Recently, PCI met with the staff at -Emerald Performance Materials to discuss questions they are often asked about successful industry approaches for optimizing performance of low- and zero-VOC coatings, and to gain insight into the company’s latest raw material innovations in specialty resins, coalescents and additives. Information in this article includes contributions from William D. Arendt, Bruce Berglund, Julie Vaughn Biege, Walter Bustynowicz, John Erbeck, Garrett Gebhardt, Shamsi P. Gravel, Emily L. McBride, Thomas Penny, Jeffrey Tyrrell and Charles Zarnitz.
Q1. How has the focus on VOC reduction impacted suppliers and the products you offer?
As industry needs have changed, the way we interact with customers and the marketplace has also greatly changed. Given the number and scope of material and formulation changes across the supply chain, we recognized we cannot innovate in a vacuum. We work even more closely today with customers to understand industry developments in order to provide competitive solutions that meet the market’s current and future needs, and we have expanded our R&D capabilities to do so.
As a supplier of additives and specialty resins, we focus on creating new products to meet the challenge of delivering low- and zero-VOC offerings, including specialty resins, coalescents/plasticizers, water-based and energy-curable colorants, foam control and silicone products. Many products we supplied to the coatings industry a decade ago have either been reformulated or replaced with next-generation materials. We are continually rolling out new materials to address common customer challenges, such as open time, gloss retention, blocking, increase in dirt pick-up, film appearance and foaming. Slow cure speed and higher viscosity have been key areas to address for low-VOC thermoset coatings.
Q2. What types of materials have you focused your efforts on as customers addressed the drive to lower VOCs?
We have not focused on one specific product platform, but rather on broadly reducing VOCs across all our product offerings. We seek to not only reduce or eliminate VOCs, but to also maintain or improve the performance characteristics of the final coating. Because our customers are replacing the polymer, the additives, or both, our product additives must be effective in various coatings systems and in conjunction with other additives in the customer’s manufacturing process and in the consumer’s ultimate application.
Q3. How has this impacted reformulation efforts of the various additives?
Achieving good overall balance in the end product is critical but challenging. We saw a number of situations in which a solution to one problem could create an unintended or undesirable consequence. The high-VOC materials had been providing a number of useful functions in the application, which had to be taken into account when designing a new product. Low-VOC formulations may need to be optimized for common customer challenges, and it may take more than one approach to address these issues.
For example, many high-VOC coalescents that were used in paint also functioned as defoamers. When these were removed from the formulation, the paint tended to generate more foam in the manufacturing process and also formed a stable microfoam. Many of the old industry-standard defoamers were not effective enough, and we took the approach of developing new next-generation zero-VOC products that address this problem.
Coalescents can have a big impact on VOCs in the coating formulation. New coalescent products are available; however, when reducing VOCs, formulators may need to adjust the levels of other useful additives, such as glycols, to optimize freeze/thaw resistance and tooling.
As VOCs were reduced in aqueous color dispersions, nozzle plugging in dispensing units was a concern, particularly for in-store zero-VOC colorants. This was not a concern for in-plant colorants, but we have focused on ensuring that all the newly reformulated zero-VOC/APE-free/formaldehyde-free colorants were stable, worked well together in a variety of systems and offered color consistency at a range of tint strengths.
In the epoxy industry, formulators often use liquid epoxy resins (LER) as an approach to lower VOCs in high-total-solids epoxy primer formulations. This extends the dry time, which is typically undesirable. We developed a product to reduce dry time and achieve an optimal balance of features: equivalent cure to solid epoxy systems, excellent solvent resistance, good formulation viscosity at about one third the VOC content of typical solid epoxy resin formulations.
We have also developed new silicone additives to overcome blocking issues that some companies have reported when switching to softer polymers. These new additives have shown promising results in trials.
Q4. It seems like foam control should be easy to address, yet there are many choices. How does a formulator proceed?
A good defoamer package can eliminate problems in production and for the end-use customer, but hundreds of available low/zero-VOC alternatives can make defoamer selection daunting. The types and levels of pigments, rheology modifiers and coalescents impact defoamer performance, so working with a supplier that can service your needs and perform screening studies can save time. Screening studies typically check compatibility in the paint first to narrow down the selection to the best chemistries (e.g., mineral oil, siloxane). Next, the initial knock-down and persistence of the foam control capabilities after accelerated heat aging and film appearance are evaluated. Typically, a series of choices at several dose levels are screened to determine the most effective choice and value in use.
Q5. Why have blocking and tack been such challenges?
As customers have changed paint formulations to lower VOCs, they often switch to lower-Tg polymers or blends of lower- and higher-Tg polymers that are inherently softer than many industry-standard polymers. Challenges with blocking in trim, window and door applications can cause problematic sticking of the painted surfaces. Similarly, challenges with tack can cause dirt pickup and appearance problems. Alternatively, formulators have utilized additives that may remain in the films longer. These approaches might create more blocking and tack issues than the traditional harder polymers that were coalesced with 100% VOC film-forming aids. Blocking and tack issues can often be addressed through reformulation.
Q6. What types of products have addressed these issues and how do they differ from previous generations?
Outside of changing to a harder polymer system, the addition of additives, fillers or crosslinkers may improve block and tack resistance, but may also come with cost and performance issues. Emerald is developing a new silicone additive technology utilizing oligomeric polysiloxanes with long-chain alkyl group functionalities, optimized to provide lubricity to coated surfaces. Initial trials indicate a three-point increase in block resistance, and the resulting coatings have improved release from painted surfaces (cured coatings) while providing for recoatability (uncured coatings).
For coalescents, customers relied heavily on TMPDMIB (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate) and glycol ethers for many years. There are now many alternatives, such as triethylene glycol di-2-ethylhexanoate and new benzoate compositions, including our patent-pending technology. The new benzoates are comprised of dibenzoate blends or monobenzoates to optimize the compatibility, performance, efficiency, economy and handling characteristics needed in paint. In side-by-side testing, we found block resistance is comparable when dropping in dibenzoates in place of traditional high-VOC coalescents at the typical low-use level for paint.
Defoamer formulations continue to evolve with the coatings in which they are used. The latest defoamer products have no VOCs or alkylphenol ethoxylates (APEs) and are low in odor. To improve compatibility in today’s paint formulations, there is an expanding palette of new organically modified silicones that provide improved efficiency over previous silicone defoamers. These products are offered at the high strength of older silicone defoamers that formulators liked, but they have excellent compatibility and are effective at low dose rates. The end results are new additives that do not create surface defects or negatively impact gloss and can reduce usage rate and inventory levels for the manufacturer.
Q7. What are effective solutions to improve scrub resistance?
Scrub resistance can be related to wear and abrasion resistance, and may be improved by using nanoparticle fillers that incorporate a hard domain into the film or crosslinkers to harden the polymer matrix and additives.
There are dibenzoate coalescents that can greatly improve scrub resistance in paint applications. This may be due to enhanced compatibility and film formation qualities over other coalescent choices, as both gloss and scrub resistance show an improvement. It is also possible that a more level application of coating to the substrate has higher scrub values, as it is devoid of thin spots that lead to failure.
In applications where coating durability is critical, acrylic/epoxy systems may be a good choice. Use of epoxy reactive crosslinkers optimizes performance, such as MEK rubs, corrosion and impact resistance in two-part enamel formulations with carboxy-functional acrylic polymers.
Q8. How can I increase the specular gloss of a formulation?
Incorporating additives into a polymer will generally cause a decrease in gloss, which can be avoided by using an effective coalescent. A better-coalesced film will be smoother and will better reflect (versus scatter) light rays, resulting in higher gloss. In screening studies of various coalescents in a typical semigloss paint formulation, we have seen up to a 10-point difference in 60° gloss between the different options.
Other additives, such as foam control products, also have an impact on gloss. Compatibility of the additive in the formulation is key to maintaining clarity. In defoamer studies, the range in gloss reduction can be 7-10 points when using traditional mineral oil defoamer products. Selection of an improved next-generation, organically modified silicone (OMS) or synthetic-based defoamer can eliminate this reduction in gloss.
Q9. Do formulators need to use different procedures to optimize performance with new additives?
Usually, new procedures are unnecessary, but order of addition may be impacted. In the rare case when optimization is challenging, often relatively simple steps can improve the performance characteristics of any additive used in the coatings formulation. Examples include higher shear mixing, longer mixing time or a change in the nonionic surfactant level or type. For example, certain defoamers are designed to withstand high shear and can be added during grinding, some are only effective in the let-down and yet others are effective in both. Your supplier should provide recommendations for the most effective results.
Q10. What about using non-water-based systems to address VOCs?
Energy-curable formulations and 100%-solids systems can also be effective low- or zero-VOC options and may be preferred in certain coatings applications. Energy-cure systems have become more popular in factory-applied and contractor-applied applications because of the production rates and short time to develop final film properties, including hardness and chemical resistance. For example, a floor coating can be completed and ready for business in hours rather than days – critical for a warehouse.
We offer a range of thermoset resin options that can be formulated into 100%-solids systems, including a chemically modified resin that provides fast cure even at low temperatures for low-VOC coatings. While epoxies can be very low in VOCs, they are also very viscous; plasticizers or reactive diluents can be utilized to improve overall performance or handling.
Factory- and contractor-applied coatings are often tinted in semi-transparent or opaque finishes. Our new line of pigment dispersions and transparent iron oxides provide a 100% solids (zero-VOC) colorant line that has been optimized for these applications.
Q11. What can be done to solve microfoam issues in low-VOC coatings?
Resin and paint manufacturers have noted increased levels of microfoam in their products, which is a challenge because it is more stable and difficult to break. Microfoam is difficult to detect with the naked eye, but could detract from the appearance of the tint strength and adhesion of the paint. Prior generations of silicones were typically only effective in the grind, and formulators needed to adjust with a mineral oil variety in the let-down. We found the new OMS types are more user friendly and can be added in both the grind and let-down and are economical due to the much lower dose rate required.
Q12. How do you make coatings that repel water and also are recoatable?
Coatings that repel water generally do so by forming continuous barriers, creating a unique surface morphology (as in the case of the Lotus effect), or having low surface energies, making them hydrophobic. However, the same additives used to make the surface water repellent may make recoating that surface with a water-based paint very challenging to obtain satisfactory wetting and film appearance. As a result, many companies stress preparation of the original surface prior to recoating, such as sanding, cleaning and/or use of chemical bonding, in order to enhance adhesion. However, the quality of surface preparation execution by the end user can vary widely, so many companies have sought to make their coatings more robust.
We developed a new alkyl modified silicone (AMS) to address this challenge. These molecules contain two domains that are optimized to balance water repellency and subsequent recoating. The new AMS product contains a low-surface-energy backbone for water repellency. Pendent alkyl groups provide domains of higher surface energy, which are more miscible with aqueous paint, and thus enable good wetting and adhesion during recoat.
Q13. How do we enhance adhesion to certain difficult-to-coat substrates?
For plastic and low-surface-energy surfaces, corona and plasma treatments have long been used, but formulators have sought alternatives to avoid this step. Some companies have developed functional polymers, specialty dispersants and modified silicone superwetters to aid in adhesion to plastics and oil-contaminated metal surfaces. Examples of these include reactive liquid polymers that extend the low-temperature flexibility/adhesion and adhesion to oily metal substrates, as well as alkoxy-modified siloxane superwetters.
In thermoset systems, incorporation of reactive liquid polymers (RLPs) in the formulation can be very effective in improving adhesion to oily surfaces. Carboxyl-terminated polymers increase the surface energy of composites (i.e. BMC and SMC) to improve paintability and rubber-modified epoxies and amine-terminated polymers improve epoxy adhesion of coatings to oily metal surfaces and to unsaturated polyester surfaces.
Q14. How does one compare VOC content of different raw materials?
Data is often reported by suppliers in many different formats, e.g., ASTM D2369, ASTM D6886, ISO 11890-2, CARB and boiling point data at various pressures. How do these relate?
Some test methods (ie., ASTM D2369) refer to standardized methods of determining VOC content by measuring weight loss under specific conditions, whereas others determine VOC via gas chromatography (ASTM D6886, ISO 11890-2). Results between oven and GC methods may not necessarily correlate to one another.
In Europe, VOCs are defined by the percentage of ingredients in the formulation with a boiling point below an arbitrary temperature, rather than relying on a weight-loss or GC method. Therefore, companies often report boiling point as a way to characterize the volatility of their material.
In comparing the volatility between ingredients, it is critical to compare the boiling point measurements at the same pressure. Typically, boiling points are reported at atmospheric pressure (760 mm Hg), which are called normal boiling points. However, some low-VOC materials have a very high boiling point, making it difficult to measure because the material may decompose before boiling. In these cases, some companies report an extrapolated value of the normal boiling point based on low-pressure boiling point data, or they report the boiling point result at the actual test pressure (vacuum). Boiling point temperatures are directly proportional to the pressures at which they are run, so the boiling point determined under a vacuum will be lower than those determined at atmospheric conditions.
Q15. What additional improvements can be made to drive sustainability?
Continue to reduce VOCs and incorporate renewable resources into products when you find viable candidates from a performance and economics standpoint that bring value to customers. One example is our specialty epoxy resin based on sorbitol/sugar. When epichlorohydrin, a key starting material, is made using glycerin-derived renewable resources, the product has a renewable content >90%. It is also an excellent bisphenol A (BPA) replacement. We have recently developed zero-VOC defoamers based on renewable resources with 85% renewable content. These typically would not be used in grinding, but are effective let-down defoamers used in place of mineral oil/petroleum-based products.
Many suppliers have an active sustainability program and manufacturing metrics, focused on the reduction of energy consumption, emissions and waste. Since our inception in 2006, we have reduced emissions by more than 50%. We attained these results through investments to eliminate or capture waste streams and reuse them. At Rotterdam, one of our largest plant sites, we joined a steam grid that produces energy from waste and shut down one of our fossil fuel boilers. This process began in June 2013 and will reduce our CO2 emissions by 40,000 tons per year.
Each of our operations has developed meaningful goals and measurements, such as 10% reduced energy use/MT production and 30% reduced CO2 emissions/MT production by 2020 as compared to our 2010 baseline. Employee engagement is a critical element of the continuous improvement process, and a variety of tools are used to continue to identify opportunities and implement projects and new practices. We also continue to look for game-changing opportunities to drive sustainability and utilize bio-based materials, partnering with customers and suppliers as these technologies continue to develop.
For more information, visit www.emeraldmaterials.com.