JP7219101B2 - 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, the present invention relates to an abrasive composition used for polishing the surface of glass magnetic disk substrates, aluminum magnetic disk substrates, etc., for which the demand for smoothness of the substrate surface after polishing has become stricter in recent years as the magnetic recording density of hard disks increases. 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, as a polishing agent composition for polishing the surface of an electroless nickel-phosphorus plating film on an aluminum magnetic disk substrate, from the viewpoint of productivity, alumina particles with a relatively large particle diameter capable of realizing a high polishing rate are added to water. Dispersed abrasive compositions have been used. However, when alumina particles are used, since the alumina particles have a considerably high hardness against the electroless nickel-phosphorus plating film of the aluminum magnetic disk substrate, the alumina particles pierce the substrate, and these pierced particles are used in the subsequent polishing process. The problem was that it had a negative impact.

As a solution to such problems, abrasive compositions in which alumina particles and silica particles are combined have been proposed (Patent Documents 1 to 4). Further, a method of polishing with only silica particles without using alumina particles has been proposed (Patent Documents 5 to 9). Further, additives for reducing edge sagging (roll-off) of a substrate when polished only with silica particles have been studied (Patent Documents 10 to 14). A proposal has also been made to improve the balance of polishing speed, pits, and surface roughness by combining two types of silica particles (Patent Document 15).

Japanese Patent Application Laid-Open No. 2001-260005 JP 2009-176397 A JP 2011-204327 A JP 2012-43493 A JP 2010-167553 A Japanese Patent Publication No. 2011-527643 JP 2014-29754 A JP 2014-29755 A JP 2012-155785 A JP-A-2002-167575 Japanese Patent Application Laid-Open No. 2003-160781 Japanese Patent Publication No. 2003-510446 JP-A-2007-63372 Japanese Patent Application Laid-Open No. 2007-130728 WO2015/146941

By combining alumina particles and silica particles as in Patent Documents 1 to 4, it is possible to remove alumina particles sticking into the substrate to some extent. However, as long as the abrasive composition containing this alumina particle is used, the possibility of the alumina particles contained in the abrasive composition sticking into the substrate still remains. In addition, since such a polishing composition contains both alumina particles and silica particles, the properties of the particles cancel each other out, resulting in a problem of deterioration in polishing speed and surface smoothness.

Therefore, a method of polishing with only silica particles without using alumina particles has been proposed. Patent Documents 5 and 6 propose a combination of colloidal silica and a polishing accelerator. Patent Documents 7 and 8 propose polishing with colloidal silica, fumed silica, surface-modified silica, silica produced by the water glass method, or the like, and a method using colloidal silica with a special shape. However, with these methods, the polishing rate is insufficient, and improvements are required. Further, Patent Document 9 proposes a method of achieving a polishing rate close to that of alumina particles by using crushed silica particles. However, in this method, there is a problem that the surface smoothness such as waviness is deteriorated, and improvement is required.

The method of polishing only with these silica particles also has a problem of poor roll-off compared to the case of using alumina particles. Various additives have also been investigated for roll-off reduction. For example, addition of nonionic surfactants (Patent Documents 10 and 11), addition of cellulose derivatives (Patent Document 12), addition of alkylbenzenesulfonic acid-based surfactants and polyoxyethylene sulfate ester-based surfactants (Patent Document 13). , 14) have been proposed. However, although the roll-off is reduced by these additives, the effect is insufficient depending on the compatibility with the silica particles, and there is also the drawback that the polishing rate is significantly reduced.

Furthermore, as the magnetic recording density of hard disks increases, the demand for surface smoothness has become stricter than before, and there is a strong demand for improvements in waviness and shallow pits.

Patent Document 15 is a proposal to improve the balance of polishing speed, pits, and surface roughness by combining colloidal silica and pulverized wet-process silica particles, but further improvement is required from the viewpoint of reducing shallow pits. . Shallow pits are dents that are shallower and smaller than conventional pits, and it has become known that shallow pits remain even when pits are reduced due to improvements in analytical equipment. Shallow pits have come to be recognized as a problem as the performance of magnetic disks improves, and in addition to eliminating conventional pits, further reduction of shallow pits has become an issue.

