JP2019029044A - Silica slurry - Google Patents

Abstract

To provide silica slurry and the like having good redispersibility of silica particles after long-term storage and capable of realizing both high polishing speed and deterioration inhibiting of substrate quality even when using after long-term storage.SOLUTION: Silica slurry according to one aspect of the present invention is used for preparation of a polishing liquid composition for a magnetic disk substrate having pH between 0.5 and 6.0 at 25°C, and contains silica particles, redispersibility improver, and water. The average primary particle diameter of the silica particles is 80nm or more, and the average secondary particle diameter of the silica particles is between 130nm and 580nm. The redispersibility improver is a water swellable inorganic layer compound and has pH between 8.0 and 12.0 at 25°C. The water swellable inorganic layer compound is preferably one or more selected from bentonite, hectorite, and saponite.SELECTED DRAWING: None

Description

  The present invention relates to a silica slurry, a polishing liquid kit including the same, and a method for producing a polishing liquid composition for a magnetic disk substrate. The present invention also relates to a method for manufacturing a magnetic disk substrate and a method for polishing the 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 improve the detection sensitivity of the magnetic signal. In view of this, technical development is underway to further reduce the flying height of the magnetic head and reduce the unit recording area. 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. From the viewpoint of achieving both improvement in surface quality and productivity, such as smoother and less scratches, such a requirement, the hard disk substrate manufacturing method includes a multi-stage polishing method having two or more polishing steps. 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 the polishing step (also referred to as rough polishing step) prior to the final polishing step, a polishing liquid composition containing alumina particles is used from the viewpoint of improving productivity. However, when alumina particles are used as the abrasive, media drive defects may be caused by the piercing of the alumina particles into the substrate.

  Therefore, a method of manufacturing a magnetic disk substrate that can reduce the sticking of particles 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 has been proposed. (Patent Documents 1 and 2).

  On the other hand, it contains water, inorganic fine particles such as anhydrous silica, an anionic surfactant, and hydrotalcite compound particles. The electrostatic repulsion between the inorganic fine particles and the hydrotalcite compound particles causes A suspension composition is disclosed in which dispersibility is maintained (Patent Document 3).

  Furthermore, it is a polishing composition for a compound semiconductor wafer edge part, which contains colloidal silica particles as abrasive particles, an inorganic layered compound such as montmorillonite or mica as an anti-settling agent, and has a pH of 7.0 to 10.5 A polishing composition is disclosed (Patent Document 4).

  Furthermore, it is a polishing composition suitable for polishing an alloy material such as an aluminum alloy and a resin material, and the volume average particle diameter of abrasive grains such as aluminum oxide particles or silicon carbide particles is 2.0 μm or more and 25.0 μm or less. A polishing composition containing a layered silicate compound is disclosed (Patent Document 5).

JP 2014-29755 A JP 2014-1116057 A Japanese Patent Laid-Open No. 2008-201984 JP 2001-44148 A Patent No. 6099067

  If a rough polishing process and a final polishing process that do not use alumina particles are employed in the polishing process of the magnetic disk substrate, the remaining alumina due to the adhesion or sticking of alumina can be suppressed, and the protrusion defects on the substrate surface after polishing can be reduced. However, when the rough polishing process is performed with silica particles having a large particle size instead of alumina particles, it has been found that a problem arises that the redispersibility of the precipitated silica particles in the silica slurry is poor. Deterioration of redispersibility causes a reduction in polishing rate and deteriorates substrate quality such as long-period defects. Therefore, it is desired to improve redispersibility of silica particles in a silica slurry after long-term storage.

  Therefore, the present invention provides a silica slurry that is used for the preparation of a polishing liquid composition for a magnetic disk substrate and has excellent redispersibility of silica particles after long-term storage. Provided is a polishing composition capable of ensuring both a high polishing rate and ensuring good substrate quality even when using a silica slurry after long-term storage.

  One aspect of the present invention is a silica slurry used for the preparation of a polishing liquid composition for a magnetic disk substrate having a pH at 25 ° C. of 0.5 or more and 6.0 or less, wherein silica particles, a redispersibility improver, And the average primary particle diameter of the silica particles is 80 nm or more, the average secondary particle diameter of the silica particles is 130 nm or more and 580 nm or less, and the redispersibility improver is a water-swellable inorganic layered compound It is related with the silica slurry whose pH in 25 degreeC is 8.0 or more and 12.0 or less.

  Another aspect of the present invention includes the silica slurry (first liquid) of the present invention and an acidic aqueous solution (second liquid) housed in a container separate from the silica slurry, and the first liquid and the The present invention relates to a polishing liquid kit having a pH at 25 ° C. of 0.5 or more and 6.0 or less when mixed with the second liquid.

  Still another aspect of the present invention is a polishing composition for a magnetic disk substrate, comprising a step of mixing the silica slurry of the present invention and an acid to adjust the pH at 25 ° C. to 0.5 or more and 6.0 or less. It relates to a manufacturing method.

  Yet another embodiment of the present invention relates to a method for producing 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 of the present invention.

  Still another aspect of the present invention includes a step of polishing a substrate to be polished using a polishing composition for a magnetic disk substrate prepared using the silica slurry of the present invention, wherein the substrate to be polished is a magnetic disk substrate. The present invention relates to a method for polishing a substrate, which is a substrate used for manufacturing the substrate.

  According to the present invention, a silica slurry having excellent redispersibility of silica particles after long-term storage can be provided. Further, according to the present invention, if the silica slurry of the present invention is used for the preparation of a polishing composition, it is possible to achieve both high polishing rate and good substrate quality even when using a silica slurry after long-term storage. The effect that it is possible can be produced.

  The silica slurry of the present invention is used for the preparation of a magnetic disk substrate polishing liquid composition (hereinafter sometimes abbreviated as “polishing liquid composition”) having a pH of 0.5 or more and 6.0 or less at 25 ° C. A silica slurry containing silica particles having an average primary particle diameter of 80 nm or more and an average secondary particle diameter of 130 nm to 580 nm as abrasive grains, and a water-swellable inorganic layered compound as a redispersibility improver And the pH at 25 ° C. is 8.0 or more and 12.0 or less, based on the knowledge that the redispersibility of the silica particles after long-term storage is excellent. In addition, since the silica slurry of the present invention is used for the preparation of the polishing liquid composition of the present invention, a high polishing rate is ensured even if the polishing liquid composition prepared using the silica slurry after long-term storage is used for rough polishing. And based on the knowledge that good substrate quality can be ensured.

