WO2019004161A1

WO2019004161A1 - Silica slurry for polishing-liquid composition

Info

Publication number: WO2019004161A1
Application number: PCT/JP2018/024104
Authority: WO
Inventors: 木村陽介
Original assignee: 花王株式会社
Priority date: 2017-06-26
Filing date: 2018-06-26
Publication date: 2019-01-03

Abstract

One embodiment of the present invention is a silica slurry for a polishing-liquid composition, said slurry comprising silica particles, a redispersion aid and water, the redispersion aid being an alkali thickening polymer emulsion, and the pH of said silica slurry being 8.0–12.0, inclusive, at 25°C. The average secondary particle size of the silica particles is preferably 150–580nm, inclusive. The silica slurry for a polishing-liquid composition preferably has a viscosity of no less than 20mPa·s at 25°C. When an acid or an oxidising agent is added to adjust the pH to 0.5–6.0, inclusive, the viscosity is preferably no more than 10mPa·s at 25°C.

Description

Silica slurry for polishing composition

The present invention relates to a silica slurry for a polishing composition, a polishing kit including the same, and a method for producing a polishing composition. The present invention also relates to a method of manufacturing a magnetic disk substrate and a method of polishing a substrate.

In recent years, the size and capacity of magnetic disk drives have been reduced, and higher recording density has been required. In order to increase the recording density, it is necessary to improve the detection sensitivity of the magnetic signal. Therefore, technology development has been advanced to further reduce the flying height of the magnetic head and to reduce the unit recording area. The magnetic disk substrate is improved in smoothness and flatness (reduction of surface roughness, waviness, edge drop) and surface defect reduction (residual abrasive grains, in order to correspond to the low floating of the magnetic head and securement of the recording area. The reduction of scratches, protrusions, pits, etc. is strictly required. From the viewpoint of achieving both surface quality improvement such as smoother and less flawed and productivity improvement in response to such a requirement, in the hard disk substrate manufacturing method, a multistage polishing method having two or more polishing steps is used. It is often adopted. Generally, in the final polishing step of the multistage polishing method, that is, in the finish polishing step, in order to meet the requirements of reduction of surface roughness and reduction of scratches such as scratches, protrusions and pits, polishing liquid composition for finishing containing colloidal silica particles In the polishing process (also referred to as a rough polishing process) prior to the final polishing process, a polishing composition containing alumina particles is used from the viewpoint of improving productivity. However, when alumina particles are used as abrasives, penetration of the alumina particles into the substrate can cause defects in the media drive.

Therefore, a method of manufacturing a magnetic disk substrate is proposed that enables reduction of particle sticking to the substrate by using a polishing liquid composition that does not contain alumina particles and contains silica particles as abrasive grains in the rough polishing step. (Patent Documents 1 and 2).

On the other hand, it is a polishing composition for polishing coated surfaces such as automobile coatings and architectural coatings, which comprises α-alumina having an average particle diameter of 0.3 to 3 μm as polishing particles and an alkali as a thickener A polishing liquid composition containing a thickening type acrylic polymer is disclosed (Patent Document 3).

Furthermore, it is a polishing liquid composition for CMP, which contains cerium oxide particles as polishing particles, and contains as a dispersing agent a polymer dispersing agent containing a polyacrylic acid ammonium salt as a copolymerization component. It is disclosed (patent document 4).

JP, 2014-29755, A JP, 2014-116057, A JP, 2010-163553, A JP 2003-059868 A

If the rough polishing process and the finish polishing process without using alumina particles are employed in the polishing process of the magnetic disk substrate, the remaining of the alumina due to adhesion of alumina, sticking and the like can be suppressed, and protrusion defects on the substrate surface after polishing can be reduced. However, it has been found that when the rough polishing process is performed using silica particles having a large particle size instead of alumina particles, the problem of poor redispersion of precipitated silica particles in the silica slurry newly occurs. Since the deterioration of the redispersibility leads to the decrease of the polishing rate and the deterioration of the substrate quality such as long cycle defects, it is desirable to improve the redispersion of the silica particles in the silica slurry after long-term storage.

Therefore, the invention provides a silica slurry for a polishing composition, which is excellent in redispersibility of silica particles after long-term storage. The present invention also provides a polishing composition capable of securing a high polishing rate and securing a favorable substrate quality even when using a silica slurry for a polishing composition after long-term storage.

One embodiment of the present invention comprises a silica particle, a redispersibility improver, and water, and the redispersibility improver is an alkali-thickening polymer emulsion, and the pH at 25 ° C. is 8.0 or more and 12.0 or less. It is a silica slurry for polishing composition.

Another aspect of the present invention is an acidic aqueous solution (second liquid) contained in a separate container from the silica slurry for polishing liquid composition of the present invention (first liquid) and the silica slurry for polishing liquid composition. And a pH of 0.5 or more and 6.0 or less at 25 ° C. when the first liquid and the second liquid are mixed.

Yet another aspect of the present invention is a polishing composition comprising the step of mixing the silica slurry for a polishing composition of the present invention with an acid to set the pH at 25 ° C. to 0.5 or more and 6.0 or less. Manufacturing method.

Yet another aspect of the present invention is a magnetic disk substrate comprising the step of polishing a substrate to be polished using the polishing composition for a magnetic disk substrate prepared using the silica slurry for a polishing composition of the present invention. It is a manufacturing method.

Yet another aspect of the present invention includes the step of polishing a substrate to be polished using a polishing composition prepared using the silica slurry for a polishing composition of the present invention, wherein the substrate to be polished is a magnetic disk It is a grinding method of a substrate which is a substrate used for manufacture of a substrate.

According to the present invention, it is possible to provide a silica slurry for a polishing composition, which is excellent in redispersibility of silica particles after long-term storage. Therefore, if the silica slurry for polishing composition of the present invention is used for preparation of the polishing composition, high polishing rate can be secured and good substrate quality even when using the silica slurry for polishing composition after long-term storage The effect is that collateral can be provided.

The silica slurry for a polishing composition according to the present invention (hereinafter sometimes referred to as "silica slurry" in some cases) contains silica particles as abrasive grains, and contains an alkali-thickening polymer emulsion as a redispersibility improver. Based on the finding that redispersibility of silica particles after long-term storage is excellent. In addition, since the silica slurry of the present invention is used to prepare the polishing composition of the present invention, high polishing speed can be ensured even if the polishing composition prepared using the silica slurry after long-term storage is used for rough polishing Based on the finding that good substrate quality can be secured.

In general, if the dispersibility of the silica particles in the polishing composition used for manufacturing the magnetic disk substrate is good, not only long-period defects but also other substrate qualities such as long-wavelength waviness are improved. In the present invention, the high polishing rate is secured, and the adverse effect on the substrate quality due to the use of the silica slurry after long-term storage is suppressed, and improvement in productivity of the magnetic disk substrate can be expected.

In the present invention, the redispersibility of the silica particles is excellent, and as a result, the details of the mechanism capable of securing a high polishing rate and securing a good substrate quality are not clear, but are presumed as follows.

In the silica slurry, silica particles having a relatively large particle size precipitate during storage due to their own weight to form a hard caking layer. When the silica slurry is stirred and mixed with other components such as acid for preparation of the polishing composition, primary particles of the silica particles are strongly aggregated with respect to the uneven surface of the substrate to be polished. As the physical force of the silica particles becomes hard to act, the polishing rate is reduced, and the particle diameter of the silica particles is increased, so that deterioration such as waviness or deterioration of long period defect removal occurs.

On the other hand, in the present invention, it hydrates (is water-soluble) under alkaline conditions and thickens by forming a three-dimensional network structure, thereby suppressing aggregation of silica particles by the three-dimensional network structure, which is acidic Below, an alkali-thickening polymer emulsion having pH-dependent viscosity switching properties is contained in the silica slurry, and the pH of the silica slurry at 25 ° C. is 8: .0 or more and 12.0 or less. Therefore, the redispersibility of the silica particles in the silica slurry is good even after long-term storage. And when adding an acid etc. to the silica slurry of this invention and preparing an acidic polishing liquid composition, even when using the silica slurry after long-term storage, the redispersion property of the silica particle in a silica slurry is favorable. Thus, in the polishing composition, it is possible to secure a high polishing rate and secure a good substrate quality. Since the alkali-thickened polymer emulsion has the above-mentioned viscosity switching property, the adverse effect of the thickening due to the inclusion of the alkali-thickened polymer emulsion on the polishing rate in an acidic polishing composition is small. Also in the polishing liquid kit of the present invention, since the silica slurry of the present invention is contained as one solution, it is possible to ensure both a high polishing rate and a good substrate quality. However, the present invention is not interpreted as being limited to these mechanisms.

