JP6656867B2 - Polishing composition for magnetic disk substrate, method for manufacturing magnetic disk substrate, and magnetic disk substrate - Google Patents

Description

  The present invention relates to a polishing composition for a magnetic disk substrate, a method for manufacturing a magnetic disk substrate using the polishing composition, and a magnetic disk substrate manufactured by the method.

  In the manufacture of a magnetic disk substrate, pre-polishing (primary polishing) is generally performed prior to a final polishing step (final polishing) performed to finish the surface of a final product with a high degree of polishing efficiency. For example, by performing at least preliminary polishing and final polishing on a disk substrate (Ni-P substrate) on which nickel phosphorus plating has been performed, a highly accurate surface can be efficiently realized. In such a polishing process, even in the polishing performed before the final polishing step as in the above-mentioned preliminary polishing, it is desirable to realize a good surface state because it contributes to the improvement of the surface accuracy in the final polishing step.

  One of the factors that affect the surface accuracy of the object to be polished is the material and properties of the abrasive grains contained in the polishing liquid. For example, according to the polishing liquid using silica as abrasive grains, the surface quality (for example, defects due to surface smoothness and piercing of abrasive grains) of the surface to be polished is improved as compared with the polishing liquid using abrasive grains such as alumina having higher hardness. Tend to. Patent Literatures 1 to 5 are given as technical literature relating to a polishing technique using silica as abrasive grains.

JP 2006-026885 A JP 2010-016344 A JP 2001-269857 A JP-A-61-136909 JP 2014-116057 A

However, polishing liquids using silica abrasive grains generally tend to have poor polishing efficiency (typically, polishing rate), such as primary polishing of a magnetic disk substrate (Ni-P substrate) plated with nickel phosphorus. When used in polishing which requires a high polishing rate, there is a possibility that such a request cannot be sufficiently satisfied.
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a polishing composition for a magnetic disk substrate that can exhibit a high polishing rate using abrasive grains containing silica particles. Another related object is to provide a method of manufacturing a magnetic disk substrate using such a polishing composition and a magnetic disk substrate manufactured by the method. Still another object is to provide a method for polishing a magnetic disk substrate using the above polishing composition.

  The polishing composition for a magnetic disk substrate provided by this specification contains abrasive grains and water. The abrasive grains include at least silica particles. In the volume-based aspect ratio distribution of the abrasive grains in the polishing composition, the cumulative 90% aspect ratio is 1.25 or more, and the cumulative 75% aspect ratio is 1.20 or more. According to the polishing composition containing such abrasive grains, a high polishing rate can be realized.

  In a preferred embodiment of the polishing composition disclosed herein, a cumulative 75% aspect ratio in the volume-based aspect ratio distribution of the abrasive grains is 1.7 or less. According to such a polishing composition, a high polishing rate and a good surface accuracy can both be achieved at a high level.

  In a preferred embodiment of the polishing composition disclosed herein, the abrasive has a volume average particle diameter of 70 nm or more measured by a dynamic light scattering method. According to such a polishing composition, a high polishing rate and a good surface accuracy can both be achieved at a high level.

  The polishing composition disclosed herein preferably has a pH of 5 or less. When the abrasive having the cumulative 90% aspect ratio and the volume average particle diameter is used in a polishing composition having such a pH, the effects of the present invention can be more suitably exerted.

  The polishing composition disclosed herein is suitable as a polishing composition used in a step before the final polishing step. For example, the polishing composition is suitably used for primary polishing of a magnetic disk substrate. Since the polishing composition disclosed herein can exhibit a high polishing rate, it is useful to be used in a polishing process requiring high polishing efficiency such as the primary polishing.

  A preferable application target of the polishing composition disclosed herein is a magnetic disk substrate (Ni-P substrate) plated with nickel phosphorus. When the polishing composition is applied to the magnetic disk substrate, a high polishing rate can be achieved. The polishing composition disclosed herein is particularly suitable for preliminary polishing (primary polishing) of a nickel-phosphorous-plated magnetic disk substrate.

  According to this specification, there is also provided a method of manufacturing a magnetic disk substrate. The manufacturing method includes a step (1) of polishing a magnetic disk substrate using any of the polishing compositions for a magnetic disk substrate disclosed herein. According to such a manufacturing method, a magnetic disk substrate can be manufactured with high productivity.

  The method for manufacturing a magnetic disk substrate may further include, after the step (1), a step (2) of polishing the magnetic disk substrate using a finish polishing composition containing colloidal silica. According to this manufacturing method, a magnetic disk substrate having a higher quality surface can be manufactured with high productivity.

  As another aspect of the magnetic disk substrate manufacturing method disclosed herein, a magnetic disk substrate manufactured by the method is provided. Such a magnetic disk substrate is preferable because it can be advantageous in terms of production cost.

  According to this specification, a method for polishing a magnetic disk substrate is further provided. The polishing method is characterized in that one of the polishing compositions for a magnetic disk substrate disclosed herein is supplied to a magnetic disk substrate to polish the magnetic disk substrate. According to such a polishing method, the magnetic disk substrate can be efficiently polished.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than matters specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on conventional techniques in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and common technical knowledge in the field.

<Abrasives>
The polishing composition disclosed herein is a polishing composition for a magnetic disk substrate (preferably for primary polishing), and contains abrasive grains containing at least silica particles. The abrasive has a specific aspect ratio distribution. That is, in the volume-based aspect ratio distribution of the abrasive grains in the polishing composition, the cumulative 90% aspect ratio is 1.25 or more, and the cumulative 75% aspect ratio is 1.20 or more. As a result, for example, a higher polishing rate can be realized as compared with a polishing composition using an abrasive having a smaller cumulative 90% aspect ratio and a smaller cumulative 75% aspect ratio instead of the abrasive.

  The reason why the above-described effects can be obtained is not particularly limited, but is considered as follows, for example. That is, from the viewpoint of polishing efficiency, the abrasive grains preferably include large-diameter particles. However, in polishing using spherical particles having a large diameter, a part of stress that can be generated by friction (sliding movement) between the particles and the substrate surface acts on the substrate surface due to the rolling movement of the particles. Easily escaped without. On the other hand, abrasive grains having a cumulative 90% aspect ratio of 1.25 or more and a cumulative 75% aspect ratio of 1.25 or more are particles having a large volume (that is, a high contribution rate to the polishing rate). The shape of large particles is distorted from spherical. Distorted particles are less likely to roll than spherical particles, so that stress can be more effectively transmitted to the surface of the substrate. This is considered to contribute to the improvement of the polishing rate.

