JP2012113802A - Method of manufacturing glass substrate for magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve circularity of glass substrates to a necessary level when a plurality of glass substrates for magnetic disk are manufactured from a stack of a plurality of plate-like glasses.SOLUTION: The method of manufacturing the glass substrates for magnetic disk includes a stack preparation process of preparing the stack of a plurality of plate-like glasses; and a grinding process of grinding the stack by moving an integrated core drill, having a large-diameter cylindrical outer peripheral grinding grindstone and a small-diameter cylindrical inner peripheral grinding grindstone arranged coaxially, in the stacking direction of the stack while rotating the integrated core drill on its axis and supplying a grinding liquid to an outer peripheral grinding surface formed as the outer peripheral grinding grindstone and plate-like glasses come into contact with each other and an inner peripheral grinding surface formed as the inner-peripheral grinding grindstone and plate-like glasses come into contact with each other, the rotating direction of the core drill and the supply direction of the grinding liquid to the outer peripheral grinding surface being adjusted so as to draw in the grinding liquid to the outer peripheral grinding surface.

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, an inner diameter cylindrical blade and an outer diameter cylindrical blade move in the laminating direction of the laminated body while rotating a coring cutter in which the inner diameter cylindrical blade and the outer diameter cylindrical blade are integrally formed on the same axis. By processing, the inner peripheral surface and the outer peripheral surface of the laminate are processed.

JP 2007-283651 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. . In the chamfering process, it is common to adjust the inner and outer diameters and form a chamfered surface by simultaneously processing the end shape using a general-purpose grindstone, that is, grinding the end surface and the chamfered surface. Known.

Here, it has become clear that if a device with a built-in hard disk is dropped, the magnetic disk is likely to be destroyed from the inner periphery, and a certain strength is maintained by eliminating cracks in the inner periphery as much as possible. There is a need.
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.

  As described above, the coring process is required to be performed with high accuracy in order to reduce cracks in the magnetic disk glass substrate. Here, in the grinding apparatus disclosed in Patent Document 1, it is difficult to uniformly supply the grinding liquid (coolant) to the outer peripheral grinding surface. For this reason, the grinding resistance and the discharge rate of glass sludge are non-uniform between the portion where the coolant is easily supplied and the portion where the coolant is difficult to be supplied on the grinding surface, and the grinding degree of the outer peripheral grinding surface of the laminate becomes non-uniform, The roundness of the outer peripheral ground surface of the annular glass after processing decreases.

In the following description, the outer peripheral grinding surface refers to the outer peripheral surface of a laminate of cylindrical plate glass that is being ground or ground (after processing) by a grinding blade, or individual circles forming the laminate. It means the outer peripheral surface of the annular glass. The inner peripheral grinding surface refers to the inner peripheral surface of a laminated sheet of cylindrical plate glass that is being ground or ground (after processing) by a grinding blade, or the inner circumference of each annular glass forming the laminated body Means the side face.
In the following description, the outer peripheral grinding surface of the core drill (coring cutter) means the outer peripheral surface of the core drill, that is, the outer surface of the cylindrical outer peripheral grinding wheel of the core drill. If there is no thickness of the outer peripheral grinding wheel, the outer peripheral grinding surface of the core drill and the outer peripheral grinding surface of the laminate are the same surface, but the outer peripheral grinding surface of the core drill is actually the thickness of the outer peripheral grinding wheel of the core drill. It is located outside the outer peripheral grinding surface of the laminate by an amount (for example, about 1 to 10 mm).
In the following description, when referring to the roundness of the outer peripheral grinding surface or the concentricity between the outer peripheral grinding surface and the inner peripheral grinding surface, the outer peripheral grinding of the laminated body or the individual sheet glass constituting the laminated body Suppose you are referring to a face.

  While rotating a core drill in which an inner peripheral grinding wheel (inner diameter cylindrical blade) and an outer peripheral grinding wheel (outer diameter cylindrical blade) are coaxially integrated with each other in the laminated direction of the laminated glass, When moving, as the core drill advances in the stacking direction of the laminated body, supply of the grinding liquid to the grinding position (tip of the core drill) is insufficient, and the processing accuracy tends to deteriorate. This is because the distance between the grinding fluid supply position and the grinding position is increased, and the grinding fluid supply path (the region between the core drill blade and the grinding surface of the laminate) is narrow. As the distance increases, the roundness of the sheet glass tends to deteriorate.

