This research investigates the effects of whey protein coating on the chemical, bacterial, and sensory properties, proximate analysis, and shelf life of common kilka during frozen storage.

For this experiment, common kilka were coated with 9% whey protein while non-coated kilka were used as a control sample. Both the coated and non-coated samples were stored at -18 oC for six months. Results showed that total bacterial counts (1.47–2.49 log CFU/g) and Staphylococcus bacteria (1.02–1.71 log CFU/g) were lower in the coated samples compared to the control samples (P > 0.05). Coliform, E. coli, and Pseudomonas bacterial contamination were undetectable in both the coated and control samples throughout the storage period. Humidity (73.92–46.18%), protein (18.24–19.07%), lipid (4.27–4.01%), ash (1.82–2.12%), and calorie (108.85–120.78 kcal/kg) were higher in the test samples compared to the control samples. Values for peroxide (0.15–5.12 meq/kgoil), free fatty acids (1.32–12.40 g/100), thiobarbituric acid (0.14–0.98 mg/kg), total volatile basic nitrogen (TVB-N) (6.32-21.79 mg/100g), and pH (6.32-7.45) were lower in the test samples.

Significant decreases in chemical factors were observed in the coated samples compared to the control samples (p<0.05). The overall acceptance score had a better quality in the coated samples (80) compared to the control samples (113) (p<0.05). According to the results of experiments and statistical analysis, the coated samples had a favorable quality until the end of the storage period but the control samples had lost their quality. Therefore, a 9% whey protein coating is recommended for kilka fish as a better alternative to using disposable packaging dishes with a cellophane coating.

Introduction

Kilka fish belong to the genus Clupeonella, in the family Clupeidae. These fish are composed of three species consisting of Clupeonalla delicatula, C. engrauliformis, and C. grimmi (Coad, 2017). They can be processed into salted, smoked, pickled conserved, dried, and frozen fish. In Iran, kilka products are sold fresh, canned, or in frozen packaging. From 2016 to 2021, the annual catch ranged from 20,138 to 22,429 tons. Approximately 10-12% of this catch was used for human consumption, and the remaining 88-90% was used for animal feeds. 6,307 – 6,626 tons of the fish were caught in the Guilan Province, of which 5-12% was used for human consumption and the remaining 88-95% for animal feeds (Program and Budget Office, 2022). Consumption of fresh kilka fish dropped from 6% to 2.20% during the period of 2004 to 2009. Consumption of canned kilka also dropped during the same period, whereas consumption of frozen kilka rose during the same years (Seifzadeh, 2014). The frozen fish packs had a much higher sales rate in comparison to the sales of fresh fish because of their longer storage time and wider distribution. Sales of frozen fish were also higher. The fish packs were frozen for less than three months because longer frozen-storage time may lead to color changes, surface dryness, and peroxide accumulation. Even so, the first indication of a decline in quality after only one month of frozen storage was a reduction in the weight of frozen packed fish, which in turn had a deteriorating effect on the texture and taste of the small-sized fish. There was a 3.5% decline in fish weight after three months of frozen storage (Moeini, 2009).

Kilka fish, which have valuable protein and digestible fats, rich vitamins, and minerals, have attained an important position in the food-product market. Overall, the value of food products, such as kilka, depends on their nutritional specifications and acceptability in society; therefore, accurate processing and the preparation of appealing product varieties are crucial for the market (Khanipor et al., 2017).

The final step of the food-production chain is packaging, which occupies the middle ground of production, distribution, and consumption. Many small and large companies all over the world are very active in packaging industry. Competition among packaging manufacturers has led to improved quality and more types of packaging. Currently, numerous packaging and preservation methods, including nonbiological decomposable synthetic chemicals, are used for food preservation. Recently, new packaging materials—such as edible films that are biologically decomposable—have entered the market (Aguilar-Rivera et al., 2023; Kandasamy et al., 2018).

Consumer demand is high for high-quality seafood products, especially those that can retain their superior quality of taste, texture, and general fresh appearance following a prolonged period of cold or frozen storage (Bayram et al., 2021). The use of edible films for packaging kilka seems to be an ideal method for proper preservation during periods of long storage.

Edible coatings are completely water soluble and glossy; they perform just like a secondary skin and have favorable properties such as rapid attachment to foodstuff, label attachment, antibacterial, and antioxidant properties (Seifzadeh, 2022). These types of coatings protect the aroma, taste, and food color as well as help to maintain the nutritional components. Coating food products with these films can lead to preservation of food moisture and the lowering of oxygen absorption, which can substantially improve the appearance of food products. These coatings are invisible to the naked eye (Londoño-Hernandez et al., 2018; Yu et al., 2019).

Whey protein is derived from milk and is composed of protein, lactose, and inorganic salts. It is anti-bacterial, antiproteolysis, and preserves food moisture (Setiadi and Sauria, 2020). Edible films made of whey protein have been used for packaging salmon, hotdogs, sausages, crackers, and frozen fish filets, and have improved their quality and shelf life (Seifzadeh, 2014). The objective of this study is to investigate the effects of a whey protein coating on the chemical, bacterial, and sensory properties, proximate analysis, and shelf life of frozen kilka.

Increasing awareness of environmental, health, and food safety issues, as well as increasing regulations on substances with potential health effects, are major driving forces for consumer behavioral changes. These behavioral changes propel the shift toward development of alternative products free from substances of concern. One such substance is Bisphenol-A (BPA), a chemical commonly found in the protective linings of food or beverage metal cans. BPA has undoubtedly become a major cause of concern, prompting serious examinations from various regulatory bodies across the world connecting BPA to adverse health effects.^1-5

Since 2015, France has issued a ban on BPA in all packaging, containers, and utensils intended to come into contact with food.1 As recently as 2018, the European Union published a regulation that further restricts the presence or use of BPA-containing substances in plastic food contact materials. The new regulation reduces the specific migration limit for BPA in varnishes and coatings for food contact applications by an order of magnitude (from 0.6 mg/kg to 0.05 mg/kg) over previous regulations.^2,3 Although the U.S. Food and Drug Administration has not issued a complete ban on the use of BPA in food can lining applications, several states such as Maryland, Connecticut, and California have placed further restrictions on its presence in food cans. Given the increasing regulatory pressure, the demand for Bisphenol-A Non-Intent (BPA-NI) metal packaging coatings will continue to increase in years to come.⁴

Resin manufacturers, can coating formulators, can makers, and brand owners are responding to this shifting market demand by actively innovating alternative solutions that can meet or exceed the performance of BPA epoxy coatings while minimizing the cost of these transitions. The performance requirements that BPA-NI can linings need to satisfy are high. The coatings must exhibit enough flexibility and adhesion to withstand the rigorous mechanical demands of can forming processes. They also need to survive high temperatures and high-pressure food sterilization processes in the presence of hydrolytic and corrosive environments such as low pH, acids, sulfur, and salts. Not only does the coating need to meet these high requirements pertaining to can forming and sterilization processes, it must also survive the storage test or pack test as part of the routine assessment of long-term shelf stability.^6,7

Polyester coatings are one of the most promising BPA-NI alternatives to BPA epoxy-based coatings. The modularity of building blocks in polyesters allow for fine-tuning of its compositions with a wide variety of monomers, enabling the achievement of balanced properties including high-glass transition temperature, flexibility, and toughness. Several notable monomers, namely 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD), 1,4-cyclohexanedimethanol (CHDM), isosorbide, and tricyclodecane dimethanol (TCDDM), have emerged as promising building blocks for superior polyester performance. In particular, TMCD is known to impart a variety of excellent properties such as good temperature resistance, toughness, chemical resistance, and hydrolytic stability. TMCD is used in BPA-free specialty plastics prevalent in sports bottles. TMCD-containing protective resin systems have demonstrated good resistance to corrosion and chemical attack while simultaneously demonstrating good flexibility and adhesion in a variety of applications, including metal packaging applications.^7,8 New product qualification in storage or pack tests is a vital step in the development and evaluation process of new metal packaging coatings. Pack tests may last from several months to several years and may involve filling and storing goods in cans at elevated temperatures. At specified time intervals, cans are opened and visually inspected for defects. Food and beverage cans come in various sizes and shapes, and coatings formulations vary across the industry. As the combination of can types and food products are numerous, this coating qualification effort can take significant time and financial investment, as well as collaboration across value chains. Given the cost, complexity, and time involved in qualifying new coatings, reducing qualification time has the potential to accelerate development cycles. A predictive analytical technique that can reduce the need for time-consuming pack tests would be highly desirable across the metal packaging value chain. Though the goal seems lofty, it is in the best interest of the metal packaging industry to develop techniques that may predict long-term performance for new coatings.

Electrochemical impedance spectroscopy (EIS) is a useful analytical technique that has been widely employed for numerous applications in industry and academia over several decades. This technique assesses the barrier properties of organic coatings and their time-dependent, long-term durability and performance in response to various experimental conditions.^9-22 EIS can reveal a wealth of information on the state of corrosion in coating prior to the visual appearance of corrosion. With EIS, a small sinusoidal alternating current (AC) wave is applied and the resulting resistance (impedance) to current flow is assessed as a function of frequency. Impedance data are collected and analyzed with relevant electrical circuit models to understand the corrosion state of the coating. Kern and colleagues employed EIS to study the performance of cans coated with various formulas and filled with different food contents. They used direct current (DC) treatments and electrolyte aging treatments to understand and predict corrosion during storage.⁹ Charge transfer capacitance, related to the delaminated metal area, and electrolyte aging, respectively, were found to be reliable parameters and procedures for quality evaluation and performance ranking of various cans. De Vooys and colleagues also employed EIS as a screening tool to evaluate the suitability of coated metal packaging cans with new food products by measuring their impedance over a two-week period.¹⁰ The evolution of complex impedance at low frequency over a two-week period with threshold impedance values was used as a pass/fail criterion for product/container combinations. Others have employed EIS as a means to quantify the adhesion of different types of lacquers for food packaging,¹¹ to measure the delamination of coatings over time when exposed to various conditions,¹² to study the water and electrolyte uptake of organic coatings,^13,14 and many other applications.^15-22

In this study, we employed an EIS technique in conjunction with aging procedures involving concentrated food simulant and elevated temperatures for a series of coatings. The aging procedure acts to accelerate the corrosion process, while EIS provides quantitative measurements that enable in-depth understanding of corrosion mechanisms. This combination enables faster coating quality evaluations and rapid selection of formulations for further evaluation. The performance evaluation from EIS is further validated using an industrially relevant enamel rater test. This work provides fundamental insight into the relative performance of polyester resins in various formulations as part of a resin development strategy.

Experimental Procedures

EMN-MP resin is a mid-molecular weight TMCD-based polyester with a number average molecular weight (M_n) in the range of 6000–8000 g/mole and T_g��~90 °C. Commercial Control resin is a non-TMCD-based, high-molecular weight resin with an M_n of > 10,000 g/mole and T_g��100–110 ºC. The two resins were formulated into white polyurethane (PU) and gold phenolic PU formulations as representative solventborne BPA-NI 3-piece food can interior lacquers. The formulation details for white PU coatings and gold phenolic PU coatings are listed in Tables 1 and 2, respectively. All resins were reduced with Aromatic 100 (A-100) solvent to 50 wt% solids. Fascat® 9102 catalyst solution was diluted with A-100 to 10% of the original supplied concentration.

The formulations were drawn down onto electro tin plate (ETP) substrate panels supplied by Lakeside Metals Inc. (0.25# Bright T-1 0.009-0.010 x 4.0 x 12.0 in.). All formulations were applied with appropriate wire-wound rods to target film weights of 10 gram per square meter (gsm) and 6 gsm for white PU and gold phenolic isocyanate coatings, respectively. The coated panels were cured at 200 ºC for 12 min in a forced air convection oven.

Electrochemical impedance spectroscopy was performed using Gamry Instrument “Reference 600” Potentiostat equipped with Gamry framework and Echem Analyst. The samples were held in a cylindrical glass cell by a clamp fixture attached to an O-ring gasket affixed to the grooved bottom of the cell. A nickel electrode and a graphite electrode were used as reference and auxiliary electrodes, respectively. The potential was applied in a range of 5 mV from open circuit potential and the frequency was varied from 10⁵ to 0.1 Hz.

Food simulants used in this study were 3% acetic acid (3 wt% acetic acid in 97 wt% DI water), 2% lactic acid (2 wt% lactic acid in 98 wt% DI water), and 5% acetic acid (5 wt% acetic acid, in 95 wt% DI water).

To perform EIS measurements for white PU panels, the drawn down panels were first retorted in the presence of 3% acetic acid solution. The EIS cell apparatus was fixed on top of the area of interest, and this area only was exposed to the electrolyte during the retort process at 131 ºC for one hour. Upon completion of retort and cooling, the first EIS measurements were performed, and subsequent measurements were taken at defined time points. To perform EIS measurements for gold phenolic PU panels, the area of interest in the drawn down panels was exposed to 2% lactic acid by fixing the EIS cell apparatus on top of the panels. Following 36 days of exposure to 2% lactic acid, the EIS measurements were obtained. All EIS measurements and aging were performed at room temperature. Enamel rater measurement was performed using WACO Digital Enamel Rater II. Test voltage was set at 6.3 V. Can lids were stamped from white PU flat panels and retorted in the presence of 5% acetic acid. Upon retort, the can lids were exposed to 5% acetic acid, and the can lids were placed in an oven maintained at 50 ºC. At defined time points, the can lids were taken out of oven and enamel rating was obtained.