In the present invention, the degree of "securement of high polishing rate" can be evaluated by the polishing rate when using a polishing composition prepared using a silica slurry immediately after production, and the rate reduction rate. The rate of decrease in speed can be calculated, for example, by the method described in the examples below.

That is, the silica slurry of the present invention comprises a silica particle (component a), a redispersibility improver (component b), and water, and the redispersibility improver (component b) is an alkali-thickened polymer emulsion , A silica slurry having a pH of 8.0 or more and 12.0 or less at 25.degree.

In the present application, “waviness” of a substrate refers to unevenness on the surface of the substrate whose wavelength is longer than the roughness. In the present application, "long wavelength waviness" refers to a waviness observed with a wavelength of 500 to 5000 μm. By reducing the long wavelength waviness of the substrate surface after polishing, the flying height of the magnetic head can be reduced in the magnetic disk drive, and the recording density of the magnetic disk can be improved.

In the present application, “PED (polish enhanced defect)” refers to a shallow concave defect that appears on the substrate surface after polishing. This PED occurs, for example, in the manufacturing process of a Ni-P plated aluminum alloy substrate. In the annealing step in the step of forming a film by plating on an aluminum alloy substrate, it refers to a portion of insufficient annealing due to water or foreign matter attached to the substrate surface, and occurs as a shallow dent on the substrate surface during polishing. The term "grind scratch" refers to the shavings of the grindstone generated in the process of grinding the aluminum alloy substrate prior to plating. PEDs and grind flaws are also collectively referred to as "long-period defects". The incidence rate of long period defects is an index for evaluating the removal rate of long period defects and can be measured using the measuring device described in the examples.

[Silica particles]
The silica slurry of the present invention contains silica particles (component a) as abrasive grains. The silica particles preferably contain non-spherical silica particles A (hereinafter also referred to as “particles A”) from the viewpoint of securing a high polishing rate, and from the viewpoint of achieving both long cycle defect reduction and securing a high polishing rate. , And preferably includes both particles A and spherical silica particles B (hereinafter also referred to as "particles B"). Examples of the silica particles include colloidal silica, fumed silica, precipitated silica, surface-modified silica and the like.

From the viewpoint of securing a high polishing rate, as the particle A, colloidal silica or precipitated silica is preferable. When the silica particles consist only of particles A, the particles A are preferably colloidal silica from the viewpoint of reduction of long period defects, and when the silica particles contain both particles A and particles B, the particles A ensure high polishing rate Precipitated silica is preferred from the viewpoint of The particles A may be one type of non-spherical silica particles, or may be a combination of two or more types of non-spherical silica particles. As the particle B, colloidal silica is preferable from the viewpoints of securing a high polishing rate and reducing long-period defects, and from the viewpoint of reducing projection defects. The particles B may be one type of spherical silica particles, or may be a combination of two or more types of spherical silica particles.

Examples of the method for producing the particle A include known methods such as the method described in Tosoh Research and Technology Report, Volume 45 (2001), pages 65 to 69. As a specific example of the method for producing the particles A, there is mentioned a precipitation method in which silica particles are precipitated by the neutralization reaction of a silicate such as sodium silicate and a mineral acid such as sulfuric acid. It is preferable to carry out the neutralization reaction at relatively high temperature under alkaline conditions, whereby the growth of primary particles of silica proceeds rapidly, and the primary particles are flocculated and precipitated to obtain the precipitated silica. Be Colloidal silica is preferably obtained from a hydrolyzate of water glass or alkoxysilane, and more preferably obtained from water glass. Silica particles obtained from water glass can be produced by a conventionally known method.

The particles B may be produced by a flame melting method, a sol gel method, and a grinding method, but in view of securing a high polishing rate and reducing long period defects, and reducing protrusion defects after rough and finish polishing. From the viewpoint, it is preferable to use a silica particle produced by a particle growth method (hereinafter also referred to as “water glass method”) using an aqueous solution of alkali silicate as a starting material. The use form of the particles B is preferably in the form of a slurry.

The content of the silica particles (component a) in the silica slurry of the present invention is preferably 10% by mass or more, more preferably 20% by mass or more, and 30% by mass or more from the viewpoint of improving redispersibility of the silica particles. From the viewpoint of production suitability, 70% by mass or less is preferable, 60% by mass or less is more preferable, and 50% by mass or less is still more preferable.

The BET specific surface area of the silica particles (component a) is preferably 5 m ² / g or more, more preferably 10 m ² / g or more, from the viewpoint of achieving both high polishing rate and reduction of long period defects, and the same From the viewpoint, 50 m ² / g or less is preferable, and 45 m ² / g or less is more preferable. The BET specific surface area of the silica particles (component a) in the case where the silica particles (component a) contain both particles A and particles B can be calculated from the BET specific surface area and the compounding ratio (mass ratio) of both particles.

The average primary particle diameter D1 of the silica particles (component a) in terms of BET conversion is preferably 50 nm or more, more preferably 70 nm or more, still more preferably 90 nm or more, from the viewpoint of securing high polishing rate and reduction of long period defects. Or 300 nm or less is preferable, 250 nm or less is more preferable, and 200 nm or less is more preferable, from the viewpoint of reduction of long period defects. In addition, D1 of a silica particle (component a) in case a silica particle (component a) contains both particle | grains A and particle | grains B can be calculated from D1 of both particle | grains, and a compounding ratio (mass ratio).

The average secondary particle diameter D2 of the silica particles (component a) is preferably 150 nm or more from the viewpoint of securing a high polishing rate and reduction of long period defects, and 580 nm or less from the viewpoint of reduction of long period defects , 500 nm or less is more preferable, 400 nm or less is more preferable, and 350 nm or less is still more preferable. In addition, D2 of a silica particle (component a) in case a silica particle (component a) contains both particle | grains A and particle | grains B can be calculated from D2 of both particle | grains, and a compounding ratio (mass ratio).

(Non-spherical silica particles)
The silica slurry of the present invention preferably contains non-spherical silica particles A from the viewpoint of securing a high polishing rate. The particles A may be one type of non-spherical silica particles, or may be a combination of two or more types of non-spherical silica particles.

The average sphericity of the particles A is preferably 0.60 or more, more preferably 0.70 or more, from the viewpoint of reduction of long period defects, and from the same viewpoint, 0.85 or less is preferable, 0.80 or less Is more preferable, and 0.75 or less is more preferable.

As used herein, the average sphericity of particle A is the 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 determining the projection area S and the projection perimeter L of the particle A using, for example, TEM observation and image analysis software.
Sphericity = 4π × S / L ²
Similar to the average sphericity, the sphericity of each particle A is preferably 0.60 or more, more preferably 0.70 or more, and from the same viewpoint, preferably 0.85 or less, 0.80 or less More preferably, 0.75 or less is more preferable.

The average minor diameter of the particles A is preferably 100 nm or more, more preferably 150 nm or more, still more preferably 180 nm or more, and 500 nm or less from the same viewpoint, from the viewpoint of securing high polishing speed and reduction of long period defects. Preferably, 450 nm or less is more preferable.

In the case where the silica particles (component a) consist only of the particles A and the particles A are colloidal silica, the average minor diameter of the particles A is preferably 100 nm or more from the viewpoint of securing high polishing rate and reduction of long period defects, 150 nm or more is more preferable, 180 nm or more is more preferable, and from the same viewpoint, 500 nm or less is preferable, 450 nm or less is more preferable, 400 nm or less is more preferable, and 300 nm or less is still more preferable.

When the silica particles (component a) contain both particles A and particles B and the particles A are precipitated silica, the average short diameter of the particles A is from the viewpoint of securing a high polishing rate and reducing long-period defects, 150 nm or more is preferable, 180 nm or more is more preferable, and from the same viewpoint, 500 nm or less is preferable, and 450 nm or less is more preferable.

In the present application, the average minor axis of the particles A is an average value of minor axes of at least 200 particles A contained in the silica slurry of the present invention. The minor axis of the particle A is the length of the short side of the rectangular when drawing the smallest rectangle circumscribing the projected image of the particle A using, for example, TEM observation and image analysis software. Similarly, the major axis of the particle A is the length of the major side of the rectangle.

The BET specific surface area of the particles A is preferably 5 m ² / g or more, more preferably 10 m ² / g or more, and 50 m from the same viewpoint, from the viewpoint of achieving both high polishing rate and reduction of long period defects. ² / g or less is preferable, 40 m ² / g or less is more preferable, and 30 m ² / g or less is more preferable.

