JP2018081733A - Polishing liquid composition for magnetic disk substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polish liquid composition for a magnetic disk substrate capable of improving polishing speed in rough polishing and reducing long wavelength waviness after the polishing.SOLUTION: The present disclosure relates to a polish liquid composition for a magnetic disk substrate containing non-spherical silica particles A and water, having a pH of 0.5 or more and 6.0 or less, if a particle diameter at which cumulative frequency is 10%, 50%, or 90% in a particle size distribution in terms of a weight conversion obtained by a centrifugal sedimentation method is D10, D50, or D90 respectively, the non-spherical silica particle A has a span represented by a formula (D90-D10) of 180 nm or more and a D50 of 180 nm or more.SELECTED DRAWING: None

Description

  The present disclosure relates to a polishing composition for a magnetic disk substrate and a method for producing a silica slurry, a method for producing a magnetic disk substrate, and a method for polishing a substrate.

  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, it is necessary to reduce the unit recording area and improve the detection sensitivity of the weakened magnetic signal. For this reason, technical development for lowering the flying height of the magnetic head has been underway. For magnetic disk substrates, the smoothness and flatness are improved (reduction of surface roughness, waviness, and edge sagging) and surface defects are reduced (residual abrasive, Reduction of scratches, protrusions, pits, etc.) is strictly demanded.

  In response to such demands, from the viewpoint of achieving both improvement in surface quality and productivity that are smoother and less scratched, a multi-stage polishing method having two or more stages of polishing processes in the method of manufacturing a magnetic disk substrate Is often adopted. In general, in the final polishing step of the multi-stage polishing method, that is, the final polishing step, a polishing composition for finishing that contains colloidal silica particles in order to satisfy the requirements of reducing surface roughness and scratches such as scratches, protrusions, and pits. In a polishing step (also referred to as a rough polishing step) prior to the final polishing step, a polishing liquid composition containing alumina particles as abrasive grains is used from the viewpoint of improving productivity. However, when alumina particles are used as abrasive grains, the piercing of alumina particles into the substrate may cause defects in the magnetic disk substrate or a magnetic disk having a magnetic layer applied to the magnetic disk substrate.

  Then, the polishing liquid composition which does not contain alumina particles but contains silica particles as abrasive grains has been proposed (Patent Documents 1 to 3).

JP 2014-1116057 A JP 2012-111869 A JP 2014-29754 A

  In a conventional polishing composition in which silica particles are used in place of alumina particles, alumina residue due to alumina adhesion or sticking can be suppressed, and protrusion defects on the substrate surface after polishing can be reduced. However, when rough polishing is performed with a polishing composition comprising silica particles instead of alumina particles, long-wave waviness on the substrate surface after polishing becomes a problem. And in order to reduce the long wavelength wave | undulation in rough | crude grinding | polishing, a polishing time longer than the polishing liquid composition containing an alumina particle is required, and there exists a problem that productivity falls.

  Accordingly, the present disclosure provides a polishing liquid composition for a magnetic disk substrate that can improve the polishing rate in rough polishing and reduce long-wave waviness on the substrate surface after rough polishing even when silica particles are used as abrasive grains. .

  The present disclosure includes non-spherical silica particles A and water, has a pH of 0.5 or more and 6.0 or less, and has a cumulative frequency of 10%, 50% in a particle size distribution in terms of weight obtained by a centrifugal sedimentation method, The non-spherical silica particles A have a span represented by the formula (D90-D10) of 180 nm or more and D50 of 180 nm or more, where the particle diameters of 90% are D10, D50, and D90, respectively. The present invention relates to a polishing liquid composition for disk substrates.

  The present disclosure includes a step of blending at least the non-spherical silica particles A and water, and the particle sizes at which the cumulative frequency is 10%, 50%, and 90% in the particle size distribution in terms of weight obtained by the centrifugal sedimentation method, respectively. When the non-spherical silica particles A are D10, D50, and D90, the span represented by the formula (D90-D10) is 180 nm or more, and D50 is 180 nm or more. The present invention relates to a method for producing a silica slurry used for production.

  The present disclosure relates to a method for manufacturing a magnetic disk substrate, including a step of polishing a substrate to be polished using the polishing composition for a magnetic disk substrate according to the present disclosure.

  The present disclosure includes a step of polishing a substrate to be polished using the polishing composition for a magnetic disk substrate according to the present disclosure, wherein the substrate to be polished is a substrate used for manufacturing a magnetic disk substrate. Regarding the method.

  According to the present disclosure, even when silica particles are used as the abrasive grains, it is possible to improve the polishing rate in the rough polishing, and to reduce the long wavelength waviness on the substrate surface after the rough polishing. As a result, the productivity of the magnetic disk substrate with improved substrate quality can be improved.

FIG. 1 is an example of a transmission electron microscope (hereinafter also referred to as “TEM”) observation photograph of a confetti type colloidal silica abrasive grain. FIG. 2 is an example of a TEM observation photograph of deformed colloidal silica abrasive grains.

  The present disclosure provides the knowledge that the polishing rate can be improved and the long wavelength waviness can be reduced by using a polishing composition containing non-spherical silica particles having a large particle size and a broad particle size distribution for rough polishing. based on. In general, in the manufacture of a magnetic disk substrate, productivity can be improved if long-wave waviness can be reduced.

