JPH01178511A - Methacrylic copolymer having low hygroscopicity - Google Patents

Abstract

PURPOSE:To obtain the title copolymer having excellent transparency, low birefringence, thermal stability, low hygroscopicity and heat resistance, by compounding two specified methacrylate units and, if required, a specified ethylenically unsatd. compd. unit. CONSTITUTION:The title copolymer is a copolymer which contains 2-30mol.% tert-butylcyclohexyl methacrylate units (A), 60-98mol.% methyl methacrylate units (B) and 0-30mol.% ethylenically unsatd. compd. units (C) of formula I [wherein R1 is H or methyl; R2 is phenyl or methyl-substd. phenyl or formula II (wherein Z is 1-8C unsubstd. of F-substd. alkyl)], wherein A+B+C=100 mol.% and having a wt.-average MW in the range of 10<4>-10<7>. The copolymer is colorless and transparent, has good moldability, low birefringence and thermal stability, and moreover, excellent low hygroscopicity and heat resistance and is suitable for a raw material of molded items for an optical element base and a light-transmitting extruded sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION [3-1 Industrial Application Field 1 The present invention relates to a novel low hygroscopic methacrylic copolymer. More specifically, the present invention provides methacrylic acid 1. e r
Specify the j-butylcyclohexyl unit, the methyl methacrylate unit, and if desired, the specific ethylenically unsaturated compound unit that can be copolymerized with these lff1 units.
It has colorlessness, transparency, moldability, low birefringence, and thermal stability, and also has low moisture absorption and excellent heat resistance.
Therefore, the present invention relates to a low hygroscopic methacrylic copolymer suitable as a material for molded products such as optical element substrates and 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, and prisms. be able to.

Examples of the light-transmissive extruded board include signboards, displays, partitions, daylight windows, television front panels, liquid crystal display front panels, and the like.

[3-2 Prior art and its problems] Conventionally, methyl methacrylate resin has excellent optical properties such as excellent transparency and low birefringence, so it has been used for optical applications such as optical disk substrates. It is widely used as a material for products that function by transmitting light, such as device substrates or transparent plates.

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 read-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 a type of read-only disc. 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.

A compact disc is a type of read-only 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 as optical discs and do not require a high FI of 17 degrees, so they are not used in practical applications. 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 read-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).
-162135 publication, 57-108012 publication)
However, even if styrene is copolymerized, the effect of improving hygroscopicity is not very large, and in order to greatly exhibit the improvement effect, increasing the content of styrene units,
The increased birefringence causes the resin to lose its original excellent characteristics, causing the problem that it cannot be used as an optical element substrate (for example, a disk substrate).Furthermore, even if styrene is copolymerized, the heat resistance is improved. Therefore, 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. 57-186241 No. 58-127754, No. 58-154751,
Publication No. 59-1518, Publication No. 60-104110 +
11). However, even if cyclohexyl methacrylate is copolymerized, the effect of improving hygroscopicity is not very large, and if the content of cyclohexyl methacrylate units is increased in order to make the improvement effect greater, heat resistance decreases significantly. , and become extremely brittle, for example, the heat generated during handling may cause the optical disk to warp or deform, making it difficult to record or read highly accurate information, or damage the optical disk during handling. This results in an undesirable situation in which its use as a vehicle 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 with cyclohexyl methacrylate (Japanese Unexamined Patent Publication No. No. 57-186241), methacrylic acid 3
, 3.5-Trimethylcyclohexyl and isobornyl methacrylate copolymerization example (Japanese Unexamined Patent Publication No. 60-1
No. 4110) is disclosed. however,
In these examples, although the hygroscopicity of the methyl methacrylate resin is improved, the obtained (M resin has low heat deformation resistance,
Further, there is a problem that mechanical strength and thermal stability are poor.

