Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B37/00—Lapping machines or devices; Accessories
  • B24B37/04—Lapping machines or devices; Accessories designed for working plane surfaces
  • B24B37/042—Lapping machines or devices; Accessories designed for working plane surfaces operating processes therefor
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers
  • G11B5/8404—Processes or apparatus specially adapted for manufacturing record carriers manufacturing base layers

Definitions

• This invention relates to a magnetic disk substrate and a production method of a magnetic disk.
• Magnetic disk devices have made a remarkable progress as external storage devices for computers owing to their superior cost performance ratio and further progress is expected.
• An aluminum type substrate has been used in the past as a substrate for a magnetic disk which is mounted to the magnetic disk device, but glass substrates, such as chemically-tempered glass and crystallized glass have gradually gained wider application because they have high impact resistance and can be easily made flat.
• the aluminum type substrate can easily provide a magnetic disk having excellent magnetic characteristics but involves the problem of lack of flatness because it suffers plastic deformation during a mechanical process such as polishing.
• the glass substrate can be easily made flat because it has high surface hardness and does not suffer the plastic deformation described above.
• polishing is generally conducted as an upper plate and a lower plate of the polishing machine are reversely rotated while the glass substrate is clamped between a pair of polishing machine plates (upper plate and lower plate) .
• Such a polishing carrier is obtained by stacking a predetermined number of prepregs made by causing a glass woven fabric to be impregnated with an epoxy resin and drying the woven fabric, for example, and by integrally heating and press-molding them.
• the polishing carrier is generally formed of a fiber reinforced resin in order to acquire high rigidity.
• the glass substrate is polished by using such a polishing carrier, however,- scratches occur due to contact between the outer end face of the glass substrate (that is, outer peripheral side surface) and the inner peripheral surface of the circular retaining holes of the polishing carrier.
• the following problems have so far been pointed out regarding the scratches of the outer end face of the glass substrate.
• the inside of the polishing carrier can be formed of a material having hardness of 100 or below (Japanese Unexamined Patent Publication
• the polishing carrier can have a notch shape (Japanese Unexamined Patent Publication (Kokai) No. 2000-288921) .
• the diameter of the retaining holes of the polishing carrier can be greater by 0.4 to 2.0 mm than the diameter of the glass substrate (Japanese ⁇ nexamined Patent Publication (Kokai) No. 2000-84834) .
• the ratio (R/r) of a radius R of the retaining holes of the polishing carrier to a radius r of the glass substrate is set to 1.030 or above (Japanese ⁇ nexamined Patent Publication (Kokai) No. 2002-326156), and so forth.
• the following problem has also been pointed out regarding the scratches on the outer end face of the glass substrate.
• chemical tempered glass contains sodium as a main alkali metal and crystallized glass contains lithium. Because the ion radius of these metal ions is small, the ions are easily mobile, particularly at a high temperature. Though this mechanism has not yet been clarified sufficiently, the sodium ions and the lithium ions that have moved to the surface of the magnetic disk react with surrounding materials, form various chemical compounds such as hydroxides and carbonates and also form protrusions on the surface of the magnetic disk, and possibly impinge against the flying head to cause a head crash. As these ions corrode the magnetic film, they invite deterioration of the characteristics of the magnetic film, cause errors during recording/reproduction and can also cause a head crash.
• polishing carriers disclosed in the first to fourth patent documents mentioned above provide certain effects in reducing the scratches of the outer end face of the glass substrate and in reducing the particles occurring upon contact with the inner peripheral surface of the accommodation container but these polishing carriers do not provide the number of scratches that can completely eliminate the protrusions that may result from the movement of the sodium ions and the lithium ions described above.
• polishing carriers limit the shape, material and hardness of the carriers, become unusable due to wear in the course of repetition of use and impede a decrease in the polishing cost.
• the method disclosed by the fifth patent document ' 155 first applies an insolubilization treatment at the outer end face of the glass substrate or a treatment for reducing the alkali metal content and then conducts polishing. Therefore, it has been found that scratches develop due to the contact between the outer end face of the glass substrate and the inner peripheral surface of circular retaining holes of the polishing carrier during polishing and the number of scratches is not reduced to the number of scratches that can completely eliminate the protrusions that may result from the movement of the sodium ions and the lithium ions described above.
• this invention provides a production method for a magnetic disk substrate that can be applied irrespective of the shape, material and hardness of the polishing carrier and can prevent the occurrence of scratches on an outer end face of the glass substrate as well as the occurrence of protrusions that may presumably result from the movement of sodium ions and lithium ions, a magnetic disk glass substrate obtained by such a method and having excellent characteristics, a production method for a magnetic disk characterized in that a magnetic recording layer is formed on such a magnetic disk glass substrate, and a magnetic disk.
• the present invention provides the following inventions.
