JPH1027390A - Method of manufacturing plastic substrate for optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the local double refraction of plastic substrates for optical disks and to obtain the substrates for the optical disks which are uniform in double refraction by averting the application of the same weight at the limited one point or several points of the substrates while oscillating the substrates at a specified frequency in an annealing treatment. SOLUTION: The plastic substrates 1 for the disks are held by a holding case 2 and while the substrates 1 are oscillated by an external oscillation device 3, the substrates are subjected to the annealing treatment. The holding case 2 is provided with stoppers 4 so as to prevent the mispositioning of the case by vibration. When charging the substrates 1 stored in the holding case 2 into a heating furnace, the substrates 1 are placed on a holder 5 already installed in the heating furnace and are oscillated at a specified frequency, for example, 1 to 100kHz, more preferably 1 to 50kHz during the annealing treatment. As a result, the annealing treatment is carried out by avoiding the application of the own weights of the substrates 1 at the limited one point or several points of the substrates 1 always at the same size. The concentration of the load is averted and the occurrence of the parts abnormal in the double refraction is prevented by the application of the oscillation and the consequent slight jumping of the substrates.

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 vibrating the plastic substrate for the optical disk, the position of the plastic substrate for the optical disk in contact with the holding case is changed, and the force applied to the same position on the outer peripheral portion of the plastic substrate for the optical disk is
I tried not to always be the same. 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 a plastic substrate for an optical disk in which a plastic substrate for an optical disk is molded and then annealed. And a method of manufacturing a plastic substrate for an optical disk.

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 vertical front view of the same, FIG. 3 is a TES waveform of a substrate processed by the method of the present invention, and FIG. TES waveforms are shown. In the figure, 1 is a substrate,
2 denotes a holding case, 3 denotes a vibration device, 4 denotes a stopper, and 5 denotes a holding table.

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. The 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 as described above is subjected to a special annealing treatment using the apparatus shown in FIGS. The annealing temperature is usually 10 to the glass transition point (TG) of the substrate resin.
A temperature 60 ° C. lower is used, preferably 1 to TG.
0 to 50 ° 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, the substrate birefringence and the substrate warpage (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 and 2 is a drawing that best illustrates the features of the present invention, in which a plastic substrate 1 for an optical disk is held by a holding case 2,
The annealing process is performed while applying vibration to the plastic substrate 1 for an optical disk by the external vibration device 3. Stopper 4 so that the position of holding case 2 does not shift due to vibration.
Is provided. The holding table 5 for transmitting the vibration generated by the external vibration device to the plastic substrate for the optical disk via the holding case is preferably made of a metal plate or the like in order to transmit the vibration well.

In the annealing process shown in the figure, when the plastic substrate for an optical disk stored in the holding case shown in the figure is put into a heating furnace (oven), it is put on the holding device 5 already installed in the heating furnace. A constant frequency during the annealing process, for example, 1 to 100 kHz, preferably 1 to 5 kHz.
By vibrating at 0 kHz, it is possible to prevent the weight of the plastic substrate for the optical disk from being always applied to one or several limited points of the plastic substrate for the optical disk with the same size, and to perform the annealing process. It is considered that by applying the vibration, the substrate 1 is rotated or slightly jumped, so that the load is not concentrated and the occurrence of the abnormal birefringence portion is prevented.

The external vibration generator 3 may be of any type as long as it vibrates the holding case 2 for storing the plastic substrate 1 for an optical disk at a constant frequency. In this embodiment, the lower surface of the holding case 2 A 5 mm-thick stainless steel holding device 5 equipped with a stopper 4 so as to support the whole and prevent the position of the holding case from shifting was used. In addition, the frequency was vibrated at 1 kHz. The power depends on the size of case 2, but is 20
50 to 20 for case 2 containing about one substrate 1
A power of about 0 w may be sufficient.

The plastic substrate 1 for an optical disk having a thickness of 1.2 mm after injection molding is subjected to a furnace temperature of 90 by the method of the present invention.
After holding at 3 ° C. for 3 hours, annealing was performed under annealing conditions of slow cooling. FIG. 3 shows a TES waveform of the outer peripheral portion (at a position of a radius of 63 mm) of the optical disk substrate having a diameter of 130 mm that has been annealed. FIG. 4 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 vibration in the same manner. T after annealing according to the present invention
It can be seen that the ES waveform clearly has improved local abnormalities as compared with the conventional waveform.

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.

[0019]

According to the present invention, it is possible to prevent the same weight from being applied to a limited point or several points of the plastic substrate for an optical disk while vibrating the plastic substrate for an optical disk at a constant frequency during the annealing process 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 longitudinal sectional front view of the apparatus shown in FIG. 1;

FIG. 3 is a TES waveform in an outer peripheral portion of an optical disk after an annealing process according to the present invention.

FIG. 4 is a TES waveform at an outer peripheral portion of a conventional optical disc.

[Explanation of symbols]

 Reference Signs List 1 plastic substrate for optical disk 2 holding case 3 external vibration generator 4 stopper 5 holding table

Claims (1)

[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 vibrating the substrate.