WO2015046528A1 - 磁気ディスク用ガラス基板の製造方法及び磁気ディスクの製造方法、並びに研削工具 - Google Patents
磁気ディスク用ガラス基板の製造方法及び磁気ディスクの製造方法、並びに研削工具 Download PDFInfo
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- WO2015046528A1 WO2015046528A1 PCT/JP2014/075940 JP2014075940W WO2015046528A1 WO 2015046528 A1 WO2015046528 A1 WO 2015046528A1 JP 2014075940 W JP2014075940 W JP 2014075940W WO 2015046528 A1 WO2015046528 A1 WO 2015046528A1
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- grinding
- glass substrate
- abrasive grains
- magnetic disk
- glass
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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
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- the present invention relates to a method for manufacturing a glass substrate for a magnetic disk mounted on a magnetic disk device such as a hard disk drive (HDD) and a method for manufacturing a magnetic disk.
- a magnetic disk device such as a hard disk drive (HDD)
- HDD hard disk drive
- a magnetic disk as one of information recording media mounted on a magnetic disk device such as a hard disk drive (HDD).
- a magnetic disk is configured by forming a thin film such as a magnetic layer on a substrate, and an aluminum substrate has been conventionally used as the substrate.
- the ratio of the glass substrate capable of narrowing the distance between the magnetic head and the magnetic disk as compared with the aluminum substrate is gradually increasing.
- the surface of the glass substrate is polished with high accuracy so as to increase the recording density so that the flying height of the magnetic head can be reduced as much as possible.
- HDDs high recording capacity and lower prices. In order to achieve this, it is necessary to further improve the quality and cost of glass substrates for magnetic disks. It is coming.
- high smoothness on the surface of the magnetic disk is indispensable for reducing the flying height (flying height) necessary for increasing the recording density.
- a substrate surface with a high smoothness is required in the end. Therefore, it is necessary to polish the glass substrate surface with high accuracy.
- further polishing is performed to reduce the surface roughness and microwaviness, thereby reducing the main surface. Has achieved extremely high smoothness.
- a diamond pad is a diamond particle or agglomerates (concentrated abrasive grains) in which several diamond particles are hardened with a binder such as glass, and then a sheet using a support material such as a resin (for example, acrylic resin). It is fixed.
- a resin layer containing diamond may be formed on the sheet, and then a groove may be formed in the resin layer to form a protrusion.
- the diamond pad referred to here is not necessarily a general name, but is referred to as a “diamond pad” for convenience of explanation in this specification.
- abrasive grains with a distorted shape are present between the surface plate and the glass and are non-uniform, so if the load on the abrasive grains is not constant and the load is concentrated, the surface of the surface plate Because of the low elasticity of cast iron, deep cracks enter the glass, the work-affected layer is deep, and the processing surface roughness of the glass also increases, so a large amount of removal was required in the subsequent mirror polishing process. It was difficult to reduce processing costs.
- the abrasive grains are uniformly present on the surface of the sheet, so that the load is not concentrated, and in addition, the abrasive is fixed to the sheet using resin. Therefore, even if a load is applied to the abrasive grains, the high elastic action of the resin fixing the abrasive grains makes the cracks (deformed layer) on the processed surface shallow, and the processed surface roughness can be reduced. The load on the machine (such as machining allowance) is reduced, and processing costs can be reduced.
- the surface roughness of the processed surface can be reduced, the load on the subsequent mirror polishing process is reduced, and the processing cost of the glass substrate is reduced.
- reduction is possible, according to the study of the present inventors, it has been found that there are the following problems.
- the present inventor also examined the cause, and found that uneven grinding, that is, partial grinding failure (a state where only a part of the glass substrate surface was ground and the rest was not ground) occurred. .
- the above-mentioned defects are remarkably generated when a mirror-finished glass substrate produced by a float process or the like is processed, or when the abrasive grain size is reduced.
- Patent Document 4 the fact that the execution pressure, that is, the processing rate is different between the upper and lower surface plates is used as it is, and the undulation is made uniform on the front and back surfaces of the substrate by reducing the undulation as the processing amount increases. It was converted.
- Patent Document 4 it has been found that there are the following problems. In other words, processing with a difference in processing rate between the upper and lower surface plates as in the prior art is unstable, and even when the technique of Patent Document 4 is applied, Although the surface plate side was sufficiently ground, the surface of the lower surface plate side had a certain percentage of defects that the whole or part of the surface was not ground.
- a glass substrate produced by the float process is usually a mirror surface having a surface roughness Ra of 5 nm or less, but it has also been found that the above-mentioned defects are remarkably generated when such a glass substrate having a mirror surface is processed.
- the present invention has been made to solve such a conventional problem, and a first object of the present invention is to perform a stable grinding process in which grinding unevenness does not occur in a grinding process using fixed abrasive grains.
- a method of manufacturing a glass substrate for a magnetic disk capable of reducing the occurrence rate of flatness defects after processing and capable of manufacturing a high-quality glass substrate, and a method of manufacturing a magnetic disk using the glass substrate obtained thereby, and A grinding tool suitable for the grinding process is provided.
- the second object is to perform stable grinding even when there is a difference in the execution pressure between the upper and lower surface plates during grinding with fixed abrasive grains, and high quality. It is providing the manufacturing method of the glass substrate for magnetic discs which can manufacture this glass substrate, and the manufacturing method of a magnetic disc using the glass substrate obtained by it.
- the present inventor has found that micro-waviness exists on the surface of the diamond pad provided with diamond abrasive grains (concentrated abrasive grains).
- diamond abrasive grains Concentrated abrasive grains.
- the present inventor has sought a solution capable of performing stable grinding by paying attention to the relationship between the protruding amount of the abrasive grains protruding from the concentrated abrasive grains and the micro waviness on the surface of the diamond pad. As a result, the present invention has been completed.
- the present inventor makes processing unstable when continuously batch-processed, and the upper surface plate side of the glass substrate is often ground, and the surface of the lower surface plate side is wholly or partially.
- Grinding is performed together with the grinding fluid, but the grinding fluid is inevitably concentrated on the lower surface plate during processing.
- grinding waste sludge is generated with the grinding process.
- the glass binder around the abrasive grains is a grinding scrap and a binder. Glass which is the same material is likely to adhere, and this is considered to occur particularly remarkably on the lower surface plate side, and the above-mentioned defects are likely to occur.
- the present inventor cannot perform stable grinding by a method that uses the difference in execution pressure, that is, the machining rate as it is with the upper and lower surface plate as in the prior art. Even when there is a difference in execution pressure between the surface plates, the present invention has been sought for a solution that can make the processing rate of the upper and lower surface plates uniform and can perform stable grinding. It came to complete. That is, in order to solve the above problems, the present invention has the following configuration.
- a method of manufacturing a glass substrate for a magnetic disk including a grinding process for grinding a main surface of a glass substrate, wherein the grinding process includes a plurality of aggregated abrasive grains in which a plurality of abrasive grains are bonded with a glass binder, A grinding tool including a resin bonded to the abrasive grains, wherein a protruding amount from the resin around the abrasive grains on the grinding surface of the grinding tool is a stylus type surface roughness meter.
- a method for producing a glass substrate for a magnetic disk comprising grinding a main surface of a glass substrate using a grinding tool higher than the maximum height of the surface shape measured using
- a method for manufacturing a glass substrate for a magnetic disk comprising a dressing process of a grinding tool and a grinding process for grinding a main surface of a glass substrate, wherein a plurality of grinding abrasive grains bonded with a glass binder, and a plurality of abrasive grains
- a grinding tool including a resin that binds the concentrated abrasive grains, and the amount of protrusion from the resin around the grinding abrasive grains on the grinding surface of the grinding tool in advance causes the grinding surface to become a stylus surface.
- a magnetic treatment characterized in that dressing is performed so as to be higher than the maximum height of the surface shape measured using a roughness meter, and the glass substrate main surface is ground using the dressed grinding tool.
- a method for producing a glass substrate for a disk comprising a dressing process of a grinding tool and a grinding process for grinding a main surface of a glass substrate, wherein a plurality of grinding abrasive grains bonded with a glass binder, and
- a grinding tool for grinding a glass substrate surface comprising a collecting abrasive grain in which a plurality of abrasive grains are bonded with a glass binder, and a resin binding the plurality of the collecting abrasive grains, the collecting abrasive grain
- a grinding tool characterized in that the protruding amount of the abrasive grains protruding from the surface is higher than the maximum height of the surface shape measured on the surface of the grinding tool using a stylus type surface roughness meter.
- (Configuration 7) Grinding that grinds the main surface of a glass substrate by sandwiching a glass substrate between an upper surface plate and a lower surface plate each having a fixed abrasive grindstone in which a plurality of abrasive grains are bonded via a glass binder.
- a method of manufacturing a glass substrate for a magnetic disk including processing, wherein a fixed abrasive grindstone and a lower surface plate on the upper surface plate side so that the ratio of the collected abrasive grains on which the sludge is not fixed is larger in the lower surface plate
- a magnetic disk manufacturing method comprising: forming at least a magnetic recording layer on a glass substrate for a magnetic disk manufactured by the method for manufacturing a glass substrate for a magnetic disk according to any one of Structures 1 to 4 and 6 to 11. Method.
- the present invention it is possible to perform stable grinding without occurrence of uneven grinding in the grinding process using fixed abrasive grains, and the occurrence rate of flatness defects after processing can be reduced. Thereby, it is possible to manufacture a high-quality glass substrate at low cost. Furthermore, a highly reliable magnetic disk can be obtained using the glass substrate obtained thereby. Moreover, the grinding tool suitable for the said grinding process can be provided. In addition, according to the present invention, stable grinding can be performed even when there is a difference in execution pressure between the upper and lower surface plates during the grinding process in the grinding process using the fixed abrasive grains. Thereby, a high quality glass substrate can be manufactured. Further, a highly reliable magnetic disk using the glass substrate obtained thereby can be manufactured.
