Method of manufacturing magnetic disk substrate polishing liquid

Abstract

To provide a method of manufacturing a polishing liquid, which enables both improvement in quality of the magnetic disk substrate polishing liquid and extension of filter life.SOLUTION: A method of manufacturing a magnetic disk polishing liquid is provided, the method comprising filtering a dispersion using a membrane filter made up of a hydrophobic polymer and a hydrophilic polymer. Also provided is a method of manufacturing a magnetic disk substrate, comprising the steps of: obtaining the magnetic disk substrate polishing liquid; and polishing a polishing target surface of a substrate to be polished by supplying the obtained magnetic disk substrate polishing liquid to the polishing target surface, bringing a polishing pad into contact with the polishing target surface, and moving at least one of the polishing pad and the substrate to be polished.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 suppressing clogging of a filter in the method for manufacturing a polishing liquid for a magnetic disk substrate, a polishing liquid for a magnetic disk substrate, and a method for manufacturing 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 promoted. In order to improve the detection sensitivity of the weakened magnetic signal, technological development has been advanced to make the flying height of the magnetic head lower. 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 improvement of smoothness and flatness represented by reduction of surface roughness, waviness, and end face sag (roll-off), and reduction of defects represented by 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 the photoresist becomes shallow, and even higher surface smoothness is desired.

[0003] In response to such requirements, for example, Patent Document 1 proposes a composite membrane having a porous substrate and a polymer layer formed using a polymer composition containing polyvinylpyrrolidone (PVP) as a composite membrane for selectively permeating and vaporizing alcohol from a mixture of alcohol and gasoline.

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 capacity of magnetic disk drives, the required characteristics for the surface quality of the substrate have become even more stringent, and it is essential to reduce scratches that affect it. However, when attempting to reduce the coarse particles contained in the polishing liquid, which is considered one of the causes of scratch generation, there is a problem that it becomes difficult to achieve both the reduction operation and the productivity of the polishing liquid.

[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 an improvement in the quality of the polishing liquid for a magnetic disk substrate and an extended service life of the filter used in the production of the polishing liquid for a magnetic disk substrate.

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, which includes a step of filtering with a membrane filter composed of a hydrophobic polymer and a hydrophilic polymer.

[0008] In one aspect, the present disclosure relates to a method for suppressing clogging of a filter used in the filtration step in the production of a polishing liquid for a magnetic disk substrate. The filtration step includes a step of filtering with a membrane filter composed of a hydrophobic polymer and a hydrophilic polymer.

[0009] In one aspect, the present disclosure relates to a method for manufacturing a magnetic disk substrate, which includes a step of obtaining 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 the polishing target surface of the substrate to be polished, bringing a polishing pad into contact with the polishing target surface, and moving at least one of the polishing pad and the substrate to be polished to polish the polishing target surface.

Effects of the Invention

[0010] According to the present disclosure, in one aspect, a method for manufacturing a polishing liquid for a magnetic disk substrate is provided, which can achieve both improvement in the quality of the obtained polishing liquid for a magnetic disk substrate and extension of the service life of a filter used in the manufacture of the polishing liquid for a magnetic disk substrate.

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 components constituting the polishing liquid for a magnetic disk substrate using a membrane filter composed of a hydrophobic polymer and a hydrophilic polymer, it is possible to improve the quality of the obtained polishing liquid for a magnetic disk substrate and extend the service life of the filter.

[0012] That is, the present disclosure relates to, in one aspect, a method for manufacturing a polishing liquid for a magnetic disk substrate (hereinafter, the manufacturing method is also referred to as "the manufacturing method of the present disclosure") having a step of filtering with a membrane filter composed of a hydrophobic polymer and a hydrophilic polymer.

[0013] Although the details of the mechanism of effect manifestation in the manufacturing method of the polishing liquid for a magnetic disk substrate of the present disclosure are not clear, it is presumed as follows. In the manufacture of a polishing liquid for a magnetic disk substrate, when removing coarse particles that cause quality degradation if remaining in the polishing liquid with a membrane filter, since the porous membrane constituting the membrane filter generally has high hydrophobicity, the liquid cannot reach the deep part of the pores due to low affinity for water, which is a commonly used medium in the manufacture of a polishing liquid for a magnetic disk substrate, and not all pores contributed to filtration. In the present disclosure, by including a hydrophilic polymer (for example, polyvinylpyrrolidone) in addition to the hydrophobic polymer (for example, polysulfone or polyethersulfone) that constitutes the membrane filter, a hydrophilic portion can be imparted to the membrane filter. As a result, a medium mainly composed of water can easily enter into the narrow part inside the pores of the membrane filter, and the flow path can be utilized to the maximum extent, so it is considered that the filter can have a longer lifespan. Furthermore, it is considered that the hydrophilic polymer inside the pores of the membrane filter swells upon contact with water, generating new sites for capturing coarse particles and improving the filtration accuracy, thereby improving the quality of the polishing liquid for magnetic disk substrates obtained. However, the present disclosure may not be construed as being limited to these mechanisms.

[0014] In the present disclosure, "coarse particles" refer to particles having a particle diameter of 0.5 μm or more, and the number of coarse particles can be evaluated by the filter liquid passing amount described in the examples below. The larger the liquid passing amount, the smaller the number of coarse particles. In the present disclosure, the coarse particles include primary particles of silica particles, aggregated particles formed by aggregation of the primary particles, and further contaminants other than silica that are unintentionally mixed in.

[0015] In the present disclosure, "scratch" is a physical property that is particularly important for high density or high integration in a memory hard disk 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 full-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] The manufacturing method of the present disclosure includes, in one or more embodiments, a step of filtering with a membrane filter composed of a hydrophobic polymer and a hydrophilic polymer.

[0017] (Membrane filter) In the present disclosure, the membrane filter belongs to the so-called surface type in which filtration is performed on the surface of the filter, and the filter medium has a membrane shape and has pores (holes) of a certain diameter. In one or more embodiments, the membrane filter used in the manufacturing method of the present disclosure is a membrane filter composed of a hydrophobic polymer and a hydrophilic polymer. In one or more embodiments, the hydrophilic polymer can be contained in either or both of the surface and the inside of the membrane filter. Usually, it is difficult for liquid to enter the narrow part inside the pores of the membrane filter, but in the present disclosure, since the hydrophilic polymer is present in at least one of the surface and the inside of the membrane filter, the narrow part inside the pores of the membrane filter can also be utilized as a liquid flow path. Therefore, it is considered that this leads to an improvement in the quality of the polishing liquid for magnetic disk substrates obtained by the manufacturing method of the present disclosure and an extension of the service life of the filter used in the production of the polishing liquid.

