JP7501007B2 - Fiber optic cable - Google Patents

Description

The present invention relates to an optical fiber cable that has excellent long-term heat resistance and ease of handling.

Plastic optical fibers with a core made of a highly transparent resin such as methyl methacrylate are used for optical information communication inside trains, airplanes, automobiles, and other vehicles, as well as in the field of factory automation (FA). In the above-mentioned optical information communication field, plastic optical fibers are usually used in the form of optical fiber cables with a resin coating on the outer periphery.

When optical fiber cables are used for wiring inside vehicles such as automobiles or communication wiring in the factory automation field, they are used in environments close to high-temperature bodies such as engines, or in high-temperature environments in the summer. Therefore, optical fiber cables with excellent long-term heat resistance are required so that transmission loss does not increase even when exposed to heat for long periods of time.

Furthermore, in the above applications, optical fiber cables are laid in a twisted state in narrow spaces, and are used as movable wiring where they are repeatedly twisted, so optical fiber cables with excellent twisting resistance are desired.

As a method for improving the long-term heat resistance of a plastic optical fiber, for example, Patent Document 1 discloses an optical fiber cable in which the material constituting the cladding and the material constituting the coating layer are optimized.
As a method for improving the long-term heat resistance and flexibility of a plastic optical fiber, for example, Patent Documents 2 and 3 disclose an optical fiber cable using a specific modified fluorine-based resin as a material for forming the cladding.

International Publication No. 2019/177105 JP 2010-28682 A JP 2012-27304 A

However, although the optical fiber cables disclosed in Patent Documents 1 to 3 have excellent long-term heat resistance, they do not have sufficient twisting resistance.

The object of the present invention is to provide an optical fiber cable that has excellent long-term heat resistance and twisting resistance.

The gist of the present invention is to provide an optical fiber cable having an optical fiber strand having a core formed of a transparent resin and at least one cladding layer formed around the core, and at least one coating layer formed on the outside of the optical fiber strand, in which the material constituting the cladding layer or the outermost layer of the cladding layer has a polymer chain containing tetrafluoroethylene units, ethylene units, hexafluoropropylene units, and perfluoro(1,1,5-trihydro-1-pentene) units, and contains a modified fluororesin having a reactive functional group having a carbonate group at the end of the main chain and/or side chain, and the material constituting the coating layer or the innermost layer of the coating layer contains an ethylene-vinyl alcohol resin.

According to an embodiment of the present invention, an optical fiber cable with excellent long-term heat resistance and twisting resistance can be provided.

1 is a schematic cross-sectional view showing an example of an optical fiber cable of the present invention. FIG. 2 is a schematic cross-sectional view showing an example of a step-index optical fiber, which is an example of an optical fiber in the optical fiber cable of the present invention. 1 is a schematic diagram of a twisting test device used for measuring the twisting light loss of the optical fiber cable of the present invention. FIG.

The following describes the embodiments of the present invention with reference to the drawings, but the present invention is not limited to these drawings.

<Optical fiber cable>
The optical fiber cable of the present invention is an optical fiber cable having an optical fiber core formed from a transparent resin described below and at least one cladding layer described below formed around the core, and at least one coating layer described below formed on the outside of the optical fiber core.
Specific embodiments of the optical fiber cable of the present invention include, for example, an optical fiber cable having one coating layer (20a) around the outer periphery of the optical fiber 10 as shown in FIG. 1(a), an optical fiber cable having two coating layers (20a (inner coating layer) and 20b (outer coating layer)) around the outer periphery of the optical fiber 10 as shown in FIG. 1(b), and an optical fiber cable having three or more coating layers (20a (inner coating layer), 20b (outer coating layer), and 20c (outermost coating layer)) around the outer periphery of the optical fiber 10 as shown in FIG. 1(c).
In the optical fiber cable of the present invention, when the coating layer is one layer, the material constituting the coating layer is an ethylene-vinyl alcohol-based resin described below. When the coating layer is two or more layers, the material constituting the innermost coating layer is an ethylene-vinyl alcohol-based resin described below. Specifically, the material constituting the coating layer (20a) in Fig. 1(a) and the inner coating layer (20a) in Fig. 1(b) and (c) is an ethylene-vinyl alcohol-based resin described below.

Furthermore, in the optical fiber cable of the present invention, the outermost layer of the cladding layer contains a modified fluororesin described below, and the innermost layer of the coating layer contains an ethylene-vinyl alcohol-based resin, so that the twisting light loss when the optical fiber cable is twisted five times from a straight state, as measured by a continuous twisting test, can be made to be 0.12 dB or less.
When the twisting light loss is 0.12 dB or less, the optical fiber cable can be laid in a twisted state in a narrow space, and can be used as a movable wiring in a state where it is repeatedly twisted.
A specific method for measuring the twisting loss of an optical fiber cable will be described later.

The diameter of the optical fiber cable of the present invention is preferably 1.2 mm to 4.0 mm, and more preferably 1.3 mm to 2.6 mm. When the diameter of the optical fiber cable is 1.2 mm or more, the optical fiber cable has excellent long-term heat resistance and torsion resistance. Furthermore, when the diameter of the optical fiber cable is 4.0 mm or less, the optical fiber cable has excellent flexibility and ease of handling.

When the coating layer is made of one coating layer and the material constituting the coating layer contains an ethylene-vinyl alcohol resin, the thickness of the coating layer is preferably 50 μm to 700 μm from the viewpoint of excellent long-term heat resistance and rotation resistance of the optical fiber cable. A more preferable thickness is 100 μm to 350 μm.