The present invention has been made in view of the problems of the prior art, and its object is to realize a high polishing rate without using alumina abrasive grains, and at the same time, reduce shallow pits and waviness. An object of the present invention is to provide an abrasive composition capable of realizing good surface smoothness and further achieving reduction in roll-off.

As a result of intensive studies to solve the above problems, the present inventors have found that by combining colloidal silica having a specific particle size configuration and wet silica formed through a pulverization process at a specific ratio, high polishing speed and waviness can be achieved. The inventors have found that it is possible to achieve good surface smoothness and roll-off reduction by reducing surface roughness and shallow pits, and have completed the present invention. That is, according to the present invention, the abrasive composition shown below is provided.

[1] Colloidal silica having an average primary particle size of 10 to 150 nm, pulverized wet-process silica particles having an average particle size of 200 to 500 nm, a water-soluble polymer compound, and water, and the colloidal particles occupying the total silica particles. The ratio of silica is 20 to 80% by mass, the ratio of the pulverized wet silica particles is 20 to 80% by mass, and the ratio of particles having a particle size of 30 to 70 nm in the colloidal silica is 10 to 90% by volume. wherein the ratio of the average particle size of the pulverized wet-process silica particles to the average primary particle size of the colloidal silica is 2.0 to 15.0, and the concentration of the total silica particles is 2 to 40% by mass. and the water-soluble polymer compound is a copolymer having a monomer having a carboxylic acid group and a monomer having an amide group as essential monomers, a monomer having a carboxylic acid group, and a sulfonic acid a copolymer having a monomer having a group as an essential monomer, a monomer having a carboxylic acid group and a monomer having an amide group, and a monomer having a sulfonic acid group as an essential monomer. An abrasive composition for magnetic disk substrates , which is at least one selected from the group consisting of polymers .

[ 2 ] When the water-soluble polymer compound is a copolymer containing, as essential monomers, a monomer having a carboxylic acid group and a monomer having an amide group, the monomer having a carboxylic acid group The abrasive composition for magnetic disk substrates according to the above [ 1 ], wherein the proportion of structural units derived from the amide group is in the range of 50 to 95 mol%, and the proportion of structural units derived from the monomer having an amide group is in the range of 5 to 50 mol%. .

[ 3 ] When the water-soluble polymer compound is a copolymer containing, as essential monomers, a monomer having a carboxylic acid group and a monomer having a sulfonic acid group, a monomer having a carboxylic acid group The abrasive for magnetic disk substrates according to the above [ 1 ], wherein the ratio of structural units derived from is in the range of 30 to 95 mol% and the ratio of structural units derived from a monomer having a sulfonic acid group is in the range of 5 to 70 mol%. Composition.

[ 4 ] When the water-soluble polymer compound is a copolymer comprising, as essential monomers, a monomer having a carboxylic acid group, a monomer having an amide group, and a monomer having a sulfonic acid group , the proportion of structural units derived from a monomer having a carboxylic acid group is 50 to 95 mol%, the proportion of structural units derived from a monomer having an amide group is 1 to 40 mol%, a monomer having a sulfonic acid group The abrasive composition for magnetic disk substrates according to the above [ 1 ], wherein the proportion of structural units derived from is in the range of 0.01 to 20 mol%.

[ 5 ] The magnetic disk substrate according to any one of [ 1 ] to [ 4 ], 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

[ 6 ] The above [ 1 ] and [ 2 ], wherein the monomer having an amide group is one or more monomers selected from acrylamide, methacrylamide, N-alkylacrylamide, and N-alkylmethacrylamide ], and the abrasive composition for magnetic disk substrates according to any one of [ 4 ].

[ 7 ] the monomer containing a sulfonic acid group is isoprenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, vinylsulfonic acid, The polishing for magnetic disk substrates according to any one of [ 1 ] , [3] and [ 4 ], wherein the monomer is selected from allylsulfonic acid, isoamylenesulfonic acid, naphthalenesulfonic acid and salts thereof. agent composition.

[ 8 ] Any one of the above [1] to [ 7 ], wherein the polishing 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.

