JP2010170650A - Polishing liquid composition for magnetic disk substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing liquid composition for a magnetic disk substrate that can reduce scratches and the surface roughness of the substrate after polishing without sacrificing productivity, and to provide a method for manufacturing the magnetic disk substrate using the polishing liquid composition. <P>SOLUTION: The polishing liquid composition comprises colloidal silica and water. An average particle diameter of the colloidal silica measured at a detection angle of 90° by a dynamic light scattering method is 1 to 40 nm, a value (CV90) of a coefficient of a variation (CV) obtained by dividing a standard deviation measured at a detection angle of 90° by the dynamic light scattering method of the colloidal silica by the average particle diameter and multiplying the obtained value by 100 is 1 to 35% and the difference (ΔCV=CV30-CV90) between a CV value (CV30) obtained by dividing a standard deviation measured at a detection angle of 30° by the dynamic light scattering method of the colloidal silica by the average particle diameter and multiplying the obtained value by 100 and the CV90 is 0 to 10%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polishing composition for a magnetic disk substrate and a method for producing a magnetic disk substrate using the same.

  In recent years, magnetic disk drives have been reduced in size and capacity, and high recording density has been demanded. In order to increase the recording density, the unit recording area is reduced, and in order to improve the detection sensitivity of the weakened magnetic signal, technological development for lowering the flying height of the magnetic head has been advanced. Magnetic disk substrates have improved smoothness and flatness (reduced surface roughness, waviness, and edge sagging) and reduced defects (scratches, protrusions, pits) in order to reduce the flying height of the magnetic head and secure a recording area. Etc.) is becoming stricter. In response to such demands, there have been proposed polishing liquid compositions in which the particle size distribution of colloidal silica is defined as polishing particles and polishing liquid compositions containing colloidal silica and anionic polymers (for example, patent documents). 1-3).

  Patent Document 1 discloses a polishing liquid composition using colloidal silica having a specific particle size distribution. According to this polishing liquid composition, the particle size distribution of the colloidal silica is reduced. It is described that the surface roughness of a memory hard disk substrate can be reduced by sharpening the thickness.

  Patent Document 2 discloses a polishing liquid composition for a polymer glass substrate having a sulfonic acid group. According to this polishing liquid composition, by adding a polymer having a sulfonic acid group, a glass substrate is obtained. It is described that surface roughness and substrate contamination can be improved.

  In Patent Document 3, a polishing composition comprising colloidal silica as an abrasive, polyacrylic acid ammonium salt as a polishing resistance reducing agent, EDTA-Fe salt as a polishing accelerator, and water is caused by vibration during polishing. It is disclosed that prevention of chamfer part damage and reduction of defects (scratches, pits) can be achieved.

JP 2004-204151 A JP 2006-167817 A JP 2001-155332 A

  However, in order to realize further increase in capacity, the conventional polishing composition is insufficient, and while maintaining productivity (without causing a decrease in polishing rate), scratching and surface roughness of the substrate after polishing are performed. It is necessary to further reduce the maximum value (AFM-Rmax).

  Furthermore, with the increase in capacity, the recording method on the magnetic disk has shifted from the horizontal magnetic recording method to the perpendicular magnetic recording method. In the manufacturing process of a perpendicular magnetic recording type magnetic disk, the texture process required for aligning the magnetization direction in the horizontal magnetic recording method is not required, and a magnetic layer is formed directly on the polished substrate surface. The required characteristics for quality are becoming stricter. The conventional polishing composition cannot satisfactorily satisfy the scratch and surface roughness maximum values (AFM-Rmax) required for the surface of a perpendicular magnetic recording substrate.

  Accordingly, the present invention provides a polishing composition for a magnetic disk substrate that can realize low scratching of the substrate after polishing and reduction of the maximum value of surface roughness (AFM-Rmax) without impairing productivity, and the same. A method of manufacturing a magnetic disk substrate is provided.

  The present invention contains colloidal silica and water, and has an average particle diameter of 1 to 40 nm measured at a detection angle of 90 ° in the dynamic light scattering method of the colloidal silica, and the dynamic light scattering method of the colloidal silica. The coefficient of variation (CV90) obtained by dividing the standard deviation measured at a detection angle of 90 ° by the average particle diameter and multiplying by 100 is 1 to 35%, and the dynamic light scattering method of the colloidal silica The difference (ΔCV = CV30−CV90) between the CV value (CV30) obtained by dividing the standard deviation measured at a detection angle of 30 ° by the average particle diameter and multiplying by 100 is 0 to 10%. The present invention relates to a polishing composition for substrates.

  The method for producing a magnetic disk substrate of the present invention is a method for producing a magnetic disk substrate including a step of polishing a substrate to be polished using the polishing composition for a magnetic disk substrate of the present invention.

  According to the polishing composition for a magnetic disk substrate of the present invention, a magnetic disk substrate, particularly a vertical disk, in which the maximum value of the scratch and the surface roughness (AFM-Rmax) is reduced without significantly impairing the productivity and the surface roughness. The effect that a magnetic disk substrate of a magnetic recording system can be manufactured is preferably achieved.

  In the polishing composition for a magnetic disk substrate containing colloidal silica, the present invention can reduce scratches on the substrate after polishing and maintain the polishing rate at a level at which productivity is not impaired by using specific colloidal silica. The surface roughness of the substrate after polishing is also based on the knowledge that it is possible to meet the demand for an increase in recording capacity.

  Specifically, in addition to the average particle diameter that has been controlled conventionally, the value of the coefficient of variation (CV value) indicating the spread of the particle size distribution, and the difference between the CV values at two different detection angles (ΔCV) It was found that by controlling the colloidal silica using these three parameters by paying attention to the value), the scratch of the substrate after polishing is greatly reduced.

  That is, in one aspect, the present invention is a polishing composition for a magnetic disk substrate, which contains colloidal silica and water, and is an average measured at a detection angle of 90 ° in the dynamic light scattering method of the colloidal silica. A coefficient of variation (CV90) having a particle diameter of 1 to 40 nm and dividing the standard deviation measured at a detection angle of 90 ° in the dynamic light scattering method of colloidal silica by the average particle diameter and multiplying by 100. CV value obtained by dividing the standard deviation measured at a detection angle of 30 ° in the colloidal silica dynamic light scattering method by the average particle diameter and multiplying by 100 (CV30) and the CV90 The difference (ΔCV = CV30−CV90) of the magnetic disk substrate is 0 to 10% (hereinafter also referred to as the polishing liquid composition of the present invention).

  In addition, the polishing liquid composition of this aspect of this aspect can also be paraphrased as follows. That is, in one embodiment, the polishing composition of the present invention contains colloidal silica and water, and the ΔCV value of the colloidal silica is 0 to 10%. Here, the ΔCV value is a dynamic light scattering method. (CV30) obtained by dividing the standard deviation based on the scattering intensity distribution at a detection angle of 30 ° by the average particle diameter based on the scattering intensity distribution and multiplying by 100 (CV30), and the standard deviation based on the scattering intensity distribution at a detection angle of 90 ° A value (ΔCV = CV30−CV90) which is a value obtained by dividing by 100 and dividing by an average particle diameter based on the scattering intensity distribution (ΔCV = CV30−CV90), and the CV90 value of the colloidal silica is 1 to 35%, And it is a polishing composition for magnetic disk substrates whose average particle diameter measured by 90 degree of detection angles in the said colloidal silica dynamic light-scattering method is 1-40 nm.

