JP2678030B2 - Good flowability, low moisture absorption, methacrylic copolymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a novel methacrylic copolymer having good fluidity and low hygroscopicity. More specifically, the present invention relates to 4-tert-butylcyclohexyl methacrylate units and methyl methacrylate units in a specific range of stereoisomeric ratios, and, if desired, specific ethylenic monomers copolymerizable with these monomer units. It contains a saturated compound unit in a specific amount ratio, has colorlessness, transparency, heat resistance, low birefringence, thermal stability, low hygroscopicity, and is excellent in moldability, and therefore an optical element. The present invention relates to a methacrylic copolymer having a low hygroscopicity, which is suitable as a material for a molded article such as a substrate and a light-transmitting extruded plate.

The optical element substrate in the present invention means a body substrate of the optical element. The term "optical element" as used herein is a generic term for instruments that utilize optical characteristics such as transmission, refraction, and reflection of light rays. Specific examples of the optical element include, for example, an optical information recording disc (hereinafter referred to as an optical disc), an optical information recording card, an optical information recording sheet, an optical information recording film, a lens, a mirror, and a prism. Can be mentioned. The light-transmitting extruded plate includes, for example, a sign, a display, a partition, a lighting window, a television front plate, a liquid crystal display front plate, and the like.

[Conventional technology]

Conventionally, methyl methacrylate resin is an optically excellent resin such as excellent transparency and small birefringence, so that light can be transmitted through, for example, an optical element substrate such as an optical disc substrate or a transparent plate. It is widely used as a material for products that exhibit their functions.

However, this methyl methacrylate resin has a high hygroscopic property, and dimensional changes, warpage, and deformation occur due to moisture absorption, and since heat resistance is not very good, deterioration of mechanical properties, warpage, and deformation under high temperature environment. However, there is a drawback in that such a situation occurs, and in reality, its use is limited.

Currently, various types of discs such as a read-only disc, a write-once disc, and a rewritable disc are put into practical use as optical discs. Various properties such as transparency, moldability, low birefringence, thermal stability, low hygroscopicity, and heat resistance are required as the base material for these discs, but resins satisfying all of these properties are required. Has not been found yet, and the fact is that conventional optical disks based on resins are subject to many restrictions. For example, in a video disk which is a kind of a read-only type disk, a methyl methacrylate resin is conventionally used as a base material. However, methyl methacrylate resin has a large hygroscopic property, and a base is formed using this resin, metal is vapor-deposited on one side, and a protective film is coated. The fact is that warping and deformation are prevented by pasting, and they are practically used.

In a compact disk (digital audio disk), which is a kind of read-only disk, a polycarbonate resin is conventionally used as a base material. In this compact disk, since the two disk substrates are not bonded to each other, the disk may be warped or deformed due to moisture absorption, and may have low heat resistance and may be deformed in a high temperature environment such as being left in a car in summer. Is not used as a disc base material. On the other hand, polycarbonate resin has poor moldability and large birefringence, but compact discs are used practically because optical discs are relatively small in size and do not require high precision.

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

To improve the hygroscopicity of methyl methacrylate resin,
A technique of copolymerizing methyl methacrylate with styrene is known (JP-A-57-33446 and JP-A-57-162135). However, if the content of styrene units is increased to exhibit a desired level of low hygroscopicity, the birefringence increases and the original excellent characteristics of the methyl methacrylate resin are lost, resulting in an optical element substrate (for example, optical disc substrate). However, since the heat resistance is not improved even when styrene is copolymerized, it cannot be used for applications requiring heat resistance higher than that of the methyl methacrylate resin.

On the other hand, there is known a technique of copolymerizing methyl methacrylate and cyclohexyl methacrylate in order to improve the hygroscopicity of a methyl methacrylate resin without increasing the birefringence too much (Japanese Patent Laid-Open No. 186241/1982). 58-127754, 58-154751, 59-1518, 60-1041
No. 10 bulletin). However, when the content of cyclohexyl methacrylate unit is increased in order to exert a desired level of low hygroscopicity, the heat resistance is remarkably lowered and becomes extremely brittle. As a result, it becomes difficult to record or read highly accurate information, or the optical disc is damaged during handling, which results in an undesired situation in which the use of the optical disc is significantly limited.

