JPS6134503A - Plastic optical transmission body - Google Patents

Abstract

PURPOSE:To provide superior heat resistance by combining a core with a clad having a lower refractive index than the core and by using a cross-linked polymer consisting of specified structural units as the material of the core. CONSTITUTION:The core is combined with the clad having a lower refractive index than the core. The core is made of a cross-linked polymer contg. structural units of glycidyl methacrylate and/or beta-methylglycidyl methacrylate by >=5mol% (expressed in terms of the monomers), and the clad is made of a homo- or copolymer of vinylidene fluoride or the like. Since a glycidyl methacrylate polymer for the core has epoxy groups in the molecule, it is effectively cross- linked by slight irradiation, has the improved heat resistance, and can be used at >=100 deg.C. The resulting plastic optical transmission body is used for applications requiring heat resistance such as an optical data link for an automobile.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a plastic optical transmission body having excellent heat resistance and comprising a core and a cladding.

[Problems with conventional technology]

Conventionally, optical transmission bodies have been manufactured using transparent quartz glass or plastic. Optical fibers using silica glass have excellent optical transmission properties and are put into practical use for long-distance communications. Although plastic optical fibers have inferior optical transmission properties compared to optical fibers made of quartz, they have advantages such as good flexibility, light weight, and ease of processing. Applications to light guides, sensors, etc. are underway.

Many of these applications require heat resistance.

For example, optical fibers used for automobile optical data links have a temperature of 100 to 120 degrees due to heat from the engine room.
It is required to withstand high temperatures such as C. However, conventional plastic optical fibers use polystyrene or polymethyl methacrylate for the core, and the normal operating temperature is only 80°C. Optical fibers made of polystyrene or polymethyl methacrylate can be heated to 80°C.
At higher temperatures, shrinkage occurs, reducing optical transmission.
Further, at high temperatures of 100° C. or higher, large shrinkage occurs, which not only reduces optical transmission properties but also breaks the fiber itself, making it completely impermeable to transmit light.

The glass transition point and melting point are physical properties that indicate the performance at high temperatures of polymethyl methacrylate and fluorine-containing polymers used in the core and cladding of conventional plastic optical fibers. The glass transition point of polymethyl methacrylate is approximately 105°C, and at temperatures above the glass transition point, the segmental motion of the polymer molecules becomes more intense, resulting in increased fluctuations and changes in the refractive index, resulting in significant light scattering loss. It becomes impossible to maintain practical performance.

For this reason, it was considered to use a polymer with a high glass transition point for the core, and addition polymerization polymers and condensation polymers were considered. Polycarbonate is a condensation polymer with good transparency, and its glass transition point is about 1450. The fiber obtained with polycarbonate as the core had good thermal properties, but the optical transmission performance was lower than that of polystyrene,
It was considerably inferior to polymethyl methacrylate. The reason is that polycarbonate obtained by condensation polymerization requires a step to remove condensation by-products such as NaCl, and it seems that the residue and contamination of impurities are unavoidable. In addition to polycarbonate, polysulfone and polyarylester are known as condensed amorphous polymers that exhibit a high glass transition point, but the fiber processing temperature is high, resulting in decomposition of the polymer, residual impurities, and contamination. However, it was not possible to obtain a fiber with good optical transmission properties.

A material with a refractive index smaller than that of the core is used as the cladding material of the plastic optical transmission body. Conventional plastic optical fibers with a core of polymethyl methacrylate include a polymer of fluoroalkyl methacrylate or a copolymer of vinylidene heptadide and tetrafluoroethylene as a cladding material, with a vinylidene fluoride content of, for example, 77 moles. copolymers are used. However, the polymer of fluoroalkyl methacrylate has a low decomposition initiation 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, when a fiber using fluoroalkyl methacrylate as a cladding is exposed to a temperature near its glass transition temperature, the transmission loss begins to increase, and at a temperature of 100'O or higher, the loss increases to such an extent that it cannot be used.

