JP2020119619A - Polishing agent composition for magnetic disk substrate - Google Patents

Abstract

To provide a polishing agent composition for a magnetic disk substrate, which achieves not only reduction of short-wavelength waviness of the substrate after polishing but also reduction of halation, without lowering productivity.SOLUTION: A polishing agent composition contains colloidal silica, a water-soluble polymer compound, and water. The water-soluble polymer compound is a copolymer having a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as essential monomers, and a molar ratio of a constitutional unit derived from the monomer having the carboxylic acid group to the constitutional unit derived from the monomer having the sulfonic acid group is in a range of 95:5 to 5:95. The water-soluble polymer compound has a weight average molecular weight of 1,000 to 1,000,000.SELECTED DRAWING: None

Description

The present invention relates to an abrasive composition used for polishing electronic parts such as magnetic recording media such as semiconductors and hard disks. In particular, it relates to an abrasive composition used for polishing the surface of a magnetic recording medium substrate such as a glass magnetic disk substrate or an aluminum magnetic disk substrate. Furthermore, the present invention relates to an abrasive composition used for surface polishing of an aluminum magnetic disk substrate for a magnetic recording medium in which an electroless nickel-phosphorus plating film is formed on the surface of an aluminum alloy substrate.

Conventionally, as an abrasive composition for polishing the surface of an electroless nickel-phosphorus plating film of an aluminum magnetic disk substrate, various improvements in polishing characteristics have been demanded in order to improve magnetic recording density. For example, in the case of scratches, the scratch portion may cause a writing or reading error, or the burr around the scratch may cause a head collision or the like.

Therefore, from the viewpoint of reducing scratches, colloidal silica has come to be used for polishing an aluminum magnetic disk substrate as an abrasive grain portion responsible for mechanical polishing of an abrasive composition. At that time, in industrial polishing, the abrasive grain portion of the abrasive composition, which is responsible for mechanical polishing, and the chemical portion, which is responsible for chemical polishing, are often mixed and used immediately before actual polishing.

However, when the colloidal silica as the abrasive grain portion and the chemical component are mixed, the colloidal silica tends to aggregate. As measures against this, removal of coarse particles and agglomerated particles, adjustment of corrosiveness of abrasives (Patent Document 1), adjustment of particle shape (Patent Document 2), adjustment of content of agglomerated particles (Patent Document 3), etc. Proposals have been made.

JP, 2009-120850, A JP, 2009-172709, A JP, 2010-170650, A

Further, from the viewpoint of improving the magnetic recording density, not only scratches but also halation and undulation are newly required. The term "halation" used herein means that a substrate total surface defect inspection machine (NS2000H manufactured by Hitachi High-Tech Fine Systems Co., Ltd.) described in the examples below can detect fine defects on the substrate surface under specific inspection conditions. Yes, it can be quantitatively evaluated as a halation count.

Halation is considered to be a phenomenon caused by the presence of some fine non-uniformity of the substrate surface in a wide range of the substrate, and the cause thereof is the polishing pad, the carrier, the substrate, and the polishing agent composition. The incongruity of the characteristics possessed is considered. Recently, the presence of halation has become a new problem as an obstacle to the improvement of magnetic recording density, and reduction of halation is required.

On the other hand, conventionally, reduction of waviness on the substrate surface has been demanded from the viewpoint of improving magnetic recording density. Among the undulations, reducing long-wave undulations (wavelength: 500 μm to 5 mm) and medium-wavelength undulations (wavelength: 100 to 500 μm) has been conventionally considered as a problem to be solved from the viewpoint of improving magnetic recording density. With the recent technological progress, reduction of short wavelength waviness (wavelength: 20 to 100 μm) has become a problem to be solved from the viewpoint of improving magnetic recording density.

An object of the present invention is to provide an abrasive composition for a magnetic disk substrate, which achieves not only reduction of short-wavelength waviness of a substrate after polishing but also reduction of halation without lowering productivity.

In order to solve the above problems, as a result of intensive studies, the following magnetic disk substrate abrasive composition was used to achieve short wavelength waviness reduction and halation reduction without lowering productivity, and reached the present invention. did.

[1] A polishing composition containing colloidal silica, a water-soluble polymer compound, and water, wherein the water-soluble polymer compound is a monomer having at least a carboxylic acid group and a sulfonic acid group. The amount of the structural unit derived from the monomer having a carboxylic acid group and the structural unit derived from a monomer having a sulfonic acid group of the water-soluble polymer compound The molar ratio of the water-soluble polymer compound is in the range of 95:5 to 5:95, and the weight average molecular weight of the water-soluble polymer compound is 1,000 to 1,000,000.

