JP2015069668A - Manufacturing method of magnetic disk glass substrate and manufacturing method of magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a magnetic disk glass substrate, capable of improving accuracy of form of an end surface of a glass substrate and allowing high quality.SOLUTION: A rotation axis of magnetic generation means for forming and holding magnetic slurry mass containing magnetic viscous fluid and polishing abrasive grain is inclined with respect to an axis orthogonal to a principal face of a glass substrate. While in this state, both a side wall surface of an end surface of the glass substrate and a chamfered face interposed between a principal face of the glass substrate and the side wall surface are polished by bringing the end surface of the glass substrate into contact with the magnetic slurry mass.

Description

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

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 substrate, and an aluminum substrate has been conventionally used as the substrate. However, recently, in response to the pursuit of higher recording density, the ratio of the glass substrate capable of narrowing the distance between the magnetic head and the magnetic disk as compared with the aluminum substrate is gradually increasing. Further, the surface of the glass substrate is polished with high accuracy so as to increase the recording density so that the flying height of the magnetic head can be reduced as much as possible. In recent years, there has been an increasing demand for HDDs with higher recording capacity and lower prices. In order to achieve this, it is necessary to further improve the quality and cost of glass substrates for magnetic disks. It is coming.

A glass substrate for a magnetic disk is usually produced by sequentially performing steps such as shape processing (end grinding and chamfering), end surface polishing, main surface grinding, main surface polishing, chemical strengthening on a glass substrate formed into a disk shape. .
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 of the glass substrate is required. The same applies not only to the main surface of the glass substrate but also to the end face shape.

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.
Patent Document 3 below discloses a magnetic fluid (magnetic powder) that is attracted to a magnetic electrode by rotating a magnetic electrode disposed away from the processing surface of the workpiece relative to the workpiece. A magnetic polishing method for processing a workpiece with held abrasive grains is disclosed.

JP-A-11-28649 JP 2005-50501 A JP 2004-291208 A

  As described above, there is a need for an inexpensive magnetic disk that can achieve a high recording density. For this purpose, the end face of the substrate is improved in quality based on a request to reduce contamination factors such as the occurrence of corrosion on the main surface of the medium. It is required to achieve both improvement in shape accuracy to reduce flutter (flutter).

  However, in the method of processing the end surface of the glass substrate by performing end surface grinding using the above-described conventional general-purpose grindstone and then performing brush end surface polishing, in mass production processing, particularly with the chamfered surface at the end surface of the substrate The variation in the edge angle between the side wall surfaces is large, and it is difficult to improve the shape accuracy of the substrate end surface.

Further, in the method of polishing the end surface of the glass substrate for magnetic disks by applying a magnetic field to the slurry containing the ferrite-based magnetic particles and the abrasive grains disclosed in Patent Document 2, the chamfered surface of the end surface of the glass substrate is used. The processing rate is different from that of the side wall surface, and it is difficult to finish both the chamfered surface and the side wall surface into a mirror surface within a predetermined processing time. In this case, if both the chamfered surface and the side wall surface are processed until they are finished to a mirror surface, there arises a problem that the processing time is increased and the shape accuracy is deteriorated.
Moreover, the above-mentioned Patent Document 3 does not disclose the end face polishing of the magnetic disk glass substrate. Assuming that the magnetic polishing method of Patent Document 3 is applied to end face polishing of a glass substrate for a magnetic disk, in order to simultaneously polish the chamfered surface and the side wall surface of the end face of the glass substrate, It is necessary to perform processing while oscillating the processing point. When considering mass production processing, it is particularly difficult to suppress variations in the finished end face shape.

  In recent years, quality requirements for glass substrates for magnetic disks, such as the shape accuracy of the end face of the glass substrate and the finished surface quality of chamfering, are increasing from the viewpoint of higher information recording density. When a large number of mass-produced glass substrates for magnetic disks are manufactured using the above-mentioned grinding method and polishing method, it is becoming increasingly difficult to stably meet the increasing quality requirements of glass substrates.

Therefore, the present invention improves the shape accuracy of the end surface of the magnetic disk glass substrate particularly from the viewpoint of meeting the demand for higher recording density of magnetic disks, which is urgently required to ensure high recording density. Another object of the present invention is to provide a method for producing a glass substrate for a magnetic disk capable of stable processing that can be finished with high quality, and a method for producing a magnetic disk using the glass substrate obtained thereby.

