JP2024109435A - Abrasive composition for magnetic disk substrates and method for polishing magnetic disk substrates - Google Patents

Abstract

To provide an abrasive composition for a magnetic disk substrate that contains intermediate alumina, improves a polishing rate, and can reduce defects and scratches on a surface of the substrate such as a magnetic disk substrate after polishing.SOLUTION: An abrasive composition for a magnetic disk substrate contains alumina particles and water. The alumina particle has α-alumina and intermediate alumina. An average particle diameter of the α-alumina is in a range of 0.2 to 0.8 μm. An average particle diameter of the intermediate alumina is in a range of 0.02 to 0.4 μm. A ratio of the average particle diameter of the intermediate alumina for the average particle diameter of the α-alumina is in a range of 0.1 to 0.6. A mass ratio between the α-alumina and the intermediate alumina is in a range of 90:10 to 50:50.SELECTED DRAWING: None

Description

The present invention relates to an abrasive composition for magnetic disk substrates and a method for polishing magnetic disk substrates. More specifically, the present invention relates to an abrasive composition for magnetic disk substrates used for polishing electronic components such as semiconductors and magnetic recording media such as hard disks, and in particular to an abrasive composition for magnetic disk substrates used for polishing the surfaces of substrates for magnetic recording media such as glass magnetic disk substrates and aluminum magnetic disk substrates.

The present invention further relates to an abrasive composition for magnetic disk substrates, which is used for polishing the surface of an aluminum magnetic disk substrate for magnetic recording media, the substrate surface of which is made of an aluminum alloy and has an electroless nickel-phosphorus plating film formed thereon, and a method for polishing magnetic disk substrates, such as glass magnetic disk substrates and aluminum magnetic disk substrates, using the abrasive composition for magnetic disk substrates.

Conventionally, from the viewpoint of productivity, abrasive compositions in which alumina particles are dispersed in water, which can achieve high polishing rates, have been used as abrasive compositions for polishing the surface of electroless nickel-phosphorus plating films on aluminum magnetic disk substrates.

In order to improve the polishing speed and reduce waviness and surface roughness, it has been proposed to use alumina particles with various crystal structures in polishing compositions that use alumina-based abrasive grains, thereby achieving both improved polishing speed and high polished surface quality, such as reduced waviness and surface roughness.

Patent Document 1 proposes that by using an abrasive composition containing alumina abrasive grains of a given size, such as γ, δ, or θ type, it is possible to increase the polishing rate and obtain a polished surface of higher quality than before.

Patent Document 2 proposes that by using an abrasive composition containing intermediate alumina, which is an alumina other than α-alumina, it is possible to reduce surface defects and improve the polishing rate.

Patent Document 3 proposes that a high polishing rate can be achieved and waviness can be reduced by using an abrasive composition containing α-alumina and intermediate alumina. However, the waviness reduction effect is insufficient, and improvements are required.

Patent Document 4 proposes that when polishing a magnetic recording medium substrate with an abrasive composition containing an abrasive, a polishing aid, and water, the polishing speed can be improved and the surface roughness can be reduced by using an aliphatic organic sulfate as the polishing aid. However, this proposal is insufficient in improving the polishing speed and reducing the surface roughness, and improvements are required.

Japanese Patent Application Publication No. 11-268911 JP 2001-89746 A JP 2005-23266 A International Publication No. WO 1998/021289

However, as in Patent Documents 1 to 4, when a magnetic disk substrate is polished using an abrasive composition to which intermediate alumina has simply been added, it is problematic in that it is not possible to simultaneously improve the polishing rate and reduce defects and scratches on the substrate surface after polishing.

In view of the above, the present invention aims to provide an abrasive composition for magnetic disk substrates that contains intermediate alumina and is capable of improving the polishing rate while reducing defects and scratches on the surface of a substrate such as a magnetic disk substrate after polishing, and a method for polishing a magnetic disk substrate.

As a result of intensive research into the above-mentioned problems, the inventors of the present application have found that the above-mentioned problems can be solved by adopting the following abrasive composition for magnetic disk substrates and a method for polishing magnetic disk substrates using the abrasive composition for magnetic disk substrates.

[1] An abrasive composition for magnetic disk substrates, comprising alumina particles and water, the alumina particles containing α-alumina and intermediate alumina, the average particle size of the α-alumina being in the range of 0.2 to 0.8 μm, the average particle size of the intermediate alumina being in the range of 0.02 to 0.4 μm, the ratio of the average particle size of the intermediate alumina to the average particle size of the α-alumina being in the range of 0.1 to 0.6, and the mass ratio of the α-alumina to the intermediate alumina being in the range of 90:10 to 50:50.

