fiber optic

Abstract

To provide an optical fiber that has excellent bending resistance and hot water resistance, and can maintain its strength even when immersed in water for a long period of time. [Solution] The optical fiber according to this disclosure comprises a glass fiber including a core and a cladding, and a coating resin layer that is in contact with the glass fiber and covers the glass fiber, wherein the cladding includes an inner cladding that covers the outer circumference of the core, a trench that covers the outer circumference of the inner cladding, and an outer cladding that covers the outer circumference of the trench, the coating resin layer has a primary resin layer that covers the glass fiber and a secondary resin layer that covers the primary resin layer, the outer cladding contains chlorine-added quartz glass, and the average chlorine mass concentration of the outer cladding is 100 ppm or more and 6000 ppm or less.

Description

Technical Field

[0001] The present disclosure relates to optical fibers.

Background Art

[0002] In recent years, the demand for high-density cables with increased packing density of optical fibers has been growing. To increase the packing density of optical fibers in a cable, it is advantageous to reduce the outer diameter of the optical fibers. When the outer diameter of an optical fiber is reduced, the bending characteristics of the optical fiber tend to deteriorate.

[0003] An optical fiber includes a glass fiber that is an optical transmission body and a coating resin layer for protecting the glass fiber. The coating resin layer has, for example, a primary resin layer in contact with the glass fiber and a secondary resin layer formed on the outer peripheral surface of the primary resin layer.

[0004] To improve the bending characteristics, reducing the Young's modulus of the primary resin layer or increasing the Young's modulus of the secondary resin layer has been considered. For example, in Patent Document 1, a resin composition containing a urethane oligomer obtained by reacting a reaction product of an aliphatic polyether diol and a diisocyanate with a monohydric alcohol and a hydroxyl group-containing (meth)acrylate has been studied to achieve both flexibility (low Young's modulus) and mechanical strength of the primary resin layer.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Optical fibers are required to maintain their strength and other properties even when immersed in water for extended periods. However, optical fibers equipped with a primary resin layer with a low Young's modulus to improve bending properties tend to have a lower degree of hardening, and when immersed in hot water, the coating resin layer may peel off from the glass fiber, reducing the strength of the optical fiber.

[0007] This disclosure aims to provide an optical fiber that exhibits excellent bending resistance and hot water resistance, and can maintain its strength even when immersed in water for a long period of time. [Means for solving the problem]

[0008] An optical fiber according to one aspect of the present disclosure comprises a glass fiber including a core and a cladding, and a coating resin layer that is in contact with and covers the glass fiber, wherein the cladding includes an inner cladding covering the outer circumference of the core, a trench covering the outer circumference of the inner cladding, and an outer cladding covering the outer circumference of the trench, the coating resin layer has a primary resin layer covering the glass fiber and a secondary resin layer covering the primary resin layer, the outer cladding includes chlorine-added quartz glass, and the average chlorine mass concentration of the outer cladding is 100 ppm or more and 6000 ppm or less. [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide an optical fiber that has excellent bending resistance and hot water resistance, and can maintain its strength even when immersed in water for a long period of time. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of an optical fiber according to this embodiment. [Modes for carrying out the invention]

[0011] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and explained.

[0012] (1) An optical fiber according to one aspect of the present disclosure comprises a glass fiber including a core and a cladding, and a coating resin layer that is in contact with and covers the glass fiber, wherein the cladding includes an inner cladding covering the outer circumference of the core, a trench covering the outer circumference of the inner cladding, and an outer cladding covering the outer circumference of the trench, the coating resin layer has a primary resin layer covering the glass fiber and a secondary resin layer covering the primary resin layer, the outer cladding includes chlorine-added quartz glass, and the average chlorine mass concentration of the outer cladding is 100 ppm or more and 6000 ppm or less.

[0013] By adding a specific amount of chlorine to the outer cladding of such optical fibers, a small amount of acidic component is generated from the glass fiber when the optical fiber is immersed in water. This allows the bond between the glass fiber and the primary resin layer to be maintained even during immersion in hot water, and the strength can be maintained even when immersed in water for a long time.

[0014] (2) In the above (1), from the viewpoint of further improving resistance to hot water, the coating resin layer may include a cured product of a resin composition containing a photopolymerizable compound including urethane (meth)acrylate and an acylphosphine oxide-based photopolymerization initiator, and the amount of phosphine oxide-based photopolymerization initiator remaining in the coating resin layer may be 0.3% by mass or less based on the total amount of optical fibers.

[0015] (3) In (1) or (2) above, from the viewpoint of further improving resistance to hot water, the primary resin layer may include a cured product of a resin composition containing a photopolymerizable compound including urethane (meth)acrylate, an acylphosphine oxide-based photopolymerization initiator, a silane coupling agent, and an organic base.

