Magnetic disk substrate

• US 5,874,376 A
• Filed: 08/18/1997
• Issued: 02/23/1999
• Est. Priority Date: 12/28/1995
• Status: Expired due to Fees

• Current Assignee: Yamamura Glass Company Limited
• Original Assignee: Yamamura Glass Company Limited
• Inventors: Ohara, Tohru, Kawai, Hideki, Taguchi, Tomoyuki, Kuriyama, Ikuo, Wakabayashi, Hajimu
• Primary Examiner(s): GROUP, KARL E
• Application Number:
  US08/912,478
• Time in Patent Office: 554 Days
• Field of Search: 428/694 ST, 428/694 SG, 501/63, 501/5, 501/7
• US Class Current: 501/63
• CPC Class Codes: C03C 10/0027 containing SiO2, Al2O3, Li2O as main constituents
• CPC Class Codes: C03C 21/002 to perform ion-exchange between alkali ions C03C21/005 takes precedence
• CPC Class Codes: C03C 3/097 containing phosphorus, niobium or tantalum
• CPC Class Codes: G11B 5/73921 Glass or ceramic substrates

Abstract

A glass composition for magnetic disk substrates comprising as oxides: from 66 to 80% by weight of SiO₂, from 5 to 15% by weight of Al₂ O₃, from 3 to 8.5% by weight of Li₂ O, from 0 to 3% by weight of Na₂ O, from 0 to 3% by weight of K₂ O, from 0.5 to 8% by weight of TiO₂, from 3.5 to 8% by weight of ZrO₂, from 0.5 to 3% by weight of P₂ O₅, from 0 to 2% by weight of Sb₂ O₃, and from 0 to 2% by weight of As₂ O₃, and having a theoretical optical basicity of 0.548 or less; a magnetic disk substrate which is prepared by forming and polishing the above glass composition, followed by chemically strengthening the polished substrate by ion exchange or by forming, heat treating, and polishing the above composition and contains Li₂ O.2SiO₂ and/or spodumene as the main crystalline phase. The glass composition for magnetic disk substrates can easily be formed, can easily be polished after crystallization of the glass by heat treatment or chemically strengthened by ion exchange of the glass after forming and polishing, and is used for preparing magnetic disk substrates which has excellent chemical durability, mechanical strength, heat resistance, surface flatness, and surface smoothness, and shows little degradation of magnetic film characteristics by alkali migration.

Claims

1. A magnetic disk substrate prepared by forming and polishing a glass composition for magnetic disk substrates comprising, expressed in terms of weight percent on the oxide basis:

from 66 to 80% SiO₂,

from 5 to 15% Al₂ O₃,

from 3 to 8.5% Li₂ O,

from 0 to 3% Na₂ O,

from 0 to 3% K₂ O,

from 0.5 to 8% TiO₂,

from 3.5 to 8% ZrO₂,

from 0.5 to 3% P₂ O₅,

from 0 to 2% Sb₂ O₃, and

from 0 to 2% As₂ O₃,

wherein the total of the contents of Li₂ O, Na₂ O and K₂ O is from 3 to 10%, and having a theoretical optical basicity of 0.548 or less, and strengthening the formed and polished glass composition by ion exchange of alkali metal ions in the surface layer of the glass composition for alkali metal ions having larger ionic radii at a temperature of from 350°

to 550°

C.

2. A magnetic disk substrate according to claim 1, comprising, expressed in terms of weight percent on the oxide basis:

from 66 to 75% SiO₂,

from 5.5 to 10% Al₂ O₃,

from 4 to 8.5% Li₂ O,

from 0 to 2% Na₂ O,

from 0 to 2% K₂ O,

from 2 to 6% TiO₂,

from 3.8 to 6.5% ZrO₂,

from 1 to 2.5% P₂ O₅,

from 0 to 2% Sb₂ O₃, and

from 0 to 2% As₂ O₃,

wherein the total of the contents of Li₂ O, Na₂ O and K₂ O is from 4 to 9%, and having a theoretical optical basicity of 0.548 or less.

3. A magnetic disk substrate according to claim 1, comprising, expressed in terms of weight percent on the oxide basis:

from 66 to 75% SiO₂,

from 5.5 to 7.5% Al₂ O₃,

from 5 to 8.5% Li₂ O,

from 0 to 2% Na₂ O,

from 0 to 2% K₂ O,

from 2 to 4% TiO₂,

from 4.1 to 6% ZrO₂,

from 1 to 2.5% P₂ O₅,

from 0 to 1% Sb₂ O₃, and

from 0 to 1% As₂ O₃,

wherein the total of the contents of Li₂ O, Na₂ O and K₂ O is from 5 to 9%, and having a theoretical optical basicity of 0.548 or less.

