JPS63139301A - Substrate for optical disc - Google Patents

Abstract

PURPOSE:To elevate the laser transmissions and to shorten the time for forming a substrate for an optical disc by hardening resin liquid consisting primarily of vinyl ester and contg. 0.015-0.025pt.wt. cobalt naphthenate as hardening accelerator in a forming die. CONSTITUTION:A lower die comprising a base material 2 adhered from the rear side to keep flat the surface of a stamper 1 for forming a guiding groove is faced oppositely to the stamper 1, and vinyl ester resin liquid 5 is injected from an injecting port 3 at the central part between a glass die 4 mounted with a space corresponding to the thickness of a substrate. 0.015-0.025pt.wt. cobalt naphthenate is added as hardening accelerator to this resin liquid, which is hardened in the forming die to obtain a substrate for an optical disc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical disc substrate forming a recording layer for optically recording and reproducing information.

Conventional technology Optical disks are high-density recording media with excellent features such as low cost relative to recording capacity, fast access speeds, and relatively high transfer rates, making them extremely useful as next-generation memories. .

Generally, the original disk is used by forming a recording layer on a transparent disk with a thickness of about 1.2 mm, and a laser beam guide groove is formed in a spiral shape on the substrate surface. Laser light is incident from the opposite side of the guide groove to record information on the recording layer formed on the guide groove.

Playback is in progress. This is an effective method for preventing dust, which greatly affects BER (pit error rate), and for facilitating handling.

Therefore, the substrate material must not be able to prevent the transmission of laser light, and currently glass and PMMA are used.

Extremely transparent materials such as polycarbonate are used. However, each of these materials also has drawbacks.

Glass is heavy and fragile, and PMMA has the highest transparency among plastic materials, but has high water absorption and poor dimensional stability. Furthermore, although polycarbonate can be easily manufactured in large quantities by injection molding, its high birefringence limits the ability to achieve high recording densities. Additionally, additives such as stabilizers have a chemical effect on the recording layer.
There were also problems with reliability.

Due to the above, in recent years, epoxy resin
A method of curing in a mold using a curable resin such as diethylene glycol bisallyl carbonate (Japanese Unexamined Patent Publication No. 68-137150) has been studied. This method has advantages such as excellent transferability of the guide grooves and no internal distortion because it is molded using a low-viscosity resin.

Problems to be Solved by the Invention However, whether epoxy resin or diethylene glycol bisallyl carbonate is used, molding takes a long time, and it takes several to ten hours from casting to demolding.

This is because they are all thermosetting resins, but vinyl ester is an example of a resin that is room temperature curable and has a low viscosity.

Vinyl ester resin has excellent corrosion resistance and mechanical strength against many chemicals including acids and alkalis.
It is used as a material that requires severe environmental characteristics, such as in chemical plants and ships. These characteristics are essential for extending the life of optical disk substrates.

However, vinyl ester resin uses cobalt naphthenate and organic peroxide as its optimal curing system;
Since this cobalt naphthenate has a coloring property, the resulting substrate will also be colored, which will impede the transmittance of laser light, so at present very little research has been done on it.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide an optical disc substrate that has a high laser light transmittance and a short molding time and is optimal for use as an original disc.

Means for Solving the Problems The optical disc substrate of the present invention to achieve this object is as follows:
A former disk substrate obtained by curing a resin liquid in a mold, comprising: 1. The resin liquid is mainly composed of vinyl ester.

Function The present invention provides an original disk substrate with the above structure that does not affect laser light transmittance, and the amount of cobalt naphthenate used as an accelerator when curing vinyl ester resin is optimized for optical disk substrates. It is intended to be set within a certain range.

In other words, the light absorption properties of this type of resin change depending on the amount of cobalt naphthenate added, but since it is sufficient as long as the light transmittance is high at the wavelength of the laser actually used, the amount added can be selected to the extent that it does not have any effect.

Normally, the wavelength of the semiconductor laser used in optical disk systems is 830 nm, but the thickness was made using 0.03 parts by weight or more of cobalt naphthenate, which is generally recommended as a curing system for vinyl ester. 1.
The transmittance of a 2 mm plate at 830 nm is 87 mm, which is lower than the 92 mm transmittance of a PMM, so there is no advantage in using it as an optical disc. However, if the amount added is 0.
When the amount is reduced from 0.03 parts by weight, the influence rapidly decreases, and a transmittance equivalent to that of PMM can be obtained.

