JP2007098483A - Glass substrate for magnetic disk, manufacturing method of magnetic disk and end face grinder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology for improving the accuracy of grinding the end face of a glass substrate, restraining the generation of dust from the end face, and keeping a grinding wheel in a good condition over a long period of time. <P>SOLUTION: In this method, a grinding means 21 where abrasive grains 23 are buried and a coolant supply means 26 for supplying a coolant to a grinding position are used to grind the end faces 12, 13 of the glass substrate 20, and the temperature of the coolant 25 is controlled to 28°C or less. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a glass substrate for a magnetic recording medium and a method for manufacturing a magnetic disk.

  In recent years, with the advancement of information technology, information recording technology, particularly magnetic recording technology, has made remarkable progress. An aluminum substrate has been widely used as a substrate for a magnetic recording medium such as an HDD (Hard Disk Drive) which is one of the magnetic recording media. However, with the miniaturization, thinning, and high-density recording of magnetic disks, glass substrates that are superior in substrate surface flatness and substrate strength compared to aluminum substrates are gradually being replaced.

  As the magnetic recording technology has been increased in density, the magnetic head has been changed from a thin film head to a magnetoresistive head (MR head) and a large magnetoresistive head (GMR head). The flying height from the center is narrowed to about 10 nm. A magnetic head equipped with such a magnetoresistive element may cause a thermal asperity failure as an inherent failure. Thermal asperity failure means that the magnetoresistive element is heated by adiabatic compression or contact of air when the magnetic head passes while flying over a minute convex or concave shape on the magnetic disk surface. This is a failure that causes a read error. Therefore, for a magnetic head equipped with a magnetoresistive element, the surface of the magnetic disk is required to have extremely high smoothness and flatness. Further, if the magnetic layer is formed with dust or foreign matter attached, a convex portion is formed. Therefore, the glass substrate is required to prevent dust generation by removing irregularities and to perform advanced cleaning to remove foreign matter.

  Furthermore, in recent years, there is a tendency for the size of a substrate to be reduced in order to mount a large-capacity magnetic recording medium in a portable device. For this reason, 1.8-inch substrates, 1-inch substrates, or even smaller substrates have been demanded from conventional 3.5-inch substrates and 2.5-inch substrates. The smaller the substrate, the smaller the allowable dimensional error, and there is a need for more precise outer shape processing.

  In the above situation, as related to chamfering of a glass substrate, as described in Patent Document 1 (Japanese Patent Application Laid-Open No. 11-267975), an end surface of the glass substrate using a pulley-like rotary grindstone has been conventionally used. A configuration for grinding is described. In Patent Document 1, the angle of incidence of the grindstone with respect to the surface of the glass substrate is specified, and by arranging a plurality of fine cooling water discharge holes on the grinding surface, chipping or crack progression at the end of the glass substrate is suppressed. You can extend the lifespan.

  The reason why the glass substrate is chamfered is to prevent the generation of chips and foreign matters by smoothing the edge of the substrate. If the surface state of the end face of the glass substrate is not smooth, resin and glass particles generated by rubbing the end face with the wall surface of the resin case, and other particles captured by the inner peripheral end face and the outer peripheral end face portion of the glass substrate However, there is a possibility that it will later adhere to the main surface of the substrate. If the magnetic layer is formed with particles adhering to the main surface of the glass substrate, it may cause film defects, or convex portions will be formed on the surface of the magnetic disk, and an appropriate glide height will not be obtained, and thermal asperity will be caused. Cause.

  Moreover, there is a possibility that the strength of the glass substrate is lowered or the accuracy of the concentricity is lowered due to the lack of the end portion. That is, the grinding of the edge portion of the substrate is a big problem in order to improve the production efficiency by reducing the incidence of chipping and to reduce the manufacturing cost.

