WO2013100157A1 - Procédé de fabrication d'un substrat de verre pour disques magnétiques - Google Patents

Procédé de fabrication d'un substrat de verre pour disques magnétiques Download PDF

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Publication number
WO2013100157A1
WO2013100157A1 PCT/JP2012/084244 JP2012084244W WO2013100157A1 WO 2013100157 A1 WO2013100157 A1 WO 2013100157A1 JP 2012084244 W JP2012084244 W JP 2012084244W WO 2013100157 A1 WO2013100157 A1 WO 2013100157A1
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Prior art keywords
base plate
polishing
glass base
glass
abrasive grains
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PCT/JP2012/084244
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English (en)
Japanese (ja)
Inventor
岩田　勝行
京介 飯泉
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Hoya株式会社
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Publication of WO2013100157A1 publication Critical patent/WO2013100157A1/fr

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    • 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

  • the present invention relates to a method for producing a glass substrate for a magnetic disk.
  • a personal computer, a notebook personal computer, or a DVD (Digital Versatile Disc) recording device has a built-in hard disk device for data recording.
  • a magnetic disk having a magnetic layer provided on a glass substrate is used, and magnetic recording information is recorded on the magnetic layer by a magnetic head (DFH (Dynamic Flying Height) head) slightly floating above the surface of the magnetic disk. Recorded or read.
  • a glass substrate is preferably used because the glass substrate is less likely to be plastically deformed than other metal substrates.
  • the magnetic disk in response to a request for an increase in storage capacity in a hard disk device, the magnetic disk has been increased in density of magnetic recording.
  • the magnetic recording information area is miniaturized by using a perpendicular magnetic recording method in which the magnetization direction in the magnetic layer is perpendicular to the surface of the substrate.
  • the storage capacity of one disk substrate can be increased.
  • the flying distance from the magnetic recording surface of the magnetic head is extremely shortened to reduce the magnetic recording information area.
  • the magnetic layer is formed smoothly so that the magnetization direction of the magnetic layer is substantially perpendicular to the substrate surface. For this reason, the surface roughness of the glass substrate is made as small as possible.
  • defects are also caused by defects such as fine particles in addition to local minute irregularities on the main surface of the magnetic disk, so that along the inner and outer circumferences of the magnetic disk in addition to the main surface of the magnetic disk The defects on the end face are also made as small as possible.
  • the main surface of the plate-like glass base plate that has become flat after press molding is ground with a fixed abrasive grain, and this grinding process leaves the main surface.
  • the main surface polishing step is included for the purpose of removing scratches and distortions.
  • a method for manufacturing a glass substrate for a magnetic disk using cerium oxide (cerium dioxide) abrasive grains as an abrasive is known in the above-mentioned main surface polishing step (Patent Document 1).
  • end face polishing of the glass base plate and polishing of the main surface using cerium oxide as loose abrasive grains (first polishing) are performed, and thereafter, the glass base plate is chemically strengthened.
  • zirconia zirconium dioxide
  • cerium oxide which is relatively difficult to obtain because of rare metals
  • a magnetic disk is produced by forming a magnetic layer on a glass substrate produced using the above zirconia as a polishing agent for loose abrasive grains of a glass base plate
  • glass produced using cerium or silica as an abrasive.
  • problems such as a head crash failure and a thermal asperity failure are more frequently caused.
  • the problem of the above problem does not occur with cerium oxide or silica under the circumstances where the flying distance of the magnetic head is extremely shortened by the DFH head and high surface accuracy of the main surface is required for the glass substrate, and zirconia is used. For the first time.
  • cerium oxide or silica is used as an abrasive, there is a method for cleaning the cerium oxide or silica fine particles, even if there is a problem of cerium oxide or silica fine particles fixed to the glass substrate. It was.
  • the present invention manufactures a glass substrate for magnetic disk that is less prone to problems such as head crash failure and thermal asperity failure when a magnetic disk glass substrate is manufactured by polishing with an abrasive of loose abrasive grains.
  • An object of the present invention is to provide a method for manufacturing a glass substrate for a magnetic disk.
  • the inventors of the present application have examined the problem of the above-mentioned problem that is not caused by cerium oxide abrasive grains or silica abrasive grains but is caused by zirconia abrasive grains.
  • zirconia particles are fixed to the main surface when the magnetic layer is formed, even after the mirror surface is polished and the main surface is sufficiently washed to remove particles and the like. I found out that there was a case.
  • a magnetic layer is laminated above the zirconia particles, and minute irregularities are formed on the surface of the magnetic layer.
  • the minute irregularities cause problems such as a head crash failure and a thermal asperity failure.
  • the zirconia particles fixed to the main surface of the glass substrate are a part of the zirconia abrasive grains used for polishing, and are fixed to the side wall surface located at the outer peripheral end of the glass base plate during the production of the glass substrate. I also found it.
  • zirconia has a higher Mohs hardness than cerium and silica, it has been found that zirconia tends to stick into minute cracks or recesses on the side wall surface of the glass substrate and stick to the side wall surface. Accordingly, the inventors of the present application have come up with the invention of the aspect described below.
  • One aspect of the present invention is a method for producing a glass substrate for a magnetic disk.
  • the manufacturing method is Holding the glass base plate on a carrier, and polishing the main surface of the glass base plate with a polishing apparatus using Mohs hardness (former Mohs hardness) of 8 or more abrasive grains as free abrasive grains;
  • Mohs hardness former Mohs hardness
  • the glass is provided with an anti-adhesion layer that prevents the loose abrasive grains from adhering to the side wall surface of the glass base plate located at the outer peripheral end portion in contact with the carrier.
  • Preparing a base plate Preparing a base plate.
  • the anti-adhesion layer can be removed by polishing after the main surface is polished.
  • another aspect of the present invention is a method for manufacturing a magnetic disk glass substrate.
  • the manufacturing method includes a step of chemically strengthening at least a side wall surface located at an outer peripheral end of a glass base plate, and holding the glass base plate subjected to the chemical strengthening on a carrier to release zirconia abrasive grains. And polishing the main surface of the glass base plate with a polishing apparatus using the abrasive grains.
  • the glass base plate has a disk shape, and when the polishing is performed, a pair of main surfaces of the glass base plate are sandwiched between polishing pads in a state where the glass base plate is held by a holding hole of the carrier. Supplying a polishing liquid containing the zirconia abrasive grains between the glass base plate and the polishing pad, and relatively moving the polishing pad and the glass base plate, thereby allowing the main plate of the glass base plate to move. It is preferable to polish the surface and form a compressive stress layer on the side wall surface of the glass base plate by the chemical strengthening.
  • the chemical toughening treatment conditions are adjusted so that the fracture toughness value K 1c of the glass base plate after the chemical strengthening is 0.7 [MPa / m 1/2 ] or more as measured by a Vickers hardness meter. Is preferred.
  • the arithmetic mean roughness Ra of the side wall surface of the glass base plate before polishing the main surface of the glass base plate is 1 ⁇ m or less.
  • the arithmetic average roughness Ra of the side wall surface is 1 ⁇ m or less by performing end surface polishing on the side wall surface of the glass base plate before polishing the main surface of the glass base plate.
  • the average particle diameter of the zirconia abrasive is preferably 0.1 to 2 ⁇ m.
  • a maximum gap of 2.1 mm or less is provided between the holding hole for holding the glass base plate of the carrier and the glass base plate.
  • the chemical strengthening is to strengthen the entire surface including the side wall surface and a pair of main surfaces of the glass base plate, and after the step of chemically strengthening the glass base plate, It is preferable to include a step of grinding the compression layer formed on the main surface of the glass base plate by the chemical strengthening before the step of polishing the surface.
  • the arithmetic average roughness Ra of the part which contacts the said glass base plate in the said carrier is 5 micrometers or less.
  • (A)-(c) is a figure explaining the magnetic disc produced using the glass substrate for magnetic discs of this invention. It is a figure which shows an example of the flow of the manufacturing method of the glass substrate of this embodiment.
  • (A) is a schematic sectional drawing of the grinding
  • (b) is sectional drawing of the carrier along XX line in (a).
  • FIGS. 1A to 1C are diagrams for explaining a magnetic disk manufactured using the magnetic disk glass substrate of the present embodiment (hereinafter simply referred to as a glass substrate).
  • the method for producing a glass substrate for a magnetic disk according to the present invention comprises the steps of holding a glass base plate on a carrier and using abrasive grains having Mohs hardness (former Mohs hardness) of 8 or more as free abrasive grains in a polishing apparatus.
  • the anti-adhesion layer is obtained by forming a compression layer on the surface of the glass base plate by chemical strengthening. Alternatively, it can be obtained by providing a separate anti-adhesion layer on the side wall surface of the glass base plate.
  • zirconia will be described as an example of abrasive grains having a Mohs hardness (former Mohs hardness) of 8 or more.
  • a compression layer compression stress layer formed on the side wall surface by chemically strengthening the glass base plate
  • a magnetic disk 1 used in a hard disk device shown in FIG. 1A has at least a magnetic layer as shown in FIG. 1B on the main surface of an annular magnetic disk glass substrate (hereinafter referred to as a glass substrate) 2.
  • Layers 3A and 3B including (perpendicular magnetic recording layer) and the like are formed. More specifically, the layers 3A and 3B include, for example, at least an adhesion layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer in order from the side closer to the main surface on the main surface of the glass substrate. Are stacked.
  • the glass substrate 2 is introduced into a vacuum-deposited film forming apparatus, and an adhesion layer to a magnetic layer are sequentially formed on the main surface of the glass substrate in an Ar atmosphere by a DC magnetron sputtering method.
  • CrTi can be used as the adhesion layer
  • CrRu can be used as the underlayer.
  • a CoTaZr / Ru / CoTaZr soft magnetic layer, a CoCrSiO 2 nonmagnetic granular underlayer, a CoCrPt—SiO 2 ⁇ TiO 2 granular magnetic layer, and the like are formed.
  • a magnetic recording medium can be formed by forming a protective layer using, for example, C 2 H 4 by CVD and performing nitriding treatment in which nitrogen is introduced into the surface in the same chamber. Thereafter, for example, PFPE (polyfluoropolyether) is applied on the protective layer by a dip coating method to form a lubricating layer.
  • PFPE polyfluoropolyether
  • each of the magnetic heads 4A, 4B of the magnetic disk 1 is 10 nm or less from the surface of the magnetic disk 1 as the magnetic disk 1 rotates at a high speed, for example, 7200 rpm. For example, it rises 5 nm. That is, the distance H in FIG. 1C is 10 nm or less, for example, 5 nm.
  • the magnetic heads 4A and 4B record or read information on the magnetic layer. As the magnetic heads 4A and 4B float, the magnetic layer is recorded or read out without sliding with respect to the magnetic disk 1, and the magnetic recording information area is miniaturized and the magnetic recording is improved. Achieve densification.
