Abrasive tool making process – material – or composition – With inorganic material – Metal or metal oxide
Reexamination Certificate
2000-07-18
2002-08-27
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
Metal or metal oxide
C106S003000, C438S692000, C438S693000, C252S079200, C501S127000, C423S625000, C423S629000
Reexamination Certificate
active
06440187
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an alumina powder characterized by having a single or multiple crystal structure selected from the group consisting &ggr;, &dgr; and &thgr;-forms, a primary particle size of 10 to 50 nm, a mean secondary particle size (mean aggregated particle size) of 100 to 500 nm, and a granular primary particle:shape, an alumina powder characterized by having an &agr;-form crystal'structure, a primary particle size of 60 to 150 nm, a mean secondary particle size (mean aggregated particle size) of 200 to 500 nm, and a granular primary particle 'shape, and processes for producing those. The present invention also relates to polishing compositions using those alumina powders as an abrasive.
The polishing compositions of the present invention can efficiently provide a smooth polished surface with high precision in polishing an aluminum disk, and therefore are useful as a final finish polishing composition. The “polishing an aluminum disk” intended herein means to polish the surface of a substrate itself of a magnetic memory disk comprising aluminum or its alloy, the surface of a layer of, for example, non-electrolysis nickel-phosphornus (Ni—P) plating or non-electrolysis nickel-boron (Ni—B) plating, formed on the substrate, particularly a hard layer of non-electrolysis nickel-phosphorus (Ni—P) plating having compositions comprising 90 to 92% Ni and 8 to 10% P, and the surface of an aluminum oxide layer.
Further, the polishing material using an abrasive of alumina according to the present invention can efficiently provide a smooth polished surface with high precision, and therefore is useful for polishing an oxide film, a nitride film or carbide film of a semiconductor device, a wiring metal of a semiconductor multilayer wiring substrate, or the like, and for final finish polishing a magnetic head, a quartz, a glass and the like.
PRIOR ART
Alumina powder comprising alumina fine particles having a mean particle size of 1 &mgr;m or less is produced by dry and/or wet grinding alumina having a crystal structure of, for example, &ggr;, &dgr;, &kgr;, &thgr;, &eegr; or &agr;-form obtained by calcining aluminum hydroxide that is produced by the Bayer process at low cost and in large amount.|
Further, high purity alumina powder of a plate-like, &ggr;-form, &dgr;-form or the like crystal structure having a primary particle size of 20 to 80 nm or high purity alumina powder of &agr;-form crystal structure having a primary particle size of 150 to 200 nm or more is commercially available.
Further, EP-A-0554908 (corresponding to JP-A-5-345611 (1993)) describes &agr;-form alumina having a primary particle size of 20 to 50 nm in which a barrier of silica is formed around boehmite particles to thereby suppress growth of particles in transferring to &agr;-form alumina.
Further, JP-A-7-089717 (1995) discloses a process for producing alumina sol of, for example, &ggr;, &dgr;, &kgr;, &thgr;, &eegr; or &agr;-form, having a mean particle size of 100 nm or less by a peptization method of contacting commercially available ultrafine alumina powder as it is, or a powder obtained by calcining the ultrafine alumina powder, with a cation-exchange resin in an aqueous phase in the presence of an acid.
A slurry obtained by mixing water, an alumina polishing material, and a polishing accelerator, and if necessary, a surface modifier, is used as a polishing composition which is used in polishing an aluminum disk. As the examples of this polishing accelerator, U.S. Pat. No. 4,705,566 (corresponding to JP-B-2-023589 (1990)) disclosed aluminum nitrate, nickel nitrate, nickel sulfate, and the like, and JP-A-2-158682 (1990) discloses sodium nitrite, potassium nitrite, calcium nitrite, magnesium nitrite, barium nitrite, zinc nitrite, aluminum nitrite or the like.
Problems to be Solved
In recent years, performance of aluminum disk has the tendency of gaining higher density and higher speed. Therefore, no surface defect of orange peel, scratch, pit, asperity or the like, and high flatness with small mean surface roughness and small maximum surface roughness are strongly demanded.
The alumina powder having a crystal structure of, for example, &ggr;, &dgr;, &kgr;, &thgr;, &eegr; or &agr;-form obtained by calcining and grinding aluminum hydroxide produced by the Bayer process has a broad particle size distribution due to the break-down method even if the alumina powder comprises alumina fine particles having a mean particle size of 1 &mgr;m or less. For this reason, a wet classification (hydraulic elutriation or the like) is conducted, but it is difficult to completely remove coarse particles. Where a polishing material having coarse particles intermixed therein is used, it is difficult to obtain a polished surface of high quality.
Further, in the alumina powder having a crystal structure of &ggr; or &dgr;-form obtained by calcining aluminum hydroxide produced by a metal alkoxide method, the particle shape is plate-like. Therefore, the material to be polished is in the state that the material slides on a pad during polishing, and a removal rate is slow, so that productivity of polishing step is poor. Furthermore, since the alumina powder having a crystal structure of &agr;-form has a primary particle size of 150 to 200 nm or more , it is difficult to obtain a polished surface of high quality.
Further, in the &agr;-form alumina having a barrier of silica as the surface layer and having a primary particle size of 20 to 50 nm, the removal rate thereof is slow due to the silica layer having a removal rate slower than that of alumina.
On the other hand, alumina sol of, for example, &ggr;, &dgr;, &kgr;, &thgr;, &eegr; or &agr;-form having a mean particle size of 100 nm or less by a peptization method of contacting commercially available ultrafine alumina powder as it is, or a powder obtained by calcining the ultrafine alumina powder, with a cation-exchange resin in an aqueous phase in the presence of an acid has a primary particle size of 10 nm or less. Therefore, the removal rate is slow and productivity of polishing step becomes poor.
SUMMARY OF THE INVENTION
The present invention has an object to provide alumina powders as an abrasive suitable for a polishing composition which can improve productivity of polishing step and decrease cost by increasing the removal rate while maintaining the polished surface of high quality, a process for producing those alumina powders, and a polishing composition.
The present inventors have found an alumina powder having a single or multiple crystal structure selected from the group consisting of &ggr;, &dgr; and &thgr;-forms, a primary particle size of 10 to 50 nm, wherein the particle size distribution is sharp, a mean secondary particle size (mean aggregated particle size) of 100 to 500 nm, and a granular primary particle shape, obtained by calcining alumina hydrate comprising rectangular plate-like primary particle having a length of one side of 10 to 50 nm and having a boehmite structure as a raw material by the production process of the present invention without using commercially available alumina powder and grinding, and an alumina powder having an &agr;-form crystal structure, a primary particle size of 60 to 150 nm in which the particle size distribution is sharp, a mean secondary particle size (mean aggregated particle size) of 200 to 500 nm, and a granular primary particle shape obtained by the same process and the same raw material. The present inventors have also found that if the alumina powder of the present invention is used as an abrasive in a polishing composition for aluminum disk, comprising an abrasive, water and a polishing accelerator, a polished surface of higher quality can be obtained as compared with the conventional polishing material for aluminum. disk, and the alumina powder has high speed polishing property.
In addition, the present inventors have found that if an alumina mixed abrasive is prepared by adding the alumina powder having a single or multiple alumina crystal structure selected from the group consisting of &gg
Ema Kiyomi
Kasai Toshio
Nishimura Tohru
Ota Isao
Marcheschi Michael
Nissan Chemical Industries Ltd.
Oliff & Berridg,e PLC
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