JP2006088321A - Brush polishing method for inner peripheral end face of substrate for recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing method for inner peripheral end faces of substrates for a plurality of disk-type recording mediums with sufficient accuracy. <P>SOLUTION: The brush polishing method is used for polishing the inner peripheral end faces of the substrates 8 for the disk-type recording mediums, and comprised of the following steps. In the first step, the plurality of substrates 8 for the disk-type recording mediums each having a circular hole exhibiting the inner peripheral end face at the center are prepared, and they are superposed on each other by positioning the circular holes to each other, to thereby form a polishing object having a cylindrical hole at the center. In the second step, the polishing object is brought into contact with abrasive slurry 7 containing abrasive. In the following step, while the slurry 7 makes contact with the polishing object, a polishing brush 4 obtained by arranging brushing bristles on a peripheral surface of a rod shaft is inserted into the cylindrical hole of the polishing object, and the polishing brush 4 is rotated about the shaft, to thereby polish the inner peripheral end faces of the respective substrates 8. According to the method, the abrasive slurry 7 is controlled such that its temperature is set to a constant value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for polishing an inner peripheral end surface of a recording medium substrate, a method for manufacturing the substrate using the same, and the like.

  As a substrate for a magnetic recording medium such as a magnetic disk, an aluminum substrate has been widely used. However, with the downsizing and thinning of a magnetic disk and high density recording, the flatness of the substrate surface and the substrate as compared with the aluminum substrate are increased. It is gradually replacing glass substrates with excellent strength. In general, in order to increase the substrate strength, a chemically strengthened glass substrate or a crystallized glass substrate whose substrate strength is increased by crystallization is used for the glass substrate for a magnetic recording medium.

  Also, the magnetic head has been changed from a thin film head to a magnetoresistive head (MR head) and a large magnetoresistive head (GMR head) as the recording density is increased. Therefore, it is expected that reproducing a magnetic recording medium using a glass substrate with a magnetoresistive head will be a major trend in the future.

  As described above, various improvements have been made to the magnetic disk for high-density recording, and along with the progress of such a magnetic disk, new problems have been generated one after another in the glass substrate for magnetic recording media. One of them is high cleaning of the glass substrate surface. This causes a problem that if a foreign substance adheres to the glass substrate surface, it may cause a film defect of a thin film formed on the glass substrate surface or a convex portion on the thin film surface. Also, when reproducing magnetic recording media using a glass substrate with a magnetoresistive head, if the flying height (flying height) of the head is lowered in order to improve the recording density, malfunction of reproduction or reproduction is impossible. You may encounter a phenomenon that becomes a problem. This is because the protrusion formed by particles on the glass substrate on the surface of the magnetic disk becomes thermal asperity, heat is generated in the magnetoresistive head, and the resistance value of the head fluctuates. This is because the electromagnetic conversion is adversely affected.

  The cause of the foreign matter on the surface of the glass substrate for magnetic recording medium as described above is that the surface state of the end surface of the glass substrate is not smooth, so that the end surface rubs against the wall surface of the resin case, and the resin or glass generated by the rub is generated. A major factor is that particles and other particles captured on the inner peripheral end surface and the outer peripheral end surface portion of the glass substrate adhere to the surface.

  Patent Document 1 (Japanese Patent Application Laid-Open No. 11-221742) discloses a method of immersing a disc-shaped glass substrate (recording medium substrate) having a circular hole in the center in a polishing liquid containing free abrasive grains, A polishing method is disclosed in which the end face is polished by rotating and contacting a polishing brush or a polishing pad using a polishing liquid containing loose abrasive grains.

