JPH08334605A - Plastic light transmission body and melt spinning device - Google Patents

Abstract

PURPOSE: To obtain high translucency and a region where a refractive index changes continuously with high productivity by discharging polymerizable compds. from a composite spinning mouthpiece having the temp. lower than the temp. of a main body in a discharge section, thereby producing a light transmission body having a specific refractive index distribution. CONSTITUTION: The plastic light transmission body internally having the continuously changing refractive index distribution by discharging the polymerizable compds. from the composite spinning mouthpiece held at the temp. in the discharge section lower than the temp. of the main body section. Namely, the polymer A contg. the nonpolymerizable compd. C is introduced by a gear pump into the inner side part 2 of a composite spinning mouthpiece having, for example, double concentric discharge holes and the polymer B contg. the nonpolymerizable compd. D into the outer part 3 if the nonpolymerizable compds. are two kinds. The respective polymers A, B are thereafter extruded simultaneously from the inner discharge hole 2 and outer discharge hole 3, respectively, of the composite spinning mouthpiece, by which the core-and-sheath type composite rod-shaped body is obtained within the composite spinning mouthpiece. The rod-shaped body is extruded into the inside 9 of the cooled discharge section lower in temp. than the heated diffused part 8, by which melt viscosity of the polymers is held at a high state at a low temp. and thereafter the rod-shaped body is discharged outside from a discharge hole 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a plastic optical transmission medium having a continuously changing refractive index distribution inside a polymer, which is effectively used for optical fibers, optical waveguides, rod lenses and the like. The present invention relates to a melt spinning device used.

[0002]

2. Description of the Related Art An optical transmission body made of quartz glass having a region where the refractive index continuously changes from the center of a linear body or rod-shaped body to the outer periphery has already been proposed and put into practical use. However, although the silica-based optical transmission material has excellent light-transmitting performance, it has problems in mechanical properties such as poor flexibility and poor impact resistance, and it is expensive. . On the other hand, the plastic type optical transmission body is inferior to the quartz type in light transmission performance, but has advantages such as light weight, good workability, good flexibility, and low cost.

Among the plastic type optical transmission bodies, a method for producing an optical transmission body having a refractive index distribution continuously decreasing from the central portion to the outer peripheral portion, which is used for rod lenses, broadband optical fibers, etc., has already been proposed. Several have been proposed.

For example, a monomer alone or a polymer-monomer mixture having a refractive index different from that of the polymer is brought into contact with the surface or hollow inner surface of the polymer mainly forming the optical transmission medium and diffused inside the polymer. To give a concentration distribution, and then polymerize (JP-B-52-5857, JP-B-56-37521, JP-A-2-33104)
JP-A-3-42604, JP-A-3-64704, JP-A-3-65
904, etc.), a method of providing a refractive index distribution by photopolymerizing two or more kinds of monomers having different refractive indexes and monomer reactivity ratios in a transparent container (Japanese Patent Publication No. 54-30301).
Japanese Patent Laid-Open No. 61-130904), spinning a polymer containing a monomer having a high volatility and a refractive index different from that of the polymer, and volatilizing the monomer from the surface to give a concentration distribution. Polymerization method (Japanese Patent Laid-Open No. 62-209402, etc.), a polymer container in which two or more kinds of monomers having different monomer reactivity ratios but substantially different refractive indices are dissolved in the monomers. There is a method of filling the inside and then polymerizing it (Japanese Patent Laid-Open Nos. 4-97302 and 4-97303).

However, all of these methods produce polymers with significantly different refractive indices (eg 0.04 or more),
And reacting two or more kinds of monomers having slightly different monomer reactivity ratios, or giving a polymer having a refractive index greatly different from that of the polymer formed previously in the polymer molded body. Since the homopolymerization reaction of the monomer is carried out, it is unavoidable that a microscopic phase-separated structure having a different refractive index is formed in the polymer in which the polymerization is completed. For this reason, there is a drawback that the light transmission performance is adversely affected.

