JPH05307769A - Optical disk substrate, apparatus and method for producing optical disk substrate - Google Patents

Abstract

PURPOSE:To prevent the generation of waving and to decrease double refractions in molding of the thin type substrate by a resin. CONSTITUTION:A stamper 4 is fixed onto a moving mold 3 by means of an inner peripheral retainer 5 and a cavity ring 6. A stationary mold 2, the moving mold 3 and the cavity ring 6 are joined and a molten resin is introduced from a nozzle 1 to the spacing formed thereof at the time of molding the substrate. The resin spreads in this spacing and is deformed in compliance with the mold. The resin is thereafter cooled to solidify and the substrate is molded. The moving mold 3, thereafter, parts together with the cavity ring 6 from the stationary mold 2 and a piercer 7 projects toward the substrate plane with a slight delay, by which a hole is formed in the inner peripheral part of the substrate. The spacing near the resin inflow port of the mold of the apparatus for producing the optical disk substrate is formed wider than the part further from the resin inflow port and the plate thickness in the inner peripheral part of the optical disk substrate to be molded is made larger than the plate thickness in the outer peripheral part. In addition the plate thickness in the outer peripheral part is made constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk substrate which is a large capacity recording medium, an apparatus and a method for manufacturing the optical disk substrate.

[0002]

2. Description of the Related Art FIG. 5 shows a sectional view of a molding section of a conventional optical disk substrate manufacturing apparatus. In FIG. 5, reference numeral 1 denotes a nozzle, and pelletized resin is heated by a heater (not shown) and melted, and then introduced into the nozzle 1. The nozzle 1 is joined to the fixed mold 2 of FIG. 3 is a movable mold, and a stamper 4 for transferring grooves and pits to the resin substrate to be molded is fixed on the movable mold 3. This stamper 4
Is generally formed of nickel or the like. The stamper 4 is fixed to the movable mold 3 by an inner presser 5 on the inner peripheral portion and a cavitation 6 on the outer peripheral portion. At the time of molding the substrate, the fixed mold 2, the movable mold 3, and the cavity ring 6 are joined, and the molten resin is guided from the nozzle 1 to the gap formed by these. The resin spreads through this gap and deforms as usual. Then, the resin is cooled and solidified to mold the substrate. After that, the movable mold 3 is separated from the fixed mold 2 together with the cavity 6 and the hole punching 7 projects in the substrate surface direction with a slight delay to form a hole in the inner peripheral portion of the substrate. Conventionally, a method has been used in which the gap between the fixed mold 2 and the movable mold 3 is opened by about 0.1 mm when the resin is inflowed, and the mold is closed after the resin is filled. This is because the birefringence is reduced, and the pressure applied to the resin is reduced, and the shear stress applied to the resin is reduced.

[0003]

The thinner the disc substrate is, the closer the pickup and the disc can be to each other, so that the aperture of the lens for condensing light can be increased. Then, since the light is narrowed down as compared with the conventional one, the density can be increased. Further, since the light emitted by the lens is reduced, the efficiency of light energy transfer is improved.

However, when a substrate having a small thickness is molded with a resin, a large shear force is required because the resin passes through a narrow gap between the molds, and waviness and birefringence occur. Further, even if the disk substrate has the same thickness as the conventional one, the same phenomenon is likely to occur when the disk substrate has a large diameter of 20 cm or more, particularly 30 cm or more, in order to increase the capacity.

In view of the above problems, the present invention provides an optical disk substrate having a small thickness and less likely to cause waviness and birefringence, an optical disk substrate manufacturing apparatus and a manufacturing method thereof.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a resin melted by heating is made wider by widening the gap between the molds after the flow direction of the inflowing resin has been changed, in the region farther from the resin inflow port than in the vicinity of the resin inflow port. Is poured into a mold, cooled and solidified to obtain an optical disk substrate having a plate thickness of an inner peripheral portion thicker than that of an outer peripheral portion.

[0007]

According to the present invention, the outer peripheral portion of the disk substrate is forced by the thick inner peripheral portion to suppress the waviness of the substrate. Further, at the time of molding, the shear stress received when the resin flows in the inner peripheral portion of the disk substrate is reduced, and the birefringence is also reduced.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a molding part of an optical disk substrate manufacturing apparatus according to a first embodiment of the present invention. Compared to FIG. 3 of the conventional example, the fixed mold 2 is recessed at the sprue portion continuing to the tip of the nozzle 1. Since the gap between the molds is widened in this portion, the pressure applied to the resin when the optical disk substrate is formed is lower than in the conventional case, and the resin is smoothly introduced. Therefore, the shear stress applied to the resin at the time when the resin flows into the portion corresponding to the inner peripheral portion of the optical disc substrate is reduced, and the birefringence of the optical disc substrate formed is reduced. Further, the outer peripheral portion of the optical disk substrate is forced by the thick inner peripheral portion, and the waviness of the substrate is suppressed.

