JP2006338815A - Manufacturing method of glass substrate for magnetic disk and manufacturing method of magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate for a magnetic disk having satisfactory shape uniformity such as uniformity of an outside diameter at a low cost and to provide the inexpensive glass substrate for the magnetic disk and the magnetic disk in large amounts. <P>SOLUTION: In a manufacturing method of the glass substrate for the magnetic disk including a step for forming glass disks by cutting a cylindrical glass base material 3 vertically to the center axis thereof, the difference between outside diameters of the thickest part and the thinnest part of the cylindrical glass base material 3 is specified to be ≤0.5 mm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a glass substrate for a magnetic disk used for a magnetic disk that is a recording medium in an information recording apparatus such as a hard disk drive (HDD).

  The present invention also relates to a method of manufacturing a magnetic disk that is a recording medium in an information recording apparatus such as a hard disk drive (HDD).

  In recent years, various information processing apparatuses have been proposed with the advancement of the information society, and a hard disk drive (HDD) has been proposed as an information recording apparatus used in these information processing apparatuses. In the hard disk drive, in order to reduce the size and performance of the information processing apparatus, it is required to increase the information recording capacity and increase the recording density, and to reduce the manufacturing cost.

  In a hard disk drive, in order to increase the information recording density, it is necessary to reduce so-called spacing loss, and the flying height (glide height) of the magnetic head that performs recording and reproduction on the magnetic disk as the recording medium Need to be reduced. However, since the magnetic disk rotates at high speed during recording and reproduction, if the flying height of the magnetic head is reduced, there is a high possibility that the magnetic head will come into contact with the surface of the magnetic disk. Therefore, in order to prevent such contact with the magnetic head, it is necessary to finish the surface of the magnetic disk as a very smooth surface.

  In order to realize such smoothness of the surface of the magnetic disk, a glass substrate is used as a magnetic disk substrate, as represented by a “2.5 inch disk”, instead of the conventionally widely used aluminum substrate. It has come to be used. This is because a glass substrate is superior in surface flatness and substrate strength compared to an aluminum substrate. Examples of such a glass substrate include a glass substrate whose strength is improved by chemical strengthening and a crystallized glass substrate whose strength is improved by crystallization.

  By the way, generally a glass substrate for a magnetic disk is a process of preparing a molten glass by heating and melting a glass raw material, a process of forming the molten glass into a plate-shaped glass disk, and processing a glass disk formed into a plate shape. Then, the glass substrate is prepared by sequentially executing a step of producing a glass substrate by polishing.

  In forming the molten glass into a plate-like glass disk, a forming method such as a press method, a flow method, or a fusion method is employed. When the pressing method is used, a plate-shaped glass disk is formed directly from molten glass. When the float method or the fusion method is used, the molten glass is formed into a rectangular plate glass, and a glass disk is cut out from the plate glass. Among these, the most widely used method is a method of producing a glass disk by a pressing method.

  As another method, as described in Patent Document 1, a method of cutting out a glass disk from a cylindrical glass base material has been proposed.

  Patent Documents 2 and 3 propose a method of making a glass disk by cutting a cylindrical glass base material with a multi-wire saw.

  The glass disk substrate for a magnetic disk is manufactured by polishing the end face and the main surface of the glass disk produced as described above and performing a strengthening process such as chemical strengthening.

JP-A-4-168629 JP-A-8-007272 Japanese Patent No. 2639270

  By the way, a hard disk drive using a glass substrate capable of realizing a high information recording surface density as described above has been able to store a sufficient amount of information even with a small magnetic disk. Accordingly, such hard disk drives are not only installed in so-called stationary computer devices, but also so-called “Car Navigation System”, “PDA (Personal Digital Assistance)”, “mobile phone”. As described above, the application has been extended to those used for information storage of mobile devices with a small housing space such as in-vehicle or portable.

  The size of a small magnetic disk mounted on such a small hard disk drive is, for example, an outer diameter of 30 mm or less, an inner diameter of 10 mm or less, and a disk thickness of 0.5 mm or less. Examples thereof include a “1 inch type disc” having a diameter of 27.4 mm, an inner diameter of 7 mm, and a disc thickness of 0.381 mm, and a “0.85 inch type disc” having an outer diameter of 21.6 mm, an inner diameter of 6 mm, and a disc thickness of 0.381 mm.

  Since such a small hard disk drive for “mobile use” is always exposed to the impact of dropping, vibration, sudden movement acceleration, etc., the glass substrate for magnetic disk and magnetic The disk is required to have sufficiently high impact resistance compared to a relatively large magnetic disk such as a conventional “2.5 inch type disk” (outer diameter 65 mm, inner diameter 20 mm, disk thickness 0.635 mm). Has reached.

  On the other hand, a recent hard disk drive has been proposed that performs a start / stop operation by the “LUL (load / unload) method”. A magnetic disk mounted on a “LUL type” hard disk drive is required to have a smoother and cleaner surface than a conventional magnetic disk. That is, the flying height of the magnetic head in the “LUL type” hard disk drive is set to 10 nm or less, and a crash failure is likely to occur as compared with the conventional “CSS (contact start stop) type” hard disk drive. Accordingly, the glass substrate for magnetic disk used in the “LUL type” hard disk drive and the surface of the magnetic disk must be sufficiently cleaned as compared with the conventional case.