[2] The abrasive composition for a magnetic disk substrate according to the above [1], wherein the colloidal silica has an average particle diameter (D50) of 1 to 100 nm and a concentration in the composition of 1 to 50% by mass.

[3] The magnetic disk substrate abrasive composition according to [1] or [2], wherein the water-soluble polymer compound has a weight average molecular weight of 5,000 to 600,000.

[4] The polishing composition further contains a surfactant, the surfactant has a sulfonate group and/or a sulfonate group, and further has an aromatic group in the main chain of the repeating unit. The magnetic disk substrate abrasive composition according to any one of the above [1] to [3], which is an ionic surfactant.

[5] The anionic surfactant having a sulfonate group and/or a sulfonate group and further having an aromatic group in the main chain of the repeating unit is a naphthalene sulfonate compound, a lignin sulfonate compound, The abrasive composition for a magnetic disk substrate according to the above [4], which is at least one selected from aromatic aminosulfonic acid compounds and salts thereof.

[6] The magnetic disk substrate according to [5], wherein the anionic surfactant that is the naphthalene sulfonic acid compound is at least one selected from the group consisting of a naphthalene sulfonic acid formaldehyde condensate and methyl naphthalene sulfonic acid. Abrasive composition.

[7] The magnetic disk substrate according to any one of [1] to [6], wherein the monomer having a carboxylic acid group is a monomer selected from acrylic acid or a salt thereof, methacrylic acid or a salt thereof. Abrasive composition.

[8] The monomer having a sulfonic acid group is isoprenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, vinylsulfonic acid, allyl. The abrasive composition for a magnetic disk substrate according to any one of the above [1] to [7], which is a monomer selected from sulfonic acid, isoamylenesulfonic acid, and salts thereof.

[9] A monomer having a carboxylic acid group, wherein the copolymer having at least a carboxylic acid group-containing monomer and a sulfonic acid group-containing monomer, which are the water-soluble polymer compounds, as essential monomers And a polishing composition for a magnetic disk substrate according to any one of the above [1] to [8], which is a copolymer containing a monomer having a sulfonic acid group and a monomer having an amide group as essential monomers. Stuff.

[10] The abrasive composition for a magnetic disk substrate according to [9], wherein the amide group-containing monomer is a monomer selected from acrylamide, methacrylamide, N-alkylacrylamide and N-alkylmethacrylamide. ..

[11] In any one of the above [1] to [10], wherein the abrasive composition further contains an acid and/or a salt thereof, and has a pH value (25° C.) in the range of 0.1 to 4.0. An abrasive composition for a magnetic disk substrate as described above.

[12] The abrasive composition for a magnetic disk substrate according to any one of [1] to [11], wherein the abrasive composition further contains an oxidizing agent.

[13] The abrasive composition for a magnetic disk substrate according to any one of the above [1] to [12], which is used for polishing an electroless nickel-phosphorus plated aluminum magnetic disk substrate.

INDUSTRIAL APPLICABILITY The polishing composition for magnetic disk substrates of the present invention enables reduction of short wavelength waviness and halation after polishing while maintaining a polishing rate.

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

1. Abrasive Composition The abrasive composition for magnetic disk substrates of the present invention is an abrasive composition containing colloidal silica, a water-soluble polymer compound, and water, and contains a surfactant, an acid and/or an optional component. It contains the salt and the oxidizing agent.

1-1. Colloidal silica The colloidal silica used in the present invention preferably has an average particle diameter (D50) of 1 to 100 nm. More preferably, it is 2 to 80 nm. Colloidal silica is obtained by a water glass method in which an alkali metal silicate such as sodium silicate or potassium silicate is used as a raw material, and the raw material is subjected to a condensation reaction in an aqueous solution to grow particles. Alternatively, it can be obtained by an alkoxysilane method in which an alkoxysilane such as tetraethoxysilane is used as a raw material, and the raw material is grown in water containing a water-soluble organic solvent such as alcohol by a condensation reaction by hydrolysis with an acid or an alkali.

Colloidal silica is known to have a spherical shape, a chain shape, a Konpeito sugar shape, 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 preferably spherical or nearly spherical. The concentration of colloidal silica in the abrasive composition is preferably 1 to 50% by mass. More preferably, it is 2 to 40 mass %.

