JPH0762721B2 - Optical material - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical material composed of a methacrylic resin, and more specifically, the present invention relates to molecular homogeneity suitable as a material for lenses, optical disks, optical fibers and the like. Excellent,
The present invention relates to an optical material made of a colorless and transparent methacrylic resin having high optical purity.

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

By the way, this methacrylic resin has recently begun to be used as an optical material for lenses, optical discs, optical fibers and the like. Therefore, in addition to the above-mentioned characteristics, for example, reduction of minute foreign matters and volatilization of residual monomers in order to improve optical purity. There are demands for reduction of components and minimization of high molecular weight gel.

Conventionally, a methacrylic resin is usually 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 cannot avoid the inclusion of impurities, polymerization aids, foreign substances, and the like, and moreover, in the pelletizing step, burns and kogation are likely to occur, and the optical purity is not always required. However, since it is molecularly inhomogeneous, it has the drawback that cloudiness or turbidity occurs in the molded product.

Therefore, as a method for improving such a defect, for example, a continuous bulk polymerization method (continuous bulk polymerization method) and a continuous solution polymerization method have been tried, but the methacrylic resin obtained by the continuous polymerization method has been 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, from the reaction composition produced by bulk polymerization or solution polymerization, volatile components such as unreacted monomers, solvents and by-products are removed to obtain a highly pure molding material. Studies are being conducted mainly for resin (Japanese Patent Publication Nos. 35-8557, 38-120 and 44-2).
No. 97, No. 45-31678, JP-A No. 47-27872, etc.), and methacrylic resin is only a few
Is only known (Japanese Patent Publication No. 52-17555,
JP-A-50-88197, etc.). 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.

Problems to be Solved by the Invention The present inventors have previously found a method for producing a methacrylic resin optical fiber having excellent optical purity, but this method is not necessarily used for reducing volatile components and improving yellowness. It wasn't satisfactory.

Under these circumstances, the object of the present invention is to obtain an excellent methacrylic resin that is excellent in molecular homogeneity, has a small amount of fine foreign matters, volatile components, high molecular weight gel, etc., and has high optical purity, and is colorless and transparent. To provide an optical material.

Means for Solving the Problems The inventors of the present invention have conducted diligent research to develop a methacrylic resin having excellent molecular homogeneity and optical purity, and as a result, treat a monomer solution having a specific composition with a specific means. Then, the dissolved oxygen amount in the solution to 1ppm or less, and after removing the fine foreign matter, continuously supply this monomer solution to the reaction zone,
Polymerization is carried out so that the polymer concentration in the reaction zone becomes a predetermined value, and then the obtained reaction composition is heat-treated under specific conditions to remove volatile components, thereby achieving the object. Based on this finding, the present invention has been completed.

That is, the present invention is selected from a methyl methacrylate homopolymer and a methyl methacrylate copolymer containing 15% by weight or less of a methyl acrylate unit or an ethyl acrylate unit, and (1) a molecular weight measured by GPC. (Mw) 70,000-1
50,000, (2) Dimer 1000ppm or less as volatile component and residual monomer 2500ppm or less, (3) Thermal decomposition index α3.0 or less,
(4) 0.5 to 25μ fine foreign matter measured by a fine particle counter 10,000 or less / g polymer and (5) Δ measured by a color difference meter
An optical material comprising a methacrylic resin having a YI of 6.00 or less is provided.
For example, in the presence of a free radical generating catalyst and a chain transfer catalyst, methyl methacrylate monomer alone or methyl methacrylate
85% by weight or more and methyl acrylate or ethyl acrylate
To a monomer solution consisting of 10 to 25% by weight of an inert solvent based on the weight of the monomer mixture with 15% by weight or less and the total reaction mixture, an inert gas was introduced to adjust the amount of dissolved oxygen in the solution. 1 ppm
After making the following, after filtering this solution with a filter of 0.5μ or less, it is continuously fed to the reaction zone, so that the polymerization conversion rate of the monomer becomes substantially constant within the range of 40 ~ 65%. To
Polymerization is carried out at a temperature of 120 to 160 ° C., then the resulting reaction composition is heated to a temperature of 200 to 290 ° C. and introduced into the reduced pressure zone, and the dimer content is 1000 ppm or less and the residual monomer content is 2500 ppm or less. It can be manufactured by devolatilizing until it becomes.

Hereinafter, the present invention will be described in more detail.

