JP2017062864A - Manufacturing method of aluminium magnetic disk substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing method of an aluminium magnetic disk substrate combining a specific rough polishing step and a specific final polishing step which achieve high polishing speed and obtain satisfactory surface smoothness without using alumina particles.SOLUTION: A manufacturing method of an aluminium magnetic disk substrate at least includes: a rough polishing step of using a first polishing agent composition containing wet-process silica particles, first colloidal silica and water for polishing; and a final polishing step of using a second polishing agent composition containing second colloidal silica, a water-soluble polymer compound and water for polishing. The average particle diameter of the first colloidal silica is smaller than that of the wet-process silica particles, and the average particle diameter of the second colloidal silica is smaller than that of the first one. The water-soluble polymer compound has a constitutional unit derived from unsaturated aliphatic carboxylic acid. The ph values of the first and second polishing agent compositions are 0.1-4.0.SELECTED DRAWING: None

Description

  The present invention relates to a method of manufacturing an aluminum magnetic disk substrate that is widely used as a magnetic recording medium substrate of a magnetic recording medium such as a hard disk. In particular, the present invention relates to a method for manufacturing an aluminum magnetic disk substrate for a magnetic recording medium in which an electroless nickel-phosphorous plating film is formed on the surface of an aluminum alloy substrate.

  In recent years, hard disks have been reduced in size and capacity, and high recording density has been demanded. Therefore, it is necessary to improve the detection sensitivity of high recording density magnetic signals, and technical developments are underway to further reduce the flying height of the magnetic head and increase the unit recording density. The magnetic disk substrate has improved smoothness and flatness (reduced surface roughness, waviness and edge sagging) and reduced surface defects (residual particles, Improvement of surface quality such as reduction of scratches, protrusions, pits, etc.) is strictly demanded.

  From the viewpoint of achieving both improvement in surface quality such as smoother and less scratches and productivity improvement in response to such demands, the method for manufacturing a magnetic disk substrate is a multi-stage polishing having two or more polishing steps. The method is often adopted. In general, in a final polishing step of a multi-stage polishing method, that is, a final polishing step, a polishing composition for finishing that contains colloidal silica in order to satisfy the demands of reducing surface roughness and scratches such as scratches, protrusions, and pits. In the polishing step (rough polishing step) prior to the final polishing step, an abrasive composition containing alumina particles has been used from the viewpoint of improving productivity.

  However, when polishing an aluminum magnetic disk substrate, the alumina particles used in the rough polishing process are considerably harder than the electroless nickel-phosphorus plating film of the aluminum magnetic disk substrate, so the alumina particles pierce the substrate. There is. It has been a problem that the pierced particles have an adverse effect on the subsequent final polishing process.

  As a solution to such a problem, an abrasive composition combining alumina particles and silica particles has been proposed (Patent Documents 1 to 6). Moreover, the method of grind | polishing only by a silica particle without using an alumina particle is proposed (patent documents 7-13).

JP 2009-176597 A JP 2011-204327 A JP 2012-43493 A JP 2014-29752 A JP 2014-29753 A JP 2014-32718 A Special table 2011-527643 gazette JP 2014-29754 A JP 2014-29755 A JP 2014-1116057 A JP 2014-210912 A Special table 2003-514950 gazette JP 2012-155785 A

  As in Patent Documents 1 to 3, by combining alumina particles and silica particles, it is possible to remove alumina particles stuck into the substrate to some extent. However, as long as the abrasive composition containing the alumina particles is used, the possibility that the alumina particles contained in the abrasive composition pierce the substrate still remains. Moreover, since such an abrasive | polishing agent composition contains both an alumina particle and a silica particle, there exists a problem that the characteristic which each particle | grain cancels mutually, and a polishing rate and surface smoothness deteriorate.

  Further, Patent Documents 4 to 6 propose a method in which alumina particles are used first, and then silica particles are used after a rinsing step. However, the sticking of alumina particles is still completely removed. It is difficult.

  Thus, a method of polishing only with silica particles without using alumina particles has been proposed. Patent Document 7 proposes a combination of colloidal silica and a polishing accelerator. Patent Documents 8 to 11 propose a method using colloidal silica, fumed silica, surface-modified silica, silica produced by a water glass method, or the like, particularly using colloidal silica having a special shape. However, these methods have an insufficient polishing rate, and improvements are required. Patent Document 12 proposes a method of using colloidal silica and fumed silica in combination. However, in this method, although the polishing rate is improved, fumed silica has a very low bulk specific gravity, so the workability such as slurrying becomes very bad, and there is a concern about the influence of dust on health. Patent Document 13 proposes a method of producing a polishing rate close to that of alumina by using crushed silica particles. However, this method has a problem that the surface smoothness deteriorates, and improvement is demanded.

  Further, in the final polishing process, it is conceivable to use fine abrasive particles in order to improve the surface smoothness, but there is a problem that the polishing rate is lowered. Further, in the production of an aluminum magnetic disk substrate, when a large number of substrates are polished continuously, the polishing rate is remarkably lowered with an increase in the number of polishings, and the productivity is deteriorated. Improvement of the reduction in the polishing rate at the time of continuous multiple polishing in this final polishing step has also been an issue of improving productivity.

  The present invention has been made in view of such problems of the prior art, and the problem is to achieve a high polishing rate and obtain good surface smoothness without using alumina particles. It is an object of the present invention to provide a method for polishing an aluminum magnetic disk substrate, which combines a specific rough polishing step that makes it possible to improve surface smoothness and a specific finish polishing step that can improve productivity.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have used a wet method silica particle obtained through a pulverization step in combination with colloidal silica in a rough polishing step, and further obtained through a pulverization step. We found that it is possible to achieve a high polishing rate and good surface smoothness by making the average particle size of colloidal silica smaller than the average particle size of wet-process silica particles. It was realized.

