JP2002071972A - Plastic optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a graded refractive index optical fiber made of a noncrystalline fluorine-containing polymer having no C-H bond in which increase in loss during bending is suppressed and the heat resistance and resistance against moisture and heat are improved. SOLUTION: The plastic optical fiber consists of an inner layer having a graded refractive index structure made of a noncrystalline fluorine-containing polymer (a) having no C-H bond and an outer layer made of a fluorine- containing polymer material (c) having a refractive index lower than that of the fluorine-containing polymer (a) and having affinity with the polymer (a).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a graded-index plastic optical fiber having low bending loss and excellent heat resistance and wet heat resistance.

[0002]

2. Description of the Related Art As a refractive index distribution type plastic optical fiber, a non-crystalline fluoropolymer having substantially no C--H bond is used as a matrix, and a substance having a different refractive index from the matrix is formed with a concentration gradient in a radial direction. A plastic optical fiber in which a refractive index distribution structure is formed by distribution is known (see JP-A-8-5848). Further, in order to improve the increase in transmission loss due to bending in such a refractive index distribution type optical fiber, an optical fiber provided with a polymer having a lower refractive index than the matrix is disclosed in Japanese Patent Application Laid-Open No. Hei 8-30.
No. 4636.

[0003]

The conventional refractive index distribution type optical fiber provided with a low refractive index polymer on the outer periphery has a long-term heat resistance (70 ° C., 1000 hours) and a thermal cycle test (70 ° C.).
/ −20 ° C. × 10 times), and a heat / moisture / heat test such as a wet heat cycle test (65 ° C., humidity 95% / − 10 ° C. × 10 times) has 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 inventor found that the separation between the outer layer made of the low refractive index polymer and the inner layer having the refractive index distribution increased, resulting in increased transmission loss. Was found to be the cause.

[0004]

The present inventors have made intensive studies based on the recognition of the above-mentioned problems, and as a result, in order to improve the adhesiveness between the inner layer and the outer layer, as a low refractive index material for the outer layer,
It has been found that it is effective to use a polymer having a high affinity for the polymer constituting the matrix of the inner layer. That is, the present invention provides a gradient index optical fiber,
By forming the outer layer using a polymer having a lower refractive index than the outermost refractive index of the inner layer and a good adhesive property on the outer side of the inner layer having the formed refractive index distribution, heat resistance, wet heat resistance is improved. An object of the present invention is to provide a new optical fiber in which an increase in transmission loss due to bending is reduced while holding the optical fiber. The present invention is the following invention based on such knowledge.

In a gradient index optical fiber having at least two concentric inner and outer layer structures, the inner layer is substantially C
An inner layer having a refractive index distribution structure made of a non-crystalline fluorine-containing polymer (a) having no -H bond, wherein the outer layer has a lower refractive index than the outermost refractive index of the inner layer, and A) a fluoropolymer material (c) selected from 2)
An optical fiber, which is an outer layer made of: 1) A fluorinated polymer (d) containing the same polymer units as the polymer units in the fluorinated polymer (a). 2) Fluoropolymer (a) and other fluorinated polymer (e)
(F).

In the optical fiber of the present invention, in order for the fluoropolymer material (c) to have high adhesiveness to the fluoropolymer (a) and not to lower the heat resistance and the wet heat resistance of the optical fiber, it is necessary to include The glass transition temperature Tgc of the fluoropolymer material (c) is 70 ° C <Tgc <Tga + 30 ° C (however,
Tga is preferably the glass transition temperature of the fluoropolymer (a). Further, the fluoropolymer (d) preferably contains at least 30 mol% of the same polymer units as the polymer units in the fluoropolymer (a). The term “polymerized unit” in the present invention refers to a repeating unit in a polymer formed by a polymerization reaction of a monomer.

Further, in order not to increase the transmission loss of the optical fiber, it is preferable that the refractive index of the fluoropolymer material (c) is lower than the outermost refractive index of the inner layer by 0.003 or more. In the present invention, the refractive index is sodium D
Refers to the refractive index for a line.

In the optical fiber of the present invention, the inner layer is 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. It is preferably an inner layer.
As the fluorinated polymer (a), a fluorinated polymer having a ring structure in the main chain as described in the above-mentioned known examples is preferable. Similarly, the fluorine-containing polymer (d) and the fluorine-containing polymer (e) are also preferably a fluorine-containing polymer having a ring structure in the main chain. Further, the optical fiber of the present invention is preferably provided with a protective coating layer made of a synthetic resin outside the outer layer. The synthetic resin is a thermoplastic resin made of a polymer other than the fluoropolymer (a), the fluoropolymer (d), and the fluoropolymer (e). Preference is given to thermoplastic resins which are used or proposed to be used.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The refractive index distribution in the radial direction of the optical fiber of the present invention is shown in FIGS.
And (D). The horizontal axis shows the diameter of the optical fiber,
The vertical axis indicates the refractive index. Inner layer of optical fiber (range (1))
Within, the center has a high refractive index distribution and the refractive index decreases as the distance from the center increases. The refractive index of the outer layer (range (2)) is lower than the refractive index of the outermost layer of the inner layer. The refractive index distribution of the inner layer shows either a gentle distribution at the outer periphery as shown in FIGS. 1A and 1B or a parabolic distribution as shown in FIGS. 2C and 2D. Good. From the viewpoint of a large transmission band, the latter having a parabolic refractive index distribution is desirable. On the other hand, FIG.
1 (A) and FIG. 2 (D), the refractive index has a distribution in which the refractive index continuously decreases to the outermost portion of the inner layer.
Alternatively, as shown in FIG. 2C, the inner layer may be continuously lowered from the center to the middle of the inner layer and the inner layer outside the center may have a constant refractive index. The outer layer in FIGS. 1B and 2D substantially functions as a cladding layer. FIG.
In FIG. 2A and FIG. 2C, a portion having a constant refractive index in the inner layer functions as a cladding layer, and the outer layer functions as a second cladding layer.

