Method of producing polishing liquid for polishing magnetic disc substrate

Abstract

To provide a method of producing polishing liquid for polishing a magnetic disc substrate, the method enabling both of quality of an obtained polishing liquid, and productivity and economic efficiency in production of the polishing liquid to be made compatible with each other.SOLUTION: A method of producing a polishing liquid for polishing a magnetic disc substrate including a silica particle and water is provided, the method includes: a filtering step of filtering a mixture including a silica particle, and water, the filtering step includes: a step (1) of filtering a mixture including the silica particle and water with a filter aid-including filter F1, thereby obtaining a filtrate (1); and a step (2) of filtering the filtrate (1) obtained by the step (1) by means of a pleat-type filter F2, where the air-flow resistance of the filter aid-including filter F1 of the step (1) is 0.02 MPa or higher, and the air-flow resistance of the pleat-type filter F2 of the step (2) is 0.2 MPa or higher.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a method for producing an abrasive liquid for polishing magnetic disk substrates, a method for suppressing clogging of a filter in the production of an abrasive liquid for polishing magnetic disk substrates, and a method for producing an abrasive liquid for polishing magnetic disk substrates and a magnetic disk substrate. [Background technology]

[0002] In recent years, magnetic disk drives have become smaller and have larger capacities, and higher recording densities are being demanded. To achieve higher recording densities, technological developments are being made to reduce the unit recording area and lower the flying height of the magnetic head in order to improve the detection sensitivity of weakened magnetic signals. In order to lower the flying height of the magnetic head and ensure a sufficient recording area, there are increasingly strict requirements for magnetic disk substrates in terms of improving smoothness and flatness, as typified by reducing surface roughness, waviness, and edge sagging (roll-off), and reducing defects, as typified by reducing scratches, protrusions, pits, etc. In the field of semiconductors, the trend towards higher integration and higher speeds is also progressing, and in particular, finer wiring is required for higher integration. As a result, in the manufacturing process of semiconductor substrates, the focal depth when exposing photoresist is becoming shallower, and even greater surface smoothness is desired.

[0003] In response to such demands, for example, Patent Document 1 proposes a method for producing a silica dispersion used in producing a polishing liquid composition for silicon wafers, the method including a filtration step of filtering a treated silica dispersion P containing silica particles A, a nitrogen-containing basic compound B, and water, in which the content of the nitrogen-containing basic compound B in the treated silica dispersion P is 1 part by mass or more and 15 parts by mass or less per 100 parts by mass of the silica particles A, and the treated silica dispersion P is substantially free of a water-soluble polymer compound, sodium, and potassium. Patent Document 2 proposes a method for producing a polishing composition using a liquid containing colloidal silica abrasive grains, in which the colloidal silica abrasive grains-containing liquid is filtered through a filter, and the filter has a filter fiber layer composed of filter fibers having an average fiber diameter of less than 1 μm. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-117847 A [Patent Document 2] JP 2015-71659 A Summary of the Invention [Problem to be solved by the invention]

[0005] As the capacity of magnetic disk drives increases, the requirements for the surface quality of substrates become more stringent. Therefore, the polishing process in the manufacture of substrates becomes increasingly important, and the quality of the polishing liquid used in the polishing process is key. One of the causes of scratches, which are one type of defect on the substrate surface of a magnetic disk drive, is coarse particles contained in the polishing liquid. Normally, coarse particles in the polishing liquid are removed by filtration during the polishing liquid manufacturing process. In filtering the polishing liquid, there is a trade-off between the quality of the resulting polishing liquid (e.g., fewer coarse particles) and the productivity and economic efficiency. In other words, if the filter diameter is made smaller to improve the quality of the resulting polishing liquid, the filling speed (productivity) decreases. In addition, if the filter diameter is made smaller, the filter is more likely to become clogged, and filter clogging leads to increased frequency of filter replacement, resulting in poor economic efficiency.

[0006] Therefore, in one aspect, the present disclosure provides a method for producing a polishing liquid for polishing magnetic disk substrates, which can achieve both high quality of the resulting polishing liquid and high productivity and cost-effectiveness. [Means for solving the problem]

[0007] In one aspect, the present disclosure relates to a method for producing an abrasive liquid for polishing magnetic disk substrates, which contains silica particles and water, comprising a filtration step of filtering a mixture containing silica particles and water, the filtration step comprising step (1): filtering the mixture containing silica particles and water through a filter aid-containing filter F1 to obtain a filtrate (1), and step (2): filtering the filtrate (1) obtained in step (1) through a pleated filter F2, wherein the filter aid-containing filter F1 in step (1) has an air resistance of 0.02 MPa or more, and the pleated filter F2 in step (2) has an air resistance of 0.2 MPa or more.

[0008] In one aspect, the present disclosure relates to a method for suppressing filter clogging in a filtration step of a mixture containing silica particles and water in the production of a polishing liquid for polishing magnetic disk substrates, the filtration step comprising: step (1): filtering a mixture containing silica particles and water through a filter aid-containing filter F1 to obtain a filtrate (1); and step (2): filtering the filtrate (1) obtained in step (1) through a pleated filter F2, wherein the filter aid-containing filter F1 in step (1) has an airflow resistance of 0.02 MPa or more, and the pleated filter F2 in step (2) has an airflow resistance of 0.2 MPa or more.

[0009] In one aspect, the present disclosure relates to a polishing liquid for polishing magnetic disk substrates, which is obtained by the method for producing a polishing liquid of the present disclosure.

[0010] In one aspect, the present disclosure relates to a method for manufacturing a magnetic disk substrate, comprising: supplying a polishing liquid for polishing magnetic disk substrates, obtained by the method for manufacturing a polishing liquid of the present disclosure, to a surface of a magnetic disk substrate to be polished; bringing a polishing pad into contact with the surface of the magnetic disk substrate to be polished; and moving the polishing pad and / or the magnetic disk substrate to be polished to polish the surface to be polished. Effect of the Invention

[0011] According to one aspect of the present disclosure, a method for producing a polishing liquid for polishing magnetic disk substrates can be provided, which can achieve both high quality of the resulting polishing liquid and high productivity and cost-effectiveness. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present disclosure is based on the finding that a polishing liquid for polishing magnetic disk substrates that is excellent in productivity and economy and has excellent quality can be produced by including a process of filtering a mixture of silica particles and water using a filter aid-containing filter F1 having a specific air resistance and a pleated filter F2 having a specific air resistance.

[0013] That is, in one aspect, the present disclosure provides a method for producing a polishing slurry for polishing magnetic disk substrates, which contains silica particles and water, the method including a filtration step of filtering a mixture containing silica particles and water, The filtration step includes the following steps (1) and (2): Step (1): filtering a mixture containing silica particles and water through a filter aid-containing filter F1 to obtain a filtrate (1); step (2): filtering the filtrate (1) obtained in step (1) through a pleated filter F2; The air flow resistance of the filter aid-containing filter F1 in step (1) is 0.02 MPa or more, The present invention relates to a method for producing an abrasive slurry for polishing magnetic disk substrates (hereinafter also referred to as "the method for producing the abrasive slurry of the present disclosure"), in which the pleated filter F2 in step (2) has an airflow resistance of 0.2 MPa or more. According to the present disclosure, it is possible to provide a method for producing an abrasive liquid for polishing magnetic disk substrates, which produces an abrasive liquid for polishing magnetic disk substrates of excellent quality and can improve productivity and cost-effectiveness.

[0014] Although the details of the mechanism by which the effect of the method for producing a polishing liquid according to the present disclosure is exerted are not clear, it is presumed as follows. When removing coarse silica particles from a mixture containing silica particles and water (for example, a silica dispersion used to manufacture a polishing liquid before filtration (treated silica dispersion)) using a pleated filter, the greater the airflow resistance of the filter, the greater the filter's ability to capture coarse particles, and therefore the fewer the number of coarse particles contained in the resulting silica dispersion or polishing liquid, i.e., the higher the quality. On the other hand, the greater the airflow resistance of the filter, the more likely it is that filter clogging will occur, and the more economical it tends to be. In the present disclosure, a filter containing a filter aid with a large airflow resistance is used in the filtration process prior to the pleated filter. This allows many coarse particles to be removed before filtration by the pleated filter, suppressing clogging of the pleated filter, making it possible to achieve both high-quality polishing liquid and economical efficiency. In addition, in general, when removing coarse particles using a filter containing a filter aid, in order to increase the filtration efficiency, the amount of the filter aid is increased or the particle diameter of the filter aid itself is reduced to increase the packing density. However, the above methods reduce the filtration rate, which leads to a deterioration in productivity. In the present disclosure, only the airflow resistance of the filter aid-containing filter is increased without changing the amount or particle size of the filter aid. This is because the filter aid has a smaller pore diameter (hereinafter also simply referred to as "pore diameter") than conventional ones (for example, 1 μm or less). This increases the capture efficiency by physically adsorbing coarse particles to the pores, but the thickness and density (weight and area) of the filter aid layer do not change, so the filtration rate is maintained and the quality of the silica dispersion after filtration is also maintained. In other words, in addition to achieving both high-quality polishing liquid and economic efficiency, productivity can also be improved. However, the present disclosure need not be construed as being limited to these mechanisms.

