# US 2025/0095682 A1 · Substrate for magnetic disk, magnetic disk, and hard disk drive apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2025/0095682 A1 - Document ID: US20250095682A1 - Status: Published application - Kind: A1 - Application number: 18/970,882 - Filed: 2024-12-05 - Published: 2025-03-20 - Earliest claimed: 2017-06-30 - Assignees: Hoya Corporation - Applicants: Hoya Corporation - Inventors: Kinobu OSAKABE - Web page: https://patentgrep.com/patent/US20250095682A1 ## CPC - G11B 5/73921: {Glass or ceramic substrates} - G11B 5/739: {Magnetic recording media substrates} - G11B 5/73911: {Inorganic substrates} - G11B 5/73917: {Metallic substrates, i.e. elemental metal or metal alloy substrates} - G11B 5/73919: {Aluminium or titanium elemental or alloy substrates} - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) ## Abstract A substrate for a magnetic disk includes a substrate main body having two main surfaces and an outer circumferential edge surface, and a film that is an alloy film containing Ni and P and provided on a surface of the substrate main body. A disk shape of the substrate main body has an outer diameter of 90 mm or more. A thickness T of the substrate that includes film thicknesses of sections of the film provided on the main surfaces is 0.520 mm or less. A total thickness D mm, which is a sum of the film thicknesses of the sections of the film on the main surfaces and the thickness T mm satisfy D≥0.0082/T−0.0015. The substrate main body at the outer circumferential edge surface forming an interface with the film provided on the outer circumferential edge surface has a surface roughness maximum height Rz of 0.5 μm or more. ## Claims ### Claim 1 A substrate for a magnetic disk, the substrate comprising: a substrate main body having two opposing main surfaces and an outer circumferential edge surface, the substrate main body being a glass substrate main body or an aluminum alloy substrate main body, the substrate main body having a disk shape; and a film that is an alloy film containing Ni and P, and provided on a surface of the substrate main body such that the film is formed continuously over the main surfaces and the outer circumferential edge surface, wherein the disk shape has an outer diameter of 90 mm or more, a thickness T of the substrate, which includes film thicknesses of sections of the film provided on the main surfaces, is 0.520 mm or less, a total thickness D (mm), which is a sum of the film thicknesses of the sections of the film provided on the main surfaces, and the thickness T (mm) of the substrate satisfy Equation (1) below, D≥0.0082/T−0.0015 (1), and the substrate main body at the outer circumferential edge surface forming an interface with the film provided on the outer circumferential edge surface has a surface roughness maximum height Rz of 0.5 μm or more. ### Claim 2 (depends on 1) The substrate for a magnetic disk according to claim 1, wherein a film thickness of a section of the film provided on the outer circumferential edge surface is larger than, and 150% or less of, one of the film thicknesses of the sections of the film provided on the main surfaces. ### Claim 3 (depends on 1) The substrate for a magnetic disk according to claim 1, wherein the film thickness of the section of the film provided on the outer circumferential edge surface is 110% or more of the one of the film thicknesses of the sections of the film provided on the main surfaces. ### Claim 4 (depends on 2) The substrate for a magnetic disk according to claim 2, wherein the film thickness of the section of the film provided on the outer circumferential edge surface is 110% or more of the one of the film thicknesses of the sections of the film provided on the main surfaces. ### Claim 5 (depends on 1) A magnetic disk, wherein a surface of the substrate for a magnetic disk according to claim 1 has at least a magnetic film. ### Claim 6 (depends on 2) A magnetic disk, wherein a surface of the substrate for a magnetic disk according to claim 2 has at least a magnetic film. ### Claim 7 (depends on 3) A magnetic disk, wherein a surface of the substrate for a magnetic disk according to claim 3 has at least a magnetic film. ### Claim 8 (depends on 4) A magnetic disk, wherein a surface of the substrate for a magnetic disk according to claim 4 has at least a magnetic film. ### Claim 9 (depends on 5) The magnetic disk according to claim 5, wherein when an impact is applied under conditions of 120 (G) and 2 (msec) in a normal direction of the main surfaces in a state in which an inner circumferential portion of the substrate is fixed, the number of times an amount of shift caused by vibration of an outer circumferential edge portion of the substrate in a thickness direction of the substrate is 0.2 mm or more is four or less. ### Claim 10 (depends on 6) The magnetic disk according to claim 6, wherein when an impact is applied under conditions of 120 (G) and 2 (msec) in a normal direction of the main surfaces in a state in which an inner circumferential portion of the substrate is fixed, the number of times an amount of shift caused by vibration of an outer circumferential edge portion of the substrate in a thickness direction of the substrate is 0.2 mm or more is four or less. ### Claim 11 (depends on 7) The magnetic disk according to claim 7, wherein when an impact is applied under conditions of 120 (G) and 2 (msec) in a normal direction of the main surfaces in a state in which an inner circumferential portion of the substrate is fixed, the number of times an amount of shift caused by vibration of an outer circumferential edge portion of the substrate in a thickness direction of the substrate is 0.2 mm or more is four or less. ### Claim 12 (depends on 8) The magnetic disk according to claim 8, wherein when an impact is applied under conditions of 120 (G) and 2 (msec) in a normal direction of the main surfaces in a state in which an inner circumferential portion of the substrate is fixed, the number of times an amount of shift caused by vibration of an outer circumferential edge portion of the substrate in a thickness direction of the substrate is 0.2 mm or more is four or less. ### Claim 13 (depends on 5) A hard disk drive apparatus comprising: ten or more magnetic disks each of which is the magnetic disk according to claim 5; and a magnetic head. ### Claim 14 (depends on 6) A hard disk drive apparatus comprising: ten or more magnetic disks each of which is the magnetic disk according to claim 6; and a magnetic head. ### Claim 15 (depends on 7) A hard disk drive apparatus comprising: ten or more magnetic disks each of which is the magnetic disk according to claim 7; and a magnetic head. ### Claim 16 (depends on 8) A hard disk drive apparatus comprising: ten or more magnetic disks each of which is the magnetic disk according to claim 8; and a magnetic head. ### Claim 17 (depends on 9) A hard disk drive apparatus comprising: ten or more magnetic disks each of which is the magnetic disk according to claim 9; and a magnetic head. ### Claim 18 (depends on 10) A hard disk drive apparatus comprising: ten or more magnetic disks each of which is the magnetic disk according to claim 10; and a magnetic head. ### Claim 19 (depends on 11) A hard disk drive apparatus comprising: ten or more magnetic disks each of which is the magnetic disk according to claim 11; and a magnetic head. ### Claim 20 (depends on 12) A hard disk drive apparatus comprising: ten or more magnetic disks each of which is the magnetic disk according to claim 12; and a magnetic head.