JPH0291108A - Methacrylic copolymer having good flowability and low moisture absorptivity - Google Patents

Abstract

PURPOSE:To lower the moisture absorptivity and to improve the flowability 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 50% or more of the stereoisomers is in the cis 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 good fluidity and low moisture absorption. More specifically, the present invention provides 4-tert-butylcyclohexyl methacrylate units and methyl methacrylate units in a specific range of stereoisomer ratios, and optionally specific ethylenic units copolymerizable with these monomer units. and an unsaturated compound unit in a specific amount ratio,
It has colorlessness, transparency, heat resistance, low birefringence, thermal stability, and low moisture absorption, and has excellent moldability, so it can be used as a material for molded products such as optical element substrates and transparent extruded plates. The present invention relates to a suitable low hygroscopic methacrylic copolymer.

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. Examples of the light-transmissive extruded board include signboards, displays, partitions, daylight windows, television front panels, liquid crystal display front panels, 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 for this reason, many optical discs based on conventional resins are The reality is that they are subject to restrictions. for example,
Methyl methacrylate resin has conventionally been used as a base material for video discs, which are one type of discs exclusively for continuous 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 causes 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. Not used as a material. 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 in size 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 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 (Japanese Unexamined Patent Publication No. 57186241, No. 58-58). 1
Publication No. 27754, No. 58-154751, No. 59-
No. 1518, No. 60-104110). 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, resulting in warpage and deformation of optical discs due to heat during handling. 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 have also reported an example in which 4-isopropylcyclohexyl acrylate and dicyclohexyl fumarate were copolymerized in addition to cyclohexyl methacrylate (JP-A-57-1999) 186241) and methacrylic acid 3.3.
5-) Example of copolymerization of lyntylcyclohexyl and isobornyl methacrylate (JP-A-60-104110)
Publication No.) has been 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
Publication No.). However, increasing the content of isobornyl methacrylate units in order to achieve a desired level of low hygroscopicity may result in significant brittleness (for example, damage to the optical disk during handling), which may impede its use as an optical disk substrate material. Even if isobornyl methacrylate is copolymerized under the normal polymerization conditions for radical polymerization described in the above publication, unreacted monomers remain in the resulting resin. A considerable amount remains, and it is extremely difficult to remove this from the resin.If unreacted monomers remain in the resin, not only the heat resistance of the resin will be significantly lowered, but also the thermal stability will be significantly lowered.

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 focus 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-
22.7909).

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.

(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 good-flowing, low-hygroscopic methacrylic copolymer that exhibits low hygroscopicity and has excellent moldability, and is therefore suitable as a material for molded products such as optical element substrates and light-transmitting extruded plates. It is.

In order to achieve this objective, there has been 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 intensive research on the above copolymers, the present inventors have discovered a new copolymer that can fully achieve the above object. It's arrived.

tert-butylcyclohexyl methacrylate has
There are three types of isomers depending on the position of the tert-butyl group bonded to the cyclohexane ring, and each of them has cis and trans forms. Among these isomers,
Methacrylic acid with a cis/trans ratio within a specific range
In a copolymer made of 4-tert-butylcyclohexyl, while maintaining the excellent transparency, mechanical strength, and low birefringence inherent to methacrylic resin, the water absorption rate (equilibrium water absorption rate) is lowered by about 50%, and heat resistance is improved. The present inventors have found that the present invention has been completed based on the findings that the present invention has been found to have improved properties and to have extremely good moldability.

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 has been made based on these findings.

(Means for Solving the Problem) That is, according to the present invention, (A) 2 to 30 mol% of 4-tert-butylcyclohexyl methacrylate units in which the cis isomer is 50% or more among the stereoisomers; (B) 60 to 98 mol% of methyl methacrylate units, (C) formula (1) [wherein R+ is a hydrogen atom or a methyl group, and R2 is a phenyl group, a methyl-substituted phenyl group, or an alkyl group substituted with an elementary atom A copolymer consisting of O to 30 mol% of at least one ethylenically unsaturated compound unit represented by , and the weight average molecular weight of the copolymer is 10
4-10? Provided is a methacrylic copolymer with good fluidity and low hygroscopicity, which is characterized in that the methacrylic copolymer has a low hygroscopicity.

In the methacrylic copolymer of the present invention, the content of 4-tert-butylcyclohexyl methacrylate units in which the cis isomer is 50% or more among the stereoisomers that are component (A) is (A) and (B). and 2 to 30 mo1% based on the total molar amount of component (C), and when the amount of component (A) is less than the above range, the low hygroscopicity and good moldability, which are the characteristics of the present invention, are fully exhibited. Not done. 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
~20IIIO1%.

