JPH08334633A - Production of base material for producing refraction index distribution type optical fiber - Google Patents

Abstract

PURPOSE: To provide a base material for producing a refractive index distribution type optical fiber. CONSTITUTION: The base material composed of a high refractive index inside layer 5 and a low refractive index outside layer 3 is produced by using an amorphous fluorinated high polymer (a) having no C-H bond and at least one kind of a material (b) >=0.001 in the difference of refractive index compared with the high polymer (a) by rotational molding and at this time, the concentration gradient of the material (b) is formed by diffusing the material (b) between the inside and outside layers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is a graded index optical fiber having high transparency and heat resistance, which has been difficult to realize with conventional optical resins (hereinafter sometimes abbreviated as GI type optical fiber). The present invention relates to a method of manufacturing a base material (preform).

Since the GI type optical fiber obtained by the present invention is a non-crystalline resin, it does not scatter light and has a very high transparency in a wide wavelength band from ultraviolet light to near infrared light, so that it has various wavelengths. It can be effectively used for optical systems. In particular, the present invention provides an optical transmission body having low loss at wavelengths of 1300 nm and 1550 nm, which are used for trunk silica fibers in the field of optical communication.

Further, the GI type optical fiber obtained by the present invention has heat resistance, chemical resistance, moisture resistance and nonflammability, which can withstand severe use conditions in the engine room of automobiles.

The refractive index distribution in a gradient index optical fiber means that the refractive index in the transverse section of the optical fiber decreases from the center of the fiber in the radial direction in a curve close to a parabola. In the GI type optical fiber, the traveling speed of light is high in the peripheral portion where the refractive index is low,
Since the light having a high refractive index is slow in the central portion, the light traveling in the peripheral portion has a long path, but the speed is high, so that the transmission speed is almost equal to that of the light traveling in the central portion, and the mode dispersion is low.

[0005]

2. Description of the Related Art As a conventionally known resin for a GI type optical fiber, an optical resin represented by a methylmethacrylate resin, a tetrafluoroethylene resin or a vinylidene fluoride resin described in WO94 / 04949 is proposed. Has been done.

The core of the graded-refraction plastic optical fiber is methyl methacrylate resin, styrene resin,
Many proposals have been made to use an optical resin such as a carbonate resin or norbornene resin and to make the clad a fluoropolymer. Further, JP-A-2-244007 proposes using a fluorine-containing resin for the core and the clad. Also, WO94 / 04949 and JP-A-3-8170.
No. 3, JP-A-3-81704, JP-A 5-1
A method of manufacturing a GI type optical fiber is described in Japanese Patent Publication No. 73026 and the like.

[0007]

DISCLOSURE OF THE INVENTION The present invention has a heat resistance required for automobiles, office automation (OA) equipment, home electric appliances, etc., which cannot be reached by optical fibers such as methyl methacrylate resin, carbonate resin and norbornene resin. G with moisture resistance, chemical resistance, and non-combustibility
The present invention provides a method for manufacturing a base material for manufacturing an I-type optical fiber.

Further, the present invention makes it possible to use ultraviolet light (wavelength 200 nm to 400 nm) and near infrared light (wavelength 700 nm to 2500 nm) which cannot be achieved by an optical transmission material such as methacrylate resin, carbonate resin, norbornene resin, Further, the present invention provides a method for manufacturing a base material for manufacturing a GI type optical fiber having a low optical transmission loss in a wide transmission region band.

[0009]

DISCLOSURE OF THE INVENTION The present inventor has found that a C—H bond (that is, a carbon-hydrogen bond) which imparts heat resistance, moisture resistance, chemical resistance, and incombustibility and causes light absorption in near infrared light. It was found that a fluorinated polymer substantially free of C—H bond is optimal for eliminating the above). This fluoropolymer has C—F bonds (that is, carbon-bonds) instead of C—H bonds.
Fluorine bond).

That is, when a substance is irradiated with light, the stretching vibration of a bond between certain atoms and the light having a wavelength that causes resonance vibration with the bending vibration are preferentially absorbed. The polymeric substances used in plastic optical fibers so far are mainly C
It was a compound having a -H bond. In the polymer substance based on this C—H bond, since the hydrogen atom is light and easily vibrates, the basic absorption is in the infrared region on the short wavelength side (3400 n).
appear in m). Therefore, in the near-infrared to infrared region (600 to 1550 nm), which is the wavelength of the light source, relatively low overtone absorption of this C—H stretching vibration appears in abrupt manner, which is a major cause of absorption loss.

