JPS6383939A - Production of optical disk substrate - Google Patents

Abstract

PURPOSE:To improve oxidation resistance and to extend life by subjecting a plastic sheet having excellent oxidation resistance performance to die molding to form guide grooves thereon, then adding a transparent resin thereon, and press-molding the resin to integrate the same with the plastic sheet. CONSTITUTION:The plastic sheet 6 is positioned and press-molded on a stamper 5 on which the guide grooves are die-molded, then a molten substrate material 7 is supplied onto the same and is press-molded by using a mold 8, by which the substrate 1 integrated with the plastic sheet 6 and the substrate material 7 is obtd. Since such substrate 1 is shut off from the penetration of moisture and monomer by the plastic sheet 6, the direct formation of the recording layer thereon is possible. The deterioration of the recording layer is thereby prevented and the reliability of the optical disk is improved.

Description

[Detailed Description of the Invention] [Summary] As a method for manufacturing an optical disk substrate with excellent oxidation resistance and long life,
A method in which a plastic sheet with excellent oxidation resistance is molded to form a guide groove, and then a transparent resin is added thereon and pressure molded to form an integral part with the plastic sheet.

[Industrial application field]

The present invention relates to a method of manufacturing an optical disk substrate made of plastic, which has excellent oxidation resistance and has a long life.

Optical disks can be classified into regular optical disks and magneto-optical disks, both of which are memories that use laser light to record high-density information, have a large storage capacity, and can perform contactless recording and playback. It also has excellent features such as being unaffected by dust.

In other words, the laser beam can be narrowed down to a small spot with a diameter of about 1 μm by a lens, and therefore 1 μm in diameter.
The area required for recording bit information is approximately 1 μm2.

In addition, since the distance to the focal plane of the laser beam narrowed down by the lens is 1 to 2 mm, non-contact is possible.Also, the diameter of the light beam is approximately 1 mm at the substrate surface, so even if the substrate surface Even if there is dust with a size of several tens of μII+2, it can be done with almost no effect on recording and reproduction.

Here, an optical disk is a read-only memory that uses a low-melting point metal as a recording medium and records and reproduces information depending on the presence or absence of a hole (focus).
), on the other hand, in a magneto-optical disk, the recording medium is made of a perpendicularly magnetized magnetic film, and the magnetization reversal caused by the temperature rise of the magnetic film irradiated with a laser is used to record and erase information, and the reflected light from the magnetic film is Alternatively, reproduction is performed by utilizing the fact that the rotation of the polarization plane of transmitted light differs depending on the magnetization direction.
- Such a recording medium is formed as a layer on a transparent substrate such as glass or plastic provided with a guide groove with a protective layer interposed therebetween, and laser light is irradiated through the transparent substrate.

The present invention relates to a method of manufacturing a plastic optical disk substrate provided with such a guide groove.

[Conventional technology]

Precise positioning is necessary to accurately record and reproduce information at any position on the disk surface, and concentric or spiral shallow guide grooves (pre-groups) are formed on the substrate at minute intervals. It is maintained and installed.

For example, the width of the guide groove is 0.7 μm and the depth is 0.07 μm.
, the mutual pitch is about 1.6 μm.

FIG. 3 is a partial cross-sectional view showing the structure of an optical disc,
A protective layer 2 is formed on the substrate 1 in which the guide groove is formed. Recording layer 3. It is formed by sequentially stacking the ff1 layer 4.

Here, when the substrate 1 is made of plastic, a transparent synthetic resin such as polymethyl methacrylate (abbreviated as r'HMA) or polycarbonate (abbreviated as PC) is used using a mold called a stamper in which guide grooves are formed in advance. A disk-shaped substrate 1 having a thickness of about 1.2 mm is produced by molding.

In addition, when the substrate 1 is made of a glass disk, an ultraviolet curable resin is applied thereon, and a stamper is pressed onto it.
A PP method has been developed in which the substrate is irradiated with ultraviolet rays to cure it, and then the stand bar is peeled off to form guide grooves.

Another method is to apply a photoresist onto a glass substrate, selectively expose and develop the photoresist to open a guide groove pattern, and then perform plasma etching to form the guide grooves.

Here, there is no problem if the substrate 1 is made of glass and the recording layer 3 is provided directly thereon, but if the substrate 1 is made of plastic such as PMM^ or PC, the protective layer 2 formation is necessary.

The reason for this is that plastic substrates such as PMMA and PC have strong moisture permeability and gas adsorption properties, which causes oxidation of the recording layer 3 and deteriorates the optical disc.

Therefore, the protective layer 2, such as silicon nitride (si: +Nt) or aluminum nitride (A#N), is not deposited to a thickness of about 1,000 layers using methods such as vacuum evaporation or vacuum deposition, and pinholes are likely to form. There is a problem.

Furthermore, coating the substrate 1 with a resin having low moisture permeability such as polyvinyl chloride or polyvinylidene chloride has been attempted, but good results have not been obtained because the shape of the guide groove is damaged.