FIG. 2 is a sectional view of a molding portion of an optical disk substrate manufacturing apparatus according to a second embodiment of the present invention. Compared with FIG. 3 of the conventional example, a portion of the inner circumference pressing member 5 on the movable mold 3 side is recessed. Since the gap between the molds near the resin inlet is wide,
For the same reason as described in the first embodiment, the shear stress applied to the resin at this portion is reduced, and the birefringence of the optical disk substrate formed is reduced. Also at this time, the outer peripheral portion of the optical disk substrate is forced by the thick inner peripheral portion to suppress the waviness of the substrate.

In the first and second embodiments of the present invention, only one side in the vicinity of the resin inlet is recessed, but of course both may be recessed. Further, although the stamper 4 is fixed to the movable mold 3 in the first and second embodiments of the present invention, it may be fixed to the fixed mold 2. In this case, the inner presser 5 and the cavity ring 6 are always joined to the fixed mold 2. The punch 7 is fixed to the movable mold 3.

As shown in FIG. 3, the sectional shape of the optical disk substrate formed in the first and second embodiments of the present invention is such that the thickness of the inner peripheral portion is larger than that of the outer peripheral portion. At this time, the plate thickness in the data area of the outer peripheral portion needs to be constant. This is because it is necessary to keep the focal length of the laser beam used for recording / erasing / reproducing data constant. Further, it is desirable that the plate thickness at the inner peripheral portion is also constant. This is because it is necessary to maintain parallelism with the data area when it is used as a support surface for holding the disk.

Although FIG. 3 shows the case where only one of the inner peripheral portions of the optical disk substrate is projected, of course, it may be projected in both directions.

FIG. 4 shows a state in which a disc using the optical disc substrate of the present invention is placed in a cartridge. Reference numeral 8 is an optical disk substrate, and 9 is a cartridge. The cartridge 9 has a function of protecting the optical disk substrate 8.
Further, the cartridge 9 is generally provided with a window (not shown) so that the window can be opened to access the recording film provided on the optical disc at the time of recording / erasing / reproducing data. At this time, the thickness of the inner peripheral portion of the optical disk substrate 8 is set so as to be flush with the surface of the cartridge 9 or slightly protrude. With this configuration, when the optical disc is fixed to the rotation shaft of the drive, a loading mechanism such as sinking the optical disc itself to the rotation shaft side or lifting the rotation shaft is not required, and the structure of the drive is simplified.

Although FIG. 4 shows the case where only one of the inner peripheral parts of the optical disk substrate is projected, it may of course be projected in both directions.

[0016]

According to the present invention, the outer peripheral portion of the optical disk substrate is forced by the thick inner peripheral portion to suppress the waviness of the substrate.

Further, at the time of molding, since the gap between the molds through which the resin flows at the inner peripheral portion of the disk substrate becomes wider than in the conventional case, the shear stress applied to the resin during the flow is reduced and the birefringence is also reduced.

Further, when the optical disk is put into the cartridge for use, the loading mechanism for holding the optical disk is simplified.

[Brief description of drawings]

FIG. 1 is a sectional view of a molding portion of an optical disk substrate manufacturing apparatus according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a molding part of an optical disk substrate manufacturing apparatus according to the second embodiment.

FIG. 3 is a sectional view of the third optical disk substrate.

FIG. 4 is a sectional view of the fourth optical disc substrate.

FIG. 5 is a cross-sectional view of a molding part of an optical disk substrate manufacturing apparatus of a conventional example.

[Explanation of symbols]

 1 Nozzle 2 Fixed Die 3 Movable Die 4 Stamper 5 Inner Circumferential Hold 6 Caviring 7 Drilling 8 Optical Disc Substrate 9 Cartridge

Claims (5)

[Claims] 1. An optical disk substrate, wherein a plate thickness of an inner peripheral portion is thicker than a plate thickness of an outer peripheral portion, and a plate thickness of a data area of the outer peripheral portion is constant. 2. The optical disk substrate according to claim 1, wherein the plate thickness between the inner peripheral portion and the outer peripheral portion is continuously changed. 3. A cartridge is provided in the periphery, and the plate thickness of the inner peripheral portion is selected such that at least one surface of the inner peripheral portion surface is substantially flush with the cartridge surface or protrudes from the cartridge surface. The optical disc substrate according to claim 1, which is characterized in that. 4. A heating means for heating a resin to a molten state, a die for molding the resin, a means for fixing a stamper for transferring a fine shape to the die, and a flow of the resin into the die. And a means for compressing the resin, characterized in that the gap between the molds after the flow direction of the inflowing resin is changed is made wider in the area farther from the resin inlet than in the vicinity of the resin inlet. Optical disk substrate manufacturing equipment. 5. The heat-melted resin is flown into the mold by widening the gap between the molds after the flow direction of the inflowing resin has been changed, from the vicinity of the resin inflow port to the part farther from the resin inflow port. A method for manufacturing an optical disk substrate that is cooled and solidified.