JPH0646243B2 - Method for manufacturing plastic optical transmission body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] The present invention relates to a method for producing a plastic optical transmission body comprising a core and a clad with improved heat resistance and solvent resistance.

[Conventional technology and its problems]

Conventionally, an optical transmission body is manufactured using quartz glass or plastic. An optical transmission body using quartz glass has an excellent optical transmission property and has been put to practical use for long-distance communication. Compared to optical transmission materials that use quartz, plastic optical transmission elements have inferior optical transmission characteristics, but they have the advantages of good flexibility, light weight, and easy processing. , Light guides, sensors, etc. are being applied. In many of these applications, heat resistance is required. For example, an optical transmitter used for an optical data link for an automobile is required to withstand a high temperature of 100 to 120 ° C. due to heat from an engine room. However, the conventional plastic optical transmission body uses polystyrene or polymethylmethacrylate for the core, and the temperature for regular use is only 80 ° C.
An optical transmission material using polystyrene or polymethylmethacrylate contracts at a high temperature of 80 ° C. or higher, and the optical transmission property deteriorates. Further, at a high temperature of 100 or higher, a large yield occurs and the optical transmission property is deteriorated. The wire itself was broken, and no light could pass through.

A glass transition point and a melting point are physical properties showing the use performance at a high temperature of polymethylmethacrylate and a fluorine-containing polymer used for the core and clad of a conventional plastic optical transmission body. The glass transition point of polymethylmethacrylate is about 105 ° C. At temperatures above the glass transition point, the segmental motion of the polymer molecules becomes more intense and the fluctuations increase, and the change in the refractive index also increases, so that the scattering loss of light becomes remarkable and the 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 type polymer with good transparency, and its glass transition point is about 145 ° C.
Is. The optical transmission material obtained by using polycarbonate as a core had good thermal characteristics, but the optical transmission property was considerably inferior to polystyrene and polymethylmethacrylate. It is considered that the reason is that the polycarbonate obtained by the condensation polymerization requires a step of removing condensation by-products such as NaCl, and inevitably the residue or contamination of impurities cannot be avoided. Polymers such as polysulfone and polyaryl ester are known as condensation type amorphous polymers that show a high glass transition point. In addition to polycarbonate, polymers such as polysulfone and polyaryl ester are known. However, it was impossible to obtain an optical transmission material having good optical transmission properties due to inevitable mixing.

A material having a smaller refractive index than the core is used as the clad material for the plastic optical transmission body. Conventionally, a polymer of fluoroalkyl methacrylate or a copolymer of vinylidene fluoride and tetrafluoroethylene is used as a clad material in a plastic optical transmission body having polymethyl methacrylate as a core. However, the fluoroalkyl methacrylate polymer has a low decomposition temperature, which not only causes problems in fiber production, but also has a glass transition temperature of the polymer in a low temperature range of 60 to 90 ° C. Therefore, an optical transmission body using a fluoroalkyl methacrylate as a cladding starts to increase the transmission loss when exposed to a temperature in the vicinity of its glass transition temperature, and the loss increases to such a degree that it cannot be used at a temperature of 10 ° C. or higher. On the other hand, a vinylidene fluoride-tetrafluoroethylene copolymer having a vinylidene fluoride content of 7
The 7 mol% copolymer has a melting point of 10 ° C. Therefore, when the optical transmission medium is exposed to a temperature near the melting point or a temperature exceeding the melting point, the transmission loss increases, and eventually the core flows and the transmission characteristics are significantly deteriorated. There are aryl methacrylate and p-phenylstyrene copolymers that give addition-polymerization polymers having a high glass transition temperature, but these monomers belong to special ones that have not been industrially produced and are practically used. To achieve this, it is necessary to start by establishing a mass production method for monomers.

[Object and Summary of Invention]

Based on the knowledge of the prior art as described above, the inventors of the present invention have earnestly studied to improve the heat resistance of a plastic optical transmission body and arrived at the present invention.