When the coating layer is made up of two layers, an inner coating layer and an outer coating layer, which are formed concentrically in that order, and the material constituting the inner coating layer contains an ethylene-vinyl alcohol resin, and the material constituting the outer coating layer contains a polyamide resin, from the viewpoint of excellent long-term heat resistance and torsion resistance of the optical fiber cable, it is preferable that the thickness of the inner coating layer is 25 μm to 350 μm, and the thickness of the outer coating layer is 25 μm to 350 μm.

When the coating layer is composed of three layers formed concentrically in the order of an inner coating layer, an outer coating layer, and an outermost coating layer, and the material constituting the inner coating layer contains an ethylene-vinyl alcohol-based resin, the material constituting the outer coating layer contains a polyamide-based resin, and the material constituting the outermost coating layer contains a polybutylene terephthalate-based resin, from the viewpoint of excellent long-term heat resistance and torsion resistance of the optical fiber cable, it is preferable that the thickness of the inner coating layer is 25 μm to 350 μm, the thickness of the outer coating layer is 25 μm to 350 μm, and the thickness of the outermost coating layer is 150 μm to 700 μm.

<Optical fiber strand>
The optical fiber strand has a core formed of a transparent resin and at least one cladding layer formed around the core, and is not particularly limited as long as it functions as an optical fiber, and any known optical fiber can be used.

Types of optical fiber strands include, for example, step-index type optical fiber, multi-step-index type optical fiber, grated-index type optical fiber, and multi-core optical fiber. Among these types of optical fiber, step-index type optical fiber and multi-core optical fiber are preferred because of their excellent heat resistance, and step-index type optical fiber is more preferred because it enables communication over longer distances.

A step-index optical fiber causes light to propagate within the core by total internal reflection at the interface between the core and the cladding.
Examples of step-index optical fibers include an optical fiber having one cladding layer 12 around a core 11 as shown in FIG. 2( a), and an optical fiber having two or more cladding layers (a first cladding layer 12 a and a second cladding layer 12 b) around a core 11 as shown in FIG. 2( b).

The optical fiber strand of the present invention has excellent stability in transmission loss values, and from the standpoint of ease of handling, etc., it is preferable to set the diameter to, for example, a range of 500 μm to 2000 μm, and more preferably a range of 700 μm to 1200 μm.

The thickness of the cladding layer of the optical fiber strand is preferably in the range of 3 to 30 μm, and more preferably in the range of 4 to 15 μm, because the mechanical strength is improved by coating with modified fluororesin, the light passing through the core is totally reflected, and the cross-sectional area occupancy rate of the core portion of the optical fiber can be sufficiently ensured.

<Core>
The transparent resin forming the core is not particularly limited as long as it is a resin with high transparency, and examples thereof include acrylic resin, styrene resin, carbonate resin, etc. These transparent resins may be used alone or in combination of two or more. Among the above-mentioned materials, acrylic resin and polycarbonate resin are preferred because they have excellent transparency at a wavelength of about 650 nm, and acrylic resin is more preferred because they have excellent long-term heat resistance at 105° C. and are suitable for longer distance communication.

Examples of the acrylic resin include homopolymers of methyl methacrylate (PMMA) and copolymers of methyl methacrylate and one or more vinyl monomers. Specific examples of the copolymers include copolymers containing 50% or more by mass of methyl methacrylate units. These acrylic resins may be used alone or in combination of two or more. Among these acrylic resins, methyl methacrylate homopolymers and copolymers containing 50% or more by mass of methyl methacrylate units (methyl methacrylate-based copolymers) are preferred because of their excellent optical properties, mechanical properties, heat resistance, and transparency. As the methyl methacrylate-based copolymers, copolymers containing 60% or more by mass of methyl methacrylate units are preferred, and copolymers containing 70% or more by mass of methyl methacrylate units are more preferred. Methyl methacrylate homopolymers are particularly preferred as core materials.
In this specification, (meth)acrylate refers to acrylate, methacrylate or both.

The refractive index of the core material such as acrylic resin is preferably from 1.485 to 1.50, and more preferably from 1.490 to 1.495.
In this specification, the refractive index is a value measured according to the method described below.

The core material can be manufactured by a known polymerization method. Examples of polymerization methods for manufacturing the core material include bulk polymerization, suspension polymerization, emulsion polymerization, and solution polymerization. Among these polymerization methods, bulk polymerization and solution polymerization are preferred because they can prevent the inclusion of foreign matter.

<Clad>
In the optical fiber cable of the present invention, the material constituting the cladding layer of the optical fiber (cladding material) has a refractive index lower than that of the core material.
The cladding layer of the optical fiber of the present invention is at least one cladding layer formed around the core.

In the optical fiber of the present invention, when the cladding layer is one layer, the material constituting the cladding layer contains a modified fluororesin, which will be described later. When the cladding layer is two or more layers, the material constituting the outermost layer of the cladding layer contains a modified fluororesin, which will be described later. Specifically, the material constituting the cladding layer (12) in FIG. 2(a) and the second cladding layer (12b) in FIG. 2(b) contains a modified fluororesin, which will be described later.

For example, in the case of a two-layer clad structure in which a first clad and a second clad are concentrically laminated in this order around the outer periphery of a core, the first clad layer located on the inside contains a fluorinated methacrylate resin having a refractive index higher than that of the modified fluororesin, and the second clad layer, which is the outermost layer of the clad layers, contains the modified fluororesin.
The two-layer clad structure allows the modified fluororesin contained in the second clad layer (the outermost clad layer) and the ethylene-vinyl alcohol resin contained in the innermost coating layer to have a high affinity, resulting in good adhesion between the optical fiber and the coating layer. As a result, the optical fiber cable has excellent twist resistance. Furthermore, the fluorinated methacrylate resin contained in the first clad layer can maintain good transparency even in high-temperature environments, which allows the optical fiber cable to have better long-term heat resistance at 105°C.