In order to solve the above problems, the present invention has the following configuration.
(Configuration 1)
A method of manufacturing a glass substrate for a magnetic disk including an end face processing for processing an end face of a disk-shaped glass substrate, wherein the end face processing is performed with respect to an axis perpendicular to the main surface of the glass substrate, With the rotation axis of the magnetism generating means for forming and holding a lump of magnetic slurry containing abrasive grains tilted, the end surface of the glass substrate is brought into contact with the lump of magnetic slurry, and the end surface of the glass substrate A method of manufacturing a glass substrate for a magnetic disk, comprising: an end surface polishing treatment for polishing a side wall surface and a chamfered surface interposed between the main surface of the glass substrate and the side wall surface.

(Configuration 2)
2. The method of manufacturing a glass substrate for a magnetic disk according to Configuration 1, wherein in the end surface polishing process, the rotation direction of the magnetism generating means is changed in the middle of processing.

(Configuration 3)
The glass substrate for a magnetic disk according to Configuration 1 or 2, wherein an inclination angle of a rotation axis of the magnetism generating unit with respect to an axis orthogonal to the main surface of the glass substrate is in a range of 3 degrees to 7 degrees. Manufacturing method.

(Configuration 4)
The glass for a magnetic disk according to any one of Structures 1 to 3, wherein a grinding process for forming both a chamfered surface and a side wall surface on the end surface of the glass substrate is performed before the end surface polishing process. A method for manufacturing a substrate.

(Configuration 5)
5. A magnetic disk manufacturing method comprising: forming at least a magnetic recording layer on a magnetic disk glass substrate manufactured by the method for manufacturing a magnetic disk glass substrate according to any one of Structures 1 to 4.

According to the present invention, the difference in processing rate between the chamfered surface of the glass substrate end surface and the side wall surface can be suppressed, the shape accuracy of the chamfered surface of the glass substrate end surface and the side wall surface is improved, and the end surface is made of high quality. Stable end surface processing that can be finished is possible, and it is possible to stably provide a glass substrate for a magnetic disk whose substrate end surface is finished with a high-precision shape and high quality.

Furthermore, by using the glass substrate for magnetic disk manufactured by this method for manufacturing a glass substrate for magnetic disk, the end surface of the substrate is finished with high precision shape and high quality. It is possible to provide a magnetic disk that can prevent the occurrence of a failure due to the state, can achieve higher recording density, and has high reliability.

It is sectional drawing which shows the end surface shape of the glass substrate for magnetic discs. (A)-(c) is a figure for demonstrating the structure of the magnetic generation means applied to the end surface grinding | polishing process of this invention, respectively. It is a perspective view for demonstrating the end surface grinding | polishing process by a magnetic slurry. It is a schematic diagram for demonstrating the state which is performing the end surface grinding | polishing process of this invention.

Hereinafter, embodiments for carrying out the present invention will be described in detail.
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. The glass substrate 1 is not shown in FIG. 1, but the whole having a circular hole in the center is formed in a disc shape, and is formed between the main surfaces 11a and 11b on the front and back sides and between these main surfaces 11a and 11b. An outer peripheral end surface and an inner peripheral end surface.

The end surface on the outer peripheral side of the glass substrate 1 is formed between the side wall surface 12 orthogonal to the pair of front and back main surfaces 11a and 11b, and between the side wall surface 12 and the front and back main surfaces 11a and 11b, respectively. It is formed in the shape which consists of two chamfered surfaces (chamfered surfaces) 13a, 13b. Moreover, although it does not show in figure about the end surface of the inner peripheral side of the said glass substrate 1, like the said outer peripheral side end surface, the side wall surface orthogonal to the main surfaces 11a and 11b, this side wall surface, and the main surface 11a of the front and back , 11b and two chamfered surfaces (chamfered surfaces) formed between them.

In the case of a magnetic disk, for example, a 2.5 inch disk, the glass substrate 1 is finished to have an outer diameter of 65 mm and an inner diameter of 20 mm. Here, the inner diameter is the inner diameter of a circular hole in the center of the glass substrate 1.

  The pair of front and back main surfaces 11a and 11b, the outer peripheral side end surface, and the inner peripheral side end surface of the magnetic disk glass substrate 1 are each finally polished (mirror polished) to have a predetermined surface roughness. Both the outer peripheral side end face and the inner peripheral side end face of the glass substrate 1 are finished to the end face shape as described above, and the surface roughness is, for example, Rz 0.2 μm or less and Ra 0.02 μm or less in a mirror surface state. It is usually required to be finished.

The glass substrate 1 for a magnetic disk is usually subjected to grinding / polishing (mirror polishing) of the end surface, grinding / mirror polishing of the main surface, chemical treatment on a glass substrate (glass disk 10) formed into a predetermined disk shape by a direct press or the like. Manufactured with sequential steps such as strengthening.
In the present invention, everything from a glass disk molded into a predetermined disk shape by direct press or the like to a final product glass substrate produced by processing, processing, etc. on this glass disk is used for convenience of explanation. It will be called 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 disk shape of a predetermined size, and has a groove shape for forming the end face shape of the glass substrate on the outer peripheral side thereof. 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.

  As the general-purpose grindstone used in the end face grinding, a so-called electrodeposition bond grindstone in which diamond abrasive grains, which are high-rigidity grindstones are hardened by electrodeposition bond, is suitable for rough grinding. In addition, for finishing precision grinding, a resin bond grindstone in which the binder for bonding abrasive grains is a resin material such as phenol resin, urethane resin, polyimide resin, polyester resin, fluororesin, or the binder is copper-based, for example. Metal bond grindstones that are metallic binders such as alloys, cast iron alloys, and titanium alloys, and vitrified grindstones whose binder is a vitreous binder are suitable, and a composite grindstone in which these binders are mixed is used. You can also Among these, a resin bond grindstone in which the adjustment of the hardness of the grindstone is relatively easy is particularly suitable. As the abrasive grains, alumina abrasive grains, cubic boron nitride abrasive grains, and the like can be used.

Further, as the grain size of the abrasive grains, for example, abrasive grains having an average grain diameter of 30 μm or less are suitable in order to maintain the grinding performance over the life of the grinding wheel while maintaining the roughness. For this, abrasive grains having an average particle diameter of 3 to 15 μm are suitable. As an abrasive grain, a diamond abrasive grain is suitable, for example. The particle size of the abrasive grains can be measured by, for example, an electrical resistance test method.

  In the end surface grinding using the above-described general-purpose grindstone, the processing is performed in such an arrangement relationship that the glass substrate and the grindstone are in the same plane. In this case, it is preferable to perform the processing while rotating the grindstone and the glass substrate in respective predetermined directions. The peripheral speed and the peripheral speed ratio of each of the grindstone and the glass substrate are appropriately set so as to be suitable for the grinding of the inner and outer peripheral side end faces. It only has to be set. The rotation direction of the grindstone and the glass substrate may be either the same direction (counter direction) or a different direction (anticounter direction).

In addition, since glass materials have processing characteristics that are easily affected by the heat generated during grinding, cooling with a grinding liquid (coolant) supplied to the end face of the glass substrate is necessary to enable stable grinding. It is desirable to increase the effect and reduce the influence of heat during grinding as much as possible. The grinding fluid (coolant) used in the present invention is not particularly limited, but a water-soluble grinding fluid having a high cooling effect and high safety at the production site is particularly suitable.

By grinding using the above-mentioned general-purpose grinding wheel, the shape of the chamfered surface and the side wall surface of the substrate end surface can be created. For example, as a precision grinding method after rough grinding using a general-purpose grinding wheel Applying a method of grinding the end face of the glass substrate by bringing the grindstone into contact with the end face of the glass substrate in a state where the rotation axis of the grindstone is inclined with respect to an axis orthogonal to the main surface of the glass substrate. Is preferred.

For example, a precision grinding process is performed in a state where the grindstone is inclined with respect to a glass substrate in which both the side wall surface and the chamfered surface are formed on the inner and outer peripheral end faces by rough grinding using a general-purpose grindstone. The grindstone used in this case is formed in a disk shape of a predetermined size, and has a groove shape on the outer peripheral side thereof in contact with the end surface of the glass substrate. It has a concave shape. Unlike the above-mentioned general shape grindstone, shape transfer is performed using a part of the groove shape.
As the grindstone used in the processing method for performing precision grinding in a state where the grindstone is inclined with respect to such a glass substrate, it is preferable to apply the above-mentioned resin bond grindstone.

Even in this case, it is preferable to perform the processing while rotating the grindstone and the glass substrate in respective predetermined directions, and the respective peripheral speeds and peripheral speed ratios may be appropriately set so as to be suitable for processing of the inner and outer peripheral side end faces. Good. The rotation direction of the grindstone and the glass substrate may be either the same direction (counter direction) or a different direction (anticounter direction).

In the case of this processing method, the grindstone that comes into contact with the end surface of the glass substrate by bringing the grindstone into contact with the end surface of the glass substrate in a state where the rotation axis of the grindstone is inclined with respect to the axis orthogonal to the main surface of the glass substrate. The processing is performed by bringing the end face of the glass substrate into contact with the grindstone so that the trajectory is not constant.
In this processing method, the trajectory of the grindstone that comes into contact with the end surface of the glass substrate is not constant, and the convex portions (abrasive grains) of the grindstone abut and act on the substrate end surface at random positions. There is little damage, and the surface roughness and in-plane variation of the ground surface are reduced, so that the ground surface with the above-described general-purpose grindstone can be finished to a higher smoothness (quasi-mirror surface state).

  In the present invention, following the end face grinding process described above, an end face polishing process using a magnetic slurry containing a magnetorheological fluid and abrasive grains is performed. The end face polishing process using the magnetic slurry is performed with high quality polishing. Although it is possible, if the pre-processing (pre-processing) is only the grinding wheel processing, the grinding surface has a high roughness, so that the machining allowance is increased to reduce the roughness in the end surface polishing process using magnetic slurry. Therefore, there is a possibility that the edge is greatly rounded, for example, due to a deviation from the shape formed by the general-purpose grindstone. Therefore, as described above, it is preferable to finish the substrate end surface in a quasi-mirror surface state by precision grinding with the grindstone tilted with respect to the glass substrate before the end surface polishing treatment using the magnetic slurry.

Next, the end face polishing process of the present invention that is performed after the end face grinding process will be described in detail.
In the end surface polishing treatment of the present invention, the rotation axis of the magnetism generating means for forming and holding a mass of magnetic slurry containing the magnetorheological fluid and the abrasive grains is inclined with respect to the axis orthogonal to the main surface of the glass substrate. In this state, the end surface of the glass substrate is brought into contact with the lump of magnetic slurry, and a side wall surface of the end surface of the glass substrate and a chamfered surface interposed between the main surface of the glass substrate and the side wall surface This is a process for polishing both surfaces simultaneously.

FIGS. 2A to 2C are views for explaining the configuration of the magnetism generating means applied to the end surface polishing process of the present invention. 3 is a perspective view for explaining an end surface polishing process using a magnetic slurry, and FIG. 4 is a schematic view for explaining a state in which the end surface polishing process of the present invention is performed.
The apparatus 20 used for the end surface polishing treatment in the present invention polishes the end surface of the glass substrate using a magnetism generating means and a magnetic slurry. 2 (a) to 2 (c), FIG. 3 and FIG. 4 each show a case where the outer peripheral side end face of the glass substrate is polished.

The outline of the apparatus 20 will be described. As shown in FIG. 2A, the apparatus 20 includes a pair of magnets 21 and 22 that are permanent magnets, a spacer 23, and a hollow cylinder made of a nonmagnetic material such as stainless steel. Shape-shaped exterior member 24. Magnets 21 and 22 and a spacer 23 are built in the exterior member 24.
If it is desired to increase the amount of contact between the magnetic slurry and the glass substrate in order to adjust the polishing rate, etc., it is necessary to insert the end portion of the glass substrate between the magnets 21 and 22 so that the exterior member 24 is processed. Is not provided.

The glass substrate 10 subjected to the end face grinding is held by a holder (not shown). The glass substrate 10 held by the holder is brought close to the exterior member 24, and a lump 26 of magnetic slurry (see FIGS. 2C and 3), which will be described later, and the outer peripheral side end surface of the glass substrate 10 are brought into contact with each other. A holder (not shown) that holds the exterior member 24 and the glass substrate 10 of the apparatus 20 is connected to a drive motor (not shown). The outer peripheral end surface of the glass substrate 10 can be polished by rotating the exterior member 24 and the holder to relatively move the outer peripheral end surface of the glass substrate 10 and the magnetic slurry lump 26. For example, the exterior member 24 and the holder for holding the glass substrate 10 (in other words, the glass substrate 10 and the magnets 21 and 22) are rotated in opposite directions (see FIG. 3), and the exterior member 24 and the glass It is preferable to rotate the substrate 10 relative to the peripheral speed of, for example, 50 to 500 m / min. If the outer peripheral side end face of the glass substrate 10 and the magnetic slurry lump 26 can be relatively moved, either the glass substrate 10 or the magnetic slurry lump 26 may be fixed and the other may be rotated. .

  More specifically, the pair of magnets 21 and 22 are close to each other, function as magnetism generating means, and form magnetic lines 25 as shown in FIG. The magnetic field lines 25 are linear magnetic field lines that proceed from the centers of the magnets 21 and 22 in the thickness direction of the glass substrate. In the example shown in FIG. 2B, a pair of magnets arranged in the thickness direction of the glass substrate 10 so that the N-pole surface and the S-pole surface are spaced apart from each other is used as the magnetism generating means. It is done. A spacer 23 made of a non-magnetic material is provided between the magnets 21 and 22 in order to set a predetermined separation distance between the N pole end face of the magnet 21 and the S pole end face of the magnet 22. It has been. As described above, without using the exterior member 24, a lump of magnetic slurry may be formed between the magnets 21 and 22, and the end of the glass substrate may be brought into contact therewith. 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.

  In the example shown in FIG. 2, a permanent magnet is used as the magnetism generating means. However, for example, an electromagnet can be used. In addition, the spacer 23 is used in order to ensure a certain 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, but the outer member 24 is not used without using the spacer 23. The magnets 21 and 22 are fixed, and 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 can be kept constant.

  As the magnetorheological fluid of the magnetic slurry used for the end face polishing, a magnetic slurry (magnetic fine particles) dispersed 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, a polishing grinding | polishing flow 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. A surfactant may be added to the magnetorheological fluid.

  As the abrasive grains contained in the magnetic slurry, known abrasive grains for 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 magnetorheological fluid, 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 magnetorheological fluid is low), it is difficult to form the lump 26, and it is difficult to perform 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. The yield stress of the magnetic slurry containing the magnetorheological fluid and 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 magnetorheological fluid 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 shear stress of the magnetorheological fluid was determined, and the obtained shear rate The yield stress of the magnetorheological fluid can be determined by approximating the relationship between the shear stress and 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, the rotation axis of the magnetic generating means for forming and holding a mass of magnetic slurry containing the magnetorheological fluid and the abrasive grains is inclined with respect to the axis orthogonal to the main surface of the glass substrate. In this state, the polishing is performed by bringing the end face of the glass substrate into contact with a lump of magnetic slurry. For example, as shown in FIG. 4, a mass 26 of magnetic slurry is formed along the direction of the magnetic force lines formed so as to advance linearly between a pair of opposed magnets 21 and 22 that are magnetism generating means. The end surface of the glass substrate 10 and the magnetic slurry lump 26 in a state where the rotation axis LM of the magnetic generating means is inclined by an angle α with respect to an axis (for example, a rotation axis) LS orthogonal to the main surface of the glass substrate 10. Make contact.

  For example, when the glass substrate is not inclined and is inserted in a plane direction perpendicular to the direction of the magnetic field lines and the end surface of the glass substrate is brought into contact with a lump of magnetic slurry, the side wall surface of the end surface of the glass substrate is more Since the amount of contact with the magnetic slurry is larger than the chamfered surface, the processing rate of the side wall surface is larger than the processing rate of the chamfered surface, and the side wall surface is processed with priority. Thus, if the processing rate differs between the chamfered surface and the side wall surface of the glass substrate end surface, it is difficult to finish both the chamfered surface and the side wall surface to the same quality within a predetermined processing time. In this case, if both the chamfered surface and the side wall surface are processed until they are finished to the same quality, there arises a problem that the processing time becomes longer and the shape accuracy of the preferentially processed side wall surface deteriorates.

  Therefore, in the present invention, the end surface of the glass substrate 10 is brought into contact with the magnetic slurry lump 26 with the rotation axis LM of the magnetism generating means inclined with respect to the axis LS orthogonal to the main surface of the glass substrate 10. As a result, the magnetic slurry contacts and acts at random positions with respect to the substrate end surface, and as a result, the contact between the chamfered surface of the substrate end surface and the magnetic slurry can be promoted more than the conventional technology. The processing pressure on the chamfer increases. 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. As a result, it is possible to improve the shape accuracy of both the chamfered surface and the side wall surface of the glass substrate end surface, and to perform stable polishing that can finish the end surface with high quality.

In the present invention, the inclination angle α of the rotation axis LM of the magnetism generating unit with respect to the axis LS orthogonal to the main surface of the glass substrate 10 is slightly different depending on the distance between magnets, the magnetic flux density, etc. It is preferable to be within the range. When the tilt angle is less than 3 degrees, it is difficult to obtain an effect of suppressing the difference in processing rate between the chamfered surface and the side wall surface of the glass substrate end surface. On the other hand, when the inclination angle is larger than 7 degrees, the holding state of the magnetic slurry is disturbed, and the processing rate of both the side wall surface and the chamfered surface is lowered.

In the end surface polishing process using the magnetic slurry of the present invention, it is preferable to change the rotation direction of the magnetism generating means in the middle of processing. For example, in FIG. 4, when the rotation of the magnetism generating means, that is, the rotation of the magnetic slurry is in the A direction, the processing pressure on the chamfered surface on the A ′ side of the glass substrate 10 is further increased. The effect which can suppress the processing rate difference of a chamfering surface becomes large. On the other hand, when the rotation of the magnetism generating means, that is, the rotation of the magnetic slurry is in the B direction, the processing pressure of the chamfered surface on the B ′ side of the glass substrate 10 is further increased, and in particular, the side wall surface and the chamfered surface on the B ′ side. The effect which can suppress the processing rate difference of becomes large. Therefore, by changing the rotation direction of the magnetism generating means in the middle of processing, the processing rate difference between the chamfered surface on the A ′ side and B ′ side and the side wall surface can be suppressed. is there.

According to the end surface polishing treatment of the present invention, as described above, it is possible to finish both the chamfered surface and the side wall surface into a mirror surface of the same quality within a predetermined processing time. The shape accuracy of both surfaces of the wall surface can be improved. For example, after the end surface polishing treatment of the present invention, the variation in the curvature radius of the edge between the chamfered surface and the side wall surface of the glass substrate and the variation in the curvature radius of the edge between the main surface and the chamfered surface of the glass substrate are both. It is possible to fit within 0.03 mm.

The machining allowance by the end surface polishing process in the present invention is about 1 to 10 μm. Further, if the thickness is 5 μm or less, the shape accuracy is further improved, which is further preferable.

In addition, although the above demonstrated the grinding | polishing of the outer peripheral side end surface of the glass substrate 10, it can grind | polish also about the inner peripheral side end surface of the glass substrate 10 by the same method. That is, the inner peripheral side end face can also be polished by passing the magnetism generating means through the circular hole in the center of the glass substrate 10 and bringing the lump of magnetic slurry into contact with the inner peripheral end face of the glass substrate 10. .

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, the end face processing including end face polishing using the magnetic slurry in the present invention is equivalent to a thick plate (for example, 0.635 mm or more) even if the glass substrate thickness to be input into the end face processing is, for example, 0.5 mm or less. The end face quality can be secured.

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. Furthermore, it is more preferable to use glass containing SiO ₂ as a main component and containing 15% by weight or less of Al ₂ O ₃ . Specifically, 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%. % To 12% by weight, ZrO ₂ is contained in an amount of 5.5% to 15% by weight as a main component, and the weight ratio of Na ₂ O / ZrO ₂ is 0.5 to 2.0, Al ₂ O _An amorphous aluminosilicate glass containing no phosphorus oxide and having a ₃ / ZrO ₂ weight ratio of 0.4 to 2.5 can be used.

As the heat-resistant glass, for example, in mol%, the SiO ₂ 50 to 75%, the _{Al 2 O 3 0~5%, 0~2} % of BaO, 0 to 3% of Li ₂ O, ZnO 0-5%, Na ₂ O and K ₂ O in total 3-15%, MgO, CaO, SrO and BaO in total 14-35%, ZrO ₂ , TiO ₂ , La ₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ and HfO ₂ are included in a total amount of ₂ to 9%, and the molar ratio [(MgO + CaO) / (MgO + CaO + SrO + BaO)] is in the range of 0.85 to 1. And glass having a molar ratio [Al ₂ O ₃ / (MgO + CaO)] in the range of 0 to 0.30 can be preferably used.
Further, the total amount of alkali metal oxides selected from the group consisting of 56 to 75 mol% SiO ₂ , 1 to 9 mol% Al ₂ O ₃ , Li ₂ O, Na ₂ O and K ₂ O is 6 to 15 mol. %, MgO, 10 to 30 _mol% in total of alkaline earth metal oxide selected from the group consisting of CaO and _{SrO, ZrO 2, TiO 2,} Y 2 O 3, La 2 O 3, Gd 2 O 3, Nb Glass containing oxides selected from the group consisting of ₂ O ₅ and Ta ₂ O ₅ in total exceeding 0% and not more than 10 mol% may be used.
In the present invention, the content of Al ₂ O ₃ in the glass composition is preferably 15% by weight or less. Furthermore, still preferably _Al 2 _{O 3} content is 5 mol% or less.

After the end face polishing process of the present invention is finished, the main surface is ground to improve the dimensional accuracy and shape accuracy of the glass substrate. This main surface grinding is usually performed by using a double-sided grinding device and grinding 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. This main surface grinding step may be performed before the end surface grinding is performed on the disk-shaped glass disk produced by the direct press method described above.

And after completion | finish of the said main surface grinding process, the mirror polishing process for obtaining a highly smooth main surface is performed.
As a mirror polishing method for a glass substrate, it is preferable to use 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 there. 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.

Here, in the present invention, Ra and Rz are roughnesses in accordance with Japanese Industrial Standard (JIS) B0601. In the present invention, the surface roughness (for example, maximum roughness Rz, arithmetic average roughness Ra) of the side wall surface and the chamfered surface is measured in a measurement region of 50 μm × 50 μm using a laser microscope with an observation magnification of 3000 times. It is a measured value.

In the present invention, chemical strengthening treatment may be performed 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. The chemical strengthening treatment is a process in which a molten chemical strengthening salt is brought into contact with a glass substrate, whereby an alkali metal element having a relatively large atomic radius in the chemical strengthening salt and a relatively small atomic radius in the glass substrate. This is a treatment in which an alkali metal element is ion-exchanged, an alkali metal element having a large ion radius is permeated into the surface layer of the glass substrate, and compressive stress is generated on the surface of the glass substrate. 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 the chemical strengthening salt, alkali metal nitrates such as potassium nitrate and sodium nitrate can be preferably used.
As described above, the magnetic disk glass substrate according to the present invention is manufactured.

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.

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. The lubricating layer can be applied and formed by a dip method.
By utilizing the glass substrate obtained by the present invention, the end surface of the substrate is finished with a high precision shape and high quality, so that the occurrence of failures due to the surface state of the substrate end surface, such as anti-corrosion, is prevented. A higher recording 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.
(Examples 1-5, Comparative Examples 1-2)
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 process First, a glass substrate (glass disk) made of disc-shaped aluminosilicate glass having a diameter of 66 mmφ and a thickness of 0.635 mm is obtained from molten glass by direct pressing using an upper die, a lower die, and a barrel die. It was. In this case, in addition to the direct press, a disk-shaped glass substrate may be obtained by cutting out with a grinding wheel from a sheet glass formed by a downdraw method or a float method. 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 grinding machine, setting a glass substrate held by a carrier between the upper and lower surface plates to which diamond pads are attached, and adjusting to a predetermined plate thickness. did.
(3) End surface grinding step Next, a cylindrical grindstone was used to make a hole in the central portion of the glass substrate, and predetermined end surface grinding (shape processing) was performed on the outer peripheral end surface and the inner peripheral end surface.
In this example, first, the outer peripheral end face of the substrate was chamfered using a general-purpose grindstone, and then grinding was performed in a state where the grindstone was tilted with respect to the glass substrate surface described above, and the chamfered surface and the side were formed on the substrate end face A wall was formed.
In addition, the kind of grindstone, the particle size, etc. selected and used appropriately.
The surface roughness of the outer peripheral side end surface of the glass substrate at this time was 1.2 μm or less in terms of Rz for both the side wall surface and the chamfered surface.
Further, the inner peripheral side end face of the substrate was chamfered using a predetermined total shape grindstone.
In addition, about the rotation direction and rotation speed of a grindstone and a glass substrate, the relative ratio of the rotation speed of a board | substrate and a grindstone, etc. are the ranges as described in the above-mentioned embodiment.

(4) End Surface Polishing Step Next, the outer peripheral side end surface of the glass substrate in which the chamfered surface and the side wall surface were formed on the substrate end surface by grinding as described above was polished. In the example, a polishing process using a magnetic slurry was performed according to the method shown in FIG.
As shown in FIG. 4, a lump of magnetic slurry was formed between two magnets using a polishing apparatus incorporating magnetism generating means composed of a pair of magnets. And the end surface of the glass substrate was grind | polished by rotating these magnetism generation means and a glass substrate mutually. The rotational directions of the two were opposite to each other as shown in FIG.
The rotational speed of the magnetism generating means (magnetic slurry lump), the rotation speed of the substrate, the relative ratio of the rotation speed of the lump of the substrate and the magnetic slurry, the magnetic flux density of the magnet, etc. are described in the above embodiment. Range.
In Examples 1 to 5, the inclination angle α (see FIG. 4) of the rotation axis of the magnetism generating unit with respect to the rotation axis of the glass substrate was set in the range of 3 to 15 degrees (see Table 1 below). In Example 5, the rotation direction of the magnetism generating means was changed in the middle, and the same time was processed before and after the change. Moreover, as Comparative Example 2, the glass substrate was processed in the same manner except that the glass substrate was not tilted (tilt angle was 0 degree). Further, as Comparative Example 1, conventional brush polishing was performed instead of polishing processing using a magnetic slurry.
In this way, the outer peripheral end face of the glass substrate was polished.
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 step Next, chemical strengthening was performed on the glass substrate after the cleaning. For chemical strengthening, a chemical strengthening solution in which potassium nitrate and sodium nitrate were mixed was prepared, the chemical strengthening solution was heated to 380 ° C., and the cleaned and dried glass substrate was immersed for about 4 hours to perform chemical strengthening treatment.

(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), a glass substrate having a smooth main surface with Rz = 1.53 nm and Ra = 0.13 nm. Got.
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, glass substrates for magnetic disks of the above examples and comparative examples were obtained.

And about 100 glass substrates produced in the same manner, the surface roughness (Rz) of the side wall surface and the two chamfered surfaces on the outer peripheral end surface of the substrate after the end face polishing is measured using a laser microscope, The results are summarized in Table 1.
Moreover, about 100 glass substrates produced similarly, each processing rate of the side wall surface of the outer peripheral end surface of a board | substrate in the said end surface grinding | polishing process and two chamfering surfaces is measured (diameter dimension change). The results are summarized in Table 1. The processing rate ratio between the chamfered surface and the side wall surface is also shown in Table 1.
In Table 1, the side wall surface is represented as “12 surface”, and the two chamfered surfaces are represented as “13a surface” and “13b surface” (see FIG. 1), respectively.

From the results in Table 1, the following can be understood.
1. Example 1 in which the polishing process was performed in the state where the rotation axis of the magnetism generating means with respect to the rotation axis of the glass substrate was inclined within the range of the inclination angle (α) of 3 degrees to 7 degrees in the end surface polishing process using the magnetic slurry. , 2, the processing rate difference between the chamfered surface and the side wall surface of the glass substrate is reduced, and both the chamfered surface and the side wall surface can be finished to the same quality mirror surface within a predetermined processing time (short time). It becomes possible. In particular, in Example 5 in which the rotation direction of the magnetism generating means was switched halfway, the difference in the machining rate between the chamfered surface and the side wall surface was very small (the machining rate ratio was close to 1.0), and further the 13a surface, It was possible to suppress the processing rate difference between the chamfered surface of the 13b surface and the side wall surface.
Further, in Examples 3 and 4 in which the inclination angle is larger than the above range, a reduction in the chamfered surface machining rate was observed.
In addition, regarding the difference in roughness (Rz) between the two chamfered surfaces and the side wall surface, compared to the case where the substrate is not inclined (Comparative Example 2), the one where the substrate is inclined (Example), It was found that the difference was small.
2. On the other hand, in Comparative Example 2 in which the polishing process was performed without inclining the rotation axis of the magnetism generating unit with respect to the rotation axis of the glass substrate, the chamfering of the glass substrate was difficult because the processing toward the chamfered surface side hardly progressed. The difference in the processing rate between the surface and the side wall surface became very large, and the processing rate of the chamfered surface was about 1/4 of the processing rate of the side wall surface.
Further, in Comparative Example 1 in which the conventional brush polishing was performed instead of the end surface polishing treatment with the magnetic slurry, the processing rate difference between the chamfered surface and the side wall surface was small, but the processing rate itself was low, and the chamfered surface and the side wall surface were In order to finish both to a mirror surface of the same quality, processing for a long time (at least about 1800 seconds) is required, and the shape accuracy of the end face may be deteriorated.

(Manufacture of magnetic disk)
The following film formation process was performed on the magnetic disk glass substrate obtained in Example 5 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 disk)
DESCRIPTION OF SYMBOLS 11 Main surface 12 of glass substrate Peripheral side end surface 12a of glass substrate Side wall surface 12b Chamfering surface 20 End surface polishing device 21, 22 Magnet 23 Spacer 24 Exterior member 25 Magnetic field line 26 Magnetic slurry lump

Claims (5)

A method of manufacturing a glass substrate for a magnetic disk including an end face processing for processing an end face of a disk-shaped glass substrate,
In the end face processing, the rotation axis of the magnetism generating means for forming and holding a mass of magnetic slurry containing the magnetorheological fluid and abrasive grains is inclined with respect to the axis orthogonal to the main surface of the glass substrate. The end surface of the glass substrate is brought into contact with the lump of the magnetic slurry to polish the side wall surface of the end surface of the glass substrate and the chamfered surface interposed between the main surface of the glass substrate and the side wall surface. The manufacturing method of the glass substrate for magnetic discs characterized by including an end surface grinding | polishing process.   2. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein in the end face polishing process, the rotation direction of the magnetism generating means is changed in the middle of processing.   3. The magnetic disk glass according to claim 1, wherein an inclination angle of a rotation axis of the magnetism generating unit with respect to an axis orthogonal to the main surface of the glass substrate is in a range of 3 degrees to 7 degrees. A method for manufacturing a substrate.   4. The magnetic disk according to claim 1, wherein a grinding process for forming both a chamfered surface and a side wall surface on the end surface of the glass substrate is performed before the end surface polishing process. A method for producing a glass substrate. 5. A method for producing a magnetic disk, comprising forming at least a magnetic recording layer on the glass substrate for a magnetic disk produced by the method for producing a glass substrate for a magnetic disk according to claim 1.

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