JPS6135404A - Plastic optical transmission body - Google Patents

Abstract

PURPOSE:To obtain a plastic optical transmission body having good heat resistance and solvent resistance by consisting a core of a homopolymer or copolymer contg. >=1 kinds of styrene, styrene deriv. and acrylate as a constitutional unit and crosslinking the same at least by radiation irradiation. CONSTITUTION:A transparent polymer is manufactured by feeding a monomer soln. mixed with refined styrene, chain transfer agent and n-butyl mercaptan into a ''Teflon(R)'' tube, putting the same into a stainless steel vessel which permits evacuation to a reduced pressure, closing a discharge valve after the evacuation and deforaming and executing thermal polymn. in a thermostatic chamber while maintaining the reduced pressure condition. The operator withdraws the polymer from the ''Teflon(R)'', puts quickly the same into a zippered PE bag and stores the same in a desiccator. On the other hand, the above-mentioned core is subjected to coating thereon by using a mixed ethyl acetate/methyl ethyl ketone soln. of a vinylidene fluoride/tetrafluoroethylene polymer as a clad. The gamma rays of Cobalt 60 are irradiated on such rod lens-shaped optical waveguide.

Description

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

[Prior art and its problems]

Conventionally, optical transmission bodies have been manufactured using quartz glass or plastic. Optical transmission bodies using quartz glass have excellent optical transmission properties and are put into practical use for long-distance communications. Plastic optical transmitters have inferior optical transmission properties compared to optical transmitters made of quartz, but they have advantages such as good flexibility, light weight, and ease of processing, and these can be utilized to create short-distance data links. , light guides, sensors, etc. are being applied. Heat resistance is often required in these applications. For example, optical transmission bodies used in optical data links for automobiles are required to withstand high temperatures of 100 to 120° C. due to heat from the engine room. However, conventional plastic optical transmission bodies use polystyrene or polymethyl methacrylate for the core, and the normal operating temperature is only 80°C.

Optical transmitters made of polystyrene or polymethyl methacrylate will shrink when exposed to high temperatures of 80'C or higher, resulting in a decrease in optical transmission properties.Furthermore, at high temperatures of 100'C or higher, significant shrinkage will occur, resulting in not only a decrease in optical transmission properties. The optical transmission body itself would break, and no light would pass through it at all.

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 transmitters. The glass transition point of polymethyl methacrylate is about 105°C. At temperatures above the glass transition point, the segmental motion of polymer molecules becomes more intense, leading to increased fluctuations and larger changes in the refractive index, resulting in significant light scattering loss, making it 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 145°C. Although the optical transmission body obtained using polycarbonate as a core had good thermal properties, the optical transmission properties were considerably inferior to those of polystyrene and polymethyl methacrylate. The reason seems to be that polycarbonate obtained by condensation polymerization requires a step to remove condensation by-products such as NaCt, and the residue and contamination of impurities are unavoidable. Polymers such as polysulfone and polyarylester are known in addition to polycarbonate as condensed amorphous polymers that exhibit a high glass transition point, but the processing temperature for optical transmitters is high, resulting in polymer decomposition, impurity residue, and contamination. However, it has not been possible to obtain an optical transmitter 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. Conventionally, a polymer of fluoroalkyl methacrylate or a copolymer of vinylidene fluoride and tetrafluoroethylene has been used as a cladding material in a plastic optical transmission body having a core of polymethyl methacrylate. However, fluoroalkyl methacrylate polymers have a low decomposition temperature, which not only poses problems in fiber production, but also has a glass transition temperature of 60 to 90°C, which is a low temperature range.

Therefore, when an optical transmission body using fluoroalkyl methacrylate as a cladding is exposed to a temperature near its glass transition temperature, transmission loss begins to increase, and at a temperature of 100° C. 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 with a vinylidene fluoride content of 77 molt has a melting point of 110°C.
It is.

Therefore, when the optical transmitter is exposed to temperatures near or above the melting point, transmission loss increases, and the core flows, resulting in a significant drop in transmission characteristics. Copolymers of aryl methacrylate and p-7 enylstyrene are examples of addition polymerization polymers that provide polymers with high glass transition temperatures, but these monomers belong to special monomers that are not manufactured industrially. For practical use, it is necessary to start by establishing a method for mass production of 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 provides a plastic optical transmission body consisting of a core and a cladding having a refractive index lower than the core, wherein the core is made of a homopolymer or copolymer containing one or more of styrene, styrene derivatives, and acrylic esters as a structural unit. The present invention is a plastic optical transmission body having good heat resistance and solvent resistance, characterized in that at least the core is crosslinked by radiation irradiation.