  Details of the mechanism by which the effects of the present disclosure are manifested are not clear, but are presumed as follows. By broadening the particle size distribution of the large non-spherical silica particles, the small-diameter particles enter between the large-diameter particle gaps, and the abrasive grains between the polishing pad being polished and the surface to be polished of the substrate It is considered that the filling rate of the is increased. For this reason, it is considered that the polishing rate can be maintained or improved by increasing the cutting area of the substrate by increasing the contact area of the abrasive grains with the surface to be polished and by making the polishing load applied to the substrate during polishing over a wide range uniform. Furthermore, it is considered that the magnitude of vibration that occurs between the polishing pad and the substrate during polishing can be reduced, and long-wave waviness can be reduced. Further, when spherical particles are further included in the polishing composition containing non-spherical silica particles having a large particle size and a broad particle size distribution, the polishing rate can be further improved and the long wavelength waviness can be further reduced. it is conceivable that. However, the present disclosure need not be interpreted as being limited to these mechanisms.

  That is, the present disclosure includes non-spherical silica particles A and water, has a pH of 0.5 or more and 6.0 or less, and has a cumulative frequency of 10% in a particle size distribution in terms of weight obtained by centrifugal sedimentation. %, 90% of the particle diameter is D10, D50, D90, respectively, the non-spherical silica particles A have a span represented by the formula (D90-D10) of 180 nm or more and D50 of 180 nm or more. And a polishing liquid composition for a magnetic disk substrate (hereinafter also referred to as “polishing liquid composition according to the present disclosure”).

  In the present disclosure, “undulation” of a substrate refers to irregularities on the surface of the substrate having a wavelength longer than the roughness. In the present disclosure, “long wavelength undulation” refers to undulation observed with a wavelength of 500 to 5000 μm. By reducing long-wave waviness on the substrate surface after polishing, the flying height of the magnetic head in the magnetic disk drive can be reduced, and the recording density of the magnetic disk can be improved. The long wavelength waviness of the substrate surface can be measured by the method described in the examples.

[Non-spherical silica particles A]
The polishing liquid composition according to the present disclosure contains non-spherical silica particles A (hereinafter also referred to as “particles A”). The particle A may be one type of non-spherical silica particle or a combination of two or more types of non-spherical silica particles.

The average particle diameter D50 in terms of weight by the centrifugal sedimentation method of the particles A (hereinafter also referred to as “average secondary particle diameter D2 _A ”) is 180 nm or more from the viewpoint of improving the polishing rate and reducing long wavelength waviness, From the viewpoint of improving the polishing rate, 200 nm or more is more preferable, and from the viewpoint of improving the polishing rate and reducing long wavelength waviness, 500 nm or less is preferable, 400 nm or less is more preferable, and 350 nm or less is more preferable. In the present disclosure, the average particle diameter D50 refers to a particle diameter having a cumulative frequency of 50% in a particle size distribution in terms of weight obtained by a centrifugal sedimentation method. Specifically, it can be calculated by the measurement method described in the examples.

The span of the particle A (hereinafter also referred to as “span S _A ”) is 180 nm or more from the viewpoint of improving the polishing rate and reducing the long wavelength waviness, and is preferably 240 nm or more from the viewpoint of improving the polishing rate, and is 360 nm or more. More preferably, from the viewpoint of improving the polishing rate and reducing long wavelength waviness, 700 nm or less is preferable, 600 nm or less is more preferable, and 500 nm or less is even more preferable. In the present disclosure, the span S _A is a value calculated by the equation (D90−D10). Here, D10 and D90 are particle diameters with cumulative frequencies of 10% and 90%, respectively, in the particle size distribution in terms of weight obtained by centrifugal sedimentation.

  The D90 of the particle A is preferably 350 nm or more, more preferably 500 nm or more, further preferably 550 nm or more from the viewpoint of improving the polishing rate, and 1000 nm or less is preferable from the viewpoint of improving the polishing speed and reducing long wavelength waviness, and 800 nm. The following is more preferable, and 700 nm or less is still more preferable.

  The D90 / D50 of the particle A is preferably 1.55 or more, more preferably 1.60 or more, further preferably 1.70 or more, from the viewpoint of reducing long wavelength waviness, and 3.00 or less from the same viewpoint. Is preferably 2.80 or less, more preferably 2.50 or less.

  As one embodiment of the method for adjusting the particle size distribution of the particles A, for example, a method of adjusting the particle growth time, the particle temperature, the particle concentration, etc. in the particle growth process in the production stage can be mentioned. Other embodiments of the method for adjusting the particle size distribution of the particles A include, for example, a method of giving a desired particle size distribution by adding particles serving as new nuclei in the particle growth process in the production stage, and different particles. Examples thereof include a method of mixing two or more kinds of silica particles having a size distribution to give a desired particle size distribution.

BET specific surface area of the particles A, from the viewpoint of improving the polishing rate and a long wavelength waviness reduction is preferably 35m ² / g or less, more preferably 30 m ² / g, still more preferably 25 m ² / g or less, and, 10 m ² / G or more is preferable, 15 m ² / g or more is more preferable, and 20 m ² / g or more is still more preferable. In the present disclosure, the BET specific surface area can be calculated by a nitrogen adsorption method (hereinafter also referred to as “BET method”). Specifically, it can be calculated by the measurement method described in the examples.

The average sphericity of the particles A is preferably 0.60 or more, more preferably 0.70 or more, and preferably 0.85 or less, more preferably 0.80 or less, from the viewpoint of improving the polishing rate and reducing long wavelength waviness. Preferably, 0.75 or less is more preferable. In the present disclosure, the average sphericity of the particles A is an average value of the sphericity of at least 200 particles A. The sphericity of the particle A can be calculated from the following equation by obtaining the projected area S and the projected perimeter L of the particle A using, for example, TEM observation and image analysis software.
Sphericality = 4π × S / L ²

  The sphericity of the individual particles A is preferably 0.60 or more, more preferably 0.70 or more, and preferably 0.85 or less, more preferably 0.80 or less, like the average sphericity. 75 or less is more preferable.