  If the roundness of the outer peripheral grinding surface of the sheet glass after grinding in the coring process is not good, it is difficult to improve the concentricity with the inner peripheral grinding surface. If the roundness of the outer peripheral grinding surface of the flat glass after processing is not good, the roundness of the outer peripheral grinding surface is improved while improving the accuracy of concentricity between the outer peripheral grinding surface and the inner peripheral grinding surface. In this chamfering process, the machining allowance of the inner and outer peripheral grinding surfaces of the laminated body or individual annular glass must be increased. In particular, if the machining allowance of the inner peripheral grinding surface is increased in the chamfering process, cracks are likely to occur on the inner peripheral end surface. Therefore, in order to reduce the machining allowance in the chamfering process and prevent the generation of cracks as much as possible, it is required to perform grinding with high accuracy in the coring process, which is the preceding process. Further, in recent years, when the rotational speed of the magnetic disk in the hard disk becomes high, there is a problem that fluttering occurs when the roundness of the outer peripheral ground surface is not good.

  Therefore, the present invention makes it possible to improve the roundness of the outer peripheral ground surface to a required level when producing a plurality of glass substrates for magnetic disks from a laminate in which a plurality of plate glasses are laminated. It aims at providing the manufacturing method of the glass substrate for magnetic discs.

  In order to solve the above problems, a method for manufacturing a glass substrate for a magnetic disk according to the present embodiment includes a laminate preparation step for preparing a laminate in which a plurality of plate glasses are laminated, and a large-diameter cylindrical outer peripheral grinding wheel. And an inner peripheral grinding surface in which the outer peripheral grinding wheel and the plate glass are in contact with each other, and an integral core drill in which a small-diameter cylindrical inner peripheral grinding wheel is coaxially disposed. A grinding step of grinding the laminate by moving the laminate in the laminating direction while supplying a grinding liquid to an inner peripheral grinding surface formed by contacting the peripheral grinding wheel and the plate glass. And adjusting the rotation direction of the core drill and the supply direction of the grinding liquid to the outer peripheral grinding surface so that the grinding liquid is drawn into the outer peripheral grinding surface.

  In the method for manufacturing a glass substrate for a magnetic disk, the supply direction of the grinding liquid to the outer peripheral grinding surface is a vector direction from a nozzle that supplies the grinding liquid to a point on the outer peripheral grinding surface, and is a plan view. It is preferable that an angle formed with the velocity vector of the core drill at the point is within a range of 0 to 15 degrees, and the vector has a downward component in the stacking direction of the stacked body.

  Further, the supply direction of the grinding liquid to the outer peripheral grinding surface is a tangential vector direction from the nozzle for supplying the grinding liquid to the outer peripheral grinding surface, and the vector is a vector toward the rotation direction of the core drill. And a vector downward in the stacking direction of the stacked body.

  Further, in the grinding step, it is preferable to supply the grinding fluid to the outer peripheral grinding surface using a plurality of nozzles arranged substantially evenly over the entire circumference of the outer peripheral grinding wheel.

  Further, in the grinding step, the grinding liquid is supplied from the nozzle to the outer peripheral grinding surface while rotating one or more nozzles arranged toward the outer peripheral grinding wheel around the axis of rotation of the outer peripheral grinding wheel. Is preferably supplied.

  Moreover, it is preferable that the roundness of the outer periphery is 5 μm or less. Furthermore, it is more preferable in it being 2 micrometers or less.

  According to the method for manufacturing a glass substrate for a magnetic disk of the present invention, when a plurality of glass substrates for a magnetic disk are created from a laminate in which a plurality of plate glasses are laminated, the roundness of the outer peripheral grinding surface is required. It can be improved to the level.

It is a figure which shows an example of the cross section of the laminated body on which the some plate glass and the adhesive agent were laminated | stacked. It is a figure which shows an example of the grinding apparatus when grind | pulverizing the laminated body of sheet glass in the coring process of embodiment. It is sectional drawing of an example of the integrated core drill used at the coring process of embodiment. It is a figure which shows the supply direction of the coolant in the surface orthogonal to a lamination direction. It is a figure explaining the target position about supply of the coolant seen by plane view. It is a figure which shows an example of a grinding device when grinding the laminated body of sheet glass in the coring process of a modification.

