JPH02206609A - Low hygroscopic methacrylic copolymer of good moldability - Google Patents

Abstract

PURPOSE:To provide the title copolymer having a specified range of molecular weight, excellent in colorlessness, transparency, heat resistance, low birefringence, thermal stability, etc., made up of t-butylcyclohexyl methacrylate unit, methyl methacrylate unit, styrene unit, etc. CONSTITUTION:The objective copolymer with the weight-average molecular weight ranging from 10<4> to 10<7>, made up of (A) 2-30 (pref. 4-20) mol% of t- butylcyclohexyl methacrylate unit, (B) 60-96 (pref. 70-93)mol% of methyl methacrylate unit, (C) 2-20 (pref. 2-15) mol% of styrene unit, and (D) 0-10 (pref. 1-6)mol% of a copolymerizable ethylenic unsaturated compound unit (e.g. methyl acrylate).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a low hygroscopic methacrylic copolymer with good moldability. More specifically, the present invention provides methacrylic acid te
It contains rt-butylcyclohexyl units, methyl methacrylate units, styrene units, and, if desired, specific ethylenically unsaturated compound units copolymerizable with these monomer units in a specific ratio, and is colorless and transparent. It has excellent moldability, heat resistance, low birefringence, thermal stability, and low moisture absorption, and is therefore suitable as a material for molded products such as optical element substrates and transparent extruded plates. This invention relates to methacrylic copolymers.

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. The light-transmitting extruded plate can be used, for example, for signboards, display displays,
This includes partitions, lighting windows, television front panels, liquid crystal display front panels, etc.

[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 it is not bonded together, so it can warp or deform due to moisture absorption.It also 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 relatively small for optical discs and do not require a high degree of precision, so they cannot be put to practical use. There is.

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 the birefringence and loses the inherent good characteristics of methyl methacrylate. ), the problem arises that it becomes unusable.
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, 58-
No. 127754, No. 58-154751, No. 59-1518, No. 60-104110)
.

However, if the content of cyclohexyl methacrylate units is increased in order to achieve a desired level of low hygroscopicity, the heat resistance will be significantly lowered and the optical disc will become extremely brittle (for example, due to heat during handling, the optical disc may warp). This deformation may make it difficult to record or read highly accurate information, or the optical disc may be damaged during handling, resulting in an undesirable situation in which the use of the optical disc is severely limited.

In addition, in order to improve the hygroscopicity of methyl methacrylate resin without increasing the birefringence, we have also reported an example in which 4-isopropylcyclohexyl acrylate and dicyclohexyl fumarate were copolymerized in addition to cyclohexyl methacrylate (Unexamined Japanese Patent Publication No. Publication No. 57-186241) and methacrylic acid 3.
3.5-) Example of copolymerization of trimethylcyclohexyl and isobornyl methacrylate (JP-A-60-1041)
No. 10) is disclosed. However, in these examples, although the hygroscopicity of the methyl methacrylate resin is improved, the resulting resins have 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
However, if the content of isobornyl methacrylate units is increased in order 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, for example. There is a problem in that it is inevitably limited in its use as a disk base material.

Even if isobornyl methacrylate is copolymerized under the normal polymerization conditions of radical polymerization described in the above publication, a considerable amount of unreacted monomer remains in the resulting resin,
This is extremely difficult to remove from the resin.

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 that contains 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 bit 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.

In addition, in order to simultaneously improve the hygroscopicity and heat resistance of methyl methacrylate resin, an example has been disclosed in which bornyl methacrylate, methacrylic M3.5-dimethyladamantyl, and fenthyl methacrylate were copolymerized (JP-A-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, even at high temperatures such as 280°C. When melt-molding, there are problems with significant discoloration and decomposition and foaming.

(Problems to be Solved by the Invention) The present invention solves the above problems, has colorlessness, transparency, thermal stability, excellent heat resistance, and maintains sufficient mechanical strength. Provides a low hygroscopic methacrylic copolymer that exhibits low hygroscopicity and has excellent moldability, and therefore has good moldability and is suitable as a material for molded products such as optical element substrates and light-transmitting extruded plates. It is something to do.