  In general, if the dispersibility of silica particles in the polishing liquid composition used for manufacturing a 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, a high polishing rate is ensured, and an adverse effect on the substrate quality due to the use of the silica slurry after long-term storage is suppressed, so that an 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 that can ensure both high polishing rate and good substrate quality are not clear, but are presumed as follows.

  A relatively large silica particle having an average primary particle diameter of, for example, 80 nm or more and an average secondary particle diameter of 130 nm or more and 580 nm or less precipitates during storage due to its own weight. When the silica slurry is stirred and mixed with other components such as acid for the preparation of the polishing composition, if the primary particles of the silica particles remain firmly aggregated, the uneven surface of the substrate to be polished Thus, the physical force of the silica particles becomes difficult to act, so that the polishing rate decreases, and the silica particles increase in particle size, thereby causing undulations and the like.

  In contrast, in the present invention, a swellable inorganic layered compound (hereinafter sometimes abbreviated as “layered compound”) that swells in an aqueous system to form a card house structure and thickens in the silica slurry. Contains. Therefore, the redispersibility of the silica particles in the silica slurry is good even after long-term storage. In addition, when an acid or the like is added to the silica slurry of the present invention to prepare a polishing composition having a pH of 0.5 or more and 6.0 or less, the polishing composition is used even when the silica slurry after long-term storage is used. Since the dispersibility of the silica particles in the product is good, good substrate quality can be ensured. In addition, when the above layered compound is sheared, the flaky crystals are arranged in parallel to the flow and the viscosity decreases, and the thixotropic property is exhibited. Therefore, the thickening due to the inclusion of the layered compound gives the polishing rate. The adverse effect is small. For this reason, the present invention is presumed to be able to ensure both a high polishing rate and good substrate quality. However, the present invention is not limited to these mechanisms.

  That is, the silica slurry of the present invention is a silica slurry used for the preparation of a polishing composition for a magnetic disk substrate having a pH at 25 ° C. of 0.5 or more and 6.0 or less. An average primary particle diameter of the silica particles is 80 nm or more, an average secondary particle diameter of the silica particles is 130 nm or more and 580 nm or less, and the redispersibility improver is water swellable. It is related with the silica slurry whose pH in 25 degreeC is 8.0 or more and 12.0 or less.

  In the present application, “undulation” of the 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.

  In the present application, “PED (polish enhanced defect)” refers to a shallow dent-like defect that appears on the substrate surface after polishing finish. This PED occurs, for example, in the manufacturing process of an Ni-P plated aluminum alloy substrate. An annealing process in the process of forming a plating film on an aluminum alloy substrate, which is a portion of insufficient annealing due to water or foreign matter adhering to the substrate surface, and occurs as a shallow dent defect on the substrate surface during polishing. The “grind scratch” refers to a grinding mark of a grindstone generated in a process of grinding an aluminum alloy substrate before plating. PED and grind scratches are collectively called “long-period defects”. The occurrence rate of long-period defects is an index for evaluating the removal rate of long-period defects, and can be measured using the measuring instrument described in the examples.

[Silica particles]
The silica slurry of the present invention contains silica particles as abrasive grains. The silica particles preferably include non-spherical silica particles A (hereinafter also referred to as “particles A”) from the viewpoint of improving the polishing rate, and are preferably particles A from the viewpoint of coexistence of reduction of long wavelength waviness and improvement of the polishing rate. And spherical silica particles (hereinafter also referred to as “particle B”). Examples of the silica particles include colloidal silica, fumed silica, and surface-modified silica.

  From the viewpoint of ensuring a high polishing rate, the particles A are preferably colloidal silica or precipitated silica particles. When the silica particles consist only of the particles A, the particles A are preferably colloidal silica from the viewpoint of reducing long-period defects, and when the silica particles include both the particles A and the particles B, the particles A can ensure a high polishing rate. From the viewpoint of, precipitated silica particles are preferable. 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. As the particle B, colloidal silica is preferable from the viewpoint of ensuring a high polishing rate, reducing long-period defects, and reducing protrusion defects. The particle B may be one type of spherical silica particle or a combination of two or more types of spherical silica particles.

  Examples of the method for producing the particles A include known methods such as the method described in Tosoh Research and Technical Report Vol. 45 (2001) pages 65 to 69. Specific examples of the method for producing the particles A include a precipitation method in which silica particles are precipitated by a neutralization reaction between a silicate such as sodium silicate and a mineral acid such as sulfuric acid. Preferably, the neutralization reaction is performed at a relatively high temperature and under alkaline conditions, whereby the primary particles of silica progress rapidly, the primary particles aggregate in a floc form and settle, and the precipitated silica particles can get. The 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 pulverization method. However, the viewpoint of ensuring a high polishing rate and reducing long-period defects, as well as reducing protrusion defects after rough polishing and final polishing. From the viewpoint, silica particles produced by a particle growth method using an alkali silicate aqueous solution as a starting material (hereinafter also referred to as “water glass method”) are preferable. The usage form of the particles B is preferably 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 more preferably 30% by mass or more from the viewpoint of improving the redispersibility of the silica particles. Further, 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 ensuring a high polishing rate and reducing long-period defects. From the viewpoint, 50 m ² / g or less is preferable, and 45 m ² / g or less is more preferable. In addition, the BET specific surface area of the silica particle (component a) when the silica particle (component a) includes both the particle A and the particle B can be calculated from the BET specific surface area and the blending ratio (mass ratio) of both particles.

