Plastic optical fiber

Abstract

To provide a plastic optical fiber usable for a sensor with a simple configuration.SOLUTION: The optical fiber 10 in the present disclosure includes a core 11, a cladding 12 disposed on an outer periphery of the core 11, and a coating layer 13 disposed on an outer periphery of the cladding 12 and at a position adjacent to the cladding 12. A gap portion 14 in which the cladding 12 and the coating layer 13 are not in direct contact with each other is provided in at least a part between the cladding 12 and the coating layer 13.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to plastic optical fibers. [Background technology]

[0002] In addition to being used for communications, optical fibers are also used as optical fiber sensors that utilize changes in the transmission characteristics of optical fibers. For example, Patent Document 1 discloses a fiber-reinforced optical fiber cable that can be molded into any shape, in which an optical fiber wire made of quartz glass or the like is covered with a resin protective layer, and a fiber-reinforced resin layer and a thermoplastic resin layer are further provided around the periphery of the wire, and an optical fiber sensor that uses the optical fiber cable. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-211642 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure aims to provide a plastic optical fiber that has superior flexibility to glass optical fibers and can be used in sensors with a simple configuration. [Means for solving the problem]

[0005] The present disclosure provides: The core and a cladding disposed on the outer periphery of the core; a coating layer disposed on the outer periphery of the clad and adjacent to the clad; Equipped with a gap portion is provided at least in a portion between the clad and the coating layer, where the clad and the coating layer are not in direct contact with each other; Provides plastic optical fiber. [Effects of the Invention]

[0006] According to the present disclosure, a plastic optical fiber that can be used for a sensor with a simple configuration can be provided. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing an example of the structure of a cross section perpendicular to the longitudinal direction of a plastic optical fiber according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view of the plastic optical fiber shown in FIG. 1 taken along line II. [Figure 3A] FIG. 3A is an image of a part of a cross section of a plastic optical fiber for which the void ratio is to be determined, the cross section passing through the central axis of the plastic optical fiber and along the length direction. [Figure 3B] FIG. 3B is an image of a part of a cross section of a plastic optical fiber for which the void ratio is to be determined, the cross section passing through the central axis of the plastic optical fiber and along the length direction. [Figure 4] FIG. 4 is a schematic cross-sectional view showing an example of a manufacturing apparatus that can be used to manufacture a plastic optical fiber according to an embodiment of the present disclosure. [Figure 5] FIG. 5 is a graph showing the results of the lateral pressure test. [Figure 6A] FIG. 6A is a graph showing the results of the environmental test (heat resistance test) for Examples 1, 2, and 5. [Figure 6B] FIG. 6B is a graph showing the results of the environmental test (heat resistance test) for Examples 3, 4, and 6. [Figure 7] FIG. 7 is an image showing the shape of the plastic optical fiber of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0008] Fig. 1 is a schematic diagram showing an example of the cross-sectional structure of a plastic optical fiber (hereinafter referred to as "POF") according to an embodiment of the present disclosure, taken perpendicular to the longitudinal direction of the POF. Fig. 2 is a cross-sectional view of the POF shown in Fig. 1 taken along line II.

[0009] The POF 10 according to this embodiment includes a core 11, a cladding 12, and a coating layer 13. The cladding 12 is disposed on the outer periphery of the core 11. The coating layer 13 is disposed on the outer periphery of the cladding 12 and adjacent to the cladding 12. A gap 14 is provided at least partially between the cladding 12 and the coating layer 13, where the cladding 12 and the coating layer 13 are not in direct contact with each other.

[0010] With the above-described configuration, the POF 10 of this embodiment can change the transmission loss (herein referred to as a specific change) even with a smaller pressure due to a change in pressure (lateral pressure) applied from the side of the POF 10. Therefore, by utilizing such a specific change in transmission loss, the POF 10 of this embodiment can detect pressure with high sensitivity and can be used as a sensor. That is, the POF 10 of this embodiment can be used as an optical fiber sensor that can detect, for example, a change in lateral pressure, with a simple configuration in which a gap 14 is provided at least partially between the cladding 12 and the coating layer 13.

[0011] The glass transition temperature Tg1 of the material of the core 11 is preferably 110° C. or higher. When the glass transition temperature Tg1 is in this range, the heat resistance temperature of the POF can be set high, and therefore it can be used for a long period of time even in harsh outdoor environments.

[0012] The glass transition temperature Tg1 of the material of the core 11 is, for example, 135° C. or lower.

[0013] In this specification, the glass transition temperature is the midpoint glass transition temperature (T mg ) means

[0014] Here, the material of the core 11 refers to the resin material that constitutes the core 11. The resin material used for the core 11 will be described in detail later.

[0015] When the glass transition temperature Tg1 of the material of the core 11 is 110° C. or higher, the glass transition temperature Tg2 of the material of the coating layer 13 may be, for example, 140° C. or higher and 150° C. or lower. In this case, the gap ratio of the POF 10, which is the ratio of the length of the gap 14 per unit length of the POF, is preferably 80% or lower, and more preferably 78% or lower.

[0016] When the glass transition temperature Tg1 of the material of the core 11 is 110°C or higher and the glass transition temperature Tg2 of the material of the coating layer 13 is 140°C or higher and 150°C or lower, the POF 10 of this embodiment can maintain a strong bond between the cladding 12 and the coating layer 13 while realizing a specific change in transmission loss due to changes in lateral pressure by setting the gap ratio to 80% or lower. This allows the lateral pressure sensor characteristics of the POF 10 to be improved with a simple configuration. Furthermore, setting the gap ratio to 78% or lower further improves the lateral pressure sensor characteristics of the POF 10.

[0017] Here, the gap ratio of the POF 10 is the ratio of the length of the gap 14 to the length of the boundary line between the cladding 12 and the coating layer 13 in a cross-sectional image of the POF 10 along its length.

[0018] The gap ratio will be explained in more detail using the example images shown in FIGS. 3A and 3B. The images shown in FIGS. 3A and 3B are images of a portion of a cross section (length: L) of a POF for which the gap ratio is to be determined, passing through the central axis of the POF and along the longitudinal direction. In each of the images shown in FIGS. 3A and 3B, the length of the boundary line between the cladding 12 and the coating layer 13 is 2L, which is the boundary line between the upper and lower sides of the image. In the images, the gap 14 is indicated by the black portion between the cladding 12 and the coating layer 13. In the image of FIG. 3A, the gap 14, where the cladding 12 and the coating layer 13 do not contact, is the entire upper boundary line (length a) and a portion of the lower boundary line (length b). In the image of FIG. 3B, the gap 14, where the cladding 12 and the coating layer 13 do not contact, is the entire upper boundary line (length c), and the lower boundary line does not include the gap 14. In this way, n images of any location on the POF for which the gap ratio is to be determined are acquired, and the length of the gap 14 is determined for each of the acquired n images. The images for determining the gap ratio are acquired by a line sensor camera. The gap ratio is calculated by the following mathematical formula (I) using the length of the gap 14 determined for each of the acquired n images.

