JPH10121034A - Composition for polishing magnetic disk substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a compsn. for polishing magnetic disk substrates which has a good polishing capability by using fine zirconium oxide particles having specified state and particle sizes together with an aluminum nitrate polishing accelerator and water. SOLUTION: This compsn. comprises fine zirconium oxide particles, a polishing accelerator, and water and can polish NiP-plated magnetic disk substrates at a high speed. The particles used are in the state of secondary particles, i.e., aggregates of primary particles, and the average secondary particle size is 0.1-1μm and the average primary particle size, 0.001-0.3μm (the smaller, the better). Pref. the particles are produced by a wet process followed by baking and crystallization. Aluminum nitrate is esp. pref. as the accelerator. Pref. the particles are contained in an amt. of 2-20wt.% in the compsn., and the accelerator, in an amt. of 1-20wt.%. A magnetic disk obtd. from a substrate polished with the compsn. has a low surface roughness and is free from the occurrence of polishing scratchs, pits, and missing pulse errors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing composition for a magnetic disk substrate, and more particularly to a polishing method 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. To a composition for use.

[0002]

2. Description of the Related Art Magnetic disks (memory hard disks) are widely used as storage means that can be accessed at high speed in external storage devices of computers and word processors. This magnetic disk has N surface on the surface of Al alloy disk.
A substrate obtained by electrolessly plating iP was used as a substrate, and after polishing the surface of the substrate, a Cr alloy base film, a Co alloy magnetic film, and a carbon protective film were coated by sequential sputtering.
If a protrusion having a height equal to or higher than the flying height of the magnetic head remains on the surface of the magnetic disk, the magnetic head flying at a high speed while flying at a predetermined height may collide with the protrusion and cause damage. If the magnetic disk substrate has protrusions or polishing scratches, C
Even when coated with an r-alloy base film or Co alloy magnetic film, projections appear on the surface and defects due to polishing scratches occur, and the magnetic disk surface does not become a highly accurate smooth surface, so it is necessary to improve the accuracy of the disk surface. Requires precise polishing of the substrate.

[0003] For this reason, various polishing compositions have been studied in which the projections are eliminated or the height thereof is reduced as much as possible in the polishing of the substrate, and polishing scratches are not generated. Conventionally proposed (1) JP-A-60-1084
89 (two-stage polishing method using aluminum oxide containing an oxidizing agent such as sodium hypochlorite and colloidal aluminum oxide or cerium dioxide);
-291674 (a method of adding sulfamic acid or phosphoric acid to alumina), (3) JP-A-62-25187 (a method of adding aluminum nitrate to alumina), (4) JP-A-1-188264 (a method of adding boehmite to alumina) Method), (5) JP-A-1-2055973 (method of adding a metal salt and boehmite to alumina), (6) JP-A-Hei2
(158) (a method of adding metal nitrite to alumina), (7) JP-A-2-158683 (a method of adding an ammonium salt of boehmite, inorganic acid or organic acid to alumina), (8) JP-A-3-106984 ( Method using alumina slurry pre-treated with an ultrasonic filter),
(9) JP-A-3-115383 (method of adding boehmite and water-soluble peroxide to alumina), (10) JP-A-4-115383
-108887 (a method of adding an amino acid to alumina), (11) JP-A-4-27587 (alumina to aluminum sulfate, aluminum chloride and peroxide, nitric acid,
(12) JP-A-4-363385 (a method of adding a chelate compound, boehmite and aluminum salt to alumina), and (13) JP-A-5-271647 (a method of adding alumina). Method of adding boehmite produced by heat treatment of primary particles having angular gibbsite), (14) JP-A-7-2400
25 (a method of adding colloidal particles of a chemical corrosive and silica).

[0004] Among these known techniques, (1) to (1)
3) uses an alumina or aluminum compound of about 1 μm as an abrasive, so that it can be polished with such an accuracy that collision of projections on a magnetic disk can be avoided in the flying height of a conventional magnetic head, but it has recently become remarkable. The high level of surface accuracy required by the increasing recording density has not been achieved. On the other hand, (14) uses colloidal particles of silica of several tens of nm as an abrasive, so that surface accuracy can be easily achieved, but the polishing rate is low, so that the required mass productivity is not sufficient. There is a problem that the outer peripheral portion is excessively polished (referred to as surface sagging).