  The average primary particle diameter D1 in terms of BET conversion of silica particles (component a) is 80 nm or more, preferably 90 nm or more, from the viewpoint of securing a high polishing rate and reducing long-period defects, and reducing long-period defects. From the viewpoint, 300 nm or less is preferable, 250 nm or less is more preferable, and 200 nm or less is still more preferable. In addition, D1 of a silica particle (component a) in case a silica particle (component a) contains both the particle | grains A and the particle | grains B is computable from D1 of both particle | grains, and a mixture ratio (mass ratio).

  The average secondary particle diameter D2 of the silica particles (component a) is 130 nm or more from the viewpoint of ensuring a high polishing rate and reducing long-period defects, and is 580 nm or less from the viewpoint of reducing long-period defects. , 500 nm or less is preferable, 400 nm or less is more preferable, and 350 nm or less is even more preferable. In addition, D2 of a silica particle (component a) in case a silica particle (component a) contains both the particle | grains A and the particle | grains B is computable from D2 of both particles, and a mixture ratio (mass ratio).

(Non-spherical silica particles)
The polishing composition of the present invention preferably contains non-spherical silica particles A from the viewpoint of ensuring a high polishing rate.

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

In the present application, 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 projection area S and the projection perimeter L of the particle A using, for example, observation with a transmission electron microscope (TEM) and image analysis software.
Sphericality = 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, 0.85 or less is preferable and 0.80 or less is preferable. More preferred is 0.75 or less.

  The average minor axis of the particles A is preferably 100 nm or more, more preferably 150 nm or more, further preferably 180 nm or more, and 500 nm or less from the same viewpoint from the viewpoint of ensuring a high polishing rate and reducing long-period defects. Preferably, 450 nm or less is more preferable, and 400 nm or less is still more preferable.

  When the silica particles (component a) are composed only of the particles A and the particles A are colloidal silica, the average short diameter of the particles A is preferably 100 nm or more from the viewpoint of securing a high polishing rate and reducing long-period defects. 150 nm or more is more preferable, 180 nm or more is further preferable, and from the same viewpoint, 500 nm or less is preferable, 450 nm or less is more preferable, 400 nm or less is further preferable, and 300 nm or less is even more preferable.

  When the silica particles (component a) include both particles A and B, and the particles A are precipitated silica particles, the average short diameter of the particles A is from the viewpoint of ensuring a high polishing rate and reducing long-period defects. 150 nm or more, preferably 180 nm or more, 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 the minor axis 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 rectangle when a minimum rectangle circumscribing the projected image of the particle A is drawn using, for example, TEM observation and image analysis software. Similarly, the major axis of the particle A is the length of the long side of the rectangle.

BET specific surface area of the particles A, from the viewpoint of reduction in the level of security and long period defect high polishing rate, preferably at least 5 m ² / g, more preferably at least 10 m ² / g, and, from the same viewpoint, 50m ² / g or less is preferable, 40 m ² / g or less is more preferable, 30 m ² / g or less is more preferable, and 20 m ² / g 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, 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 preferably 10 m ² / g or more, more preferably 20 m ² / g or more, and from the same viewpoint, 50 m 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 particle (component a) includes both the particle A and the particle B, and the particle A is a precipitated silica particle, the BET specific surface area of the particle A is from the viewpoint of ensuring 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, and 30 m ² / g or less is more preferable. 20 m ² / g or less is even more preferable.

In the present application, the average primary particle diameter D1 of the particles A can be calculated from the following formula 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 diameter (nm) = 2727 / S

  The average primary particle diameter D1 in terms of BET of the particle A is preferably 50 nm or more, more preferably 70 nm or more, still more preferably 80 nm or more, and even more preferably 90 nm or more, from the viewpoint of ensuring a high polishing rate and reducing long-period defects. Preferably, from the viewpoint of reducing long-period defects, 300 nm or less is preferable, 250 nm or less is more preferable, and 200 nm or less is even more preferable.

  When the silica particle (component a) is composed of only the particle A and the particle A is colloidal silica, D1 of the particle A is 80 nm or more and 90 nm or more from the viewpoint of securing a high polishing rate and reducing long-period defects. In view of reducing long-period defects, it is preferably 300 nm or less, more preferably 250 nm or less, still more preferably 200 nm or less, still more preferably 150 nm or less, and even more preferably 120 nm or less.

  When the silica particle (component a) includes both the particle A and the particle B and the particle A is a precipitated silica particle, D1 of the particle A is 90 nm from the viewpoint of ensuring a high polishing rate and reducing long-period defects. The above is preferable, 120 nm or more is more preferable, and from the viewpoint of reducing long-period defects, 300 nm or less is preferable, 250 nm or less is more preferable, and 200 nm or less is even more preferable.

  The average secondary particle diameter D2 of the particles A is preferably 100 nm or more, preferably 130 nm or more, more preferably 150 nm or more, still more preferably 180 nm or more, from the viewpoint of ensuring a high polishing rate and reducing long-period defects. From the viewpoint of reducing long-period defects, 580 nm or less is preferable, 500 nm or less is more preferable, 400 nm or less is further preferable, and 350 nm or less is even more preferable.

  When the silica particle (component a) is composed of only the particle A and the particle A is colloidal silica, D2 of the particle A is 130 nm or more and 150 nm or more from the viewpoint of securing a high polishing rate and reducing long-period defects. 180 nm or more is more preferable, and from the viewpoint of reducing long-period defects, 400 nm or less is preferable, 350 nm or less is more preferable, 300 nm or less is further preferable, and 250 nm or less is even more preferable.

  When the silica particle (component a) includes both the particle A and the particle B and the particle A is a precipitated silica particle, D2 of the particle A is 150 nm from the viewpoint of securing a high polishing rate and reducing long-period defects. The above is preferable, 200 nm or more is more preferable, 220 nm or more is further preferable, 250 nm or more is even more preferable, 300 nm or more is further more preferable, and 580 nm or less is preferable and 500 nm or less is more preferable from the viewpoint of reducing long-period defects. Preferably, 400 nm or less is more preferable, and 350 nm or less is even 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 a scattering intensity distribution measured by a light scattering method. In this application, “scattering intensity distribution” is obtained by dynamic light scattering (DLS), quasielastic light scattering (QLS), or static light scattering (laser diffraction / scattering). This refers to the particle size distribution in terms of volume of the submicron particles or less. The average secondary particle diameter D2 of the particles A in the present application can be specifically obtained by the method described in the examples.

