JP6572082B2 - Polishing composition for magnetic disk substrate, method for producing 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 producing a magnetic disk substrate using the polishing composition, and a magnetic disk substrate produced by the method.

  In the manufacture of a magnetic disk substrate, in general, preliminary polishing (primary polishing) with an emphasis on polishing efficiency is performed before the final polishing step (finish polishing) performed to finish the surface accuracy of the final product. For example, a highly accurate surface can be efficiently realized by performing at least preliminary polishing and final polishing on a disk substrate (Ni-P substrate) subjected to nickel phosphorus plating. 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.

  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, a polishing liquid using silica as an abrasive grain improves surface quality of the surface to be polished (for example, defects due to surface smoothness or abrasive piercing) compared to a polishing liquid using abrasive grains such as alumina with higher hardness. Tend to. Patent documents 1-4 are mentioned as technical literature about polish technology which uses silica as an abrasive grain.

Japanese Patent Laid-Open No. 2006-026885 JP 2010-016344 A JP 2001-269857 A JP-A-61-136909

However, generally, a polishing liquid using silica abrasive grains tends to be inferior in polishing efficiency (typically a polishing rate). For example, primary polishing of a magnetic disk substrate (Ni-P substrate) plated with nickel phosphorus is used. When used in polishing that requires a high polishing rate, there is a possibility that such a request cannot be fully met.
This invention is made | formed in view of such a situation, Comprising: It aims at providing the polishing composition for magnetic disk substrates which can exhibit a high polishing rate using the abrasive grain containing a silica particle. 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 is a polishing composition for a magnetic disk substrate that is supplied to the magnetic disk substrate and used for polishing the magnetic disk substrate. This polishing composition contains abrasive grains and water. The abrasive grains include at least silica particles. The volume average particle diameter of the abrasive grains in the polishing composition is Da, and the volume average particle diameter of the abrasive grains after a standard polishing test for polishing a nickel phosphorus plating substrate using the polishing composition is Db. The particle diameter change rate X calculated by the following formula: X = (Db / Da) × 100; is 80% or more and 115% or less. According to the polishing composition containing such abrasive grains, a high polishing rate can be realized.

  In the polishing composition disclosed herein, the particle diameter change rate X is preferably 90% or more. According to such a polishing composition, a higher quality surface can be realized while maintaining a high polishing rate.

  The polishing composition disclosed herein preferably has a pH of 5 or less. When the abrasive having the particle diameter change rate X is used in a polishing composition having such a pH, the effects of the present invention can be more suitably exhibited.

  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 useful to be used in a polishing process that requires high polishing efficiency such as the primary polishing.

  A preferred application object of the polishing composition disclosed herein is a magnetic disk substrate (Ni-P substrate) on which nickel phosphorus plating has been applied. 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 primary polishing of a magnetic disk substrate on which nickel phosphorous plating has been performed.

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

  The method of manufacturing the magnetic disk substrate may further include a step (2) of polishing the magnetic disk substrate using a final polishing composition containing colloidal silica after the step (1). 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 magnetic disk substrate polishing compositions disclosed herein is supplied to the magnetic disk substrate to polish the magnetic disk substrate. According to this polishing method, the magnetic disk substrate can be polished efficiently.

  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>
The polishing composition disclosed herein is a polishing composition for a magnetic disk substrate (preferably for primary polishing) that is supplied to a magnetic disk substrate and used for polishing the magnetic disk substrate, and includes an abrasive containing silica particles. Contains grains. The abrasive grains have little change in particle diameter before and after polishing. That is, the volume average particle diameter of the abrasive grains in the polishing composition is Da, and the volume average particle diameter of the abrasive grains after a standard polishing test for polishing a nickel phosphorus plating substrate using the polishing composition is Db,
The following formula: X = (Db / Da) × 100;
The particle diameter change rate X calculated by the above is 80% or more and 115% or less. As a result, a high polishing rate can be realized.

In the present specification, the particle diameter change rate X of the abrasive grains is determined by performing a standard polishing test on the nickel phosphorus plated substrate under the following polishing conditions using the polishing composition as a polishing liquid as it is before and after polishing. A value calculated based on the above formula from the volume average particle diameters Da and Db of the abrasive grains is employed.
[Polishing conditions]
Polishing device: Double-side polishing machine manufactured by System Seiko Co., Ltd., model “9.5B-5P”
Polishing pad: Polyurethane pad manufactured by FILWEL, trade name “CR200”
Number of inserted Ni-P substrates: 15 (5 / carrier x 3 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 2.2μm in total on both sides of each substrate
Polishing object: Nickel phosphorus plating substrate (diameter 3.5 inches, thickness 1.75 mm)

  The volume average particle diameters Da and Db of the abrasive grains can be grasped by measuring the particle diameter based on the dynamic light scattering method. As a specific procedure, the polishing liquid (polishing composition) used in the standard polishing test and the polishing waste liquid collected after polishing are used as measurement samples. Irradiate the measurement sample with laser light, adjust the scattering intensity suitable for measurement while diluting the measurement sample with phosphoric acid aqueous solution or sodium hydroxide aqueous solution having the same pH as the measurement sample, and then detect the scattered light Thus, the particle diameter is measured. 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.

  The particle diameter change rate X of the abrasive grains is generally 80% or more and 115% or less, preferably 85% or more and 110% or less, more preferably 90% or more and 110% or less. By setting the particle diameter change rate X to 80% or more and 115% or less, the polishing rate can be improved better. The reason why such an effect is obtained is not particularly limited, but may be considered as follows, for example. That is, in polishing using abrasive grains having a large or small particle diameter change rate X before and after polishing, some of the stress (energy) that may be generated by friction between the particles and the substrate surface may be agglomeration between particles or chipping of particles. This makes it difficult to transmit stress to the substrate surface. On the other hand, the abrasive grains having a particle diameter change rate X before and after polishing of 80% or more and 115% or less are less likely to agglomerate particles or chip during the polishing. It can transmit stress more effectively. This is considered to contribute to the improvement of the polishing rate.

  The particle diameter change rate X of the abrasive grains is, for example, that the material of the abrasive grains contained in the polishing composition is changed, or when the abrasive grains are a mixture of two or more kinds of abrasive grains, the material and content thereof It can also be adjusted by changing the ratio. For example, the silanol group density of silica particles is thought to affect the aggregation of silica particles due to dehydration condensation polymerization, but it also acts as a site that controls electrostatic interactions, so interactions between particles and polishing by-products It is thought that it will also affect. That is, the change in the particle size before and after polishing differs depending on the silanol group density of the silica particles and the material. Therefore, the particle diameter change rate X described above can be adjusted to an appropriate range disclosed herein by appropriately selecting the ratio of the material and content of abrasive grains contained in the polishing composition. In a preferred embodiment, the abrasive grains contained in the polishing composition are a mixture of small diameter particles having a high silanol group density and large diameter particles having a low silanol group density. In this way, changes in the particle diameter before and after polishing can be suppressed, and good workability can be imparted.

  The volume average particle diameter Da of the abrasive grains in the polishing composition is not particularly limited as long as the particle diameter change rate X is satisfied with the Db, but from the viewpoint of the polishing rate and the like, preferably 100 nm or more, More preferably, it is 200 nm or more, More preferably, it is 300 nm or more, Most preferably, it is 350 nm or more. The upper limit of the volume average particle diameter Da of the abrasive grains is not particularly limited, but is preferably 600 nm or less, more preferably 500 nm or less, and still more preferably 400 nm or less from the viewpoint of obtaining a higher quality surface. Further, the difference (| Da−Db |) between Da and Db is preferably 100 nm or less, more preferably 50 nm or less, still more preferably 40 nm or less, and particularly preferably 10 nm or less.

  The volume average particle diameter Db of the abrasive grains after the standard polishing test is not particularly limited as long as the relationship of the particle diameter change rate X with the Da is satisfied, but is preferably 80 nm from the viewpoint of the polishing rate and the like. More preferably, it is 150 nm or more, more preferably 300 nm or more, and particularly preferably 350 nm or more. Further, the volume average particle diameter Db after polishing of the abrasive grains is preferably 700 nm or less, more preferably 600 nm or less, and further preferably 400 nm or less, from the viewpoint of obtaining a higher quality surface.

