Medium substrate, production method thereof and magnetic disk device

• US 6,673,474 B2
• Filed: 03/27/2001
• Issued: 01/06/2004
• Est. Priority Date: 08/09/2000
• Status: Expired due to Fees

• Current Assignee: Showa Denko KK (Resonac Holdings Corp.)
• Original Assignee: Fujitsu Limited
• Inventors: Yamamoto, Kenrou
• Primary Examiner(s): KILIMAN, LESZEK B
• Application Number:
  US09/818,764
• Publication Number:
  US 20020037437A1
• Time in Patent Office: 1,015 Days
• Field of Search: 428/694.ST, 428/694.SG, 428/900, 427/128-130, 427/131, 65/301, 65/301.4, 65/31, 65/601, 65/605
• US Class Current: 428/846.9
• CPC Class Codes: C03C 3/089 containing boron
• CPC Class Codes: G11B 5/73921 Glass or ceramic substrates
• CPC Class Codes: G11B 5/8404 manufacturing base layers
• CPC Class Codes: Y10S 428/90 Magnetic feature

Abstract

A medium substrate comprising a borosilicate glass containing silica as a main component and having on the surface thereof a continuous texture derived from the porous structure, the medium substrate being used as a substrate in the production of a magnetic recording medium and other. The method for the production of the textured medium substrate is also disclosed, along with a magnetic recording medium using the medium substrate and a magnetic disk device.

Claims

1. A medium substrate for use as a substrate in magnetic recording mediums and the like, said medium substrate comprising silica (SiO₂) glass having a purity of 99% or more as a main component, the silica glass being a sea component of phase-separated borosilicate glass having an islands-in-sea structure, and having on the surface thereof a continuous texture derived from the porous structure of the silica glass, the texture having a surface roughness Ra of 1 to 10 nm and a pore size of 5 to 250 nm.

2. The medium substrate as recited in claim 1, wherein the borosilicate glass is sodium borosilicate glass formed starting from Na₂O, B₂O₃ and SiO₂.

3. The medium substrate as recited in claim 2, wherein the sodium borosilicate glass has the following composition:

Na₂O 10 to 30% by weight,

B₂O₃ 10 to 30% by weight, and

SiO₂ 50 to 80% by weight.

4. The medium substrate as recited in claim 3, wherein the sodium borosilicate glass comprises 10% by weight of Na₂O, 30% by weight of B₂O₃ and 60% by weight of SiO₂.

5. The medium substrate as recited in claim 1, wherein the borosilicate glass is lithium borosilicate glass formed starting from Li₂O, B₂O₃ and SiO₂.

6. The medium substrate as recited in claim 5, wherein the lithium borosilicate glass has the following composition:

Li₂O 5 to 30% by weight,

B₂O₃ 10 to 30% by weight, and

SiO₂ 50 to 80% by weight.

7. The medium substrate as recited in claim 6, wherein the lithium borosilicate glass comprises 5% by weight of Li₂O, 30% by weight of B₂O₃ and 65% by weight of SiO₂.

8. The medium substrate as recited in claim 1, wherein the porous structure of the borosilicate glass is formed by way of phase separation during a heat treatment of the glass and elution of components during an acid treatment subsequent to the phase separation.

9. The medium substrate as recited in claim 1, wherein the continuous texture is selectively formed on the surface of the substrate.

10. A method for producing a medium substrate for use as a substrate in magnetic recording mediums and the like, said medium substrate comprising silica (SiO₂) glass having a purity of 99% or more as a main component, the silica glass being a sea component of phase-separated borosilicate glass having an islands-in-sea structure, and having on the surface thereof a continuous texture derived from the porous structure of the silica glass, the texture having a surface roughness Ra of 1 to 10 nm and a pore size of 5 to 250 nm,

the method comprising the steps of:

heat-treating a disk of borosilicate glass at a temperature of 500 to 750°

C. to cause phase separation, thereby forming the phase-separated borosilicate glass; and

treating the phase-separated borosilicate glass with an acid selected from the group consisting of nitric acid, sulfuric acid, hydrochloric acid and acetic acid to dissolve out an islands component from the phase-separated borosilicate glass and thereby render the borosilicate glass porous.

