JP7219097B2 - Abrasive composition for magnetic disk substrate - Google Patents

Description

TECHNICAL FIELD 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 magnetic recording medium substrates such as glass magnetic disk substrates and aluminum magnetic disk substrates. Further, the present invention relates to an abrasive composition used for polishing the surface 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.

Conventionally, various improvements in polishing properties have been demanded for polishing compositions for polishing the surfaces of electroless nickel-phosphorus plating films on aluminum magnetic disk substrates in order to improve the magnetic recording density. For example, with regard to scratches, the scratched portion may cause writing or reading errors, and burrs formed around the scratch may cause head collision.

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

However, when the colloidal silica as the abrasive grain portion and the drug component are mixed, the colloidal silica tends to agglomerate. As countermeasures, removal of coarse particles and aggregated particles, adjustment of abrasive corrosiveness (Patent Document 1), adjustment of particle shape (Patent Document 2), adjustment of content of aggregated particles (Patent Document 3), etc. A proposal is made.

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

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

Halation is considered to be a phenomenon resulting from the existence of some kind of fine non-uniformity on the substrate surface over a wide area of the substrate. A disharmony of the characteristics possessed is considered. Recently, the presence of halation has become a new problem as an obstacle to improving the magnetic recording density, and there is a demand for reducing halation.

On the other hand, conventionally, reduction of waviness on the substrate surface has been demanded from the viewpoint of improving the magnetic recording density. Among the undulations, reduction of long-wavelength undulation (wavelength: 500 μm to 5 mm) and medium-wavelength undulation (wavelength: 100 to 500 μm) has conventionally been studied as a problem to be solved from the viewpoint of improving magnetic recording density. Along with recent technological progress, reduction of short-wavelength waviness (wavelength: 20 to 100 μm) has also 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 magnetic disk substrates that achieves not only reduction in short-wavelength waviness of polished substrates but also reduction in halation without lowering productivity.

In order to solve the above problems, as a result of intensive studies, the present invention was achieved by using the following abrasive composition for magnetic disk substrates to reduce short-wavelength waviness and halation without lowering productivity. bottom.

[1] A polishing composition containing colloidal silica, a water-soluble polymer compound, and water, wherein the water-soluble polymer compound comprises at least a monomer having a carboxylic acid group and a monomer having a sulfonic acid group. is a copolymer containing a sulfonic acid group as an essential monomer, and the amount of structural units derived from a monomer having a carboxylic acid group and a monomer having a sulfonic acid group in the water-soluble polymer compound electroless nickel-phosphorus plating , wherein the molar ratio is in the range of 90:10 to 10:90 , and the water - soluble polymer compound has a weight average molecular weight of 1,000 to 1,000,000 An abrasive composition for magnetic disk substrates , which is used for final polishing of aluminum magnetic disk substrates .

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

[3] The abrasive composition for magnetic disk substrates 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 abrasive composition further contains a surfactant, the surfactant has a sulfonic acid group and/or a sulfonic acid group, and a shadow having an aromatic group in the main chain of the repeating unit. The abrasive composition for magnetic disk substrates according to any one of [1] to [3], which is an ionic surfactant.

[5] The anionic surfactant having a sulfonic acid group and/or a sulfonic acid group and further having an aromatic group in the main chain of the repeating unit is a naphthalenesulfonic acid-based compound, a ligninsulfonic acid-based compound, The abrasive composition for magnetic disk substrates according to [4] above, 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, which is the naphthalenesulfonic acid compound, is at least one selected from the group consisting of naphthalenesulfonic acid-formaldehyde condensates and methylnaphthalenesulfonic acid. Abrasive composition for

[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 its salts and methacrylic acid or its salts. Abrasive composition for

[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 magnetic disk substrates according to any one of [1] to [7], wherein the monomer is selected from sulfonic acid, isoamylenesulfonic acid and salts thereof.

[9] The copolymer containing at least a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as essential monomers, which is the water-soluble polymer compound, is a monomer having a carboxylic acid group. and a monomer having a sulfonic acid group and a monomer having an amide group as essential monomers. thing.

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

[11] 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 The abrasive composition for magnetic disk substrates described above.

[12] The abrasive composition for magnetic disk substrates according to any one of [1] to [11], which further contains an oxidizing agent.

