WO2001000745A1

WO2001000745A1 - Composition for polishing substrate for magnetic disk and method for producing substrate for magnetic disk

Info

Publication number: WO2001000745A1
Application number: PCT/JP2000/004245
Authority: WO
Inventors: Norihiko Miyata
Original assignee: Showa Denko K.K.
Priority date: 1999-06-28
Filing date: 2000-06-28
Publication date: 2001-01-04
Also published as: AU5704300A; TW581803B; MY128169A; CN1152104C; CN1315991A

Abstract

A composition for polishing a substrate for a magnetic disk, which comprises water, fine titanium oxide particles and a polishing promoter, characterized in that 90 to 100 % of the titanium oxide constituting said particles has the same crystal structure; and a method for producing a substrate for a magnetic disk using the composition. The composition can be used for polishing a substrate for a magnetic disk, at an economical polishing rate, so as to have a reduced surface roughness and to become free from the occurrence of fine defects such as projections, scraches by abrasion and micropits.

Description

Description: Polishing composition for magnetic disk substrate and method for manufacturing magnetic disk substrate

The present invention relates to a polishing composition for a magnetic disk substrate, and more particularly to a polishing composition for a magnetic disk substrate capable of obtaining a highly accurate magnetic disk surface suitable for flying a magnetic head with a low flying height. The present invention relates to a composition and a method for producing a magnetic disk substrate. Background art

Magnetic disks (memory hard disks) are widely used as a means of accessing at high speed in external storage devices such as computers and word processors. A typical example of this magnetic disk is an A1 alloy substrate with NiP electrolessly plated on its surface as an original plate, and after polishing the surface of this original plate, a Cr alloy base film, a Co alloy magnetic film And a carbon protective film formed sequentially by sputtering.

By the way, if a protrusion having a height equal to or higher than the magnetic head flying height remains on the surface of the magnetic disk, the magnetic head flying at a high speed while flying at a predetermined height collides with the protrusion and is damaged. Cause. In addition, if the magnetic disk substrate has protrusions or polishing scratches, when Cr alloy base film or Co alloy magnetic film is formed, protrusions appear on the surface of those films, and defects due to polishing scratches occur. However, since the surface of the magnetic disk does not become a smooth surface with high accuracy, it is necessary to precisely polish the substrate in order to increase the accuracy of the disk surface.

Therefore, in polishing a magnetic disk substrate, many polishing compositions have been proposed as polishing compositions which eliminate projections or reduce the height thereof as much as possible and which hardly cause polishing scratches. For example, an abrasive that uses an alumina or aluminum compound with a particle size of about 1 μιη as abrasive grains can be polished with such accuracy that collision of projections on a magnetic disk can be avoided at the conventional magnetic head flying height. However, it has not been possible to achieve the high level of surface accuracy required for the increase in recording density, which has recently become remarkable.On the other hand, those using colloidal particles of silica of several tens of nm as abrasive grains have high surface accuracy. Accuracy is easy to achieve, but the polishing rate is low, so the required mass productivity is not sufficient, and if the polishing is performed for a long time, the outer peripheral portion will be polished excessively (called surface sagging).

On the other hand, the polishing composition described in Japanese Patent Application Laid-Open No. H10-112135 uses titanium oxide (titania) fine particles of sub-micron as abrasive grains, so that high surface precision and high polishing can be achieved. Speed is easy to achieve. In the composition of this patent, rutile-type titanium oxide is excellent in polishing efficiency because of its small crystal cell and dense and high in hardness, but is susceptible to polishing scratches. It is considered that the rutile type titanium oxide (rutilization ratio) is desirably 10 to 80%.

According to the above patent, titanium oxide having a rutile ratio of 10 to 80% is preferable.If titanium oxide having a different crystal structure is present, the disintegration or pulverization of fine particles is uniformly performed. And the particle size distribution is difficult to sharpen accurately. As a result, micro defects such as micro pits and micro scratches are generated at a low frequency, which causes a problem that the production yield of the substrate is deteriorated.

The quality required of a polishing composition for an aluminum magnetic disk substrate that enables high-density magnetic recording is to achieve a high-precision disk surface that enables low flying of the head. Disclosure of the invention

It is an object of the present invention to achieve high-density recording with low surface roughness of a magnetic disk, and no generation of fine defects such as protrusions, polishing scratches, micropits, and micro scratches, and at an economical speed. An object of the present invention is to provide a polishing composition for a magnetic disk substrate that can be polished and a method for manufacturing a magnetic disk substrate.

