JP2011095762A - Plastic optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a refractive index distribution type optical fiber having suppressed initial transmission loss and loss increase upon bending and enhanced heat resistance and wet heat resistance, and having a non-crystalline fluorine-containing polymer which has no C-H bond as its material. <P>SOLUTION: In the refractive index distribution type optical fiber having concentric inner and outer at least two layer structure, an inner layer has an amorphous fluorine-containing polymer (a) substantially having no C-H bond as its material; an outer layer comprises an amorphous fluorine-containing polymer substantially having no C-H bond, has a refractive index lower than that of the outermost part of the inner layer and comprises only a fluorine-containing polymer (d) obtained by polymerizing a monomer, containing a compound represented by formula (1) or a fluorine-containing polymer material (c) to be a mixture of the fluorine-containing polymer (d) and an another material. The formula (1) is CF<SB>2</SB>=CF-O-CR<SP>1</SP>R<SP>2</SP>-CR<SP>3</SP>R<SP>4</SP>-CF=CF<SB>2</SB>. In the formula, R<SP>1</SP>, R<SP>2</SP>, R<SP>3</SP>and R<SP>4</SP>each independently denotes F, CF<SB>3</SB>or OCF<SB>3</SB>and at least one among them denotes CF<SB>3</SB>or OCF<SB>3</SB>. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a plastic optical fiber.

  As a refractive index distribution type plastic optical fiber, a non-crystalline fluorine-containing polymer having substantially no CH bond is used as a matrix, and a material having a refractive index different from that of the matrix is distributed with a concentration gradient in the radial direction. A plastic optical fiber having a distributed structure is known (see Patent Document 1). Further, in order to improve an increase in transmission loss due to bending in such a gradient index optical fiber, an optical fiber having a polymer having a refractive index lower than that of a matrix on its outer periphery is known (Patent Documents 2 and 3). reference).

JP-A-8-5848 JP-A-8-304636 JP 2002-71972 A

  The conventional refractive index distribution type optical fiber provided with the low refractive index polymer on the outer periphery has a lower initial transmission loss than the refractive index distribution type optical fiber without the outer layer due to the influence of the interface irregularity between the inner layer and the outer layer. Long-term heat resistance (70 ° C, 1000 hours), thermal cycle test (70 ° C / -20 ° C x 10 times), wet heat cycle test (65 ° C, humidity 95% /-10 ° C x 10 times), etc. When the test is performed, there is a problem that transmission loss increases. As a result of analyzing the fiber after the heat cycle test and the wet heat cycle test, the present inventor has found that separation occurs between the outer layer made of the low refractive index polymer and the inner layer in which the refractive index profile is formed. I found out that it was the cause.

  As a result of intensive studies based on recognition of the above problems, the present inventor has found that a polymer constituting an inner layer matrix as a low refractive index material for the outer layer in order to improve the adhesion between the inner layer and the outer layer. It was found that it was effective to use a polymer having the same basic skeleton. That is, the present invention provides a refractive index distribution type optical fiber having the same basic skeleton having a refractive index lower than the outermost refractive index of the inner layer on the outer side of the inner layer where the refractive index distribution is formed and having good adhesion. By forming the outer layer using the above polymer, an optical fiber in which the increase in the transmission loss due to the initial transmission loss and bending is reduced while maintaining the heat resistance and moist heat resistance is newly provided. This invention is the following invention based on this knowledge.

The present invention relates to a refractive index distribution type optical fiber having a concentric inner / outer at least two-layer structure, wherein the inner layer is made of a non-crystalline fluoropolymer (a) having substantially no CH bond. A non-crystalline fluoropolymer having an index distribution structure, the outer layer having substantially no C—H bond, and having a refractive index lower than the outermost refractive index of the inner layer; Fluorine-containing polymer material (c) which is only a fluorine-containing polymer (d) obtained by polymerizing a monomer containing a compound represented by), or a mixture of the fluorine-containing polymer (d) and other materials. A plastic optical fiber is provided.
_{^{CF 2 = CF-O-CR}} 1 R 2 -CR 3 R 4 -CF = CF 2 ··· (1)
(R ¹ , R ² , R ³ and R ⁴ are each independently F, CF ₃ or OCF ₃ , and at least one is CF ₃ or OCF _3. )

With the optical fiber of the present invention, it has become possible to have extremely low loss of light from ultraviolet light to the near infrared, suppress increase in loss during bending, and have both heat resistance and moisture heat resistance.

(A) And (B) is a figure showing the refractive index distribution of the radial direction in the cross section of the optical fiber of this invention, respectively. (C) and (D) are diagrams showing the refractive index distribution in the radial direction in the cross section of the optical fiber of the present invention.

