JPH0141961B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an optical transmission fiber having a core-sheath structure and having excellent heat resistance. Optical transmission fibers have conventionally been manufactured using glass-based materials as a base material, and are widely used as optical signal transmission media for measurement control between and within devices, for data transmission, for medical purposes, for decoration, and for image transmission. However, optical transmission fibers based on glass-based materials,
Recently, various attempts have been made to make fibers made of plastic because they have the disadvantage of poor flexibility unless they are made from fibers with a thin inner diameter, and they also break easily, have a high specific gravity, and are expensive, including the connector. Proposed. The main characteristics of using plastic are that it is lightweight, and even fibers with a thick inner diameter are strong and flexible.Therefore, high apertures and large diameters are possible, and it is easy to combine with light receiving and emitting elements. It has excellent operability. The general method for manufacturing such optical transmission fibers using plastic is to use a plastic with a high refractive index and good light transmittance as a core component, and then use a transparent plastic with a lower refractive index as a core component. The fiber has a core-sheath structure in which the sheath component is . This method transmits light by reflecting it at the core-sheath interface, and the larger the difference in refractive index between the plastics that make up the core and the sheath, the better the light transmission properties. Amorphous materials are preferable as plastics with high light transmittance, and polymethyl methacrylate and polystyrene are attracting attention industrially (for example, Japanese Patent Publication No. 43-8978, Japanese Patent Publication No. 53-21660).
Publication No.). However, such plastic optical transmission fibers suffer from a drop in transmission loss as the temperature rises, and the reduction value is large, sometimes resulting in a lack of reliability as an optical signal medium. In addition, there is a drawback in heat resistance,
When applied to moving objects such as automobiles, ships, aircraft, or robots, there are restrictions on the uses and locations of application. The upper limit temperature at which polymethyl methacrylate and polyethylene can be used is approximately 80°C, and at temperatures higher than that, thermal contraction increases, deformation occurs, and microstructural fluctuations occur, making it difficult to function as an optical transmission fiber. Moreover, once it is used at a temperature of 80℃ or higher, the optical transmission loss becomes large even if the temperature is returned to room temperature, making it impossible to use it again. However, there was a need for the development of a plastic optical transmission fiber with excellent heat resistance. In view of the current situation, the inventors of the present invention have conducted intensive studies to develop a plastic light transmission fiber that has excellent heat resistance and light transmission properties, and as a result, they have arrived at the present invention. That is, the present invention uses a polymer comprising a methacrylic acid ester having an alicyclic hydrocarbon group having 8 or more carbon atoms in the ester moiety as a core component, and a transparent polymer having a refractive index that is at least 3% smaller than that of the core component. The present invention provides an optical transmission fiber with excellent heat resistance characterized by having a sheath component. The optical transmission fiber of the present invention can be used in a temperature range from room temperature to around 80 degrees Celsius.Compared to conventionally proposed optical transmission fibers that use polymethyl methacrylate as a core component, the optical transmission fiber of the present invention has a tendency to reduce light guide loss that occurs as the temperature increases. The rate of decrease in the optical signal is small, and the reliability as an optical signal transmission medium can be significantly improved. Furthermore, unexpectedly, it is possible to provide an optical transmission fiber in which the light guide loss hardly decreases even at temperatures at which the conventionally proposed optical transmission fibers described above cannot be used at all. In the present invention, the monomer constituting the polymer consisting of a methacrylic acid ester having an alicyclic hydrocarbon group having 8 or more carbon atoms in the ester moiety used as the core component has the formula (Here, R is a hydrocarbon group having 0 to 2 carbon atoms, and A is an alicyclic hydrocarbon group having 8 or more carbon atoms.) The monomer combines methacrylic acid or more preferably its acid chloride with an alicyclic hydrocarbon of the formula ROH.
