JP2006106779A - Optical plastic material, graded-refractive-index optical fiber and method for manufacturing graded-refractive-index optical plastic material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel graded-refractive-index optical plastic material which has heat resistance, humidity resistance, chemical resistance and nonflammability and is capable of transmitting light from ultraviolet light up to near infrared light with extremely low loss. <P>SOLUTION: The graded-refractive-index optical plastic material is composed of an amorphous fluoropolymer and at least one kind of material which differs from the amorphous fluoropolymer in refractive index by at least 0.001, wherein at least one kind of the material is distributed in the fluoropolymer so as to have a concentration gradient along a specific direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a refractive index distribution type optical resin material (hereinafter sometimes abbreviated as an optical resin material) having high transparency and heat resistance, which has been difficult to realize with conventional optical resins, and a method for producing the same. Is.

The optical resin material of the present invention itself may be an optical transmission body such as an optical fiber, or may be a base material of an optical transmission body such as an optical fiber preform.

  The optical transmission material, which is the optical resin material of the present invention, is an amorphous resin, so there is no light scattering, and the transparency is very high in a wide wavelength band from ultraviolet light to near infrared light. It can be used effectively in the optical system. In particular, the present invention provides an optical transmission body having a low loss at wavelengths of 1300 nm and 1550 nm, which are wavelengths used for a trunk silica fiber in the optical communication field.

  In addition, the optical transmission material that is the optical resin material of the present invention has heat resistance, chemical resistance, moisture resistance, and nonflammability that can withstand severe use conditions in an engine room of an automobile.

The optical transmission material, which is the optical resin material of the present invention, is a refractive index distribution type optical fiber, rod lens, optical waveguide, optical splitter, optical multiplexer, optical demultiplexer, optical attenuator, optical switch, optical isolator, optical The present invention is useful as a wide variety of refractive index distribution type optical transmitters such as a transmitter module, an optical receiver module, a coupler, a deflector, and an optical integrated circuit. Here, the refractive index distribution means a region in which the refractive index continuously changes along a specific direction of the optical transmission body. For example, the refractive index distribution of the refractive index distribution type optical fiber is a radial direction from the center of the fiber. The refractive index is decreasing along a curve close to a parabola.

  When the optical resin material of the present invention is a base material of an optical transmission body, it can be spun by hot drawing or the like to produce an optical transmission body such as a gradient index optical fiber.

  Conventionally known resins for refractive index distribution type plastic optical transmission bodies include optical resins typified by methyl methacrylate resins, and tetrafluoroethylene resins and vinylidene fluoride resins described in Patent Document 1. Has been.

Many proposals have been made for a step-refractive plastic optical fiber in which an optical resin such as methyl methacrylate resin, styrene resin, carbonate resin, norbornene resin is used as a core and a clad is made of a fluorine-containing polymer. Patent Document 2 also proposes using a fluorine-containing resin for the core and the clad.
International Publication No. 94/4949 Pamphlet JP-A-2-244007

  The present invention, which could not be achieved by an optical transmission body such as methyl methacrylate resin, carbonate resin, norbornene resin, required heat resistance, moisture resistance, and chemical resistance required for automobiles, office automation (OA) equipment, home appliances, etc. An optical resin material having incombustibility is provided.

  In addition, 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) that could not be achieved by an optical transmission body such as methacrylate resin, carbonate resin, norbornene resin, etc. An object of the present invention is to newly provide an optical resin material having a low optical transmission loss in the transmission region band and a manufacturing method thereof.

  As a result of intensive studies based on recognition of the above problems, the present inventor has imparted heat resistance, moisture resistance, chemical resistance, nonflammability, and C—H bond (wherein light absorption occurs in near infrared light) That is, in order to eliminate the carbon-hydrogen bond), it was found that a fluoropolymer substantially free of C—H bonds is optimal. This fluoropolymer has a C—F bond (that is, a carbon-fluorine bond) instead of a C—H bond.

  That is, when a substance is irradiated with light, light having a wavelength that causes stretching vibration of a bond between certain atoms or resonance vibration and bending vibration is preferentially absorbed. Until now, the polymer substances used in plastic optical fibers have been mainly compounds having C—H bonds. In the high molecular weight substance based on this C—H bond, hydrogen atoms are light and easily vibrate, so that the fundamental absorption appears on the short wavelength side (3400 nm) in the infrared region. Therefore, in the near-infrared to infrared region (600 to 1550 nm), which is the wavelength of the light source, relatively low harmonic overtone absorption of this C—H stretching vibration appears rapidly, which causes a large absorption loss.