- a glass substrate for a magnetic disk is usually manufactured through shape processing, main surface grinding, end surface polishing, main surface polishing, chemical strengthening, and the like.
- a glass substrate is obtained by cutting into a predetermined size from a sheet-like glass produced by a float method or a downdraw method.
- a sheet-like plate glass produced by pressing from molten glass may be used.
- the present invention is suitable when a glass substrate having a mirror-like main surface is used at the start of grinding.
- the glass substrate is subjected to a grinding process for improving dimensional accuracy and shape accuracy.
- a main surface of the glass substrate is generally ground using a double-side grinding apparatus and using hard abrasive grains such as diamond.
- a predetermined plate thickness and flatness are processed, and a predetermined surface roughness is obtained.
- the present invention relates to the improvement of this grinding process.
- the grinding process in the present invention is, for example, a grinding process using a grinding wheel including diamond particles as a fixed abrasive.
- a double-side grinding apparatus for example, an upper and lower surface plate to which a diamond pad is attached as a grinding tool. Both main surfaces of the glass substrate are brought into close contact with each other by moving the glass substrate and the upper and lower surface plates relatively while holding the glass substrate with a predetermined pressure by the upper and lower surface plates Grinding at the same time.
- a lubricating liquid (coolant) is supplied to cool the working surface or to promote the processing.
- the grinding tool (fixed abrasive grindstone) used for the grinding treatment in the present invention is, for example, a diamond pad, and its configuration is schematically shown in FIG.
- the diamond pad 1 shown in FIG. 1 has an abrasive agglomerate (referred to as “gathered abrasive” in the present invention) 3 in which some diamond particles 5 (see FIG. 2) are hardened with a binder such as glass. It is affixed to the sheet 2 using a support material such as resin (for example, acrylic resin).
- resin for example, acrylic resin
- the term “fixed abrasive grain” means a grinding abrasive grain fixed in a grinding wheel (grinding tool) such as the above-mentioned concentrated abrasive grain unless otherwise specified.
- the average particle diameter of the abrasive grains means the average particle diameter of the abrasive grains.
- the present inventor has conducted intensive studies focusing on the relationship between the protruding amount of the abrasive grains protruding from the concentrated abrasive grains and the micro waviness on the surface of the diamond pad, and as a result, the abrasive grains protruded from the concentrated abrasive grains. It has been found that stable grinding can be performed by grinding using a diamond pad (grinding tool) whose protrusion amount is higher than the fine waviness on the surface of the diamond pad.
- the grinding process in the present invention includes, as in the above-described configuration 1, a concentrated abrasive in which a plurality of abrasive grains are bonded with a glass binder, and a resin in which the plurality of the concentrated abrasive grains are bonded.
- a grinding tool such as a diamond pad, wherein the amount of protrusion from the resin around the abrasive grains on the grinding surface of the grinding tool is measured using a stylus type surface roughness meter
- the glass substrate main surface is ground using a grinding tool that is higher than the maximum height of the shape.
- the fine undulations existing on the surface of the grinding tool will inhibit the abrasive grains from contacting the glass surface. Since there are many abrasive grains that cannot sufficiently act on the surface (weak effect on the glass surface), the above-mentioned partial grinding failure occurs, and as a result, the occurrence rate of flatness failure after processing increases.
- the abrasive grains are made of glass even if there are micro waviness on the surface of the grinding tool. Since the contact with the surface is not hindered, the abrasive grains work stably on the glass surface, and stable grinding can be performed without uneven grinding. It is also possible to improve the later flatness defect rate to 0%, for example.
- the maximum height of the surface shape of the grinding tool described above is the maximum height difference Rz (JIS B 0601) in the line roughness curve measured with a stylus type surface roughness meter on the grinding surface of the grinding tool surface. : 2001), which is used as an index of the size of the micro-waviness existing on the surface of the grinding tool.
- the measurement width (measurement length) is preferably 2 to 3 mm on the surface of the grinding tool.
- the measurement width is 2.5 mm.
- the measurement location is the grinding surface in contact with the surface of the substrate to be processed among the surfaces of the grinding tool, so if there are grooves or the like on the surface of the grinding surface, make sure to avoid that part. Needless to say.
- the protrusion amount of the abrasive grain of said grinding tool is measured as follows. 10% and 50% from the inner circumference when the distance from the inner circumference to the outer circumference is 100% with respect to the grinding tools on the upper and lower surface plates (usually formed in a disk shape) before grinding. A total of 6 samples (pad pieces) each having a size of 2.5 mm ⁇ 2.5 mm are cut out from the 90% position.
- the maximum height difference between the concentrated abrasive grains and the resin part around the concentrated abrasive grains is measured by cross-sectional shape analysis, etc., and the average of the height differences of all the concentrated abrasive grains The value is defined as the protruding amount of the abrasive grains of the grinding tool of the surface plate. The protruding amount is adjusted so that it is almost equal between the upper and lower surface plates.
- the protruding amount of the grinding abrasive grains of the present invention is higher than the maximum height of the surface shape
- a double-sided grinding device used for grinding is also applied to dressing, and the surface of a grinding tool such as a diamond pad provided on the upper and lower surface plates is controlled to have an appropriate thickness variation # 400.
- the dressing process can be performed with the # 3000 grindstone in contact with the upper and lower surface plates of the double-side grinding apparatus rotated. The smaller the count, the more the resin near the fixed abrasive is scraped and the greater the amount of protrusion.
- the maximum height of the micro waviness on the surface of the grinding tool can be adjusted by appropriately changing the maximum height of the micro waviness on the surface of the grindstone used for dressing.
- it may be processed using a dressing grindstone having a value smaller than the target value of the maximum height of the microwaviness on the surface of the grinding tool.
- the rotation speed of the surface plate may be appropriately selected within the range of 1 to 30 rpm and the surface plate load on the dressing grindstone within the range of 10 to 200 g / cm 2 .
- the material of the grindstone used for the dressing process is not particularly limited, but for example, an alumina grindstone is suitable.
- the dressing process may be performed step by step using a plurality of dressing grindstones having different counts and micro waviness. For example, after first adjusting the protrusion of the grinding tool surface using a dressing stone with a small count and large microwaviness, use a dressing stone with a large count and small microwaviness. It is easy to obtain the desired characteristics of the grinding tool surface by adjusting the height.
- the fine waviness of the dressing grindstone can be measured in the same manner as the fine waviness on the surface of the grinding tool.
- the abrasive grains are preferably diamond grains.
- the average particle diameter of the diamond abrasive grains is preferably in the range of 1.5 to 12 ⁇ m.
- the average particle diameter of the diamond abrasive grains is less than the above range, the cut into the mirror-like glass substrate becomes shallow and the biting into the glass substrate is difficult to proceed.
- the average particle diameter of the diamond abrasive grains exceeds the above range, the roughness of the finish becomes rough, so that there is a possibility that the machining allowance load in the subsequent process becomes large.
- the abrasive grain with an average particle diameter of 3.0 micrometers or less.
- the abrasive grain cannot stably act on the glass substrate, and the occurrence of the above-mentioned grinding unevenness was remarkable. Since the grinding tool managed so that the protruding amount of the abrasive grains is higher than the maximum height of the surface shape of the grinding tool is applied, such a conventional problem can be solved.
- the average grain size of the concentrated abrasive grains is preferably 15 to 50 ⁇ m.
- the average particle diameter is a point where the cumulative curve is 50% when the cumulative curve is obtained with the total volume of the powder group in the particle size distribution measured by the laser diffraction method as 100%. (Hereinafter referred to as “cumulative average particle diameter (50% diameter)”).
- the cumulative average particle diameter (50% diameter) is a value that can be measured using a particle diameter / particle size distribution measuring device.
- the load during processing is preferably 100 g / cm 2 to 150 g / cm 2 .
- the processing load is below the above range, the abrasive grains do not act on the surface of the glass substrate on the mirror surface, and the grinding is difficult to proceed.
- the processing load exceeds the above range, the bite of the abrasive grains with respect to the glass increases, so that the finish roughness becomes rough, and the machining allowance load in the subsequent process may increase.
- a fixed abrasive grindstone in which a plurality of abrasive grains are bonded via a glass binder is provided between an upper surface plate and a lower surface plate, each provided on a grinding surface.
- the fixed abrasive wheel on the upper platen side and the fixed abrasive on the lower platen side so that the difference in processing speed between the upper and lower platen becomes smaller
- the dressing process is performed under different conditions for each surface of the grain grindstone.
- processing with a difference in processing rate with an up-and-down surface plate like the prior art is unstable, and the upper surface plate side of the glass substrate is sufficient when batch processing is performed continuously. Although it is ground, the surface of the lower surface plate side has a defect that the whole or a part is not ground.
- the above-described defects are remarkably generated.
- a glass binder around the abrasive grains is used.
- glass which is grinding waste generated during processing, is likely to adhere, and this is considered to be particularly prominent on the lower surface plate side where the grinding liquid tends to concentrate, and the above-described defects are likely to occur.
- the present inventor cannot perform stable grinding by a method that uses the difference in execution pressure, that is, the machining rate as it is with the upper and lower surface plate as in the prior art.
- the upper surface is set so that the difference in processing speed is reduced between the upper and lower surface plates. It has been found that it is preferable to perform dressing under different conditions on the respective surfaces of the fixed abrasive wheel on the board side and the fixed abrasive wheel on the lower surface plate side.
- the dressing process it is preferable to remove the attached grinding scraps from the surface of the fixed abrasive grindstone. Then, the dressing treatment is performed under different conditions for each surface of the fixed abrasive wheel on the upper surface plate side and the fixed abrasive wheel on the lower surface plate side so that the processing speed decreases between the upper and lower surface plates. In this case, it is preferable to perform a removal process in which the amount of grinding scraps removed from the surface of the fixed abrasive wheel provided on the lower surface plate side is larger than that of the fixed abrasive wheel provided on the upper surface plate side.