As a result of intensive studies, the present inventor has found that titanium oxide abrasives having different crystal structures do not coexist in many cases and have a single structure as much as possible so that the particle size distribution becomes sharper during crushing and pulverization. It has been found that a high-precision surface of a magnetic disk substrate that enables low flying height of the magnetic disk can be obtained, and that not only ordinary polishing scratches but also fine defects with particularly small polishing scratches can be prevented. The present invention is based on this finding. Titanium oxide has one of these crystal structures (single crystal structure) Any crystal structure may be used as long as the content is 90% or more.

That is, the present invention comprises at least water, titanium oxide fine particles, and a polishing accelerator, wherein the titanium oxide has a single crystal structure of titanium oxide in an amount of 90 to 100%. It is.

The method for producing a magnetic disk substrate of the present invention includes a step of supplying the polishing composition.

The polishing composition of the present invention can be used for a substrate for high recording density (typically, 1 GbitZnch) represented by a magnetic disk for a magnetic head utilizing the magnetoresistance (MR) effect.

^Two or more recording density having a) can be advantageously applied to, but can be effectively applied from the standpoint of improving reliability with respect to the magnetic disk to have a less recording density. BEST MODE FOR CARRYING OUT THE INVENTION

Conventionally, the depth of polishing scratches, which has been regarded as a problem on a magnetic disk substrate, is about 10 nm or more, but especially on a low-floating type hard disk substrate aimed at by the present invention. The presence of minute polishing flaws with a depth of about 5 nm that was not observed also causes errors in the magnetic properties and is judged to be outside the permissible range for practical use.

The titanium oxide fine particles contained as an abrasive in the polishing composition of the present invention have a single crystal structure of 90 to 100%. That is, 90 to 100% of any one of anatase type, rutile type, and brookite type titanium oxide is used. The remaining less than 10% may have another crystal structure. For example, anatase-type titanium oxide is 90% or more, and the remainder is less than 10% of rutile-type and / or brookite-type titanium oxide. If titanium oxide having a single crystal structure is less than 90%, that is, 10% or more of other crystal structures coexist, the particle size distribution becomes difficult to be sharp.

The crystal structure of titanium oxide can be identified by X-ray diffraction (using CuKct rays) as follows. The ratio of rutile titanium oxide can be calculated from the peak intensity ratio of the X-ray diffraction between the rutile (1 10) plane and the anatase (101) plane. Although the anatase (101) plane overlaps with the blue kite (1 20) plane, the blue kite (1 2 1) plane (relative strength 90%) does not overlap with all the anatase planes. The intensity of the blue kite (120) plane (100Z90 times) can be determined from the peak intensity and the peak intensity of the anatase (101) plane can be used to determine the content ratio of both.

In the present invention, the method for producing titanium oxide is not particularly limited, and the ilmenite or titanium slag is reacted with sulfuric acid, and the sulfuric acid method comprising the steps of dissolution, hydrolysis, and calcination, or rutile ore is heated red heat. After dehydration, a chlorine method is used in which titanium gas is vaporized as chloride by passing chlorine gas through a chlorine gas furnace heated to about 800 ° C, and this is directly pyrolyzed from titanium tetrachloride obtained by distillation. It is a target.

Regarding the crystal structure of titanium oxide, for example, in the case of a gas phase method produced by a mixed combustion method of titanium tetrachloride and oxygen, the anatase type is formed and stable at the lowest temperature. When this is heat-treated and burned, a bullish kite type at 816 to 1040 ° C is obtained, and a rutile-type structure is obtained at higher temperatures (Ichititanium acid, 3rd edition, RIKEN, p. 5 14-5 1 5).

Since titanium oxide having a single crystal structure of 90% or more is commercially available, it can be used in the present invention by adjusting the particle size by grinding or removing coarse particles as necessary.

In the particle size distribution of the titanium oxide used in the present invention, the particle size distribution of the secondary particles is such that the cumulative particle size is 90% by weight and the particle size is D 90 (the particle size of D 90 or less is 9 ° weight /.) And the cumulative value is 10 The ratio D 90ZD 10 with respect to the weight% of the particle diameter 1310 (the particle diameter of D 10 or less is 10 weight./.) Is preferably within 3 and more preferably within 2.7. The smaller the ratio, the sharper the particle size distribution.