  When polishing the end face of the substrate using the slurry and the polishing brush as described above, it is aligned with the center hole of the disk-shaped substrate having the center hole and the center hole of the object to be polished in which a plurality of substrates are stacked. Then, while dripping the slurry or with the object to be polished immersed in the slurry, a rod-shaped polishing brush is inserted into the center hole and polishing is performed by rotating the brush. In such a polishing method, the temperature rises due to friction between the object to be polished, the abrasive slurry, and the polishing brush. This temperature rise fluctuates the polishing rate, making it difficult to perform polishing with an accurate processing amount. On the other hand, at the end surfaces of the stacked substrates, since each substrate is chamfered, a recessed portion is formed between the chamfered portions of the upper and lower substrates. It is difficult to polish such a recessed portion with the same processing accuracy as other end edge surfaces. In the disk-shaped recording medium substrate, it is required to increase the dimensional accuracy of the center hole, and therefore it is necessary to increase the processing accuracy of the polishing of the inner peripheral end face.

JP-A-11-221742

  Accordingly, an object of the present invention is to provide a method for polishing an inner peripheral end surface of a substrate, which can be performed with sufficient processing accuracy when polishing inner peripheral end surfaces of a plurality of disk-shaped recording medium substrates.

  The present invention provides the following brush polishing method for the inner peripheral end surface of a disk-shaped recording medium substrate and a method for manufacturing a substrate using the same.

(1) A brush polishing method for an inner peripheral end face of a disk-shaped recording medium substrate,
A plurality of disc-shaped recording medium substrates having a circular hole having an inner peripheral end face at the center is prepared, the circular holes are aligned and stacked, and an object to be polished having a circular hole at the center is formed. thing,
Bringing an abrasive slurry containing an abrasive into contact with the object to be polished;
In a state where the slurry is in contact with the object to be polished, a polishing brush provided with brush bristles around a rod-shaped shaft is inserted into the circular hole of the object to be polished, and the polishing brush is centered on the shaft. Rotating to polish the inner peripheral edge of the substrate,
And polishing the inner slurry end surface of the disc-shaped recording medium substrate, wherein the abrasive slurry is controlled at a constant temperature.

  (2) The brush polishing method according to (1), wherein polishing is performed by rotating the polishing brush and reciprocating the polishing brush in the brush insertion direction with respect to the object to be polished.

(3) A method for manufacturing a disk-shaped recording medium substrate, comprising the step of performing the brush polishing method according to (1) or (2) above in the method for manufacturing a disk-shaped recording medium substrate.
(4) A substrate manufactured by the method for manufacturing a disk-shaped recording medium substrate according to (3).
(5) A method for producing a magnetic recording medium, comprising the step of performing the brush polishing method according to (1) or (2).

  In the polishing method of the present invention, since the temperature of the abrasive slurry is controlled to be constant, the polishing rate of the inner peripheral end surface of the substrate can be maintained constant, and as a result, polishing processing is performed with high dimensional accuracy. Can do.

  The polishing method of the present invention is a method of simultaneously polishing the inner peripheral end surfaces of a plurality of laminated disc-shaped recording medium substrates using a slurry containing an abrasive and a polishing brush provided with brush bristles around a rod. It is. FIG. 1 is a schematic cross-sectional view of a polishing apparatus that can be used in the polishing method of the present invention. The polishing apparatus 100 includes a polishing apparatus container 1, a holding table 2, a substrate holder 3 installed on the holding table 2, a polishing rotating brush 4, and a rotation driving unit 5. The polishing apparatus container 1 is filled with an abrasive slurry 7, passes through the substrate holder 3 through the abrasive slurry flow port 6, and uses the abrasive slurry 7 to make the inside of the brush 4 and the substrate 8. The peripheral end face is brought into rotational contact. In this apparatus 100, the substrate is immersed in the abrasive slurry 7, thereby bringing the substrate into contact with the slurry 7.