1-2. Water-Soluble Polymer Compound The water-soluble polymer compound used in the present invention is a copolymer containing at least a carboxylic acid group-containing monomer and a sulfonic acid group-containing monomer as essential monomers. The molar ratio of the structural unit derived from the monomer having a carboxylic acid group to the structural unit derived from the monomer having a sulfonic acid group is in the range of 95:5 to 5:95. Further, the water-soluble polymer compound has a weight average molecular weight of 1,000 to 1,000,000. The details will be described below.

1-2-1. Monomer Having Carboxylic Acid Group As the monomer having a carboxylic acid group, unsaturated aliphatic carboxylic acids and salts thereof are preferably used. Specific examples include acrylic acid, methacrylic acid, maleic acid, itaconic acid and salts thereof. Examples of the salt include sodium salt, potassium salt, magnesium salt, ammonium salt, amine salt, alkylammonium salt and the like.

Among the water-soluble polymer compounds, the pH value of the water-soluble polymer compound indicates whether the ratio of the monomer having a carboxylic acid group is in the acid state or in the salt state. Can be evaluated with. The higher the proportion of the acid, the lower the pH value, and the higher the proportion of the salt, the higher the pH value. In the present invention, for example, a water-soluble polymer compound having a pH value (25° C.) of 1 to 13 in a water-soluble polymer compound aqueous solution having a concentration of 10% by mass can be used.

1-2-2. Sulfonic acid group-containing monomer Specific examples of the sulfonic acid group-containing monomer include isoprenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, and styrene. Examples thereof include sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, isoamylene sulfonic acid and salts thereof. Preferably, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid and salts thereof are mentioned.

1-2-3. Other Monomers The water-soluble polymer compound used in the present invention is essentially a monomer having a carboxylic acid group and a monomer having a sulfonic acid group, but other monomers Can also be used. For example, a monomer having an amide group can also be used. That is, the water-soluble polymer compound used in the present invention is a copolymer in which a monomer having a carboxylic acid group, a monomer having a sulfonic acid group and a monomer having an amide group are essential monomers. Is also preferable. As the monomer having an amide group, specifically, acrylamide, methacrylamide, N-alkylacrylamide, N-alkylmethacrylamide, or the like can be used.

Specific examples of N-alkyl acrylamide and N-alkyl methacrylamide include N-methyl acrylamide, N-ethyl acrylamide, Nn-propyl acrylamide, N-iso-propyl acrylamide, N-n-butyl acrylamide and N-iso. -Butylacrylamide, N-sec-butylacrylamide, N-tert-butylacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, Nn-propylmethacrylamide, N-iso-propylmethacrylamide, Nn- Examples thereof include butyl methacrylamide, N-iso-butyl methacrylamide, N-sec-butyl methacrylamide, and N-tert-butyl methacrylamide.

1-2-4. Copolymer The water-soluble polymer compound used in the present invention is a copolymer in which a monomer having a carboxylic acid group and a monomer having a sulfonic acid group are essential monomers. The amount ratio of the structural unit derived from the monomer having a carboxylic acid group and the structural unit derived from the monomer having a sulfonic acid group of the compound is in the range of 95:5 to 5:95 in terms of mol ratio. That is, the proportion of the constituent units derived from the monomer having a carboxylic acid group in the copolymer is 5 to 95 mol%, preferably 8 to 92 mol%, and more preferably 10 to 90 mol%. .. The ratio of the structural unit derived from the monomer having a sulfonic acid group is 5 to 95 mol%, preferably 8 to 92 mol%, more preferably 10 to 90 mol%.

1-2-5. Production Method of Water-Soluble Polymer Compound The production method of the water-soluble polymer compound is not particularly limited, but an aqueous solution polymerization method is preferable. According to the aqueous solution polymerization method, the water-soluble polymer compound can be obtained as a uniform solution. The polymerization solvent for the above aqueous solution polymerization is preferably an aqueous solvent, and particularly preferably water.
In addition, in order to improve the solubility of the above-mentioned monomer components in the solvent, an organic solvent may be appropriately added within a range that does not adversely affect the polymerization of each monomer. Examples of the organic solvent include alcohols such as isopropyl alcohol and ketones such as acetone. These may be used alone or in combination of two or more.

The method for producing a water-soluble polymer compound using the above aqueous solvent will be described below. In the polymerization reaction, known polymerization initiators can be used, but radical polymerization initiators are particularly preferably used. Examples of the radical polymerization initiator include persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate, hydroperoxides such as t-butyl hydroperoxide, water-soluble peroxides such as hydrogen peroxide, and methyl ethyl ketone peroxide. Ketone peroxides such as oxides and cyclohexanone peroxide, oil-soluble peroxides such as di-t-butyl peroxide, dialkyl peroxides such as t-butylcumyl peroxide, azobisisobutyronitrile, 2,2 -Azo compounds such as azobis(2-methylpropionamidine)dihydrochloride. These peroxide-based radical polymerization initiators may be used alone or in combination of two or more. Among the above-mentioned peroxide type radical polymerization initiators, persulfates and azo compounds are preferable, and azobisisobutyronitrile is particularly preferable, because the molecular weight of the water-soluble polymer compound to be generated can be easily controlled. ..