• a production method for a magnetic disk substrate which polishes a glass substrate by holding the glass substrate in a polishing carrier, characterized in that polishing is carried out by using a polishing carrier in which an inner surface capable of coming into contact with an outer end face of the glass substrate is coated with a resin.
• thermoplastic resin is a polyester, polyamide, polyolefin, ABS or polystyrene resin.
• thermosetting resin is an epoxy, phenol, unsaturated polyester or polyimide resin.
• the resin is not fiber reinforced.
• this invention provides a production method for a magnetic disk substrate capable of preventing the occurrence of scratches on an outer end face of the glass substrate, a magnetic disk glass substrate obtained by such a method and having excellent characteristics, a production method of a magnetic disk characterized in that a magnetic recording layer is formed on such a magnetic disk glass substrate, and a magnetic disk.
• polishing is carried out by using a polishing carrier in which the inner surface can come into contact with an outer end face of the glass substrate and is coated with resin when the glass substrate is held and polished by the polishing carrier.
• Amorphous, chemically tempered or crystallized glass that has generally been used for the magnetic disk substrate can be used as the glass substrate in the invention.
• glasses such as soda lime, aluminosilicate, lithium silicate, lithium aluminosilicate, aluminoborosilicate, and so forth.
• the chemical tempered glass glass that is brought into contact with a molten salt at a high temperature to cause ion exchange of alkali ions in the glass with different kinds of alkali ions in the molten salt and is tempered by the compressive stress is suitable.
• the crystallized glass are those which are obtained by re ⁇ heating glass under a controlled condition and precipitating and growing a large number of fine crystals.
• Concrete examples are an Al 2 Os-SiO 2 -Li 2 O type, a B 2 O 3 -Al 2 O 3 -SiO 2 -Li 2 O type, and so forth.
• the invention can prevent the occurrence of the scratches of the outer end face of the glass substrate and the occurrence of protrusions on a magnetic film, a protective film, etc, that may presumably result from the movement of sodium ions and lithium ions when glass of the glass substrate contain the alkali metal.
• the thicknesses of such glass substrates are generally selected from the range of about 0.1 to about 2 mm.
• Polishing in the invention can include lapping and polishing as long as they can be carried out by using the polishing carrier.
• Lapping is defined as pre-process for polishing.
• lapping is generally carried out by abrading the surface of the glass substrate and a plate through a polishing slurry prepared by dispersing free abrasives in water, or the like.
• the polishing slurry is used for all of amorphous, chemically tempered and crystallized glasses.
• the abrasives are cerium oxide, zirconium oxide, silicon dioxide, and so forth, but cerium oxide is suitable from the aspect of a polishing speed.
• polishing operations can be carried out in a customary manner in the invention but it is necessary that polishing is carried out by using the polishing carrier in which the inner surface capable of coming into contact with the outer end face of the glass substrate is coated with resin.
• the resin used for resin coating is a thermoplastic resin such as polyester, polyamide, polyolefin, ABS or polystyrene resin or a thermosetting resin such as epoxy, phenol, unsaturated polyester or polyimide resin, but an epoxy resin is most suitable.
• these resins are not fiber reinforced.
• the thickness of the resin coating is in the range of about
• the polishing carrier itself that is resin coated in the invention, is generally formed of a fiber reinforced resin.
• the resin in this fiber reinforced resin include thermoplastic resins such as polyester, polyamide, polyolefin, ABS or polystyrene resin or thermosetting resins such as epoxy, phenol, unsaturated polyester or polyimide resin, but the resin need not be same as the resin in the resin coating.
• the resin in the fiber reinforced resin is generally a glass fiber, a carbon fiber or an aramide fiber.
• the invention further provides a glass substrate polishing carrier formed of the fiber reinforced resin and a glass substrate polishing carrier in which the inner surface can come into contact with an end face of the glass substrate and is coated with resin (preferably with a resin that is not fiber reinforced) .
• the resulting magnetic disk substrate is polished. (When the polishing is lapping, the end ' face on the inner peripheral side facing inner diameter holes and the end face on the outer peripheral side are chamfered, respectively, the resulting inner peripheral side end face and outer peripheral side end face are polished to mirror surface and the main surface of the glass substrate is polished) . Thereafter, the magnetic disk substrate is washed and dried in a customary manner and is used for the production of a magnetic disk. For example, texturing for forming texture grooves in a head traveling direction is first applied to the substrate, whenever necessary. Next, a base film made of a Cr alloy is formed by sputtering on this substrate.
• a magnetic recording layer made of a Co base alloy is formed to a thickness of about 10 to 100 nm on this base film, for example.
• a protective film of carbon, or the like, is preferably formed further on this magnetic recording layer to improve corrosion resistance, sliding resistance, etc.
• Hydrogenated carbon, by sputtering, or diamond-like carbon, by CVD, as examples, are formed to a film thickness of about 1 to about 50 nm on the carbon.