  In recent hard disk drives, a magnetic head mounted with a magnetoresistive element or a large magnetoresistive element is used. This also requires that the magnetic disk glass substrate and the surface of the magnetic disk be smoother and cleaner than before. That is, a magnetic head equipped with a magnetoresistive element or a large magnetoresistive element may cause a thermal asperity failure if the magnetic disk surface has insufficient smoothness and cleanliness. Therefore, in a magnetic disk from which information is reproduced by a magnetoresistive element, the surface must be sufficiently smooth and clean compared to a magnetic disk from which information is reproduced by a conventional thin film element.

  Conventionally, in the production of a glass substrate for a magnetic disk, as described above, a method of producing a glass disk from molten glass using a pressing method has been the mainstream. In addition, a method of creating a sheet glass from molten glass by a float method or the like and cutting a glass disk from the sheet glass has been performed.

  However, when a glass disk is produced by such a method, there is a problem that a lot of glass debris and pieces of glass are discharged. That is, among the molten glass used as a raw material, there is a lot of glass that is finally discarded without being processed into a glass disk. In other words, it is difficult to improve the material utilization rate. Further, there is a problem that it is difficult to improve the number of glass disks that can be produced per unit time, that is, the mass productivity of glass disks.

  Therefore, in the production of a glass disk, it is difficult to sufficiently facilitate manufacturing and reduce manufacturing costs only by using a method that has been used as a mainstream from the past.

  As a method for solving such a problem, a method of manufacturing a glass disk as described in Patent Documents 1 to 3 described above is also conceivable. However, in such a manufacturing method, there is a problem that burrs or chips are generated in the vicinity of the end surface portion of the glass disk obtained by cutting the cylindrical glass base material, or the thickness of the glass disk is not uniform. Arise. Moreover, in such a manufacturing method, the subject that it is difficult to obtain the glass disc by which both the main surfaces of the front and back were mutually made parallel with high precision arises.

  Therefore, the present invention is proposed in view of the above-mentioned circumstances, and the first object of the present invention is to provide a magnetic material having good end face shape, parallelism of both main surfaces, and uniformity of plate thickness. The object is to provide a glass substrate for a disk at a low cost, and to provide a large number of inexpensive glass substrates and magnetic disks for a magnetic disk.

  A second object of the present invention is to provide a large amount of a magnetic disk glass substrate and a magnetic disk excellent in impact resistance at low cost.

  A third object of the present invention is to provide a large amount of small-sized glass substrates for magnetic disks and magnetic disks having an outer diameter of 30 mm or less, for example.

  Furthermore, a fourth object of the present invention is to provide a large amount of a glass substrate and a magnetic disk for a magnetic disk mounted on a “LUL type” hard disk drive at low cost.

  In order to solve the above-described problems and achieve the above object, the present invention comprises any one of the following configurations.

[Configuration 1]
A method of manufacturing a glass substrate for a magnetic disk including a step of cutting a columnar or cylindrical glass base material perpendicularly to its central axis to produce a glass disk, wherein the columnar or cylindrical glass base material is The difference between the outer diameter at the thickest part and the outer diameter at the thinnest part is 0.5 mm or less.

[Configuration 2]
A method of manufacturing a glass substrate for a magnetic disk having Configuration 1, wherein a columnar or cylindrical glass base material has a difference between an outer diameter of the thickest part and an outer diameter of the thinnest part of 0.3 mm or less. It is characterized by that.

[Configuration 3]
A method of manufacturing a glass substrate for a magnetic disk having Configuration 1 or Configuration 2, wherein the columnar or cylindrical glass base material has an average outer diameter of 30 mm or less. .

[Configuration 4]
A method for producing a glass substrate for a magnetic disk, comprising a step of cutting a columnar or cylindrical glass base material perpendicularly to its central axis to produce a glass disk, wherein the columnar or cylindrical glass base material After the side surface portion is ground or polished, the difference between the outer diameter at the thickest part and the outer diameter at the thinnest part of the columnar or cylindrical glass base material is reduced to 0.5 mm or less, and then cut. Processing is performed.

[Configuration 5]
A method of manufacturing a glass substrate for a magnetic disk having any one of configurations 1 to 4, wherein a side surface portion of a columnar or cylindrical glass base material and a wire saw are brought into contact with each other, and the side surface portion and the wire saw are The glass disk is produced by cutting the columnar or cylindrical glass base material by relative movement.

[Configuration 6]
A method of manufacturing a glass substrate for a magnetic disk having any one of Configurations 1 to 4, wherein a side surface portion of a columnar or cylindrical glass base material is brought into contact with a blade saw, the side surface portion and the blade saw Are moved relative to each other to cut the columnar or cylindrical glass base material to produce a glass disk.

[Configuration 7]
A method of manufacturing a glass substrate for a magnetic disk having any one of Configurations 1 to 6, wherein after annealing a columnar or cylindrical glass base material to relieve internal stress, the columnar or cylindrical glass A glass disk is produced by cutting a base material.

[Configuration 8]
At least a recording layer is formed on a glass substrate manufactured by the method for manufacturing a magnetic disk glass substrate having any one of Configurations 1 to 7.

  In the method for manufacturing a magnetic disk glass substrate according to the present invention, a magnetic disk glass substrate including a step of cutting a columnar or cylindrical glass base material perpendicularly to its central axis to produce a glass disk. In the manufacturing method, since the difference between the outer diameter at the thickest part and the outer diameter at the thinnest part of the columnar or cylindrical glass base material is 0.5 mm or less, the outer diameter has good uniformity. Glass disk can be obtained.

