JP2011138590A - Method for manufacturing glass substrate for magnetic disk and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a glass substrate for magnetic disk to efficiently machine the glass substrate for magnetic disk having a magnetic layer formed only on one side thereof. <P>SOLUTION: The method for manufacturing a glass substrate for magnetic disk by using a glass blank produced by cutting and pressing molten glass, includes: a glass blank molding step to mold the glass blank which is equipped with a first principal surface having surface roughness Ra of 0.01-10 μm and a second principal surface having a shear mark and which has flatness necessary for a glass substrate for magnetic disk; and a surface machining step to machine only the first principal surface of the glass blank. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a glass substrate and a magnetic recording medium used in a magnetic disk device.

Currently, annular magnetic disks are widely used in hard disk drive devices (HDD devices). In general, a magnetic disk is manufactured by subjecting a blank material to a shape processing step (coring, chamfering, etc.), a grinding step (lapping), a polishing step (polishing), etc., and manufacturing a magnetic disk substrate. It is manufactured by forming a magnetic layer or the like on the substrate.
Today, hard disk drives are built in personal computers, notebook personal computers, DVD (Digital Versatile Disc) recording devices, and the like. In particular, in a hard disk device used in a device such as a notebook personal computer that is assumed to be portable, a glass substrate is preferably used because it is less likely to be plastically deformed than a metal substrate or the like.

  In the polishing process of the main surface in the method for manufacturing a magnetic disk substrate, a carrier holding the magnetic disk substrate is placed between a pair of surface plates (upper surface plate and lower surface plate), and pressure is applied between the upper and lower surface plates. Then, the carrier is sandwiched, the upper surface plate and the lower surface plate are rotated reversely, and both main surfaces of the magnetic disk substrate are polished while supplying the abrasive (Patent Document 1).

The recording density of magnetic disks is increasing year by year, and magnetic disks of 100 GB or more on one side have been developed. The magnetic disk satisfies the recording density required for both sides, but an electronic device that does not require a high recording density can satisfy the recording density required for only one side.
If it becomes possible to satisfy the required recording density on only one side, it is possible to provide a single magnetic head for one magnetic disk on the HDD device side, thereby reducing costs and reducing the thickness of the device. be able to. Therefore, the need for a magnetic disk having a magnetic layer only on one side is expected to increase in the future.

JP 2007-90452 A

  When manufacturing a glass substrate for a magnetic disk having a magnetic layer only on one surface, the surface quality required for the surface on which the magnetic layer is not formed (non-recording surface) is required for the surface on which the magnetic layer is formed (recording surface). The surface quality is not as high. The required surface quality is, for example, the surface roughness of a magnetic disk glass substrate.

  An object of this invention is to provide the manufacturing method of the glass substrate for magnetic discs which can process efficiently the glass substrate for magnetic discs provided with a magnetic layer only on one side.

  The method for producing a glass substrate for a magnetic disk according to the present invention is a method for producing a glass substrate for a magnetic disk by using a glass blank that is obtained by cutting molten glass and having a surface roughness Ra of 0.01 μm. A glass blank forming step of forming a glass blank having a flatness necessary for a magnetic disk glass substrate, the first main surface being 10 μm or less and a second main surface having a sheer mark; and the glass A surface processing step of processing only the first main surface of the blank.

  The glass blank forming step includes a cutting step of cutting molten glass, a step of dropping a lump of glass formed by being cut by the cutting step, and a surface roughness Ra of 0.01 μm to 10 μm. Using the first mold and the second mold, the first mold is pressed by pressing the glass lump from a substantially horizontal direction while the lump of glass is falling. Preferably, the first main surface is formed, and the second mold includes a pressing step of forming the second main surface including the sheer mark.

  In addition, the pressing step uses the first mold having a surface roughness Ra of 0.01 μm or more and 10 μm or less, and the second mold having a surface roughness Ra of 0.005 μm or less, and the lump of glass. Is preferably pressed.

  In addition, the pressing step uses a first mold having a surface roughness Ra of 0.01 μm or more and 1 μm or less and a second mold having a surface roughness Ra of 0.005 μm or less, and the lump of glass. Is preferably pressed.

  Moreover, it is preferable to have a scribe process which scribes the said glass blank between the said glass blank shaping | molding process and the said surface processing process.

  The surface processing step includes a grinding step of grinding the first main surface using fixed abrasive grains, and a polishing step of polishing the first main surface using loose abrasive grains after the grinding step. It is preferable.

  The grinding step is preferably performed using fixed abrasive grains containing diamond particles.

  Further, the flatness required as a glass substrate for a magnetic disk is preferably 4 μm or less.

  The magnetic recording medium of the present invention includes a glass substrate for magnetic disk manufactured by the method for manufacturing a glass substrate for magnetic disk and a first main surface of the glass blank among the main surfaces of the glass substrate for magnetic disk. And a magnetic layer formed only on the main surface on the processed side.

  According to the method for manufacturing a glass substrate for magnetic disk of the present invention, a glass substrate for magnetic disk having a magnetic layer only on one side can be processed efficiently.

(A) is a figure which shows an example of the glass substrate for magnetic discs manufactured with the manufacturing method of this embodiment, (b) is a figure which shows an example of a glass blank. It is a flowchart which shows an example of the manufacturing method of the glass substrate for magnetic discs of this embodiment. (A)-(c) is a figure which shows an example of a glass blank shaping | molding process. (A) is a general view of the surface processing apparatus used in the present embodiment, and (b) is a diagram showing a carrier used in the surface processing apparatus shown in (a). It is sectional drawing along the AA line of FIG.4 (b). (A)-(c) is a figure which shows the other example of a glass blank shaping | molding process. It is a figure which shows an example of a grinding process. It is a figure which shows the other example of a grinding process.