On the other hand, a copolymer of vinylidene fluoride and tetrafluoroethylene containing 77 moles of vinylidene fluoride has a melting point of 1100.

Therefore, if the fiber is exposed to temperatures near or above its melting point, transmission loss will increase, and the core will flow, resulting in a significant drop in transmission characteristics.

Copolymers of aryl methacrylate and P-7 enyl styrene are addition polymers that provide polymers with high glass transition temperatures, but these monomers belong to special monomers that are not manufactured industrially and are not practical. It is necessary to start by establishing an economical mass production method for monomers.

[Purpose and outline of the invention]

Based on the knowledge of the prior art described above, the present inventors conducted extensive studies on improving the heat resistance of plastic optical transmission bodies and arrived at the present invention. .

The present invention uses a polymer containing structural units of glycidyl methacrylate and/or β-methylglycidyl methacrylate having a molar ratio of 5 or more in terms of monomer molar ratio as the core, and the outer region has a refractive index lower than that of the core. The present invention relates to a plastic optical transmission body formed by forming a cladding of a polymer, and at least the core thereof is crosslinked by radiation irradiation or the like.

[Effects and Detailed Description of the Invention] According to the present invention, heat resistance can be improved by efficient radiation crosslinking, which cannot be used with conventional plastic optical transmission materials having cores of polymethyl methacrylate or polystyrene. In addition, a plastic optical transmission body that can be used even at a temperature of 100'0 or more can be obtained. In addition to plastic optical fibers, the plastic optical transmission body according to the present invention can be used in a wide range of applications such as waveguides for optical integrated circuits, optical couplers, optical demultiplexers, and advertising displays.

Polymethyl methacrylate is easily decomposed by radiation rather than cross-linked efficiently, and when the irradiation distance is large (d), it may generate decomposition gases such as Co, CO2, H2, and bubbles in the polymer. It is difficult to improve heat resistance by cross-linking polymethyl methacrylate, a homopolymer of methacrylate, with radiation.However, when a group that can be easily cross-linked by radiation is introduced into the structural unit of the polymer, there There is a possibility that crosslinking can be achieved effectively even with a relatively small dose of radiation, and the present inventors focused on this point and proceeded with their research, and found that polymers with epoxy groups introduced into their molecules are suitable for radiation crosslinking.

The present invention first uses a polymer containing structural units of glycidyl methacrylate and/or β-methylglycidyl methacrylate having a molar ratio of 5 or more in terms of monomer molar ratio. When making a copolymer, glycidyl methacrylate
The following monomers can be cited as co-electrical monomers with 1 and/or β-methylgrindyl methacrylate: methylmethacrylate 1, ethyl methacrylate
1, isopropyl methacrylate-1, 1-butyl methacrylate, cyclohegycyl methacrylate, phenyl methacrylate-1, benzyl methacrylate-1, furfuryl methacrylate-1, styrene, methyl acrylate, ethyl acrylate, etc. It is.

Generally, when monomers M+ and M2 are copolymerized, the copolymers obtained according to the monomer reactivity ratios rl and r2 have different main chain structures such as random, block, and alternating structures. Differences in composition in the main chain, such as in block copolymers, are undesirable because they cause light scattering due to density fluctuations, microphase separation, etc., and reduce light transmission. Therefore, simply combining glycidyl methacrylate and/or β-methylglycidyl methacrylate with any other monomer and polymerizing it to obtain a copolymer does not necessarily result in low-loss optical transmission. A practical copolymer can be obtained by selecting from among the above-mentioned methacrylic acid ester monomers, acrylic acid ester monomers, and styrene monomers and combining them with silk.

The monomer to be copolymerized with glycidyl methacrylate and/or β-methylglycidyl methacrylate is preferably used in a range of 95 moles in terms of monomer moles. If more than 95 moles of these are contained in the copolymer, the content of epoxy groups in the copolymer will be too low and crosslinking will be insufficient for electron beam irradiation, making it impossible to achieve the objective of improving heat resistance. Note that the electron beam irradiation conditions are set to optimal values depending on the composition, molecular weight, content of epoxy groups, etc. of the polymer, and crosslinking is performed.