Therefore, when hydrogen atoms are replaced with fluorine atoms, the wavelengths of their overtone absorption peaks shift to the long wavelength side, and the absorption amount in the near infrared region decreases. From the theoretical value, in the case of PMMA (polymethylmethacrylate) having a C—H bond, the absorption loss of the C—H bond is estimated to be 105 dB / km at a wavelength of 650 nm, and 10,000 dB at a wavelength of 1300 nm. / Km
That's all.

On the other hand, in a substance in which hydrogen atoms are replaced by fluorine atoms, there is practically no loss due to absorption at a wavelength of 650 nm, and even at a wavelength of 1300 nm, 1 dB / s between the 6th and 7th tones of the stretching vibration of the C—F bond. It is on the order of km and it can be considered that there is no absorption loss. For that we are C
It is proposed to use compounds with a -F bond. Further, it is desirable to exclude a functional group such as a carboxyl group or a carbonyl group, which is a factor that hinders heat resistance, moisture resistance, chemical resistance, and incombustibility. Further, a carboxyl group absorbs near infrared light, and a carbonyl group absorbs ultraviolet light. Therefore, it is desirable to exclude these groups. Further, in order to reduce the transmission loss due to light scattering, it is important to use an amorphous polymer.

Further, in the case of the graded index optical fiber, multimode light propagates while being reflected at the interface between the core and the clad. Therefore, modal dispersion occurs and the transmission band is reduced. However, in the graded index optical fiber, mode dispersion hardly occurs and the transmission band increases.

The inventor of the present invention, therefore, used as a material for a GI type optical fiber, an amorphous fluoropolymer having substantially no C—H bond, particularly a fluoropolymer having a ring structure in the main chain, and the polymer. We have newly found a GI type optical fiber in which substances having different refractive indices are used as compared with the combination, and the concentration of the substances having different refractive indices has a gradient in a specific direction. The present invention is the following invention relating to a method for producing a base material for producing this GI type optical fiber.

In the method for producing a base material for producing a gradient index optical fiber, an amorphous fluoropolymer (a) having substantially no C--H bond and a fluoropolymer (a).
In comparison with at least one substance (b) having a difference in refractive index of 0.001 or more, a cylindrical molded body made of a low refractive index material selected from at least one of the above materials is used as a mold. At least one layer made of a layer-forming material having a relatively high refractive index selected from at least one of the above-mentioned materials is formed on the inner surface by rotational molding to form a cylindrical or columnar structure having at least two inner and outer layers. A method for producing a base material for producing a gradient index optical fiber, which comprises producing a base material made of a molded body.

In the method for producing a base material for producing a gradient index optical fiber, an amorphous fluoropolymer (a) having substantially no C--H bond and a fluoropolymer (a).
In comparison with, at least one substance (b) having a difference in refractive index of 0.001 or more is used to manufacture a plurality of layer forming materials having different refractive indexes, and the layer forming materials are sequentially placed in a rotating cylindrical drum. To produce a base material composed of a cylindrical or cylindrical molded body in which the inner layer of the molded article has a higher refractive index than the outer layer, and the production of a base material for producing a gradient index optical fiber. Method.

First, the fluoropolymer (a), the substance (b), and the GI type optical fiber, which are the materials for the GI type optical fiber, will be described, and then the method for producing the above base material will be described.

<Fluorine-containing polymer (a)> As the fluorine-containing polymer, tetrafluoroethylene resin, perfluoro (ethylene-propylene) resin, perfluoroalkoxy resin, vinylidene fluoride resin, ethylene-tetrafluoroethylene has hitherto been used. Resins, chlorotrifluoroethylene resins and the like are widely known. However, since these fluorine-containing resins have crystallinity,
Light is scattered and the transparency is not good, which is not preferable as a material for a plastic optical fiber.