[0005]

The basis for considering a polishing composition is an abrasive. In general, when a material having a high hardness as a material is used as an abrasive, there is an inherent problem that polishing scratches are easily generated during polishing. It is necessary to select a polishing material having an appropriate hardness in consideration of the hardness of the NiP plating surface on the surface of the magnetic disk substrate. Considering the quality (degree of polishing scratches and pits) required of the low flying height type aluminum magnetic disk, a submicron abrasive having a sharp particle size distribution is required. As described in the section of the prior art, α-alumina is generally used as an abrasive for polishing an aluminum magnetic disk substrate. However, α alumina is Ni
When α-alumina is used as an abrasive for low-flying height aluminum magnetic disks, it is necessary to strictly define the crystal structure, particle size distribution, etc. of α-alumina because the hardness is significantly higher than that of the P-plane. . In order to obtain alumina fine particles industrially, fine pulverization is usually performed. However, there is a problem that the production yield of necessary particles is low and the productivity of alumina fine particles is poor.

On the other hand, when silica is used as an abrasive, the hardness of the silica is low, so that polishing scratches are hardly generated on the disk substrate, but the polishing rate is low and there is a problem in productivity. Next, regarding the surface accuracy of the magnetic disk, the average roughness (Ra)
It is not only a matter of the presence or absence of a protrusion, but also whether an error occurs or not in a write / read inspection in a predetermined format described later. It has been confirmed by recent analysis that this error is caused by polishing scratches or polishing pits remaining in the polishing process, and it is required to solve these problems.

The present invention provides a polishing composition for a magnetic disk substrate which has a small surface roughness of a magnetic disk, does not generate protrusions or polishing scratches, can have a high recording density, and can be polished at a high speed. Things. This polishing composition can be applied to a substrate for high recording density (500 Mbit / inch ² or more in recording density) typified by, for example, a magnetic disk for a magnetic head utilizing the magnetoresistance (MR) effect, but has a magnetic property of less than that. It can be effectively applied to discs from the viewpoint of improving reliability.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the use of alumina and silica as abrasives as described above, and have found that zirconium oxide fine particles are regarded as abrasives. Was found to be excellent, and the present invention was achieved. That is, the present invention is a composition for polishing a magnetic disk substrate, comprising water, zirconium oxide fine particles, a polishing accelerator or a water-soluble oxidizing agent.

In making the present invention, the inventor first examined which level of polishing scratches and polishing pits would cause an error when reading a magnetic disk. Magnetic disks prototyped by various polishing methods were inspected with a glide certifier tester RQ3000 manufactured by Hitachi DECO, and the frequency of read errors and the state of the magnetic disk surface were precisely compared and examined. The measurement conditions of the tester were as follows. Track width 3 μm Recording density Flux variation per inch 70,000 Head flying height 2.0 μinch (50.8 nm) Slice level 65% Those that do not reach this slice level, that is, those whose output waveform is less than 65% of the input waveform Treated as a missing pulse error, the depth and size of the polishing flaw and the depth and size of the polishing pit corresponding to the missing pulse error were determined. The number of missing pulse errors was also determined. The depth of the polishing scratches and polishing pits was determined by using an optical unevenness inspection device (Topo-3D manufactured by WYKO, a three-dimensional non-constant surface profiler), and the maximum depth that did not cause a missing pulse error was measured. It was measured. As a result, it was found that scratches and pits having a depth of 15 nm or less had no problem in recording / reproducing to / from a magnetic disk. As a result, a polishing scratch and a polishing pit having a depth of 15 nm or less were accepted.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The abrasive used in the present invention is zirconium oxide fine particles. The fine particles preferably have an average secondary particle diameter of 0.1 to 1.0 μm and a sharp particle size distribution. Zirconium oxide fine particles exist in the form of secondary particles, which are aggregates of fine primary particles. For the primary particles, the particle diameter (average value of the major and minor axes) is determined from an SEM photograph, and for the secondary particles, the particle size can be measured with a laser diffraction particle size analyzer. The polishing action of zirconium oxide largely depends on the secondary particles, and the polishing action increases as the secondary particles become larger. On the other hand, polishing scratches not only tend to occur when the secondary particles are large, but also tend to occur when the primary particles are large. Therefore, it is considered that secondary particles having a size within a certain range and small primary particles are preferable as having a large polishing action and preventing generation of polishing scratches.