As for the polymerization method, since methacrylate having a highly reactive epoxy group is used as a monomer, a bulk polymerization method is preferable since there is no risk of contamination with impurities, but it is possible to use a solution polymerization method or It is also possible to produce by a suspension polymerization method.

As the cladding material used in the present invention, a copolymer containing polyvinylidene fluoride units as a main component is suitable, and the melting point of the polymer is preferably 1200 or higher. 100 if the melting point is less than 120°C
This is because when exposed to temperatures of up to 120° C., transmission loss increases and the device becomes unusable. However, if the core and cladding are crosslinked by simultaneously irradiating the core with an electron beam after the core is clad, the melting point of the cladding material before crosslinking may be less than 1200. Vinylidene fluoride copolymers that can be used in the present invention include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene,
In addition to fluorine-containing vinyl compounds such as vinyl fluoride, chlorotrifluoroethylene, and perfluoroalkyl vinyl ether, methyl methacrylate and butyl methacrylate-1
Examples include copolymers of tutaacrylic acid esters such as ・and vinyl acetate. When using a copolymer of vinylitine fluoride and tetrafluoroethylene, if the content of tetrafluoroethylene exceeds 60 mol, the crystallinity of the copolymer becomes too strong and the adhesion with the core decreases considerably. It's not nice. In addition to the vinylidene fluoride copolymer, the present invention also includes a copolymer of polyvinylidene fluoride copolymer and glycidyl methacrylate, and/or a copolymer of β-methylglycidyl methacrylate and nystelt methacrylate. Glycidyl methacrylate and/or β
- Mixtures of methylglydyl methacrylate and copolymers of methacrylic acid esters can also be used as cladding materials. In this case, by adjusting the content of epoxy groups in the mixture, it is possible to easily control the irradiation crosslinking properties of the cladding, suppress crystallization of the vinylidene fluoride copolymer, and improve adhesion to the core. can. The mixing ratio of the vinylidene heptadide-based polymer and the above-mentioned methacrylic acid ester copolymer can be changed over a wide range, but the refractive index difference between the core and the cladding must be set within a range of 1 inch or more of the refractive index of the core. is preferred.

There are no particular restrictions on the means for coating the core with the cladding, such as a method of coating the core with a solution of the cladding material by a coating method after molding the core, a method of coating the core material and the cladding material with a composite spinning nozzle having a core-sheath structure. Any conventionally known method may be used, such as a method of forming by melt-spinning using.

Bulk polymerization is preferable for producing the polymer used for the core, and in order to obtain an optical transmission body with low loss, it is preferable to prepare a preform free from foreign matter as follows and melt-mold it.

The core material used in the present invention is a monomer that has been purified by methods such as microfiltering, distillation, and recrystallization to remove impurities and polymerization inhibitors contained in each monomer, and is purified in a closed system or in a dust-free clean atmosphere. The mixture is mixed, a chain transfer agent for controlling the molecular weight of the polymer and a polymerization initiator are added, and the mixture is introduced into a polymerization vessel in a closed system or in a clean atmosphere and thermally polymerized. The size of the preform is determined by the polymerization container and the amount of monomer used, but for example, 10 m
Diameter from m to 30mm, 200mm to 1000m
A length of m can be easily made. In order to obtain a preform without air bubbles that cause light scattering, it is necessary to remove the air dissolved in the monomer by freezing and degassing before polymerization, and to polymerize in a vacuum-sealed tube or to install a piston in the polymerization container. It is preferable to carry out polymerization while pressurizing the monomer solution during polymerization so that there is no surface.

