JP7494084B2 - Polishing composition for magnetic disk substrates - Google Patents

Description

This disclosure relates to a polishing composition for magnetic disk substrates, and a method for manufacturing and polishing magnetic disk substrates using the same.

In recent years, magnetic disk drives have become smaller and have larger capacities, and there is a demand for higher recording density. To achieve higher recording density, technological developments are underway 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. To accommodate the lower flying height of the magnetic head and ensure the recording area, there are increasingly strict requirements for magnetic disk substrates in terms of improved smoothness and flatness, as typified by reduced surface roughness, waviness, and edge sagging (roll-off), as well as reduced defects, as typified by reduced scratches, protrusions, pits, etc.

In response to such demands, for example, Patent Document 1 discloses an abrasive composition which contains silica, an acid, a surfactant, an oxidizing agent, and water, and in which the surfactant is an anionic surfactant having a repeating unit and a sulfonic acid (salt) group in the molecule and further having an aromatic group in the main chain of the repeating unit.
Patent Document 2 discloses a polishing composition for magnetic disk substrates, which contains inorganic particles, a specific diallylamine polymer, an acid, and water, and in which the content of the diallylamine polymer in the polishing composition is 0.008 to 0.1% by weight.

JP 2012-142064 A JP 2010-135052 A

As the capacity of magnetic disk drives increases, the requirements for the surface quality of substrates are becoming more stringent, and there is a demand for the development of polishing compositions that can reduce scratches on the substrate surface while improving the polishing speed. In general, there is a trade-off between polishing speed and scratches; for example, there is a problem that increasing the polishing speed increases scratches.

Therefore, the present disclosure provides a polishing composition that can improve the polishing rate while reducing scratches on the substrate surface after polishing, as well as a method for manufacturing a magnetic disk substrate and a method for polishing a substrate using the same.

In one aspect, the present disclosure relates to a polishing liquid composition for magnetic disk substrates, which contains inorganic particles (component A), a water-soluble polymer (component B), an acid (component C), and water, and the component B is a copolymer containing a structural unit a having a hydroxyl group (excluding a hydroxyl group as a substituent of an aromatic ring) and a structural unit b (excluding structural unit a) derived from a monomer containing at least one functional group selected from an amino group, a quaternary ammonium group, and a salt thereof.

In another aspect, the present disclosure relates to a method for manufacturing a magnetic disk substrate, comprising a step of polishing a substrate to be polished using the polishing composition of the present disclosure.

In another aspect, the present disclosure relates to a method for polishing a substrate, the method comprising polishing a substrate to be polished with the polishing composition of the present disclosure, the substrate to be polished being a substrate used in the manufacture of magnetic disk substrates.

In one or more embodiments, the polishing composition of the present disclosure can achieve the effect of simultaneously improving the polishing rate and reducing scratches on the substrate surface after polishing.

This disclosure is based on the finding that by using a specific water-soluble polymer, it is possible to suppress an increase in scratches on the substrate surface after polishing, even if the polishing speed is increased.

That is, in one aspect, the present disclosure relates to a polishing liquid composition for magnetic disk substrates (hereinafter also referred to as the "polishing liquid composition of the present disclosure") which contains inorganic particles (component A), a water-soluble polymer (component B), an acid (component C), and water, wherein the component B is a copolymer containing a structural unit a having a hydroxyl group (excluding a hydroxyl group as a substituent of an aromatic ring) and a structural unit b (excluding the structural unit a) derived from a monomer containing at least one functional group selected from an amino group, a quaternary ammonium, and a salt thereof.
According to one or more embodiments of the present disclosure, the polishing rate can be improved and an increase in scratches on the substrate surface after polishing can be suppressed. Also, according to one or more other embodiments of the present disclosure, the polishing rate can be improved and scratches on the substrate surface after polishing can be reduced.

Although the details of the mechanism by which the effects of the present disclosure are manifested are not clear, it is presumed as follows.
A substrate to be polished is usually polished by sandwiching the substrate between plates to which polishing pads are attached, supplying a polishing composition to a polishing machine, and moving the plates and the substrate to be polished. In such polishing, if inorganic particles get into the holes of the polishing pad, the number of inorganic particles acting in polishing is reduced, and the polishing rate is thought to decrease.
In the present disclosure, it is believed that the hydroxyl groups (structural unit a) of the water-soluble polymer (component B) are adsorbed to the inorganic particles (component A), and the amino groups or quaternary ammonium groups (structural unit b) are adsorbed to the polishing pad or substrate through electrostatic interaction, thereby increasing the number of inorganic particles acting in the polishing, thereby contributing to an improvement in the polishing rate.
Furthermore, the water-soluble polymer (component B) is adsorbed onto the polishing pad, softening the surface of the polishing pad and reducing the indentation stress of the inorganic particles caused by the polishing pad, which is believed to contribute to reducing scratches.
However, the present disclosure need not be construed as being limited to these mechanisms.

In the present disclosure, scratches on the substrate surface can be detected, for example, by an optical defect inspection device and can be quantitatively evaluated as the number of scratches. Specifically, the number of scratches can be evaluated by the method described in the Examples.