The amount of the radical polymerization initiator used is not particularly limited, but is 0.1 to 15% by mass, particularly 0.5 to 10% by mass, based on the total mass of all monomers of the water-soluble polymer compound. Preference is given to using. By setting this ratio to 0.1% by mass or more, the copolymerization rate can be improved, and by setting it to 15% by mass or less, the stability of the water-soluble polymer compound can be improved.

In some cases, the water-soluble polymer compound may be produced by using a water-soluble redox polymerization initiator. As the redox-based polymerization initiator, an oxidizing agent (for example, the above-mentioned peroxide) and a reducing agent such as sodium bisulfite, ammonium bisulfite, ammonium sulfite, sodium hydrosulfite, and a combination of iron alum, potassium alum, etc. Can be mentioned.

In the production of the water-soluble polymer compound, a chain transfer agent may be appropriately added to the polymerization system in order to adjust the molecular weight. As the chain transfer agent, for example, sodium phosphite, sodium hypophosphite, potassium hypophosphite, sodium sulfite, sodium hydrogen sulfite, mercaptoacetic acid, mercaptopropionic acid, thioglycolic acid, 2-propanethiol, 2- Examples thereof include mercaptoethanol and thiophenol.

The polymerization temperature for producing the water-soluble polymer compound is not particularly limited, but the polymerization temperature is preferably 60 to 100°C. When the polymerization temperature is 60° C. or higher, the polymerization reaction proceeds smoothly and the productivity is excellent, and when the polymerization temperature is 100° C. or lower, coloring can be suppressed.

Further, the polymerization reaction can be carried out under pressure or reduced pressure, but it is preferable to carry out the polymerization reaction under normal pressure because the cost for providing equipment for pressurization or reduced pressure is required. The polymerization time is preferably 2 to 20 hours, particularly preferably 3 to 10 hours.

After the polymerization reaction, neutralization with a basic compound is carried out if necessary. Examples of the basic compound used for neutralization include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide, ammonia water, and monoethanolamine. And organic amines such as diethanolamine and triethanolamine. The pH value (25° C.) after neutralization is preferably 2 to 9, and more preferably 3 to 8 in the case of an aqueous solution having a water-soluble polymer compound concentration of 10% by mass.

1-2-6. Weight average molecular weight The water-soluble polymer compound used in the present invention is a copolymer having a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as essential monomers, and the weight average molecular weight is It is 1,000 to 1,000,000, preferably 3,000 to 800,000, and more preferably 5,000 to 600,000. The weight average molecular weight of the water-soluble polymer compound is measured by gel permeation chromatography (GPC) in terms of polyacrylic acid. When the weight average molecular weight of the water-soluble polymer compound is less than 1,000, waviness after polishing is deteriorated. On the other hand, when it exceeds 1,000,000, the viscosity of the aqueous solution becomes high, and the handling becomes difficult.

1-2-7. Concentration The concentration of the water-soluble polymer compound in the abrasive composition is preferably 0.0001 to 3.0% by mass, more preferably 0.001 to 2.0% by mass in terms of solid content, and Preferably it is 0.005-1.0 mass %. If the concentration of the water-soluble polymer compound is less than 0.0001% by mass, the effect of adding the water-soluble polymer compound cannot be sufficiently obtained, and if it is more than 3.0% by mass, The effect of addition will reach a ceiling, and more water-soluble polymer compounds will be added than necessary, which is not economical.

1-3. Surfactant In the present invention, for the purpose of further reducing waviness and halation, the surfactant used as an optional component has a sulfonate group and/or a sulfonate group, and further has a repeating unit in the main chain. It is an anionic surfactant having an aromatic group.