[0015] In the present disclosure, "coarse particles" refers to coarse silica particles having a particle diameter of 0.5 μm or more, and the number of coarse particles in a mixture containing silica particles and water can be evaluated by the amount of liquid passing through a 0.20 μm pore size filter described in the Examples below. The greater the amount of liquid passing through, the fewer the number of coarse particles in the mixture containing silica particles and water, and the higher the filtration accuracy. In the present disclosure, the silica particles in the mixture containing silica particles and water include not only primary particles but also aggregated particles formed by aggregation of primary particles.

[0016] In this disclosure, a "scratch" is a physical property that is important for high density or high integration in hard disk substrates or semiconductor device substrates, particularly in hard disk substrates, and is a fine scratch on the substrate surface with a depth of 1 nm or more but less than 100 nm, a width of 5 nm or more but 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).

[0017] [Filtration process] The method for producing a polishing liquid for polishing magnetic disk substrates according to the present disclosure includes a filtration step, and the filtration step includes the following steps (1) and (2). Step (1): A step of filtering a mixture containing silica particles and water through a filter aid-containing filter F1 to obtain a filtrate (1) Step (2): filtering the filtrate (1) obtained in step (1) through a pleated filter F2. In the present disclosure, the term "filtrate" refers to the filtrate that has passed through a filter in one or more embodiments. The filtrate may be the filtrate itself, or in some cases, it may be a diluted or concentrated filtrate. The filtrate obtained by filtering a mixture containing silica particles and water is a mixture containing silica particles and water, but when the term "mixture containing silica particles and water" is used without any particular explanation in the present disclosure, it refers to the "mixture containing silica particles and water" that is the material to be treated before the filtration process. In the present disclosure, the "mixture containing silica particles and water" that is the material to be treated before the filtration process is also referred to as the "treated silica dispersion".

[0018] (Filter containing filter aid F1) The filter aid-containing filter F1 in step (1) is a filter containing at least a filter aid. The air resistance of the filter aid-containing filter F1 is, from the viewpoints of improving the quality of the polishing liquid and economy, 0.02 MPa or more, preferably 0.03 MPa or more, and more preferably 0.044 MPa or more, and from the viewpoint of improving productivity, preferably 1.0 MPa or less, more preferably 0.5 MPa or less, and even more preferably 0.1 MPa or less. In the present disclosure, the airflow resistance can be measured, for example, by an airflow resistance tester in accordance with the air permeability A method (Fragile type method) specified in JIS L1096, specifically, by the method described in the Examples. The airflow resistance of the filter aid-containing filter F1 can be adjusted by selecting and blending a filter aid having an optimal pore diameter when producing the filter.

[0019] Examples of the filter aid contained in the filter aid-containing filter F1 include insoluble mineral substances such as silicon dioxide, kaolin, acid clay, diatomaceous earth, perlite, bentonite, talc, etc. In the present disclosure, the filter aid contained in the filter aid-containing filter F1 is preferably one or more selected from silicon dioxide, diatomaceous earth, and perlite, more preferably one or more selected from diatomaceous earth and perlite, and even more preferably one containing diatomaceous earth, from the viewpoint of improving productivity. The ratio of one or more types selected from diatomaceous earth and perlite in the filter aid contained in the filter aid-containing filter F1 is preferably 50% or more by mass, more preferably 75% or more, even more preferably 95% or more, and even more preferably 100%. The proportion of diatomaceous earth in the filter aid contained in the filter aid-containing filter F1 is preferably 50% or more by mass, more preferably 75% or more, even more preferably 95% or more, and still more preferably 100%.

[0020] From the viewpoint of reducing coarse particles, the laser average particle size of the filter aid is preferably 1 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and even more preferably 15 μm or more, and from the same viewpoint, it is preferably 100 μm or less, more preferably 60 μm or less, even more preferably 50 μm or less, even more preferably 40 μm or less, even more preferably 20 μm or less, even more preferably 18 μm or less, and even more preferably 17 μm or less. In the present disclosure, the "laser average particle size" of the filter aid refers to the average particle size of the filter aid particles measured by a laser particle size distribution measuring device, and in the present disclosure, it is a value calculated by measuring the scattering intensity distribution obtained by the Marquardt method at a detection angle of 90°. In one or more embodiments, it can be measured by the method described in the Examples.

[0021] From the viewpoint of increasing the product yield, the pore diameter of the filter aid is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more, and from the same viewpoint, it is preferably 1 μm or less, more preferably 0.9 μm or less, even more preferably 0.85 μm or less, even more preferably 0.81 μm or less, and even more preferably 0.70 μm or less. In the present disclosure, the pore diameter of the filter aid is a value calculated by observation with an electron microscope and image analysis. In one or more embodiments, the pore diameter of the filter aid can be measured by the method described in the Examples.

[0022] The filter aid-containing filter F1 may contain the filter aid on either or both of the filter surface and the inside of the filter. The filter aperture is preferably 10 μm or less, more preferably 5 μm or less, even more preferably 3 μm or less, and even more preferably 2 μm or less from the viewpoint of preventing leakage of the filter aid, and is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.3 μm or more, and even more preferably 0.5 μm or more from the viewpoint of improving productivity and improving the filter passing speed. Examples of methods for using the filter aid include the precoat method and the body feed method. Here, the precoat method is a method for forming a cake filter, which is a method for forming a filter aid layer (cake layer) with a thickness of about several mm on a filter material (filter medium) described later. For example, a method is exemplified in which filter aid particles are dispersed in water, and the filter aid is filtered out with a filter medium to form a filter aid layer. In the present disclosure, the thickness of the filter aid layer (cake layer) of the filter aid-containing filter F1 is preferably 1 mm or more, more preferably 2 mm or more, even more preferably 3 mm or more, and preferably 10.0 mm or less, more preferably 8 mm or less, and even more preferably 5 mm or less. In the present disclosure, the density of the filter aid layer of the filter aid-containing filter F1 is preferably 0.05 g / cm 2 More preferably, 0.1 g / cm 2 More preferably, 0.2 g / cm 2 and preferably 1 g / cm 2 Less than or equal to 0.8 g / cm 2 More preferably, 0.5 g / cm 2 The body feed method is a method of filtering the raw liquid to be filtered by cake while adding a certain amount of filter aid, and the purpose is to improve the filterability of the raw liquid. It is effective for raw liquid with small particle size that immediately maximizes the cake resistance (making it impossible to filter).

[0023] The content of the filter aid in the filter aid-containing filter F1 (g / cm 2 ) is preferably 0.001 g / cm from the viewpoint of reducing coarse particles.2 More preferably, 0.005 g / cm 2 More preferably, 0.01 g / cm 2 More preferably, 0.02 g / cm 2 More preferably, 0.04 g / cm 2 More preferably, 0.1 g / cm 2 From the viewpoints of improving productivity and economy, and of improving the filtration rate, it is preferably 1 g / cm 2 Less than or equal to 0.8 g / cm 2 More preferably, 0.6 g / cm 2 More preferably, 0.4 g / cm 2 More preferably, 0.3 g / cm 2 More preferably, 0.2 g / cm 2 The following is the result.

[0024] Examples of the filter material (filter medium) of the filter aid-containing filter F1 include paper, synthetic resins such as polyethylene, polypropylene, polyethersulfone, cellulose acetate, nylon, polycarbonate, and Teflon (registered trademark), ceramics, and metals. From the viewpoint of maintaining the quality of the mixture containing silica particles and water after filtration, paper and synthetic resins such as polyethylene, polypropylene, polyethersulfone, cellulose acetate, nylon, polycarbonate, and Teflon (registered trademark) are preferred, one or more selected from paper, polyethylene, polypropylene, polyethersulfone, cellulose acetate, and nylon, and combinations thereof are more preferred, and one or more selected from paper, polyethylene, and polypropylene, and combinations thereof are even more preferred.