[0019] Gap ratio (%) = {Σp / (2L×n)}×100 (I) p: length of gap in each image L: Length of POF in each image n: Number of images used to identify the gap ratio

[0020] If the gap ratio is calculated using the two images shown in FIGS. 3A and 3B, Σp=a+b+c n=2 Therefore, the gap ratio is {(a+b+c) / 2L×2}×100(%).

[0021] The length L of the POF in each image is, for example, 500 μm, and the number of images used to identify the gap ratio is, for example, 20.

[0022] When the glass transition temperature Tg1 of the material of the core 11 is 110°C or higher and the glass transition temperature Tg2 of the material of the coating layer 13 is 140°C or higher and 150°C or lower, the void ratio of the POF 10 is preferably 40% or higher. This configuration makes it easier for the POF 10 to realize a specific change in transmission loss due to a change in lateral pressure, thereby further improving the lateral pressure sensor characteristics of the POF 10. In this case, the void ratio of the POF 10 may be 74% or higher.

[0023] When the glass transition temperature Tg1 of the material of the core 11 is 110° C. or higher, the glass transition temperature Tg2 of the material of the coating layer 13 may be 110° C. or higher and 120° C. or lower. In this case, the gap ratio of the POF 10, which is the ratio of the length of the gap 14 per unit length of the POF, is preferably 15% or lower, and more preferably 12% or lower.

[0024] When the glass transition temperature Tg1 of the material of the core 11 is 110°C or higher and the glass transition temperature Tg2 of the material of the coating layer 13 is 110°C or higher and 120°C or lower, by setting the gap ratio to 15% or lower, the POF 10 of this embodiment can maintain a strong bond between the cladding 12 and the coating layer 13 while realizing a specific change in transmission loss due to changes in lateral pressure. This allows the lateral pressure sensor characteristics of the POF 10 to be improved with a simple configuration. Furthermore, by setting the gap ratio to 12% or lower, the lateral pressure sensor characteristics of the POF 10 can be further improved.

[0025] When the glass transition temperature Tg1 of the material of the core 11 is 110°C or higher and the glass transition temperature Tg2 of the material of the coating layer 13 is 110°C or higher and 120°C or lower, the void ratio of the POF 10 is preferably 3% or higher. This configuration makes it easier for the POF 10 to realize a specific change in transmission loss due to a change in lateral pressure, thereby further improving the lateral pressure sensor characteristics of the POF 10. In this case, the void ratio of the POF 10 may be 11% or higher.

[0026] When the difference between the glass transition temperature Tg1 of the material of the core 11 and the glass transition temperature Tg2 of the material of the coating layer 13 is ΔTg, for example, the following (A) or (B) may be satisfied. (A) ΔTg≦8° C., and the gap ratio, which is the ratio of the length of the gap 14 per unit length of the POF 10, is 12% or less. (B) 8° C.<ΔTg, and the gap ratio, which is the ratio of the length of the gap 14 per unit length of the POF 10, is 78% or less.

[0027] By satisfying the above (A) or (B), the POF 10 of this embodiment can maintain a strong bond between the cladding 12 and the coating layer 13 and realize a specific change in transmission loss due to a change in lateral pressure. This allows the lateral pressure sensor characteristics of the POF 10 to be improved with a simple configuration.

[0028] When the POF 10 of this embodiment satisfies the above (A), the gap ratio may be 3% or more, or may be 11% or more.

[0029] When the POF 10 of this embodiment satisfies the above (B), the gap ratio may be 40% or more, or may be 74% or more.

[0030] The gap 14 may be provided, for example, in a spiral shape around the core 11. With this configuration, the POF 10 of this embodiment can detect pressure more accurately even when pressure is applied from various directions by reducing the difference depending on the direction in which the pressure is applied.

[0031] Each component of the POF 10 of this embodiment will be described in more detail below.

[0032] (Core 11) The core 11 is a region that transmits light. The core 11 is made of a resin material that has a higher refractive index than the cladding 12. With this configuration, light that enters the core 11 is confined within the core 11 by the cladding 12 and propagates through the POF 10.

[0033] Core 11 includes a first resin. Core 11 may include the first resin as a main component. Here, "core 11 includes the first resin as a main component" means that the component contained in core 11 in the largest amount by mass is the first resin. Core 11 may include 75% by mass or more, 80% by mass or more, or 85% by mass or more of the first resin.

[0034] The core 11 may further contain an additive in addition to the first resin. The additive is, for example, a refractive index adjuster. That is, the core 11 may be formed of a resin composition containing the first resin and an additive such as a refractive index adjuster. As the refractive index adjuster, for example, a known refractive index adjuster used in the material of the core 11 of the POF 10 may be used. The material of the core 11 may contain an additive other than the refractive index adjuster.

[0035] When the POF 10 is, for example, a graded index (GI) type, the core 11 has a refractive index profile in which the refractive index varies in the radial direction (see the arrows in FIG. 1 ). Such a refractive index profile can be formed, for example, by adding a refractive index adjuster to the first resin and diffusing (for example, thermally diffusing) the refractive index adjuster in the first resin.

[0036] The first resin contained in the core 11 is not particularly limited as long as it is a resin having high transparency. Examples of the first resin include fluorine-containing resins, acrylic resins such as methyl methacrylate, styrene-based resins, and carbonate-based resins.

[0037] The first resin contained in the core 11 may be at least one selected from the group consisting of a fully fluorinated resin, a partially fluorinated resin, a partially chlorinated resin, and a partially deuterated resin. The terms partially fluorinated resin, partially chlorinated resin, and partially deuterated resin refer to resins known in the art as core materials for POFs in which some of the hydrogen atoms in C-H bonds have been substituted with fluorine, chlorine, and deuterium, respectively. The term fully fluorinated resin refers to resins known in the art as core materials for POFs in which all of the hydrogen atoms in C-H bonds have been substituted with fluorine. Examples of resins known in the art as core materials include acrylic resins such as methyl methacrylate, styrene resins, and carbonate resins, as described above. Polymers having an alicyclic structure, such as a polymer having a dioxolane structure, may also be used.

[0038] The first resin is preferably at least one selected from the group consisting of fully fluorinated resins and partially fluorinated resins, that is, the first resin is preferably a fluorine-containing resin.

[0039] The first resin of core 11 is preferably a fluororesin containing a fluoropolymer. Hereinafter, the fluororesin contained in core 11 will be referred to as the first fluororesin, and the fluoropolymer contained in the first fluororesin will be referred to as the first fluoropolymer.

[0040] From the viewpoint of suppressing light absorption due to the stretching energy of C-H bonds, the first fluorine-containing polymer contained in the first fluorine-containing resin preferably contains substantially no hydrogen atoms, and particularly preferably has all hydrogen atoms bonded to carbon atoms substituted with fluorine atoms. That is, the first fluorine-containing polymer preferably contains substantially no hydrogen atoms and is perfluorinated. In this specification, "the fluorine-containing polymer contains substantially no hydrogen atoms" means that the content of hydrogen atoms in the fluorine-containing polymer is 1 mol% or less.

