Abstract: In an optical recording medium wherein grooves or lands formed on the supporting substrate are used for the recording tracks, and wherein prepits are also formed, production of the supporting substrate and high density recording are facilitated. This medium comprises a supporting substrate and a recording layer on the substrate wherein the surface of the supporting substrate on which the recording layer is formed is formed with alternating continuous convex portions and continuous concave portions which are substantially parallel to each other. The adjacent continuous convex portions are connected by bridging convex portions extending in transverse direction, and the bridging convex portion has a planar configuration that its width is minimum at or near the center between the adjacent continuous convex portions. The supporting substrate is produced by using a master disk which has a resist layer formed with mother patterns of each of the continuous convex portions, continuous concave portions, and prepits.

Abstract: In an optical information medium comprising a supporting substrate, an information recording layer thereon, and a light-transmitting layer wherein a recording/reading laser beam enters the recording layer through the light-transmitting layer, the light-transmitting layer is formed of a resin and has a tensile strength at break of 5-40 MPa, a tensile elongation at break of 15-100%, and a tensile modulus of 40-1,000 MPa. The medium has improved recording/reading characteristics when a laser beam defines a beam spot having a small diameter of up to 300 &mgr;m and the medium is rotated at a high linear velocity of at least 8 m/s.

Abstract: In the multi-layer information medium having a plurality of information-storing layers according to the present invention, distance between the adjacent information-storing layers is reduced with no increase in cross talk between these layers. The optical information medium has at least two information-storing layers each storing recorded information and/or servo information, and at least one of the information-storing layers is recorded or read by the recording beam or the reading beam which has passed through other information-storing layer(s). The medium has a filter layer between the adjacent information-storing layers, and in the spectral absorption characteristics in the wavelength range of 300 to 1000 nm of this filter layer, a wavelength range exhibiting an absorption of 80% or higher and a wavelength range exhibiting an absorption of 20% or lower are present.

Abstract: An optical information medium includes a disk-shaped substrate (100) having a center hole (101), an annular information recording area thereon, and an annular resin-based light-transmitting layer (102) thereon by which recording/reading laser beam is transmitted to the information recording area. The light-transmitting layer (102) terminates at a radially inner periphery which forms an annular raised rim (6). The rim is effective for protecting the light-transmitting layer from damages and dust adhesion, and when a plurality of such media are stacked, preventing the media from intimate contact.

Abstract: A method and apparatus is provided for preparing an optical information medium comprising a disk-shaped substrate having a center hole, an information recording layer thereon, and a resin-based light-transmitting layer thereon by which recording/reading laser beam is transmitted. The apparatus includes a rotating table (2) for holding and rotating the substrate (100) having the information recording layer borne thereon, a plug means (3) including a disk member (31) for closing the center hole (101) and an integral support shaft (32), and a nozzle (4) for feeding a coating fluid containing the resin to the outer periphery of the support shaft (32), wherein the coating fluid is flowed from the support shaft to the disk member, then over the substrate, thereby forming the light-transmitting layer having a minimized thickness variation.

Abstract: An optical information medium which has excellent abrasion resistance and which further exhibits sufficient smudge-proof properties is provided. The optical information medium is coated on at least one surface with a film of a silane coupling agent containing a water- or oil-repellent substituent, said silane coupling agent being represented by the following formula (1): R1—Si(X)(Y)(Z) wherein R1 is the water- or oil-repellent substituent; X, Y and Z are independently a monovalent group; and at least one of X, Y and Z is a group which is capable of forming Si—O—Si bond by polycondensation with silanol group; and said medium has an underlying layer formed in contact with said silane coupling agent film, and at least the surface of said underlying layer comprises a compound having a chemical bond represented by the formula (2): M—A wherein M is a metal atom (including a semimetal), and A is a chalcogen atom selected from O, S, Se, and Te, nitrogen atom, or carbon atom.

Abstract: The invention provides an optical disc comprising a circular glass substrate (2) having information-carrying means (3) on one major surface. A protective member (4) of a resin includes a circular flat portion (42) and an annular rim (41) extending perpendicular from the periphery of the flat portion (42). The glass substrate (2) is integrally joined to the protective member (4) such that the information-carrying means (3) of the glass substrate (2) may face the covering portion (42) of the protective member (4). The outer side of the glass substrate (2) is surrounded by the protective member rim (41) to leave a shock absorbing space therebetween. The invention prevents the glass substrate from failure at its corner when impact is applied to the disc.

Abstract: A mechanical property such as axial acceleration of an injection molded resin disc substrate or an optical disc comprising the same is determined by measuring a variation in radius or diameter of the substrate or disc in its circumferential direction, and determining the mechanical property of the substrate or disc from the measurement.

Abstract: An optical recording medium of phase change type, and in particular, a dual side medium prepared by adhering two single side media is provided. In this medium, deformation of record marks generated in the overwriting due to difference in light absorption between the record marks and the region other than the record marks is prevented by providing a reflective layer of high light transmission, and increase in jitter and failure of track servo and focus servo caused by uneven coating of the adhesive layer and the resin protective layer are prevented. The optical recording medium comprises a substrate, a recording layer of phase change type on the surface side of the substrate, and a reflective layer and a light absorption layer disposed in this order on the surface side of the recording layer.