[ 9 ] The abrasive composition for magnetic disk substrates according to any one of [1] to [ 8 ], which further contains an oxidizing agent.

[10] The abrasive composition for magnetic disk substrates according to any one of [ 1 ] to [ 9 ], which is used for polishing electroless nickel-phosphorus plated aluminum magnetic disk substrates.

The abrasive composition of the present invention uses a combination of two specific types of silica particles in a specific ratio when polishing the surface of a magnetic disk substrate, resulting in a high polishing rate, reduced waviness, and reduced shallow pits. It makes it possible to achieve good smoothness and further reduce roll-off.

FIG. 5 is a diagram for explaining roll-off measurement when the surface of a substrate is polished;

Embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments, and within the scope of the present invention, based on the ordinary knowledge of those skilled in the art, the following It should be understood that any suitable modifications, improvements, etc., to the embodiment are also included in the scope of the present invention.

1. Abrasive Composition The abrasive composition of the present invention is an aqueous composition containing at least colloidal silica and wet silica particles. The average primary particle size of colloidal silica is 10 to 150 nm, and the average particle size of wet silica particles is 200 to 500 nm. Here, the wet-process silica particles are crushed by pulverization in the manufacturing process. That is, the manufacturing process of wet-process silica particles includes a pulverization process. Further, in the abrasive composition of the present invention, the proportion of colloidal silica in the total silica particles is 20 to 80% by mass, and the proportion of pulverized wet-process silica particles is 20 to 80% by mass. Furthermore, the ratio of particles having a particle size of 30 to 70 nm in the colloidal silica is 10 to 90% by volume, and the ratio of the average particle size of the pulverized wet-process silica particles to the average primary particle size of the colloidal silica is 2.0%. 0 to 15.0, and the concentration of all silica particles is 2 to 40% by mass.

(1) Colloidal Silica The colloidal silica contained in the abrasive composition of the present invention generally has an average primary particle size of 10 to 150 nm, preferably 20 to 100 nm. When the average primary particle size is 10 nm or more, a decrease in polishing rate can be suppressed. When the average primary particle size is 150 nm or less, deterioration of surface smoothness such as shallow pits can be suppressed. Further, the proportion of particles having a particle diameter of 30 to 70 nm in the colloidal silica is 10 to 90% by volume, preferably 12 to 80% by volume, thereby further improving surface smoothness such as shallow pits.

Colloidal silica is known to have a spherical shape, a chain shape, a confetti shape (particles having convex portions 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 preferably spherical or nearly spherical colloidal silica. By using spherical or nearly spherical colloidal silica, surface smoothness such as shallow pits can be improved.

Colloidal silica uses sodium silicate or potassium silicate as a raw material, the water glass method in which the raw material is subjected to a condensation reaction in an aqueous solution to grow particles, and condensation by hydrolysis of alkoxysilane such as tetraethoxysilane with acid or alkali. It can be obtained by the alkoxysilane method or the like, in which particles are grown by reaction.

(2) Wet-process silica particles The wet-process silica particles used in the present invention are wet-process silica obtained as precipitated silicic acid by adding an aqueous alkali silicate solution and an inorganic acid or an aqueous inorganic acid solution to a reaction vessel. It refers to particles to be prepared, and wet-process silica particles do not include the colloidal silica described above.

Examples of the aqueous alkali silicate solution, which is a raw material for wet-process silica, include aqueous sodium silicate solution, aqueous potassium silicate solution, aqueous lithium silicate solution and the like, but generally aqueous sodium silicate solution is preferably used. Examples of inorganic acids include sulfuric acid, hydrochloric acid, nitric acid and the like, and generally sulfuric acid is preferably used. After completion of the reaction, the reaction solution is filtered, washed with water, and then dried with a drier so that the water content becomes 6% or less. The dryer may be a static dryer, a spray dryer, or a fluidized bed dryer. Then, it is pulverized by a pulverizer such as a jet mill, and further classified to obtain wet process silica particles. The particle shape of the wet-process silica particles pulverized by the pulverization step in this way has corners and has a higher polishing ability than nearly spherical particles.

