JPS61141749A - Optical disc - Google Patents

Abstract

PURPOSE:To provide an optical disc which has a low birefringence index, low hygroscopicity and good transparency, heat distortion temp. and mechanical strength and little causes discoloration, consisting of a resin obtd. by incorporating a small quantity of an antioxidant in a methacrylate resin. CONSTITUTION:An optical disc is obtd. by using, as a material for the main body of a disc, a resin obtd. by using, as a main component, a copolymer (A) composed of 30-60wt% methyl methacrylate, 10-40wt% methacrylate ester wherein a 3-8C hydrocarbon group is attached to an acid radical (e.g. cyclohexyl methacrylate) and 10-50wt% arom. monoalkenyl monomer as essential ingredients and incorporating 0.01-1.5wt% (based on the quantity of component A) antioxidant [e.g. n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] in component A.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an optical information recording disk (hereinafter abbreviated as an optical disk) in which recorded signals are read out by reflection or transmission of a laser beam.

[Background technology]

The optical information recording/reproducing method, in which a spot beam of laser light is applied to a disk and the signals recorded by minute bits on the disk are read out by detecting the amount of reflected or transmitted light, can significantly increase the recording density. Since the images and sounds reproduced from it have excellent characteristics, it is expected that it will be widely used for recording and reproducing images and sounds, recording and reproducing large amounts of information, etc. The disks used in this recording/reproducing system are required not only to be transparent so that laser beams can pass through the disk body, but also to have optical homogeneity to reduce reading errors. Birefringence occurs when the laser beam passes through the disk body due to thermal stress caused by single molecule orientation during the cooling and flow process of the resin during disk body molding, residual stress due to volume changes in the disk body material near the softening point, etc. arise. This large optical non-uniformity caused by birefringence is a fatal flaw for optical discs. In addition, dimensional changes and warping of optical discs (molded products) due to moisture absorption can increase reading errors, so hygroscopicity is also much lower than that of optical discs that use conventional methacrylic resin. requested.

Moreover, in addition to imparting these characteristics,
It is naturally required that the properties of methacrylic resin, such as transparency, heat distortion temperature, mechanical strength, etc., are not reduced.

The inventors have found that methyl methacrylate, methacrylic esters in which a hydrocarbon group having 3 to 8 carbon atoms is bonded to an acid group, and heptanoamines are used as resins for optical discs that can basically satisfy the above-mentioned required performance. A resin copolymerized with a lukenyl aromatic monomer has already been discovered. However, it has been found that this copolymer resin has the following problems.

That is, in the manufacture of optical discs that require high precision and low birefringence, the resin that forms the disc body is molded at high temperature by injection molding or the like. The problem is that when exposed to high temperatures during molding for a certain period of time, the resin thermally decomposes and the molded disk body becomes colored. The disc body is not necessarily colored uniformly; for example, the disc body may be colored in shading, with colored parts scattered in spots. In this way, when the disc is colored in shading, a fatal problem arises for the disc body in that when the disc body is irradiated with a laser beam, the amount of transmitted and reflected light of the laser beam changes.

[Purpose of the invention]

This invention was made in view of these circumstances, and has a very low birefringence, low hygroscopicity, and satisfactorily satisfies transparency, heat distortion temperature, and mechanical strength. Moreover, it is an object of the present invention to provide an optical disc with a very low degree of coloration.

[Disclosure of the invention]

The inventors attempted to achieve the above object by using, for the disk body, a resin that is an improved version of the copolymer resin that the inventors had already discovered. □As a result, 0.01~1
．． The present invention was completed based on the discovery that it is sufficient to include an antioxidant in the resin at a ratio of 5% by weight.

Therefore, this invention provides methyl methacrylate 30-6
0% by weight, 10% to 40% by weight of methacrylic acid ester in which a hydrocarbon group having 3 to 8 carbon atoms is bonded to an acid group, and 10% to 50% by weight of a monoalkenyl aromatic monomer as essential raw materials. The gist of the optical disc is an optical disc whose disc main body material is a resin containing an antioxidant in an amount of 0.01 to 1.5% by weight relative to the copolymer. The present invention will be explained in detail below.

As mentioned above, the optical disc according to the present invention uses methyl methacrylate, a methacrylic ester in which a hydrocarbon group having 3 to 8 carbon atoms is bonded to an acid group (hereinafter simply referred to as "methacrylic ester"), and A resin containing as a main component a copolymer whose essential raw material is a monoalkenyl aromatic monomer (including styrene, styrene derivatives, etc.) is used as the material for the disk body. Examples of the hydrocarbon group of the methacrylic acid ester include a chain hydrocarbon group such as an alkyl group, a cyclic hydrocarbon group, and the like.