  In this specification, the “cumulative 90% aspect ratio” of the abrasive grains means the cumulative volume distribution curve in which the total volume of the aspect ratio distribution obtained on a volume basis is 100%, from the side having the smaller aspect ratio. Is the aspect ratio of the point where the cumulative volume becomes 90%. The “cumulative 75% aspect ratio” of the abrasive grains means that the cumulative volume from the side having the smaller aspect ratio is 75% in the cumulative volume distribution curve in which the total volume of the aspect ratio distribution obtained on a volume basis is 100%. Is the aspect ratio of the point. These cumulative volume aspect ratios mean the cumulative volume aspect ratio that is grasped as the overall characteristics of the abrasive grains contained in the polishing composition. Therefore, when the abrasive grains contained in the polishing composition are, for example, a mixture of two types of abrasive grains X and Y, the above-mentioned cumulative volume aspect ratio indicates that the abrasive grains (that is, the mixture of the abrasive grains X and Y) It can be determined by measuring the aspect ratio and volume of a plurality of abrasive grains contained in the abrasive grains as a measurement sample.

As a specific procedure, using a scanning electron microscope (SEM), abrasive grains to be measured (one kind of abrasive grains may be used, and a mixture of two or more kinds of abrasive grains may be used. (For example, 100 to 1000, typically 200) particles are observed. Then, for the smallest rectangle circumscribing each particle image, the value obtained by dividing the length of the long side (the value of the long axis) by the length of the short side (the value of the short axis) is the ratio of the long diameter / short diameter of each particle ( (Aspect ratio). Moreover, to calculate the value obtained by 4πr ^3/3 from the radius r of the ideal yen (perfect circle) having an area equal to the projected area of each particle image as the volume of each particle. Here, the aspect ratio and the volume are calculated by counting particles independently dispersed in the polishing composition as one particle, regardless of whether the particles are primary particles or secondary particles. I do. Then, by deriving the cumulative volume distribution curve of the aspect ratio distribution from the aspect ratio and the volume of the predetermined number of particles, each of the above-described cumulative volume aspect ratios can be obtained. Such a cumulative volume aspect ratio can be determined using general image analysis software.

<Cumulative 90% aspect ratio>
The technology disclosed herein is implemented in a mode that includes abrasive grains having a cumulative 90% aspect ratio of 1.25 or more. The cumulative 90% aspect ratio of the abrasive grains is preferably 1.3 or more, more preferably 1.4 or more, further preferably 1.5 or more, and particularly preferably 1.6 or more, from the viewpoint of the polishing rate or the like. . In addition, the cumulative 90% aspect ratio of the abrasive grains is usually preferably 3.0 or less from the viewpoints of durability (for example, resistance to collapse due to stress) of the abrasive grains and stability of polishing. Yes, preferably 2.5 or less, more preferably 2.0 or less (for example, less than 2.0). For example, a polishing composition containing abrasive grains having a cumulative 90% aspect ratio of more than 1.25 and less than 3.0 (more preferably 1.31 or more and 2.2 or less, more preferably 1.52 or more and 1.96 or less). Things are preferred.

<Cumulative 75% aspect ratio>
As the abrasive grains, those having a cumulative 75% aspect ratio of 1.20 or more can be used. The 75% cumulative aspect ratio of the abrasive grains is preferably 1.22 or more, more preferably 1.25 or more. Higher polishing rates may be achieved by increasing the cumulative 75% aspect ratio. Further, the cumulative 75% aspect ratio of the abrasive grains is preferably 1.7 or less, more preferably 1.6 or less, still more preferably 1.5 or less, from the viewpoint of obtaining a surface with higher surface accuracy. It is preferably at most 1.4, particularly preferably at most 1.3. The technology disclosed herein is, for example, such that the cumulative 75% aspect ratio of the abrasive grains is 1.2 or more and less than 1.7 (more preferably 1.2 or more and 1.7 or less, for example, 1.2 or more and 1.5 or less) )).

  The ratio value (A90 / A75) between the cumulative 90% aspect ratio (A90) and the cumulative 75% aspect ratio (A75) is preferably 1.05 or more, more preferably 1.1 or more, from the viewpoint of the polishing rate or the like. , More preferably 1.2 or more. The value of the above ratio (A90 / A75) is preferably 1.6 or less, more preferably 1.5 or less, from the viewpoint of obtaining a higher quality surface.

  The volume-based aspect ratio distribution of the abrasive grains can be adjusted by selecting abrasive grains to be used or a combination thereof. For example, A90 and A75 in the above-described aspect ratio distribution are adjusted to an appropriate range disclosed herein by using a mixture of large-diameter particles having a large aspect ratio and smaller-diameter particles at an appropriate weight ratio. Can be.

<Volume average particle size>
Typically, the volume average particle diameter of the abrasive grains is preferably 70 nm or more. The volume average particle diameter of the abrasive grains is preferably 100 nm or more, more preferably 150 nm or more, further preferably 200 nm or more, particularly preferably 250 nm or more, from the viewpoint of the polishing rate or the like. The volume average particle diameter of the abrasive grains may be, for example, 600 nm or less. From the viewpoint of obtaining a higher quality surface, the volume average particle diameter is preferably 500 nm or less, more preferably 450 nm or less, further preferably 400 nm or less, and particularly preferably 350 nm or less. The technology disclosed herein can be preferably implemented, for example, in an embodiment using abrasive grains having a volume average particle diameter of 70 nm or more and less than 500 nm (more preferably 120 nm or more and less than 400 nm, for example, 180 nm or more and less than 350 nm).