  The refractive index distribution in the radial direction of the optical fiber of the present invention is shown in FIGS. 1 (A) and 1 (B) and FIGS. 2 (C) and 2 (D). The horizontal axis indicates the diameter of the optical fiber, and the vertical axis indicates the refractive index. In the inner layer (range (1)) of the optical fiber, the center has a high refractive index and a refractive index distribution in which the refractive index decreases as the distance from the center increases. The refractive index of the outer layer (range (2)) is lower than the outermost refractive index of the inner layer. The refractive index distribution of the inner layer is either one showing a gentle distribution at the outer periphery as shown in FIGS. 1 (A) and 1 (B), or one showing a parabolic distribution as shown in FIGS. 2 (C) and 2 (D). Good. From the viewpoint of a high transmission band, the latter having a parabolic refractive index profile is desirable. On the other hand, even those having a distribution in which the refractive index continuously decreases to the outermost part of the inner layer as shown in FIGS. 1 (B) and 2 (D) are as shown in FIGS. 1 (A) and 2 (C). Alternatively, the inner layer may be continuously lowered from the center to the middle of the inner layer, and the inner layer outside thereof may have a certain refractive index. The outer layer in FIGS. 1B and 2D substantially functions as a cladding layer. 1A and 2C, the portion having a constant refractive index functions as a cladding layer, and the outer layer functions as a second cladding layer.

  The refractive index of the outer layer is preferably 0.003 or more lower than the outermost refractive index of the inner layer in order to reduce bending loss. A more preferable refractive index difference is 0.005 or more. The numerical aperture NA calculated by the maximum refractive index of the central portion and the minimum refractive index of the outer layer is 0.20 or more, preferably 0.23 or more, more preferably 0.25 or more. Usually, the upper limit of the numerical aperture is 0.5. In general, the bending loss varies depending on the core diameter of the optical fiber, and the bending loss increases as the core diameter increases. The core diameter of the optical fiber in the present invention is not particularly limited, but is desirably 1000 μm or less, preferably 500 μm or less, and more preferably 200 μm or less. Usually, the lower limit of the core diameter is 30 μm. In addition, the core part of the optical fiber in the present invention refers to a part having a refractive index higher than the lowest refractive index of the inner layer by 5% or more of the difference between the highest refractive index of the inner layer and the lowest refractive index of the inner layer.

  In the optical fiber of the present invention, a protective coating layer may be provided on the outer side of the outer layer. The material of the protective coating layer is not particularly limited as long as it is a synthetic resin, and a thermoplastic resin or a cured product of a curable resin other than the fluorine-containing polymer (a) and the fluorine-containing polymer (d). Can be used. Among them, a synthetic resin that has been conventionally used or proposed for use as a protective coating layer of an optical fiber is preferable. When it is required to increase the mechanical strength as the role of the protective coating layer, a layer having a certain thickness or more is necessary, and it is preferable to use a synthetic resin having a high tensile strength and elastic modulus. As a material for the protective coating layer, a thermoplastic resin is preferable, and among them, an acrylic resin, a polycarbonate resin, and a cyclic polyolefin resin are particularly preferable. The protective coating layer may be a multilayer of two or more layers, one of which is a relatively soft thermoplastic resin such as a vinyl chloride resin, a polyolefin resin, a polyvinylidene fluoride resin, or an ethylene-tetrafluoroethylene copolymer resin. It may be.

  In the present invention, as a method for forming the refractive index distribution of the inner layer, there is a method of forming a refractive index distribution structure by using a fluoropolymer (a) as a matrix and distributing substances (b) having different refractive indexes in the matrix. preferable. In addition, a fluorine-containing polymer (a) in which the polymerization composition ratio changes in the radial direction from the center by combining two or more fluorine-containing monomers capable of forming a polymer whose refractive index changes according to the polymerization composition ratio The method of forming the inner layer which consists of may be sufficient. The fluoropolymer (a) is an amorphous fluoropolymer in order to reduce transmission loss and has a C—H bond so that optical communication in the near-infrared wavelength band is possible. It is necessary that the substance (b) has a chemical structure that can be similarly dissolved in the fluoropolymer and does not have a C—H bond.

The fluoropolymer material (c) constituting the outer layer needs to be a material having a lower refractive index than the outermost refractive index of the inner layer and has high adhesion to the inner layer made of the fluoropolymer (a). Therefore, it is necessary to have a chemical structure which is an amorphous fluoropolymer and does not have a C—H bond. The fluorinated polymer material (c) is composed of only the fluorinated polymer (d) obtained by polymerizing the monomer containing the compound represented by the formula (1), or the fluorinated polymer (d) and other materials. It is a mixture of
_{^{CF 2 = CF-O-CR}} 1 R 2 -CR 3 R 4 -CF = CF 2 ··· (1)
(R ¹ , R ² , R ³ , R ⁴ are each independently F, CF ₃ or OCF ₃ and at least one is CF ₃ or OCF ₃ ).