  The average minor axis of the particles A is preferably 160 nm or more, more preferably 180 nm or more, further preferably 185 nm or more from the viewpoint of improving the polishing rate, and preferably 500 nm or less from the viewpoint of improving the polishing speed and reducing long wavelength waviness. 450 nm or less is more preferable, and 400 nm or less is still more preferable. In the present disclosure, the average minor axis of the particles A is an average value of the minor axes of at least 200 particles A. The minor axis of the particle A is the length of the short side of the rectangle when a minimum rectangle circumscribing the projected image of the particle A is drawn using, for example, TEM observation and image analysis software.

The average primary particle diameter D1 _A of the particles _A is preferably 100 nm or more, more preferably 120 nm or more, still more preferably 150 nm or more, from the viewpoint of improving the polishing rate and reducing the long wavelength waviness, and from the viewpoint of reducing the long wavelength waviness, 400 nm or less is preferable, 300 nm or less is more preferable, and 250 nm or less is still more preferable. In the present disclosure, the average primary particle diameter D1A of the particles _A is a number average value of particle diameters obtained as an equivalent circle diameter in an electron microscope (TEM) observation image. Specifically, it can be calculated by the measurement method described in the examples.

  Examples of the particles A include colloidal silica, fumed silica, and surface-modified silica. From the viewpoint of improving the polishing rate and reducing long wavelength waviness, the particle A is preferably colloidal silica, and more preferably colloidal silica having the following specific shape.

  From the viewpoint of improving the polishing rate and reducing long wavelength waviness, the shape of the particles A is, for example, silica particles having a particle diameter smaller than the secondary particle diameter of the particles A as precursor particles, and a plurality of precursor particles are aggregated or A fused shape is mentioned. From the same point of view, the particle A is preferably at least one silica particle selected from a confetti-type silica particle Aa, a deformed-type silica particle Ab, and a deformed and confetti-type silica particle Ac. Silica particles Ab are more preferable.

  In the present disclosure, confetti-type silica particles Aa (hereinafter, also referred to as “particles Aa”) refer to silica particles having unique hook-shaped protrusions on the surface of spherical particles (see FIG. 1). The particle Aa preferably has a shape in which the largest precursor particle a1 and one or more precursor particles a2 having a particle size of 1/5 or less of the precursor particle a1 are aggregated or fused. The particles Aa are preferably in a state in which a plurality of precursor particles a2 having a small particle size are partially embedded in one precursor particle a1 having a large particle size. The particles Aa can be obtained, for example, by the method described in JP 2008-137822 A. The particle diameter of the precursor particles can be obtained as an equivalent circle diameter measured in one precursor particle in an observation image by TEM or the like, that is, the diameter of a circle having the same area as the projected area of the precursor particles. The particle diameters of the precursor particles in the silica particles Ab and the silica particles Ac can be obtained in the same manner.

  In the present disclosure, irregular-shaped silica particles Ab (hereinafter also referred to as “particles Ab”) have a shape in which two or more precursor particles, preferably two or more and ten or less precursor particles are aggregated or fused. This refers to silica particles (see FIG. 2). The particle Ab preferably has a shape in which two or more precursor particles having a particle size of 1.5 times or less are aggregated or fused on the basis of the particle size of the smallest precursor particle. The particles Ab can be obtained, for example, by the method described in JP-A-2015-86102.

  In the present disclosure, irregular and confetti-type silica particles Ac (hereinafter also referred to as “particles Ac”) have the particle Ab as the precursor particle c1, the largest precursor particle c1, and the particle size of the precursor particle c1. It is a shape in which one or more precursor particles c2 which are 1/5 or less are aggregated or fused.

  The particle A can include, for example, one or more selected from particles Aa, Ab, and Ac. The total amount of the particles Aa, Ab, and Ac in the particles A is preferably 50% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more, from the viewpoint of improving the polishing rate and reducing the long wavelength waviness. 90% by mass or more is even more preferable, and substantially 100% by mass is even more preferable.

  The particles A may be produced by a flame melting method, a sol-gel method, and a pulverization method from the viewpoint of improving the polishing rate and reducing the long wavelength waviness. Silica particles produced by “water glass method”) are preferred. The usage form of the particles A is preferably a slurry.

  The content of the particles A in the polishing liquid composition is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and further preferably 1% by mass or more, from the viewpoint of improving the polishing rate and reducing long wavelength waviness. Preferably, 2% by mass or more is still more preferable, and from the viewpoint of economy, 30% by mass or less is preferable, 25% by mass or less is more preferable, 20% by mass or less is further preferable, and 15% by mass or less is even more preferable. .

[Spherical silica particles B]
The polishing composition according to the present disclosure preferably further contains spherical silica particles B (hereinafter also referred to as “particles B”) from the viewpoint of reducing long wavelength waviness. The particle B may be one type of spherical silica particle or a combination of two or more types of spherical silica particles.

The average particle diameter D50 in terms of weight by the centrifugal sedimentation method of the particles B (hereinafter, also referred to as “average secondary particle diameter D2 _B ”) is preferably 20 nm or more from the viewpoint of improving the polishing rate and reducing long wavelength waviness, and 50 nm. The above is more preferable, 90 nm or more is further preferable, and from the same viewpoint, 200 nm or less is preferable, 180 nm or less is more preferable, and 160 nm or less is still more preferable. The average particle diameter D50 (average secondary particle diameter D2 _B ) of the particle _B can be calculated by the same method as the average particle diameter D50 of the particle A.