  The volume average particle diameter of the abrasive grains can be determined by measuring the particle diameter based on a dynamic light scattering method using an abrasive-containing liquid containing the abrasive grains as a measurement sample. As a specific procedure, water is added to an abrasive-containing liquid containing abrasive particles to be measured (one type of abrasive particles or a mixture of two or more types of abrasive particles). An aqueous solution of sodium oxide is added to prepare an abrasive-containing liquid having a pH of 10 (abrasive concentration: 10% by weight). Then, the particles are dispersed for 90 seconds by a 50 kHz ultrasonic dispersing machine, and the particles (which may be in the form of primary particles and / or secondary particles) dispersed in the abrasive-containing liquid are irradiated with laser light, and water is applied. After adjusting the scattering intensity suitable for measurement while diluting with a sodium oxide aqueous solution (pH 10 adjustment), the particle diameter is measured by detecting the scattered light. The refractive index used for the measurement is 1.45. This particle size measurement can be performed using, for example, a model “UPA-UT151” manufactured by Nikkiso Co., Ltd. Further, as the ultrasonic dispersing machine, for example, model "Tetora150" manufactured by Nikkaki Bios Co., Ltd. can be used.

  The silica particles contained in the abrasive grains may be various types of silica particles containing silica as a main component. Here, the silica particles containing silica as a main component are particles in which 90% by weight or more (normally 95% by weight or more, typically 98% by weight or more) of the particles is silica. Examples of the silica particles that can be used include, but are not particularly limited to, colloidal silica, precipitated silica, sodium silicate silica, alkoxide silica, fumed silica, dried silica, explosive silica, and the like. Examples of usable silica particles further include silica obtained using the above silica particles (ie, precipitated silica, sodium silicate method silica, alkoxide method silica, fumed silica, dried silica, explosion method silica, etc.) as a raw material. Particles. Examples of such silica particles include the above-mentioned raw material silica particles (hereinafter also referred to as “raw silica”), heat treatment such as heating, drying and baking, pressure treatment such as autoclave treatment, crushing and pulverization ( Silica particles obtained by applying one or more treatments selected from mechanical treatments such as crushing) and surface modification (for example, introduction of functional groups, chemical modification such as metal modification). obtain. The abrasive in the technology disclosed herein may include one kind of such silica particles alone or in combination of two or more kinds.

  For example, silica particles obtained by heat-treating raw silica (hereinafter also referred to as “heat-treated silica”), specifically, heated silica particles, dried silica particles, calcined silica particles, and the like. Can be preferably used. Here, the heated silica particles are typically obtained through a process of maintaining the silica particles in an environment of 60 ° C. or more and less than 110 ° C. for a certain time or more (for example, 15 minutes or more, typically 30 minutes or more). Silica particles. The dried silica particles are typically used in an environment of 110 ° C. or more and less than 500 ° C. (preferably 300 ° C. or more and less than 500 ° C.) for a given time or more (eg, 15 minutes or more, typically 30 minutes). Above) refers to silica particles obtained through a holding process. And, the calcined silica particles (hereinafter also referred to as “calcined silica”) are typically 500 ° C. or more, preferably 700 ° C. or more, more preferably 900 ° C. or more for a certain time or more (for example, This refers to silica particles obtained through a holding process for 15 minutes or more, typically 30 minutes or more. The silica particles obtained through the process of heat-treating any of the above-mentioned raw material silicas (precipitated silica, sodium silicate silica, alkoxide silica, fumed silica, dried silica, explosive silica, etc.) It is a typical example included in the concept of silica.

  The technology disclosed herein can be preferably implemented in a mode in which the abrasive grains contained in the polishing composition include heat-treated silica alone or a combination of heat-treated silica and other silica particles. In such an embodiment in which the abrasive grains contain at least the heat-treated silica, the content of the heat-treated silica in the abrasive grains is not particularly limited. From the viewpoint of the polishing rate, the content of the above-mentioned heat-treated silica is preferably 10% by weight or more of the abrasive grains, more preferably 20% by weight or more (for example, 25% by weight or more), and further preferably 30% by weight or more. is there. The upper limit of the content of the heat-treated silica in the abrasive grains is not particularly limited, and may be substantially 100% by weight (typically 99% by weight or more). From the viewpoint of balancing various performances (eg, polishing rate, undulation of the surface to be polished, etc.), the content of the heat-treated silica in the abrasive grains is preferably 90% by weight or less, more preferably 80% by weight or less (for example, 75% by weight or less), and more preferably 60% by weight or less.

  In a preferred embodiment, heat-treated silica (first silica particles) and colloidal silica (second silica particles) are used in combination as abrasive grains contained in the polishing composition. By using colloidal silica in addition to heat-treated silica, the aspect ratio distribution of the abrasive grains can be suitably adjusted, and a high polishing rate and good surface accuracy can be achieved at a high level. In this case, the content of colloidal silica in the abrasive grains is preferably 40% by weight or more, and more preferably 50% by weight or more. The content of colloidal silica in the abrasive grains may be, for example, 65% by weight or more, or 70% by weight or more.

  In another preferred embodiment, the abrasive grains contained in the polishing composition contain colloidal silica alone. By using colloidal silica alone, better surface accuracy (surface with reduced waviness) can be realized while maintaining a high polishing rate.

  The polishing composition disclosed herein can contain particles other than silica particles as abrasive grains having the cumulative 90% aspect ratio and the cumulative 75% aspect ratio. As particles other than silica particles, any of inorganic particles, organic particles, and organic-inorganic composite particles can be used. Specific examples of the inorganic particles include oxide particles such as alumina particles, cerium oxide particles, chromium oxide particles, titanium dioxide particles, zirconium oxide particles, magnesium oxide particles, manganese dioxide particles, zinc oxide particles, and red iron oxide particles; silicon nitride particles. And nitride particles such as boron nitride particles; carbide particles such as silicon carbide particles and boron carbide particles; diamond particles; carbonates such as calcium carbonate and barium carbonate; Examples of the alumina particles include α-alumina, intermediate alumina other than α-alumina, and composites thereof. Intermediate alumina is a general term for alumina particles other than α-alumina, and specific examples include γ-alumina, δ-alumina, θ-alumina, η-alumina, κ-alumina, and composites thereof. Specific examples of the organic particles include polymethyl methacrylate (PMMA) particles and poly (meth) acrylic acid particles (here, (meth) acrylic acid means acrylic acid and methacrylic acid comprehensively). And polyacrylonitrile particles. These particles other than silica particles can be used alone or in combination of two or more.