[0041] The first fluorine-containing polymer preferably has a fluorine-containing alicyclic structure. The fluorine-containing alicyclic structure may be contained in the main chain of the fluorine-containing polymer or in a side chain of the first fluorine-containing polymer. The first fluorine-containing polymer has, for example, a structural unit (A) represented by the following formula (1): [ka]

[0042] In formula (1), R ff 1 ~R ff 4 R each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. ff 1 and R ff 2 may be linked to form a ring. "Perfluoro" means that all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. In formula (1), the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5, more preferably 1 to 3, and even more preferably 1. The perfluoroalkyl group may be linear or branched. Examples of perfluoroalkyl groups include a trifluoromethyl group, a pentafluoroethyl group, and a heptafluoropropyl group.

[0043] In formula (1), the number of carbon atoms in the perfluoroalkyl ether group is preferably 1 to 5, and more preferably 1 to 3. The perfluoroalkyl ether group may be linear or branched. Examples of the perfluoroalkyl ether group include a perfluoromethoxymethyl group.

[0044] R ff 1 and R ff 2When these are linked to form a ring, the ring may be a 5-membered ring or a 6-membered ring. Examples of this ring include a perfluorotetrahydrofuran ring, a perfluorocyclopentane ring, and a perfluorocyclohexane ring.

[0045] Specific examples of the structural unit (A) include structural units represented by the following formulas (A1) to (A8). [ka]

[0046] Of the structural units represented by the above formulas (A1) to (A8), the structural unit (A) is preferably the structural unit (A2), ie, the structural unit represented by the following formula (2). [ka]

[0047] The first fluorine-containing polymer may contain one or more types of structural unit (A). In the first fluorine-containing polymer, the content of the structural unit (A) is preferably 20 mol % or more, more preferably 40 mol % or more, based on the total of all structural units. When the structural unit (A) is contained in an amount of 20 mol % or more, the first fluorine-containing polymer tends to have higher heat resistance. When the structural unit (A) is contained in an amount of 40 mol % or more, the first fluorine-containing polymer tends to have higher transparency and high mechanical strength in addition to high heat resistance. In the first fluorine-containing polymer, the content of the structural unit (A) is preferably 95 mol % or less, more preferably 70 mol % or less, based on the total of all structural units.

[0048] The structural unit (A) is derived from, for example, a compound represented by the following formula (3): ff 1 ~R ff 4is the same as formula (1). The compound represented by formula (3) can be obtained by a known production method, such as the production method disclosed in JP-A-2007-504125. [ka]

[0049] Specific examples of the compound represented by the above formula (3) include compounds represented by the following formulae (M1) to (M8). [ka]

[0050] The fluorine-containing polymer may further contain other structural units in addition to the structural unit (A). Examples of the other structural units include the following structural units (B) to (D).

[0051] The structural unit (B) is represented by the following formula (4). [ka]

[0052] In formula (4), R 1 ~R 3 R each independently represents a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms. 4 represents a perfluoroalkyl group having 1 to 7 carbon atoms. The perfluoroalkyl group may have a ring structure. Some of the fluorine atoms may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkyl group may be substituted with halogen atoms other than fluorine atoms.

[0053] The fluorine-containing polymer may contain one or more types of structural unit (B). In the fluorine-containing polymer, the content of the structural unit (B) is preferably 5 to 10 mol % based on the total of all structural units. The content of the structural unit (B) may be 9 mol % or less, or may be 8 mol % or less.

[0054] The structural unit (B) is derived from, for example, a compound represented by the following formula (5): In formula (5), R 1 ~R 4 is the same as formula (4). The compound represented by formula (5) is a fluorine-containing vinyl ether such as perfluorovinyl ether. [ka]

[0055] The structural unit (C) is represented by the following formula (6). [ka]

[0056] In formula (8), R 5 ~R 8 each independently represents a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms. The perfluoroalkyl group may have a ring structure. Some of the fluorine atoms may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkyl group may be substituted with halogen atoms other than fluorine atoms.

[0057] The fluorine-containing polymer may contain one or more types of structural unit (C). In the fluorine-containing polymer, the content of the structural unit (C) is preferably 5 to 10 mol % based on the total of all structural units. The content of the structural unit (C) may be 9 mol % or less, or may be 8 mol % or less.

[0058] The structural unit (C) is derived from, for example, a compound represented by the following formula (7): 5 ~R 8 is the same as formula (6). The compound represented by formula (7) is a fluorine-containing olefin such as tetrafluoroethylene or chlorotrifluoroethylene. [ka]

[0059] The structural unit (D) is represented by the following formula (8). [ka]

[0060] In formula (8), Z is an oxygen atom, a single bond, or —OC(R 19 R 20 )O-, R 9 ~R 20 each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a perfluoroalkoxy group having 1 to 5 carbon atoms. Some of the fluorine atoms may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkyl group may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkoxy group may be substituted with halogen atoms other than fluorine atoms. s and t each independently represent an integer of 0 to 5, and s+t is an integer of 1 to 6 (provided that Z is -OC(R 19 R 20 )O-, s+t may be 0).

[0061] The structural unit (D) is preferably represented by the following formula (9): The structural unit represented by the following formula (9) is the structural unit represented by the above formula (8) in which Z is an oxygen atom, s is 0, and t is 2. [ka]

[0062] In formula (11), R 141 , R 142 , R 151 , and R 152each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a perfluoroalkoxy group having 1 to 5 carbon atoms. Some of the fluorine atoms may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkyl group may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkoxy group may be substituted with halogen atoms other than fluorine atoms.

[0063] The fluorine-containing polymer may contain one or more types of structural unit (D). In the fluorine-containing polymer, the content of the structural unit (D) is preferably 30 to 67 mol% based on the total of all structural units. The content of the structural unit (D) is, for example, 35 mol% or more, and may be 60 mol% or less, or may be 55 mol% or less.

