Interior architectural coatings today do much more than hide blemishes in walls and ceilings. They often play a key role in the overall decorating scheme and are chosen in concert with furnishings and room accessories. In addition, consumers today expect these coatings to have minimal impact on the environment and have low odor while also offering a multitude of performance properties, from high hiding power to stain resistance. Increasingly, consumers also want interior architectural coatings to have advanced functionality, from biocidal properties to the ability to degrade harmful chemicals in the air. The growing demand for higher and more varied performance is occurring at a time when the market for these coatings is expanding. Driven by healthy construction sectors in mature economies and rising incomes in emerging markets, the value of the global interior architectural coatings segment is growing from $39.8 billion in 2018 at a CAGR of 6.4% and will, according to IMARC Group, reach $57.8 billion by 2024.

Many Fundamental Properties

Opacity and brightness are two of the most important attributes for interior architectural paints, along with color, and much research revolves around color trends, according to Aggie Lotz, vice president of The ChemQuest Group and the ChemQuest Technology Institute. “The most important attributes for an interior paint are to provide color as well as protection to the surface,” agrees Stan Cook, Architectural Coatings marketing director at Dow Coating Materials. Flatter sheens are also becoming a strong consumer desire. From the pigment perspective, color consistency is the most important attribute that end users look for from interior architectural coatings, both from a can-to-can and visit-to-visit standpoint, adds Michael T. Venturini, marketing director for Coatings with Sun Chemical. “There is an expectancy that no matter what day of the week and no matter the can of paint, that color will be a seamless match. That puts a big demand on ensuring pigment color consistency, tinter consistency, and dosing,” he observes.

Other required attributes for interior architectural coatings vary based on the project and overall demand of the paint job, according to Nate Hardy, product manager at Kelly-Moore Paint Company. “More heavily used or high traffic areas, such as kitchens, bathrooms, commercial buildings, schools, and doors and trim, may require a coating with higher durability to provide resistance to cleaning, moisture, scuffing, and damage. In low-traffic areas such as living spaces or offices, however, the most important attribute may be the coating’s aesthetics. Determining the most important attributes of a coating really comes down to the specific project and desired outcome,” he explains. For residential consumers, for instance, Mark Coward, technical leader Paints & Coatings, BU Industrial & Consumer Specialties at Clariant, notes that in high-humidity areas, premium paints contain additives to prevent mold and mildew formation, while in kitchen and dining areas, coatings should provide resistance to fingerprints and food staining. Commercial and institutional end users, on the other hand, prefer low-VOC paints with consistent gloss, low odor, and quick drying times for fast return to service. “Consumers and contractors expect a competitively priced, low-VOC paint that applies easily, with minimal splattering or running, exhibits maximum hiding/coverage, holds up to daily wear and tear, and delivers color,” he summarizes.

Increasingly, consumers also want interior architectural coatings to have advanced functionality, from biocidal properties to the ability to degrade harmful chemicals in the air.

Some of the basic requirements for interior architectural coatings do depend on the applicator, however. In addition to being brand loyal, contractors require paint that applies quickly and easily, hides well, touches up, and minimizes call backs. “Generally, how the paint applies with a brush, roller, or sprayer is a key selection criterion,” notes Eric Dumain, global marketing director, Liquid Resins, Arkema. In addition, for commercial and institutional jobs, the paint must have the appropriate Master Painters Institute (MPI) specification. Do-it-yourselfers, on the other hand, are influenced by consumer marketing ads, available color palette, social media trends, and third-party testing (i.e., Consumer Reports®). They are, according to Dumain, looking for decorating help, durability, stain resistance, and one-coat hide. An overall trend, he adds, is a desire for anti-scuff capability for coatings used in hallways, while trim paints need to provide excellent block and hardness, and bathroom paints must exhibit superior humidity resistance. “Protection has evolved into a more sophisticated concept that includes resistance to stains, burnishing, and other conditions previously understood as normal wear and tear,” comments Pablo León Escobar, global marketing director at OMNOVA Solutions. Surface cleanability is also part of enhanced protection especially with regards to matte finishes and texturized applications, he observes.

Sustainability is a key driver of new coatings technology research. End users (both consumers and manufacturers) seek paints that can be applied with simpler techniques, that have lower energy footprints, and reduced coating-related waste. There is also growing interest in plant-based resins and coatings based on recycled materials, according to Lotz. “Environmental regulations continue to become stricter, especially at international and state levels, and that could affect architectural coatings, while a surging awareness of the value of sustainable products (low/no-VOCs and isocyanate-, NMP-, BPA-, formaldehyde-, and metal-free) is leading to higher demand for ‘green’ coatings,” she says. In particular, Lotz points to LEED and other third-party certifications as becoming increasingly important to the interior architectural coatings market.

Shift to Greater Functionality

Another key shift for interior architectural coatings, according to Lotz, is a move from decorative to functional. “The main functionality drivers for coatings remain aesthetics and protection; end users want the coating to make the surface look good, reduce wear over time, and be able to be maintained easily,” Hardy remarks. “Coatings,” he continues, “must retain their color and finish, adhere to the surface, resist damage, and be able to be cleaned and touched up. Some coatings also need special functionalities, such as moisture, mildew, or chemical resistance, in order to protect against exposure to certain environments.” In general, according to Coward, people are looking to change the interior appearance of their homes, personalizing them to their unique tastes, in part to create a “look” that is brought alive by paint. They want this look to last, and to remain fresh, through the use of various functionalities.
More “basic” multifunctional coatings, therefore, can be anti-microbial, anti-corrosion, self-cleaning and/or self-healing. “Consumers want functionality that will ease their pain points and deliver on unmet needs. They aren’t, however, looking for specific functionality, but to have their unmet needs addressed,” notes Michael Burriss, Industrial Coatings industry manager at DSM Coating Resins.