  The average particle diameter D50 of the particles B is preferably smaller than the average particle diameter D50 of the particles A from the viewpoint of improving the polishing rate and reducing long wavelength waviness. The ratio B / A of the average particle diameter D50 of the particles B to the average particle diameter D50 of the particles A is preferably 0.12 or more, more preferably 0.20 or more, and further preferably 0.30 or more from the viewpoint of improving the polishing rate. Preferably, from the viewpoint of improving the polishing rate and reducing long wavelength waviness, 0.85 or less is preferable, 0.80 or less is more preferable, and 0.70 or less is even more preferable.

The span of the particle B (hereinafter also referred to as “span S _B ”) is preferably 10 nm or more, more preferably 30 nm or more, still more preferably 100 nm or more, from the viewpoint of improving the polishing rate and reducing long wavelength waviness, and the same From the viewpoint, 500 nm or less is preferable, 450 nm or less is more preferable, and 400 nm or less is even more preferable. In the present disclosure, span S _B can be measured in the same manner as span S _A.

Span S _B particles B, from the viewpoint of improving the polishing rate and a long wavelength waviness reduction, preferably less than the span S _A particle A. The difference in span between the particles A and the particles B is a value calculated by the formula (S _A −S _B ), and is preferably 250 nm or more, more preferably 260 nm or more, and more preferably 340 nm or more from the viewpoint of improving the polishing rate. Further, from the viewpoint of improving the polishing rate and reducing long wavelength waviness, it is preferably 700 nm or less, more preferably 600 nm or less, and still more preferably 550 nm or less.

  In the present disclosure, the average sphericity of the particles B is preferably 0.86 or more, more preferably 0.88 or more, and 1.00 from the same viewpoint from the viewpoint of improving the polishing rate and reducing the long wavelength waviness. Or less, preferably 0.95 or less. The average sphericity of the particle B can be calculated by the same method as the average sphericity of the particle A. The sphericity of each individual particle B is preferably 0.86 or more, more preferably 0.88 or more, and is 1.00 or less, preferably 0.95 or less, like the average particle size.

  The average minor axis of the particles B is preferably 30 nm or more, more preferably 45 nm or more, further preferably 85 nm or more, more preferably 200 nm or less, and more preferably 150 nm or less, from the viewpoint of improving the polishing rate and reducing long wavelength waviness. More preferably, it is 130 nm or less. The average minor axis of the particle B can be calculated by the same method as the average minor axis of the particle A.

  The average minor axis of the particles B is preferably smaller than the average minor axis of the particles A from the viewpoint of improving the polishing rate and reducing long wavelength waviness. The ratio of the average minor axis of particle A to the average minor axis of particle B (average minor axis of particle A) / (average minor axis of particle B) is preferably more than 1.0, more preferably 1.5 or more, and 2 0.0 or more is more preferable, 2.5 or more is more preferable, 3.0 or more is more preferable, 30.0 or less is preferable, 15.0 or less is more preferable, 10.0 or less is further preferable, and 7. 0 or less is more preferable, and 4.0 or less is more preferable.

The average primary particle diameter D1 _B of the particles _B is preferably 35 nm or more, more preferably 40 nm or more, still more preferably 50 nm or more, and more preferably 150 nm or less from the viewpoint of improving the polishing rate and reducing long wavelength waviness. Preferably, 120 nm or less is more preferable, and 100 nm or less is still more preferable. The average primary particle diameter D1 _B of the particles _B can be calculated by the same method as the average primary particle diameter D1 _{A of the} particles _A.

  Examples of the particles B include colloidal silica, fumed silica, and surface-modified silica. As the particle B, for example, commercially available colloidal silica may be applicable. From the viewpoint of improving the polishing rate and reducing long wavelength waviness, the particles B are preferably colloidal silica.

  The particles B may be produced by a flame melting method, a sol-gel method, and a pulverization method from the viewpoint of improving the polishing rate and reducing long wavelength waviness, but are preferably silica particles produced by a water glass method. The usage form of the particles B is preferably a slurry.

  When the polishing liquid composition according to the present disclosure contains the particles B, the content of the particles B in the polishing liquid composition is preferably 0.1% by mass or more from the viewpoint of improving the polishing rate and reducing long wavelength waviness, 0.5 mass% or more is more preferable, 1.0 mass% or more is still more preferable, and 20.0 mass% or less is preferable from a viewpoint of economical efficiency, 15.0 mass% or less is more preferable, 10.0 A mass% or less is more preferable.

  When the polishing liquid composition according to the present disclosure contains the particles A and the particles B, the ratio A / B of the content of the particles A to the content of the particles B in the polishing liquid composition is an improvement in polishing rate and long wavelength waviness. From the viewpoint of reduction, 10/90 or more is preferable, 20/80 or more is more preferable, 50/50 or more is more preferable, 70/30 or more is more preferable, and from the same viewpoint, 90/10 or less is preferable, 85/15 or less is more preferable. When the particle B is a combination of two or more kinds of spherical silica particles, the content of the particle B refers to the total content thereof. The same applies to the content of the particles A.

  When the polishing liquid composition according to the present disclosure contains silica particles other than the particles A and the particles B, the total content of the particles A and the particles B with respect to the entire silica particles in the polishing liquid composition increases the polishing rate and From the viewpoint of reducing long wavelength waviness, 98.0% by mass or more is preferable, 98.5% by mass or more is more preferable, 99.0% by mass or more is further preferable, 99.5% by mass or more is further more preferable, and 99. 8% by mass or more is even more preferable, and substantially 100% by mass is even more preferable.