Produced by esterification with monools. Alicyclic hydrocarbons/monols include 1-adamantanol, 2-adamantanol, 3-methyl-1-adamantanol, 3,5-dimethyl-
1-adamantanol, 3-ethyladamantanol, 3-methyl-5-ethyl-1-adamantanol, 3,5,8-triethyl-1-adamantanol and 3,5-dimethyl-8-ethyl-
1-adamantanol, octahydro-4,7-
Methanoinden-5-ol, octahydro-
4,7-methanoinden-1-ylmethanol,
p-menthanol 8, p-menthanol-2,3
-Hydroxy-2,6,6-trimethyl-bicyclo[3,1,1]heptane, 3,7,7-trimethyl-4-hydroxy-bicyclo[4,1,0]
Heptane, borneol, isoborneol, 2
Examples include alicyclic hydrocarbons and monools such as -methylcarphanol and 2,2,5-trimethylcyclohexanol, and corresponding polymers or copolymers of methacrylic esters. can. The reason why it is limited to alicyclic hydrocarbon groups is that aromatic hydrocarbon groups cause large light guide loss in optical transmission fibers, which limits their use as optical signal transmission media. Among the alicyclic hydrocarbon groups having 8 or more carbon atoms, particularly preferably the alicyclic hydrocarbon groups having 10 or more carbon atoms have a high contribution rate to improving heat resistance. Among these methacrylic acid esters, particularly preferred are 1-adamantyl methacrylate, 2-adamantyl methacrylate, and 3,5-methacrylate.
-Dimethyl-1-adamantyl, bornyl methacrylate, isobornyl methacrylate, phenthyl methacrylate, L-menthyl methacrylate, p-menthane methacrylate, 2-methylcamphane methacrylate, 2,2,5-trimethylcyclohexane methacrylate can be given. The polymer made of the methacrylic acid ester exhibits a high refractive index and thus has favorable properties as a light transmission fiber. The component to be copolymerized with these methacrylic esters is selected from alkyl acrylates and alkyl methacrylates having an alkyl group having 1 to 6 carbon atoms, such as methyl, ethyl, n-
Alkyl acrylates or alkyl methacrylates having alkyl groups such as propyl, n-butyl, and cyclohexyl can be effectively used. When a methacrylic acid ester having an alicyclic hydrocarbon group having 7 or less carbon atoms is used, heat resistance does not improve. Further, even when the number of carbon atoms is 8 or more, linear hydrocarbon groups such as methacrylic acid esters such as n-octyl methacrylate and n-dodecyl methacrylate do not contribute to improving heat resistance. Alicyclic hydrocarbons having up to about 20 carbon atoms are preferred; beyond this, the mechanical strength of the polymer tends to decrease. The core component polymer is a polymer comprising 20 to 100%, more preferably 30 to 95%, of a methacrylic acid ester in which the ester moiety has an alicyclic hydrocarbon group having 8 or more carbon atoms. The content of the methacrylic acid ester component is preferably 20% or more in order to ensure heat resistance, dimensional stability at high temperatures, and flexibility as an optical transmission fiber. The sheath component, which is another important component of the present invention, is a transparent polymer having a refractive index that is at least 3% lower than the core component. If the refractive index is smaller than 3%, the proportion of light reflected by the sheath component will be small and the light guide loss will be large. Preferred transparent polymers include vinyl fluoride,
Vinylidene fluoride, trifluoroethylene, tetrafluoroethylene, hexafluoropropene, trifluoromethyl trifluorovinyl ether,
Examples include fluorine-containing polymers such as perfluoropropyl trifluorovinyl ether and perfluoro-t-butyl methacrylate, polymethyl methacrylate, polyethyl methacrylate, and copolymers thereof. Among these fluorine-containing polymers, particularly preferred are vinylidene fluoride-tetrafluoroethylene copolymer, trifluoroethylene-vinylidene fluoride copolymer, and vinylidene fluoride-tetrafluoroethylene-hexafluoropropene copolymer. and perfluoro-t-butyl methacrylate polymer. The specific refractive index is 1.42 or less, it is a non-crystalline and nearly amorphous polymer, and
It is desirable that the adhesive has good adhesion to the methacrylic acid ester of the core component. These sheath component polymers can be produced by conventionally known methods. In the case of sheath component polymers, the manufacturing method does not have as much of an effect on optical transmission as in the case of core component polymers, so the sheath component polymers should be manufactured with special care taken to avoid contamination with foreign matter such as dust. Bye. Conventional optical transmission fibers made of plastic have generally been produced by synthesizing a core component and a sheath component by a suspension polymerization method, and supplying this to a fiber manufacturing apparatus. Since this method uses a large amount of water, foreign substances contained therein are likely to mix into the polymer.