Examples of properties that are still sought, according to Jan van Dongen, AkzoNobel marketing director for Innovation and Insights, are dirt repellency/easy-to-clean and anti-scratch/anti-scuff. The former paints would be longer lasting and stay clean longer, while the latter would stay bright longer, particularly in high-traffic areas. “Overall,” says Cook, “end users across the board are looking for paints and coatings that do more. Paints and coatings are being asked to provide properties that go beyond the traditional decorative and protective functions, from anti-microbial and sound absorbing properties to formaldehyde abatement and many more.”

Paint + Primer in One products are one example of highly functional coatings, according to Cook. “These products were initially developed from binder technology solutions to deliver outstanding stain-blocking functionality without jeopardizing the classic topcoat properties of a premium interior architectural coating,” he says. Easy-clean coatings have also been on the market for several years, but improvements are still being introduced with next-generation products, according to van Dongen. He notes that anti-scratch solutions and brighter colors are on the market as well, but here again new insights are enabling continually improved performance.

. . . for commercial and institutional jobs, the paint must have the appropriate Master Painters Institute (MPI) specification. Do-it-yourselfers, on the other hand, are influenced by consumer marketing ads, available color palette, social media trends, and third-party testing.

Coward points to surfactants with increasingly broad compatibility and improved thickener technologies combined with better economics on pigments that allow more pigments to be used in the architectural arena as other important advances. Recently, wetting and dispersing additives containing both hydrophilic groups and hydrophobic groups that, upon drying, orientate so the hydrophilic groups face towards the pigment particles and the hydrophobic groups face out into the coating have been introduced that hydrophobize��the entire paint film and thus reduce the tendency for water uptake, according to Christopher Mosinski, BYK’s end-use manager for Wood Coatings in the United States. “These additives provide great pigment stabilization and viscosity reduction, while also minimizing any negative impacts on other important properties such as stain resistance,” he says.

For Shandi Ramirez, Architectural Coatings industry manager with DSM Coating Resins, the fact that the coatings industry has waterborne paints is a testament to the need for functionality. “Across our industry we have been able to develop polymers not meant to go into water. There is an intended functionality to every paint that is designed and part of that functionality is to ease the pain points of a consumer and deliver on unmet needs. For example, faster drying resins were developed that still delivered excellent gloss development. Coatings that erode vs peel have better toughness by adding various functionalities. The trend for paint has always been moving toward improving efficiency. Painting is a laborious job; when we can make it easier on the consumer, that is the functionality that will be used,” she states.

Indeed, some interior architectural coatings today have “smart” functionality, although the definition of this type of coating can vary widely. For van Dongen, smart coatings for interior applications may be antibacterial or aseptic coatings; have active air-cleaning capability; exhibit thermal activities, such as insulation coatings; provide sound isolation; or act as sensors. Escobar considers smart functionalities to include self-cleaning properties, odor-absorption technology, and thermochromic capabilities to monitor disinfection in hospitals or temperature changes in specific rooms. He also includes anti-microbial coatings that provide resistance to mold and/or mildew formation. Hardy adds that coatings that are breathable, stain-release, self-cleaning, rust-converting, etc. are available to meet specific project needs. “Smart functionalities at their core are attribute benefits beyond aesthetics and protection,” he concludes.

Need to Achieve Balance

Developing these highly functional coatings requires the ability to balance many opposing properties and expectations. “One of the largest challenges we tend to forget is that a coating is a very thin layer. Laws of physics are restricting the effect that a thin layer can have on thermal and sound isolating properties, for instance,” says van Dongen. Creating functional interior architectural coatings at a product cost that makes sense for the market is also difficult. “Technology exists to produce extremely high-performance coatings. Unfortunately, this technology is expensive and does not always fit architectural painting budgets,” Hardy observes.�� There are, agrees Escobar, many raw materials and process technologies commercially available and transferable from other industries with relative success in coatings, but that come at a cost. “Consumers, contractors, and retailers must be willing to adopt these new functionalities for the added value gained despite the higher price tags for such coatings,” he states.

It becomes important for formulators to find not only the best solution for viscosity reduction and pigment stabilization, but also minimize the impact that doing so can have on water sensitivity and stain resistance.

It is also essential to balance the critical performance needs per application, according to Ramirez. “For example,” she says, “in wall paint, some key performance requirements are low VOCs, wash and scrub resistance, and stain resistance. Achieving these requirements can become a balancing act.�� This issue is particularly apparent when considering the addition of a functionality such as adhesion to various substrates, especially engineered substrates,” she notes. Other challenges exist when formulating functional coatings such as compatibility of ingredients, Hardy adds. “Often times, when one ingredient is added to improve a functionality, other functionalities are negatively impacted,” he explains. As an example, Mosinski points to the need for wetting and dispersing additives in waterborne��coatings, which in turn creates the need to find ways to eliminate the negative impact their hydrophilic nature can have on such properties. “It becomes important for formulators to find not only the best solution for viscosity reduction and pigment stabilization, but also minimize the impact that doing so can have on water sensitivity and stain resistance,” he explains.

Smart coatings for interior applications may be antibacterial or aseptic coatings; have active air-cleaning capability; exhibit thermal activities, such as insulation coatings; provide sound isolation; or act as sensors.

The situation is complicated by the need to create formulations that are zero-VOC, odor-free, and do not contain many traditional ingredients due to environmental concerns. “Designers and formulators have fewer degrees of freedom in material selection,” Dumain asserts. Finally, van Dongen notes that safety has to be kept in mind, which can be particularly challenging for functional coatings that interact with electrical power. Finding multifunctional raw materials and streamlining formulas is often the best route, according to Coward.