[0025] The shape of the filter aid-containing filter F1 is not particularly limited, but from the viewpoint of ease of handling and increasing the efficiency of reducing coarse particles, a sheet type, a cylindrical type, a disk type, or a folded type is preferred, a sheet type, a disk type, or a folded type is more preferred, and a disk type or a folded type is even more preferred.

[0026] The number of stages of the filter aid-containing filter F1 is preferably 1 to 5 stages, more preferably 1 to 3 stages, and even more preferably 1 or 2 stages, from the viewpoints of improving filtration accuracy, productivity, and economic efficiency.

[0027] (Pleated filter F2) The airflow resistance of the pleated filter F2 in step (2) is 0.2 MPa or more, preferably 0.3 MPa or more, and more preferably 0.4 MPa or more from the viewpoint of reducing coarse particles, and is preferably 3.0 MPa or less, more preferably 1.0 MPa or less, and even more preferably 0.8 MPa or less from the viewpoints of economy and safety of the device. The airflow resistance of the pleated filter F2 can be adjusted, for example, by the mesh size of the filter.

[0028] When the airflow resistance of the filter aid-containing filter F1 is VR1 and the airflow resistance of the pleated filter F2 is VR2, the value represented by the formula (VR1) × (VR2) × 100 is preferably 0.9 or more, more preferably 1.0 or more, and even more preferably 1.5 or more, from the viewpoint of reducing coarse particles and improving productivity, and is preferably 500.0 or less, more preferably 50.0 or less, and even more preferably 8.0 or less, from the viewpoint of improving productivity.

[0029] In the present disclosure, the pleated filter F2 refers to a filter material that has been molded into a pleated shape. The pleated filter F2 can be applied to either a depth type filter that captures particles at each portion in the thickness direction, or a surface type filter that captures particles on the filter surface, but it is preferable that the pleated filter F2 is a surface type filter formed into a pleated shape. Examples of surface-type filters include membranes and punchings. Among these, membranes using any one selected from polyethersulfone, polysulfone, polypropylene, nylon, polytetrafluoroethylene, and acetylcellulose are preferred, membranes using any one selected from polyethersulfone, polysulfone, nylon, and polypropylene are more preferred, and membranes using any one selected from nylon and polyethersulfone are even more preferred.

[0030] The pleated filter F2 may be used in one stage or in multiple stages (eg, in a series arrangement).

[0031] The pore size of the pleated filter F2 is preferably 0.1 μm or more from the viewpoint of improving the productivity and economy in the production of the polishing liquid of the present disclosure and extending the service life of the filter, and is preferably 1.0 μm or less, more preferably 0.8 μm or less, and even more preferably 0.6 μm or less, from the viewpoint of reducing coarse particles. Furthermore, when the pleated filter F2 is a surface-type filter, the surface-type filter constituting the pleated filter F2 may have a built-in filter mechanism, i.e., a prefilter, having a pore size larger than that of the main filter, at the upstream stage of the main filter (two-layer structure). The filter material molded into pleats of the pleated filter F2 may be further molded, and a preferred example of the further molded shape is a hollow cylindrical shape.

[0032] [Process(0)] In one or more other embodiments, the filtration step may include a step of filtering a mixture containing silica particles and water with a depth filter F0 to obtain a filtrate (0) before step (1). In this case, in step (1), the filtrate (0) is filtered with a filter aid-containing filter F1 to obtain a filtrate (1). By filtering with the depth filter F0 prior to step (1), it is believed that the depth filter F0 can remove particularly large coarse particles, and the performance of the filter aid-containing filter F1 can be further enhanced. Therefore, in one or more other embodiments, the filtration step may include the following steps (0) to (2). Step (0): A step of filtering a mixture containing silica particles and water through a depth filter F0 to obtain a filtrate (0) Step (1): A step of filtering the filtrate (0) obtained in step (0) through a filter aid-containing filter F1 to obtain the filtrate (1). Step (2): filtering the filtrate (1) obtained in step (1) through a pleated filter F2.

[0033] (Depth filter F0) As described above, the depth type filter F0 means a filter that captures particles at each part in the thickness direction. More specifically, the pore structure of the filter medium is coarse at the inlet side, fine at the outlet side, and becomes finer continuously or stepwise from the inlet side to the outlet side. Therefore, among the coarse particles, the larger particles are captured near the inlet side, and the smaller particles are captured near the outlet side. The depth type filter F0 uses this depth type filter, and its shape can be a bag type or a cartridge type with a hollow cylindrical shape. In addition, since a depth type filter molded into a pleat shape naturally has the function of the depth type filter F0, when a depth type filter molded into a pleat shape is used before the step of filtering with the filter aid-containing filter F1 to obtain the filtrate (1), the depth type filter molded into a pleat shape is classified as a depth type filter F0 in the present disclosure.

[0034] The depth type filter F0 may be used in a single stage, or in a combination of multiple stages (for example, in a direct arrangement), or in a combination of multiple stages of filters having different pore sizes in descending order of pore size.Furthermore, a bag type filter and a cartridge type filter may be used in combination.

[0035] The filtration accuracy of the depth-type filter F0 is preferably 5.0 μm or less, more preferably 3.0 μm or less, even more preferably 2.0 μm or less, even more preferably 1.0 μm or less, and even more preferably 0.5 μm or less, from the standpoint of productivity and economy in the manufacturing method of the polishing liquid of the present disclosure, and from the standpoint of extending the life of the filter, and from the standpoint of reducing coarse particles in the polishing liquid of the present disclosure described below. Here, the filtering accuracy of the depth type filter F0 refers to the particle size at which 99.8% of the particles present in the liquid being filtered can be removed on a number basis.

[0036] In the filtration step, the filtration pressure in step (1) and step (2) is preferably 0.16 MPa or more, more preferably 0.18 MPa or more, and even more preferably 0.20 MPa or more, from the viewpoint of reducing coarse particles and improving productivity and economy, and from the same viewpoints, is preferably 0.59 MPa or less, more preferably 0.55 MPa or less, even more preferably 0.50 MPa or less, and still more preferably 0.45 MPa or less. In the present disclosure, "filtration pressure" refers to the difference between the pressure on the feed side and the pressure on the filtrate side of the filter aid-containing filter F1 and the pleated filter F2. When the filtration step includes a step (0), the suitable range of the filtration pressure in the step (0) is the same as the suitable range of the filtration pressure in the step (1) and the step (2).

[0037] In the filtration step, the filtration flow rate in step (1) and step (2) is preferably 10.0 kg / (min m) from the viewpoint of reducing coarse particles and improving productivity and economy. 2 ) or more, and more preferably 12.0 kg / (min m 2 ) or more, and more preferably 14.0 kg / (min m 2) or more, and from the same viewpoint, preferably 40.0 kg / (min m 2 ) or less, and more preferably 38.0 kg / (min m 2 ) or less, and more preferably 36.0 kg / (min m 2 ) or less. In this disclosure, the "filtration flow rate" refers to the mass filtered per unit area of ​​the filter per time, and in one or more embodiments, can be adjusted by adjusting the valve on the secondary side, which is the outlet of the filter. When the filtration step includes a step (0), the suitable range of the filtration flow rate in the step (0) is the same as the suitable filtration flow rates in the steps (1) and (2).

[0038] The filtration method in the steps (1), (2), and (0) may be a circulation method in which filtration is repeated, or a one-pass method. A batch method in which one-pass methods are repeated may also be used. The circulation method, one-pass method, and batch method may be performed for each step, or each method may be performed again after completing steps (1) to (2), or steps (0) to (2). As for the liquid passing method, a pump is preferably used in the circulation method to apply pressure, and in the one-pass method, in addition to using a pump, a pressure filtration method in which the fluctuation range of the filter inlet pressure is small by introducing air pressure or the like into the tank may be used.

[0039] In the manufacturing method of the polishing liquid of the present disclosure, in addition to the above-mentioned filtration step, a general dispersion step or particle removal step may be provided. For example, a dispersion step using a high-speed dispersion device or a high-pressure dispersion device such as a high-pressure homogenizer, or a coarse particle settling step using a centrifugal separator or the like may be used. When using these, each may be used alone or in combination of two or more types, and there is no restriction on the order of the combination. In addition, the processing conditions and the number of times of processing may be appropriately selected and used.