Further, a manufacturing method which is capable of imparting excellent translucency even though it is a gradient index plastic optical transmission body has already been proposed as Japanese Patent Application No. 3-274354. This is different from the conventional manufacturing method in which monomers with different refractive indices are polymerized to form a refractive index distribution, and because a non-polymerizable material is used, light scattering due to phase separation based on the difference in polymerization rate is suppressed. This is a manufacturing method capable of reducing the light guide loss.
However, according to this method, although it is possible to obtain a gradient index optical transmitter excellent in light transmission performance, the method proposed here is in the hollow of the polymer hollow tube prepared in advance, The polymer of the hollow tube is dissolved and filled with a polymerizable solution containing a high refractive index non-polymerizable compound (a substance generally called a plasticizer), and the periphery of the high refractive index non-polymerizable compound in the filling solution is filled. Since it is a batch-type production method of polymerizing to obtain a rod-shaped preform while promoting diffusion to a part, and then melting and stretching so as to have a desired diameter, the productivity is extremely poor and the quality is high. There is a big problem as an industrialized technology such as non-uniformity.

Therefore, there is a particular method of continuously producing a transparent diffusive material having a refractive index different from that of a polymer while diffusing toward the peripheral portion or the central portion, or by diffusing and then extrusion-melt-molding. It has already been proposed as Japanese Patent Application No. 4-238811.

[0008]

According to this method, since a non-polymerizable compound (a substance generally called a plasticizer) is used for forming a refractive index distribution, for example, a thermoplastic polymer serving as a base. Polymethyl methacrylate (PMMA, n
D ²⁰ = 1.492) to obtain a refractive index difference of about 0.015 or more between the central part of the core and the clad, which is useful as a gradient index optical transmitter, and is a transparent non-polymerizable compound that is easily available ( nD ²⁰ = 1.50 to 1.65), it is necessary to add about 15 to 20 parts by weight in the high refractive index portion, and as a result, the glass transition temperature of the polymer decreases and the melt viscosity also increases. descend.

A thermoplastic polymer containing such a non-polymerizable compound is charged into a heating cylinder and melted, and two or three extrusion nozzles equipped with the heating cylinder are concentrically emitted. Multiple openings are arranged so that the mouths are located sequentially from upstream to downstream, and the diffusible material (non-polymerizable compound) contained in the molten polymer filled in the cylinder is diffused between the nozzles, and then the bottom The optical transmission body is obtained by discharging from the nozzle.

The higher the heating temperature of this diffusion region, the better
In addition to the decrease in the melt viscosity of the polymer that becomes the polymer, the molecular motion of the diffusible material (non-polymerizable compound) that diffuses in the melt polymer increases, so that the diffusion rate increases and the desired Obtaining the concentration distribution (refractive index distribution) is advantageous in terms of productivity.

However, in the structure used in the prior art for discharging from the lowermost nozzle (base hole) having the thermal diffusion area, the heating temperature of the diffusion area is higher than that of the lower surface nozzle (base hole). Melt viscosity (1
The temperature is limited to 10,000 to 150,000 poise). Furthermore, PMMA (weight average molecular weight 5) is used as a polymer generally used for plastic light transmission materials.
30,000-100,000) as an example, this polymer has a non-polymerizable compound (for example, a molecular weight of 150-350,
When a material containing about 10 parts by weight of a boiling point of 250 to 350 ° C. is used, when it is discharged from the nozzle (base hole) in the molten state to the outside, it is released from the pressure of extrusion, so the heating temperature is high and the melt viscosity is low. And foams due to the volatile components contained. Therefore, in order to obtain a clean optical transmission body without generation of bubbles, for example, under these conditions, the heating temperature is 19
The temperature is limited to about 0 ° C or lower, and the heat diffusion is forced in the state where the melt viscosity is relatively high. It takes a very long time to form a refractive index distribution (concentration distribution) capable of obtaining a transmission band that is sufficiently wider than that of a step index type optical transmitter, and a heating area such as the nozzle (base) length is required. However, it has a drawback in that it is inferior in terms of productivity, for example, it is necessary to take a long time and slow the spinning speed. The same applies when a conventional composite spinneret as shown in FIG. 1 is used.