  In the method of the present invention, the temperature of the slurry 7 is kept constant, thereby keeping the polishing rate constant. The temperature of the slurry 7 is measured by a temperature sensor 9 in cooperation with the chiller unit / temperature controller 10, and the slurry is cooled by a cooling tank 13 so as to have a predetermined set temperature. The slurry 7 from the polishing apparatus 100 passes through the slurry pipe 11 and is preferably filtered by the filter 12 to remove the ground material and the like generated by the polishing process, and then enters the cooling tank 13. The cooling tank 13 has a double structure, the slurry 7 is held on the inner side, and the cooling water circulates on the outer side through the cooling water pipe 16. A stirrer 15 is provided in the cooling tank 13 to make the temperature of the slurry uniform and to prevent the abrasive in the slurry from settling. The temperature control of the cooling tank 13 can be performed by adjusting the temperature of a constant amount of cooling water, adjusting the flow rate of cooling water at a constant temperature, or adjusting both the amount and temperature of the cooling water. The slurry 7 controlled to a desired temperature is returned to the polishing apparatus 100 through a pump 14. In this way, the temperature of the slurry 7 during polishing is kept constant. The temperature of the slurry 7 may be constant in order to make the polishing rate constant, and may be any temperature.

Next, FIG. 2 shows a cross-sectional view of a laminated substrate which is an object to be polished. The inner peripheral end face 21 of each substrate is composed of an end face 22 and a chamfer 23. A recessed portion 24 formed by the chamfered portion 23 is formed between the end surfaces 21 of the upper and lower substrates. The indented portion 24 is less likely to be in contact with the brush 4 or has a lower contact pressure, so that it is less likely to be polished than the edge surface 22. For this reason, if the brush 4 can move up and down with respect to the laminated substrate which is the object to be polished, in addition to the rotational movement, better and precise polishing can be performed. The vertical movement can be performed by the vertical movement of the brush 4 or the vertical movement of the substrate holder 3.
The “up” and “down” directions in the present invention are based on the up and down directions in FIG.

  The abrasive used in the polishing method of the present invention and the slurry containing the same are not particularly limited, and any abrasive and abrasive slurry known in the art may be used. Specifically, abrasives such as rare earth oxides, iron oxides, zirconium oxides, and silicon dioxides can be used, but for polishing the surface of glass substrates, polishing is performed in comparison with iron oxides, zirconium oxides, and silicon dioxides. An abrasive mainly composed of a rare earth oxide, particularly cerium oxide, can be used because the speed is several times better. Although not limited thereto, an abrasive slurry containing cerium oxide will be described below as an example.

  The abrasive slurry can be obtained by dispersing an abrasive mainly composed of a rare earth oxide containing cerium oxide in water. The slurry includes a dispersant, a chelating agent, and the like as necessary.

  Examples of the abrasive mainly composed of a rare earth oxide mixture containing cerium oxide contained in the abrasive slurry include bust nesite and rare earth chloride-based low cerium polishing having a cerium oxide content of about 50% by mass. Materials, synthetic high cerium abrasives having a cerium oxide content of 70 to 90% by mass, and high-purity cerium oxide having a cerium oxide content of 99% by mass or more.

Bustnessite-based abrasives are obtained by crushing bustness stone, which is a rare earth element fluorinated carbonate mineral, and through chemical treatment, drying, roasting, crushing, classification, and finishing processes. In addition to about 50% by mass, other rare earth elements coexist as basic fluorides such as LaOF, NdOF, and PrOF. A rare earth chloride-based abrasive is a hydroxide cake made from a rare earth chloride, dried and then baked as a partial sulfate, pulverized, classified, and finished. It contains about 50% by mass of cerium oxide. In addition, other rare earth elements coexist as basic anhydrous sulfates such as La ₂ O ₃ .SO ₃ , Nd ₂ O ₃ .SO ₃ , and Pr ₅ O ₁₁ .SO ₃ .

Synthetic high cerium abrasives are roasted from raw materials such as bustness stone, dissolved in nitric acid, heated while adjusting pH with dilute ammonia water to hydrolyze Ce ⁴⁺ to form hydroxide This is produced through filtration, drying, roasting, pulverization, classification and finishing, and contains 70 to 90% by mass of cerium oxide. High-purity cerium oxide dissolves rare earth oxides in nitric acid, extracts Ce ⁴⁺ in aqueous solution with tributyl phosphate-benzene, transfers it to the organic phase, and further uses a reducing agent such as sodium nitrite. It is obtained by back-extracting with an aqueous phase containing cerium oxalate and then roasting. The purity of cerium oxide usually reaches 99.9% by mass or more.

  Cerium oxide has a Mohs hardness of 5.5 to 6.5, which is the same as or slightly higher than that of glass, and can be finely adjusted. Therefore, it can be suitably used as a glass abrasive. Both low cerium abrasives and high cerium abrasives have excellent polishing power, but high cerium abrasives have a particularly long life. There is no particular limitation on the particle size of the abrasive mainly composed of a rare earth oxide mixture containing cerium oxide used in the abrasive composition, but generally the volume measured by JIS R 6002, “6. Electrical Resistance Test Method” An abrasive having a particle size of 0.5 to 3 μm corresponding to a cumulative value of 50% can be suitably used. The crystal system of cerium oxide is preferably a cubic system.

  The abrasive slurry can contain a chelating agent as required. By containing a chelating agent, the reactivity of the glass component produced by polishing can be reduced. In the conventional glass surface finish polishing, the abrasive slurry is usually circulated and used, but as the usage time becomes longer, the glass component as the object to be polished increases in the circulated slurry. If the glass component uniformly covers the surface of the abrasive particles, not only will the precipitate of the abrasive become very hard, but it will also reattach to the glass surface due to its high affinity with the glass surface. Worsen.

  When the abrasive slurry contains a chelating agent, the reactivity between the surface of the abrasive particle and the glass surface is reduced, and the abrasive particle surface is prevented from being covered with a glass component, and thus a hard precipitate may be generated. Therefore, deterioration of the cleaning property is prevented. Preferable specific examples of the chelating agent include o-phenanthroline, gluconic acid and its salt, amino acid, ethylenediaminetetraacetic acid and the like. Examples of gluconic acid and its salts include gluconic acid and its sodium, calcium, zinc, and ferrous salts.

  The amino acid to be contained is not particularly limited, and for example, acidic amino acids, neutral amino acids, basic amino acids, metal salts thereof, some of the amino group's amino groups are alkyl groups, hydroxylalkyl groups, alkoxyl groups, etc. Substituted compounds and the like can be used. However, when the abrasive slurry becomes acidic, the chemical effect on glass polishing of cerium oxide itself is reduced and the processing speed is reduced. Therefore, when using an acidic amino acid, it is preferable to use it in combination with a basic amino acid. . In addition, as the amino acid, either a natural product or a synthetic product can be used. Furthermore, in the case of an amino acid having an optical isomer, either D-type or L-type can be used.

  Examples of amino acids that can be used in the abrasive slurry include glycine, alanine, valine, leucine, isoleucine, serine, threonine, cysteine, cystine, methionine, aspartic acid, glutamic acid, lysine, arginine, phenylalanine, tyrosine, histidine, Examples include tryptophan, proline, hydroxyproline, diiodotyrosine, thyroxine, hydroxylysine, β-alanine, γ-aminobutyric acid, anthranilic acid, m-aminobenzoic acid, p-aminobenzoic acid and the like. Among these, glycine and arginine can be particularly preferably used. An amino acid can be used individually by 1 type and can also be used in combination of 2 or more type.

  Among the above chelating agents, o-phenanthroline, gluconic acid and salts thereof are preferable. The chelating agent content is preferably 0.05 to 0.3% by mass. If the content is less than 0.05% by mass, the effect of suppressing the reactivity of the glass component is poor. Conversely, if the content exceeds 0.3% by mass, the polishing rate is lowered.

  The abrasive slurry can further contain an acetonato complex of aluminum having 1 to 3 acetonato ligands. By including an acetonato complex of aluminum, it is possible to suppress the adhesion of the abrasive to the glass substrate or the polishing apparatus, and to prevent the cleaning performance from being deteriorated. Usually, the abrasive is an ultrafine powder having an average particle size of about 1 to 2 μm, and exists in a certain agglomerated state in the polishing slurry due to its surface activity. These agglomerated grains serve to reduce the apparent surface area and suppress the adhesion of the abrasive to the glass substrate or polishing apparatus, but the particles in the outermost shell exist while maintaining the activity, so the glass substrate once If it adheres to each part of the polishing apparatus, it cannot be removed by washing with running water or ultrasonic irradiation. A normal abrasive tends to adhere to a glass substrate or a polishing apparatus. In contrast, for abrasives containing an aluminum acetonate complex, the interaction between the aluminum acetonate complex and abrasive agglomerated particles in the abrasive slurry suppresses the adhesion of the abrasive and prevents degradability. Is done.

  Specific examples of the aluminum acetonato complex used include complexes having an acetylacetonate (R = methyl) ligand such as aluminum tris (acetylacetonate), and ethylacetoacetate such as aluminum tris (ethylacetoacetate) ( And a complex having an R = ethoxy) ligand. Among these, aluminum tris (acetylacetonate) is preferable. The acetonato complex of aluminum may be a complex having two or three different acetonato ligands in one molecule, and the acetonato complex of aluminum may be used alone or in combination of two or more. Also good. The content of the acetonato complex of aluminum is preferably 0.05 to 0.3% by mass. When the content is less than 0.05% by mass, the effect of preventing the adhesion of the abrasive is poor, and when it exceeds 0.3% by mass, the polishing rate decreases.

  Abrasive slurry is made of glycols such as ethylene glycol and polyethylene glycol, phosphates such as tripolyphosphate and hexametaphosphate, and polyacrylate as necessary to improve particle dispersibility, prevent sedimentation and improve workability. Polymeric dispersants such as, cellulose ethers such as methylcellulose and carboxymethylcellulose, and water-soluble polymers such as polyvinyl alcohol may be added. The addition amount with respect to these abrasives is usually in the range of 0.05 to 20% by mass, preferably 0.1 to 15% by mass, and more preferably 0.1 to 10% by mass.

  The abrasive slurry is generally used as a slurry having a concentration of about 5 to 30% by weight in a dispersion medium such as water. Water or a water-soluble organic solvent is used as the dispersion medium. Examples of the water-soluble organic solvent include alcohol, polyhydric alcohol, acetone, tetrahydrofuran and the like, but water is usually used. In addition, auxiliary agents commonly used in ordinary cerium oxide-based abrasives can be added.

  The slurry used in the method of the present invention may be prepared by mixing raw materials, and is not particularly limited. Preferably, the slurry may be mechanically mixed and prepared at the above mixing ratio by a ball mill, a high speed mixer or the like.

  The substrate end surface polishing is generally performed after a circular hole is formed in the center of the glass substrate and chamfering is performed on the inner peripheral end surface and the outer peripheral end surface. Thereafter, the substrate is subjected to polishing of the recording surface, and may be further chemically strengthened with a potassium nitrate or sodium nitrate chemical strengthening solution, if necessary.

  A magnetic recording medium can be manufactured by sequentially laminating an underlayer, a magnetic layer, a protective layer, and a lubricating layer on the substrate prepared as described above. In addition, although not necessarily limited, as a base layer, nonmagnetic materials, such as Cr, Mo, Ta, W, V, B, and Al, can usually be used. In addition, a magnetic film containing Co as a main component can be used as the magnetic layer. As the protective layer, a Cr film, a carbon film, or the like can be used, and as the lubricating layer, a liquid lubricant obtained by diluting perfluoroether with a fluoro solvent, and applying and drying can be used.

The present invention is not limited to the examples, but the method of the present invention will be described in more detail below using examples.
Example 1
Laminated 150 glass substrates for hard disk (HD) with a diameter of 65 mm (outer diameter), 20 mm diameter (inner diameter of the central hole), and 0.635 μm thickness (TS-10SX manufactured by OHARA INC.) Under the following conditions. The inner peripheral end face was polished using a polishing apparatus as shown in FIG.
The inner peripheral end face of the substrate consisted of an edge surface of 0.335 μm and a chamfered portion of 0.150 μm on both sides thereof.