  And by making the abrasive composition used in the final polishing process present a water-soluble polymer compound, it has been found that even when a large number of substrates are polished continuously, a decrease in the polishing rate can be suppressed. The present invention was completed by combining with.

  That is, according to the present invention, the following method for manufacturing an aluminum magnetic disk substrate is provided.

[1] In polishing an aluminum magnetic disk substrate after electroless nickel-phosphorous plating,
A rough polishing step prior to the final stage, which is polished using a first abrasive composition containing wet method silica particles obtained through a pulverization step, a first colloidal silica, and water;
Polishing with a second abrasive composition comprising a second colloidal silica, a water-soluble polymer compound, and water, and a final polishing step in the final stage;
Having at least two polishing steps including
The average particle size of the first colloidal silica is smaller than the average particle size of the wet method silica particles,
The average particle size of the second colloidal silica is smaller than the average particle size of the first colloidal silica,
The water-soluble polymer compound is a polymer or copolymer having a structural unit derived from an unsaturated aliphatic carboxylic acid,
A method for producing an aluminum magnetic disk substrate, wherein the first abrasive composition in the rough polishing step and the second abrasive composition in the final polishing step have a pH value of 0.1 to 4.0.

[2] In the rough polishing step, in [1], an average particle diameter of the wet process silica particles is 0.1 to 1.0 μm, and an average particle diameter of the first colloidal silica is 5 to 200 nm. A manufacturing method of the aluminum magnetic disk substrate as described.

[3] In the rough polishing step, a total concentration of the wet method silica particles and the first colloidal silica is 1 to 50% by mass in the first abrasive composition,
The ratio of the wet method silica particles to the entire silica particles in the first abrasive composition is 5 to 95 mass%, and the ratio of the first colloidal silica is 5 to 95 mass%. [1] The method for producing an aluminum magnetic disk substrate according to [2].

[4] In the final polishing step, an average particle diameter of the second colloidal silica is 1 to 50 nm, and a concentration of the second colloidal silica contained in the second abrasive composition is 1 to 50 mass. % Of the method for producing an aluminum magnetic disk substrate according to any one of [1] to [3].

[5] In the final polishing step, the water-soluble polymer compound has a weight average molecular weight of 500 to 50,000, and the concentration of the water-soluble polymer compound in the second abrasive composition is 0.0001 to 1. The method for producing an aluminum magnetic disk substrate according to any one of [1] to [4], which is 0.0 mass%.

[6] The method according to any one of [1] to [5], further including a structural unit derived from a hydrophobic monomer when the water-soluble polymer compound is a copolymer in the final polishing step. A method of manufacturing an aluminum magnetic disk substrate.

  The method for polishing an aluminum magnetic disk substrate of the present invention can realize a high polishing rate and good surface smoothness by a combination of a specific rough polishing step and a specific finish polishing step.

  Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments, and based on ordinary knowledge of those skilled in the art without departing from the spirit of the present invention. It should be understood that modifications, improvements, and the like appropriately added to the embodiments described above fall within the scope of the present invention.

  The method for producing an aluminum magnetic disk substrate of the present invention is characterized by a step of polishing an aluminum magnetic disk substrate having an electroless nickel-phosphorous plating film formed on the surface of an aluminum alloy substrate (hereinafter also referred to as “polishing step”). It is what has. In the method for producing an aluminum magnetic disk substrate of the present invention, the polishing step includes two or more polishing steps including at least a rough polishing step before the final step and a final polishing step of the final step.

1. Rough Polishing Step In the method for producing an aluminum magnetic disk substrate of the present invention, the rough polishing step is at least one of the polishing steps performed before the final polishing step, which is the final step, in two or more polishing steps. It is.

1-1. 1st abrasive | polishing agent composition A rough | crude grinding | polishing process is performed in presence of the 1st abrasive | polishing agent composition containing the wet process silica particle obtained through the grinding | pulverization process, 1st colloidal silica, and water.

  In the rough polishing step, the first colloidal silica having an average particle size smaller than the average particle size of the wet process silica particles obtained through the pulverization step is used. Thereby, compared with the case where each silica particle is used alone, an unexpectedly high polishing rate is achieved, and at the same time, good surface smoothness is achieved. The average particle diameter of the wet process silica particles obtained through the pulverization step is preferably 0.1 to 1.0 μm, and the average particle diameter of the first colloidal silica is preferably 5 to 200 nm. In addition, the average particle diameter in this application is a median diameter (D50).

  In general, when a combination of a large particle size (wet method silica particle in the present invention) and a small particle size (first colloidal silica in the present invention) is used, the polishing rate and The surface smoothness tends to be governed by the polishing rate and surface smoothness provided by the large particle size. That is, in general, the polishing rate does not greatly exceed the polishing rate by the large particle size, and the surface smoothness becomes the surface smoothness by polishing the large particle size, and the surface by the small particle size Inferior in smoothness. However, in the rough polishing step in the present invention, the polishing rate is significantly higher than that in the case where each of the wet method silica particles and the first colloidal silica is used alone, and good surface smoothness is maintained. .

  Hereinafter, the wet method silica particles and the first colloidal silica used in the rough polishing step of the present invention will be described in more detail.

1-2. Wet process silica particles Wet process silica particles are particles prepared from wet process silica obtained as precipitated silicic acid by adding an alkali silicate aqueous solution and an inorganic acid or an inorganic acid aqueous solution to a reaction vessel. In the present invention, the wet process silica particles do not include colloidal silica.

