JP2018174010A - Polishing composition and manufacturing method for magnetic disk substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing composition capable of achieving both a high polishing rate and an undulation reduction.SOLUTION: Provide is a polishing composition which is used for polishing a magnetic disk substrate and containing abrasive grains. In a volume based pore size distribution of the abrasive grains, a difference between a pore diameter PV90 corresponding to an accumulation 90% diameter from a mall-diameter side and a pore diameter PV10 corresponding to an accumulation 10% diameter is 50Å or more and 760Å or less, and a specific surface area conversion particle size by a BET method is 35 nm or more and 100 nm or less.SELECTED DRAWING: None

Description

  The present invention relates to a polishing composition and a method for producing a magnetic disk substrate using the polishing composition.

  Conventionally, a polishing process using a polishing composition is performed on the surface of a material such as a metal, a semimetal, a nonmetal, or an oxide thereof. In this type of polishing process, in general, pre-polishing with more emphasis on polishing efficiency is performed before the final polishing step for finishing the surface accuracy of the final product. In such a polishing process, even in the polishing performed before the final polishing step as in the preliminary polishing, it contributes to the improvement of the surface accuracy in the final polishing step, so it is desirable to realize a good surface state. Patent Documents 1 and 2 are cited as technical documents related to polishing techniques using abrasive grains.

JP 2014-1116057 A Japanese Patent Laying-Open No. 2015-204127

  One of the factors that influence 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 composition using silica as the abrasive grains, the surface quality of the surface to be polished tends to be improved as compared with the polishing composition using abrasive grains such as alumina having higher hardness. However, polishing compositions using abrasive grains such as silica generally tend to be inferior in polishing rate. For example, primary polishing of a magnetic disk substrate (hereinafter also referred to as “nickel phosphorus substrate”) on which nickel phosphorus plating has been applied. When used in polishing where a high polishing rate is required, there is a possibility that such a request cannot be fully met.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a polishing composition capable of achieving both a high polishing rate and surface accuracy. Another related object is to provide a method of manufacturing a magnetic disk substrate using the polishing composition.

  According to the present invention, a polishing composition containing abrasive grains is provided. In the volume-based pore diameter distribution of the abrasive grains measured by the nitrogen gas adsorption method, the difference between the pore diameter PV90 corresponding to the cumulative 90% diameter from the small diameter side and the pore diameter PV10 corresponding to the cumulative 10% diameter. However, it is 50 to 760 mm, and the specific surface area converted particle diameter by the BET method of the abrasive grains is 35 to 100 nm. According to the polishing composition containing abrasive grains satisfying the above characteristics, a high polishing rate and excellent surface accuracy can be achieved at a high level.

  In a preferred embodiment of the polishing composition disclosed herein, the abrasive grains include silica particles. By using silica as the abrasive, the effect of the present invention can be more preferably exhibited.

  The polishing composition disclosed herein is used for polishing a magnetic disk substrate. Among these, a nickel phosphorus substrate is mentioned as a preferable polishing object. When the polishing composition is applied to the magnetic disk substrate, the surface accuracy of the surface of the magnetic disk substrate after polishing is improved, and a high polishing rate can be achieved.

  The polishing composition disclosed here is suitable as a polishing composition used in a pre-process of a final polishing process. 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 particularly useful to be used in a polishing process that requires high polishing efficiency such as the primary polishing.

  The present invention also provides a method for manufacturing a magnetic disk substrate. The manufacturing method includes a step of polishing a magnetic disk substrate using any of the polishing compositions disclosed herein. According to such a manufacturing method, a magnetic disk substrate having a high-quality surface can be manufactured with high productivity.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

<Abrasive>
(Pore size distribution, specific surface area equivalent particle size)
The polishing composition disclosed herein contains abrasive grains. This abrasive grain has a pore diameter PV90 corresponding to a cumulative 90% diameter from a small diameter side and a pore diameter PV10 corresponding to a cumulative 10% diameter from a small diameter side in a volume cumulative pore diameter distribution curve measured by a nitrogen gas adsorption method. The difference PV90-PV10 is 50 to 760 and the specific surface area equivalent particle diameter Dsa is 35 to 100 nm. Here, the “pore diameter PV90” refers to the pore diameter at which the cumulative pore volume from the side where the pore diameter is small becomes 90% in the volume cumulative pore diameter distribution curve. Further, the “pore diameter PV10” refers to the pore diameter at which the cumulative pore volume from the smaller pore diameter side becomes 10% in the volume cumulative pore diameter distribution curve. The volume cumulative pore diameter distribution curve shows that the total volume of pores having a pore diameter of 10 to 1000 mm measured by the nitrogen gas adsorption method is 100%, the horizontal axis is the pore diameter, and the vertical axis is the small pore diameter. It is represented by a graph with cumulative pore volume (%) from the side. The pore diameter is typically a pore diameter when the pore shape is assumed to be cylindrical. The specific surface area equivalent particle diameter Dsa is calculated from the specific surface area measured by the BET method according to the formula: Dsa [nm] = 6000 / (true density [g / cm ³ ] × specific surface area [m ² / g]). This refers to the calculated particle size, and can typically be the average primary particle size of the abrasive grains. For example, when the abrasive grains are silica particles, the specific surface area equivalent particle diameter can be calculated by Dsa = 2727 / specific surface area [m ² / g]. The abrasive grains having the difference PV90-PV10 of 50 to 760 and the specific surface area equivalent particle diameter Dsa of 35 to 100 nm are effective in achieving both a high polishing rate and swell reduction in polishing of the substrate to be polished. Can contribute.

