PURPOSE: To obtain a disk substrate with superior resistance to heat, moisture, impact and chemicals, superior transparency, resistance to optical rotation, fidelity in molding, etc. by using a specified polymer composition.
CONSTITUTION: A magnetic layer which can be changed by light energy is formed on one side of an optically transparent plate made of a polymer composition contg. repeating units represented by the formula, and a metallic coating layer having a specular surface is formed on the surface of the recording layer. Information is reproduced by irradiating laser light from the reverse side of the metallic coating layer. The polymer composition contg. repeating units represented by the formula is poly-(N-ethylene trimellitic imide) resin consisting of the repeating units, a copolymer contg. the repeating units, or a polymer blend of a copolymer contg. the repeating units with other polymer. The front and rear sides of a disk substrate 3 can be utilized as recording and reproducing surfaces by forming surface protective layers 3', 6 on the substrate 3 and by joining a metallic coating layer 5 face to face by adhesion 7.
ICHIKAWA RINJIROU
UNO KEIICHI