[0064] The structural unit (D) is derived from a compound represented by the following formula (10): In formula (10), Z, R 9 ~R 18 , s and t are the same as in formula (8). The compound represented by formula (10) is a fluorine-containing compound which has two or more polymerizable double bonds and is capable of cyclopolymerization. [ka]

[0065] The structural unit (D) is preferably derived from a compound represented by the following formula (11): 141 , R 142 , R 151 , and R 152 is the same as equation (9). [ka]

[0066] Specific examples of the compound represented by formula (10) or formula (11) include the following compounds. CF2=CFOCF2CF=CF2 CF2=CFFOCF(CF3)CF=CF2 CF2=CFOCF2CF2CF=CF2 CF2=CFOCF2CF(CF3)CF=CF2 CF2=CFOCF(CF3)CF2CF=CF2 CF2=CFOCFClCF2CF=CF2 CF2=CFOCCl2CF2CF=CF2 CF2=CFOCF2OCF=CF2 CF2=CFOC(CF3)2OCF=CF2 CF2=CFOCF2CF(OCF3)CF=CF2 CF2=CFCF2CF=CF2 CF2=CFCF2CF2CF=CF2 CF2=CFCF2OCF2CF=CF2 CF2=CFOCF2CFClCF=CF2 CF2=CFOCF2CF2CCl=CF2 CF2=CFOCF2CF2CF=CFCl CF2=CFOCF2CF(CF3)CCl=CF2 CF2=CFOCF2OCF=CF2 CF2=CFOCCl2OCF=CF2 CF2=CClOCF2OCCl=CF2

[0067] The first fluorine-containing polymer may further contain other structural units than the structural units (A) to (D), but preferably does not substantially contain other structural units than the structural units (A) to (D). Here, "the fluorine-containing polymer does not substantially contain other structural units than the structural units (A) to (D)" means that the total of the structural units (A) to (D) is 95 mol % or more, preferably 98 mol % or more, of the total of all structural units in the fluorine-containing polymer.

[0068] The polymerization method for the first fluorine-containing polymer is not particularly limited, and for example, a general polymerization method such as radical polymerization can be used. The polymerization initiator for polymerizing the fluorine-containing polymer may be a perfluorinated compound.

[0069] The first fluorine-containing polymer constitutes a first fluorine-containing resin used as the first resin. The first resin has a first glass transition temperature of, for example, more than 105°C and not more than 140°C, and may be 110°C or 120°C or higher.

[0070] As described above, the glass transition temperature Tg1 of the material of core 11 is preferably, for example, 110° C. or higher. When core 11 is formed of, for example, a resin composition containing a first resin and a refractive index adjuster, the glass transition temperature of the resin composition corresponds to the glass transition temperature Tg1 of the material of core 11.

[0071] (Clad 12) In the POF 10 of this embodiment, the cladding 12 includes, for example, a second resin. The cladding 12 may include the second resin as a main component. Here, "the cladding 12 includes the second resin as a main component" means that the component that is contained in the cladding 12 in the largest amount by mass ratio is the second resin. The cladding 12 may include 80% by mass or more of the second resin, 90% by mass or more, or 95% by mass or more of the second resin. The cladding 12 may be made only of the second resin. The cladding 12 may further include an additive in addition to the second resin.

[0072] The second resin contained in the clad 12 is not particularly limited as long as it is a resin having high transparency. Examples of the second resin are the same as those exemplified as the resin that can be used as the first resin. As with the first resin, a fluorine-containing resin is preferably used as the second resin.

[0073] The second resin of the clad 12 is preferably a fluororesin containing a fluoropolymer. Hereinafter, the fluororesin contained in the clad 12 will be referred to as the second fluororesin, and the fluoropolymer contained in the second fluororesin will be referred to as the second fluoropolymer.

[0074] As the second fluorine-containing resin, any of the fluorine-containing resins exemplified as the fluorine-containing resin that can be used as the first fluorine-containing resin can be used.

[0075] As the second fluorine-containing resin, a fluorine-containing resin containing a fluorine-containing polymer having an amorphous structure and further containing a constituent unit (E) represented by the following formula (12), and a fluorine-containing plasticizer may be used. [ka] (In formula (12), Z is an oxygen atom, a single bond, or —OC(R 31 R 32 )O-, R 21 ~R 32 each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a perfluoroalkoxy group having 1 to 5 carbon atoms. "Perfluoro" means that all hydrogen atoms bonded to carbon atoms have been substituted with fluorine atoms. Some of the fluorine atoms may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkyl group may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkoxy group may be substituted with halogen atoms other than fluorine atoms. s and t each independently represent an integer of 0 to 5, and s+t is an integer of 1 to 6 (provided that Z is not -OC(R 31 R 32 ) In the case of O-, s+t may be 0. u and v are each independently 0 or 1.

[0076] The fluorine-containing polymer containing the structural unit (E) may further contain a structural unit (F) represented by the following formula (13). [ka] (In formula (13), R 33 ~R 36 each independently represents a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms. The perfluoroalkyl group may have a ring structure. Some of the fluorine atoms may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkyl group may be substituted with halogen atoms other than fluorine atoms.

[0077] When the second fluorine-containing polymer is the above copolymer, the ratio of the structural unit (E) to the structural unit (F) is optional and is not particularly limited.

[0078] The second fluorine-containing polymer is preferably, for example, at least one selected from the group consisting of fluorine-containing polymer A and fluorine-containing polymer B shown below.

[0079] The fluorine-containing polymer A contains a structural unit (G) represented by the following formula (14) and a structural unit (H) represented by the following formula (15). 23 , R 24 , R 31 , and R 32 is the same as the above equation (12).

[0080] [ka] [ka] (In formula (15), R 37 ~R 40 each independently represents a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms. The perfluoroalkyl group may have a ring structure. Some of the fluorine atoms may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkyl group may be substituted with halogen atoms other than fluorine atoms.

[0081] The fluorine-containing polymer B contains a structural unit (I) represented by the following formula (16): 21 ~R 24 , R 27 ~R 30 , R 31 , and R 32 is the same as the above equation (12). [ka]

[0082] The above-mentioned fluorine-containing polymer A and fluorine-containing polymer B have very high transparency and can have a refractive index that is very low compared with the general refractive index of the first fluorine-containing resin used as the material for the core 11. Therefore, the second fluorine-containing resin containing at least one selected from the group consisting of fluorine-containing polymer A and fluorine-containing polymer B as the second fluorine-containing polymer can further reduce the refractive index while maintaining the high transparency of the cladding 12. As a result, the difference between the refractive index of the core 11 and the refractive index of the cladding 12 can be made even larger, which further improves the effect of confining light in the core 11 by the cladding 12 and makes it easier to achieve low transmission loss in the optical fiber 10.

[0083] The second fluorine-containing polymer preferably contains a structural unit (J) represented by the following formula (17). [ka] (In formula (17), m and n are any integers.)

[0084] The fluorine-containing plasticizer is preferably a fluorine-containing polyether, more preferably a perfluoropolyether.

[0085] Specific examples of perfluoropolyethers include organic compounds represented by the following formula (18) or (19): In the following formulas (18) and (19), p1, q1, p2, and q2 each represent an arbitrary integer. CF3-[(O(CF3)CFCF2) p1 -(OCF2) q1 ]OCF3(18) CF3-[(OCF2CF2) p2 -(OCF2) q2 ]OCF3(19)

[0086] The second fluorine-containing polymer constitutes a second fluorine-containing resin used as the second resin. The second glass transition temperature Tg3 of the second resin is not particularly limited and may be, for example, higher than 105°C and not higher than 170°C, or 125°C or higher.

[0087] (Coating layer 13) Examples of materials for the coating layer 13 include various engineering plastics such as polycarbonate, polyester, cycloolefin polymer, cycloolefin copolymer, polytetrafluoroethylene (PTFE), modified PTFE, and tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), or copolymers or mixtures thereof.