In the present invention, the zirconium oxide fine particles preferably have an average particle diameter of 1.0 μm or less as secondary particles in order to prevent polishing scratches. Further, in order to enhance the polishing effect, the secondary particle diameter is preferably 0.1 μm or more in average particle diameter. And when the secondary particles are in the above range,
The primary particles have an average particle size in the range of 0.001 to 0.3 μm, and among these, smaller ones are preferable. Regarding the particle size distribution of the zirconium oxide particles, even if the average particle size is the same, a large particle size distribution will include large particles,
A sharp particle size distribution is preferable since it causes polishing scratches. For example, 90% by weight of the secondary particles in the particle size distribution is cumulative.
It is particularly preferable that the ratio D90 / D10 of the particle diameter of the particles to the particle diameter of 10% by weight is within 3.0.

Next, a method for producing zirconium oxide particles will be described. Since zirconium oxide is fine particles,
The production method is preferably a wet method, for example, a method of hydrolyzing a Zr alkoxide compound, ZrOCl ₂ , Zr (NO ₃ ) _4, or the like. For example, when an alkaline compound such as aqueous ammonia is added to these compounds and hydrolyzed to a pH of 0 to 4, a colloidal sol is obtained. This sol is further neutralized with ammonia, etc.
Is set to 7 to 8, the colloidal sol aggregates and precipitates. The obtained precipitate is washed with water and filtered to remove ammonium chloride and hydrochloric acid.

After washing, the precipitate collected by filtration is dried to obtain a colloidal zirconium oxide precursor (hydrate of zirconium or amorphous zirconium oxide). Next, the colloidal zirconium oxide precursor is fired to obtain crystalline zirconium oxide. The firing temperature of this precursor is 4
00-1100 degreeC is preferable. If the calcination temperature is lower than 400 ° C., crystallization of zirconium oxide is insufficient.
If the temperature exceeds 100 ° C., the crystal diameter (primary particles and secondary particles) of the zirconium oxide particles increases, and the polishing performance decreases.

It is preferable that the crystalline zirconium oxide powder obtained by firing has a sharp particle size distribution as described above, if necessary, by classification or filtering. This zirconium oxide powder is dispersed in water to form a slurry. The dispersion method is preferably a method in which zirconium oxide powder and water are put into, for example, a ball mill and rotated to sufficiently pulverize the powder. By this method, the dispersibility of the zirconium oxide fine particles in water is improved, and a stable slurry can be obtained.

In the polishing composition of the present invention, zirconium 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. Aluminum nitrate (Al (NO ₃ ) ₃ ), aluminum sulfate (A
l ₂ (SO ₄ ) ₃ ), aluminum oxalate (Al ₂ (C ₂
O ₄ ) ₃ ), iron nitrate (Fe (NO ₃ ) ₃ ), aluminum lactate (Al (C ₃ H ₅ O ₃ ) ₃ ), gluconic acid (C ₆
H ₁₂ O _7), malic acid (C ₄ H ₆ O ₅₎ or the like is used. Of these, aluminum salts are preferred, and aluminum nitrate is particularly preferred. The polishing accelerator chemically acts on the substrate such as a corrosive action, and a mechanical polishing action of zirconium oxide is added to the chemical, thereby greatly improving the polishing efficiency. Further, addition of a water-soluble oxidizing agent in addition to the polishing accelerator is also effective in improving the polishing performance. Hydrogen peroxide (H ₂ O ₂ ), nitric acid, potassium permanganate (KMnO ₄ ), perchloric acid (HCl)
O ₄ ), sodium perchlorate (NaClO ₄ ), sodium hypochlorite (NaClO) and the like are used. Since the effect is not increased even if the concentration is too high, 10% by weight or less is appropriate.

The composition for polishing a magnetic disk substrate of the present invention is basically a slurry composed of the above-mentioned zirconium oxide fine particles, a polishing accelerator and water, and a water-soluble oxidizing agent is further added if necessary. However, a surfactant, a preservative, and an acid or an alkali for pH adjustment may be added. Preferred pH when an acidic salt of aluminum such as aluminum nitrate is used as a polishing accelerator
Ranges from 2 to 5. The concentration of each component in the polishing composition of the present invention is preferably 2 to 20% by weight of zirconium oxide. If it is less than 2% by weight, the polishing rate is low, and a long time is required for polishing. If it exceeds 20% by weight, the polishing rate does not increase and it is economically disadvantageous.