Also, the ratio of cis and trans in (A) component is 5 for the cis form.
It is 0% or more. When the ratio of the cis isomer is less than 50%, the effect of improving moldability is small.

In addition, methacrylic acid-4tert- which has a high cis isomer content
Butylcyclohexyl monomer was obtained from a cis and trans mixture through separation steps such as crystallization and rectification.

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,
Transparency, moldability, and low birefringence, which are originally excellent properties of methyl methacrylate, deteriorate, and when this range is exceeded, the low moisture absorption and heat resistance intended by the present invention become insufficient, which is not preferable.

The preferred content of component (B) is 70 to 94 mo1%.

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 COZ (Z is a carbon number of 1
~8 unsubstituted or fluorine atom-substituted alkyl group)]. Examples of such monomers include methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, and di-acrylate.
Acrylic acid alkyl esters such as ethylhexyl: trifluoromethyl acrylate, acrylic acid 1,1.1-
Acrylic acid fluorinated alkyl esters such as trifluoroethyl; or styrene, α-methylstyrene, p-
Aromatic vinyl compounds such as methylstyrene can be mentioned.

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 O to 30 mo1%, preferably 2 to 20 ra, based on the total molar amount of components (A), (B), and (C).
It is 01%.

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.

In the case of solution polymerization, the polymer consists of 4-tert-butylcyclohexyl methacrylate, methyl methacrylate, and, if desired, an ethylenically unsaturated compound of formula (1), in which the cis isomer is 50% or more of the stereoisomers. A solution prepared by dissolving a monomer 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. As the quantitative ratio of each component of the monomer mixture, use the quantitative ratio that is substantially the same as the quantitative ratio of the monomer units of components (A), (B), and (C) of the target copolymer. be able to.

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 10' to 10
? is within the range of 105 to 10 when obtaining a molded product such as a light-transmitting plate by direct polymerization such as a casting method.
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 1X1OS. . In this case, if the weight average molecular weight is less than 10', the mechanical strength will decrease and 2
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 a more preferable range is 1.5 x 105 to 2.5 x 10'.
It is. In this case, if the weight average molecular weight is less than 1X10', sufficient mechanical strength and dimensional stability cannot be obtained;
If it exceeds ', it cannot be extruded 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-4tert constituting the copolymer of the present invention
- The content of each of butylcyclohexyl, methyl methacrylate, or the ethylenically unsaturated compound unit represented by the formula (1) copolymerizable with these is determined by pyrolysis gas chromatography and 13C-NMR method (nuclear magnetic resonance method). It can be measured by In the 11C-NMR method, the copolymer was prepared using deuterated solvents CCDCl5, ChDb,
CD3NO2, DMSO (dimethyl 5ulf
The 130-nucleus can be quantified by dissolving it in 130-d6] and performing spectral analysis of the 130-nucleus at room temperature or at a high temperature.

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 the copolymer, it is preferable to apply a conventional method for removing the residual monomer. Examples of the method for removing the residual monomer include a method of heating the obtained copolymer under an air flow, a method of heating the obtained copolymer 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, desensitizers, impact resistance improvers, antistatic agents, flame retardants, preservatives, dyes, and 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. Temperature conditions during extrusion and withdrawal are selected depending on the characteristics of the extruded plate or its intended use, 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, 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, it is necessary for the foundation of write-once discs and rewritable discs, including magneto-optical discs, which require higher precision than video discs and compact discs, have a large amount of information, and are used under harsh conditions. Although an optical disk substrate that fully satisfies all of the characteristics 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 the copolymer ■ Nuclear magnetic resonance absorption (NMR) method A spectrum analysis of the I30 nucleus at a specific site of 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-c16, and the analysis was conducted in quantitative mode at a temperature of 70° C. and 12,000 cumulative 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 molecule N (Mw) Prepare a sample solution by dissolving the bead-like polymer obtained by polymerization in dichloromethane (50 mg/30 ml), and use Get Permeation 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 Measurements were performed based on ASTM-D63B.

The test piece was a raft-shaped M that was annealed at 96℃ for 2 hours.
Measurements were carried out under conditions (48 hours at 23° C. and 52% relative humidity).

(5) Heating 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 based on ASTM-Dl 003.

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

(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%.

To measure the warpage, the distance between the center of the disk base and a plane passing through two points on the outer periphery of the disk base was measured every time to determine the maximum amount of warp.

