JP2012203960A - Manufacturing method for glass substrate for magnetic information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a glass substrate for a magnetic information recording medium with excellent impact resistance and planarity and with no optical distortion.SOLUTION: A manufacturing method for a glass substrate for a magnetic information recording medium includes: a disc processing step of providing a glass substrate having an approximate circular shape out of molten glass; an annealing step of correcting the shape of the glass substrate obtained in the disc processing step, by heating; a wrapping step of grinding a surface of the glass substrate obtained in the annealing step; a polishing step of polishing a surface of the glass substrate obtained in the wrapping step; and a stress measurement step of measuring optically the remaining stress of the glass substrate obtained in the polishing step. In the stress measurement step, the measurement is preferably performed on the birefringence quantity at a plurality of locations on the glass substrate. The method preferably further includes a selection step of selecting the glass substrate obtained in the stress measurement step as the glass substrate employed as the glass substrate for the magnetic information recording medium.

Description

  The present invention relates to a method for producing a glass substrate for a magnetic information recording medium.

  A magnetic information recording apparatus records information on an information recording medium by using magnetism, light, magneto-optical, and the like. A typical example is a hard disk drive device. A hard disk drive device is a device that magnetically records information on a magnetic disk as an information recording medium having a recording layer formed on a substrate by a magnetic head. As a base material of such an information recording medium, a so-called substrate, a glass substrate is preferably used.

  In addition, the hard disk drive device records information on the magnetic disk while rotating it at a high speed by only a few nanometers without contacting the magnetic head with the magnetic disk. Furthermore, in recent years, the recording density of hard disks has been further improved, and accordingly, the difference between the magnetic head and the magnetic disk (hereinafter referred to as the head flying height) has been reduced. In particular, in a hard disk having a DFH (Dynamic Flying High) mechanism, a head flying height of 3 nm or less has been developed. However, in the DFH mechanism, since the head flying height is extremely small, a problem that the head crashes due to the collision between the magnetic head and the magnetic disk frequently occurs.

  Also, recent hard disk drive devices have been required to have excellent impact resistance and flatness of substrates used in the hard disks and have low optical distortion due to their improved recording density. Improvement of impact resistance has been realized by providing chemical strengthening in the manufacturing process of the magnetic information recording medium substrate. This chemical strengthening reinforces the glass substrate by giving internal stress by replacing ions (for example, Li, Na ions) in the glass substrate with those having a larger ion radius (for example, Na ions, K ions). It is a method of making it. However, even with such chemical strengthening, a substrate having low impact resistance was generated. Further, there has been a problem that the flatness of the substrate is deteriorated by chemical strengthening.

  On the other hand, in order to impart excellent flatness to the glass substrate, a step of heating the glass substrate (hereinafter referred to as an annealing step) is provided before the step of polishing the surface of the glass substrate, and distortion inside the glass substrate is reduced. The surface scratches that are newly generated in the subsequent polishing process are reduced (Patent Document 1). However, even in the glass substrate subjected to such an annealing process, optical distortion still remains.

JP 2008-287779 A

  The present invention has been made in view of the above prior art, and the problem to be solved is a method for producing a glass substrate for a magnetic information recording medium having excellent impact resistance and flatness and having no optical distortion. The purpose is to provide.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive studies paying attention to the time when the annealing process should be performed in the manufacturing process of the glass substrate for magnetic information recording media and the optical stress of the glass substrate. As a result, by performing an annealing process immediately after the disk processing process, measuring the stress at multiple locations on the glass substrate that has undergone all the processes such as the lapping process, polishing process, and cleaning process, and selecting those that do not vary It has been found that a glass substrate for optical magnetic information recording medium free from optical distortion can be produced. Furthermore, if it is a glass substrate for magnetic information recording media obtained by such a manufacturing method, it can be provided with sufficient impact resistance without performing a chemical strengthening step, and excellent flatness can be obtained. I found it.

  The method for manufacturing a glass substrate for a magnetic information recording medium according to the present invention includes a disk processing step for obtaining a glass substrate having a substantially annular shape from molten glass, and a shape obtained by applying heat to the glass substrate obtained by the disk processing step. An annealing process for correcting, a lapping process for grinding the surface of the glass substrate obtained by the annealing process, a polishing process for polishing the surface of the glass substrate obtained by the lapping process, and the glass obtained by the polishing process And a stress measuring step for optically measuring the residual stress of the substrate.