As described above, according to the conventional method, it is difficult to produce a plastic optical transmission medium having a good productivity and a continuous refractive index distribution.

Therefore, the present invention solves the above-mentioned drawbacks of the prior art, has high productivity, has a light transmission performance comparable to that of a polymethylmethacrylate-based step index type optical transmission body, and has a continuous refractive index. It is an object of the present invention to provide a method and an apparatus for manufacturing a plastic optical transmission body having a region that changes from one to another.

[0014]

In order to achieve this object, the present invention continuously changes the inside by discharging from a composite spinneret in which the temperature of the discharging part is lower than that of the main part. A method of manufacturing a plastic optical transmission medium, which is an optical transmission medium having a refractive index distribution.

As such a plastic light transmission body, a transparent non-polymerizable compound having a refractive index different from that of the polymer is contained in a transparent polymer, and the plastic non-polymerizable compound has a concentration distribution based on diffusion of the non-polymerizable compound. And a plastic optical transmission body having a region where the refractive index continuously changes.

The polymer used in the present invention may be any polymer as long as it has high transparency, and is preferably colorless. For example, methacrylic acid ester (the ester substituent is, for example, methyl, ethyl, isopropyl, t-butyl, cyclohexyl, 4-methylcyclohexyl, phenyl, 1-phenylethyl, 1-phenylcyclohexyl, benzyl,
n-bornyl, isobornyl and the like), fluorinated alkyl methacrylate (the fluorinated alkyl group is, for example, 2,2,2-
Trifluoroethyl, 2,2,3,3-tetrafluoropropyl, 2,2,3,3,4,4,5,5-octafluoropropyl, 2,2,3,
4,4,4-hexafluoropropyl and the like), α-fluoroacrylic acid alkyl (the alkyl group is, for example, methyl, ethyl, isopropyl and the like), α-fluoroacrylic acid fluorinated alkyl (the fluorinated alkyl group is, for example, 2,2,
2-trifluoroethyl, 2,2,3,3-tetrafluoropropyl, 2,2,3,3,4,4,5,5-octafluoropropyl, 2,2,3,
4,4,4-hexafluoropropyl etc.), styrene, substituted styrene (the substituents are, for example, methyl, dimethyl, t-
Butyl, chloro, dichloro, bromo, fluoro, phenyl, etc.), vinylidene fluoride, tetrafluoroethylene, and other homopolymers or copolymers of a polymerized monomer.

The number of polymers used is not limited to one, and a large number may be used. The non-polymerizable compound used in the present invention is compatible with the polymer and can be uniformly dispersed in the polymer, is transparent, is non-polymerizable, and the homopolymer is a base polymer. It is necessary not to form a copolymer with a monomer that forms a coalescence. When such a non-polymerizable compound is used, a microscopic phase-separated structure having a different refractive index is not formed in the polymer, and it is possible to prevent the deterioration of the light transmission performance. Furthermore, it is necessary that its boiling point be higher than the melt molding temperature of the polymer.

Further, the number of the non-polymerizable compound is not limited to one, and a large number may be used. However, at least one of them needs to have a refractive index different from that of the polymer forming the optical transmission medium, for example, 0.02 or more.