The average particle size of the wet silica particles is usually 200-500 nm, preferably 250-400 nm. When the average particle size is 200 nm or more, it is possible to suppress a decrease in polishing rate. When the average particle size is 500 nm or less, deterioration of surface smoothness such as shallow pits can be suppressed.

(3) Relationship between colloidal silica and wet-process silica particles The ratio (B/A) of the average particle size (B) of wet-process silica particles to the average primary particle size (A) of colloidal silica is 2.0 to 15. .0, preferably 2.5 to 12.0, more preferably 3.0 to 10.0. When the average particle size ratio is 2.0 or more, the polishing rate can be improved. When the average particle size ratio is 15.0 or less, deterioration of surface smoothness such as shallow pits can be suppressed.

The total concentration of colloidal silica and wet-process silica particles is 2 to 40% by mass, preferably 3 to 30% by mass, based on the total abrasive composition. More preferably, it is 3 to 20% by mass. When the total concentration of silica particles is 2% by mass or more, a decrease in polishing rate can be suppressed. When the total concentration of silica particles is 40% by mass or less, a sufficient polishing rate can be maintained without using more silica particles than necessary.

The proportion of colloidal silica in the total silica particles is 20-80% by mass, preferably 30-70% by mass. When the proportion of colloidal silica is 20% by mass or more, deterioration of surface smoothness such as shallow pits can be suppressed. When the proportion of colloidal silica is 80% by mass or less, a decrease in polishing rate can be suppressed.

The proportion of wet-process silica particles in the total silica particles is 20 to 80% by mass, preferably 30 to 70% by mass. When the proportion of the wet-process silica particles is 80% by mass or less, deterioration of surface smoothness can be suppressed. When the proportion of the wet silica particles is 20% by mass or more, a decrease in polishing rate can be suppressed.

The abrasive composition of the present invention may contain silica particles other than colloidal silica and wet-process silica particles. For example, it may contain fumed silica. Fumed silica is produced by hydrolyzing a volatile silane compound (generally silicon tetrachloride is used) in a mixed gas flame of oxygen and hydrogen (around 1000°C). Pure silica particles. Compared with colloidal silica, colloidal silica exists as individually dispersed primary particles, while in fumed silica, a large number of primary particles are aggregated and connected in chains to form secondary particles. Formation of the secondary particles increases the holding power to the polishing pad, and improves the polishing speed.

(4) Water-Soluble Polymer Compound The abrasive composition of the present invention preferably contains a water-soluble polymer compound. The water-soluble polymer compound preferably used in the present invention includes (a) a copolymer having a monomer having a carboxylic acid group and a monomer having an amide group as essential monomers, (b) a carboxylic acid (c) a monomer having a carboxylic acid group, a monomer having an amide group, and a sulfone A copolymer containing a monomer having an acid group as an essential monomer can be mentioned.

(4-1) 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.

(4-2) Amide Group-Containing Monomer Examples of the amide group-containing monomer include acrylamide, methacrylamide, N-alkylacrylamide, and N-alkylmethacrylamide. One or more of these can be selected and used as a monomer. For example, acrylamide and N-alkylacrylamide may be selected and used in combination. Methacrylamide and N-alkylmethacrylamide may be selected and used together.

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. Among them Nn-butylacrylamide, N-iso-butylacrylamide, n-sec-butylacrylamide, N-tert-butylacrylamide, Nn-butylmethacrylamide, N-iso-butylmethacrylamide, N-sec-butyl Methacrylamide, N-tert-butylmethacrylamide and the like are preferred.

(4-3) Monomers Having Sulfonic Acid Groups Specific examples of monomers having sulfonic acid groups include isoprenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and 2-methacrylamido-2-methyl Propanesulfonic acid, styrenesulfonic acid, vinylsulfonic acid, allylsulfonic acid, isoamylenesulfonic acid, naphthalenesulfonic acid, salts thereof, and the like. Preferred are 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid and salts thereof.