[PH adjuster]
The polishing composition according to the present disclosure preferably contains a pH adjusting agent from the viewpoint of improving the polishing rate, reducing long wavelength waviness, and adjusting the pH. As a pH adjuster, 1 or more types chosen from an acid and a salt are preferable from the same viewpoint.

  Examples of the acid include inorganic acids such as nitric acid, sulfuric acid, sulfurous acid, persulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, polyphosphoric acid, and amidosulfuric acid; organic phosphoric acid and organic phosphonic acid Organic acids such as, and the like. Among these, at least one selected from phosphoric acid, sulfuric acid, and 1-hydroxyethylidene-1,1-diphosphonic acid is preferable, and at least one selected from sulfuric acid and phosphoric acid is preferable from the viewpoint of improving the polishing rate and reducing long-wave waviness. More preferred is sulfuric acid.

  As a salt, the salt of said acid and at least 1 sort (s) chosen from a metal, ammonia, and an alkylamine is mentioned, for example. Specific examples of the metal include metals belonging to Groups 1 to 11 of the periodic table. Among these, from the viewpoint of improving the polishing rate and reducing long wavelength waviness, a salt of the above acid with a metal belonging to Group 1 or ammonia is preferable.

  The content of the pH adjusting agent in the polishing liquid composition is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, from the viewpoint of reducing long wavelength waviness without significantly impairing the polishing rate. 0.05% by mass or more is more preferable, 0.1% by mass or more is further more preferable, and from the same viewpoint, 5.0% by mass or less is preferable, 4.0% by mass or less is more preferable, 3.0% The mass% or less is further preferable, and the 2.5 mass% or less is even more preferable.

[Oxidant]
The polishing liquid composition according to the present disclosure may contain an oxidizing agent from the viewpoint of improving the polishing rate and reducing long wavelength waviness. Examples of the oxidizing agent include peroxide, permanganic acid or a salt thereof, chromic acid or a salt thereof, peroxo acid or a salt thereof, oxygen acid or a salt thereof, nitric acid, sulfuric acid, and the like from the same viewpoint. . Among these, at least one selected from hydrogen peroxide, iron nitrate (III), peracetic acid, ammonium peroxodisulfate, iron sulfate (III) and ammonium iron sulfate (III) is preferable. Hydrogen peroxide is more preferred from the viewpoint of preventing metal ions from adhering to the surface and the viewpoint of availability. 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 mass or more, more preferably 0.05% by mass or more, still more preferably 0.1% by mass or more, from the viewpoint of improving the polishing rate. From the viewpoint of improving the polishing rate and reducing long wavelength waviness, 4.0% by mass or less is preferable, 2.0% by mass or less is more preferable, and 1.5% by mass or less is more preferable.

[water]
The polishing liquid composition according to the present disclosure contains water as a medium. Examples of water include distilled water, ion exchange water, pure water, and ultrapure water. The content of water in the polishing liquid composition can be the remainder of the particles A, the particles B, and the pH adjusting agent, the oxidizing agent, and other optional components described later, if necessary.

[Other optional ingredients]
The polishing liquid composition according to the present disclosure may contain other optional components as necessary. Examples of other optional components include a thickener, a dispersant, a rust inhibitor, a basic substance, a polishing rate improver, a surfactant, and a polymer compound. The other optional component is preferably contained in the polishing liquid composition within a range not impairing the effects of the present disclosure, and the content of the other optional component in the polishing liquid composition is 0% by mass or more. Preferably, more than 0% by mass is more preferable, 0.1% by mass or more is further preferable, 10% by mass or less is preferable, and 5% by mass or less is more preferable.

[Alumina abrasive]
In the polishing liquid composition according to the present disclosure, the content of alumina abrasive grains is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, from the viewpoint of reducing protrusion defects, and 0.02% by mass. The following is more preferable, and it is further preferable that the alumina abrasive grains are not substantially contained. In the present disclosure, “substantially free of alumina abrasive grains” means that no alumina particles are contained, no alumina particles functioning as abrasive grains, or an amount of alumina particles that affect the polishing result. May not be included. The content of alumina particles in the polishing liquid composition is preferably 2% by mass or less, more preferably 1% by mass or less, still more preferably 0.5% by mass or less, based on the total amount of abrasive grains in the polishing liquid composition. Even more preferably, it is substantially 0% by weight.

[PH]
The pH of the polishing composition according to the present disclosure is 0.5 or higher, preferably 0.7 or higher, more preferably 0.9 or higher, from the viewpoint of improving the polishing rate and reducing long wavelength waviness, and more preferably 1.0 or higher. The above is more preferable, 1.2 or more is still more preferable, 1.4 or more is still more preferable, and from the same viewpoint, it is 6.0 or less, 4.0 or less is preferable, and 3.0 or less is more Preferably, 2.5 or less is further preferable, and 2.0 or less is even more preferable. It is preferable to adjust pH using the above-mentioned pH adjuster. The above pH is the pH of the polishing composition at 25 ° C. and can be measured using a pH meter, and is preferably a value two minutes after the electrode of the pH meter is immersed in the polishing composition.

