Filler-containing polypropylene resin composition and process for producing the same

A filler-containing polypropylene resin composition comprises (a) from 27 to 87% by weight of a polypropylene resin, (b) from 3 to 15% by weight of a modified poly­propylene resin containing from 0.1 to 3 mol% of an un­saturated dicarboxylic acid anhydride repeating unit, (c) from 5 to 30% by weight of an ethylene copolymer (melt index 0.5 to 800) composed of 82 to 98.7 mol% of an ethylene repeating unit, 1 to 15 mol% of an ester repeating unit which is Cl-8 alkyl acrylate or methacrylate, and from 0.3 to 3 mol% of an unsaturated dicarboxylic acid anhydride repeating unit, and (d) from 5 to 40% by weight of a filler which may have an organosilane coating. The composition can be made by melt-kneading all the components, but preferably by melt-mixing components (a), (b), and (d) and then melt-mixing the resulting mixture with component (c). The resin composition has excellent finishing properties, including adhesion, coating properties, and printability, as well as improved rigidity and thermal properties for use e.g. as automobile parts.