  Furthermore, in the method for manufacturing a glass substrate for a magnetic disk according to the present invention, the difference between the outer diameter at the thickest part and the outer diameter at the thinnest part of the columnar or cylindrical glass base material is 0.3 mm or less. Further, it is possible to obtain a glass disk having a better outer diameter uniformity.

  In the method for producing a glass substrate for a magnetic disk according to the present invention, a small-diameter glass disk can be satisfactorily prepared by setting the average value of the outer diameter of the columnar or cylindrical glass base material to 30 mm or less. .

  And in the manufacturing method of the glass substrate for magnetic discs which concerns on this invention, the glass for magnetic discs which includes the process of cutting a column-shaped or cylindrical glass base material perpendicularly | vertically with respect to the central axis, and producing a glass disc In the substrate manufacturing method, by grinding or polishing the side surface of the columnar or cylindrical glass base material, the outer diameter at the thickest part and the outermost part at the thinnest part of the columnar or cylindrical glass base material are obtained. Since the difference from the diameter is 0.5 mm or less, it is possible to obtain a glass disk with good outer diameter uniformity.

  Further, in the above-described method for manufacturing a glass substrate for a magnetic disk, the cylindrical glass base material is cut by bringing the side surface portion of the cylindrical glass base material into contact with the wire saw and relatively moving the side surface portion and the wire saw. By processing to produce a glass disk, the cylindrical glass base material can be easily and quickly cut.

  Further, in each of the above-described methods for manufacturing a glass substrate for a magnetic disk, the cylindrical glass base material is obtained by bringing the side surface portion of the cylindrical glass base material into contact with the blade saw and relatively moving the side surface portion and the blade saw. By producing a glass disk by cutting, the cylindrical glass base material can be easily and quickly cut.

  Further, in the above-described method for manufacturing a glass substrate for a magnetic disk, before the cylindrical glass base material is cut, the cylindrical glass base material is annealed to relieve internal stress, thereby reducing the cylindrical glass base material. The cutting process can be performed satisfactorily.

  And in the manufacturing method of the magnetic disk which concerns on this invention, since the glass substrate manufactured by the manufacturing method of the glass substrate for magnetic disks which concerns on this invention mentioned above is used, the shape of an end surface part, the parallelism of both main surfaces, and It is created in a state where the thickness uniformity is good.

  That is, the present invention can provide a magnetic disk glass substrate having good shape uniformity, such as uniformity of outer diameter, at a low cost, and can provide a large number of inexpensive glass substrates and magnetic disks. It can be done.

  In addition, the present invention can provide a large number of glass substrates and magnetic disks for magnetic disks that are excellent in impact resistance at low cost.

  Such a glass substrate for a magnetic disk and a magnetic disk are also suitable for application to a small magnetic disk. That is, the present invention can provide a large amount of a small glass substrate and magnetic disk for a magnetic disk having an outer diameter of 30 mm or less, for example, at low cost.

  Such a magnetic disk glass substrate and magnetic disk are also suitable for application to a magnetic disk mounted in a “LUL system” hard disk drive. That is, the present invention can provide a large amount of a glass substrate and a magnetic disk for a magnetic disk mounted on a “LUL system” hard disk drive at low cost.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  The method for producing a glass substrate for a magnetic disk according to the present invention is for producing a glass substrate for a magnetic disk used as a glass substrate of a magnetic disk mounted on a hard disk drive (HDD) or the like, for example. This magnetic disk is a recording medium capable of performing high-density information signal recording and reproduction by, for example, a perpendicular magnetic recording method.

  This glass substrate for magnetic disk has an outer diameter of 15 to 30 mm, an inner diameter of 5 to 12 mm, and a plate thickness of 0.2 to 0.5 mm. For example, “0.8 inch type magnetic disk” (inner diameter of 6 mm, outer 21.6 mm diameter, plate thickness 0.381 mm), “1.0 inch type magnetic disk” (inner diameter 7 mm, outer diameter 27.4 mm, plate thickness 0.381 mm), etc. . Further, it may be manufactured as a magnetic disk such as a “2.5 inch magnetic disk” or a “3.5 inch magnetic disk”. Here, the “inner diameter” is the inner diameter of the circular hole at the center of the glass substrate.

  FIG. 1 is a perspective view showing a configuration of a glass substrate for magnetic disk manufactured by the method for manufacturing a glass substrate for magnetic disk according to the present invention.

  The method for manufacturing a glass substrate for a magnetic disk according to the present invention is a method for manufacturing a glass substrate for a magnetic disk for manufacturing a glass substrate 2 for a magnetic disk having a circular hole 1 at the center as shown in FIG. Since the glass substrate for magnetic disk is made of glass, it can achieve excellent smoothness by mirror polishing, has high hardness, and high rigidity, and thus has excellent impact resistance. In particular, since a magnetic disk used for a hard disk drive mounted on a portable (carried) or in-vehicle information device is required to have high impact resistance, a glass substrate is used in such a magnetic disk. Usefulness is high.