When the silica particles (component a) consist only of particles A and the particles A are colloidal silica, the BET specific surface area of the particles A is 5 m ² / g or more from the viewpoint of securing a high polishing rate and reducing long period defects. Is preferable, 10 m ² / g or more is more preferable, 20 m ² / g or more is further preferable, and from the same viewpoint, 50 m ² / g or less is preferable, 40 m ² / g or less is more preferable, 30 m ² / g or less Is more preferred.

When the silica particles (component a) contain both particles A and particles B and the particles A are precipitated silica, the BET specific surface area of the particles A is from the viewpoint of securing a high polishing rate and reducing long-period defects, 5 m ² / g or more is preferable, 10 m ² / g or more is more preferable, and from the same viewpoint, 50 m ² / g or less is preferable, 40 m ² / g or less is more preferable, 30 m ² / g or less is more preferable, 20 m < ² > / g or less is still more preferable.

In the present application, the average primary particle diameter D1 of the particles A can be calculated from the following equation using the BET specific surface area S (m ² / g). Specifically, it can be calculated by the measurement method described in the examples.
Average primary particle size (nm) = 2727 / S

The average primary particle diameter D1 of the particles A in terms of BET is preferably 50 nm or more, more preferably 70 nm or more, still more preferably 90 nm or more, from the viewpoint of securing a high polishing rate and reducing long period defects, and long period defects From the viewpoint of reduction of the above, 300 nm or less is preferable, 250 nm or less is more preferable, and 200 nm or less is more preferable.

When the silica particles (component a) consist only of the particles A and the particles A are colloidal silica, D1 of the particles A is preferably 50 nm or more, 70 nm or more from the viewpoint of securing a high polishing rate and reduction of long period defects. Is more preferably 90 nm or more, and 300 nm or less is preferable, 250 nm or less is more preferable, 200 nm or less is more preferable, 150 nm or less is still more preferable, and 120 nm or less is more preferable from the viewpoint of reduction of long period defects. preferable.

When the silica particle (component a) contains both particle A and particle B and particle A is precipitated silica, D1 of particle A is 90 nm or more from the viewpoint of securing a high polishing rate and reducing long period defects. Is more preferably 120 nm or more, and 300 nm or less is preferable, 250 nm or less is more preferable, and 200 nm or less is more preferable from the viewpoint of reduction of long period defects.

The average secondary particle diameter D2 of particles A is preferably 150 nm or more from the viewpoint of securing a high polishing rate and reduction of long period defects, and from the viewpoint of reduction of long period defects, preferably 580 nm or less, 500 nm or less More preferably, 400 nm or less is more preferable, and 350 nm or less is even more preferable.

When the silica particles (component a) consist only of the particles A and the particles A are colloidal silica, D2 of the particles A is preferably 150 nm or more from the viewpoint of securing a high polishing rate and reduction of long period defects, From the viewpoint of reduction of long period defects, 400 nm or less is preferable, 350 nm or less is more preferable, 300 nm or less is more preferable, and 250 nm or less is still more preferable.

When the silica particle (component a) contains both particle A and particle B and particle A is precipitated silica, D2 of particle A is 150 nm or more from the viewpoint of securing a high polishing rate and reducing long-period defects. Is preferably 200 nm or more, more preferably 220 nm or more, still more preferably 250 nm or more, still more preferably 300 nm or more, and from the viewpoint of reduction of long period defects, preferably 580 nm or less, more preferably 500 nm or less And 400 nm or less is more preferable, and 350 nm or less is still more preferable.

In the present application, the average secondary particle diameter D2 of the particles A refers to a volume-based average particle diameter based on the scattering intensity distribution measured by the light scattering method. In the present application, “scattered intensity distribution” is determined by dynamic light scattering (DLS), quasi-elastic light scattering (QLS), or static light scattering (laser diffraction / scattering method). , Submicron particle size distribution of particle size conversion. The average secondary particle diameter D2 of the particles A in the present application can be obtained specifically by the method described in the examples.

The particle diameter ratio (D2 / D1) between the average secondary particle diameter D2 of the particles A and the average primary particle diameter D1 is preferably 1.4 or more, from the viewpoint of securing a high polishing rate and reducing long period defects. .7 or more is more preferable, 4.0 or less is preferable, 3.0 or less is more preferable, and 2.8 or less is more preferable.

In the present application, the particle size ratio (D2 / D1) can mean the degree of deformation of the particle A. In general, the average secondary particle diameter D2 measured by the light scattering method takes into consideration the length in the long direction and the short direction because the light scattering in the long direction is detected and processed when the particles are irregular shaped particles. The greater the degree of anomaly, the larger the value. The average primary particle diameter D1 converted from the specific surface area value measured by the BET method is expressed as spheres based on the volume of the particles to be obtained, and therefore becomes smaller than the average secondary particle diameter D2. From the viewpoint of securing a high polishing rate, it is preferable that the particle diameter ratio (D2 / D1) is also large in the above range.

The shape of the particles A is preferably a shape in which a plurality of primary particles are aggregated from the viewpoint of securing a high polishing rate and reducing long-period defects.

The content of particles A in the silica slurry of the present invention is preferably 10% by mass or more, more preferably 20% by mass or more, and further preferably 25% by mass or more from the viewpoint of securing a high polishing rate and reducing long cycle defects. From the viewpoint of economy, 70% by mass or less is preferable, 60% by mass or less is more preferable, 50% by mass or less is more preferable, and 35% by mass or less is even more preferable.

(Spherical silica particles B)
As described above, the polishing composition of the present invention is preferably spherical silica particles B (hereinafter also referred to as "particles B") as the component a from the viewpoint of reduction of long period defects and securing of high polishing rate. In particular, when particle A is precipitated silica, it preferably contains particle B from the viewpoint of securing a high polishing rate.

In the present application, the average sphericity of the particles B is preferably greater than 0.85 from the viewpoints of securing a high polishing rate and reduction of long period defects, and reduction of projection defects after rough polishing and finish polishing, 0.87 or more is more preferable, and from the same viewpoint, 1.00 or less is preferable, and 0.95 or less is more preferable. The sphericity of the individual particles B is preferably greater than 0.85, more preferably 0.87 or more, and preferably 1.00 or less, more preferably 0.95 or less. The average sphericity and sphericity of particle B can be calculated in the same manner as particle A.

The average sphericity of the particles B is preferably larger than the average sphericity of the particles A from the viewpoint of reduction of long-period defects. The difference between the average sphericity of the particles A and the particles B is preferably 0.02 or more, more preferably 0.05 or more, still more preferably 0.08 or more, and still more preferably 0.1 or more from the viewpoint of reducing waviness. From the same viewpoint, 0.50 or less is preferable, 0.40 or less is more preferable, and 0.30 or less is more preferable.

The average minor axis of particle B is smaller than the average minor axis of particle A. The average minor diameter of the particles B is preferably 20 nm or more, more preferably 30 nm or more, and still more preferably 40 nm or more, from the viewpoint of securing a high polishing rate, and preferably 200 nm or less from the viewpoint of reduction of long period defects, 150 nm or less is more preferable, and 110 nm or less is more preferable. The average minor axis of the particles B can be calculated by the same method as the particles A.

The ratio of the average minor axis of particles A and particles B in the polishing composition of the present invention (average minor axis of particles A) / (average minor axis of particles B) is the high polishing rate and long period defects. From the viewpoint of reduction, 1.3 or more is preferable, 1.5 or more is more preferable, 2.0 or more is further preferable, and 2.5 or more is further preferable, and from the viewpoint of securing a high polishing rate, 13.0 The following is preferable, 10.0 or less is more preferable, 8.0 or less is more preferable, 6.0 or less is still more preferable.

The BET specific surface area of the particles B is preferably 5 m ² / g or more, more preferably 10 m ² / g or more, still more preferably 20 m ² / g or more, from the viewpoint of securing a high polishing rate and reducing long-period defects. From the same viewpoint, 55 m ² / g or less is more preferable, 45 m ² / g or less is more preferable, and 35 m ² / g or less is still more preferable.

The average primary particle diameter D1 of the particles B in terms of BET is preferably 20 nm or more, more preferably 30 nm or more, still more preferably 40 nm or more, from the viewpoint of securing a high polishing rate and reducing long period defects. Therefore, 150 nm or less is preferable, 120 nm or less is more preferable, and 100 nm or less is more preferable. The average primary particle diameter of the particles B in BET conversion can be calculated by the same method as the particles A.