Many Areas of Exploration

Interior coatings are waterborne and, therefore, normally acrylics. Some paints are based on pure acrylics, while others rely on acrylic hybrid resins to increase the range of properties exhibited. For many functionalities, other ingredients are added to the formulation to create the desired effect, according to van Dongen, but for some attributes such as easy-clean and anti-scratch coatings, the nature and quality of the resin is clearly important. “It is less important to understand the resin chemistries used, and more important to understand the problem that is trying to be solved. One resin or chemistry cannot do it all. Formulators need many technologies in their toolbox in order to be able to develop the best-performing products that address customer challenges,” Burriss says. He also notes that polymer design has become more complex to balance the various performance requirements and today requires “thinking outside of the box” to identify resin chemistries that have multi-functions to them, such as hybrids and tribrids. Furthermore, Burriss stresses that a deeper understanding of all ingredients used in the formulation is required, and not just a focus on the resin or polymer itself.

Companies that are exploring biobased and/or recycled materials will have an advantage, because these ingredients represent different chemistries and provide the opportunity to leverage new polymerization and crosslinking technologies.

As this understanding increases, ingredient suppliers and formulators will continue to develop more advanced interior architectural coatings with increasingly complex functionalities. “Because each paint ingredient plays a part in overall performance, many raw material manufacturers are striving to innovate to consumer demands,” Coward states. He also expects that end users will be willing to pay for game-changing coatings that bring tangible benefits.

Researchers are exploring new hybrid and multiphase technologies to provide stain-resistant systems and higher levels of block and hardness at zero VOC, according to Dumain. In the pigment realm, Venturini notes that the desire is to continuously improve sustainability, lightfastness in certain color spaces, dispersibility, and achieving these developments at the necessary price point. Dow is interested in simplifying the painting process through the development of technologies that can be combined to deliver a coating that enables a painting prep process that is significantly less onerous—less taping, spackling, and sanding, while also serving as a first coat in the painting process.��“This is a very demanding requirement to fulfill, but would serve a part of the market that is typically in need of solutions to increase speed and efficiency while minimizing dusting and EHS concerns,” Cook observes. Work is also needed, notes van Dongen, on antibacterial/antiseptic coatings given the limited options available in different places due to varying regulations. AkzoNobel is also interested in safe conductive coatings that function as sensors, which is a challenging target. “Several layers are needed to create a functional system, and in case of small damages, it must remain safe for all customers,” he says. Technologies that could improve indoor air quality in all its aspects from chemicals to particulate matter are being investigated, but most are still in very explorative phases. The holy grail, according to van Dongen, would be a coating that generates electricity from light that enters a room, but this technology is very far away from anything currently in scope.

In �ƶ��̾�’s recently released U.S. Market Analysis for the Paint and Coatings Industry (2018–2023) (see paint.org/market), ChemQuest has identified several notable development areas as well, including: multifunctional pigments for multiple surfaces; connectivity and/or conductivity through paint technology for lighting and other applications; inclusion of biocides and/or bacteria resistance in paints (desired by the older community who fear that one bad staph infection will be life threatening); odor absorbing/grease resistance for home kitchens and medical applications, hospitality, and other venues where odors/grease could be a concern; radon blocking for radon-producing regions; and changeable wall technology whereby colors change from solar impacts (time of day), upon exposure to artificial lighting, or through controls sent via a phone.

Researchers are exploring new hybrid and multiphase technologies to provide stain-resistant systems and higher levels of block and hardness at zero VOC.

Multiple Expectations Always a Factor

Underlying the development of these novel functional coatings, the key trends outlined above will continue to be important going forward. “Sustainability is going to impact the interior architectural coatings market and will play a role in how the coatings will evolve, whether functional or not,” Venturini insists. Technologies that increase application efficiency, solve routine problems, and reduce the cost of labor for commercial and residential do-it-for-me jobs will be in demand, and these coatings will need to perform more functions, according to Dumain. “Consumers will continue to look for new solutions to common issues but no longer be willing to sacrifice finish appearance for performance,” Hardy asserts. They will also look for more cost-effective offerings with better convenience and reduced maintenance time and costs, adds Escobar. “Customers will expect more added value benefits in the field of performance as well as well-being; from passive to active coatings,” van Dongen concludes.

Achieving these goals in the face of ever-tightening restrictions on the materials available for use in coatings is creating the need for a new problem-solving approach, according to Dumain. Arkema is working with its customer partners and looks forward to developing effective solutions, he notes. Clariant, too, is positioning its offerings in the paints and coating market to address the demand for enhanced functionality while becoming greener and addressing a globalized market, according to Coward. “As industries shift and materials change in cost structure and functionality, new approaches can be incorporated and brought to the architectural market,” he says. Collaborations will, in fact, be necessary to help the industry overcome the challenges they face with respect to the need to balance the right amount of performance with the price demands of the market, according to Hardy. Companies that are exploring biobased and/or recycled materials will have an advantage, because these ingredients represent different chemistries and provide the opportunity to leverage new polymerization and crosslinking technologies, observes van Dongen. He also says that, particularly for interior coatings, aesthetics continue to be extremely important. “Color guidance to support customers in selecting the right color combination will be as important as the selection of the right functional formulation, with color visualization technology and color science contributing to significant changes in the landscape.”

CoatingsTech | Vol. 17, No. 2 | February 2020

Introduction

Per- and polyfluoroalkyl substances (PFAS) have been used historically in paint formulations for their hydrophobic and oleophobic properties in addition to their surface properties. In waterborne coating formulations, they are often present as fluorosurfactants (FS). This study explores the development of high-performance waterborne coatings that do not require fluorosurfactants and maintain or exceed the performance of legacy FS-containing systems.

