PURPOSE: To prepare a disk plate having excellent transparency, moisture warpage resistance, heat deformation resistance and formability, by using a copolymer resin composed of specific amounts of methyl methacrylate, alkyl acrylate, maleic anhydride and an aromatic vinyl monomer, as a substrate.
CONSTITUTION: A copolymer resin is prepared by the polymerization of (a) 41W97.5mol%, preferably 41W70mol% of methyl methacrylate, (b) 0W5mol% of a 1W4C alkyl acrylate (preferably methyl, ethyl or butyl acrylate), (c) 1W26mol%, preferably 5W12mol% of maleic anhydride, and (d) 1.5W60mol%, preferably 18W 30mol% of an aromatic vinyl monomer (preferably styrene or p-methylstyrene), preferably in the presence of a radical initiator and chain transfer agent. The obtained copolymer resin is used as a substrate of a disk plate. Preferably, the amount of the residual monomer in the copolymer resin is ≤1.0wt%, and especially, that of the residual maleic anhydride is ≤0.1wt%.
TOYOSHIMA SHINICHI
ITOU MAKOTO