  Examples of the alkali silicate aqueous solution that is a raw material of the wet process silica include a sodium silicate aqueous solution, a potassium silicate aqueous solution, and a lithium silicate aqueous solution. Among these aqueous alkali silicate solutions, generally, an aqueous sodium silicate solution is preferably used. Examples of inorganic acids include sulfuric acid, hydrochloric acid, nitric acid and the like. Of these inorganic acids, sulfuric acid is generally preferably used. After completion of the reaction, the reaction solution is filtered and washed with water, and then dried with a dryer so that the water content is 10% or less. The dryer may be any of a stationary dryer, a spray dryer, and a fluid dryer. Then, it grind | pulverizes with grinders, such as a jet mill, and also classifies, and obtains a wet process silica particle.

  The particle shape of the wet-process silica particles crushed by pulverization in this way has corners and has higher polishing ability than particles that are nearly spherical.

  The average particle size of the wet process silica particles is preferably 0.1 to 1.0 μm, more preferably 0.2 to 1.0 μm, and still more preferably 0.2 to 0.8 μm. When the average particle size is 0.1 μm or more, a reduction in the polishing rate can be suppressed. When the average particle size is 1.0 μm or less, deterioration of surface smoothness can be suppressed.

1-3. First colloidal silica The average particle size of the first colloidal silica is preferably 5 to 200 nm. When the average particle size is 5 nm or more, a decrease in the polishing rate can be suppressed. When the average particle size is 200 nm or less, deterioration of surface smoothness can be suppressed. The average particle size of the first colloidal silica is more preferably 10 to 200 nm, still more preferably 20 to 200 nm.

  Colloidal silica is known to have a spherical shape, a chain shape, a confetti shape (particle shape having a convex portion on the surface), an irregular shape, and the like, and primary particles are monodispersed in water to form a colloidal shape. The colloidal silica used in the present invention is particularly preferably spherical or nearly spherical colloidal silica. Surface smoothness can be further improved by using spherical or nearly spherical colloidal silica. Colloidal silica is obtained by a water glass method using sodium silicate or potassium silicate as a raw material, a method of hydrolyzing an alkoxysilane such as tetraethoxysilane with an acid or alkali, and the like.

1-4. Wet method silica particles and first colloidal silica The ratio of the average particle size of the wet method silica particles to the average particle size of the first colloidal silica is preferably 2.0 to 30.0, more preferably 2.5. It is -20.0, More preferably, it is 3.0-16.0. When the average particle size ratio is 2.0 or more, the polishing rate can be improved. When the average particle size ratio is 30.0 or less, deterioration of surface smoothness can be suppressed.

  The total concentration of the wet process silica particles and the first colloidal silica is preferably 1 to 50% by mass, more preferably 2 to 40% by mass, based on the entire abrasive composition used in the rough polishing step. When the total concentration of the silica particles is 1% by mass or more, a decrease in the polishing rate can be suppressed. When the total concentration of silica particles is 50% by mass or less, a sufficient polishing rate can be maintained without using excessive silica particles.

  It is preferable that the ratio of the wet method silica particle to the whole silica particle is 5-95 mass%, More preferably, it is 20-80 mass%. When the ratio of the wet process silica particles is 95% by mass or less, deterioration of the surface smoothness can be suppressed. When the ratio of the wet method silica particles is 5% by mass or more, a decrease in the polishing rate can be suppressed.

  It is preferable that the ratio of the 1st colloidal silica to the whole silica particle is 5-95 mass%, More preferably, it is 20-80 mass%. When the ratio of the first colloidal silica is 5% by mass or more, deterioration of the surface smoothness can be suppressed. When the ratio of the first colloidal silica is 95% by mass or less, a decrease in the polishing rate can be suppressed.

1-5. Other Components An acid and / or a salt thereof and an oxidizing agent can be preferably used for the first abrasive composition.

  As the acid, an inorganic acid, an organic acid, or both may be present. Specific examples of the inorganic acid include nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, and tripolyphosphoric acid. Specific examples of organic acids include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), and diethylenetriaminepenta (methylenephosphonic acid). Organic phosphonic acids such as ethane-1,1-diphosphonic acid and methanehydroxyphosphonic acid, aminocarboxylic acids such as glutamic acid and aspartic acid, citric acid, tartaric acid, oxalic acid, nitroacetic acid, maleic acid, malic acid, succinic acid, etc. These carboxylic acids are mentioned. There are no particular limitations on the counter ion when these acids are used as salts, and specific examples include counter ions of metals, ammonium, alkylammonium, and the like.

  The concentration of the acid and / or salt thereof used in the first abrasive composition in the abrasive composition can be determined according to the pH set in the first abrasive composition.

  Examples of the oxidizing agent include peroxide, permanganic acid or a salt thereof, chromic acid or a salt thereof, and the like. Specific examples include hydrogen peroxide, sodium peroxide, barium peroxide, potassium permanganate and the like. Of these, hydrogen peroxide is preferred.

  The concentration of the oxidizing agent used in the first abrasive composition in the abrasive composition is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, from the viewpoint of improving the polishing rate. From the viewpoint of improving the surface smoothness during rough polishing, the content is preferably 6% by mass or less, and more preferably 4% by mass or less.

  Water used in the first abrasive composition is used as a medium, and examples thereof include distilled water, ion exchange water, and pure water. The content of water in the first abrasive composition is preferably 50 to 99% by mass, more preferably 60 to 98% by mass.

  The pH value of the first abrasive composition is 0.1 to 4.0, preferably 0.5 to 3.0. When the pH value is 0.1 or more, deterioration of surface smoothness can be suppressed. When the pH value is 4.0 or less, a decrease in the polishing rate can be suppressed. In general, electroless nickel-phosphorus plating is usually performed under conditions of a pH value of 4-6. Under a pH value of 4 or less, nickel tends to dissolve, so that plating is difficult to proceed. On the other hand, in polishing, since nickel tends to dissolve under conditions of pH 4 or lower, it is easy to increase the polishing rate.