Architectural coatings are expected to deliver a balance of performance properties. Among the most critical performance attributes is block resistance, especially in high-traffic and high-touch environments such as kitchens, bathrooms, cabinetry, and institutional settings. Removing fluorosurfactant from formulations often leads to trade-offs in performance, particularly in block resistance, tack resistance, and durability. Traditional approaches to improve block resistance, such as increasing pigment volume concentration (PVC), raising glass transition temperature (T_g), or adding waxes, can negatively impact gloss, durability, or VOC content. Therefore, another approach is necessary.

By optimizing polymer design, focusing on��T_g, particle morphology, crosslinking, and monomer selection, this research demonstrates that coatings can achieve excellent block resistance, tack resistance, washability, and durability without the use of fluorosurfactants. Comparative performance data across gloss levels and environmental conditions validate the efficacy of these optimized systems, offering a resin-based approach to eliminating FS from waterborne acrylic coating formulations.

This article presents a comprehensive study on the development of an optimized all-acrylic polymer system that eliminates fluorinated additives while maintaining or improving key performance metrics.

Materials and Methods

This study focuses on an all-acrylic polymer that does not contain fluorosurfactant while delivering high-performance properties. A high-gloss (HG) polymer was specifically designed to achieve gloss levels above 80 GU at 60°, with a minimum film formation temperature (MFFT) of 21 °C and utilizing self-crosslinking monomer.

Resins with higher��T_g��or elevated MFFT typically exhibit desirable hardness characteristics, such as reduced surface tack. However, increasing hardness often requires additional coalescent, which can raise VOC levels in the final coating formulation. To balance these factors, the HG polymer was engineered to minimize coalescent demand while maintaining surface performance. The incorporation of a self-crosslinking monomer further enhanced hardness without increasing VOC content, as crosslinking occurred after film formation rather than during application. The resin system was evaluated against an FS-containing control resin.

Four coating base formulations using the optimized polymer are shown in��Table 1. The deep base formulas in this study were tinted with 12 oz of colorant per 100 gal.

Experimental

The following tests were conducted.

Hot Block Resistance

Hot block resistance was evaluated with a 3-mil drawdown dried at 70 °F and 50% relative humidity (RH). Small squares were cut at dimensions of 1.5 in. by 1.5 in. and the coated sides were placed together and put in a 120 °F oven with a 1000 g weight on top. Then, samples were kept at room temperature for 30 min before the samples were pulled apart and the block resistance was rated on a scale of 0-10, with a rating of a 0 indicating fully adhered, and a rating of 10 indicating no adhesion and the squares pulled apart from each other with essentially no force needed.

Cotton Ball Tack Resistance

The tack resistance of the HG surface was evaluated by allowing the coated sample to dry for 24 h under controlled conditions of 70 °F and 50% RH. After drying, a cotton ball was placed on the surface, and a 500 g weight was applied directly on top. The setup was then transferred to an oven and exposed to 120 °F for 60 min. Following heat exposure, the sample was allowed to rest at room temperature for 30 min. After this rest period, the cotton ball was removed and evaluated for cotton residue.

High-Traffic Durability

The “light switch test” was conducted to simulate high traffic and high contact conditions. Lotion was applied to half of each test panel and allowed to sit for 2 h. After the exposure period, the lotion was wiped off, and the panels were stained with a combination of mineral oil and a dirt particulate, as well as a rusty water solution. These stains were allowed to dry for 2 h before being wiped with a paper towel. The panels were then subjected to 100 wash cycles using a sponge and a nonabrasive scrub medium. Finally, the color change (ΔE) of the stains was measured to assess the coating’s chemical resistance and ability to resist softening and staining.��Figure 1��shows a panel that was prepared and washed.

The main objective of this study is to generate formulating knowledge that can be applied for selecting appropriate solar reflective pigments and fillers for exterior wall coatings of various colors while retaining other important coating properties. A low pigment volume concentration (PVC), all acrylic, white formulation was used as the tint base for all colorants, conventional and infrared (IR) reflective. The key tests included rheology of the wet paints and color, gloss, hiding, and solar reflectance of dry coating films. Commercially available solar reflective materials, such as hollow spherical inorganic and organic particulate fillers and mixed-metal-oxide black and other color pigments and their equivalent conventional pigments were studied. Particular attention was focused on the issue of viscosity instability of tint base when tinted with colorants. Solar reflectance gains from IR-reflective pigments will be presented in comparison to coatings of the same color and other properties, formulated with conventional colorants. Results of this study can be used to estimate cooling energy savings due to incorporation of IR-reflective pigments.

Introduction

The earth receives about 50% of its solar power in the form of ultraviolet (UV) and visible radiation whereas the remaining 50% is in the form of infrared (IR).¹ The need for solar power to sustain all forms of life on earth is an unarguable fact. However, excessive amounts of solar power can cause harmful effects. An example of this is the phenomenon known as the heat-island effect.² Within a highly developed urban center, roofs and pavements receive and trap excessive amounts of solar energy in the form of heat causing greater needs for cooling the interiors of urban structures located in warm climatic regions. The need for cooling adds to the building maintenance cost, increases the building’s carbon footprint, and contributes to air pollution.

