To provide a substrate which is excellent in dimensional accuracy at the time of molding and has high dimensional stability at the time of practical usage by forming the substrate of cyclic olefinic copolymer selected from the copolymers of α-olefin of straight chain type or branched chain type which has specified carbon numbers and either of two kinds of cyclic olefin, and the copolymers of these monomers and aromatic vinyl compounds.
This substrate for magnetic recording medium is composed of cyclic olefinic copolymer which is selected from the copolymer of α-olefin A of straight chain type or branched chain type which has 2-20 carbon numbers and cyclic olefin B represented by the formula I or the formula II, and the copolymer of component A, component B and aromatic vinyl compound. In the formula, (n), (k) denotes 0 or 1, (m) denotes 0 or an integer, R1-18, Ra, Rb denotes hydrogen atom, halogen atom or hydrocarbon, (p), (q) denotes 0 or an integer, (r), (s) denotes 0, 1 or 2 and R21-39 denotes hydrogen atom, halogen atom, aliphatic or aromatic hydrocarbon group, etc. That is, ethylene- norbornane-styrene copolymer, etc., are preferably used.
MOMOTAKE HIROYUKI
NISHIJIMA SHIGETOSHI