On the other hand, the non-crystalline fluoropolymer is excellent in transparency because it does not scatter light due to crystals.
As the fluoropolymer (a) in the present invention, C-H
There is no limitation as long as it is a non-crystalline fluoropolymer having no bond, but a fluoropolymer having a ring structure in its main chain is preferable. The fluorine-containing polymer having a ring structure in the main chain, a fluorine-containing aliphatic ring structure, a fluorine-containing imide ring structure,
A fluoropolymer having a fluorine-containing triazine ring structure or a fluorine-containing aromatic ring structure is preferable. Among the fluoropolymers having a fluorinated aliphatic ring structure, those having a fluorinated aliphatic ether ring structure are more preferable.

The fluorine-containing polymer having a fluorine-containing alicyclic structure has a thermal stretching or melting property which will be described later as compared with a fluorine-containing polymer having a fluorine-containing imide ring structure, a fluorine-containing triazine ring structure or a fluorine-containing aromatic ring structure. It is a more preferable polymer because it is difficult for the polymer molecules to be oriented even when it is made into fibers by spinning, and as a result, light is not scattered.

The viscosity of the fluorinated polymer (a) in the molten state is from 10 ^{3 at} a melting temperature of 200 ° C. to 300 ° C.
10 ⁵ poise is preferred. If the melt viscosity is too high, not only is melt spinning difficult, but it is necessary to form a refractive index distribution.
Diffusion of the substance (b) is less likely to occur, making it difficult to form a refractive index distribution. In addition, if the melt viscosity is too low, there will be a practical problem. That is, when it is used in electronic devices, automobiles, etc., it is exposed to high temperatures and softens, and the optical transmission performance deteriorates.

The number average molecular weight of the fluoropolymer (a) is
It is preferably 10,000 to 5,000,000, more preferably 50,000 to 1,000,000. If the molecular weight is too small, heat resistance may be impaired, and if it is too large, it becomes difficult to form an optical fiber having a refractive index distribution, which is not preferable.

The polymer having a fluorinated alicyclic structure is obtained by polymerizing a monomer having a fluorinated cyclic structure, or a fluorinated monomer having at least two polymerizable double bonds is cyclopolymerized. A polymer having a fluorinated alicyclic structure in the main chain obtained as described above is suitable.

A polymer having a fluorinated alicyclic structure in its main chain, which is obtained by polymerizing a monomer having a fluorinated alicyclic structure, is known from Japanese Patent Publication No. 63-18964. That is, perfluoro (2,2-dimethyl-
1,3-dioxole) and other monomers having a fluorine-containing alicyclic structure are homopolymerized, and this monomer is also radical-polymerizable monomer such as tetrafluoroethylene, chlorotrifluoroethylene, and perfluoro (methyl vinyl ether). A polymer having a fluorinated alicyclic structure in its main chain can be obtained by copolymerizing with.

Further, a polymer having a fluorine-containing aliphatic ring structure in its main chain obtained by cyclopolymerization of a fluorine-containing monomer having at least two polymerizable double bonds is disclosed in JP-A-63-
It is known from JP-A-238111 and JP-A-63-238115. That is, by cyclopolymerizing monomers such as perfluoro (allyl vinyl ether) and perfluoro (butenyl vinyl ether), or by using such monomers as tetrafluoroethylene, chlorotrifluoroethylene, perfluoro (methyl vinyl ether), etc. A polymer having a fluorine-containing alicyclic structure in its main chain can be obtained by copolymerizing with the radical-polymerizable monomer.

Further, perfluoro (2,2-dimethyl-
Monomers having a fluorinated alicyclic structure such as 1,3-dioxole) and perfluoro (allyl vinyl ether)
A polymer having a fluorinated alicyclic structure in its main chain can also be obtained by copolymerizing a fluorinated monomer having at least two polymerizable double bonds such as or perfluoro (butenyl vinyl ether).

Specific examples of the above-mentioned polymer having a fluorinated alicyclic structure include those having a repeating unit selected from the following formulas (I) to (IV). The fluorine atoms in the polymers having these fluorine-containing alicyclic structures may be partially substituted with chlorine atoms in order to increase the refractive index.

[0028]

Embedded image

[In the above formulas (I) to (IV), 1 is 0 to 5, m is 0 to 4, n is 0 to 1, and l + m + n is 1 to 1.
6, o, p and q are 0 to 5, respectively, and o + p + q is 1 to
6, R is F or CF ₃ , R ₁ is F or CF ₃ , R ₂ is F
Or CF ₃ , X ₁ is F or Cl, X ₂ is F or Cl
Is. The polymer having a fluorinated alicyclic structure is preferably a polymer having a ring structure in its main chain, but a polymer containing 20 mol% or more, preferably 40 mol% or more of polymer units having a ring structure is preferable. It is preferable in terms of transparency and mechanical properties.