Results and Discussion

The electrochemical impedance spectroscopy technique has been employed for decades for measuring and monitoring of time-dependent changes of organic coatings.^9-22 The measured impedance values are presented in Nyquist or Bode plots and fitted to relevant and appropriate electrical equivalent circuits consisting of resistive and capacitive elements in various configurations that help with the physical interpretation of the impedance data.^15-17 With this technique, the penetration of electrolyte into the coating can be followed and the initiation of corrosion at the metal/coating interface can be detected. Figure 1 shows the stages of corrosion, relevant electrical circuits, and the expected shape of Bode plots at different stages of corrosion when a coated panel is exposed to electrolyte. In Stage 0, at the start of immersion, the coatings are dry and behave like a pure capacitance. The appropriate circuit configuration is that of electrolyte resistance and coating capacitance in series. The coating capacitance depends on coatings thickness. In Stage 1, the coatings begin to absorb the electrolyte until the film micropores become saturated with the electrolyte. In this phase, the coatings can be represented by a resistance and a capacitance component in parallel. As the film continuously absorbs electrolyte, the coatings capacitance increases with increasing electrolyte content, whereas the resistance component decreases until the film becomes saturated. The film affinity towards the electrolyte and crosslinking density influence the speed of electrolyte penetration in the film. Coatings capacitance can be used to determine the change in coatings porosity or electrolyte diffusion coefficient according to the Brasher-Kingsbury equation.²² In Stage 2, as the electrolyte reaches the coatings/metal interface, corrosion is initiated and blisters in the coating begin to develop. The newly formed oxidized layer can be represented using a double layer capacitance and a charge transfer resistance in parallel, or the “two time-constants” as commonly used in EIS. There might be no visible sign of corrosion at this stage, but the magnitude of the complex impedance at low frequency continues to drop. In the subsequent stage, delamination starts, and pore breakthrough occurs along with a diffusion-limited corrosion reaction as the reactant gets delivered to the surface. A Warburg impedance component is added to the equivalent circuit in this stage.

There are many ways to interpret or use the results of resistive and capacitive elements from relevant electrochemical circuits. McIntyre and Pham¹⁸ used R_po (pore resistance) and C_dl (double layer capacitance) terms to estimate the degree of delamination in can coatings. They also used C_c (coating capacitance) to estimate the coating porosity and correlate it with flavor scalping performance. Hu et al. used a coating capacitance term to monitor water uptake and diffusion of chlorine ions in epoxy-coated aluminum alloys in the presence of NaCl solutions.¹³ Kern et al. used charge transfer capacitance in a slightly more complicated circuit configuration to estimate the delaminated area after exposure to food simulants.⁹ De Vooys et al. simply relied on the evolution of the shape of Bode plots over time and assigned relevant electrical circuits to fit the data. The magnitude of overall impedance of the coated metals exposed to food simulant over two weeks was used as a pass/fail criterion. McIntyre and Pham also used EIS to track the low-frequency impedance over several weeks and showed that the rate of decrease in impedance has some correlation with the coating porosity.¹⁸

In this study, we compare EIS responses to characterize the progress of corrosion as a proxy for long-term performance in a pack test. The magnitude of impedance at low frequency (0.1 Hz) is used to compare the relative performance of different coatings as appropriate. EMN-MP resin and Commercial Control resin were each formulated into white PU formulations (Table 1) and drawn down on tinplate. The coatings were then subjected to a retort procedure in an autoclave at 131 ºC for one hour in the presence of 3% acetic acid in a custom-made set up that exposes only the intended area to the food simulant.

Figure 2 shows the frequency-dependent impedance values immediately after retort and after a subsequent 48 h of immersion in 3% acetic acid. At the beginning of the test, both coatings were at the same corrosion stage (Stage 1, electrolyte penetration). However, after the subsequent 48 h of exposure, the Commercial Control coating had progressed into Stage 2 corrosion, as apparent by its Bode plot shape indicating initiation of corrosion, whereas the coating based on EMN-MP resin was still in the stage of electrolyte penetration (Stage 1). This observation is supported by the general shapes of the Nyquist plots shown in Figure 3.

At zero hours, both coatings showed one semi-circle indicating Stage 1 corrosion. After 48 h of exposure, two semi-circles began to emerge in Nyquist plot of Commercial Control coating indicative of Stage 2 corrosion, while only a semi-circle was observed for EMN-MP coating, indicative of Stage 1 corrosion. The decrease of impedance at low frequency (0.1 Hz) for both formulas is traced in Figure 4a and consistently shows that Commercial Control coating has lower corrosion resistance over the exposure time. As the impedance values plateau at longer times, it is apparent that the corrosion slows after the initial retort exposure. EMN-MP coating demonstrates better corrosion resistance of 2.56 Mega Ohms as compared to 0.44 Mega Ohms conferred by Commercial Control coating in this post-retort plateau region (Figure 4b).

Both resins were also formulated into gold phenolic PU formulations (Table 2) and drawn down onto tin plates. Upon curing, the panels were exposed/soaked in 2% lactic acid solution and aged for 36 days at room temperature. Figure 5 shows the frequency-dependent impedance measurement of both panels after 36 days of exposure in 2% lactic acid. Figure 6 compares the Nyquist plots of both panels at the end of 36 days of exposure in 2% lactic acid. Comparing the curve shape from the Nyquist plots, it is evident that EMN-MP coating was still in Stage 1 corrosion as indicated by one semi-circle, whereas Commercial Control coating has entered into Stage 2 corrosion as evidenced from the appearance of two semi-circles. The low frequency (0.1 Hz) impedance values over 48 h of observation are shown in Figure 7a, and the corrosion resistance of both coatings are compared in Figure 7b. Again, the EMN-MP coating exhibited significantly better corrosion resistance of 53.7 Mega Ohms as compared to 2.47 Mega Ohms with Commercial Control coating in gold, phenolic isocyanate formulation at the same dry film thickness. Perhaps the higher hydrophobicity of EMN-MP resin and, therefore, its lower propensity to absorb 2% lactic acid food simulant, might contribute to the delay in corrosion development. The superior corrosion resistance observed with EMN-MP resin can be, at least in part, attributed to the hydrophobic contribution of TMCD. As evident from the two examples above, EIS techniques coupled with different aging procedures can produce quantitative and qualitative assessments that guide the development and evaluation of resin and coating performance.

To validate the EIS results, we also compare the performance of each of these resins with enamel rater testing commonly used in industry, as documented in various patents and articles.^23-27 The test included an accelerated aging approach using 5% acetic acid (2% higher than the concentration of acetic acid used for EIS experiment on white coatings) at 50 ºC over several days of exposure. This experiment was performed on stamped can lids, a notably harsher mechanical treatment than flat metal panels. It was expected that the high concentration of simulant and higher temperature would accelerate the corrosion process. Enamel rater is a DC-based technique that applies a constant 6.3-volt potential across the coating during four seconds and measures the resulting current. The enamel rating is an index of the amount of metal exposed or delaminated from the coating during exposure to food simulant. A higher current flow indicates a worse coating performance. Figure 8 tracks the current flow of can lids coated with white PU coatings exposed to 5% acetic acid at 50 ºC over seven days. The coating based on EMN-MP resin demonstrates a better corrosion resistance than Commercial Control coating at the end of seven days of exposure as evidenced by its lower current flow relative to that of Commercial Control coating.

At the end of the experiment, the exposed can lids were subjected to a tape-pull test for qualitative assessment of coating adhesion. Figure 9 shows the pictures of stamped can lids based at the seven-day exposure interval, before and after the tape-pull test. It is evident that the coating based on EMN-MP resin exhibits a qualitatively better coatings adhesion at the end of this accelerated aging test. It is also worth noting that signs of underfilm corrosion were already visible in the case of Commercial Control even prior to the tape-pull test. The tape-pull test further revealed underfilm corrosion in Commercial Control case. Signs of underfilm corrosion were also present in the exposed surface of EMN-MP coating after the tape-pull test, but the exposed area is qualitatively smaller than in Commercial Control coating, owing to better coating adhesion although quantitative assessment was not performed. The results observed in the enamel rating test are, thus, in agreement with the results of the EIS evaluation.

Conclusions

Electrochemical impedance spectroscopy is employed as a screening tool in the innovation process of new BPA-NI metal packaging resins. The resins in this study were formulated into coatings, which were subjected to aging treatments with several food simulants at relatively high concentrations. Time-dependent impedance measurements by EIS reveal the progress of corrosion in the coatings and provide quantitative measurements of corrosion resistance. EMN-MP resin in white PU coatings exhibited better barrier properties with slower corrosion kinetics and higher corrosion resistance relative to Commercial Control resin in white PU formulation. Similarly, in the gold phenolic PU formulations EMN-MP coating exhibits better barrier properties relative to Commercial Control coating. The EMN-MP resin system also shows better barrier properties in the enamel rater test on white PU coatings. The results from the enamel rater test are consistent with results observed with EIS. This work demonstrates the utility of EIS and the more commonly available enamel rater tests as powerful tools in understanding the barrier properties and corrosion kinetics of coatings as part of a resin design strategy. The data provided by these techniques can help to enable quantitative data-based decision making and faster coatings development cycles.

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CoatingsTech | Vol. 17, No. 8 | August 2020

Homebound consumers are creating a bright spot in the DIY paint segment—and inspiring innovations in packaging.

The COVID-19 pandemic has had terrible health and economic consequences for the world. Stay-at-home orders and closures of non-essential businesses have resulted in a decline in global growth for this year, with predictions that a return to pre-pandemic conditions will not fully occur until near the end of this decade. Under such dire circumstances—and with the novel coronavirus SARS-CoV-2 still spreading across the globe, including in areas where business has been at least partially restarted—it is difficult to find good news. In the paint and coatings industry, there is one bright light, however, in the do-it-yourself (DIY) sector, which has experienced a measurable increase in sales as consumers, more than ever, look for sustainable, easy-to-use products. Packaging of DIY paint products, which not only educates, but also reflects the sustainability commitments of coating manufacturers, is playing an increasingly important role in the consumer buying decision.

Staying Home

Industry experts say stay-at-home orders related to the COVID-19 pandemic have driven the DIY paint market. “After sheltering in place for months, with more time expected, many people are hyper-aware of how their home makes them feel, and it’s become increasingly important for them to create a space that reflects how they want to feel during an unsettling time,” says Alison Bruce, senior marketing manager for PPG.

Home has, for many, become central to their lives during this global pandemic, agrees Kathryn Ledson, AkzoNobel’s global marketing director for consumer paints. “Home has been a sanctuary, where everything happens—families living, working, and playing indoors together, sometimes all at once. The home environment also affects mental health and well-being, especially during periods of long confinement. Ordinary people have been digging deep to adapt to this way of living,” she observes. In countries where DIY painting is prevalent, many people are doing jobs they have been putting off, and others are creating colorful spaces out of necessity—like working from home or refreshing the spaces that they are now spending more time in, according to Ledson.

The trend in online purchases is expected to continue, not only due to continued presence of the virus, but as the result of the rapid response by paint companies to make digital purchasing easy.

“As a result of stay-at-home orders, consumers are more engaged than ever to tackle home improvement projects. They are spending less on travel and dining and using discretionary money to re-invest in their homes,” notes Harriette Martins, senior manager for product marketing at Benjamin Moore. The paint company recently broadened its DIY footprint with an assortment of Benjamin Moore paints now available at more than 3,500 participating Ace Hardware stores nationwide. This is in addition to Benjamin Moore’s existing network of 5,000+ locally owned and operated independent retailers.

Given the uncertainty in the economy, even consumers who would not necessarily call themselves do-it-yourselfers are looking for ways to revitalize their homes on a tight budget, adds Randy Austin, director of product management at Scholle IPN. “Painting a space, a door, or a piece of furniture within the home is one of the easiest ways to create a new look,” he says. Shelter-in-place orders and social distancing are, in fact, reversing the recent trend towards “do-it-for-me” back to DIY, according to Nathan Hardy, director product management with Kelly-Moore Paint Company.

As a result, home improvement and DIY projects have experienced a nationwide surge. According to a , which has been monitoring 1,000 consumers during the pandemic, home improvement purchases grew from 55% on March 23 to over 80% by April 13. Much of this activity has occurred online. “Readily armed with technology, homeowners have shifted how they purchase home improvement products. The top product that was searched for online is paint, up 700% from March 16 to April 5. In fact, in recent months, PPG has experienced triple-digit percentage increases in online paint sales, indicating that purchasing paint online may become the new normal for homeowners,” comments Bruce. Retailers, notes Ledson, have had to rapidly adapt, meeting shifts in demand while maintaining safe environments for customers and employees.

The trend in online purchases is expected to continue, not only due to continued presence of the virus, but as the result of the rapid response by paint companies to make digital purchasing easy. One big focus area has been on providing color selection support. “We are finding in DIY markets that newer homeowners have fewer skills than previous generations, so there is a need to provide more guidance than in the past. Color choice is often an area where people appreciate a helping hand, and applications such as AkzoNobel’s virtual advisor or mobile visualizer tool give the control to people in their home. It also means we can provide this help on mass scale,” Ledson explains.

Paints that are easy to use are also in demand by DIYers.

Behr Paint Company is helping the new generation of consumers entering the DIY paint market throughout the entire painting process from inspiration to completion by providing how-tos, color Q&As, online color selection tools, and more,” says company CMO Jodi Allen. Behr Express was introduced in 2019 but has become widely used since the COVID-19 pandemic emerged. This tool enables DIYers to select paint colors from a curated collection of Behr’s most popular paints using a simple online quiz. Along with the paint, customers receive everything they need to tackle a project in an all-in-one painting kit, including supplies such as paint brushes and rollers. “This approach is designed specifically for the next generation of DIY painters, allowing them to get everything they need to transform their space, delivered to their door in a simple, beautiful package,” Allen remarks.

PPG is now offering free virtual color consultations in the United States to help DIYers accomplish their projects. This virtual solution allows consumers to get recommendations from PPG color experts from the comfort of their home, according to Bruce. When submitting a request, customers are asked to provide details about their project, initial color preferences, and photos of the space. Then through text, e-mail, or video conference, PPG color experts provide color recommendations and details on how to order free color swatches from www.ppgpaints.com. Once a color is selected, customers can schedule curbside pickup at a PPG Paints store or order paint online from The Home Depot.