JP-A-11-267975

  A grindstone (grinding means) for grinding the end face of the glass substrate is worn or worn. If the worn grindstone is continuously used, the glass substrate is often chipped. For this reason, it is necessary to replace or readjust (repair the shape) the grindstone according to the state.

  The standard for exchanging and re-adjusting the grindstone is the roundness of the glass substrate, the profile of the end face, and the visual inspection that is performed after every 100 pieces are ground (the end face is observed with a halogen lamp). This is done by checking appearance defects such as cracks. In addition, readjustment of a grindstone is performed by applying sapphire. This replacement or readjustment is necessary, but if it is frequent, the productivity is lowered and the manufacturing cost is increased.

  Since the inventors reduced the chipping of the glass substrate by exchanging or re-adjusting the grindstone, the inventors investigated the state of the grindstone at this time and investigated the cause of the chipping.

  FIG. 5 is an enlarged view of a grinding surface of a conventional rotary grindstone. As shown in FIG. 5A, the grindstone has a configuration in which diamond abrasive grains 51 are bonded to a base material 50 with nickel 52. And when the grindstone in the state which needs replacement | exchange was observed, as shown in FIG.5 (b), it turned out that the abrasive grain 51 slipped out and the hollow 53 was made in the grindstone. Also, it was found that dust and abrasives were attached in the recess 53. That is, if grinding is performed with a grindstone from which the abrasive grains 51 have been removed, grinding cannot be performed satisfactorily, the processed surface becomes uneven, and the surface becomes rough. For this reason, it is considered that defects such as chips and cracks occur on the end surface of the glass substrate.

  Furthermore, the inventors studied the cause of the abrasive grains 51 of the grindstone coming off. Then, when the temperature at the time of grinding was high, it turned out that the abrasive grain 51 tends to fall out. On the other hand, cooling is conventionally performed with a cooling liquid during grinding, but since the cooling liquid is circulated, it has been found that the temperature is increased by continuous grinding. Here, it is also conceivable to replace nickel as an adhesive with one having high heat resistance. However, it is not easy to develop alternative materials because there are many required conditions such as mechanical strength to hold abrasive grains, low melting point to melt diamond abrasive grains without burning, and resistance to continuous load by polishing. Absent.

  Accordingly, an object of the present invention is to provide a technique capable of improving the precision of end grinding of a glass substrate, suppressing dust generation from the end face, and maintaining a grindstone in a good state for a long period of time.

  In order to solve the above problems, a typical configuration of a method for manufacturing a glass substrate for a magnetic disk according to the present invention includes a grinding unit in which abrasive grains are embedded, and a cooling liquid supply unit that supplies a cooling liquid to a grinding position. And a method of grinding an end face of a glass substrate, wherein the temperature of the cooling liquid is adjusted to 28 ° C. or lower. The temperature of the cooling liquid is preferably further adjusted to 25 ° C. or lower, or 23 ° C. or higher and 25 ° C. or lower. Thereby, the temperature of a grinding means can be lowered | hung and an omission of an abrasive grain can be prevented. For this reason, the dimensional accuracy of the glass substrate can be improved, and dust generation from the end face of the glass substrate can be prevented to prevent thermal asperity. Further, the life of the grinding means can be extended, and the productivity can be improved.

  The abrasive grains may be diamond abrasive grains, and may be embedded in nickel as an adhesive with respect to the base material of the grinding means. In such a case, it is possible to prevent the abrasive grains from being removed particularly effectively.

  The grinding means may chamfer the end surface of the plate glass. In such a case, a grinding means in which abrasive grains are embedded is preferably used.

  The plate-like glass may be made of aluminosilicate glass. In such a case, an excellent glass substrate for a magnetic disk can be obtained.

  A typical configuration of the magnetic disk manufacturing method according to the present invention is characterized in that at least a magnetic layer is formed on the surface of the magnetic disk glass substrate obtained by the method for manufacturing a magnetic disk glass substrate. . Thereby, a magnetic disk having extremely high smoothness and flatness can be manufactured.

