By Cynthia Challener, Contributing Writer
Numerous changes in end-use markets, both existing and new, are driving the development of low-temperature cure powder coating technologies. For existing automotive, aerospace, and general industrial applications, the growing demand for more sustainable products and processes is a key contributing factor.
Powder coatings contain no solvent (e.g., volatile organic compounds), and the application process results in minimal product waste. They also enable the rapid application of high-film builds with excellent appearance and protection against chipping, abrasion, chemicals, corrosion, and weathering. However, energy consumption is still an issue for traditional coatings that cure at relatively high temperatures. These high temperatures also prevent the use of traditional powder coatings on temperature-sensitive substrates including wood, medium-density fiberboard (MDF), most plastics, composites, and some metals, such as aluminum.
Very large metal components are also unsuitable for powder coatings due to the need to heat the large substrate masses involved. With the emphasis on lightweighting that exists today in the automotive and aerospace industries, many temperature-sensitive substrates are increasingly used. In addition, a growing number of components for a wide range of applications are produced today using three-dimensional (3D) or additive printing technologies, and there is a need for coating technologies suitable for these substrates that can provide a similar appearance across many surfaces.
The global market for low-temperature powder coatings (polyesters and polyester-epoxy hybrids, epoxies, polyurethanes, and acrylics) is estimated by market research firm Markets and Markets to be expanding at a compound annual growth rate (CAGR) of 5.7% from $1.4 million in 2018 to $1.8 million by 2023.1 End-use markets covered in the study include the furniture, appliances, automotive, architectural, electronics and medical sectors, with the highest growth occurring in the furniture market.
Notably, the non-metal segment is expected to experience the highest CAGR during the forecast period and account for the larger share of the low-temperature powder coatings market. With respect to resin chemistry, polyesters and polyester hybrids are the most widely used and will continue to be so through 2023. The major low-temperature powder coating manufacturers include AkzoNobel, Axalta Coating Systems, Jotun, PPG Industries, and The Sherwin-Williams Company, among others.
Achieving lower-temperature cure has required increased reactivity of the resin chemistries used in powder coating formulations, as well as the introduction of new curing mechanisms. Today, binders are available that allow curing of powder coating formulations via heating at temperatures as low as 130–160 °C. Other low-temperature powder coatings on the market today are cured using infrared radiation ovens. The latter approach is ideal for temperature-sensitive substrates because the intensity and/or duration of the radiative heat source can be reduced or even completely removed if the temperature of the substrate becomes too elevated. This solution works with powder coatings with curing mechanisms that can be interrupted without affecting the properties of the coating once curing is completed.
In September 2020, AkzoNobel expanded its powder coatings offerings with the acquisition of Stahl Performance Powder Coatings, which included its range of products for heat-sensitive substrates.2 The low-temperature curing technologies include both UV and thermally curing powders that cure at ultra-low (80–100 °C) temperatures and are ideally suited for use on MDF, plywood, thermoplastics, and composites.
“The clearly differentiating UV technology in particular is expected to see significant growth and will further strengthen our position as a complete provider of sustainable solutions for heat-sensitive substrates in particular for our wood coatings customers,” said Daniela Vlad, business director of AkzoNobel Powder Coatings. AkzoNobel already offers a range of Interpon Low-E (Low Energy) polyester powder coatings (Interpon 610 Low-E and Interpon Coarse Texture Low-E) that cure between 150 and 170 °C and offer anti-gassing technology, making them suitable for porous substrates, as well as other substrates found in many applications including industrial steel products, street and garden furniture, and agricultural and construction equipment. In addition, they are effective in both interior and exterior environments.
Meanwhile, Cleveland-based coatings producer Keyland Polymer develops, formulates, manufactures, and sells UV-cured powder coatings for use on MDF and other heat-sensitive substrates, including MDF, plastics, composites, metals, and other materials.3 The coatings are used by neighbor DVUV, a manufacturer of custom powder-coated components and parts for the retail, store fixture, POP display, healthcare, educational, and office furniture industries.
In the coating process, the MDF parts are hung on the line and sprayed with compressed air to remove any dust and then heated for one minute in a low-temperature preheat oven to encourage outgassing and bring moisture to the surface for increased conductivity. The coating is then electrostatically applied using an automating spraying system, and the parts are once again heated at low temperature for one minute to melt/gel the powder. The coating is then instantly cured under UV lamps. The entire process takes about 20 minutes.
Advances in biobased low-temperature powder coating technologies have also occurred in recent years.4 For example, allnex developed a line of biobased carboxyl polyesters based on renewable monomers derived from C5 and C6 sugars that can be used in a variety of powder coating systems, including epoxy-polyester hybrids, polyester-HAA (hydroxyl-alkyl amide), and TGIC-cured formulas.
Battelle Memorial Institute developed low-temperature curing powder coatings based on highly aliphatic polyester amide resins prepared from long-chain aliphatic diacids synthesized from high oleic soybean oil and di-ethanol amine. Powder coatings with 85% biobased content formulated with resins prepared using this approach and various glycidyl functional and hydroxyl-alkyl amide curing agents were found to exhibit excellent film properties even when cured at 135 °C. The resins have been produced at the pilot scale and application trials performed at infrared curing test facilities and MDF powder coating operations. It is
also worth noting that allnex offers a range of low-temperature curing polyester powder resins (CRYLCOAT) for both indoor and outdoor applications, including hybrid, standard durable, and superdurable systems.
References
- Markets and Markets, “Low Temperature Powder Coatings Market by Substrate (Non-metal, Metal), Resin (Polyester & Hybrids, Epoxy & Hybrids, PU, Acrylic), End-use Industry (Furniture, Appliances, Automotive, Architectural, Electronics, Medical), and Region – Forecast to 2023,” December 2018. https://www.marketsandmarkets.com/Market-Reports/low-temperature-
powder-coating-market-171394651.html (accessed Oct 12, 2020). - AkzoNobel, “AkzoNobel gains unique low cure technology with acquisition of Stahl’s powder activities,” Sept 2, 2020. https://www.akzonobel.com/en/for-media/media-releases-and-features/akzonobel-gains-unique-low-cure-technology-acquisition-stahl%E2%80%99s
(accessed Oct 12, 2020). - Copeland, L. “UV-Cured Powder Coating Speeds MDF Application
Process Time,” UV+EB Technology, Feb 25, 2020. https://uvebtech.com/articles/2020/uv-cured-powder-coating-speeds-mdf-application-
process-time/ (accessed Oct 12, 2020). - Biller, K. “Recent Advancements in Bio-based PowderCoating Technology,” Powder Coated Touch, Mar 22, 2019. https://www.powdercoatedtough.com/
News/ID/5111/Recent-Advancements-in-Bio-based-Powder-Coating-Technology (accessed Oct 12, 2020).
CoatingsTech | Vol. 17, No. 11 | November/December 2020