ABS resins are widely used because of their good workability and superior impact resistance but have a disadvantage of being poor in heat resistance which is usually expressed in terms of a heat distortion temperature.
Polycarbonates are superior in impact strength, heat resistance, and transparency. However, they have disadvantages in that molten fluidity is poor, the impact strength of moldings of increased thickness is low, and they are expensive.
In order to compensate for the foregoing defects of ABS resins and polycarbonates, it has been extensively attempted to blend the ABS resins and polycarbonates together; see, for example, Japanese Patent Publication No. 15225/63. That is, the heat resistance of ABS resins is improved by blending with polycarbonates, and the workability of polycarbonates is improved by blending with ABS resins.
In accordance with conventional methods, however, if the intent is to significantly increase the heat resistance of ABS resins, it is inevitably necessary to add large amounts of polycarbonates. This will increase the production costs and reduce workability which is one of the desirable features of ABS resins. On the other hand, if the intent is to improve the workability of polycarbonates by adding ABS resins, the heat resistance of the polycarbonates is reduced to undesirably low levels.
In order to overcome the foregoing problems, various compositions have been proposed, including a composition comprising a graft copolymer prepared by graft polymerization of styrene, acrylonitrile and methyl methacrylate onto a rubber, an .alpha.-methylstyrene/methyl methacrylate/acrylonitrile copolymer, and 50% or less of a polycarbonate (see Japanese Patent Publication No. 504/77); and a composition comprising a graft copolymer prepared by graft polymerization of vinyl monomers onto a rubber, an .alpha.-methylstyrene/acrylonitrile copolymer and 50% or less of a polycarbonate (see Japanese Patent Application (OPI) Nos. 83540/82 and 55945/82). The term "OPI" as used herein means a published unexamined Japanese patent application. These compositions, however, fail to sufficiently overcome the above-described problems.