[0018] In the present disclosure, the hydrophobic polymer, which is one of the components constituting the membrane filter, means that when 10 g of the polymer is mixed with 100 g of ion-exchanged water, the solubility in ion-exchanged water is 1 g or less. Preferable examples of the hydrophobic polymer, which is one of the components constituting the membrane filter, include polysulfone, polyethersulfone, polyvinylidene fluoride, polytetrafluoroethylene, cellulose acetate, nitrocellulose, polypropylene, polyester, and polyamide. In the present disclosure, the hydrophobic polymer preferably contains the polymers listed as preferable examples of the above hydrophobic polymer. When the hydrophobic polymer, which is one of the components constituting the membrane filter in the present disclosure, contains the polymers listed above, it means that the hydrophobic polymer may have, in addition to the monomers constituting the above homopolymers, other monomers as the structural units of the hydrophobic polymer. That is, in the present disclosure, the hydrophobic polymer may be a copolymer of the monomers constituting the above homopolymers and other monomers. Among these, from the viewpoints of improving the quality of the polishing liquid for magnetic disk substrates obtained by the manufacturing method of the present disclosure and extending the service life of the filter used in the production of the polishing liquid, in the present disclosure, the hydrophobic polymer, which is one of the components constituting the membrane filter, more preferably contains at least one selected from polysulfone (PS) and polyethersulfone (PES), and from the same viewpoint, the hydrophobic polymer, which is one of the components constituting the membrane filter, is more preferably at least one selected from polysulfone and polyethersulfone. In the present disclosure, materials such as support materials, core materials, and protective materials for holding the membrane filter in a certain shape, which do not directly participate in the filtering function, are not included in the components constituting the membrane filter. Further, a prefilter that is integrated with the membrane filter and installed in the front stage of the membrane filter is not included in the components constituting the membrane filter in the present disclosure even if the prefilter is a membrane filter.

[0019] In the present disclosure, the hydrophilic polymer, which is one of the components constituting the membrane filter, means that when 10 g of the polymer is mixed with 100 g of ion-exchanged water, the solubility in the ion-exchanged water is more than 1 g. Suitable examples of the hydrophilic polymer, which is one of the components constituting the membrane filter, include polyvinylpyrrolidone (PVP), poly(2-hydroxyethyl methacrylate) (HEMA), poly(N-vinylacetamide), and poly(meth)acrylamide. In the present disclosure, the hydrophilic polymer preferably contains the polymers exemplified as suitable examples of the above hydrophilic polymer. That the hydrophilic polymer contains the polymers exemplified above in the present disclosure means that the hydrophilic polymer may have monomers other than the monomers constituting the above homopolymers as constitutional units of the hydrophilic polymer. That is, in the present disclosure, the hydrophilic polymer may be a copolymer of the monomers constituting the above homopolymers and other monomers. Among these, from the viewpoints of improving the quality of the polishing liquid for magnetic disk substrates obtained by the manufacturing method of the present disclosure and extending the service life of the filter used in the production of the polishing liquid, it is preferable that the hydrophilic polymer, which is one of the components constituting the membrane filter in the present disclosure, contains polyvinylpyrrolidone. That the hydrophilic polymer, which is one of the components constituting the membrane filter in the present disclosure, contains polyvinylpyrrolidone means that the hydrophilic polymer is one selected from those consisting of polyvinylpyrrolidone, those consisting of polyvinylpyrrolidone and a hydrophilic polymer other than polyvinylpyrrolidone, and those that are copolymers of vinylpyrrolidone monomer and a monomer other than vinylpyrrolidone monomer. In the present disclosure, it is more preferable that the hydrophilic polymer, which is one of the components constituting the membrane filter, consists of polyvinylpyrrolidone.

[0020] From the viewpoints of improving the quality of the polishing liquid for magnetic disk substrates obtained by the manufacturing method of the present disclosure and extending the service life of the filter used in the production of the polishing liquid, the content ratio of the hydrophilic polymer to the hydrophobic polymer constituting the membrane filter is preferably 0.1% or more, more preferably 1% or more, still more preferably 10% or more, still more preferably 15% or more. And from the same viewpoints, it is preferably less than 50%, more preferably 40% or less, still more preferably 30% or less, and even more preferably 20% or less. In the present disclosure, the content ratio of the hydrophilic polymer to the hydrophobic polymer constituting the membrane filter can be calculated from the ratio of the peak intensities at specific wavelengths by infrared absorption spectrum. In the present disclosure, when the hydrophobic polymer constituting the membrane filter is polyethersulfone or polysulfone and the hydrophilic polymer is polyvinylpyrrolidone, the ratio can be calculated by the ratio of the intensity of the peak at 1650 cm -1 to the intensity of the peak at 1500 cm -1 as the hydrophobic polymer.

[0021] Examples of the method for manufacturing the membrane filter containing the hydrophilic polymer include centrifugation, thermally induced phase separation, non-solvent induced phase separation, track etching, and the like.

[0022] From the viewpoint of extending the filter life, the molecular weight of the hydrophobic polymer, which is the main component constituting the membrane filter, is preferably 10,000 or more, more preferably 50,000 or more, and still more preferably 65,000 or more. From the viewpoints of improving the quality of the polishing liquid for magnetic disk substrates and reducing coarse particles obtained by the manufacturing method of the present disclosure, it is preferably 150,000 or less, more preferably 100,000 or less, and still more preferably 80,000 or less. In the present disclosure, the molecular weight of the hydrophobic polymer can be referred to the numerical values described in catalogs and the like.