[0016] (4) In the above (3), from the viewpoint of improving storage stability, the organic base may be δ-valerolactam or ε-caprolactam.

[0017] (5) In any of the above (1) to (4), the Young's modulus of the primary resin layer may be 0.6 MPa or less at 23°C, from the viewpoint of having excellent lateral pressure characteristics.

[0018] [Details of the embodiments of this disclosure] Specific examples of optical fibers according to the embodiments of this disclosure will be described with reference to the drawings. This disclosure is not limited to these examples and is intended to include all modifications within the meaning and scope equivalent to the claims as indicated by the claims. In the following description, the same elements as in the description of the drawings are denoted by the same reference numerals, and redundant descriptions are omitted. In this embodiment, (meth)acrylate means acrylate or the corresponding methacrylate, and the same applies to other similar expressions such as (meth)acrylic acid. In this specification, ppm indicates a mass ratio.

[0019] (Optical fiber) The optical fiber according to this embodiment comprises a glass fiber including a core and a cladding, and a coating resin layer that is in contact with the glass fiber and covers the glass fiber, wherein the cladding includes an inner cladding that covers the outer circumference of the core, a trench that covers the outer circumference of the inner cladding, and an outer cladding that covers the outer circumference of the trench, the coating resin layer has a primary resin layer that covers the glass fiber and a secondary resin layer that covers the primary resin layer, the outer cladding contains chlorine-added quartz glass, and the average chlorine mass concentration of the outer cladding is 100 ppm or more and 6000 ppm or less.

[0020] Figure 1 is a schematic cross-sectional view showing an example of an optical fiber according to this embodiment. The optical fiber 10A comprises a glass fiber 13 including a core 11 and a cladding 12, and a coating resin layer 16 including a primary resin layer 14 and a secondary resin layer 15 provided on the outer circumference of the glass fiber 13. In the optical fiber 10A, the cladding 12 includes an inner cladding 121 that covers the outer circumference of the core 11 and is in contact with the outer surface of the core 11, a trench 122 that covers the outer circumference of the inner cladding 121 and is in contact with the outer surface of the inner cladding 121, and an outer cladding 123 that covers the outer circumference of the trench 122 and is in contact with the outer surface of the trench 122.

[0021] The core 11 and the cladding 12 mainly contain glass such as quartz glass. For the core 11, quartz glass added with germanium or pure quartz glass can be used. For the inner cladding 121, pure quartz glass, quartz glass added with fluorine, or quartz glass added with chlorine can be used. From the perspective of hot water resistance characteristics, the inner cladding 121 may contain quartz glass added with chlorine, and the average chlorine mass concentration of the inner cladding 121 may be, for example, 500 ppm or more and 5000 ppm or less, or 500 ppm or more and 3000 ppm or less. For the trench 122, quartz glass added with fluorine can be used.

[0022] From the perspective of maintaining the strength even when the optical fiber is immersed in water for a long time, quartz glass added with chlorine can be used for the outer cladding 123. The average chlorine mass concentration of the outer cladding 123 is 100 ppm or more and 6000 ppm or less, and from the perspective of further enhancing the glass strength when immersed in water for a long time, it may be 200 ppm or more and 5500 ppm or less, 300 ppm or more and 5300 ppm or less, 400 ppm or more and 5000 ppm or less, 450 ppm or more and 4000 ppm or less, or 480 ppm or more and 3500 ppm or less. The average OH mass concentration of the outer cladding 123 is substantially zero. Here, substantially zero specifically means 50 ppm or less.

[0023] In FIG. 1, for example, the outer diameter (D2) of the glass fiber 13 may be 100 μm or more and 125 μm or less, and the diameter (D1) of the core 11 constituting the glass fiber 13 may be 7 μm or more and 15 μm or less. The thickness of the coating resin layer 16 may be, for example, 22 μm or more and 70 μm or less. The thickness of each of the primary resin layer 14 and the secondary resin layer 15 may be 5 μm or more and 50 μm or less.

[0024] The outer diameter (D2) of the glass fiber 13 may be 125 μm or more and 220 μm or less, 150 μm or more and 210 μm or less, or 170 μm or more and 190 μm or less. The outer diameter of the optical fiber 10 may be 200 μm or more and 250 μm or less, 210 μm or more and 240 μm or less, or 220 μm or more and 230 μm or less.

[0025] The coating resin layer 16 contains a cured product of a resin composition containing a photopolymerizable compound and an acylphosphine oxide-based photopolymerization initiator, and the amount of phosphine oxide-based photopolymerization initiator remaining in the coating resin layer 16 may be 0.3% by mass or less based on the total amount of optical fiber. This makes it possible to obtain optical fibers with reduced changes in adhesion over time.