Specific methacrylic acid esters include, for example, cyclohexyl methacrylate (cyclohexyl methacrylate), isopropyl methacrylate, and n-methacrylate.
Butyl (n-butyl methacrylate), isobutyl methacrylate, 2-ethylhexyl methacrylate, full-n-propyl methacrylate, 5ec-butyl methacrylate, isoamyl methacrylate, t-amyl methacrylate, neopentyl methacrylate, methacrylic acid -3,
Examples include 3-dimethylbutyl, which may be used alone or in combination of two or more. Examples of monoalkenyl aromatic monomers include styrene, p-methylstyrene, 0-methylstyrene, m-methylstyrene, α-methylstyrene, and other styrene derivatives, and others, which may be used alone. Alternatively, two or more types may be used in combination. From the viewpoint of color resistance, it is preferable to use styrene without substituents.In copolymerizing the above-mentioned monomers, 30 to 60% by weight of methyl methacrylate and 10 to 10% by weight of ester methacrylate are used. 40
% by weight, monoalkenyl aromatic monomer 10-50% by weight
It is necessary to use the ratio of When copolymerized at such a ratio, optical homogeneity such as birefringence, mechanical properties such as mechanical strength, hygroscopicity, transparency, heat distortion temperature (heat distortion resistance), etc. are suitable as a material for the disk body. It is obtained as a copolymer.

The photoelastic coefficient of the copolymer is -10, OX 10-”cd
/dyne or more, +10. OX 10-”c+J
It is preferable to make it less than /dyne, −8,
0X10-'3aJ/dyne or more, +8. Q
It is more preferable to adjust the copolymer's birefringence to less than or equal to I Q -" ci /dyne. This is because the birefringence of the copolymer becomes even smaller. The adjustment of the photoelastic coefficient is carried out by adjusting the photoelastic coefficient of a monomer that is a resin with a positive photoelastic coefficient. This can be carried out by copolymerizing a suitable combination of a monomer and a monomer forming a negative resin.

Antioxidants are added to the resin. Examples of antioxidants include phenolic antioxidants.

Examples include phosphorus-based antioxidants and sulfur-based antioxidants.

In order to achieve the objectives of this invention, it is necessary that the antioxidant be stable at the processing temperature. Also,
It is also necessary that the resin has good compatibility with the resin and is non-colored. Phenolic antioxidants include monophenols, bisphenols, and polymeric phenols, but at least one of the two ortho positions of the phenolic hydroxyl group is bulky (such as a t-butyl group).
Substituted with a bulky hydrocarbon group is preferred. In addition, when using a phenolic antioxidant, it is preferable that the 5% weight loss hot water temperature measured by a thermogravimetric analysis (TGA) device is 280° C. or higher.

Examples of phenolic antioxidants include the following (
A) n-octadecyl-3-(3,5
-di-tert-butyl-4-hydroxyphenyl) propionate (Yoshitomi Pharmaceutical's Tominox SS, etc.), (B)
4,4'-Butylidene-bis-(3-
Methyl-6-tert-butylphenol) (Sumilizer 88M, etc. from Sumitomo Chemical Co., Ltd.), tetrakis-[methylene-3-(3',5'-di-tert-butyl-4) shown by formula (C) [-Hydroxyphenyl)prohyonate] methane (Sumilizer BP-10 from Sumiya Chemical Industry ■)
1, etc.), 2-tert-butyl-6 represented by the formula (D)
-(3''-tert-butyl-5'-methyl-2'-hydroxybenzyl)-4-methylphenyl acrylate (Sumilizer GM, Sumitomo Chemical Co., Ltd., etc.), 1, 3 shown in formula (E) .5-trimethyl-2,4,6-dolisu(3,5-di-tert-butyl-4-hydroxybenzyl)benzene (Elanox-33 from Asano Chemicals ■)
0, etc.), 2,2'-methylene- shown in formula (F)
Bis-(4-ethyl-6-tert-butylphenol (Swanox 425 from Maruzen Petrochemical), (G) mark AO-20 from Adeka Argus ■, (H)
Gutudrych's Gutdrite 312 shown by the formula
5, 4,4'-thiobis-(3
-Methyl-6-tert-butylphenol) (Yoshitomi Pharmaceutical-
Yoshinox SR), (J) shown in formula 2, 2
4,4'-methylene-bis-(2゜6-di-tert-butylphenol) (Cipro Kasei's Seenox 226M, etc.), tris-(2-methyl-4-hydroxy-5-tert-butylphenyl)butane (Cipro Kasei's Seenox 336B, etc.) may be used, and a plurality of types may be used in combination.

(Left below) The amount of CH3 antioxidant added is 0.00% relative to the copolymer (resin).
0.01 to 1.5% by weight, and 0.02 to 0.02% by weight.
It is preferably 5% by weight. Added amount is 0゜01% by weight
If the amount is less than 1.5% by weight, the effect on heat decomposition resistance and coloring resistance will not be sufficiently obtained, and if it exceeds 1.5% by weight, not only will the effect of addition not be improved, but it will be difficult to mix uniformly into the resin.

When using the above-mentioned phenolic antioxidants as antioxidants, sulfur-based antioxidants generally known as secondary antioxidants, such as dimilisnarnaodizo 1) HJ, /, -1(2, t-CHt C
Hz COOCr a H2W ) z ) etc. may be used in combination without impairing the purpose of the present invention.

In addition, for the purpose of improving the performance of optical discs, the above-mentioned monomers, namely methyl methacrylate, methacrylate ester, and monoalkenyl aromatic monomer, may be added as necessary to the extent that does not impede the purpose of the present invention. A polymerizable monomer may be used together with the polymer.

The copolymer may be produced by any of the known polymer production methods, such as bulk polymerization, suspension polymerization, solution polymerization, and emulsion polymerization.

Stamper is used as a component of the resin that becomes the disc body material.
For example, silicone, wax, fatty acids, and fatty acid esters for the purpose of improving mold release properties.

Auxiliary agents (mold release agents) such as fatty acid metal salts and fatty acid alcohols, and auxiliary agents (antistatic agents) such as sulfonate salts of higher alcohols and quaternary ammonium salts for the purpose of preventing static electricity.
may be used in combination with the above-mentioned copolymer within a range that does not impair the achievement of the objects of the present invention.

The optical disc of the present invention is manufactured, for example, in the following manner. First, a resin made by adding an antioxidant and additives used as necessary to a copolymer is injection molded or press molded, and pits that become recording signals are transferred using a mold equipped with a stamper. , mold the disk body (substrate). Molding must be performed under conditions that minimize residual stress. Next, in the case of a duplicate disk, a reflective layer is generally formed on the pit transfer surface by a method such as vacuum vapor deposition of metal, sputtering, or ion blasting.
In addition, in the case of memory disks, after the pits that serve as tracking signals are transferred in the same manner as described above, the bit surface is further coated with a protective coating of a reflective layer as required. depositing or coating a user-writable recording layer of quality rare metals or compounds that can be thermally decomposed by a laser;
Further, if necessary, a reflective layer or a protective coating as described above can be formed to manufacture an optical disk for memory.

The optical disc of the present invention obtained in the above manner has high optical homogeneity and a very high birefringence because it uses a resin mainly composed of the above-mentioned copolymer. It is small, has a high heat distortion temperature, and has very low hygroscopicity. Furthermore, since the resin used has good heat decomposition resistance due to the inclusion of an antioxidant, the degree of coloration is also very low.

Next, Example 1 to explain Examples and Comparative Examples
~6, the proportions shown in Table 1 (
We decided to use a resin to which a phenolic antioxidant was added (in proportion to the copolymer) as the disc body material.

On the other hand, in Comparative Examples 1 to 3, a copolymer obtained by copolymerizing monomers at the blending ratio shown in Table 1 was used as it was as the resin for the disk body material. However, the copolymerization reaction was carried out using a suspension polymerization method. Example 1
6 and Comparative Examples 1 to 3, thermal decomposition temperature 1 colorability, water absorption, and photoelastic coefficient were measured to determine thermal stability. The results are shown in Table 1. However, the water absorption rate is J
According to the measurement method specified in IS K 691),
The thermal decomposition temperature, colorability, and photoelastic coefficient were determined as follows.

■ Heat decomposition temperature (thermal stability test) Accurately weigh approximately 20 mg of sample and conduct thermogravimetric analysis (TGA).
Using an apparatus, the temperature of the sample was raised at a rate of 5° C./min, and the temperature at which the weight loss reached 5% was measured. This temperature is an index of thermal stability (thermal decomposition resistance).

■ Coloration test The degree of coloration was measured based on the method for measuring object color shown in JIS Z 8722.

The samples used were obtained by preparing a 10% chloroform solution of each resin, applying the solution to a thickness of several μm on a 5×5 cm glass plate, and drying it to form a film. After placing the sample in an oven at 280°C for 30 minutes, the sample was placed in a colorimeter (Murakami Color Research Institute model CMS).
1200). The measurement will be performed by placing a sample glass plate with a film on a standard white plate and measuring the spectral reflectance.
Among them, B1, which seems to have the largest difference, was adopted as the degree of coloration. B' is an index representing yellowness, and the larger the value, the thicker the degree of coloring.

■ Photoelastic coefficient Using each resin, prepare a test piece with a thickness of 6 mm with the side surface shown in Fig.
The photoelastic coefficient was measured by the method described in "Photoelasticity Experimental Method" published by Riken Keiichi. However, in Figure 1, a is lQ
im, b is 34w, C is 40fl, and the arrows indicate the direction of the external force applied during measurement.

(Margins below) From Table 1, it can be seen that the resins of Examples 1 to 6 and Comparative Examples 1 to 3 have sufficiently satisfactory performance in terms of water absorption and photoelastic coefficient for use as disc body materials. is within a preferable range, and as a result, a disk body with a very small birefringence can be obtained. It can be seen that the temperature is high and the coloring resistance is also excellent.

A disk body was made by injection blow molding using the resin as described above. Then, a reflective layer was formed on the disc body, and a protective coating was applied to the reflective layer to obtain optical discs of Examples 1 to 6 and Comparative Examples 1 to 3.

The optical discs of Examples 1 to 6 and Comparative Examples 1 to 3 were
All of them had low hygroscopicity and very low birefringence, but while those of Examples 1 to 6 were transparent with no coloring, those of Comparative Examples 1 to 3 were not colored. Ta.

〔Effect of the invention〕

The optical disc according to the present invention contains 30 to 60% by weight of methyl methacrylate, 10 to 40% by weight of a methacrylic acid ester in which a hydrocarbon group having 3 to 8 carbon atoms is bonded to an acid group, and 10 to 10% by weight of a monoalkenyl aromatic monomer. Since the main component of the disc is a copolymer containing ~50% by weight as an essential raw material and a resin containing an antioxidant at a ratio of 0.01 to 145% by weight relative to the copolymer, the birefringence is extremely low. It is small in size, has low hygroscopicity, satisfies transparency, heat distortion temperature, and mechanical strength, and has a very low degree of coloration.

[Brief explanation of drawings]

FIG. 1 is a side view of a test piece for measuring photoelastic coefficient. Agent: Takehiko Matsumoto, Patent Attorney No. 1, Monthly L4, 3/4, 1985, No. 263494, No. 2, Title of Invention: Optical Disk 3, Patent applicant address: 1048 Kadoma, Kadoma City, Osaka Prefecture
Name (5 & ()) Representative of Matsushita Electric Works Co., Ltd. (Sadao Fujii 4, Agent 6, Specification subject to amendment 7, Contents of amendment (1) Page 23 of the specification, line 9 to page 1θ of the same page The line that says "injection blow molding" should be corrected to "injection molding."

Claims (5)

[Claims] (1) Methyl methacrylate 30-60% by weight, carbon number 3
The main component is a copolymer containing 10 to 40% by weight of methacrylic acid ester in which ~8 hydrocarbon groups are bonded to acid groups and 10 to 50% by weight of monoalkenyl aromatic monomer as essential raw materials, and contains an antioxidant. 0.0 in proportion to the copolymer
An optical disc whose main body material is a resin containing 1 to 1.5% by weight. (2) The methacrylic acid ester is cyclohexyl methacrylate, isopropyl methacrylate, n-methacrylate
Butyl, isobutyl methacrylate and methacrylic acid-
The optical disc according to claim 1, wherein the optical disc is at least one selected from the group consisting of 2-ethylhexyl. (3) The monoalkenyl aromatic monomer is styrene, p-
The optical disc according to claim 1 or 2, which is at least one selected from the group consisting of methylstyrene, o-methylstyrene, m-methylstyrene, and α-methylstyrene. (4) The optical disc according to any one of claims 1 to 3, wherein the antioxidant is a phenolic antioxidant. (5) The resin composition has a photoelastic coefficient of -10.0×10^
-^1^3cm^2/dyne or more, +10.0x10
The optical disc according to any one of claims 1 to 4, which has a particle size of ^-^1^3 cm^2/dyne or less.