GB2385057A

GB2385057A - Polishing composition

Info

Publication number: GB2385057A
Application number: GB0229161A
Authority: GB
Inventors: Tomohide Kamiya; Junichi Hirano; Noboru Yasufuku; Noritaka Yokomichi; Toshiki Owaki
Original assignee: Fujimi Inc
Current assignee: Fujimi Inc
Priority date: 2001-12-20
Filing date: 2002-12-13
Publication date: 2003-08-13
Anticipated expiration: 2022-12-13
Also published as: CN1285686C; CN1427055A; GB0229161D0; MY131820A; JP4095798B2; GB2385057B; CN1854224A; JP2003183630A

Abstract

A polishing composition to be used for polishing a magnetic disk substrate, which comprises one member selected from a phosphate and a phosphorus compound, or two members selected from phosphoric acid, a phosphate and a phosphorus compound; silica; and water; wherein when phosphonic acid is contained alone aluminium nitrate is not contained. Another polishing composition is shown that comprises at least one member from a phosphoric acid, a phosphate and a phosphorus compound; silica; water; and diammonium ethylenediamine tetraacetate. The phosphorus compound may be pyrophosphoric acid, phosphonic acid, phosphinic acid, hydroxyethylidene diphosphonic acid, nitrotri(methylene phosphonic acid) or phosphonobutane tricarboxylic acid, or a salt thereof.

Description

c 2385057 - 1 - POLISHING COMPOSITION

The present invention relates to a polishing composition to be used for polishing a magnetic disk substrate. s In a process for producing a magnetic disk, it is common to carry out polishing by means of a polishing composition in order to remove waviness or irregularities of a magnetic disk substrate to make it flat and smooth.

As the polishing composition to be used for such lo polishing of a magnetic disk substrate, various compositions have been proposed wherein various abrasives are combined with polishing accelerators or other additives. The present inventors have closely examined the 15 surfaces of magnetic disk substrates polished by means of conventional polishing compositions, and have found new surface defects which are presently not yet recognized as particularly problematic but which are likely to be influential over the characteristics of magnetic disks in so future, as the surface precision required for magnetic

- 2 - disk substrates becomes stricter along with the demand for higher capacities of magnetic disks. Such surface defects are characterized in that (1) they are formed on a part of the surface or over the entire surface of a 5 magnetic disk substrate, (2) they are assemblages of fine scratches with depths of from about 3 to 7 nm, and (3) such scratches extend substantially in a certain specific direction (in many cases, in the radial direction of the magnetic disk substrate). However, at present, the lo causes for the formation of such defects have not yet been known.

It is an object of the present invention to provide a polishing composition which is capable of suppressing the formation of such surface defects having the above characteristics (1) to (3) which have been found anew by the present inventors.

In a first aspect, the present invention provides a polishing composition to be used for polishing a magnetic disk substrate, which 20 comprises (A) one member selected from a phosphate and a phosphorus compound, or two members selected from phosphoric acid, a phosphate and a phosphorus compound, (B) silica, and (C) water, wherein when phosphoric acid is contained alone as the compound of (A), (D) aluminum 25 nitrate is not contained.

In a second aspect, the present invention provides such a polishing composition which further contains (E)

diammonium iron ethylenediamine tetraacetate.

In a third aspect, the present invention provides a polishing composition to be used for polishing a magnetic disk substrate, which comprises (A) at least one member 5 selected from phosphoric acid, a phosphate and a phosphorus compound, (B) silica, (C) water, and (E) diammonium iron ethylenediamine tetreacetate.

Now, the present invention will be described in detail with reference to a preferred embodiment.

lo The polishing composition in this embodiment comprises (A) at least one member selected from phosphoric acid, a phosphate and a phosphorus compound, (B) silica, (C) water, and (E) diammonium iron ethylenediamine tetraacetate.

15 Firstly, the phosphoric acid, the phosphate and the phosphorus compound of component (A) will be described.

The phosphoric acid, the phosphate and the phosphorus compound will play a role as a polishing accelerator to polish a magnetic disk substrate by a 20 chemical action. Further, at the same time, they will play a role of suppressing the formation of the surface defects having the abovementioned characteristics (1) to (3), when a magnetic disk substrate is polished by means of the polishing composition of this embodiment. The 25 phosphoric acid, the phosphate and the phosphorus compound are considered to form a protecting film on the surface of the magnetic substrate and to suppress the

- 4 - formation of the above surface defects by the function of such a protective film.