Further, an example in which 4-isopropylcyclohexyl acrylate and dicyclohexyl fumarate are copolymerized in addition to cyclohexyl methacrylate in order to improve the hygroscopicity of a methyl methacrylate resin without increasing the birefringence (JP-A-57- 186241) and an example in which 3,3,5-trimethylcyclohexyl methacrylate and isobornyl methacrylate are copolymerized (JP-A-60-104110). However, in these examples, although the hygroscopicity of the methyl methacrylate resin is improved, there is a problem that the obtained resin has low thermal deformation resistance, and mechanical strength and thermal stability are poor.

Furthermore, in order to improve both the hygroscopicity and heat resistance of the methyl methacrylate resin, a technique of copolymerizing methyl methacrylate with isobornyl methacrylate is known (JP-A-59-227909 and JP-A-60). -115605 publication). However, when the content of isobornyl methacrylate unit is increased in order to exert a desired level of low hygroscopicity, the content becomes significantly brittle, and therefore, the optical disc is damaged during handling, which limits its use as an optical disc substrate material. There is a problem that you cannot escape. Even when isobornyl methacrylate was copolymerized under the usual polymerization conditions of radical polymerization as described in the above-mentioned publication, a considerable amount of unreacted monomer remained in the obtained resin. It is extremely difficult to remove. When unreacted monomers remain in the resin, not only the heat resistance of the resin is significantly reduced, but also the thermal stability is significantly reduced. Therefore, even if an attempt is made to obtain a molded article from a resin containing a large amount of residual monomer, the molded article may be colored during molding, cannot be molded due to foaming, or may be molded, but the obtained molded article is colored. And the heat resistance is not as good as expected, so it is inevitable to be subject to application restrictions. Moreover, the resin obtained by copolymerizing isobornyl methacrylate is originally low in thermal stability, and for example, even in a resin in which the residual monomer is reduced by a purification method in which the obtained resin is dissolved in a solvent and reprecipitated, When performing high-temperature melt molding such as 280 ° C, which is used to obtain high pit reproducibility in injection molding for optical disk substrates, it is difficult to obtain good molded products because significant coloring and decomposition and foaming occur at the same time. .

Further, in order to simultaneously improve the hygroscopicity and heat resistance of a methyl methacrylate resin, an example in which bornyl methacrylate, 3,5-dimethyladamantyl methacrylate, and phenethyl methacrylate are copolymerized is disclosed (Japanese Patent Application Laid-Open No. Sho 61-96). 59-22
7909 publication). However, in this example, although the hygroscopicity of the methyl methacrylate resin is improved, the mechanical strength of the obtained resin is low and the thermal stability is poor,
When melt-molding at a high temperature such as 280 ° C, there is a problem that remarkable coloring and decomposition foaming occur.

(Problems to be Solved by the Invention) The present invention solves the above problems, has colorlessness, transparency, and thermal stability, is excellent in heat resistance, and is excellent in low mechanical strength while maintaining sufficient mechanical strength. The present invention provides a methacrylic copolymer having good flowability and low hygroscopicity, which exhibits hygroscopicity and further has excellent moldability, and therefore is suitable as a material for molded articles such as optical element substrates and light-transmitting extruded plates. is there.

In order to achieve this object, there is a report on a resin obtained by copolymerizing methyl methacrylate and at least tert-butylcyclohexyl methacrylate. (JP-A-63-017915, JP-A-63-017401) As a result of further diligent research on the above-mentioned copolymer, the present inventors have found a new copolymer that can sufficiently achieve the above-mentioned object. I arrived.

In tert-butylcyclohexyl methacrylate, depending on the position of the tert-butyl group attached to the cyclohexane ring,
There are three kinds of isomers, and each of them has a cis-form and a trans-form, and among these isomers, methacrylic acid-4-tert having a cis / trans ratio in a specific range.
-In butyl cyclohexyl copolymer, while maintaining the original transparency, mechanical strength and low birefringence inherent in methacrylic resin, the water absorption rate (center water absorption rate) is reduced by about 50% and heat resistance is improved. Then, they found that the moldability was extremely good, and completed the present invention.