[Inorganic particles (component A)]
As the inorganic particles (hereinafter also referred to as "component A") contained in the polishing composition of the present disclosure, inorganic particles generally used for abrasive grains in polishing compositions can be used, and examples thereof include metal, metal or semimetal carbide, nitride, oxide, or boride, diamond, etc. The metal or semimetal element is derived from group 2A, 2B, 3A, 3B, 4A, 4B, 5A, 6A, 7A, or 8 of the periodic table (long period type). Examples of component A include silicon oxide (hereinafter referred to as silica), aluminum oxide (hereinafter referred to as alumina), silicon carbide, diamond, manganese oxide, magnesium oxide, zinc oxide, titanium oxide, cerium oxide (hereinafter referred to as ceria), zirconium oxide, etc., and it is preferable to use one or more of these from the viewpoint of improving the polishing rate. Among them, silica particles are preferred as component A from the viewpoint of improving the polishing rate and reducing scratches. Examples of silica particles include colloidal silica, fumed silica, pulverized silica, and silica surface-modified therewith, and colloidal silica is preferred. Component A may be one type or a combination of two or more types.

From the viewpoint of improving the polishing rate, the average particle size of component A is preferably 1 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more, and from the viewpoint of reducing scratches, it is preferably 100 nm or less, more preferably 70 nm or less, even more preferably 40 nm or less, and even more preferably 30 nm or less. From the same viewpoint, the average particle size of component A is preferably 1 nm or more and 100 nm or less, more preferably 5 nm or more and 70 nm or less, even more preferably 10 nm or more and 40 nm or less, and even more preferably 10 nm or more and 30 nm or less. In this disclosure, the "average particle size of inorganic particles" refers to the average particle size based on the scattering intensity distribution measured at a detection angle of 90° in the dynamic light scattering method. The average particle size of inorganic particles can be specifically determined by the method described in the examples.

The content of component A in the polishing composition of the present disclosure is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.5% by mass or more from the viewpoint of improving the polishing rate, and is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and even more preferably 1.5% by mass or less from the viewpoint of reducing scratches. From the same viewpoint, the content of component A in the polishing composition of the present disclosure is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.2% by mass or more and 5% by mass or less, even more preferably 0.5% by mass or more and 3% by mass or less, and even more preferably 0.5% by mass or more and 1.5% by mass or less from the viewpoint of improving the polishing rate and reducing scratches. When component A is a combination of two or more kinds, the content of component A refers to the total content thereof. In addition, when component A is silica, the content of component A is a value converted to SiO ₂ .

[Water-soluble polymer (component B)]
The water-soluble polymer (hereinafter also referred to as "component B") contained in the polishing composition of the present disclosure is a copolymer containing a structural unit a having a hydroxyl group (excluding hydroxyl groups as a substituent of an aromatic ring) and a structural unit b (excluding structural unit a) derived from a monomer containing at least one functional group selected from an amino group, a quaternary ammonium group, and a salt thereof, from the viewpoint of improving the polishing rate and reducing scratches. Component B may be one type or a combination of two or more types. In the present disclosure, "water-soluble" means having a solubility of 0.5 g/100 mL or more, preferably 2 g/100 mL, in water at 20°C.

(Structural unit a)
The structural unit a is a structural unit having a hydroxyl group (excluding a hydroxyl group as a substituent of an aromatic ring), and from the viewpoint of improving the polishing rate, is preferably a structural unit derived from a compound having a hydroxyl group (excluding a hydroxyl group as a substituent of an aromatic ring) and an ethylenically unsaturated bond, or a structural unit derived from a compound having an epoxy group.
As the compound having a hydroxyl group (excluding a hydroxyl group as a substituent of an aromatic ring) and an ethylenically unsaturated bond, from the viewpoint of improving the polishing rate, an acrylamide having a hydroxyl group is preferable, and examples thereof include hydroxyethylacrylamide.
An example of a compound having an epoxy group is epichlorohydrin.
In one or a plurality of embodiments, from the viewpoint of improving the removal rate, the structural unit a is preferably a structural unit derived from hydroxyethylacrylamide or epichlorohydrin.

(Structural unit b)
The structural unit b is a structural unit derived from a monomer containing at least one functional group selected from an amino group, a quaternary ammonium group, and a salt thereof. The structural unit b does not include the structural unit a. That is, a structural unit having an amino group but a hydroxyl group corresponds to the structural unit a. In one or more embodiments, the amino group is a primary amino group, a secondary amino group, or a tertiary amino group. From the viewpoint of improving the polishing rate and reducing scratches, examples of the monomer forming the structural unit b include an amine compound having an allyl group, an amine compound having an alkyl group, ammonia, and salts thereof. An example of an amine compound having an allyl group is allylamine. An example of an amine compound having an alkyl group is dialkylamine such as dimethylamine. Examples of salts include hydrochloride, hydrobromide, acetate, sulfate, nitrate, sulfite, phosphate, amidosulfate, methanesulfonate, and the like, and examples of the structural unit b include a structural unit derived from allylamine, a structural unit derived from dimethylamine, and a structural unit derived from ammonia. The structural unit b may be one type or a combination of two or more types.

The content of structural unit a in all structural units of component B is preferably 5 mol% or more, more preferably 20 mol% or more, and even more preferably 30 mol% or more, from the viewpoint of improving the polishing speed, and is preferably 95 mol% or less, more preferably 80 mol% or less, and even more preferably 60 mol% or less, from the viewpoint of improving the polishing speed and reducing scratches.