  Although glass is a brittle material, the fracture strength can be improved by a strengthening treatment such as chemical strengthening or air cooling strengthening or by means of crystallization. A preferable glass as a material for such a glass substrate is aluminosilicate glass. This is because the aluminosilicate glass can realize an excellent smooth mirror surface and can increase the breaking strength by, for example, chemical strengthening.

The aluminosilicate _{glass, SiO} 2: 62 to 75 _wt%, Al _{2 O} 3: 5 to 15 wt%, _Li 2 O: 4 to 10 wt%, _Na 2 O: 4 to 12 wt%, _ZrO 2: 5 0.5 to 15 wt% as a main component, the weight ratio of Na ₂ O to ZrO ₂ is 0.5 to 2.0, and the weight ratio of Al ₂ O ₃ to ZrO ₂ is 0.4 to 2 A glass for chemical strengthening of .5 is preferred.

Further, in such a glass substrate, in order to eliminate the protrusion of the glass substrate surface undissolved product of ZrO ₂ occurs causes a SiO ₂ 57 to 74 mol%, a ZrO ₂ 0 to 2.8 mol%, Al ₂ It is preferable to use a chemically strengthening glass containing ₃ to 15 mol% of O ₃ , 7 to 16 mol% of LiO ₂ and 4 to 14 mol% of Na ₂ O. The aluminosilicate glass having such a composition has an increased bending strength, a deep compressive stress layer, and an excellent Knoop hardness when chemically strengthened.

  In addition, the material which comprises the glass substrate for magnetic discs manufactured in this invention is not necessarily limited to what was mentioned above. That is, as the material of the glass disk, in addition to the aluminosilicate glass described above, for example, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, or crystallized glass Examples thereof include glass ceramics.

  FIG. 2 is a cross-sectional view showing the shape of the inner peripheral end face of the circular hole 1 of the magnetic disk glass substrate 2.

  The glass substrate for a magnetic disk produced according to the present invention is preferably one in which the ridges on both sides of the end face portion are chamfered. That is, the outer peripheral side end surface portion of the magnetic disk glass substrate 2 and the inner peripheral side end surface portion of the circular hole 1 are chamfered from the inner peripheral end surface portion toward the main planes on both sides as shown in FIG. (C surface) 1b, 1b is formed, and the outer peripheral side end surface portion of the glass substrate for magnetic disk 2 is chamfered from the outer peripheral side end surface portion toward the main planes on both sides ( C surface) is formed.

  A portion between the chamfered portions 1b and 1b in the inner peripheral side end surface portion of the magnetic disk glass substrate 2 is a cylindrical side surface (T surface) formed of a plane perpendicular to the main plane of the magnetic disk glass substrate 2. 1a. The aforementioned inner diameter of the circular hole 1 is the inner diameter of the side surface 1a. Further, in the outer peripheral side end surface portion of the magnetic disk glass substrate 2, the portion between the chamfered portions is a cylindrical side surface (T surface) formed of a plane perpendicular to the main plane of the magnetic disk glass substrate 2. ing. The above-mentioned diameter of the glass substrate for a magnetic disk is the diameter of this side surface. In this glass substrate for magnetic disk, the crushing of the edge portion of the end face portion increases the breaking strength. In the description of the present invention, the side surface and the chamfered surface are collectively referred to as an end surface portion.

  FIG. 3 is a process diagram showing each process of the method for manufacturing a magnetic disk glass substrate according to the present invention.

  Hereinafter, the manufacturing method of the glass substrate for magnetic disks which concerns on this invention is demonstrated in order of a process.

(1) Step of obtaining cylindrical glass base material In the method for manufacturing a magnetic disk glass substrate according to the present invention, as shown in FIG. 3, first, a cylindrical glass base material 3 is formed into a predetermined shape and prepared. To do. As described above, the columnar glass base material 3 is preferably made of aluminosilicate glass. The cylindrical glass base material 3 has a diameter slightly larger than the diameter of the magnetic disk glass substrate 2 to be manufactured, and has a length corresponding to the thickness in a state where a large number of the magnetic disk glass substrates 2 are laminated. For example, it has a length of about 300 mm to 600 mm.

  That is, when a glass substrate for a magnetic disk for “0.8 inch type magnetic disk” (outer diameter 21.6 mm) or “1.0 inch type magnetic disk” (outer diameter 27.4 mm) is prepared. The average value of the outer shape of the cylindrical glass base material 3 is desirably 30 mm or less. In this case, the maximum diameter of the columnar glass base material 3 is desirably 30 mm or less.

  And it is preferable that this cylindrical glass preform | base_material 3 eases an internal stress by annealing treatment.

  The cylindrical glass base material 3 may be provided with a central hole along the central axis before a cutting process described later.

(2) The step of surface-treating the side surface portion of the cylindrical glass base material The cylindrical glass base material 3 has a circular cut surface that appears when it is cut substantially perpendicularly to its central axis. The roundness represented by the difference between the diameter and the minimum diameter is preferably 200 μm or less. Furthermore, it is more preferable that the roundness of the circular cut surface is 50 μm or less.

  In the Japanese Industrial Standard (JISB0021), the roundness is expressed by the difference between the radius of the maximum diameter portion and the radius of the minimum diameter portion. The difference from the minimum diameter (diameter) is the roundness.

  The cylindrical glass base material 3 has a roundness of 200 μm or less, or 50 μm or less when the circular cut surface appears when the side surface portion is cut or ground by grinding. Can be kept.