[0040] [Mixture containing silica particles and water (treated silica dispersion)] In the present disclosure, the mixture containing silica particles and water (treated silica dispersion) refers to a slurry containing silica in one or more embodiments, and refers to a slurry before step (0) if the filtration step in the present disclosure includes step (0), and before step (1) if the filtration step in the present disclosure does not include step (0). In one or more embodiments, the treated silica dispersion may contain an additive (e.g., an acid, an oxidizing agent, a heterocyclic aromatic compound, an amine compound, etc., which will be described later) that can be blended in the polishing liquid of the present disclosure.

[0041] <Silica particles (component A)> Examples of silica particles (hereinafter also referred to as "component A") contained in the mixture containing silica particles and water (treated silica dispersion) include colloidal silica, fumed silica, pulverized silica, and silica obtained by surface modification of these, from the viewpoint of improving the polishing rate and reducing scratches, and among these, colloidal silica is preferred. Colloidal silica can be obtained, for example, by a method of producing it from an aqueous silicic acid solution. In addition, these particles can be surface-modified or surface-modified with functional groups, or composite particles made with surfactants or other abrasives. Component A may be one type or a combination of two or more types.

[0042] The shape of component A may be spherical or non-spherical. The use form of Component A is preferably a slurry-like polishing liquid component.

[0043] From the viewpoint of improving the quality of the polishing liquid for polishing magnetic disk substrates and reducing scratches, the average primary particle diameter of component A is preferably 1 nm or more, more preferably 3 nm or more, even more preferably 5 nm or more, even more preferably 10 nm or more, and even more preferably 12 nm or more, and from the viewpoint of reducing scratches, it is preferably 100 nm or less, more preferably 80 nm or less, even more preferably 50 nm or less, even more preferably 30 nm or less, and even more preferably 25 nm or less. In the method for producing a polishing liquid of the present disclosure, the average primary particle diameter of silica particles is determined based on the specific surface area S (m2 The average primary particle size can be measured by the method described in the Examples.

[0044] In the manufacturing method of the polishing liquid of the present disclosure, the content of component A in the mixture containing silica particles and water (treated silica dispersion) is preferably 1 mass % or more, more preferably 5 mass % or more, even more preferably 10 mass % or more, and even more preferably 15 mass % or more from the viewpoint of improving productivity, and is preferably 70 mass % or less, more preferably 60 mass % or less, even more preferably 50 mass % or less, and even more preferably 45 mass % or less from the viewpoint of reducing scratches. When component A is a combination of two or more kinds, the content of component A refers to the total content thereof.

[0045] <Water> In the manufacturing method of the polishing liquid of the present disclosure, examples of the water contained in the mixture containing silica particles and water (treated silica dispersion) include ion-exchanged water, distilled water, ultrapure water, etc. The content of water in the treated silica dispersion can be the remainder obtained by subtracting component A and additives (such as acids, oxidizing agents, heterocyclic aromatic compounds, amine compounds, anionic water-soluble polymers, etc. described below) from 100 mass%. The content of each component in the mixture containing silica particles and water (treated silica dispersion) can be the content or blending amount of each component in the polishing liquid of the present disclosure.

[0046] In one or more embodiments, the pH of the mixture containing silica particles and water (treated silica dispersion) is preferably 8.5 or more, more preferably 8.8 or more, and even more preferably 9.0 or more, and is preferably 11 or less, more preferably 10.8 or less, and even more preferably 10.5 or less, from the viewpoint of improving productivity and reducing scratches. 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 a value at 25°C, and is a value measured using a pH meter. Specifically, it can be measured by the method described in the examples.

[0047] [Method for preventing filter clogging in the manufacture of polishing fluid for polishing magnetic disk substrates] In one or more embodiments, by subjecting the treated silica dispersion to the filtration step, it is possible to obtain a filtrate (silica dispersion after the filtration step) having reduced coarse particles while suppressing clogging of the filter used in the filtration step. Therefore, in another aspect, the present disclosure relates to a method for suppressing filter clogging in a filtration process of a mixture containing silica particles and water in the production of a polishing liquid for polishing magnetic disk substrates, the filtration process including the following steps (1) and (2) (hereinafter also referred to as the "filter clogging suppression method of the present disclosure"). Step (1): filtering a mixture containing silica particles and water through a filter aid-containing filter F1 to obtain a filtrate (1); step (2): filtering the filtrate (1) obtained in step (1) through a pleated filter F2; Here, the airflow resistance of the filter aid-containing filter F1 in step (1) is 0.02 MPa or more, and the airflow resistance of the pleated filter F2 in step (2) is 0.2 MPa or more. In addition, in one or more other embodiments, the filtration step of the filter clogging suppression method of the present disclosure may include the following steps (0) to (2). Step (0): A step of filtering a mixture containing silica particles and water through a depth filter F0 to obtain a filtrate (0) Step (1): A step of filtering the filtrate (0) obtained in step (0) through a filter aid-containing filter F1 to obtain the filtrate (1). Step (2): filtering the filtrate (1) obtained in step (1) through a pleated filter F2. According to the method of suppressing filter clogging disclosed herein, by producing an abrasive liquid for polishing magnetic disk substrates using the method described in the above-mentioned steps (1), (2), and, if necessary, (0), it is possible to suppress filter clogging in the filtration step of producing an abrasive liquid for polishing magnetic disk substrates.

[0048] In the method for producing a polishing liquid and the method for suppressing filter clogging of the present disclosure, the pH of the filtrate obtained by subjecting the treated silica dispersion to a filtration step, i.e., the pH of the silica dispersion after filtration, is preferably the same as the pH of the silica dispersion before being subjected to step (1), step (2), and step (0), respectively. In the present disclosure, if the difference in pH is ±0.2, the pH is considered to be the same. The pH of the silica dispersion after filtration can be measured by the method described in the Examples.

[0049] In the method for producing a polishing liquid and the method for suppressing filter clogging of the present disclosure, the content of each component in the silica dispersion after filtration can be the same as that of the treated silica dispersion before the filtration.

[0050] In the disclosed method for producing a polishing liquid and the disclosed method for suppressing filter clogging, the amount of the silica dispersion passing through the filter after filtration (unit: g) is, from the viewpoint of improving the quality of the polishing liquid for polishing magnetic disk substrates, preferably 1 g or more, more preferably 5 g or more, even more preferably 10 g or more, still more preferably 50 g or more, still more preferably 100 g or more, and still more preferably 120 g or more, and from the viewpoint of improving productivity, is preferably 3000 g or less, more preferably 2000 g or less, and even more preferably 1500 g or less. In the present disclosure, the method for measuring the amount of silica dispersion passing through the filter after filtration is to place the silica dispersion after filtration in a container equipped with a specific filter, pressurize the silica dispersion to pass through the specific filter, and measure the amount of the silica dispersion passing through the filter until the filter is clogged. In the present disclosure, the amount of silica dispersion passing through the filter after filtration is calculated by the method described in the examples using a specific filter.

[0051] In general, the polishing liquid contains raw silica, water and additives as required.In one or more embodiments of the manufacturing method of the polishing liquid of the present disclosure, the mixture (processed silica dispersion liquid) containing silica particles and water is subjected to the above-mentioned filtration process (step (1), step (2), and step (0) as required) to obtain the silica dispersion liquid, and the obtained silica dispersion liquid can be used as the polishing liquid for magnetic disk substrate polishing, and additives (such as acid, oxidizing agent, heterocyclic aromatic compound, amine compound, anionic water-soluble polymer, etc., which will be described later) can be added to obtain the polishing liquid for magnetic disk substrate polishing. Alternatively, in one or a plurality of embodiments, the polishing liquid of the present disclosure can be obtained by subjecting a "mixture containing silica particles and water (treated silica dispersion)" containing an additive to step (0) as necessary, and then subjecting it to the above-mentioned steps (1) and (2). Among these, from the viewpoint of the quality of the polishing liquid for polishing magnetic disk substrates, it is preferable that the polishing liquid of the present disclosure is obtained by subjecting a mixture containing silica particles and water (treated silica dispersion) to the above-mentioned filtration step, and mixing the obtained silica dispersion with additives. Therefore, in one or more embodiments, the method for producing the polishing liquid of the present disclosure may include a step of blending a mixture containing silica particles and water (including before, during, and after filtration) with at least one selected from an acid, an oxidizing agent, a heterocyclic aromatic compound, an amine compound, and an anionic water-soluble polymer before, during, or after the filtration step. In the present disclosure, "blending" includes mixing silica particles, water, and, if necessary, the exemplified compounds (acid, oxidizing agent, heterocyclic aromatic compound, amine compound, anionic water-soluble polymer) simultaneously or in any order. The blending can be performed using a mixer such as a homomixer, a homogenizer, an ultrasonic disperser, and a wet ball mill. In the present disclosure, an additive refers to a component other than raw silica that can be blended in the polishing liquid used for polishing the magnetic disk substrate to be polished. Examples of the component other than raw silica include an acid, an oxidizing agent, a heterocyclic aromatic compound, an amine compound, and an anionic water-soluble polymer, which will be described later.