[2] The abrasive composition for magnetic disk substrates according to [1], wherein the average particle size of the α-alumina is in the range of 0.38 to 0.5 μm, the average particle size of the intermediate alumina is in the range of 0.07 to 0.2 μm, and the ratio of the average particle size of the intermediate alumina to the average particle size of the α-alumina is in the range of 0.1 to 0.5.

[3] The abrasive composition for magnetic disk substrates described in [1] above, in which the alumina particles are ground using a grinding aid.

[4] The abrasive composition for magnetic disk substrates according to [3], wherein the grinding aid is a phosphorus-containing inorganic compound or a phosphorus-containing organic compound.

[5] The abrasive composition for magnetic disk substrates according to [4], wherein the phosphorus-containing inorganic compound is a phosphorus-containing inorganic acid and/or a salt thereof, and the phosphorus-containing inorganic acid and/or a salt thereof is at least one compound selected from phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, tripolyphosphoric acid, and/or a salt thereof, or sodium hexametaphosphate.

[6] The abrasive composition for magnetic disk substrates according to the above [4], wherein the phosphorus-containing organic compound is an organic phosphonic acid and/or a salt thereof, and the organic phosphonic acid and/or a salt thereof is at least one compound selected from 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, α-methylphosphonosuccinic acid, and/or a salt thereof.

[7] The abrasive composition for magnetic disk substrates according to [1] above, further comprising an acid and/or a salt thereof, and having a pH value (25°C) in the range of 0.1 to 4.0.

[8] The abrasive composition for magnetic disk substrates according to [1] above, further containing an oxidizing agent.

[9] The abrasive composition for magnetic disk substrates described in [1] above is used in a multi-stage polishing method for polishing a magnetic disk substrate for a magnetic recording medium, the magnetic disk substrate having an electroless nickel-phosphorus plating film formed on the surface of an aluminum alloy substrate, and is used in a pre-stage polishing performed prior to the final polishing of the magnetic disk substrate.

[10] A method for polishing a magnetic disk substrate, comprising the following steps (1) to (3), said steps (1) to (3) being carried out using a single polishing machine, wherein an abrasive composition for magnetic disk substrates according to any one of [1] to [9] above is used as abrasive composition A in step (1):
Step (1): Supplying abrasive composition A to a polishing machine to perform pre-stage polishing of a magnetic disk substrate; Step (2): Rinse the magnetic disk substrate obtained in step (1); Step (3): Supplying abrasive composition B containing colloidal silica and water to a polishing machine to perform post-stage polishing of a magnetic disk substrate.

The abrasive composition for magnetic disk substrates of the present invention contains intermediate alumina and has the excellent effect of improving the polishing rate and reducing defects and scratches on the surface of a substrate such as a magnetic disk substrate after polishing. The method for polishing a magnetic disk substrate of the present invention involves polishing a magnetic disk substrate using the abrasive composition for magnetic disk substrates of the present invention.

The following describes the embodiments of the present invention, but the present invention is not limited to the following embodiments. It should be understood that modifications and improvements to the following embodiments, based on the ordinary knowledge of those skilled in the art, fall within the scope of the present invention, as long as they do not deviate from the spirit of the present invention.

1. Abrasive Composition for Magnetic Disk Substrate The abrasive composition for magnetic disk substrate of the present invention (hereinafter simply referred to as "abrasive composition") is characterized in that it is an aqueous composition comprising alumina particles and water, and further comprising an acid and/or a salt thereof, and an oxidizing agent as other optional components.

2. Alumina Particles The alumina particles constituting the polishing composition of the present invention are composed of "α-alumina particles" and "intermediate alumina" which is an alumina other than α-alumina particles. Here, examples of intermediate alumina other than α-alumina include γ-alumina, δ-alumina, and θ-alumina.

It is generally known that α-alumina has a higher degree of crystallinity and higher hardness than intermediate alumina. Therefore, when α-alumina is used as a polishing composition, scratches tend to form on the surface of the object to be polished, such as a substrate (substrate surface).

On the other hand, intermediate aluminas such as γ-alumina, δ-alumina, and θ-alumina are known to have a lower degree of crystallinity and lower hardness than the above-mentioned α-alumina. Therefore, when intermediate alumina is used as a polishing composition, it is less likely to scratch the substrate surface, but the polishing rate tends to be lower than that of α-alumina. Therefore, by taking into account the advantages and disadvantages of both α-alumina and intermediate alumina and using them together, an abrasive composition that is excellent in polishing rate and has a good balance of leaving a good surface condition of the polished object after polishing is prepared.

Here, the production of alumina particles will be described in more detail. The main alumina raw materials used for producing alumina particles are well known to be gibbsite: Al ₂ O _{3.3H 2} O, boehmite: Al ₂ O _{3.H 2} O, pseudoboehmite: Al ₂ O _{3.nH 2} O (n = 1 to 2), etc. These alumina raw materials are prepared by the methods described below, respectively, to produce desired alumina particles.