[0088] As described above, the material of the coating layer 13 may be, for example, a material having a glass transition temperature Tg2 of 140°C or higher and 150°C or lower, or a material having a glass transition temperature Tg2 of 110°C or higher and 120°C or lower.

[0089] The thickness of the coating layer 13 is preferably, for example, 50 μm or more and 250 μm or less. When the thickness of the coating layer 13 is 50 μm or more, the core 11 and the cladding 12 can be sufficiently protected by the coating layer 13, thereby obtaining a highly reliable POF 10. When the thickness of the coating layer 13 is 250 μm or less, a highly flexible POF 10 can be obtained.

[0090] The POF 10 of this embodiment is suitable for use in sensors, but can also be used as a POF for communications.

[0091] (POF manufacturing method) The POF 10 of this embodiment is manufactured by, for example, a melt spinning method. That is, an example of a manufacturing method of the POF 10 of this embodiment is as follows: melting a core material and extruding it into a fiber shape to produce a fiber-shaped molded body made of the core material; melting a clad material and extruding it to cover the surface of the molded body, thereby producing a first laminate in which the core material and the clad material are concentrically laminated; a material for forming a coating layer is melted and extruded to cover the surface of the first laminate, thereby producing a second laminate in which the core material, the cladding material, and the material for forming the coating layer are concentrically laminated; Includes:

[0092] The core material includes, for example, a first resin. The clad material includes, for example, a second resin. Examples of materials for forming the coating layer are as described above.

[0093] When producing a fiber-shaped molded body made of a core material, a first core material containing a refractive index control agent may be extruded first to form an inner core layer, and then a second core material may be extruded so as to cover the outer periphery of the inner core layer 2 formed of the first core material 1a. In this case, the refractive index control agent contained in the first core material is diffused toward the outer periphery of the core formed of the second core material, thereby forming a core 11 having a refractive index profile.

[0094] The gap 14 can be formed at least partially between the cladding 12 and the coating layer 13 by, for example, adjusting the glass transition temperatures of the materials forming each layer of the POF 10, or, when the POF 10 is manufactured by melt spinning, by controlling the temperature during spinning and applying lateral pressure to the filament immediately after spinning (i.e., the second laminate described above). The gap ratio can be adjusted by appropriately combining these methods. An example of the combination of the glass transition temperatures of the materials forming each layer of the POF 10 is adjusting the glass transition temperature Tg1 of the material of the core 11 and the glass transition temperature Tg2 of the material of the coating layer 13. Examples of the combination of the glass transition temperature Tg1 of the material of the core 11 and the glass transition temperature Tg2 of the material of the coating layer 13 are as described above.

[0095] FIG. 4 is a schematic cross-sectional view showing an example of a manufacturing apparatus that can be used to manufacture the POF 10 shown in FIG.

[0096] The apparatus 1000 shown in FIG. 4 includes a first extrusion device 101a for extruding a first core material, a second extrusion device 101b for extruding a second core material, a third extrusion device 101c for extruding a cladding material, and a fourth extrusion device 101d for forming a coating layer.

[0097] The first extrusion device 101a has a first storage section 102a that stores the first core material 1a and a first extrusion section 103a that extrudes the first core material 1a stored in the first storage section 102a from the first storage section 102a. The first extrusion device 101a is further provided with a heating section (not shown) so that the first core material 1a can be melted in the first storage section 102a and the molten first core material 1a can be maintained in a molten state until it is molded. A rod-shaped first core material (preform) 1a is inserted into the first storage section 102a through an upper opening and is heated and melted in the first storage section 102a.

[0098] In the first extrusion device 101a, the first core material 1a is extruded by gas extrusion from the first storage section 102a through the first extrusion section 103a to form the inner core layer section 2. The first core material 1a extruded through the first extrusion section 103a to form the inner core layer section 2 then moves vertically downward and is supplied to the first chamber 110.

[0099] The second extrusion device 101b has a second storage section 102b that stores the second core material 1b and a second extrusion section 103b that extrudes the second core material 1b stored in the second storage section 102b from the second storage section 102b. The second extrusion device 101b extrudes the molten second core material so as to cover the outer periphery of the inner core layer section 2 formed from the first core material 1a extruded from the first extrusion device 101a. Specifically, the second core material extruded from the second extrusion device 101b is supplied to a first chamber 110. In the first chamber 110, the inner core layer section 2 formed from the first core material 1a is covered with the second core material, thereby forming an outer core section 3 that covers the outer periphery of the inner core layer section 2. The laminate 4 formed of the inner core layer portion 2 and the outer core portion 3 covering the outer periphery of the inner core layer portion 2 moves from the first chamber 110 to the diffusion tube 120 arranged vertically below the first chamber 110. A heater (not shown) for heating the laminate is arranged in the diffusion tube 120. The diffusion tube 120 diffuses the refractive index adjuster and the like contained in the inner core layer portion 2 of the laminate 4 passing through the inside of the diffusion tube 120 toward the outer core portion 3. In other words, the inner core layer portion 2 and the outer core portion 3 ultimately form a core.

[0100] The third extrusion device 101c has a third housing section 102c that houses the clad material 1c and a third extrusion section 103c that extrudes the clad material 1c housed in the third housing section 102c from the third housing section 102c. The third extrusion device 101c extrudes the molten clad material 1c so as to coat the outer periphery of the laminate 4 that has passed through the diffusion tube 120. Specifically, the clad material 1c extruded from the third extrusion device 101c is supplied to a second chamber 130. In the second chamber 130, the laminate 4 (i.e., the core) is coated with the clad material 1c, thereby forming a clad 5 that covers the outer periphery of the core. Hereinafter, the laminate 4 will be referred to as the core 4. The laminate formed of the core 4 and the clad 5 moves from the second chamber 130 to a third chamber 140 located vertically below the second chamber 130.

[0101] The fourth extrusion device 101d includes a fourth storage section 102d that stores the material 1d for forming the coating layer, a screw 104 disposed in the fourth storage section 102d, and a hopper 105 connected to the fourth storage section 102d. In the fourth extrusion device 101d, the material 1d, for example, in pellet form, is supplied to the fourth storage section 102d through the hopper 105. The material 1d supplied to the fourth storage section 102d is kneaded by the screw 104 while being heated, thereby softening and becoming flowable. The softened material 1d is extruded from the fourth storage section 102d by the screw 104.

[0102] The material 1d extruded from the fourth extrusion device 101d is supplied to the third chamber 140. In the third chamber 140, the surface of the first laminate formed of the core 4 and the clad 5 is coated with the material 1d, thereby forming a coating layer 6 that covers the outer periphery of the clad 5.

[0103] The second laminate 7, in which the core 4, the clad 5, and the coating layer 6 are concentrically laminated, flows from the third chamber 140 into the internal flow path through the inlet of the nozzle 150. The second laminate 7 is reduced in diameter as it passes through the internal flow path, and is discharged from the outlet of the nozzle 150 in the form of a fiber.