(4-4) Copolymer The water-soluble polymer compound used in the present invention is preferably a copolymer by combining and polymerizing these monomer components. Combinations of copolymers include combinations of acrylic acid and/or its salts and N-alkylacrylamides, combinations of acrylic acid and/or its salts and N-alkylmethacrylamides, methacrylic acid and/or its salts and N-alkyl A combination of acrylamide, a combination of methacrylic acid and/or its salt and N-alkyl methacrylamide, a combination of acrylic acid and/or its salt and a monomer having a sulfonic acid group, methacrylic acid and/or its salt and a sulfonic acid group a combination of acrylic acid and/or a salt thereof and N-alkylacrylamide and a monomer having a sulfonic acid group, acrylic acid and/or a salt thereof and an N-alkylmethacrylamide and a sulfonic acid group a combination of methacrylic acid and/or its salt and N-alkylacrylamide and a monomer having a sulfonic acid group; methacrylic acid and/or its salt and N-alkylmethacrylamide and a sulfonic acid group A combination of monomers is preferably used.

When the water-soluble polymer compound is (a) a copolymer containing, as essential monomers, a monomer having a carboxylic acid group and a monomer having an amide group, it is derived from the monomer having a carboxylic acid group. The proportion of the structural units is preferably 50-95 mol %, more preferably 60-93 mol %. The ratio of structural units derived from monomers having amide groups is preferably 5 to 50 mol %, more preferably 7 to 40 mol %. (b) In the case of a copolymer containing a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as essential monomers, the proportion of structural units derived from the monomer having a carboxylic acid group is 30. ~95 mol% is preferred, and 40 to 90 mol% is more preferred. The ratio of the monomer having a sulfonic acid group is preferably 5-70 mol %, more preferably 10-60 mol %. (c) in the case of a copolymer containing a monomer having a carboxylic acid group, a monomer having an amide group, and a monomer having a sulfonic acid group as essential monomers, a monomer having a carboxylic acid group The proportion of structural units derived from is preferably 50 to 95 mol%, more preferably 60 to 93 mol%, and even more preferably 70 to 90 mol%. The ratio of structural units derived from monomers having an amide group is preferably 1 to 40 mol%, more preferably 3 to 30 mol%, even more preferably 5 to 20 mol%. The ratio of structural units derived from a monomer having a sulfonic acid group is preferably 0.01 to 20 mol%, more preferably 0.1 to 10 mol%, even more preferably 0.2 to 5 mol%.

(4-5) Method for producing water-soluble polymer compound The method for producing a 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. As a polymerization solvent for the aqueous solution polymerization, an aqueous solvent is preferable, and water is particularly preferable. 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 and 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 reduced pressure requires cost. The polymerization time is preferably 2 to 20 hours, particularly 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.) of the water-soluble polymer compound after neutralization or without neutralization is preferably from 1 to 13, and from 2 to 9 is more preferred, and 3-8 is more preferred.

(4-6) Weight average molecular weight The weight average molecular weight of the water-soluble polymer compound is preferably 1,000 to 1,000,000, more preferably 2,000 to 800,000, and still more preferably 3,000. ~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, the surface smoothness is deteriorated. On the other hand, when it exceeds 1,000,000, the viscosity of the aqueous solution becomes high and handling becomes difficult.

(4-7) Content The content of the water-soluble polymer compound in the abrasive composition is preferably 0.0001 to 2.0% by mass, more preferably 0.001 to 1.0% by mass in terms of solid content. %, more preferably 0.005 to 0.5% by mass. If the content 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 2.0% by mass, the water-soluble polymer The effect of adding the compound reaches a plateau, and the water-soluble polymer compound is added more than necessary, which is not economical.

(5) 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 such as nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, phosphonic acid, pyrophosphoric acid, tripolyphosphoric acid and/or salts thereof.

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. and a combination of phosphoric acid and an organic phosphonate.

