JP2002082202A - Optical resin material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical resin material having improved birefringent performance while retaining transparency, rigidity (high elastic modulus) and low water absorbing property as superior features of a hydrogenated styrene resin material. SOLUTION: The optical resin material comprises a partially hydrogenated styrene polymer and has the following characteristics (a)-(f);(a) the content of styrene bond units and hydrogenated styrene bond units in the partially hydrogenated styrene polymer is >=80 wt.%, (b) the proportion of completely hydrogenated aromatic rings contained in the partially hydrogenated styrene polymer is 85-96 mol%, that of unhydrogenated aromatic rings is 15-4 mol% and that of partially hydrogenated aromatic rings is 4-0 mol%, (c) >=85% total light transmittance, (d) >=100 deg.C glass transition temperature, (e) >=15,000 kg/cm2 elastic modulus and (f) <0.1 wt.% water absorption. The birefringence of a molded article is made substantially zero while retaining performances such as transparency, rigidity (high elastic modulus) and low water absorbing property.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical resin material having excellent optical properties such as birefringence and light transmittance, and also having excellent heat resistance, rigidity and low water absorption.

[0002]

2. Description of the Related Art Conventionally, glass has been widely used as a transparent optical material. However, in recent years, utilizing the excellent features of resin materials such as moldability, light weight, impact resistance, etc., optical lenses, prisms, mirrors, optical disks, optical fibers, sheets and films for liquid crystal displays, light guide plates for liquid crystal display devices, etc. Transparent resin materials have come to be used for optical components.

As typical transparent resin materials used for optics, polymethacrylic resin (hereinafter abbreviated as PMMA) and polycarbonate resin (hereinafter abbreviated as PC) are typical. However, since these resin materials have high water absorption, the surface accuracy of the optical component is easily changed as compared with glass, and there is a major drawback in that the reliability is poor. Furthermore, PMMA does not have sufficient heat resistance, and PC has large birefringence, which is an optical distortion, and has a problem in optical characteristics depending on the use.

[0004] An optical disk is an example of an optical resin material that requires particularly high optical performance. Since optical recording using a laser enables recording, storage and reproduction of high-density information, improvement and development of optical disks are being actively promoted. An optical disk is basically composed of a transparent substrate and various recording media coated thereon. For the transparent substrate of the optical disk, a colorless and transparent synthetic resin is often used. Typical examples are PC and PMMA.
These resins have excellent colorless transparency and excellent mechanical performance as a resin material, and are widely used as substrates of optical disks.

However, PC has a problem of high birefringence or a decrease in light transmittance in a short wavelength region due to its aromatic ring, and also has a problem in water absorption or water permeability.
On the other hand, PMMA has problems in heat resistance, water absorption or water permeability, and impact resistance. The water absorption and water permeability of PC and PMMA indicate that the substrate absorbs moisture in the environment (moisture absorption).
And cause warpage by expansion. In addition, the permeation of moisture through the substrate causes corrosion of the recording medium and shortens the life of the optical disk.

In the current state of the art for optical disks, a PC having large birefringence is formed by suppressing the birefringence by devising molding conditions. Specifically, an injection compression molding method is generally used, and the birefringence and the molding distortion are suppressed by performing molding by increasing the mold temperature and the resin temperature to near limits. The optical disk obtained in this way is widely used for CDs (compact disks) having a relatively moderate birefringence limit, DVDs (digital versatile disks) with low recording density, and MOs (magneto-optical disks). .

However, the recent increase in the density of recorded information is accompanied by the use of shorter wavelength lasers and higher NA (numerical aperture) of optical lens systems. In particular, in DVDs, the use of laser light having a short wavelength of about 350 to 410 nm and an NA value of 0.6 or more has been studied, and limitations have been pointed out on the birefringence of PC and light transmittance in a short wavelength range. Further, there is a problem that the high density of recording is more susceptible to the influence of the deformation process of the disk due to moisture absorption and the tilt due to warpage, during the cooling process after high-temperature molding.

[0008] Several measures have already been proposed for the demand for solving the problems with these optical materials. PMM
Investigations include those with an alicyclic hydrocarbon group introduced into the side chain to improve the heat resistance and water absorption of A, and those with a phenyl or fluorenyl group introduced into the side chain to reduce the birefringence of PC. It has been. Further, blends of polymers having different birefringence directions, for example, a polymer alloy of PC and a styrene-based resin, a PC grafted with a styrene-based polymer, and the like have been studied. However, none of them have been widely used yet.

