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CN-120530456-B - Magnetic disk substrate

CN120530456BCN 120530456 BCN120530456 BCN 120530456BCN-120530456-B

Abstract

The present invention aims to provide a substrate for a magnetic disk, which is particularly thin, but effectively suppresses occurrence of head crashes by effectively suppressing undulation existing in an outer peripheral side region of a surface of the disk. The present invention provides a magnetic disk substrate, wherein the maximum value of an arithmetic average height Sa defined in ISO25178 is below 0.50 nm in a middle wavelength side region by using a scanning type optical interferometry through a Gaussian filter with a cut-off wavelength of 1.0 mm in a plurality of view field regions located in an outer peripheral side region of at least one surface, and the standard deviation of the arithmetic average height Sa is below 0.10 nm.

Inventors

  • HIDEYUKI HATAKEYAMA
  • Ichiro Haokou

Assignees

  • 古河电气工业株式会社
  • 株式会社UACJ

Dates

Publication Date
20260505
Application Date
20240126
Priority Date
20230201

Claims (5)

  1. 1. A substrate for a magnetic disk, wherein the maximum value of the arithmetic mean height Sa defined in ISO25178 is 0.50 nm or less in each of the intermediate wavelength side regions measured by a Gaussian filter having a cut-off wavelength of 1.0 mm by using a scanning optical interferometry in 8 view field regions located in the outer peripheral side region of at least one surface, The standard deviation of the arithmetic mean height Sa is 0.10 nm or less, The eight field areas are arranged at equal intervals of 45 DEG so as to contact the inner side of a concentric circle of 0.1 to 1mm on the center side with respect to the outer peripheral edge of the substrate.
  2. 2. The magnetic disk substrate according to claim 1, wherein the arithmetic average height Sa has an average value of 0.40 nm or less.
  3. 3. The substrate for a magnetic disk according to claim 1 or 2, wherein the thickness dimension is less than 0.50 mm.
  4. 4. The substrate for a magnetic disk according to claim 1 or 2, wherein an outer diameter is 95 mm or more.
  5. 5. A magnetic disk having a maximum value of 0.50 nm or less when an arithmetic average height Sa specified in ISO25178 is measured in a medium wavelength side region via a Gaussian filter having a cut-off wavelength of 1.0 mm by using a scanning optical interferometry in 8 view field regions located in an outer peripheral side region of at least one surface, The standard deviation of the arithmetic mean height Sa is 0.10 nm or less, The eight field areas are arranged at equal intervals of 45 DEG so as to contact the inner side of a concentric circle of 0.1 to 1mm on the center side with respect to the outer peripheral edge of the substrate.

Description

Magnetic disk substrate Technical Field The present invention relates to a magnetic disk substrate. More specifically, the present invention relates to a magnetic disk substrate which is thin but effectively suppresses occurrence of head crashes by effectively suppressing undulation existing in an outer peripheral region of a surface of a disk. Background In recent years, due to rapid spread of cloud computing, a high capacity is demanded for a hard disk used in a data center. Accordingly, countermeasures such as increasing the number of substrates to be arranged by increasing the diameter and thinning of the disk substrate have been taken, but the size of the hard disk case has been standardized, and thus it has been difficult to achieve a further increased diameter. Therefore, further thinning of the magnetic disk substrate is strongly desired. However, it is known that the thinned substrate tends to be deformed due to insufficient rigidity, and hence the disk tends to undulate during high-speed rotation. The undulation is a main cause of collision of the magnetic disk with the magnetic head, and therefore, is preferably suppressed. Hitherto, some studies have been made for reducing physical errors such as head crashes in hard disks. For example, patent document 1 discloses a glass substrate which is easily obtained with high cleanliness and high smoothness of a surface (specifically, an average surface roughness (Ra) of the surface is smoothed to less than 0.3 nm) by acid treatment. [ Prior Art literature ] (Patent literature) Patent document 1 Japanese patent No. 3959588 Disclosure of Invention [ Problem to be solved by the invention ] The glass substrate described in patent document 1 is a glass substrate whose surface is smoothed by adjusting the surface so as to reduce the average surface roughness (Ra) which is a two-dimensional surface property state measured based on a line. In the case of the thinned substrate, deformation is likely to occur due to insufficient rigidity, and therefore, the head crash may not be suppressed merely by adjusting the two-dimensional surface property state. The present invention aims to provide a substrate for a magnetic disk, which is thin, but can effectively inhibit the occurrence of head collision by effectively inhibiting the fluctuation existing in the peripheral side area of the surface of the disk. [ Means of solving the problems ] As a result of intensive studies, the present inventors have found that if a disk substrate having a smaller arithmetic average height Sa on at least one outer peripheral side region is used, the fluctuation of the outer peripheral side region is suppressed, and as a result, head crashes are less likely to occur, leading to completion of the present invention. In order to achieve the above object, the gist of the present invention is as follows. (1) A substrate for a magnetic disk, wherein a maximum value of an arithmetic mean height Sa defined in ISO25178 is 0.50 nm or less in a middle wavelength side region, and a standard deviation of the arithmetic mean height Sa is 0.10 nm or less, respectively, using a scanning optical interferometry, through a Gaussian (Gaussian) filter having a cutoff wavelength of 1.0 mm in a plurality of view field regions located in an outer peripheral side region of at least one surface. (2) The magnetic disk substrate according to (1), wherein the arithmetic average height Sa has an average value of 0.40 nm or less. (3) The substrate for a magnetic disk according to the above (1) or (2), wherein the thickness dimension is less than 0.50 mm. (4) The magnetic disk substrate according to any one of the above (1) to (3), wherein the outer diameter is 95 mm or more. (5) A magnetic disk having a maximum value of 0.50 nm or less in a plurality of view field regions located in an outer peripheral side region of at least one surface, the maximum value being measured in a middle wavelength side region by using a scanning optical interferometry through a gaussian filter having a cut-off wavelength of 1.0 mm, and the standard deviation of the arithmetic average height Sa being 0.10 nm or less. (Effects of the invention) According to the present invention, there is provided a substrate for a magnetic disk, which is particularly thin, but which effectively suppresses occurrence of head crashes by effectively suppressing undulation existing in an outer peripheral side region of a surface of the disk. Drawings Fig. 1 is a plan view of a magnetic disk substrate according to the present invention, showing an example of an outer peripheral region of an upper surface and a plurality of field regions for measuring an arithmetic mean height Sa. Fig. 2 is a flowchart showing an example of a process for manufacturing an aluminum alloy substrate for magnetic disk according to the present invention. FIG. 3 is a flowchart showing an example of a process for producing a glass substrate for magnetic disk according to the present inv