JP3237199B2 - How to attach a magnetic plate to a disk substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for mounting a magnetic plate disposed on a disk substrate of an information signal recording disk on which a desired information signal is recorded, such as an optical disk or a magneto-optical disk.

[0002]

2. Description of the Related Art Hitherto, there has been proposed an information signal recording disk on which a desired information signal is recorded, such as an optical disk or a magneto-optical disk. This kind of disc is capable of recording information signals at a high density, so that a very small disc has been proposed. For example, there has been proposed an optical disk or a magneto-optical disk having a diameter of about 64 mm and capable of recording about 74 minutes with a tone signal.

A magneto-optical disk having such a small diameter and capable of recording information signals at a high density is mounted on a disk rotation drive and rotated at a high speed. Then, while being rotated at a high speed, a fine recording track provided on a signal recording layer formed on one main surface of the magneto-optical disk is irradiated with a light beam emitted from the optical pickup device, and a magnetic field is emitted. A desired information signal is recorded by applying an external magnetic field modulated from a magnetic field generator such as a head according to the information signal to be recorded.

In order to accurately irradiate a fine recording track with a light beam while being rotated and driven at a high speed, the magneto-optical disk is surely integrated with a disk table of a disk rotation driving device and a shaft of the disk table is rotated. It is necessary to mount the rotation center on the heart with high precision. Conventionally, to achieve this purpose,
A metal plate made of a magnetic material is arranged on the magneto-optical disk side,
A disk mounting method has been proposed in which the magneto-optical disk is chucked on the disk table by attracting the magnetic disk with a magnet provided on the disk table side.

A magneto-optical disk used in a magnet chucking system utilizing the attraction of a magnet is
As shown in FIG. 9, a disk substrate 5 formed by molding a synthetic resin such as a transparent polycarbonate resin into a disk shape.
1 is provided. One main surface 5 of the disk substrate 51
On the side of 1a, an information signal recording layer on which a desired information signal is recorded is formed. The disc substrate 51 has the other main surface 51b opposite to the one main surface 51a on which the information signal recording layer is formed as the information signal write / read surface,
By irradiating the signal recording layer with a light beam from the writing / reading surface side, recording or reproduction of a desired information signal is performed.

Further, a center hole 52 is formed in the center of the disk substrate 51 so that a centering member provided on the disk rotation driving device side can be engaged. Further, a disk-shaped magnetic plate 53 made of a metal material is provided in the center of the center hole 5 in the central portion on one main surface 51a side of the disk substrate 51.
2 is arranged to close. Such a magnetic plate 53
Are arranged on one main surface 51a side of the disk substrate 51 so as to fit into a magnetic plate housing recess 54 formed around the center hole 52. The magnetic plate 53 disposed in the magnetic plate storage recess 54 has a protrusion (not shown) that projects inwardly of the recess 54 by ultrasonically processing the peripheral edge of the magnetic plate storage recess 54. Do.)
It is stored and held in the disk substrate 51.

The disk substrate 51 of the magnetic plate 53
Attachment is performed as follows.

First, as shown in FIG. 10, a disk substrate 51 is placed on a disk receiving table 55. Disk support 55
Is a magnetic plate storage recess 54 provided on the disk substrate 51.
And a projection fitting recess 57 for receiving the disk substrate 51 therein. A disk receiving portion 58 formed as an annular protrusion for supporting the write / read surface 51b of the disk substrate 51 is formed on the outer peripheral edge of the protrusion fitting concave portion 57. The disk receiving base 55 is provided with a fitting projection 59 for positioning the disk substrate 51 facing the center hole 52 of the disk substrate 51 at the center of the projection fitting recess 57. Further, the disk receiving base 55 has suction holes 6 connected to a vacuum air pump for securely fixing the disk substrate 51 to the disk receiving base 55.
0 is provided. The suction holes 60 are
Receiving portion 58 supporting write / read surface 51b
It is provided as a continuous through hole to the base end.

The projection 56 of the disk substrate 51 is fitted into the projection fitting recess 57 of the disk receiving base 55 thus configured, and the center hole 52 is made to face the fitting projection 59. As a result, the disk substrate 51 is placed in a state of being positioned with respect to the disk receiving table 55 by the fitting projection 59.

