Method of manufacturing magnetic disk substrate polishing liquid

Abstract

To provide a method of manufacturing a magnetic disk substrate polishing liquid, which enables both improvement in quality of the magnetic disk substrate polishing liquid and extension of filter life.SOLUTION: An aspect of the present invention relates to a method of manufacturing a magnetic disk substrate polishing liquid containing silica particles (component A) and water, the method comprising a step of filtering a treatment target silica dispersion containing silica particles (component A) and water using a membrane filter to obtain a filtered silica dispersion, where the membrane filter has an average pore diameter of 2.4 μm or less and an average aperture ratio of 10% or greater.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a polishing liquid for a magnetic disk substrate, a method for manufacturing a magnetic disk substrate, and a method for suppressing clogging of a filter in the manufacture of a polishing liquid for a magnetic disk substrate.

Background Art

[0002] In recent years, magnetic disk drives have been miniaturized and increased in capacity, and further higher recording density has been demanded. To achieve this, reduction of the unit recording area has been advanced. In order to improve the detection sensitivity of the weakened magnetic signal, technological development to lower the flying height of the magnetic head has been advanced. Therefore, for the magnetic disk substrate, in order to cope with the reduction of the flying height of the magnetic head and the securing of the recording area, the requirements for improving smoothness and flatness represented by the reduction of surface roughness, waviness, and end face sag (roll-off), and the reduction of defects represented by the reduction of scratches, protrusions, pits, etc. have become stricter. Also, in the semiconductor field, high integration and high speed are progressing. Particularly in high integration, miniaturization of wiring is required. As a result, in the manufacturing process of semiconductor substrates, the depth of focus when exposing photoresist becomes shallow, and even higher surface smoothness is desired.

[0003] In response to such requirements, Patent Document 1 proposes an asymmetric microporous membrane suitable for high-throughput application examples, which has a network-like porous surface and contains a polymer material having a bubble point normalized serum retention time of less than about 2, as a membrane suitable for filtration of a large amount of fluid and high-speed filtration of a fixed amount of liquid.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] With the increase in the storage capacity of magnetic disk drives, the required characteristics for the surface quality of the substrate have become even more stringent. Therefore, the importance of the polishing process in the manufacture of the substrate is increasing, and the quality of the polishing liquid used in the polishing process is the key. One of the causes of scratches, which are one of the defects on the surface of the substrate of a magnetic disk drive, is the coarse particles contained in the polishing liquid. Usually, the coarse particles in the polishing liquid are removed by filtration in the manufacturing process. In the filtration of the polishing liquid, there is a problem of a trade-off between the quality of the obtained polishing liquid (for example, the small amount of coarse particles) and the long life of the filter used in the manufacture of the polishing liquid. That is, if the aperture of the filter used in the manufacturing process is reduced to improve the quality of the obtained polishing liquid, the filter is likely to be clogged and the filter life is shortened. On the other hand, if the pore diameter of the filter is increased to extend the filter life, it becomes difficult to ensure the quality of the silica dispersion liquid after filtration.

[0006] Therefore, in one aspect, the present disclosure provides a method for manufacturing a polishing liquid for a magnetic disk substrate that can achieve both the quality of the obtained polishing liquid and the long life of the filter.

Means for Solving the Problems

[0007] In one aspect, the present disclosure relates to a method for manufacturing a polishing liquid for a magnetic disk substrate containing silica particles (component A) and water, the method including a step of filtering a silica dispersion liquid to be treated containing silica particles (component A) and water with a membrane filter to obtain a silica dispersion liquid after filtration, wherein the average pore diameter of the membrane filter is 2.4 μm or less and the average aperture ratio of the membrane filter is 10% or more.

[0008] In one aspect, the present disclosure relates to a method for manufacturing a magnetic disk substrate, which includes a step of manufacturing a polishing liquid for a magnetic disk substrate by the method for manufacturing a polishing liquid for a magnetic disk substrate of the present disclosure, and a step of supplying the polishing liquid for a magnetic disk substrate obtained in this step to a surface to be polished of a substrate to be polished, bringing a polishing pad into contact with the surface to be polished, and moving one or more selected from the polishing pad and the substrate to be polished to polish the surface to be polished.

[0009] In one aspect, the present disclosure is a method for suppressing clogging of a filter used in a filtration step in the manufacture of a polishing liquid for a magnetic disk substrate containing silica particles (component A) and water. The filtration step includes a step of filtering with a membrane filter, the average pore diameter of the membrane filter is 2.4 μm or less, and the average aperture ratio of the membrane filter is 10% or more.

Advantages of the Invention

[0010] According to the present disclosure, in one aspect, it is possible to provide a method for manufacturing a polishing liquid for a magnetic disk substrate that can achieve both an improvement in the quality of the obtained polishing liquid and an extended service life of the filter.

Embodiments for Carrying Out the Invention

[0011] The present disclosure is based on the finding that in a method for manufacturing a polishing liquid for a magnetic disk substrate, by having a step of filtering a silica dispersion to be treated using a membrane filter having a specific average pore diameter and average aperture ratio, the quality of the silica dispersion after filtration can be improved, and both an improvement in the quality of the obtained polishing liquid for a magnetic disk substrate and an extended service life of the filter used in the manufacture of the polishing liquid for a magnetic disk substrate can be realized.

[0012] That is, in one aspect, the present disclosure relates to a method for manufacturing a polishing liquid for a magnetic disk substrate containing silica particles (component A) and water, the method including a step of filtering a silica dispersion to be treated containing silica particles (component A) and water through a membrane filter to obtain a silica dispersion after filtration, wherein the average pore diameter of the membrane filter is 2.4 μm or less, and the average aperture ratio of the membrane filter is 10% or more (hereinafter, the manufacturing method is also referred to as "the manufacturing method of the present disclosure"). According to the present disclosure, it is possible to provide a method for manufacturing a polishing liquid for a magnetic disk substrate that can extend the service life of a filter in the manufacture of the polishing liquid for a magnetic disk substrate without deteriorating the quality of the obtained polishing liquid for a magnetic disk substrate.

[0013] Although the details of the mechanism of the effect manifestation in the manufacturing method of the present disclosure are not clear, it is presumed as follows. In the manufacture of a polishing liquid for a magnetic disk substrate, in order to increase the efficiency of removing coarse particles derived from silica particles (component A) contained in the polishing liquid for a magnetic disk substrate by filtration, one method is to reduce the mesh size of the filter used for filtration. When the filter used for filtration is a membrane filter, it is necessary to reduce the average pore diameter of the membrane filter. However, when the average pore diameter is reduced, there is a problem that the captured coarse particles easily block the pores of the membrane filter, and the filter becomes clogged prematurely. In the present disclosure, by setting the average pore diameter to 2.4 μm or less and the average aperture ratio of the membrane filter to 10% or more, it is possible to increase the number of pores while keeping the average pore diameter small, so that a flow path for the silica dispersion can be secured, and it is considered that both the quality of the silica dispersion after filtration and the extended service life of the filter used in the filtration step can be achieved. However, the present disclosure should not be construed as being limited to these mechanisms.

[0014] In the present disclosure, "coarse particles" refer to coarse silica particles having a particle diameter of 0.5 μm or more. The number of coarse particles in the silica dispersion can be evaluated by the amount of liquid passing through the filter described in the examples below. The larger the amount of liquid passing through, the smaller the number of coarse particles in the silica dispersion, which means higher dispersibility and filtration accuracy. In the present disclosure, the coarse silica particles in the silica dispersion include not only primary particles but also aggregated particles formed by aggregation of primary particles.

