JPH11265527A - Disk-type recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately mold an entire substrate along with a center hole and to surely attach a clamping plate. SOLUTION: This medium is provided with a disk substrate 2 where a center hole 4 is punched by a center punch 28 whose tip part 28a is projected inside a cavity 25 in advance, and with a clamping plate 3 where an attachment flange 3a is bent at an outer peripheral part and attached to a recessed part 5 where the center hole 4 of the disk substrate 2 is formed. On the disk substrate 2, an annular locking projection part 6 whose diameter is smaller than the attachment flange 3a is integrally formed along a center hole opening edge on the clamping plate attaching surface of the recessed part 5. On a molding die 20, the diameter of the opening part 27a of a nozzle 27 is made larger than the tip 28a of the center punch 28 and the locking projection part 6 is formed by the larger diameter part 27b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a disk-shaped recording medium such as an optical disk, a magneto-optical disk, or a magnetic disk.

[0002]

2. Description of the Related Art For example, an optical disk is used exclusively for reproducing an information signal or the like recorded in advance, and a pit having a concavo-convex pattern corresponding to the information signal and the like is formed on a surface of a disk substrate and a light reflection layer is formed. It becomes. The magneto-optical disk also enables recording while reproducing information signals and the like. A pre-groove forming a recording track on which a desired information signal and the like are recorded is formed on the surface of the disk substrate, and a signal comprising a magnetic film layer is formed. A recording layer and a light reflection layer are formed.

[0003] In these optical disks and magneto-optical disks, a disk substrate is molded by a molding die using a synthetic resin material having optical transparency, for example, a polycarbonate resin. A stamper for transferring and forming the above-mentioned pits and pregrooves to the disk substrate is incorporated in the molding die, and a center hole is formed in the center of the disk substrate by a center punch projecting into the cavity.

[0004] When an optical disc is loaded into a reproducing apparatus,
The center portion is chucked by the disk rotation drive mechanism and driven to rotate, and the information signal and the like recorded by the optical pickup are reproduced. When a magneto-optical disk is loaded into a recording and / or reproducing (hereinafter simply referred to as "recording / reproducing") device, a central portion of the magneto-optical disk is similarly chucked by a disk rotation driving mechanism, and is driven to rotate. The information signal and the like recorded by the pickup are reproduced, and the information signal and the like are recorded by the optical pickup and the magnetic head mechanism.

For example, a magneto-optical disk 100 has a concave portion 102 having a center hole 101 at the center as shown in FIG.
A clamping plate 103 made of a magnetic material such as a metal plate is attached to the concave portion 102. When the magneto-optical disk 100 is loaded in the recording / reproducing apparatus, the bottom surface 102a of the recess 102 is magnet-clamped on the disk table 105 of the disk rotation drive mechanism 104. Disk table 105
Is mounted on a rotating shaft 107 of a spindle motor 106 and driven to rotate.

In the disk table 105, a magnet 108 is mounted on a disk mounting surface 105a, and three positioning balls 110 are mounted on a projection 109 as shown in FIGS. Convex part 1
Reference numeral 09 denotes a diameter slightly smaller than the inner diameter of the center hole 101 of the magneto-optical disk 100. Positioning ball 110
Are arranged at equal intervals in the circumferential direction, and each of them is exposed to the outer peripheral portion of the convex portion 109 and is assembled to the convex portion 109. Two of the positioning balls 110 are provided with a projecting behavior toward the outside by springs (not shown).

The magneto-optical disk 100 includes a magnet 10
The clamping plate 103 is attracted by 8 and is magnet-clamped on the disk table 105 with the bottom surface 102a of the recess 102 as a mounting reference surface. In this state, the projection 109 of the disk table 105 enters the center hole 101 in this state, and the center of rotation is established by the positioning balls 110 being pressed against the inner peripheral wall of the center hole 101 as shown in FIG. Positioned.