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-63-17915, JP-A-63-1740
However, although this resin has sufficient low hygroscopicity, it sometimes lacks fluidity in applications requiring high mobility, and improvements have been desired.

However, if the molecular weight is simply lowered in order to improve fluidity, there is a problem in that the mechanical strength, which is one of the characteristics of this resin, decreases.

As a result of further extensive research into the above-mentioned copolymers, the present inventors have discovered a new copolymer that can fully achieve the above-mentioned objectives.

The copolymer obtained by copolymerizing tert-butylcyclohexyl methacrylate, methyl methacrylate, and styrene has excellent transparency, heat resistance, The present invention was completed based on the discovery that the molding processability was significantly improved by improving fluidity while maintaining low moisture absorption and mechanical strength, and at the same time, reducing residual monomer and improving thermal stability. reached.

In the development of optical disk substrate materials, it has traditionally been important to keep moisture absorption warpage to a low level, but in order to improve moisture absorption warpage, it is necessary to sacrifice moldability, birefringence, and mechanical strength. The reality is that we have been plagued by technical dilemmas. Therefore, the present invention is revolutionary because it solves this technical dilemma and makes it possible to suppress water absorption to about 50% lower than that of methyl methacrylate resin. It is expected that it will be useful not only as a material for optical element substrates, but also as a material for other products such as light-transmitting extruded plates, for which warping has traditionally been a major problem.The present invention is based on these findings. It was made by

[Means to solve the problem]

That is, according to the present invention, (A) methacrylic acid tert-
2 to 30 mol% of butylcyclohexyl units, (B) 60 to 96 mol% of methyl methacrylate units, 2 to 20 mol% of CC'') styrene units, (D) 0 to 10 mol of copolymerizable ethylenically unsaturated compound units. %, (A) + (
B)+(C)+CD) -100 mol%, and the weight average molecular weight of the copolymer is IO4-1
Provided is a low hygroscopic methacrylic copolymer with good moldability characterized by a moisture absorption in the range of 0''.

In the methacrylic copolymer of the present invention, the content of tert-butylcyclohexyl methacrylate units, which is component (A), is (A), (B), (<1:) and (D
) 2 to 30 moj based on the total molar amount of the components! %, and if the amount of component (A) is less than the above range, the low hygroscopicity and heat resistance that are the characteristics of the present invention will not be fully exhibited. If the above range is exceeded, moisture absorption and heat resistance will improve, but
The preferred content of component (A), which is undesirable because it reduces mechanical strength, is 4 to 20%.

Tert-butylcyclohexyl methacrylate has ortho, meta, and rose isomers, and each of these has cis and trans isomers.

In the present invention, any of them can be used,
Moreover, mixtures in any proportion can be used. Their content in the copolymers of the invention can be determined by pyrolysis gas chromatography analysis.

The content of methyl methacrylate units as component (B) is 60 to 96% by weight based on the total molar amount of components (A), (B), (C) and (D). If it is less than this range, the original excellent properties of methyl methacrylate, such as transparency, moldability, and low birefringence, will be poor (and if it exceeds this range, the low hygroscopicity and heat resistance intended by the present invention will be poor). This is insufficient and undesirable.

The preferred content of component (B) is 70 to 93 mof%.

The content of styrene units as component (C) is (A),
It is 2 to 20 moffi% based on the total molar amount of components (B), (C) and CD). If it is less than this range,
The effect of reducing residual monomers in the copolymer is reduced, and the effect of improving moldability and thermal stability is also reduced.

Moreover, if the content exceeds this range, the low birefringence will deteriorate and the heat resistance will deteriorate, which is not preferable.The preferable content of the component (C) is 2 to 15 II of %.

The copolymer according to the present invention may contain, as component (D), an ethylenically unsaturated compound unit copolymerizable with component (A), component CB), and component (C), if desired.

Examples of such monomers include methyl acrylate, (
(meth)acrylic acid alkyl esters such as ethyl meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate 5, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate; trifluoroacrylate Methyl, acrylic acid 1.1.1-
) acrylic acid fluorinated alkyl esters such as trifluoroethyl.