  The reason why the above effects can be obtained is considered as follows, for example. That is, the pore size distribution of the abrasive grains measured by the nitrogen gas adsorption method is obtained from the pore size distribution of the powder obtained from the slurry dried product described later, and the primary particles or a plurality of primary particles in the powder are associated. This is caused by the vacancies existing in the secondary particles, that is, the surface pores of the primary particles and the gaps between the primary particles. The tendency is that the larger the primary particles are, and the more distorted particles are, the larger the gap is. On the other hand, when there are many fine particles filling the gap, the gap is considered to be small. The pore size distribution can serve as an index that can substitute a contribution model to the processing of abrasive grains in the slurry. That is, the pore size distribution in polishing is regarded as one index reflecting the distribution of the action points and the local pressure distribution on the contact surface between the abrasive grains and the surface to be polished from a microscopic viewpoint. Specifically, in an area where abrasive grains that form large pore diameters are processed at a high local pressure with a small number of points of action, a contribution to a high polishing rate can be expected. On the other hand, in areas where abrasive grains that form small pore diameters are processed at a low local pressure at a large number of points of action, it can be expected to contribute to reducing waviness of the polishing substrate. Therefore, it is considered that there is an appropriate pore size distribution for the polishing rate and swell. Further, Dsa can be used as a substitute for the average primary particle diameter as an index indicating the average working point density of the abrasive grains and the working depth of the abrasive grains. Specifically, the lower the Dsa is, the higher the average action point density is, but the average action depth is shallower. The higher the Dsa is, the lower the average action point density is, but the average action depth tends to be deeper. For this reason, it is considered that Dsa also has a region suitable for the polishing rate and the swell. By using an abrasive having a value of the difference PV90-PV10 of 50 to 760 and having a specific surface area equivalent particle diameter Dsa of 35 to 100 nm, the action point distribution, the local pressure distribution, and the average action of the abrasive It is presumed that the point density and the working depth are optimized to achieve both a high polishing rate and a reduction in waviness at a high level. However, it is not limited to this reason.

  From the above viewpoint, the difference PV90-PV10 is preferably 60 mm or more, more preferably 70 mm or more, further preferably 80 mm or more, and particularly preferably 85 mm or more. The difference PV90-PV10 is preferably 745 mm or less, more preferably 740 mm or less. For example, the difference PV90−PV10 may be, for example, 700 mm or less, and typically 650 mm or less.

  The pore diameter PV90 of the abrasive grains is not particularly limited as long as the above difference PV90-PV10 is satisfied. In a preferred embodiment, from the viewpoint of polishing rate and the like, the pore diameter PV90 is 80 mm or more, more preferably 100 mm or more, further preferably 140 mm or more, and particularly preferably 160 mm or more. The pore diameter PV90 may be, for example, 180 mm or more, and typically 195 mm or more. The pore diameter PV90 is usually suitably 950 mm or less, more preferably 900 mm or less, further preferably 850 mm or less, particularly preferably 830 mm or less from the viewpoint of surface quality and the like. For example, a polishing composition containing abrasive grains having a pore diameter PV90 of 195 to 830 mm is suitable.

  The pore diameter PV10 of the abrasive grains is not particularly limited as long as the above difference PV90-PV10 is satisfied. In a preferred embodiment, from the viewpoint of polishing rate and the like, the pore diameter PV10 is 30 mm or more, more preferably 40 mm or more, further preferably 50 mm or more, and particularly preferably 60 mm or more. The pore diameter PV10 is usually suitably 600 mm or less from the viewpoint of surface quality and the like, preferably 550 mm or less, more preferably 500 mm or less, further preferably 480 mm or less, and particularly preferably 445 mm or less. It is. For example, a polishing composition containing abrasive grains having a pore diameter PV10 of 60 to 445 mm is suitable.

  Further, the pore diameter PV50 corresponding to the 50% cumulative diameter from the small diameter side in the volume cumulative pore diameter distribution curve measured by the nitrogen gas adsorption method disclosed herein is not particularly limited. Here, the “pore diameter PV50” refers to the pore diameter at which the cumulative pore volume from the small diameter side where the pore diameter is small becomes 50% in the volume cumulative pore diameter distribution curve. The abrasive according to a preferred embodiment has a pore diameter PV50 of 50 mm or more. By using such abrasive grains, a high polishing rate is realized. The pore diameter PV50 is more preferably 60 mm or more, further preferably 70 mm or more, particularly preferably 80 mm or more, for example 90 mm or more, from the viewpoint of the polishing rate and the like. Further, the pore diameter PV50 of the above-mentioned abrasive grains is usually suitably 900 mm or less from the viewpoint of durability (for example, being hard to collapse due to stress), polishing stability, etc. The following is preferable, 700 Å or less is more preferable, and 630 Å or less is more preferable. For example, a polishing composition containing abrasive grains having a pore diameter PV50 of 90 to 630 mm is suitable.

