Method of manufacturing magnetic disk substrate polishing liquid

Abstract

To provide a method of manufacturing a silica dispersion, which enables both improvement in quality of a resultant magnetic disk substrate polishing liquid and extension of filter life in manufacturing of the magnetic disk substrate polishing liquid.SOLUTION: An aspect of the present invention relates to a method of manufacturing a magnetic disk substrate polishing liquid containing silica particles (component A) and water, the method comprising a step of filtering a treatment target silica dispersion containing silica particles (component A) and water using a membrane filter to obtain a filtered silica dispersion, where the membrane filter has a ratio U / D, representing a ratio of a primary-side average pore diameter U to a secondary-side average pore diameter D, of 3.0 or less and an average pore diameter of 0.5 μm or greater.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] In recent years, magnetic disk drives have been miniaturized and increased in capacity, and further higher recording density has been demanded. In order to achieve this, reduction of the unit recording area has been promoted, but in order to improve the detection sensitivity of the weakened magnetic signal, reduction of the flying height of the magnetic head has been promoted. In response to this, for magnetic disk substrates, there are strict 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. Also, in the semiconductor field, high integration and high speed are progressing, and particularly in high integration, miniaturization of wiring is required. As a result, in the manufacturing process of semiconductor substrates, the depth of focus when exposing photoresist becomes shallow, and even higher surface smoothness is desired.

[0003] In response to such requirements, for example, Patent Document 1 proposes a method of filtering a liquid containing a polishing additive with a filter having characteristics that the average pore diameter P measured by a palm porometer is 0.15 μm or less, and the pore diameter gradient (Sin / Sout), which is the ratio of the average pore diameter Sin on the inlet side (primary side) to the average pore diameter Sout on the outlet side (secondary side) measured by SEM observation, is 3 or less.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As the capacity of magnetic disk drives increases, the required characteristics for the surface quality of the substrate, as described above, are becoming even more stringent. One of the indicators of the surface quality of the substrate is scratch, and one of the causes of its occurrence, the coarse particles in the polishing liquid, is usually removed by filtration in the manufacturing process of the polishing liquid. However, this filtration causes a trade-off problem between the quality of the polishing liquid (e.g., the small amount of coarse particles) and the improvement of productivity / economy due to the extended life of the filter.

[0006] Therefore, in one aspect, the present disclosure provides a method for manufacturing a polishing liquid for a magnetic disk substrate that enables both the quality of the obtained polishing liquid for a magnetic disk substrate and the extended life of the filter in the manufacture 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 containing silica particles (component A) and water, the method including a step of filtering a silica dispersion to be treated containing silica particles (component A) and water with a membrane filter to obtain a filtered silica dispersion, wherein the ratio U / D of the primary side average pore diameter U to the secondary side average pore diameter D of the membrane filter is 3.0 or less, and the average pore diameter of the membrane filter is 0.5 μm or more.

[0008] In one aspect, the present disclosure relates to a method for manufacturing a magnetic disk substrate, the method including a step of manufacturing a polishing liquid for a magnetic disk substrate by the method for manufacturing a polishing liquid for a magnetic disk substrate of the present disclosure, and a step of supplying the polishing liquid 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 one or more selected from the polishing pad and the substrate to be polished to polish the polishing target surface.

[0009] 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 containing silica particles (component A) and water, wherein the filter is a membrane filter, and the ratio U / D of the primary-side average pore diameter U to the secondary-side average pore diameter D of the membrane filter is 3.0 or less, and the average pore diameter of the membrane filter is 0.5 μm or more.

Effect of the Invention

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

Embodiments for Carrying Out the Invention

[0011] Based on the finding that by filtering a silica dispersion to be treated containing silica particles (component A) and water using a membrane filter with a ratio U / D of the primary-side average pore diameter U to the secondary-side average pore diameter D of the membrane filter being a predetermined value or less and the average pore diameter of the entire membrane filter being a predetermined value or more to obtain a filtered silica dispersion, the quality of the filtered silica dispersion is improved, the quality of the polishing liquid for a magnetic disk substrate is also improved, and furthermore, an extended service life of the filter used in the production of the polishing liquid for a magnetic disk substrate can be achieved.

[0012] That is, in one aspect, the present disclosure relates to a method for producing a polishing liquid for a magnetic disk substrate containing silica particles (component A) and water, the method including a step of filtering a silica dispersion to be treated containing silica particles (component A) and water with a membrane filter to obtain a filtered silica dispersion, wherein the ratio U / D of the primary-side average pore diameter U to the secondary-side average pore diameter D of the membrane filter is 3.0 or less, and the average pore diameter of the membrane filter is 0.5 μm or more (hereinafter, also referred to as "the method for producing a polishing liquid for a magnetic disk substrate of the present disclosure"). According to the present disclosure, it is possible to provide a method for manufacturing a polishing liquid for a magnetic disk substrate that can improve the quality of the obtained polishing liquid for a magnetic disk substrate and can extend the service life of a filter in the production of the polishing liquid for a magnetic disk substrate.

[0013] Although the details of the mechanism of effect manifestation in the method for manufacturing a polishing liquid for a magnetic disk substrate of the present disclosure are not clear, it is presumed as follows. When removing coarse particles of silica mixed in the silica particles contained in the polishing liquid for a magnetic disk substrate with a membrane filter, not only the capture of coarse particles by the pores on the primary side (the upstream side where the filtrate flows into the membrane filter) of the membrane filter, but also the capture of coarse particles inside the pores up to the secondary side (the downstream side where the filtrate flows out from the membrane filter) of the membrane filter, and small-diameter particles aggregate densely in the narrow part inside the pores to cause aggregation (aggregation foreign matter), resulting in filter clogging, so the filter life tends to be shortened. In the present disclosure, by making the average pore diameter D on the secondary side relatively larger than the average pore diameter U on the primary side of the membrane filter, it is possible to reduce the generation of aggregation foreign matter inside the pores, and it is considered possible to achieve both an improvement in the quality of the polishing liquid for a magnetic disk substrate using the silica filtered by the filter and an extension of the service life of the filter during the production of the polishing liquid. Also, usually, if the average pore diameter of the entire membrane filter is made too small, the filter life tends to deteriorate significantly. In the present disclosure, it is considered that the filter can have a longer service life by making the average pore diameter of the entire membrane filter 0.5 μm or more. However, the present disclosure may not be construed as being limited to these mechanisms.