  • the magnetic heads 4A and 4B can be accurately operated in a state where the distance H is maintained at 10 nm or less, more preferably 5 nm or less from the center of the glass substrate 2 of the magnetic disk 1 to the outer peripheral edge 5.
  • the arithmetic average roughness Ra JIS B 0601: 2001
  • a thickness of 0.03 to 0.15 nm is preferable for accurately operating the magnetic heads 4A and 4B while keeping the distance H at 10 nm or less.
  • the arithmetic average roughness Ra of the main surface of the glass substrate 2 is preferably 0.1 nm or less.
  • the arithmetic average roughness Ra is a value obtained by measuring 256 points ⁇ 256 points in a measurement area of 1 ⁇ m ⁇ 1 ⁇ m on the surface of the glass substrate 2 using an atomic force microscope.
  • the manufacturing method using the present embodiment is a head crash failure or a problem that has been a problem even when the main surface is polished using zirconia abrasive grains. It is possible to obtain a glass substrate for a magnetic disk in which troubles such as a thermal asperity failure hardly occur.
  • aluminosilicate glass soda lime glass, borosilicate glass, alkali aluminosilicate glass, alkali borosilicate glass, or the like can be used.
  • alkali aluminosilicate glass can be suitably used in that it can be chemically strengthened and a glass substrate for a magnetic disk excellent in flatness of the main surface and strength of the glass substrate can be produced. .
  • Amorphous glass is more preferable because the surface roughness can be extremely reduced.
  • the composition of the magnetic disk glass substrate of the present embodiment is not limited, but the glass substrate 2 of the present embodiment is preferably converted to oxide standards and expressed in mol%.
  • ⁇ SiO 2 50 to 75%
  • ⁇ Al 2 O 3 1 to 15%
  • At least one component selected from Li 2 O, Na 2 O and K 2 O a total of 5 to 35%
  • An amorphous alkali aluminosilicate glass having a composition having The glass substrate 2 is an annular thin glass substrate.
  • the size of the glass substrate 2 is not limited, for example, it is suitable for a glass substrate for a magnetic disk having a nominal diameter of 2.5 inches.
  • the manufacturing process of the glass substrate 2 will be described. However, the order of the steps described below may be changed as appropriate.
  • FIG. 2 is a diagram illustrating an example of a flow of the glass substrate manufacturing method of the present embodiment.
  • a float method In the formation of a plate-shaped glass blank, for example, a float method is used.
  • molten glass is continuously poured into a bath filled with a molten metal such as tin to obtain, for example, a sheet glass having the above-described composition.
  • the molten glass flows along the traveling direction in a bathtub that has been subjected to a strict temperature operation, and finally a plate-like glass adjusted to a desired thickness and width is formed. From this plate-like glass, a plate-shaped glass blank having a predetermined shape that is the basis of the glass substrate for magnetic disk is cut out.
  • a press molding method can be used for forming the plate-shaped glass blank.
  • a glass gob glass lump made of molten glass is supplied onto a lower mold that is a receiving gob forming mold, and an upper mold that is a lower gob and an opposing gob forming mold is used.
  • the glass gob is press-molded. Thereby, the disk-shaped glass blank used as the origin of the glass substrate for magnetic discs is produced.
  • a plate-shaped glass blank can be manufactured not only using the method mentioned above but well-known manufacturing methods, such as a downdraw method, a redraw method, and a fusion method.
  • a disk-shaped glass blank serving as a base for a glass substrate for a magnetic disk is cut out from a sheet glass made by a known manufacturing method such as a float method, a downdraw method, a redraw method, or a fusion method.
  • a chamfering step for forming a chamfered surface at the ends (outer peripheral end surface and inner peripheral end surface) of the disk-shaped glass base plate is performed.
  • the outer peripheral surface and the inner peripheral surface of the glass base plate processed into an annular shape by the coring step are chamfered by, for example, a metal bond grindstone using diamond abrasive grains.
  • the end portion of the glass base plate has a side wall surface perpendicular to the main surface that is not chamfered and a chamfered chamfered surface.
  • the side wall surface and the chamfered surface are collectively referred to as an end surface.
  • End face polishing step (S18) End face polishing (edge polishing) of the annular glass base plate is performed.
  • the inner peripheral end surface and the outer peripheral end surface of the annular glass base plate are mirror-finished by brush polishing.
  • the plurality of glass base plates laminated with the spacers sandwiched between the glass base plates are simultaneously polished using a polishing brush.
  • the polishing liquid used for end face polishing contains fine particles such as cerium oxide having an average particle diameter (diameter) of 0.5 to 5 ⁇ m as free abrasive grains.
  • the arithmetic average roughness Ra of the side wall surface of the glass base plate is 1 ⁇ m or less, for example, 0.001 to 0.5 ⁇ m.
  • the arithmetic mean roughness Ra of the side wall surface is set to 1 ⁇ m or less because the zirconia abrasive grains described later bite into and adhere to the concave and convex portions on the side wall surface of the glass base plate during the first polishing described later.
  • zirconia has a Mohs hardness (old Mohs hardness) of 8 or more and higher Mohs hardness (old Mohs hardness) than conventional cerium oxide and silica, it will be described later in the concave and convex recesses on the side wall surface of the glass base plate. It is thought that the zirconia abrasive grains tend to bite and stick.
  • the first polishing uses zirconia abrasive grains having a particle size limited as free abrasive grains so that the surface roughness of the main surface falls within the target roughness range.