Hereinafter, the manufacturing method of the glass substrate for magnetic disks is demonstrated based on embodiment.
<First Embodiment>
The glass substrate for magnetic disks manufactured in this embodiment will be described. FIG. 1A is a view showing an example of a glass substrate for a magnetic disk manufactured in the present embodiment. As shown in FIG. 1A, the magnetic disk glass substrate manufactured in this embodiment has a main surface (recording surface) on which magnetic data is written and a main surface on which no magnetic data is written. (Non-recording surface).
Since a magnetic layer is formed on the recording surface and magnetic data is written, high surface quality is required. On the other hand, since no magnetic data is written on the non-recording surface, the surface quality is not as high as that of the recording surface.
FIG.1 (b) is a figure which shows an example of the glass blank B used as the origin of the glass substrate for magnetic discs shown by Fig.1 (a). As will be described later, the recording surface of the magnetic disk glass substrate is formed by subjecting the first main surface of the glass blank B to a surface processing step. Further, the second main surface of the glass blank B is a non-recording surface of the magnetic disk glass substrate. The surface roughness Ra of the first main surface of the glass blank B is larger than the surface roughness Ra of the second main surface.

As will be described later, a shear mark may be formed on a glass blank formed by press molding. A shear mark is a collection of small bubbles that are concentrated between a certain depth from the surface near the center of a disk-shaped glass. It has been clarified that the shear mark is formed by a cut surface when the molten glass is cut.
If the shear mark is formed on the recording surface of the glass substrate, there is a possibility that the writing of magnetic data may be hindered. For this reason, when the shear mark is formed on the main surface of the glass blank on the recording surface side of the glass substrate, it is necessary to remove the shear mark by grinding or polishing. However, depending on the state of the shear mark, the shear mark may be removed by grinding or polishing. May not be removed. On the other hand, since no magnetic data is written on the non-recording surface, when the shear mark is formed on the non-recording surface of the glass substrate, it is not necessary to remove the shear mark by grinding or polishing.
Therefore, in the present embodiment, the glass blank for the magnetic disk satisfying the required surface quality by processing the glass blank so that the main surface on the side on which the sheer mark is formed becomes the non-recording surface of the magnetic disk. A substrate is produced.

  Hereinafter, with reference to FIG. 2, the manufacturing method of the glass substrate for magnetic disks of this embodiment is demonstrated. FIG. 2 is a flowchart showing an example of a method of manufacturing a magnetic disk glass substrate according to this embodiment. As shown in FIG. 2, the method for manufacturing a magnetic disk glass substrate of the present embodiment mainly includes a glass blank forming step and a surface processing step. Here, the surface processing step includes a grinding step, a first polishing step, and a second polishing step. Furthermore, the manufacturing method of the glass substrate for magnetic disks of this embodiment includes a scribe process, a shape processing process, an end surface polishing process, and a chemical strengthening process. Hereinafter, each step will be described in detail.

(Glass blank molding process)
With reference to FIG. 3, the glass blank forming step (step S100) will be described. In the glass blank forming step, a glass blank B is formed by pressing a molten glass lump (gob). FIG. 3 is a diagram illustrating an example of a glass blank forming process. FIG. 3A shows a state before the gob is formed. FIG.3 (b) is a figure which shows the state in which the gob was formed. FIG.3 (c) is a figure which shows the state by which the gob was pressed.

First, as shown in FIG. 3 (a), the molten glass L _G is continuously flown out from the glass outlet 100. Next, as shown in FIG. 3 (b), the cutting blade 110 which is disposed below the glass outlet 100, to cut the molten glass L _G that is continuously flowing out from the glass outlet 100. Cut molten glass L _G becomes a gob G _G substantially spherical due to surface tension. In this way, a molten glass lump (gob) _GG is formed.
In the present embodiment, each time of cutting the molten glass _{L G} by the cutting blade 110, as gob _{G G} radius of about 10mm is formed, the outflow rate of the molten glass _{L G,} the cutting blade 110 is a molten glass _{L G} The timing for cutting is controlled.

Gob G _G substantially spherical, which is formed by the molten glass L _G is cut by the cutting blade 110 and falls vertically. As shown in FIG. 3 (b), on both sides of the path of the gob G _G drops, the first mold 120, a second mold 130, it is disposed.
The first press surface 122 that is the press surface of the first die 120 and the second press surface 132 that is the press surface of the second die 130 have different surface roughness Ra. Specifically, the surface roughness Ra of the second press surface 132 of the second die 130 is smaller than the surface roughness Ra of the first press surface 122 of the first die 120.
Further, as will be described later, in order to make the distance between the first press surface 122 and the second press surface 132 constant when the gob _GG is pressed with the first die 120 and the second die 130, The mold 120 includes a protruding spacer 124 on the first press surface 122 side.

As will be described later, of the main surfaces of the glass blank B, the main surface pressed by the first press surface 122 (first main surface) was used as the recording surface of the glass substrate and was pressed by the second press surface 132. The main surface (second main surface) is used as a non-recording surface of the glass substrate.
As described above, the recording surface of the glass substrate is required to have high surface quality. The surface roughness Ra required for the recording surface of the glass substrate is, for example, 0.2 nm or less. In addition to the surface roughness Ra, the recording surface of the glass substrate is also required to have surface quality such as flatness. Since it is difficult to satisfy the surface quality required for the recording surface only by the glass blank forming process, the first main surface of the glass blank B needs to be subjected to a grinding process and a polishing process described later. Therefore, the glass substrate which satisfy | fills the surface quality requested | required of a recording surface is produced by performing the grinding | polishing process and grinding | polishing process which are mentioned later on the 1st main surface of the glass blank B.

As the material of the glass substrate, aluminosilicate glass, soda lime glass, borosilicate glass, or the like can be used. 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.
As aluminosilicate glass, by mol%, a SiO ₂ 57-74%, the ZnO ₂ 0 to 2.8%, the _Al 2 _{O 3} 3 to 15%, the LiO ₂ 7 to 16%, a Na ₂ O It is preferable to use a glass material for chemical strengthening containing 4 to 14% as a main component.

On the other hand, the surface quality required for the non-recording surface of the glass substrate is not as high as the surface quality required for the recording surface, but the upper limit of the surface roughness Ra required for the non-recording surface of the glass substrate is 0.005 μm. It is. When the surface roughness Ra of the non-recording surface of the glass substrate is larger than 0.005 μm, the particles may adhere to the non-recording surface of the glass substrate, or the particles may bite into the surface irregularities of the non-recording surface. Is expensive. If particles adhere to the non-recording surface of the glass substrate, the particles are likely to scatter when the magnetic disk rotates and adhere to the surface of the magnetic disk, thereby causing a high thermal asperity or head crash.
Therefore, if the 2nd main surface of the glass blank B shape | molded in a glass blank formation process satisfy | fills the surface quality requested | required of the non-recording surface of a glass substrate, it is a grinding process with respect to the 2nd main surface of the glass blank B. There is no need to perform a polishing process. In order to further prevent generation of particles on the second main surface, a first polishing step described later may be performed on the second main surface.

In the present embodiment, the surface roughness Ra of the first press surface 122 is preferably 0.01 μm or more and 10 μm or less. The surface roughness Ra of the second press surface 132 is preferably 0.005 μm or less.
As will be described later, when the outer diameter of the glass blank B is larger than 65 mm, which is the outer diameter of the final product, and it cannot be processed as it is, it is preferable to perform a scribe process. In order to suitably form a cutting line in the scribing step, the surface roughness Ra of the first press surface 122 is more preferably 0.01 μm or more and 1 μm or less.

Here, the flatness can be measured using, for example, a flatness tester FT-900 manufactured by Nidek. Moreover, the roughness of the main surface is defined by JIS B0601: 2001 and expressed by arithmetic average roughness Ra. When the roughness is 0.006 μm or more and 200 μm or less, for example, it is measured by a Mitutoyo Corporation roughness measuring machine SV-3100, It can be calculated by a method defined in JIS B0633: 2001. As a result, when the roughness is 0.03 μm or less, for example, the roughness can be calculated by a method defined by JIS R1683: 2007 by measuring with a scanning probe microscope (atomic force microscope) manufactured by SII Nano Technologies.
This time, about the surface roughness of a plate-shaped glass material, using the result measured using Mitutoyo Corporation roughness measuring machine SV-3100, about the surface roughness of the glass substrate after grinding | polishing, the said scanning probe microscope ( The results measured with an atomic force microscope were used.

Then, when the gob G _G are dropped into a vertical direction is passing between the first mold 120 and second mold 130, the first mold 120 and second mold 130 with each other The first mold 120 and the second mold 130 are moved in the approaching horizontal direction. Thereafter, as shown in FIG. 3C, the gob _GG is pressed between the first mold 120 and the second mold 130.
A first mold 120 and second mold 130 is moved in a direction approaching each other, from the gob _{G G} is in contact with the first press surface 122 or the second pressing surface 132, the spacer 124 to the second pressing surface 132 The time until the first mold 120 and the second mold 130 are brought into a completely closed state is about 0.06 seconds, for example.

A first mold 120 as described above when the second mold 130 is pressed gob G _G, gob G _G while spreading between the first press surface 122 second press surface 132 in the shape of a disc, It is cooled rapidly and solidifies as amorphous glass. Since the first mold 120 is provided with a projecting spacer 124, by pressing the gob G _G between the first mold 120 and second mold 130, the glass blank B of a predetermined thickness is formed.
In the present embodiment, for example, a disk-shaped glass blank B having a diameter of 65 mm to 80 mm and a thickness of about 1 mm is formed.

As described above, when the first mold 120 and the second mold 130 are closed within a very short time such as within 0.1 seconds, the gob _GG is moved to the first press surface 122 and the second mold 130. It contacts the press surface 132 substantially simultaneously. Therefore, it can suppress that the 1st press surface 122 and the 2nd press surface 132 are heated locally.
Moreover, before the heat of the gob G _G moves to the first mold 120 and second mold 130, since the disk-shaped glass blank B is formed from the gob G _G, the temperature distribution of the glass blank B is approximately one It becomes like. As a result, when the glass blank B is cooled, it is possible to suppress the occurrence of distortion caused by the local shrinkage distribution.
That is, until the gob starts to be pressed and becomes a glass blank B, the first main surface and the second main surface are in a substantially thermal balance, and no thermal distortion occurs, resulting in flatness. It is possible to form an excellent glass blank. This point cannot be achieved by the conventional pressing method.

  The shapes of the first press surface 122 and the second press surface 132 are transferred to the glass blank B. Therefore, the glass blank B whose surface roughness Ra of the 1st main surface of the glass blank B is 0.01 micrometer or more and 10 micrometers or less and whose surface roughness Ra of the 2nd main surface is 0.005 micrometer or less can be shape | molded. .

  By setting the surface roughness Ra of the first main surface of the glass blank B to 0.01 μm or more, it is possible to efficiently perform grinding with fixed abrasive grains described later. Further, by setting the surface roughness Ra of the first main surface of the glass blank B to 10 μm or less, a large machining allowance (polishing amount) is required in the polishing step in order to remove cracks caused by grinding described later. It can be suppressed. Further, by setting the surface roughness Ra of the first main surface of the glass blank to 10 μm or less, it is possible to reliably adjust to Ra required as a glass substrate for a magnetic disk. Furthermore, by setting the surface roughness Ra of the first main surface of the glass blank B to 0.01 μm or more and 1 μm or less, scribing described later can be performed efficiently.

Here, when the cutting blade cuts the molten glass, the molten glass is locally cooled at the cutting point. Therefore, it is generally known that the viscosity of the cut portion is increased and the cut portion is formed as a shear mark on the glass blank after the molten glass is pressed. Also in glass blank forming process of the present embodiment, the molten glass L _G is the glass blank B after being pressed, cut part is formed as a shear mark.

Further, the shear mark is always formed on the same side of either the first mold 120 side or the second mold 130 side. The detailed mechanism by which the shear mark is formed on the same side has not been elucidated. When the gob G _G is pressed by the first press surface 122 and the second pressing surface 132, the gob G _G is not to contact at exactly the same time in both the first press surface 122 and the second pressing surface 132, It is considered that the first press surface 122 or the second press surface 132 is contacted slightly earlier. Therefore, those who gob G _G are in contact earlier of the first press surface 122 or the second pressing surface 132, or, for those in contact slow is believed that shear marks are formed. Therefore, the outflow rate of the molten glass L _G, the timing at which the cutting blade 110 cuts the molten glass L _G, if conditions such as speed and timing of the first mold 120 and second mold 130 is moved is the same, the sheer mark Can always be formed on the same side.

