JPH09138313A - Production of distributed refractive index plastic optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a refractive index distribution uniform in a longitudinal direction and to make this distribution smooth in a radial direction by applying solns. prepd. by dissolving polymers and low-refractive index compds. into monomers on the circumference of a plastic rod and polymerizing these monomers, thereby forming polymer layers. SOLUTION: The polymer (polymethyl methacrylate) which is the center of the fiber is melt extruded to a fiber form and the soln. contg. the monomer as a solvent is applied on the surface of the fibrous polymer 10 by a coating applying nozzle 11. The polymer 10 coated with the soln. passing a UV irradiation region 21 is irradiated with UV rays from a UV source 11, by which the monomer is polymerized and solidified. This operation is successively repeated by the coating applying nozzles 12 to 15, the UV light sources 22 to 25 and the UV irradiation regions 32 to 35. The 60% polymers composed of methyl methacrylate and dibutyl sebacate are used as the first to fourth solns.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method of manufacturing a gradient index plastic optical fiber.

[0002]

2. Description of the Related Art Refractive index distribution type [GI (graded index)]
[Type] Plastic A method for manufacturing a plastic for an optical fiber is disclosed in JP-A-7-5329 and JP-A-7-533.
No. 1 publication. In these methods, in order to form a refractive index distribution, a plurality of solutions (coating solutions) having different refractive indexes are used, and the solutions are sprayed or coated. Since the solution does not flow, it must have a certain degree of viscosity, but it is difficult to apply a highly viscous solution uniformly. On the other hand, the viscosity that can be applied causes liquid sagging.

Further, since the viscosity of the solution affects the thickness of the formed layer, it is necessary to precisely adjust the viscosity. However, the viscosity should be constantly adjusted to be constant by evaporation of volatile components such as a solvent. It is difficult. Even if the coating or spraying conditions are controlled, it is very difficult to make the refractive index distribution uniform in the length direction and / or the radial direction. Moreover, it is difficult to completely remove the solvent and the like from the applied solution layer.

Japanese Unexamined Patent Publication (Kokai) No. 7-13029 discloses a method of growing a graded index plastic optical fiber preform by spraying raw material vapors having different blending ratios and thus different refractive indexes onto the lower end portion of the support rod. Has been done. However, with this method, it is considered difficult to accurately control the thickness of each layer and form the refractive index distribution in a predetermined manner.

Another method for manufacturing a preform for a gradient index plastic optical fiber is disclosed in Japanese Patent Laid-Open No. 7-2792.
No. 84 is described. This method, by diffusing a transparent non-polymerizable compound having a different refractive index, which is compatible with the polymer, into a molded product of the transparent polymer,
A refractive index distribution is formed in the polymer molding. However, it is almost impossible to precisely control the refractive index distribution by diffusion. There is a part where the refractive index is low, or there is a boundary between the high refractive index part and the low refractive index part.
A continuous refractive index distribution cannot be obtained.

[0006] All of the above-mentioned conventional techniques are methods for producing an optical fiber preform, and are therefore inadequate from the viewpoint of continuously producing the final product, the optical fiber. International Application Publication No. WO94 / 04949 discloses one method for continuously producing a gradient index plastic optical fiber. This method is 2
Extruding a clear plastic melt from the outer port of a heavy cylindrical nozzle, providing diffusible material from the inner tube to control the index of refraction, and diffusing the diffusible material from the center of the plastic to the periphery. Thereby forming a region in which the refractive index continuously changes.

However, the method of WO94 / 04949 for diffusing this diffusible material into a plastic melt has various drawbacks. First, it is difficult to control the distribution of the refractive index. The refractive index is controlled by the diffusion of the diffusible material. However, unless the direction and speed of the flow until the plastic melt reaches the nozzle are strictly controlled, the diffusion state of the diffusible material is Since it changes in the longitudinal direction of the melt, it is not possible to obtain a homogeneous plastic optical fiber. next,
The diffusable material may collect around the nozzle of the inner tube without flowing, and the diffusable material may be pushed out without being diffused. In this case, an optical fiber having a refractive index distributed as designed cannot be obtained. As described above, in this conventional method, since the refractive index distribution may change in the longitudinal direction of the extruded plastic melt, it is possible to continuously and stably manufacture an optical fiber having a constant refractive index distribution. Have difficulty.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method capable of continuously producing a gradient index plastic optical fiber having a constant refractive index profile in the longitudinal direction and a smooth radial index. Is.

[0009]

According to the present invention, the above object is to apply a solution of a polymer and a low refractive index compound dissolved in a monomer around a plastic rod forming the center of a plastic optical fiber. Since a monomer is polymerized to form a first polymer layer having a lower refractive index than a plastic core, and a n-th polymer layer having a lower refractive index is sequentially formed by the same procedure as necessary. This can be solved by the method for producing a gradient index plastic optical fiber.