  • the arithmetic average roughness Ra of the side wall surface is obtained by measuring the stylus type roughness meter while sliding it on the circumference of the side wall surface.
  • the removal allowance (wrapping amount + grinding amount) by lapping of (2) and fixed abrasive grains of (6) (lapping amount + grinding amount) including lapping, grinding and polishing described later (lapping amount + grinding amount + polishing amount). Is about 80 to 90 ⁇ m. Further, the above allowance by the lapping of (2) and grinding by the fixed abrasive of (6) is about 30 to 40 ⁇ m when the allowance including lapping, grinding, and polishing described later is about 0.05 mm. is there.
  • Chemical strengthening step (S22) the annular glass base plate after being ground with the fixed abrasive is chemically strengthened.
  • the chemical strengthening liquid for example, a mixed melt of potassium nitrate (60% by mass) and sodium nitrate (40% by mass) can be used.
  • the chemical strengthening solution is heated to, for example, 250 ° C. to 500 ° C., and the cleaned glass base plate is preheated to, for example, 200 ° C. to 300 ° C., and then the annular glass base plate is placed in the chemical strengthening solution. For example, it is immersed for 0.5 to 5 hours.
  • a cage holding the ends of a plurality of annular glass base plates so as to chemically strengthen both main surfaces of the annular glass base plates.
  • Li ions and Na ions on the main surface, side wall surface and chamfered surface of the glass base plate have a relative ion radius in the chemical strengthening solution.
  • Large Na ions and K ions, respectively are strengthened by forming a compression layer on the side wall surface and the pair of main surfaces of the glass base plate.
  • the chemically strengthened annular glass base plate is washed. For example, after washing with sulfuric acid, it is washed with pure water or the like.
  • the compressed layer corresponds to an anti-adhesion layer for preventing free abrasive grains from adhering to the side wall surface, as will be described later.
  • the fracture toughness value K 1c of the glass workpiece after chemical strengthening processing conditions for chemical strengthening so as measured by Vickers hardness tester with 0.7 [MPa / m 1/2] or more is adjusted Is preferred.
  • various chemical treatment conditions may be changed in advance to determine a treatment condition that achieves the target fracture toughness value K1c .
  • the fracture toughness value K 1c is more preferably 1.0 [MPa / m 1/2 ] or more. Moreover, it is still more preferable in it being 1.3 [MPa / m 1/2 ] or more.
  • Fracture toughness value K 1c is preferably higher, the upper limit of the fracture toughness value K 1c is not particularly provided.
  • the fracture toughness value K 1c is a sharp diamond indenter of known Vickers hardness meter can this be measured by a method of pushing the glass workpiece. That is, the fracture toughness value K1c is obtained by the following equation from the size of the indentation of the indenter remaining on the glass base plate when the Vickers indenter is pushed in and the length of the crack generated from the corner of the indentation.
  • P is the indentation load [N] of the Vickers indenter
  • a is the length [m] half of the diagonal length of the Vickers indentation.
  • E is the Young's modulus [Pa] of the glass base plate
  • C is the length [m] that is half the length of the string.
  • the chemical strengthening treatment conditions include the type of chemical strengthening solution (for example, the mixing ratio of potassium nitrate and sodium sulfate), the temperature of the chemical strengthening solution, the chemical strengthening treatment time, and the like. It is also possible to select a glass composition of the glass base plate such that the fracture toughness value K 1c of the glass base plate after chemical strengthening is 0.7 [MPa / m 1/2 ] or more as described above.
  • the main surface of the glass base plate is a measurement target of the fracture toughness value K1c , but the chemical strengthening is performed because the side wall surface of the end face of the glass base plate is chemically strengthened in the same manner as the main surface.
  • fracture toughness K 1c of the side wall surface of the glass workpiece is the same as the measurement results of fracture toughness K 1c of the main surface can be replaced by fracture toughness K 1c of the main surface.
  • polishing which uses a zirconia abrasive grain as a loose abrasive grain is given to the main surface of the annular
  • the machining allowance by the first polishing is, for example, about 10 to 20 ⁇ m when the machining allowance including lapping, grinding, and first polishing and second polishing described later is about 0.1 mm, for example. When it is about 0.05 mm, it is about 5 to 10 ⁇ m, for example.
  • the purpose of the first polishing is to remove scratches, distortion, waviness, and fine waviness remaining on the main surface by grinding.
  • the average particle diameter (diameter) of the zirconia abrasive grains is, for example, 0.1 to 2 ⁇ m, and preferably 0.2 to 0.8 ⁇ m.
  • the average particle diameter (diameter) is defined by 50% particle diameter (median diameter) measured by SALD-2200 manufactured by Shimadzu Corporation.
  • the polishing liquid (slurry) using zirconia abrasive grains contains, for example, 5 to 15% by mass of zirconia abrasive grains with respect to the polishing liquid.
  • the slurry may further contain a dispersant such as sodium hexametaphosphate or potassium pyrophosphate, or a hard cake inhibitor such as cellulose, maltose or fructose as additives.
  • a dispersant such as sodium hexametaphosphate or potassium pyrophosphate
  • a hard cake inhibitor such as cellulose, maltose or fructose
  • the polishing liquid is circulated and used repeatedly in the polishing step, it is preferable to use these dispersant and hard cake-preventing agent at the same time because a decrease in the polishing rate can be suppressed over a long period of time.
  • As the polishing pad a urethane polishing pad, a suede pad, or the like is used.
  • FIG. 3A is a schematic cross-sectional view of the polishing apparatus 10 used in the first polishing process.