PPG expects the COVID-19 pandemic will impact color preferences going forward. “The pandemic has spurred a feeling of unrest and anxiety among consumers, who are now craving colors that instill a sense of comfort, like cool blues and other neutrals. We anticipate that COVID-19 will influence designers and consumers to shift towards natural colors, which represent our innate desire to achieve internal peacefulness and reconnect with nature in an age where sustainability and mental and physical wellbeing is crucial,” Bruce observes. PPG also anticipates that commercial design preferences will pivot. “For example,” she says, “restaurants will likely space out their seating arrangements and add more windows, allowing patrons to sit farther apart and create an open atmosphere. Architects will likely incorporate more balconies in their future multi-family living designs, as balconies have provided residents with a sense of freedom and a connection to nature, while maintaining social distance from others.”

Easy and Sustainable

For many years, demand for paints with a sustainability benefit and for paints that do more has been increasing. “While the COVID-19 pandemic and online accessibility will drive how customers buy paint, sustainability and transparency of the paint will be drivers of the products purchased,” Hardy says. DIYers want paints that do not impact the environment or their health.

One area of growing consumer awareness, according to Ledson, is around indoor air pollution, especially in larger cities. “While this issue has been a focus in China for many years, we are now seeing this trend on the rise in other regions,” she says, as people are becoming increasingly conscious of their health and well-being.

According to a from Farnsworth, which has been monitoring 1,000 consumers during the pandemic, home improvement purchases grew from 55% on March 23 to over 80% by April 13.

Paints that are easy to use are also in demand by DIYers. Ledson highlights easy-to-clean properties as the top demand of DIYers in most markers. AkzoNobel recently introduced Easycare mark-resist paint in Poland in response to this consumer preference. “The paint structure means that any DIYer can now achieve a beautiful interior finish, and the walls won’t be prone to the unsightly black scuff marks that appear with everyday wear and tear,” Ledson notes.

Paint manufacturers will also be looking for more ways to reuse or recycle paint, reduce environmental impact, and minimize the amount of product that is thrown away, all while providing a safe, user-friendly, and practical product for consumers, according to Anastasia Khodakova, global marketing director for Liquibox.

Allen describes a similar strategy at Behr, remarking that, “with sustainability increasingly becoming an important trend in the DIY market, we are working to address this issue in not only our products, but also in our packaging.”

Packaging and the DIY Decision

Indeed, it is not just the paint that consumers want to be sustainable. They are also looking for paint products to come in more sustainable packaging that provides needed information and supports their ability to easily complete painting projects. “Packaging plays a huge role in the DIY market, because customers first and foremost seek convenience, along with products that perform and are durable,” says Allen.

“The container and the labeling have important roles for the DIY customer,” adds Hardy. The container needs to preserve the material and minimize impact on the environment, while the label needs to clearly define the product and be a trustworthy source of information regarding what is in the product, how it is used, and the necessary precautions.

Packaging should also provide the consumer with a clear understanding of product usage and attributes in order to simplify the selection process, observes Martins.

DIY Packages Must Do More

It should be no surprise, then, that successful packaging solutions for DIY products are those that quickly and clearly educate the consumer, or that packaging continues to be an important element of the purchasing experience for DIY buyers. “While many consumers tend to rely on the expertise of in-store sales associates, professionals, or their own experience with products, they still look to the packaging to clearly and effectively communicate product attributes,” Bruce notes. The language on product packaging has, therefore, become increasingly more concise and simplified, a trend that is continuing to help consumers better understand product features, she says.

“Consumers should be able to easily understand key product benefits and use cases and determine if a product is the right one for their needs,” Martins adds.

The packaging should also be sustainable and provide the clear and transparent information in a memorable way, according to Hardy. Basic critical features for paint packaging, adds Austin, include being easy to open, close, and reopen after first use. He also points to matching package size to the right amount of paint for the job and evacuation of the paint from the container as other important properties.

“An ideal packaging solution for DIY paint must be durable and lightweight, as well as easy to transport, store, and dispose of. It should be easy and safe for consumers to use without creating a mess, and it must protect paint from drying and forming crust over time,” says Khodakova.

Sustainability Drives Change in DIY Packaging

In response to all of these needs and trends, consumer packaging continues to evolve, with the information shared on the package becoming more transparent in the DIY market. “DIY customers want simple, clear information on their packaging about product use and the potential hazards. New consumer warnings and ingredient lists are becoming commonplace to help protect the user. Sustainability is also becoming a key purchasing driver. Sustainable containers that can be recycled are also preferred as sustainable packaging becomes more desirable. Recycled materials have developed significantly and are becoming the go-to for different packaging solutions,” Hardy observes. He also notes that while some sustainable paint and packaging solutions exist, more development is happening every day. “Fully sustainable paint solutions are in development and should be the long-term goal,” he asserts.

For AkzoNobel, reduction of packaging footprint is the lead driver around many of the company’s packaging decisions, according to Ledson. “Consumers are exposed to packaging in many other categories, and they have expectations that well-known brands are reducing their carbon footprint and limiting material use,” she says. Overall, Ledson adds, the company aims to design and manufacture the best quality products in the most sustainable way, and where possible, the overall amount of packaging needed is reduced and recycled materials, including paper and plastics, are used. “We recently announced our ambition to be a zero-waste company and cut our carbon emissions by 50% by 2030 and to have a minimum of 50% recycled content in our paint packing for deco Europe by 2025,” Ledson comments. For DIYers, in particular, AkzoNobel looks at format and has recently introduced sponge tubes to replace aerosol use in fillers and has also begun incorporating bio-based materials in some of its packaging.

Behr, meanwhile, recently introduced the BEHR Simple Pour Lid, a first-of-its-kind plastic lid that does not require a key and has an attachable spout for a more precise pour, according to Allen. “The new lid,” she explains, “eliminates mess and rust and helps keep paint fresher longer.” If you are a DIYer who prefers to dip your brush directly into the paint can, you can still do that by simply removing the Simple Pour Lid. The BEHR Simple Pour Lid is currently available on select products and will be rolling out exclusively at The Home Depot stores nationwide.

Consumers are exposed to packaging in many other categories, and they have expectations that well-known brands are reducing their carbon footprint and limiting material use.

Khodakova believes that packaging manufacturers have done a good job in meeting consumer needs with respect to convenience and easy cleanup. As an example, Austin points to easy pour packaging and better handles to reduce waste. Khodakova also highlights the significant effort companies are making to downgauge packaging as far as possible while still ensuring it provides adequate product protection and is recyclable where possible. “There is still an opportunity in the DIY market, however,” Khodakova insists, “to find the best solution for disposing of this hazardous packaging waste products without harming the environment by burning or burying unused product in landfills.” She adds that there has been a lot of effort by the industry to find ways to reuse or recycle paint and to reduce the amount of product thrown away to a minimum. “For now, though, she says, “in most countries any packaging that has been in contact with paint is classified as hazardous waste and is sent to incineration.” Ledson agrees that post-use recycling schemes are becoming increasingly important to help close the loop on paint waste and notes that AkzoNobel encourages consumers to recycle packaging and old paint wherever possible. There are also still some opportunities for labeling, according to Austin. For example, given that store-printed labels often fade, peel, or get covered with paint, he poses, “How do we clearly communicate the exact name and color on the package for long-term storage?”

Flexible Packaging Gains Traction

A packaging format that is extremely lightweight and reduces the product and packaging waste, as well as carbon emissions in transport and storage, will help paint companies meet their sustainability objectives, according to Khodakova. Flexible packaging, adds Austin, can also help DIYers deal with the two biggest painting challenges—how to store unused paint and how to dispose of paint containers—by preserving unused paint in a highly space-
efficient manner and helping to fully evacuate the paint for easy disposal of the package.

To help reduce the amount of contaminated packaging, Liquibox (USA), a global packaging manufacturer with over 50 years of experience, has designed a bag-in-box solution for paint, coatings, and varnishes. “Bag-in-box packaging tackles the problem of wasted product as the air-tight bag prevents the paint from drying up for as long as two years after opening, allowing users to dispense just the right amount and keep the rest for later use without worrying about a crust forming on the top of the product,” Khodakova explains. She adds that in terms of CO₂��emissions, the new packaging represents only a 10% carbon footprint of aluminum tins of the same size and optimizes logistics due to its perfectly square shape. In addition, bag-in-box packaging from Liquibox can be equipped with a handy dispensing system that allows one-hand serving and ensures no product leaks, splashing, or glugging. The only part of the bag-in-box that is in contact with the paint is a thin and resistant flexible bag. The outer cardboard box that protects the bag during transport and handling is made of recycled material, is foldable and 100% recyclable. Once the flexible bag is empty, it is still clean on the outside and consumes very little space, reducing disposal effort and cost, according to Khodakova.

Liquibox also offers paint in pouches for e-commerce sales, as well as for product testing and sampling. A variety of durable films including metPET with PE laminate, clear EVOH with PE and biaxially-oriented nylon (BON) laminate, and metPET with PE laminate protect the product from oxygen and UV light while ensuring product quality and safety, according to Khodakova. The company’s research and development team is also continually investigating new film and fitment innovations, including ways to improve the sustainability of its flexible packaging. Goals include light weighting the bags, shifting to mono-material film structures, and the use of more eco-friendly materials that will enhance compatibility with existing recycling streams.

Scholle IPN also has a range of bag-in-box and stand-up pouch solutions for the DIY paint market that can help differentiate a brand on store shelves and provide convenience to consumers, such as easy-to-carry designs, user-friendly closures, and space-saving formats. “Our bag-in-box and pouch products reduce hazards, messes, and waste while increasing safety and efficiency for both commercial and retail consumer use,” Austin says. The flexible package is made of a secure and durable film that is strong enough to keep even acidic, caustic, or basic products from eating away at the packaging wall, reducing risk during shipment and storage, he notes. Scholle IPN’s controlled bag-in-box dispensing systems are, according to Austin, designed for accurate mixing, which reduces the risk of product waste, errors, and exposure to harsh or hazardous materials. Also, the user-friendly fitment designs eliminate glugging and spilling, allowing users to dispense quickly and precisely for increased efficiency and safety. Overall, he says the packages are designed to reduce costs while minimizing waste and environmental impact, making the product not only safer for the DIYer, but also for the people who manufacture and those that transport paint products. Bag-in-box products come in a range of sizes from one liter for DIYers to 300 gallons for industrial applications. Current research at Scholle IPN is focused on increasing oxygen barrier performance and minimizing waste through propriety film and closure developments, according to Austin.

CoatingsTech | Vol. 17, No. 8 | August 2020

Packaging design trends in 2019 are a mix of adaptability, functionality, and simplicity, with an emphasis on sustainability. Topping the list of the desired packaging features is flexibility, which is driving increased use of flexible packaging for a growing range of consumer and food/beverage products.¹ Advancements in production and materials have developed flexible packaging solutions with easy-to-use features, such as resealable food packages. Flexible packaging is also highly adaptable, lightweight, and recyclable, making it a sustainable choice.

Innovations in shape and construction are crucial when it comes to attracting the eye and providing protective functionality, longevity, and full product use.

Sustainability remains a priority in the packaging industry because consumers are increasingly aware of the environmental impact of the goods they purchase—and that extends to the products’ packaging. Today’s consumers want packaging that is recyclable and/or biodegradable and produced using eco-friendly materials. So, while brands need to attract buyers’ attention through more personalized and unusual packaging designs, they must also use smarter or less packaging materials for shipping and transport, an issue that becomes more imperative as e-commerce continues to grow. To meet consumer expectations and lower transportation costs, packaging innovators are producing lightweight, adaptable options that use less material and help reduce fuel consumption.

The advancements in packaging designs also include a growing interest in vintage-inspired packaging—a trend that spans many product segments. The simple yet distinctive look and feel of retro-style packaging taps into the consumer nostalgia reflected in the resurgence of vinyl records and a renewed interest in 1980s television shows.

This return to simplicity influences other design elements as well. Some packaging designs are more streamlined and offer greater transparency, such as additional product information.² Flat illustrations, which originated in printed materials, have migrated to minimalist packaging solutions with crisp, clean designs.³ Black and white, as well as neutral tones and pastels, are prominent in the minimalist themes, creating a sleek and sophisticated look. Subtle and bright gradients move from the background and into the overall designs, allowing the colors to stand out.² Bold typography and geometric shapes are showing up as graphic elements, and some brands are experimenting with storytelling approaches. As for the physical packaging itself, innovations in shape and construction are crucial when it comes to attracting the eye and providing protective functionality, longevity, and full product use.

Assisting in the continuous evolution of packaging design are packaging coatings. Coatings add aesthetic, functional, and haptic elements to packaging that help create the visual and tactile experiences for the consumer. More important, coatings provide chemical and corrosion resistance and prevent contamination, which protects the integrity of product and ensures consumer safety. Among the resin technologies used in packaging coatings, epoxies are used most often, followed by acrylics, polyurethanes, polyolefins, and polyesters.⁴

The packaging coatings market, which includes coatings for all types of substrates, from paper to cans, sees significant growth as more packaging innovations enter the supply chain. Allied Market Research estimates the packaging coating market is expanding at a compound annual growth rate (CAGR) of 4.6% from $2.83 billion in 2016 to $3.865 billion by 2023.⁵ A report from Mordor Intelligence predicts the market will expand more rapidly at a CAGR of 5.12% through 2024.⁴

LEONHARD KURZ, part of the KURZ Group, is one coatings company contributing to the market growth with its developments in thin-film technology. At Luxe Pack Monaco 2019 in September, LEONHARD KURZ introduced “expressive packaging,” a concept the company says reflects the spirit and lifestyles of the times. “By offering a diverse selection of unusual patterns, we inspire designers and brand name manufacturers to break away from customary design patterns, to look at packaging design in a new way, and to rediscover the world of hot stamping technology,” the company said in a press release.⁶

The packaging coatings market, which includes coatings for all types of substrates, from paper to cans, sees significant growth as more packaging innovations enter the supply chain.