Examples of the non-polymerizable compound include phthalic ester compounds (the ester substituents thereof are, for example, benzyl n-butyl, dimethyl, diethyl, diallyl, dibutyl, diisobutyl, dicyclohexyl, di n-octyl,
Di-2-ethylhexyl, etc., benzoic acid ester type (the ester substituents are, for example, benzyl, etc.), adipic acid ester type (the ester substituents are, for example, dicapryl, diisooctyl, etc.), sebacic acid ester type (the ester substituents Are, for example, dibutyl, di2-ethylhexyl, etc.), phosphoric acid compounds (eg, tributyl phosphate, triphenyl phosphate, diphenylcresyl phosphate, triphenyl phosphite, etc.), benzene compounds (eg, bromobenzene). , Dichlorobenzene, bromoiodobenzene, diphenyl ether, bromodiphenyl ether,
Diphenyl sulfide, phenoxytoluene, etc.), naphthalene compounds (bromonaphthalene, bromomethylnaphthalene, methylnaphthalene, dimethylnaphthalene, ethylnaphthalene, isopropylnaphthalene, etc.) and the like. When the polymer composition is mainly composed of a fluorinated monomer, a fluorinated product of the non-polymerizable compound may be used.

In carrying out the present invention, in order for the optical transmission medium to have a condensing property, the refractive index of the central portion of the optical transmission medium may be set higher than that of the peripheral portion thereof, and conversely the light divergence property may be improved. In order to have the refractive index, the refractive index of the central portion may be set lower than that of the peripheral portion. To form such a refractive index distribution as a continuous distribution, Japanese Patent Application Nos. 3-274354 and 4-2 are applicable.
As already proposed as No. 38811, it is preferable to diffuse a non-polymerizable compound having a refractive index different from that of the polymer inside the polymer.

However, as in the prior art, in the structure in which the lowermost nozzle (base hole) having the used thermal diffusion area is used for discharging, the heating temperature of the diffusion area is from the lowermost nozzle (base hole). The discharged polymer is limited to the melt viscosity temperature at which it can be spun, and if the heating temperature is high and the melt viscosity is low, the pressure of extrusion is released when discharging from the nozzle (base hole) in the molten state to the outside. , Foams because of the volatile components it contains. Therefore, in order to obtain a clean optical transmission body without generation of bubbles, it is necessary to obtain a desired concentration distribution (refractive index distribution) because heat diffusion in a state where the melt viscosity is relatively high is forced. It requires a long time, and it is necessary to take a long heating region such as the length of the nozzle (base) and slow the spinning speed, which is a disadvantage in terms of productivity.

Therefore, according to the present invention, by discharging from a composite spinneret in which the temperature of the discharge portion is lower than that of the main body portion, a plastic light is used as a light transmission body having a refractive index distribution that continuously changes inside. Get the transmitter.

In the production method of the present invention, the non-polymerizable compound is thermally diffused at a relatively high temperature in the heat diffusion region inside the main body of the composite spinneret at a relatively low melt viscosity of the polymer, or while the non-polymerizable compound is thermally diffused. After extruding to the discharge part of the spinneret and making the melt viscosity of the polymer high at a relatively low temperature inside the cooling discharge part where the temperature is relatively lower than the heating diffusion part, from the discharge hole (spout hole) to the outside Discharge. By adopting this method, the heating temperature of the diffusion region is not limited to the melt viscosity temperature at which the polymer discharged from the nozzle (mouth hole) can be spun, and the viscosity of the molten polymer when discharged is Since it is low, it can be freely set even at a high temperature at which it cannot be spun as it is due to foaming due to the contained volatile components. This enables thermal diffusion of the non-polymerizable compound in the polymer at high temperature and low melt viscosity, which was impossible with the conventional techniques. As a result, it becomes possible to obtain a desired concentration distribution (refractive index distribution) in a relatively short time compared to the conventional diffusion in a polymer having a relatively low temperature and a high melt viscosity, which is technically and productivity-friendly. But I got an advantage.

PMMA (weight average molecular weight of 50,0) is used as a polymer generally used for plastic optical transmission media.
00 to 100,000, for example, a non-polymerizable compound (for example, a molecular weight of 150 to 350, a boiling point of 2) is added to this polymer.
When 50% to 350 ° C.) is used in an amount of 10 parts by weight, a heating temperature of 190 ° C. is obtained under the above conditions in order to obtain a clean optical transmission body when the molten state is discharged from the nozzle (base hole) to the outside. It is limited to about ℃ or less, and is forced to diffuse heat in a relatively high melt viscosity state.
It takes a very long time to obtain a desired concentration distribution (refractive index distribution).

