JPH0614127B2 - Method for manufacturing plastic optical transmission body - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a plastic optical transmission body having a core and a clad and having excellent heat resistance.

[Conventional technology and problems]

Conventionally, an optical transmission body is manufactured by using transparent quartz glass or plastic. An optical fiber using quartz glass has an excellent optical transmission property and has been put to practical use for long-distance communication. Plastic optical fibers are inferior in optical transmission to optical fibers using quartz, but they have the advantages of good flexibility, light weight, and easy processing. It is being applied to guides and sensors. In many of these applications, heat resistance is required. For example, an optical fiber used for an optical data link for automobiles is
It is required to endure high temperatures such as 100 to 120 ° C. due to heat from the engine room. However, the conventional plastic optical fiber uses polystyrene or polymethylmethacrylate in the core, and the temperature for normal use is only 80 ° C. An optical fiber made of polystyrene or polymethylmethacrylate shrinks at a high temperature of 80 ° C. or higher, resulting in a decrease in optical transmission property.
At a high temperature such as 0 ° C. or higher, a large shrinkage occurs, and not only the optical transmission property is deteriorated, but also the fiber itself is broken and no light is transmitted.

The glass transition point and the melting point are physical properties that indicate the performance at high temperatures of the polymethylmethacrylate and fluorine-containing polymers used in the core and cladding of conventional plastic optical fibers. The glass transition point of polymethylmethacrylate is about 105 ° C, and at temperatures above the glass transition point, segmental motion of polymer molecules becomes vigorous and fluctuations increase, and the change in refractive index also increases, resulting in significant light scattering loss. Practical performance cannot be maintained.

Therefore, it is considered to use a polymer having a high glass transition point in the core, and addition polymerization type polymers and condensation type polymers have been studied. Polycarbonate is a condensation polymer having good transparency, and its glass transition point is about 145 ° C. The fiber obtained by using the polycarbonate as the core had good thermal characteristics, but the optical transmission property was polystyrene,
It was considerably inferior to polymethylmethacrylate. The reason seems to be that the polycarbonate obtained by condensation polymerization requires a step of removing condensation by-products such as NaCl, and inevitably residual impurities and contamination. Polycarbonate and other polymers such as polysulfone and polyaryl ester are known as condensation type non-polymeric polymers showing a high glass transition point, but the fiber processing temperature is high, and the decomposition of the polymer and the residual and mixing of impurities are known. However, it was not possible to obtain a fiber with good optical transmission properties.

A material having a smaller refractive index than the core is used as the clad material for the plastic optical transmission body. In a conventional plastic optical fiber having polymethylmethacrylate as a core, a fluoroalkyl methacrylate polymer or a copolymer of vinylidene fluoride and tetrafluoroethylene as a clad material has a vinylidene fluoride content of, for example, 77 mol%. Copolymers have been used. However, the fluoroalkyl methacrylate polymer has a low decomposition initiation temperature,
Not only is there a problem in fiber production, but the glass transition temperature of the polymer is in the low temperature range of 60 to 90 ° C. Therefore, the fiber using fluoroalkyl methacrylate as the cladding starts to increase the transmission loss when exposed to the temperature near the glass transition temperature, and the loss increases to the extent that it cannot be used at a temperature of 100 ° C. or higher.

On the other hand, a copolymer of vinylidene fluoride and tetrafluoroethylene having a vinylidene fluoride content of 77 mol% has a melting point of 110 ° C. Therefore, when the fiber is exposed to a temperature near the melting point or at a temperature exceeding the melting point, the transmission loss increases, which in turn causes the core to flow and significantly deteriorate the transmission characteristics.

As an addition polymerization type polymer which gives a polymer having a high glass transition temperature, there is a copolymer of arylmethacrylate P-phenylstyrene, but these monomers belong to a special one which has not been industrially produced and are put to practical use. On the other hand, it is necessary to start by establishing an economical mass production method for monomers.

[Object and Summary of Invention]

Based on the knowledge and the basis of the above-mentioned conventional techniques, the present inventors have arrived at the present invention through intensive studies on improvement of heat resistance of a plastic optical transmission body.

