Elastomeric Coatings for Automotive Plastics
THIS ARTICLE describes elastomeric coatings that are suitable for painting flexible plastic substrates. In particular, the
coatings systems described are those that find utility in automotive exterior applications, where the requirements of
appearance and durability are most severe. Wire coatings, for example, are not discussed even though they definitely have
a demanding flexibility requirement. The article also focuses on substrates that have a high degree of flexibility, so it does
not include coatings systems for more rigid plastics, such as fiberglass-reinforced polyester sheet molding composites or
the more rigid nylon substrates, although some of the coatings systems described would certainly perform well in these
applications.
More general information about the selection and application of organic coatings is available in the article "Painting" in
this Volume.
Types of Elastomeric Coatings for Automotive Plastics
Flexible plastic substrates became popular for automotive use in the 1970s, when legislation mandated that automobiles
should sustain little or no damage in low-speed collisions. As a result, the use of plastic bumpers and fascia capable of
receiving these low-speed impacts without damage became widespread. These substrates are still widely used, including
EPDM (ethylene-propylene-diene monomers), reaction injected molded polyurethane, glass-filled reaction injection
molded polyurethane, and thermoplastic polyurethane. More recently, rubber-modified poly-propylene thermoplastic
olefin has been used for many automotive exterior applications.
Paints that are used for these substrates must meet the automotive exterior requirements that the paint on the steel portion
must meet. Among the most critical issues are durability, adhesion, appearance, and color match capability. In addition,
flexibility of the painted substrate over a wide range of temperatures is a minimum requirement. Certainly the paint must
be flexible enough that the part can be handled and attached to the car body in the assembly plant. However, many of the
automotive specifications (e.g., Ref 1) require that the painted substrate be capable of being bent 180° over a 25 mm (1
in.) mandrel at temperatures below -18 °C (0 °F) with little or no cracking of the paint or substrate. In addition to
performance requirements, elastomeric coatings must now comply with federal and local regulations that pertain to
volatile organic compounds and hazardous air pollutants. All of these requirements have led to a wealth of research
directed toward solving these challenges. Over the years elastomeric coatings have changed from low-solids enamels to
high-solids basecoat clearcoat systems and, most recently, to water-based systems.
The types of chemistries that have been used for elastomeric coatings fall into two general categories:
· Modified polyester/polyurethane cross-linked with either melamine formaldehyde resin or
polyisocyanate
· Modified acrylics cross-linked with either melamine formaldehyde resin or polyisocyanate
The details of these systems will be discussed as they pertain to structure, synthesis, and formulation.

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