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 (Japanese Patent Laid-Open No. 59-227909, 1986-115
Publication No. 605). However, even if isobornyl methacrylate is copolymerized, the effect of improving hygroscopicity is not very large, and if the content of isobornyl methacrylate units is increased in order to exhibit a large effect of improving hygroscopicity, it becomes extremely brittle. For example, there is a problem in that the optical disc may be damaged during handling, and its use as an optical disc base material γ-F cannot be avoided. Even if isobornyl methacrylate is copolymerized under the normal polymerization conditions for radical polymerization described in the above publication, no reaction occurs in the resulting resin! i! There is a lot of residue remaining, and it is extremely difficult to remove it from the resin. If unreacted 111' remains 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, plastics made of resin containing a large amount of residual monomer
Even if you try to obtain a product B, it may be colored or foamed during molding and cannot be molded, or even if it can be molded, the resulting molded product may be colored or have poor heat resistance.
However, it may not be very good, so it has its limitations. Moreover, the resin obtained by copolymerizing isobornyl methacrylate originally has low thermal stability, and for example, the residual W polymer has been reduced by a purification method in which the obtained resin is dissolved in a solvent and reprecipitated. Even with resin, when performing high-rise melt molding at 280°C, which is used to obtain high bit reproducibility in injection molding for optical disk substrates, significant coloring and decomposition and foaming occur simultaneously, making it difficult to obtain a good molded product. is the circuit.

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 Publication 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, and cannot be melt-molded at high temperatures such as 280°C. In this case, there is a problem of significant discoloration and decomposition and foaming.

The object of the present invention is to provide an optical element that has colorlessness, transparency, moldability, thermal stability, excellent heat resistance, and exhibits excellent low moisture absorption while maintaining sufficient mechanical strength. The object of the present invention is to provide a low hygroscopic methacrylic copolymer suitable as a material for molded products such as substrates and light-transmitting extruded plates.

As a result of intensive research to achieve the objective, the present inventors have found that methyl methacrylate and at least te
The resin obtained by copolymerizing with rt-butylcyclohexyl has the excellent transparency, moldability, and low birefringence inherent to methyl methacrylate resin, and maintains mechanical strength while maintaining water absorption (equilibrium). It was surprisingly discovered that the water absorption rate of methyl methacrylate resin can be suppressed to about 1%, compared to about 2% for methyl methacrylate resin. 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 in obtaining the desired results. 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 various products such as light-transmitting extruded plates, for which warping has been a major problem in the past.The present invention is based on these findings. It was made by

[Means and actions for solving 3-3 problems] Immediately,
According to the present invention, (A) 2 to 30 mol% of tert-butylcyclohexyl methacrylate units, (B) 60 to 98 mol% of methyl methacrylate units, (C) formula (1) [wherein, R9 is a hydrogen atom] or a methyl group, R8 is a phenyl group, and a methyl-substituted phenyl group represents an alkyl group substituted with a fluorine atom. + (C) = 100 mol%, and the weight average molecular weight of the copolymer is in the range of 1O4 to 1O''. Ru.

In the methacrylic copolymer of the present invention, the content of tert-butylcyglohexyl methacrylate units, which is the (A)-component, is 2 to 2 to 30 mo1%, methacrylic acid te
If the amount of rt-butylcyclohexyl units is less than the above range, the low hygroscopicity and high heat resistance, which are the characteristics of the present invention, will not be fully exhibited.6 If the amount exceeds the above range, the hygroscopicity and heat resistance will improve, but The preferred content of r, ert -butylcyclohexyl units is 5 to 20 II lo 1%, which is undesirable because the mechanical strength decreases.

jerL-butylcyclohexyl methacrylate has ortho, meta, and rose cystic forms, and each of these forms has cis and trans forms.

In the present invention, any of them can be used, or a mixture of any proportion can be used.6 The content of these in the copolymer of the present invention can be determined by gas chromatography analysis. It is possible.

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 envisioned by the present invention will deteriorate. This is insufficient and undesirable. (8) The preferred content of the component is 70 to 94 m
o1%.

The copolymer according to the present invention may contain, as component (C), an ethylenically unsaturated compound unit copolymerizable with component (8) and component (B), if desired. Such an ethylenic compound monomer has one formula (1) [wherein, R1 is a hydrogen atom or a methyl group, R3 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 acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, and 2-ethylhexyl acrylate; trifluoromethyl acrylate; acrylic acid 1,1. Examples include acrylic acid fluorinated alkyl esters such as 1-1-lifluoroethyl; and aromatic vinyl compounds such as styrene, α-methylstyrene, and p-methylstyrene.

By containing an ethylenically unsaturated compound unit as component (C), it is possible to improve thermal stability, fluidity during molding, or hygroscopicity, but excessive use may cause a decrease in thermal properties. (C)
The content of the component is O to 30 mo1%, preferably 2 to 20 mole, based on the total molar amount of components (A), (B), and (C).
The mo is 1%.

