JPH1011748A - Blank material for crystallized glass substrate for magnetic disk, and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to stably produce crystallized glass substrates free from warpage by preventing the warpage of the crystallized glass substrates at the time of finishing both surfaces of a blank material for the crystallized glass substrates for magnetic disk by polishing. SOLUTION: Both of the main surfaces 5a, 5b, 9a, 9b on both sides of the blank materials 5, 9 are recessed surfaces or projecting surfaces. Amorphous glass plates manufactured to have a nearly uniform thickness are held between the transfer surfaces of plural hold-down plates. The transfer surfaces of these hold-down plates are formed as projecting surfaces or recessed surfaces. The respective main surfaces of the amorphous glass plates are respectively brought into contact with the transfer surfaces of the respective hold-down plates and in this state, the amorphous glass plates are softened to correct the warpage of the amorphous glass plates. Crystals are then grown in the original glass and while the state of correcting the warpage of the amorphous glass plates is maintained, the amorphous glass plates are solidified, by which the blank materials 5, 9 are produced. The blank materials 5, 9 are subjected to finish polishing, by which the crystallized glass substrates are produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a blank material for a crystallized glass substrate for a magnetic disk and a method for producing the same.

[0002]

2. Description of the Related Art Main components of a magnetic storage device such as a computer are a magnetic recording medium and a magnetic head for magnetic recording and reproduction. As a material for a substrate for a hard disk as a magnetic recording medium, an aluminum alloy has been mainly used. However, recently, as the size of hard disk drives has been reduced and the recording density has been increased, the flying height of the magnetic head has been significantly reduced. Accordingly, extremely high precision is required for the smoothness of the surface of the magnetic disk. Generally, the maximum height of the irregularities on the surface of the magnetic disk must be less than half the flying height of the magnetic head. For example, in a hard disk drive having a flying height of 75 nm, the maximum height of irregularities on the disk surface must be 38 nm or less. In particular, recently, it has been required that the center line average surface roughness Ra in the read / write zone of the magnetic disk substrate be 20 Å or less. However, in the case of an aluminum alloy substrate, since the hardness is low, even if polishing is performed using high-precision abrasive grains and a machine tool, the polished surface is plastically deformed. Surfaces are difficult to manufacture. For example, even if nickel phosphorus plating is performed on the surface of an aluminum alloy substrate, it is not possible to form a smooth surface of the above level.

In order to solve this problem, a magnetic disk substrate made of glass has been put to practical use as a material for a magnetic disk substrate. However, since a particularly high strength is required for a magnetic disk substrate for an HDD, it is necessary to use a tempered glass such as a chemically strengthened glass or a glass ceramic. Examples of the glass constituting the magnetic disk substrate include chemically strengthened glass such as soda lime glass, crystallized glass, non-alkali glass, and aluminosilicate glass. Among them, chemically strengthened glass and crystallized glass are preferable in terms of strength.

[0004] In particular, crystallized glass has less variation in hardness and flexural strength than chemically strengthened glass, and therefore has higher strength reliability. In particular, it is very preferable to reduce the thickness of the magnetic disk substrate to 0.5 mm or less and to maintain a desired strength.

[0005]

However, there have been the following problems in mass-producing such a magnetic disk substrate made of crystallized glass. That is, in the conventional manufacturing method, for example,
When manufacturing a 2.5 inch diameter glass substrate, first,
A part of the molten glass is placed in a mold and pressed to produce a disc-shaped amorphous glass molded body having a thickness of about 1.2 mm to 1.5 mm. Alternatively, a cylindrical amorphous glass molded body is cut to obtain a disk-shaped amorphous glass plate, and the amorphous glass plate is further ground or polished as needed to obtain a thickness of 1.2 to 1.2 mm. A disk-shaped glass plate of about 1.5 mm is prepared. These amorphous glass plates are heated and crystallized to produce semi-finished products (so-called blanks) before polishing. Then, both sides are finish-polished, that is, the upper and lower surfaces of the semi-finished product are simultaneously wrapped and polished to finish a crystallized glass substrate for a magnetic disk having a thickness of, for example, 0.635 mm.