  Therefore, when hydrogen atoms are replaced with fluorine atoms, the wavelength of those overtone absorption peaks shifts to the longer wavelength side, and the amount of absorption 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 or more.

  On the other hand, a substance in which a hydrogen atom is replaced with a fluorine atom has substantially no loss due to absorption at a wavelength of 650 nm, and even at a wavelength of 1300 nm, the order is 1 dB / km between the sixth harmonic and the seventh harmonic of the C—F bond stretching vibration. It can be considered that there is no absorption loss. To that end, we propose to use compounds with C—F bonds.

  In addition, it is desirable to exclude functional groups such as a carboxyl group and a carbonyl group, which are factors that inhibit heat resistance, moisture resistance, chemical resistance, and nonflammability. In addition, if there is a carboxyl group, it absorbs near-infrared light, and if there is a carbonyl group, it absorbs ultraviolet light, it is desirable to exclude these groups. Further, in order to reduce transmission loss due to light scattering, it is important to use an amorphous polymer.

  Furthermore, in the case of a graded index optical fiber, multimode light propagates while being reflected at the interface between the core and the clad. As a result, mode dispersion occurs and the transmission band decreases. However, in the graded index optical fiber, mode dispersion hardly occurs and the transmission band increases.

  Therefore, an amorphous fluoropolymer having substantially no C—H bond as an optical resin material, particularly a fluoropolymer having a ring structure in the main chain, and a substance having a refractive index different from that of the polymer. An optical resin material having a gradient in the specific direction and a method for producing the same have been found out, and the present inventions (1) to (2) described below have been achieved.

(1) At least 1 having a difference in refractive index of 0.001 or more in comparison between the amorphous fluoropolymer (a) having substantially no C—H bond and the fluoropolymer (a). A refractive index distribution type optical resin material comprising a kind of substance (b), wherein the substance (b) is distributed in the fluoropolymer (a) with a concentration gradient along a specific direction.

(2) The amorphous fluoropolymer (a) having substantially no C—H bond is melted, and the fluoropolymer (a) is added to the center of the melt of the fluoropolymer (a). In comparison with the above, at least one kind of substance (b) having a refractive index difference of 0.001 or more, or a fluoropolymer (a) containing the substance (b) is injected, and the substance (b) is diffused. Or a method of producing a refractive index distribution type optical resin material, wherein a region where the refractive index continuously changes is formed by molding after being diffused.

  In the present invention, by using an amorphous fluororesin in a wide variety of plastic optical transmission bodies such as a graded index optical fiber, a graded index optical waveguide, and a graded index rod lens, the ultraviolet light to the near infrared are used. It has become possible to transmit light up to light with extremely low loss.

  In particular, the gradient index optical fiber is flexible and easy to branch and connect despite its large fiber diameter, making it ideal for short-distance optical communications. However, no practical low-loss optical fiber has been proposed so far. . The present invention provides a low-loss optical fiber that can be used for short-distance optical communication.

  Moreover, the optical transmission body of the present invention is a plastic optical transmission body with heat resistance, chemical resistance, moisture resistance, and nonflammability that can withstand severe use conditions in automobile engine rooms, OA equipment, plants, home appliances, etc. It is to provide. Furthermore, the gradient index optical resin material of the present invention can be used not only as an optical fiber but also as a flat plate or rod type lens. In that case, it can function as a convex lens and a concave lens depending on whether the refractive index change from the central part to the peripheral part is lowered or raised.

  Conventionally known as fluoropolymers are tetrafluoroethylene resin, perfluoro (ethylene-propylene) resin, perfluoroalkoxy resin, vinylidene fluoride resin, ethylene-tetrafluoroethylene resin, chlorotrifluoroethylene resin, and the like. Yes. However, since these fluorine-containing resins have crystallinity, light scattering occurs, transparency is not good, and it is not preferable as a material for a plastic optical transmission body.

  On the other hand, an amorphous fluoropolymer is excellent in transparency because it does not scatter light by crystals. The fluoropolymer (a) in the present invention is not limited as long as it is an amorphous fluoropolymer having no C—H bond, but a fluoropolymer having a ring structure in the main chain is preferred. The fluorine-containing polymer having a ring structure in the main chain is preferably a fluorine-containing polymer having a fluorine-containing aliphatic ring structure, a fluorine-containing imide ring structure, a fluorine-containing triazine ring structure or a fluorine-containing aromatic ring structure. Of the fluorine-containing polymers having a fluorine-containing aliphatic ring structure, those having a fluorine-containing aliphatic ether ring structure are more preferable.