(ii) Extruded board An extruded board cut into a size of 2 x 300 x 300 ma+ was used as a test piece, one side of which was covered with Saran film and left in an atmosphere at a temperature of 50°C and a relative humidity of 90% for 48 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 A separable glass flask with a content of 1 (liter) was filled with 51.
Potassium polyacrylate 50e1 and 1.5 g of sodium hydrogen phosphate were added and stirred at a temperature of 30 to 35°C to prepare an aqueous phase. Meanwhile, in another glass container, methacrylic acid-4
-tert-butylcyclohexyl [cis form/trans form = 90/10 (w/w) 3171 g (4 mo1%)
, 1796 g (94 mo1%) of methyl methacrylate and 33 g (2 mo1%) of methyl acrylate were added, and 3 g (0
, 15 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 the separable flask with nitrogen, polymerization was carried out by keeping the mixture at a temperature of 75° C. for 2 hours while stirring. 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.
A colorless bead-like polymer was obtained by washing with water and drying.

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) are produced by extruding into strands at 30m+mHg or higher and cutting them with a cutter.
I got it.

A test piece was obtained by injection molding the obtained pellet at 230° C. using a 3 oz single-screw injection molding machine. At this time, the minimum injection pressure (S S P) required to completely fill the mold was 650 Kg/cm.
Shown in Table and 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-200/800DM>
300mmφ with information sign on one side, thickness 1.2mm
got the foundation. The injection molding temperature was 290° C., and the injection pressure and speed were 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. . The results are shown in Table 3.

Example 14 (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. Using this pellet, the melt viscosity was determined at 270°C and a shear rate of 1005 ec-', and it was found to be 1220°C poise.
Using a IIIIIIφ vented twin-screw extruder, 230
C. and a vent vacuum of 730 mmHg or higher, and the extruded resin melt was taken on a take-up roll heated to 120.degree. C. or higher to obtain a colorless and transparent extruded plate with a good appearance. Moisture absorption warping properties of this extrusion sample were measured. The results are shown in Table 4.

Examples 16-21 (Extrusion plate) Monomer composition, molecules! Example 1 except that the amount of regulator (n-octyl mercaptan) added was changed as shown in Table 4.
Polymerization was carried out in the same manner as in Example 15, and the melt viscosity of the pellets and the hygroscopic warpage of the extruded plate were measured under the same conditions as in Example 15.

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 1% methyl methacrylate 98a+o and 1% methyl acrylate were used as monomers.
The characteristics of the fibers were evaluated. 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 the properties of the polymers were evaluated. The results are shown in Table 6.

Comparative Examples 9 to 16 Polymerization was carried out in the same manner as in Example 1, except that the monomer composition and the amount of molecular weight regulator added were changed as shown in Table 7. The melt viscosity of the pellets was was measured.

The results are shown in Table 7.

(The following is a blank space) [Effects of the Invention] The methacrylic copolymer of the present invention not only has the excellent transparency, low birefringence, and thermal stability that are characteristics of methyl methacrylate resin, but also has the characteristics of methyl methacrylate resin. This is a new resin that has significantly improved hygroscopicity, heat resistance, and moldability, but without sacrificing mechanical strength.The methacrylic copolymer has these excellent characteristics. Therefore, the molded products can be advantageously used for various purposes, especially optical information recording disks (optical disks), optical information recording cards, optical information recording sheets, optical information recording films, Suitable for use as a substrate for optical elements such as lenses, mirror prisms, and optical transmission fibers, or as a light-transmitting plate for use in signboards, display displays, partitions, daylight windows, television front panels, liquid crystal display front panels, etc. .

Patent applicant: Asahi Kasei Industries, Ltd.

Claims (1)

[Claims] 1. (A) 2 to 30 mol% of 4-tert-butylcyclohexyl methacrylate units in which 50% or more of the stereoisomers are cis-isomers, (B) 60 methyl methacrylate units.
~98 mol%, (C) Formula (1) ▲Mathematical formula, chemical formula, table, 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 ▲Mathematical formula, There are chemical formulas, tables, etc. ▼ (Z represents an alkyl group having 1 to 8 carbon atoms, unsubstituted or substituted with a fluorine atom)] 0 to 30 mol% of at least one ethylenically unsaturated compound unit represented by It consists of (A) + (B) + (
C) = 100 mol%, and the weight average molecular weight of the copolymer is in the range of 10^4 to 10^7, a good fluidity low moisture absorption methacrylic copolymer. Combined.