The abrasive composition for magnetic disk substrates of the present invention can reduce short-wavelength waviness and halation after polishing while maintaining the polishing rate.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. The present invention is not limited to the following embodiments, and can be changed, modified, and improved without departing from the scope of the invention.

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

1-1. Colloidal Silica The colloidal silica used in the present invention preferably has an average particle size (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 alkali metal silicates such as sodium silicate and potassium silicate are used as raw materials, and the raw materials are subjected to a condensation reaction in an aqueous solution to grow particles. Alternatively, alkoxysilane such as tetraethoxysilane is used as a raw material, and the raw material is hydrolyzed with acid or alkali in water containing a water-soluble organic solvent such as alcohol to cause particles to grow through a condensation reaction.

Colloidal silica is known to have shapes such as spheres, chains, confetti, and irregular shapes, and primary particles are monodispersed in water to form a colloid. The colloidal silica used in the present invention is preferably spherical or nearly spherical colloidal silica. The concentration of colloidal silica in the polishing composition is preferably 1 to 50% by mass. More preferably, it is 2 to 40% by mass.

1-2. Water-Soluble Polymer Compound The water-soluble polymer compound used in the present invention is a copolymer containing at least a monomer having a carboxylic acid group and a monomer having a sulfonic acid group 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. A detailed description will be given below.

1-2-1. Carboxylic acid group-containing monomer As the carboxylic acid group-containing monomer, unsaturated aliphatic carboxylic acids and salts thereof are preferably used. Specific examples include acrylic acid, methacrylic acid, maleic acid, itaconic acid and salts thereof. Salts include sodium salts, potassium salts, magnesium salts, ammonium salts, amine salts, alkylammonium salts and the like.

The pH value of the water-soluble polymer compound determines whether the proportion of the monomer having a carboxylic acid group in the water-soluble polymer compound is high in the acid state or in the salt state. can be evaluated with The greater the proportion present as an acid, the lower the pH value, and the greater the proportion present as a salt, the higher the pH value. In the present invention, for example, a water-soluble polymer compound having a pH value (25° C.) in the range 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. Monomers Having a Sulfonic Acid Group Specific examples of monomers having a sulfonic acid group include isoprenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, and styrene. sulfonic acid, vinylsulfonic acid, allylsulfonic acid, isoamylenesulfonic acid and salts thereof; Preferred are 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid and salts thereof.

1-2-3. Other monomers In the water-soluble polymer compound used in the present invention, a monomer having a carboxylic acid group and a monomer having a sulfonic acid group are essential monomers, but monomers other than these can also be used. For example, monomers with amide groups can also be used. That is, the water-soluble polymer compound used in the present invention is a copolymer comprising, as essential monomers, a monomer having a carboxylic acid group, a monomer having a sulfonic acid group, and a monomer having an amide group. It is also preferable that As a monomer having an amide group, specifically, acrylamide, methacrylamide, N-alkylacrylamide, N-alkylmethacrylamide and the like can be used.

Specific examples of N-alkylacrylamide and N-alkylmethacrylamide include N-methylacrylamide, N-ethylacrylamide, Nn-propylacrylamide, N-iso-propylacrylamide, Nn-butylacrylamide, N-iso -butylacrylamide, N-sec-butylacrylamide, N-tert-butylacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, Nn-propylmethacrylamide, N-iso-propylmethacrylamide, Nn- Butyl methacrylamide, N-iso-butyl methacrylamide, N-sec-butyl methacrylamide, N-tert-butyl methacrylamide and the like.

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

1-2-5. Method for Producing Water-Soluble Polymer Compound The method for producing the water-soluble polymer compound is not particularly limited, but an aqueous solution polymerization method is preferred. According to the aqueous solution polymerization method, a water-soluble polymer compound can be obtained as a uniform solution. The polymerization solvent for the aqueous solution polymerization is preferably an aqueous solvent, particularly preferably water.
Moreover, in order to improve the solubility of the 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 can be used individually by 1 type or in combination of 2 or more types.