  • FIG. 3B is a cross-sectional view taken along line XX in FIG.
  • the grinding device used in the above-described grinding step (S20) and the polishing device used in the second polishing step (S26) described later can also have the same configuration as this polishing device.
  • the polishing apparatus 10 is a processing apparatus that polishes both main surfaces of a planetary gear motion type glass base plate.
  • the polishing apparatus 10 includes a polishing apparatus main body A and a slurry circulation device B.
  • the polishing apparatus main body A has a polishing pad 11, holding plates 13a and 14a, upper and lower surface plates (upper surface plate 13 and lower surface plate 14), a carrier 15, a sun gear 16 and an internal gear 17 as polishers. is doing.
  • the plurality of polishing pads 11 are made of, for example, soft foamed urethane.
  • Holding plates 13 a and 14 a for holding the polishing pad 11 are attached to the opposed surfaces of the upper surface plate 13 and the lower surface plate 14.
  • the upper surface plate 13 and the lower surface plate 14 rotate in opposite directions.
  • the sun gear 16 and the internal gear 17 are disposed between the upper surface plate 13 and the lower surface plate 14, and a plurality of carriers 15 are disposed between the sun gear 16 and the internal gear 17.
  • five carriers 15 are provided, but the number is not limited to this.
  • the carrier 15 holds a plurality of glass base plates in the holding holes. In FIG.3 (b), although the four glass base plates are provided in the one carrier 15, it is not limited to this number.
  • an epoxy resin containing glass fiber is used for the carrier 15.
  • the glass base plate is set in a holding hole of the carrier 15 using a setting mechanism (not shown).
  • a gear that meshes with the sun gear 16 and the internal gear 17 is formed on the outer periphery of the carrier 15.
  • the sun gear 16 and the internal gear 17 rotate along with the rotation of the upper and lower surface plates 13 and 14, whereby the carrier 15 rotates and revolves (planetary gear motion).
  • the glass base plate 12 held by the carrier 15 is brought into close contact between the upper and lower surface plates 13 and 14 to which the polishing pad 11 is attached, and the carrier 15 is attached to the sun gear 16 and the internal gear 17.
  • the glass base plate 12 is clamped by the upper and lower surface plates 13 and 14.
  • a polishing liquid containing an abrasive is supplied between the polishing pad 11 and the polishing surface of the glass base plate 12 and rotated to rotate the glass base plate 12 while rotating on the upper and lower surface plates 13 and 14. (Planet gear movement) and mirror polishing both sides at the same time.
  • the slurry circulating apparatus B shown in FIG. 3A includes a liquid feed pipe 22 (supply path), a drain pipe 23 (discharge path), a liquid feed groove 24, a drain receiver 25, a liquid feed pump 26, and a slurry tank 27. It has.
  • the polishing liquid supplied from the liquid supply pipe 22 is supplied between the polishing pad 11 and the glass base plate 12 as necessary and sufficient through the liquid supply groove 24.
  • a filter 28 is provided at the end of the liquid supply pipe 22 and a filter 29 is provided at the end of the drainage pipe 23 so as to remove dust generated during polishing.
  • the slurry is circulated and used by a series of circulation paths from the liquid feed pump 26 to the slurry tank 27.
  • the liquid feeding pipe 22 is attached to the liquid feeding pump 26, and the other end is attached to the liquid feeding groove 24.
  • the liquid feeding groove 24 is attached to the upper part of the upper surface plate 13, and supplies the slurry to the polishing apparatus 10 (between the upper surface plate 13 and the lower surface plate 14) through a plurality of holes drilled in the upper surface plate 13.
  • the drainage pipe 23 has one end attached to the drainage receiver 25 and the other end attached to the slurry tank 27.
  • the drainage receiver 25 is for receiving the slurry discharged from the lower surface plate 14, and is connected to the drainage pipe 23 through a plurality of holes drilled in the bottom thereof.
  • the slurry tank 27 is a container that temporarily stores the slurry discharged from the drainage pipe 23.
  • the liquid feed pump 26 sucks up the slurry in the slurry tank 27 and supplies it again to the upper surface plate 13 via the liquid feed pipe 22 and the liquid feed groove 24.
  • the filter 28 is provided between the liquid feeding pipe 22 and the liquid feeding groove 24, and filters the dust mixed in the slurry before introducing the slurry into the polishing apparatus 10.
  • the filter 29 is provided between the drainage pipe 23 and the slurry tank 27, filters dust mixed in the discharged slurry, and introduces the slurry into the slurry tank 27.
  • a pair of main surfaces of the glass base plate 12 are sandwiched between the polishing pads 11 in a state where the glass base plate 12 is held by the holding holes of the carrier 15.
  • a polishing liquid containing zirconia abrasive grains is supplied between the polishing pad 12 and the polishing pad 11 and the glass base plate 12 are moved relatively to polish the main surface of the glass base plate 12.
  • it has a maximum gap of 0.2 to 1.0 mm.
  • the maximum gap is less than 0.1 mm, it is difficult to efficiently take out the glass base plate 12 from the holding hole and to set the glass base plate 12 into the holding hole efficiently.
  • this maximum gap exceeds 2.1 mm, the impact that the glass base plate 12 receives from the holding hole during polishing is increased, and the zirconia abrasive grains are likely to sink into the side wall surface of the glass base plate 12, The zirconia abrasive grains break down and are likely to adhere to the recesses on the side wall surface of the glass base plate 12, and the zirconia abrasive grains or part of the zirconia abrasive grains are likely to cause problems such as head crash failure and thermal asperity failure. .