The content of structural unit b in all structural units of component B is preferably 5 mol% or more, more preferably 20 mol% or more, and even more preferably 40 mol% or more, from the viewpoint of improving the polishing rate and reducing scratches, and from the same viewpoint, is preferably 95 mol% or less, more preferably 80 mol% or less, and even more preferably 70 mol% or less.

The molar ratio (a/b) of structural unit a to structural unit b among all structural units of component B is preferably 5/95 or more, more preferably 20/80 or more, and even more preferably 30/70 or more, from the viewpoint of improving the polishing speed, and is preferably 95/5 or less, more preferably 80/20 or less, and even more preferably 60/40 or less, from the viewpoint of improving the polishing speed and reducing scratches.

From the viewpoint of improving the polishing speed, the total content of structural units a and structural units b in all structural units of component B is preferably 60 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, and even more preferably 100 mol%.

In the present disclosure, as the content (mol %) of a certain constituent unit among all constituent units constituting component B, depending on the synthesis conditions, the amount (mol %) of the compound for introducing the constituent unit charged in the reaction tank among the compounds for introducing all constituent units charged in the reaction tank in all steps of the synthesis of component B may be used. Also, in the present disclosure, as the constituent ratio (molar ratio) of two constituent units constituting component B, depending on the synthesis conditions, the amount ratio (molar ratio) of the compounds for introducing the two constituent units charged in the reaction tank in all steps of the synthesis of component B may be used.

Component B may be, for example, a compound having a structure represented by the following formula (I) or the following formula (II).

In formula (I), X ₁ ^- and X ₂ ^- represent a monovalent anion, p, q and r each satisfy 60≦p+q+r≦100, and in formula (II), X ₃ ^- represents a monovalent anion, m and n each satisfy 60≦m+n≦100.

In formula (I), X ₁ ^- , X ₂ ^- and X ₃ ^- are, for example, a halide ion or a hydroxide ion. X ₁ ^- , X ₂ ^- and X ₃ ^- may each be one kind alone or two or more kinds.
From the viewpoint of improving the polishing rate, q is preferably 5 or more, more preferably 20 or more, and even more preferably 30 or more, and from the viewpoint of improving the polishing rate and reducing scratches, q is preferably 95 or less, more preferably 80 or less, and even more preferably 60 or less.
From the viewpoints of improving the polishing rate and reducing scratches, p+r is preferably 5 or more, more preferably 20 or more, and even more preferably 40 or more, and from the same viewpoints, it is preferably 95 or less, more preferably 80 or less, and even more preferably 70 or less.
From the viewpoints of improving the polishing rate and reducing scratches, r/p is preferably 0 or more, and from the same viewpoints, it is preferably 5 or less, more preferably 1 or less, and even more preferably 0.5 or less.
From the viewpoint of improving the polishing rate, p+q+r is preferably 60≦p+q+r, more preferably 70≦p+q+r, even more preferably 80≦p+q+r, still more preferably 90≦p+q+r, and still more preferably p+q+r=100.

In formula (II), from the viewpoint of improving the polishing rate, m is preferably 5 or more, more preferably 20 or more, and even more preferably 30 or more, and from the viewpoint of improving the polishing rate and reducing scratches, m is preferably 95 or less, more preferably 80 or less, and even more preferably 60 or less.
From the viewpoints of improving the polishing rate and reducing scratches, n is preferably 5 or more, more preferably 20 or more, and even more preferably 30 or more, and from the same viewpoints, n is preferably 95 or less, more preferably 80 or less, and even more preferably 70 or less.
From the viewpoint of improving the polishing rate, m+n is preferably 60≦m+n, more preferably 70≦m+n, even more preferably 80≦m+n, still more preferably 90≦m+n, and still more preferably m+n=100.

Component B may be, from the viewpoint of improving the polishing speed and reducing scratches, an ammonia/epichlorohydrin/dimethylamine copolymer, an epichlorohydrin/dimethylamine copolymer, an allylamine/hydroxyethylacrylamide copolymer, etc.

Component B may further contain other structural units in addition to structural unit a and structural unit b. Examples of other structural units include structural unit c derived from a monomer containing a sulfonic acid group. Examples of structural unit c include isoprene sulfonic acid, 2-methacrylamide-2-methylpropane sulfonic acid, styrene sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, phenyl sulfonic acid, naphthalene sulfonic acid, and toluene sulfonic acid. Structural unit c may be one type or a combination of two or more types.

The arrangement of each of the constituent units constituting component B may be random, block, or graft.

When component B is an ammonia/epichlorohydrin/dimethylamine copolymer, component B can be obtained, for example, by synthesis through a ring-opening reaction of epichlorohydrin with ammonia-dimethylamine in an aqueous solvent.
When component B is an epichlorohydrin/dimethylamine copolymer, component B can be obtained, for example, by synthesis through a ring-opening reaction of epichlorohydrin with dimethylamine in an aqueous solvent.
When component B is an allylamine/hydroxyethylacrylamide copolymer, component B can be obtained, for example, by synthesis through radical polymerization of allylamine and hydroxyethylacrylamide in a polar solvent.

From the viewpoint of improving the polishing rate and reducing scratches, the weight average molecular weight of component B is preferably 500 or more, more preferably 1,000 or more, and even more preferably 1,500 or more, and from the same viewpoint, it is preferably 1,000,000 or less, more preferably 750,000 or less, and even more preferably 500,000 or less. From the same viewpoint, the weight average molecular weight of component B is preferably 500 or more and 1,000,000 or less, more preferably 1,000 or more and 750,000 or less, and even more preferably 1,500 or more and 500,000 or less. In this disclosure, the weight average molecular weight is a value measured using gel permeation chromatography (GPC) under the conditions described in the examples.

From the viewpoints of improving the polishing rate and reducing scratches, the content of component B in the polishing liquid composition of the present disclosure is preferably 0.000001 mass% or more, more preferably 0.00001 mass% or more, even more preferably 0.0001 mass% or more, even more preferably 0.0005 mass% or more, and even more preferably 0.001 mass% or more, and from the same viewpoints, it is preferably 0.01 mass% or less, more preferably less than 0.01 mass%, even more preferably 0.009 mass% or less, even more preferably 0.006 mass% or less, and even more preferably 0.005 mass% or less. From the same viewpoint, the content of component B in the polishing liquid composition of the present disclosure is preferably 0.000001 mass% or more and 0.01 mass% or less, more preferably 0.00001 mass% or more and 0.01 mass% or less, even more preferably 0.0001 mass% or more and 0.009 mass% or less, even more preferably 0.0005 mass% or more and 0.006 mass% or less, and even more preferably 0.001 mass% or more and 0.005 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.

The mass ratio of component B to component A in the polishing liquid composition of the present disclosure (content of component B/content of component A) is preferably 0.00001 or more, more preferably 0.0001 or more, and even more preferably 0.0002 or more, from the viewpoint of improving the polishing rate and reducing scratches, and is preferably 0.02 or less, more preferably 0.01 or less, and even more preferably 0.005 or less, from the viewpoint of improving the polishing rate. And, the mass ratio of component B to component A in the polishing liquid composition of the present disclosure is preferably 0.00001 or more and 0.02 or less, more preferably 0.0001 or more and 0.01 or less, and even more preferably 0.0002 or more and 0.005 or less, from the viewpoint of improving the polishing rate and reducing scratches.

[Acid (Component C)]
The polishing composition of the present disclosure contains an acid (component C). In the present disclosure, the use of an acid includes the use of an acid or a salt thereof. Component C may be one type or a combination of two or more types.

Examples of component C 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 them, from the viewpoint of improving the polishing rate and reducing scratches, at least one selected from inorganic acids and organic phosphonic acids is preferred. As inorganic acids, at least one selected from nitric acid, sulfuric acid, hydrochloric acid, perchloric acid, and phosphoric acid is preferred, and at least one of phosphoric acid and sulfuric acid is more preferred. As organic phosphonic acids, at least one selected from 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), aminotri(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), and diethylenetriaminepenta(methylenephosphonic acid) is preferred, and HEDP is more preferred. 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 metals include metals belonging to Groups 1 to 11 of the periodic table. Among these, salts of the above acids with metals belonging to Group 1A or ammonia are preferred from the viewpoint of improving the polishing rate and reducing scratches.

From the viewpoint of improving the polishing rate, the content of component C in the polishing liquid composition 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, and from the viewpoint of reducing scratches, it is preferably 5 mass% or less, more preferably 4 mass% or less, and even more preferably 3 mass% or less. From the viewpoint of improving the polishing rate and reducing scratches, the content of component C in the polishing liquid composition of the present disclosure is preferably 0.01 mass% or more and 5 mass% or less, more preferably 0.1 mass% or more and 4 mass% or less, and even more preferably 0.5 mass% or more and 3 mass% or less. When component C is a combination of two or more types, the content of component C refers to the total content thereof.

The mass ratio C/A of component C to component A (content of component C/content of component A) in the polishing liquid composition of the present disclosure is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more, from the viewpoint of improving the polishing rate, and is preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less, from the viewpoint of reducing scratches. And, from the viewpoint of improving the polishing rate and reducing scratches, the mass ratio C/A is preferably 0.1 or more and 5 or less, more preferably 0.2 or more and 4 or less, and even more preferably 0.3 or more and 3 or less.

[water]
The polishing composition of the present disclosure contains water as a medium. Examples of water include distilled water, ion-exchanged water, pure water, and ultrapure water. The content of water in the polishing composition of the present disclosure can be the remainder excluding component A, component B, component C, and any optional components described below.

[Oxidizing agent (component D)]
The polishing composition of the present disclosure may further contain an oxidizing agent (hereinafter also referred to as "component D") from the viewpoint of improving the polishing rate and reducing scratches. In one or more embodiments, component D is an oxidizing agent that does not contain a halogen atom. Component D may be one type or a combination of two or more types.

Component D, from the viewpoint of improving the polishing rate and reducing scratches, may be, for example, 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. 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 substrate to be polished, and ease of availability.

From the viewpoint of improving the polishing rate, the content of component D in the polishing liquid composition 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 from the viewpoint of reducing scratches, it is preferably 4 mass% or less, more preferably 2 mass% or less, and even more preferably 1.5 mass% or less. From the viewpoint of improving the polishing rate and reducing scratches, the content of component D in the polishing liquid composition of the present disclosure is preferably 0.01 mass% or more and 4 mass% or less, more preferably 0.05 mass% or more and 2 mass% or less, and even more preferably 0.1 mass% or more and 1.5 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.

[Other ingredients]
In one or more embodiments, the polishing liquid composition of the present disclosure may contain other components as necessary within a range that does not impair the effects of the present disclosure. Examples of other components include heterocyclic aromatic compounds, aliphatic amine compounds, alicyclic amine compounds, thickeners, dispersants, rust inhibitors, basic substances, polishing rate enhancers, surfactants, water-soluble polymers other than Component B, etc.

[pH of polishing composition]
The pH of the polishing liquid composition of the present disclosure is preferably 6 or less, more preferably 5 or less, even more preferably 4 or less, and even more preferably 3 or less, from the viewpoint of improving the polishing rate, and is preferably 0.5 or more, more preferably 0.8 or more, and even more preferably 1 or more, from the viewpoint of reducing scratches. And, from the viewpoint of improving the polishing rate and reducing scratches, the pH of the polishing liquid composition of the present disclosure is preferably 0.5 to 6 or less, more preferably 0.8 to 5 or less, even more preferably 1 to 4 or less, and even more preferably 1 to 3 or less. The pH can be adjusted using the above-mentioned acid (component C) or a known pH adjuster. In the present disclosure, the above pH is the pH of the polishing liquid composition at 25 ° C., and can be measured using a pH meter, and can be, for example, the value after 2 minutes of immersing the electrode of the pH meter in the polishing liquid composition.

[Method of producing the polishing composition]
The polishing liquid composition of the present disclosure can be produced, for example, by blending component A, component B, component C, and water, and, if desired, optional components (component D and other components) by a known method. For example, in one or more embodiments, the polishing liquid composition of the present disclosure can be produced by blending at least component A, component B, component C, and water. Therefore, in another aspect, the present disclosure relates to a method for producing a polishing liquid composition, which includes a step of blending at least component A, component B, component C, and water. In the present disclosure, "blending" includes mixing component A, component B, component C, and water, and optional components (component D and other components) as necessary, simultaneously or in any order. The inorganic particles of component A (component A) may be mixed in the state of a concentrated slurry, or may be mixed after diluting with water or the like. When component A is composed of multiple types of inorganic particles, the multiple types of inorganic particles can be blended simultaneously or separately. When component B is composed of multiple types of water-soluble polymers, the multiple types of water-soluble polymers can be blended simultaneously or separately. When component C is composed of multiple types of acids, the multiple types of acids can be blended simultaneously or separately. The blending can be carried out using a mixer such as a homomixer, a homogenizer, an ultrasonic disperser, a wet ball mill, etc. The preferred blending amount of each component in the method for producing the polishing liquid composition can be the same as the preferred content of each component in the polishing liquid composition of the present disclosure described above.

In the present disclosure, "the content of each component in the polishing liquid composition" refers to the content of each component at the time of use, i.e., at the time when the polishing liquid composition is started to be used for polishing. The polishing liquid composition of the present disclosure may be stored and supplied in a concentrated state to the extent that its storage stability is not impaired. In this case, it is preferable in that the manufacturing and transportation costs can be further reduced. When used, the concentrate of the polishing liquid composition of the present disclosure may be appropriately diluted with the above-mentioned water as necessary. The dilution ratio is not particularly limited as long as the above-mentioned content of each component (at the time of use) can be secured after dilution, and may be, for example, 10 to 100 times.

[Polishing liquid kit]
In another aspect, the present disclosure relates to a kit for producing the polishing liquid composition of the present disclosure (hereinafter, also referred to as the "polishing liquid kit of the present disclosure"). The polishing liquid kit of the present disclosure includes, for example, a polishing liquid kit (two-liquid type polishing liquid composition) containing an abrasive dispersion containing component A and water, and an additive aqueous solution containing component B and component C in a mutually unmixed state. The abrasive dispersion and the additive aqueous solution are mixed at the time of use, and diluted with water as necessary. The water contained in the abrasive dispersion may be the entire amount of water used in preparing the polishing liquid composition, or may be a part of the amount. The additive aqueous solution may contain a part of the water used in preparing the polishing liquid composition. The abrasive dispersion and the additive aqueous solution may each contain the above-mentioned optional components (component D and other components) as necessary. According to the polishing liquid kit of the present disclosure, a polishing liquid composition capable of simultaneously improving the polishing rate and reducing scratches on the substrate surface after polishing can be obtained.

[Polished substrate]
In one or more embodiments, the substrate to be polished is a substrate used for manufacturing a magnetic disk substrate. In one or more embodiments, the surface of the substrate to be polished is polished with the polishing composition of the present disclosure, and then a magnetic layer is formed on the substrate surface by sputtering or the like, thereby manufacturing a magnetic disk substrate.

Materials of the substrate to be polished that are preferably used in the present disclosure include, for example, metals or semimetals such as silicon, aluminum, nickel, tungsten, copper, tantalum, and titanium, or alloys thereof, glassy materials such as glass, glassy carbon, and amorphous carbon, ceramic materials such as alumina, silicon dioxide, silicon nitride, tantalum nitride, and titanium carbide, and resins such as polyimide resins. In particular, the substrate to be polished is preferably one containing metals such as aluminum, nickel, tungsten, and copper, and alloys mainly composed of these metals. As the substrate to be polished, for example, Ni-P plated aluminum alloy substrates and glass substrates such as crystallized glass, reinforced glass, aluminosilicate glass, and aluminoborosilicate glass are more suitable, and Ni-P plated aluminum alloy substrates are even more suitable. In the present disclosure, the term "Ni-P plated aluminum alloy substrate" refers to an aluminum alloy substrate whose surface is ground and then electrolessly plated with Ni-P.