A method for producing a water-soluble polymer compound using the aqueous solvent is described below. In the polymerization reaction, a known polymerization initiator can be used, and a radical polymerization initiator is particularly preferably used. Examples of radical polymerization initiators include persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate; hydroperoxides such as t-butyl hydroperoxide; water-soluble peroxides such as hydrogen peroxide; oxide, ketone peroxides such as cyclohexanone peroxide, oil-soluble peroxides such as dialkyl peroxides such as di-t-butyl peroxide and 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 peroxide-based radical polymerization initiators described above, persulfates and azo compounds are preferable, and azobisisobutyronitrile is particularly preferable, since 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. It is preferred to use By making this ratio 0.1% by mass or more, the copolymerization rate can be improved, and by making this ratio 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 using a water-soluble redox polymerization initiator. As a redox polymerization initiator, a combination of an oxidizing agent (for example, the above peroxide), a reducing agent such as sodium bisulfite, ammonium bisulfite, ammonium sulfite, sodium hydrosulfite, iron alum, potash alum, etc. can be mentioned.

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

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

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

After the polymerization reaction, neutralization is performed with a basic compound, if necessary. Basic compounds 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, aqueous ammonia, and monoethanolamine. , diethanolamine, and triethanolamine. The pH value (25° C.) after neutralization is preferably 2 to 9, 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, 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. If the weight-average molecular weight of the water-soluble polymer compound is less than 1,000, waviness after polishing becomes worse. On the other hand, when it exceeds 1,000,000, the viscosity of the aqueous solution becomes high and handling becomes difficult.

1-2-7. Concentration The concentration of the water-soluble polymer compound in the polishing 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 further It is preferably 0.005 to 1.0% by mass. If the concentration of the water-soluble polymer compound is less than 0.0001% by mass, the effect of addition of the water-soluble polymer compound cannot be sufficiently obtained, and if it is more than 3.0% by mass, the concentration of the water-soluble polymer compound is reduced. The effect of addition hits a ceiling, and more water-soluble polymer compound than necessary is added, which is not economical.

1-3. Surfactant In the present invention, the surfactant used as an optional component for the purpose of further reducing waviness and halation has a sulfonic acid group and/or a sulfonic acid group, and further has a It is an anionic surfactant with an aromatic group.

Specific examples include polyalkylarylsulfonic acid compounds such as naphthalenesulfonic acid formaldehyde condensates, methylnaphthalenesulfonic acid formaldehyde condensates, and anthracene sulfonic acid formaldehyde, melamine formalin resin sulfone compounds such as melamine sulfonic acid formaldehyde condensates, and lignin. Examples include ligninsulfonic acid compounds such as sulfonic acid and modified ligninsulfonic acid, and aromatic aminosulfonic acid compounds such as aminoarylsulfonic acid-phenol-formaldehyde condensates. Among polyalkylarylsulfonic acid compounds, naphthalenesulfonic acid-based compounds such as naphthalenesulfonic acid-formaldehyde condensates and methylnaphthalenesulfonic acid-formaldehyde condensates, ligninsulfonic acid-based compounds, aromatic aminosulfonic acid-based compounds, and these is preferred. Among the naphthalenesulfonic acid compounds, naphthalenesulfonic acid-formaldehyde condensates, methylnaphthalenesulfonic acid-formaldehyde condensates, and salts thereof are particularly preferred.

In addition, counter ions in the respective salts include alkali metal salts such as sodium and potassium, alkaline earth metal salts such as calcium, ammonium salts, primary amine salts such as monoethanolamine, and secondary amine salts such as diethanolamine. , tertiary amine salts such as triethanolamine, quaternary ammonium salts such as tetramethylammonium, and the like.

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

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

Inorganic acids and/or salts thereof include inorganic acids and/or salts thereof such as nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, phosphonic acid, pyrophosphoric acid, and tripolyphosphoric acid.

Organic acids and/or salts thereof 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 or salts thereof, organic phosphonic acids and/or salts thereof, and the like. One or more of these acids and/or salts thereof can be used.

Organic phosphonic acids and/or salts thereof 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 More than one species of compound is included.

It is also a preferred embodiment to use two or more 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 combination of phosphoric acid and an organic phosphonate and a combination of.

1-5. Oxidizing Agent In the present invention, an oxidizing agent can be used as a polishing accelerator. The oxidizing agents used include peroxides, permanganic acid or its salts, chromic acid or its salts, peroxo acids or their salts, halogen oxoacids or their salts, oxyacids or their salts, and two of these oxidizing agents. A mixture of more than one species, etc. can be used.

Specifically, hydrogen peroxide, sodium peroxide, barium peroxide, potassium peroxide, potassium permanganate, metal salts of chromic acid, metal salts of dichromic acid, persulfuric acid, sodium persulfate, potassium persulfate, persulfate ammonium sulfate, peroxolinic acid, sodium peroxoborate, performic acid, peracetic acid, hypochlorous acid, sodium hypochlorite, calcium hypochlorite, and the like. Among them, hydrogen peroxide, persulfuric acid and its salts, hypochlorous acid and its salts are preferred, and hydrogen peroxide is more preferred.

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

2. Physical properties (pH) of abrasive composition
The pH value (25° C.) of the polishing composition of the present invention preferably ranges from 0.1 to 4.0. It is more preferably 0.5 to 3.0. When the pH value (25° C.) of the polishing composition is 0.1 or more, 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 suppress a decrease in polishing rate.

The abrasive composition of the present invention can be used for polishing various electronic parts such as magnetic recording media such as hard disks. In particular, it is suitably used for polishing aluminum magnetic disk substrates. More preferably, it can be used for polishing an aluminum magnetic disk substrate plated with electroless nickel-phosphorus. Electroless nickel-phosphorus plating is usually performed under the condition of pH value (25° C.) of 4.0-6.0. When the pH value (25°C) is 4.0 or less, nickel tends to dissolve, making 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, the polishing rate can be increased by using the polishing composition of the present invention. .

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

As a method for applying the abrasive composition of the present invention, for example, a polishing pad is attached to the surface plate of a polishing machine , and an abrasive is applied to the surface to be polished of an object to be polished (for example, an aluminum disc) or to the polishing pad. There is a method of supplying a composition and rubbing the surface to be polished with a polishing pad. For example, when 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 respectively attached to the upper surface plate and the lower surface plate. In this method, an aluminum disk 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 simultaneously to obtain an aluminum disc. Polish the front and back of the disc. Incidentally, in the normal polishing of magnetic disk substrates, it is common to carry out the main polishing after implementing the dummy polishing. Dummy polishing here means that after attaching a polishing pad to the surface plate of the polishing machine, pad dressing is performed as necessary, and then before the main polishing is performed, the same kind of substrate as the object to be polished is applied. is separately prepared and polished as a dummy substrate. The abrasive composition of the present invention can be used only for dummy polishing, only for main polishing, or both for dummy polishing and main polishing.

Any type of polishing pad can be used. There are polishing pads of non-woven fabric type and suede type, but the suede type is often used. Examples of the material of the surface foam 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 the present invention is not limited to these examples, and it goes without saying that the present invention can be implemented in various aspects as long as it belongs to 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 contained the materials shown in Table 1 in the amounts shown in Table 1. In Table 1, the abbreviation for acrylic acid is AA, the abbreviation for 2-acrylamido-2-methylpropanesulfonic acid is ATBS, and the abbreviation for N-tert-butylacrylamide is TBAA. As the sodium naphthalenesulfonate formaldehyde condensate, Labelin FM-45 manufactured by Daiichi Kogyo Seiyaku Co., Ltd. was used.

[Weight average molecular weight]
As the water-soluble polymer compound, as shown in Table 1, polymers of Synthesis Nos. 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: 0.2 M phosphate buffer/acetonitrile = 9/1 (volume ratio)
Flow rate: 1.0ml/min
Temperature: 40°C
Detection: 210 nm (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 Kagaku Co., Ltd., American Polymer Standards Corp.)

[Particle size of colloidal silica]
The particle size (Heywood diameter) of colloidal silica was obtained by photographing a field of view at a magnification of 100,000 times using a transmission electron microscope (TEM) (manufactured by JEOL Ltd., JEM2000FX (200 kV)). The Heywood diameter (equivalent diameter of projected area circle) was measured by analysis using analysis software (Mac-View Ver.4.0, manufactured by Mountec Co., Ltd.) The average particle diameter of colloidal silica was determined by the method described above. Analyze the particle diameter of about 2000 colloidal silica, and the particle diameter at which the cumulative particle size distribution (cumulative volume basis) from the small particle size side is 50% is calculated using the above analysis software (manufactured by Mountech Co., Ltd., Mac-View Ver. .4.0) is the average particle diameter (D50) calculated using

[Polishing conditions]
An electroless nickel-phosphorus-plated aluminum magnetic disk substrate having an outer diameter of 95 mm was roughly polished, and the object to be polished was polished.

Polishing machine: 9B double-sided polishing machine manufactured by Speedfam Co., Ltd. Polishing pad: P2 pad manufactured by FILWEL Co., Ltd. Surface plate rotation speed: Upper surface plate −6.7 rpm
Lower surface plate 20.0rpm
Abrasive composition supply rate: 100 ml/min
Polishing time: 300 seconds Processing pressure: 14 kPa
After each component was mixed to prepare an abrasive composition, a polishing test was carried out. 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 being 1 (reference value). Table 3 shows relative values with Comparative Example 3 being 1 (reference value).

[Evaluation of polished disk]
[Polishing speed]
The polishing rate was calculated based on the following formula by measuring the mass of the aluminum magnetic disk substrate that had 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 of 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 1024×1024
Filter Band Pass
Cut Off Short 20.000 μm
Long 100.000 μm
Measuring point radius 30.00mm
36 points for every 10° angle

[Method for evaluating halation on substrate surface after polishing]
Halation was measured using NS2000H manufactured by Hitachi High-Tech Fine Systems Co., Ltd., which is a substrate full surface defect inspection machine. 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 fine defects 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, compared to the case of using the acrylic acid homopolymer of Comparative Example 1 as the water-soluble polymer compound, acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid of Examples 1 to 8 It can be seen that the polishing rate, short wavelength waviness and halation count are all improved when the copolymer is used. In Examples 9 to 16, in which a surfactant (sodium naphthalenesulfonate formaldehyde condensate) was further added, short wavelength waviness and halation count were further improved.

Incidentally, Examples 2, 3 and 10, 11 are different from Examples 1 and 9 in that acrylic acid/2-acrylamido-2-methylpropanesulfonic acid copolymer of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid Experimental examples with different ratios.

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

Examples 8 and 16 are experimental examples in which an acrylic acid/2-acrylamido-2-methylpropanesulfonic acid/N-tert-butylacrylamide copolymer containing an amide group in the water-soluble polymer was used in Examples 1 and 9. is.

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

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

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 to be added is different from that of Example 18.

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

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

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

The abrasive 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. Furthermore, it can be used for final 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.

Claims (12)

A polishing composition containing colloidal silica, a water-soluble polymer compound, and 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 essential monomers,
The molar 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 in the water-soluble polymer compound is 90:10 to 10 : 9 . is in the range of 0 ,
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, and is used for final polishing of electroless nickel-phosphorus plated aluminum magnetic disk substrates . 2. The abrasive composition for magnetic disk substrates according to claim 1, wherein the colloidal silica has an average particle size (D50) of 1 to 100 nm and a concentration in the composition of 1 to 50% by mass. 3. The abrasive composition for magnetic disk substrates 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 any one of claims 1 to 3, wherein the surfactant has a sulfonic acid group and/or a sulfonic acid group and further has an aromatic group in the main chain of the repeating unit. Abrasive composition for magnetic disk substrates. The anionic surfactant having a sulfonic acid group and/or a sulfonic acid group and further having an aromatic group in the main chain of the repeating unit is a naphthalenesulfonic acid compound, a ligninsulfonic acid compound, an aromatic amino 5. The abrasive composition for magnetic disk substrates according to claim 4, which is at least one selected from sulfonic acid compounds and salts thereof. 6. The abrasive composition for magnetic disk substrates according to claim 5, wherein said anionic surfactant which is said naphthalenesulfonic acid compound is at least one selected from the group consisting of naphthalenesulfonic acid-formaldehyde condensate and methylnaphthalenesulfonic acid. thing. 7. The abrasive composition for magnetic disk substrates according to claim 1, wherein the monomer having a carboxylic acid group is a monomer selected from acrylic acid or its salts and methacrylic acid or its salts. thing. 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, 8. The abrasive composition for magnetic disk substrates according to claim 1, which is a monomer selected from isoamylenesulfonic acid and salts thereof. The water-soluble polymer compound comprising at least a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as essential monomers is a monomer having a carboxylic acid group and a sulfonic acid group. The abrasive composition for magnetic disk substrates according to any one of claims 1 to 8, which is a copolymer comprising a group-containing monomer and an amide group-containing monomer as essential monomers. 10. The abrasive composition for magnetic disk substrates according to claim 9, wherein said monomer having an amide group is a monomer selected from acrylamide, methacrylamide, N-alkylacrylamide and N-alkylmethacrylamide. The magnetic disk according to any one of claims 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. Abrasive composition for substrates. 12. The abrasive composition for magnetic disk substrates according to claim 1, further comprising an oxidizing agent.