JPH0462123A - Mold for optical disc base sheet - Google Patents

Abstract

PURPOSE:To obtain a mold providing an optical disc base with small internal strain and a few errors for recording and reproducing of information by providing a inclined face in such a way that a part projected in a cavity of an inner peripheral holder ring becomes higher to the outer peripheral side and specifying the height of the projected part. CONSTITUTION:A mold for an optical disc base provides a fixed mirror face 1 and a movable mirror face 2 to form a cavity 3 wherein a molten resin is filled. A inner peripheral holder ring 8 has a projected part in the cavity 3 and when a resin is filled, the resin receives a shearing stress. Magnitude of the shearing stress is determined in accordance with the slope theta to a stamper 12 of the projected part and the height h determined by using the stamper 12 of the inner peripheral holder ring 8 as a standard. The taper angle theta and the height h are 0 deg.<theta<90 deg. and 0mm<h<=1.2mm. When this inner peripheral holder ring is used, the molten resin easily passes between the fixed mirror and the inner peripheral holder ring and shearing stress generated becomes thereby small. In addition, as the optical disc base is easily released from the movable mirror face after molding, no strain is produced in the base during releasing.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a mold for forming an optical disk substrate.

[Prior Art] A magneto-optical disk, which is one type of optical disk on which information is recorded and reproduced by irradiation with a laser beam, has a large recording capacity, and its uses are expanding. Among them, magneto-optical disks having a diameter of 3.5 inches are small and easy to carry, and are therefore expected to be widely used in the near future.

Disc-shaped plastic substrates used in magneto-optical disks are often formed by injection molding because of their high productivity and low cost.

As a method for continuously molding disc-shaped plastic substrates by injection molding, a gate cut method is often adopted (see Japanese Patent Publication No. 58-58214 and Japanese Patent Application Laid-open No. 247532-1982). According to the gate cut method, molten resin is applied to the center of the fixed mirror surface into a cavity formed by fitting a movable mirror surface with a stamper having an uneven structure to be transferred onto the substrate and a fixed mirror surface. A disc-shaped plastic substrate is obtained by injecting the resin from the plastic substrate. The stamper used in the gate cutting method is fixed to a movable mirror surface by an inner holder ring and an outer holder ring that are arranged concentrically with respect to the center of the stamper. When the molten resin is injected into the cavity, the resin passes over the inner holder ring and is filled from the center of the cavity to the outer periphery. Therefore, an inner holder ring mark (hereinafter referred to as a gate mark) is formed on the obtained plastic substrate. A shearing core force is applied to the periphery of the inner holder ring during the acid form, and the plastic substrate around the gate mark has a larger internal strain than other parts.

[Problems to be Solved by the Invention] If the area where information is recorded/reproduced includes a portion with large internal distortion, information recording errors/errors may occur in this portion.
Playback errors are likely to occur. Therefore, it is necessary to determine the size of the recording/reproducing area so that a sufficient distance is maintained between the portion having internal distortion and the recording/reproducing area. However, in a magneto-optical disk having a diameter of 3.5 inches, if the above-mentioned distance is increased, the recording/reproducing area becomes significantly smaller, resulting in a problem that the recording capacity of the magneto-optical disk becomes smaller.

To solve the above problem, an inner holder ring with a small outer diameter may be used. However, since the center hole of the magneto-optical disk substrate is determined to have a diameter of 15 cm, when using an inner holder ring with a small outer diameter, it is necessary to install it near the center of the inner holder ring. The wall thickness of the cut bin and ejector turbine must be reduced. As a result, the mechanical strength of the cut bin and ejector turbine is reduced and they become easily broken, and in order to replace these parts, the molding machine must be stopped and continuous molding must be interrupted.

The purpose of the present invention is to reduce internal distortion and prevent information recording errors.
It is an object of the present invention to provide a molding die that provides an optical disk substrate that rarely causes playback errors.

[Means for Solving the Problems] According to the present invention, the above-mentioned object is achieved by applying a molten glass to a cavity formed by fitting a movable mirror surface to which a stamper is fixed by an inner holder ring and a fixed mirror surface. A mold in which an optical disc substrate is formed by filling resin from the center of a fixed mirror surface, and the part of the inner holder ring that protrudes into the cavity is gradually raised higher than the stamper from the center side to the outer circumference side. This is achieved by providing a mold for forming an optical disk substrate, which has a surface inclined so that the protruding portion has a height of 1.2 cm or less based on the stamper. Ru.

