Glass-ceramic substrate for an information storage medium

• US 6,174,827 B1
• Filed: 03/15/1999
• Issued: 01/16/2001
• Est. Priority Date: 03/23/1998
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Ohara
• Original Assignee: Kabushiki Kaisha Ohara
• Inventors: Ishioka, Junko, Goto, Naoyuki, Kawashima, Yasuyuki
• Primary Examiner(s): Group, Karl
• Application Number:
  US09/267,743
• Time in Patent Office: 673 Days
• Field of Search: 501/4, 501/5, 65/338, 65/61, 428/694.ST, 428/694.SG
• US Class Current: 501/4
• CPC Class Codes: C03C 10/0027 containing SiO2, Al2O3, Li2O as main constituents
• CPC Class Codes: C12N 2510/00 Genetically modified cells
• CPC Class Codes: C12N 2517/04 Cells produced using nuclear transfer
• CPC Class Codes: G11B 5/73921 Glass or ceramic substrates
• CPC Class Codes: Y10S 428/90 Magnetic feature

Abstract

A glass-ceramic substrate for an information storage medium includes, as a predominant crystal phase, lithium disilicate (Li₂O·2SiO₂) or a combination of lithium disilicate and at least one crystal phase selected from the group consisting of α-quartz (α-SiO₂), α-quartz solid solution (α-SiO₂ solid solution), α-cristobalite (α-SiO₂) and α-cristobalite solid solution (α-SiO₂ solid solution). This substrate has Young'"'"'s modulus (GPa)/specific gravity of 37 or over, surface roughness Ra (arithmetic mean roughness) of 5.0 Å or below, a coefficient of thermal expansion within a temperature range from −50° C. to +70° C. which ranges from +65×10⁻⁷/° C. to +130×10⁻⁷/° C. and bending strength of 400 MPa or over.

Claims

1. A glass-ceramic substrate for an information storage medium comprising, as a predominant crystal phase, lithium disilicate (Li₂O·

2SiO₂) having a crystal grain diameter (average) of 0.05 μ

m or below.

2. A glass-ceramic substrate as defined in claim 1 wherein Young'"'"'s modulus (GPa)/specific gravity is 37 or over.

4. A glass-ceramic substrate as defined in claim 1 wherein the degree of crystallization of the lithium disilicate crystal phase is within a range of 3% to 20% crystallinity.

5. A glass-ceramic substrate as defined in claim 1 comprising further at least one crystal phase selected from the group consisting of α

-quartz (α

-SiO₂), α

-quartz solid solution (α

-SiO₂) solid solution), degree of crystallization of the α

-quartz (α

-SiO₂) and the α

-quartz solid solution (α

-SiO₂ solid solution) being within a range of from 5% to 25% crystallinity and a crystal grain diameter thereof (average) being 10 μ

m or below.

6. A glass-ceramic substrate as defined in claim 1 comprising further at least one crystal phase selected from the group consisting of α

-cristobalite (α

-SiO₂), α

-cristobalite solid solution (α

-SiO₂) solid solution), degree of crystallization of the α

-cristobalite (α

-SiO₂) and the α

-cristobalite solid solution (α

-SiO₂ solid solution) being within a range of from 2% to 10% crystallinity and a crystal grain diameter thereof (average) being 10 μ

m or below.

7. A glass-ceramic substrate as defined in claim 1 comprising, as predominant crystal phases, lithium disilicate (Li₂O·

2SiO₂) and at least one crystal phase selected from the group consisting of α

-quartz (α

-SiO₂), α

-quartz solid solution (α

-SiO₂ solid solution), α

-cristobalite (α

-SiO₂) and α

-cristobalite solid solution (α

-SiO₂ solid solution).

8. A glass-ceramic as defined in claim 1 wherein crystal grains of the lithium disilicate are fine and substantially of a globular shape.

9. A glass-ceramic substrate as defined in claim 1 which is substantially free of Na₂O and PbO.

10. A glass-ceramic substrate as defined in claim 1 which has a surface roughness Ra (arithmetic mean roughness) after polishing of 5.0 Å

or below.

11. A glass-ceramic substrate as defined in claim 1 which has a coefficient of thermal expansion within a range from +65×

1<sup>−

7</sup>/°

C. to +130×

10<sup>−

7</sup>/°

C in a temperature range from −

50°

C. to +70°

C.

12. A glass-ceramic substrate as defined in claim 1 which has bending strength of 400 MPa or over.

13. A glass-ceramic substrate as defined in claim 1 having a composition which consists in weight percent of:

14. A method for manufacturing a glass-ceramic substrate for an information storage medium as defined in claim 1 which comprises steps of heat treating a base glass for nucleation under a temperature within a range from 500°

C. to 600°

C. for one to seven hours and further heat treating the glass for crystallization under a temperature within a range from 700°

C. to 780°

C. for one to twelve hours and thereafter polishing the glass-ceramic to a surface roughness Ra (arithmetic mean roughness) of 5°

C. or below.

15. An information storage disk provided by forming a magnetic film and other layers including Ni—

P plating, an undercoat layer, a protective layer and a lubricating layer, on a glass-ceramic substrate as defined in claim 1.

3. A glass-ceramic substrate consisting of a crystal phase or phases and an amorphous phase and having a crystal grain diameter (average) of 0.05 μ

m or below and comprising SiO₂ in the amount of 70-77% and Li₂O in the amount of 8-12% wherein Young'"'"'s modulus (Gpa)/specific gravity is 37 or over.