As for the particle diameter of titanium oxide in the present invention, the secondary particles preferably have an average particle diameter of 0.1 to 1.0 / xm. The average particle diameter of the secondary particles is a value measured using a laser Dobler-frequency analysis type particle size distribution analyzer, Microtrac UPA150 (manufactured by Honeywell 11).

The polishing rate of titanium oxide fine particles largely depends on the secondary particle diameter, and as the secondary particle diameter increases, the polishing rate increases, but polishing scratches are more likely to occur, which may cause errors in magnetic properties. However, it is difficult to suppress the polishing scratches to a practically acceptable level as a low-floating hard disk substrate. Therefore, oxidation The average particle diameter of the secondary particles of tanium is preferably 1.0 μπι or less. On the other hand, the average particle diameter of the secondary particles is preferably 0.1 μπι or more from the viewpoint of increasing the polishing rate and reducing the surface sag.

Furthermore, even if the size of the primary particles is large, polishing flaws are liable to occur, and the average particle size of the secondary particles is within the above range and the primary particles are small. Since the polishing rate is high and polishing scratches can be prevented, the average primary particle diameter (average of major and minor diameters) determined from SEM photographs is in the range of 0.01 to 0.6 m. Is more preferred.

Regarding the concentration of titanium oxide in the polishing composition of the present invention, when the concentration is low, the polishing rate is low. The polishing rate increases as the concentration increases, but the weight is 15 weight. Beyond this, the rate of increase in polishing rate slows down. In consideration of economy, the upper limit is practically 20% by weight. Therefore, the concentration of titanium oxide in the polishing composition is preferably in the range of 2 to 20% by weight.

In the polishing composition of the present invention, titanium oxide has a mechanical polishing action. However, in order to further enhance the polishing efficiency, a polishing accelerator which chemically acts on the substrate is added. The polishing accelerator aluminum nitrate (A 1 (N_〇 ₃₎ _3), aluminum sulfate _{_{(A 1 2 (S0 4)}} 3), aluminum oxalate (A 1 _₂ (C ₂

0 _4)), iron nitrate (F e (N0 ₃₎₎ of aluminum lactate _{(A 1 (C 3 H 0} 3) 3), Darukon acid _{_{_{(C 6 H 12 0 7)}}} , malic acid (C ₄ Eta _beta 0 ₅ ) etc. are used. Of these, aluminum salts and nitrates are preferred, and aluminum nitrate is particularly preferred. These polishing accelerators may be used alone or in combination of two or more. The polishing accelerator chemically acts on the substrate such as a corrosive action, and the mechanical polishing action of titanium oxide is added to the chemical action, thereby greatly improving the polishing efficiency. Further, addition of a water-soluble oxidizing agent in addition to the polishing accelerator is also effective in enhancing the polishing performance. Hydrogen peroxide as the water-soluble oxidizing agent (H ₂ 0 _2), nitric acid, permanganic acid strength Riumu (KMn_〇 _4), perchloric acid (HC 10 _4), perchloric acid sodium (N a C 1 0 ₄ ), One or more of sodium hypochlorite (Na CIO) is used. Since the effect is not increased even if the concentration is too high, the concentration is suitably 10% by weight or less. The addition amount of the polishing accelerator is 0.1 to 20% by weight, preferably 1 to 15% by weight. If the addition amount of the polishing accelerator is less than 0.1% by weight, the polishing rate is reduced, and the polishing time required for polishing a predetermined amount is prolonged, thereby increasing the surface sag. When the addition amount is increased, the polishing rate increases up to 15% by weight, but the polishing rate does not increase even when the addition amount exceeds 15% by weight. Therefore, even if added in excess of 15% by weight, there is no adverse effect on the polished surface, but considering economics, 20% by weight is determined to be the upper limit.

The above-mentioned component concentrations are the concentrations when polishing the magnetic disk substrate. When a polishing composition is manufactured and transported, it is more efficient to use a composition II which is thicker than the above concentration, and dilute it to the above concentration before use.