(6) 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 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. More preferably, it is 0.5 to 3.0. When the pH value (25°C) of the abrasive composition is 0.1 or more, surface roughness 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 to 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 polishing method to which the abrasive composition of the present invention can be applied, for example, a polishing pad is attached to the surface plate of a polishing machine, and the surface to be polished of an object to be polished (for example, an aluminum disk) or the polishing pad is polished. There is a method of supplying an agent composition and rubbing the surface to be polished with a polishing pad (called polishing). 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 7 , Reference Examples 1 to 5, and Comparative Examples 1 to 6 were abrasives containing the materials shown in Table 1 in the contents or added amounts shown in Table 1. composition. In each example and comparative example, the concentration of all silica particles in the polishing composition was 4.0% by mass (Examples 1, 3 to 7 , Reference Examples 1, 3 to 5, Comparative Examples 1, 3 to 6) or 6.0% by mass (Example 2, Reference Example 2, Comparative Example 2). Also, the amount of sulfuric acid added was adjusted so that the pH of all the polishing compositions was 1.2. In Tables 1 and 2, the abbreviation for acrylic acid is AA, the abbreviation for N-tert-butylacrylamide is TBAA, and the abbreviation for 2-acrylamido-2-methylpropanesulfonic acid is ATBS. Table 2 shows the results of the polishing tests of Examples 1 to 7 , Reference Examples 1 to 5, and Comparative Examples 1 to 6.

[Particle size of colloidal silica]
The particle diameter (Heywood diameter) of colloidal silica is determined by taking a photograph of a field of view at a magnification of 100,000 times using a transmission electron microscope (TEM) (manufactured by JEOL Ltd., transmission electron microscope JEM2000FX (200 kV)). This photograph was analyzed using analysis software (Mac-View Ver. 4.0, manufactured by Mountec Co., Ltd.) to measure the Heywood diameter (equivalent diameter of projected area circle). For the average particle size of colloidal silica, analyze the particle size of about 2000 colloidal silica particles by the method described above, and determine the particle size at which the cumulative particle size distribution (based on cumulative volume) from the small particle size side is 50%. Average particle size (D50) calculated using software (Mac-View Ver 4.0, manufactured by Mountec Co., Ltd.).

[Average particle size of wet silica particles]
The average particle size of the wet silica particles was measured using a dynamic light scattering particle size analyzer (Microtrac UPA manufactured by Nikkiso Co., Ltd.). The average particle size of the wet-process silica particles is the average particle size (D50) at which the cumulative particle size distribution from the small particle size side on the basis of volume is 50%.

[Weight average molecular weight]
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.)

[Polishing conditions]
An electroless nickel-phosphorus plated aluminum disc having an outer diameter of 95 mm was used as a polishing object, and polishing was performed under the following polishing conditions.

Polishing machine: SPEEDFAM (Ltd.), 9B double-sided polishing machine Polishing pad: FILWEL Co., Ltd., P1 pad Surface plate rotation speed: Upper surface plate -7.7 rpm
Lower surface plate 23.5rpm
Abrasive composition supply rate: 90 ml/min
Polishing time: Polish until the amount of polishing is 1.2 to 1.5 μm/side (240 to 720 seconds).
Processing pressure: 120kPa

[Polishing speed ratio]
The polishing rate was calculated based on the following formula by measuring the mass of the aluminum disk that had decreased after polishing.
Polishing rate (μm/min)=mass loss of aluminum disc (g)/polishing time (min)/area of one side of aluminum disc (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 disc is 65.9 cm ² and the density of the electroless nickel-phosphorus plating film is 8.0 g/cm ³ ).
The polishing speed ratio is a relative value when the polishing speed of Comparative Example 1 obtained using the above formula is set to 1 (reference).

[Shallow pit]
Shallow pits were measured using a three-dimensional surface structure analysis microscope (New View 8300) manufactured by Ametech Co., Ltd. using scanning white light interferometry.
The measurement conditions are as follows.
Lens 1.4x ZOOM 0.5x 1 field of view measurement area 12mm x 12mm
Measurement Type Surface
Measurement Mode CSI
Scan Length 5 μm

A square with a side of 95 mm covering the entire aluminum disk was set, divided into 100 sections, and the entire surface of the aluminum disk with a diameter of 95 mm was scanned. At that time, each scan data was set to overlap by 20%. Next, the obtained scan data were combined and the entire surface of the aluminum disk was observed. When observing each section, the presence or absence of shallow pits was confirmed while enlarging with a mouse. As a result of observing the entire surface of the aluminum disc, when almost no shallow pits were observed, it was evaluated as "Good". When shallow pits were slightly observed, it was evaluated as "Δ (acceptable)". When a large number of shallow pits were observed, it was evaluated as "x (impossible)".

