JP5356606B2 - Manufacturing method of glass substrate for magnetic disk - Google Patents

Abstract

A method for manufacturing a magnetic-disk glass substrate is provided such that, when a plurality of magnetic-disk glass substrates are manufactured from a stack in which a plurality of glass plates are stacked, the circularity deviations of inner holes of the magnetic-disk glass substrates can be improved to a desired level while the cycle-time merits of machining stacked glass plates are maintained. In a stack preparation process, a stack (5) in which a plurality of glass plates are stacked is prepared. In a grinding process, an integrated core drill (20) in which a cylindrical large-diameter grindstone for outer circumference grinding and a cylindrical small-diameter grindstone for inner circumference grinding are coaxially disposed is moved in the stacking direction of the stack (5) while also being rotated about a shaft, and the stack (5) is thereby cylindrically ground. At this time, the grindstone for inner circumference grinding has a grit number greater than that of the grindstone for outer circumference grinding.

Description

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

  2. Description of the Related Art Today, a personal computer, a DVD (Digital Versatile Disc) recording device, or the like has a built-in hard disk device (HDD: Hard Disk Drive) for data recording. In particular, in a hard disk device used in a portable computer such as a notebook personal computer, a magnetic disk in which a magnetic layer is provided on a glass substrate is used, and the magnetic head slightly floats above the surface of the magnetic disk. Magnetic recording information is recorded on or read from the magnetic layer by a (DFH (Dynamic Flying Height) head). As a substrate for this magnetic disk, a glass substrate is preferably used because it has a property that it is less likely to be plastically deformed than a metal substrate (aluminum substrate) or the like.

  Further, in response to a request for an increase in storage capacity in a hard disk device, the density of magnetic recording has been increased. For example, the magnetic recording information area is miniaturized by using a perpendicular magnetic recording method in which the magnetization direction in the magnetic layer is perpendicular to the surface of the substrate. Thereby, the storage capacity of one disk substrate can be increased. Furthermore, in order to further increase the storage capacity, the flying distance from the magnetic recording surface of the magnetic head can be made extremely short to further improve the accuracy of information recording / reproduction (improve the S / N ratio). Has been done. In such a magnetic disk substrate, the magnetic layer is formed flat so that the magnetization direction of the magnetic layer is substantially perpendicular to the substrate surface. For this reason, the surface irregularities of the substrate of the magnetic disk are made as small as possible.

In the process of producing the glass substrate for magnetic disk, for example, a coring process for forming a sheet glass into an annular shape, a chamfering process for chamfering the inner peripheral end face and the outer peripheral end face of the annular plate glass, And an edge polishing step of performing mirror finishing of the inner peripheral end face and the outer peripheral end face.
Conventionally, the coring process was performed individually one by one (single-wafer processing), but multiple annular glass sheets were produced at the same time by grinding multiple glass sheets at the same time. A processing method is known in which the tact time of manufacturing is shortened (Patent Document 1). According to this conventional method, the inner peripheral grinding wheel and the outer peripheral grinding wheel move in the stacking direction of the stacked body while rotating the integrated core drill in which the inner peripheral grinding wheel and the outer peripheral grinding wheel are integrally configured coaxially. By processing, the inner peripheral surface and the outer peripheral surface of the laminate are processed. Moreover, in the said patent document 1, it is characterized by the grinding capability of an inner periphery grinding stone being higher than the grinding capability of an outer periphery grinding stone, for example, making the count of an outer periphery grinding stone larger than the count of an inner periphery grinding stone. Good points are disclosed.

JP 2008-97690 A

By the way, in recent years, there is an increasing demand for further improvement in the roundness of the inner hole of the glass substrate for magnetic disks, for the following reason.
As described above, in the magnetic disk for the hard disk device, the magnetic recording information area using the perpendicular magnetic recording method is miniaturized, and the width of the area (magnetic domain) used for 1-bit recording is extremely narrow. The width of a plurality of tracks (storage areas) formed concentrically from the inner hole to the outer edge of the magnetic disk is also becoming extremely narrow. Therefore, if the play between the inner hole and the spindle is large when the inner hole of the magnetic disk is attached to the spindle in the hard disk device, a read error (so-called TMR: Track Miss-Read) may occur between adjacent tracks. There is. Therefore, high accuracy of, for example, 2 μm or less is required as the roundness of the inner hole of the magnetic disk glass substrate.

On the other hand, as a roundness of the inner hole of the glass substrate for magnetic disks, for example, in order to realize a high accuracy roundness of 2 μm or less, grinding is performed with high accuracy in the coring process (grinding process). This is necessary for the following reason.
That is, when the roundness of the inner hole formed in the coring process is not good, the machining allowance must be increased in the subsequent chamfering process, for example, by making the abrasive grains rough. However, if the machining allowance in the chamfering process is increased, the inner peripheral end face is likely to crack. Therefore, in order to reduce the allowance of the inner peripheral end face in the chamfering process so as not to generate cracks as much as possible, it is required to perform grinding with high accuracy in the coring process, which is the preceding process. .

Here, it has become clear that when a device with a built-in hard disk is dropped, the magnetic disk is easily destroyed from the inner periphery. Need to keep.
In addition, the above-described reduction of cracks on the glass substrate for magnetic disk not only ensures the required strength in the drop test of the hard disk device, but also the following recent attempts to achieve higher density recording of the magnetic disk. It is also requested by technology.

  That is, in recent years, a magnetic material (high Ku magnetic material) having a high magnetic anisotropy energy such as an Fe—Pt system or a Co—Pt system is used for the purpose of achieving higher density recording of a magnetic disk. It is being considered. In order to achieve high-density recording, it is necessary to reduce the particle size of the magnetic particles. On the other hand, when the particle size is reduced, deterioration of magnetic properties due to thermal fluctuation becomes a problem. High Ku magnetic materials are less susceptible to thermal fluctuations and are expected to contribute to high density recording. However, the high Ku magnetic material needs to obtain a specific crystal orientation state in order to realize a high Ku. Therefore, it is necessary to perform film formation at a high temperature or heat treatment at a high temperature after film formation. Therefore, in order to form a magnetic recording layer made of these high Ku magnetic materials, the glass substrate must have high heat resistance that can withstand the above high temperature processing, that is, high glass transition temperature (for example, 600 to 700 degrees Celsius). Is required. Here, when the crack has arisen in the end surface of a glass substrate, a crack progresses in the process of the said heat processing, and there exists a possibility that target intensity | strength cannot be ensured. Therefore, as a premise for achieving high density recording by using a high Ku magnetic material, there is a demand for further reduction of cracks than in the past.

In order to reduce cracks on the magnetic disk glass substrate, as described above, the coring process is required to be performed with high accuracy. However, in the coring process disclosed in Patent Document 1, In forming the inner hole, it is difficult to perform high-precision processing. That is, the coring process disclosed in Patent Document 1 is characterized in that the grinding ability of the inner peripheral grinding wheel of the core drill is higher than the grinding ability of the outer peripheral grinding wheel. Although it is disclosed that the diameter of the peripheral grinding wheel is larger than that of the peripheral grinding wheel, in such a setting of the internal grinding wheel and the peripheral grinding wheel, the processing for the inner hole becomes rough, and the roundness of, for example, 2 μm or less is set. It is difficult to realize the surface roughness for realizing.
In addition, it is conceivable to increase the processing accuracy of the outer peripheral part as well as the inner hole by increasing both the counts of the inner peripheral grinding wheel and the outer peripheral grinding wheel. The merit of processing by lamination is lost.

  Therefore, the present invention provides a magnetic disk glass while maintaining the advantages of processing by lamination in terms of tact time when producing a plurality of magnetic disk glass substrates from a laminate in which a plurality of plate glasses are laminated. It is an object of the present invention to provide a method for manufacturing a glass substrate for a magnetic disk that can improve the roundness of an inner hole of the substrate to a required level.

One embodiment of the present invention provides:
A laminate preparation step of preparing a laminate in which a plurality of plate-like glasses are laminated;
By rotating an integrated core drill in which a large-diameter cylindrical outer peripheral grinding wheel and a small-diameter cylindrical inner peripheral grinding wheel are coaxially arranged around the axis, moving in the stacking direction of the laminate, And a grinding step of grinding the laminated body into a cylindrical shape. Here, the count of the inner peripheral grinding wheel is set larger than the count of the outer peripheral grinding wheel.

  In the method for manufacturing a glass substrate for a magnetic disk, the grinding step includes an outer peripheral grinding surface in which the outer peripheral grinding wheel and the plate glass are in contact, and an inner periphery in which the inner peripheral grinding wheel and the plate glass are in contact with each other. Grinding is performed while supplying the grinding fluid to the grinding surface, and the amount of grinding fluid supplied per unit circumference of the inner peripheral grinding surface per unit time is the grinding fluid supplied per unit circumference of the outer peripheral grinding surface. It is preferable that it is larger than the amount of.

  In the method for manufacturing a glass substrate for a magnetic disk, the count of the inner peripheral grinding wheel may be 150 or more and 800 or less, and the count of the outer peripheral grinding wheel may be 120 or more and 600 or less.

  The method for manufacturing a glass substrate for a magnetic disk may include a machining process for polishing an end face of the plate glass after grinding.

  When producing a plurality of glass substrates for magnetic disks from a laminated body in which a plurality of plate glasses are laminated, while maintaining the merit of processing by lamination in terms of tact time, Roundness can be improved to the required level.

The figure which shows the cross section of the laminated body on which several plate glass and the adhesive agent were laminated | stacked. The figure which shows the grinding device when grinding the laminated body of sheet glass in the coring process of embodiment. The figure which shows the cross section of the integrated core drill used at the coring process of embodiment.

  Hereinafter, the manufacturing method of the glass substrate for magnetic disks of this embodiment is demonstrated in detail.

[Magnetic disk glass substrate]
Aluminosilicate glass, soda lime glass, borosilicate glass, or the like can be used as the material for the magnetic disk glass substrate in the present embodiment. In particular, aluminosilicate glass can be suitably used in that it can be chemically strengthened and a glass substrate for a magnetic disk excellent in the flatness of the main surface and the strength of the substrate can be produced.

Although the composition of the glass substrate for magnetic disks of this embodiment is not limited, the composition of a preferable glass substrate is as follows.
For example, a glass substrate of this embodiment is _preferably, SiO 2: 58-75 _{wt%, Al} 2 O 3: _{5~23 wt%,} Li 2 O: _{3~10 wt%,} Na 2 O: _4~13 weight % As a main component.
Glass substrate of the present embodiment is particularly _preferred, SiO 2: _{62~75 wt%, Al} 2 O 3: _{5~15 wt%,} Li 2 O: _{4~10 wt%,} Na 2 O: _4~12 wt% ZrO ₂ : 5.5 to 15% by weight as a main component, the Na ₂ O / ZrO ₂ weight ratio is 0.5 to 2.0, and the Al ₂ O ₃ / ZrO ₂ weight ratio is 0.8. It is aluminosilicate glass which is 4-2.5.
As another suitable glass, expressed in terms of _{weight%, SiO 2: 61~70%,} Al 2 O 3: 9~18%, Li 2 O: 2~3.9%, Na 2 O: 6 ˜13%, K ₂ O: 0 to 5%, R ₂ O: 10 to 16% (provided that R ₂ O = Li ₂ O + Na ₂ O + K ₂ O), MgO: 0 to 3.5%, CaO: 1 ~ 7%, SrO: 0~ 2 %, BaO: 0~2%, RO: 2~10%, ( provided _{that, RO = MgO + CaO + SrO} + BaO), TiO 2: 0~2%, CeO 2: 0~2%, Fe Mention may be made of aluminosilicate glasses containing ₂ O ₃ : 0 to 2%, MnO: 0 to 1%, TiO ₂ + CeO ₂ + Fe ₂ O ₃ + MnO = 0.01 to 3%.

  The glass substrate for a magnetic disk in the present embodiment is an annular thin glass substrate. The size of the glass substrate for the magnetic disk is not limited, but is suitable as a glass substrate for a magnetic disk having a nominal diameter of 2.5 inches or a smaller diameter (for example, 1 inch), for example.

[Method of manufacturing glass substrate for magnetic disk]
Hereinafter, the manufacturing method of the glass substrate for magnetic disks of this embodiment is demonstrated for every process. However, the order of each step may be changed as appropriate.

(1) Forming and lapping process of sheet glass by float method In the process of forming sheet glass by float process, for example, molten glass having the above-described composition is continuously poured into a bath filled with molten metal such as tin. A plate-like glass is obtained. The molten glass flows along the traveling direction in a bathtub that has been subjected to a strict temperature operation, and finally a plate-like glass adjusted to a desired thickness and width is formed. From this plate-like glass, a plate-shaped glass having a predetermined shape that is the basis of the glass substrate for magnetic disks is cut out. Since the surface of the molten tin in the bath is horizontal, the flat glass obtained by the float process has a sufficiently high flatness. The plate-like glass obtained by the above method has a thickness of 0.6 to 1.4 mm and a surface roughness Ra (arithmetic average roughness) of 0.01 μm or less.
In addition, plate glass can be manufactured using well-known manufacturing methods, such as a press molding, a down draw method, a redraw method, a fusion method, not only a float glass method.

  Next, lapping processing using alumina-based loose abrasive grains is performed on both main surfaces of the sheet glass cut into a predetermined shape, if necessary. Specifically, the lapping platen is pressed on both sides of the plate glass from above and below, a grinding liquid (slurry) containing free abrasive grains is supplied onto the main surface of the plate glass, and these are moved relatively. Perform lapping. In addition, when plate glass is molded by the float process, the lapping process may be omitted because the accuracy of the roughness of the main surface after molding is high.

(2) Laminate Preparation Step The plate-like glass cut out in the step (1) is, for example, a plate-like glass having a predetermined rectangular shape (for example, a square shape) slightly larger than the size of the target magnetic disk glass substrate. It is. (For example, when producing a 2.5-inch magnetic disk glass substrate, a rectangular shape of 75 mm × 75 mm).
In the laminate preparation step, a laminate in which a plurality of plate glasses are laminated is prepared by sequentially applying or sticking an adhesive or a spacer between two plate glasses. This laminated body is produced in order to integrally process a plurality of plate glasses in a coring process described later. Further, this laminate may be integrally processed in a chamfering process and an edge polishing process performed after the coring process.
FIG. 1 shows a cross section of a laminate in which a plurality of plate glasses and an adhesive are laminated. FIG. 1 discloses a laminate 5 produced by applying or sticking an adhesive 5b between the plate-like glasses 5a. Here, the adhesive 5b may be anything as long as the glass sheets can be bonded or separated. For example, since the ultraviolet curable resin is easily solidified by irradiation with ultraviolet rays having a predetermined wavelength, the bonding operation is easy. Further, as the ultraviolet curable resin, a resin that can easily peel off the glass sheet bonded with warm water or an organic solvent is preferable. As the adhesive, in addition to the UV curable resin, wax, photo curable resin, visible light curable resin, or the like can be used. Since the wax softens at a predetermined temperature to become a liquid and becomes a solid at room temperature, it is easy to bond and separate. When a spacer is attached instead of the adhesive, a thin spacer made of a resin material, a fiber material, a rubber material, a metal material, or a ceramic material can be used. The thickness of the adhesive or the spacer is, for example, about 0.01 to 2 mm.

(3) Coring step The coring step includes grinding a laminated body 5 in which a plurality of plate glasses are laminated using an integrated core drill, and a laminated body of annular plate glasses in which inner holes are formed. It is a process to do.

  Hereinafter, the coring process (grinding process) of this embodiment will be described with reference to FIGS. FIG. 2 is a view showing a grinding device for grinding a laminated sheet of glass sheets in the coring step of the present embodiment. FIG. 3 is a view showing a cross section of the integrated core drill used in the coring step of the present embodiment.

In the coring process of this embodiment, the grinding apparatus shown in FIG. 2 is used.
In this grinding apparatus, the main device 10 has a function of driving the integrated core drill 20 and a function of supplying coolant as a grinding fluid to the integrated core drill 20. The integral core drill 20 has a substantially cylindrical shape as a whole, and is supported by, for example, a shaft 12 made of a highly rigid stainless material. The cylindrical shaft 12 is supported so as to be able to rotate with respect to the main device 10 and is driven to rotate at a desired number of rotations by a spindle motor (not shown) in the main device 10. The shaft 12 and the integrated core drill 20 are concentric, and the integrated core drill 20 can rotate at high speed with almost no axial center shake due to the rotation of the shaft 12. Therefore, the laminated body 5 can be ground with high precision into an annular plate-like glass laminated body having an inner hole, and the initial stage of processing in which the tip of the integrated core drill 20 contacts the surface of the laminated body 5. The glass on the surface of the laminate 5 is not damaged.

As shown in FIG. 2, in the coring process, a mounting table 30 on which the stacked body 5 is mounted is disposed below the integrated core drill 20. Although not shown, the mounting table 30 is provided with a stopper for the stacked body 5 so that the stacked body 5 is not displaced laterally on the mounting surface of the mounting table 30 during the grinding process. It is preferable.
The grinding apparatus according to the present embodiment can move the main apparatus 10 up and down by a servo mechanism (not shown), thereby integrally moving up and down the integrated core drill 20, shaft 12, and coolant supply hose 15 (described later). It is possible.

  As shown in FIG. 3, the integrated core drill 20 has a large-diameter cylindrical outer peripheral grinding wheel 20a and a small-diameter cylindrical inner peripheral grinding stone 20b arranged coaxially. In addition, as shown in FIG. 2, on the mounting table 30 on which the stacked body 5 is mounted, the outer peripheral grinding wheel 20 a and the inner peripheral grinding wheel 20 b of the integrated core drill 20 collide with the mounting surface of the mounting table 30. An outer peripheral grinding wheel escape groove 30a and an inner peripheral grinding wheel escape groove 30b are provided for prevention.

As shown in FIG. 2, a plurality of coolant supply hoses 15 are attached to the main device 10. In the example shown in FIG. 2, two coolant supply hoses 15 are provided, but the present invention is not limited to this. Any number of three or more coolant supply hoses 15 can be provided along the outer edge of the cylindrical integrated core drill 20. Each coolant supply hose 15 is a flexible hose, and the nozzle 15a at the tip of the coolant supply hose 15 has a coolant on an outer peripheral grinding surface in which the outer peripheral grinding stone 20a of the integrated core drill 20 and the laminate 5 are in contact with each other before grinding. It is directed to a position where it can be supplied.
Further, a coolant supply pipe 17 is installed inside the shaft 12, and the inner peripheral grinding stone 20 b of the integrated core drill 20 and the laminate 5 are in contact with each other by a nozzle 17 a at the tip of the coolant supply pipe 17. Coolant can be supplied to the peripheral grinding surface.
In the grinding apparatus shown in FIG. 2, a tank for storing the coolant supplied to the outer peripheral grinding surface and the inner peripheral grinding surface, and a coolant supply hose 15 and a coolant supply pipe by discharging the coolant from the tank. The pump and piping for guiding to 17 are not shown.

In the coring step of the present embodiment, the laminated body 5 is ground as follows using the grinding apparatus shown in FIG.
First, as shown in FIG. 2, the laminate 5 is prepared at a predetermined position on the mounting table 30. In a state where the laminated body 5 is placed at the predetermined position, the laminated body 5 is located below the integrated core drill 20. Next, the shaft 12 is rotated at, for example, about 1500 to 15000 rpm while lowering the main device 10. Accordingly, the integrated core drill 20 is moved in the stacking direction of the stacked body 5 (that is, downward) while rotating around the central axis of the shaft 12. The lowering of the integrated core drill 20 is performed until the integrated core drill 20 comes into contact with the outer peripheral grinding wheel escape groove 30a and the inner peripheral grinding wheel escape groove 30b of the mounting table 30. During grinding of the laminate 5 by the integrated core drill 20, coolant is supplied from the nozzle 15 a of the coolant supply hose 15 and the nozzle 17 a of the coolant supply pipe 17. During the grinding of the laminate 5 by the integrated core drill 20, the coolant supplied from the nozzle is sufficiently permeated into the outer peripheral grinding surface and the inner peripheral grinding surface, so that a small amount of processing (for example, about several hundred μm) is performed each time a certain amount of machining is performed. ) The integrated core drill 20 may be raised and the coolant may be drawn into the grinding surface (particularly the inner peripheral grinding surface) of the laminate 5 and the processing may proceed again. In order to increase the grinding efficiency, it is preferable that the integral core drill 20 is vibrated slightly by an ultrasonic vibrator (not shown) in the vertical direction during the grinding process. As an example of the ultrasonic vibration, the frequency is 20 kHz and the amplitude is about 5 to 7 μm.

The outer peripheral grinding wheel 20a and the inner peripheral grinding wheel 20b of the integrated core drill 20 of this embodiment will be further described.
The outer peripheral grinding stone 20a and the inner peripheral grinding stone 20b are, for example, metal bond grindstones including diamond as abrasive grains and bronze or cast iron as a binder, but are not limited thereto. Not only a metal bond grindstone, but also a resin bond grindstone containing a resin-based binder, a vitrified bond grindstone containing a ceramic (glassy) binder, or an electrodeposited bond grindstone using electrolytic plating may be used. The thickness of the tip of the outer peripheral grinding stone 20a is 1 to 10 mm, and the thickness of the tip of the inner peripheral grinding stone 20b is 1 to 10 mm.

In the integrated core drill 20 of the present embodiment, the count of the inner peripheral grinding wheel 20b is set larger than the count of the outer peripheral grinding wheel 20a. That is, the abrasive grains of the inner peripheral grinding stone are made finer than the abrasive grains of the outer peripheral grinding stone.
As for the range of the count of the inner grinding wheel, the lower limit value is determined based on the required specification of the roundness of the inner hole of the glass substrate for magnetic disks, and the upper limit value is determined by the processing time (processing tact time). The For example, in order to realize a roundness with a high accuracy of 2 μm or less as the roundness of the inner hole of the glass substrate for a magnetic disk, the surface roughness is set as close as possible to the roundness in the coring process. It is necessary. This is to reduce the allowance of the inner peripheral end face in the subsequent chamfering process so that cracks are not generated as much as possible. From this viewpoint, the count of the inner peripheral grinding wheel is preferably 150 or more. Moreover, it is preferable that the count of the inner peripheral grinding wheel is 800 or less because of the limitation of the processing time of the entire coring process. In addition, grinding resistance of the inner peripheral grinding surface of the laminate 5 becomes larger than that of the outer peripheral grinding surface by making the abrasive grains of the inner peripheral grinding wheel finer. However, since the inner peripheral grinding surface has a shorter processing length, the grinding resistance is reduced. Increase is not at a problematic level.
On the other hand, the range of the count of the outer peripheral grinding wheel may be generally coarser than that of the inner peripheral grinding wheel, but the concentricity (for example, 5 μm or less) which is a target for the inner and outer circumferences as a glass substrate for a magnetic disk. ) Is preferably set to 120 or more. Further, since the outer peripheral grinding surface has a long processing length, it is preferable that the outer peripheral grinding wheel has a count of 600 or less so as not to hinder the grinding process due to an increase in grinding resistance.

  In the integrated core drill 20 of this embodiment, it is preferable that the tip of the inner peripheral grinding stone 20b protrudes from the tip of the outer peripheral grinding stone 20a. Thereby, an inner peripheral part will be processed ahead of an outer peripheral part, and a process axis will become easy to stabilize.

  In the grinding device of this embodiment, the amount of coolant supplied per unit peripheral length of the inner peripheral grinding surface in unit time (that is, the amount of coolant supplied from the nozzle 17a of the coolant supply pipe 17) is It is preferable that the amount of coolant supplied per unit circumferential length of the grinding surface (that is, the amount of coolant supplied from the nozzle 15a of one or more coolant supply hoses 15) is larger. In the present embodiment, the count of the inner peripheral grinding wheel is set to be larger than the count of the outer peripheral grinding wheel, so that the inner peripheral grinding surface has a larger grinding resistance than the outer peripheral grinding surface, and the integrated core drill 20 The processing speed (that is, the traveling speed of the integrated core drill 20 in the stacking direction of the stacked body 5) depends on the grinding speed of the inner periphery. In other words, since the grinding ability of the outer peripheral grinding wheel is higher, while the inner peripheral grinding surface is ground over time, the outer peripheral grinding surface is finished early and not substantially ground ( Is idle). Therefore, by making the amount of coolant supplied per unit circumferential length of the inner peripheral grinding surface per unit time larger than the amount of coolant supplied per unit peripheral length of the outer peripheral grinding surface, the circumferential unit length If it sees now, more coolant will be supplied to an inner peripheral grinding surface rather than an outer peripheral grinding surface. Thereby, the lubrication capability between the inner peripheral grinding wheel and the laminate 5 on the inner peripheral grinding surface, and the chip discharging capability on the inner peripheral grinding surface are relatively improved compared to the outer peripheral grinding surface, and the inner peripheral grinding surface is processed. Since the time is shortened, the processing time in the coring process can be shortened.

(4) Chamfering step After the coring step, a chamfering step of forming a chamfered surface at the ends (outer peripheral end surface and inner peripheral end surface) is performed. In the chamfering step, chamfering is performed on the outer peripheral surface and the inner peripheral surface of the laminated body processed into a cylindrical shape by the coring step by, for example, a metal bond grindstone using diamond abrasive grains.

(5) End face polishing process (machining process)
Next, end face polishing (edge polishing) of the annular plate glass is performed.
In the end face polishing, the inner peripheral end face and the outer peripheral end face of the annular plate glass are mirror-finished by brush polishing. At this time, a slurry containing fine particles such as cerium oxide as free abrasive grains is used. By polishing the end face, removal of contamination such as dust, damage or scratches attached to the end face of the annular plate glass prevents the occurrence of thermal asperity and corrosion such as sodium and potassium. It is possible to prevent the occurrence of ion precipitation causing the above.

(6) Laminate Separation Process The laminate 5 is processed by the coring process, the chamfering process, and the edge polishing process, and then the laminate 5 is separated into each annular plate-like glass. Is done. For example, depending on the type of the adhesive 5b, the adhesive 5b is softened by immersing the laminate in warm water (80 to 90 degrees Celsius), and the laminate 5 is separated into each annular plate-like glass. Can do.

(7) Grinding process with fixed abrasive In the grinding process with fixed abrasive, grinding is performed on the main surface of the annular plate-shaped glass using a double-sided grinding device. The machining allowance by grinding is, for example, about several μm to 100 μm. The double-sided grinding apparatus has a pair of upper and lower surface plates (upper surface plate and lower surface plate), and an annular plate glass is sandwiched between the upper surface plate and the lower surface plate. Then, by moving either the upper surface plate or the lower surface plate, or both, by moving the annular plate glass and each surface plate relatively, both of the annular plate glasses can be moved. The main surface can be ground.

(8) First Polishing (Main Surface Polishing) Step Next, first polishing is performed on the main surface of the ground annular plate glass. The machining allowance by the first polishing is, for example, about several μm to 50 μm. The purpose of the first polishing is to remove scratches and distortions remaining on the main surface by grinding with fixed abrasive grains. In the first polishing, for example, a double-side grinding apparatus used in a grinding process using fixed abrasive grains is used. At this time, the point different from the grinding by the fixed abrasive is that a free abrasive that is turbid in the slurry is used instead of the grinding pad and a resin polisher is used.
As the free abrasive grains used for the first polishing, for example, fine particles (particle size: about 1 to 2 μm in diameter) such as cerium oxide suspended in the slurry are used.

(9) Chemical Strengthening Step Next, the annular plate glass after the first polishing is chemically strengthened.
As the chemical strengthening solution, for example, a mixed solution of potassium nitrate (60% by weight) and sodium sulfate (40% by weight) can be used. In the chemical strengthening, the chemical strengthening liquid is heated to, for example, 300 ° C. to 400 ° C., and the washed annular plate glass is preheated to, for example, 200 ° C. to 300 ° C., and then the annular plate glass is in the chemical strengthening solution. For example, 3 hours to 4 hours. In the case of this immersion, it can be performed in a state of being housed in a holder so that a plurality of annular plate glasses are held at the end faces so that both main surfaces of the annular plate glasses are chemically strengthened. preferable.
Thus, by immersing the annular plate glass in a chemical strengthening solution, lithium ions and sodium ions on the surface layer of the annular plate glass are sodium ions and potassium having a relatively large ion radius in the chemical strengthening solution. Each is replaced by an ion to strengthen the annular plate-like glass. The chemically strengthened annular plate glass is washed. For example, after washing with sulfuric acid, washing with pure water, IPA (isopropyl alcohol), or the like.

(10) Second Polishing (Final Polishing) Step Next, the annular polishing plate glass that has been chemically strengthened and sufficiently cleaned is subjected to second polishing. The machining allowance by the second polishing is, for example, about 1 μm. The second polishing is intended for mirror polishing of the main surface. In the second polishing, for example, the double-side grinding apparatus used in the grinding with the fixed abrasive and the first polishing is used. At this time, the difference from the first polishing is that the type and particle size of the free abrasive grains are different and the hardness of the resin polisher is different.
As the free abrasive grains used for the second polishing, for example, fine particles (particle size: diameter of about 0.1 μm) such as colloidal silica made turbid in the slurry are used.
The polished annular plate glass is washed with a neutral detergent, pure water, IPA or the like to obtain a glass substrate for a magnetic disk.

[Magnetic disk]
A magnetic disk is obtained as follows using a glass substrate for magnetic disk (hereinafter, glass substrate).
A magnetic disk has a configuration in which, for example, at least an adhesion layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer are laminated on the main surface of a glass substrate in order from the side closer to the main surface. .
For example, the substrate is introduced into a film forming apparatus that has been evacuated, and a film is sequentially formed from an adhesion layer to a magnetic layer on the main surface of the substrate in an Ar atmosphere by a DC magnetron sputtering method. For example, CrTi can be used as the adhesion layer, and CrRu can be used as the underlayer. After the film formation, a magnetic recording medium can be formed by forming a protective layer using C ₂ H ₄ by CVD, for example, and performing a nitriding treatment in which nitrogen is introduced into the surface in the same chamber. . Thereafter, for example, PFPE (polyfluoropolyether) is applied on the protective layer by a dip coating method, whereby a lubricating layer can be formed.

  In the following, the present invention is further illustrated by examples. However, this invention is not limited to the aspect shown in the Example.

(1) Production of molten glass The raw materials were weighed and mixed to obtain a compounded raw material so that a glass having the following composition was obtained. This raw material was put into a melting vessel, heated and melted, clarified and stirred to produce a homogeneous molten glass free from bubbles and unmelted materials. In the obtained glass, bubbles, undissolved material, crystal precipitation, refractory constituting the melting vessel and platinum contamination were not recognized.
[Glass composition]
Glass containing SiO ₂ : 58 to 75 wt%, Al ₂ O ₃ : 5 to 23 wt%, Li ₂ O: 3 to 10 wt%, Na ₂ O: 4 to 13 wt% as main components.

(2) Production of Laminate A plate-like glass having a thickness of 1.0 mm was obtained by a float method in which molten glass having the above-described composition was continuously poured into a bath filled with molten metal containing tin. The surface roughness Ra of the plate glass was 0.01 μm. The plate-like glass was cut out, and the cut-out plate-like glass was laminated on the surface after uniformly applying a visible light curable resin material as an adhesive to produce a laminate. Further, the resin material was cured by irradiating visible light while compressing the laminated body from both sides, so that the laminated glass sheets were not separated.
[Laminated body of Example]
-Size of plate glass: 75mm x 75mm
-Number of layers: 25-Adhesive: Visible light curable resin (Adel, Clear Presto CP4022)
-Adhesive layer thickness: 30 μm

