Automotive topcoats types

The nonleafing grade aluminum types are manufactured using oleic acid. They do not possess the required surface tension to leaf and consequently the aluminum platelets are randomly located within the paint film. The nonleafing grade is primarily used in automotive topcoats where they impart an aesthetically pleasing sparkle to the finish. 

Automotive Topcoats. The types of automotive topcoats that have been (or will be) used are shown in Table VI. Examination of these topcoats offers a good illustration of the projected progress of HS coatings. 

Table VII distributes automotive topcoat usage by type, with predictions for 1987. The progression from low-solids, high-emission coatings to high-solids systems is shown. Research and development of HS-E are active at each of the auto companies and at every major coatings supplier and raw materials producer. Certainly, problems such as specific polymer design and cross-linker choice still exist—as well as application, flow, and aluminum flake orientation. However, current and future research and development should reduce these problems rapidly to manageable levels.

The stronger and more economical types with fine particle sizes are also found in transparent paints. If it is to be used in two-coat metallics, however, the application of the pigment must be combined with UV absorbants in topcoats to render it weatherfast enough to be applied in original automotive finishes. 

Salt spray test. The model coatings of Table I are of the high solid type used in automotive top coats. Their primary function is not corrosion protection since this is first of all a matter of phosphate layer, electrocoat and/or primer. However, the topcoats may contribute to corrosion protection by their barrier function for water, oxygen and salts. Therefore their permeability is important as one of the factors in the corrosion protection by the total coating system. We feel that a salt spray test of the model coatings directly applied to a steel surface is of little relevance for their corrosion protection performance in a real system. 

PyGC is also an effective method for identifying and differentiating the organic binder of paint. In some cases, paint additives may readily be detected and identified. Automotive paint binder types can be identified on mg-sized samples of topcoat. Challinor [567] has evidenced various phthalates (DBP, BBP, BCP) in a methyl methacrylate (MMA)-butyl methacrylate (BMA) copolymer, BBP in a MMA-BMA-MA (methacrylic acid) terpolymer, DBP and BCP in MMA-MA copolymer and BBP in MMA-EA (ethylacrylate) copolymer. Paint additives may also be identified in architectural paints. Dimethyl orthophthalate (DMOP) was detected in an architectural alkyd enamel which had been subjected to simultaneous pyrolysis methylation (SPM) [635]. Industrial finishes on a beverage can also contain a variety of plasticisers (DMA, DMOP, DMIP), as also determined by SMP-GC [567]. 

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