Abstract: A glass substrate for a magnetic disk of the invention is a disk-shaped glass substrate for a magnetic disk where the substrate has a main surface and end face and is subjected to chemical reinforcement treatment, and is characterized in that the penetration length in the uppermost-portion stress layer on the main surface is 49.1 ?m or less, and that assuming that an angle between the main surface and compressive stress in the stress profile by a Babinet compensator method is ?, a value y of {12·t·ln(tan ?)+(49.1/t)} is the penetration length in the uppermost-portion stress layer or less.

Abstract: An aspect of the present invention relates to a glass substrate for a magnetic recording medium, which is comprised of glass with a glass transition temperature of equal to or greater than 600° C., an average coefficient of linear expansion at 100 to 300° C. of equal to or greater than 70×10?7/° C., a Young's modulus of equal to or greater than 81 GPa, a specific modulus of elasticity of equal to or greater than 30 MNm/kg, and a fracture toughness value of equal to or greater than 0.9 MPa·m1/2.

Abstract: An aspect of the present invention relates to glass for a magnetic recording medium substrate, which comprises, denoted as molar percentages, 50 to 75 percent of SiO2, 0 to 5 percent of Al2O3, 0 to 3 percent of Li2O, 0 to 5 percent of ZnO, a total of Na2O and K2O of 3 to 15 percent, a total of MgO, CaO, SrO, and BaO of 14 to 35 percent, a total of ZrO2, TiO2, La2O3, Y2O3, Yb2O3, Ta2O5, Nb2O5, and HfO2 of 2 to 9 percent, with a molar ratio of {(MgO+CaO)/(MgO+CaO+SrO+BaO)} falling within a range of 0.85 to 1, and a molar ratio of {Al2O3/(MgO+CaO)} falling within a range of 0 to 0.30.

Abstract: The present invention relates to recording glass substrates molar percentages: 56-75 SiO2, 1-11 Al2O2, more than 0-4 Li2O, 1-15 Na2O. more than 0 less than 3 K2O, no BaO. total Li2O, Na2O and K2O 6-15, (Li2O Na2O) less than 0.50, {K2O/(Li2O, Na2O and K2O)} equal or less than 0.13, total MgO, CaO and SrO 10-30, MgO and CaO 10-30, {(MgO+CaO)/(MgO+CaO+SrO)} equal or more than 0.86, alkali oxides to alkaline earth oxides equal to or more than 0.50. total ZrO2, TiO2, Y2O3, La2O3, Gd2O3, Nb2O5, and Ta2O5 more than 0 equal to or less than 10, molar ratio {(ZrO2, TiO2, Y2O3, La2O3, Gd2O3, Nb2O5, and Ta2O5)/Al2O2 equal or more than 0.40, Tg equal to or higher than 600° C., average coefficient linear expansion equal or higher than 70×10?7/°C. at 100-300° C. and Young's modulus equal to or higher than 80 GPa.

Abstract: Disclosed are a thin-sheet cover glass that is high in quality and has high mechanical strength, and a display equipped with the aforementioned cover glass. The cover glass is used to cover the image display unit of a display and to make images displayed by the aforementioned image display unit opaque. The cover glass is formed from a glass that comprises, in an oxide base conversion indicated in mol %, 60 to 75% SiO2, 0 to 12% Al2O3 (provided that the total content of SiO2 and Al2O3 is 68% or more), 0 to 10% B2O3, 5 to 26% Li2O and Na2O in total, 0 to 8% K2O (provided that the total content of Li2O, Na2O, and K2O is 26% or less), 0 to 18% MgO, CaO, SrO, BaO in total, and ZnO, and 0 to 5% ZrO2, TiO2, and HfO2 in total, as well as a total of 0.1 to 3.5 mass % of an Sn oxide and a Ce oxide relative to the total mass, wherein (Sn oxide content/(Sn oxide content+Ce oxide content)) is 0.01 to 0.99, and the content of an Sb oxide is 0 to 0.1%; and has a plate thickness of no more than 1.0 mm.