( ₁ ) _Gibbsite : _Al2O3.3H2O
It is obtained by dissolving bauxite in a hot solution of sodium hydroxide, removing the insoluble components by filtration, cooling the resulting solution and drying the resulting precipitate.

( ₂ ) _Boehmite : _Al2O3.H2O
It is obtained by hydrolysis of aluminum alkoxide: Al(OR) ₃ , which is obtained by reacting metallic aluminum with alcohol.

(3) Pseudoboehmite: Al ₂ O _{3.nH 2} O (n=1 to 2)
It is obtained by treating gibbsite with water vapor in an alkaline atmosphere.

By further calcining the product obtained by any of the above (1) to (3) at a high temperature, α-alumina, etc. can be obtained.

The average particle size of α-alumina, which is part of the alumina particles constituting the polishing compound composition of the present invention, is in the range of 0.2 to 0.8 μm, and preferably in the range of 0.38 to 0.5 μm. In this specification, the "average particle size of α-alumina" is sometimes expressed as "D50α". If the average particle size of α-alumina is 0.2 μm or less, the polishing rate decreases, which is undesirable from the viewpoint of productivity. On the other hand, if the average particle size of α-alumina exceeds 0.8 μm, defects and scratches are likely to occur on the substrate surface after polishing, causing problems in terms of surface precision.

It is known that the average particle size of commercially available α-alumina is usually on the order of several tens of μm. The abrasive composition of the present invention uses α-alumina that has been obtained and further pulverized to adjust the average particle size so that it falls within the range of the average particle size specified for the abrasive composition of the present invention.

The grinding of α-alumina is not particularly limited, and it is possible to use ordinary grinding machines such as ball mills, vibration mills, and jet mills that are well known in the art, and either dry grinding or wet grinding can be used.

To explain the grinding process in detail, for example, when performing the grinding process by wet grinding, a slurry liquid in which the α-alumina to be ground is slurried with water is used. In this case, when adjusting the average particle size of the α-alumina to 0.5 μm or less, a grinding aid may be further added to the abrasive composition of the present invention in order to prevent a decrease in grinding efficiency due to an increase in the viscosity of the α-alumina slurry liquid.

The grinding aid added to the abrasive composition is not particularly limited, but may be, for example, a phosphorus-containing inorganic compound and/or a phosphorus-containing organic compound, as in the grinding process for intermediate alumina described below.

On the other hand, the average particle size of intermediate alumina, which is part of the alumina particles constituting the abrasive composition of the present invention, is in the range of 0.02 to 0.4 μm, and preferably in the range of 0.07 to 0.2 μm. In this specification, the "average particle size of intermediate alumina" is sometimes referred to as "D50 intermediate."

When the average particle size of intermediate alumina is 0.4 μm or less, intermediate alumina can easily penetrate into the gaps between α-alumina particles, making it possible to reduce unevenness caused by polishing and reducing waviness and scratches on the substrate surface after polishing.

In addition, the mass ratio of α-alumina to intermediate alumina contained in the alumina particles can be in the range of α-alumina:intermediate alumina = 90:10 to 50:50.

Here, by making the mass ratio of intermediate alumina at least 10 mass% or more, the gaps between the α-alumina particles can be filled, and as described above, by reducing the gaps between the particles, it is possible to reduce polishing unevenness and reduce defects such as waviness and scratches on the substrate surface after polishing. On the other hand, by making the mass ratio of intermediate alumina not exceed 50 mass%, it is possible to maintain the frequency and number of contacts between the α-alumina and the substrate surface at a specified level or higher, and suppress a decrease in the polishing rate.

The average particle size of commercially available intermediate alumina is known to be typically on the order of several tens of μm. The abrasive composition of the present invention uses intermediate alumina that has been obtained and further pulverized to adjust the average particle size to fall within the range of the average particle size specified in the present invention. Here, the intermediate alumina can be pulverized using a conventional pulverizer such as a ball mill, which is well known in the art, in the same manner as in the pulverization of α-alumina described above, and either dry pulverization or wet pulverization can be used.

When wet grinding intermediate alumina, as with the wet grinding of α-alumina described above, if the average particle size is adjusted to 0.5 μm or less, a decrease in grinding efficiency due to an increase in the viscosity of the intermediate alumina slurry liquid may be observed. In particular, when the average particle size of intermediate alumina is 0.45 μm or less, the viscosity of the intermediate alumina increases significantly, making subsequent grinding processing difficult.

Therefore, in order to suppress the increase in viscosity of intermediate alumina, a grinding aid may be further added to the abrasive composition of the present invention, as in the grinding process of α-alumina. It is known that the phenomenon of increasing viscosity as the grinding process progresses is particularly noticeable in intermediate alumina compared to α-alumina.

