Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2000-08-04
2002-07-30
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S141000, C428S065100, C428S690000
Reexamination Certificate
active
06426155
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
This invention relates to a Ni—P electroless-plated magnetic hard disc substrate made of an aluminum alloy which is a high capacity-type, such as those using a MR head or the like, and a process for manufacturing the magnetic disc.
b) Description of the Prior Art
A magnetic hard disc substrate can be generally obtained by punching a roll coil made of an aluminum alloy to prepare a blank, grinding the blank to remove flaws, waviness, and the like to obtain a substrate, then electroless plating the substrate with Ni—P, finish-polishing the plated substrate, then forming a magnetic film by magnetic sputtering, and coating the magnetic film with an overcoat to obtain a sputtering media. In order to allow the surface roughness and the flatness to fall in prescribed ranges respectively in these steps, the grinding of the magnetic hard disc substrate (blank) prior to the Ni—P electroless plating is performed by the following method: the substrate is put onto a polishing board to which a nonwoven fabric polishing cloth made of an organic polymer is applied and (a) the polishing operation is performed under a fixed pressure while supplying, to the polishing face, a polishing solution produced by dispersing metal oxide particles, such as alumina, titania, and zirconia with an average grain size of 0.3 to 5 &mgr;m, in an organic acid-type etchant wherein the polishing operation consists of a first stage polishing using abrasive grains of a larger size and successively second stage polishing using abrasive grains of a smaller size; or (b) the polishing operation is performed using a polishing solution produced by dispersing colloid particles of silica, zirconia, titania, or the like, with an average grain size of 0.01 to 0.3 &mgr;m, in an acid-type or alkali-type etchant.
In general, the magnetic hard disc substrate made of an aluminum alloy which is electroless plated with Ni—P and is used for a hard disc of memory devices such as a computer, is improving in recording density from year to year. There is a great demand for more improvement in the recording density. There is also a tendency to a higher density and larger capacity. It is therefore important to finish the magnetic hard disc substrate used in these fields so that the substrate has the prescribed surface roughness and flatness. Particularly, the realization of high density recording is due to a remarkable progress in low floatation technologies based on the improvement of the head, which requires the reduction of the interval between the head and the medium. With the reduction in the interval, the magnetic disc needs to have a smooth surface and mostly reduced surface defects. Specifically, the following polishing qualities are required: the surface roughness Ra<5 angstroms, the surface roughness Rmax≦80 angstroms, and the surface is free from scratches with a depth of 50 angstroms or more and from pits with a depth of 50 angstroms or more. In the conventional method in which the polishing is performed using a polishing solution containing abrasive grains composed of a metal oxide such as alumina, titania, or zirconia, particles with a large grain size cannot be prevented from getting slightly mixed therein during a classification stage because these oxides are produced by grinding a massive raw material and classifying the ground material. The contaminant particles with a large grain size cause the production of scratches with a depth of 50 angstroms.
In the method (a) among the aforementioned conventional methods, though the waviness of the substrate decreases, the obtained value of Ra is about 10 angstroms and polishing flaws with a depth as long as 100 &mgr;m or more remains. In the method (b), in turn, the obtained value of Ra is about 3 angstroms and the polishing flaws decrease in depth to about 50 angstroms or less, but the waviness of the substrate remains. Also, the polishing speed is low, which requires a polishing time as long as about 5 minutes or more to attain the object Ra value. Magnetic hard disc substrates obtained after the polishing step in the conventional methods inevitably have the features that the surface roughness Ra is in a range from 7 to 15 angstroms, the surface roughness Rmax is in a range from 80 to 150 angstroms, and several scratches with a depth of 80 to 150 angstroms, some pits with a depth of 100 angstroms or less, and micro-waviness are produced. When using a suspension of known micro-sized and uniform silica particles to polish in order to avoid this situation, it takes a long time to polish because the particles are small. If erosive chemicals are added to accelerate the polishing, the silica will gel to-cause the silica particles to lose their uniformity. Thus a surface with the surface roughness Ra ≦5 angstroms and the surface roughness Rmax≦80 angstroms cannot be achieved at present.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the above prior art problems and to provide a magnetic hard disc substrate with a smooth surface and decreased defects which makes it possible to achieve high density recording and also to provide a process for manufacturing the magnetic disc.
Another object of the present invention is to provide a magnetic hard disc substrate which has a surface roughness Ra≦5 angstroms and is free from scratches (grinding flaws) with a depth of 50 angstroms or more and from micro-waviness.
A further object of the present invention to provide a magnetic disc which has a surface roughness Ra≦5 angstroms and a surface roughness Rmax≦80 angstroms and is free from scratches with a depth of 50 angstroms or more and from pits with a depth of 50 angstroms or more.
A still further object of the present invention is to provide a process for manufacturing the magnetic hard disc substrate in a short time and in a simple manner.
A still further object of the present invention relates to the above process using silica abrasive grains and is to provide a process for manufacturing the magnetic hard disc substrate having excellent surface properties in an efficient manner by adding, to the polishing agent, additives for avoiding gelation and for improving the rate of polishing.
Still further objects will be clear from the descriptions herein below.
The present invention resides to a polishing process in succession to a Ni—P electroless plating process in a process for manufacturing an aluminum alloy magnetic hard disc substrate and comprises: dividing the polishing process into plural polishing stages, polishing a subject material using a polishing solution containing metal oxide abrasive grains with an average grain size of 0.3 to 5 &mgr;m in a polishing stage preceding a final polishing stage, and polishing the treated subject material using a polishing solution containing colloid particles with a grain size of 0.01 &mgr;m to 0.3 &mgr;m in the final polishing stage. It is noted that the polishing process using a metal oxide abrasive grains, which is followed by the final polishing process, may be divided into a plurality of polishing steps using particles with different grain sizes respectively.
According to a further aspect of the present invention, there is provided a process for manufacturing a magnetic hard disc substrate comprises: processing a subject material until the surface roughness Ra is 15 angstroms or less and the surface roughness Rmax is 200 angstroms or less and then polishing the treated subject material using a colloidal abrasive agent containing silica particles with a grain size of 0.5 &mgr;m or less, to which are added additives for preventing gelation and accelerating the rate of polishing.
Preferably the above additive contains 0.01 mol/l of a trivalent iron ion as an inorganic acid salt or organic acid salt in the present invention.
Other examples of the additive include 0.1 to 2.0 mol/l of hydroxyacetic acid, 0.1 to 2.0 mol/l of molybdenum oxide (hexavalent), 0.01% or more of hydrogen peroxide, 0.03 to 4.0 mol/l of aluminum nitrate, 0.03 to 2.0 mol/l of nitric
Awaya Kurata
Tada Kiyoshi
Tomita Kenji
Utashiro Tomoya
Flynn ,Thiel, Boutell & Tanis, P.C.
Resan Stevan A.
Showa Denko K.K.
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