JP3576224B2 - Plastic optical fiber - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a plastic optical fiber that can be used as an optical information communication medium.
[0002]
[Prior art]
At present, optical transmitters that have been put into practical use are classified into quartz-based and plastic-based optical transmitters according to the type of material. The transmission mode is classified into a single mode type and a multi-mode type. Optical transmission is widely used for communication trunks because it has a large capacity and is not affected by electromagnetic noise at all. Quartz single-mode fibers that are commercially available on a large scale are characterized by overwhelmingly low loss and broadband, and are used for long-distance large-capacity communication trunks by taking advantage of these features.
[0003]
As for the plastic type, a multi-mode type of step index (SI) is commercially available, which is not only a silica type single mode fiber but also a silica type graded index (GI) fiber and a plastic clad silica core fiber. Since the light source has a large diameter and a high numerical aperture, alignment of the light source and the like are easy, and it is flexible and easy to handle, connection operations such as disconnection are easy. In addition, since expensive equipment is not required for such a work, the connection cost is low. Taking advantage of this feature, applications to short-range communication such as data links and sensors are becoming widespread. In the future, quartz fiber will not be introduced due to the high cost of quartz-based fiber, such as in a facility network such as a LAN between devices inside and outside the floor such as for FA and OA, as well as in terminal wiring to ordinary households. It is expected as a distance information transmission line. Furthermore, because of its excellent flexibility, it is less likely to be damaged or deteriorated even in a vibrating environment. In this regard, it is far superior to quartz-based materials, and is applied to signal transmission lines such as networks in mobiles such as cars, trains, and airplanes. Has become very popular in recent years.
[0004]
In such a moving body, the external environment is not constant, and reliability such as high heat resistance that can withstand various environments such as temperature and humidity is required as a required characteristic. In addition, in short-distance communication applications, in recent years, the usage environment has been increasing, such as inside and outside of buildings, and further heat resistance has been desired.
[0005]
On the other hand, in general plastic optical fibers, those using poly (methyl methacrylate) as a core material are mainly used because the core material has low transmission loss and has no problem in mechanical properties and weather resistance. However, the maximum use temperature of an optical fiber having polymethyl methacrylate as a core is limited to at most about 105 ° C. even when a heat-resistant coating or the like is applied. Heat resistance is insufficient for outdoor use.
[0006]
As a method for improving the heat resistance of a plastic optical fiber, there are conventionally a method of increasing the glass transition temperature of a core material and a method of providing a heat-resistant coating. As the former, the glass transition temperature of the core material is raised. (1) Polycarbonate having a high glass transition point as a polymer alone is used as the core material (Japanese Patent Application Laid-Open No. 61-262706); (3) using an olefin copolymer containing a monomer as a core material (Japanese Patent Laid-Open No. 61-213315), and (3) using a copolymer of a methyl methacrylate monomer and another comonomer having a high glass transition point as a core material. In addition, those using an aromatic maleimide as a comonomer (Japanese Patent Publication No. 5-82405, Japanese Patent Publication No. 5-82406), those using an aliphatic maleimide (Japanese Patent Application Laid-Open No. 63-80205), alicyclic methacrylates (JP-A-61-260205).
[0007]
[Problems to be solved by the invention]
However, the above-mentioned (1) and (2) have sufficient dimensions and mechanical stability at high temperatures, but have a large transmission loss characteristic as compared with polymethyl methacrylate-based optical fibers. Further, there is a drawback that the change with time under high temperature is large. This is because it is difficult to remove impurities and coloring proceeds by by-products and decomposition products. In the case of (3), the system using aliphatic maleimide has the best characteristics in terms of the balance between transmission loss, heat resistance and mechanical characteristics. In comparison, there is a problem that transmission loss is large and the transmission distance is limited to a short distance.
[0008]
In addition, since cables must be laid out in a limited space in a moving body such as an automobile, the number of bent portions increases, so that it is necessary to increase a margin for transmission loss. However, there is a problem that transmission loss must be sacrificed to some extent in any case in which the heat resistance is improved as in the examples of (1) to (3) described above.
[0009]
An object of the present invention is to solve such problems and to provide a heat-resistant plastic optical fiber having excellent low transmission loss characteristics comparable to polymethyl methacrylate.