The plastic forming the center of the plastic optical fiber is preferably a colorless and highly transparent polymer. As a monomer that gives such a polymer,
The following methacrylic acid esters, styrene compounds, fluorinated acrylic acid esters, fluorinated methacrylic acid esters, etc. can be exemplified: (a) Methacrylic acid ester Methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, methacrylic acid T-Butyl acid, benzyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, diphenylmethyl methacrylate, etc .; (b) Styrene compound styrene, α-methylstyrene, chlorostyrene, bromostyrene, dichlorostyrene, dibromostyrene, etc .; c) Fluorinated acrylic acid ester 2,2,2-trifluoroethyl acrylate and the like; (d) Fluorinated ethyl methacrylate 1,1,2-trifluoroethyl methacrylate and the like. In the present invention, the refractive index can be adjusted by appropriately selecting and using one kind or two or more kinds from the above monomers.

Such monomers are preferably radically polymerized to obtain a center-forming polymer, which is melt extruded to form the center of the optical fiber. In the manufacturing method of the present invention, an optical fiber is manufactured by laminating a polymer layer having a sequentially lowered refractive index around the center.

The refractive index of the polymer to be laminated around the center is adjusted by using a compound having a lower refractive index than the polymer obtained from the monomer when the center plastic is produced from one kind of monomer, Adjust the concentration appropriately. The low refractive index compound used here is non-polymerizable, has a refractive index difference of 0.02 or more with the central polymer, has good compatibility with the monomer and the polymer, and has a high boiling point, for example, 20
It is preferably at least 0 ° C. When polymethylmethacrylate is used as the polymer at the center, alkyl ester sebacate (such as dibutyl sebacate) and saturated dibasic acid alkyl ester can be used as the non-polymerizable compound having a low refractive index.

When the central polymer is produced from two or more kinds of monomers, it is also possible to adjust the refractive index of the polymer to be laminated by using polymers having different refractive indexes and similar reactivity ratios. it can. However, in the method of copolymerization using two or more kinds of monomers, optical transmission loss increases (transparency decreases) due to phase separation based on a microscopic heterogeneous structure. Therefore, it is desirable to use one monomer and a non-polymerizable low refractive index compound.

The solution of the polymer to be laminated can be prepared by dissolving the polymer and the compound having a low refractive index in a monomer. The mixture of the monomer and the compound having a low refractive index is subjected to polymerization conditions, For example, heating is performed to temporarily stop the polymerization in a state where the polymerization of the monomer that is the solvent has progressed from 50% to 70%,
The obtained solution can also be used as a coating solution.
In the latter case, a higher purity solution can be obtained, which is preferable.

The polymerization of the monomer in the applied solution can be promoted by heating, irradiation with radiation (for example, irradiation with ultraviolet rays) or the like depending on the kind of the monomer. In the case of heating, it is not necessary to raise the temperature so that the polymer melts, and the polymerization can be performed at a relatively low temperature at which the monomer does not volatilize.

Next, using a solution prepared by dissolving a polymer having a refractive index lower than that of the first polymer layer and a compound having a low refractive index in a monomer, the second method is performed in the same manner as above.
To form a polymer layer. In this way, a desired gradient index plastic optical fiber is obtained by sequentially stacking polymer layers having a lowered refractive index. The number of polymer layers to be laminated and the thickness of each layer can be appropriately set based on the refractive index distribution and the diameter of the optical fiber. Usually, the number of coating layers is 2.
10 to 10, preferably 3 to 6, and the thickness of each layer is 0.
It is from 05 to 0.3 mm, preferably from 0.08 to 0.2 mm, but it may deviate somewhat above and below this range. The diameter of the center is usually 0.03 to 0.2 mm, preferably 0.05 to 0.15 mm, but it may deviate somewhat above and below this range.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings. FIG.
Shows an example of a preferable apparatus used in the manufacturing method of the present invention. This apparatus has ultraviolet ray irradiation regions 21 to 21 having coating nozzles 11 to 15 for coating a solution containing a polymer and a reflecting plate for polymerizing monomers in the coated solution.
25 and ultraviolet light sources 31 to 35. In the manufacturing method of the present invention, first, a polymer serving as the center of the fiber is melt-extruded into a fibrous form, and a solution or gel containing a monomer as a solvent is applied to the surface of the fibrous polymer 10 by the application nozzle 11. The polymer 10 coated with the solution passing through the ultraviolet irradiation region 21 is irradiated with ultraviolet rays from the ultraviolet light source 11 to polymerize and solidify the monomer. This operation is sequentially repeated by the coating nozzles 12 to 15, the ultraviolet light sources 22 to 25, and the ultraviolet irradiation regions 32 to 35 to form five coating layers to manufacture a gradient index plastic optical fiber.

On the surface of the previous polymer layer wetted by the solution applied in the next step, the monomer penetrates and swells, so that the compound having a low refractive index easily moves toward the center. Therefore, the step of the refractive index at the boundary of each layer is reduced or eliminated, and a smooth refractive index distribution can be formed.

[0019]

Example 1 Polymethylmethacrylate was used as the polymer forming the center of the optical fiber. Polymethylmethacrylate was obtained as follows. In a polymerization vessel, add 0.3 wt% benzoyl peroxide (polymerization initiator) to methyl methacrylate and n-
After adding 0.2 wt% of butyl mercaptan (chain transfer agent) and replacing the inside of the container with nitrogen gas, the temperature was changed to 20 at 60 ° C.
Polymerization was performed by heating for a time. Then, in order to complete the polymerization, heat treatment was carried out at 90 ° C. for 10 hours and further at 110 ° C. for 4 hours to obtain a rod-shaped polymer.

