JPH1027389A - Method of manufacturing plastic substrate for optical disk - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a plastic substrate for an optical disk having no birefringence abnormal portion on the outer peripheral edge. SOLUTION: A substrate supporting portion is not fixed to a specific portion by performing an annealing process after injection molding while oscillating the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a substrate used for an optical disk for recording or reproducing information by optical means. More specifically, the present invention relates to a method for obtaining a substrate having small birefringence by annealing a disk substrate obtained by molding a synthetic resin.

[0002]

2. Description of the Related Art In recent years, optical recording media have attracted attention as large-capacity, high-speed memory media. As an optical recording medium, a read-only optical disk (CD, CD-ROM, etc.), a read / write optical disk (rewritable type) and the like are known. As a substrate of these optical recording media, a substrate made of a synthetic resin (polycarbonate resin, acrylic resin, or the like) is generally used.

[0003] These disk substrates are usually formed by injection molding or injection compression molding in terms of productivity. According to this method, an annular flat stamper having preformat information is mounted in a cavity formed between a fixed mold and a movable mold in a mold clamped state, and a molten resin material is introduced into the cavity. In this method, a disk substrate on which preformat information such as a signal (pit) of a stamper and a laser guide groove is transferred is formed.

[0004]

However, the disk substrate made of synthetic resin obtained in this manner is:
The birefringence due to molecular orientation distortion during injection molding is large, and signal characteristics (for example, C
/ N ratio) is inferior, and reduction of birefringence during molding has been studied by various methods.

[0005] The birefringence of the substrate is mainly observed as the sum of birefringence due to molecular orientation (shear stress) and birefringence due to thermal stress during molding. Birefringence due to shear stress can be reduced by optimizing molding conditions and mold compression allowance during injection molding. In addition, distortion due to thermal stress during molding is reduced by heat treatment (annealing treatment) of the disk substrate obtained by injection molding, and birefringence due to thermal stress can be reduced.

Various methods have been proposed for the annealing treatment. (1) A method in which a substrate is leaned against a holding case and an annealing process is performed in a state where two outer peripheral points of the substrate are supported inside the case (for example, see JP-A-3-248345). (2) A method in which a support is penetrated through a center hole of a substrate, and the substrate is supported by the support and an annealing process is performed (for example, Japanese Unexamined Patent Application Publication No.
-248345).

However, when annealing is performed by the method (1), the circumferential distribution of birefringence in the portion where the substrate is in contact with the case, that is, the supporting position of the outer peripheral portion of the substrate is locally changed. When an optical disc is manufactured due to local change in refraction, there is a problem that the envelope of the reproduced signal changes when the reproduced signal is read.
In the above method (2), since the center hole of the substrate is supported by the support, distortion occurs due to its own weight in the support and the contact portion of the center hole of the substrate, and a relatively high temperature required for reducing the vertical birefringence. When the annealing process is performed, there is a problem that the substrate is deformed and the mechanical characteristics of the optical disc are deteriorated.

[0008] In view of the above problems, the present invention provides a method for annealing plastic substrates for optical discs.
By performing the annealing process while rocking the plastic substrate for the optical disk, the position of the plastic substrate for the optical disk in contact with the holding case and the force applied to the same position on the outer peripheral portion of the plastic substrate for the optical disk are not always the same. did. That is, an object of the present invention is to provide a method of manufacturing a plastic substrate for an optical disk in which local birefringence abnormality is eliminated by avoiding that a load of the same magnitude is always applied only to a certain portion of the plastic substrate for an optical disk. I do.

[0009]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a method of manufacturing an optical disk plastic substrate in which a plastic substrate for an optical disk is molded and then annealed. A method for manufacturing a plastic substrate for an optical disk, characterized in that

According to the manufacturing method of the present invention, when annealing the plastic substrate for an optical disk, the weight of the plastic substrate for the optical disk is not always supported at a limited point or several points by the same force, and the local weight is reduced. It is possible to avoid applying to a plastic substrate for an optical disk only at one or a few points where the local force is limited, and it is possible to prevent the occurrence of local birefringence abnormality. That is, the time during which the same weight is applied to a fixed point on the plastic substrate for an optical disk during the annealing process is set to about 10 minutes or less to prevent the occurrence of local birefringence abnormality.

An example of the method of the present invention will be further described with reference to the drawings. FIG. 1 is a schematic side view of an example of an apparatus used in the method of the present invention, FIG. 2 is a drawing similar to FIG. 1 showing a swinging state, FIG. 3 is a vertical schematic front view of the apparatus shown in FIG. FIG. 5 shows the TES waveform of the substrate obtained by the present invention, and FIG. 5 shows the TES waveform of the substrate obtained by the conventional method. In the figure, 1 is a plastic substrate for an optical disk, 2 is a holding case, 3 is a holding table, 4 is a frame, 5 is a running wheel, 6 is a rail, and 7 is a base.

The optical disc substrate 1 is usually formed of a synthetic resin, for example, a polycarbonate resin or an acrylic resin, by using an injection molding method or an injection compression method. This molding method is performed by mounting an annular flat stamper having preformat information in a cavity formed between a fixed mold and a movable mold. By introducing the molten synthetic resin into the cavity, a disk substrate to which preformat information such as a signal (pit) of a stamper and a laser guide groove is transferred is formed. After molding, the mold is opened while blowing air for release, and the substrate is removed from the mold.