The accompanying figure shows in a triangular view the area covered by the invention. In the figure, the shaded area is the area.

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, and optionally an ethylenically unsaturated compound of formula (1) is added to an aromatic hydrocarbon such as toluene or ethylbenzene. A solution prepared by dissolving it in a solvent 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 a quantitative ratio that is substantially the same as the quantitative ratio of monomer units of components (A), CB), 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, such as azo compounds such as azobis-1'tubyronitrile, hensyl peroxide, lauroyl peroxide, T,erL-butylperoxy-2-ethylhexyl Organic peroxides such as noates are particularly preferred. The amount used is generally in the range 0.01-10% by weight of the total amount of monomer. 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, thio Particularly preferred are mercaptan compounds such as 2-ethylhexyl glycolic acid.

The temperature at which the copolymer of the present invention is polymerized is not particularly limited, but is usually 0 to 150°C, preferably 50-1
Selected within the range of 20°C. Optimal polymerization L@degree is the polymerization method,
It is determined in consideration of the polymerization equipment, polymerization initiator, molecular weight regulator, characteristics of the resulting copolymer resin, etc. Polymerization is about 12
After curing for 0 to 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 invention is lO"~IQ
' range. 1) When producing a molded product with a light transmittance of 1 layer by α-adhesive polymerization as in the casting method, it is 10゛~
A relatively high gLi''V distribution prediction of lO'' can be taken. When the object is an injection molded product such as a disk base, the range is usually 1 x 10' to 2XIO', preferably 5 x 101 to 1.5Xlo', and more preferably 5 ×10". In this case, weight! If the distribution is less than 10”, the mechanical strength will decrease, and 2×
If it exceeds 10°, the degree of mold transfer tR during molding will decrease.

In addition, when the target is an extruded product such as a light-transmitting extruded plate, the weight average molecular weight is l x 10' to 3XIO'
The more preferable range is 1.5×101 to 2
．． 5X10'', in which case the weight average molecular weight is 1X
If it is less than 10", sufficient mechanical strength and dimensional stability cannot be obtained, and if it exceeds 3XIO", it cannot be extruded under normal extrusion molding conditions, and thermal decomposition and coloration occur when 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.

The content of each of the tert-butylcyclohexyl methacrylate, methyl methacrylate, or the ethylenically unsaturated compound unit represented by the formula (1) copolymerizable with these constituting the copolymer of the present invention is determined by C-NMR method ( It can be measured by nuclear magnetic resonance method). That is, the copolymer was dissolved in a deuterated solvent [CD(1,,C,D,,CD,No.
,, DMSO (dimethyl 5ulroxide
) −d, ) and at room temperature or at high temperature °
°C - can be quantified by nuclear spectral analysis.

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 modified 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 sequestrants, lubricants, mold release agents, plasticizers, impact resistance improvers, antistatic agents, snow 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 that take advantage of the various properties of the copolymer of the present invention by molding methods well known in the field of plastics technology.

By subjecting the copolymer resin of the present invention to extrusion molding, a 11-light transmitting extruded plate can be obtained. 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 flexibility during extrusion and withdrawal is 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. A light-transmitting extruded plate obtained by extrusion molding can be used, for example, for signboards, displays, partitions, etc.
, TV t) ij ili Jfi, liquid crystal display device ti
ij il'i Vi, etc., and exhibits high performance because it is excellent in low moisture absorption, high heat resistance, transparency, thermal stability, mechanical strength, etc.

Further, by the casting method, it is possible to obtain a light-transmitting material made of the copolymer resin of the present invention which has a high weight average molecular weight and high strength, 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. This ability can be advantageously obtained by injection molding for automobile tail lamps, meter covers, etc.

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. It can be obtained by providing a protective film or a protective film and, if necessary, bonding the two sheets together with or without providing an intermediate layer of gas or solid. 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 read-only discs, write-once discs, and rewritable discs.

In addition to disks made of a single substrate such as compact discs, the term also includes disks made of two substrates bonded together such as video discs. Furthermore, on the surface of the board,
In addition to general disks with minute irregularities that are or should be signals, it also includes disks with a smooth substrate surface coated with a memory layer of metal, pigment, etc. This also includes magneto-optical disks that are optical discs.

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 humidity and high temperatures. , it can be used even under harsher conditions.

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 the basis for write-once discs and rewritable discs, including magneto-optical discs, which require higher precision, contain a larger amount of information, and are used under harsher conditions than video discs and compact discs. Although an optical disk substrate that satisfactorily satisfies all of the necessary properties has not been obtained in the past, the disk substrate made of the copolymer (sealant) of the present invention can be preferably used for this purpose as well.

[3-4 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.

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

(2) Component composition in the copolymer Nuclear magnetic resonance absorption (NMR) method: ? Then, we conducted a Subekk≧R analysis of the C nucleus of the specific part of each component of the residual hair coalescence.
The composition ratio was determined. , 11 Quantitative analysis ('l is the test Ft copolymer dissolved in DMSO-d, and analysis was carried out in quantitative mode at 11 N and 70° C. for 12,000 cumulative times.

(3) Weight average molecular weight (M w ) The bead-like polymer obtained by polymerization was dissolved in dichloromethane (50 x 730 river 1) to prepare a solution.
graphy (GPC) measurements were performed. alq
From the 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 ASTM-D638. After annealing the test piece at 96°C for 2 hours, the condition condition m (
The measurements were carried out at 23° C. and 52% relative humidity for 48 hours.

(5) Heat deflection temperature (HDT) Measurement was performed based on ASi'MD648. 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-DIO03.

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

(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.

(ti) 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 test piece was heated for 48 hours in an atmosphere of 50°C and 90% relative humidity. 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 1 5Q of water was added to a glass separable flask with an internal capacity of 1OQ,
Potassium polyacrylate 50α and sodium hydrogen phosphate 1.5 g were added and stirred at a temperature of 30 to 35°C to prepare an aqueous phase. Meanwhile, in another glass container, methacrylic acid p-
Add 188 g (2 mo1%) of tert-butylcyclohexyl [cis form/trans form = 23/77 (w/w), 1870 g (96 mo1%) of methyl methacrylate, and 33 g (2 mo1%) of methyl methacrylate,
Furthermore, the total amount of these monomers is ffiffi2000g.
A monomer phase was prepared by adding 3 g of azobisisobutyronitrile <'q, 1 part of 15 mm) and 4 g of n-octyl mercaptan (0.20 parts by weight) to 100 parts by weight of α.

This monomer phase was added to the aqueous phase and suspended by stirring, and after replacing the air in the separable flask with nitrogen, the mixture was kept at a temperature of 75°C for 2 hours while stirring. Polymerization was carried out. 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-shaped polymer is extruded into a strand shape using a vented twin-screw extruder with a screw diameter of 30 m + aφ at 230°C and a vent vacuum degree of 730 mH'g or more, and is cut with a cutter to form granules ( pellet)
I got it.

A test piece was obtained by injection molding the obtained pellet at 230° C. using a 3 oz screw injection molding machine. Tables 1 and 2 show the analysis results of the bead-like polymers and test pieces prepared above.

Examples 2 to 12 Polymerization, molding, and evaluation were carried out in the same manner as in Example 1, except that the type and composition of the monomer and the amount of the separation nail regulator (n-octyl mercaptan) were changed as shown in Table 1. Ta. These results are shown in Tables 1 and 2.

Example 13 O-jerj-butylcyclohexyl methacrylate [cis form/iso form = 23777 (w/w)] was used instead of p-tert-butylcyclohexyl methacrylate, and the composition of each monomer was as shown in Table 1. Polymerization, molding, and evaluation were carried out in the same manner as in Example 1 except for the following changes. These results are shown in Tables 1 and 2.

Example 14 m-tert, -butylcyclohexyl methacrylate [cis form/iso form = 23/77 (w/w)] was used instead of p -sert-butylcyclohexyl methacrylate, and each W and total mer composition were Polymerization, molding, and evaluation were carried out in the same manner as in Example 1 except for the changes shown in Table 1. These results are shown in Tables 1 and 2.

Example 15 (Optical disk base) The pellet obtained in Example 1 was molded into a precision injection molding machine (
Using Meijin Seisakusho M-200/800DM), a base of 300 mmφ and 1.2 mm thick with an information mark on one side was obtained. 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 one side was coated with a UV coating (an acrylic resin coated and crosslinked by ultraviolet and l!iI irradiation) as a protective film. A vapor deposition substrate was prepared.The birefringence and moisture absorption warpage of this single-sided vapor deposition substrate were measured.The results are shown in Table 3.