The “Box next to Box”�� is a decorated drawer box that contains a trend collection with different themes: Archive celebrates the rediscovery of “old treasures and resources”; Supa Func focuses on efficiency, function, order, and structure; Black Mirror encourages “the contemplation of reflection and self-determination in times of omnipresent digitalization and artificial intelligence”; and Clearance reflects “the desire for true sustainability, new materials, and better consumer behavior.” To illustrate each trend, KURZ developed metallized-transfer products with surprising optical effects and unusual colors. One style features underprinted designs shining through translucent silver, a matte terra cotta, and a fluorescent orange. To complement the unique color motifs and optical effects, KURZ enhanced the tactile experience with textures and embossing using stamping die technology from its subsidiary, Hinderer and Mühlich.

KURZ also exhibited its new technology Trustseal SFX Mosaic, which uses holographic lenses confined within a strictly symmetrical arrangement to create striking contrasts and a multiple, repeating-depth effect.

Other companies are also exploring cutting-edge transfer technologies for packaging applications. Toray Plastics (America) made headlines in 2016 when it introduced Lumirror MR20, a polyester metal-transfer film. Lumirror MR20 transfers aluminum deposited on the film with adhesive to paper or paperboard packaging, producing a bright, reflective surface that can be used to create a luxurious look for mass-produced products.⁷

Also developing coatings in the luxury/specialty space is Diamond Packaging. It produces two metallic UV coatings as part of its Sustainable Chic line™: Liquid Metal™ and MiraFoil®. The company says the Sustainable Chic packaging coatings deliver “beauty without compromise” using advancements in converting technologies.⁸ A combination of flexo and offset printing creates the Liquid Metal effects, which Diamond Packaging touts as a more sustainable alternative to metallized substrates and foil stamping. Meanwhile, MiraFoil’s satin metallic effects are achieved through a process that Diamond Packaging says is “an economical, in-line alternative to film and foil laminates.” Diamond Packaging’s specialty coatings also include the award-winning DiamondGlitter and DiamondReticulate. DiamondGlitter is a shimmering finish that catches the eye, while DiamondReticulate’s subtle texture adds a tactile quality that engages the consumer.⁹

As the coatings industry continues to develop high-performance packaging coatings that both market and protect products, companies such as Diamond Packaging, KURZ, and Toray will continue to acknowledge consumer environmental concerns, emphasizing the sustainability best practices used to manufacture packaging coatings and products’ recyclability for the life cycle of the packaging.

References

1. Haverfield, C., “5 Packaging Trends Emerging in 2019,” Packaging Design, March 18, 2019, https://www.packagingdigest.com/packaging-design/5-packaging-trends-emerging-in-2019-2019-03-18 (accessed Oct. 9, 2019).
2. Williams, D., “Packaging Design Trends 2019: Innovations to Look Out For,” Packaging Gateway, March 18, 2019, https://www.packaging-gateway.com/features/packaging-design-trends-2019/ (accessed Oct. 9, 2019).
3. Lupus, M., “9 Inspiring Packaging Design Trends for 2019,” 99 Designs, https://99designs.com/blog/trends/packaging-design-trends-2019/ (accessed Oct. 9, 2019).
4. Mordor Intelligence, “Packaging Coatings Market—Growth, Trends, and Forecast (2019–2024),” Market Report Summary, https://www.mordorintelligence.com/industry-reports/packaging-coatings-market (accessed Oct. 10, 2019).
5. Allied Market Research, “Packaging Coatings Market by Type (Epoxy Thermoset, Urethane, UV-Curable, BPA Free, and Soft Touch UV-Curable & Urethane), Substrate (Metal, Rigid Plastic, Glass, Liquid Cartons, Paper-based Containers, Flexible Packaging, and Others), Application (Food Cans, Beverage Cans, Caps & Closures, Aerosols & Tubes, Industrial Packaging, Promotional Packaging, and Specialty Packaging), and End User (Food & Beverages, Cosmetics, Pharmaceuticals, Consumer Electronics, and Automotive Components)—Global Opportunity Analysis and Industry Forecast, 2017–2023,” Market Report Summary, July 2017, https://www.alliedmarketresearch.com/packaging-coatings-market (accessed Oct. 10, 2019).
6. LEONHARD KURZ Stiftung & Co. KG, “Packaging as an Expression of Lifestyle,” Sept. 9, 2019, https://www.pressebox.de/pressemitteilung/leonhard-kurz-stiftung-co-kg/Packaging-as-an-expression-of-lifestyle/boxid/972528 (accessed Oct. 10, 2019).
7. McTigue, Pierce, L., “Metallized Film Transfers to Paperboard to Create Premium Packages,” Packaging Digest, Sept. 16, 2016, https://www.packagingdigest.com/
   foils/metallized-film-transfers-to-paperboard-to-create-premium-packages-2016-09-16 (accessed Oct. 10, 2019).
8. Diamond Packaging, “Environmentally-Friendly Metallic Coatings,” https://www.diamondpackaging.com/expertise/printing-effects/metallic-coatings (accessed Oct. 14, 2019).
9. Diamond Packaging, “Diamond Packaging Wins Four Awards in 2019 Excellence Awards Competition,” Sept. 12, 2019, https://www.diamondpackaging.com/Diamond-Packaging-Wins-Four-Awards-in-2019-Excellence-Awards-Competition (accessed Oct. 10, 2019).

CoatingsTech | Vol. 16, No. 11 | November/December 2019

1. Design out waste and pollution;
2. Keep products and materials in use;
3. Regenerate natural systems.

Consumers increasingly believe that companies should address environmental issues, especially as they relate to the proper disposal of plastics. As the Ocean Conservancy reports (www.oceanconservancy.org/
trash-free-seas/plastics-in-the-ocean), at least eight million metric tons of plastic end up in the ocean every year. This is the equivalent of dumping one garbage truck every minute into the ocean. At that rate, by 2050, there would be more weight in garbage than fish! Obviously, this is not a sustainable practice if we care about our planet. Retailers are responding by setting their own sustainability goals. For example, Walmart wants to achieve 100% recyclable, reusable, or compostable packaging for private brands by 2025. Target is working with its suppliers to change how they produce, use, and reuse plastic packaging, and PepsiCo is working towards 100% recyclable, compostable, or bio-degradable packaging by 2025. In addition, national and regional governments in the United States and Europe are mandating sustainable solutions through laws and ordinances to reduce plastic waste.

Packaging material suppliers are working on innovative approaches to increase their participation in the circular economy. Increasingly, raw materials used to produce plastics are bio-renewable and compostable. Even university researchers are heeding the call by submitting grant proposals focused on using carbohydrate-based chemicals to produce plastics. As this chemistry becomes commercially available, packaging suppliers will offer more biobased options for the market. In the meantime, suppliers are lightweighting plastic containers by removing plastic from bottles and using unique shapes and forms to add strength where needed. They are utilizing sophisticated software tools to redesign packaging to increase stack height to ship more freight per truckload. Container suppliers are also adding more post-consumer recycled materials to their bottles. Compostable smart adhesives are beginning to emerge for use on paper stock, plastics, and fibers to ensure a good quality certified compost. In short, packaging suppliers are working through the entire value chain to support the circular economy.

Packaging innovation in the paint and coatings industry began in 1877 when Sherwin-Williams patented the resealable paint can. Although the paint can is recyclable, improvements to product packaging can also increase recycling efforts. This can be done by designing more efficient pallet patterns, using less plastic shrink wrap, eliminating secondary overwraps, and reducing cardboard usage. Similar to the packaging industry, the coatings industry can participate in the circular economy through more effective use of materials throughout its entire value chain.

Dr. Victoria Scarborough is owner and principle advisor at Materia Prima Ventures; (vscarborough@matprimeve.com)

CoatingsTech | Vol. 16, No. 11 | November/December 2019

Consumer and regulatory pressure to replace bisphenol-A (BPA)-based materials in food contact metal packaging coatings has increased in recent years. Regardless of the controversy around BPA, consumers expect canned foods to be free of substances perceived to have negative health impacts while maintaining current shelf life and flavor characteristics. To address the market needs, formulators must innovate to deliver BPA-non-intent (BPA-NI) solutions that can meet or exceed the performance of BPA-based materials. This presents a challenge with regard to improving the resistance to food sterilization and stability during pack testing, and simultaneously balancing mechanical performance that allows the BPA-NI coating to withstand the aggressive canning process.

One response to these technical challenges has been the development of BPA-NI polyester resin technology through innovation on a monomer basis. This monomer innovation provides protective performance attributes such as resistance to corrosion and chemical attack, while enabling flexibility and adhesion through innovative resin and formulation design. Fundamental techniques such as electrochemical impedance spectroscopy (EIS) and cathodic disbonding were employed in combination with industrial fitness-for-use evaluations to demonstrate the improved protective barrier properties of novel non-BPA resins in formulated coatings. In addition, hydrophobicity and interfacial properties were studied to understand the impact of resin structure on coating performance from both experimental and computational perspectives. Applying this suite of methods and analysis builds strong structure-property correlations as part of a resin development strategy for novel non-BPA resins in metal packaging coating applications.

INTRODUCTION

Bisphenol-A (BPA) is a chemical commonly used in food contact plastics and coatings applications such as the BPA-epoxy-based linings of metal cans containing food or beverages. In recent years, the use of BPA in food contact applications has come under scrutiny. The 2003–2004 National Health and Nutrition Examination Survey (NHANES III) conducted by the Centers for Disease Control and Prevention (CDC) found detectable levels of BPA in 93% of 2517 urine samples from people six years and older.¹ In 2008, the National Toxicology Program of National Institute of Health (NIH) determined that BPA may pose risks to human development, raising concerns for early puberty, prostate effects, breast cancer, and behavioral impacts from early-life exposures.² Due to the potential health concerns, France has banned the use of BPA in all packaging, containers, and utensils intended to come into direct contact with food since 2015.³

With increasing pressure from food brands, formulators and can makers are actively looking for alternative solutions that can meet or exceed the performance of BPA-based coatings. From a technical standpoint, it is challenging to find the right alternatives due to the rigorous performance requirements for the coatings as well as the low price of BPA-epoxy resins. For example, the coating must be able to endure high temperatures, high pressure food sterilization, and long-time direct contact while exposed to the food materials, which include hydrolytic and corrosive environments such as low pH, acids, sulfur, and salt. Adhesion of the coating to the metal can is also crucial for both preventing corrosion and withstanding the can forming process. To respond to the technical challenges, coating scientists and chemists must innovate to develop new resin technologies.

Among all the new resin technologies today, polyesters with a balance of key performance attributes have emerged as one of the most promising alternative solutions. For polyester resins in this application, it should be noted that enabling high glass transition temperature (T_g) in combination with good mechanical properties, such as flexibility and toughness, is critical to the final film performance. These considerations are often applied when selecting monomers for resin design. Therefore, several qualified specialty glycol monomers such as 1, 4–cyclohexanedimethanol (CHDM), isosorbide, tricyclodecane dimethanol (TCDDM), and 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD) have received broad attention as building blocks. TMCD also demonstrated superior hydrolytic stability to other specialty monomers in a degradation kinetics study based on model compounds (Figure 1). Through previous work, polyesters containing TMCD are also known to demonstrate a variety of excellent properties such as good temperature resistance, toughness, chemical resistance, and hydrolytic stability. They have been successfully used in BPA-free specialty plastics applications such as durable water bottles.^4-6 Applying the monomer innovation to resin development, TMCD-based resin systems have shown attractive performance attributes such as resistance to corrosion and chemical attack, while enabling flexibility and adhesion through innovative resin and formulation design.

To better understand the structure–property relationships of polyester resins, a series of fundamental methodologies including electrochemical impedance spectroscopies (EIS) and cathodic disbonding tests were developed to study barrier properties, interfaces, and adhesion of metal packaging coatings. EIS is a widely used corrosion evaluation tool based on an electrical analogue of corrosion processes. It uses simple electrical circuits typically comprising of resistive and capacitive elements. For polymer coated metal systems, the EIS test is sensitive to the electrochemical changes at metallic interfaces as well as the resistive properties of organic coatings in a variety of aggressive or corrosive environments. In the past decades, both academia and industry have been using this technique to characterize coating barrier properties including diffusivity and polarity,⁷ to characterize water uptake,⁸ to detect formation of blisters and pinholes, and to recognize the loss of adhesion.⁹ The cathodic disbonding test is also an effective electrochemical technique to evaluate adhesion performance. Cathodic disbonding is an important delamination mechanism associated with interfacial corrosion of organic coatings on metal substrates that lead to an exposure of bare metal to the aqueous food environment.¹⁰

In this study, the electrochemical techniques have been employed in combination with industrial fitness-for-use (FFU) evaluations to better understand the barrier properties, interface, and adhesion of metal packaging coatings. This work provides fundamental insights on the relative performance of polyester resins in a variety of formulations where improved barrier properties and enhanced coating-
metal interfacial strength is observed with the TMCD-based resins.

Experimental Procedures

Materials and Sample Preparation

In this study, BPA-NI Resin A and Resin B were TMCD-based polyester resins developed and produced by Eastman Chemical Company, while Control A and Control B are the benchmark resins based on commercial BPA-NI polyesters. All of the polyester resins were classified by molecular weight: both Resin A and Control A (Category A) have absolute-number average molecular (Mn) greater than 10,000 g/mol while Resin B and Control B (Category B) have absolute-Mn in the range of 4,000–7,000 g/mol. Formulation components in this study were chosen for the purpose of representing BPA-NI interior lacquers. All coatings based on these polyester resins were formulated and applied in the Eastman Chemical coating development laboratories. The details of resins and formulation components are given in Table 1 and Table 2.

Prior to formulating, Resin A and Control A were reduced with Aromatic 100 to achieve 50% solids; Resin B was reduced with Aromatic 100 to 55% solids; Fascat 9102 catalyst was diluted to 10% of the original supplied concentration with Aromatic 100; likewise, Nacure 5925 catalyst was also diluted to 20% of the original supplied concentration with Aromatic 100. The formulation details of gold benzoguanamine phenolic formulation, clear PU formulation, and white PU formulation are provided in Table 3 and Table 4, respectively.