On the other hand, as a relatively new resin material used for optics, amorphous cycloolefin resin (hereinafter referred to as C)
Abbreviated as OP. ) Has been developed. These are PC,
Unlike improvements of conventional polymers such as PMMA, it has short wavelength light transparency, low birefringence, low water absorption and heat resistance. However, although COP has low birefringence, further improvement in birefringence performance is required depending on the required level or molding conditions. In COP, a transition metal catalyst is used as a polymerization catalyst, but the remaining transition metal causes coloring and a decrease in light transmittance. Therefore, in order to use it as an optical material, it is necessary to demine the transition metal after synthesizing the polymer. This demineralization step causes an increase in COP production cost, and improvement in this point is also required.

Further, there is a styrene-based polymer as a technique closest to the present invention. Styrene-based polymers have the characteristics that they can be obtained at low cost, have excellent light transmittance, and have almost no water absorption. In addition, a styrene-based polymer obtained by a radical polymerization is also characterized in that a metal catalyst that requires a deashing step is not used. However, the styrene-based polymer has a fatal defect that it has large birefringence and is inferior in heat resistance and weather resistance and is easily colored, so that its use as an optical material itself is limited.

On the other hand, a polymer obtained by hydrogenating an aromatic ring of a styrene polymer, that is, a polyvinylcyclohexane resin is
It has the same excellent optical characteristics as OP. This kind of polyvinylcyclohexane resin (having the same structure as a hydrogenated styrene resin) has been known for a long time. For example,
No. 11425 relates to a polymer composition (blend) of polyvinylcyclohexane. The specification states that a homopolymer of vinylcyclohexane is already known at the time of filing and is a transparent hard resin. The fact that the birefringence is small can be easily understood from the chemical structural formula and the Lorentz-Lorentz relational formula.

[0012] In recent years, proposals have been made to limit the use of vinylcyclohexane resins by utilizing their optical performance such as transparency and low birefringence. For example, JP-A-63-43
No. 910 relates to an optical disk material, and discloses the use of a vinylcyclohexane-based polymer for an optical disk substrate. Japanese Patent Application Laid-Open No. 01-132603 relates to an optical material, and discloses the use of a hydrogenated vinyl aromatic hydrocarbon polymer as an optical material. The claim states that the hydrogenation rate of the vinyl aromatic hydrocarbon polymer is 3
It is limited to 0% or more, and according to the description in the specification, it is generally preferable that the hydrogenation rate be higher.

[0013]

The birefringence of a molded product is determined by the properties of the material and the interaction between orientation and strain depending on molding conditions. Further, the properties inherent to the material can be evaluated by the intrinsic birefringence and photoelastic coefficient. Generally, a hydrogenated styrene resin is brittle, and a high molecular weight is required to increase the strength. A high molecular weight leaves strain stress and orientation in the molded body, and as a result, large birefringence is likely to occur. Therefore, although the hydrogenated styrene-based resin has a relatively small intrinsic birefringence, the molded article shows high birefringence depending on molding conditions, and further improvement of the intrinsic birefringence is required. That is, the problem to be solved by the present invention is to maintain transparency, rigidity (high elastic modulus) and low water absorption, which are the excellent features of the hydrogenated styrene resin material,
It is intended to further improve the birefringence performance.

[0014]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies on the improvement of the birefringence performance of a hydrogenated styrene resin material, and have achieved the present invention. That is, the optical resin material composed of a partially hydrogenated styrene polymer having a specific structure has extremely excellent birefringence while maintaining its excellent short-wavelength light transmittance, mechanical performance and low water absorption. The inventors have found what can be achieved, and have accomplished the present invention.

In order to facilitate understanding of the present invention, the birefringence performance of the optical resin material of the present invention will be described with reference to specific examples. However, it is to be understood that the scope of the present invention is set forth in the appended claims and is not limited to the following description. It is well known that styrene polymers have large negative values of intrinsic birefringence. This is a major reason why the molded article exhibits birefringence. On the other hand, it was known that the birefringence due to the orientation of the hydrogenated styrene polymer was relatively small, but the quantitative value of intrinsic birefringence, including positive and negative, was not known at all. Conventionally, it has been considered that the higher the hydrogenation rate, the better the performance as an optical resin material.

