Abstract: A magnetic disk used in a hard disk drive device includes a substrate; a magnetic recording layer; and a heat insulating layer provided between the substrate and the magnetic recording layer. Even though a substrate has low heat resistance, as a result of providing the heat insulating layer, the substrate can be used as a substrate for a magnetic disk that can withstand heat treatment (high-temperature annealing).

Abstract: A substrate for a magnetic disk has a disk shape. The substrate has a diameter D of 85 mm or more and a thickness T of 0.6 mm or less. When an impact is applied to the substrate under conditions of 70 (G) and 2 (msec) in a normal direction of main surfaces of the substrate in a state in which an inner circumferential end portion of the substrate is fixed, the maximum amplitude of vibration in a thickness direction of an outer circumferential end portion of the substrate is 0.25 mm or less, the substrate is a non-magnetic metal substrate, and regarding the Young's modulus E and the thickness T of the substrate, a value of E·T3 is 3 to 18 (GPa·mm3).

Abstract: A method for manufacturing the ring-shaped glass spacer to be arranged in contact with a magnetic disk in a hard disk drive apparatus, including: preparing a ring-shaped glass blank; and grinding main surfaces of the ring-shaped glass blank by using grinding pads that include diamond particles as fixed abrasive particles.

Abstract: A ring-shaped glass spacer is configured to be arranged in contact with a magnetic disk in a hard disk drive apparatus. A surface resistivity of a surface of a glass material of the glass spacer at 22 (° C.) is lower than a surface resistivity of an inner portion of the glass material at 22 (° C.).

Abstract: A disk-shaped substrate for a magnetic disk has a diameter D of 85 mm or more and a thickness T of 0.6 mm or less, and a material of the substrate has a Young's modulus E of 90 GPa or more.

Abstract: A method for manufacturing the ring-shaped glass spacer to be arranged in contact with a magnetic disk in a hard disk drive apparatus, including: preparing a ring-shaped glass blank; and grinding main surfaces of the ring-shaped glass blank by using grinding pads that include diamond particles as fixed abrasive particles.

Abstract: In order to suppress the occurrence of adhesion between magnetic disks and spacers when the magnetic disks and the spacers are removed from a hard disk drive apparatus in which the magnetic disks and the spacers are installed, a surface roughness Ra of a main surface of a ring-shaped glass spacer to be arranged in contact with a magnetic disk is set to be not larger than 1.0 ?m, and an average inclination R?a of the main surface is set to be at least 0.02.

Abstract: A ring shaped glass spacer is configured to be arranged in contact with a magnetic disk in a hard disk drive apparatus. A surface resistivity of a surface of a glass material of the glass spacer at 22 (° C.) is lower than a surface resistivity of an inner portion of the glass material at 22 (° C.).

Abstract: A disk-shaped substrate for a magnetic disk has a diameter D of 85 mm or more and a thickness T of 0.6 mm or less, and a material of the substrate has a Young's modulus E of 90 GPa or more.

Abstract: A glass material of a glass spacer has a surface resistivity of 103 to 109 (?/sq) at 22 (° C.). The surface resistivity of a surface of the glass material of the glass spacer at 22 (° C.) is lower than the surface resistivity of an inner portion of the glass material at 22 (° C.). The glass spacer contains at least one oxide selected from the group consisting of TiO2, Nb2O5, WO3, and Bi2O3, as a glass component.

Abstract: In order to suppress the occurrence of adhesion between magnetic disks and spacers when the magnetic disks and the spacers are removed from a hard disk drive apparatus in which the magnetic disks and the spacers are installed, a surface roughness Ra of a main surface of a ring-shaped glass spacer to be arranged in contact with a magnetic disk is set to be not larger than 1.0 ?m, and an average inclination R?a of the main surface is set to be at least 0.02.

Abstract: In order to suppress the occurrence of adhesion between magnetic disks and spacers when the magnetic disks and the spacers are removed from a hard disk drive apparatus in which the magnetic disks and the spacers are installed, a surface roughness Ra of a main surface of a ring-shaped glass spacer to be arranged in contact with a magnetic disk is set to be not larger than 1.0 ?m, and an average inclination R?a of the main surface is set to be at least 0.02.

Abstract: A glass material of a glass spacer has a surface resistivity of 103 to 109 [?/sq] at 22 [° C.]. The surface resistivity of a surface of the glass material of the glass spacer at 22 [° C.] is lower than the surface resistivity of an inner portion of the glass material at 22 [° C.]. The glass spacer contains at least one oxide selected from the group consisting of TiO2, Nb2O5, WO3, and Bi2O3, as a glass component.

Abstract: In order to suppress the occurrence of adhesion between magnetic disks and spacers when the magnetic disks and the spacers are removed from a hard disk drive apparatus in which the magnetic disks and the spacers are installed, a surface roughness Ra of a main surface of a ring-shaped glass spacer to be arranged in contact with a magnetic disk is set to be not larger than 1.0 ?m, and an average inclination R?a of the main surface is set to be at least 0.02.

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: 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: 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: 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.