JP2730053B2 - Substrate forming material for optical disks - Google Patents

Description

The present invention relates to a material for forming a substrate for an optical disk, and more particularly, it comprises a polyvinylcyclohexane-based block copolymer which can be suitably used as a substrate material for various types of optical disks. The present invention relates to a substrate forming material for an optical disk.

[Prior Art] Optical recording using a laser is capable of high-density information recording, storage and reproduction, 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.

In many cases, a transparent substrate of an optical disk is made of a colorless and transparent synthetic resin, and typical examples thereof include polycarbonate (hereinafter abbreviated as “PC”) and polymethyl methacrylate (hereinafter abbreviated as “PMMA”). ). Although these resins excel in colorless transparency, they also have excellent properties unique to each,
Not all of the requirements for optical materials, especially optical disk substrates, are met, and there are problems to be solved. 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 with heat resistance, water absorption and toughness have been pointed out in PMMA.

As described above, each of these resins is used with inherent problems inherent therein. However, in practice, the relationship with a recording medium coated on a transparent substrate made of these resins is further increased. , A new problem as described below has arisen.

On the other hand, a wide variety of recording media have been conventionally developed according to 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 or alloy compound in the write-once type, and Gd / Fe in the erasable type.
/ TbFe, rare earth-transition metal amorphous alloy compounds such as Gd.Fe.Co/Tb.FeCo and other inorganic materials are predominant.Generally, dry processing such as sputtering under a high vacuum is applied to a transparent substrate. It is formed by forming a film.

On the other hand, an organic dye-based material soluble in an organic solvent has also been studied as a recording medium, and if it can be formed into a medium by a coating method, a special and expensive device such as an inorganic material is used. It is said that there is no need to use it, and it will open up a great way to reduce costs in the future in conjunction with the improvement in productivity.

[Problems to be Solved by the Invention] However, conventional resins for substrates represented by PC and 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 in this direction. Was a major factor that hindered the deployment.

An object of the present invention is to solve the above-described conventional problems and to provide a transparent resin material for an optical disk substrate that can be applied not only to a conventional inorganic recording medium but also to a coating type organic dye-based recording medium. .

[Means and Actions for Solving the Problems] The substrate forming material for an optical disk of the present invention comprises a styrene block containing 60 to 99% of a styrene polymer segment and 40 to 1% by weight of a conjugated diene polymer segment. The hydrogenation rate obtained by hydrogenating the aromatic ring of the polymer is 80%.
It is characterized by comprising the above-mentioned polyvinylcyclohexane-based block copolymer.

That is, the present inventors have conducted intensive studies to achieve the above object, and as a result, according to the polyvinylcyclohexane-based resin obtained by hydrogenating the aromatic ring of a specific styrene-based resin with nucleus hydrogenation, extremely good results were obtained. The inventors have found that the present invention can be obtained, and completed the present invention.

 Hereinafter, the present invention will be described in detail.

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

As the styrene monomer (vinyl aromatic hydrocarbon) of the A segment, styrene, p-methylstyrene, α-
Methylstyrene and the like can be mentioned, and styrene is a typical example. These are one kind alone,
Alternatively, two or more kinds can be used in combination.

On the other hand, as the conjugated diene constituting the B segment,
1,3-butadiene, isoprene, 2,3-dimethyl-1,3-
Examples thereof include butadiene, 1,3-pentadiene, and 1,3-hexadiene, and among these, 1,3-butadiene and isoprene are particularly common.

The styrenic block copolymer according to the present invention, the A segment and the B segment are known methods called so-called ripening anion polymerization, for example, using an organic lithium compound as an initiator, hexane, in a hydrocarbon solvent such as heptane Can be easily obtained by polymerization.

In such a block copolymer, the ratio of the A segment to the B segment is in the range of 60/40 to 99/1, preferably 80/20 to 99/1, and more preferably 90/10 to 99/1. It is said. 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. On the other hand, 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 a resin having a softening point of 140 ° C. or higher, more preferably 150 ° C. or higher, as measured by a thermomechanical analyzer.

The polyvinylcyclohexane-based resin of the present invention is obtained by nucleating the aromatic ring of such a styrene-based block copolymer in the presence of a hydrogenation catalyst having an aromatic hydrogenation ability. 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. Among them, Raney nickel,
Raney cobalt, stabilized nickel and carbon or alumina supported catalysts of ruthenium, rhodium or platinum are preferred in terms of reactivity.

The nuclear hydrogenation reaction uses a saturated hydrocarbon solvent such as cyclohexane, methylcyclohexane, n-octane, decalin, tetralin, or naphtha as a solvent under a pressure of 50 to 250 kg / cm ² and a temperature of 100 to 200 ° C. It is preferable to carry out.

Incidentally, usually, in the nuclear hydrogenation of the styrene polymer,
As a side reaction, the molecular chain of the polymer is cut. 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% or more, preferably 90% or more, and more preferably 95% or more. If the nuclear hydrogen rate 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 preferably 30 nm or less when molded as an optical disk substrate.

The molecular weight of the polyvinylcyclohexane-based resin obtained in this way depends on the composition of the styrene-based polymer as a raw material,
Although it depends on the molecular weight, hydrogenation (hydrogenation) conditions, etc., in consideration of both mechanical properties and workability during melt molding, it is desirable that the number average molecular weight is greater than 30,000, preferably greater than 50,000. . Further, 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 determined from the viewpoint of moldability, but is usually 300,000 or less in number average molecular weight.

In order to manufacture an optical disk substrate using the substrate forming material of the present invention composed of such a polyvinylcyclohexane-based block copolymer, a stabilizer is optionally added to the block copolymer, 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 made of the substrate-forming material of the present invention manufactured in this manner can of course be sufficiently tested in a system using a conventional inorganic recording medium, but a system using a coating type recording medium as described above. The main feature is that the method can be applied without any trouble. Examples of such a coating type optical recording medium include an organic dye compound having a laser absorbing ability, which is dissolved in a ketone solvent at a high concentration, has an absorption in a wavelength band of 600 to 900 nm, and has a molecular extinction coefficient. Those having a density of 10 ⁴ to 10 ⁵ cm ^-1 are preferable. Examples of the ketone solvent used include acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. When using a solvent, a mixture of these solvents or a solvent such as ketone alcohol or ether alcohol may be used in combination as long as the solubility of the dye compound is not impaired.

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

General formula [I] (Wherein, rings A ¹ and B ¹ represent a benzene ring or a naphthalene ring which may have a substituent, -R ¹ and -R ² represent a C _{1 to} C ₃ alkyl group or alkenyl group, n represents an integer of 0 to 4, and X ⁻ represents an anion.) General formula [II] (Where A ² and B ² are Or 0, and R ³ , R ⁴ , R ⁵ , and R ⁶ represent a hydrogen atom, an alkyl group, an alkoxy group, an alkoxyalkoxy group, a halomethyl group, or a halogen atom, and R ⁷ and R ⁸ represent a hydrogen atom or a halogen atom. Show. ) General formula [III] (Wherein, one of R ⁹ and R ¹⁰ is —O (C ₂ H ₄ O) _p R
¹¹ (provided that R ¹¹ represents an optionally branched alkyl group,
p represents the number of 1-6, respectively. ), The other is a hydrogen atom, and A ³ is VO, Cu, Ni or Co. ) General formula [IV] (Wherein M represents a metal atom; rings A ⁴ and B ³ may have a substituent; K represents a residue of a substituted or unsubstituted aromatic amine; Z ⁻ represents an anion; The compounds represented by the general formulas [I] to [IV] or those represented by the following structural formulas [A] to [D] can be exemplified.

The film formation of the recording medium by coating can be performed by, for example, 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.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples, Comparative Examples, and Reference Examples. However, the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded.

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

Number average molecular weight: gel permeation chromatography (GP
According to C), the same measurement as in polystyrene was performed using tetrahydrofuran (THF) as a solvent, and the molecular weight in terms of polystyrene was determined.

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

Softening point (° C): Using a Dupont thermomechanical analyzer,
The softening temperature was measured at a heating rate of 5 ° C./min.

Light transmittance (%) of optical disk substrate: Measured in accordance with JIS K 6714.

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 ): ASTM for injection piece separately molded under the same conditions as disk molding
-Measured according to D638.

Chemical resistance: The disc was tilted 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 Example 1 Styrene-butadiene-styrene block copolymer (butadiene content: 20% by weight) was subjected to nucleus hydrogenation to give a polyvinyl number average molecular weight of 81,000 and a nucleus hydrogenation rate of 99%. A cyclohexane block copolymer was obtained.

As a stabilizer for this resin, tetrakis [methylene-3]
-(3,5-di-t-butyl-4-hydroxyphenyl)
Propionate methane (Irgano manufactured by Ciba-Geigy Japan)
x1010 ") and tetrakis (2,4-di-t-butylphenyl) -4,4'-biphenylenephosphonite" Irgap
"hos P-EPQ" 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 give a number average molecular weight of 50,000.
Polyvinylcyclohexane having a nucleus hydrogenation ratio of 99% was obtained.

This resin was injection-molded under the same conditions as in Example 1, but cracks were observed at 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 obtain a polyvinylcyclohexane-based block copolymer having a number average molecular weight of 65,000 and a nuclear hydrogenation rate of 99%.

 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 obtain a polyvinylcyclohexane-based block copolymer having a number average molecular weight of 55,000 and a nuclear hydrogenation rate of 99%.

 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.

Reference Example 1 A styrene-butadiene-styrene block copolymer (butadiene content 35% by weight) was subjected to nuclear hydrogenation to obtain a polyvinylcyclohexane-based block copolymer having a number average molecular weight of 85,000 and a nuclear hydrogenation rate of 99%. 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.

Table 1 shows 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.

Example 4, Comparative Examples 2 and 3 0.15 g of an organic dye compound represented by the following structural formula was dissolved in 10 g of methyl ethyl ketone, and the solution was filtered through 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 application, at 60 ° C
After drying for 10 minutes, the effect on the substrate after application was examined.

For comparison, the same examination was performed on injection molded disks of PC (Comparative Example 2) and PMMA (Comparative Example 3).

 The results are shown in Table 2.

From Table 2, it is recognized that the substrate forming material of the present invention can be applied to a coating type recording medium.

[Effects of the Invention] As described above in detail, the optical disk substrate forming material of the present invention has extremely excellent heat resistance, excellent mechanical properties such as toughness and elastic modulus, and excellent chemical resistance. Therefore, the substrate forming material 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 type medium. Thus, its optical properties are also significantly higher.

In particular, in the present invention, the styrene-based block copolymer used for the hydrogenation, the styrene-based polymer segment 80-99.
In the case of containing by weight, an extremely excellent effect can be obtained.

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Claims (2)

(57) [Claims] 1. A styrene polymer segment comprising 60 to 99% by weight, and a conjugated diene polymer segment comprising 40 to 1% by weight.
A substrate forming material for an optical disk comprising a polyvinylcyclohexane-based block copolymer having a degree of hydrogenation of 80% or more, obtained by hydrogenating an aromatic ring of a styrene-based block copolymer containing the same. 2. The optical disk substrate-forming material according to claim 1, wherein the styrene-based block copolymer contains 80 to 99% of a styrene-based polymer segment.