  In the stress measurement step, it is preferable to measure the amount of birefringence at a plurality of locations on the glass substrate. If it is such a structure, it will become possible to manufacture the glass substrate for magnetic information recording media with higher productivity by measuring the amount of birefringence.

  It is preferable that the method further includes a selection step of selecting a glass substrate obtained by the stress measurement step as a glass substrate employed for the glass substrate for a magnetic information recording medium. With such a configuration, a glass substrate without optical distortion can be produced efficiently.

  In the selecting step, it is preferable to select a glass substrate in which the difference between the maximum value and the minimum value of the birefringence amount at the plurality of locations is 50% or more with respect to the maximum value. With such a configuration, a glass substrate with less optical distortion can be obtained.

  It is preferable that the glass substrate having a minimum value of birefringence at the plurality of locations less than 50% of the maximum value is further subjected to an annealing step. According to such a configuration, a glass substrate without optical distortion can be mass-produced by subjecting the glass substrate not selected in the stress measurement step to the annealing step again.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the glass substrate for magnetic information recording media which has the outstanding impact resistance and flatness, and does not have an optical distortion can be provided.

It is a manufacturing process figure explaining the process in manufacture of the glass substrate for magnetic information recording media concerning this embodiment. It is a top view which shows the glass substrate for magnetic information recording media manufactured by the manufacturing method of the glass substrate for magnetic information recording media concerning this embodiment. It is a schematic sectional drawing which shows an example of the grinding | polishing apparatus used at the rough grinding | polishing process and the precision grinding | polishing process in the manufacturing method of the glass substrate for magnetic information recording media which concerns on this embodiment. 1 is a partial cross-sectional perspective view showing a magnetic disk as an example of a magnetic recording medium using a glass substrate for magnetic information recording medium manufactured by the method for manufacturing a glass substrate for magnetic information recording medium according to the present embodiment.

  Hereinafter, although the embodiment concerning the present invention is described, the present invention is not limited to these.

  The method for manufacturing a glass substrate for a magnetic information recording medium according to the present embodiment includes a disk processing step for obtaining a glass substrate having a substantially annular shape from molten glass, and a shape obtained by applying heat to the glass substrate obtained by the disk processing step. Obtained by the polishing step, the lapping step for grinding the surface of the glass substrate obtained by the annealing step, the polishing step for polishing the surface of the glass substrate obtained by the lapping step, and the polishing step And a stress measurement step for optically measuring the residual stress of the glass substrate.

  Moreover, the manufacturing method of the glass substrate for magnetic information recording media according to the present embodiment includes an annealing process between the disk processing process and the lapping process, and includes a stress measurement process after all the processes. There is no particular limitation, and any known production method may be used.

  Examples of the method for producing a glass substrate for a magnetic information recording medium include a disk processing step, an annealing step, a first lapping step, a shape processing step, a second lapping step, a rough polishing step (primary polishing step), and a precision polishing step ( A secondary polishing step), a cleaning step, and the like. The steps may be performed in this order, or the order of the precision polishing step (secondary polishing step) and the cleaning step may be switched. Furthermore, a method including steps other than these may be used. For example, you may provide what performs an end surface grinding | polishing process between a lapping process and a rough grinding | polishing process (primary grinding | polishing process).

  In particular, the cleaning process may be performed after the rough polishing process or after the precision polishing process, and may be performed once after each of the rough polishing process and the precision polishing process.

  Here, the stress measurement process in the manufacturing method of this invention is explained in full detail.

<Stress measurement process>
The stress measurement step is performed after all the steps such as the shape processing step, the lapping step, the polishing step, and the cleaning step.

  Specifically, the amount of birefringence at a plurality of locations on the glass substrate is measured. The amount of birefringence is the phase difference between two refracted lights when light passes through the substance for a unit length. Usually, the optical distortion of glass is defined as the amount of birefringence.

  The amount of birefringence is measured using PA-100 (manufactured by Photonic Lattice) or the like.

  As described above, if the minimum value of the birefringence measured at a plurality of locations is 50% or more with respect to the maximum value, a glass substrate having a small optical distortion can be selected (selection step). That is, the amount of birefringence obtained by this measurement process is a process before performing the selection process before shipping the glass substrate. If the minimum value of the birefringence amount is less than 50% with respect to the maximum value, it can be determined that the balance of stress values in the glass substrate is poor. And a glass substrate without optical distortion can be produced in a larger quantity by subjecting this glass substrate with a poor stress value balance to an annealing process again.