In the present embodiment, so as to always shear marks are formed on the pressed second main surface with a second press surface 132, in advance, the timing at which the outflow rate of the molten glass L _G, the cutting blade 110 cuts the molten glass L _G The conditions such as the moving speed and timing of the first mold 120 and the second mold 130 are adjusted in advance. Therefore, a shear mark is always formed on the second main surface of the glass blank B.
However, as described above, in the present embodiment, since the second main surface of the glass blank B is used as the non-recording surface of the glass substrate, it is not necessary to remove the shear mark by grinding or polishing.

  As described above, according to the glass blank forming step of the present embodiment, the required surface quality is obtained by grinding or polishing only the first main surface of the glass blank B in the grinding step or polishing step described later. A glass blank B capable of producing a glass substrate can be formed.

(Scribe process)
Next, the scribe process (Step S110) will be described. In the scribing step, two concentric cutting lines are formed on the main surface of the glass blank B using a scriber. The scriber blade is formed of, for example, a super steel alloy or diamond particles.
When the scribed glass blank B is partially heated, the glass blank B is separated at the cutting line of the outer concentric part due to the difference in thermal expansion coefficient of the glass blank B. In this way, the glass blank B is processed into an annular shape.

  Here, in general, when a surface having a surface roughness Ra larger than 1 μm is scribed, the scriber does not follow the surface irregularities, and it is difficult to uniformly provide a cutting line. When performing scribing on the first main surface side, the surface roughness Ra of the first main surface of the glass blank B described above is preferably set to 1 μm or less in order to suitably form a cutting line using a scriber. .

(Shaping process)
Next, the shape processing step (step S120) will be described. The shape processing step includes a coring step and a chamfering step.
In the coring process, for example, when the scribe process is not performed, a hole is formed in the glass blank B processed into a disk shape using a cylindrical diamond drill. In this way, the glass blank B is processed into an annular shape.
In the chamfering step, the inner peripheral end surface and the outer peripheral end surface are ground with a diamond grindstone, and a predetermined chamfering process is performed on the glass blank B processed into an annular shape.

(Grinding process)
Next, the grinding process (step S130) will be described. The glass blank B processed into an annular shape is ground with fixed abrasive grains. The particle size of the fixed abrasive is, for example, about 10 μm. The machining allowance (grinding amount) in the grinding process is, for example, about several μm to 100 μm.
Here, with reference to FIG.4 and FIG.5, the structure of the surface processing apparatus 200 is demonstrated. FIG. 4A is a diagram illustrating an overall configuration of the surface processing apparatus 200, and FIG. 4B is a diagram illustrating a carrier used in the surface processing apparatus 200. FIG. 5 is a cross-sectional view taken along the line AA in FIG.

4 and 5, the surface processing apparatus 200 includes a lower surface plate 202, an upper surface plate 204, an internal gear 206, a carrier 208, a diamond sheet 210, a plate-like body 211, a sun plate, A gear 212, an internal gear 214, and a container 216 are provided.
The surface processing apparatus 200 sandwiches an internal gear 206 between the lower surface plate 202 and the upper surface plate 204 from the vertical direction. A plurality of carriers 208 are held in the internal gear 206 during grinding. FIG. 4B shows five carriers 208. A diamond sheet 210 is planarly bonded to the lower surface plate 202. A plate-like body 211 is planarly bonded to the upper surface plate 204.

  For example, epoxy glass or SUS (stainless steel) is used as the material of the plate-like body 211. The material of the plate-like body 211 is not particularly limited as long as it can prevent the non-recording surface of the glass blank B from being polished. Further, the thickness and shape of the plate-like body 211 are not particularly limited.

  As shown in FIG. 5, the first main surface of the glass blank B abuts on the diamond sheet 210 on the lower surface plate 202, and the second main surface of the glass blank B contacts the plate-like body 211 on the upper surface plate 204. The carrier 208 is disposed so as to contact. By grinding in such a state, only the 1st main surface of the glass blank B processed into the annular | circular shape can be ground. In addition, the 2nd main surface of the glass blank B is not ground substantially.

  As shown in FIG. 4B, an annular glass blank B is held in a circular hole provided in each carrier 208. On the other hand, the glass blank B is held on the lower surface plate 202 by a carrier 208 having a gear 209 on the outer periphery. The carrier 208 meshes with a sun gear 212 and an internal gear 214 provided on the lower surface plate 202. By rotating the sun gear 212 in the arrow directions shown in FIG. 4B, each carrier 208 revolves while rotating as a planetary gear in each arrow direction. Thereby, the glass blank B is ground using the diamond sheet 210.

  As shown in FIG. 4A, a coolant 218 is accommodated in the container 216. The coolant 218 accommodated in the container 216 is supplied into the upper surface plate 204 by the pump 220 and is collected from the lower surface plate 202. The recovered coolant 218 is returned to the container 216. The coolant 218 removes the facets generated during grinding from the grinding surface. Specifically, when circulating the coolant 218, the surface processing apparatus 200 filters the coolant 218 with the filter 222 provided in the lower surface plate 202 and retains the facets in the filter 222.

When the surface roughness Ra of the first main surface of the glass blank B is less than 0.01 μm, it is difficult to perform grinding using fixed abrasive grains such as the diamond sheet 210. As described above, the glass blank B of the present embodiment has a first main surface with a surface roughness Ra of 0.01 μm or more, and therefore can be ground using a fixed abrasive such as a diamond sheet.
In the present invention, fixed abrasive grains are used as in the past by using a glass blank having excellent flatness, specifically, a glass blank having flatness (for example, 4 μm or less) required for a magnetic disk. There is no need to perform a grinding step (grinding with a surface plate using loose abrasive grains such as alumina) for adjusting the flatness before the grinding step.