(3) Processing of laminated body The laminated body was fixed on the mounting table as in the arrangement shown in Fig. 2, and grinding by coring was performed. At this time, the rotation speed of the integrated core drill was set to 5000 rpm, and grinding was performed while ultrasonic vibration (20 kHz, amplitude 5 to 7 μm) in the vertical direction, and 2.5 inch circular plate-like glass (inner hole diameter φ20 mm) , Outer diameter φ65 mm). Further, during the grinding process, the amount of coolant shown in Table 1 was supplied to the inner peripheral grinding surface and the outer peripheral grinding surface. The outer peripheral grinding wheel and inner peripheral grinding wheel are metal bond wheels (bonding material: cast iron) using diamond abrasive grains. As shown in Table 1 below, the inner grinding wheel count and the outer grinding wheel count The tact time was measured by grinding with a plurality of combinations.
In Table 1, Comparative Example 1 is an example in which the count of the inner peripheral grinding wheel is smaller than the count of the outer peripheral grinding wheel, and Comparative Example 2 has the count of the inner peripheral grinding wheel and the count of the outer peripheral grinding wheel. This is an example of equality. Examples 1-4 are all examples in which the count of the inner peripheral grinding wheel is larger than the count of the outer peripheral grinding wheel. In Examples 1, 2 and 4, the amount of coolant supplied per unit circumferential length of the inner peripheral grinding surface per unit time is larger than the amount of coolant supplied per unit peripheral length of the outer peripheral grinding surface. Example 3 is an example when the condition is not satisfied.
After grinding of the core ring, chamfering is performed on the outer peripheral surface and inner peripheral surface of the laminated body processed into a cylindrical shape by diamond chamfering and chamfering processing using a metal bond grindstone (bonding material: cast iron). gave. The count of the metal bond grindstone at this time was 400.

(4) Separation of laminated body and end face polishing Next, the cylindrical laminated body was immersed in warm water (80 to 90 degrees Celsius) and separated into a plurality of annular plate glasses. At this time, no abnormality was found on the surface of each annular plate glass. Thereafter, a slurry containing fine particles of cerium oxide as free abrasive grains was used, and the inner peripheral end face and outer peripheral end face of the annular plate glass were mirror-finished by brush polishing to obtain a glass substrate.

(5) Evaluation of the roundness of the inner circumference of the glass substrate The roundness of the obtained glass substrate was measured, and the results of observation with a laser microscope for the presence or absence of cracks on the inner circumference end surface of the glass substrate were as follows. It is shown in 1.

As shown in Table 1, by increasing the count of the inner peripheral grinding wheel to be larger than the count of the outer peripheral grinding wheel, the tact time is achieved while achieving the target roundness (2 μm) without generating cracks. I was able to reduce my time.
The reason why the roundness deteriorates in Comparative Example 1 is that the processing resistance of the outer peripheral grinding wheel is larger than the processing resistance of the inner peripheral grinding wheel, so that when the inner and outer periphery is processed coaxially, a difference in processing speed occurs. This is probably because stable machining is no longer possible.
Also, when the condition that the amount of coolant supplied per unit circumferential length of the inner peripheral grinding surface per unit time is larger than the amount of coolant supplied per unit peripheral length of the outer peripheral grinding surface is not satisfied (Example) In 3), the tact time was extended as compared with the case where the condition was satisfied (Example 2).

  As mentioned above, although the manufacturing method of the glass substrate for magnetic discs of this invention was demonstrated in detail, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, even if various improvement and a change are carried out. Of course it is good.

DESCRIPTION OF SYMBOLS 5 Laminated body 5a Sheet glass raw material 5b Adhesive 10 Main apparatus 12 Shaft 15 Coolant supply hose 15a Nozzle 17 Coolant supply pipe 17a Nozzle 20 Integrated core drill 20a Outer peripheral grinding wheel 20b Inner peripheral grinding wheel 30 Mounting base 30a Outer peripheral grinding wheel escape Groove 30b Inner peripheral grinding wheel relief groove

Claims (4)

A laminate preparation step of preparing a laminate in which a plurality of plate-like glasses are laminated;
By rotating an integrated core drill in which a large-diameter cylindrical outer peripheral grinding wheel and a small-diameter cylindrical inner peripheral grinding wheel are coaxially arranged around the axis, moving in the stacking direction of the laminate, A grinding step of grinding the laminate into a cylindrical shape,
The method of manufacturing a glass substrate for a magnetic disk, wherein the count of the inner peripheral grinding wheel is larger than the count of the outer peripheral grinding wheel. In the grinding step, the grinding liquid is applied to the outer peripheral grinding surface formed by contact between the outer peripheral grinding wheel and the plate glass, and the inner peripheral grinding surface formed by contact between the inner peripheral grinding wheel and the plate glass. Grinding while supplying,
The amount of the grinding fluid supplied per unit circumferential length of the inner peripheral grinding surface in a unit time is larger than the amount of the grinding fluid supplied per unit circumferential length of the outer peripheral grinding surface. Manufacturing method of glass substrate for magnetic disk.   3. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein a count of the inner peripheral grinding stone is 150 or more and 800 or less, and a count of the outer peripheral grinding wheel is 120 or more and 600 or less.   The method for manufacturing a glass substrate for a magnetic disk according to any one of claims 1 to 3, further comprising a machining step of polishing an end face of the plate glass after the grinding.

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