However, as a result of intensive studies of the present invention, it has been found that a partially hydrogenated styrene resin having a specific structure does not substantially exhibit orientation birefringence. This means that molding conditions, that is, mold temperature conditions, injection conditions, and the like are not limited to lower the birefringence of the molded body, and the practical effect is extremely large. As a result of diligent studies on this reason as well, it has been found that the birefringence of the hydrogenated styrene polymer has a positive value, and that the birefringence becomes substantially zero by canceling out plus and minus under a specific hydrogenation rate condition. .

That is, the present invention is as set forth in the appended claims. A partially hydrogenated styrene polymer obtained by partially hydrogenating an aromatic ring of a styrene monomer obtained by polymerizing or copolymerizing a styrene monomer and a monomer copolymerizable with the styrene monomer, Optical resin materials having the characteristics of a) to (f): (a) the content of a styrene bond unit and a hydrogenated styrene bond unit in a partially hydrogenated styrene-based polymer is 80% by weight or more, and (b) a partially hydrogenated styrene The ratio of the hydrogenation rate of the aromatic ring contained in the system polymer is in the following range, a fully hydrogenated aromatic ring 85 to 96 mol%, an unhydrogenated aromatic ring 15 to 4 mol%, a partially hydrogenated aromatic ring 4 to 0 (C) Total light transmittance is 85% or more, (d) glass transition temperature is 100 ° C. or more, (e) elastic modulus is 15000 kg / cm ² or more (f) water absorption is less than 0.1 wt%

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. The partially hydrogenated styrene-based polymer used in the optical resin material of the present invention must contain at least 80% by weight of a styrene bond unit and its hydrogen bond unit. It is preferably at least 90% by weight, more preferably at least 95% by weight. Unless the styrene bonding unit and its hydrogenated bonding unit are contained in an amount of 80% by weight or more, it is not possible to sufficiently exhibit optical characteristics such as transparency and low birefringence based on the hydrogenated aromatic ring or mechanical performance as a resin material. A styrene-bonded unit and its hydrogenated-bonded unit having 100% by weight, that is, a partially hydrogenated styrene polymer is a preferred example.

The copolymerizable monomer in the styrenic polymer of the present invention varies depending on the polymerization method. Generally, monomers such as vinyl aromatic monomers other than styrene, conjugated diene monomers, methacrylates, acrylates and the like can be mentioned. Examples of the vinyl aromatic monomer include α-methylstyrene, 4-methylstyrene, 2-methylstyrene, p-tertbutylstyrene, 4-phenylstyrene, p-methoxystyrene, vinylnaphthalene and the like.

Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene and 1,3-cyclohexadiene. And the like. Examples of methacrylates include methyl methacrylate, ethyl methacrylate, propyl methacrylate,
Alkyl acrylates such as butyl methacrylate and 2-ethylhexyl methacrylate, cyclohexyl methacrylate, methylcyclohexyl methacrylate, t-butylcyclohexyl methacrylate, bornyl methacrylate, isobornyl methacrylate, methacrylic acid Cycloalkyl methacrylates such as adamantyl, phenyl methacrylate, benzyl methacrylate, aromatic esters of methacrylate such as naphthyl methacrylate, fluorobenzyl methacrylate,
Methacrylic acid-substituted aromatic esters such as chlorophenyl methacrylate and bromobenzyl methacrylate; halogenated alkyl methacrylates such as fluoromethyl methacrylate, fluoroethyl methacrylate, chloroethyl methacrylate, and bromoethyl methacrylate And hydroxyalkyl methacrylate, glycidyl methacrylate, aminoalkyl methacrylate, cyanoalkyl methacrylate and the like.

Examples of the acrylate include alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate and 2-ethylhexyl acrylate, cyclohexyl acrylate, methylcyclohexyl acrylate, t-acrylate. −
Butylcyclohexyl, bornyl acrylate, isobornyl acrylate, cycloalkyl acrylate such as adamantyl acrylate, phenyl acrylate, benzyl acrylate, aromatic acrylate such as naphthyl acrylate, fluorobenzyl acrylate, chlorophenyl acrylate, Acrylic acid-substituted aromatic esters such as bromobenzyl acrylate, fluoromethyl acrylate, fluoroethyl acrylate, chloroethyl acrylate, alkyl acrylate halides such as bromoethyl acrylate, hydroxyalkyl acrylate, glycidyl acrylate, acrylic Acid aminoalkyl esters and cyanoalkyl acrylates.