By containing an ethylenically unsaturated compound unit as component (D), thermal stability, fluidity during molding, or hygroscopicity can be improved, but excessive use may lead to a decrease in heat resistance. Therefore, the content of component (D), which is not preferable, is 0 to 10 vaol 1%, preferably 1 to 6 mof%, based on the total molar amount of components (A), (B), (C) and (D).

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 mixture consisting of tert-butylcyclohexyl methacrylate, methyl methacrylate, styrene, and optionally a copolymerizable ethylenically unsaturated compound is added to an aromatic hydrocarbon solvent such as toluene or ethylbenzene. A solution prepared by dissolving it in 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.

Initiators used when polymerizing the resin of the present invention include:
Any initiator commonly used in radical polymerization can be used, such as azo compounds such as azobisisobutyronitrile, benzoyl peroxide, lauroyl peroxide, tert-butylperoxy-2-ethylhexanoate, etc. Particularly preferred are organic peroxides. The amount used is generally in the range of 0.01 to 10% by weight based on the total amount of monomers.When polymerizing the resin of the present invention, the molecular weight regulator used as needed is generally used in radical polymerization. Any molecular weight regulator can be used, and mercaptan compounds such as butyl mercaptan, octyl mercaptan, dodecyl mercaptan, 2-ethylhexyl thioglycolate are particularly preferred.

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°C.
-120°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.

The weight average molecular weight of the copolymer according to the present invention is 104 to 1
07 range. When obtaining a molded product such as a light-transmitting plate by direct polymerization such as a casting method, 10S to 1
A relatively high weight average molecular weight of 0.07 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 1.5xio', 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 10s to 3 x 10', and a more preferable range is 1.5 XIO' to 2.5
10'.

In this case, if the weight average molecular weight is less than 1X10', sufficient mechanical strength and dimensional stability cannot be obtained, and if it exceeds 3X10', it will not be possible to extrude under normal extrusion molding conditions, and if extrusion is attempted at high temperature, thermal decomposition will occur. or discoloration may occur.

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

tert-methacrylic acid constituting the copolymer of the present invention
The content of butylcyclohexyl, methyl methacrylate, styrene, or ethylenically unsaturated compound units copolymerizable with these can be determined by pyrolysis gas chromatography,
and ' ``Can be measured by C-NMR method (nuclear magnetic resonance method).'' In C-NMR method, the copolymer is mixed with a deuterated solvent [CDCl1,1, C6D&, CD! NO
1. DMSO (dimethyl 5ulfoxide)
) −+L+) at room temperature or at high temperature.
The 3C-nuclei can be quantified by spectral analysis.

The copolymers according to the invention can be used alone, but
Polymethyl methacrylate, acrylonitrile-styrene copolymer, etc., within a range that does not impair its characteristics such as excellent transparency, moldability, low birefringence, thermal stability, low moisture absorption, and high heat resistance. It can also be used in a blend with other resins such as methyl methacrylate-styrene copolymer and polystyrene.

If the copolymer of the present invention contains a large amount of residual monomers, the high heat stability, etc., as well as the high heat resistance, which is one of the characteristics of the copolymer of the present invention, 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. The remaining monomers can be removed by heating the obtained copolymer under air flow or under reduced pressure.

There is a method of 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 substrate can also be obtained by obtaining a flat plate by cast polymerization or extrusion molding, and then compression molding this flat plate. , 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, hygroscopicity, which is a drawback of methyl methacrylate resin, is 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, it can be used even under high temperature conditions because the resin has low hygroscopicity.

Furthermore, 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) An acetone sample containing residual monomer n-butyl alcohol as an internal standard substance was dissolved and quantified by heating gas chromatography.

(2) Composition of components in copolymer (a) Nuclear magnetic resonance absorption (NMR) method A spectrum analysis of the 13c nucleus at a specific site of each component of the copolymer was conducted to determine the composition ratio. The measurement conditions were as follows: sample copolymer in DMSO-
d, and the number of integration times is 12.00 at a temperature of 70°C.
Analysis was performed in quantitative mode 0 times.

(b) Pyrolysis gas chromatography furnace temperature 45
The polymer was thermally decomposed at 0°C, and the decomposed gas was quantified by chromatography to determine the composition ratio.

