Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1999-12-15
2001-10-23
Banks, Derris H. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S028000
Reexamination Certificate
active
06306013
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of producing a polishing cloth for texturing the surface of a magnetic hard disk substrate by using free abrading particles.
In general, the texturing of the surface of a disk substrate, say, of an aluminum alloy by means of free abrading particles is carried out by pressing a polishing cloth on the target surface to be polished while supplying onto the surface a liquid slurry serving as the free particles and rotating the disk substrate while adjusting the pressure on the polishing cloth. The liquid slurry may be one obtained by mixing abrading particles of aluminum oxide, silicon carbide or diamond with an aqueous solution containing a surfactant and stirring the mixture together. In the past, woven cloths produced by weaving plastic fibers were frequently used for such a texturing process. Such a cloth may be produced, for example, by weaving both longitudinally and transversely woven bundles of plastic fibers of polyester or tetron and cut in the shape of a circle or a tape.
With the recent increase in the memory capacity of magnetic hard disks, there is a demand to increase the density of various memory media. As a result, it has become necessary to reduce and stabilize the floating distance of a magnetic head over the surface of a magnetic hard disk substrate and the surface texturing on such disk surfaces is required to be ever finer and more uniform than before. By a texturing process with the use of free abrading particles and a polishing cloth as described above, however, abnormal protrusions, waviness and irregular patches are generated on the textured surface and it was not possible to carry out a fine and uniform texturing of a surface of a magnetic hard disk substrate. In other words, it has been very difficult to reduce and stabilize the floating distance of a magnetic head, and this has been a cause of collisions or adhesion between the magnetic head and a hard disk.
Next will be explained the reasons for finding abnormal protrusions, waviness and patches on a textured surface of a magnetic hard disk substrate.
FIG. 2
shows the conditions of a polishing surface of a conventional polishing cloth
20
produced by weaving woven bundles
23
of plastic fibers longitudinally and transversely to serve as its base
21
having a polishing surface
22
. As can been seen in FIG.
2
(
a
) in which a small portion B of the polishing surface
22
is enlarged, the polishing surface
22
of a prior art polishing cloth
20
has many protrusions and indentations. If a polishing cloth with such protrusions and indentations on its polishing surface is used in a texturing process by means of free abrading particles, the target surface to be polished experiences compressive forces of different magnitude, depending on whether it is being pressed by one of the protrusions or indentations on the surface of the polishing cloth. The liquid slurry which is supplied onto the target surface will not be pressed uniformly, and patches are finally left on the finished surface. As a result, abnormal protrusions may be formed on the surface of the disk substrate or a waviness may be generated. Grooved lines cannot therefore be formed at a high density, and it is concluded that prior art polishing cloth is not suited for a fine and uniform texturing process.
With the recent increase in the demand for magnetic hard disks, it is also coming to be severely required to shorten the time spent for the texturing of magnetic hard disk substrates and to thereby increase the throughput.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a method of producing an improved polishing cloth with which the surface of a magnetic hard disk substrate can be finely and uniformly textured.
It is an additional object of this invention to provide a method of producing an improved polishing cloth with which the time required for texturing a disk substrate can be shortened such that the production throughput can be improved.
A polishing cloth embodying this invention, with which the above and other objects can be accomplished, may be characterized as comprising a base material of a woven cloth formed by weaving in woven bundles of plastic fibers having a surface layer formed by portions of these woven bundles which are cut and raised so as to stand up from a surface. Such a polishing cloth can be produced by preparing a woven cloth as its base material by weaving in woven bundles of plastic fibers, cutting portions of these woven bundles over a surface of the woven cloth, and forming a surface layer by raising the cut portions of the woven bundles from a surface. When such a polishing cloth is used for texturing a target surface of a disk substrate, the target surface is rubbed with such a cloth while a liquid slurry containing free abrasive particles is supplied to the surface. With a polishing cloth according to this invention, the target surface can be pressed more uniformly and gently and the removed particles from the target surface can be effectively captured inside the surface layer with raised plastic fibers.
REFERENCES:
patent: 3280517 (1966-10-01), Copeland
patent: 4136221 (1979-01-01), Okamoto et al.
patent: 4381805 (1983-05-01), Troy
patent: 4668553 (1987-05-01), Sctte et al.
patent: 5396737 (1995-03-01), Englund et al.
patent: 6074284 (2000-06-01), Tani et al.
Aoyama Yoshitomo
Horie Yuji
Banks Derris H.
Coudert Brothers
Nihon Micro Coating Co., Ltd.
Shakeri Hadi
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