  In the polishing composition disclosed herein, the content of the silica particles in the solid content contained in the polishing composition is not particularly limited. The content of the silica particles is preferably 40% by weight or more, more preferably 50% by weight or more, even more preferably 60% by weight or more of the entire solid content from the viewpoint of easily exhibiting the effect of the present invention. Even more preferably, it is 80% by weight or more, particularly preferably 90% by weight or more (for example, 99% by weight or more). Substantially all of the solid content contained in the polishing composition may be the silica particles.

  The polishing composition disclosed herein can be preferably implemented in a mode substantially free of alumina abrasive grains (for example, α-alumina abrasive grains). According to such a polishing composition, deterioration in quality (for example, generation of scratches and depressions, residual alumina, puncturing defects of the abrasive grains, and the like) due to use of the alumina abrasive grains is prevented. In the present specification, the phrase "substantially does not contain predetermined abrasive grains (for example, alumina abrasive grains)" means that the proportion of the abrasive grains is 1% by weight or less (more preferably, the total amount of solids contained in the polishing composition). Is 0.5% by weight or less, typically 0.1% by weight or less). A polishing composition in which the proportion of alumina abrasive grains is 0% by weight, that is, a polishing composition containing no alumina abrasive grains is particularly preferred. Further, the polishing composition disclosed herein can be preferably practiced in a mode substantially free of α-alumina abrasive grains.

  The polishing composition disclosed herein can also be preferably practiced in an aspect that does not substantially contain particles (non-silica particles) other than silica particles. Here, the term "substantially free of non-silica particles" means that the proportion of non-silica particles in the total solid content of the polishing composition is 1% by weight or less (more preferably 0.5% by weight or less, typically Means 0.1% by weight or less). In such an embodiment, the application effects of the technology disclosed herein can be suitably exhibited.

<Polishing composition>
(water)
The polishing composition disclosed herein typically contains water in which the abrasive grains are dispersed, in addition to the abrasive grains as described above. As the water, ion-exchanged water (deionized water), pure water, ultrapure water, distilled water and the like can be preferably used.

  The polishing composition (typically, a slurry-like composition) disclosed herein is preferably implemented, for example, in a form having a non-volatile content (NV) of 5 g / L to 300 g / L. obtain. A form in which the NV is 10 g / L to 200 g / L is more preferable.

(acid)
The polishing composition disclosed herein may be preferred in aspects that include an acid as a polishing accelerator. Examples of acids that can be suitably used include inorganic acids and organic acids (for example, organic carboxylic acids having 1 to 10 carbon atoms, organic phosphonic acids, organic sulfonic acids, amino acids and the like). Not limited. The acids can be used alone or in combination of two or more.

  Specific examples of the inorganic acid include phosphoric acid, nitric acid, sulfuric acid, hydrochloric acid, hypophosphorous acid, phosphonic acid, boric acid, and sulfamic 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, crotonic acid, nicotinic acid, acetic acid , Adipic acid, formic acid, oxalic acid, propionic acid, valeric acid, caproic acid, caprylic acid, capric acid, cyclohexanecarboxylic acid, phenylacetic acid, benzoic acid, crotonic acid, methacrylic acid, glutaric acid, fumaric acid, phthalic acid, isophthalic acid Acid, terephthalic acid, glycolic acid, tartronic acid, glyceric acid, hydroxybutyric acid, hydroxyacetic acid, hydroxybenzoic acid, salicylic acid, isocitric acid, methylene succinic acid, gallic acid, ascorbic acid, nitroacetic acid, oxaloacetic acid, glycine, alanine, glutamic acid , Aspartic acid, valine, leucine, a Leucine, serine, threonine, cysteine, methionine, phenylalanine, tryptophan, tyrosine, proline, cystine, glutamine, asparagine, lysine, arginine, nicotinic acid, picolinic acid, methyl acid phosphate, ethyl acid phosphate, ethyl glycol acid phosphate, isopropyl acid phosphate 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, Tan-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, α-methylphosphono Examples include succinic acid, aminopoly (methylene phosphonic acid), methanesulfonic acid, ethanesulfonic acid, aminoethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and 2-naphthalenesulfonic acid.

  Preferred acids from the viewpoint of polishing efficiency include phosphoric acid, nitric acid, sulfuric acid, sulfamic acid, phytic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, methanesulfonic acid and the like. Of these, nitric acid, sulfuric acid, phosphoric acid, sulfamic acid and methanesulfonic acid are preferred.

  When the polishing composition contains an acid, its content is not particularly limited. Usually, the content of the acid is appropriately 1 g / L or more, preferably 3 g / L or more, more preferably 5 g / L or more (for example, 10 g / L or more). When the content of the acid is too small, the polishing rate tends to be insufficient, which may not be practically preferable. Usually, the content of the acid is suitably 100 g / L or less, preferably 50 g / L or less, and more preferably 30 g / L or less (for example, 15 g / L or less). If the content of the acid is too large, the surface accuracy of the object to be polished tends to decrease, which may not be practically preferable.

The acid may be used in the form of a salt of the acid. Examples of the salt include a metal salt (for example, an alkali metal salt such as a lithium salt, a sodium salt, and a potassium salt) and an ammonium salt (for example, a tetramethylammonium salt, a tetraethylammonium salt, and the like) of the above-described inorganic acids and organic acids. Quaternary ammonium salts), alkanolamine salts (for example, monoethanolamine salts, diethanolamine salts, and triethanolamine salts).
Specific examples of the salt include alkali metal phosphates and alkali metal phosphates such as tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate. Hydrogen phosphate; alkali metal salts of the organic acids exemplified above; other alkali metal salts of glutamic acid diacetate, alkali metal salts of diethylenetriaminepentaacetic acid, alkali metal salts of hydroxyethylethylenediaminetriacetic acid, and triethylenetetramine hexaacetic acid. Alkali metal salts; and the like. The alkali metal in these alkali metal salts can be, for example, lithium, sodium, potassium and the like.

  As a salt that can be included in the polishing composition disclosed herein, a salt of an inorganic acid (for example, an alkali metal salt or an ammonium salt) can be preferably used. For example, potassium chloride, sodium chloride, ammonium chloride, potassium nitrate, sodium nitrate, ammonium nitrate, potassium phosphate and the like can be preferably used.