  Moreover, this invention uses colloidal silica and anionic polymer (water-soluble polymer which has anionic group) which satisfy | fill the prescription | regulation of said three parameters (average particle diameter, CV90, and (DELTA) CV) as another aspect. Therefore, the maximum value (AFM-Rmax) of the scratch and the surface roughness of the substrate after polishing can be further reduced while maintaining the polishing rate in polishing. That is, the present invention, as another embodiment, contains colloidal silica, a water-soluble polymer having an anionic group, and water, and is an average particle measured at a detection angle of 90 ° in the dynamic light scattering method of the colloidal silica. A coefficient of variation (CV90) having a diameter of 1 to 40 nm and dividing the standard deviation measured at a detection angle of 90 ° in the colloidal silica dynamic light scattering method by the average particle diameter and multiplying by 100 CV value (CV30) obtained by dividing the standard deviation measured at a detection angle of 30 ° in the dynamic light scattering method of the colloidal silica by the average particle diameter and multiplying by 100 and the CV90. The present invention relates to a polishing liquid composition for a magnetic disk substrate having a difference (ΔCV = CV30−CV90) of 0 to 10%. In addition, the polishing liquid composition of this aspect of this aspect can also be paraphrased as follows. That is, in another aspect, the polishing composition of the present invention contains colloidal silica, a water-soluble polymer having an anionic group, and water, and the ΔCV value of the colloidal silica is 0 to 10%. Polishing liquid for magnetic disk substrate whose CV90 value of colloidal silica is 1-35%, and whose average particle diameter is 1-40 nm based on the scattering intensity distribution of 90 degrees of detection angles by the dynamic light scattering method of said colloidal silica Relates to the composition.

  By adding a small amount of a water-soluble polymer having an anionic group (preferably having a low molecular weight), the generation of the silica aggregates generated during polishing is suppressed, and the friction vibration during polishing is reduced, thereby reducing the polishing pad. It is presumed that the maximum value (AFM-Rmax) of the scratch and surface roughness of the substrate after polishing is remarkably reduced by preventing the silica agglomerates from dropping from the openings. However, the present invention is not limited to these estimation mechanisms.

  According to the polishing liquid composition of the present invention, a magnetic disk substrate, particularly a vertical disk, in which the maximum value of scratch and surface roughness (AFM-Rmax) is reduced without impairing productivity (without causing a decrease in polishing rate). There is an effect that a magnetic recording type magnetic disk substrate can be manufactured.

[ΔCV value]
In this specification, the ΔCV value of colloidal silica is the standard deviation of the particle diameter measured based on the scattering intensity distribution at a detection angle of 30 ° (forward scattering) by the dynamic light scattering method, and the detection angle of 30 by the dynamic light scattering method. Scattering with a coefficient of variation (CV30) multiplied by 100 divided by the average particle diameter measured based on the scattering intensity distribution of ° C (CV30) and a detection angle of 90 ° (side scattering) by the dynamic light scattering method A coefficient of variation (CV90) obtained by dividing the standard deviation of the particle diameter measured based on the intensity distribution by the average particle diameter measured based on the scattering intensity distribution at a detection angle of 90 ° by the dynamic light scattering method and multiplying by 100. ) (ΔCV = CV30−CV90) and a value indicating the angular dependence of the scattering intensity distribution measured by the dynamic light scattering method. Specifically, the ΔCV value can be measured by the method described in Examples.

  The present inventors have found that there is a correlation between the ΔCV value of colloidal silica and the number of scratches, and that there is a correlation between the ΔCV value of colloidal silica and the content of non-spherical silica. . Although the mechanism for reducing scratches is not clear, 50-200 nm silica aggregates (non-spherical silica) produced by agglomeration of primary particles of colloidal silica are the causative substances of the occurrence of scratches. Estimated to be reduced.

  That is, by paying attention to the ΔCV value, it is possible to easily detect the presence of non-spherical particles in a particle dispersion sample that has been difficult to detect in the past. Therefore, a polishing liquid composition containing such non-spherical particles Can be avoided, and as a result, a reduction in scratches can be achieved.

Here, whether the particles in the particle dispersion sample are spherical or non-spherical is generally determined by a method using the angle dependency of the diffusion coefficient (D = Γ / q ² ) measured by the dynamic scattering method as an index (for example, Jpn. Pat. Appln. KOKAI Publication No. 10-195152). Specifically, the smaller the angle dependency shown in the graph plotting Γ / q ² with respect to the scattering vector q ^{2, the} more the average shape of the particles in the dispersion is judged to be spherical, and the angle dependency is The larger the particle size, the more the average shape of the particles in the dispersion is judged to be non-spherical. That is, the conventional method using the angular dependence of the diffusion coefficient measured by the dynamic scattering method as an index assumes that the uniform particle is dispersed throughout the system, and the shape and particle size of the particle are determined. It is a method of detecting and measuring. Therefore, it is difficult to detect non-spherical particles present in a part of the dispersion sample in which spherical particles are predominant.

  On the other hand, in the dynamic light scattering method, when measuring a spherical particle dispersion solution of 200 nm or less in principle, the measurement result does not depend on the detection angle because the scattering intensity distribution is almost constant regardless of the detection angle. . However, the scattering intensity distribution of dynamic light scattering of a spherical dispersion containing non-spherical particles varies greatly depending on the detection angle due to the presence of non-spherical particles, and the distribution of the scattering intensity distribution becomes broader at lower detection angles. . Therefore, the measurement result of the scattering intensity distribution of dynamic light scattering depends on the detection angle, and the ΔCV value, which is one of the indicators of “angle dependency of the scattering intensity distribution measured by the dynamic light scattering method”, is It is considered that a few non-spherical particles existing in the spherical particle dispersion solution can be measured by measuring. Note that the present invention is not limited to these mechanisms.

[Scattering intensity distribution]
In this specification, “scattering intensity distribution” means three particle size distributions of sub-micron or less particles obtained by dynamic light scattering (DLS) or quasielastic light scattering (QLS). It means the particle size distribution of scattering intensity among (scattering intensity, volume conversion, number conversion). Usually, the sub-micron particles have Brownian motion in a solvent, and the intensity of scattered light changes (fluctuates) with time when irradiated with laser light. For this fluctuation of scattered light intensity, for example, an autocorrelation function is obtained using a photon correlation method (JIS Z 8826), and a diffusion coefficient (D) indicating a Brownian motion velocity is calculated by cumulant method analysis. Furthermore, the average particle diameter (d: hydrodynamic diameter) can be obtained using the Einstein-Stokes equation. In addition to polydispersity index (PI) by cumulant method, particle size distribution analysis includes histogram method (Marquardt method), Laplace inverse transformation method (CONTIN method), non-negative least square method (NNLS method), etc. There is.

In the particle size distribution analysis of the dynamic light scattering method, the polydispersity index (PI) by the cumulant method is generally widely used. However, in the detection method that enables detection of non-spherical particles that are slightly present in the particle dispersion, the average particle size (from the particle size distribution analysis by the histogram method (Marquardt method) or the Laplace inverse transform method (CONTIN method)) It is preferable to obtain d50) and the standard deviation, calculate a CV value (Coefficient of variation: a value obtained by dividing the standard deviation by the average particle size and multiply by 100), and use the angular dependence (ΔCV value).
(Reference document)
Text of the 12th Scattering Study Group (held on November 22, 2000) Scattering Basic Course "Dynamic Light Scattering Method" (Professor Mitsuhiro Shibayama, The University of Tokyo)
Text of the 20th Scattering Study Group (held on December 4, 2008) Measurement of size distribution of nanoparticles by dynamic light scattering (Doshisha University, Professor Yasushi Mori)

[Angle dependence of scattering intensity distribution]
In this specification, “angle dependency of the scattering intensity distribution of the particle dispersion” means scattering according to the scattering angle when the scattering intensity distribution of the particle dispersion is measured at different detection angles by the dynamic light scattering method. The magnitude of fluctuation in intensity distribution. For example, if the difference in the scattering intensity distribution between the detection angle of 30 ° and the detection angle of 90 ° is large, it can be said that the angle dependency of the scattering intensity distribution of the particle dispersion is large. Therefore, in this specification, the measurement of the angle dependence of the scattered intensity distribution includes obtaining a difference (ΔCV value) between measured values based on the scattered intensity distribution measured at two different detection angles.

