Over the past two or three decades, there has been a well-publicized amount of consolidation within the paint and coatings industry that has often trudged behind the demise of large customers such as Sears, Roebuck and Co. (1889-2018).

Sears-branded paint accounted for 43% of DeSoto Paint Co. coatings, and losing this large customer was the beginning of the end. One of my personal favorite house paints of all time was the Sears Ultralight Latex Interior House Paint, which—with almost imperceptible drops of color added to a gallon of white satin paint—provided a subtle, color-shifting visage to any room. Hints of color danced on the walls, depending on the day’s weather—sunny or cloudy—and even upon the type of light bulbs used in lamps and chandeliers. Unfortunately, both DeSoto and Sears are now distant memories, swallowed up by other companies or private equity groups, their products visible in aging family photographs.

Maximizing a coating’s durability is a complex equation that must account for multiple factors.¹ Making matters even more challenging is the fact that formulators have been missing a critical piece of information about how titanium dioxide (TiO₂) can influence durability—until now.

Today’s paint producers and formulators are under heightened pressure to create highly durable coatings for exterior architectural and industrial applications capable of standing up against harsh UV rays, rising temperatures, and severe weather events. At the same time, many applications also demand greater efficiency via longer-lasting coatings that increase the length of service before recoating and reduce material and labor costs.

TiO₂, a critical component of high-quality, highly protective coatings, is known to have several effects on paint durability that formulators must consider.^2-10 As a strong UV light absorber, TiO₂ protects underlying resin from direct interactions with the UV component of sunlight. However, TiO₂ can convert some of the UV light energy into chemical energy in the form of radicals, which can then attack the binder or react with other molecules at the surface that can lead to further paint degradation. In addition to the inherent photoactivity of the TiO₂ pigment, the degree of TiO₂ dispersion also plays an important role in determining a paint’s durability.

It is logical for formulators to assume that by decreasing the photoactivity they can create a more durable coating. However, a more nuanced approach shows that TiO₂ grade can affect paint durability beyond simple TiO₂ photoactivity.

Closing a Crucial Information Gap

It has been previously established that initial paint gloss—a paint characteristic that is highly representative of pigment dispersion—has an effect on gloss retention independent of TiO₂ photocatalytic activity.¹¹ However, the effect of degree of dispersion on color stability (fade) of paints has not been studied in the same way. This is because the durability of paints with poor TiO₂ dispersion is seldom measured. Durability testing is expensive and time-consuming, whereas TiO₂ opacity testing—which is also related to degree of dispersion—can be used to identify and reject poorly dispersed paints quickly and for little cost.
As such, there is limited information available that separates the effect of TiO₂ dispersion on paint durability from the effect of TiO₂ photocatalytic activity. This information gap has made creating coatings that maximize paint durability challenging for formulators.

To create high-quality paints that provide a high level of protection from the elements, formulators must fully understand the relative importance of photoactivity and TiO₂ dispersion on paint durability. At Chemours, we wanted to measure and quantify this relationship to help formulators make the highest-quality products possible. To do so, we conducted an experiment to shine a light on this process and uncover exactly how the degree of TiO₂ dispersion can affect color stability, a critical aspect of a coating’s durability.

Continue reading in the �Ǵ���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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From the very first paints to today, the discovery and development of the purest of materials and pigments has been a goal for artists and designers alike. The search for the blackest of black pigments is likely now at its end, or nearly so, with the development of carbon nanotube-based paints that swallow more than 99% of light across the visible spectrum.

The focus of our paint development over the last five years has been on creating the blackest matte-black paints using carbon nanotubes and tailoring them for use across the ultraviolet, visible, and infrared. Vertically aligned carbon nanotube arrays (VANTA) hold the record as the world’s blackest, most highly absorbing materials, and this is due both to their chemical composition and their structure.

The optical properties of carbon nanotubes are crystallographically dependent, as their structure is highly anisotropic. Nanotubes are similar to graphite, which has different in-plane and thru-thickness optical constants, except that in carbon nanotubes, the planes are wrapped into a tubular shape. As a result, VANTA coatings are not very black at grazing-angle incidence, due to that structural anisotropy. The VANTA coatings are synthesized at >500 °C, limiting the materials that can host such a material.

To address this and other issues, we have researched and developed optically absorbing carbon nanotube-loaded paints (now marketed as Singularity Black). These use a more randomized structure that has been tailored for high-optical and infrared absorption at normal and grazing-angle incidence. describes the structures necessary for highly absorbing black coatings and reviews the approach and data collected for two products, Singularity Black paint, and our version of vertically aligned nanotube arrays, adVANTA.

Color selection and pigment development go hand in hand. End users gather data on trends in consumer color preferences to determine new colors for upcoming product lines. Those color selections then must be realized using existing or new pigment technologies developed to address attributes such as hue, opacity, brightness, and appearance.

Color selection and formulation are complex processes. There are, according to Hannah Yeo, manager of color marketing and development for Benjamin Moore, hundreds of unique color spaces, but that is only part of the story.

There are also different shades within each unique color space, which can result in colors being unique for each vendor based on their manufacturing process and raw materials. The overall color selection process, therefore, must involve the product designer, paint formulator, and pigment manufacturer.

“A close partnership is of utmost importance to ensure a regular exchange on market needs and trends on the one hand and coloration possibilities and innovations on the other hand,” says Tom Landuydt, head of industry management for automotive coatings with the BASF Colors & Effects® pigment business. “Long-term collaboration enables services around the colorant and mutual understanding about the requirements for ideal pigment selection based on color and performance,” he adds. “Moreover, it forms the basis for the development of next-generation pigments for future color selections.”

COLOR FORECASTING AND PALETTE DEVELOPMENT

Color selection for future product development depends on many factors. Customer preference is a top consideration, but with larger products such as vehicles, product design can also be important. “Color selection is a dynamic process,” says Craig Swift, senior mastering specialist at the Ford Motor Company Product Development Center. “And at Ford, we often use coatings to differentiate our vehicle series from the competition.”

Some color spaces, he adds, may allow for emphasis of a particular set of attributes, but everything must adhere to production standards. In addition, the rapid move toward automotive electrification creates additional challenges around pigment detection and interference with advanced sensor systems, and some series on the same vehicle platforms can have different needs. Finally, Swift says that while Ford pays close attention to trends, the company is not so rigid that it can’t be a trendsetter.

Coating formulators help their end customers with color selection by providing insights on color trends. PPG, for instance, offers a broad palette of more than 2,000 architectural coating shades but also curates specific palettes that reflect annual trends to make the selection process simpler for its customers, according to Kristi Kauffman, PPG senior technical manager for architectural coatings, research and development, color.

Benjamin Moore’s portfolio contains 3,500-plus colors that are appropriate for architectural coatings and meeting the needs of customers, but the company also develops curated palettes for project-specific products chosen based on in-depth research on demand and usage in that specific application, Yeo says.

The specific palettes at PPG are developed once PPG’s global color styling team builds industry color trends based on global, cross-cultural lifestyle, fashion, and design insights. “We always develop colors that are not only trending and resonate with consumers, but that can also pass all finishing tolerances set by customer standards,” says Vanessa Peterson, PPG’s color design manager for consumer electronics.

For automotive applications, pigments are selected that guarantee the necessary durability, stability, and workability, while also enabling sustainability, innovation, and coatings compatibility with new vehicle technologies (i.e., radar and LIDAR) needed for assisted and autonomous driving, according to Federico Menta, PPG global technical director for automotive OEM coatings.

In PPG’s automotive refinish and commercial fleet/industrial business, formulas are provided that meet repair needs specific to each market and match the variation of colors seen on vehicles on the road. PPG’s team of color formulation experts located at various ports of entry are a crucial component of the company’s success because they identify new color variations as soon as vehicles are introduced to the U.S. market, notes Natalie Scott, PPG marketing manager, automotive refinish color, in North America.

PIGMENT AND COLOR INNOVATION

When it comes to developing new colorant and pigment technologies, some drivers apply to all pigments, while others can be application-specific. Jerry Powers, technical director—Coatings Americas for Chromaflo Technologies, identifies four development buckets: to satisfy the market need for improved technology; to create products that meet regulatory requirements and anticipate future changes; to achieve product sustainability in a competitive market that can also be impacted by raw material costs and availability; and to “think outside the box” and enable market disruption (the fun bucket).

Paul Nowak, director of sales and marketing in the Americas at Korean pigment manufacturer CQV, identifies four primary drivers for pigment innovation: the market demand for unique materials; emerging color trends; the need for functionality or other physical properties to meet customer requirements or create a competitive advantage; and upgrades in manufacturing processes and changes in application technologies.

Regardless of how development drivers are categorized, the overall goals, according to Landuydt, are expanding the color and effect space and improving performance and processability. In general, he adds, new pigment chemistries enable formulators to reach the vibrant shades requested by consumers and designers across all applications.

Regulatory drivers, including reduced use of biocides, elimination of heavy metal pigments, the need for APEO (alkylphenol ethoxylate)-free and low-VOC colorants and DCB (dichlorobenzidine)- and PCB (polychlorinated byphenyl)-free pigments, and the desire for increased sustainability, which is driving the shift from solventborne to water-based coatings, are also common across applications, says Gabriela Seefeldt, head of industry management architectural and industrial coatings at BASF Colors & Effects. She also points to a general expectation for increased durability and a greater ease of use, such as easy dispersible pigment preparations and innovative technologies like dry dosing at the point of sale.

Companies are also always looking to optimize the “cost” of pigments either on a cost-by-weight or cost-to-performance basis, according to Mark Ryan, marketing manager at The Shepherd Color Company. Functionality beyond color gains is also increasingly important. As examples, he cites adding hyperspectral properties to coatings in the near-infrared (IR), which keep materials cooler and can also create visually invisible markings that are readable by autonomous driving vehicles.

Improvements in manufacturability can entail a multitude of advances in manufacturing equipment and process control. Nowak of CQV notes examples such as computer-metered addition of raw materials for reduced operator errors, use of artificial intelligence to monitor chemical reactions for greater operational efficiencies, in-line sensing to obtain real-time feedback for more consistent manufacturing processes. “All of these approaches lead to higher quality, more cost-efficient products,” he says.

New pigment chemistries enable formulators to reach the vibrant shades requested by consumers and designers across all applications.

Changes in end-user technologies can also create a need for new pigment chemistries, according to Nowak. The ink industry, for instance, is shifting to energy-cure and digital printing and away from traditional liquid heat set processes. The movement from liquid to powder coatings for some applications is also requiring modification of existing pigment chemistries. Air vs. electrostatic spray application may also require changes in particle size or the creation of more robust pigments that can handle the extrusion process used for powder coating production.

The “holy grail” for a pigment supplier is to develop a colorant that can provide a new, fresh, never-before-seen, widely applicable, visual experience that is globally accepted across multiple markets and product lines, Nowak says. “Such tools, when put into the hands of a creative design person, can spark a global wildfire leading to economic prosperity for the colorant manufacturer and the manufacturers of consumer products,” he says.

When it comes to choosing pigments for a specific application, Nowak adds that expected life cycle (warranties), consumer protections in the form of governmental safety or environmental requirements, ability to change colors easily and often, cost, are all determinants in what colorants are used. If a supplier wishes to sell into a specific industry or for a specific application, the pigment/colorant must be suitable and meet the minimum requirements for that application or industry, and that, he says, may require product development.

“To achieve competitive advantage, pigments might be made brighter, more chromatic, more easily dispersed, more durable, non-dusting, or more environmentally acceptable (sustainable, lower carbon footprint during manufacture, or suitable for recycling) or have added functionality, such as anti-corrosive properties, acid etch resistance, better adhesion, or improved resistance to outside detrimental influences like pollution, depending on the specific application,” Nowak explains.

For different industry segments, some specific drivers are worth mentioning. For automotive coatings, bright, highly transparent, and durable pigments are essential. Pigments must also be compatible with new resins, and there is growing demand for LIDAR-ready pigments, according to Andreas Harz, head of preparations coatings in the Americas at Clariant. “These evolving technologies, like self-driving cars, require unique road markings to function safely and effectively; consequently, a lot of attention is being paid to what is needed for those developing transportation concerns,” he says.

