JP2016126808A - Method for manufacturing substrate for magnetic disk and end surface polishing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a substrate for a magnetic disk, in which a productivity can be further improved by improving a polishing rate at an end surface of the substrate for a magnetic disk.SOLUTION: A method polishes an end surface on the outer peripheral side of a disk-shaped substrate by forming a magnetic slurry mass containing a magnetic substance and abrasive grains in a ring shape by magnetism generating means, bringing the end surface on the outer peripheral side of the disk-shaped substrate into contact with the inner peripheral side of the magnetic slurry mass formed in the ring shape, and moving the magnetic slurry mass formed in the ring shape and the disk-shaped substrate relatively.SELECTED DRAWING: Figure 2

Description

  The present invention is used for a method of manufacturing a magnetic disk substrate used in a magnetic disk mounted on a magnetic recording apparatus such as a hard disk drive (hereinafter abbreviated as “HDD”), and for end polishing of the magnetic disk substrate. The present invention relates to an end surface polishing apparatus.

  One of information recording media mounted on a magnetic recording device such as an HDD is a magnetic disk. A magnetic disk is configured by forming a thin film such as a magnetic layer on a disk-shaped substrate, and an aluminum alloy substrate or a glass substrate is used as the substrate. A glass substrate is harder than an aluminum alloy substrate, and has an advantage of excellent impact resistance. The surfaces of these substrates are polished and smoothed with high precision so as to reduce the flying height of the magnetic head as much as possible, thereby realizing high recording density. In recent years, the demand for further increase in recording capacity and price of HDDs has increased, and in order to realize this, it has become necessary to further improve the quality and cost of magnetic disk substrates. ing.

A magnetic disk substrate is usually manufactured by sequentially performing steps such as shape processing (end surface grinding and chamfering), end surface polishing, main surface grinding, main surface polishing, and chemical strengthening on a disk-shaped substrate.
As described above, there is a demand for a magnetic disk that is inexpensive and can achieve a high recording density. However, in order to increase the recording density of the magnetic disk, a high level of processing accuracy is required for the substrate. The same applies to the end surface shape as well as the main surface.

As disclosed in the following Patent Document 1, conventionally, the end surface of a glass substrate for a magnetic disk is generally processed by polishing the end surface using a grindstone and then polishing the end surface of the brush. It was.
Patent Document 2 below discloses a method of polishing an end surface of a glass substrate for a magnetic disk by applying a magnetic field to a slurry containing ferrite magnetic particles and abrasive grains.

JP-A-11-28649 JP 2005-50501 A

  As described above, there is a demand for an inexpensive magnetic disk substrate that can achieve a high recording density, and further improvement in productivity is desired with respect to the polishing of the end face of the substrate.

  However, the method of polishing the end face of the glass substrate using a conventional polishing brush has a limit in improving the polishing rate, and it has been difficult to further improve productivity.

  Further, even when the magnetic disk and the method for polishing the end surface of the glass substrate for magnetic disk by applying a magnetic field to the slurry containing ferrite-based magnetic particles and abrasive grains disclosed in Patent Document 2 described above, the distance between the magnetic body and the magnet is small. Since they are separated from each other, there is a problem that the force for holding the magnetic body is weak and the processing time is long.

  Therefore, the present invention improves the polishing rate of the end face of the magnetic disk substrate and enables further improvement of production efficiency, and the end face suitably used for the end face polishing treatment of the magnetic disk substrate. An object is to provide a polishing apparatus.

  The inventor forms and holds a magnetic slurry lump 26 including a magnetic body and abrasive grains between a pair of magnets 21 and 22 as magnetism generating means, and a disk-shaped glass substrate for a magnetic disk there. A conventional method was studied in which end face polishing was performed while contacting the outer peripheral side end faces of 10 and rotating both the magnetism generating means and the glass substrate (see FIG. 4). According to the study of the present inventor, it has been found that in this case, the magnetic body and the abrasive grains held between the magnets 21 and 22 are gradually scattered during processing by the rotation of the magnetism generating means. Therefore, the shear stress that the glass substrate receives from the lump of magnetic slurry during processing changes, and a problem that a stable processing rate cannot be obtained occurs.

Therefore, as a result of further investigation, the inventor has formed a magnetic slurry lump in a ring shape by the magnetism generating means, and the glass substrate is formed on the inner peripheral side of the magnetic slurry lump formed in the ring shape. It has been found that the above-mentioned problem can be solved by bringing the outer peripheral side end face into contact (that is, inscribed) and performing the end face polishing treatment.
That is, in order to solve the above problems, the present invention has the following configuration.

(Configuration 1)
A method of manufacturing a magnetic disk substrate including an end surface processing for processing an end surface of a disk-shaped substrate, wherein the end surface processing is performed by ringing a lump of magnetic slurry containing a magnetic body and abrasive grains by a magnetism generating means. An outer peripheral side end surface of the disk-shaped substrate is brought into contact with an inner peripheral side of the magnetic slurry lump formed in the ring shape and the magnetic slurry lump formed in the ring shape is formed. A method of manufacturing a magnetic disk substrate, comprising: an end surface polishing process for polishing an outer peripheral side end surface of the disk-shaped substrate while relatively moving the disk-shaped substrate.