The average secondary particle diameter D2 of particle B by dynamic scattering method is preferably 20 nm or more, more preferably 30 nm or more, and still more preferably 40 nm or more, from the viewpoint of securing a high polishing rate and reducing long-period defects. From the same viewpoint, 200 nm or less is preferable, 150 nm or less is more preferable, and 120 nm or less is more preferable. The average secondary particle diameter of the particles B can be calculated by the same measurement method as the particles A.

The content of the particles B in the silica slurry of the present invention is preferably 5% by mass or more, more preferably 10% by mass or more, from the viewpoint of securing a high polishing rate and reducing long-period defects, and economical aspect Therefore, 35 mass% or less is preferable, 30 mass% or less is more preferable, and 25 mass% or less is still more preferable.

The mass ratio A / B of the particles A to the particles B in the silica slurry of the present invention is preferably 10/90 or more, more preferably 15/85 or more, from the viewpoint of securing a high polishing rate and reducing long period defects. 25/75 or more is more preferable, 40/60 or more is further more preferable, and from the same viewpoint, 99/1 or less is preferable, 90/10 or less is more preferable, and 75/25 or less is still more preferable. In the case where particle B is a combination of two or more types of spherical silica particles, the content of particle B refers to the total content thereof. The content of particles A is also the same.

When the silica slurry of the present invention contains silica particles other than the particle A and the particle B, the total content of the particle A and the particle B with respect to the whole silica particle in the silica slurry ensures high polishing rate and long period defects. From the viewpoint of reduction, 98.0% by mass or more is preferable, 98.5% by mass or more is more preferable, 99.0% by mass or more is more preferable, 99.5% by mass or more is still more preferable, 99.8% by mass The above is even more preferable, and substantially 100% by mass is even more preferable.

[Redispersibility improver]
The silica slurry of the present invention contains an alkali-thickening polymer emulsion as a redispersibility improver (component b). Under alkaline conditions, alkali-thickened polymer emulsions are hydrated (water-soluble) and adsorbed by silica particles to form a three-dimensional network structure and thickened, and under acidic conditions, they exist as spheres in water And pH-dependent viscosity switching properties. Here, "water-soluble" means having a solubility of 2 g / 100 mL or more in water (20 ° C.).

Since the silica slurry of the present invention contains the redispersibility improver (component b), an acid or the like is added to the silica slurry of the present invention, and the pH at 25 ° C. is, for example, 0.5 or more. When the viscosity is 0 or less, preferably 1.0 or more and 3.0 or less, the viscosity of the silica slurry at 25 ° C. is preferably 10 mPa · s or less, more preferably 7.0 mPa · s or less, still more preferably 5.0 mPas · S or less, and preferably 0.5 mPa · s or more, more preferably 1.0 mPa · s or more, still more preferably 1.5 mPa · s or more, still more preferably 2.0 mPa · s or more it can.

As an alkali-thickening type polymer emulsion, it is granular in water at pH 1.0 or more and 3.0 or less from the viewpoint of improvement of redispersibility of silica particles, and the acid group is neutralized at pH 8.0 or more and 12.0 or less Polymer which is solubilized and diffused in water is preferable, an alkali-thickened carboxylic acid polymer having an acid group of carboxyl group is more preferable, a carboxylic acid copolymer is more preferable, and the carboxylic acid copolymer is more preferable. The acid-based copolymer is a carboxylic acid-based copolymer containing two or more of the following first monomer units, and a carboxylic acid-based copolymer containing the following first monomer units and the following second monomer units At least one polymer selected from coalescing is preferable, and a carboxylic acid copolymer containing the following first monomer unit and the following second monomer unit is more preferable.

When the alkali-thickening polymer emulsion is the carboxylic acid copolymer, the alkali-thickening polymer emulsion contains only the first monomer unit and the second monomer unit as monomer units. Although it is preferable, it is preferable to further contain the following third monomer unit in addition to the first monomer unit and the second monomer unit. A cross-linking agent etc. are mentioned as a 3rd single unit, As a cross-linking agent, the diallyl phthalate with a high thickening effect is preferable.

The sum of the mole% of the first monomer unit and the mole% of the second monomer unit with respect to all the monomer units contained in the carboxylic acid polymer ensures a high polishing rate and reduces long-period defects. 90% by mass or more is preferable, 94% by mass or more is more preferable, 98% by mass or more is more preferable, and 100% by mass or less is preferable, and 99.9% by mass or less is more preferable from the same viewpoint. 8 mass% or less is further preferable, 99.5 mass% or less is further preferable, and 99.0 mass% or less is still more preferable.

Examples of the method for producing the alkali-thickening type polymer emulsion include methods such as emulsion polymerization, suspension polymerization and solution polymerization. The alkali-thickened polymer emulsion is in a state of being neutralized by alkali in water. Examples of the salt include ammonium salts; alkanolamine salts such as triethanolamine; and alkali metal salts such as sodium and potassium. These can be used alone or in combination of two or more.

The first monomer is preferably at least one selected from unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid and itaconic acid, and salts thereof, from the viewpoint of improving the redispersibility of silica particles. And more preferably at least one selected from acrylic acid, methacrylic acid and salts thereof. As the salt, ammonium salts or alkali metal salts such as sodium and potassium are preferable.

As the second monomer, monomers other than the aforementioned unsaturated carboxylic acids and salts thereof are preferable, and (meth) acrylics such as methyl (meth) acrylate, ethyl (meth) acrylate and butyl (meth) acrylate Among these, alkyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, acrylamide and the like can be mentioned, among them, methyl (meth) acrylate and ethyl (meth) acrylate from the viewpoint of improving redispersibility of silica particles. And at least one selected from

The molar ratio of the first monomer unit to the second monomer unit (mol% of the first monomer unit / mol% of the second monomer unit) in the carboxylic acid copolymer is silica particles From the viewpoint of improving the redispersibility of the polymer, it is preferably 10/90 or more, more preferably 20/80 or more, still more preferably 30/70 or more, still more preferably 35/65 or more, and from the same viewpoint Preferably it is 90/10 or less, More preferably, it is 80/20 or less, More preferably, it is 70/30 or less, More preferably, it is 60/40 or less, More preferably, it is 50/50 or less.

In the carboxylic acid polymer, from the viewpoint of improving redispersibility of silica particles, preferably, the first monomer is at least one selected from acrylic acid, methacrylic acid and salts thereof, The second monomer which forms a carboxylic acid polymer with one monomer is preferably at least one selected from alkyl acrylate and alkyl (meth) acrylate, and the third monomer is diallyl phthalate. Is preferable.

The number average molecular weight of the carboxylic acid copolymer is preferably 500,000 or more from the viewpoint of improving the redispersibility of the silica particles, and preferably 5,000,000 or less, more preferably 400 from the same viewpoint. It is at most 10,000, more preferably at most 3,000,000. The number average molecular weight can be measured, for example, as follows.

The said number average molecular weight can be measured by the gel permeation chromatography (GPC) method of the following conditions.
<GPC conditions>
Column: Guard column α, analytical column α-M 2 series Eluent: 60 mmol / L H3PO4, 50 mmol / L LiBr / DMF
Flow rate: 1.0 mL / min
Column temperature: 40 ° C
Detection: RI
Reference material: polystyrene

Specific examples of preferable commercially available products of alkali-thickened carboxylic acid copolymers include Aron series A-7075, A-7055, B-300K, B-500, manufactured by Toagosei Co., Ltd. Primal TT-615 and TT-935 (both of which are copoly methacrylic acid aqueous emulsions) manufactured by Haas Co., Ltd., and the like.

The mass ratio of the silica particles to the redispersibility improver in the silica slurry of the present invention is preferably 0.1 parts by mass or more with respect to 100 parts by mass of the silica particles from the viewpoint of improving the redispersibility of the silica particles. 2 parts by mass or more is more preferable, 0.3 parts by mass or more is further preferable, and from the same viewpoint, 5 parts by mass or less is preferable, 3 parts by mass or less is more preferable, and 1 part by mass or less is more preferable.

The content of the redispersibility improver in the silica slurry of the present invention is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, in terms of solid content, from the viewpoint of improving the redispersibility of the silica particles. The content is preferably 0.15% by mass or more, and from the viewpoint of economy, 1.0% by mass or less is preferable, 0.5% by mass or less is more preferable, and 0.3% by mass or less is more preferable.

