JPH07107746B2 - Optical information recording medium and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to optical information, such as a compact disk, a video disk, an optical disk memory for a computer, which performs writing and reading of information by irradiating a light beam. The present invention relates to a method of manufacturing a disk substrate applied to a recording disk.

[Conventional technology]

In recent years, as the optical information recording disk substrate, a substrate obtained by injection-molding a polymer substance has been attracting attention because it is inexpensive in manufacturing cost and is lightweight and easy to handle.

However, injection molded products of polymeric materials are not only susceptible to the appearance of defects such as weld lines and sink marks at the gates, push-cuts, and uneven thicknesses, but also the injection pressure and temperature distribution during molding. Uneven, and
There is a problem that strain is likely to occur in the disk substrate due to the orientation when the molten polymer substance flows on the cavity surface of the mold. Polycarbonate, polymethylmethacrylate, and other materials with excellent light-transmitting properties are used as polymer substances applied to the production of disk substrates. Among these polymer substances, polycarbonate and others have a large photoelastic coefficient and However, there is a problem that an optical anisotropic body is likely to be formed due to the introduction of the mechanical strain, and birefringence is likely to occur.

The optical information recording disk writes information on the recording layer by irradiating the recording layer formed on the inner surface of the disk substrate from the outside of the disk substrate with information, and detects the intensity of reflected light from the recording layer. As a result, the information recorded on the recording layer is read out.Therefore, when the light beam incident on the disk substrate causes birefringence, the circularly polarized light beam causes elliptical deflection, and the normal information Recording and reproduction becomes impossible. In particular, in order to realize a magneto-optical disk, which is attracting attention as an erasable / rewritable optical information recording disk, a disk substrate having a significantly smaller birefringence than that of a read-only disk or a draw-type disk is required. However, it cannot be put to practical use in a state of being injection-molded.

From the above requirements, a method for manufacturing a disk substrate having a small birefringence is desired.

Conventionally, as an injection molding method to prevent appearance defects such as weld lines and sink marks and residual stress during molding, ultrasonic vibration is applied to the gate part, push-cut part, and uneven thickness part of the mold. A method of applying a voltage is known (Japanese Patent Laid-Open No. 52-109556). Further, as an injection molding method for preventing optical distortion due to the orientation of the molten polymer material at the time of injection molding, there is a method of molding while applying ultrasonic vibration to the polymer material that has flowed into the mold. Known (JP Sho
58-140222). Further, as a method of increasing the fluidity of the molten polymer substance, after the polymer substance is filled in the mold,
A method is known in which the polymer substance is instantaneously melted by high frequency (Japanese Patent Laid-Open No. 450-45039).

[Problems to be solved by the invention]

However, removal of the above-mentioned conventional residual strain disturbs the molecular arrangement of the molded product by melting the solidified molded product again, and aims at homogenizing the optical properties. The substance is easily heated to an unreasonably high temperature, which may cause a new problem that the polymer substance is deteriorated. Further, in order to carry out the above-mentioned residual strain removing method, it is necessary to incorporate a special device such as an ultrasonic wave generator or a high frequency coil into the mold, and the mold manufacturing cost, that is, However, there is a problem that the manufacturing cost of the disk substrate becomes high.

[Means for solving problems]

The present invention has been made in order to solve the above-mentioned problems of the prior art, and regarding an optical information recording medium, as a transparent resin substrate of the optical information recording medium, thermal deformation of a resin material constituting the substrate is performed. The structure is such that an annealing treatment is performed at a temperature below the temperature and the birefringence index in a single pass is adjusted to 40 nm or less.

Regarding the method for manufacturing the optical information recording medium, after a disc substrate having a predetermined shape is injection-molded with a resin material, the disc substrate is annealed at a temperature equal to or lower than the thermal deformation temperature of the resin material, and a single pass Birefringence 40nm
The configuration includes the step of producing the adjusted disk substrate below.

〔Example〕

The outline of the method for manufacturing the optical information recording disk substrate according to the present invention will be described below with reference to FIG.

First, as shown in FIG. 1 (a), the molds 1 and 2 are integrally combined, and the cavity 4 is inserted from the spool 3 formed in the mold 1.
The polymer material melted inside is injected at high pressure. Mold filled with molten polymer material in the cavity 4
1, 2 are cooled to solidify the polymer substance, and as shown in FIG. 1 (b), the disk substrate 5 having a predetermined shape is taken out. Then, the disk substrate injection-molded as described above is housed in a heating furnace 6 as shown in FIG. 1 (c), and the temperature is higher than the heat deformation temperature of the polymer substance forming the disk substrate 5. Hold at a slightly low temperature and then slowly cool.

