Plastics are ubiquitous in modern life. They are used to make components of the everyday items we rely on from cars to smartphones. Plastics are painted for both decorative and functional reasons. Coatings are not just a protective skin, but also influence the customer’s experience and buying decision. In every industry, painting plastic parts is becoming more common. Making the most of the qualitative characteristics of the surface to facilitate individualization is one challenge for plastics coatings formulators. These aesthetics must be achieved without negatively impacting the durability of the coating.
The plastic coatings market was valued at USD $7.33 Billion in 2020 and is projected to reach $11.19 Billion by 2028, growing at a compound annual growth rate of 5.4% from 2021 to 2028. Painting is frequently one of the highest cost processes in any manufacturing sequence. Paint suppliers are continuously optimizing their products to maximize efficient use of resources while improving product quality. Cost pressures and demand for environmentally sound practices coupled with decreasing lot sizes and expanded color palettes require flexibility from coatings formulators and applicators. Well-known plastics coatings Rose Ryntz says, “The three most important parameters to developing an automotive coating are cost, cost and cost.” Of course, factors such as ease of application and reduced scrap rates contribute to the final cost per painted part, which is the best metric for process efficiency.
Automotive applications
About one-third of automotive components are made from plastic. Some models contain even more; remember the Pontiac Fiero or the early Saturn models? The advantages of using plastics include light-weighting, design flexibility and ease of fabrication. Automotive applications are the largest plastics coatings market segment with an estimated annual market value of $3.5 billion. Coatings for automotive components require coatings capable of adhesion to low surface energy substrates like thermoplastic polyolefin (TPO) and polypropylene. A wide range of plastics is used in exterior automotive components. These often require different formulations tailored to the various curing conditions specific to the base material. A particular challenge is color harmony between these various coating formulations when used on close-fitting adjacent parts.
LiDAR reflective coatings for exterior automotive applications
Autonomous vehicles need to see and be seen by other AI-guided vehicles. LiDAR is a common method of achieving this objective. LiDAR is an acronym that stands for “light detection and ranging,” though sometimes people like to fit “imaging” between the first two words. A common wavelength of light to use in these systems is 1500 nanometers (nm), which falls in the Near-Infrared portion of the spectrum, outside of human vision. Unfortunately, this corresponds to a very strong absorbance band of carbon black pigments (PBk).
Many automotive stylings rely on carbon black pigment to achieve their coloristic values. Car buyers establish an emotional connection with color to the extent that 40% of buyers will select another vehicle brand or model if their preferred color is not available. Since even small amounts of carbon black pigments strongly absorb energy at 1500 nm, eliminating carbon black from exterior automotive coatings is vital to LiDAR detection. Pigment suppliers are developing products to meet auto buyers’ expectations of color choice while facilitating LiDAR visibility for coming generations of self-driving cars. Sun Chemical introduced Spectrasense Black EH 8082 to the market to help coatings formulators accomplish this goal. This jet black NIR transparent pigment allows for true black color shades with excellent LiDAR detection properties.
Plastics have revolutionized car and truck interiors over the last forty years. Virtually everything in the passenger compartment except seating, carpeting and headliners are molded from plastic. Consumers demand a luxurious experience while driving, and interior coatings help deliver it. The right coating transforms a plain, hard piece of injection-molded plastic into a warm, touch-friendly door or instrument panel. Coatings often are used to enhance the feel or haptics of an interior automotive component as well as protect it from wear, dirt pick-up and damage from chemicals. Plastics coatings play an important role in safety as well. They must help reduce glare and reflections, which can distract the driver.
Consumer electronics
As in automotive interiors, surface haptics and resistance to specific chemicals from cosmetics and cleaners are key properties for consumer electronics coatings. Unique colors and effects which define and differentiate brands are better achieved with coatings than with molded-in-color plastics. Coated plastics parts enable the customization craved by today’s personal electronics buyers. Since they are meant to be handheld and used daily, microbial resistance can be an added value proposition for this market. The coronavirus pandemic has spurred the development of coatings with antiviral properties targeting many applications, including consumer electronics.
Recycling of coated plastic components
It is estimated that almost five billion tons of plastic waste ended up in landfills or in the environment between 1950 and 2015. If even ten percent of this plastic was coated, that would translate to 500 million tons of painted plastics. Coatings can complicate the recycling process or even make it impractical. Formulating coatings with maximum adhesion to the desired substrate is a primary goal of the chemist. But to enable easy recycling, the coating must be removed from the substrate when needed. In fact, the EU has funded the DECOAT Project to research methods of facilitating the recycling of painted plastics.
The main goal of the EU DECOAT Project is to develop smart additives for use in paints and primers that, when activated by a specific trigger condition, will enable paint disbonding. The focus is on recycling the bulk material, but the project will investigate methods to recycle coating materials as well. Recycling of painted plastic automotive facias, also referred to as bumpers, has also been the subject of numerous studies and pilot programs. The Plastics Industry Association estimates that over 145 million pounds of TPO fascias are landfilled every year. A PIA case study in cooperation with Ultra-Poly Corporation found that targeted recycling of TPO bumpers from auto body shops could produce material with 85 to 90% of the mechanical properties of virgin material while annually diverting up to one million pounds of plastics from landfills.
Plastics coatings will be a growing area of coatings technology development for many years to come. Future growth opportunities include coatings for renewable substrates (both plant-based and recycled), bio-based raw materials for the coatings themselves, low-temperature cure powder coatings for plastics, and direct-to-substrate coatings which can eliminate priming and simplify surface preparation as a way to reduce cost and waste.
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Further reading
“Painting Trends in Plastics Processing” Plastics Decorating, March 23, 2014.
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