Specific examples thereof include polyalkylaryl sulfonic acid type compounds such as naphthalene sulfonic acid formaldehyde condensate, methyl naphthalene sulfonic acid formaldehyde condensate, anthracene sulfonic acid formaldehyde, melamine formalin resin sulfone type compounds such as melamine sulfonic acid formaldehyde condensate, lignin. Examples thereof include lignin sulfonic acid compounds such as sulfonic acid and modified lignin sulfonic acid, and aromatic amino sulfonic acid compounds such as aminoaryl sulfonic acid-phenol-formaldehyde condensate. Among them, naphthalene sulfonic acid formaldehyde condensates of polyalkylaryl sulfonic acid compounds, naphthalene sulfonic acid compounds such as methyl naphthalene sulfonic acid formaldehyde condensate, lignin sulfonic acid compounds, aromatic amino sulfonic acid compounds, and those Are preferred. Among the naphthalenesulfonic acid type compounds, naphthalenesulfonic acid formaldehyde condensate, methylnaphthalenesulfonic acid formaldehyde condensate and salts thereof are particularly preferable.

When used as a salt, the counter ion may be an alkali metal salt such as sodium or potassium, an alkaline earth metal salt such as calcium, an ammonium salt, a primary amine salt such as monoethanolamine, or a secondary amine salt such as diethanolamine. , Tertiary amine salts such as triethanolamine, and quaternary ammonium salts such as tetramethylammonium.

The content of the surfactant in the abrasive composition is preferably 0.0001 to 2.0 mass%, more preferably 0.001 to 1.0 mass%. If it is less than 0.0001% by mass, the effect of reducing the waviness cannot be sufficiently obtained. If it exceeds 2.0% by mass, the polishing rate will decrease.

1-4. Acid and/or salt thereof In the present invention, an acid and/or salt thereof can be used for pH adjustment or as an optional component. Examples of the acid and/or its salt used include inorganic acid and/or its salt and organic acid and/or its salt.

Examples of the inorganic acid and/or its salt include nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, phosphonic acid, pyrophosphoric acid, tripolyphosphoric acid and the like and/or salts thereof.

Examples of the organic acid and/or its salt include aminocarboxylic acids such as glutamic acid and aspartic acid and/or salts thereof, carboxylic acids such as citric acid, tartaric acid, oxalic acid, nitroacetic acid, maleic acid, malic acid and succinic acid, and/or Alternatively, salts thereof, organic phosphonic acids and/or salts thereof and the like can be mentioned. These acids and/or salts thereof may be used alone or in combination of two or more.

Examples of the organic phosphonic acid and/or its salt include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid). Acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2. At least one selected from diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, α-methylphosphonosuccinic acid, and salts thereof. Included are one or more compounds.

It is also a preferred embodiment to use two or more kinds of the above compounds in combination, specifically, a combination of sulfuric acid and phosphoric acid, a combination of phosphoric acid and an organic phosphonic acid, or a phosphoric acid and an organic phosphonate. And the like.

1-5. Oxidizing Agent In the present invention, an oxidizing agent can be used as a polishing accelerator. Examples of the oxidizing agent used include peroxide, permanganic acid or a salt thereof, chromic acid or a salt thereof, peroxo acid or a salt thereof, halogenoxo acid or a salt thereof, oxygen acid or a salt thereof, and these oxidizing agents. A mixture of two or more species can be used.

Specifically, hydrogen peroxide, sodium peroxide, barium peroxide, potassium peroxide, potassium permanganate, chromic acid metal salt, dichromic acid metal salt, persulfuric acid, sodium persulfate, potassium persulfate, persulfate. Examples thereof include ammonium sulfate, peroxophosphoric acid, sodium peroxoborate, performic acid, peracetic acid, hypochlorous acid, sodium hypochlorite, calcium hypochlorite and the like. Among them, hydrogen peroxide, persulfuric acid and salts thereof, hypochlorous acid and salts thereof and the like are preferable, and hydrogen peroxide is more preferable.

The content of the oxidizing agent in the abrasive composition is preferably 0.01 to 10.0% by mass. More preferably, it is 0.1 to 5.0 mass %.

2. Physical properties of abrasive composition (pH)
The range of pH value (25° C.) of the polishing composition of the present invention is preferably 0.1 to 4.0. More preferably, it is 0.5 to 3.0. When the pH value (25° C.) of the polishing composition is 0.1 or more, the surface roughness of the substrate after polishing can be suppressed. When the pH value (25° C.) of the polishing composition is 4.0 or less, it is possible to prevent the polishing rate from decreasing.

The polishing composition of the present invention can be used for polishing various electronic components such as magnetic recording media such as hard disks. Particularly, it is preferably used for polishing an aluminum magnetic disk substrate. More preferably, it can be used for polishing an electroless nickel-phosphorus plated aluminum magnetic disk substrate. The electroless nickel-phosphorus plating is usually plated under the condition that the pH value (25° C.) is 4.0 to 6.0. Under the condition that the pH value (25° C.) is 4.0 or less, nickel tends to dissolve, which makes plating difficult. On the other hand, in polishing, for example, nickel tends to dissolve under the condition that the pH value (25° C.) is 4.0 or less. Therefore, by using the abrasive composition of the present invention, the polishing rate can be increased. ..

