JPH0772213B2 - Method for producing methacrylic resin - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a methacrylic resin. More specifically, the present invention relates to a method for producing a colorless and transparent methacrylic resin, which has excellent molecular homogeneity and high optical purity, which is preferably used in the optical field of lenses, optical disks, optical fibers and the like. Is.

[0002]

BACKGROUND OF THE INVENTION Methacrylic resins are widely used in, for example, lighting fixtures, signboards, various ornaments and nameplates because of their excellent transparency, good mechanical properties, processability, and beautiful appearance of molded products. Besides, it is also used for automobile parts and tableware.

By the way, recently, this methacrylic resin has begun to be used in optical fields such as lenses, optical disks, and optical fibers. Therefore, in addition to the above-mentioned characteristics, in order to improve optical purity, for example, reduction of minute foreign matters, residual monomer, etc. There is a demand for reduction of volatile components such as, and minimization of high molecular weight gel.

Conventionally, a methacrylic resin has been produced as a molding material by polymerizing methyl methacrylate or a component copolymerizable therewith by an aqueous suspension method or an aqueous emulsion method. However, the methacrylic resin obtained by such a method contains impurities,
Mixing of polymerization aids and foreign substances is unavoidable, and further, burns and kogation are likely to occur in the pelletizing process,
It cannot be said that it is necessarily excellent in optical purity, and in addition, since it is molecularly inhomogeneous, it has drawbacks such as cloudiness or turbidity occurring in the molded product.

Therefore, as a method for improving such a defect, for example, a continuous bulk polymerization method (continuous bulk polymerization method) or a continuous solution polymerization method has been tried. However, the methacrylic resin obtained by the continuous polymerization method has hitherto been used. However, even if the homogeneity of the molecule is improved, satisfactory results have not always been obtained for the improvement of optical purity.

By the way, a method of removing volatile components such as unreacted monomers, solvents and by-products from a reaction composition produced by bulk polymerization or solution polymerization to obtain a highly pure molding material has hitherto been mainly used. Studies are proceeding mainly on styrene-based resins (Japanese Patent Publication No. 35-8557 and No. 38, 38).
-120 gazette, the same 44-20097 gazette, the same 45-
No. 31678, No. 47-27872, etc.) and a few methacrylic resins are known (Japanese Patent Publication No. 52-17555 and No. 50-88197). Gazette). However, in the methods for these methacrylic resins, there is a problem that the obtained resin is significantly deteriorated and colored due to long-term residence at high temperature, and there are many side reaction products. I can't get it.

[0007]

The present inventors have previously found a method for producing a methacrylic resin optical fiber having excellent optical purity. However, this method does not always reduce volatile components and improve yellowness. It wasn't satisfactory.

Under these circumstances, the object of the present invention is to provide an excellent methacrylic compound which is excellent in the homogeneity of molecules, has a small amount of fine foreign matters, volatile components, high molecular weight gels, etc., and has a high optical purity, and is colorless and transparent. It is to provide a method for producing a resin.

[0009]

Means for Solving the Problems As a result of intensive studies to develop a methacrylic resin having excellent molecular homogeneity and optical purity, the present inventors have found that a monomer solution having a specific composition can be obtained by a specific means. Treatment to reduce the amount of dissolved oxygen in the solution to 1 ppm
After the following, and after removing the fine foreign matter, this monomer solution was continuously supplied to the reaction zone, polymerization was carried out so that the polymer concentration in the reaction zone was a predetermined value, and then obtained It was found that the object can be achieved by heating the reaction composition under a specific condition to remove volatile components, and the present invention has been completed based on this finding.