[Example code] Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 FIG. 1 shows a schematic cross-sectional view of one example of a molding die for an optical disk substrate of the present invention. The mold for forming an optical disk substrate of the present invention includes a fixed mirror surface 1 and a movable mirror surface 2, which are fitted together to form a cavity 3 filled with molten resin. A sprue bush 4 having a molten resin introduction path 11 is attached to the fixed mirror surface l. The movable mirror surface 2 has a molten resin introduction path 1 after the cavity 3 is filled with resin.
A sprue ejector turbine 6 that closes the sprue ejector turbine 1 and a cut bin 5 that makes a center hole in the optical disk substrate are provided, and air is ejected from the movable mirror surface 2 to separate the optical disk substrate formed on the outer periphery of the sprue ejector turbine 6. 7, a rod cover 9 that fixes the eject turbine 7 to the movable mirror surface 2, and an inner circumferential holder ring 8 that fixes the inner circumference of the stand bar 12. The outer periphery of the stand bar 12 is fixed to the movable mirror surface 2 by an outer periphery holder ring 10.

FIG. 2 shows an enlarged schematic sectional view of the AN shown in FIG. 1. As shown in FIG. 2, the inner holder ring 8 has a portion that projects into the cavity 3. As shown in FIG. When this portion is filled with molten resin, it becomes harmful and the resin is subjected to shearing core force. The magnitude of the shear core force is determined by the inclination θ of the protruding portion with respect to the stand bar 2 at the center side (hereinafter referred to as the Taber angle) and the height of the inner holder ring 8 with respect to the stand bar 12 (hereinafter referred to as This is called the height).

In the inner circumferential holder ring provided in the molding die for the optical disc substrate of the present invention, the above-mentioned Taber angle θ and height h
satisfy the following formulas.

0°〈θ＜90°, Omm＜h≦1.2m＋＋＋If you use this inner holder ring, the molten resin will pass between the fixed mirror surface and the inner holder ring when filling the cavity. Because it is easy, the shear core force generated is small. Moreover, if you use the inner holder ring,
Since the optical disk substrate after molding is easily peeled off from the movable mirror surface, no distortion occurs in the substrate during peeling.

Therefore, the internal strain of the obtained optical disc substrate is small. The above Taber angle θ and height h are 15
°〈θ〈45° and Offim<h≦0, 6mm
It is preferable to satisfy the above conditions because an optical disk substrate having an extremely small internal strain can be obtained.

A magneto-optical disk having a diameter of 3.5 inches at the end is produced using the optical disk substrate molding mold of the present invention using an optical disk substrate molded from polycarbonate resin. Figure 3 shows the resulting signal waveform.

It is clear from FIG. 3 that the signal waveform has little disturbance.

Although the magneto-optical disk has been described in detail above, the mold for forming an optical disk substrate of the present invention can also be used to mold a substrate for a read-only optical disk, a substrate for a write-once optical disk, and the like.

Comparative Example 1 In an optical disc molding mold having the same structure as in Example 1, an inner holder ring having a Taber angle θ of 90° and a height h of 1.41 was used, and Example 1 was used. A magneto-optical disk having a diameter of 35 inches was manufactured using an optical disk substrate obtained by molding under the same conditions as in . FIG. 4 shows a signal waveform obtained by reproducing the format signal of the inner peripheral portion of this magneto-optical disk. By comparing FIG. 3 and FIG. 4, it is clear that in Comparative Example 1, there is a lot of disturbance in the signal waveform.

[Effects of the Invention] According to the present invention, internal distortion is small and information recording errors and
A molding die is provided that provides an optical disc substrate that is less prone to playback errors.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of an example of a mold for forming an optical disk substrate of the present invention, FIG. 2 is an enlarged schematic sectional view of section A shown in FIG. 1, and FIGS. 3 and 4 are magneto-optical FIG. 3 is a diagram showing a signal waveform obtained by reproducing a disc format signal. DESCRIPTION OF SYMBOLS 1... Fixed mirror surface, 2... Movable mirror surface, 3... Capitei, 4... Suburbunyu, 5... Cut bin, 6... Sprue eject turbine, 7... Eject turbine, 8... - Inner circumference holder ring, 9... Rod cover 10... Outer circumference holder ring, 1... Molten resin introduction path, 12... Stand bar. Patent applicant RiRa Shi Co., Ltd.

Claims (1)

[Claims] An optical disk substrate is formed by filling the cavity formed by fitting the movable mirror surface, on which the stamper is fixed with the inner holder ring, with the fixed mirror surface, from the center of the fixed mirror surface, from the center of the fixed mirror surface. The mold is such that the part of the inner holder ring that protrudes into the cavity has an inclined surface that gradually becomes higher with respect to the stamper from the center side to the outer circumferential side, and the stamper of the protruding part is A mold for forming an optical disk substrate, characterized in that a reference height is 1.2 mm or less.