2. Final polishing step In the method for producing an aluminum magnetic disk substrate of the present invention, the final polishing step is a polishing step performed as the final step in two or more polishing steps.

2-1. 2nd abrasive | polishing agent composition A final grinding | polishing process is performed in presence of the 2nd abrasive | polishing agent composition containing 2nd colloidal silica, a water-soluble polymer compound, and water.

2-2. Second Colloidal Silica The average particle size of the second colloidal silica used in the second abrasive composition is preferably 1 to 50 nm. When the average particle size is 1 nm or more, a decrease in the polishing rate can be suppressed. When the average particle size is 50 nm or less, deterioration of surface smoothness can be suppressed. The average particle size of the second colloidal silica is more preferably 2 to 40 nm, and further preferably 3 to 40 nm.

  Colloidal silica has known shapes such as a spherical shape, a chain shape, a confetti shape (particle shape having a convex portion on the surface), an irregular shape, and the like, and primary particles are monodispersed in water to form a colloidal shape. As the second colloidal silica, spherical or nearly spherical colloidal silica is preferable. Surface smoothness can be further improved by using spherical or nearly spherical colloidal silica. Colloidal silica is obtained by a water glass method using sodium silicate or potassium silicate as a raw material, or a method of hydrolyzing an alkoxysilane such as tetraethoxysilane with an acid or an alkali.

  Abrasive composition used in the final polishing step (second abrasive) rather than the average particle size of the first colloidal silica used in the abrasive composition (first abrasive composition) used in the rough polishing step The average particle size of the second colloidal silica used in the composition is small. Thereby, the surface smoothness after the finish polishing step is good.

  It is preferable that the density | concentration of a 2nd colloidal silica is 1-50 mass% of the whole 2nd abrasive | polishing agent composition, More preferably, it is 2-40 mass%. When the concentration of the second colloidal silica is 1% by mass or more, a decrease in the polishing rate can be suppressed. When the concentration of the second colloidal silica is 50% by mass or less, a sufficient polishing rate can be maintained without using unnecessary colloidal silica.

2-3. Water-soluble polymer compound The water-soluble polymer compound contained in the second abrasive composition is a polymer or copolymer having a structural unit derived from an unsaturated aliphatic carboxylic acid. That is, the water-soluble polymer compound is a polymer compound polymerized using an unsaturated aliphatic carboxylic acid and / or a salt thereof as a monomer, and a structural unit derived from the unsaturated aliphatic carboxylic acid is an essential structural unit. Is a polymer compound. Examples of unsaturated aliphatic carboxylic acids and salts thereof include acrylic acid, methacrylic acid, maleic acid, itaconic acid and salts thereof.

  In the water-soluble polymer compound, at least a part of the structural unit derived from the unsaturated aliphatic carboxylic acid may be contained as a carboxylic acid salt. Examples of the carboxylic acid salt include sodium salt, potassium salt, magnesium salt, ammonium salt, amine salt, alkylammonium salt and the like.

  In order to contain the structural unit derived from the unsaturated aliphatic carboxylic acid as the carboxylic acid in the water-soluble polymer compound, the unsaturated aliphatic carboxylic acid may be polymerized as a monomer, or the unsaturated aliphatic carboxylic acid may be polymerized. After polymerizing a carboxylic acid salt as a monomer, it may be converted to a carboxylic acid by cation exchange. Further, in order to contain a structural unit derived from an unsaturated aliphatic carboxylic acid as a carboxylic acid salt in the water-soluble polymer compound, the unsaturated aliphatic carboxylic acid salt may be polymerized as a monomer. The salt of carboxylic acid may be formed by polymerizing an unsaturated aliphatic carboxylic acid as a monomer and then neutralizing with a base.

  In order to evaluate the ratio of the structural unit contained as the carboxylic acid and the structural unit contained as the carboxylic acid salt in the water-soluble polymer compound, it is necessary to use the pH value of the aqueous solution of the water-soluble polymer compound. it can. When the pH value of the water-soluble polymer compound aqueous solution is low, it can be evaluated that the content ratio of the structural unit contained as the carboxylic acid is high. On the other hand, when the pH value of the water-soluble polymer compound aqueous solution is high, it can be evaluated that the content ratio of the structural unit contained as a carboxylic acid salt is high. In the present invention, for example, a water-soluble polymer compound having a pH value of 1 to 13 in a water-soluble polymer compound aqueous solution having a concentration of 10% by mass can be used.

  When the water-soluble polymer compound is a copolymer having a structural unit derived from an unsaturated aliphatic carboxylic acid, as a monomer used for copolymerization in combination with an unsaturated aliphatic carboxylic acid and / or a salt thereof, An example is a hydrophobic monomer. Hydrophobic monomers include unsaturated aliphatic carboxylic acid esters such as acrylic acid esters, methacrylic acid esters, maleic acid esters and itaconic acid esters, and N-substituted unsaturated amides such as N-alkyl acrylamides and N-alkyl methacrylamides. And aromatic monomers such as (N-substituted α, β-ethylenically unsaturated amide), styrene, α-methylstyrene, divinylbenzene, N-phenylmaleimide and the like. Preferable specific examples of the hydrophobic monomer include n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, t-butyl acrylate, t-butyl methacrylate, pentyl acrylate, and methacrylic acid. Pentyl, hexyl acrylate, hexyl methacrylate, heptyl acrylate, heptyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, Nn-butylacrylamide, N-iso-butyl Acrylamide, N-sec-butylacrylamide, N-tert-butylacrylamide, Nn-butylmethacrylamide, N-iso-butylmethacrylamide, N-sec-butylmethacrylamide, N-ter - butyl methacrylamide, and the like. Among them, Nn-butylacrylamide, N-iso-butylacrylamide, N-sec-butylacrylamide, N-tert-butylacrylamide, Nn-butylmethacrylamide, N-iso-butylmethacrylamide, N-sec -Butyl methacrylamide and N-tert-butyl methacrylamide are particularly preferred.