  Preferred examples of the abrasive grains disclosed herein are those having a volume average particle diameter Da of 100 nm to 600 nm and a volume average particle diameter Db of 80 nm to 700 nm; a volume average particle diameter Da of 200 nm to 500 nm. The volume average particle diameter Db is 180 nm or more and 550 nm or less; the volume average particle diameter Da is 300 nm or more and 400 nm or less, and the volume average particle diameter Db is 280 nm or more and 430 nm or less; etc. Is mentioned.

  As said abrasive grain, that whose number average aspect ratio is 1.4 or less can be used, for example. By reducing the number average aspect ratio, the surface accuracy after polishing can be improved. The number average aspect ratio of the abrasive grains is preferably 1.3 or less, more preferably 1.2 or less, and still more preferably 1.1 or less, from the viewpoint of obtaining a surface with further reduced waviness. Further, the number average aspect ratio of the abrasive grains is 1.0 or more in principle, and is suitably 1.01 or more from the viewpoint of the polishing rate, preferably 1.04 or more. For example, a polishing composition containing abrasive grains having a number average aspect ratio of 1.01 to less than 1.2 (more preferably 1.04 to less than 1.1) is suitable. In addition, when the abrasive grains are a mixture of two or more kinds of abrasive grains, it is also preferable that at least one abrasive grain having a number average aspect ratio of 1.25 to 1.40 is included. For example, silica particles having a heat-treated number average aspect ratio of 1.25 or more are less likely to be chipped during processing, and can serve as abrasive grains imparting good processability.

  The number average aspect ratio of the abrasive grains can be grasped by, for example, observation with an electron microscope. As a specific procedure for grasping the number average aspect ratio, for example, a minimum number circumscribing each particle image of a predetermined number (for example, 200) of abrasive particles capable of recognizing the shape of independent particles using SEM. Draw a rectangle. For the rectangle drawn for each particle image, the value obtained by dividing the length of the long side (major axis value) by the length of the short side (minor axis value) is the major axis / minor axis ratio (aspect ratio). ). The number average aspect ratio can be obtained by arithmetically averaging the aspect ratios of the predetermined number of particles.

  The average primary particle diameter of the abrasive is preferably 10 nm or more, more preferably 20 nm or more, still more preferably 30 nm or more, and particularly preferably 35 nm or more. Higher polishing rates can be achieved by increasing the average primary particle size. Further, from the viewpoint of obtaining a surface with higher surface accuracy, the average primary particle diameter is preferably 150 nm or less, more preferably 100 nm or less, still more preferably 80 nm or less, and particularly preferably 60 nm or less.

In the technology disclosed herein, the average primary particle diameter of the abrasive grains refers to the average particle diameter determined based on the BET method. For example, when the abrasive grains are silica abrasive grains (that is, abrasive grains made of silica particles), the average primary particle diameter of the silica abrasive grains is D1 (nm) from the specific surface area S (m ² / g) measured by the BET method. ) = (6000 / 2.2) / S. In this equation, 2.2 is the value of the specific gravity of silica, which is the particle diameter as silica. The specific surface area can be measured using, for example, a surface area measuring device manufactured by Micromeritex Corporation, a trade name “Flow Sorb II 2300”.

  The silica particles contained in the abrasive grains may be various silica particles mainly composed of silica. Here, silica particles containing silica as a main component refer to particles in which 90% by weight or more (usually 95% by weight or more, typically 98% by weight or more) of the particles is 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 obtained by using the above silica particles (that is, precipitated silica, sodium silicate silica, alkoxide silica, fumed silica, dry silica, explosive silica, etc.) as raw materials. 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 firing, pressure treatment such as autoclave treatment, pulverization and pulverization ( Includes silica particles obtained by applying one or more treatments selected from mechanical treatment such as crushing), surface modification (for example, introduction of functional groups, chemical modification such as metal modification), etc. obtain. 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.