• Perfluoropolyether or a product obtained by esterifying or amidating the terminals of the former is diluted with a solvent and is applied by spraying, dipping, spin coating, etc to a film thickness of about 0.5 to 5 nm, as a lubrication layer, to the surface of this carbon protective film, and the durability, the reliability, etc can be further improved.
• the magnetic glass substrate obtained by the method of the invention has a small number of scratches on the outer end face and can prevent the occurrence of protrusions on the magnetic film and the protective film that may result from the movement of sodium ions and lithium ions when the magnetic disk is produced by using this glass substrate.
• the invention will be explained in further detail with reference to Examples thereof, the invention is not limited to these Examples unless the invention exceeds the gist thereof.
• the occurrence of scratches on the end face of the glass substrate is determined by setting magnification of an optical microscope to 120X and observing the entire periphery of the outer end face through the optical microscope.
• the occurrence of the protrusions on the surface of the magnetic disk is confirmed in the following way. (1) The glass substrates are charged into a magnetic disk production process and magnetic disks are obtained. (2) The magnetic disks are accommodated inside a magnetic disk drive and are left standing under a constant temperature/constant humidity condition of 85°C and 90%.
• each magnetic disk taken out is inspected and measured by eye and with halogen light.
• the outer peripheral portions of the protrusions occurring on the surfaces of the magnetic disk appear slightly opaque when observed by eye under halogen light.
• the degree of occurrence of a slightly opaque portion is judged in the following five levels: Level 0: No opaque portion.
• Level 1 Up to two slightly opaque portions of 5 mm or less in the circumferential direction per surface.
• Level 1.5 Three to four slightly opaque portions of 5 mm or less in the circumferential direction per surface.
• Level 2 Five to ten slightly opaque portions of 5 mm or less in the circumferential direction per surface.
• Level 3 Eleven or more slightly opaque portions of 5 mm or less in the circumferential direction per surface, or slightly opaque portions greater than 5 mm in the circumferential direction occur in less than 1/3 of entire circumference.
• Level 4 Slightly opaque portions greater than 5 mm in the circumferential direction occur in more than 1/3 to less than 4/5 of entire circumference.
• Level 5 Slightly opaque portions greater than 5 mm in the circumferential direction occur in more than 4/5 of entire circumference.
• Example 1 A 2.5-in. lithium silicate-type crystallized glass substrate was polished by using a polishing carrier (material: glass fiber reinforced epoxy resin) in which the inner surface was resin coated. The resin coating (without reinforcing fiber) was formed of an epoxy resin (Konishi Bond E set: two-component mixing chemical reaction-type epoxy resin adhesive) to a thickness of 50 ⁇ m. In polishing, cerium oxide polishing slurry (concentration 10 mass%) was supplied and polishing was carried out at a rate of revolution of the plates of 35 rpm and a processing pressure of 70 g/cm 2 (about 6,864 Pa) for 40 minutes.
• the resulting substrate was subjected to texture processing by using diamond slurry and a non- woven fabric and was fitted to a sputtering apparatus.
• a base film of a chromium alloy and a magnetic film of a cobalt alloy were formed by sputtering on both surfaces of the substrate.
• a diamond-like carbon film was formed by sputtering on both surfaces and "Fonblin Z- Tetraol" (product of Solvay Solexis Co.) as a lubricant was further coated to form a magnetic disk.
• the total thickness of the films formed was 90 nm and the thickness of the film formed by CVD was 10 nm.
• a glass substrate and a magnetic disk were produced in the same way as in Example 1 with the exception that a polishing carrier with notches that could come into contact with the glass substrate was used. When the occurrence of the scratches on the outer end face of the resulting glass substrate was observed, the number of scratches was 198. The resulting magnetic disk had a Level 2 to 3 and protrusions were observed on the surfaces of the magnetic disk. Comparative Example 2 :
• a glass substrate and a magnetic disk were produced in the same way as in Example 1 with the exception that a polishing carrier in which the inner surface was not resin coated was used. When the occurrence of scratches on the outer end face of the resulting glass substrate was observed, the number of scratches was 376. The resulting magnetic disk had the Level 4 to 5 and protrusions were observed on the surfaces of the magnetic disk.
• this invention provides a production method for a magnetic disk substrate that can be applied irrespective of shape, material and hardness of a polishing carrier and can prevent the occurrence of scratches on an outer end face of the glass substrate, a magnetic disk glass substrate obtained by such a method and having excellent characteristics, a production method of a magnetic disk characterized in that a magnetic recording layer is formed on such a magnetic disk glass substrate, and a magnetic disk.

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• 2005
  • 2005-06-07 JP JP2005166959A patent/JP2006088314A/ja active Pending
  • 2005-08-26 WO PCT/JP2005/016052 patent/WO2006022445A1/en active Application Filing
  • 2005-08-26 CN CNA2005800281589A patent/CN101005924A/zh active Pending
  • 2005-08-26 US US11/661,194 patent/US20070298688A1/en not_active Abandoned

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