  The fluorine-containing polymer having a fluorine-containing aliphatic ring structure is a fiber obtained by hot drawing or melt spinning, 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. This is a more preferable polymer because the polymer molecules are difficult to be oriented during the formation, and as a result, light scattering does not occur.

The viscosity of the fluoropolymer (a) in the molten state is preferably 10 ³ to 10 ⁵ poise at a melting temperature of 200 ° C. to 300 ° C. If the melt viscosity is too high, melt spinning is not only difficult, but also the diffusion of the substance (b) necessary for forming the refractive index distribution hardly occurs and the refractive index distribution is difficult to form. Moreover, when melt viscosity is too low, a problem will arise practically. 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 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 inhibited, and if it is too large, formation of an optical transmission body having a refractive index distribution becomes difficult, which is not preferable.

  The polymer having a fluorine-containing aliphatic ring structure is obtained by polymerizing a monomer having a fluorine-containing ring structure, or obtained by cyclopolymerizing a fluorine-containing monomer having at least two polymerizable double bonds. A polymer having a fluorinated aliphatic ring structure in the main chain is preferred.

  A polymer having a fluorine-containing aliphatic ring structure in the main chain obtained by polymerizing a monomer having a fluorine-containing aliphatic ring structure is known from JP-B 63-18964. That is, by homopolymerizing a monomer having a fluorine-containing aliphatic ring structure such as perfluoro (2,2-dimethyl-1,3-dioxole), this monomer is converted into tetrafluoroethylene, chlorotrifluoroethylene, perfluoro. By copolymerizing with a radical polymerizable monomer such as (methyl vinyl ether), a polymer having a fluorine-containing aliphatic ring structure in the main chain is obtained.

  Further, polymers having a fluorinated aliphatic ring structure in the main chain obtained by cyclopolymerizing a fluorinated monomer having at least two polymerizable double bonds are disclosed in JP-A-63-238111 and No. 63-238115 is known. That is, by cyclopolymerizing monomers such as perfluoro (allyl vinyl ether) and perfluoro (butenyl vinyl ether), or such monomers as tetrafluoroethylene, chlorotrifluoroethylene, perfluoro (methyl vinyl ether), etc. A polymer having a fluorine-containing aliphatic ring structure in the main chain is obtained by copolymerizing with the radical polymerizable monomer.

  In addition, a monomer having a fluorinated aliphatic ring structure such as perfluoro (2,2-dimethyl-1,3-dioxole) and at least two polymerizable properties such as perfluoro (allyl vinyl ether) and perfluoro (butenyl vinyl ether). A polymer having a fluorine-containing aliphatic ring structure in the main chain can also be obtained by copolymerizing with a fluorine-containing monomer having a double bond.

  Specific examples of the polymer having a fluorinated alicyclic structure include those having a repeating unit selected from the following formulas (I) to (IV). In addition, in order to raise a refractive index, the fluorine atom in the polymer which has these fluorine-containing aliphatic ring structures may be partially substituted by the chlorine atom.

[In the above formulas (I) to (IV), l is 0 to 5, m is 0 to 4, n is 0 to 1, l + m + n is 1 to 6, o, p and q are 0 to 5, and o + p + q is 1 respectively. 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. ]
The polymer having a fluorine-containing aliphatic ring structure is preferably a polymer having a ring structure in the main chain, but a polymer containing a polymer unit having a ring structure is 20 mol% or more, preferably 40 mol% or more is transparent. From the viewpoints of properties and mechanical properties.

  The substance (b) is at least one substance having a refractive index difference of 0.001 or more in comparison with the fluoropolymer (a), and has a higher refractive index than the fluoropolymer (a). Or a low refractive index. In an optical fiber or the like, a substance having a higher refractive index than that of the fluoropolymer (a) is usually used.

  The substance (b) is preferably a low molecular compound, oligomer or polymer containing an aromatic ring such as a benzene ring, a halogen atom such as chlorine, bromine or iodine, or a linking group such as an ether bond. Moreover, it is preferable that a substance (b) is a substance which does not have a C-H bond substantially for the same reason as the fluoropolymer (a). The difference in refractive index from the fluoropolymer (a) is preferably 0.005 or more.

  The substance (b) which is an oligomer or a polymer is composed of a polymer of a monomer that forms the fluoropolymer (a) as described above, and the difference in refractive index is 0 in comparison with the fluoropolymer (a). It may be an oligomer or polymer that is .001 or more. The monomer is selected from those that form a polymer having a refractive index difference of 0.001 or more in comparison with the fluoropolymer (a). For example, two types of fluorine-containing polymers (a) having different refractive indexes can be used, and one polymer (a) can be distributed as a substance (b) in another polymer (a).