On the other hand, if the technique of the present invention is used, 300 ° C.
It is possible to thermally diffuse the non-polymerizable compound in the polymer at the above temperature. However, when a polymer such as PMMA that is easily depolymerized at a high temperature is used, it is preferable to thermally diffuse the polymer at a temperature not higher than the depolymerization temperature. When using PMMA, the temperature is preferably 250 ° C or lower.

Further, the non-polymerizable compound is diffused inside the polymer containing no non-polymerizable compound, or the content of the non-polymerizable compound is relatively small (for example, the difference is 5).
(Part by weight or more) When diffused inside the polymer to form a continuous refractive index distribution, a large gradient of the content of the non-polymerizable compound is formed inside the polymer. As a result, the melt viscosities are partially different, and there are problems such as difficulty in spinning and difficulty in diffusion in the higher melt viscosities. Therefore, the non-polymerizable compound content in the polymer is different from each other. It is preferable that the phases are substantially the same.

Further, the optical transmission medium of the present invention is preferably obtained by a method in which two or more non-polymerizable compounds having different refractive indexes are mutually diffused between two phases. The number of this phase may be large. The optical transmission body thus obtained exhibits optical characteristics that are stable against temperature changes.

Furthermore, 85 ° C., such as for use in communication
When high heat resistance is required, the non-polymerizable compound having a higher refractive index and a lower refractive index than the polymer can be used among two or more kinds of non-polymerizable compounds having different refractive indexes that diffuse inside the polymer. Is preferably included. When diffusing only a high refractive index non-polymerizable compound or only a low refractive index non-polymerizable compound by diffusing such a high refractive index non-polymerizable compound and a low refractive index non-polymerizable compound in opposite directions Compared with, the amount of non-polymerizable compound contained in the polymer to obtain the same difference in refractive index is relatively reduced. For this reason, the Tg of the polymer, which generally decreases depending on the amount of the non-polymerizable compound contained, becomes relatively high, and the heat resistance of the resulting optical transmission body is also improved. The optical transmission body thus obtained can have heat resistance of 85 ° C., which was difficult with the conventional technique, even when polymethylmethacrylate or the like was used as the polymer.

In the case of manufacturing an optical fiber, for example, the non-polymerizable compound inside the polymer is sufficiently diffused by heat, and the refractive index distribution which continuously decreases from the center to the periphery is obtained from the center. The closer to a distribution proportional to the square of the distance, the wider the transmission band of the optical fiber. When this is cut into a rod lens without being stretched to have an appropriate length, the image has no distortion.

The method for carrying out the present invention will be described by way of examples, but the present invention is not limited thereto.

First, a monomer mixture in which one or more kinds of monomers, a polymerization initiator and, if necessary, a molecular weight adjusting agent are mixed is supplied to a polymerization apparatus, and this is subjected to thermal polymerization or photopolymerization. To obtain a polymer. As the polymerization initiator, for example, an azo compound such as azobisisobutyronitrile, an ordinary radical polymerization initiator such as peroxide such as benzoyl peroxide, and as a molecular weight modifier, a mercaptan such as n-butyl mercaptan is used. A usual radical chain transfer agent such as a class is used.

The polymer thus obtained is mixed with a non-polymerizable compound so as to have a uniform concentration to prepare a transparent polymer containing a non-polymerizable compound. A known method for producing a polymer containing a plasticizer may be used for this production. Also,
A non-polymerizable compound-containing polymer may be obtained by mixing the non-polymerizable compound in the polymerizable monomer before the polymerization and then polymerizing.