  In the stress measurement step, the measurement time is significantly shorter than in other stress measurements, and measurement of a glass substrate over a wide range is possible. Other general stress measuring devices include a polarimeter and the like, but since the measuring range is in units of several millimeters, productivity deteriorates.

  Furthermore, the glass substrate excellent in impact resistance can be obtained by performing this stress measurement process and the selection process. That is, the impact resistance of the glass substrate is determined not only by the hardness and the number of microcracks, but also by the residual stress inside the substrate. The hardness of the glass substrate depends on the composition of the glass and the number of microcracks depends on the surface Ra, but the value of the residual stress inside the substrate is determined at the time of press molding of the glass substrate and can be increased by subsequent chemical strengthening.

  However, it is known that when the chemical strengthening step is performed, the flatness of the substrate is deteriorated, and even if the chemical strengthening step is performed, a substrate having poor strength is generated. This is because the total amount of internal stress is increased by chemical strengthening, but a portion where the internal stress is locally weak cannot be increased so much by the chemical strengthening process.

  Therefore, the glass substrate obtained by the production method of the present invention performs birefringence measurement, and by selecting one having a good balance of internal stress values, not only through the chemical strengthening step, but also without optical distortion, A substrate having high impact resistance can be obtained.

<Disk processing process>
In the disk processing step, a through-hole 10a is formed in the center portion of a glass base plate formed from a glass material having a predetermined composition so that the inner periphery and the outer periphery are concentric circles as shown in FIG. This is a process of processing into a disk-shaped glass base plate 10. Specifically, the direct press method can be taken.

  For example, molten glass is supplied onto the lower mold forming surface of a press mold, pressed with the lower mold forming surface and the upper mold forming surface opposite to the molding surface to form a glass blank, and then the glass blank is The mold is released from the upper mold surface in a state of being placed on the molding surface, cooled, and then taken out from the press mold.

As a material of the glass substrate, for example, soda lime glass mainly composed of SiO ₂ , Na ₂ O, CaO; mainly composed of SiO ₂ , Al ₂ O ₃ , R ₂ O (R = K, Na, Li) Aluminosilicate glass; borosilicate glass; Li ₂ O—SiO ₂ glass; Li ₂ O—Al ₂ O ₃ —SiO ₂ glass; R′O—Al ₂ O ₃ —SiO ₂ glass (R ′ = Mg) , Ca, Sr, Ba) and the like can be used. Among these, aluminosilicate glass and borosilicate glass are particularly preferable because they are excellent in impact resistance and vibration resistance. The press-molded glass substrate precursor can be obtained by opening a hole in the central portion with a core drill or the like provided with a diamond grindstone or the like in the cutter portion.

  In this disk processing step, for example, the outer diameter r1 is 2.5 inches (about 64 mm), 1.8 inches (about 46 mm), 1 inch (about 25 mm), 0.8 inches (about 20 mm), etc., and the thickness is It is processed into a disk-shaped glass base plate of 2 mm, 1 mm, 0.63 mm or the like. Further, when the outer diameter r1 is 2.5 inches (about 64 mm), the inner diameter r2 is processed to 0.8 inches (about 20 mm) or the like.

<Annealing process>
The annealing process is performed before the first lapping process, which is a grinding process. This annealing process is a process in which a glass substrate for an information recording medium is sandwiched between setter jigs and heated in a heat treatment furnace. By adding this annealing process, the inside of the glass substrate generated in the disk processing process, which is the previous process, The distortion can be released.

  In particular, in a process where glass is melted and formed by pressing, the glass cooling temperature is not uniform, and stress distortion occurs inside the glass. Due to this stress strain, if lapping or polishing is performed without performing the annealing step, minute cracks are generated according to the strain. Abrasives or foreign substances enter the cracks, and even if high-precision polishing is repeated, convex portions are generated, resulting in defective products. This stress strain inside the glass can be released by annealing immediately after the disk processing step, and even if lapping or polishing is performed thereafter, cracks are not generated and the occurrence of defective products can be reduced.

  The temperature of the annealing step is preferably 30 to 70 ° C. higher than the glass transition temperature (Tg). If the temperature is lower than the above range, the flatness cannot be corrected. On the other hand, when the temperature is higher than the above range, the temperature becomes close to the softening point, and the glass and the jig for annealing are stuck together, or the flatness is deteriorated. The holding time at the annealing temperature is preferably 120 minutes or more and less than 1440 minutes.

