Glass substrate for magnetic recording medium, magnetic recording medium, and method of manufacturing the same

• US 20020142191A1
• Filed: 02/14/2002
• Published: 10/03/2002
• Est. Priority Date: 08/19/1998
• Status: Active Grant

• Current Assignee: Hoya Corporation
• Original Assignee: Hoya Corporation
• Inventors: Sakai, Hiroyuki, Ono, Katsutoshi, Matsuda, Syoji
• Granted Patent: US 6,548,139 B2
• Time in Patent Office: Days
• US Class Current: 428/694R
• CPC Class Codes: B82Y 15/00 Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
• CPC Class Codes: C03C 15/00 Surface treatment of glass, not in the form of fibres or filaments, by etching etching or surface-brightening compositions, in general C09K13/00
• CPC Class Codes: C03C 15/02 for making a smooth surface
• CPC Class Codes: C03C 19/00 Surface treatment of glass, not in the form of fibres or filaments, by mechanical means sand-blasting, grinding, or polishing glass B24
• CPC Class Codes: C03C 2204/08 Glass having a rough surface
• CPC Class Codes: G11B 5/8404 manufacturing base layers
• CPC Class Codes: Y10T 428/24355 Continuous and nonuniform or irregular surface on layer or component [e.g., roofing, etc.]

Abstract

In a glass substrate for use in a magnetic recording medium, a surface roughness of at least a principal surface of the glass substrate is measured by the use of the interatomic force microscope (AFM), Ra falls within the range between 0.2 and 2.5 nm, Rmax falls within the range between 3 and 25 nm, and Rmax/Ra falls within the range between 3 and 35.

Claims

1. A glass substrate which is for use in a magnetic recording medium and which has surface roughness Ra and Rmax, where Ra is representative of a center-line mean roughness, Rmax is defined as a maximum height representative of a difference between a highest point and a lowest point wherein:

a surface roughness of at least a principal surface of the glass substrate is measured by the use of the interatomic force microscope (AFM),

Ra falls within the range between 0.2 and 2.6 nm,

Rmax falls within the range between 3 and 25 nm, and

Rmax/Ra falls within the range between 3 and 35.

2. A glass substrate as claimed in claim 1, wherein:

a surface parallel to a virtual principal surface is defined as a contour surface when it is assumed that the principal surface of said glass substrate is completely flattened,

when roughness formed on the principal surface are cut by the use of the contour surface, a percentage rate of a total area of the principal surface for sum of areas of the cut cross sectional surface is defined as a bearing ratio,

the contour surface having the bearing ratio of 50% is defined as a referential surface,

each distance from the referential surface to each contour surface having each bearing ratio is specified as a bearing height,

the bearing height of the contour surface having the bearing ratio of 2.5% is defined as B.H. (2.5) while the bearing height of the contour surface having the bearing ratio of 5.0% is defined as B.H. (5.0), and

B.H. (2.5)/Rmax falls within the range between 0.1 and 0.5 or B.H. (5.0)/Rmax falls within the range between 0.1 and 0.45.

3. A glass substrate as claimed in claim 1, wherein;

the surface roughness of at least the principal surface is measured by the use of the interatomic force microscope (AEM),

Rmax falls within the range between 5 and 25 nm, and

B.H. (2.5)/Rmax falls within the range between 0.1 and 0.5 or B.H. (5.0)/Rmax falls within the range between 0.1 and 0.45.

4. A glass substrate as claimed in any one of claims 1 through 3, wherein;

said glass substrate contains at least alkali metal oxide and alkali earth oxide, and

the content of the alkali earth oxide is not exceeding 3 mol %.

5. A glass substrate as claimed in any one of claims 1 through 4, wherein:

said glass substrate is used for a magnetic disk which has a glide height having 1.2 μ

inch or less.

6. A magnetic recording medium, wherein:

at least a magnetic layer is formed on the principal surface of the glass substrate claimed in any one of claims 1 through 5.

