Abrasive composition for magnetic disk substrate and method for polishing magnetic disk substrate

Abstract

To provide an abrasive composition capable of realizing a high polishing speed without using alumina particles and good surface smoothness, especially a surface state where silica particles are not adhered by eliminating fine concave defects called "shallow pits".SOLUTION: An abrasive composition for magnetic disk substrates contains colloidal silica having an average particle size of 10 to 120 nm, wet type silica having an average particle size of 200 to 600 nm, an oxidizing agent, an acid, and water. A proportion of particles with a particle size of 30 to 70 nm in the colloidal silica is 10 to 90% by volume, a rate of the average particle size of the wet type silica to the average particle size of colloidal silica is in a range of 2.0 to 30.0, and the acid is a phosphorus-containing inorganic acid and / or a phosphorus-containing organic acid.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polishing agent composition for a magnetic disk substrate and a method for polishing a magnetic disk substrate, and more particularly to a polishing agent composition for a magnetic disk substrate (hereinafter simply referred to as "polishing agent composition") that can be used for polishing a magnetic disk substrate constituting electronic components such as magnetic recording media such as semiconductors and hard disks, and a method for polishing a magnetic disk substrate.

[0002] In particular, the present invention relates to a polishing agent composition that can be used for polishing the substrate surface of a magnetic disk substrate for a magnetic recording medium such as a glass magnetic disk substrate or an aluminum magnetic disk substrate, and a method for polishing a magnetic disk substrate. Further, the present invention relates to a polishing agent composition that can be suitably used for polishing an aluminum magnetic disk substrate having an electroless nickel-phosphorus plating film formed on the surface of a substrate made of an aluminum alloy, and a method for polishing a magnetic disk substrate using the polishing agent composition.

Background Art

[0003] Conventionally, as a polishing agent composition for polishing the surface of an electroless nickel-phosphorus plating film on an aluminum magnetic disk substrate, a polishing agent composition in which alumina particles having a relatively large particle size, which can achieve a high polishing rate, are dispersed in water has been widely used from the viewpoint of productivity such as production efficiency.

[0004] However, alumina particles have a physical property of higher hardness than the electroless nickel-phosphorus plating film formed on the substrate surface, and are held in a state where the alumina particles pierce the substrate surface during polishing. There is a problem that such alumina particles may affect the final polishing step (finishing polishing step) performed as the next step of the polishing process.

[0005] To solve the above problems, for example, the use of an abrasive composition in which components of alumina particles and components of silica particles are mixed at a predetermined ratio and combined has been proposed (see Patent Documents 1 to 4). Further, a polishing method using an abrasive composition that does not contain alumina particles and contains only components of silica particles has also been proposed (see Patent Documents 5 to 10).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Patent Document 10

Summary of the Invention

Problems to be Solved by the Invention

[0007] The abrasive compositions shown in the above Patent Documents 1 to 10, or the polishing methods using the abrasive compositions, may have the following problems.

[0008] For example, by using an abrasive composition that combines the components of alumina particles and silica particles shown in Patent Documents 1 to 4, it was possible to somewhat improve the penetration of alumina particles into the substrate surface of a magnetic disk substrate. However, since it contains at least alumina particles, the possibility of the alumina particles penetrating the substrate surface still remained. In addition, since the abrasive composition is composed of both components of alumina particles and silica particles, the characteristics of the individual particle components offset each other, and there was a problem that the characteristics of the abrasive composition such as polishing rate and surface smoothness decreased conversely.

[0009] Therefore, an abrasive composition composed only of silica particles without using alumina particles, and a polishing method using such an abrasive composition have been proposed. For example, a combination of colloidal silica and a polishing accelerator is known (see Patent Documents 5 and 6). Furthermore, polishing methods using colloidal silica, fumed silica, surface-modified silica, silica produced by the water glass method, etc., especially polishing methods using colloidal silica having a special shape have already been proposed (see Patent Documents 7 and 8). However, in the case of the proposed polishing methods above, there is a possibility that the polishing performance such as insufficient polishing rate is inferior compared to conventional abrasive compositions, and further improvement has been demanded.

[0010] Furthermore, a polishing method using an abrasive composition that combines colloidal silica and fumed silica has been proposed (see Patent Document 9). However, in the case of the polishing method using such an abrasive composition, although an improvement in the polishing rate is recognized, due to the low bulk specific gravity of fumed silica, it is difficult to make the abrasive composition into a slurry, which may affect workability. Furthermore, a polishing method has been proposed that can achieve a polishing rate close to that of using alumina particles by using crushed silica particles (see Patent Document 10). However, in the case of such a polishing method, there is a problem that the surface smoothness deteriorates compared to conventional abrasive compositions, and further improvement has been demanded.

[0011] Furthermore, in the polishing method using an abrasive composition containing only silica particles, silica particles may adhere to and remain on the surface of the substrate after the polishing step. Therefore, if the remaining silica particles cannot be removed even after cleaning the surface of the substrate after the polishing step, the workload in the final polishing step after the polishing step may be high. Therefore, it has been required to use an abrasive composition that does not adhere silica particles to the surface of the substrate after the polishing step or can be easily removed by a relatively simple cleaning operation.

[0012] Therefore, the present invention has been made in view of the problems of the above prior art, and without using alumina particles, it is possible to achieve a high polishing rate, and good surface smoothness, particularly eliminating fine concave defects called "shallow pits", and providing an abrasive composition capable of achieving a surface state without adhesion of silica particles, and a method for polishing a magnetic disk substrate using the abrasive composition.

Means for Solving the Problems

[0013] As a result of intensive studies by the inventors of the present application to solve the above problems, by using an abrasive composition containing colloidal silica and wet-process silica in combination, and further containing an oxidizing agent, a phosphorus-containing inorganic acid and / or a phosphorus-containing organic acid as an acid, and preferably a water-soluble polymer compound, it has been found that a high polishing rate, good surface smoothness, and particularly elimination of fine concave defects called shallow pits and a surface state without adhesion of silica particles can be achieved, and the abrasive composition and the method for polishing a magnetic disk shown below have been completed.