In the architectural space, Harz notes, exterior coatings such as those for decks require improved resistance to mildew and color permanency, which is leading to the development new coatings systems, and colorants must be compatible with these new technologies. Similarly, IR-reflecting pigments aid “cool coatings” for roof and wall coverings but also must meet requirements for color fastness and resistance to efflorescence. Meanwhile, for interior applications, antimicrobial (antibacterial, antiviral) coatings are receiving significant attention, and thus pigments and additives that can help improve microbial resistance have become important, according to Harz.

COLLABORATION ACROSS THE SUPPLY CHAIN

Truly successful color and pigment development involves cooperation between experts at end users, formulators and pigment manufacturers. Ford, for instance, works closely with both paint and colorant suppliers to evaluate new pigments that can enhance a traditional color space in a new and exciting way, according to Swift. Typically, the big coating suppliers to the automotive industry hold shows each year to introduce their different color lines. “Sometimes these formulations can be used as is except to ensure they meet all production specifications, but other times alternative colors are needed to fit a specific theme,” Swift says.

Car manufacturers face different challenges. “It is a very complex process to get all the different paint chemistries that go on all the different substrates and geometries to look the same as you walk around a vehicle,” Swift says. Sheet metal is painted at the plant with one coating technology; an ABS spoiler is made by one supplier and painted with a totally different chemistry; and the TPO facia comes from another supplier and is coated with yet another chemistry. “In addition, the paints used on all of the different parts of one vehicle may come from five or six different paint suppliers. The key is developing effective color masters and working closely with suppliers to help them adjust processing parameters so all of the components, regardless of substrate and paint chemistry, end up with an applied color that matches the master,” Swift explains.

Formulators, meanwhile, work with both customers and pigment suppliers to develop optimal coatings with the right color performance. Benjamin Moore, for instance, is in constant contact with architects, designers, and contractors to understand their needs and ensure they are equipped with appropriate product and color, Yeo says. For new product launches, department members from Product, Color Marketing & Development, Color Technology, and R&D work together to provide the best solution. They gather as much information as possible from pigment suppliers to ensure that the company’s proprietary chemistries marry well with pigments in the target color spaces to deliver dispersions with robust chroma that deliver the broadest palettes, Yeo explains.

The team also meets regularly with pigment suppliers to discuss technological advances in pigment chemistries, novel new color spaces, logistics, regulations, and more. “Creating pigment dispersions is a delicate balance of chemistry and physics. The chemistries required to do this are specific not only to colors, but often to the vendor as well,” Yeo says. “Our laboratory works closely with vendors, procurement, and manufacturing to ensure we have the highest quality pigments for use in efficient manufacturing processes and that we deliver an outstanding customer experience.”

One of PPG’s core principles is to partner with customers to create mutual value. As a best practice, Kauffman notes, the company aims to anticipate the needs of customers and work alongside them to leverage PPG’s longstanding, insights-driven approach to innovation and color trends. In the auto industry, for instance, new color programs are built in partnership with each automakers’ design team to ensure that the uniqueness of each brand and their designs are taken into consideration.

The key is developing effective color masters and working closely with suppliers to help them adjust processing parameters so all of the components, regardless of substrate and paint chemistry, end up with an applied color that matches the master.

PPG customers across businesses visit the company for face-to-face color workshops, but in light of the COVID-19 pandemic, it is more common to discuss options via remote workshops, according to Peterson. Digitalization in general is becoming increasingly important as part of the color-creation process. Menta says that PPG is creating future-forward digital tools to increase collaboration and intimacy with its customers, allowing increased efficiency and shortening the time to market.

Working with pigment suppliers is equally important for formulators. “Our customers are always looking for the latest trends and that which will separate them from the competition,” Peterson says. “Color trends push boundaries within the industry and lead to experimentation in new ways of preserving color, especially within electronic materials and industrial coatings. It’s vital that we continue to work closely with suppliers to inspire them and educate them on the needs of the clients in the hope that these desired effects will be manufactured.”

For the automotive market, PPG predicts needs in the early stages of the design process and works closely with pigment suppliers to develop new products/pigments in order to provide differentiated color developments for its customers, according to Menta. “We strive to reduce our complexity in order to be able to drive sustainable innovation and environmental stewardship,” Menta says. “Those goals are in part achieved by delivering new pigments and effects each year based on the work done with our suppliers.”

Pigment suppliers, meanwhile, have the deep knowledge and understanding of their technologies and are best positioned to recommend optimal pigment solutions for a given application, particularly when they have expertise with a broad palette of both organic and inorganic pigments, according to Frank P. Lavieri, executive vice president of sales and marketing at DCL.

Based on Chromaflo’s experience, having a range of options that suit different market segments is crucial for guiding colorant selection because what colors/colorants a coatings company requires can depend on the application. Input from formulators is absolutely crucial as well, Powers adds.

“While there are industry-accepted standards and methods, sometimes coatings companies have expectations that can be higher than typical benchmarks or may add other requirements specific to their technical objectives,” he explains. “Considering the application that the colorants will be used in and the potential exposure requirements before the color project begins is also necessary for identifying the pigment choices that provide longer-term value. The key element to a successful outcome of this process is to have a thorough technical discussion at the beginning of the project to determine the requirements of the colorant and the impact on the coating performance.”

At BASF Colors & Effects, pigment experts are also engaged throughout the coating production process to ensure that customer requirements are well-translated into the correct product selection and highest level of service, according to Seefeldt. Those services can include recommendation of a pigment that adds the required benefit to a formulation, guidance to ensure optimal processing, and laboratory, heat management, and mixing-system calculation support for optimization of the complete coating system.

Clariant shares its color trends knowledge and formulation ideas with coating technicians in the architectural and automotive industries through webinars and in-person meetings and works closely with manufacturers to develop new pigments and dispersions that support their product development objectives, according to Harz.

Shepherd Color also brings experimental products to the attention of the company’s key industry partners to gauge interest in new technologies. “Since our products are often used in high-durability coatings, getting new pigments into long-term testing as early as possible allows them to be used at the earliest possible time,” Ryan notes.

CQV makes a point of staying in regular contact with the entire chain of teams responsible for developing a color, including those responsible for fleshing out “trend colors,” purchasing, personnel responsible for testing and dispersion, and formulators responsible for commercialization, according to Nowak. In addition to offering guidance on global and regional color trends, the company offers prototype examples of those trends using our colorants, providing data on manufacturing specifications, physical properties, and regulatory compliance.

During the pandemic, Shepherd Color has been exploring ways to communicate color by using interactive 3D displays of color space, providing formulators with another context for understanding the potential of new shades and products. Landuydt says through advances in virtual color technology, appearance and color travel can be effectively shown as well, allowing both sides to understand the properties of a colorant even in remote locations.

CUSTOMIZATION WHEN NECESSARY

While both formulators and pigment suppliers have robust portfolios that meet most end-user needs, there are occasions when projects have unique color and appearance requirements and thus the need for unique pigment/colorant solutions. Nowak notes that the need for customized solutions has been growing in recent years.

The key element to a successful outcome of this process is to have a thorough technical discussion at the beginning of the project to determine the requirements of the colorant and the impact on the coating performance.

“Over time, companies have developed their own unique resin chemistries and formulations that have taken many divergent paths. The result is that no one pigment may be universal for all of these variants, and therefore a tailored approach is needed to make pigments and colorants suitable for a specific resin and formulation chemistry,” he explains. Examples may include added surface treatments, changes in pigment chemistry, or entire pigment reconstruction.

Established relationships between formulators and pigment suppliers become even more important for these projects. “Close relationships with pigment suppliers enables us as a formulator to order samples quickly and then rapidly develop the desired colors,” Peterson explains.

A robust R&D program is also essential for successful, tailored development of pigments for specific customer applications, according to Lavieri. Of course, the development work and resources required for such customized project must make business sense, Powers stresses. “These conversations take place quite regularly. Sometimes the customer may not be aware that a certain colorant technology already available within our existing product lines will meet their needs,” he says.

In some cases, specialized projects can lead to new product lines. For Clariant, that was the case when a customer struggling with flocculation resistance and color development in a resin system with a specific color index required an improved solventborne industrial dispersion system.

The newly developed technology solution led to the introduction of Clariant’s newest product range—Hostatint^™ SI dispersions for solvent-based industrial coatings. “Our easily dispersible pigments were designed for a very specific application and that technology has provided major cost savings in the manufacturing of coatings by reducing the need for expensive media mills,” says Romesh Kumar, Clariant’s senior technical sales manager for coatings in North America.

SPOTLIGHT ON NEW TECHNOLOGIES

Depending on the pigment industry in question (organic vs. inorganic vs. flake effect pigments), there have been numerous developments in pigment technology. In the organic space, the development of pigments that can be supplied as easily dispersed, non-dusting powders, eliminating the need for additional secondary processing, is one notable achievement, according to Nowak. Another is colorant dispersions based on hyper-dispersed organic pigments created using sonic dispersion equipment, which are less prone to agglomeration, resulting in stronger, cleaner, more durable pigments that approach the appearance of a dye.

BASF Colors & Effects, for instance, introduced eXpand!^® stir-in slurries for waterborne automotive coatings, including eXpand!^® Red EH 3530 in 2020, the first universal grade enabling intense shades in various coating systems. Pacific Yellow and Pacific Orange are other examples of universal pigments from BASF Colors & Effects with a good balance of properties, according to Seefeldt.

Clariant has also focused on the development of all-in-one solutions, and recently introduced Hostaperm® Scarlet GO, Hostaperm® Yellow H3G, and Novoperm® Orange HL70 universal pigments. The Hostafine® and Hostatint™ A 100-ST ranges of super-transparent dispersions for waterborne and solvent-based coatings, respectively, offer alternatives to traditional dyes and provide improved performance in terms of migration resistance, color permanency and color stability in coatings for wood, automotive, and consumer goods, Kumar says.

Increasing durability and pigment loading while reducing VOCs has been a focus for Chromaflo. The company has introduced new low-VOC pigments and colorant technologies for the architectural market that help coatings formulators with opacity and durability in both interior and exterior applications, according to Powers.

One example is the Colortrend Pearls 2020® line of 11 solid colorants for waterborne architectural and industrial applications in the EMEA market. “This alternative, dry colorant technology is biocide-free and can be volumetrically dosed due to the narrow particle size distribution of the product,” Powers says.

Close relationships with pigment suppliers enable formulators to order samples quickly and the rapidly develop the desired colors.

New colorant lines from Chromaflo are also enabling industrial coating formulators to move away from traditional solventborne systems. The new Chroma-Chem FLV series of biobased colorants are, Powers adds, a comprehensive improvement from older, standardized industrial colorants for use in industrial epoxy, polyaspartic, and polyurethane flooring applications. For industrial waterborne applications, the Chroma-Chem 897 line also enables industrial coating formulators to move away from solventborne systems, according to Powers.

DCL provides value beyond color with its new range of very opaque and strong organic pigments that enable low-cost formulas with excellent light and weather fastness properties, especially for liquid industrial coatings, says Lavieri.

Several companies have developed both inorganic and organic pigments intended to expand existing color spaces. Shepherd Color has improved on existing cobalt blues, which offer bright red shades, but with lower opacity and higher oil absorption than other inorganic pigments. By radically reducing the physical surface area without changing the chemistry, the company developed Blue 10C595, which offers lower oil absorption and much higher loading levels for greater coating opacity while still giving higher gloss and better flow, leveling, and distinctness of image, according to Ryan.

Shepherd Color’s patented NTP Yellow pigment chemistry, meanwhile, enables bright chromatic yellows with high opacity and excellent weathering. “When you pair the NTP Yellow with our RTZ Orange pigment, you can cover a wide range of the yellow color space with all inorganic, highly durable pigmentation,” Ryan says.

Bismuth Vanadate RMXS from DCL, according to Lavieri, is the strongest, most opaque bismuth vanadate pigment and allows for highly durable, lighter weight yellow vehicle coatings that lead to savings on fuel costs. BASF Colors & Effects recently launched highly chromatic inorganic pigments Sicopal® Turquoise and Red also provide for super-durable coatings without having to limit the color palette, according to Seefeldt.