In the polishing composition, at least one member selected from the phosphoric acid, the phosphate and the 5 phosphorus compound, is incorporated as the compound of (A). Namely, as the compound of (A), phosphoric acid, a phosphate, a phosphorus compound, or any one of combinations of phosphoric acid and a phosphate, phosphoric acid and a phosphorus compound, a phosphate 10 and a phosphorus compound, and phosphoric acid, a phosphate and a phosphorus compound, is incorporated. It is particularly preferred to incorporate at least two members in combination. It is most preferred to incorporate phosphoric acid and a phosphate, or 15 phosphoric acid and a phosphorus compound, in combination.

When phosphoric acid (H3PO4) is to be incorporated to the polishing composition, its amount is preferably from 0.001 to 0.5 mol/Q, more preferably from 0.01 to 0.2 molly, most preferably from 0.02 to 0.1 moldy so As a specific example of the phosphate, an ammonium salt (NH4H2PO4, (NH4)2HPO4, or (NH4)3PO4), a sodium salt, (NaH2PO4, Na2HPO4 or Na3PO4) or a potassium salt (KH2PO4, K2HPO4 or K3PO4) may be mentioned. In a case where such a phosphate is incorporated to the polishing composition in combination with phosphoric acid, the amount of phosphoric acid to be incorporated, is preferably from 50 to 150 mol%, more preferably from 75 to 125 mol%, most

- 5 preferably from 95 to 105 mol%.

The phosphorus compound may be selected from phosphoric acids, phosphoric acids and phosphinic acids. As a specific example of the phosphorus compound, pyrophosphoric acid, phosphoric acid, phosphinic acid, hydroxyethylidene diphosphonic acid (HEDP), nitrotri(methylenephosphonic acid) (NTMP) or phosphonobutane tricarboxylic acid (PBTC), or a salt thereof, may be mentioned. In a case where the phosphorus compound is incorporated to the polishing composition, its amount is preferably from 0.001 to 0.5 lo mol/0, more preferably from 0.01 to 0.2 mold, most preferably from 0.02 to 0.1 mol/Q.

Now, the silica of (B) will be described.

The silica (silicon dioxide) will play a role as an abrasive to polish a magnetic disk substrate by a 5 mechanical action. As a specific example of silica, colloidal silica, fumed silica or precipitated silica may be mentioned. Among them, colloidal silica is preferred.

The particle diameter of the silica is preferably from 5 to 200 nm, more preferably from 10 to 150 nm, most 20 preferably from 15 to 100 no, as an average particle size obtained from the surface area measured by a BET method.

The amount of the silica to be incorporated, is preferably from 0.1 to 40 wt%, more preferably from 1 to 30 wt%, most preferably from 3 to 25 wt%.

25 Now, the water of (C) will be described.

The water playing a role as a dispersing medium and a solvent, is preferably one containing impurities as

- 6 - little as possible. Specifically, one obtained by filtering deionized water, or distilled water, is preferred. Now, diammonium iron ethylenediamine tetraacetate of 5 (E) will be described.

The diammonium iron ethylenediamine tetraacetate (EDTA Fe 2NH4OH) will play a role as a polishing accelerator to polish a magnetic disk substrate by a chemical action. The amount of the diammonium iron 10 ethylenediamine tetraacetate to be incorporated, is preferably from 0.1 to 10 wt%, more preferably from 0.5 to 8 we%, most preferably from 1 to 5 wt%.

Now, the polishing composition comprising the above-

described (A) at least one member selected from 15 phosphoric acid, a phosphate and a phosphorus compound, (B) silica, (C) water and (E) diammonium iron ethylenediamine tetraacetate, will be described.

The polishing composition of this embodiment is prepared by mixing and dissolving or dispersing (A) at 20 least one member selected from phosphoric acid, a phosphate or a phosphorus compound, (B) silica and (E) diammonium iron ethylenediamine tetraacetate, in (C) water. The dispersing method is optional, and for example, stirring by a vane-type stirring machine or 25 ultrasonic dispersion may be mentioned.

Further, the pH of the polishing composition is preferably at least 1.5 and less than 7.

The polishing composition of this embodiment is used for polishing a magnetic disk substrate. Among magnetic disk substrates, it is preferably employed for polishing a Ni-P substrate having a nickel-phosphorus alloy 5 electroless-plated on the surface of a blank material.