[0023] From the viewpoint of extending the filter life, the molecular weight of the hydrophilic polymer contained in the membrane filter is preferably 100 or more, more preferably 1,000 or more, and still more preferably 10,000 or more. From the viewpoints of improving the quality of the polishing liquid for magnetic disk substrates and reducing coarse particles obtained by the manufacturing method of the present disclosure, it is preferably 150,000 or less, more preferably 100,000 or less, and still more preferably 30,000 or less. In the present disclosure, the molecular weight of the hydrophilic polymer can be referred to the numerical values described in catalogs and the like.

[0024] From the viewpoints of improving the quality of the polishing liquid for magnetic disk substrates obtained by the manufacturing method of the present disclosure and extending the life of the filter used in the production of the polishing liquid, the average pore diameter of the membrane filter is preferably 0.5 μm or more, more preferably 0.8 μm or more, and still more preferably 1.0 μm or more. From the same viewpoints, it is preferably 2.4 μm or less, more preferably 2.0 μm or less, still more preferably 1.5 μm or less, and even more preferably 1.16 μm or less. In the present disclosure, the average pore diameter is the average value of the diameters of the pores (holes) on the side where the filtrate flows into the membrane filter. The average pore diameter can be adjusted by the solvent composition and solvent evaporation time during film formation. The average pore diameter can be measured by the method described in the examples.

[0025] From the viewpoints of improving the quality of the polishing liquid for magnetic disk substrates obtained by the manufacturing method of the present disclosure and extending the service life of the filter used in the production of the polishing liquid, the spreading degree of the dropping liquid of the membrane filter is preferably 1.5 or more, more preferably 2 or more, still more preferably 3 or more, and from the same viewpoints, preferably 10 or less, more preferably 5 or less, still more preferably 4 or less. The spreading degree of the dropping liquid is one of the indexes of the hydrophilicity of the membrane filter. The larger the numerical value of the spreading degree of the dropping liquid, the higher the hydrophilicity of the membrane filter, indicating that the diameter of the circle of wet spreading from the primary side to the secondary side of the filter tends to be larger. The spreading degree of the dropping liquid can be measured by the method described in the examples. The spreading degree of the dropping liquid can be adjusted by changing the content of the hydrophilic polymer contained in the membrane filter or the content ratio of the hydrophilic polymer to the hydrophobic polymer of the membrane filter in one or more embodiments.

[0026] From the viewpoints of improving the quality of the polishing liquid for magnetic disk substrates obtained by the manufacturing method of the present disclosure and extending the service life of the filter used in the production of the polishing liquid, the membrane potential of the membrane filter is preferably -62 mV or more, more preferably -58 mV or more, still more preferably -53 mV or more, and from the same viewpoints, preferably 0 mV or less, more preferably -10 mV or less, still more preferably -20 mV or less. When the material of the membrane filter is polyethersulfone, the membrane potential is preferably -58 mV or more, more preferably -52 mV or more, and preferably 0 mV or less, more preferably -10 mV or less, still more preferably -20 mV or less. When the material of the membrane filter is polysulfone, the membrane potential is preferably -62 mV or more, more preferably -60 mV or more, and preferably 0 mV or less, more preferably -10 mV or less, still more preferably -20 mV or less. In the present disclosure, the membrane filter has a reduced negative charge by containing a hydrophilic polymer as a constituent component. Since the coarse particles to be removed in the present disclosure also have a negative charge, suppressing the negative charge of the membrane filter can prevent the membrane filter and the coarse particles from repelling each other, and it is considered that the filter can efficiently capture them. The membrane potential can be measured, for example, by the method described in the examples.

[0027] From the viewpoint of improving the quality of the polishing liquid for magnetic disk substrates obtained by the production method of the present disclosure and extending the life of the filter used in the production of the polishing liquid, the membrane filter may be a pleated filter (hereinafter, also simply referred to as "pleated filter") in which the membrane as the filter medium is formed into a pleated shape. The pleated filter may be further processed, and a preferred example of the further processed form is a cartridge type having a hollow cylindrical shape.

[0028] The membrane filter may be used in a single stage or in multiple stages (for example, in a series arrangement).

[0029] The step of filtering with a membrane filter composed of a hydrophobic polymer and a hydrophilic polymer in the production method of the present disclosure (hereinafter, also referred to as "the filtering step of the present disclosure") is a step of filtering the components (filtered components to be described later) to be subjected to the step of filtering with the membrane filter with the membrane filter. From the viewpoint of improving the quality of the polishing liquid for magnetic disk substrates obtained by the production method of the present disclosure and extending the life of the filter used in the production of the polishing liquid, the filtration pressure in the filtering step of the present disclosure is preferably 0.16 MPa or more, more preferably 0.18 MPa or more, still more preferably 0.20 MPa or more, and from the same viewpoint, preferably 0.49 MPa or less, more preferably 0.45 MPa or less, still more preferably 0.40 MPa or less, and even more preferably 0.30 MPa or less. In the present disclosure, the "filtration pressure" means the difference between the pressure on the feed liquid side and the pressure on the filtrate side of the membrane filter. 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.

[0030] From the viewpoints of improving the quality of the polishing liquid for magnetic disk substrates obtained by the manufacturing method of the present disclosure and extending the service life of the filter used in the production of the polishing liquid, the filtration flow rate in the filtration process of the present disclosure 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. And from the same viewpoints, it 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" is the weight per unit area per unit time of filtration, and in one or more embodiments, it can be adjusted by adjusting the valve on the secondary side, which is the filter outlet.

[0031] As the filtration method in the filtration process of the present disclosure, a cyclic method of repeated filtration may be used, or a one-pass method may be used. Also, a batch method of repeating the one-pass method may be used. For the liquid passing method, in order to apply pressure, a pump is preferably used in the cyclic method. In addition to using a pump in the one-pass method, a pressure filtration method with a small variation range of the filter inlet pressure can be used by introducing air pressure or the like into the tank.

[0032] In the manufacturing method of the present disclosure, in addition to using the above-described filter, 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 by 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.

[0033] (Pre-filtration step) The manufacturing method of the present disclosure preferably includes a step of filtering using at least one filter selected from a filter aid-containing filter and a depth filter before the step of filtering with the membrane filter, that is, a pre-filtration step.