[0052] [Polishing fluid for polishing magnetic disk substrates] In one aspect, the present disclosure relates to a polishing liquid for polishing magnetic disk substrates (hereinafter also referred to as the "polishing liquid of the present disclosure") obtained by the method for producing a polishing liquid of the present disclosure. In one or a plurality of embodiments, the polishing liquid of the present disclosure may include, in addition to silica particles (component A) and water, optional components (for example, an acid, an oxidizing agent, a heterocyclic aromatic compound, an amine compound, an anionic water-soluble polymer, other components, etc., which will be described later).

[0053] <Silica particles (component A) 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, they are derived from the filtered silica dispersion. The content of Component A in the polishing liquid of the present disclosure is preferably 0.05 mass % or more, more preferably 0.1 mass % or more, and even more preferably 0.2 mass % or more from the viewpoint of improving the polishing rate, and is preferably 10 mass % or less, more preferably 7.5 mass % or less, and even more preferably 5 mass % or less, from the viewpoint of improving dispersibility and storage stability.

[0054] <Water> Examples of water contained in the polishing liquid of the present disclosure include ion-exchanged water, distilled water, ultrapure water, etc. The content of water in the polishing liquid of the present disclosure corresponds to the remainder obtained by subtracting component A and optional components (component B, component C, component D, component E, component F, other components, etc. described below) from 100 mass%, and is preferably 60 mass% or more, more preferably 80 mass% or more, and is preferably 99 mass% or less, more preferably 97 mass% or less.

[0055] In one or more embodiments, the polishing liquid of the present disclosure preferably further contains at least one 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). These components B to F are described below.

[0056] <Acid (component B)> The polishing liquid of the present disclosure preferably further contains an acid (hereinafter also referred to as "component B"). In the present disclosure, the acid includes an acid or a salt thereof. Component B may be one type or a combination of two or more types.

[0057] 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, amidosulfuric acid, etc.; organic acids such as organic phosphoric acid, organic phosphonic acid, carboxylic acid, etc. Among these, component B preferably contains an inorganic acid and an organic phosphonic acid, more preferably contains an inorganic acid, and further preferably contains only an inorganic acid, from the viewpoint of improving the polishing rate and reducing scratches. The inorganic acid is preferably at least one selected from nitric acid, sulfuric acid, hydrochloric acid, perchloric acid and phosphoric acid, and more preferably phosphoric acid. The organic phosphonic acid is preferably at least one selected from 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), aminotri(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), and diethylenetriaminepenta(methylenephosphonic acid), and HEDP is more preferable. Examples of 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.

[0058] 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 mass % or more, more preferably 0.1 mass % or more, and even more preferably 0.5 mass % or more, from the viewpoint of improving the quality of the polishing liquid, such as increasing the polishing rate and reducing scratches, and from the same viewpoint, is preferably 5 mass % or less, more preferably 4 mass % or less, even more preferably 3 mass % or less, and even more preferably 2 mass % or less. When component B is a combination of two or more types, the content of component B refers to the total content thereof.

[0059] <Oxidizing agent (component C)> From the viewpoint of improving the quality of the polishing liquid, such as increasing the polishing rate and further reducing scratches, it is preferable that the polishing liquid of the present disclosure 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.

[0060] Examples of component C include peroxides, permanganic acid or its salts, chromic acid or its salts, peroxoacid or its salts, oxyacid or its salts, metal salts, nitric acids, sulfuric acids, etc., from the viewpoint of improving the polishing rate and the quality of the polishing liquid, such as scratches. Among these, at least one selected from hydrogen peroxide, iron (III) nitrate, peracetic acid, ammonium peroxodisulfate, iron (III) sulfate, and ammonium iron (III) sulfate is preferred, and hydrogen peroxide is more preferred from the viewpoint of improving the polishing rate, preventing metal ions from adhering to the surface of the magnetic disk substrate to be polished, and ease of availability.

[0061] 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 mass % or more, more preferably 0.05 mass % or more, and even more preferably 0.1 mass % or more, and is preferably 4 mass % or less, more preferably 2 mass % or less, and even more preferably 1 mass % or less, from the viewpoint of improving the quality of the polishing liquid, such as further improving the polishing rate and further reducing scratches. When component C is a combination of two or more types, the content of component C refers to the total content thereof.

[0062] <Heterocyclic aromatic compounds (component D)> In one or more embodiments, the polishing liquid of the present disclosure preferably further contains a heterocyclic aromatic compound (including a salt thereof) (component D) from the viewpoint of improving the quality of the polishing liquid, such as further improving the polishing rate and further reducing scratches. Component D may be one type or a combination of two or more types.

[0063] From the viewpoint of improving the quality of the polishing liquid, such as further increasing the removal rate and further reducing scratches, component D 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, and preferably having nine or less nitrogen atoms in the heterocycle, more preferably having five or less nitrogen atoms in the heterocycle, and even more preferably having four or less nitrogen atoms in the heterocycle.

[0064] In one or more embodiments, component D is preferably 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 alkyl or amine substituted derivatives thereof. Examples of the alkyl group of the alkyl substituent include lower alkyl groups having 1 to 4 carbon atoms, and in one or more embodiments, methyl and ethyl groups. In one or more embodiments, examples of the amine substituent include 1-[N,N-bis(hydroxyethylene)aminomethyl]benzotriazole, 1-[N,N-bis(hydroxyethylene)aminomethyl]tolyltriazole, and the like. Among these, from the viewpoint of further reducing scratches, component D is more preferably at least one selected from 1H-benzotriazole (BTA), 1H-tolyltriazole, 2-aminobenzotriazole, and 3-aminobenzotriazole, and further preferably 1H-benzotriazole (BTA).

[0065] 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, and even more preferably 0.02% by mass or more, from the viewpoint of improving the quality of the polishing liquid, such as further improving the polishing rate and further reducing scratches, and from the viewpoint of improving the polishing rate, 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 types, the content of component D refers to the total content thereof.

[0066] <Amine compound (ingredient E)> In one or more embodiments, the polishing liquid of the present disclosure preferably further contains an amine compound (component E) from the viewpoint of improving the quality of the polishing liquid, such as further improving the polishing rate and further reducing scratches. A preferred example of the functional group contained in the amine compound is an amino group. 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 one type or a combination of two or more types.

[0067] As the amine compound, aliphatic amine compounds or alicyclic amine compounds are preferably mentioned. In one or more embodiments, the aliphatic amine compound is preferably 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, more preferably at least one selected from N-aminoethylethanolamine, N-aminoethylisopropanolamine, and N-aminoethyl-N-methylethanolamine, and even more preferably N-aminoethylethanolamine (AEA). In one or a plurality of embodiments, from the viewpoint of improving the quality of the polishing liquid, such as further improving the polishing rate and further reducing scratches, the alicyclic amine compound is preferably at least one selected from piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, 1-amino-4-methylpiperazine, N-methylpiperazine, and hydroxyethylpiperazine (HEP), and more preferably hydroxyethylpiperazine (HEP).

[0068] 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, and even more preferably 0.02% by mass or more from the viewpoint of improving the quality of the polishing liquid, such as improving the polishing rate and further reducing scratches, and is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even 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 types, the content of component E refers to the total content thereof.

[0069] <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 (component F) from the viewpoint of improving the quality of the polishing liquid, such as further improving the polishing rate and further reducing scratches. The anionic water-soluble polymer 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 in water (20°C), preferably a solubility of 2 g / 100 mL or more. Component F may be one type or a combination of two or more types.