- the double-sided grinding machine used for grinding is also applied to the dressing process, with a fixed abrasive grain surface in contact with, for example, a # 400-3000 grinding wheel, and the upper and lower surface plates of the double-sided grinding machine rotated. Can be dressed.
- the material of the grindstone used for the dressing process is not particularly limited, for example, an alumina grindstone, a silicon carbide grindstone, or the like is preferable.
- the dressing process is performed under different conditions for each surface of the fixed abrasive wheel on the upper surface plate side and the fixed abrasive wheel on the lower surface plate side so that the difference in processing speed is reduced between the upper and lower surface plates.
- conditions such as the number of platen rotations at the time of dressing, the processing time, and the number of processings (frequency) are changed on the upper and lower surface plates. Accordingly, it is possible to perform a removal process in which the amount of grinding waste removed from the surface of the fixed abrasive wheel provided on the lower surface plate side is larger than that of the fixed abrasive wheel provided on the upper surface plate side.
- the above-mentioned dressing processing time is suitably in the range of, for example, about 5 to 120 seconds. Set too long.
- the processing time of the upper surface plate can be set in the range of 5 to 60 seconds
- the processing time of the lower surface plate can be set in the range of 20 to 120 seconds.
- the number of times of dressing for example, it is appropriate to carry out every 10 to 100 batches (100 sheets per batch).
- the dressing processing is performed every 20 to 100 batch processing for the upper surface plate processing and every 10 to 50 batch processing for the lower surface processing.
- the conditions such as the surface plate rotation speed, processing time, processing frequency (frequency), etc. at the time of dressing need not be changed on the upper and lower surface plates. At least one of the conditions may be changed.
- the dressing conditions can be set so that the effective abrasive grain ratio after dressing (which can be confirmed with a microscope) is an appropriate ratio between the upper and lower surfaces so that the difference in processing speed is reduced between the upper and lower surface plates. .
- the fixed abrasive is preferably a diamond abrasive.
- the average particle diameter of the diamond abrasive grains is preferably about 1 to 10 ⁇ m.
- the average particle diameter of the diamond abrasive grains is less than the above, the cut into the mirror-like glass substrate becomes shallow, and the bite into the glass substrate is difficult to proceed.
- the average particle diameter of the diamond abrasive grains exceeds the above, the roughness of the finish becomes rough, so there is a possibility that the machining allowance load in the subsequent process becomes large.
- the surface of the glass substrate put into the grinding process is suitable when, for example, Ra is in a mirror surface state of 5 nm or less.
- a grinding tool in which fixed abrasive grains are dispersed such as a diamond pad
- the surface roughness of the glass substrate after completion of the grinding treatment is preferably finished in the range of 0.080 to 0.130 ⁇ m in Ra.
- the glass constituting the glass substrate is preferably an amorphous aluminosilicate glass.
- a glass substrate can be finished to a smooth mirror surface by mirror polishing the surface, and the strength after processing is good.
- an aluminosilicate glass for example, a glass containing SiO2 as a main component and containing 20 wt% or less of Al2O3 is preferable. Further, it is more preferable to use glass containing SiO2 as a main component and containing Al2O3 or less by 15% by weight or less.
- SiO2 is 62% by weight to 75% by weight
- Al2O3 is 5% by weight to 15% by weight
- Li2 ⁇ O is 4% by weight to 10% by weight
- Na2O is 4% by weight to 12% by weight
- ZrO2 is contained in an amount of 5.5% to 15% by weight as a main component
- the weight ratio of Na2O / ZrO2 is 0.5 to 2.0
- the weight ratio of Al2O3 / ZrO2 is 0.4 to 2.5.
- Amorphous aluminosilicate glass that does not contain the following phosphorous oxide can be used.
- SiO2 is 50 to 75%
- Al 2 O 3 is 0 to 5%
- BaO is 0. ⁇ 2%
- MgO, CaO, SrO and BaO in total 14-35%
- molar ratio [(MgO + CaO) / (MgO + CaO + SrO + BaO)] is in the range of 0.85 to 1
- molar ratio [Al2O3 / (MgO + CaO) ] In the range of 0 to 0.30 can be preferably used.
- the glass may contain more than 0% and not more than 10 mol% in total.
- the content of Al 2 O 3 in the glass composition is preferably 15% by weight or less.
- Al 2 O 3 content is 5 mol% or less.
- mirror polishing is performed to obtain a highly accurate plane.
- the amount of removal in the subsequent mirror polishing process can be reduced, the processing load can be reduced, and the processing cost can be reduced.
- a polishing pad of a polisher such as polyurethane while supplying a slurry (polishing liquid) containing a metal oxide abrasive such as cerium oxide or colloidal silica.
- a slurry polishing liquid
- a metal oxide abrasive such as cerium oxide or colloidal silica.
- a glass substrate having high smoothness is obtained, for example, by polishing with a cerium oxide-based abrasive (first polishing process) and then with final polishing (mirror polishing) (second polishing process) using colloidal silica abrasive grains. It is possible.
- the surface of the glass substrate after mirror polishing is preferably a mirror surface having an arithmetic average surface roughness Ra of 0.2 nm or less, more preferably 0.1 nm or less.
- the arithmetic average roughness Ra is a roughness calculated in accordance with Japanese Industrial Standard (JIS) B0601.
- JIS Japanese Industrial Standard
- the surface roughness (the arithmetic average roughness Ra) is practically preferable to be the surface roughness of the surface shape obtained when measuring 5 ⁇ m square with a resolution of 256 ⁇ 256 with an atomic force microscope (AFM). .
- chemical strengthening treatment can be performed.
- a method of the chemical strengthening treatment for example, a low-temperature ion exchange method in which ion exchange is performed in a temperature range not exceeding the glass transition temperature is preferable.
- the chemical strengthening treatment is a process in which a molten chemical strengthening salt is brought into contact with a glass substrate, whereby an alkali metal element having a relatively large atomic radius in the chemical strengthening salt and a relatively small atomic radius in the glass substrate.
- This is a treatment in which an alkali metal element is ion-exchanged, an alkali metal element having a large ion radius is permeated into the surface layer of the glass substrate, and compressive stress is generated on the surface of the glass substrate. Since the chemically strengthened glass substrate is excellent in impact resistance, it is particularly preferable for mounting on a HDD for mobile use, for example.
- the present invention also provides a method for manufacturing a magnetic disk using the above glass substrate for a magnetic disk.
- the magnetic disk is produced by forming at least a magnetic recording layer (magnetic layer) on the magnetic disk glass substrate according to the present invention.
- a magnetic recording layer magnetic layer
- a hexagonal CoCrPt-based or CoPt-based ferromagnetic alloy having a large anisotropic magnetic field can be used.
- a method of forming the magnetic layer it is preferable to use a method of forming a magnetic layer on a glass substrate by a sputtering method, for example, a DC magnetron sputtering method.
- a protective layer and a lubricating layer may be formed on the magnetic recording layer.
- the protective layer an amorphous carbon-based protective layer is suitable.
- a lubricating layer a lubricant having a functional group at the end of the main chain of the perfluoropolyether compound can be used.
- Example 1-1 (1) Substrate preparation, (2) Shape processing, (3) End surface polishing, (4) Main surface grinding, (5) Main surface polishing (first polishing), (6) Chemical strengthening, (7) Main A glass substrate for a magnetic disk of this example was manufactured through surface polishing (second polishing).
- Substrate preparation A large glass plate made of aluminosilicate glass having a thickness of 1 mm produced by the float method was prepared, and cut into a 70 mm ⁇ 70 mm square piece using a diamond cutter. Subsequently, it processed into the disk shape of outer diameter 65mm and internal diameter 20mm using the diamond cutter.
- this aluminosilicate glass SiO 2 : 62 to 75 wt%, ZrO 2: 5.5 to 15 wt%, Al 2 O 3 : 5 to 15 wt%, Li 2 O: 4 to 10 wt%, Na 2 O
- a chemically strengthenable amorphous glass containing 4 to 12% by weight was used.
- the surface of the obtained substrate was a mirror surface with a surface roughness Ra of 5 nm or less.
- This main surface grinding process uses a double-sided grinding machine, and collects aggregated abrasive grains obtained by solidifying a plurality of diamond abrasive grains with a glass binder and a resin binding the plurality of aggregated abrasive grains.
- a glass substrate held by a carrier was set between the upper and lower surface plates to which the fixed abrasive grindstone (diamond pad) provided was attached.
- the diamond pad a diamond pad having an average particle diameter (D50) of diamond abrasive grains of about 3.0 ⁇ m and an average particle diameter (D50) of concentrated abrasive grains of 30 ⁇ m was used. Moreover, it carried out using the lubricating liquid.
- the rotation speed of the surface plate and the load on the glass substrate were adjusted as appropriate.
- dressing was performed using an alumina grindstone before grinding.
- the protruding amount of the abrasive grains was 2 ⁇ m and the maximum height of the surface shape was measured.
- the thickness was 0.5 ⁇ m.
- the first polishing was performed using a hard polisher (hard foamed urethane) as the polisher.
- the polishing liquid was pure water in which cerium oxide was dispersed as an abrasive, and the load and polishing time were appropriately set.
- the glass substrate after the first polishing step was sequentially immersed in cleaning baths of neutral detergent, pure water, IPA (isopropyl alcohol), and IPA (steam drying), ultrasonically cleaned, and dried.
- Chemical strengthening was performed on the glass substrate after the cleaning.
- a chemical strengthening solution in which potassium nitrate and sodium nitrate were mixed was prepared, the chemical strengthening solution was heated to 380 ° C., and the cleaned and dried glass substrate was immersed for about 4 hours to perform chemical strengthening treatment.
- Example 1-2 In the main surface grinding process of Example 1-1, a diamond pad having an average grain size of approximately 9.0 ⁇ m, a protruding amount of abrasive grains of 7 ⁇ m, and a maximum surface shape height of 5 ⁇ m was used. Except for this, grinding was carried out in the same manner as in Example 1-1 to produce a magnetic disk glass substrate.