[0014] In the present disclosure, the "coarse particles" are coarse silica particles having a particle diameter of 0.5 μm or more, and the number of coarse particles in the polishing liquid for a magnetic disk substrate can be evaluated by the filter liquid passing amount described in the following examples. The larger the liquid passing amount, the smaller the number of coarse particles in the polishing liquid for a magnetic disk substrate, which means higher filtration accuracy. In the present disclosure, the silica particles in the polishing liquid for a magnetic disk substrate include not only primary particles but also aggregated particles formed by aggregation of primary particles. In the present disclosure, "aggregated foreign matter" refers to matter generated by aggregation within pores when particles having a particle size suitable for a polishing liquid for a magnetic disk substrate pass through a membrane filter before filtration by the membrane filter, and it clogs the filter. Although the aggregated foreign matter is not directly observable in the present disclosure, it greatly affects the life of the filter.

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

[0016] [Filtration step] In one or more embodiments, the method for manufacturing a polishing liquid for a magnetic disk substrate of the present disclosure includes a step of filtering a silica dispersion to be treated containing silica particles (component A) and water with a membrane filter having a ratio U / D of the primary side average pore diameter U to the secondary side average pore diameter D of 3.0 or less and an average pore diameter of 0.5 μm or more (hereinafter, also referred to as "the filtration step of the present disclosure").

[0017] (Membrane filter) In the present disclosure, the membrane filter belongs to a so-called surface type in which filtration is performed on the surface of the filter, and the filter medium has a film shape and has openings (pores) of a certain diameter. In one or more embodiments, the membrane filter used in the filtration process of the present disclosure is a membrane filter (hereinafter, also referred to as "the membrane filter of the present disclosure") in which the ratio U / D of the primary-side average pore diameter U to the secondary-side average pore diameter D is 3.0 or less, and the average pore diameter is 0.5 μm or more. Since the ratio U / D of the primary-side average pore diameter U to the secondary-side average pore diameter D of the membrane filter of the present disclosure is a predetermined value or less, coarse particles can be captured on the primary side (upstream side, surface) of the filter, the generation of aggregated foreign matter inside the pores can be suppressed, the occurrence of filter clogging can be suppressed, and it is considered that both the quality improvement of the silica dispersion liquid after filtration and the long life of the filter can be achieved. The primary side of the membrane filter is the side (upstream side) where the filtrate, that is, the silica dispersion liquid to be treated, flows into the membrane filter, and the secondary side of the membrane filter is the side (downstream side) where the silica dispersion liquid after filtration flows out from the membrane filter. In the present disclosure, the primary-side average pore diameter U of the membrane filter is obtained by photographing the primary side of the membrane filter with an electron microscope and calculating the average value of the diameters of the portions corresponding to the openings of the membrane filter using image analysis software. The secondary-side average pore diameter D of the membrane filter is obtained by similarly photographing / analyzing the secondary side of the membrane filter, and the unit of both is μm. The primary-side average pore diameter U and the secondary-side average pore diameter D of the membrane filter can be measured, for example, by the method described in the examples.

[0018] From the viewpoint of extending the life of the filter, the primary-side average pore diameter U of the membrane filter of the present disclosure is preferably 0.1 μm or more, more preferably 0.2 μm or more, still more preferably 0.4 μm or more. From the viewpoints of improving the quality of the silica dispersion liquid after filtration and reducing coarse particles, it is preferably 2.4 μm or less, more preferably 1.5 μm or less, still more preferably 1.0 μm or less, and even more preferably 0.7 μm or less. The primary-side average pore diameter can be adjusted by adjusting the conditions during the film formation of the membrane filter. Also, a membrane filter that satisfies the above primary-side average pore diameter can be selected from off-the-shelf products.

[0019] The secondary-side average pore diameter D of the membrane filter of the present disclosure is preferably 0.3 μm or more, more preferably 0.5 μm or more, still more preferably 1.0 μm or more, and even more preferably 1.2 μm or more from the viewpoint of extending the filter life. From the viewpoints of improving the quality of the silica dispersion after filtration and reducing coarse particles, it is preferably 2.4 μm or less, more preferably 2.0 μm or less, and still more preferably 1.5 μm or less. The secondary-side average pore diameter can be adjusted by adjusting the conditions during film formation. It is also possible to select a membrane filter that satisfies the above secondary-side average pore diameter from off-the-shelf products.

[0020] The ratio U / D of the primary-side average pore diameter U to the secondary-side average pore diameter D of the membrane filter of the present disclosure is preferably 0.1 or more, more preferably 0.2 or more, still more preferably 0.3 or more from the viewpoint of extending the filter life. From the viewpoints of improving the quality of the silica dispersion after filtration and reducing coarse particles, it is 3.0 or less, preferably 2.0 or less, more preferably 1.5 or less, still more preferably 1.0 or less, and even more preferably 0.4 or less.