11. A method for producing a medium substrate as recited in claim 10, wherein the borosilicate glass is sodium borosilicate glass formed starting from Na₂O, B₂O₃ and SiO₂.

12. The method for producing a medium substrate as recited in claim 11, wherein the sodium borosilicate glass has the following composition:

Na₂O 10 to 30% by weight,

B₂O₃ 10 to 30% by weight, and

SiO₂ 50 to 80% by weight.

13. A method for producing a medium substrate as recited in claim 12, wherein the sodium borosilicate glass comprises 10% by weight of Na₂O, 30% by weight of B₂O₃ and 60% by weight of SiO₂.

14. The method for producing a medium substrate as recited in claim 10, wherein the borosilicate glass is lithium borosilicate glass formed starting from Li₂O, B₂O₃ and SiO₂.

15. The method for producing a medium substrate as recited in claim 14, wherein the lithium borosilicate glass has the following composition:

Li₂O 5 to 30% by weight,

B₂O₃ 10 to 30% by weight, and

SiO₂ 50 to 80% by weight.

16. The method for producing a medium substrate as recited in claim 15, wherein the lithium borosilicate glass comprises 5% by weight of Li₂O, 30% by weight of B₂O₃ and 65% by weight of SiO₂.

17. The method for producing a medium substrate as recited in claim 10, wherein the borosilicate glass is heat-treated at a temperature of 600 to 700°

C. for 5 to 24 hours to control the pore size of the porous structure to the range from 5 to 250 nm.

18. The method for producing a medium substrate as recited in claim 10, wherein after the borosilicate is heat-treated to cause phase separation, the acid treatment is performed while allowing a masking element to be present in the region exclusive of the landing zone of a magnetic head to selectively render the landing zone porous.

19. A magnetic recording medium comprising a substrate having applied thereon at least a magnetic recording layer, said substrate comprising silica (SiO₂) glass having a purity of 99% or more as a main component, the silica glass being a sea component of phase-separated borosilicate glass having an islands-in-sea structure, and having on the surface thereof a continuous texture derived from the porous structure of the silica glass, the texture having a surface roughness Ra of 1 to 10 nm and a pore size of 5 to 250 nm.

20. The magnetic recording medium as recited in claim 19, wherein the borosilicate glass comprises sodium borosilicate glass formed starting from Na₂O, B₂O₃ and SiC₂ or lithium borosilicate glass formed starting from Li₂O, B₂O₃ and SiO₂.

21. A method for producing a magnetic recording medium comprising a substrate having applied thereon at least a magnetic recording layer, in which said substrate comprises silica (SiO₂) glass having a purity of 99% or more as a main component, the silica glass being a sea component of phase-separated borosilicate glass having an islands-in-sea structure, and having on the surface thereof a continuous texture derived from the porous structure of the silica glass, the texture having a surface roughness Ra of 1 to 10 nm and a pore size of 5 to 250 nm,

the method comprising the steps of:

heat treating a disk of borosilicate glass at a temperature of 500 to 750°

C. to cause phase separation, thereby forming the phase-separated borosilicate glass; and

treating the phase separated borosilicate glass with an acid selected from the group consisting of nitric acid, sulfuric acid, hydrochloric acid and acetic acid to dissolve out an islands component from the phase-separated borosilicate glass, thereby producing said substrate.

22. A magnetic disk device comprising a recording head part for recording information in a magnetic recording medium and a reproducing head part for reproducing the information, wherein the magnetic recording medium is a magnetic recording medium comprising a nonmagnetic substrate having provided thereon a magnetic recording layer and the substrate comprises silica (SiO₂) glass having a purity of 99% or more as a main component, the silica glass being a sea component of phase-separated borosilicate glass having an islands-in-sea structure, and having on the surface thereof a continuous texture derived from the porous structure of the silica glass, the texture having a surface roughness Ra of 1 to 10 nm and a pore size of 5 to 250 nm.

23. The magnetic disk device as recited in claim 22, wherein the borosilicate glass is sodium borosilicate glass or lithium borosilicate glass.