In the development of optical disk base materials, it has been important to keep the moisture absorption warpage property low, but if we try to improve the moisture absorption warpage property, we must sacrifice molding processability, birefringence, and mechanical strength. The reality is that I have been troubled by a technical dilemma. Therefore, the present invention that solves such a technical dilemma and enables the water absorption to be suppressed to about 50% lower than that of methyl methacrylate resin is a breakthrough, and the present invention is an epoch-making one. It is expected to be useful not only as an optical element substrate but also as a material for other products such as a light-transmitting extruded plate, for which warpage has conventionally 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 methacrylic acid-4-tert-butylcyclohexyl unit whose cis isomer is 50% or more of the stereoisomer, and (B) methyl methacrylate unit of 60 to 98 Mol%, (C) formula (1) [In the formula, R ₁ is a hydrogen atom or a methyl group, R ₂ is a phenyl group,
Methyl-substituted phenyl group or (Z represents an alkyl group having 1 to 8 carbon atoms, which is unsubstituted or substituted with a fluorine atom), and is composed of 0 to 30 mol% of at least one ethylenically unsaturated compound unit (A) + (B) + (C)
= 100 mol%, and a good flowable low hygroscopic methacrylic copolymer, characterized in that the weight average molecular weight of the copolymer is in the range of 10 ⁴ to 10 ^7. It

In the methacrylic copolymer of the present invention, the content of 4-tert-butylcyclohexyl methacrylate unit whose cis isomer is 50% or more in the stereoisomers as the component (A) is (A), (B). And 2 to 30 mol% with respect to the total molar amount of the component (C), and when the amount of the component (A) is less than the above range, the low hygroscopicity and good moldability, which are the features of the present invention, are sufficiently exhibited Not done. If it exceeds the above range, the hygroscopicity and the heat resistance are improved, but the mechanical strength is lowered, which is not preferable. The preferred content of component (A) is 5 to 20 mol.
%.

The ratio of cis and trans of component (A) is 50 for cis.
% Or more. When the ratio of cis isomer is less than 50%, the effect of improving moldability is small.

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

The content of the methyl methacrylate unit as the component (B) is 60 to 98 mol% based on the total molar amount of the components (A), (B) and (C). If the amount is less than this range, transparency, moldability and low birefringence, which are inherent properties of methyl methacrylate, are deteriorated. If the amount exceeds this range, the low moisture absorption and heat resistance intended by the present invention are impaired. It is not preferable because it is sufficient. The preferred content of the component (B) is 70 to 94 mol%.

In the copolymer according to the present invention, if desired, (A)
An ethylenically unsaturated compound unit copolymerizable with the component and the component (B) can be contained as the component (C). Such an ethylenically unsaturated compound monomer has the formula (1) [In the formula, R ₁ is a hydrogen atom or a methyl group, R ₂ is a phenyl group,
Methyl-substituted phenyl group or (Z represents an alkyl group having 1 to 8 carbon atoms, which is unsubstituted or substituted with a fluorine atom)]. Examples of such monomers include alkyl acrylates such as methyl acrylate, ethyl acrylate, butyl actylate, isobutyl acrylate, 2-ethylhexyl acrylate; trifluoromethyl acrylate, 1,1,1 acrylate. Examples thereof include acrylic acid fluorinated alkyl esters such as 1-trifluoroethyl; and aromatic vinyl compounds such as styrene, α-methylstyrene and p-methylstyrene. By containing an ethylenically unsaturated compound unit as the component (C), thermal stability, fluidity at the time of molding, or hygroscopicity can be improved, but excessive use causes deterioration of heat resistance. Not preferable. The content of the component (C) is 0 to 30 mol%, preferably 2 to 20 mol% with respect to the total molar amount of the components (A), (B) and (C).