Electro tin plate (ETP) substrate panels were described by the vendor, Lakeside Metals Inc. as 0.25 # Bright T-1 0.009–0.010 x 4.0 x 12.0 in. All formulated paints were drawn down onto 4.0 x 12.0 in. (10.16 cm x 30.48 cm) tinplates (provided by Lakeside Materials Inc.) using an appropriate wire wound rod targeting a dry film thickness (DFT) of 0.4 mils (10.2 μm) for clear and gold formulations, or 0.6 mils (15.2 μm) for white formulations. Following a 15 min room temperature flash-off at constant temperature and humidity conditions (73°F ± 2, 50% RH ± 5), panels were baked at 200°C for 12 min in an air oven.

Testing and Evaluations

Electrochemical Impedance Spectroscopy (EIS)

A Gamry Instrument “Reference 600” Potentiostat, equipped with Gamry framework and Echem Analyst, was used in electrochemical impedance measurements. The flat coated panels (3.0 x 4.0 in.) were masked by a Gamry designated masking tape with a hollow circle at the center. A cylindrical glass cell with a rubber O-ring attached to the grooved bottom of the cylindrical cell and a clamp fixture was used to hold the samples. A nickel electrode and a graphite electrode were used as reference and auxiliary electrodes, respectively. To simulate food, several food simulants were used as the electrolyte and corrosive environments. The potential was applied in a range of ± 5 mV from open circuit potential and the frequency was varied from 10⁵ to 10^-1 Hz.

Cathodic Disbonding Test

The cathodic disbonding test is an internally developed coating disbonding test modified from a number of standard test methods.¹¹ It helps to differentiate coatings on the basis of their susceptibility to adhesion failure in the presence of a defect. The scheme of the cathodic disbonding experimental setup and the lab setup are shown in Figure 2a and 2b. The flat coated panels (3.0 x 4.0 in.) were masked by a Gamry designated masking tape with a hollow circle at the center. In the unmasked area at the center, the coatings were scribed with an “X” mark (as shown in Figure 2b using a knife. A cylindrical glass cell with a rubber O-ring attached to the grooved bottom of it and a clamp fixture was used to hold the samples. A coated panel with X scribe (cathode) was connected with the negative electrode of the voltage supply while a graphite (anode) was connected with the positive electrode of a direct current (DC) voltage supplier. Between cathode and anode, the cylindrical glass cell was filled with electrolyte made by 3.5 wt% NaCl solution with 150 ppm Manoxol OT solution to ensure both parallel electrodes were submerged in the electrolyte solution. The DC voltage applied between the parallel cathode and anode was 5 volts (V) for 60 sec. After this electrochemical process was completed, the sample was rinsed with DI water and followed by air drying.

Under the applied DC electric field, the hydrogen bubbles were initially generated at the X scribe and then propagated to the coating-tinplate interface following the cathode reaction as shown in equation (1). In addition to the hydrogen bubbles generated at the metal surface lifting up the coating from the tinplate, the generation of ����¯ also weakens the coating–tinplate adhesion, resulting in coating delamination.

(1)

Food Simulants and Retort

The recipes of food simulants used in this study are shown below:

(i) Lactic acid–Acetic acid-Salt (LAS) food simulant: 1 wt% lactic acid, 1 wt% acetic acid, and 1 wt% NaCl in 97 wt% DI water;

(ii) 3% Acetic acid food simulant: 3% acetic acid in 97% DI water; and

(iii)�� 2% Lactic acid food simulant: 2% lactic acid in 98% DI water.

A coupon measuring 2.5 x 4.0 in. was cut from the coated panel for retort testing. The coupons were scribed by a knife with an X mark on the bottom-half of the panel and then placed in 250 mL closed-cap glass jars half filled with 3% acetic acid food simulant where half the coupon is out of the food simulant and the other half is submerged in food simulant. The retort test was conducted on a coated panel with an X scribe at 131°C for 60 min in an autoclave.

Computational Modeling

Calculated LogP values which estimate the value of the octanol-water partitioning coefficient were determined by using ACD/Labs Chemsketch software. The calculated logP values were also validated by ChemBioDraw Ultra 13.0, Molinspiration and Accelrys Materials Studio 5.5. Molecular structures of trimer model compounds represented as glycol1-terephthalate-glycol2 (G1-T-G2) with hydroxyl end groups were used in the experiments and calculations.¹²

Solubility parameters were calculated for 30x30x30 ų amorphous cells with 1 g/cm³ cell density for 3 terephthalate and glycol units that were constructed by using Accelrys Materials Studio 5.5 software. PCFF forcefield was used to build and minimize cells and calculate cohesive energies, which led to the calculation of cohesive energy densities followed by calculation of solubility parameters.¹³ Average solubility parameters were calculated for 500 different amorphous cells followed by 5000 steps of molecular mechanics geometry optimization with Ewald Summation method¹⁴ and 12.5 Å vdW cut-off distance for each composition.

Results and Discussion

EIS and Corrosion Mechanisms

EIS is a powerful technique to understand corrosion mechanisms and barrier properties of coatings by providing an accurate in-situ measurement for characterizing polymer-coated metals and changes in coating performance during exposure in corrosive environments. The term “impedance” refers to the frequency-dependent resistance to current flow of circuit elements such as resistors, capacitors, inductors, etc. In practice, the corrosion resistance is integrated from all types of resistance involved and can be approximately estimated by using |Z(w®0)|, the impedance value at low frequencies. In this study, corrosion resistance is identified by the impedance value at 0.1 Hz. However, to describe the corrosion process quantitatively, Bode plots are fitted using electrical equivalent circuits corresponding to the appropriate stage of corrosion.

Stage Zero: Dry Film

Like a dielectric layer, before immersion in an electrolyte solution a dry polymer film often plays a role like a pure capacitor as shown in Figure 3.�� When the film responds to the frequency, the overall impedance can be presented as shown in equation (2):

(2) therein ω = 2πf

where j is the complex number (  j ²=-1); R_sis the solution resistance which is the resistance of the food simulant; C_cis the coating capacitance; w is the angular frequency; and_�� f _����is the frequency. The Bode plot for Stage zero is simply demonstrated in Figure 3.

��

Stage I: Food Simulant Absorption

Before the corrosion process starts, the dry coating must absorb the electrolyte until the polymer film gets fully saturated by the electrolyte as shown in Figure 4. The electrolyte is the food simulant in this case. In Stage I, the coating is no longer a pure capacitance due to the presence of water and ions. Instead, the combination of the capacitance component and the resistance component of the coating contribute to the overall impedance. With higher water and ion uptake, the value of the capacitance component increases while the value of the resistance component decreases. They change independently as a function of time before the film gets fully saturated by the food simulant. In general, the diffusion kinetics are highly dependent on the physical properties of the polymer film such as crosslinking density. When the film responds to the frequency, the overall impedance can be presented as shown in equation (3):

(3) where j is the complex number (  j ²=-1); R_sis the solution resistance which is the resistance of the food simulant; C_c�� is the coating capacitance; w is the frequency; and R_c��is the coating resistance. As shown in Figure 4, a single time-constant can be indicated by a frequency–independent impedance plateau at low frequency followed by a frequency–dependent impedance plot in the medium frequency region. The increase of C_cas a function of exposure can be used to determine the diffusion coefficient as well as the food simulant uptake.

Stage II: Corrosion Initiation

After the film gets fully saturated, water and ions in the food simulant start to be delivered to the coating-tinplate interface and initiate the corrosion process. In this process, the redox reactions between the metal and food simulant (H⁺��either from food simulant or from hydrolyzed water) lead to corrosion. At this stage, the newly formed oxidized layer with semi-dielectric character exists under the polymer film, playing a role as the combination of a double layer capacitance and a charge transfer resistance, as presented in equation (4):

(4)
where R_s��is the solution resistance which is the resistance of the food simulant; C_c�� is the coating capacitance; w is the angular frequency; C_dl is the double layer capacitance; R_ct�� is the charge transfer resistance; and R_c�� is the coating resistance.

Stage III ~ IV: Pore/breakthrough Formation and Delamination

A process that depends on diffusion of reactants toward or away from the surface has a particular low-frequency character. The impedance with this characteristic is usually described as “Warburg” impedance (as shown in Figure 7), which indicates the breakthrough of a barrier and localized disbonding. At this stage, the overall impedance can be presented as shown in equation (4) (pore/breakthrough formation) and equation (5), (delamination), respectively:

(5)

(6) where R_s�� is the solution resistance which is the resistance of the food simulant; C_c�� is the coating capacitance;�� w is the frequency; C_dl�� is the double layer capacitance; R_ct�� is the charge transfer resistance; R_po�� is the pore resistance; k is the redox reaction rate; and D is the diffusion coefficient at this stage. At Stage III ~ IV, the barrier has been damaged locally, even though the defects might not be able to be detected by the naked eye. In this case, R_ct�� representing pore resistance is used to describe the concept of “coating resistance” because this value now is highly dependent on the number of pores in the film or capillary channels resulting from the formation of ionically conducting paths through the coating, instead of the intrinsic physical properties of the coating barrier.

To demonstrate the progression of coating failure as a function of LAS food simulant exposure time, Control B was chosen to formulate a clear coating, then subjected to the EIS test in LAS food simulant. As shown in Figure 7, Control B in a clear PU formulation starts to show Stage I corrosion (one time-constant) after 4 min of exposure, indicating that the food simulant absorption has begun. After 15 min, the characteristics of Stage II corrosion (e.g., two time-constants) have been observed, and this is followed by the Bode plot with Warburg character (Stage III ~ IV) after 5 h of exposure in LAS food simulant.

To compare BPA-NI polyester resins in clear PU formulations, Resin A and commercial Control A were selected to formulate the paints followed by appropriate baking. A comparison of the EIS spectrum of Resin A and Control A in these two coatings in Figure 8a shows similar corrosion resistance and barrier properties after 5 h of exposure. Resin A-based clear PU shows a corrosion resistance of 53.7 mega Ohms, which is slightly higher than that of the Control A-based coating (39.8 mega Ohms). Both coatings demonstrate excellent barrier properties and almost two orders of magnitude improvement on corrosion resistance after 5 h of exposure as compared to the low T_g polyester control in the same formulation (0.69 mega Ohms, as shown in Figure 7).

In Figure 8, Resin A was formulated in both clear PU and gold benzoguanamine phenolic formulations. Through the comparison of EIS data after 5 h of exposure (Stage I corrosion), it has been found that the gold benzoguanamine phenolic formulation exhibits significantly better corrosion resistance (170 mega Ohms) as compared to the corrosion resistance of clear PU formulation (53.7 mega Ohms) at the same dry film thickness. The authors believe that the presence of triazine and aromatic structures in benzoguanamine-formaldehyde and phenolic-formaldehyde crosslinkers may provide better hydrophobicity and barrier properties as compared to IPDI trimer-based PU structures.

Time-based Corrosion Resistance

In many cases, corrosion is an electrochemical process that requires multiple steps, and each step is associated with a different mechanism and kinetics. The estimation or prediction of long-term corrosion performance, such as the corrosion observed in a pack test, often relies on continuous time-based corrosion observations over a relatively long interval of testing instead of a single data point at a short exposure time. As part of a resin design strategy, a continuous in-situ EIS test has been conducted on white PU coatings based on four BPA-NI polyester resins including Control A (high-T_g high Mn polyester), Control B (low-T_g low Mn polyester), Resin A (high-T_g high Mn polymer), and Resin B (med-T_g low Mn polyester) in 2% lactic acid food simulant. The EIS test in one testing period was set up to continuously run for 48 h. Ten hours of relaxation time was given prior to the next testing period. Figure 9a and 9b demonstrate a decay of corrosion resistance as a function of exposure time for each sample during the 1st and 2nd 48-h test intervals. After a total of 106 h of exposure, all the white PU samples still remain in the Stage I corrosion process. During the 2nd 48-h test period, the decay of corrosion resistance for each sample becomes significantly slower, followed by a plateau of impedance at longer times. The two high Mn polyesters seem to be separated from the other two low Mn polyesters after the 2nd 48-h interval, where the high Mn polyester-based coatings show higher values of corrosion resistance. By the end of the test, the comparison of all four white PU coatings shows a ranking on corrosion resistance: Resin A > Control A > Resin B > Control B in white PU formulations (Figure 10). Since all of the samples are still in Stage I corrosion, the decay kinetics indicate the diffusion coefficient while the films absorb the food simulant, whereas the plateau level reflects the solubility of the electrolyte solution in the coating film. Therefore, higher corrosion resistance correlates with higher hydrophobicity or lower solubility in 2% lactic acid food simulant in this case. In Figure 11, LogP and Hildebrand solubility parameters were calculated for glycol (G1)-terephthalic acid (T)-glycol (G2) trimer model compounds through computational modeling. In general, a higher LogP value or lower Hildebrand solubility parameter indicates better hydrophobicity of a polymer. With the same molecular weight (trimers) and acid composition (terephthalic acid) in the model compounds, it has been hypothesized that the glycols with higher LogP values or lower Hildebrand solubility parameter lead to a lower concentration of the aqueous food simulant in the bulk of the film, thus reducing the rate of corrosion.¹² Considering the molecular weight contributions in the resins, the comparison between a TMCD-based resin and a control polyester resin at a similar molecular weight and T_g range (Resin A vs Control A and Resin B vs Control B) indicates that the improvement of corrosion resistance in coatings formulated with Resin A and Resin B is primarily due to the hydrophobicity contributions from TMCD (Figure 11).

Interface and Adhesion

To better understand what happened during late stage corrosion, the EIS comparison between Resin A- and Control A-based clear PU coatings (shown in Figure 8a) was extended to longer exposure times. After 12 days in LAS food simulant, it has been observed that both Resin A- and Control A-based clear PU coatings are in Stage III ~ IV corrosion with clear Warburg impedance in the Bode plots (Figure 12). Although the pores and capillary channels that provide conducting paths (e.g., Warburg impedance) through a coating have already formed in both Control A- and Resin A-based clear PU coatings, the interface, with its excellent double-layer capacitance and charge transfer resistance, can still provide excellent corrosion prevention.