That is, in order to finish a semi-finished product (blank material) obtained by crystallizing amorphous glass into a final product (crystallized glass substrate for a magnetic disk), in view of the thickness of the blank material, Half or more of the thickness must be removed by polishing. Moreover, the crystallized glass after crystallization is compared to the amorphous glass before crystallization.
Since the hardness is further increased, much time is required for polishing, and there is a problem that the production cost is increased. Naturally, in order to reduce this cost, it is preferable to finish as thin as possible in the state of the amorphous glass, but if it is simply crystallized in this state, the glass plate warps at the stage of crystallization, It was almost impossible to correct this by double-side polishing. Moreover, the more the thickness of the blank material is reduced, the more difficult it is to correct this warpage. Therefore, in the conventional method, an amorphous glass having a certain thickness (that is, a thickness of about 1.2 to 1.5 mm) has to be crystallized and used as a blank material.

The flatness required for a magnetic disk substrate having a diameter of 2.5 inches is usually 5 μm or less.

[0008] To solve this problem, the present applicant has
In the specification of Japanese Patent Application No. 7-258792, an amorphous glass plate having a substantially uniform thickness is formed by two pressers made of a material which does not react with the amorphous glass and does not deform during crystallization. In this state, the amorphous glass plate is softened by heating it to a temperature higher than the yield point of the original glass, the warpage of the amorphous glass plate is corrected, and then the amorphous glass plate is crystallized. It has been disclosed that the temperature is raised to a temperature at which growth occurs, and crystals are grown in the original glass, thereby solidifying the amorphous glass plate while maintaining the state where the warpage of the amorphous glass plate is corrected. That is, at the stage where the glass is amorphous, that is, at the stage where the hardness is relatively low and the polishing is easy, the amorphous glass plate is polished, and the thickness of the amorphous glass plate is reduced to the final product, the crystal for magnetic disk The glass substrate was uniformly finished to a thickness close to the thickness of the glass substrate, and was crystallized. At the same time, the warpage, that is, the flatness of the polished amorphous glass plate was corrected. Thereby, the amount of polishing from the blank material having high hardness after crystallization to the final product can be significantly reduced.

However, as a result of further study by the present inventor, it has been found that there is still the following problem. That is,
Before the blank material is polished on both sides, the blank material has an arcuate or corrugated shape having a flatness of 15 μm or less. By polishing and finishing both surfaces of the blank material, the bow or corrugated shape is corrected, and a crystallized glass substrate having a flatness of 5 μ or less is manufactured. However, it has been found that warpage remains in the crystallized glass substrate and the yield decreases.

An object of the present invention is to prevent the warpage of a crystallized glass substrate when polishing both sides of a blank of a crystallized glass substrate for a magnetic disk, and to provide a stable and warped crystallized glass. To be able to produce substrates.

[0011]

SUMMARY OF THE INVENTION The present invention relates to a blank material before polishing for producing a crystallized glass substrate for a magnetic disk, wherein both main surfaces on both sides of the blank material are concave. Or, a blank material of a crystallized glass substrate for a magnetic disk, characterized by having a convex surface.

Further, the present invention provides an amorphous glass plate having a substantially uniform thickness, which is made of a material which does not react with the amorphous glass, does not deform during crystallization, and has a transfer surface. It is sandwiched between two holding plates, and at this time, each main surface of the amorphous glass plate is brought into contact with the transfer surface of each holding plate,
In this state, the amorphous glass plate is softened by heating it to a temperature equal to or higher than the yield point of the original glass so that the principal surface is along the transfer surface and the warpage of the amorphous glass plate is corrected. By heating the glass plate to the temperature at which crystal growth occurs and growing crystals in the original glass, the amorphous glass plate is solidified while maintaining the state in which the warpage of the amorphous glass plate has been corrected. The present invention relates to a method for manufacturing a blank material, wherein a transfer surface of a pressing plate is a convex surface or a concave surface, and main surfaces on both sides of the blank material are a concave surface or a convex surface.

