JP7611048B2 - Polishing composition, substrate manufacturing method and polishing method - Google Patents

Description

The present invention relates to a polishing composition used for polishing magnetic disk substrates, a method for manufacturing the substrates, and a polishing method.

Conventionally, the manufacturing process for magnetic disk substrates, which require a highly accurate surface, includes a step of polishing the substrate, which is the raw material of the substrate, with a polishing liquid. For example, in the manufacture of nickel-phosphorus plated disk substrates (hereinafter also referred to as Ni-P substrates), polishing that places emphasis on polishing efficiency (primary polishing) and final polishing (finish polishing) that is performed to achieve the surface accuracy of the final product are generally performed. Patent Document 1 is an example of a technical document related to a polishing composition used for polishing magnetic disk substrates.

JP 2018-081733 A

In polishing magnetic disk substrates, efforts to improve the quality of the substrate surface are being continuously made to increase the recording capacity. In recent years, in order to improve the quality of the substrate surface after finish polishing, silica abrasive grains have been used instead of alumina abrasive grains from the primary polishing stage. Compared to polishing with alumina abrasive grains, polishing with silica abrasive grains does not pierce the substrate with abrasive grains, is excellent in reducing defects such as scratches, and is easy to obtain high surface quality. On the other hand, polishing with silica abrasive grains is difficult to obtain the processing power of a slurry containing alumina abrasive grains, and improving the processing power is an issue. In addition, in polishing with silica abrasive grains, the flatness of the substrate surface after polishing is also an issue. For example, Patent Document 1 proposes improving the polishing speed and reducing long-wavelength waviness by using a polishing composition containing non-spherical silica particles.

By the way, a polishing composition for polishing a magnetic disk substrate is often prepared by mixing an abrasive dispersion containing silica abrasive grains in water at a higher concentration than the polishing liquid (working slurry) supplied to the object to be polished and used to polish the object to be polished, with a solution containing other components such as an acid. The present inventors have investigated a magnetic disk substrate polishing composition that uses silica abrasive grains to improve the polishing rate and suppress microwaviness on the substrate surface after polishing, and have found that even a polishing composition that initially exhibits a polishing performance that balances a high polishing rate and low microwaviness exhibits a phenomenon in which the polishing performance such as microwaviness significantly decreases when the abrasive dispersion before use is stored for a long period of time (hereinafter referred to as "change in polishing performance over time"). If a technology is provided that provides good initial polishing performance and suppresses change in the polishing performance over time in a magnetic disk substrate polishing composition containing silica abrasive grains, it would be beneficial from the viewpoints of reducing the management costs of the abrasive dispersion and improving the quality stability of the polishing composition.

The present invention was created in view of the above circumstances, and aims to provide a polishing composition for magnetic disk substrates that contains silica abrasive grains and has good initial polishing performance and suppresses changes in the polishing performance over time. Another related object is to provide a method for manufacturing and polishing a substrate using the above polishing composition.

According to this specification, a polishing composition for use in polishing magnetic disk substrates is provided. This polishing composition contains silica particles as abrasive grains and water. The silica particles have an average aspect ratio of 1.1 or more based on SEM image analysis, and in a weight-based particle size distribution based on a light transmission centrifugal sedimentation method, the ratio of the cumulative 99% particle diameter D ₉₉ to the cumulative 90% particle diameter D ₉₀ (D ₉₉ /D ₉₀ ) is 1.4 or more, and the cumulative 90% particle diameter D ₉₀ is 250 nm or less. The polishing composition of this configuration can achieve good initial polishing performance and suppression of the change in the polishing performance over time.

In some embodiments, the silica particles have a cumulative 50% particle size _D50 of 170 nm or less in a particle size distribution based on weight based on a light transmission centrifugal sedimentation method. According to the technology disclosed herein, in polishing using silica abrasive grains having a _D50 of 170 nm or less, it is possible to realize an initial performance that achieves a good balance between a high polishing rate and low microwaviness, and to suitably suppress changes in the initial performance over time.

In some preferred embodiments, the silica particles satisfy at least one of the following: the cumulative 90% particle diameter _D90 is 210 nm or less, and the average aspect ratio is 1.25 or less. By including such silica particles as abrasive grains, the change in polishing performance over time can be better suppressed.

In some preferred embodiments, the polishing composition further contains an acid and an oxidizing agent. By using a polishing composition containing a combination of the silica particles, an acid, and an oxidizing agent, it becomes easier to achieve a practical polishing rate when polishing magnetic disk substrates.

The present specification also provides a method for producing a magnetic disk substrate. The method includes step (1) of polishing a substrate to be polished using any of the polishing compositions disclosed herein. This method allows for the efficient production of a magnetic disk substrate having a high-quality surface. In some embodiments, the method for producing the substrate further includes step (2) of polishing the substrate to be polished using a finish polishing composition after step (1). The finish polishing composition preferably contains colloidal silica. By carrying out step (2) after step (1), a magnetic disk substrate having a higher quality surface can be efficiently produced.

The present specification also provides a method for polishing a substrate. The polishing method includes step (1) of supplying any one of the polishing compositions disclosed herein to a substrate to be polished and polishing the substrate. Such a polishing method can efficiently improve the surface quality of the polished object. In some embodiments, the method for polishing a substrate further includes step (2) of supplying a finish polishing composition to the substrate to be polished after step (1) and polishing the substrate to be polished. The finish polishing composition preferably contains colloidal silica. By carrying out step (2) after step (1), a substrate surface of higher quality can be obtained.

The following describes preferred embodiments of the present invention. Note that matters other than those specifically mentioned in this specification that are necessary for implementing the present invention can be understood as design matters of a person skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and common technical knowledge in the relevant field.

<Polishing Composition>
(Silica particles)
The polishing composition disclosed herein contains silica particles as abrasive grains. The silica particles have an average aspect ratio of 1.1 or more based on SEM image analysis, and in the weight-based particle size distribution based on a light transmission centrifugal sedimentation method, the ratio of the cumulative 99% particle diameter D ₉₉ to the cumulative 90% particle diameter D ₉₀ (D ₉₉ /D ₉₀ ) is 1.4 or more, and the cumulative 90% particle diameter D ₉₀ is 250 nm or less. In the polishing composition having such a configuration, it is possible to suitably realize good initial polishing performance and suppression of the change in the polishing performance over time. In the following description, the cumulative 90% particle diameter D ₉₀ , the cumulative 99% particle diameter D ₉₉ , and the ratio of the cumulative 99% particle diameter D ₉₉ to the cumulative 90% particle diameter D ₉₀ (D ₉₉ /D ₉₀ ) may be simply referred to as D ₉₀ , D ₉₉ , and the ratio (D ₉₉ /D ₉₀ ), respectively.

