We present a novel approach that introduces mass as a fundamental metric for characterizing the size and structure of pigments and nanoparticles. This offers the potential to establish a new standard for particle size determination. Leveraging measurement techniques developed in aerosol sciences, we apply them to uniquely analyze pigment particles in an application-oriented manner.

Engineered nanomaterials are produced at a massive scale, ranging from 10³ to 10⁷ tons per year. The physical properties of individual particles, aggregates, fibers, etc., profoundly influence the application performance of these materials. Traditional methods for characterizing physical dimensions are either expensive and time-consuming (e.g., TEM imaging) or limited to equivalent diameters. For instance, laser diffraction size analysis requires the refractive indices for a wide range of color pigments and struggles to accurately measure nonspherical or aggregated particles.

Moreover, various material properties are mass-based metrics, facilitating the calculation of other essential values. For instance, using skeletal density (g/cm³) or specific surface area (m²/g), one can derive absolute particle volume or surface area and key performance indicators like the number of particles per gram or particles per dollar. Additionally, we measure the mobility diameter, enabling the calculation of particle bulk densities, fractality, porosities, and more.

To introduce the potential of this measurement concept, we present the results of three commercially available iron red pigments, three carbon blacks, and a coated iron yellow pigment. First, some background information is provided on the relation between particle mass and diameter, collectively defining the particle structure, and then the experimental setup is briefly discussed.

Background: Mass Plus Diameter Equals Structure

The structure of a particle population is encoded in the relation between mass and diameter of the individual particles. The scaling relation between particle mass (m) and the particle diameter (d) can be expressed by Equation (1):

with a constant (k) and the fractal index (fi). While a fractal index of 3 indicates scaling of a solid object, a fractal index below 3 (and above 2, which would indicate plate-like scaling) signifies the scaling of an increasingly more porous material (see Figure A1). In the context of color pigments, the fractal index describes the branching of the aggregates itself and varies for every material. To visualize that, we examine the effective density, i.e., the density of a particle with mass m and diameter d assuming sphericity. Inserting Equation (1) for the diameter gives Equation (2).

The scaling for three structurally different particle types is illustrated in Figure 1. Solid particles with a fractal index of 3 exhibit a constant effective density (in this special case, equal to the skeletal density). The effective densities of aggregated particles, here, as the example shows, columns and spheres (Figure 1), decreases with increasing mass, indicating a fractal index below 3. The stronger the decrease, the lower the fractal index and the higher the aggregation level of the particles.

FIGURE 1 Particle effective density as a function of particle mass for three structurally different particle types: Solid spheres (top), aggregated columns (middle), and aggregated spheres (bottom). Gray circles indicate a diameter estimate for visual guidance. Note: Same skeletal density is assumed. Particle mass axis is logarithmic.

The electrical mobility analysis is used to measure the geometric dimensions of a particle. Unlike other diameter estimates, the mobility diameter is not affected by the material density and refractive index. The mass is an intrinsic property of a particle and, unlike any equivalent diameter, it does not require any prior assumption and is independent of the measurement method. Therefore, the particle mass is well-suited to serve as a standard for the particle size.

Methods

We utilized a PowMaster system (femtoG AG, Switzerland), a combination of dedicated particle dispersion systems and the newly developed Mass & Mobility Aerosol Spectrometer (M2AS, Cambustion Ltd., UK), which enables the rapid measurement of size distributions for both absolute particle mass and a diameter (electrical mobility) within 5 to 15 minutes.

Powder analysis was initiated by an aerosolization of the powder material. Here we suspended 0.2 g of a pigment in 100 mL ultrapure water. The particles were deagglomerated by a finger-type ultrasound probe until an energy input of 100 J/ml was reached. Subsequently, the suspension was nebulized and the droplets were dried to retrieve the initial pigment particles. By producing small droplets and working with dilute suspensions, re-agglomeration during the drying process could be prevented.

Different aesthetic requirements for powder coatings necessitate formulators to be able to produce finishes in any level of sheen, from full gloss down to dead matte. By default, a basic powder coating formulation will exhibit a 60° specular gloss of 90 or higher. A number of different methods can be employed to reduce the luster to a semigloss or matte finish. Some of these techniques involve the incorporation of mineral fillers or wax additives to impart the desired appearance, while others utilize resin chemistry to create a microscopic texture on the coating’s surface, as shown in Figure 1.

FIGURE 1 Polyester/GMA acrylic close-up showing microtexture of the surface

Extender Pigments

Extender pigments are inert, typically inorganic filler materials that are added to a formula to reduce overall formula cost, but they can also provide an aesthetic or performance-enhancing function. The most commonly used extenders in powder formulating are calcium carbonate and barium sulfate, though the particle-size distribution of the mineral filler has more influence on the appearance of a powder coating than the chemical makeup.

Powder coatings are sensitive to high oil-absorption components such as fumed silica and organoclays.

Whereas solventborne liquid coatings can incorporate high levels of fine particle size fillers for their matting needs, the viscosity of powder coatings increases incrementally with the incorporation of high oil-absorption additives to the point of extreme texture and film incontinuity. If used at a low level (e.g., under 4% by formula weight), they can decrease gloss or impart a subtle texture without losing mechanical properties.

On the other end of the particle-size spectrum, larger particle-size extender pigments may be used to affect a powder coating’s sheen. Particles larger than 44 microns (325 mesh) may protrude from the surface, creating unattractive defects known as bits or seeds. However, mineral fillers with a narrow particle-size distribution and a median in the 10-to-20-micron range can disrupt the surface in a uniform way, creating a semigloss finish of 50 gloss units or lower.

This method is particularly viable in dark coatings that only require a low loading level of colorant pigment to attain opacity. In white or pastel coatings that require a higher loading of prime pigments, it may be difficult to incorporate enough filler to substantially reduce the gloss.

Wax Additives

Waxes used in powder coatings are typically synthetically produced and are characterized by their melt point. They are nominally incorporated at a level of 0.5-5.0%. Because powder coatings are normally extruded around 100 °C, low-melting waxes such as paraffin and carnauba melt below the typical extrusion temperatures and are intimately mixed with the polymeric binder during extrusion. Other waxes such as Fischer-Tropsch and polyethylene are dispersed as a particle in the extruder and melt during the curing cycle, which can be up to 200 °C or higher. (See Table 1.)

Either way, while the binder melts and cures in the oven, wax additives are driven to the surface of the coating; this positioning on the surface can have both positive and negative effects on the coating. On the positive side, the use of wax additives can improve the slip and mar properties of the coating. In addition, with proper selection, they can be used to reduce the gloss to as low as 40 gloss units.