That is, in the present invention, methyl methacrylate monomer alone or 85% by weight or more of methyl methacrylate and 15% by weight or less of methyl acrylate or ethyl acrylate are used in the presence of a free radical generating catalyst and a chain transfer catalyst. An inert gas was introduced into a monomer solution composed of the monomer mixture and 10 to 25% by weight based on the weight of the entire reaction mixture of an inert polymerization solvent to reduce the amount of dissolved oxygen in the solution to 1 ppm or less. Then, this solution is filtered through a filter of 0.5 μm or less, and then continuously fed to the reaction zone so that the polymerization conversion rate of the monomer becomes substantially constant within the range of 40 to 65%.
GPC, characterized in that polymerization is carried out at a temperature of 120 to 160 ° C., then the obtained reaction composition is heated to a temperature of 200 to 290 ° C., introduced into a reduced pressure zone, and devolatilized.
The molecular weight (Mw) measured by 70,000 to 150,000, the thermal decomposition index is 3.0 or less, and 0.5 to 2 measured by a fine particle counter.
It is intended to provide a method for producing a methyl methacrylate homopolymer or a methyl methacrylate copolymer having 5 μm of minute foreign matters of 10,000 / g polymer or less and ΔYI of 6.00 or less measured by a color difference meter.

The present invention will be described in more detail below. The methacrylic resin obtained by the method of the present invention is a methyl methacrylate homopolymer or a methyl methacrylate copolymer containing 15% by weight or less of methyl acrylate units or ethyl acrylate units.
It is a methyl methacrylate copolymer containing 88 to 99% by weight of a methyl methacrylate unit and 12 to 1% by weight of a methyl acrylate unit or an ethyl acrylate unit. In this copolymer, the methyl methacrylate unit and the methyl acrylate unit or the ethyl acrylate unit are composed of random bonds, and the methyl methacrylate unit improves heat resistance and mechanical strength properties. Yes, on the other hand, methyl acrylate units and ethyl acrylate units are
It is intended to improve the fluidity and thermal decomposability of this resin during molding.

This methyl methacrylate homopolymer or copolymer has a weight average molecular weight (Mw) of 70,000 to GPC (gel permeation chromatography).
It must be in the range of 150,000, preferably 80,000 to 120,000. If the molecular weight is less than 70,000, the molded product is fragile and cannot withstand industrial use. On the other hand, if it has a molecular weight of more than 150,000, the fluidity at the time of melting is significantly lowered and the birefringence of the molded product is increased. Is not preferable.

The content of volatile components in the resin is preferably 1000 ppm or less for dimers of polymerization by-products, and 2500 ppm or less for residual monomers such as unreacted monomers and thermal decomposition products. It is necessary to be.
If the content of the dimer exceeds 1000 ppm, the heat-deformation resistance of the obtained molded article is lowered, and the practical use range is narrowed, which is not preferable. Further, when the residual monomer content exceeds 2500 ppm, when molding is carried out at a high temperature, the surface of the obtained molded product is damaged, such as the occurrence of silver streaks, which makes it impractical. This monomer or dimer is generally difficult to remove because the vapor pressure is relatively high when the polymer is removed by decompression treatment in a molten state. Although there is an unfavorable tendency to decompose to form a monomer, this resin preferably reduces the volatile components to the above range. In such a resin, the content of dimer and residual monomer in the resin is usually 1
It is in the range of 0 to 1000 ppm and 500 to 2500 ppm.

Further, regarding the thermal decomposition resistance of the resin obtained by the method of the present invention, it is necessary that the thermal decomposition index α is 3.0 or less. If this value exceeds 3.0, the thermal decomposition resistance becomes inferior, gas is generated strongly during high temperature injection molding, and there is a problem that the application range of the resin is unavoidably limited. In particular, when it is used for a disc, it is not preferable because the generated gas hinders the transfer of the recording signal and remarkably deteriorates the quality of the disc.

Regarding the content of fine foreign matter in the resin obtained by the method of the present invention, it is necessary that the fine foreign matter of 0.5 to 25 μm measured by a fine particle counter is 10,000 or less / g polymer. If it exceeds 10,000 units / g polymer, the transmission loss of light becomes large and it cannot be used.

The resin obtained by the method of the present invention is excellent in colorless transparency and has a ΔYI measured by a color difference meter.
(Yellow index based on air) is 6.0 or less. If this value exceeds 6.0, the yellowness of the resin will be increased and the light transmittance will be significantly reduced.

In a preferred embodiment of the method of the present invention,
First, in the presence of a free radical generating catalyst and a chain transfer catalyst, methyl methacrylate monomer alone or methyl methacrylate 85
More than weight% and methyl acrylate or ethyl acrylate 1
A monomer solution is prepared consisting of up to 5% by weight of the monomer mixture and 10-25% by weight of the inert polymerization solvent, based on the weight of the total reaction mixture.

