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Recently, R-PP (Rubber modified Polypropylene) has been often used in automotive exterior parts, but is difficult to use for longer parts because of the limit of it's dimensional stability. Studies of the thermal expansion mechanism of R-PP by the rule of mixtures and FEM indicated that optimization of the volume elasticity ratio of PP/rubber is a key point to design the low thermal expansion alloy. And the selection of rubber which is partially compatible with the PP is also important. The developed new alloys are used for automotive longer exterior parts such as the rocker panel and side moldings which have better dimensional stability than the usual R-PP and R-RIM(Reinforced Reaction Injection Molding).

New vibration damping plastic alloys were developed using blends of nylon-6 or polypropylene (PP) with modifiers and damping agent. The damping properties and stiffness were compared with commercially available nylon-6 and PP. As trials, we have attempted to make these plastic alloys construction of engine such as cylinder head cover and timing velt cover. These plastic alloys were molded into engine parts such as the front cover, rocker cover and timing belt cover. The purpose was to reduce the noise levels approximately 4.0 dB lower than that of aluminum covers. The newly developed plasitic alloy engine covers have great potential to reduce engine noise.