  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, in the case of producing a 2.5-inch magnetic disk glass substrate, a 75 mm × 75 mm rectangular plate glass is cut out.

  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 and / 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.

  Here, with reference to FIG. 1, the structure of the laminated body of this embodiment is demonstrated. FIG. 1 is a cross-sectional view showing an example of a laminated body of the present embodiment. As shown in FIG. 1, the laminate 5 of the present embodiment is configured by laminating a plurality of plate glasses 5a and adhesives 5b alternately. The laminated body 5 is produced by applying or sticking an adhesive 5b between the plate-like glasses 5a.

As long as the adhesive 5b can adhere | attach or isolate | separate sheet glass 5a, what kind of thing may be sufficient as it. 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 diagram showing a grinding device for grinding the laminated body 5 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.

As shown in FIG. 2, the grinding device includes a main device 10, a shaft 12, a coolant supply hose 15, and an integrated core drill 20. The main device 10 drives the integrated core drill 20. The main device 10 supplies coolant to the interior of the integrated core drill 20.
The integral core drill 20 is substantially cylindrical as a whole. The integrated core drill 20 is supported by a shaft 12 made of, for example, 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, the integrated core drill 20 is disposed above the stacked body 5 mounted on the mounting table 30. 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 of the present embodiment can move the main apparatus 10 up and down by a servo mechanism (not shown), and thereby can integrally lift the integrated core drill 20, the shaft 12, and the coolant supply hose 15. It has become.

Here, as shown in FIG. 3, in the integrated core drill 20, a large-diameter cylindrical outer peripheral grinding stone 20a and a small-diameter cylindrical inner peripheral grinding stone 20b are arranged coaxially.
Further, as shown in FIG. 2, the mounting table 30 on which the stacked body 5 is mounted is provided with an outer peripheral grinding wheel escape groove 30 a and an inner peripheral grinding wheel escape groove 30 b. The outer peripheral grinding wheel escape groove 30a and the inner peripheral grinding wheel escape groove 30b are used to prevent the outer peripheral grinding wheel 20a and the inner peripheral grinding wheel 20b of the integrated core drill 20 from colliding with the mounting surface of the mounting table 30. It is a groove.

  As shown in FIG. 2, a coolant supply pipe 17 is installed inside the shaft 12. The coolant is supplied to the inner peripheral grinding surface formed by the contact between the inner peripheral grinding wheel 20b of the integrated core drill 20 and the laminated body 5 by the nozzle 17a at the tip of the coolant supply pipe 17.

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, an example in which the main apparatus 10 includes two coolant supply hoses 15a and 15b will be described, but the number of coolant supply hoses 15 is not limited to this. Although the number of coolant supply hoses 15 may be two, it is preferable that three or more coolant supply hoses 15 of three or more are provided along the outer edge of the cylindrical integrated core drill 20.
The plurality of coolant supply hoses 15 are preferably arranged substantially evenly over the entire circumference of the outer peripheral grinding wheel 20a.

Each coolant supply hose 15 is a flexible hose. Further, the nozzle 16 at the tip of each coolant supply hose 15 is predetermined so that the coolant is drawn into the outer peripheral grinding surface of the integrated core drill 20 formed by the contact between the outer peripheral grinding wheel 20a of the integrated core drill 20 and the laminate 5. It is adjusted in advance to a position where coolant can be supplied from the direction.
The coolant is preferably supplied as an ejected flow or jet whose diameter, speed (flow velocity), and directivity are appropriately adjusted. In this way, when the coolant supply position (the position where the coolant and the core drill come into contact) is controlled, or when the integrated core drill 20 and / or the coolant supply hose is moving, the coolant and the peripheral grinding wheel It becomes possible to control the relative speed between 20a and / or the laminate.

Here, with reference to FIG. 2 and FIG. 4, the supply direction of the coolant with respect to the outer peripheral grinding surface of the integrated core drill 20 will be described. FIG. 4 is a diagram conceptually illustrating a coolant supply direction in a plane orthogonal to the stacking direction.
As shown in FIG. 4, a vector in a tangential direction from the nozzle 16 toward the outer peripheral grinding surface 32 of the integrated core drill 20 in a plane orthogonal to the stacking direction of the stacked body 5, and the rotation of the integrated core drill 20. Coolant is supplied in the direction of the vector toward the direction. Specifically, there are two vectors in the tangential direction from the nozzle 16a toward the outer peripheral grinding surface 32, which are the vector a and the vector a ′ shown in FIG. Coolant is supplied from the nozzle 16a in the direction of the vector a. Similarly, coolant is supplied from the nozzle 16b in the direction of the vector b.