[0021] The average pore diameter of the membrane filter of the present disclosure is 0.5 μm or more, preferably 0.7 μm or more, more preferably 0.9 μm or more from the viewpoint of extending the filter life. From the viewpoints of improving the quality of the silica dispersion after filtration and reducing coarse particles, it is preferably 2.4 μm or less, more preferably 1.5 μm or less, still more preferably 1.16 μm or less, and even more preferably 1.1 μm or less. The average pore diameter of the membrane filter means the average of the diameters of all the pores (both on the primary side and the secondary side) of the membrane filter. The average pore diameter of the membrane filter can be calculated by taking the average value of the numerical values obtained by calculating the primary-side average pore diameter U and the secondary-side average pore diameter D of the membrane filter. Specifically, the average pore diameter of the membrane filter can be measured by the method described in the examples. The average pore diameter of the membrane filter can be adjusted by adjusting the conditions during film formation. It is also possible to select a membrane filter that satisfies the above average pore diameter from off-the-shelf products. Further, when a pre-filter is attached to the membrane filter, even if the pre-filter is a membrane filter, the numerical values of its diameter (on the primary side and the secondary side) are not included in the derivation of the primary side average pore diameter U, the secondary side average pore diameter D, and the average pore diameter.

[0022] When the average pore diameter of the membrane filter of the present disclosure is defined as APD, the value represented by the formula: (U / D) × {(APD) 3} is preferably 0.1 or more, more preferably 0.15 or more, still more preferably 0.2 or more, even more preferably 0.28 or more, from the viewpoint of extending the life of the filter and from the viewpoint of the quality of the polishing liquid for magnetic disk substrates obtained, and from the same viewpoint, it is preferably 6.5 or less, more preferably 3 or less, still more preferably 2 or less, even more preferably 1.5 or less, even more preferably 1.0 or less, and even more preferably 0.5 or less.

[0023] Examples of the method for manufacturing a membrane filter that satisfies the ratio U / D and the average pore diameter APD include centrifugation, thermally induced phase separation, non-solvent induced phase separation, track etching, and the like.

[0024] As components constituting the membrane filter of the present disclosure, in one or more embodiments, from the viewpoint of improving the quality of the polishing liquid for magnetic disk substrates obtained and extending the life of the filter, it is preferable to contain one or more selected from polysulfone (PS) and polyethersulfone (PES). The mass ratio of one selected from polysulfone (PS) and polyethersulfone (PES) in all components constituting the membrane filter of the present disclosure is preferably more than 50% by mass, more preferably 75% by mass or more, still more preferably 90% by mass or more, and even more preferably 100% by mass. As components constituting the membrane filter of the present disclosure, in one or more embodiments, it is preferably one selected from polysulfone (PS) and polyethersulfone (PES). The mass ratio of one or more selected from polysulfone (PS) and polyethersulfone (PES) in all components constituting the membrane filter of the present disclosure, when a prefilter is attached to the membrane filter, even if the prefilter is a membrane filter, the numerical value of its mass is not included in the derivation of the mass ratio of one or more selected from polysulfone (PS) and polyethersulfone (PES) of the membrane filter of the present disclosure.

[0025] The thickness of the membrane filter layer of the present disclosure is preferably 0.05 μm or more, more preferably 0.10 μm or more, and preferably 0.20 μm or less, more preferably 0.15 μm or less. The membrane filter of the present disclosure may be a pleated filter having a membrane filter layer in which the ratio U / D of the primary side average pore diameter U to the secondary side average pore diameter D is 3.0 or less and the average pore diameter of the membrane filter is 0.5 μm or more from the viewpoints of maintaining the quality of the silica dispersion liquid after filtration and extending the life of the filter. Examples of the pleated filter include those in which the membrane is formed into a corrugated (pleated) shape to form a hollow cylindrical cartridge type.

[0026] The filtration pressure in the filtration 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 viewpoints, 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 in the filtration step of the present disclosure" means the difference between the pressure on the primary side and the pressure on the secondary side of the membrane filter of the present disclosure. In one or more embodiments, the filtration pressure in the filtration step of the present disclosure can be adjusted by adjusting the pressure applied to the primary side.

[0027] In the filtration process of the present disclosure, the filtration flow rate is preferably 40.0 kg / (min·m 2 ), more preferably 50.0 kg / (min·m 2 ), still more preferably 60.0 kg / (min·m 2 ) or more, and from the same perspective, 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 ). In the present disclosure, the "filtration flow rate in the filtration process of the present disclosure" refers to the mass per unit area of the membrane filter of the present disclosure 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.

[0028] As the filtration method in the filtration process of the present disclosure, a circulating type in which filtration is repeated may be used, or a one-pass method may be used. Also, a batch type in which the one-pass method is repeated may be used. As the liquid passing method, in order to apply pressure, a pump is preferably used in the circulating type, and in addition to using a pump in the one-pass method, a pressure filtration method with a small fluctuation range of the filter inlet pressure can be used by introducing air pressure or the like into the tank.

[0029] The membrane filter may be used in one stage or in multiple stages (for example, in a series arrangement).

[0030] In the filtration process of the present disclosure, in one or more other embodiments, from the perspective of improving the quality of the polishing liquid for magnetic disk substrates obtained and extending the life of the filter, before the step of filtering with the membrane filter, a step of filtering using one or more selected from a filter aid-containing filter and a depth filter may be included. Therefore, in one or more other embodiments, the filtration process may include the following steps (1) and (2). Step (1): Filtering a silica dispersion to be treated, which contains silica particles and water, using one or more selected from a filter aid-containing filter and a depth filter Step (2): Filtering the silica dispersion obtained in Step (1) using the membrane filter of the present disclosure In other one or more embodiments, from the viewpoints of reducing coarse particles, improving the quality of the silica dispersion after filtration, and extending the service life of the filter, it is preferable to filter the silica dispersion to be treated in the order of one or more selected from a filter aid-containing filter and a depth filter, and then the membrane filter of the present disclosure. By using one or more selected from a filter aid-containing filter and a depth filter in the front stage of the membrane filter, particularly large coarse particles can be removed, and it is considered that the performance of the membrane filter of the present disclosure in the subsequent stage can be more easily exerted.