  Further, the columnar glass base material 3 has a difference between the outer diameter at the thickest part and the outer diameter at the thinnest part, that is, the cylindricity is 0.5 mm or less, more preferably 0.3 mm or less. It is desirable.

  In the Japanese Industrial Standard (JISB0021), the cylindricity is expressed by the difference between the radius of the largest diameter portion and the radius of the smallest diameter portion in the cylinder. The difference between the outer diameter (diameter) and the outer diameter (diameter) at the narrowest part is defined as cylindricity.

  The cylindrical glass base material 3 has a shape in which the difference between the outer diameter at the thickest part and the outer diameter at the thinnest part is 0.5 mm or less, or 0 by grinding or polishing the side surface part. 3 mm or less.

  In this step, grinding of the outer peripheral side surface or polishing may be performed with a brush or the like using an abrasive, but it is desirable to perform cylindrical grinding. Further, a centerless grinding process (center-less finishing method) may be performed. As shown in FIG. 4, the centerless grinding process is performed by using the cylindrical glass base material 3 as a reference on the outer periphery without supporting the cylindrical glass base material 3, which is a cylindrical workpiece, with a center hole. In this method, the cylindrical glass base material 3 is supported by a blade (supporting blade) 6 and an adjusting roll (adjusting wheel) 7 and the outer peripheral surface of the cylindrical glass base material 3 is polished by a cylindrical grindstone 8.

  Furthermore, you may process the cylindrical glass preform | base_material 3 in the predetermined shape mentioned above by performing an etching process.

  Next, the side surface part (circumferential surface) of the outer periphery of the columnar glass base material 3 is subjected to surface treatment to obtain a grained surface or a pear surface. Alternatively, the outer peripheral side surface of the columnar glass base material 3 may be a rough surface having a predetermined surface roughness by grinding or polishing. Moreover, as a surface treatment for the outer peripheral side surface portion of the cylindrical glass base material 3, a blast treatment may be used.

  This blast treatment is performed by spraying various powders such as non-metallic particles such as silica sand and metal particles at a high speed on the side surface of the outer periphery of the cylindrical glass base material 3 to roughen the surface, It is processing that performs processing, satin processing, and embossing.

  These surface treatments are for the purpose of accurately performing a cutting process described later.

  In this step, when the central hole is formed in the columnar glass base material 3, the inner peripheral side surface (circumferential surface) of the central hole is polished and mirror-finished.

  Further, in this step, as shown in FIG. 5, a V-shaped groove 4 which becomes a chamfered surface of the outer periphery when the glass substrate for a magnetic disk is formed on the side surface portion of the outer periphery of the cylindrical glass base material 3. May be provided in an annular shape along the circumferential direction.

(3) Step of cutting (slicing) the glass base material Next, by cutting the cylindrical glass base material 3 perpendicularly to the central axis, the thickness is slightly thicker than the thickness of the magnetic disk glass substrate. Get a glass disk. At this time, a large number of glass disks are obtained from one cylindrical glass base material 3.

  The cutting process of the columnar glass base material 3 in this step can be performed by using, for example, a multi-wire saw. As shown in FIG. 6, the multi-wire saw has a plurality of multi-groove rollers arranged at predetermined intervals, and a plurality of endless wires are wound around the grooves of the multi-groove rollers, and the endless wires are placed on the side surfaces of the glass base material. It is an apparatus which cut | disconnects this columnar glass base material 3 by pressing. That is, the cylindrical glass base material 3 is cut by bringing the side surface part of the cylindrical glass base material 3 into contact with the wire saw and relatively moving the side surface part and the wire saw.

  By this cutting process, a large number of glass disks are obtained. Here, the side surface of the outer periphery of the columnar glass base material 3 is made of grain, pear ground, or a rough surface with a predetermined surface roughness, so that the wire saw is a side surface of the columnar glass base material 3. Slipping in the lateral direction (the axial direction of the cylindrical glass base material 3) with respect to the portion is prevented, so that a large number of glass disks having a predetermined thickness and good thickness uniformity can be obtained. It is done. In addition, since the cylindrical glass base material 3 has a predetermined shape, the main surface has good roundness, has a predetermined outer diameter, and has good outer diameter uniformity. A large number of glass discs can be obtained.

  Further, instead of the wire saw, the cylindrical glass base material 3 is cut by bringing the side surface portion of the cylindrical glass base material 3 into contact with the multi-plated saw and relatively moving the side surface portion and the multi-blade saw. You may make it process. The multi-ply saw is a large number of plaid saws installed in parallel to each other, and is a device that cuts the cylindrical glass base material 3 by pressing the plaid saw against the side surface of the cylindrical glass base material 3.

(4) Step of forming center hole in glass disk Next, a center hole having a predetermined size is formed along the center axis of the glass disk. This central hole is the central hole 1 in the magnetic disk glass substrate 2 and is formed as a hole having an inner diameter slightly smaller than the inner diameter of the central hole 1 in the magnetic disk glass substrate 2.

  As described above, the center hole may be formed before the cylindrical glass base material 3 is cut. In this case, the above-described cutting process is performed on the cylindrical glass base material in which the center hole is formed to be cylindrical.

(5) Shape processing step, lapping step In this step, the glass disk obtained by cutting the columnar glass base material 3 is trimmed and the main surface is lapped. In the lapping process, processing is performed using a double-sided lapping apparatus and alumina abrasive grains, and the dimensional accuracy and shape accuracy of the glass disk are set to predetermined values.