  It is preferable to polymerize or copolymer by polymerizing these monomer components alone or in combination. As the combination of copolymerization, a combination of acrylic acid and / or a salt thereof and an acrylic ester, a combination of acrylic acid and / or a salt thereof and a methacrylic ester, a combination of acrylic acid and / or a salt thereof and N-alkylacrylamide, Combination of acrylic acid and / or salt thereof and N-alkylmethacrylamide, combination of methacrylic acid and / or salt thereof and acrylate ester, combination of methacrylic acid and / or salt thereof and methacrylic ester, methacrylic acid and / or thereof A combination of a salt and N-alkyl acrylamide, a combination of methacrylic acid and / or a salt thereof and N-alkyl methacrylamide is preferably used. Among them, a combination of acrylic acid and / or a salt thereof and N-alkylacrylamide, a combination of acrylic acid and / or a salt thereof and N-alkylmethacrylamide, a combination of methacrylic acid and / or a salt thereof and N-alkylacrylamide, More preferred is a combination of an acid and / or a salt thereof and N-alkyl methacrylamide, wherein the alkyl group of N-alkyl acrylamide or N-alkyl methacrylamide is an n-butyl group, an iso-butyl group, a sec-butyl group, a tert- Those which are at least one selected from the group consisting of butyl groups are particularly preferably used.

  The weight average molecular weight of the water-soluble polymer compound is preferably 500 or more and 50000 or less, more preferably 1000 or more and 30000 or less. The weight average molecular weight is measured in terms of polyacrylic acid by gel permeation chromatography (GPC).

  The concentration of the water-soluble polymer compound in the abrasive composition is preferably 0.0001% by mass or more and 1.0% by mass or less, more preferably 0.001% by mass or more, 0 in terms of solid content. It is 0.5 mass% or less, More preferably, it is 0.005 mass% or more and 0.2 mass% or less. Especially preferably, it is 0.01 mass% or more and 0.1 mass% or less.

2-4. Other Components An acid and / or a salt thereof and an oxidizing agent can be preferably used for the second abrasive composition.

  As the acid, an inorganic acid, an organic acid, or both may be present. Specific examples of the inorganic acid include nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, and tripolyphosphoric acid. Specific examples of organic acids include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), and diethylenetriaminepenta (methylenephosphonic acid). Organic phosphonic acids such as ethane-1,1-diphosphonic acid and methanehydroxyphosphonic acid, aminocarboxylic acids such as glutamic acid and aspartic acid, citric acid, tartaric acid, oxalic acid, nitroacetic acid, maleic acid, malic acid, succinic acid, etc. These carboxylic acids are mentioned. There are no particular limitations on the counter ion when these acids are used as salts, and specific examples include counter ions of metals, ammonium, alkylammonium, and the like.

  The concentration of the acid and / or salt thereof used in the second abrasive composition in the abrasive composition can be determined according to the pH set in the second abrasive composition.

  Examples of the oxidizing agent include peroxide, permanganic acid or a salt thereof, chromic acid or a salt thereof, and the like. Specific examples include hydrogen peroxide, sodium peroxide, barium peroxide, potassium permanganate and the like. Of these, hydrogen peroxide is preferred.

  The concentration of the oxidizing agent used in the second abrasive composition in the abrasive composition is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, from the viewpoint of improving the polishing rate. From the viewpoint of surface smoothness after the finish polishing step, it is preferably 5% by mass or less, and more preferably 3% by mass or less.

  The water used for the second abrasive composition is used as a medium, and examples thereof include distilled water, ion exchange water, and pure water. The content of water in the second abrasive composition is preferably 50 to 99 mass%, more preferably 60 to 98 mass%.

  The pH value of the second abrasive composition is 0.1 to 4.0, preferably 0.5 to 3.0. When the pH value is 0.1 or more, deterioration of surface smoothness can be suppressed. When the pH value is 4.0 or less, a decrease in the polishing rate can be suppressed.

3. Polishing method of rough polishing step and finish polishing step As a polishing method, a polishing pad is attached to a surface plate of a polishing machine, and a polishing composition is supplied to the surface of the aluminum magnetic disk substrate to be polished or the polishing pad, and the surface to be polished Is generally rubbed with a polishing pad (referred to as polishing), and both single-side polishing and double-side polishing can be employed.

  In the case of double-sided polishing, first prepare two polishing surface plates with a polishing pad attached, put the polishing pad of one polishing surface plate on the front surface of the substrate, and polish the polishing pad of the other polishing surface plate Is applied to the back surface of the substrate, so that the substrate is sandwiched between the polishing pads. Then, in this state, a slurry-like abrasive composition in which an abrasive is dispersed between the polishing pad and the front surface (front surface or back surface) of the substrate is supplied, and at the same time, a polishing platen or substrate is mounted. By moving, the surface of the substrate is rubbed with a polishing pad. Single-side polishing is a method in which a single polishing surface plate is used and a polishing pad is applied to the front surface or the back surface of a substrate to polish one surface at a time.

  With this operation, the convex portion on the surface of the object is scraped off while the abrasive rolls on the surface of the object or moves while being held by the polishing pad. As a result, the front surface of the substrate and the back surface of the substrate are polished simultaneously.

  As the polishing pad, any other type such as a urethane type, a suede type, a non-woven fabric type, and a two-layer type in which these are laminated can be used. A polishing pad containing various additives such as carbon and ceria can also be used.