3. Method for Polishing Magnetic Disk Substrate The abrasive composition of the present invention is suitable for use in polishing a magnetic disk substrate such as an aluminum magnetic disk substrate or a glass magnetic disk substrate. In particular, it is suitable for use in polishing an electroless nickel-phosphorus plated aluminum magnetic disk substrate (hereinafter referred to as an aluminum disk).

As a method to which the polishing composition of the present invention can be applied, for example, a polishing pad is attached to a polishing platen, and the polishing composition is applied to a surface to be polished of a polishing object (for example, an aluminum disk) or a polishing pad. There is a method of supplying an object and rubbing the surface to be polished with a polishing pad. For example, in the case of simultaneously polishing the front surface and the back surface of an aluminum disk, there is a method of using a double-side polishing machine in which polishing pads are attached to the upper surface plate and the lower surface plate, respectively. In this method, an aluminum disc is sandwiched between polishing pads attached to an upper surface plate and a lower surface plate, an abrasive composition is supplied between the polishing surface and the polishing pad, and the two polishing pads are rotated at the same time. Polish the front and back of the disc. Incidentally, in the usual polishing of the magnetic disk substrate, it is general that the main polishing is performed after the dummy polishing. Dummy polishing is the same type as the substrate that is the object to be polished, after the polishing pad is attached to the surface plate of the polishing machine, pad dressing is performed if necessary, and before the main polishing is performed thereafter. Is prepared separately and polished as a dummy substrate. The polishing composition of the present invention can be used only for dummy polishing, only for main polishing, or for both dummy polishing and main polishing.

Any type of polishing pad can be used. There are non-woven type and suede type polishing pads, but suede type is often used. Examples of the material of the foamed surface layer that comes into contact with the abrasive include polyurethane elastomer, polystyrene, polyester, polyvinyl chloride and the like, and polyurethane elastomer is often used.

Hereinafter, the present invention will be specifically described based on Examples, but it goes without saying that the present invention is not limited to these Examples and can be carried out in various modes within the technical scope of the present invention. Nor.

[Method for preparing abrasive composition]
The abrasive compositions used in Examples 1 to 22 and Comparative Examples 1 to 4 are the abrasive compositions containing the materials shown in Table 1 in the contents shown in Table 1. In Table 1, the abbreviation of acrylic acid is AA, the abbreviation of 2-acrylamido-2-methylpropanesulfonic acid is ATBS, and the abbreviation of N-tert-butylacrylamide is TBAA. As the sodium naphthalene sulfonate formaldehyde condensate, Laberin FM-45 manufactured by Dai-ichi Kogyo Seiyaku was used.

[Weight average molecular weight]
As the water-soluble polymer compound, as shown in Table 1, polymers of synthesis numbers 1 to 10 were used. The weight average molecular weight of the water-soluble polymer compound is measured by gel permeation chromatography (GPC) in terms of polyacrylic acid, and the GPC measurement conditions are shown below.

[GPC conditions]
Column: G4000PWXL (manufactured by Tosoh Corporation) + G2500PWXL (manufactured by Tosoh Corporation)
Eluent: 0.2M phosphate buffer/acetonitrile=9/1 (volume ratio)
Flow rate: 1.0 ml/min
Temperature: 40°C
Detection: 210nm (UV)
Sample: Concentration 5 mg/ml (injection volume 100 μl)
Polymer for calibration curve: Polyacrylic acid Molecular weight (peak top molecular weight: Mp) 115,000, 28,000, 4100, 1250 (Sowa Chemical Co., Ltd., American Polymer Standards Corp.)

[Particle size of colloidal silica]
The particle size of the colloidal silica (Heywood diameter) was taken with a transmission electron microscope (TEM) (JEOL Ltd., transmission electron microscope JEM2000FX (200 kV), and a field of view of 100,000 times was photographed. The analysis was performed using analysis software (Mac-View Ver. 4.0, manufactured by Mountech Co., Ltd.) to measure as a Heywood diameter (diameter equivalent to a projected area circle). Approximately 2,000 particles of colloidal silica are analyzed, and the particle size at which the cumulative particle size distribution (accumulation volume basis) from the small particle size side is 50% is determined by the above analysis software (Mac-View Ver, manufactured by Mountech Co., Ltd.). It is an average particle diameter (D50) calculated by using (4.4.0).

