Abrasive tool making process – material – or composition – With inorganic material
Reexamination Certificate
2001-04-17
2003-05-27
Wood, Elizabeth D. (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
C051S308000, C051S309000, C106S003000, C438S692000, C438S693000, C216S089000, C252S079100, C252S079200, C252S079300, C252S079400, C252S079500
Reexamination Certificate
active
06569215
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a polishing composition used in the manufacture of a magnetic disk substrate used as a storage device for a computer or the like. More particularly, the present invention relates to a composition for polishing a magnetic disk substrate that can provide a magnetic disk surface with high precision suitable for use in combination with a magnetic head that floats at a low level, and to a method of producing the above-mentioned polishing composition.
BACKGROUND OF THE INVENTION
Among the external storage devices for a computer or word processor, a magnetic disk (a memory hard disk) is widely used as a high-speed accessible means. One typical example of the magnetic disk is a disk obtained by subjecting an Al-alloy base material to electroless plating of NiP to form a substrate, polishing a surface of the substrate, and successively sputtering a Cr-alloy undercoat layer, a Co-alloy magnetic layer, and a carbon protective layer on the substrate in that order.
If a protrusion with a height that exceeds the floating level of the magnetic head remains on the magnetic disk surface, the magnetic head travels and collides with the protrusion while floating at a predetermined height. As a result, the protrusion will cause damage to the magnetic head. In addition, when a protrusion or a scratch caused by polishing exists on the magnetic disk substrate, the protrusion also appears on the Cr-alloy undercoat layer and the Co-alloy magnetic layer even when such layers are overlaid, and a flaw caused by the scratch is produced, whereby the magnetic disk is not provided with a smooth surface having high precision. Accordingly, it is necessary to precisely polish the substrate to enhance the precision of the disk surface.
For the polishing of the magnetic disk substrate, many polishing compositions are proposed that can remove the protrusion completely or buff the protrusion down to as low a height as possible without easily producing any scratches.
Japanese Laid-Open Patent Application No. 10-121035 discloses the use of a composition prepared by adding aluminum nitrate (serving as a polishing accelerator) to titania. In the aforementioned application, sub-micron particles of titanium oxide are used as abrasive grains. When such a composition is used for polishing the magnetic disk substrate, the surface precision can become higher and the polishing speed can be increased compared with when conventional compositions are used. However, in consideration of the hardness of the abrasive grain material, it is difficult to attain such a level of surface precision as is currently desired.
Japanese Laid-Open Patent Application No. 9-204657 discloses the use of a composition prepared by adding aluminum nitrate and an anti-gelling agent to colloidal silica. In Japanese Laid-Open Patent Application No. 9-204658 there is disclosed a use of a composition prepared by adding aluminum nitrate to fumed silica. Each of the compositions disclosed in the above-mentioned applications comprises finely-divided particles of silicon oxide with low hardness as the abrasive grains so that the surface precision can be easily obtained, although it is difficult to achieve a polishing speed suitable for real production.
Further, in Japanese Laid-Open Patent Application No. 10-204416, the use of many kinds of oxidizing agents and the use of Fe-salts are separately proposed to accelerate the polishing speed. However, the obtained polishing speed is still insufficient in light of real production in practice.
SUMMARY OF THE INVENTION
A composition for polishing an aluminum magnetic disk substrate that realizes high-density magnetic recording is required to provide a disk surface with high precision which enables a head to float at a low level.
Accordingly, an object of the present invention is to provide a composition for polishing a magnetic disk substrate capable of realizing high-density magnetic recording. The composition can provide a magnetic disk substrate having a low surface roughness with no protrusions or scratches caused by polishing, and can polish the magnetic disk substrate at a cost-effective speed.
The inventors of the present invention have intensively investigated an abrasive that can provide a polished surface with high precision required for an aluminum magnetic disk for use with a low floating magnetic head. As a result, the inventors have found a polishing composition that exhibits excellent properties in polishing an aluminum magnetic disk, especially, with a Ni-P plated aluminum magnetic disk. The present invention has been accomplished based on the above-mentioned finding.
Namely, the present invention basically provides the following aspects:
(1) A polishing composition comprising an aqueous medium together with alkali metal ions, abrasive grains, a carboxylic acid, an oxidizing agent, and an anti-gelling agent which are contained in said aqueous medium.
(2) The polishing composition as described in (1) above, wherein said alkali metal ions are contained in an amount of 0.001 to 5% by mass.
(3) The polishing composition as described in (1) or (2) above, wherein said alkali metal ions are supplied by alkali metal hydroxide.
(4) The polishing composition as described in (1) or (2) above, wherein said alkali metal ions comprise at least one ion selected from the group consisting of lithium, sodium, potassium, rubidium, and cesium ions.
(5) The polishing composition as described in (1) or (2) above, wherein said alkali metal ions are potassium ions.
(6) The polishing composition as described in (1) or (2) above, wherein said abrasive grains comprise at least one material selected from the group consisting of alumina, titania, silica, and zirconia.
(7) The polishing composition as described in (1) or (2) above, wherein said abrasive grains have a secondary particle with a mean particle diameter of 0.03 to 0.5 &mgr;m.
(8) The polishing composition as described in (1) or (2) above, wherein said abrasive grains are in the form of colloidal particles.
(9) The polishing composition as described in (1) or (2) above, wherein said carboxylic acid is an organic carboxylic acid comprising at least one COOH group or COO— group in a molecule thereof.
(10) The polishing composition as described in (1) or (2) above, wherein said carboxylic acid comprises at least one acid selected from the group consisting of gluconic acid, lactic acid, tartaric acid, glycolic acid, glyceric acid, malic acid, citric acid, formic acid, acetic acid, propionic acid, acrylic acid, oxalic acid, malonic acid, succinic acid, adipic acid, maleic acid, itaconic acid, glycine, lysine, aspartic acid, and glutamic acid.
(11) The polishing composition as described in (1) or (2) above, wherein said oxidizing agent comprises at least one material selected from the group consisting of a peroxide, a persulfate, a nitrate, an oxyacid salt, and an iron salt.
(12) The polishing composition as described in (1) or (2) above, wherein said oxidizing agent comprises a hydrogen peroxide.
(13) The polishing composition as described in (1) or (2) above, wherein said anti-gelling agent comprises at least one material selected from the group consisting of a phosphonic acid compound, phenanthroline, and aluminum acetylacetonate.
(14) The polishing composition as described in (1) or (2) above, wherein said anti-gelling agent comprises at least one material selected from the group consisting of phosphoric acid, 1-hydroxyethane-1,1-diphosphonic acid, aminotrimethylenephosphonic acid, phenanthroline, and aluminum acetylacetonate.
(15) The polishing composition as described in (1) or (2) above, wherein said composition has a pH value in a range of about 1 to about 5.
(16) The polishing composition as described in (1) or (2) above, wherein said composition comprises 3 to 30% by weight of abrasive grains, 0.1 to 8% by weight of a carboxylic acid, 0.2 to 5% by weight of an oxidizing agent, and 2% or less by weight of an anti-gelling agent.
(17) The polishing composition as described in (1) or (2) above, wherein said polishi
Showa Denko Kabushiki Kaisha
Sughrue & Mion, PLLC
Wood Elizabeth D.
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