The present inventors investigated the heat resistance of plastic optical transmission bodies.

Focusing on crosslinking of polymers as a means to improve solvent resistance, we investigated crosslinking by radiation irradiation. As a result, optical transmitters with methyl methacrylate homopolymer cores are not effectively crosslinked by radiation irradiation, and when the irradiation dose is increased, decomposed gases such as Co and CO2°H2 are generated, and bubbles are formed in the core. However, no improvement in properties due to crosslinking was realized.

However, when a homopolymer or copolymer containing one or more selected from styrene derivatives and acrylic esters as a structural unit is used as a core, and when irradiated with radiation, crosslinking occurs between the polymer molecules, resulting in heat resistance and solvent resistance. The present inventors have found that this significantly improves the performance of the present invention, and have completed the present invention. In addition to optical fibers, the plastic optical transmission body of the present invention includes waveguides for optical integrated circuits, optical couplers, optical demultiplexers, optical lenses, etc., and can be used for a wide range of purposes.

[Supplementary explanation of the invention]

The core material used in the present invention is one selected from styrene or its derivatives such as styrene, chlorstyrene, fromstyrene, and 2,5-diclostyrene, and acrylic esters such as methyl acrylate, ethyl acrylate, phenyl acrylate, and benzyl acrylate. A homopolymer or copolymer containing the above as a structural unit,
Copolymerization of methyl methacrylate may be used as long as the crosslinking effect caused by radiation irradiation is not significantly impaired.

Generally monomer M1. When M2 is copolymerized, the copolymers obtained with a monomer reactivity ratio of '++'2 have different main chain structures such as random, block, and alternating structures. Differences in composition in the main chain, such as in block copolymers, cause light scattering due to density fluctuations and microphase separation, reducing optical transmission properties, so copolymerization does not necessarily result in a low-loss optical transmission material. I can't. In addition, if crystal and amorphous parts coexist in the polymer, light scattering becomes significant, so the combination of monomers and polymer composition must be selected. The polymers of styrene and styrene derivative monomers described above generally become amorphous polymers, but since homopolymers of acrylic acid esters contain crystals, they can be used as copolymers with styrene, styrene derivatives, and methyl methacrylate. Preferably used in the present invention.

As the polymerization method for the core used in the present invention, a bulk polymerization method with less risk of contamination with impurities is preferable, but it is also possible to manufacture the core by a solution polymerization method or a suspension polymerization method by appropriately selecting the solvent and dispersant. .

As the cladding material used in the present invention, polyvinylidene fluoride or a copolymer containing vinylidene fluoride units as a main component is suitable, and the melting point of the polymer is preferably 120° C. or higher. 100~ when the melting point is less than 120℃
This is because when exposed to temperatures such as 120° C., transmission loss increases and the device becomes unusable. However, if the cladding material is simultaneously crosslinked by applying radiation to the core after forming the core into the shape of an optical transmission body, the melting point of the cladding material before crosslinking may be lower than 120°C. Vinylidene fluoride copolymers that can be used in the present invention include vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene.

Examples include copolymers of fluorine-containing vinyl compounds such as vinyl fluoride, chlorotrifluoroethylene, and perfluoroalkyl vinyl ether, methacrylic acid esters such as methyl methacrylate and butyl methacrylate, and vinyl acetate. When using a copolymer of vinylidene fluoride and tetrafluoroethylene, if the content of tetrafluoroethylene is 60 molt or more, the crystallinity of the copolymer increases and the adhesion with the core decreases, which is undesirable. .

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

The polymer used for the core is bulk polymerized as described above.

Although it can be manufactured by solution polymerization or suspension polymerization, bulk polymerization is preferable, and in order to obtain a low-loss optical transmitter, a preform that does not contain foreign substances is prepared as follows, and this is melt-molded, or Alternatively, it is preferable to complete the polymerization and molding simultaneously in a mold having the final shape.

The raw material monomer for the core used in the present invention is first filtered to remove impurities and polymerization inhibitors using a microfilter.