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

When solution polymerization is carried out, it is composed of 4-tert-butylcyclohexyl methacrylate, methyl methacrylate having a cis-form of 50% or more of stereoisomers, and optionally an ethylenically unsaturated compound of the formula (1). A solution prepared by dissolving the monomer mixture in a solvent of aromatic hydrocarbon such as toluene or ethylbenzene can be used. When polymerizing by suspension polymerization or emulsion polymerization, the polymerization can be performed using water as a medium. When polymerizing by bulk polymerization, the polymerization can be started by free radicals generated by ordinary heating or irradiation. The amount ratio of each component of the monomer mixture is substantially the same as the amount ratio of the monomer units of the target copolymers (A), (B) and (C). be able to.

As the initiator used when polymerizing the resin of the present invention, any initiator generally used in radical polymerization can be used, for example, an azo compound such as azobisisobutyronitrile, benzoyl peroxide,
Lauroyl peroxide, tert-butylperoxy-
Organic peroxides such as 2-ethylhexanoate are particularly preferred. The amount used is generally based on the total amount of monomers.
It is in the range of 0.01 to 10% by weight. When polymerizing the resin of the present invention, as the molecular weight regulator used as needed, any molecular weight regulator generally used in radical polymerization can be used, for example, butyl mercaptan,
Mercaptan compounds such as octyl mercaptan, dodecyl mercaptan and 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 to 120 ° C.
Is selected in the range. The optimum polymerization temperature is determined in consideration of a polymerization method, a polymerization apparatus, a polymerization initiator, a molecular weight regulator, characteristics of a copolymer resin obtained, and the like. After the polymerization is carried out for about 120 to 150 minutes, it is further cured for about 1 hour to obtain the copolymer of the present invention.

The weight average molecular weight of the copolymer according to the invention is in the range from 10 ⁴ to 10 ⁷ . It can take a relatively high weight average molecular weight of 10 ⁵ to 10 ⁷ in the case of obtaining a molded article such as a light transmissive plate by direct polymerization as casting method. When an injection molded product such as an optical disk substrate is targeted, it is usually in the range of 1 × 10 ⁴ to 2 × 10 ⁵ , preferably 5 × 10 ⁴ to 5 × 10 ⁴ .
It is 1.5 × 10 ⁵ , more preferably 5 × 10 ⁴ to 1 × 10 ⁵ . In this case, if the weight average molecular weight is less than 10 ⁴ , the mechanical strength decreases, and if it exceeds 2 × 10 ⁵ , the mold transfer accuracy during molding decreases. When an extrusion-molded product such as a light-transmissive extruded plate is used, the weight average molecular weight is in the range of 1 × 10 ^{5 to} 3 × 10 ⁵ , and more preferably 1.5 × 10 ^{5 to} 2.5 × 10 ^{5. Is 5} . In this case, if the weight average molecular weight is less than 1 × 10 ⁵ , sufficient mechanical strength and dimensional stability cannot be obtained, and if it exceeds 3 × 10 ⁵ , it will not be extruded under normal extrusion molding conditions, and it will be extruded at a high temperature. Then, thermal decomposition and coloring occur.

Here, the weight average molecular weight is measured by GPC (gel permeation chromatography) using standard polystyrene as a standard sample.

Methacrylic acid-4-tert constituting the copolymer of the present invention
-Butylcyclohexyl, methyl methacrylate or the content of each ethylenically unsaturated compound unit represented by the formula (1) copolymerizable therewith is determined by thermal decomposition gas chromatography and ¹³ C-NMR method (nuclear magnetic resonance method). ) Can be measured. ^{In the 13} C-NMR method, the copolymer was treated with a deuterated solvent [CDCl ₃ , C ₆ D ₆ , CD ₃ NO ₂ , DMSO (dimethyl
It can be quantified by dissolving it in sulfoxide) -d ₆ ] and performing spectral analysis of ¹³ C-nucleus at room temperature or high temperature.

The copolymer according to the present invention can be used alone, but does not impair the characteristics such as excellent transparency, moldability, low birefringence, thermal stability, low hygroscopicity and high heat resistance. Within the range, it may be used by blending with other resins such as polymethylmethacrylate, acrylonitrile-styrene copolymer, and methylmethacrylate-styrene copolymer.