  In addition, if the cooling speed is high (rapid cooling), another warp is generated, so it is preferable that the cooling speed is low.

As the material of the setter member, stainless steel (austenite or martensite), casting (FC or FCD), heat-resistant alloy (Co or Ni), ceramics (SiC or SiCN ₃ ), etc. can be used. . In addition, the surface of the pressing member can be subjected to treatment such as CR plating and Ni-P electroless plating which are hard and difficult to oxidize. As for the shape of the pressing surface, it is desirable that the upper and lower surfaces are flat and the upper and lower surfaces are parallel to each other. Since the shape of the setter surface changes depending on the temperature, it is determined in consideration of the use temperature, the expansion characteristics of the mold material, and the like so as to obtain a desired shape when the main surface of the glass substrate is pressed.

<First wrapping process>
The lapping step is a step of processing the glass base plate to a predetermined plate thickness. Specifically, the process etc. which grind | polish (lapping) the both surfaces of a glass base plate are mentioned. By processing in this way, the parallelism, flatness and thickness of the glass base plate can be adjusted. Further, this lapping step may be performed once or twice or more. For example, when it is performed twice, the parallelism, flatness and thickness of the glass base plate are preliminarily adjusted in the first lapping process (first lapping process), and glass is used in the second lapping process (second lapping process). It becomes possible to finely adjust the parallelism, flatness and thickness of the base plate.

  More specifically, examples of the first lapping step include a step of making the entire surface of the glass base plate have a substantially uniform surface roughness. At that time, for example, when the arithmetic average roughness Ra of the glass base plate is measured at a plurality of locations, the difference between the minimum value and the maximum value of Ra obtained is preferably about 0.01 to 0.4 μm.

<Shaping process>
The shape processing step is a step of processing the inner and outer diameters by grinding the outer peripheral end surface and the inner peripheral end surface of the glass substrate with a grinding wheel such as a drum-shaped diamond.

  The inner peripheral and outer peripheral end faces of the glass substrate are polished by brush polishing in the inner peripheral and outer peripheral end face processing steps. The brush is preferably made of nylon, polypropylene or the like having a diameter of about 0.2 to 0.3 mm. The polishing liquid is preferably cerium oxide having a particle size of about several μm. As a result of brush polishing, the surface roughness of the inner and outer end faces is preferably such that Rmax is 0.2 to 0.4 μm and Ra is about 0.02 to 0.04 μm. The shape of the end surface of the glass substrate that has undergone the shape processing step is such that the corner formed by the main surface and the end surface is removed, and the end surface is sag from the position of about 0.2 mm to 0.5 mm from the outer peripheral end surface.

<Second wrapping process>
The second lapping step may include a process of grinding the main surface of the roughened glass substrate using a fixed abrasive polishing pad. In this second wrapping step, for example, a roughened glass substrate is set in a wrapping apparatus, and a three-dimensional fixed abrasive with a surface pattern such as diamond tile is used. The surface can be wrapped.

  When the second lapping step is performed, polishing performed in a rough polishing step described later can be performed efficiently. Further, the surface roughness Ra of the glass base plate used in the polishing step performed by the second lapping step is preferably 0.10 μm or less, and more preferably 0.05 μm or less.

<Rough polishing process>
The rough polishing step (primary polishing step) is a step of rough polishing the surface of the glass base plate that has been subjected to the lapping step. This rough polishing is intended to remove scratches and distortions remaining in the lapping step described above, and is performed using the following polishing method.

  The surface to be polished in the rough polishing step is a main surface and / or an end surface. The main end surface is a surface parallel to the surface direction of the glass base plate. The end surface is a surface composed of an inner peripheral end surface and an outer peripheral end surface. Moreover, an inner peripheral end surface is a surface which has an inclination with respect to the surface of an inner peripheral side perpendicular | vertical to the surface direction of a glass base plate, and the surface direction of a glass base plate. Moreover, an outer peripheral end surface is a surface which has an inclination with respect to the surface direction of the outer peripheral side perpendicular | vertical to the surface direction of a glass base plate, and the surface direction of a glass base plate.

  The polishing apparatus used in the rough polishing step is not particularly limited as long as it is a polishing apparatus used for manufacturing a glass substrate. Specifically, there is a polishing apparatus 1 as shown in FIG. FIG. 3 is a schematic cross-sectional view showing an example of the polishing apparatus 1 used in the rough polishing process and the precision polishing process in the method for manufacturing a glass substrate for a magnetic information recording medium according to the present embodiment.

