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In this study, for the composite polypropylene in instrument panel, mechanical and chemical properties of primer-less waterborne paint is investigated by formulations of paint composition and material properties according to process conditions are also investigated. Primer-less waterborne paint with 30% of polyolefin modified acryl emulsion, 15% of alkyl methacrylate emulsion, 3% of cross-linked polymethacrylate bead, 2% of amide modified polyethylene wax had good adhesion properties onto polypropylene substrate without adhesion promoter and showed better properties on long term reliability test. In production line test, IR curing condition was insufficient for waterborne paint due to high latent heat of evaporation and complicated feature of instrument panel. Waterborne primer-less paint was sensitive to painting environment compared with solvent-borne paint.

Physical properties of waterborne soft feel coatings for instrument panel were investigated. Soft feel coatings give warm and velvet touch for cold and hard plastic materials. A waterborne soft feel coating is composed of two parts. Part A contains polyester polyurethane dispersion (PE-PUD), OH-functional water dispersible polyurethane resin (PC-PUD) and OH-functional water dispersible alkyd resin (OH-PA). Part B contains hydrophilic hexamethylene diisocyanate trimer (HHDI). The soft feeling of a coated panel is related with the amounts of PC-PUD and OH-PA. The physical properties of coated panel are controlled by the NCO/OH ratio from Part A and Part B. The results from all reliability tests satisfied soft feeling, scratch, chemical resistance and fogging.

Physical properties of sprayed polyurethane skin for instrument panel were investigated. Optimized sprayed PU(polyurethane) composition for instrument panel was determined by reaction speed measurement, which were polyol of 6000 molecular weight and modified MDI (NCO=25%). For making sprayed PU skin, raw material was sprayed from 15 cm of distance, at 15 g/min of spraying rate, on 70°C of mold, with 75°C of raw material. Sprayed PU skin had lower density than PVC skin when investigating cross sections of skins using scanning electron microscope (SEM). But the reliability test results satisfied all the specification requirements like scratch, chemical resistance, contamination resistance and fogging. Tensile strength, hardness and elongation of sprayed PU skin were slightly changed during heat aging, but the changing rate was much smaller than those of PVC skin.