The polymerization temperature can be a normal thermal polymerization temperature, for example, 60°C or higher, but it is better to carry out the polymerization at a temperature as high as possible because the polymerization time is shorter and the structure and composition of the resulting copolymer is more irregular. This makes it possible to obtain an optical transmission body with lower loss. Preferably a temperature of 60°C to 140°C is chosen. When polymerization is started at a relatively low temperature of 60 to 80°C, the temperature is raised at the end of the polymerization to reach a temperature higher than the glass transition temperature of the final polymer, and the polymerization is completed at this temperature. , preferably a preform.

Note that it is suitable to heat and melt a preform and draw it for a simple-shaped optical transmission body such as a plastic optical fiber, but when manufacturing a complex-shaped optical waveguide, etc., it is necessary to draw it without going through a preform. It is also possible to complete polymerization into the final shape by injecting the monomer solution into a mold of the desired shape.

The preform can be made into a fiber by melt spinning. An effective method is to use a ram extruder equipped with a cylinder and a piston to heat and melt the preform in the cylinder and move it at a constant pressure or speed to supply a fixed amount of the molten polymer that will become the core to the spinning die. can. Alternatively, it is also possible to use Fi, or a method of supplying a fixed amount of core polymer to a spinning die by charging a preform into a cylinder, melting it, and pressurizing it with an inert gas such as N2 gas instead of a piston. The preform does not necessarily need to be taken out from the polymerization vessel; a spinning die may be attached to the bottom of the polymerization tube in advance, and after the polymerization is completed, the preform may be pressurized with an inert gas, heated and melted, and drawn.

At least the core of the plastic optical transmission body of the present invention is cross-linked by radiation irradiation, but the radiation includes α-rays, β-rays, and R-rays, as in general radiation chemical reactions.

Ionizing radiation such as X-rays, neutron beams, and electron beams is used. In the present invention, it is advantageous to use gamma radiation of up to 60% (Kobal) or an electron beam obtained from an electron beam accelerator.

[Embodiments of the invention]

The present invention will be specifically explained below with reference to Examples, but the present invention is not limited thereto.

Example 1 β-methylglycidyl methacrylate was purified by distillation under reduced pressure to form polymerized form 1 by removing the agent. Commercially available reagent grade methyl methacrylate], 10g of Na per OOml
5% NaOH aqueous solution in which C1 was dissolved 200
After washing, anhydrous sodium sulfate was added, drying was performed, and precision purification was performed by distillation under reduced pressure.

The precision purification receiver for methyl methacrylate was equipped with a weighing line and was equipped with piping so that the required amount of monomer could be transferred to the mixing container without contact with 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 to the polymerization vessel using a PTFE stopper.

Purified β-methylglycidyl methacrylate-1146ml (
], 0 mol) was weighed on a clean bench and poured into a mixing container. Purified methyl methacrylate 107ml (1
, 0 mol) was transferred to a mixing container and mixed with magnetic starch. As a polymerization initiator, 2゜21-azobis(isobutyronitrile), which had been recrystallized twice in methanol, was added in an amount of 0.01% of the sum of the moles of each monomer, stirred and dissolved, and then chained. Lobutyl mercaptan purified by vacuum distillation was used as a transfer agent at 0.4 Om.
l: (1,,5X 1. Q ”mat/monomer 100
100O was added and the mixture was further stirred and mixed. The monomer solution was transferred from the mixing vessel to the polymerization vessel via a Teflon tube from the outlet to the polymerization vessel to avoid contamination. The polymerization container was made of quartz glass and had a pipe shape with an inner diameter of 30 mm, the upper and lower ends of which were tapered to an inner diameter of 6 mm, and the lower end was melt-sealed.

After the monomer solution was transferred to a polymerization container, dissolved air was removed by evacuation from the upper end, and the quartz glass tube portion with an inner diameter of 6 mm at the upper end was heated and melt-sealed with a burner under reduced pressure. Furthermore, the polymerization container was immersed in liquid nitrogen, and the monomer solution was repeatedly frozen and heated and thawed to remove dissolved gas.