These substances (b) preferably have a difference in solubility parameter within 7 (cal / cm ³ ) ^1/2 in comparison with the matrix. Here, the solubility parameter is a characteristic value that is a measure of the mixing property between substances. The solubility parameter is δ, the molecular cohesive energy of the substance is E, and the molecular volume is V. The formula δ = (E / V) ¹ Represented by ^{/ 2} .

  Examples of the low molecular weight compound include halogenated aromatic hydrocarbons that do not contain a hydrogen atom bonded to a carbon atom. In particular, 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 in terms of compatibility with the fluorine-containing polymer (a). Moreover, 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 the formula Φ _r -Z _b [Φ _r is a b-valent fluorinated aromatic ring residue in which all of the hydrogen atoms are replaced by fluorine atoms, and Z is a halogen other than fluorine. An atom, -Rf, -CO-Rf, -O-Rf, or -CN; 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 Aromatic rings include benzene and naphthalene rings. The perfluoroalkyl group or polyfluoroperhaloalkyl group as 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 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 the substance (b) which is a polymer or oligomer, among the compounds having the repeating units (I) to (IV), a fluorine-containing polymer having a refractive index different from that of the combined fluorine-containing polymer (a) (for example, , A combination of a fluorine-containing polymer containing only fluorine atoms as halogen atoms and a fluorine-containing polymer containing fluorine atoms and chlorine atoms, and two types of polymers obtained by polymerizing two or more monomers of different types or in different proportions. Combinations of fluoropolymers) are preferred.

In addition to the fluorine-containing polymer having a ring structure in the main chain as described above, it comprises a monomer not containing a hydrogen atom such as tetrafluoroethylene, chlorotrifluoroethylene, dichlorodifluoroethylene, hexafluoropropylene, and perfluoroalkyl vinyl ether. Oligomers and copolymerized oligomers of two or more of these monomers can also be used as the substance (b). In addition, perfluoropolyether having a structural unit of —CF ₂ CF (CF ₃ ) O— or — (CF ₂ ) _n O— (n is an integer of 1 to 3) can be used. The molecular weight of these oligomers is selected from the molecular weight range that is amorphous, and the number average molecular weight is preferably from 300 to 10,000. Considering the ease of diffusion, the number average molecular weight is more preferably 300 to 5,000.

  A particularly preferred substance (b) is a chlorotrifluoroethylene oligomer because of its good compatibility with the fluoropolymer (a), particularly a fluoropolymer having a ring structure in the main chain. Due to the good compatibility, the fluoropolymer (a), in particular, 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, after dissolving and mixing in a fluorine-containing solvent, both can be mixed uniformly by removing a solvent. The preferred molecular weight of the chlorotrifluoroethylene oligomer is a number average molecular weight of 500-1500.

  The optical resin material of the present invention is most preferably a gradient index optical fiber. In this 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 that of the fluoropolymer (a), and the substance (b) has a concentration gradient in which the concentration decreases along the peripheral direction from the center of the optical fiber. It is a distributed optical fiber. 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. The optical fiber is also useful. The former optical transmission body such as an optical fiber can be usually manufactured by arranging the substance (b) in the center and diffusing in the peripheral direction. The latter optical transmission body such as an optical fiber can be manufactured by diffusing the substance (b) from the periphery toward the center.

  The optical transmission material which is the optical resin material of the present invention has a wavelength of 700 to 1,600 nm and a 100 m transmission loss of 100 dB or less. In particular, in a fluoropolymer having an aliphatic ring structure in the main chain, the transmission loss at 100 m can be reduced to 50 dB or less at the same wavelength. 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 it is an inexpensive light source compared to the conventional plastic optical fiber that has to use a wavelength shorter than 700 to 1,600 nm. There is an advantage that it can be done. In the production of the optical resin material of the present invention, the molding of the resin and the formation of the refractive index profile may be performed simultaneously or separately. For example, the optical resin material of the present invention can be manufactured by forming a refractive index distribution at the same time as forming a refractive index distribution by spinning or extrusion molding. Further, the refractive index distribution can be formed after the resin is molded by spinning or extrusion molding. Furthermore, an optical resin material such as an optical fiber can be manufactured by manufacturing a preform (base material) having a refractive index distribution and molding (for example, spinning) the preform. As described above, the optical resin material of the present invention also means a preform having the above refractive index distribution.