  Further, in the case where the V-shaped groove is not provided in the side surface portion of the columnar glass base material 3 before the cutting process, in this step, chamfering is performed on the outer peripheral side end surface portion and the inner peripheral side end surface portion of the glass disk. Apply.

(6) 1st grinding | polishing process Next, a 1st grinding | polishing process is given as a main surface grinding | polishing process. The first polishing process is mainly intended to remove scratches and distortions remaining on the main surface in the lapping process described above. This process can be performed using a planetary gear mechanism using a double-side polishing apparatus and a hard resin polisher. As the abrasive, cerium oxide abrasive grains are preferably used.

(7) Second Polishing Step Next, a second polishing step is performed as a mirror polishing step for the main surface. The purpose of this second polishing step is to finish the main surface into a mirror surface. This step can be performed using a planetary gear mechanism using a double-side polishing apparatus and a soft foam resin polisher. As the abrasive, it is preferable to use fine cerium oxide abrasive grains as compared with the cerium oxide abrasive grains used in the first polishing step.

(8) Chemical strengthening process Next, the glass disk which finished the above-mentioned polishing process is chemically strengthened. For chemical strengthening, for example, a chemical strengthening solution prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) is prepared, and this chemically strengthened solution is heated to about 380 ° C. and preheated to 300 ° C. The glass disk is immersed for a predetermined time.

  Thus, by immersing in the chemical strengthening solution, the lithium ions and sodium ions in the surface layer of the glass disk are replaced with sodium ions and potassium ions in the chemical strengthening solution, respectively, and the glass disk is strengthened.

(9) 1st washing | cleaning process The glass disk which finished the chemical strengthening process is immersed in the concentrated sulfuric acid heated to about 40 degreeC, and is wash | cleaned, Furthermore, the glass disk which finished the sulfuric acid washing | cleaning is made into a pure water and a pure water. , IPA (isopropyl alcohol) and IPA (steam-dried) are sequentially immersed in each cleaning tank for cleaning. In addition, it is preferable to apply an ultrasonic wave to each washing tank.

(10) Second cleaning step The glass substrate after the first cleaning step is sequentially immersed in each cleaning bath of neutral detergent, neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying). And wash. In addition, it is preferable to apply an ultrasonic wave to each washing tank. In this way, a magnetic disk glass substrate is obtained.

(11) Final inspection step As the final inspection step, the surface roughness and cleanliness of the main surface and inner and outer peripheral end surfaces of the magnetic disk glass substrate obtained through the aforementioned steps are measured.

(12) Magnetic Disk Manufacturing Process Using the magnetic disk glass substrate thus manufactured, at least a magnetic layer is formed on the main surface portion of the magnetic disk glass substrate, so that head crashes and thermal asperities are formed. It is possible to configure a magnetic disk in which the parity failure is prevented.

  As the magnetic layer, a Co—Pt alloy magnetic layer having a high anisotropic magnetic field (Hk) is preferable. In addition, an underlayer may be appropriately formed between the magnetic disk glass substrate and the magnetic layer from the viewpoint of achieving crystal orientation of the magnetic layer and making the grains uniform and fine. As a method for forming these underlayer and magnetic layer, for example, a DC magnetron sputtering method can be used.

  Moreover, it is preferable to provide a protective layer for protecting the magnetic layer on the magnetic layer. Examples of the material for the protective layer include a carbon-based protective layer. As the carbon-based protective layer, hydrogenated carbon or nitrogenated carbon can be used. For the formation of this protective layer, plasma CVD or DC magnetron sputtering can be used.

  Furthermore, it is preferable to form a lubricating layer for reducing the impact from the magnetic head on the protective layer. An example of the lubricating layer is a perfluoropolyether lubricating layer. In particular, an alcohol-modified perfluoropolyether lubricating layer having a hydroxyl group having excellent affinity with the protective layer is preferable. This lubricating layer can be formed using a dip method.

  Examples of the present invention will be described in detail below.

[Example 1]
In Example 1, a magnetic disk glass substrate was manufactured through the following steps.

(1) Step of obtaining a columnar glass base material In this example, a columnar glass base material made of aluminosilicate glass was prepared.

  The cylindrical glass base material had a diameter of 28.7 mm and a length of 600 mm.

(2) The step of surface-treating the inner and outer peripheral side surfaces of the glass base material By rounding the side surfaces of the cylindrical glass base material, the roundness of the circular cut surface that appears when the cut processing is performed is 50 μm or less. It was made to become. Further, the difference between the outer diameter at the thickest part and the outer diameter at the thinnest part of the cylindrical glass base material 3 was set to 0.3 mm or less.

  And the side part of the outer periphery of a columnar glass base material was surface-treated, and it was set as the pear ground. The surface roughness of the side surface portion was confirmed to be 0.1 μm to 5 μm in Ra and / or 1 μm to 50 μm in Rmax.

  Then, when the dimension measurement of the side part of a cylindrical glass preform was performed, the diameter (outer diameter) was 27.4 mm.

(3) Step of cutting (slicing) the cylindrical glass base material Next, the cylindrical glass base material is cut to be perpendicular to the central axis so that it is slightly thicker than the thickness of the magnetic disk glass substrate. A glass disk having a thickness of 0.6 mm was obtained. At this time, many glass disks were obtained from one cylindrical glass base material.