The method for polymerizing the styrenic polymer is not particularly limited. Radical polymerization or thermal radical polymerization using a radical initiator, or polymerization using a known anionic polymerization catalyst, cationic polymerization catalyst, Ziegler catalyst, or Kaminsky catalyst can be used. The most preferred polymerization method is a radical polymerization method using no metal catalyst. The use of a metal catalyst is generally not preferable because an optical resin material generally requires a deashing step for removing a metal, which increases the production cost.

Usually, the polymerization of the monomer is carried out without a solvent or using a solvent. The polymerization solvent that can be used varies depending on the polymerization method, but in general, benzene, toluene, aromatic solvents such as xylene, pentane, hexane, heptane, octane, cyclopentane, cyclohexane, and aliphatic solvents such as methylcyclohexane, Halogenated hydrocarbon solvents such as methyl chloride, methylene chloride, 1,2-dichloroethane, 1,1,1-trichloroethane and 1,1,2-trichloroethylene can be used.

The polymerization temperature is generally -100 to 200.
C, more generally in the range of 0 to 150C. The pressure at the time of polymerization is generally not lower than the lower limit pressure at which the system can be kept in a liquid phase. The styrene-based polymer is converted into a partially hydrogenated styrene-based polymer by hydrogenation after polymerization. It is necessary to perform partial hydrogenation at a controlled rate by hydrogenation in the presence of a hydrogenation catalyst having the ability to hydrogenate aromatic rings. The hydrogenation catalyst used is not particularly limited. For example, nickel, cobalt, ruthenium, rhodium, platinum, metals such as palladium, or oxides, salts, complexes thereof and activated carbon, diatomaceous earth,
Those supported on alumina, silica and the like can be mentioned. Among these, catalysts supported on carbon, alumina and silica of platinum group metals such as rhodium, ruthenium and platinum are preferred in terms of catalytic activity and removal of the catalyst after hydrogenation.

The hydrogenation reaction is generally carried out at normal pressure to 250 kg.
/ Cm ² , at a temperature of 50 to 200 ° C., as a solvent, a saturated hydrocarbon solvent such as cyclohexane, methylcyclohexane, n-octane, decalin, naphtha, or TH
This is performed using an ether solvent such as F. When a hydrogenation reaction is performed, the reactivity can be increased by adding a small amount of an alcohol or an ether compound. The amount of the alcohol or ether used for such purpose is 0.5 to 5 parts by weight, preferably 1 to 3 parts by weight, based on 100 parts by weight of the solvent.

The hydrogenation rate of the styrenic polymer is birefringence performance,
In particular, the intrinsic birefringence is determined. Since it is extremely difficult to measure the intrinsic birefringence, it was calculated here by calculation. It has been known that the intrinsic birefringence of a polymer material is represented by the Lorentz-Lorentz equation. From the formula, the intrinsic birefringence of the polymer substance is determined by the direction of the dielectric polarizability of the molecule. Δn ⁰ = 2 / 9π × (n ² +2) ² / n × ΔP · d · N /
M where Δn ⁰ = intrinsic birefringence ΔP = dielectric polarizability difference (ΔP = P ₁ −P ₂ ) P ₁ = dielectric polarizability in the molecular chain axis direction P ₂ = dielectric polarizability in the direction perpendicular to the molecular chain axis n = Refractive index d = Density N = Avogadro number M = Molecular weight The directionality of the dielectric polarizability mentioned here, that is, the dielectric polarization tensor, can be calculated by the molecular orbital method as one method in recent years. For example, MOPAC97 (WinMOPACV
2.0, transplanter: Fujitsu's AM1 method or PM3 method.