  Further, a typical configuration of an end surface grinding apparatus for a magnetic disk glass substrate according to the present invention includes a grinding means in which abrasive grains are embedded, a cooling liquid supply means for supplying a cooling liquid to a grinding position, and a temperature of the cooling liquid. And a temperature adjusting means for adjusting. Thereby, the edge part of a glass substrate can be ground with high dimensional accuracy, and a grinding means can be used in a favorable state over a long time.

  ADVANTAGE OF THE INVENTION According to this invention, the precision of the end surface grinding of a glass substrate can be improved, and at the same time dust generation can be suppressed and the production efficiency of a glass substrate and a magnetic disk can be improved. Further, since the grinding means for end face grinding can be kept in a good state for a long time, productivity can be improved.

  Embodiments of a magnetic disk glass substrate, a magnetic disk manufacturing method, and an end surface grinding apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining a forming process for chamfering an end surface of a glass substrate, FIG. 2 is an enlarged view of a main portion of a grinding position, FIG. 3 is an overall configuration diagram of an end surface grinding apparatus, and FIG. It is a figure explaining the change of the incidence rate of a chip.

  The forming step of chamfering the end surface of the glass substrate is performed on an annular glass substrate 10 in which a circular hole 11 is formed at the center of a disk-shaped glass substrate, as shown in FIG.

  As shown in FIG. 1B, an inner grindstone 20 as an example of a grinding means is inserted into the circular hole 11, and an outer grindstone 21 as an example of a grinding means is also arranged outside the glass substrate 10. The inner grindstone 20 and the outer grindstone 21 are pressed so as to sandwich the glass substrate 10 in the radial direction by a pressing means (not shown). The inner grindstone 20 and the outer grindstone 21 are pulley-shaped rotary grindstones, and have a grinding surface to be described later on the outer peripheral surface. The glass substrate 10, the inner grindstone 20, and the outer grindstone 21 are each driven to rotate by driving means (not shown), and the rotation directions are set to be opposite directions at the respective contacts. In the figure, the support mechanism and the rotation drive mechanism of the glass substrate 10 are omitted.

  Then, the inner peripheral end face 12 and the outer peripheral end face 13 of the glass substrate 10 are ground to form chamfered portions 12a and 13a, respectively, as shown in FIG.

  FIG. 2 is an enlarged view of the main part of the grinding position. However, since the description overlaps with the inner grindstone 20 and the outer grindstone 21, only the outer grindstone 21 will be described here. On the outer peripheral surface of the base material 21a of the outer grindstone 21, a central flat portion 22a for forming a flat portion at the central portion in the thickness direction of the outer peripheral end surface 13 and an inclined portion 22b for forming the chamfered portion 13a are formed. Has been. In the surface layer of the central flat portion 22a and the inclined portion 22b, diamond abrasive grains 23 as examples of abrasive grains are embedded in nickel 24. The surface of the glass substrate 10 is ground by the abrasive grains 23. Since high heat is generated by grinding, a coolant nozzle 26 as an example of coolant supply means is disposed in the vicinity of the grinding position, and the coolant 25 is discharged toward the grinding position.

  As shown in FIG. 3, the coolant 25 is circulated in the end surface grinding apparatus. That is, the cooling liquid discharged to the grinding position falls into the collection tank 27 and is collected and stored in the first tank 28. Then, it is sent to the separation device 29 by a pump to remove foreign matters such as grinding powder, and then stored in the second tank 30. Then, it is supplied again to the grinding position and discharged.

  Here, in the present embodiment, a cooling coil 32 (evaporator) connected to a cooler 31 as an example of temperature adjusting means is disposed in a second tank 30 that is a tank immediately before being supplied to a grinding position. The temperature of the coolant 25 discharged from the coolant nozzle 26 at the grinding position can be lowered. Control of the power of the cooler 31 may be known, and for example, the opening / closing of the expansion valve may be controlled by the refrigerant pressure in the temperature sensing cylinder, or the operation of the compressor may be controlled using a thermostat.