The reason why the above-described configuration achieves the effects of the technique disclosed herein is thought to be as follows, although this is not to be construed as being particularly limiting.
When silica particles are used as abrasives in polishing magnetic disk substrates, if the polishing rate is improved by simply increasing the particle size, it tends to be difficult to maintain low microwaviness as the polishing rate increases. The use of silica particles with a larger average aspect ratio can be an effective means for improving the polishing rate while suppressing microwaviness. However, while silica particles with a larger average aspect ratio are suitable for improving the polishing rate of magnetic disk substrates, they tend to aggregate more easily than silica particles with a smaller average aspect ratio. Among the abrasive dispersions in which such silica particles are dispersed in water, some of the silica particles aggregate and settle as the storage period passes. As the size of the silica particles increases, the aggregated particles are more likely to settle. It is considered that such aggregation and sedimentation are one of the factors that increase the change in polishing performance over time.
Therefore, the inventors of the present invention have conducted extensive research and found that by restricting the particle diameter of silica particles, particularly the particle diameter at 90% cumulative frequency (D ₉₀ ), to a predetermined value or less, it is possible to suppress the above-mentioned particle aggregation and sedimentation, or to favorably redisperse the sedimented particles, and thus to favorably suppress the change in polishing performance over time. Furthermore, it has been found that in silica particles having an average aspect ratio of a predetermined value or more, if D ₉₀ is restricted to a predetermined value or less, the increase in microwaviness can be suppressed even if D ₉₉ is large, and a large D ₉₉ advantageously contributes to improving processability. Specifically, it has been found that when the average aspect ratio of silica particles is 1.1 or more and the ratio of D ₉₉ to D ₉₀ (D ₉₉ /D ₉₀ ) is 1.4 or more, a high polishing rate and low microwaviness can be achieved at a high level in a well-balanced manner.
It should be noted that the above explanation is the inventor's consideration based on experimental results, and the technology disclosed herein should not be interpreted as being limited to the above mechanism.

From the viewpoint of maintaining or improving processability, the average aspect ratio of silica particles is more preferably 1.15 or more, more preferably 1.20 or more (for example, 1.25 or more).In addition, from the viewpoint of efficiently improving surface quality, in some embodiments, the average aspect ratio is suitably 2.50 or less, preferably 2.0 or less, more preferably 1.70 or less, more preferably 1.50 or less, and may be 1.35 or less.In silica particles having an average aspect ratio in such a range, the effect of setting _D90 and ratio ( _D99 / _D90 ) to a predetermined range is preferably exhibited.

From the viewpoint of more suitably suppressing the change over time of polishing performance, the D ₉₀ of the silica particles is preferably 240 nm or less (e.g., 235 nm or less), more preferably 220 nm or less, even more preferably 210 nm or less, and particularly preferably 200 nm or less. From the viewpoint of suppressing the sedimentation of the silica particles during storage of the abrasive dispersion, the D ₉₀ of the silica particles is suitably 195 nm or less (e.g., 190 nm or 185 nm or less), and may be 180 nm or less, or may be 175 nm or less. Moreover, from the viewpoint of processability, the D ₉₀ is preferably 50 nm or more, more preferably 100 nm or more, and may be 150 nm or more. According to the technology disclosed herein, in the embodiment using silica particles having the D ₉₀ limited as described above, the change over time of polishing performance can be more suitably suppressed.

In some embodiments, from the viewpoint of further enhancing the processing power, the _D90 of the silica particles may be 185 nm or more, 200 nm or more, 210 nm or more, 220 nm or more, or 230 nm or more, so long as it is within the range of 250 nm or less. According to the technology disclosed herein, even in embodiments in which silica particles having a relatively large _D90 are used, the change in polishing performance over time can be effectively suppressed.

In some embodiments, silica particles having the average aspect ratio of 1.30 or less, 1.27 or less, or 1.25 or less (e.g., 1.20 or less) can be preferably used. As described above, silica particles having such an average aspect ratio have a relatively large _D90 within the range of 250 nm or less, so even if they settle, they are easy to redisperse well. This makes it possible to achieve both good initial polishing performance and suppression of the deterioration of the polishing performance.

From the viewpoint of maintaining or improving processability, the ratio ( _D99 / _D90 ) of silica particles is more preferably 1.5 or more, even more preferably 2.0 or more, and may be 2.4 or more (for example, 2.5 or more). In some embodiments, the ratio ( _D99 / _D90 ) is suitably 5.0 or less, preferably 4.5 or less, may be 4.0 or less, may be 3.5 or less, or may be 3.0 or less. In the embodiment using silica particles having the ratio ( _D99 / _D90 ) limited as above, the change over time of polishing performance can be more suitably suppressed.

Regarding the silica particles, the cumulative 50% particle diameter D ₅₀ (hereinafter also simply referred to as D ₅₀ ) in the weight-based particle size distribution based on the light transmission type centrifugal sedimentation method is not particularly limited as long as the above-mentioned D ₉₀ and ratio (D ₉₉ /D ₉₀ ) are realized. In some embodiments, D ₅₀ is suitably 200 nm or less, preferably 170 nm or less, may be 150 nm or less, or may be 130 nm or less. According to silica particles having such D ₅₀ , it is easy to obtain a suitable D ₉₀ and ratio (D ₉₉ /D ₉₀ ) suitable for solving the problems in the technology disclosed in this specification. The lower limit of D ₅₀ is not particularly limited, but from the viewpoint of improving the polishing rate, it is suitable to be 20 nm or more, advantageously 30 nm or more, preferably 40 nm or more, and more preferably 50 nm or more (for example, 55 nm or more).

The average aspect ratio of silica particles (silica abrasive grains) as abrasive grains is measured, for example, by the following method. Specifically, a scanning electron microscope (SEM) is used to observe a predetermined number of particles contained in the abrasive grains to be measured (which may be one type of abrasive grains or a mixture of two or more types of abrasive grains) in an SEM image containing 50 or more particles in one field of view. The observation magnification is 10,000 to 50,000 times. For the abrasive grains in the observation image, the smallest rectangle circumscribing each particle image is drawn. Then, for the rectangle drawn for each particle image, the value obtained by dividing the length of the long side (long axis value) by the length of the short side (short axis value) is calculated as the long axis/short axis ratio (aspect ratio). The average aspect ratio can be obtained by arithmetically averaging the aspect ratios of the predetermined number of particles. The average aspect ratio can be obtained using general image analysis software.
In addition, the above-mentioned predetermined number, i.e., the number of particles for which the aspect ratio of each particle is calculated, is usually appropriate to be 1000 or more, and preferably 1500 or more, from the viewpoint of improving measurement accuracy and reproducibility. The upper limit of the above-mentioned predetermined number is not particularly limited. From the viewpoint of measurement efficiency, the above-mentioned predetermined number may be, for example, 5000 or less, or may be 2500 or less. For the above measurement, for example, a scanning electron microscope "SU8000" manufactured by Hitachi High-Technologies Corporation or image analysis type particle size distribution measurement software "Mac-View" manufactured by Mountec Co., Ltd. is used. The same applies to the examples described later.

The _D90 and _D99 of the silica particles can be calculated from the particle size distribution based on weight obtained by the particle size measurement based on the light transmission centrifugal sedimentation method. The details of the light transmission centrifugal sedimentation method will be described in the examples below.

Silica particles having the above average aspect ratio, D ₉₀ , and ratio (D ₉₉ /D ₉₀ ) can be adjusted by selecting the type of silica particles used, selecting or adjusting the silica manufacturing method, mixing two or more types of silica particles having different particle shapes, etc. For example, based on the description of this specification and taking into consideration common technical knowledge, one type of particle group having a specific particle size and aspect ratio is selected, or two or more types of particle groups are selected and mixed in an appropriate ratio, thereby obtaining the silica particles disclosed herein. Also, based on the description of this specification and taking into consideration common technical knowledge, it is possible to adopt, for example, a method of crushing porous silica gel under appropriate conditions to obtain irregularly shaped particles, or a method of growing the obtained irregularly shaped particles by adding a predetermined amount of silicate under appropriate conditions (pH, temperature conditions, etc.) to obtain irregularly shaped particles having a desired particle size. By mixing one type of particle obtained in this way alone or with other silica particles having different particle properties, the silica particles disclosed herein can be obtained.

The silica particles are not particularly limited as long as they satisfy the predetermined average aspect ratio, D ₉₀ , and ratio (D ₉₉ /D ₉₀ ), and various silica particles mainly composed of silica can be used. Here, the silica particles mainly composed of silica refer to particles in which 90% by weight or more, for example 95% by weight or more, typically 98% by weight or more of the particles are silica. Examples of silica particles that can be used are not particularly limited, and include colloidal silica, agglomerated silica, precipitated silica (also called precipitated silica), sodium silicate silica, alkoxide silica, fumed silica, dried silica, and detonation silica. Furthermore, silica particles obtained from the above silica particles as raw materials can also be used. Examples of such silica particles include silica particles obtained by applying one or more treatments selected from heat treatments such as heating, drying, and firing, pressure treatments such as autoclaving, mechanical treatments such as crushing and pulverization, and surface modification to the above raw silica particles (hereinafter also called "raw silica"). Examples of surface modification include chemical modification such as introduction of a functional group, metal modification, etc. The silica particles in the technology disclosed herein may contain one type of silica particles as described above alone or two or more types in combination.

In the technology disclosed herein, the silica particles may be in the form of secondary particles formed by agglomeration of multiple primary particles, or in the form of secondary particles formed by association of multiple primary particles. Furthermore, silica particles in the form of primary particles and silica particles in the form of secondary particles may be mixed.

The content of silica particles in the polishing composition is not particularly limited, and is, for example, 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1% by weight or more, even more preferably 3% by weight or more, and particularly preferably 5% by weight or more. When multiple types of silica particles are contained, the above content is the total content of them. By increasing the content of silica particles, higher processability tends to be obtained. From the viewpoint of the surface smoothness of the substrate after polishing and the stability of polishing, the above content is appropriately 30% by weight or less, preferably 25% by weight or less, more preferably 15% by weight or less, and even more preferably 10% by weight or less.

In the polishing composition disclosed herein, the content of silica particles in the solid content contained in the polishing composition is preferably 90% by weight or more of the total solid content, more preferably 95% by weight or more, and even more preferably 98% by weight or more, for example 99% by weight or more, from the viewpoint of better exerting the effects of the technology disclosed herein. In this specification, the solid content contained in the polishing composition refers to the residual content, i.e., non-volatile content, after evaporating water from the polishing composition at a temperature at which bound water is not removed, for example 60°C.

The polishing composition disclosed herein can be preferably implemented in an embodiment that is substantially free of alumina particles. Examples of alumina particles include α-alumina particles. Such a polishing composition prevents quality degradation caused by the use of alumina particles. Examples of quality degradation include the occurrence of scratches and dents, residual alumina, and puncture defects. In this specification, "substantially free of alumina particles" means that the proportion of alumina particles in the total amount of solids contained in the polishing composition is 1% by weight or less, more preferably 0.5% by weight or less, and typically 0.1% by weight or less. A polishing composition with a proportion of alumina particles of 0% by weight, i.e., a polishing composition that does not contain alumina particles, is particularly preferred. The polishing composition disclosed herein can also be preferably implemented in an embodiment that is substantially free of α-alumina particles.

The polishing composition disclosed herein may also be preferably implemented in an embodiment that is substantially free of particles other than silica particles, i.e., non-silica particles. Here, "substantially free of non-silica particles" means that the proportion of non-silica particles in the total solid content contained in the polishing composition is 1% by weight or less, more preferably 0.5% by weight or less, typically 0.1% by weight or less. In such an embodiment, the application effect of the technology disclosed herein can be suitably exhibited.

(acid)
The polishing composition disclosed herein may contain an acid as a polishing accelerator. The acid may be either an inorganic acid or an organic acid. The organic acid may be, for example, an organic carboxylic acid, an organic sulfonic acid, or an amino acid having about 1 to 18 carbon atoms, typically about 1 to 10 carbon atoms. The acid may be used alone or in combination of two or more kinds.

Specific examples of inorganic acids include phosphoric acid (orthophosphoric acid), nitric acid, sulfuric acid, hydrochloric acid, boric acid, sulfamic acid, phosphinic acid, phosphonic acid, pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, hexametaphosphoric acid, carbonic acid, hydrofluoric acid, sulfurous acid, thiosulfuric acid, chloric acid, perchloric acid, chlorous acid, hydroiodic acid, periodic acid, iodic acid, hydrobromic acid, perbromic acid, bromic acid, chromic acid, and nitrous acid.

Specific examples of organic acids include citric acid, maleic acid, malic acid, glycolic acid, succinic acid, itaconic acid, malonic acid, iminodiacetic acid, gluconic acid, lactic acid, mandelic acid, tartaric acid, formic acid, acetic acid, propionic acid, butyric acid, adipic acid, oxalic acid, valeric acid, enanthic acid, caproic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, cyclohexanecarboxylic acid, phenylacetic acid, benzoic acid, crotonic acid, oleic acid, linoleic acid, linolenic acid, ricinoleic acid, and methacrylic acid. , glutaric acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, tartronic acid, glyceric acid, hydroxybutyric acid, hydroxyacetic acid, hydroxybenzoic acid, salicylic acid, isocitric acid, methylenesuccinic acid, gallic acid, ascorbic acid, nitroacetic acid, oxaloacetic acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid, and other organic carboxylic acids; glycine, alanine, glutamic acid, aspartic acid, valine, leucine, isoleucine, serine, threonine, cysteine, methionine, phenylalanine, tryptophan, tyrosine, proline, Amino acids such as lysine, cystine, glutamine, asparagine, lysine, and arginine; nicotinic acid; picric acid; picolinic acid; phytic acid; 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethanehydroxy-1,1,2-triphosphonic acid, ethane-1 , organic phosphonic acids such as 2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, α-methylphosphonosuccinic acid, and aminopoly(methylenephosphonic acid); organic sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, aminoethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, 2-naphthalenesulfonic acid, sulfosuccinic acid, 10-camphorsulfonic acid, isethionic acid, and taurine.

Examples of acids that are preferred from the viewpoint of polishing efficiency include phosphoric acid, phosphonic acid, maleic acid, hydrochloric acid, nitric acid, sulfuric acid, sulfamic acid, phytic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, methanesulfonic acid, etc. Among these, phosphoric acid, phosphonic acid, maleic acid, hydrochloric acid, nitric acid, and sulfuric acid are preferred.

The acid may be used in the form of a salt of the acid. Examples of the salt include metal salts, ammonium salts, alkanolamine salts, etc. of the above-mentioned inorganic acids and organic acids. Examples of the metal salts include alkali metal salts such as lithium salts, sodium salts, and potassium salts. Examples of the ammonium salts include quaternary ammonium salts such as tetramethylammonium salts and tetraethylammonium salts. Examples of the alkanolamine salts include monoethanolamine salts, diethanolamine salts, and triethanolamine salts.
Specific examples of salts include alkali metal phosphates and alkali metal hydrogen phosphates such as tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, etc.; alkali metal salts of the organic acids exemplified above; and, in addition, alkali metal salts of glutamic acid diacetate, alkali metal salts of diethylenetriaminepentaacetic acid, alkali metal salts of hydroxyethylethylenediaminetriacetic acid, alkali metal salts of triethylenetetraminehexaacetic acid; etc. The alkali metal in these alkali metal salts may be, for example, lithium, sodium, potassium, etc.

As salts that may be contained in the polishing composition disclosed herein, salts of inorganic acids, such as alkali metal salts and ammonium salts, may be preferably used. For example, potassium chloride, sodium chloride, ammonium chloride, potassium nitrate, sodium nitrate, ammonium nitrate, potassium phosphate, etc. may be preferably used.

The acids and their salts may be used alone or in combination of two or more (e.g., two or three). In some preferred embodiments, an acid may be used in combination with a salt of an acid different from the acid. The acid is preferably an inorganic acid. The salt of the acid is preferably an inorganic acid.

The molar concentration of the acid in the polishing composition (when multiple types of acids are included, the total molar concentration of the acids) is not particularly limited, and is preferably 0.001 mol/L or more, more preferably 0.01 mol/L or more, more preferably 0.05 mol/L or more, even more preferably 0.07 mol/L or more, and particularly preferably 0.09 mol/L or more. By increasing the molar concentration of the acid, higher processability can be achieved. From the viewpoint of the surface quality after polishing and the stability of polishing, the molar concentration of the acid is preferably 1.2 mol/L or less, more preferably 1 mol/L or less, more preferably 0.8 mol/L or less, even more preferably 0.5 mol/L or less, and particularly preferably 0.3 mol/L or less (for example, 0.2 mol/L or less).

(Oxidizing Agent)
The polishing composition disclosed herein may contain an oxidizing agent. Examples of oxidizing agents include, but are not limited to, peroxide, nitric acid or its salt, periodic acid or its salt, peroxo acid or its salt, permanganic acid or its salt, chromic acid or its salt, oxygen acid or its salt, metal salts, sulfuric acid, etc. The oxidizing agent may be used alone or in combination of two or more. Specific examples of the oxidizing agent include hydrogen peroxide, sodium peroxide, barium peroxide, nitric acid, iron nitrate, aluminum nitrate, ammonium nitrate, peroxomonosulfuric acid, ammonium peroxomonosulfate, metal peroxomonosulfate, peroxodisulfate, ammonium peroxodisulfate, metal peroxodisulfate, peroxolinic acid, peroxosulfuric acid, sodium peroxoborate, performic acid, peracetic acid, perbenzoic acid, perphthalic acid, hypobromous acid, hypoiodous acid, chloric acid, bromic acid, iodic acid, periodic acid, perchloric acid, hypochlorous acid, sodium hypochlorite, calcium hypochlorite, potassium permanganate, metal chromate, metal dichromate, iron chloride, iron sulfate, iron citrate, ammonium iron sulfate, etc. Preferred examples of the oxidizing agent include hydrogen peroxide, iron nitrate, periodic acid, peroxomonosulfuric acid, peroxodisulfuric acid, and nitric acid. It preferably contains at least hydrogen peroxide, and more preferably consists of hydrogen peroxide.

The content of the oxidizing agent in the polishing composition is preferably 0.05 mol/L or more, more preferably 0.1 mol/L or more, even more preferably 0.15 mol/L or more, and particularly preferably 0.3 mol/L or more, in consideration of the rate at which the polishing object is oxidized and therefore the processability. In addition, the content of the oxidizing agent in the polishing composition is preferably 1 mol/L or less, more preferably 0.8 mol/L or less, and even more preferably 0.6 mol/L or less, in consideration of maintaining surface precision.

(water)
The polishing composition disclosed herein typically contains water to disperse the abrasive grains in addition to the above-mentioned abrasive grains. As the water, ion-exchanged water, pure water, ultrapure water, distilled water, etc. can be preferably used. The ion-exchanged water can typically be deionized water.

The polishing composition disclosed herein can be preferably implemented, for example, in a form in which the solid content is 0.5% by weight to 30.0% by weight. More preferably, the solid content is 1.0% by weight to 20.0% by weight. The polishing composition can typically be a slurry-like composition.

(Other ingredients)
The polishing composition disclosed herein may further contain, as necessary, known additives that can be used in polishing compositions, such as surfactants, water-soluble polymers, dispersants, chelating agents, preservatives, antifungal agents, basic compounds, etc., to the extent that the effects of the present invention are not significantly impeded.

The surfactant is not particularly limited, and any of anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants can be used. The use of surfactants can improve the dispersion stability of the polishing composition. The surfactants can be used alone or in combination of two or more. The surfactants can typically be water-soluble organic compounds with a molecular weight of less than 1×10 ⁶ .
Specific examples of anionic surfactants include polyoxyethylene alkyl ether acetates, polyoxyethylene alkyl sulfates, alkyl sulfates, polyoxyethylene alkyl sulfates, alkyl sulfates, alkyl benzene sulfonates, alkyl phosphates, polyoxyethylene alkyl phosphates, polyoxyethylene sulfosuccinates, alkyl sulfosuccinates, alkyl naphthalene sulfonates, alkyl diphenyl ether disulfonic acids, polyacrylic acids, sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzene sulfonate, polyoxyethylene alkyl ether sodium sulfate, polyoxyethylene alkyl phenyl ether ammonium sulfate, polyoxyethylene alkyl phenyl ether sodium sulfate, and salts thereof.
Other specific examples of the anionic surfactant include polyalkylarylsulfonic acid compounds such as naphthalenesulfonic acid formaldehyde condensates, methylnaphthalenesulfonic acid formaldehyde condensates, anthracenesulfonic acid formaldehyde condensates, and benzenesulfonic acid formaldehyde condensates; melamine formalin resin sulfonic acid compounds such as melaminesulfonic acid formaldehyde condensates; ligninsulfonic acid compounds such as ligninsulfonic acid and modified ligninsulfonic acid; aromatic aminosulfonic acid compounds such as aminoarylsulfonic acid-phenol-formaldehyde condensates; polyisoprene sulfonic acid, polyvinylsulfonic acid, polyallylsulfonic acid, polyisoamylenesulfonic acid, polystyrenesulfonic acid; and salts thereof. As the salt, alkali metal salts such as sodium salts and potassium salts are preferred.
Specific examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene alkyl amines, and alkyl alkanolamides.
Specific examples of the cationic surfactant include alkyltrimethylammonium salts, alkyldimethylammonium salts, alkylbenzyldimethylammonium salts, and alkylamine salts.
Specific examples of amphoteric surfactants include alkyl betaine type, fatty acid amidopropyl betaine type, alkyl imidazole type, amino acid type, and alkyl amine oxide type.

In the polishing composition containing a surfactant, the surfactant content is suitably, for example, 0.0005% by weight or more. From the viewpoint of surface smoothness after polishing, the content is preferably 0.001% by weight or more, more preferably 0.002% by weight or more. From the viewpoint of processability, the content is suitably 3.0% by weight or less, preferably 0.5% by weight or less, for example 0.1% by weight or less.

The polishing composition disclosed herein may contain a water-soluble polymer. By containing a water-soluble polymer, the surface quality after polishing can be improved. Examples of water-soluble polymers include polyalkylarylsulfonic acid compounds such as naphthalenesulfonic acid formaldehyde condensates, methylnaphthalenesulfonic acid formaldehyde condensates, and anthracenesulfonic acid formaldehyde; melamine formalin resin sulfonic acid compounds such as melamine sulfonic acid formaldehyde condensates; ligninsulfonic acid compounds such as ligninsulfonic acid and modified ligninsulfonic acid; aromatic aminosulfonic acid compounds such as aminoarylsulfonic acid-phenol-formaldehyde condensates; and others such as polyisoprene sulfonic acid, polyvinyl sulfonic acid, polyaryl Examples of the water-soluble polymer include sulfonic acid, polyisoamylene sulfonic acid, polystyrene sulfonate, polyacrylate, polyvinyl acetate, polymaleic acid, polyitaconic acid, polyvinyl alcohol, polyglycerin, polyvinylpyrrolidone, copolymer of isoprene sulfonic acid and acrylic acid, polyvinylpyrrolidone-polyacrylic acid copolymer, polyvinylpyrrolidone-vinyl acetate copolymer, diallylamine hydrochloride-sulfur dioxide copolymer, carboxymethylcellulose, salt of carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, pullulan, chitosan, and chitosan salts. The water-soluble polymer can be used alone or in combination of two or more.

In an embodiment of the polishing composition that contains a water-soluble polymer, the content of the water-soluble polymer in the polishing composition is, for example, 0.001% by weight or more. In an embodiment that contains multiple water-soluble polymers, the above content is the total content of them. From the viewpoint of surface smoothness of the polished object after polishing, the above content is preferably 0.003% by weight or more, more preferably 0.005% by weight or more, and even more preferably 0.007% by weight or more. From the viewpoint of processability, the above content is preferably 1.0% by weight or less, and is preferably 0.5% by weight or less, for example 0.1% by weight or less. Note that the technology disclosed herein can also be preferably implemented in an embodiment in which the polishing composition does not substantially contain a water-soluble polymer from the viewpoint of processability.

Examples of dispersants include polycarboxylic acid-based dispersants such as sodium polycarboxylate and ammonium polycarboxylate; naphthalene sulfonic acid-based dispersants such as sodium naphthalene sulfonate and ammonium naphthalene sulfonate; alkylsulfonic acid-based dispersants; polyphosphoric acid-based dispersants; polyalkylene polyamine-based dispersants; quaternary ammonium-based dispersants; alkyl polyamine-based dispersants; alkylene oxide-based dispersants; polyhydric alcohol ester-based dispersants; etc. Dispersants can be used alone or in combination of two or more.

Examples of chelating agents include aminocarboxylic acid chelating agents and organic phosphonic acid chelating agents. Examples of aminocarboxylic acid chelating agents include ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetate, nitrilotriacetic acid, sodium nitrilotriacetate, ammonium nitrilotriacetate, hydroxyethylethylenediaminetriacetic acid, sodium hydroxyethylethylenediaminetriacetate, diethylenetriaminepentaacetic acid, sodium diethylenetriaminepentaacetate, triethylenetetraminehexaacetic acid, and sodium triethylenetetraminehexaacetate. Examples of organic phosphonic acid chelating agents include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetrakis(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, and α-methylphosphonosuccinic acid. Of these, organic phosphonic acid chelating agents are more preferred, and among these, ethylenediaminetetrakis(methylenephosphonic acid) and diethylenetriaminepenta(methylenephosphonic acid) are particularly preferred. A particularly preferred chelating agent is ethylenediaminetetrakis(methylenephosphonic acid). The chelating agents can be used alone or in combination of two or more.

Examples of preservatives and antifungal agents include isothiazoline preservatives such as 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one, paraoxybenzoic acid esters, phenoxyethanol, etc.

The polishing composition may contain a basic compound as necessary. Here, a basic compound refers to a compound that has the function of increasing the pH of the polishing composition when added to the composition. Examples of basic compounds include alkali metal hydroxides, carbonates and hydrogen carbonates, quaternary ammonium or salts thereof, ammonia, amines, phosphates and hydrogen phosphates, organic acid salts, etc. The basic compounds may be used alone or in combination of two or more.

(pH)
The pH of the polishing composition disclosed herein is not particularly limited. The pH of the polishing composition may be, for example, 12.0 or less, typically 0.5 to 12.0, or 10.0 or less, typically 0.5 to 10.0. From the viewpoint of processability, surface quality, and the like, the pH of the polishing composition may be 7.0 or less, for example 0.5 to 7.0, more preferably 5.0 or less, typically 1.0 to 5.0, and even more preferably 4.0 or less, for example 1.0 to 4.0. The pH of the polishing composition may be, for example, 3.0 or less, typically 1.0 to 3.0, preferably 1.0 to 2.0, and more preferably 1.0 to 1.8. In order to realize the above pH in the polishing liquid, a pH adjuster such as an organic acid, an inorganic acid, or a basic compound may be contained as necessary. The above pH may be preferably applied to a polishing composition for a magnetic disk substrate such as a nickel phosphorus substrate. In particular, it may be preferably applied to a polishing composition for primary polishing.

(Polishing fluid)
The polishing composition disclosed herein is typically supplied to an object to be polished in the form of a polishing liquid containing the polishing composition, and used to polish the object to be polished. The polishing liquid may be prepared, for example, by diluting the polishing composition. Here, dilution typically refers to dilution with water. Alternatively, the polishing composition may be used as a polishing liquid as it is. That is, the concept of the polishing composition in the technology disclosed herein includes both a polishing liquid (working slurry) that is supplied to an object to be polished and used to polish the object to be polished, and a concentrated liquid that is diluted and used as a polishing liquid. Such a polishing composition in the form of a concentrated liquid is advantageous from the viewpoints of convenience and cost reduction during production, distribution, storage, etc. The concentration ratio can be, for example, about 1.5 to 50 times. From the viewpoint of storage stability of the concentrated liquid, a concentration ratio of, for example, 2 to 20 times, typically about 2 to 10 times, is appropriate.

<Polishing composition preparation set>
The polishing composition disclosed herein may be a one-component type or a multi-component type, including a two-component type. For example, a first composition containing silica particles (silica abrasive grains) as abrasive grains and a second composition containing at least a part of the remaining components contained in the polishing composition may be mixed and used to polish an object to be polished. In some preferred embodiments, the first composition and the second composition before being mixed are stored separately from each other as components of a polishing composition preparation set containing them. As the first composition, an abrasive dispersion containing silica particles disclosed herein and water to disperse the silica particles can be preferably used. The abrasive dispersion used as the first composition may be adjusted to an appropriate pH using a pH adjuster as necessary. The abrasive dispersion may or may not further contain a dispersant. An example of a component contained in the second composition is an acid. In addition, the second composition may contain a water-soluble polymer and other additives. Therefore, this specification provides a polishing composition preparation set comprising a first composition comprising an abrasive dispersion containing silica particles disclosed herein and water dispersing the silica particles, and a second composition containing at least an acid. When mixing, an oxidizing agent such as hydrogen peroxide can be further mixed. For example, when the oxidizing agent is supplied in the form of an aqueous solution, the aqueous solution can be the third composition constituting the multi-agent type polishing composition. The polishing composition preparation set disclosed herein may include the third composition as a component stored separately from the first and second compositions. In addition, when mixing, water for dilution, a pH adjuster, etc. can be further mixed.

(First composition)
The content of silica particles in the first composition (i.e., abrasive dispersion liquid) is not particularly limited, and may be, for example, about 5% by weight to 50% by weight. In some embodiments, the content of the silica particles is suitably about 10% by weight or more, may be 20% by weight or more, may be 30% by weight or more, or may be 40% by weight or more (for example, about 45% by weight) from the viewpoint of saving storage space of the first composition and convenience during production, distribution, etc. In addition, the upper limit of the content of the silica particles is not particularly limited, but is suitably about 60% by weight or less, may be 55% by weight or less, or may be 50% by weight or less from the viewpoint of ease of preparation of the polishing composition.

The pH of the first composition is not particularly limited, and may be, for example, about 1.5 to 12.0. In some embodiments, from the viewpoint of dispersion stability of the silica particles, the pH of the first composition is suitably 7.0 or more, preferably 7.5 or more, and may be 8.0 or more, or may be 8.5 or more. In addition, from the viewpoint of preventing dissolution of the silica particles, the pH of the first composition is suitably 12.0 or less, preferably 11.0 or less, and may be 10.5 or less, or may be 10.0 or less. A pH adjuster such as a basic compound may be contained as necessary so that the above pH is realized in the first composition.

(Second Composition)
The second composition contains at least an acid, and typically further contains water. As the acid, for example, those described above can be used without any particular limitation. In addition, the molar concentration of the acid in the second composition (when a plurality of types of acids are contained, the total molar concentration thereof) is not particularly limited, and is suitably set to, for example, 0.1 mol/L or more, preferably 0.5 mol/L or more, and more preferably 1.0 mol/L or more. In addition, the molar concentration of the acid is suitably set to 8.0 mol/L or less, preferably 6.0 mol/L or less, and more preferably 4.0 mol/L or less. In addition, the second composition can contain any component other than the acid as necessary. As such an optional component, for example, the oxidizing agent and other components as described above can be used.

<Method of producing polishing composition>
The polishing composition as the polishing liquid or its concentrate can be produced by, for example, a method including mixing a first composition (i.e., an abrasive dispersion) containing silica particles and water dispersing the silica particles disclosed herein with other components contained in the polishing composition. For example, in the case of a polishing composition containing an acid, the polishing composition can be prepared by mixing the first composition with a second composition containing at least an acid. Thus, this specification provides a method for producing a polishing composition, which includes preparing a first composition consisting of an abrasive dispersion containing silica particles and water dispersing the silica particles disclosed herein, and a second composition containing at least an acid; and mixing the first composition with the second composition. The first composition and the second composition are preferably stored separately from each other before use. The first composition and the second composition can be mixed with any mixing means applied to mixing this type of composition without any particular restrictions.

If sedimentation of silica particles is observed during use of the first composition (during preparation of the polishing composition), it is preferable to use the first composition after redispersing it by applying a known redispersion means. Examples of such redispersion means include, but are not limited to, shaking, stirring, and application of ultrasonic vibration. The above redispersion means can be used alone or in appropriate combination of two or more. When two or more redispersion means are used in combination, they may be used simultaneously or in stages. In addition, the timing of applying the means for redispersing silica particles is not limited to when the first composition is used, and may be applied at any time during storage of the first composition, or the above redispersion means may be applied while mixing the first composition with other components, or may be applied at any time after mixing and before supplying the composition to the object to be polished.

<Applications>
The polishing composition disclosed herein can be preferably applied to polishing magnetic disk substrates such as nickel phosphorus substrates, glass substrates, and carbon substrates. In addition, the plating material may be a disk substrate having a metal layer or a metal compound layer other than a nickel phosphorus plating layer on the surface of a substrate disk. In particular, it is suitable as a polishing composition for a nickel phosphorus plated substrate having a nickel phosphorus plating layer on an aluminum alloy substrate disk. In such applications, it is particularly meaningful to apply the technology disclosed herein.

The polishing composition disclosed herein can be used particularly effectively in applications requiring high polishing efficiency, such as the preliminary polishing step in the manufacturing process of magnetic disk substrates, which requires a highly accurate surface after the final polishing step. When there are multiple preliminary polishing steps prior to the final polishing step, the polishing composition can be used in any of the preliminary polishing steps, and the same or different polishing compositions can be used in these preliminary polishing steps. The polishing composition disclosed herein is suitable, for example, as a polishing composition used in the primary polishing step, i.e., the first polishing step, of magnetic disk substrates. In particular, the polishing composition can be preferably used in the first polishing step, i.e., the first polishing step, after nickel phosphorus plating in the manufacturing process of nickel phosphorus substrates.

The polishing composition disclosed herein is suitable for use in polishing a magnetic disk substrate having a surface roughness of about 20 Å to 300 Å as measured by a laser scanning surface roughness meter "TMS-3000WRC" manufactured by Schmitt Measurement System Inc., and adjusting the surface roughness of the magnetic disk substrate to 10 Å or less. In such applications, it is particularly meaningful to apply the technology disclosed herein. The surface roughness referred to here means the arithmetic mean roughness (Ra).

<Polishing method>
The polishing composition disclosed herein can be suitably used for polishing a magnetic disk substrate as an object to be polished, for example, in an embodiment including the following operations. A preferred embodiment of a method for polishing an object to be polished using the polishing composition disclosed herein is described below. Hereinafter, the object to be polished is also referred to as a substrate to be polished.
That is, prepare a polishing liquid (working slurry) containing any of the polishing compositions disclosed herein. The preparation of the polishing liquid may include adjusting the concentration or pH of the polishing composition to prepare the polishing liquid. The concentration adjustment may be, for example, dilution. Alternatively, the polishing composition may be used as it is as a polishing liquid.

The polishing liquid is then supplied to the object to be polished, and polished in a conventional manner. For example, the object to be polished is set in a general polishing device, and the polishing liquid is supplied to the surface of the object to be polished, i.e., the surface to be polished, through the polishing pad of the polishing device. Typically, the polishing liquid is continuously supplied while the polishing pad is pressed against the surface of the object to be polished, causing the two to move relative to one another. The movement can be, for example, a rotational movement. Through this polishing process, the polishing of the object to be polished is completed.

There are no particular limitations on the polishing pad that can be used. For example, polishing pads of hard foam polyurethane type, nonwoven fabric type, suede type, etc. can be used. The suede type may be a buff pad, and typically may be a polishing pad in a non-buffed state in which the surface has not been buffed (so-called non-buff pad). Such suede type polishing pads (typically polyurethane polishing pads) are easy to process and can easily achieve high quality on the substrate surface. Note that the polishing pads used in the technology disclosed herein do not contain abrasive grains.

After polishing (specifically, after the primary polishing of the magnetic disk substrate), it is preferable to wash the substrate (washing step). The washing step is typically performed using a washing machine. In the washing step, a washing liquid may be used, or washing may be performed using only running water without using a washing liquid. Ultrasonic treatment may be performed in which ultrasonic waves are applied to the substrate immersed in the washing liquid or water. By performing such a washing step, silica remaining on the substrate after polishing can be efficiently removed.

The polishing machine used in the polishing process may be a double-sided polishing machine that polishes both sides of the object to be polished simultaneously, or a single-sided polishing machine that polishes only one side of the object to be polished. When the above-mentioned polishing process is a preliminary polishing process, in some embodiments, a double-sided polishing machine may be preferably used as the polishing machine that performs the polishing process. When a finish polishing process is performed after the primary polishing process, a single-sided polishing machine may be preferably used as the polishing machine that performs the finish polishing process.

The polishing step as described above can be part of a manufacturing process for a magnetic disk substrate, for example a nickel phosphorus substrate. Therefore, this specification provides a manufacturing method and a polishing method for a magnetic disk substrate that include the above polishing step.

The polishing composition disclosed herein can be preferably used in a preliminary polishing step of an object to be polished, for example, a primary polishing step. According to this specification, a manufacturing method and a polishing method for a magnetic disk substrate are provided, which include a step of performing preliminary polishing using any of the polishing compositions described above. The above method includes a step (1) of supplying the polishing composition disclosed herein to the object to be polished and polishing the object to be polished. The above method may include a finish polishing step after the preliminary polishing step. The polishing composition used in the finish polishing step is not particularly limited. Therefore, the matters disclosed by this specification include a manufacturing method and a polishing method for a magnetic disk substrate, which include, in this order, a step (1) of polishing the object to be polished with a polishing composition containing abrasive grains disclosed herein, and a step (2) of polishing the object to be polished with a polishing composition (e.g., a finish polishing composition) different from the polishing composition used in step (1). According to such a manufacturing method, a magnetic disk substrate can be efficiently manufactured.

The abrasive grains used in step (2) are not particularly limited, and for example, colloidal silica is preferably used. By using colloidal silica, a polished product with high surface accuracy can be efficiently manufactured. The particle shape of the colloidal silica is not particularly limited, and for example, it may be spherical or non-spherical, but spherical colloidal silica is preferably used.

The final polishing composition that can be used in step (2) contains, for example, water in addition to abrasive grains. In addition, the final polishing composition can contain the same components as the polishing composition described above (acid, oxidizing agent, basic compound, various additives, etc.) as necessary.

Several examples of the present invention are described below, but it is not intended that the present invention be limited to those examples.

<Experimental Example 1>
[Examples 1 to 3, Comparative Example 1]
<Preparation of Polishing Composition>
Abrasive dispersions (Samples E1-3, C11) containing silica abrasive grains at a concentration of 45±3% by weight in deionized water were prepared. The pH was about 9 to 9.5. The average aspect ratio, 50% cumulative frequency particle size (D ₅₀ ), 90% cumulative frequency particle size (D ₉₀ ), 99% cumulative frequency particle size (D ₉₉ ) and ratio (D ₉₉ /D ₉₀ ) of the silica abrasive grains were as shown in Table 1.

The prepared abrasive dispersion was mixed with phosphoric acid, 31% hydrogen peroxide solution, and deionized water, either without storage or after storage under the conditions below for the periods shown in Table 1, to prepare a polishing composition with an abrasive concentration of 7 wt%, phosphoric acid concentration of 0.1 mol/L, and hydrogen peroxide concentration of 0.4 mol/L. The pH of this polishing composition was 1.5.

The average aspect ratio of the silica abrasive grains was determined based on the above-mentioned SEM image analysis. The _D50 , _D90 , _D99 and ratio ( _D99 / _D90 ) of the silica abrasive grains were determined from the weight-based particle size distribution obtained by dispersing each abrasive grain dispersion in ion-exchanged water to prepare a measurement slurry with an abrasive grain concentration of 2% by weight, and measuring the particle size distribution of each sample using a light transmission centrifugal sedimentation method. Specifically, the weight-based particle size distribution was determined using a disk centrifugal particle size distribution measuring device "DC24000 UHR" manufactured by CPS Instruments, USA, in accordance with JIS Z 8823-2 under the following conditions.
[Measurement conditions]
Test solution introduced into the cell: Aqueous sucrose solution with a minimum concentration of 8% by weight and a maximum concentration of 24% by weight. Amount of test solution introduced into the cell: 12 mL.
Silica concentration of the slurry to be measured: 2% by weight
Amount of slurry injected for measurement: 0.1 mL
Disk rotation speed: 24000 rpm
Measurement range: 0.025 μm to 1.0 μm

The abrasive dispersion was stored by placing 2 liters of the abrasive dispersion in a 2-liter polypropylene container (round bottle, hereinafter also referred to as "PP container") and leaving it at room temperature (approximately 25°C). In Table 1, 1M, 2M, ... 15M indicate storage periods of 1 month, 2 months ... 15 months, respectively. When using the first composition after storage to prepare a polishing composition, if settling of abrasive particles was observed in the PP container, the PP container was shaken by hand to thoroughly redisperse the settled abrasive particles before use.

<Evaluation of initial performance>
The polishing performance of the polishing composition prepared using the initial (i.e., unstored) abrasive dispersion was evaluated as follows.

[Disc polishing]
The polishing composition according to each example was used as a polishing liquid as it was, and polishing of the object to be polished was carried out under the following conditions. The object to be polished was an aluminum substrate for a hard disk having an electroless nickel phosphorus plating layer on its surface. The diameter of the object to be polished (substrate to be polished) was 3.5 inches (a doughnut shape with an outer diameter of about 95 mm and an inner diameter of about 25 mm), the thickness was 1.75 mm, and the surface roughness Ra (the arithmetic mean roughness of the nickel phosphorus plating layer measured by a laser scanning surface roughness meter "TMS-3000WRC" manufactured by Schmitt Measurement System Inc.) before polishing was 130 Å.

(Polishing conditions)
Polishing equipment: System Seiko double-sided polishing machine, model "9.5B-5P"
Polishing pad: Polyurethane pad manufactured by FILWEL, product name "CR200"
Number of substrates to be polished: 15 (3 substrates/carrier x 5 carriers)
Polishing liquid supply rate: 135 mL/min Polishing load: 120 g/ ^cm2
Upper platen rotation speed: 27 rpm
Lower surface plate rotation speed: 36 rpm
Sun gear rotation speed: 8 rpm
Amount polished: total thickness of about 2.2 μm on both sides of each substrate. The amount polished was calculated based on the following formula.
Polishing amount [μm]=weight loss of substrate due to polishing [g]/(substrate area [cm ² ]×density of nickel phosphorus plating [g/cm ³ ])×10 ⁴

[Processability]
The polishing rates on both sides of the substrate to be polished under the above polishing conditions were calculated. The polishing rates were calculated based on the following formula. The results were converted into relative values, with the polishing rate in Example 1 taken as 100%, and shown in the "initial polishing rate" column of Table 1. When the polishing rate is 75% or more, it is evaluated that the processability is favorably maintained.
Polishing rate [μm/min]=weight loss of substrate due to polishing [g]/(area of substrate [cm ² ]×density of nickel phosphorus plating [g/cm ³ ]×polishing time [min])×10 ⁴

[Micro waviness]
After polishing using the polishing composition according to each example, one Ni-P substrate was randomly selected from the Ni-P substrates (substrates after polishing) set in each carrier during the polishing, for a total of three Ni-P substrates. Microwaviness was measured for the front and back surfaces of these three Ni-P substrates, a total of six surfaces, using a non-contact surface profiler "NEWVIEW5032" manufactured by ZYGO Corporation, under the conditions of an objective lens magnification of 2.5 times, an intermediate lens magnification of 0.5 times, and a bandpass filter of 80 to 500 μm. Measurements were performed for each of the six surfaces at four points spaced at 90° intervals from the center of the polished substrate to a position 37 mm radially outward, and the average value of these 24 points was taken as the value of microwaviness (Å). The obtained values were converted into relative values with the value of Example 1 taken as 100%, and shown in the "initial microwaviness" column of Table 1. When the value is 120% or less, it is evaluated that the microwaviness is suitably suppressed.