(3) Weight average molecular weight (Mw) Prepare a sample solution by dissolving the bead-like polymer obtained by polymerization in dichloromethane ('5 k/30d),
Gel Pero+ation Chromato
graphy (GPC) measurement was 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 Measured based on 437M-0638. 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) Measurement was performed based on ASTM-0648. The specimens were annealed at 96°C for 2 hours and then conditioned (
Measurements were carried out at 23° C., relative humidity 52% for 48 hours).

(6) Equilibrium water absorption rate Measured at 23°C according to ASTM-0570.

(7) Total light transmittance Measured at 23°C according to ASTM-01003.

(8) Thermal stability A heating loss test was conducted under the conditions of N2 atmosphere and temperature increase rate of 10° (:/Llin), and the temperature at the time of 5 wt% loss was measured.

(9) Birefringence Birefringence of a disc with an information label on one side was measured using a polarizing microscope at a portion 50fflI11 from the center.

0. Moisture Absorption Warpage (i) Optical disk substrate A warpage 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.

(if) Extruded plate An extruded plate cut into a size of 2 x 300 x 300 m was used as a test piece, one side of which was covered with Saran 0 film, and the temperature was 50°C and the relative humidity was 90%.
I left it for a while.

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: Into a glass separable flask with an internal capacity of 102, 52 ml of water was added.
50 g of calcium polyacrylate, 1 sodium hydrogen phosphate. 5 g was added and stirred at a temperature of 30 to 35°C to prepare a separate aqueous phase. Meanwhile, in another glass container, methacrylic acid
4-tart-butylcyclohexyl [cis/trans-23/77 (w/W)) 172g (4w
+offi%), 1756 g of methyl methacrylate (
92moi! %), 40 g styrene (2tso
1%) and 32 g (2sof%) of methyl acrylate, and the total weight of these monomers was 2000 g.
(100 parts by weight), azobisisobutyronitrile 5g (0.25 parts by weight), n-octyl mercaptan 4
g (0.20 parts by weight) to prepare a monomer phase.

This monomer phase was added to the aqueous phase and suspended by stirring, and after replacing the air in separable flask 1' with nitrogen, the mixture was kept at a temperature of 75'C for 2 hours while stirring. Polymerization was carried out. Furthermore, 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 (bellets) were obtained by extruding into strands using 30 WRag or more and cutting the strands with a cutter.

A test piece was obtained by injection molding the obtained pellet at 230° C. using a 3 oz screw type injection molding machine. At this time, the minimum injection pressure (SSP) required to completely fill the mold was 680 kg/cd, and the thermal stability of the pellet was 0 or higher at a temperature of 325°C at the time of 5 wt% reduction. Tables 1 and 2 show the analysis results of the bead-like polymers and test pieces.

Examples 2-6 Monomer composition, molecular 1tJi moderating agent (n-octyl mercaptan), and polymerization initiator (azobisbutyronitrile)
Polymerization, molding, and evaluation were carried out in the same manner as in Example 1, except that the amount of was changed as shown in Table 1.

These results are shown in Tables 1 and 2.

Example 7 O-tert-butylcyclohexyl methacrylate [cis form/trans form -23/77 (w/w)) was used instead of p-tert-butylcyclohexyl methacrylate, and the composition of each monomer was changed to the first Polymerization, molding, and evaluation were performed in the same manner as in Example 1 except for the changes shown in the table. These results are shown in Tables 1 and 2.

Example 8 5-tert-butylcyclohexyl methacrylate [cis form/trans form -23/77 (w/w) instead of p-ter<-butylcyclohexyl methacrylate
), and polymerization, molding, and evaluation were carried out in the same manner as in Example 1, except that the composition of each monomer was changed as shown in Table 1.

These results are shown in Tables 1 and 2.

Example 9 (Optical disk base) The pellet obtained in Example 1 was molded into a precision injection molding machine (
Molded using each machine manufacturing company M-200/800DM),
300fflIlφ with information label on one side, thickness 1.
A 2 m base was obtained. The injection molding temperature was 290° C., the injection pressure, and the injection speed was high pressure and high speed.