  By reducing the temperature of the coolant 25 as described above, the temperatures of the inner grindstone 20 and the outer grindstone 21 can be lowered, and the removal of the abrasive grains 23 from the nickel 24 can be prevented. For this reason, the dimensional accuracy of the end surface grinding of the glass substrate can be improved. Further, since the accuracy is improved, dust generation from the end face of the glass substrate can be prevented and thermal asperity can be prevented, so that the production efficiency of the glass substrate and the magnetic disk can be improved. In addition, the grinding means for end face grinding can be kept in good condition for a long time, so that frequent replacement and readjustment of the grinding wheel can be avoided, improving productivity and reducing manufacturing costs. Can be planned.

  The adjustment temperature of the coolant 25 under the control of the cooler 31 may be 28 ° C. or lower when the diamond abrasive grains 23 are embedded in the nickel 24. However, since the temperature of the coolant 25 varies depending on the operation of the cooler 31, the target temperature is preferably about 25 ° C. Moreover, since the effect does not change even if the temperature is lowered too much, it is preferably set in the range of 23 ° C. to 25 ° C. from the viewpoint of energy efficiency.

[Example]
Examples of a glass substrate for a magnetic disk and a method for manufacturing the magnetic disk to which the present invention is applied will be described below.

(1) Shape processing step and first lapping step First, the melted aluminosilicate glass was molded into a disk shape by direct pressing using an upper die, a lower die, and a barrel die to obtain an amorphous plate glass. In addition, the glass for chemical strengthening was used as aluminosilicate glass. The obtained disk-shaped plate-like glass had a diameter of 96 mm and a plate thickness of 1.8 mm. In this case, in addition to the direct press, a disk-shaped glass substrate for a magnetic disk may be obtained by cutting a sheet glass formed by a downdraw method or a float method with a grinding wheel. As the aluminosilicate _glass, SiO 2: 58 to 75 _{wt%, Al} 2 O 3: _{5~23 wt%,} Li 2 O: 3 to 10 _wt%, Na 2 O: 4 to 13 principal component weight% Chemically strengthened glass contained as

  Next, both main surfaces of the plate glass were lapped to form a disk-shaped glass base material. This lapping process was performed using alumina free abrasive grains with a double-sided lapping apparatus using a planetary gear mechanism. Specifically, the lapping platen is pressed on both sides of the plate glass from above and below, the grinding liquid containing free abrasive grains is supplied onto the main surface of the plate glass, and these are moved relative to each other for lapping. went. By this lapping process, a glass base material having a flat main surface was obtained. Moreover, the plate | board thickness of the glass base material was reduced rather than plate glass by this lapping process, and became 0.6 mm.

(2) Cutting process (coring, forming)
Next, the glass base material was cut using a diamond cutter, and a glass substrate having a diameter of 29 mm was cut out from the glass base material. The diameter of the glass base material was 96 mm, and six glass substrates could be collected from one glass base material.

  Next, using a cylindrical diamond drill, a circular hole was formed in the center of the glass substrate to obtain an annular glass substrate (coring). Then, the inner peripheral end face and the outer peripheral end face were ground with a diamond grindstone and subjected to predetermined chamfering (forming).

  Here, in the forming process, the temperature of the coolant 25 is adjusted by the cooler 31 as described above, and then discharged to the grinding position. In this embodiment, the set temperature of the coolant 25 is 25 ° C.

  FIG. 4 is a diagram for explaining a change in the occurrence rate of chipping by adjusting the temperature of the coolant. In FIG. 4, until the middle of the sixth week, the forming process was performed by the conventional method, and the temperature of the coolant 25 was approximately 31 ° C. From the middle of the sixth week, the temperature of the coolant 25 was adjusted and cooled to 25 ° C. The vertical axis represents the occurrence rate of chipping in the inspection of the glass substrate, that is, the rate of defective products.

