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: 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: 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: Provided are a magnetic disk substrate and a method of manufacturing the same, wherein the magnetic disk substrate has very few defects present on its surface with an arithmetic mean roughness (Ra) at a level in the vicinity of 0.1 nm and thus is suitable as a substrate for a magnetic disk with high recording density. The magnetic disk glass substrate is such that the arithmetic mean roughness (Ra) of the main surface of the glass substrate measured using an atomic force microscope with a resolution of 256×256 pixels in a 2 ?m×2 ?m square is 0.12 nm or less and the number of defects detected to have a size of 0.1 ?m to 0.6 ?m in plan view and a depth of 0.5 nm to 2 nm is less than 10 per 24 cm2, wherein the defects are each detected using a shift in wavelength between incident light and reflected light upon irradiating and scanning helium neon laser light with a wavelength of 632 nm on the main surface of the glass substrate.

Abstract: The present invention provides a glass substrate for magnetic disk in which surface irregularity of a principal surface is suppressed and a method for efficiently manufacturing a glass substrate for magnetic disk. The method includes the steps of: forming a sheet glass material by performing press forming to molten glass, a principal surface of the sheet glass material having target flatness for the glass substrate for magnetic disk, the sheet glass material having a surface shape to be ground using a grinding abrasive grain; grinding the sheet glass material using a fixed abrasive grain; and polishing the sheet glass material using a loose abrasive grain, the sheet glass material having surface irregularity of the principal surface ground using the fixed abrasive grain.

Abstract: The present invention provides a method for efficiently manufacturing a glass substrate for magnetic disk having good accuracy of a surface irregularity and an impact resistance. The method includes the steps of: performing press forming to molten glass to prepare a sheet glass material, the sheet glass material having a roughness of the principal surface of 0.01 ?m or less and target flatness of a glass substrate for magnetic disk; chemically strengthening the sheet glass material by dipping the sheet glass material in a chemically strengthening salt, thereby preparing a disk substrate; polishing the principal surfaces of the disk substrate. A thickness of the sheet glass material prepared in the press forming step is larger than a target thickness of the glass substrate for magnetic disk by a polishing quantity of the principal surface polishing step.

Abstract: A magnetic disk glass substrate including compressive stress layers at main surfaces and a tensile stress layer between the compressive stress layers formed by chemical strengthening. When the glass substrate has a thickness of less than 0.5 mm and the tensile stress layer has a thickness L and a tensile stress of Pt (kg/mm2), the following relation holds: 0.4 (kg/mm)?L·Pt?2.

Abstract: Provided are a magnetic disk substrate that can be adapted to a reduction in flying height of a head in an HDD and to an increase in rotational speed therein, and a method of manufacturing such a substrate. In an annular glass substrate for a magnetic recording medium, a main surface (12) of the glass substrate is uniformly inclined from an inner peripheral end (13) to an outer peripheral end (14) and has an isotropic shape with respect to an axis passing through the center of the glass substrate. That is, it is rotationally symmetric with respect to an arbitrary angle rotation about the axis passing through the center of the glass substrate.

Abstract: A magnetic disk glass substrate including compressive stress layers at main surfaces and a tensile stress layer between the compressive stress layers formed by chemical strengthening. When the glass substrate has a thickness of less than 0.5 mm and the tensile stress layer has a thickness L and a tensile stress of Pt (kg/mm2), the following relation holds: 0.4 (kg/mm)?L·Pt?2.0 (kg/mm).

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: A magnetic disk glass substrate manufacturing method includes a step of polishing a surface of a glass substrate to a mirror surface, a gas heating process step of causing a heated atmosphere and the glass substrate to contact each other so as to heat the glass substrate at a temperature T0, a step of causing a chemically strengthening salt melted exceeding a freezing temperature TF and the glass substrate to contact each other so as to chemically strengthen the glass substrate at a temperature T1, a gas cooling process step of causing a gas coolant and the glass substrate to contact each other so as to cool the glass substrate to a temperature T2, and a liquid cooling process step of causing a liquid coolant and the glass substrate to contact each other so as to cool the glass substrate to a temperature T3, the above-mentioned steps being included in this order, wherein the temperature T2 is set to a temperature less than the freezing temperature TF of the chemical strengthening salt in a gas cooling process