[Polishing conditions]
The aluminum magnetic disk substrate having an outer diameter of 95 mm, which was electrolessly nickel-phosphorus plated, was roughly polished, and was polished as a polishing object.

Polishing machine: Speedfam Co., Ltd., 9B double-sided polishing machine Polishing pad: FILWEL Co., Ltd. P2 pad Surface plate rotation speed: Upper surface plate -6.7 rpm
Lower surface plate 20.0 rpm
Abrasive composition supply rate: 100 ml/min
Polishing time: 300 seconds Processing pressure: 14kPa
After preparing the polishing composition by mixing the respective components, a polishing test was conducted. The polishing test results are shown in Tables 2 and 3. The values of the following evaluation items are shown in Table 2 as relative values with the value of Comparative Example 1 as 1 (reference value). In Table 3, Comparative Example 3 is shown as a relative value with 1 (reference value).

[Evaluation of polished disc]
[Polishing speed]
The polishing rate was calculated based on the following formula by measuring the mass of the aluminum magnetic disk substrate that decreased 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 )/density of electroless nickel-phosphorus plating film (g/ cm ³ )/2×10 ⁴
(However, in the above formula, the area of one side of the aluminum magnetic disk substrate is 65.9 cm ² , and the density of the electroless nickel-phosphorus plating film is 8.0 g/cm ³ )

[Method for evaluating short-wavelength waviness on substrate surface after polishing]
The short wavelength waviness of the substrate was measured using a three-dimensional optical profiler New View 8300 manufactured by Ametech Co., Ltd.
The measurement conditions are as follows.

Lens 10x Mirau type ZOOM 1.0x Measurement Type Surface
Measure Mode CSI
Scan Length 5 μm
Camera Mode 1024 x 1024
Filter Band Pass
Cut Off Short 20.000 μm
Long 100.000 μm
Measuring point radius 30.00mm
36 points for every 10 degrees

[Method of evaluating halation on substrate surface after polishing]
Halation was measured using a substrate all-surface defect inspection machine NS2000H manufactured by Hitachi High-Tech Fine Systems Co., Ltd. The measurement conditions are as follows.

PMT/APD Power Control Voltage
Hi-Light 1 OFF
Hi-Light 2 900V
Scan Pitch 3 μm
Inner/Outer Radius 18.0000-47.0000mm
Positive Level 76mV
H2 White Spot Level 80.0mV

Halation is detected as a fine defect on the substrate surface under the above measurement conditions, and can be quantitatively evaluated as a halation count.

[Discussion]
As is clear from Table 2, as compared with the case of using the acrylic acid homopolymer of Comparative Example 1 as the water-soluble polymer compound, the acrylic acid/acrylamido-2-methylpropanesulfonic acid of Examples 1 to 8 was used. It can be seen that when the copolymer is used, the polishing rate, short wavelength waviness, and halation count are all improved. Further, in Examples 9 to 16 in which a surfactant (sodium naphthalene sulfonate formaldehyde condensate) was added, the short wavelength swell and halation count were further improved.

Incidentally, Examples 2, 3 and 10, 11 are the same as Examples 1 and 9 except that acrylic acid of 2-acrylic acid-2-acrylamido-2-methylpropanesulfonic acid copolymer and acrylic acid of 2-acrylamido-2-methylpropanesulfonic acid were used. This is an experimental example in which the ratio is different.

Examples 4 to 7 and 12 to 15 are experimental examples in which the weight average molecular weight of the water-soluble polymer compound added in Examples 1 and 9 is different.

Examples 8 and 16 are the same as Examples 1 and 9 except that an acrylic acid/2-acrylamido-2-methylpropanesulfonic acid/N-tert-butylacrylamide copolymer containing an amide group in the water-soluble polymer was used. Is.

On the other hand, when the 2-acrylamido-2-methylpropanesulfonic acid homopolymer of Comparative Example 2 is used, the polishing rate is improved as compared with Comparative Example 1, but the short wavelength waviness and the halation count are deteriorated. ..

Even in Table 3 in which the average particle diameters of the colloidal silica abrasive grains are different, the acrylic acid/2-acrylamide-2 of Example 17 was compared with the case where the acrylic acid homopolymer of Comparative Example 3 was used as the water-soluble polymer compound. It can be seen that the polishing rate, short wavelength waviness, and halation count are all improved when the -methylpropanesulfonic acid copolymer is used. It can be seen that in Example 18 in which a surfactant (sodium naphthalene sulfonate formaldehyde condensate) was further added, the short wavelength swell and the halation count were further improved.