[0104] The second laminate 7 discharged in a fiber form from the discharge port of the nozzle 150 flows into the internal space 161 of the cooling pipe 160, is cooled while passing through the internal space 161, and is discharged from the opening to the outside of the cooling pipe 160. The second laminate 7 discharged from the cooling pipe 160 passes between two rolls 171 and 172 of the nip roll 170, and further passes through guide rolls 173 to 175 to be taken up on a take-up roll 176 as a POF 10. A displacement meter 180 for measuring the outer diameter of the POF 10 may be further provided near the take-up roll 176, for example, between the guide roll 175 and the take-up roll 176. [Example]

[0105] Example 1 [Preparation of first fluorine-containing resin] As the first fluorine-containing resin, a polymer of perfluoro-4-methyl-2-methylene-1,3-dioxolane (PFMMD) was prepared. Perfluoro-4-methyl-2-methylene-1,3-dioxolane was synthesized by first synthesizing 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane, fluorinating it, and then separating the resulting carboxylate by decarboxylation. Perfluorobenzoyl peroxide was used as the polymerization initiator for the polymerization of perfluoro-4-methyl-2-methylene-1,3-dioxolane.

[0106] The synthesis of 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane, the fluorination of 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane, the synthesis of perfluoro-4-methyl-2-methylene-1,3-dioxolane, and the polymerization of perfluoro-4-methyl-2-methylene-1,3-dioxolane are described in detail below.

[0107] <Synthesis of 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane> A 3 L three-neck flask equipped with a water-cooled condenser, a thermometer, a magnetic stirrer, and a pressure-equalizing dropping funnel was prepared. 139.4 g (1.4 mol total) of a mixture of 2-chloro-1-propanol and 1-chloro-2-propanol was added to the flask. The flask was cooled to 0 °C, and methyl trifluoropyruvate was slowly added and stirred for an additional 2 hours. 100 mL of dimethyl sulfoxide (DMSO) and 194 g of potassium carbonate were added over 1 hour, followed by stirring for an additional 8 hours to obtain a reaction mixture. The resulting reaction mixture was mixed with 1 L of water, and the aqueous phase was separated. This was then extracted with dichloromethylene. The dichloromethylene solution was mixed with the organic reaction mixture phase, and the resulting solution was dried over magnesium sulfate. After removing the solvent, 245.5 g of crude product was obtained. This crude product was fractionally distilled under reduced pressure (12 Torr) to obtain 230.9 g of purified 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane. The boiling point of the purified product was 77-78°C, and the yield was 77%. The purified product was confirmed to be 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane by HNMR and 19 This was confirmed by FNMR.

[0108] HNMR(ppm):4.2-4.6,3.8-3.6(CHCH2,multiplet,3H),3.85-3.88(COOCH3,multiplet,3H),1.36-1.43(CCH3,multiplet,3H) 19 FNMR(ppm):-81.3(CF3,s,3F)

[0109] <Fluorination of 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane> A 10 L stirred reactor was charged with 4 L of 1,1,2-trichlorotrifluoroethane. Nitrogen was introduced into the stirred reactor at a flow rate of 1340 cc / min, and fluorine was introduced at a flow rate of 580 cc / min, creating a nitrogen / fluorine atmosphere. Five minutes later, 290 g of the previously prepared 2-carbomethyl-2-trifluoromethyl-4-methyl-1,3-dioxolane was dissolved in 750 mL of 1,1,2-trichlorotrifluoroethane solution, and this solution was added to the reactor at a rate of 0.5 mL / min. The reactor was cooled to 0°C. After adding all the dioxolane over 24 hours, the fluorine gas flow was stopped. After purging with nitrogen, an aqueous potassium hydroxide solution was added until the mixture became slightly alkaline.

[0110] After removing volatile materials under reduced pressure, the reaction vessel was cooled to ambient temperature and then dried under reduced pressure at 70°C for 48 hours to obtain a solid reaction product. The solid reaction product was dissolved in 500 mL of water, and excess hydrochloric acid was added to separate the product into an organic phase and an aqueous phase. The organic phase was separated and distilled under reduced pressure to obtain perfluoro-2,4-dimethyl-1,3-dioxolane-2-carboxylic acid. The boiling point of the main distillate was 103°C-106°C / 100 mmHg. The fluorination yield was 85%.

[0111] <Synthesis of perfluoro-4-methyl-2-methylene-1,3-dioxolane> The distillate was neutralized with aqueous potassium hydroxide to obtain perfluoro-2,4-dimethyl-2-potassium carboxylate-1,3-dioxolane. The potassium salt was vacuum dried at 70°C for 1 day. The salt was decomposed at 250-280°C under a nitrogen or argon atmosphere. Condensation was carried out in a cold trap cooled to -78°C to obtain perfluoro-4-methyl-2-methylene-1,3-dioxolane in 82% yield. The boiling point of the product was 45°C / 760mmHg. 19 The products were identified using FNMR and GC-MS.

[0112] 19 FNMR:-84ppm(3F,CF3),-129ppm(2F,=CF2) GC-MS:m / e244(Molecular ion)225,197,169,150,131,100,75,50.

[0113] <Polymerization of perfluoro-4-methyl-2-methylene-1,3-dioxolane> 100 g of the perfluoro-4-methyl-2-methylene-1,3-dioxolane obtained above and 1 g of perfluorobenzoyl peroxide were sealed in a glass tube. The glass tube was degassed by freeze-degassing, then refilled with argon and heated at 50°C for several hours. The contents became solid, but further heating at 70°C overnight yielded 100 g of a transparent rod.

[0114] The obtained transparent rod-like substance was dissolved in Fluorinert FC-75 (manufactured by Sumitomo 3M), and the obtained solution was poured onto a glass plate to obtain a thin film of the polymer. The obtained polymer had a glass transition temperature of 117°C and was completely amorphous. The transparent rod-like substance was dissolved in hexafluorobenzene, and chloroform was added thereto to cause precipitation, thereby purifying the product. The glass transition temperature of the purified polymer was approximately 131°C. This polymer was designated as the first fluorine-containing resin.

[0115] [Refractive index adjuster] Chlorotrifluoroethylene oligomer (molecular weight 700 to 850) was used as the refractive index adjuster. Specifically, Daikin Industries, Ltd.'s "Dafloil #10" was distilled, and the component with a molecular weight of 700 to 850 was separated. The separated component with a molecular weight of 700 to 850 was filtered through a 40 nm pore size filter "DFA1ANDESW44" (PALL Corporation) to obtain the refractive index adjuster.

[0116] [First core material] The first fluorine-containing resin prepared by the above method was dissolved in a solvent, Vertrel XF-UP (manufactured by Mitsui-Chemours Fluoroproducts). The solution was filtered twice using a 100 nm pore size filter, "LPJ-CTA-001-N3" (manufactured by Roki Techno Corporation), and the filtrate was dropped into a Hastelloy container heated to 260°C to evaporate the solvent and dry the mixture. The filtered fluorine-containing resin obtained by drying and solidifying it and the refractive index modifier were melt-mixed at 260°C to prepare a resin composition. The concentration of the refractive index modifier in the resulting resin composition was 12% by mass. This resin composition was used as the first core material.