[0015] In the present disclosure, "scratch" refers to a physical property that is particularly important for high density or high integration in a memory hard disk substrate or a semiconductor element substrate, and is a fine scratch on the substrate surface with a depth of 1 nm or more and less than 100 nm, a width of 5 nm or more and less than 500 nm, and a length of 100 μm or more. This scratch can be detected by an optical surface defect inspection machine (OSA6100: manufactured by KLA-Tencor) described in the examples below and can be quantitatively evaluated as the number of scratches. Furthermore, the depth and width can be measured using an atomic force microscope (AFM).

[0016] [Filtration step] In one or more embodiments, the manufacturing method of the present disclosure includes a step of filtering a silica dispersion to be treated containing silica particles (component A) and water with a membrane filter having an average pore diameter of 2.4 μm or less and an average aperture ratio of 10% or more (hereinafter, also simply referred to as "the filtration step of the present disclosure").

[0017] (Membrane filter) In the present disclosure, the membrane filter belongs to a so-called surface type in which filtration is performed on the surface of the filter, and the filter medium is in a film shape and has pores (holes) of a certain diameter. In the present disclosure, examples of the filter material of the membrane filter preferably include polyethersulfone (PES), polytetrafluoroethylene (PTFE), nylon, polysulfone (PS), polyvinylidene fluoride, and cellulose derivatives. Among these, one selected from polyethersulfone and polysulfone is more preferable, and polyethersulfone is even more preferable. In the present disclosure, the thickness of the membrane filter layer is preferably 0.05 μm or more, more preferably 0.10 μm or more, and preferably 0.20 μm or less, more preferably 0.15 μm or less. In one or more embodiments, the membrane filter used in the filtration step of the present disclosure is a membrane filter having an average pore diameter of 2.4 μm or less and an average aperture ratio of 10% or more. In the present disclosure, the average pore diameter is the average value of the diameters of the pores of the membrane filter, and the average aperture ratio is the ratio occupied by the pore portion in the membrane filter expressed as a percentage (%) of the area. In the present disclosure, the average pore diameter and the average aperture ratio refer to those on the side (primary side) where the filtrate of the membrane filter flows in. The membrane filter having an average pore diameter of 2.4 μm or less and an average aperture ratio of 10% or more (hereinafter, also referred to as "the membrane filter of the present disclosure") used in the filtration step of the present disclosure can secure a flow path for the silica dispersion liquid because the average pore diameter is 2.4 μm or less and the average aperture ratio is 10% or more, and can achieve both the quality of the silica dispersion liquid after filtration and the long life of the filter used in the filtration step.

[0018] From the viewpoint of extending the life of the filter, the average pore diameter (APD, unit: μm) of the membrane filter of the present disclosure is preferably 0.1 μm or more, more preferably 0.3 μm or more, still more preferably 0.5 μm or more, and from the viewpoints of maintaining the quality of the silica dispersion liquid after filtration and reducing coarse particles, it is 2.4 μm or less, preferably 1.5 μm or less, more preferably 1.2 μm or less, still more preferably 1.0 μm or less. The average pore diameter can be measured by the method described in the examples. The average pore diameter can be selected from membrane filters satisfying the above average pore diameter from off-the-shelf products, or adjusted by adjusting the conditions during film formation.

[0019] The average aperture ratio (AAR, unit: %) of the membrane filter of the present disclosure is 10% or more, preferably 15% or more, more preferably 18% or more, still more preferably 20% or more, from the viewpoint of extending the life of the filter. From the viewpoints of maintaining the quality of the silica dispersion after filtration and reducing coarse particles, it is preferably 50% or less, more preferably 30% or less, and still more preferably 25% or less. The average aperture ratio can be measured by the method described in the examples. The average aperture ratio can be adjusted by selecting a membrane filter that satisfies the above average aperture ratio from off-the-shelf products or by adjusting the conditions during preparation.

[0020] When the average pore diameter of the membrane filter of the present disclosure is APD (unit: μm) and the average aperture ratio is AAR (unit: %), the value represented by the formula: (AAR) / (APD) is preferably 10 or more, more preferably 14 or more, still more preferably 20 or more, from the viewpoints of extending the filter life and maintaining the quality of the silica dispersion after filtration. And it is preferably 50 or less, more preferably 40 or less, and still more preferably 30 or less.

[0021] From the viewpoints of maintaining the quality of the silica dispersion after filtration and extending the life of the filter, the membrane filter of the present disclosure may be a pleated filter (hereinafter, also simply referred to as "pleated filter") having a membrane filter layer with an average pore diameter of 2.4 μm or less and an average aperture ratio of 10% or more. Examples of the pleated filter with an average pore diameter of 2.4 μm or less and an average aperture ratio of 10% or more include those obtained by shaping a membrane that satisfies the above average pore diameter and average aperture ratio into a corrugated (pleated) shape to form a hollow cylindrical cartridge type. The pleated filter is preferable because it can increase the filtration area and thus improve the filtration efficiency.

[0022] The membrane filter may be used in a single stage or in multiple stages (for example, in a series arrangement).

[0023] In the filtration process of the present disclosure, the filtration pressure is preferably 0.16 MPa or more, more preferably 0.18 MPa or more, still more preferably 0.20 MPa or more, from the viewpoints of maintaining the quality of the silica dispersion after filtration, extending the life of the filter, and improving productivity, and, from the same viewpoints, is preferably 0.49 MPa or less, more preferably 0.45 MPa or less, still more preferably 0.40 MPa or less, still more preferably 0.30 MPa or less. In the present disclosure, the "filtration pressure in the filtration process of the present disclosure" refers to the difference between the pressure on the side (primary side) where the filtrate of the membrane filter of the present disclosure flows in and the pressure on the side (secondary side) where the filtrate flows out, and in one or more embodiments, the filtration pressure in the filtration process of the present disclosure can be adjusted by adjusting the pressure applied to the primary side.

[0024] In the filtration process of the present disclosure, the filtration flow rate is preferably 40.0 kg / (min·m 2 ) or more, more preferably 50.0 kg / (min·m 2 ) or more, still more preferably 60.0 kg / (min·m 2 ) or more, from the viewpoints of maintaining the quality of the silica dispersion after filtration, extending the life of the filter, and improving productivity, and, from the same viewpoints, is preferably 120.0 kg / (min·m 2 ) or less, more preferably 100.0 kg / (min·m 2 ) or less, still more preferably 80.0 kg / (min·m 2 ) or less. In the present disclosure, the "filtration flow rate in the filtration process of the present disclosure" refers to the mass per unit time filtered per unit area of the membrane filter of the present disclosure, and the unit is kg / (min·m 2 ). In one or more embodiments, it can be adjusted by adjusting the valve on the secondary side (the side where the filtrate flows out), which is the outlet of the filter.

[0025] As a filtration method in the filtration process of the present disclosure, a cyclic filtration method that repeats filtration or a one-pass method may be used. Also, a batch method that repeats the one-pass method may be used. As for the liquid passing method, in order to apply pressure, in the cyclic method, a pump is preferably used. In the one-pass method, in addition to using a pump, a pressure filtration method with a small fluctuation range of the filter inlet pressure can be used by introducing air pressure or the like into the tank.