  A polishing apparatus 11 as shown in FIG. 3 is an apparatus capable of simultaneous grinding on both sides. The polishing apparatus 11 includes an apparatus main body 11a and a polishing liquid supply unit 11b that supplies a polishing liquid to the apparatus main body 11a.

  The apparatus main body 11a includes a disk-shaped upper surface plate 12 and a disk-shaped lower surface plate 13, and they are arranged vertically spaced apart so that they are parallel to each other. Then, the disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13 rotate in directions opposite to each other.

  A polishing pad 15 for polishing both the front and back surfaces of the glass base plate 10 is attached to the opposing surfaces of the disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13. The polishing pad 15 used in the rough polishing step is not particularly limited as long as it is a polishing pad used in the rough polishing step. Specifically, for example, a hard polishing pad made of polyurethane or the like can be used.

  A plurality of rotatable carriers 14 are provided between the disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13. The carrier 14 is provided with a plurality of base plate holding holes 51, and the glass base plate 10 can be fitted into the base plate holding holes 51. For example, the carrier 14 may include 100 base plate holding holes 51 so that 100 glass base plates 10 can be fitted and arranged. Then, 100 glass base plates 10 can be processed by one processing (1 batch).

  The carrier 14 sandwiched between the surface plates 12 and 13 through the polishing pad is the same as the lower surface plate 13 with respect to the rotation center of the surface plates 12 and 13 while rotating while holding the plurality of glass base plates 10. Revolve in the direction. The disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13 can be operated by separate driving. In the polishing apparatus 11 operating as described above, the polishing slurry 16 is supplied between the upper surface plate 12 and the glass base plate 10 and between the lower surface plate 13 and the glass base plate 10, so that the glass base material is supplied. Rough polishing of the plate 10 can be performed.

  The polishing slurry supply unit 11b includes a liquid storage unit 110 and a liquid recovery unit 120. The liquid reservoir 110 includes a liquid reservoir main body 110a and a liquid supply pipe 110b having a discharge port 110e extending from the liquid reservoir main body 110a to the apparatus main body 11a. The liquid recovery part 120 was extended to the liquid recovery part main body 120a, the liquid recovery pipe 120b extended from the liquid recovery part main body 120a to the apparatus main body part 11a, and the polishing slurry supply part 11b from the liquid recovery part main body 120a. And a liquid return pipe 120c.

  Then, the polishing slurry 7 put in the liquid storage unit main body 110a is supplied from the discharge port 110e of the liquid supply pipe 110b to the apparatus main body part 11a, and from the apparatus main body part 11a through the liquid recovery pipe 120b, the liquid recovery part main body 120a. To be recovered. The recovered polishing slurry 16 is returned to the liquid storage part 110 via the liquid return pipe 120c and can be supplied again to the apparatus main body part 11a.

  The polishing liquid 16 used here is a liquid in which an abrasive is dispersed in water, that is, a slurry liquid.

  Further, the polishing pad 15 used here is a foam of synthetic resin such as urethane or polyester containing a cerium oxide abrasive.

The polishing liquid 7 is in a state where the abrasive is dispersed in water, and the content of CeO ₂ is preferably 3 to 15% by mass with respect to the total amount of the polishing liquid. By doing so, the glass substrate for information recording media excellent in impact resistance can be manufactured, the polishing rate can be further increased, and the glass substrate for information recording media having higher smoothness can be manufactured.

  The abrasive has a maximum particle size distribution of 3.5 μm or less measured by the laser diffraction scattering method, and a cumulative 50 volume% diameter D50 in the particle size distribution measured by the laser diffraction scattering method is 0.4 to 0.4. It is preferable that it is 1.6 μm.

  When the particle size of the abrasive is too small, the polishing rate tends to decrease. When the particle size of the abrasive is too large, scratches that can be formed on the glass base plate due to polishing tend to occur.

<Precision polishing process (secondary polishing process)>
The precision polishing process is a mirror polishing process that finishes a smooth mirror surface having a surface roughness (Rmax) of about 6 nm or less, for example, while maintaining the flat and smooth main surface obtained in the rough polishing process. The precision polishing step is performed, for example, by using a polishing apparatus similar to that used in the rough polishing step and replacing the polishing pad from a hard polishing pad to a soft polishing pad. The surface to be polished in the precision polishing step is the main surface, similar to the surface to be polished in the rough polishing step.