  As a combination of the two detection angles used in the measurement of the angle dependence of the scattering intensity distribution, a combination of forward scattering and side or back scattering is preferable from the viewpoint of improving the accuracy of detection of non-spherical particles. From the same viewpoint, the forward scattering detection angle is preferably 0 to 80 °, more preferably 0 to 60 °, still more preferably 10 to 50 °, and still more preferably 20 to 40 °. From the same viewpoint, the side or backscattering detection angle is preferably 80 to 180 °, more preferably 85 to 175 °. In the present invention, 30 ° and 90 ° are used as two detection angles for obtaining the ΔCV value.

[Colloidal silica]
The colloidal silica used in the polishing composition of the present invention may be obtained by a known production method or the like produced from an aqueous silicic acid solution. The usage form of the silica particles is preferably a slurry from the viewpoint of operability.

  The “average particle size of colloidal silica” in the present invention refers to the average particle size based on the scattering intensity distribution measured by the dynamic light scattering method, and unless otherwise specified, the “average particle size of colloidal silica” The average particle diameter based on the scattering intensity distribution measured at a detection angle of 90 ° in the dynamic light scattering method. The average particle diameter of the colloidal silica in the present invention can be specifically obtained by the method described in Examples.

  The average particle diameter of the colloidal silica used in the present invention is 1 to 40 nm, preferably 5 to 37 nm, from the viewpoint of reducing the maximum value of the scratch and surface roughness (AFM-Rmax) without impairing the productivity. More preferably, it is 10-35 nm.

  The CV value of the colloidal silica used in the present invention is 1 to 35%, preferably 5 to 34, from the viewpoint of reducing the maximum value of the scratch and the surface roughness (AFM-Rmax) without impairing the productivity. %, More preferably 10 to 33%. Here, the CV value is a value of a coefficient of variation obtained by dividing the standard deviation based on the scattering intensity distribution by the average particle diameter and multiplying by 100 in the dynamic light scattering method. The CV value measured at ° (side scatter) is called CV90, and the CV value measured at a detection angle of 30 ° (forward scatter) is called CV30. Specifically, the CV value of colloidal silica can be obtained by the method described in Examples.

  The ΔCV value of the colloidal silica used in the present invention is 0 to 10%, preferably 0.01% from the viewpoint of reducing the maximum value of the scratch and the surface roughness (AFM-Rmax) without impairing the productivity. -10%, more preferably 0.01-7%, even more preferably 0.1-5%. Here, the ΔCV value of colloidal silica is obtained by dividing the standard deviation obtained by measurement based on the scattering intensity distribution at a detection angle of 30 ° (forward scattering) by the dynamic light scattering method by the average particle diameter and multiplying by 100. The coefficient of variation (CV90) obtained by dividing the standard deviation by the average particle diameter and multiplying by 100 (CV90) obtained by the measurement based on the value of the coefficient of variation (CV30) and the scattering intensity distribution at a detection angle of 90 ° (side scatter). (CV30-CV90), specifically, it can be measured by the method described in the examples.

Examples of the method for adjusting the ΔCV value of colloidal silica include the following methods for preventing formation of 50 to 200 nm silica aggregates (non-spherical silica) in the preparation of the polishing composition.
A) Method by filtration of polishing liquid composition B) Method by process control at the time of colloidal silica production

  In the above A), ΔCV can be reduced by removing silica aggregates of 50 to 200 nm by, for example, centrifugation or fine filter filtration (Japanese Patent Laid-Open No. 2006-102829 and Japanese Patent Laid-Open No. 2006-136996). Specifically, a colloidal silica aqueous solution appropriately diluted so that the silica concentration is 20% by weight or less can be removed under conditions where 50 nm particles calculated from the Stokes equation can be removed (for example, 10,000 G or more, centrifuge tube height of about 10 cm). ΔCV can be reduced by a method of centrifuging for 2 hours or more, a method of pressure filtration using a membrane filter having a pore size of 0.05 μm or 0.1 μm (for example, Advantech, Sumitomo 3M, Millipore).

The colloidal silica particles are usually 1) a mixed solution (seed solution) of less than 10% by weight of No. 3 sodium silicate and seed particles (small particle silica) in a reaction layer, and heated to 60 ° C. or higher. 2) An acidic active silicic acid aqueous solution in which No. 3 sodium silicate is passed through a cation exchange resin and an alkali (alkali metal or quaternary ammonium) are dropped to grow a spherical particle with a constant pH. 3) It can be obtained by concentrating by evaporation or ultrafiltration after aging (Japanese Patent Application Laid-Open No. 47-1964, Japanese Patent Publication No. 1-223412, Japanese Patent Publication No. 4-55125, Japanese Patent Publication No. 4-55127). However, it is often reported that non-spherical particles can be produced by slightly changing the process in the same production process. For example, activated silicic acid is very unstable, and when a polyvalent metal ion such as Ca or Mg is intentionally added, an elongated silica sol can be produced. Further, the temperature of the reaction layer (evaporates when the boiling point of water is exceeded and the silica is dried at the gas-liquid interface), the pH of the reaction layer (silica particles are liable to be linked below 9), the SiO ₂ / M ₂ O of the reaction layer. (M is an alkali metal or quaternary ammonium), and non-spherical silica can be produced by changing the molar ratio (selectively producing non-spherical silica at 30 to 60) (Japanese Patent Publication No. 8-5657, Patent 2803134, JP, 2006-80406, JP, 2007-153671). Therefore, in the above-mentioned B), ΔCV can be adjusted to be small by performing process control so as not to be a condition for generating non-spherical silica locally in a known spherical colloidal silica production process.

  The method for adjusting the particle size distribution of the colloidal silica is not particularly limited, but a method of giving a desired particle size distribution by adding particles as a new nucleus in the particle growth process in the production stage, or a different particle size Examples thereof include a method of mixing two or more types of silica particles having a distribution to give a desired particle size distribution.

  The content of colloidal silica particles in the polishing liquid composition of the present invention is preferably 0.5% by weight or more, more preferably 1% by weight or more, and further preferably 3% by weight or more, from the viewpoint of improving the polishing rate. More preferably, it is 4% by weight or more, and from the viewpoint of further improving the flatness of the substrate surface, it is preferably 20% by weight or less, more preferably 15% by weight or less, still more preferably 13% by weight or less, and even more. Preferably it is 10 weight% or less. That is, the content of the silica particles is preferably 0.5 to 20% by weight, more preferably 1 to 15% by weight, still more preferably 3 to 13% by weight, and even more preferably 4 to 10% by weight.

[Water-soluble polymer having an anionic group]
The polishing composition of the present invention is a water-soluble polymer having an anionic group (hereinafter referred to as an anionic water-soluble polymer) from the viewpoint of reducing the maximum value (AFM-Rmax) of scratches and surface roughness of the substrate after polishing. (Also referred to as a molecule). The polymer reduces frictional vibration during polishing to prevent the silica agglomerates from dropping from the openings of the polishing pad, and increases the maximum value (AFM-Rmax) of the scratch and surface roughness of the substrate after polishing. It is estimated to decrease.