  The particle diameter ratio (D2 / D1) between the average secondary particle diameter D2 and the average primary particle diameter D1 of the particles A is preferably 1.3 or more from the viewpoint of securing a high polishing rate and reducing long-period defects. 0.5 or more is more preferable, 1.7 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) may mean the degree of deformation of the particles A. In general, the average secondary particle diameter D2 measured by the light scattering method takes into account the length in the long direction and the short direction in order to detect and process light scattering in the long direction when the particles are irregularly shaped particles. Thus, the greater the degree of deformity, the larger the numerical value. Since the average primary particle diameter D1 converted from the specific surface area value measured by the BET method is expressed in terms of a sphere based on the obtained particle volume, it is a smaller numerical value than the average secondary particle diameter D2. From the viewpoint of securing a high polishing rate, the particle size ratio (D2 / D1) is preferably 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 the 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 ensuring a high polishing rate and reducing long-period defects. From the viewpoint of economy, it is preferably 70% by mass or less, more preferably 60% by mass or less, still more preferably 50% by mass or less, and even more preferably 35% by mass or less.

(Spherical silica particles B)
As described above, the polishing composition of the present invention preferably further contains spherical silica particles B as component a from the viewpoint of reducing long-period defects and ensuring a high polishing rate. When the precipitated silica particles are used, the particles B are preferably contained from the viewpoint of securing a high polishing rate.

  In the present application, the average sphericity of the particles B is preferably more than 0.85 from the viewpoints of securing a high polishing rate and reducing long-period defects, and reducing protrusion defects after rough polishing and finish polishing. .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 each particle B is preferably more 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 the particle B can be calculated by the same method as the particle A.

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

  The average minor axis of the particle B is smaller than the average minor axis of the particle A. The average minor axis of the particle B is preferably 20 nm or more, more preferably 30 nm or more, still more preferably 40 nm or more from the viewpoint of improving the polishing rate, and 200 nm or less is preferable from the viewpoint of reducing long-period defects, and 150 nm or less. Is more preferable, and 110 nm or less is still more preferable. The average minor axis of the particle B can be calculated by the same method as that for the particle A.

  The ratio of the average minor axis between the particles A and the particles B in the polishing liquid composition of the present invention (average minor axis of particles A) / (average minor axis of particles B) is such that high polishing rate is ensured and long-period defects. From the viewpoint of coexistence of reduction, 1.5 or more is preferable, 2.0 or more is more preferable, 2.5 or more is more preferable, and 13.0 or less is preferable from the viewpoint of ensuring a high polishing rate. 0 or less is more preferable, and 8.0 or less is more preferable.

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

  The average secondary particle diameter of the particle B by the dynamic scattering method is preferably 20 nm or more, more preferably 30 nm or more, still more preferably 40 nm or more, from the viewpoint of coexistence of ensuring a high polishing rate and reducing long-period defects. From the same viewpoint, it is preferably 200 nm or less, more preferably 150 nm or less, and still more preferably 120 nm or less. The average secondary particle diameter of the particle B can be calculated by the same measurement method as that for the particle 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, and economical efficiency from the viewpoint of achieving both a high polishing rate and long-period defects. In view of the above, 35% by mass or less is preferable, 30% by mass or less is more preferable, and 25% by mass or less is still more preferable.

  The mass ratio A / B between the particles A and 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 achieving both a high polishing rate and reducing long-period defects. Preferably, 25/75 or more is further 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 more preferable. When the particle B is a combination of two or more types 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 silica slurry of the present invention contains silica particles other than particles A and particles B, the total content of particles A and particles B with respect to the entire silica particles in the silica slurry is from the viewpoint of improving the polishing rate and reducing waviness. 98.0% by mass or more, preferably 98.5% by mass or more, more preferably 99.0% by mass or more, still more preferably 99.5% by mass or more, and even more preferably 99.8% by mass or more. Preferably, substantially 100% by weight is even more preferred.

[Redispersibility improver]
The polishing liquid composition of the present invention contains a water-swellable inorganic layered compound as a redispersibility improver. Here, “water swellability” means that the test method defined in the 15th revised Japanese Pharmacopoeia is applied mutatis mutandis, and the swelling force expressed by the swelling volume (cm ³ ) of 2 g of clay mineral is 20 cm ³ / g or more. It means what is.

  The inorganic layered compound is, for example, a water-swellable clay mineral, and examples of the water-swellable clay mineral include bentonite (including natural or synthetic bentonite), montmorillonite (including natural or synthetic montmorillonite), beidellite, nontronite, Laponite, saconite, hectorite (including natural or synthetic hectorite), saponite (including natural or synthetic saponite), smectite clay minerals such as stevensite, vermiculite, swellable synthetic fluorinated mica (Na-type, Li-type synthetic mica) ) And swellable mica. Among these, from the viewpoint of improving redispersibility of silica particles, one or more selected from bentonite, montmorillonite, beidellite, nontronite, laponite, hectorite, and saponite are preferable, bentonite, hectorite, And one or more selected from saponite are more preferred.

  Commercially available water-swelling clay minerals include Polagel (made by American Colloid), Laponite (made by Big Chemie Japan), Wenger (made by Toyoshun Mining Co., Ltd.), Lucentite (made by Corp Chemical), Kunipia (Kunimine Industries) ), Benclay (Mizusawa Chemical Co., Ltd.), Bee Gum (Vanderbilt Co., Ltd.), Smecton (Kunimine Kogyo Co., Ltd.), Optigel (Sud-chemie Co., Ltd.), etc. can do. These can be used alone or in combination of two or more.

  The average particle size of the water-swellable clay mineral is preferably 1 to 5000 nm, more preferably 5 to 3000 nm, and still more preferably 10 to 15000 nm or more when dispersed with water. The average particle diameter of the water-swellable clay mineral is the median diameter (particle diameter at which the cumulative particle amount is 50% by volume) measured by a laser diffraction method of the water-swellable clay mineral dispersed with 50 times the mass of water. Yes, it can be measured by a measuring instrument: Shimadzu laser diffraction particle size distribution analyzer SALD-2200.