The grinding aid added to the intermediate alumina is preferably, for example, a phosphorus-containing inorganic compound and/or a phosphorus-containing organic compound, and among these, a phosphorus-containing organic compound is particularly preferred from the viewpoint of suppressing the increase in viscosity of the intermediate alumina.

Specific examples of phosphorus-containing inorganic compounds include phosphorus-containing inorganic acids and/or salts thereof. Specific examples of phosphorus-containing inorganic acids and/or salts thereof include at least one compound selected from phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, tripolyphosphoric acid, and/or salts thereof, or sodium hexametaphosphate.

Among the above, sodium hexametaphosphate is particularly preferably used. By using sodium hexametaphosphate as a grinding aid to carry out grinding, the increase in viscosity of the intermediate alumina that accompanies the progress of grinding is suppressed, and intermediate alumina with a small particle size can be efficiently obtained.

On the other hand, specific examples of phosphorus-containing organic compounds include organic phosphonic acids and/or salts thereof. Specific examples of organic phosphonic acids and/or salts thereof include at least one compound selected from 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, α-methylphosphonosuccinic acid, and/or salts thereof.

Among the above, 1-hydroxyethylidene-1,1-diphosphonic acid and the sodium salt of 1-hydroxyethylidene-1,1-diphosphonic acid are particularly preferred. By using such 1-hydroxyethylidene-1,1-diphosphonic acid and/or the sodium salt of 1-hydroxyethylidene-1,1-diphosphonic acid as a grinding aid to carry out grinding, the increase in viscosity of the intermediate alumina that accompanies the progress of grinding is suppressed, and intermediate alumina with a small particle size can be efficiently obtained.

The grinding aid may further comprise a combination of the phosphorus-containing inorganic acid and/or its salt and an organic phosphonic acid and/or its salt. For example, sodium hexametaphosphate and 1-hydroxyethylidene-1,1-diphosphonic acid (salt) may be used in combination.

In addition, the ratio of the average particle size of intermediate alumina (D50 intermediate) to the average particle size of alpha-alumina (D50α) satisfies the condition "D50 intermediate/D50α = 0.1 to 0.6", preferably in the range of 0.1 to 0.5, and particularly preferably in the range of 0.1 to 0.3.

By keeping the D50 midpoint/D50α value at 0.6 or less, it is possible to reduce surface defects and scratches on the substrate surface after polishing while maintaining a high polishing rate.

This is believed to be due to the following mechanism. That is, because the average particle size of low-hardness intermediate alumina is smaller than the average particle size of high-hardness alpha-alumina, the low-hardness intermediate alumina can easily penetrate into the gaps between the particles of high-hardness alpha-alumina, reducing unevenness in the polishing of the substrate surface and suppressing the occurrence of scratches and surface defects without compromising the polishing power of alpha-alumina.

On the other hand, when the average particle size of low-hardness intermediate alumina is larger than that of high-hardness α-alumina, the contact frequency and contact pressure of α-alumina with the substrate surface are both reduced, and therefore the polishing rate is presumably lower. However, the present invention is not limited to these presumptions.

The concentration of the alumina particles, including α-alumina and intermediate alumina, in the polishing composition of the present invention is preferably in the range of 1 to 50 mass %, more preferably in the range of 2 to 40 mass %. By making the concentration of the alumina particles 1 mass % or more, it is possible to suppress a decrease in the polishing rate, while by making the concentration of the alumina particles 50 mass % or less, it is possible to suppress the unnecessary use of alumina particles, and polishing can be performed under economically advantageous conditions with reduced polishing costs.

3. Acid and/or Salt Thereof The polishing compound of the present invention may contain an acid and/or a salt thereof for pH adjustment or as an optional component. Examples of the acid and/or a salt thereof used herein include inorganic acids and/or salts thereof, and organic acids and/or salts thereof.

Inorganic acids and/or salts thereof include inorganic acids and/or salts thereof such as nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, phosphonic acid, pyrophosphoric acid, and tripolyphosphoric acid. On the other hand, organic acids and/or salts thereof include aminocarboxylic acids and/or salts thereof such as glutamic acid and aspartic acid, carboxylic acids and/or salts thereof such as citric acid, tartaric acid, oxalic acid, nitroacetic acid, maleic acid, malic acid, and succinic acid, and organic phosphonic acids and/or salts thereof. One or more of these acids and/or salts thereof can be used.

The organic phosphonic acid and/or its salt may be at least one compound selected from 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, α-methylphosphonosuccinic acid, and salts thereof.

It is also a preferred embodiment to use two or more of the above compounds in combination. Specific examples include a combination of sulfuric acid and/or a salt thereof with an organic phosphonic acid and/or a salt thereof, and a combination of phosphoric acid and/or a salt thereof with an organic phosphonic acid and/or a salt thereof.