However, if incorporated at too high of a level, the wax additives can impart haze and burnish, inviting fingerprints. They also can prevent intercoat adhesion in a multiple coat or recoat situation. Additionally, some waxes are not weatherable and not recommended for coatings requiring high UV durability. Because of these potential side effects, the formulator must take care to select the proper wax for gloss reduction and monitor coating properties at various addition levels to ensure coating performance is not negatively impacted.

Differential Cure

Differential cure can be achieved by combining two compatible powder coating formulations with disparate functionality. The two components react and cure at different rates such that during the cure cycle, the faster-reacting components will crosslink, and flow will become restricted in those domains, while the slower-reacting components continue to flow. Finally, the slower-reacting components will crosslink. This differential-cure mechanism results in a microtexture on the film’s surface, which appears as a smooth, low-gloss finish.

In particular, the conference organizers are asking for new and innovative presentations with “valuable information which improves powder coating operations, discusses industry trends, and provides ideas to enhance business practices.”

The PCI Events Subcommittee will give high consideration to presentations that include interaction, demonstrations, videos, and show and tell items; that are submitted along with abstracts from exhibiting companies; and that are on the following topics: justifying operational costs, future trends, new technologies, conversion from liquid to powder, IoT updates and implementation, formulation and raw materials, media blasting/coating removal, the benefits of a quality department, improving line efficiency, managing shortages and supply chain issues, automation to improve performance or efficiency, case studies, and troubleshooting and correcting defects.

Those people who the subcommittee selects to present at the conference will receive a full technical conference registration with access to all technical conference sessions, the tabletop exhibition, and meal functions and will be featured, along with their company, in all promotional materials, including print and digital publications and on all social media outlets.

The technical conference is set for March 12–13, 2024, in Orlando, FL, and is part of Powder Coating Week 2024.

Abstracts must be submitted using the online form at powdercoating.org/page/Abstract24. For more information on the conference and abstract submission, visit .

The past year marked a rebound in powder coating revenue as well as investment in R&D. In particular, both the North American and Latin American powder markets showed growth of 3.5% and 1.8%, respectively, in 2022.¹ These growth figures coincided with the introduction of several innovations in sustainability, low-temperature cure, corrosion resistance, outdoor durability, thin films, and thermoplastic application technology.

Sustainability

Sherwin-Williams recently introduced a powder coating product line based on post-consumer recycled plastic. PowduraÂź ECO powder coatings are formulated with polyester resins based on recycled polyethylene terephthalate plastic (rPET). Earlier versions of PowduraÂź ECO powder coatings were based on pre-consumer waste plastic that is generated in factories. This latest development will have an impact on recycling post-consumer plastic that comes mainly from beverage bottles.

According to the company, one pound of Powdura ECO TGIC/TGIC-free (triglycidyl isocyanurate) coatings contains the rPET equivalent of about sixteen 16-ounce water bottles, depending on the final product formulation Sherwin-Williams estimates that one pound of Powdura ECO hybrid coatings contains approximately the rPET of seven to ten 16-ounce water bottles, depending on the formulation.

Low-Temperature Cure

Pengchen (Simon) Yang, a senior researcher in allnex’s Corporate Innovation Group located in Wageningen, Netherlands, introduced a potentially game-changing powder technology at the 2023 European Coatings Conference. The breakthrough was described in his presentation, “Ultra Low Temperature Curing Powder Coating via Real Michael Addition.”

Yang’s work introduces a new chemistry to the low-temperature-cure powder coating universe. This fascinating technology is based on Real Michael Addition (RMA) chemistry that includes an innovative catalysis system that provides cure latency to this highly reactive chemistry. An RMA reaction relies on a combination of a “Michael donor” in the form of a nucleophile with an α,ÎČ-unsaturated carbonyl to create a Michael adduct. The allnex team, led by Yang, crafted this chemistry into solid polymers/oligomers that are extrudable and capable of film formation at relatively low temperatures, i.e., < 120 °C. In addition, these polymers/oligomers are reportedly stable at room temperature storage conditions.

This chemistry is comprised of two crosslinkable species: component A is a material containing C-H acidic moieties, and component B is an unsaturated polymer. The most preferred component A is a malonate functional polyester resin, and methacrylated polymers (polyester-, epoxy-, or urethane-based) are the most preferred B component.

The catalysis system is rather complex and is based on a catalyst precursor (P1) in combination with a catalyst activator (C1). P1 is a weak base (DABCOℱ or tetramethyl guanidine) that reacts with C1, generally an epoxide compound, to produce a strong base catalyst. The epoxide compound can be TGIC, glycidyl methacrylate (GMA) acrylic resin, or Aralditeℱ PT-910/912. This catalyst technology is quite reactive; therefore, a retarder, typically a carboxylate, is used to introduce a degree of latency. Latency is critical to enable processing through the conventional extrusion techniques that are common in the powder coating industry.

Latency is further enhanced by macro-physically separating reactive species in independent compounded mixtures. For example, the C1 catalyst activator may be extruded into binder components independent of the P1 catalyst precursor/retarder blend. Two powder materials are generated that are then post-blended into a pseudo-2K powder mixture that is then applied to a substrate and cured at low temperatures, typically about 110–130 °C.

This groundbreaking technology is comprehensively detailed in the international patent application WO-2022/236519 A1, which was issued on November 17, 2022. It is the author’s hope that the powder coating world will take notice of Yang’s fascinating low-temperature RMA-curing technology and that this will open a spectrum of opportunities for growth into new markets and applications.

In other developments, AkzoNobel debuted Interpon W, a product group specially formulated for application to heat-sensitive substrates. Not only can these products be used to coat wood and engineered boards, but they can also be used on various plastics, gypsum, and plastic composites. Interpon W includes thermoset as well as UV-curable powder technologies. Allnex Resins is also supporting the development of low-temperature-cure powder coatings with the introduction of ultra-low-temperature-cure polyester resins. These include UVECOAT (UV cure) and Crylcoat (thermoset) resins specifically designed to cure at temperatures 80–135 °C.

Continue reading in the of CoatingsTech.

Introduction

Epoxy-based products are used in many applications that face aggressive operating environments. Some examples (Figure 1) are electrically insulative encapsulants or powder coatings (e.g., inside electrical motors), chemical-resistant pipe linings, adhesives, and composite parts. Under extreme service conditions (e.g., regarding heat, chemical exposure, and mechanical stresses, often in combination), many traditional epoxy formulations fail because they suffer from a loss of integrity over time. Traditional solutions require switching from epoxy to alternate chemistries such as cyanate ester, bismaleimide, and polyimides, which, while suitable, can add complexity to the process and increase cost.

