Abstract: Optical recording media include substrates of a larger diameter formed by injection molding a copolymer of ethylene with a cyclic olefin. The media are adapted for high speed rotation with the benefits of a high output, high C/N, and low noise level. When a protective substrate of glass is attached to the polyolefin substrate such that the recording layer is inside, there is obtained a light-weight rigid disk which experiences minimal axial runouts and hence, minimal focusing errors during high rotational speed operation.

Abstract: An optical recording disk is constructed using an injection molded substrate of a cyclic polyolefin having a recurring structural unit of the formula: ##STR1## wherein R.sub.1 and R.sub.2 are independently selected from hydrocarbon groups. The disk has a diameter of at least 200 mm, and is rotated at 1,800 rpm or higher during recording/reproducing operation. Despite a larger diameter, the disk experiences minimized occurrence of double refraction during high speed rotation, ensuring high outputs with a high C/N and a low noise level.

Abstract: In a magneto-optical recording medium comprising a perpendicular magnetizable thin film layer formed from an amorphous rare earth metal-transition metal alloy on a substrate with or without an intermediate layer, and a first protective layer formed from a plasma-polymerized film on the magnetizable layer; a second protective layer is formed on the first protective layer by curing a radiation-curable compound coating and/or an undercoat layer of a plasma-polymerized film is formed on the substrate in order to improve the moisture proofness of the magnetic layer. The substrate may be plasma treated to improve adherence. Covering the overall outside surface of the medium with a cured film of a radiation-curable compound ensures best shelf stability.