  For example, silica particles obtained by subjecting raw material silica to heat treatment, specifically, heated silica particles, dried silica particles, baked silica particles, and the like 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 predetermined time or longer (for example, 15 minutes or longer, typically 30 minutes or longer). This refers to the produced silica particles. The dried silica particles are typically 110 ° C. or more and less than 500 ° C. (preferably 300 ° C. or more and less than 500 ° C.) for a certain period of time (for example, 15 minutes or more, typically 30 minutes). The above refers to silica particles obtained through the holding treatment. The fired silica particles (hereinafter also referred to as “fired silica”) are typically held in an environment of 500 ° C. or higher for a predetermined time or longer (for example, 15 minutes or longer, typically 30 minutes or longer). This refers to silica particles obtained through the treatment. The silica particles obtained through the process of heat-treating any of the above-described raw material silicas (precipitated silica, silica silicate method silica, alkoxide method silica, fumed silica, dry silica, explosive method silica, etc.) It is a typical example included in the concept of silica.

  In a preferred embodiment, the abrasive grains contained in the polishing composition contain heat-treated silica alone, or contain heat-treated silica and other silica particles. Thus, in the aspect in which an abrasive grain contains a heat-processed silica at least, content of the heat-processed silica in an abrasive grain is not specifically limited. The content of the 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 40% by weight or more from the viewpoint of the polishing rate. is there. The upper limit of the content of 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 (for example, polishing rate, waviness 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), more preferably 60% by weight or less.

  In a preferred embodiment, heat-treated silica and colloidal silica are used in combination as abrasive grains contained in the polishing composition. By using colloidal silica in addition to heat-treated silica, a high polishing rate and good surface accuracy can be achieved at a high level.

In a preferred embodiment, the polishing composition contains silica abrasive grains (that is, abrasive grains made of silica particles), and the average silanol group density of the silica abrasive grains is 1.25 / nm ² or less. Here, the silanol group density means the number of silanol groups per 1 nm ² of the surface area of the silica particles. The silanol group density (hereinafter sometimes referred to as “SD”) is calculated from the specific surface area (BET specific surface area) of silica particles measured by the BET method and the amount of silanol groups measured by titration. The More specifically, the SD of silica particles is measured according to the following silanol group density measurement method.

[Silanol group density measurement method]
A dispersion containing 1% by weight of silica particles is adjusted to pH 3.5 to 3.8 with hydrochloric acid, and then adjusted to pH 4.0 with a 0.1 mol / L aqueous sodium hydroxide solution as a titration sample. . The titration sample is titrated in a pH 4.0 to pH 9.0 range using a 0.1 mol / L sodium hydroxide aqueous solution. From the titration amount and the BET specific surface area of the silica particles, The silanol group density [number / nm ² ] is calculated.

Further, in this specification, the average silanol group density (hereinafter sometimes referred to as “SD _AVE ”) of the silica abrasive grains is the overall silica abrasive grains contained in the polishing composition disclosed herein. It means silanol group density (SD) grasped as a characteristic. When the silica abrasive grains contained in the polishing composition are, for example, a mixture of two types of silica particles X and Y, SD _AVE uses the silica abrasive grains (that is, a mixture of silica particles X and Y) as a measurement sample. It can obtain | require by applying the silanol group density measuring method. Also, usually, at least as a practically sufficient approximate value, the SD of each component (here, silica particles X and Y) constituting the silica abrasive grains and the weight of the silica particles X and Y in the silica abrasive grains A value calculated from the ratio can be adopted as SD _AVE . The same applies when the silica abrasive grains contained in the polishing composition are a mixture of three or more types of silica particles.

