JPS63215739A - Production of optical disc base - Google Patents

Abstract

PURPOSE:To obtain an optical disc base small in double refraction, water absorptivity, etc., by molding a disc base containing a thermoplastic resin, a monomer having a plurality of ethylenically unsaturated groups and a photopolymerization initiator and crosslinking this base by irradiation with a radiation. CONSTITUTION:A disc base based on a thermoplastic resin (e.g., acrylate polymer or a polycarbonate), a monomer having at least two ethylenically unsaturated groups in the molecule (e.g., ethylene glycol dimethacrylate) and a photopolymerization initiator (e.g., acetophenone) is produced. This base is irradiated with a radiation from a mercury vapor lamp, xenon lamp or the like to form crosslinkages in it. In this way, an optical disc base small in double refraction, good in transferability of groove pattern, excellent in dimensional stability because of low water absorptivity, and excellent in heat softening resistance can be produced in good efficiency.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an optical disc substrate, and more specifically to a resin for substrates of information recording bodies such as video discs, compact discs, audio discs, and information file discs for computers. Regarding.

[Prior Art] Transparent resins are used for the substrates of disks, and at present, polymethyl methacrylate and polycarbonate are the most preferred materials in practical use in terms of light transmittance, moldability, etc. As the molding method, injection molding or compression molding is usually used.

However, in polymethyl methacrylate,
It has a large specific water absorption capacity, and is prone to dimensional changes due to moisture absorption, warpage of the board, or cracks due to long-term repeated drying and moisture absorption.It also has a tendency to remarkable thermal softening at around 100 to 110℃, and has poor heat softening resistance. There is an inherent problem that this is not necessarily sufficient.

On the other hand, in polycarbonate, orientation tends to occur during injection molding or compression molding, resulting in high birefringence.
Since rapid thermal softening is observed at around 0° C., there was a problem in that the thermal softening resistance was poor.

In order to prevent these drawbacks, a method of casting polymerization using a thermosetting resin has been proposed.

For example, JP-A-58-08042, JP-A-6
In JP 1-281114 and the like, a crosslinked structure is generated by a cast polymerization method using a difunctional or higher functional methacrylic ester. Similarly, the inventors of the present invention
JP-A-275080 proposes a method for obtaining a resin for disk substrates made of a polymer having a crosslinked structure by a cast polymerization method.

[Problems to be solved by the invention] However, methods using these thermosetting resins,
Since the molding method is cast polymerization, it takes a long time to cure the resin, which poses a major problem in productivity.

The present invention aims to eliminate the drawbacks of the prior art, and uses highly productive molding methods such as injection molding and compression molding, and also improves the warping of the substrate due to water absorption, heat softening resistance, and birefringence. An object of the present invention is to provide a method for efficiently manufacturing an optical disk substrate that is excellent in both aspects.

[Means for solving bad luck] The present invention has the following configuration in order to achieve the above object.

That is, in the present invention, a disk substrate is molded using a mixture whose main components are a thermoplastic resin, a monomer having two or more ethylenically unsaturated groups in the molecule, and a photopolymerization initiator, and then the This is a method for manufacturing an optical disk substrate, characterized in that a crosslinked structure is generated by irradiating the substrate with radiation light.

As the thermoplastic resin in the present invention, a transparent resin that can be molded into a disk substrate by injection molding, compression molding, or the like can be used. However, since the disk substrate must not be deformed during handling after molding, it is preferable that the glass transition temperature of the resin is 50° C. or higher. moreover,
The process of recording and reproducing information on an optical disc is performed using laser light. Therefore, the resin used for the disc is required to have high light transmittance. Therefore,
It is preferable that the light transmittance of the resin is 80% or more.

Examples of such resins include polystyrene, acrylic ester polymers, methacrylic ester polymers, polycarbonate, etc. However, in terms of light transmittance, moldability, birefringence, etc. Acid ester polymers and polycarbonates are preferred.

Examples of acrylic ester polymers and methacrylic ester polymers include methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, Polymers or copolymers of benzyl methacrylate and their corresponding acrylic acids are used.

In addition, aromatic monomers such as methane dilylic acid and styrene, methylstyrene, α-methylstyrene, etc. are added to these polymers or copolymers to improve the water absorption and heat resistance of the acrylic acid polymer. It may also be added as a copolymerization component.

Moreover, as the polycarbonate, a polycarbonate resin obtained by reacting an aromatic diol with phosgene, diphenyl carbonate, etc. is preferable. Examples of aromatic diols used in this case include bis-(4-hydroxyphenyl)methane, 1,1-bis-(4°-hydroxyphenyl)ethane, 1,1-bis-(4′-hydroxyphenyl) Propane, 2.2-bis-(4°-hydroxyphenyl)propane (hereinafter referred to as "bisphenol A"), 2.2-bis-(4"-hydroxyphenyl)
Butane, 2,2-bis-(4°-hydroxyphenyl)
Pentane, 2,2-bis-(4"-hydroxyphenyl)isopentane, 2,2-bis-(4"-hydroxyphenyl)hexane, 2,2-bis-(4"-hydroxyphenyl)inhexane, 4, 4-dihydroxyphenylmethane, 1.1-bis=(4-hydroxyphenyl)
Cyclohexane, 2,2-bis-(4“-hydroxy-
3'-methylphenyl)propane, 2,2-bis(4
Particularly preferred aromatic diols include one or more selected from bisphenols such as ゛-hydroxy-3°, 5゛-dimethylphenyl)propane, dihydroxydiphenyl ether, dihydroxydiphenyl sulfone, and dihydroxydiphenyl sulfide. Examples include bisphenol A.

In addition, examples of monomers having two or more ethylenically unsaturated groups in the molecule include ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, and 1,6-hexane. Thiol dimethacrylate, 1,4-dimethacryloxybenzene,
2.2-bis(4-methacryloxyethoxyphenyl)
Sulfone, 2,2-bis(4-methacryloxyethoxyphenyl)methane, 2,2-bis(4-methacryloxyphenyl)propane, 2,2-bis(4-methacryloxyethoxyphenyl)propane, 2,2- Dimethacrylates such as bis(4-methacryloxypolyethoxyphenyl)propane and corresponding diacrylates, tri(meth)acrylates such as trimethylolethane trimethacrylate, trimethylolpropane trimethacrylate, and trimethylolpropane triacrylate; , polyfunctional acrylic esters and methacrylic esters having four or more functional groups, such as dipentaerythritol hexaacrylate, tetramethylolmethanetetraacrylate, and pentaerythritol tetraacrylate, and aromatic divinyl esters such as divinylbenzene. There are compounds, etc. These compounds may be used alone or in combination of two or more. However, it is necessary to select a monomer that has good compatibility with the thermoplastic resin so that the substrate becomes transparent upon crosslinking. The blending ratio of these compounds cannot be uniformly limited depending on the compound used, but if it is less than 5% by weight, the crosslinking effect will be insufficient, and if it exceeds 60% by weight, the molding will be insufficient. It is preferably at most 10% by weight, particularly preferably from 10 to 50% by weight.

In the present invention, the above-mentioned thermoplastic resin and a compound having two or more ethylenically unsaturated groups in the molecule are uniformly mixed, and then a photopolymerization initiator, a thermal polymerization inhibitor, etc. are added. This thermal polymerization inhibitor is added to suppress the reaction of the unsaturated groups when the reaction of the unsaturated groups occurs during molding, making molding difficult.

A photopolymerization initiator, a thermal polymerization inhibitor, and the like may be dissolved in advance into the polyfunctional monomer before mixing the thermoplastic resin and the polyfunctional monomer.

Conventionally known photopolymerization initiators can be used, such as acetophenone, 2,2-jethoxyacetophenone, p-dimethylaminoacetophenone,
Benzophenone, 2-talolopenzophenone, benzyl, benzoin, benzoin methyl ether, benzoin ethyl ether, azobisbutyronitrile, etc. can be used, and the above-mentioned compound 1 having an ethylenically unsaturated group
The content is suitably 0.05 parts by weight or more and 10 parts by weight or less per 00 parts by weight.

Conventionally known thermal polymerization inhibitors can be used, including hydroquinone, phenols such as butylcatechol, quinones such as benzoquinone, aromatic amines such as phenylamine, mercaptans and dithio Sulfur compounds such as carbamates, etc.
A suitable amount is 0.0001 to 5 parts by weight per 100 parts by weight of the above-mentioned compound having an ethylenically unsaturated group.

In addition to the above-mentioned essential ingredients, silicone,
Contains mold release agents such as fatty acids, fatty acid esters, and aliphatic alcohols, antistatic agents such as higher alcohol sulfonates and quaternary ammonium salts, and anti-coloring agents such as triphenylphosphine and triphenylantimony. Good too.

Next, the manufacturing method will be explained. A mixture of the above-mentioned thermoplastic resin, a monomer having two or more ethylenically unsaturated groups in the molecule, a photopolymerization initiator, a thermal polymerization inhibitor, etc. is injection molded or A disk substrate onto which the information signals of the stamper are transferred is molded by compression molding or the like. The stamper used in this invention is not particularly limited, and may be produced by a known normal process. After the substrate is removed from the mold, the disk substrate is irradiated with radiation to create a crosslinked structure. As the light source of the radiant light, a low pressure mercury lamp, a high pressure mercury lamp, an ultra-high pressure mercury lamp, a xenon lamp, a metal halide lamp, a carbon arc, an ultraviolet fluorescent lamp, etc. are used. In addition, the crosslinking reaction can be promoted by heating the substrate to the extent that the physical properties of the substrate are not adversely affected when the crosslinked structure is generated by this light.

In the present invention, by using a thermoplastic resin containing a monomer having two or more ethylenically unsaturated groups in the molecule as described above, the resin has good fluidity during molding, and improves moldability and stampability. The transferability of the grooves is improved. Moreover,
Since the residual stress of the resin is reduced, the birefringence of the substrate after molding is also extremely small. In addition, after forming the disk substrate,
By irradiating the disk with radiation light at room temperature, a crosslinking reaction is caused, so that uniform crosslinking occurs and an increase in birefringence before and after irradiation with radiation light can be prevented. The thus obtained disk substrate has a crosslinked structure introduced into the substrate, thereby increasing the heat softening resistance of the substrate and preventing deformation such as warping under high temperature conditions. Furthermore, even when a highly hygroscopic resin such as polymethyl methacrylate resin is used as the thermoplastic resin, warping of the substrate due to moisture absorption can be suppressed.

[Examples] In order to clarify the gist of the present invention, Examples are given below, but the present invention is not limited to these Examples. In addition, in Examples and Comparative Examples, various physical properties were measured by the following test methods.

(1) Heat Softening Resistance: Based on ASTM-D1525 <: According to the VICAT heat softening test method, the needle penetration amount is determined by increasing the temperature to 150°C. The criteria are A: Needle penetration amount is 0.5 mm or less (good) B: Needle penetration amount is 0.5 mm
C: Needle penetration exceeds 1.0 mm (defective)
After being immersed in water for 24 hours, the amount of warpage was measured.

(3) Birefringence: Using an automatic elliplimator DVA-36L, a 5-inch (Jlei pa
Measured by th.

Example 1 75 parts by weight of polymethyl methacrylate, 25 parts by weight of trimethylolmethanetetraacrylate, 2 parts by weight of benzyl dimethyl ketal, 4 parts by weight of 2,6-ditertiary-butyl
- After stirring and mixing uniformly using ethyl acetate and 0.5 parts by weight of methylphenol as a solvent, the solvent was removed and vacuum dried to obtain a transparent blend. This blend was injection molded at a cylinder temperature of 210° C. and a mold temperature of 60° C. to obtain a transparent disk substrate with a diameter of 12 cm and a thickness of 1.2 mm.

This disk substrate was tested at 50°C in the VICAT heat softening test.
The needle penetration amount was 1.0 m or more. Next, the substrate was simultaneously irradiated with ultraviolet rays from both sides for 10 minutes using an ultra-high pressure mercury lamp to cause a crosslinking reaction. The obtained disk substrate is
It is transparent, has heat softening resistance level A (VICAT heat softening test, even when heated to 150°C, the penetration amount of the needle is less than 0.5 mm), and the amount of deformation and warpage in water is 1.2 mm, which is excellent, and has excellent birefringence. Δnd was also extremely small at 3 nm.

The results are shown in Table 1.

Example 2 50 parts by weight of polymethyl methacrylate, 2,2-bis-
A disk substrate was obtained in the same manner as in Example 1 except that (4-acryloxyethoxyphenyl)propane was used in an amount of 50 parts by weight. The results obtained are shown in Table 1.

Comparative Example 1 A disk substrate having a diameter of 12c+n and a thickness of 1.2 mm was obtained by injection molding using polymethyl methacrylate resin.

The results obtained are shown in Table 1.

Comparative Example 2 60 parts by weight of 2.2-bis(4-acryloxyethoxyphenyl)propane was dissolved in 40 parts by weight of methane. 0.61 parts by weight of azobisisobutyronitrile as a polymerization initiator was added to this mixed solution, and after thorough mixing, dissolved gas such as air was degassed under vacuum to carry out cell cast polymerization. Cell cast polymerization was performed as follows. Inject the monomer mixture having the above composition into a mold equipped with a stand bar on one side. Polymerization started at 60'C and reached 120'C.
The temperature was raised to 'C in 3 hours to complete the polymerization. The disk plate thus obtained had a heat softening resistance level A and a birefringence And of as small as 31 m.

However, in order to cause less strain due to polymerization and to completely react unreacted monomers, it is necessary to
It was necessary to heat the polymer for 3 hours in a temperature range of up to 20° C. for polymerization and curing.

[Effects of the Invention] According to the method for manufacturing an optical disk substrate of the present invention, birefringence is small, groove transferability is good, water absorption is low, so dimensional stability is excellent, and heat softening resistance is excellent. Optical disk substrates can be efficiently produced.

Claims (3)

[Claims] (1) Molding a disk substrate mainly composed of a thermoplastic resin, a monomer having two or more ethylenically unsaturated groups in the molecule, and a photopolymerization initiator, and then irradiating the substrate with radiant light. A method for producing an optical disc substrate, characterized in that a crosslinked structure is generated by (2) The method for manufacturing an optical disk substrate according to claim (1), wherein the thermoplastic resin has a glass transition temperature of 50° C. or higher and a light transmittance of 80% or higher. . (3) The monomer having two or more ethylenically unsaturated groups in the molecule is at least one type selected from bifunctional or higher functional acrylic esters, methacrylic esters, and aromatic divinyl compounds. A method for manufacturing an optical disc substrate according to claim (1).