  Further, as the abrasive used in the precision polishing step, an abrasive that causes fewer scratches even if the abrasiveness is lower than the abrasive used in the rough polishing step is used. Specifically, for example, a polishing agent containing silica-based abrasive grains (colloidal silica) having a particle diameter lower than that of the polishing agent used in the rough polishing step. The average particle diameter of the silica-based abrasive is preferably about 20 nm. And the polishing slurry liquid containing the said abrasive | polishing agent is supplied to a glass base plate, a polishing pad and a glass base plate are slid relatively, and the surface of a glass base plate is mirror-polished.

<Washing process>
The cleaning step is a step of cleaning the glass base plate that has been subjected to the rough polishing step.

  The glass base plate after the rough polishing by the rough polishing step is preferably cleaned by a cleaning step. The washing process is not particularly limited. Specifically, for example, the following washing steps are mentioned.

  First, the glass base plate is washed with an alkaline detergent having a pH of 13 or more, and the glass base plate is rinsed. Next, the glass base plate is washed with an acid detergent having a pH of 1 or less, and the glass base plate is rinsed. Moreover, it is preferable to use a rinse tank after each washing. In some cases, a surfactant, a dispersing agent, a chelating agent, a reducing material, and the like may be added to these detergents. Moreover, it is preferable to apply an ultrasonic wave to each washing tank and to use deaerated water for each detergent. Finally, the glass base plate is taken out, rinsed with pure water, and IPA dried.

The glass substrate after the rough polishing is cleaned so that the amount of cerium oxide on the surface of the glass substrate is 0.125 ng / cm ² or less. When the amount of cerium oxide on the surface of the glass base plate is too large, the flatness of the glass base plate tends not to be good.

(Film formation process)
FIG. 4 is a partial cross-sectional perspective view showing a magnetic disk which is an example of a magnetic recording medium using the glass substrate for magnetic information recording medium manufactured by the method for manufacturing a glass substrate for magnetic information recording medium according to the present embodiment. is there. The magnetic disk D includes a magnetic film 102 formed on the main surface of a circular glass substrate 101 for a magnetic information recording medium. For the formation of the magnetic film 102, a known method is used. For example, a formation method (spin coating method) for forming a magnetic film 102 by spin-coating a thermosetting resin in which magnetic particles are dispersed on a glass substrate 101 for a magnetic information recording medium, or a glass substrate for a magnetic information recording medium Examples include a formation method (sputtering method) for forming the magnetic film 102 on the substrate 101 by sputtering, a formation method (electroless plating method) for forming the magnetic film 102 on the glass substrate 101 for magnetic information recording medium by electroless plating, and the like. It is done.

  The thickness of the magnetic film 102 is about 0.3 to 1.2 μm when the spin coating method is used, and is about 0.04 to 0.08 μm when the sputtering method is used. In some cases, the thickness is about 0.05 to 0.1 μm. From the viewpoint of thinning and densification, film formation by sputtering is preferable, and film formation by electroless plating is preferable.

  The magnetic material used for the magnetic film 102 can be any known material and is not particularly limited. The magnetic material is preferably, for example, a Co-based alloy based on Co having high crystal anisotropy in order to obtain a high coercive force, and Ni or Cr added for the purpose of adjusting the residual magnetic flux density. More specifically, CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, CoCrPtSiO, and the like whose main component is Co can be given.

The magnetic film 102 has a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa, etc.) divided by a nonmagnetic film (for example, Cr, CrMo, CrV, etc.) in order to reduce noise. May be. Magnetic material used for the magnetic layer 102, in addition to the magnetic material, ferrite or iron - may be a rare earth, also, Fe in a non-magnetic film made of _SiO 2, BN, etc., Co, FeCo, CoNiPt and the like A granular material having a structure in which the magnetic particles are dispersed may be used. In addition, for recording on the magnetic film 102, either an inner surface type or a vertical type recording format may be used.

  In order to improve the sliding of the magnetic head, the surface of the magnetic film 102 may be thinly coated with a lubricant. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a freon-based solvent.

  Furthermore, an underlayer or a protective layer may be provided on the magnetic film 102 as necessary. The underlayer in the magnetic disk D is appropriately selected according to the magnetic film 102. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. For example, in the case of the magnetic film 102 containing Co as a main component, the material of the underlayer is preferably Cr alone or a Cr alloy from the viewpoint of improving magnetic characteristics.