Abstract: Glass is mass-produced with a glass melting furnace comprising a melting tank, at least a wall surface in contact with molten glass thereof being made of refractory material, at least one pair of electrodes placed so as to be in contact with the molten glass held in the melting tank for ohmically heating the molten glass held in the melting tank; and at least one metallic member, at least a surface of which is made of metal and placed so as to be substantially always in contact with the molten glass held in the melting tank. Every metallic member is, when the melting tank is filled with the molten glass, placed so as to be substantially always outside an electric current flowing region which is formed by the electrodes into the molten glass held in the melting tank.

Abstract: According to one aspect of the present invention, provided is glass for use in substrate for information recording medium, which comprises, denoted as molar percentages, a total of 70 to 85 percent of SiO2 and Al2O3, where SiO2 content is equal to or greater than 50 percent and Al2O3 content is equal to or greater than 3 percent; a total of equal to or greater than 10 percent of Li2O, Na2O and K2O; a total of 1 to 6 percent of CaO and MgO, where CaO content is greater than MgO content; a total of greater than 0 percent but equal to or lower than 4 percent of ZrO2, HfO2, Nb2O5, Ta2O5, La2O3Y2O3 and TiO2; with the molar ratio of the total content of Li2O, Na2O and K2O to the total content of SiO2, Al2O3, ZrO2, HfO2, Nb2O5, Ta2O5, La2O3, Y2O3 and TiO2((Li2O+Na2O+K2O)/(SiO2+Al2O3+ZrO2+HfO2+Nb2O5+Ta2O5+La2O3+Y2O3+TiO2)) being equal to or less than 0.28.

Abstract: According to one aspect of the present invention, provided is glass for use in substrate for information recording medium, which comprises, denoted as molar percentages, a total of 70 to 85 percent of SiO2 and Al2O3, where SiO2 content is equal to or greater than 50 percent and Al2O3 content is equal to or greater than 3 percent; a total of equal to or greater than 10 percent of Li2O, Na2O and K2O; a total of 1 to 6 percent of CaO and MgO, where CaO content is greater than MgO content; a total of greater than 0 percent but equal to or lower than 4 percent of ZrO2, HfO2, Nb2O5, Ta2O5, La2O3 Y2O3 and TiO2; with the molar ratio of the total content of Li2O, Na2O and K2O to the total content of SiO2, Al2O3, ZrO2, HfO2, Nb2O5, Ta2O5, La2O3, Y2O3 and TiO2 ((Li2O+Na2O+K2O)/(SiO2+Al2O3+ZrO2+HfO2+Nb2O5+Ta2O5+La2O3+Y2O3+TiO2)) being equal to or less than 0.28.

Abstract: A method of manufacturing a glass blank for a magnetic recording medium glass substrate in which, after a pair of press molds placed so as to be opposed to each other in a horizontal direction with press-molding surfaces thereof and the temperatures of the press-molding surfaces being substantially the same are brought into contact with a molten glass gob substantially at the same time, press molding is carried out to produce plate glass and the plate glass continues to be pressed with the pair of molds, and then, when the plate glass is taken out, the duration time of pressing the plate glass is controlled so that the flatness of the glass blank is 10 ?m or less, and a method of manufacturing a magnetic recording medium glass substrate, a method of manufacturing a magnetic recording medium, and an apparatus for manufacturing a glass blank for a magnetic recording medium glass substrate using the same.

Abstract: An aspect of the present invention relates to a glass substrate for a magnetic recording medium, which is comprised of glass with a glass transition temperature of equal to or greater than 600° C., an average coefficient of linear expansion at 100 to 300° C. of equal to or greater than 70×10?7/° C., a Young's modulus of equal to or greater than 81 GPa, a specific modulus of elasticity of equal to or greater than 30 MNm/kg, and a fracture toughness value of equal to or greater than 0.9 MPa·m1/2.