The addition amount of the polishing accelerator is 1 to 20% by weight, preferably 2 to 15% by weight. If the addition amount of the polishing accelerator is less than 1% by weight, the polishing rate decreases, and the polishing time required for polishing a predetermined amount increases, 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 an amount of 15% by weight or more, there is no adverse effect on the polished surface.
% By weight is determined to be the upper limit. The above-mentioned respective component concentrations are the concentrations when polishing the magnetic disk substrate. When a polishing composition is manufactured and transported, it is efficient to use a composition having a concentration higher than the above concentration and dilute it to the above concentration before use.

The magnetic disk substrate on which the polishing composition of the present invention is used is NiP-plated, Ni-Cu-P-plated,
Examples are an o-P plated aluminum (including alloy) plate, an anodized aluminum plate, and the like. The polishing method is a method in which a polishing pad generally used for a slurry-like abrasive is rubbed on the surface of a magnetic disk substrate, and the pad or the substrate is rotated while supplying slurry between the pad and the substrate. A magnetic disk made from a substrate polished with the polishing composition of the present invention has very few protrusions and scratches, and has a surface roughness (Ra) of about 3 to 5 °, and is excellent in smoothness.

[0019]

EXAMPLES In a 2 liter beaker, zirconium oxychloride _{(ZrOCl 2 · 8H 2 O)} 250g, pure water 26
After mixing 0 ml and 2.8 N ammonia water 320 ml, the mixed solution was transferred to a 1 liter glass autoclave, and heated and pressurized at 130 ° C. for 7 hours with stirring. After the solution was cooled to room temperature, the reaction solution was taken out, and the entire reaction solution was a milky white colloidal sol and passed through filter paper. When this sol is neutralized with aqueous ammonia to a pH of 7 to 8, the colloidal sol aggregates and precipitates, and can be washed and filtered. Ammonium chloride and hydrochloric acid produced by repeating water washing and filtration three times Was removed. After washing, the precipitate collected by filtration was dried at 150 ° C. for 3 hours to obtain 104 g of a colloidal zirconium oxide precursor powder. The specific surface area of this precursor is 1
It was 76.8 m ² / g. Then 90 g of this precursor
Was fired in an alumina crucible at 500 ° C. for 30 minutes to obtain zirconium oxide powder. The obtained powder was identified as a monoclinic phase batterite by the identification of the crystal phase by X-ray diffraction. The specific surface area of this powder was 65.8 m ² / g.
The average particle size of the primary particles of the powder particles was 0.05 μm by SEM measurement, and the average particle size of the secondary particles was 0.37 μm by laser particle size measurement. In the particle size distribution of the zirconium oxide secondary particles, the ratio D90 / D10 between the cumulative particle size of 90% by weight and the particle size of 10% by weight is about 2.8. This particle size distribution was measured by a measuring instrument SALD-2000 manufactured by Shimadzu Corporation. This fired powder 80
g was placed in a 0.7 liter nylon pot mill together with 187 ml of pure water and zirconium oxide balls having a diameter of 5 mm, and the mixture was disintegrated and dispersed at a pot rotation speed of 80 rpm for 96 hours. After the crushing was completed, the pH of the dispersion slurry recovered from the pot was 4.9 due to HCl remaining in a small amount.
This zirconium oxide slurry, even after standing for one week,
The dispersion was stable with only a slight precipitate visible. In the pulverization, the zirconium oxide particle size hardly changes, so that the primary and secondary particle sizes of the zirconium oxide particles in the slurry are the above values.

The alumina used in the comparative example was obtained by finely pulverizing α-alumina, and had an average particle diameter of 0.8 μm. Colloidal silica is NS-2 manufactured by Nissan Chemical Industries, Ltd. and has a particle size of about 0.06 μm. The magnetic disk substrate used for polishing was a 3.5 inch (95 mm) diameter, 0.8 mm thick NiP plated aluminum alloy disk. This substrate was polished under the following conditions. After polishing, the substrate was washed and dried, the weight loss before and after polishing was measured, and the polishing rate was expressed as the thickness (μm) polished per unit time (min).

