JP2007026488A - Water abrasive for magnetic disk substrate and manufacturing method of magnetic disk substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water abrasive for a magnetic disk substrate, wherein polishing properties of a Ni-P surface of the magnetic disk substrate are excellent and an organic residue does not remain on a polished surface after polishing. <P>SOLUTION: The water abrasive for the magnetic disk substrate contains abrasive fine particles, a higher fatty acid and a polyethylene glycol ether type non-ionic surfactant. The abrasive fine particles consist of diamond fine particles, wherein a dispersion liquid formed by dispersing the fine particles in pure water in a ratio of 20 carat/L has a pH value of ≥7.0. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an aqueous abrasive for a magnetic disk substrate, and more particularly to an aqueous abrasive for a magnetic disk substrate in which abrasive fine particles are diamond fine particles and a method for producing a magnetic disk substrate including a substrate polishing step using the aqueous abrasive. .

  Magnetic disks (hard disk memories) are widely used as external storage devices that can be accessed at high speed by computers.

  A typical example of a magnetic disk is a chromium underlayer, a cobalt magnetic film layer, a carbon protective film layer on a magnetic disk substrate having a nickel phosphorus (Ni-P) layer formed by electroless plating on an aluminum alloy substrate. The surface of the Ni-P layer is textured by polishing.

  The surface roughness of the magnetic disk has a significant effect on the quality of the magnetic disk. In particular, the presence of protrusions on the surface of the magnetic disk that exceed the flying height of the magnetic head can cause damage to both the magnetic head and the magnetic disk. Therefore, the surface of the magnetic disk is finished to an extremely smooth surface.

  Causes of protrusions on the surface of the magnetic disk include protrusions existing on the surface of the magnetic disk substrate, adhesion of fine particles of each layer laminated by sputtering, etc., adhesion of dust after film formation, etc. Since the protrusions on the surface of the magnetic disk substrate are inherited by the layers stacked thereon, the surface of the magnetic disk substrate is precisely polished so as to have a predetermined texture before the layers are stacked.

  Known polishing methods for texturing the surface of a magnetic disk substrate include a method using a polishing tape (Patent Document 1 and the like), a punishing method (Patent Document 2 and the like), a honing method (Patent Document 3), and the like. A variety of abrasives are used.

  The abrasive used in these methods is obtained by dispersing fine particles of an abrasive in a dispersion medium that also serves as a coolant that removes heat generated during polishing. For example, an abrasive containing diamond fine particles as an abrasive ( Patent Documents 4, 5, etc.), abrasives containing aluminum oxide fine particles (Patent Documents 6, 7, 8, 9 etc.), colloidal silica-based abrasives (Patent Document 10, etc.) and the like are known.

  In order to form the desired texture on the surface of the magnetic disk substrate, the abrasive fine particles need to have an extremely small particle size and dispersion stability that is uniformly and stably dispersed in the abrasive. The abrasive contains various surfactants as a dispersant for the abrasive fine particles, and water is suitably used as a dispersion medium that also serves as a coolant.

  In recent years, diamond fine particles have been included as abrasive fine particles, and a mixture mainly composed of a higher fatty acid alkanolamine salt type nonionic surfactant and a polyethylene glycol ether type nonionic surfactant as a dispersant. An aqueous abrasive (Patent Document 11) is attracting attention because of its excellent abrasiveness.

JP-A 64-086320 Japanese Patent Laid-Open No. 03-273523 Japanese Patent Laid-Open No. 03-290822 JP-A-62-157327 JP-A 63-197030 Japanese Patent Laid-Open No. 60-108489 JP-A-62-025187 Japanese Patent Laid-Open No. 01-188264 Japanese Patent Laid-Open No. 04-275387 Japanese Patent Laid-Open No. 07-240025 JP-A-11-185249

  The aqueous abrasive containing the mixture of the diamond fine particles and the nonionic surfactant has excellent abrasiveness, but there is considerable variation in the abrasiveness, and even after cleaning the magnetic disk substrate, the substrate It can be seen that organic residues remain on top and stick.