Hereinafter, the problem solving method according to the present invention will be further described. The present inventor specifically attempts to manufacture a blank having a thickness close to the thickness of a crystallized glass substrate for a magnetic disk as a final product by a method as described below, and to polish and finish the blank. I was going. This step will be described with reference to the respective schematic cross-sectional views of FIGS.

As shown in FIG. 1A, the polishing disks 1A and 1A
B and the blank 2. The thickness of the blank 2 is substantially uniform throughout, and a mounting hole 30 is formed in the center of the blank 2. The blank 2 is warped so as to be slightly arcuate as a whole. However, in FIGS. 1A to 1D, the size of the warp of the blank material 2 is exaggerated for easy understanding of the reader. Actually, the flatness of each main surface 2a, 2b of the blank material 2 is within 15 μm, respectively.
Therefore, the magnitude of the warp is also only within 15 μm. It is considered that such a slight warpage is caused by stress inside the blank material during the crystallization process.

Next, as shown in FIG. 1B, pressure is applied to the blank material 2 by the polishing disks 1A and 1B, and polishing and finishing are performed in this state. As the polishing progresses,
As shown in (c), the thickness of the blank 2 is reduced,
A crystallized glass substrate 3 as a final product is produced.
Even in this state, the main surfaces 3a, 3b of the crystallized glass substrate 3
Are in contact with the polishing disks 1A and 1B. Then
As shown in FIG. 1D, the polishing disks 1A and 1B are released from the crystallized glass substrate. However, at this time, the crystallized glass substrate 3 sometimes slightly warped. In this case, the yield is reduced because the product is defective.

The present inventor has also studied reducing the warpage of the crystallized glass substrate by increasing the thickness of the blank material and increasing the polishing amount. However, according to this method, the time of a high-cost process of precision polishing of a crystallized glass substrate having high hardness becomes longer, and the polishing amount increases.

The inventor of the present invention has conceived that, as described above, both surfaces of a blank made of crystallized glass are either concave or convex. First, the case where both surfaces of the blank material are concave will be described. As shown in FIG. 2A, the main surfaces 5a and 5b on both sides of the blank 5
Each is concave. That is, the thickness s of the outer peripheral portion 7 is larger than the thickness t of the central portion 6. However, since the variation in the overall thickness of the blank material 5 is 15 μm or less, the difference between s and t is also only 15 μm or less.

Next, polishing and finishing are performed, and FIG.
As shown in FIG. 7, a crystallized glass substrate 8 having a thickness u is obtained. Next, the polishing disks 1A and 1B are removed from the main surfaces 8a and 8b of the crystallized glass substrate 8.

It is important that the blank 5 is not deformed by pressure during the polishing process. This is because, as shown in FIG. 2A, at the stage where the blank 5 is sandwiched between the polishing disks, the outer peripheral portion 7 of the blank 5 mainly contacts the polishing disk. The outer peripheral portion 7 is polished. At this stage, pressure is applied to the outer peripheral portion 7 in the thickness direction, and polishing of the outer peripheral portion 7 proceeds from both sides. Then, after this polishing reaches the central portion 6, by polishing a small amount, a crystallized glass substrate 8 having a sufficiently flat main surface is obtained as shown in FIG. 2 (b).

On the other hand, in the example shown in FIGS. 1A to 1D, pressure is applied to the slightly bowed blank material 2 as shown in FIG. Polishing proceeds with both surfaces of the blank 2 flattened as shown in FIG. While the polishing is in progress, a bending stress is applied to the inside of the blank material 2, and when the polishing is completed, when the crystallized glass substrate 3 is released from the pressure of the polishing plate, the crystallized glass substrate is removed. The substrate 3 warps due to the residual bending stress.

Next, a case where both surfaces of the blank material are convex surfaces will be described. As shown in FIG. 2C, the main surfaces 9a and 9b on both sides of the blank material 9 are convex surfaces. That is, the thickness w of the central portion 10 is larger than the thickness v of the outer peripheral portion 11.

