JP2010167553A - 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 surface roughness of the substrate after polishing without sacrificing productivity, and a method for manufacturing the magnetic disk substrate using the polishing liquid composition. <P>SOLUTION: The polishing liquid composition includes a colloidal silica, water, an acid, and an oxidizing agent; wherein the colloidal silica satisfies all of the following requirements (a) to (d): (a) a sphericity ratio is 0.75-1; (b) surface roughness (SA1/SA2) calculated from a specific surface area (SA1) according to a sodium titration method and a specific surface area (SA2) converted from an average particle diameter (S2) obtained by observation with a transmission type electron microscope is at least 1.3; (c) the average particle diameter (S2) is 1-40 nm; (d) a ΔCV value (ΔCV=CV30-CV90) is 0-10%, which is defined as a difference between a value (CV30) of CV (coefficient of variatin) measured at a detection angle of 30 degrees by a dynamic light scattering method and a CV value (CV90) measured at a detection angle of 90 degrees by the dynamic light scattering method. <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, polishing liquid compositions in which the particle size distribution of colloidal silica is controlled as polishing particles and polishing liquid compositions in which the shape of the polishing particles is defined have been proposed (see, for example, Patent Documents 1 to 4). ).

  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 containing true spherical abrasive particles having a specific particle size distribution. According to this polishing liquid composition, by using true spherical particles, It describes that surface roughness and surface waviness can be improved.

  Patent Documents 3 and 4 disclose polishing compositions containing gold flat sugar-like silica fine particles. According to this polishing composition, the productivity of a magnetic disk substrate can be obtained by using gold flat sugar-like fine particles. It describes that (polishing rate) can be improved.

JP 2004-204151 A JP 2008-93819 A JP 2008-137822 A JP 2008-169102 A

  However, in order to realize a further increase in capacity, it is necessary to further reduce the scratches and surface roughness of the substrate after polishing while maintaining productivity (without causing a decrease in the polishing rate).

  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 sufficiently satisfy the scratch and surface roughness required for the surface of a perpendicular magnetic recording substrate.

  With the polishing liquid composition of Patent Document 1, the surface roughness of the substrate can be reduced, but the scratch and surface roughness required for the surface of a perpendicular magnetic recording substrate cannot be sufficiently satisfied.

  With the polishing composition of Patent Document 2, the surface roughness of the substrate can be reduced, but the polishing rate is not sufficient and the productivity cannot be satisfied.

  With the polishing liquid compositions of Patent Documents 3 and 4, productivity can be improved, but surface roughness (especially, the maximum height of the surface roughness: Rmax) and scratch required for the substrate surface of the perpendicular magnetic recording system Cannot be reduced sufficiently.

  Accordingly, the present invention provides a polishing composition for a magnetic disk substrate capable of realizing low scratching and reduction of surface roughness of the substrate after polishing without impairing productivity, and a method for producing a magnetic disk substrate using the same. To do.

The present invention relates to a polishing composition for a magnetic disk substrate that contains colloidal silica, water, an acid, and an oxidizing agent, and the colloidal silica satisfies all the following requirements (a) to (d).
(A) The sphericity measured by observation with a transmission electron microscope is 0.75 to 1.
(B) Surface roughness calculated from specific surface area (SA1) measured by sodium titration method and specific surface area (SA2) converted from average particle diameter (S2) measured by transmission electron microscope observation (SA2) The value of (SA1 / SA2) is 1.3 or more.
(C) The average particle size (S2) is 1 to 40 nm.
(D) CV (100) obtained by dividing the standard deviation of the particle diameter measured at a detection angle of 30 degrees by the dynamic light scattering method by the average particle diameter measured at the detection angle of 30 degrees by the dynamic light scattering method. The coefficient of variation) (CV30) and the standard deviation of the particle diameter measured at a detection angle of 90 degrees by the dynamic light scattering method are divided by the average particle diameter measured at a detection angle of 90 degrees by the dynamic light scattering method. The ΔCV value (ΔCV = CV30−CV90), which is the difference from the CV value (CV90) multiplied by 100, is 0 to 10%.