[0070] In one or more embodiments, a suitable example of a monomer having an anionic group in the molecule is a vinyl monomer. The anionic group of the vinyl monomer having an anionic group in the molecule is preferably a carboxylic acid group or a sulfonic acid group. The vinyl monomer having a carboxylic acid group in the molecule is preferably at least one selected from acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, styrenesulfonic acid, and salts thereof. The vinyl monomer having a sulfonic acid group in the molecule is preferably 2-acrylamido-2-methylpropanesulfonic acid. Suitable examples of a water-soluble polymer having a vinyl monomer having an anionic group in the molecule as a constituent unit include acrylic acid / 2-acrylamido-2-methylpropanesulfonic acid copolymer (AA / AMPS), polystyrenesulfonic acid, and salts thereof. Examples of salts include alkali metal salts, ammonium salts, and organic amine salts. In one or more embodiments, component F may be a condensate or salt of an aromatic compound having a sulfonic acid group or a salt thereof, a polymer or salt thereof containing a structural unit derived from an aromatic vinyl monomer having a sulfonic acid group or a salt thereof, etc. Examples of the salt include an alkali metal salt, an ammonium salt, and an organic amine salt. From the viewpoint of further reducing scratches, the condensate or salt of an aromatic compound having a sulfonic acid group or a salt thereof is preferably a condensate or salt thereof having a structure in which at least one hydrogen atom of an aromatic ring constituting a main chain is substituted with a sulfonic acid group, and more preferably at least one selected from a phenolsulfonic acid condensate, a naphthalenesulfonic acid condensate, and salts thereof. In one or more embodiments, a suitable example of a monomer having an anionic group in the molecule is an aromatic compound containing a sulfonic acid group or a salt thereof. As the aromatic compound containing a sulfonic acid group or a salt thereof, a compound having a structure in which at least one hydrogen atom of an aromatic ring is substituted with a sulfonic acid group or a salt thereof is preferred, and at least one selected from phenolsulfonic acid, naphthalenesulfonic acid, and salts thereof is preferred. Examples of the salt include alkali metal salts, ammonium salts, and organic amine salts. In this disclosure, a monomer having an anionic group in the molecule and also having a vinyl group is considered to be a vinyl-based monomer having an anionic group in the molecule. Suitable examples of the water-soluble polymer having an aromatic compound containing a sulfonic acid group or a salt thereof in the molecule as a constituent unit include 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) (BisS / PhS), and salts thereof.

[0071] From the viewpoint of improving the quality of the polishing liquid, such as further increasing the removal rate and further reducing scratches, the weight average molecular weight of component F is preferably 500 or more, more preferably 1,000 or more, and even more preferably 1,500 or more, and is preferably 50,000 or less, more preferably 30,000 or less, even more preferably 20,000 or less, even more preferably 10,000 or less, and even more preferably 5,000 or less.

[0072] 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 mass % or more, more preferably 0.005 mass % or more, even more preferably 0.01 mass % or more, and preferably 1 mass % or less, more preferably 0.5 mass % or less, and even more preferably 0.1 mass % or less, from the viewpoint of improving the quality of the polishing liquid, such as further improving the polishing rate and further reducing scratches. When component F is a combination of two or more types, the content of component F refers to the total content thereof.

[0073] <Other ingredients> The polishing liquid of the present disclosure may contain other components as necessary. In one or more embodiments, the other components may include a thickener, a surfactant, and the like.

[0074] The content of each component of the polishing liquid of the present disclosure described above is the content when used in the polishing process, and the polishing liquid of the present disclosure may be in a concentrated state. In this case, it is preferable in that the manufacturing and transportation costs can be further reduced. When the polishing liquid of the present disclosure is in a concentrated state, it can be appropriately diluted with the above-mentioned water as necessary and used in the polishing process. The dilution ratio can be 5 to 100 times.

[0075] 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, even more preferably 0.7 or more, and even more preferably 1.1 or more from the viewpoint of ensuring safety, and is preferably 4.0 or less, more preferably 3.0 or less from the viewpoint of high polishing rate. In the present disclosure, the pH of the polishing liquid of the present disclosure can be measured by the same method as that of the above-mentioned silica dispersion liquid.

[0076] An embodiment of the polishing liquid of the present disclosure may be a so-called one-component type in which all components are premixed and supplied to the market, or a so-called two-component type in which components are mixed at the time of use.

[0077] [Polishing method] The polishing liquid of the present disclosure is supplied, for example, between a nonwoven organic polymer-based polishing cloth or the like (polishing pad) and a magnetic disk substrate to be polished, that is, the polishing liquid of the present disclosure is supplied to the polishing surface of a substrate sandwiched between polishing plates to which a polishing pad is attached, and is used in the polishing process while contacting the substrate by moving the polishing plates and / or the substrate under a predetermined pressure. This polishing can significantly suppress the occurrence of scratches. Therefore, in one aspect, the present disclosure relates to a method for polishing a substrate, which includes supplying the polishing liquid of the present disclosure to a surface to be polished of a magnetic disk substrate to be polished, contacting the surface to be polished with a polishing pad, and moving the polishing pad and / or the magnetic disk substrate to be polished to perform polishing.

[0078] The polishing liquid of the present disclosure is particularly suitable for polishing substrates of magnetic recording media such as magnetic disks and magneto-optical disks.

[0079] The polishing liquid of the present disclosure is particularly effective in a polishing process, but can also be applied to other polishing processes, such as a lapping process.

[0080] Suitable materials for the polishing object (magnetic disk substrate) using the polishing liquid of the present disclosure include, for example, silicon, aluminum, nickel, tungsten, copper, tantalum, titanium, and other metals or semimetals, or alloys thereof, glass, glassy carbon, amorphous carbon, and other glassy materials, alumina, silicon dioxide, silicon nitride, tantalum nitride, titanium carbide, and other ceramic materials, and polyimide resin and other resins. Among these, it is suitable for the polishing object (magnetic disk substrate) containing metals such as aluminum, nickel, tungsten, copper, and alloys mainly composed of these metals. For example, it is more suitable for Ni-P plated aluminum alloy substrates and glass substrates such as crystallized glass and reinforced glass, and Ni-P plated aluminum alloy substrates are even more suitable.

[0081] The shape of the object to be polished (magnetic disk substrate to be polished) is not particularly limited, and the polishing liquid of the present disclosure can be used for objects having a flat surface such as a disk, plate, slab, or prism, or a curved surface such as a lens. In particular, the polishing liquid is excellent for polishing a disk-shaped object to be polished (magnetic disk substrate to be polished).

[0082] [Method of manufacturing 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 supplying a polishing liquid of the present disclosure to a surface to be polished of a magnetic disk substrate to be polished, contacting a polishing pad with the surface to be polished, and moving the polishing pad and / or the magnetic disk substrate to be polished to polish the surface to be polished. In the substrate manufacturing method of the present disclosure, when there are multiple polishing steps, it is preferable to use the polishing liquid obtained by the method for manufacturing the polishing liquid of the present disclosure in the second step or later, and more preferably to use it in a final polishing step. The final polishing step refers to the last polishing step when there are multiple polishing steps. When there are multiple polishing steps, a separate polishing machine may be used for each step in order to avoid contamination with abrasives or polishing liquid from the previous step, and when separate polishing machines are used for each step, it is preferable to clean the substrate after each step. The polishing machine is not particularly limited. According to the substrate manufacturing method of the present disclosure, it is possible to efficiently manufacture magnetic disk substrates with reduced scratches on the substrate surface. EXAMPLES

[0083] The present disclosure will be described in more detail below with reference to examples, but these are merely illustrative and the present disclosure is not limited to these examples.

[0084] 1. Parameter Measurement [pH Measurement of Treated Silica Dispersion, Filtered Silica Dispersion, and Polishing Liquid of the Present Disclosure] The pH values ​​at 25°C of the treated silica dispersion, the filtered silica dispersion, and the polishing liquid of the present disclosure are values ​​measured using a pH meter (Toa Denpa Kogyo Co., Ltd., HM-30G) and are values ​​measured 1 minute after the electrode was immersed in the silica dispersion or the polishing liquid.

[0085] [Average primary particle size of silica particles] The average primary particle diameter of silica was measured by drying the silica dispersion at 110°C for 12 hours with hot air and crushing it in an agate mortar to obtain a powdered silica particle sample, pre-drying the obtained sample at 200°C for 15 minutes immediately before measuring the BET specific surface area, and measuring the specific surface area S (m2) by the BET method using a Micromeritic automatic specific surface area measuring device "Flowsorb III2305" (Shimadzu Corporation). 2 / g) was measured and the specific surface area S obtained was substituted into the following formula to calculate. Average primary particle diameter (nm)=2727 / S

[0086] [Method for measuring the average particle size of filter aids using laser] Each filter aid was measured using a laser diffraction / scattering particle size distribution analyzer (product name LA-920, manufactured by Horiba, Ltd.), and the volume-based median diameter was determined as the laser average particle diameter.