4. Oxidizing Agent The polishing composition of the present invention may further contain an oxidizing agent as a polishing accelerator. The oxidizing agent may be a peroxide, permanganic acid or a salt thereof, chromic acid or a salt thereof, peroxoacid or a salt thereof, halogen oxoacid or a salt thereof, oxygen acid or a salt thereof, or a mixture of two or more of these oxidizing agents.

Specific examples include hydrogen peroxide, sodium peroxide, barium peroxide, potassium peroxide, potassium permanganate, metal salts of chromate, metal salts of dichromate, persulfuric acid, sodium persulfate, potassium persulfate, ammonium persulfate, peroxolinic acid, sodium perborate, performic acid, peracetic acid, hypochlorous acid, sodium hypochlorite, calcium hypochlorite, etc. Among these, hydrogen peroxide, persulfuric acid and its salts, hypochlorous acid and its salts, etc. are preferred, and hydrogen peroxide is more preferred.

The oxidizing agent content in the polishing composition is preferably in the range of 0.01 to 10.0 mass%, and more preferably in the range of 0.1 to 5.0 mass%.

5. Other Additives The polishing composition of the present invention may contain other additives in addition to the above-mentioned components. Examples of other additives include conventionally known surfactants, water-soluble polymers, corrosion inhibitors, thickeners, dispersants, preservatives, and rust inhibitors.

6. Properties of the Polishing Agent Composition The pH value (25°C) of the polishing agent composition of the present invention is preferably in the range of 0.1 to 4.0, more preferably in the range of 0.5 to 3.0. When the pH value (25°C) of the polishing agent composition is 0.1 or more, surface roughness can be suppressed. On the other hand, when the pH value (25°C) of the polishing agent composition is 4.0 or less, a decrease in the removal rate can be suppressed.

The abrasive composition of the present invention can be used for polishing various electronic components such as magnetic recording media such as hard disks. In particular, it is suitable for polishing aluminum magnetic disk substrates. It is even more suitable for polishing aluminum magnetic disk substrates that have been electrolessly nickel-phosphorus plated. Electroless nickel-phosphorus plating is usually performed under conditions of a pH value (25°C) of 4 to 6. Under conditions of a pH value (25°C) of 4 or less, nickel tends to dissolve, making plating difficult. On the other hand, in polishing, for example, nickel tends to dissolve under conditions of a pH value (25°C) of 4.0 or less, so the polishing rate can be increased by using the abrasive composition of the present invention.

7. Method for polishing magnetic disk substrate The polishing compound composition of the present invention is suitable for use in polishing magnetic disk substrates for magnetic recording media, such as aluminum magnetic disk substrates and glass magnetic disk substrates, and is particularly suitable for use in polishing aluminum magnetic disk substrates having an electroless nickel-phosphorus plating film formed on the surface of an aluminum alloy substrate.

Furthermore, when polishing electrolessly nickel-phosphorus plated aluminum magnetic disk substrates (hereinafter referred to as aluminum disks) by a multi-stage polishing method, the composition is suitable for use in a polishing step (rough polishing step) prior to the final polishing step. In particular, the composition is suitable for use as abrasive composition A used in step (1) in a method for polishing a magnetic disk substrate in which the rough polishing steps consisting of the following steps (1) to (3) are carried out using the same polishing machine.
(1) a step of supplying an abrasive composition A to a polishing machine to perform a pre-stage polishing of a magnetic disk substrate; (2) a step of rinsing the magnetic disk substrate obtained in step (1); and (3) a step of supplying an abrasive composition B containing colloidal silica and water to the polishing machine to perform a post-stage polishing of the magnetic disk substrate.

A polishing method to which the abrasive composition of the present invention can be applied is, for example, a method in which a polishing pad is attached to the platen of a polishing machine, the abrasive composition of the present invention is supplied to the polishing surface of the object to be polished (e.g., an aluminum disk, etc.) or to the polishing pad, and the surface to be polished is rubbed with the polishing pad (known as polishing).

For example, when polishing the front and back surfaces of an aluminum disk simultaneously, one method is to use a double-sided polisher with polishing pads attached to both the upper and lower plates. In this method, the aluminum disk is sandwiched between the polishing pads attached to the upper and lower plates, an abrasive composition is supplied between the polishing surface and the polishing pad, and the two polishing pads are rotated simultaneously to polish the front and back surfaces of the aluminum disk. Any type of polishing pad can be used, including urethane, suede, and nonwoven fabric types.

The present invention will be described in detail below with reference to examples, but it goes without saying that the present invention is not limited to these examples and can be implemented in various forms as long as they fall within the technical scope of the present invention.

(1) Pulverization of Alumina The α-alumina and intermediate alumina used in Examples 1 to 6 and Comparative Examples 1 to 11 were each subjected to a pulverization treatment by wet pulverization using a ball mill. Commercially available α-alumina and intermediate alumina were used here, and the alumina was added to water as a dispersion medium so that the alumina concentration was 50 mass% for α-alumina and 30 mass% for intermediate alumina, and a grinding aid was further added in a ratio relative to the alumina solid content shown in Table 1 below, and then pulverization was performed.

The α-alumina in Comparative Example 2 and the intermediate alumina in Comparative Example 6 became highly viscous during the grinding process, making it difficult to continue grinding thereafter. As a result, it was not possible to obtain alumina with the expected average particle size, and it was therefore not possible to carry out the subsequent polishing test.

(2) Method for preparing abrasive composition Abrasive composition A used in the pre-stage polishing of step (1) in Examples 1 to 6 and Comparative Examples 1 to 11 was prepared so as to contain the materials shown in Table 1 in the amounts shown in Table 1. Here, abrasive composition A corresponds to the abrasive composition for magnetic disk substrates (abrasive composition) in the present invention.

The alumina particles used had an average particle size adjusted by the above-mentioned grinding process. The pH value (25°C) of the polishing agent composition A was 1.2, and the polishing agent composition B used in the polishing step subsequent to step (3) in Examples 1 to 6 and Comparative Examples 1 to 11 was a polishing agent composition of the same composition as shown in Table 1. The pH value (25°C) of the polishing agent composition B was 1.2. The results of the polishing test are shown in Table 2.

(3) Average particle size of alumina particles The average particle size of alumina particles was measured using a laser diffraction particle size distribution analyzer (SALD 2200, manufactured by Shimadzu Corporation). The average particle size of alumina particles is the average particle size (D50) at which the cumulative particle size distribution from the small particle size side based on volume becomes 50%. In this way, the average particle size of α-alumina (D50α) and the average particle size of intermediate alumina (D50 intermediate) were calculated.

(4) Average Particle Diameter of Colloidal Silica The particle diameter (Heywood diameter) of colloidal silica was measured as the Heywood diameter (diameter equivalent to a circle having a projected area) by photographing a field of view at a magnification of 100,000 times using a transmission electron microscope (TEM) (JEM2000FX (200 kV) manufactured by JEOL Ltd.) and analyzing the photograph using analysis software (Mac-View Ver. 4.0 manufactured by Mountec Co., Ltd.).

The average particle size of colloidal silica is the average particle size (D50) calculated by analyzing the particle sizes of approximately 2,000 colloidal silica particles using the method described above, and using the above analysis software (Mountec Co., Ltd., Mac-View Ver. 4.0) to determine the particle size at which the cumulative particle size distribution (accumulated volume basis) from the small particle size side is 50%.

(5) Polishing conditions (conditions for steps (1) to (3) in the polishing process)
(5-1) Step (1) Conditions for Pre-Polishing Polishing machine: 9B double-sided polishing machine manufactured by SpeedFam Co., Ltd. Polishing pad: P1 pad manufactured by FILWEL Co., Ltd. Platen rotation speed: Upper platen -7.5 rpm
Lower surface plate 22.5 rpm
Amount of polishing compound supplied: 100 ml/min
Polishing time: 4.5 minutes Processing pressure: 80g/ ^cm2
In the polishing step (1), abrasive composition A is used.

(5-2) Step (2) Rinse conditions Polishing machine: same as in the previous polishing Polishing pad: same as in the previous polishing Platen rotation speed: same as in the previous polishing Rinse liquid supply rate: 3 L/min
Rinse time: 20 seconds Processing pressure: 15 g/ ^cm2
In addition, pure water is used as the rinse liquid.

(5-3) Step (3) Polishing conditions for the second polishing stage Polishing machine: same as the first polishing stage Polishing pad: same as the first polishing stage Rotation speed of the platen: same as the first polishing stage Supply amount of the polishing agent composition: 100 ml/min
Polishing time: 80 seconds Processing pressure: 80g/ ^cm2
In the latter polishing step, abrasive composition B was used.

(6) Polishing Rate Ratio The polishing rate ratio is expressed as a relative value when the polishing rate value of Comparative Example 3 calculated using the following formula for calculating the polishing rate is set as 1 (reference).
Polishing rate (μm/min)=Amount of mass reduction of aluminum disk (g)/Polishing time (min)/Area of one side of aluminum disk (cm ² )/Density of electroless nickel-phosphorus plating film (g/cm ³ )/2×10 ⁴
(In the above formula, the area of one side of the aluminum disk is 69 cm ² , and the density of the electroless nickel-phosphorus plating film is 8.0 g/cm ³ .)