In Figure 12, Resin A shows a higher plateau in the middle—frequency range, which indicates the value of charge transfer resistance corresponding to equation (6). When a redox reaction occurs, electrons enter the metal and metal ions diffuse into the electrolyte. Thus, charge is being transferred. The current density of the charge transfer process at the applied potential follows Faradays Law [equation (7)]:

(7) where i_o��is exchange current density;�� C_o is the concentration of oxidant at the electrode surface; C_o*����is the concentration of oxidant in the bulk; C_R�� is the concentration of reductant at the electrode surface; C_R*������is the concentration of reductant in the bulk; h is the overpotential (difference between applied potential and open circuits potential, OCP); F is Faradays constant; T is absolute temperature; R is the ideal gas constant; a is the reaction order; and n is the number of electrons involved. When the overpotential is very small (± 5 mV vs OCP in this experiment) and the electrochemical system is at equilibrium (C_o�� =�� C_o*���� and�� C_{R����}=  C_R*����), charge transfer resistance can be represented, as shown in equation (8):

(8) With the same experimental conditions, the difference between the two clear PU coatings on charge transfer resistance is believed to be due to the number of electrons involved, which correlates to the percentage of area without polymeric barrier due to the loss of adhesion. Several studies^15-17 for different applications have found that charge transfer resistance is correlated to adhesion experimentally. For the comparison shown in Figure 12, the authors believe that the Resin A-based clear PU with significantly higher charge transfer resistance indicates that Resin A provides a clear PU coating with a stronger coating-tinplate interface and better adhesion as compared to Control A.

Besides the EIS tests, gloss loss after a 3% acetic acid retort test was measured as a way to evaluate the barrier performance of the coatings. As the retort test was conducted on a coated panel at 131°C for 60 min in an autoclave, the presence of high temperature and pressure has significantly accelerated the corrosion formation at the coating-tinplate interface, causing the development of “blisters” as the result of under-film corrosion. This process often leads to gloss loss due to (i) the changes in surface and interface smoothness caused by under-film corrosion; (ii) rust stains the coating surface caused by broken “blisters”; and (iii) a change in coating refractive index caused by water retention. Similar to what occurs during the late stage corrosion process, the corrosion development and coating delamination at X scribes could be much faster than that in other areas because the barrier layer has been broken through manually. In this scenario, adhesion performance can be evaluated based on a visual observation. As shown in Figure 13a, no significant difference can be observed between Resin A- and Control A-based clear PU coatings from gloss reduction, indicating that Resin A provides similar barrier properties as Control A in the clear PU formulation. This retort result is consistent with the insights obtained from EIS data (Figure 8a).

In Figure 13b, when the aggressive cathodic disbonding test was applied under 5V on X scribed panels, the Control A-based clear PU coating with a large disbonded area (less desirable) is differentiated from the Resin A-based coating with very little disbonded area (more desirable). The disbonded area was identified by a high-resolution camera and the areas of bare tinplate were quantified by pixel-counting image analysis software (Figure 14). In this case, the disbonded area, in percentage of the total area, of Control A-based clear PU coating was determined as approximately 52%, while only a minor disbonded area (< 5% disbonded area) was found for Resin A-based clear PU coating. In this case, a smaller disbonded area indicates better adhesion or interfacial strength. The cathodic disbonding result in Figure 13b is consistent with the EIS results (Figure 12) regarding adhesion performance. The combination of EIS and cathodic disbonding results indicates that Resin A provides a stronger interface to tinplate as compared to Control A. Considering the molecular weight and T_g effects, the comparison between TMCD-based Resin A and Control A polyester resin at a similar molecular weight and T_g range indicates that the improvement of adhesion in coatings containing Resin A could be due to the hydrophobicity contributions from TMCD.

CONCLUSIONS

In this study, fundamental methodologies based on EIS and cathodic disbonding tests were successfully developed and applied to understand the barrier properties, interfaces, and adhesion of BPA-NI metal packaging coatings. Corresponding to EIS Bode plot characteristics, a series of equivalent circuit models indicating the stages of corrosion process were developed to demonstrate the degradation mechanisms including (i) food simulant absorption, (ii) corrosion initiation, and (iii) pore/breakthrough formation. These circuit models also enable quantitative analysis of coating performance to design resins that are in tune with coating properties in metal packaging applications.

A combination of electrochemical techniques and industrially relevant FFU evaluations were conducted to differentiate the corrosion resistance of TMCD containing vs non-TMCD containing clear and white PU coatings. In the early stage corrosion process, Resin A exhibited a slightly improved barrier performance in the coatings as compared to Control A due to the low permeability after being fully saturated by the food simulants. This is believed to be due to the hydrophobicity contribution from TMCD in polyester Resin A. A similar conclusion has been obtained when comparing the TMCD-containing Resin B to the Control B resin in both white and clear PU coatings.

In addition to PU formulations, TMCD containing Resin A and Control A resin were also formulated with benzoguanamines and phenolic crosslinkers to evaluate these resins in gold lacquer applications. A comparable barrier performance was observed during the early stage corrosion processes in a clear PU coating with Resin A in and Control A. However, the comparison between Resin A in the clear PU formulation and gold benzoguanamine phenolic formulations indicates that the gold formulation is significantly better on barrier performance with the same resin and film thickness.

EIS results for a late-stage corrosion process based on Resin A- and Control A-based clear PU coatings are consistent with the results obtained from cathodic disbonding tests. Analysis of these results demonstrates that the coating made with TMCD-containing Resin A provides a significantly improved coating-tinplate interface that leads to superior adhesion performance as compared to Control A resin in a clear PU formulation.

ACKNOWLEDGMENT

Technical expertise provided by Damiano Beccaria, Sandra Case, Peter Chapman, Alain Cagnard, Samuel Puaud, John Maddox and Carlos Carvajal from Eastman Chemical Company is gratefully acknowledged. The Computational Modeling results presented in this paper were generated in collaboration with Erol Yildirim, Harold Freeman, and Melissa Pasquinelli, Fiber and Polymer Science Program, North Carolina State University. The contribution made by Dr. Yildirim for this paper is highly appreciated. The authors also appreciate the technical support from Dr. Li-piin Sung through the Polymer Surface Interface Consortium, Engineering Laboratory, National Institute of Standards and Technology.

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*This paper received the Best Paper Award at the 2019 CoatingsTech Conference, sponsored by the American Coatings Association, April 8–10, in Cleveland, OH.

CoatingsTech | Vol. 16, No. 6 | June 2019

The global market for flexible packaging is, according to market research firm Grand View Research, expanding at a compound annual growth rate (CAGR) of nearly 4.7% from a value of $221.82 billion in 2016. Flexible packaging is used most widely in the food and beverage industries, but also has applications in the pharmaceutical and medical, cosmetic and personal care, pet food, consumer goods, and industrial sectors. Coatings, including acrylics, epoxies, and polyurethanes, among others, are used to enhance the appearance and/or functionality of flexible packaging solutions. The global market for flexible plastic packaging coatings was valued by Transparency Market Research at $1.53 billion in 2017 and is forecast to expand at a CAGR of 4.0% from 2018 to 2026.

Flexible packaging offers brands a lightweight and more durable option through the shipping process and minimizes costs associated with production, returns, and shipping, according to Arica Drake, global marketing manager, Flexible Packaging at Michelman. “As e-commerce continues to grow, there is no denying the importance of safe and effective packaging. E-commerce brands are leveraging flexible packaging by using a wide range of material options, shipping more product with less weight, and protecting products from exposure to oxygen and moisture,” she says.

In addition, flexible packaging is being used to enhance the consumer experience. “Through the use of different haptics coatings, brand owners can use packaging to not only protect and safeguard their products, but also to communicate their brand messages,” Drake observes. These coatings range from matte finishes to different textures including soft touch, velvet feel, sandy or course feel, and various combinations. As such, haptics coatings can provide packaging differentiation with different visuals and textures and be utilized to convey messages that denote premium, natural, or “good for you” products, she notes.

Through the use of different haptics coatings, brand owners can use packaging to not only protect and safeguard their products, but also to communicate their brand messages.

The key challenge with flexible packaging is its lack of recyclability, at least for current multi-layer technologies. “Currently,” comments Drake, “recycling flexible packaging is difficult due to the multiple layers of different materials used to achieve packaging performance.” Most new regulatory developments stem from the desire to improve the sustainability of packaging. Drake points to many new material-use bans, and in particular those targeting single-use plastics. Other initiatives require the use of recycled content in flexible packaging. While some of these initiatives are official bans or requirements, others are goals for future years, according to Drake. She notes that many companies are signing on to the Ellen MacArthur Foundation’s New Plastics Economy Global Commitment, which has targets including:

• Elimination of problematic or unnecessary plastic packaging and movement away from single-use to reusable packaging models;
• Innovation to ensure 100% of plastic packaging can be easily and safely reused, recycled, or composted by 2025; and
• Circulation of the plastic that has already produced throughout the economy by significantly increasing the amounts of plastics reused or recycled and made into new packaging or other products.

As flexible packaging manufacturers seek solutions for improving sustainability, they are frequently turning to coatings. Coatings are being developed to replace some of the layers of polymers traditionally used in flexible packaging, providing needed functionality while having minimal impact on recyclability, according to Drake. For instance, she notes that a polyester film with an applied coating can go through the polyester recycle-stream successfully, while a polyester film extruded to a polyethylene layer cannot.

Performance requirements vary depending on the product being packaged. Food and beverage coatings should be compliant with U.S. FDA regulations (or similar organizations’ regulations in other countries), while all coatings used in the medical segment have requirements for sterilization processes, for instance. Within the food sector, different products often have different requirements. Packaging for a fresh meat product will have different functionality needs than packaging for a confectionary product, according to Drake. “Fresh meat generally needs coatings that provide an oxygen barrier to prevent bacteria growth, a moisture barrier to keep the meat moist in the package, and excellent clarity to allow the consumer to inspect the meat before purchasing. A confectionary package might not need a strong oxygen barrier, but may need a moisture barrier to prevent the product from becoming soggy. It may also require a coating that can be sealed at low temperatures, because many confectionery products contain chocolate, which is very sensitive to heat,” she explains.

Coatings are being developed to replace some of the layers of polymers traditionally used in flexible packaging, providing needed functionality while having minimal impact on recyclability.

New flexible packaging solutions with mono-material structures that are recyclable are being developed by flexible packaging producers. Coatings are playing a vital role in these structures by adding functionality that might be missing due to the elimination of other polymer layers. “A full polyolefin pouch, for instance, is recyclable with other polyolefin materials. However, while polyolefin materials provide a good moisture barrier, they are considered very breathable. For oxygen-sensitive products, therefore, an oxygen barrier coating can be applied to the structure to add that functionality without affecting the recyclability,” Drake observes. She adds that polyolefin materials are not very heat-resistant during package production, creating the possibility of material distortion, which can negatively impact appearance. “Here again,” she says, “a coating can be used to give the structure heat resistance while still maintaining recyclability.” These types of developments are available today, but Drake believes additional improvements in technology will be introduced over the coming years so that sustainable packaging will be able to meet or exceed the performance and economic needs of current packaging.

Michelman offers a wide range of water-based coatings designed specifically for the flexible packaging market. These coatings include primers, barrier coatings, overprint varnishes, and heat-seal coatings. Recently, the company introduced a clear, water-based, high-oxygen-barrier coating designed for use on plastic packaging films. According to Drake, the coating is very durable, can withstand flex cracking, and can be combined with metallization and other barrier coating processes for protective and enhanced oxygen barrier performance. Michelman is also working on a portfolio of haptics coatings that will be launched in 2019, including a variety of matte and gloss finishes, soft touch and sandy coarse feels, and an anti-skid coating.

CoatingsTech | Vol. 16, No. 3 | March 2019

The antimicrobial properties of two disparate bio-based coating additives were evaluated in a polyvinyl alcohol (PVA) food packaging coating for antimicrobial activity. Chitosan, a shrimp and crustacean shell derived polysaccharide, and an antimicrobial peptide were evaluated in a dissolvable food package coating for reductions in microbial growth after contacting agar patties serving as food simulants. Where the antimicrobial components of such packaging coatings are chosen to be generally recognized as safe by worldwide regulatory agencies, migration from the packaging into headspaces and food-contact surfaces can provide enhanced efficacy against foodborne pathogens, including viruses. The techniques and coatings presented in this article suggest that dramatic improvements in food safety can be achieved using coatings containing non-toxic bio-based biocides.

Introduction

Food packaging is an asset that can preserve foods going to market and extend shelf-life, but it can also become a liability when the packaged food itself is contaminated or becomes so during the packaging process. The economic damage to the food industry of reduced shelf-life for packaged foods is great, and contamination of packaged food is a major public health concern. There are several contamination points during food preparation and packaging and numerous examples of outbreaks of foodborne illness leading to the recall of goods.^1-3 Major incidences have occurred around the world over the decades (e.g., E. coli O157:H7 contamination from the United States Jack in the Box restaurant,⁴ E. coli O104:H4 spread from German sprouts,⁵ listeriosis throughout Europe in frozen corn,⁶ E. coli O157:H7 on Canadian pork,⁷ listeriosis from processed meat in South Africa⁸) and continue today. Table 1 highlights the diversity of products and pathogens associated with some of the most recent outbreaks in the United States.⁹ Even as recently as July 2018, there was a recall of packaged vegetable trays due to a multistate outbreak of parasitic cyclosporiasis in the United States.¹⁰

Such outbreaks have led not only to changes in guidelines and adoption of new regulations,^11-13 but also spurred interest in new technologies such as “smart” packaging.^14,15 Packaging coatings that can reduce such contamination while the food is traveling to its point of sale are long-sought goals of the food industry. Research for improved food packaging has generally focused on two areas: edible films that can be applied directly to food and are safe to eat,^16-19 and chemical or physical modifications to plastic packaging materials that are permanent and specifically do not leach onto or into the packaged food product.^20-22 In this work, we combined the best attributes of both research areas into one product by retaining the physical barrier properties afforded by plastic packaging film and gaining the effectiveness of dissolvable (but safe to eat) bio-based antimicrobial additives. Bio-based additives have the advantage of often having low toxicity to humans, and many have notifications with the Food and Drug Administration that they have been determined to be Generally Recognized as Safe (GRAS). Though not a prerequisite for development of an antimicrobial food contact coating in the present study, the selection of materials, whether polymeric coating components or bio-based additives, with GRAS notices previously filed was a consideration. Both polyvinyl alcohol and chitosan fall into this category and were chosen for this study.^23-26 Other considerations were the likely efficacy of the additive against microorganisms commonly associated with foodborne illness (i.e., bacteria like Escherichia coli), known general lack of toxicity, and biodegradability. Finally, as the numbers and types of foodborne pathogens are varied, consideration was given to bio-based biocides that were potentially capable of controlling not only bacteria, but also spores of Gram-positive species, fungi, algae, and viruses (ergo, the inclusion of antimicrobial peptides).