(Polishing conditions) Polishing machine; 4-way double-side polishing machine SFDL-
98-PP (manufactured by Speed Fam Co., Ltd.) (platen diameter 640)
mmφ) Polishing pad; Suede type (Polytex DG Rodale Co., Ltd.) Lower platen rotation speed: 60 rpm Slurry (coarse composition for polishing) supply amount: 50 ml / min Working pressure: 50 g / m ^{2 On the} polished substrate A 100-nm-thick Cr layer, a 25-nm-thick Co ₈₆ Cr ₁₂ Ta ₂ magnetic layer and a 15-nm-thick carbon protective film are formed by a DC sputtering device. Finally, a lubricant (perfluoropolyether-based lubricant) is added. Each was coated to a thickness of 2 nm to produce a magnetic disk.

The surface roughness (Ra) of the magnetic disk was measured by Taristep and Taridata 2000 (both manufactured by Rank Taylor Hobson). The presence or absence of polishing scratches on the magnetic disk was visually determined in a dark room under the light of a halogen lamp. The surface defect was measured by a differential interference microscope (50 times) and expressed by the number of pits existing on one surface of the magnetic disk. The rising characteristics of the magnetic head were measured for each magnetic disk. When the flying height of the head was lowered using the glide certifier tester, the height at which the head started to collide with the projection was measured and defined as the flying height. The glide-certifier tester described above was used to check the recording / reproduction of the magnetic disk for any problems.
The number of missing pulse errors was measured using a head at 5%.

Examples 1 to 16 Polishing compositions containing zirconium oxide, aluminum nitrate and the like in the proportions shown in Table 1 were prepared. In Table 1, the balance is water. Comparative Examples 1 and 2 Comparative Example 1 is an example using alumina as an abrasive, and Comparative Example 2 is an example using colloidal silica. Using the polishing compositions of these Examples and Comparative Examples, the substrate was polished, the polishing rate was measured, polishing flaws were visually observed, the surface roughness, the number of pits were measured, and then the magnetic field was measured. After the disk was formed, the flying height of the magnetic head and the missing pulse error were measured. Table 2 shows the results.

[0024]

[Table 1]

[0025]

[Table 2]

As can be seen from the above results, when alumina is used as the abrasive, the polishing rate is high but the surface roughness of the magnetic disk is large, polishing scratches and pits are generated, the flying height of the magnetic head is large, and the Many pulse errors.
When colloidal silica is used as an abrasive, there is no problem in magnetic properties and the like, but the polishing rate is low. On the other hand, the polishing composition of the present invention satisfied all the characteristics, and provided an overall excellent effect.

[0027]

The polishing composition of the present invention can polish a magnetic disk substrate at a high polishing rate, and a magnetic disk using the substrate has a small surface roughness, does not generate polishing scratches and pits, and has a recording property. And no missing pulse error in reproduction. Also, the flying height of the magnetic head is small. This indicates that there is no protrusion or the protrusion is very small on the surface of the magnetic disk. For this reason, for example, it is possible to provide a high-recording-density magnetic disk using an MR head.

Claims (8)

[Claims] 1. A polishing composition for a magnetic disk substrate, comprising water, zirconium oxide fine particles and a polishing accelerator. 2. A polishing composition for a magnetic disk substrate, comprising water, zirconium oxide fine particles, a polishing accelerator and a water-soluble oxidizing agent. 3. The average particle diameter of the zirconium oxide fine particles is 0.1 to 1.0 μm for secondary particles and 0.001 for primary particles.
The polishing composition according to claim 1, wherein the thickness is from 0.3 to 0.3 μm. 4. The polishing composition according to claim 1, wherein the concentration of the zirconium oxide fine particles in the polishing composition is 2 to 20% by weight. 5. The polishing composition according to claim 1, wherein the polishing accelerator is an aluminum salt. 6. The polishing composition according to claim 1, wherein the aluminum salt is aluminum nitrate. 7. The polishing composition wherein the concentration of the polishing accelerator is 1%.
The polishing composition according to any one of claims 1 to 6, wherein the amount is from 20 to 20% by weight. 8. The polishing composition according to claim 2, wherein the concentration of the water-soluble oxidizing agent in the polishing composition is 10% by weight or less.