Adhesion of Polyurethane Foam to Automotive Interior Thermoplastics

A method was adapted to measure the adhesion strength of polyurethane, semi-flexible foams to thermoplastic substrates. This method (lap-joint shear) was used to determine the effect of six (6) variables upon adhesion. These variables were: 1.) the type of substrate material, 2.) the type of polyurethane foam, 3.) the weight percentage of water in the polyurethane formulation (the degree to which the foam is blown and the chemical constituents), 4.) the chemical index of the polyurethane (the ratio of isocyanate to polyol resin), 5.) the surface roughness of the substrate, and 6.) the temperature of the polyurethane materials. Five (5) typical automotive interior thermoplastic substrates were studied: 1.) Polypropylene with preblended glass, 2.) Polycarbonate/ABS, 3.) PPO/HIPS with preblended glass, 4.) SMA with in-house dry blended glass, and 5.) SMA with preblended glass. Along with these five (5) substrates, two (2) water-blown, polyurethane, semi-flexible foams were chosen, typical of present-day automotive instrument panel padding. Adhesion values in psi and N/cm², and surface roughnesses in micro inches and microns are reported. This information is particularly useful to those working on automotive interior trim projects, most significantly those working on door panels and instrument panels that use pour-in-place foam as padding.