Two quantitative assays were developed to analyze effectiveness of the coatings using modern microbiological methods and statistical software. The first used clear-coated plastic disks through which bacterial colonies could be enumerated on the agar surface beneath. The second used agar “patties” serving as a food simulant in a vacuum-sealed food packaging system. The contaminated agar can be contacted on one or both sides with an antimicrobial coating and the microbial growth inhibition evaluated. Statistical evaluation was undertaken to detect antagonistic, additive, and/or synergistic relationships between chitosan and an antimicrobial peptide, AMP7, in the food contact coating.^27-29 The assays were successful in detecting antimicrobial activity against E. coli for both the bio-based additives analyzed, and the statistical methods used detected an antagonistic effect at most of the concentrations evaluated and only slightly antagonistic or additive effects at higher concentrations. These methods proved useful in screening the candidate bio-based additives presented here and are currently being used to evaluate other promising bio-based additives for incorporation into food packaging.

Materials and Methods

Reagents and Bacterial Strains

Polyvinyl alcohol (PVA) was obtained from Sigma-Aldrich (Cat# 348406, reported Mw 13,000-23,000, 98% hydrolyzed). Chitosan was obtained from bulksupplements.com. E. coli K12 was obtained from Presque Isle Cultures (Erie, PA), and the peptide AMP7 was obtained from Reactive Surfaces, Ltd. (Austin, TX). Isopropanol (91%) was purchased locally. All growth media used Difco Tryptic Soy Agar (TSA) or tryptic soy broth from Becton, Dickinson, and Co. (Sparks, MD). MacConkey, Eosin Methylene Blue (EMB), and Luria-Bertani (LB) agar were obtained from Carolina Biological Supply Co. (Burlington, NC). 4-Methylumbelliferyl-β-D-glucuronide dehydrate (MUG) was obtained from Fisher Scientific (Waltham, MA).

Preparation of Coated Films

Disks of 0.5-in. diameter were cut using a 40W CO2 laser (Glowforge®, Seattle, WA) from a 3-mil thick sheet of clear Dura-Lar polyester (Grafix, Maple Heights, OH) substrate. For the vacuum-sealed food simulant experiment, 8.5 cm diameter disks were hand-cut from Dura-Lar sheets, or from commercial substrates, including Opalen™ (Bemis, Parc de L’Alliance Braine L’Alleud, Belgium), a clear, PET film and Trayforma™ (Stora Enso, Stockholm, Sweden), a PET-coated paperboard. A 5% (w/w) PVA solution, 1% (w/w) chitosan in 2% (v/v) acetic acid solution, and 10% (w/w) AMP7 in 5% (w/w) PVA solution were prepared and mixed before application to create the final concentrations indicated in the following experiments. In each case, the bio-based additive levels reported are based on the percentage by weight in the final, dry coating. All Dura-Lar films were coated by applying a specific volume of the liquid coating directly to the film, so that the final film thickness was approximately 1 mil. The coated films were left to dry at room temperature overnight before being used in any of the antimicrobial tests.

Antimicrobial Coated Disk Treatment of E. coli Contaminated Agar Plates

Traditional zone of inhibition testing uses paper disks infused with the target active. The paper disks are incubated with microbes, and the zone of clearing seen around the disk (i.e., lack of microbial colony growth due to leaching of the active from the disk) is measured to indicate the effectiveness of the active. In our experiments, using the transparent disks with a clear, dissolvable coating allowed inspection of cell growth directly beneath the disk as well as any observable zone of inhibition (Figure 1). A cotton swab was dipped into a suspension of E. coli K12 (~5×106 CFUs/mL) and was spread over 15 cm diameter TSA plates (done in triplicate). After the plates had dried for approximately 15 min, the disks were placed, coated side down, on top of the E. coli layer. The plates were incubated at 30°C to 36°C overnight. Each disk was photographed using a dissecting microscope for magnification, and colonies were counted using ImageJ software from the National Institutes of Health (Bethesda, MD). The dose response of individual additives was evaluated using log-logistic regression model with the R package drc.³⁰ For experiments involving the combination of bio-based additives in coatings, the interaction between the two bioadditives (i.e., synergistic, additive, antagonistic) was evaluated using the zero interaction potency (ZIP) model with the R package synergyfinder.³¹

Preparation of Vacuum-Sealed Food Simulants

To mimic packaged food, agar patties were cast into petri dishes and then gently removed from the dishes once firm to serve as food-patty simulants. These patties were vacuum sealed with plastic film inserts containing mixtures of PVA, chitosan, and AMP7 as studied in the small disk assays (Figure 2). Several selective and differential agar media were evaluated for visualization of E. coli colonies. These included MacConkey agar, LB agar with MUG, and EMB agar. It was determined that MacConkey agar consistently produced clearly visible and easily observable E. coli colonies, and thus was primarily used. Each agar patty was placed in a vacuum bag, and an aliquot of diluted E. coli was spread over one surface so that approximately 200 CFUs were added (each test done in triplicate). Coated films sized to match the agar patties were placed, coating side facing the bacteria, on the agar patties, and uncoated films were used as controls. The vacuum seal bags were sealed using the “Low” vacuum setting and the default seal setting on a Harvest Keepers Commercial vacuum sealer. The vacuumed samples were incubated for 24 h at 30°C, and colonies were counted using ImageJ software. For experiments measuring the effect of AMP7 and chitosan combinations, the interaction between the two bioadditives (i.e., synergistic, additive, antagonistic) was evaluated using the R package synergyfinder, with the Bliss model being used to calculate predicted response because the number of combinations was low.

Experiments and Results

Clear Disk Antimicrobial Assay

The efficacy of the bio-based antimicrobials in food-safe coatings was assessed by placing the coated 0.5-in. diameter Dura-Lar disks, coating-side down, onto prepared lawns of E. coli (Figure 3). The disks were coated with PVA-based coatings dosed with AMP7 at concentrations from 5,000 [0.5% (w/w)] to 20,000 ppm [2% (w/w)], and with chitosan at concentrations from 10,400 [1.04% (w/w)] to 90,800 ppm [9.08% (w/w)], or combinations of these two additives.

The dose response, as determined by percent reduction in colony numbers compared to the PVA negative control, was determined for AMP7 and chitosan. The effective dose to kill 50% of the bacterial population (ED50) of AMP7 was around 4,500 ppm and 30,000 ppm for chitosan (Figures 4A and 4B). The responses of the bacteria to various combinations are displayed in the heatmap (Figure 4C), which shows the relative response as a color from red (highest percent growth inhibition) to green (lowest percent growth inhibition). To test whether antagonism or synergy exists between these two compounds, the responses from AMP7 and chitosan combinations were used to determine the synergy score using the ZIP method, which returns a score based on the deviation of the actual response from the expected response.³² These scores are visualized for each combination in a contour plot (Figure 4D), which suggests that the two antimicrobials generally interact in an antagonistic manner, with the highest regions of antagonism existing for concentrations of AMP7 between 5,000 ppm [0.5% (w/w)] and 10,000 ppm [1.0% (w/w)] and for concentrations of chitosan ranging from 10,400 ppm [1.04% (w/w)] to 47,600 ppm [4.76% (w/w)]. However, beyond this region of antagonism, all other combinations of AMP7 and chitosan appear to interact with reduced levels of antagonistic behavior. This suggests that the AMP7 peptide and chitosan are interfering with each other’s function, but that the negative interaction can be overcome as the concentrations of both additives increase. The antagonistic response could be happening because both additives target the cellular membrane of microbes to produce a biocidal effect.

Moist-Food Simulant Packaging Study

To test the scalability of the results from the clear disk assay, we simulated the common vacuum-sealed storage of moist foods (meats, fruits, vegetables, etc.) using a nutrient agar patty contacting a bio-based antimicrobial coated plastic disk while stored inside a vacuum sealed bag. Single additives were tested as well as combinations at corresponding concentrations. These results are summarized in the table in Figure 5A. Addition of 1% (w/w) AMP7 to 2.17% (w/w) chitosan-PVA coatings markedly worsened the efficacy of chitosan at this concentration, suggesting stronger antagonistic behavior in this concentration regime, which is consistent with the original model from the small disk study. Interaction between the two additives was evaluated by calculating synergy scores, using the Bliss model to calculate predicted responses. The contour plot of these scores is shown in Figure 5B. Although the combination of 0.5% (w/w) AMP7 with 2.17% (w/w) chitosan-PVA coating exhibited improved antimicrobial activity compared with the 0.5% AMP7 or 2.17% chitosan PVA coatings alone, the percent growth inhibition was less than predicted for an additive combination response, resulting in a negative synergy score (Figure 5B). Representative plates for this combination, as well as for the single additives and control, are shown in Figure 6.

Commercial Packaging Study at Elevated Concentrations and Reduced Coating Thickness

The vacuum-sealed patty studies had good agreement with the results seen in the disk assay, which confirmed that the disk assay is a good method for screening the effectiveness of these bio-based additives alone and in combination. To complete our study with this combination of materials, we wanted to overcome the antagonistic effects of these two components by increasing the final concentration in the PVA coating to 16% (w/w) chitosan and 1.5% (w/w) AMP7, and evaluating if cost-effective materials could be made by reducing the overall coating thickness on the test films. Because the bioactive coatings used in these studies are soluble, dosage of the active ingredients can be varied both by their concentrations in the coating mixture and by the amount of the coating added to the films (higher volumes applied to the films resulted in thicker coatings and a higher dose of actives). This test was conducted using disks of commercial packaging products. Disks of both types of commercial packaging were tested with either a 0.2-mil thick coating or a 0.6-mil thick coating (compared to the 1-mil thick coatings used in the earlier studies). As seen in Figure 7, it was confirmed that the bio-based additives could be used with commercial packaging materials to get efficient kill of E. coli contamination by controlling coating thickness to achieve enough of the chitosan and AMP7 to overcome their antagonistic effects (see Table 2).

Conclusions

Individually, and in combination, AMP7 and chitosan in a simple PVA coating demonstrated effective antimicrobial activity in reducing bacterial growth in a food simulant contacting the food packaging coating. It was determined that combinations of AMP7 and chitosan had an antagonistic interaction, rather than additive or synergistic activity. This was not unexpected, as these additives, though biochemically dissimilar with one being a polysaccharide and the other an amino acid oligomer, act upon the same cellular target (the external cell membrane of bacteria and other microorganisms). When combined, they may compete for physical interaction with the cellular membrane to disrupt the membrane and produce a biocidal effect; so it is possible that one interfered with the other’s effectiveness. The antagonistic effects were shown to be overcome at high concentrations of both additives, and they are both still good candidates for the development of antimicrobial food packaging systems because they have demonstrated antimicrobial activity and are known to possess low toxicity; for example, chitosan has previously been used in antimicrobial edible coatings^33,34 and the antimicrobial peptide used has previously been demonstrated to exhibit no discernable toxicity in rodent oral administration evaluations.³⁵

The analytical methods used here offer a powerful tool for screening potential bio-based actives for additive, antagonistic, or synergistic activity. Other bio-based antimicrobials can be selected to act on different cellular targets, and combinations that target different cellular components would likely produce additive or synergistic antimicrobial effects. Selection of antimicrobials that interact synergistically in combination is ideal, because this increases the antimicrobial activity of both additives while decreasing the concentration needed, thereby reducing overall production costs in a commercial application. Enzymatic additives may be selected to catalyze destructive reactions on lipids, proteins, sugars, and cellular wall components that sustain microbial life. Enzymes can be selected to be specific to the biochemistry of target microorganisms, such as selecting an enzyme that preferentially degrades bacterial cell walls vs the cell walls of fungi. Alternatively, some enzymatic additives could be selected to exert nonspecific antimicrobial effects, such as certain oxidases that produce reactive oxygen species that attack most microbial biomolecules, including DNA. Other non-enzymatic peptide bio-additives, such as nisin and AMP7, have varying modes of action, typically through disrupting microbial membranes and cell walls, but due to their small molecular sizes, may be more suitable for applications where diffusion from a food preservative coating may aid in getting better protective coverage of the food item during storage. Future studies using different combinations of these types of bio-additives may produce coatings to safely enhance the shelf-life of food, and in some cases, be tailored to protection of specific food items from microbes, particularly pathogens, that preferentially contaminate those products.

References

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*Tyler W. Hodges is also affiliated with William Carey University, Hattiesburg, MS.
**Aayushma Kunwar is also affiliated with Reactive Surfaces.

CoatingsTech | Vol. 15, No. 9 | September 2018

Throughout the life of a coating product, from the earliest phases of product development to commercialization and ongoing customer support during its time on the market, extensive testing is required for many reasons. Most large coatings companies and raw material suppliers have routine analytical capabilities, while smaller manufacturers may have limited resources for establishing testing facilities. In addition, often highly specialized analyses must be performed that require not only dedicated testing instruments, but analytical scientists with specialized skills and expertise. Consequently, third-party testing laboratories are widely used in the coatings industry to help facilitate product development and problem solving.