(End face polishing process)
Next, the end surface polishing step (step S140) will be described. In the end surface polishing step, the inner peripheral side end surface and the outer peripheral side end surface of the glass blank B are mirror-polished by a brush polishing method. At this time, as the abrasive grains, for example, a slurry containing cerium oxide abrasive grains (free abrasive grains) can be used. By removing the contamination, damage, and scratches on the end surface of the glass substrate by this end surface polishing step, it is possible to suppress the occurrence of ion precipitation that causes corrosion such as sodium and potassium.

(First polishing process)
Next, the first polishing process (step S150) will be described. In the first polishing step, the first main surface of the glass blank B is polished. The machining allowance (polishing amount) in the first polishing step is, for example, about several μm to 10 μm. In addition, the 2nd main surface of the glass blank B is not grind | polished substantially.
In the first polishing step, scratches and distortions remaining on the recording surface are removed by grinding with fixed abrasive grains. In the first polishing process, the surface processing apparatus 200 used in the above-described grinding process (step S130) is used.

The first polishing step is different from the grinding step in that free abrasive grains turbid in the slurry, no coolant is used, and a resin polisher is used instead of the diamond sheet 210. Other than that is the same as that described in the grinding step.
As the free abrasive grains used in the first polishing step, for example, fine particles such as cerium oxide made turbid in the slurry are used. The size of the fine particles is about 1 μm to 2 μm in diameter.

(Chemical strengthening process)
Next, the chemical strengthening step (Step S160) will be described.
In the chemical strengthening step, the chemical strengthening solution is heated to 300 ° C. to 400 ° C., for example. Moreover, after the glass blank B which wash | cleaned is heated by 200 to 300 degreeC, for example, the glass blank B is immersed in a chemical strengthening liquid for 3 hours-4 hours, for example. At this time, the glass blank B is immersed in the chemical strengthening solution in a state of being accommodated in the holder so that the plurality of glass blanks B are held at the end surfaces so that both main surfaces of the glass blank B are chemically strengthened. Is preferred. As the chemical strengthening liquid, for example, a mixed liquid of potassium nitrate (60%) and sodium nitrate (40%) is used.

  Thus, by immersing the glass blank B in the chemical strengthening solution, the lithium ions and sodium ions on the surface layer of the glass blank B are replaced with sodium ions and potassium ions having a relatively large ion radius in the chemical strengthening solution, respectively. Is done. Thereby, the glass blank B is chemically strengthened.

(Second polishing step)
Next, the second polishing process (step S170) will be described.
In the second polishing step, the first main surface of the glass blank B that has been chemically strengthened and sufficiently cleaned is polished. The machining allowance (polishing amount) in the second polishing step is, for example, about 1 μm.
In the second polishing step, the first main surface of the glass blank B is mirror-polished. In the second polishing process, the surface processing apparatus used in the above-described grinding process using the fixed abrasive grains (step S130) and the first polishing process (step S150) is used. In addition, the 2nd main surface of the glass blank B is not grind | polished substantially.

In the second polishing step, the type and particle size of the loose abrasive grains are different from those in the first polishing step. Further, the hardness of the resin polisher used in the first polishing step is different. Other than that is the same as that described in the first polishing step.
As the free abrasive grains used in the second polishing step, for example, fine particles such as colloidal silica made turbid in the slurry are used. The size of the fine particles is about 0.1 μm in diameter.

The glass blank B polished in the second polishing step is washed with, for example, a neutral detergent, pure IPA (isopropyl alcohol).
By the second polishing step, a magnetic disk glass substrate having a recording surface with a surface roughness Ra of 0.2 nm or less is obtained. A magnetic disk is formed by laminating a magnetic layer on the recording surface of the magnetic disk glass substrate.

According to the glass blank forming step of the present embodiment, a glass blank including a first main surface having a surface roughness Ra of 0.01 μm or more and 10 μm or less and a second main surface including a sheer mark can be formed. .
Further, according to the present embodiment, in the glass blank forming step, the first press surface 122 is substantially transferred to the first main surface of the glass blank B, and the second press surface 132 is approximately transferred to the second main surface of the glass blank B. Transcribed. Therefore, by forming the surface roughness Ra of the first press surface 122 and the second press surface 132 differently, a glass blank in which the surface roughness Ra of the first main surface and the surface roughness Ra of the second main surface are different is formed. can do. As a result, a glass blank including a first main surface having a surface roughness Ra of 0.01 μm or more and 10 μm or less and a second main surface having a surface roughness Ra of 0.005 μm or less can be formed.

The reason why the surface roughness Ra of the first main surface is 0.01 μm or more is to perform grinding with fixed abrasive grains efficiently. In addition, the surface roughness Ra of the first main surface is set to 10 μm or less to suppress an increase in machining allowance (polishing amount) required in the polishing process and to perform conventional grinding for adjusting flatness. This is because the surface roughness required for the glass substrate for a magnetic disk is surely adjusted without performing the process. In addition, the surface roughness Ra of the second main surface is set to 0.005 μm or less because foreign matters from the second main surface enter the first main surface, causing problems such as thermal asperity and head crash. It is for suppressing.
Note that grinding with fixed abrasive grains is different from grinding using loose abrasive grains, and the convex portions of the irregularities on the first main surface of the glass blank B are selectively ground, so that grinding can be performed efficiently. it can.

  As described above, the surface roughness Ra of the first main surface of the glass blank B before the surface processing step is adjusted to a value larger than the surface roughness Ra of the second main surface. This is because grinding with a fixed abrasive is efficiently performed. At this time, since the upper limit of the surface roughness Ra of the first main surface is 10 μm, the machining allowance (grinding amount, polishing amount) by grinding and polishing can be suppressed. Further, by performing the surface processing step, the surface roughness Ra of the recording surface of the glass substrate can be set to a necessary roughness (for example, 0.2 nm or less) as the recording surface.

In this embodiment, a sheer mark is formed on the second main surface of the glass blank. However, since the second main surface of the glass blank is used as the non-recording surface of the glass substrate for magnetic disks, conditions such as the surface roughness Ra of the second main surface of the glass blank are required for the non-recording surface of the glass substrate. If the surface quality is satisfied, the surface quality required for the non-recording surface of the magnetic disk glass substrate can be satisfied without grinding or polishing the second main surface.
As a result, according to the manufacturing method of the magnetic disk glass substrate of the present embodiment described above, the magnetic disk glass substrate having a magnetic layer only on one side can be efficiently processed.

In addition, the glass blank shaping | molding process mentioned above is an example, and shape | molding a glass blank provided with the 1st main surface whose surface roughness Ra is 0.01 micrometer or more and 10 micrometers or less, and the 2nd main surface provided with a sheer mark. If possible, the forming method is not limited to the method described above.
Moreover, the manufacturing method of the glass substrate for magnetic disks demonstrated with reference to FIG. 2 is an example, and the order of each process is not limited to this. As long as the glass blank forming process (step S100), the grinding process (step S130), the first polishing process (step S150), and the second polishing process (step S170) are performed in this order, the scribing process (step S110), the shape processing The order of each step of the step (step S120), the end surface polishing step (step S140), and the chemical strengthening step (step S160) can be changed as appropriate.

(Modification 1)
In glass blank forming process of the first embodiment, by using the cutting blade 110, by cutting the molten glass L _G that flows out from the glass outlet 100, to form the gob G _G substantially spherical. However, if the viscosity of the molten glass L _G is small, the only cutting the molten glass L _G, the glass material which is cut is not a generally spherical. Therefore, in such a case, it is preferable to use a gob mold for forming the gob in the glass blank molding step. Hereinafter, with reference to FIG. 6, the glass blank shaping | molding process of this modification is demonstrated.

FIG. 6 is a diagram showing a glass blank forming process of the present modification. Fig.6 (a) is a figure which shows the state before a gob is formed. FIG. 6B is a diagram illustrating a state where the gob is formed. FIG. 6C is a diagram illustrating a state where the gob is pressed.
As shown in FIG. 6, the gob mold 112 is disposed below the cutting blade 110. The gob molding die 112 is a block-like member having a hemispherical recess 112a formed in the upper portion thereof, and is divided into two blocks 113 and 114 around the recess 112a.

In the state of FIG. 6A, the cutting blades 110 are separated from each other. Further, the blocks 113 and 114 of the gob mold 112 are in close contact with each other to form a recess 112a. In this state, the molten glass _{L G} that is continuously flowing out from the glass outlet 100 is received in the recess 112a of the gob mold 112.
Next, as shown in FIG. 6 (b), the cutting blade 110 which is disposed below the glass outlet 100, to cut the molten glass L _G that is continuously flowing out from the glass outlet 100. Further, the blocks 113 and 114 are moved so as to be separated from each other. Thus, falling molten glass L _G held in the recess 112a of the gob mold 112, the gob G _G substantially spherical by the surface tension of the molten glass L _G. In this way, a molten glass lump (gob) _GG is formed.

Gob G _G substantially spherical, which is formed by the molten glass L _G is cut by the cutting blade 110 and falls vertically. Then, when the gob G _G are dropped into a vertical direction is passing between the first mold 120 and second mold 130, the first mold 120 and second mold 130 with each other The first mold 120 and the second mold 130 are moved in the approaching direction. Thereafter, as shown in FIG. 6C, the gob _GG is pressed between the first mold 120 and the second mold 130. Similar to the first embodiment, the surface roughness Ra of the second press surface 132 of the second die 130 is smaller than the surface roughness Ra of the first press surface 122 of the first die 120. Also in this modification, always as shear marks are formed on the pressed second main surface with a second press surface 132, in advance, the outflow rate of the molten glass L _G, the cutting blade 110 is a molten glass L _G Conditions such as the cutting timing, the speed and timing at which the first mold 120 and the second mold 130 move are adjusted. Therefore, a shear mark is always formed on the second main surface of the glass blank B.
Since this step is the same as that of the first embodiment described with reference to FIG. 3C, detailed description thereof is omitted.

As described above, in this modification, the use of gob mold 112 hemispherical recess 112a is formed in the upper, even if the viscosity of the molten glass L _G is small, substantially spherical gob G _G Can be formed. Thereby, the glass blank provided with the 1st main surface whose surface roughness Ra is 0.01 micrometer or more and 10 micrometers or less, and the 2nd main surface provided with a sheer mark can be shape | molded.

(Modification 2)
In the first embodiment, the first main surface of the glass blank B contacts the diamond sheet 210 on the lower surface plate 202, and the second main surface of the glass blank B contacts the plate-like body 211 on the upper surface plate 204. Thus, although the carrier 208 is arrange | positioned, arrangement | positioning of the diamond sheet 210, the plate-shaped body 211, and the carrier 208 is not limited to this.
Hereinafter, with reference to FIG. 7, the grinding process of this modification is demonstrated. In addition, although the following description demonstrates a grinding process, this modification can be applied similarly also in a grinding | polishing process.

FIG. 7 is a diagram illustrating an example of a grinding process according to the present modification. As shown in FIG. 7, a plate-like body 211 is bonded to the lower surface plate 202 in a planar manner. A diamond sheet 210 is planarly bonded to the upper surface plate 204. Other configurations are the same as those of the first embodiment.
As shown in FIG. 7, the second main surface of the glass blank B abuts on the plate-like body 211 on the lower surface plate 202, and the first main surface of the glass blank B contacts the diamond sheet 210 on the upper surface plate 204. The carrier 208 is disposed so as to contact. By grinding in such a state, only the 1st main surface of the glass blank B processed into the annular | circular shape can be ground.
According to this modification, only the first main surface of the glass blank B can be ground. When only one surface of the glass substrate is used as the magnetic recording layer, the second main surface that does not need to be ground can be protected and ground. In particular, when the sheer mark is formed on the second main surface of the glass blank B, it is not necessary to remove the sheer mark, so that the glass blank B can be surface-processed efficiently.

(Modification 3)
In 1st Embodiment and the modification 2, although the process of grinding the glass blank B using the one carrier 208 in the direction perpendicular | vertical to a surface plate between the lower surface plate 202 and the upper surface plate 204 was demonstrated. However, the present invention is not limited to this.
Hereinafter, the grinding process of this modification will be described with reference to FIG. In addition, although the following description demonstrates a grinding process, this modification can be applied similarly also in a grinding | polishing process.