Examples 16 to 28 (Optical disk substrate) Optical disk disks were prepared in the same manner as in Example 15 using the pellets obtained in Examples 2 to 14, respectively, and the birefringence and hygroscopic warpage were 4 [11] constant. I did it. The results are shown in Table 3.

Example 29 (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. Obtained a beret on the machine. Next, this pellet was put into a bent type 2 with a screw diameter of 30 II and 1 mφ equipped with a flat plate die.
Using a axial extruder, 230℃, vent vacuum degree 730mm
By extruding under conditions of Hg or higher 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. Moisture absorption warping properties of this extrusion sample were measured. The results are shown in Table 4.

Examples 30 to 35 (extruded plate) 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.
Polymerization was carried out in the same manner as in Example 2, and an extruded plate was produced under the same conditions as in Example 2, and the moisture absorption warping property was determined to be: Table 4 shows the 1' fruit.

Comparative Example I As shown in Table 5, polymerization and molding were carried out in the same manner as in Example 1, except that methyl methacrylate 98 + no 1% and methyl acrylate 2 mo 1% were used as monomers, and the properties were evaluated. Ta. The results are shown in Table 6.

Comparative Examples 2 and 3 Polymerization and molding were carried out in the same manner as in Example 1, except that the monomer 411l2 was changed as shown in Table 1S5, and the properties of the polymers were evaluated. The results are shown in Table 6.

Comparative Example 4 As shown in Table 5, methacrylic acid p-r, ert-
Polymerization and molding were carried out in the same manner as in Example 3, except that isobutyl acrylate was used instead of butylcyclohexyl, and the properties of the polymer were evaluated. The results are shown in Table 6.

Comparative Example 5 As shown in Table 5, methacrylic acid p-LQr11. −
Polymerization and molding were carried out in the same manner as in Example 3, except that cyclohexyl methacrylate or cyclohexyl phosphate was used instead of butylcyclohexyl, and the properties of the polymer were evaluated. The results are shown in Table 6.

Comparative Examples 6 to 1O J obtained in Comparative Examples 1 to 5 respectively (the polymer was pelletized and an optical disc was formed in the same manner as in Example 15,
What about the evaluation of the characteristics? It became 7. The results are shown in Table 7.

Table 6 Table 7 [3-5 Effects of the invention] The methacrylic copolymer of the present invention has excellent transparency, moldability, low birefringence, which are characteristics of methyl methacrylate resin,
This is a new resin that not only has four thermal stability but also has significantly improved hygroscopicity and heat resistance, which are disadvantages of methyl methacrylate resin, 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, mirrors, prisms, optical transmission fibers, etc., or as signboards, display displays, partitions, lighting windows, TV front panels, and liquid crystal displays. It is suitable for use as a light-transmitting plate used as a front panel of an apparatus.

[Brief explanation of the drawing]

The figure is a triangular view showing the area covered by the present invention. In Figure 0, the area indicated by diagonal lines is the area of the present invention.

Claims (1)

[Claims] 1. (A) 2 to 30 mol% of tert-butylcyclohexyl methacrylate units, (B) 60 to 98 mol% of methyl methacrylate units, (C) Formula (1) ▲ Numerical formula, chemical formula, table ▼ [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 ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (Z is an unsubstituted or fluorine atom with 1 to 8 carbon atoms represents an alkyl group substituted with)] A copolymer consisting of 0 to 30 mol% of ethylenically unsaturated compound units represented by (A) + (B) + (C) = 100 mol% A low hygroscopic methacrylic copolymer, characterized in that the weight average molecular weight of the copolymer is in the range of 10^4 to 10^5. 2. The ethylenically unsaturated compound unit (C) is 1 to 10 mol%, and R_1 in general formula (1) is H, R_2
▲There are mathematical formulas, chemical formulas, tables, etc.▼, Z has 1 to 1 carbon number
The low hygroscopic methacrylic copolymer according to claim 1, which is an alkyl group of No. 8. 3. Low moisture absorption according to claim 1, wherein the ethylenically unsaturated compound unit (C) is 5 to 30 mol%, and R_2 in general formula (1) is a phenyl group or a methyl-substituted phenyl group. methacrylic copolymer.