In addition, Example 19 is an experimental example in which the ratio of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid in the acrylic acid/2-acrylamido-2-methylpropanesulfonic acid copolymer is different from that of Example 18.

Examples 20 and 21 are experimental examples in which the weight average molecular weight of the water-soluble polymer compound added is different from that of Example 18.

Example 22 is an experimental example in which the acrylic acid/2-acrylamido-2-methylpropanesulfonic acid/N-tert-butylacrylamide copolymer containing an amide group was used as the water-soluble polymer in Example 18.

On the other hand, when the 2-acrylamido-2-methylpropanesulfonic acid homopolymer of Comparative Example 4 is used, the polishing rate is improved as compared with Comparative Example 3, but the short wavelength waviness and the halation count are deteriorated. ..

From the above, it is understood that the use of the water-soluble polymer compound of the present invention improves the balance of the polishing rate, the short wavelength waviness, and the halation count. It can be seen that the short wavelength waviness and the halation count are further improved by further combining a specific surfactant.

The polishing composition of the present invention can be used for polishing electronic parts 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 disk substrates and aluminum magnetic disk substrates. Further, it can be used for finish polishing of an aluminum magnetic disk substrate for a magnetic recording medium having an electroless nickel-phosphorus plating film formed on the surface of an aluminum alloy substrate.

Claims (13)

Colloidal silica, a water-soluble polymer compound, a polishing composition containing water,
The water-soluble polymer compound is a copolymer having at least a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as an essential monomer,
The amount ratio of the structural unit derived from the monomer having a carboxylic acid group and the structural unit derived from the monomer having a sulfonic acid group of the water-soluble polymer compound is 95:5 to 5:95 in terms of mol ratio. Is a range
An abrasive composition for magnetic disk substrates, wherein the water-soluble polymer compound has a weight average molecular weight of 1,000 to 1,000,000. The abrasive composition for a magnetic disk substrate according to claim 1, wherein the colloidal silica has an average particle diameter (D50) of 1 to 100 nm and a concentration in the composition of 1 to 50% by mass. The abrasive composition for a magnetic disk substrate according to claim 1, wherein the water-soluble polymer compound has a weight average molecular weight of 5,000 to 600,000. The abrasive composition further contains a surfactant,
4. The anionic surfactant according to claim 1, wherein the surfactant has a sulfonate group and/or a sulfonate group, and further has an aromatic group in the main chain of the repeating unit. The magnetic disk substrate abrasive composition of. The anionic surfactant having a sulfonate group and/or a sulfonate group and further having an aromatic group in the main chain of the repeating unit is a naphthalene sulfonate compound, a lignin sulfonate compound, or an aromatic amino group. The abrasive composition for magnetic disk substrates according to claim 4, which is at least one selected from sulfonic acid compounds and salts thereof. The abrasive composition for a magnetic disk substrate according to claim 5, wherein the anionic surfactant that is the naphthalenesulfonic acid-based compound is at least one selected from the group consisting of a naphthalenesulfonic acid formaldehyde condensate and methylnaphthalenesulfonic acid. Stuff. The magnetic disk substrate abrasive composition according to any one of claims 1 to 6, wherein the monomer having a carboxylic acid group is a monomer selected from acrylic acid or a salt thereof, and methacrylic acid or a salt thereof. Stuff. The monomer having a sulfonic acid group is isoprenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, vinylsulfonic acid, allylsulfonic acid, The abrasive composition for magnetic disk substrates according to claim 1, which is a monomer selected from isoamylene sulfonic acid and salts thereof. The water-soluble polymer compound is a copolymer having at least a carboxylic acid group-containing monomer and a sulfonic acid group-containing monomer as essential monomers, a carboxylic acid group-containing monomer and a sulfonic acid group. The abrasive composition for a magnetic disk substrate according to claim 1, which is a copolymer containing a monomer having a group and a monomer having an amide group as essential monomers. The abrasive composition for magnetic disk substrates according to claim 9, wherein the monomer having an amide group is a monomer selected from acrylamide, methacrylamide, N-alkylacrylamide and N-alkylmethacrylamide. The magnetic disk according to claim 1, wherein the abrasive composition further contains an acid and/or a salt thereof and has a pH value (25° C.) in the range of 0.1 to 4.0. Substrate abrasive composition. The abrasive composition for magnetic disk substrates according to claim 1, wherein the abrasive composition further contains an oxidant. The abrasive composition for a magnetic disk substrate according to claim 1, which is used for polishing an electroless nickel-phosphorus-plated aluminum magnetic disk substrate.