Aromatic dianhydrides such as BTDA¼ (3,3’,4,4’-benzophenone tetracarboxylic dianhydride) have been known to impart high crosslinking densities to epoxy formulations.^1,2 See details on this molecule in Table 1 and its chemical structure in Figure 2. The resulting dense crosslinking, in combination with the structure of the BTDA linkages, leads to epoxy powder coatings with high glass-transition temperatures (Tg) and heat resistance. These formulations also offer superior dielectric properties, mechanical properties, and chemical resistance. As a result, BTDA-based powder coatings find uses in aggressive environments such as those that are high temperature, involve chemical exposure, or are for long-term electrical applications. It is noteworthy that such successes are achieved using simple, bisphenol-A based solid epoxy resins (Figure 2). Specialized resins such as epoxy novolacs and other multifunctional resins can certainly raise the performance but are not necessary when using a dianhydride curing agent.

A Note on Proper Stoichiometric Treatment of Dianhydride-Epoxy Formulations

To properly design dianhydride-epoxy formulations, a few points require consideration. Dianhydrides cure epoxy formulations to extremely high levels of crosslinking through esterification reactions. A proper review of the complex reaction mechanism^3-6 is outside the scope of this paper. Figure 3 describes a simplified two-step esterification reaction model that has been adopted by the epoxy industry. In the overall esterification reaction, one epoxide group reacts with one anhydride group. At first glance, this reaction implies a stoichiometric ratio of anhydride to epoxide groups (A/E ratio) to be 1.0. However, optimum A/E ratios for most dianhydride-epoxy formulations are far less than 1.0, typically between 0.65 and 0.80 for powder coatings. There are two main reasons for this.

First, an A/E ratio less than 1.0 helps address the side-reaction of epoxy etherification (also known as homopolymerization), a process which can consume epoxides without participation from anhydride groups⁷ (Figure 4). This is a well-established fact, and epoxy formulations using mono-anhydrides such as methyl tetrahydrophthalic anhydride (MTHPA) routinely use A/E ratios in the range of 0.90–0.96 for this reason. This approach minimizes residual anhydride groups after cure while optimizing the Tg and other properties.

However, dianhydrides require a second, crucial consideration due to the extremely high levels of crosslinking that they produce. At near-stoichiometry, formulations will readily vitrify before full cure, thus locking in unreacted functional groups, which are undesirable for long-term performance. Although it is true that post-curing at elevated temperature can lead to full cure, in many cases, the final crosslink density may be too high for the application, thus leading to suboptimal performance.

Therefore, in most epoxy powder coatings, the dianhydride usage must be well below stoichiometric—typically at A/E ratios in the range of 0.65–0.80. Any excess epoxide groups in the formulation will be consumed via etherification side reactions (epoxy homopolymerization). This approach helps avoid over-crosslinking while optimizing performance. The optimum A/E ratio for a specific application is best determined experimentally, but the recommendations in Table 2 are a good starting point.

Continue reading in the ŽÇŽÚÌęCoatingsTech.

I’m going to get a little personal in this column and take the opportunity to recount my illustrious career in the powder coating industry. I got my start in powder coatings in March 1978. This was before computers, digital scales, Excel spreadsheets, email, and smart phones. Interestingly, even though the tools to develop coating technology continuously evolve, the fundamentals of formulating a high-performance powder coating really haven’t changed that much.

The Beginning

I had just celebrated my 20th birthday, still too young to legally purchase a bottle of wine but filled with an eager enthusiasm to conquer the challenges facing this fledgling industry. Powder coatings were conceived in the mid-1950s as a laboratory curiosity by Dr. Erwin Gemmer, a German scientist. By the 1970s, this technology had found a commercial home as a thick-film, functional coating used to protect pipelines, steel rebar, and electrical equipment. The late 1960s and ’70s ushered in thermoset polymers, the use of extrusion to compound formulas, and electrostatic spray techniques capable of applying relatively thin films.

My inauspicious entry into the industry paralleled powder’s introduction to the major appliance and automotive industries where high performance was required. Typical applications were dryer drums; washer tops and lids; and automotive suspension springs, battery trays, and other under-hood components. I entered the industry as a lab technician at The Glidden Paint Co.’s Research Center in Strongsville, OH, in a maelstrom of fervent product development. At the time, I was laser focused on meeting the coating requirements of a rapidly growing number of enterprising fabricators who recognized the advantages of replacing porcelain enamels and solventborne paints with this groundbreaking finishing technology.

Moving On Up

I completed my chemistry degree four years into my budding career, which vaulted me onto the corporate ladder and provided a path to laboratory project leader and eventually group leader roles. These were dizzying times for the powder coating community. Each year promised double-digit growth of greater than 20%, along with a mind-blowing array of technical dragons to slay and processing mountains to scale.

The powder industry was on fire throughout the 1980s and, even more so, the 1990s. Tier-one automotive suppliers introduced clear polyester powders as the topcoat for aluminum alloy wheels. Automakers installed dozens of finishing systems that utilized powder as a body coat, initially as an intermediate coat (i.e., a primer surfacer), and eventually as the clear topcoat for BMW’s 5 and 7 series cars manufactured in Germany. Concurrently, clever chemists invented low-temperature-cure technologies, including the world’s first UV-curable powder coatings for application to pre-assembled electric motors. Seemingly everything metal that could fit into a cure oven was now being powder coated.

At this juncture, the large multinational paint makers began to realize that powder coatings were here to stay and entered the fray by building their own powder businesses, along with unrelenting acquisition of already-established powder businesses. Glidden, where I spent the first 15 years of my career, was purchased by the UK-based ICI Paints, making it a global powerhouse. This development afforded me the opportunity for a two-year assignment as part of a pan-

European powder group located in Birmingham, England. Upon my return to the United States, ICI sold off most of its industrial coatings businesses, including the powder coating group. I left the day Ferro Corp. bought our powder business to join the Herberts Group, a Germany-based powder producer.

Branching Out

After 19 years toiling away at these two global paint titans, I transitioned into an entrepreneurial realm, initially as an independent consultant and soon thereafter as a small business owner. Since making the break with the corporate world, I have owned two custom powder manufacturing businesses, served as an editor to a few coatings publications, and in 2007 founded the Powder Coating Research Group.