  Examples of the anionic group of the anionic water-soluble polymer include a carboxylic acid group, a sulfonic acid group, a sulfate ester group, a phosphate ester group, and a phosphonic acid group. Among these, those having a carboxylic acid group and / or a sulfonic acid group are more preferable from the viewpoint of reducing scratches. These anionic groups may take the form of neutralized salts.

  The water-soluble polymer having a carboxylic acid group and / or a sulfonic acid group is selected from the group consisting of a structural unit derived from a monomer having a carboxylic acid group and a structural unit derived from a monomer having a sulfonic acid group. Examples thereof include (co) polymers having at least one structural unit or salts thereof. Examples of the monomer having a carboxylic acid group include itaconic acid, (meth) acrylic acid, maleic acid and the like. Examples of the monomer having a sulfonic acid group include isoprene sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, styrene sulfonic acid, methallyl sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, isoamido Examples thereof include lensulfonic acid and naphthalenesulfonic acid. The anionic water-soluble polymer may contain two or more types of structural units derived from a monomer having a carboxylic acid group and structural units derived from a monomer having a sulfonic acid group.

  Among these, as an anionic water-soluble polymer, the following general formula (1) is used from the viewpoint of reducing the maximum value (AFM-Rax) of the scratch and the surface roughness of the substrate after polishing without impairing the productivity. A polymer having the structural unit represented is preferred.

上記式（１）中、Ｒは水素原子、メチル基又はエチル基であり、Ｘは水素原子、アルカリ金属原子、アルカリ土類金属原子（１／２原子）、アンモニウム基又は有機アンモニウム基である。

In the above formula (1), R is a hydrogen atom, a methyl group or an ethyl group, and X is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom (1/2 atom), an ammonium group or an organic ammonium group.

  Examples of the (meth) acrylic acid-based (co) polymer having the structural unit represented by the general formula (1) and salts thereof include (meth) acrylic acid / sulfonic acid copolymer, (meth) acrylic acid / maleic acid. Acid copolymers, poly (meth) acrylic acid and their salts are preferred, and (meth) acrylic acid / sulfonic acid copolymers, poly (meth) acrylic acid and their salts are more preferred. The anionic water-soluble polymer may be one type of these (co) polymers or may contain two or more types. In the present invention, (meth) acrylic acid refers to acrylic acid or methacrylic acid.

  The (meth) acrylic acid / sulfonic acid copolymer refers to a copolymer containing a structural unit derived from (meth) acrylic acid and a structural unit derived from a sulfonic acid group-containing monomer. The (meth) acrylic acid / sulfonic acid copolymer may contain two or more structural units derived from the sulfonic acid group-containing monomer.

  As the sulfonic acid group-containing monomer, isoprenesulfonic acid and 2- (meth) acrylamide-2-methylpropanesulfonic acid are preferable from the viewpoint of reducing scratches, and 2- (meth) acrylamide-2-methylpropanesulfonic acid is preferable. Is more preferable. In the present invention, 2- (meth) acrylamide-2-methylpropanesulfonic acid refers to 2-acrylamido-2-methylpropanesulfonic acid or 2-methacrylamide-2-methylpropanesulfonic acid.

  The (meth) acrylic acid / sulfonic acid copolymer is a structural unit derived from a monomer other than the sulfonic acid group-containing monomer and the (meth) acrylic acid monomer within the scope of the effects of the present invention. It may contain components.

  The content rate of the structural unit derived from the sulfonic acid group-containing monomer in all the structural units constituting each of the (meth) acrylic acid / sulfonic acid copolymer or salt thereof is 10 to 90 from the viewpoint of reducing scratches. Although it is possible to consider it as mol%, 15-80 mol%, or 15-50 mol%, it is preferable that it is 3-97 mol%, More preferably, it is 50-95 mol%, More preferably, it is 70-90 mol %. Here, the (meth) acrylic acid monomer containing a sulfonic acid group is counted as a sulfonic acid group-containing monomer.

  Preferred (meth) acrylic acid / sulfonic acid copolymers include (meth) acrylic acid / isoprenesulfonic acid copolymers, (meth) acrylic acid / 2- (meth) acrylamide-2-methyl, from the viewpoint of reducing scratches. Examples thereof include propanesulfonic acid copolymer, (meth) acrylic acid / isoprenesulfonic acid / 2- (meth) acrylamide-2-methylpropanesulfonic acid copolymer, and the like.

  The (meth) acrylic acid / maleic acid copolymer refers to a copolymer containing a structural unit derived from (meth) acrylic acid and a structural unit derived from maleic acid.

  The (meth) acrylic acid / maleic acid copolymer is a structural unit component derived from a monomer other than the maleic acid monomer and the (meth) acrylic acid monomer within the scope of the effects of the present invention. You may contain.

  The content of the structural unit derived from maleic acid in all the structural units constituting the (meth) acrylic acid / maleic acid copolymer is 10 to 90 mol%, 20 to 80 mol% from the viewpoint of reducing nanoscratches, Although it is considered to be 30 to 70 mol%, it is preferably 5 to 95 mol%, more preferably 50 to 95 mol%, still more preferably 70 to 90 mol%.

  The (co) polymer is obtained by, for example, converting a base polymer containing a diene structure or an aromatic structure into a known method, for example, edited by The Chemical Society of Japan, New Experimental Chemistry Course 14 (Synthesis and Reaction of Organic Compounds III, 1773, 1978).

上記一般式（２）で表される構成単位を有する重合体としては、スクラッチ低減及び研磨速度の向上の観点から、該重合体の全構成単位中に占める上記一般式（２）で表される構成単位の割合が５０モル％を超える重合体であることが好ましく、７０モル％以上がより好ましく、９０モル％以上がさらに好ましく、９７モル％以上がさらにより好ましく、上記一般式（２）で表される構成単位の繰り返し構造のみで表わされる重合体であることがさらにより好ましい。さらに該重合体の分子末端が水素で封鎖されていることが好ましい。 A polymer having a structural unit represented by the following general formula (2) is also preferably used as the water-soluble polymer having a carboxylic acid group and / or a sulfonic acid group.

The polymer having the structural unit represented by the general formula (2) is represented by the general formula (2) occupying in all the structural units of the polymer from the viewpoint of reducing scratches and improving the polishing rate. The proportion of the structural unit is preferably a polymer exceeding 50 mol%, more preferably 70 mol% or more, still more preferably 90 mol% or more, still more preferably 97 mol% or more, and in the above general formula (2) It is even more preferable that the polymer is represented only by the repeating structure of the structural unit represented. Furthermore, it is preferable that the molecular terminal of the polymer is blocked with hydrogen.

In the general formula (2), M is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom (1/2 atom), an ammonium group or an organic ammonium group, and the alkali metal is preferably sodium or potassium. In the general formula (2), n is 1 or 2, and is preferably 1 from the viewpoint of improving scratch reduction. Moreover, as for the “polymer mainly composed of the structural unit represented by the general formula (2)” as a whole, n preferably has an average value of 0.5 or more and 1.5 or less. Furthermore, in the general formula (2), the sulfonic acid group (—SO ₃ M) may be bonded to any position of the naphthylene group, but from the viewpoint of improving scratch reduction, the 6-position or the 7-position. Is preferably bonded to the 6 position. In the present specification, the general formula (2) can be referred to for the positions of the 6th and 7th positions of the naphthalene group.

