JP2962291B2 - Optical disk substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical disk substrate, and more particularly to an optical disk substrate made of a polyvinylcyclohexane-based block copolymer.

[0002]

2. Description of the Related Art Optical recording using a laser is capable of recording, storing, and reproducing information at high density, and has been actively developed in recent years. An example of such optical recording is an optical disk. Generally, an optical disc is basically composed of a transparent substrate and various recording media coated thereon.

[0003] In many cases, a transparent substrate of an optical disk is made of a colorless and transparent synthetic resin. Typical examples thereof include polycarbonate (hereinafter abbreviated as "PC") and polymethyl methacrylate (hereinafter "PMMA"). Abbreviations). These resins excel in colorless transparency and have excellent properties unique to each.However, they do not have all the requirements for optical materials, especially for optical disc substrates. have. For example, PC has a problem of birefringence caused by the aromatic ring, and also has a problem of water absorption or water permeability. On the other hand, problems in terms of heat resistance, water absorption and toughness have been pointed out in PMMA.

[0004] As described above, these resins are used while incorporating their own inherent problems. In practice, however, a recording medium coated on a transparent substrate made of these resins is further used. In this connection, a new problem described below has arisen.

On the other hand, various developments have been made on recording media in accordance with the use of optical disks. For example, a write-once type dedicated to recording and reproduction is a drilling type, and an erasable type is a recording-reproduction-erasing-re-recording type of a phase transition type utilizing a crystal transition phenomenon. And a magneto-optical type utilizing the magneto-optical effect are known. These recording medium materials include tellurium or its oxide and alloy compounds in the write-once type, and Gd.Fe / TbFe and Gd.Fe.Co/Tb in the erasable type.
-Inorganic materials such as rare earth-transition metal amorphous alloy compounds such as FeCo are mainly used, and are generally formed by forming a film on a transparent substrate by a dry processing method such as sputtering under a high vacuum. .

On the other hand, an organic dye-based material soluble in an organic solvent has been studied as a recording medium, and if it can be formed into a medium by a coating method, a special and expensive material such as an inorganic material is used. It is no longer necessary to use a simple device, and it is said that, in conjunction with the improvement in productivity, a great road to cost reduction in the future will be opened.

[0007]

However, PCs,
Conventional substrate resins represented by PMMA are inferior in solvent resistance, so that it is difficult to apply them to the above-mentioned coating type organic dye-based recording medium, and this has been a major obstacle to development in this direction.

An object of the present invention is to solve the above-mentioned conventional problems and to provide an optical disk substrate made of a transparent resin material applicable to not only a conventional inorganic recording medium but also a coating type organic dye-based recording medium. Aim.

[0009]

An optical disk substrate according to the present invention comprises a styrene-based block copolymer containing 60 to 99% by weight of a styrene-based polymer segment and 40 to 1% by weight of a conjugated diene-based polymer segment. It is made of a polyvinylcyclohexane-based block copolymer obtained by hydrogenating an aromatic ring, and has a birefringence of 30 nm or less.

That is, the present inventors have conducted intensive studies in order to achieve the above object, and as a result, the use of a polyvinylcyclohexane-based resin obtained by hydrogenating the aromatic ring of a specific styrene-based resin with a nucleus is extremely effective. The present inventors have found that a good optical disk substrate can be obtained, and have completed the present invention.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

The styrenic block copolymer used in the present invention comprises a styrenic monomer, that is, a polymer segment of a vinyl aromatic hydrocarbon (hereinafter abbreviated as "A segment"), and at least one or more kinds. A conjugated diene-based polymer segment mainly comprising a conjugated diene (hereinafter, abbreviated as “B segment”), and the weight ratio of A segment to B segment is 60/40 to 99/1, preferably 80 /. 20-99 / 1, more preferably 90 / 10-9
It is a block copolymer in the range of 9/1. This block copolymer preferably has a total light transmittance of 80% or more.

Examples of the styrene monomer (vinyl aromatic hydrocarbon) in the A segment include styrene, p-methylstyrene, α-methylstyrene and the like, and styrene is particularly typical. These are 1
These can be used alone or in combination of two or more.

On the other hand, conjugated dienes constituting the B segment include 1,3-butadiene, isoprene, and 2,3-butadiene.
Dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene and the like can be mentioned, and among these, 1,3-butadiene and isoprene are particularly common.

The styrenic block copolymer according to the present invention can be prepared by a known method wherein the A segment and the B segment are so-called ripening anion polymerizations, for example, using an organolithium compound as an initiator, and a hydrocarbon such as hexane or heptane. It can be easily obtained by polymerization in a system solvent.

[0016] In such a block copolymer, the ratio of the A segment to the B segment is 60/40 to 40/40.
The range is 99/1, preferably 80/20 to 99/1, more preferably 90/10 to 99/1. If the ratio is less than 60/40, the resin obtained after hydrogenation has a low elastic modulus, is unsuitable as an optical disk substrate, and has a low softening temperature, which is insufficient in terms of heat resistance. Also,
If it exceeds 99/1, the toughness is insufficient, and the problem of cracking of the molded piece during injection molding occurs, which is not preferable.

The heat resistance of the resin is preferably 140 ° C. or higher, more preferably 150 ° C. or higher, as measured by a thermomechanical analyzer.

The polyvinylcyclohexane-based block copolymer resin of the present invention is obtained by nucleating the aromatic ring of the styrene-based block copolymer in the presence of a hydrogenation catalyst having an aromatic hydrogenation ability. Things. Examples of the hydrogenation catalyst that can be used include, for example, metals such as nickel, cobalt, ruthenium, rhodium, platinum, and palladium or oxides, salts, and complexes thereof, and activated carbon, diatomaceous earth, and those supported on a carrier such as alumina. No. Of these, Raney nickel, Raney cobalt, stabilized nickel and ruthenium, rhodium or platinum carbon or alumina supported catalysts are particularly preferred from the viewpoint of reactivity.

The nuclear hydrogenation reaction is carried out at 50 to 250 kg / cm ^2.
At a pressure of 100 to 200 ° C. as a solvent, cyclohexane, methylcyclohexane, n-octane,
It is preferable to use a saturated hydrocarbon solvent such as decalin, tetralin, naphtha or the like.

In general, the nuclear hydrogenation of a styrenic polymer is accompanied by cleavage of the polymer molecular chain as a side reaction.
In order to prevent this molecular chain scission, hydrogenation is preferably performed at a hydrogen pressure as high as possible and in a short time.

The degree of hydrogenation of the aromatic nucleus by the nuclear hydrogenation reaction is 80%.
Above, preferably 90% or more, more preferably 95% or more. If the nucleus hydrogenation ratio is less than this range, there are problems such as a decrease in heat resistance of the resin and an increase in birefringence, which is not preferable. The birefringence is 30 nm or less when molded as an optical disk substrate.

The molecular weight of the polyvinylcyclohexane-based block copolymer resin thus obtained depends on the composition, molecular weight, hydrogenation (hydrogenation) conditions, etc. of the styrene-based polymer as a raw material. In consideration of both the workability during melt molding, the number average molecular weight is desirably greater than 30,000, preferably greater than 50,000. From the viewpoint of toughness, the smaller the content of the diene-based polymer, the higher the molecular weight is required.
The upper limit of the molecular weight is defined from the viewpoint of moldability, but is usually 300,000 or less in number average molecular weight.

In order to manufacture the optical disk substrate of the present invention using such a polyvinylcyclohexane-based block copolymer, a stabilizer is mixed with the block copolymer, if necessary, followed by injection molding. In this case, the method of mixing the stabilizer is not particularly limited, but usually, the block copolymer and the stabilizer are mixed with a ribbon blender, a tumbler blender, a Henschel mixer, and the like, and thereafter, a Banbury mixer, a single screw extruder, The mixture is melt-kneaded in a twin-screw extruder or the like, and mixed by forming into a pellet shape. Then, using the pellets thus obtained, injection molding is performed at a molding temperature of 270 ° C. to 330 ° C.

The optical disk substrate of the present invention thus manufactured exhibits good characteristics as an optical disk substrate with a birefringence of 30 nm or less. The birefringence of the optical disk substrate
Use the commonly used compensator method, transmission method, etc.
(For example, see "Polymer Dictionary" Maruzen, etc.).

The optical disk substrate of the present invention can of course be adequately tested on a system using a conventional inorganic recording medium, but can be applied to a system using a coating type recording medium without any hindrance as described above. The major feature is that it can be done. As such a coating type optical recording medium, an organic dye-based compound having a laser absorbing ability, which can be dissolved in a ketone-based solvent at a high concentration, may be used.
And has an absorption coefficient of 10 ⁴
It is preferred those wherein to 10 ⁵ cm ^-1. As the ketone solvent used, acetone, methyl ethyl ketone,
Examples thereof include methyl isobutyl ketone and cyclohexanone. When using a solvent, a mixture of these solvents or a solvent such as a ketone alcohol or an ether alcohol may be used in combination as long as the solubility of the coloring compound is not impaired.

Examples of the organic dye compounds having high solubility in such ketone solvents include compounds represented by the following general formulas [I], [II], [III] and [IV].

[0027]

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[0028]

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[0029]

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[0030]

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Representative examples of the compounds represented by the general formulas [I] to [IV] include the following structural formulas [a] to [d].
Can be exemplified.

[0032]

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[0033]

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The film formation of the recording medium by coating can be performed, for example, by spin-coating such an organic dye compound as it is or dissolved in a ketone solvent together with a binder. Any binder can be used as long as it can be dissolved in a ketone solvent.

[0035]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples, Comparative Examples and Reference Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. .

Various physical properties in Examples, Comparative Examples and Reference Examples were measured by the following methods.

Number average molecular weight: gel permeation chromatography (GP
C), using tetrahydrofuran (THF) as a solvent, the same measurement as for polystyrene was performed, and the molecular weight in terms of polystyrene was determined. Nuclear hydrogenation rate (%): Polyvinylcyclohexane resin is dissolved in THF,
It was measured by V absorption. Softening point (° C.): The softening temperature was measured at a rate of 5 ° C./min using a thermomechanical analyzer manufactured by Dupont. Light transmittance (%) of optical disk substrate: Measured according to JIS K6714. Toughness: The presence or absence of cracks in the injection-molded disk was confirmed and evaluated according to the following evaluation criteria. ○ = No crack generation × = Crack generation Elastic modulus (kg / cm ² ): AST for injection molded separately under the same conditions as disk molding
It measured based on MD638. Chemical resistance: The disk was inclined at 30 degrees, 5 drops of each solvent were dropped, and the flow trace was observed after air drying at room temperature, and evaluated according to the following evaluation criteria. ＝= No flow trace × = With flow trace Birefringence: 546 by polarizing microscope Type 104 manufactured by NIKON
at a wavelength of 20 nm from the injection gate of the injection molded product.
The position birefringence was measured. Example 1 A styrene-butadiene-styrene block copolymer (butadiene content: 20% by weight) was subjected to nuclear hydrogenation to obtain a polyvinylcyclohexane-based block copolymer having a number average molecular weight of 81,000 and a nuclear hydrogenation rate of 99%. Was.

As a stabilizer for this resin, tetrakis [methylene-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate methane (“Irganox1010” manufactured by Ciba Geigy Japan) and tetrakis (2 , 4-Di-t-butylphenyl) -4,4'-biphenylenephosphonite "Irgaphos PE
PQ "was added in an amount of 0.2% by weight, and injection molding was performed at 300 ° C. to form a disc-shaped disk substrate having a thickness of 1.2 mm and a diameter of 130 mm.

Table 1 shows the physical properties of the resin and the molded substrate.

Comparative Example 1 A styrene homopolymer was subjected to nuclear hydrogenation to obtain polyvinylcyclohexane having a number average molecular weight of 50,000 and a nuclear hydrogenation rate of 99%.

This resin was injection-molded under the same conditions as in Example 1, but cracks were observed in the center of the disc-shaped substrate at a ratio of one out of ten molded substrates. Table 1 shows the physical properties of the resin and the molded substrate.

Example 2 A styrene-butadiene-styrene block copolymer (butadiene content: 5% by weight) was subjected to nuclear hydrogenation to give a polyvinylcyclohexane-based block copolymer having a number average molecular weight of 65,000 and a nuclear hydrogenation rate of 99%. A coalescence was obtained.

This resin was molded in the same manner as in Example 1. Table 1 shows the physical properties of the resin and the molded substrate.

Example 3 A styrene-butadiene-styrene block copolymer (butadiene content: 10% by weight) was subjected to nuclear hydrogenation to give a polyvinylcyclohexane-based block copolymer having a number average molecular weight of 550,000 and a nuclear hydrogenation rate of 99%. A coalescence was obtained.

This resin was molded in the same manner as in Example 1. Table 1 shows the physical properties of the resin and the molded substrate.

The ginseng Reference Example 1 styrene - butadiene - styrene block copolymer (butadiene content 35 wt%) and nuclear hydrogenated, the number-average molecular weight 85,000, nuclear water hydrogenation ratio of 99% polyvinyl cyclohexane-based block copolymer A polymer was obtained. This resin was molded in the same manner as in Example 1.

Table 1 shows the physical properties of the resin and the molded substrate. From Table 1, it is recognized that the disk substrate formed from the substrate forming material of the present invention has excellent heat resistance, mechanical properties, and optical properties, and also has good chemical resistance.

[0048]

[Table 1]

Example 5 , Comparative Examples 3 and 4 0.15 g of an organic dye compound represented by the following structural formula was dissolved in 10 g of methyl ethyl ketone, and filtered with a 0.2 μm filter to obtain a dye solution. 5 ml of this dye solution was dropped on the disk-shaped disk substrate obtained by injection molding in Example 1, and applied at a rotation speed of 800 rpm by a spinner method. After the application, the substrate was dried at 60 ° C. for 10 minutes, and the influence on the substrate after the application was examined.

[0050]

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For comparison, PC (Comparative Example 3 ), PMMA
The same examination was performed on the injection molded disk of (Comparative Example 4 ). Table 2 shows the results.

[0052]

[Table 2]

Table 2 shows that the optical disk substrate of the present invention can be applied to a coating type recording medium.

[0054]

As described in detail above, the optical disc substrate of the present invention has excellent heat resistance, excellent mechanical properties such as toughness and elastic modulus, and good chemical resistance. Therefore,
The optical disk substrate of the present invention can be effectively applied not only to an optical disk using a conventional inorganic recording medium but also to an optical disk substrate using a coating type organic dye-based medium.
Thus, its optical properties are also significantly higher.

Particularly, in the present invention, when the styrene-based block copolymer used for nuclear hydrogenation contains 80 to 99% by weight of a styrene-based polymer segment, extremely excellent effects can be obtained.

──────────────────────────────────────────────────の Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C08F 8/04 C08F 297/04 C08L 53/02

Claims (2)

(57) [Claims] 1. A styrenic polymer segment of 60 to 9
9% by weight, and a conjugated diene polymer segment of 40 to
An optical disk substrate comprising a polyvinylcyclohexane-based block copolymer obtained by hydrogenating an aromatic ring of a styrene-based block copolymer containing 1% by weight and having a birefringence of 30 nm or less. 2. The optical disk substrate according to claim 1, wherein the styrene-based block copolymer contains 80 to 99% by weight of a styrene-based polymer segment.