  Examples of the method for producing the optical resin material of the present invention include the following methods (1) to (7). However, it is not limited to these. A particularly preferred method is the method (1).

(1) The fluoropolymer (a) is melted, and the substance (b) or the fluoropolymer (a) containing the substance (b) is injected into the center of the melt of the fluoropolymer (a). A method of forming the material (b) while diffusing or after diffusing.

  In this case, in order to inject the substance (b), not only the substance (b) is injected into the central part but also the substance (b) may be injected into the central part in multiple layers. Examples of the molding include extrusion melt molding suitable for molding a rod-shaped base material such as an optical fiber preform, and melt spinning molding suitable for molding an optical fiber.

(2) A method of repeatedly dip-coating a substance (b) or a fluoropolymer (a) containing the substance (b) on a core comprising the fluoropolymer (a) obtained by melt spinning or stretching. .

(3) A tube made of a hollow fluorine-containing polymer (a) is formed using a rotating glass tube and the like, and the substance (b) or fluorine-containing heavy containing the substance (b) inside the polymer tube A method in which the monomer phase forming the coalescence (a) is sealed and polymerized while rotating at low speed.

  In the case of this interfacial gel copolymerization, in the polymerization process, the tube made of the fluoropolymer (a) swells in the monomer phase to form a gel phase, and the monomer molecules are polymerized while selectively diffusing into the gel phase. The

(4) A fluorine-containing polymer (a) produced by using two types of monomers that form the fluorine-containing polymer (a) and the monomer that forms the substance (b) and have different reactivity. ) And the substance (b) is a method in which the polymerization reaction proceeds so that the composition ratio continuously changes from the periphery toward the center.

(5) A mixture obtained by uniformly mixing the fluorine-containing polymer (a) and the substance (b) in a solvent or a solvent, and then removing only the solvent by volatilization and removing the mixture by hot stretching or melt extrusion. A method of forming a refractive index distribution by forming a fiber and then (or immediately after forming the fiber) contacting an inert gas under heating to volatilize the substance (b) from the surface. Alternatively, after forming the fiber, the fiber is immersed in a solvent that dissolves only the substance (b) without dissolving the fluoropolymer (a), and the substance (b) is eluted from the fiber surface, thereby refraction index. A method of forming a distribution.

(6) The rod or fiber made of the fluoropolymer (a) is coated only with the substance (b) having a refractive index smaller than that of the fluoropolymer (a), or the fluoropolymer (a) and the substance A method of forming a refractive index distribution by coating the mixture with (b) and then diffusing the substance (b) by heating.

(7) A high-refractive index polymer and a low-refractive index polymer are mixed in a solution state containing heat-melting or a solvent, and both are extruded together (or after extrusion) with each other in a different mixing ratio. A method of diffusing and finally obtaining a fiber having a refractive index profile. In this case, the high refractive index polymer may be a fluorine-containing polymer (a) and the low refractive index polymer may be a substance (b), the high refractive index polymer may be a substance (b), and the low refractive index polymer may be a substance (b). )

  Next, examples of the present invention will be described more specifically, but it is needless to say that the description does not limit the present invention.

“Synthesis Example 1”
35 g of perfluoro (butenyl vinyl ether) [PBVE], 5 g of 1,1,2-trichlorotrifluoroethane (R113), 150 g of ion-exchanged water, and ((CH ₃ ) ₂ CHOCOO) ₂ as a polymerization initiator 90 mg was 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 carried out at 40 ° C. for 22 hours. As a result, 28 g 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 the 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 was 465 ° C., the solubility parameter was 5.3 (cal / cm ³ ) ^1/2 , and the refractive index was 1.34. FIG. 1 shows the light transmittance of the polymer A.

“Synthesis Example 2”
Perfluoro (2,2-dimethyl-1,3-dioxole) [PDD] and tetrafluoroethylene are radically polymerized at a weight ratio of 80:20, and a polymer having a number average molecular weight of about 5 × 10 ⁵ at a glass transition point of 160 ° C. (Hereinafter referred to as polymer B). The polymer B was colorless and transparent, the refractive index was 1.3, and the light transmittance was high.

PDD and chlorotrifluoroethylene (CTFE) were radically polymerized at a weight ratio of 75:25 to obtain a polymer having a number average molecular weight of about 3 × 10 ⁵ at a glass transition point of 150 ° C. (hereinafter referred to as polymer C). The polymer C was colorless and transparent, the refractive index was 1.4, and the light transmittance was high.