- Example 1-3 In the main surface grinding of Example 1-1, a diamond pad was used in which the average grain size of the diamond abrasive grains was about 1.5 ⁇ m, the protruding amount of the abrasive grains was 3 ⁇ m, and the maximum height of the surface shape was 1 ⁇ m. Except for this, grinding was carried out in the same manner as in Example 1-1 to produce a magnetic disk glass substrate.
- Example 1-4 In the main surface grinding process of Example 1-1, a diamond pad in which the average grain size of the diamond abrasive grains is about 1.5 ⁇ m, the protruding amount of the abrasive grains is 2 ⁇ m, and the maximum height of the surface shape is 0.5 ⁇ m. Except for the use, grinding was performed in the same manner as in Example 1-1 to produce a magnetic disk glass substrate. (Example 1-5) In the main surface grinding process of Example 1-1, except that a diamond pad having an average grain size of about 12 ⁇ m, a protruding amount of grinding grain of 9 ⁇ m, and a maximum surface shape height of 6 ⁇ m was used. Were ground in the same manner as in Example 1-1 to produce a magnetic disk glass substrate.
- Example 1-1 In the main surface grinding process of Example 1-1, a diamond pad having an average grain size of approximately 3.0 ⁇ m, a protruding amount of the abrasive grain of 2 ⁇ m, and a maximum surface shape height of 2 ⁇ m was used. Except for this, grinding was carried out in the same manner as in Example 1-1 to produce a magnetic disk glass substrate.
- Comparative Example 1-2 In the main surface grinding process of Example 1-1, a diamond pad was used in which the average grain size of the diamond abrasive grains was about 3.0 ⁇ m, the protruding amount of the abrasive grains was 2 ⁇ m, and the maximum height of the surface shape was 3 ⁇ m. Except for this, grinding was carried out in the same manner as in Example 1-1 to produce a magnetic disk glass substrate.
- Example 1-3 In the main surface grinding of Example 1-1, a diamond pad having an average grain size of about 3.0 ⁇ m, a protruding amount of grinding grain of 2 ⁇ m, and a maximum surface shape height of 5 ⁇ m was used. Except for this, grinding was carried out in the same manner as in Example 1-1 to produce a magnetic disk glass substrate.
- Comparative Example 1-4 In the main surface grinding process of Example 1-1, a diamond pad having an average grain size of approximately 9.0 ⁇ m, a protruding amount of abrasive grains of 7 ⁇ m, and a maximum surface shape height of 7 ⁇ m was used. Except for this, grinding was carried out in the same manner as in Example 1-1 to produce a magnetic disk glass substrate.
- Example 1-5 In the main surface grinding process of Example 1-1, a diamond pad having an average grain size of approximately 9.0 ⁇ m, a protruding amount of the abrasive grain of 7 ⁇ m, and a maximum surface shape height of 8 ⁇ m was used. Except for this, grinding was carried out in the same manner as in Example 1-1 to produce a magnetic disk glass substrate.
- Comparative Example 1-6 In the main surface grinding process of Example 1-1, a diamond pad in which the average grain size of the diamond abrasive grains was about 9.0 ⁇ m, the protruding amount of the abrasive grains was 7 ⁇ m, and the maximum height of the surface shape was 10 ⁇ m was used. Except for this, grinding was carried out in the same manner as in Example 1-1 to produce a magnetic disk glass substrate.
- Example 1--7 In the main surface grinding process of Example 1-1, a diamond pad was used in which the average grain size of the diamond abrasive grains was about 1.5 ⁇ m, the protruding amount of the abrasive grains was 2 ⁇ m, and the maximum height of the surface shape was 2 ⁇ m. Except for this, grinding was carried out in the same manner as in Example 1-1 to produce a magnetic disk glass substrate.
- the main surface grinding was performed for a total of 100 sheets per batch.
- the flatness of 20 sheets per batch is measured for a glass substrate after grinding using a flat nesting tester, and a predetermined standard (3 ⁇ m or less) is regarded as a good product, and this standard is not satisfied.
- the occurrence rate of glass substrates was calculated, and the results are shown in Table 1. Further, the results of the surface roughness (Ra) measured by AFM on the glass substrate after the grinding process are shown in Table 2 as ratios based on the values of Example 1.
- the flatness of 20 sheets per batch was measured for a glass substrate after grinding using a flat nesting tester, and a predetermined standard (3 ⁇ m or less)
- the occurrence rate of glass substrates exceeding that (the occurrence rate of defective flatness) was calculated, and the results are shown in Table 1.
- the abrasive grain size is the average particle size (D50) of the diamond fine particles contained in the concentrated abrasive grains.
- the abrasive grain protrusion amount is the aggregate abrasive grains from the resin portion around them. Is a distance protruding from the plane.
- Example 1-1 using the fixed abrasive grindstone in which the protruding amount of the abrasive grains is higher than the maximum height of the surface shape the abrasive grains stably act on the glass surface.
- the flatness defect occurrence rate is 0%, and stable grinding without uneven grinding can be performed. 2.
- the maximum height is 5 ⁇ m and the protruding amount of the abrasive grains is 7 ⁇ m, so that the protruding amount of the abrasive grains is larger than the maximum height of the surface shape.
- Example 1-2 using a high fixed abrasive grindstone, the abrasive grains stably act on the glass surface, and the flatness defect occurrence rate is 0%.
- the surface roughness of the substrate after processing increases compared to Example 1-1 (see Table 2). This is probably because the abrasive grain size is large and the grinding force acting on the glass surface is large.
- Comparative Examples 1-5 and 1-6 in which the abrasive grain size is 9.0 ⁇ m and the protruding amount of the grinding grain is lower than the maximum height of the surface shape, Comparative Examples 1-5 and 1-6 with respect to the glass surface
- the action of the abrasive grains was weak, and the flatness failure was an occurrence rate of 80%. 3.
- the protruding amount of abrasive grains is A and the maximum height of micro-waviness on the ground surface is B
- the grain size of the abrasive grains (diamond fine particles) is 3 ⁇ m or less.
- the defect rate is likely to deteriorate. That is, it can be seen that the present invention is particularly effective when the grain size of the abrasive grains (diamond fine particles) is 3 ⁇ m or less.
- Example 2-1 Through the same steps as in Example 1-1, a glass substrate for a magnetic disk of the following example was produced.
- Substrate preparation A large glass plate made of amorphous aluminosilicate glass having a thickness of 1 mm manufactured by the float method was prepared, and cut into 70 mm ⁇ 70 mm square pieces using a diamond cutter. Subsequently, it processed into the disk shape of outer diameter 65mm and internal diameter 20mm using the diamond cutter.
- This aluminosilicate glass contains SiO2: 62-75 wt%, ZrO2: 5.5-15 wt%, Al2O3: 5-15 wt%, Li2O: 4-10 wt%, Na2O: 4-12 wt% Glass that can be chemically strengthened was used.
- This main surface grinding process uses a double-sided grinding machine, and the upper and lower surfaces where a fixed abrasive grindstone (diamond pad) containing agglomerate grains obtained by solidifying a plurality of diamond particles with a glass binder is attached.
- a glass substrate held by a carrier was set between the surface plates.
- a diamond pad a diamond pad was used in which the average grain size (D50) of the diamond abrasive grains was about 2.5 ⁇ m and the average grain diameter (D50) of the concentrated abrasive grains was 25 ⁇ m.
- D50 average grain size
- D50 average grain diameter
- dressing of the fixed abrasive grindstone was performed on the way. Specifically, first, brushing was performed to remove the grinding liquid and sludge adhering to the surface of the fixed abrasive grains. Next, dressing was performed in a state where the # 1000 alumina grindstone was brought into contact with the surface of the fixed abrasive grains and the upper and lower surface plates of the double-side grinding apparatus were rotated.
- the platen rotation speed, processing time, and processing frequency (frequency) at the time of dressing were set as follows.
- Surface plate rotation speed 20 rpm (same for upper and lower surface plates) Processing time (once): Upper surface plate 60 seconds, lower surface plate 120 seconds
- Processing frequency Upper surface plate is processed every 20 batches (1 batch is 100 sheets), and lower surface plate is processed every 20 batches
- Example 1-1 Main surface polishing (first polishing) Next, the first polishing for removing the scratches and distortions remaining in the grinding process described above was performed in the same manner as in Example 1-1. (6) Chemical Strengthening Next, the glass substrate that had been cleaned was chemically strengthened in the same manner as in Example 1-1. (7) Main surface polishing (second polishing) Next, the second polishing was performed in the same manner as in Example 1-1.
- Example 2-2 In the main surface grinding process of Example 2-1, the number of platen rotations, the processing time, and the number of processing (frequency) during dressing were set as follows.
- Surface plate rotation speed 20 rpm (same for upper and lower surface plates) Processing time (once): Upper surface plate 10 seconds, lower surface plate 20 seconds Processing frequency: Upper surface plate is processed every 40 batches continuously, Lower surface plate is processed every 20 batches, except for the same as Example 2-1. Thus, a glass substrate for a magnetic disk was produced.
- Example 2-3 In the main surface grinding process of Example 2-1, the number of platen rotations, the processing time, and the number of processing (frequency) during dressing were set as follows.
- Surface plate rotation speed 20 rpm (same for upper and lower surface plates) Processing time (once): Upper surface plate 10 seconds, lower surface plate 20 seconds Processing frequency: Upper surface plate is processed every 100 batches continuously, Lower surface plate is processed every 50 batches, except for the same as Example 2-1. Thus, a glass substrate for a magnetic disk was produced.
- Example 2-1 In the main surface grinding process of Example 2-1, the number of platen rotations, the processing time, and the number of processing (frequency) during dressing were set as follows.