The rod-shaped polymer was extruded at a melting temperature of 190 ° C. and molded into a fiber having a diameter of 0.6 mm. This fibrous polymer 10 is introduced into a nozzle 11 for applying the first solution,
The solution was applied to the surface. If the viscosity of the solution to be applied is too low, dripping or non-uniformity will occur, and if the viscosity is too high, it will be difficult to apply it to the surface.
Use a solution prepared to 000 poise. In this example, a 60% polymer of methyl methacrylate and dibutyl sebacate was used as the first to fourth solutions. Viscosity is 60,
000 poise.

The first solution for forming the first layer was prepared by mixing 8% by volume of dibutyl sebacate with methyl methacrylate, and adding 0.5% by weight of benzoyl peroxide as an initiator to this mixture as a chain transfer agent. 0.2 wt% of n-butyl mercaptan was added, and this was polymerized at 60 ° C. in a reaction vessel filled with nitrogen gas, and when the polymerization was 60%, heating was stopped to prepare. The second, third and fourth solutions had dibutyl sebacate concentrations of 12, 16 and 25 vol, respectively.
% Was prepared.

The first to fourth solutions were polymerized in the reaction vessels directly connected to the coating nozzles 11 to 14, respectively, and were sent to a storage tank in a state where 60% polymerization proceeded, and were supplied to the nozzles.
Polymerization was carried out in the reaction vessel as needed while once stored in the storage tank. This solution was applied onto the polymer surface from an application nozzle adjusted so that the wet thickness was 0.1 mm.
The solution applied to a thickness of 0.1 mm was thinned by polymerization shrinkage, and the diameter of the fiber after the fifth layer was finally formed was 1 mm.

After the application of each solution, the fibrous polymer was introduced into a reactor where infrared lamps 31 to 34 were arranged, the monomers were polymerized, and the coating solution layer was solidified. The reactor in which the coating nozzle and the ultraviolet lamp are lined up is completely sealed so as not to come into contact with the outside (not shown), and the inside thereof is under a nitrogen gas atmosphere. Further, a cylindrical reflection plate is attached to the inner wall of the reaction container so as to surround the fiber so that the ultraviolet rays are uniformly irradiated. Each step was exposed to UV light for 4 hours to completely polymerize the monomer.

After forming the fourth layer, a clad layer was formed as the fifth layer. As a solution for forming the fifth layer, 1, 2,
Polymerization rate of 2-trifluoroethyl methacrylate of 60 to
A 70% solution was used. Apply this to the surface of the fourth layer,
The clad layer was used. Finally, the fibrous polymer forming the first to fifth layers was wound around the winding roller 40 while stretching.

In order to evaluate the light transmission performance of the gradient index optical fiber thus produced, the transmission loss was measured by the cutback method. As a result, transmission loss is 165 dB / km
Met. When the distribution state of the refractive index was measured by an interference microscope, it was found to have a refractive index distribution as shown in FIG.

[0026]

According to the manufacturing method of the present invention, the length of the obtained optical fiber does not depend on the size of the preform, and the optical fiber can be continuously manufactured. In addition, since the monomer itself is used as the solvent, the problem of "solvent removal" found in the method using a solvent other than the monomer does not occur. Furthermore, since the refractive index distribution is not formed by diffusing a compound having a low refractive index, but is formed by coating a plurality of layers having different refractive indexes a plurality of times, the refractive index distribution can be precisely controlled. According to the manufacturing method of the present invention, it is possible to continuously manufacture a plastic optical fiber having a refractive index distribution suitable for high-speed transmission, and the light transmission performance of the optical fiber is higher than that of the SI type plastic optical fiber. You can get a comparable product.

[Brief description of the drawings]

FIG. 1 is a schematic view of an example of a polymerization apparatus used in the production method of the present invention.

FIG. 2 is a diagram showing a refractive index distribution of the plastic optical fiber preform obtained in Example 1.

Claims (4)

[Claims] 1. A solution having a polymer and a low refractive index compound dissolved in a monomer is applied around the plastic rod forming the center of the plastic optical fiber, and the monomer is polymerized to have a refractive index lower than that of the plastic core. 1. A method of manufacturing a gradient index plastic optical fiber, comprising forming a polymer layer No. 1 and, if necessary, forming a polymer layer up to the n-th polymer layer having a sequentially decreased refractive index by the same procedure. 2. The production method according to claim 1, wherein the monomer is a radiation ray-polymerizable monomer, and the monomer is polymerized by irradiation with radiation. 3. The production method according to claim 2, wherein the monomer is an ultraviolet polymerizable monomer, and the monomer is polymerized by irradiating with ultraviolet light. 4. The monomer in which the polymer and the low refractive index compound are dissolved is prepared by previously polymerizing a part of the monomer in a solution in which the low refractive index compound is dissolved in the monomer. The manufacturing method according to any one.