[water]
The silica slurry of the present invention contains water as a medium. Examples of water include distilled water, ion-exchanged water, pure water and ultrapure water. The content of water in the silica slurry is preferably 45% by mass or more, more preferably 50% by mass or more, still more preferably 55% by mass or more, from the viewpoint of facilitating the handling of the silica slurry, and from the same viewpoint 85 mass% or less is preferable, 80 mass% or less is more preferable, and 75 mass% or less is still more preferable. 70 mass% or less is still more preferable, and 65 mass% or less is still more preferable.

[Other ingredients]
The silica slurry of the present invention may contain other components as needed. Other components include pH adjusters, thickeners, dispersants, rust inhibitors, basic substances, polishing rate improvers, surfactants, polymer compounds and the like. The other components are preferably contained in the silica slurry as long as the effects of the present invention are not impaired, and the content of the other components in the silica slurry is preferably 0% by mass or more, and more than 0% by mass Is more preferably 0.01% by mass or more, still more preferably 0.1% by mass or more, and 10% by mass or less is preferable, and 5% by mass or less is more preferable.

[PH adjuster]
The pH of the silica slurry of the present invention is alkaline from the viewpoint of improving the redispersibility of silica particles, and is 8.0 or more and 12.0 or less. A pH adjuster may be used when necessary in the preparation of the silica slurry of the present invention. The pH adjuster is, for example, an alkali compound, and examples thereof include ammonia, and inorganic alkali compounds such as potassium hydroxide and sodium hydroxide; and organic alkali compounds such as alkylamines and alkanolamines. Among them, at least one selected from ammonia, sodium hydroxide and alkylamine is preferable, and at least one selected from ammonia and sodium hydroxide is more preferable, from the viewpoint of improving the redispersibility of the silica particles.

[Alumina particles]
The content of the alumina particles is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and still more preferably 0.02% by mass or less from the viewpoint of reducing projection defects. Preferably, it is further preferable to be substantially free of alumina particles. In the present invention, "substantially free of alumina particles" means that the particles do not contain alumina particles, does not contain an amount of alumina particles that functions as an abrasive, or an amount of alumina particles that affects the polishing result. It may include not including. The content of the alumina particles in the silica slurry 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 particles in the silica slurry. It is even more preferable that it is mass%.

[PH]
The pH of the silica slurry of the present invention is 8.0 or more, preferably 8.2 or more, more preferably 8.5 or more, and still more preferably 9.0 or more, from the viewpoint of improving the redispersibility of the silica particles. And from the same viewpoint, it is 12.0 or less, preferably 11.0 or less, more preferably 10.8 or less, still more preferably 10.5 or less, and still more preferably 10.0 or less. The adjustment of pH is preferably performed using the above-mentioned pH adjuster. The above pH is the pH of the silica slurry at 25 ° C. and can be measured using a pH meter, and preferably the value after 30 seconds of immersing the electrode of the pH meter in the polishing composition.

The viscosity of the silica slurry of the present invention is preferably 20 mPa · s or more, more preferably 50 mPa · s or more, still more preferably 100 mPa · s or more, from the viewpoint of improving the redispersibility of the silica particles, and similar viewpoints Therefore, the viscosity is preferably 10,000 mPa · s or less, more preferably 5,000 mPa · s or less, still more preferably 1,000 mPa · s or less, and still more preferably 800 mPa · s or less. The viscosity is the value at 25 ° C. silica slurry.

[Method of producing polishing composition]
The polishing composition of the present invention comprises, for example, the silica slurry of the present invention, an acid, and, if desired, an oxidizing agent and other components according to a known method, and has a pH at 25.degree. It can manufacture by setting it as 6.0 or less, preferably 1.0 or more and 3.0 or less. Accordingly, the present invention relates to a method for producing a silica slurry used for producing a polishing composition, which comprises the steps of blending at least a silica particle, a redispersibility improver, and water. Furthermore, the present invention includes a step of blending at least a silica particle, a redispersibility improver and water, and the pH at 25 ° C. is 0.5 to 6.0, preferably 1.0 to 3 if necessary. The present invention relates to a method for producing a polishing composition, which comprises the step of adjusting to 0 or less.

In the present invention, "blending" means mixing silica particles, redispersion improver and water simultaneously or in any order, silica slurry, acid, if necessary, oxidizing agent and other components simultaneously or optional Mixing in the order of The mixing can be performed, for example, using a propeller stirrer, a homomixer, a homogenizer, a mixer such as an ultrasonic disperser, a wet ball mill, or the like. The preferred compounding amounts of the respective components in the method for producing a polishing composition are the same as the preferred contents of the respective components in the polishing composition.

An example of the method for producing the polishing composition of the present invention preferably includes the following steps from the viewpoint of the dispersibility of the silica particles.
Step 1: A process of mixing water, an acid and optionally an oxidizing agent and other components, and adjusting an acidic aqueous solution having a pH of 6.0 or less at 25 ° C. Step 2: The above acidic aqueous solution and the silica slurry of the present invention And mixing the pH of the resulting acidic aqueous solution in step 1 so that the pH of the polishing composition becomes a desired value, preferably 3.0 or less, and 0. Five or more are preferable.

An example of the method for producing a polishing composition of the present invention may include the step of adding water before or after mixing the acidic aqueous solution with the silica slurry of the present invention. When water is added prior to mixing the acidic aqueous solution with the silica slurry of the present invention, water may be added to the silica slurry of the present invention, for example. The water may be water contained in the silica slurry. In particular, when the content of silica particles in the silica slurry of the present invention is 10% by mass to 70% by mass, it is preferable that the method of producing a polishing composition of the present invention includes the step of adding the water. .

[Abrasive liquid composition]
The content of the silica particles in the polishing composition of the present invention is preferably 0.5% by mass or more, more preferably 2% by mass or more, from the viewpoint of securing a high polishing rate and reducing long-period defects. % Or more is more preferable, and from the viewpoint of economy, 10% by mass or less is preferable, 8% by mass or less is more preferable, and 6% by mass or less is still more preferable.

The content of the redispersibility improver in the polishing composition of the present invention is preferably 0.005% by mass or more, and 0.01% by mass or more, from the viewpoint of securing a high polishing rate and reducing long cycle defects. More preferably, it is 0.02 mass% or more, and from the viewpoint of economy, 1.0 mass% or less is preferable, 0.5 mass% or less is more preferable, and 0.1 mass% or less is still more preferable.

[PH]
The pH of the polishing composition of the present invention at 25 ° C. is preferably 0.5 or more, more preferably 0.7 or more, and still more preferably 0.9 or more from the viewpoint of securing a high polishing rate and reducing long cycle defects. Preferably, 1.0 or more is more preferable, 1.2 or more is still more preferable, 1.4 or more is even more preferable, and from the same viewpoint, 6.0 or less is preferable and 4.0 or less is more preferable 3.0 or less is more preferable, 2.5 or less is still more preferable, and 2.0 or less is even more preferable. The adjustment of pH is preferably performed using an acid described later, if necessary, an oxidizing agent. The above pH is the pH of the polishing composition at 25 ° C., and the measurement method is the same as the measurement method of the pH of the silica slurry.

[acid]
Examples of the acid include inorganic acids such as nitric acid, sulfuric acid, sulfurous acid, persulfuric acid, hydrochloric acid, perchloric acid, amidosulfuric acid, phosphoric acid, polyphosphoric acid and phosphonic acid; organic acids such as organic phosphoric acid and organic phosphonic acid; Can be mentioned. Among them, at least one selected from phosphoric acid, sulfuric acid and 1-hydroxyethylidene-1,1-diphosphonic acid is preferable from the viewpoint of securing a high polishing rate and reducing long-cycle defects, and is selected from sulfuric acid and phosphoric acid. At least one is more preferable, and phosphoric acid is more preferable.

The content of the acid in the polishing composition is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, from the viewpoint of securing a high polishing rate and reducing long-cycle defects. % Or more is more preferable, 0.1% by mass or more is still more preferable, and from the same viewpoint, 5.0% by mass or less is preferable, 4.0% by mass or less is more preferable, and 3.0% by mass or less More preferably, 2.5% by mass or less is even more preferable.

[Oxidant]
The polishing composition of the present invention may contain an oxidizing agent from the viewpoint of securing a high polishing rate and reducing long cycle defects. Examples of the oxidizing agent include, from the same viewpoint, peroxides, permanganic acid or salts thereof, chromic acid or salts thereof, peroxy acids or salts thereof, oxygen acids or salts thereof, and the like. Among these, at least one selected from hydrogen peroxide, iron (III) nitrate, peracetic acid, ammonium peroxodisulfate, iron (III) sulfate and ammonium iron (III) sulfate is preferable, from the viewpoint of securing a high polishing rate, Hydrogen peroxide is more preferable from the viewpoint that metal ions are not attached to the surface of the polishing substrate and from the viewpoint of availability. You may use these oxidizing agents individually or in mixture of 2 or more types.

