Abrasive tool making process – material – or composition – With inorganic material – Clay – silica – or silicate
Reexamination Certificate
2001-01-31
2002-09-24
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
Clay, silica, or silicate
C106S003000, C252S079200, C252S079400, C510S167000, C216S096000, C216S089000, C216S103000
Reexamination Certificate
active
06454820
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polishing composition. More particularly, the present invention relates to a polishing composition which improves a polishing rate, and reduces surface roughness (Ra) and waviness (Wa), thereby giving a high-quality polished surface; a polishing process using the polishing composition; a magnetic disc substrate having improved surface smoothness; and a process for manufacturing the magnetic disc substrate.
2. Discussion of the Related Art
There have been ever increasing demands for improving the recording density of the hard disc, and in order to reduce the floating amount of the magnetic head, it has been required to improve the degree of flatness (surface smoothness) of the disc substrate. Concretely, there have been required to have such surface smoothness that each of the surface roughness (Ra) and the waviness (Wa) of the disc substrate is 3 Å or less. Especially, it has been a great concern to reduce waviness which causes breakdown of the magnetic disc devices or causes errors in read-write of information. Conventionally, in order to obtain a desired surface smoothness, there has been carried out a process comprising polishing a substrate with a polishing liquid comprising abrasive grains such as alumina, and thereafter further polishing with a polishing liquid comprising silica particles having finer sizes as abrasive grains. However, the polishing liquid using the silica particles has a defect of slow polishing rate, so that a further improvement in the polishing rate has been required. For instance, there have been proposed a process comprising adding a compound such as iron citrate, iron oxalate or iron chloride to a polishing liquid comprising abrasive grains composed of silica particles in Japanese Patent Laid-Open No. Hei 11-167711; a process comprising adding a colloidal silica and a compound such as iron citrate, ammonium iron citrate or ammonium iron oxalate in Japanese Patent Laid-Open No. Hei 10-204416; and the like. In both methods, the improvements in the polishing rate is insufficient.
An object of the present invention is to provide a polishing composition which can increase a polishing rate and give little surface defects such as scratches and pits, and improves surface smoothness such as surface roughness (Ra) and waviness (Wa); a polishing process using the polishing composition; a magnetic disc substrate having improved surface smoothness such as surface roughness (Ra) and waviness (Wa); and a process for manufacturing the magnetic disc substrate.
These and other objects of the present invention will be apparent from the following description.
SUMMARY OF THE INVENTION
According to the present invention, there are provided:
[1] a polishing composition comprising silica particles, water, and Fe salt and/or Al salt of a polyaminocarboxylic acid;
[2] the polishing composition according to item [1] above, further comprising an inorganic acid and/or an organic acid;
[3] a polishing process comprising applying the polishing composition of item [1] or [2] above;
[4] a process for manufacturing a magnetic disk substrate, comprising the step of polishing a substrate with the polishing composition of item [1] or [2] above; and
[5] a magnetic disk substrate manufactured by applying the polishing composition of item [1] or [2] above.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a metal salt of a polyaminocarboxylic acid (Fe salt and/or Al salt) is used, from the viewpoints of improving the surface smoothness such as surface roughness (Ra) and waviness (Wa), and increasing the polishing rate. The polyaminocarboxylic acid moiety of the metal salt of a polyaminocarboxylic acid has a multidentate ligand for forming a chelate compound by binding with a metal ion, and has two or more carboxyl groups. The molecular weight of the polyaminocarboxylic acid is preferably from 80 to 1000, more preferably from 140 to 600, from the viewpoints of increasing the polishing rate, suppressing precipitation of metal ions, and improving the solubility. In addition, the number of carboxyl groups of the polyaminocarboxylic acid is preferably 3 or more, from the viewpoint of increasing the polishing rate, and that the number of carboxyl groups is preferably 10 or less, more preferably 8 or less, more preferably 6 or less, from the viewpoint of improving the solubility. Concrete examples of the polyaminocarboxylic acid include ethylenediaminetetraacetic acid, hydroxyethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenettiaminepentaacetic acid, triethylenetetraminehexaacetic acid, 4 dicarboxymethyl glutamic acid, hydroxyethylimino diacetic acid, dihydroxyethyl glycine, 1,3-propanediamine tetraacetic acid, 1,3-diamino-2-hydroxypropane tetraacetic acid, and the like. Among them, ethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenetiiaminepentaacetic acid, dicarboxymethyl glutamic acid and 1,3-propanediamine tetraacetic acid are preferable, and ethylenediaminetetraacetic acid is especially preferable.
In addition, as the metal ions usable for the metal salt of a polyaminocarboxylic acid, Fe ions and Al ions are preferable, from the viewpoints of increasing the polishing rate of the polishing composition and preventing the reduction of dispersibility of the silica abrasive grains. Fe ions are more preferable, and Fe ions with a valence number of 3 are especially preferable. In addition, the metal salt may be those containing ammonium ions or sodium ions, from the viewpoint of improving the solubility. In the present specification, the Fe salt of a polyaminocarboxylic acid refers to any salts containing iron atom, encompassing not only iron salts but also iron sodium salts and iron ammonium salts. The same can be said for the Al salt, and it encompasses not only aluminum salts but also aluminum sodium salts and aluminum ammonium salts.
Preferred examples of the metal salt of a polyaminocarboxylic acid include iron ethylenediaminetetraacetate, aluminum ethylenediaminetetraacetate, aluminum ammonium ethylenediaminetetraacetate, iron diethylenetriaminepentaacetate, iron 1,3-propanediamine tetraacetate, aluminum diethylenetriaminepentaacetate, aluminum 1,3-propanediamine tetraacetate, iron ammonium ethylenediaminetetraacetate, iron sodium ethylenediaminetetraacetate, iron ammonium 1,3-propanediamine tetraacetate, iron ammonium diethylenetriaminepentaacetate, iron sodium diethylenetiaminepentaacetate, and the like. In addition, these polyaminocarboxylates can be previously formed into a necessary metal salt, or a desired salt can be obtained by mixing an inorganic acid salt such as nitrate, sulfate or phosphate, or an organic acid salt such as acetate, each inorganic salt or organic salt containing these metals, with a polyaminocarboxylic acid and/or a polyaminocarboxylate of other than an Fe salt and an Al salt to carry out chelate exchange in the polishing composition.
The content of the metal salt of a polyaminocarboxylic acid is preferably 0.02% by weight or more, more preferably 0.05% by weight or more, still more preferably 0.1% by weight or more, especially preferably 0.5% by weight or more, of the polishing composition, from the viewpoint of increasing the polishing rate, and the content of the metal salt is preferably 20% by weight or less, more preferably 15% by weight or less, still more preferably 10% by weight or less, especially preferably 5% by weight or less, of the polishing composition, from the viewpoints of reducing the surface roughness and waviness, and reducing the surface defects such as pits and scratches, thereby improving the surface quality. The content is preferably from 0.02 to 20% by weight, more preferably from 0.05 to 15% by weight, still more preferably from 0.1 to 10% by weight, especially preferably from 0.5 to 5% by weight.
In the present invention, silica particles are used, from the viewpoints of reducin
Fujii Shigeo
Hagihara Toshiya
Naito Koichi
Birch & Stewart Kolasch & Birch, LLP
Kao Corporation
Marcheschi Michael
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