Next, the vacuum air pump is operated, and the suction holes 6
The disk substrate 51 placed on the disk receiving portion 58 is supported by suction through the “0”. Thereby, the disk substrate 51
Are securely fixed to the disk receiving table 55.

Thereafter, a cylindrical horn 61 is brought into contact with the peripheral edge of the opening of the magnetic plate accommodating recess 54 of the disk substrate 51, and ultrasonic vibration from an ultrasonic oscillator (not shown) is transmitted to the horn 61. As a result, the magnetic plate storage recess 54
Is thermally deformed, and the resin at the periphery of the opening protrudes inwardly of the concave portion 54 due to the pressurization caused by the sinking of the horn 61 to form an annular projection. Thus, the magnetic plate 53 is stored and supported in the magnetic plate storage recess 54 in a loosely fitted state.

[0012]

However, even if a method of vacuuming the disk substrate 51 using a vacuum air pump is used, the disk substrate 51 vibrates due to the application of ultrasonic vibration to the disk substrate 51, and the position of the disk substrate 51 shifts. Occurs. If the disk substrate 51 shifts during swaging,
The ultrasonic vibration leaks to the entire disk substrate 51, making it impossible to concentrate the ultrasonic vibration at a predetermined position, and cracks are generated around the predetermined position. Cracks do not occur immediately after swaging, but gradually occur over time.

Further, in the prior art, as shown in FIG.
The disk substrate 51 is also fixed to the disk receiving table 55 by applying a constant external force F thereto. Even with this method, it is difficult to securely fix the disk substrate 51, and the position of the disk substrate 51 shifts due to the application of ultrasonic vibration, and cracks occur in portions that are thermally deformed.

Therefore, the present invention has been proposed in view of the above technical problem, and reliably holds a disk substrate at the time of swaging and concentrates ultrasonic vibrations at a predetermined position where thermal deformation occurs. It is an object of the present invention to provide a method of attaching a magnetic plate to a disk substrate that can be swaged by being swung.

[0015]

According to the present invention, a magnetic plate is provided in a magnetic plate storage recess provided at the center of a disk substrate, and the disk substrate is mounted on a disk mounting means. The ultrasonic generating means is brought into contact with the upper peripheral edge of the magnetic plate storage concave portion in a state where the magnetic disk device is placed and pressed and held by the disk pressing means, so that the upper peripheral edge of the magnetic plate storage concave portion is inward of the concave portion. A protruding portion protruding toward the disk is formed, and the magnetic plate is supported on the disk substrate by the protruding portion.

When swaging, the inner peripheral portion of the disk substrate on which the information signal recording layer is not formed is held by the disk pressing means and the disk mounting means. At this time, the disk pressing means and the disk mounting means are provided with annular projections which come into contact with the inner peripheral portion of the disk substrate where the information signal recording layer is not formed. Further, a dust collecting mechanism is provided in the disc holding means.

[0017]

According to the method of the present invention, the disk substrate is swaged while being mounted on the disk mounting means and pressed and held by the disk pressing means, so that the disk substrate is securely fixed to the disk mounting means and applied. The ultrasonic vibration is concentrated on the portion where the protrusion is formed. Therefore, the weld time is shortened, and the occurrence of cracks in the thermally deformed portion is prevented.

Since the disc mounting means and the disc holding means hold the inner peripheral portion of the disc substrate on which the information signal recording layer is not formed, the information signal recording layer is not damaged. Further, since the disc holding means is provided with the dust collecting mechanism, swaging can be performed in a dust-free and always clean state.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below in detail with reference to the drawings. This embodiment is an example in which the present invention is applied to a magneto-optical disk having a diameter of 64 mm.

First, a magneto-optical disk to which the present invention is applied will be described. As shown in FIG. 1, such a magneto-optical disk 1 has a disk substrate 2 formed by integrally molding a synthetic resin material such as a transparent polycarbonate resin.
Is provided. This disk substrate 2 has a diameter of approximately 64 m.
m and a disk shape with a thickness of about 1.2 mm.

The magneto-optical disk 1 constituted by using the disk substrate 2 has a signal recording section in which an information signal recording layer for recording a desired information signal is formed on one main surface 2a side of the disk substrate 2. The other main surface 2b on the opposite side is used as a writing / reading surface for information signals, and recording / reproducing of information signals is performed by irradiating the signal recording layer with a light beam from the writing / reading surface side. Is configured to be performed.