Probably one of my most unintentional but consequential decisions occurred around the turn of the century when I was asked to author a regular Q&A column for a company newsletter. My colleagues at the time suggested the column to be titled “Ask Kevin.” I thought such a humdrum title would attract few, if any, readers and offered in its stead an alternate nom de plume and hence, “Joe Powder” was born. My real name was not attached to the column for the first few years, which created a swirl of intrigue in our staid industry. Through the years, the “Ask Joe Powder” column has appeared on three continents in 10 different publications. In 2020, the Ask Joe Powder “powdcast” debuted and can be accessed through most popular podcast services and on the ChemQuest website, chemquest.com.

The timing of my career moves may not have been stellar, as nearly every time I made a major transition an economic storm was brewing. When I shed my corporate identity in the late 1990s, the powder industry was enduring monumental headwinds with the economic recession of 2000–2001, along with issues with production overcapacity, consolidation, shrinking profit margins, and globalization.

Later that decade, I launched my powder technology group, unbeknownst that the Great Recession was looming in the shadows. Throughout this period, paint companies were tightening their spending budgets, including reductions in R&D, which probably benefitted our technology start-up by providing opportunities where understaffed technical groups couldn’t cover all the organization’s innovation objectives.

I weathered these storms undaunted and continued to thrive, leading an entrepreneurial technology outpost dedicated to crafting the next generations of powder coating technology. In 2021, our business was acquired by The ChemQuest Group, which broadened our resources and expanded our capacity, building a strong platform for future growth.

I recently handed over the reins of our powder coating R&D enterprise to my colleague, Nathan Biller, and the erudite team at ChemQuest. While I have stepped down from full-time employment after 45 exciting years as a technologist in this amazing industry, I won’t disappear any time soon as I will continue consulting work, as well as writing, teaching, and other engagements in the industry.

Future Developments

My rear-view mirror captures an exceptionally rewarding experience in a dynamic industry. Throughout my career, I have collaborated with some of the most ingenious technologists and, most importantly, some of the finest human beings I have ever met. It has been an honor and a privilege to share in the triumphs of this extraordinary technology, and I am enthusiastic to continue to contribute to its bright future.

Kevin Biller, founder of the former Powder Coating Research Group, serves as director of ChemQuest Powder Coating Research. Email: kbiller@chemquest.com.

Powder coatings continue to be an attractive technology, primarily due to reduced volatile organic compound (VOC) emissions, ability to recycle overspray, and the exceptional film mechanical properties that can be attained.¹ Despite the appeal, there are major drawbacks that need to be resolved for the technology to be effectively substitutable for liquid coatings.

Powder History and Today’s Market

Powder coating is a relatively new technology with significant improvements in the last few decades. The combination of history and a brief review of today’s market demonstrate a need for continued innovation, specifically the need for low temperature cure (LTC) capabilities.

Launch of Thermoset Powder Technology—Innovation and Low VOC Initiatives: Circa 1950–1990

The first thermoset powder coating appeared in the late 1950s based on research work done at Shell Chemicals.² By the early 1960s, modern extrusion methods were developed, allowing for more reproducible powder coatings.^2–4 Within the same year, the development of electrostatic application further solidified powder coating as a viable coating technology.³

These technological advancements later led to increased market growth and subsequently decreased production costs.² By the 1970s, powder coating prices were starting to be comparable to liquid coating costs. This was due to the solvent price increases following the 1970s energy crisis.² In addition, during this era, the coatings industry was determined to find innovative technologies to reduce VOCs due to restrictions established by the Clean Air Act.⁵

Liquid coatings of course continued to dominate the coatings market, but the growth of powder coatings made it evident that that technology was here to stay, as thermoset powder coatings see a growth of nearly 240% during the 1980s.⁴ Powder coatings were beginning to emerge in several markets by the 1990s, including major appliances, general metal coatings, automotive components, industrial machinery, and metal fabrication.³ However, many of these formulations still required very high bake temperatures, as conventional thermosets require bake temperatures greater than 200 °C.

Continued Growth in a Variety of Markets—Postmillennial

By the mid-2010s, the powder coatings global market was being valued at an estimated $7.15 billion with an annual growth rate of approximately 5–8%.¹ By the end of the 2010s, powder coatings held approximately 6% of the total coating market and an even larger percentage of factory-applied coatings.

Before the turn of the decade, in 2019, the global powder coatings market was estimated to be between $10.6 billion and 11.6 billion.⁶ Several applications are currently utilizing powder coatings, inclusive of widespread usage in automotive, general appliances, furniture, and architecture.⁷ A large area where powder coatings have been successful is in the agricultural, construction, and earthmoving equipment (ACE) industry.6 Powder coatings have even found their way into medical devices, and of course, general industrial applications.

Some thermosets have now been utilized for lower bake temperatures, but many of the conventional systems used globally still require higher bake temperatures. Most common thermosets require peak metal temperatures (PMT) of 180–190 °C or higher.

Despite the high energy costs of these bake systems, the market continues to grow today. Preceding the COVID-19 pandemic, analyses of the total global coatings market projected a 3.9% compound annual growth rate (CAGR) by 2024 and a 5.4% CAGR by 2026, reaching a total estimated value of $15 billion.⁶

Continue reading in the January-February digital issue of CoatingsTech.

Color has a way of creating impact and enhancing spaces and objects. There is evidence all around us to suggest that people are drawn to colorful, shiny things. While color perceptions are subjective and deeply personal, there are some color and gloss effects that have universal meaning. Perhaps it is because many cultures have come to associate gloss with wealth, luxury, and beauty.

Luminosity, iridescence, and holographic effects are a few of the ways that the love for metallic and pearlescent finishes has evolved. These additives enhance color by adding shimmer and brilliance, providing contrast and metamerism for the entire color palette.

New technologies are making strong statements in all aspects of coatings and design, allowing colors to appear and disappear in light in a kaleidoscope of color displays and illumination across the entire color spectrum. The luminosity of metallic and pearlescent finishes stands out, immediately grabbing our attention.¹

Specialized metallic and pearlescent pigments have been developed that allow coated surfaces to exhibit a more glamorous appearance, with luster and brilliance that sets them apart from finishes produced by using conventional pigments.

Appliances, vehicles, cosmetics, printing inks, packaging, soaps, and even food and beverages are a few of the markets that have taken advantage of these additives to project beauty and command attention in a crowded world.

Today’s natural inorganic pigments have come a long way since prehistoric times when natural ochre, charcoal, and clays were used as color pigments. The pigment industry began to develop in earnest in the 18th  century, after which new discoveries and technological advancements led to today’s focus on better performing, less toxic, and more ecologically friendly effect pigments of all kinds.