  Further, the underlayer is not limited to a single layer, and may have a multilayer structure in which the same or different layers are stacked. Examples of such an underlayer having a multilayer structure include multilayer underlayers such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, and NiAl / CrV. Examples of the protective layer that prevents wear and corrosion of the magnetic film 102 include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be continuously formed with the underlayer and the magnetic film 102 by an in-line sputtering apparatus. These protective layers may be a single layer, or may be a multi-layer structure composed of the same or different layers.

Note that another protective layer may be formed on the protective layer or instead of the protective layer. For example, instead of the protective layer, a SiO ₂ layer may be formed on the Cr layer. Such a SiO ₂ layer is formed by dispersing and applying colloidal silica fine particles in a tetraalkoxysilane diluted with an alcohol-based solvent on the Cr layer and further baking.

  In such a magnetic recording medium based on the glass substrate 101 for magnetic information recording medium according to this embodiment, the glass substrate 101 for magnetic information recording medium is formed with the above-described composition. It can be done with high reliability.

  In addition, although the case where the glass substrate 101 for magnetic information recording media in this embodiment was used for a magnetic recording medium was demonstrated above, it is not limited to this, The glass substrate for magnetic information recording media in this embodiment 101 can also be used for magneto-optical disks, optical disks, and the like.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

  After going through the steps as described below, the measured stress value of each substrate was measured to produce a glass substrate.

(Disc machining process)
First, molten glass was prepared by melting a glass material. The molten glass was poured into a lower mold and directly pressed using an upper mold and a barrel mold to obtain a disk-shaped glass substrate precursor having a diameter of 66 mmφ and a thickness of 1.2 mm. Aluminosilicate glass was used as the glass material. Next, a hole was made by grinding the central portion of the glass substrate precursor with a core drill having a diamond grindstone or the like in the cutter portion. In this way, a hole having an inner diameter of 20 mm (diameter of the hole 1H in the central part) was formed in the central part of the glass substrate precursor having an outer diameter of 65 mm.

(Annealing process)
The temperature of the annealing step was 50 ° C. higher than the glass transition temperature (Tg). The holding time at the annealing temperature was 720 minutes.

(First lapping process)
Next, the glass substrate precursor is set in a double-sided wrapping apparatus, and alumina abrasive grains having a particle size of # 400 (particle size of about 40 to 60 μm) are used, and the load on the surface plate on alumina is set to about 100 kg. The front and back surfaces of the glass substrate precursor were polished. The glass substrate precursor thus housed in the carrier had a surface accuracy of 0 μm to 1 μm on both sides and a surface roughness Rmax of about 6 μm.

(Internal / external machining process)
Next, chamfering of the outer peripheral end surface and the inner peripheral end surface of the glass substrate precursor was performed. As a result, the surface roughness of the end surface of the glass substrate precursor was about 2 μm in Rmax.

(End face polishing process)
Subsequently, the outer peripheral end surface and the inner peripheral end surface of the glass substrate precursor were polished while rotating the glass substrate precursor by a brush polishing method using a slurry (free abrasive particles) containing cerium oxide abrasive grains as polishing abrasive grains. . Here, polishing was performed until the surface roughness of the outer peripheral end face and the inner peripheral end face of the glass substrate precursor was about 0.4 μm in Rmax and about 0.1 μm in Ra.

  The above-mentioned inner peripheral side end face was further polished by a magnetic polishing method to be processed into a mirror surface state that prevents generation of particles and the like. And after grind | polishing the inner peripheral end surface in this way, the main surface of the glass substrate precursor was wash | cleaned with water.

(Second wrapping process)
Next, in the fine lapping process, both the front and back surfaces of the glass substrate precursor were set in a double-side grinding machine using a planetary gear mechanism. Then, using a diamond sheet, the weight of the platen applied to the glass substrate precursor is changed from 60 g / cm ² to 120 g / cm ² , the rotation speed of the platen is changed from 10 rpm to 30 rpm, and the rotation speed of the upper platen is decreased. The front and back surfaces of the glass substrate precursor were polished at a rate slower by about 30% to 40% than the platen rotation speed. Thus, lapping was performed until the surface roughness Ra of the main surface of the glass substrate precursor was 0.1 μm or less and the flatness was 7 μm or less.