[0034] (Pre-filtration step by filter aid-containing filter) A filter aid-containing filter is a filter containing at least a filter aid. Examples of the filter aid preferably include insoluble mineral substances such as silicon dioxide, kaolin, acid clay, diatomaceous earth, perlite, bentonite, and talc. Among the above filter aids, from the viewpoint of improving productivity, one or more selected from silicon dioxide, diatomaceous earth, and perlite are more preferable, one or more selected from diatomaceous earth and perlite are still more preferable, and diatomaceous earth is even more preferable.

[0035] (Pre-filtration step by depth filter) In the present disclosure, a depth filter is a filter having a pore structure of the filter medium that is coarse on the 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 in the shape of a bag and a cartridge type in a hollow cylindrical shape. Also, a material obtained by molding a 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.

[0036] The depth-type filter may be used in a single stage, or the same filter may be used in combination in series of two or more, or depth-type filters with different pore diameters and non-depth-type filters may be combined and used in such a manner that the filtrate passes through them 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 by the depth-type filter. Further, these may be used in combination of a bag type and a cartridge type.

[0037] From the viewpoints of improving productivity and extending the life of the filter, the pore diameter of the depth-type filter is preferably 0.1 μm or more, and from the viewpoints of improving the quality of the polishing liquid for a magnetic disk substrate obtained by the manufacturing method of the present disclosure 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, and even more preferably 1.0 μm or less. In the manufacturing method of the present disclosure, it is more preferable that it includes a filtration step by a depth-type filter before the filtration step of the present disclosure.

[0038] [Component to be filtered] In the filtration step of the present disclosure, the component (hereinafter also referred to as "component to be filtered") to be subjected to the step of filtering with the membrane filter is preferably a silica particle and water-containing one (silica dispersion). The component to be filtered may contain other components that can be blended in the polishing liquid for a magnetic disk substrate obtained by the manufacturing method of the present disclosure described later in one or more embodiments. Preferable examples of other components that can be blended in the polishing liquid for a magnetic disk substrate obtained by the manufacturing method of the present disclosure include at least one selected from an acid, an oxidizing agent, a heterocyclic aromatic compound, an amine compound, and an anionic water-soluble polymer.

[0039] In the manufacturing method of the present disclosure, it is more preferable that the component to be filtered consists of silica particles and water.

[0040] [Silica particles (Component A)] As the silica particles (hereinafter also referred to as "Component A") preferably contained in the component to be filtered in the present disclosure, from the viewpoints of improving the polishing rate of the magnetic disk and reducing scratches by the polishing liquid for the magnetic disk substrate obtained by the production method of the present disclosure, colloidal silica, fumed silica, and pulverized silica can be mentioned, and among these, colloidal silica is more 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, those obtained by forming composite particles with a surfactant or other abrasive materials, etc. can also be used. Component A may be one kind or a combination of two or more kinds.

[0041] The shape of Component A may be spherical or non-spherical. Component A is preferably a silica particle dispersion dispersed in an aqueous medium.

[0042] From the viewpoint of improving the quality of the polishing liquid for the magnetic disk substrate obtained by the production method of the present disclosure, 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, even more preferably 12 nm or more, and from the same viewpoint, 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, and even more preferably 25 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 of Component A can be measured by the method described in the examples.

[0043] In the component to be filtered in the present disclosure, the content of component A 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. And from the viewpoint of improving the quality of the polishing liquid for magnetic disk substrates obtained by the production method of the present disclosure, it is preferably 60% by mass or less, more preferably 55% by mass or less, still more preferably 50% by mass or less, and even more preferably 45% by mass or less. When component A is a combination of two or more kinds, the content of component A in the component to be filtered is the total content thereof.

[0044] <Water> Preferred examples of water that the component to be filtered in the present disclosure preferably contains include ion-exchanged water, distilled water, ultrapure water, and the like. The content of water in the component to be filtered in the present disclosure can be the residue obtained by subtracting component A and other components added as necessary from 100% by mass. The component to be filtered in the present disclosure may contain components other than component A and water. Preferred examples of components other than component A and water include other components that can be blended into the polishing liquid for magnetic disk substrates obtained by the production method of the present disclosure. Preferred examples of other components that can be blended into the polishing liquid for magnetic disk substrates obtained by the production method of the present disclosure include acids, oxidants, heterocyclic aromatic compounds, amine compounds, and anionic water-soluble polymers. That is, the production method of the present disclosure is preferably at least one selected from a method of performing the filtration step of the present disclosure using silica particles and water as the component to be filtered and blending other components that can be blended into the polishing liquid for magnetic disk substrates, and a method of performing the filtration step of the present disclosure using silica particles, water, and other components that can be blended into the polishing liquid for magnetic disk substrates as the component to be filtered. Among them, from the viewpoint of improving the quality of the polishing liquid for magnetic disk substrates obtained by the production method of the present disclosure and extending the service life of the filter used in the production of the polishing liquid, a method of performing the filtration step of the present disclosure using silica particles and water as the component to be filtered and blending other components that can be blended into the polishing liquid for magnetic disk substrates is more preferred.

[0045] In one or more embodiments, the pH of the component to be filtered in the present disclosure is preferably 8.5 or higher, more preferably 8.8 or higher, still more preferably 9.0 or higher, and also preferably 11 or lower, more preferably 10.8 or lower, still more preferably 10.5 or lower, from the viewpoints of improving the quality of the polishing liquid for magnetic disk substrates obtained by the production method of the present disclosure and extending the service life of the filter used in the production of the polishing liquid. The pH of the component to be filtered in the present disclosure can be adjusted by known pH adjusters. 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.

[0046] The suitable pH of the component to be filtered after filtration, which is obtained by passing the component to be filtered through the filtration step, is the same as the pH of the component to be filtered described above. The pH of the component to be filtered after filtration can be measured by the same method as the measurement of the pH of the component to be filtered.

[0047] It is preferable that the content and pH of each component in the component to be filtered after filtration in the present disclosure are substantially the same as those of the silica dispersion to be treated. In the present disclosure, "substantially the same" means that the composition of the silica dispersion to be treated and the silica dispersion after filtration does not change except for coarse particles.