  An object of the present invention is to provide an aqueous abrasive containing diamond fine particles, which have no variation in abrasiveness and in which no organic residue remains after washing, as an abrasive. Another object of the present invention is to provide a method of manufacturing a magnetic disk substrate having a smooth surface free from protrusions that damage the magnetic head and the magnetic disk.

  As a result of diligent research to achieve the above object, the present inventors have found that there is a large difference in the dispersibility of diamond fine particles in a dispersion in which diamond fine particles that are commercially available as abrasives are dispersed in pure water. Although there is no difference, the pH value of the dispersion has a large difference of about 3 to about 8, and the dispersibility of the diamond fine particles depends on the pH value of the dispersion in an aqueous system containing a higher fatty acid. As a result, the present invention has been completed.

  The aqueous abrasive for magnetic disk substrate of the present invention is an aqueous abrasive for magnetic disk substrate containing abrasive fine particles, higher fatty acid and polyethylene glycol ether type nonionic surfactant, wherein the abrasive fine particles are It is characterized by comprising diamond fine particles having a pH value of 7.0 or more in a dispersion liquid in which fine particles are dispersed in pure water at a rate of 20 carats / liter.

  In the present invention, the diamond fine particles may be diamond fine particles that have been washed with water until the pH value of a dispersion of 20 carats / liter in pure water becomes 7.0 or more. The higher fatty acid is selected from the group consisting of nonanoic acid, ricinoleic acid and mixtures thereof.

  The method of manufacturing a magnetic disk substrate according to the present invention includes a step of polishing the magnetic disk substrate using the aqueous abrasive for magnetic disk substrate and a step of washing the polished magnetic disk substrate surface with water.

  In the water-based abrasive of the present invention, the diamond fine particles of the abrasive are excellent in dispersibility. Therefore, in the polishing of the magnetic disk substrate using the abrasive, not only the desired textured surface is obtained but also the dispersion of the diamond fine particles. By selecting a combination of a higher fatty acid and a polyethylene glycol ether type nonionic surfactant as an agent, organic substances can be efficiently removed from the substrate surface by washing with water after polishing. As a result, in the polishing process of the magnetic disk substrate using the aqueous abrasive of the present invention, the occurrence rate of poor polishing is reduced and the yield of products is remarkably improved.

  In the water-based abrasive of the present invention, as a grinding material, commercially available diamond fine particles or diamond fine particles obtained by washing them with water and having a pH of 7 dispersed in pure water at a concentration of 20 carats / liter. Contains diamond fine particles exhibiting 0.0 or more.

Commercially available diamond fine particles contain impurities such as Cl, NO ₃ and SO ₄ as anions and Ca, Mg and Na as cations, depending on the production method and the cleaning method after production. The dispersion dispersed at a concentration of 20 carats / liter exhibits a wide range of pH values from 3.3 to 8.1 as shown in Table 1.

  As shown in Table 1, the particle diameters of the diamond fine particles in the pure water dispersion are not greatly different regardless of the pH values indicated by these dispersions, and the pH dependence of the particle diameter is not recognized.

  On the other hand, when each of these diamond fine particles is added and dispersed in a 5% nonanoic acid aqueous solution, agglomeration is observed in a part of the diamond fine particles, particularly diamond fine particles having a pure water dispersion having a pH value of 4.5 or less. The aggregated particle size depends on the pH value of the aqueous dispersion as shown in Table 1. FIG. 1 shows the pH dependence of the particle size of the diamond fine particles in the pure water dispersion and in the nonanoic acid solution dispersion.

  In the aqueous abrasive of the present invention, diamond fine particles having a pH value of 7.0 or higher in a pure water dispersion in which no large aggregation is observed in the nonanoic acid solution dispersion are used. Diamond fine particles in which the pH value of the pure water dispersion is 7.0 or more by washing with water can also be used. The blending amount of the diamond fine particles is 0.1 to 2.0 carat / liter, preferably 0.3 to 1.3 carat / liter in weight.

  In the aqueous abrasive of the present invention, the higher fatty acid is a saturated or unsaturated aliphatic carboxylic acid having 8 to 18 carbon atoms and a hydroxycarboxylic acid such as octanoic acid, nonanoic acid, lauric acid, myristic acid, palmitic acid, stearin. Acids, azelaic acid, sebacic acid, oleic acid, ricinoleic acid and the like, preferably selected from nonanoic acid, ricinoleic acid and mixtures thereof. The blending amount of the higher fatty acid is 0.1 to 30% by weight, preferably 0.5 to 5% by weight, based on the weight of the aqueous abrasive.

In the aqueous abrasive of the present invention, the polyethylene glycol ether type nonionic surfactant is derived from polyethylene glycol having a degree of polymerization of 5 to 9 and a higher alcohol of C _{12 to} C ₁₈ or an alkyl phenol of C _{8 to} C _9. It is a nonionic surfactant. The blending amount of the polyethylene glycol type nonionic surfactant is in the range of 0.1 to 30% by weight, preferably 0.5 to 5% by weight, based on the weight of the aqueous abrasive.

Aqueous abrasives Each of the diamond fine particles of Sample Nos. 1 to 11 shown in Table 1 was mixed with ricinoleic acid 1% and a polyethylene glycol ether type nonionic surfactant (polyethylene glycol ether of n-butyl carbitol: Wako Pure Chemical Industries, Ltd.) An aqueous abrasive was prepared by dispersing it in an aqueous solution containing 1% at a concentration of 1 carat / liter.

Polishing of magnetic disk substrate A polishing tape is pressure-bonded to a Ni-P layer surface of a 3.5-inch magnetic disk substrate made of an aluminum alloy substrate on which a Ni-P layer is formed by electroless plating with a contact roller. The magnetic disk substrate was rotated while each of these was dropped and polished for 1 minute.

Cleaning Ultrasonic cleaning was performed in a cleaning agent for 1 minute and then rinsed with pure water for 2 minutes while air-drying while applying a water shower so that the substrate surface after polishing was not dried.

Evaluation The number of adhered particles on the surface of each magnetic disk substrate after the cleaning treatment and the presence or absence of organic residues were evaluated using a surface inspection apparatus OSA6100 (manufactured by Canberra Instruments). Table 2 shows the number of particles adhering to the magnetic disk substrate surface, and FIG. 2 shows the relationship between the pH of the diamond fine particle dispersion and the number of adhering particles.

  The operation of separating and filtering the sample No. 4 diamond fine particles after dispersing and washing in pure water under stirring at a concentration of 20 carats / liter was repeated three times. The pH value of the washed aqueous dispersion of diamond fine particles having a concentration of 20 carats / liter was 7.1.

  A magnetic disk substrate was polished and cleaned under the same conditions as in Example 1 using an aqueous abrasive prepared under the same conditions as in Example 1 except that the obtained washed diamond fine particles were used. The substrate surface was evaluated in the same manner as described above. The number of adhered particles on the substrate surface was 10, and no organic residue was observed.

The graph which shows the pH dependence in the aqueous dispersion and nonanoic acid solution dispersion of the particle diameter of a diamond fine particle. 3 is a graph showing the relationship between the pH of the diamond fine particle dispersion obtained in Example 1 and the number of attached particles.

Claims (4)

  An aqueous abrasive for a magnetic disk substrate containing abrasive fine particles, higher fatty acid and polyethylene glycol ether type nonionic surfactant, wherein the abrasive fine particles are contained in pure water at a rate of 20 carats / liter. An aqueous abrasive for magnetic disk substrates, comprising diamond fine particles having a pH of 7.0 or higher in the dispersion dispersed in (1).   The aqueous abrasive for magnetic disk substrate according to claim 1, wherein the diamond fine particles are diamond fine particles washed with water until the pH of a dispersion of 20 carats / liter in pure water becomes 7.0 or higher. .   2. The aqueous abrasive for magnetic disk substrates according to claim 1, wherein the higher fatty acid is selected from the group consisting of nonanoic acid, ricinoleic acid and mixtures thereof. A magnetic disk comprising: a step of polishing a magnetic disk substrate using the aqueous abrasive for magnetic disk substrate according to claim 1; and a step of washing the polished magnetic disk substrate surface with water. A method for manufacturing a substrate.

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