  Further, as shown in FIG. 2, the coolant is supplied from the nozzle 16 in the direction in which the integrated core drill 20 moves (downward in FIG. 2) in the stacking direction of the stacked body 5. Specifically, the coolant is supplied from the nozzle 16a in the direction including the component of the vector z shown in FIG. The same applies to the nozzle 16b.

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 above description, the coolant supply direction from the nozzle 16 is the tangential vector direction toward the outer peripheral grinding surface 32 of the integrated core drill 20, but the thickness of the outer peripheral grinding wheel 20a of the integrated core drill 20 is as follows. Since it is smaller than the diameter of the laminated body, it may be considered as a tangential vector direction toward the outer peripheral grinding surface of the laminated body.

In the coring process of the present embodiment, grinding is performed on the laminated body 5 as follows using the grinding apparatus shown in FIG.
First, as shown in FIG. 2, the integrated core drill 20 is disposed above the stacked body 5 placed on the placing table 30. Next, the shaft 12 is rotated while the main device 10 is lowered. The rotational speed of the shaft 12 is, for example, about 1500 to 15000 rpm. 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 16 of the coolant supply hose 15 and the nozzle 17 a of the coolant supply pipe 17.

  During grinding of the laminated body 5 by the integrated core drill 20, the coolant is sufficiently penetrated into the outer peripheral grinding surface and the inner peripheral grinding surface. And the coolant may be drawn into the grinding surface (especially 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.

Here, 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 preferably set to be substantially the same as or larger than the count of the outer peripheral grinding wheel 20a. In addition, it is still more preferable that the count of the inner peripheral grinding stone 20b is set larger than the count of the outer peripheral grinding stone 20a. That is, it is preferable that the abrasive grains of the inner peripheral grinding wheel are substantially the same as or finer than the abrasive grains of the outer peripheral grinding wheel.
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. ) 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. As a result, it becomes easy to reduce the roundness of the outer peripheral grinding surface of each sheet glass constituting the laminated body after processing, so the concentricity between the outer peripheral grinding surface and the inner peripheral grinding surface of the sheet glass is also reduced. It becomes easy to do.

As described above, in the coring process of the present embodiment, the position at which the coolant is supplied, the flow velocity and the diameter of the coolant flow so as to be drawn into the gap between the outer peripheral grinding wheel 20a of the rotating integrated core drill 20 and the laminate. Control etc. For example, the rotation direction of the integrated core drill 20 and the supply direction of the coolant to the outer peripheral grinding surface 32 are adjusted so that the coolant is drawn into the outer peripheral grinding surface 32. More specifically, a vector in a tangential direction from the nozzle 16 for supplying the coolant to the outer peripheral grinding surface 32, and a vector on a surface orthogonal to the lamination direction toward the rotation direction of the integrated core drill 20, and the laminate 5 It is preferable that the coolant is supplied from the nozzle 16 in the direction of a vector obtained by combining the downward vector in the stacking direction. At this time, coolant is supplied toward the position of the contact point between the outer surface of the peripheral grinding wheel (that is, the peripheral ground surface of the integrated core drill 20) and the uppermost surface of the laminate (that is, the coolant is applied). Is preferred.
In the above description, the coolant supply direction from the nozzle 16 is the tangential vector direction toward the outer peripheral grinding surface 32 of the integrated core drill 20, but the thickness of the outer peripheral grinding stone 20a of the integrated core drill 20 is as follows. Since it is smaller than the diameter of the laminated body, it may be considered as a tangential vector direction toward the outer peripheral grinding surface of the laminated body.

  Note that the target position for applying the coolant (the position where the center of the coolant flow with a predetermined diameter hits; hereinafter referred to as the “target position of the coolant”) according to the rotational speed of the core drill and the coolant flow velocity is referred to as 1) the contact point. It may be a little more on the front side (that is, the center side of the laminated body), or 2) slightly above the contact point while maintaining the contact between the integrated core drill 20 and the coolant flow. In this way, even when the tip of the outer peripheral grinding wheel of the integrated core drill 20 advances into the laminated body as the grinding progresses, the coolant can be actively drawn into the tip of the outer peripheral grinding wheel. The discharge of the generated sludge and the cooling of the grinding part can be maintained satisfactorily by the coolant, and the roundness of the outer peripheral grinding surface of the sheet glass constituting the laminated body after processing can be prevented.