[0048] From the viewpoint of improving the quality of the polishing liquid for magnetic disk substrates obtained by the production method of the present disclosure, the filter throughput (g) of the component to be filtered 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, even more preferably 180 g or more, and from the viewpoint of improving productivity, it is preferably 3,000 g or less, more preferably 2,000 g or less, still more preferably 1,500 g or less. In the present disclosure, the filter throughput of the filtered component to be filtered is determined by placing the filtered component to be filtered in a container or syringe equipped with a filter having a specific pore size, and applying pressure or vacuum to pass the filtered component to be filtered through the filter, and measuring the throughput until the filter becomes clogged. In the present disclosure, the filter throughput of the filtered component to be filtered is measured by the method described in the examples using a hydrophilic PTFE membrane filter with a pore size of 0.20 μm. The filtered component to be filtered can be applied in various fields such as abrasives, coating agents, fillers, ceramic binders, catalyst carriers, adsorbents, etc. Further, the filtered component to be filtered 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] In one or more embodiments, the manufacturing method of the present disclosure may include a step of blending other components that can be blended in the polishing liquid for a magnetic disk substrate obtained by the manufacturing method of the present disclosure into the component to be filtered before the filtering step and / or into the filtered component to be filtered after the filtering step by a known method. In the present disclosure, "blending" includes mixing the component to be filtered and / or the filtered component to be filtered with the other component simultaneously or in any order. The other components include components that can be blended in the polishing liquid for a magnetic disk substrate obtained by the manufacturing method of the present disclosure. Suitable examples thereof include acids, oxidizing agents, heterocyclic aromatic compounds, amine compounds, and anionic water-soluble polymers. The blending can be performed, for example, using a mixer such as a homomixer, homogenizer, ultrasonic disperser, and wet ball mill.

[0050] [Polishing liquid for magnetic disk substrate obtained by the manufacturing method of the present disclosure] In one aspect, the present disclosure relates to a polishing liquid for a magnetic disk substrate obtained by the manufacturing method of the present disclosure (hereinafter also referred to as "the polishing liquid of the present disclosure"). In one or more embodiments, the polishing liquid of the present disclosure preferably contains one or more selected from an acid, an oxidizing agent, a heterocyclic aromatic compound, an amine compound, and an anionic water-soluble polymer in addition to silica particles and water. The polishing liquid of the present disclosure is obtained by filtering silica particles and water in the filtering step of the present disclosure to obtain a filtered component after filtration, and further blending other components that can be blended into the polishing liquid for a magnetic disk substrate. It also means both the polishing liquid for a magnetic disk substrate obtained by blending, and the filtered component after filtration obtained by filtering silica particles, water, and other components that can be blended into the polishing liquid for a magnetic disk substrate in the filtering step of the present disclosure and using it as the polishing liquid for a magnetic disk substrate.

[0051] <Silica Particles 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 filtered component (filtrate) after the filtration. From the viewpoint of improving the polishing rate, the content of silica particles 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, and from the viewpoints 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 filtered component after the filtration, but it may be added separately during the preparation of the polishing liquid of the present disclosure, or a part of it may be distilled off. Further, when the polishing liquid of the present disclosure is further blended with other components that can be blended into the polishing liquid described later, those brought in along with these may also be acceptable. The content of water in the polishing liquid of the present disclosure corresponds to the remainder obtained by subtracting Component A and other components that can be blended into the polishing liquid for a magnetic disk substrate 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] <Other Components That Can Be Blended into the Polishing Liquid of the Present Disclosure> In one or more embodiments, the polishing liquid of the present disclosure preferably further contains at least one selected from an acid, an oxidizing agent, a heterocyclic aromatic compound, an amine compound, and an anionic water-soluble polymer. These 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; and the like. Among these, from the viewpoint of scratch reduction, Component B preferably contains an inorganic acid and an organic phosphonic acid, and more preferably contains an inorganic acid. 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 and 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 scratch reduction, 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. When Component B is a combination of two or more kinds, the content of Component B refers to their total content.

[0057] <Oxidizing agent (Component C)> From the viewpoint of further reducing scratches, the polishing liquid of the present disclosure preferably contains an oxidizing agent (hereinafter also referred to as "Component C"). Component C may be one kind or a combination of two or more kinds.

[0058] Examples of Component C include, from the viewpoint of further reducing scratches, for example, peroxides, permanganic acid or its salts, chromic acid or its salts, peroxy acids or their salts, oxyacids or their salts, metal salts, nitrates, sulfates, and the like. 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 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, 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. When Component C is a combination of two or more kinds, the content of Component C refers to their total content.

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

[0061] As Component D, from the perspective of further reducing scratches, it is preferably a heterocyclic aromatic compound containing two or more nitrogen atoms in the heterocycle, more preferably having three or more nitrogen atoms in the heterocycle, still more preferably three to nine, still more preferably three to five, and still more preferably three or four.

[0062] In one or more embodiments, as Component D, 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 mentioned. Examples of the amine-substituted derivative include 1-[N,N-bis(hydroxyethylene)aminomethyl]benzotriazole, 1-[N,N-bis(hydroxyethylene)aminomethyl]tolyltriazole, etc. 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 still more preferred.

[0063] When the polishing liquid of the present disclosure contains Component D, the content of Component D 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, and preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 1% by mass or less, and even more preferably 0.2% by mass or less from the viewpoint of improving the polishing rate. 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, the polishing liquid of the present disclosure preferably further contains an amine compound (hereinafter also referred to as "Component E") from the viewpoint of further reducing scratches. From the viewpoint of further reducing scratches, 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] As the amine compound, one or more selected from aliphatic amine compounds and alicyclic amine compounds are preferable. As the aliphatic amine compound, in one or more embodiments, from the viewpoint 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 still 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 preferred, and hydroxyethylpiperazine (HEP) is more preferred.

[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 perspective of further reducing scratches, 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 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 perspective 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 structural 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 monomers having an anionic group in the molecule include vinyl monomers in one or more embodiments. 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 salts thereof. 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 salts thereof. When component F is a water-soluble polymer having a vinyl monomer having an anionic group in the molecule as a constituent unit, component F may have a vinyl monomer other than the vinyl monomer having an anionic group in the molecule. When 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 component F preferably include acrylic acid / 2-acrylamido-2-methylpropanesulfonic acid copolymer (AA / AMPS), polystyrenesulfonic acid, and salts thereof.

[0069] Suitable examples of monomers having an anionic group in the molecule include aromatic compound monomers containing a sulfonic acid group or a salt thereof in one or more embodiments. The aromatic compound monomer containing a sulfonic acid group or a salt thereof preferably has a structure in which at least one hydrogen atom of the aromatic ring is substituted with a sulfonic acid group or a salt thereof, and more preferably includes at least one selected from phenolsulfonic acid, naphthalenesulfonic acid, and salts thereof. Examples of the salt include alkali metal salts, ammonium salts, organic amine salts, and the like. When 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, the water-soluble polymer having 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. Specific examples thereof preferably include one or more constituent units selected from a methylene group and a bis(4-hydroxyphenyl)sulfone (BisS) group. When 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, preferred examples of Component F include at least one selected from a formalin condensate of phenolsulfonic acid (PhS), a formalin condensate of naphthalenesulfonic acid (NaS), a formalin condensate of bis(4-hydroxyphenyl)sulfone (BisS) and phenolsulfonic acid (PhS), and salts thereof.

[0070] From the viewpoint of further reducing scratches, 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, still 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, from the viewpoint of further reducing scratches, 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. 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 of the present disclosure can contain other components as needed. Examples of other components include, in one or more embodiments, thickeners, dispersants, rust inhibitors, surfactants, and the like.

[0073] The content of each component described above is the content during use in the polishing process. 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 that the manufacturing and transportation costs can be further reduced. The concentrated liquid of the polishing liquid can be appropriately diluted with the aforementioned water as needed 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, and 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 productivity. The pH of the polishing liquid of the present disclosure can be measured by the same method as the above-described components to be filtered.

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

[0076] [Method for suppressing clogging of filter] In one aspect, the present disclosure relates to 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, the filtration step including a step of filtering with a membrane filter composed of a hydrophobic polymer and a hydrophilic polymer, and relates to a method for suppressing clogging of a filter in a method for producing a polishing liquid for a magnetic disk substrate.

[0077] That is, the present disclosure has a step of filtering with a membrane filter composed of a hydrophobic polymer and a hydrophilic polymer in the method for producing a polishing liquid for a magnetic disk substrate, thereby achieving a longer filter life without degrading the quality of the obtained polishing liquid for a magnetic disk substrate and enhancing the productivity of the polishing liquid for a magnetic disk substrate.

[0078] [Method for manufacturing a magnetic disk substrate] In one aspect, the present disclosure relates to a method for manufacturing a magnetic disk substrate, including a step of obtaining 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 the 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 at least one of the polishing pad and the substrate to be polished to polish the polishing target surface. That is, the method for manufacturing a magnetic disk substrate of the present disclosure is preferably a method for manufacturing a magnetic disk substrate having step III following step I or step II below. Step I: A step of filtering silica particles and water in the filtering step of the present disclosure as components to be filtered, and further, if necessary, adding other components that can be incorporated into the polishing liquid for a magnetic disk substrate to the components to be filtered to obtain a polishing liquid I for a magnetic disk substrate Step II: A step of filtering silica particles, water, and other components that can be incorporated into the polishing liquid for a magnetic disk substrate in the filtering step of the present disclosure to obtain a polishing liquid II for a magnetic disk substrate Step III: A step of supplying polishing liquid I for a magnetic disk substrate or polishing liquid II for a magnetic disk substrate to a polishing target surface of a substrate to be polished, bringing a polishing pad into contact with the polishing target surface, and moving at least one of the polishing pad and the substrate to be polished to polish the polishing target surface Among these, a method for manufacturing a magnetic disk substrate in which step III is carried out following step I is preferred. In the method for manufacturing a magnetic disk substrate of the present disclosure (hereinafter, also referred to as "the substrate manufacturing method of the present disclosure"), suitable substrates to be polished include metals or semi-metals such as silicon, aluminum, nickel, tungsten, copper, tantalum, titanium, etc., or alloys thereof, glassy substances such as glass, glassy carbon, amorphous carbon, etc., ceramic materials such as alumina, silicon dioxide, silicon nitride, tantalum nitride, titanium carbide, etc., and substrates of resins such as polyimide resin. Among these, substrates containing metals such as aluminum, nickel, tungsten, copper, etc. and alloys mainly composed of these metals are more preferable, glass substrates such as Ni-P plated aluminum alloy substrates, crystallized glass, and strengthened glass are even more preferable, and Ni-P plated aluminum alloy substrates are even more preferable. 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 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. 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 wash 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.

Examples

[0079] Hereinafter, the present disclosure will be described by way of examples, but the present disclosure is not limited thereto.

[0080] The pH of the components to be filtered, the average primary particle diameter of the silica particles, and the molecular weight of the anionic water-soluble polymer are determined by the following methods.

[0081] [Measurement of pH of Components to be Filtered, Components to be Filtered after Filtration, and Polishing Liquid for Magnetic Disk Substrate] The pH at 25°C of the component to be filtered, the component to be filtered after filtration, and the polishing liquid for magnetic disk substrates is the value measured using a pH meter (Toa Denpa Kogyo Co., Ltd., HM-30G), and is the value one minute after immersion of the electrode in the component to be filtered, the component to be filtered after filtration, and the polishing liquid for magnetic disk substrates.

[0082] [Measurement of the average primary particle size of silica particles] First, collect 1.5 g per minute of the solid content of the colloidal silica slurry 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, dissolve it with a stirrer, 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, perform a blank test and read the amount (g) (B) of the sodium hydroxide standard solution required for the titration of the blank test. 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)

[0083] [Measurement of the weight average molecular weight of an anionic water-soluble polymer] The weight average molecular weight of the anionic water-soluble 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: 0.2M phosphate buffer / CH 3 CN = 9 / 1 (volume ratio) Temperature: 40°C Flow rate: 1.0 mL / min Sample size: 5 mg / mL Detector: RI Standard substance: Sodium polyacrylate (molecular weight (Mp): 115,000, 28,000, 4,100, 1,250 (manufactured by Sowa Kagaku and American Polymer Standards Corp.))