In the embodiment in which the silica abrasive grains contain two or more types of silica particles, the SD of the silica particles for each type is not particularly limited, and the SD _{AVE of} silica abrasive grains containing these silica particles in an appropriate weight ratio is in the desired range. Any SD can be obtained. From the viewpoint of dispersion stability and the like, usually, silica particles having SD of 0.3 particles / nm ² or more can be preferably used. From the viewpoint of obtaining a polished surface with higher accuracy, SD is 0.4 pieces / nm ² or more (more preferably 0.5 pieces / nm ² or more, for example, 0.6 pieces / nm ² or more, and further 0.7 pieces. / Nm ² or more) can be preferably used. Further, since it is easy to realize the preferred SD _AVE disclosed herein, the SD is usually 10 / nm ² or less (preferably 5 / nm ² or less, more preferably 2.5 / nm ² or less. For example, 2.0 particles / nm ² or less) can be preferably used. From the viewpoint of polishing rate, etc., SD can be preferably used silica particles of 1.5 / nm ² or less (more preferably 1.3 pieces / nm ² or less, for example 1.25 / nm ² or less). SD may be used silica particles of 1.1 pieces / nm ² or less (e.g., 1.0 pieces / nm ² or less).

In the technology disclosed herein, the silica abrasive grains include silica particles K and silica particles L, and the silanol group density (SD _K ) of the silica particles _K is lower than the silanol group density (SD _L ) of the silica particles L. Can be preferably implemented. In such embodiments, SD _K is, for example, less than 1.25 / nm ^2, is usually preferably 1.2 pieces / nm ² or less, preferably 1.1 pieces / nm ² or less, more preferably 1.05 Pieces / nm ² or less. SD _K can be preferably used silica particles K is less than 1.0 pieces / nm ² (eg 0.9 / nm ² or less). The silica particles L, can be suitably used SD _L is, for example, 1.0 pieces / nm ² or more. Polishing compositions disclosed herein, SD _L is 1.1 pieces / nm ² or more (e.g., 1.2 pieces / nm ² or more) of silica particles L are preferably implemented in a manner that use of a high polishing rate and Good surface accuracy can be achieved in a well-balanced manner.

  The polishing composition disclosed herein may contain particles other than silica particles as abrasive grains having the particle diameter change rate X. 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 alumina particles, cerium oxide particles, chromium oxide particles, titanium dioxide particles, zirconium oxide particles, magnesium oxide particles, manganese dioxide particles, zinc oxide particles, bengara particles, etc .; 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 is a generic term for acrylic acid and methacrylic acid). And polyacrylonitrile particles. These particles other than silica particles can be used singly or in combination of two or more.

  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 (eg 99% by weight or more). The silica particles may be substantially all of the solid content contained in the polishing composition.

  The polishing composition disclosed herein can be preferably implemented in an embodiment that is substantially free of alumina abrasive grains (for example, α-alumina abrasive grains). According to such a polishing composition, deterioration in quality due to the use of alumina abrasive grains (for example, generation of scratches and dents, residual alumina, abrasive sticking defects, etc.) is prevented. In the present specification, “substantially free of predetermined abrasive grains (for example, alumina abrasive grains)” means that the ratio of the abrasive grains in the total amount of solids contained in the polishing composition is 1% by weight or less (more preferably Is 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 (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 5% by weight or less (more preferably 1% by weight or less, typically 0). .5% by weight or less). In such an aspect, the application effect of the technique disclosed herein can be suitably exhibited.

  The content of abrasive grains in the polishing composition (in the case where plural kinds 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. It is preferable that it is 30 g / L or more. A higher polishing rate tends to be realized by increasing the content of abrasive grains. From the viewpoint of the surface smoothness of the substrate after polishing and the stability of polishing, the content of the abrasive grains is usually suitably 250 g / L or less, preferably 200 g / L or less, more preferably 150 g / L or less. More preferably, it is 100 g / L or less.

<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 exchange water (deionized water), pure water, ultrapure water, distilled water and the like can be preferably used.

  The polishing composition disclosed herein (typically a slurry-like composition) is preferably implemented, for example, in a form in which its non-volatile content (NV) is 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 an embodiment containing 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, etc.). It is not limited. An acid can be used individually by 1 type or in combination of 2 or more types.

  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 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). 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 100 g / L or less, preferably 50 g / L or less, more preferably 30 g / L or less (for example 15 g / L 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 (for example, alkali metal salts such as lithium salt, sodium salt and potassium salt) and ammonium salts (for example, tetramethylammonium salt and tetraethylammonium salt) of the inorganic acids and organic acids described above. Quaternary ammonium salts), alkanolamine salts (for example, monoethanolamine salts, diethanolamine salts, triethanolamine salts) and the like.
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 (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.

