Dynamic magnetic information storage or retrieval – Fluid bearing head support – Disk record
Reexamination Certificate
1999-03-09
2001-03-13
Miller, Brian E. (Department: 2652)
Dynamic magnetic information storage or retrieval
Fluid bearing head support
Disk record
Reexamination Certificate
active
06201663
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates a magnetic head having excellent machine processability and surface characteristics and having a good friction characteristic with respect to a magnetic disk.
Recent development of multimedia technology has resulted in processing of a large volume of data for image and voice. To cope with this situation, a rapid progress has been made for changing an HDD (hard disk) device which is a main external recording medium of a computer to one of a larger capacity and a higher speed. Keeping pace with this tendency, an inductive type thin film magnetic head is being replaced by a magneto-resistive head (MR head) in the field of a thin film magnetic head. Further, as a future type of magnetic head, a giant magneto-resistive head (GMR head) has become an object of attention.
In operation, the current hard disk device rotates a hard disk at a high speed and performs writing on and reading from the hard disk by means of a magnetic head which in operation is not in contact with the surface of the hard disk. In a hard disk device employing a CSS (contact start and stop) system, in order to prevent sticking of the magnetic head slider to the magnetic disk, a processing (mechanical texturing) is performed according to which a mechanical grinding is made for leaving substantially concentric circumferential machining traces on a magnetic disk substrate. There are also performed alternative texturing processings on a magnetic disk such as an etching processing, a sputtering processing and a laser processing. It is also proposed to produce crystal grains having a special crystal structure on the surface of a disk substrate and thereby obviate the above mentioned texturing processings. As to a magnetic head, the following proposals have been made for coping with the problem relating to the CSS system.
Japanese Patent Application Laid-open No. Sho 56-169264 proposes a magnetic head in which a non-contact type film is formed on a slider surface which opposes the surface of a magnetic medium for preventing sticking of the slider. Japanese Patent Application Laid-open No. Hei 5-182189 proposes a method for preventing sticking by forming a photo-sensitive glass layer on a rail port ion of a magnetic head which contacts the surface of a magnetic disk substrate and forming a pattern of projections and depressions on the surface of this photo-sensitive glass layer. Japanese Patent Application Laid-open No. Sho 63-60127 discloses high strength and high thermal expansion glass-ceramics for a magnetic head substrate having &agr;-quartz and spinel as its predominant crystal phase.
However, in the magnetic head having a non-contact type film, powder produced as a result of wear of the film is liable to cause difficulty in the sliding movement in case the film is made of a solid material while, in case the film is made of a liquid material, it is liable to cause wear and stripping off due to wear and resulting sticking to the slider with resulting decrease in efficiency.
In the magnetic head using the photo-sensitive glass, there is a problem of stripping off of the glass layer from the magnetic head. Besides, the photo-sensitive processing or etching processing must be made for forming the pattern of projections and depressions which is labor-consuming and costly. The glass-ceramics having &agr;-quartz and spinel as its crystal phase has a high strength but its processability is poor. There is also a magnetic head material which uses an alumina-titanium-carbide sintered material but this material is very hard and its processability is poor. Moreover, this material has many voids and this reduces productivity and make it difficult to manufacture the magnetic head with this material at a low cost.
It is an object of the present invention to eliminate the above described defects of the prior art and provide a magnetic head having excellent surface characteristics.
SUMMARY OF THE INVENTION
Accumulated studies and experiments made by the inventors of the present invention for achieving the above described object of the invention have resulted in the finding, which has led to the present invention, that a glass-ceramic obtained by subjecting to heat treatment, under specific heating conditions, a base glass of SiO
2
—Li
2
O—P
2
O
5
system has a mixed crystal structure in which either or both of globular crystal grains of &agr;-quartz (&agr;-SiO
2
) each consisting of aggregated particles and globular grains of a -cristobalite have randomly grown in a fine crystal of lithium disilicate (Li2O.2SiO
2
) and that differences in mechanical and chemical actions caused by the polishing processing between the lithium disilicate crystal phase which is mechanically and chemically instable and the aggregated globular grains of &agr;-quartz or globular grains of &agr;-cristobalite which is mechanically and chemically stable cause projections and depressions to be produced on the surface, and further that, by controlling the size of either or both of the aggregated globular grains of &agr;-quartz and the globular grains of &agr;-cristobalite, a material having excellent surface characteristics after polishing as the magnetic head substrate can be obtained.
For achieving the above described object of the invention, there is provided a magnetic head having a slider comprising a glass-ceramic substrate which has as its predominant crystal phase a mixed crystal of lithium disilicate (Li
2
O.2SiO
2
) and either or both of &agr;-quartz (&agr;-SiO
2
) and &agr;-cristobalite (&agr;-SiO
2
), said &agr;-quartz having a globular grain structure each globular crystal grain being made of aggregated particles and having a grain diameter within a range from 0.1 &mgr;m to 3.0 &mgr;m, said &agr;-cristobalite having a globular grain structure each globular grain having a grain diamter within a range from 0.1 &mgr;m to 1.0 u&mgr;m, and surface roughness (Ra) of said glass-ceramic substrate after polishing being within a range from 5 Å to 50 Å.
In one aspect of the invention, the glass-ceramic substrate of the magnetic head is obtained by subjecting to heat treatment a base glass comprising in weight percent:
SiO
2
65-83%
Li
2
O
8-13%
K
2
O
0-7%
MgO + ZnO + PbO
0.5-5.5%
in which MgO
0.5-5.5%
ZnO
0-5%
PbO
0-5%
P
2
O
5
1-4%
Al
2
O
3
0-7%
As
2
O
3
+ Sb
2
O
3
0-2%
and thereafter polishing the surface of the substrate to surface roughness (Ra) of 5 Å to 50 Å.
In another aspect of the invention, the glass-ceramic substrate for a magnetic head is characterized in that said glass-ceramic substrate is obtained by subjecting to heat treatment a base glass comprising in weight percent:
SiO
2
70-82%
Li
2
O
8-12%
K
2
O
1-6%
MgO + ZnO
1.5-5.5%
in which MgO
1-5%
ZnO
0.2-5%
P
2
O
5
1-3%
Al
2
O
3
1-6%
As
2
O
3
+ Sb
2
O
3
0-2%.
and thereafter polishing the surface of the substrate to surface roughness (Ra) of 5 Å to 50 Å.
According to the invention, the glass-ceramic substrate of the magnetic head has as its predominant crystal phase a mixed crystal of lithium disilicate (Li
2
O.2SiO
2
) and either or both of &agr;-quartz (&agr;-SiO
2
) and &agr;-cristobalite (&agr;-SiO
2
), the &agr;-quartz has a globular grain structure each globular crystal grain being made of aggregated particles and having a grain diameter within a range from 0.1 &mgr;m to 3.0 &mgr;m, the &agr;-cristobalite has a globular grain structure each globular grain having a grain diamter within a range from 0.1 &mgr;m to 1.0 &mgr;m, and surface roughness (Ra) of the glass-ceramic substrate after polishing is within a range from 5 Å to 50 Å whereby the invention can provide a magnetic head having a slider which has a surface rougness which does not need the laser texturing or mechanical or chemical textureing which has been required in the prior art magnetic head substrates for improving the CSS characteristics of the magnetic disk device.
Further, since the surface roughness within the above described range can be easily obtained by simply changi
Goto Naoyuki
Yamaguchi Katsuhiko
Hedman & Costigan ,P.C.
Kabushiki Kaisha Ohara
Miller Brian E.
LandOfFree
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