In fact, in 2015, the FDA issued a final approval ruling whereby mica-based pearlescent pigments could even be used as color additives in Easter egg decorating kits and distilled spirits that contained 18-23% alcohol.² Most cordials, liqueurs, flavored alcoholic malt beverages, wine coolers, and cocktails currently contain some form of FDA-approved pearlescent pigment to add an aesthetic component to adult beverages.

Pigments that produce lustrous, brilliant, glittery surfaces are known as effect pigments. Effect pigments react to light in a unique way because of the high aspect ratio (width to height) of the platelet geometry. This allows for a large variety of colors and special effects including shimmer, metamerism, or metallic reflection.

Several factors combine to influence the finish, luster, and glitter effects on the surface. These include flake orientation, particle size, pigment concentration, layering effects, and coating-film transparency.

There are three main classes of effect pigments commonly used in various applications. The three pigment categories are defined by their interaction with light—specifically absorption, metallic, and pearlescent.

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The powder coatings market in 2020 is estimated to be about $12 billion and represents about 12.5% of the industrial coatings market. After a trying 2020 for both business and operations the global powder market is forecast to grow 4.5% in 2021 with the Asia Pacific region leading the way at about 6% and North America at a more modest 3.4%.¹

Growth is expected to be fueled by recovery in the gross domestic product, a rebound in the automotive market, and increased housing starts and construction. An environmental regulatory push for lower volatile organic compounds (VOCs) will also cause a modest incentive to transition from solventborne paints to powder coatings.

Overall, 2020 was a slow year for powder coating innovations, but many development programs were in the works before the COVID-19 pandemic and are now emerging as the market landscape has stabilized somewhat.

Advances in low-temperature cure were introduced recently as well as powders capable of meeting high durability standards such as American Architectural Manufacturers Association (AAMA) 2605 and Qualicoat Class 3 (both require 10 years Florida durability).

To meet these specifications the coating must pass the following tests: dry adhesion, wet adhesion, boiling water adhesion, impact resistance, abrasion resistance, muriatic acid resistance, mortar resistance, nitric acid resistance, detergent resistance, window cleaner resistance, 4000 h humidity resistance, 4000 h salt spray resistance and 10 years South Florida durability with a maximum ΔE color change of 5.0 units and 50% gloss retention.

These architectural specifications represent the most demanding coating requirements for commercial buildings such as skyscrapers and stadiums. In addition, sustainable technologies are emerging based on either recycled plastic feedstocks or biobased raw materials. Moreover, binders exhibiting enhanced corrosion resistance and edge coverage have been recently debuted. Corresponding new developments have occurred in testing and application technology.

SUSTAINABILITY

A number of strides have been made in sustainable raw materials developed specifically for powder coatings. Defining sustainability can be elusive and concrete examples are sometimes difficult to pinpoint.

Investopedia offers this succinct definition: “Sustainability focuses on meeting the needs of the present without compromising the ability of future generations to meet their needs. The concept of sustainability is composed of three pillars: economic, environmental, and social—also known informally as profits, planet, and people.”²

Sustainability can be represented in different ways. Renewable resources such as plant-based feedstocks are obvious, but other less obvious materials and processes can be found under the sustainability umbrella. For example, low-temperature cure products use less energy and therefore create a smaller carbon footprint.

Coatings with greater durability (corrosion resistance and UV durability) save materials, energy and labor. The following captures some of the latest sustainable developments in powder coatings.

BIOBASED AND RECYCLED

The coating resins company allnex has committed to sustainability with the development of polyester resins based on C5 and C6 sugars, which have been derived from plants.³ This product portfolio includes carboxyl polyesters designed for hybrids (epoxy cure), HAA (hydroxy alkyl amide) and TGIC (triglycidyl isocyanurate) cure powders.

In another sustainable initiative they have developed a series of polyester resins that utilize up to 25% pre-consumer recycled PET (polyethylene terephthalate). PET is commonly used to make the popular two-liter beverage bottles. Interestingly the feedstock is preconsumer waste. This significantly decreases plant-generated waste streams.

Mirroring allnex’s recent developments, Sherwin Williams debuted its PowduraÂź ECO Hybrid Coatings line.⁴ The company notes that the polyester resin used in these coatings contains 25% pre-consumer recycled plastic (rPET). On average one pound of powder coatings contains the rPET equivalent of seven to 10 single-use water bottles depending upon final product formulation.

Sherwin Williams touts these coatings as being easy to apply (better first pass transfer efficiency), having wide cure capability over a significant temperature range, and aligning with certain third-party certifications that define and measure sustainability standards, such as Leadership in Energy and Environmental Design (LEED), GreenGuard and the Business and Institutional Furniture Manufacturers Association (BIFMA), a not-for-profit organization that was formed with the purpose of creating voluntary standards that would promote safe working environments).

Battelle Memorial Institute has developed a biobased powder resin that checks two boxes of sustainability—renewable plant-based feedstocks and low-temperature cure. This polyester-amide resin boasts an 85% biobased content and is capable of cure as low as 130 °C.⁵

In addition, its aliphatic chemistry affords excellent ultraviolet (UV) resistance as evidenced in laboratory testing (less than 50% gloss loss at 4,000 h in QUV-B accelerated indoor weather testing). Prototypes have been submitted to a limited number of powder manufacturers for their evaluation with hopes for eventual commercialization.

Most powder coatings are thermoset, accounting for nearly 95% of the market. However, it is important to note that a sustainable, very high-performance polymer accounts for approximately 22% of the thermoplastic powder industry.

Polyamide 11, a member of the nylon family of polymers, is produced by the polymerization of 11-amino-undecanoic acid. The source of this organic acid is castor beans. Arkema produces this polymer and markets it under the trade name RilsanÂź. PA-11 is used for a variety of products requiring high performance including dishwasher racks, auto parts, potable water pipelines, outdoor furniture, medical instruments, and commercial grade outdoor lighting. ⁶

LOW-TEMPERATURE CURE

Low-temperature cure is another subgenre of sustainable products. Reducing the energy requirements to cure coatings reduces carbon footprint and saves operating costs. Major resin companies offer products that reduce the typical powder-cure requirement of 15 to 20 minutes at 190 to 200 °C to a more energy efficient 10 to 15 minutes at 150 to 160 °C.

AkzoNobel recently introduced its Interpon Low-E (low-emissivity) collection of polyester powder coatings, which are designed to reduce the curing temperature and/or curing time without sacrificing the quality and properties of the coating. ⁷

AkzoNobel’s Interpon Low-E polyester powder coatings have a recommended bake temperature of between 150 and 170°C and cure in 8 to 40 minutes. By using this range, coaters can reduce their energy consumption and/or increase the productivity of their application process. This contributes to lower costs and improves its ecological footprint. Axalta debuted a similar line based on TGIC-free polyester technology called Alesta BE+ in Mexico in 2020.