  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 (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 may contain an oxidizing agent as necessary. Examples of the oxidizing agent include peroxide, nitric acid or a salt thereof, peroxo acid or a salt thereof, permanganic acid or a salt thereof, chromic acid or a salt thereof, oxygen acid or a salt thereof, metal salt, sulfuric acid, and the like. However, it is 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, peroxodisulfuric acid, ammonium peroxodisulfate, 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 Examples thereof include acid, sodium hypochlorite, calcium hypochlorite, potassium permanganate, metal chromate, metal dichromate, iron chloride, iron sulfate, iron citrate, and iron iron sulfate. Preferable 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, the content thereof is preferably 1 g / L or more, more preferably 3 g / L or more, and further preferably 4 g / L or more, based on the amount of 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 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 30 g / L or less on the basis of the amount of active ingredients, More preferably, it is 15 g / L 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 (for example, sodium salt, potassium salt); and the like.
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) within a range that does not significantly impair the effects of the present invention. For example, you may further contain the well-known additive which can be used for the polishing composition for magnetic disk substrates like a Ni-P board | substrate etc. 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 a surfactant (typically a water-soluble organic compound having a molecular weight of less than 1 × 10 ⁴ ), 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.
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 amphoteric surfactants include alkyl betaines and alkyl amine oxides.

  In the polishing composition containing the 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. Further, from the viewpoint of 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 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; Others, 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 including the water-soluble polymer, the content of the water-soluble polymer in the polishing liquid (in the embodiment including a plurality of water-soluble polymers, the total content thereof) is, for example, 0.01 g / L or more is appropriate. The content is preferably 0.05 g / L or more, more preferably 0.08 g / L or more, and still more preferably 0.0, from the viewpoint of the surface smoothness of an object to be polished (for example, a magnetic disk substrate) after polishing. 1 g / L or more. Further, from the viewpoint of polishing rate and the like, the content is suitably 10 g / L or less, preferably 5 g / L or less, for example 1 g / L 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.

  The polishing composition disclosed herein may be a one-part type or a multi-part type including a two-part type. For example, the A liquid containing a part of the constituents of the polishing composition (typically components other than water) and the B liquid containing the remaining components are mixed to polish the 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 can be, for example, 12.0 or less (typically 0.5 to 12.0), and 10.0 or less (typically 0.5 to 10.0). Also 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), and is 5.0 or less (typically 1.0 to 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 pH can be preferably applied to, for example, a polishing composition for polishing (particularly primary polishing) of a magnetic disk substrate having a nickel phosphorus plating layer.

(Use)
The polishing composition disclosed herein can be preferably applied to polishing of a magnetic disk substrate (Ni-P substrate) having a nickel phosphorus plating layer on the surface of a base disk, for example. The base disk can be made of, for example, aluminum alloy, glass, glassy carbon, or the like. A disk substrate provided with a metal layer or metal compound layer other than the nickel phosphorus plating layer on the surface of such a base disk may be used. Especially, it is suitable as a polishing composition for Ni-P board | substrates which have a nickel phosphorus plating layer on the base material disk made from an aluminum alloy. In such applications, it is particularly meaningful 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 manufacturing process of an abrasive (for example, a magnetic disk substrate) that requires a highly accurate surface after the final polishing step. Can be used with particular significance. When having a plurality of preliminary polishing steps as a pre-process 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 step (first polishing step) of an object to be polished. Especially, in the manufacturing process of a Ni-P board | substrate, it can be preferably used in the first grinding | polishing process (primary grinding | polishing process) after nickel phosphorus plating.

  The polishing composition disclosed herein has, for example, a surface roughness (arithmetic average roughness (Ra)) measured by a laser scanning surface roughness meter “TMS-3000WRC” manufactured by Schmitt Measurement System Inc. of 20 μm to 20 μm. It is suitable for applications in which a magnetic disk substrate of about 300 mm is polished (typically primary polishing) and the magnetic disk substrate is adjusted to a surface roughness (arithmetic average roughness (Ra)) of 10 mm or less. In such applications, it is particularly meaningful to apply the technology disclosed herein.