[0031] (Filter aid-containing filter) The filter aid-containing filter is a filter containing at least a filter aid.

[0032] Examples of the filter aid include insoluble mineral substances such as silicon dioxide, kaolin, acid clay, diatomaceous earth, perlite, bentonite, and talc. Among the filter aids, from the viewpoint of improving productivity, silicon dioxide, diatomaceous earth, and perlite are preferable, diatomaceous earth and perlite are more preferable, and diatomaceous earth is even more preferable.

[0033] (Depth filter) Examples of the depth filter include bag-type filters (such as those of Sumitomo 3M Co., Ltd.) and cartridge-type filters (such as those of Advantec Toyo Co., Ltd., Nippon Pall Co., Ltd., CUNO Inc., and Daiwa Bow Co., Ltd.). Here, a depth-type filter means a type of filter in which filtration is performed inside the filter. The pore structure of the filter medium is coarse on the inlet side, fine on the outlet side, and has the characteristic of becoming finer continuously or stepwise 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-type filter include a bag-type bag shape and a hollow cylindrical cartridge shape. In addition, a filter medium having the above characteristics simply formed into a pleated shape has the function of a depth-type filter and is thus classified as a depth-type filter.

[0034] The depth-type filter may be used in a single stage, or the same filter may be used in combination in series with two or more. Also, non-depth-type filters with different pore diameters may be combined so 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 using a depth-type filter. Furthermore, these may be used in combination with a bag type and a cartridge type.

[0035] 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. From the viewpoints of improving the quality of the silica dispersion liquid after filtration and reducing coarse particles, it is preferably 5.0 μm or less, more preferably 3.0 μm or less, still more preferably 2.0 μm or less, even more preferably 1.0 μm or less, and even more preferably 0.5 μm or less.

[0036] In the method for producing a polishing liquid for a magnetic disk substrate 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 using a centrifugal separator or the like can also be used. When processing using these, they may be processed alone or in combination of two or more, and there is no limitation on the combination processing order. Also, the processing conditions and the number of processing times can be appropriately selected and used.

[0037] [Silica dispersion to be processed] In one or more embodiments, the "silica dispersion to be processed" in the present disclosure refers to a silica dispersion (silica slurry) in which silica particles are dispersed in water before being subjected to the filtration process in the filtration step of the present disclosure. That is, the silica dispersion to be processed in the present disclosure contains silica particles and water in one or more embodiments. The silica dispersion to be processed in the present disclosure may further contain one or more selected from acids, oxidizing agents, heterocyclic aromatic compounds, amine compounds, and anionic water-soluble polymers, which are preferably used as other components that can be incorporated into the polishing liquid for magnetic disk substrates described below. In the production method of the present disclosure, it is more preferable that the silica dispersion to be processed consists of silica particles and water.

[0038] The method for producing the polishing liquid for magnetic disk substrates of the present disclosure includes a step of filtering the silica dispersion to be processed with the membrane filter of the present disclosure. Specifically, a method of subjecting a silica dispersion to be processed containing silica particles, water, and optionally other components that can be incorporated into the polishing liquid for magnetic disk substrates to the filtration step of the present disclosure, or a method of subjecting a silica dispersion to be processed containing silica particles and water to the filtration step of the present disclosure and then mixing other components that can be incorporated into the polishing liquid for magnetic disk substrates with the obtained filtered silica dispersion is preferably selected. Among them, from the viewpoint of ease of operation in producing the polishing liquid for magnetic disk substrates, a method of subjecting a silica dispersion to be processed containing silica particles and water to the filtration and then mixing other components that can be incorporated into the polishing liquid for magnetic disk substrates with the obtained filtered silica dispersion is more preferable.

[0039] [Silica particles (Component A) contained in the silica dispersion to be processed] As the silica particles contained in the silica dispersion to be processed (hereinafter also simply referred to as "Component A"), from the viewpoints of improving the polishing rate and reducing scratches of the polishing liquid for magnetic disk substrates obtained, colloidal silica, fumed silica, pulverized silica, silica with its surface modified, etc. can be mentioned, and among these, colloidal silica is preferable. Colloidal silica can be obtained, for example, by a production method of generating it from an aqueous silicic acid solution. Also, those in which these particles are surface-modified or surface-modified with a functional group, those made into 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.

[0040] The shape of Component A may be spherical or non-spherical. As the usage form of Component A, it is preferable that it is a silica slurry in which silica particles are dispersed in a medium containing water.

[0041] From the viewpoints of improving the polishing rate, productivity, and reducing scratches of the polishing liquid for magnetic disk substrates obtained, 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 viewpoints, it is preferably 100 nm or less, more preferably 80 nm or less, still more preferably 50 nm or less, even more preferably 40 nm or less, even more preferably 30 nm or less, even more preferably 25 nm or less, and even more preferably 20 nm or less. In the present disclosure, the average primary particle diameter of the silica particles is calculated using the specific surface area S (m 2 / g) calculated from the amount of surface silanol groups. Specifically, the average primary particle diameter can be measured by the method described in the examples.

[0042] The content of component A in the silica dispersion to be treated is preferably 1% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, and even more preferably 15% by mass or more from the viewpoint of improving productivity, and preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 45% by mass or less, and even more preferably 40% by mass or less from the viewpoint of reducing scratches of the polishing liquid for magnetic disk substrates obtained.

[0043] <Water contained in the silica dispersion to be treated> Examples of the water contained in the silica dispersion to be treated include ion-exchanged water, distilled water, ultrapure water, etc. The content of water in the silica dispersion to be treated can be the remainder after subtracting component A and other components added as necessary from 100% by mass.

[0044] The pH of the silica dispersion to be treated is preferably 8.5 or more, more preferably 8.8 or more, still more preferably 9.0 or more, and preferably 11 or less, more preferably 10.8 or less, still more preferably 10.5 or less from the viewpoints of improving productivity and reducing scratches of the polishing liquid for magnetic disk substrates obtained. The pH of the silica particle dispersion to be treated can be adjusted with a known pH adjuster. Preferred pH adjusters include sodium hydroxide, potassium hydroxide, ammonia, and tetramethylammonium hydroxide. In the present disclosure, 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.

[0045] [Silica dispersion after filtration] The silica dispersion after filtration is a silica dispersion obtained by subjecting the silica dispersion to be treated to the filtration step of the present disclosure. By including the silica dispersion after filtration in the polishing liquid for magnetic disk substrates, a polishing liquid for magnetic disk substrates capable of manufacturing a substrate with reduced scratches can be obtained.

[0046] The preferred pH of the silica dispersion after filtration is the same as that of the silica dispersion to be treated described above. The pH of the silica dispersion after filtration can be measured in the same manner as the pH of the silica dispersion to be treated described above.

[0047] The content and pH of each component in the silica dispersion after filtration are preferably substantially the same as those of the silica dispersion to be treated, except for the coarse particles. In the present disclosure, "the content and pH of each component are 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 the number of coarse particles.

[0048] The filter throughput (g) of the silica dispersion after filtration is preferably 1 g or more, more preferably 50 g or more, still more preferably 100 g or more, even more preferably 150 g or more, even more preferably 162 g or more, and even more preferably 180 g or more from the viewpoint of improving the quality of the polishing liquid for magnetic disk substrates to be obtained. From the viewpoint of improving productivity, it is preferably 3,000 g or less, more preferably 2,000 g or less, and still more preferably 1,500 g or less. In the present disclosure, as a method for measuring the filter throughput of the silica dispersion after filtration, the silica dispersion after filtration is put into a container or syringe equipped with a predetermined filter, and the silica dispersion after filtration is passed through the predetermined filter by applying pressure or reducing pressure, and the throughput until the predetermined filter is blocked is measured. In the present disclosure, a membrane filter with a pore diameter of 0.20 μm is used as the predetermined filter. In the present disclosure, the filter throughput of the silica dispersion after filtration can be calculated by the method described in the examples. The silica dispersion after filtration can be applied to various fields such as abrasives, coating agents, fillers, ceramic binders, catalyst carriers, adsorbents, etc. Further, the silica dispersion after filtration can be suitably used as abrasive grains of a polishing liquid used for polishing a substrate to be polished such as a semiconductor substrate or a magnetic disk substrate.

[0049] Generally, a polishing liquid for a magnetic disk substrate is prepared by blending raw material silica particles, water, and additives as required. Suitable examples of additives used in the polishing liquid for a magnetic disk substrate include acids, oxidizing agents, heterocyclic aromatic compounds, amine compounds, and anionic water-soluble polymers. Therefore, in one or more embodiments, the method for manufacturing a polishing liquid for a magnetic disk substrate according to the present disclosure preferably includes a step of mixing at least one selected from acids, oxidizing agents, heterocyclic aromatic compounds, amine compounds, and anionic water-soluble polymers into the silica dispersion after filtration. In the present disclosure, "mixing" means, after the filtration step, that is, simultaneously or in any order, mixing at least one selected from acids, oxidizing agents, heterocyclic aromatic compounds, amine compounds, and anionic water-soluble polymers and, if necessary, additives other than the above examples into the silica dispersion after filtration and water. The mixing can be performed using a mixer such as a homomixer, homogenizer, ultrasonic disperser, and wet ball mill.

[0050] [Polishing Liquid for Magnetic Disk Substrate] In one aspect, the present disclosure relates to a polishing liquid for a magnetic disk substrate (hereinafter also referred to as "the polishing liquid of the present disclosure") manufactured by the method for manufacturing a polishing liquid for a magnetic disk substrate according to the present disclosure. In one or more embodiments, the polishing liquid of the present disclosure includes, in addition to silica particles (component A) and water, optional components (for example, acids, oxidizing agents, heterocyclic aromatic compounds, amine compounds, anionic water-soluble polymers, and other components described later).

[0051] [Silica Particles (Component A) Contained in the Polishing Liquid of the Present Disclosure]< The silica particles (component A) contained in the polishing liquid of the present disclosure are derived from the silica particles (component A) contained in the silica dispersion to be treated, that is, from the silica dispersion after filtration. From the perspective of improving the polishing rate, the content of component A in the polishing liquid of the present disclosure is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.2% by mass or more, and from the perspective 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] <The 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 to-be-treated silica dispersion liquid and the silica dispersion liquid after filtration, but may be separately added during the preparation of the polishing liquid of the present disclosure, and a part of it may be distilled off. Further, when the polishing liquid of the present disclosure further contains one or more selected from the acids, oxidizing agents, heterocyclic aromatic compounds, amine compounds, and anionic water-soluble polymers described later, it may include the water brought in concomitantly therewith. The content of water in the polishing liquid of the present disclosure corresponds to the remainder obtained by subtracting component A and the acids, oxidizing agents, heterocyclic aromatic compounds, amine compounds, anionic water-soluble polymers, and other components described later from 100% by mass, preferably 60% by mass or more, more preferably 80% by mass or more, and preferably 99% by mass or less, more preferably 97% by mass or less.

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

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

[0055] Examples of Component B include inorganic acids such as nitric acid, sulfuric acid, sulfurous acid, persulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, tripolyphosphoric acid, and amidosulfuric acid; organic acids such as organic phosphoric acid, organic phosphonic acid, and carboxylic acid; and the like. Among these, Component B preferably contains inorganic acid and organic phosphonic acid, and more preferably contains inorganic acid, from the viewpoints of improving the polishing rate and reducing the scratch of the polishing liquid. As the inorganic acid, at least one selected from nitric acid, sulfuric acid, hydrochloric acid, perchloric acid, and phosphoric acid is preferable, and phosphoric acid is more preferable. As the organic phosphonic acid, at least one selected from 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), aminotri(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), and diethylenetriaminepenta(methylenephosphonic acid) is preferable, and HEDP is more preferable. Examples of the salts of these acids include salts of the above acids 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 same viewpoint, 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, from the viewpoints of improving the polishing rate and reducing the scratch of the polishing liquid. When Component B is a combination of two or more, the content of Component B refers to their total content.

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

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

[0059] When the polishing liquid of the present disclosure contains component C, 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, from the viewpoints of further improving the polishing rate and further reducing scratches. When component C is a combination of two or more, the content of component C refers to their total content.

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

[0061] As component D, from the viewpoint of further reducing scratches, a heterocyclic aromatic compound containing two or more nitrogen atoms in the heterocyclic ring is preferable, more preferably having three or more nitrogen atoms in the heterocyclic ring, and preferably having nine or less nitrogen atoms in the heterocyclic ring, more preferably having five or less nitrogen atoms in the heterocyclic ring, and still more preferably having four or less nitrogen atoms in the heterocyclic ring.

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

[0063] When the polishing liquid of the present disclosure contains component D, from the viewpoint of further reducing scratches, 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, and from the viewpoint of improving the polishing rate, it is 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. When component D is a combination of two or more, the content of component D refers to their total content.

[0064] <Amine compound (component E)> In one or more embodiments, from the perspective of further reducing scratches, the polishing liquid of the present disclosure preferably further contains an amine compound (hereinafter also referred to as "Component E"). From the perspective 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, an aliphatic amine compound or an alicyclic amine compound is preferably exemplified. In one or more embodiments, as the aliphatic amine compound, from the perspective of further reducing scratches, at least one selected from ethylenediamine, N,N,N',N'-tetramethylethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,4-diaminobutane, hexamethylenediamine, 3-(diethylamino)propylamine, 3-(dibutylamino)propylamine, 3-(methylamino)propylamine, 3-(dimethylamino)propylamine, N-aminoethylethanolamine, N-aminoethylisopropanolamine, and N-aminoethyl-N-methylethanolamine is preferred, at least one selected from N-aminoethylethanolamine, N-aminoethylisopropanolamine, and N-aminoethyl-N-methylethanolamine is more preferred, and N-aminoethylethanolamine (AEEA) is even more preferred. In one or more embodiments, as the alicyclic amine compound, 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 viewpoint 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 viewpoint of improving the polishing rate. When component E is a combination of two or more, the content of component E refers to their total content.

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

[0068] Suitable examples of the monomer having an anionic group in the molecule include 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 their salts. Specific examples of the vinyl monomer having a sulfonic acid group in the molecule preferably include one or more selected from 2-acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid and their salts. 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 the component F is a water-soluble polymer having a vinyl monomer having an anionic group in the molecule as a constituent unit, specific examples of the component F include acrylic acid / 2-acrylamido-2-methylpropanesulfonic acid copolymer (AA / AMPS), polystyrene sulfonic acid, and salts thereof.

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

[0070] The weight average molecular weight of Component F is preferably 500 or more, more preferably 1,000 or more, still more preferably 1,500 or more, and preferably 50,000 or less, more preferably 30,000 or less, still more preferably 20,000 or less, even more preferably 10,000 or less, and even more preferably 5,000 or less, from the viewpoint of further reducing scratches.

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

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

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

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

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

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

[0077] Suitable materials for the substrate to be polished using the polishing liquid of the present disclosure include, for example, 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 containing 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 preferred, one selected from Ni-P plated aluminum alloy substrates, glass substrates such as crystallized glass or strengthened glass is more preferred, and Ni-P plated aluminum alloy substrates are even more preferred.

[0078] In the method for manufacturing a substrate of the present disclosure, when there are a plurality of polishing steps, it is preferable to use the polishing liquid obtained by the method for manufacturing a polishing liquid of the present disclosure after the second step, and it is more preferable to use it in the final polishing step. The final polishing step refers to at least one final polishing step when there are a plurality of polishing steps. When there are multiple polishing steps, in order to avoid contamination of the abrasive and polishing liquid from the previous step, separate polishing machines may be used for each step. Also, when separate polishing machines are used for each step, it is preferable to clean the substrate for each step. Note that the polishing machine is not particularly limited. According to the substrate manufacturing method of the present disclosure, a magnetic disk substrate with reduced scratches on the substrate surface can be efficiently manufactured.

[0079] [Method for Suppressing Filter Clogging] In one or more other embodiments, by passing the silica dispersion to be treated through the filtration step of the present disclosure, a silica dispersion (filtered silica dispersion) with reduced coarse particles can be obtained while suppressing clogging of the filter to be used. Therefore, the present disclosure, in other aspects, is a method for suppressing clogging of a filter used in a filtration step in the production of a polishing liquid for a magnetic disk substrate containing silica particles (component A) and water, wherein the filter is a membrane filter, and the ratio U / D of the primary side average pore diameter U to the secondary side average pore diameter D of the membrane filter is 3.0 or less, and the average pore diameter of the membrane filter is 0.5 μm or more. That is, the present disclosure can suppress clogging of the filter in the production of the polishing liquid for a magnetic disk substrate by using the filter in the production of the polishing liquid for a magnetic disk substrate.

Examples

[0080] Hereinafter, the present disclosure will be described by way of examples, but the present disclosure is not limited thereto.

[0081] 1. Parameter Measurement [pH Measurement of Silica Dispersion to be Treated, Filtered Silica Dispersion, and Polishing Liquid] The pH at 25°C of the silica dispersion to be treated, the filtered silica dispersion, and the polishing liquid is the value measured using a pH meter (Toa Denpa Kogyo Co., Ltd., HM-30G), and is the value 1 minute after the electrode is immersed in the silica dispersion to be treated, the filtered silica dispersion, and the polishing liquid.

[0082] [Method for Measuring Average Primary Particle Size of Silica Particles (Component A)] First, collect 1.5 g of the colloidal silica slurry in terms of solid content into a 200 mL beaker, add 100 mL of ion-exchanged water, and mix with a stirrer. Next, using a potentiometric titration apparatus, adjust the pH of the sample solution to 3.0 with a 0.1 mol / L hydrochloric acid standard solution. Add 30.0 g of sodium chloride, 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] [Method for Measuring Weight-Average Molecular Weight of Anionic Water-Soluble Polymer] The weight-average molecular weight of the anionic water-soluble polymer is measured by gel permeation chromatography (GPC) method under the following measurement conditions. (GPC Conditions) Column: TSKgel G4000PWXL + TSKgel G2500PWXL (manufactured by Tosoh Corporation) Guard column: TSKguardcolumn PWXL (manufactured by Tosoh Corporation) Eluent: 0.2 M phosphate buffer / CH 3 CN = 9 / 1 (volume ratio) Temperature: 40 °C Flow rate: 1.0 mL / min Sample size: 5 mg / mL Detector: RI Standard substance: Polyacrylic acid Na (molecular weight (Mp): 115,000, 28,000, 4100, 1250 (manufactured by Sowa Kagaku and American Polymer Standards Corp.))

[0084] 2. Treated silica dispersion liquid As the treated silica dispersion liquid, a colloidal silica slurry (pH 9.0, manufactured by Nichiyu Catalyst Kasei Co., Ltd., average primary particle diameter 18.0 nm, silica particle concentration 40% by mass) was used.

[0085] 3. Preparation of membrane filter [Preparation Examples 1, 2] A membrane filter having a membrane filter layer (porous membrane, membrane thickness: 0.12 mm, porous membrane material: polysulfone, polyethersulfone) that satisfies the ratio U / D of the primary side average pore diameter U to the secondary side average pore diameter D shown in Table 1 and the average pore diameter APD is prepared by the non-solvent induced phase separation method as follows. Preparation Example 1 Polysulfone (PS: Udel P3500 manufactured by Solvay, molecular weight 59,000) is dissolved in a solvent (dimethylacetamide manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to a concentration of 20% by mass, and thoroughly stirred to obtain a uniform casting solution. The casting solution is uniformly coated on a 10 cm square metal plate to a thickness of 0.12 mm. Immediately afterwards, it is immersed in 1 L of ion-exchanged water adjusted to 15°C together with the metal plate for 10 minutes. The polymer coagulated in the ion-exchanged water is taken out and dried at 25°C overnight, and the porous membrane is obtained because the water vapor bubbles in the gaps disappear. This is used as the membrane filter of Preparation Example 1. At this time, the side in contact with the metal plate is the primary side, and the other side is the secondary side. Preparation Example 2 Polyethersulfone (PES: Sumikaexcel 5003PS manufactured by Sumitomo Chemical Co., Ltd., molecular weight 50,000) is dissolved in a solvent (dimethylacetamide manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to a concentration of 30% by mass, and a membrane filter is obtained in the same manner as described in Preparation Example 1, and this is used as the membrane filter of Preparation Example 2. [Commercially available products 1, 2, 3] 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 K010A025A (manufactured by Advantec, membrane material: polycarbonate, filtration accuracy 0.1 μm, membrane thickness 0.12 mm) Commercially available product 3, Water Fine WFN002 (manufactured by Paul Co., membrane material: polysulfone, filtration accuracy: 0.2 μm, membrane thickness: 0.12 mm)

[0086] The ratio U / D of the primary-side average pore diameter U to the secondary-side average pore diameter D of the membrane filter, and the average pore diameter is determined by the following method. [Ratio U / D of the primary-side average pore diameter U to the secondary-side average pore diameter D of the membrane filter and average pore diameter APD of the membrane filter] The membrane filter to be measured was cut out into a 30 mm square, observed with an SEM (manufactured by Hitachi High-Technologies, FE-4800, 30 kV, 1 to 100,000 times), the obtained photo was taken into the personal computer as image data with a scanner, and the image of the membrane filter opening was analyzed using image analysis software (Mitani Trading Co., "WinROOF2017"). The 500 pore diameters on the primary side of the membrane filter were calculated individually, and the average value was taken as the primary-side average pore diameter U of the filter. The 500 pore diameters on the secondary side of the membrane filter were calculated individually, and the average value was taken as the secondary-side average pore diameter D of the filter. Then, the ratio U / D of the membrane filter was calculated. Also, the average value of all the observed pores was taken as the average pore diameter APD. The results are shown in Table 1.

[0087] 4. Filtration treatment (filtration process) One piece of each membrane filter cut to φ25 mm was set in a plastic holder (PP-25) manufactured by ADVANTEC, and the silica dispersion liquid to be treated was filtered under the conditions of a pressure of 0.2 MPa and a filtration rate of 50 g / min to obtain a silica dispersion liquid after filtration (pH: 9.0).

[0088] 5. Evaluation of filtration performance [Filter liquid throughput (MF value)] The silica dispersion liquid after filtration obtained above was passed through a hydrophilic PTFE 0.20 (pore diameter) μm filter manufactured by ADVANTEC, model: 25HP020AN, under a constant pressure of an air pressure of 0.30 MPa, and the liquid throughput (g) until the filter was blocked was determined as the MF value and shown in Table 1. Also, it was shown in Table 1 as a relative value with the MF value of Comparative Example 1 taken as 100%. Here, if the dropping liquid did not fall within 30 seconds, it was determined that the filter was clogged. In addition, the liquid passing amount of the filter under this condition can be used as an index for reducing scratches when the silica dispersion is used for preparing the polishing liquid. That is, the higher the MF value, the more it is evaluated that a polishing liquid capable of reducing scratches can be obtained.