As the above-mentioned inert polymerization solvent, a solvent which can adjust the molecular weight of the resin to be produced in the range of 70,000 to 150,000 is used. Preferred solvents include ethylbenzene and methyl isobutyl ketone, with ethylbenzene being particularly preferred. The amount of this solvent used is selected in the range of 10 to 25% by weight based on the weight of the total reaction mixture. If this amount is less than 10% by weight, the viscosity of the weight reaction system is high and it is difficult to control the weight reaction.
If it exceeds, the load on the devolatilization step increases sharply, which is not industrially preferable.

The above-mentioned free radical generating catalyst is a polymerization initiator which generates a free radical.
Organic peroxides such as benzoyl peroxide, cumene hydroperoxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, and azo initiators such as 1,1- Azobis (1-
Cyclohexanecarbonitrile), 2,2-azobis (2,4,4-trimethylpentane) and the like can be used, but 3,3,5-trimethylcyclohexane-di-t-butyl peroxide is particularly preferable. The amount of these free radical generating catalysts used is preferably in the range of 0.001 to 0.03% by weight based on the weight of the entire reaction mixture.

On the other hand, as the chain transfer catalyst, mercaptans, particularly butyl mercaptan, octyl mercaptan, dodecyl mercaptan and the like are preferable, and the amount of these chain transfer catalysts is usually 0.1 to 0 based on the weight of the whole reaction mixture. It is selected within the range of 0.5% by weight.

Next, an inert gas is introduced into the thus-prepared monomer solution to adjust the amount of dissolved oxygen in the solution to 1
Keep it below ppm. When the amount of dissolved oxygen exceeds 1 ppm, the colorless transparency of the resin obtained is impaired. There is no particular limitation on the method for reducing the amount of dissolved oxygen in the monomer solution to 1 ppm or less, but it is preferable to continuously supply the solution to a countercurrent contact tower to feed an inert gas such as nitrogen gas. It is desirable to use a method in which the dissolved oxygen is expelled into the inert gas stream by utilizing gas-liquid equilibrium and is effectively removed by the flow contact. Dissolved oxygen is reduced to 1 by the inert gas bubbling method in the feed tank that is usually performed.
It is difficult to reduce to below ppm,
Since the limit is about ppm, it is not preferable.

In the present invention, after the amount of dissolved oxygen in the monomer solution is reduced to 1 ppm or less in this way,
It is necessary to filter the solution with a filter of 0.5 μ or less. As the filter, for example, an Enflon filter (MCY 4463FRE) manufactured by Pall Ltd. is preferably used. The polymer obtained by such filtration treatment has a particle count of 0.5 measured by a fine particle counter.
The content of minute foreign matter of ˜25 μ is 10,000 pieces / g polymer or less.

Next, the monomer solution which has been subjected to the above-mentioned dissolved oxygen removal treatment and minute foreign matter removal treatment is continuously supplied to the reaction zone, and the polymerization conversion rate of the monomer is in the range of 40 to 65%. Polymerization is carried out at a temperature in the range of 120 to 160 ° C. so that it is substantially constant within. When the conversion rate is less than 40%, the load of the devolatilization step due to volatile components is large, and in particular, volatilization may be insufficient due to the restriction of the heat transfer area of the preheater,
On the other hand, when it exceeds 65%, the pressure loss of the piping from the polymerization reactor to the preheater becomes large, and it becomes difficult to transport the reaction composition, which is not preferable. If the polymerization temperature is less than 120 ° C, the reaction rate is too slow to be practical, and if it exceeds 160 ° C, the reaction rate is too fast, and it becomes difficult to control the polymerization conversion rate, and side reactions occur, or the product is colored. Is not preferred.

The polymerization pressure is not particularly limited, and the reaction may be carried out under normal pressure or under pressure, but when the reaction is carried out under pressure, 4.0 kg /
A pressure of cm ² or less is preferred. The stirring of the reaction solution depends on the shape and size of the polymerization reactor, the viscosity of the reaction solution, etc., but it is preferable to use a double helical ribbon or a pitched paddle type stirring blade.

In the method of the present invention, in order to remove the volatile components in the reaction composition obtained by such a polymerization reaction, the reaction composition is heated to a temperature of 200 to 290 ° C.
After removing the volatile components, the volatile components can be further reduced by feeding them to a devolatilization tank under a reduced pressure with a sufficient space above.

By the way, a conventional method for obtaining a polymer product by removing volatile components such as unreacted monomer, solvent and by-products of polymerization reaction from the reaction composition is to vacuum the reaction composition while heating it to a high temperature. It is a method of introducing into the atmosphere and performing volatilization separation. If the volatile component is less than 10% by weight,
It can be efficiently separated by a twin-screw extruder with multi-stage pent, and the volatile component remaining in the finally obtained methacrylic resin is 1.0 wt% or less, and methacrylic resin molding with good physical properties. The material or extruded plate can be obtained.

When the amount of volatile components is more than 10% by weight, when a multi-stage vented extruder is used, the foaming of the resin is severe due to the gasification of the volatile components and the vent holes are clogged with the foamed polymer. Often occurs, the colorless and transparent properties of the obtained resin are significantly impaired, the yellowness is particularly increased, and it is difficult to perform stable operation for a long time.

When a multi-stage vented extruder is not used, it is difficult to raise the temperature of the polymer composition and, in addition, a method for conveying a high-viscosity fluid after removing volatile components, and further, a high temperature and long time Problems such as polymer deterioration and side reaction products due to retention over time occur.

Degradation of the polymer due to long-term residence at high temperature, coloring, and side reaction products are fatal defects for the methacrylic resin excellent in optical purity which is the object of the present invention.

According to the method of the present invention, the reaction composition containing a large amount of volatile components can be efficiently heated, and vacuum flushing can be performed while giving a stable flow state, whereby the volatile components can be efficiently removed. .

In the method of the present invention, 20 parts of the reaction composition are used.
The volatile components are removed simultaneously with heating at a temperature in the range of 0 to 290 ° C, preferably 220 to 270 ° C. At this time, it is preferable to use a flat plate type preheating plate. If the heating temperature is lower than 200 ° C, the fluidity of the reaction composition is low and the volatile components are not sufficiently removed. If the heating temperature exceeds 290 ° C, the polymer is thermally deteriorated.

The reaction composition thus heated is passed through a narrow outlet formed in the gap between the heating plates to a devolatilization tank having a sufficient space in the upper part thereof which is maintained in a high vacuum state. be introduced. The function of the narrowed outlet is, firstly, to cause a pressure loss required at the boundary between the polymerization reaction region and the devolatilization region, and secondly to increase the flow rate of the reaction composition released. Is mentioned.

In the method of the present invention, the devolatilization condition is particularly important from the viewpoint of the color tone of the resin, and it is necessary to avoid conditions of high temperature and long time as much as possible.

The reaction composition introduced into the devolatilization tank kept in a high vacuum state causes an instantaneous volatilization of the volatile components and thereby foaming to form an extremely large evaporation area and efficiently and in a short time. The volatile components are removed at.

As the conditions in this devolatilization tank, a heating temperature and a vacuum degree are required so that the residual volatile components in the reaction composition can be reduced to a desired content, and the optimum conditions are a temperature of 220 to 250 ° C. , Vacuum degree is 20-100
It is selected in the Toll range.

In the devolatilization tank, the viscosity of the composition changes from several thousand poises to tens of thousands poises and becomes extremely viscous, but the residence time is usually about 1 to 20 minutes. When the residence time becomes long, the resulting resin is liable to be colored and deteriorated, and it becomes difficult to obtain a resin having excellent optical purity for the purpose of the present invention.

The devolatilized polymer is discharged by a gear pump installed below the devolatilization tank. As a result of such devolatilization treatment, the polymer becomes 1000
It will contain less than ppm dimer and less than 2500 ppm residual monomer.

By the manufacturing method as described above,
(1) The molecular weight (Mw) measured by GPC is 70,000 to 15
(2) 1000 ppm or less of dimer as a volatile component and 2500 ppm or less of residual monomer, (3) Pyrolysis index α of 3.0 or less, (4) 0.5-25 μm fine foreign matter measured by a fine particle counter. Of less than 10,000 / g polymer and (5) ΔYI of 6.00 or less measured by a color difference meter can be easily obtained.

[0039]

The methacrylic resin obtained by the method of the present invention is a methyl methacrylate homopolymer or a copolymer of methyl methacrylate and methyl acrylate or ethyl acrylate, and has excellent molecular homogeneity, and It has excellent characteristics such as high optical purity and being colorless and transparent, and is preferably used particularly in the optical field of lenses, optical disks, optical fibers and the like.

[0040]

EXAMPLES The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto. The properties of the polymer were determined as follows.

(1) Measurement of molecular weight by GPC Measurement was carried out according to the method described on pages 97 to 122 of "Gel chromatography (basic edition)" (published by Kodansha). That is, two HSG-20, 50 [manufactured by Shimadzu Corporation] were used as columns, and a calibration curve was prepared using standard polystyrene manufactured by Plessia Chemical Co., Ltd.
Was dissolved in 30 ml of methyl ethyl ketone, the elution curve obtained was equally divided, the height at the divided point was measured, and Mw was calculated by the following equation.

[0042]

[Equation 1]

However, Hi is the height of the elution curve at the dividing point, Mi (p) is the molecular weight of standard polystyrene at the dividing point i, and Qm and Qp are the Q factors of the copolymer and polystyrene, which are 40 and 41, respectively. .

(2) Measurement of Pyrolysis Index α Using pyrolysis gas chromatography, the polymer is decomposed at 450 ° C. under N 2 atmosphere, and the total decomposition gas decomposed in 60 minutes is detected and integrated, which is designated as X, The gas decomposed and generated at 270 ° C. for 30 minutes was integrated, and this was defined as Y, and α was calculated with the thermal decomposition index α = (Y / X) × 100.

(3) Measurement of minute foreign matter (using HIAC-ROYCO) 5 g of the polymer was weighed and dissolved in 30 ml of dichloroethane, and the scattering of laser light was detected by a counter previously calibrated to give 0.5 to 25μ particles were measured.

(4) Measurement of ΔYI by color difference meter 5 ounces of resin was molded using an injection molding machine, and 15 × 22
A test piece of 5 × 3 mm was obtained. The test piece was set in a color difference meter manufactured by JASCO Corporation, and the YI value in the long optical path (225 mm) direction was measured.

Example 1 As a polymerization feed liquid, 78% by weight of methyl methacrylate, 2% by weight of methyl acrylate, 20% by weight of ethylbenzene, 1,1-bis (t-butylperoxy) -3,
A material containing 150 ppm of 3,5-trimethylcyclohexane and 2500 ppm of octyl mercaptan was used, and this solution was continuously supplied to a nitrogen-feed liquid countercurrent contact tower (nitrogen-feed ratio = 1/50 wt%) to obtain a raw material. After adjusting the concentration of oxygen dissolved in the feed liquid to 0.55 ppm, a filter manufactured by Pall Co., Ltd. (particle cut rate of 0.5 μm or more: 85%) was used to measure 0.5-25 ppm in the feed liquid.
The fine particles of μ were reduced to 300 particles / (feed liquid 1 ml) to obtain a high-purity feed liquid.

The attached drawing is a flow sheet of an apparatus used for polymerizing and devolatilizing this high-purity feed liquid. That is, in this figure, the high-purity feed liquid was supplied to the polymerization reaction tank 1, the polymerization temperature was 135 ° C., the polymerization pressure was 1.3 kg / cm ² , the monomer conversion rate was 62.5%,
Polymerization was carried out under the condition that the solid component content of the polymerization system was 50% by weight, and 50% by weight of methacrylic resin having a weight average molecular weight (Mw) of 100,000 measured by GPC, unreacted monomer, initiator and chain transfer. A reaction composition containing the residue of the agent, the decomposed product, and 50% by weight of the solvent was obtained.

Then, the reaction composition was constantly taken out by the metering pump 2, heated to 260 ° C. by the heating plate 3 and cast into the devolatilization tank 4 through the gap between the heating plates. The devolatilization tank was maintained at 30 Torr and 200 ° C. to remove residual volatile components. 22 residual dimers in the polymer
ppm and residual monomer 10 ppm. This polymer was extruded through an extrusion die 5. The residual monomer of the obtained pellet was 2500 ppm, and the residual dimer was 20 ppm. Next, this pellet was molded by a 3 ounce injection molding machine to prepare a test piece. The appearance of this product is colorless and transparent, 4000 fine foreign matters per gram of polymer, ΔYI of 4.52 measured by a color difference meter, and thermal decomposition index α of 2.
It was 1.

Examples 2 to 6 The same operation as in Example 1 was carried out except that the conditions in Example 1 were changed as shown in the following table. The results are shown in the table below.

[0051]

[Table 1]

Example 7 The same operation as in Example 1 was carried out except that the dissolved oxygen concentration was changed to 1 ppm. The ΔYI of the obtained test piece was 5.55 and the thermal decomposition index α was 2.12.

Comparative Example 1 The procedure of Example 1 was repeated except that the concentration of dissolved oxygen was changed to 40 ppm. The obtained test piece has a ΔYI of 13.55 and a thermal decomposition index α of 3.66.
Met.

Comparative Example 2 The reaction composition obtained in Example 1 was constantly taken out by a metering pump 2 and supplied to a twin-screw devolatilizing extruder.
The extrusion temperature was 260 ° C to 280 ° C, the amount of gas generated from the reaction composition was very large, polymer clogging occurred in the first vent and the second vent, and stable devolatilization extrusion was difficult.

Example 8 The same operation as in Example 1 was carried out except that the polymerization conversion rate of the monomer in Example 1 was changed to 65% by weight. The residual dimer of the polymer before forming the pellet was 35 ppm, the residual monomer was 10 ppm, the residual dimer of the pellet was 15 ppm, and the residual monomer was 2300 ppm. Further, the appearance of the test piece was colorless and transparent, and 4100 fine foreign matters per 1 g of the polymer, ΔYI measured by a color difference meter were 4.55, and thermal decomposition index α was 2.0.

Comparative Example 3 The same operation as in Example 1 was carried out except that the polymerization conversion rate of the monomer was changed to 75% by weight in Example 1, and the reaction composition was constantly extracted with a metering pump. Was difficult to obtain, the amount of withdrawal was constantly changing, and the colorless and transparent test piece obtained as a result was impaired, and ΔYI was 23.0.

Comparative Example 4 The same operation as in Example 1 was carried out except that the operation for reducing fine particles using a filter was not carried out in Example 1. The amount of fine foreign matter per 1 g of the obtained polymer is 3,400.
It was 0.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an example of a polymerization and devolatilization step in producing a methacrylic resin by the method of the present invention.

[Explanation of symbols]

 1 polymerization reaction tank 2 metering pump 3 heating plate 4 devolatilization tank 5 extrusion die

Claims (1)

[Claims] 1. A free radical generating catalyst and chain transfer in continuously polymerizing methyl methacrylate monomer alone or methyl methacrylate monomer and methyl acrylate monomer or ethyl acrylate monomer. In the presence of a catalyst, methyl methacrylate monomer alone or methyl methacrylate 85
More than weight% and methyl acrylate or ethyl acrylate 1
5% by weight or less of the monomer mixture, and 10 to 25% by weight based on the weight of the total reaction mixture of a monomer solution of an inert polymerization solvent, an inert gas is introduced into the solution, and dissolved oxygen in the solution is introduced. After adjusting the amount to 1 ppm or less, this solution was filtered through a filter of 0.5 μ or less and continuously supplied to the reaction zone, and the polymerization conversion rate of the monomer was substantially within the range of 40 to 65%. Polymerization was carried out at a temperature of 120 to 160 ° C. so as to be constant, and then the obtained reaction composition was added to 200 to 2
The molecular weight (Mw) measured by GPC is 7 which is characterized in that it is heated to a temperature of 90 ° C., introduced into a reduced pressure zone, and devolatilized.
10,000 to 150,000, thermal decomposition index α is 3.0 or less, and 0.5 to 25μ fine foreign matter measured by a fine particle counter is 10,000 / g
A method for producing a methyl methacrylate homopolymer or a methyl methacrylate copolymer having a polymer or less and a ΔYI measured by a color difference meter of 6.00 or less.