<Regarding the substance (b)> The substance (b) has a difference in refractive index of 0. 1 as compared with the fluoropolymer (a).
It is at least one kind of substance of 001 or more and may have a higher refractive index or a lower refractive index than the fluoropolymer (a). In the present invention, a substance having a higher refractive index than that of the fluoropolymer (a) is usually used.

The substance (b) is preferably a low molecular weight compound, an oligomer or a polymer containing an aromatic ring such as a benzene ring, a halogen atom such as chlorine, bromine or iodine, and a bonding group such as an ether bond. In addition, the substance (b) is preferably a substance that does not substantially have a C—H bond for the same reason as that of the fluoropolymer (a). The difference in refractive index with the fluoropolymer (a) is preferably 0.005 or more.

The substance (b) which is an oligomer or polymer is a polymer of the monomer forming the above-mentioned fluoropolymer (a), and has a refractive index in comparison with that of the fluoropolymer (a). It may be an oligomer or a polymer having a difference of 0.001 or more. As a monomer,
It is selected from those which form a polymer having a difference in refractive index of 0.001 or more in comparison with the fluoropolymer (a). For example, two kinds of fluoropolymers (a) having different refractive indexes can be used, and one polymer (a) can be distributed as the substance (b) in the other polymer (a).

These substances (b) have a solubility parameter difference of 7 (cal) in comparison with the above matrix.
/ Cm ³ ) ^1/2 is preferable. Here, the solubility parameter is a characteristic value that is a measure of the mixing property between substances, and the solubility parameter is δ, the molecular cohesive energy of the substance is E, and the molecular volume is V. The equation δ = (E / V) ¹ Expressed as ^{/ 2} .

Examples of the low molecular weight compound include halogenated aromatic hydrocarbons containing no hydrogen atom bonded to a carbon atom. Particularly, a halogenated aromatic hydrocarbon containing only a fluorine atom as a halogen atom or a halogenated aromatic hydrocarbon containing a fluorine atom and another halogen atom is preferable from the viewpoint of compatibility with the fluoropolymer (a). It is more preferable that these halogenated aromatic hydrocarbons do not have a functional group such as a carbonyl group or a cyano group.

Examples of such halogenated aromatic hydrocarbons include those represented by the formula Φ _r -Z _b [Φ _r is a b-valent fluorinated aromatic ring residue in which all hydrogen atoms are replaced by fluorine atoms, and Z is fluorine. Halogen atoms other than -Rf, -CO-Rf,-
O-Rf, or -CN. However, Rf is a perfluoroalkyl group, a polyfluoroperhaloalkyl group, or a monovalent Φ _r . b is 0 or an integer of 1 or more. ] There is a compound represented by. The aromatic ring includes a benzene ring and a naphthalene ring. The perfluoroalkyl group or polyfluoroperhaloalkyl group which is Rf preferably has 5 or less carbon atoms. As a halogen atom other than fluorine, a chlorine atom or a bromine atom is preferable.

Specific compounds include, for example, 1,3-
Dibromotetrafluorobenzene, 1,4-dibromotetrafluorobenzene, 2-bromotetrafluorobenzotrifluoride, chloropentafluorobenzene,
Examples include bromopentafluorobenzene, iodopentafluorobenzene, decafluorobenzophenone, perfluoroacetophenone, perfluorobiphenyl, chloroheptafluoronaphthalene, and bromoheptafluoronaphthalene.

As the substance (b) which is a polymer or an oligomer, among the substances having the repeating units (I) to (IV), a fluorine-containing polymer having a refractive index different from that of the fluoropolymer (a) to be combined is used. A compound (for example, a combination of a fluoropolymer containing only a fluorine atom as a halogen atom and a fluoropolymer containing a fluorine atom and a chlorine atom, obtained by polymerizing two or more monomers of different types or different ratios) Combinations of different fluoropolymers) are preferred.