The content of the oxidizing agent in the polishing composition is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and further preferably 0.1% by mass or more from the viewpoint of securing a high polishing rate. From the viewpoint of securing a high polishing rate and reducing long-period defects, the content is preferably 4.0% by mass or less, more preferably 2.0% by mass or less, and still more preferably 1.5% by mass or less.

[water]
The polishing composition of the present invention contains water as a medium. Examples of water include distilled water, ion-exchanged water, pure water and ultrapure water. From the viewpoint of facilitating the handling of the polishing composition, the content of water in the polishing composition is preferably 61% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more. % Or more is further more preferable, and from the same viewpoint, 99% by mass or less is preferable, 98% by mass or less is more preferable, and 97% by mass or less is more preferable.

[Other ingredients]
The polishing composition of the present invention may contain other components as required. Other components include thickeners, dispersants, rust inhibitors, basic substances, polishing rate improvers, surfactants, polymer compounds and the like. The other components are preferably contained in the polishing composition as long as the effects of the present invention are not impaired, and the content of the other components in the polishing composition is preferably 0% by mass or more. More than 0 mass% is more preferable, 0.1 mass% or more is further more preferable, and 10 mass% or less is preferable, and 5 mass% or less is more preferable.

In the present invention, the "content of each component in the polishing composition" refers to the content of each component at the time of using the polishing composition for polishing. Therefore, when the polishing composition of the present invention is prepared as a concentrate, the content of each component may be increased by the concentration.

[viscosity]
The viscosity of the polishing composition of the present invention is preferably 10 mPa · s or less, more preferably 7.0 mPa · s or less, and 5.0 mPa · s or less from the viewpoint of securing a high polishing rate and reducing long-period defects. From the same viewpoint, 0.5 mPa · s or more is preferable, 1.0 mPa · s or more is more preferable, 1.5 mPa · s or more is more preferable, and 2.0 mPa · s or more is still more preferable. The viscosity is the viscosity of the polishing composition at 25 ° C., and the measuring method is the same as the measuring method of the viscosity of the silica slurry.

[Abrasive fluid kit]
The polishing liquid kit of the present invention relates to a kit for producing a polishing liquid composition, which comprises a container-enclosed silica slurry in which a silica slurry containing the silica particles is housed in a container. The polishing liquid kit of the present invention may further include an acidic aqueous solution having a pH of 6.0 or less stored in a separate container from the container-containing silica slurry. According to the present invention, it is possible to provide a polishing solution kit capable of obtaining a polishing composition capable of securing a high polishing rate and reducing long cycle defects even when silica particles are used as the abrasive.

The polishing solution kit of the present invention includes, for example, a silica slurry (first solution) containing the above-mentioned silica particles, and an acidic aqueous solution (second solution) containing other components that can be blended in the polishing composition used for polishing a workpiece. And a polishing solution kit (two-component polishing solution composition) in which the solutions are stored in a state where they are not mixed with each other and these are mixed at the time of use. As a component which may be mix | blended with acidic aqueous solution, an acid, an oxidizing agent, etc. are mentioned, for example. The first liquid and the second liquid may contain optional components as required. Examples of the optional components include thickeners, dispersants, rust inhibitors, basic substances, polishing rate improvers, surfactants, polymer compounds and the like.

[Substrate to be polished]
The polishing composition of the present invention is a substrate to be used in the production of a substrate to be polished and a magnetic disk substrate, for example, an Ni-P plated aluminum alloy substrate, silica glass, aluminosilicate glass, crystals And glass substrates such as tempered glass and tempered glass, and from the viewpoint of cost and ease of handling, Ni-P plated aluminum alloy substrates are preferable. In the present invention, the "Ni-P plated aluminum alloy substrate" refers to one that has been subjected to electroless Ni-P plating treatment after grinding the surface of the aluminum alloy substrate. After the step of polishing the surface of the substrate to be polished using the polishing composition according to the present disclosure, a magnetic disk can be manufactured by performing the step of forming a magnetic layer on the surface of the substrate by sputtering or the like. The shape of the substrate to be polished includes, for example, a shape having a flat portion such as a disk, plate, slab, or prism, or a shape having a curved portion such as a lens, preferably a disk to be polished It is. In the case of a disk-shaped substrate to be polished, its outer diameter is, for example, 10 to 120 mm, and its thickness is, for example, 0.5 to 2 mm.

Generally, in a magnetic disk, a substrate to be polished which has been subjected to a grinding process is polished through a rough polishing process and a finish polishing process, and is manufactured through a magnetic layer forming process. The polishing composition of the present invention is preferably used for polishing in a rough polishing process.

[Method of manufacturing magnetic disk substrate]
The present invention comprises a step of polishing a substrate to be polished using the polishing composition of the present invention (hereinafter, also referred to as "polishing step using the polishing composition of the present invention"). (Hereafter, it is also called "the board | substrate manufacturing method of this invention.").

In the polishing step using the polishing composition of the present invention, for example, the substrate to be polished is sandwiched by a platen to which a polishing pad is attached, the polishing composition of the present invention is supplied to the polishing surface, and polishing is performed while applying pressure. The substrate to be polished is polished by moving either or both of the pad and the substrate to be polished.

The polishing load in the polishing step using the polishing composition of the present invention is preferably 30 kPa or less, more preferably 25 kPa or less, and still more preferably 20 kPa or less, from the viewpoint of reducing long cycle defects without significantly reducing the polishing rate. And 3 kPa or more is preferable, 5 kPa or more is more preferable, and 7 kPa or more is still more preferable. In the present invention, the term "polishing load" refers to the pressure of a platen applied to the surface to be polished of a substrate to be polished during polishing. The adjustment of the polishing load can be performed by the load of air pressure or weight on the platen, substrate or the like.

The amount of polishing per 1 cm ^{2 of the} substrate to be polished in the polishing step using the polishing composition of the present invention is preferably 0.20 mg or more, from the viewpoint of reducing long cycle defects without significantly reducing the polishing rate. .30 mg or more is more preferable, 0.40 mg or more is further 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 still more preferable.

The supply rate of the polishing composition per 1 cm ^{2 of the} substrate to be polished in the polishing step using the polishing composition of the present invention is preferably 2.5 mL / min or less, and 2.0 mL / min or less from the economical viewpoint. Is more preferably 1.5 mL / min or less, and from the viewpoint of securing a high polishing rate, 0.01 mL / min or more is preferable per 1 cm ^{2 of the} substrate to be polished, and 0.03 mL / min or more is more preferable. 0.05 mL / min or more is more preferable.

As a method of supplying the polishing liquid 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 the polishing composition is supplied to the polishing machine, it is divided into a plurality of component liquids in consideration of the storage stability of the polishing composition, etc., in addition to the method of supplying one solution containing all the components. , Can also be supplied in two or more solutions. In the latter case, the plurality of blending component liquids are mixed, for example, in a supply pipe or on a substrate to be polished, to form the polishing composition of the present invention.

According to the substrate manufacturing method of the present invention, since it is possible to reduce long period defects without largely deteriorating the polishing rate in rough polishing, there is an effect that it is possible to efficiently produce a magnetic disk substrate with reduced projection defects. It can be played.

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

By using the polishing method of the present invention, it is possible to reduce long period defects without largely reducing the polishing rate in rough polishing, thereby improving the productivity of a magnetic disk substrate in which protrusion defects are reduced. An effect can be achieved. Specific polishing methods and conditions can be the same as those of the substrate manufacturing method of the present invention described above.

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

1. Preparation of Abrasive Particle Slurry The abrasive particles (non-spherical silica particles A1 to A3, non-spherical alumina particles A4 and spherical silica particles B1) of Table 1, the redispersibility improver of Table 3 (component b) or the comparative object thereof, Abrasive grain slurries of Examples 1 to 14 and Comparative Examples 1 to 7 were prepared using water. The content of each component in the abrasive grain slurry is 30-50% by mass of abrasive grains (A1: 40% by weight, A2: 40% by weight, A3: 30% by weight, A4: 45% by weight, B1: 50% by weight A redispersibility improver (component b) or its comparison target: the amount described in Table 3, the balance is water. The pH of the abrasive slurry of Examples 1 to 14 and Comparative Examples 1 to 7 at 25 ° C. is 10. The details of the particles A and the particles B are as described in Table 1.