However, if it is too small, the curability of the vinyl ester will be affected, mechanical properties will be reduced, and a large amount of unreacted residual monomer will have an adverse effect on the production of the recording film.

Percoll hardness is a value that directly indicates the degree of hardening, and when we investigated changes in the amount of cobalt naphthenate added, we found that it shows a constant value above a certain amount.

There is a range that exhibits the highest values in both transmittance and curability, and it is desirable to use this range in the present invention.

EXAMPLE Hereinafter, an optical disc substrate according to an example of the present invention will be described with reference to the drawings.

Figure 1 shows the stamper 1 and a lower mold made of a base material 2 bonded from the back side in order to maintain the flatness of the stamper 1 and the stamper 1, which are used to form guide grooves. 3 is a sectional view showing a state in which vinyl ester resin liquid 5 is injected from an injection port 3 provided at the center between glass molds 40 placed with a gap equivalent to that of the glass mold 40. FIG. The vinyl ester resin liquid 5 contains 33 parts by weight of styrene monomer as a reactive diluent, and 0.0 parts by weight of cobalt naphthenate as a curing accelerator.
Made by Kayaku Nouri Co., Ltd. (product number: 328), which was developed exclusively for vinyl ester as a hardening agent.
E) was used, and the amount added was 1%.

In the above composition, the gelation time was 12 minutes and the peak time was 18 minutes. Demold 30 minutes after injection 60
After-cure was performed at 80'C for 30 minutes and 3 hours at 80'C.

The laser beam (s3o
The transmittance (nm) was 91.6%, the hardness was 48, and it had sufficient characteristics as an optical disc substrate.

Figure 2 shows the results obtained by changing the amount of cobalt naphthenate added.
It shows the light absorption characteristics of an optical disk substrate molded by the method shown in the figure. In Figure 2, ■ indicates the amount of cobalt naphthenate added is 0.015 parts by weight, ■ indicates 0.020 parts by weight, and ■ indicates 0.0 parts by weight.
26 parts by weight, and ■ is 0.03 parts by weight. The horizontal axis shows the wavelength of light, and the vertical axis shows the laser light transmittance.

From Figure 2, when the amount of cobalt naphthenate added is 0.03 parts by weight, the transmittance is 87.5% at a wavelength of 830 nm, whereas when the amount of cobalt naphthenate is 0.026 parts by weight, the transmittance is 91.6% and 0.0 parts by weight.
It can be seen that the transmittance is within the practical range when the amount added is 0.026 parts by weight or less, which is 92 inches for 20 and 0.016 parts by weight. Figure 3 shows the results when the amount of cobalt naphthenate added is varied. It shows changes in Percoll hardness, with the horizontal axis representing the amount of cobalt naphthenate added and the vertical axis representing Percoll hardness.

As can be seen from the results in FIG. 3, when the amount of cobalt naphthenate added is 0.016 parts by weight or less, the Percoll hardness gradually decreases.

Based on the above results, the amount of cobalt naphthenate added was 0.0.
By limiting the content to a range of 15 parts by weight or more and 0.025 parts by weight or less, the properties required for an optical disc substrate can be satisfied.

Effects of the Invention As described above, the present invention provides a resin solution containing vinyl ester as a main component in a range of 0.015 parts by weight to 0.01 parts by weight of cobalt naphthenate.
By molding in the presence of 0.25 parts by weight, it is possible to provide a substrate optimal for optical discs, which has high laser light transmittance and short molding time.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a resin liquid injected into a mold used in an embodiment of the present invention, FIG. 2 is an absorption characteristic diagram of substrates prepared by varying the amount of cobalt naphthenate added, and FIG. The figure is a characteristic diagram showing changes in Percoll hardness of substrates produced by varying the amount of cobalt naphthenate added. 1... Stun bar 12... Base material,
3...Inlet, 4...Glass mold, 5...
...Vinyl ester resin liquid. Name of agent: Patent attorney Toshio Nakao and 1 other person1-
Stamper 2-Base material 3-La main entrance 4-Glass mold No. 1 Figure 5-Vinyl ester sugar 1
S liquid Figure 2 - Jk 4C (nm)

Claims (2)

[Claims] (1) An optical disc substrate characterized in that it is obtained by curing a resin liquid mainly composed of vinyl ester in a mold. (2) The optical disc substrate according to claim 1, wherein the resin liquid contains a curing accelerator of 0.015 parts by weight to 0.025 parts by weight of cobalt naphthenate.