# US 6,718,799 B2 · Die and glass material for forming glass substrate, method for manufacturing glass substrate, and magnetic disk glass substrate

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- Number: US 6,718,799 B2
- Document ID: US6718799B2
- Status: Granted
- Kind: B2
- Application number: 10/358,468
- Filed: 2003-02-04
- Published: 2003-07-03
- Granted: 2004-04-13
- Earliest claimed: 1999-04-30
- Assignees: Matsushita Electric Industrial Co., Ltd.
- Inventors: Kazuaki Takagi; Kunio Hibino; Tomokazu Tokunaga; Fujio Okuyama; Minoru Onoda
- Web page: https://patentgrep.com/patent/US6718799B2

## CPC

- C03B 11/12: Cooling, heating, or insulating the plunger, the mould, or the glass-pressing machine; {cooling or heating of the glass in the mould}(C03B9/38 takes precedence)
- C03B 11/082: {having profiled, patterned or microstructured surfaces}
- C03B 11/088: {Flat discs}
- C03B 2215/41: Profiled surfaces
- C03B 2215/44: Flat, parallel-faced disc or plate products
- C03B 2215/46: Lenses, e.g. bi-convex
- C03B 2215/65: Means for releasing gas trapped between glass and press die
- C03B: MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES

## Abstract

A glass material (4) is placed in a forming die including a pair of upper and lower dies (1, 2) and a control member (3) for controlling the space between the upper and the lower die, and then heated, softened, and molded by pressure into a glass substrate in the shape of a parallel plate. The amount of thermal contraction of the control member is smaller than that of the glass material. Therefore, the glass substrate is released from the die when cooled after molding. The present invention can provide a glass substrate that is excellent in smoothness and form accuracy of the surface, and that is suitable for recording media such as magnetic disks that are inexpensive and suitable for mass production.

## Claims

### Claim 1

A glass forming die for molding a glass substrate into a shape of a parallel plate comprising:
a pair of upper and lower dies;
a glass material disposed between the upper and lower dies, the glass material having a shape that provides a point-contact with the upper and lower dies when placed therein, and as a contact portion between the glass material and the upper and lower dies is increased by pressure molding, the glass material is transformed continuously so as to prevent air from entering the contact portion; and
a control member for controlling a space between the upper and the lower dies;
wherein the glass material has a coefficient of thermal expansion larger than that of the control member.

### Claim 2 (depends on 1)

The glass forming die according to claim 1, wherein a relationship between an outer diameter X and a thickness Y of the glass material satisfies X>40 Y.

### Claim 3 (depends on 1)

The glass forming die according to claim 1, wherein a vertical cross section of the glass material is circular or elliptical.