In addition to the fluorine-containing polymer having a ring structure in the main chain as described above, it does not contain hydrogen atoms such as tetrafluoroethylene, chlorotrifluoroethylene, dichlorodifluoroethylene, hexafluoropropylene and perfluoroalkyl vinyl ether. Oligomers composed of monomers, copolymerized oligomers of two or more of those monomers, and the like can also be used as the substance (b). Also, -C
F ₂ CF (CF ₃₎ O- or _{- (CF 2) n O- (} n is 1-3
Perfluoropolyether having a structural unit of (integer of) can also be used. The molecular weight of these oligomers is selected from the range of molecular weight at which they become amorphous, and the number average molecular weight is 300.
~ 10,000 is preferred. Considering the ease of diffusion, a number average molecular weight of 300 to 5000 is more preferable.

The particularly preferred substance (b) is a chlorotrifluoroethylene oligomer because of its good compatibility with the fluoropolymer (a), especially the fluoropolymer having a ring structure in its main chain. Since the compatibility is good, the fluoropolymer (a), particularly the fluoropolymer having a ring structure in the main chain, and the chlorotrifluoroethylene oligomer are easily mixed by heating and melting at 200 to 300 ° C. be able to. Moreover, both can be mixed uniformly by dissolving in a fluorine-containing solvent and mixing and then removing the solvent. A preferred molecular weight of the chlorotrifluoroethylene oligomer is a number average molecular weight of 500 to 1
500.

<About GI type optical fiber> In the cross section of the GI type optical fiber, the substance (b) is distributed in the fluoropolymer (a) with a concentration gradient from the center to the peripheral direction. Preferably, the substance (b) is a substance having a higher refractive index than the fluoropolymer (a), and the substance (b) has a concentration gradient in which the concentration decreases from the center of the optical fiber to the peripheral direction. It is a distributed optical fiber. In some cases, the substance (b) is a substance having a lower refractive index than the fluoropolymer (a), and this substance is distributed with a concentration gradient in which the concentration decreases from the periphery of the optical fiber toward the center. Fiber optics are also useful.
The former optical fiber can be usually manufactured by arranging the substance (b) at the center and diffusing it toward the peripheral direction. The latter optical fiber can be manufactured by diffusing the substance (b) from the periphery toward the center.

The GI type optical fiber obtained by the present invention can have a transmission loss of 100 db or less at 100 m at wavelengths of 700 to 1,600 nm. Especially at a similar wavelength in a fluoropolymer having an alicyclic structure in the main chain,
The transmission loss of 100 m can be 50 db or less. At relatively long wavelengths of 700 to 1,600 nm, such a low level of transmission loss is extremely advantageous. That is, since the same wavelength as that of the quartz optical fiber can be used, connection with the quartz optical fiber is easy, and it is a cheaper light source than the conventional plastic optical fiber which has to use a wavelength shorter than 700 to 1,600 nm. It has the advantage of being completed.

<Production Method of the Present Invention> The present invention is G
The present invention relates to a method for producing a base material (preform) for producing an I-type optical fiber by rotational molding. First, a cylindrical molded body made of a material having a relatively low refractive index selected from the above materials is manufactured in advance, and at least one layer made of a material having a high refractive index is formed on the inner surface of the molded body as a mold. Is formed by rotational molding, and a base material made of a cylindrical or cylindrical molded product having at least two inner and outer layers is manufactured. Another invention is a method for producing the same base material by forming the outer layer molded body by rotational molding and subsequently forming the inner layer by rotational molding. The base material does not necessarily have to have a refractive index distribution (a refractive index distribution can be formed during post-treatment or spinning of the base material), but a certain or more refractive index distribution must be formed in the base material. Is preferred. By forming the refractive index distribution in the base material to a certain extent or more, it becomes easy to form the refractive index distribution in the post-treatment or spinning, and the GI
The manufacturing efficiency of the optical fiber is also improved.

In the production of the base material, it is necessary to diffuse the substance (b) from one layer into the fluoropolymer (a) of the other layer between adjacent layers in order to form the refractive index distribution. For example, when manufacturing a base material having two layers of a central portion and a peripheral portion, in order to form a refractive index distribution, the substance (b) is diffused from the central layer to the peripheral layer (the substance (b) Has a higher refractive index than the fluoropolymer (a)) or diffuses the substance (b) from the peripheral layer to the central layer (the substance (b) is more than the fluoropolymer (a)). Also has a low refractive index). The substance (b) can be diffused by thermal diffusion. This diffusion can be carried out continuously while rotomolding, or after rotomoulding is complete.

In addition to the diffusion of the substance (b) in the production of the base material, it is also possible to produce a base material having a refractive index change close to the refractive index distribution by sequentially changing the refractive index of the material to be laminated. That is, lamination is performed while sequentially increasing the refractive index of the material supplied into the rotating cylindrical drum (for example, while sequentially increasing the concentration of the high refractive index substance (b) with respect to the fluoropolymer (a)). The base material can be manufactured. In addition to this method, diffusion of the substance (b) can be used together.

The form of the above-mentioned material to be subjected to rotational molding is not limited as long as it has a liquid form such as a melt, a solution or a dispersion. In the case of a solution or dispersion, a liquid medium such as a solvent can be molded while removing the liquid medium by evaporative removal after supplying the solution or the like to the rotating cylindrical drum. It is desirable to adjust the molding conditions and the like so that the materials are not mixed between different layers formed during molding. The means for supplying the material to the rotating cylindrical drum is not particularly limited, and for example, a melt extrusion supply method, a flow curtain method, a spray method or the like can be appropriately adopted. In order to uniformly supply the material in the axial direction, the material is preferably supplied over the entire axial length of the rotating cylindrical drum.

For example, in the case of producing a base material composed of a two-layer molded product, a cylindrical body made of an outer layer forming material having a low refractive index is used, or an outer layer forming material having a low refractive index is supplied to a rotating cylindrical drum to form an outer layer. After forming, an inner layer forming material having a high refractive index is supplied to form an inner layer. As a result, a cylindrical or columnar molded body having two inner and outer layers can be obtained. As the outer layer forming material, for example, a fluoropolymer (a) is used, and as the inner layer forming material, for example, a mixture of the fluoropolymer (a) and a substance (b) having a higher refractive index than that is used. Similarly, a molded product having a multi-layer structure of three or more layers can be manufactured.

As a specific example of rotational molding, a schematic vertical sectional view of a rotary cylindrical drum is shown in FIG. 1, and a horizontal sectional view thereof is shown in FIG. 1 and 2, the molding apparatus includes a rotary cylindrical drum 1 that rotates about a cylindrical shaft as a rotation axis and a material extruding die 2, and an outer layer forming material having a relatively low refractive index is supplied from the die 2. The outer layer 3 is formed, and the inner layer forming material 4 having a relatively high refractive index is supplied to the inner surface thereof in a molten state to form the inner layer 5. The outer layer 3 may be formed by inserting a preformed cylindrical molded body into the rotary cylindrical drum 1. After the desired layer is formed, it can be kept in a heated state while continuing rotation to perform thermal diffusion. Thermal diffusion is preferably carried out in the molten state of the material.
After that, the molded body is cooled and solidified and taken out from the rotary cylindrical drum 1, whereby a target base material is obtained.

The material of the rotating cylindrical drum is not particularly limited, but it is preferably made of a material such as corrosion resistant metal or glass. The diameter of the formed base material is 20 to 100
It is preferably mm. If the diameter is too small, it is difficult to form the inner layer, and the production efficiency of the GI type optical fiber is low. If the diameter is too large, it is a substance (b).
It takes a great deal of time to diffuse. Further, the thickness of the outer layer with respect to the inner layer is not particularly limited, but is appropriately about 0.5 to 2 times, and preferably about 1 to 1.5 times. Further, as the base material, a cylindrical shape is preferable to a cylindrical shape because it is easy to mold, and it is efficient to degas volatile components in the material during or after molding.

The concentric layers having different refractive indexes in the base material may be present not only in two layers but also in three or more layers. Even in that case, basically, the central portion and the layers near the central portion are made of a material having a higher refractive index than the layers far from the center. As described above, the substance (b) may have a higher refractive index or a lower refractive index than the fluoropolymer (a). Therefore, when the substance (b) has a higher refractive index than that of the fluoropolymer (a), the substance (b) is present at a higher concentration in the central portion or in a layer closer to the central portion, and the substance (b) is contained. When the refractive index is lower than that of the fluoropolymer (a), the substance (b) is present in a higher concentration in the outermost layer or a layer closer to the outermost layer.