Furthermore, there is a possibility that foreign matter may be mixed in during the dehydration process. Furthermore, in order to melt-spun the produced polymer into fibers, a step of pelletizing is required, and the polymer production equipment and the fiber production process are located separately, so foreign substances may be generated. It has drawbacks such as being easily mixed in and causing coloration because it is placed in an environment where it is oxidized by air. Therefore, a desirable method for manufacturing the optical transmission fiber of the present invention is to carry out the manufacturing step of the core component polymer and the manufacturing step of the optical transmission fiber in a continuous process, and to increase the polymerization of the core component polymer. A two-step production method is preferred: a continuous bulk polymerization step at high temperature, followed by a continuous separation step of volatiles mainly consisting of residual unreacted monomers. Alternatively, a production method in which the core component is bulk polymerized, and then the core component and sheath component are formed from the obtained polymer by a double extrusion method is also desirable. In the bulk polymerization method, for example, 2,2'-azobis(isobutyronitrile), 1,1'-azobis(cyclohexanecarbonitrile), 2,2'-azobis(2,4 azo compounds such as -dimethylvaleronitrile), azobisisobutanol diacetate, and di-
Examples include organic peroxides such as tert-butyl peroxide, dicumyl peroxide, methyl ethyl ketone peroxide, di-tert-butyl perphthalate, di-tert-butyl peracetate, and di-tert-amyl peroxide. Further, in the polymerization system, in order to control the molecular weight, tert-butyl, n-butyl, n-octyl, n-dodecyl mercaptan, etc. are added as a chain transfer agent in an amount of about 1 mol % or less based on the monomers. As mentioned above, the present invention greatly expands the applicable temperature range of conventional plastic optical transmission fibers by using specific polymers for the core component and the sheath component in optical transmission fibers having a core-sheath structure. The present invention provides an optical transmission fiber with excellent heat resistance, and its industrial value is extremely high. Since the normal operating temperature can be 110°C or higher, it can be applied to, for example, automobiles, ships, aircraft, or robots. Furthermore, the range of application will be expanded by easing temperature conditions in on-premises and in-building communications. Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto. The light guide loss in the examples was measured by using a diffraction grating spectrometer with a halogen tungsten lamp as the light source, and reading the output intensities of the measured optical transmission fiber and the reference optical transmission fiber at a wavelength of 650 nm with a silicon photodiode. The light guide loss α for the fiber length L (Km) was determined from the intensities I ₁ and I ₂ using the following equation. α (dB/Km)=10/Llog(I ₂ /I ₁ ) From this equation, it is shown that the smaller the α value, the better the optical transmission performance. Further, the heat resistance test was conducted by heating the obtained optical transmission fiber for a predetermined period of time, and then measuring and comparing the light guide loss at the initial stage and after heating. Example 1 Methacrylic acid-1- purified by vacuum distillation
87 parts of adamantyl, 13 parts of methyl acrylate, n
-0.05 part of dodecyl mercaptan and 2,2'-azobis(2,4-dimethylvaleronitrile)
A mixture consisting of 0.05 parts is prepared in the absence of oxygen,
The chloroform solution was sent to a reaction tank maintained at 150℃ for prepolymerization for 8 hours, then sent to a screw conveyor maintained at 200℃ to complete polymerization after a residence time of 2 hours. A polymer with an intrinsic viscosity [η] of 0.70 and a refractive index of 1.547 was obtained. Furthermore, this polymer was supplied to a vented extruder heated to 255°C, and while the polymer in the form of a strand with a diameter of 1 mm was discharged as a core component from the center of a double extrusion nozzle maintained at 235°C, a fluorophore was added. Vinylidene fluoride-tetrafluoroethylene copolymer [vinylidene fluoride 70%, refractive index 1.405, melt flow index 140 (230
°C)] as a sheath component to obtain a strand with a core-sheath structure. The blending ratio of the core-sheath polymer was set at 90:10. Next, this strand was stretched 1.8 times to give it mechanical toughness.