The above phenomena and issues have been well recognized for over four decades.³ To mitigate the problems associated with excessive solar heating, solar reflective and heat emission technologies have been developed and widely adapted for roofs and, to a significant extent, to pavements.^3-9 According to the Cool Roof Rating Council’s (CRRC) website,¹⁰ currently there are 3180 certified roof coating products. Due to the heightened awareness of global warming and ever-rising energy costs, there is a need to extend solar reflective technologies beyond roofs and pavements to other surfaces, such as exterior walls. According to a recent study by Lawrence Berkley National Laboratory’s Heat Island Group, there is great untapped potential for cool coatings for walls.¹¹ However, there are only a few solar reflective coating products for walls, and only 147 certified products are listed on the CRRC website. A literature survey has shown that, although there is increased research activity on heat-reflective coatings for walls, formulation data for commercially viable exterior wall coatings are very limited. The primary objective of this study is to contribute to filling this knowledge gap and enable formulators to develop their own successful products.

Initially, the study focused on understanding and quantifying the heat-reflective performance of conventional waterborne exterior architectural coatings and optimizing the formulations for solar reflectance without the use of specialty heat-reflective materials. All experimental coatings were prepared according to commercially viable formulations. In addition to solar reflectance, other key properties of the coatings, both at wet state and as dry films, were monitored. Results from these types of studies should enable formulators to select solar reflective grades of common raw materials while retaining other important coating properties. The solar reflective materials studied include hollow-spherical inorganic and organic particulate fillers and mixed-metal oxides.

The rheology modifiers used in all formulations in this study are associative thickeners that are sensitive to many formulation variables, including the colorants. As our previous studies have demonstrated,¹² this sensitivity used to be a huge problem causing unpredictable viscosity drops of tint bases when tinted with predispersed colorants. A secondary objective of the current study is to assess the magnitude of the associative thickener sensitivity to today’s colorants, both conventional and solar reflective.

Experimental Materials and Methods

All raw materials used in formulating the coatings are routinely used by the paint and coating industry and were obtained from commercial suppliers. The initial filler (calcium carbonate and nepheline syenite) evaluations were conducted with an exterior flat white formulation, at a pigment volume concentration (PVC) of 43.4 containing predispersed TiO2 and filler (Base Formulation 1 (BF1)). The next set of formulations was prepared with TiO2 in dry powder form (BF2). An example of the latter type, 25 PVC formulation, is shown in Table 1. Our most recent experiments were conducted with a 17.5 PVC, direct-to-metal (DTM) formulation identical to a published study.¹³ Formulations were mixed with an EMI MXML-STD disperser using a Cowles type blade in pint-sized paint cans at approximately 400 g total weight. The grind step was conducted at 1600 rpm and the let-down step at 1000 rpm.

Continue reading in the����issue of CoatingsTech

Introduction

In this article, we introduce a new applied method, brush workability, for determining the open time of architectural coatings, that offers good reproducibility and high level of differentiation in lab testing. This method shows validated correlation to real world application, using a selection of commercial paints in a double-blind contractor study.

Open time in architectural coatings is defined as the time after applying a single coat of paint where the film remains wet and workable. It is distinct from the full cure time or time before a second coat may be applied. Poor open time is evidenced by the inability to smoothly blend two areas of coating on a large substrate (within a single coat) and is also correlated to poor leveling as the film dries which can result in brush marks or visible roller pattern. Open time can also be evident during the coating application, where paints with poor open time may exhibit roller picking and poor drag between the drying film and the brush or roller.

There are multiple stages in paint drying, including: (1) Diffusion of water through the coating to the air interface and evaporation; (2) Film compaction and particle jamming; (3) Latex particle deformation under capillary force; final evaporation of water; and (4) Final cure/film compaction and coalescence via polymer entanglement. ^1-3 Workable open time is defined by the first two stages.

Current industry standards for measuring open time include ASTM methods such as wet edge,⁴ dry to touch (DTT),⁵ and use of automated dry time recorders.¹ These methods may be subjective in the ways they are rated and/or applied. Furthermore, many scientists and customers have noted that such methods do not translate well to actual paint application and/or are not physically representative of practical workable open time. This underscores the need for better methods with reduced subjectivity and better correlation to real world application, such as our new method.

Materials and Methods

Table 1 details the commercial paints used in this study, with information on technical properties. All paints are eggshell sheen, interior paints. Paint viscosities were measured using the lab viscometers (KU Stormer, ICI, Brookfield LV3/6 rpm). All testing was performed blind, using the paint IDs in Table 1 such that the applicator did not know which commercial paint was being tested. All lab open time tests were performed in a temperature-controlled lab at 75 °F and 50% RH.

Wet Edge: The wet edge test is adapted from ASTM D7488, using two vertical parallel lines running the length of the chart rather than six independent X marks at each time point. Paint was drawn down on a Leneta BK chart using a square bar with 5-mil gap. Immediately following the drawdown, the timer was started and two lines were drawn down the center of the wet film using two parallel tongue depressors. At 1-min intervals, the wet film was brushed over with 15 brush strokes in one direction. The brush was not dipped in fresh paint each time, ensuring a harsher, quicker test. The wet edge open time is the last time when the vertical lines are not able to be seen.

Dry to Touch (DTT): DTT testing was performed using 3 mil drawdowns on BK charts. Following the drawdown, a gloved fingertip was placed in the center of the wet drawdown at 1-min time intervals, and then the wet fingertip was pressed on the chart outside the drawdown area to leave a fingerprint. The paint is considered dry to touch when no finger mark is left. This method is adapted from ASTM D1640.5

Automated Dry Time Measurements: A Gardco circular path dry time recorder was also used for automated drying time measurements of paints. The machine consists of a Teflon ball stylus with a weight on the arm to control force, which moves in a circle through the wet film at a set speed. Tests were done using the 1-h setting, and 5-mil drawdowns on BK charts. The stylus was set approximately in the middle/center of the drawdown. Once complete and dry, the dry path was inspected for four types of signatures according to ASTM procedure D5895.1 There is a transparent overlay to mark the time points corresponding to the positions of each signature.

