Abstract: Information recording discs comprise a disc substrate having a recording layer on one side thereof, one hub having an insertion portion to be inserted into a center hole of the disc substrate and a flange portion to cover the disc substrate in the vicinity of the center hole, at least an apex of the insertion portion being composed of a magnetic material, the hub being inserted into the center hole so that the flange portion is positioned on the recording layer side of the disc substrate, and an adhesive layer is provided between the flange portion and the disc substrate. By this construction, a portion of the hub which protrudes from the back surface of the disc substrate, facing toward the spindle of a turn table can be altered in dimension and/or the diameter of the protrusion portion of the hub can be made smaller than that of the center hole of the disc substrate.

Abstract: An active energy ray-curable composition comprising (A) an epoxy resin, (B) a compound selected from the group consisting of sulfonium salts and cyclopentadienyl iron compounds, (C) a compound selected from the group consisting of acrylates, methacrylates and oligomers thereof, and (D) an organic peroxide, and optionally (E) a rubber component. The composition is useful for an adhesive layer of an optical recording medium.

Abstract: A curable resin composition comprising:(A) a compound having at least one curable acrylic radical, methacrylic radical or vinyl radial, or a mixture thereof;(B) an organic solvent containing an alcoholic organic solvent with an amount of not less than 40% by weight;(C) a compound having at least one pentavalent P with phosphoryl bonding; and(D) a polymerization initiator whichwhen coated on the surface of molded inorganic or organic materials, the coating shows superiority in curing under atmosphere and the cured composition has excellent adhesion, surface hardness, resistance to scratch, resistance to abrasion, surface luster, transparency and antistatic property.

Abstract: Information recording discs comprise a disc substrate having a recording layer on one side thereof, one hub having an insertion portion to be inserted into a center hole of the disc substrate and a flange portion to cover the disc substrate in the vicinity of the center hole, at least an apex of the insertion portion being composed of a magnetic material, the hub being inserted into the center hole so that the flange portion is positioned on the recording layer side of the disc substrate, and an adhesive layer is provided between the flange portion and the disc substrate. By this construction, a portion of the hub which protrudes from the back surface of the disc substrate, facing toward the spindle of a turn table can be altered in dimension and/or the diameter of the protrusion portion of the hub can be made smaller than that of the center hole of the disc substrate.

Abstract: An information recording disc including a plurality of disc substrates (2), at least one of which has a recording medium containing layer (1), two pieces of hubs mounted over the center hole of said disc substrates on both sides thereof, each hub having a portion to be inserted into said center hole and a flange portion to cover a portion of said disc substrate in the vicinity of said center hole, and an adhesive layer (13, 14) formed between said hubs and said disc substrates and between said two hubs. An adhesive layer (7) laminates the substrates (2a, 2b) to one another.

Abstract: Improvement in an information recording medium comprising two transparent resin substrates combined with each other, at least one of which has a recording layer provided on the inner surface thereof, two hubs mounted over the center hole of said disc substrates on both sides thereof, each hub having a insertion portion to be inserted into said center hole and a flange portion to cover a portion of said disc substrate in the vicinity of said center hole, wherein a notch is provided on the peripheral surface of each hub, adhesive layers are formed at least in the notch, between the inner peripheral surface of the center hole and the outer peripheral surface of the insertion portion of said hubs and between the hubs and a specific photo-curable composition may be used for the adhesive layer.

Abstract: In an information recording medium having laminated two disc substrates by an adhesive, each disc substrate comprising a substrate and a recording layer, so that the recording layers are disposed opposite to each other, this invention provides an information recording medium wherein said adhesive is a hot melt adhesive having a softening point of 130.degree. C. or more. Said information recording medium forms no deviation betweeen two laminated disc substrates thereof and decreased deformation such as warpage even when exposed to an atmosphere at high temperature and humidity for a long time.

Abstract: A process for producing a magnetic hub for an optical disc which is fixed to the spindle of a disc drive by means of a magnetic clamp system, which process comprises positioning and setting an annular metal plate composed of a ferromagnetic substance having burrs on one side thereof produced by punching in a mold and then injecting a resin into the mold.

Abstract: An injection-molding polyethylene composition consisting essentially of ultrahigh-molecular-weight polyethylene having a molecular weight of at least about 1,650,000 and low-molecular-weight to high-molecular-weight polyethylene having a molecular weight of, for example, about 1500 to about 360,000. This composition is produced by a multistep polymerization process comprising a step of producing the ultrahigh-molecular-weight polyethylene and a step of producing the low-molecular-weight or high-molecular-weight polyethylene.

Abstract: A resin composition for spacers of an information recording disc which comprises: (A) a random copolymer of ethylene and at least one cycloolefin having an intrinsic viscosity [.eta.] of from 0.05 to 10 dl/g, as measured in decalin at a temperature of 135.degree. C., and (B) from 0.01 to 5 parts by weight, based on 100 parts by weight, of said copolymer A, of an inorganic particles such as titania and silica having a particle size of not more than 300 .mu.m. Spacers made of the composition described herein can be welded to disc substrates within a shortened period of ultrasonic vibration to produce an information recording disc having a reduced warp angle.

Abstract: A process for producing an information recording disc of an air sandwich structure by ultrasonic welding two disc substrates, at least one of which has a recording medium containing layer, to each other through outer and inner peripheral spacers lying therebetween, which process is characterized in that the outer peripheral spacer is first welded to the disc substrate on one side, the disc substrate on the other side is then superposed through the inner peripheral spacer on said outer peripheral spacer-welded disc substrate turned inside out, and said outer peripheral spacer and disc substrate on the other side, and said inner peripheral spacer and disc substrates on both sides are ultrasonic welded together simultaneously.

Abstract: A process for producing information recording discs of an air sandwich structure by ultrasonic welding together two disc substrates, at least one of which has a recording medium containing layer, through outer and inner peripheral spacers lying therebetween, which process is characterized in that the ultrasonic welding is carried out by the use of a horn and an anvil which are so designed that each of said horn and said anvil has a difference in height along the axial direction between its portion corresponding to the outer peripheral spacer and its portion corresponding to the inner peripheral spacer, wherein the sum of differences in height of said horn and said anvil corresponds to the difference in thickness between the outer peripheral poritons of said two disc substrates plus the outer peripheral spacer and the inner peripheral portions of said two disc substrates plus the inner peripheral spacer.