BASF Colors & Effects has also expanded the red to blue color space with Lumina^® Royal Exterior Blue Russet S6903D, which Landuydt notes also provides superior sparkle to automotive OEM and refinish, aerospace, general industrial, and powder coatings.

To address the unique needs of pigments for coatings on autonomous vehicles, BASF Colors & Effects has developed functional black pigments such as Spectrasense^TM Black L 0086 and Sicopal® Black L 0095. In addition to providing detection of autonomous vehicle applications, these pigments also allow formulators to produce colors that meet heat management targets for architectural and industrial applications, according to Seefeldt. “Ultimately, the development of functional black pigments enables formulators to surpass new performance requirements without giving in on the color,” she says.

There have also been numerous advances in effect pigment technology. One that Nowak highlights includes the development of aluminum-flake pigments that are supplied as non-hazardous, easily dispersed, dry powders that are universally compatible (water/solvent/powder), circulation-degradation resistant, and available in thin silver dollar geometries, allowing the creation of brighter, cleaner, effects with smaller particle-size distributions. He also points to the development of colored aluminum pigments that allow the creation of highly chromatic colors with good opacity in the red, orange, gold, and copper color spaces as being notable.

Others worth mentioning, according to Nowak, include extremely thin, aluminum-based pigments that approach a liquid-metal effect; “real” white pearlescent pigments based on synthetic mica that are neutral in hue (not too warm “yellow” nor too cool “blue”) with good luster; and higher chroma, smaller particle-size-distribution effect pigments (< 25 um d(90)) in the red, blue, and violet color spaces.

Finally, two developments in colorant systems should be noted. In 2018, PPG developed FormulaPro™ High Strength Colorant, a new state-of-the-art colorant system used to develop colors for PPG’s architectural coatings. During the development of this system, PPG benchmarked commercially available colorant systems and worked closely with pigment providers to select features that would provide industry-leading performance with respect to durability, colorfastness, hiding power and range of colors, according to Kauffman.

Separately, BASF Colors & Effects introduced the XF200 dispenser, a solid dispensing system for point-of-sale (POS) use. The Xfast^® Easy Color software allows dosing of customized formulations of solid colorants directly into base paints. “By tackling three of the major cost factors of liquid systems—service, colorant viscosity changes, and sedimentation—it reduces expenses significantly and improves the everyday handling of POS systems,” Seefeldt says.

ALWAYS LOOKING TO EXPAND

Despite the numerous advances in pigment and colorant technologies that have been made over the years, there remain areas for improvement—and challenges to addressing them. “Our R&D team is constantly looking into new pigment varieties that can improve performance properties, make the life of coatings formulators easier and expand the color space, but they must be economical solutions; achieving the optimal cost-performance balance is the challenge,” Landuydt says. In addition, he notes that coating formulators ultimately would like a “one fits all” solution—a pigment that is compatible with all paint systems, provides the highest performance properties, can be stirred in and thus eliminate the need for milling, and achieves the highest variety of colors for a low price.

Kumar agrees, noting, “True universal colorants that can reduce the overall number of products needed to tint coatings and pigments for bright, opaque yellow, red, and orange shades are desired.”

The regulatory hurdles that must be overcome to get new pigment chemistries approved present another set of challenges, according to Ryan. “When you factor in the time and cost of these regulatory hurdles and then the restrictions placed on new chemistries, to bring new pigment technologies out to the market becomes a daunting task that requires a broad range of laboratory, regulatory, production and marketing resources,” he explains.

Development needs also differ for organic and inorganic pigments. As the demand for more chromatic shades increases in coating applications, so does the need for increasingly durable organic pigments capable of meeting strict exterior industry specifications, according to Seefeldt.

In fact, Kauffman notes, PPG is always looking for pigments that can offer more durability and hiding power, especially for organic pigments. Conversely, Seefeldt says that inorganic pigments with improved chroma would be well received by the industrial markets. From a coloristic point of view, she points to highly durable exterior coatings in the bluish-red area, especially formulations of magentas and violets, as the biggest challenge.

Ryan agrees that a red that performs like other high-performance inorganic pigments is the “holy grail.” The gap created by the necessary exit of heavy metal pigments for industrial coatings applications remains to be filled, Powers adds. “Bright, chromatic, durable (exposure to chemicals and weathering) pigments required for creating deep blues, greens, and especially yellows and reds, are needed in the market today,” he says.

For effect pigment manufacturers, Nowak says that there is yet another layer of difficulty created by the laws of physics, which will need to be broken if the current substrate oxide coating technology model continues to be applied.

“Our challenge is to find a new method to somehow engineer color and effect using a totally new model, which requires a breakthrough in some manufacturing process or discovery of a new raw material,” he says. “In the meantime, we must identify various permutations to the standard model that have unique properties but also are sustainable, environmentally friendly, low-carbon-footprint variants of our existing technologies.”

Nowak notes that there is a particular need for an exterior durable neutral shade yellow-effect pigment that is not too red or too green, an effect pigment that gives a true “chrome” or liquid-metal look, and cost-effective optically variable pigments fine-tuned to have very specific color travel that can be consistently produced. PPG is also receiving requests for tonal color shifts, or metallic effect pigments that can shift along with deep fluctuations within the same tonal color family, according to Peterson.

Sustainable solutions—pigments derived from biomass and that take less energy to produce—and those designed to support the electrification of vehicles are in demand in the automotive industry, according to Swift. The need for LIDAR reflectivity, and radar transmissivity place severe limits on the colors and thus pigments that can be used in exterior coatings for these vehicles. Coatings containing flake pigment based on aluminum cannot be detected efficiently at all angles, and dark colors are nearly impossible to detect. In fact, pure solid white exhibits the best performance.

“Many aluminum pigments will interfere with radar and LIDAR detection systems, so there is significant effort being focused on exploring how this issue can be resolved so that specific colors can still be achieved. One alternative is to use inert substances such as mica, but it is difficult to create a silver look without aluminum,” he says.

In addition, Nowak notes that how hot the surface temperature of a vehicle gets is a concern for autonomous vehicles. “Total Solar Reflectivity needs to be controlled with light reflective pigments and color spaces,” he says. Swift says he believes that as more companies such as Ford delve into autonomous vehicle technologies, how much more they need to learn will become more evident.

FEBRUARY 2021 | VOL. 18, NO. 2

Pigment dispersion quality in pastes and paints may be tested by one of several different techniques. Probably the most common method in labs and plants is taking readings with a grind gauge, usually the Hegman type (ASTM D1210). The main reason for doing this for pastes usually is to see whether the dispersion process has reached the required end point for that pigment. Another reason would be to find out whether the dispersion equipment was adequate to achieve the target reading in a reasonable length of time. Hegman readings of 6 and 7 correspond to particle sizes of 25 and 12.5 mm, respectively, yet the average pigment particle size will be a fraction of that, perhaps as little as 1/10th. With a grind gauge, we only see the boulders, the largest particles (aggregates, agglomerates). Beginners find grind gauges frustrating to use and their precision is poor, but experienced users can produce rapid, repeatable, and meaningful results.

Tint strength (ASTM D387, ISO 787/16) is a useful test that measures the color strength of a colored paste let down into a white base by comparison with a standard. Formulators use tint strength to test the color development of the pigment being dispersed, which depends on the degree of deagglomeration and freedom from flocculation of the paste as well as the quality of the pigment itself. The test may be used for quality control and to evaluate pigment from different suppliers, batches of pigment, effect of process changes and equipment, etc.

There are several techniques for measuring the particle size and size distribution in pigment pastes and paints, but my favorite device is an optical microscope with a digital camera connected to a computer with image analysis software. I like to see the pigment particles and be able to record and save what I have seen. I recommend a compound (conventional) optical microscope at 200–500X with transmitted light and dark field. This combination also can be used to look for flocculation and seeds. Pastes usually are difficult to evaluate because there are so many particles jammed together. It is possible to dilute the paste (with the paint vehicle, not just solvent), but this must be done with great care to prevent flocculation. It usually is better to observe the paint made from the paste rather than the paste itself. A paste-paint comparison is shown in Figures 1 and 2. The specimens were produced by placing a small drop of pigment paste or paint on a microscope slide. The picture of the paste does not supply useful information, whereas that of the paint shows what turns out to be loose flocculation, but otherwise a homogeneous mixture.

Regarding pigment flocculation, most production paints show this phenomenon to some extent. In fact, a little flocculation in a paint is good. It prevents pigment settling and reduces sag and the tendency to form surface defects.
In multi-pigment paints, slight co-flocculation of the pigments improves color uniformity and reduces the possibility of convection flow related defects on drying or baking. Co-flocculation with extender pigments can be particularly effective in these respects. How can we tell if there is too much flocculation? That situation usually causes problems such as off color, flooding and floating, Bénard cells, or rough film. For example, a blue paint may be a lighter shade than specified. A mistake may have been made in its preparation (too much white pigment), or the paint may be flocculated. We can use a simple test called rub-up to determine which scenario is more likely. The technique involves rubbing the wet paint film in a circular motion with a gloved forefinger and observing the result. If the problem is one of flocculation, the color in the rubbed area will be the correct one. The rubbing action dispersed the pigment in the paint.

There are other, instrument-based particle size methods such as dynamic light scattering, laser diffraction, and dynamic imaging (ASTM D8090). Light scattering techniques have been around for many years and can provide excellent data. However, the specimen must be diluted considerably, and larger particles may be filtered out during the process. I have seen where microscopy showed a bimodal particle size distribution (large, small) and light scattering did not. The cause of the paint problem turned out to be the large particles.

Viscosity is an important aspect of pigment dispersion, yet we rarely measure it or need to do so. Paste viscosity varies with the pigment, its loading, its vehicle demand, the pigment/binder ratio, the wetting efficiency of the dispersant, the order of addition of the components and the temperature. High viscosity causes poor mixing, a poor flow rate, poor pumping, high temperature, and packing of the media (sometimes to the point of clogging the mill). Low viscosity produces poor dispersion quality and efficiency due to a lack of shearing action. There is a possibility of splashing and cavitation in the mill and settling is likely in the resultant pigment paste. Viscosity problems may occur where there are changes in the paste formula such as raising pigment loadings (which may cause shear thickening leading to jamming of pumps and mills), changing dispersants, adding a wetting agent (likely to lower viscosity), etc. When such changes are made, it is a good idea to measure the viscosity vs shear rate behavior of the new paste and compare it to that of a control paste. Adjustments can then be made to bring the new paste into line.

CoatingsTech | Vol. 17, No. 7 | July 2020

Direct-to-metal (DTM) coatings are designed to provide the performance of traditional primer–topcoat systems, but in one coat. As technologies for the development of DTM coatings have advanced and led to more desirable properties during application and in applied films, demand for these coatings has been increasing. As a result, while DTM coatings today still account for a small percentage of the overall metal coatings market, they have become one of the fastest-growing subsegments of this market.

Adhesion is a primary feature; if the coating does not stick to the metal substrate, it does not matter how well it performs, says Hillary Hamp, market segment manager, industrial with BASF. Second, she notes, is the provision of substantial protection from corrosion, erosion and chalking. Because they are monocoat applications with no topcoat, aesthetics may play a larger role as well. “In other words, DTM coatings are expected to provide aesthetic and protective benefits as an all-in-one solution, with attributes such as gloss retention and hardness development equally important in the customers’ decision-making process for some applications,” Hamp says. Successful DTM coatings, therefore, must achieve the right compromise between substrate protection (e.g., against corrosion, improved adhesion), application issues (e.g., foaming behavior, optimized sag resistance), and optical performance (e.g., leveling, gloss), according to Heiko Juckel, head of global enduse marine & protective at BYK.

Benefits of DTM coatings that provide the desired level of performance are numerous, from convenience and ease of application to cost savings and enhanced sustainability. For DTM coatings, convenience and ease of application actually address a couple of hurdles that have to be overcome with these types of systems, according to Tom Vanheertum, marketing manager for industrial metal at allnex. “Metal cannot be regarded as one substrate as there are many variations between alloys, pretreatments, or residual chemicals from the production process like galvanization, sandblasting, residual lubricating oil from a cold rolling process, etc. These all have a significant impact on adhesion to the substrate,” he explains. In fact, in most industrial coating applications, DTM coatings are not applied directly to metal substrates, but on some type of pretreatment, adds Andrew Carroll, vice president of industrial coatings, Americas for PPG. “It is critical to understand the pretreatment/coating synergy, the real-world application, and online test results versus a lab environment on controlled panels,” he states.