- Surface plate rotation speed 20 rpm (same for upper and lower surface plates)
- Processing time once: Upper surface plate 10 seconds, lower surface plate 10 seconds (same upper and lower surface plates)
- Processing frequency Upper surface plate is processed every 50 batches, lower surface plate is processed every 50 batches (same upper and lower surface plates)
- a glass substrate for a magnetic disk was produced in the same manner as in Example 2-1, except for this.
- the ratio of the concentrated abrasive grains (collected abrasive grains to which sludge is not fixed) that acts effectively at the time after the end of the dressing process after 200 batches of the main surface grinding step is calculated.
- Table 3 shows the results of investigation using the upper and lower surface plates. In addition, it judged with sludge having adhered when the sludge covered almost the whole collection abrasive grain, and when adhesion of sludge to the collection abrasive grain was slight, it did not determine with adhesion.
- the ratio of the effective fixed abrasive grains was confirmed by observing the surface of the diamond pad with a microscope and observing a fixed number (upper and lower 100) of fixed abrasive grains. Further, Table 3 shows the ratio of the processing speeds of the upper and lower surface plates of the 201st batch (lower surface processing speed / upper surface processing speed). The ratio of the processing speed is preferably closer to 1, but when it is 1.05 to 0.95, the processing balance of the upper and lower surface plates is improved, and stable processing can be continued.
- the frequency of occurrence of defects in a state where the whole or a part of the substrate surface on the lower surface plate side is not processed is represented by a defective batch rate, and the results are shown in Table 4.
- the defective batch rate is preferably less than 5%.
- On the upper surface plate side no processing defects were found on any of the substrates.
- a total of 201 batch processes were performed. Whether or not it is defective can be determined by visually observing the main surface of the glass substrate using a condenser lamp and whether or not the mirror surface remains.
- the grinding process using the fixed abrasive grains of the present invention is performed properly, the substrate surface becomes white and cloudy and is not a mirror surface. However, when the grinding process is not performed, the portion remains a mirror surface and no cloudiness is observed.
- the one where the ratio (%) of the effective fixed abrasive on the lower surface plate side is higher is better.
- the difference between the upper and lower surface plates is preferably within 20%, more preferably 10% or less (Example 2-1).
- the difference in the effective abrasive grain ratio between the upper and lower surface plates is that the lower surface plate is more than 5% than the upper surface plate, and the processing balance is improved and the defective batch rate is improved. 2.
- Comparative Example 2-1 in which the dressing treatment was performed on the surfaces of the fixed abrasive wheel on the upper platen side and the fixed abrasive wheel on the lower platen side, the lower platen side with a small effective pressure was used.
- the ratio of the effective fixed abrasive grains is lower than the ratio of the effective fixed abrasive grains on the upper surface plate side, and this causes the processing balance in the upper and lower surface plates to deteriorate and the frequency of occurrence of defects increases.
- the following film forming steps were performed on the magnetic disk glass substrates obtained in Examples 1-1 and 2-1 to obtain a magnetic disk for perpendicular magnetic recording. That is, an adhesion layer made of a Ti-based alloy thin film, a soft magnetic layer made of a CoTaZr alloy thin film, an underlayer made of a Ru thin film, a perpendicular magnetic recording layer made of a CoCrPt alloy, a protective layer, and a lubricating layer are sequentially formed on the glass substrate. Filmed. As the protective layer, a hydrogenated carbon layer was formed. The lubricating layer was formed by dipping a liquid lubricant of alcohol-modified perfluoropolyether.
- the obtained magnetic disk was installed in an HDD equipped with a DFH head, and a load / unload durability test was conducted for one month while operating the DFH function in a high temperature and high humidity environment of 80 ° C. and 80% RH. There were no particular obstacles and good results were obtained.
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- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Manufacturing Of Magnetic Record Carriers (AREA)
- Grinding And Polishing Of Tertiary Curved Surfaces And Surfaces With Complex Shapes (AREA)
- Grinding-Machine Dressing And Accessory Apparatuses (AREA)