<Modified fluororesin>
In the optical fiber of the present invention, the material constituting the cladding layer or the outermost layer of the cladding layer contains a modified fluororesin having a polymer chain containing tetrafluoroethylene units, ethylene units, hexafluoropropylene units, and perfluoro(1,1,5-trihydro-1-pentene) units and having a reactive functional group having a carbonate group at the end of the main chain and/or the side chain. The modified fluororesin provides an optical fiber cable with excellent long-term heat resistance and twisting resistance.

From the viewpoint of providing an optical fiber cable with better long-term heat resistance and twisting resistance, the modified fluororesin is preferably a modified fluororesin having a polymer chain containing 24 to 58 mol % tetrafluoroethylene units, 30 to 68 mol % ethylene units, 7 to 28 mol % hexafluoropropylene units, and 1 to 10 mol % perfluoro(1,1,5-trihydro-1-pentene) units, and having a reactive functional group having a carbonate group at the end of the main chain and/or side chain.

The modified fluororesin has a reactive functional group having a carbonate group (carbonyldioxy group) in the main chain or side chain, which can further improve the adhesion between the optical fiber strand and the coating layer containing the ethylene-vinyl alcohol-based thermoplastic resin. As a result, it is possible to impart excellent resistance to twisting to the optical fiber cable. The modified fluororesin into which a reactive functional group having a carbonate group has been introduced can be easily introduced by using peroxycarbonate as a polymerization initiator during polymerization of the modified fluororesin.

The modified fluororesin preferably has a melting point in the range of 120 to 200°C. If the melting point is within this range, it is possible to suppress shape variations in the core and cladding layer during the manufacture of the optical fiber, and further, it is preferable because it can be manufactured at a temperature that suppresses thermal decomposition of the transparent resin of the core.

The modified fluororesin preferably has a melt flow index of 5 to 100 g/10 min, measured at 230°C under a load of 3.8 kg. If the melt flow index is within this range, it is preferable because it is possible to suppress shape variations in the core and cladding layer during the manufacture of the optical fiber, and further, it is possible to manufacture the optical fiber at a temperature that suppresses thermal decomposition of the transparent resin of the core.

The modified fluororesin preferably has a refractive index of 1.34 to 1.41 for sodium D lines measured at 23°C using an Abbe refractometer in accordance with ISO 13468. If the refractive index is within this range, the numerical aperture of the optical fiber strand is sufficiently large, ensuring a sufficient amount of light reception, making it suitable for long-distance communications.

The material constituting the clad layer preferably contains 85% by mass or more of the modified fluororesin, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

As such modified fluororesins, commercially available products such as Neoflon EFEP RP4020 and RP5000 manufactured by Daikin Industries, Ltd. and Fluon LM-ETFE AH2000 manufactured by Asahi Glass Co., Ltd. can be used.
Neoflon EFEP RP4020 and RP5000 are tetrafluoroethylene/ethylene/hexafluoropropylene/perfluoro(1,1,5-trihydro-1-pentene) copolymers having reactive functional groups having carbonate groups at the ends of the main chain and/or side chains of the polymer chain.

<Fluorinated methacrylate resin>
In the optical fiber cable of the present invention, when the cladding layer is formed of two or more layers, the fluorinated methacrylate resin is a material constituting the first cladding layer located on the inside.
As the fluorinated methacrylate resin, from the viewpoint of high transmittance and excellent heat resistance and moldability, a fluoroalkyl (meth)acrylate polymer containing a fluorine-containing (meth)acrylate unit such as a fluoroalkyl (meth)acrylate unit or an α-fluoro-fluoroalkyl (meth)acrylate unit, or a fluoroalkyl (meth)acrylate-alkyl (meth)acrylate copolymer is preferred.
Furthermore, by using a copolymer containing fluoroalkyl (meth)acrylate units and methyl methacrylate units, the refractive index can be controlled while maintaining the transparency and mechanical strength of the cladding material, which is preferable.

Examples of fluoroalkyl (meth)acrylates include long-chain fluoroalkyl (meth)acrylates such as 2-(perfluorohexyl)ethyl methacrylate (13FM) and 2-(perfluorooctyl)ethyl methacrylate (17FM) shown in the following general formula (1); and short-chain fluoroalkyl (meth)acrylates such as 2,2,2-trifluoroethyl methacrylate (3FM) shown in the following general formula (2).

(In the formula, m is 1 or 2, n is an integer from 5 to 13, R is a hydrogen atom or a methyl group, and X is a hydrogen atom or a fluorine atom.)

(In the formula, m is 1 or 2, n is an integer from 1 to 4, R is a hydrogen atom or a methyl group, and X is a hydrogen atom or a fluorine atom.)