[0117] [Second core material] The first fluororesin prepared by the above method was filtered in the same manner as in the filtration of the fluororesin used in preparing the first core material to obtain a filtered fluororesin, which was used as the second core material.

[0118] [Clad materials] A second fluorine-containing resin was prepared as a clad material. Teflon AF1600 (manufactured by Mitsui-Chemours Fluoroproducts) as the second fluorine-containing resin and Fomblin YR (manufactured by Solvay) as a plasticizer were dissolved in a Vertrel XF-UP solvent (manufactured by Mitsui-Chemours Fluoroproducts). The mass ratio of Teflon AF1600 to Fomblin YR was 7:3. The resulting solution was filtered through a 300 nm pore size filter, LPA-SLF-003-N2 (manufactured by Roki Techno Co., Ltd.). The filtrate was then dropped into a Hastelloy container heated to 260°C to evaporate the solvent and dry the mixture. The resulting resin composition was used as a clad material.

[0119] [Materials for forming the coating layer] Xylex 7200 (manufactured by SABIC, glass transition temperature: 113° C.) was used as a material for forming the coating layer.

[0120] [POF fabrication] Using the first core material, second core material, cladding material, and material for forming the coating layer prepared by the above-mentioned methods, a POF having a structure similar to that of POF 10 shown in Fig. 1 was fabricated by melt spinning. In this example, the manufacturing apparatus shown in Fig. 4 was used to manufacture the POF.

[0121] In this example, the inner diameter (diameter) of the diffusion tube 120 was 6.3 mm. The length of the diffusion tube 120 was set so that the diffusion time was 120 minutes.

[0122] In this example, the melting temperature of the first core material was 250°C, the melting temperature of the second core material was 255°C, the melting temperature of the cladding material was 260°C, and the melting temperature of the material for forming the coating layer was 240°C. The temperature of the diffusion tube 120 was set to 275°C. A core was formed from the first core material and the second core material. The drawing temperature of the second laminate consisting of the core, cladding, and coating layer was 240°C.

[0123] The melt extrusion was carried out with the volume ratio of each material being 1:1.6 for the second core material, 0.1 for the cladding material, and 48.6 for the material for forming the coating layer.

[0124] In the first chamber 110 shown in Fig. 4, the temperature of the converging mold used when coating the core inner layer portion formed of the first core material with the second core material was set to 260°C. In the second chamber 130 shown in Fig. 4, the temperature of the converging mold used when coating the core with the clad material was set to 205°C. In the third chamber 140 shown in Fig. 4, the temperature of the converging mold used when coating the surface of the laminate formed of the core and clad with the coating layer material was set to 250°C.

[0125] In Example 1, the nip rolls were set so that a lateral pressure of about 0.18 MPa was applied to the second laminate immediately after it was released from the cooling pipe 160 .

[0126] The sample was taken 38 hours after the start of melt extrusion.

[0127] The POF produced in Example 1 had a core diameter (outer diameter of the core) of 50 μm, an outer diameter of the clad of 60 μm, and an outer diameter of the coating layer of 232 μm, all of which were measured by the method described below.

[0128] Example 2 In producing the POF, the nip rolls were set so that no lateral pressure was applied to the second laminate immediately after it was released from the cooling pipe 160. The sample used was taken 41 hours after the start of melt extrusion. Except for these points, the POF was produced in the same manner as in Example 1.

[0129] Example 3 Panlite L-1225LM (Teijin Limited, glass transition temperature: 144°C) was used as the resin composition for forming the coating layer. Furthermore, in the production of the POF, the nip rolls were set so that a lateral pressure of about 0.18 MPa was applied to the second laminate immediately after it was released from the cooling pipe 160. Furthermore, the temperature at which the second laminate consisting of the core, cladding, and coating layer was drawn down was set to 235°C. The sample taken 23 hours after the start of melt extrusion was used. Except for these points, the POF was produced in the same manner as in Example 1.

[0130] Example 4 Panlite L-1225LM (manufactured by Teijin Limited, glass transition temperature: 144°C) was used as the resin composition for forming the covering layer. Furthermore, in producing the POF, the nip rolls were set so that no lateral pressure was applied to the second laminate immediately after it was released from the cooling pipe 160. The temperature for drawing down the second laminate consisting of the core, cladding, and covering layer was set to 235°C. The sample taken 10 hours after the start of melt extrusion was used. Except for these points, the POF was produced in the same manner as in Example 1.

[0131] Example 5 The POF of Example 5 was produced in the same manner as in Example 1, except that the sample was taken 36.5 hours after the start of melt extrusion.

[0132] Example 6 Panlite L-1225LM (manufactured by Teijin Limited, glass transition temperature: 144°C) was used as the resin composition for forming the coating layer. Furthermore, in producing the POF, the nip rolls were set so that a lateral pressure of about 0.18 MPa was applied to the second laminate immediately after it was released from the cooling pipe 160. The sample used was taken 38.5 hours after the start of melt extrusion. Except for these points, the POF was produced in the same manner as in Example 1.

[0133] [Evaluation of gap ratio] The gap ratio was calculated using the above formula (I) in the manner described in the embodiment. 20 images of randomly selected locations on the POF were acquired. The images used to determine the gap ratio were acquired using a line sensor camera. The length L of the POF in each image was 500 μm. The results are shown in Table 1. [Table 1]

[0134] [Lateral pressure test] A lateral pressure test was conducted using the POFs of Examples 1 and 5. The loss change was measured when the POF was sandwiched between two 10 cm diameter circular compression plates and compressed. In Example 1, the area of ​​the POF where peeling of the coating layer was observed was sandwiched between the two compression plates. In Example 5, the area of ​​the POF where no peeling was observed was sandwiched between the two compression plates. An autograph (AG-X Plus manufactured by Shimadzu Corporation) was used to compress the POF. The loss was measured and the loss change was determined using the following method. An OTDR (product name: LOR-220, manufacturer: Luciol Instruments) was prepared. The loss change was measured at a wavelength of 850 nm and a pulse width of 7 ns. The results are shown in Figure 5. As shown in Figure 5, the loss change when lateral pressure was applied was confirmed when the POF had peeling (gaps) in the coating layer compared to the POF without peeling (gaps) in the coating layer. Therefore, it is understood that a POF having peeling in the coating layer (that is, having a gap) can be used as a sensor characteristic compared to a POF not having peeling in the coating layer (that is, not having a gap).