Circumstances under which coatings are applied can also vary by applicator and sometimes even by season, ranging from low temperature and high humidity to high temperature and dry conditions, according to Vanheertum. “These differences usually have an effect on cure speed, dry time, and overcoat times. Coatings companies are, therefore, trying to develop one-size-fits-all solutions, while applicators are looking for the best performance in their given conditions. Adding complexity to the challenge is the fact that regulatory pressure on the market is very different by region, where Europe has already made a transition into waterborne for some industries, the United States is still mainly solventborne and allowing the use of certain exempt solvents, and in Asia, mainly China is in a transitional phase where some industries are afraid that they need to change systems overnight similar to the change that happened in the container coatings business,” he explains.

As more longer-term data becomes available, the industry is realizing that high-performance DTM coating systems not only offer a labor- and cost-effective solution for light- to medium-duty steel structures, but in many cases these systems can be used in a larger swathe of the steel protection market in both fabrication shops and in the field.

Indeed, DTM coatings allow simplification of the coating system by replacing traditional primer/topcoat systems with one or more coats of a single coating that performs all of the functions of both primer and topcoat. “There is no doubt that the use of a simpler DTM system drives greater convenience for end users, allowing them to stock fewer coating SKUs and simplify coating lines in factory settings,” asserts Leo Procopio, principal scientist—TS&D with Dow. The main driver of liquid DTM coatings for the industrial applications, such as agriculture and construction or general industrial, agrees Carroll, is to improve productivity by eliminating a layer (typically a primer) in the coatings process. The reduced time and labor and simplification of the coating process that DTM coatings provide result in reduction of the overall applied cost per square foot per year, which is often the metric that the asset owner carefully considers, adds Steven Reinstadtler, infrastructure marketing manager, Covestro LLC.

It is important to remember, according to Liz Blankenhorn, market segment manager, transportation at BASF, that like for most technologies, interest in DTM coatings is application-dependent. “For monocoat applications primarily used in the industrial market space,” she remarks, “the drivers are often economic. Reducing the number of coats a customer applies to his/her equipment often results in reduction of complexity and labor costs, as well as an increase in throughput for newly coated equipment. Added benefits come when performing maintenance: fewer coats means easier application—and reduced downtime when a piece of equipment needs to be re-coated. For automotive refinishes where these coatings are typically used as a primer, ease of application is the primary interest.

The challenge, according to Carroll, is to provide equivalent or enhanced performance over the existing multi-layer coatings system. Additionally, if these new DTM products are difficult to apply and vary in performance due to marginal pretreatment, it really makes it difficult to see the true value proposition of the technology. It is the expectation of equivalent performance to the primer/topcoat system that is a key factor in decisions by the end user to use DTM finishes and a key driver in development efforts by raw material and coatings manufacturers, Procopio adds.
As a raw material manufacturer, Dow finds there is a continual push for higher-performing products with improvements in properties, such as corrosion resistance, exterior durability, and hardness. One consistent need from the market, Procopio observes, has been the ability to move towards thinner films, mainly for cost reasons, without sacrificing performance, such as corrosion resistance. “As more longer-term data becomes available, the industry is realizing that high-performance DTM coating systems not only offer a labor- and cost-effective solution for light- to medium-duty steel structures, but in many cases these systems can be used in a larger swathe of the steel protection market in both fabrication shops and in the field,” Reinstadtler asserts. In general, adds Marco Heuer, head of applied research & technology industrial coatings EMEA at Evonik, only 12% of the total costs of a painting process are related to the liquid paint material. It is, therefore, more cost-efficient to pay a little bit more for a high-end material because the money and time saved by reducing coating layers is much greater than the incremental cost.

Sustainable Formulations on ‘Everybody’s Wish List’

Maintaining or improving DTM properties while lowering volatile organic compound (VOC) content has also been a consistent regulatory theme for many years and is an important driver of R&D efforts in both waterborne and high solids coatings. “Glossy films with enhanced corrosion resistance at lower VOC are on everybody’s wish list,” Procopio says. Regulatory compliance, especially VOC reduction, is a key factor when it comes to formulating waterborne DTM coatings that can deliver the same performance as solventborne solutions, agrees Sel Avci, global marketing director, Solvay Novecare Coatings. “Formulators are searching for technologies to address specific DTM challenges, such as adhesion to difficult substrates, anticorrosion, hydrophobicity or overall durability, particularly when it comes to segments such as metal structures, shipping containers, etc. Coatings for these segments are being converted to waterborne products that must meet the same performance requirements as their solvent-based counterparts,” he observes. For primer applications, pot-life and dry times become important features to help automotive refinish shops increase their throughput, making solventborne solutions more common in this space, according to Blankenhorn. For some applications, though, she notes that there is also a push towards waterborne technologies, with regulatory drivers influencing this segment of the market as well. The desire to meet sustainability goals is also driving the shift in the liquid spray coatings industry move to high solids solvent-based resins with robust application windows, according to Carroll.

There is more to the sustainability of DTM coatings than VOC reduction, however. In coating markets, according to Amber Goodyear, business development manager, industrial coatings at Arkema Coating Resins, sustainability and high performance are, in fact, linked. “When we speak of sustainability, we include, of course, the reduction of VOC emissions, but also the fact that we will avoid toxic compounds and the fact that coatings will increase the service life of steel structures. Reducing the number of coating layers applied can also, in certain situations, enhance sustainability,” she says. Carroll agrees that elimination of
the use of hazardous heavy metals like lead and chrome and the development of alternative corrosion inhibitors and non-hazardous color pigments are important advances in the DTM and other coating segments.

The replacement of two or more coating layers with DTM solutions has largely occurred for DTM formulations based on higher-quality chemistries, according to Heuer. Examples include two-component (2K) polyurethane or non-isocyanate-curable coatings, in some cases with the use of high-performance co-binders and usually incorporating additives designed specifically for DTM coatings. “It is difficult to distinguish where the main advances have happened, as it is very difficult to only change one component of a formulation. Keeping the formulated product in mind is important when developing a new component. That is why we have intimate cooperation between our additives and resins labs and also reach out to co-suppliers in the market,” Vanheertum comments. PPG continues to see coatings raw material suppliers innovate in all of areas, with advances usually aligned with various macro trends, by geographical region, and as appropriate to the types of coatings of interest, according to Carroll.

Lately, according to Procopio, the most advances have happened within resin/binder chemistry. “Because the resin is such a large component of any coating and affects so many properties for a coating, many advancements are dependent on improvements in the design of the resin system. As manufacturers adopt new resin technologies, however, formulations need to be re-optimized, which often requires the incorporation of new additives.”

Most resin advances involve evolution of existing technologies towards more compliant, cost-efficient and more robust performance, according to Vanheertum. “For waterborne coatings, that translates to low-VOC, low-aromatic-content waterborne epoxies, as well as waterborne one-component (1K) acrylics that reach higher anti-corrosion standards while maintaining excellent durability expected from a topcoat or a monocoat system,” he says. Solvay is seeing more and more styrene acrylic and acrylic-based waterborne DTM coatings replacing solventborne systems, because they can provide the same full balance of properties expected from a metal-protective system.

Indeed, improved understanding of structure-property relationships has led to the introduction of new acrylic latex products for high-performing DTMs that display an excellent balance of properties, such as corrosion resistance, hardness, metal adhesion, low-VOC, and exterior durability, according to Procopio. Specific advancements in 1K waterborne acrylic DTMs have included more hydrophobic binders that facilitate coatings with greater corrosion resistance and binders with complex latex morphologies, which in turn allow for good hardness properties at low-VOC content, he notes. “These advancements are driven by end-user needs for improvements in these properties. In particular, a need for low-VOC waterborne acrylic DTM finishes below 50 g/L with good hardness (related to properties such as block, tack, dirt pickup resistance) has been expressed by the industry,” he explains. Additionally, waterborne epoxy systems are becoming more in demand because of the durability properties of epoxy resins, according to Avci.

Ten to fifteen years ago, polyaspartic-based DTM coatings were thought of as a light- to medium-duty solution for a particularly limited portion of the protective coatings market. Now, after over a decade of actual in-field use, formulators and specifiers understand that this a proven technology with demonstrated long-term performance.

Some polymers other than urethane acrylic chemistries have also shown some promise as DTMs. Carroll points to polyureas, polyaspartics, and polyesters, along with various hybrids. “Advances in these chemistries have led to improvements in application robustness,” he says. As asset owners and specifiers have become much more educated on coatings technologies, Reinstadtler adds, they have begun asking resin manufacturers specifically for resins that reduce their long-term operating costs while being easier to apply and maintain. One technology that supports this requirement is the fast-curing and higher film build properties of polyaspartic DTM coatings. “Ten to fifteen years ago, polyaspartic-based DTM coatings were thought of as a light- to medium-duty solution for a particularly limited portion of the protective coatings market. Now, after over a decade of actual in-field use, formulators and specifiers understand that this a proven technology with demonstrated long-term performance, allowing for their use in a larger segment of this market space,” he states. In addition, by tweaking the polyaspartic resins that are used in the recipe, Reinstadtler notes that manufacturers have been able to formulate DTM polyaspartic systems with excellent hang at high single-layer film builds while also curing quickly even in cooler climates. This extends the contractor’s season as well as their daily output.

Resin chemistries under development are new progressions of existing technologies designed to fill gaps in performance related to durability, lower VOC emissions, and easier-to-use levels in formulations, according to Heuer. There is also a trend to move from 2K to 1K solutions, of course without compromising performance. PPG, Carroll observes, is focused on developing new water-based resin chemistries to accommodate customer needs and specific regional regulations. “The challenge has been application robustness and cost versus traditional solvent-based resins,” he notes. DTM binder technologies have also faced issues with gloss, adhesion, and block and corrosion resistance compared to high-VOC solventborne or multi-coat systems, adds Goodyear. “Recent developments, however, have displaced the idea that performance expectations must be lowered when transitioning to waterborne systems,” she asserts. Avci points to the launch of new waterborne epoxy systems and DTM binders, such as styrene/acrylic-based emulsion polymers and alkyd emulsions, that deliver equal, and sometimes even better, corrosion resistance (longer salt spray hours) and better adhesion to multiple metal substrates. He does say, however, that a good balance of film hardness and low VOC is something that can often be difficult to achieve. “Advances that have happened in the last few years in water-based binders have been closely aligned to new developments in additives, as the compatibility and synergy of these ingredients is what ultimately gives a formulated coating its balance of properties,” Procopio adds. He stresses, too, that the industry is continually working on the next generations of waterborne acrylic DTM binders, looking for new advances in corrosion, adhesion, hardness, and low VOC.

While only a small percentage of the overall formulation, additives play important roles in determining DTM coating performance. “Using additives, it is absolutely possible to improve corrosion, adhesion and humidity resistance, or to improve the early water resistance as well,” asserts Juckel. “That means, however,” he continues, “that every DTM system is only as good as the single raw materials used in in its formulation. Choosing the right combination of ingredients is the key to the production of successful DTM coatings.” It is best practice, therefore, to test different additive technologies with new binder systems to determine the optimum combination that gives the formulator the highest amount of freedom with proven quality, according to Heuer. “For example, a silicone-based defoamer will not work with a silicone resin. With the help of our high-throughput equipment, Evonik is able to run these trials in a short time-frame, offering our customers a fast service for reliable recommendations with respect to additive technologies and dosage levels,” he comments.

Several advances have been made with respect to additive chemistries that are targeted at DTM coatings. “Standard additives can indeed provide good one-dimensional results in certain cases. For example, there are many good wetting and dispersing additives on the market, but they do not always find the right compromise between the different requirements of DTM coatings,” says Juckel. The trend is toward 100% or high-solid-containing additives to support VOC reduction in the overall coating formulation. “Next to these requirements,” Heuer observes, “new regulations such as new limits for substances of very high concern (SVHC) lead to new or modified products that fulfill current and future demands for waterborne, solventborne, and 100% coatings.” For instance, he points to the toolbox of organic and organo-modified siloxane technologies as offering many new additive options that offer improved adhesion promotion, substrate wetting, and surface interactions. Dow has also observed a growing interest in additive technologies that moderate applications under different conditions—for example, technologies that accommodate not just room temperature applications, but applications across an expanded cold and hot temperature range, Procopio observes.