A polymerization container sealed under reduced pressure was heated at 130° C. for 916 hours for polymerization. After cutting the glass tube at the top and unsealing it, it was immediately transferred to a vacuum dryer and heated under vacuum at 100° C. for 948 hours to remove volatile components in the copolymer, thereby obtaining a transparent preform with no air bubbles.

Using a wire drawing device equipped with a heating furnace for the polymerization container, a cladding coating die, a cladding drying furnace, and a winder, the temperature of the heating furnace was set in advance at 190 to 210°O. The glass tube at the lower end was cut, placed in a heating furnace, and pressurized with N2 gas at 1 kg/cm2 from the upper end. As the temperature of the preform rises, the polymer is melted and extruded from the nozzle at the bottom of the polymerization vessel, so that the core diameter is approximately 1.5 mm. , Om
The take-up speed was adjusted and set so that On the other hand, a 30% solution of vinylidene fluoride-tetrafluoroethylene copolymer (melting point 132 O, composition 80/20 molar ratio) in ethyl acetate was used as the cladding material, and the cladding material was filled into a pot for cladding coaching. The resulting core was passed through a pot and die and a drying oven held at 160'O to remove ethyl acetate and have an outer diameter of 1.0 mm% and a cladding film thickness of 20μ.
It was molded into a plastic optical fiber of m.

Next, cobalt 60 gamma rays were applied to the 6X1.0 plastic optical fiber, which was wound to a diameter of 200 mm.
A total dose of 25 megarads was irradiated at 25°C at a dose rate of 'r/hr. Table 1 shows the properties of the obtained plastic optical fiber.

The acetone extraction loss of the core after irradiation was 8.5 inches, and the core was immersed in a mixed solvent of xylene and metacresol (1:1) at 100°C.
It just swelled.

Example 2 20 moles of β-methylglycidyl methacrylate, 50 mole% of purified styrene purified by 3-pressure distillation of purified methyl methacrylate, 2. 2'-azobis(isobutyronitrile) at 0.01% of the sum of moles of each monomer, n-butyl mercaptan at 1.5X
A plastic optical fiber was produced in the same manner as in Example 1, except that a monomer solution mixed at a ratio of 10" mol/total of monomers of 100 Oml was used, and gamma rays were irradiated. The properties of the obtained plastic optical fiber were determined. It is shown in Table 1.The acetone extraction loss of the core after irradiation was 1.4.
10 for a mixed solvent of xylene and metacresol
There was only slight swelling at 0°C.

Example 3 10 moles of β-methylglycidyl methacrylate, 257 moles of methyl acrylate purified by distillation, and 65 moles of methyl methacrylate purified by distillation, and 0.2 moles of 2,2'-azobis(isobutyronitrile) based on the sum of the moles of each monomer. 01%,
1,5 x 10” mob of n-butyl mercaptan
A plastic optical fiber was manufactured in the same manner as in Example 1 except for using a monomer solution mixed at a ratio of 10,100 O/monomer, and irradiated with gamma rays. however,
The polymerization container sealed under reduced pressure was heated at 100°C for 16 hours.
The monomer solution was polymerized by heating at 40°C for 12 hours. Table 1 shows the properties of the obtained plastic optical fiber.

The acetone extraction loss of the core after irradiation was 12.4%,
It was only swollen in a mixed solvent of xylene and metacresol at 100C.

Example 4 Glycidyl methacrylate 25 purified by vacuum distillation
Miruchi, purified methyl methacrylate 75 mol%, 2.2
'-azobis(isobutyronitrile) 0.01% of the sum of moles of each monomer, n-butyl mercaptan 5
A monomer solution mixed at a ratio of 10-3 mol/monomer total of 1000 m7 was injected into a Teflon tube with an inner diameter of 4 mm and a length of 100 mm (the lower end was sealed with a glass rod).
Polymerization was carried out by heating at 80°C for 924 hours and at 130'0° for 5 hours to produce a transparent polymer with a diameter of 4 mmC. Teflon tea
The polymer was removed from the bag, and immediately placed in a polyethylene bag with a zipper and stored in a desiccator so as not to be touched. On the other hand, vinylidene fluoride with clad material and 1
Tetrafluoroethylene copolymer (melting point 132°O, A
(80/20 molar ratio) and the β-methylglycidyl methacrylate-methyl methacrylate copolymer before irradiation for the core obtained by polymerization in Example 1.
A 30% ethyl acetate solution was prepared containing:

A 4 mm core stored in a desiccator was coated with a 20 μm thick cladding, and then cobalt-60 gamma rays were used at a dose rate of 6 x 10'r/hr for a total dose of 3.5
Megarads were irradiated at 25°C. The optical transmission loss of the rod-lens optical waveguide obtained in this way @1) is 25°C.
and 0.35dB15.

It was 0.92 dB/5 crn at 120°C.

The acetone extraction loss of the core was 11.5%, and it was only swollen in a mixed solvent of xylene and metacresol at 100'O.

Comparative Example 1 Purified methyl methacrylate 107 mt (1.0 mol),
Purification 2.21-azobis(isobutyronitrile) 0.0
1, n-butyl mercaptan 0.17 ml (1,5
A plastic optical fiber was manufactured in exactly the same manner as in Example 1 except that the monomer solution composition was 10-2 mol of X/100,100 O of monomer, and irradiated with gamma rays.

Table 1 shows the properties of the obtained fiber. The acetone extraction loss of the core after irradiation was 96 inches, and it was dissolved in a mixed solvent of xylene and metacresol at 100'0 without retaining its shape.

Comparative Example 2 Purified β-methylglycidyl methacrylate 5.8mt (
0.04 mol), purified methyl methacrylate 103 ml
(0.96 mol), purified 2.2'-7zopis(isobutyronitrile) 0.01%, n-butyl mercaptan 0.
Example 1 except that the monomer solution composition consisted of 17 mt.
A plastic optical fiber was manufactured in exactly the same manner as above and irradiated with gamma rays. Table 1 shows the properties of the obtained fiber. After irradiation, the core was extracted with acetone, and the weight loss was 74 cm, and the core was extracted with 100 cm in a mixed solvent of xylene and metacresol.
It swelled significantly in O and collapsed.

-22= Specification! 'I'QF (no change in content) Table 1 Optical transmission loss is 5
- Cut the cross section using a 10m good test.

Specification: No.1) Wataru 1; (No change in content) While performing the polishing 1'f9, the incident 1110 I light h1 was measured with an optical power meter and the average value of the transmission loss was determined (as in the trial of Example 4). 1′
+1 was measured for a length of 5 cm). The transmission loss I- is given by the following equation, where β is the length.

Here, ■0 is the amount of incident light, and ■ is the amount of output light. 120℃
The optical transmission loss was measured by using a 5 m test r1, passing 3.5 m through a thermostatic oven for 1 time, taking out the light input and output ends outside the 1 nm temperature oven, and measuring at a closed temperature.

Procedural amendment letter G 59.12.20 Showa year, month, day 1, case description a person making the amendment 4, agent 〒100 residence 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Telephone Tokyo (216) 1611 ( Major Representative) b, Raku Yuishi Q Feng Yut Egg Yuerippon ゎ λ3 Yugu, Trout ° Masa's 19th farewell 5. Cheer, i1 chant hook

Claims (1)

[Claims] 1. In a plastic optical transmission body consisting of a core and a cladding having a refractive index lower than that of the core, the core contains glycidyl methacrylate and/or β-glycidyl methacrylate in an amount of 5 mol % or more in terms of monomer mol %. 1. A plastic optical transmitter, which is made of a polymer containing a structural unit of methylglycidyl methacrylate, and wherein at least the core is crosslinked. 2. The plastic optical transmission body according to claim 1, wherein polyvinylidene fluoride or a copolymer having vinylidene fluoride units as a main component is used as the cladding component.