  The mass ratio of the silica particles and the redispersibility improver in the silica slurry of the present invention (silica particles / redispersibility improver) is preferably 100 / 0.1 or less from the viewpoint of improving the redispersibility of the silica particles, 100 / 0.2 or less is more preferable, 100 / 0.5 or less is more preferable, and from the same viewpoint, 100 / 20.0 or more is preferable, 100 / 10.0 or more is more preferable, and 100/5. 0 or more is more preferable.

  From the viewpoint of improving the redispersibility of the silica particles, the content of the redispersibility improver in the silica slurry of the present invention is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and 1.0% More preferably, the content is more than mass%, and from the viewpoint of economy, it is preferably 10.0 mass% or less, more preferably 8.0 mass% or less, and even more preferably 5.0 mass% or less.

[water]
The silica slurry of the present invention contains water as a medium. Examples of water include distilled water, ion exchange water, pure water, and ultrapure water. From the viewpoint of easy handling of the silica slurry, the content of water in the silica slurry is preferably 30% by mass or more, preferably 40% by mass or more, more preferably 50% by mass or more, and from the same viewpoint, 90 mass% or less is preferable, 80 mass% or less is more preferable, and 70 mass% or less is still more preferable.

[Other ingredients]
The silica slurry of the present invention may contain other components as necessary. Examples of other components include a pH adjuster, a thickener, a dispersant, a rust inhibitor, a basic substance, a polishing rate improver, a surfactant, and a polymer compound. The other components are preferably contained in the silica slurry as long as the effects of the present invention are not impaired. 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 preferable, 0.01% by mass or more is further preferable, 0.1% by mass or more is further more preferable, 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. When preparing the silica slurry of the present invention, a pH adjuster may be used as necessary. Examples of the pH adjuster include alkali compounds such as ammonia and inorganic alkali compounds such as potassium hydroxide and sodium hydroxide; organic alkali compounds such as alkylamine and alkanolamine; and the like. Among these, from the viewpoint of improving the redispersibility of the silica particles, 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.

[Alumina particles]
In the silica slurry of the present invention, the content of alumina particles is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and further 0.02% by mass or less from the viewpoint of reducing protrusion defects. Preferably, it is more preferable that the alumina particles are not substantially contained. In the present invention, “substantially free of alumina particles” means that no alumina particles are contained, no alumina particles functioning as abrasive grains are contained, or an amount of alumina particles that affects the polishing result. May not be included. The content of 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, and substantially 0% with respect to the total amount of abrasive grains in the silica slurry. It is still 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, still more preferably 9.0 or more, from the viewpoint of improving redispersibility of silica particles. 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 pH is preferably adjusted using the above-described pH adjusting agent. The above pH is the pH of the silica slurry at 25 ° C. and can be measured using a pH meter. Preferably, the pH is a value 30 seconds after the electrode of the pH meter is immersed in the polishing composition.

  The viscosity of the silica slurry of the present invention is preferably 10 mPa · s or more, more preferably 20 mPa · s or more, still more preferably 30 mPa · s or more, from the viewpoint of improving redispersibility of silica particles, and the same viewpoint To 10,000 mPa · s or less, more preferably 5,000 mPa · s or less, and even more preferably 1,000 mPa · s or less. The viscosity is a value in a silica slurry at 25 ° C.

[Method for producing polishing composition]
The polishing composition of the present invention is prepared by, for example, blending the silica slurry of the present invention, an acid, and, if desired, an oxidizing agent and other components by a known method, and adjusting the pH to 0.5 or more and 6.0 or less. , Preferably it can manufacture by setting it as 1.0-2.0. Therefore, this invention relates to the manufacturing method of the silica slurry used for manufacture of polishing liquid composition including the process of mix | blending a silica particle, a redispersibility improvement agent, and water at least. Further, the present invention includes a step of blending at least silica particles, a redispersibility improver and water, and the pH at 25 ° C. is 0.5 or more and 6.0 or less, preferably 1.0 or more and 2. It is related with the manufacturing method of polishing liquid composition including the process adjusted to 0 or less.

  In the present invention, “mixing” means mixing silica particles, redispersibility improver and water simultaneously or in any order, silica slurry, acid, and further, if necessary, oxidizing agent and other components simultaneously or arbitrarily. In order. The blending can be performed using, for example, a mixer such as a homomixer, a homogenizer, an ultrasonic disperser, and a wet ball mill. The preferable compounding quantity of each component in the manufacturing method of polishing liquid composition is the same as the preferable content of each component in polishing liquid composition.

The method for producing a polishing liquid composition of the present invention preferably includes the following steps from the viewpoint of dispersibility of silica particles.
Step 1: Step of mixing water, an acid, and optionally an oxidizing agent and other components to adjust an acidic aqueous solution having a pH of 6.0 or less Step 2: Mixing the acidic aqueous solution and silica slurry Step 1 The pH of the acidic aqueous solution obtained is preferably adjusted so that the pH of the polishing composition becomes a desired value.

[Polishing 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 coexistence of ensuring a high polishing rate and reducing long-period defects. 3 mass% or more is still more preferable, and 10 mass% or less is preferable from an economical viewpoint, 8 mass% or less is more preferable, and 6 mass% or less is still more preferable.

  The content of the redispersibility improver in the polishing composition of the present invention is preferably 0.001% by mass or more, and 0.01% by mass from the viewpoint of ensuring both high polishing rate and reducing long-period defects. The above is more preferable, 0.10% by mass or more is further preferable, 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 further preferable. preferable.

[PH]
The pH of the polishing composition of the present invention is preferably 0.5 or more, more preferably 0.7 or more, and still more preferably 0.9 or more, from the viewpoint of ensuring both high polishing rate and reducing long-period defects. 1.0 or more is still more preferable, 1.2 or more is still more preferable, 1.4 or more is further more preferable, and, from the same viewpoint, 6.0 or less is preferable, 4.0 or less is more preferable, 3.0 or less is still more preferable, 2.5 or less is still more preferable, and 2.0 or less is still more preferable. The pH is preferably adjusted using the acid described above and, if necessary, an oxidizing agent. The above pH is the pH of the polishing composition at 25 ° C., and the measuring method is the same as the measuring method of the pH of the silica slurry.