Abstract: A glass substrate for a magnetic disk of the invention is a disk-shaped glass substrate for a magnetic disk where the substrate has a main surface and end face and is subjected to chemical reinforcement treatment, and is characterized in that the penetration length in the uppermost-portion stress layer on the main surface is 49.1 ?m or less, and that assuming that an angle between the main surface and compressive stress in the stress profile by a Babinet compensator method is ?, a value y of {12·t·ln(tan ?)+(49.1/t)} is the penetration length in the uppermost-portion stress layer or less.

Abstract: An aspect of the present invention relates to a glass substrate for a magnetic recording medium, which is comprised of glass comprising, denoted as molar percentages, 56 to 75 percent of SiO2, 1 to 11 percent of Al2O3, more than 0 percent but equal to or less than 4 percent of Li2O, equal to or more than 1 percent but less than 15 percent of Na2O, equal to or more than 0 percent but less than 3 percent of K2O, and substantially no BaO, with a total content of Li2O, Na2O, and K2O falling within a range of 6 to 15 percent, with a molar ratio (Li2O/Na2O) being less than 0.50, with a molar ratio {K2O/(Li2O+Na2O+K2O)} being equal to or less than 0.13, with a total content of MgO, CaO, and SrO falling within a range of 10 to 30 percent, with a total content of MgO and CaO falling within a range of 10 to 30 percent, with a molar ratio {(MgO+CaO)/(MgO+CaO+SrO)} being equal to or more than 0.

Abstract: A glass substrate for a magnetic disk of the invention is a disk-shaped glass substrate for a magnetic disk where the substrate has a main surface and end face and is subjected to chemical reinforcement treatment, and is characterized in that the penetration length in the uppermost-portion stress layer on the main surface is 49.1 ?m or less, and that assuming that an angle between the main surface and compressive stress in the stress profile by a Babinet compensator method is ?, a value y of {12·t·ln(tan ?)+(49.1/t)} is the penetration length in the uppermost-portion stress layer or less.

Abstract: According to one aspect of the present invention, provided is glass for use in substrate for information recording medium, which comprises, denoted as molar percentages, a total of 70 to 85 percent of SiO2 and Al2O3, where SiO2 content is equal to or greater than 50 percent and Al2O3 content is equal to or greater than 3 percent; a total of equal to or greater than 10 percent of Li2O, Na2O and K2O; a total of 1 to 6 percent of CaO and MgO, where CaO content is greater than MgO content; a total of greater than 0 percent but equal to or lower than 4 percent of ZrO2, HfO2, Nb2O5, Ta2O5, La2O3 Y2O3 and TiO2; with the molar ratio of the total content of Li2O, Na2O and K2O to the total content of SiO2, Al2O3, ZrO2, HfO2, Nb2O5, Ta2O5, La2O3, Y2O3 and TiO2 ((Li2O+Na2O+K2O)/(SiO2+Al2O3+ZrO2+HfO2+Nb2O5+Ta2O5+La2O3+Y2O3+TiO2)) being equal to or less than 0.28.

Abstract: According to one aspect of the present invention, provided is glass for use in substrate for information recording medium, which comprises, denoted as molar percentages, a total of 70 to 85 percent of SiO2 and Al2O3, where SiO2 content is equal to or greater than 50 percent and Al2O3 content is equal to or greater than 3 percent; a total of equal to or greater than 10 percent of Li2O, Na2O and K2O; a total of 1 to 6 percent of CaO and MgO, where CaO content is greater than MgO content; a total of greater than 0 percent but equal to or lower than 4 percent of ZrO2, HfO2, Nb2O5, Ta2O5, La2O3, Y2O3 and TiO2; with the molar ratio of the total content of Li2O, Na2O and K2O to the total content of SiO2, Al2O3, ZrO2, HfO2, Nb2O5, Ta2O5, La2O3, Y2O3 and TiO2 ((Li2O+Na2O+K2O)/(SiO2+Al2O3+ZrO2+HfO2+Nb2O5+Ta2O5+La2O3+Y2O3+TiO2)) being equal to or less than 0.28.

Abstract: Provided are a method of manufacturing a glass blank, the method including press-molding a molten glass gob under a state in which a separation mark formed on an upper surface of the molten glass gob faces at least one of the molding surface sides of a pair of press molds arranged facing each other in a horizontal direction, when the molten glass gob falls into a space between the pair of press molds, and a method of manufacturing a magnetic recording medium substrate and a method of manufacturing a magnetic recording medium, both using the glass blank.

Abstract: Provided is a method of manufacturing a glass blank for a magnetic recording medium glass substrate, including: manufacturing a glass blank by at least press molding a falling molten glass gob with a pair of press molds both so as to face each other in a direction perpendicular to a direction in which the molten glass gob falls, in which: the molten glass gob is formed of a glass material having a glass transition temperature of 600° C. or more; and when the press molding is carried out so that the molten glass gob is completely extended by pressure and molded into a flat glass between press-molding surfaces of the pair of press molds, at least a region in contact with the flat glass in each of the press-molding surfaces of the pair of press molds forms a substantially flat surface.

Abstract: In a perpendicular magnetic recording medium which includes a substrate (1) of a nonmagnetic material, first and second nonmagnetic underlayers (4 and 5) formed on the substrate, and a perpendicular magnetic recording layer (6) formed on the first and the second nonmagnetic underlayers, the first nonmagnetic underlayer is made of an amorphous nonmagnetic metal material containing a metal element which forms a face-centered cubic (fcc) crystal structure by a simple substance. The second nonmagnetic underlayer is formed on the first nonmagnetic underlayer in contact with the first nonmagnetic underlayer and made of a nonmagnetic material containing a hexagonal close packed structure. The perpendicular magnetic recording layer is formed on the second nonmagnetic underlayer in contact with the second nonmagnetic layer.

Abstract: An aspect of the present invention relates to glass for a magnetic recording medium substrate, which comprises, denoted as molar percentages, 50 to 75 percent of SiO2, 0 to 5 percent of Al2O3, 0 to 3 percent of Li2O, 0 to 5 percent of ZnO, a total of Na2O and K2O of 3 to 15 percent, a total of MgO, CaO, SrO, and BaO of 14 to 35 percent, a total of ZrO2, TiO2, La2O3, Y2O3, Yb2O3, Ta2O5, Nb2O5, and HfO2 of 2 to 9 percent, with a molar ratio of {(MgO+CaO)/(MgO+CaO+SrO+BaO)} falling within a range of 0.85 to 1, and a molar ratio of {Al2O3/(MgO+CaO)} falling within a range of 0 to 0.30.

Abstract: The provided are a glass for a magnetic recording medium substrate permitting the realization of a magnetic recording medium substrate affording good chemical durability and having an extremely flat surface, a magnetic recording medium substrate comprised of this glass, a magnetic recording medium equipped with this substrate, and methods of manufacturing the same. Glasses for a magnetic recording medium substrate are, glass I comprised of an oxide glass, comprising, denoted as mass percentages: Si 20 to 40 percent, Al 0.1 to 10 percent, Li 0.1 to 5 percent, Na 0.1 to 10 percent, K 0 to 5 percent (where the total content of Li, Na, and K is 15 percent or less), Sn 0.005 to 0.6 percent, and Ce 0 to 1.2 percent; the Sb content is 0 to 0.1 percent; and not comprising As or F; glass II comprised of oxide glass, comprising, as converted based on the oxide, denoted as molar percentages: SiO2 60 to 75 percent, Al2O3 1 to 15 percent, Li2O 0.1 to 20 percent, Na2O 0.