As the non-polymerizable compound-containing polymer, two or more kinds of non-polymerizable compounds having different refractive indexes are prepared. When there are two kinds of non-polymerizable compound-containing polymers, the non-polymerizable compound C is added to the inner portion (2) of the composite spinning outlet gold having double concentric discharge holes as shown in FIG.
The non-polymerizable compound D-containing polymer B is introduced into the outer portion (3) of the content polymer A by a gear pump. When three or more kinds of non-polymerizable compound-containing polymers are used, a composite spinneret having multiple concentric discharge holes or a multi-stage composite spinneret capable of double-compositing and then sequentially compounding. Use the same procedure as above. The steps of polymerization, mixing of non-polymerizable compound, and spinneret up to this point are preferably continuous, but may be performed in different steps.

After that, the non-polymerizable compound C-containing polymer A and the non-polymerizable compound D-containing polymer B are simultaneously extruded from the inner ejection hole (2) and the outer ejection hole (3) of the composite spinning outlet gold, respectively. To form a core-sheath composite rod-shaped body inside the composite spinning outlet. When the number of the non-polymerizable compound-containing polymers is three or more, the rod-shaped body is a multilayer composite.

Next, in the heat diffusion portion (8) inside the composite spinning outlet, the core-sheath composite rod-shaped body is heated for a certain period of time at a high temperature in a state of relatively low melt viscosity. Since the non-polymerizable compounds C and D are compatible with the polymers A and B, the non-polymerizable compound C contained in the polymer A is added to the non-polymerizable compound D-containing polymer B in the The non-polymerizable compound D contained in the polymer B diffuses into the polymer A containing the non-polymerizable compound C. As a result, the non-polymerizable compounds C and D are
Each of the initially contained phases is dispersed to the adjacent other phase with a continuously decreasing concentration distribution in a facing direction to form a continuously changing refractive index distribution inside the rod-shaped body. The same applies to the case of a multilayer composite rod-shaped body.

After that, the rod-shaped body is extruded into the inside of the cooling discharge portion (9) whose temperature is relatively lower than that of the heating diffusion portion (8) as shown in FIG. 2, and the melt viscosity of the polymer is relatively low. After making it high, discharge hole (base hole) (7)
From the outside. The melt viscosity at the time of this discharge is 1
It is preferably 50,000 to 150,000 poise. More preferably, 20,000-100,000
Poise.

The optical transmission body thus obtained may be wound up on a winding drum as it is via a roller, but in order to have more practicality, it is coated for the purpose of preventing dissipation of the non-polymerizable compound. Is preferred.

It is preferable that the non-polymerizable compound is hard to be compatible with this coating component. For example, in the case of the hydrocarbon-based non-polymerizable compound, a fluorine-based resin (for example, vinylidene fluoride, tetrafluoroethylene, the fluorinated alkyl methacrylate, the α-fluoroacrylic acid alkyl ester, the α-fluoroacrylic acid fluorinated resin) is used. Copolymers such as alkyl halides). In the case of a fluorine-based non-polymerizable compound, there is a hydrocarbon resin. However, there are some compounds that are not compatible with a specific resin due to the polarity of the non-polymerizable compound, and this property can be utilized.

The coating method may be carried out in a separate step,
It may be continuously performed before being wound on the winding drum after the die is discharged. Alternatively, the outer peripheral portion of the optical transmission body that forms the refractive index distribution is formed by using a composite spinneret having multiple concentric circular ejection holes or a multi-stage composite spinneret that can be doubled and then sequentially combined. Alternatively, melt spinning may be performed at the same time.

When the obtained optical transmission body is used as an optical fiber, it may be stretched before the winding drum or in another step after winding so as to have a desired wire diameter. . Further, when a rod lens is manufactured, it may be cut into a predetermined length without winding and used as a rod lens.

The plastic optical transmission body obtained by the present invention is used for an optical fiber, a rod lens, etc., but is also effectively used for an optical waveguide and the like.

[0042]

EXAMPLES The present invention will be further described below with reference to examples.

In the evaluation in each example, the refractive index distribution was measured using an inter-faco interference microscope, and the optical transmission loss was measured by the cutback method.