[0087] [Filter aid pore diameter] The diameter of the pores in the filter aid components was confirmed by the following method. The filter aid to be measured was observed with a SEM (Hitachi High-Technologies Corporation, FE-4800, 30 kV, 10,000 to 100,000 times magnification), and the obtained photograph was scanned into a personal computer as image data. The projection images of the diameters of the pores in 500 filter aid components were analyzed using image analysis software (Mitani Shoji "WinROOF2017") to calculate the individual pore diameters, and the average value of all observed pore diameters was taken as the pore diameter of the filter aid components.

[0088] [Method for measuring the weight-average molecular weight of anionic polymers] The weight average molecular weight of the anionic polymer was measured by gel permeation chromatography (GPC) under the following measurement conditions. (GPC conditions) Column: TSKgel G4000PWXL + TSKgel G2500PWXL (Tosoh) Guard column: TSKguardcolumn PWXL (manufactured by Tosoh) Eluent: 0.2M phosphate buffer / CH 3 CN=9 / 1 (volume ratio) Temperature: 40℃ Flow rate: 1.0mL / min Sample size: 5mg / mL Detector: RI Conversion standard: Sodium polyacrylate (molecular weight (Mp): 115,000, 28,000, 4100, 1250 (manufactured by Sowa Kagaku and American Polymer Standards Corp.))

[0089] 2. Preparation of treated silica dispersion As the silica dispersion to be treated, a colloidal silica slurry (pH 9.0, manufactured by JGC Catalysts and Chemicals, average primary silica particle size 18.0 nm, silica particle concentration 40% by mass) was used.

[0090] 3. Preparation of Filter Aid-containing Filter F1 The following filter aids (diatomaceous earth 1 to 7) were used to prepare a filtration-containing filter F1 (disk type). [Filter aid] Diatomaceous earth 1: Radiolite No. 100 (Showa Chemical Industry Co., Ltd.) (Laser average particle size: 15.7 μm, pore size: 0.51 μm) Diatomaceous earth 2: Mixture of diatomaceous earth 1 (8.0 g) and diatomaceous earth 7 (2.0 g) (laser average particle size: 16.2 μm, pore size: 0.65 μm) Diatomaceous earth 3: Mixture of diatomaceous earth 1 (5.0 g) and diatomaceous earth 7 (5.0 g) (laser average particle size: 16.9 μm, pore size: 0.71 μm) Diatomaceous earth 4: Mixture of diatomaceous earth 1 (2.0 g) and diatomaceous earth 7 (8.0 g) (laser average particle size: 17.5 μm, pore size: 0.81 μm) Diatomaceous earth 5: NA100 (manufactured by ADVANTEC) (Laser average particle size: 16.0 μm, pore size: 0.82 μm) Diatomaceous earth 6: PED020 (manufactured by ROKI TECHNO CO., LTD.) (Laser average particle size: 16.7 μm, pore size: 1.5 μm)

[0091] [Preparation of a filter containing a filter aid] (Filter F1 containing filter aids using diatomaceous earth 1 to 4) 100 mL of ion-exchanged water was added to 10 g of filter aid (diatomaceous earth 1-4), and the mixture was stirred and mixed to obtain a filter aid dispersion solution. Next, a filter paper (No. 5A (7 μm mesh size): manufactured by Advantec Co., Ltd.) was placed in a 90 mmφ flat-plate SUS housing (INLET90-TL manufactured by Sumitomo 3M Co., Ltd.) and the filter aid dispersion solution was filtered at a pressure of 0.1 MPa or less to obtain a uniform cake layer of filter aid (thickness: 3 mm, density: 0.5 g / cm) on the filter paper. 3 After forming the filter aid, the filter aid was washed with 2 L of ion-exchanged water to obtain a filter F1 containing a filter aid. The content of the filter aid in the filter F1 was 0.18 g / cm 2It was. (Filter F1 containing filter aids using diatomaceous earth 5 and 6) The filter F1 containing the filter aid made of diatomaceous earth 5 and 6 has a cake layer (thickness: 3 mm, density: 0.5 g / cm 3 ) A preformed, commercially available filter aid-containing filter.

[0092] [Method for measuring the airflow resistance of the filter aid-containing filter F1] Filter aid-containing filter F1 with a diameter of 90 mm, a thickness of 3.0 mm, and a weight of 10.0 g was adjusted to a square of 50 mm to be used as a sample for measuring airflow resistance. According to the air permeability A method (Fragile type method) specified in JIS L1096, the airflow resistance was measured using an airflow resistance tester (device name: KES-F8-AP1, manufactured by Kato Tech Co., Ltd.), and the average value of 10 samples was taken as the airflow resistance of each filter aid-containing filter F1. The results are shown in Table 1. The airflow resistance of the filter aid-containing filter F1 under these conditions is an index of the occurrence rate of clogging of the rear-stage pleated filter F2. That is, the higher the airflow resistance of the filter aid-containing filter F1, the more coarse particles it can remove, and the filter aid-containing filter F1 can be evaluated as being capable of reducing the load on the rear-stage pleated filter F2. Even if the airflow resistance increases while the weight, thickness, and area of ​​the filter remain the same, that is, while the thickness and density of the filter aid layer remain constant, there is no effect on the filtration rate, and it is considered that the filtration rate (productivity) can be maintained.

[0093] 4. Preparation of pleated filter F2 The following was prepared as the pleated filter F2. Pleats 1: TCS020 [Advantech, pleated filter with polyethersulfone membrane, main filter pore size: 0.20 μm, prefilter pore size: 0.45 μm] Pleats 2: EMC020 [3M, 66 nylon membrane pleated filter, pore size: 0.20 μm, no prefilter] Pleats 3: EMC045 [3M, 66 nylon membrane pleated filter, pore size: 0.45 μm, no prefilter]

[0094] [Method for measuring the airflow resistance of pleated filter F2] The pleated filter F2, 0.1 mm thick and 0.5 g heavy, was cut into a 50 mm square to be used as a sample for measuring airflow resistance. Airflow resistance was measured using an airflow resistance tester (device name: KES-F8-AP1, manufactured by Kato Tech Co., Ltd.) in accordance with the air permeability A method (Fragile type method) specified in JIS L1096, and the average value of 10 samples was taken as the airflow resistance of each pleated filter F2. The results are shown in Table 1. The airflow resistance of the pleated filter F2 under these conditions correlates with the MF value, which is an index of scratches, when the silica dispersion is used to prepare a polishing liquid. In other words, the higher the airflow resistance of the pleated filter F2, the more the filter can be evaluated as one that can improve its MF value. Even if the weight, thickness, and area of ​​the filter remain the same and only the airflow resistance increases, the filtration speed is not affected.

[0095] 5. Filtration process (filtration process) Steps (1) and (2) were carried out using a filtration system in which the prepared filter aid-containing filter F1 and pleated filter F2 were combined. [Step (1): Filtration treatment using filter aid-containing filter F1] The filter aid-containing filter F1 thus prepared was not dried but was wet with cleaning water, and was subjected to a filtration pressure of 0.3 MPa and a flow rate of 40 g / min (filtration flow rate: 35 kg / (min m 2 The treated silica dispersion was filtered under the conditions of (1) and (2) to obtain a filtrate (1) (pH: 9.4). [Step (2): Filtration using pleated filter F2] One pleated filter F2 cut to φ25 mm was set in an ADVANTEC plastic holder (PP-25) and filtered at a filtration pressure of 0.3 MPa and a flow rate of 50 g / min (filtration flow rate: 35 kg / (min m 2 The filtrate (1) was filtered through the pleated filter F2 under the conditions of (1) and (2). The pH of the silica dispersion filtered through the pleated filter F2 was 9.4.

[0096] 6. Preparation of Polishing Solution 1H-benzotriazole Na salt (component D), N-aminoethylethanolamine (component E), acrylic acid / acrylamide-2-methylpropanesulfonic acid copolymer sodium salt (molar ratio 90 / 10, weight average molecular weight 2000, manufactured by Toagosei Co., Ltd.) (component F), phosphoric acid (component B), and hydrogen peroxide (component C) were added to ion-exchanged water, and the silica dispersion filtered through the pleated filter F2 was added to the aqueous solution under stirring so that the content of silica particles (component A) was 5% by mass, to prepare the polishing liquid (pH 1.8) of the present disclosure. The contents of each component in the prepared polishing liquid were 5.0% by mass for component A, 1.0% by mass for component B, 0.3% by mass for component C, 0.1% by mass for component D, 0.04% by mass for component E, 0.02% by mass for component F, and 93.54% by mass for water. Furthermore, polishing solutions of Examples 2 to 5 and Comparative Examples 1 and 2 were prepared in the same manner as in Example 1, except that the combinations of the filter aid-containing filter F1 and the pleated filter F2 were as shown in Table 1.