  The cylindrical glass base material was cut in this step by using a multi-wire saw. At this time, the variation in the thickness of each glass disk obtained was 30 μm or less.

  In addition, when the surface roughness of the main surface portion of the glass disk can be sufficiently good by this cutting treatment, a lapping step to be described later can be omitted. In this case, a glass disk having a thickness of 0.45 mm close to the thickness of the magnetic disk glass substrate is obtained by a cutting process.

(4) Step of forming center hole in glass base material Next, a center hole was formed along the center axis of the glass disk. The inner diameter of this central hole was 5.9 mm.

(5) Lapping step Here, the inner diameter of the glass disk obtained by the cutting process is 5.9 mm, the outer diameter is 27.4 mm, and the plate thickness is 0.6 mm. By lapping and polishing of the main surface portion, A glass disk having a predetermined dimension of a “1.0 inch type” magnetic disk glass substrate was used. Further, it was confirmed that the flatness of the main surface was 10 μm or less.

  Further, chamfering was performed, and it was confirmed that the width of the chamfered surface was 0.21 mm and the angle of the chamfered surface with respect to the main surface portion was 45 °.

  And the main surface of this glass disk was lapped. In the lapping process, processing is performed using a double-sided lapping apparatus and alumina abrasive grains, and the dimensional accuracy and shape accuracy of the glass substrate are set to be predetermined. The obtained glass disk has an inner diameter of 7 mm, an outer diameter of 27.4 mm, and a plate thickness of 0.45 mm. After polishing the main surface portion, the predetermined dimensions of the “1.0 inch type” magnetic disk glass substrate It was confirmed that this was a glass disk.

  When the surface shape of the surface of the glass disk was observed, it was confirmed that the flatness of the main surface was 3 μm or less. The surface roughness of the main surface was about 2 μm for Rmax and about 0.3 μm for Ra.

(6) 1st grinding | polishing process Next, the 1st grinding | polishing process was performed as a main surface grinding | polishing process. The first polishing process is mainly intended to remove scratches and distortions remaining on the main surface in the lapping process described above. Main surface polishing was performed using a planetary gear mechanism using a double-side polishing machine and a hard resin polisher. A cerium oxide abrasive was used as the abrasive.

(7) Second Polishing Step Next, a second polishing step was performed as a mirror polishing step for the main surface. The purpose of this second polishing step is to finish the main surface into a mirror surface. Mirror polishing of the main surface was performed using a planetary gear mechanism using a double-side polishing machine and a soft foam resin polisher. As the polishing agent, fine cerium oxide abrasive grains were used as compared with the cerium oxide abrasive grains used in the first polishing step.

  The plate thickness of the obtained glass disk was 0.381 mm.

(8) Chemical strengthening process Next, the glass disk which finished the above-mentioned grinding | polishing process was chemically strengthened. For chemical strengthening, a chemically strengthened solution prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) is prepared, and this chemically strengthened solution is heated to 380 ° C. and preheated to 300 ° C. Was immersed for a predetermined time. Here, regarding the chemical strengthening conditions, the treatment temperature was set to a constant temperature of 380 ° C., and the treatment was performed for a predetermined treatment time.

  Thus, by immersing in the chemical strengthening solution, the lithium ions and sodium ions in the surface layer of the glass disk are replaced with sodium ions and potassium ions in the chemical strengthening solution, respectively, and the glass disk is strengthened. Note that the thickness of the compressive stress layer formed on the surface layer of the glass disk increases as the processing time increases.

  The glass base material that had been subjected to chemical strengthening was immersed in a 20 ° C. water bath for rapid cooling and maintained for about 10 minutes.

(9) 1st washing | cleaning process It wash | cleaned by immersing the glass disk which finished quenching in the concentrated sulfuric acid heated to about 40 degreeC. Furthermore, the glass disk which finished the sulfuric acid cleaning was immersed in each cleaning tank of pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying) in order and cleaned. In addition, ultrasonic waves were applied to each cleaning tank.

(10) Second cleaning step The glass substrate after the first cleaning step is sequentially immersed in each cleaning bath of neutral detergent, neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying). And washed. In addition, ultrasonic waves were applied to each cleaning tank.

(11) Final Inspection Step The surface roughness of the inner peripheral side end face portion of the magnetic disk glass substrate obtained through the above-described steps is 0 at Rmax for both the chamfered surface (C surface) and the cylindrical surface (T surface). 0.4 μm and Ra was 0.02 μm.

  The surface roughness of the outer peripheral side end face portion was 0.4 μm in Rmax and 0.02 μm in Ra for both the chamfered surface (C surface) and the cylindrical surface (T surface). Each end face portion was finished in a mirror shape.

  The surface roughness was measured with an atomic force microscope, and the numerical values were calculated in accordance with Japanese Industrial Standard (JIS) B0601. Also, the mirror surface state was confirmed by both observation with an electron microscope and observation with an optical microscope.

  The obtained glass substrate for magnetic disk was subjected to “Dana impact test method” using “AVEX-SM-110-MP” manufactured by Air Brown. In this impact test, a magnetic disk glass substrate is assembled into a dedicated impact test jig, and a sine half-wave pulse impact is sequentially applied in a direction perpendicular to the main surface from 1000 G to 5000 G. Went by seeing. As a result, it was confirmed that the obtained glass substrate for magnetic disk withstands an impact of 3000 G.