The polymer having the structural unit represented by the general formula (2) may be prepared by a known method, for example, by introducing a sulfonic acid group into a naphthalene monomer using a sulfonating agent such as concentrated sulfuric acid, It can be synthesized by adding formalin water for condensation and further neutralizing with an inorganic salt such as Ca (OH) ₂ or Na ₂ SO ₄ . Commercially available products (for example, trade name: Dimor N and trade name: Mighty 150, both manufactured by Kao Corporation) may be used as the polymer mainly composed of the structural unit represented by the general formula (2). it can. Reference can be made to documents [JP 9-279127 A, JP 11-188614 A, and JP 2008-227098 A] for the polymer having the structural unit represented by the general formula (2).

  In addition, the anionic water-soluble polymer can contain structural unit components other than those described above. Examples of monomers that can be used as other structural unit components include aromatic vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, and p-methylstyrene, methyl (meth) acrylate, and ethyl (meth) acrylate. (Meth) acrylic acid alkyl esters such as octyl (meth) acrylate, aliphatic conjugated dienes such as butadiene, isoprene, 2-chloro-1,3-butadiene, 1-chloro-1,3-butadiene, (meta ) Vinyl cyanide compounds such as acrylonitrile and phosphoric acid compounds. These monomers can be used alone or in combination of two or more. Examples of a preferable copolymer of a water-soluble polymer having a carboxylic acid group and / or a sulfonic acid group having other structural unit components include a styrene / isoprenesulfonic acid copolymer from the viewpoint of reducing scratches.

  The counter ion of the water-soluble polymer having an anionic group is not particularly limited, and specific examples include ions of metals, ammonium, alkylammonium and the like. Specific examples of the metal include metals belonging to the periodic table (long-period type) 1A, 1B, 2A, 2B, 3A, 3B, 4A, 6A, 7A, or Group 8. Among these metals, metals belonging to Group 1A, 3B, or Group 8 are preferable from the viewpoint of surface roughness and nanoscratch reduction, and sodium and potassium belonging to Group 1A are more preferable. Specific examples of alkylammonium include tetramethylammonium, tetraethylammonium, tetrabutylammonium and the like. Among these salts, ammonium salts, sodium salts, and potassium salts are more preferable.

  The weight average molecular weight of the anionic water-soluble polymer is preferably 500 or more and 100,000 or less, more preferably 500 or more and 50,000 or less, still more preferably 500 or more and 20,000 or less, and even more, from the viewpoint of reducing scratches and maintaining productivity. Preferably they are 1000 or more and 10,000 or less, Especially preferably, they are 1500 or more and 5000 or less. Specifically, the weight average molecular weight is measured by the measurement method described in Examples.

  The content of the anionic water-soluble polymer in the polishing composition is preferably 0.001 to 1% by weight or more, more preferably 0.005 to 0.005%, from the viewpoint of achieving both scratch reduction and productivity. It is 5% by weight, more preferably 0.01 to 0.2% by weight, even more preferably 0.01 to 0.1% by weight, and particularly preferably 0.01 to 0.075% by weight.

  Further, the concentration ratio of the colloidal silica and the anionic water-soluble polymer [silica concentration (% by weight) / anionic water-soluble polymer concentration (% by weight)] in the polishing liquid composition improves the polishing rate, From the viewpoint of surface roughness and scratch reduction, 5 to 5000 is preferable, 10 to 1000 is more preferable, and 25 to 500 is more preferable.

[water]
Water in the polishing composition of the present invention is used as a medium, and examples thereof include distilled water, ion exchange water, and ultrapure water. From the viewpoint of the surface cleanliness of the substrate to be polished, ion exchange water and ultrapure water are preferable, and ultrapure water is more preferable. The content of water in the polishing composition is preferably 60 to 99.4% by weight, and more preferably 70 to 98.9% by weight. Moreover, you may mix | blend organic solvents, such as alcohol, in the range which does not inhibit the effect of this invention.

[acid]
The polishing liquid composition of the present invention preferably contains an acid and / or a salt thereof. The acid used in the polishing composition of the present invention is preferably a compound having a pK1 of 2 or less from the viewpoint of improving the polishing rate, and preferably has a pK1 of 1.5 or less from the viewpoint of reducing scratches. More preferably, it is a compound exhibiting strong acidity that cannot be expressed by pK1, more preferably 1 or less. Preferred acids are inorganic acids such as nitric acid, sulfuric acid, sulfurous acid, persulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, tripolyphosphoric acid, amidosulfuric acid, 2-aminoethylphosphonic acid, 1- Hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid), ethane-1,1, -diphosphonic acid, ethane-1,1,2 -Triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxy Phosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4 Organic phosphonic acids such as tricarboxylic acid and α-methylphosphonosuccinic acid, aminocarboxylic acids such as glutamic acid, picolinic acid and aspartic acid, carboxylic acids such as citric acid, tartaric acid, oxalic acid, nitroacetic acid, maleic acid and oxaloacetic acid Is mentioned. Of these, inorganic acids, carboxylic acids, and organic phosphonic acids are preferred from the viewpoint of reducing scratches. Among inorganic acids, nitric acid, sulfuric acid, hydrochloric acid, and perchloric acid are more preferable, and phosphoric acid and sulfuric acid are more preferable. Among the carboxylic acids, citric acid, tartaric acid, and maleic acid are more preferable, and citric acid is more preferable. Among organic phosphonic acids, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid), and salts thereof are more preferable. More preferred are -hydroxyethylidene-1,1-diphosphonic acid and aminotri (methylenephosphonic acid). These acids and salts thereof may be used alone or in combination of two or more, but from the viewpoint of improving the polishing rate, reducing nanoprotrusions and improving the cleaning property of the substrate, use two or more in combination. It is more preferable to use a mixture of two or more acids selected from the group consisting of phosphoric acid, sulfuric acid, citric acid and 1-hydroxyethylidene-1,1-diphosphonic acid. Here, pK1 is a logarithmic value of the reciprocal of the first acid dissociation constant (25 ° C.) of the organic compound or inorganic compound. The pK1 of each compound is described in, for example, the revised 4th edition Chemical Handbook (Basic Edition) II, pp316-325 (Edited by Chemical Society of Japan).

  There are no particular limitations on the counter ion when these acid salts are used, and specific examples include ions of metals, ammonium, alkylammonium, and the like. Specific examples of the metal include metals belonging to the periodic table (long-period type) 1A, 1B, 2A, 2B, 3A, 3B, 4A, 6A, 7A, or Group 8. Among these, a salt with a metal belonging to Group 1A or ammonium is preferable from the viewpoint of reducing scratches.

  The content of the acid and its salt in the polishing composition is preferably 0.001 to 5% by weight, more preferably 0.01 to 4% by weight, from the viewpoints of improving the polishing rate, surface roughness, and reducing scratches. More preferably, it is 0.05 to 3% by weight, and still more preferably 0.1 to 2.0% by weight.

[Oxidant]
The polishing composition of the present invention preferably contains an oxidant. As an oxidizing agent that can be used in the polishing liquid composition of the present invention, from the viewpoint of improving the polishing rate, peroxide, permanganic acid or a salt thereof, chromic acid or a salt thereof, peroxo acid or a salt thereof, oxygen acid or an acid thereof Examples thereof include salts, metal salts, nitric acids, sulfuric acids and the like.

  Examples of the peroxide include hydrogen peroxide, sodium peroxide, barium peroxide, etc., examples of the permanganic acid or salt thereof include potassium permanganate, and examples of the chromic acid or salt thereof include chromium. Acid metal salts, metal dichromates, and the like. Peroxo acids or salts thereof include peroxodisulfuric acid, ammonium peroxodisulfate, peroxodisulfate metal salts, peroxophosphoric acid, peroxosulfuric acid, sodium peroxoborate, and performic acid. Peroxyacetic acid, perbenzoic acid, perphthalic acid, etc., and oxygen acids or salts thereof include hypochlorous acid, hypobromite, hypoiodous acid, chloric acid, bromic acid, iodic acid, hypochlorous acid. Examples thereof include sodium chlorate and calcium hypochlorite. Examples of metal salts include iron (III) chloride, iron (III) sulfate, iron (III) nitrate, and iron citrate. III), ammonium iron (III), and the like.

  Preferable oxidizing agents include hydrogen peroxide, iron (III) nitrate, peracetic acid, ammonium peroxodisulfate, iron (III) sulfate, and iron (III) ammonium sulfate. As a more preferable oxidizing agent, hydrogen peroxide is mentioned from the viewpoint that metal ions do not adhere to the surface and are generally used and inexpensive. These oxidizing agents may be used alone or in admixture of two or more.

  The content of the oxidizing agent in the polishing liquid composition is preferably 0.01% by weight or more, more preferably 0.05% by weight or more, and further preferably 0.1% by weight or more from the viewpoint of improving the polishing rate. In view of surface roughness, waviness and scratch reduction, it is preferably 4% by weight or less, more preferably 2% by weight or less, and further preferably 1% by weight or less. Therefore, in order to improve the polishing rate while maintaining the surface quality, the content is preferably 0.01 to 4% by weight, more preferably 0.05 to 2% by weight, and still more preferably 0.1 to 1. % By weight.

[Other ingredients]
In the polishing composition of the present invention, other components can be blended as necessary. Examples of other components include a thickener, a dispersant, a rust inhibitor, a basic substance, and a surfactant. 0-10 weight% is preferable and, as for content of these other arbitrary components in polishing liquid composition, 0-5 weight% is more preferable.

[PH of polishing composition]
The pH of the polishing composition of the present invention is preferably 3.0 or less from the viewpoint of improving the polishing rate, more preferably 2.5 or less, still more preferably 2.0 or less, and even more preferably 1.8 or less. . Moreover, 0.5 or more is preferable from a viewpoint of surface roughness reduction, More preferably, it is 0.8 or more, More preferably, it is 1.0 or more, More preferably, it is 1.2 or more. In addition, the waste liquid pH of the polishing composition is preferably 3 or less, more preferably 2.5 or less, still more preferably 2.2 or less, and even more preferably 2.0 or less, from the viewpoint of improving the polishing rate. Further, from the viewpoint of reducing the surface roughness, the waste liquid pH of the polishing composition is preferably 0.8 or more, more preferably 1.0 or more, still more preferably 1.2 or more, and even more preferably 1.5 or more. It is. The waste liquid pH refers to the polishing waste liquid in the polishing step using the polishing liquid composition, that is, the pH of the polishing liquid composition immediately after being discharged from the polishing machine.

[Method for preparing polishing liquid composition]
The polishing liquid composition of the present invention is, for example, a known method comprising water, colloidal silica, and optionally an anionic water-soluble polymer, an acid and / or salt thereof, an oxidizing agent, and other components. Can be prepared by mixing. Under the present circumstances, colloidal silica may be mixed in the state of the concentrated slurry, and may be mixed after diluting with water etc. Although content and density | concentration of each component in the polishing liquid composition of this invention are the ranges mentioned above, you may prepare the polishing liquid composition of this invention as a concentrate as another aspect.

  Another aspect of the present invention is a method for preparing a polishing liquid composition for a magnetic disk substrate containing colloidal silica, wherein the average particle diameter measured at a detection angle of 90 ° in a dynamic light scattering method is 1 to 40 nm. Yes, the CV value (CV90) obtained by dividing the standard deviation measured at a detection angle of 90 ° in the dynamic light scattering method by the average particle size and multiplying by 100 is 1 to 35%, and the dynamic light scattering method Colloidal silica in which the difference (ΔCV = CV30−CV90) between the CV value (CV30) obtained by dividing the standard deviation measured at a detection angle of 30 ° by the average particle diameter and multiplying by 100 is 0 to 10% It is possible to provide a method for preparing a polishing liquid composition for a magnetic disk substrate, comprising selecting and / or using The polishing composition for a magnetic disk substrate using the colloidal silica can reduce scratches after polishing. Of course, the polishing composition of the present invention can also be produced by this method of preparing a polishing composition for a magnetic disk substrate.

[Method of manufacturing magnetic disk substrate]
As another aspect, the present invention relates to a method of manufacturing a magnetic disk substrate (hereinafter also referred to as a manufacturing method of the present invention). The manufacturing method of the present invention includes a step of polishing a substrate to be polished using the above-described polishing liquid composition of the present invention (hereinafter, also referred to as “polishing process using the polishing liquid composition of the present invention”). It is a manufacturing method of a disk substrate. Thereby, it is possible to preferably provide a magnetic disk substrate in which a decrease in the polishing rate can be suppressed, and scratching of the substrate after polishing is reduced without significantly impairing the productivity and the surface roughness of the substrate after polishing. The manufacturing method of the present invention is particularly suitable for a method for manufacturing a magnetic disk substrate for perpendicular magnetic recording. Therefore, as another aspect, the manufacturing method of the present invention is a method of manufacturing a magnetic disk substrate for a perpendicular magnetic recording system including a polishing step using the polishing composition of the present invention.

  As a specific example of a method for polishing a substrate to be polished using the polishing composition of the present invention, the substrate to be polished is sandwiched between a surface plate to which a polishing pad such as a non-woven organic polymer polishing cloth is attached. A method of polishing the substrate to be polished by moving the surface plate or the substrate to be polished while supplying the polishing composition of the invention to the polishing machine can be mentioned.

  In the case where the polishing process of the substrate to be polished is performed in multiple stages, the polishing process using the polishing composition of the present invention is preferably performed in the second stage and more preferably in the final polishing process. At that time, in order to avoid mixing of the polishing material and polishing liquid composition in the previous process, different polishing machines may be used, and in the case of using different polishing machines, polishing is performed for each polishing process. It is preferable to clean the substrate. Further, the polishing composition of the present invention can also be used in cyclic polishing in which the used polishing liquid is reused. The polishing machine is not particularly limited, and a known polishing machine for polishing a magnetic disk substrate can be used.

  In one embodiment, the production method of the present invention has an average particle diameter of 1 to 40 nm measured at a detection angle of 90 ° in the dynamic light scattering method, and is measured at a detection angle of 90 ° in the dynamic light scattering method. The CV value (CV90) of the average particle diameter is 1 to 35%, and the standard deviation measured at a detection angle of 30 ° in the dynamic light scattering method is divided by the average particle diameter and multiplied by 100 ( It may include selecting and / or confirming and using a polishing composition containing colloidal silica having a difference between CV30) and CV90 (ΔCV = CV30−CV90) of 0 to 10%. The polishing liquid composition containing the colloidal silica naturally includes the polishing liquid composition of the present invention.

[Polishing pad]
The polishing pad used in the present invention is not particularly limited, and a polishing pad of a suede type, a nonwoven fabric type, a polyurethane closed-cell foam type, or a two-layer type in which these are laminated can be used. From the viewpoint, a suede type polishing pad is preferable.

  The average pore diameter of the surface member of the polishing pad is preferably 50 μm or less, more preferably 45 μm or less, still more preferably 40 μm or less, and even more preferably 35 μm or less, from the viewpoint of scratch reduction and pad life. From the viewpoint of holding the polishing liquid of the pad, the average pore diameter is preferably 0.01 μm or more, more preferably 0.1 μm or more, and still more preferably, in order to keep the polishing liquid in the pores and prevent the liquid from running out. It is 1 μm or more, more preferably 10 μm or more. Further, the maximum value of the pore size of the polishing pad is preferably 100 μm or less, more preferably 70 μm or less, still more preferably 60 μm or less, and particularly preferably 50 μm or less from the viewpoint of maintaining the polishing rate. Therefore, the manufacturing method of this invention is a manufacturing method whose average pore diameter of the surface member of the polishing pad used at the process using the polishing liquid composition of this invention is 10-50 micrometers as another aspect.

[Polishing load]
The polishing load in the polishing step using the polishing liquid composition of the present invention is preferably 5.9 kPa or more, more preferably 6.9 kPa or more, and further preferably 7.5 kPa or more. Thereby, since the fall of a grinding | polishing speed | rate can be suppressed, productivity can be improved. In the production method of the present invention, the polishing load refers to the pressure of the surface plate applied to the polishing surface of the substrate to be polished during polishing. In the polishing step using the polishing composition of the present invention, the polishing load is preferably 20 kPa or less, more preferably 18 kPa or less, and further preferably 16 kPa or less. Thereby, generation | occurrence | production of a scratch can be suppressed. Accordingly, in the polishing step using the polishing composition of the present invention, the polishing pressure is preferably 5.9 to 20 kPa, more preferably 6.9 to 18 kPa, and further preferably 7.5 to 16 kPa. The polishing load can be adjusted by applying air pressure or weight to at least one of the surface plate and the substrate to be polished.

[Supply of polishing liquid composition]
From the viewpoint of reducing scratches, the supply rate of the polishing composition of the present invention in the polishing step using the polishing composition of the present invention is preferably 1 to 15 mL / min per 1 cm ^{2 of the} substrate to be polished. More preferably 0.06 to 10 mL / min, still more preferably 0.07 to 1 mL / min, even more preferably 0.08 to 0.5 mL / min, even more preferably 0.12 to 0.5 mL / min. Minutes.

  As a method for supplying the polishing composition of the present invention to a polishing machine, for example, a method of continuously supplying using a pump or the like can be mentioned. When supplying the polishing composition to the polishing machine, in addition to the method of supplying one component containing all the components, considering the stability of the polishing composition, etc., it is divided into a plurality of compounding component liquids, Two or more liquids can be supplied. In the latter case, for example, the plurality of compounding component liquids are mixed in the supply pipe or on the substrate to be polished to obtain the polishing liquid composition of the present invention.

[Polished substrate]
Examples of the material of the substrate to be polished preferably used in the present invention include metals, metalloids such as silicon, aluminum, nickel, tungsten, copper, tantalum, and titanium, or alloys thereof, glass, glassy carbon, and amorphous. Examples thereof include glassy substances such as carbon, ceramic materials such as alumina, silicon dioxide, silicon nitride, tantalum nitride, and titanium carbide, and resins such as polyimide resin. Among these, a substrate to be polished containing a metal such as aluminum, nickel, tungsten, copper, or an alloy containing these metals as a main component is preferable. It is particularly suitable for Ni-P plated aluminum alloy substrates and glass substrates such as crystallized glass and tempered glass, among which Ni-P plated aluminum alloy substrates are suitable.

  In addition, according to the present invention, it is possible to provide a magnetic disk substrate in which the maximum value (AFM-Rmax) of the scratch and the surface roughness of the polished substrate is highly reduced without impairing the productivity. Therefore, it can be suitably used for polishing a perpendicular magnetic recording type magnetic disk substrate that requires high performance.

  There is no restriction | limiting in particular in the shape of the said to-be-polished substrate, For example, what is necessary is just the shape which has planar parts, such as a disk shape, plate shape, slab shape, prism shape, and the shape which has curved surface parts, such as a lens. Of these, a disk-shaped substrate to be polished is suitable. In the case of a disk-shaped substrate to be polished, the outer diameter is, for example, about 2 to 95 mm, and the thickness is, for example, about 0.5 to 2 mm.

[Polishing method]
As another aspect, the present invention relates to a method for polishing a substrate to be polished, which comprises polishing the substrate to be polished while bringing the above-mentioned polishing composition into contact with a polishing pad. By using the polishing method of the present invention, the substrate to be polished can be polished without impairing the productivity, and both the surface roughness and the scratch are reduced, particularly the magnetic disk substrate of the perpendicular magnetic recording system. Is preferably provided. Examples of the substrate to be polished in the polishing method of the present invention include those used in the manufacture of a magnetic disk substrate and a magnetic recording medium substrate as described above. A substrate used for production is preferred. The specific polishing method and conditions can be as described above.

  According to the present invention, it is possible to provide a magnetic disk substrate having a reduced surface roughness without impairing productivity. In particular, the maximum height Rmax of the surface roughness obtained by observing the surface of the magnetic disk substrate with an atomic force microscope (AFM) is improved to, for example, less than 3 nm, preferably less than 2 nm, more preferably less than 1.5 nm. In particular, a perpendicular magnetic recording type magnetic disk substrate can be preferably provided.

  A polishing liquid composition was prepared using colloidal silica and the anionic water-soluble polymer shown in Table 1 below, the substrate to be polished was polished, and scratches and surface roughness of the polished substrate were evaluated. The evaluation results are shown in Table 2 below. A method for preparing the polishing liquid composition, a method for measuring each parameter, a polishing condition (polishing method), and an evaluation method are as follows.

[Method for preparing polishing liquid composition]
Colloidal silica (A to G, K to Q, T: JGC Catalysts & Chemicals, HJ, S: DuPont Air Products Nanomaterials, R: Nissan Chemical Industries) and Table 1 below An anionic water-soluble polymer, sulfuric acid (special grade manufactured by Wako Pure Chemical Industries, Ltd.), HEDP (1-hydroxyethylidene-1,1-diphosphonic acid, manufactured by Solusia Japan, dequest 2010), hydrogen peroxide Example 1 containing colloidal silica shown in Table 2 below and optionally an anionic water-soluble polymer by adding water (concentration: 35% by weight, manufactured by Asahi Denka) to ion-exchanged water and mixing them Polishing liquid compositions of -16 and Comparative Examples 1-14 were prepared. The contents of sulfuric acid, HEDP, and hydrogen peroxide in the polishing composition were 0.4 wt%, 0.1 wt%, and 0.4 wt%, respectively.

[Measuring method of average particle diameter, CV value, and ΔCV value of colloidal silica]
[Average particle size and CV value]
Colloidal silica shown above, sulfuric acid, HEDP, and hydrogen peroxide water were added to ion-exchanged water, and these were mixed to prepare a standard sample. The contents of colloidal silica, sulfuric acid, HEDP, and hydrogen peroxide in the standard sample were 5% by weight, 0.4% by weight, 0.1% by weight, and 0.4% by weight, respectively. The area of the scattering intensity distribution obtained by the Cumulant method at a detection angle of 90 ° when this standard sample is accumulated 200 times according to the instructions attached by the manufacturer using the dynamic light scattering device DLS-6500 manufactured by Otsuka Electronics Co., Ltd. The average particle size of colloidal silica was determined. Further, the CV value was obtained by dividing the standard deviation in the scattering intensity distribution measured according to the above measurement method by the average particle diameter and multiplying by 100 to obtain the CV value.
[ΔCV value]
A value obtained by subtracting the CV value (CV90) of the colloidal silica particles at a detection angle of 90 ° from the CV value (CV30) of the colloidal silica particles at a detection angle of 30 °, which was measured according to the above measurement method, was obtained as a ΔCV value.
(Measurement conditions for DLS-6500)
Detection angle: 90 °
Sampling time: 4 (μm)
Correlation Channel: 256 (ch)
Correlation Method: TI
Sampling temperature: 26.0 (° C.)
Detection angle: 30 °
Sampling time: 10 (μm)
Correlation Channel: 1024 (ch)
Correlation Method: TI
Sampling temperature: 26.0 (° C.)

[Method for measuring weight average molecular weight of polymer]
[Weight Average Molecular Weight of Polymer Having Carboxylic Acid Group]
The weight average molecular weight of the copolymer having a carboxylic acid group was measured under the following conditions by gel permeation chromatography (GPC).
(GPC conditions)
Column: G4000PWXL (manufactured by Tosoh Corporation) + G2500PWXL (manufactured by Tosoh Corporation)
Eluent: 0.2M phosphate buffer / acetonitrile = 9/1 (volume ratio)
Flow rate: 1.0 mL / min
Temperature: 40 ° C
Detection: 210nm
Sample: concentration 5 mg / mL (injection volume 100 μL)
Calibration curve polymer: polyacrylic acid Molecular weight (Mp): 115,000, 28,000, 4100, 1250 (manufactured by Sowa Kagaku Co., Ltd. and American Polymer Standards Corp.)

[Weight average molecular weight of styrene / isoprene sulfonic acid copolymer]
The weight average molecular weight of the styrene / isoprene sulfonic acid copolymer was measured by gel permeation chromatography (GPC) under the following conditions.
(GPC conditions)
Guard column: TSK guard column α (Tosoh)
Column: TSKgel α-M + TSKgel α-M (Tosoh)
Flow rate: 1.0 ml / min
Temperature: 40 ° C
Sample concentration: 3 mg / ml
Detector: RI
Conversion standard: Polystyrene

[Polishing]
Using the polishing liquid compositions of Examples 1 to 16 and Comparative Examples 1 to 14 prepared as described above, the following substrate to be polished was polished under the following polishing conditions. Next, the scratch and surface roughness of the polished substrate were measured and evaluated based on the following conditions. The results are shown in Table 2 below. The data shown in the following Table 2 is obtained by polishing four substrates for each example and each comparative example, and measuring both surfaces of each substrate to be polished. Averaged. In addition, it shows below also about the measuring method of the scratch shown in following Table 2, surface roughness, and polishing rate.

[Polished substrate]
As the substrate to be polished, a substrate obtained by rough polishing an aluminum alloy substrate plated with Ni-P in advance with a polishing composition containing an alumina abrasive was used. The substrate to be polished has a thickness of 1.27 mm, an outer diameter of 95 mm, an inner diameter of 25 mm, a center line average roughness Ra measured by AFM (Digital Instrument Nanoscope IIIa Multi Mode AFM), 1 nm, and a long wavelength. The amplitude of the undulation (wavelength 0.4 to 2 mm) was 2 nm, and the amplitude of the short wavelength undulation (wavelength 50 to 400 μm) was 2 nm.

[Polishing conditions]
Polishing tester: "Fast double-sided 9B polishing machine" manufactured by Speedfam
Polishing pad: Fujibo's suede type (thickness 0.9mm, average hole diameter 30μm)
Polishing liquid composition supply amount: 100 mL / min (supply rate per 1 cm ^{2 of} polishing substrate: 0.072 mL / min)
Lower platen rotation speed: 32.5 rpm
Polishing load: 7.9 kPa
Polishing time: 4 minutes

[Scratch measurement method]
Measuring instrument: OSA6100, manufactured by Candela Instruments
Evaluation: Four substrates were randomly selected from the substrates put into the polishing tester, and each substrate was irradiated with a laser at 10,000 rpm to measure scratches. The total number of scratches (both) on each of the four substrates was divided by 8 to calculate the number of scratches per substrate surface.

[Measurement method of surface roughness]
Using the AFM (Digital Instrument NanoScope IIIa Multi Mode AFM), the central part of the inner and outer peripheral edges of each substrate is measured one by one on the front and back sides under the following conditions, and the center line average roughness AFM-Ra and the maximum Regarding the height AFM-Rmax, the average values of four sheets (a total of eight surfaces) were set to AFM-Ra and AFM-Rmax shown in Table 2, respectively.
(AFM measurement conditions)
Mode: Tapping mode
Area: 1 × 1μm
Scan rate: 1.0 Hz
Cantilever: NCH-10V
Line: 512 × 512

[Measurement method of polishing rate]
The weight of each substrate before and after polishing was measured using a weigh scale ("BP-210S" manufactured by Sartorius) to determine the weight change of each substrate, and the average value of 10 substrates was used as the weight reduction amount, which was used as the polishing time. The value obtained by dividing by was used as the weight reduction rate. This weight reduction rate was introduced into the following formula and converted into a polishing rate (μm / min).
Polishing rate (μm / min) = weight reduction rate (g / min) / substrate single-sided area (mm ² ) / Ni-P plating density (g / cm ³ ) × 10 ⁶
(Substrate single-sided area: 6597 mm ² , Ni—P plating density: calculated as 7.9 g / cm ³ )

  As shown in Table 2, when the polishing liquid compositions of Examples 1 to 16 were used, the scratches and surface roughness of the substrate after polishing (especially AFM) were achieved without reducing the polishing rate as compared with Comparative Examples 1 to 14. -Rmax) could be reduced.

  According to the present invention, for example, a magnetic disk substrate suitable for increasing the recording density can be provided.

Claims (7)

A polishing composition for a magnetic disk substrate containing colloidal silica and water,
The average particle diameter measured at a detection angle of 90 ° in the dynamic light scattering method of the colloidal silica is 1 to 40 nm,
The coefficient of variation (CV90) obtained by dividing the standard deviation measured at a detection angle of 90 ° by the average particle diameter and multiplying by 100 in the dynamic light scattering method of the colloidal silica is 1 to 35%,
The difference (ΔCV = CV) between the CV value (CV30) obtained by dividing the standard deviation measured at a detection angle of 30 ° by the average particle size and multiplying by 100 in the dynamic light scattering method of the colloidal silica and the CV90.
30-CV90) is a polishing liquid composition for a magnetic disk substrate, which is 0 to 10%.   The polishing composition for a magnetic disk substrate according to claim 1, further comprising a water-soluble polymer having an anionic group. The polishing liquid composition for a magnetic disk substrate according to claim 2, wherein the water-soluble polymer having an anionic group is a polymer having a structural unit represented by the following general formula (1).

(In the formula, R is a hydrogen atom, a methyl group or an ethyl group, and X is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom (1/2 atom), ammonium or organic ammonium.) The polishing composition for a magnetic disk substrate according to claim 2, wherein the water-soluble polymer having an anionic group is a polymer having a structural unit represented by the following general formula (2).

(In the formula, M is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom (1/2 atom), ammonium or organic ammonium, and n is 1 or 2.)   The polishing composition for a magnetic disk substrate according to claim 2, wherein the water-soluble polymer having an anionic group is a styrene / isoprene sulfonic acid copolymer.   The polishing composition for a magnetic disk substrate according to claim 1, further comprising an acid and an oxidizing agent.   A method for producing a magnetic disk substrate, comprising a step of polishing a substrate to be polished using the polishing composition for a magnetic disk substrate according to claim 1.