The non-spherical silica particles A1 and A2 are colloidal silica, the non-spherical silica particles A3 are precipitated silicas, and the particles B are colloidal silica produced by the water glass method. The pH of the abrasive grain slurry was measured using a pH meter (manufactured by Toa DK Co., Ltd.), and the electrode was immersed in the polishing composition and the value after 30 seconds was adopted (the same applies hereinafter).

Each of A-7075, A-7055, B-500, and B-300K in Table 3 is an alkali-thickening polymer emulsion, and is a carboxylic acid copolymer, and all of them are the first monomer unit and It contains a second monomer unit.

2. Preparation of Polishing Composition [Preparation of Polishing Composition Used for Rough Polishing]
An acidic aqueous solution (pH = 1.5) was adjusted by mixing an acid (phosphoric acid), an oxidizing agent (hydrogen peroxide) and water. Immediately after preparation of the abrasive slurry prepared by the method described in “1. Preparation of abrasive slurry” or after standing for 3 months, the abrasive slurry and acidic aqueous solution of Examples 1 to 14 and Comparative Examples 1 to 7 The mixture was mixed with the above to prepare polishing composition 1 to 21. The content of each component in the polishing composition 1 to 21 was 5.0 wt% of abrasive grains, the redispersibility improver (component b) or the comparative object thereof: the amount described in Table 3, phosphoric acid: 1.5 mass%, hydrogen peroxide: 0.8 mass%. The remaining amount is water. The pH of the polishing composition 1 to 21 at 25 ° C. is 1.6.

[Preparation of Polishing Composition C Used for Finishing Polishing]
Using the colloidal silica particles (abrasive grain a) of Table 2, sulfuric acid, hydrogen peroxide and water, a polishing composition C to be used for final polishing was prepared. The content of each component in the polishing composition C was 5.0 mass% of colloidal silica particles, 0.5 mass% of sulfuric acid, and 0.5 mass% of hydrogen peroxide. The pH of the polishing composition C was 1.4. This polishing composition C was used in the below-mentioned finish polishing process. The details of the abrasive grains a are as described in Table 2.

3. Measuring method of each parameter [Method of measuring BET specific surface area of abrasive grains]
The BET specific surface area S is subjected to the following [pre-treatment], and then about 0.1 g of the measurement sample is refined to 4 digits after the decimal point (0.1 mg digit) in the measurement cell, and 110 ° C. After drying for 30 minutes in an atmosphere of the above, it was measured by the BET method using a specific surface area measuring apparatus (Micromeritic automatic specific surface area measuring apparatus "Flowsorb III 2305" manufactured by Shimadzu Corporation).
[Preprocessing]
The slurry-like 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 ground in an agate mortar to obtain a measurement sample.

[Method of measuring BET specific surface area of abrasive grains and average primary particle diameter D1]
The average primary particle size (nm) of the abrasive grains was calculated by the following equation using the specific surface area S (m ² / g) calculated by the BET (nitrogen adsorption) method.
(1) Average Primary Particle Size of Silica Particles (nm) = 2727 / S = 6 / (ρ × S)
ρ: density of substance (kg / m ³ )
(2) Average primary particle size of alumina particles (nm) = 1508 / S

[Method of measuring average secondary particle size of abrasive grains]
(1) Method of Measuring Average Secondary Particle Size of Silica Particles A1, A2 and B1 The silica particles were diluted with ion exchanged water to prepare a dispersion containing 1 mass% of silica particles. Then, the dispersion was charged into the following measuring device to obtain a volume particle size distribution of silica particles. The particle size (Z-average value) at which the cumulative volume frequency of the obtained volume particle size distribution is 50% was defined as the secondary particle size.
Measurement equipment: Malvern Zetasizer Nano "Nano S"
Measurement conditions: Sample volume 1.5 mL
: Laser He-Ne, 3.0 mW, 633 nm
: Scattered light detection angle 173 °

(2) Method of measuring average secondary particle diameter of silica particles A3 (2-1) Silica particles A3
Water is introduced as a dispersion medium into the following measuring apparatus, and then a sample (silica particles A3) is introduced so that the transmittance is 75 to 95%, and then ultrasonic waves are applied for 5 minutes, and then the particle size is obtained. Was measured.
(2-2) Alumina particles A4
An aqueous solution containing 0.5% by mass of Poise 530 (manufactured by Kao Corporation, polycarboxylic acid type polymer surfactant) as a dispersion medium is introduced into the following measuring apparatus, and then the transmittance becomes 75 to 95%. The sample (alumina particles 4A) was charged as described above, and then ultrasonic waves were applied for 5 minutes, and then the particle size was measured.
Measuring equipment: Horiba, Ltd. Laser diffraction / scattering type particle size distribution analyzer LA920
Circulation strength: 4
Ultrasonic intensity: 4

[Method of measuring average minor diameter and average sphericity of abrasive grains]
A photograph of the abrasive grains observed by TEM (“JEM-2000FX”, 80 kV, 1 to 50,000 times by Nippon Denshi Co., Ltd.) is captured as image data by a scanner into a personal computer, and analysis software (Mitani Shoji “WinROOF (Ver. 6) “) was used to analyze the projected images of 500 abrasive grains as follows.
The minor diameter of each abrasive grain was determined, and the average value of the minor diameter (average minor diameter) was obtained. Furthermore, the sphericity of each abrasive grain was calculated from the area S and the circumferential length L of each abrasive grain according to the following equation, and the average value of the sphericity (average sphericity) was obtained.
Sphericity = 4π × S / L ²

[D10, D50, and D90 of abrasive grain a]
A 1% by mass dispersion obtained by diluting the abrasive grains a with ion-exchanged water was introduced into the following measuring apparatus to obtain a volume particle size distribution of the silica abrasive grains.
Measurement equipment: Malvern Zetasizer Nano "Nano S"
Measurement conditions: Sample volume 1.5 mL
: Laser He-Ne, 3.0 mW, 633 nm
: Scattered light detection angle 173 °
Then, the particle sizes at which the cumulative volume frequency of the obtained volume particle size distribution is 10%, 50% and 90% are respectively designated D10, D50 (volume average particle size), and D90.

4. Redispersibility The redispersibility of the silica particles in the silica slurry was evaluated by the sedimentation rate (%). The sedimentation rate is the ratio of the amount of sedimentation (g) to the total solid content, assuming that the total solid content is 100. The silica slurry, which has been allowed to stand for 3 months after preparation, is shaken with a shaker ("MW-YS" manufactured by Miyamoto Riken Kogyo Co., Ltd.) for 30 seconds at a rotational speed of 100 rpm, and the supernatant liquid removed is sedimented Amount. The smaller the sedimentation rate, the better the redispersibility of the silica slurry.
[Evaluation criteria]
A: Settability 0% or more and less than 1% B: Settability 1% or more and less than 3% C: Settability 3% or more

5. Polishing conditions Polishing of the substrate to be polished was performed according to the following steps (1) to (3). The conditions of each process are shown below. Step (3) was carried out using a polishing machine separate from the polishing machine used in step (1).
(1) Rough polishing step: a step of polishing the surface to be polished of the substrate to be polished using the polishing composition 1 to 21.
(2) Washing step: a step of washing the substrate obtained in step (1).
(3) Finishing polishing step: a step of polishing the surface to be polished of the substrate obtained in step (2) using the polishing composition C.

[Substrate to be polished]
As a substrate to be polished, a Ni-P plated aluminum alloy substrate was used. The substrate to be polished had a thickness of 1.27 mm and a diameter of 95 mm.

[Step (1): rough polishing]
Polishing machine: Double-sided polishing machine (9B type double-sided polishing machine, made by Speed Femme)
Number of substrates to be polished: 10 sheets Abrasive liquid: Abrasive liquid composition 1 to 21
Polishing pad: suede type (foamed layer: polyurethane elastomer), thickness: 1.0 mm, average pore diameter: 30 μm, surface layer compression ratio: 2.5% (manufactured by Filwel)
Plate rotation speed: 35 rpm
Polishing load: 9.8 kPa (set value)
Polishing fluid supply amount: 100 mL / min (0.076 mL / min per 1 cm ^{2 of the} substrate to be polished)
Equivalent to
Polishing time: 6 minutes

[Step (2): Cleaning]
The substrate obtained in step (1) was washed under the following conditions.
First, the substrate obtained in step (1) is immersed for 5 minutes in a bath containing an alkaline cleaner composition of pH 12 consisting of a 0.1% by mass KOH aqueous solution. Next, the substrate after immersion is rinsed with ion exchange water for 20 seconds. Then, the substrate after the rinse is transferred to the scrub cleaning unit in which the cleaning brush is set and cleaned.