[0084] Preparation Examples 1 and 2 Preparation of Membrane Filters The method for preparing a membrane filter in which the hydrophilic polymer of a membrane filter composed of a hydrophobic polymer and a hydrophilic polymer contains polyvinylpyrrolidone is as follows (non-solvent induced phase separation method). Preparation Example 1: Mix polysulfone (Udel P3500 manufactured by Solvay, molecular weight 59,000), polyvinylpyrrolidone (K25 manufactured by Fujifilm Wako Pure Chemical Industries, molecular weight 25,000), and dimethylacetamide (reagent manufactured by Fujifilm Wako Pure Chemical Industries) in a mass ratio of 20:5:75, and stir well to obtain a uniform membrane-forming stock solution. The above membrane-forming stock solution is uniformly coated on a 10 cm square metal plate with a thickness of 0.12 mm. Immediately thereafter, the metal plate is immersed in 1 L of ion-exchanged water adjusted to 30 °C for 10 minutes. Dimethylacetamide, which is a solvent, dissolves well in water, but the above polymer hardly dissolves in water and thus solidifies. The polymer solidified in the ion-exchanged water is taken out and dried overnight, and the air bubbles of water vapor in the gaps disappear, resulting in a porous membrane. This is designated as the membrane filter of Preparation Example 1. At this time, the side in contact with the metal plate is defined as the primary side, and the other side is defined as the secondary side. Preparation Example 2: Mix polyethersulfone (Sumikaexcel 5003PS manufactured by Sumitomo Chemical, molecular weight 50,000), polyvinylpyrrolidone (the same as above), and dimethylacetamide (the same as above) in a mass ratio of 20:5:75, and obtain the membrane filter of Preparation Example 2 in the same manner as the method described in Preparation Example 1. [Commercially Available Products 1 and 2 Membrane Filters] Commercially Available Product 1: Tocell TCS002 (manufactured by Advantec, membrane material: polyethersulfone / polyvinylpyrrolidone, filtration accuracy 0.2 μm, membrane thickness 0.12 mm) Commercially available product 2: Water Fine WFN002 (manufactured by Paul Co., membrane material: polysulfone, filtration accuracy: 0.2 μm, membrane thickness: 0.12 mm)

[0085] The PVP content ratio, average pore diameter, dropwise liquid spreading degree, and membrane potential of the membrane filter are determined by the following methods.

[0086] [Hydrophilic polymer content ratio of membrane filter] Each membrane filter to be measured was cut into a 10 mm square and measured by FTIR (manufactured by Thermo Fisher Scientific, Nicolet i5, number of integrations: 10 times, measurement wave number: 500 - 4000 cm -1 ) to obtain an infrared absorption spectrum. The peak of polyethersulfone (PES) or polysulfone (PS) was used as a reference at 1500 cm -1 , and the peak of polyvinylpyrrolidone (PVP: hydrophilic polymer) was used as a reference at 1650 cm -1 . The peak intensity ratio of the two was calculated as a percentage by the following formula and taken as the PVP content ratio. [Intensity of peak at 1650 cm -1 / Intensity of peak at 1500 cm -1 ×100 The results are shown in Table 1.

[0087] [Average pore diameter of membrane filter] The membrane filter to be measured was cut into a 30 mm square, and the primary side and the secondary side were observed by SEM (manufactured by Hitachi High-Technologies, FE-4800, 30 kV, 1 to 100,000 times). The obtained photos were scanned into a personal computer as image data for 500 pores on each side, and the individual pore diameters were calculated using image analysis software (Mitani Trading Co., "WinROOF2017"). The average value of the diameters of all the observed pores was taken as the average pore diameter. The results are shown in Table 1.

[0088] [Dropwise liquid spreading degree of membrane filter] Cut out each membrane filter to be measured to a diameter of φ90 mm, with the primary side of the membrane filter facing up. Drop 0.02 g of a blue-colored wetting tension test mixture (No. 73.0, manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) with a surface tension of 73 mN / m at 25°C onto it. Calculate the diameter of the blue-colored circle on each of the primary side and the secondary side of the membrane filter, and calculate the diameter ratio using the following formula to obtain the droplet spreading degree. The results are shown in Table 1. It can be judged that the higher the numerical value of the droplet spreading degree, the higher the hydrophilicity of the membrane filter. Droplet spreading degree = (Diameter of the colored circle on the secondary side of the membrane filter / Diameter of the colored circle on the primary side of the membrane filter) × 100

[0089] [Membrane potential of the membrane filter] Cut out each membrane filter to be measured to a diameter of φ15 mm, and measure it with a streaming potential measurement device (Surpass3 manufactured by Anton Paar, temperature 25°C, pH = 9, electrolyte 1 mmol / L KCl aqueous solution, electrode Ag / AgCl). Obtain the zeta potential on the surface of the membrane filter from the Helmholtz-Smoluchowski equation using the attached analysis software. The average value of three measurements for each membrane filter was taken as the membrane potential. The results are shown in Table 1.

[0090] Pre-filtration Prepare 2000 g of colloidal silica slurry (pH 9.0, manufactured by Nippon Shokubai Catalysts & Chemicals, Ltd., average primary particle diameter 18.0 nm, silica particle concentration 40% by mass, the balance is water), and perform pre-filtration using a Profile II filter (nominal filtration accuracy 1.0 μm, depth type filter) manufactured by Pall Corporation to obtain a pre-filtered colloidal silica slurry that is the filtered component of the present disclosure.

[0091] Examples 1-1 to 3-1 and Comparative Example 1-1 Filtration process Set one membrane filter cut to φ25 mm in a plastic holder (PP-25) manufactured by ADVANTEC, with a pressure of 0.2 MPa, a filtration rate of 50 g / min, and a filtration flow rate of 70 kg / (min·m 2Under the conditions of , the pre-filtered colloidal silica slurry, which is the component to be filtered, was filtered to obtain the component to be filtered after filtration (pH: 9.0).