As shown in FIG. 2, the center of a disk substrate 2 constituting the magneto-optical disk 1 is located at the center of a disk table constituting a disk rotation drive provided in a recording / reproducing apparatus. A center hole 3 into which a provided centering member (not shown) is engaged is formed. The center hole 3 is formed as a circular hole through the disk substrate 2 so that the center of the center hole 3 matches the center of curvature of a recording track formed concentrically or spirally in the signal recording layer. It is formed as follows.

An annular protruding portion 4 is formed integrally with the center surface of the disk substrate 2 on the other main surface 2b side so as to surround the center hole 3. The protruding portion 4 is provided with a centering member provided on the disk table side on which the magneto-optical disk 1 is mounted without increasing the depth of the center hole 3 formed in the thin disk substrate 2. The function of ensuring that the centering operation for mounting the magneto-optical disk 1 with the rotation center of the magneto-optical disk 1 aligned with the axis of the disk table is ensured without increasing the amount of protrusion from the center hole 3. Further, the tip surface 4a of the projection 4
Functions as a mounting reference surface for the disk table.

The protruding portion 4 is formed at least in a non-signal recording area on the inner peripheral side of the disk substrate 2 where no signal recording layer is formed, and is formed so as to have a protruding amount substantially equal to the thickness of the disk substrate 2. I have. Therefore, the portion of the disk substrate 2 where the protruding portion 4 is formed is about twice as thick as the substrate main body.

Then, one main surface 2a of the disk substrate 2
An annular magnetic plate storage recess 6 is formed in the center on the side where the magnetic plate 5 for magnet attraction is disposed surrounding the center hole 3. The magnetic plate housing recess 6 has a diameter smaller than the outer diameter of the protrusion 4 and is formed at a depth substantially equal to the thickness of the disk substrate 2. This magnetic plate storage recess 6
Is larger than the opening diameter of the center hole 3. Therefore, at the bottom of the magnetic plate storage recess 6,
An annular flat surface 6a is provided. This flat surface 6a
Is a mounting surface on which the magnetic plate 5 is mounted.

On the other hand, the magnetic plate 5 housed and held in the magnetic plate housing recess 6 is formed by punching a metal material such as a stainless steel plate into a disk shape.
The magnetic plate 5 is formed as a disk large enough to be stored in the magnetic plate storage recess 6, and when stored in the magnetic plate storage recess 6, its outer peripheral surface 5a is It is formed in such a size that it does not contact the inner peripheral wall 6b of the recess 6. At the center of the magnetic plate 5,
A small circular hole 7 used for handling in the manufacturing process is provided.

The magnetic plate 5 formed as described above is mounted on the disk substrate 2 by a mounting device having the following ultrasonic wave generating means. As shown in FIG. 3, the mounting device includes a disk substrate support table 8 as a disk mounting means for mounting the disk substrate 2 and an ultrasonic wave generating means as an ultrasonic wave generating means for applying ultrasonic waves to the disk substrate 2. And a mechanical unit 9.

The disk substrate support table 8 is configured so as to be able to position the mounted disk substrate 2, and the disk substrate 2 is placed on the upper surface side of a flat support table body 10. A disk substrate mounting table 11 for positioning and mounting is provided. As shown in FIG. 4, the disk substrate mounting table 11
A fitting projection 12 which is a projection into which the center hole 3 of the disk substrate 2 fits is provided at the center, and the projection 4 of the disk substrate 2 is loosely fitted around the outside of the fitting projection 12. And a projection fitting recess 13 that fits into the projection.

The fitting projection 12 is formed as a columnar projection having an outer diameter substantially equal to the opening diameter of the center hole 3.
The center hole 3 of the disk substrate 2 faces the inside of the magnetic plate storage recess 6. An inclined surface is provided on the peripheral edge on the distal end side of the fitting protrusion 12 so that the disk substrate 2 can be easily inserted into the fitting protrusion 12. The height of the fitting projection 12 is such that the tip end surface does not protrude from the bottom surface 6a of the magnetic plate housing recess 6 of the disk substrate 2 when the disk substrate 2 is placed. I have.

The protrusion fitting recess 13 provided on the outer periphery of the fitting protrusion 12 is formed as an annular concave enough to accommodate the protrusion 4 of the disk substrate 2 therein. When stored, a predetermined gap is opened between the inner peripheral wall 13a and the outer peripheral surface 4b of the protruding portion 4.
Therefore, the disk substrate 2 is positioned on the disk substrate mounting table 11 by fitting the center hole 3 into the fitting projection 12.

Further, on the outer periphery of the protrusion fitting recess 13,
A disk receiving portion 14 for supporting a main surface 2b of the disk substrate 2 serving as a read / write surface for information signals is provided. The disk receiving portion 14 is formed as an annular protrusion near the opening periphery of the magnetic plate housing concave portion 6 where the information signal recording layer of the disk substrate 2 is not formed, and is formed on the annular flat surface 14a. The disk substrate 2 is supported in a surface contact state. Further, the disk receiving portion 14 is formed of a relatively soft material such as silicon rubber in order to prevent the disk substrate 2 from being damaged. Although not shown, a vacuum pump is used on the disk substrate support table 8 configured as described above using a vacuum pump in order to securely fix the disk substrate 2 mounted on the disk substrate mounting table 11. A suction mechanism for sucking is provided.

On the other hand, as shown in FIG. 3, the ultrasonic generating mechanism 9 mainly includes an ultrasonic vibrator 15 for converting electric energy generated from an ultrasonic oscillator into mechanical vibration, and a mechanical device for the ultrasonic vibrator 15. A cone 16 for amplifying the vibration, and a horn 17 for transmitting the amplified mechanical vibration to the workpiece
It is composed of The ultrasonic transducer 15, the cone 16, and the horn 17 are integrated in a vertical line in that order, and are moved up and down with respect to the disk substrate 2 by the air cylinder 18. Compressed air is introduced into the air cylinder 18 via a pneumatic circuit. In addition, a control panel is provided between the disk substrate support table 8 and the ultrasonic oscillator, so that the pressing force and amplitude of the horn 17 on the disk substrate 2 and the swaging depth are controlled. An air pressure circuit is connected to this control panel, and the amount of compressed air to be sent to the air cylinder 18 is finely adjusted.

The ultrasonic wave generating mechanism 9 is provided with a disk pressing means 20 which moves up and down in conjunction with the lowering operation of the horn 17. The disc holding means 20
The ultrasonic transducer 15, the cone 16, and the horn 17 are supported by a coil spring 22 at the distal end of a transducer support 21 that internally supports the ultrasonic transducer 15, and are attached to the transducer support 21 so as to move up and down. . The disc holding means 20 is formed as a cylindrical body large enough to accommodate the horn 17 therein, and has a disc-shaped disc holding member 23 at the tip.

The disk pressing member 23 is provided with a disk pressing portion 24 for securely fixing the disk substrate 2 to the disk substrate mounting table 11.
The disc holding portion 24 is formed as a ring-shaped projection at a position opposed to the preceding disc receiving portion 14, that is, at a position near the opening edge of the magnetic plate housing recess 6 where the information signal recording layer of the disc substrate 2 is not formed. The disk substrate 2 is supported in a surface contact state by the formed flat surface 24a having an annular shape. In addition, this disc holding part 2
Similarly to the disc receiving portion 14, the disc 4 is made of silicon rubber or the like to prevent the disc substrate 2 from being damaged. Also, the horn 17 is attached to the disc holding member 23.
Is provided with a circular horn introduction hole 25 for facing the horn.

Further, the disc holding part 24 has a dust collecting mechanism for sucking dust existing in the space surrounded by the disc holding part 24 when the disc substrate 2 is pressed and held by the disc holding means 20. Vacuum hose 26 connected to the vacuum air pump to be constituted
Is installed. At a portion where the vacuum hose 26 is attached, a suction hole 27 penetrating from the outside to the inside of the disc holding portion 24 is provided. Therefore, dust and the like existing in the space surrounded by the disc pressing portion 24 during the swaging of the disc substrate 2 are guided to the vacuum hose 26 through the suction hole 27.

The mounting of the magnetic plate 5 to the disk substrate 2 using the mounting device is performed as follows. First, FIG.
The disk substrate 2 is mounted on the disk substrate mounting table 11 as shown in FIG. That is, the disk substrate 2 is inserted into the fitting projection 12 provided on the disk substrate mounting table 11.
The center hole 3 of the disk substrate 2 is fitted and the projection 4 of the disk substrate 2 is stored and held in the projection fitting recess 13. Thereby, the disk substrate mounting table 1 of the disk substrate 2
1 and the disk substrate 2
The main surface 2b serving as a writing / reading surface is supported by the disk receiving portion 14 in a surface contact state.

After that, the disk substrate mounting table 11
By operating a suction mechanism built in the disk substrate 2, the disk substrate 2 is vacuum-suctioned and fixed on the disk substrate mounting table 11.

Next, the magnetic plate storage recess 6 of the disk substrate 2
The magnetic plate 5 is put inside. Next, the horn 17 is lowered by the air cylinder 18. Then, as shown in FIG. 5, the disk pressing means 20 descends in advance in conjunction with the lowering operation of the horn 17, and the disk pressing portion 24 provided at the tip thereof contacts the disk substrate 2. At this time, the disc holding portion 24 supports the peripheral edge of the opening of the magnetic plate housing recess 6 where the information signal recording layer of the disc substrate 2 is not formed, so that the information signal recording layer is not damaged.

When the horn 17 is further lowered, a pressing force is applied to the disc pressing means 20 by the coil spring 22. The disk substrate 2 is pressed and held on the disk substrate mounting table 11 by the pressing force at this time.

Then, as shown in FIG. 6, when the horn 17 comes into contact with the disk substrate 2, ultrasonic vibration is applied. The ultrasonic wave applied here may be so-called longitudinal vibration caused by intermittently moving up and down in the axial direction of the horn 17, or in a clockwise direction and a counterclockwise direction around the axis of the horn 17. A so-called torsional vibration may be achieved by intermittently moving the horn 17 in the in-plane direction.

While the ultrasonic vibration is being applied, a constant pressure F is applied to the horn 17, and the vacuum air pump of the dust collecting mechanism is operated to perform vacuum.

Then, the peripheral edge of the opening of the magnetic plate housing recess 6 with which the horn 17 is in contact is softened by frictional heat. The pressing force F applied to the horn 17 causes the peripheral edge of the opening of the magnetic plate housing recess 6 to form a recess corresponding to the size of the horn 17 as shown in FIG. It protrudes toward the inner peripheral side of the recess 6. As a result, horn 1
A projection 19 is formed at a portion where the projection 7 comes into contact with the magnetic plate housing recess 6 so as to protrude toward the inner peripheral side. Such protrusion 19
Are formed to project in an annular shape so as to cover the outer peripheral edge portion 5a of the magnetic plate 5 housed in the magnetic plate housing concave portion 6, and
From the disk substrate 2 is prevented.

In the swaging state, since the disk substrate 2 is pressed and held on the disk substrate mounting table 11 by the disk pressing means 20, all the ultrasonic vibrations generated by the horn 17 are generated by this. It concentrates on the portion of the disk substrate 2 that receives the thermal deformation.
Therefore, the swaging can be performed satisfactorily, the weld time can be reduced, and the occurrence of cracks in the projecting portion 19 can be prevented. In this example, the time can be reduced by about 0.1 second as compared with the conventional method. In addition, since swaging is performed while vacuuming, the disk substrate 2 can always be swaged in a clean state,
Adhesion of dust and the like can be avoided.

After the completion of the swaging, the horn 1
7 and the disc holding means 20 are raised with respect to the disc substrate 2, the vacuum suction is released, and the disc substrate 2 is taken out. As a result, as shown in FIG. 8, the magneto-optical disk 1 in which the magnetic plate 5 is held in a loosely fitted state with respect to the disk substrate 2 is manufactured. In such a magneto-optical disk 1, since the ultrasonic vibration can be concentrated on the portion of the disk substrate 2 where the projecting portion 19 is formed, the thickness of the projecting portion 19 can be controlled with high precision. A certain clearance C is secured between the plate 5 and the projecting portion 19 formed over the plate 5. That is, the magnetic plate 5
With a preset clearance C
Can be loosely fitted and held. Therefore, it is possible to prevent the disk substrate 2 from being deformed due to a difference in thermal expansion coefficient between the disk substrate 2 made of a synthetic resin and the magnetic plate 5 made of a metal material.

In this embodiment, an example in which the present invention is applied to a magneto-optical disk has been described. However, the present invention also has a disk substrate made of a synthetic resin and has a magnetic plate for magnet chucking. Can be widely applied to information signal recording disks having

[0046]

As described above, in the method of the present invention, since the swaging is performed while the disk substrate is pressed and held on the disk substrate mounting table by the disk pressing means, the ultrasonic vibration is applied. Even if the disk substrate is not displaced, the ultrasonic vibration can be concentrated on the portion of the disk substrate where the thermal deformation is to be performed. Can be avoided, and the weld time can be shortened.

Further, according to the method of the present invention, since the ultrasonic vibration can be concentrated on the portion to be thermally deformed, the thickness of the protrusion formed by the thermal deformation can be controlled with high accuracy. The magnetic plate can be stored and held in the magnetic plate storage recess of the disk substrate in a loosely fitted state. Therefore, it is possible to prevent the magnetic plate from being fixedly attached to the main surface of the disk substrate while being inclined, and to generate a disk due to a difference in thermal expansion coefficient between the disk substrate made of synthetic resin and the magnetic plate made of metal material. Deformation of the substrate can be prevented. As a result, the information signal recording disk configured using this disk substrate can be stably mounted on the disk table of the disk rotation drive mechanism.

Further, according to the method of the present invention, the information signal recording layer is formed on the disk substrate and the inner peripheral portion thereof is not formed by the disk mounting means and the disk pressing means. There is no damage to the recording layer. Further, at the time of swaging, dust and the like existing in the space near the thermal deformation are sucked by the dust collecting mechanism, so that swaging can be always performed in a clean state. Therefore, a highly reliable information signal recording disk free of dust and the like can be manufactured.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a magneto-optical disk to which the present invention is applied.

FIG. 2 is a sectional view showing an exploded state of a magneto-optical disk to which the present invention is applied.

FIG. 3 is a front view showing a magnetic plate mounting device to which the present invention is applied.

FIG. 4 is a cross-sectional view showing a state in which a magnetic plate is loaded on a disk substrate.

FIG. 5 is a cross-sectional view showing a state in which a disk pressing portion is brought into contact with a disk substrate.

FIG. 6 is a cross-sectional view showing a state where the horn is in contact with the disk substrate.

FIG. 7 is a sectional view showing a swaging state.

FIG. 8 is a sectional view of the magneto-optical disk after swaging is completed.

FIG. 9 is a cross-sectional view showing a state where the disk substrate is fixed to the disk substrate mounting table by vacuum.

FIG. 10 is a cross-sectional view showing a state where the outer peripheral edge of the disk substrate is pressed by a disk holder and the disk substrate is fixed to a disk substrate mounting table.

[Explanation of symbols]

Reference Signs List 1 magneto-optical disk, 2 disk substrate, 3 center hole, 5 magnetic plate, 6 magnetic plate storage recess, 8
Disk substrate support table, 9 ultrasonic generating mechanism,
11 disk board mounting table, 12 fitting projection, 14 disk receiving part, 15 ultrasonic transducer,
16 cone, 17 horn, 18 air cylinder, 19 protrusion, 20 disc holding means,
24 Disc holding part, 26 Vacuum hose

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-208784 (JP, A) JP-A-6-4907 (JP, A) JP-A-4-54069 (JP, A) JP-A-4-208 143494 (JP, A) Radio Technology, Vol. 45, No. 12, Heisei 12-12-12, p. 152-155 (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 23/00 601 G11B 7/26

Claims (4)

(57) [Claims] A magnetic plate is disposed in a magnetic plate storage recess provided at the center of a disk substrate, and the disk substrate is mounted on disk mounting means and pressed and held by disk pressing means. by abutting the ultrasound generating means to the upper rim <br/> plate housing recess to form a protrusion protruding inwardly of the recess from the top peripheral edge of the magnetic plate housing recess, the protrusion A method of mounting the magnetic plate on the disk substrate, wherein the magnetic plate is supported by the disk substrate. 2. The magnetic recording medium according to claim 1, wherein the disc holding means and the disc mounting means hold an inner peripheral portion of the disc substrate on which an information signal recording layer is not formed. How to mount the board. 3. The disk pressing means and the disk mounting means are provided with annular projections which are in contact with an inner peripheral portion of the disk substrate on which the information signal recording layer is not formed. The method for attaching a magnetic plate to a disk substrate according to claim 1. 4. The method for mounting a magnetic plate on a disk substrate according to claim 1, wherein the disk holding means is provided with a dust collecting mechanism.