Generally, according to Goodyear, coatings must acquire a certain degree of surface levelling in order to have an acceptable surface appearance. Therefore, a rheology modifier that displays good thixotropic properties helps to achieve the best compromise between sag resistance and levelling. “This is an essential feature for DTM coatings that have to be thick to protect the substrate and to have initial aesthetically pleasing film appearance, because they are not covered by top coats,” she explains. More efficient rheology modifiers also allow the formulator to achieve the right viscosity profile for the coating without adding too much hydrophilic material, which can have a negative effect on the corrosion resistance, adds Procopio. Proper defoaming is critical as well, not just for appearance, but also corrosion resistance, he notes.

Of course, corrosion resistance is a paramount feature of DTM coatings. “Corrosion protection from high-gloss waterborne DTM coatings has improved as binder technologies have advanced, but formulating waterborne solutions requires that every component contribute to anti-corrosion performance,” comments Avci. One additive that must be included in all waterborne DTM coatings is a flash rust inhibitor to protect the metal during the drying process. “More people are now using, along with wetting agents, phosphate ester surfactants that also inhibit flash-rust, and thus offer multifunctional performance,” Avci says. Another example of new chemistry that enhances the corrosion performance of DTM coatings is magnesium-based materials. “At PPG, we have developed proprietary technology that incorporates these types of materials into a liquid DTM formula and significantly enhances the corrosion performance,” Carroll notes.

Formulation know-how is an additional component to the creation of high-performing DTM coatings. “Developing new technology in additives and resins creates value for customers and end-users; however, it is critical to formulate these new technologies into real-world products that work day in and day out on a paint line. The best technology in the world will not be successful if it is difficult to apply on a paint line or requires additional capital investment or unique equipment to work,” states Carroll. As an example, Vanheertum points to waterborne 1K acrylic binder technologies, which can be less robust in DTM applications than alkyd- or epoxy-based technologies with formulation optimization using new resins and additives to maximize hydrophobicity and minimize transportation of ions and oxygen through the film. “Achieving this type of performance at the lowest possible VOC without using anti-corrosive pigments requires much more attention from formulators, but also from resin or additive developers,” he remarks. Hamp adds that for waterborne chemistries, formulation has always been critical to ultimate coating performance. “Any new formulation component must be assessed for compatibility with the whole system. To achieve this goal, in the last five years formulators have been increasingly using Electrochemical Impedance Spectroscopy (EIS) to characterize and predict a system’s corrosion protection performance, because this analytical method allows formulators to quantify the benefits of individual formulation components,” she observes.

Company and New Product Roundup

allnex has introduced a new range of waterborne acrylics (SETAQUA® DTM 6850; SETAQUA 6899) and the anionic pigment dispersant ADDITOL® XW 6588 to enable formulators to achieve robust anti-corrosion properties in monocoat systems. allnex itself has achieved 500 h+ salt spray resistance without noticeable blistering and while limiting delamination to less than 3 mm on various metal substrates with film thicknesses below 80 mm. DUROFTAL FC 2828/75 BAC, a 2K polyester-polyol for DTM-monocoats with exceptional appearance, enables formulation of systems with 270–320 g/L VOC that still exhibit very fast cure speed even at reduced curing temperatures and without sacrificing pot-life, according to Vanheertum. “These features will be of particular use in the ACE market, where larger components are stored in cold areas and need to be heated to achieve full curing. Moving these parts out to a storage area is critical to optimize output in an assembly plant,” he states.

Products like these three examples are developed through close collaboration between scientists in the allnex resin and additives labs. “Such a close working relationship allows the creation of synergistic enhancements that can be formulated into new DTM technologies,” says Tim Kittler, market manager for additives and marine and protective. “Through this unique cooperation we have also been able to bring new dispersant chemistries to the market that allow improved corrosion performance and stability,” he adds. allnex’s marketing and technical teams also continually monitor the regulatory changes that are being made globally and how they will impact the coating industry. “Using this research, we are continually trying to stay ahead of changes that will impact our markets,” Kittler remarks.

Arkema has developed very high solid acrylic polyol technology for low-VOC, 2K DTM coatings. “This new technology allows for 2K polyurethane paints with VOCs below 250 g/L,” Goodyear says. She adds that when new binder is formulated into low-VOC DTM coatings, it demonstrates performance with respect to dry time, gloss capability, adhesion direct-to-metal, chemical resistance, and durability (including water and corrosion resistance and UV exposure) on par with higher VOC systems. “As a result,” she concludes, “this new technology is useful for reducing VOCs and in certain cases reducing the number of coating layers that need to be applied to protect the metal substrate.”

BASF in 2020 is introducing two new resin products: solventborne JONCRYL® xDTM and waterborne ACRONAL® PRO 770. “Typically, when formulating with conventional polyols, formulators may add a tin catalyst to reduce dry times, but this tactic often negatively impacts pot-life. When using BASF’s JONCRYL xDTM, the use of a tin catalyst still allows formulators to reduce dry times but does not affect the pot-life —a major benefit in comparison to conventional polyol resins, making application easier and less expensive,” Blankenhorn says. JONCRYL xDTM is a low VOC-capable solventborne polyol specifically designed for DTM application that exhibits superior dry and wet adhesion to multiple metal substrates, performing particularly well on EZG and galvanneal steel, she says. “This new resin also offers reliable corrosion resistance and high gloss retention and hardness, eliminating the need to compromise between technical performance and aesthetic goals, according to Blankenhorn. Meanwhile, “in the current regulatory environment, many in the industry are switching to waterborne coatings and demanding higher corrosion protection performance from waterborne systems,” Hamp observes. BASF’s answer is ACRONAL PRO 770, a water-based resin that can achieve C3 or higher-level protection in a true DTM monocoat system, she says. “By eliminating the need for corrosion inhibitors and active pigments, PRO 770, which offers best-in-class corrosion protection coupled with superior wet and dry adhesion, reduces formulation cost and complexity,” Hamp comments.

As an innovative company, BYK is continually working to advance existing technologies and develop novel additives to enhance the performance of existing and future formulations based on the latest resin technologies, according to Juckel. Two examples include DISPERBYK-2080 and RHEOBYK-440. DISPERBYK-2080 was developed specifically for waterborne DTM coatings that require improved water resistance. The rheology modifier RHEOBYK-440, also designed for use in water-based DTM coatings, enhances both the appearance and performance of applied systems. “We have many other additives that have been specifically developed for the DTM sector, many of which are based on local requirements and that have been developed in response to customer requests,” Juckel says.

Covestro has been addressing increasingly lower VOC and exempt solvent limits by formulating new polyaspartic guide formulas with novel lower viscosity polyaspartic resin blends and unique aliphatic hardener packages, according to Reinstadtler. “This approach addresses the market need for easy-to-use DTM polyaspartic coatings that can both meet future VOC challenges and the possible elimination of exempt solvents, as well as retain the desired fast return-to-service attributes that end users have come to expect,” he explains. The company has also used more refined modeling techniques to create an advanced digital predictive modeling tool that takes the concept of the standard Design of Experiments (DoE) to the next level, according to Reinstadtler. The formulation mapping tool uses years of formulating experience to set boundaries that enable specific algorithms to focus in on a more distinct set of ranges for a desired polyaspartic formula. “Often, the DoE output is only as good as the expertise of the person reading it. This limitation is addressed by having the data interface with a very user-friendly ‘dashboard’ that allows the scientist to dial in virtual gauges to determine if the desired attributes exist anywhere on the DoE surface. If an option is identified, the program can instantly spit out a starting point formula, significantly shortening the coating development process,” he explains.

Dow’s waterborne AVANSETM Resin technology has led to a new paradigm for how latex particles and pigment particles interact in the wet state, Procopio asserts. “The formation of latex–pigment composites in the wet paint leads to improved pigment dispersion in the dry film and results in improved barrier properties for the film versus a conventional binder. The improved barrier properties give the formulator a method to reach higher levels of corrosion resistance without the need for corrosion inhibitors,” he comments. AVANSETM Resin technology is used in several products within Dow’s portfolio of DTM resins, including the new product MAINCOTETM 5045, which facilitates formulation of gloss finishes below 25 g/L and, according to Procopio, surpasses the performance of other products that are limited to only 50 g/L. “This resin displays excellent corrosion resistance, adhesion, and exterior durability, while also having good block resistance and dirt pickup resistance. Designed for light- to medium-duty industrial maintenance and commercial architectural DTM applications, MAINCOTETM 5045 has good adhesion to steel, as well as tough-to-stick-to metals like untreated aluminum and galvanized steel,” he adds.

MAINCOTETM AEH Acrylic-Epoxy Hybrid technology from Dow is an example of a 2K hybrid system that combines the best features of epoxies (chemical/solvent resistance, hardness, corrosion resistance) and acrylics (durability, fast dry). An epoxy-functional resin is imbibed into an acrylic latex particle. The acrylic particle acts as a carrier for the epoxy resin and constitutes Part A of a 2K coating. Formulators have flexibility in choosing the Part B crosslinker, and either waterborne amine hardeners or carboxyl-functional acrylic latexes such as MAINCOTETM AE-58 can be used to crosslink the MAINCOTETM AEH emulsions, allowing for a range of performance, according to Procopio. “For example,” he says, “when using an acrylic crosslinker, a 2K coating with excellent chemical/solvent resistance and corrosion resistance can be achieved, approaching that of solventborne epoxy/amine systems. At the same time, these coatings have excellent durability that far surpasses the poor chalk resistance and gloss retention of solventborne epoxies, and suggests these systems would be especially useful in applications where epoxies are used as weathering DTM finishes, such as for rail cars or storage tanks.”

Finally, Dow has also introduced ACRYSOLTM RM-3030 Rheology Modifier, a new HEUR thickener that efficiently builds ICI viscosity and is useful in DTMs where brush application is needed, and DOWSILTM 107F, a new defoamer that delivers efficacy and improved compatibility in low-VOC formulations, as well as with specialized dispersants targeting organic pigments that meet evolving color demands.

The formation of latex–pigment composites in the wet paint leads to improved pigment dispersion in the dry film and results in improved barrier properties for the film versus a conventional binder.

Evonik is in the final phase of development for a new patented hardener technology that allows silicone-based resins to cure within in a shorter time frame at room temperature. This attribute enables customers to formulate a DTM coating layer that is heat-resistant up to 550–600 °C and 99% VOC-free and offers outstanding UV- and corrosion-resistance, according to Heuer. “The new hardener technology combined with our silicone binders is able to create a DTM formulation on critical substrates like cold rolled steel. Adhesion on such kinds of critical substrates without any special pre-treatment is highly demanded from the market,” he observes. Heuer also notes that in addition to being ultra-low-VOC, these coatings can be produced and applied using existing equipment. Separately, Evonik has developed many new co-binders and additives over the last several years that are designed to substantially reduce VOC emissions. “For instance,” Heuer says, “by using our newly designed pigment concentrates with reduced solvent content, which are produced using new grinding resins and dispersing additives, along with their well-known main binders, formulators can reduce the level of VOC emissions tremendously. As a result, the formulator has much more freedom to develop DTM formulations that meet not only current but future regulatory demands.”

Car Engine Valve close-up

PPG invests more in research and development than any other coatings company, according to Carroll. “We invest in innovation because it is the primary driver of our growth. Our combined resources in resin synthesis, formulation expertise across all coating layers and within a broad range of businesses, and real-world application centers uniquely position us to deliver new technologies like DTMs in industrial coatings,” he states. One recent innovation related to PPG’s powder technology. ENVIROCRON® Extreme Protection Edge is proprietary powder DTM technology that improves the corrosion performance of exposed metal edges. “This technology is unique because it will significantly reduce edge corrosion without sacrificing the appearance like existing technologies in the market,” Carrol remarks.