[0089] [Filter life] In the filtration test of the above membrane filter, the total liquid passing amount when the filtration rate decreased to 17 g / min (1 / 3 of the initial rate) was calculated. Then, by multiplying the liquid passing amount by the ratio of the effective filtration area of φ25 mm to the total effective filtration area assumed for actual machine production, the filter life equivalent to the actual machine production scale was obtained. The results are shown in Table 1.

[0090] 6. Preparation of polishing liquid The components, ion-exchanged water, and the silica dispersion after filtration through the membrane filters of Preparation Examples 1 and 2 and Commercial Products 1 to 3 were mixed so that the contents in the obtained polishing liquid were 5% by mass of silica particles, 0.1% by mass of 1H-benzotriazole Na salt, 0.03% by mass of N-aminoethylethanolamine, 0.02% by mass of sodium acrylate / acrylamide-2-methylpropanesulfonic acid copolymer (AA / AMPS, molar ratio 90 / 10, weight average molecular weight 2000, manufactured by Toagosei Co., Ltd.), 1.0% by mass of phosphoric acid, and 0.4% by mass of hydrogen peroxide, to prepare the polishing liquids (pH 1.8) of Examples 1 to 3 and Comparative Examples 1 to 2.

[0091] 7. Polishing of substrate using polishing liquid Polishing was performed under the following polishing conditions using the polishing liquids of Examples 1 to 3 and Comparative Examples 1 to 2 prepared as described above, and the number of scratches on each polished substrate was evaluated. The evaluation results of the polishing are shown in Table 1 below. [Substrate to be polished] As the substrate to be polished, a substrate obtained by preliminarily coarsely polishing an aluminum alloy substrate plated with Ni-P with a polishing liquid containing silica abrasive grains was used. This substrate to be polished had a thickness of 0.6 mm, an outer diameter of 97 mm, and an inner diameter of 25 mm, and the center line average roughness Ra measured by AFM (Digital Instrument NanoScope IIIa Multi Mode AFM) was 1 nm. The ratio of Ni to P in the Ni-P plating was 88:12 by mass ratio. 〔Finishing polishing conditions〕 Polishing machine: Double-sided polishing machine (Type 9B double-sided polishing machine, manufactured by Speedfam Co., Ltd.) Number of substrates to be polished: 10 Polishing liquid: The polishing liquid of the present disclosure and the polishing liquid of the comparative example 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 Supply rate per 1 cm of the substrate to be polished 2 : 0.076 mL / min Polishing amount per 1 cm of the substrate to be polished 2 : 0.23 mg Polishing time: 6 minutes

[0092] 8. Evaluation of the polishing liquid [Evaluation of scratches] Measuring instrument: "Candela OSA7100" manufactured by KLA-Tencor Corporation Evaluation: Among the substrates put into the polishing tester, 4 sheets were randomly selected, and each substrate was irradiated with a laser at 10,000 rpm to measure the number of scratches. The total number of scratches (pieces) on both sides of each of the 4 substrates was divided by 8 to calculate the number of scratches per substrate surface. The evaluation results of the number of scratches are shown in Table 1 as relative values with Comparative Example 1 taken as 100.

[0093]

Table 1

[0094] As shown in Table 1, in Examples 1 to 3 using a membrane filter with a U / D ratio of 3.0 or less and an average pore diameter APD of 0.5 μm or more, compared with Comparative Example 2 using a membrane filter with a U / D ratio exceeding 3.0 and an average pore diameter APD of 0.5 μm or more, and Comparative Example 1 using a membrane filter with a U / D ratio of 3.0 or less and an average pore diameter APD of less than 0.5 μm, the filter life was improved, and the quality of the polishing liquid for magnetic disk substrates obtained was improved, and scratches were reduced.

Industrial Applicability

[0095] The polishing liquid for magnetic disk substrates manufactured using the manufacturing method of the present disclosure is useful as a polishing liquid for finish polishing, and further, it is possible to suppress clogging of the filter used in the manufacture of the polishing liquid for magnetic disk substrates.

Claims

1. A method for producing a polishing liquid for a magnetic disk substrate containing silica particles (component A) and water, comprising: a step of filtering a silica dispersion to be treated containing silica particles (component A) and water with a membrane filter to obtain a silica dispersion after filtration; wherein a ratio U / D of a primary-side average pore diameter U to a secondary-side average pore diameter D of the membrane filter is 3.0 or less; and the average pore diameter of the membrane filter is 0.5 μm or more. A method for producing a polishing liquid for a magnetic disk substrate.

2. When the average pore diameter of the membrane filter is APD, the value represented by the formula: (U / D) × {(APD) 3} is 0.1 or more and 6.5 or less. The method for producing a polishing liquid for a magnetic disk substrate according to claim 1.

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

4. A method for producing a magnetic disk substrate, comprising: a step of producing a polishing liquid for a magnetic disk substrate by the method for producing a polishing liquid for a magnetic disk substrate according to any one of claims 1 to 3; supplying the polishing liquid 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 one or more selected from the polishing pad and the substrate to be polished to polish the surface to be polished.

5. A method for suppressing clogging of a filter used in a filtration step in the production of a polishing liquid for a magnetic disk substrate containing silica particles (component A) and water, wherein the filter is a membrane filter, a ratio U / D of a primary-side average pore diameter U to a secondary-side average pore diameter D of the membrane filter is 3.0 or less, and the average pore diameter of the membrane filter is 0.5 μm or more. A method for suppressing clogging of a filter.

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