JPH0291107A - Highly-temperature-resistant and lowly-moisture-absorptive methacrylic copolymer - Google Patents

Abstract

PURPOSE:To lower the moisture absorption and to improve the heat resistance by polymerizing a specific 4-t-butylcyclohexyl methacrylate with methyl methacrylate and an ethylenically unsaturated compound. CONSTITUTION:A monomer mixture comprising 4-t-butylcyclohexyl methacrylate (A) wherein 85% or more of the stereoisomers is in the trans form, methyl methacrylate (B), and if desired, one or more ethylenically unsaturated compounds (C) of formula I [wherein R1 is H or CH3; R2 is (methyl-substituted) phenyl or a group of formula II wherein Z is a 1-8C (fluorine-substituted) alkyl] is polymerized in the presence of an initiator in an amount of 0.01-10wt.% of the mixture in a solvent at 0-150 deg.C for 120-150min, and the product is cured for about 1hr to obtain the title copolymer which has a weight-average molecular weight of 10<4>-10<7> and comprises 2-30mol% component (A), 60-98mol% component (B) and 0-30mol% component (C).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a novel methacrylic copolymer with high heat resistance and low moisture absorption. More specifically, the present invention provides specific ranges of stereoisomeric ratios of 4-tart-butylcyclohexyl methacrylate units and methyl methacrylate units, and optionally specific ethylenically unsaturated units copolymerizable with these monomer units. and compound units in a specific ratio, and has colorlessness, transparency, moldability, low birefringence, thermal stability, and low hygroscopicity, and also has excellent heat resistance. The present invention also relates to a highly heat-resistant, low-hygroscopic methacrylic copolymer suitable as a material for molded products such as light-transmitting extruded plates.

The optical element substrate as used in the present invention means a body substrate of an optical element. Moreover, the optical element here is a general term for instruments that utilize optical properties such as transmission, refraction, and reflection of light rays.

Specific examples of optical elements include optical information recording disks (hereinafter referred to as optical disks), optical information recording cards, optical information recording sheets, optical information recording films, lenses, mirrors, prisms, etc. can be mentioned. Light-transmitting extruded plates include, for example, signboards, displays, partitions, lighting windows, television front plates, liquid crystal display front plates, and the like.

[Conventional technology]

Conventionally, methyl methacrylate resin is an optically superior resin with excellent transparency and low birefringence, so it has been used in materials such as optical element substrates such as optical disk substrates, or transparent plates that allow light to pass through. It is widely used as a material for products that perform functions by doing so.

However, this methyl methacrylate resin has a high hygroscopicity, and absorption of moisture causes dimensional changes, warping, and deformation.Also, it does not have very good heat resistance, so it cannot be used in high-temperature environments. However, the actual situation is that its use is limited.

Currently, various types of optical discs are in practical use, such as continuous-only discs, write-once discs, and rewritable discs. The base material for these discs has the following characteristics: transparency, moldability, low birefringence, thermal stability,
Although properties such as low moisture absorption and heat resistance are required, a resin that satisfies all of these properties has not yet been found, and as a result, conventional optical discs based on resin have many limitations. The reality is that we are receiving this. For example, methyl methacrylate resin has conventionally been used as a base material for video discs, which are one type of discs that are only available for subsequent use. However, methyl methacrylate resin is highly hygroscopic, and if a base is molded using this resin, metal is vapor-deposited on one side, and a protective film is coated, the moisture absorption will cause warping and deformation, so two sheets are used. In reality, bonding prevents warping and deformation and is used in practical applications.

Compact disc (
Polycarbonate resin has conventionally been used as a base material for digital audio discs. In this compact disc, the disc base 2
Methyl methacrylate resin is used for disk substrates because the sheets are not pasted together, causing warping and deformation due to moisture absorption.Moreover, methyl methacrylate resin has low heat resistance and is likely to deform in high-temperature environments such as when left in a car in the summer. On the other hand, polycarbonate resin has poor moldability and high birefringence, but compact discs are used practically as optical discs because they are relatively small and do not require high precision. .

Therefore, an optical disc using a resin as a base material that has the characteristics of methyl methacrylate resin, such as excellent transparency, moldability, low birefringence, and thermal stability, and also has low moisture absorption and excellent heat resistance, has been developed. If obtained, it can be advantageously used as any type of disc, such as a continuous-only disc, a write-once disc, or a rewritable disc.

In order to improve the hygroscopicity of methyl methacrylate resin, a technique is known in which methyl methacrylate is copolymerized with styrene (Japanese Unexamined Patent Publication No. 57-33446, No. 57-16).
Publication No. 2135). However, increasing the content of styrene units in order to achieve the desired level of low hygroscopicity increases birefringence and loses the inherent good characteristics of methyl methacrylate resin, making it difficult for optical element substrates (e.g. The problem arose that it became unusable for the optical disk base (optical disk base),
Furthermore, copolymerizing styrene does not improve heat resistance, so it cannot be used in applications that require higher heat resistance than that of methyl methacrylate resin.

On the other hand, in order to improve the hygroscopicity of methyl methacrylate resin without increasing the birefringence too much, a technique is known in which methyl methacrylate and cyclohexyl methacrylate are copolymerized (JP-A-57-186241, 5B-
No. 127754, No. 58-154751, No. 59
-1518 Publication, 60-104110 Publication). However, if the content of cyclohexyl methacrylate units is increased in order to achieve a desired level of low moisture absorption, the heat resistance will be significantly reduced and the optical disc will become extremely brittle, causing warpage and deformation of the optical disc due to heat during handling, for example. This may make it difficult to record or read highly accurate information, or the optical disc may be damaged during handling.
This brings about an undesirable situation in which the use of the optical disc is inevitably severely restricted.

In addition, in order to improve the hygroscopicity of methyl methacrylate resin without increasing the birefringence, we also copolymerized 4-isopropylcyclohexyl acrylate and dicyclohexyl fumarate in addition to cyclohexyl methacrylate (
JP-A-57-186241), methacrylic M3,
Example of copolymerization of 3.5-trimethylcyclohexyl and isobornyl methacrylate (JP-A-6O-1()41
No. 10) is disclosed. However, in these examples, although the hygroscopicity of the methyl methacrylate resin is improved, the resulting resin has a problem of low heat deformation resistance (and poor mechanical strength and thermal stability).

Furthermore, in order to improve both the hygroscopicity and heat resistance of methyl methacrylate resin, a technique is known in which methyl methacrylate is copolymerized with isobornyl methacrylate (JP-A-59-227909, JP-A-60 -115605
Publication No.). However, when the content of isobornyl methacrylate units is increased to achieve a desired level of low moisture absorption, the optical disc becomes extremely brittle, which may cause damage to the optical disc during handling, which limits its use as an optical disc base material. There is a problem that cannot be avoided. Even if isobornyl methacrylate is copolymerized under the normal polymerization conditions for radical polymerization described in the above publication, a considerable amount of unreacted monomer remains in the resulting resin, and this monomer is removed from the resin. It is extremely difficult to remove. If unreacted monomers remain in the resin, not only the heat resistance of the resin will be significantly reduced, but also the thermal stability will be significantly reduced.

Therefore, even if you try to obtain a molded product from a resin containing a large amount of residual monomer, it may become colored or foam during molding and cannot be molded, or even if it can be molded, the resulting molded product will be colored or foamed. In some cases, the heat resistance is not as good as expected, so there are limitations in its use. Moreover, resins obtained by copolymerizing isobornyl methacrylate originally have low thermal stability. 28 is used to obtain high pit reproducibility in injection molding on optical disk substrates.
When performing melt molding at a high temperature such as 0° C., significant coloring and decomposition and foaming occur simultaneously, making it difficult to obtain a good molded product.

Furthermore, in order to simultaneously improve the hygroscopicity and heat resistance of methyl methacrylate resin, an example has been disclosed in which bornyl methacrylate, 3,5-dimethyladamantyl methacrylate, and fentyl methacrylate were copolymerized (Japanese Patent Application Laid-open No. 59-
227909).

However, although this example improves the hygroscopicity of the methyl methacrylate resin, the resulting resin has low mechanical strength and poor thermal stability, resulting in melting at high temperatures such as 280°C. When molding, there are problems with significant discoloration and decomposition and foaming.

[Problem to be solved by the invention]

The present invention solves the above problems, has colorlessness, transparency, moldability, thermal stability, exhibits excellent low moisture absorption while maintaining sufficient mechanical strength, and has further excellent heat resistance. have,
Therefore, the present invention provides a methacrylic copolymer with high heat resistance and low moisture absorption, which is suitable as a material for molded products such as optical element substrates and light-transmitting extruded plates.

In order to achieve this objective, there is a report on a resin obtained by copolymerizing methyl methacrylate and at least tert-butylcyclohexyl methacrylate. (
JP-A-63-017915, JP-A-63-017401
) As a result of further extensive research into the above copolymers, the present inventors have discovered a new copolymer that can fully achieve the above objectives.

Tert-butylcyclohexyl methacrylate has three types of isomers depending on the position of the tert-butyl group bonded to the cyclohexane ring, and each of these has cis and trans forms. Among these isomers,
Methacrylic acid-4 with a cis-trans ratio within a specific range
- In the copolymer consisting of tert-butylcyclohexyl, the excellent transparency and moldability inherent to methacrylic resin,
The present inventors have discovered that while maintaining mechanical strength and low birefringence, the water absorption rate (medium water absorption rate) can be lowered and the heat resistance can be greatly improved, and the present invention has been completed.

[Means to solve the problem]

That is, according to the present invention, (A) methacrylic acid-4-tert- in which 85% or more of the stereoisomers are trans isomers;
2 to 30 mol% of butylcyclohexyl units, (B) 60 to 98 mol% of methyl methacrylate units, (C) formula (1) [wherein, R8 is a hydrogen atom or a methyl group, R2 is a phenyl group, a methyl-substituted phenyl group or COZ (Z is carbon number 1
~8 unsubstituted or fluorine atom-substituted alkyl groups)], consisting of 0 to 30 mol% of at least one ethylenically unsaturated compound unit represented by (A) + (B
)+(C)=100 mol%,
A highly heat resistant, low hygroscopic methacrylic copolymer is also provided, which is characterized in that the weight average molecular weight of the copolymer is in the range of 104,107.

In the methacrylic copolymer of the present invention, the content of 4-tert-butylcyclohexyl methacrylate units in which the trans isomer is 85% or more of the stereoisomer that is component (A) is (A) and (B). and 2 to 39 mo1% based on the total molar amount of component (C), and if the amount of component (A) is less than the above range, the low hygroscopicity and high heat resistance that are the characteristics of the present invention will not be fully exhibited. . If it exceeds the above range, the hygroscopicity and heat resistance will improve, but mechanical strength will decrease, which is not preferable. The preferred content of component (A) is 5
~20mo1%.

In addition, the ratio of cis to trans in component (A) is 85% or more in the trans form. When the ratio of trans isomer is less than 85%, the effect of improving heat resistance is small. In addition, 4-tert-butylcyclohexyl methacrylate monomer with a high trans-isomer content can be obtained by crystallization from a cis-trans mixture, rectification,
It was obtained through a separation process such as

The content of methyl methacrylate units as component (B) is 60 to 98 mo1% based on the total molar amount of components (A), (B), and (C). If it is less than this range, the original excellent properties of methyl methacrylate, such as transparency, moldability, and low birefringence, will deteriorate, and if it exceeds this range, the low hygroscopicity and heat resistance intended by the present invention will be impaired. This is not enough and is not desirable.

The preferred content of component (B) is 70 to 940101%.

The copolymer according to the present invention may contain, as component (C), an ethylenically unsaturated compound unit copolymerizable with component (A) and component (B), if desired. Such an ethylenically unsaturated compound monomer has the formula (1) [wherein, R is a hydrogen atom or a methyl group, R2 is a phenyl group, a methyl-substituted phenyl group, or C0Z (Z has 1 to 1 carbon atoms)]
8) represents an unsubstituted or fluorine atom-substituted alkyl group. Examples of such monomers include acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate; trifluoromethyl acrylate, acrylic acid 1.1. 1-)
Examples include acrylic acid fluorinated alkyl esters such as lifluoroethyl; and aromatic vinyl compounds such as styrene, α-methylstyrene, and p-methylstyrene.

By containing an ethylenically unsaturated compound unit as component (C), thermal stability, fluidity during molding, or hygroscopicity can be improved, but excessive use may lead to a decrease in heat resistance. So I don't like it. The content of component (C) is 0 to 30 mo1%, preferably 2 to 20 mo1%, based on the total molar amount of components (A), (B), and (C).
It is 1%.

The copolymer of the present invention can be produced by commonly used polymerization methods such as cast polymerization, bulk polymerization, suspension polymerization, solution polymerization, and emulsion polymerization.

When carrying out solution polymerization, a monomer consisting of 4tert-butylcyclohexyl methacrylate, methyl methacrylate, in which the trans isomer accounts for 85% or more of the stereoisomers, and optionally an ethylenically unsaturated compound of formula (1). A solution prepared by dissolving the mixture in an aromatic hydrocarbon solvent such as toluene or ethylbenzene can be used. When polymerizing by suspension polymerization or emulsion polymerization, water can be used as a medium. When polymerizing by bulk polymerization, the polymerization can be initiated by free radicals generated by ordinary heating or by irradiation with radiation. The quantitative ratio of each component of the monomer mixture is substantially the same as the quantitative ratio of the monomer units of components (A), (B), and (C) of the target copolymer. Can be used.

Initiators used when polymerizing the resin of the present invention include:
Any initiator commonly used in radical polymerization can be used, for example azo compounds such as azobisisobutyronitrile, benzoyl peroxide, lauroyl peroxide, tert-butylperoxy-
Particularly preferred are organic peroxides such as 2-ethylhexanoate. The amount used generally ranges from 0.01 to 10% by weight of the total monomer amount. As the molecular weight regulator used as necessary when polymerizing the resin of the present invention, any molecular weight regulator generally used in radical polymerization can be used, such as butyl mercaptan, octyl mercaptan, dodecyl mercaptan,
Particularly preferred are mercaptan compounds such as 2-ethylhexyl thioglycolate.

The temperature at which the copolymer of the present invention is polymerized is not particularly limited, but is usually 0 to 150°C, preferably 50 to 150°C.
Selected within the range of 20°C. The optimum polymerization temperature is determined in consideration of the polymerization method, polymerization equipment, polymerization initiator, molecular weight regulator, characteristics of the resulting copolymer resin, etc. Polymerization is about 120
After curing for ~150 minutes, the copolymer of the present invention can be obtained by further curing for about 1 hour.

The weight average molecular weight of the copolymer according to the present invention is 104 to 10
The range is 7. When obtaining a molded product such as a light-transmitting plate by direct polymerization such as a casting method, it is 10' to 10
A relatively high weight average molecular weight of 7.7 can be obtained. When the target is an injection molded product such as an optical disk substrate, the range is usually 1X10' to 2X10', preferably 5X10' to 1.5X10', and more preferably 5X10' to 1X10'. In this case, if the weight average molecular weight is less than 104, the mechanical strength will decrease and 2X10
If it exceeds ', the mold transfer accuracy during molding will decrease. In addition, when dealing with extruded products such as transparent extruded plates,
The weight average molecular weight is in the range of 1 x 10' to 3 x 10', and the more preferable range is 1.5 x 10' to 2.5 x 10'.
It is. In this case, if the weight average molecular weight is less than 1 x 10S, sufficient mechanical strength and dimensional stability cannot be obtained;
If it exceeds S, it will not be possible to extrude under normal extrusion molding conditions, and thermal decomposition and coloring will occur if extrusion is attempted at high temperatures.

The weight average molecular weight referred to herein is measured by GPC (gel permeation chromatography) using standard polystyrene as a standard sample.

methacrylic acid-4-ter constituting the copolymer of the present invention
The content of each of t-butylcyclohexyl, methyl methacrylate, or ethylenically unsaturated compound units represented by formula (1) copolymerizable with them was determined by pyrolysis gas chromatography and 13 cm NMR method (nuclear magnetic resonance method).
It can be measured by "In the C-NMR method, the copolymer is mixed with deuterated solvents CCDC1z, CbDb
, CI) INOx, DMSO (dimethyl
5ulfoxide)-d6] and conducts spectral analysis of the z-co-C-nucleus at room temperature or at high temperature for quantitative determination.

The copolymers according to the invention can be used alone, but
Polymethyl methacrylate, acronitrile-styrene copolymer, and other It can also be used in combination with other resins such as methyl methacrylate-styrene copolymer.

If the copolymer according to the present invention contains a large amount of residual monomers, the high heat stability, which is one of the characteristics of the copolymer according to the present invention, as well as high thermal stability will be impaired. The content of residual monomers is preferably 5% by weight or less, preferably 2% by weight or less, and more preferably 1% by weight or less. The copolymer of the present invention can be polymerized under the above-mentioned normal polymerization conditions to have a sufficiently low residual monomer content for practical use. In order to obtain this, it is preferable to apply a conventional residual monomer removal method. Methods for removing the residual monomer include heating the obtained copolymer under air flow, heating under reduced pressure, and vent extrusion under reduced pressure using a vented extruder.

Various properties of the resin can be improved by adding generally known additives to the copolymer resin of the present invention within a range that does not significantly impair its excellent characteristics. For example, various antioxidants, heat stabilizers, ultraviolet absorbers, metal sequestering agents, lubricants, mold release agents, plasticizers, impact resistance improvers, antistatic agents, flame retardants, preservatives, dyes, pigments, etc. can be added.

The methacrylic copolymer resin of the present invention can be used to produce various useful molded products by making use of the properties of the copolymer of the present invention by molding methods well known in the field of plastics technology.

A light-transmitting extruded plate can be obtained by subjecting the copolymer resin of the present invention to extrusion molding. That is, the copolymer resin of the present invention, which has been melted in an extruder, is taken up onto a take-up roll whose temperature is appropriately controlled to be processed into a flat plate. The temperature conditions during extrusion and withdrawal are selected depending on the characteristics of the extruded plate, its use, etc., but it is generally appropriate to carry out extrusion molding at a temperature in the range of 200 to 280°C. The light-transmitting extruded plates obtained by extrusion molding are used, for example, in signboards, display displays, partitions, daylight windows, television front panels, liquid crystal display front panels, etc., and have low moisture absorption,
It exhibits high performance due to its excellent heat resistance, transparency, thermal stability, mechanical strength, etc.

Furthermore, a light-transmitting plate made of the copolymer resin of the present invention having a high weight average molecular weight and high strength can be obtained by the casting method, and can be advantageously used in various applications.

The copolymer resin of the present invention can be molded into various optical element substrates by injection molding or compression molding.
In view of dimensional accuracy, it is preferable to use injection molding. As mentioned above, the optical element base means the body base of the optical element. Specific examples of optical elements include optical information recording disks (hereinafter referred to as optical disks), optical information recording cards, optical information recording sheets, optical information recording films, lenses, mirrors, and prisms. be able to. In addition, automobile tail lamps, meter covers, etc. can also be advantageously obtained by injection molding.

Optical discs are manufactured by injection molding the methacrylic copolymer resin of the present invention using a disc-shaped mold with minute irregularities on one side to obtain a base, and then applying a memory function film or a reflective film to the base. This can be obtained by providing a protective film. In addition to injection molding of methacrylic resin as described above, the base can also be obtained by obtaining a flat plate by cast polymerization or extrusion molding, and then compression molding this flat plate. It can also be obtained directly by cast polymerization.

Optical discs are optical information recording discs that record information using light or read information recorded using light, and include various types of discs such as continuous-only discs, write-once discs, and rewritable discs.

Furthermore, in addition to general disks that have minute irregularities on the surface of the substrate that are signals or should serve as signals, it also includes disks that have a smooth substrate surface coated with a memory layer such as metal or pigment. It also includes magneto-optical disks in which the memory layer is made of a magnetic material.

As mentioned above, the optical disk base obtained by molding the methacrylate copolymer of the present invention has excellent transparency, moldability, low birefringence, and thermal stability, which are characteristics of methyl methacrylate resin. Moreover, the hygroscopicity and heat resistance, which are disadvantages of methyl methacrylate resin, are significantly improved. When an optical disc base made of the copolymer resin of the present invention is used for a video disc base that conventionally uses methyl methacrylate resin, the resin has low hygroscopicity and high heat resistance, so it can withstand high temperatures, high temperatures, etc. It can be used even under harsher conditions.

In addition, when an optical disc base made of the copolymer resin of the present invention is used for a compact disc base that conventionally uses polycarbonate resin, the birefringence of the resin is small (
Since it has good moldability, it is easy to obtain discs with higher precision.

Further, the optical disk substrate of the present invention is preferably used for optical disks that are larger than compact disks and have a large amount of recorded information and are composed of a single substrate similar to compact disks, which has been difficult to put into practical use in the past.

Furthermore, the characteristics required for the foundation of write-once disks and rewritable disks, including magneto-optical disks, which require higher precision than video disks and compact disks, have a large amount of information, and are used under harsh conditions. Although an optical disk substrate that satisfactorily satisfies all of the above requirements has not been obtained in the past, the optical disk substrate made of the copolymer resin of the present invention can be preferably used for this purpose as well.

〔Example〕

EXAMPLES In order to describe the present invention in more detail, Examples will be described, but the scope of the present invention is not limited to these Examples.

Each physical property in the examples was measured by the following method.

(1) A sample was dissolved in acetone containing residual monomer n-butyl alcohol as an internal standard substance, and quantified by temperature-rising gas chromatography.

(2) Composition of components in copolymer ■ Nuclear magnetic resonance absorption (NMR) method Spectral analysis of IIC nuclei at specific sites in each component of the copolymer was conducted to determine the composition ratio. The measurement conditions were as follows: The sample copolymer was dissolved in DMSO-d, and the analysis was conducted in quantitative mode at a temperature of 70° C. for a total of 12,000 times.

(2) Pyrolysis gas chromatography method The polymer was thermally decomposed at a furnace temperature of 450°C, and the decomposed gas was quantified by gas chromatography to determine the composition ratio.

(3) Weight average molecular weight (MW) A sample solution was prepared 8 times by dissolving the bead-like polymer obtained by polymerization in dichloromethane (50 mg/30 ml), and then gel permeation chromat.
ography (GPC') measurements were performed. From the measurement results, the weight average molecular weight was calculated using a calibration curve obtained by measuring the molecular weight of standard polystyrene and converted to polymethyl methacrylate.

(4) Tensile breaking strength Measurements were performed based on ASTM-D638.

The test pieces were annealed at 96° C. for 2 hours and then conditioned (48 hours at 23° C. and 52% relative humidity) for measurement.

(5) Heat deflection temperature (HDT) Measurements were performed based on ASTM-D648.

The test pieces were annealed at 96° C. for 2 hours and then conditioned (48 hours at 23° C. and 52% relative humidity) for measurement.

(6) Equilibrium water absorption rate Measured at 23°C based on ASTM-D570.

(7) Total light transmittance Measured at 23°C according to ASTM-D 1003.

(8) Birefringence Birefringence of a disc with an information label on one side was measured at a 50 mm distance from the center using a polarizing microscope.

(9) Moisture absorption warpage (i) Optical disk substrate A warping test was conducted for 10 hours at a temperature of 50° C. and a relative humidity of 90%.

The warpage was measured by measuring the distance between the center of the disk base and a plane passing through at least two points on the outer periphery of the disk base for each time to determine the maximum amount of warp.

(ii) Extruded board An extruded board cut into a size of 2 x 300 x 300 mm was used as a test piece, one side of which was covered with Saran film, and the temperature was 50°C and the relative humidity was 90%.
It was left for 8 hours.

Next, the warping deformation (difference in height between the center and the midpoint of the side when the flat plate is placed on a horizontal surface) of this test piece was measured.

Example 1 51 g of water, 5 (lt) of potassium polyacrylate, and 1.5 g of sodium hydrogen phosphate were added to a glass separable flask with contents of ff1101 and stirred at a temperature of 30 to 35°C to prepare an aqueous phase. 4-tert-butylcyclohexyl methacrylate [cis form/
Trans body = 2/98 (W/W)) 171g (4mo
1%), methyl methacrylate 1796g (94mol
%) and methyl acrylate (2mol%) were added, and the total weight of these monomers was 2000g (10
3 g of azobisisobutyronitrile (0 parts by weight)
(0.15 parts by weight), n-octyl mercaptan 4
g (0.20 parts by weight) was added to prepare the monomer phase.

This monomer phase was added to the aqueous phase and suspended by stirring, and after replacing the air in the separable flask with nitrogen, polymerization was carried out by keeping the mixture at a temperature of 75° C. for 2 hours while stirring. Further, in order to complete the polymerization reaction, the temperature was raised to 95° C. and then maintained at this temperature for 1 hour. Next, the polymerization system was cooled to room temperature, and the contents were filtered, washed with water, and dried to obtain a colorless bead-like polymer.

The obtained bead-like polymer was heated at 230° C. with a vent vacuum degree of 7 using a vented twin-screw extruder with a screw diameter of 30 mmφ.
Granules (pellets) were obtained by extruding into strands at 30 mmHg or higher and cutting the strands with a cutter.

A test piece was obtained by injection molding the obtained pellet at 230°C using a 3oz screw type injection molding machine.The analysis results of the bead-like polymer and test piece obtained are shown in Table 1 and Table 1. It is shown in Table 2.

Examples 2 to 7 Polymerization, molding, and evaluation were carried out in the same manner as in Example 1, except that the types and compositions of monomers were changed as shown in Table 1. These results are shown in Tables 1 and 2.

Example 8 (Optical disk base) The pellets obtained in Example 1 were placed in a precision injection molding machine (
Molded using Meiki Seisakusho M-200/8000M),
300mmφ, thickness 1.2m with information sign on one side
Obtained the basis of m. Injection molding temperature is 290℃, injection pressure,
The injection speed was high pressure and high speed.

This substrate was fixed to a vapor deposition device, and aluminum ram vapor deposition was performed under a vacuum of 10 mmHg, and a UV coat (coated with acrylic resin and cross-linked by ultraviolet irradiation) was further coated as a protective film to create a single-sided vapor deposition substrate. The birefringence and moisture absorption warpage of this single-sided vapor-deposited substrate were measured.

The results are shown in Table 3.

Examples 9 to 14 (Optical disk substrate) Optical disk disks were prepared in the same manner as in Example 8 using the pellets obtained in Examples 2 to 7, and birefringence and hygroscopic warpage were measured. . Table 3 shows the results.

Example 15 (Extrusion plate) Polymerization was carried out in the same manner as in Example 1 except that the amount of N-octyl mercaptan added was changed to 0.16 parts by weight, and a bead-shaped polymer was obtained and further extruded. Pellets were obtained using a machine. Next, the pellets were heated to 230° C. and vented to a vacuum degree of 730 mmHg using a vented twin-screw extruder with a screw diameter of 30 mm equipped with a flat plate die.
By extruding under the above conditions and then taking the extruded resin melt onto a take-up roll heated to 120° C. or higher, a colorless and transparent extruded plate with a good appearance was obtained.

The moisture absorption warping properties of this extruded plate were measured. 4th result
Shown in the table.

Examples 16 to 21 (Extrusion plate) Polymerization was carried out in the same manner as in Example 1, except that the monomer composition and the amount of molecular weight regulator (n-octyl mercaptan) added were changed as shown in Table 4. An extruded plate was produced under the same conditions as in Example 15, and its moisture absorption warping property was measured. The results are shown in Table 4.

Comparative Example 1 As shown in Table 5, polymerization and molding were carried out in the same manner as in Example 1, except that 98 mo1% of methyl methacrylate and 2 mo1% of methyl acrylate were used as monomers, and various properties were evaluated. Ta. The results are shown in Table 6.

Comparative Examples 2 to 8 Polymerization and molding were carried out in the same manner as in Example 1, except that the monomer composition was changed as shown in Table 5, and various properties were evaluated. The results are shown in Table 6.

(The following are blank spaces) Table 2 Table 3 Table 6 Due to these excellent characteristics, the molded product can be used advantageously for various purposes, especially for optical discs (optical discs). ), optical information recording cards, optical information recording sheets, optical information recording films, lenses, mirror prisms, optical transmission fibers, etc., or as optical element substrates, signboards, displays, partitions, daylight windows, etc. It is suitable for use as a light-transmitting plate for use in front panels of televisions, front panels of liquid crystal display devices, and the like.

〔Effect of the invention〕

Claims (1)

[Scope of Claims] 1. (A) 2 to 30 mol% of 4-tert-butylcyclohexyl methacrylate units in which 85% or more of the stereoisomers are trans-isomers; (B) 60 to 98 methyl methacrylate units; Mol%, (C) Formula (1) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (1) [In the formula, R_1 is a hydrogen atom or a methyl group, R_2 is a phenyl group, a methyl-substituted phenyl group, or ▲ Numerical formula, chemical formula, There are tables, etc. ▼ (Z is the number of carbon atoms 1 to 8
at least one ethylenically unsaturated compound unit represented by
Consisting of 30 mol%, (A) + (B) + (C) = 100
% by mole, and the weight average molecular weight of the copolymer is in the range of 10^4 to 10^7.