FIG. 8 is a diagram illustrating an example of a grinding process according to the present modification. As shown in FIG. 8, a diamond sheet 210 is planarly bonded to the lower surface plate 202. A diamond sheet 210 is planarly bonded to the upper surface plate 204.
One carrier 208 is arranged so that the first main surface of the glass blank B comes into contact with the diamond sheet 210 on the lower surface plate 202. Further, another carrier 208 is arranged so that the first main surface of the glass blank B comes into contact with the diamond sheet 210 on the upper surface plate 204. A plate-like body 211 is arranged between the two carriers 208. By grinding in such a state, only the upper surface (first main surface) of the glass blank B held on the upper carrier 208 is ground, and the glass blank B held on the lower carrier 208 is lower ( Only the first main surface) is ground.

  According to this modification, only the first main surface of the glass blank B can be ground. When only one surface of the glass substrate is used as the magnetic recording layer, the second main surface that does not need to be ground can be protected and ground. In particular, according to this modification, the production efficiency can be doubled by using two carriers 208 and disposing the plate-like body 211 between the two carriers 208.

  An adhesive layer, a soft magnetic layer, a non-magnetic underlayer, a perpendicular magnetic recording layer, a protective layer, and a lubricating layer are sequentially laminated on the recording surface of the magnetic disk glass substrate thus obtained. Can be produced. For example, a Cr alloy is used for the adhesion layer, and functions as an adhesion layer with the glass substrate. For the soft magnetic layer, for example, a CoTaZr alloy or the like is used. As the nonmagnetic underlayer, for example, a granular nonmagnetic layer is used. For example, a granular magnetic layer is used for the perpendicular magnetic recording layer. In addition, a material made of hydrogen carbon is used for the protective layer, and a fluorine resin or the like is used for the lubricating layer, for example.

More specifically, an in-line sputtering apparatus is used for a glass substrate, and a CrTi adhesion layer, a CoTaZr / Ru / CoTaZr soft magnetic layer, and a CoCrSiO ₂ non-coating layer are formed on both main surfaces of the glass substrate. A magnetic granular underlayer, a CoCrPt—SiO ₂ · TiO ₂ granular magnetic layer, and a hydrogenated carbon protective film are sequentially formed. Further, a perfluoropolyether lubricating layer is formed on the formed uppermost layer by dipping.

  In the magnetic disk, the magnetic head of the hard disk device floats about 5 nm from the surface of the magnetic disk as the magnetic disk rotates at a high speed, for example, 7200 rpm. In this state, the magnetic head records or reads information on the magnetic layer. By flying the magnetic head, the magnetic layer can be recorded or read at a close distance without sliding against the magnetic disk, thus miniaturizing the magnetic recording information area and increasing the magnetic recording density. To do.

In order to confirm the effect of the present invention, a plurality of glass blanks B having different surface roughness Ra on the first main surface were formed, and then a glass substrate for a magnetic disk was produced by each step shown in FIG. Table 1 shows the surface roughness Ra of the first main surface, the surface roughness Ra of the second main surface, and the flatness of each example and each comparative example.
The glass material is aluminosilicate glass (SiO ₂ 57-74%, ZnO ₂ 0-2.8%, Al ₂ O ₃ 3-15%, LiO ₂ 7-16%, Na ₂ O 4-4 14%) was used. In Examples 1 to 7 and Comparative Examples 2 to 6, a sheer mark is formed on the second main surface of the glass blank B. In Comparative Example 1, a sheer mark is formed on the first main surface of the glass blank B. Is done.

The scribing shown in step S110 was performed on the glass blank B of each example and each comparative example.
As shown in Table 1, in the glass blanks B of Examples 1 to 5 and Comparative Examples 1 and 2, the surface roughness Ra of the first main surface is 1 μm or less. Therefore, in the scribing step (step S110), the scriber A cutting line could be suitably formed on the first main surface side using. On the other hand, since the glass roughness B of Examples 6 and 7 and Comparative Examples 3 to 6 has a surface roughness Ra of the first main surface larger than 1 μm, it is cut using a scriber in the scribe process (step S110). It was difficult to form the lines uniformly.
Here, in the glass blanks B of Examples 6 and 7 and Comparative Examples 3 to 6, the surface roughness Ra of the first main surface is larger than 1 μm, but the surface roughness Ra of the second main surface is 1 μm or less. Therefore, a cutting line could be formed on the second main surface side.
In addition, when the glass blank B is a perfect circle and it is not necessary to adjust the size of the outer diameter, it is not necessary to perform scribing, and an inner hole may be formed using a core drill or the like.

Further, the glass blank B of each example and each comparative example was ground with the fixed abrasive shown in step S130.
As shown in Table 1, since the glass blanks B of Examples 1 to 7 and Comparative Examples 1 and 3 to 6 have a surface roughness Ra of the first main surface of 0.01 μm or more, a grinding process (step S130). ) Could be ground with fixed abrasive grains. On the other hand, the glass blank B of Comparative Example 2 has a surface roughness Ra of the first main surface smaller than 0.01 μm and cannot be ground with fixed abrasive grains in the grinding step (step S130). It was.

Moreover, the 1st grinding | polishing process (step S150) and the 2nd grinding | polishing process (step S170) were further given with respect to the glass blank B of each Example and each comparative example (except the comparative example 2).
In the first polishing step (step S150), polishing was performed using cerium oxide (average particle size; diameter 1 to 2 μm) and a hard urethane pad. The machining allowance (polishing amount) was 3 μm.
In the second polishing step (step S170), polishing was performed using colloidal silica (average particle size; diameter 0.1 μm) and a soft polyurethane pad. The machining allowance (polishing amount) was 1 μm.

On the recording surface of the produced glass substrate, using an in-line type sputtering apparatus, a CrTi adhesion layer, a CoTaZr / Ru / CoTaZr soft magnetic layer, a CoCrSiO ₂ non-magnetic granular underlayer, CoCrPt—SiO ₂ · TiO ₂ A granular magnetic layer and a hydrogenated carbon protective film were sequentially formed. Thereafter, a perfluoropolyether lubricating layer was formed on the formed uppermost layer by dipping. Thereby, a magnetic disk was obtained.