[0135] [Environmental testing] The heat resistance of the POFs in Examples 1 to 6 was evaluated by measuring the loss of a 40-m POF. The POFs were maintained at 85°C or 60°C (85% rh in the case of 60°C), and the loss change over time was determined. More specifically, the loss of the POFs was measured using an optical time domain reflectometer (OTDR) (product name: LOR-220, manufacturer: Luciol Instruments) at a wavelength of 850 nm and a pulse width of 7 ns, and the loss change was determined. Figure 6A shows the results for Examples 1, 2, and 5, and Figure 6B shows the results for Examples 3, 4, and 6. As shown in Figure 6A, when the glass transition temperature Tg2 of the coating layer material was 110°C or higher and 120°C or lower, it was confirmed that the heat resistance of the POF was improved by setting the gap ratio to 12% or less. Furthermore, as shown in FIG. 6B, when the glass transition temperature Tg1 of the coating layer material is 140°C or higher and 150°C or lower, the heat resistance of the POF is improved by setting the void ratio to 78% or lower.

[0136] [POF shape] An arbitrary location of the POF in Example 1 was photographed. Then, the POF was rotated by 90 degrees and photographed again. The results are shown in Figure 7. As the rotation occurred, the position of the peeling (gap) changed as shown in Figure 7, and it was found that the peeling (gap) in the POF was arranged in a spiral shape around the core.

[0137] [Note] To summarize the above, one aspect of the present disclosure is as follows.

[0138] (1) The core and a cladding disposed on the outer periphery of the core; a coating layer disposed on the outer periphery of the clad and adjacent to the clad; Equipped with a gap portion is provided at least in a portion between the clad and the coating layer, where the clad and the coating layer are not in direct contact with each other; Plastic optical fiber.

[0139] (2) The glass transition temperature Tg1 of the core material is 110°C or higher. The plastic optical fiber according to (1) above.

[0140] (3) the glass transition temperature Tg2 of the material of the coating layer is 140°C or higher and 150°C or lower; The gap ratio, which is the ratio of the length of the gap per unit length of the plastic optical fiber, is 80% or less. The plastic optical fiber according to (2) above. Here, the gap ratio is the ratio of the length of the gap to the length of the boundary line between the cladding and the coating layer in a cross-sectional image along the longitudinal direction of the plastic optical fiber.

[0141] (4) The gap ratio is 78% or less. The plastic optical fiber according to (3) above.

[0142] (5) The gap ratio is 40% or more. The plastic optical fiber according to (3) or (4) above.

[0143] (6) The glass transition temperature Tg2 of the material of the coating layer is 110°C or higher and 120°C or lower, The gap ratio, which is the ratio of the length of the gap per unit length of the plastic optical fiber, is 15% or less. The plastic optical fiber according to (2) above. Here, the gap ratio is the ratio of the length of the gap to the length of the boundary line between the cladding and the coating layer in a cross-sectional image along the longitudinal direction of the plastic optical fiber.

[0144] (7) The gap ratio is 12% or less. The plastic optical fiber according to (6) above.

[0145] (8) The gap ratio is 3% or more. The plastic optical fiber according to (6) or (7) above.

[0146] (9) When the difference between the glass transition temperature Tg1 of the core material and the glass transition temperature Tg2 of the coating layer material is ΔTg, the following (A) or (B) is satisfied: The plastic optical fiber according to (1) above. (A) ΔTg≦8° C., and the gap ratio, which is the ratio of the length of the gaps per unit length of the plastic optical fiber, is 12% or less. (B) 8° C.<ΔTg, and the gap ratio, which is the ratio of the length of the gaps per unit length of the plastic optical fiber, is 78% or less. Here, the gap ratio is the ratio of the length of the gap to the length of the boundary line between the cladding and the coating layer in a cross-sectional image along the longitudinal direction of the plastic optical fiber.

[0147] (10) The gap is provided spirally around the core. The plastic optical fiber according to any one of (1) to (9) above. [Industrial Applicability]

[0148] The POF of the present disclosure is suitable for use in optical fiber sensors. [Explanation of symbols]

[0149] 1a First core material 1b Second core material 1c Cladding material 1d Materials for forming the coating layer 2. Core inner layer 3 Core outer periphery 4 Laminate (core) 5. Clad 6 Covering layer 7 Second laminate 10 POF 11 cores 12 Clad 13 Covering layer 14 Gap 101a First extrusion device 101b Second extrusion device 101c Third extrusion device 101d Fourth extrusion device 102a First storage section 102b Second storage section 102c Third Storage Unit 102d 4th Storage Unit 103a First extrusion section 103b Second extrusion section 103c Third extrusion section 104 Screw 105 Hopper 110 Room 1 120 Diffusion tube 130 Room 2 140 Room 3 150 nozzles 160 Cooling pipe 161 Interior Space 170 Nip Roll 171,172 rolls 173,174,175 Guide Roll 176 Winding Roll 180 Displacement Meter 1000 manufacturing equipment

Claims

1. The core and a cladding disposed on the outer periphery of the core; a coating layer disposed on the outer periphery of the clad and adjacent to the clad; Equipped with a gap portion is provided at least in a portion between the clad and the coating layer, where the clad and the coating layer are not in direct contact with each other; Plastic optical fiber.

2. The glass transition temperature Tg of the core material 1 is 110°C or higher, The plastic optical fiber according to claim 1.

3. The glass transition temperature Tg of the material of the coating layer 2 is 140°C or higher and 150°C or lower, The gap ratio, which is the ratio of the length of the gap per unit length of the plastic optical fiber, is 80% or less. The plastic optical fiber according to claim 2. Here, the gap ratio is the ratio of the length of the gap to the length of the boundary line between the cladding and the coating layer in a cross-sectional image along the longitudinal direction of the plastic optical fiber.

4. The gap ratio is 78% or less. The plastic optical fiber according to claim 3.

5. The gap ratio is 40% or more.

5. The plastic optical fiber according to claim 3 or 4.

6. The glass transition temperature Tg of the material of the coating layer 2 is 110°C or higher and 120°C or lower, The gap ratio, which is the ratio of the length of the gap per unit length of the plastic optical fiber, is 15% or less. The plastic optical fiber according to claim 2. Here, the gap ratio is the ratio of the length of the gap to the length of the boundary line between the cladding and the coating layer in a cross-sectional image along the longitudinal direction of the plastic optical fiber.

7. The gap ratio is 12% or less. The plastic optical fiber according to claim 6.

8. The gap ratio is 3% or more.

8. The plastic optical fiber according to claim 6 or 7.

9. The glass transition temperature Tg of the core material 1 and the glass transition temperature Tg of the material of the coating layer. 2 When the difference between the temperature and the temperature is ΔTg, the following (A) or (B) is satisfied: The plastic optical fiber according to claim 1. (A) ΔTg≦8° C., and the gap ratio, which is the ratio of the length of the gaps per unit length of the plastic optical fiber, is 12% or less. (B) 8° C.<ΔTg, and the gap ratio, which is the ratio of the length of the gap per unit length of the plastic optical fiber, is 78% or less. Here, the gap ratio is the ratio of the length of the gap to the length of the boundary line between the cladding and the coating layer in a cross-sectional image along the longitudinal direction of the plastic optical fiber.

10. The gap is provided spirally around the core. The plastic optical fiber according to claim 1.

Images