An optical transmission fiber with a diameter of approximately 0.75 mm was obtained. When the light guide loss was measured at 25°C and 70°C, it was 340 dB/Km and 370 dB/Km at a wavelength of 650 nm, respectively. After heat-treating this optical transmission fiber at 120°C for 3 hours, the light guide loss was measured again and was 400 dB/Km, indicating excellent heat resistance. Examples 2 to 6 Optical transmission fibers were obtained in the same manner as in Example 1 by changing the core component polymer and the sheath component polymer, and then their heat resistance was examined. All of them were optical transmission fibers that exhibited excellent heat resistance (Table 1). Comparative Example For comparison, by the same operation as in Example 1,
An optical transmission fiber having a core-sheath structure using polymethyl methacrylate as the core component and vinylidene fluoride-tetrafluoroethylene copolymer as the sheath component was obtained. When the light guide loss was measured at 25℃ and 70℃, it was found that at a wavelength of 650nm,
It was 350dB/Km and 500dB/Km. this thing
When heat treated at 105℃ for 7 hours, 110℃ for 3 hours, 120℃ for 3 hours, or 150℃ for 3 hours, each showed a transmission loss of 1000dB/Km or more.
Heat resistance was low. Further, optical transmission fibers obtained using polymers consisting of benzyl methacrylate or n-octyl methacrylate as a core component also exhibited transmission losses of 1000 dB/Km or more after heat treatment at 100° C. for 2 hours. Examples 7 and 8 Optical transmission fibers were made using the core component polymer and sheath component polymer as shown in Table 2 by the same operation as in Example 1, and the heat resistance was examined, and the results are shown in Table 2. . All exhibited excellent heat resistance.

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Claims (1)

[Scope of Claims] 1. A polymer comprising a methacrylic acid ester having an alicyclic hydrocarbon group having 8 or more carbon atoms in the ester moiety as a core component, and at least 3% more than the core component.
An optical transmission fiber with excellent heat resistance characterized by having a transparent polymer having a small refractive index as a sheath component. 2 A methacrylic acid ester having an alicyclic hydrocarbon group having 8 or more carbon atoms in the ester moiety has the formula (Here, R is a hydrocarbon group having 0 to 2 carbon atoms, and A is an alicyclic hydrocarbon group having 8 or more carbon atoms.) optical transmission fiber. 3 A polymer consisting of a methacrylic acid ester having an alicyclic hydrocarbon group having 8 or more carbon atoms in the ester moiety is adamantyl methacrylate, -3,5-dimethyl-1-adamantyl methacrylate, bornyl methacrylate, isobornyl methacrylate. The optical transmission fiber according to claim 1, which is a polymer consisting of p-menthane methacrylate, phenthyl methacrylate, or L-menthyl methacrylate. 4. The transparent polymer having a refractive index at least 3% lower than the core component is vinylidene fluoride-tetrafluoroethylene copolymer, trifluoroethylene-
Vinylidene fluoride copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropene copolymer, or perfluoro-t-methacrylic acid
The optical transmission fiber according to claim 1, which is a butyl polymer.