As described above, the magneto-optical disk 100 is
Disk table 105 of disk rotation drive mechanism 104
The center of rotation is positioned by pressing the positioning ball 110 against the inner peripheral wall of the center hole 101. Therefore, in the magneto-optical disk 100, the positioning accuracy of the rotation center is determined by the hole accuracy of the center hole 101, that is, the surface accuracy of the inner peripheral wall (the tolerance of unevenness). When the positioning ball 110 is engaged with the large concave portion 101a formed on the inner peripheral wall of the magneto-optical disk 100 due to poor hole accuracy of the center hole 101, as shown in FIG. The rotation is driven in a state where the rotation center is eccentric. When recording and reproduction of information signals and the like are performed in this state, the magneto-optical disk 100 may cause a tracking error due to an eccentric component, thereby causing a tracking error.

In the conventional magneto-optical disk 100,
The specification of the accuracy of the inner peripheral wall surface of the center hole 101 was set to 70 μmpp. Therefore, in the magneto-optical disk 100, even if the center hole 101 is punched and formed by a center punch in a forming die at the time of forming the disk substrate as described above, it is possible to sufficiently conform to this specification.

[0010]

By the way, in the magneto-optical disk 100, the recording track pitch is narrowed, for example, to 0.6 times that of the conventional specification, so that high-density recording of information signals and the like can be achieved. Have been. This high-density recording magneto-optical disk 100 needs to be rotationally driven with the rotation center positioned with higher precision.
The surface accuracy specification of the inner peripheral wall of the center hole 101 is strictly set to, for example, about 40 μmpp compared to the conventional specification (specification of the low-density recording magneto-optical disk 100) of 70 μmpp.

The high-density recorded magneto-optical disk 100 is formed by punching a center hole by a high-precision center punch on a disk substrate formed with high dimensional accuracy, and the degree of abrasion of the center punch and the like is also determined. It must be strictly managed. High density recording magneto-optical disk 100
In addition, the method involves forming a molding die including a stamper and a center punch with high accuracy, and also requires processes such as management and re-grinding of the center punch, resulting in increased costs and poor productivity.

Conventionally, the surface accuracy of the center hole 101 of the disk substrate is 40 μmpp or more, which is almost the same as the required specification of the high density recording magneto-optical disk 100 described above. In addition to the need for a 100% inspection process for the manufactured disk substrates, the productivity is lowered, and depending on the change in the molding conditions, a substrate having a size outside the specified size is formed, thereby lowering the yield.

In the magneto-optical disk 100, the positioning ball 110 of the disk table 105 is relatively engaged with the center hole 101 at a certain depth in the axial direction. That is, the disk table 105
The configuration is such that the positioning ball 110 is not pressed against the center hole 101 of the magneto-optical disk 100 at a position, for example, at most 0.6 mm or more from the mounting reference surface 102a. Therefore, the magneto-optical disk 100 has the center hole 1
01, the surface accuracy of the inner peripheral wall
It is sufficient that the portion from the bottom surface 102a of the concave portion 102, which is a reference surface when the magnetic chuck 05 is magnet chucked, to a depth position of 0.6 mm conforms to the above specification.

The disk substrate is formed directly by the outer periphery of the center punch, has a small internal stress, and is sharply cut by the center punch to form a shear surface. Is manufactured with extremely high precision. On the other hand, the inner surface of the disk substrate gradually increases as the punching operation by the center punch proceeds, and a fracture surface is generated.
center hole 10 as the depth from
1, the surface accuracy of the inner peripheral wall is deteriorated.

Focusing on such molding characteristics, the disk substrate is formed by a molding die 120 shown in FIG.
1 is at least 0.6 m from the mounting reference surface 102a with which the positioning ball 110 relatively engages,
m and molded to meet the required specifications in the area below m. The molding die 120 is composed of a fixed die 121 and a movable die 122 that is arranged to face the fixed die 121 and that is moved toward and away from the fixed die 121. Mold 12
Numeral 0 indicates that a cavity forming portion is formed on each of the main surfaces of the fixed mold 121 and the movable mold 122 facing each other, and a cavity 125 which is a molding space of the disk substrate 2 is formed in a mold clamped state.

A sprue bush 126 is mounted on the fixed die 121 at the center of the cavity 123. The sprue bush 126 includes a movable mold 1 described later.
A nozzle 127 is provided at a position corresponding to the center hole 101 of the disk substrate to be punched and removed by the center punch 128 on the 22 side. The nozzle 127 is
A molten synthetic resin material, for example, a transparent polycarbonate resin injected and supplied from the injection molding machine side is used for the cavity 1.
Inject into 25.

A stamper 129 for transferring and recording recording tracks on the main surface of the disk substrate is mounted on the cavity forming surface of the movable mold 122. Movable mold 12
2, a center punch 128 and an eject pin 130 are provided. The center punch 128 is fixed die 1
While being located opposite the nozzle 127 on the 21 side,
The distal end portion 128 a is combined with the movable mold 122 in a state of protruding into the cavity 125. After the disk substrate is formed, the center punch 128 is protruded into the cavity 125 to punch and form the center hole 101 in the disk substrate.

More specifically, the center punch 128
28a has a height h of 0.3 from the mounting reference plane 102a.
mm. Therefore, the center hole 101 has an inner peripheral wall surface whose entire depth dimension t = 0.8.
The portion from the mounting reference surface 102a to 0.3 mm with respect to the mm is directly formed by the center punch 128. The remaining portion of the center hole 101 is punched and formed by the center punch 128. in this case,
The inner peripheral wall surface of the center hole 101 is constituted by a molding surface, a shear surface, and a fracture surface. Center hole 101
Is generated at a position at least 0.6 mm from the mounting reference plane 102a.

As described above, the molding die 120 is used to mold a disk substrate in which a substantial portion of the center hole 101 is formed with high precision. As shown in FIG.
Since the resin flow path 131 between the distal end portion 128a of the nozzle 8 and the injection port 127a of the nozzle 127 becomes narrow, the fluidity of the molten resin deteriorates. Therefore, it is difficult for the molding die 120 to optimally control the molding conditions such as the mold temperature and the injection pressure of the molten resin, and the surface deviation, the birefringence, the skew or the groove due to the deterioration of the surface accuracy of the disk substrate to be molded. This causes a problem that the variation in transferability is increased.

On the other hand, in the magneto-optical disk 100,
As described above, the recess 102
The clamping plate 103 is attached to the internal space of the. The clamping plate 103 is provided with the concave portion 10.
After being mounted in the internal space of No. 2, the opening edge of the concave portion 102 is subjected to a swaging process for applying ultrasonic waves, and is prevented from coming off by a plurality of stopper convex portions formed by melting. Since the clamping plate 103 is attached to the internal space of the concave portion 102 in a non-fixed state as described above, it may fall off depending on the amount of protrusion of the stopper convex portion. In addition, the clamping plate 103 may move inside the recess 102 due to the clearance between the outer peripheral portion and the inner peripheral wall of the recess 102 to generate shavings. The shavings adhere to the surface of the disk substrate and deteriorate recording / reproducing characteristics of information signals and the like.

Therefore, according to the present invention, the center hole is formed with high precision at least in the region where the positioning means of the center of rotation relatively engages, and the entire disk substrate is formed with high precision. It has been proposed for the purpose of providing a disc-shaped recording medium to which a clamping plate can be securely attached.

[0022]

A disk-shaped recording medium according to the present invention, which achieves this object, has a disk substrate formed by a molding die using synthetic resin as a material, and is loaded into a recording / reproducing apparatus. Recording / reproduction of information signals and the like is performed by being rotationally driven by the disk drive mechanism in a state where the rotation center is positioned by the center hole which is chucked by the magnet chucking means and engages with the positioning means. The disc-shaped recording medium is formed by a molding die using a synthetic resin as a material, and is formed by punching a center hole constituting a rotation center at a center portion by a center punch having a tip portion previously projected into a cavity; A clamping plate attached to a recess formed in a central region surrounding the center hole of the disk substrate, which is formed in a substantially shallow dish shape by bending a mounting flange portion on an outer peripheral portion using a metal plate as a material; Is provided. The disk-shaped recording medium has a smaller diameter than the mounting flange along the opening edge of the center hole on the clamping plate mounting surface side of the recessed portion on the disk substrate, and an annular locking projection for locking the inner peripheral surface thereof. The part is formed integrally.

According to the disk-shaped recording medium of the present invention configured as described above, at least a portion of the center hole where the positioning means of the recording / reproducing device is engaged is directly formed by the outer peripheral portion of the center punch. Since the stress generation is small and formed by the initial part of the punching operation that is sharply cut by the center punch, it is formed with high precision close to a perfect circle. Therefore, the disc-shaped recording medium can use a center punch which has a gentle dimensional tolerance and does not require strict wear control, and the conditions of the punching process by the center punch are also eased, so that a high-precision disk substrate can be used. Is produced efficiently. In addition, since the disc-shaped recording medium is positioned and mounted on the recording and / or reproducing apparatus with high precision, tracking control conditions are relaxed,
Accurate recording / reproduction of information signals and the like is performed even under high-density specifications or severe use conditions. Further, in the disc-shaped recording medium, since the portion corresponding to the locking projection forms a resin flow path with a sufficient interval between the center punch and the center hole,
The fluidity of the material resin is maintained and the disk substrate runs out,
The skew or the variation in the transferability of the groove or the like is formed with high accuracy and small variation.

[0024]

Embodiments of the present invention will be described below in detail with reference to the drawings. As an embodiment, the disc-shaped recording medium shown in FIGS. 1 and 2 is a magneto-optical recording medium of a high-density recording specification capable of reproducing information signals recorded at high density and recording information signals at high density. Disc 1
It is. The magneto-optical disk 1 includes a disk substrate 2 and a clamping plate 3, and is rotatably housed in a thin box-shaped cartridge (not shown). The disk substrate 2 is made of a light-transmitting synthetic resin material, for example, a polycarbonate resin as a material.
Formed by

Although not described in detail, a pregroove forming a recording track on which a desired information signal or the like is recorded is formed in a spiral shape at a narrow track pitch on the disk substrate 2 and a signal recording made of a magnetic film layer is performed. And a light reflection layer. The disc substrate 2 has, for example, a thickness dimension a of 0.8 mm, and is formed integrally with a recess 5 having a center hole 4 formed in the center thereof by swelling toward one main surface side. The disk substrate 2 accommodates a clamping plate 3 made of a magnetic material such as a metal plate on the bottom surface 5b of the internal space 5a of the recess 5. Disk substrate 2
When the magneto-optical disk 1 is mounted on the recording / reproducing apparatus as described later, the mounting reference surface 5c
Is configured. The concave portion 5 is formed on the inner peripheral portion of the disk substrate 2 where no recording track is formed.

The center hole 4 is formed in the molding die 2 as described later.
When the disk substrate 2 is molded by the method of FIG. The center hole 4 has a hole diameter b of, for example, 11 mm, and the inner peripheral wall has irregularities of about 10 μmpp at least from the mounting reference plane 5 c to a portion having a depth dimension of 0.6 mm, and at most 25 μmpp.
It is formed with the following high surface accuracy.

An annular locking projection 6 is formed integrally with the disc substrate 2 along the opening edge of the center hole 4 on the bottom surface 5 b of the internal space 5 a of the recess 5. The locking protrusion 6 has a height dimension c of 0.1 mm or more and 1.0 mm or less, and an outer diameter d of 12.5 mm or less. Therefore, the height e of the disk substrate 2 is maintained at 0.9 mm or more and 1.8 mm or less even at the opening of the center hole 4 with respect to the thickness of 0.8 mm at the bottom surface of the recess 5. The gap between the mounting reference plane set on the conventional magneto-optical disk 100 and the clamping plate 103 is maintained. Thus, the magneto-optical disk 1 can be used with compatibility with the conventional magneto-optical disk 100 without changing the specifications of the recording / reproducing apparatus.

The outer diameter of the clamping plate 3 is slightly smaller than the inner diameter of the internal space 5a of the concave portion 5, and a flange-shaped locking portion 3a having a crank-shaped cross section on the outer peripheral portion is formed around the entire circumference. It is formed so as to be bent integrally. The dimensions of the clamping plate 3 are the same as those of the conventional clamping plate 103. The height of the inner surface of the clamping plate 3 from the reference mounting surface 5c is not less than 1.8 mm, and the flange-shaped locking portion 3a is provided. Has an inner diameter of 12.5 mm or more.

The disk substrate 2 is subjected to a swaging process for applying an ultrasonic wave to the opening edge of the concave portion 5 in a state where the clamping plate 3 is housed in the internal space 5a, as shown in FIG. A plurality of stopper protrusions 7 protruding in the center direction are formed by melting. The disk substrate 2
The magneto-optical disk 1 is configured by locking the flange-shaped locking portions 3 a by these stopper projections 7 so that the clamping plates 3 do not fall out of the concave portions 5. The basic configuration of the magneto-optical disk 1 is the same as that of the conventional magneto-optical disk 100.

When the magneto-optical disk 1 is loaded in the recording / reproducing apparatus, it is chucked on the disk table 10 of the disk rotation drive mechanism as shown in FIGS. It is driven to rotate.
The disk table 10 is provided with the concave portion 5 of the magneto-optical disk 1.
The outer diameter of the stepping motor is slightly larger than the outer diameter of the stepping motor. The disk table 10 has a projection 11 at the center of the main surface 10a.
An annular magnet 12 is provided so as to surround 1. The magnet 12 magnetically chucks the magneto-optical disk 1 by attracting the clamping plate 3 as described later.

The outer diameter of the engaging projection 11 is slightly smaller than the inner diameter of the center hole 4 of the magneto-optical disk 1 and the height is slightly lower than the thickness of the recess 5. In the outer periphery of the engagement protrusion 11, ball attachment recesses 13 (13a to 13c) which are located at regular intervals in the circumferential direction and have a substantially hemispherical shape are formed. Further, the engaging projection 11 is provided with a spring mounting groove 14 (14a, 14b) connected to the bottom of the first ball mounting recess 13a and the second ball mounting recess 13b.

Three positioning balls 15 (15a to 15c) and two coil springs 16 (16a, 16b) are assembled to the engagement projection 11. Each of the positioning balls 15 is assembled in each of the ball mounting recesses 13 in such a manner that a part of the peripheral surface is exposed outward and is prevented from coming off. Coil spring 1
As shown in FIG. 3, the reference numerals 6 are respectively assembled in the spring installation grooves 14 in a compressed state. The coil spring 16 couples the first positioning ball 15a and the second positioning ball 15b assembled to the first ball mounting recess 13a and the second ball mounting recess 13b with the engaging projection 11
Bias in the direction protruding from Therefore, each positioning ball 15 has a state in which the first positioning ball 15a and the second positioning ball 15b are movable in the diametrical direction and the third positioning ball 15c is fixed in the diametrical direction. It is assembled to the engaging projection 11.

When the magneto-optical disk 1 is loaded in the recording / reproducing apparatus, the clamping plate 3 is attracted by the magnet 12 and is magnet-clamped on the main surface 10a of the disk table 10. The rotation center of the magneto-optical disk 1 is positioned on the disk table 10 by engaging the engaging projections 11 with the center hole 4 and pressing the positioning balls 15 against the inner peripheral wall of the center hole 4. Be attached. Magneto-optical disk 1
When the disk rotation drive mechanism is driven in this state,
It is driven to rotate integrally with the disk table 10.

The magneto-optical disk 1 reproduces information signals and the like recorded on recording tracks by an optical pickup (not shown). The magneto-optical disk 1 is applied with an external magnetic field modulated by a magnetic head according to an information signal or the like to be recorded by a magnetic head in a state where a laser beam emitted from an optical pickup irradiates a recording track. Recording of signals and the like is performed. The operation of recording / reproducing such information signals is exactly the same as that of the conventional device. Therefore,
The magneto-optical disk 1 does not require a new configuration for the recording / reproducing device.

As described above, in the magneto-optical disk 1, the inner peripheral wall of the center hole 4 at a position at least 0.6 mm from the mounting reference plane 5c is formed with high surface accuracy with irregularities of about 10 μmpp. On the other hand, the disk table 10
The configuration is such that the positioning ball 15 does not press against the center hole 4 of the magneto-optical disk 1 at a position having an upper limit of 0.6 mm or more in the axial direction. Accordingly, the magneto-optical disk 1 does not have a large eccentric rotation center due to the positioning ball 15 engaging with the large concave portion formed on the inner peripheral wall surface of the center hole 4.
The magnet is chucked by being accurately positioned on the zero.

Since the magneto-optical disk 1 is driven to rotate via the disk table 5 in a state where there is no blur, the magneto-optical disk 1 is recorded on a recording track formed at a narrow track pitch without performing high-precision tracking control. Accurate reproduction of the information signal or the like or recording of the information signal or the like is performed. In addition, the magneto-optical disk 1 can accurately reproduce an information signal or the like or record an information signal or the like even when vibration or the like is applied.

The disk substrate 2 of the above-described magneto-optical disk 1 is molded by the molding die 20 shown in FIG.
The molding die 20 also has the same basic configuration as that of the conventional molding die. As shown in the figure, a stationary die 21 is disposed opposite to the stationary die 21 and a contact / separation operation is performed. And a movable mold 22 to be used. Mold 20
The mold of the injection molding machine is manufactured by mounting the fixed mold 21 to the fixed mold block 23 via mounting bolts and the like and the movable mold 22 to the movable mold block 24 via mounting bolts and the like. It is attached to the attachment part. The molding die 20 includes a fixed die 21 and a movable die 2.
A cavity constituting portion is formed on each of the main surfaces facing 2. The molding die 20 has a cavity 25 which is a molding space of the disk substrate 2 in a state where the movable die 22 is moved and joined to the fixed die 21 as described later (in a clamped state). You.

A sprue bush 26 is attached to the fixed mold 21 at the center of the cavity 25.
The sprue bush 26 has a nozzle 27 which opens at a portion corresponding to the center hole 4 of the disk substrate 2 which is punched and removed by a center punch 28 on the movable mold 22 side described later.
Is provided. The nozzle 27 injects a molten synthetic resin material, for example, a transparent polycarbonate resin, which is injected and supplied from the injection molding machine side, into the cavity 25 from the nozzle opening 27a.

By the way, the nozzle 27 is
The inner diameter of a is substantially equal to the inner diameter of the center hole 4, in other words, the outer diameter of the center punch 28, but an enlarged diameter portion 27 b is formed at the leading end thereof. The enlarged diameter portion 27b has a depth dimension of 0.1 mm or more and 1.0 m or more.
m and the outer diameter is 12.5 mm or less. In other words, the enlarged diameter portion 27b is a portion where the above-mentioned locking projection 6 of the disk substrate 2 is formed.

A stamper 29 for transferring recording tracks to the main surface of the disk substrate 2 formed in the cavity 25 is mounted on the cavity forming surface of the movable mold 22. The movable mold 22 is provided with a center punch 28 and a plurality of eject pins 30. The center punch 28 is positioned so as to face the nozzle 27 on the fixed mold 21 side, and is combined with the movable mold 22 with its tip 28a protruding into the cavity 25 as described in detail later. I have. After the disk substrate 2 is formed, the center punch 28 is protruded into the cavity 25 to punch and form the center hole 4 in the disk substrate 2.

The eject pin 30 is arranged on the outer peripheral portion of the center punch 28 corresponding to the concave portion 5 of the disk substrate 2 and is combined with the movable mold 22. The eject pins 30 are fixed to the fixed mold 2 when the disk substrate 2 is formed.
In the state where the movable mold 22 performs the mold opening operation with respect to
To eject.

When the movable mold 22 is joined to the fixed mold 21, the molding mold 20 is
From 7, a molten polycarbonate resin is injected into the cavity 25. In the molding die 20, the fixed state of the fixed die 21 and the movable die 22 is maintained for a predetermined time until the injected polycarbonate resin is slightly cured. The molding die 20 removes the molding distortion generated in the disk substrate 2 which is formed by the movable molding 22 moving to the fixed mold 21 and being subjected to the compression molding operation.

In the molding die 20, the center punch 28 is operated before the injected polycarbonate resin is completely cured, and the center hole 4 is formed by punching out the center hole 4 of the disk substrate 2 protruded into the cavity 25 and molded. I do. In the molding die 20, the fixed state of the fixed die 21 and the movable die 22 is maintained until the polycarbonate resin is completely cured.

After a predetermined hardening time has elapsed, the movable mold 22 is separated from the fixed mold 21 to perform the mold opening operation. The molding die 20 performs an opening operation in a state where the disk substrate 2 is attached to the movable die 22 side, and performs an ejecting operation in which the disk substrate 2 is pushed down from the movable die 22 by a projecting operation of the eject pin 30. Will be Further, in the molding die 20, the runner portion remaining in the nozzle 27 along with the ejecting operation of the disk substrate 2 is cut by an appropriate structure. The disk substrate 2 formed by the molding die 20 as described above
Is manufactured as the magneto-optical disk 1 through a process such as a process of attaching the clamping plate 3 to the recess 5.

Incidentally, in the molding die 20, the tip portion 28a of the center punch 28 is configured to protrude into the cavity 25 in advance as described above. Specifically, the center punch 28 is set so that the height h from the cavity surface forming the mounting reference surface 5c is about 0.6 mm. The molding die 20 molds the disk substrate 2 having a thickness of 0.8 mm. When the center punch 28 projects into the cavity 25 with a projection amount of about 0.6 mm as described above, the nozzle opening is formed. 27a and center punch 2
8, that is, the flow path of the molten resin is deteriorated, that is, the resin flow path is narrowed.

In the molding die 20, since the enlarged diameter portion 27b is formed at the tip of the nozzle opening 27a, the sectional area of this portion 25a is sufficiently ensured, and the fluidity of the molten resin does not deteriorate. . Therefore, the molding die 20
The molding of the disk substrate 2 can be performed by setting the mold temperature and the injection speed of the molten resin in the optimum ranges. Thus, the molding die 20 forms the disk substrate 2 which is excellent in surface deflection, birefringence or skew characteristics.

On the other hand, the molding die 20 has the entire depth dimension e.
For the center hole 4 (0.9 mm or more and 1.8 mm or less), the distance from the cavity surface forming the mounting reference surface 5c is 0.6
The part up to mm is directly formed by the center punch 28. Further, the molding die 20 is formed by punching the remaining portion of the center hole 4 by the center punch 28. Therefore, the center hole 4 has an inner peripheral wall surface formed with a molding surface,
It will be composed of a shear surface and a fracture surface.

The center hole 4 is thus fitted with the mounting reference surface 5c.
Since the side opening part is directly formed by the outer peripheral surface of the center punch 28 to a part having a depth dimension of up to 0.6 mm,
It is formed with high surface accuracy approximating a perfect circle with an extremely small degree of irregularity. In addition, since the center hole 4 is punched and formed by the center punch 28 at a portion 0.6 mm or more from the mounting reference surface 5c, the degree of unevenness is slightly larger than that of the opening portion. However, 0.6
From the millimeter to a slightly deeper position, the degree of concavity and convexity is formed at a maximum value of about 10 μmpp because of the sheared surface as described above, which is an extremely small value as compared with the conventional magneto-optical disk 100.

Incidentally, in the magneto-optical disk 1,
The tolerance of the unevenness generated on the inner peripheral wall surface of the center hole 4 needs to be 25 μmpp or less in order to conform to the required specification (40 μmpp) in consideration of the margin. Of course,
The tolerance of the concave and convex of the center hole 4 only needs to be maintained at least to a position 0.6 mm from the mounting reference surface 5c with which the positioning ball 15 of the disk table 10 relatively engages. As described above, in the magneto-optical disk 1, the center hole 4 of the disk substrate 2 is formed so as to sufficiently satisfy the tolerance of the unevenness.

In the molding die 20, as described above, the center punch 28 is moved 0.6 mm from the mounting reference surface 5 c.
Although the projection is made to project into the cavity 25 in advance with a projection dimension h of 2 mm, the center hole 4 conforming to the required specifications of the magneto-optical disk 1 can be formed if it is at least 0.2 mm or more. . That is, the center hole 4 is formed with a shearing surface having a relatively good surface accuracy at a position of 0.4 mm by the center punch 28 following the forming surface directly formed by the outer peripheral portion of the center punch 28.
In other words, the center punch 28 is provided with respect to the cavity 25 for molding the disk substrate 2 having a thickness of 0.8 mm by not less than 1/3 of the thickness in consideration of a margin.
What is necessary is just to make it project in advance with a projection amount of 2 or less.

In the molding die 20, since the center punch 28 is assembled by the above-described configuration, the dimensional accuracy of the formation portion of the center punch 28 and the center hole 4 is greatly eased, and the center hole 4 is formed by the center punch 28. Can be formed under relatively mild conditions. Further, the molding die 20 includes a center punch 28.
The wear control of the disk substrate 2 is also eased, the productivity of the disk substrate 2 is improved, and the high-precision disk substrate 2 with good yield is obtained.
Is molded.

In the above-described embodiment, the magneto-optical disk 1 has a thickness of 0.8 mm, is magnetically chucked on the disk table 10, and is positioned at the center of rotation by the positioning ball 15. However, the present invention is not limited to the magneto-optical disk 1. The present invention is also applicable to other disk-shaped recording media, such as magnetic disks, which are magnet chucked on a disk table and whose rotation center is positioned by positioning balls.

[0053]

As described above in detail, according to the disk-shaped recording medium of the present invention, at least a portion of the center hole where the positioning means is engaged is formed by the outer peripheral portion of the center punch which is previously projected into the cavity. Since it is directly formed, it is formed with high precision, and is positioned and mounted on the recording / reproducing device with high precision, so that the tracking control conditions are relaxed, and the information signal etc. can be obtained even under high-density specifications or severe use conditions. Accurate recording / reproduction is performed. In addition, the disc-shaped recording medium can use a center punch which has a gradual dimensional tolerance and does not require strict wear control, and the conditions of the punching process by the center punch are also eased to reduce the cost. Produced efficiently. Further, in the disk-shaped recording medium, since the portion corresponding to the locking projection forms a resin flow path with a sufficient space between the center punch and the center hole, the fluidity of the material resin is maintained and the surface runout is maintained. In addition, variations such as birefringence, skew and transferability of grooves are small, and they are formed with high precision.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a main part of a magneto-optical disk shown as an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of a main part showing a state where the magneto-optical disk is chucked on a disk table.

FIG. 3 is an explanatory diagram showing details of the chucking state.

FIG. 4 is a longitudinal sectional view of a main part of a molding die for molding a disk substrate of the magneto-optical disk.

FIG. 5 is a schematic configuration diagram of a conventional magneto-optical disk and a disk drive.

FIG. 6 is an explanatory diagram showing details of a chucking state of the magneto-optical disk.

FIG. 7 is a longitudinal sectional view of a main part of a molding die for molding a conventional disk substrate.

[Explanation of symbols]

1 magneto-optical disk (disk-shaped recording medium), 2 disk substrate, 3 clamping plate, 4 center hole, 5
Recessed part, 5a internal space, 5c bottom surface (mounting reference surface),
6 locking projection, 7 stopper projection, 10 disk table, 11 engagement projection, 12 magnet, 15 positioning ball (positioning means), 20 disk substrate molding die, 21 fixed die, 22 movable die, 25 cavities, 27 nozzles, 27a nozzle openings, 27b
Enlarged portion, 28 Center punch, 28a Tip, 29
Stamper, 30 eject pins

Claims (4)

[Claims] 1. A disk substrate molded by a molding die using a synthetic resin as a raw material, and having a center hole punching and forming a center of rotation at a center portion by a center punch having a tip portion previously projected into a cavity; A clamping plate is formed in a substantially shallow dish shape by bending a mounting flange portion on an outer peripheral portion using a metal plate as a material, and is mounted in a concave portion formed in a central region surrounding the center hole of the disk substrate. A plate having a smaller diameter than the mounting flange along the opening edge of the center hole on the side of the clamping plate mounting surface of the recess, the inner surface of which is locked. A disc-shaped recording medium, wherein the locking projections are integrally formed. 2. The clamping plate, wherein the mounting flange portion, the inner peripheral surface of which is locked by the locking convex portion, is formed so that its outer peripheral surface protrudes inward at an opening edge of the concave portion. 2. The disk-shaped recording medium according to claim 1, wherein the disk-shaped recording medium is held in a recess of the disk substrate by being locked by a stopper convex portion. 3. The molten resin is formed between an opening of a nozzle for injecting the molten resin material into the cavity and a tip of the center punch protruded into the cavity. The disk-shaped recording medium according to claim 1, wherein the recording medium is formed by a wide-diameter portion that holds a flow path of a material. 4. The upper limit of a positioning means for positioning the center of rotation of the center hole, the tip of which is at least one-third of a thickness dimension from a mounting reference plane of the recess, and is relatively engaged to position the center of rotation. 4. The disk-shaped recording medium according to claim 3, wherein the recording medium is punched and formed by the center punch previously projected into the cavity with a projection amount equal to or less than the joint position.