[Method for producing polishing composition]
The polishing composition according to the present disclosure is prepared by, for example, blending a silica slurry containing the particles A and, if desired, a pH adjusting agent, an oxidizing agent and other components by a known method, and adjusting the pH to 0.5 or more and 6 It can be manufactured by setting it to 0.0 or less. The silica slurry may further include particles B. For example, the polishing liquid composition according to the present disclosure can be a polishing liquid composition comprising at least particles A and water and having a pH of 0.5 or more and 6.0 or less. Therefore, this indication is related with the manufacturing method of the silica slurry used for manufacture of polishing liquid composition including the process of blending at least particles A and water. Further, the present disclosure includes a step of blending at least the particles A and water, and a step of adjusting the pH to 0.5 or more and 6.0 or less as necessary (hereinafter referred to as “a polishing liquid composition production method”). Also referred to as “a method for producing a polishing liquid composition according to the present disclosure”. Furthermore, in the present disclosure, “mixing” means mixing particles A and water, and if necessary, at least one selected from particles B, a pH adjuster, an oxidizing agent and other components simultaneously or in any order. including. The said mixing | blending can be performed using mixers, such as a homomixer, a homogenizer, an ultrasonic disperser, and a wet ball mill, for example. The compounding quantity of each component in the manufacturing method of the polishing liquid composition which concerns on this indication can be made the same as content of each component in the above-mentioned polishing liquid composition which concerns on this indication.

The manufacturing method of the polishing liquid composition according to the present disclosure preferably includes the following steps from the viewpoint of dispersibility of silica particles.
Step 1: Step of mixing water, a pH adjuster, and optionally an oxidizing agent to prepare a dispersion medium having a pH of 6.0 or less Step 2: Step of mixing the dispersion medium and silica slurry containing particles A In step 1, the pH of the resulting dispersion medium is preferably adjusted so that the pH of the polishing composition becomes a desired value.

  In the present disclosure, the “content of each component in the polishing liquid composition” refers to the content of each component at the time when the polishing liquid composition is used for polishing. Therefore, when the polishing liquid composition according to the present disclosure is prepared as a concentrate, the content of each component can be increased by the concentration.

[Polishing liquid kit]
The present disclosure relates to a polishing liquid kit for manufacturing a polishing liquid composition, which includes a container-containing slurry in which a silica slurry containing the particles A is stored in a container. The polishing liquid kit according to the present disclosure may further include a dispersion medium having a pH of 6.0 or less housed in a container different from the container-containing slurry. According to the present disclosure, even when silica particles are used as abrasive grains, a polishing composition capable of obtaining a polishing liquid composition capable of reducing long-wave waviness on the substrate surface after rough polishing without greatly impairing the polishing rate in rough polishing. A liquid kit can be provided.

  As a polishing liquid kit according to the present disclosure, for example, a solution (second liquid) containing silica slurry (first liquid) containing particles A and other components that can be blended in a polishing liquid composition used for polishing an object to be polished. Liquid) are stored in a state where they are not mixed with each other, and a polishing liquid kit (two-component polishing liquid composition) in which these are mixed at the time of use is mentioned. Examples of other components that can be blended in the polishing liquid composition include a pH adjuster and an oxidizing agent. The first liquid may further contain particles B. The first liquid and the second liquid may each contain an optional component as necessary. Examples of the optional component include a thickener, a dispersant, a rust inhibitor, a basic substance, a polishing rate improver, a surfactant, and a polymer compound.

[Polished substrate]
The substrate to be polished by the polishing composition according to the present disclosure is a substrate used for manufacturing a magnetic disk substrate. For example, a Ni-P plated aluminum alloy substrate, silicate glass, aluminosilicate glass is used. In addition, glass substrates such as crystallized glass and tempered glass can be mentioned, and an aluminum alloy substrate plated with Ni—P is preferable from the viewpoint of strength and ease of handling. In the present disclosure, the “Ni—P plated aluminum alloy substrate” refers to a surface of an aluminum alloy base material that has been subjected to electroless Ni—P plating after being ground. A magnetic disk can be manufactured by performing a step of forming a magnetic layer on the surface of the substrate by sputtering or the like after the step of polishing the surface of the substrate to be polished using the polishing composition according to the present disclosure. Examples of the shape of the substrate to be polished include a shape having a flat portion such as a disk shape, a plate shape, a slab shape, and a prism shape, and a shape having a curved surface portion such as a lens, and preferably a disk-shaped substrate to be polished. It is. In the case of a disk-shaped substrate to be polished, the outer diameter is, for example, 10 to 120 mm, and the thickness is, for example, 0.5 to 2 mm.

  In general, a magnetic disk is manufactured through a magnetic layer forming process in which a substrate to be polished that has undergone a grinding process is polished through a rough polishing process and a final polishing process. The polishing composition according to the present disclosure is preferably used for polishing in the rough polishing step.

[Method of manufacturing magnetic disk substrate]
The present disclosure includes a step of polishing a substrate to be polished using the polishing liquid composition according to the present disclosure (hereinafter, also referred to as “polishing step using the polishing liquid composition according to the present disclosure”). The present invention relates to a manufacturing method (hereinafter also referred to as “substrate manufacturing method according to the present disclosure”).

  In the polishing process using the polishing liquid composition according to the present disclosure, for example, the substrate to be polished is sandwiched by a surface plate with a polishing pad attached thereto, the polishing liquid composition according to the present disclosure is supplied to the polishing surface, and pressure is applied. The substrate to be polished is polished by moving the polishing pad and the substrate to be polished.

  The polishing load in the polishing step using the polishing liquid composition according to the present disclosure is preferably 30 kPa or less, more preferably 25 kPa or less, still more preferably 20 kPa or less, and further 3 kPa, from the viewpoints of improving the polishing rate and reducing long wavelength waviness. The above is preferable, 5 kPa or more is more preferable, and 7 kPa or more is still more preferable. In the present disclosure, “polishing load” refers to the pressure of the surface plate applied to the surface to be polished of the substrate to be polished during polishing. The polishing load can be adjusted by applying air pressure or weight to the surface plate or the substrate.