Abstract: Chemical strengthening treatment is performed by first providing a granular chemical strengthening salt so as to prevent spread in atmosphere at the time of introduction of chemical strengthening salt in a treating vessel, introducing the chemical strengthening salt in a treating vessel, melting the chemical strengthening salt into molten chemical strengthening salt and bringing a glass disc into contact with the molten chemical strengthening salt. The granular chemical strengthening salt is, for example, one obtained by forming of a powdery chemical strengthening salt material into grains. A chemically strengthened glass substrate for magnetic disk can be obtained through the process of carrying out chemical strengthening treatment of magnetic disk glass substrates. A magnetic disk can be obtained by forming at least a magnetic layer on the chemically strengthened glass substrate for magnetic disk.

Abstract: To provide a magnetic-disk glass substrate manufacturing method that can reduce the inner diameter dimensional error.

Abstract: The present invention provides a method for producing a glass substrate for a magnetic disk in which the occurrence of micro-waviness on the glass substrate is prevented in a cooling step after a chemically strengthening step so that the glass substrate has a significantly smooth principal surface, and provides a method for producing a magnetic disk in which head crash, thermal asperity failures, and the like are prevented, the flying height of a magnetic head can be decreased, and high-density recording is enabled.

Abstract: A process for producing a glass substrate for magnetic disk through chemical strengthening operation, in which the distribution of compressive stress is uniformed at a surface layer portion of the glass substrate to thereby, while preventing failures such as head crash and thermal asperity, realize a low flying height of magnetic head, attaining high-density information recording. In particular, the provided glass substrate for magnetic disk is suitable for application to compact magnetic disks for portable information equipment.

Abstract: A magnetic disk glass substrate including compressive stress layers at main surfaces and a tensile stress layer between the compressive stress layers formed by chemical strengthening. When the glass substrate has a thickness of less than 0.5 mm and the tensile stress layer has a thickness L and a tensile stress of Pt (kg/mm2), the following relation holds: 0.4 (kg/mm)?L·Pt?2.

Abstract: A method for manufacturing a magnetic disk glass substrate including a chemical strengthening step is provided. In the method, chemical strengthening treatment is sufficiently performed over the entire main surfaces of a glass substrate. Consequently, the resulting magnetic disk glass substrate can provide a magnetic disk allowing the magnetic head to have a low flying height and achieving high-density information recording, and particularly a magnetic desk suitably used in small hard disk drives for portable information apparatuses. In the chemical strengthening step, a chemical strengthening agent is brought into contact with a glass substrate to perform ion exchange by allowing the chemical strengthening agent to flow with respect to the glass substrate, or by moving the glass substrate with respect to the chemical strengthening agent.

Abstract: A magnetic disk glass substrate manufacturing method includes a step of polishing a surface of a glass substrate to a mirror surface, a gas heating process step of causing a heated atmosphere and the glass substrate to contact each other so as to heat the glass substrate at a temperature T0, a step of causing a chemically strengthening salt melted exceeding a freezing temperature TF and the glass substrate to contact each other so as to chemically strengthen the glass substrate at a temperature T1, a gas cooling process step of causing a gas coolant and the glass substrate to contact each other so as to cool the glass substrate to a temperature T2, and a liquid cooling process step of causing a liquid coolant and the glass substrate to contact each other so as to cool the glass substrate to a temperature T3, the above-mentioned steps being included in this order, wherein the temperature T2 is set to a temperature less than the freezing temperature TF of the chemical strengthening salt in a gas cooling process

Abstract: In a method of processing a glass substrate for a magnetic disk, the glass substrate containing alkali ions, the glass substrate is processed by the use of a first alkali ion having a first ion radius greater than the smallest ion radius of the smallest alkali ion among the alkali ions contained the glass substrate. Subsequently, the glass substrate is processed by the use of a second alkali ion having a second ion radius greater than the first ion radius of the first alkali ion.