The target position of the coolant will be further described with reference to FIG. FIG. 5 is a diagram illustrating a target position for coolant supply as viewed in a plan view. FIG. 5 shows the position of the nozzle for supplying the coolant and the outer peripheral grinding surface 32 of the core drill (the outer peripheral surface of the core drill; a circle in plan view). In FIG. 5, an angle formed by a line connecting a point on the outer peripheral grinding surface 32 of the core drill (target position of the coolant) from the nozzle and a tangent to the circle of the outer peripheral grinding surface 32 of the core drill at that point is α degrees. In other words, when viewed in a plan view, the angle formed by the vector from the nozzle toward the point on the outer peripheral grinding surface of the core drill (target position of the coolant) and the velocity vector of the core drill at that point is α degrees. For example, when the coolant is supplied from the nozzle in a direction in contact with the outer peripheral grinding surface 32 of the core drill, α = 0 (d1 in FIG. 5), and when the coolant is supplied from the nozzle toward the center of the outer peripheral grinding surface 32. Is α = 90 (d0 in FIG. 5). At this time, it is preferable that the coolant supply direction from the nozzle viewed in a plan view is directed to a direction in which α is in the range of 0 to 15 degrees. That is, the coolant supply direction may not be α = 0 (the direction in contact with the outer peripheral grinding surface 32 of the core drill). Since the coolant flow from the nozzle has a predetermined diameter, the coolant can be sufficiently drawn into the outer peripheral grinding surface 32 even if it is slightly closer to the center side of the laminate (α = 0 to 15) than when α = 0. Become. Note that FIG. 5 is a plan view, but the coolant supply direction from the nozzle is laminated with a vector (α = 0 to 15) directed in the rotation direction of the integrated core drill 20 on the horizontal plane shown in FIG. This is the direction of a vector that is combined with the downward vector of the body stacking direction. That is, the vector from the nozzle to the point on the outer peripheral grinding surface of the core drill (the target position of the coolant) has a downward component in the stacking direction of the stacked body.
In the above description, the range of the coolant supply direction from the nozzle 16 is based on the outer peripheral grinding surface 32 of the integrated core drill 20, but the thickness of the outer peripheral grinding wheel 20a of the integrated core drill 20 is the diameter of the laminate. Therefore, the outer peripheral grinding surface of the laminate may be considered as a reference. That is, the coolant target position may be considered as a point on the outer peripheral grinding surface of the laminate.

Regarding the flow rate of the coolant, when the speed is decomposed into a lateral speed in a plane perpendicular to the stacking direction of the laminate and a downward speed in the stacking direction of the stack, the lateral speed is reduced to the coolant. The linear velocity of the outer peripheral grinding wheel of the integrated core drill 20 at the target position is preferably substantially the same. By doing so, the coolant flow rate and the linear velocity of the outer peripheral grinding wheel are almost the same, so that the coolant is less likely to be reflected (hard to be repelled) by the rotation of the core drill. As a result, the coolant passes between the outer peripheral grinding wheel and the laminate. It becomes easy to move downward (it becomes easy to be pulled in). The coolant speed may be adjusted as appropriate so that the coolant is not reflected (does not repel) by the rotation of the core drill. That is, even when the front end of the outer peripheral grinding wheel advances downward in the stacking direction of the laminate, the coolant easily reaches the grinding site (that is, the front end of the outer peripheral grinding wheel). As a result, even when the grinding of the laminated body proceeds, the discharge of sludge caused by grinding and the cooling of the grinding part can be favorably maintained by the coolant. Thereby, it becomes possible to prevent the roundness of the outer peripheral ground surface of the sheet glass constituting the processed laminated body from deteriorating.
The nozzle diameter is preferably about 2 mm to 8 mm. Moreover, it is preferable to make it a nozzle shape so that the diameter of the coolant flow after jetting does not widen.