JCT CoatingsTech spoke to experts at five different analytical service providers to learn more about the role they play in supporting coating customers: Marie Halliday, global coating specialist with Element Materials Technology; Scott Moore, paints & coatings specialist with EAG Laboratories; Ian Priestnall, technical consultant, Vibrational Spectroscopy at Intertek; Cynthia L. O’Malley, consulting and laboratory services manager for KTA-Tator; and Paul Lewis, technical manager for Coatings, Adhesives, Sealants, and Elastomers, Craig Larner, technical manager for Lab Services & Analytical Testing, and Dejana Drew, director of technical solutions from Nexeo Solutions, LLC.

Q. What testing activities do coatings formulators typically outsource?

Scott Moore, EAG: Formulators tend to use third-party laboratories when they have problems they can’t solve or testing they cannot perform. These requests are usually focused on basic formulation, deformulation, and raw material substitution for existing materials. We have also received requests for the new bio-based materials coming into the marketplace or for finding substitutes for materials being discontinued. Many times, these projects involve performance-based testing, comparing the new product to the existing one.

Craig Larner, Nexeo Solutions: We classify coating testing into three basic categories: product performance testing; testing to support research and development, typically to address specific issues; and general chemical analysis, which often involves problem solving or testing to establish regulatory compliance, in particular VOC content.

Ian Priestnall, Intertek: We work with formulators and their suppliers on a daily basis covering a whole range of assurance solutions supporting the product lifecycle from early concept R&D support, end-use application performance testing, registration compliance requirements through to addressing issues associated with the end use.

We assist new product development and research through detailed analysis to help fundamental understanding about the coating product or substrates, while competitive product deformulation and performance-type testing help our clients to determine that the new product performs well for the end use.

Depending on the application and industry, some products have to meet stringent regulatory requirements, and our assurance programs incorporate testing and/or advisory guidance. We also work with formulators to address failure investigations including product contamination or end-use performance issues right through to helping clients protect their products in the marketplace with analysis for patent defense or infringement disputes.

Cynthia L. O’Malley, KTA-Tator: Coating manufacturers consistently use third party testing to be able to provide independent unbiased data on coating performance, such as corrosion protection. Coating testing by a third-party independent laboratory assists coating manufacturers in providing competitive coating materials for the intended environment without sacrificing performance. This approach provides a greater degree of confidence that the coating system will provide long-term asset protection. Additionally, testing coating performance reduces the risk of the coating failing to perform in the intended environment.

Q. What drives��the need to outsource testing in the coatings industry?

Cynthia L. O’Malley, KTA-Tator: Specification compliance, qualified product lists, and comparable performance data are probably the three biggest drivers for outsourcing of testing. Specifications are designed for the intended purpose of asset protection and obtaining quality materials, applied such that material performance is optimized. Therefore, it makes sense that coating materials are tested prior to application to ensure that they meet the criteria specified. Similarly, a qualified products list is a listing of coatings that have been tested by a third-party testing laboratory and subsequently have associated data that is comparable across products tested for a specific performance environment.

Paul Lewis, Nexeo Solutions: Much of the equipment required for coating analyses and testing is very expensive. It doesn’t make economic sense for companies to invest in these types of instruments if they use them infrequently. In addition, the analyses require trained and skilled experts to utilize them, and it isn’t possible for a company to hire experts who won’t have a steady work stream. Retaining these experts becomes very challenging in situations where they are not exposed to continuous development opportunities.

Ian Priestnall, Intertek: Large multi-nationals as well as smaller, more specialized companies see a benefit to being able to select complex analytical techniques off the shelf without having to directly invest the required capital expenditure to bring everything in house. Coating formulators will have excellent formulation, engineering, or processing expertise but may have gaps in their analytical expertise that a third party provider can fill.

Scott Moore, EAG: Basically, a lack of technical expertise, knowledge or analytical equipment in a specific area, capacity as well as a need for unbiased testing results can drive the need. These results can be valuable for sales brochures in new product introduction, or are often used in product failure and litigation support.

Dejana Drew, Nexeo Solutions: Many startups that are developing cutting-edge products are using raw materials that have not been traditionally developed for coatings applications. These companies also have limited analytical resources. Third-party testing labs with experience dealing with a broad range of chemicals can provide the flexibility and expertise needed to aid the product development efforts at these innovative firms. This ability allows them to focus on their core competencies rather than over-extend themselves.

Q. Do testing needs vary depending on the stage of product development/commercialization?

Ian Priestnall, Intertek: Absolutely. Analytical needs vary enormously depending on the client and the stage of commercialization. Development of a new coating formulation may start, in some cases, with an assessment of competitors’ products. Spectroscopic analysis for product deformulation can help clients understand the competition and the raw materials that they are using in their formulations. In the product development phase, the emphasis may be on end-use performance testing whether that be mechanical properties, scratch resistance, conductivity, thermal properties such as thermal stability, or developing an understanding of how formulations affect cure profiles. In the final or pre-production phase, the important questions could be around quality control, quality assurance testing, or regulatory requirements, for example for food contact approval. In all of these cases, finding the right third-party provider with relevant expertise can be critical in getting a product to market.

Marie Halliday, Element Materials Technology: Within the coatings industry, testing partners support the testing needs of formulators and raw materials suppliers at two critical points in laboratory work. First, at the development stage to help create a prototype formulation to meet a business case, including specific standards, which is necessary to move to the next point in a stage gate development process. Anticorrosive testing or mechanical testing are common at this point. The next step is within product support, to help maximize return on investment (ROI) by ensuring that products can be used to the maximum number of end-user specifications. It is at this stage that any prequalification tests linked to end-user specifications that were not required during development are signed off.

Cynthia L. O’Malley, KTA-Tator: For smaller coating manufacturers, we are a resource that can be used for performance testing of formulations before commercialization. Outsourcing lab testing in the earlier stages of development makes sense for these smaller companies. Larger organizations engage third party testing to obtain unbiased coating performance and may look for comparison testing with competitor products that are established and available in the market. Therefore, larger organizations usually engage third party labs at a later stage of product commercialization.

Scott Moore, EAG: We tend to see more demand in the early, conceptual stages for basic product ideas, and��then toward the end of the process for fine-tuning and product testing.

Q. What are the most common tests/analyses��that are��outsourced in the coating industry?

Scott Moore, EAG:�� Deformulation and product failure are the most common requests we receive, likely due to the amount of analytical equipment and knowledge required. The second-most-requested area is performance testing using ASTM or other test methods.

Ian Priestnall, Intertek: In general terms, I think that compositional analysis, end-use application performance testing, and regulatory compliance testing cover the major categories, but they all require different types of “tests” depending on the circumstances. Quite often, when the coating industry outsources analyses, they are not just looking for “testing” but they are looking for real, informed insight that can help their decision-making process to either accelerate product development or assure product quality through achieving compliance or resolve issues rapidly.

Marie Halliday, Element: As previously mentioned, anticorrosive testing or mechanical testing are common testing procedures required at the development stage, while there are a range of standardized tests in demand at the product support stage. Three areas of particular importance in testing outsourcing are cyclic anticorrosion testing, fire protection testing, and linings testing. The tests are not simply required to meet industry standards, but also additional, specific government standards that are relative to each geographical location.

Cynthia L. O’Malley, KTA-Tator: Coating manufacturers, as previously mentioned regarding early stages of product development, routinely request performance testing that is aligned with the needs of the market segment that they are intending to service. Another area where third-party independent analysis is necessary is for regulatory compliance. Therefore, VOC testing, hazardous metal content, and the like are generally outsourced tests in order to obtain unbiased data.

Q. What are the key characteristics/traits companies in the coatings industry should look for when selecting third-party testing labs?

Cynthia L. O’Malley, KTA-Tator: Quality of data and, therefore, accreditation as well as capacity for testing in order to meet established timelines are essential criteria for selection of a third-party testing laboratory. In addition, variables associated with test protocols and standard requirements are complicated. To receive applicable, accurate data that is of benefit for the intended use requires a laboratory that is accustomed to providing a tailored approach to the specific needs of each individual company.

Craig Larner, Nexeo Solutions: Third-party testing labs need to not only have a deep understanding of coating chemistry and testing methods, but also be able to communicate that knowledge in a value-added manner. Many customers don’t know which questions to ask and need help figuring out what analyses need to be performed. Scientists at third-party labs need to be able to explain which tests are needed, why, and where the customer will benefit.

Once tests are completed, high-quality testing labs also take the time to explain the results. One-on-one conversations with customers to review final project reports are necessary to properly convey the information, particularly for complex analyses performed to aid in product development. Interactions on this level are highly valued because they provide customers with close access to the knowledge base at the third-party lab.

In addition, for specific types of testing, such as for VOC measurements, there are multiple options with advantages and disadvantages depending on the intended application. Testing labs need to have an understanding of the testing methods in order to be able to recommend the most appropriate choice.

It is also imperative that labs stay up to date on the latest standard test methods. These methods are always evolving, and it is crucial for analytical service providers to remain aware of and fully implement all of the latest methods.

Marie Halliday, Element: Testing partners in the coatings industry must deliver strategic support to their clients—it is not enough for a testing company to complete test plans at an arm’s length. Instead, testing partners should provide an integrated service comprising testing and consultancy.

The best and most trusted testing partners in the coatings industry will combine technical and operational excellence with the right capabilities to solve commercial challenges. Testing to recognized standards is central to this, so companies that have experts on standards committees can help clients to truly understand their testing requirements. Moreover, sitting on these committees involves collaboration with other industry stakeholders, which delivers benefits in knowledge-sharing.
Ultimately, testing partners that understand client requirements and can deliver excellent performance in first-time right (FTR) and on-time delivery (OTD) metrics are at an advantage. For example, reporting standards are crucial because reports are readily passed from clients to end users as part of the prequalification process.

Ian Priestnall, Intertek: I think it’s critical that third-party laboratories clearly demonstrate their competence, their experience, and their ability to deliver what the client needs. Clients should be quite rightly concerned if they are placing any aspect of their product development, and, therefore, their reputation, in the hands of a third party, and they need to have the confidence that a third-party supplier will be able to help them in a synergistic way. For example, adding a third party’s specialized analytical expertise to the client’s formulation knowledge should provide greater benefits to the client.

Paul Lewis, Nexeo Solutions: Having experience with a wide range of different chemical compounds can be really beneficial for third-party testing labs. As a chemical distributor, we have found that our familiarity with and knowledge of a very wide range of raw materials has provided us with a strategic advantage, particularly with respect to problem solving. We can link this knowledge to product development and performance testing results and are able to provide more comprehensive recommendations and evaluations.

For instance, a customer was faced with a solvent-based contaminant. The solvent was quickly identified as hydrocarbon-based, but that level of information was insufficient for the customer to identify its source. We were able to identify the actual compounds in the solvent mixture due to our familiarity with these materials. As a result, the customer was able to pinpoint the source and solve the problem.

Scott Moore, EAG:�� We have a lot of repeat business because we provide scientifically proven answers to our customers’ questions. Our new customers come to us because of our reputation, knowledge, and reliability. Most companies value these traits more than the actual cost.

Most recently, to provide greater value to our customers throughout their entire product development and commercialization processes, we recently aligned all of our brands under the name EAG Laboratories. We have a tremendous amount of capability and services for our coating customers, but they were previously offered under different brands. The new singular company brings a complete offering to market.

Q. What��do you��perceive to be��the biggest challenges for companies in the coatings industry when working with��third-party testing labs?

Paul Lewis, Nexeo Solutions: Many coating companies find it difficult to identify the right third-party testing labs that can meet their needs.�� There are no obvious places to find this information, so it can be very difficult to find specific labs that have specialized capabilities. One place to start is the Underwriter’s Laboratories (UL) website, which has some tools to help find laboratories, although it is not comprehensive. Google searches can provide some leads; however, the leads found in this manner are not always easy to validate and engage with.�� It would be better to develop strategic partnerships and use expert recommendations.�� Companies should expect, though, that it will take time to identify the best labs for their individual needs.

Marie Halliday, Element: Lead times remain a challenge, with meeting agreed timescales for testing and reporting critical to commercial success. Testing partners with an extensive geographic footprint of quality laboratories provide coatings companies with easier access to reduce project times and increase quality.

Scott Moore, EAG:�� Companies are always concerned about protecting both their intellectual property and the confidential information related to the tests we have developed for them. We take this very seriously, and have strict policies in place to protect this information. We have a strong track record of doing so.

The next issue we see is managing expectations when it comes to resources. We work for multiple clients simultaneously, and must allocate our time to each customer accordingly. Depending on our current workload, this sometimes can lead to responsiveness issues. We have overcome these issues by clearly setting expectations at the outset of the project.

Finally, an ill-defined project scope can create major issues. When doing in-house projects, companies can change scope or direction many times without cost considerations. When this is done with an outside lab, and the project needs to change scope or move in a different direction, there may be costs associated with this change.

Ian Priestnall, Intertek: One challenge for the providers is for us to help the clients see beyond the simple test or to see us as simply outsourcing providers and consider who or what they are looking for as development partners who have a focus on product quality assurance.

Q. What would you like to see improved regarding your interactions with coatings industry companies?

Scott Moore, EAG: For developmental work, we’d like to initiate better communication of project goals up front, including all the information we will need to move forward with the project.

Cynthia L. O’Malley, KTA-Tator: Continuous improvement is always needed. However, the interactions between coating manufacturers and laboratory test services have been predominately positive. Perhaps the one area where improvements could be made is to better bridge the specification developers and testing service providers to clarify the intent of performance specification language, which could ease the challenges faced by many coating manufacturers.

Marie Halliday, Element: Overall, the coatings industry would benefit from greater integration between testing partners and clients. Working on testing methods and applications as part of a joint venture (JV) or joint industry project (JIP) from the outset can give clients a greater commercial advantage, particularly if the test method developed is very niche and not easy for competitors to replicate. More broadly, the wider industry can benefit from JIPs that involve a broad spectrum of end users, suppliers, and testing partners. These projects can, for example, build on testing research and technology to help evaluate and develop methods creating stronger standards and more consistent and realistic test methods.