Abrading – Abrading process – Utilizing fluent abradant
Reexamination Certificate
2002-07-31
2004-10-05
Eley, Timothy V. (Department: 3724)
Abrading
Abrading process
Utilizing fluent abradant
C051S298000, C051S307000, C428S903000, C442S351000, C442S366000, C442S405000, C451S037000, C451S041000, C451S059000, C451S063000, C451S532000, C451S550000
Reexamination Certificate
active
06800019
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to an abrasive ground fabric used for the production of magnetic recording media and similar media which require high-accuracy surface finish. Specifically, it relates to an abrasive ground fabric suitably used for texturing in the production of magnetic recording substrates such as hard disks and to a polishing method using the same.
2. Description of the Prior Art
Along with recent progress made in information processing technologies such as computers, high-accuracy surface finish is required for magnetic recording media and silicon wafers. For example, to produce a magnetic recording substrate such as a hard disk as a magnetic recording medium, the surface of aluminum or glass is smoothened and plated with a non-magnetic material such as nickel-P, a magnetic thin film of a cobalt-based alloy is formed on the surface, and then a surface protective layer such as a carbon layer is formed on the film. The requirement for an abrasive ground fabric used to smooth the above surface is becoming higher and higher. Particularly in the final stage of smoothing the surface of this magnetic recording substrate, a surface treatment called “texturing” using a slurry containing abrasive grains dispersed therein and an abrasive ground fabric is carried out to form fine grooves in the surface of the disk and the development of the optimum abrasive ground fabric for increasing the capacity and density of the disk has been awaited from the market.
As the abrasive ground fabric used for texturing has been used a fabric woven of fine fibers of about 5 &mgr;m in diameter or a sheet transplanted with fibers of 14 &mgr;m in diameter. However, the above fabric has problems that polishing with fine fibers of 5 &mgr;m in diameter is unsatisfactory and the freedom of fibers is low, and the above sheet has problems that the surface of the substrate is easily scratched deeply and a magnetic recording medium having low reliability is obtained because thick fibers are transplanted perpendicular to the surface.
To solve the above problems, JP-A 9-277175 (the term “JP-A” as used herein means an “unexamined published Japanese Patent Application”) proposes an abrasive sheet which is a nonwoven fabric composed of intertwined fine fibers of 10 &mgr;m or less in diameter and having a raised surface. However, a nonwoven fabric obtained by a melt blow method has a problem that the strength of fibers is low and a nonwoven fabric composed of ordinary split fibers has a problem that fine fibers readily fall off because they are physically intertwined. In general texturing, the nonwoven fabric is used in the form of a tape. In this method, a reinforcing layer must be laminated as the strength of the tape is unsatisfactory. JP-A 11-138407 proposes abrasive cloth produced by cutting part of a bundle of a fabric and raising it. However, it is difficult to produce the abrasive cloth on an industrial scale because part of the bundle of the obtained fabric must be cut and fine fibers of less than 2 &mgr;m in diameter must be raised.
Further, JP-A 2000-237951 proposes abrasive cloth which is a nonwoven fabric comprising fine fibers of 0.3 dtex or less and having a hydrophilic surface. This abrasive cloth is a nonwoven fabric composed of fiber bundles, each consisting of 30 or less fine fibers which are polyethylene terephthalate fibers and relatively uniform in diameter from the viewpoint of a production method thereof. It is difficult to maintain both the strength and polishing accuracy of the abrasive ground fabric at high levels as the number of fine fibers constituting each bundle is relatively small and the fibers are uniform in diameter.
PROBLEM TO BE SOLVED BY THE INVENTION
It is an object of the present invention which has been made to solve the above problems to provide an abrasive ground fabric which is capable of polishing uniformly without producing a deep scratch in the surface of a substrate by variations in polishing conditions when the surface of a magnetic recording medium or the like is subjected to precision polishing such as texturing and has sufficiently high strength and a method of polishing a magnetic recording substrate using the same.
MEANS FOR SOLVING THE PROBLEMS
According to researches conducted by the inventors of the present invention, it has been found that the object of the present invention is attained by an abrasive ground fabric which is a composite ground fabric comprising a fiber substrate and a elastic polymer filled in the fiber substrate, wherein (1) the fiber substrate is composed of fiber bundles, each consisting of 20 to 3,000 fine fibers, and (2) the average diameter (D1) of fine fibers existent in a center portion from the center of the cross section perpendicular to a lengthwise direction of each fiber bundle to ½ of the radius of each fiber bundle is 0.3 to 10 &mgr;m, the average diameter (D2) of fine fibers existent in a peripheral portion from ½ of the radius to the end of each fiber bundle is 0.05 to 1 &mgr;m, and the D1/D2 ratio is 1.5 or more. Further, it has been found that the object of the present invention is attained by an abrasive ground fabric which has (a) a water absorption height on one side of 20 mm/hr or more and a water absorption height on the other side of 5 mm/hr or less, and (b) one raised side.
The abrasive ground fabric of the present invention will be described in more detail hereinbelow.
The abrasive ground fabric of the present invention is a composite ground fabric which comprises a fiber substrate and a elastic polymer filled in the fiber substrate. This fiber substrate is composed of fiber bundles of fine fibers and the elastic polymer is mainly existent outside the fiber bundles in the inside of the fiber substrate other than the surface layer of the fiber substrate. That is, the elastic polymer is substantially existent in spaces between the fiber bundles. Each fiber bundle consists of 20 to 3,000 fine fibers, preferably 50 to 2,000 fine fibers, the most preferably 100 to 1,600 fine fibers. When the number of fine fibers is smaller than 20, the number of fibers in the peripheral portion becomes small and the effect obtained by the difference in average diameter between the center portion and the peripheral portion which will be described hereinafter is hardly obtained. From the viewpoint of production, the total fineness of the fine fibers of each bundle is preferably 1 to 10 dtex, more preferably 2 to 5 dtex.
As for the fine fibers of each bundle, the average diameter (D1) of fine fibers existent in the center portion from the center of the cross section perpendicular to the lengthwise direction of the bundle to ½ of the radius of the bundle must be 0.3 to 10 &mgr;m (about 0.0008 to about 0.94 dtex), preferably 0.5 to 2 &mgr;m (about 0.0024 to about 0.038 dtex). When the average diameter (D1) of the fine fibers of the center portion is smaller than 0.3 &mgr;m, the strength of the fine fibers lowers and the strength of the obtained composite ground fabric also lowers. When the average diameter (D1) is larger than 10 &mgr;m, a substrate to be polished is easily scratched by polishing.
The average diameter (D2) of fine fibers existent in the peripheral portion must be 0.05 to 1 &mgr;m (about 0.00002 to about 0.0094 dtex), more preferably 0.1 to 0.7 &mgr;m (about 0.0001 to about 0.0046 dtex), the most preferably 0.2 to 0.5 &mgr;m (about 0.00038 to about 0.0024 dtex). When the average diameter (D2) is smaller than 0.05 &mgr;m, the strength of fine fibers lowers and the fine fibers fall off at the time of polishing. When the average diameter (D2) is larger than 1 &mgr;m, there is no difference between the conventional product and the obtained product of the present invention.
Further, the largest diameter of a fine fiber of each bundle is preferably 10 &mgr;m (about 0.94 dtex) or less, more preferably 3 &mgr;m (about 0.1 dtex) or less. The smallest diameter of a fine fiber is preferably 0.01 &mgr;m (about 0.000001 dtex) or more. When the
Kitawaki Shusuke
Mimura Masahisa
Suzuki Yoshiyuki
Tanaka Manabu
Eley Timothy V.
Teijin Limited
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