[undulation]
The waviness of the aluminum disk was measured using a three-dimensional surface structure analysis microscope using scanning white light interferometry manufactured by Ametech. The measurement conditions are a measuring device manufactured by Ametech (New View 8300 (lens: 1.4 times, zoom: 1.0 times), a wavelength of 100 to 500 μm, a measurement area of 6 mm × 6 mm, and analysis software manufactured by Ametech. (Mx) was used for the analysis.

[Roll-off ratio]
As an evaluation of the shape of the end surface, roll-off, which is a numerical value of the degree of drooping of the end surface, was measured. The roll-off was measured using a measuring device (New View 8300 (lens: 1.4x, zoom: 1.0x) manufactured by Ametech) and analysis software (Mx) manufactured by Ametech.

A method of measuring roll-off will be described with reference to FIG. FIG. 1 shows a cross-sectional view of an electroless nickel-phosphorus plated aluminum disk with an outer diameter of 95 mm, which is the object to be polished, passing through the center of the disk and perpendicular to the polished surface. In measuring the roll-off, first, a perpendicular line h was provided along the outer peripheral edge of the disc, and from the perpendicular line h to the center of the disc on the polished surface, parallel to the perpendicular line h and at a distance of 3.90 mm from the perpendicular line h. A certain line j was provided, and a point A was set at a position where the line of the cross section of the disc intersects with the line j. Also, a line k parallel to the perpendicular line h and at a distance of 0.30 mm from the perpendicular line h was provided, and a point B was defined as a position where the line of the cross section of the disc intersects the line k. A line m connecting the points A and B is provided, and a line t perpendicular to the line m is provided. Point C is the position where the line of the cross section of the disk intersects the line t, and point D is the position where the line m intersects the line t. and Then, the distance at which the distance between points CD is maximum was measured as roll-off. The roll-off ratio is a relative value when the roll-off of Comparative Example 1 measured using the above method is set to 1 (reference).

[Discussion]
From the comparison between Reference Example 1 and Comparative Example 1, it can be seen that when the proportion of particles having a particle diameter of 30 to 70 nm in colloidal silica is 10% by volume or more, the polishing rate is improved, shallow pits are significantly reduced, and waviness and It can be seen that the roll-off balance is also improved.

A comparison of Reference Example 2 and Comparative Example 2 also reveals the same. That is, both when the total silica concentration is 4.0% by mass ( Reference Example 1 and Comparative Example 1) and when the total silica concentration is 6.0% by mass ( Reference Example 2 and Comparative Example 2), It can be seen that when the proportion of particles having a particle diameter of 30 to 70 nm is 10% by volume or more, the polishing speed is improved, shallow pits are significantly reduced, and the balance between waviness and roll-off is also improved.

A comparison between Reference Example 5 and Comparative Example 3 also reveals the same. That is, both when the average particle diameter of the wet silica particles is 300 nm ( Reference Example 1 and Comparative Example 1) and when it is 350 nm ( Reference Example 5 and Comparative Example 3), the particles in the colloidal silica have a particle diameter of 30 to 70 nm. is 10% by volume or more, the polishing speed is improved, shallow pits are significantly reduced, and the balance between waviness and roll-off is improved.

Reference Examples 3 and 4 are the results of using abrasive compositions in which the proportion of particles with a particle size of 30 to 70 nm in colloidal silica is greater than in Reference Example 1. The result is an improved balance of speed, shallow pit, swell, and roll-off.

Examples 1 , 3 , and 4 are the results of using the abrasive composition of Reference Example 1 to which a water-soluble polymer compound was added . It can be seen that it is even better than 1. Similarly, Example 2, in which a water-soluble polymer compound was added to the abrasive composition of Reference Example 2 , exhibited a further improved balance of polishing rate, shallow pits, waviness, and roll-off compared to Reference Example 2. It can be seen that

Example 5 is the result of using the abrasive composition of Reference Example 3 to which a water-soluble polymer compound was added . You can see that it is improving. Example 6 is the result of using the abrasive composition of Reference Example 4 to which a water-soluble polymer compound was added . You can see that it is improving. Example 7 is the result of using the abrasive composition of Reference Example 5 to which a water-soluble polymer compound was added . You can see that it is improving.

From the comparison between Reference Example 5 and Comparative Example 4, it can be seen that when the average particle size of the wet-process silica particles exceeds 500 nm, the number of shallow pits increases and waviness and roll-off also deteriorate.

From the comparison between Reference Example 1 and Comparative Example 5, it can be seen that when the proportion of colloidal silica in the total silica exceeds 80% by mass, the polishing rate is greatly reduced and the roll-off is also deteriorated.

From the comparison between Reference Example 1 and Comparative Example 6, it can be seen that when the proportion of colloidal silica in the total silica is less than 20% by mass, the number of shallow pits increases remarkably and waviness worsens.

From the above, it is clear that the use of the abrasive composition of the present invention improves the balance of polishing rate, shallow pits, waviness and roll-off.

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. Further, it can be used for 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 (10)

Colloidal silica having an average primary particle size of 10 to 150 nm,
pulverized wet-process silica particles having an average particle size of 200 to 500 nm;
a water-soluble polymer compound;
contains water,
The proportion of the colloidal silica in the total silica particles is 20 to 80% by mass, and the proportion of the pulverized wet silica particles is 20 to 80% by mass,
The proportion of particles with a particle size of 30 to 70 nm in the colloidal silica is 10 to 90% by volume,
The ratio of the average particle size of the pulverized wet-process silica particles to the average primary particle size of the colloidal silica is 2.0 to 15.0,
The concentration of the total silica particles is 2 to 40 mass% ,
The water-soluble polymer compound is a copolymer containing a monomer having a carboxylic acid group and a monomer having an amide group as essential monomers, a monomer having a carboxylic acid group and a monomer having a sulfonic acid group. A copolymer containing a monomer as an essential monomer, a copolymer containing a monomer having a carboxylic acid group, a monomer having an amide group, and a monomer having a sulfonic acid group as essential monomers An abrasive composition for magnetic disk substrates , which is at least one selected from the group . When the water-soluble polymer compound is a copolymer containing, as essential monomers, a monomer having a carboxylic acid group and a monomer having an amide group, it is derived from the monomer having a carboxylic acid group. 2. The abrasive composition for magnetic disk substrates according to claim 1 , wherein the proportion of structural units is in the range of 50 to 95 mol %, and the proportion of structural units derived from monomers having amide groups is in the range of 5 to 50 mol % . When the water-soluble polymer compound is a copolymer containing a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as essential monomers, it is derived from the monomer having a carboxylic acid group. 2. The abrasive composition for magnetic disk substrates according to claim 1 , wherein the proportion of structural units is in the range of 30 to 95 mol %, and the proportion of structural units derived from monomers having sulfonic acid groups is in the range of 5 to 70 mol %. . When the water-soluble polymer compound is a copolymer containing, as essential monomers, a monomer having a carboxylic acid group, a monomer having an amide group, and a monomer having a sulfonic acid group, the carboxylic acid 50 to 95 mol% of structural units derived from monomers having groups, 1 to 40 mol% of structural units derived from monomers having amide groups, derived from monomers having sulfonic acid groups 2. The abrasive composition for magnetic disk substrates according to claim 1 , wherein the ratio of the structural units is in the range of 0.01 to 20 mol % . 5. 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. Claims 1 , 2 , and 4, wherein the monomer having an amide group is one or more monomers selected from acrylamide, methacrylamide, N-alkylacrylamide, and N-alkylmethacrylamide . The abrasive composition for magnetic disk substrates according to any one of the above items. The sulfonic acid group-containing monomer is isoprenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, vinylsulfonic acid, and allylsulfonic acid. , isoamylenesulfonic acid, naphthalenesulfonic acid, and salts thereof . The magnetic disk according to any one of claims 1 to 7, 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. 9. The abrasive composition for magnetic disk substrates according to claim 1, further comprising an oxidizing agent . The abrasive composition for magnetic disk substrates according to any one of claims 1 to 9 , which is used for polishing electroless nickel-phosphorus plated aluminum magnetic disk substrates .

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