The shape of the substrate to be polished can be, for example, a disk-shaped, plate-shaped, slab-shaped, prism-shaped, or other shape with a flat surface, or a lens-shaped, or other shape with a curved surface. Of these, a disk-shaped substrate to be polished is suitable. In the case of a disk-shaped substrate to be polished, the outer diameter is, for example, about 2 to 95 mm, and the thickness is, for example, about 0.4 to 2 mm.

In one or more embodiments, the polishing liquid composition of the present disclosure can be suitably used for polishing a substrate after rough polishing. The substrate to be polished can be a substrate after rough polishing. Examples of abrasive grains used for rough polishing include alumina, silica, and the like.

[Method of manufacturing magnetic disk substrate]
In general, a magnetic disk is manufactured by polishing a substrate to be polished through a grinding process, a rough polishing process, and a finish polishing process, and forming a magnetic disk in a recording part forming process. The polishing composition of the present disclosure can be used in a polishing process, preferably a finish polishing process, for polishing a substrate to be polished in a method for manufacturing a magnetic disk substrate. That is, in another aspect, the present disclosure relates to a method for manufacturing a magnetic disk substrate (hereinafter also referred to as a "substrate manufacturing method of the present disclosure") including a process for polishing a substrate to be polished using the polishing composition of the present disclosure (hereinafter also referred to as a "polishing process using the polishing composition of the present disclosure"). The substrate manufacturing method of the present disclosure is particularly suitable for a method for manufacturing a magnetic disk substrate for a perpendicular magnetic recording system.

In one or more embodiments, the polishing process using the polishing liquid composition of the present disclosure is a process in which the polishing liquid composition of the present disclosure is supplied to the surface of the substrate to be polished, a polishing pad is brought into contact with the surface to be polished, and at least one of the polishing pad and the substrate to be polished is moved to perform polishing. In another one or more embodiments, the polishing process using the polishing liquid composition of the present disclosure is a process in which the substrate to be polished is sandwiched between a platen to which a polishing pad such as a nonwoven organic polymer-based polishing cloth is attached, and the platen and the substrate to be polished are moved while the polishing liquid composition of the present disclosure is supplied to the polishing machine to polish the substrate to be polished.

When the polishing process of the substrate to be polished is performed in multiple stages, the polishing process using the polishing liquid composition of the present disclosure is preferably performed in the second stage or later, and more preferably in the final polishing process or finish polishing process. In this case, a separate polishing machine may be used for each step to avoid contamination with abrasive grains or polishing liquid composition from the previous step, and when separate polishing machines are used, it is preferable to clean the substrate to be polished after each polishing process. Furthermore, the polishing liquid composition of the present disclosure can be used in circulating polishing in which the used polishing liquid is reused. There are no particular limitations on the polishing machine, and any known polishing machine for substrate polishing can be used.

The polishing pad used in the present disclosure is not particularly limited, and may be, for example, a suede type, a nonwoven fabric type, a polyurethane independent foam type, or a two-layer type in which these are laminated, and from the viewpoint of improving the polishing speed, a suede type polishing pad is preferred.

The polishing load in the polishing process using the polishing liquid composition of the present disclosure is preferably 5.9 kPa or more, more preferably 6.9 kPa or more, and even more preferably 7.5 kPa or more, from the viewpoint of improving the polishing rate, and is preferably 20 kPa or less, more preferably 18 kPa or less, and even more preferably 16 kPa or less, from the viewpoint of reducing scratches. In the manufacturing method of the present disclosure, the polishing load refers to the pressure of the platen applied to the polishing surface of the substrate to be polished during polishing. The polishing load can be adjusted by applying air pressure or a weight to at least one of the platen and the substrate to be polished.

In a polishing process using the polishing liquid composition of the present disclosure, the supply rate of the polishing liquid composition of the present disclosure is, from the viewpoint of reducing scratches, preferably ^0.05 mL/min or more and 15 mL/min or less, more preferably 0.06 mL/min or more and 10 mL/min or less, even more preferably 0.07 mL/min or more and 1 mL/min or less, and even more preferably 0.07 mL/min or more and 0.5 mL/min or less, per 1 cm2 of the substrate to be polished.

The polishing composition of the present disclosure can be supplied to the polishing machine, for example, by continuously supplying the composition using a pump or the like. When supplying the polishing composition to the polishing machine, in addition to supplying the composition as a single liquid containing all the components, the composition can be divided into multiple blending component liquids and supplied as two or more liquids, taking into consideration the stability of the polishing composition. In the latter case, the multiple blending component liquids are mixed, for example, in the supply pipe or on the substrate to be polished, to produce the polishing composition of the present disclosure.

According to the substrate manufacturing method of the present disclosure, by using the polishing composition of the present disclosure, it is possible to produce high-quality magnetic disk substrates with reduced scratches on the substrate surface after polishing with high yield and good productivity.

[Polishing method]
In another aspect, the present disclosure relates to a method for polishing a substrate (hereinafter also referred to as the "polishing method of the present disclosure"), which includes polishing a substrate to be polished using the polishing liquid composition of the present disclosure, and the substrate to be polished is a substrate used in the manufacture of a magnetic disk substrate. By using the polishing method of the present disclosure, it is possible to produce a high-quality magnetic disk substrate with reduced scratches on the substrate surface after polishing with high yield and good productivity. As described above, the substrate to be polished in the polishing method of the present disclosure includes those used in the manufacture of magnetic disk substrates, and among them, substrates used in the manufacture of magnetic disk substrates for perpendicular magnetic recording are preferred. The specific polishing method and conditions can be the same as those of the substrate manufacturing method of the present disclosure described above.

In one or more embodiments, polishing a substrate to be polished using the polishing liquid composition of the present disclosure means supplying the polishing liquid composition of the present disclosure to the surface of the substrate to be polished, contacting the surface to be polished with a polishing pad, and moving at least one of the polishing pad and the substrate to be polished to perform polishing, or sandwiching the substrate to be polished between plates to which a polishing pad such as a nonwoven organic polymer-based polishing cloth is attached, and polishing the substrate to be polished by moving the platen and the substrate to be polished while supplying the polishing liquid composition of the present disclosure to a polishing machine.

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

1. Preparation of polishing compositions (Examples 1 to 14 and Comparative Examples 1 to 7)
The polishing liquid compositions of Examples 1 to 14 and Comparative Examples 1 to 7 shown in Table 1 were prepared by mixing and stirring colloidal silica (component A), water-soluble polymers B1 to B8 (component B or non-component B) shown in Table 1, phosphoric acid (component C), hydrogen peroxide (component D), and ion-exchanged water. The content (effective amount) of each component in each polishing liquid composition is as shown in Table 1. The content of ion-exchanged water is the remainder excluding component A, component B or non-component B, component C, and component D.

In preparing each polishing composition, the following components B, non-component B, component C and component D were used.
(Component B)
B1: Ammonia/epichlorohydrin/dimethylamine copolymer (molar ratio: 5/50/45) [manufactured by Senka Corporation, weight average molecular weight: 10,000]
B2: epichlorohydrin/dimethylamine copolymer (molar ratio: 50/50) [manufactured by Senka Corporation, weight average molecular weight: 8,000]
B3: Allylamine/hydroxyethylacrylamide copolymer (molar ratio: 70/30) neutralized with hydrochloric acid [manufactured by Kao Corporation, weight average molecular weight: 9,000]
B4: Allylamine/hydroxyethylacrylamide copolymer (molar ratio: 50/50) neutralized with hydrochloric acid [manufactured by Kao Corporation, weight average molecular weight: 10,000]
(Non-Component B)
B5: Aminobenzenesulfonic acid-phenol-formaldehyde condensate (molar ratio 45/5/50) [manufactured by Kao Corporation, weight average molecular weight: 10,000]
B6: DADMAC (poly N,N diallyl(N,N-methyl)ammonium chloride) [manufactured by Nitto Boseki Co., Ltd., weight average molecular weight: 8,500]
B7: DADMAC/SO ₂ (copolymer of N,N diallyl(N,N dimethyl)ammonium chloride/sulfur dioxide) (molar ratio: 50/50) [manufactured by Nitto Boseki Co., Ltd., weight average molecular weight: 4,000]
B8: Polyvinyl alcohol [weight average molecular weight: 88,000]
(Component C)
Phosphoric acid [Wako Pure Chemical Industries, Ltd., special grade]
(Component D)
Hydrogen peroxide solution [concentration 35% by mass, manufactured by ADEKA]

2. Measurement of each parameter (1) Average particle size of colloidal silica (component A) Component A (colloidal silica) and component C (phosphoric acid) used in the preparation of the polishing composition were added to ion-exchanged water and stirred to prepare a standard sample. The contents of components A and C in the standard sample were 1% by mass and 0.45% by mass, respectively. The standard sample was subjected to a dynamic light scattering apparatus (DLS-6500 manufactured by Otsuka Electronics Co., Ltd.) according to the manufacturer's attached instructions, and the particle size at which the area of the scattering intensity distribution obtained by the Cumulant method at a detection angle of 90° when integrated 200 times was 50% of the total was determined, and this was taken as the average particle size of the colloidal silica. The results are shown in Tables 1 to 3.

(2) Weight-average molecular weight of water-soluble polymer (component B and non-component B) The weight-average molecular weight of component B and non-component B was measured by gel permeation chromatography (GPC) under the following conditions. The results are shown in Tables 1 to 3.
<Measurement conditions>
Column: TSKgel GMPWXL + TSKgel GMPWXL (Tosoh Corporation)
Eluent: 0.2 M phosphate buffer/CH ₃ CN=7/3 (volume ratio)
Temperature: 40°C
Flow rate: 1.0 mL/min Sample size: 2 mg/mL
Detector: RI
Standard substance: sodium polystyrene sulfonate (weight average molecular weight: 1,100, 3,610, 14,900, 152,000, manufactured by POLMER STANDARDS SERVICE)

(3) Measurement of pH The pH of the polishing composition was measured at 25° C. using a pH meter (manufactured by DKK-TOA Corporation), and the value measured 2 minutes after immersing the electrode in the polishing composition was recorded. The results are shown in Tables 1 to 3.