[Step (3): Finish Polishing]
Polishing machine: Double-sided polishing machine (type 9B double-sided polishing machine, manufactured by Speed Fam Co., Ltd.), the number of polishing substrates to be polished separately from the polishing machine used in step (1): 10 sheets Polishing solution: Polishing solution composition C
Polishing pad: suede type (foamed layer: polyurethane elastomer), thickness: 0.9 mm, average pore diameter: 5 μm, compression ratio of surface layer: 10.2% (manufactured by Fujibo)
Plate rotation speed: 40 rpm
Polishing load: 9.8 kPa
Polishing liquid supply amount: 100 mL / min (corresponding to 0.076 mL / min per 1 cm ^{2 of the} substrate to be polished)
Polishing time: Washing was performed after the step (3) for 2 minutes. The washing conditions were the same as in the step (2).

6. Evaluation method [Measurement method and evaluation of polishing rate in step (1)]
The weight per substrate before and after polishing was measured using a measure ("Sortorius, BP-210S" manufactured by Sartorius), and the amount of mass loss was determined from the mass change of each substrate. The value obtained by dividing the average mass loss of all ten sheets by the polishing time was calculated as the polishing rate by the following equation, and the results are shown in Table 3.
Mass loss (g) = {mass before polishing (g)-mass after polishing (g)}
Polishing rate (mg / min) = mass loss (mg) / polishing time (min)

The rate of decrease in speed (%) was calculated according to the following equation, and the results are shown in Table 3.
Speed reduction rate (%) = Polishing speed after standing for 100-3 months ÷ Polishing speed immediately after production × 100
Rate reduction rate: Evaluation-5% or more and less than 5%: "A: Excellent polishing rate, and further improvement of substrate yield can be expected"
5% or more and less than 10%: "B: The polishing rate is good, and substrate yield improvement can be expected"
10% or more: "C: Need for improvement in actual production"

[Method for evaluating long period defects on substrate surface after step (1)]
Step (2) was carried out on both sides (total 20 points) of the ten substrates after polishing of step (1), and then the occurrence rate (%) was determined by measurement under the following conditions. When the small spot which can be checked with the naked eye on the substrate surface is PED and it could be confirmed even at one point on the substrate surface, the surface was regarded as having a long period defect.
Long cycle defect rate (%)
= (Number of substrate surfaces with long-period defects / 20) x 100
The long cycle defect incidence rate was evaluated in five levels based on the following criteria. That is, the larger the evaluation value, the lower the incidence of long-period defects. The results are shown in Table 3.
[Evaluation criteria]
Long cycle defect occurrence rate: Evaluation 10% or less: "5: occurrence is extremely suppressed, and substrate yield improvement can be expected"
10% over 20% or less: "4: Real production possible"
20% over 30% or less: "3: Need for improvement in actual production"
30% or more and 50% or less: "2: substrate yield is significantly reduced"
50% over: "1: far from the actual production (same level as when using general silica abrasive)"
[measuring equipment]
Optical interference surface profiler: OptiFLAT III (manufactured by KLA Tencor) Radius Inside / Out: 14.87 mm / 47.83 mm
Center X / Y: 55.44 mm / 53.38 mm
Low Cutoff: 2.5mm
Inner Mask: 18.50 mm
Outer Mask: 45.5 mm
Long Period: 2.5 mm
Wa Correction: 0.9
Rn Correction: 1.0
No Zernike Terms: 8

[Evaluation method of alumina residue]
The surface of each substrate after polishing was observed at a magnification of 10,000 with a scanning electron microscope (manufactured by Hitachi, Ltd .: S-4000), and the following three-step evaluation was performed.
A: No alumina residue observed on the surface B: A slight alumina residue observed on the surface C: An alumina residue observed on the surface

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

For example, when Example 2 and Comparative Example 2 are compared, as shown in Table 3, the sedimentation rate of the silica slurry of Example 2 is significantly smaller than that of the silica slurry of Comparative Example 2, The redispersibility of the silica particles is improved by the inclusion of the redispersibility improver. The same applies to the comparison between Example 1 and Comparative Example 1 and Example 6 and Comparative Example 3.

In addition, when using an abrasive composition prepared using a silica slurry immediately after production, no noticeable difference is found in the polishing rate for Example 2 and Comparative Example 2, but leaving still for 3 months from production In the case of using the abrasive composition prepared using the later silica slurry, in Comparative Example 2, the polishing rate was significantly reduced, but in Example 2, there was almost no change. In addition, when using an abrasive composition prepared using a silica slurry after standing for 3 months from production, the incidence of long period defects is significantly lower in Example 2 than in Comparative Example 2. The The same applies to the comparison between Example 1 and Comparative Example 1 and Example 6 and Comparative Example 3.

In the silica slurry of Comparative Example 5 using PEG (weight average molecular weight 6,000) well known as a dispersant, the redispersibility of the silica particles was poor. In Comparative Example 6, by using PEG having a larger weight average molecular weight, the evaluation of redispersibility was good, but the polishing rate was slow. The polyacrylic acid used to prepare the silica slurry of Comparative Example 7 is a carboxylic acid-based polymer but is not affected by the alkali-thickening polymer emulsion.

As shown in Table 3, the silica slurries of Examples 1 to 14 which contain an alkali-thickening polymer emulsion as a redispersibility improver are the silicas of Comparative Examples 1 to 4 which do not contain the alkali-thickening polymer emulsion. The redispersibility of silica particles after long-term storage is superior to that of a slurry. And, polishing compositions 1 to 14 prepared using the silica slurry of Examples 1 to 14 stored for a long period of time have high polishing speed and long period defects compared with polishing compositions 15 to 21. It is possible to reduce.

According to the present invention, even after long-term storage, it is possible to ensure both high polishing speed and suppression of deterioration of the substrate quality such as long period defects, so the productivity of manufacturing the magnetic disk substrate with good substrate quality is improved. it can. The present invention can be suitably used for manufacturing a magnetic disk substrate.

Claims

Silica particles, redispersibility improver, and water
The redispersibility improver is an alkali-thickened polymer emulsion,
The silica slurry for polishing liquid composition whose pH in 25 degreeC is 8.0 or more and 12.0 or less.
The silica slurry for polishing composition according to claim 1, wherein the viscosity at 25 ° C of the silica slurry for polishing composition is 20 mPa · s or more.
The silica slurry for polishing composition according to claim 1 or 2, wherein the viscosity at 25 ° C is 10 mPa · s or less when the pH is 0.5 or more and 6.0 or less.
The silica slurry for polishing composition according to any one of claims 1 to 3, wherein the redispersibility improver is an alkali-thickened carboxylic acid-based polymer.
The silica slurry for polishing composition according to any one of claims 1 to 4, wherein the silica particles include non-spherical silica particles.
The silica slurry for polishing composition according to claim 5, wherein an average secondary particle diameter of the non-spherical silica particles is 150 nm or more and 580 nm or less.
The silica slurry for polishing composition according to any one of claims 1 to 6, wherein the polishing composition is a polishing composition for a magnetic disk substrate.
An acidic aqueous solution (second example) housed in a separate container from the silica slurry (first liquid) for a polishing composition according to any one of claims 1 to 7 and the silica slurry for the polishing composition. A polishing solution kit, wherein the pH at 25 ° C. when mixing the first solution and the second solution is 0.5 or more and 6.0 or less.
A polishing composition comprising a step of mixing the silica slurry for a polishing composition according to any one of claims 1 to 7 with an acid to make the pH at 25 ° C 0.5 or more and 6.0 or less. Method of manufacturing objects.
The method for producing a polishing composition according to claim 9, wherein the content of silica particles in the silica slurry for a polishing composition is 10% by mass to 70% by mass, and water is further mixed in the step.
A magnetic disk substrate comprising a step of polishing a substrate to be polished using a polishing composition for a magnetic disk substrate prepared using the silica slurry for a polishing composition according to any one of claims 1 to 7. Manufacturing method.
The method of manufacturing a magnetic disk substrate according to claim 11, wherein the substrate to be polished is a Ni-P plated aluminum alloy base.
A process of polishing a substrate to be polished using a polishing composition prepared using the silica slurry for a polishing composition according to any one of claims 1 to 7,
The method for polishing a substrate, wherein the substrate to be polished is a substrate used for manufacturing a magnetic disk substrate.