Claims
- 1. A glass-ceramic substrate for an information storage medium having a Young's modulus of GPa/specific gravity of 37 or over and comprising 5.3 to 8 weight percent, expressed on the basis of the oxide, of Al2O3.
- 2. A glass-ceramic substrate as defined in claim 1 wherein the Young's modulus is within a range of from 95 GPa to 120 GPa and the specific gravity is within a range of from 2.4 to 2.6.
- 3. A glass-ceramic substrate as defined in claim 1 wherein a coefficient of thermal expansion is within a range from 65×10−7/° C. to 130×10−7/° C. within a temperature range from −50° C. to +70° C.
- 4. A glass-ceramic substrate as defined in claim 1 wherein a surface roughness Ra, expressed as the arithmetic mean roughness, after polishing is 9 Å or below.
- 5. A glass-ceramic as defined in claim 1 which has crystal phases wherein the predominant crystal phases are lithium disilicate (LiO.2SiO2) and α-quartz (α-SiO2).
- 6. A glass-ceramic substrate as defined in claim 1 which is substantially free of Na2O and PbO.
- 7. A glass-ceramic substrate as defined in claim 1 wherein crystal grains of the crystal phases are fine globular grains.
- 8. A glass-ceramic substrate as defined in claim 1 wherein a average diameter of crystal grains of crystal phases is 0.30 μm or below.
- 9. A glass-ceramic substrate as defined in claim 1 comprising 0.3 weight percent or over, expressed on the basis of the oxide, of MgO.
- 10. A glass-ceramic substrate as defined in claim 1 having a composition which consist in weight percent expressed on the basis of the weight of the oxides of:SiO271-81%LiO2 8-11%K2O0-3%MgO0.3-2% ZnO0-1%P2O51-3%ZrO20.5-5% TiO20-3%Al2O35.3-8% Sb2O30.1-0.5%SnO20-5%MnO30-3%NiO0-2%CoO0-3%Cr2O30-3%which has crystal phases and having, as predominant crystal phases, lithium disilicate (Li2O.2SiO2) and α-quartz (α-SiO2).
- 11. An information storage medium provided by forming a magnetic film and other layers including an undercoat layer, a protective layer and a lubricating layer, on a glass-ceramic substrate as defined in claim 1.
Priority Claims (3)
Number |
Date |
Country |
Kind |
10-094020 |
Mar 1998 |
JP |
|
10-125316 |
Apr 1998 |
JP |
|
10-351682 |
Dec 1998 |
JP |
|
Parent Case Info
The present application is a continuation of 09/260,768 filed Mar. 2, 1999 and claims priority to Japanese Application Nos. 94020/1998 filed Mar. 23, 1998, 125316/1998, filed Apr. 20, 1998, and 351682, filed Dec. 10, 1998.
US Referenced Citations (7)
Foreign Referenced Citations (6)
Number |
Date |
Country |
0781 731 |
Feb 1997 |
EP |
0779612 |
Jun 1997 |
EP |
0788093 |
Aug 1997 |
EP |
0810586 |
Dec 1997 |
EP |
0875886 |
Nov 1998 |
EP |
0917135 |
May 1999 |
EP |
Non-Patent Literature Citations (3)
Entry |
Patents Abstracts of Japan, vol. 097, No. 006, #09035234 Feb. 7, 1997. |
Patents Abstracts of Japan, vol. 011, No. 268, #62072547 Apr. 3, 1987. |
European Search Report, The Hague, Aug. 17, 1999, Examiner Heywood, C. |
Continuations (1)
|
Number |
Date |
Country |
Parent |
09/260468 |
Mar 1999 |
US |
Child |
09/260768 |
|
US |