As a result of calculation by the AM1 method, the difference in dielectric polarizability of the styrene bond unit in the polymer = −31 AU,
A difference in dielectric polarizability of the hydrogenated styrene bond unit = + 4.5 AU was obtained. The intrinsic birefringence of the polymer corresponding to each binding unit is calculated to be -0.11 and +0.013, respectively. Although there are some prerequisites for the partially hydrogenated styrene resin, it can be determined that its intrinsic birefringence is approximately the volume average of the above-mentioned bonding unit. When calculated from this, 10.6 vol% of the hydrogenated styrene polymer, that is, 9.
When 5% by weight is included, the intrinsic birefringence can be calculated to be almost zero.

It has been confirmed as experimental results that the partially hydrogenated styrene polymer exhibits an extremely low orientation birefringence when the residual amount of unhydrogenated aromatic rings is in the range of 15 to 4 mol%. The reason can be well explained by the above calculation results. The calculation results explained the birefringence performance of the resin material very well. That is, the absolute value ΔP of the dielectric polarizability difference is 30 × 10 ^−25.
When it is less than cm ³ , the orientation birefringence has a remarkably low value.

The complete hydrogenation rate of aromatic rings contained in the partially hydrogenated styrene polymer, that is, the content of cyclohexane rings is 85.
The range is from 96 to 96 mol%, preferably from 87 to 95 mol%, particularly preferably from 89 to 94 mol%. Complete hydrogenation means that the aromatic ring is hydrogenated to the cyclohexane ring. The residual ratio of the aromatic ring contained in the partially hydrogenated styrene-based polymer is in the range of 15 to 4 mol%, preferably 13 to 5 mol%, particularly preferably 11 to 6 mol%. If the residual ratio of the aromatic ring exceeds 15 mol%, undesirably, the orientation birefringence due to the residual aromatic ring and the absorption in a low wavelength region increase. If the residual ratio of the aromatic ring is less than 4 mol%, the orientation birefringence and the birefringence due to the photoelastic coefficient increase, which is also not preferable.

A partially hydrogenated aromatic ring means a structure in which an aromatic ring is partially hydrogenated and one or two double bonds remain in the ring structure. The content of the partially hydrogenated aromatic ring is 4 mol% or less, preferably 2 mol% or less, more preferably 1 mol% or less,
In particular, it is preferably at most 0.5 mol%. When the amount of the partially hydrogenated aromatic ring increases, the heat resistance or weather resistance of the optical resin material decreases, which is not preferable. The bond distribution between the remaining aromatic ring and the hydrogenated aromatic ring in the partially hydrogenated styrene-based polymer chain of the optical resin material of the present invention must be uniform to such an extent that microphase separation does not occur. When the distribution of bonds in the polymer chain of the residual aromatic ring and the hydrogenated aromatic ring is a mixture containing block or unhydrogenated products, light scattering is caused by fluctuations in the microscopic refractive index in the resin material, which is preferable. Absent.
That is, it is preferably substantially random.

The weight average molecular weight of the partially hydrogenated styrene polymer of the optical resin material of the present invention is preferably 100,00.
0 to 1,000,000, more preferably 150,0
00 to 500,000, particularly preferably 200,000
４００400,000. When the weight average molecular weight of the partially hydrogenated styrene polymer is 100,000 or less, the mechanical properties such as the strength and impact resistance of the optical resin material are unpreferably reduced. If it is more than 1,000,000, the molding and workability of the optical resin material is unpreferably reduced.

The total light transmittance (the method of JIS-K-6714) of the optical resin material of the present invention must be 85% or more. Preferably at least 88%, particularly preferably 9%
0% or more. If the total light transmittance is less than 85%, sufficient performance as an optical material cannot be exhibited. Also, 350-4
The transmittance of ultraviolet light having a wavelength of 10 nm is preferably 80% or more, more preferably 85% or more, and particularly preferably 88%.
% Or more. The wavelength in this region is necessary for writing and reading with a short wavelength laser beam when used for an optical disk.

Further, glass of the optical resin material of the present invention
The transition temperature is preferably 100 ° C. or higher, more preferably
The temperature is 110 ° C or higher, particularly preferably 120 ° C or higher. Moth
The lath transition temperature is measured by a differential thermal analyzer (DSC).
When the glass transition temperature is less than 100 ° C., resistance to optical material
Thermal properties are insufficient for some applications and are not preferred. Of the present invention
The elastic modulus of the optical resin material, particularly the flexural modulus, is 15,000.
0Kg / cm ^TwoIt is preferable that it is above. Even more preferred
Or 20,000 Kg / cm^TwoAnd particularly preferably 2
3,000Kg / cm^TwoThat is all. Modulus too low
Is easily deformed and scratched by external force,
Difficult to use.