(Configuration 2)
The chamfered surface of at least one of the chamfered surface between the side wall surface of the outer peripheral side end surface of the disk-shaped substrate and the two main surfaces of the disk-shaped substrate and the side wall surface is simultaneously polished. A manufacturing method of a magnetic disk substrate according to Configuration 1.

(Configuration 3)
The disk-shaped substrate is brought into contact with the magnetic slurry lump so that the rotation axis of the disk-shaped substrate is not perpendicular to a plane formed by the magnetic slurry lump formed in the ring shape, and end face polishing treatment is performed. A method for manufacturing a magnetic disk substrate according to Configuration 1 or 2, wherein the method is performed.

(Configuration 4)
4. The method for manufacturing a magnetic disk substrate according to any one of Structures 1 to 3, wherein the disk-shaped substrate is a stacked body in which a plurality of disk-shaped substrates are stacked.

(Configuration 5)
An end surface polishing apparatus used for end surface polishing processing for polishing an end surface of a disk-shaped substrate for a magnetic disk, and a magnetic slurry lump including a magnetic body and abrasive grains is formed and held in a ring shape. And a magnetic slurry lump formed in the ring shape, wherein the outer peripheral side end surface of the disk-shaped substrate is brought into contact with an inner circumferential side of the lump of magnetic slurry formed in the ring shape. An end surface polishing apparatus for polishing an outer peripheral side end surface of a disk-shaped substrate while relatively moving the disk-shaped substrate.

According to the present invention, the polishing rate of the end face of the magnetic disk substrate can be improved, and the production efficiency can be further improved. In addition, it is possible to improve the shape accuracy of the chamfered surface and the side wall surface of the substrate end surface, and to perform stable end surface processing that can finish the end surface with high quality.
Moreover, the end surface polishing apparatus of the present invention can be suitably used for the end surface polishing processing of the magnetic disk substrate of the present invention.

It is sectional drawing which shows the end surface shape of the glass substrate for magnetic discs. It is principal part sectional drawing for demonstrating the end surface grinding | polishing process using the magnetic slurry of this invention. It is sectional drawing along the plane which the lump of the magnetic slurry in FIG. 2 comprises. It is a principal part perspective view for demonstrating the end surface grinding | polishing process using the conventional magnetic slurry.

Hereinafter, embodiments for carrying out the present invention will be described in detail. As described above, an aluminum alloy-based substrate also exists as a magnetic disk substrate. Here, a glass substrate will be described as an example.
FIG. 1 is a cross-sectional view of the outer peripheral end of a magnetic disk glass substrate 1 to which the present invention is applied. Although the glass substrate 1 is not shown in FIG. 1, the whole having a circular hole in the center is formed in a disk shape, and the main surfaces 11, 11 on the front and back sides thereof and between these main surfaces 11, 11 are formed. An outer peripheral end surface and an inner peripheral end surface are formed.

  The end surface on the outer peripheral side of the glass substrate 1 has a side wall surface 12a orthogonal to the main surface 11 and two chamfered surfaces formed between the side wall surface 12a and the front and back main surfaces 11, 11 ( Chamfered surfaces) 12b and 12b. Moreover, although it does not show in figure about the end surface of the inner peripheral side of the said glass substrate 1, similarly to the said outer peripheral side end surface, the side wall surface orthogonal to the main surface 11 and the main surfaces 11 and 11 of this side wall surface and front and back Are formed in a shape composed of two chamfered surfaces (chamfered surfaces) formed between the two.

  In the case of a magnetic disk, for example, a nominal 2.5 inch disk, the outer diameter of the glass substrate 1 is 65 mm and the inner diameter is 20 mm. In the case of a nominal 3.5 inch disk, the outer diameter of the glass substrate 1 is 95 mm and the inner diameter is Finished to 25 mm. Here, the inner diameter is the inner diameter of a circular hole in the center of the glass substrate 1.

  The main surface 11, the outer peripheral side end surface, and the inner peripheral side end surface of the glass substrate 1 for magnetic disk are all polished (mirror polished) to have a predetermined surface roughness. Both the outer peripheral side end surface and the inner peripheral side end surface of the glass substrate 1 are finished to the end face shape as described above, and the surface roughness is finished to a mirror surface state with Rz of 1 μm or less and Ra of 0.1 μm or less, for example. It is usually sought to be.