  The present invention also relates to a method for producing a magnetic disk substrate including a step of polishing the substrate using the polishing composition for a magnetic disk substrate of the present invention.

  The polishing composition for a magnetic disk substrate of the present invention preferably has the effect of being able to produce a magnetic disk substrate with reduced scratches and surface roughness, particularly a perpendicular magnetic recording type magnetic disk substrate, without significantly degrading the polishing rate. Can play.

  In the polishing composition for a magnetic disk substrate containing colloidal silica, the present invention can maintain the polishing rate at a level that does not impair the productivity by using a specific colloidal silica. This is based on the knowledge that the recording capacity can be reduced and the demand for a larger recording capacity can be met.

  Specifically, in addition to the true sphericity, surface roughness, and average particle size, the present inventors have conventionally added a difference in CV values (ΔCV value) at two different detection angles. It was found that the scratch and surface roughness of the substrate after polishing were greatly reduced by paying attention and controlling the colloidal silica.

That is, in one aspect, the present invention includes a colloidal silica, water, an acid, and an oxidizing agent, and the colloidal silica satisfies all the following requirements (a) to (d): , Also referred to as a polishing composition of the present invention).
(A) The sphericity measured by transmission electron microscope observation is 0.75 to 1,
(B) Surface roughness (SA1) calculated from the specific surface area (SA1) measured by the sodium titration method and the specific surface area (SA2) converted from the average particle diameter (S2) measured by transmission electron microscope observation / SA2) is 1.3 or more,
(C) The average particle size (S2) is 1 to 40 nm, and
(D) CV (100) obtained by dividing the standard deviation of the particle diameter measured at a detection angle of 30 degrees by the dynamic light scattering method by the average particle diameter measured at the detection angle of 30 degrees by the dynamic light scattering method. The coefficient of variation) (CV30) and the standard deviation of the particle diameter measured at a detection angle of 90 degrees by the dynamic light scattering method are divided by the average particle diameter measured at a detection angle of 90 degrees by the dynamic light scattering method. The ΔCV value (ΔCV = CV30−CV90), which is the difference from the CV value (CV90) multiplied by 100, is 0 to 10%.

  According to the polishing liquid composition of the present invention, a magnetic disk substrate with reduced scratches and surface roughness, particularly a perpendicular magnetic recording type magnetic disk substrate, is obtained without impairing productivity (without causing a decrease in polishing rate). The effect that it can manufacture can be show | played.

  The inventor has 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 silica aggregates. Although the mechanism of reducing scratches is not clear, it is estimated that 50-200 nm silica aggregates produced by agglomeration of primary particles of colloidal silica are the causative substances of scratch generation, and scratches are reduced because there are few such aggregates. is doing.

  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 light 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 light scattering method as an index assumes that the uniform particle is dispersed throughout the system, and the particle shape, particle size, etc. This is a method for 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" (Mitsuhiro Shibayama, 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 Yasumori 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 degrees and the detection angle of 90 degrees is large, it can be said that the angle dependence 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 detection angle of the forward scattering is preferably 0 to 80 degrees, more preferably 0 to 60 degrees, further preferably 10 to 50 degrees, and still more preferably 20 to 40 degrees. From the same viewpoint, the side or backscattering detection angle is preferably 80 to 180 degrees, more preferably 85 to 175 degrees. In the present invention, 30 degrees and 90 degrees 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.

[Sphericity ratio]
In this specification, the sphericity ratio measured by observation with a transmission electron microscope of colloidal silica is the projected area (A1) of one silica particle obtained by a transmission electron microscope and the circle whose circumference is the circumference of the particle. The ratio to the area (A2), that is, the value of “A1 / A2”, preferably the value of “A1 / A2” for any 50 to 100 colloidal silicas in the polishing composition of the present invention. The average value of Specifically, the sphericity of colloidal silica can be measured by the method described in Examples. From the viewpoint of reducing scratches and surface roughness without impairing productivity, the sphericity of the colloidal silica used in the polishing composition of the present invention is 0.75 to 1, and 0.75 to 0.00. 95 is preferable, and 0.75 to 0.85 is more preferable.

[Surface roughness]
In this specification, the surface roughness of colloidal silica is the specific surface area (SA2) converted from the specific surface area (SA1) measured by the sodium titration method and the average particle diameter (S2) measured by transmission electron microscope observation. The value of “SA1 / SA2”, which is a ratio to the above, is specifically measured by the method described in the examples. Here, the specific surface area (SA1) measured by the sodium titration method is to determine the specific surface area of the silica from the consumption of the sodium hydroxide solution when the sodium hydroxide solution is titrated against the silica. It can be said that it reflects the surface area. Specifically, the specific surface area (SA1) increases as the surface of the silica is richer in undulations or ridges. On the other hand, the specific surface area (SA2) calculated from the average particle diameter (S2) measured by a transmission electron microscope is calculated assuming that silica is an ideal spherical particle. Specifically, the specific surface area (SA2) decreases as the average particle size (S2) increases. The specific surface area indicates the surface area per unit mass, and the value of the surface roughness (SA1 / SA2) is larger as the silica is spherical and has more ridge-like projections on the silica surface. As shown in the figure, the smaller and smoother the ridge-like protrusions on the silica surface, the smaller the value and the value approaches 1. The surface roughness of the colloidal silica used in the polishing composition of the present invention is 1.3 or more from the viewpoint of reducing scratches and surface roughness without impairing productivity, and 1.3 to 2.5. Is preferable, and 1.3 to 2.0 is more preferable.

[Average particle size]
In this specification, the average particle diameter of colloidal silica includes two kinds of average particle diameters, that is, an average particle diameter (S2) measured by transmission electron microscope observation and an average measured by a dynamic light scattering method. Particle size is used. These average particle diameters are measured by the method described in the examples.

  The average particle diameter (S2) measured by transmission electron microscope observation of the colloidal silica used in the present invention is 1 to 40 nm from the viewpoint of reducing scratches and surface roughness without impairing productivity. -37 nm is preferable, and 10-35 nm is more preferable. In addition, the average particle size of colloidal silica based on the scattering intensity distribution measured by the dynamic light scattering method is 1 from the viewpoint of reducing the maximum value of the scratch and the surface roughness (AFM-Rmax) without impairing the productivity. -40 nm is preferable, More preferably, it is 5-37 nm, More preferably, it is 10-35 nm.

[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 degrees (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 size measured based on the scattering intensity distribution in degrees (CV30) and a detection angle of 90 degrees (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 degrees by the dynamic light scattering method and multiplying by 100. ) (ΔCV = CV30−CV90), specifically, it can be measured by the method described in the examples. The ΔCV value of the colloidal silica used in the polishing liquid composition of the present invention is 0 to 10%, preferably 0.01 to 10%, from the viewpoint of reducing scratches and surface roughness without impairing productivity. More preferably, it is 0.01 to 7%, and still more preferably 0.1 to 5%.

  In the present specification, the CV value of colloidal silica is a value of a coefficient of variation obtained by dividing the standard deviation based on the scattering intensity distribution in the dynamic light scattering method by the average particle size and multiplying by 100. They are represented by CV90 and CV30, and specifically can be obtained by the method described in the examples. The CV90 of colloidal silica used in the polishing composition of the present invention is preferably 1 to 35%, more preferably 5 to 34%, from the viewpoint of reducing scratches and surface roughness without impairing productivity. ~ 33% is more preferred.

  The sphericity, surface roughness (SA1 / SA2), and average particle diameter of colloidal silica can be adjusted using a conventionally known method for producing colloidal silica. For example, the production methods described in JP 2008-137822 A and JP 2008-169102 A can be exemplified, but the present invention is not limited thereto.