  As can be seen from FIG. 4, in the first, third, and sixth weeks, the chipping rate gradually increased to 3%, and the grindstone was replaced here. In addition, even when a new grindstone is used, it can be seen that chipping of about 1% occurs on average. On the other hand, after starting the temperature control, the chipping rate is about 0.3% on average and at most about 0.5%, the productivity is greatly improved, and the grindstone is good for a long time. It can be seen that the state is maintained.

(3) End surface polishing process Next, the end surface of the glass substrate was mirror-polished by a brush polishing method. At this time, as the abrasive grains, a slurry (free abrasive grains) containing cerium oxide abrasive grains was used. Next, the inner peripheral side end face was mirror polished by a magnetic polishing method. And the glass substrate which finished the end surface grinding | polishing process was washed with water. By this end surface polishing step, the end surface of the glass substrate was processed into a mirror surface state capable of preventing generation of particles and the like. As a result, the diameter of the glass substrate becomes 27.4 mm, which can be used as a substrate for a 1-inch magnetic disk.

  In this end surface polishing step, the glass substrate is overlapped and the end surface is polished. In this case, in order to avoid scratches on the main surface of the glass substrate, before the first polishing step described later, Alternatively, it may be performed before and after the second polishing step.

(4) Second Lapping Step Next, a second lapping process was performed on both main surfaces of the obtained glass substrate in the same manner as in the first lapping step. By performing this second lapping step, it is possible to remove in advance the fine unevenness formed on the main surface in the cutting step and end surface polishing step, which are the previous steps, and shorten the subsequent polishing step on the main surface. Will be able to be completed in time.

(5) Main surface polishing step As the main surface polishing step, first, a first polishing step was performed. This first polishing step is mainly intended to remove scratches and distortions remaining on the main surface in the lapping step described above. In the first polishing step, the main surface was polished using a hard resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, cerium oxide abrasive grains were used.

  The glass substrate that has finished the first polishing step is sequentially immersed in cleaning baths of neutral detergent, pure water (1), pure water (2), IPA (isopropyl alcohol), and IPA (steam drying), and cleaned. did.

  Next, a second polishing step was performed as the main surface polishing step. The purpose of this second polishing step is to finish the main surface into a mirror surface. In the second polishing step, mirror polishing of the main surface was performed using a soft foamed resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, cerium oxide abrasive grains finer than the cerium oxide abrasive grains used in the first polishing step were used.

  After the second polishing process, the glass substrate is made of neutral detergent (1), neutral detergent (2), pure water (1), pure water (2), IPA (isopropyl alcohol), IPA (steam-dried). It was immersed in each washing tank in order and washed. Note that ultrasonic waves were applied to each cleaning tank.

(6) Chemical strengthening process Next, the glass substrate which finished the above-mentioned lapping process and grinding | polishing process was chemically strengthened. For chemical strengthening, a chemical strengthening solution prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) is prepared, and the chemically strengthened solution is heated to 400 ° C., and the cleaned glass substrate is heated to 300 ° C. The sample was preheated and immersed in a chemical strengthening solution for about 3 hours. In this immersion, in order to chemically strengthen the entire surface of the glass substrate, it was carried out in a state of being accommodated in a holder so that a plurality of glass substrates were held at the end surfaces.

  Thus, by immersing in a chemical strengthening solution, the lithium ion and sodium ion of the surface layer of a glass substrate are each substituted by the sodium ion and potassium ion in a chemical strengthening solution, and a glass substrate is strengthened. The thickness of the compressive stress layer formed on the surface layer of the glass substrate was about 100 μm to 200 μm.

  The glass substrate that had been subjected to the chemical strengthening treatment was immersed in a water bath at 20 ° C. for rapid cooling and maintained for about 10 minutes. And the glass substrate which finished quenching was immersed in the concentrated sulfuric acid heated at about 40 degreeC, and was wash | cleaned (dealkali process). Further, the glass substrate after the sulfuric acid cleaning was cleaned by immersing in a cleaning bath of pure water (1), pure water (2), IPA (isopropyl alcohol) and IPA (steam drying) sequentially. In addition, ultrasonic waves were applied to each cleaning tank.

