# US 9,038,417 B2 · Method for producing glass substrate for magnetic disk and method for manufacturing magnetic disk

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- Number: US 9,038,417 B2
- Document ID: US9038417B2
- Status: Granted
- Kind: B2
- Application number: 14/275,630
- Filed: 2014-05-12
- Published: 2014-09-04
- Granted: 2015-05-26
- Earliest claimed: 2006-03-24
- Assignees: Hoya Corporation
- Applicants: Hoya Corporation
- Inventors: Toshio Takizawa; Takumi Koshimizu; Yoshinori Marumo; Masahiro Katagiri
- Web page: https://patentgrep.com/patent/US9038417B2

## CPC

- B24B 7/241: {Methods}
- C03C 19/00: Surface treatment of glass, not in the form of fibres or filaments, by mechanical means (sand-blasting, grinding, or polishing glass B24)
- C03C 23/0075: {Cleaning of glass (specially adapted to plate glass B08B11/00)}
- G11B 5/8404: {manufacturing base layers}
- B24B: MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING (grinding of gear teeth B23F, of screw-threads B23G1/36; by electro-erosion B23H; abrasive or related blasting B24C; tools for grinding, buffing or sharpening B24D; polishing compositions C09G1/00; abrasives C09K3/14; electrolytic etching or polishing C25F3/00; grinding arrangements for use on assembled railway tracks E01B31/17); DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- C03C: CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- 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

When mirror polishing is performed on a glass substrate by bringing a polishing pad into contact with the surface of the glass substrate while supplying a polishing liquid containing polishing grains to the substrate surface, the pH of the polishing liquid is maintained within a certain range or the agglomeration degree or dispersion degree of the polishing liquid is controlled. Consequently, an adequate mirror polishing rate can be maintained and there can be obtained a glass substrate having a good end shape.

## Claims

### Claim 1

A method of making a glass substrate for a magnetic disk, comprising a mirror polishing step which includes contacting a polishing pad with a surface of a multi-component glass substrate, supplying a polishing liquid containing polishing grains to the surface of said glass substrate, and relatively moving said glass substrate and said polishing pad to polish the surface of said glass substrate, said magnetic disk allowing a magnetic head to fly at a floating height of 8 nm or less, wherein:
colloidal silica grains having a grain size of not larger than 80 nm are used as the polishing grains;
said polishing step being carried out under the conditions that the polishing liquid contains an inorganic acid and a buffer agent for preventing change in pH of the polishing liquid, that the pH value of the polishing liquid is kept at 3.0 or less, and that a zeta potential of said polishing grains contained in the polishing liquid is not higher than −24.7 mV, in order to control a degree of coagulation or dispersion in said polishing liquid so that a Duboff value which shapes an end contour of the resulting glass substrate obtained by the mirror polishing step falls within ±10 nm.

### Claim 2 (depends on 1)

The method of making a glass substrate for a magnetic disk as defined in claim 1, wherein the multi-component glass is an aluminosilicate glass.

### Claim 3 (depends on 1)

The method of making a glass substrate for a magnetic disk as defined in claim 1, wherein said buffer agent is composed of an organic acid.

### Claim 4 (depends on 1)

The method of making a glass substrate for a magnetic disk as claimed in claim 1, wherein the mirror polishing step includes polishing the glass substrate so that the surface roughness of the glass substrate is 0.3 nm or less in arithmetic mean roughness (Ra) and is 2 nm or less in maximum peak (Rp).

### Claim 5 (depends on 1)

The method of making a glass substrate for a magnetic disk as claimed in claim 1, further comprising a step of pre-polishing the glass substrate using cerium oxide grains having a grain size of less than 4 μm.

### Claim 6 (depends on 1)

The method of making a glass substrate for a magnetic disk as claimed in claim 1, wherein the mirror polishing step is carried out while the zeta potential is kept at −30 mV or less.

### Claim 7 (depends on 1)

A method of manufacturing a magnetic disk, wherein a magnetic layer is formed on the glass substrate manufactured by the use of a method of making a glass substrate for a magnetic disk as defined in claim 1.