  The acids and salts thereof can be used alone or in combination of two or more. In one preferred embodiment of the polishing composition disclosed herein, an acid (preferably an inorganic acid) and a salt of an acid different from the acid (preferably a salt of an inorganic acid) can be used in combination.

(Oxidant)
The polishing composition disclosed herein can contain an oxidizing agent as needed. Examples of the oxidizing agent include peroxide, nitric acid or a salt thereof, peroxoacid or a salt thereof, permanganic acid or a salt thereof, chromic acid or a salt thereof, oxyacid or a salt thereof, metal salt, and sulfuric acid. However, it is not limited to these. The oxidizing agents can 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, peroxodisulfuric acid, ammonium peroxodisulfate, metal peroxodisulfate, peroxophosphoric acid, and peroxosulfuric acid. , Sodium peroxoborate, formic acid, peracetic acid, perbenzoic acid, perphthalic acid, hypobromous acid, hypoiodic acid, chloric acid, bromic acid, iodic acid, periodic acid, perchloric acid, hypochlorous acid Examples include acids, sodium hypochlorite, calcium hypochlorite, potassium permanganate, metal chromates, metal dichromates, iron chloride, iron sulfate, iron citrate, and iron ammonium sulfate. Preferred oxidizing agents include hydrogen peroxide, iron nitrate, peroxodisulfuric acid and nitric acid. It preferably contains at least hydrogen peroxide, and more preferably consists of hydrogen peroxide.

  When the polishing composition contains an oxidizing agent, its content is preferably at least 1 g / L, more preferably at least 3 g / L, even more preferably at least 4 g / L, based on the amount of the active ingredient. If the content of the oxidizing agent is too small, the rate of oxidizing the object to be polished becomes slow, and the polishing rate decreases, which may not be practically preferable. When the polishing composition contains an oxidizing agent, its content is preferably 30 g / L or less, more preferably 15 g / L or less, based on the amount of the active ingredient. If the content of the oxidizing agent is too large, the surface accuracy of the object to be polished is likely to decrease, which may not be practically preferable.

(Basic compound)
The polishing composition can contain a basic compound as necessary. Here, the basic compound refers to a compound having a function of increasing the pH of the polishing composition when added to the polishing composition. Examples of the basic compound include alkali metal hydroxides, carbonates and bicarbonates, quaternary ammonium or its salts, ammonia, amines, phosphates and hydrogen phosphates, and organic acid salts. The basic compounds can be used alone or in combination of two or more.

Specific examples of the alkali metal hydroxide include potassium hydroxide, sodium hydroxide and the like.
Specific examples of carbonates and hydrogen carbonates include ammonium hydrogen carbonate, ammonium carbonate, potassium hydrogen carbonate, potassium carbonate, sodium hydrogen carbonate, sodium carbonate, and the like.
Specific examples of the quaternary ammonium or a salt thereof include quaternary ammonium hydroxides such as tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetrabutylammonium hydroxide; alkali metals of such quaternary ammonium hydroxides Salts (eg, sodium salts and potassium salts);
Specific examples of the amine include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, monoethanolamine, N- (β-aminoethyl) ethanolamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, and anhydrous piperazine. , Piperazine hexahydrate, 1- (2-aminoethyl) piperazine, N-methylpiperazine, guanidine, azoles such as imidazole and triazole, and the like.
Specific examples of phosphates and hydrogen phosphates include alkali salts such as tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate. Metal salts.
Specific examples of the organic acid salt include potassium citrate, potassium oxalate, potassium tartrate, potassium sodium tartrate, ammonium tartrate and the like.

(Other components)
The polishing composition disclosed herein includes a polishing composition (such as a surfactant, a water-soluble polymer, a dispersant, a chelating agent, a preservative, and a fungicide) as long as the effects of the present invention are not significantly impaired. For example, a known additive that can be used in a polishing composition for a magnetic disk substrate such as a Ni-P substrate or the like may be further contained as necessary.

The surfactant is not particularly limited, and any of anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants can be used. Use of a surfactant (typically, a water-soluble organic compound having a molecular weight of less than 1 × 10 ⁴ ) can improve the dispersion stability of the polishing composition. One type of surfactant can be used alone, or two or more types can be used in combination.
Specific examples of the anionic surfactant include polyoxyethylene alkyl ether acetic acid, polyoxyethylene alkyl sulfate, alkyl sulfate, polyoxyethylene alkyl sulfate, alkyl sulfate, alkylbenzene sulfonic acid, alkyl phosphate, polyoxyethylene. Alkyl phosphate ester, polyoxyethylene sulfosuccinic acid, alkyl sulfosuccinic acid, alkyl naphthalene sulfonic acid, alkyl diphenyl ether disulfonic acid, polyacrylic acid, sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzene sulfonate, sodium polyoxyethylene alkyl ether sulfate, Ammonium polyoxyethylene alkyl phenyl ether sulfate, polyoxyethylene alkyl phenyl ether sulfate Sodium, and salts thereof.
Other specific examples of anionic surfactants include polyalkylaryl sulfonic acid compounds such as naphthalene sulfonic acid formaldehyde condensate, methyl naphthalene sulfonic acid formaldehyde condensate, anthracene sulfonic acid formaldehyde condensate, and benzene sulfonic acid formaldehyde condensate Melamine formalin resin sulfonic acid compounds such as melamine sulfonic acid formaldehyde condensate; lignin sulfonic acid compounds such as lignin sulfonic acid and modified lignin sulfonic acid; aromatic amino sulfonic acids such as aminoaryl sulfonic acid-phenol-formaldehyde condensate Polyisoprenesulfonic acid, polyvinylsulfonic acid, polyallylsulfonic acid, polyisoamylenesulfonic acid, polystyrenesulfonic acid; and the like. Etc. The. As the salt, an alkali metal salt such as a sodium salt and a potassium salt is preferable.
Specific examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyalkylene alkyl ether, sorbitan fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, and alkyl alkanolamide. .
Specific examples of the cationic surfactant include an alkyltrimethylammonium salt, an alkyldimethylammonium salt, an alkylbenzyldimethylammonium salt, and an alkylamine salt.
Specific examples of the amphoteric surfactant include alkyl betaine and alkylamine oxide.