When the copolymer according to the present invention contains a large amount of residual monomer, other than high heat resistance, which is one of the characteristics of the copolymer of the present invention, high thermal stability is impaired. The content of the residual monomer 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 made into a sufficiently low residual monomer for practical use by polymerizing under the above-mentioned ordinary polymerization conditions, but a copolymer having a remarkably low residual monomer content can be used. In order to obtain it, it is preferable to apply a usual residual monomer removal method. Examples of the method for removing the residual monomer include a method of heating the obtained copolymer under an air stream, a method of heating under reduced pressure, and a method of vent extruding under reduced pressure by an extruder with a vent.

Various properties of the resin can also be improved by adding generally known additives to the copolymer resin of the present invention as long as the excellent characteristics are not significantly impaired. For example, various antioxidants, heat stabilizers, UV absorbers, sequestering agents, lubricants, mold release agents, plasticizers, impact resistance improvers, antistatic agents, flame retardants, preservatives, dyes, pigments, etc. Can be added.

With the methacrylic copolymer resin of the present invention, various useful molded articles utilizing the properties of the copolymer of the present invention can be obtained by a molding method well known in the field of plastics technology.

A light-transmissive 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 melted by an extruder is processed into a flat plate by drawing it on a take-up roll whose temperature is appropriately controlled. The temperature conditions at the time of extrusion and withdrawal are selected depending on the characteristics of the extruded plate, the use, and the like. The light-transmissive extruded plate obtained by extrusion molding is, for example, a signboard, a display, a partition, a daylighting window, a TV front plate, a liquid crystal display front plate, etc., and has low hygroscopicity, heat resistance, transparency, thermal stability and mechanical properties. Since it is excellent in dynamic strength, etc., it exhibits high performance.

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

The copolymer resin of the present invention can be used to form various optical element substrates by injection molding or compression molding. However, injection molding is preferred in view of productivity, dimensional accuracy, and the like. As described above, the optical element base means the body base of the optical element. Specific examples of the optical element include, for example, an optical information recording disk (hereinafter, referred to as an optical disk), an optical information recording card, an optical information recording sheet, an optical information recording film, a lens, a mirror, and a prism. be able to. In addition, tail lamps and meter covers for automobiles can be advantageously obtained by injection molding.

An optical disc is obtained by injection-molding the methacrylic copolymer resin of the present invention using a disc-shaped mold having one side having minute irregularities, and then a substrate is obtained. Or by providing a protective film. As a method of obtaining a base, as described above,
In addition to injection-molding the methacrylic resin, it can be obtained by obtaining a flat plate by cast polymerization or extrusion and then compression-molding this flat plate, or directly by cast polymerization.

The optical disc is an optical information recording disc that records information by light or reads information recorded by light, and includes various types of discs such as a read-only disc, a write-once disc, and a rewritable disc. In addition to general discs that have a signal, or have fine irregularities that should become a signal on the surface of the substrate, in addition to discs that have a smooth substrate surface coated with a memory layer such as metal or dye, It also includes a magneto-optical disk in which the memory layer is a magnetic material.

As described above, the optical disk substrate obtained by molding the methacrylate copolymer of the present invention has excellent transparency, moldability, low birefringence, and thermal stability, which are the characteristics of methyl methacrylate resin. In addition, the hygroscopicity, which is a drawback of the methyl methacrylate resin, is significantly improved. When an optical disk substrate made of the copolymer resin of the present invention is used for a video disk substrate in which a methyl methacrylate resin is conventionally used, since the resin has low hygroscopicity, it can be used even in a high humidity condition.

In addition, when an optical disk substrate made of the copolymer resin of the present invention is used for a compact disk substrate in which a polycarbonate resin is conventionally used, the resin has low birefringence and good moldability, so that a more accurate disk can be easily manufactured. Is obtained.

In addition, the optical disk substrate of the present invention is preferably used for an optical disk having a large recording information amount, which is conventionally larger than a compact disk and has a large amount of recorded information, which is similar to a compact disk.

Furthermore, from video disk and compact disk,
Conventionally, optical disk substrates that fully satisfy all the characteristics required for write-once disks that require high accuracy, large amounts of information, or used under severe conditions, and rewritable disks including magneto-optical disks Although not obtained, an optical disk substrate made of the copolymer resin of the present invention can be preferably used for this purpose.