The magnetic disk glass substrate 1 is formed by subjecting a glass plate 10 obtained by processing, for example, a glass plate obtained by a direct press method or a float method into a predetermined disc shape, and grinding and polishing an end face ( (Mirror polishing), grinding of the main surface, mirror polishing, chemical strengthening, etc. are performed in order.
In the present invention, a glass plate obtained by processing a glass plate obtained by a direct press method or a float method into a predetermined disc shape (glass base plate) is processed and processed on the glass substrate. For the sake of convenience of explanation, all of the final product glass substrates are referred to as a glass substrate or a magnetic disk glass substrate.

First, the end face grinding process will be described.
Usually, the end face grinding can be performed using a so-called general-purpose grindstone.
This total shape grindstone is formed in a cylindrical shape of a predetermined size, and has a groove shape for forming an end face shape of the glass substrate on its outer peripheral surface. Specifically, the glass substrate The groove shape is such that the shape of both the side wall surface and the chamfered surface can be transferred to the outer peripheral side end surface. This total shape grindstone is formed in a predetermined dimensional shape in consideration of the target dimensional shape of the ground surface of the glass substrate.

  For example, a grindstone in which diamond abrasive grains, which are high-rigidity grindstones, are fixed by an electrodeposition bond, a metal bond, a resin bond, or the like is suitable as the total shape grindstone used in the end face grinding. As the abrasive grains, alumina abrasive grains, cubic boron nitride abrasive grains, and the like can be used. Moreover, it can also be set as the multistage grinding using the grindstone which changed the abrasive grain and the fixing method of the abrasive grain.

In the present invention, subsequent to the above-described end surface grinding, an end surface polishing process using a magnetic slurry containing a magnetic body and abrasive grains is performed.
Next, the end surface polishing treatment of the present invention will be described in detail.
In the end surface polishing treatment of the present invention, a magnetic slurry lump including a magnetic material and abrasive grains is formed in a ring shape by a magnetism generating means, and the inner peripheral side of the magnetic slurry lump formed in the ring shape The outer peripheral side end face of the glass substrate is polished while the outer peripheral side end face of the glass substrate is brought into contact with and the mass of the magnetic slurry formed in the ring shape and the glass substrate are relatively moved.

  Further, the end surface polishing treatment of the present invention includes a magnetic generating means for forming and holding a lump of a magnetic slurry including a magnetic material and abrasive grains in a ring shape, and the magnet formed in the ring shape. The outer peripheral side end surface of the glass substrate while the outer peripheral side end surface of the glass substrate is brought into contact with the inner peripheral side of the slurry lump and the magnetic slurry lump formed in the ring shape and the glass substrate are relatively moved. An end surface polishing apparatus for polishing the surface can be preferably used.

  2 and 3 are diagrams for explaining an end surface polishing process using the magnetic slurry of the present invention, and FIG. 2 is a cross-sectional view of a main part for describing an end surface polishing process using the magnetic slurry of the present invention. FIG. 3 is a cross-sectional view taken along a plane formed by the lump of magnetic slurry in FIG.

In the end surface polishing treatment in the present invention, the end surface of the glass substrate is polished using a lump of magnetic slurry formed in a ring shape. This magnetic slurry includes a magnetic material and abrasive grains.
As shown in FIG. 2, for example, a pair of magnets 21 and 22 that are permanent magnets and a stopper portion 23 are included. In addition, you may cover the said magnets 21 and 22 and the stopper part 23 within the exterior member formed from the nonmagnetic material as needed.

  In one embodiment shown in FIG. 2, the pair of magnets 21 and 22 as magnetism generating means are both formed in a cylindrical shape, and the stopper portion 23 is interposed between the cylindrical magnets 21 and 22. Is arranged. The lump 25 of the magnetic slurry is formed and held in a ring shape between the magnets 21 and 22 and inside the stopper portion 23. Then, the outer peripheral side end face of the glass substrate 10 is brought into contact with the inner peripheral side of the magnetic slurry lump 26 formed in the ring shape, and the magnetic slurry lump 26 formed in the ring shape and the glass substrate 10 are relatively moved. The outer peripheral side end surface of the glass substrate is polished while being moved. The stopper portion 23 is made of, for example, a non-magnetic material, and maintains a predetermined distance between the magnets 21 and 22, and also includes a magnetic body or polishing abrasive contained in the magnetic slurry lump 26 formed in the ring shape. The particles are prevented from splashing outside during processing.

  The pair of magnets 21 and 22 are close to each other and function as magnetism generating means, and form lines of magnetic force between these magnets 21 and 22. In the example shown in FIG. 2, for example, a pair of magnets arranged in the thickness direction of the glass substrate 10 so as to be separated from each other so that the N-pole surface and the S-pole surface face each other is used as the magnetism generating means. Between the magnets 21 and 22, as described above, a stopper made of a non-magnetic material is used to set a predetermined distance between the end face of the N pole of the magnet 21 and the end face of the S pole of the magnet 22. A portion 23 is provided. Since the magnetic slurry lump 26 is a portion that contacts the outer peripheral side end surface of the glass substrate 10 and moves relative to the end surface, the magnetic slurry lump 26 has a certain degree of magnetic force in order to ensure the rigidity of the magnetic slurry lump 26. Is desired. For this reason, it is preferable that the separation distance between the end face of the N pole of the magnet 21 and the end face of the S pole of the magnet 22 is short, but if it is too short, it becomes difficult to carry out when inserting the glass substrate between the magnets. Therefore, it is preferable that the separation distance between the end face of the N pole of the magnet 21 and the end face of the S pole of the magnet 22 is set within a certain predetermined range.

  The magnetism generating means is not limited to a permanent magnet, and an electromagnet can be used, for example.

  The glass substrate 10 is rotatably held by holding means (not shown). The glass substrate 10 held by the holding means is brought close to the inner peripheral side of the magnetic slurry lump 26 formed in a ring shape between the magnets 21 and 22, and the magnetic slurry lump 26 and the outer peripheral side end surface of the glass substrate 10 are Contact. The magnetism generating means comprising the pair of magnets 21 and 22 and the holding means for holding the glass substrate 10 are connected to a drive motor (not shown). Therefore, the outer peripheral side end surface of the glass substrate 10 is polished by rotating the magnets 21 and 22 and the glass substrate 10 to relatively move the outer peripheral side end surface of the glass substrate 10 and the magnetic slurry lump 26. Can do.

  As the magnetic material of the magnetic slurry used for the end surface polishing, a material obtained by dispersing magnetic particles (magnetic particles) in a dispersion medium is used. The magnetic particles may be any ferromagnetic material, and from the viewpoint that the magnetic force is particularly strong, particles made of Fe are preferable. Moreover, you may use what mixed Fe and ferromagnetic materials other than Fe. The particle size of the magnetic particles is preferably within the range of 0.1 to 10 μm. By setting it as the said range, an abrasive grain can be hold | maintained suitably. As the dispersion medium, nonpolar oil or polar oil can be suitably used. As a dispersion medium, when using nonpolar oil or polar oil, it is preferable that it has a viscosity of 100-1000 (mPa * second) at room temperature (20 degreeC), for example. Further, a surfactant may be added to the magnetic material.

  Moreover, as abrasive grains contained in the magnetic slurry, known abrasive grains of glass substrates such as cerium oxide, colloidal silica, zirconia oxide, alumina abrasive grains, and diamond abrasive grains can be used. The particle size of the abrasive grains is, for example, 0.5 to 3 μm. By using abrasive grains having a particle size in this range, the end face of the glass substrate can be satisfactorily polished. The abrasive grains are preferably contained in the magnetic slurry, for example, about 3 to 15% by volume.

  The viscosity of the magnetic slurry is preferably 1000 to 2000 mPa · sec at room temperature (20 ° C.) by adjusting the concentration of the magnetic material, from the viewpoint of forming the magnetic slurry lump 26 and performing end face polishing efficiently. If the viscosity is low (the concentration of the magnetic material is low), it is difficult to form the lump 26, and it is difficult to perform the relative movement while being pressed against the end face of the glass substrate 10 for polishing. On the other hand, when the viscosity of the magnetic slurry is excessively high, it is difficult to form a uniform pressed state. The magnetic flux density in the magnetism generating means is preferably 0.3 to 0.8 Tesla from the viewpoint of forming the magnetic slurry lump 26 and efficiently polishing the end face. In addition, the yield stress of the magnetic slurry containing the magnetic material and the abrasive grains is preferably 30 kPa or more, more preferably 30 to 60 kPa, with a 0.4 Tesla magnetic field applied.

  Here, the yield stress (yield shear stress) of the magnetic slurry can be obtained, for example, by the following method. Using a device incorporating a magnetic field application means (permanent magnet, electromagnet, etc.) capable of applying a predetermined magnetic field to a rotational viscometer, the relationship between the shear rate and the shear stress of the magnetic slurry was determined, and the obtained shear rate and The yield stress of the magnetic slurry can be obtained by approximating the relationship of the shear stress using the known Casson equation.

  The yield stress affects the pressure that the glass substrate receives from the magnetic slurry, that is, the shear stress, when the magnetic slurry held by the magnetic field and the edge of the glass substrate move relative to each other. Therefore, the higher the yield stress of the magnetic slurry (the higher the shear stress during the magnetic slurry flow), the more efficiently the polishing by contact between the abrasive grains and the glass substrate can be achieved, and the processing rate can be improved.

  In the end surface polishing process of the present invention, as described above, a magnetic slurry lump containing a magnetic material and abrasive grains is formed in a ring shape by the magnetism generating means, and the magnetic slurry formed in this ring shape is formed. The outer peripheral side end surface of the glass substrate can be polished while the outer peripheral side end surface of the glass substrate is brought into contact with the inner peripheral side of the lump, and the lump of the magnetic slurry formed in the ring shape and the glass substrate are relatively moved. It is a feature.

It is preferable to rotate the glass substrate 10 and the magnets 21 and 22 (or magnetic slurry lump) so that the relative speeds of the peripheral speeds at the processing position (contact position) are 50 to 500 m / min. At this time, both rotation directions may be opposite to each other (up cut) or the same direction (down cut) at the processing position.
In the present invention, it is preferable that the absolute value of the peripheral speed of the glass substrate 10 is larger than the absolute value of the peripheral speed of the magnets 21 and 22 from the viewpoint of improving the shape accuracy of the glass substrate after processing. In the opposite case, the roundness of the outer peripheral edge of the glass substrate may be deteriorated by processing.

  In the end surface polishing process of the present invention, when the magnets 21 and 22 are rotating, the ring-shaped magnetic slurry lump 26 formed and held between the magnets 21 and 22 is scattered to the outside by centrifugal force. Can be prevented. Therefore, the shear stress that the glass substrate receives from the magnetic slurry lump hardly changes during processing, and a stable processing rate can be obtained over a long period of time, and stable processing with less shape variation after processing becomes possible. .

  As described above, for example, as shown in FIG. 4, when the outer peripheral side end face of the glass substrate 10 is brought into contact with the outer peripheral side of the magnetic slurry lump (so-called circumscribing), polishing is performed. Due to the rotation of the generating means, the magnetic slurry held between the magnets 21 and 22 is gradually scattered during processing, so that the shear stress that the glass substrate receives from the mass of magnetic slurry during processing changes and is stable. This causes a problem that the processed rate cannot be obtained.

According to the end surface polishing treatment of the present invention, the side wall surface 12a of the outer peripheral side end surface of the glass substrate 10 and the two chamfered surfaces 12b between both the main surfaces 11 and 11 of the glass substrate 10 and the side wall surface 12a. At least one chamfered surface can be polished simultaneously.
In the present invention, the contact between the chamfered surface of the substrate and the magnetic slurry can be promoted by inclining the horizontal plane of the glass substrate in an appropriate direction with the lump 26 of the magnetic slurry. it can. As a result, it is possible to suppress the difference in processing rate between the chamfered surface and the side wall surface of the glass substrate end surface, and it is possible to finish both the chamfered surface and the side wall surface to the same quality mirror surface within a predetermined processing time. It becomes.

  Further, in the present invention, the glass substrate is made of the magnetic slurry in a state where the rotation axes of the magnets 21 and 22 holding the magnetic slurry lump 26 are inclined with respect to the axis orthogonal to the main surface of the glass substrate 10. You may make it contact an lump and perform an end surface grinding | polishing process. Also by this, it can suppress that the difference in a processing rate arises with the chamfering surface and side wall surface of a glass substrate end surface.

  The machining allowance by the end surface polishing treatment in the present invention is preferably in the range of 1 to 30 μm. Further, if it is 10 μm or less, the shape accuracy is further improved, and if it is 5 μm or less, it is even better.

  Moreover, although this embodiment demonstrated grinding | polishing of the outer peripheral side end surface of the glass substrate 10, the grinding | polishing method using a magnetic slurry is applicable also to the inner peripheral side end surface of the glass substrate 10. FIG. For example, the magnetic generating means for holding the magnetic slurry as shown in FIG. 4 is passed through the circular hole at the center of the glass substrate 10, and the lump of magnetic slurry is brought into contact with the inner peripheral side end surface of the glass substrate 10. The end face can be polished.

In addition, a plurality of magnets are arranged in a state of being separated from each other in the vertical direction, a magnetic slurry lump is formed between the magnets, and a plurality of glass substrates are laminated on the multi-stage magnetic slurry lump. The end surfaces of a plurality of laminated glass substrates can be processed simultaneously by bringing the end portions into contact with each other.
Further, a plurality of substrates may be processed at the same time so that end surfaces of a plurality of laminated glass substrates are put between a pair of magnets. In the end surface polishing process of the present invention, when the magnets 21 and 22 are rotating, the ring-shaped magnetic slurry lump 26 formed and held between the magnets 21 and 22 is scattered to the outside by centrifugal force. It is possible to hold the magnetic slurry even if the distance between the magnets increases and the magnetic field weakens, and the productivity can be dramatically increased by stacking multiple substrates. .

In the present invention, the glass constituting the glass substrate is preferably an amorphous aluminosilicate glass. Such a glass substrate can be finished to a smooth mirror surface by mirror polishing the surface, and the strength after processing is good. As such an aluminosilicate glass, for example, a glass containing SiO ₂ as a main component and containing 20 wt% or less of Al ₂ O ₃ is preferable. Specifically, for example, SiO ₂ is 62 wt% to 75 wt%, Al ₂ O ₃ is 5 wt% to 15 wt%, Li ₂ O is 4 wt% to 10 wt%, and Na ₂ O is 4 wt%. Wt% to 12 wt%, ZrO ₂ is contained in an amount of 5.5 wt% to 15 wt% as a main component, and the weight ratio of Na ₂ O / ZrO ₂ is 0.5 to 2.0, Al ₂ An amorphous aluminosilicate glass containing no phosphorus oxide and having a weight ratio of O ₃ / ZrO ₂ of 0.4 to 2.5 can be used.

  After the end face polishing process of the present invention is completed, the glass substrate is ground (lapped) to improve the dimensional accuracy and shape accuracy. This main surface grinding is usually performed by using a double-sided lapping machine to grind the main surface of the glass substrate using hard abrasive grains such as diamond. By grinding the main surface of the glass substrate in this way, a predetermined plate thickness and flatness are processed, and a predetermined surface roughness is obtained.

And after completion | finish of the said main surface grinding process, the mirror polishing process for obtaining a highly smooth main surface is performed.
The mirror polishing method for the main surface of the glass substrate is performed using a polishing pad of a polisher such as polyurethane while supplying a slurry (polishing liquid) containing a metal oxide abrasive such as cerium oxide or colloidal silica. Is preferred. A glass substrate having high smoothness is obtained, for example, by polishing with a cerium oxide-based abrasive (first polishing process) and then with final polishing (mirror polishing) (second polishing process) using colloidal silica abrasive grains. It is possible.

In the present invention, chemical strengthening treatment may be applied to improve the substrate strength. As a method of the chemical strengthening treatment, for example, a low-temperature ion exchange method in which ion exchange is performed in a temperature range not exceeding the glass transition temperature is preferable. Since the chemically strengthened glass substrate is excellent in impact resistance, it is particularly preferable for mounting on a HDD for mobile use, for example.
As described above, the magnetic disk substrate according to the present invention is manufactured.

  The above description has been given of the case of a glass substrate as an example of a magnetic disk substrate. However, as described above, an aluminum alloy-based substrate also exists as a magnetic disk substrate. The end surface polishing treatment using the magnetic slurry of the present invention can be preferably applied, and the polishing rate of the substrate end surface can be improved to further improve the production efficiency. The aluminum alloy substrate includes an aluminum alloy substrate and an aluminum alloy substrate having a NiP alloy formed on the surface thereof.

  The present invention also provides a method for manufacturing a magnetic disk using the above glass substrate for a magnetic disk. In the present invention, the magnetic disk is manufactured by forming at least a magnetic layer on the magnetic disk glass substrate according to the present invention. As a material for the magnetic layer, a hexagonal CoCrPt-based or CoPt-based ferromagnetic alloy having a large anisotropic magnetic field can be used. As a method of forming the magnetic layer, it is preferable to use a method of forming a magnetic layer on a glass substrate by a sputtering method, for example, a DC magnetron sputtering method. Further, by interposing an underlayer between the glass substrate and the magnetic layer, the orientation direction of the magnetic grains of the magnetic layer and the size of the magnetic grains can be controlled. For example, by using a cubic base layer such as a Cr-based alloy, for example, the magnetization easy direction of the magnetic layer can be oriented along the magnetic disk surface. In this case, a magnetic disk of the in-plane magnetic recording system is manufactured. Further, for example, by using a hexagonal underlayer containing Ru or Ti, for example, the easy magnetization direction of the magnetic layer can be oriented along the normal of the magnetic disk surface. In this case, a perpendicular magnetic recording type magnetic disk is manufactured. The underlayer can be formed by sputtering as with the magnetic layer.

In addition, a protective layer and a lubricating layer may be formed in this order on the magnetic layer. As the protective layer, an amorphous hydrogenated carbon-based protective layer is suitable. For example, the protective layer can be formed by a plasma CVD method. Further, as the lubricating layer, a lubricant having a functional group at the end of the main chain of the perfluoropolyether compound can be used. In particular, it is preferable that the main component is a perfluoropolyether compound having a terminal hydroxyl group as a polar functional group. The lubricating layer can be applied and formed by a dip method.
By utilizing the glass substrate obtained by the present invention, the end face of the substrate is finished with a high precision shape and high quality, so that the occurrence of a failure due to the surface state of the end face of the substrate is prevented, and further higher recording is achieved. Density can be realized and a highly reliable magnetic disk can be obtained.

Hereinafter, embodiments of the present invention will be specifically described with reference to examples. In addition, this invention is not limited to a following example.
Example 1
The following (1) substrate preparation step, (2) main surface grinding step, (3) end surface grinding step, (4) end surface polishing step, (5) main surface polishing step (first polishing step), (6) chemical strengthening A glass substrate for a magnetic disk was manufactured through steps (7) and a main surface polishing step (second polishing step).

(1) Substrate preparation step First, a glass substrate (glass base plate) made of aluminosilicate glass having a diameter of 66 mmφ and a thickness of 0.635 mm by direct press using molten glass from an upper mold, a lower mold, and a body mold. Got. In this case, in addition to the direct press, a disk-shaped glass substrate may be obtained by cutting out from a sheet glass formed by a downdraw method or a float method with a grinding wheel. As the aluminosilicate _glass, SiO 2: 62 to 75 _wt%, ZrO 2: _{5.5~15 wt%, Al} 2 O 3: _{5~15 wt%,} Li 2 O: _4~10 wt%, Na ₂ O: Glass for chemical strengthening containing 4 to 12% by weight was used.

(2) Main surface grinding process This main surface grinding process is performed by using a double-sided lapping machine and setting a glass substrate held by a carrier between the upper and lower surface plates to which diamond pads are affixed, and adjusting to a predetermined plate thickness. did.
(3) End face grinding step Next, a cylindrical grindstone was used to make a hole in the center portion of the glass substrate, and a predetermined end face grinding (shape processing) was performed on the outer peripheral end face and the inner peripheral end face using a general-purpose grindstone. .

(4) End surface polishing process Next, the grinding | polishing process of the outer peripheral side end surface of the glass substrate which formed the chamfering surface and the side wall surface in the substrate end surface by grinding as mentioned above was performed. In this example, the end surface polishing process using a magnetic slurry was performed according to the method shown in FIG.
As shown in FIG. 2, a ring-shaped magnetic slurry lump was formed between two magnets using a polishing apparatus incorporating magnetism generating means composed of a pair of magnets. The magnetic substance and abrasive grains described in the present specification (described above) were used. And the end surface of the glass substrate was grind | polished by rotating these two magnets and a glass substrate mutually. The rotational directions of the two were opposite to each other, and the rotational speed was appropriately adjusted.
In this way, the outer peripheral end face of the glass substrate was polished. The surface roughness of the outer peripheral end surface of the substrate after processing was 0.1 μm or less in terms of Rz for both the side wall surface and the chamfered surface.
Moreover, about the inner peripheral side of the glass substrate, it grind | polished using the conventional grinding | polishing brush.
As described above, the glass substrate after the end face polishing was washed.

(5) Main surface polishing step (first polishing step)
Next, the 1st grinding | polishing process for removing the flaw and distortion which remain | survived by the main surface grinding process mentioned above was performed using the double-side polish apparatus. In a double-side polishing machine, a glass substrate held by a carrier is closely attached between an upper and lower polishing surface plate to which a polishing pad is attached, and this carrier is engaged with a sun gear (sun gear) and an internal gear (internal gear). The glass substrate is sandwiched between upper and lower surface plates. Thereafter, a polishing liquid is supplied and rotated between the polishing pad and the polishing surface of the glass substrate, whereby the glass substrate revolves while rotating on the surface plate to simultaneously polish both surfaces. The glass substrate after the first polishing step was washed and dried.

(6) Chemical strengthening process Next, the glass substrate which finished the said washing | cleaning was chemically strengthened. The chemical strengthening was performed by immersing the glass substrate in a chemical strengthening solution in which potassium nitrate and sodium nitrate were mixed and heated and melted for about 4 hours.

(7) Main surface polishing step (second polishing step)
Next, the second polishing step was performed using the same double-side polishing apparatus as used in the first polishing step. In this second polishing step, for example, the surface roughness of the main surface of the glass substrate is 0.2 nm in terms of Ra (measured with an atomic force microscope) while maintaining the flat surface obtained in the first polishing step described above. This is a mirror polishing process for finishing the surface to a smooth mirror surface. The glass substrate after the second polishing step was washed and dried.

When the surface roughness of the main surface of the glass substrate obtained through the above steps was measured with an atomic force microscope (AFM), glass having an ultra-smooth main surface with Rz = 1.53 nm and Ra = 0.13 nm. A substrate was obtained.
The obtained glass substrate had an outer diameter of 65 mm, an inner diameter of 20 mm, and a plate thickness of 0.635 mm.
Thus, a glass substrate for magnetic disk of this example was obtained.

(Comparative Example 1)
A glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except that in the end surface polishing step, the outer peripheral side end surface was polished using conventional brush polishing. Brush polishing was performed by laminating 25 substrates.

(Comparative Example 2)
A glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except that in the end surface polishing step, an end surface polishing process using a magnetic slurry was performed according to the method shown in FIG.
In addition, the same thing as Example 1 was used for the magnetic body and the abrasive grain, the rotation direction of the magnet and the glass substrate was made into the mutually opposite direction, and the rotation speed was adjusted suitably.

In addition, the grinding allowance of outer peripheral end face grinding | polishing in the above Example 1 and Comparative Examples 1 and 2 is all 10 micrometers.
About the glass substrate (100 pieces for each example) manufactured under the conditions of Example 1 and Comparative Examples 1 and 2 above, the edge portion between the chamfered surface and the side wall surface on the outer peripheral end surface of the substrate (FIG. 1). The radius of curvature of part A) was determined one by one, and the variation in each example was determined. The variation here is a difference between the maximum value and the minimum value of the data of the 100 obtained substrates. The curvature radius was evaluated using a stylus evaluation device.

  A variation of 0.02 mm or less in 100 substrates is level 1, a level greater than 0.02 mm and 0.03 mm or less is level 2, and a level 3 is greater than 0.03 mm. The smaller the level, the better. The results are summarized in Table 1. In Table 1, for convenience, Example 1 is described as inscribed magnetic polishing, and Comparative Example 2 is described as circumscribed magnetic polishing.

From the results in Table 1, the following can be understood.
1. The outer peripheral side end surface of the glass substrate is brought into contact with the inner peripheral side of the magnetic slurry lump formed in the ring shape, and the magnetic slurry lump formed in the ring shape and the glass substrate are relatively moved (in this embodiment, In Example 1 in which the end surface polishing process for polishing the outer peripheral side end surface of the glass substrate was performed while rotating, the processing time can be shortened even with the same polishing allowance compared with Comparative Examples 1 and 2, and the polishing rate should be improved. Can do. Moreover, the result of the variation in the radius of curvature of the edge portion between the chamfered surface and the side wall surface at the outer peripheral end surface was good, and the machining accuracy was also good.
2. On the other hand, in Comparative Example 1 in which the end surface polishing process was performed by the conventional brush polishing, the processing time was very long, and the variation in the radius of curvature of the edge portion between the chamfered surface and the side wall surface was large and good shape accuracy was achieved. Was not obtained.
Moreover, although it is an end surface grinding | polishing process using a magnetic slurry, in the comparative example 2 implemented by the conventional circumscribed type | mold (FIG. 4), processing time takes a little longer than Example 1, and a chamfer surface and a side wall surface are The variation in the radius of curvature of the edge portion between them was also worse than that in Example 1.

(Manufacture of magnetic disk)
The following film formation process was performed on the magnetic disk glass substrate obtained in Example 1 to obtain a magnetic disk for perpendicular magnetic recording.
That is, an adhesion layer made of a Ti-based alloy thin film, a soft magnetic layer made of a CoTaZr alloy thin film, an underlayer made of a Ru thin film, a perpendicular magnetic recording layer made of a CoCrPt alloy, a carbon protective layer, and a lubricating layer are sequentially formed on the glass substrate. A film was formed. The protective layer is for preventing the magnetic recording layer from deteriorating due to contact with the magnetic head, and is made of hydrogenated carbon, and provides wear resistance. The lubricating layer was formed by dipping a liquid lubricant of alcohol-modified perfluoropolyether.
The obtained magnetic disk was installed in an HDD equipped with a DFH head, and a load / unload durability test was conducted for one month while operating the DFH function in a high temperature and high humidity environment of 80 ° C. and 80% RH. There were no particular obstacles and good results were obtained.

1 Glass substrate for magnetic disk 10 Disc-shaped glass substrate (glass base plate)
DESCRIPTION OF SYMBOLS 11 Main surface 12 of glass substrate Outer peripheral side end surface 12a of glass substrate Side wall surface 12b Chamfered surfaces 21, 22 Magnet 23 Stopper portion 25, 26 Mass of magnetic slurry

Claims (5)

A method for manufacturing a magnetic disk substrate including an end surface processing for processing an end surface of a disk-shaped substrate,
The end face processing is
A magnetic slurry lump containing a magnetic body and abrasive grains is formed in a ring shape by a magnetism generating means,
The outer peripheral side end surface of the disk-shaped substrate is brought into contact with the inner peripheral side of the ring-shaped magnetic slurry lump, and the ring-shaped magnetic slurry lump and the disk-shaped substrate are relatively A method of manufacturing a magnetic disk substrate, comprising: an end surface polishing process for polishing an outer peripheral side end surface of the disk-shaped substrate while moving the disk-shaped substrate.   The chamfered surface of at least one of the chamfered surface between the side wall surface of the outer peripheral side end surface of the disk-shaped substrate and the two main surfaces of the disk-shaped substrate and the side wall surface is simultaneously polished. A method for manufacturing a magnetic disk substrate according to claim 1.   The disk-shaped substrate is brought into contact with the magnetic slurry lump so that the rotation axis of the disk-shaped substrate is not perpendicular to a plane formed by the magnetic slurry lump formed in the ring shape, and end face polishing treatment is performed. The method for manufacturing a magnetic disk substrate according to claim 1, wherein the method is performed.   4. The method for manufacturing a magnetic disk substrate according to claim 1, wherein the disk-shaped substrate is a stacked body in which a plurality of disk-shaped substrates are stacked. An end surface polishing apparatus used for end surface polishing processing for polishing an end surface of a disk-shaped substrate for a magnetic disk,
A magnetic generating means for forming and holding a lump of magnetic slurry including a magnetic body and abrasive grains in a ring shape;
The outer peripheral side end surface of the disk-shaped substrate is brought into contact with the inner peripheral side of the ring-shaped magnetic slurry lump, and the ring-shaped magnetic slurry lump and the disk-shaped substrate are relatively An end face polishing apparatus for polishing an outer peripheral side end face of the disk-shaped substrate while moving it periodically.

Images