[0026] (Filter containing filter aid) In other one or more embodiments of the production method of the present disclosure, from the viewpoints of reducing coarse particles, maintaining the quality of the silica dispersion after filtration, and extending the life of the filter, it is preferable to have a step of filtering using a filter containing a filter aid before the filtration step of the present disclosure. Therefore, the production method of the present disclosure may include the following steps (1) and (2) in other one or more embodiments. (1) Step of filtering the silica dispersion to be treated with a filter containing a filter aid (2) Step of filtering the silica dispersion obtained in step (1) with the membrane filter of the present disclosure The filter containing a filter aid is a filter containing at least a filter aid.

[0027] Examples of the filter aid include insoluble mineral substances such as silicon dioxide, kaolin, acid clay, diatomaceous earth, perlite, bentonite, and talc. Among the filter aids, from the viewpoint of improving productivity, silicon dioxide, diatomaceous earth, and perlite are preferable, diatomaceous earth and perlite are more preferable, and diatomaceous earth is even more preferable.

[0028] From the viewpoints of maintaining the quality of the silica dispersion liquid after filtration, reducing coarse particles, reducing scratches, and extending the filter life, it is preferable that the filter aid is pretreated with an acid. The pretreatment with an acid refers to a process of immersing the filter aid in an acid aqueous solution such as an inorganic acid or an organic acid for a certain period of time. In one or more embodiments, examples include treatment with hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, phosphonic acid, oxalic acid, citric acid, etc. From the same viewpoints, treatment with hydrochloric acid, sulfuric acid, nitric acid, or phosphonic acid is more preferable, and treatment with hydrochloric acid, sulfuric acid, or phosphonic acid is even more preferable.

[0029] Examples of the filter material of the filter aid-containing filter include paper, polyethylene, polypropylene, polyethersulfone, cellulose acetate, nylon, polycarbonate, plastics such as Teflon (registered trademark), ceramics, metal meshes, etc. From the viewpoint of maintaining the quality of the silica dispersion liquid after filtration, plastics such as paper, polyethylene, polypropylene, polyethersulfone, cellulose acetate, nylon, polycarbonate, Teflon (registered trademark) are preferable, paper, polyethylene, polypropylene, polyethersulfone, cellulose acetate, nylon are more preferable, and paper, polyethylene, polypropylene are even more preferable.

[0030] The shape of the filter aid-containing filter is not particularly limited, but from the viewpoints of ease of handling and maintaining the quality of the silica dispersion liquid after filtration, a sheet type, cylindrical type, disk type, or folded type is preferable, a sheet type, disk type, or folded type is more preferable, and a disk type or folded type is even more preferable.

[0031] From the viewpoints of improving filtration accuracy and productivity, the number of stages of the filter aid-containing filter is preferably 1 to 5 stages, more preferably 1 to 3 stages, and even more preferably 1 to 2 stages.

[0032] (Depth filter) In other one or more embodiments, from the viewpoints of reducing coarse particles, maintaining the quality of the silica dispersion after filtration, and extending the service life of the filter, the manufacturing method of the present disclosure preferably includes a step of filtering using a depth filter before the filtration step of the present disclosure. Therefore, in other one or more embodiments, the manufacturing method of the present disclosure may include the following steps (1') and (2'). (1') A step of filtering the silica dispersion to be treated with a depth filter (2') A step of filtering the silica dispersion obtained in step (1') with the membrane filter Here, the depth filter means a type of filter in which filtration is performed inside the filter. More specifically, it means a filter having a characteristic that the aperture of the filter medium is coarse on the filtrate inlet side, fine on the outlet side, and becomes continuously or stepwise finer from the inlet side to the outlet side. Therefore, among the coarse particles, large particles are collected near the inlet side, and small particles are collected near the outlet side. Examples of the shape of the depth filter include a bag type and a cartridge type with a hollow cylindrical shape. In addition, a material obtained by forming the filter medium having the above characteristics into a pleated shape has the function of a depth filter and is thus classified as a depth filter. Examples of commercially available depth filters include bag type (Bag 500 series of 3M), cartridge type (TCPD series of Advantec Toyo Co., Ltd., Profile II series of Nippon Pall Co., Ltd., GPJ series of 3M, Wave Star II series of Daiwa Bow Co., Ltd., SHP type manufactured by Rocktechno Co., Ltd.).

[0033] The depth filter may be used in one stage, or the same filter may be used in combination in series with two or more, or depth filters with different pore diameters may be combined so that the filtrate passes through in the order from the one with a larger pore size to the one with a smaller pore size, which is also a pre-filtration step using a depth filter. Furthermore, these may be used in combination with a bag type and a cartridge type.

[0034] From the viewpoints of improving productivity and extending the filter life, the aperture of the depth-type filter is preferably 0.1 μm or more. From the viewpoints of maintaining the quality of the silica dispersion after filtration and reducing coarse particles, it is preferably 5.0 μm or less, more preferably 3.0 μm or less, still more preferably 2.0 μm or less, even more preferably 1.0 μm or less, and even more preferably 0.5 μm or less.

[0035] In the production method of the present disclosure, in addition to using the membrane filter of the present disclosure, a general dispersion step or particle removal step may be provided. For example, a dispersion step using a high-pressure dispersion device such as a high-speed dispersion device or a high-pressure homogenizer, or a sedimentation step of coarse particles using a centrifugal separator or the like can also be used. When processing using these, each can be processed alone or in combination of two or more, and there is no limitation on the processing order of the combination. Also, the processing conditions and the number of processing times can be appropriately selected and used.

[0036] [Silica dispersion to be treated] In the present disclosure, the "silica dispersion to be treated" refers to a silica dispersion (silica slurry) in which silica particles (component A) are dispersed in water before being subjected to the filtration treatment in the filtration step in one or more embodiments. That is, the silica dispersion to be treated in the present disclosure contains silica particles (component A) and water in one or more embodiments. The silica dispersion to be treated in the present disclosure may further contain one or more selected from an acid (component B), an oxidizing agent (component C), a heterocyclic aromatic compound (component D), an amine compound (component E), and an anionic water-soluble polymer (component F), which are preferably used as other components that can be blended into the polishing liquid for a magnetic disk substrate described later. In the production method of the present disclosure, it is more preferable that the silica dispersion to be treated consists of silica particles and water.

[0037] In the manufacturing method of the present disclosure, specifically, a method of subjecting a silica dispersion to be treated containing silica particles (component A), water, and other components that can be blended into a polishing liquid for a magnetic disk substrate, if necessary, to the filtration step of the present disclosure, or a method of subjecting a silica dispersion to be treated containing silica particles (component A) and water to the filtration step of the present disclosure, and then mixing other components that can be blended into a polishing liquid for a magnetic disk substrate with the obtained silica dispersion after filtration, is preferably selected from among them. Among these, from the viewpoint of enhancing the quality of the obtained polishing liquid for a magnetic disk substrate, a method of subjecting a silica dispersion to be treated containing silica particles (component A) and water to the filtration step of the present disclosure, and then mixing other components that can be blended into a polishing liquid for a magnetic disk substrate with the obtained silica dispersion after filtration is more preferable.

[0038] <Silica particles (component A) contained in the silica dispersion to be treated> In the present disclosure, as the silica particles (hereinafter also simply referred to as "component A") contained in the silica dispersion to be treated, from the viewpoints of improving the polishing rate and reducing the scratchability of the polishing liquid, colloidal silica, fumed silica, pulverized silica, silica obtained by surface-modifying them, and the like can be mentioned. Among these, colloidal silica is preferable. Colloidal silica can be obtained, for example, by a production method of generating it from an aqueous silicic acid solution. Further, those obtained by surface-modifying or surface-modifying these particles with a functional group, and those obtained by forming composite particles with a surfactant or other inorganic compounds can also be used. Component A may be one kind or a combination of two or more kinds.