That is, the present invention provides (a) as monomers, 10 mol% of purified methyl acrylate obtained by removing commercially available reagent grade methyl acrylate by distillation to remove the polymerization inhibitor and purifying commercially available reagent grade methyl methacrylate by distillation. 30 mol% of purified methyl methacrylate obtained by removing the agent and purified, and 60 mol% of purified styrene obtained by distilling styrene under reduced pressure to remove the polymerization inhibitor and purified are put into a mixing vessel and mixed by stirring with a magnetic stirrer. (B) 0.01% by mole of a special grade of azotertiary butane as a polymerization initiator with respect to the number of moles of the mixed monomer is added to the mixing vessel, and then distillation purification under reduced pressure is performed as a chain transfer agent. Monomer 1000 with mixed n-butyl mercaptan
a step of adding 1.5 × 10 ⁻² mol to ml and stirring and mixing; and (c) a quartz glass-made tube made of a fluorinated ethylene propylene resin tube from a mixing container so that the stirred and mixed monomer solution is not contaminated. Cylindrical, the upper end and the lower end are narrowed down, and the lower end is transferred to a sealed polymerization container, and While heating and sealing the quartz glass part at the top with a burner, (e) dip the vacuum-sealed polymerization vessel in liquid nitrogen and freeze and thaw the monomer solution repeatedly to sufficiently remove the dissolved gas. And (f) heat the polymerization vessel at 130 ° C. for 16 hours to perform thermal polymerization, cut the glass tube at the upper end and unseal, immediately transfer to a vacuum dryer, and heat at 100 ° C. for 48 hours. Copolymer The process of removing the volatile components in the product to obtain a transparent preform free from air bubbles, and (g) a drawing furnace in which a heating furnace for a polymerization container, a clad coating die, a clad drying furnace, and a winding machine are arranged in a vertical shape Using the equipment, set the temperature of the heating furnace in advance to 190-210 ° C, cut the glass tube at the lower end of the quartz glass polymerization container, and attach it in the heating furnace. From the upper end, 1 kg / cm ² with N ₂ gas. A step of pressurizing, and (h) a step of adjusting and setting the take-up speed so that the core has a predetermined thickness when the temperature of the preform rises and the copolymer is melt-extruded from the nozzle at the lower end of the polymerization container. (I) As a clad material, Tarad using a solution obtained by mixing a 30% ethyl acetate and a methylethylketone of a copolymer of 80 mol% vinylidene fluoride and 20 mol% tetrafluoroethylene in a ratio of 1: 1 Coating A plastic optical fiber by forming a clad film on the outer periphery of the core by filling the pot for molding with the drawn core through a pot, a clad die, and a drying oven held at 160 ° C. to remove the solvent. ) A method for producing a plastic optical transmission medium, which comprises irradiating the plastic optical fiber with a gamma ray of cobalt 60 at a dose rate of 6 × 10 ⁴ r / h at a total dose of 15 megarads at 25 ° C. is there.

The present inventors have focused on polymer crosslinking as a means for improving the heat resistance and solvent resistance of a plastic optical transmission medium, and have studied crosslinking by irradiation with radiation. As a result, the light transmission body having a core of a homopolymer of methyl methacrylate is not effectively cross-linked by irradiation with radiation, and when the irradiation dose is increased, decomposed gas such as CO, CO ₂ and H ₂ is generated, and it is generated in the core. The formation of bubbles did not lead to the improvement of the properties due to crosslinking. However, when a styrene derivative and an acrylic acid ester copolymer are used for the core and radiation is applied, cross-linking between polymer molecules is performed, and heat resistance and solvent resistance are remarkably improved, and the present invention is completed. I arrived.

[Supplementary explanation of the invention]

The core material used in the present invention is a copolymer of styrene and methyl acrylate, to which methyl methacrylate is copolymerized within a range that does not significantly impair the crosslinking effect by irradiation with radiation.

Generally, when the monomers M ₁ and M ₂ are copolymerized, the copolymers obtained by the monomer reactivity ratios r ₁ and r ₂ have different main chain structures such as random blocks and alternations.
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, it is not always possible to obtain a low-loss optical transmission medium by copolymerizing arbitrary monomers in combination. In addition, when crystals and amorphous portions coexist in the polymer, light scattering becomes remarkable, so that the combination of monomers and the polymerization composition must be selected. The styrene described above generally becomes an amorphous polymer, and the homopolymer of acrylic acid ester contains crystals, so that it is used in the present invention as a copolymer with styrene, methyl acrylate, and methyl methacrylate.

As the polymerization method of the core used in the present invention, a bulk polymerization method which is less likely to contain impurities is desirable.

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
If it is less than 0 ° C, the transmission loss increases when exposed to a temperature of 100 to 120 ° C, and it becomes unusable. The vinylidene fluoride copolymer used in the present invention is a copolymer of vinylidene fluoride and tetrafluoroethylene. Incidentally, the copolymer of vinylidene fluoride and tetrafluoroethylene, when the content of tetrafluoroethylene is 60 mol% or more, the crystallinity of the copolymer becomes large, and the adhesiveness with the core decreases, In the present invention, a copolymer of vinylidene fluoride of 80 mol% and tetrafluoroethylene of 20% (melting point 132 ° C.) is used.

As a means for coating the clad on the outer periphery of the core, the present invention employs a method of coating the clad material solution by a coating method after molding the core.

The polymer used for the core is produced by the bulk polymerization method as described above, but in order to obtain a low loss optical transmission medium which is preferably bulk polymerization, a preform in which foreign matter is not mixed is prepared and melted as follows. Need to be molded.

The raw material monomer for the core used in the present invention is a polymer obtained by mixing impurities and a polymerization inhibitor with a microfilter, distilling, and purifying the monomer purified by a method such as recrystallization in a closed system or in a dust-free clean atmosphere. It can be obtained by adding a chain transfer agent for controlling the molecular weight and a polymerization initiator, introducing it into a polymerization vessel in a closed system or a clean atmosphere, and conducting thermal polymerization. The size of the preform to be prepared depends on the polymerization container and the amount of monomers used, but for example, a diameter of 10 mm to 30 mm and a length of 200 to 1000 mm can be easily prepared. It is necessary to remove air dissolved in the monomer by freeze degassing and to perform polymerization in a vacuum sealed tube before the initiation of thermal polymerization in order to obtain a bubble-free preform that causes light scattering. .

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. 130 is preferable because an optical transmission body with lower loss can be obtained.

A melt spinning method can be applied to manufacture a fibrous optical transmission body from a preform. In the present invention, the core polymer is extruded from the lower end of the polymerization container by heating and melting the preform in the polymerization container and pressurizing with an inert gas such as N ₂ gas, and the core polymer is quantitatively supplied to the spinning die.

At least the core of the plastic optical transmission article of the present invention is crosslinked by irradiation with radiation. In the present invention, the r-ray of cobalt-60 is used.

〔Example〕

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

(Example 1) Styrene was distilled under reduced pressure to remove the polymerization inhibitor and was purified. The styrene precision refining receiver used had a weighing line, and was equipped with piping so that the required amount of monomer could be transferred without touching the mixing container. The mixing container is a rotor made of polytetrafluoroethylene (Teflon, trade name of Du Pont, Inc.) for stirring, a monomer for copolymerization, a polymerization initiator, an input port for adding a chain transfer agent, polytetrafluoroethylene (Du
Equipped with an outlet to the polymerization container using a stopper made by Pont Co., Ltd. (Teflon, trade name).

A commercially available reagent grade methyl acrylate was purified by distillation to remove the polymerization inhibitor. Commercially available reagent grade methyl methacrylate was purified by removing the polymerization inhibitor by distillation as in the case of methyl acrylate.

18 ml (0.2 mol) of purified methyl acrylate was weighed on a clean bench and charged into a mixing container, and 64 ml (0.6 mol) of purified methyl methacrylate was weighed on a clean bench and charged into a mixing container. Purified styrene 1
The mixture was transferred to a 38 ml (1.2 mol) mixing vessel and mixed by stirring with a magnetic stirrer. To start the polymerization, azotertiary butane of a special grade reagent was added to the mixing container in an amount of 0.01 of the total number of moles of each monomer, and then n-butyl mercaptan 0.35 m which was subjected to vacuum distillation purification as a chain transfer agent.
1 (1.5 × 10 ⁻² mol / 1000 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 polytetrafluoroethylene (Teflon, trade name of Du Pont Co., Ltd.) tube to the polymerization container so as not to be contaminated. The polymerization vessel is made of quartz glass and has a cylindrical shape with an inner diameter of 30 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 a polymerization vessel, the upper end was evacuated under reduced pressure to remove dissolved air, and the evacuated evacuated quartz glass portion having an inner diameter of 6 mm was heat-sealed with a burner. Next, the pressure-sealed polymerization vessel was immersed in liquid nitrogen, and freezing and heating and thawing of the monomer solution were repeated to sufficiently remove the dissolved gas. The polymerization container was heated at 130 ° C. for 16 hours to carry out thermal polymerization. The glass tube at the upper end was cut and unsealed, then immediately transferred to a vacuum dryer and heated at 100 ° C. for 48 hours to remove volatile components in the copolymer to obtain a transparent preform having no bubbles. . A heating furnace for the polymerization vessel, a clad coating die, a clad drying furnace, and a wire drawing device in which a winding machine is vertically arranged are used, and the temperature of the heating furnace is set in advance to 190 to 210 ° C. The glass tube at the lower end of the container 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 copolymer is melt extruded from the nozzle at the lower end of the polymerization container, so the core is about 0.5 mm.
The take-up speed was adjusted and set so that On the other hand, as a clad material, a vinylidene fluoride-tetrafluoroethylene copolymer (melting point 132 ° C., composition 80/20 molar ratio) 30
% Ethyl acetate-methyl ketone mixed (1/1) solution was used to fill a clad coating pot, and the drawn core was passed through the pot, the clad die, and a drying oven held at 160 ° C. to remove the solvent, and the outer diameter was 0. It was molded into a plastic optical fiber of 0.5 mm and a clad film thickness of 20 μm.

Next, using a gamma ray of cobalt 60 on the above-mentioned plastic optical fiber wound to a diameter of 200 mm, 6 × 10 ⁴ r /
A total dose of 15 megarads was irradiated at 25 ° C. at a dose rate of h. The properties of the obtained plastic optical fiber are shown in Table 1.

The acetone extraction weight loss of the core after irradiation was 13%, and it only swelled at 100 ° C. in a mixed solvent (1/1) of xylene and metacresol.

(Comparative Example 1) 107 ml (1.0 mol) of purified methyl methacrylate,
Purified 2,2′-azobis (isobutyronitrile) 0.01% as a polymerization initiator, chain transfer agent n-butyl mercaptan 0.17 ml (1.5 × 10 ⁻² mol / monomer 1)
A plastic optical fiber was manufactured in the same manner as in Example 1 except that the monomer solution composition was 000 ml), and gamma rays were irradiated. The properties of the obtained optical fiber are shown in Table 1. Acetone extraction weight loss of core after irradiation is 96
% And 10 in a mixed solvent of xylene and metacresol.
It dissolved at 0 ° C. without stopping the shape.

(Comparative Example 2) The optical transmission loss of the plastic optical fiber prepared in Example 1 before gamma ray irradiation was 0.40 dB / m at 25 ° C, but at 120 ° C, light was not transmitted and measurement was impossible. In addition, the core before gamma ray irradiation was 100% in the acetone extraction test.
% Dissolved in acetone.

[Effects of the Invention] As described in detail above, the plastic optical transmission article produced by the production method of the present invention is excellent in heat resistance and solvent resistance, and has high industrial practicality. is there.

Claims (1)

[Claims] 1. (a) As a monomer, a commercially available reagent grade methyl acrylate is distilled to remove a polymerization inhibitor and purified, and 10 mol% of purified methyl acrylate and a commercially available reagent grade methyl methacrylate are subjected to distillation to prevent polymerization. 30 mol% of purified methyl methacrylate obtained by removing the agent and purified, and 60 mol% of purified styrene obtained by distilling styrene under reduced pressure to remove the polymerization inhibitor and purified are put into a mixing vessel and mixed by stirring with a magnetic stirrer. (B) 0.01% by mole of a special grade of azotertiary butane as a polymerization initiator with respect to the number of moles of the mixed monomer is added to the mixing vessel, and then distillation purification under reduced pressure is performed as a chain transfer agent. Monomer 1000 with mixed n-butyl mercaptan
a step of adding 1.5 × 10 ⁻² mol to ml and stirring and mixing; and (c) a quartz glass-made tube made of a fluorinated ethylene propylene resin tube from a mixing container so that the stirred and mixed monomer solution is not contaminated. Cylindrical, the upper end and the lower end are narrowed down, and the lower end is transferred to a sealed polymerization container, and While heating and sealing the quartz glass part at the top with a burner, (e) dip the vacuum-sealed polymerization vessel in liquid nitrogen and freeze and thaw the monomer solution repeatedly to sufficiently remove the dissolved gas. And (f) heat the polymerization vessel at 130 ° C. for 16 hours to perform thermal polymerization, cut the glass tube at the upper end and unseal, immediately transfer to a vacuum dryer, and heat at 100 ° C. for 48 hours. Copolymer A step of removing the volatile components in the solution to obtain a transparent preform free of air bubbles, and (g) a drawing in which the heating furnace for the polymerization vessel, the clad coating die, the clad drying furnace, and the winding machine are arranged in a rigid pattern. Using the equipment, set the temperature of the heating furnace in advance to 190-210 ° C, cut the glass tube at the lower end of the quartz glass polymerization container, and attach it in the heating furnace. From the upper end, 1 kg / cm ² with N ₂ gas. A step of pressurizing, and (h) a step of adjusting and setting the take-up speed so that the core has a predetermined thickness when the temperature of the preform rises and the copolymer is melt-extruded from the nozzle at the lower end of the polymerization container. (I) 80% by mol of vinylidene fluoride and 2 in a solvent obtained by mixing ethyl acetate and methyl ethyl ketone in a ratio of 1: 1.
A clad coating pot was filled with a solution in which 30% of a clad copolymer consisting of 0 mol% tetrafluoroethylene was dissolved, and the drawn core was passed through a pot, a clad die and a drying oven maintained at 160 ° C. to obtain a solvent. Except for the step of forming a clad film on the outer circumference of the core to form a plastic optical fiber, and (j) using a gamma ray of cobalt 60 on the plastic optical fiber to give a total dose of 15 megarads at a dose rate of 6 × 10 ⁴ r / h. And a step of irradiating at 25 ° C.