  In the polishing composition containing a surfactant, it is appropriate that the content of the surfactant is, for example, 0.005 g / L or more. The content is preferably 0.01 g / L or more, more preferably 0.1 g / L or more, from the viewpoint of the smoothness of the surface after polishing. From the viewpoint of the polishing rate and the like, the content is suitably 100 g / L or less, preferably 50 g / L or less, for example, 10 g / L or less.

  The polishing composition disclosed herein may contain a water-soluble polymer. By including a water-soluble polymer, surface accuracy after polishing can be improved. Examples of the water-soluble polymer include polyalkylarylsulfonic acid compounds such as naphthalenesulfonic acid formaldehyde condensate, methylnaphthalenesulfonic acid formaldehyde condensate and anthracenesulfonic acid formaldehyde; melamine formalin resin sulfone such as melaminesulfonic acid formaldehyde condensate Acid compounds; Lignin sulfonic acid compounds such as lignin sulfonic acid and modified lignin sulfonic acid; Aromatic amino sulfonic acid compounds such as aminoaryl sulfonic acid-phenol-formaldehyde condensate; others, polyisoprene sulfonic acid and polyvinyl sulfonic acid , Polyallylsulfonic acid, polyisoamylenesulfonic acid, polystyrenesulfonic acid salt, polyacrylate, polyvinyl acetate, polymaleic acid, polyitaconic acid, polyvinyl Alcohol, polyglycerin, polyvinylpyrrolidone, copolymer of isoprenesulfonic acid and acrylic acid, polyvinylpyrrolidone polyacrylic acid copolymer, polyvinylpyrrolidone vinyl acetate copolymer, diallylamine hydrochloride sulfur dioxide copolymer, carboxymethylcellulose, carboxymethylcellulose , Hydroxyethylcellulose, hydroxypropylcellulose, pullulan, chitosan, chitosan salts and the like. The water-soluble polymers can be used alone or in combination of two or more.

  In the polishing composition of the embodiment containing a water-soluble polymer, the content of the water-soluble polymer in the polishing liquid (in the embodiment containing a plurality of water-soluble polymers, the total content thereof) is, for example, 0.01 g / It is appropriate to be L or more. The content is preferably 0.05 g / L or more, more preferably 0.08 g / L or more, and further preferably 0.1 g / L or more, from the viewpoint of the surface smoothness of the object to be polished (for example, a magnetic disk substrate) after polishing. It is 1 g / L or more. From the viewpoint of the polishing rate and the like, the content is suitably 10 g / L or less, and preferably 5 g / L or less, for example, 1 g / L or less. The technique disclosed herein can be preferably implemented even in an embodiment in which the polishing composition does not substantially contain a water-soluble polymer.

  Examples of dispersants include polycarboxylic acid-based dispersants such as sodium polycarboxylate and ammonium polycarboxylate; naphthalenesulfonic acid-based dispersants such as sodium naphthalenesulfonic acid and ammonium naphthalenesulfonic acid; alkylsulfonic acid Dispersants; polyphosphoric acid dispersants; polyalkylene polyamine dispersants; quaternary ammonium dispersants; alkyl polyamine dispersants; alkylene oxide dispersants; polyhydric alcohol ester dispersants;

  Examples of the chelating agent include an aminocarboxylic acid-based chelating agent and an organic phosphonic acid-based chelating agent. Examples of aminocarboxylic acid-based chelating agents include ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetate, nitrilotriacetic acid, sodium nitrilotriacetate, ammonium nitrilotriacetate, hydroxyethylethylenediaminetriacetic acid, sodium hydroxyethylethylenediaminetriacetate, and diethylenetriaminepentaacetic acid. , Sodium diethylene triamine pentaacetate, triethylene tetramine hexaacetic acid and sodium triethylene tetramine hexaacetate. Examples of the organic phosphonic acid chelating agent include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetrakis (methylenephosphonic acid), and diethylenetriaminepenta (methylenephosphonic acid). 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-methylphosphonic acid Includes nosuccinic acid. Of these, organic phosphonic acid-based chelating agents are more preferred, and particularly preferred are ethylenediaminetetrakis (methylenephosphonic acid) and diethylenetriaminepenta (methylenephosphonic acid). Particularly preferred chelating agents include ethylenediaminetetrakis (methylenephosphonic acid).

  Examples of preservatives and fungicides include isothiazoline preservatives such as 2-methyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, and paraoxybenzoates. Phenoxyethanol and the like.

  Note that the polishing composition disclosed herein may be a one-pack type or a multi-part type including a two-pack type. For example, a solution A containing a part of components (typically components other than water) of the constituents of the polishing composition and a solution B containing the remaining components are mixed to polish a polishing object. It may be configured to be used.

(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), and may be 10.0 or less (typically 0.5 to 10.0). Is also good. From the viewpoints of polishing rate, surface accuracy, and the like, the pH of the polishing composition can be set to 7.0 or less (for example, 0.5 to 7.0), and 5.0 or less (typically 1.0 to 1.0). 5.0), more preferably 4.0 or less (for example, 1.0 to 4.0). The pH of the polishing composition is, for example, 3.0 or less (typically 1.0 to 3.0, preferably 1.0 to 2.0, more preferably 1.0 to 1.8). it can. The above pH can be preferably applied to, for example, a polishing composition for polishing (particularly for primary polishing) a magnetic disk substrate having a nickel phosphorus plating layer.

(Application)
The polishing composition disclosed herein can be preferably applied to, for example, polishing of a magnetic disk substrate (Ni-P substrate) having a nickel phosphorus plating layer on the surface of a base disk. The base disk may be made of, for example, aluminum alloy, glass, glassy carbon, or the like. A disk substrate provided with a metal layer or a metal compound layer other than the nickel phosphorus plating layer on the surface of such a base disk may be used. Among them, it is suitable as a polishing composition for a Ni-P substrate having a nickel phosphorus plating layer on a base disk made of an aluminum alloy. In such an application, it is particularly significant to apply the technology disclosed herein.

  The polishing composition disclosed herein is used in applications where high polishing efficiency is required, such as a preliminary polishing step in a process of manufacturing a polishing object (for example, a magnetic disk substrate) that requires a highly accurate surface after the final polishing step. Can be used in a particularly meaningful way. When a plurality of pre-polishing steps are provided as a pre-step of the final polishing step, the pre-polishing steps can be used, and the same or different polishing compositions can be used in these pre-polishing steps. The polishing composition disclosed herein is suitable, for example, as a polishing composition used in a primary polishing step (first polishing step) of an object to be polished. Above all, it can be preferably used in the first polishing step (primary polishing step) after nickel phosphorus plating in the manufacturing process of the Ni-P substrate.

  The polishing composition disclosed herein has, for example, a surface roughness (arithmetic average roughness (Ra)) of 20 ° or more measured by a laser scan type surface roughness meter “TMS-3000WRC” manufactured by Schmitt Measurement System Inc. It is suitable for use in polishing a magnetic disk substrate of about 300 ° (typically primary polishing) to adjust the surface roughness (arithmetic average roughness (Ra)) of the magnetic disk substrate to 10 ° or less. In such an application, it is particularly significant to apply the technology disclosed herein.

(Polishing liquid)
The polishing composition disclosed herein is typically supplied to an object to be polished (for example, a magnetic disk substrate) in the form of a polishing liquid containing the polishing composition, and used for polishing the object to be polished. The polishing liquid may be, for example, one prepared by diluting a polishing composition (typically, diluting 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 a polishing liquid (working slurry) that is supplied to a polishing target and used for polishing the polishing target, and a concentration that is diluted and used as a polishing liquid. Liquid. Such a polishing composition in the form of a concentrated solution is advantageous from the viewpoints of convenience, cost reduction, and the like during production, distribution, storage, and the like. The concentration ratio can be, for example, about 1.5 to 50 times. From the viewpoint of the storage stability of the concentrate, a concentration ratio of about 2 to 20 times (typically, 2 to 10 times) is appropriate. Further, the polishing composition may be a one-pack type or a multi-pack type including a two-pack type. For example, the polishing composition may be configured such that a liquid A containing a part of the constituent components of the polishing composition and a liquid B containing the remaining components are mixed and used for polishing a polishing object.

  The content of the abrasive grains in the polishing liquid (when a plurality of types of abrasive grains are included, the total content thereof) is not particularly limited, but is typically 5 g / L or more and 10 g / L or more. , And more preferably 30 g / L or more. Increasing the abrasive content tends to achieve higher polishing rates. From the viewpoint of the surface smoothness of the substrate after polishing and the stability of polishing, the content is usually suitably 250 g / L or less, preferably 200 g / L or less, more preferably 150 g / L or less, and still more preferably. Is 100 g / L or less.

  The pH of the polishing liquid can be the same as the pH of the polishing composition described above. If necessary, a pH adjuster such as an organic acid or an inorganic acid can be contained so that the above-mentioned pH is realized in the polishing liquid.

<Polishing process>
The polishing composition disclosed herein can be suitably used for polishing an object to be polished (here, a magnetic disk substrate) in a mode including the following operation, for example. Hereinafter, a preferred embodiment of a method for polishing an object to be polished using the polishing composition disclosed herein will be described.
That is, a polishing liquid (working slurry) containing any of the polishing compositions disclosed herein is prepared. Preparing the polishing liquid may include preparing the polishing liquid by performing operations such as concentration adjustment (for example, dilution) and pH adjustment on the polishing composition. Alternatively, the polishing composition may be used as a polishing liquid as it is.

  Next, the polishing liquid is supplied to the object to be polished and polished by a conventional method. For example, an object to be polished is set in a general polishing apparatus, and a polishing liquid is supplied to the surface of the object to be polished (surface to be polished) through a polishing pad of the polishing apparatus. Typically, while continuously supplying the polishing liquid, a polishing pad is pressed against the surface of the object to be polished, and the two are relatively moved (for example, rotationally moved). Through such a polishing step, polishing of the object to be polished is completed.

  The polishing step as described above can be a part of a manufacturing process of a magnetic disk substrate (for example, a Ni-P substrate). Therefore, according to this specification, there is provided a method of manufacturing a magnetic disk substrate including the above polishing step.

  The polishing composition disclosed herein can be preferably used for a preliminary polishing step (for example, a primary polishing step) of a polishing object. According to this specification, there is provided a method for producing a polished article, which includes a step of performing preliminary polishing using any of the polishing compositions (preliminary polishing compositions) described above. The method for producing a polished object may include a finish polishing step after the preliminary polishing step. The polishing composition (final polishing composition) used in the final polishing step is not particularly limited. For example, a finish polishing composition containing colloidal silica as abrasive grains can be preferably employed. Accordingly, matters disclosed in this specification include a step (1) of polishing a polishing target with a polishing composition containing abrasive grains having the above-mentioned cumulative 90% aspect ratio and the above-mentioned cumulative 75% aspect ratio, and colloidal silica. And a step (2) of polishing the object to be polished using a finish polishing composition containing the above in this order. According to this manufacturing method, a magnetic disk substrate can be manufactured efficiently.

  As described above, in the finish polishing composition containing colloidal silica, the cumulative 90% aspect ratio and the cumulative 75% aspect ratio of the abrasive grains contained in the finish polishing composition are not particularly limited. From the viewpoint of the surface accuracy after the final polishing, the cumulative 90% aspect ratio of the abrasive grains contained in the final polishing composition is smaller than the cumulative 90% aspect ratio of the abrasive grains contained in the preliminary polishing composition. preferable. Further, the cumulative 75% aspect ratio of the abrasive grains contained in the finish polishing composition is preferably smaller than the cumulative 75% aspect ratio of the abrasive grains contained in the preliminary polishing composition.

  In the finish polishing composition containing colloidal silica, the content of colloidal silica is not particularly limited. The content of the colloidal silica is preferably 40% by weight or more, more preferably 50% by weight or more, further preferably 60% by weight or more (for example, 80% by weight) of the total solid content contained in the finish polishing composition. Above). Substantially all (for example, 99% by weight or more) of the solid content contained in the polishing composition may be colloidal silica.

  Finish polishing compositions typically include water in addition to the abrasive grains. In addition, the same component (acid, oxidizing agent, basic compound, various additives, etc.) as the above-mentioned polishing composition can be contained in the final polishing composition as necessary. Although not particularly limited, the pH of the finish polishing composition can be the same as the polishing composition described above. The pH of the finish polishing composition can be, for example, 12.0 or less (typically 0.5 to 12.0), preferably 7.0 or less (eg, 0.5 to 7.0), More preferably, it is 5.0 or less (typically 1.0 to 5.0), and still more preferably 4.0 or less (for example, 1.0 to 4.0). In a preferred embodiment, the pH of the finish polishing composition is 3.0 or less (typically 1.0 to 3.0, preferably 1.0 to 2.0, more preferably 1.0 to 1.8. ).