However, the application of the polishing composition of this embodiment is not limited to the polishing of a Ni-P substrate, and it may, of course, be used for polishing magnetic disk substrates other than the NiP substrate, 0 such as a Ni-Fe substrate, a boron carbide substrate and a carbon substrate.

Further, the polishing composition of this embodiment is preferably employed for finish polishing in the polishing process of a magnetic disk substrate.

5 However, it may, of course, be used for polishing before the finish polishing.

Now, the effects obtainable by this embodiment will be described.

By the polishing composition of this embodiment, it 20 is possible to suppress the formation of surface defects having the above-mentioned characteristics (1) to (3) found anew by the present inventors. Further, such an effect can further be improved if two or more members selected from phosphoric acid, a phosphate and a 25 phosphorus compound, are used in combination, and the effect will still further be improved if phosphoric acid and a phosphate, or phosphoric acid and a phosphorus

compound, are used in combination.

Diammonium iron ethylenediamine tetraacetate which functions as a polishing accelerator, is incorporated, whereby the polishing efficiency (the stock removal rate) can be improved. Here, diammonium iron ethylenediamine tetraacetate does not influence the effect for suppressing the above-mentioned surface defects, whereby the polishing efficiency can be improved without impairing the effect for suppressing the surface defects.

10 On the other hand, in a case where an aluminum nitrate or the like which has been commonly employed as a polishing accelerator, is incorporated instead of diammonium iron ethylenediamine tetraacetate, the effect for suppressing the above surface defects will substantially decrease.

Further, the above-described embodiment may be modified as follows.

The polishing composition may be constituted by omitting diammonium iron ethylenediamine tetraacetate in the above-described embodiment.

20 However, JP-A-61-291674 discloses a polishing composition comprising phosphoric acid, colloidal silica and water. Accordingly, in the case where diammonium iron ethylenediamine tetraacetate is to be omitted, a case wherein phosphoric acid is used alone as the : compound of (A), shall not be included in the present invention. Further, JP-A-9-208934 discloses a polishing

- 9 composition which comprises phosphoric acid, fumed silica, water and aluminum nitrate. Accordingly, in the case where diammonium iron ethylenediamine tetraacetate is to be omitted, a case wherein phosphoric acid used alone as 5 the compound of (A) and aluminum nitrate is contained, shall not be included in the present invention.

Namely, to constitute the polishing composition by omitting diammonium iron ethylenediamine tetraacetate, means to change the constitution of the polishing lo composition so that it comprises (A) one member selected from a phosphate and a phosphorus compound, or two members selected from phosphoric acid, a phosphate and a phosphorus compound, (B) silica, and (C) water, wherein when phosphoric acid is contained alone as the compound of (A), (D) aluminum nitrate is not contained.

To the polishing composition of the above embodiment, various additives which are commonly used in conventional polishing compositions, may be incorporated.

The polishing composition may be prepared as a stock so solution having a relatively high concentration, so that it may be diluted with water at the time of using it for the polishing operation. By this construction, it is possible to improve the handling efficiency for the storage or the transportation.

25 Now, the present invention will be described in further detail with reference to Examples and Comparative Examples.

- 10 EXAMPLES 1 to 11 and COMPARATIVE EXAMPLES 1 to 5 Colloidal silica and various compounds as identified in the following Table 1 were mixed in deionized water to prepare the respective polishing compositions.

5 With respect to the polishing composition of each of Examples 1 to 11 and Comparative Examples 1 to 5, the pH was measured, and with respect to the following two items, measurements and evaluation were carried out. The results are show in Table 1.

0 1. Polishing efficiency Using the polishing composition of each Example, a magnetic disk substrate (a Ni-P substrate) was polished under the following polishing conditions, and the value of the polishing efficiency was obtained by the 15 calculation formula shown below. However, the value of the polishing efficiency in Table 1 is an average value of 10 sheets per batch.

