JPS62162257A - Production of optical disk substrate - Google Patents

Abstract

PURPOSE:To reduce the warpage and reggedness of the titled substrate and to improve the flatness by completely curing the cross-linking plastic plate of vinyl ester resin, polyester resin, etc., which has been primarily cured in a mold and released from the mold in an inert liq. such as fluorocarbon. CONSTITUTION:A soln. (6%) of cobalt naphthenate in naphthenic acid is added by 0.5% to a phenyol novolak type resinous soln. contg. 36% styrene monomer as a curing accelerator, and then 1.5% org. peroxide is added as a curing agent. The soln. is defoamed, charged into a mold, and then allowed to stand at 25 deg.C for 20min to primarily cure the resin. The obtained plastic substrate is released from the mold, and worked into a specified size to obtain an optical disk substrate. The optical disk substrate 1 and a substrate holder 2 are immersed in an inert liq. 4 such as fluorocarbon which is stored in a liq. container 3. The liq. is heated at the rate of 10 deg.C/min from 25 deg.C-90 deg.C, and kept at 90 deg.C for 1hr to completely cure the plastic of the substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing an optical disc substrate for 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 high transfer rates, making them extremely useful as next-generation memories.

Generally, in an optical disk, a recording layer is formed on a disc-shaped transparent glass substrate, and information is recorded and reproduced by vertically entering a laser beam from the opposite surface of the recording layer. Therefore, the plastic substrate is required to have high laser light transmittance, and the optical paths of the incident light and the returned light must be completely the same. In other words, if the plastic substrate is warped or has irregularities, the optical path of the returned light will fluctuate or it will be misaligned with the incident light, which not only prevents stable recording and reproduction, but also causes errors. The minute irregularities on the surface cause irregular diffused reflection of laser light, which is also a cause of substrate noise.

For these reasons, efforts are being made to improve the flatness of optical disc substrates by eliminating warps and irregularities.

Epoxy N resin, vinyl ester resin, polyester resin, etc. are used as crosslinkable transparent plastics. After the epoxy resin is heated and hardened in the mold, it is then slowly cooled over a long period of time to prevent molding distortion. In this way, the substrate is completely cured within the mold, resulting in a substrate with less warpage.

Problems to be Solved by the Invention However, the above-mentioned method has the drawback of high cost because it takes several hours to more than ten hours to mold one substrate.

On the other hand, vinyl ester resins and polyester resins are curable at room temperature and have sufficient rigidity for handling without heating, and reach a hardness that allows them to be removed from the mold after several tens of minutes of curing in the mold. Of course, for complete hardening, it is necessary to heat and harden after demolding. However, in this case, since a large number of substrates can be processed at once, the cost is lower than that of the epoxy resin mentioned above. The disadvantage of the method of heating and curing after demolding is that the crosslinking reaction is not completely completed and, like thermoplastic resins, it is easily deformed by heating.

These deformations are largely caused by deflection of the substrate due to gravity and non-uniform heating.

Another drawback when using vinyl ester resins and polyester resins as optical disk substrates is that several dozen styrene monomers are used to completely cure the resin and to lower the viscosity of the resin liquid and improve moldability. However, some of this styrene monomer volatilizes from the surface during the curing reaction, causing deterioration of the surface properties of the cured product. 1LK (
In other words, it was necessary to heat the product after leaving it at a low temperature for a long time.

The present invention was made to solve the above problems, and provides a method for manufacturing an optical disk substrate with good flatness.

Means for Solving the Problems In order to achieve this object, the method for manufacturing an optical disk substrate of the present invention uses a crosslinkable transparent plastic board such as vinyl ester resin or polyester resin that is primarily cured in a mold and then released from the mold. Complete curing is performed in an inert liquid.

Function The present invention provides a method for manufacturing an optical disc substrate having good flatness with less anti-9 and unevenness by the above method.
By heating an incompletely cured substrate in an inert liquid, the problems associated with conventional heat curing in air are solved.