In order to evaluate the flying stability of the magnetic head with respect to the obtained magnetic disk, an LUL durability test (600,000 times) was performed. LUL endurance test means that the HDD is placed in a constant temperature and humidity chamber with a temperature of 70 ° C and humidity of 80%, and the head is moved in a cycle of lamp-> ID stop->lamp-> ID stop->. This is a test to investigate the occurrence of abnormalities such as dirt and wear on the head after the test. Ten units were used for one experimental level, and as a result of the LUL test of 80,000 times / day × 7.5 days = 600,000 times, when even one HDD showed an abnormality, it was evaluated as rejected.
Table 1 shows the flatness after processing, the surface roughness after processing, and the LUL durability test results (pass and fail) in Examples 1 to 7 and Comparative Examples 1 and 3 to 6.

  As shown in Table 1, since the glass blanks B of Examples 1 to 7 and Comparative Examples 1 and 3 have a flatness of 4 μm or less, the flatness of the processed glass substrate can be 4 μm or less. It was. On the other hand, since the flatness of the glass blanks B of Comparative Examples 4 to 6 was larger than 4 μm, the flatness of the glass substrate after processing was larger than 4 μm.

Moreover, as Table 1 shows, since the glass blank B of Examples 1-7 and Comparative Examples 1 and 4-6 has surface roughness Ra of the 1st main surface of 10 micrometers or less, it is a grinding process (step S130). ) In order to remove cracks, it is possible to suppress an increase in the machining allowance (polishing amount) required in the first polishing step (step S150) and the second polishing step (step S170). Therefore, by performing the first polishing step (step S150) and the second polishing step (step S170), a glass substrate for magnetic disk having a surface roughness Ra after processing of 0.2 nm or less can be manufactured. In this way, it is possible to adjust to Ra required as a magnetic disk glass substrate.
On the other hand, the glass blank B of Comparative Example 3 has a surface roughness Ra of the first main surface larger than 10 μm. Therefore, in order to remove cracks generated in the grinding process (step S130), the first polishing process (step In S150), the machining allowance (polishing amount) required in the second polishing step (step S170) is larger than those in Examples 1-7 and Comparative Examples 1, 4-6. Therefore, by performing the first polishing step (step S150) and the second polishing step (step S170), a glass substrate for a magnetic disk having a surface roughness Ra after processing of 0.2 nm or less could not be manufactured. .

  Moreover, since the glass roughness B of Examples 1-7 has surface roughness Ra of the 2nd main surface being 0.005 micrometer or less, the result of the LUL durability test was a pass. However, since the glass blank B of Comparative Example 1 had a sheer mark formed on the first main surface, the result of the LUL durability test was unacceptable.

  In addition, this invention is not limited to the said embodiment, a modified example, and the form of an Example, It can implement by changing suitably. The numerical values, materials, sizes, processing procedures, and the like in the above-described embodiments and modifications are examples, and can be appropriately changed and implemented within a range where the effects of the present invention are exhibited. Other modifications can be made as appropriate without departing from the scope of the object of the present invention.

DESCRIPTION OF SYMBOLS 100 Glass outlet 110 Cutting blade 112 Gob mold 113,114 Block 120 1st type | mold 122 1st press surface 124 Spacer 130 2nd type | mold 132 2nd press surface 200 Surface processing apparatus 202 Lower surface plate 204 Upper surface plate 206 Inter Null gear 208 Carrier 209 Gear 210 Diamond sheet 211 Plate body 212 Sun gear 214 Internal gear 216 Container 218 Coolant 220 Pump 222 Filter B Glass blank L _G molten glass G _G gob

Claims (9)

A method for producing a glass substrate for a magnetic disk, using a glass blank that is cut by cutting molten glass,
A glass blank having a first main surface having a surface roughness Ra of 0.01 μm or more and 10 μm or less and a second main surface having a sheer mark and having a flatness necessary as a glass substrate for a magnetic disk is formed. A glass blank molding process;
A surface processing step of processing only the first main surface of the glass blank;
A method for producing a glass substrate for a magnetic disk, comprising: The glass blank forming step
A cutting step of cutting the molten glass;
Dropping the lump of glass formed by being cut by the cutting step;
Using the first mold having a surface roughness Ra of 0.01 μm or more and 10 μm or less, and the second mold, while the glass lump is falling, the glass lump is removed from the substantially horizontal direction. A pressing step in which the first mold molds the first main surface and the second mold molds the second main surface with the sheer mark by pressing;
The manufacturing method of the glass substrate for magnetic discs of Claim 1 which has these.   In the pressing step, the glass block is pressed using a first mold having a surface roughness Ra of 0.01 μm or more and 10 μm or less and a second mold having a surface roughness Ra of 0.005 μm or less. The manufacturing method of the glass substrate for magnetic discs of Claim 2.   In the pressing step, the glass lump is pressed using a first mold having a surface roughness Ra of 0.01 μm or more and 1 μm or less and a second mold having a surface roughness Ra of 0.005 μm or less. The manufacturing method of the glass substrate for magnetic discs of Claim 2. Between the glass blank forming step and the surface processing step, a scribe step for scribing the glass blank is provided.
The manufacturing method of the glass substrate for magnetic discs of Claim 4. The surface processing step includes
A grinding step of grinding the first main surface using fixed abrasive grains;
After the grinding step, a polishing step for polishing the first main surface using loose abrasive grains;
The manufacturing method of the glass substrate for magnetic discs in any one of Claims 1 thru | or 5 which has these.   The said grinding process is a manufacturing method of the glass substrate for magnetic discs of Claim 6 ground using the fixed abrasive grain containing a diamond particle.   The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the flatness required for the glass substrate for a magnetic disk is 4 μm or less. A glass substrate for a magnetic disk manufactured by the method for manufacturing a glass substrate for a magnetic disk according to any one of claims 1 to 8,
Of the main surface of the glass substrate for magnetic disk, a magnetic layer formed only on the main surface on the side where the first main surface of the glass blank is processed,
A magnetic recording medium comprising: