JP2000000851A - Metal mold for disk substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the influence of the gases of low molecular weight components of a synthetic resin material, a mold release agent, and others effectively by forming a sealing part which contacts the peripheral side part of the back part of a stamper and seals the gap between the back part of the stamper and a stamper mounting surface on a stamper mounting surface of a mold. SOLUTION: A metal mold for a disk substrate is equipped with a fixed metal mold 1 and a movable metal mold 2 which are arranged opposite to each other, and between a stamper mounting surface 3 which is a main surface part of the fixed metal mold 1 and the main surface part of the movable metal mold 2, when the molds 1, 2 are butted against each other, a molding cavity 4 of a shape corresponding to the disk substrate to be molded is formed. An O-ring 12 to be a sealing member is arranged in the peripheral part of the stamper mounting surface 3 of the fixed metal mold 1. Accordingly, since the gap between the back part of a stamper 8 and the stamper mounting surface 3 is sealed by the O-ring 12, the intrusion of the gases of low molecular weight components, a mold release agent, and others generated in the mold is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disk substrate mold for producing a disk substrate of a recording disk such as an optical disk or a magneto-optical disk by injection molding.

[0002]

2. Description of the Related Art Conventionally, recording disks such as optical disks and magneto-optical disks have been proposed. These recording disks are configured by forming a signal recording layer on the main surface of a disk-shaped disk substrate made of a synthetic resin material. The disk substrate is manufactured using a disk substrate mold.

[0003] As shown in FIG. 4, the die for a disk substrate is brought into contact with each other to form a cavity 1.
The fixed mold 102 and the movable mold 103 forming the first and second molds 01 and 01 are formed. The cavity 101 is a closed space, and a disk substrate is manufactured by injecting a synthetic resin material 104 to be a material of the disk substrate into the cavity 101 through the nozzle portion 105. In this disk substrate die, the fixed die 10
A disk-shaped stamper 106 is attached to at least one of the movable mold 103 and the movable mold 103. This stamper 1
06 is provided by an annular stamper holding member 107.
It is fixed and attached to the fixed mold 102 or the movable mold 103 in a state where the back surface is in close contact with the fixed mold 102 or the movable mold 103. On the surface of the stamper 106, irregularities corresponding to irregularities such as groups and pits to be formed on the main surface of the disk substrate are formed.
In other words, the disk substrate is molded in such a manner that the resin material 104 melted into the cavity 101 is injected, so that the irregularities formed on the surface of the stamper 106 located in the cavity 101 are transferred.

The fixed die 102 of the disk substrate die
Alternatively, the surface portion of the movable mold 103 to which the back surface of the stamper is in close contact, that is, the stamper mounting surface (signal surface mirror portion or stamper mirror portion) 108 is HRC.
The surface of a mold made of 50 or more hardened steels is polished (wrapped) to a mirror surface having a surface roughness of about 0.03S, and further coated with TiC, TiN, or the like.

[0005]

By the way, in the above-mentioned mold for a disk substrate, the stamper expands when the synthetic resin material heated above the melting temperature is injected and when the synthetic resin material is cooled. The shrinkage causes friction between the stamper mounting surface and minute irregularities are formed by a so-called fretting phenomenon. The unevenness thus formed is transferred as a shape error to the disk substrate to be molded. An error in the shape of the disk substrate caused by such transfer, particularly a convex shape, may cause a tracking servo error or the like in a recording disk formed using the disk substrate.

[0006] As the information recording density on the recording disk increases, the influence of a minute change in the shape of the disk substrate increases, and the maximum allowable shape error decreases. Therefore, in this case, the number of times that a disk substrate can be molded in one disk substrate mold without a shape error exceeding an allowable value is reduced. If the shape error of the disk substrate to be molded exceeds an allowable value, the mold must be disassembled and the stamper mounting surface must be polished again. Therefore, as the density of information recording on the recording disk increases, the productivity of the disk substrate deteriorates.

[0007] The formation rate of the irregularities on the stamper mounting surface depends on the low molecular weight component of the synthetic resin material generated when the molten synthetic resin material is injected into the mold and a gas such as a release agent. It turns out that it is accelerating.

[0008] As a countermeasure against such gas generation,
As proposed in Japanese Patent Application No. 3-8412,
It is conceivable to provide a hole for gas escape in the mold. However, when holes are provided in the mold as a countermeasure against the generation of gas, the temperature of the mold must be extremely high, and the molding of a disk substrate used for a high-density recording disk is required. Does not provide a very good effect.

In addition, a measure has been proposed in which the interior of the mold is evacuated to remove gas before the injection of the synthetic resin.
However, in this measure, it is difficult to sufficiently remove the gas in the mold, a large-scale apparatus is required, and the structure of the mold is complicated.

Further, as a countermeasure against such gas generation, it is conceivable to cut low molecular weight components of the synthetic resin material. However, when this countermeasure is adopted, the production of the synthetic resin material becomes difficult and the production cost increases, so that an inexpensive recording disk cannot be provided.

Accordingly, the present invention has been proposed in view of the above-mentioned circumstances, and has been proposed in view of the low molecular weight component of the synthetic resin material, the release agent, etc., without complicating the configuration and increasing the size. An object of the present invention is to provide a disk substrate mold capable of effectively preventing the influence of gas and maintaining the productivity of the disk substrate in a good state even when the information recording on the recording disk is increased in density. It is.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a disk substrate mold according to the present invention has a fixed mold and a movable mold which form a cavity by being butted against each other. A disk on which a stamper is attached to at least one of a mold and a movable mold, positioned in the cavity, a molten resin material is injected into the cavity, and irregularities formed on the surface of the stamper are transferred. In a disk substrate mold for molding a substrate, a stamper mounting surface of a fixed die or a movable die to which a back portion of the stamper is attached, and an outer peripheral portion of the back portion of the stamper are brought into contact with a back surface portion of the stamper. A seal member is provided for sealing the space between the stamper mounting surface.

In the disk substrate mold, the low molecular weight component of the synthetic resin material and the gas of the release material generated when the synthetic resin material is injected are prevented from entering between the stamper and the stamper mounting surface. This makes it possible to stabilize the characteristics of the molded disk substrate and extend the wear life of the stamper mounting surface.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

A mold for a disk substrate according to the present invention is a mold for forming a disk substrate by injection molding using a synthetic resin material such as polycarbonate or polymethylmethacrylate which has optical transparency. It is. This disk substrate constitutes a recording disk such as a so-called optical disk or magneto-optical disk by forming a signal recording layer on a main surface portion.

As shown in FIG. 1, the disk substrate mold includes a fixed mold 1 and a movable mold 2 which are arranged to face each other. When the fixed mold 1 and the movable mold 2 are abutted with each other, a space between the stamper mounting surface 3 which is the main surface of the fixed mold 1 and the main surface of the movable mold 2 corresponds to the disk substrate to be molded. The molding cavity 4 having the following shape is formed. That is, the forming cavity 4 has a substantially disk shape.

At the center position of the fixed die 1, that is, at the center position of the stamper mounting surface 3 constituting the molding cavity 4 of the fixed die 1, an insertion hole is formed perpendicular to the stamper mounting surface 3. . A substantially annular sprue bush support ring 5 is inserted and disposed in an insertion hole formed in the fixed mold 1. The sprue bush support ring 5 has a substantially cylindrical sprue bush 6.
Are fitted and arranged. The sprue bush 6 has a resin injection nozzle 7 formed along a central axis.
This sprue bush 6 is formed via a resin injection nozzle 7
A molten synthetic resin material supplied from an injection device (not shown) is caused to flow into the molding cavity 4. The sprue bush 6 is disposed such that a tip end portion thereof is slightly protruded from the stamper mounting surface 3 of the fixed mold 1. In other words, the sprue bush 6 has its tip end portion entering the molding cavity 4, and the tip end surface of the resin injection nozzle 7 where the opening end is formed faces the molding cavity 4. The sprue bush support ring 5 has a step-like reduced diameter at the front end facing the molding cavity 4 and a flange-shaped flange at the rear end. The front end of the sprue bush support ring 5 is substantially flush with the stamper mounting surface 3 of the stationary mold 1 and forms a part of the inner surface of the molding cavity 4.

The molding cavity 4 of the fixed mold 1
The stamper 8 for transferring an information signal or a concavo-convex pattern corresponding to a pre-groove forming a recording track is mounted on the stamper mounting surface 3 constituting the recording track. The stamper 8 is formed of a material such as nickel into a thin disk shape having a center hole 8a at the center.
The stamper 8 is positioned by fitting the center hole 8 a to the tip side portion of the sprue bush 6. That is, the inner diameter of the center hole 8 a corresponds to the outer diameter of the sprue bush 6. The stamper 8 has an inner peripheral edge portion of the center hole 8a,
The flange 5 provided at the front end of the sprue bush support ring 5 presses the sprue bush 5 toward the fixed mold 1.

The outer peripheral edge of the stamper 8 is supported by being sandwiched between the stamper 8 and the fixed mold 1 by an outer stamper holder 9 attached to the fixed mold 1. The outer peripheral side stamper holder 9 is formed in a substantially annular shape, and is attached to an outer peripheral side portion of the fixed mold 1 by a fixing screw 9a as shown in FIG. Has made.

The fixed mold 1 is provided with a stamper suction mechanism for sucking and holding the stamper 8. This stamper suction mechanism discharges air between the fixed mold 1 and the stamper 8 to the outside by a vacuum pump (not shown) through an annular suction slit 10 provided in the fixed mold 1. Is configured. That is, as shown in FIG. 3, the suction slit 10 is opened on the stamper mounting surface 3, and the tunnel section 1 pierced in the fixed mold 1.
It communicates with the outside through 1. This tunnel section 11
Are formed in the radial direction of the molding cavity 4 from the center side of the fixed mold 1 to the outer side surface.

A suction hose (not shown) is attached to the outer surface of the fixed mold 1 so as to communicate with the tunnel section 11. This suction hose is connected to a vacuum pump via a valve device. That is, when the valve device is in the open state, the vacuum pump is connected to the stamper mounting surface 3 of the fixed mold 1 through the suction hose, the tunnel section 11 and the suction slit 10.
And the air between the stamper 8 is sucked and discharged to the outside. When the valve device is closed, the space between the stamper mounting surface 3 of the fixed mold 1 and the stamper 8 is closed to the outside. At this time, the stamper 8
It is held by suction on the stamper mounting surface 3.

As shown in FIG. 1, an O-ring 12 serving as a sealing member is provided on the outer peripheral side of the stamper mounting surface 3 of the fixed mold 1. This O-ring 12
Is inserted into an annular groove 12a formed in the stamper mounting surface 3, as shown in FIG. This O-ring 12 is located on the back side of the stamper 8 and is in contact with the back side of the stamper 8. The O-ring 12
As shown in FIG. 2, on the surface of the stamper 8, it is located outside the region where the disk substrate is formed, and is located outside the suction slit 10. When the O-ring 12 is located inside the area where the disk substrate is formed,
This is because the stamper 8 may be deformed by the injection pressure of the synthetic resin material injected into the cavity 4.

That is, as shown in FIG. 2, if the diameter of the disk substrate to be molded is A, the diameter of the O-ring is a, and the diameter of the center line of the O-ring is X, X = A + a + d is established. ing. a is about 1 mm to 3 mm. d is usually set to 0.5 mm to 1 mm or more.

As the material forming the O-ring 12, a soft material having a small surface frictional resistance, such as a silicon-based material, is selected. this is,
This is to prevent the movement of the stamper 8 due to expansion and contraction from being hindered, and to obtain an accurate disk substrate. When movement due to expansion and contraction of the stamper 8 is hindered, deformation of the group transferred to the disk substrate occurs.

On the other hand, an insertion hole is formed at the center position of the upper movable mold 2 as shown in FIG. The insertion hole is provided at a position facing the front end surface of the sprue bush 6 supported by the fixed mold 1. A sleeve 13 having a substantially cylindrical shape is inserted and disposed in an insertion hole formed in the movable mold 2. The sleeve 13 has its front end face facing the molding cavity 4 slightly immersed in the movable mold 2 more than the main surface of the movable mold 2, and can be moved toward the fixed mold 1. In addition, this sleeve 13
Is provided with a cylindrical punch 14 fitted therein. The punch 14 is movable with respect to the sleeve 13 and is supported by the sleeve 13. The punch 14 has a front end face facing the molding cavity 4 projecting slightly beyond the front end face of the sleeve 13.

In order to form a disk substrate in the disk substrate mold configured as described above, first, the movable mold 2 is abutted against the fixed mold 1 to form the molding cavity 4. Then, the synthetic resin material 1 such as polycarbonate melted in the molding cavity 4 through the resin injection nozzle 7 of the sprue bush 6 by an injection device.
04 is injection-filled. At this time, the synthetic resin material 10
4 flows in the molding cavity 4 from the center toward the outer periphery. Then, the movable mold 2 is moved to the fixed mold 1 side, and the synthetic resin material filled in the molding cavity 4 is compressed by a predetermined mold clamping pressure, so-called mold clamping is performed, followed by cooling. Then, the synthetic resin material 104 filled in the molding cavity 4 is solidified to form a disk substrate having a shape corresponding to the molding cavity 4.

On the other hand, the punch 14 projects a center hole in the disk substrate by protruding toward the fixed mold 1 side. In the disk substrate mold, when molding the disk substrate, the mold clamping pressure, the timing of the punching of the center hole by the punch 14, and the curing timing of the synthetic resin material 104 forming the disk substrate are appropriately changed. The adjustment makes it possible to control the birefringence characteristics of the disk substrate to have desired characteristics. The birefringence characteristic is a characteristic that expresses the amount of birefringence that occurs when a light beam passes through a medium having a so-called refractive index anisotropy, and the x direction and the x direction that are orthogonal to the traveling direction of the light beam and to each other. It is indicated by the phase difference between the polarization components of the light beam in the y direction.

In the disk substrate mold,
By opening the mold to separate the movable mold 2 from the fixed mold 1 while projecting the sleeve 13 toward the fixed mold 1, the molded disk substrate is released from the movable mold 2. Then, the disk substrate is separated from the fixed mold 1 to complete the molding of the disk substrate. One main surface of the disk substrate is a signal recording portion forming surface molded by a stamper 8. That is,
When a read-only optical disk is configured using this disk substrate, the concave / convex pattern is formed on the signal recording portion forming surface of the disk substrate on which the concave / convex pattern corresponding to the information signal is formed by means such as vapor deposition or sputtering. A reflective film made of aluminum or the like is formed by covering. This concavo-convex pattern is formed by transferring the concavo-convex pattern of the stamper 8. These concavo-convex pattern and the reflection film become a signal recording layer.

When a magneto-optical disk for both recording and reproduction is formed using this disk substrate, a signal recording portion forming surface of the disk substrate on which a pre-groove forming a recording track on which an information signal is recorded is formed. Then, a signal recording layer made of a magnetic material is formed so as to cover the pregroove. The pre-groove is formed by transferring the concavo-convex pattern of the stamper 8.

In this die for a disk substrate, the space between the back surface of the stamper 8 and the stamper mounting surface 3 is sealed by the O-ring 12, so that the space between the rear surface of the stamper 8 and the stamper mounting surface 3 is maintained. When the synthetic resin material melted into the mold is injected into the mold, gas such as a low molecular weight component of the synthetic resin material and a release agent does not enter, and the formation speed of the irregularities on the stamper mounting surface is reduced. Is not accelerated.

Here, the disk substrate mold according to the present invention was compared with a disk substrate mold having no O-ring as a sealing member. In any of the dies, the material of the dies was quenched with stainless steel, and the stamper mounting surface had a Rockwell hardness of 53 degrees.
After mirror finishing, the coating process of TiN is 1.8
It is applied with a thickness of μm. Using these molds,
A disk substrate for a magneto-optical (MO) disk having a storage capacity of 1 GB (gigabyte) was continuously molded. Then, it was observed how the tracking servo signal obtained from the magneto-optical disk constituted by using this disk substrate changes with respect to the number of moldings (the number of shots).

As a result, in the disk substrate mold having no O-ring, the tracking servo signal exceeded the allowable value in the magneto-optical disk using the disk substrate molded after 7,000 to 10,000 times molding. However, in the disk substrate mold according to the present invention provided with the O-ring, the 4
Even with a magneto-optical disk using a disk substrate molded after 0000 moldings, the tracking servo signal was within the allowable value.

As shown in FIG. 1, when the stamper 8 is pressed by the flange portion 5a also on the inner peripheral portion, an O-ring serving as a sealing member is also provided on the inner peripheral portion of the stamper 8. It is possible to provide. This is because deformation of the stamper 8 due to injection pressure of the synthetic resin material can be prevented if the seal member is provided at a position below the flange portion 5a.

When the suction slit 10 is positioned outside the O-ring 12, the low molecular weight component of the synthetic resin material generated when the molten synthetic resin material is injected into the mold. A gas such as a mold release agent can be discharged out of the mold by the vacuum pump through the suction slit 10.

[0035]

As described above, in the mold for a disk substrate according to the present invention, when the molten synthetic resin material is injected, gas such as a low molecular weight component of the synthetic resin material and a release material is released. By preventing entry between the stamper and the stamper mounting surface, the wear rate of the stamper mounting surface is suppressed, and the life of the mold is extended.
Expensive surface treatment for extending the life of the stamper mounting surface is not required, and the stamper can be manufactured at low cost. Also,
In this disk substrate die, the quality and characteristics of the disk substrate to be molded can be stabilized, and the interval of the die inspection can be extended.

That is, according to the present invention, the configuration is complicated,
Effectively preventing the effects of gases such as low molecular weight components of synthetic resin materials and mold release agents without increasing the size of the resin material, and improving the productivity of the disk substrate even when the density of information recording on the recording disk is increased. An object of the present invention is to provide a disk substrate mold that can be maintained in a good state.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a configuration of a disk substrate mold according to the present invention.

FIG. 2 is a vertical sectional view of a main part showing a structure of a main part of the disk substrate mold.

FIG. 3 is a plan view showing a configuration of a fixed die of the disk substrate die.

FIG. 4 is a longitudinal sectional view showing a configuration of a conventional disk substrate mold.

[Explanation of symbols]

1 fixed mold, 2 movable mold, 3, 4 cavity,
5, 6, 7, 8 stamper, 9, 10 suction slit, 11 tunnel section, 12 O-ring, 104 synthetic resin material

Claims (2)

[Claims] 1. A fixed mold and a movable mold that form a cavity by being abutted with each other, and a stamper is attached to at least one of the fixed mold and the movable mold to be positioned in the cavity. A disk substrate mold for injecting a molten resin material into the cavity to mold a disk substrate on which the irregularities formed on the surface of the stamper are transferred, wherein the back surface of the stamper is mounted. A seal member is provided on the stamper mounting surface of the fixed mold or the movable mold to contact the outer peripheral portion of the back surface of the stamper to seal the space between the back surface of the stamper and the stamper mounting surface. A mold for a disk substrate, characterized by being made. 2. A method according to claim 1, wherein the fixed or movable mold to which the stamper is attached is suctioned through a back surface of the stamper attached to the stamper attachment surface through an opening provided in the stamper attachment surface to attach the stamper. 2. The disk substrate mold according to claim 1, further comprising a suction means for adsorbing to the stamper mounting surface.