  In the present invention, the polishing process has two or more stages of polishing processes including at least a rough polishing process before the final stage and a final polishing process of the final stage. That is, the polishing step has at least one rough polishing step before the final polishing step. In addition, it is necessary that the average particle diameter of the second colloidal silica in the finishing step is smaller than the average particle diameter of the first colloidal silica in the final rough polishing step. The number of rough polishing steps is not particularly limited, but is usually 1 to 3 from the viewpoint of work efficiency.

  A rinsing process and / or a cleaning process may be interposed between the rough polishing process and the final polishing process, that is, before the final polishing process. By sandwiching the rinsing process and / or the cleaning process, polishing scraps and residual particles generated in the rough polishing process are removed, and the workability of the final polishing process can be improved. In addition, the rinsing step and / or the cleaning step can also be performed for the purpose of rinsing or cleaning the abrasive composition during the same polishing step (rough polishing step or final polishing step). For example, in an arbitrary rough polishing step, rough polishing is performed using the first abrasive composition, a rinsing step and / or a cleaning step are performed, and then the same or different first as the first abrasive composition. It is possible to further perform rough polishing using the abrasive composition. Alternatively, in the final polishing step, the second polishing composition is used for final polishing, and a rinsing step and / or a cleaning step are performed. Thereafter, the second polishing is the same as or different from the second polishing composition. Further polishing can be performed using the agent composition.

  Hereinafter, the present invention will be specifically described based on examples. The present invention is not limited to these examples, and can be carried out in various modes as long as they belong to the technical scope of the present invention.

  The finish polishing process in each of the following examples and comparative examples was performed using a substrate polished under the conditions of the rough polishing process in the corresponding examples and comparative examples.

[Method for Preparing First Abrasive Composition]
The abrasive | polishing agent composition (1st abrasive | polishing agent composition) used by the rough | crude grinding | polishing process used in Examples 1-8 and Comparative Examples 1-4 is an abrasive | polishing agent composition which consists of the following component and water. Table 1 shows the results of polishing using these abrasive compositions.

(Examples 1, 2, 8 and Comparative Examples 1, 4)
2. Wet method silica particles (average particle size (D50): 0.3 μm, commercially available wet method silica) 3.0 mass%, first colloidal silica (average particle size (D50): 51 nm, commercially available colloidal silica) 0% by mass (the mass ratio of the wet process silica particles to the first colloidal silica is 5: 5, the total concentration is 6.0% by mass), the sulfuric acid is 0.7% by mass, and the hydrogen peroxide is 1.2% by mass.

(Example 3)
Wet method silica particles (average particle size (D50): 0.3 μm, commercially available wet method silica) 4.2 mass%, first colloidal silica (average particle size (D50): 51 nm, commercially available colloidal silica) 8% by mass (the mass ratio of the wet process silica particles to the first colloidal silica is 7: 3, the total concentration is 6.0% by mass), the sulfuric acid is 0.7% by mass, and the hydrogen peroxide is 1.2% by mass.

Example 4
3. Wet method silica particles (average particle size (D50): 0.3 μm, commercially available wet method silica) 1.8% by mass, first colloidal silica (average particle size (D50): 51 nm, commercially available colloidal silica) 2% by mass (mass ratio of wet process silica particles and first colloidal silica is 3: 7, total concentration is 6.0% by mass), sulfuric acid 0.7% by mass, hydrogen peroxide 1.2% by mass.

(Example 5)
2. Wet method silica particles (average particle size (D50): 0.4 μm, commercially available wet method silica) 3.0 mass%, first colloidal silica (average particle size (D50): 51 nm, commercially available colloidal silica) 0% by mass (the mass ratio of the wet process silica particles to the first colloidal silica is 5: 5, the total concentration is 6.0% by mass), the sulfuric acid is 0.7% by mass, and the hydrogen peroxide is 1.2% by mass.

(Example 6)
2. Wet method silica particles (average particle size (D50): 0.8 μm, commercially available wet method silica) 3.0 mass%, first colloidal silica (average particle size (D50): 51 nm, commercially available colloidal silica) 0% by mass (the mass ratio of the wet process silica particles to the first colloidal silica is 5: 5, the total concentration is 6.0% by mass), the sulfuric acid is 0.7% by mass, and the hydrogen peroxide is 1.2% by mass.

(Example 7)
2. Wet method silica particles (average particle size (D50): 0.3 μm, commercially available wet method silica) 3.0 mass%, first colloidal silica (average particle size (D50): 80 nm, commercially available colloidal silica) 0% by mass (the mass ratio of the wet process silica particles to the first colloidal silica is 5: 5, the total concentration is 6.0% by mass), the sulfuric acid is 0.7% by mass, and the hydrogen peroxide is 1.2% by mass.

(Comparative Example 2)
Colloidal silica (average particle size (D50): 51 nm, commercially available colloidal silica) 6.0% by mass, sulfuric acid 0.7% by mass, hydrogen peroxide 1.2% by mass.

(Comparative Example 3)
Wet method silica particles (average particle size (D50): 0.3 μm, commercially available wet method silica) 6.0% by mass, sulfuric acid 0.7% by mass, hydrogen peroxide 1.2% by mass.

[Method for Preparing Second Abrasive Composition]
The abrasive | polishing agent composition (2nd abrasive | polishing agent composition) used by the final polishing process used in Examples 1-8 and Comparative Examples 1-4 is an abrasive | polishing agent composition which consists of the following component and water. Table 2 shows the results of performing the final polishing process on the substrates polished under the conditions of the rough polishing process of the corresponding examples and comparative examples using these second abrasive compositions.