The refractive index of the outer layer is preferably lower than the refractive index of the outermost layer by 0.003 or more in order to reduce bending loss. A more preferable refractive index difference is 0.005 or more. Further, it is desirable that the numerical aperture NA calculated from the highest refractive index of the central portion and the lowest refractive index of the outer layer is 0.20 or more, preferably 0.23 or more, more preferably 0.25 or more. In general, the bending loss changes depending on the core diameter of the optical fiber, and the bending loss increases as the core diameter increases. Although the core diameter of the optical fiber in the present invention is not particularly limited, it is 1000 μm or less, preferably 500 μm or less.
μm or less, more preferably 200 μm or less. Note that the core portion of the optical fiber in the present invention refers to a portion having a refractive index that is higher than the lowest refractive index of the inner layer by at least 5% of the difference between the highest refractive index of the inner layer and the lowest refractive index of the inner layer.

[0011] In the optical fiber of the present invention, a protective coating layer may be provided further outside the outer layer. The material of the protective coating layer is not particularly limited as long as it is a synthetic resin, and is a thermoplastic resin which is a material other than the fluoropolymer (a), the fluoropolymer (d), and the fluoropolymer (e). Or a cured product of a curable resin. Among them, a synthetic resin which has been conventionally used or proposed to be used 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 of a certain thickness or more is necessary,
Further, it is preferable to use a synthetic resin having high tensile strength and elastic modulus. As a material of 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. Also,
This protective coating layer may be a multilayer of two or more layers,
The layer may be a relatively soft thermoplastic resin such as a vinyl chloride resin, a polyolefin resin, a polyvinylidene fluoride resin, an ethylene-tetrafluoroethylene copolymer resin.

In the present invention, as a method of forming the refractive index distribution of the inner layer, the fluoropolymer (a) is used as a matrix,
It is preferable to form a refractive index distribution structure by distributing substances (b) having different refractive indexes in the matrix. Also,
Composed of two or more fluorine-containing monomers capable of forming a polymer whose refractive index changes according to the polymerization composition ratio, and is composed of a fluorine-containing polymer (a) having a polymerization composition ratio changed radially from the center. A method of forming an inner layer may be used. The fluoropolymer (a) is a non-crystalline fluoropolymer in order to reduce transmission loss and has a CH bond so that optical communication in the near infrared wavelength band is possible. It is necessary that the substance (b) also has a chemical structure that is soluble in the fluoropolymer and has no C—H bond.

The fluoropolymer material (c) constituting the outer layer
Must be a material having a lower refractive index than the outermost refractive index of the inner layer. The fluorinated polymer (d) contains the same polymerized unit as the polymerized unit in the fluorinated polymer (a). The mixture (f) is a mixture of the fluorinated polymer (a) and another fluorinated polymer (e). The fluoropolymer (d)
And the fluoropolymer (e) may be the same polymer.

The more the fluorinated polymer (d) contains the same polymerized units as the polymerized unit (hereinafter referred to as polymerized unit a) in the fluorinated polymer (a), the more the fluorinated polymer (d) adheres to the fluorinated polymer (a). In order to maintain the predetermined refractive index difference, since the difference in the refractive index between the two fluoropolymers is reduced, it is preferable that the heat resistance and the wet heat resistance are easily maintained. The ratio of the polymerized unit a in the fluoropolymer (d) is naturally limited. Further, as the polymerized unit a, 1
The polymer units are not limited to the same, and when both fluoropolymers are copolymers, two or more of the polymer units may be common. The ratio of the polymer units a to the total polymer units in the fluoropolymer (d) is preferably at least 20 mol%, particularly preferably at least 30 mol%. The upper limit is not limited as long as a predetermined refractive index difference between both fluoropolymers can be maintained, but is usually 95 mol%, preferably 85 mol%.
Further, the fluoropolymer (d) is preferably optically transparent, but is not always essential. In order to enhance the adhesiveness with the fluoropolymer (a), it is preferable that the polymer is an amorphous polymer. The polymer unit a is preferably a polymer unit having a fluorinated aliphatic ring structure in the description of the fluoropolymer (a) described below.

In the case of the mixture (f) as well, the higher the proportion of the fluoropolymer (a) contained therein, the better in terms of improving the adhesiveness and the like, but the mixture has a predetermined refractive index with the fluoropolymer (a). In order to maintain the difference, the ratio is naturally limited.
The mixture (f) is preferably optically homogeneous and highly transparent, but is not always essential. On the other hand, the fluorinated polymer (e) and the fluorinated polymer (a) are preferably polymers that can be mixed uniformly, in order to improve the adhesion to the inner layer. For this purpose, the fluorine-containing polymer (e) must be a polymer having a high affinity for the fluorine-containing polymer (a), and therefore, like the above-mentioned fluorine-containing polymer (d), the fluorine-containing polymer containing the polymerized unit a. Polymers are preferred. That is, the fluoropolymer (e) is preferably the same as the fluoropolymer (d). However, the polymerization unit a in the fluoropolymer (e)
May be lower than the above preferable ratio of the polymerized unit a in the fluoropolymer (d). Since the fluorinated polymer (e) is used by mixing with the fluorinated polymer (a), the fluorinated polymer (a) can be used even if the proportion of the polymerized unit a in the fluorinated polymer (e) is small. This is because the adhesiveness of the existing mixture (f) to the inner layer is improved.

The proportion of the fluoropolymer (a) in the mixture (f) is preferably 90% by mass or less, particularly preferably 70% by mass or less. If the ratio is too large, the predetermined refractive index difference between the inner layer and the outer layer cannot be maintained. There is no particular lower limit on the ratio. This is because when the fluoropolymer (e) is the fluoropolymer (d), the fluoropolymer (a)
This is because the object can be achieved without the presence of, and the proportion of the fluoropolymer (a) in the mixture (f) can be extremely small. However, in order to further improve adhesion and the like, the content is preferably 5% by mass or more, particularly preferably 10% by mass or more. When the fluoropolymer (e) is not the fluoropolymer (d) (that is, when it does not have the polymerized unit a), the proportion of the fluoropolymer (a) in the mixture (f) is 10% by mass. Above, particularly preferably 30% by mass or more.

The glass transition temperature Tgc of the fluoropolymer material (c) is preferably 70 ° C. <Tgc <Tga + 30 ° C. If the Tgc is less than 70 ° C., thermal deformation occurs and transmission loss increases. In the case of an optical fiber having a protective coating layer, a gap occurs between the outer layer and the protective coating layer during a high-temperature and low-temperature cycle. As a result, the fiber end face is easily protruded or retracted. On the other hand, Tgc is (Tga + 3
(0 ° C.) or more, a difference in shrinkage speed occurs between the inner layer and the outer layer during cooling during spinning of the optical fiber, and distortion occurs in the inner layer, which tends to cause scattering loss. Therefore, the difference between Tgc and Tga is preferably within 10 ° C. The melt viscosity of the fluoropolymer material (c) is preferably as close as possible to the melt viscosity of the fluoropolymer (a) in the inner layer for the same reason.

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

The fluoropolymer material (c) is preferably a material having no C—H bond, but it is not essential that the material has no C—H bond. That is, the fluoropolymer (d) or the fluoropolymer (e) may be a polymer having a C—H bond. The outer layer is not mainly a portion where light propagates, but reflects light leaked from the inner layer when the optical fiber is bent. Therefore, the fluoropolymer material (c) absorbs light due to the presence of C—H bonds. This is because it is not considered to have a great influence on the transmission of the light having the occurring wavelength. When the fluorinated polymer material (c) has a C—H bond, that is, when the fluorinated polymer (d) or the fluorinated polymer (e) has a C—H bond, the carbon atom in the polymer is The ratio of the bonded hydrogen atoms is preferably 5% by mass or less, particularly preferably 1% by mass or less. If the ratio is too high, the refractive index of the polymer increases, and it becomes impossible to maintain a predetermined difference in refractive index with respect to the inner layer. Examples of the polymer unit having a CH bond of the fluorine-containing polymer having a small amount of CH bond include one of a fluorine atom or a chlorine atom of a monomer for producing a fluorine-containing polymer (a) described below. Examples thereof include a polymerized unit derived from a monomer having two or more hydrogen atoms.

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

The viscosity of the fluoropolymer (a) in the molten state is 10 ³ to 1 at a melting temperature of 200 to 300 ° C.
0 ⁵ poise is preferred. If the melt viscosity is too high, the melt spinning is difficult, and the substance (b) necessary for forming the refractive index distribution is used.
Diffusion hardly occurs, and it becomes difficult to form a refractive index distribution. On the other hand, if the melt viscosity is too low, practical problems arise.
That is, when used as an optical transmitter in an electronic device, an automobile, or the like, it is exposed to a high temperature and softened, and the light transmission performance is reduced.

The number average molecular weight of the fluoropolymer (a) is 1
× 10 ^{4 to} 5 × 10 ⁶ is preferable, and 5 × 10 ⁴ to 1 × 1
0 ⁶ is more preferable. If the molecular weight is too small, heat resistance may be impaired, and if it is too large, it becomes difficult to form a light transmitting body having a refractive index distribution. When this molecular weight is expressed by intrinsic viscosity [η], it is 30 in perfluoro (2-butyltetrahydrofuran) [hereinafter referred to as PBTHF].
0.1 to 1.0 at ° C, particularly 0.2
It is preferably from 0.5 to 0.5.

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

A polymer having a fluorinated alicyclic structure in the main chain obtained by polymerizing a monomer having a fluorinated alicyclic structure is known from JP-B-63-18964. That is, by homopolymerizing a monomer having a fluorinated aliphatic ring structure such as perfluoro (2,2-dimethyl-1,3-dioxole), a radical having no C—H bond with this monomer is obtained. By copolymerizing with a polymerizable monomer, a polymer having a fluorinated aliphatic ring structure in the main chain can be obtained.

As the radical polymerizable monomer containing no CH bond, a polyfluoroolefin having no CH bond or a vinyl ether monomer having no CH bond is preferable. Specific examples of the polyfluoroolefin having no C—H bond include a perfluoroolefin such as tetrafluoroethylene and a perhalopolyfluoroolefin such as chlorotrifluoroethylene. Polyfluoroolefin or C having no CH bond
As a vinyl ether monomer having no -H bond,
Specifically, for example, perfluoro (alkyl vinyl ether), perhalopolyfluoro (alkyl vinyl ether) in which a part of the fluorine atom is substituted by a chlorine atom,
There is perfluoro ((alkoxyalkyl) vinyl ether) having an etheric oxygen atom between carbon atoms of the alkyl group of perfluoro (alkyl vinyl ether).
The polyfluoroolefin preferably has 2 to 4 carbon atoms, and the vinyl portion of the vinyl ether-based monomer may have an etheric oxygen atom and has 10 carbon atoms.
The following 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 238
No. 111, Japanese Patent Application Laid-Open No. 63-238115, and the like. That is, by subjecting a monomer such as perfluoro (allyl vinyl ether) or perfluoro (butenyl vinyl ether) to cyclopolymerization, or by combining such a monomer with tetrafluoroethylene, chlorotrifluoroethylene, perfluoro (methyl vinyl ether), or the like. A copolymer having a fluorinated aliphatic ring structure in the main chain can be obtained by copolymerizing the above with a radical polymerizable monomer.

Also, perfluoro (2,2-dimethyl-
Monomers having a fluorinated aliphatic ring structure such as 1,3-dioxole) and perfluoro (allyl vinyl ether)
A polymer having a fluorinated aliphatic ring structure in the main chain can also be obtained by copolymerizing a fluorinated monomer having two or more polymerizable double bonds such as perfluoro (butenyl vinyl ether) or the like.

The polymer having a fluorinated aliphatic ring structure is
What contains 20 mol% or more, especially 40 mol% or more of the polymer units having the fluorinated aliphatic ring structure with respect to all the polymerized units of the polymer having the fluorinated aliphatic ring structure is transparent,
It is preferable in terms of mechanical properties and the like.

Specific examples of the above-mentioned polymer having a fluorinated aliphatic ring structure include those having a polymerized unit selected from the following chemical formula. Formulas 1 and 2 below are examples of polymerized units formed by polymerization of a monomer having a fluorinated ring structure. Formulas 3 and 4 below are examples of polymerized units formed by cyclopolymerization of a fluorine-containing monomer having two polymerizable double bonds. In the following formulas 1 to 4, X
^{1 to} X ¹⁰ each independently represent a fluorine atom or a perfluoroalkyl group, a part of the fluorine atom may be substituted by a chlorine atom, and a part of the fluorine atom in the perfluoroalkyl group is substituted by a chlorine atom. You may. The number of carbon atoms in the perfluoroalkyl group is from 1 to 5
Is particularly preferable, and 1 is particularly preferable. Z represents an oxygen atom, a single bond, or —OC (R ⁹ R ¹⁰ ) O—. Preferred Z is an oxygen atom.

R ^{1 to} R ¹⁰ are each independently a fluorine atom,
Represents a perfluoroalkyl group or a perfluoroalkoxy group, and part of a fluorine atom may be substituted with a chlorine atom, and part of a fluorine atom in the perfluoroalkyl group and the perfluoroalkoxy group may be substituted with a chlorine atom . The number of carbon atoms in the perfluoroalkyl group and the perfluoroalkoxy group is 1 to 5
Is particularly preferable, and 1 is particularly preferable. Further, R ¹ and R ² and R ³ and R ⁴ may together form a fluorinated aliphatic ring, and when p or q is 2 or more, a substituent bonded to a different substituted methylene group is Similarly, a fluorinated aliphatic chain may be formed jointly. For example, R ¹ and R ² may together represent a C 2-6 perfluoroalkylene group. p is an integer of 1 to 4, q is an integer of 1 to 5,
s and t are each independently an integer of 0 to 5 and s + t is an integer of 1 to 6 (however, when Z is -OC (R ⁹ R ¹⁰ ) O-,
+ T may be 0). Where p, q,
When s and t are integers of 2 or more, the types of the substituents in the plurality of substituted methylene groups defined by the numbers may be different. For example, when p is 2, two R ¹ may be different, and two R ² may also be different. Preferred p is 1 or 2, and preferred q is 2. s and t
Is preferably an integer of 0 to 4 and s + t is 1 to 4.

[0031]

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A monomer forming a polymerized unit represented by the formula (1)
Represents a fluorinated aliphatic ring structure represented by the following formula 5:
Having a monomer (having p = 1) and a monomer represented by the following formula 6
A monomer having a fluoroaliphatic ring structure (where p is 2)
preferable. Further, a unit forming the polymerized unit represented by Formula 2
As the monomer, a fluorinated aliphatic ring system represented by the following formula 7
Monomers having a structure (q is 2) are preferred. The following formula
At R¹¹, R¹²Is R¹The same as R^{twenty one}, R
^{twenty two}Is R^TwoThe same as R³¹, R³²Is R^ThreeSame as
Of R⁴¹, R⁴²Is R^FourRepresents the same as In addition,
As we did, R ¹¹And R^{twenty two}, R³¹And R⁴²Is joint
To form a fluorinated aliphatic ring. Equations 5 to 7
As the compound represented, X¹~ X^FourAre all fluorine
Atom, R ¹, R^Two, R¹¹, R¹², R^{twenty one}, R^{twenty two}, R³¹, R
³², R⁴¹, R⁴²Are independently a fluorine atom,
Oromethyl or chlorodifluoromethyl
Compounds are preferred. The most preferred compound is represented by Formula 5
X¹, X^TwoAre all fluorine atoms and R¹And R^TwoSquat
A compound whose deviation is also a trifluoromethyl group [ie,
Perfluoro (2,2-dimethyl-1,3-dioxo)
Le)].

[0033]

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Specific examples of preferred compounds represented by the formulas 5 to 7 include the following compounds.

[0035]

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The fluorine-containing monomer having two polymerizable double bonds forming the polymerization units represented by the formulas 3 and 4 by cyclization polymerization includes a monomer represented by the following formula. In the compound represented by the formula 8, Z is an oxygen atom or -O
C (R ⁹ R ¹⁰ ) O—, s is 0 or 1, t is 0 to 4 and s + t is 1 to 4 (provided that Z is —OC (R ⁹ R ¹⁰ ) O
-May be 0), X ^{5 to} X ¹⁰ are all fluorine atoms, or at most two are chlorine atoms, trifluoromethyl groups or chlorodifluoromethyl groups and the others are fluorine atoms, Compounds in which R ^{5 to} R ¹⁰ are each independently a fluorine atom, a chlorine atom (but at most one bond per carbon atom), a trifluoromethyl group or a chlorodifluoromethyl group are preferred.

[0037]

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The compound represented by the formula 8 includes the following formula 9
To the compounds of formula 11 are preferred. The compound represented by the following formula 9 is a compound wherein Z is an oxygen atom, s is 0 and t is 1 in the formula 8, and the compound represented by the following formula 10 is a compound wherein Z is an oxygen atom and s is 0 in the formula 8. , T is 2, and the compound represented by the formula 11 is a compound in which, in the formula 8, Z is —OC (R ⁹ R ¹⁰ ) O—, s, and t are all 0. In the following formulas, R ⁷¹ and R ⁷² represent the same as R ^7, and R ⁸¹ and R ⁸² represent the same as R ⁸ . In the compound represented by the formula 9, X ^{5 to} X ¹⁰ are all fluorine atoms or 1 to 2 thereof (provided that X ⁵ to
At most at most 1 and X ⁸ to X ¹⁰ in X ⁷ is preferably one) is another fluorine atom a chlorine atom. R ⁷
And R ⁸ are preferably all fluorine atoms or one is a chlorine atom or a trifluoromethyl group and the other is a fluorine atom. The most preferred compound represented by the formula 9 is a compound in which X ^{5 to} X ¹⁰ , R ⁷ and R ⁸ are all fluorine atoms [that is, perfluoro (allyl vinyl ether)].

In the compound represented by the formula 10, X^Five~
X^TenAre all fluorine atoms or 1 to 2 of them
(However, X^Five~ X⁷At most one and X⁸~ X^Tenof
At most one) is chlorine and the others are fluorine
Is preferred. R⁷¹, R⁷², R ⁸¹, R⁸²Are all fluorine atoms
Are at least two chlorine atoms or
It is a trifluoromethyl group and the other is a fluorine atom
preferable. The most preferred compound of formula 10 is X^Five
~ X^Ten, R⁷¹, R⁷², R⁸¹, R⁸²Are all fluorine atoms
[Ie, perfluoro (butenylvinyl)
Ether)]. The compound represented by the formula 11
And X^Five~ X^TenAre all fluorine atoms or
1 or 2 (however, X^Five~ X⁷At most one and X
⁸~ X^TenAt most one) is a chlorine atom and the other is a fluorine atom
It is preferable that R⁹And R^TenAre all fluorine atoms
Or one of them is chlorine atom or trifluoromethyl group
And the other is preferably a fluorine atom. Most favorable
A compound represented by the formula 11 is preferably X^Five~ X^Ten, R⁹, R
^TenAre all fluorine atoms [ie, per
Fluoro {bis (vinyloxy) methane)}].

[0040]

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Specific examples of the compounds represented by formulas 9 to 11 include the following compounds. _{CF 2 = CFOCF 2 CF = CF} 2 CF 2 = CFOCF (CF 3) CF = CF 2 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 ₂ OCF = CF ₂ CF ₂ = CFOC (CF ₃ ) ₂ OCF = CF ₂ CF ₂ = CFOCCl ₂ OCF = CF ₂ CF ₂ = CCClOCF ₂ OCCl = CF ₂

The polymer units other than the polymer units a in the fluoropolymer (d) (hereinafter referred to as polymer units d) are the same as the above-mentioned fluorinated fatty acids unless they are the same as the polymer units a in the fluoropolymer (a). It may be a polymerized unit having an aromatic ring structure. Further, it may be a polymerized unit formed by polymerization of a monomer having no fluorinated aliphatic ring structure, such as a radical polymerizable monomer containing no C—H bond. The polymerization unit d is preferably a fluorine atom-containing polymerization unit containing no C—H bond, but may be a polymerization unit containing a small number of hydrogen atoms. As the radical polymerizable monomer containing no C—H bond, as described above, a polyfluoroolefin having no C—H bond or a vinyl ether monomer having no C—H bond is preferable. Perfluoro (alkyl vinyl ether) which may have an etheric oxygen atom in the alkyl moiety is preferred. The polymerized unit containing a small number of hydrogen atoms may be a polymerized unit having a fluorinated aliphatic ring structure or a polymerized unit having no fluorinated aliphatic ring structure. As the former, there is a polymerized unit in which a part of X ^{1 to} X ¹⁰ and R ^{1 to} R ^{10 in} the above formulas 1 to 4 is a hydrogen atom.

The substance (b) has a refractive index difference of 0.0 as compared with the fluoropolymer (a) as the matrix resin.
Preferably, the substance is at least 05, and the fluoropolymer (a)
The refractive index may be higher or lower than the refractive index. 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 to the peripheral direction of the optical fiber. Is an optical fiber distributed. In some cases, the substance (b) is a substance having a lower refractive index than the fluoropolymer (a), and this substance has a concentration gradient that decreases from the periphery of the optical fiber toward the center. Optical fibers are also useful. The former optical fiber is usually a substance (b)
Can be manufactured by arranging them at the center and diffusing them toward 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 the fluoropolymer (a) is usually used as the substance (b). That is, the substance (b) is a substance having substantially no C—H bond for the same reason as the fluoropolymer (a), and has a refractive index larger than that of the fluoropolymer (a) by 0.05 or more. It is more preferable that, when the refractive index is higher, the content of (b) necessary for forming a desired refractive index distribution can be smaller, so that the decrease in the glass transition temperature can be reduced, and as a result, Since the heat resistance of the optical fiber increases,
It is particularly preferred that it is larger than 0.1.

As this substance (b), a benzene ring or the like
Aromatic ring, halogen atom such as chlorine, bromine, iodine, etc.
Including a bonding group such as a ter bond, a low molecular compound, an oligomer,
Polymers are preferred, but polymers have higher molecular weights.
When it becomes less, the compatibility with the fluoropolymer (a) decreases, and
As a result, the light scattering loss increases, and the molecular weight is too large.
Nothing is good. Conversely, the molecular weight has been reduced.
In the case of the compound, in the mixture with the fluoropolymer (a)
Lower glass transition temperature, lower heat-resistant temperature of optical fiber
Too small an amount is not preferable because it may cause the occurrence of the above. Therefore
The number average molecular weight of the compound (b) is 3 × 10^Two~ 2 × 1
0^ThreeIs preferably 3 × 10^Two~ 1 × 10 ^ThreeIs more preferred
No.

Specific examples of the compound of the substance (b) include oligomers, which are pentamers and octamers of chlorotrifluoroethylene, and pentamers of dichlorotrifluoroethylene as described in JP-A-8-5848. Oligomers that are dimers,
Alternatively, 2 to 2 obtained by polymerizing a monomer (for example, a monomer having a chlorine atom) that gives an oligomer having a high refractive index among the monomers forming the fluoropolymer (a).
There are pentameric oligomers.

In addition to the halogen-containing aliphatic compounds such as the above-mentioned oligomers, halogenated aromatic hydrocarbons containing no hydrogen atoms bonded to carbon atoms and halogen-containing polycyclic compounds can also be used. In particular, a fluorinated aromatic hydrocarbon or a fluorinated polycyclic compound containing only a fluorine atom as a halogen atom (or containing a relatively small number of chlorine atoms relative to a fluorine atom) is in phase with the fluorinated polymer (a). It is preferable in terms of solubility.
Further, these halogenated aromatic hydrocarbons and halogen-containing polycyclic compounds more preferably do not have a polar functional group such as a carbonyl group and a cyano group.

Examples of such a halogenated aromatic hydrocarbon include, for example, the formula Φr-Zb [Φr is a b-valent fluorinated aromatic ring residue in which all hydrogen atoms are substituted by fluorine atoms, Z
Is a halogen atom other than fluorine, -Rf, -CO-Rf,
—O—Rf, or —CN. Here, Rf is a perfluoroalkyl group, a polyfluoroperhaloalkyl group, or a monovalent Φr. b is 0 or an integer of 1 or more. ] The compound represented by these. The aromatic ring includes a benzene ring and a naphthalene ring. 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 compounds include, for example,
1,3-dibromotetrafluorobenzene, 1,4-dibromotetrafluorobenzene, 2-bromotetrafluorobenzotrifluoride, chloropentafluorobenzene, bromopentafluorobenzene, iodopentafluorobenzene, decafluorobenzophenone, perfluoroacetophenone, perfluoro Examples include biphenyl, chloroheptafluoronaphthalene, and bromoheptafluoronaphthalene.

As examples of the fluorine-containing polycyclic compound, the following compounds (b-1) to (b-3) as exemplified in JP-A-11-167030 are preferred. (B-1) a fluorinated ring 2 which is a carbocyclic or heterocyclic ring and has a fluorine atom or a perfluoroalkyl group;
At least one is a fluorine-containing non-condensed polycyclic compound linked by a bond containing at least one selected from the group consisting of a triazine ring, oxygen, sulfur, phosphorus and a metal, and is substantially C-H
Compound having no bond. (B-2) Fluorine-containing ring 3 which is a carbocyclic or heterocyclic ring and has a fluorine atom or a perfluoroalkyl group
At least one is a fluorine-containing non-fused polycyclic compound bonded directly or by a bond containing carbon, and is substantially C-H
Compound having no bond. (B-3) a condensed polycyclic compound composed of three or more carbocycles or heterocycles and substantially C—H
A fused fluorine-containing polycyclic compound having no bond.

Particularly preferred substance (b) is that it has good compatibility with the fluoropolymer (a), especially a fluoropolymer having a ring structure in the main chain, and has good heat resistance. Chlorotrifluoroethylene oligomer, perfluoro (triphenyltriazine), perfluoroterphenyl, perfluoroquatrophenyl, perfluoro (triphenylbenzene), perfluoroanthracene. Due to the good compatibility, the fluoropolymer (a), particularly 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 done. In addition, after dissolving and mixing in a fluorine-containing solvent, the two can be uniformly mixed by removing the solvent.

As a specific method for producing an optical fiber by distributing the substance (b) in the fluoropolymer (a) to form a refractive index distribution structure, there is, for example, the following method. 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) on the central axis is manufactured, and the substance (b) is diffused in a radial direction from the central axis by thermal diffusion to thereby obtain a refractive index distribution. And then forming an optical fiber by using the obtained cylindrical molded body as a preform (1). 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 a fluoropolymer (a) is melt-extruded into a fibrous shape while being extruded into a fiber to produce an optical fiber, a high concentration of the substance (b) is present at the central axis, and light is diffused while thermally diffusing the substance (b). A method for producing a fiber (3). In the method (3), a columnar preform having a refractive index distribution formed by extrusion molding is manufactured, and then an optical fiber is manufactured from the preform (4).

The substance (b) is dissolved in a monomer capable of forming the fluoropolymer (a), and the solution is placed in a rotating cylindrical mold, and the solution is rotated from the periphery of the cylindrical mold to the center. A method of producing an optical fiber by forming a refractive index distribution by advancing polymerization of a monomer in a direction, and using the obtained cylindrical molded body as a preform (5). In this method (5), since the solubility of the substance (b) in the polymer is usually lower than that of the monomer, the polymerization proceeds from the periphery of the cylinder to the unpolymerized monomer rather than the polymerized portion. The substance (b) is distributed at a high concentration in the portion, and consequently the high concentration of the substance (b) is present in the central axis where the polymer formation is slowest, and the concentration of the substance (b) is increased in the radial direction from 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 substance (b) in the method (5). When the polymerizability of the polymerizable monomer (hereinafter referred to as a precursor monomer) is lower than the polymerizability of the monomer capable of forming the fluoropolymer (a), the polymerization of the precursor monomer is slower. As in the case of the method (5), a concentration distribution in which a high concentration of the polymer of the precursor monomer (that is, the substance (b)) exists in the central axis portion is formed.

The outer layer can be formed, for example, as follows. A cylindrical body made of the fluorinated polymer material (c) is manufactured, and an inner layer made of the fluorinated polymer (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. Fluoropolymer material (c) to be an outer layer on the outer periphery of the preform obtained by the above method or the like
Is formed by a method such as coating, and an optical fiber is manufactured using a preform having this layer. Fluoropolymer material (c) having an inner diameter larger than the outer shape of the preform
Is manufactured, and an optical fiber is manufactured by integrally spinning a cylinder having a preform fitted therein. In the melt extrusion method, the fluoropolymer material (c) is extruded as an outer layer at the same time as the inner layer to produce a preform having the outer layer or directly at the same time as the extrusion to produce an optical fiber. After manufacturing the 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, an optical fiber is obtained by producing a preform having a refractive index distribution, fitting the preform to a cylindrical body made of a fluoropolymer material (c), and spinning the preform. An optical fiber can also be obtained by manufacturing a cylindrical body comprising an inner layer and an outer layer before diffusion of the substance (b), heating the cylindrical body to diffuse the substance (b) into a preform, and then spinning. Can be

The GI optical fiber obtained by the present invention can have a transmission loss of 100 dB or less at a wavelength of 700 to 1,600 nm of 50 dB or less. In particular, in a fluoropolymer having an aliphatic ring structure in the main chain, 1
The transmission loss of 00m can be 10 dB or less.
At a relatively long wavelength of 700 to 1600 nm, it is extremely advantageous to have such a low level of transmission loss. In other words, by using the same wavelength as the quartz optical fiber, the connection with the quartz optical fiber is easy, and compared with the conventional plastic optical fiber which has to use a wavelength shorter than 700 to 1,600 nm.
There is an advantage that an inexpensive light source is sufficient.

[0056]

Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to these specific examples. Examples 1 to 7 below
Is an example of polymer synthesis, Examples 8 to 14 are Examples, and Example 15
Examples 17 to 17 show comparative examples.

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
Was placed in a pressure-resistant glass autoclave having an internal volume of 200 ml. After purging the system 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. Intrinsic viscosity [η] of 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 at room temperature, it was a tough and transparent glassy polymer. The 10% thermal decomposition temperature is 46
The temperature was 8 ° C., and the refractive index was 1.342.

Example 2 27 g of PBVE, perfluoro (2,2-dimethyl-1,3-dioxole) [hereinafter P
DD] 3 g ion-exchanged water 150 g, methanol 1
0 g and 0.15 g of diisopropyl peroxydicarbonate were put into a pressure-resistant glass autoclave having an internal volume of 200 ml. After purging the system three times with nitrogen, 40
Suspension polymerization was performed at 22 ° C. for 22 hours. As a result, 27 g of a polymer (hereinafter, referred to as polymer B) was obtained. The intrinsic viscosity [η] of the polymer B was 0.25 at 30 ° C. in PBTHF.
From the analysis of the IR spectrum, the content of the repeating unit formed by the polymerization reaction of PDD [hereinafter referred to as PDD polymerization unit; the same applies to the repeating unit formed by the polymerization reaction of another monomer] was 11 mol%. Glass transition temperature of polymer B measured by TMA is 112 ° C.,
At room temperature, it was a tough and transparent glassy polymer. The 10% thermal decomposition temperature is 465 ° C., and the refractive index is 1.33.
It was 6.

(Example 3) PBVE 15 g, PDD 8.5
g, tetrafluoroethylene [hereinafter referred to as TFE] 4.
5 g, 100 g of ion-exchanged water, 17 g of methanol, and 0.28 g of diisopropyl peroxydicarbonate as a polymerization initiator were put into a 200 ml stainless steel autoclave. After purging the system three times with nitrogen,
Suspension polymerization was performed at 40 ° C. for 22 hours. As a result, 27 g of a polymer (hereinafter, referred to as polymer C) was obtained. The intrinsic viscosity [η] of the polymer C was 0.30 in PBTHF at 30 ° C. From the analysis of the NMR spectrum, PBVE polymerized units:
The molar ratio of DD polymerization unit: TFE polymerization unit is 38: 2
7:35. The glass transition temperature of Polymer C measured by TMA was 104 ° C., and at room temperature, it was a tough and transparent glassy polymer. The 10% thermal decomposition temperature is 4
The temperature was 70 ° C., and the refractive index was 1.328.

Example 4 18 g of PBVE, perfluoro (5-methyl-3,6-dioxa-1-nonene) [CF
₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ C
F ₃ ; hereinafter referred to as PHVE] 9 g, TFE 3.5 g, ion-exchanged water 120 g and diisopropyl peroxydicarbonate 0.15 g were placed in a 200 ml stainless steel autoclave. After purging the system with nitrogen three times, suspension polymerization was performed at 40 ° C. for 20 hours. As a result, 13 g of a polymer (hereinafter, referred to as polymer D) was obtained. The intrinsic viscosity [η] of the polymer D was 0.3 in PBTHF at 30 ° C.
29. From the analysis of the NMR spectrum, the molar ratio of PBVE polymerization unit: PHVE polymerization unit: TFE polymerization unit was 49:13:38. The glass transition temperature of Polymer D measured by TMA was 55 ° C., and at room temperature, it was a tough and transparent glassy polymer. The 10% thermal decomposition temperature was 460 ° C., and the refractive index was 1.336.

Example 5 Perfluoro (2-methylene-4)
-Methyl-1,3-dioxolane) [hereinafter referred to as PMMD] 15 g, TFE 14 g, dichloropentafluoropropane solvent [hereinafter referred to as R225] 20 g, and 46 of perfluorobenzoyl peroxide as a polymerization initiator.
mg was placed in a 200 ml stainless steel autoclave. After purging the inside of the system three times with nitrogen,
Solution polymerization was performed for hours. As a result, 16 g of a polymer (hereinafter, referred to as polymer E) was obtained. Intrinsic viscosity [η] of polymer E
Was 0.33 at 30 ° C. in PBTHF. From the analysis of the NMR spectrum, the molar ratio of PMMD polymerized unit: TFE polymerized unit was 60:40. The glass transition temperature of polymer E measured by TMA was 78 ° C., and at room temperature, it was a tough and transparent glassy polymer. Also 10%
The thermal decomposition temperature was 427 ° C. and the refractive index was 1.336.

(Example 6) 10 g of PMMD, 14 g of TFE,
10 g of PHVE, 10 g of R225 and 40 mg of perfluorobenzoyl peroxide were added to a 200 ml internal volume.
In a stainless steel autoclave. After the inside of the system was replaced with nitrogen three times, solution polymerization was performed at 70 ° C. for 5 hours. As a result, 16 g of a polymer (hereinafter, referred to as polymer F) was obtained. The intrinsic viscosity [η] of the polymer F is 30 ° C. in PBTHF.
Was 0.33. From the analysis of the NMR spectrum, the PM
MD polymerization unit: TFE polymerization unit: m of PHVE polymerization unit
The ol ratio was 52: 39: 9. The glass transition temperature of Polymer F measured by TMA was 78 ° C., and at room temperature, it was a tough and transparent glassy polymer. Also 10%
The thermal decomposition temperature was 423 ° C., and the refractive index was 1.332.