Since the fluorinated methacrylate resin can reduce transmission loss, a copolymer consisting of 10 to 50 mass% of long-chain fluoroalkyl (meth)acrylate units shown in the above formula (2), 20 to 90 mass% of short-chain fluoroalkyl (meth)acrylate units shown in the above formula (3), and 0 to 50 mass% of other copolymerizable monomer units is preferred. Specifically, a 17FM-3FM-methyl methacrylate-methacrylic acid copolymer or a 13FM-3FM-methyl methacrylate-methacrylic acid copolymer having the above content is preferred.
The fluorinated methacrylate resin preferably has a glass transition temperature within a range of 70 to 150° C. If the glass transition temperature is within this range, it is possible to suppress shape variations in the core and cladding layer during the manufacture of the optical fiber, and further, it is preferable because the optical fiber can be manufactured at a temperature at which thermal decomposition of the transparent resin of the core can be suppressed.
The fluorinated methacrylate resin preferably has a melt flow index in the range of 5 to 100 g/10 min measured at 230° C. under a load of 3.8 kg. A melt flow index in this range is preferable because it can suppress shape variations in the core and cladding layer during the manufacture of the optical fiber and can also be manufactured at a temperature that can suppress thermal decomposition of the transparent resin of the core.
The fluorinated methacrylate resin can have a refractive index of sodium D line measured at 23° C. using an Abbe refractometer in the range of 1.42 to 1.48 in accordance with ISO 13468. If the refractive index is within this range, the numerical aperture of the optical fiber becomes sufficiently large, and a sufficient amount of light can be received, making it suitable for long-distance communications.

<Method of manufacturing optical fiber>
The optical fiber can be manufactured by a known manufacturing method, for example, a melt spinning method.
The production of an optical fiber by melt spinning can be carried out, for example, by melting a core material and a cladding material separately and composite spinning them.
When an optical fiber cable is used in an environment with a large temperature difference, it is preferable to anneal the optical fiber to suppress pistoning. The conditions of the annealing treatment may be set appropriately depending on the material of the optical fiber. The annealing treatment may be performed continuously or in batches.

<Coating Layer>
The optical fiber cable of the present invention has at least one coating layer formed on the outside of the optical fiber strand, and the material constituting the innermost layer of the coating layer can be configured to contain an ethylene-vinyl alcohol-based resin described below.

Furthermore, the optical fiber cable of the present invention may have a coating layer consisting of at least two layers, with an inner coating layer and an outer coating layer formed concentrically in that order. In this case, the material constituting the inner coating layer may include an ethylene-vinyl alcohol resin, and the material constituting the outer coating layer may include a polyamide resin.

Furthermore, the optical fiber cable of the present invention may further have an outermost coating layer on the outer circumference of the outer coating layer. In this case, the material constituting the outermost coating layer may include a polybutylene terephthalate resin.

The inner coating layer, the outer coating layer, and the outermost coating layer will be described below in this order.
The term "inner coating layer" is synonymous with "the innermost coating layer."
(Inner coating layer)
When the coating layer is composed of two or more layers, the inner coating layer refers to the innermost coating layer.

The material constituting the inner coating layer may contain an ethylene-vinyl alcohol resin (hereinafter referred to as "EVOH resin").
EVOH resin is a copolymer resin containing units derived from ethylene (hereinafter abbreviated as "ethylene units") and units derived from vinyl alcohol (hereinafter abbreviated as "vinyl alcohol units").

Since the EVOH resin has a high affinity with the modified fluororesin, the adhesion between the coating layer and the optical fiber is high, and as a result, the twisting resistance of the optical fiber cable can be improved.

Furthermore, since EVOH resin has high oxygen barrier properties, it is possible to suppress an increase in transmission loss due to oxidative deterioration of the optical fiber in a high-temperature environment, thereby improving the long-term heat resistance of the optical fiber cable.
The content of EVOH resin in the low oxygen permeability material is not particularly limited as long as it is within a range in which the effects of the present invention can be obtained. From the viewpoint of obtaining a more sufficient oxygen barrier property, however, the content is preferably in the range of 90 to 100 mass %, more preferably in the range of 95 to 100 mass %, and it is particularly preferable that the low oxygen permeability material is EVOH resin.

The ethylene-vinyl alcohol resin is not particularly limited, but is preferably a copolymer in which the content of ethylene units and vinyl alcohol units is in the range of 20 mol% to 50 mol% and 50 mol% to 80 mol% of vinyl alcohol units per 100 mol of the total amount of monomer units constituting the EVOH resin. The total amount of ethylene units and vinyl alcohol units is preferably 90 mol% or more, more preferably 95 mol% or more, per 100 mol of the total amount of monomer units constituting the EVOH resin.

The upper limit of the content of vinyl alcohol units in the EVOH resin is not particularly limited, but from the viewpoint of improving the mechanical strength of the optical fiber cable, it is preferably 80 mol% or less relative to 100 mol% of the total amount of monomer units constituting the ethylene-vinyl alcohol resin. 77 mol% or less is more preferable, and 74 mol% or less is even more preferable. The lower limit of the content of vinyl alcohol units is not particularly limited, but from the viewpoint of improving the long-term heat resistance at 105°C of the optical fiber cable, it is preferably 50 mol% or more relative to 100 mol% of the total amount of monomer units constituting the ethylene-vinyl alcohol resin. 56 mol% or more is more preferable, 65 mol% or more is even more preferable, and 69 mol% or more is particularly preferable.

The upper limit of the content of ethylene units in the EVOH resin is not particularly limited, but from the viewpoint of obtaining good heat resistance at 105°C of the optical fiber cable, it is preferably 50 mol% or less relative to 100 mol% of the total amount of monomer units constituting the ethylene-vinyl alcohol resin. 44 mol% or less is more preferable, 35 mol% or less is even more preferable, and 31 mol% or less is particularly preferable. The lower limit of the content of ethylene units is not particularly limited, but from the viewpoint of obtaining good mechanical strength of the optical fiber cable, it is preferably 20 mol% or more relative to 100 mol% of the total amount of monomer units constituting the ethylene-vinyl alcohol resin. 23 mol% or more is more preferable, and 26 mol% or more is even more preferable.