[0092] The evaluation of the filtration performance was carried out as follows. [Filter liquid passing volume] The components to be filtered after filtration obtained in the above Examples 1-1 to 3-1 and Comparative Example 1-1 were passed through a filter manufactured by Advantec (model: 25HP020AN, hydrophilic PTFE, 0.20 (pore size) μm) under a constant air pressure of 0.30 MPa, and the liquid passing volume (unit: g) until the filter was blocked was determined and shown in Table 1. Also, it was shown in Table 1 as a relative value with the liquid passing volume of Comparative Example 1-1 taken as 100. Here, if the dropping liquid did not fall for 30 seconds, it was judged that the filter was blocked. In addition, the filter liquid passing volume under this condition can be used as an index for the degree of scratch reduction of the polishing liquid prepared using the component to be filtered after filtration. That is, the larger the liquid passing volume, the more it can be evaluated as a polishing liquid for a magnetic disk substrate capable of reducing scratches.

[0093] [Filter life] In the above filtration process, the liquid passing volume when the filtration rate decreased to 17 g / min (1 / 3 of the initial rate) was calculated. Then, by multiplying the ratio of the effective filtration area of φ25 mm to the total effective filtration area used in actual machine production by the liquid passing volume when the filtration rate decreased to 17 g / min, the filter life equivalent to the actual machine production scale (unit: ton) was obtained. The results are shown in Table 1.

[0094] Examples 1-2 to 3-2 and Comparative Example 1-2 Preparation of polishing liquid for magnetic disk substrate To ion-exchanged water, 0.1% by mass of Na salt of 1H-benzotriazole, 0.03% by mass of N-aminoethylethanolamine, 0.02% by mass of sodium salt of acrylic acid / 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. While stirring the aqueous solution, colloidal silica slurry after filtration obtained with the membrane filters obtained in Examples 1-1 to 3-1 and Comparative Example 1-1 was added to a concentration of 5% by mass, and polishing liquids (pH 1.8) for magnetic disk substrates of Examples 1-2 to 3-2 and Comparative Example 1-2 were prepared.

[0095] Substrate polishing using the polishing liquid Using the polishing liquids for magnetic disk substrates of Examples 1-2 to 3-2 and Comparative Example 1-2 prepared as described above, finish polishing was performed under the following polishing conditions. The number of scratches on each polished substrate was evaluated. The evaluation results of the finish polishing are shown in Table 1 below. 〔Substrate to be polished〕 As the substrate to be polished, a Ni-P plated aluminum alloy substrate that had been preliminarily rough-polished 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. 〔Finish polishing conditions〕 Polishing machine: Double-sided polishing machine (Type 9B double-sided polishing machine, manufactured by Speedfam Co., Ltd.) Number of substrates to be polished: 10 Polishing liquid: Polishing liquids for magnetic disk substrates of Examples 1-2 to 3-2 and Comparative Example 1-2 Polishing pad: Suede type (foam layer: polyurethane elastomer, thickness 0.9 mm, average pore diameter 10 μm, manufactured by Fujibo Co., Ltd.) Platen rotation speed: 32.5 rpm Polishing load: 10.5 kPa (set value) Polishing liquid supply rate: 100 mL / min 1 cm of the substrate to be polished 2 Supply rate per 1 cm: 0.076 mL / min 1 cm of the substrate to be polished 2 Amount of polishing per 1 cm: 0.23 mg Polishing time: 6 minutes

[0096] Evaluation of the polishing liquid for magnetic disk substrates [Evaluation of scratches] Measuring instrument: "Candela OSA7100" manufactured by KLA-Tencor Evaluation: Among the substrates put into the polishing tester, 4 pieces were randomly selected, and each substrate was irradiated with a laser at 10,000 rpm to measure the number of scratches. The sum of the 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 Examples 1-2 taken as 100.

[0097]

Table 1

[0098] As shown in Table 1, in Examples 1-2 to 3-2 using a membrane filter with a polyvinylpyrrolidone content ratio (relative to the entire membrane filter) of 0.1 or more as the hydrophilic polymer, compared with Comparative Example 1-2 using a membrane filter containing no hydrophilic polymer, the filter life was improved, and the quality of the components to be filtered after filtration was improved, resulting in a reduction in scratches.

Industrial applicability

[0099] The manufacturing method of the present disclosure is useful as a manufacturing method of a polishing liquid for magnetic disk substrates that can exhibit high performance when used as a polishing liquid for finish polishing.

Claims

1. A method for manufacturing a polishing liquid for a magnetic disk substrate, comprising a step of filtering with a membrane filter composed of a hydrophobic polymer and a hydrophilic polymer.

2. The method for manufacturing a polishing liquid for a magnetic disk substrate according to claim 1, wherein the content ratio of the hydrophilic polymer to the hydrophobic polymer constituting the membrane filter is 0.1% or more.

3. The method for manufacturing a polishing liquid for a magnetic disk substrate according to claim 1 or 2, wherein the hydrophilic polymer contains polyvinylpyrrolidone.

4. The method for manufacturing a polishing liquid for a magnetic disk substrate according to any one of claims 1 to 3, wherein the hydrophobic polymer contains at least one selected from polysulfone and polyethersulfone.

5. The method for manufacturing a polishing liquid for a magnetic disk substrate according to any one of claims 1 to 4, wherein the average pore diameter of the membrane filter is 0.5 μm or more and 2.4 μm or less.

6. The method for manufacturing a polishing liquid for a magnetic disk substrate according to any one of claims 1 to 5, wherein the droplet spreading degree of the membrane filter is 1.5 or more.

7. The method for manufacturing a polishing liquid for a magnetic disk substrate according to any one of claims 1 to 6, wherein the membrane potential of the membrane filter is -62 mV or more.

8. The method for manufacturing a polishing liquid for a magnetic disk substrate according to any one of claims 1 to 7, wherein the filtering step includes a step of filtering using a depth filter before the step of filtering with the membrane filter.

9. The method for manufacturing a polishing liquid for a magnetic disk substrate according to any one of claims 1 to 8, wherein the components subjected to the step of filtering with the membrane filter contain silica particles and water.

10. A method for suppressing clogging of a filter used in a filtering step in the manufacture of a polishing liquid for a magnetic disk substrate, wherein the filtering step is a method for suppressing clogging of a filter in a method for manufacturing a polishing liquid for a magnetic disk substrate, the method having a step of filtering with a membrane filter composed of a hydrophobic polymer and a hydrophilic polymer.

11. 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 9; and a step of supplying the polishing liquid for a magnetic disk substrate obtained in the 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 at least one of the polishing pad and the substrate to be polished to polish the surface to be polished.

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