(Rough polishing process)
First, the rough polishing process for removing the flaw and distortion which remained in the fine lapping process was performed using the double-side polish apparatus mentioned above. In this rough polishing step, the front and back surfaces of the glass substrate precursor were polished under the following conditions using a polishing pad whose polisher was a suede pad.

Polishing liquid: Cerium oxide (average particle size 1.3 μm) + water Load: 80 to 100 g / cm ²
Polishing time: 30 minutes to 50 minutes Removal method: 35 μm to 45 μm

(Precision polishing process)
Subsequently, by performing a precision polishing step, the front and back surfaces of the glass substrate precursor are polished on the glass substrate precursor using a polishing pad that is a soft polisher (suede), and 1 μm from the main surface of the glass substrate precursor. The thickness of was removed. In addition, as an abrasive | polishing agent used at a precision grinding | polishing process, the silica abrasive grain finer than the cerium oxide used at the rough | crude grinding | polishing process was used.

(Final cleaning process)
The glass substrate precursor after the polishing treatment was washed with a neutral detergent and pure water and dried.

<Example 1>
The birefringence was measured after the polishing process. A substrate having a value with the smallest birefringence of 50% or more with respect to a large value was extracted. The place where the birefringence was measured is a circumferential point of r1.25 mm. (The central part of the substrate was set to r0, and the birefringence values were measured in the circumferential direction at a point of 1.25 mm from there, and compared.)

<Example 2>
In the birefringence measurement, a substrate having a minimum birefringence of 80% or more with respect to a large value was extracted.

<Example 3>
In Example 1, the annealing process was performed on the minimum value less than 50% of the maximum value. The annealing process is a process in which a glass substrate is sandwiched between setter jigs and heated in a heat treatment furnace. By including this annealing step, the flatness can be corrected.

  The glass substrate subjected to the annealing step was again subjected to birefringence measurement, and a substrate having a value with the smallest birefringence of 50% or more with respect to a large value was extracted. The yield in this case was 85%. That is, it became clear that the birefringence of the glass substrate was changed by this annealing process.

<Comparative Example 1>
After passing through each process as mentioned above, the glass substrate was manufactured without performing the birefringence measurement process.

(Evaluation of crack test)
Each substrate was formed and then incorporated into a hard disk drive to conduct a cracking test. In this crack test, a plurality of HDDs were dropped so that an impact of 1000 G (1G: 9.80665 m / s ² ) was applied to the HDD. At that time, it was visually confirmed whether or not the magnetic disk built in the HDD was cracked, and the ratio of cracking was calculated.

  In addition, each value of following Table 1 is an average value after selecting 100 glass substrates in each Example and a comparative example.

  As is apparent from the results in Table 1, by measuring the residual stress of the glass substrate optically, it becomes possible to select a glass substrate having a high impact strength, and as a result, a magnetic recording medium having a high impact strength can be obtained. I was able to show that.

DESCRIPTION OF SYMBOLS 10 Glass substrate 11 Polishing apparatus 12 Upper surface plate 13 Lower surface plate 16 Pump 101 Glass substrate for magnetic information recording media

Claims (5)

A disk processing step of obtaining a glass substrate having a substantially annular shape from molten glass;
An annealing step of correcting the shape by applying heat to the glass substrate obtained by the disk processing step;
A lapping step of grinding the surface of the glass substrate obtained by the annealing step;
A polishing step of polishing the surface of the glass substrate obtained by the lapping step;
A stress measurement step for optically measuring the residual stress of the glass substrate obtained by the polishing step;
The manufacturing method of the glass substrate for magnetic information recording media provided with.   The method of manufacturing a glass substrate for a magnetic information recording medium according to claim 1, wherein the stress measurement step measures birefringence at a plurality of locations on the glass substrate.   The magnetic information recording medium according to claim 1, further comprising a selection step of selecting a glass substrate obtained by the stress measurement step as a glass substrate employed for the glass substrate for the magnetic information recording medium. Method for manufacturing glass substrate.   4. The glass substrate for a magnetic information recording medium according to claim 3, wherein in the selection step, a glass substrate in which a minimum value of birefringence at the plurality of locations is 50% or more with respect to a maximum value is selected. Production method. 5. The glass substrate for a magnetic information recording medium according to claim 3, wherein a glass substrate having a minimum value of birefringence at the plurality of locations of less than 50% of the maximum value is further subjected to an annealing step. Manufacturing method.

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