As shown in FIG. 2C, when the blank 9 is sandwiched between the polishing disks, the central portion 10 of the blank 9 is removed.
Mainly comes into contact with the polishing plate, so that the central portion 10 is mainly polished in the initial stage of polishing. At this stage, pressure is applied to the central portion 10 in the thickness direction, and polishing of the central portion 10 proceeds from both sides. Then, after the polishing reaches the outer peripheral portion 11, by polishing a small amount, the substrate 8 having a sufficiently flat main surface is obtained as shown in FIG.

The difference between the thickness of the central portion and the thickness of the outer peripheral portion of the blank is preferably 5 μm or less, whereby the effect of the present invention becomes more remarkable. Further, by setting the difference between the thickness of the central portion and the thickness of the outer peripheral portion of the blank material to 5 μm or less, the amount of polishing at the time of polishing finishing can be reduced.

If the main surfaces on both sides of the blank material are concave, the outer peripheral portion 7 will be described particularly with reference to FIG.
Is particularly preferable because the blank comes into contact with the polishing disc, so that the blank 5 is held in a stable state between the polishing discs and there is no possibility of swinging.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A particularly preferred embodiment of the present invention will be described below with reference to FIGS. First, cast the molten glass into a mold, cool it to produce a cylindrical shaped body, and cut it with a band saw, wire saw, or inner peripheral blade slicing machine, etc.
A disk-shaped amorphous glass plate is manufactured. FIG. 3A schematically shows a cutting method using a band saw. Here, the cylindrical large-sized molded body 13 has a pair of end surfaces 13b and a peripheral surface 13a. As shown by arrow C, the cutting blade 14 is moved in a direction parallel to each end face 13b.
It is made to enter the peripheral surface 13a, and a disk-shaped molded body having a predetermined thickness is cut out.

By grinding or polishing both sides of the disc-shaped amorphous glass plate thus obtained, the unevenness of the cut surface formed at the time of cutting is removed, and the amorphous glass plate having a uniform thickness is obtained. Is produced. However, if the variation in the thickness of the disc-shaped amorphous glass plate obtained by cutting is small, the next grinding or polishing process is not required,
The process can proceed to the crystallization step.

The grinding method or the polishing method at this stage is not limited, but usually, the method shown in FIG.
As shown in FIG. 3, the carrier 15 is sandwiched between the grindstone 18A of the upper mold 17A and the grindstone 18B of the lower mold 17B.
Then, each of the cut amorphous glass plates 16 is held. By rotating the carrier 15 as shown by the arrow D, each amorphous glass plate 16 can be ground to a predetermined thickness.

After the amorphous glass plate 16 polished or ground to a predetermined thickness is crystallized, final polishing (lapping and polishing) is performed to produce a crystallized glass substrate. Here, in order to minimize the final polishing amount, the difference between the thickness of the finished amorphous glass plate and the thickness of the crystallized glass substrate as the final product is 0.1 mm (100 μm). The thickness is preferably not more than 0.05 mm (50 μm), and more preferably not more than 0.05 mm (50 μm). For example, a crystallized glass substrate for a magnetic disk
In the case of a magnetic disk substrate having a diameter of 2.5 inches, the thickness of the final product is 0.635 mm. At this time, the thickness of the finished amorphous glass plate is 0.73 mm.
It is preferably 5 mm or less, more preferably 0.685 mm or less.

The thickness of the finished amorphous glass plate is preferably uniform, and is preferably within ± 10 μm. In the subsequent step (ie, the crystallization step), since the warpage (ie, flatness) is corrected at the same time, the amorphous glass plate at this stage may be warped.

Further, the amorphous glass plate can be manufactured by a press molding method, and the amorphous glass plate is polished or ground.

In the actual magnetic disk substrate, a circular hole is formed in the center of the disk to fix the disk.
It is necessary to perform a process for increasing the accuracy of the inner and outer diameters of the substrate. Further, it is necessary to chamfer the outer periphery of the disk and the inner periphery of the circular hole (not shown). These processes can be performed on an amorphous glass plate, and can also be performed after crystallization. However, amorphous glass is easier to process than crystallized glass,
It is preferable that the above processing is performed on the amorphous glass plate.