In the polishing step using the polishing liquid composition according to the present disclosure, the polishing amount per 1 cm ^{2 of the} substrate to be polished is preferably 0.20 mg or more, and preferably 0.30 mg or more from the viewpoint of improving the polishing rate and reducing long wavelength waviness. More preferably, 0.40 mg or more is more preferable, and from the same viewpoint, 2.50 mg or less is preferable, 2.00 mg or less is more preferable, and 1.60 mg or less is more preferable.

The supply rate of the polishing liquid composition per 1 cm ^{2 of the} substrate to be polished in the polishing step using the polishing liquid composition according to the present disclosure is preferably 2.5 mL / min or less from the viewpoint of economy, and is 2.0 mL / min. The following is more preferable, 1.5 mL / min or less is further preferable, and from the viewpoint of improving the polishing rate, 0.01 mL / min or more per 1 cm ^{2 of the} substrate to be polished is preferable, 0.03 mL / min or more is more preferable, 0.05 mL / min or more is more preferable.

  Examples of a method for supplying the polishing liquid composition according to the present disclosure to a polishing machine include a method of continuously supplying using a pump or the like. When supplying the polishing liquid composition to the polishing machine, in addition to the method of supplying it with one liquid containing all the components, considering the storage stability of the polishing liquid composition, etc., it is divided into a plurality of component liquids for blending. 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 according to the present disclosure.

  According to the substrate manufacturing method according to the present disclosure, long wavelength waviness on the substrate surface after rough polishing can be reduced without significantly impairing the polishing rate in rough polishing, so that a magnetic disk substrate with improved substrate quality can be efficiently manufactured. The effect that it is possible can be produced.

[Polishing method]
The present disclosure relates to a substrate polishing method (hereinafter, also referred to as a polishing method according to the present disclosure) including a polishing step using the polishing composition according to the present disclosure.

  By using the polishing method according to the present disclosure, it is possible to reduce long-wave waviness of the substrate surface after rough polishing without significantly impairing the polishing rate in rough polishing, and thus the productivity of a magnetic disk substrate with improved substrate quality. The effect that it can improve can be show | played. The specific polishing method and conditions can be the same as those of the substrate manufacturing method according to the present disclosure described above.

  Hereinafter, the present disclosure will be described in more detail by way of examples. However, these examples are illustrative, and the present disclosure is not limited to these examples.

1. Preparation of polishing liquid composition Examples using the abrasive grains (non-spherical silica particles A, spherical silica particles B), pH adjusters (sulfuric acid), oxidizing agents (hydrogen peroxide), and water shown in Tables 1 and 2 1 to 11 and Comparative Examples 1 to 5 were prepared (Table 3). The preparation was performed by mixing water, a pH adjuster, and an oxidizing agent in advance to prepare a dispersion medium, and mixing the dispersion medium and a slurry containing abrasive grains. The content of each component in the polishing liquid compositions of Examples 1 to 11 and Comparative Examples 1 to 5 is: abrasive grains: 6.5 mass%, sulfuric acid: 0.5 mass%, hydrogen peroxide: 0.5 mass %Met. The polishing liquid compositions of Examples 1 to 11 and Comparative Examples 1 to 5 do not contain alumina abrasive grains. Particles A and B are colloidal silica particles produced by a water glass method. The pH of the polishing composition of Examples 1 to 11 and Comparative Examples 1 to 5 was 1.4. The pH was measured using a pH meter (manufactured by Toa DKK Co., Ltd.), and the value after 2 minutes after the electrode was immersed in the polishing composition was adopted (hereinafter the same).

2. Measuring method of each parameter [Measuring method of average primary particle diameter, average minor diameter, and average sphericity of silica particles]
A photograph obtained by observing silica particles with a TEM (“JEM-2000FX” manufactured by JEOL Ltd., 80 kV, 1 to 50,000 times) is captured as image data with a scanner on a personal computer, and analyzed software (Mitani Corporation “WinROOF (Ver. 3) .6) ") and the projection image of 500 silica particles was analyzed as follows.
The number average of the particle diameters determined as the equivalent circle diameters of the individual silica particles was obtained as the average primary particle diameter. Furthermore, the short diameter of each silica particle was calculated | required and the average value (average short diameter) of the short diameter was obtained. Furthermore, from the area S and the perimeter length L of each silica particle, the sphericity of each silica particle was calculated by the following formula, and the average value of sphericity (average sphericity) was obtained.
Sphericality = 4π × S / L ²

[Measurement method of BET specific surface area of silica particles]
The BET specific surface area S was subjected to the following [pre-treatment], then weighed about 0.1 g of the measurement sample into the measurement cell to 4 digits after the decimal point (0.1 mg digit), and 110 ° C. immediately before the measurement of the specific surface area. After being dried for 30 minutes under the above atmosphere, measurement was performed by the BET method using a specific surface area measuring device (Micromeritic automatic specific surface area measuring device, Flowsorb III2305, manufactured by Shimadzu Corporation).
<Pretreatment>
Slurry particles were placed in a petri dish and dried in a hot air dryer at 150 ° C. for 1 hour. The dried sample was finely pulverized in an agate mortar to obtain a measurement sample.