Examples of the method for adjusting the ΔCV value of colloidal silica include the following methods A and B which prevent the formation of a 50 to 200 nm silica aggregate 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), for example, the ΔCV value can be reduced by removing silica aggregates of 50 to 200 nm by centrifugation or precision 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 silica agglomerates can be produced if the steps are changed slightly 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 alkali metal or quaternary ammonium), and a silica aggregate 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), in the known spherical colloidal silica production process, the ΔCV value can be adjusted to be small by performing process control so as not to be a condition for locally producing a silica aggregate.

  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]
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 composition of the present invention contains an acid. In this specification, the use of an acid includes the use of 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 contains an oxidizing agent. 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 include sodium chlorate, calcium hypochlorite, and metal salts include iron (III) chloride, iron (III) nitrate, iron (III) sulfate, 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.

[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 adsorbs to the polishing pad to reduce frictional vibration during polishing, prevents the silica agglomerates from dropping from the opening of the polishing pad, and reduces the scratch and surface roughness of the substrate after polishing. Presumed to be.

  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 a polymer having at least one structural unit or a salt 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, naphthalenesulfonic acid, and salts thereof. 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, from the viewpoint of reducing the maximum value (AFM-Rmax) of the scratch and the surface roughness of the substrate after polishing without impairing the productivity, the following general formula (1) A polymer having the structural unit represented is preferred.

［上記式中、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, 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 polymer having the structural unit represented by the general formula (1) include (meth) acrylic acid / sulfonic acid copolymer, (meth) acrylic acid / maleic acid copolymer, poly (Meth) acrylic acid and salts thereof are preferable, and (meth) acrylic acid / sulfonic acid copolymer, poly (meth) acrylic acid and salts thereof are more preferable. The anionic water-soluble polymer may be one of these 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 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 a salt thereof is 5 to 95 from the viewpoint of reducing scratches. It is preferable that it is 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 preferably 10 to 90 mol%, more preferably 20 from the viewpoint of reducing nanoscratches. It is -80 mol%, More preferably, it is 30-70 mol%.

  For example, the polymer may be a base polymer containing a diene structure or an aromatic structure by a known method, for example, edited by The Chemical Society of Japan, New Experimental Chemistry Course 14 (Synthesis and Reaction of Organic Compounds III, pages 1773, 1978) and the like.

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 more than 50 mol%, more preferably 70 mol% or more, still more preferably 90 mol% or more, still more preferably 97 mol% or more, and the structure represented by the general formula (2) It is even more preferable that the polymer is represented only by the repeating structure of the unit. 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. The weight average molecular weight refers to the weight average molecular weight in terms of polyacrylic acid in gel permeation chromatography (GPC). The GPC measurement conditions are shown below.
[GPC conditions]
Column: G4000PWXL (manufactured by Tosoh Corporation) + G2500PWXL (manufactured by Tosoh Corporation)
Eluent: 0.2M phosphate buffer / acetonitrile = 9/1 (volume ratio)
Flow rate: 1.0 mL / min
Temperature: 40 ° C
Detection: 210nm
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.)

  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.

[Other ingredients]
The polishing composition of the present invention can further contain other components 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 composition of the present invention can be obtained by, for example, mixing water, colloidal silica, acid, oxidizing agent, and optionally an anionic water-soluble polymer and other components by a known method. Can be prepared. 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.

[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.

[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 of the scratch and the surface roughness of the polished substrate is highly reduced without impairing the productivity, so that high surface smoothness is required. It can be suitably used for polishing a perpendicular magnetic recording type magnetic disk substrate.

  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 with reduced scratches and surface roughness without impairing productivity. In particular, according to the present invention, the maximum height Rmax of the surface roughness obtained by reducing the scratches and observing the surface of the magnetic disk substrate with an atomic force microscope (AFM) is preferably less than 2 nm, more preferably 1 In particular, a perpendicular magnetic recording type magnetic disk substrate can be preferably provided.