FIG. 3 (c) is a cross-sectional view schematically showing a state in which the outer and inner peripheries of the disc are processed with respect to the amorphous glass plate before crystallization. The polished surface of the molded body 19 polished or ground is opposed to the processing tool 24. The processing tool 24 is provided with a ring-shaped or annular-shaped outer peripheral grindstone 23A and an inner peripheral grindstone 23B. The polishing surface is brought into contact with these blades, and the processing tool 24 is rotated about the rotation shaft 22 in, for example, the direction of arrow E. Thereby, the outer peripheral portion of the molded body is deleted along the position of the broken line 20, and the dimension of the outer periphery of the molded body is controlled according to a predetermined specification. At the same time,
The inner peripheral portion of the molded body 19 is deleted along the position of the broken line 21, and a circular hole having a predetermined shape and size is formed.

In the crystallization step, when carbon is used as the material of the holding plate, when the amorphous glass plate is sandwiched between the holding plates and heated to soften, the holding plate and the amorphous glass plate react with each other. do not do. In addition, when the flatness of the holding plate is determined, the hardness of the material is low, so that a high flatness can be easily obtained by polishing. In addition, as a material of the holding plate, a material that does not react with or adhere to glass besides carbon and that is chemically and mechanically stable at a crystallization temperature can be used. In particular, carbon-coated ceramics and the like, or metals such as stainless steel can be suitably used.

Further, by setting the atmosphere in the furnace to an inert atmosphere such as nitrogen, it is possible to prevent the holding plate from deteriorating due to the reaction between carbon and metal or the like and oxygen during heating, and to prevent seizure between the glass and the holding plate. Can be. From this viewpoint, this atmosphere may be a reducing atmosphere.

When the crystallization of the amorphous glass is performed on an industrial scale, a large number of amorphous glass plates are collectively prepared.
It is necessary to process simultaneously and continuously. Therefore, it is preferable to use a flat holding plate, to form a laminate by alternately stacking the holding plate and the amorphous glass plate, and to process the stack in a furnace at once. . Further, it is preferable to use a tunnel furnace and continuously move and process a plurality of laminates in the tunnel furnace. FIG. 4 is a diagram schematically showing such a mass production process.

In the heat treatment furnace of FIG. 4, the upper furnace 26A
The heater 27A is installed in the inside, and the heater 27B is installed in the lower furnace 26B. Each laminate 25A,
25B, 25C, and 25D are each viewed from below.
The pressing plate 28 and the amorphous glass plate 29 are alternately laminated. Pressing plates 28 are provided on the lowermost and uppermost sides of each laminate, respectively. This laminate can be moved in the direction of arrow F by a moving device such as a conveyor (not shown). The temperature in the furnace can be adjusted in accordance with each step of raising the temperature of the laminate from room temperature, heating to a temperature above the yield point, and heating to the crystallization temperature.

Here, in each of the laminates, a configuration as shown in FIGS. 5 and 6 can be adopted. In FIG. 5, the holding plate 33 and the amorphous glass plate are alternately laminated on the flat surface 32 of the surface plate 31B having a predetermined weight, and the heat treatment is performed. The main surfaces 33a and 33b on both sides of the holding plate 33 are convex. At this time, the surface plate 31A having a predetermined weight is placed on the uppermost pressing plate 33, and a predetermined pressure is applied to the entire laminate. In this way, after sandwiching the amorphous glass plate between the two holding plates, by applying pressure to the holding plate, the convex shape of the surface of the holding plate can be more accurately formed on the amorphous glass plate. Is transcribed.

In FIG. 6, the main surfaces 37a and 37b on both sides of the holding plate 37 are concave. A platen 31A having a predetermined weight is placed on the uppermost holding plate 37, and a predetermined pressure is applied to the entire laminate. As a result, the shapes of the concave surfaces 37a and 37b of the holding plate 37 are accurately transferred to the amorphous glass plate, and the convex surfaces 9a and 9b are formed on both sides of the crystallized glass substrate 9.
Is formed.

Examples of crystallized glass suitable for producing the magnetic disk substrate of the present invention include Li ₂ O—Al ₂ O
Examples include, but are not limited to, _3- SiO ₂ -based crystallized glass.