[Measuring method of average secondary particle diameter of silica particles, D10 and D90]
Silica particles were diluted with ion-exchanged water to prepare a dispersion containing 0.04 to 0.4% by mass of silica particles as a sample, and the particle size distribution was measured by centrifugal sedimentation using the following measuring device. In the particle size distribution in terms of weight obtained by the centrifugal sedimentation method, the particle diameters with cumulative frequencies of 10%, 50%, and 90% were defined as D10, D50 (average secondary particle diameter), and D90, respectively.
<Measurement conditions>
Measuring device: “CPS DC24000 UHR” manufactured by CPS Instruments
Measurement range: 0.02 to 3 μm
Particle extinction coefficient: 0.1
Particle shape factor: 1.2 or 1.0
Rotation speed: 18,000rpm-22,000rpm

3. Polishing of Substrates Using the prepared polishing liquid compositions of Examples 1 to 11 and Comparative Examples 1 to 5, the substrate to be polished was polished under the following polishing conditions.

<Polishing conditions>
Polishing machine: Double-side polishing machine (9B-type double-side polishing machine, manufactured by Speed Fam Co.)
Substrate to be polished: Ni-P plated aluminum alloy substrate, thickness: 1.27 mm, diameter 95 mm, number of sheets: 10 polishing liquid: polishing composition polishing pad: suede type (foam layer: polyurethane elastomer), thickness: 1 0.0 mm, average pore diameter: 30 μm, compression ratio of surface layer: 2.5% (manufactured by Filwel)
Plate rotation speed: 40 rpm
Polishing load: 9.8 kPa (set value)
Polishing liquid supply amount: 60 mL / min
Polishing time: 5 minutes 00 seconds

4). Evaluation method [Evaluation of polishing rate]
The polishing rates of the polishing liquid compositions of Examples 1 to 11 and Comparative Examples 1 to 5 were evaluated as follows. First, the weight per substrate before and after polishing was measured (measured by Sartorius, “BP-210S”), and the amount of mass reduction was determined from the change in mass of each substrate. A value obtained by dividing the average mass reduction amount of all 10 sheets by the polishing time was defined as a polishing rate, and was calculated by the following formula.
Weight loss (g) = {mass before polishing (g) −mass after polishing (g)}
Polishing speed (mg / min) = mass reduction amount (mg) / polishing time (min)

[Evaluation of long wavelength swell]
Measurements were made on the following conditions for 10 surfaces after polishing, a total of 20 surfaces. The average value of the measured values on the 20 surfaces was calculated as the long wavelength waviness of the substrate. In this evaluation, the long wavelength waviness is preferably 3.0 mm or less, more preferably 2.7 mm or less, further preferably 2.4 mm or less, and further preferably 2.1 mm or less, from the viewpoint of improving the recording density of the magnetic disk.
<Measurement conditions>
Measuring equipment: “OptiFLAT III” manufactured by KLA Tencor
Radius Inside / Out: 14.87mm / 47.83mm
Center X / Y: 55.44mm / 53.38mm
Low Cutoff: 2.5mm
Inner Mask: 18.50mm
Outer Mask: 45.5mm
Long Period: 2.5mm
Wa Correction: 0.9
Rn Correction: 1.0
No Zernike Terms: 8

5. Results The results of each evaluation are shown in Table 3.

  As shown in Table 3, Examples 1 to 11 containing predetermined non-spherical silica particles ensure a high polishing rate as compared with Comparative Examples 1 to 5 not including predetermined non-spherical silica particles. Long wavelength waviness after polishing was reduced.

  According to the present disclosure, it is possible to reduce the long-wave waviness after polishing while ensuring the polishing rate, so that the productivity of manufacturing the magnetic disk substrate can be improved. The present disclosure can be suitably used for manufacturing a magnetic disk substrate.

Claims (10)

Comprising non-spherical silica particles A and water,
pH is 0.5 or more and 6.0 or less,
When the particle diameters with a cumulative frequency of 10%, 50%, and 90% in the particle size distribution in terms of weight obtained by the centrifugal sedimentation method are D10, D50, and D90, respectively, the non-spherical silica particles A are represented by the formula (D90 A polishing liquid composition for a magnetic disk substrate, wherein the span represented by -D10) is 180 nm or more and D50 is 180 nm or more.   2. The polishing composition for a magnetic disk substrate according to claim 1, wherein D90 / D50 of the non-spherical silica particles A is 1.55 or more and 3.00 or less. 3. The polishing composition for a magnetic disk substrate according to claim 1, wherein the non-spherical silica particles A have a BET specific surface area of 35 m ² / g or less. Further comprising spherical silica particles B;
The polishing composition for a magnetic disk substrate according to any one of claims 1 to 3, wherein the spherical silica particles B have an average sphericity of 0.85 or more and 1.00 or less.   The polishing composition for a magnetic disk substrate according to claim 4, wherein a span of the spherical silica particles B is smaller than a span of the non-spherical silica particles A.   6. The polishing composition for a magnetic disk substrate according to claim 4, wherein a ratio of the content of the non-spherical silica particles A to the content of the spherical silica particles B is 10/90 or more and 90/10 or less.   7. The polishing composition for a magnetic disk substrate according to claim 1, wherein the content of the alumina abrasive grains is 0.1% by mass or less. Having a step of blending at least non-spherical silica particles A and water,
When the particle diameters with a cumulative frequency of 10%, 50%, and 90% in the particle size distribution in terms of weight obtained by the centrifugal sedimentation method are D10, D50, and D90, respectively, the non-spherical silica particles A are represented by the formula (D90 A method for producing a silica slurry used for producing a polishing composition for a magnetic disk substrate, wherein the span represented by -D10) is 180 nm or more and D50 is 180 nm or more.   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.   A step of polishing a substrate to be polished using the polishing composition for a magnetic disk substrate according to any one of claims 1 to 7, wherein the substrate to be polished is a substrate used for production of a magnetic disk substrate. A method for polishing a substrate.