The present invention is characterized in that the disk substrate obtained above is mounted on the apparatus shown in FIGS. 1 to 3 and an annealing process is performed. The annealing temperature is usually 10 to 6 with respect to the glass transition point (TG) of the substrate resin.
A 0 ° C. lower temperature is used, preferably 10 to TG.
５０50 ° C. lower temperature. When a polycarbonate resin is used, the temperature is preferably in the range of usually 80 to 120C. If the annealing process is performed at a temperature lower than the TG by less than 10 ° C., when the substrate is taken out from the annealing device, the disk substrate may be deformed, or the groove or pit shape of the substrate may be deformed during the annealing process.

[0014] The annealing time is 30 minutes or more, preferably 30 minutes to 5 hours. If the annealing time is less than 30 minutes, birefringence of the substrate and warpage of the substrate (Til)
Since t) is in the process of changing, the characteristics may change in an accelerated test at high temperature and high humidity. The apparatus shown in FIGS. 1 to 3 is an example of an apparatus for performing the method of the present invention. The plastic substrate 1 for the optical disk is held by the holding case 2,
Annealing is performed while rocking the optical disc plastic substrate 1. Specifically, when the optical disc plastic substrate 1 accommodated in the holding case 2 shown in FIGS. 1 to 3 is put into a heating furnace (oven), the plastic substrate 1 is placed on a rail 6 already installed in the heating furnace. Anneal while carrying and running. As shown in FIG. 2, the rails 6 are configured to swing the holding case 2 with different heights of the left and right rails 6, and in FIG. 2, the height of the right rail 6 is increased. At other positions, the height of the left rail 6 is increased.

The height of the left and right rails 6 provided on the base 7 is alternately changed so that the holding case 2
Is swingable, but in addition to the swinging method using the rails 6 and the running wheels 5 as shown in the figure, a roller conveyor type, a belt conveyor type, a hanging type, and the like are conceivable. It is also conceivable that a pressure cylinder is provided below the holding table 3 on which the holding case 2 is provided, and the traveling wheel 5 is moved up and down by the pressure cylinder to swing. The swinging method may be appropriately selected depending on the case, and in any case, the height of the running path of the holding case 2 may be made different from each other.

The holding case 2 includes a frame 4 provided on a holding table 3.
If the structure is such that it is placed inside, and if it is a structure that can be separated from the holding table 3, it is convenient for handling. The plastic substrate 1 for an optical disk having a thickness of 1.2 mm after the injection molding was annealed by a method of the present invention at a furnace temperature of 90 ° C. for 3 hours.
The maximum inclination angle was alternately set to 15 degrees with respect to the horizontal plane. The angle change was performed once every three minutes. After the annealed optical disk substrate having a diameter of 130 mm is gradually cooled, an outer peripheral portion TES waveform of the substrate is shown in FIG. FIG. 5 is a graph showing the TES of the outer peripheral portion of the plastic substrate 1 that has been subjected to the annealing process without applying the swing in the same manner. It can be seen that the TES waveform after the annealing treatment according to the present invention is clearly improved in local anomalies as compared with that according to the conventional method. This is presumably because the swing of the substrate 1 prevents the weight of the substrate 1 from being concentrated on the portion where the substrate 1 contacts the holding case 2.

According to the present invention, a remarkable improvement in local birefringence abnormality was observed. As a result of a sample test of the plastic substrate for an optical disk obtained in the embodiment, the local birefringence abnormality was 0%. , Confirmed its effect.

[0018]

According to the present invention, the plastic substrate for an optical disk is swung during the annealing process of the plastic substrate for an optical disk, so that the same weight is not applied to one or several points of the plastic substrate for an optical disk. As a result, it is possible to eliminate the local birefringence abnormality of the plastic substrate for optical discs and obtain a plastic substrate for optical discs having uniform birefringence. An optical disk manufactured using the plastic substrate for an optical disk can be an optical disk having no local abnormality in a recording / reproducing signal and a TES waveform.

[Brief description of the drawings]

FIG. 1 is a schematic side view of an example of an apparatus used in the method of the present invention.

FIG. 2 is a schematic side view showing a swinging state.

FIG. 3 is a schematic vertical sectional front view of the apparatus shown in FIG. 1;

FIG. 4 shows TES at the outer peripheral portion of the substrate obtained by the present invention.
Waveform.

FIG. 5 shows a TES waveform at an outer peripheral portion of a substrate obtained by a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plastic substrate for optical disks 2 Holding case 3 Holding table 4 Frame 5 Running wheel 6 Rail 7 Base

Claims (2)

[Claims] In a method for manufacturing a plastic substrate for an optical disk, the method comprises the steps of:
A method for producing a plastic substrate for an optical disk, wherein the method is performed while the substrate is rocked. 2. When performing an annealing process while holding a plastic substrate for an optical disc in a holding case and moving the plastic substrate in a furnace, the height of the track of the holding case is alternately changed so as to swing the holding case. 2. The method according to claim 1, wherein the plastic substrate is moved.