<Evaluation of polishing performance after storage>
The polishing rate and microwaviness of the polishing composition prepared using the first composition after storage were measured in the same manner as above, and the obtained values were converted into relative values with the value of Example 1 taken as 100%. The evaluation results of microwaviness are shown in the corresponding columns of Table 1.

As shown in Table 1, the microwaviness suppression performance was comparable in Examples 1 to 3 and Comparative Example 1 for the polishing compositions prepared using the initial first composition, but as the storage period of the first composition increased, the microwaviness suppression performance of Comparative Example 1 decreased significantly. In Examples 1 to 3, the decrease in microwaviness suppression performance due to the longer storage period of the first composition was smaller than in Comparative Example 1.

In addition, in all of Examples 1 to 3 and Comparative Example 1, the change in the polishing rate (relative value with the value in Example 1 taken as 100%) due to the storage period of the first composition was smaller than the change in the microwaviness suppression performance. More specifically, the decrease in the polishing rate when the first composition was used after 10 months of storage compared to when the initial first composition was used was within 10% in all cases, and particularly within 5% in Examples 1 and 2.

In the above experiment, it was confirmed that in the abrasive dispersions of Examples 1, 3 and Comparative Example 1, silica particles aggregate and settle at the bottom of the PP container as the storage period progresses. On the other hand, in the abrasive dispersion of Example 2, such aggregation and settling of silica particles was not confirmed. In addition, the abrasive dispersions of Examples 1, 3 and Comparative Example 1 were all used to prepare a polishing composition after shaking the PP container well before use to redisperse the silica particles, but since there was a clear difference in the degree of change over time between Examples 1, 3 and Comparative Example 1, the situation when redispersed was examined in detail, and it was found that in Comparative Example 1, it was necessary to shake the PP container better to redisperse the silica particles compared to Examples 1 and 3. In addition, in comparison between Example 1 and Example 3, Example 1 was easier to redisperse. Therefore, referring to Table 1, it was inferred that there is a correlation between the size of _D90 of silica particles and redispersibility, so the following experiment was carried out to analyze this correlation in detail.

<Experimental Example 2>
[Examples 1 to 10, Comparative Examples 1 to 6]
Abrasive dispersions E4 to E10 and C12 to C16 were prepared containing silica abrasive grains at a concentration of 45±3% by weight in deionized water. The pH was about 9 to 9.5. The _D50 , _D90 , _D99 , ratio ( _D90 / _D99 ), and average aspect ratio of the silica particles contained in each abrasive dispersion are shown in the corresponding columns of Table 2.
The polishing compositions of each example were prepared in the same manner as in the first test, except that the abrasive dispersions of Samples E4 to E10 and C12 to C16 were used, and the initial performance was evaluated in the same manner. The obtained values are shown in Table 2, together with the initial performances of Examples 1 to 3 and Comparative Example 1 obtained in Experimental Example 1, converted into relative values with Comparative Example 1 being 100%.
As shown in Table 2, in Comparative Examples 5 and 6, in which silica particles with a ratio ( _D99 / _D90 ) lower than 1.4 were used, the polishing rates were significantly lower than those of the other examples. Therefore, the following storage stability test was omitted for the abrasive dispersions of Samples C15 and C16.

<Storage stability test>
[Sedimentation]
A sedimentation test was carried out by weighing out 2 L of the abrasive dispersion liquid of samples E1 to 10 and C11 to 14, placing it in the PP container, and leaving it at room temperature (about 25°C) for two months. Then, it was visually confirmed whether or not sedimentation of silica particles occurred on the bottom surface of each PP container. The results are shown in the "Sedimentation" column of Table 2.

[Redispersibility]
For samples in which sedimentation was confirmed in the sedimentation test, the redispersibility of the silica particles was evaluated by shaking the PP container from side to side while it was turned sideways. The shaking was performed at 110±5 reciprocations/min, with a width of 10 cm from the center to the left and right. If the time required from the start of shaking until a good redispersion state was obtained was within 1 minute, the redispersibility was marked as "◎", if it was more than 1 minute and within 3 minutes, the redispersibility was marked as "○", and if it took more than 3 minutes to redisperse, the redispersibility was marked as "×", and these were indicated in the corresponding columns of Table 2. The results are shown in the "redispersibility" column of Table 2. For samples in which sedimentation of silica particles was not confirmed, the redispersibility test was not performed, and the redispersibility column was marked as "-".

As shown in Table 2, in an abrasive dispersion in which the average aspect ratio of silica particles is 1.1 or more and the ratio ( _D99 / _D90 ) is 1.4 or more, it was confirmed that if _D90 is 250 nm or less, sedimentation is unlikely to occur, and even if sedimentation does occur, redispersibility is good. From this, it is considered that by using silica particles that satisfy the above conditions, the change over time in polishing performance can be suitably suppressed.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples given above.

Claims (8)

A polishing composition for use in polishing a magnetic disk substrate, comprising:
The method includes the steps of:
The silica particles have an average aspect ratio of 1.1 or more based on SEM image analysis, and in a weight-based particle size distribution based on a light transmission centrifugal sedimentation method, a ratio of a cumulative 99% particle diameter D ₉₉ to a cumulative 90% particle diameter D ₉₀ (D ₉₉ /D ₉₀ ) of 1.4 or more, and the cumulative 90% particle diameter D ₉₀ is 250 nm or less. The polishing composition according to claim 1, wherein the silica particles have a cumulative 50% particle diameter _D50 of 170 nm or less in a weight-based particle size distribution based on a light transmission centrifugal sedimentation method. The silica particles are
The cumulative 90% particle size _D90 is 210 nm or less, and the average aspect ratio is 1.25 or less.
The polishing composition according to claim 1 or 2, which satisfies at least one of the above. The polishing composition according to any one of claims 1 to 3, further comprising an acid and an oxidizing agent. A method for manufacturing a magnetic disk substrate, comprising step (1) of polishing a substrate to be polished using the polishing composition according to any one of claims 1 to 4. A method for polishing a substrate, comprising step (1) of supplying the polishing composition according to any one of claims 1 to 4 to a substrate to be polished and polishing the substrate. A method for producing a polishing composition for use in polishing a magnetic disk substrate, comprising the steps of:
preparing a first composition containing silica particles as abrasive grains and water in which the silica particles are dispersed, and a second composition containing at least an acid;
mixing the first composition with the second composition;
wherein the silica particles have an average aspect ratio of 1.1 or more, and in a weight-based particle size distribution based on a light transmission centrifugal sedimentation method, a ratio of a cumulative 99% particle diameter _D99 to a cumulative 90% particle diameter _D90 ( _D99 / _D90 ) of 1.4 or more, and the cumulative 90% particle diameter _D90 is 250 nm or less. A set for preparing a polishing composition for use in polishing a magnetic disk substrate, comprising:
A first composition including silica particles as abrasive grains and water for dispersing the silica particles;
A second composition comprising at least an acid;
Including,
the silica particles have an average aspect ratio of 1.1 or more, and in a weight-based particle size distribution based on a light transmission centrifugal sedimentation method, a ratio of a cumulative 99% particle diameter D ₉₉ to a cumulative 90% particle diameter D ₉₀ (D ₉₉ /D ₉₀ ) is 1.4 or more, and the cumulative 90% particle diameter D ₉₀ is 250 nm or less;
A polishing composition preparation set, wherein the first composition and the second composition are stored separately from each other.