Solvay Novecare Coatings has developed over the past several years the Sipomer® PAM series of phosphate-based specialty monomers, primarily for waterborne DTM applications. “These specialty monomers offer excellent adhesion to different metal substrates and superior corrosion resistance,” Avci says. Adding to the Sipomer PAM-100 and 200 ranges of monomers, the company recently launched the new specialty monomer Sipomer PAM 600, which is specifically designed for DTM applications and offers improved durability, sustainability, adhesion, corrosion resistance and new functionalities, particularly when used in combination with Solvay’s other specialty monomers and surfactants, according to Avci. Rhodafac® phosphate ester surfactants from Solvay can be used as emulsifiers for making DTM binders and as wetting agents in DTM formulations.

As more longer-term data becomes available, the industry is realizing that high-performance DTM coating systems not only offer a labor- and cost-effective solution for light- to medium-duty steel structures, but in many cases these systems can be used in a larger swathe of the steel protection market in both fabrication shops and in the field.

Ten to fifteen years ago, polyaspartic-based DTM coatings were thought of as a light- to medium-duty solution for a particularly limited portion of the protective coatings market. Now, after over a decade of actual in-field use, formulators and specifiers understand that this a proven technology with demonstrated long-term performance.

The formation of latex–pigment composites in the wet paint leads to improved pigment dispersion in the dry film and results in improved barrier properties for the film versus a conventional binder.

CoatingsTech | Vol. 17, No. 6 | June 2020

This restoration project is different than any previous project performed at the museum. It is taking place in a special glass chamber that has been constructed in front of the painting so that it can remain on display and visitors to the museum can observe the restoration process. The restoration effort is also being stream live online (), and the thousands of image that will be obtained will be made available to the public.

“Operation Night Watch”, which began in July 2019, includes experts from the Rijksmuseum and other museums and universities around the world, as well as AkzoNobel color specialists. The team will first try to determine how the painting was made, what its original appearance was intended to be, its current condition and what alterations have bee made to it and why.

To find the answers, 11,400 photographs with a resolution of 5,430 dpi will be taken using a purpose-built imaging frame. Special scanners will also be used to investigate the cracks and crevices of the painting, and the pigments will be examined at a nano level using a hi-tech laser.  The many terabytes of data gathered during this research phase will be analyzed to identify the best method for restoring The Night Watch.

AkzoNobel and the Rijksmuseum have signed a three-year partnership focused on this restoration project. It is not the first time they have worked together. AkzoNobel supplied approximately 8,000 liters of paint to the museum for its own decade-long renovation, which required the development of a special color palette known as the Sikkens RIJKS Colors that matches the colors originally used by architect Pierre Cuypers.

“We’re about to rock the world of paintings conservation and do things that have never been attempted before,” says Robert van Langh, the Rijksmuseum’s head of Conservation and Science. “First of all, we need to find out what we’re up against. With a partner like AkzoNobel on board, we’re confident we’ll take our understanding of paint to the next level – and I don’t just mean one level, I’m talking three or four levels.” AlzoNobel, meanwhile, is proud to be the main partner for the innovative project, according to CEO Thierry Vanlancker. “As a company which believes in taking its innovation beyond generations, we’re excited to be contributing our expertise and passion for paint to help restore a cultural icon,” he says.

While there is an intuitive connection between wall brightness and the electrical demand for illuminating a room, there has been little data reported to quantify this relationship. Here, we report the relative electrical load needed to light a room at the 500 lux level specified by European lighting standard EN12464-1:2011, as a function of wall brightness. A room was painted white, black, and two intermediate shades of gray, and room brightness was measured at multiple locations and directions using four light levels (controlled with a light dimmer), for both warm and cool fluorescent bulbs. Results were compared to computer modeling. Based on these results, we determined the expected electrical requirements for rooms painted with over a dozen “colors of the year,” as designated by major décor coatings manufacturers. The results were compared to the electrical requirement for a white wall. Significant energy savings are possible when painting a dark wall white.

INTRODUCTION

It is well known that reduction of electricity consumption in regions with hot summer climates can be realized by painting the exterior surfaces of buildings, particularly their roofs, white (or another bright color). This maximizes the reflection of solar radiation and so minimizes the amount of heat absorbed by these buildings. This concept is centuries old, but over the last decade it has received renewed interest and attention in the form of “white roof” or “white building” initiatives.¹

While these benefits are well recognized, there is a second, less recognized, energy advantage associated with bright colors. This savings applies to the amount of electricity required to light a room brightly enough to carry out the tasks intended for that room. Depending on the location and orientation of the task (for example, writing on a table), and the locations of the light fixtures, a significant fraction of the incident brightness can be from light reflected by the room walls. Obviously, the brightness of the walls will affect the quantity of light reflected from it.

Electricity consumption for lighting is significant. In the U.S. residential sector, inefficient incandescent lights are being actively replaced with more efficient alternatives (primarily LEDs and compact fluorescent bulbs). However, this conversion is far from complete. At the end of 2017, more than half of the bulbs used in residential lighting were still incandescent.² That year, 9% of total residential energy consumption was for lighting.³

Although Europe is overall more complete in their conversion from incandescent bulbs to more energy efficient light sources, a significant amount of electricity is still consumed there for residential lighting. In 2017, 13% of electricity used in the UK was for all lighting.⁴ Energy consumption for lighting in Continental Europe is more difficult to quantify because lighting is combined with electrical appliances in EU energy use statistics. Globally, however, it is estimated that all lighting accounts for 15% of total energy consumption, and that lighting demand will increase 50% between 2015 and 2030.⁵

Painting a room with a bright color results in both direct and indirect electrical savings. The direct savings are obvious—as brightness increases, less light is needed. Indirect savings are obtained during periods when the room is actively cooled. The ultimate fate of most of the light generated in a light fixture is heat. This is especially true for incandescent lamps, where as little as 2% to 3% of the incoming energy is converted into visible light; the rest is released as heat. By decreasing the energy used to generate adequate light, we decrease the electrical load on the cooling system.

We can compare the electricity used for lighting to that used to cool buildings. In the United States, it is estimated that 9.6% of the electricity used residentially in 2017 was for cooling.⁶ Globally, in 2017, 10% of overall electrical usage was for cooling.⁷ While both types of energy consumption are roughly equal, we note that cool roofing is a topic of current interest to the public, while bright rooms is not.

That said, architects are aware that reflectivity affects room brightness, and during building design sometimes include wall reflectivity in their calculations to determine the number and location of lighting fixtures. The basis of these models is theoretical. These models have been used to optimize lighting in office settings,⁸ but to our knowledge, there has been no experimental data reported that measures the energy required to adequately illuminate an actual room as a function of wall brightness.

In this article, we detail the results of our experiment to determine electric energy requirements as a function of wall brightness for an average size interior office room. We then compare the results of our experiment to results calculated by a well-known architecture software model.

EXPERIMENTAL

An interior office was painted with achromatic paints of four brightnesses: brightest white, two shades of gray, and black. The tristimulus Y reflectance values for these paints are 91, 60, 20, and 5, respectively. A schematic of the room, showing the measurement and light fixture locations, and a picture of the room, painted black, are shown in Figures 1 and 2. The room had a standard acoustical tile ceiling (tristimulus Y reflectance value of 84) and mid/dark carpeting (tristimulus Y reflectance value of 35). The ceiling height was 3.0 m, and most measurements were made 90 cm from the floor. The exceptions were measurements made 60 cm underneath each lighting fixture. These measurements were used to determine the luminosities of the light sources, with the intention being that all light measured at those positions comes directly from the light sources, rather than being reflected from the walls.

Luminance was measured at six locations in the room, with the meter oriented at different angles for these locations (e.g., Horizontal, 45°, facing the nearest wall or facing the interior) and with two different dimmable fluorescent bulbs (25 W 4100K and 32 W 6500K). There were two light fixtures in the room, centrally located, and each fixture accommodated four bulbs. A diffusion panel was placed on each fixture. Within a set wall brightness and bulb type, four electrical power levels were explored at each location and orientation. Brightness was varied with a standard light dimmer.

A total of 776 brightness values were measured, including one set of measurements done in triplicate. These were of the lighter gray room using the 4100K lamps and measuring at all room locations and orientations. From this we calculate an average standard deviation of 14.1 lux for light intensity and 0.5 Watts for the power setting.

Typical results are shown in Figure 3. Here we display luminance values (on the y-axis), for each room color (separate line), for the middle of the room with an up-facing orientation of the light meter, as a function of the four different dimmer settings (on the x-axis) for the 4100K lamps. Lux values of 500 and 800 are highlighted in red. These span the values typically recommended for reading and other activities (see below). As indicated by the high Pearson R-squared values given in Figure 3, there is an excellent linearity between the power setting and the luminance value for each wall color. For these data, an R-squared value above 0.980 (R value above 0.990) is significant at the 0.01 level. This condition is met by all four experimental lines in Figure 3, confirming that the relationship between light intensity and power is linear over this range. Linearity is expected as it indicates that the illumination efficacy of a light does not change with power over the range we studied.⁹

RESULTS AND DISCUSSION

We intentionally used an interior room, rather than one with a window, in this study. A window would add complexity and confound the results. We would expect less electricity use during the day, when the room benefits from a bright outdoors, but significantly more electricity use at night, when most of the light falling on the windows is lost to the outdoors. The balance between savings during the day and losses at night is difficult to quantify since it depends on the room’s use (work or home), the length of the day, and the number of active hours during daytime and nighttime. In addition, many offices do not have windows—in a 2015 survey of office employees, 61.2% reported that they did not sit near a window and so had very little natural light.¹⁰

Our interest is in two lux levels: 500 lux, which is specified by European lighting standard EN12464-1:2011, and 800 lux, which was preferred by 60% of European office employees in a 2015 survey⁶ and is recommended for workers 45 years or older.¹¹ We found that the response of luminance to power level to be linear in all cases (see Figure 3 for an example), and so the percent extra electricity needed to illuminate the room to 500 lux, for a given room color and lamp type, is the same as the percent extra electricity needed to illuminate the room to 800 lux (that is, luminance is linear with electrical power).

The luminosity of the lights at each of the four light settings was determined by placing a photo meter directly below each light fixture. This was measured for each room color, to confirm that the radiation being measured was entirely from the lights themselves, with only an insignificant amount, if any, coming from the walls. This was confirmed to be the case.

Our analysis included all data points, but for brevity not all of these points will be detailed in this article. Instead, we will focus on a subset of results that we believe to be representative of the entire data set. This subset consisted of:

• Room center; meter oriented facing up; 4100K bulbs
• Room center; meter oriented at 45°; 4100K bulbs
• Against the wall (“Wall 2” in Figure 1); meter oriented facing up; 4100K bulbs
• Against the wall (“Wall 2” in Figure 1); meter oriented at 45° into the room; 4100K bulbs

Our reason for analyzing these particular locations and orientations is that we believe them to be relevant to different usages of the room. If the room is used as a conference room, then the most likely location for a table would be the center of the room. If it is used as an office, then the most likely location for a desk would be along a wall. The two different orientations (facing up and at 45°) are those used for observing an object flat on the table or desk, or for holding a book at these locations.

Our chief interest in this work is to determine the relative amount of extra energy needed to illuminate the room to the same level for different wall darkness. We consider the white room results to be the baseline, with an assigned value of 1.0, and calculate how much more energy, relative to the baseline value, is required to illuminate the room to the same level of brightness as the white room. Averaged values are reported in Table 1 and plotted in Figure 4. Note that one data point was omitted from our analysis—the room center, at 45° orientation, for the light gray room—because it was anomalous.

Results for the room center, with the meter held horizontally, were the least sensitive to wall brightness. This is expected since this is beneath the lights, and so most illumination will be directly from the source. The wall location, facing 45° into the room, was the next least sensitive. Here the meter was pointed nearly at the lights, but since this location is further away than the center location, the electrical need is greater than for the center location. The location and orientation most sensitive to wall brightness was the wall, facing up. This is understandable since a significant portion of light striking this surface will come from the wall.*

Overall, we find that, for the black paint, between 41% and 85% additional lighting is required compared to the white room. While this is an extreme case (rooms, especially those with no windows, are seldom painted black), even for a light gray paint, between 21% and 31% additional lighting is required compared to the white room. This is a significant increase in electricity requirements which, as detailed above, constitutes a significant portion of the overall electricity demand globally.