As described above, when the polymer material in which the strain remains due to the injection molding is annealed, the oriented molecular arrangement is recombined into a non-oriented state again to form an optically isotropic body.

Next, some specific examples will be given to show the difference in birefringence from the disk substrate that is not annealed.

First Example A polycarbonate resin having an average molecular weight of 15,000 was injection-molded as shown in FIG.
A disk substrate having a thickness of 0 mm and a thickness of 1.2 mm was manufactured. Next, this disk substrate was placed in a 60 ° C. pake oven, held for 1 hour, and then gradually cooled to room temperature for annealing treatment. still,
The heat distortion temperature of polycarbonate resin is about 125 ° C.

Second Example A disk substrate manufactured in the same manner as in the first example was placed in a bake oven at 80 ° C., held for 1 hour, then gradually cooled to room temperature and annealed.

Third Example A disk substrate manufactured in the same manner as in the first and second examples was placed in a bake oven at 100 ° C., held for 1 hour, and then annealed by slowly cooling to room temperature.

Fourth Example A disk substrate manufactured in the same manner as in the first to third examples was placed in a bake oven at 120 ° C., held for 1 hour, and then annealed by slowly cooling to room temperature.

FIG. 2 shows a comparison of the birefringence generated on a disk substrate manufactured by the method of the present invention with the birefringence generated on an as-molded disk substrate. The horizontal axis of this graph shows the distance from the center of the disk substrate, and the vertical axis shows the magnitude of birefringence. The birefringence was measured by a transmission method using an ellipsometer with a laser wavelength of 633 nm.

As is clear from this graph, the birefringence of the disk substrate annealed after the injection molding is smaller than that of the disk substrate as it is injection-molded. The ratio of the maximum birefringence of the disk substrate annealed after injection molding to the value of the maximum birefringence of the as-injection-molded disk substrate is
36% when annealed at 60 ° C (first embodiment), 80 ° C
31% when annealed at 2 ° C (second embodiment), 16% when annealed at 100 ° C (third embodiment), and 15% when annealed at 120 ° C (fourth embodiment). It was found that the higher the annealing temperature, the more effective the reduction of birefringence. In particular, the birefringence at the inner peripheral portion and the outer peripheral portion of the disk substrate is remarkably improved, and the uniformity of the disk substrate in the radial direction is improved.

The polymer substance applied to the present invention is not limited to polycarbonate, and any thermoplastic transparent polymer substance having a required refractive index such as PMMA and vinyl chloride can be used. Can be used.

Further, in each of the above-described embodiments, only the case where the disk substrate is heated in the bake furnace has been described, but the heating means is not limited to this, and a thermal battle such as laser, infrared ray or microwave is irradiated. Alternatively, any means such as putting in a hot air circulation furnace can be adopted.

Furthermore, the conditions such as temperature and heating rate and cooling rate during annealing are not limited to those in the above-mentioned examples, and it is needless to say that they can be arbitrarily adjusted depending on the type of polymer substance used. . .

〔The invention's effect〕

As described above, according to the present invention, the transparent resin substrate of the optical information recording medium is annealed at a temperature equal to or lower than the thermal deformation temperature of the resin material forming the substrate, and has a birefringence index in a single pass. Since the one adjusted to 40 nm or less is used, the birefringence of the recording / reproducing light transmitted through the substrate can be reduced, and the optical information recording medium having excellent recording / reproducing characteristics can be manufactured.

[Brief description of drawings]

FIG. 1 is a process explanatory view showing a method for manufacturing a disk substrate according to the present invention, and FIG. 2 is a birefringence generated in a disk substrate manufactured by the method of the present invention and a disk substrate as injection-molded. It is a graph which compares with a birefringence. 1, 2: Mold, 3: Spool, 4: Cavity, 5: Disc substrate, 6: Heating furnace

Claims (4)

[Claims] 1. A transparent resin substrate for an optical information recording medium, which has been annealed at a temperature not higher than a heat deformation temperature of a resin material constituting the substrate and whose birefringence index in a single pass is adjusted to 40 nm or less. An optical information recording medium characterized by using. 2. The resin material is a thermoplastic resin material typified by polycarbonate, polymethylmethacrylate, or vinyl chloride.
An optical information recording medium according to the item. 3. A transparent resin substrate obtained by annealing an injection-molded polycarbonate substrate (heat deformation temperature 125 ° C.) at a temperature of 80 ° C. to 120 ° C .. Optical information recording medium. 4. A disc substrate having a predetermined shape is injection-molded from a resin material, and the disc substrate is annealed at a temperature not higher than the heat deformation temperature of the resin material so that the birefringence index in a single pass is 40 nm or less. A method of manufacturing an optical information recording medium, comprising a step of manufacturing an adjusted disk substrate.