  Hereinafter, some examples of the present invention will be described, but the present invention is not intended to be limited to those shown in the examples.

<Polishing composition>
A plurality of types of silica particles having different aspect ratios and average particle sizes were prepared. Abrasive grains containing these silica particles alone or in combination, phosphoric acid, 31% hydrogen peroxide solution, and deionized water are mixed to obtain 45 g / L abrasive grains and 12.5 g / phosphoric acid. L, hydrogen peroxide _(H 2 _{O 2)} was prepared polishing composition of examples 1-9 containing 40 g / L. The pH of this polishing composition was 1.5. Table 1 summarizes the types of silica particles used, the cumulative 90% aspect ratio of the abrasive grains, the cumulative 75% aspect ratio, and the volume average particle diameter of the polishing composition according to each example.

  Note that the cumulative 90% aspect ratio and the cumulative 75% aspect ratio of the abrasive grains in each example were determined according to the above-described method based on SEM observation. In addition, the volume average particle diameter is a volume average particle diameter measured by the above method using “Nanotrac Wave-UT151” manufactured by Nikkiso Co., Ltd. as a measurement sample using the abrasive particle-containing liquid containing the abrasive particles of each example.

<Disk polishing>
Polishing of the object to be polished was performed under the following conditions using the polishing composition according to each example as a polishing liquid as it was. As an object to be polished, an aluminum substrate for a hard disk having an electroless nickel phosphorus plating layer on the surface was used. The object to be polished (hereinafter also referred to as "Ni-P substrate") has a diameter of 3.5 inches (a toroidal shape having an outer diameter of about 95 mm and an inner diameter of about 25 mm), a thickness of 1.75 mm, and a surface before polishing. The roughness Ra (arithmetic average roughness of the nickel phosphorus plating layer measured by a laser scanning type surface roughness meter “TMS-3000WRC” manufactured by Schmitt Measurement System Inc.) was 130 °.

[Polishing conditions]
Polishing device: Double-sided polishing machine manufactured by System Seiko Co., Ltd., model "9.5B-5P"
Polishing pad: polyurethane pad manufactured by FILWEL, trade name "CR200"
Number of Ni-P substrates loaded: 15 (5 / carrier x 3 carriers)
Polishing liquid supply rate: 135 mL / min Polishing load: 120 g / cm ²
Upper platen rotation speed: 27 rpm
Lower platen rotation speed: 36 rpm
Sun gear (sun gear) rotation speed: 8 rpm
Polishing amount: Thickness of about 2.2 μm in total on both sides of each substrate

<Polishing rate>
The polishing rate when the Ni—P substrate was polished under the above polishing conditions using the polishing composition according to each example was calculated. The polishing rate was determined based on the following formula.
Polishing rate [μm / min] = Amount of weight loss of substrate by polishing [g] / (substrate area [cm ² ] × density of nickel phosphorus plating [g / cm ³ ] × polishing time [min]) × 10 ⁴
The obtained value was converted to a relative value when the polishing rate of Example 7 was set to 1, and is shown in the column of “polishing rate” in Table 1.

<Long wavelength swell>
Using "Optiflat III" manufactured by KLA Tencor (USA), the arithmetic mean waviness (Wa) of the arithmetic mean waviness (Wa) measured under the condition of a cutoff value of 5 mm in a range of a radius of 20 mm to 44 mm from the center of the polished Ni-P substrate. The value was measured. Then, the obtained measurement value was evaluated as “○” when the measured value was less than 5 °, and “△” when the measured value was 5 ° or more. The results are shown in the column of "Waviness" in Table 1.

  As shown in Table 1, in Examples 1 to 6 using abrasive grains having a cumulative 90% aspect ratio of 1.25 or more and a cumulative 75% aspect ratio of 1.25 or more, Examples 7 to 11 In comparison, better results were obtained with the polishing rate. From these results, according to the polishing composition using abrasive grains having a cumulative 90% aspect ratio of 1.25 or more and a cumulative 75% aspect ratio of 1.25 or more, a high polishing rate can be realized. Was confirmed. Further, comparing Examples 1 to 6, in Examples 2 to 6 using abrasive grains having a cumulative 75% aspect ratio of 1.2 or more and 1.7 or less, a remarkable decrease in surface accuracy (undulation of undulation) was observed as in Example 1. No increase), and showed a high polishing rate. From this, it has been confirmed that according to the polishing composition using abrasive grains having a cumulative 75% aspect ratio of 1.2 or more and 1.7 or less, a high polishing rate and good surface accuracy can be compatible at a high level. Was.

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

Claims (7)

A polishing composition for a magnetic disk substrate comprising abrasive grains and water,
The abrasive grains include at least silica particles,
In the volume-based aspect ratio distribution of the abrasive grains in the polishing composition, the cumulative 90% aspect ratio is 1.25 or more and 3.0 or less , and the cumulative 75% aspect ratio is 1.20 or more and 1.6. The following polishing composition for a magnetic disk substrate.   The polishing composition for a magnetic disk substrate according to claim 1, wherein the abrasive has a volume average particle size of 70 nm or more as measured by a dynamic light scattering method.   The polishing composition for a magnetic disk substrate according to claim 1 or 2, wherein the pH is 5 or less.   The polishing composition for a magnetic disk substrate according to any one of claims 1 to 3, which is used in a step before the final polishing step. A method for manufacturing a magnetic disk substrate, comprising:
A method for manufacturing a magnetic disk substrate, comprising the step (1) of polishing a magnetic disk substrate using the polishing composition for a magnetic disk substrate according to any one of claims 1 to 4.   6. The method of manufacturing a magnetic disk substrate according to claim 5, further comprising, after the step (1), a step (2) of polishing the magnetic disk substrate using a finish polishing composition containing colloidal silica. A method for polishing a magnetic disk substrate, comprising supplying the polishing composition for a magnetic disk substrate according to any one of claims 1 to 4 to a magnetic disk substrate and polishing the magnetic disk substrate.