  In addition, in a hard disk drive (HDD) equipped with a magnetic disk using a glass substrate manufactured under conditions that can withstand an impact of 3000 G, it was confirmed that no cracks would occur in the magnetic disk even after a drop test (2000 G). Has been.

[Example 2]
In Example 2, a magnetic disk was manufactured by the following process using the glass substrate for magnetic disk prepared in Example 1 described above.

  A Ni-Ta alloy first underlayer, a Ru second underlayer, and a Co-Cr-Pt-B alloy magnetic layer are formed on both main surfaces of the above-described magnetic disk glass substrate by using a stationary opposed DC magnetron sputtering apparatus. Then, a hydrogenated carbon protective layer was sequentially formed. Next, an alcohol-modified perfluoropolyether lubricating layer was formed by a dip method. In this way, a magnetic disk for the perpendicular magnetic recording system was obtained.

  About the obtained magnetic disk, it confirmed that the defect did not generate | occur | produce in films | membranes, such as a magnetic layer, by the foreign material. In addition, when the glide test was performed, no hit (the head bited against the protrusion on the surface of the magnetic disk) or crash (the head collided with the protrusion on the surface of the magnetic disk) was not recognized. Furthermore, when a reproduction test was conducted with a magnetoresistive head, no malfunction of reproduction due to thermal asperity failure was found.

  The above test was performed as a test method for a magnetic disk having an information recording density per square inch equivalent to 40 gigabits. Specifically, the flying height of the magnetic head was 10 nm, and in the recording / reproducing test, the information line recording density was 700 fci.

  That is, it was found that the magnetic disk according to the present invention was able to avoid the problem due to foreign matter on the surface of the glass substrate and was produced as a good magnetic disk for the magnetoresistive head.

It is a perspective view which shows the structure of the glass substrate for magnetic discs manufactured by the manufacturing method of the glass substrate for magnetic discs which concerns on this invention. It is sectional drawing which shows the shape of the inner peripheral side end surface of the circular hole of the said glass substrate for magnetic discs. It is process drawing which shows each process of the manufacturing method of the glass substrate for magnetic discs which concerns on this invention. In the manufacturing method of the glass substrate for magnetic discs which concerns on this invention, it is a perspective view which shows the state which is performing the centerless grinding process with respect to the side part of a cylindrical glass base material. In the manufacturing method of the glass substrate for magnetic discs concerning this invention, it is sectional drawing which shows the shape of the groove | channel provided in the side part of the columnar glass base material. In the manufacturing method of the glass substrate for magnetic discs which concerns on this invention, it is a perspective view which shows the state which has cut | disconnected the cylindrical glass base material with the multi-wire saw.

Explanation of symbols

1 circular hole 2 glass substrate for magnetic disk 3 glass base material

Claims (8)

A method of manufacturing a glass substrate for a magnetic disk, including a step of cutting a columnar or cylindrical glass base material perpendicularly to its central axis to produce a glass disk,
The columnar or cylindrical glass base material has a difference between the outer diameter of the thickest part and the outer diameter of the thinnest part of 0.5 mm or less. Method. It is a manufacturing method of the glass substrate for magnetic discs of Claim 1, Comprising:
The columnar or cylindrical glass base material has a difference between an outer diameter of the thickest part and an outer diameter of the thinnest part of 0.3 mm or less. Method. A method for producing a glass substrate for a magnetic disk according to claim 1 or claim 2,
The columnar or cylindrical glass base material has an average outer diameter of 30 mm or less. A method of manufacturing a glass substrate for a magnetic disk, wherein: A method of manufacturing a glass substrate for a magnetic disk, including a step of cutting a columnar or cylindrical glass base material perpendicularly to its central axis to produce a glass disk,
By grinding or polishing the side surface of the columnar or cylindrical glass base material, the difference between the outer diameter at the thickest part and the outer diameter at the thinnest part of the columnar or cylindrical glass base material The method of manufacturing a glass substrate for a magnetic disk is characterized in that the cutting process is performed after setting the thickness to 0.5 mm or less. It is a manufacturing method of the glass substrate for magnetic discs as described in any one of Claims 1 thru | or 4, Comprising:
The side surface portion of the columnar or cylindrical glass base material is brought into contact with the wire saw, the side surface portion and the wire saw are moved relative to each other to cut the columnar or cylindrical glass base material, A method for producing a glass substrate for a magnetic disk, comprising producing a glass disk. It is a manufacturing method of the glass substrate for magnetic discs as described in any one of Claims 1 thru | or 4, Comprising:
The side surface portion of the columnar or cylindrical glass base material and a blade saw are brought into contact with each other, and the side surface portion and the blade saw are relatively moved to cut the columnar or cylindrical glass base material, A method for producing a glass substrate for a magnetic disk, comprising producing the glass disk. It is a manufacturing method of the glass substrate for magnetic discs as described in any one of Claims 1 thru | or 6, Comprising:
A glass substrate for a magnetic disk, wherein the columnar or cylindrical glass base material is annealed to relieve internal stress, and then the cylindrical or cylindrical glass base material is cut to form a glass disk. Manufacturing method.   A method for manufacturing a magnetic disk, comprising forming at least a recording layer on a glass substrate manufactured by the method for manufacturing a glass substrate for a magnetic disk according to claim 1.

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