This substrate was fixed to a vapor deposition device and aluminum was vapor-deposited under a vacuum of 10-”ffllllHg, and a UV coat (acrylic resin coated 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 10 to 16 (Optical disk substrate) Optical disk disks were prepared in the same manner as in Example 9 using the pellets obtained in Examples 2 to 8, respectively, and birefringence and hygroscopic warping properties were measured. . The results are shown in Table 3.

Example 17 (Extrusion plate) Polymerization was carried out in the same manner as in Example 2 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. Obtained a beret on the machine. Using this beret, at 270℃,
The melt viscosity under the condition of a shear rate of 1005 ec-' was determined to be 11800 poise.Next, the pellet was passed through a screw diameter 30a equipped with a plate die.
By extruding using an aφ vented twin-screw extruder at 230°C and a vent vacuum of 730m5+Hg or more, and then taking the extruded resin melt onto a take-up roll heated to 120°C or more. A colorless and transparent extruded plate with a good appearance was obtained. The moisture absorption warping properties of this extruded plate were measured. The results are shown in Table 4.

Examples 18-20 (extrusion plate) Monomer composition, molecular weight wiry agent (n-octyl mercaptan) and polymerization initiator (azobisisobutyronitrile)
Example 1 except that the amount added was changed as shown in Table 4.
Polymerization was carried out in the same manner as in Example 17, and the melt viscosity of the pellets and the hygroscopic warpage of the extruded plate were measured under the same conditions as in Example 17.

The results are shown in Table 4.

Comparative Example 1 As shown in Table 5, 98mof! of methyl methacrylate was used as a monomer! Polymerization and molding were carried out in the same manner as in Example 1, except that 1% of methyl acrylate and 0.15 parts by weight of a polymerization initiator (azobisisobutyronitrile) were used, and the properties of the polymer were evaluated. The results are shown in Table 6.

Comparative Examples 2 to 8 Same as Example 1 except that the monomer composition, polymerization initiator (azobisisobutyronitrile), and molecular weight regulator (n-octyl mercaptan) addition amounts were changed as shown in Table 5. Polymerization and molding were performed, and the properties of the material were evaluated. The results are shown in Table 6.

Comparative Examples 9 to 16 The copolymers obtained in Comparative Examples 1 to 8 were pelletized, and optical disks were formed in the same manner as in Example 9, and the disk properties were evaluated. The results are shown in Table 7.

Comparative Examples 17 to 19 Same as Example 1 except that the monomer composition, molecular weight regulator (n-octyl mercaptan), and polymerization initiator (azobisisobutyronitrile) addition amount were changed as shown in Table 8. Polymerization was carried out in the same manner as in Example 17, and the melt viscosity of the pellet and the moisture absorption warping property of the extruded plate were measured. The results are shown in Table 8.

Margins below [Effects of the Invention] The methacrylic copolymer of the present invention not only has the excellent transparency, low birefringence, and thermal stability that are the characteristics of methyl methacrylate resin, but also has the disadvantages of methyl methacrylate resin. It is a novel resin with significantly improved certain hygroscopic properties, heat resistance and moldability without sacrificing mechanical strength. Because the methacrylic copolymer has such excellent characteristics, its molded products can be advantageously used in various applications, especially optical information recording discs (optical discs), optical information recording discs, etc. As optical element substrates such as cards, optical information recording sheets, optical information recording films, lenses, mirror prisms, optical transmission fibers, etc., or as signboards, displays, partitions, daylight windows, TV front panels, and liquid crystal display devices. It is suitable for use as a light-transmitting plate for use in front panels, etc.

Patent applicant: Asahi Kasei Industries, Ltd.

Claims (1)

[Claims] 1, (A) tert-butylcyclohexyl methacrylate units 2 to 30 mol%, (B) methyl methacrylate units 60 to 96 mol%, (C) styrene units 2 to 20 mol%
, (D) copolymerizable ethylenically unsaturated compound unit 0-
Consisting of 10 mol%, (A) + (B) + (C) + (D)
= 100 mol%, and the weight average molecular weight of the copolymer is in the range of 10^4 to 10^7. A low moisture absorption methacrylic copolymer with good moldability. union