  In the final polishing step, 100 substrates that were previously polished under the conditions of the rough polishing step of the predetermined example or comparative example were prepared, and the final polishing was performed continuously from the first to the 100th. Table 10 shows the polishing rate and scratch evaluation results when finishing polishing for the 10th and 50th substrates in the middle of the continuous finish polishing, and the last 100th substrate, in each example and comparative example. Then, the polishing rate and scratch transition of the finish polishing process were compared.

The acrylic polymers used in the examples as water-soluble polymer compounds are shown below.
Acrylic polymer 1 (acrylic acid / N-tert-butylacrylamide = 86/14 (mol ratio), weight average molecular weight 9000)
The pH value of a 10% by mass aqueous solution of acrylic polymer 1 is usually 3.8. In Examples 1, 3 to 8, and Comparative Examples 2 and 4, this normal acrylic polymer 1 was used.
Acrylic polymer 2 (acrylic acid / N-tert-butylacrylamide = 86/14 (mol ratio), weight average molecular weight 4000)
The pH value of a 10% by mass aqueous solution of acrylic polymer 2 is usually 3.4. In Example 2, this normal acrylic polymer 2 was used.

(Examples 1, 3-7 and Comparative Example 2)
Second colloidal silica (average particle size (D50): 29 nm, commercially available colloidal silica) 5.6% by mass, phosphoric acid 2.0% by mass, hydrogen peroxide 0.6% by mass, acrylic polymer 1 0.02% by mass %.

(Example 2)
Second colloidal silica (average particle size (D50): 29 nm, commercially available colloidal silica) 5.6% by mass, phosphoric acid 2.0% by mass, hydrogen peroxide 0.6% by mass, acrylic polymer 2 0.02% by mass %.

(Example 8)
Second colloidal silica (average particle size (D50): 21 nm, commercially available colloidal silica) 5.6% by mass, phosphoric acid 2.0% by mass, hydrogen peroxide 0.6% by mass, acrylic polymer 1 0.02% by mass %.

(Comparative Example 1)
Colloidal silica (average particle diameter (D50): 29 nm, commercially available colloidal silica) 5.6% by mass, phosphoric acid 2.0% by mass, hydrogen peroxide 0.6% by mass.

(Comparative Example 3)
Since the pits are frequent due to rough polishing, the final polishing process is not performed.

(Comparative Example 4)
Colloidal silica (average particle diameter (D50): 80 nm, commercially available colloidal silica) 5.6% by mass, phosphoric acid 2.0% by mass, hydrogen peroxide 0.6% by mass, acrylic polymer 1 0.02% by mass.

  In Tables 1 and 2, the average particle size of the wet method silica particles, the average particle size of the first colloidal silica, and the second colloidal silica are measured by the following methods.

  The average particle size of the wet method silica particles was measured using a dynamic light scattering particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., Microtrac UPA) for particles of 0.4 μm or less. Moreover, about the particle | grains larger than 0.4 micrometer, it measured using the laser diffraction type particle size distribution measuring machine (Corporation | KK Shimadzu Corporation make, SALD2200). The average particle size of the wet process silica particles is an average particle size (D50) at which the cumulative particle size distribution from the small particle size side with respect to volume is 50%.

  The particle diameter of the colloidal silica (Heywood diameter) was taken with a transmission electron microscope (TEM) (manufactured by JEOL Ltd., transmission electron microscope JEM2000FX (200 kV)) with a field of view at a magnification of 100,000 times, By analyzing this photograph using analysis software (Mac-View Ver. 4.0, manufactured by Mountech Co., Ltd.), the Heywood diameter (projected area equivalent circle diameter) was measured. The average particle size of the colloidal silica is analyzed by analyzing the particle size of about 2000 colloidal silica by the above-mentioned method, and the particle size at which the integrated particle size distribution (accumulated volume basis) from the small particle size side becomes 50% is calculated by the above analysis software. It is the average particle diameter (D50) calculated using (Mount Tech Co., Ltd. product, Mac-View Ver.4.0).

[Polishing conditions for rough polishing process]
Polishing was performed under the following polishing conditions using an electroless nickel-phosphorous plated aluminum magnetic disk substrate having an outer diameter of 95 mm as a polishing target.
Polishing machine: manufactured by System Seiko Co., Ltd., 9B double-side polishing machine polishing pad: manufactured by FILWEL Co., Ltd., P1 pad surface plate rotation speed: upper surface plate -13.0 min ^-1
Lower surface plate 16.0min ^-1
Abrasive composition supply amount: 70 ml / min
Polishing time: Polishing is performed until the polishing amount becomes 1.2 to 1.5 μm / one side.
(130-1500 seconds)
Processing pressure: 12kPa

[Polishing conditions for finish polishing process]
Polishing was performed under the following polishing conditions using the aluminum magnetic disk substrate polished in the rough polishing step as a polishing target.
Polishing machine: Speedfam Co., Ltd., 9B double-side polishing machine Polishing pad: FILWEL Co., Ltd. P2 pad surface plate rotation speed: upper surface plate -8.3 min ^-1
Lower surface plate 25.0min ^-1
Abrasive composition supply amount: 100 ml / min
Polishing time: 300 seconds Processing pressure: 11 kPa

[Evaluation of polished disc surface]
[Polishing speed ratio (rough polishing process, final polishing process)]
The polishing rate was calculated based on the following formula by measuring the mass of the aluminum magnetic disk substrate reduced after polishing.
Polishing rate (μm / min) = mass reduction of aluminum magnetic disk substrate (g) / polishing time (min) / area of one side of aluminum magnetic disk substrate (cm ² ) / electroless nickel-phosphorus plating film density (g / cm ³ ) / 2 × 10 ⁴ (formula)
(However, in the above formula, the area of one surface of the aluminum magnetic disk substrate is 65.9 cm ² , and the density of the electroless nickel-phosphorous plating film is 8.0 g / cm ³ )
The polishing rate ratio is a relative value in the rough polishing step (Table 1) when the polishing rate of Comparative Example 2 obtained using the above formula is 1 (reference), and in the final polishing step (Table 2). These are relative values when the polishing rate obtained using the above formula when the 10th substrate is finish-polished in Comparative Example 1 is 1 (reference). The polishing rate of Comparative Example 2 in the rough polishing step is 0.131 μm / min, and the polishing rate when the 10th substrate is finish-polished in Comparative Example 1 in the final polishing step is 0.102 μm / min. Met.