[acid]
The polishing composition of the present invention contains an acid from the viewpoint of coexistence of ensuring a high polishing rate and reduction of long-period defects, and adjusting the pH.

  Examples of the acid include nitric acid, sulfuric acid, sulfurous acid, persulfuric acid, hydrochloric acid, perchloric acid, amidosulfuric acid, phosphoric acid, polyphosphoric acid, phosphonic acid, and other inorganic acids; organic phosphoric acid, organic phosphonic acid, and other organic acids; etc. Is mentioned. Among these, from the viewpoint of ensuring both high polishing rate and reduction of long-period defects, at least one selected from phosphoric acid, sulfuric acid, and 1-hydroxyethylidene-1,1-diphosphonic acid is preferable. From sulfuric acid and phosphoric acid At least one selected 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 achieving both a high polishing rate and reducing long-period defects. 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, and 3.0% by mass. The following is more preferable, and 2.5% by mass or less is even more preferable.

[Oxidant]
The polishing composition of the present invention may contain an oxidant from the viewpoint of achieving both a high polishing rate and a reduction in long-period defects. 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, 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. From the viewpoint of preventing metal ions from adhering to the surface and the availability, hydrogen peroxide is more preferable. 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, further preferably 0.1% by mass or more, from the viewpoint of improving the polishing rate. And 4.0 mass% or less is preferable from a viewpoint of coexistence of the ensuring of a high grinding | polishing speed | rate and reduction of a long period defect, 2.0 mass% or less is more preferable, and 1.5 mass% or less is still more preferable.

[water]
The polishing composition of the present invention 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 is preferably 61% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, and 85% by mass from the viewpoint of easy handling of the polishing liquid composition. % Or more is more preferable, and from the same viewpoint, 99 mass% or less is preferable, 98 mass% or less is more preferable, and 97 mass% or less is still more preferable.

[Other ingredients]
The polishing composition of the present invention may contain other components as necessary. Examples of other components include thickeners, dispersants, rust inhibitors, basic substances, polishing rate improvers, surfactants, and polymer compounds. The other components are preferably contained in the polishing liquid composition within a range not impairing the effects of the present invention, and the content of the other components in the polishing liquid composition is preferably 0% by mass or more, More than 0 mass% is more preferable, 0.1 mass% or more is still more preferable, 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 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 of the present invention is prepared as a concentrate, the content of each component can be increased by the concentration.

[viscosity]
The viscosity of the polishing composition of the present invention is preferably 20.0 mPa · s or less, more preferably 10 mPa · s or less, and 9.0 mPa · s or less, from the viewpoint of achieving both a high polishing rate and reducing long-period defects. The following is more preferable, 7.0 mPa · s or less is still more preferable, and from the same viewpoint, 0.5 mPa · s or more is preferable, 1.0 mPa · s or more is more preferable, and 2.0 mPa · s or more is further Preferably, 3.0 mPa · s or more is even 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.

[Polishing liquid kit]
The polishing liquid kit of this invention is a kit for manufacturing polishing liquid composition, Comprising: It is related with the polishing liquid kit containing the silica slurry containing the said silica slurry containing the silica particle accommodated in the container. The polishing liquid kit of the present invention may further include an acidic aqueous solution having a pH of 6.0 or less housed in a container different from the silica slurry in the container. ADVANTAGE OF THE INVENTION According to this invention, even when the silica particle with a large particle diameter is used as an abrasive grain, the polishing liquid kit which can obtain the polishing liquid composition which can perform both ensuring of high polishing speed and reduction of a long period defect can be provided. .

  As the polishing liquid kit of the present invention, for example, an acidic aqueous solution (second liquid) containing a silica slurry (first liquid) containing the silica particles 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 composition include an acid and an oxidizing agent. 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 of the present invention is a substrate used for manufacturing a magnetic disk substrate. For example, a Ni-P plated aluminum alloy substrate, silicate glass, aluminosilicate glass, Examples thereof include glass substrates such as crystallized glass and tempered glass, and an aluminum alloy substrate plated with Ni—P is preferable from the viewpoint of strength and ease of handling. In the present invention, 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 produced 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 invention. 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 of the present invention is preferably used for polishing in the rough polishing step.

[Method of manufacturing magnetic disk substrate]
The present invention provides a method for producing a magnetic disk substrate, comprising a step of polishing a substrate to be polished using the polishing liquid composition of the present invention (hereinafter also referred to as “polishing step using the polishing liquid composition of the present invention”). (Hereinafter also referred to as “the method for producing a substrate of the present invention”).

  In the polishing step using the polishing liquid composition of the present invention, for example, the substrate to be polished is sandwiched by a surface plate to which a polishing pad is attached, the polishing liquid 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 the pad or the substrate to be polished.

  The polishing load in the polishing step using the polishing liquid composition of the present invention is preferably 30 kPa or less, more preferably 25 kPa or less, and even more preferably 20 kPa or less, from the viewpoint of reducing long-period defects without significantly impairing 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 “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 of the present invention, the polishing amount per 1 cm ^{2 of the} substrate to be polished is preferably 0.20 mg or more from the viewpoint of reducing long-period defects without significantly impairing the polishing rate. .30 mg or more is more preferable, 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 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 preferably 2.0 mL / min or less from the viewpoint of economy. Is more preferably 1.5 mL / min or less, 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, and 0 .05 mL / min or more is more preferable.

  As a method for supplying the polishing composition of the present invention to a polishing machine, for example, a method of continuously supplying using a pump or the like can be mentioned. When supplying the polishing 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 of the present invention.

  According to the substrate manufacturing method of the present invention, since long-period defects can be reduced without significantly reducing the polishing rate in rough polishing, an effect of efficiently manufacturing a magnetic disk substrate with reduced protrusion defects can be achieved.

[Polishing method]
The present invention relates to a magnetic disk substrate polishing method (hereinafter, also referred to as a polishing method according to the present disclosure) 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 significantly reducing the polishing rate in rough polishing, so that the productivity of a magnetic disk substrate with reduced protrusion defects can be improved. sell. The specific polishing method and conditions can be the same as those of the substrate manufacturing method of the present invention 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 Silica Slurry The silica slurries of Examples 1-8 and Comparative Example 1 were prepared using the abrasive grains (non-spherical silica particles A, spherical silica particles B), redispersibility improvers, and water shown in Table 1. The content of each component in the silica slurry is 40% by mass of silica particles, the redispersibility improver is the amount shown in Table 3, and the balance is water. The pH of the silica slurries of Examples 1-8 and Comparative Example 1 at 25 ° C. is 10. Details of the particles A and the particles B are as shown in Table 1.

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

2. Preparation of polishing liquid composition [Preparation of polishing liquid composition used for rough polishing]
An acid aqueous solution (pH = 1.4) was prepared by mixing an acid (phosphoric acid), an oxidizing agent (hydrogen peroxide), and water. Immediately after preparation of the silica slurry prepared by the method described in “1. Preparation of silica slurry” or after standing for 3 months, the silica slurries of Examples 1 to 8 and Comparative Example 1, phosphoric acid and hydrogen peroxide Polishing liquid compositions 1-9 were prepared by mixing an acidic aqueous solution containing water. The content of each component in the polishing composition 1-9 is 5.0% by mass for abrasive grains, 1.5% by mass for phosphoric acid, 0.8% by mass for hydrogen peroxide, and the redispersibility improver is As described in Table 3. The remaining amount is water. The pH of the polishing composition 1 to 9 at 25 ° C. is 1.6.

[Preparation of polishing composition C used for finish polishing]
Using the colloidal silica particles (abrasive grains a) shown in Table 2, sulfuric acid, hydrogen peroxide, and water, a polishing liquid composition C used for final polishing was prepared. The content of each component in the polishing liquid composition C was colloidal silica particles: 5.0 mass%, sulfuric acid: 0.5 mass%, and hydrogen peroxide: 0.5 mass%. The pH of the polishing composition C was 1.4. This polishing composition C was used in the finish polishing step described later. Details of the abrasive grains a are as shown in Table 2.

3. Measurement method of each parameter [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 measurement device (Micromeritic automatic specific surface area measurement device “Flowsorb III2305” manufactured by Shimadzu Corporation).
[Preprocessing]
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 primary particle diameter of silica particles by BET conversion]
The average primary particle diameter in terms of BET of silica particles was calculated from the following formula using the BET specific surface area S (m ² / g).
Average primary particle diameter (nm) = 2727 / S

[Measurement method of average secondary particle diameter of silica particles]
(1) Measuring method of average secondary particle diameter of silica particles A1 and B1 Silica particles were diluted with ion-exchanged water to prepare a dispersion containing 1% by mass of silica particles. And this dispersion liquid was thrown in into the following measuring apparatus, and the volume particle size distribution of the silica particle was obtained. The particle size (Z-average value) at which the cumulative volume frequency of the obtained volume particle size distribution was 50% was defined as the secondary particle size.
Measuring equipment: Malvern Zetasizer Nano “Nano S”
Measurement conditions: Sample volume 1.5 mL
: Laser He-Ne, 3.0 mW, 633n
: Scattered light detection angle 90 °

(2) Measuring method of average secondary particle diameter of silica particle A2 Using water as a dispersion medium, the sample is introduced into the following measuring device, and then a sample (silica particle A2) is introduced so that the transmittance is 75 to 95%. Then, after applying ultrasonic waves for 5 minutes, the particle size was measured.
Measuring instrument: Laser diffraction / scattering particle size distribution measuring device LA920 manufactured by Horiba, Ltd.
Circulation strength: 4
Ultrasonic intensity: 4

[Measuring method of average minor axis 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 analysis software (Mitani Corporation “WinROOF (Ver. 3. 6) ”) was used to analyze the projected images of 500 silica particles as follows.
The minor axis and major axis of each silica particle were determined, and the average value of the minor axis (average minor axis) 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

[D10, D50, and D90 of abrasive grains a]
A 1% by mass dispersion obtained by diluting the abrasive grains a with ion-exchanged water was put into the following measuring apparatus to obtain a volume particle size distribution of the silica abrasive grains.
Measuring 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 °
The particle sizes at which the cumulative volume frequency of the obtained volume particle size distribution becomes 10%, 50%, and 90% were defined as D10, D50 (volume average particle diameter), and D90, respectively.

4). Redispersibility The redispersibility of silica particles in a silica slurry was evaluated by the sedimentation rate (%). The sedimentation rate is the ratio of the sedimentation amount (g) to the total solid content when the total solid content is 100. The silica slurry, which was allowed to stand for 3 months after the preparation, was shaken for 30 seconds with a shaking machine (“MW-YS” manufactured by Miyamoto Riken Kogyo Co., Ltd.) at a rotational speed of 100 rpm, and the remaining amount after removing the supernatant was settled. It was. The smaller the sedimentation rate, the better the redispersibility of the silica slurry.
[Evaluation criteria]
A: Sedimentation rate 0% or more and less than 1% B: Sedimentation rate 1% or more and less than 3% C: Sedimentation rate 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 for each step are shown below. Step (3) was performed with 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 1-9.
(2) Cleaning step: A step of cleaning the substrate obtained in step (1).
(3) Final polishing step: A step of polishing the polishing target surface of the substrate obtained in step (2) using the polishing composition C.

[Polished substrate]
The substrate to be polished was an aluminum alloy substrate plated with Ni-P. This substrate to be polished had a thickness of 1.27 mm and a diameter of 95 mm.