3. Polishing Method The polishing compositions of Examples 1 to 14 and Comparative Examples 1 to 7 prepared as described above were used to polish the following substrates under the following polishing conditions. Then, the polishing rate and the number of scratches were measured by the measuring methods described below, and the results are shown in Tables 1 to 3.
In addition, since silica aggregated in Comparative Example 5, polishing was not performed using the polishing composition of Comparative Example 5.

[Polished substrate]
The substrate to be polished was a Ni-P plated aluminum alloy substrate that had been roughly polished with a polishing composition containing alumina abrasive grains. The substrate had a thickness of 0.8 mm, an outer diameter of 95 mm, an inner diameter of 25 mm, and a center line average roughness Ra of 1 nm as measured by an AFM (Digital Instrument NanoScope IIIa Multi Mode AFM).

[Polishing conditions]
Polishing test machine: Speedfam's "Double-sided 9B polishing machine"
Polishing pad: Fujibo suede type (foam layer: polyurethane elastomer, thickness 0.9 mm, average pore size 10 μm)
Amount of polishing composition supplied: 100 mL/min (supply rate per ¹ cm2 of substrate to be polished: 0.076 mL/min)
Lower platen rotation speed: 32.5 rpm
Polishing load: 13.0 kPa
Polishing time: 6 minutes Number of substrates: 10

4. Evaluation [Evaluation of polishing rate]
The weight of each substrate before and after polishing was measured using a machine (manufactured by Sartorius, "BP-210S"), and the mass loss was calculated from the change in mass of each substrate. The average mass loss of all 10 substrates was divided by the polishing time to obtain the polishing rate, which was calculated using the following formula. The polishing rate measurement results of Examples 1 to 6 and Comparative Examples 1 to 5 are shown in Table 1 as relative values with Comparative Example 1 set to 100. The polishing rate measurement results of Examples 7 to 10 and Comparative Example 6 are shown in Table 2 as relative values with Comparative Example 6 set to 100. The polishing rate measurement results of Examples 11 to 14 and Comparative Example 7 are shown in Table 3 as relative values with Comparative Example 7 set to 100.
Mass reduction amount (g) = {mass before polishing (g) - mass after polishing (g)}
Polishing rate (mg/min)=mass reduction (mg)/polishing time (min)

[Scratch Evaluation]
Measuring equipment: KLA Tencor "Candela OSA7100"
Evaluation: Four of the substrates were randomly selected from the substrates put into 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 (lines) on both sides of each of the four substrates was divided by 8 to calculate the number of scratches per substrate surface. The measurement results of the number of scratches in Examples 1 to 6 and Comparative Examples 1 to 5 are shown in Table 1 as relative values with Comparative Example 1 set to 100. The measurement results of the number of scratches in Examples 7 to 10 and Comparative Example 6 are shown in Table 2 as relative values with Comparative Example 6 set to 100. The measurement results of the number of scratches in Examples 11 to 14 and Comparative Example 7 are shown in Table 3 as relative values with Comparative Example 7 set to 100.

As shown in Table 1 above, the polishing compositions of Examples 1 to 6 improved the polishing rate and effectively reduced scratches compared to the polishing compositions of Comparative Examples 1 to 5.

As shown in Tables 2 and 3 above, the polishing compositions of Examples 7 to 14 showed the same tendency as Examples 1 to 6, and the polishing rate was improved and scratches were reduced compared to the polishing compositions of Comparative Examples 6 and 7.

This disclosure makes it possible to provide, for example, a magnetic disk substrate suitable for high recording density.

Claims (9)

Contains inorganic particles (component A), a water-soluble polymer (component B), an acid (component C) and water,
the component B is a copolymer containing a structural unit a having a hydroxyl group (excluding a hydroxyl group as a substituent of an aromatic ring) and a structural unit b (excluding the structural unit a) derived from a monomer containing at least one functional group selected from an amino group, a quaternary ammonium group, and a salt thereof ,
The polishing composition for magnetic disk substrates, wherein the structural unit a is a structural unit derived from hydroxyethylacrylamide or epichlorohydrin . The polishing composition according to claim 1, wherein the content of structural unit a in all structural units of component B is 5 to 95 mol %, and the content of structural unit b is 5 to 95 mol %. The polishing composition according to claim 1 or 2, wherein component B further contains a structural unit c derived from a monomer containing a sulfonic acid group. The polishing composition according to any one of claims 1 to 3, wherein the total content of structural units a and structural units b in all structural units of component B is 60 mol % or more. 5. The polishing composition according to claim 1, wherein Component B is a compound represented by the following formula (I) or (II):

In formula (I), X ₁ ^- and X ₂ ^- represent a monovalent anion, p, q and r each satisfy 60≦p+q+r≦100, and in formula (II), X ₃ ^- represents a monovalent anion, m and n each satisfy 60≦m+n≦100. The polishing composition according to claim 1 , wherein the content of Component B is 0.01 mass % or less. The polishing composition according to claim 1 , further comprising an oxidizing agent (component D). A method for producing a magnetic disk substrate, comprising a polishing step of polishing a substrate to be polished with the polishing composition according to claim 1 . 8. A method for polishing a substrate, comprising polishing a substrate to be polished with the polishing composition according to claim 1 , wherein the substrate to be polished is a substrate used in the manufacture of magnetic disk substrates.