[Pit (rough polishing process)]
The pits were measured using a three-dimensional surface structure analysis microscope using a scanning white interference method manufactured by Zygo. The measurement was performed using a measuring apparatus (New View 5032 (lens: 2.5 times, zoom: 0.5 times)) manufactured by Zygo and analysis software (Metro Pro) manufactured by Zygo. In the obtained shape profile, when almost no pits were recognized, it was evaluated as “◯ (good)”. When a pit was recognized, it was evaluated as “× (impossible)”. When the evaluation was “x (impossible)”, the pits could be observed visually.

[Scratch ratio (finish polishing process)]
The number of scratches was measured using a MicroMAX VMX-4100 manufactured by Vision Cytec Co., Ltd., and the number of scratches on the substrate was measured under a measurement condition tilt angle of -5 ° and a magnification of 20 times. The scratch ratio is a relative value when the number of scratches when the 10th substrate is finish-polished in Comparative Example 1 is 1 (reference).

[Discussion]
In the rough polishing step (Table 1), wet method silica obtained through the pulverization step as the first abrasive composition from the comparison between Example 1 and Comparative Example 2 and the comparison between Example 1 and Comparative Example 3 By using the particles and colloidal silica in combination, the polishing rate was improved and the pits were better than when each silica particle was used alone.

  From the comparison between Example 1 and Comparative Example 1 and the comparison between Example 2 and Comparative Example 1 in the final polishing step (Table 2), the presence of a water-soluble polymer compound in the second abrasive composition In addition, the initial value of the polishing rate was improved, and the decrease in the polishing rate was suppressed even in continuous multiple polishing. In addition, scratches decreased and surface quality improvement effect was confirmed.

  In the method for producing an aluminum magnetic disk substrate of the present invention, the water-soluble polymer compound is present in the abrasive composition (second abrasive composition) used in the final polishing step, so that the polishing pad is clogged, etc. Therefore, it is estimated that the polishing rate can be maintained high even in the case of continuous multiple polishing.

  In the finish polishing step (Table 2), the first colloidal silica used in the rough polishing step is used as the second colloidal silica used in the second abrasive composition by comparing Example 1 and Comparative Example 4. When colloidal silica having a larger average particle diameter than the above was used, although the polishing rate was improved, the scratch was greatly deteriorated.

  From the above, it can be seen that the combination of the specific rough polishing step and the specific finish polishing step can improve the productivity of the polishing step without deteriorating the product quality of the aluminum magnetic disk substrate.

  The method for producing an aluminum magnetic disk substrate of the present invention can be used for surface polishing of a substrate for a magnetic recording medium in which a nickel-phosphorous plating film is formed on the surface of an aluminum alloy substrate.

Claims (6)

In polishing aluminum magnetic disk substrate after electroless nickel-phosphorous plating,
A rough polishing step prior to the final stage, which is polished using a first abrasive composition containing wet method silica particles obtained through a pulverization step, a first colloidal silica, and water;
Polishing with a second abrasive composition comprising a second colloidal silica, a water-soluble polymer compound, and water, and a final polishing step in the final stage;
Having at least two polishing steps including
The average particle size of the first colloidal silica is smaller than the average particle size of the wet method silica particles,
The average particle size of the second colloidal silica is smaller than the average particle size of the first colloidal silica,
The water-soluble polymer compound is a polymer or copolymer having a structural unit derived from an unsaturated aliphatic carboxylic acid,
A method for producing an aluminum magnetic disk substrate, wherein the first abrasive composition in the rough polishing step and the second abrasive composition in the final polishing step have a pH value of 0.1 to 4.0.   2. The aluminum magnetism according to claim 1, wherein in the rough polishing step, an average particle diameter of the wet process silica particles is 0.1 to 1.0 μm, and an average particle diameter of the first colloidal silica is 5 to 200 nm. A manufacturing method of a disk substrate. In the rough polishing step, the total concentration of the wet process silica particles and the first colloidal silica is 1 to 50% by mass in the first abrasive composition,
The ratio of the wet process silica particles in the entire silica particles in the first abrasive composition is 5 to 95 mass%, and the ratio of the first colloidal silica is 5 to 95 mass%. 3. A method for producing an aluminum magnetic disk substrate according to 1 or 2.   In the final polishing step, the average particle diameter of the second colloidal silica is 1 to 50 nm, and the concentration of the second colloidal silica contained in the second abrasive composition is 1 to 50% by mass. The manufacturing method of the aluminum magnetic disc board | substrate of any one of Claims 1-3.   In the final polishing step, the water-soluble polymer compound has a weight average molecular weight of 500 to 50,000, and the concentration of the water-soluble polymer compound in the second abrasive composition is 0.0001 to 1.0 mass. 5. The method for manufacturing an aluminum magnetic disk substrate according to claim 1, wherein the manufacturing method is aluminum.   6. The aluminum magnetic disk substrate according to claim 1, further comprising a structural unit derived from a hydrophobic monomer when the water-soluble polymer compound is a copolymer in the finish polishing step. 7. Manufacturing method.