As the base material, the substance (b) is a substance (b) having a higher refractive index than the fluoropolymer (a) [hereinafter, this substance (b) is a substance (b ')], and the substance ( It is preferable that b ′) is present in the inner layer forming material in a relatively high concentration. In this case, the material for forming the inner layer is composed of only the substance (b ') or a mixture of the substance (b') and the fluoropolymer (a). The material for forming the inner layer is preferably composed of a mixture of the substance (b ') and the fluoropolymer (a), because the mechanical properties and moldability of the substance (b') are often insufficient. The outer layer forming material consists of the fluoropolymer (a) only or a mixture of the fluoropolymer (a) and the substance (b ') (provided that the substance (b')
Is lower than the concentration of the inner layer forming material). The outer layer forming material may be a material composed of a mixture of the fluoropolymer (a) and a substance (b) having a lower refractive index than that. When the base material is composed of a multi-layered structure having three or more layers, the layer closer to the center has a higher concentration of the substance (b ') (however, lower than the concentration in the center) and the outermost layer or the layer closer to the outermost layer. A material having a low concentration of the substance (b ′) is used. The substance (b) having a refractive index lower than that of the fluoropolymer (a) may be arranged in the outermost layer or a layer close to the outermost layer.

The fiberizing method for producing an optical fiber using the obtained base material is not particularly limited, and a conventionally known method can be adopted. For example, the desired GI optical fiber can be obtained by heat drawing or melt spinning the base material. The conditions such as the heating temperature and the fiberizing rate for heat drawing and melt spinning can be appropriately determined depending on the kind of the material such as the fluoropolymer (a).

[0052]

EXAMPLES Next, examples of the present invention will be described more specifically, but it goes without saying that the description does not limit the present invention.

"Synthesis Example 1" 35 parts by weight of perfluoro (butenyl vinyl ether) [PBVE], 1,1,2-
5 parts by weight of trichlorotrifluoroethane (R113), 150 parts by weight of ion-exchanged water, and 0.09 parts by weight of ((CH ₃ ) ₂ CHOCOO) ₂ as a polymerization initiator,
It was placed in a pressure-resistant glass autoclave. After purging the system with nitrogen three times, suspension polymerization was carried out at 40 ° C. as a result,
28 parts by weight of a polymer having a number average molecular weight of about 1.5 × 10 ⁵ (hereinafter referred to as polymer A) was obtained.

The intrinsic viscosity [η] of polymer A was 0.50 at 30 ° C. in perfluoro (2-butyltetrahydrofuran) [PBTHF]. The glass transition point of the polymer A was 108 ° C., and it was a tough and transparent glassy polymer at room temperature. The 10% thermal decomposition temperature is 465 ° C,
The solubility parameter was 5.3 (cal / cm ³ ) ^1/2 and the refractive index was 1.34.

The polymer A obtained by the above synthesis was treated with PBTHF.
It dissolves in a solvent and has a CTFE of 800 with a number average molecular weight of 800.
The oligomer was added (the ratio of TFE oligomer to the polymer mixture was 30% by weight) to obtain a mixed solution. This mixed solution is desolvated to give a transparent mixed polymer (hereinafter referred to as polymer B
I got). The CTFE oligomer had a refractive index of 1.41, and the difference in solubility parameter from the polymer A was 1.4 (cal / cm ³ ) ^1/2 .

[Example 1] Inner diameter 50 mm, length 300 m
The glass rotary cylindrical drum of m was rotated at about 60 rotations / second, and the atmospheric temperature of the drum and the inside of the drum was adjusted to 300 ° C. The molten polymer A was introduced into the inner surface of the drum to make the thickness 1
An outer layer of 0 mm was formed. Then, the molten polymer B was supplied in a thin film form from a slit die having substantially the same length as the drum to form an inner layer having a thickness of 10 mm. Rotation was continued for 8 hours under the same temperature conditions as above, and then cooled to obtain a cylindrical base material having an inner diameter of 30 mm and an outer diameter of 50 mm.

Using the base metal obtained, 300
The fiber was stretched at a temperature of ℃ to form a GI optical fiber having a diameter of 600 μm.

The optical transmission characteristics of the obtained optical fiber are 7
280 dB / km at 80 nm, 120 d at 1550 nm
It was B / km, and was an optical fiber capable of favorably transmitting light from visible light to near infrared.