We will discuss the implications of these results to real world room colors below.

*We can see this by imagining that the wall is a mirror. In this case, roughly half the illumination will come from the lights in the room, and half from the lights in the mirror. Replacing the mirror with black paint, therefore, is expected to decrease illumination at the wall by roughly half.

MODELING

Modeling was done using DIALux software.¹² This software is widely available and heavily used by architects and building designers.

While we would have liked to model each of the four room locations and orientations, this software is limited to modeling only horizontal orientations. In addition, the minimum wall brightness was 0.10, rather than the 0.05 that we achieved experimentally. We, therefore, modelled the horizontal center and wall locations at wall reflectance values of 0.90, 0.60, 0.20, and 0.10. The light sources available for modeling did not match either of our two lamps, and so a 32 Watt fluorescent, 5208K source was used in the model. This should have no impact on our conclusions, since we are concerned with analyzing energy needs on a relative basis (relative to bright white) rather than an absolute basis.

As was done with the experimental results, we report, in Table 2, the relative electricity requirements at equal brightness, for the four wall colors, at each of the two locations. This data is shown graphically in Figure 5.

Comparing the results in Tables 1 and 2 graphically (Figure 5), we see that the model agrees well with the experimental results for the center reading, but is 8% higher than the experiment for the measurement near the wall. This is seen in the slopes of the best fit lines in Figure 5 (see Table 3). The slope of the line is a measure of the sensitivity of the brightness at that location and orientation to wall darkness. Assuming that our results are representative of most offices, this suggests that architects may be specifying brighter light intensities than is necessary in some cases. We cannot offer an explanation for this discrepancy, since we do not know the details of how the model bases its calculations.

IMPLICATIONS FOR PAINT CONSUMERS

Color is a leading consideration for interior architectural (décor) paints, and color choice is quite often the first question asked of a customer entering a paint store. While statistics are not available as to which colors are popular among business and home owners, the traditional choice is an off white. However, many interior designers recommend darker, bolder colors to their clients as a way to stand out and make a fashion statement. This is reflected in the choice of “color of the year” made by many interior architectural producers. We have collected 19 of these colors from the last two years. Tristimulus Y values and corresponding L* values for these paints are given in Table 4.

As can be seen from Table 4, the “color of the year” paints are relatively dark (the average tristimulus Y value is 23.3 and an average L* value of 49.8). This is consistent with many of their names, such as “Dark Navy” and “Deep Onyx.”

To estimate the lighting costs associated with these colors, we have indicated their reflectance values in Figure 6 along with the best fit lines for the four location/orientation pairs that we analyzed (from Figure 5). We tabulate the additional electrical load for the four location/orientation pairs for our room in Table 4. We see from this table that the additional electricity requirements for these paints vary from 12% to 84% versus white walls. It is clear that the additional electricity burden of using relatively dark paints on interior walls is very real.

ECONOMIC AND ENVIRONMENTAL CONSEQUENCES

From our data we can calculate the monetary cost of lighting rooms with bright walls over rooms with dark walls. While electricity cost varies globally, we will calculate these costs for one specific region as an indicator of the value of bright walls in general. For this calculation we will use data from the United States, where the average user cost of a kilowatt hour of electricity is $0.133.¹³ We assume that the room is used five days a week for nine hours per day.

The results of these calculations for our room are shown in Table 5, averaged over the two light types. Here we consider two lighting levels (500 lux and 800 lux) and two measurement locations (wall and room center, both oriented up). The financial cost of a dark room, compared to a white room, is substantial—over one year, the additional electricity cost of the black room varies from $16.40 to $84.23, depending on lighting level and where in the room light intensity is measured. Over the service life of the paint, the additional cost of lighting a black room far exceeds the initial cost of the paint, and the cost of using greater amounts of TiO₂ to brighten a room is quickly offset by the electricity savings.

In addition to the monetary cost of a dark wall, there is an important environmental cost. This cost is the amount of CO₂ released to the environment, both in making the TiO₂ pigment and in generating the electricity consumed by the lights. We can quantify this cost in terms of a payback period—how long it takes for the CO₂ savings from using less electricity to offset the CO₂ generated when making the TiO₂ white pigment. For this calculation, we assume that each kilowatt hour of generated electricity results in the release of 0.71 lb of CO₂,¹⁴ that the white paint contains 2.5 lb of TiO₂ per gallon, and that production of each pound of TiO₂ results in the release of 5.0 lb of CO₂.

As seen in Table 5, this environmental payback period is quite short—a little over eight weeks for the least sensitive location (room center) at lowest illumination target, and less than two weeks for the most sensitive location (at the wall) and highest illumination level.

COMPARISON TO WHITE  ROOF ENERGY SAVINGS

Over the years there have been numerous initiatives to decrease electrical consumption, both to reduce cost and to protect the environment. One such program is the cool roof (or white building) initiative. The concept is straightforward—by replacing dark roofs with light roofs, much solar energy can be reflected away from a structure, rather than be absorbed in to it in the form of heat. This could significantly decrease the cooling burden on the structure during hot summer months.

Note that this not only results in less overall electricity use, but it does so during peak electricity demand times, since in many cities the greatest electrical use occurs on the hottest days of the year. By decreasing peak demands, the number of power plants needed to service a city will be fewer, since this number is determined by the peak (maximum) electricity requirement, rather than the average requirement.

An estimate of the electricity savings gained by increasing the albedo of roofs from a solar reflectance value of 0.2 to a value of 0.6, in 27 cities around the globe, was reported in 2007.¹⁵ These savings are, of course, greater in cities characterized by very hot summers than in more moderate climates. Overall, the summer electrical savings were estimated to be between 11% and 75% for this level of brightness increase. These estimates are quite comparable to the savings potential we estimate for painting rooms with bright colors, reinforcing the consequences of using a dark interior color to overall electricity consumption.

CONCLUSIONS

Our work quantifies, for our test room, the relative energy required to meet lighting targets as a function of wall reflectance. While we studied only one room, we believe the conclusions we draw from it to be valid for similar rooms, at least at the semi-quantitative level.

We found that the amount of electricity required to light the room to 500 lux, the minimum level generally accepted as adequate for office work, and 800 lux, the level preferred by many, correlates very strongly with the brightness of the room paint. This energy demand was linear over the range we studied. Electricity requirements increased by as much as a factor of 1.85 between the bright white and black paints.

While this is an extreme brightness range (very few rooms are expected to be painted black), some “colors of the year,” as chosen by paint manufacturers, are quite dark. For the colors that we examined, we estimate the additional electricity requirements for them, relative to the requirement for a white wall, to vary by factors of 1.12 to 1.84. These values are quite significant—as a point of reference, depending on location, cool roofs are estimated to reduce cooling costs by between 11% and 75% when the reflectivity of the roof is increased from 0.20 to 0.60. On a percentage basis, these savings are quite comparable to the electricity savings we demonstrated for a bright white room compared to a room painted with a “color of the year” (between 12% and 84%).

The increase in electricity consumption for dark rooms comes at a cost—both financial and environmental. The annual additional cost of lighting a dark room ranges, for our room, from $16.40 to $84.23, depending on how the room is used (office or conference room). As for environmental considerations, our analysis showed that there is a very fast breakeven time (a few weeks) for both the monetary cost of the TiO₂ used in the white paint and the CO₂ released in the production of the TiO₂.

We also found that a popular architecture modeling program overestimated the effect of wall color on lighting needs by up to 8%. Relying on this model alone would lead to brighter lighting than necessary, but at the expense of additional cost and environmental burden.

While personal preference will always be a major factor in color choice, it is important that the consumer be aware of all costs of a given color option—not only in terms of monetary costs (in the form of higher electricity bills), but also environmental costs (emissions from power plants). Those consumers wanting a “green” paint may find the color they are looking for is, in fact, white.

References

1. “Cool Roofs,” https://www.energy.gov/energysaver/energy-efficient-home-design/cool-roofs.
2. “Annual Energy Outlook 2018,” https://www.cooperative.com/news/documents/eia-annual-energy-outlook-2018.pdf).
3. “How Much Electricity Is Used for Lighting in the United States,” https://www.eia.gov/tools/faqs/faq.php?id=99&t=3.
4. “Energy Consumption in the UK ECUK 2018,” https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/729317/Energy_Consumption_in_the_UK__ECUK__2018.pdf).
5. “Rise and Shine—Lighting the World with 10 Billion LED Bulbs,” https://www.energy.gov/articles/rise-and-shine-lighting-world-10-billion-led-bulbs).
6. “How Much Electricity Is Used for Cooling in the United States,” https://www.eia.gov/tools/faqs/faq.php?id=1174&t=1.
7. “Air Conditioning Use Emerges as One of the Key Drivers of Global Electricity-Demand Growth,” https://www.iea.org/newsroom/news/2018/may/air-conditioning-use-emerges-as-one-of-the-key-drivers-of-global-electricity-dema.html.
8. “The Impact of Artificial Light in Architectural Spaces,” Thesis, Ana Teresa Luis Negrao, https://fenix.tecnico.ulisboa.pt/downloadFile/395145552805/EXTENDED%20ABSTRACT_Ana%20Negr%C3%A3o_2013.pdf.
9. “Lux, Lumens and Watts: Our Guide,” https://greenbusinesslight.com/resources/lighting-lux-lumens-watts/.
10. “New Zumtobel Research on Lighting Quality Perceived in Offices,” https://www.thefuturebuild.com/news/new-zumtobel-research-on-lighting-quality-perceived-in-offices.
11. “Philips Lighting Questions Proper Light-Level Standards for Office Workers,” https://www.ledsmagazine.com/articles/iif/2015/03/philips-lighting-questions-proper-light-level-standards-for-office-workers.html.
12. “DIALux family for lighting designer and manufacturer,” https://www.dial.de/en/dialux.
13. “Greenhouse Gases Equivalence Calculator,” https://www.epa.gov/energy/greenhouse-gases-equivalencies-calculator-calculations-and-references.
14. “Electricity Rates by State (Updated March 2019),” https://www.electricchoice.com/electricity-prices-by-state/.
15. Synnefa, A., Santamouris, M., and Akbari, H., “Estimating the Effect of Using Cool Coatings on Energy Loads and Thermal Comfort in Residential Buildings in Various Climatic Conditions,” Energy and Buildings 39 (2007) 1167–1174 (10.1016/j.enbuild.2007.01.004).

CoatingsTech | Vol. 16, No. 9 | September 2019

Introduction

Powder coatings are solvent-free coating systems used for many applications due to their durability, ease of application, and environmental advantages vs liquid coating systems. Powder paints are applied to a substrate electrostatically and cured at relatively high temperatures to form a continuous, durable film. The advantages of powder coatings are that no solvents are used when they are sprayed, minimizing environmental issues related to volatile organic compounds (VOCs). Additionally, any material that does not adhere to the substrate after spraying, known as “overspray,” can be collected and used again, resulting in very little waste.

Powder coatings are typically made by combining resins, a crosslinker, fillers, organic or inorganic absorption pigments, and additives together in an extruder. The resin is melted, and the ingredients are intensely mixed into the resin. The extruded resin is collected and milled to a fine particle size distribution to then be sprayed.

Effect pigments owe a significant portion of their color and appearance to their structure and shape. In the case of aluminum pigments, a silver to gray metallic appearance is observed due to their shape. Most aluminum pigments are micron sized platelets with large aspect ratios (pigment width/pigment height). In an application, aluminum pigments behave like “micro-mirrors,” reflecting nearly all the light that interacts with them in a specular or near-specular angle. These pigments display the so-called “flip-flop” effect, which is a light to dark color travel when viewing a display head-on vs at a diffuse angle.

Additionally, aluminum pigments have a bright, silvery appearance that is defined by their brightness (L*) values and gloss. Platelet-shaped aluminum pigments have excellent hiding power when compared to spherical pigments. Because of their shape, they are very susceptible to bending and breakage under high shear mixing, like extrusion, and are typically incorporated into powder coatings in subsequent processing steps.