The water absorption of the optical resin material of the present invention is 0.1.
It must be less than wt%. Preferably 0.05w
It is less than t%, particularly preferably less than 0.02 wt%.
If the water absorption rate is high, deformation due to expansion and corrosion of the optical disk recording medium due to permeation of moisture are caused, which is not preferable.
It is preferable that the metal content of the optical resin material of the present invention is less than 10 ppm. It is more preferably at most 5 ppm, particularly preferably at most 1 ppm. If the metal content exceeds 10 ppm, the light transmittance is undesirably reduced. In particular, when used as an optical disk material, it causes a bit error of recorded information, which is not preferable.

The optical elasticity of the optical resin material of the present invention is 30.
It is preferably less than × 10 ⁻¹³ cm ² / dyne.
More preferably, less than 20 × 10 ⁻¹³ cm ² / dyne,
Particularly preferably, it is less than 15 × 10 ⁻¹³ cm ² / dyne. If the photoelastic coefficient is large, the birefringence due to the distortion of the molded article increases, which is not preferable. In the optical resin material of the present invention, a known resin additive not specified in the present invention may be added. For example, it is obvious that a known effect can be achieved by adding a stabilizer, an ultraviolet absorber, a plasticizer, and the like. The timing and method of mixing these resin additives with the optical resin material of the present invention are not particularly limited. It can be mixed in a solution stage at the time of polymerization production, or can be mixed at the time of mixing resin components or at the time of molding.

Examples of the stabilizer include a hindered phenol stabilizer, a sulfur stabilizer, a phosphorus stabilizer and the like. It is preferable to use a hindered phenol-based stabilizer and a phosphorus-based stabilizer in combination from the viewpoint of improving the heat deterioration resistance. In particular, when used for an optical disk substrate, a stabilizer that does not absorb light in the wavelength region of laser light used for writing and erasing information is preferable.

Specific examples of the hindered phenol stabilizer usable in the present invention include tetrakis [methylene-3]
-(3,5-di-t-butyl-4-hydroxyphenyl) propionate methane, 3,9-bis [1,1,-
Dimethyl-2- {β- (3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy} ethyl] 2,4,8,10-tetraoxaspro [5,5]
Undecane, 1,3,5-tris (3,5-di-t-butyl-4-hydroxybenzyl-s-triazine-2,
4,6- (1H, 3H, 5H) -trione, 1,3,5
-Trimethyl-2,4,6-tris (3,5-di-t-
Butyl-4-hydroxybenzyl) benzene and the like.

Specific examples of the phosphorus-based stabilizer include tetrakis (2,4-di-t-butylphenyl) -4,
4'-bisphenylenephosphonite, bis (2,6-
Di-butyl-4-methylphenyl) pentaerythritol-di-phosphite. The preferred amount of the stabilizer is 0.001 to 100 parts by weight of the resin component.
1 part by weight. In addition, even with a stabilizer, the optical resin material of the present invention has a certain level of stability, and depending on the composition, the stabilizer may be preferable in some cases. Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Various polymer structures and resin performances in the following Examples and Comparative Examples were measured and evaluated by the following methods. (1) Measurement of hydrogenation rate: Analysis was performed based on a proton NMR spectrum. (2) Molecular weight measurement: The molecular weight of each polymer was determined by gel permeation chromatography (GPC) using TH
The measurement was performed using F as a solvent. (3) Birefringence: The birefringence at the center of the molded body was measured with a deflection microscope. The measured resin temperature is 25 ° C. The description is an absolute value. (4) Total light transmittance: using a 3 mm thick plate, JIS K-
It was measured according to 6714.