(Concentrated liquid)
The polishing composition disclosed herein may be in a concentrated form (that is, in the form of a polishing liquid concentrate) before being supplied to the magnetic disk substrate. The thus-concentrated polishing composition (concentrated liquid) is advantageous from the viewpoints of convenience, cost reduction, etc. during production, distribution, storage, and the like. The concentration factor can be, for example, about 1.5 to 50 times in terms of volume, and usually about 2 to 20 times is appropriate. Such concentrated liquid can be used in such a manner that a polishing composition (polishing liquid) is prepared by diluting at a desired timing and the polishing liquid is supplied to the magnetic disk substrate. The dilution can be typically performed by adding water to the concentrated solution and mixing. The polishing composition may be a one-part type or a multi-part type including a two-part type. For example, the liquid A containing a part of the constituent components of the polishing composition and the liquid B containing the remaining components may be mixed and used for polishing an object to be polished.

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

  Next, the polishing liquid is supplied to the object to be polished and polished by a conventional method. For example, a polishing object is set in a general polishing apparatus, and a polishing liquid is supplied to the surface (polishing object surface) of the polishing object through a polishing pad of the polishing apparatus. Typically, while supplying the polishing liquid continuously, the polishing pad is pressed against the surface of the object to be polished, and both are relatively moved (for example, rotated). 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 (eg, a Ni-P substrate). Therefore, according to this specification, a method of manufacturing a magnetic disk substrate including the polishing step is provided.

  The polishing composition disclosed herein can be preferably used in a preliminary polishing step (for example, a primary polishing step) of an object to be polished. According to this specification, there is provided a method for producing a polished article, including a step of performing preliminary polishing using any of the above-described polishing compositions (preliminary polishing composition). This method for manufacturing a polished article may include a final polishing step after the preliminary polishing step. The polishing composition (composition for final polishing) 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. Therefore, the matter disclosed by this specification includes a step (1) of polishing a polishing object with a polishing composition containing abrasive grains having the particle diameter change rate X, and a final polishing composition containing colloidal silica. And a step (2) of polishing the object to be polished using the above in this order. According to this manufacturing method, the magnetic disk substrate can be manufactured efficiently.

  Thus, in the composition for final polishing containing colloidal silica, the particle diameter change rate X2 of the abrasive grain contained in this final polishing composition is not specifically limited. From the viewpoint of surface accuracy after finish polishing, the particle diameter change rate X2 of the abrasive grains contained in the finish polishing composition is preferably 110% or less.

  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) based on the total solid content contained in the finish polishing composition. Above). Colloidal silica may be used for substantially all (for example, 99% by weight or more) of the solid content contained in the polishing composition.

  The finish polishing composition typically contains water in addition to the silica abrasive grains. In addition, the finish polishing composition can contain the same components (acid, oxidizing agent, basic compound, various additives, and the like) as the above-described polishing composition as necessary. Although not particularly limited, the pH of the polishing composition for finishing can be the same as that of 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 (for example, 0.5 to 7.0). More preferably, it is 5.0 or less (typically 1.0-5.0), More preferably, it is 4.0 or less (for example, 1.0-4.0). In a preferred embodiment, the finish polishing composition has a pH of 3.0 or less (typically 1.0 to 3.0, preferably 1.0 to 2.0, more preferably 1.0 to 1.8. ).

  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.

<Polishing composition>
A plurality of types of silica particles having different volume particle size distributions were prepared. Abrasive grains containing these silica particles alone or in combination, phosphoric acid, 31% hydrogen peroxide water, and deionized water are mixed to obtain phosphoric acid at 12.5 g / L, 31% hydrogen peroxide. The polishing composition of Examples 1-9 containing 40 g / L of water was prepared. The content of abrasive grains in the polishing composition was 45 g / L in Examples 1 to 4 and 8, and 62 g / L in Examples 5 to 7 and 9. The pH of the polishing composition was 1.5 for Examples 1 to 5, 7 to 9, and 2.1 for Example 6.