IFS Coatings debuted a new product line for FBE (fusion-bonded epoxy) applications mainly for the functional markets including gas and oil pipelines and rebar (concrete reinforcement bar).⁸ IFS Pureflex Fastcure is a flexible, corrosion- resistant, single coat, thermosetting FBE powder with built-in rapid reactivity, which allows coaters increased line speeds along with energy savings from lower oven temperatures. This FBE powder will gel in 2-3 seconds and cure in only 12-15 seconds, depending on the temperature of the incoming bar.

HYPER-DURABILITY

Longevity of a coating and hence the durability of the coated item is another aspect of sustainability. The need to refresh or repaint products is costly, labor intensive and can involve field applied coatings possessing high VOC content.

Furthermore, if coating failure (e.g., severe corrosion) renders an item inoperable, the cost of replacement and disposal is antithetical to environmental stewardship. The powder coating industry recognizes this and has developed technology that significantly enhances the longevity of a coated asset.

The two most common powder approaches to coating longevity are UV durability and corrosion resistance. Hyper-durable powder coating technology is well positioned to take on the high-performance architectural market for skyscrapers and other monumental building products.

The North American architectural market abides by the AAMA specifications: 2603 (one year Florida durability), 2604 (five years Florida durability) and 2605 (10-plus years Florida durability).

Powder coatings meeting the AAMA 2604 specification have existed for decades and have a sterling track record of performance in the field. These are typically based on “superdurable” polyester binders combined with high performance pigments, fillers and additives. Superdurable solid polyester resins are based on isophthalic acid and corresponding aliphatic glycols and maintain greater than 50% gloss with minimal color change after five years of exposure in south Florida.⁹

Powder coatings meeting the more stringent AAMA 2605 requirements have recently been commercialized and are gaining momentum in the architectural market. These powders are based of fluoropolymer binders and can last up to 20 years in UV-intense environments such as south Florida.

Leaders in this arena include IFS Coatings, PPG, Axalta, ProTech and AkzoNobel. Prominent building projects have touted the use of AAMA 2605 powder coatings including the PNC Plaza in Pittsburgh (PPG Coraflon), and 55 Hudson Yards (PPG Coraflon) and 10 & 30 Hudson Yards (AkzoNobel Fluoromax) in Manhattan.

AAMA 2605 compliant powder coating technology is based on proprietary FEVE (fluoro-ethylene vinyl ether) resin technology that comes from AGC Chemicals America. These resins, dubbed LumiflonÂź are hydroxyl functional fluoropolymers and typically cure with aliphatic blocked isocyanate crosslinkers commonly used in polyurethane powder coatings.

A myriad of coating colors, gloss and surface profiles can be produced with this fluoropolymer binder system including satins, gloss and textures to meet the discerning eyes of architectural design engineers.

OTHER TECHNOLOGY TRENDS IN POWDER COATINGS

Several new developments are emerging across the powder coating technology spectrum. An unexpected shift in the use of curing agents has occurred largely due to supply chain difficulties. New approaches to antimicrobial performance continue to develop as companies try to help manufacturers stay ahead of the concerns for infectious viral spread.

Novel techniques for bonding special-effect pigments to powder coatings have been identified in university research laboratories. Instrumentation techniques continue to evolve with the development of surface profile characterization innovations. Control technology for powder application equipment has advanced with more sophisticated software to fine-tune application parameters.

SHIFT IN POLYESTER CURING AGENT TECHNOLOGY

An ongoing technical trend in the industry involves a transition of crosslinkers used to cure polyester powder coatings. TGIC has been the predominate curing agent for polyester powder coatings since the 1970s.

PrimidÂź XL-552 was introduced by Rohm & Haas in the 1980s as an alternative to TGIC. Chemically this material is a beta hydroxyl alkyl amide and hence is referred to generically as HAA. Powders using this crosslinker are also described as “TGIC-Free Polyesters.”

HAA took a while to gain acceptance in the powder industry. However, a watershed moment occurred in the early 1990s when the nascent European Union identified TGIC as a potential mutagen and required new labeling for products containing it. This strict labeling requirement, including a skull-and-crossbones image, motivated European powder manufacturers to shift polyester curing systems from TGIC to HAA.

It was a different story in North America. Neither the EPA nor OSHA required such labeling, nor did the state of California. Consequently, TGIC continued to hold the lion’s share of the market in the United States.

HAA-based polyester powders crept into the market mainly through multinational producers of powder coatings, oftentimes as part of their global powder coating platforms. In other cases, the improved first pass transfer efficiency observed with HAA polyesters prompted the change. In a few isolated cases it was related to food contact requirements.

Recently the pace of transition from TGIC to HAA has increased. Some of this is due to shortages of supply of TGIC, most of which is produced in China. Two TGIC production sites recently suspended production because of state inspections regarding environment compliance.

This tightened the supply of TGIC which, in turn, encouraged powder producers to make a switch to HAAbased polyester powders. PCR Group’s 2019 market analysis pegged the North American share of HAA powders at a paltry 3.2% compared to TGIC’s robust 43.5% share of the powder market.¹⁰

The current North American market share for HAA powders is now estimated to be 5.7% and climbing at the expense of TGIC polyesters. This trend is expected to continue throughout 2021.

ANTIMICROBIAL COATINGS

The COVID-19 pandemic has brought an increased focus on materials technology capable of creating hygienic surfaces. Multiple organizations have been feverishly pursuing a solution to stem the spread of the novel coronavirus.

Industrial Engineering Chemical Research Journal reports that scientists in China and from Western Ontario University have developed an improved technique to use silver ions to kill infectious microbes including the novel coronavirus. ¹¹

Their technique involves chemically bonding silver nanoparticles to Ag, Cu, and Zn ternary zeolites using alpha lipoic acid then encapsulated by hydrophilic polymers. They claim that this combination controls the release of silver ions and thereby significantly increases the longevity of efficacy provided by the silver ions. They offer test data that shows a 99.99% of kill rate of various bacteria after being wiped 1,200 times with cleaning solution.

Raising the bar even higher, Keyland Polymer has developed a special antimicrobial coating that is not only a powder coating but also can be cured within minutes at 100 to 125°C because it is based on UV cure powder technology.¹²

Unlike thermosetting powders, UV curable powder coating technology separates the melt phase from the curing phase, allowing for consistent, even film formation before the crosslinking reaction kicks in.

