Challenges for topcoats in Automotive Coatings
Curable or thermosetting powder coating compositions are widely used, particularly for topcoats in automotive and other industrial coatings. Basecoat/clearcoat composite coatings are topcoats that offer exceptional gloss, depth of color, distinctness of image or special metallic effects. The automotive industry has made extensive use of basecoat/clearcoat composite coatings for automotive body panels. Single-layer topcoats and clearcoats usually require an extremely high degree of clarity and gloss to achieve the desired visual effect. Furthermore, they must maintain their clarity and gloss over long periods of time in the face of environmental challenges.
Clearcoats, the outermost automotive coating, are subject to damage caused by numerous elements, including environmental fallout; exposure to ultraviolet radiation from sunlight; exposure to high relative humidity at high temperature; and defects made by impact from small, hard objects resulting in chipping. Topcoat can be formulated to reduce so-called scratch and mar, and environmental etch. Scratch and mar refers to damage from impact, rubbing or abrasion that produces visible scratches or marring that sometimes can be rubbed out. Environmental etch is a term applied to a type of exposure degradation that is characterized by spots or marks on or in the finish of the coating that often cannot be rubbed out.
To be commercially successful, a coating should provide as many favorable characteristics as possible. Accordingly, it is most preferable to produce a coating that has an optimum mix of characteristics with regard to various forms of damage resistance. For example, it is desirable to provide an increase in scratch and mar protection without hampering the environmental etch protection.