[0044] Example 1 100 parts by weight of methyl methacrylate in the polymerization apparatus, nD ²⁰ 1 obtained by polymerizing azobisisobutyronitrile 0.015 parts by weight, the mixture having 0.2 parts by weight n- butyl mercaptan .492 polymethylmethacrylate (PMM
A) 93 parts by weight of diphenyl sulfide (nD ²⁰ 1.6
3) 7 parts by weight of the mixture was introduced to the inner part of the spinneret having double concentric discharge holes, and 93 parts by weight of PMMA and dimethyl adipate (nD ²⁰⁾ were added to the outer part of the same spinneret.
1.43) 7 parts by weight of the mixture was introduced and simultaneously extruded into the die body to form a double composite rod having a diameter of 4 mm. In this state, the inside of the 230 ° C base (80 cm long)
The continuous diffusion of the non-polymerizable compound promoted the mutual diffusion of the non-polymerizable compound. Then, it was continuously extruded to the die discharge part (10 cm length) set at 180 ° C., cooled at the discharge part, and then wound at 5 m / min while being discharged to the outside to obtain an optical fiber having a diameter of 0.5 mm. It was When the refractive index distribution of the obtained optical fiber was measured, it was found that the distribution gradually decreased from the center toward the periphery. The refractive index difference between the central portion and the peripheral portion was about 0.015. Optical transmission loss measurement at room temperature showed a low value of 150 dB / km at a wavelength of 650 nm.

[0045] Example 2 100 parts by weight of methyl methacrylate in the polymerization apparatus, azobisisobutyronitrile 0.015 parts by weight, n- butyl mercaptan 0.20 nD ²⁰ 1 of the mixture was obtained by polymerizing with parts .492 polymethylmethacrylate (PMM
A) 92 parts by weight and bromonaphthalene (nD ²⁰ 1.66)
8 parts by weight of the mixture were introduced into the inner part of the spinneret having triple concentric discharge holes, and 93 parts by weight of PMMA and bromodiphenyl ether were added to the outer part of the spinneret next to this.
7 parts by weight of ter (nD ²⁰ 1.61) was introduced, and further, a mixture of 93 parts by weight of PMMA and 7 parts by weight of tributyl phosphate (nD ²⁰ 1.42) was introduced to the outer side of the mixture, and the inside of the die body was introduced. Were simultaneously extruded into a triple composite rod shape having a diameter of 4 mm. In this state, the mutual diffusion of the non-polymerizable compound was promoted while continuously flowing through the inside of the die at 230 ° C. (80 cm length). Then, extrude to the die discharge part (20 cm long) set at 180 ° C., cool at the discharge part, and then discharge to the outside at 10 m / mi.
It was wound up with n to obtain an optical fiber having a diameter of 0.5 mm.

When the refractive index distribution of the obtained optical fiber was measured, it was found that the distribution gradually decreased from the center toward the peripheral portion. The difference in refractive index between the central part and the peripheral part is
It was about 0.016. Optical transmission loss measurement at room temperature showed a low value of 140 dB / km at a wavelength of 650 nm.

[0047] Comparative Example 1 100 parts by weight of methyl methacrylate in the polymerization apparatus, nD ²⁰ 1 obtained by polymerizing azobisisobutyronitrile 0.015 parts by weight, the mixture having 0.2 parts by weight n- butyl mercaptan .492 polymethylmethacrylate (PMM
A) 93 parts by weight of diphenyl sulfide (nD ²⁰ 1.6
3) 7 parts by weight of the mixture was introduced to the inner part of the spinneret having double concentric discharge holes, and 93 parts by weight of PMMA and dimethyl adipate (nD ²⁰⁾ were added to the outer part of the same spinneret.
1.43) 7 parts by weight of the mixture was introduced and simultaneously extruded into the die body to form a double composite rod having a diameter of 4 mm. In this state, the inside of the 230 ° C base (base length 80c
In m), the continuous diffusion of the non-polymerizable compound was promoted. When the polymer was extruded as it was to the mouthpiece discharge part and was discharged to the outside, the polymer vigorously foamed and an optical transmission body was not obtained.