Polishing efficiency (pm/min) = weight reduction (g) of the magnetic substrate by polishing. (surface area (cm2) 20 of the polished surface of the magnetic substrate x density (g/cm3) of nickel/phosphorus plating x polishing time (min)) x 10,000 Polishing conditions Substrate to be polished: A 3.5" (.95 mm) z5 electroless Ni-P substrate preliminarily polished so that the surface roughness Ra measured by Chapman 2000 PLUS (manufactured by Chapman Instruments) would be about 10 A,

- 11 machine: double surface polishing machine (SFDL-9B, manufactured by SpeedFam Co., Ltd.), polishing pad: BELLATRIX N0058 (manufactured by Kanebo, Ltd.), polishing pressure: 100 g/cm2 (-.10 kPa), lower platen rotational 5 speed: 20 rem, supply amount of the polishing composition: 30 ml/min, polishing time: 15 min 2. Surface defects The surface of the magnetic disk substrate after the polishing was observed by means of a differential 10 interference microscope (MX50, manufactured by Olympus Optical Co., Ltd., object lens: 5 magnifications, eye lens: 10 magnifications). A total of 20 surfaces including the front and rear surfaces of 10 magnetic disk substrates, were observed, whereby if the number of surfaces on which surface defects having the above-

mentioned characteristics (1) to (3) were observed, was not more than two surfaces, such was evaluated to be id, if from 3 to 5 surfaces, such was evaluated to be O. and if 6 surfaces or more, such was evaluated to be X.

U O O O _ O _ -0

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- 13 -

__ O X X X X

0 ret rat O O o o o o o _ O O Ln (A N 0 rn -1 C> Cat _ = one l l l l N 'O a of O 1 u H =m O I O =0 _ JJ h h h P P P Pg O X O X O X O X O X

V 1 V Iq V W V lull V 111

- 14 As shown in Table 1, with respect to each of the polishing compositions of Examples, the evaluation with respect to the surface defects, was good. Among them, when phosphoric acid and a phosphate were used in 5 combination, the evaluation with respect to the surface defects tended to be particularly good. Further, in Examples 9 to 11 wherein diammonium iron ethylenediamine tetraacetate was incorporated, a result was obtained which shows improvement of the polishing efficiency.

lo Now, the technical concept which can be grasped from the above Examples will be described.

A polishing composition comprising (A) one member selected from a phosphate and a phosphorus compound (excluding phosphoric acid) or at least two members selected from phosphoric acid, a phosphate and a phosphorus compound (inclusive of phosphoric acid), (B) silica and (C) water.

A polishing composition comprising phosphoric acid, silica and water, and not containing aluminum nitrate.

20 A polishing composition comprising (A) phosphoric acid and a phosphate, (B) silica, and (C) water. By this construction, it is possible to effectively suppress the formation of surface defects having the abovementioned characteristics (1) to (3) found anew by the present 25 inventors.

A polishing composition comprising (A) phosphoric acid and a phosphorus compound, (B) silica and (C) water.

- 15 By this construction, it is possible to effectively suppress the formation of surface defects having the above-mentioned characteristics (1) to (3) found anew by the present inventors.

5 The present invention has the above-described construction and thus provides the following effects.

According to the first to third aspects of the present invention, it is possible to suppress the formation of surface defects having the following lo characteristics (1) to (3) found anew by the present inventors. (1) They are formed on a part of the surface or on the entire surface of the magnetic disk substrate. (2) They are assemblages of fine scratches with depths of from about 3 to 7 nm. (3) The scratches extend substantially in a certain specific direction (in many cases, in the radial direction of the magnetic disk substrate). Further, according to the second and third aspects 20 of the present invention, it is possible to improve the polishing efficiency.

Claims

- 16 CLAIMS:

1. A polishing composition to be used for polishing a magnetic disk substrate, which comprises (A) one member selected from a phosphate and a phosphorus compound, or s two members selected from phosphoric acid, a phosphate and a phosphorus compound, (B) silica, and (C) water, wherein when phosphoric acid is contained alone as the compound of (A), (D) aluminum nitrate is not contained.

2. The polishing composition according to Claim 1,

lo which further contains (E) diammonium iron ethylenediamine tetraacetate.

3. A polishing composition to be used for polishing a magnetic disk substrate, which comprises (A) at least one member selected from phosphoric acid, a phosphate and a 5 phosphorus compound, (B) silica, (C) water, and (E) diammonium iron ethylenediamine tetraacetate.

4. The polishing composition according to any one of Claims 1 to 3, wherein the phosphorus compound is pyrophosphoric acid, phosphoric acid, phosphinic acid, 20 hydroxyethylidene diphosphonic acid, nitrotri(methylenephosphonic acid) or phosphonobutane tricarboxylic acid, or a salt thereof.

5. A polishing composition substantially as any one of the Examples herein.

6. A method of polishing a magnetic disk substrate using a polishing composition according to any one of claims l to 5.