Abrasive tool making process – material – or composition – With inorganic material – Clay – silica – or silicate
Reexamination Certificate
2001-01-23
2002-11-12
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
Clay, silica, or silicate
C051S307000, C051S309000, C106S003000, C438S692000, C438S693000
Reexamination Certificate
active
06478835
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an abrasive composition for polishing magnetic recording disk substrates, and more particularly, to an abrasive composition for polishing magnetic recording disk substrates that allows the obtaining of a magnetic recording disk surface of high accuracy suitable for enabling the flying height of a magnetic head from the disk to be reduced.
2. Description of Related Art
Magnetic recording disks (memory rigid disks) are widely used in the external memories of computers and word processors as means of allowing high-speed access. A typical example of such a magnetic recording disk is one which is produced by preparing a substrate by subjecting an Al alloy substrate to electroless plating of NiP on the surface, surface-polishing the substrate, and thereafter sequentially forming a Cr-alloy underlayer, a Co-alloy magnetic film, and a carbon protective film by sputtering.
When irregularities or protrusions which are higher than the flying height of a magnetic head remain on the surface of a magnetic recording disk, the magnetic head, which flies over the disk at a predetermined flying height and high speed, may hit such protrusions, causing damage to the head. When a magnetic recording disk substrate has protrusions and polishing scratches, in the case of formation of a Cr-alloy underlayer or a Co-alloy magnetic film on the substrate, protrusions and defects attributed to the polishing scratches arise on the surface of the film, and thus the resulting magnetic recording disk fails to have an even surface of high accuracy. Therefore, in order to produce a magnetic recording disk having a surface of high accuracy, the substrate of the disk must be accurately polished.
Consequently, there have been proposed many abrasive compositions which remove protrusions, minimize the height of protrusions or rarely form polishing scratches during polishing of magnetic recording disk substrates. For example, although Japanese Unexamined Patent Application, First Publication No. 10-121035 (use of a composition comprising the addition of aluminum nitrate to titania) easily achieves high surface accuracy and abrasion rate as compared with the prior art as a result of using submicron titanium oxide particles for the abrasive particles, it is difficult to achieve the level of surface accuracy required at present due to the effects of hardness of the abrasive particles. In addition, although Japanese Unexamined Patent Application, First Publication No. 11-167715 (use of a composition comprising the addition of aluminum nitrate to colloidal silica) makes it easy to obtain surface accuracy as a result of using fine particles of silicon dioxide having low hardness for the abrasive particles, it was difficult to achieve an abrasion rate that can be used in actual production.
BRIEF SUMMARY OF THE INVENTION
The quality required of abrasive compositions for polishing aluminum magnetic recording disk substrates that enable high-density magnetic recording is such that a highly accurate disk surface is achieved that allows reduction of the head flying height.
The object of the present invention is to provide an abrasive composition for polishing magnetic recording disk substrates that lowers the surface roughness of a magnetic recording disk, allows the attaining of high-density recording without the occurrence of protrusions or polishing scratches, and enables polishing to be performed at an economical high speed.
As a result of conducting extensive research on abrasive compounds for attaining a highly accurate polished surface required by aluminum magnetic recording disks having a low flying height, the inventors of the present invention found that an abrasive composition that uses silicon dioxide for the abrasive material and blends aluminum nitrate, antigelling agent and hydrogen peroxide therein demonstrates superior performance, thereby leading to completion of the present invention. Namely, the present invention is composed of each of the following inventions:
(1) an abrasive composition for polishing magnetic recording disk substrates comprising: water, silicon dioxide, antigelling agent, aluminum nitrate and hydrogen peroxide;
(2) an abrasive composition for polishing magnetic recording disk substrates according to (1) above, wherein the silicon dioxide is one or more types selected from colloidal silica, fumed silica and precipitated silica;
(3) an abrasive composition for polishing magnetic recording disk substrates according to either of (1) or (2) above, wherein the average particle size of secondary particles of the silicon dioxide is 0.03-0.5 &mgr;m;
(4) an abrasive composition for polishing magnetic recording disk substrates according to any of (1) through (3) above, wherein the concentration of silicon dioxide in the composition is 3-30 wt %;
(5) an abrasive composition for polishing magnetic recording disk substrates according to any of (1) through (4) above, wherein the antigelling agent is one or more types selected from a phosphonic acid compound, phenanthroline and acetylacetone aluminum salt; and,
(6) an abrasive composition for polishing magnetic recording disk substrates according to (5) above, wherein the phosphonic acid compound is 1-hydroxyethane-1,1-diphosphonic acid.
According to the present invention, an abrasive composition for polishing magnetic recording disk substrates that is comprised of water, silicon dioxide, antigelling agent, aluminum nitrate and hydrogen peroxide such that, due to the presence of the three ingredients of antigelling agent, aluminum nitrate and hydrogen peroxide, a higher abrasion rate is obtained.
Although the abrasive composition for polishing of the present invention can be advantageously applied to, for example, a substrate for high-density recording such as a magnetic recording disk for magnetic heads utilizing magnetoresistance (MR) effects (normally having a recording density of 1 Gbit/inch
2
or more), it can also be applied effectively to magnetic recording disks having a lower recording density from the standpoint of improving reliability.
When disks are polished using the abrasive composition for polishing of the present invention, surface roughness can be reduced significantly and polishing can be performed at a high abrasion rate. A magnetic recording disk using a polished disk is useful as a low flying height rigid disk, and enables high-density recording.
In particular, a magnetic recording disk using a polished disk has a high degree of usefulness as a high-density recording medium typically represented by media for MR heads (having a recording density of 1 Gbit/inch
2
or more). It is also useful for magnetic recording disks having a lower recording density from the viewpoint of being a highly reliable medium.
DETAILED DESCRIPTION OF THE INVENTION
There are no particular restrictions on the silicon dioxide contained as abrasive material in the abrasive composition for polishing of the present invention, colloidal silica, fumed silica or precipitated silica may be used, and the average particle size of the secondary particles is preferably 0.03-0.5 &mgr;m. The average particle size of the secondary particles refers to the value measured by means of the MICROTRAC UPA 150 (manufactured by Honeywell), which is a laser Doppler frequency analysis type of particle size distribution measuring instrument.
Although it becomes easier to inhibit fine gelling and aggregation when the size of the secondary particles of the silicon dioxide increases, since the probability of the existence of coarse particles also increases, this can cause the occurrence of polishing scratches. In addition, if the size of the secondary particles decreases, there is increased susceptibility to the above gelling and aggregation, which also causes the occurrence of polishing scratches. Thus, the average particle size of the secondary particles of the silicon dioxide contained as abrasive material in the abrasive composition for polishing of the present invention is preferably 0.03-0.5 &mgr;m
Miyata Norihiko
Tada Kiyoshi
Tomita Kenji
Marcheschi Michael
Showa Denko K.K.
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