  The value obtained by dividing the difference PV90-PV10 by the pore diameter PV50, that is, the value of (PV90-PV10) / PV50 is preferably 0.1 or more, more preferably 0.3 or more, from the viewpoint of the polishing rate and the like. More preferably, it is 0.45 or more, and particularly preferably 0.52 or more. The value of (PV90-PV10) / PV50 is preferably 15 or less, more preferably 12 or less, still more preferably 9 or less, particularly preferably 8.3 or less from the viewpoint of obtaining a higher quality surface. is there.

  The pore diameter distribution of the abrasive grains can be adjusted by selecting the abrasive grains to be used or a combination thereof. For example, a plurality of particles having various particle diameters and particle shapes are selected and mixed at an appropriate weight ratio, commercially available abrasive particles are heated, dried, fired, etc. under appropriate conditions, autoclaved, etc. The pore diameter PV90, the pore diameter PV10, and the pores in the above-mentioned pore diameter distribution by subjecting to pressure treatment, mechanical treatment such as crushing and crushing, and surface modification such as chemical modification The diameter PV50 can be adjusted to the appropriate range disclosed herein.

  In the present specification, the pore diameter distribution serving as a reference for the pore diameter PV90, the pore diameter PV10, and the pore diameter PV50 is the pore diameter distribution grasped as an overall characteristic of the abrasive grains contained in the polishing composition. Means. 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 pore size distribution is obtained using the abrasive grains, that is, a mixture of abrasive grains X and Y as a measurement sample. It can be determined by measuring the pore size distribution of the abrasive grains. The pore size distribution of the abrasive grains can be grasped from the pore size distribution of the powder obtained from the dried product of the polishing composition (slurry). Specifically, as a pretreatment, a slurry part containing abrasive grains is adjusted to pH 4 with an ion exchange resin and then dried at 105 ° C. for 24 hours. The obtained powder is further evacuated at 105 ° C. for 90 minutes to obtain a measurement sample. In the nitrogen gas adsorption method, an isotherm obtained by changing the relative pressure between 0 and 1 with an equilibrium interval of 10 seconds using nitrogen gas as the adsorbed gas and liquid nitrogen as the refrigerant is analyzed by the BJH method. Then, the pore size distribution at the time of nitrogen desorption is collected in the range of 10 to 1000 mm. From the volume cumulative pore diameter distribution curve obtained from the results measured here, the values of the pore diameter PV90, the pore diameter PV10, and the pore diameter PV50 can be obtained. The measurement of the pore distribution can be performed using, for example, a pore distribution measuring device manufactured by Micromerex, Inc., trade name “TriStar II 3020”. The same applies to the embodiments described later.

  The specific surface area equivalent particle diameter Dsa of the abrasive grains disclosed herein is usually 100 nm or less. The specific surface area equivalent particle diameter Dsa is suitably 90 nm or less, for example 85 nm or less, typically 80 nm or less. In a preferred embodiment, the specific surface area equivalent particle diameter Dsa of the abrasive grains is 78 nm or less. Abrasive grains having Dsa of a predetermined value or less include fine particles at a ratio of a predetermined value or more. By using such abrasive grains, the waviness can be preferably reduced by the action of fine particles, specifically by miniaturization of processing points on the substrate surface, while obtaining a high polishing rate. The specific surface area equivalent particle diameter Dsa of the abrasive grains is about 35 nm or more, preferably 38 nm or more, more preferably 40 nm or more, still more preferably 42 nm or more, for example 45 nm or more.

(Specific surface area)
The specific surface area of the abrasive grain disclosed here is not particularly limited. Usually, abrasive grains having a specific surface area of 27 m ² / g or more are used. The specific surface area is suitably 30 m ² / g or more, for example 32 m ² / g or more, typically 34 m ² / g or more. The specific surface area of the abrasive is suitably about 78 m ² / g or less, preferably 72 m ² / g or less, more preferably 68 m ² / g or less, and even more preferably 65 m ² / g or less. . The specific surface area can be measured using, for example, a surface area measuring device manufactured by Micromeritex, Inc., a trade name “Flow Sorb II 2300”. The same applies to the embodiments described later.

(Abrasive grain type)
As long as the difference PV90-PV10 is within a predetermined range, the material and properties of the abrasive grains disclosed herein are not particularly limited, and are appropriately selected according to the purpose of use and usage of the polishing composition. can do. As examples of the abrasive grains, any of inorganic particles, organic particles, and organic-inorganic composite particles can be used. Specific examples of the inorganic particles include silica particles, alumina particles, cerium oxide particles, chromium oxide particles, titanium dioxide particles, zirconium oxide particles, magnesium oxide particles, manganese dioxide particles, zinc oxide particles, oxide particles such as bengara particles; Examples thereof include nitride particles such as silicon nitride particles and 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, poly (meth) acrylic acid particles, and polyacrylonitrile particles. Here, (meth) acrylic acid means to generically refer to acrylic acid and methacrylic acid. The said abrasive grain can be used individually by 1 type or in combination of 2 or more types.

(Silica particles)
The polishing composition according to a preferred embodiment includes silica particles as abrasive grains. The silica particles contained in the abrasive grains may be various silica particles mainly composed of silica. Here, the silica particles mainly composed of silica refer to particles in which 90% by weight or more, usually 95% by weight or more, and typically 98% by weight or more of the particles are silica. Examples of silica particles that can be used include, but are not limited to, colloidal silica, precipitated silica, sodium silicate method silica, alkoxide method silica, fumed silica, dry silica, and explosion method silica. Examples of silica particles that can be used further include silica particles obtained using the silica particles as raw materials. Examples of such silica particles include silica particles (hereinafter also referred to as “raw silica”) of the above raw materials, heat treatment such as heating, drying and firing, pressure treatment such as autoclave treatment, pulverization and pulverization, etc. Silica particles obtained by applying one or more treatments selected from mechanical treatment, surface modification and the like may be included. Examples of the surface modification include chemical modification such as introduction of a functional group and metal modification. The abrasive grains in the technology disclosed herein may contain one kind of such silica particles alone or in combination of two or more kinds.

  Examples of the silica particles include silica particles obtained by subjecting raw material silica to heat treatment (hereinafter also referred to as “heat treated silica”), specifically, heated silica particles, dried silica particles, and firing. The silica particles and the like that have been used can be preferably used. Here, the heated silica particles are typically obtained through a treatment for holding in an environment of 60 ° C. or higher and lower than 110 ° C. for a certain time or longer, for example, 15 minutes or longer, typically 30 minutes or longer. Refers to silica particles. The dried silica particles are typically 110 ° C. or higher and lower than 500 ° C., preferably 300 ° C. or higher and lower than 500 ° C., for a certain time or longer, for example, 15 minutes or longer, typically 30 minutes or longer. This refers to silica particles obtained through a holding process. The calcined silica particles (hereinafter also referred to as “calcined silica”) are typically 500 ° C. or higher, preferably 700 ° C. or higher, more preferably 900 ° C. or higher, for a predetermined time or longer, for example 15 It refers to silica particles obtained through a treatment for holding for 30 minutes or more, typically 30 minutes or more. The silica particles obtained through the process of heat-treating any of the raw material silicas described above, that is, precipitated silica, sodium silicate method silica, alkoxide method silica, fumed silica, dry silica, explosion method silica, etc. are referred to herein. It is a typical example included in the concept of heat-treated silica. When the silica abrasive grains contain heat treated silica, the heat treated silica contained in the silica abrasive grains may be one kind or two or more kinds having different production conditions and / or physical properties. The silica abrasive grains may be composed of one or more kinds of heat-treated silica, and contain a combination of heat-treated silica and other silica particles, that is, unheat-treated silica particles. Also good.

  Colloidal silica is mentioned as another suitable example of the silica particle which can be used as a structural component of the silica abrasive grain in the technique disclosed here. Of these, colloidal silica synthesized through particle growth in an aqueous phase, such as sodium silicate method silica and alkoxide method silica, is preferably used. According to the silica abrasive grains containing this type of colloidal silica, a high polishing rate and good surface accuracy can be suitably achieved. When the silica abrasive grain disclosed here contains colloidal silica, the colloidal silica contained in the silica abrasive grain may be one kind or two or more kinds having different production conditions and / or physical properties. . The silica abrasive grains may be composed of one or more colloidal silicas, and include a combination of colloidal silica and other silica particles, that is, silica particles other than colloidal silica. Also good.

  The particle shape of colloidal silica is not particularly limited, and may be, for example, spherical or non-spherical. Specific examples of the non-spherical shape include a peanut shape, a bowl shape, a shape with a protrusion, and a rugby ball shape. The peanut shape can be, for example, the shape of a peanut shell. The shape with protrusions can be, for example, a confetti shape.

The technique disclosed here can be preferably implemented in such a manner that the abrasive grains contained in the polishing composition contain heat treated silica alone or in combination with heat treated silica and other silica particles. Thus, in the aspect in which the silica abrasive grain contains at least heat-treated silica, the content of the heat-treated silica in the silica abrasive grain is not particularly limited.
The technique disclosed here can also be preferably implemented in an embodiment in which the silica abrasive grains contained in the polishing composition contain a combination of heat-treated silica and colloidal silica. By using colloidal silica in addition to heat-treated silica, higher surface accuracy can be realized.

  In the polishing composition disclosed herein, the content of 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, and still more preferably 60% by weight or more based on the total solid content from the viewpoint of easily exerting 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. In the present specification, the solid content contained in the polishing composition refers to a residue, that is, a non-volatile content after water is evaporated 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 does not substantially contain alumina abrasive grains. Examples of the alumina abrasive grains include α-alumina abrasive grains. According to such a polishing composition, quality deterioration due to the use of alumina abrasive grains is prevented. Examples of the deterioration in quality include generation of scratches and dents, residual alumina, and piercing defects in abrasive grains. In the present specification, “substantially free of predetermined abrasive grains, such as alumina abrasive grains” means that the ratio of the abrasive grains in the total amount of solids contained in the polishing composition is preferably 1% by weight or less. Means 0.5 wt% or less, typically 0.1 wt% or less. A polishing composition in which the proportion of alumina abrasive grains is 0% by weight, that is, a polishing composition not containing alumina abrasive grains is particularly preferred. Moreover, the polishing composition disclosed here can be preferably implemented in an embodiment that does not substantially contain α-alumina abrasive grains.

  The polishing composition disclosed herein can also be preferably implemented in an embodiment that does not substantially contain particles other than silica particles, that is, non-silica particles. Here, “substantially free of non-silica particles” means that the proportion of non-silica 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. Means 0.1% by weight or less. In such an aspect, the application effect of the technique 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 water, ion-exchanged water, pure water, ultrapure water, distilled water or the like can be preferably used. The ion exchange 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 wt% to 30.0 wt%. A form in which the solid content is 1.0% by weight to 20.0% by weight is more preferable. The polishing composition can typically be a slurry-like composition.

(acid)
The polishing composition disclosed herein can be preferably implemented in an embodiment containing an acid as a polishing accelerator. Examples of acids that can be suitably used include, but are not limited to, inorganic acids and organic acids. An acid can be used individually by 1 type or in combination of 2 or more types. Examples of the organic acid include organic carboxylic acids having 1 to 10 carbon atoms, organic phosphonic acids, organic sulfonic acids, and amino acids.

  Specific examples of the inorganic acid include phosphoric acid, nitric acid, sulfuric acid, hydrochloric acid, hypophosphorous acid, phosphonic acid, boric acid, sulfamic acid and the like.

  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 (methylenephosphonic 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 preferable.

  When an acid is contained in the polishing composition, the content is not particularly limited. The acid content is usually suitably 0.1% by weight or more, preferably 0.3% by weight or more, more preferably 0.5% by weight or more, for example 1.0% by weight or more. If the acid content is too small, the polishing rate tends to be insufficient, which may be undesirable in practice. The acid content is usually suitably 20.0% by weight or less, preferably 10.0% by weight or less, more preferably 5.0% by weight or less, for example 3.0% by weight or less. When there is too much content of an acid, the surface precision of a grinding | polishing target object will fall easily, and it may be unpreferable practically.

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, and the like of the inorganic acids and organic acids described above. As a metal salt, alkali metal salts, such as lithium salt, sodium salt, potassium salt, are mentioned, for example. Examples of the ammonium salt include quaternary ammonium salts such as tetramethylammonium salt and tetraethylammonium salt. Examples of the alkanolamine salt include a monoethanolamine salt, a diethanolamine salt, and a triethanolamine salt.
Specific examples of the salt include tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate and the like alkali metal phosphates and alkali metals Hydrogen phosphate salt; alkali metal salt of organic acid exemplified above; other alkali metal salt of glutamic acid diacetic acid, alkali metal salt of diethylenetriaminepentaacetic acid, alkali metal salt of hydroxyethylethylenediaminetriacetic acid, 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 contained in the polishing composition disclosed herein, a salt of an inorganic acid such as 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.

  An acid and its salt can be used individually by 1 type or in combination of 2 or more types. In a preferred embodiment of the polishing composition disclosed herein, an acid and a salt of an acid different from the acid can be used in combination. The acid is preferably an inorganic acid. The acid salt is preferably a salt of an inorganic acid.

(Oxidant)
The polishing composition disclosed herein may contain an oxidizing agent as necessary. Examples of oxidizing agents are peroxides, nitric acid or salts thereof, periodic acid or salts thereof, peroxo acids or salts thereof, permanganic acid or salts thereof, chromic acid or salts thereof, oxygen acids or salts thereof, metal salts And sulfuric acids, but are not limited to these. An oxidizing agent can be used individually by 1 type or in combination of 2 or more types. 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, peroxomonosulfuric acid metal salt, peroxodisulfuric acid, peroxodioxide. Ammonium sulfate, peroxodisulfate metal salt, peroxophosphoric acid, peroxosulfuric acid, sodium peroxoborate, performic acid, peracetic acid, perbenzoic acid, perphthalic acid, hypobromite, 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, Examples thereof include iron citrate and ammonium iron sulfate. Examples of preferable oxidizing agents 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.

  When the polishing composition contains an oxidizing agent, the content is preferably 0.1% by weight or more, more preferably 0.3% by weight or more, and still more preferably 0.4% by weight based on the amount of active ingredients. % By weight or more. 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 is lowered, which may be undesirable in practice. Moreover, when an oxidizing agent is included in polishing composition, it is preferable that the content is 3.0 weight% or less on the basis of the amount of active ingredients, More preferably, it is 1.5 weight% or less. When there is too much content of an oxidizing agent, the surface precision of a grinding | polishing target object will fall easily, and it may be unpreferable practically.

(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 composition when added to the polishing 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 and the like. A basic compound can be used individually by 1 type or in combination of 2 or more types.

Specific examples of the alkali metal hydroxide include potassium hydroxide and sodium hydroxide.
Specific examples of the carbonate and bicarbonate include ammonium bicarbonate, ammonium carbonate, potassium bicarbonate, potassium carbonate, sodium bicarbonate, 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, tetrabutylammonium hydroxide; alkali metals of such quaternary ammonium hydroxides Salt; and the like. Examples of the alkali metal salt include sodium salt and potassium salt.
Specific examples of amines include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, monoethanolamine, N- (β-aminoethyl) ethanolamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, 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 alkalis such as tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate. Metal salts are mentioned.
Specific examples of the organic acid salt include potassium citrate, potassium oxalate, potassium tartrate, potassium sodium tartrate, ammonium tartrate and the like.