  A polishing 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 the polishing rate, the scratch of the substrate after polishing, and the surface roughness 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 (ID in Table 2 below: a1-a3, b, c1-2, d, e, f1-2, gl; manufactured by JGC Catalysts & Chemicals Co., Ltd.) and sulfuric acid (manufactured by Wako Pure Chemical Industries, Ltd.) 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP, manufactured by Solusia Japan), hydrogen peroxide solution (manufactured by Asahi Denka), and an anionic water-soluble polymer A- selectively shown in Table 1 below C and C were added to ion-exchanged water, and these were mixed to prepare polishing liquid compositions of Example 1-13 and Comparative Example 1-10 shown in Table 2 below. The contents of colloidal silica, anionic water-soluble polymer, sulfuric acid, HEDP and hydrogen peroxide in the polishing composition are 5% by weight, 0.05% by weight (when added) and 0.5% by weight, respectively. 0.1% by weight and 0.5% by weight. The colloidal silica a1-3 has the same SA1, SA2, surface roughness, and sphericity, but has a different ΔCV value. The same applies to colloidal silica c1-2 and f1-2.

[Measurement method of sphericity of colloidal silica]
A sample containing colloidal silica is observed according to the instructions attached by the manufacturer using a transmission electron microscope (TEM) trade name “JEM-2000FX” (80 kV, 1 to 50,000 times, manufactured by JEOL Ltd.) A TEM image was taken. This photograph is taken into a personal computer as image data by a scanner, and the projected area (A1) of one particle and the circumference of the particle are defined as the circumference using analysis software “WinROOF ver. 3.6” (distributor: Mitani Corporation). The area (A2) of the circle to be measured was measured, and the ratio (A1 / A2) between the projected area (A1) of the particles and the area (A2) obtained from the circumference of the particles was calculated as the true sphere ratio. In addition, the numerical value of following Table 2 calculates these average values, after calculating | requiring the sphericity rate of 100 silica particles.

[Measurement method of surface roughness of colloidal silica]
As shown below, specific surface area (SA2) converted from specific surface area (SA1) measured by sodium titration method and average particle diameter (S2) measured by transmission electron microscope observation was obtained, and the ratio ( SA1 / SA2) was calculated as the surface roughness.

[Method for obtaining specific surface area (SA1) of colloidal silica by sodium titration method]
1) A sample containing colloidal silica corresponding to 1.5 g as SiO ₂ is collected in a beaker and transferred to a constant temperature reaction tank (25 ° C.), and pure water is added to make the liquid volume 90 ml. The following operation is performed in a constant temperature reaction tank maintained at 25 ° C.
2) A 0.1 mol / L hydrochloric acid solution is added so that the pH is 3.6 to 3.7.
3) Add 30 g of sodium chloride, dilute to 150 ml with pure water and stir for 10 minutes.
4) A pH electrode is set, and 0.1 mol / L sodium hydroxide solution is added dropwise with stirring to adjust the pH to 4.0.
5) The sample adjusted to pH 4.0 was titrated with 0.1 mol / L sodium hydroxide solution, and the titer and pH value in the range of pH 8.7 to 9.3 were recorded at 4 points or more. A calibration curve is prepared, where X is the titer of 1 mol / L sodium hydroxide solution and Y is the pH value at that time.
6) The consumption V (ml) of the 0.1 mol / L sodium hydroxide solution required for pH 4.0 to 9.0 per 1.5 g of SiO ₂ was determined from the following formula (1), and the following [a] Specific surface area SA1 [m ² / g] is determined according to ~ [b].
[A] The value of SA1 is obtained by the following formula (2), and when the value is in the range of 80 to 350 m ² / g, the value is set to SA1.
[B] When the value of SA1 by the following formula (2) exceeds 350 m ² / g, SA1 is obtained again by the following formula (3), and the value is set to SA1.
V = (A × f × 100 × 1.5) / (W × C) (1)
SA1 = 29.0V−28 (2)
SA1 = 31.8V−28 (3)
However, the meanings of the symbols in the above formula (1) are as follows.
A: Titration amount of 0.1 mol / L sodium hydroxide solution required for pH 4.0 to 9.0 per 1.5 g of SiO ₂ (ml)
f: titer of 0.1 mol / L sodium hydroxide solution C: SiO ₂ concentration of sample (%)
W: Sample collection amount (g)

[Method for obtaining average particle diameter (S2) and specific surface area (SA2) by observation with a transmission electron microscope]
A sample containing colloidal silica is observed according to the instructions attached by the manufacturer using a transmission electron microscope (TEM) trade name “JEM-2000FX” (80 kV, 1 to 50,000 times, manufactured by JEOL Ltd.) Take a TEM image. This photograph is taken into a personal computer as image data by a scanner, and an equivalent circle diameter of each silica particle is obtained using analysis software “WinROOF ver. 3.6” (distributor: Mitani Corp.), which is used as the particle diameter. Thus, after calculating | requiring the particle diameter of 1000 or more silica particles, the average value is computed and it is set as the average particle diameter (S2) measured by transmission electron microscope observation. Next, the value of the average particle diameter (S2) obtained above is substituted into the following formula (4) to obtain the specific surface area (SA2).
SA2 = 6000 / (S2 × ρ) (4) (ρ: density of sample)
ρ: 2.2 (in the case of colloidal silica)

[Measuring Method of Average Particle Size, CV Value, and ΔCV Value Measured by Colloidal Silica Dynamic Light Scattering Method]
[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 degrees when this standard sample is integrated 200 times with the dynamic light scattering device DLS-6500 manufactured by Otsuka Electronics Co., Ltd. according to the instructions attached by the manufacturer. The average particle size of colloidal silica was determined. 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 (CV90).
[ΔCV value]
A value obtained by subtracting the CV value (CV90) of the colloidal silica particles at a detection angle of 90 degrees from the CV value (CV30) of the colloidal silica particles at a detection angle of 30 degrees, 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.)

[Polishing]
The following to-be-polished substrate was grind | polished on the grinding | polishing conditions shown below using the polishing liquid composition of Example 1-13 and Comparative Example 1-10 prepared as mentioned above. 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} substrate to be polished: 0.07
2mL / min)
Lower platen rotation speed: 32.5 rpm
Polishing load: 7.9 kPa
Polishing time: 8 minutes

[Scratch measurement method]
Measuring instrument: Kela Tencor, Candela OSA6100
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. The results are shown in Table 2 below as relative values with Comparative Example 1 taken as 100. In Comparative Examples 7 to 9, measurement was not possible because the number of scratches exceeded the upper limit of measurement.

[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 composition of Example 1-13 is used, the scratch and surface roughness of the substrate after polishing can be reduced without reducing the polishing rate as compared with Comparative Example 1-10. It was.

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

Claims (5)

A polishing composition for a magnetic disk substrate, comprising colloidal silica, water, an acid and an oxidizing agent, wherein the colloidal silica satisfies all the following requirements (a) to (d).
(A) The sphericity measured by transmission electron microscope observation is 0.75 to 1,
(B) Surface roughness calculated from specific surface area (SA1) measured by sodium titration method and specific surface area (SA2) converted from average particle diameter (S2) measured by transmission electron microscope observation (SA2) SA1 / SA2) is 1.3 or more,
(C) The average particle size (S2) is 1 to 40 nm, and
(D) CV (100) obtained by dividing the standard deviation of the particle diameter measured at a detection angle of 30 degrees by the dynamic light scattering method by the average particle diameter measured at the detection angle of 30 degrees by the dynamic light scattering method. The coefficient of variation) (CV30) and the standard deviation of the particle diameter measured at a detection angle of 90 degrees by the dynamic light scattering method are divided by the average particle diameter measured at a detection angle of 90 degrees by the dynamic light scattering method. The ΔCV value (ΔCV = CV30−CV90), which is the difference from the CV value (CV90) multiplied by 100, 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.)   A method for producing a magnetic disk substrate, comprising a step of polishing the substrate using the polishing composition for a magnetic disk substrate according to claim 1.   The method for manufacturing a magnetic disk substrate according to claim 4, wherein the substrate is a Ni—P plated aluminum alloy substrate.