Copolymer resins of vinyl cyanide-based heat resistant - for increasing the vinyl aromatic

The present invention provides a method for improving an aromatic vinyl - cyanide vinyl based copolymer resin, the heat resistance, by compounding the aromatic vinyl - vinyl cyanide-based resin, the heat resistance can be improved without aromatic vinyl damage - excellent transparency vinyl cyanide-based resin, and the molded product can be obtained having an excellent appearance. According to the present invention can provide a method for improving an aromatic vinyl - cyanide vinyl based copolymer resin heat resistance, comprising: 45 to 85 mass% of an aromatic vinyl monomer unit, from 5 to 45 mass% (meth) acrylate monomer units, 10 to 20 mass% of unsaturated dicarboxylic anhydride monomer units, said copolymer as measured according to 2mm thick ASTM D1003 of total light transmittance of 88% or more.