<Disk polishing>
The polishing composition according to each example was directly used as a polishing liquid, and a standard polishing test was performed to polish an object to be 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 above polishing object (hereinafter also referred to as “Ni-P substrate”) has a diameter of 3.5 inches (a donut shape having an outer diameter of about 95 mm and an inner diameter of about 25 mm) and a thickness of 1.75 mm. The roughness Ra (the arithmetic average roughness of the nickel phosphorus plating layer measured by a laser scan type surface roughness meter “TMS-3000WRC” manufactured by Schmitt Measurement System Inc.) was 130 mm.

[Polishing conditions]
Polishing device: Double-side polishing machine manufactured by System Seiko Co., Ltd., model “9.5B-5P”
Polishing pad: Polyurethane pad manufactured by FILWEL, trade name “CR200”
Number of inserted Ni-P substrates: 15 (5 / carrier x 3 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 2.2μm in total on both sides of each substrate

  Table 1 shows the types of silica particles used, the volume average particle diameter Da of the abrasive grains, the volume average particle diameter Db after the standard polishing test, the particle diameter change rate X, and the number average aspect ratio of the polishing composition according to each example. Shown together. The volume average particle diameters Da and Da are measured by using the abrasive-containing liquid prepared by the above-described method from the polishing liquid used in the standard polishing test and the polishing waste liquid collected after polishing, as a measurement sample, “Nanotrac Wave-” manufactured by Nikkiso Co., Ltd. It was measured using “UT151”.

<Polishing rate>
The polishing rate when the Ni-P substrate was polished in the standard polishing test 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 Comparative Example 1 is 1, and is shown in the “Polishing Rate” column of Table 1.

<Long wavelength swell>
Using “Optiflat III” manufactured by KLA Tencor (USA), the arithmetic average waviness (Wa) measured under the condition of a cut-off value of 5 mm in a radius range of 20 mm to 44 mm from the center of the Ni-P substrate after polishing. The value was measured. And the obtained measured value was evaluated as “◯” when the measured value was less than 5 mm, and “Δ” when the measured value was 5 mm or more. The results are shown in the “undulation” column of Table 1.

  As shown in Table 1, in Examples 1 to 4 using abrasive grains having a particle diameter change rate X of 80% or more and 115% or less, better results were obtained at the polishing rate than in Examples 5 to 9. . From this result, it was confirmed that a high polishing rate could be realized with a polishing composition using abrasive grains having a particle size change rate of 80% to 115%. In Examples 1 to 3 using abrasive grains having a number average aspect ratio of 1.3 or less, higher surface accuracy was obtained than in Example 4.

  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 (7)

A polishing composition for a magnetic disk substrate that is supplied to a magnetic disk substrate and used for polishing the magnetic disk substrate,
Including abrasive grains and water,
The abrasive includes at least silica particles,
The volume average particle diameter of the abrasive grains in the polishing composition is Da,
The volume average particle diameter of the abrasive grains after a standard polishing test for polishing a nickel phosphorus plating substrate using the polishing composition is represented by the following formula:
X = (Db / Da) × 100;
A polishing composition for a magnetic disk substrate, wherein the particle diameter change rate X calculated by the above is 80% or more and 115% or less.   The polishing composition for a magnetic disk substrate according to claim 1, wherein the particle diameter change rate X is 90% or more.   The polishing composition for a magnetic disk substrate according to claim 1 or 2, wherein the pH is 5 or less.   The magnetic disk substrate polishing composition according to any one of claims 1 to 3, which is used in a pre-process of a final polishing process. A method of manufacturing a magnetic disk substrate, comprising:
A method for producing a magnetic disk substrate comprising the step (1) of polishing a magnetic disk substrate using the magnetic disk substrate polishing composition according to claim 1.   6. The method of manufacturing a magnetic disk substrate according to claim 5, further comprising a step (2) of polishing the magnetic disk substrate using a final polishing composition containing colloidal silica after the step (1).   A magnetic disk substrate polishing method, comprising: supplying the polishing composition for a magnetic disk substrate according to claim 1 to the magnetic disk substrate to polish the magnetic disk substrate.