7. A method of manufacturing a glass substrate which is for use in a magnetic recording medium, comprising the steps of:

preparing a glass member in which Ra falls within the range between 0.1 and 1.0 nm when a surface roughness of a principal surface of said glass member is measured by the use of the interatomic force microscope (AFM), and

chemically processing the surface so that Ra falls within the range between 0.2 and 2.5 nm, Rmax falls within the range between 3 and 25 nm, and Rmax/Ra falls within the range between 3 and 35,

said glass member having surface roughness Ra and Rmax, where Ra is representative of a center-line mean roughness, Rmax is defined as a maximum height representative of a difference between a highest point and a lowest point,

9. A method as claimed in claim 7 or 8, further comprising the steps of:

polishing at least the principal surface by the use of abrasive materiel containing free abrasive grain having grain diameter between 0.3 and 3.0 μ

m before the chemical surface process or the surface process due to the hydrofluosilic acid.

10. A method as claimed in claim 9, wherein:

the chemical surface process or the surface process due to the hydrofluosilic acid processes the surface so that a portion having relatively high remaining distortion forms an island or peak in remaining stress distribution which is generated at a portion of abrasive trace due to the abrasive grain in the polishing step of the glass member.

11. A method as claimed in any one of claims 8 through 10, wherein:

the hydrofluosilic acid has concentration between 0.15 and 3.0 by weight %.

12. A method as claimed in any one of claims 7 through 9, wherein:

the glass constituting said glass member contains at least alkali metal oxide and alkali earth oxide, and

content of the alkali earth oxide is not exceeding 3 mol %.

13. A method as claimed in claim 12, wherein:

the glass constituting said glass member contains SiO₂ between 58 and 75 weight %. Al₂O₃ between 5 and 23 weight %, Li₂O between 3 and 10 weight %, and Na₂O between 4 and 13 weight % as main components.

14. A method as claimed in claim 13, wherein:

the glass contains SiO₂ between 62 and 75 weight %, Al₂O₃ between 5 and 15 weight %, Li₂O between 4 and 10 weight %, Na₂O between 4 and 12 weight %, and ZrO₂ between 5.5 and 15 weight % as main components, and

weight ratio of Na₂O/ZrO₂ falls within the range between 0.5 and 2.0 while weight ratio of Al₂O₃/ZrO₂ falls within the range between 0.4 and 2.5.

15. A method as claimed in any one of claims 7 through 14, wherein:

the step of chemically processing the surface or a chemical reinforcement process is carried out after the surface process due to the hydrofluosilic acid.

16. A method of manufacturing a magnetic recording medium, wherein:

at least a magnetic layer is formed on the principal surface of the glass substrate manufactured by the method claimed in any one of claims 7 through 15.

8. A method of manufacturing a glass substrate which is for use in a magnetic recording medium, comprising the steps of:

preparing a glass member in which Ra falls within the range between 0.1 and 1.0 nm when a surface roughness of a principal surface of said glass member is measured by the use of the interatomic force microscope (AFM), and

processing at least the principle surface by the use of hydrofluosilic acid,

said glass member having surface roughness Ra where Ra is representative of a center-line mean roughness.

17. A method of manufacturing a glass substrate which is for use in a magnetic recording medium and which has surface roughness Ra and Rmax, where Ra is representative of a center-line mean roughness, Rmax is defined as a maximum height representative of a difference between a highest point and a lowest point, comprising the steps of:

specifying a surface state of said glass substrate to improve flying characteristic of a magnetic head at every kinds of the magnetic head within a specific range Ra, Rmax and Rmax/Ra measured by the use of the interatomic force microscope (AFM);

processing the surface of the glass substrate under various surface processing conditions;

determining the surface processing condition so that Ra, Rmax and Rmax/Ra measured by the use of the interatomic force microscope (AFM) after the process falls within the specific range; and

processing the surface of said glass substrate based upon the determined surface processing condition.