[0010]
[Means for Solving the Problems]
The gist of the present invention is a plastic optical fiber having a core-cladding structure, wherein the core has 1 to 40% by weight of N-cyclohexylmaleimide and / or N-lower alkylmaleimide (A) and 99 to 98% of methyl methacrylate (B). A plastic optical fiber comprising a uniform mixture of 60 to 99% by weight of a copolymer consisting of 40% by weight and 40 to 1% by weight of a low molecular weight product having a molecular weight of 100 to 1000; Alternatively, 1 to 40% by weight of N-cyclohexylmaleimide and / or N-lower alkylmaleimide (A), 99 to 40% by weight of methyl methacrylate (B), and 30% by weight or less of aromatic vinyl compound (C) Plastic optical fiber using a copolymer of
[0011]
Considering the factors of transmission loss of a methyl methacrylate copolymer obtained by copolymerizing a monomer having a high glass transition point to impart heat resistance, the transmission loss increased by copolymerization is due to the absorption loss of the monomer having a high glass transition point. There are factors due to Rayleigh scattering loss based on microphase separation by the block portion of the copolymer. The former is a factor determined when the monomer is selected, and thus is determined in consideration of heat resistance. Therefore, the present inventors studied a method for reducing the light scattering loss caused by the latter, and as a result, it was possible to introduce a low molecular dopant having a good affinity for the copolymer as a scattering reducer into the core material. The present invention has been found to be effective and has been completed. That is, the scattering loss is due to micro-phase separation and micro-density of the copolymer, micro-refractive index fluctuation based on fluctuation of concentration, and macro-refractive index irregularities such as voids and micro bubbles. There is something. These fluctuations and irregularities are, in other words, discontinuous portions of the refractive index, and the low-molecular dopant is considered to play a role of continuously connecting such discontinuous portions.
[0012]
The N-cyclohexylmaleimide and / or N-lower alkylmaleimide (A) constituting the copolymer used as the core material of the present invention mainly has a role as a heat-resistance imparting component. Examples of the N-lower alkylmaleimide include N-methylmaleimide, N-ethylmaleimide, N-isopropylmaleimide, Nnpropylmaleimide, Nt-butylmaleimide, Nn-butylmaleimide and the like. N-isopropylmaleimide and N-cyclohexylmaleimide are preferred in consideration of the balance between heat resistance, physical properties such as mechanical properties, transmission loss properties, and low moisture absorption.
[0013]
The aromatic vinyl compound (C) is effective for greatly improving the copolymerizability of the component (A). If the amount of the monomer exceeds 30% by weight, the optical properties become unsatisfactory. Therefore, the proportion of the monomer in the copolymer must be 30% by weight.
[0014]
Examples of the aromatic vinyl compound (C) include styrene, alkylstyrene, for example, o-, m-, p-methylstyrene, 1,3-dimethylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tertiary butyl Styrene, monovinylidene aromatic hydrocarbons such as α-methylstyrene, α-ethylstyrene, α-methyl-p-methylstyrene, vinylnaphthalene, o-, m- and p-chlorostyrene, 2,4-dibromostyrene , 2-methyl-4-chlorostyrene and the like.
[0015]
It is useful in industrial production to use α-methylstyrene when it is desired to further improve heat resistance, and to use styrene and vinyltoluene when improving productivity.
[0016]
Examples of the low molecular weight compounds having a molecular weight of 100 to 1000 used in the present invention include benzyl-n-butyl phthalate, 1-methoxyphenyl-1-phenylethane, benzyl benzoate, bromobenzene, o-dichlorobenzene, and m-dibutylbenzene. Chlorobenzene, 1,2-dibromoethane, 3-phenyl-1-propanol and the like can be mentioned.
[0017]
If the molecular weight of the low molecular weight material is too low, the diffusion rate is large and the material is easily volatilized by heat, so that the fiber performance becomes unstable with respect to heat. On the other hand, if the molecular weight is too high, the dispersibility in the polymer decreases, and the light scattering loss increases.
[0018]
The content of the low molecular weight substance is determined in consideration of optical properties and mechanical properties, but an appropriate range is 1 to 40% by weight as a guide. If it is too large, heat resistance and mechanical properties are adversely affected by the plasticizing effect of the core material. If the amount is too small, the effect of reducing the loss is impaired. More preferably, the content is 10 to 30% by weight.
[0019]
As the cladding material of the plastic optical fiber of the present invention, fluorinated methacrylate-based polymers and copolymers, copolymers of fluorinated methacrylate and methacrylate-based resins, vinylidene fluoride-tetrafluoroethylene copolymer, α-fluoromethacrylate-based Resins, and mixtures thereof, may be mentioned. In terms of improving heat resistance, an α-fluoromethacrylate resin having a high glass transition point is preferable.
[0020]
The optical fiber of the present invention comprises: (1) a method in which a low molecular weight substance is previously mixed with a raw material monomer in a continuous bulk polymerization direct spinning process, and after polymerization, supplied to a spinning nozzle and introduced into a core material; In the spinning process, a method of introducing a low-molecular-weight material into the core material after the polymerization and degassing and extrusion processes, and (3) a method in which a low-molecular-weight material is dispersed and mixed in the core material in advance using a screw-type extruder. Extrusion method, (4) After shaping a fiber having a core-clad structure in advance, the fiber is immersed in a single substance of a low molecular weight substance or a mixture or a solution thereof, and optionally heated as necessary to remove the low molecular weight substance. It can be manufactured by a method such as a method of infiltrating.
[0021]
Of these methods, the continuous bulk polymerization direct spinning method is preferably used to sufficiently reduce the transmission loss. In addition, the method of infiltrating a low molecular weight substance by post-treatment is preferable in terms of productivity since large-scale equipment is not required since the post-treatment can be performed after shaping the fiber by a conventional method.
[0022]
【Example】
Hereinafter, the present invention will be specifically described based on examples.
Example 1
A monomer mixture of methyl methacrylate / isopropylmaleimide was copolymerized by a bulk polymerization method in the presence of benzyl-n-butyl phthalate to give a copolymer 90 of methyl methacrylate / isopropylmaleimide = 74/26 (% by weight). % By weight and a mixture of 10% by weight of benzyl-n-butyl phthalate was used as a core material. Further, a copolymer of trifluoroethyl α-fluoroacrylate / methyl α-fluoroacrylate = 85/15 (molar ratio) was used as the cladding material. The core material and the clad material were supplied to a screw-type extruder and subjected to composite spinning to obtain a plastic optical fiber having a core-clad structure having a fiber diameter of 1000 μm and a core diameter of 980 μm.
[0023]
The transmission loss of this plastic optical fiber was 200 dB / km (measurement method; 50 m-5 m cutback method, wavelength: 650 nm, incident NA = 0.1). When this optical fiber was heat-treated at 125 ° C. for 1000 hours, the transmission loss was kept at 209 dB / km or less, and good heat resistance was exhibited.
[0024]
Example 2
An optical fiber spun continuously was obtained in the same manner as in Example 1. This optical fiber was cut into 50 fibers in units of 50 m, and the transmission loss at a wavelength of 650 nm was measured for the 50 fibers by a cutback method. The average of the measured values was 210 dB / km. The ratio showing a value of 280 dB / km or more in all the measured values was 2%.
[0025]
Example 3
A monomer mixture of methyl methacrylate / isopropylmaleimide / styrene was copolymerized by a bulk polymerization method in the presence of benzyl-n-butyl phthalate, and methyl methacrylate / isopropylmaleimide / styrene = 75/17/8 (% by weight) A mixture of 90% by weight of the copolymer (1) and 10% by weight of benzyl-n-butyl phthalate was obtained and used as a core material. Further, a copolymer of trifluoroethyl α-fluoroacrylate / methyl α-fluoroacrylate = 85/15 (molar ratio) was used as the cladding material. The core material and the clad material were supplied to a screw-type extruder and subjected to composite spinning to obtain a plastic optical fiber having a core-clad structure having a fiber diameter of 1000 μm and a core diameter of 980 μm.
[0026]
The transmission loss of this plastic optical fiber was 235 dB / km (measurement method: 50 m-5 m cutback method, wavelength: 650 nm, incident NA = 0.1). When this optical fiber was heat-treated at 125 ° C. for 1000 hours, the transmission loss was maintained at 237 dB / km or less, showing good heat resistance.
[0027]
Comparative Example 1
A plastic optical fiber was obtained in the same manner as in Example 1, except that benzyl-n-butyl phthalate as a low molecular weight product was not mixed. The transmission loss of this plastic optical fiber was 245 dB / km.
[0028]
Comparative Example 2
A plastic optical fiber was obtained in the same manner as in Example 2 except that benzyl-n-butyl phthalate as a low molecular weight product was not mixed, and the transmission loss was measured. The average value was 250 dB / km. In addition, the ratio showing a value of 280 dB / km or more in all the measured values was 6%.
[0029]
Comparative Example 3
A plastic optical fiber was obtained in the same manner as in Example 3, except that benzyl-n-butyl phthalate as a low molecular weight product was not mixed. The transmission loss of this plastic optical fiber was 255 dB / km.
[0030]
【The invention's effect】
The plastic optical fiber of the present invention has excellent low transmission loss characteristics comparable to poly (methyl methacrylate) as well as heat resistance.

Claims (2)

A plastic optical fiber having a core-cladding structure, wherein the core comprises 1 to 40% by weight of N-cyclohexylmaleimide and / or N-lower alkylmaleimide (A) and 99 to 40% by weight of methyl methacrylate (B). A plastic optical fiber comprising a uniform mixture of 60 to 99% by weight of a copolymer and 40 to 1% by weight of a low molecular weight product having a molecular weight of 100 to 1000. A plastic optical fiber having a core-cladding structure, wherein the core comprises 1 to 40% by weight of N-cyclohexylmaleimide and / or N-lower alkylmaleimide (A), and 99 to 40% by weight of methyl methacrylate (B); A plastic optical fiber comprising a uniform mixture of 60 to 99% by weight of a copolymer comprising 30% by weight or less of an aromatic vinyl compound (C) and 40 to 1% by weight of a low molecular weight compound having a molecular weight of 100 to 1,000.