[0097] 7. Polishing the substrate using polishing fluid Finish polishing was carried out under the following polishing conditions using the polishing solutions of Examples 1 to 5 and Comparative Examples 1 and 2 prepared as described above. The number of scratches on the substrate after each polishing was evaluated. The evaluation results of the finish polishing are shown in Table 1 below. [Magnetic Disk Substrate to be Polished] The magnetic disk substrate to be polished was an aluminum alloy substrate plated with Ni-P and roughly polished with a polishing solution containing silica abrasive grains. The magnetic disk substrate to be polished had a thickness of 0.6 mm, an outer diameter of 97 mm, an inner diameter of 25 mm, and a center line average roughness Ra of 1 nm measured by an AFM (Digital Instrument NanoScope IIIa Multi Mode AFM). The ratio of Ni to P in the Ni-P plating was 88:12 by mass. [Finish polishing conditions] Polishing machine: Double-sided polishing machine (9B type double-sided polishing machine, manufactured by SpeedFam) Number of magnetic disk substrates to be polished: 10 Polishing liquid: Polishing liquids obtained in Examples 1 to 5 and Comparative Examples 1 and 2 Polishing pad: Suede type (foam layer: polyurethane elastomer, thickness 0.9 mm, average pore size 10 μm, Fujibo Co., Ltd.) Plate rotation speed: 32.5 rpm Polishing load: 10.5kPa (set value) Polishing liquid supply amount: 100mL / min Magnetic disk substrate to be polished 1cm 2 Feed rate per: 0.076mL / min Magnetic disk substrate to be polished 1cm 2 Polishing amount per piece: 0.23mg Polishing time: 6 minutes

[0098] 8. Evaluation of filtration performance [Clogging rate of pleated filter F2] 2000 g of silica dispersion after filtration through the filter aid-containing filter F1 was prepared, and filtration was performed through the pleated filter F2 under the filtration treatment conditions for the pleated filter F2. The criterion for determining filter clogging was whether or not it was possible to filter a total amount of liquid passing through the filter of more than 1500 g. The clogging rate was calculated by dividing the number of times clogging occurred when filtration was performed 50 or more times with different filters by the number of filtrations.

[0099] [Product yield] When filtering about 2000 g of silica dispersion with the filter aid-containing filter F1 and the pleated filter F2, 100 g of the filtrate filtered with the pleated filter F2 (filtered silica dispersion) is collected and the MF value of each sample is measured. The MF value of Comparative Example 1 is set to 100%, and samples with an MF value of less than 100% are considered defective. The number of times that 2000 g of silica dispersion is filtered multiple times is defined as the number of filtrations. The number of samples collected is 2000 g / 100 g=20. The product yield was calculated from the following formula. If the product yield is low, the economic efficiency is deteriorated. Defective product occurrence rate (%) = (number of defective products) / {(number of filtrations) x (number of samples taken)} Product yield (%) = 100 - (defective product occurrence rate) For example, in the case of Example 3, the number of defective products was 4, the number of samples taken was 20, and 2000 g filtration was performed 5 times, so the defective product rate was calculated as 4 / (5×20)×100=4%, and the product yield rate was calculated as 100-4=95%.

[0100] 9. Evaluation of Silica Dispersion (After Filtration) and Polishing Fluid [0.20μm filter passing volume (MF value)] The silica dispersion obtained by the above filtration (filtration through the filter aid-containing filter F1 and the pleated filter F2) was filtered through a predetermined filter (Advantech membrane filter, model: 25HP020AN, filter material: hydrophilic PTFE, pore size: 0.20 μm, effective filtration area: 4.0 cm 2 ) and the liquid was passed through the filter under a constant air pressure of 0.30 MPa, and the amount of liquid (g) that passed until the filter was clogged was determined as the MF value, which is shown in Table 1. The MF values ​​shown in Table 1 are also relative values, with the MF value of Comparative Example 1 taken as 100%. The MF values ​​shown in Table 1 are average values ​​when 2000 g of the silica dispersion was entirely filtered. It can be seen that the greater the amount of liquid passing through the filter under these conditions, the fewer the number of scratches. In other words, it can be determined that the higher the MF value, the more likely it is that the silica dispersion or polishing liquid is capable of reducing scratches.

[0101] [Scratch rating] Measuring equipment: KLA-Tencor "Candela OSA7100" Evaluation: Four substrates were randomly selected from the substrates placed in the polishing tester, and each substrate was irradiated with a laser at 10,000 rpm to measure the number of scratches. The total number of scratches on both sides of each of the four 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 a relative value with Comparative Example 1 set to 100.

[0102] [Table 1]

[0103] As shown in Table 1, in Examples 1 to 5, in which a filter aid-containing filter F1 having an air resistance of 0.02 MPa or more and a pleated filter F2 having an air resistance of 0.2 MPa or more were used in the filtration process, the number of scratches was reduced when polishing was performed with the resulting polishing liquid for polishing magnetic disk substrates, and the polishing liquid for polishing magnetic disks was superior in productivity and economy in the production of the polishing liquid for polishing magnetic disks, compared to Comparative Example 1, in which a pleated filter F2 having an air resistance of less than 0.2 MPa was used, and Comparative Example 2, in which a filter aid-containing filter F1 having an air resistance of less than 0.02 MPa was used. [Industrial Applicability]

[0104] The method for producing a polishing liquid according to the present disclosure is useful as a method for producing a polishing liquid for polishing magnetic disk substrates, which can achieve both high quality of the resulting polishing liquid and high productivity and cost-effectiveness.

Claims

1. A method for producing a polishing solution for polishing magnetic disk substrates containing silica particles and water, The process includes a filtration step of filtering a mixture containing silica particles and water. The filtration process includes the following steps (1) and (2): Step (1): A step of filtering a mixture containing silica particles and water through a filter F1 containing a filter aid to obtain a filtrate (1); Step (2): A step of filtering the filtrate (1) obtained in step (1) with a pleated filter F2; The airflow resistance of the filter F1 containing the filtration aid in step (1) is 0.02 MPa or higher. A method for manufacturing a polishing liquid for polishing magnetic disk substrates, wherein the airflow resistance of the pleated filter F2 in step (2) is 0.2 MPa or more.

2. A method for producing a polishing liquid for polishing magnetic disk substrates according to claim 1, wherein the filter aid contained in the filter aid containing filter aid F1 contains diatomaceous earth.

3. The filtration step includes, prior to step (1), a step of filtering a mixture containing silica particles and water through a depth-type filter F0 to obtain a filtrate (0), A method for producing a polishing liquid for polishing magnetic disk substrates according to claim 1 or 2, comprising filtering the filtered material (0) with a filter aid-containing filter F1 to obtain filtered material (1) in step (1).

4. A method for producing a polishing solution for polishing magnetic disk substrates according to claim 1 or 2, comprising the step of blending a mixture containing silica particles and water with at least one selected from an acid, an oxidizing agent, a heterocyclic aromatic compound, an amine compound, and an anionic water-soluble polymer, before, during, or after the filtration step.

5. A method for suppressing filter clogging in the filtration process of a mixture containing silica particles and water in the manufacture of a polishing solution for polishing magnetic disk substrates, A method for preventing blockage of a filter, comprising the filtration step including the following steps (1) and (2). Step (1): A step of filtering a mixture containing silica particles and water through a filter F1 containing a filter aid to obtain a filtrate (1); Step (2): A step of filtering the filtrate (1) obtained in step (1) with a pleated filter F2; Here, the airflow resistance of the filter F1 containing the filter aid in step (1) is 0.02 MPa or higher. The airflow resistance of the pleated filter F2 in step (2) is 0.2 MPa or higher.

6. A polishing liquid for polishing magnetic disk substrates obtained by the method for manufacturing a polishing liquid for polishing magnetic disk substrates according to claim 1 or 2.

7. A method for manufacturing a magnetic disk substrate, comprising supplying the polishing liquid for polishing a magnetic disk substrate according to claim 6 to the surface to be polished of a magnetic disk substrate to be polished, bringing a polishing pad into contact with the surface to be polished of the magnetic disk substrate to be polished, and moving the polishing pad and / or the magnetic disk substrate to be polished to polish the surface to be polished.