Plastics coatings grow: as the demand for plastics grows, so has the market for coating applied...

In North America, as the demand for plastics has grown, so has the market for coatings applied to plastic materials. According to the ChemQuest Group, a management consulting firm located in Cincinnati, Ohio, the plastic substrate coatings market totalled $958 million based on a volume of 32

million gallons. As with all other types of coatings, reduction of waste and minimisation of emissions of volatile organic compounds (VOCs) is a significant issue for those applying coatings to plastic parts. New technologies developed in North America address these concerns and still enable the production of highly decorated plastic products.

The automotive sector accounts for approximately 50% of the market for painted plastic goods, where painted plastics parts are used in both exterior (bumper fascia, mirror housings, door guards, etc.) and interior) applications. While colour can be incorporated into the molding process, painting of plastics provides durability (gloss protection and scratch resistance) that cannot be achieved otherwise. Vinyl flooring is the second largest market for painted plastics in North America. After that the market is highly fragmented.

Red Spot is the leading supplier of coatings for plastics in North America. The company focuses on high performance coatings for automotive plastics, but is also pioneering new coatings for plastics used in the sports and consumer products industries. Other producers include Akzo Nobel, PPG, Sherwin Williams, and DuPont. BASF has developed UV curable paints designed specifically for application on plastic substrates.

Adhesion of coatings to these low surface energy materials has posed the biggest challenge to paint manufacturers, according to Michael D. Brown, vice president of the ChemQuest Group. 'Finding ways to overcome this issue has been a major focus for the research and development teams,' he adds. Eastman is the leading provider of adhesion promoters. The company's chlorinated and non-chlorinated adhesion promoters are available for use in both 1K and 2K topcoats for untreated polyethylene, polypropylene, and TPO. DuPont Dow Elastomers also offers adhesion promoters for plastic substrates. PPG offers base coats for novel self-priming plastics that have adhesion promoters incorporated into the polyolefin resin.

Developments

New technologies developed within the last several years in North America have made it possible to significantly improve the decorating process of injection-molded plastics. 'These technologies incorporate the decorating step into the molding process, virtually eliminating the inefficiency, waste, and environmental emissions concerns associated with the application of liquid coatings to the surface of formed plastic part,' Brown explains.

The first technology, offered by Avery Dennison and Soliant, utilises dry paint film, which is inserted into the injection mold. The film, which looks like dried paint, is created via a process similar to printing, and can include any desired graphic design as well as incorporate special effects. The film has a backing composed of the same plastic material of which the part is made and melts into the part. The use of high performance films can provide enhanced durability for the final coatings.

Soliant's Fluorex Paint Films can be applied on most any plastic substrate utilising existing equipment, use the same colour matching technology as traditional paint systems, and offer a total system cost advantage over traditionally painted plastic components, according to the company. They also do not chip or flake, don't experience 'orange peel,' and have excellent weatherability and solvent resistance properties. They are used extensively in automotive applications as well as for recreational vehicles, outdoor signs, and appliances in many different processes including thermoforming, injection molding, extrusion, compression molding, pressure sensitive, and metal forming.

Omnova Solutions introduced a technology that involves injection of liquid coatings into the mold at a specific point in the molding cycle. As with the dry paint film approach, the part is painted while it is still in the mold, and thus offers the same elimination of waste and reduction of VOC emissions. With this process, there is more flexibility in the chemistry of the liquid coatings. Omnova's coatings are integrated into the manufacture of fiber glass vehicles and components for land and marine applications and can be used as a primer or quality topcoat.

While these two technologies have seen only limited use outside of North America, they should be attractive to other regions of the world. According to Brown, the plastic molding industry is more consolidated in North America, which has enabled companies to establish long term relationships with customers and implement the technologies for specific products. In Europe and Asia, the industry is much more fragmented, with most production conducted on a custom basis.

In addition, the big three automakers in the US have embraced the technologies, whereas car manufacturers in Europe and Japan have not yet done so. Lastly, the companies offering the technologies do not yet have a significant presence in Europe and Asia. It is likely, though, that the benefits of the technologies will lead to their global adoption. 'These technologies are extremely well suited for developing nations,' says Brown. 'Plastic molders don't need to make the heavy investments associated with application of liquid coatings to formed parts. They can implement this technology from the beginning and produce products in a cost effective and environmentally friendly way without any significant added capital cost.'

Cynthia A Challener is the proprietor of US-based C & N Consulting Email: challener@vtlink.net