1. Polishing 1.1. Types of abrasive slurry abrasives, particle size: cerium oxide (SHOROX A-10, Showa Denko KK), average particle size 1.4 μm
Dispersion medium: water dispersant: abrasive concentration in sodium hexametaphosphate slurry: 10% by mass
Brush material, hair length, hair diameter: nylon, 4mm, φ0.15mm
Brush rotation speed: 2400rpm
Polishing time: 20 minutes The temperature of the polishing slurry was controlled at 25 ° C. by the mechanism shown in FIG.

Comparative Example 1
Polishing was performed in the same manner as in Example 1 above, but temperature control was not performed. The temperature at the start of polishing was 26 ° C. and increased to 30 ° C. at the end of polishing.

2. Evaluation test 2.1. Surface Defect Observation Surface defects were observed on the substrates polished in the above examples and comparative examples. The surface defect was observed under the Olympus microscope 200 ×, and the entire circumference of the inner peripheral end face was observed.

2.2. Dimensional inspection of inner peripheral end face Dimensional measurements were performed on a total of three substrates, the outermost two substrates polished in the above-described examples and comparative examples, and the central substrate. The results are shown in Table 1 below. In addition, a result shows the average value of the dimension of three board | substrates.

  From the above test results, it was confirmed that both Example 1 and Comparative Example 1 had no scratches or pits by surface defect observation. On the other hand, the dimension of the inner peripheral end face was 19 μm, which was 3 μm higher than the planned polishing amount in Comparative Example 1, while it was 16 μm of the planned polishing amount in Example 1. By controlling the temperature at the time of polishing to be constant, the polishing speed (processing speed) is stabilized, and an inner diameter substantially equal to the target value can be obtained. Further, variations in the inner diameter due to fluctuations in the hardness of the brush due to a local temperature rise can be suppressed.

The schematic sectional drawing of the polisher which can be used with the polish method of the present invention is shown. Sectional drawing of the laminated | stacked board | substrate is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polishing apparatus container 2 Holding stand 3 Substrate holder 4 Polishing rotating brush 5 Rotation drive part 6 Abrasive slurry distribution port 7 Abrasive slurry 8 Substrate 9 Temperature sensor 10 Chiller unit / temperature controller 11 Slurry piping 12 Filter 13 Cooling tank 14 Pump 15 Stirrer 16 Cooling water piping 100 Polishing device

Claims (5)

A brush polishing method for an inner peripheral end surface of a disk-shaped recording medium substrate,
A plurality of disc-shaped recording medium substrates having a circular hole having an inner peripheral end face at the center is prepared, the circular holes are aligned and stacked, and an object to be polished having a circular hole at the center is formed. thing,
Bringing an abrasive slurry containing an abrasive into contact with the object to be polished;
In a state where the slurry is in contact with the object to be polished, a polishing brush provided with brush bristles around a rod-shaped shaft is inserted into the circular hole of the object to be polished, and the polishing brush is centered on the shaft. Rotating to polish the inner peripheral edge of the substrate,
And polishing the inner slurry end surface of the disc-shaped recording medium substrate, wherein the abrasive slurry is controlled at a constant temperature.   The brush polishing method according to claim 1, wherein the polishing is performed by rotating the polishing brush and reciprocating the polishing brush in the brush insertion direction with respect to the object to be polished.   A method for manufacturing a disk-shaped recording medium substrate, comprising the step of performing the brush polishing method according to claim 1 or 2 in the method for manufacturing a disk-shaped recording medium substrate.   A substrate manufactured by the method for manufacturing a disk-shaped recording medium substrate according to claim 3.   A method for manufacturing a magnetic recording medium, comprising the step of performing the brush polishing method according to claim 1.

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