(5) Photoelastic coefficient: A mercury lamp (wavelength = 54) was measured using a photoelasticity measuring device (RI-KEN Keiki Co., Ltd. PA-150).
6 nm) as a light source. Measurement resin temperature is 100
° C. The description is an absolute value. (6) Glass transition temperature Measured using a differential thermal analyzer (DSC). (7) Flexural modulus ASTM D790 (kg / cm
It was measured according to ² ). (8) Water absorption: A molded sheet having a thickness of 1 mm
Weight increase when immersed in water for hours (wt%)

[0041]

Example 1 In a nitrogen atmosphere, 100 parts by weight of a styrene monomer were mixed with 300 parts by weight of a cyclohexane solvent, and AIB was added.
Solution polymerization was carried out using N (azobisisobutyronitrile) as an initiator. After completion of the polymerization, the cyclohexane 30
The mixture was diluted with 0 parts by weight, and hydrogenated under pressure through a column packed with a catalyst supporting palladium on alumina while applying hydrogen pressure. After hydrogenation, the mixed alumina-supported catalyst was removed by filtration, and the polymer was dried and recovered.

As a result of analysis, it was found that the weight average molecular weight was 280,000 and the degree of hydrogenation was 94 mol%. Palladium metal residual ratio 1p
pm. The glass transition temperature was 142 ° C. The obtained polymer was heated at a mold temperature of 9 using an injection molding machine.
0mm, resin temperature 240 ° C, 120mm square, thickness 1.2
mm sheet was formed and the birefringence was measured. The total light transmittance was measured on a 3 mm thick sheet. Table 1 shows the analysis results of the polymer structure and the measurement and evaluation results of the resin performance.

[0043]

Examples 2 and 3 and Comparative Examples 1 and 2 A commercially available polystyrene resin (polystyrene G8259 A & M)
100 parts by weight of Styrene Co., Ltd.) were dissolved in 500 parts by weight of cyclohexane solvent, and then passed through a column filled with a palladium-supported alumina catalyst while applying hydrogen pressure.
Hydrogenated under pressure. The hydrogenation rate was controlled by adjusting the hydrogen pressure at this time. After hydrogenation, the mixed alumina-supported catalyst was removed by filtration, and the polymer was dried and recovered.
Table 1 shows the analysis results of each polymer structure and the measurement and evaluation results of resin performance.

[0044]

[Table 1]

[0045]

The optical resin material substantially comprising the partially hydrogenated styrenic polymer of the present invention has transparency, rigidity (high elastic modulus), and low water absorption which are excellent features of the hydrogenated styrenic polymer. By further improving the birefringence performance while maintaining the performance such as properties, the birefringence of the obtained molded article is made substantially zero.

Claims (7)

[Claims] An optical resin material comprising a partially hydrogenated styrene-based polymer and having the following characteristics (a) to (f): (A) the content of the styrene bond unit and the hydrogenated styrene bond unit in the partially hydrogenated styrene-based polymer is 80% by weight or more; (b) the ratio of the hydrogenation rate of the aromatic ring contained in the partially hydrogenated styrene-based polymer Is the following range: 85-96 mol% of completely hydrogenated aromatic rings 15-4 mol% of partially hydrogenated aromatic rings 4-0 mol% (c) Total light transmittance is 85% or more, (D) a glass transition temperature of 100 ° C. or more, (e) an elastic modulus of 15,000 kg / cm ² or more, (f) a water absorption of less than 0.1 wt% 2. The optical resin material according to claim 1, further having the following features (g) to (i): (G) The transmittance of ultraviolet light having a wavelength of 350 to 410 nm is 80.
% Or more; (h) the average main polarizability difference of the bonding units constituting the polymer is 30;
Less than × 10 ⁻²⁵ cm ³ , (i) the residual metal content is less than 10 ppm, 3. The optical resin material according to claim 1, wherein the partially hydrogenated styrene-based polymer has the following characteristics (f) and (g). (F) the distribution of bonds in the polymer chain between the residual aromatic ring and the hydrogenated aromatic ring in the partially hydrogenated styrene-based polymer is substantially random; (d) the weight average molecular weight of the partially hydrogenated styrene-based polymer is 1
In the range of 00,000-1,000,000, 4. The optical resin material according to claim 1, wherein the partially hydrogenated styrene polymer is a partially hydrogenated styrene homopolymer. 5. The non-birefringent optical resin material according to claim 1, wherein the styrene polymer is obtained by a radical polymerization method. 6. The optical resin material according to claim 1, which is obtained by using a supported catalyst of a platinum group metal for hydrogenation of the styrene-based polymer. 7. An optical disc characterized by reading recorded information with a laser beam through a cover layer made of the resin material for optical use according to claim 1 and having a thickness of 0.01 to 0.6 mm.