  • the surface which contacts the side wall surface of the glass base plate 12 of the holding hole of the carrier 15 is obtained by measuring in the circumferential direction (of the holding hole of the carrier) using a stylus type roughness meter.
  • Second polishing (final polishing) step (S26) second polishing is performed on the first polished glass base plate.
  • the machining allowance by the second polishing is, for example, about 1 to 2 ⁇ m.
  • the second polishing is intended for mirror polishing of the main surface.
  • a polishing apparatus having the same configuration as the first polishing is used.
  • the difference from the first polishing is that the type and particle size of the free abrasive grains are different and the hardness of the polishing pad is different.
  • the polishing pad a urethane polishing pad such as foamed urethane or a suede pad is used.
  • the free abrasive grains used in the second polishing for example, fine particles (average particle diameter: about 10 to 50 nm) such as colloidal silica made of silica suspended in a polishing liquid are used. These fine particles are finer than the free abrasive grains used in the first polishing.
  • the slurry which is a polishing liquid in which fine particles such as colloidal silica are turbid, contains, for example, 0.1 to 40% by mass, preferably 3% to 30% by mass of silica with respect to the slurry. It is preferable in terms of securing and increasing the surface roughness.
  • the polished glass base plate is cleaned.
  • the cleaning it is preferable to use a neutral cleaning solution or an alkaline cleaning solution from the viewpoint of not forming defects such as scratches on the glass surface by the cleaning and further reducing the surface roughness.
  • the arithmetic average roughness Ra of the main surface can be set to 0.15 nm or less, for example, 0.03 to 0.15 nm.
  • a plurality of cleaning processes using pure water, IPA, or the like can be performed. It is preferable that at least the cleaning with the acidic cleaning liquid and the cleaning with the alkaline cleaning liquid are not used in combination on the polished glass base plate. In this way, the glass substrate 2 for magnetic disks is produced by washing
  • the chemically strengthened glass base plate is polished with zirconia.
  • polishing using cerium oxide or the like may be performed between the chemical strengthening and the polishing of zirconia.
  • the side wall surface positioned at the outer peripheral end of the chemically strengthened glass base plate is also chemically strengthened. ing. Therefore, it is possible to suppress the zirconia abrasive grains from adhering to the side wall surface and the zirconia abrasive grains from being stuck into the concave portion of the side wall surface during the first polishing.
  • the free abrasive grains used in the first polishing were cerium abrasive grains or alumina abrasive grains having a hardness lower than that of zirconia abrasive grains. These abrasive grains did not stick or sink. That is, conventionally, problems such as a head crash failure and a thermal asperity failure of a magnetic disk have been extremely rare.
  • zirconia abrasive grains are used as the free abrasive grains for the first polishing, problems such as a head crash failure and thermal asperity failure of the magnetic disk occur. Therefore, the first polishing is performed after the glass base plate is chemically strengthened as in this embodiment. This is an effective solution for suppressing problems such as head crash failure and thermal asperity failure of the magnetic disk.
  • a compression layer is formed as an anti-adhesion layer for preventing loose abrasive grains from adhering to the side wall surface located at the outer peripheral edge that contacts the carrier of the glass base plate.
  • a form in which an anti-adhesion layer is separately provided on the side wall surface of the glass base plate can also be used.
  • diamond-like carbon can be formed on the side wall surface of the glass base plate by vapor deposition or thermal CVD. In this case, the diamond-like carbon formed as an anti-adhesion layer may be removed before the final product by ashing with oxygen plasma or the like, or may be left as the final product.
  • the anti-adhesion layer can be removed by polishing the glass base plate including the anti-adhesion layer.
  • the anti-adhesion layer may be a layer made of a resin material that can be removed from the outer peripheral side end surface of the glass substrate by applying heat, light, or electromagnetic waves.
  • the anti-adhesion layer may be a thermosetting resin adhesive mixed with a material having a heat melting property or a heat decomposability, for example, a decomposable adhesive in which a thermoplastic adhesive is added to a known epoxy resin adhesive.
  • the layer which consists of an agent is mentioned.
  • an acrylic resin that can be cured by ultraviolet rays and can be removed by heating may be used as the anti-adhesion layer.
  • thermoplastic resin adhesives can also be used as the anti-adhesion layer.
  • the anti-adhesion layer may be removed from the glass base plate by applying light or electromagnetic waves.
  • a method using excimer light for example, Japanese Patent Application Laid-Open No. 2012-1601
  • electromagnetic waves high-frequency electromagnetic waves
  • JP 2007-314711 A, etc. a method by induction heating
  • problems such as a head crash failure and thermal asperity failure of a magnetic disk caused by using zirconia having a Mohs hardness (former Mohs hardness) of 8 or more as abrasive grains have been solved.
  • the same problem occurs when the abrasive grains having a Mohs hardness (former Mohs hardness) of 8 or more are used. Therefore, in this embodiment, the glass base plate is held on the carrier, and the main surface of the glass base plate is polished by a polishing apparatus using abrasive grains having a Mohs hardness (former Mohs hardness) of 8 or more as free abrasive grains. You can also.
  • cubic zirconia is suitably used in this embodiment because it has a very high Mohs hardness (formerly Mohs hardness) of about 8.5 and a high polishing rate.
  • Mohs hardness now Mohs hardness
  • the outer peripheral end surface in contact with the carrier during polishing is likely to be pierced, and the pierced cubic zirconia cannot be removed by ordinary cleaning. For this reason, when it uses when grind
  • stabilized zirconia obtained by adding about 4 to 15% of yttrium, calcium, magnesium, hafnium or the like to zirconia is called cubic stabilized zirconia or simply cubic zirconia.