(Other ingredients)
The polishing composition disclosed herein is a polishing composition such as a surfactant, a water-soluble polymer, a dispersant, a chelating agent, an antiseptic, and an antifungal agent, as long as the effects of the present invention are not significantly hindered. You may further contain the well-known additive which can be used for a thing as needed.

The surfactant is not particularly limited, and any of an anionic surfactant, a nonionic surfactant, a cationic surfactant, and an amphoteric surfactant can be used. By using the surfactant, the dispersion stability of the polishing composition can be improved. Surfactant can be used individually by 1 type or in combination of 2 or more types. The surfactant may typically be a water-soluble organic compound having a molecular weight of less than 1 × 10 ⁴ .
Specific examples of the anionic surfactant include polyoxyethylene alkyl ether acetic acid, polyoxyethylene alkyl sulfate ester, alkyl sulfate ester, polyoxyethylene alkyl sulfate, alkyl sulfate, alkylbenzene sulfonic acid, alkyl phosphate ester, 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, Polyoxyethylene alkyl phenyl ether ammonium 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, benzene sulfonic acid formaldehyde condensate Melamine formalin resin sulfonic acid compound such as melamine sulfonic acid formaldehyde condensate; lignin sulfonic acid compound such as lignin sulfonic acid and modified lignin sulfonic acid; aromatic amino sulfonic acid such as aminoaryl sulfonic acid-phenol-formaldehyde condensate Compounds such as polyisoprene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, polyisoamylene sulfonic acid, polystyrene sulfonic acid; and these Etc. The. As the salt, alkali metal salts such as sodium salt and potassium salt are 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, alkyl alkanolamide and the like. .
Specific examples of the cationic surfactant include alkyltrimethylammonium salt, alkyldimethylammonium salt, alkylbenzyldimethylammonium salt, alkylamine salt and the like.
Specific examples of the amphoteric surfactant include alkyl betaine type, fatty acid amidopropyl betaine type, alkyl imidazole type, amino acid type, alkyl amine oxide type and the like.

  In the polishing composition containing the surfactant, it is appropriate that the content of the surfactant is, for example, 0.0005% by weight or more. The content is preferably 0.001% by weight or more, more preferably 0.002% by weight or more from the viewpoint of the smoothness of the surface after polishing. Further, from the viewpoint of polishing rate and the like, 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 accuracy after polishing can be improved. Examples of water-soluble polymers include polyalkylaryl sulfonic acid compounds such as naphthalene sulfonic acid formaldehyde condensate, methyl naphthalene sulfonic acid formaldehyde condensate, anthracene sulfonic acid formaldehyde condensate; melamine formalin resin sulfone such as melamine sulfonic 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 condensates; other polyisoprene sulfonic acid, polyvinyl sulfonic acid , Polyallylsulfonic acid, polyisoamylenesulfonic acid, polystyrene sulfonate, polyacrylate, polyvinyl acetate, polymaleic acid, polyitaconic acid, polyvinyl Lucol, polyglycerin, polyvinylpyrrolidone, copolymer of isoprenesulfonic acid and acrylic acid, polyvinylpyrrolidone polyacrylic acid copolymer, polyvinylpyrrolidone vinyl acetate copolymer, diallylamine hydrochloride sulfur dioxide copolymer, carboxymethylcellulose, carboxymethylcellulose Salt, hydroxyethyl cellulose, hydroxypropyl cellulose, pullulan, chitosan, chitosan salts and the like. A water-soluble polymer can be used singly or in combination of two or more.

  In the polishing composition containing the water-soluble polymer, it is appropriate that the content of the water-soluble polymer in the polishing liquid is, for example, 0.001% by weight or more. The content is the total content in an embodiment including a plurality of water-soluble polymers. The content is preferably 0.003% by weight or more, more preferably 0.005% by weight or more, and further preferably 0.007% by weight or more from the viewpoint of the surface smoothness of the polished object after polishing. . Further, from the viewpoint of polishing rate and the like, the content is suitably 1.0% by weight or less, preferably 0.5% by weight or less, for example 0.1% by weight or less. In addition, the technique disclosed here can be preferably implemented even in an embodiment in which the polishing composition does not substantially contain a water-soluble polymer.

  Examples of the dispersing agent include polycarboxylic acid-based dispersants such as polycarboxylic acid sodium salt and polycarboxylic acid ammonium salt; naphthalenesulfonic acid-based dispersants such as naphthalenesulfonic acid sodium salt and naphthalenesulfonic acid ammonium salt; Polydisperse dispersants; polyalkylene polyamine dispersants; quaternary ammonium dispersants; alkyl polyamine dispersants; alkylene oxide dispersants; polyhydric alcohol ester dispersants; and the like.