The methacrylic resin used as the optical material of the present invention is selected from methyl methacrylate homopolymers and methyl methacrylate copolymers containing 15% by weight or less of methyl acrylate units or ethyl acrylate units, but preferred. What is a methyl methacrylate copolymer containing 88 to 99% by weight of methyl methacrylate units and 12 to 1% by weight of methyl acrylate units or ethyl acrylate units. 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 characteristics. On the other hand, the methyl acrylate unit and the ethyl acrylate unit improve the fluidity and thermal decomposability of the resin during molding.

These methyl methacrylate homopolymers or copolymers are GPC (Gel Permeation Chromatography)
It is necessary that the weight average molecular weight (Mw) measured by the method is in the range of 70,000 to 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.

Further, the content of volatile components in the resin is required to be 1000 ppm or less for the dimer of the polymerization by-product and 2500 ppm or less for the residual monomer such as unreacted monomer or thermal decomposition product monomer. If the content of the dimer exceeds 1000 ppm, the heat-deformation resistance of the obtained molded article is deteriorated 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 silver streaks, and the surface becomes impractical. This monomer or dimer
Generally, when removing a polymer by depressurizing it in a molten state,
Since its vapor pressure is relatively high, it is difficult to remove it, and by heating and melting, there is an unfavorable tendency that the methacrylic resin is thermally decomposed to produce a monomer, but the optical material of the present invention is The volatile component is reduced to the above range. In the optical material of the present invention, the content of dimer and residual monomer in the resin is usually 10 ~
It is in the range of 1000 ppm and 500 to 2500 ppm.

Furthermore, regarding the thermal decomposition resistance of the optical material of the present invention, it is necessary that the thermal decomposition index α is 3.0 or less. This value is
If it 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 restricted. 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 optical material of the present invention, the fine foreign matter of 0.5 to 25 μ measured with a fine particle counter is 10,000 pieces / g.
It is necessary that the amount is not more than the polymer, and if it exceeds 10,000 pieces / g polymer, light transmission loss becomes large and it cannot be used.

Further, the optical material of the present invention is excellent in colorless transparency and has a ΔYI (yellow index based on air) measured by a color difference meter of 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.

Suitable methods for producing the resin of the present invention include, for example, in the presence of a free radical generating catalyst and a chain transfer catalyst, methyl methacrylate monomer alone or methyl methacrylate 85% by weight or more and methyl acrylate or ethyl acrylate 15% by weight. 10% or less based on the weight of the monomer mixture and the total reaction mixture
There is a continuous solution polymerization method carried out using a monomer solution consisting of 25% by weight of an inert polymerization solvent.

As the inert polymerization solvent, a solvent that can adjust the molecular weight of the produced resin to a 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 polymerization reaction system is high, and it is difficult to control the polymerization reaction. If it exceeds 25% by weight, the load on the devolatilization step increases sharply, which is industrially undesirable. .

The above-mentioned free radical generating catalyst is a polymerization initiator that generates free radicals, and examples thereof include organic peroxides such as benzoyl peroxide, cumene hydroperoxide, and 1,1-bis (t). -Butylperoxy) -3,
It is possible to use 3,5-trimethylcyclohexane and the like, and azo-based initiators such as 1,1-azobis (1-cyclohexanecarbonitrile) and 2,2-azobis (2,4,4-trimethylpentane). However, 3,3,5-trimethylcyclohexane-di-t-butyl peroxide is particularly preferable. The amount of these free radical generating catalysts used is selected in the range of 0.001 to 0.03% by weight, based on the weight of the total reaction mixture.

On the other hand, as the chain transfer catalyst, mercaptans, especially butyl mercaptan, octyl mercaptan, dodecyl mercaptan and the like can be preferably used.

Next, an inert gas is introduced into the thus-prepared monomer solution to reduce the dissolved oxygen content in the solution to 1 ppm or less. 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 preferably the solution is continuously supplied to a countercurrent contact tower to direct 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. It is difficult to reduce the dissolved oxygen to 1 ppm or less by a commonly used inert gas bubbling method in a feed tank, etc., and the limit is about 10 to 20 ppm, which is not preferable.

In the preparation of the optical material of the present invention, it is necessary to reduce the dissolved oxygen amount in the monomer solution to 1 ppm or less in this way, and then filter the solution with a filter of 0.5 μ or less. As the filter, for example, Enflon filter (MCY4463FRE) manufactured by Pall Ltd. is preferably used. By such a filtration treatment, the content of fine foreign matters of 0.5 to 25 μm measured by a fine particle counter in the obtained polymer becomes 10,000 or less / g polymer.

Next, the monomer solution that 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 substantially within the range of 40 to 65%. Polymerization is carried out at a temperature in the range of 120 to 160 ° C. so that the temperature becomes constant. If the conversion rate is less than 40%, the load of the devolatilization process due to volatile components is large, and the devolatilization may be insufficient due to the restriction of the heat transfer area of the preheater. Since the pressure loss of the pipe to the preheater becomes large, 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, making it difficult to control the polymerization conversion rate, and causing a side reaction or coloring the product. Is not preferred.

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

In the preparation of the optical material 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. to remove volatile components, and then fed to a devolatilization tank under a reduced pressure with a sufficient space above to further reduce the volatile components. Can be done by

By the way, a conventional method for removing a volatile component such as an unreacted monomer, a solvent and a by-product of a polymerization reaction from a reaction composition to obtain a polymer product is to heat the reaction composition at a high temperature in a vacuum atmosphere. It is a method of conducting volatile separation. When the volatile component is less than 10% by weight, it can be efficiently separated by a twin-screw extruder with a multistage vent, etc., and the volatile component remaining in the finally obtained methacrylic resin is 1.
It is 0% by weight or less, and a methacrylic resin molding material having good physical properties or an extruded plate can be obtained.

When the amount of volatile components exceeds 10% by weight, when using an extruder with a multi-stage vent, resin foaming is severe due to gasification of the volatile components, and the vent holes often cause blockage due to foamed polymer. The colorless transparency of the obtained resin is remarkably impaired, the yellowness is particularly strengthened, and it is difficult to carry out stable operation for a long time.

When not using a multi-vented extruder,
It is difficult to raise the temperature of the polymer composition, and there are problems such as a method of transporting a high-viscosity fluid after removing volatile components, deterioration of the polymer due to high temperature and long-term retention, and side reaction products. .

Deterioration 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 above-mentioned method, the reaction composition containing a large amount of volatile components can be efficiently heated, and vacuum flushing can be performed while providing a stable fluidized state to efficiently remove the volatile components.

When preparing the optical material of the present invention, the reaction composition was adjusted to 200 to 2
At the same time as heating at a temperature of 90 ° C., preferably in the range of 220 to 270 ° C., the volatile components are removed at the same time. At this time, it is preferable to use a flat plate type preheating plate. Heating temperature
If the temperature is less than 200 ° C, the fluidity of the reaction composition is low and the volatile components are not sufficiently removed. If the temperature exceeds 290 ° C, the polymer is thermally deteriorated.

The reaction composition thus heated is introduced into a devolatilization tank having a sufficient space in the upper part held in a high vacuum state through a narrow outlet formed in a gap between heating plates. . 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 preparation of the optical material of the present invention, devolatilization conditions are 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 maintained in a high vacuum state causes the instantaneous volatilization of the volatile components and the resulting foaming, forming an extremely large evaporation area, and efficiently volatile components in a short time. Are removed.

As the conditions in this devolatilization tank, a heating temperature and a degree of vacuum that can reduce the residual volatile components in the reaction composition to a desired content are necessary.
220-250 ℃, vacuum degree is selected in the range of 20-100 Torr.

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. By such a devolatilization treatment, the polymer contains, as volatile components, 1000 ppm or less of dimer and 2500 ppm or less of residual monomer.

According to the production method as described above, (1) the molecular weight (Mw) measured by GPC is 70,000 to 150,000, (2) the dimer as a volatile component is 1000 ppm or less, and the residual monomer is 2500 ppm or less, (3 ) A methacrylic resin having a thermal decomposition index α of 3.0 or less, (4) 10,000 or less fine foreign matters of 0.5 to 25 μm measured by a fine particle counter and (5) ΔYI of 6.00 or less measured by a color difference meter Easily obtained.

EFFECTS OF THE INVENTION The optical material of the present invention is a methyl methacrylate homopolymer or a copolymer of methyl methacrylate and methyl acrylate or ethyl acrylate, which has excellent molecular homogeneity and high optical purity, and is colorless. It has excellent characteristics such as transparency, and is particularly preferably used as a material for lenses, optical discs, optical fibers and the like.

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

The properties of the polymer were determined as follows.

(1) GPC molecular weight measurement “Gel Chromatography (Basic)” (Published by Kodansha)
It was measured according to the method described on pages 97-122.

That is, a sample in which two HSG-20, 50 (manufactured by Shimadzu Corporation) were used as columns, a calibration curve was prepared using standard polystyrene manufactured by Plessia Chemical Co., and 75 mg of the polymer was dissolved in 30 ml of methyl ethyl ketone. The elution curve obtained using the solution was equally divided, the height at the division point was measured, and Mw was calculated by the following equation.

Where 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, Qm and Qp are the Q factor of the copolymer and polystyrene, respectively 40 and
41.

(2) Measurement of thermal decomposition index α Using thermal decomposition gas chromatography, the polymer is decomposed at 450 ° C under N2 atmosphere, and the total decomposition gas decomposed in 60 minutes is detected and integrated, and this is defined as X, and at 270 ° C The amount of gas decomposed and generated in 30 minutes is integrated, and this is defined as Y.
X was calculated as X) × 100.

(3) Measurement of minute foreign matter (using HIAC-ROYCO) Weigh 5 g of polymer, dissolve in 30 ml of dichloroethane, and measure the scattering of laser light with a counter that has been calibrated beforehand to measure 0.5 to 25μ particles. did.

(4) Measurement of ΔYI by color difference meter 5 ounces of resin was molded using an injection molding machine and 15 × 225 × 3
I got a mm piece. This sample 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) -3,3,5-trimethylcyclohexane 150ppm, octyl mercaptan 2500pp
Using a liquid containing m, this liquid is continuously fed into a nitrogen-feed liquid countercurrent contact tower (nitrogen-feed ratio = 1/50% by weight).
The oxygen concentration of 0.55
After adjusting to ppm, use a filter manufactured by Ball Co. (85% particle cut rate of 0.5μ or more) to 0.5-25μ in the feed solution.
The number of fine particles was reduced to 300 / (feed solution 1 ml) to obtain a high-purity feed solution.

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, and the polymerization temperature was 135 ° C. and the polymerization pressure was 1.3 Kg / c.
50% by weight of methacrylic resin with a weight average molecular weight (Mw) of 100,000 measured by GPC was carried out under the conditions of m ² , polymerization conversion rate of monomer 62.5%, and solid content of polymerization system 50% by weight. When,
Unreacted monomer, initiator, residue of chain transfer agent, decomposition product,
A reaction composition containing 50% by weight of solvent was obtained.

Next, the reaction composition was constantly taken out by the metering pump 2, heated to 260 ° C. by the heating plate 3, and cast and dropped 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. 22ppm residual dimer in the polymer, 10ppm residual monomer
It was. 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, and the minute foreign matter per 1 g of polymer is 4000
Individually, △ YI measured with a color difference meter is 4.52, thermal decomposition index α is 2.
It was 1.

Examples 2 to 6 The same operations as in Example 1 were performed except that the conditions in Example 1 were changed as shown in the following table. The results are shown in the table below.

Example 7 The same operation as in Example 1 was performed 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 dissolved oxygen concentration was changed to 40 ppm. The ΔYI of the obtained test piece was 13.55 and the thermal decomposition index α was 3.66.

Comparative Example 2 The reaction composition obtained in Example 1 was constantly taken out by the metering pump 2 and supplied to the 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 was changed to 65% by weight. The residual dimer of the polymer before making 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. The appearance of the test piece was colorless and transparent, and 4100 fine foreign matters per 1 g of the polymer, ΔYI of 4.55 measured by a color difference meter, and thermal decomposition index α of 2.0.

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

[Brief description of drawings]

The figure is a flow sheet showing an example of the polymerization and devolatilization step in the production of the optical material of the present invention. In the figure, reference numeral 1 is a polymerization reaction tank, 2 is a metering pump, 3 is a heating plate, 4 is devolatilization. tank,
5 is an extrusion die.

Claims (1)

[Claims] 1. A methyl methacrylate homopolymer and a methyl methacrylate copolymer containing 15% by weight or less of methyl acrylate units or ethyl acrylate units, and (1) the molecular weight measured by GPC ( Mw) 70,000-150,000,
(2) Dimer 1000ppm or less and residual monomer 2500ppm or less as volatile components, (3) Thermal decomposition index α3.0 or less, (4)
0.5-25μ fine foreign particles measured by a particle counter 10,000 or less / g polymer and (5) ΔYI6.00 measured by a color difference meter
An optical material comprising a methacrylic resin having the following: