Optical molding material, and optical disk substrate and production method thereof

Abstract

Provided is an optical molding material comprising a cyclic polyolefin resin having a glass transition temperature (Tg) of 120° C. to 170° C., wherein the melt viscosity of the resin at 260° C. is 5,000 to 50,000 poises as measured at a shear rate of 10 sec and 200 to 1,000 poises at a shear rate of 10,000 sec , and the melt viscosity of the resin at 320° C. is 500 to 5,000 poises at a shear rate of 10 sec and 100 to 800 poises at a shear rate of 10,000 sec . An optical molding material comprising a cyclic polyolefin resin, an optical molded product and an optical disk substrate, wherein a variation range of retardation of the resin is within ±10% of the retardation at 590 nm when the wavelength is changed from 400 nm to 830 nm, are provided. The material is molded into, for example, the optical disk substrate. A method for producing an optical disk substrate comprises injection-molding a thermoplastic resin comprising a cyclic polyolefin resin under conditions of a resin temperature of (Tg+100)° C. to 400° C., a mold temperature of (Tg−100)° C. to (Tg−5)° C., a shear rate of 4×10 to 1×10 sec and average residence time of the resin in a molding machine of 5 to 200 seconds. The cyclic polyolefin resin is preferably composed of a norbornene derivative.