GLASS-CERAMIC SUBSTRATE FOR AN INFORMATION STORAGE MEDIUM

• US 20020031670A1
• Filed: 03/02/1999
• Published: 03/14/2002
• Est. Priority Date: 03/23/1998
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Ohara
• Original Assignee: Kabushiki Kaisha Ohara
• Inventors: GOTO, NAOYUKI, KAWASHIMA, YASUYUKI, ISHIOKA, JUNKO
• Granted Patent: US 6,383,645 B1
• Time in Patent Office: Days
• US Class Current: 428/426
• 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

There is provided a glass-ceramic substrate for an information storage medium usable in an information storage device of the ramp loading system. The glass-ceramic substrate has Young'"'"'s modulus (GPa)/specific gravity of 37 or over and includes 0 to less than 10 weight percent (expressed on oxide basis) of Al₂O₃. The glass-ceramic substrate has, as its predominant crystal phases, lithium disilicate (Li₂O.2SiO₂) and α-quartz (α-SiO₂), has a coefficient of thermal expansion within a range from 65×10⁻⁷/° C. to 130×10⁻⁷/° C. wtihin a temperature range from −50° C. to +70° C. and has a surface roughness (Ra) (arithmetic mean roughness) of 9 Å or below.

Claims

1. A glass-ceramic substrate for an information storage medium having Young'"'"'s modulus (GPa)/specific gravity of 37 or over and comprising 0 to less than 10 weight percent (expressed on oxide basis) of A₂O₃.

2. A glass-ceramic substrate as defined in claim 1 wherein the Young'"'"'s modulus is within a range from 95 GPa to 120 GPa and the specific gravity is within a range 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<sup>−

7</sup>/°

C. to 130×

10<sup>−

7</sup>/°

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 (arithmetic mean roughness) after polishing is 9 Å

or below.

5. A glass-ceramic substrate as defined in claim 1 wherein predominant crystal phases are lithium disilicate (Li₂O.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 an average diameter of crystal grains of crystal phases is 0.30 μ

m or below.

9. A glass-ceramic substrate as defined in claim 1 comprising 0.3 weight percent or over (expressed on the basis of composition of the oxide) of MgO.

10. A glass-ceramic substrate as defined in claim 1 having a composition which consists in weight percent expressed on the basis of composition of oxides of:

13. An information storage medium provided by forming a magnetic film and, if necessary, other layers including an undercoat layer, a protective layer and a lubricating layer, on a glass-ceramic substrate as defined in claim 1.

11. A glass-ceramic substrate for an information storage medium having, as its predominant crystal phases, lithium disilicate (Li₂O.2SiO₂) and α

-quartz (α

-SiO₂) which have fine globular crystal grains and having a surface roughness Ra (arithmetic mean roughness) after polishing of 9 Å

or below.

12. A method for manufacturing a glass-ceramic substrate for an information storage medium which comprises steps of:

melting a base glass having a composition which consists in weight percent expressed on the basis of composition of oxides of;

SiO₂71-81%Li₂O8-11%K₂O0-3%MgO0.3-2%ZnO0-1%P₂O₅1-3%ZrO₂0.5-5%TiO₂0-3%Al₂O₃4-8%Sb₂O₃0.1-0.50%SnO₂0-5%MoO₃0-3%NiO0-2%CoO0-3%Cr₂O₃0-3%

forming molten glass, annealing formed glass and then heat treating the formed glass for nucleation under nucleation temperature within a range from 550°

C. to 650°

C. for one to twelve hours and further heat treating the formed glass for crystallization under cyrstallization temperature within a range from 680°

C. to 800°

C. for one to twelve hours and polishing the glass-ceramic to a surface roughness (Ra) of 9 Å

or below.