The polishing composition for a magnetic disk substrate of the present invention comprises the aforementioned anatase-type titanium oxide 910%, rutile-type titanium oxide 910%, or brookite-type titanium oxide 910%. % Of titanium oxide, a polishing accelerator and water, and a water-soluble oxidizing agent is added if necessary.In addition, a surfactant, a preservative and an acid or alkali for adjusting pH are added. It can be accompanied by calories. When an acid salt of aluminum such as aluminum nitrate is used as the polishing accelerator, the preferred pH range is 25. If the pH is less than 2, corrosion of the polishing machine or the like will occur, and if it exceeds 5, the polishing efficiency will be impaired.

The polishing composition of the present invention can be prepared by suspending titanium oxide having the above crystal structure in water and adding a polishing accelerator or the like to water, similarly to the conventional polishing composition.

Although the magnetic disk substrate to which the polishing composition of the present invention is applied is not particularly limited, the composition of the present invention is applied to an aluminum substrate, particularly, for example, an aluminum substrate in which NiP is electrolessly plated. By applying the method, the mechanical polishing action by titanium oxide and the chemical polishing action by the polishing accelerator are combined, and a high-quality polished surface can be industrially advantageously obtained.

The polishing method is generally a method in which a polishing pad used for a slurry-like abrasive is rubbed on a magnetic disk original plate, and the pad or the original plate is rotated while supplying slurry between the pad and the original plate.

A magnetic disk made from a substrate polished by the polishing composition of the present invention is a magnetic disk. The frequency of occurrence of minute defects such as pit pits and micro scratches is extremely low, and the surface roughness (Ra) is about 3-5A, which is excellent in smoothness. Example

Hereinafter, examples of the present invention will be specifically described, but the present invention is not limited to these examples.

(Example:! ~ 16)

Showa Titanium Co., Ltd.'s high-purity titanium oxide, super titania F110 (98% by weight of rutile titanium oxide, anatase-type titanium oxide double weight ⁰ /.) And Supertitania F-4 (anatase-type titanium oxide 95 (Weight: rutile-type titanium oxide 5% by weight) was pulverized with a medium stirring mill to remove a small amount of coarse particles to obtain titanium oxide having an average particle diameter of 0.3 μπι. The crystal structure and content of titanium oxide were measured using RAD-2 2 manufactured by Rigaku Corporation. These are shown in Table 1 as Titania II and Titania II, respectively.

The particle diameter was measured with a laser Doppler frequency analysis type particle size distribution analyzer, Microtrack UPA150 (manufactured by Honeywell). Table 1 shows the measured particle size.

Next, the above-mentioned titanium oxide and a polishing accelerator as a polishing material, and optionally an oxidizing agent were further added in the proportions shown in Table 2, to prepare various aqueous polishing compositions, and the following polishing apparatus and polishing conditions were used. Was polished. When aluminum nitrate was used as a polishing accelerator, the pH value was 2.3 to 4.1. Polishing

Substrate used

Polishing equipment and polishing conditions using 3.5 inch aluminum disk with NiP electroless plating

Polishing test machine 4-way double-side polishing machine

Polishing pad suede type (Polytex DG, Dale mouth) Lower platen rotation speed 60 r pm

Slurry feed rate 5 Om 1 / min

Polishing time 5 min

Processing pressure 50 g / cm ² Evaluation of polishing characteristics

Polishing rate Converted from weight loss before and after polishing of aluminum disk Surface roughness Taristep, Taridata 2000 (made by Rank Taylor Hobson) is used

The depths of the polishing scratches and polishing pits were determined by three-dimensional mode analysis using a stylus-type surface analyzer P-12 (manufactured by TENCOR).

Table 2 shows the evaluation results of the polishing characteristics. The polishing flaw A in Table 2 has a polishing flaw depth of 5 nm or less, and the pit A has a pit depth of 5 nm or less. Polishing scratch B has a polishing scratch depth of 5 to 10 nm, and pit B has a pit depth of 5 to 10 nm. No abrasive scratch depth of more than 10 nm or pit depth of more than 10 nm occurred in any of the examples and comparative examples.

