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: A manufacturing method of a glass blank for magnetic disk including a pair of principal surfaces, the method including: dropping process for dropping a lump of molten glass; pressing process for forming a sheet glass material by sandwiching simultaneously the lump from both sides of the dropping path of the lump with surfaces of the pair of dies facing together, and performing press forming to the lump; and temperature adjusting process for adjusting temperature of the lump before the pressing process such that viscosity variation of the lump is reduced with respect to positions over the entirety of the lump in the pressing process.

Abstract: The present invention provides a manufacturing method of a sheet glass material excellent in flatness. A manufacturing method of glass substrate for magnetic disk including a pair of principal surfaces, the method comprising the steps of: dropping process for dropping a lump of molten glass; pressing process for forming a sheet glass material by performing press forming to the lump while sandwiching the lump from both sides of the dropping path of the lump with facing surfaces of a pair of dies, the pair of dies being set to substantially the same temperature; and processing process for processing the sheet glass material, while the lump drops down while revolving around its dropping axis.

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

Abstract: A manufacturing method of a glass blank for magnetic disk including a pair of principal surfaces, the method including: dropping process for dropping a lump of molten glass; pressing process for forming a sheet glass material by sandwiching simultaneously the lump from both sides of the dropping path of the lump with surfaces of the pair of dies facing together, and performing press forming to the lump; and temperature adjusting process for adjusting temperature of the lump before the pressing process such that viscosity variation of the lump is reduced with respect to positions over the entirety of the lump in the pressing process.

Abstract: A manufacturing method of a glass substrate for magnetic disk including a pair of principal surfaces is disclosed The method includes the steps of: dropping process for dropping a lump in vertically downward direction, the lump made by cutting molten glass; pressing process for forming a sheet glass material by sandwiching substantially simultaneously the lump from both sides of the dropping path of the lump with surfaces of the pair of dies at the timing when at least a cut mark of the lump protrudes from a pair of dies facing together, and performing press forming to the lump; and removing process for removing the glass material protruding from the pair of dies.

Abstract: There are provided, a method for efficiently manufacturing a glass substrate for magnetic disk in which the degree of surface irregularity of the principal surface is suppressed, and the glass substrate for magnetic disk. When manufacturing a glass substrate for magnetic disk including a pair of principal surfaces, a glass blank is formed by pressing molten glass or softened glass with planar press forming surfaces of dies in such a way that the molten glass or the softened glass is sandwiched from the both sides. Temperature condition is equalized around the pair of principal surfaces of the glass blank during the pressing.

Abstract: The present invention provides a manufacturing method of a sheet glass material excellent in flatness. A manufacturing method of glass substrate for magnetic disk including a pair of principal surfaces, the method comprising the steps of: dropping process for dropping a lump of molten glass; pressing process for forming a sheet glass material by performing press forming to the lump while sandwiching the lump from both sides of the dropping path of the lump with facing surfaces of a pair of dies, the pair of dies being set to substantially the same temperature; and processing process for processing the sheet glass material, while the lump drops down while revolving around its dropping axis.

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