That is, by holding a plastic substrate in a liquid, the gravity acting on the substrate is avoided, so that deformation of the substrate due to gravity is eliminated. Furthermore, in the case of curing in air, a temperature gradient occurs between the parts of the substrate that are in contact with the holder that holds the substrate and the parts that are not, resulting in a difference in curing speed and causing deformation of the substrate. The active liquid, such as a fluorocarbon-based inert liquid, has a heat transfer coefficient about five times greater than that of air, so any part of the substrate can be uniformly heated and deformation can be reduced.

Conventionally, styrene monomers blended into vinyl ester resins and unsaturated polyester resins partially volatilize when heated in the air, deteriorating surface properties, but when heated in an inert liquid as in the present invention, the styrene monomer gas is removed. Curing is suppressed and the surface remains smooth during curing. In addition, by placing the surface of the substrate in an inert atmosphere, discoloration due to surface oxidation of the resin is suppressed, and there is no loss of the curing agent or the like due to oxidation, so that a completely cured product can be obtained.

EXAMPLE Hereinafter, a method of manufacturing an original disk substrate according to an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the method for manufacturing an optical disk substrate of the present invention.

In FIG. 1, reference numeral 1 denotes a plurality of vinyl ester optical disk substrates held by a substrate holder 2. As shown in FIG. The optical disk substrate 1 made of vinyl ester is made of a phenol novolanoque solution containing 36% styrene monomer and a naphthenic acid solution of cobalt nanthenate (6%) as a curing accelerator.
After adding o, s% of %), 1.5% of organic peroxide (Kayaku Nury Co., Ltd., 328E) was added as a curing agent.
After defoaming, pour it into the mold and leave it at 25°C for 20 minutes.
After the next hardening, the plastic substrate was removed from the mold to the specified size (
130 pieces in outer diameter and 15 mm in inner diameter). The optical disc substrate 1 and substrate holder 2 are
It is immersed in a fluorocarbon-based inert liquid (manufactured by Sumitomo 3M, FC-4o) 4 stored in an inert liquid container 3. This inert liquid 4 is constantly circulated through a heating device 5 and a filter 6 (pore size 0.2 μm). With this configuration, it is easy to set the heating temperature, dust generated from the substrate is filtered out, and curing can be performed in a clean atmosphere at all times.

With the above configuration, the heating temperature was raised at a rate of 10°C/min in the range of 25°C to 90'C, and then held at 90'C for 1 hour.

The amount of warpage of the optical disc substrate thus obtained (two maximum displacements from the plane with the center of the substrate as a reference) is 0.
05 or less, and 0.1 to 1. Compared to the conventional method which lacked practicality due to the large amount of warpage (○), this method is sufficiently convenient for use as an optical disk substrate. Also, the surface roughness is Ra=:O,○
04, which can be significantly improved compared to the conventional method where Ra=O, O○5 to ○o1.

In this example, vinyl ester resin was used, but the same effect can be obtained using polyester resin.

Effects of the Invention As described above, the present invention completely cures a crosslinkable plastic plate such as vinyl ester resin or polyester resin that has been primarily cured in a mold and removed from the mold in an inert liquid such as a fluorocarbon-based liquid. By doing so, it is possible to provide a method for manufacturing an optical disk substrate with good flatness and less warpage and unevenness.

[Brief explanation of drawings]

The figure is a configuration diagram showing a method of manufacturing an optical disk substrate in an embodiment of the present invention. 1-1-- Optical disc substrate, 2... Substrate holder, 3-- Inert liquid container, 4... Inert liquid,
5... Heating device, 6... Filter. Name of agent: Patent attorney Toshio Nakao and 1 other person/-
4 Te "chair 7 basic level 2 -1 + - Ushizu T ()] Lder 3-11 Fu to book 1 East Fuyu, number, 4- Fu〉卦生う fLf book, 5---10 season Byeki 6---Filter

Claims (3)

[Claims] (1) A method for producing an optical disk substrate, which comprises completely curing a crosslinkable transparent plastic plate that has been primarily cured in a mold and removed from the mold in an inert liquid. (2) The method for manufacturing an optical disk substrate according to claim 1, wherein the crosslinkable plastic is vinyl ester or unsaturated polyester. (3) The method for manufacturing an optical disk substrate according to claim 1, wherein the inert liquid is a fluorocarbon-based inert liquid.