Commercially available products of the above EVOH resins include, for example, Soarnol D, DT, DC, Soarnol E, ET, A, and AT (product names, manufactured by Mitsubishi Chemical Corporation).

The upper limit of the melting point of the EVOH resin is not particularly limited, but is preferably 195° C. or lower, more preferably 180° C. or lower, and the melt flow index measured at 210° C. and a load of 5 kgf in accordance with JIS K7210 is preferably in the range of 25 to 80 g/10 min from the viewpoint of excellent molding stability of the optical fiber cable. The lower limit of the melting point of the EVOH resin is not particularly limited, but is preferably 155° C. or higher, more preferably 165° C. or higher. If the melting point is too low, there is a risk of reduced molding stability when providing an inner coating layer.
In this specification, the melting point is a value measured by a differential scanning calorimeter in accordance with ISO 3146:2000.

(Outer coating layer)
When the coating layer is composed of two or more layers, the outer coating layer refers to a layer formed on the outer periphery of the inner coating layer.
The material constituting the outer coating layer may include a polyamide resin.
By forming the outer coating layer from a material containing a polyamide-based resin, the excellent heat resistance, chemical resistance, and mechanical strength of the polyamide-based resin can provide the optical fiber cable with good heat resistance and mechanical strength.

Examples of polyamide resins include aliphatic polyamides such as polyamide 6, polyamide 66, polyamide 612, polyamide 11, polyamide 12, and polyamide 1010; semi-aromatic polyamides such as polyamide 4T (copolymer of 1,4-butanediamine and terephthalic acid), polyamide 6T (copolymer of 1,6-hexanediamine and terephthalic acid), polyamide MXD6 (copolymer of meta-xylylenediamine and adipic acid), polyamide 6I (copolymer of 1,6-hexanediamine and isophthalic acid), and polyamide 9T (copolymer of 1,9-nonanediamine and terephthalic acid). These polyamide resins (N) may be used alone or in combination of two or more. Among these polyamide-based resins (N), polyamide 6, polyamide 66, polyamide 612, polyamide 11, polyamide 12, polyamide 1010, polyamide MXD6, polyamide 6T, and polyamide 9T are preferred because they have excellent heat resistance and oxygen barrier properties, and polyamide 6, polyamide 66, polyamide 12, polyamide 11, and polyamide MXD6 are more preferred, and polyamide 66, polyamide 12, and polyamide 11 are even more preferred.

The lower limit of the content of polyamide-based resin (N) in the material constituting the outer coating layer is not particularly limited, but since the optical fiber cable has excellent long-term heat resistance at 105°C and excellent laser welding properties with the ferrule, it is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on 100% by mass of the material constituting the outer coating layer. The upper limit of the content of polyamide-based resin (N) is not particularly limited, but since the optical fiber cable has excellent adhesion between the inner coating layer and the outer coating layer, it is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less, based on 100% by mass of the material constituting the outer coating layer.

The melting point of the polyamide resin (N) is preferably 150° C. to 300° C., and more preferably 180° C. to 280° C. When the melting point of the polyamide resin (N) is 150° C. or higher, the optical fiber cable has excellent heat resistance. When the melting point of the polyamide resin (N) is 300° C. or lower, the optical fiber cable has excellent processability.
In this specification, the melting point is a value measured by a differential scanning calorimeter in accordance with ISO 3146:2000.

Furthermore, in the optical fiber cable of the present invention, the material constituting the outer coating layer may be a mixture of a polyamide resin and an ethylene-vinyl alcohol resin.
By including an ethylene-vinyl alcohol resin in the material constituting the outer coating layer, an affinity is obtained between the outer coating layer and the inner coating layer, and good adhesion can be achieved between the outer coating layer and the inner coating layer of the optical fiber cable.
The ethylene-vinyl alcohol-based resin constituting the outer coating layer may be the same as the EVOH resin described in the section on the inner coating layer. From the viewpoint of improving the adhesion between the outer coating layer and the inner coating layer, it is preferable that the EVOH resin used in the material constituting the inner coating layer and the ethylene-vinyl alcohol-based resin used in the material constituting the outer coating layer are the same.

In the outer coating layer, the blending ratio of the polyamide resin to the ethylene-vinyl alcohol resin is preferably 10 to 30 parts by mass, and more preferably 15 to 25 parts by mass, of the ethylene-vinyl alcohol resin per 100 parts by mass of polyamide resin. When the content of the ethylene-vinyl alcohol resin is 10 parts by mass or more, the adhesion between the inner coating layer and the outer coating layer of the optical fiber cable can be improved. When the content of the ethylene-vinyl alcohol resin is 30 parts by mass or less per 100 parts by mass of polyamide resin, the effect of the polyamide resin can be fully obtained.

The polyamide resin and the ethylene-vinyl alcohol resin can be mixed, for example, by melt kneading using a known device such as a twin-screw extruder.

The temperature for melt-kneading the material constituting the outer coating layer is preferably 200°C to 300°C, and more preferably 220°C to 280°C. If the temperature for melt-kneading the material constituting the outer coating layer is 200°C or higher, the material constituting the outer coating layer can be sufficiently kneaded. If the temperature for melt-kneading the material constituting the outer coating layer is 300°C or lower, the polyamide resin can be kneaded without impairing its inherent performance.

(Outermost coating layer)
When the coating layer is composed of three or more layers, the outermost coating layer refers to a layer formed on the outer periphery of the outer coating layer.
The material constituting the outermost coating layer may include a polybutylene terephthalate resin (hereinafter, referred to as "PBT resin").
Since the outermost coating layer is made of a material containing PBT resin, the excellent heat resistance, chemical resistance, and mechanical strength of PBT resin provide the optical fiber cable with good heat resistance, chemical resistance, and mechanical strength under high temperature and high humidity conditions.
The PBT resin is a polymer containing, as a main constituent unit, an oligopoly-1,4-butylene terephthalate unit represented by the following general formula (4) synthesized by polycondensation of bishydroxybutyl terephthalate (BHT) or its oligomer obtained by an esterification reaction between 1,4-butanediol (tetramethylene glycol) and terephthalic acid, or an ester exchange reaction between 1,4-butanediol and dimethyl terephthalate.

(where n is a positive integer)

More specifically, the PBT resin suitable for the present invention is preferably an elastomer resin that contains oligopoly 1,4-butylene terephthalate represented by the above general formula (4) as a hard segment unit (crystalline phase) and a block unit represented by the following general formula (5) synthesized by polycondensation of an aliphatic polyether having a molecular weight in the range of 200 to 5000 (e.g., polytetramethylene glycol (PTMG)) with at least one of terephthalic acid, dimethyl terephthalate, diethyl terephthalate, dipropyl terephthalate, and dibutyl terephthalate, or a block unit of poly(ε-caprolactone) (PCL) represented by the following general formula (6) or a block unit of an aliphatic polyester such as polybutylene adipate (PBA), as a soft segment unit (amorphous phase).

(In the formula, p is an integer of 4 to 12, q is an integer of 2 to 20, and m is a positive integer.)

(In the formula, r is an integer of 1 or more, and l is a positive integer.)

Among the above PBT resins, a PBT resin having a block unit containing an aliphatic polyether unit represented by the above general formula (5) as a soft segment unit is particularly preferred in terms of maintaining the optical performance of the optical fiber cable and the mechanical strength of the coating layer under high temperature and high humidity conditions. In particular, a PBT resin that is a block copolymer containing a hard segment portion (A) (structure represented by formula (4)) made of oligopoly 1,4-butylene terephthalate and a soft segment portion (B) (structure when p = 4 in formula (5)) made of a polycondensate of terephthalic acid or terephthalate and polytetramethylene glycol (PTMG) having a molecular weight in the range of 200 to 600 is preferred because it has excellent optical performance of the optical fiber cable and mechanical strength of the coating layer under high temperature and high humidity conditions.

Furthermore, in the above PBT resin, the ratio (a/b) of the total number of moles (a) of 1,4-butylene terephthalate units contained in the hard segment portion (A) to the total number of moles (b) of 1,4-butylene terephthalate units contained in the soft segment portion (B) is preferably in the range of 15/85 to 30/70. If this ratio (a/b) is too small, the number of ether bond units in the polymer main chain increases, making the PBT resin susceptible to degradation due to hydrolysis under high temperature and high humidity conditions, and the soft segment content increases, making the material itself flexible and susceptible to deformation, resulting in a decrease in pull-out strength. Conversely, if this ratio (a/b) is too large, the hard segment content increases, raising the melting point and decreasing the coating stability. This ratio (a/b) is more preferably 18/82 or more, and even more preferably 22/78 or more. On the other hand, this ratio is more preferably 27/73 or less, and even more preferably 25/75 or less.

Furthermore, the melting point of the PBT resin is preferably in the range of 155°C or more and 230°C or less. If the melting point is too low, there is a risk of the adhesion with the inner coating layer being reduced. On the other hand, if the melting point is too high, there is a risk of the optical properties of the optical fiber being reduced due to the influence of the thermal history when the outermost coating layer is provided. The melting point of the PBT resin is more preferably 220°C or less, and even more preferably 210°C or less. The melting point of the PBT resin is more preferably 165°C or more, and even more preferably 175°C or more.
In this specification, the melting point is a value measured by a differential scanning calorimeter in accordance with ISO 3146:2000.

Such PBT resins can be selected from, for example, Hytrel 8068, 5547F, 6037F, and 7237F (trade names) manufactured by DuPont-Toray Co., Ltd., DURANEX series (trade name) manufactured by Polyplastics Co., Ltd., Pelprene S type and P type (trade name) manufactured by Toyobo Co., Ltd., Novaduran 5010N6-3X (trade name) manufactured by Mitsubishi Engineering Plastics Corporation, and Crastin series (trade name) manufactured by DuPont.
Among these, it is more preferable to use Hytrel 7237F (product name) manufactured by DuPont-Toray Co., Ltd. or Novaduran 5010N6-3X manufactured by Mitsubishi Engineering Plastics Corporation, because of their excellent flame retardancy.

In the material constituting the outermost coating layer, the lower limit of the content of PBT resin is not particularly limited, but from the viewpoint of improving the long-term heat resistance at 105°C and plasticizer resistance of the optical fiber cable, it is preferably 70% by mass or more relative to 100% by mass of the material constituting the outermost coating layer. 80% by mass or more is more preferable, and 90% by mass or more is even more preferable. The upper limit of the content of PBT resin in the material constituting the outermost coating layer is not particularly limited, and may be 100% by mass.

<Method of manufacturing optical fiber cable>
As a method for coating the outer circumference of an optical fiber with a coating layer, for example, a method using an extrusion coating device equipped with a crosshead die can be mentioned. In particular, when coating a plastic optical fiber with a coating layer, a method using an extrusion coating device equipped with a crosshead die is preferable because it can obtain an optical fiber cable with a uniform diameter.
When the coating layers are formed concentrically around the outside of the optical fiber core in the order of an inner coating layer and an outer coating layer, and when an outermost coating layer is further formed around the outer periphery of the outer coating layer, the coating layers may be formed one by one in order, or multiple coating layers may be formed simultaneously.

The extrusion temperature when coating the coating layer on the outer periphery of the optical fiber is preferably 200°C to 300°C, and more preferably 220°C to 280°C. When the extrusion temperature when coating the coating layer on the outer periphery of the optical fiber is 200°C or higher, the optical fiber cable has an excellent appearance. When the extrusion temperature when coating the coating layer on the outer periphery of the optical fiber is 300°C or lower, the original performance of the material that constitutes the coating layer is not impaired.

The optical fiber cable of the present invention has a wide transmission bandwidth and excellent long-term heat resistance, flexibility, and mechanical durability, and can therefore be suitably used for optical information communication, for example, inside trains, airplanes, automobiles, and other vehicles, and inside buildings, as well as in the field of factory automation (FA). It is particularly suitable for use in a bent state in a narrow space, such as inside an automobile or other vehicle, where it is exposed to mechanical stress and high temperature environments.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

(Measurement of refractive index)
A film-like test piece having a thickness of 200 μm was prepared by melt pressing, and the refractive index of sodium D line at 23° C. was measured in accordance with ISO 13468 using an Abbe refractometer (model name “NAR-3T”, manufactured by Atago Co., Ltd.).

(Melt Flow Index)
The melt flow index was measured in accordance with Japanese Industrial Standard JIS K7210 from the amount of resin extruded from a nozzle having a diameter of 2 mm and a length of 8 mm for 10 minutes under conditions of 230° C. and a load of 3.8 kg.

(Melting Point)
The melting point was measured by differential scanning calorimetry, using a differential scanning calorimeter (model: EXSTAR DSC6200, manufactured by Seiko Instruments Inc.) by raising the temperature of the sample at a heating rate of 20° C./min.

(Measurement of long-term heat resistance)
The optical fiber cables obtained in the examples and comparative examples were exposed to an environment at a temperature of 105° C. for 3000 hours, and were measured by a 25 m-1 m cutback method under conditions of a wavelength of 650 nm and an excitation NA of 0.1.
Measurements using the 25m-1m cutback method were performed in accordance with IEC 60793-1-40:2001. Specifically, a 25m optical fiber was set in the measurement device, and the output power P2 was measured, after which the optical fiber was cut to the cutback length (1m from the input end), the output power P1 was measured, and the optical transmission loss (unit: dB/km) was calculated using the following formula (1). The above measurements were performed in a light-shielded environment.

(Measurement of torsion resistance)
As an index of the twist resistance of the optical fiber cable, the twist light loss was measured by the following method using a homemade twist resistance tester.
A twisting test device used for measuring the twisting light loss of an optical fiber cable will be described with reference to FIG.
Using a homemade torsion test device, one end of a 2 m long optical fiber cable 31 near the center (approximately 25 cm) was fixed to one chuck (2) 32' of a pair of chucks 32, 32' (250 mm apart) arranged horizontally in the torsion test device.
An LED light source 33 (product name "TOTX170A", wavelength 660 nm) was connected to one end of an optical fiber cable having a length of 2 m, and an optical power meter 35 (product name "AQ1135E", manufactured by Ando Electric Co., Ltd., receiving sensitivity -70 dBm) equipped with a photodiode detector 34 was connected to the other end of the cable.
Next, a 500 gf weight 37 was hung via a pulley 36 on one side of the optical fiber cable 31 near the chuck (1) 32, thereby applying a tensile force to the optical fiber cable to hold it straight, and the amount of light (T1) after one minute was recorded.
Next, while maintaining a tension of 500 gf applied to the optical fiber cable, one of the chucks (2) 32' on one side of the optical fiber cable was rotated five times around the central axis of the optical fiber cable, and the light quantity (T2) after one minute was recorded. The twisting light quantity loss (unit: dB) was calculated using the following formula (2).

(material)
The following materials were used for the core material constituting the core of the optical fiber and the cladding material constituting the cladding.
First clad material (B-1): Fluorine resin (13FM/3FM/MMA/MAA copolymer, refractive index 1.417)
Second clad material (C-1): Fluorine resin (product name: RP4020, manufactured by Daikin Industries, Ltd., a copolymer containing tetrafluoroethylene units, ethylene units, hexafluoropropylene units, and perfluoro (1,1,5-trihydro-1-pentene units, and having reactive functional groups having carbonate groups at the ends of the main chain and/or side chain of the polymer chain. Refractive index: 1.380, melting point: 160°C, melt flow index: 11 g/10 min)
Second clad material (C-2): Fluorine resin (VDF/TFE/HFP copolymer, VDF:TFE:HFP=60:35:5 (molar ratio), refractive index 1.374, melting point 129°C, melt flow index 37g/10min)
EVOH resin (E-1): Ethylene-vinyl alcohol copolymer resin containing 29 mol% ethylene units. Oxygen permeability: 0.2 cc·20 μm/(m2·day·atm), melt flow index: 15 g/10 min (product name: Soarnol D2908, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.)
Polyamide resin (N-1): Polyamide 12. Oxygen permeability: 580 cc/20 μm/(m2/day/atm) (product name: Grilamid XE3926, manufactured by EMS-GRIVORY, melt flow index: 84 g/10 min)
Polybutylene terephthalate resin (X-1): PBT resin containing pigment (ultramarine blue) (product name "NOVADURAN5010N6-3X", manufactured by Mitsubishi Engineering Plastics Corporation)
In addition, "MMA" is an abbreviation for methyl methacrylate, "MAA" is an abbreviation for methacrylic acid, "13FM" is an abbreviation for 2-(perfluorohexyl)ethyl (meth)acrylate, "3FM" is an abbreviation for 2,2,2-trifluoroethyl (meth)acrylate, "VDF" is an abbreviation for vinylidene fluoride, "TFE" is an abbreviation for tetrafluoroethylene, and "HFP" is an abbreviation for hexafluoropropylene.

[Production Example 1] (Production of Optical Fiber)
The core material was polymethyl methacrylate (refractive index 1.492), the material of the first clad layer was the first clad material (B-1), and the material of the second clad layer was the second clad material (C-1). These were spun using a three-layer concentric composite spinning nozzle and stretched to twice the size in the fiber axis direction in a hot air heating furnace at 140°C, to obtain an optical fiber wire with a diameter of 1.0 mm, with a first clad layer thickness of 5 μm and a second clad layer thickness of 10 μm.

[Example 1]
The material constituting the inner coating layer was EVOH resin (E-1), the material constituting the outer coating layer was a mixture of 80 parts of polyamide resin (N-1) and 20 parts of EVOH resin (E-1), and the material constituting the outermost coating layer was polyethylene terephthalate resin (X-1). These materials were supplied to a resin coating crosshead type 40 mm cable coating device (manufactured by Hijiri Seisakusho Co., Ltd.), and the outer circumference of the optical fiber wire produced in Production Example 1 was coated with an inner coating layer (thickness 100 μm), an outer coating layer (thickness 155 μm), and an outermost coating layer (thickness 395 μm), to obtain an optical fiber cable with a diameter of 2.30 mm. The evaluation results of the obtained optical fiber cable are shown in Table 1.

[Comparative Example 1]
An optical fiber cable was obtained in the same manner as in Example 1, except that the material constituting the second cladding was changed as shown in Table 1. The evaluation results of the obtained optical fiber cable are shown in Table 2.

The optical fiber cable obtained in Example 1 was excellent in long-term heat resistance and ripening resistance.
On the other hand, the optical fiber cable obtained in Comparative Example 1 was inferior in twisting resistance to the optical fibers of the Examples.

10: Optical fiber 11: Core 12: Clad layer 12a: Clad (first clad layer)
12b Clad (second clad layer)
20 Covering layer 20a Covering layer (inner covering layer)
20b Coating layer (outer coating layer)
20c Coating layer (outermost coating layer)
31 Optical fiber cable 32 Chuck (1)
32' Chuck (2)
33 LED light source 34 Photodiode detector 35 Optical power meter 36 Pulley 37 Weight (500 g)

Claims (12)

An optical fiber having a core made of a transparent resin and at least one clad layer formed around the core; and
An optical fiber cable having at least one coating layer formed on the outside of the optical fiber,
a material constituting one of the clad layers, or a material constituting an outermost layer of two or more of the clad layers, comprises a modified fluororesin having a polymer chain containing tetrafluoroethylene units, ethylene units, hexafluoropropylene units, and perfluoro(1,1,5-trihydro-1-pentene) units, and having a reactive functional group having a carbonate group at an end of the main chain and/or a side chain;
An optical fiber cable , wherein a material constituting one of said coating layers, or a material constituting an innermost layer of said two or more coating layers , is made solely of an ethylene-vinyl alcohol-based resin. 2. The optical fiber cable according to claim 1, wherein a twisting loss of light when the optical fiber cable is twisted five times from a straight state is 0.12 dB or less as measured in a continuous twisting test. The optical fiber cable according to claim 1 or 2, wherein the content of vinyl alcohol units in the ethylene-vinyl alcohol resin is 50 to 80 mol % relative to 100 mol % of the total molar amount of the monomer units constituting the ethylene-vinyl alcohol resin. The optical fiber cable according to any one of claims 1 to 3, wherein the modified fluororesin is a fluororesin containing 24 to 58 mol% tetrafluoroethylene units, 30 to 68 mol% ethylene units, 7 to 28 mol% hexafluoropropylene units, and 1 to 10 mol% perfluoro(1,1,5-trihydro-1-pentene) units. The optical fiber cable according to any one of claims 1 to 4, wherein the modified fluororesin has a melting point in the range of 120 to 200°C. The optical fiber cable according to any one of claims 1 to 5, wherein the modified fluororesin has a refractive index of 1.34 to 1.41 at sodium D line measured at 23°C using an Abbe refractometer in accordance with ISO 13468. The optical fiber cable according to any one of claims 1 to 6, wherein the modified fluororesin has a melt flow index of 5 to 100 g/10 min measured at 230°C under a load of 3.8 kg. The coating layer is composed of at least two layers concentrically formed in the order of an inner coating layer and an outer coating layer,
8. The optical fiber cable according to claim 1, wherein a material constituting the inner coating layer includes an ethylene-vinyl alcohol-based resin, and a material constituting the outer coating layer includes a polyamide-based resin. An outermost coating layer is further provided around the outer coating layer,
9. The optical fiber cable according to claim 8, wherein a material constituting the outermost coating layer includes a polybutylene terephthalate resin. The optical fiber cable according to claim 8 or 9, wherein the material constituting the outer coating layer is a mixture of polyamide resin and ethylene-vinyl alcohol resin. The clad layer is composed of two or more layers,
a material constituting the first clad layer located on the inside includes a fluorinated methacrylate resin having a refractive index greater than that of the modified fluororesin;
The optical fiber cable according to any one of claims 1 to 10, wherein a material constituting the second cladding layer located on the outside contains the modified fluororesin. The optical fiber cable according to claim 11, wherein the fluorinated methacrylate resin is a copolymer containing fluoroalkyl (meth)acrylate units and methyl methacrylate units.