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Abstract
Description
上記特許文献2等に開示されているような固定砥粒による研削加工を行った場合、加工後の平坦度不良の発生率が高くなることがある。本発明者はその原因についても検討したところ、研削ムラ、つまり部分的な研削不良(ガラス基板表面の一部のみが研削されて残りは研削されていない状態)が発生していることを突き止めた。特に、フロート法等により作製した鏡面のガラス基板を加工する場合や、研削砥粒粒径を小さくした場合に、上述の不良が顕著に発生することも判明した。
従来、ダイヤモンド粒子等を含む固定砥粒(ダイヤモンドパッド)が研削面に配備された上下定盤の間にガラス基板を挟んでガラス基板の表面を研削加工する場合、上定盤と下定盤とでは実行圧力が異なり、通常は上定盤の方が下定盤よりも実行圧力が大きく、加工レートが高いことが知られている。
上記特許文献4には、上定盤側にガラス基板のうねりの大きい面を配置し、下定盤側にうねりの小さい面を配置して研削加工を行うことが開示されている。フロート法等により作製したガラス基板には、表裏で表面うねりに差が生じており、研削装置の上下定盤間にガラス基板を表裏関係なくランダムに配置し、そのまま実行圧力の異なる上下定盤で多数枚のガラス基板を研削加工すると、各ガラス基板で表面うねりの異なるガラス基板が多数生じてしまうことになる。そこで、特許文献4では、表面うねりの大きい面のみを、実行圧力の大きい上定盤によって加工することによって、多数枚のガラス基板を加工した場合でも表裏面のうねりが微小かつ均一なガラス基板を製造することができるとしている。
つまり、従来技術のような上下定盤で加工レートに差がある状態での加工は不安定であり、特許文献4の技術を適用しても、連続でバッチ加工した際に、ガラス基板の上定盤側は十分に研削されるものの、下定盤側の表面は全体あるいは一部が研削されないという不良が一定割合で発生した。フロート法により作製したガラス基板は通常、表面粗さRaが5nm以下の鏡面であるが、このような鏡面のガラス基板を加工する場合に、上述の不良が顕著に発生することも判明した。
研削加工は研削液とともに加工を行うが、加工中に研削液はどうしても下定盤側に集中してしまう。また、研削加工に伴い、研削くず(スラッジ)が発生する。前記ダイヤモンドパッドのような、複数のダイヤモンド砥粒を例えばガラス結合材で固めた固定砥粒(集結砥粒)を用いた場合、砥粒周辺にあるガラス結合材に、研削くずであり結合材と同じ材料であるガラスが付着しやすくなり、これが特に下定盤側で顕著に発生するものと考えられ、上述の不良が発生しやすくなる。
すなわち、上記課題を解決するため、本発明は以下の構成を有する。
ガラス基板の主表面を研削する研削処理を含む磁気ディスク用ガラス基板の製造方法であって、前記研削処理では、複数の研削砥粒がガラス結合材で結合された集結砥粒と、複数の当該集結砥粒を結合している樹脂とを含む研削工具であって、前記研削工具の研削面における前記研削砥粒の周囲の樹脂からの突出し量が、前記研削面を触針式表面粗さ計を用いて測定された表面形状の最大高さよりも高い研削工具を用いて、ガラス基板主表面の研削を行うことを特徴とする磁気ディスク用ガラス基板の製造方法。
研削工具のドレス処理とガラス基板の主表面を研削する研削処理を含む磁気ディスク用ガラス基板の製造方法であって、複数の研削砥粒がガラス結合材で結合された集結砥粒と、複数の当該集結砥粒を結合している樹脂とを含む研削工具であって、予め、前記研削工具の研削面における前記研削砥粒の周囲の樹脂からの突出し量が、前記研削面を触針式表面粗さ計を用いて測定された表面形状の最大高さよりも高くなるようにドレス処理を行い、該ドレス処理された研削工具を用いて、ガラス基板主表面の研削を行うことを特徴とする磁気ディスク用ガラス基板の製造方法。
前記研削砥粒はダイヤモンド砥粒を含むことを特徴とする構成1又は2に記載の磁気ディスク用ガラス基板の製造方法。
(構成4)
主表面が鏡面状態のガラス基板に対して前記研削処理を行うことを特徴とする構成1乃至3のいずれかに記載の磁気ディスク用ガラス基板の製造方法。
複数の研削砥粒がガラス結合材で結合された集結砥粒と、複数の当該集結砥粒を結合している樹脂とを含む、ガラス基板表面を研削する研削工具であって、前記集結砥粒から突出された前記研削砥粒の突出し量が、研削工具表面を触針式表面粗さ計を用いて測定された表面形状の最大高さよりも高いことを特徴とする研削工具。
複数の研削砥粒がガラス結合材を介して結合された固定砥粒砥石が研削面にそれぞれ配備された上定盤及び下定盤の間にガラス基板を挟んでガラス基板の主表面を研削する研削加工処理を含む磁気ディスク用ガラス基板の製造方法であって、上下定盤間での加工速度の差が小さくなるように、上定盤側の固定砥粒砥石と下定盤側の固定砥粒砥石の各々の表面に対して異なる条件でドレス処理を行うことを特徴とする磁気ディスク用ガラス基板の製造方法。
複数の研削砥粒がガラス結合材を介して結合された固定砥粒砥石が研削面にそれぞれ配備された上定盤及び下定盤の間にガラス基板を挟んでガラス基板の主表面を研削する研削加工処理を含む磁気ディスク用ガラス基板の製造方法であって、スラッジが固着していない集結砥粒の割合が下定盤の方が多くなるように、上定盤側の固定砥粒砥石と下定盤側の固定砥粒砥石の各々の表面に対して異なる条件でドレス処理を行うことを特徴とする磁気ディスク用ガラス基板の製造方法。
下定盤側の固定砥粒砥石と上定盤側の固定砥粒砥石とで、前記除去処理の時間及び/又は頻度を変更することを特徴とする構成6又は7に記載の磁気ディスク用ガラス基板の製造方法。
(構成9)
前記ドレス処理は、砥石を用いて行うことを特徴とする構成6乃至8のいずれかに記載の磁気ディスク用ガラス基板の製造方法。
前記固定砥粒砥石はダイヤモンド砥粒を含むことを特徴とする構成6乃至9のいずれかに記載の磁気ディスク用ガラス基板の製造方法。
(構成11)
主表面が鏡面状態のガラス基板に対して前記研削加工処理を行うことを特徴とする構成6乃至10のいずれかに記載の磁気ディスク用ガラス基板の製造方法。
構成1乃至4、6乃至11のいずれかに記載の磁気ディスク用ガラス基板の製造方法により製造された磁気ディスク用ガラス基板上に、少なくとも磁気記録層を形成することを特徴とする磁気ディスクの製造方法。
また、本発明によれば、固定砥粒による研削処理において、研削処理時に上下定盤の間で実行圧力の差が存在する場合においても、安定した研削加工を行うことが可能である。これにより、高品質のガラス基板を製造することができる。またそれによって得られるガラス基板を利用した信頼性の高い磁気ディスクを製造することができる。
磁気ディスク用ガラス基板は、通常、形状加工、主表面研削、端面研磨、主表面研磨、化学強化、等を経て製造される。
本発明の磁気ディスク用ガラス基板の製造方法においては、フロート法やダウンドロー法で製造されたシート状ガラスから所定の大きさに切り出してガラス基板を得る。また、これ以外に、溶融ガラスからプレスで作製したシート状板ガラスを用いてもよい。本発明は、研削加工開始時に主表面が鏡面状のガラス基板を使用する場合に好適である。
この研削加工は、通常両面研削装置を用い、ダイヤモンド等の硬質砥粒を用いてガラス基板主表面の研削を行う。こうしてガラス基板主表面を研削加工することにより、所定の板厚、平坦度に加工するとともに、所定の表面粗さを得る。
前にも説明したとおり、本発明者は、前述の従来技術において、部分的な研削不良が発生する理由について詳細に検討した結果、ダイヤモンド砥粒(集結砥粒)を備えたダイヤモンドパッドの表面には微小うねりが存在しており、砥粒がガラス表面に接触することが阻害され、ガラス表面に対して十分に作用できない砥粒が存在するため、上述の部分的な研削不良が発生することを突き止めた。そこで、本発明者は、集結砥粒から突出された研削砥粒の突出し量とダイヤモンドパッドの表面の微小うねりとの関係に着目して鋭意検討した結果、集結砥粒から突出された研削砥粒の突出し量が、ダイヤモンドパッドの表面の微小うねりよりも高いダイヤモンドパッド(研削工具)を用いて研削を行うことにより、安定した研削加工を行うことが可能であることを見出したわけである。
研削加工実施前の上下それぞれの定盤の研削工具(通常、円盤状に形成されている)に対して、内周から外周までの距離を100%としたとき、内周から10%、50%、90%の位置から、それぞれ2.5mm×2.5mmの大きさの合計6サンプル(パッド片)を切り出す。この6サンプルのそれぞれについて、例えばレーザー顕微鏡を用いて得られた観察画像(表面形状データ)から任意に選んだ集結砥粒5個(測定サンプルが多い方が突出し量の測定精度は向上するが、非常に多くの工数がかかり現実的でない。一方、サンプル数が5個より少ない場合、突出し量の測定精度が大幅に悪くなり管理上問題となる。このため、生産性と品質安定化を両立出来る測定個数として5個が適切である。)に対し、断面形状解析等により、集結砥粒とその集結砥粒周辺の樹脂部との最大高低差を測定し、全集結砥粒の高低差の平均値をもってその定盤の研削工具の研削砥粒の突出し量と定義する。なお、突出し量は上下の定盤でほぼ同等となるように調整されている。
一方、研削工具表面の微小うねりの最大高さは、ドレス処理に用いる砥石表面の微小うねりの最大高さを適宜変更することで調節することができる。ドレス処理用砥石表面の微小うねりの最大高さが小さいほど、ドレス処理後の研削工具表面の微小うねりの最大高さが小さくなる。具体的には、研削工具表面における微小うねりの最大高さの狙い値よりも小さい値を持つドレス処理用砥石を用いて処理すればよい。
ダイヤモンド砥粒の平均粒子径が上記の範囲を下回ると鏡面状ガラス基板に対する切り込みが浅くなりガラス基板への食い込みが進行し難くなる。一方、ダイヤモンド砥粒の平均粒子径が上記の範囲を上回ると仕上りの粗さが粗くなるため後工程の取り代負荷が大きくなるおそれがある。
また、集結砥粒の平均粒径は15~50μmであることが好ましい。上記範囲より小さいと、特に鏡面ガラス基板の表面に対して加工初期に砥粒を食い込ませ難くなり、研削レートが悪化する場合がある。また、上記範囲より大きいと、研削後の表面粗さが高くなりすぎる場合がある。
本発明における研削加工処理の第2の実施の形態は、複数の研削砥粒がガラス結合材を介して結合された固定砥粒砥石が研削面にそれぞれ配備された上定盤及び下定盤の間にガラス基板を挟んでガラス基板の主表面を研削する研削加工処理において、加工速度の差が上下定盤間で小さくなるように、上定盤側の固定砥粒砥石と下定盤側の固定砥粒砥石の各々の表面に対して異なる条件でドレス処理を行うことを特徴とするものである。
また、上記のドレス処理時間としては例えば5~120秒程度の範囲が適当であるが、上下定盤でドレス処理時間の条件を変更する場合、下定盤の処理時間を上定盤の処理時間よりも長く設定する。例えば、上定盤の処理時間を5~60秒の範囲で設定し、下定盤の処理時間を20~120秒の範囲で設定することができる。この場合、上下定盤の処理時間比は、上定盤:下定盤=4:5~1:2とすることが好ましい。
なお、ドレス処理時の定盤回転数、処理時間、処理回数(頻度)等の条件を上下定盤ですべて変更しなくてもよい。少なくともいずれか1つの条件を変更するようにしてもよい。
加工速度の差が上下定盤間で小さくなるように、たとえばドレス処理後の有効砥粒割合(顕微鏡で確認できる)が、上下で適切な比率になるようにドレス処理条件を設定することができる。
また、本発明においては、研削処理終了後のガラス基板の表面粗さが、Raで0.080~0.130μmの範囲に仕上がることが好ましい。このように仕上がりの粗さを低く抑えることで、後の工程の加工負荷を減らすことができる。
また、SiO2を56~75モル%、Al2O3を1~9モル%、Li2O、Na2OおよびK2Oからなる群から選ばれるアルカリ金属酸化物を合計で6~15モル%、MgO、CaOおよびSrOからなる群から選ばれるアルカリ土類金属酸化物を合計で10~30モル%、ZrO2、TiO2、Y2O3、La2O3、Gd2O3、Nb2O5およびTa2O5からなる群から選ばれる酸化物を合計で0%超かつ10モル%以下、含むガラスであってもよい。
本発明において、ガラス組成におけるAl2O3の含有量が15重量%以下であると好ましい。さらには、Al2O3の含有量が5モル%以下であるとなお好ましい。
また、本発明において表面粗さ(上記算術平均粗さRa)は、原子間力顕微鏡(AFM)で5μm四方を分解能256x256で測定したときに得られる表面形状の表面粗さとすることが実用上好ましい。
本発明において磁気ディスクは、本発明による磁気ディスク用ガラス基板の上に少なくとも磁気記録層(磁性層)を形成して製造される。磁性層の材料としては、異方性磁界の大きな六方晶系であるCoCrPt系やCoPt系強磁性合金を用いることができる。磁性層の形成方法としてはスパッタリング法、例えばDCマグネトロンスパッタリング法によりガラス基板の上に磁性層を成膜する方法を用いることが好適である。
本発明によって得られる磁気ディスク用ガラス基板を利用することにより、信頼性の高い磁気ディスクを得ることができる。
(実施例1-1)
以下の(1)基板準備、(2)形状加工、(3)端面研磨、(4)主表面研削加工、(5)主表面研磨(第1研磨)、(6)化学強化、(7)主表面研磨(第2研磨)、を経て本実施例の磁気ディスク用ガラス基板を製造した。
フロート法により製造された厚さ1mmのアルミノシリケートガラスからなる大板ガラスを準備し、70mm×70mmの正方形の小片にダイヤモンドカッターを用いて裁断した。次いで、ダイヤモンドカッターを用いて、外径65mm、内径20mmの円盤形状に加工した。このアルミノシリケートガラスとしては、SiO2:62~75重量%、ZrO2:5.5~15重量%、Al2O3:5~15重量%、Li2O:4~10重量%、Na2O:4~12重量%を含有する化学強化可能なアモルファスのガラスを使用した。
得られた基板の表面は、表面粗さRaが5nm以下の鏡面であった。
次に、ダイヤモンド砥石を用いてガラス基板の中央部分に孔を空けると共に、外周端面および内周端面に所定の面取り加工を施した。
(3)端面研磨
次いで、ブラシ研磨により、ガラス基板を回転させながらガラス基板の端面(内周、外周)を研磨した。
この主表面研削加工は両面研削装置を用い、複数のダイヤモンド砥粒をガラス結合材で固めた集結砥粒と、複数の当該集結砥粒を結合している樹脂とを備えた固定砥粒砥石(ダイヤモンドパッド)が貼り付けられた上下定盤の間にキャリアにより保持したガラス基板をセットして行なった。ダイヤモンドパッドは、ダイヤモンド砥粒の平均粒径(D50)が約3.0μm、集結砥粒の平均粒径(D50)が30μmのダイヤモンドパッドを使用した。また、潤滑液を使用しながら行った。また、定盤の回転数、ガラス基板への荷重は、適宜調整して行った。
また、研削加工の前にアルミナ砥石を用いてドレス処理を行った。本実施例で使用した上記ダイヤモンドパッドにおける研削砥粒の突出し量及び表面形状の最大高さ(微小うねり)を前述の方法で測定した結果、研削砥粒の突出し量は2μm、表面形状の最大高さは0.5μmであった。
次に、上述した研削加工で残留した傷や歪みを除去するための第1研磨を両面研磨装置を用いて行なった。両面研磨装置においては、研磨パッドが貼り付けられた上下研磨定盤の間にキャリアにより保持したガラス基板を密着させ、このキャリアを太陽歯車(サンギア)と内歯歯車(インターナルギア)とに噛合させ、上記ガラス基板を上下定盤によって挟圧する。その後、研磨パッドとガラス基板の研磨面との間に研磨液を供給して回転させることによって、ガラス基板が定盤上で自転しながら公転して両面を同時に研磨加工するものである。具体的には、ポリシャとして硬質ポリシャ(硬質発泡ウレタン)を用い、第1研磨を実施した。研磨液としては酸化セリウムを研磨剤として分散した純水とし、荷重、研磨時間は適宜設定した。上記第1研磨工程を終えたガラス基板を、中性洗剤、純水、IPA(イソプロピルアルコール)、IPA(蒸気乾燥)の各洗浄槽に順次浸漬して、超音波洗浄し、乾燥した。
次に、上記洗浄を終えたガラス基板に化学強化を施した。化学強化は硝酸カリウムと硝酸ナトリウムの混合した化学強化液を用意し、この化学強化溶液を380℃に加熱し、上記洗浄・乾燥済みのガラス基板を約4時間浸漬して化学強化処理を行なった。
次いで上記の第1研磨で使用したものと同じ両面研磨装置を用い、ポリシャを軟質ポリシャ(スウェード)の研磨パッド(発泡ポリウレタン製)に替えて第2研磨を実施した。この第2研磨は、上述した第1研磨で得られた平坦な表面を維持しつつ、例えばガラス基板主表面の表面粗さをRaで0.2nm程度以下の平滑な鏡面に仕上げるための鏡面研磨加工である。研磨液としてはコロイダルシリカを分散した純水とし、荷重、研磨時間は適宜設定した。上記第2研磨工程を終えたガラス基板を、中性洗剤、純水、IPA、IPA(蒸気乾燥)の各洗浄槽に順次浸漬して、超音波洗浄し、乾燥した。
実施例1-1の主表面研削加工において、ダイヤモンド砥粒の平均粒径が約9.0μm、研削砥粒の突出し量が7μm、表面形状の最大高さが5μmの状態のダイヤモンドパッドを使用したこと以外は、実施例1-1と同様にして研削加工を行い、磁気ディスク用ガラス基板を作製した。
(実施例1-3)
実施例1-1の主表面研削加工において、ダイヤモンド砥粒の平均粒径が約1.5μm、研削砥粒の突出し量が3μm、表面形状の最大高さが1μmの状態のダイヤモンドパッドを使用したこと以外は、実施例1-1と同様にして研削加工を行い、磁気ディスク用ガラス基板を作製した。
実施例1-1の主表面研削加工において、ダイヤモンド砥粒の平均粒径が約1.5μm、研削砥粒の突出し量が2μm、表面形状の最大高さが0.5μmの状態のダイヤモンドパッドを使用したこと以外は、実施例1-1と同様にして研削加工を行い、磁気ディスク用ガラス基板を作製した。
(実施例1-5)
実施例1-1の主表面研削加工において、ダイヤモンド砥粒の平均粒径が約12μm、研削砥粒の突出し量が9μm、表面形状の最大高さが6μmの状態のダイヤモンドパッドを使用したこと以外は、実施例1-1と同様にして研削加工を行い、磁気ディスク用ガラス基板を作製した。
実施例1-1の主表面研削加工において、ダイヤモンド砥粒の平均粒径が約3.0μm、研削砥粒の突出し量が2μm、表面形状の最大高さが2μmの状態のダイヤモンドパッドを使用したこと以外は、実施例1-1と同様にして研削加工を行い、磁気ディスク用ガラス基板を作製した。
(比較例1-2)
実施例1-1の主表面研削加工において、ダイヤモンド砥粒の平均粒径が約3.0μm、研削砥粒の突出し量が2μm、表面形状の最大高さが3μmの状態のダイヤモンドパッドを使用したこと以外は、実施例1-1と同様にして研削加工を行い、磁気ディスク用ガラス基板を作製した。
実施例1-1の主表面研削加工において、ダイヤモンド砥粒の平均粒径が約3.0μm、研削砥粒の突出し量が2μm、表面形状の最大高さが5μmの状態のダイヤモンドパッドを使用したこと以外は、実施例1-1と同様にして研削加工を行い、磁気ディスク用ガラス基板を作製した。
(比較例1-4)
実施例1-1の主表面研削加工において、ダイヤモンド砥粒の平均粒径が約9.0μm、研削砥粒の突出し量が7μm、表面形状の最大高さが7μmの状態のダイヤモンドパッドを使用したこと以外は、実施例1-1と同様にして研削加工を行い、磁気ディスク用ガラス基板を作製した。
実施例1-1の主表面研削加工において、ダイヤモンド砥粒の平均粒径が約9.0μm、研削砥粒の突出し量が7μm、表面形状の最大高さが8μmの状態のダイヤモンドパッドを使用したこと以外は、実施例1-1と同様にして研削加工を行い、磁気ディスク用ガラス基板を作製した。
(比較例1-6)
実施例1-1の主表面研削加工において、ダイヤモンド砥粒の平均粒径が約9.0μm、研削砥粒の突出し量が7μm、表面形状の最大高さが10μmの状態のダイヤモンドパッドを使用したこと以外は、実施例1-1と同様にして研削加工を行い、磁気ディスク用ガラス基板を作製した。
実施例1-1の主表面研削加工において、ダイヤモンド砥粒の平均粒径が約1.5μm、研削砥粒の突出し量が2μm、表面形状の最大高さが2μmの状態のダイヤモンドパッドを使用したこと以外は、実施例1-1と同様にして研削加工を行い、磁気ディスク用ガラス基板を作製した。
上記各実施例において、研削加工後のガラス基板について、フラットネステスターを用いて、1バッチあたり20枚の平坦度の測定を行い、所定の基準(3μm以下)を良品とし、この基準を満たさないガラス基板の発生率(平坦度不良発生率)を算出し、結果を表1に示した。また、研削加工後のガラス基板について、AFMにて測定した表面粗さ(Ra)の結果を、実施例1の値を基準としたときの比率で表2に示した。
また、上記各比較例において、上記実施例と同様に、研削加工後のガラス基板について、フラットネステスターを用いて、1バッチあたり20枚の平坦度の測定を行い、所定の基準(3μm以下)を超えるガラス基板の発生率(平坦度不良発生率)を算出し、結果を表1に示した。
なお、表1において研削砥粒粒径とは、集結砥粒の中に含まれるダイヤモンド微粒子の平均粒径(D50)であり、砥粒突出し量とは、集結砥粒がその周囲の樹脂部分からなる平面から突き出した距離である。
1.研削砥粒粒径が3.0μmの場合、研削砥粒の突出し量が表面形状の最大高さよりも低い固定砥粒砥石を用いた比較例では、ガラス表面に対する研削砥粒の作用が弱く、平坦度不良は100%の発生率であった。また、研削砥粒の突出し量を表面形状の最大高さと同等にした比較例では、平坦度不良の発生率が20%に低減するが、ガラス表面に十分に作用できない砥粒が存在するため、一部で研削ムラが発生している。これに対して、研削砥粒の突出し量が表面形状の最大高さよりも高い固定砥粒砥石を用いた実施例1-1では、ガラス表面に研削砥粒が安定的に作用するようになり、平坦度不良発生率は0%となり、研削ムラのない安定した研削加工を行える。
2.また、研削砥粒粒径が9.0μmの場合においても、最大高さが5μmで、研削砥粒の突出し量を7μmとすることにより、研削砥粒の突出し量が表面形状の最大高さよりも高い固定砥粒砥石を用いた実施例1-2では、ガラス表面に研削砥粒が安定的に作用するようになり、平坦度不良発生率は0%となる。但し、この場合、加工後の基板の表面粗さが実施例1-1と比べると上昇する(表2参照)。砥粒粒径が大きいため、ガラス表面に作用する研削力が大きいことによるものと考えられる。一方、研削砥粒粒径が9.0μmで、研削砥粒の突出し量が表面形状の最大高さよりも低い固定砥粒砥石を用いた比較例1-5、1-6においても、ガラス表面に対する研削砥粒の作用が弱く、平坦度不良は80%の発生率であった。
3.砥粒突出し量をA、研削面における微小うねりの最大高さをBとしたとき、A-Bで得られる値が同じ例同士を比較すると、研削砥粒(ダイヤモンド微粒子)の粒径が3μm以下になると不良率が悪化しやすい。すなわち、研削砥粒(ダイヤモンド微粒子)の粒径が3μm以下の場合に特に本発明が有効であることがわかる。
上記実施例1-1と同様の工程を経て以下の実施例の磁気ディスク用ガラス基板を製造した。
(1)基板準備
フロート法により製造された厚さ1mmのアモルファスのアルミノシリケートガラスからなる大板ガラスを準備し、70mm×70mmの正方形の小片にダイヤモンドカッターを用いて裁断した。次いで、ダイヤモンドカッターを用いて、外径65mm、内径20mmの円盤形状に加工した。このアルミノシリケートガラスとしては、SiO2:62~75重量%、ZrO2:5.5~15重量%、Al2O3:5~15重量%、Li2O:4~10重量%、Na2O:4~12重量%を含有する化学強化可能なガラスを使用した。
次に、ダイヤモンド砥石を用いてガラス基板の中央部分に孔を空けると共に、外周端面および内周端面に所定の面取り加工を施した。
(3)端面研磨
次いで、ブラシ研磨により、ガラス基板を回転させながらガラス基板の端面(内周、外周)を研磨した。
この主表面研削加工は両面研削装置を用い、複数のダイヤモンド粒子をガラス結合材で固めた凝集体砥粒を含む固定砥粒砥石(ダイヤモンドパッド)が貼り付けられた上下定盤の間にキャリアにより保持したガラス基板をセットして行なった。ダイヤモンドパッドは、ダイヤモンド砥粒の平均粒径(D50)が約2.5μm、集結砥粒の平均粒径(D50)が25μmと定義したダイヤモンドパッドを使用した。また、潤滑液を使用しながら行った。また、定盤の回転数、ガラス基板への荷重は、適宜調整して行った。
具体的には、まず、固定砥粒表面に付着している研削液やスラッジを除去するために、ブラッシングを行った。次に、固定砥粒表面に#1000のアルミナ砥石を接触させ、上記両面研削装置の上下定盤を回転させた状態でドレス処理を行った。ドレス処理時の定盤回転数、処理時間、処理回数(頻度)はそれぞれ以下のように設定した。
定盤回転数:20rpm(上下定盤同一)
処理時間(1回):上定盤60秒、下定盤120秒
処理頻度:上定盤は連続20バッチ(1バッチは100枚)加工毎、下定盤についても連続20バッチ加工毎
次に、上述した研削加工で残留した傷や歪みを除去するための第1研磨を実施例1-1と同様にして行なった。
(6)化学強化
次に、上記洗浄を終えたガラス基板に実施例1-1と同様にして化学強化を施した。
(7)主表面研磨(第2研磨)
次いで上記実施例1-1と同様にして第2研磨を実施した。
実施例2-1の主表面研削加工において、ドレス処理時の定盤回転数、処理時間、処理回数(頻度)はそれぞれ以下のように設定した。
定盤回転数:20rpm(上下定盤同一)
処理時間(1回):上定盤10秒、下定盤20秒
処理頻度:上定盤は連続40バッチ加工毎、下定盤は連続20バッチ加工毎
これ以外は、実施例2-1と同様にして磁気ディスク用ガラス基板を作製した。
実施例2-1の主表面研削加工において、ドレス処理時の定盤回転数、処理時間、処理回数(頻度)はそれぞれ以下のように設定した。
定盤回転数:20rpm(上下定盤同一)
処理時間(1回):上定盤10秒、下定盤20秒
処理頻度:上定盤は連続100バッチ加工毎、下定盤は連続50バッチ加工毎
これ以外は、実施例2-1と同様にして磁気ディスク用ガラス基板を作製した。
実施例2-1の主表面研削加工において、ドレス処理時の定盤回転数、処理時間、処理回数(頻度)はそれぞれ以下のように設定した。
定盤回転数:20rpm(上下定盤同一)
処理時間(1回):上定盤10秒、下定盤10秒(上下定盤同一)
処理頻度:上定盤は連続50バッチ加工毎、下定盤は連続50バッチ加工毎(上下定盤同一)
これ以外は、実施例2-1と同様にして磁気ディスク用ガラス基板を作製した。
なお、この有効固定砥粒の割合は、ダイヤモンドパッド表面を顕微鏡観察し、一定数(上、下各100個)の固定砥粒を観察することで確認した。
また、201バッチ目の上下定盤の加工速度の比(下定盤加工速度/上定盤加工速度)を表3に示す。加工速度の比は1に近いほどよいが、1.05~0.95であると上下定盤の加工バランスがよくなり、安定した加工が継続してできるようになる。
不良であるか否かは、ガラス基板の主表面を集光ランプを用いて目視で観察し、鏡面が残っているか否かで判断することができる。本発明の固定砥粒による研削加工がきちんと行われた場合、基板表面は白く濁ったようになり鏡面ではなくなる。しかし、研削加工が行われなかった場合、その部分は鏡面のままであり、白濁が観察されない。
1.上定盤側の固定砥粒砥石と下定盤側の固定砥粒砥石の各々の表面に対して異なる条件でドレス処理を行い、下定盤側に配備された固定砥粒砥石表面から研削くずを除去する量を、上定盤側に配備された固定砥粒砥石と比べて多くする除去処理を行った実施例2-1~2-3においては、結果的に加工速度の差が上下定盤間で小さくなり、不良の発生頻度を著しく低下させることができ、これによって固定砥粒を用いた研削加工において安定した加工を行うことができる。また、下定盤側の有効固定砥粒の割合(%)が高い方がよい。また、上下定盤の差が20%以内であると好ましく、より好ましくは10%以下(実施例2-1)である。また、上下定盤の有効砥粒割合の差は、下定盤の方が上定盤よりも5%超ある方が加工のバランスが取れて不良バッチ率が改善する。
2.一方、上定盤側の固定砥粒砥石と下定盤側の固定砥粒砥石の各々の表面に対して同じ条件でドレス処理を行った比較例2-1においては、実行圧力の小さい下定盤側の有効固定砥粒の割合が上定盤側の有効固定砥粒の割合よりも低下してしまい、これが原因で上下定盤における加工のバランスが悪くなり、不良の発生頻度が高くなってしまう。
上記実施例1-1および2-1で得られた磁気ディスク用ガラス基板に以下の成膜工程を施して、垂直磁気記録用磁気ディスクを得た。
すなわち、上記ガラス基板上に、Ti系合金薄膜からなる付着層、CoTaZr合金薄膜からなる軟磁性層、Ru薄膜からなる下地層、CoCrPt合金からなる垂直磁気記録層、保護層、潤滑層を順次成膜した。保護層は、水素化カーボン層を成膜した。また、潤滑層は、アルコール変性パーフルオロポリエーテルの液体潤滑剤をディップ法により形成した。
得られた磁気ディスクについて、DFHヘッドを備えたHDDに組み込み、80℃かつ80%RHの高温高湿環境下においてDFH機能を作動させつつ1ヶ月間のロードアンロード耐久性試験を行ったところ、特に障害も無く、良好な結果が得られた。
2 シート
3 集結砥粒
4 ペレット
5 ダイヤモンド粒子
10 ガラス基板
Claims (12)
- ガラス基板の主表面を研削する研削処理を含む磁気ディスク用ガラス基板の製造方法であって、
前記研削処理では、複数の研削砥粒がガラス結合材で結合された集結砥粒と、複数の当該集結砥粒を結合している樹脂とを含む研削工具であって、前記研削工具の研削面における前記研削砥粒の周囲の樹脂からの突出し量が、前記研削面を触針式表面粗さ計を用いて測定された表面形状の最大高さよりも高い研削工具を用いて、ガラス基板主表面の研削を行うことを特徴とする磁気ディスク用ガラス基板の製造方法。 - 研削工具のドレス処理とガラス基板の主表面を研削する研削処理を含む磁気ディスク用ガラス基板の製造方法であって、
複数の研削砥粒がガラス結合材で結合された集結砥粒と、複数の当該集結砥粒を結合している樹脂とを含む研削工具であって、予め、前記研削工具の研削面における前記研削砥粒の周囲の樹脂からの突出し量が、前記研削面を触針式表面粗さ計を用いて測定された表面形状の最大高さよりも高くなるようにドレス処理を行い、該ドレス処理された研削工具を用いて、ガラス基板主表面の研削を行うことを特徴とする磁気ディスク用ガラス基板の製造方法。 - 前記研削砥粒はダイヤモンド砥粒を含むことを特徴とする請求項1又は2に記載の磁気ディスク用ガラス基板の製造方法。
- 主表面が鏡面状態のガラス基板に対して前記研削処理を行うことを特徴とする請求項1乃至3のいずれかに記載の磁気ディスク用ガラス基板の製造方法。
- 複数の研削砥粒がガラス結合材で結合された集結砥粒と、複数の当該集結砥粒を結合している樹脂とを含む、ガラス基板表面を研削する研削工具であって、
前記集結砥粒から突出された前記研削砥粒の突出し量が、研削工具表面を触針式表面粗さ計を用いて測定された表面形状の最大高さよりも高いことを特徴とする研削工具。 - 複数の研削砥粒がガラス結合材を介して結合された固定砥粒砥石が研削面にそれぞれ配備された上定盤及び下定盤の間にガラス基板を挟んでガラス基板の主表面を研削する研削加工処理を含む磁気ディスク用ガラス基板の製造方法であって、
上下定盤間での加工速度の差が小さくなるように、上定盤側の固定砥粒砥石と下定盤側の固定砥粒砥石の各々の表面に対して異なる条件でドレス処理を行うことを特徴とする磁気ディスク用ガラス基板の製造方法。 - 複数の研削砥粒がガラス結合材を介して結合された固定砥粒砥石が研削面にそれぞれ配備された上定盤及び下定盤の間にガラス基板を挟んでガラス基板の主表面を研削する研削加工処理を含む磁気ディスク用ガラス基板の製造方法であって、
スラッジが固着していない集結砥粒の割合が下定盤の方が多くなるように、上定盤側の固定砥粒砥石と下定盤側の固定砥粒砥石の各々の表面に対して異なる条件でドレス処理を行うことを特徴とする磁気ディスク用ガラス基板の製造方法。 - 下定盤側の固定砥粒砥石と上定盤側の固定砥粒砥石とで、前記除去処理の時間及び/又は頻度を変更することを特徴とする請求項6又は7に記載の磁気ディスク用ガラス基板の製造方法。
- 前記ドレス処理は、砥石を用いて行うことを特徴とする請求項6乃至8のいずれかに記載の磁気ディスク用ガラス基板の製造方法。
- 前記固定砥粒砥石はダイヤモンド砥粒を含むことを特徴とする請求項6乃至9のいずれかに記載の磁気ディスク用ガラス基板の製造方法。
- 主表面が鏡面状態のガラス基板に対して前記研削加工処理を行うことを特徴とする請求項6乃至10のいずれかに記載の磁気ディスク用ガラス基板の製造方法。
- 請求項1乃至4、6乃至11のいずれかに記載の磁気ディスク用ガラス基板の製造方法により製造された磁気ディスク用ガラス基板上に、少なくとも磁気記録層を形成することを特徴とする磁気ディスクの製造方法。
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