  When the fluoropolymer material (c) is a mixture of the fluoropolymer (d) and other materials, the proportion of the fluoropolymer (d) in the mixture is 20 to 99% on a mass basis. It is preferable that it is 40 to 99%.

  The glass transition temperature Tgc of the fluoropolymer material (c) is preferably 70 ° C. <Tgc <Tga + 30 ° C. If Tgc is 70 ° C. or lower, thermal deformation will occur and transmission loss will increase, or in the case of an optical fiber with a protective coating layer, a deviation will occur between the outer layer and the protective coating layer during high temperature and low temperature cycles. As a result, the fiber end face tends to protrude or retract. On the other hand, if Tgc is (Tga + 30 ° C.) or more, a difference in shrinkage rate occurs between the inner layer and the outer layer during cooling when spinning an optical fiber, and distortion occurs in the inner layer, which is likely to cause scattering loss. Therefore, as Tgc, the difference from Tga is preferably within 15 ° C. That is, it is preferable that Tga-15 <Tgc <Tga + 15. Tga, which is the glass transition temperature of the fluoropolymer (a), is preferably 70 <Tga. Further, the melt viscosity of the fluoropolymer material (c) is preferably as close as possible to the melt viscosity of the inner layer fluoropolymer (a) for the same reason.

  When the fluorine-containing polymer material (c) is a mixture of two or more polymers, the Tg of the mixture is 1 corresponding to the mass ratio of each polymer when the two or more polymers are sufficiently uniformly mixed. Tg appears. In this case, one Tg of this mixture is the above Tgc. However, when the mixture is not sufficiently uniform, Tg based on each polymer (Tg of 2 or more) may appear as the Tg of the mixture. In this case, the polymer mixture in the present invention is preferably one in which the Tg of each polymer is within the above range.

  The fluoropolymer material (c) is a material having no C—H bond.

  In the present invention, the fluoropolymer (a) is not particularly limited as long as it is non-crystalline and has substantially no C—H bond that absorbs light in the near infrared light. However, a fluorine-containing polymer having a fluorine-containing aliphatic ring structure in the main chain is preferable. Having a fluorine-containing aliphatic ring structure in the main chain means that at least one carbon atom constituting the aliphatic ring is a carbon atom in the carbon chain constituting the main chain, and the carbon atom constituting the aliphatic ring is It means having a structure in which a fluorine atom or a fluorine-containing group is bonded to at least a part. The atoms constituting the ring may have an oxygen atom or a nitrogen atom in addition to the carbon atom. As the fluorine-containing aliphatic ring structure, a fluorine-containing aliphatic ether ring structure is more preferable.

The viscosity of the fluoropolymer (a) in the molten state is preferably 10 ³ to 10 ⁵ poise at a melting temperature of 200 to 300 ° C. If the melt viscosity is too high, melt spinning is difficult, and the diffusion of the substance (b) necessary for the formation of the refractive index distribution hardly occurs and the refractive index distribution is difficult to form. In addition, if the melt viscosity is too low, there is a practical problem. That is, when it is used as an optical transmission body in an electronic device or an automobile, it is softened by being exposed to a high temperature, and the light transmission performance is lowered.

The number average molecular weight of the fluoropolymer (a) is preferably 1 × 10 ^{4 to} 5 × 10 ^{6, and} more preferably 5 × 10 ⁴ to 1 × 10 ⁶ . 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 transmission body having a refractive index distribution. When this molecular weight is represented by intrinsic viscosity [η], it is preferably 0.1 to 1.0 dL / g at 30 ° C. in perfluoro (2-butyltetrahydrofuran) [hereinafter referred to as PBTHF], particularly 0.2 It is preferable that it is -0.5dL / g.

  As the polymer having a fluorine-containing aliphatic ring structure, a monomer having a fluorine-containing ring structure (a monomer having a polymerizable double bond between a carbon atom constituting a ring and a carbon atom not constituting a ring, or Cyclization of a polymer obtained by polymerizing a monomer having a polymerizable double bond between two carbon atoms constituting the ring) or a fluorinated monomer having two or more polymerizable double bonds A polymer having a fluorine-containing aliphatic ring structure in the main chain obtained by polymerization is preferred.