[0014] [1] Colloidal silica having an average particle size in the range of 10 to 120 nm, wet-process silica having an average particle size in the range of 200 to 600 nm, an oxidizing agent, an acid, and water and a water-soluble polymer compound and, the ratio of particles having a particle size of 30 to 70 nm in the colloidal silica is 10 to 90% by volume, the value of the ratio of the average particle size of the wet-process silica to the average particle size of the colloidal silica is in the range of 2.0 to 30.0, and the acid is a phosphorus-containing inorganic acid and / or a phosphorus-containing organic acidwhich is a copolymer having at least a monomer having a carboxylic acid group and a monomer having an amide group as essential monomers, and / or a copolymer having at least a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as essential monomers is wherein the average count number per field of view of silica adhesion on the substrate surface after the polishing process under the condition of an observation magnification of 20,000 times using a scanning electron microscope is 20 or less A polishing agent composition for a magnetic disk substrate.

[0015] [2] The polishing agent composition for a magnetic disk substrate according to [1], wherein the proportion of the particles having a particle diameter of 30 to 70 nm in the colloidal silica is in the range of 12 to 80% by volume.

[0016] [3] The polishing agent composition for a magnetic disk substrate according to [1] or [2], wherein the average particle diameter of the wet-process silica is in the range of 200 to 500 nm.

[0017] [4] The polishing agent composition for a magnetic disk substrate according to any one of [1] to [3], wherein the phosphorus-containing inorganic acid is at least one selected from the group consisting of phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, and tripolyphosphoric acid.

[0018] [5] The polishing agent composition for a magnetic disk substrate according to any one of [1] to [3], wherein the phosphorus-containing organic acid is at least one 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, and methanehydroxyphosphonic acid.

[0021] 6 The polishing agent composition for a magnetic disk substrate according to any one of [1] to 5 , wherein the pH value (25 °C) is in the range of 0.1 to 4.0.

[0022] 7 The polishing agent composition for a magnetic disk substrate according to any one of [1] to 6 , which is used for polishing an electroless nickel-phosphorus plated aluminum magnetic disk substrate as an object to be polished.

[0023] 8 The 7 ​​​A method for polishing a magnetic disk substrate using the abrasive composition for a magnetic disk substrate according to any one of [[ID=]], comprising a polishing step and a final polishing step performed after the polishing step, wherein the abrasive composition for a magnetic disk substrate is a method for polishing a magnetic disk substrate used in the polishing step before the final polishing step.

Advantages of the Invention

[0024] In the present invention, when polishing the surface of a magnetic disk substrate, by using an abrasive composition containing two types of silica particles, an oxidizing agent, and a phosphorus-containing inorganic acid and / or a phosphorus-containing organic acid as an acid, a high polishing rate can be achieved, and there are no fine concave defects called shallow pits on the surface of the substrate after polishing, and a smooth substrate without adhesion of silica particles can be obtained.

Embodiments for Carrying Out the Invention

[0025] Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the following embodiments, and modifications, corrections, and improvements can be made without departing from the scope of the invention.

[0026] 1. Abrasive Composition (Abrasive Composition for Magnetic Disk Substrate) The abrasive composition of the present invention is an abrasive composition containing colloidal silica, wet-process silica, an oxidizing agent, a phosphorus-containing inorganic acid and / or a phosphorus-containing organic acid as an acid, and water as essential components. Further, it may preferably be an abrasive composition containing a water-soluble polymer compound.

[0027] 1.1 Colloidal Silica The colloidal silica contained in the abrasive composition of the present invention has an average particle size in the range of 10 to 120 nm, preferably in the range of 10 to 110 nm, and more preferably in the range of 15 to 100 nm. When the average particle size of the colloidal silica is 10 nm or more, a decrease in the polishing rate can be suppressed. In other words, when the average particle size of the colloidal silica is less than 10 nm, the polishing rate of the abrasive composition may decrease, which may affect the working efficiency in the polishing process. On the other hand, when the average particle size of the colloidal silica is 120 nm or less, the generation of fine concave defects called "shallow pits" can be suppressed, and the surface smoothness can be kept good. In other words, when the average particle size of the colloidal silica exceeds 120 nm, shallow pits are likely to occur, and the surface smoothness of the object to be polished may be poor.

[0028] In addition, the proportion of particles having a particle size of 30 to 70 nm in the colloidal silica is in the range of 10 to 90% by volume, preferably in the range of 12 to 80% by volume. By setting the proportion of particles having a particle size of 30 to 70 nm in the range of 10 to 90% by volume, it has the effect of suppressing the generation of shallow pits. That is, in the colloidal silica used, when the particle size is not in the predetermined range, the generation of shallow pits cannot be suppressed, and sufficient surface smoothness cannot be ensured.

[0029] Colloidal silica is known to have shapes such as spherical, chain-like, confectionery sugar type (particulate with convex portions on the surface), and irregular shapes, and the primary particles are monodispersed in water to form a colloidal state. As the colloidal silica used in the present invention, colloidal silica having a spherical shape or a shape close to spherical is particularly preferred. By using such spherical or nearly spherical colloidal silica, the surface smoothness can be further improved. Note that colloidal silica can be formed by adopting conventionally well-known methods such as the water glass method using sodium silicate or potassium silicate as a raw material, the alkoxysilane method of hydrolyzing alkoxysilanes such as tetraethoxysilane with an acid or an alkali, or a method of reacting metallic silicon with water in the presence of an alkali catalyst to generate hydrogen while forming silica particles.

[0030] 1.2 Wet Process Silica The wet process silica contained in the abrasive composition of the present invention is prepared from silica particles obtained as precipitated silica by adding an aqueous alkali silicate solution and an inorganic acid or an aqueous inorganic acid solution to a reaction vessel. Note that the colloidal silica described above is not included in the wet process silica in this specification.

[0031] Examples of the aqueous alkali silicate solution used as a raw material for wet process silica include an aqueous sodium silicate solution, an aqueous potassium silicate solution, and an aqueous lithium silicate solution, etc., and generally, the use of an aqueous sodium silicate solution is preferred. On the other hand, examples of the inorganic acid added into the reaction vessel together with the aqueous sodium silicate solution include sulfuric acid, hydrochloric acid, and nitric acid, etc., and generally, the use of sulfuric acid is preferred.

[0032] An alkaline silicate aqueous solution serving as a raw material for wet-process silica and each component such as an inorganic acid are added into a reaction vessel. After the reaction is completed, the reaction solution is filtered, washed with water, and then dried by a dryer so that the moisture content becomes 6% or less. Here, the dryer to be used is not particularly limited, and for example, any of a static dryer, a spray dryer, a fluidized dryer, etc. may be used. Then, it is pulverized by a pulverizer such as a jet mill, and further classified to obtain the above-mentioned wet-process silica that has been pulverized.