Abstract: An optical disc is constructed by joining a pair of resin substrates through an adhesive layer so that information carrying means is disposed inside. The resin substrate has a diameter-to-thickness ratio d/t.gtoreq.180. The adhesive layer has a Young's modulus of 0.1-1 kgf/mm.sup.2 at 20.degree. C. and a mechanical dissipation factor (tan.delta.) of 0.6-5.0 at 20.degree. C. The adhesive layer is formed of a hot melt adhesive, pressure-sensitive adhesive, room temperature curable adhesive or ultraviolet curable adhesive. The disc is resistant to both heat and vibration.

Abstract: A magneto-optical disc comprising a recording layer and a protective coating on a substrate is operated for magneto-optical recording in a magnetic field modulation mode such that the protective coating is in sliding contact with a magnetic head. The protective coating is obtained by curing with radiation a polymerizable composition which contains a fatty acid ester and radiation-curable compounds including a monofunctional (meth)acrylic monomer, a polyfunctional (meth)acrylic monomer, and optionally, an acrylic oligomer.

Abstract: A magneto-optical recording disc adapted for magneto-optical recording in the magnetic field modulation system by means of a magnetic head in continuous contact with the disc includes a recording layer on a substrate and a wear resistant resinous coating thereon. The coating is formed of a resin containing carbon particles having a mean particle size of 1 to 15 .mu.m. The magnetic head is in sliding contact with the surface of the coating during operation. The coating is effective for reducing friction with the magnetic head and retains such reduced friction over a long time.

Abstract: A magneto-optical disc includes a substrate, a recording layer, and a protective coating comprised of a resin and a lubricant. The disc is operated for magneto-optical recording in a magnetic field modulation mode such that the protective coating is in sliding contact with a magnetic head. The lubricant is a higher fatty acid ester R.sup.1 --COO--R.sup.2 wherein R.sup.1 is a saturated or unsaturated aliphatic C.sub.10 -C.sub.30 hydrocarbon residue, and R.sup.2 is a saturated or unsaturated aliphatic C.sub.10 -C.sub.30 hydrocarbon residue. Alternatively, the protective coating is formed by curing with radiation a composition containing a lubricant and a radiation-curable compound such that micropores are locally formed in or near the outer surface of the protective coating, the lubricant being distributed in the micropores. In either case, the protective coating is effective for minimizing friction with the magnetic head.

Abstract: An optical recording medium comprising a recording layer on a substrate and an intermediate layer between the substrate and the recording layer exhibits high reflectance and corrosion resistance when the intermediate layer comprises silicon, aluminum, oxygen, nitrogen, and at least one element selected from the group consisting of yttrium, lanthanide elements and actinide elements, and contains 0.1 to 2 atom % of the element and 20 to 90 atom % of silicon and nitrogen combined or 2 to 35 atom % of the element and 20 to 95 atom % of silicon and nitrogen combined.

Abstract: A magneto-optical disc includes a recording layer (4) and a protective film (7) of radiation-cured resin on a substrate (2). Information is written in the recording layer with the aid of a magnetic head in sliding contact with the disc. In a first form, when the protective film is subject to a micro-vibration scratch test by setting the disc in a thin film scratch tester equipped with a diamond indentor having a radius of curvature R of up to 50 .mu.m, the relationship: 0.8.ltoreq.L/R.sup.2 .ltoreq.2.7 is met wherein L is the critical load (N.m) under which the thin film is scratched. In a second form, the protective film has a dynamic modulus of 5.0.times.10.sup.9 to 4.0.times.10.sup.10 dyn/cm.sup.2 at 100.degree. C. The disc is highly durable.

Abstract: An optical disk is configured as comprising a pair of substrates one of which has a recording layer borne thereon, the substrates being joined together through an adhesive so that the recording layer is interposed therebetween. In one form, one of the substrates is of glass, the other substrate is of a resin. In another form, both the substrates are of glass or resin. Delamination is prevented by using the adhesive having a specific glass transition temperature, Young's modulus, and dynamic loss factor.

Abstract: A protective coating made of resin, preferably a radiation curable resin containing fluoroplastic fine particles having a low surface energy is provided in the form of the uppermost layer facing a magnetic head, thereby improving the frictional properties and durability of a magneto-optical disc that is used with a magnetic field modulation system in which the magnetic head comes in constant contact therewith.

Abstract: An optical recording disk includes a resin substrate having a recording layer thereon and a protective glass substrate, which are joined into an integral disk such that the recording layer is inside. The resin substrate is formed of a resin composition comprising a specific cyclic polyolefin and an optional alkyl phenol condensate. The resulting lightweight, rigid disk is adapted for recording/reproducing operation at high rotational speeds with few focusing errors due to minimized axial runouts.

Abstract: An optical recording disk is constructed using a substrate which is injection molded from a mixture of a cyclic polyolefin and up to 2% by weight of an alkyl phenol condensate. A recording layer remains firmly adhered to the substrate even in a hot humid environment.

Abstract: An optical disk is configured as comprising a pair of substrates one of which has a recording layer borne thereon, the substrates being joined together through an adhesive so that the recording layer is interposed therebetween. In one form, one of the substrates is of glass, the other substrate is of a resin. In another form, both the substrates are of glass or resin. Delamination is prevented by using the adhesive having a specific glass transition temperature, Young's modulus, and dynamic loss factor.