[0039] The shape of component A may be spherical or non-spherical. As the usage form of component A, it is preferable that component A is a silica slurry dispersed in a medium containing water.

[0040] The average primary particle diameter of Component A is preferably 1 nm or more, more preferably 3 nm or more, still more preferably 5 nm or more, even more preferably 10 nm or more, and even more preferably 12 nm or more, from the viewpoints of improving polishing rate, productivity, and scratch reduction property of the polishing liquid. From the same viewpoints, it is preferably 100 nm or less, more preferably 80 nm or less, still more preferably 50 nm or less, even more preferably 30 nm or less, even more preferably 25 nm or less, and even more preferably 20 nm or less. In the present disclosure, the average primary particle diameter of Component A is calculated from the amount of silanol calculated by potentiometric titration. Specifically, the average primary particle diameter can be measured by the method described in the Examples.

[0041] The content of Component A in the silica dispersion to be treated is preferably 1% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, and even more preferably 15% by mass or more, from the viewpoint of improving productivity in the production method of the present disclosure. From the viewpoint of scratch reduction of the obtained polishing liquid, it is preferably 50% by mass or less, more preferably 45% by mass or less, and still more preferably 40% by mass or less.

[0042] [Water contained in the silica dispersion to be treated] Examples of the water contained in the silica dispersion to be treated include ion-exchanged water, distilled water, and ultrapure water. The content of water in the silica dispersion to be treated can be the remainder obtained by subtracting Component A and other components contained as necessary from 100% by mass.

[0043] [pH of the silica dispersion to be treated] The pH of the treated silica dispersion is, in one or more embodiments, preferably 8.5 or higher, more preferably 8.8 or higher, still more preferably 9.0 or higher, from the viewpoints of productivity improvement and scratch reduction property of the polishing liquid, and is preferably 11 or lower, more preferably 10.8 or lower, still more preferably 10.5 or lower. The pH of the treated silica dispersion can be adjusted by a known pH adjuster. Preferred pH adjusters include sodium hydroxide, potassium hydroxide, ammonia, and tetramethylammonium hydroxide. In the present disclosure, the pH is the value at 25°C and is the value measured using a pH meter. Specifically, it can be measured by the method described in the examples.

[0044] [Silica dispersion after filtration] The silica dispersion after filtration is a silica dispersion obtained by subjecting the treated silica dispersion to the filtration step of the present disclosure. By including the silica dispersion after filtration in the polishing liquid for a magnetic disk, a polishing liquid for a magnetic disk capable of manufacturing a substrate with reduced scratches can be obtained.

[0045] A suitable pH of the silica dispersion after filtration is the same as that of the treated silica dispersion described above. The pH of the silica dispersion after filtration can be measured in the same manner as the treated silica dispersion described above.

[0046] The content and pH of each component in the silica dispersion after filtration are preferably substantially the same as those of the treated silica dispersion except for coarse particles. In the present disclosure, "the content and pH of each component are substantially the same" means that the composition of the treated silica dispersion and the silica dispersion after filtration does not change except for the number of coarse particles.

[0047] The filter throughput (g) of the silica dispersion after filtration is preferably 1 g or more, more preferably 50 g or more, still more preferably 100 g or more, even more preferably 150 g or more, even more preferably 162 g or more, and even more preferably 180 g or more from the viewpoint of improving the quality of the polishing liquid for magnetic disk substrates to be obtained. From the viewpoint of improving productivity, it is preferably 3,000 g or less, more preferably 2,000 g or less, and still more preferably 1,500 g or less. In the present disclosure, as a method for measuring the filter throughput, the silica dispersion after filtration is put into a container or syringe equipped with a predetermined filter, and the silica dispersion after filtration is passed through the filter by applying pressure or decompression, and the throughput until the filter is blocked is measured. In the present disclosure, a membrane filter with a pore size of 0.20 μm is used as the predetermined filter. In the present disclosure, the filter throughput can be calculated by the method described in the examples.

[0048] The silica dispersion after filtration can be applied to various fields such as abrasives, coating agents, fillers, ceramic binders, catalyst carriers, and adsorbents. Furthermore, the silica dispersion after filtration can be suitably used as abrasive grains of a polishing liquid used for polishing a substrate to be polished such as a semiconductor substrate or a magnetic disk substrate.

[0049] Generally, a polishing liquid is prepared by blending raw silica, water, and additives as required. Therefore, the production method of the present disclosure can include, in one or more embodiments, a step of blending the silica dispersion after filtration, water, and additives after the filtration step of the present disclosure. In the present disclosure, "blending" includes mixing the silica dispersion after filtration, water, and additives as required simultaneously or in any order. The blending can be performed using a mixer such as a homomixer, homogenizer, ultrasonic disperser, and wet ball mill. That is, the production method of the present disclosure preferably has a step of further mixing at least one selected from an acid, an oxidizing agent, a heterocyclic aromatic compound, an amine compound, and an anionic water-soluble polymer with the silica dispersion after filtration. In the present disclosure, the additive refers to components other than silica particles (component A) and water that can be blended into the polishing liquid used for polishing the substrate to be polished. Examples of components other than silica particles (component A) and water include, for example, an acid (component B), an oxidizing agent (component C), a heterocyclic aromatic compound (component D), an amine compound (component E), and an anionic water-soluble polymer (component F) described later.

[0050] [Polishing Liquid for Magnetic Disk Substrate] In one aspect, the present disclosure relates to a polishing liquid for a magnetic disk substrate obtained by the production method of the present disclosure (hereinafter, the polishing liquid is also referred to as "the polishing liquid of the present disclosure"). In one or more embodiments, the polishing liquid of the present disclosure further includes one or more selected from an acid (component B), an oxidizing agent (component C), a heterocyclic aromatic compound (component D), an amine compound (component E), and an anionic water-soluble polymer (component F) in addition to silica particles (component A) and water. The polishing liquid of the present disclosure is obtained by filtering silica particles (component A) and water in the filtration step of the present disclosure to obtain a filtered silica dispersion, and further blending other components that can be blended into the polishing liquid for a magnetic disk substrate. It also means both a polishing liquid for a magnetic disk substrate obtained by blending other components that can be blended into the polishing liquid for a magnetic disk substrate with the filtered silica dispersion obtained by filtering silica particles (component A), water, and other components that can be blended into the polishing liquid for a magnetic disk substrate in the filtration step of the present disclosure.

[0051] [Silica Particles (Component A) Contained in the Polishing Liquid of the Present Disclosure]< The silica particles (component A) contained in the polishing liquid of the present disclosure are derived from the silica particles (component A) contained in the treated silica dispersion, that is, from the filtered silica dispersion. From the viewpoint of improving the polishing rate of the polishing liquid of the present disclosure, the content of component A in the polishing liquid of the present disclosure is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.2% by mass or more. From the viewpoint of improving dispersibility and storage stability, it is preferably 10% by mass or less, more preferably 7.5% by mass or less, still more preferably 5% by mass or less.

[0052] <Water contained in the polishing liquid of the present disclosure> The water contained in the polishing liquid of the present disclosure is derived from the water contained in the silica dispersion liquid after filtration, but may be added separately during the preparation of the polishing liquid of the present disclosure, and a part thereof may be distilled off. Further, when the polishing liquid of the present disclosure is further blended with one or more selected from the following optional components: acid (component B), oxidizing agent (component C), heterocyclic aromatic compound (component D), amine compound (component E), and water-soluble polymer having an anionic group (component F), those carried in with these may also be acceptable. The content of water in the polishing liquid of the present disclosure corresponds to the remainder obtained by excluding component A and the following acid, oxidizing agent, heterocyclic aromatic compound, amine compound, anionic water-soluble polymer, and other components from 100% by mass. It is preferably 60% by mass or more, more preferably 80% by mass or more, and preferably 99% by mass or less, more preferably 97% by mass or less.

[0053] In one or more embodiments, the polishing liquid of the present disclosure preferably further contains at least one selected from acid (component B), oxidizing agent (component C), heterocyclic aromatic compound (component D), amine compound (component E), and anionic water-soluble polymer (component F). These components B to F will be described below.

[0054] <Acid (Component B)> The polishing liquid of the present disclosure preferably contains an acid (hereinafter also referred to as "component B"). In the present disclosure, the acid includes an acid or its salt. Component B may be one kind or a combination of two or more kinds.

[0055] Examples of component B include inorganic acids such as nitric acid, sulfuric acid, sulfurous acid, persulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, tripolyphosphoric acid, and amidosulfuric acid; organic acids such as organic phosphoric acid, organic phosphonic acid, and carboxylic acid; etc. Among these, component B preferably contains inorganic acids and organic phosphonic acids, and more preferably contains inorganic acids, from the viewpoints of improving the polishing rate and reducing the scratch of the polishing liquid. As the inorganic acid, at least one selected from nitric acid, sulfuric acid, hydrochloric acid, perchloric acid, and phosphoric acid is preferable, and phosphoric acid is more preferable. As the organic phosphonic acid, at least one selected from 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), aminotri(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), and diethylenetriaminepenta(methylenephosphonic acid) is preferable, and HEDP is more preferable. Examples of the salts of these acids include salts of the above acids with at least one selected from metals, ammonia, and alkylamines. Examples of the above metals include metals belonging to Groups 1 to 11 of the periodic table.

[0056] When the polishing liquid of the present disclosure contains Component B, the content of Component B in the polishing liquid of the present disclosure is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.5% by mass or more, and from the viewpoint of improving the polishing rate and reducing scratches of the polishing liquid, preferably 5% by mass or less, more preferably 4% by mass or less, still more preferably 3% by mass or less, and even more preferably 2% by mass or less.

[0057] <Oxidizing agent (Component C)> From the viewpoints of improving the polishing rate and further reducing scratches during polishing with the polishing liquid of the present disclosure, the polishing liquid of the present disclosure preferably further contains an oxidizing agent (hereinafter also referred to as "Component C"). Component C may be one type or a combination of two or more types.

[0058] Examples of Component C include, from the viewpoints of improving the polishing rate and further reducing scratches during polishing with the polishing liquid of the present disclosure, for example, peroxides, permanganic acid or its salts, chromic acid or its salts, peroxyacids or their salts, oxyacids or their salts, metal salts, nitrates, sulfates, etc. Among these, at least one selected from hydrogen peroxide, iron(III) nitrate, peracetic acid, ammonium peroxydisulfate, iron(III) sulfate, and ammonium iron(III) sulfate is preferable, and hydrogen peroxide is more preferable from the viewpoints of improving the polishing rate, preventing metal ions from adhering to the surface of the substrate to be polished, and easy availability.

[0059] When the polishing liquid of the present disclosure contains Component C, from the viewpoint of further improving the polishing rate and further reducing scratches during polishing with the polishing liquid of the present disclosure, the content of Component C in the polishing liquid of the present disclosure is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, still more preferably 0.1% by mass or more, and preferably 4% by mass or less, more preferably 2% by mass or less, still more preferably 1% by mass or less.

[0060] <Heterocyclic aromatic compound (Component D)> In one or more embodiments, the polishing liquid of the present disclosure preferably further contains a heterocyclic aromatic compound (including its salts, hereinafter also referred to as "Component D") from the viewpoint of further reducing scratches during polishing with the polishing liquid of the present disclosure. Component D may be one type or a combination of two or more types.

[0061] As Component D, from the viewpoint of further reducing scratches during polishing with the polishing liquid of the present disclosure, it is preferably a heterocyclic aromatic compound containing two or more nitrogen atoms in the heterocyclic ring, more preferably having three or more nitrogen atoms in the heterocyclic ring, and preferably having nine or less nitrogen atoms in the heterocyclic ring, more preferably having five or less nitrogen atoms in the heterocyclic ring, and still more preferably having four or less nitrogen atoms in the heterocyclic ring.

[0062] As component D, in one or more embodiments, at least one selected from 1,2,4-triazole, 3-amino-1,2,4-triazole, 5-amino-1,2,4-triazole, 3-mercapto-1,2,4-triazole, 1H-tetrazole, 5-aminotetrazole, 1H-benzotriazole (BTA), 1H-tolyltriazole, 2-aminobenzotriazole, 3-aminobenzotriazole, and their alkyl-substituted or amine-substituted derivatives is preferred. Examples of the alkyl group of the alkyl-substituted derivative include lower alkyl groups having 1 to 4 carbon atoms, and in one or more embodiments, a methyl group and an ethyl group are included. Examples of the amine-substituted derivative include 1-[N,N-bis(hydroxyethylene)aminomethyl]benzotriazole, 1-[N,N-bis(hydroxyethylene)aminomethyl]tolyltriazole, etc. in one or more embodiments. Among these, from the perspective of further reducing scratches, as component D, at least one selected from 1H-benzotriazole (BTA), 1H-tolyltriazole, 2-aminobenzotriazole, and 3-aminobenzotriazole is more preferred, and 1H-benzotriazole (BTA) is even more preferred.

[0063] When the polishing liquid of the present disclosure contains component D, from the perspective of further reducing scratches, the content of component D in the polishing liquid composition of the present disclosure is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, even more preferably 0.02% by mass or more, and from the perspective of improving the polishing rate, it is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and even more preferably 0.2% by mass or less. When component D is a combination of two or more, the content of component D refers to their total content.

[0064] <Amine compound (component E)> In one or more embodiments, from the perspective of further reducing scratches during polishing with the polishing liquid of the present disclosure, it is preferable that the polishing liquid of the present disclosure further contains an amine compound (hereinafter also referred to as "Component E"). From the perspective of further reducing scratches of the polishing liquid of the present disclosure, the number of amino groups in the molecule of Component E is preferably 2 or more and 4 or less. Component E may be of one type or a combination of two or more types.

[0065] In the present disclosure, preferable examples of the amine compound (Component E) include aliphatic amine compounds and alicyclic amine compounds. As the aliphatic amine compound, in one or more embodiments, from the perspective of further reducing scratches, at least one selected from ethylenediamine, N,N,N’,N’-tetramethylethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,4-diaminobutane, hexamethylenediamine, 3-(diethylamino)propylamine, 3-(dibutylamino)propylamine, 3-(methylamino)propylamine, 3-(dimethylamino)propylamine, N-aminoethylethanolamine, N-aminoethylisopropanolamine, and N-aminoethyl-N-methylethanolamine is preferable, at least one selected from N-aminoethylethanolamine, N-aminoethylisopropanolamine, and N-aminoethyl-N-methylethanolamine is more preferable, and N-aminoethylethanolamine (AEEA) is even more preferable. As the alicyclic amine compound, in one or more embodiments, from the perspective of further reducing scratches, at least one selected from piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, 1-amino-4-methylpiperazine, N-methylpiperazine, and hydroxyethylpiperazine (HEP) is preferable, and hydroxyethylpiperazine (HEP) is more preferable.

[0066] When the polishing liquid of the present disclosure contains Component E, the content of Component E in the polishing liquid of the present disclosure is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, still more preferably 0.02% by mass or more, from the viewpoint of further reducing scratches during polishing with the polishing liquid of the present disclosure, and preferably 1% by mass or less, more preferably 0.5% by mass or less, still more preferably 0.1% by mass or less, from the viewpoint of improving the polishing rate. When Component E is a combination of two or more, the content of Component E refers to their total content.

[0067] <Anionic water-soluble polymer (Component F)> In one or more embodiments, the polishing liquid of the present disclosure preferably further contains an anionic water-soluble polymer from the viewpoint of further reducing scratches during polishing with the polishing liquid of the present disclosure. The anionic water-soluble polymer (hereinafter also referred to as "Component F") is a water-soluble polymer having a monomer having an anionic group in the molecule as a constituent unit. In the present disclosure, "water-soluble" means having a solubility of 0.5 g / 100 mL or more, preferably 2 g / 100 mL or more, in water (20 °C). Component F may be one kind or a combination of two or more kinds.

[0068] Suitable examples of the monomer having an anionic group in the molecule include, in one or more embodiments, vinyl monomers having an anionic group in the molecule. Preferred examples of the anionic group of the vinyl monomer having an anionic group in the molecule include a carboxylic acid group and a sulfonic acid group. Specific examples of the vinyl monomer having a carboxylic acid group in the molecule preferably include at least one selected from acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and their salts. Specific examples of the vinyl monomer having a sulfonic acid group in the molecule preferably include at least one selected from 2-acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, and their salts. The water-soluble polymer having a vinyl monomer having an anionic group in the molecule as a constituent unit may have a vinyl monomer other than the vinyl monomer having an anionic group in the molecule. When the component F is a water-soluble polymer having a vinyl monomer having an anionic group in the molecule as a constituent unit, specific examples of the component F include acrylic acid / 2-acrylamido-2-methylpropanesulfonic acid copolymer (AA / AMPS), polystyrene sulfonic acid, and salts thereof.

[0069] Suitable examples of the monomer having an anionic group in the molecule include, in one or more embodiments, aromatic compound monomers containing a sulfonic acid group or a salt thereof. As the aromatic compound monomer containing a sulfonic acid group or a salt thereof, a compound having a structure in which at least one hydrogen atom of the aromatic ring is substituted with a sulfonic acid group or a salt thereof is preferred, and at least one selected from phenol sulfonic acid, naphthalene sulfonic acid, and salts thereof is more preferably mentioned. Preferred examples of the salt include alkali metal salts, ammonium salts, and organic amine salts. The water-soluble polymer in which the component F has an aromatic compound monomer containing a sulfonic acid group or a salt thereof in the molecule as a constituent unit preferably has a constituent unit other than the aromatic compound monomer containing a sulfonic acid group or a salt thereof in the molecule, and specific examples thereof preferably include one or more constituent units selected from a methylene group and a bis(4-hydroxyphenyl)sulfone (BisS) group. When the component F is a water-soluble polymer having an aromatic compound monomer containing a sulfonic acid group or a salt thereof in the molecule as a constituent unit, suitable examples of the component F include at least one selected from a formalin condensate of phenol sulfonic acid (PhS), a formalin condensate of naphthalene sulfonic acid (NaS), a formalin condensate of bis(4-hydroxyphenyl)sulfone (BisS) and phenol sulfonic acid (PhS), and salts thereof.

[0070] From the perspective of scratch reduction of the polishing liquid of the present disclosure, the weight-average molecular weight of Component F is preferably 500 or more, more preferably 1,000 or more, still more preferably 1,500 or more, and preferably 50,000 or less, more preferably 30,000 or less, still more preferably 20,000 or less, even more preferably 10,000 or less, and even more preferably 5,000 or less. In the present disclosure, the weight-average molecular weight of Component F can be measured by the method described in the examples.

[0071] When the polishing liquid of the present disclosure contains Component F, the content of Component F in the polishing liquid of the present disclosure is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, still more preferably 0.01% by mass or more, and preferably 1% by mass or less, more preferably 0.5% by mass or less, still more preferably 0.1% by mass or less, from the perspective of scratch reduction of the polishing liquid of the present disclosure. When Component F is a combination of two or more types, the content of Component F refers to their total content.

[0072] <Other components> The polishing liquid in the present disclosure can contain other components as necessary. Examples of other components include thickeners, surfactants, etc. in one or more embodiments.

[0073] The content of each component described above is the content during use in the polishing process, and the polishing liquid of the present disclosure may be stored and supplied in a concentrated state as long as its storage stability is not impaired. In this case, it is preferable in terms of further reducing the manufacturing and transportation costs. The concentrated liquid of the polishing liquid can be appropriately diluted with the aforementioned water as necessary and used in the polishing process. The dilution ratio can be 1.5 to 100 times.

[0074] The pH of the polishing liquid of the present disclosure at 25°C is preferably 0.1 or more, more preferably 0.5 or more, still more preferably 0.7 or more, and even more preferably 1.0 or more from the viewpoint of scratch reduction of the polishing liquid, and is preferably 4.0 or less, more preferably 3.0 or less, still more preferably 2.5 or less, and even more preferably 2.0 or less from the viewpoint of ensuring a high polishing rate. In the present disclosure, the pH of the polishing liquid can be measured by the same method as the above-described silica dispersion to be treated.

[0075] The embodiments of the polishing liquid of the present disclosure may be a so-called one-component type in which all components are supplied to the market in a pre-mixed state, or a so-called two-component type in which they are mixed at the time of use.

[0076] [Method for manufacturing a magnetic disk substrate] In one aspect, the present disclosure relates to a method for manufacturing a magnetic disk substrate (hereinafter, also referred to as "the substrate manufacturing method of the present disclosure"), which includes a step of manufacturing the polishing liquid of the present disclosure by the manufacturing method of the present disclosure, and a step of supplying the polishing liquid for a magnetic disk substrate obtained in this step to a polishing target surface of a substrate to be polished, bringing a polishing pad into contact with the polishing target surface, and moving one or more selected from the polishing pad and the substrate to be polished to polish the polishing target surface.

[0077] In the substrate manufacturing method of the present disclosure, suitable materials for the substrate to be polished include metals or semi-metals such as silicon, aluminum, nickel, tungsten, copper, tantalum, and titanium, or alloys thereof, glassy substances such as glass, glassy carbon, and amorphous carbon, ceramic materials such as alumina, silicon dioxide, silicon nitride, tantalum nitride, and titanium carbide, and resins such as polyimide resin. Among these, metals such as aluminum, nickel, tungsten, and copper and alloys mainly composed of these metals are preferable, and for example, one selected from Ni-P plated aluminum alloy substrates, glass substrates such as crystallized glass and tempered glass is more preferable, and a Ni-P plated aluminum alloy substrate is even more preferable.

[0078] In the substrate manufacturing method of the present disclosure, when there are a plurality of polishing steps, it is preferable to use the polishing liquid obtained by the manufacturing method of the present disclosure after the second step, and it is more preferable to use it in the finish polishing step. The finish polishing step refers to the last polishing step when there are a plurality of polishing steps.

[0079] When there are a plurality of polishing steps, in order to avoid contamination of the abrasive and polishing liquid in the previous step, different polishing machines may be used respectively. Also, when different polishing machines are used respectively, it is preferable to clean the substrate for each step. Note that the polishing machine is not particularly limited. According to the substrate manufacturing method of the present disclosure, a magnetic disk substrate with reduced scratches on the substrate surface can be efficiently manufactured.

[0080] [Method for Suppressing Filter Clogging] In one or more other embodiments, by passing the silica dispersion to be treated through the filtration step, it is possible to obtain a silica dispersion (filtered silica dispersion) with reduced coarse particles while suppressing clogging of the filter to be used. Therefore, the present disclosure is, in other aspects, a method for suppressing clogging of a filter used in a filtration step in the production of a polishing liquid for a magnetic disk substrate containing silica particles (component A) and water, wherein the filtration step includes a step of filtering with a membrane filter, the average pore diameter of the membrane filter is 2.4 μm or less, and the average aperture ratio of the membrane filter is 10% or more. That is, the present disclosure has a step of filtering with the membrane filter of the present disclosure in the production method of the polishing liquid for a magnetic disk substrate, so that the life of the filter can be extended without deteriorating the quality of the obtained polishing liquid for a magnetic disk substrate, and the productivity of the polishing liquid for a magnetic disk substrate can be increased.

Examples

[0081] Hereinafter, the present disclosure will be described by way of examples, but the present disclosure is not limited thereto.

[0082] 1. Parameter Measurement [Measurement of pH of Treated Silica Dispersion, Filtered Silica Dispersion, and Polishing Liquid] The pH values of the treated silica dispersion, the filtered silica dispersion, and the polishing liquid were measured at 25 °C using a pH meter (HM-30G, manufactured by Toa Denpa Kogyo Co., Ltd.), and are the values measured 1 minute after immersing the electrode in the treated silica dispersion, the filtered silica dispersion, and the polishing liquid respectively.

[0083] [Method for Measuring Average Primary Particle Size of Silica Particles (Component A)] First, collect 1.5 g of the colloidal silica slurry in terms of solid content into a 200 mL beaker, add 100 mL of ion-exchanged water, and mix with a stirrer. Next, using a potentiometric titration apparatus, adjust the pH of the sample solution to 3.0 with a 0.1 mol / L hydrochloric acid standard solution. Add 30.0 g of sodium chloride and dissolve it with a stirrer, then add ion-exchanged water up to the 150 mL mark of the beaker and mix with a stirrer. Immerse it in a constant temperature water bath (20 ± 2 °C) for about 30 minutes. Perform titration with a 0.1 mol / L sodium hydroxide standard solution using a potentiometric titration apparatus, and read the amount (g) (A) of the sodium hydroxide standard solution used when the pH changes from 4.0 to 9.0. At the same time, conduct a blank test and read the amount (g) (B) of the sodium hydroxide standard solution required for the blank test titration. Then, calculate the average primary particle size (nm) using the following calculation formula. Average primary particle size (nm) = 3100 ÷ 26.5 × (A - B) ÷ sample collection amount (g)

[0084] [Method for Measuring Weight-Average Molecular Weight of Anionic Polymer] The weight-average molecular weight of the anionic polymer was measured by gel permeation chromatography (GPC) method under the following measurement conditions. (GPC Conditions) Column: TSKgel G4000PWXL + TSKgel G2500PWXL (manufactured by Tosoh Corporation) Guard column: TSKguardcolumn PWXL (manufactured by Tosoh Corporation) Eluent: 0.2 M phosphate buffer / CH 3 CN = 9 / 1 (volume ratio) Temperature: 40 °C Flow rate: 1.0mL / min Sample size: 5mg / mL Detector: RI Standard material: Sodium polyacrylate (molecular weight (Mp): 115,000, 28,000, 4100, 1250 (manufactured by Sowa Kagaku and American Polymer Standards Corp.))

[0085] 2. Preparation of treated silica dispersion As the silica dispersion to be treated, colloidal silica slurry (pH 9.0, JGC Catalysts and Chemicals The silica particle concentration was 40% by mass and the average primary particle diameter was 18.0 nm.

[0086] 3. Preparation of Membrane Filters The membrane filters used in Examples 1 and 2 are prepared according to the following procedure. Preparation Example 1: Polysulfone (Udel P3500, Solvay, molecular weight 59,000) is dissolved in a solvent (dimethylacetamide, Fujifilm Wako Pure Chemical Industries, Ltd.) to a concentration of 20% by mass, and thoroughly stirred to obtain a uniform membrane-forming solution. The membrane-forming solution is uniformly applied to a 10 cm square metal plate to a thickness of 0.12 mm. Immediately thereafter, the metal plate is immersed in 1 L of ion-exchanged water adjusted to 15°C for 10 minutes. The polymer solidified in the ion-exchanged water is removed and dried overnight at 25°C, and this is used as the membrane filter of Preparation Example 1. At this time, the side in contact with the metal plate is the primary side (the side into which the filtrate flows). Preparation Example 2: Polyethersulfone (SumikaExcel 5003PS, molecular weight 50,000, manufactured by Sumitomo Chemical) was dissolved in a solvent (dimethylacetamide, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to a concentration of 30% by mass, and a membrane filter was obtained in the same manner as in Preparation Example 1. This membrane filter was used as the membrane filter of Preparation Example 2. In Examples 3 and 4 and Comparative Examples 1 to 3, the following commercially available filters were used. Commercially available product 1: Tocell TCS002 (Advantech, material: polyethersulfone, filtration accuracy 0.2 μm, membrane thickness 0.12 mm) Commercially available product 2: LifeASSURE EMC020 (manufactured by 3M, material: polypropylene, filtration accuracy: 0.2 μm, film thickness: 0.12 mm) Commercially available product 3: LifeASSURE EPF020 (manufactured by 3M, material: polyethersulfone, filtration accuracy: 0.2 μm, film thickness: 0.12 mm) Commercially available product 4: K020A047A (manufactured by Advantec, material: polycarbonate, filtration accuracy: 0.45 μm, film thickness: 0.12 mm) Commercially available product 5: LifeASSURE EMC045 (manufactured by 3M, material: PP, filtration accuracy: 0.45 μm, film thickness: 0.12 mm) was also obtained in the same manner.

[0087] [Average pore diameter (APD) of the membrane filter] The average pore diameter and average aperture ratio of the membrane filter are determined by the following method. The membrane portions of the membrane filters obtained in Preparation Examples 1 and 2 and the commercially available product filters were cut out into 30 mm squares, observed by SEM (Hitachi High-Technologies, FE-4800, 30 kV, 1 to 100,000 times), and the obtained photos were captured as image data by a scanner into a personal computer. The projection images of 1000 filter pores on the primary side were analyzed using image analysis software (Miyaya Shosha "WinROOF2017"). The individual pore diameters were calculated, and the average value of all observed pores was taken as the average pore diameter. The results are shown in Table 1.

[0088] [Average aperture ratio (AAR) of the membrane filter] From the individual pore diameters obtained from the above image analysis by SEM, assuming that each pore is a perfect circle, the total sum of the pore areas in one field of view is calculated. The pore diameter aperture ratio is calculated by dividing the total sum of the pore areas by the area of one field of view. Observation is carried out at a magnification at which about 100 pores can be measured per field of view, and the average value of the pore diameter aperture ratios of 10 fields of view is taken as the average aperture ratio. The results are shown in Table 1.

[0089] [(AAR) / (APD)] Taking the above average pore diameter as APD and the above average aperture ratio as AAR, the ratio (AAR) / (APD) of AAR to APD is calculated. The results are shown in Table 1.

[0090] 4. Filtration process (filtration step) The membrane filters obtained in Preparation Examples 1 and 2 and a commercially available filter were cut into φ25 mm, set in a plastic holder (PP-25) manufactured by ADVANTEC, and the silica dispersion to be treated was filtered under the conditions of a pressure of 0.2 MPa and a filtration rate of 50 g / min to obtain a silica dispersion after filtration.

[0091] 5. Preparation of finishing polishing liquid To ion-exchanged water, 0.1% by mass of 1H-benzotriazole Na salt, 0.03% by mass of N-aminoethylethanolamine, 0.02% by mass of sodium acrylate / acrylamide-2-methylpropanesulfonic acid copolymer (AA / AMPS, molar ratio 90 / 10, weight average molecular weight 2000, manufactured by Toagosei Co., Ltd.), 1.0% by mass of phosphoric acid, and 0.4% by mass of hydrogen peroxide were added and mixed. Under stirring of the aqueous solution, the silica dispersion after filtration obtained above was added so that the solid content of silica particles (component A) became 5% by mass, and polishing liquids (pH 1.8) of Examples 1 to 4 and Comparative Examples 1 to 3 were prepared.

[0092] 6. Polishing of substrate using finishing polishing liquid Using the polishing liquids of Examples 1 to 4 and Comparative Examples 1 to 3 prepared as described above, finishing polishing was performed under the following polishing conditions. The number of scratches on each polished substrate was evaluated. The evaluation results of the finishing polishing are shown in Table 1 below. 〔Substrate to be polished〕 As the substrate to be polished, a substrate obtained by preliminarily rough-polishing an aluminum alloy substrate plated with Ni-P with a polishing liquid containing silica abrasive grains was used. This substrate to be polished had a thickness of 0.6 mm, an outer diameter of 97 mm, and an inner diameter of 25 mm, and the center line average roughness Ra measured by AFM (Digital Instrument NanoScope IIIa Multi Mode AFM) was 1 nm. The ratio of Ni to P in the Ni-P plating was 88:12 by mass ratio. 〔Finishing polishing conditions〕 Polishing machine: Double-sided polishing machine (Type 9B double-sided polishing machine, manufactured by Speedfam) Number of substrates to be polished: 10 sheets Abrasive liquid: The abrasive liquids of Examples 1 to 4 and Comparative Examples 1 to 3 Polishing pad: Suede type (foam layer: polyurethane elastomer, thickness 0.9 mm, average pore diameter 10 μm, manufactured by Fujibow Co., Ltd.) Platen rotation speed: 32.5 rpm Polishing load: 10.5 kPa (set value) Abrasive liquid supply rate: 100 mL / min Substrate to be polished: 1 cm 2 Supply rate per cm: 0.076 mL / min Substrate to be polished: 1 cm 2 Amount of polishing per cm: 0.23 mg Polishing time: 6 minutes

[0093] 7. Evaluation of filtration performance [Filter liquid passing volume (MF value)] The filtered silica dispersion obtained above was passed through a predetermined filter (manufactured by Advantec, hydrophilic PTFE 0.20 (pore diameter) μm filter, model: 25HP020AN) under a constant pressure of air pressure 0.30 MPa, and the liquid passing volume (g) until the filter was blocked was determined as the MF value and shown in Table 1. Also, it was shown in Table 1 as a relative value with the MF value of Comparative Example 1 taken as 100%. In addition, the filter liquid passing volume under these conditions can be used as an index for reducing scratches when the filtered silica dispersion obtained in the filtration step of the present disclosure is used in the preparation of the abrasive liquid. That is, the higher the MF value, the more it can be evaluated as a silica dispersion or abrasive liquid capable of reducing scratches.

[0094] [Filter life] In the filtration test of the above membrane filter, the total liquid passing volume when the filtration rate decreased to 17 g / min (1 / 3 of the initial rate) was calculated. Then, by multiplying the liquid passing volume by the ratio of the effective filtration area of φ25 mm to the total effective filtration area assumed for use in actual machine production, the filter life equivalent to the actual machine production scale was obtained. The results are shown in Table 1.

[0095] 8. Evaluation of abrasive liquid [Evaluation of scratches] Measuring instrument: "Candela OSA7100" manufactured by KLA-Tencor Corporation Evaluation: Out of the substrates loaded into the polishing tester, 4 substrates were randomly selected, and each substrate was irradiated with a laser at 10,000 rpm to measure the number of scratches. The total number of scratches (pieces) on both sides of each of the 4 substrates was divided by 8 to calculate the number of scratches per substrate surface. The evaluation results of the number of scratches are shown in Table 1 as relative values with Comparative Example 1 set to 100.

[0096]

Table 1

[0097] As shown in Table 1, in Examples 1 to 4 using a membrane filter with an average pore diameter of 2.4 μm or less and an average aperture ratio of 10% or more, compared with Comparative Example 1 using a membrane filter with an average pore diameter exceeding 2.4 μm and an average aperture ratio less than 10%, Comparative Example 2 using a membrane filter with an average pore diameter of 2.4 μm or less but an average aperture ratio less than 10%, and Comparative Example 3 using a membrane filter with an average aperture ratio of 10% or more but an average pore diameter exceeding 2.4 μm, the filter life was improved, and the quality of the silica dispersion was maintained or improved, and scratches were reduced.

Industrial Applicability

[0098] The polishing liquid for a magnetic disk substrate manufactured using the manufacturing method of the present disclosure is particularly useful as a polishing liquid for a magnetic disk substrate for finish polishing.

Claims

1. A method for manufacturing a polishing liquid for a magnetic disk substrate containing silica particles (Component A) and water, comprising: a step of filtering a silica dispersion to be treated containing silica particles (Component A) and water with a membrane filter to obtain a silica dispersion after filtration; wherein the average pore diameter of the membrane filter is 2.4 μm or less; and the average aperture ratio of the membrane filter is 10% or more. A method for manufacturing a polishing liquid for a magnetic disk substrate.

2. The method for manufacturing a polishing liquid for a magnetic disk substrate according to Claim 1, wherein when the average pore diameter of the membrane filter is APD and the average aperture ratio is AAR, the value represented by the formula: (AAR) / (APD) is 10 or more.

3. The method for manufacturing a polishing liquid for a magnetic disk substrate according to Claim 1 or 2, further comprising a step of further mixing at least one selected from an acid, an oxidizing agent, a heterocyclic aromatic compound, an amine compound, and an anionic water-soluble polymer with the silica dispersion after filtration.

4. A method for manufacturing a magnetic disk substrate, comprising: a step of manufacturing a polishing liquid for a magnetic disk substrate by the method for manufacturing a polishing liquid for a magnetic disk substrate according to any one of Claims 1 to 3; and a step of supplying the polishing liquid for a magnetic disk substrate obtained in this step to a surface to be polished of a substrate to be polished, bringing a polishing pad into contact with the surface to be polished, and moving one or more selected from the polishing pad and the substrate to be polished to polish the surface to be polished.

5. A method for suppressing clogging of a filter used in a filtration step in the manufacture of a polishing liquid for a magnetic disk substrate containing silica particles (Component A) and water, comprising: the filtration step includes a step of filtering with a membrane filter; wherein the average pore diameter of the membrane filter is 2.4 μm or less; and the average aperture ratio of the membrane filter is 10% or more. A method for suppressing clogging of a filter.

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