“Synthesis Example 3”
8 g of PBVE, 2 g of PDD, 10 g of PBTHF, and 20 mg of ((CH ₃ ) ₂ CHOCO) ₂ as a polymerization initiator were placed in a pressure-resistant glass ampoule having an internal volume of 50 ml. After the inside of the system was replaced with nitrogen three times, polymerization was carried out at 40 ° C. for 20 hours. As a result, 6.7 g of a transparent polymer (hereinafter referred to as polymer D) having a number average molecular weight of about 2 × 10 ⁵ was obtained.

The polymer D had a glass transition point of 157 ° C., a refractive index of 1.32, and an absorbance of 1930 cm ^{−1 in} the IR spectrum.

Further, 2 g of PBVE, 8 g of PDD, 10 g of PBTHF, and 20 mg of ((CH ₃ ) ₂ CHOCO) ₂ as a polymerization initiator were put in a pressure-resistant glass ampoule having an internal volume of 50 ml. The system was frozen and degassed three times, and then polymerized at 30 ° C. for 20 hours. As a result, 7 g of a transparent polymer (hereinafter referred to as polymer E) having a number average molecular weight of about 3 × 10 ⁵ was obtained.

The polymer E had a glass transition point of 210 ° C., a refractive index of 1.29, and the polymer unit content of PDD determined from the absorbance of absorption at 1930 cm ⁻¹ of the IR spectrum was 82% by weight.

"Example 1"
The polymer A obtained by the above synthesis was dissolved in a PBTHF solvent, and the refractive index was 1.52 and the difference in solubility parameter from the polymer A was 3.2 (cal / cm ³ ) ^1/2 . Some 1,3-dibromotetrafluorobenzene (DBTFB) was added at 12% by weight to obtain a mixed solution. This solution was desolvated to obtain a transparent mixed polymer (hereinafter referred to as polymer F).

  The polymer A was melted and melt-spun at 300 ° C. while injecting the polymer F as a melt into the center of the polymer A, whereby an optical fiber having a refractive index that gradually decreased from the center to the periphery was obtained.

  The optical transmission characteristics of the obtained optical fiber were 300 dB / km at 780 nm and 130 dB / km at 1550 nm, and it was confirmed that the optical fiber was able to transmit light from visible light to near infrared light well.

"Example 2"
40 g of PBVE and 500 ml of ((CH ₃ ) ₂ CHOCOO) ₂ as a polymerization initiator were added to a glass tube, freeze degassed, and then polymerized while rotating at high speed. The synthesized hollow tube was taken out from the glass tube to obtain a tube made of a polymer having a number average molecular weight of about 1 × 10 ⁵ . 20 g of PBVE, 2 g of DBTFB as a high refractive index substance, and 200 ml of ((CH ₃ ) ₂ CHOCOO) ₂ as a polymerization initiator were added to the hollow portion of the tube, and the tube was sealed and polymerized while rotating at low speed.

  In the polymerization process, since the polymer of the tube swells into the monomer phase and a gel phase is formed, the polymerization reaction is promoted by the gel effect in the gel phase, and the polymer phase is formed from the periphery. At this time, the monomer molecules are selectively diffused into the gel phase because the molecular size is smaller than that of the high-refractive-index material molecules, and the high-refractive-index materials are collected and polymerized in the central portion, so that from the central portion. A refractive index distribution in which the refractive index gradually decreases toward the peripheral portion is formed. The preform thus obtained was hot-stretched to obtain an optical fiber having a refractive index distribution.

  The optical transmission characteristics of the obtained optical fiber were 500 dB / km at 650 nm and 150 dB / km at 1550 nm, and it was confirmed that the optical fiber can transmit light from visible light to near infrared light well.

"Example 3"
A core material of 30 microns was prepared from the polymer D obtained by the synthesis. Further, a solution containing polymer D at a concentration of 1% by weight in a PBTHF solvent (hereinafter referred to as solution D) was prepared. Similarly, a solution (hereinafter referred to as solution E) containing 1% by weight of polymer E in a PBTHF solvent was prepared. The solution D was pulled up on the core material of the polymer D at a speed of 6 cm and dried at 180 ° C. It was confirmed that the diameter of the polymer D increased by 100 nm.
The solution E was added to this solution D by 1/250 by weight, and dip coating and drying were repeated 500 times in the same manner. Finally, dip coating and drying were repeated 5 times for the solution E having a concentration of 10% by weight and dried at 180 ° C. for 2 hours. An optical fiber having a diameter of about 600 microns and a refractive index that gradually decreases from the center toward the periphery was obtained.