10. A magnetic disk substrate according to claim 1, wherein decrease in weight is 6×

10^-7 g/cm² ·

h or less in a water elution test of a glass in accordance with the grain test for chemical durability.

11. A magnetic disk substrate according to claim 2, wherein decrease in weight is 6×

10^-7 g/cm² ·

h or less in a water elution test of a glass in accordance with the grain test for chemical durability.

12. A magnetic disk substrate according to claim 3, wherein decrease in weight is 6×

10^-7 g/cm² ·

h or less in a water elution test of a glass in accordance with the grain test for chemical durability.

4. A magnetic disk substrate which is prepared by forming, heating treating, and polishing a glass composition for magnetic disk substrates comprising, expressed in terms of weight percent on the oxide basis:

from 66 to 80% SiO₂,

from 5 to 15% Al₂ O₃,

from 3 to 8.5% Li₂ O,

from 0 to 3% Na₂ O,

from 0 to 3% K₂ O,

from 0.5 to 8% TiO₂,

from 3.5 to 8% ZrO₂,

from 0.5 to 3% P₂ O₅,

from 0 to 2% Sb₂ O₃, and

from 0 to 2% As₂ O₃,

wherein the total of the contents of Li₂ O, Na₂ O and K₂ O is from 3 to 10%, and having a theoretical optical basicity of 0.548 or less, and has a main crystalline phase comprising at least one kind selected from the group consisting of Li₂ O.2SiO₂ and spodumene.

5. A magnetic disk substrate as claimed in claim 4, comprising, expressed in terms of weight percent on the oxide basis:

from 66 to 75% SiO₂,

from 5.5 to 10% Al₂ O₃,

from 4 to 8.5% Li₂ O,

from 0 to 2% Na₂ O,

from 0 to 2% K₂ O,

from 2 to 6% TiO₂,

from 3.8 to 6.5% ZrO₂,

from 1 to 2.5% P₂ O₅,

from 0 to 2% Sb₂ O₃, and

from 0 to 2% As₂ O₃,

wherein the total of the contents of Li₂ O, Na₂ O and K₂ O is from 4 to 9%, and having a theoretical optical basicity of 0.548 or less.

6. A magnetic disk substrate as claimed in claim 4, comprising, expressed in terms of weight percent on the oxide basis:

from 66 to 75% SiO₂,

from 5.5 to 7.5% Al₂ O₃,

from 5 to 8.5% Li₂ O,

from 0 to 2% Na₂ O,

from 0 to 2% K₂ O,

from 2 to 4% TiO₂,

from 4.1 to 6% ZrO₂,

from 1 to 2.5% P₂ O₅,

from 0 to 1% Sb₂ O₃, and

from 0 to 1% As₂ O₃,

wherein the total of the contents of Li₂ O, Na₂ O and K₂ O is from 5 to 9%, and having a theoretical optical basicity of 0.548 or less.

7. A magnetic disk substrate according to claim 4, wherein the total degree of crystallization is 20% by volume or more.

8. A magnetic disk substrate according to claim 5, wherein the total degree of crystallization is 20% by volume or more.

9. A magnetic disk substrate according to claim 6, wherein the total degree of crystallization is 20% by volume or more.

13. A magnetic disk substrate according to claim 4, wherein decrease in weight is 6×

10^-7 g/cm² ·

h or less in a water elution test of a glass-ceramic in accordance with the grain test for chemical durability.

14. A magnetic disk substrate according to claim 5, wherein decrease in weight is 6×

10^-7 g/cm² ·

h or less in a water elution test of a glass-ceramic in accordance with the grain test for chemical durability.

15. A magnetic disk substrate according to claim 6, wherein decrease in weight is 6×

10^-7 g/cm² ·

h or less in a water elution test of a glass-ceramic in accordance with the grain test for chemical durability.

16. A magnetic disk substrate according to claim 7, wherein decrease in weight is 6×

10^-7 g/cm² ·

h or less in a water elution test of a glass-ceramic in accordance with the grain test for chemical durability.

17. A magnetic disk substrate according to claim 8, wherein decrease in weight is 6×

10^-7 g/cm² ·

h or less in a water elution test of a glass-ceramic in accordance with the grain test for chemical durability.

18. A magnetic disk substrate according to claim 9, wherein decrease in weight is 6×

10^-7 g/cm² ·

h or less in a water elution test of a glass-ceramic in accordance with the grain test for chemical durability.