  As described above, in the coring step, the coolant supplied from the nozzle 16 is less likely to be reflected by the integrated core drill 20 that rotates at high speed, and the coolant is easily drawn into the outer peripheral grinding surface 32. Therefore, sludge is uniformly removed (discharged) on the circumference of the outer peripheral grinding surface, the degree of grinding on the outer peripheral grinding surface of the laminate becomes more uniform, and the roundness of the outer peripheral grinding surfaces of the individual glass sheets constituting the laminate is increased. The degree is improved. In addition, even when the tip of the outer peripheral grinding wheel enters the inside of the laminate as processing progresses, it is possible to maintain the discharge of sludge generated by grinding and the cooling of the grinding part well with the coolant, so that lamination after processing is possible. It becomes possible to prevent the roundness of the outer peripheral grinding surface of each sheet glass constituting the body from deteriorating.

(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 process, the outer peripheral surface and the inner peripheral surface of the laminated body processed into a cylindrical shape by the coring process are chamfered by, for example, a metal bond grindstone or an electrodeposition 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: for example, 0.01 to 0.1 μm in diameter) 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, for example, C ₂ H ₄ by CVD and performing nitriding treatment in which nitrogen is introduced into the surface in the same chamber. . Thereafter, for example, PFPE (polyfluoropolyether) is applied on the protective layer by a dip coating method, whereby a lubricating layer can be formed.

(Modification)
Next, a modified example of the above-described method for manufacturing a magnetic disk glass substrate will be described. The manufacturing method of the magnetic disk glass substrate of this modification is different from the embodiment described above in the coring process. Steps other than the coring step are the same as in the above-described embodiment. Hereinafter, the coring process of this modification will be described with reference to FIG.

FIG. 6 is a diagram showing a grinding device for grinding the laminated body 5 in the coring process of this modification. As shown in FIG. 6, the grinding apparatus includes a main device 10, a shaft 12, a rotating unit 14, a coolant supply hose 15, and an integrated core drill 20. The shaft 12, the coolant supply hose 15, and the integrated core drill 20 are the same as those in the above-described embodiment.
In the grinding device of this modification, a rotating portion 14 is provided on the outer peripheral portion of the main device 10. The rotating unit 14 is provided with a coolant supply hose 15. The main apparatus 10 can drive the rotary unit 14 to rotate about the same axis as the rotation axis of the outer peripheral grinding wheel independently of the integrated core drill 20. The rotating unit 14 preferably rotates in the same direction as the direction of rotation of the integrated core drill 20.
The coolant supply direction with respect to the outer peripheral grinding surface is the same as in the above-described embodiment.

In the coring process of the present modification, grinding is performed on the laminate 5 as follows using the grinding apparatus shown in FIG.
First, as shown in FIG. 6, the integrated core drill 20 is arranged above the stacked body 5 placed on the placing table 30. Next, the shaft 12 is rotated while the main device 10 is lowered. The rotational speed of the shaft 12 is, for example, about 1500 to 15000 rpm. 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 main device 10 rotates the rotating unit 14. The rotation speed of the rotation unit 14 is, for example, about 10 to 100 rpm. Thereby, the coolant supply hose 15 provided in the rotation part 14 rotates coaxially with the rotating shaft of the outer peripheral grinding wheel.

  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 16 of the coolant supply hose 15 and the nozzle 17 a of the coolant supply pipe 17.

  In the coring process of this modification, the coolant is supplied from the nozzle to the outer peripheral grinding surface of the integrated core drill 20 while rotating the nozzle disposed toward the outer peripheral grinding wheel about the rotation axis of the outer peripheral grinding wheel. . Thereby, sludge is removed more uniformly on the periphery of the outer peripheral grinding surface, the degree of grinding on the outer peripheral grinding surface becomes more uniform, and the roundness of the outer peripheral grinding surface is improved.

  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, Clearpresto (registered trademark) 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 the coring was ground. 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). Here, the diameter of the inner peripheral grinding wheel and the outer peripheral grinding wheel of the integrated core drill is such that the diameter of the inner hole of the annular plate glass is φ20 mm and the outer diameter is φ65 mm after the grinding of the core ring and the subsequent chamfering process. Was set to be. The thickness of each grinding wheel (grinding drill) was 2 mm.

During the grinding process, an amount of 17 liters of coolant per minute was supplied from the nozzle 17a to the inner peripheral ground surface. As the coolant, Chemicool (registered trademark) C-798S (manufactured by Chemic Co., Ltd.) was used. Further, as shown in FIG. 4, the coolant is supplied to the outer peripheral grinding surface by two nozzles 16a and 16b arranged on the object around the rotation axis of the integrated core drill. In the outer peripheral grinding surface, nozzles 16a and 16b are arranged in a tangential direction vector from the nozzle toward the outer peripheral grinding surface in a plane orthogonal to the stacking direction of the laminate, and in the vector direction toward the rotation direction of the integrated core drill. The coolant was supplied in an amount of 20 liters per minute. More specifically, it is a vector direction obtained by synthesizing a vector tangential from the nozzle toward the outer peripheral grinding surface of the core drill and a rotation direction of the integrated core drill and a downward vector in the stacking direction of the laminate. Coolant is supplied to the position of the contact point between the outer surface of the outer peripheral grinding wheel and the uppermost surface of the laminate at a flow rate such that the speed (lateral component) in the plane perpendicular to the lamination direction of the laminate is 18 m / sec. Even if the grinding process progressed, the coolant was drawn sufficiently.
Here, the linear velocity of the outer peripheral grinding wheel of the core drill is calculated as 69 (mm) × π × 5000 (rpm) ÷ 60 (sec / min) ≈18 (m / sec). Note that 69 (mm) is taken into account the thickness of the core drill. That is, the coolant flow rate and the outer peripheral grinding wheel linear velocity were made substantially the same.
The outer peripheral grinding wheel and the inner peripheral grinding wheel were metal bond wheels (bonding material: cast iron) using diamond abrasive grains. The count of the inner grinding wheel was 600, and the count of the outer grinding wheel was 300.

  After the coring grinding, the outer peripheral surface and the inner peripheral surface of the laminate processed into a cylindrical shape were chamfered by chamfering using an electrodeposition grindstone using diamond abrasive grains. The count of the grindstone at this time was 800.

(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.

After the coring grinding, some samples were separated into a plurality of annular plate glasses without chamfering. The annular plate glass thus obtained is referred to as the annular plate glass of Example 1.
Also, in the plane perpendicular to the stacking direction of the laminate, there is no tangential component from the nozzle to the outer peripheral grinding surface, and the coring is ground while supplying the coolant from the nozzle toward the circle center of the outer peripheral grinding surface. It processed and isolate | separated into the some annular | circular shaped plate glass, without performing a chamfering process. The annular plate glass thus obtained is referred to as the annular plate glass of Comparative Example 1.
Further, the coolant is supplied at a position between the uppermost surface of the laminate and the outer surface of the outer peripheral grinding wheel of the core drill so that the target position at which the coolant is supplied is between Example 1 and Comparative Example 1. Modified samples were made. Let the annular plate-like glass obtained by this sample be Reference Examples 1-3. Specifically, in Reference Examples 1 to 3, a circle formed by the direction from the nozzle toward the target position of the coolant and the outer peripheral grinding surface of the core drill at the target position in a plane orthogonal to the stacking direction of the stacked body. The angle α (see FIG. 5) formed with the tangent line was set at 15, 30, and 60 degrees, respectively. In FIG. 5, the coolant supply direction in Example 1 is d1, and the coolant supply direction in Comparative Example 1 is d0.
In any of the above examples, comparative examples, and reference examples, the target position where the coolant is supplied is a contact point between the uppermost surface of the laminate and the outer surface of the outer peripheral grinding wheel of the core drill, and the flow rate of the coolant is The speed (lateral component) in a plane perpendicular to the stacking direction of the stacked body was made constant at 18 m / sec.

(5) Evaluation of roundness and crack For each of the 25 annular plates in the examples, comparative examples and reference examples, the roundness of the outer circumference and the concentricity of the outer and inner circles before chamfering. The degree was measured, and the largest values were taken as the roundness and concentricity in each case. When the roundness of the outer periphery of the annular plate glass of Example 1 and Comparative Example 1 was measured, the roundness of the outer periphery of Example 1 was 2.0 μm, and the roundness of the outer periphery of Comparative Example 1 was 6 μm. 0.0 μm. Thus, as in Example 1, in the plane orthogonal to the stacking direction of the stacked body, the vector of the tangential direction from the nozzle toward the outer peripheral grinding surface of the core drill and the vector direction toward the rotation direction of the integrated core drill In addition, it can be seen that the roundness of the outer periphery at the end of grinding of the core ring is improved by supplying the coolant from the nozzle to the outer peripheral grinding surface. The concentricity of Example 1 was as good as 1.5 μm.
Moreover, the roundness of the outer periphery of Reference Examples 1 to 3 was 2.0 μm, 3.3 μm, and 5.2 μm, respectively. In Reference Example 1, the roundness equivalent to that in Example 1 was obtained because the coolant jet had a certain size in diameter, so that the laminated body with respect to the tangential direction from the nozzle toward the outer peripheral grinding surface of the core drill. Even if the direction of the coolant flow slightly deviates toward the center side, it is assumed that the amount of coolant drawn into the outer peripheral grinding surface is the same.

(6) Other Examples In addition to measuring the roundness of the inner periphery of the glass substrate (25 sheets) obtained by the steps (1) to (5) above, the cracks on the inner peripheral end face of the glass substrate are measured. The presence or absence was observed with a laser microscope. Let the glass substrate obtained by the process of said (1)-(5) be the glass substrate of Example 2. FIG.
The roundness of the inner circumference of the glass substrate (25 sheets) of Example 2 was 1.3 μm at the maximum. Moreover, as a result of observing the inner peripheral and outer peripheral end faces of the glass substrate of Example 2 with a laser microscope, no cracks were observed. Thus, according to the present Example, the target roundness (2 μm) could be achieved on both the inner and outer circumferences without generating cracks.

  Furthermore, as shown in FIG. 6, the core ring was ground, and a sample of the laminate was prepared while rotating the two nozzles in the same direction as the rotation direction of the integrated core drill. The rotation speed of the nozzle was 10 rpm. An annular plate glass obtained by this sample is referred to as Example 3. When the roundness value (25 maximum values) of the outer periphery of the annular plate-like glass of Example 3 was measured, it was 1.5 μm. That is, the roundness of the annular plate glass of Example 3 was further improved than that of Example 1.

  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 5b Adhesive 10 Main apparatus 12 Shaft 14 Rotating part 15 Coolant supply hose 16 Nozzle 17 Coolant supply pipe 17a Nozzle 20 Integrated core drill 20a Outer grinding wheel 20b Inner grinding wheel 30 Mounting base 30a Outer grinding wheel Escape groove 30b Inner peripheral grinding wheel escape groove 32 Outer peripheral grinding surface

Claims (6)

A laminate preparation step of preparing a laminate in which a plurality of plate-like glasses are laminated;
An integral core drill in which a large-diameter cylindrical outer peripheral grinding wheel and a small-diameter cylindrical inner peripheral grinding wheel are arranged coaxially is rotated around an axis, and the outer peripheral grinding wheel and the plate glass are in contact with each other. The laminate is moved in the laminating direction of the laminate while supplying the grinding liquid to the outer peripheral grinding surface and the inner peripheral grinding surface formed by contacting the inner peripheral grinding wheel and the plate glass. A grinding process for grinding,
A method of manufacturing a glass substrate for a magnetic disk, comprising adjusting a rotation direction of the core drill and a supply direction of the grinding liquid with respect to the outer peripheral grinding surface so that the grinding liquid is drawn into the outer peripheral grinding surface. The direction in which the grinding fluid is supplied to the outer peripheral grinding surface is the direction of a vector from the nozzle that supplies the grinding fluid to a point on the outer peripheral grinding surface, and the velocity vector of the core drill at the point when seen in plan view Is within the range of 0 to 15 degrees,
2. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the vector has a downward component in the stacking direction of the stacked body.   The direction in which the grinding fluid is supplied to the outer peripheral grinding surface is a vector direction in a tangential direction from the nozzle that supplies the grinding fluid to the outer peripheral grinding surface, and the vector is a vector in the rotation direction of the core drill; The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the laminated body is combined with a downward vector in the stacking direction.   The grinding liquid is supplied to the outer peripheral grinding surface in the grinding step using a plurality of nozzles arranged substantially uniformly over the entire circumference of the outer peripheral grinding wheel. The manufacturing method of the glass substrate for magnetic discs in any one of -3.   In the grinding step, the grinding liquid is supplied from the nozzle to the outer peripheral grinding surface while rotating one or a plurality of nozzles arranged toward the outer peripheral grinding wheel coaxially with the rotation axis of the outer peripheral grinding wheel. The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 4, wherein:   6. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the roundness of the outer periphery is 5 [mu] m or less.

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