Monomers purified by methods such as distillation or recrystallization are mixed in a closed system or in a clean atmosphere without dust, and a chain transfer agent and a polymerization initiator are added to adjust the molecular weight of the polymer. It can be obtained by introducing it into a polymerization container and thermally polymerizing it. When making a preform, the size is determined by the polymerization container and the amount of monomer used, but for example, a diameter of 10 mm to 30 mm, a length of 200 to 1000 m.
A length of m can be easily made. In order to obtain a preform without air bubbles that cause light scattering, the air dissolved in the monomer must be removed by freezing and degassing before the start of thermal polymerization, and the polymerization must be carried out in a vacuum-sealed tube or a piston must be installed in the polymerization container. It is preferable to carry out the polymerization while pressurizing the monomer solution during polymerization so that there are no free surfaces.

The polymerization temperature can be a normal thermal polymerization temperature, for example, 60°C or higher, but the higher the temperature, the shorter the polymerization time, and the structure and composition of the copolymer produced will be more irregular. An optical transmission body with lower loss can be obtained.

Preferably a temperature of 60°C to 140°C is chosen. 6
When polymerization is started at a relatively low temperature such as 0 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 to form the preform. It is preferable to do so.

Melt spinning can be applied to produce preforms or fibrous light transmitters. An effective method is to use a ram extruder equipped with a cylinder and 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. Available. Alternatively, a method can also be used in which the core polymer is quantitatively supplied to the spinning die by charging the preform into a cylinder, melting it, and pressurizing it using 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, 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 can be alpha, beta, or gamma rays, as in general radiochemical reactions.

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

〔Example〕

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

Example 1 The polymerization inhibitor was purified by adding styrene dropwise under reduced pressure.

The styrene precision purification receiver was equipped with a weighing wire and was equipped with piping so that the required amount of monomer could be transferred to the mixing container without touching it. The mixing vessel is equipped with a Teflon rotor for stirring, an inlet for adding a copolymerization monomer, a polymerization initiator, and a chain transfer agent, and an outlet to the polymerization vessel using a Teflon stopper.

Commercially available reagent grade methyl acrylate was purified by removing the polymerization inhibitor using a dropless method. Commercially available reagent grade methyl methacrylate was purified by removing the polymerization inhibitor using a dropless method as in the case of methyl acrylate.

18 mJ (0.2 mol) of purified methyl acrylate was weighed on a clean bench and charged into a mixing container.

Purified methyl methacrylate 61m7! (0.6 mol) was weighed on a clean bench and charged into a mixing container.

138 m (1.2 mol) of purified styrene was transferred to a mixing container and mixed with stirring using a magnetic stirrer.

As a polymerization initiator, 0.01% of the sum of the moles of each monomer was added to a mixing container with reagent-grade azo-tertiary-butane, and then as a chain transfer agent, vacuum lid purification was carried out.
Butyl mercaptan 0.35m7! (1,5X 10-
2 mol/1000 rnl of monomer) was added thereto, and the mixture was further stirred and mixed. The monomer solution was transferred from the mixing vessel to the polymerization vessel through a Teflon tube from the outlet to the polymerization vessel to avoid contamination. The polymerization container is made of quartz glass.
Cylindrical shape with an inner diameter of mm, and the upper and lower ends have an inner diameter of 6 mm.
It is narrowly drawn and the bottom end is brushed and sealed. After the monomer solution was transferred to a polymerization container, dissolved air was removed from the upper end by vacuum evacuation, and while the vacuum was being evacuated, a quartz glass portion with an inner diameter of 6 mm at the upper end was heated and melt-sealed with a burner. Next, the polymerization container sealed under reduced pressure was immersed in liquid nitrogen, and the monomer solution was repeatedly frozen and heated and thawed to sufficiently remove dissolved gas.

Thermal polymerization was carried out by heating the polymerization container at 130° C. for 16 hours. After cutting the glass tube at the two ends and unsealing it, it was immediately transferred to a vacuum dryer and heated at 100°C for 948 hours to remove the volatile components in the copolymer, resulting in a transparent preform with no air bubbles. Ta. A heating furnace for the polymerization vessel, a cladding coating guide, a cladding drying furnace, and a winder are arranged vertically in a drawing device, and the temperature of the heating furnace is set in advance at 190 to 210°C. Cut the glass tube at the bottom end of the container, install it in the heating furnace, and inject 1 kg/kg of N2 gas from the top end.
A pressure of cm2 was applied. As the temperature of the preform rose, the copolymer was melted and extruded from the nozzle at the lower end of the polymerization vessel, so the take-up speed was adjusted and set so that the core was about 0.5 mm. On the other hand, vinylidene fluoride-tetrafluoroethylene copolymer (melting point 132°C2) was used as a cladding material.
A clad coating pot was filled with a mixed (1/1) solution of 30 thioethyl acetate and methyl ethyl ketone (composition 80/20 molar ratio), and the drawn core was placed between the pot and cladding and kept at 160°C. The solvent was removed through a drying oven, and the fiber was molded into a plastic optical fiber having an outer diameter of 0.5 mm% and a cladding film thickness of 20 μm.

