JPH01318015A - Optical disc - Google Patents

Abstract

PURPOSE:To obtain with high productivity an optical disc having improved heat resistance and moldability and being effectively usable under a severe thermal condition by using a polyvinylcyclohexane having specified MW and softening point. CONSTITUTION:This optical disc has a base formed of a polyvinylcyclohexane resin having a number-average MW of 50,000 or larger and a softening point of 150 deg.C or higher. Said polyvinylcyclohexane resin is obtd. by performing pref. nuclear hydrogenation of a styrene polymer. As the raw material styrene polymer, vinyl arom. hydrocarbon polymers or vinyl arom. hydrocarbon block copolymers are cited. As the latter block copolymers, those copolymers consisting of a vinyl arom. hydrocarbon polymer segment and at least one conjugated diene polymer segment are cited.

Description

[Detailed Description of the Invention] [Field of Application in Industry A] The present invention relates to an optical disk, and in particular to a substrate made of a polyvinylcyclohexane resin having a specific molecular weight and softening point, which has excellent heat processing stability, etc. The present invention relates to an optical disc having:

[Conventional technology] Optical recording using lasers is capable of high-density information recording, storage,
Since it can be recycled and regenerated, its development has been actively carried out in recent years. An optical disk can be cited as an example of such optical recording. In general, an optical disk basically consists of a transparent substrate and various recording media coated thereon.

Colorless and transparent synthetic resins are often used for the transparent substrates of optical discs, and typical examples include polycarbonate (hereinafter abbreviated as rPCJ) and polymethyl methacrylate (hereinafter abbreviated as rPMMAJ). I can do it. Although these resins are excellent in colorless transparency and have unique and excellent properties, they do not meet all the requirements for optical materials, especially optical disk substrates, and there are problems that need to be solved. It has points. For example, PC has a problem with birefringence due to its aromatic ring, and also has problems with water absorption or water permeability. On the other hand, problems with PMMA in terms of heat resistance, water absorption, and toughness have been pointed out for some time.

In this way, these resins are used with their own inherent problems, but in reality, there are also
In relation to recording media coated on transparent substrates made of these resins, new problems have arisen as described below.

On the other hand, regarding recording media, a wide variety of developments have been carried out depending on the use of optical discs.
The write-once type is a hole-drilling type that is only for recording and playback, and the erasable type is a phase change type that utilizes crystalline phenomena, and the erasable type is a type that uses the crystalline phenomenon. Magneto-optical types that utilize magnetic effects are known. These recording media materials include tellurium or its oxide, alloy compound, etc. for the write-once type, and GdFe, GdFe, etc. for the erasable type.
Inorganic materials such as rare earth-transition metal amorphous alloy compounds such as TbFe, GdFeCo, and TbFeCo are mainstream, and are generally formed by forming a film on a transparent substrate using a dry process such as sputtering under a high vacuum. has been done.

By the way, the hygroscopicity and water permeability of PC% PMMA, on the one hand, cause the problem of warpage due to expansion of the substrate itself when it absorbs moisture, but on the other hand, on the other hand, it causes corrosion of the recording medium due to moisture permeation through the substrate. This causes the lifespan of the optical disk board to be shortened.

Further, regarding the heat resistance of the substrate resin, there are the following problems. That is, optical discs, especially light discs,
For optical discs such as once type and erasable type,
The temperature of the recording medium during writing and erasing of records reaches 200° C. or higher. For this reason, even though this heat is not directly applied to the disk substrate, it is expected that the substrate will reach a considerably high temperature when writing and erasing records, and resins with low heat resistance may cause deformation of the substrate or group formation. Problems such as deformation may occur.

On the other hand, in the production process of optical discs, a heat treatment process is often incorporated in order to prevent aging of the substrate or recording medium. It is desirable to shorten the time.

From this point of view as well, if the heat resistance of the resin is low, a high treatment temperature cannot be used and productivity cannot be increased.

For these reasons, PMMA, which has low heat resistance, is completely insufficient to withstand the high temperatures of the optical disc production process and usage conditions, and conventionally, PC, which has higher heat resistance, has been exclusively considered as a transparent substrate material. has been done. However, even PC is not necessarily evaluated as having sufficient heat resistance, and the emergence of resin materials with higher heat resistance is desired.

To compensate for the drawbacks of conventional resins such as PC and PMMA, JP-A-63-43910. Patent application 1986-157324
, a method of using polyvinylcyclohexane resin as an optical disk substrate has been proposed.

[Problems to be Solved by the Invention] However, even when polyvinylcyclohexane resin is used, it is not always possible to obtain a high-performance optical disk substrate, and satisfactory results have not been obtained in terms of heat resistance, etc. is the current situation.