  • abrasive grains having a Mohs hardness (formerly Mohs hardness) of 8 or more include alumina and diamond in addition to zirconia.
  • the glass base plate provided with the said anti-adhesion layer including the compression layer formed in the glass base plate by chemical strengthening is an intermediate product obtained from a manufacturer different from the supplier that polishes the main surface of the glass base plate. It may be.
  • the method for producing a glass substrate for a magnetic disk is such that the glass base plate is held on a carrier and abrasive grains having a Mohs hardness (former Mohs hardness) of 8 or more are used as free abrasive grains in a polishing apparatus.
  • the step of polishing the surface and the anti-adhesion preventing the free abrasive grains from adhering to the side wall surface of the glass base plate located at the outer peripheral edge contacting the carrier before the main surface is polished.
  • the step of preparing the glass base plate includes setting the glass base plate in the holding hole of the carrier of the polishing apparatus.
  • polishing of the main surface of this is performed.
  • a difference between the pair of main surfaces on both sides tends to occur in the amount of polishing (polishing amount) of the main surface of the glass base plate.
  • the thickness and stress value of the compression layer of the chemically strengthened glass base plate may not be the same between the pair of main surfaces on both sides, and the glass base plate may be warped.
  • the glass base material is chemically strengthened. It is preferable to provide a step of grinding the compressed layer formed on the main surface of the plate. At this time, the grinding of the main surface of the glass base plate is performed, for example, by the same method (grinding method using fixed abrasive grains) as in step S20 shown in FIG.
  • diamond abrasive grains hardened with resin or the like are used as fixed abrasive grains.
  • loose abrasive grains are used in this grinding, loose abrasive grains are sandwiched between the carrier and the glass base plate, and the side wall surface of the glass base plate is easily damaged.
  • fixed abrasive grains it is preferable to use fixed abrasive grains.
  • the manufacturing method of the glass substrate for magnetic disks of this embodiment is an outer diameter of 65 mm (2.5 inches) or 95 mm (3.5 inches), and with respect to a glass substrate having a thickness of 0.5 mm or more, It is preferably applied from the viewpoint of efficiently exhibiting the effects of the present embodiment described above.
  • Examples and Comparative Examples In order to confirm the effect of the glass substrate manufacturing method of the present embodiment, a 2.5-inch magnetic disk is manufactured from the manufactured glass substrate, a DFH touchdown test is performed, and a glass suitable for a magnetic head (DFH) is obtained. Whether it was a substrate was evaluated. The composition of the manufactured glass substrate satisfies the glass composition described above.
  • the press forming method used in the method for producing a glass substrate for a magnetic disk described in JP2011-138589A was used for forming the glass blank of (1).
  • alumina-based free abrasive grains having an average particle diameter of 20 ⁇ m were used.
  • a plurality of glass blanks laminated with a spacer sandwiched between glass blanks was polished using a polishing brush with cerium oxide having an average particle diameter of 1 ⁇ m as free abrasive grains.
  • grinding is performed using a grinding apparatus in which diamond sheets using diamond abrasive grains (average particle diameter: 1 to 20 ⁇ m) as fixed abrasives are attached to the upper and lower surface plates. did.
  • a mixed liquid of potassium nitrate (60 mass%) and sodium nitrate (40 mass%) or the like is used, the temperature of the chemical strengthening liquid is 380 ° C., and a glass blank preheated to 100 ° C. is 60 Dipped for a minute.
  • the polishing apparatus 10 was used to polish using zirconia abrasive grains having an average particle diameter of 0.5 ⁇ m (polishing amount 10 ⁇ m).
  • polishing was performed using colloidal silica having an average particle diameter of about 40 nm using a polishing apparatus similar to the polishing apparatus 10 (polishing amount 1 ⁇ m).
  • the arithmetic average roughness Ra JIS B 0601: 2001
  • the arithmetic average roughness Ra is a value obtained by measuring 256 points ⁇ 256 points using an atomic force microscope with respect to a measurement area of 1 ⁇ m ⁇ 1 ⁇ m on the surface of the glass substrate 2.
  • the glass blank after the second polishing was cleaned using a neutral cleaning solution and an alkaline cleaning solution.
  • a magnetic disk was formed on the obtained glass substrate to produce a magnetic disk, and a DFH touchdown test was performed.
  • Evaluation was performed as follows according to the protrusion amount of the DFH head element portion. 5.0 nm or more (level 2 to level 5) is acceptable. Level 1: Less than 5.0 nm Level 2: 5.0 nm or more, less than 6.0 nm Level 3: 6.0 nm or more, less than 7.0 nm Level 4: 7.0 nm or more, less than 8.0 nm Level 5: 8.0 nm or more Here, the higher the number of levels, the better, and level 5 is the best.
  • Example 1 In Example 1, as described above, (1) glass blank molding, (2) lapping step, (3) coring step, (4) chamfering step, (5) end surface polishing step, The grinding process with the fixed abrasive grains of (6), the chemical strengthening process of (7), the first polishing (main surface polishing) process of (8), and the second polishing (final polishing) process of (9) in this order. Went to.
  • Comparative Example In the comparative example, (1) glass blank molding, (2) lapping step, (3) coring step, (4) chamfering step, (5) end face polishing step (machining step) ), (6) After performing the grinding step with the fixed abrasive, (8) first polishing (main surface polishing) step is performed, and then (7) chemical strengthening step, (9) second polishing step. The polishing (final polishing) step was performed in this order.