[Problem that the invention seeks to solve]

Recording and reproduction of information on an optical disk is performed by irradiating the recording layer 3 with laser light through the substrate 1. If the substrate 1 is made of glass, the recording layer will not deteriorate much;
If it is made of plastic, it will deteriorate significantly due to moisture permeation and migration of adsorbed gases and monomers, so to prevent this, please use 8! Formation of layer 2 is necessary.

Here, since glass substrates with guide grooves have poor manufacturing efficiency and are expensive, it is desirable to use plastic substrates.Therefore, it has been desired to put into practical use substrates with excellent oxidation resistance and moisture resistance.

[Means for solving problems]

The above problem can be solved after the transparent substrate is molded with a plastic sheet with excellent oxidation resistance on the stand bar to form the guide groove.
This problem can be solved by a method of manufacturing an optical disc substrate in which a transparent resin is added thereon, pressure molded, and integrated with the plastic sheet.

[Effect]

The present invention changes the conventional structure of an optical disc, which requires that the substrate 1 is a supporting carrier for the recording layer 3 and is also made of an optically excellent material. By forming the protective layer 2 from a different material, the need for the protective layer 2 is eliminated.

That is, since resins such as vinyl chloride, vinylidene chloride, vinyl alcohol, vinyl fluoride, and vinylidene fluoride have low moisture permeability and excellent oxidation resistance, they form an adjoining body of the recording layer 3, and The substrate body is formed using a substrate material such as P)11'lA or PC, which has excellent optical properties.

Next, it is necessary to form a guide groove in the adjacent body of the recording layer 3, but the thinner the plastic sheet is, the better the moldability is in order to mold such fine irregularities.

Therefore, as shown in FIG. 1, the present invention first places plastic sheets 1 and 6 on top of a stamper 5 on which guide grooves are molded.
After positioning and pressure molding, a molten substrate material 7 is supplied onto this and pressure molding is performed using a mold 8 to obtain a substrate 1 in which the plastic sheet 6 and the substrate material 7 are integrated. It is.

Since the plastic sheet 6 prevents moisture, monomer, etc. from penetrating into such a substrate, the recording layer 3 can be directly formed thereon.

〔Example〕

Vinyl fluoride (thickness 200μm) as a plastic sheet
) to vinylidene fluoride (thickness 200 μm) + vinyl chloride (
thickness 160μm) + vinylidene chloride (thickness 230μmL)
Using vinyl alcohol (thickness: 300 μm), use a pressure molding machine in a stand bar at a temperature of 100°C and a weight of 40 kg/c.
Pressure is applied under the conditions of m2, width 0.7 μm, depth 0.07 μm
Guide grooves with a pitch of 1.6 μm and a pitch of 1.6 μm were transferred onto a plastic sheet.

Next, PMM in the molten state (150°C) is
A was placed on a plastic sheet and pressure molded under the same conditions as before (temperature 100°C, 40 kg/cm2) to form a substrate with a thickness of 1.2 mm.

Further, for comparison, a substrate was formed using only PMMA.

Next, terbium was deposited on the substrate by sputtering.
Iron-cobalt (Te Fe Co) was formed to a thickness of 1100 nm to form a recording layer 3, and silicon nitride (SiJ4) was then sputtered to a thickness of 1100 nm to form a coating layer 4 on top of this to form a magneto-optical disk. Formed.

Figure 2 shows these various magneto-optical disks using a semiconductor laser at a frequency of 0.5 MHz and an output of 2.5 mW.
These are the results of an accelerated test in which data was recorded at 80° C. and reproduced at an output of 0.8 mW.

In other words, Comparative Example 9, in which the recording layer 3 was provided directly on PMMAO, rapidly deteriorated after only about 100 hours, whereas optical disc 10.11, which used a sheet of vinyl fluoride and vinylidene fluoride, had a C/N ( Carrier-1 level/N
o1se-1evel) is small and stable, and the optical disk 12.13 using a sheet of vinyl chloride and vinylidene chloride and the optical disk 14 using vinyl alcohol also suppress deterioration in black color compared to Comparative Example 9. was completed.

〔Effect of the invention〕

As described above, by carrying out the present invention, when a plastic substrate is used, it is possible to suppress deterioration of the recording layer due to moisture permeation, monomer, etc., thereby making it possible to improve the reliability of the optical disc.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a method of manufacturing an optical disc substrate, FIG. 2 is a diagram showing changes over time in an example, and FIG. 3 is a partial sectional view showing the structure of an optical disc. In the figure, 1 is a substrate, 2 is a protective layer, 3 is a recording layer,
4 is a covering layer, 5 is a plastic sheet, 6 is a plastic sheet, and 7 is a substrate material.

Claims (1)

[Claims] An optical disc in which a protective layer, a recording layer, and a coating layer are sequentially formed on a transparent substrate provided with a guide groove, wherein the transparent substrate is formed by molding a plastic sheet with excellent oxidation resistance into a stamper. A method for manufacturing an optical disk substrate, characterized in that after forming a guide groove, a transparent resin is added thereon and pressure molded to form the guide groove integrally with the plastic sheet.