〔Example〕

The present invention is described by way of examples in order to describe the present invention in more detail, 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) Residual monomer A sample was dissolved in acetone containing n-butyl alcohol as an internal standard substance, and quantified by a temperature rising gas chromatography method.

(2) Component composition in the copolymer Nuclear magnetic resonance absorption (NMR) method The ¹³ C nucleus of a specific portion of each component of the copolymer was spectrally analyzed to determine the composition ratio. The measurement condition is that the sample copolymer is dissolved in DMSO-d ₆ and the temperature is 70 ° C.
The analysis was performed once in the quantitative mode.

Pyrolysis gas chromatography method The polymer was pyrolyzed at a furnace temperature of 450 ° C., and the decomposition gas was quantified by the gas chromatography method to determine the composition ratio.

(3) Weight average molecular weight (w) A bead-like polymer obtained by polymerization was dissolved in dichloromethane (50 mg / 30 ml) to prepare a sample solution, and Gel P was added.
ermeation Chromatography (GPC) measurement was performed. From the measurement results, the calibration curve obtained by measuring the molecular weight of standard polystyrene was converted into polymethyl methacrylate, and the weight average molecular weight was calculated.

(4) Tensile breaking strength Measurement was performed based on ASTM-D638. Test piece is 96 ° C
After annealing for 2 hours at, the condition was adjusted (48 hours at 23 ° C. and 52% relative humidity) for measurement.

(5) Heat deflection temperature (HDT) Measurement was performed based on ASTM-D648. Test piece is 96 ° C
After annealing for 2 hours at, the condition was adjusted (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-D1003.

(8) Birefringence With respect to a disc having an information mark on one surface, the birefringence was measured at a portion 50 mm from the center using a polarization microscope.

(9) Moisture absorption warpage property (i) Optical disk substrate A warp deformation test was performed on the optical disk substrate for 10 hours at a temperature of 50 ° C and a relative humidity of 90%. For the measurement of the warpage, a maximum warpage amount was obtained by measuring a distance between a center of the disk substrate and a plane passing through at least two points on the outer periphery of the disk substrate every time.

(Ii) Extruded plate Test the extruded plate cut into a size of 2 x 300 x 300 mm
Used as a piece, one side of which is Saran Cover with film, warm
In an atmosphere with a temperature of 50 ° C and a relative humidity of 90% for 48 hours.
Was. Next, warp deformation of this test piece (place a flat plate on a horizontal surface)
(The difference in height between the center and the midpoint of the side).

Example 1 Water 5 was placed in a glass separable flask having a content of 10;
Potassium polyacrylate 50, sodium hydrogen phosphate 1.
5 g was added and stirred at a temperature of 30 to 35 ° C to prepare an aqueous phase.
On the other hand, in a separate glass container, 4-tert-butyl cyclohexyl methacrylate [cis / trans isomer = 90/10 (w /
w)] 171g (4mol%), methyl methacrylate 1796g (94mo
1%) and 33 g (2 mol%) of methyl acrylate, and 3 g (0.15 parts by weight) of azobisisobutyronitrile, and n- with respect to the total weight of these monomers of 2000 g (100 parts by weight).
4 g (0.20 parts by weight) of octyl mercaptan was added to prepare a monomer phase.

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

Using a vent-type twin-screw extruder with a screw diameter of 30 mmφ, the obtained bead-like polymer was subjected to 230 ° C. and a vacuum degree of 730 mmHg.
As described above, the material was extruded into a strand and cut with a cutter to obtain a granular material (pellet).

A test piece was obtained by subjecting the obtained pellet to injection molding at 230 ° C. using a 3 oz screw injection molding machine. At this time, the minimum injection pressure (SSP) required to completely fill the mold was 650 Kg / cm ² . Tables 1 and 2 show the analysis results of the beaded polymer and the test piece obtained as described above.

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

Example 8 (optical disk substrate) The pellet obtained in Example 1 was molded by using a precision injection molding machine (M-200 / 800DM, manufactured by Meiki Seisakusho), and a 300 mmφ, 1.2 mm thick substrate with an information sign on one side. Got Injection molding temperature is 290 ℃, injection pressure, injection speed is high,
Performed at high speed.

This substrate was fixed on a vapor deposition device, aluminum was vapor-deposited under a vacuum of 10 ^-8 mmHg, and a UV-coated protective coating (coated with acrylic resin and cross-linked by ultraviolet irradiation) was used to create a single-sided vapor-deposited substrate. did. The birefringence and moisture-absorbing warpage of this single-sided vapor-deposited substrate were measured. The results are shown in Table 3.

Examples 9 to 14 (optical disk substrate) Using the pellets obtained in Examples 2 to 7 respectively, an optical disk was prepared in the same manner as in Example 8, and the birefringence and the moisture absorption warpage were measured. The results are shown in Table 3.

Example 14 (Extruded plate) Polymerization was performed in the same manner as in Example 1 except that the addition amount of N-octyl mercaptan was changed to 0.16 parts by weight in Example 1, a bead-shaped polymer was obtained, and the bead-shaped polymer was further placed in an extruder. To obtain pellets. Using this pellet, the melt viscosity at 270 ° C and a shear rate of 100 sec ^-1 was determined.
It was 20 ° C poise. Next, the pellets were extruded at a temperature of 230 ° C. and a degree of vent vacuum of 730 mmHg or more using a vent-type twin screw extruder with a screw diameter of 30 mmφ equipped with a plate die, and the extruded resin melt was heated to 120 ° C. or more. Then, an extruded plate having a colorless, transparent, and good appearance was obtained by drawing the film on a take-up roll heated to a temperature of 1 mm. With respect to this extruded plate, the moisture absorption warpage property was measured. The results are shown in Table 4.

Examples 16 to 21 (extruded plate) Polymerization was carried out in the same manner as in Example 1 except that the monomer composition and the amount of the molecular weight modifier (n-octyl mercaptan) added were changed as shown in Table 4. Under the same conditions as in Example 15, the melt viscosity of the pellets and the hygroscopic warpage of the extruded plate were measured.
The results are shown in Table 4.

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

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

Comparative Examples 9 to 16 Polymerization was carried out in the same manner as in Example 1 except that the monomer composition and the addition amount of the molecular weight modifier were changed as shown in Table 7.
The melt viscosity of the pellet was measured under the same conditions as in Example 15.
The results are shown in Table 7.

[Effects of the Invention] The methacrylic copolymer of the present invention has excellent transparency, low birefringence, and thermal stability, which are features of the methyl methacrylate resin, and also has a drawback of the methyl methacrylate resin, which is the moisture absorption. It is a novel resin whose properties, heat resistance and moldability are greatly improved without sacrificing mechanical strength. Since the methacrylic copolymer has such excellent characteristics, the molded product can be advantageously used in various applications, particularly for optical information recording discs (optical discs) and optical information recording discs. As an optical element substrate such as a card, an optical information recording sheet, an optical information recording film, a lens, a mirror, a prism, an optical transmission fiber, or a signboard, a display, a partition, a lighting window, a television front plate, a liquid crystal display device. It is suitable for use as a light-transmissive plate used as a front plate or the like.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location (C08F 220/14 220: 18 212: 08) (C08F 220/14 220: 18 220: 22)

Claims (1)

(57) [Claims] 1. (A) 2 to 30 mol% of methacrylic acid-4-tert-butylcyclohexyl unit whose cis isomer is 50% or more of stereoisomers, and (B) methyl methacrylate unit of 60 to
98 mol%, (C) formula (1) [In the formula, R ₁ is a hydrogen atom or a methyl group, R ₂ is a phenyl group,
Methyl-substituted phenyl group or (Z represents an alkyl group having 1 to 8 carbon atoms which is unsubstituted or substituted with a fluorine atom)] and is composed of 0 to 30 mol% of at least one ethylenically unsaturated compound unit, and (A) + (B) +
(C) = 100 mol% copolymer, and the weight average molecular weight of the copolymer is in the range of 10 ⁴ to 10 ⁷ , a good flowable low hygroscopic methacrylic copolymer. .