Example 7 10 g of PBVE, 10 g of 2,2-bis (trifluoromethyl) -1,3-dioxole (hereinafter referred to as HFDD), 8 g of TFE, 10 g of R225
g and perfluorobenzoyl peroxide 50 mg
Was placed in a 200 ml stainless steel autoclave. After the inside of the system was replaced with nitrogen three times, solution polymerization was performed at 70 ° C. for 5 hours. As a result, the polymer (hereinafter referred to as polymer G)
4.7 g). Intrinsic viscosity [η] of polymer G
Was 0.29 at 30 ° C. in PBTHF. From the analysis of the NMR spectrum, the molar ratio of PBVE polymerization unit: HFDD polymerization unit: TFE polymerization unit was 35:33:32. The glass transition temperature of the polymer G measured by TMA was 84 ° C., and at room temperature, it was a tough and transparent glassy polymer. The 10% thermal decomposition temperature was 462 ° C., and the refractive index was 1.336.

(Example 8) The polymer A obtained in Example 1 was melted in a cylindrical vessel at 250 ° C., and a chlorotrifluoroethylene oligomer (average molecular weight) was used as a refractive index distribution forming substance (b) in the center thereof. 760) was injected and diffused, and the time was adjusted so that the concentration at the center became 15% by mass, to prepare a preform having a refractive index distribution. A hollow tube made of the polymer B obtained in Synthesis Example 2 was put on the outside of the preform, and the tube was placed in a cylindrical electric heating furnace at 240 ° C.
The fiber was spun from the tip at ℃ to obtain an optical fiber. When the transmission loss of this optical fiber was measured by the cutback method, it was 181 dB / km at a wavelength of 1300 nm. In addition, an increase in transmission loss when winding around a rod having a radius of 10 mm and bending at 180 degrees was measured (hereinafter, R1).
It was 0.26 dB. For comparison, an optical fiber was prepared in the same manner using polymer A instead of polymer B, and the R10 bending loss was measured to be 2.39 dB. Therefore, it can be seen that the bending loss was reduced by one digit by providing the outer layer having a refractive index lower than that of the innermost layer by 0.006. Further, the above optical fiber was heated at 65 ° C. and a humidity of 95% and −10 ° C. for 10 hours.
After performing a reciprocating test (referred to as a wet heat cycle test), the transmission loss was measured. As a result, no deterioration in performance was observed at 189 dB / km. Further, the optical fiber was cut, and the cross section was observed with a scanning electron microscope. As a result, it was confirmed that the adhesion between the inner layer and the outer layer was good.

(Examples 9 to 14) Polymer A was used as the matrix resin of the inner layer, tris (pentafluorophenyl) -1,3,5-triazine was used as the refractive index distribution forming substance (b), and Examples 3 to 7 were used as the outer layer. Table 1 shows the results of an evaluation test of a graded index optical fiber produced in the same manner as in Example 8 by using each of the above polymers. Example 10,
Examples 12 and 13 are examples using a polymer mixture,
The types of the mixed polymers and the mixing mass ratios in [] are shown in the table.

(Example 15) [Comparative Example] An optical fiber was prepared in the same manner as in the example by using a PDD / TFE copolymer (trade name: Teflon AF) manufactured by DuPont as the outer layer, and the transmission loss was 324 dB / km. there were. The optical fiber was cut, and the cross section was observed with a scanning electron microscope. As a result, it was found that the inner layer and the outer layer were peeled off and the adhesion was poor.

(Examples 16 and 17) [Comparative Examples] Polymer A as the matrix resin for the inner layer and tris (pentafluorophenyl)-as the refractive index distribution forming substance (b)
Using 1,3,5-triazine, and using polymer E and polymer F as the outer layer, respectively, a refractive index distribution type optical fiber similar to that of Example 8 was prepared, and the evaluation test result was shown in Table 1. Show.

[0068]

[Table 1]

[0069]

According to the optical fiber of the present invention, it is possible to reduce the loss of light from ultraviolet light to near-infrared light at a very low level, suppress the increase in loss during bending, and also have heat resistance and wet heat resistance.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams showing a refractive index distribution in a radial direction in a cross section of an optical fiber of the present invention.

FIGS. 2C and 2D are diagrams showing radial refractive index distributions in a cross section of the optical fiber of the present invention.

[Explanation of symbols]

 1 Inner layer 2 Outer layer 3 Outermost refractive index level of inner layer 4 Refractive index level of outer layer

Claims (7)

[Claims] 1. A gradient index optical fiber having at least two concentric inner and outer layer structures, wherein an inner layer is substantially C
Having a refractive index distribution structure made of a non-crystalline fluorine-containing polymer (a) having no -H bond, wherein the outer layer has a lower refractive index than the outermost refractive index of the inner layer, and the following 1) and 2)
A plastic optical fiber comprising a fluoropolymer material (c) selected from the group consisting of: 1) A fluorinated polymer (d) containing the same polymer units as the polymer units in the fluorinated polymer (a). 2) Fluoropolymer (a) and other fluorinated polymer (e)
(F). 2. A fluorine-containing polymer material (c) constituting an outer layer
Has a glass transition temperature Tgc in the following range (however,
The plastic optical fiber according to claim 1, wherein ga is the glass transition temperature of the fluoropolymer (a). 70 ° C <Tgc <Tga + 30 ° C 3. The fluoropolymer (d) contains at least 30 polymer units identical to the polymer units in the fluoropolymer (a).
The plastic optical fiber according to claim 1 or 2, which contains mol%. 4. The plastic optical fiber according to claim 1, wherein the fluoropolymer material (c) has a refractive index lower by 0.003 or more than the outermost refractive index of the inner layer. 5. An inner layer comprising a fluoropolymer (a) as a matrix and a substance (b) having a different refractive index in the matrix.
5. The plastic optical fiber according to claim 1, wherein the plastic optical fiber is an inner layer formed by forming a refractive index distribution structure by dispersing the refractive index distribution. 6. The plastic optical fiber according to claim 1, wherein the fluoropolymer (a) is a fluoropolymer having a ring structure in its main chain. 7. The plastic optical fiber according to claim 1, further comprising a protective coating layer made of a thermoplastic resin outside the outer layer.