The present invention comprises purified β-methylglycidyl methacrylate purified by distillation under reduced pressure to remove the polymerization inhibitor, and 10 g per 100 ml of commercial grade reagent grade methyl methacrylate.
200 ml of 5% NaOH aqueous solution in which NaCl of
After washing twice with the above, anhydrous sodium sulfate was added and dried, and then purified methyl methacrylate prepared by precision purification by vacuum distillation was prepared, and the purified β-methylglycidyl methacrylate was 10 to 50 mol%. As described above, 2,2′-azobis (isobutyronitrile) recrystallized in methanol as a mixing initiator is charged into a mixing vessel together with the purified methyl methacrylate and stirred and mixed by a magnetic stirrer in the number of moles of each monomer. 0.01% of the sum of the above was added to a mixing vessel and dissolved by stirring, and then n-butyl mercaptan purified by distillation under reduced pressure as a chain transfer agent was added at a concentration of 1.5 × 10 ^-2 mol per 1000 ml of each monomer and mixed by stirring. After that, the stirred monomer solution is transferred from the mixing container to a polymerization container with an open upper end so as not to be contaminated. A propylene resin tube, and then vacuum-exhausted from the upper end of the polymerization container to remove dissolved air and heat-seal the upper end with a burner under reduced pressure.
Dissolve the dissolved gas by immersing the polymerization vessel in liquid nitrogen and repeating freezing and temperature thawing of the monomer solution, and heating the polymerization vessel sealed under reduced pressure at a temperature of 60 to 140 ° C. to polymerize the solution. After that, the polymerization container whose upper end was cut and unsealed was immediately transferred to a vacuum drier and vacuum-heated at a temperature of 100 to 140 ° C. to remove volatile components in the copolymer to obtain a transparent preform having no bubbles. Is formed, and then 190 to
The polymerization container having the opening cut out at the lower end was attached to a heating furnace set to 210 ° C., and 1 kg / cm ^{2 of} N ₂ gas was applied from the upper end to melt-extrude the polymer from the lower end of the polymerization container. Then, the take-up speed is adjusted and set so as to obtain a predetermined core diameter, and a 30% ethyl acetate solution of vinylidene fluoride-tetrafluoroethylene copolymer as a clad material is applied to the outer periphery of the drawn core polymer. S 160
Molded into a plastic optical fiber through a drying oven maintained at 0 ° C., and then using 60 gamma rays of cobalt 60 on the plastic optical fiber at a dose rate of 6 × 10 ⁴ r / hr,
The present invention relates to a method for producing a plastic optical transmission body, which comprises irradiating a total dose of 2.5 megarads at 25 ° C.

[Effects and Detailed Description of Invention]

According to the present invention, it is possible to improve heat resistance by efficient radiation cross-linking, and by taking care so that the core polymer is not contaminated during the manufacturing process, it is possible to use plastic light with conventional polymethylmethacrylate or polystyrene as the core. It is possible to obtain a low-loss plastic optical transmission body that can be used even at 100 ° C. or higher, which was not possible with a transmission body.

Polymethylmethacrylate is easily decomposed rather than efficiently crosslinked by radiation, and when the irradiation dose is large, decomposed gases such as CO, CO ₂ and H ₂ are generated and bubbles may be generated in the polymer. Therefore, it is difficult to improve the heat resistance by irradiation crosslinking of polymethylmethacrylate, which is a homopolymer of methylmethacrylate. However, when a group that can be easily crosslinked by radiation is introduced into the structural unit of the polymer, it may be possible to effectively crosslink even at a relatively small dose, and the present inventors have focused their attention on this point and proceeded with research, We have found that polymers with epoxy groups introduced into the molecule are suitable for irradiation crosslinking.

The present invention firstly converts 10 to 50 mol% in terms of monomer mol%.
The polymer containing the structural unit of β-methylglycidylmethacrylate is used. When a copolymer is used, examples of the monomer to be copolymerized with β-methylglycidyl methacrylate include methyl methacrylate, styrene, and methyl acrylate.

Generally, the copolymer obtained by copolymerizing the monomers M ₁ and M ₂ with the monomer reactivity ratios r ₁ and r ₂ has different main chain structures such as radam, block, and alternation.
Differences in the composition of the main chain, such as block copolymers, are undesirable because they cause light scattering due to density fluctuations, microphase separation, and the like, and reduce light transmission properties. Therefore, even if the copolymer is obtained by simply combining β-methylglycidyl methacrylate with any other monomer and polymerizing the copolymer, it is not always possible to obtain a low-loss optical transmission property. However, from the above-mentioned methyl methacrylate, styrene, and methyl acrylate, When selected and combined, a practical copolymer can be obtained.

The above-mentioned monomer copolymerized with β-methylglycidyl methacrylate is preferably used in the range of 90 mol% or less in terms of monomer mol%. If these are 90
If it is contained in the copolymer in an amount of more than mol%, the content of the epoxy group in the copolymer becomes too low and the crosslinking is insufficient for electron beam irradiation, so that the purpose of improving heat resistance cannot be achieved.

As a polymerization method, since methyl methacrylate having an epoxy group which is highly reactive with a monomer is used, it is desirable to use a bulk polymerization method in which impurities are not likely to be mixed.

As the clad material used in the present invention, a copolymer containing a vinylidene fluoride unit as a main component is suitable, and the melting point of the polymer is preferably 120 ° C. or higher. Melting point 12
This is because if the temperature is less than 0 ° C., the transmission loss increases when exposed to a temperature of 100 to 120 ° C., making it unusable. In the present invention, a copolymer of vinylidene fluoride and tetrafluoroethylene is used. The composition ratio of vinylidene fluoride and tetrafluoroethylene is 80/20 molar ratio, and the melting point thereof is 132 ° C.

As a means for coating the clad on the core, after drawing the core, the core is passed through a pot containing a 30% ethyl acetate solution of the clad material to apply the coating, and the core is passed through a heating furnace set at 160 ° C. for coating. Adopt the method.

As the method for producing the polymer used for the core, bulk polymerization is preferable, and in order to obtain a low loss optical transmission medium, it is preferable to prepare a preform in which no foreign matter is mixed and melt-mold the preform as follows.

The core material used in the present invention is a mixture of impurities and polymerization inhibitors contained in each monomer, which are purified by a method such as filtration with a microfilter, distillation, recrystallization, etc. in a closed system or in a dust-free clean atmosphere. And a chain transfer agent n-butyl mercaptan for controlling the molecular weight of the polymer and a polymerization initiator 2,2'-azobis (isobutyronitrile)
Is added to a polymerization vessel in a closed system or in a clean atmosphere to carry out thermal polymerization. The size of the preform is determined by the polymerization container and the amount of monomers used, but for example, a preform having a diameter of 10 mm to 30 mm and a length of 200 mm to 1000 mm can be easily prepared. In order to obtain a preform free from bubbles that cause light scattering, the air dissolved in the monomer should be removed by freezing and degassing before polymerization, and the polymerization in the vacuum sealed tube or the piston should be placed in the polymerization container. It is preferable to carry out the polymerization while pressurizing the monomer solution during the polymerization so that there is no surface.

The polymerization temperature may be a normal thermal polymerization temperature, for example, a temperature of 60 ° C. or higher, but the higher the temperature, the shorter the polymerization time, and the more irregular the structure and composition of the resulting copolymer. Therefore, it is possible to obtain an optical transmission body with lower loss. Preferably a temperature of 60 ° C. to 140 ° C. is chosen. When the polymerization is started at a relatively low temperature of 60 to 80 ° C., the temperature is raised at the final stage of the polymerization to reach a temperature not lower than the glass transition temperature of the polymer to be finally produced, and the polymerization is completed at this temperature to obtain a preform. It is preferable that

In addition, it is suitable to heat and melt a preform to draw a simple optical transmission body such as a plastic optical fiber.

The preform can be made into a fiber by a melt spinning method. The preform is melted in a heating furnace set at 190 to 210 ° C. and pressurized with N ₂ gas at 1 kg / cm ² to spin the core polymer. The preform is not taken out of the polymerization container, and after completion of the polymerization, a hole is formed in the lower part of the polymerization container, followed by pressurizing with an inert gas, heating and melting, and drawing.

At least the core of the plastic optical transmission article of the present invention is crosslinked by irradiation with radiation. As the radiation, r-ray by cobalt-60 is used. Irradiation is performed at a dose rate of 6 × 10 ⁴ r / hr and a total dose of 2.5 megarads at 25 ° C.

Example of Invention

 The present invention will be specifically described below with reference to examples.

(Example 1) 100 ml of commercially available reagent grade methyl methacrylate obtained by removing β-methylglycidyl methacrylate from a polymerization inhibitor by distillation under reduced pressure was purified, and washed twice with 200 ml of a 5% NaOH aqueous solution in which 10 g of NaCl was dissolved. After that, anhydrous sodium sulfate was added and dried, and precision purification was performed by distillation under reduced pressure.

The precision purification receiver for methyl methacrylate used had a weighing line, and the pipe was used so that the required amount of monomer could be transferred to the mixing container without being exposed to the outside air. The mixing vessel is equipped with a PTFE rotor for stirring, an inlet for adding a polymerization initiator and a chain transfer agent, and an outlet for the polymerization vessel using a PTFE stopper.

Purified β-methylglycidyl methacrylate 146 ml
(1.0 mol) was weighed on a clean bench and put into a mixing container. Purified methyl methacrylate 107 ml
(1.0 mol) was transferred to a mixing vessel and mixed by stirring with a magnetic stirrer. As a polymerization initiator, 2,2′-azobis (isobutyronitrile) recrystallized twice in methanol was added to a mixing vessel in an amount of 0.01% of the total number of moles of each monomer, and dissolved by stirring. Next, 0.40 of n-butyl mercaptan purified by distillation under reduced pressure was used as a chain transfer agent.
ml (1.5 × 10 ⁻² mol / 100 ml of monomer) was added, and the mixture was further stirred and mixed. The monomer solution was transferred from the mixing container to the polymerization container through a tube made of fluoroethylene propylene resin (Teflon) so as not to be contaminated, and transferred to the polymerization container. Polymerization container is made of quartz glass 3
It has a pipe shape with an inner diameter of 0 mm, the upper and lower ends are narrowed to an inner diameter of 6 mm, and the lower end is sealed.

After the monomer solution was transferred to the polymerization vessel, the upper end was evacuated under reduced pressure to remove dissolved air, and the quartz glass tube portion having an inner diameter of 6 mm at the upper end was heat-sealed with a burner under reduced pressure. Further, the polymerization vessel was immersed in liquid nitrogen, and the dissolved gas was removed by repeating freezing and temperature thawing of the monomer solution. 1 polymerization vessel sealed under reduced pressure
Polymerization was carried out by heating at 30 ° C. for 16 hours. Cut the glass tube at the top and unseal it, then immediately transfer to a vacuum dryer.
The copolymer was heated in vacuum at 48 ° C. for 48 hours to remove the volatile components in the copolymer to obtain a transparent preform having no bubbles.

Using a wire drawing device equipped with a heating furnace for a polymerization container, a clad coating die, a clad drying furnace, and a winder, the temperature of the heating furnace is set to 190 to 210 ° C. in advance, and the lower end of the quartz glass polymerization container is used. The glass tube of No. 2 was cut, mounted in a heating furnace, and pressurized with 1 kg / cm ^{2 of} N ₂ gas from the upper end. When the temperature of the preform rises, the polymer is melt-extruded from the nozzle at the lower end of the polymerization container, so the take-up speed was adjusted and set so that the core diameter was about 1.0 mm. On the other hand, a 30% ethyl acetate solution of vinylidene fluoride-tetrafluoroethylene copolymer (melting point 132 ° C., composition 80/20 molar ratio) was used as a clad material, filled in a clad coating pot, and drawn as described above. Core pots and dies and 16
It was molded into a plastic optical fiber having an outer diameter of 1.0 mm and a clad film thickness of 20 μm by removing ethyl acetate through a drying furnace kept at 0 ° C.

Next, gamma rays of cobalt 60 were applied to the above plastic optical fiber wound to a diameter of 200 mm to obtain 6 × 10 ⁴ r /
A total dose of 2.5 megarads was irradiated at 25 ° C. with a dose rate of hr. The properties of the obtained plastic optical fiber are shown in Table 1.
It was shown to.

The acetone extraction weight loss of the core after irradiation was 8.5%, and it was only swollen at 100 ° C. in a mixed solvent of xylene and metacresol (1: 1).

(Example 2) 20 mol% of β-methylglycidyl methacrylate, 30 mol% of purified methyl methacrylate, 50 mol% of styrene purified by distillation under reduced pressure, and 2,2′-azobis (isobutyronitrile) were added in a molar ratio of each monomer. 0.01% of sum, n-
A plastic optical fiber was manufactured in the same manner as in Example 1 except that a monomer solution in which butyl mercaptan was mixed at a ratio of 1.5 × 10 ^-2 mol / sum of monomers and 1000 ml was used, and gamma rays were irradiated. The properties of the obtained plastic optical fiber are shown in Table 1. The acetone extraction weight loss of the core after irradiation was 1.4%, and it slightly swelled at 100 ° C. in a mixed solvent of xylene and metacresol.

(Example 3) 10 mol% of β-methylglycidyl methacrylate, 25 mol% of distilled and purified methyl acrylate, 65 mol% of purified methyl methacrylate, and 2,2′-azobis (isobutyronitrile) were added in the sum of the number of moles of each monomer. 0.01% of
A plastic optical fiber was manufactured in the same manner as in Example 1 except that a monomer solution in which n-butyl mercaptan was mixed at a ratio of 1.5 × 10 ⁻² mol / sum of monomers of 1000 ml was used, and gamma rays were irradiated. However, the polymerization vessel sealed under reduced pressure was heated at 100 ° C. for 16 hours and then at 140 ° C. for 2 hours to polymerize the monomer solution. The properties of the obtained plastic optical fiber are shown in Table 1. The acetone extraction weight loss of the core after irradiation was 12.4%, and it only swelled in a mixed solvent of xylene and metacresol at 100 ° C.

(Comparative Example 1) 107 ml (1.0 mol) of purified methyl methacrylate,
Purified 2,2'-azobis (isobutyronitrile) 0.0
1%, 0.17 ml of n-butyl mercaptan (1.5 x
A plastic optical fiber was manufactured in the same manner as in Example 1 except that the composition of the monomer solution was 10 ⁻² mol / 100 ml of the monomer), and gamma rays were irradiated. The properties of the obtained fiber are shown in Table 1. The acetone extraction weight loss of the core after irradiation was 96%, and the core was dissolved in a mixed solvent of xylene and metacresol at 100 ° C. without stopping the form.

(Comparative Example 2) Purified β-methylglycidyl methacrylate 5.8 ml
(0.04 mol), purified methyl methacrylate 103 m
1 (0.96 mol), purified 2,2'-azobis (isobutyronitrile) 0.01%, and n-butyl mercaptan 0.17 ml in the same manner as in Example 1 except that a monomer solution composition was prepared. A plastic optical fiber was manufactured and irradiated with gamma rays. The properties of the obtained fiber are shown in Table 1. Acetone extraction weight loss of core after irradiation is 74%
And a mixed solvent of xylene and meta-cresol is 100
It swelled and collapsed remarkably at ℃.

Claims (2)

[Claims] 1. Purified β-methylglycidyl methacrylate purified by distillation under reduced pressure to remove the polymerization inhibitor, and 1 to 100 ml of commercial grade reagent grade methyl methacrylate.
5% NaOH aqueous solution 200 in which 0 g of NaCl was dissolved 200
After washing twice with ml, anhydrous sodium sulfate was added and dried, and then purified methyl methacrylate prepared by precision purification by vacuum distillation was prepared, and the purified β-methylglycidyl methacrylate was 10 to 50 mol%. As described above, the purified methyl methacrylate was charged into a mixing vessel, stirred and mixed with a magnetic stirrer, and recrystallized in methanol as a polymerization initiator.
-Azobis (isobutyronitrile) was added to a mixing vessel in an amount of 0.01% of the total number of moles of each monomer and dissolved by stirring, and then n-butyl mercaptan purified by distillation under reduced pressure was used as a chain transfer agent for each monomer. 1.5 x 10 per 1000 ml
^-After adding ² mol and stirring and mixing, transfer the stirred monomer solution from the mixing container to a polymerization container with an open top through a tube made of fluorinated ethylene propylene resin so as not to be contaminated, and reduce the pressure from the top of the polymerization container. Exhaust to remove dissolved air, heat and seal the upper end with a burner under reduced pressure, and further immerse the polymerization vessel in liquid nitrogen to freeze and thaw the monomer solution repeatedly to remove dissolved gas, and then seal under reduced pressure. After heating the tubed polymerization vessel at a temperature of 60 to 140 ° C. for polymerization, the polymerization vessel opened by cutting the upper end is immediately transferred to a vacuum dryer and heated at a temperature of 100 to 140 ° C. under vacuum. To remove volatiles in the copolymer to form a transparent preform with no bubbles at all,
The polymerization container having the opening cut out at the lower end was attached to a heating furnace set to 0 to 210 ° C., and N ₂ was added from the upper end.
A pressure of 1 kg / cm ^{2 was} applied with a gas, and the take-up speed was adjusted and set so that the polymer was melt-extruded from the lower end of the polymerization vessel to a predetermined core diameter, and at the same time, vinylidene fluoride-tetrafluoroethylene as a clad material was used. A 30% solution of the polymer in ethyl acetate was applied to the outer periphery of the drawn core polymer 1
A plastic optical fiber was molded through a drying oven maintained at 60 ° C., and then a gamma ray of cobalt 60 was applied to the plastic optical fiber at a dose rate of 6 × 10 ⁴ r / hr and a total dose of 2.5 megarads at 25 ° C. A method of manufacturing a plastic optical transmission body, which comprises irradiating. 2. Either of styrene purified by distillation under reduced pressure or methyl acrylate purified by distillation is purified β-
The method for producing a plastic optical transmission article according to item 1, wherein the mixing container is charged with methyl glycidyl methacrylate and the purified methyl methacrylate.