Example 2 Polymer A was used to form a cylinder having an outer diameter of 50 mm, a wall thickness of 10 mm and a length of 300 mm in advance, and the cylinder was inserted into a metal cylindrical support material to obtain Example 1. Similarly rotate and heat to 250 ° C. to polymer A
The molten polymer B was supplied to the inner surface of the cylinder in the same manner as in Example 1 to form an inner layer having a thickness of 10 mm. Then at 300 ° C for 8
A base material was manufactured by performing a time thermal diffusion treatment. Using this base material, a GI type optical fiber having a diameter of 600 μm was manufactured in the same manner as in Example 1.

The optical transmission characteristics of the obtained optical fiber were similar to those of Example 1.

[0061]

The present invention is a method for efficiently producing a base material for producing a gradient index optical fiber by using a rotational molding method, and efficiently forms a gradient index distribution by thermal diffusion of a substance (b). You can In the gradient index optical fiber obtained by the present invention, by using an amorphous fluororesin having no C—H bond, it is possible to transmit light from ultraviolet light to near infrared light with extremely low loss. Became possible.

This graded index optical fiber is also suitable for short-distance optical communication because it is flexible and easy to branch and connect despite its large fiber diameter.
It is possible to obtain a practically low-loss optical fiber.
Further, the gradient index optical fiber obtained according to the present invention is used in an engine room of an automobile, OA equipment, a plant,
It has heat resistance, chemical resistance, moisture resistance, and nonflammability that can withstand the harsh conditions of use in home appliances.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a rotating cylindrical drum.

FIG. 2 is a cross-sectional view of a rotating cylindrical drum.

[Explanation of symbols]

 1 Rotating Cylindrical Drum 2 Extrusion Die 3 Outer Layer 4 Inner Layer Forming Material 5 Inner Layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location G02B 6/18 G02B 6/18 // G02B 3/00 3/00 B

Claims (9)

[Claims] 1. A method for producing a base material for producing a graded index optical fiber, comprising a non-crystalline fluoropolymer (a) having substantially no C—H bond and a fluoropolymer (a). In comparison with at least one substance (b) having a difference in refractive index of 0.001 or more, and using as a mold a cylindrical molded body made of a low refractive index material selected from at least one of the above materials. At least one layer made of a layer-forming material having a relatively high refractive index selected from at least one of the above-mentioned materials is formed on the inner surface by rotational molding to form a cylindrical or columnar structure having at least two inner and outer layers. A method for producing a base material for producing a gradient index optical fiber, which comprises producing a base material made of a molded body. 2. From a layer containing a relatively high concentration of substance (b) during or after rotational molding, containing one of the adjacent layers with a relatively high concentration of substance (b). The manufacturing method according to claim 1, wherein the substance (b) is thermally diffused to the other layer. 3. The method according to claim 1, wherein the fluoropolymer (a) is a fluoropolymer having a ring structure in its main chain. 4. The method according to claim 1, 2 or 3, wherein the substance (b) is a substance having substantially no C—H bond. 5. A method for producing a base material for producing a graded index optical fiber, which comprises a non-crystalline fluoropolymer (a) having substantially no C—H bond and a fluoropolymer (a). In comparison with, at least one substance (b) having a difference in refractive index of 0.001 or more is used to manufacture a plurality of layer forming materials having different refractive indexes, and the layer forming materials are sequentially placed in a rotating cylindrical drum. To produce a base material composed of a cylindrical or cylindrical molded body in which the inner layer of the molded article has a higher refractive index than the outer layer, and the production of a base material for producing a gradient index optical fiber. Method. 6. A layer containing a relatively high concentration of the substance (b), which is contained in one of adjacent layers in a relatively high concentration of the substance (b), during or after rotational molding. The method according to claim 5, wherein the substance (b) is thermally diffused to the other layer. 7. The method according to claim 5, wherein the fluoropolymer (a) is a fluoropolymer having a ring structure in its main chain. 8. The method according to claim 5, 6 or 7, wherein the substance (b) is a substance having substantially no C—H bond. 9. The substance (b) is a substance having a higher refractive index than the fluorinated polymer (a), and after forming an inner layer containing the substance (b) at a relatively high concentration, inside the rotating cylindrical drum. The method according to claim 5, 6, 7, or 8, wherein the substance (b) is thermally diffused from the inner layer to the outer layer by the method.