(7) Evaluation method for defects and scratches on the substrate surface (defect count ratio, L scratch count ratio)
After the latter stage polishing of step (3), the defects and scratches on the substrate surface were evaluated. First, a substrate full surface defect inspection machine (NS2000H manufactured by Hitachi High-Tech Fine Systems Co., Ltd.) was used to measure the defect count and L scratch count. Here, the defect count is the number of all the fine defects on the substrate surface that are detected, including the residue.

The measurement conditions for the defect count and the L scratch count are as follows. The defect count ratio and the L scratch count ratio are expressed as relative values when the respective values of Comparative Example 3 are set to 1 (standard).
Hi-Light 1, 2: 830V
scan pitch: 15μm
Inner/Outer Radius: 15.5-48.0mm
Positive Level: 100mV
White Spot Level: 0-500mV
Long Scratch Length: ≧3000μm

(8) Observation In comparison with Comparative Example 3 in which the average particle size of α-alumina (D50α) and the average particle size of intermediate alumina (D50 intermediate) are the same value (0.42 μm), Example 3 in which the average particle size of intermediate alumina is set to about half of the average particle size of α-alumina showed almost the same results in terms of polishing speed as Comparative Example 3, and the defect count and L scratch count were significantly improved. That is, it is presumed that, as in the mechanism shown above, intermediate alumina easily penetrates into the gaps between particles of α-alumina, and polishing unevenness is reduced.

On the other hand, in Comparative Example 7, in which the average particle size of α-alumina was made smaller than in Comparative Example 3, it was observed that the polishing rate was significantly lower than in Comparative Example 3, and the defect count and L scratch count were not improved to the same extent as in Example 3. From these results, it is presumed that the decrease in the polishing rate in Comparative Example 7 is due to the reduced contact frequency and contact pressure of the high-hardness α-alumina with the substrate surface.

Furthermore, it was confirmed that in Comparative Examples 4 and 5, in which the average particle size of the intermediate alumina was made larger than the average particle size of α-alumina, the polishing speed decreased compared to Comparative Example 3, and the defect count and L scratch count worsened. The decrease in polishing speed in Comparative Examples 4 and 5 is presumed to be due to the fact that the average particle size of the intermediate alumina became larger than the average particle size of α-alumina, resulting in a decrease in the frequency and contact pressure of the high-hardness α-alumina with the substrate surface. From the above results, it is recognized that under conditions in which the average particle size of the intermediate alumina is larger than the average particle size of α-alumina, the polishing speed, defect count, and L scratch count all deteriorate.

Comparative Example 1 is an example in which the average particle size of α-alumina is larger than that of Comparative Example 3, and while the polishing speed improves due to the larger particle size of the high-hardness α-alumina, the results show that both the defect count and L scratch count significantly worsen.

On the other hand, in Examples 1 and 2, the intermediate alumina is smaller than in Comparative Example 1, and the average particle size ratio of α-alumina and intermediate alumina (D50 intermediate/D50α) is 0.6 or less. The polishing speed shows the same performance as Comparative Example 1, and the defect count and L scratch count are improved compared to Comparative Example 1.

In Example 4, the average particle size ratio (D50 intermediate/D50α) was increased from 0.48 to 0.24 by further reducing the average particle size of the intermediate alumina in Example 3, and it was shown that the defect count and L scratch count were further improved.

Example 5 is the result of using the same mass ratio of α-alumina and intermediate alumina (α-alumina: intermediate alumina = 90:10) as Comparative Example 8, and changing the average particle size ratio (D50 intermediate/D50α) from 1.0 to 0.24, and the polishing speed shows the same performance, and the defect count and L scratch count are improved. On the other hand, Comparative Example 10, in which the mass ratio of α-alumina and intermediate alumina is 95:5, which falls outside the scope of the rights of the polishing compound composition of the present invention, shows a lower polishing speed than Example 5, and the defect count and L scratch count are worse.

Example 6 is the result of using the same mass ratio of α-alumina and intermediate alumina (α-alumina: intermediate alumina = 50:50) as Comparative Example 9, and changing the average particle size ratio (D50 intermediate/D50α) from 1.0 to 0.24, and shows the same polishing speed performance, and significant improvements in defect count and L scratch count. On the other hand, Comparative Example 11, in which the mass ratio of α-alumina and intermediate alumina is 40:60, which falls outside the scope of the rights of the polishing compound composition of the present invention, shows a lower polishing speed than Example 6, and the defect count and L scratch count are worse.

As already mentioned, the average particle size of commercially available α-alumina and intermediate alumina, which are relatively easy to obtain, is approximately several tens of μm. However, as in the polishing composition of the present invention, by performing a grinding process such as wet grinding to reduce the average particle size and further using a phosphorus-containing inorganic compound (e.g., sodium hexametaphosphate) as a grinding aid, it is possible to suppress the increase in viscosity of the alumina particles until the average particle size reaches approximately 0.5 μm. Although the polishing performance decreases, polishing tests can be performed as in Comparative Examples 1 and 5.

However, in both α-alumina and intermediate alumina, by performing the grinding process so that the average particle size was 0.5 μm or less, as clearly shown in Comparative Examples 2 and 6, even when a phosphorus-containing inorganic compound was used as a grinding aid, it was not possible to prevent the alumina particles from becoming highly viscous, and it was not possible to carry out a polishing test.

On the other hand, in both α-alumina and intermediate alumina, when the grinding process is performed to reduce the average particle size to 0.5 μm or less, it has been shown that by using a phosphorus-containing organic compound (e.g., 1-hydroxyethylidene-1,1-diphosphonic acid) as a grinding aid, it is possible to suppress the alumina from becoming highly viscous, making it possible to carry out polishing tests.

As explained above, the polishing compound composition of the present invention has alumina particles that contain α-alumina and intermediate alumina, and the ratio of the average particle size of α-alumina to the average particle size of intermediate alumina (D50 intermediate/D50α) is within a specific range, and the average particle sizes of α-alumina and intermediate alumina are each within a specific range, and the mass ratios of α-alumina and intermediate alumina are each within a specific range, thereby improving surface precision while maintaining a good balance between the performance of the polishing rate, defect count on the substrate surface, and L scratch count.

The abrasive composition of the present invention can be used for polishing electronic parts such as semiconductors and magnetic recording media such as hard disks. In particular, it can be used for polishing the surface of substrates for magnetic recording media such as glass magnetic disk substrates and aluminum magnetic disk substrates. Furthermore, it can be used for polishing the surface of aluminum magnetic disk substrates for magnetic recording media, which have an electroless nickel-phosphorus plating film formed on the surface of an aluminum alloy substrate.

Claims (10)

Alumina particles;
and water,
The alumina particles are
Contains alpha alumina and intermediate alumina,
The average particle size of the α-alumina is in the range of 0.2 to 0.8 μm;
The average particle size of the intermediate alumina is in the range of 0.02 to 0.4 μm,
the ratio of the average particle size of the intermediate alumina to the average particle size of the α-alumina is in the range of 0.1 to 0.6;
The abrasive composition for magnetic disk substrates comprises the α-alumina and the intermediate alumina in a mass ratio ranging from 90:10 to 50:50. The average particle size of the α-alumina is in the range of 0.38 to 0.5 μm;
The average particle size of the intermediate alumina is in the range of 0.07 to 0.2 μm;
2. The abrasive composition for magnetic disk substrates according to claim 1, wherein the ratio of the average particle size of said intermediate alumina to the average particle size of said α-alumina is in the range of 0.1 to 0.5. The alumina particles are
2. The abrasive composition for magnetic disk substrates according to claim 1, which is pulverized using a pulverization aid. The grinding aid is
4. The abrasive composition for magnetic disk substrates according to claim 3, which is a phosphorus-containing inorganic compound or a phosphorus-containing organic compound. The phosphorus-containing inorganic compound is
a phosphorus-containing inorganic acid and/or its salt;
The phosphorus-containing inorganic acid and/or its salt is
5. The abrasive composition for magnetic disk substrates according to claim 4, which is at least one compound selected from phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, tripolyphosphoric acid, and/or salts thereof, or sodium hexametaphosphate. The phosphorus-containing organic compound is
an organic phosphonic acid and/or its salt,
The organic phosphonic acid and/or its salt is
5. The abrasive composition for magnetic disk substrates according to claim 4, which is at least one compound selected from the group consisting of 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, α-methylphosphonosuccinic acid, and/or a salt thereof. Further comprising an acid and/or a salt thereof,
2. The abrasive composition for magnetic disk substrates according to claim 1, which has a pH value (25° C.) in the range of 0.1 to 4.0. The abrasive composition for magnetic disk substrates according to claim 1, further comprising an oxidizing agent. It is used in the multi-stage polishing of magnetic disk substrates for magnetic recording media, which have an electroless nickel-phosphorus plating film formed on the surface of an aluminum alloy substrate.
2. The abrasive composition for magnetic disk substrates according to claim 1, which is used in pre-stage polishing carried out prior to final polishing of the magnetic disk substrate. A method for polishing a magnetic disk substrate, comprising the following steps (1) to (3), the steps (1) to (3) being carried out using a single polishing machine:
10. A method for polishing a magnetic disk substrate, comprising using the abrasive composition for magnetic disk substrates according to any one of claims 1 to 9 as abrasive composition A in step (1).
Step (1): Supplying abrasive composition A to a polishing machine to perform pre-stage polishing of a magnetic disk substrate; Step (2): Rinse the magnetic disk substrate obtained in step (1); Step (3): Supplying abrasive composition B containing colloidal silica and water to a polishing machine to perform post-stage polishing of a magnetic disk substrate.