A polymer having a fluorinated aliphatic ring structure in the main chain obtained by cyclopolymerization of a fluorinated monomer having two or more polymerizable double bonds is disclosed in JP-A-63-238111 and It is known from Japanese Utility Model Laid-Open No. 63-238115, Japanese Patent Application Laid-Open No. 4-346957, WO 03/037838, Japanese Patent Application Laid-Open No. 2002-5000811, and the like. That is, perfluoro (allyl vinyl ether), perfluoro (butenyl vinyl _{ether), CF 2 = CFOCF 2 CF} (CF 3) CF = CF 2, CF 2 = CFOCF (CF 3) CF 2 CF = CF 2, CF 2 = CFOCF 2 Cyclopolymerization of monomers such as CF (OCF ₃ ) CF═CF ₂ gives a polymer having a fluorinated aliphatic ring structure in the main chain.

  The polymer having a fluorinated alicyclic structure has a polymer unit having a fluorinated alicyclic structure of 20 mol% or more, particularly 40 mol%, based on the total polymerized units of the polymer having a fluorinated alicyclic structure. What is contained above is preferable in terms of transparency, mechanical properties, and the like.

Specifically, the polymer having a fluorine-containing aliphatic ring structure is a polymer obtained by cyclopolymerizing a fluorine-containing monomer having two polymerizable double bonds selected from the following chemical formula: Is exemplified. The following formula (2) is an example of a fluorine-containing monomer having two polymerizable double bonds.
^{CX 1 X 2 = CX 3 -O} -CR 5 R 6 -CR 7 R 8 -CR 9 = CX 4 X 5 ··· (2).

In the compound represented by the formula (2), X ^{1 to} X ⁵ are all fluorine atoms, or 1 to 2 thereof (provided that at most ¹ of X ^{1 to} X ³ and X ^{4 to} X ⁵ It is preferred that at most one) is a chlorine atom and the other is a fluorine atom. R ⁵ , R ⁶ , R ⁷ , R ⁸ , and R ⁹ are all fluorine atoms, or at most two are chlorine atoms, trifluoromethyl groups, or trifluoromethoxy groups, and the others are fluorine atoms. preferable. The most preferable compound represented by the formula (2) as the fluorine-containing polymer (a) is a compound in which all of X ^{1 to} X ⁵ , R ⁵ , R ⁶ , R ⁷ , R ⁸ and R ⁹ are fluorine atoms [ie , Perfluoro (butenyl vinyl ether)].

Specific examples of the compound represented by the formula (2) include the following compounds. _{CF 2 = CFOCF 2 CF 2 CF} = CF 2, CF 2 = CFOCF 2 CF (CF 3) CF = CF 2, CF 2 = CFOCF 2 CFClCF = CF 2, CF 2 = CFOCCl 2 CF 2 CF = CF 2, CF ₂ = CFOCF ₂ CF ₂ CCl = CF ₂ , CF ₂ = CFOCF ₂ CF ₂ CF = CFCl, CF ₂ = CFOCF ₂ CF (CF ₃ ) CCl = CF ₂ , CF ₂ = CFOCF (CF ₃ ) CF ₂ CF = CF ₂ , CF ₂ = CFOC (CF ₃ ) ₂ CF ₂ CF = CF ₂ , CF ₂ = CFOCF (OCF ₃ ) CF ₂ CF = CF ₂ , CF ₂ = CFOCF ₂ CF (OCF ₃ ) CF = CF ₂
The substance (b) is preferably a substance having a refractive index difference of 0.005 or more in comparison with the fluoropolymer (a) which is a matrix resin, and has a higher refractive index than the fluoropolymer (a). Or a low refractive index. Further, the fluorine-containing polymer (a) containing 15% by mass of the substance (b) in the fluorine-containing polymer (a) as the matrix resin, and the fluorine-containing polymer (a) not containing the substance (b) And the refractive index difference is preferably 0.003 or more. 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 along the peripheral direction. Are distributed optical fibers. In some cases, the substance (b) is a substance having a lower refractive index than that of the fluoropolymer (a), and this substance is distributed with a concentration gradient in which the concentration decreases from the periphery of the optical fiber along the central direction. An optical fiber is also useful. The former optical fiber can usually be manufactured by placing the substance (b) in the center and diffusing in the peripheral direction. The latter optical fiber can be manufactured by diffusing the substance (b) from the periphery toward the center.

  In the present invention, a substance having a higher refractive index than that of the fluoropolymer (a) is usually used as the substance (b). That is, the substance (b) is a substance that has substantially no C—H bond for the same reason as the fluoropolymer (a), and has a refractive index of 0.05 or more higher than that of the fluoropolymer (a). It is more preferable. If the refractive index is higher, the content of (b) necessary for forming a desired refractive index distribution may be smaller, so that the glass transition temperature can be reduced less. As a result, the heat resistance of the optical fiber is reduced. Since it increases, it is especially preferable that it is 0.1 or more.