[0033] The obtained wet-process silica may be further subjected to a firing treatment. For example, a firing treatment can be performed using a general firing device such as an electric furnace or a rotary kiln. In this case, the firing temperature related to the firing treatment of the wet-process silica can be set in the range of 600°C to 1100°C. Note that after the firing treatment, the above-mentioned pulverization treatment may be performed. The wet-process silica pulverized by such a pulverization treatment is configured to have a plurality of corners in its particle shape, and is expected to have high polishing performance compared with the particles of general spherical wet-process silica that has not been subjected to the pulverization treatment.

[0034] The average particle diameter of the obtained wet-process silica is in the range of 200 to 600 nm, preferably in the range of 200 to 500 nm. When the average particle diameter of the wet-process silica is 200 nm or more, a decrease in the polishing rate can be suppressed. In other words, when the average particle diameter of the wet-process silica is less than 200 nm, sufficient polishing performance cannot be achieved, and there is a possibility that the polishing rate may decrease. On the other hand, when the average particle diameter is 600 nm or less, deterioration of fine concave defects called shallow pits and surface roughness on the polished substrate can be suppressed. In other words, when the average particle diameter exceeds 600 nm, shallow pits are generated, and it becomes difficult to maintain a good surface state.

[0035] Here, when the average particle diameter of colloidal silica is defined as "A" and the average particle diameter of wet-process silica is defined as "B", the value of the ratio of the average particle diameter of wet-process silica to the average particle diameter of colloidal silica (= B / A) is in the range of 2.0 to 30.0, preferably in the range of 2.5 to 25.0, and more preferably in the range of 3.0 to 20.0. When the value of B / A is 2.0 or more, an improvement in the polishing rate is expected. On the other hand, when the value of B / A is 30.0 or less, deterioration of the surface roughness can be suppressed.

[0036] In addition, the total concentration of colloidal silica and wet-process silica, in other words, the "total concentration of silica particles", is preferably in the range of 1 to 50% by mass, more preferably in the range of 2 to 40% by mass, based on the weight of the entire polishing composition containing other components. When the total concentration of silica particles in the abrasive composition is 1% by mass or more, a decrease in the polishing rate can be suppressed. In other words, when the total concentration of the silica particles is less than 1% by mass, it becomes difficult to polish at a sufficient polishing rate. On the other hand, when the total concentration of silica particles is 50% by mass or less, a sufficient polishing rate can be maintained without using more silica particles than necessary. In other words, when the total concentration of silica particles exceeds 50% by mass, no further improvement in the polishing rate can be expected.

[0037] Here, the ratio of colloidal silica in the total mass of colloidal silica and wet-process silica is preferably in the range of 10 to 90% by mass, more preferably in the range of 20 to 80% by mass. When the ratio of colloidal silica is 10% by mass or more, fine concave defects called shallow pits can be suppressed, and the surface state can be kept good. In other words, when the ratio of colloidal silica is less than 10% by mass, shallow pits are generated, and it becomes difficult to maintain a good surface state. On the other hand, when the ratio of colloidal silica is 90% by mass or less, a decrease in the polishing rate can be suppressed. In other words, when the ratio of colloidal silica exceeds 90% by mass, the polishing rate may decrease.

[0038] The proportion of wet-process silica in the total mass of colloidal silica and wet-process silica is preferably in the range of 10 to 90% by mass, more preferably in the range of 20 to 80% by mass. By the proportion of wet-process silica being 90% by mass or less, deterioration of the surface roughness of the substrate after polishing can be suppressed. In other words, when the proportion of wet-process silica exceeds 90% by mass, there is a risk that the surface roughness of the substrate after polishing deteriorates. On the other hand, by the proportion of wet-process silica being 10% by mass or more, a decrease in the polishing rate can be suppressed. In other words, when the proportion of wet-process silica is less than 10% by mass, it becomes difficult to polish at a sufficient polishing rate.

[0039] 1.3 Other silica particles Examples of the silica particles contained in the polishing agent composition of the present invention include, in addition to colloidal silica and wet-process silica, the use of fumed silica and the like.

[0040] Fumed silica is obtained by hydrolyzing a volatile silane compound (generally silicon tetrachloride is used) in a flame of a mixed gas of oxygen and hydrogen (around 1000 °C), and is extremely fine and high-purity silica particles. Compared with colloidal silica, while colloidal silica exists as primary particles individually dispersed, fumed silica has a large number of primary particles aggregated and connected in a chain-like manner to form secondary particles. Due to the formation of these secondary particles, the holding force on the polishing pad becomes high, and the polishing rate can be improved.

[0041] 1.4 Oxidizing agent Examples of the oxidizing agent contained in the polishing agent composition of the present invention include peroxides, permanganic acid or its salts, chromic acid or its salts, periodic acid or its salts, and the like. Specific examples include hydrogen peroxide, sodium peroxide, barium peroxide, potassium permanganate, orthoperiodic acid, sodium metaperiodate, and the like. Among these, hydrogen peroxide is preferred.

[0042] The content of the oxidizing agent in the abrasive composition is usually used in the range of 0.1 to 10.0% by mass. When the oxidizing agent is contained in an amount of 0.1% by mass or more, the polishing rate is improved. Even when the oxidizing agent is contained in an amount of 10.0% by mass or more, no improvement in the polishing rate is observed, which is economically disadvantageous.

[0043] 1.5 Acid The abrasive composition of the present invention contains a phosphorus-containing inorganic acid and / or a phosphorus-containing organic acid as an acid.

[0044] By containing a phosphorus-containing inorganic acid and / or a phosphorus-containing organic acid in the abrasive composition, the adhesion of silica on the substrate surface after polishing can be reduced. Examples of the phosphorus-containing inorganic acid include phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, and tripolyphosphoric acid.

[0045] Examples of the phosphorus-containing organic acid include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), ethane-1,1-diphosphonic acid, and methanehydroxyphosphonic acid.

[0046] For the phosphorus-containing inorganic acid and / or the phosphorus-containing organic acid, the combined use of the phosphorus-containing inorganic acid and the phosphorus-containing organic acid is preferable for enhancing the effects of the present invention. Further, the phosphorus-containing inorganic acid and / or the phosphorus-containing organic acid can be used in combination with nitric acid, sulfuric acid, hydrochloric acid, etc. Also, it can be used in combination with polyvalent carboxylic acids such as citric acid, tartaric acid, oxalic acid, and maleic acid, or aliphatic sulfonic acids and aromatic sulfonic acids.

[0047] Examples of the aliphatic sulfonic acid include methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, 1-butanesulfonic acid, and trifluoromethanesulfonic acid.

[0048] Examples of the aromatic sulfonic acid include benzenesulfonic acid, p-toluenesulfonic acid, m-xylenesulfonic acid, cumenesulfonic acid, and dodecylbenzenesulfonic acid.

[0049] The amount of the acid used can be appropriately determined according to the setting of the pH value (25 °C) of the abrasive composition.

[0050] 1.6 Water-soluble polymer compound Examples of the water-soluble polymer compound preferably used in the abrasive composition of the present invention include polyacrylic acid-based water-soluble polymer compounds, polyamide-based water-soluble polymer compounds, polyvinyl alcohol-based water-soluble polymer compounds, and polyol-based water-soluble polymer compounds. In particular, the use of the copolymer shown below is preferred.

[0051] By further containing a water-soluble polymer compound, the abrasive composition of the present invention can reduce the adhesion of silica on the surface of the substrate after polishing. Among the water-soluble polymer compounds preferably used in the present invention, the following two types of copolymers will be described.

[0052] As the water-soluble polymer, a copolymer having at least a monomer having a carboxylic acid group and a monomer having an amide group as essential monomers, and a copolymer having at least a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as essential monomers can be preferably used in the present invention. Furthermore, it is more preferable to use the above two copolymers in combination.

[0053] More specifically, examples of the monomer having a carboxylic acid group include acrylic acid, methacrylic acid, maleic acid, itaconic acid, and salts thereof.

[0054] Examples of the monomer having an amide group include acrylamide, methacrylamide, N-alkylacrylamide, and N-alkylmethacrylamide.

[0055] Preferred examples of the monomers having an amide group, N-alkylacrylamide and N-alkylmethacrylamide, include N-methylacrylamide, N-ethylacrylamide, N-n-propylacrylamide, N-isopropylacrylamide, N-n-butylacrylamide, N-isobutylacrylamide, N-sec-butylacrylamide, N-tert-butylacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-n-propylmethacrylamide, N-isopropylmethacrylamide, N-n-butylmethacrylamide, N-isobutylmethacrylamide, N-sec-butylmethacrylamide, and N-tert-butylmethacrylamide, etc.

[0056] Among them, those using N-n-butylacrylamide, N-isobutylacrylamide, N-sec-butylacrylamide, N-tert-butylacrylamide, N-n-butylmethacrylamide, N-isobutylmethacrylamide, N-sec-butylmethacrylamide, and N-tert-butylmethacrylamide are particularly preferred.

[0057] On the other hand, examples of the monomers having a sulfonic acid group include isoprene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 2-methacrylamido-2-methylpropane sulfonic acid, styrene sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, vinyl naphthalene sulfonic acid, and their salts, etc.

[0058] It is preferable to form a copolymer by combining and polymerizing these monomer components. In the case of a copolymer having at least a monomer having a carboxylic acid group and a monomer having an amide group as essential monomers, for example, a combination of acrylic acid and / or its salt and N-alkylacrylamide, a combination of acrylic acid and / or its salt and N-alkylmethacrylamide, a combination of methacrylic acid and / or its salt and N-alkylacrylamide, and a combination of methacrylic acid and / or its salt and N-alkylmethacrylamide can be preferably used. It is particularly preferable to use those in which the alkyl group of N-alkylacrylamide or N-alkylmethacrylamide is at least one selected from the group consisting of an n-butyl group, an iso-butyl group, a sec-butyl group, and a tert-butyl group.

[0059] In the case of a copolymer having at least a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as essential monomers, for example, a combination of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid, a combination of acrylic acid and 2-methacrylamido-2-methylpropanesulfonic acid, a combination of methacrylic acid and 2-acrylamido-2-methylpropanesulfonic acid, and a combination of methacrylic acid and 2-methacrylamido-2-methylpropanesulfonic acid are exemplified.

[0060] The water-soluble polymer compound preferably used in the present invention includes copolymers having at least a monomer having a carboxylic acid group and a monomer having an amide group as essential monomers, and copolymers having at least a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as essential monomers. However, monomers other than the two types listed above may also be used.

[0061] For example, a copolymer obtained by copolymerizing three types of monomers, i.e., a monomer having a carboxylic acid group, a monomer having an amide group, and a monomer having a sulfonic acid group, can be used.

[0062] In a copolymer having at least a monomer having a carboxylic acid group and a monomer having an amide group as essential monomers, the ratio of the structural unit derived from the carboxylic acid group to the structural unit derived from the amide group is preferably in the range of 95:5 to 5:95 in terms of molar ratio as the amount ratio of the structural unit derived from the carboxylic acid group to the structural unit derived from the amide group, and more preferably in the range of 90:10 to 10:90 in terms of molar ratio.

[0063] In a copolymer having at least a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as essential monomers, the ratio of the structural unit derived from the carboxylic acid group to the structural unit derived from the sulfonic acid group is preferably in the range of 95:5 to 5:95 in terms of molar ratio as the amount ratio of the structural unit derived from the carboxylic acid group to the structural unit derived from the sulfonic acid group, and more preferably in the range of 90:10 to 10:90 in terms of molar ratio.

[0064] The weight average molecular weight of the water-soluble polymer compound is preferably in the range of 2,000 or more and 1,000,000 or less, and more preferably in the range of 4,000 or more and 800,000 or less. The weight average molecular weight of the water-soluble polymer compound is measured in terms of polyacrylic acid by gel permeation chromatography (GPC).

[0065] The concentration of the water-soluble polymer compound in the abrasive composition is preferably in the range of 0.0001% by mass or more and 1.0% by mass or less in terms of solid content, more preferably in the range of 0.001% by mass or more and 0.5% by mass or less, and still more preferably in the range of 0.005% by mass or more and 0.2% by mass or less.

[0066] 1.7 Water The water used in the abrasive composition of the present invention is a medium for dispersing other components of the abrasive composition, and pure water, ultrapure water, distilled water, etc. can be preferably used. Further, in order to disperse other components of the abrasive composition smoothly, a small amount of an organic medium such as alcohol may be contained in the water.

[0067] 1.8 Other Components As particles contained in the abrasive composition, in addition to colloidal silica and wet-process silica, other particles can be contained. However, from the viewpoint of reducing the penetration of alumina particles into the substrate to be polished, it is preferable not to contain alumina particles. In addition, the abrasive composition may contain a fungicide, an antibacterial agent, etc. in addition to the above-mentioned components.

[0068] 1.9 Physical properties The pH value (25 °C) of the abrasive composition is preferably 0.1 to 4.0, more preferably 0.5 to 3.0. By setting the pH value (25 °C) of the abrasive composition to 0.1 or more, deterioration of surface smoothness can be suppressed. On the other hand, by setting the pH value of the abrasive composition to 4.0 or less, a decrease in the polishing rate can be suppressed.

[0069] In the polishing of an electroless nickel-phosphorus plated aluminum magnetic disk substrate to which the abrasive composition of the present invention is preferably applied, since the electroless nickel-phosphorus plating film tends to dissolve under the condition of a pH value (25 °C) of 4.0 or less, from the viewpoint of improving the polishing rate, an abrasive composition having a pH value (25 °C) of 4.0 or less is preferably used.

[0070] 2. Polishing method for magnetic disk substrate As a polishing method to which the abrasive composition of the present invention can be applied, for example, a polishing pad is attached to the surface plate of a polishing machine, and the abrasive composition is supplied to the surface to be polished (for example, an aluminum magnetic disk substrate) or the polishing pad, and the surface to be polished is rubbed with the polishing pad.

[0071] Furthermore, when polishing the front and back surfaces of the aluminum magnetic disk substrate simultaneously, a double-sided polishing machine with a polishing pad attached to each of the upper surface plate and the lower surface plate is used.

[0072] In such a method, an aluminum magnetic disk substrate is sandwiched between polishing pads respectively attached to the upper platen and the lower platen, a polishing agent composition is supplied between the polishing surface and the polishing pads, and the two polishing pads are rotated simultaneously to polish the front and back surfaces of the aluminum magnetic disk substrate.

[0073] The method for polishing a magnetic disk substrate of the present invention comprises a polishing step and a final polishing step carried out after the polishing step. The polishing agent composition of the present invention is used in the polishing step (= rough polishing step) carried out before the final polishing step (= finishing polishing step). More preferably, it is used for polishing an electroless nickel-phosphorus plated aluminum magnetic disk substrate, and even more preferably, it is used for the polishing step carried out before the final polishing step of an electroless nickel-phosphorus plated aluminum substrate. By using the polishing agent composition of the present invention in such a polishing step, the effects of the present invention can be fully enjoyed.

[0074] In addition, the polishing pad used in the polishing step is not particularly limited, and polishing pads such as non-woven fabric type and suede type can be used. In particular, suede type polishing pads are generally used. Further, as the material of the surface foam layer in contact with the polishing agent composition, materials such as polyurethane elastomer, polystyrene, polyester, and polyvinyl chloride can be used. In particular, those made of polyurethane elastomer are generally used.

Examples

[0075] Hereinafter, the present invention will be specifically described based on examples. However, the present invention is not limited to these examples, and it goes without saying that it can be implemented in various modes as long as it belongs to the technical scope of the present invention.

[0076] 3. Preparation method of polishing agent composition Examples 3、4,12,1 3、 Reference Examples 1 to 9The abrasive compositions of Examples and Comparative Examples 1 to 5 were configured by using the components described in Table 1 shown below and containing the addition amounts described in Table 1. All Examples 3、4,12,1 3, Reference Examples 1 to 9 In Examples 3 and Comparative Examples 1 to 5, the total silica concentration in the abrasive composition was prepared to be 4.0% by mass.

[0077] Here, in Table 1, "HEDP" represents 1-hydroxyethylidene-1,1-diphosphonic acid, "AA" represents acrylic acid, "TBAA" represents N-tert-butylacrylamide, and "ATBS" represents 2-acrylamido-2-methylpropanesulfonic acid, respectively. Hereinafter, in this specification as well, the abbreviations such as the above HEDP will be appropriately used for explanation.

[0078]

Table 1

[0079] The following are Examples 3、4,12,1 3, Reference Examples 1 to 9 The specific preparation methods of the abrasive compositions of Examples 3 and Comparative Examples 1 to 5 are shown below. · Reference Example 1 Commercially available colloidal silica I (average particle diameter (D50) = 50 nm, proportion of particles with particle diameter of 30 to 70 nm = 60% by volume), commercially available wet-process silica I (average particle diameter (D50) = 300 nm), phosphoric acid, and hydrogen peroxide were stirred and mixed while diluting with pure water to the contents described in Table 1, Reference and the abrasive composition of Example 1 was obtained. Here, phosphoric acid corresponds to the acid in the present invention, and hydrogen peroxide solution corresponds to the oxidizing agent in the present invention.

[0080] · Reference Example 2 Reference In the preparation of the abrasive composition of Example 1, HEDP corresponding to the acid in the present invention was additionally added to the content described in Table 1, Reference and the abrasive composition of Example 2 was obtained. Otherwise Reference it was the same as the preparation of the abrasive composition of Example 1.

[0081] · Example 3 Reference In the preparation of the abrasive composition of Example 2, polymer 1 (copolymer type A) corresponding to the water-soluble polymer in the present invention was additionally added so as to have the content described in Table 1, and the abrasive composition of Example 3 was obtained. Otherwise Reference it is the same as the preparation of the abrasive composition of Example 2.

[0082] · Example 4 Reference In the preparation of the abrasive composition of Example 2, polymer 2 (copolymer type B) corresponding to the water-soluble polymer in the present invention was additionally added so as to have the content described in Table 1, and the abrasive composition of Example 4 was obtained. Otherwise Reference it is the same as the preparation of the abrasive composition of Example 2.

[0083] · Reference Example 3 Reference In the preparation of the abrasive composition of Example 1, the contents of colloidal silica and wet-process silica were changed to the contents described in Table 1, Reference Example 3 and the abrasive composition of was obtained. Otherwise, it is the same as the preparation of the abrasive composition of Example 1.

[0084] · Reference Example 4 Reference In the preparation of the abrasive composition of Example 1, the contents of colloidal silica and wet-process silica were changed to the contents described in Table 1, Reference Example 4 and the abrasive composition of was obtained. Otherwise Reference it is the same as the preparation of the abrasive composition of Example 1.

[0085] · Reference Example 5 Reference In the preparation of the abrasive composition of Example 1, colloidal silica V (average particle diameter (D50) = 15 nm, ratio of particles having a particle diameter of 30 to 70 nm = 25% by volume) was used instead of colloidal silica I,Reference Example 5 A polishing agent composition was obtained. Otherwise, Reference it is the same as the preparation of the polishing agent composition of Example 1.

[0086] · Reference Example 6 Reference In the preparation of the polishing agent composition of Example 1, colloidal silica II (average particle diameter (D50) = 100 nm, ratio of particles with a particle diameter of 30 to 70 nm = 14% by volume) was used instead of colloidal silica I, Reference Example 6 A polishing agent composition was obtained. Otherwise, Reference it is the same as the preparation of the polishing agent composition of Example 1.

[0087] · Reference Example 7 Reference In the preparation of the polishing agent composition of Example 1, colloidal silica III (average particle diameter (D50) = 100 nm, ratio of particles with a particle diameter of 30 to 70 nm = 11% by volume) was used instead of colloidal silica I, Reference Example 7 A polishing agent composition was obtained. Otherwise, Reference it is the same as the preparation of the polishing agent composition of Example 1.

[0088] · Reference Example 8 Reference In the preparation of the polishing agent composition of Example 1, wet-process silica II (average particle diameter (D50) = 400 nm) was used instead of wet-process silica I, Reference Example 8 A polishing agent composition was obtained. Otherwise, Reference it is the same as the preparation of the polishing agent composition of Example 1.

[0089] · Reference Example 9 Reference In the preparation of the polishing agent composition of Example 1, wet-process silica III (average particle diameter (D50) = 550 nm) was used instead of wet-process silica I, Reference Example 9 A polishing agent composition was obtained. Otherwise,Reference It is the same as the preparation of the abrasive composition of Example 1.

[0090] · Example 12 Reference In the preparation of the abrasive composition of Example 1, Polymer 1 was additionally added so as to have the content described in Table 1, and the abrasive composition of Example 12 was obtained. Otherwise Reference It is the same as the preparation of the abrasive composition of Example 1.

[0091] · Example 13 Reference In the preparation of the abrasive composition of Example 2, Polymer 1 and Polymer 2 were additionally added so as to have the content described in Table 1, and the abrasive composition of Example 13 was obtained. Otherwise Reference It is the same as the preparation of the abrasive composition of Example 2.

[0092] · Comparative Example 1 Reference In the preparation of the abrasive composition of Example 1, sulfuric acid was used instead of phosphoric acid so as to have the content described in Table 1, and the abrasive composition of Comparative Example 1 was obtained. Otherwise Reference It is the same as the preparation of the abrasive composition of Example 1.

[0093] · Comparative Example 2 Reference In the preparation of the abrasive composition of Example 1, the abrasive composition of Comparative Example 2 was obtained by not adding wet-process silica. Otherwise Reference It is the same as the preparation of the abrasive composition of Example 1.

[0094] · Comparative Example 3 Reference In the preparation of the abrasive composition of Example 1, the abrasive composition of Comparative Example 3 was obtained by not adding colloidal silica. Otherwise Reference It is the same as the preparation of the abrasive composition of Example 1.

[0095] · Comparative Example 4 ReferenceIn the preparation of the abrasive composition of Example 1, wet-process silica IV (average particle diameter (D50) = 800 nm) was used instead of wet-process silica I to obtain the abrasive composition of Comparative Example 4. Otherwise Reference it was the same as the preparation of the abrasive composition of Example 1.

[0096] · Comparative Example 5 Reference Example 7 In the preparation of the abrasive composition, colloidal silica IV (average particle diameter (D50) = 100 nm, proportion of particles with a particle diameter of 30 to 70 nm = 8% by volume) was used instead of colloidal silica III to obtain the abrasive composition of Comparative Example 5. Otherwise Reference Example 7 it was the same as the preparation of the abrasive composition.

[0097] 4. Measurement, Conditions, and Evaluation of Each Physical Property, etc. 4.1 Weight-Average Molecular Weight of Water-Soluble Polymer Compound The weight-average molecular weight of the water-soluble polymer compound was measured in terms of polyacrylic acid by gel permeation chromatography (GPC), and the GPC measurement conditions are shown below.

[0098] (GPC Measurement Conditions) Column: TSKgel G4000PWXL (manufactured by Tosoh Corporation) + G2500PWXL (manufactured by Tosoh Corporation) + SHODEX OHpak SB-806M-HQ (manufactured by Showa Denko KK) Eluent: 0.2 M phosphate buffer / acetonitrile = 9 / 1 (volume ratio) Flow rate: 1.0 ml / min Temperature: 40 °C Detection: Differential refractive index (RI) Sample: Concentration 0.1 wt% (injection volume 100 μL) Calibration curve polymer: Polyacrylic acid molecular weight (Mp) 115,000, 28,000, 4,100, 1,250 (Sowa Kagaku Co., Ltd., American Polymer Standards Corp.)

[0099] 4.2 Method for Measuring Particle Diameter and Average Particle Diameter of Colloidal Silica The particle size (Heywood diameter) of the colloidal silica was measured as the Heywood diameter (equivalent diameter of the projected area circle) by taking a photograph of a field of view at a magnification of 100,000 times using a transmission electron microscope (TEM) (manufactured by JEOL Ltd., transmission electron microscope JEM2000FX (200 kV)) and analyzing this photograph using analysis software (manufactured by Mountech Co., Ltd., Mac-View Ver. 4.0).

[0100] The average particle size of the colloidal silica was determined by analyzing the particle sizes of about 2,000 colloidal silica particles by the method described above, and calculating the particle size at which the cumulative particle size distribution (cumulative volume basis) from the small particle size side becomes 50% using the above analysis software ((manufactured by Mountech Co., Ltd., Mac-View Ver. 4.0) as the average particle size (D50)).

[0101] The proportion of particles with a particle size of 30 to 70 nm in the colloidal silica was determined by analyzing the particle sizes of about 2,000 colloidal silica particles by the method described above, calculating the proportion (%) of the cumulative particle size distribution (cumulative volume basis) from the small particle size side at a particle size of 30 nm and the proportion (%) of the cumulative particle size distribution (cumulative volume basis) from the small particle size side at a particle size of 70 nm using the above analysis software (manufactured by Mountech Co., Ltd., Mac-View Ver. 4.0), and can be calculated from the following formula (1). Proportion of particles with a particle size of 30 to 70 nm (%) = Proportion of cumulative particle size distribution at a particle size of 70 nm (%) - Proportion of cumulative particle size distribution at a particle size of 30 nm (%) ··· Formula (1)

[0102] 4.3 Method for Measuring the Average Particle Size of Wet Process Silica For wet process silica with an average particle size of 400 nm or less, a dynamic light scattering particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., Microtrac UPA) was used, and for particles larger than 400 nm, a laser diffraction particle size distribution measuring instrument (manufactured by Shimadzu Corporation, SALD2200) was used. The average particle size of the wet process silica is the average particle size (D50) at which the cumulative particle size distribution from the small particle size side based on volume becomes 50%.

[0103] 4.4 Polishing Conditions An electroless nickel-phosphorus plated aluminum disk substrate with an outer diameter of 95 mm was used as the object to be polished, and polishing was carried out under the following polishing conditions. Polishing machine: 9B double-sided polishing machine manufactured by SPEEDFAM Polishing pad: P1 pad manufactured by FILWEL Co., Ltd. Rotational speed of the upper platen: -7.7 rpm Rotational speed of the lower platen: 23.5 rpm Supply rate of the abrasive composition: 90 ml / min Polishing time: Polish until the polishing amount reaches 1.2 - 1.5 μm / single side. (240 - 720 seconds) Processing pressure: 120 kPa

[0104] 4.5 Polishing speed ratio The polishing speed was calculated based on the following formula (2) by measuring the mass of the aluminum disk substrate that decreased after polishing. Polishing speed (μm / min) = Mass reduction of the aluminum disk substrate (g) / Polishing time (min) / Area of one side of the aluminum disk substrate (cm 2 ) / Density of the electroless nickel-phosphorus plating film (g / cm 3 ) / 2×10 4 ··· Formula (2) (However, in the above formula (2), the area of one side of the aluminum disk substrate is 65.9 cm 2 , and the density of the electroless nickel-phosphorus plating film is calculated as 8.0 g / cm 3 ) The polishing speed ratio was calculated as the relative value when the polishing speed of the abrasive composition in Comparative Example 2 obtained using the above formula (2) was taken as 1 (reference).

[0105] 4.6 Measurement and evaluation of shallow pits The shallow pits were measured using a three-dimensional surface structure analysis microscope (New View 8300) that utilizes the scanning white interference method manufactured by Ametek. <Measurement conditions> Lens 1.4 times ZOOM 0.5 times Measurement area of one field of view 12 mm × 12 mm Measurement Type Surface Measurement Mode CSI Scan Length 5μm

[0106] A square with a side length of 95 mm that covers the entire aluminum disk substrate is set, divided into 100 sections, and the entire surface of the 95 mm diameter aluminum disk substrate is scanned. At this time, each scan data is set to have a 20% overlap. The obtained scan data is joined together to observe the entire surface of the aluminum disk substrate. When observing each section, the presence or absence of shallow pits was confirmed while magnifying with the mouse.

[0107] The entire surface of the aluminum disk substrate was visually observed, · When almost no shallow pits are observed, 「○ (Good)」 · When a few shallow pits are observed, 「△ (Fair)」 · When many shallow pits are observed, 「× (Poor)」 and each was evaluated accordingly.

[0108] 4.7 Surface Roughness Ratio The surface roughness of the aluminum disk substrate was measured using a three-dimensional surface structure analysis microscope that utilizes the scanning white interference method manufactured by Ametek. The measurement conditions were as follows: a measuring device manufactured by Ametek (New View 8300 (lens: 10.0 times, zoom: 1.0 times)), a wavelength of 20 to 100 μm, a measurement area of 0.8 mm × 0.8 mm, and analysis was performed using analysis software (Mx) manufactured by Ametek. In Table 3 below, "unmeasurable surface roughness" indicates a state where many shallow pits are observed and the surface roughness cannot be measured by the above measurement method. The surface roughness ratio is a relative value when the surface roughness of Comparative Example 4 measured using the above method is set to 1 (reference).

[0109] 4.8 Evaluation of Silica Adhesion For the purpose of evaluating the presence or absence of silica adhesion, which is abrasive residue on the surface of the aluminum disk substrate after polishing, scanning electron microscope observation was used, and it was evaluated as the count of silica adhesion under the following conditions. <Measurement Conditions> Measuring device: Manufactured by JEOL Ltd., field emission scanning electron microscope "JSM-7100" Measurement conditions: Acceleration voltage 15 kV, observation magnification 20,000 times Measurement method: Observe 12 fields on the back surface and count the number of deposits on the substrate surface. Evaluate based on the average per field.

[0110] · When the count of silica adhesion is 0 to 30, "〇 (good)" · When the count of silica adhesion is 31 to 60, "△ (fair)" · When the count of silica adhesion is 61 or more, "× (poor)" And each was evaluated accordingly.

[0111] Examples 3、4,12,1 3, Reference Examples 1 to 9 The results of the polishing tests using the abrasive compositions of Examples 3 and Comparative Examples 1 to 5 are shown in Tables 2 and 3 below. In Table 2, Polymer 1 (A) represents a copolymer having a monomer with a carboxylic acid group and a monomer with an amide group as essential monomers, and Polymer 2 (B) represents a copolymer having a monomer with a carboxylic acid group and a monomer with a sulfonic acid group as essential monomers.

[0112]

Table 2

[0113]

Table 3

[0114] 5. Discussion As is clear from Tables 2 and 3 shown above, compared with Comparative Example 1 using sulfuric acid as the acid in the abrasive composition, Example 1 using phosphoric acid as the acid in the abrasive composition Reference is confirmed to have significantly improved silica adhesion. Furthermore, compared with Comparative Example 2 using an abrasive composition not containing wet-process silica, Example 1 using an abrasive composition containing wet-process silica Reference shows an improvement in polishing rate.

[0115] In Comparative Example 3 using an abrasive composition not containing colloidal silica, a large number of shallow pits were confirmed, whereas in Reference Example 1 using an abrasive composition containing colloidal silica, almost no shallow pits were observed, and an improvement in the smoothness of the substrate surface of the aluminum disk substrate was confirmed.

[0116] In Comparative Example 4 using an abrasive composition containing wet-process silica with an average particle diameter exceeding 600 nm, some shallow pits were observed and the surface roughness value was large, whereas in Example 1 using an abrasive composition containing wet-process silica with an average particle diameter of 600 nm or less Reference almost no shallow pits were observed, and in addition, the surface roughness value was significantly reduced, and an improvement in the smoothness of the substrate surface was confirmed.

[0117] In Comparative Example 5 using an abrasive composition in which the ratio of particles having a particle diameter of 30 to 70 nm in the colloidal silica in the abrasive composition is less than 10% by volume, a large number of shallow pits were observed, whereas in Example using an abrasive composition having the same average particle diameter as Comparative Example 5 and in which the ratio of particles having a particle diameter of 30 to 70 nm in the colloidal silica exceeds 10% by volume Reference Example 7 only some shallow pits were observed, and in Example having the same average particle diameter as Comparative Example 5 and in which the ratio of particles having a particle diameter of 30 to 70 nm in the colloidal silica exceeds 12% by volume Reference Example 6 almost no shallow pits were observed, and it can be seen that the ratio of particles having a particle diameter of 30 to 70 nm in the colloidal silica in the abrasive composition is an important factor for reducing shallow pits.

[0118] Reference Example 2 shows Reference the results when phosphoric acid and HEDP are used in combination as acids in the abrasive composition in Example 1, Reference and it was confirmed that the characteristics of silica adhesion were further improved compared to Example 1.

[0119] Example 3 ReferenceThis shows the results when a water-soluble polymer compound (Polymer 1) is added to the abrasive composition in Example 2. Reference It was confirmed that the polishing rate was improved compared to Example 2, and the silica adhesion was significantly improved.

[0120] Example 4 Reference This shows the results when a water-soluble polymer compound (Polymer 2) is added to the abrasive composition in Example 2. Reference It was confirmed that the silica adhesion was significantly improved compared to Example 2.

[0121] Reference Example 3 and Reference Example 4 shows Reference the results when the ratio of colloidal silica and wet-process silica in the abrasive composition is changed in Example 1. Reference Example 5 and Reference Example Reference 6 shows Reference the results when the average particle size of colloidal silica in the abrasive composition is changed in Example 1. Reference Example 7 shows Reference Example 6 shows the results when the ratio of particles with the same average particle size of colloidal silica and ranging from 30 to 70 nm is different.

[0122] Reference Example 8 and Reference Example 9 shows Reference the results when the average particle size of wet-process silica in the abrasive composition is changed in Example 1. Example 12 Reference shows the results when a water-soluble polymer compound (Polymer 1) is added to the abrasive composition in Example 1. Reference It was confirmed that the polishing rate was improved compared to Example 1, and the silica adhesion was significantly improved.

[0123] Example 13 ReferenceThis shows the results when a water-soluble polymer compound (used in combination with Polymer 1 and Polymer 2) is added to the abrasive composition in Example 2. Reference It was confirmed that the polishing rate was improved compared to Example 2, and the silica adhesion was significantly improved.

[0124] From the above, it is clear that by using the abrasive composition of the present invention, a magnetic disk substrate with a high polishing rate and excellent balance of shallow pits, surface roughness, and silica adhesion can be obtained.

Industrial Applicability

[0125] The abrasive composition of the present invention can be used for polishing electronic components such as magnetic recording media such as semiconductors and hard disks. In particular, it can be used for surface polishing of substrates for magnetic recording media such as glass magnetic disks and aluminum magnetic disks. Furthermore, it can be used for surface polishing of aluminum substrates for magnetic recording media formed with electroless nickel-phosphorus plating films. In particular, it can be used in a polishing step prior to the final polishing step of an aluminum substrate for a magnetic recording media formed with an electroless nickel-phosphorus plating film.

Claims

1. Colloidal silica having an average particle diameter in the range of 10 to 120 nm, Wet-process silica having an average particle diameter in the range of 200 to 600 nm, An oxidizing agent, An acid, Water, A water-soluble polymer compound are contained, The proportion of particles having a particle diameter of 30 to 70 nm in the colloidal silica is 10 to 90% by volume, The value of the ratio of the average particle diameter of the wet-process silica to the average particle diameter of the colloidal silica is in the range of 2.0 to 30.0, The acid is a phosphorus-containing inorganic acid and / or a phosphorus-containing organic acid, The water-soluble polymer compound is a copolymer having at least a monomer having a carboxylic acid group and a monomer having an amide group as essential monomers, and / or a copolymer having at least a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as essential monomers, and the average count number per field of view of silica adhesion on the substrate surface after the polishing step under the condition of an observation magnification of 20,000 times using a scanning electron microscope is 20 or less, a polishing agent composition for a magnetic disk substrate.

2. The polishing agent composition for a magnetic disk substrate according to claim 1, wherein the proportion of the particles having a particle diameter of 30 to 70 nm in the colloidal silica is in the range of 12 to 80% by volume.

3. The polishing agent composition for a magnetic disk substrate according to claim 1 or 2, wherein the average particle diameter of the wet-process silica is in the range of 200 to 500 nm.

4. The phosphorus-containing inorganic acid is at least one selected from the group consisting of phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, and tripolyphosphoric acid, the polishing agent composition for a magnetic disk substrate according to any one of claims 1 to 3.

5. The phosphorus-containing organic acid is at least one 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, and methanephosphonic acid, the polishing agent composition for a magnetic disk substrate according to any one of claims 1 to 3.

6. The polishing agent composition for a magnetic disk substrate according to any one of claims 1 to 5, having a pH value (25 °C) in the range of 0.1 to 4.

0.

7. The abrasive composition for a magnetic disk substrate according to any one of claims 1 to 6, which is used for polishing an electroless nickel-phosphorus plated aluminum magnetic disk substrate as a polishing target.

8. A method for polishing a magnetic disk substrate using the abrasive composition for a magnetic disk substrate according to any one of claims 1 to 7, comprising: a polishing step and a final polishing step performed after the polishing step; wherein the abrasive composition for a magnetic disk substrate is: A method for polishing a magnetic disk substrate used in the polishing step before the final polishing step.

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