  Examples of chelating agents include aminocarboxylic acid chelating agents and organic phosphonic acid chelating agents. Examples of aminocarboxylic acid chelating agents include ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid sodium, nitrilotriacetic acid, nitrilotriacetic acid sodium, nitrilotriacetic acid ammonium, hydroxyethylethylenediaminetriacetic acid, hydroxyethylethylenediamine sodium triacetate, diethylenetriaminepentaacetic acid Diethylenetriamine sodium pentaacetate, triethylenetetramine hexaacetic acid and sodium triethylenetetramine hexaacetate. 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-methylphospho Nosuccinic acid is included. Of these, organic phosphonic acid-based chelating agents are more preferable, and ethylenediaminetetrakis (methylenephosphonic acid) and diethylenetriaminepenta (methylenephosphonic acid) are particularly preferable. A particularly preferred chelating agent is ethylenediaminetetrakis (methylenephosphonic acid).

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

(Polishing liquid)
The polishing composition disclosed herein is typically supplied to a polishing object in the form of a polishing liquid containing the polishing composition and used for polishing the polishing object. The polishing liquid may be prepared, for example, by diluting a polishing composition. Here, the dilution is typically dilution with water. Or you may use polishing composition as polishing liquid as it is. That is, the concept of the polishing composition in the technology disclosed herein is used as a polishing liquid diluted with a polishing liquid (working slurry) that is supplied to a polishing object and used for polishing the polishing object. Both concentrates are included. Such a polishing composition in the form of a concentrated solution is advantageous from the viewpoints of convenience, cost reduction, etc. during production, distribution, storage and the like. The concentration factor can be set to about 1.5 to 50 times, for example. From the viewpoint of the storage stability of the concentrate, a concentration factor of usually 2 to 20 times, typically about 2 to 10 times is appropriate.

  The content of the abrasive grains in the polishing liquid is not particularly limited, but is typically 0.5% by weight or more, preferably 1.0% by weight or more, and more preferably 2.0% by weight or more. preferable. The above content is the total content thereof when a plurality of types of abrasive grains are included. A higher polishing rate tends to be realized by increasing the content of abrasive grains. From the viewpoint of surface smoothness of the substrate after polishing and polishing stability, the content is usually suitably 25.0% by weight or less, preferably 20.0% by weight or less, more preferably 15.0%. % By weight or less, more preferably 10.0% by weight or less.

(PH)
The pH of the polishing composition disclosed herein is not particularly limited. The polishing composition can have a pH of, for example, 12.0 or less, typically 0.5 to 12.0, or 10.0 or less, typically 0.5 to 10.0. Good. From the viewpoint of polishing rate, surface accuracy, etc., the pH of the polishing composition can be 7.0 or less, for example, 0.5 to 7.0, 5.0 or less, typically 1.0 to 5.0 is more preferable, and 4.0 or less, for example, 1.0 to 4.0 is further preferable. 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. A pH adjusting agent such as an organic acid, an inorganic acid, a basic compound, or the like can be included as necessary so that the above pH is realized in the polishing liquid. The pH can be preferably applied to a polishing composition for polishing a magnetic disk substrate such as a nickel phosphorus substrate. In particular, it can be preferably applied to a polishing composition for primary polishing.

(Multi-drug polishing composition)
The polishing composition disclosed herein may be a one-part type or a multi-part type including a two-part type. For example, a constituent component of the polishing composition, typically, a liquid A containing a part of components other than water and a liquid B containing the remaining components are mixed to polish a polishing object. It may be configured to be used. The multi-component polishing composition according to a preferred embodiment is composed of a liquid A containing abrasive grains and a liquid B containing components other than abrasive grains. The liquid A containing abrasive grains may further contain a dispersant. Examples of components other than the abrasive grains contained in the liquid B include acids, water-soluble polymers, and other additives. They are usually stored separately prior to use and can be mixed at the time of use. The term “in use” as used herein can be typically a time of polishing a substrate to be polished. During 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 a C liquid constituting the multi-drug polishing composition.

  The polishing composition disclosed herein can be preferably applied to polishing, for example, a nickel phosphorus substrate, a glass substrate, a carbon substrate, and the like. Further, the plating substrate may be a disk substrate provided with a metal layer or a metal compound layer other than the nickel phosphorus plating layer on the surface of the base disk. Especially, it is suitable as a polishing composition for nickel phosphorus plating substrates having a nickel phosphorus plating layer on a base disk made of aluminum alloy. In such applications, it is particularly meaningful to apply the technology disclosed herein.

  The polishing composition disclosed herein is particularly significant in applications requiring high polishing efficiency, such as a preliminary polishing step in a magnetic disk substrate manufacturing process that requires a highly accurate surface after a final polishing step. Can be used. In the case of having a plurality of preliminary polishing steps as a pre-step of the final polishing step, it can be used for any preliminary polishing step, and the same or different polishing composition can be used in these preliminary polishing steps. The polishing composition disclosed herein is suitable as a polishing composition used in, for example, a primary polishing process of a magnetic disk substrate, that is, an initial polishing process. Especially, in the manufacturing process of a nickel phosphorus substrate, it can be preferably used in the first polishing step after nickel phosphorus plating, that is, the primary polishing step.

  The polishing composition disclosed herein, for example, polishes a magnetic disk substrate having a surface roughness measured by a laser scanning surface roughness meter “TMS-3000WRC” manufactured by Schmitt Measurement System Inc. of about 20 to 300 mm. Thus, it is suitable for use in adjusting the surface roughness of the magnetic disk substrate to 10 mm or less. In such applications, it is particularly meaningful to apply the technology disclosed herein. The surface roughness as used herein refers to arithmetic average roughness (Ra).

<Polishing process>
The polishing composition disclosed herein can be suitably used for polishing using a magnetic disk substrate as an object to be polished, for example, in an embodiment including the following operations. Hereinafter, a preferred embodiment of a method for polishing a polishing object using the polishing composition disclosed herein will be described. Hereinafter, the object to be polished is also referred to as a substrate to be polished.
That is, a polishing liquid (working slurry) containing any of the polishing compositions disclosed herein is prepared. Preparing the polishing liquid may include preparing a polishing liquid by adding operations such as concentration adjustment and pH adjustment to the polishing composition. Examples of the concentration adjustment include dilution. Or you may use polishing composition as 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, that is, the surface to be polished, through a polishing pad of the polishing apparatus. Typically, while supplying the above-mentioned polishing liquid continuously, a polishing pad is pressed against the surface of the object to be polished to move both relatively. The movement can be a rotational movement, for example. The polishing of the object to be polished is completed through this polishing step.

  The polishing process as described above can be part of a manufacturing process for a magnetic disk substrate, such as a nickel phosphorous substrate. Therefore, according to this specification, a manufacturing method and a polishing method of a magnetic disk substrate including the polishing step are provided.

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

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

<Examples 1-12>
[Preparation of polishing composition]
Plural types of silica particles having different pore diameters PV10, PV50, and PV90 were prepared. Polishing compositions of Examples 1 to 12 were prepared by mixing these silica particles, phosphoric acid, 31% hydrogen peroxide water, and deionized water. The content of abrasive grains in the polishing composition was 4.5% by weight, and the content of 31% hydrogen peroxide water was 4.0% by weight. The content of phosphoric acid in the polishing composition was such that the polishing composition had a pH of 1.5. Table 1 shows the pore diameter PV10, pore diameter PV50, pore diameter PV90, PV90-PV10, specific surface area, and specific surface area converted particle diameter of the abrasive grains used in each example.

[Disk polishing]
The polishing composition according to each example was used as it was for the polishing liquid, and the polishing object was polished under the following conditions. As an object to be polished, an aluminum substrate for hard disk having an electroless nickel phosphorus plating layer on the surface was used. The substrate had a donut shape with a diameter of 3.5 inches, an outer diameter of about 95 mm, and an inner diameter of about 25 mm, a thickness of 1.75 mm, and a surface roughness Ra before polishing of 130 mm. The surface roughness Ra is an arithmetic average roughness of the nickel phosphorus plating layer measured by a laser scan surface roughness meter “TMS-3000WRC” manufactured by Schmitt Measurement System Inc.

(Polishing conditions)
Polishing device: Double-side polishing machine manufactured by System Seiko Co., Ltd.
Polishing pad: Polyurethane pad manufactured by FILWEL, trade name “CR200”
Number of substrates to be polished: 15 (3 / carrier x 5 carriers)
Polishing liquid supply rate: 135 mL / min Polishing load: 120 g / cm ²
Upper platen rotation speed: 27rpm
Lower platen rotation speed: 36rpm
Sun gear (sun gear) rotation speed: 8rpm
Polishing amount: about 2.2 μm in total on both sides of each substrate

[Polishing rate]
The polishing rate when the polishing target 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 calculation formula.
Polishing rate [μm / min] = Reduction in weight of substrate by polishing [g] / (Substrate area [cm ² ] × Nickel phosphorus plating density [g / cm ³ ] × Polishing time [min]) × 10 ⁴
The obtained value is converted into a relative value when the polishing rate of Example 2 is 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 value of the arithmetic average waviness (Wa) measured under the condition of a cutoff value of 5 mm in a radius range of 20 mm to 44 mm from the center of the substrate after polishing was measured. did. The obtained value is converted into a relative value when the arithmetic average waviness (Wa) of Example 2 is 1, and is shown in the “waviness” column of Table 1.

  As shown in Table 1, Examples 1 to 1 using abrasive grains having a difference between the pore diameter PV90 and the pore diameter PV10 of 50 to 760 and a specific surface area equivalent particle diameter of 35 to 100 nm The polishing composition of No. 7 was able to achieve both a high polishing rate and a reduction in waviness at a high level as compared with Examples 8-12. From this result, it can be seen that according to the technique disclosed herein, a high polishing rate and a reduction in waviness can be achieved at a high level.

  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 changes of the specific examples illustrated above.

Claims (4)

A polishing composition containing abrasive grains,
In the volume-based pore diameter distribution of the abrasive grains, the difference between the pore diameter PV90 corresponding to the cumulative 90% diameter from the small diameter side and the pore diameter PV10 corresponding to the cumulative 10% diameter is 50 mm or more and 760 mm or less. ,
A polishing composition used for polishing a magnetic disk substrate, wherein the abrasive grain has a specific surface area converted particle diameter by BET method of 35 nm or more and 100 nm or less.   The polishing composition according to claim 1, wherein the abrasive grains include silica particles.   The polishing composition according to claim 1 or 2, which is used in a pre-process of a final polishing process.   A method for manufacturing a magnetic disk substrate, comprising a step of polishing the magnetic disk substrate using the polishing composition according to claim 1.