Metallic pigments can be dry blended into a powder coating. However, because this only makes a physical mixture between two powders, this can cause issues during application of the powder coating, where the pigment and coating particles separate due to electrostatically charging differences. This causes the overspray to be unusable due to inconsistent color.

To mitigate these issues, a process called bonding is often used to incorporate metallic pigments into a powder coating. During bonding, the powder coating is heated to just above its softening point and combined with effect pigments under moderate shear, causing the pigments to adhere to the surface of the powder coating. Such a process provides sprayed parts that have excellent pigment orientation, resulting in the best appearance for powder-
coated articles.

In addition to their shape, aluminum pigments have certain chemical properties that impact their orientation in powder coatings. Aluminum pigments are typically made by ball milling a three-component system of aluminum grit, hydrocarbon solvent, and lubricant. For powder coating applications, the solvent is removed, but the lubricant stays behind on the surface of the pigment. Typical lubricants are saturated and unsaturated analogues of C18 fatty acids, namely stearic and oleic acid, respectively.

When saturated fatty acids are used, the aluminum pigments will have a low surface energy, causing them to rise to the air-coating interface. The pigments crowd the surface and have superior alignment in the coating, resulting in a minimization of scattering centers and a highly glossy appearance. These types of pigments are known as leafing. When unsaturated fatty acids are used, the pigment surface is wetted by the coating, and the pigments are evenly distributed through the thickness of the coating, giving a duller metallic appearance known as nonleafing behavior.

This behavior can have a profound impact on the appearance of two otherwise identical pigments. For example, a nonleafing cornflake will have lower brightness, flop, and gloss when compared to its leafing analogue. Moreover, the hiding power of the leafing pigment will be higher, resulting in reduced pigment loading requirements for nonleafing pigments. Leafing pigments have the drawback that, since most of the pigment is located on the surface of a coating, they are more susceptible to scuffs and staining than nonleafing pigments.

In powder coatings, a solvent-free effect pigment powder must be used, which can cause a large release of dust as it is being processed and handled.  For metallic pigments, the dust not only poses an inhalation hazard, but is potentially explosive if clouds of dust are generated. This risk increases with the fineness of the pigments and requires special safety precautions to mitigate.

It is well known in the powder coating industry that aluminum pigments need to be handled with care as the coupled effect of small size and reactivity mean that aluminum pigments have a low minimum ignition energy (MIE) and high k_ST. The MIE and k_ST are measures of how much energy is required to ignite a powder or dust and the strength of that explosion, respectively.  It is typically a function of the particle size of the dust. Dry, powdered aluminum pigments, which can have a d50 of as low as 5 µm, have a low MIE (<5 mJ) and high k_ST (>300 bar m/s).¹ These hazards increase as the size of the aluminum pigments decrease.

In other industries where aluminum needs are used in a solvent-free form (e.g., plastic masterbatch), aluminum is often combined with a resin, extruded, and dried to make a pelletized product. The pellet mitigates dust, increasing the MIE and decreasing the likelihood of an explosion. If this approach could be applied to an aluminum pigment intended for use in powder coating, it could provide a benefit to converters who need to work with fine aluminum pigments. For such a preparation to work, however, the pellet would need to be easily friable and dispersible in a powder coating while the compounding resin would need to be widely compatible with many different powder coating types.

In this article, a pelletized aluminum preparation for powder coatings is presented that combines a fine (d50 = 9 µm), leafing aluminum pigment with a polyester resin. These products have an aluminum content of 85%, with the remaining fraction being the resin, which allows formulators to use these products without having a dramatic impact on the resin content of the base paint. The pellet is highly friable and can be incorporated into most polyester-based powder coatings by either high shear dry blending or bonding to give an appearance that is like a bonded aluminum powder of equivalent size and composition. A description of the test methods used and results in polyester and other resin chemistries are presented.

Materials and Methods

Description of Aluminum Pellets

In the following examples, the pelletized aluminum pigments are made using a fine, leafing corn flake pigment with a d50 particle size distribution of 9 mm. They are composed of approximately 85% aluminum flake and 15% of a polyester resin. The pellets are dry and approximately 5 mm in diameter, as seen in Figure 1.

Incorporation into Powder Coating

The pelletized pigments can be incorporated into powder coating by two different methods: high shear dry blending or bonding. For high shear dry blending, the pellets are added to a powder coating base at 1.25% total metal loading and mixed at 50% of the speed/time for a typical bonding step. These samples were compared to a dry-blended leafing aluminum (Benda-Lutz Leafing 2081) that was incorporated under the same conditions and at the same loading. Bonding of the pelletized and unpelletized aluminum was carried out at 1% total metal loading using standard bonding protocols. The pigmented powder coating bases were applied to stainless steel panels and cured according to the parameters of the base.

The 60^o gloss, brightness (L*15, measured at 45^o incident light and 15^o aspecular) and the flop index (FI), which is determined by equation (1):

where L*45 and L*110 are brightness measured at 45^o incident light and 45^o and 110^o aspecular reflection angles, respectively. All color measurements were performed on an X-Rite MA-98 multiangle spectrophotometer. Gloss measurements were performed on an Elcometer 6015 Novo-Gloss IQ Glossmeter.

Results & Discussion

Dust Testing

The MIE of a dust cloud is the lowest energy discharge required to ignite the dust/air mixture at room temperature. Table 1 shows the MIE for a fine aluminum pigment and a 2 mm diameter pellet made using the same. Modification of the pigment’s physical form is one of the few ways to raise the MIE as it allows for a decrease in dust concentration and significantly larger suspended particles.  In standard MIE testing, only particles less than 75 mm are tested. The pelletized product has increased the MIE of the fine aluminum powder by two orders of magnitude, which is a substantial change. Further increases in the pellet’s size are expected to yield a larger MIE value.

This data is important as it affects the transportation and storage requirements for different forms of aluminum pigments. Aluminum pastes, powders, and pellets fall into specific categories for transportation and storage in each region depending on local regulations. Because of their reactive nature, aluminum powders are classified in the United States by the Department of Homeland Security as “Chemicals of Interest.” As such, there are specific guidelines depending on quantities to ensure against their misuse.  There are also specific guidelines for transportation set by the various agencies in North America and Europe. Aluminum powders can be classified as hazardous materials by the U.S. Department of Transportation (DOT), or dangerous goods under the European Agreements Concerning International Carriage of Dangerous Goods by Road and Rail (ADR/RID). In China, Decree 591 sets guidelines specifying certified warehouses for storage of aluminum powders.

Pellets, however, and specifically pellets designed for powder coatings, are exempt and not regulated as dangerous goods per the applicable hazardous material transportation regulations. This can significantly simplify the supply chain and logistics for using pellets as compared to aluminum powders.

Another smaller consideration that is growing in importance is packaging materials. Aluminum powders and pastes are commonly packaged in steel drums while pellets are packaged in a bag-in-carton containers.  Steel drums can be problematic for some manufacturers to recycle by introducing another waste stream while bag-in-cartons neatly fit into warehouse racking systems and can be easily recycled.

Appearance Testing

Figure 2 shows the L*15 (a, d, and g), flop index (b, e, and h), and brightness (c, f, and i) of the pelletized aluminum and the leafing aluminum control (2081) after being incorporated into either a triglycidyl isocyanurate (TGIC)-cured (a–c) or a b-hydroxyalkyl-amide (HAA)-cured (d–f) polyester powder coating. Figure 2g–i shows the results for the aluminum pellet in a polyurethane-type of powder coating. In addition to a comparison of the different forms of aluminum, Figure 2 also shows the different appearances that can be achieved depending on the incorporation method used, whether it is high-shear dry blending (red and blue bars) or bonding (green and yellow bars).

Focusing on the TGIC examples first (Figure 2a–c), reveals that the pelletized aluminum pigment has a similar brightness to the 2081 in this system. More surprising is that, in this system, the dry blended and bonded pellets are superior in flop compared to blended or bonded, unpelletized aluminum. The dry blended and bonded pellets have similar gloss, and both are less glossy (Figure 2c) than the bonded aluminum. In all cases, the dry blended leafing pigment is the most inferior in flop and gloss for the TGIC-cured polyester.

This data shows that the pelletized aluminum can be incorporated by two different methods to give a bright metallic finish that is comparable to the bonded, loose aluminum. Moreover, the flop data suggest that the pellets have a better overall orientation in this powder coating compared to unpelletized pigments. Indeed, the inclusion of the resin may help to pull the aluminum into a flat configuration when the powder coating is cured.

The gloss is best for the bonded aluminum, with the bonded, pelletized aluminum coming in second. This is not particularly surprising considering that gloss in powder coatings can be driven by the resins in the system. Depending on the resin compatibility, this could result in a smoother finish that is aided by the superior orientation of the aluminum, increasing the gloss.

If this is the case, it is not unreasonable to expect that the pelletized aluminum may exhibit different types of behavior in different resin systems and classes. The dry-blended aluminum has the worst gloss, even when compared to the dry-blended pellet. This suggests that the pelletized aluminum may be better wetted out by the resin in the powder coating, which helps to drive its alignment.

The difference in incorporation behavior is demonstrated for the HAA-cured polyester shown in Figure 2d–f. In this instance, the dry-blended pellet has the higher L*15 and flop index, while the bonded pellet has the highest gloss. The pelletized pigments outperform the pigment powders, regardless of their incorporation method. This could be due to a similar phenomenon above, where the pellet resin positively affects the interaction between the aluminum and the powder coating matrix, acting almost like a dispersant.

Finally, Figure 2g–i shows the incorporation behavior in a polyurethane-based powder coating. In this instance, the pelletized aluminum is optically superior to the unpelletized aluminum in every case, even when comparing a dry-blended pellet to the bonded, unpelletized pigment.

While this data shows that the pelletized aluminums are compatible with different powder coating systems, it is likely that formulators would need to optimize performance of these pellets for a particular powder coating system.

Reclaim Testing

To test for the ability to reclaim a powder coating, a cyclone test was performed that mimics the reclaim for a large production. Cyclone separators use an airstream to separate the finer, lighter particles from a powder based on their weight and density. This test assesses whether a powder will separate when it is reclaimed.

Based on the good results from Figure 2 for the blended pellet, a test on the reclaim for powder coating containing this product was completed and compared to blended and bonded 2081 aluminum. Powder coatings containing each of the samples (in fact, the same powder coatings used in Figure 2a–c), were passed through a cyclone apparatus and a panel was sprayed and evaluated to give “Pass 1.” The process was repeated on the Pass 1 material to give Pass 2.

The results of the cyclone test are shown in Figure 3, which shows how the brightness (L*, Figure 3a), flop (Figure 3b), and gloss (Figure 3c) change with repeated cyclone cycles.

It is observed that upon repeated cyclone cycles, the brightness, flop, and gloss all are reduced. An interesting feature is the blended and bonded metallic pigment appear to change according to the same slope in all aspects, while the blended, pelletized aluminum has different behavior. This is unexpected, but not entirely surprising considering that there is an additional resin in these samples. The pelletized product shows a faster decline in brightness and flop, but an intermediate decline in gloss when compared to the unpelletized products. It is unclear as to why this is, but it may be due to the presence of the secondary resin and whether this drives different separation behavior.

In all instances, there was a visible degradation of the finish of the powder coatings. Under visible observation, the blended metallic pigment showed the least metallic finish, while the bonded metallic and the blended pellet had similar metallic effects. Finally, it is worth noting that this method does not test whether a powder will electrostatically separate when it is sprayed (transfer efficiency).

Conclusions

Powder coatings are a well-established paint technology, delivering many performance, economic, and environmental advantages. Aluminum flakes are widely used in all coating types because of their brightness, opacity, durability, and formulation flexibility. Aluminum flakes, however, require specific handling and storage techniques to maximize their appearance and for safe usage. Aluminum pellets are an alternative delivery form that can be incorporated using existing methods of dry blending or bonding to give equal or better appearance in a variety of paint chemistries. Pellets maintain the versatility and appearance benefits of aluminum powder while offering lower dusting and significantly higher MIE. The combined benefits and versatility of pellets make them an attractive option in powder paint manufacturing.

References

1. OSHA 3371-08 2009 “Hazard Communication Guidance of Combustible Dusts.”

CoatingsTech | Vol. 16, No. 7 | July 2019