The inventors of the present invention have made the following findings as a result of a detailed study on the problems in manufacturing an optical disk using the polyvinylcyclohexane resin proposed in the above patent application as a substrate material.

Polyvinylcyclohexane resin is usually obtained by hydrogenating the aromatic ring of a vinyl aromatic polymer, and is generally known as a brittle polymer similar to polystyrene.

As mentioned above, optical disks such as write-once type and erasable type are subjected to considerable heat history during their use and production process, so high heat resistance is required of the resin substrate.

Further, the resin material for the disk substrate is required to have at least a degree of toughness that will not cause damage during mold release during injection molding.

From this point of view, we investigated the case of manufacturing optical disk substrates using the polyvinylcyclohexane resin described in the above-mentioned conventional applications, and found that the polymers disclosed in these conventional applications do not meet the above requirements. It was found that the characteristics could not be satisfied. That is, a polymer having a high nuclear hydrogenation rate and high heat resistance has a low molecular weight and may break during injection molding, so that a satisfactory disk substrate cannot be obtained. On the other hand, polymers with small molecular weight reductions had low nuclear hydrogenation rates and insufficient heat resistance.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and provide an optical disk equipped with a substrate made of a polyvinylcyclohexane resin that has excellent heat resistance and good moldability.

[Means and effects for solving the problems] The optical disc of the present invention is characterized by having a substrate made of a polyvinylcyclohexane resin having a number average molecular weight of more than 50.000 and a softening point of 150° C. or higher. .

That is, as a result of intensive studies on improving the heat resistance and moldability of the above-mentioned polyvinylcyclohexane-based resin, the present inventors have found that by using a polyvinylcyclohexane-based resin with a specific molecular weight and softening point, a light-once type, The inventors have discovered that it is possible to obtain, with high productivity, an optical disk that can be effectively used even under severe thermal conditions, such as an erasable disk, and have thus arrived at the present invention.

If the number average molecular weight of the polyvinylcyclohexane resin used in the present invention is 50,000 or less, the resin will have poor toughness and the substrate will be damaged during mold release during injection molding.

Further, if the softening point is less than 150° C., problems such as the substrate warping and the group deforming occur due to the heat generated during writing and erasing of records in write-once type, erasable type, etc. optical disks. In addition, the heat treatment temperature in the optical disk production process must be lowered, which results in lower productivity, especially compared to conventional PCs.

The present invention will be explained in detail below.

The polyvinylcyclohexane resin used in the present invention is preferably obtained by nuclear hydrogenation of a styrene polymer.

Examples of the raw material styrenic polymer include vinyl aromatic hydrocarbon polymers and vinyl aromatic hydrocarbon block copolymers. The latter vinyl aromatic hydrocarbon block copolymer includes a vinyl aromatic hydrocarbon polymer segment (hereinafter referred to as "A segment") and a conjugated diene polymer segment having at least 1 fffi (hereinafter referred to as "B segment"). ).

Examples of the vinyl aromatic hydrocarbon used as the binder include styrene, p-methylstyrene, and α-methylstyrene, with styrene being a particularly representative example.

As the vinyl aromatic hydrocarbon polymer, a homopolymer consisting of 1 ffl or 2 ffl of these vinyl aromatic hydrocarbons is used.
Copolymers of more than one species can be mentioned. In particular, when adhesion is required, unsaturated products with polar groups that can be copolymerized with the vinyl aromatic hydrocarbons mentioned above! It is preferable to use a copolymer obtained by copolymerizing the vinyl aromatic hydrocarbon polymer with #mer to the extent that the properties of the vinyl aromatic hydrocarbon polymer are not lost.

Next, examples of the A segment in the vinyl aromatic hydrocarbon block copolymer include those similar to those of the vinyl aromatic hydrocarbon polymer described above. In addition, examples of the conjugated diene of the B segment in the block copolymer include 1,3-butadiene, isoprene, 2゜3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, etc. In particular, 1,3-butadiene and isoprene are common. A block copolymer consisting of an A segment and a B segment can be easily produced by a known method called living anion polymerization, such as a method in which polymerization is performed using an organic lithium compound as an initiator in a hydrocarbon solvent such as hexane or heptane. can be obtained. In addition, the content of A segment in such a block copolymer is 8
The content is 0% by weight or more, preferably 90% by weight or more, and more preferably 93% by weight or more. A segment content is 8
If it is less than 0% by weight, the heat resistance of the resin obtained after hydrogenation will decrease, making it unsuitable for use as an optical disk substrate.

In the present invention, the molecular weight of such raw material styrenic polymer is preferably 80,000 or more in terms of number average molecular weight. If the molecular weight of the styrenic polymer is too low, the heat resistance and toughness of the resin obtained after hydrogenation will decrease. The lower the content of the diene polymer in the polymer, the more remarkable the decrease in toughness accompanying the decrease in molecular weight. Therefore, for polymers that do not contain diene polymers, the number average molecular weight is 100.
．． A dog is more preferable than 000. - On the other hand, there is no particular restriction on the upper limit of the molecular weight, but in normal cases, 400
．． 000 or less is preferable.

Polyvinylcyclohexane resin can be obtained by nuclear hydrogenating such a styrene polymer in the presence of a hydrogenation catalyst capable of aromatic hydrogenation. Examples of the hydrogenation catalyst used here include metals such as nickel, cobalt, ruthenium, rhodium, platinum, and palladium, or their oxides, salts, and complexes, and activated carbon, diatomaceous earth, and their oxides, salts, and complexes.
Examples include those supported on a carrier such as alumina. Among these, Raney nickel, Raney cobalt, stabilized nickel and ruthenium, rhodium or platinum supported catalysts on carbon or alumina are particularly preferred from the viewpoint of reactivity.

The nuclear hydrogenation reaction is carried out at a pressure of 50 to 250 kg/c and a temperature of 100 to 200 °C using a saturated hydrocarbon solvent such as cyclohexane, methylcyclohexane, n-octane, decalin, tetralin, or naphtha as a solvent. It is preferable to use .

Note that nuclear hydrogenation of styrenic polymers usually involves scission of the molecular chains of the polymer as a side reaction. In order to prevent this molecular chain scission, hydrogenation is carried out at as high a hydrogen pressure as possible.
It is also preferable to carry out the process in a short period of time.

It is preferable that the nuclear hydrogenation rate of the aromatic nucleus by the nuclear hydrogenation reaction is 90% or more, particularly 95% or more. Nuclear hydrogenation rate is low, 9
If it is less than 0%, there are problems such as a decrease in the heat resistance of the resulting resin and an increase in birefringence, which is not preferable.

In the present invention, the molecular weight of the polyvinylcyclohexane resin thus obtained depends on the composition, molecular weight, hydrogenation conditions, etc. of the styrene polymer as a raw material, and its appropriate range also depends on the composition. Although it varies, the number average molecular weight is usually greater than 50,000, preferably 60.
．． It is greater than 000. From the standpoint of toughness, the smaller the diene polymer content, the higher the molecular weight is required, and for those containing no diene polymer, the molecular weight is preferably greater than 60,000. is 70,0
It is necessary to be a dog than 00. The upper limit of molecular weight is
It is specified from the aspect of moldability, but usually the number average molecular weight is 3.
00.000 or less. Further, its softening point is 150°C or higher, preferably 160°C or higher, as measured by a thermomechanical analyzer.

Since the polyvinylcyclohexane resin according to the present invention is a hydrocarbon resin, water in the resin can be removed by a simple drying treatment, and it can be used for molding such as injection molding. Note that during molding, additives such as heat stabilizers and antioxidants may be added as necessary to prevent deterioration of the resin during molding.

In manufacturing the substrate of the optical disc of the present invention, first,
Additives such as stabilizers are added to the above polyvinylcyclohexane resin as necessary, and the mixture is mixed using a ribbon blender, tumbler blender, Henschel mixer, etc., and then
Banbury mixer: Melt and knead using a single-screw extruder, twin-screw extruder, etc., and mix by forming into a pellet shape. By injection molding the pellet thus obtained at a molding temperature of 270 to 330[deg.] C., it is possible to obtain an optical disk substrate with excellent transparency, heat resistance, etc. and low optical distortion.

When manufacturing the optical disk of the present invention using such an optical disk substrate, Te is deposited on the surface of the substrate by metal vapor deposition or the like.
or its oxides, alloy compounds, etc., or TbFe, Tb
Rare earths such as FeCo, TbCo, and DyFeCo-1
It is possible to adopt a method such as providing a film of a recording medium such as an amorphous alloy compound of a black metal and further covering the film with a protective film.

[Examples] The present invention will be described in more detail with reference to Examples and Comparative Examples below, but the present invention is not limited to the following Examples unless it exceeds the gist thereof.

In addition, various physical properties in the following Examples and Comparative Examples were measured by the following methods.

■ Number average molecular weight Nigel permeation chromatography (GPC)
) using tetrahydrofuran (THF) as a solvent in the same manner as polystyrene to determine the number average molecular weight in terms of polystyrene.

(2) Nuclear hydrogenation rate (%): Polyvinylcyclohexane resin was dissolved in tetrahydrofuran (THF) and measured by UV absorption.

(2) Softening point (° C.): The softening temperature was measured at a heating rate of 5° C./min using a Neal Analyzer manufactured by Dupont and Surso. In addition,
The load was 5 g, and the thickness of the test piece was 3 mm.

■ Measurement of heat resistance of optical discs: Recording media and optical discs with protective films are measured using a dynamic characteristic detector equipped with a PIN photodiode differential detector to measure the carrier level (C/N ratio) (Od when using AJ2 film).
B) was measured. Measurements were performed before and after heat treatment at 100° C. for 2 hours, and the results were compared.

The recording and reproducing conditions were as follows.

Recording conditions: CAV (constant angular velocity) 1800 rpm radius 30
mm position, recording on the groove Recording frequency 0.5 MHz duty 50% Reproduction conditions: CAV 1800 rpm reproduction power 0.
8 mW Example 1 Tetrakis [methylene -3-(3,5-di-t-butyl-4-hydroxyphenyl)cobrobionate methane (IrganoxlO10, manufactured by Ciba Geigy, Japan) and tetrakis(2,4-di-t-butylphenyl-4,
4'-biphenylene phosphonite (I rgaph
os-PEPQ) was added, and melt-kneaded at 260° C. using an extruder to form pellets.

The pellets were molded using an injection molding machine (rM-140AJ manufactured by Meiki Co., Ltd.).
), attach a stamper with a group to the movable mold side, and stamp a stamper with a thickness of 1.2 mm and a diameter of 130 mm at a resin temperature of 300°C.
A disc-shaped optical disk substrate with a diameter of mm was molded.

The obtained substrate is loaded into a sputtering device, and first
The atmosphere was evacuated to below 10-'torr, and a Ta target was reactively sputtered using a mixed gas of Ar and 02 to form an interference layer (Jg, zaooA) made of Ta205. Next, by simultaneous binary sputtering with Ar gas using a Tb target and a FeCo target, Tb
A FeCo recording layer (thickness: 30 OA) was provided. Furthermore, T
A reflective layer having a thickness of 300 A was formed by sputtering an A.degree. C. tube on which an i-chip was placed in Ar gas.

The carrier level (C/
The N ratio) was 60.8 dB and remained unchanged even after heat treatment. There was also no change in group shape.

Example 2 Styrene-butadiene-styrene block copolymer synthesized by anionic polymerization (butadiene content: 5%)
Using a polyvinylcyclohexane-(ethylene-butene-1)-vinylcyclohexane block copolymer with a number average molecular weight of 61.000, a nuclear hydrogenation rate of 99%, and a softening point of 165°C obtained by nuclear hydrogenation of Similar to 1, substrate molding,
A recording layer was formed.

The carrier level (C/
The N ratio) was 60.5 dB and remained unchanged even after heat treatment. There was also no change in group shape.

Comparative Example 1 Injection molding was carried out in the same manner as in Example 1 using polyvinylcyclohexane, which was obtained by nuclear hydrogenation of a styrene homopolymer and had a number average molecular weight of 35,000, a nuclear hydrogenation rate of 97%, and a softening point of 156°C. I did it. As a result, since the molecular weight was low and the resin was brittle, cracks appeared in the substrate when the mold was released, and a normal substrate could not be obtained. Therefore, it was not possible to evaluate it as an optical disc.

Comparative Example 2 Using a vinylcyclohexane-styrene copolymer obtained by nuclear hydrogenation of a styrene homocopolymer, having a number average molecular weight ao, ooo, a nuclear hydrogenation rate of 82%, and a softening point of 125°C, Example 1 The substrate molding and recording layer formation were carried out in the same manner as described above.

When the obtained optical disk was subjected to heat treatment, the group shape force (changed) due to its low heat resistance.

The above results are summarized in Table 1.

As is clear from Table 1, the present invention provides an optical disk with excellent thickness z, heat resistance, and magneto-optical recording characteristics.

[Effects of the Invention] As detailed above, the optical disc of the present invention has excellent heat resistance, transparency, etc., low hygroscopicity, I birefringence, and extremely good optical characteristics. Substrate formability,
An optical disc with good productivity is provided.

Agent: Patent attorney Tsuyoshi Shigeno

Claims (1)

[Claims] (1) An optical disc characterized by having a substrate made of a polyvinylcyclohexane resin having a number average molecular weight of more than 50,000 and a softening point of 150° C. or more.