JPH10302305A - Optical disk substrate and optical disk - Google Patents

Abstract

(57) [Problem] To provide an optical disk substrate and an optical disk having a good balance of birefringence, heat resistance and water absorption. An optical disk substrate made of a polymer containing a structural unit represented by the following general formula (1), and an optical disk having an inorganic thin film laminated on the substrate. Embedded image In the formula, R ¹ represents a hydrogen atom, a hydrocarbon group having 1 to 25 carbon atoms, an alicyclic hydrocarbon group, or a substituted hydrocarbon group, and n represents a positive integer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical disk substrate and an optical disk made of a specific resin.

[0002]

2. Description of the Related Art Since compact disks (CDs) and laser disks (LDs) were marketed in the early 1980s, optical disks have rapidly become widespread. At present, it is further desired to digitally record a moving image comparable to that of an LD on a CD-size optical disk, and various types of thin and high-density optical disks have been developed (1992).
Lectures at Autumn Society of Applied Physics 17p-T-11, 17p-T-1
3, Lecture at the Japan Society of Applied Physics Spring 1993 29-a-
B-8, 29a-B-5, etc.).

[0003] The substrate of such an optical disk is formed by an injection molding method which can be mass-produced at low cost, and polymethyl methacrylate or polycarbonate has been proposed as a resin for the substrate.

[0004]

However, although this polymethyl methacrylate has a low birefringence, it is problematic in that it has low heat resistance and high water absorption. On the other hand, polycarbonate has a problem in that although it has excellent heat resistance and water absorption, it has a large birefringence. In order to cope with the recent increase in the density of optical information, it is necessary to reduce the birefringence, and a substrate that balances birefringence, heat resistance and water absorption is desired.

[0005]

The gist of the present invention resides in an optical disk substrate made of a polymer containing a structural unit represented by the following general formula (1), and an optical disk in which an inorganic thin film is laminated on this substrate. It is in.

[0006]

Embedded image

In the formula, R ¹ represents a hydrogen atom, a hydrocarbon group having 1 to 25 carbon atoms, an alicyclic hydrocarbon group, or a substituted hydrocarbon group, and n represents a positive integer.

The polymer comprising the repeating unit represented by the general formula (1) has a positive value of birefringence. The methyl methacrylate polymer has a negative value of birefringence. That is, the present invention provides an optical disk substrate having a birefringence of zero or near zero.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The content of the repeating unit of the general formula (1) is not particularly limited.
It is preferably at least 40% by weight or more. If the content is too small, the heat resistance tends to be insufficient. As the repeating unit component of the general formula (1) of the polymer, R ¹ is preferably a methyl group or a compound having 6 or more carbon atoms from the viewpoint of heat resistance, and methyl, cyclohexyl and tricyclodecanyl are preferred. And an adamantyl group. Components other than the repeating unit of the general formula (1) of the polymer include (meth) acrylates such as methyl methacrylate and methyl acrylate, styrene, α-
Examples include methylstyrene and acrylonitrile,
Methyl methacrylate is most preferred in terms of transparency and birefringence. In the present invention, the thickness of the obtained optical disc substrate is 1.2
mm or less, more preferably 1.0 mm or less. "Optical Technology Contact" 23, No.
As described in equation (4) on page 451 of 7,1985, the thickness and the numerical aperture of 3 are formed on the inclined optical disk molded substrate.
Coma aberration having a magnitude proportional to the power is generated. Therefore, if the thickness is too large, the use of an objective lens having a high numerical aperture to increase the density of the optical disk will increase the coma aberration, and as a result, the crosstalk will increase when the disk substrate is tilted, and at the same time the return from the disk will occur. Since the amount of light is reduced, the S / N ratio is deteriorated and the jitter is undesirably increased.

In the present invention, the birefringence of the optical disk substrate in a double pass is preferably 70 × 10 ⁻⁶ or less, more preferably 40 × 10 ⁻⁶ or less. If the birefringence is too large, it is not preferable because the data error rate of the read signal increases and the tracking becomes unstable. Incidentally, the birefringence is a value obtained by dividing a measured value in a double pass with a light beam having a wavelength of 546 nm by the thickness of the disk substrate.

The optical disk substrate of the present invention can be formed by an injection molding method, an injection compression molding method or the like. Injection conditions such as a cylinder temperature, a mold temperature, a mold clamping pressure, and an injection speed are selected as appropriate for the resin composition.

An optical disk can be obtained by laminating an inorganic thin film on the optical disk substrate. Examples of the inorganic thin film include simple metals such as aluminum and gold, or metals containing these as main components, and inorganic dielectrics such as silicon oxide, silicon nitride, and zirconium oxide. The type, thickness, film composition, etc. of the inorganic thin film formed here are determined by the type of the optical disk. For example, in a normal read-only optical disk, an aluminum film is formed with a thickness of 50 nm or more in order to obtain sufficient reflectance and durability. In a write-once optical disk and a rewritable optical disk, it is common to form a dielectric and a metal by laminating them.

[0013]

The present invention will be described below in detail with reference to examples. The “%” used in the examples is all parts by weight and weight%. In the present invention, an injection molding machine (Meiki Seisakusho Co., Ltd. Dynamelter M-70A-DM) is used, and a die equipped with a stamper having pits and grooves having a pitch of 0.8 to 1.0 μm is used. An optical disk substrate having a thickness of 120 mm and a thickness of 0.6 mm was injection molded, and the following items were evaluated for the substrate.

Saturated water absorption The injection molded product was dried at 90 ° C, weighed, and then immersed in warm water at 25 ° C until the weight reached equilibrium. The weight after the equilibrium was measured and determined by the following equation. Saturated water absorption (%) = [(water absorption−dry weight) / dry weight] × 100 Birefringence The value in a double pass with a light having a wavelength of 546 nm was measured using a polarizing microscope. The value obtained by dividing the measured value by the thickness is the birefringence. It was measured by Tg DSC.

Example 1 In a flask having a capacity of 2 liters, 824 g (4 mol) of tricyclodecanyl acrylate, 160 g (4 mol) of paraformaldehyde having a purity of 75%, 60 g of 1,4-diazabicyclo [2,2,2] octane (0.53 g) mol), p-methoxyphenol 616 mg, t-butyl alcohol 120 g while bubbling air with 80
The reaction was carried out at 5 ° C. for 5 days. After the completion of the reaction, the reaction solution was poured into 3 L of methanol and stirred for 30 minutes. Then, the mixed solution was allowed to stand at −20 ° C. overnight, and bis (α-hydroxymethyl acrylate tricyclodecanyl) ether as white crystals was obtained.
712 g (79.2% yield) was obtained.

In a 5 L flask containing 2500 ml of toluene as a solvent, 250 g of bis (α-hydroxymethyl acrylate tricyclodecanyl) ether and 250 g of methyl methacrylate (MMA) were put and dissolved. To this solution was added 3 g of pertetra A (manufactured by NOF Corporation, purity: 20 wt.%) As an initiator, and the mixture was stirred for 40 minutes while purging with nitrogen. Thereafter, the mixture was heated to 95 ° C. to start the polymerization, and the polymerization was performed for 7 hours.

This reaction solution was put into a large amount of methanol to precipitate a polymer, which was filtered and washed with methanol. This is vacuum dried to obtain 455 g of a powdery polymer (yield:
91%). The Tg of this polymer was 150 ° C.

An optical disk substrate is molded from the polymer under the molding conditions of a cylinder temperature of 290 ° C., a mold temperature of 80 ° C., and a mold clamping pressure of 20 tons.
120mm outer diameter with 0.6m thickness with μm pits and grooves
m substrates were obtained. The birefringence of this substrate was 15 × 10 ⁻⁶ , and the saturated water absorption was 0.9%.

Next, an aluminum film having a thickness of 70 nm was formed by a vacuum evaporation method, and an optical disk was manufactured. Specifically, film formation was performed under the following conditions.・ Preliminary evacuation: evacuation time 0.5h, degree of vacuum reaching 1 × 10 ^-5 T
orr Evaporation method: resistance heating Deposition rate: 0.8 to 1.2 nm / sec.

Comparative Example 1 A polycarbonate resin (AD9000TG manufactured by Teijin Chemicals Ltd.) was used, and molding conditions were a cylinder temperature of 370 ° C. and a mold temperature of 1
An optical disk substrate is formed under the conditions of 20 ° C. and a mold clamping pressure of 10 tons, and a track pitch of 0.8 to 1.0 μm is formed on the substrate surface.
120mm outer diameter with m pits and grooves, 0.6mm thick
Was obtained. Although the saturated water absorption was 0.4%, the birefringence of the substrate was as large as 75 × 10 ⁻⁶ .

[0021]

The optical disk substrate of the present invention is excellent in birefringence, heat resistance and water absorption, so that it is possible to input image data to the optical disk at a high density. It is extremely large.

Claims (3)

[Claims] 1. An optical disk substrate comprising a polymer containing a structural unit represented by the following general formula (1). Embedded image (In the formula, R1 represents a hydrogen atom or a hydrocarbon group having 1 to 25 carbon atoms, an alicyclic hydrocarbon group, or a substituted hydrocarbon group, and n represents a positive integer.) 2. The optical disk substrate according to claim 1, wherein the birefringence is 70 × 10 ⁻⁶ or less in a double pass. 3. An optical disk comprising the optical disk substrate according to claim 1 and an inorganic thin film laminated thereon.