[0048] Comparative Example 2 100 parts by weight of methyl methacrylate in the polymerization apparatus, nD ²⁰ 1 obtained by polymerizing azobisisobutyronitrile 0.015 parts by weight, the mixture having 0.2 parts by weight n- butyl mercaptan .492 polymethylmethacrylate (PMM
A) 93 parts by weight of diphenyl sulfide (nD ²⁰ 1.6
3) 7 parts by weight of the mixture was introduced to the inner part of the spinneret having double concentric discharge holes, and 93 parts by weight of PMMA and dimethyl adipate (nD ²⁰⁾ were added to the outer part of the same spinneret.
1.43) 7 parts by weight of the mixture was introduced and simultaneously extruded into the die body to form a double composite rod having a diameter of 4 mm. In this state, the inside of the base at 190 ° C (base length 80c
In m), the continuous diffusion of the non-polymerizable compound was promoted. 5m / m while discharging to the outside of the base
It was wound with in to obtain an optical fiber having a diameter of 0.5 mm.

As in Example 1, the difference in refractive index between the central portion and the peripheral portion was about 0.015. Optical transmission loss measurement at room temperature showed a low value of 150 dB / km at a wavelength of 650 nm.

However, when the refractive index distribution of the obtained optical fiber was measured, it was found that the distribution gradually decreased from the center toward the peripheral portion. It was 1/3 or less of 1. In order to obtain the same optical fiber, it was necessary to set the winding speed to 1 m / min or less.

[0051]

EFFECT OF THE INVENTION By using the manufacturing method and the melt spinning apparatus of the present invention, it is possible to obtain a refractive index distribution of a smooth profile curve which is highly transparent and has little local fluctuation utilizing a diffusion phenomenon. It is possible to continuously manufacture the plastic optical transmission body having the stable quality with high productivity.

[Brief description of drawings]

FIG. 1 is a schematic view of a composite spinning outlet device used in a conventional technique.

FIG. 2 is a schematic vertical cross-sectional view showing an example of a composite spinning outlet device used for carrying out the present invention.

FIG. 3 is a diagram showing a refractive index distribution curve of the optical transmission body produced in Example 1.

FIG. 4 is a diagram showing a refractive index distribution curve of an optical transmission body manufactured in Comparative Example 2.

[Explanation of symbols]

 1: Double concentric spinning outlet gold composite part 2: Its inner discharge hole 3: Its outer discharge hole 4: Non-polymerizable compound polymer mixture leading to inner discharge hole 5: Non-polymerizable compound polymer leading to outer discharge hole Mixture 6: Non-polymerizable compound heating diffusion part 7: Spinning discharge hole 8: Double concentric spinning outlet gold heating diffusion part 9: Double concentric spinning outlet gold cooling discharging part

Claims (3)

[Claims] 1. An optical transmission medium having a continuously changing refractive index distribution is produced by discharging from a composite spinneret in which the temperature of the discharging unit is lower than that of the main body. Manufacturing method of plastic optical transmitter. 2. A transparent polymer contains a transparent non-polymerizable compound having a refractive index different from that of the polymer, and the refractive index continuously changes according to the concentration distribution based on the diffusion of the non-polymerizable compound. In the method for producing a plastic optical transmission body having a region, the polymer containing the non-polymerizable compound is introduced into a composite spinning spinneret in a molten state, and the non-polymerizable compound is diffused inside the spinneret. 2. The method for producing a plastic optical transmission body according to claim 1, wherein the temperature is lower than that of the main body portion from the composite spinneret hole. 3. A melt spinning apparatus used for producing an optical transmission medium having a continuously changing refractive index distribution therein, wherein the temperature of the discharge section is lower than that of the main body section. A melt spinning apparatus comprising a spinneret.