Automotive coatings cross-linkers

Water-borne adhesives are preferred because of restrictions on the use of solvents. Low viscosity prepolymers are emulsified in water, followed by chain extension with water-soluble glycols or diamines. As cross-linker PMDI can be used, which has a shelf life of 5 to 6 h in water. Water-borne polyurethane coatings are used for vacuum forming of PVC sheeting to ABS shells in automotive interior door panels, for the lamination of ABS/PVC film to treated polypropylene foam for use in automotive instmment panels, as metal primers for steering wheels, in flexible packaging lamination, as shoe sole adhesive, and as tie coats for polyurethane-coated fabrics. PMDI is also used as a binder for reconstituted wood products and as a foundry core binder. 

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.

Carter et al. [402] have addressed the chemical assessment of automotive clearcoats (usually melamine-cross-linked systems), which requires evaluation of the cross-linker type, HALS and UV absorbers. Coating systems require a variety of chemical analytical techniques for their evaluation [403], including UV microspectroscopy [402, 404], /xFTIR [402,405], /xRS [406,407], NMR [408], ESR [409], ToF-SIMS [410,411] and hydroperoxide titration [412]. Ideally, what is needed for industrial evaluation purposes is a set of techniques that can follow chemical changes in individual layers of a full automotive paint system, typically consisting of 45 /xm clearcoat, 25 /xm basecoat, 35 /xm primer, and 35 /xm E-coat on metal. The clearcoat must shield underlayers from UV. Unlike the case for IR radiation, examination of 30 /xm and thinner clearcoat layers with 0.3 to 0.4 /xm radiation lends itself quite well to the use of microscopes and microspectroscopic techniques. UV microspectroscopy of 10 /xm paint system cross-sections is the method of choice cfr. also Chp. 1.1). UV microspectroscopy... 

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