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, or a bonding group such as an ether bond. When the molecular weight is increased, the compatibility with the fluoropolymer (a) is decreased, and as a result, the light scattering loss is increased. On the other hand, in the case of a compound having a small molecular weight, the glass transition temperature in the mixture with the fluoropolymer (a) is lowered and the heat resistance temperature of the optical fiber is lowered. Therefore, the number average molecular weight of the compound (b) is preferably from ^{3 × 10 2 ~2 × 10 3} , more preferably ^{3 × 10 2 ~1 × 10 3} .

  Specific examples of the substance (b) include oligomers that are chlorotrifluoroethylene 5- to 8-mer and dichlorodifluoroethylene 5- to 8-mer as described in JP-A-8-5848. 2 to 5 amounts obtained by polymerizing an oligomer or a monomer (for example, a monomer having a chlorine atom) which gives an oligomer having a high refractive index among the monomers forming the fluoropolymer (a) There are body oligomers.

  In addition to halogen-containing aliphatic compounds such as the above oligomers, halogenated aromatic hydrocarbons and halogen-containing polycyclic compounds that do not contain a hydrogen atom bonded to a carbon atom can also be used. In particular, a fluorinated aromatic hydrocarbon or a fluorine-containing polycyclic compound containing only a fluorine atom as a halogen atom (or a fluorine atom and a relatively small number of chlorine atoms) is in a phase with the fluorine-containing polymer (a). It is preferable in terms of solubility. Moreover, it is more preferable that these halogenated aromatic hydrocarbons and halogen-containing polycyclic compounds do not have a polar functional group such as a carbonyl group or a cyano group.

Examples of such a halogenated aromatic hydrocarbon include, for example, the formula Φr-Z _b [Φr is a b-valent fluorinated aromatic ring residue in which all of the hydrogen atoms are substituted with fluorine atoms, Z is a halogen atom other than fluorine, -Rf, -CO-Rf, -O-Rf, or -CN. Rf is a perfluoroalkyl group, a polyfluoroperhaloalkyl group, or a monovalent Φr. b is 0 or an integer of 1 or more. There is a compound represented by Aromatic rings include benzene and naphthalene rings. The number of carbon atoms of the perfluoroalkyl group or polyfluoroperhaloalkyl group as Rf is preferably 5 or less. As a halogen atom other than fluorine, a chlorine atom or a bromine atom is preferable. Specific examples of the compound include 1,3-dibromotetrafluorobenzene, 1,4-dibromotetrafluorobenzene, 2-bromotetrafluorobenzotrifluoride, chloropentafluorobenzene, bromopentafluorobenzene, iodopentafluorobenzene, There are decafluorobenzophenone, perfluoroacetophenone, perfluorobiphenyl, chloroheptafluoronaphthalene, bromoheptafluoronaphthalene and the like.

  As examples of the fluorine-containing polycyclic compound, the following compounds (b-1) to (b-3) as exemplified in JP-A-11-167030 are preferable. (B-1) one or more selected from the group of triazine ring, oxygen, sulfur, phosphorus and metal, wherein two or more of the fluorine-containing rings which are carbon rings or heterocyclic rings and have a fluorine atom or a perfluoroalkyl group A fluorine-containing non-condensed polycyclic compound bonded with a bond, and having substantially no C—H bond. (B-2) a fluorine-containing non-condensed polycyclic compound in which three or more fluorine-containing rings having a carbon ring or a heterocyclic ring and having a fluorine atom or a perfluoroalkyl group are bonded directly or with a bond containing carbon A compound having substantially no C—H bond. (B-3) A fluorine-containing condensed polycyclic compound which is a condensed polycyclic compound composed of three or more carbon rings or heterocyclic rings and substantially has no C—H bond.

  A particularly preferred substance (b) is chlorotrifluoromethane because of its good compatibility with the fluoropolymer (a), particularly the fluoropolymer having a ring structure in the main chain, and good heat resistance. Ethylene oligomers, perfluoro (triphenyltriazine), perfluoroterphenyl, perfluoroquatrophenyl, perfluoro (triphenylbenzene), perfluoroanthracene. Due to good compatibility, the fluoropolymer (a), in particular, the fluoropolymer (a) having a ring structure in the main chain and the substance (b) are easily mixed by heating and melting at 200 to 300 ° C. Can be made. Moreover, after dissolving and mixing in a fluorine-containing solvent, both can be mixed uniformly by removing a solvent.

  Specific methods for producing an optical fiber by forming a refractive index distribution structure by distributing the substance (b) in the fluoropolymer (a) include the following methods. However, it is assumed that the substance (b) has a higher refractive index than the fluoropolymer (a). A columnar molded body made of a fluoropolymer (a) having a high concentration of the substance (b) in the central axis is manufactured, and the refractive index distribution is obtained by diffusing the substance (b) in the radial direction from the central axis by thermal diffusion. A method (1) of forming an optical fiber using the cylindrical molded body obtained as a preform. In the method (1), a method (2) in which the thermal diffusion of the substance (b) is performed simultaneously with the production of the optical fiber. When producing an optical fiber by forming a fiber by melting and extruding the fluoropolymer (a), a high concentration of the substance (b) is present in the central axis, and the substance (b) is subjected to heat diffusion while being thermally diffused. Method (3) for manufacturing a fiber. In the method (3), a cylindrical preform having a refractive index distribution formed by extrusion molding is manufactured, and then an optical fiber is manufactured from the preform.

  The substance (b) is dissolved in the monomer capable of forming the fluoropolymer (a), and this solution is put into a rotating cylindrical mold and is rotated from the periphery of the cylindrical mold to the center direction. (5) A method for producing an optical fiber by forming a refractive index distribution by proceeding polymerization of a monomer, and using the obtained cylindrical molded body as a preform. In this method (5), since the substance (b) is usually less soluble in the polymer than the monomer, the monomer that is unpolymerized than the polymerized part when the polymerization proceeds from the periphery of the cylindrical body The substance (b) is distributed at a high concentration in the part, and as a result, the substance (b) having a high concentration exists in the central axis part where the polymer formation is the slowest, and the concentration of the substance (b) is more radial than the central axis. A decreasing concentration distribution is formed, and a refractive index distribution is formed. A method (6) in which a polymerizable monomer is used as a precursor of the material (b) in the method (5). If the polymerizability of this polymerizable monomer (hereinafter referred to as precursor monomer) is lower than the polymerizability of the monomer capable of forming the fluoropolymer (a), the polymerization of the precursor monomer is slow. Similar to the case of the method (5), a concentration distribution is formed in which a polymer (that is, the substance (b)) of a high concentration of precursor monomer exists in the central axis portion.

  The outer layer can be formed, for example, as follows. A cylindrical body made of the fluoropolymer material (c) is manufactured, and an inner layer made of the fluoropolymer (a) and the substance (b) is formed inside the cylindrical body according to the above method, and has an outer layer. A preform is manufactured, and an optical fiber is manufactured using the preform. A layer of the fluoropolymer material (c) as an outer layer is formed on the outer periphery of the preform obtained by the above method by a method such as coating, and an optical fiber is manufactured using the preform having this layer. A cylindrical body made of the fluoropolymer material (c) having an inner diameter larger than that of the preform is manufactured, and an optical fiber is manufactured by integrally spinning a cylindrical body fitted with the preform. . In the melt extrusion method, the fluoropolymer material (c) is extruded as an outer layer simultaneously with the inner layer to produce a preform having the outer layer, or directly spun simultaneously with extrusion to produce an optical fiber. After manufacturing an optical fiber having no outer layer, the outer layer is formed by coating or the like. In the method (5), a preform integrated with the cylindrical mold is manufactured using a cylindrical mold made of the fluoropolymer material (c), and an optical fiber is manufactured using the preform.

  For example, after producing a preform having a refractive index distribution, an optical fiber is obtained by fitting and spinning this preform on a cylindrical body made of the fluoropolymer material (c). An optical fiber can also be obtained by manufacturing a cylindrical body composed of an inner layer and an outer layer before diffusion of the substance (b), heating the cylindrical body to diffuse the substance (b) to form a preform, and then spinning it. It is done.

  The GI type optical fiber obtained by the present invention has a wavelength of 700 to 1,600 nm and a transmission loss of 100 m can be 10 dB or less. Such a low level of transmission loss is extremely advantageous at a relatively long wavelength of 700 to 1,600 nm. That is, by using the same wavelength as the quartz optical fiber, it is easy to connect to the quartz optical fiber, and is less expensive than the conventional plastic optical fiber that has to use a wavelength shorter than 700 to 1,600 nm. There is an advantage that a simple light source is sufficient.

  Hereinafter, the present invention will be described with specific examples, but the present invention is not limited to these specific examples. Examples 1 to 5 below are examples of polymer synthesis, Examples 6 to 10 are examples, and Example 11 is a comparative example.

(Example 1)
30 g of perfluoro (butenyl vinyl ether) [hereinafter referred to as PBVE], 150 g of ion-exchanged water, 10 g of methanol and 0.15 g of diisopropyl peroxydicarbonate as a polymerization initiator were placed in a pressure-resistant glass autoclave having an internal volume of 200 ml. After the system was replaced with nitrogen three times, suspension polymerization was performed at 40 ° C. for 22 hours. As a result, 26 g of a polymer (hereinafter referred to as polymer A) was obtained. The intrinsic viscosity [η] of the polymer A was 0.24 at 30 ° C. in PBTHF. The glass transition temperature of polymer A measured by thermomechanical analysis (hereinafter referred to as TMA) was 108 ° C., and it was a tough and transparent glassy polymer at room temperature. Further, the 10% thermal decomposition temperature was 468 ° C., and the refractive index measured by Abbe refractometer of a film prepared by press molding the polymer was 1.342.

(Example 2)
An autoclave made of pressure-resistant glass having an internal volume of 200 ml was charged with 80 g of water, CF ₂ = CFCF ₂ CF (CF ₃ ) OCF = CF ₂ 15 g (45.7 mmol), 38 mg of perfluorobenzoyl peroxide, and 2.4 g of methanol. After the autoclave was purged with nitrogen, the autoclave was heated until the internal temperature of the autoclave reached 70 ° C., and polymerization was carried out at 70 ° C. for 20 hours. The obtained polymer was washed with ion-exchanged water and methanol and then dried at 200 ° C. for 1 hour. As a result, 12.5 g of a polymer (hereinafter referred to as polymer B) was obtained. The yield of the obtained polymer was 83%.

  When a part of the polymer was dissolved in PBTHF and the intrinsic viscosity was measured, it was 0.31 dl / g. The refractive index was 1.328, and the glass transition temperature measured by differential scanning calorimetry (DSC) was 124 ° C. When the tensile properties of the polymer were measured, the tensile modulus was 1280 MPa, the yield stress was 38 MPa, and the elongation at break was 5.1%. Moreover, it was 5200 Pa.s when the zero shear viscosity in 230 degreeC was measured with the rotary melt viscoelasticity measuring apparatus.

(Example 3)
CF ₂ = CFOCF ₂ CF (CF ₃ ) CF = CF ₂ 35 g, ion-exchanged water 150 g, methanol 10 g and 0.15 g of polymerization initiator diisopropyl peroxydicarbonate were placed in a pressure-resistant glass autoclave having an internal volume of 200 ml. . After the system was replaced with nitrogen three times, suspension polymerization was performed at 40 ° C. for 22 hours. As a result, 30 g of a polymer (hereinafter referred to as polymer C) was obtained. The intrinsic viscosity [η] of the polymer C was 0.21 at 30 ° C. in PBTHF. The glass transition temperature of the polymer C measured by TMA was 118 ° C., and it was a tough and transparent glassy polymer at room temperature. The refractive index was 1.338.

(Example 4)
Water (80 g), CF ₂ = CFOCF ₂ CF (OCF ₃ ) CF═CF ₂ (15 g, 43.6 mmol), and perfluorobenzoyl oxide (38 mg) were placed in a pressure-resistant glass autoclave having an internal volume of 200 mL. After the autoclave was purged with nitrogen, the autoclave was heated until the internal temperature of the autoclave reached 70 ° C., and polymerization was carried out at 70 ° C. for 20 hours. The obtained polymer was washed with ion-exchanged water and methanol and then dried at 200 ° C. for 1 hour. As a result, 10.5 g of a polymer (hereinafter referred to as polymer D) was obtained. The yield of the obtained polymer D was 70%.

  When a part of the polymer D was dissolved in PBTHF and the intrinsic viscosity was measured, it was 0.25 dl / g. When the tensile properties of the polymer D produced by press molding were measured, the tensile modulus was 1330 MPa, the yield stress was 35 MPa, and the elongation at break was 3.5%. Moreover, it was 5300 Pa.s when the zero shear viscosity in 230 degreeC was measured with the rotary melt viscoelasticity measuring apparatus. The glass transition temperature of the polymer C measured by TMA was 113 ° C., and it was a tough and transparent glassy polymer at room temperature. The refractive index was 1.334.

(Example 5)
In an autoclave made of pressure resistant glass having an internal volume of 200 ml, water 80 g, PBVE 7 g (25.2 mmol), CF ₂ ═CFOCF (CF ₃ ) CF ₂ CF═CF ₂ 6.7 g (20.5 mmol), perfluorobenzoyl peroxide 38 mg, CHCl ₃ 0.10 g was charged. After the autoclave was purged with nitrogen, the autoclave was heated until the internal temperature of the autoclave reached 70 ° C., and polymerization was carried out at 70 ° C. for 20 hours. The obtained polymer was washed with ion-exchanged water and methanol and then dried at 200 ° C. for 1 hour. As a result, 10 g of a polymer (hereinafter referred to as polymer E) was obtained. The yield of the obtained polymer was 73%.

  A part of the polymer was dissolved in PBTHF and the intrinsic viscosity was measured to find that it was 0.27 dl / g. The refractive index was 1.332, and the glass transition temperature measured by DSC was 115 ° C.

(Example 6)
The polymer A obtained in Example 1 was melted at 250 ° C. in a cylindrical container, and chlorotrifluoroethylene oligomer (average molecular weight 760) was injected and diffused as a refractive index distribution-forming substance (b) into the central part. The preform was formed with a refractive index distribution by adjusting the time so that the concentration at the center was 15% by mass. The preform was covered with a hollow tube made from the polymer B obtained in Example 2 and spun from the tip at 240 ° C. in a cylindrical electric heating furnace to obtain an optical fiber. When the transmission loss of this optical fiber was measured by the cutback method, it was 25 dB / km at a wavelength of 1300 nm. Further, the increase in transmission loss was measured when the wire was wound around a rod having a radius of 10 mm and bent at 180 degrees (hereinafter referred to as R10 bending loss), which was 0.03 dB. As a comparison, an optical fiber was similarly prepared using the polymer A instead of the polymer B, and the R10 bending loss was measured to be 2.39 dB. Therefore, it can be seen that the bending loss is reduced by two orders of magnitude by providing the outer layer whose refractive index is 0.014 lower than the outermost layer of the inner layer. Further, after performing a test (referred to as a wet heat cycle test) in which the above optical fiber was reciprocated 10 times between 65 ° C. and a humidity of 95% and −10 ° C., the transmission loss was measured and the performance was 26 dB / km. No deterioration was observed. Moreover, although the optical fiber was cut | disconnected and the cross section was observed with the scanning electron microscope, it has confirmed that the adhesiveness of an inner layer and an outer layer was favorable.

(Examples 7 to 10)
Example 6 and Example 6 using polymer A as the matrix resin for the inner layer, perfluoro (1,3,5-triphenylbenzene) as the refractive index distribution-forming substance (b), and the polymers of Examples 3 to 5 as the outer layer, respectively. Table 1 shows the result of producing a similar gradient index optical fiber and conducting an evaluation test thereof. In addition, Example 10 is an example using a polymer mixture, and the mixing mass ratio is shown in [] in the table and the kind of polymer mixed.

(Example 11) (Comparative example)
When an optical fiber was prepared in the same manner as in the example using perfluoro (2,2-dimethyl-1,3-dioxole) / tetrafluoroethylene copolymer as the outer layer, the transmission loss was 312 dB / km. This optical fiber was cut and the cross section was observed with a scanning electron microscope, but it was found that the inner layer and the outer layer were separated and the adhesion was poor.

1: inner layer 2: outer layer 3: outermost refractive index level of inner layer 4: refractive index level of outer layer

Claims (6)

A refractive index distribution type optical fiber having a concentric inner and outer at least two-layer structure, wherein the inner layer has a refractive index distribution structure made of an amorphous fluoropolymer (a) having substantially no CH bond. Have
A compound represented by formula (1), wherein the outer layer is a non-crystalline fluoropolymer having substantially no C—H bond, and has a refractive index lower than the outermost refractive index of the inner layer. A plastic comprising only a fluoropolymer (d) obtained by polymerizing a monomer containing it, or a fluoropolymer material (c) which is a mixture of the fluoropolymer (d) and another material Optical fiber.
_{^{CF 2 = CF-O-CR}} 1 R 2 -CR 3 R 4 -CF = CF 2 ··· (1)
(R ¹ , R ² , R ³ and R ⁴ are each independently F, CF ₃ or OCF ₃ , and at least one is CF ₃ or OCF _3. ) The plastic optical fiber according to claim 1, wherein the glass transition temperature Tgc of the fluoropolymer material (c) constituting the outer layer is in the following range (where Tga is the glass transition temperature of the fluoropolymer (a)).
70 ° C <Tgc <Tga + 30 ° C   The plastic optical fiber according to claim 1 or 2, wherein the refractive index of the fluoropolymer material (c) is lower by 0.003 or more than the outermost refractive index of the inner layer.   The inner layer is an inner layer formed by using a fluoropolymer (a) as a matrix and distributing a substance (b) having a different refractive index in the matrix to form a refractive index distribution structure. The plastic optical fiber described in 1.   The plastic optical fiber according to any one of claims 1 to 4, wherein the fluoropolymer (a) is a fluoropolymer having a fluorinated aliphatic ring structure in the main chain.   The plastic optical fiber according to any one of claims 1 to 5, further comprising a protective coating layer made of a thermoplastic resin outside the outer layer.

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