Continue reading in the issue of CoatingsTech

Correlating paint film integrity in the lab with wood grain crack resistance in real-world exposure is a challenging task. In 2020, we reported on early correlations between adhesion and film mechanics that when combined could fit a grain cracking predictive model to outdoor weathering.¹��In this study, we sought to further challenge our own model by greatly expanding our study to include 79 more paints on various substrates. Our aim was to elucidate potential correlations between paint film mechanical properties and realworld exposure performance and to test the validity of our early model.

Through our analysis, we identified several significant factors and developed a statistical model. Although it is still in its early stages, this model shows promise in providing insights into the performance of paints under real-world exterior conditions. Further refinement and validation of this model could have significant implications for the paint industry. Such a model could enhance the durability and quality of wood coatings and accelerate the development timeline.

Introduction

The correlation between laboratory tests and real-world applications of paint is a critical area of research within the paint industry. While laboratory tests provide valuable insights into paint properties and performance in controlled environments, they often fail to accurately replicate the complex and dynamic conditions found in real-world environments.² Consequently, investigating the correlation between laboratory results and real-world scenarios, particularly concerning grain cracking in paint, becomes essential.

Grain cracking is a prevalent issue that occurs when paint applied to dimensionally unstable wood substrates undergoes cyclic stress from temperature fluctuations, moisture, and other environmental factors. However, reproducing these conditions accurately within a laboratory setting proves challenging, potentially leading to results that do not truly reflect the behavior of paint in the field. Understanding the correlation between laboratory tests and real-world applications of paint becomes critical in developing more accurate and reliable testing methods, as well as improving paint design and formulation. By studying this correlation, researchers and professionals in the paint industry can develop more effective strategies for preventing grain cracking and other forms of paint degradation. This, in turn, leads to enhanced durability, aesthetics, and overall quality of paint products. Therefore, investigating the relationship between laboratory tests and real-world applications is a vital endeavor that holds significant implications for the paint industry and its consumers.

In our previous study, we focused on evaluating the mechanical performance of 18 different paints.¹ The aim was to establish correlations between the performance of these paints and their real-world exposure results. To achieve this, we employed multiple linear regression (MLR) models. During the course of our research, we discovered that the results obtained from various laboratory and accelerated test methods were significantly confounded. These results did not yield easily decipherable trends.

To overcome these challenges, we expanded our study to include additional parameters. Specifically, we measured the tensile elongation at multiple conditions, adhesion to water-conditioned surfaces, and film hardness. By incorporating these factors, we were able to develop a predictive model that exhibited a high degree of accuracy. It is important to note, however, that this model is currently limited to the scope of a single commercial paint study.

To progress the development of highperformance exterior wood coatings, it is crucial to validate and expand on our findings. This entails conducting a similar study that encompasses a broader range of paints, covering a wider spectrum of mechanical performance. By doing so, we can further investigate and identify correlations between mechanical properties and real-world exposure results. This expanded research will ultimately serve to enhance the predictive model and transform it into a valuable tool for the development of high-performance exterior wood coatings.

In this study, we examined 79 paints with different formulations, colors, sheens, and significant variations in mechanical performance. These paints were applied to various substrates and evaluated every six months to determine if we could establish a correlation between accelerated testing and long-term real-world exposure results. This comprehensive analysis aims to provide a more robust understanding of the correlation between laboratory tests and real-world applications of paint, ultimately contributing to the advancement of paint technology and the development of superior paint products.

Experimental Setup
Paints
In this study, the 79 paints used included 16 experimental waterborne acrylic architecture paints and 63 commercial waterborne architecture paints purchased from hardware or paint stores. The paints were selected to cover a wide range of formulations, pigment volume concentrations (PVC), mechanical properties, and historical exposure results based on our own in-field benchmarking results. Table 1 provides information on the number of paints used in the study based on different sheens and bases. The sheens include semi-gloss, satin, and flat, while the bases include a white and deep (tinted with 12 oz per gallon black colorant) from each sheen.

As the coatings industry moves towards lower volatile organic content (VOC) or near-zero VOC, achieving good film formation in waterborne systems without sacrificing other coating properties has become challenging. Low-VOC coatings are softer and tackier due to the use of low T_g resin, which makes them more susceptible to capturing dirt and dust, especially in warmer and more humid climates. Of all the tradeoffs in low-VOC formulations, dirt pick-up resistance is one of the most noticeable changes, particularly in traditional exterior house paints. Although dirt pick-up is a complex process, the interaction of the resulting paint film with environmental particles, weather, and other variables is ultimately defined by the surface properties, which affect the accumulation of dirt. This study will explore the effects of siloxane and silica additive technologies on dirt pick-up resistance using an accelerated test method, and the mechanism of action of these additives will be discussed.

Introduction

Dirt pick-up resistance (DPUR) is a topic of high interest in exterior architectural coatings. Consumers want paint that can resist staining while also being easy to clean. In developing dirt-resistant paints, outdoor exposure is necessary for providing real-world data; however, these tests can take many months, or years, before a coating’s performance can truly be understood. Hence, accelerated DPUR tests are critical to enabling formulation development and providing insights into how various components may contribute to the DPUR of a coating. Unfortunately, there is currently no standard accelerated DPUR method in the coatings industry; several methods focus on a dry deposition of a dirt source, meanwhile methods developed in wetter climates feature dirt application using a dirt/water slurry.¹ In general, existing accelerated DPUR methods follow a procedure consisting of 1) applying the paints to panels, 2) curing the coated panels under conditions of controlled temperature and humidity, 3) exposing the cured panels to ultraviolet (UV) irradiation and higher temperature, 4) applying and removing the dirt from the conditioned panels, and 5) analyzing the extent of dirt pick-up and removal from each panel. However, the dirt application and removal step has been acknowledged to be the greatest source of low reproducibility for these ^methods.2 In this work, a new accelerated DPUR test method was developed to facilitate studying both initial pickup of dry dirt and how well that dirt could be rinsed off when subjected to a rinsing process.

While siloxanes have traditionally been utilized to enhance surface slip, flow, and leveling,³ recent research has demonstrated that siloxane surface control agents can also significantly boost block resistance of coatings.^4,5 In a similar vein, spherical silica particles have been found to increase burnish and wet scrub resistance of architectural coatings due to their effect on the dry coating film.⁶ These results motivated us to investigate the impact of various polyether-modified siloxanes, emulsions of higher molecular weight and crosslinked siloxanes, aqueous dispersions of fumed silicas, and spherical precipitated silicas on dirt adhesion and its release.

Experimental

A commercial low-VOC waterborne, self-crosslinking acrylic exterior satin paint was chosen to evaluate various siloxane and dispersed silica additives. Siloxane-based surface control additives (SCAs) were post-added at 0.50 wt % to the commercial paint, mixed well, and the paints were allowed to stand overnight before use. Similarly, dispersed silica additives (DSAs) were post-added at 1.0 wt % to the commercial paint, mixed well, and the paints were allowed to stand overnight before use. The characteristics of the additives tested are summarized in Tables 1 and 2.

A low-VOC waterborne, self-crosslinking acrylic exterior flat paint with a 76% PVC was formulated (Table 3) and it was used to evaluate the effects of full volume-to-volume replacement of calcium carbonate filler with spherical silica fillers (SPHs) of varying particle size (Table 4). Similarly, once mixed, the formulations in Table 3 were allowed to rest overnight to release residual foam from mixing.

The commercial paint samples to which had been post-added various siloxane and dispersed silica additives and the coating formulations in Table 3 were applied to scrub charts using a 150-mm wide bird-type film applicator for a 4-mil wet film thickness. After two days of drying in a standard conditioning atmosphere of 21–25 °C and 45–55% relative humidity (ASTM D4332-22), the scrub charts were trimmed to the test panel size (12.7 cm x 10.8 cm; center of coating) and cured in a Q-SUN Xe-3 Xenon Test Chamber (Ser. No. 20-34603-79-X3HBSE; from Q-Lab) at 40 °C and 45% relative humidity using a full-spectrum sunlight filter with an irradiance of 0.89 W/m2 at 340 nm for three days. The test panels were removed and allowed to rest for two hours before dirt deposition. A number of studies have revealed that typical outdoor dirt particles that soil exterior coatings have a number median diameter of approximately 100 nm.^7-9 Hence, for this study, Lamp Black 101 (carbon black from Orion Engineered Carbons), and BAYFERROX® 509 (iron oxide from Lanxess) were chosen. These dirts were applied via fine-mesh sifters to achieve a complete and uniform coverage of the test panels. After one day, the dirt was removed by lifting the panels upright and tapping 15 times against the benchtop. The panels were then rinsed at an upright position with 15 misting sprays of DI water from a spray bottle at a distance of 20 cm. The residual water was removed by tapping the panels 15 times, after which they were returned to a horizontal position and dried overnight.

Sufficient open time is essential for achieving painting efficiency and delivering aesthetically pleasing results in architectural coatings. The open time can vary widely for an exterior coating because the wet coat may experience extreme weather conditions from humidity and temperature changes to varying wind speeds. Additionally, the open timeof the coating can be influenced by solids, pigment volume concentration, polymer composition, rheology modifiers, additives like humectants, and solvents.

The open time and early rain resistance are seemingly diametrically opposed properties, and it is difficult to improve the early rain resistance without negatively influencing open time. Through the use of statistical design of experiments, this study identified polymer structure factors that can influence the open time and early rain resistance of the paints. The rain resistance was tested using the shower head test method, while the open time was tested using conventional methods such as ASTM 7488 and Gardco Quadracycle drying time.

Further insight on open time was gained by a novel test method using diffusing wave spectroscopy which provides information on critical steps of the film formation process such as water evaporation-concentration, particle packing, particle deformation, and film dry through. Combining this data with polymer structure study allowed for the elucidation of structure-property relationships, specifically regarding open time. The resulting novel insights helped in the development of new polymer prototypes that positively influence both early rain resistance and open time.

Introduction

Weather, especially rain, has a severe impact on the film formation of freshly applied paint on an exterior wall. A fastdrying paint will provide early resistance to rain. However, developing^1,2��a fast-drying paint with sufficient open time is challenging. The open time³��of paints has been defined as the period of time during which a painter can make corrections to the freshly applied wet paint film without leaving brush marks. Sufficient open time is essential for achieving painting efficiency and delivering aesthetically pleasing results in architectural coatings. The open time of the coating can be influenced^4,5��by solids, pigment volume concentration, polymer composition, rheology modifiers, additives like humectants, and solvents.

Film formation^6,7 from polymer dispersions is schematically depicted in Figure 1. It is expected that water-based paints undergo similar stages, such as water evaporation-concentration, particle packing, particle deformation, and particle coalescence-interdiffusion, to form a coating. The water evaporation stage strongly influences the open time of the paint. The drying conditions of the paint, including temperature, humidity, and air flow, have a significant impact on the water evaporation rate and open time. Low temperature, high humidity, and stagnant air will slow down water evaporation and increase open time. Conversely, high temperature, low humidity, and high-velocity air flow will speed up water evaporation and reduce open time.