  The optical transmission characteristic of the obtained optical fiber is 1050 dB / km at 650 nm, 460 dB / km at 950 nm, 130 dB / km at 1300 nm, and is an optical fiber that can transmit light from visible light to near infrared light well. I confirmed.

Example 4
Equal amounts of the polymer B and the polymer C synthesized above were dissolved in a PBTHF solvent and mixed. This was desolvated to obtain a transparent polymer mixture (B + C). The polymer B is melted, and the polymer mixture (B + C) melted inside is melt-spun while injecting the polymer C melted further into the center, whereby the refractive index gradually increases from the center to the periphery. A decreasing optical fiber was obtained.

  The optical transmission characteristics of the obtained optical fiber were 550 dB / km at 650 nm and 130 dB / km at 1550 nm, and it was confirmed that the optical fiber can transmit light from visible light to near infrared light well.

"Example 5"
An optical fiber was obtained in the same manner as in Example 1 except that 30% by weight of CTFE oligomer having a number average molecular weight of 800 was used instead of 12% by weight of DBTFB. The refractive index of this oligomer was 1.41, and the difference in solubility parameter from the polymer A was 1.4 (cal / cm ³ ) ^1/2 . The obtained optical fiber had a refractive index that gradually decreased from the center to the periphery.

  The optical transmission characteristics of this optical fiber were 280 dB / km at 780 nm and 120 dB / km at 1550 nm, and it was confirmed that the optical fiber can transmit light from visible light to near infrared well.

"Example 6"
Reactivity ratio r ¹ (ratio of PDD homopolymer production rate constant to PDD / PBVE copolymer production rate constant) of 1.9 PDD and reactivity ratio r ² (PDD / PBVE copolymer production) The ratio of the PBVE homopolymer production rate constant to the rate constant) was 0.19 PBVE 50 parts, and 1 part dialkoxyacetophenone dissolved in 5 parts HCFC225 as a photoinitiator was placed in a glass ampoule 3 times in the system. After freezing and degassing, photopolymerization was performed using a low-pressure mercury lamp. As a result, a preform having a continuous refractive index distribution with a central refractive index of 1.31 and a central portion of 1.33 was obtained. This was hot stretched to obtain an optical fiber having a refractive index distribution.

  The optical transmission characteristics of the obtained optical fiber were 320 dB / km at 650 nm and 250 dB / km at 1550 nm, and it was confirmed that the optical fiber can transmit light from visible light to ultraviolet light satisfactorily.

"Example 7"
85 parts of polymer A and 15 parts of DBTFB were melted and mixed to form a rod. The rod was heated and stretched at 200 ° C. to prepare a fiber. At this time, a 1 m long electric furnace heated to 120 ° C. is passed through the fiber coming out of the heating and stretching section. In this electric furnace, dry air heated to 120 ° C. in advance was allowed to flow, whereby DBTFB was volatilized from the surface of the fiber, and an optical fiber having a refractive index distribution was obtained.

  The optical transmission characteristics of the obtained optical fiber are 420 dB / km at 650 nm, 250 dB / km at 780 nm, 110 dB / km at 1300 nm, and it was confirmed that the optical fiber can transmit light from visible light to near infrared well. .

"Example 8"
A polymer having a number average molecular weight of about 2 × 10 ⁵ (hereinafter referred to as polymer F) was obtained by polymerizing 90 parts of PBVE and 10 parts of CTFE. A CTFE oligomer having a number average molecular weight of 800 was melted and uniformly mixed with the polymer F to obtain a rod having an oligomer content of 20% by weight.

  This was hot-drawn to prepare a fiber having a diameter of 500 μm. The fiber was passed through ethanol to elute the CTFE oligomer, and then dried by passing through a cylindrical heating furnace heated to 200 ° C. with a residence time of about 10 seconds. As a result, an optical fiber having a refractive index distribution with a refractive index of 1.38 at the center of the refractive index of 1.36 was obtained.

  The optical transmission characteristics of the obtained optical fiber were 250 dB / km at 650 nm and 150 dB / km at 1550 nm, and it was confirmed that the optical fiber can transmit light from visible light to ultraviolet light satisfactorily.

"Example 9"
The polymer C was spun by extrusion at 270 ° C., and the obtained fiber was immediately passed through a hexafluoropropylene oxide (HFPO) oligomer (number average molecular weight 2100) heated to 220 ° C. so that the residence time was 3 minutes. I let you. As a result, an optical fiber having an outer diameter of 600 μm was obtained in which the HFPO oligomer diffused and penetrated into the fiber and the refractive index continuously changed from the outer periphery toward the center. At this time, the refractive index of the outer peripheral portion was 1.34, and the refractive index of the central portion was 1.35.

  The optical transmission characteristics of the obtained optical fiber were 300 dB / km at 650 nm and 130 dB / km at 1550 nm, and it was confirmed that the optical fiber can transmit light from visible light to ultraviolet light satisfactorily.

"Example 10"
By polymerizing PDD and PBVE, a polymer having a PDD content of 20% by weight and a number average molecular weight of about 1 × 10 ⁵ (hereinafter referred to as polymer G) and 60% by weight of a number average molecular weight of about 5 × 10 ⁵ (Hereinafter referred to as polymer H) was synthesized. The refractive index was 1.33 for polymer G and 1.31 for polymer H, respectively.

  Polymers G and H were each dissolved in perfluorotributylamine / perfluorooctane = 20/80 (weight ratio) so that the polymer concentration was 20% by weight, and then both were mixed in the ratio shown in Table 1. 11 After preparing various types of solutions, a part of the solvent was volatilized by heating to obtain a gel-like solution of about 30000 cP. The 11 types of gels with different mixing ratios were heated to 80 ° C., and multilayer fibers were extruded concentrically using a multilayer nozzle. This fiber was passed through a heating furnace (about 150 to 200 ° C.) in which air was passed to remove residual solvent. As a result, a fiber having a refractive index distribution was obtained.

  The optical transmission characteristics of the obtained optical fiber are 350 dB / km at 650 nm, 150 dB / km at 950 nm, 120 dB / km at 1300 nm, and it is confirmed that the optical fiber can transmit light from visible light to near infrared well. It was.

"Comparative example"
In the refractive index distribution type plastic optical fiber, the optical transmission loss of PMMA is about 400 dB / km at a wavelength of 650 nm, and the transmission loss is very large at wavelengths of 780 nm, 1300 nm, and 1550 nm, making it impractical as an optical transmission body.

  Further, in a step-index plastic optical fiber, a fluororesin optical fiber having a core and a clad can transmit light from visible light to near infrared light, but its optical transmission loss is reported to be about 300 dB / km.

  In contrast, the gradient index transparent fluororesin optical fiber according to the present invention can transmit light from visible light to near infrared light with extremely low loss.

The figure which shows the light transmittance of the polymer A. FIG.

Claims (11)

At least one substance having a difference in refractive index of 0.001 or more in comparison between the amorphous fluoropolymer (a) having substantially no CH bond and the fluoropolymer (a) A refractive index distribution type optical resin material comprising (b), wherein the substance (b) is distributed in the fluorine-containing polymer (a) with a concentration gradient along a specific direction. The optical resin material according to claim 1, wherein the fluoropolymer (a) is a fluoropolymer having a ring structure in the main chain. The optical resin material according to claim 2, wherein the fluorine-containing polymer having a ring structure in the main chain is a fluorine-containing polymer having a fluorine-containing aliphatic ring structure in the main chain. The optical resin material according to claim 1, 2 or 3, wherein the substance (b) is substantially a substance having no CH bond. The optical resin material according to claim 1, wherein the optical resin material is a gradient index optical fiber. At least one substance having a difference in refractive index of 0.001 or more in comparison between the amorphous fluoropolymer (a) having substantially no CH bond and the fluoropolymer (a) (B) A refractive index distribution type optical fiber in which the substance (b) is distributed in the fluoropolymer (a) with a concentration gradient from the center to the peripheral direction. The refractive index according to claim 6, wherein the substance (b) has a refractive index higher than that of the fluoropolymer (a) and has a concentration gradient in which the concentration decreases from the center along the peripheral direction. Distributed optical fiber. The gradient index optical fiber according to claim 6 or 7, wherein the fluoropolymer (a) is a fluoropolymer having a ring structure in the main chain. 9. The gradient index optical fiber according to claim 6, 7 or 8, wherein the substance (b) is substantially free of C—H bonds. In comparison with the fluorine-containing polymer (a), the amorphous fluorine-containing polymer (a) having substantially no C—H bond is melted, and the melt of the fluorine-containing polymer (a) is melted. Injecting at least one substance (b) having a refractive index difference of 0.001 or more, or a fluoropolymer (a) containing the substance (b) and diffusing the substance (b) A method for producing a refractive index distribution type optical resin material, comprising forming a region where the refractive index continuously changes by molding after forming. The manufacturing method according to claim 10, wherein the molding is extrusion melt molding or melt spinning.

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