  • Example 1 passed and the comparative example failed.
  • the particles were fixed between the glass substrate and the magnetic layer.
  • the particles were found to be zirconia. It turned out to be a particle. That is, it was found that the residue of the zirconia abrasive grains used for the first polishing adhered to the main surface of the glass substrate was the cause of the failure of the durability test. From this, it can be seen that performing the chemical strengthening step and the first polishing (main surface polishing) step hardly causes problems such as a head crash failure and a thermal asperity failure.
  • Example 2 to Example 6 Further, as in the present embodiment, after the chemical strengthening step (7), the first polishing (main surface polishing) step (8) is performed, and the strengthening temperature and the immersion time in the chemical strengthening step are changed. As shown in Table 1, glass substrates with various fracture toughness values K 1c were produced. Except for the fracture toughness value K1c , the same conditions as in Example 1 were used. At this time, each of Examples 2 to 6 was subjected to a DFH touchdown test. Table 1 below shows the fracture toughness value K1c and the evaluation results of the DFH touchdown test. In Table 1, level 2 is represented by ⁇ , level 3 is represented by ⁇ , level 4 is represented by OO, and level 5 is represented by OO. Here, the higher the number of levels, the better, and the level 5 is the best. Therefore, ⁇ is better than ⁇ , and more ⁇ is better.
  • the fracture toughness value K 1 c is preferably 0.7 [MPa / m 1/2 ] or more.
  • the arithmetic average roughness Ra of the side wall surface of the glass base plate was changed by changing the polishing time of the end face polishing in (5) using cerium oxide as loose abrasive grains. The same conditions as in Example 1 were used except for the polishing time.
  • the arithmetic average roughness Ra was determined by measuring while sliding a stylus type roughness meter on the circumference of the side wall surface. The average particle size of cerium oxide was 0.5 to 5 ⁇ m.
  • the DFH touchdown test was done and evaluated. Table 2 below shows the fracture toughness value K1c and the evaluation results of the DFH touchdown test. In Table 2, level 2 is represented by ⁇ , level 3 is represented by ⁇ , and level 4 is represented by ⁇ .
  • the arithmetic average roughness Ra is preferably 1 ⁇ m or less, more preferably the arithmetic average roughness Ra as in Example 7 is preferably 0.5 ⁇ m or less.
  • Example 10 to 12 Next, by changing the size of the holding hole of the carrier 15 of the polishing apparatus 10 used for the first polishing, the maximum gap between the glass blank 12 and the holding hole is changed, and the glass substrate in each maximum gap is changed. Produced. The same conditions as in Example 1 were used except for the size of the holding hole. The glass substrate was subjected to a DFH touchdown test and evaluated in the same manner as in the above examples. From Table 3 below, it can be seen that the maximum gap between the glass blank 12 and the holding hole of the carrier 15 is preferably 2.1 mm or less, and more preferably 1.0 mm or less. As described above, the lower limit of the maximum gap is 0.1 mm, for example. In Table 3, level 2 is indicated by ⁇ , level 3 is indicated by ⁇ , and level 4 is indicated by ⁇ .

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Manufacturing Of Magnetic Record Carriers (AREA)
  • Magnetic Record Carriers (AREA)

Abstract

Le procédé de fabrication d'un substrat de verre pour disques magnétiques selon l'invention comprend : une étape dans laquelle une ébauche de verre plate est maintenue sur un support et la surface principale de l'ébauche de verre plate est polie grâce à une machine à polir au moyen de grains abrasifs ayant une dureté de Mohs (dureté de Mohs ancienne) supérieure ou égale à 8, tels que des grains abrasifs libres ; et une étape dans laquelle une couche de prévention d'adhérence pour empêcher les grains abrasifs libres d'adhérer à une surface de paroi latérale qui est positionnée dans une partie périphérique externe de l'ébauche de verre plate, ladite partie périphérique externe étant en contact avec le support, est formée avant de polir la surface principale. Un disque magnétique utilisant un substrat de verre pour disques magnétiques fabriqué grâce à ce procédé n'est pas sujet à des problèmes tels qu'un écrasement de tête et une aspérité thermique.
PCT/JP2012/084244 2011-12-29 2012-12-29 Procédé de fabrication d'un substrat de verre pour disques magnétiques WO2013100157A1 (fr)

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JP2005203080A (ja) * 2003-12-19 2005-07-28 Asahi Glass Co Ltd 磁気ディスク用ガラス基板およびその製造方法
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JP2006053965A (ja) * 2004-08-10 2006-02-23 Fuji Electric Device Technology Co Ltd 磁気記録媒体用基板の製造方法並びにそれに用いる両面研磨装置及び基板研磨用キャリア
JP5102261B2 (ja) * 2009-08-19 2012-12-19 Ｈｏｙａ株式会社 情報記録媒体用ガラス基板の製造方法
JP4760975B2 (ja) * 2009-12-22 2011-08-31 旭硝子株式会社 データ記憶媒体用ガラス基板の製造方法及びガラス基板
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JP2005203080A (ja) * 2003-12-19 2005-07-28 Asahi Glass Co Ltd 磁気ディスク用ガラス基板およびその製造方法
JP2010029981A (ja) * 2008-07-29 2010-02-12 Toray Ind Inc 研磨布
JP2011207626A (ja) * 2009-06-04 2011-10-20 Ohara Inc 情報記録媒体用結晶化ガラス基板およびその製造方法

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