FIGURE 1 Film formation in polymer dispersions.^{6, 7}

In this research, we studied the polymer composition to improve the open time without compromising early rain resistance. Statistical design of experiments was used to identify polymer structure factors that can influence the open time and early rain resistance of the paints. Multi-speckle diffusing wave spectroscopy^8,9 was used to gain understanding on the critical steps of the film formation process such as water evaporation-concentration, particle packing, particle deformation, and film dry through. Diffusing wave spectroscopy is an extension⁸ of classical dynamic light scattering to concentrated and opaque media. The diffusing wave spectroscopy and polymer structure factor data were analyzed to develop new polymers with improved open time without compromising early rain resistance.

Experiments

To study the effect of polymer composition on the open time and early rain resistance, a custom design of experiment using JMP® was carried out. The design consisted of eight structure factors of a control polymer dispersion and the details of the design are given in Table 1. Paint formulated using this control polymer provided better early rain resistance and equal open time compared to a leading national brand commercial paint. The goal is to improve the open time of this paint by changing the control polymer structure without reducing the early rain resistance of the paint.

Sixteen different polymer dispersions were synthesized using this design strategy and the composition differences of these polymer dispersions are given in Table 2. These polymer dispersions were synthesized by conventional emulsion polymerization using unsaturated monomers, emulsifiers, and initiators. These polymer dispersions have approximately 53% solids content. Two polymer dispersions, Nos. 1 and 14, were not stable and so they were eliminated from the study. For studying the main effects using this JMP® custom design, the minimum number of runs required is only 9.

Introduction

Coatings’ application performance, such as ease of application, superior coverage, and faster return-toservice, continue to be a key consideration for both consumers and contractors when choosing architectural coating products. Based on the claim analysis of commercial architectural coatings, paint application related properties are among the top claimed product performance in architectural coatings, as shown in Figure 1¹ The rheological properties of coatings play critical roles in determining various aspects of coatings application, including sag and leveling balance, spatter resistance, application feel, roller pattern, and applied hide. In addition to rheology of coatings, paint application process and results are highly dependent on environmental conditions, roller cover, paint applicator, and substrates. Traditionally, evaluating the appearance of coating and spatter resistance has heavily relied on visual assessment, which could be influenced by inconsistencies in human visual perception. To address this, we have conducted a series of roller application studies in different formulation spaces and employed advanced image analysis technologies to enable more reliable and quantitative evaluation of spatter resistance and roller patterns. In this article, we will share the insights gained from our study and discuss the impact of rheology modifiers on the performance of roller applications.

FIGURE 1 Top paint claims from commercial architectural coating products in the market in 2023.

Introduction of Spatter Resistance

Spatter resistance is an important roller application property. Paint spatters are tiny droplets of liquid paint that can be ejected from the roller/substrate as coatings are applied on substrates. The liquid droplets can land on adjacent surfaces or areas not meant to be painted. Coatings with good spatter resistance will reduce the work associated with preparing the surface and cleaning up after painting as well as help painters get the work done more efficiently.

Spatter resistance is highly influenced by the rheology of the coatings. A series of rheology modifiers were evaluated in four different formulations, including standard acrylic interior flat formulations with or without hydroxyethyl cellulose (HEC), premium acrylic flat formulation, premium composite-forming acrylic flat formulation, and economy acrylic/PVA blend flat formulations with or without HEC. In addition, nine commercial paints from leading paint manufacturers were also included in the study as benchmarks.

Rheology modifiers that were evaluated included both hydrophobically modified ethoxylated urethanes (HEURs) and hydrophobically modified alkali-swellable emulsions (HASEs), with rheology profiles spanning from shear-thinning to more Newtonian. Roller application was conducted on primed drywall (4′ × 4′) using woven roller cover, 7″ long, 3/8″ nap. A professional painting contractor conducted all roller applications. For each roller application trial, two vinyl charts are taped at the bottom of the drywall panel to capture spatter of the coating. Figure 2 shows an example of paint spatters on a black vinyl chart from a commercial interior flat paint, which has poor spatter resistance. The white dots on the charts are the spattered paint droplets. The top portion of the chart is closer to the drywall, which showed more paint spatters. The number of paint spatters decreased as the distance from the drywall increased.

FIGURE 2 Example of paint spatters captured on a black vinyl chart.

Image Analysis Algorithm Overview

Spatter resistance is rated by evaluating the paint spatter on vinyl charts. Several factors are included for evaluation, including the number of paint droplets, the size of droplets, and the intensity or contrast of droplets vs. background. Traditionally, this evaluation is done by visual assessment, where an operator would assign a score based on a set of standards or industry guidelines. However, this approach is prone to inconsistencies due to human visual perception.

A robust method has been developed for quantifying spatter resistance using image analysis for the detection and rating. To ensure consistent lighting and imaging condition among different spatter charts, images are captured using an imaging station under controlled light environment and imaging parameters. The captured images undergo image-processing techniques, such as image thresholding, to remove background noise. A blob-detection algorithm is then applied to identify individual spatter droplets. The algorithm identifies the blobs or a group of white pixels to capture the spatter. The algorithm was further refined based on fundamental physics of spatter-droplet generation to exclude the experimental artifacts from the group of detected spatters. Most of the spatters that result from the paint application will be circular shaped because the droplets experience free fall before landing on the test panel. The angle of incidence on these droplets can be assumed to be +/- 20 degrees, which will keep most of the droplets in a circular shape with constant diameter. On the other hand, experimental artifacts or unintentional paint marks on the test panel mostly occur in the form of streaks with large aspect ratio. Figure 3 shows the original image of the black vinyl chart that has undergone spatter-resistance testing on the left and the processed image with the detected spatters on the right. The figure shows one of the experimental artifacts in a non-circular shape located in the upper right corner. The blob detection highlights paint spatters in red circles, and the algorithm successfully identifies the experimental artifact, which was not included in the detection.