[0040]

EXAMPLES Example 1 76.1% by weight of SiO ₂ , 11.8% by weight of Li ₂ O, 7.1% by weight of Al ₂ O ₃ , 2.8% by weight of K ₂ O, P Powders such as oxides and carbonates of various metals are mixed so that the oxide weight ratio of ₂ O ₅ is 2.0% by weight and Sb ₂ O ₃ is 0.2% by weight, and the mixture is heated at 1400 ° C.
And melted. The obtained melt was press-molded to obtain a disk-shaped molded body having an outer diameter of 68 mm and a thickness of 1.5 mm, which was gradually cooled to remove internal strain to obtain a raw glass molded body.

Both sides of the obtained raw glass molded body were subjected to GC wrapping to obtain a disk having a thickness of 0.70 mm. This disk is processed with a diamond grindstone,
An annular amorphous glass plate having a diameter of 9.5 mm and an outer diameter of 66.0 mm was obtained (see FIG. 3C).

The obtained amorphous glass plate was sandwiched between pressing plates 33 as shown in FIG. 5 and laminated. The pressing plate 33 has a flatness of 3 to 5 μm and a convex surface 33 protruding from the center.
A carbon plate having a and 33b was used. Amorphous glass plates were laminated in 10 stages. At the top and bottom of the stack,
Plates 31A and 31B also serving as weights were installed. The flatness of the flat surface of the surface plate is on the order of submicrons.

The laminate was held horizontally in an atmosphere tubular furnace made of alumina tubes. In this state, the furnace was sealed, N ₂ gas was flowed into the furnace at a rate of 1 liter / min, and the temperature was maintained at 550 ° C. for 2 hours.
And then cooled to room temperature.

With respect to the ten blank materials thus obtained, the flatness was measured on the upper surface side and the lower surface side, and the measurement results are shown in Table 1. However, in Tables 1 to 3, each numerical value indicates the flatness of each surface, the sign “−” indicates a concave surface, and the sign “+” indicates a convex surface. As a result, even if the amorphous glass had any shape, both surfaces could be corrected to have a concave shape.

[0045]

[Table 1]

The blank material of sample No. 1 was wrapped to a thickness of 0.66 mm with GC abrasive grains of # 2000, and then wrapped in # 40.
The sample was wrapped with a GC grain of 00 to a thickness of 0.645 mm. Thereafter, the resultant was polished with cerium oxide to a thickness of 0.635 mm. As a result, the flatness of the upper surface of the obtained crystallized glass substrate was 2 μm, and the flatness of the lower surface was 1.3 μm.

Comparative Example 1 An amorphous glass plate having the same shape as in Example 1 was sandwiched and laminated between presser plates 33 as shown in FIG. No platen was used. As shown in FIG. 7A, the lowermost holding plate 4
OA was directly placed on the surface 42a of the catalon plate 42. The holding plate is laminated in 24 steps, and 1.7 kg is placed on the laminated body.
With a weight. This laminate was formed in two rows, and
Crystallization was performed in the same manner as described above.

Under these conditions, the lowermost amorphous glass plate and the second lowermost amorphous glass plate were slightly bowed as shown in FIG. 1 (a). . The convex surface of the holding plate was transferred to the third or higher stage amorphous glass from the bottom. Each flatness of the upper surface and the lower surface was measured, and the measurement results are shown in Table 2.

[0049]

[Table 2]

Next, the blank material of sample No. 13 was
After wrapping to a thickness of 0.66 mm with 2000 GC abrasives, wrapping was performed to a thickness of 0.645 mm with # 4000 GC abrasives. Thereafter, the resultant was polished with cerium oxide to a thickness of 0.635 mm. As a result, the flatness of the upper surface of the obtained crystallized glass substrate was −9.8 μm,
The flatness of the lower surface was +16.2 µm.