Next, the above plastic optical fiber wound to a diameter of 200 mm was irradiated with cobalt 60 gamma rays and 6X10'
A total dose of 15 megarads was irradiated at 25° C. at a dose rate of γ/h. Table 1 shows the properties of the obtained plastic optical fiber.

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

Example 2 NH styrene 115rm (1.0 mol), chain transfer agent n
-butyl mercaptan 0.18rnl (1,5Xl0-
Pour the monomer solution (2m01/monomer 1000ml) into a Teflon tube with an inner diameter of 2 mm and a length of 100 mm (seal the bottom end with a glass rod), put it in a stainless steel container that can be evacuated under reduced pressure, and then close the exhaust pulp after degassing under reduced pressure. Thermal polymerization was carried out for 4 hours at 130'0.16 hours + 180°G in a constant temperature bath while maintaining a reduced pressure state to produce a transparent polymer having a diameter of 2 mm. The polymer was removed from the Teflon cheep, and immediately placed in a polyethylene bag with a zipper so as not to be touched, and stored in a desiccator. on the other hand,
Vinylidene fluoride-tetrafluoroethylene copolymer as cladding (melting point 132°C 1 composition 80/20 molar ratio)
30 thiacetate - methyl ethyl ketone mixture (1/1
) solution and place 2 on top of the 2 mm diameter core above.
It was coated with a thickness of 0 μm. This rod lens-shaped optical waveguide was irradiated with cobalt-60 gamma rays at a dose rate of 6 x 10'/h and a total dose of 30 Megaland at 25°C. The optical transmission loss of the obtained optical waveguide was 0.0 at 25°C.
It was 32 dB/5cm. The weight loss of the core when extracted with acetone was 7 inches, and it was only swollen in a mixed solvent of xylene and metacresol at 100°C.

Comparative example 1 Purified methyl methacrylate 107 m/(1.0 mol).

Except for the monomer solution composition consisting of purified 2,21-azobis(imbutyronitrile) o,oi* as a polymerization initiator and 0.17 ml of n-butyl mercaptan as a chain transfer agent (1,5X 10-2 mol/monomer 100,100 O). A plastic optical fiber was manufactured in exactly the same manner as in Example 1 and irradiated with gamma rays.The properties of the obtained optical fiber are shown in Table 1.The acetone extraction loss of the core after irradiation was 9
6%, and 1% in a mixed solvent of xylene and metacresol.
It melted without retaining its shape at 00°C.

Comparative Example 2 The optical transmission loss of the plastic optical fiber produced in Example 1 before gamma ray irradiation was 0.40 dB/m at 25°C, but no light was transmitted at 120°C and it could not be measured.

In addition, the core before gamma ray irradiation was found to be 10% in the acetone extraction test.
Dissolved in 0% acetone.

Comparative Example 3 The optical transmission loss of the plastic optical waveguide prepared in Example 2 before gamma ray irradiation was 0.30 dB15 cm at 25°C. When a plastic optical waveguide before gamma ray irradiation was subjected to an acetone extraction test, 100 pieces of it dissolved and did not retain its shape.

Table 1 [Note 1] Optical transmission loss is 5 to 10 m using a He Ne laser as a light source.
While cutting and polishing the cross section of a sample with a length of , the amount of incident and output light was measured using an optical power meter, and the average value of transmission loss was determined.

The transmission loss is given by the following formula, where 1 is the sample length.

However, Io is the amount of incident light, and Io is the amount of output light.

Measurement of optical transmission loss at 120°C uses a 5m sample.
rn was passed through a thermostatic oven, the light input and output ends were taken out of the thermostatic oven, and measurements were taken at room temperature.

〔Effect of the invention〕

As explained above in detail, the plastic optical transmission body of the present invention has excellent heat resistance and solvent resistance, and is highly practical in industry.

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 is a homopolymer or 1. A plastic optical transmitter made of a copolymer, wherein at least the core is crosslinked by radiation irradiation. 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.