This technology, dubbed UVMax¼ Defender, provides added antimicrobial protection for Keyland Polymer’s entire line of UV-cured powder coatings. These products use silver ion technology and third-party testing showed reproduction of E. coli and Staphylococcus microbes were reduced by more than 99.99% with these coatings.

UVMax Defender can be used on plastic, composite, medium density fiberboard (MDF), wood, and metal substrates and is ideal for healthcare, public transportation, hospitality, education, food service, consumer goods, or other coated products where harmful bacteria can be prevalent.

BONDED METALLIC POWDERS

Progress in Organic Coatings journal published a paper in 2020 that detailed a new technique to bond metallic particles such as aluminum flake to powder coatings.¹³ The concept of bonded metallics is nothing new, but these researchers from China and Western Ontario offer a new twist.

They developed a technique using microwave energy instead of the heat generated from high-intensity mechanical mixing to fuse the metallic particles to the organic powder coating.

They claim that the microwave process gets the job done at a significantly lower temperature (<80 °C) than the conventional method which can approach the Tg (transition temperature) of a powder coating binder, typically ranging from 85 to 90 °C.

In addition, they purport that a higher degree of bonding occurs with their method. It will be interesting to see how these pioneers approach commercializing this type of process on a production scale.

INSTRUMENTATION AND TESTING

AkzoNobel and BYK-Gardner collaborated to address a complex issue plaguing the powder coating industry—how to quantify surface texture. This partnership spawned the development of the spectro2profiler, which concisely and consistently measures the textured surface of a powder coating.¹⁴

Until now, this aesthetic property could only be described qualitatively through visual inspection. The spectro2profiler can measure color, gloss, and three-dimensional topography of surface texture.

BYK-Gardner explains that the spectro2profiler uses a circumferential illumination at 45° with 0° viewing. The circumferential illumination is essential to achieve repeatable measurement results on textured surfaces.

The extra-large measurement spot with homogeneous illumination guarantees highly reliable and representative readings. This sounds like a game changer for characterizing the appearance of textured powder coatings.

Defelsko developed a new generation PosiTector Gage Body. This major innovation has a plethora of new features such as a larger 2.8-inch impact-resistant color touchscreen with redesigned keypad for quick menu navigation which can include touchscreen keyboard for quickly renaming batches, adding notes, and more.

This new-generation product is more user friendly with a help feature in the software that explains menu items at the touch of a button and an updated, stylized user interface retains the same familiar menu structure for easy one-handed menu navigation with or without gloves.

Furthermore, durability has been upgraded with a weatherproof, dustproof, and water-resistant IP65-rated enclosure and shock-absorbing rubber holster ideal for the toughest environmental conditions including an unexpected rainstorm.

APPLICATION EQUIPMENT SOFTWARE

Powder coating equipment makers have introduced more sophisticated coating-application control software in the form of user-friendly apps. GEMA’s OptiStar¼ 4.0 controls crucial coating parameters such as pneumatic and electrostatic parameters.

These relevant coating data can be then accessed on a mobile device with the company’s Electrostatic App. Moreover, its DVC technology ensures precise and reproducible powder output and ensures consistent film thickness. Finally, GEMA’s PCC and SuperCorona software improves penetration, reduces back ionization, orange peel, and picture framing.

Nordson recently introduced new application control software dubbed EncoreÂź Engage. It features an easy-to-understand, 15-inch touchscreen with modern graphics and intuitive symbol-driven navigation.

In addition, a guided recipe feature provides step-by-step navigation with preset options to help operators confidently create new recipes. Video tutorials and guided instructions provide greater visibility to key information and give additional support for critical tasks. For operators around the world, Encore EngageÂź includes several screen language options and its controller interface delivers easy navigation and enables industrial internet of things (IIoT)/Industry 4.0 functionality for powder coating application.

Parker Ionics has focused on improving its exclusive Pulse-Power gun control technology. Its new GX8500A powder application system features a 3G patented Super Pulse Power coronacharging technology that provides superior first pass transfer efficiencies on all shapes and substrates.

In addition, it is fully digital with simple controls featuring 250-recipe capacity. Parker explains that the GX8500A is excellent for coating boxes, wheels, piping, MDF and extrusions and that it possesses the highest transfer efficiency in the industry, resulting in lower operating costs.

The dynamic powder coating industry is emerging from the doldrums of 2020 with introducing innovation and game changing technology to advance the performance, consistency and reliability of the finish it gives to a universe of durable products.

References

1. Powder Coatings Research Group. Powder Coating Market, internal report, February 2021.
2. Grant, Mitchell. Sustainable Investing Terms: Sustainability. Investopedia. Updated Oct 13, 2020. (accessed May 6, 2021).
3. Allnex Coatings Resins website.  (accessed May 6, 2021).
4. The Sherwin Williams Company. Powdura ECO Powder Coatings | General Industrial Coatings
5. Biller, K.M. Recent Advances in iobased Powder Coating Technology: Improvements in Low Temperature and Outdoor Durability. Presented at Advanced Coatings Technology 2018, Sosnowiec, Poland.
6. Arkema website. Rilsan ^¼—Polyamide 11.  (accessed May 6, 2021).
7. AkzoNobel website. Interpon Low-E: Low cure polyester powder coating | Interpon
8. IFS Coatings website. IFS Pureflex functional powder coating.
9. Powder Coating Research Group. Internal laboratory test data. nd.
10. Powder Coating Research Group. Powder Coating Market, internal report, 2019.
11. Cui, J.; Yeasmin, R.; Shao, Y.; Zhang, Haiping; Zhang, Hui; Zhu, J. Fabrication of Ag+, Cu2+, and Zn2+ Ternary Ion-Exchanged Zeolite as an Antimicrobial Agent in Powder Coating, Ind. Eng. Chem. Res. 2020, vol. 59, no. 2, pp 751–762.
12. Coatings World, VideoBite: Keyland Polymer Material Science, 23 Feb 2021,Ìę.
13. Liu, W.; Zhang, H.; Shao, Y.; Zhang, H.; and Zhu, J. Preparation of aluminium metallic pigmented powder coatings with high color stability using a novel method: Microwave bonding. Progress in Organic Coatings, October 2020, vol. 147, 105787.
14. AkzoNobel and BYK-Gardner Launch spectro2profiler to Measure and Control Textured Powder Coating Surfaces,ÌęIPCM, April 5, 2020.

Numerous changes in end-use markets, both existing and new, are driving the development of low-temperature cure powder coating technologies. For existing automotive, aerospace, and general industrial applications, the growing demand for more sustainable products and processes is a key contributing factor.

Powder coatings contain no solvent (e.g., volatile organic compounds), and the application process results in minimal product waste. They also enable the rapid application of high-film builds with excellent appearance and protection against chipping, abrasion, chemicals, corrosion, and weathering. However, energy consumption is still an issue for traditional coatings that cure at relatively high temperatures. These high temperatures also prevent the use of traditional powder coatings on temperature-sensitive substrates including wood, medium-density fiberboard (MDF), most plastics, composites, and some metals, such as aluminum.

Very large metal components are also unsuitable for powder coatings due to the need to heat the large substrate masses involved. With the emphasis on lightweighting that exists today in the automotive and aerospace industries, many temperature-sensitive substrates are increasingly used. In addition, a growing number of components for a wide range of applications are produced today using three-dimensional (3D) or additive printing technologies, and there is a need for coating technologies suitable for these substrates that can provide a similar appearance across many surfaces.

The global market for low-temperature powder coatings (polyesters and polyester-epoxy hybrids, epoxies, polyurethanes, and acrylics) is estimated by market research firm Markets and Markets to be expanding at a compound annual growth rate (CAGR) of 5.7% from $1.4 million in 2018 to $1.8 million by 2023.¹ End-use markets covered in the study include the furniture, appliances, automotive, architectural, electronics and medical sectors, with the highest growth occurring in the furniture market.

Notably, the non-metal segment is expected to experience the highest CAGR during the forecast period and account for the larger share of the low-temperature powder coatings market. With respect to resin chemistry, polyesters and polyester hybrids are the most widely used and will continue to be so through 2023. The major low-temperature powder coating manufacturers include AkzoNobel, Axalta Coating Systems, Jotun, PPG Industries, and The Sherwin-Williams Company, among others.

Achieving lower-temperature cure has required increased reactivity of the resin chemistries used in powder coating formulations, as well as the introduction of new curing mechanisms. Today, binders are available that allow curing of powder coating formulations via heating at temperatures as low as 130–160 °C. Other low-temperature powder coatings on the market today are cured using infrared radiation ovens. The latter approach is ideal for temperature-sensitive substrates because the intensity and/or duration of the radiative heat source can be reduced or even completely removed if the temperature of the substrate becomes too elevated. This solution works with powder coatings with curing mechanisms that can be interrupted without affecting the properties of the coating once curing is completed.

In September 2020, AkzoNobel expanded its powder coatings offerings with the acquisition of Stahl Performance Powder Coatings, which included its range of products for heat-sensitive substrates.² The low-temperature curing technologies include both UV and thermally curing powders that cure at ultra-low (80–100 °C) temperatures and are ideally suited for use on MDF, plywood, thermoplastics, and composites.

“The clearly differentiating UV technology in particular is expected to see significant growth and will further strengthen our position as a complete provider of sustainable solutions for heat-sensitive substrates in particular for our wood coatings customers,” said Daniela Vlad, business director of AkzoNobel Powder Coatings. AkzoNobel already offers a range of Interpon Low-E (Low Energy) polyester powder coatings (Interpon 610 Low-E and Interpon Coarse Texture Low-E) that cure between 150 and 170 °C and offer anti-gassing technology, making them suitable for porous substrates, as well as other substrates found in many applications including industrial steel products, street and garden furniture, and agricultural and construction equipment. In addition, they are effective in both interior and exterior environments.

Meanwhile, Cleveland-based coatings producer Keyland Polymer develops, formulates, manufactures, and sells UV-cured powder coatings for use on MDF and other heat-sensitive substrates, including MDF, plastics, composites, metals, and other materials.³ The coatings are used by neighbor DVUV, a manufacturer of custom powder-coated components and parts for the retail, store fixture, POP display, healthcare, educational, and office furniture industries.

In the coating process, the MDF parts are hung on the line and sprayed with compressed air to remove any dust and then heated for one minute in a low-temperature preheat oven to encourage outgassing and bring moisture to the surface for increased conductivity. The coating is then electrostatically applied using an automating spraying system, and the parts are once again heated at low temperature for one minute to melt/gel the powder. The coating is then instantly cured under UV lamps. The entire process takes about 20 minutes.

Advances in biobased low-temperature powder coating technologies have also occurred in recent years.⁴ For example, allnex developed a line of biobased carboxyl polyesters based on renewable monomers derived from C5 and C6 sugars that can be used in a variety of powder coating systems, including epoxy-polyester hybrids, polyester-HAA (hydroxyl-alkyl amide), and TGIC-cured formulas.

Battelle Memorial Institute developed low-temperature curing powder coatings based on highly aliphatic polyester amide resins prepared from long-chain aliphatic diacids synthesized from high oleic soybean oil and di-ethanol amine. Powder coatings with 85% biobased content formulated with resins prepared using this approach and various glycidyl functional and hydroxyl-alkyl amide curing agents were found to exhibit excellent film properties even when cured at 135 °C. The resins have been produced at the pilot scale and application trials performed at infrared curing test facilities and MDF powder coating operations. It is
also worth noting that allnex offers a range of low-temperature curing polyester powder resins (CRYLCOAT) for both indoor and outdoor applications, including hybrid, standard durable, and superdurable systems.

References

1. Markets and Markets, “Low Temperature Powder Coatings Market by Substrate (Non-metal, Metal), Resin (Polyester & Hybrids, Epoxy & Hybrids, PU, Acrylic), End-use Industry (Furniture, Appliances, Automotive, Architectural, Electronics, Medical), and Region – Forecast to 2023,” December 2018. https://www.marketsandmarkets.com/Market-Reports/low-temperature-
   powder-coating-market-171394651.html (accessed Oct 12, 2020).
2. AkzoNobel, “AkzoNobel gains unique low cure technology with acquisition of Stahl’s powder activities,” Sept 2, 2020. https://www.akzonobel.com/en/for-media/media-releases-and-features/akzonobel-gains-unique-low-cure-technology-acquisition-stahl%E2%80%99s
   (accessed Oct 12, 2020).
3. Copeland, L. “UV-Cured Powder Coating Speeds MDF Application
   Process Time,” UV+EB Technology, Feb 25, 2020. https://uvebtech.com/articles/2020/uv-cured-powder-coating-speeds-mdf-application-
   process-time/ (accessed Oct 12, 2020).
4. Biller, K. “Recent Advancements in Bio-based PowderCoating Technology,” Powder Coated Touch, Mar 22, 2019. https://www.powdercoatedtough.com/
   News/ID/5111/Recent-Advancements-in-Bio-based-Powder-Coating-Technology (accessed Oct 12, 2020).

CoatingsTech | Vol. 17, No. 11 | November/December 2020