No Postcure RRIM for Automotive Exteriors 2001-01-3061
Reinforced reaction injection molding (RRIM) has re-emerged as an important method in automotive exterior applications. Presently composite applications demand higher productivity and improved part performance. Stability at higher heat to endure E-coat oven bake, improvements in fillers yielding easier processing at high loading, improved toughness at high modulus, and higher productivity have already been realized with RRIM in Europe and NAFTA.
Now the kinetics of one new material, Bayflex 190 is such that reaction is essentially complete at demold. In the past RRIM molded parts were required to be baked at 120°C and above to complete chemical reactions, attain complete physical properties, and de-gas parts prior to painting. In current E-coat applications postcure of 190°C is typical. Elimination of postcure means significant savings in energy, increased productivity, decreased handling and lower capital expense. Bayflex 190 polyurea attains virtually all properties at demold. After molding parts can be washed and primed directly. Dynamic mechanical analysis shows that further heating to 200°C anneals and strengthens the composite.
Several very sensitive analytical methods have been employed to characterize the degree of cure at demold. Differential scanning calorimetry (DSC) shows no exothermic chemical reaction up to 200°C. Thermal gravimetric analysis (TGA) shows no CO2 loss from unreacted isocyanates. And Fourier transform infrared spectroscopy (FTIR) scans indicate no free isocyanate in freshly molded samples. Parts painted in production exhibit no defects associated with elimination of postcure.