  As described above, by applying the first lapping step, the cutting step, the end surface polishing step, the second lapping step, the first and second polishing steps, the precision cleaning, and the chemical strengthening step, a flat and smooth, high rigidity A glass substrate for a magnetic disk was obtained.

(7) Texture processing step Polishing and circumferential texture processing were performed using a tape-type texture device. A woven fabric type tape was used as the tape, and a slurry in which polycrystalline diamond having an average particle size of 0.125 μm was dissolved in a dispersant / lubricant (glycerin) was used as the hard abrasive.

(8) Magnetic disk manufacturing process A seed layer, Cr underlayer, CrMo underlayer, CoPtCrTa magnetic layer, hydrogenation on both surfaces of the glass substrate that has been textured through the above-described steps, using a single wafer sputtering device. A carbon protective layer was formed, and a perfluoropolyether lubricating layer was formed by a dip method to produce a magnetic disk.

  The obtained magnetic disk was confirmed to be free from defects in the film such as the magnetic layer due to foreign matter. In addition, when the glide test was performed, no hit (the head bited against the protrusion on the surface of the magnetic disk) or crash (the head collided with the protrusion on the surface of the magnetic disk) was not recognized. Furthermore, when a reproduction test was conducted with a magnetoresistive head, no malfunction of reproduction due to thermal asperity was found.

  The present invention can be used as a method for producing a glass substrate and a magnetic disk for a magnetic recording medium.

It is a figure explaining the forming process which chamfers to the end surface of a glass substrate. It is a principal part enlarged view of a grinding position. It is a whole block diagram of an end surface grinding apparatus. It is a figure explaining the change of the generation | occurrence | production rate of a chip | tip by the temperature control of a cooling fluid. It is an enlarged view of the grinding surface of the conventional rotary grindstone.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Glass substrate 11 ... Circular hole 12 ... Inner peripheral end surface 12a ... Chamfering part 13 ... Outer peripheral end surface 13a ... Chamfering part 20 ... Inner whetstone 21 ... Outer whetstone 21a ... Base material 22a ... Central flat part 22b ... Inclined part 23 ... Abrasive grain 24 ... Nickel 25 ... Coolant 26 ... Coolant nozzle 27 ... Recovery tank 28 ... First tank 29 ... Separation device 30 ... Second tank 31 ... Cooler 32 ... Cooling coil 50 ... Base material 51 ... Abrasive grain 52 ... Nickel 53 ... depression

Claims (8)

A method of grinding an end face of a glass substrate using a grinding means for embedding abrasive grains and grinding an end face of a glass substrate, and a cooling liquid supply means for supplying a cooling liquid to a grinding position,
A method of manufacturing a glass substrate for a magnetic disk, wherein the temperature of the cooling liquid is adjusted to 28 ° C. or lower. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the temperature of the cooling liquid is adjusted to 25 ° C. or lower. 2. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the temperature of the coolant is adjusted to 23 ° C. or more and 25 ° C. or less. 2. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the abrasive grains are diamond abrasive grains and are embedded in nickel as an adhesive with respect to the base material of the grinding means. . 2. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the grinding means is a method for chamfering an end face of the plate glass. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the glass substrate is made of aluminosilicate glass. A method for producing a magnetic disk, comprising forming at least a magnetic layer on the surface of the glass substrate for a magnetic disk obtained by the method for producing a glass substrate for a magnetic disk according to claim 1. . Grinding means embedded with abrasive grains;
Coolant supply means for supplying coolant to the grinding position;
An apparatus for grinding an end face of a glass substrate for a magnetic disk, comprising temperature adjusting means for adjusting the temperature of the cooling liquid.

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