The present inventors have studied the causes of the lowermost amorphous glass plate and the second lowermost amorphous glass plate along the bow. As shown in FIG. 7A, the surface 42a of the catalon plate 42 has microscopic irregularities. On this catalon plate 42, a holding plate 40A, an amorphous glass plate 41
A, a holding plate 40B, an amorphous glass plate 41B, and a holding plate 40C are stacked in this order. For this reason, the load applied to the catalon plate 42 is particularly low in the pressing plate 4 near the lowermost step.
0A, 40B and the central portions of the amorphous glasses 41A, 41B, and as shown in FIG. 7B, the holding plates 40A, 40B and the amorphous glasses 41A, 41B.
The central portion of B was recessed downward, and the holding plate followed the bow. As a result, it was found that the shape of the holding plate along the bow shape was transferred to the amorphous glass plates 41A and 41B.

In other words, the pressing plate was initially convex on both sides, but the lowermost plate and the second lower pressing plate 40A,
In 40B, especially as a result of the holding plate following the bow shape,
It is probable that one surface of the holding plate became a convex surface protruding more than the first, and the other surface became a concave surface.

(Prevention of Warpage of Lower Amorphous Glass Plate) In order to accurately transfer the transfer surface of the holding plate to the amorphous glass plate, the holding plate is heated and the load or the weight of the laminated body is reduced. It is necessary that the holding plate does not bend in the bow shape even in the state in which is added. For this purpose, as the most preferable method, the lowermost holding plate can be placed on a surface plate having no warpage on the surface.

Actually, in Comparative Example 1, the platen was laid below the lowermost holding plate, and the holding plate and the amorphous glass plate were each laminated on the 24th stage. 0.85kg in the upper row
Was placed and crystallized in the same manner as in Comparative Example 1.
As a result, the flatness of the upper surface of the lowermost crystallized glass substrate was −3.2 μm, and the flatness of the lower surface was −2.5 μm.
m.

(Example 2) An amorphous glass plate having the same shape as in Example 1 was laminated and crystallized in the same manner as in Example 1. However, in Example 2, as shown in FIG. 6, a carbon plate 37 having a flatness of 3 to 5 μm and having concave surfaces 37 a and 37 b protruding at the outer peripheral portion was used as the holding plate 37. Amorphous glass plates were laminated in 10 stages. A platen 31 serving as a weight is placed on the top and bottom of the laminate.
A, 31B were installed.

Three blanks were selected from the ten blanks thus obtained, and the flatness was measured on each of the upper surface side and the lower surface side. Table 3 shows the measurement results. Here, the sample number 15 is the blank material at the top, and the sample number 1
6 is the fifth blank material from the top, and sample number 17 is the lowest blank material. As a result, it was found that even if the amorphous glass had any shape, both surfaces could be corrected to have a convex shape.

[0057]

[Table 3]

The blank material of sample No. 15 was
After wrapping to a thickness of 0.66 mm with GC abrasive grains of # 4,
Wrapped to a thickness of 0.645 mm with 000 GC abrasives. Thereafter, the resultant was polished with cerium oxide to a thickness of 0.635 mm. As a result, the flatness of the upper surface of the obtained crystallized glass substrate was 1.8 μm, and the flatness of the lower surface was 2.3 μm.

[0059]

As described above, according to the present invention, it is possible to prevent the warpage of the crystallized glass substrate when polishing and finishing both surfaces of the blank of the crystallized glass substrate for a magnetic disk. Thus, a crystallized glass substrate without warpage can be produced.

[Brief description of the drawings]

1 (a), (b), (c) and (d) show steps of manufacturing a crystallized glass substrate 3 by polishing and finishing a blank material 2 slightly warped in an arc shape. It is sectional drawing which shows typically.

FIG. 2A is a cross-sectional view schematically showing a step of finishing and polishing a blank material 5 having both concave surfaces,
(B) is a cross-sectional view schematically showing a step of obtaining a crystallized glass substrate 8 by finish-polishing the blank material 5, and (c) is a finish-polishing process of the blank material 9 having both convex surfaces. FIG. 4 is a cross-sectional view schematically showing a step of performing the process.

FIG. 3A is a perspective view schematically showing a process of cutting out a disk-shaped molded body having a predetermined thickness from a large molded body 13, and FIG. 3B is a perspective view schematically showing a step of grinding the grinding wheel 18A of the upper die 17A. It is a perspective view schematically showing a state in which the amorphous glass plate 16 is sandwiched between the grinding wheel 18B of the lower mold 17B and the grinding wheel 18B,
(C) is a sectional view schematically showing a state in which the outer and inner peripheral portions of the molded body after polishing are ground.

FIG. 4 is a schematic diagram schematically showing a heat treatment furnace suitable for mass production.

FIG. 5 is a cross-sectional view schematically illustrating a state in which platens 31A and 31B, a holding plate 33 having both convex surfaces, and a crystallized glass substrate 5 are stacked.

FIG. 6 is a cross-sectional view schematically showing a state in which platens 31A and 31B, a holding plate 37 having concave surfaces on both sides, and a crystallized glass substrate 9 are stacked.

FIGS. 7A and 7B are schematic cross-sectional views for explaining states of a holding plate and an amorphous glass plate at a lowermost stage and an upper stage in Comparative Example 1. FIGS.

[Explanation of symbols]

1A, 1B Polishing machine 5, 9 Blank material 5
a, 5b concave surface 6 central part of blank material 5 7 peripheral part of blank material 5 8 crystallized glass substrate 9
a, 9b convex surface 10 central part 10 of blank material 9
11 Peripheral part of blank 9 16, 29 Amorphous glass plate 25A, 25B, 25C, 25D Laminated body 28, 33, 37 Holding plate 31A, 31B surface plate 32 Flat surface of surface plate 33a, 33b Convex surface of holding plate 33 37a, 37b Concave surface of holding plate 37

Claims (6)

[Claims] 1. A blank material before polishing for manufacturing a crystallized glass substrate for a magnetic disk, wherein both main surfaces on both sides of the blank material are concave surfaces.
Blank material of crystallized glass substrate for magnetic disk. 2. A presser comprising an amorphous glass plate having a substantially uniform thickness and made of a material which does not react with the amorphous glass and does not deform during crystallization and has a transfer surface. In this case, the main surfaces of the amorphous glass plate are brought into contact with the transfer surfaces of the holding plates, and in this state, the amorphous glass plate is held at a temperature higher than the yield point of the original glass. Softening by heating to a temperature, correcting the warpage of the amorphous glass plate along with the main surface along the transfer surface, and then raising the temperature of the amorphous glass plate to a temperature at which crystal growth occurs. By growing a crystal in the raw glass, the amorphous glass plate is solidified while maintaining the state in which the warpage of the amorphous glass plate has been corrected, and the transfer surface of the holding plate is made a convex surface here. The main surfaces on both sides of the blank are concave. Characterized method of the blank according to claim 1 magnetic disk crystallized glass substrate for description. 3. The method for producing a blank of a crystallized glass substrate for a magnetic disk according to claim 2, wherein a carbon plate is used as said holding plate. 4. A blank before polishing for producing a crystallized glass substrate for a magnetic disk, wherein both main surfaces on both sides of the blank are convex.
Blank material of crystallized glass substrate for magnetic disk. 5. An amorphous glass plate made of a material having a substantially uniform thickness, which is made of a material which does not react with the amorphous glass, does not deform during crystallization, and has a transfer surface. In this case, the main surfaces of the amorphous glass plate are brought into contact with the transfer surfaces of the holding plates, and in this state, the amorphous glass plate is held at a temperature higher than the yield point of the original glass. Softening by heating to a temperature, correcting the warpage of the amorphous glass plate along with the main surface along the transfer surface, and then raising the temperature of the amorphous glass plate to a temperature at which crystal growth occurs. By growing crystals in the original glass, the amorphous glass plate is solidified while maintaining the state of correcting the warpage of the amorphous glass plate, and the transfer surface of the holding plate is made concave here. Main surfaces on both sides of the blank material are convex surfaces Wherein, according to claim 4 production process of the blank of the crystallized glass substrate for a magnetic disk according. 6. The method for producing a blank material for a crystallized glass substrate for a magnetic disk according to claim 5, wherein a carbon plate is used as said holding plate.