[Step (1): Rough polishing]
Polishing machine: Double-side polishing machine (9B-type double-side polishing machine, manufactured by Speed Fam Co., Ltd.)
Number of substrates to be polished: 10 polishing liquid: polishing liquid compositions 1-9
Polishing pad: Suede type (foam 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 liquid supply amount: 100 mL / min (0.076 mL / min per 1 cm ^{2 of} substrate surface to be polished)
Equivalent to
Polishing time: 6 minutes

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

[Step (3): Final polishing]
Polishing machine: double-side polishing machine (9B type double-side polishing machine, manufactured by Speedfam Co., Ltd.), polishing machine separate from the polishing machine used in step (1) Number of substrates to be polished: 10 polishing liquid: polishing liquid composition C
Polishing pad: Suede type (foam 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} substrate surface to be polished)
Polishing time: 2 minutes After the step (3), washing was performed. The washing conditions were the same as in the above 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 (measured by Sartorius, “BP-210S”), and the amount of mass reduction was determined from the change in mass of each substrate. The value obtained by dividing the average mass reduction amount of all 10 sheets by the polishing time was calculated as the polishing rate by the following formula, and the results are shown in Table 3.
Weight loss (g) = {mass before polishing (g) −mass after polishing (g)}
Polishing speed (mg / min) = mass reduction amount (mg) / polishing time (min)

Further, the rate of decrease in speed (%) was calculated by the following formula, and the results are shown in Table 3.
Rate decrease rate (%) = Polishing rate after standing for 100-3 months ÷ Polishing rate immediately after production × 100
Rate reduction rate: Evaluation −5% or more and less than 5%: “A: Excellent polishing rate and further improvement in substrate yield can be expected”
5% or more and less than 10%: “B: Good polishing rate and expected improvement in substrate yield”
10% or more: “C: Actual production needs improvement”

[Method for evaluating long-period defects on substrate surface after step (1)]
After performing the step (2) on both surfaces (total of 20 points) of the 10 substrates after the polishing in the step (1), the measurement was performed under the following conditions to obtain the long-period defect occurrence rate (%). When a small spot that can be confirmed with the naked eye on the substrate surface is PED and even one spot can be confirmed on the substrate surface, the surface is considered to have a long-period defect.
Long-period defect rate (%)
= (Number of substrate surfaces on which long-period defects are generated / 20) × 100
The long-period defect occurrence rate was evaluated in five stages according to the following criteria. That is, the larger the value, the lower the occurrence rate of long-period defects. The results are shown in Table 3.

[Evaluation criteria]
Long-period defect occurrence rate: Evaluation: 10% or less: “5: generation is extremely suppressed, and improvement in substrate yield can be expected”
Over 10% and below 20%: “4: Real production possible”
Over 20% and below 30%: “3: Improvement is required for actual production”
More than 30% and 50% or less: “2: Substrate yield decreases significantly”
More than 50%: “1: Far from actual production (same level as when using general silica abrasive grains)”
[measuring equipment]
Optical interference type surface shape measuring machine: “OptiFLAT III” (manufactured by KLA Tencor) Radius Inside / Out: 14.87 mm / 47.83 mm
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

[Alumina residue evaluation method]
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-stage evaluation was performed.
A: No alumina residue is observed on the surface B: A slight alumina residue is observed on the surface C: Alumina residue is observed on the surface

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

  When Examples 1-8 are compared with Comparative Example 1, the silica slurry of Examples 1-8 has a significantly lower sedimentation rate than the silica slurry of Comparative Example 1, and includes a redispersibility improver. This improves the redispersibility of the silica particles.

  Moreover, when the abrasive | polishing agent composition prepared using the silica slurry immediately after manufacture is used, about Example 1-8 and the comparative example 1, although a remarkable difference is not looked at at a grinding | polishing rate, it is 3 months from manufacture. When using the abrasive | polishing agent composition prepared using the silica slurry after stationary, in Comparative Example 1, although the grinding | polishing speed fell notably, in Examples 1-8, there was almost no change. Moreover, when using the abrasive | polishing agent composition prepared using the silica slurry after standing for 3 months from manufacture, the direction of Examples 1-8 is more remarkable than the comparative example 1 in the incidence of long-period defects. It was low.

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

Claims (12)

A silica slurry used in the preparation of a polishing composition for a magnetic disk substrate having a pH at 25 ° C. of 0.5 or more and 6.0 or less,
Silica particles, a redispersibility improver, and water,
The average primary particle diameter of the silica particles is 80 nm or more,
The average secondary particle diameter of the silica particles is 130 nm or more and 580 nm or less,
The redispersibility improver is a water-swellable inorganic layered compound,
A silica slurry having a pH at 25 ° C. of 8.0 or more and 12.0 or less.   The silica slurry according to claim 1, wherein the water-swellable inorganic layered compound is at least one selected from bentonite, hectorite, and saponite.   The silica slurry according to claim 1 or 2, wherein the silica particles include non-spherical silica particles.   The silica slurry according to claim 3, wherein the nonspherical silica particles have an average sphericity of 0.85 or less.   The silica slurry according to claim 3 or 4, wherein the silica particles further contain spherical silica particles.   The silica slurry according to claim 5, wherein a mass ratio (A / B) between the non-spherical silica particles and the spherical silica particles is 10/90 or more and 99/1 or less.   The silica slurry according to any one of claims 1 to 6, wherein the content of alumina particles is 0% by mass or more and 0.1% by mass or less.   The silica slurry (first liquid) according to any one of claims 1 to 7, and an acidic aqueous solution (second liquid) housed in a container different from the silica slurry, wherein the first liquid A polishing liquid kit capable of producing a polishing liquid composition for a magnetic disk substrate having a pH at 25 ° C. of from 0.5 to 6.0 when mixed with the second liquid.   A polishing liquid composition for a magnetic disk substrate, comprising a step of mixing the silica slurry according to any one of claims 1 to 7 with an acid to adjust the pH at 25 ° C to 0.5 or more and 6.0 or less. Manufacturing method.   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 prepared using the silica slurry according to any one of claims 1 to 7.   The method of manufacturing a magnetic disk substrate according to claim 10, wherein the substrate to be polished is a Ni—P plated aluminum alloy substrate. A step of polishing a substrate to be polished using a polishing composition for a magnetic disk substrate prepared using the silica slurry 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.