The same effect was obtained when the blue-kit type titanium oxide was 90 to 100%. (Comparative Examples 1 and 2)

Showa Titanium Co., Ltd.'s titanium oxide super titania F-1 (rutile titanium oxide 50 weight ⁰ /., Anatase titanium oxide 50 weight ⁰ /.) And F-2 (rutile titanium oxide 16 weight%) , Anatase-type titanium oxide (84% by weight), and aqueous polishing compositions shown in Table 2 were prepared and polished in the same manner as in Examples. The results are shown in Table 2. Table 1 shows the measured particle size. In the table, titania ③ represents F-2 above, and titania ④ represents F-1. Titanium oxide Primary particle diameter of titanium oxide Secondary particle diameter D 90 / type Crystal structure and content (average) (average) D 10

(β m) (β m) Titania-rutile type 0.2 0 0.3 2

98

Anatase type

2 Titania ② anatase type 0. 05 0. 3 2. 6

95

Rutile type

5 Titania ③ Rutile type 0.06 0.3 0.34

1 6

Anatase type

84 Titania rutile type 0.1 0.5 0.5

50

Anatase type

50

Table 2

Abrasives Polishing accelerators

表 Table [& さレレ⁰しレ⁰レ，種類種類種類種類種類種類種類種類種類種類種類

m l n) (A) 夹她 1 丄 titania ① 1 aluminum nitrate 5.0 Λ Λ

丄 / Λ

2 〃 5 II 5.00, 254 A A

10 // o.0 (J.b A A

〃 4 20 〃 5.0 .0 0.30 6 A A

5 〃 5 0.05 0.10 5 A A

"6 〃 5 〃〇. 1 ― 0.1 3 4 A A

"75 〃 1.0 .0-0.174 A A

〃 2.0 U. 1 A Λ Λ

Δ 丄 r o Ο ρ 5

〃 9 "5 10.0 .0 1 .29 4 A A

"10 Titania 5 II 5 .0 0.28 4 A A

"1 1 titania _{① 5 II 2. 0 H 2} 0 2 1. 0 0. 25 4 AA

1 2 〃 5 II 2.0

1 3 Titania 5 Aluminum oxalate 2.0 0.16 A A

"14 〃 5 iron nitrate 2.0 0 0.25 A A

"15 5 5 Aluminum lactate 2 • 0 0.1 5 A A

〃 16 〃 5 Dalconic acid 1 • 0 0.1 7 5 A A Comparative example 1 Titania ③ 5 Aluminum nitrate 5.0 0. 21 4 B B

〃 2 Titania ④ 5 〃 5. 0 0.23 6 BB

Industrial applicability

When a disk is polished using the polishing composition of the present invention, a polished surface having a low surface roughness and a very low frequency of occurrence of minute defects such as micropits and microscratch can be obtained, and at a high speed. Can be polished. A magnetic disk using a polished disk is useful as a low-floating type hard disk, and enables high-density recording.

In particular, it is highly useful as a high recording density medium (having a recording density of 1 Gbit / inch ² or more) typified by an MR head media utilizing the magnetoresistive effect of a magnetic disk using a polished disk. However, it is useful from the viewpoint that there is a highly reliable medium even in the lower media.

Claims

The scope of the claims

1. At least water, titanium oxide fine particles, and a polishing accelerator, wherein the titanium oxide contains 90 to 100% of titanium oxide having a single crystal structure, and is characterized in that it is used for polishing a magnetic disk substrate. Composition.

2. Cumulative 90% by weight particle size and 10% by weight in the particle size distribution of secondary titanium oxide fine particles. 2. The polishing composition according to claim 1, wherein the particle diameter ratio D90ZD10 of the particles is within 3.0.

3. The polishing composition according to claim 1, wherein the secondary particles of the titanium oxide fine particles have an average particle diameter of 0.1 to 1.0 μm.

4. The polishing composition according to any one of claims 1 to 3, wherein the polishing accelerator is an aluminum salt or a nitrate.

5. The polishing composition according to claim 4, wherein the aluminum salt is aluminum nitrate.

6. The polishing composition according to any one of claims 1 to 5, further comprising a water-soluble oxidizing agent.

7. A method for producing a magnetic disk substrate, comprising a step of supplying the polishing composition according to any one of claims 1 to 6 to the surface of a magnetic disk original plate.

8. While supplying the polishing composition according to any one of claims 1 to 6, between the magnetic disk master and the polishing pad, at least one of the magnetic disk master or the polishing pad is supplied. A method for manufacturing a magnetic disk substrate, comprising a step of rotating.