[0026] The content of acylphosphine oxide-based photopolymerization initiators in optical fibers can be adjusted by changing the amount of acylphosphine oxide-based photopolymerization initiator incorporated into the resin composition used to form the coating resin layer, the manufacturing speed when producing optical fibers, and the time until additional ultraviolet irradiation is performed after optical fiber production.

[0027] Examples of acylphosphine oxide-based photopolymerization initiators include 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Omnirad TPO N, manufactured by IGM Resins BV), ethyl(2,4,6-trimethylbenzoyl)-phenylphosphinenate (Omnirad TPO-L, manufactured by IGM Resins), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (Omnirad 819, manufactured by IGM Resins BV), and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

[0028] Acylphosphine oxide-based photopolymerization initiators can aggregate if they remain in the coating resin layer, potentially becoming a starting point for interfacial delamination between the glass fiber 13 and the coating resin layer 16; therefore, it is preferable to minimize the amount remaining. The amount of acylphosphine oxide-based photopolymerization initiator remaining in the coating resin layer may be 0.3% by mass or less, 0.2% by mass or less, or 0.1% by mass or less, from the viewpoint of improving adhesion between the glass fiber and the coating resin layer.

[0029] The resin composition according to this embodiment may further contain other photopolymerization initiators different from acylphosphine oxide-based photopolymerization initiators. The other photopolymerization initiators can be appropriately selected from known radical photopolymerization initiators. Examples of other photopolymerization initiators include 1-hydroxycyclohexylphenyl ketone (Omnirad 184, IGM Resins), 2,2-dimethoxy-2-phenylacetophenone (Omnirad 651, IGM Resins), 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one (Omnirad 907, IGM Resins).

[0030] The content of the photopolymerization initiator in the resin composition may be 1 to 10 parts by mass, 2 to 8 parts by mass, or 3 to 7 parts by mass per 100 parts by mass of the total amount of the photopolymerizable compound. The content of the photopolymerization initiator may be 0.2 parts by mass or more, 0.4 parts by mass or more, or 0.6 parts by mass or more, or 6 parts by mass or less, 5 parts by mass or less, or 4 parts by mass or less per 100 parts by mass of the total amount of the photopolymerizable compound.

[0031] The photopolymerizable compound may include urethane (meth)acrylate from the viewpoint of adjusting the Young's modulus of the coating resin layer. As urethane (meth)acrylate, for example, reaction products with polyol compounds, polyisocyanate compounds, and hydroxyl group-containing (meth)acrylate compounds can be used. One type of urethane (meth)acrylate may be used alone or a mixture of two or more types.

[0032] Examples of polyol compounds include polytetramethylene glycol, polypropylene glycol, and bisphenol A-ethylene oxide addition diols. Examples of polyisocyanate compounds include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane 4,4'-diisocyanate. Examples of hydroxyl group-containing (meth)acrylate compounds include 2-hydroxyethyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 1,6-hexanediol mono(meth)acrylate, pentaerythritol tri(meth)acrylate, 2-hydroxypropyl (meth)acrylate, and tripropylene glycol mono(meth)acrylate.

[0033] From the viewpoint of adjusting the Young's modulus of the primary resin layer, the number-average molecular weight (Mn) of the polyol compound may be 1000 to 10000, 1500 to 9000, 2000 to 8000, or 3000 to 6000. From the viewpoint of adjusting the Young's modulus of the secondary resin layer, the Mn of the polyol compound may be 300 to 3000, 400 to 2500, or 500 to 2000.

[0034] Organotin compounds are generally used as catalysts in the synthesis of urethane (meth)acrylates. Examples of organotin compounds include dibutyltin dilaurate, dibutyltin diacetate, dibutyltin maleate, dibutyltin bis(2-ethylhexyl mercaptoacetate), dibutyltin bis(isooctyl mercaptoacetate), and dibutyltin oxide. Dibutyltin dilaurate or dibutyltin diacetate may be used as catalysts due to their availability or catalytic performance.

[0035] Lower alcohols with 5 or fewer carbon atoms may be used when synthesizing urethane (meth)acrylates. Examples of lower alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 2-methyl-2-butanol, 3-methyl-2-butanol, and 2,2-dimethyl-1-propanol.

[0036] The photopolymerizable compound according to this embodiment may further include photopolymerizable compounds other than urethane (meth)acrylate (hereinafter referred to as "monomers").

[0037] Examples of monomers include monofunctional monomers having one polymerizable group and polyfunctional monomers having two or more polymerizable groups. Two or more monomers may be used in mixture form.

[0038] Examples of monofunctional monomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, s-butyl (meth)acrylate, tert-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, isoamyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, iso Octyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 3-phenoxybenzyl acrylate, phenoxydiethylene glycol acrylate, phenoxypolyethylene glycol acrylate, 4-tert-butylcyclohexanol acrylate, tetrahydrofurfuryl (meth)acrylate, benzyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopenta (Meth)acrylate monomers such as nyl(meth)acrylate, nonylphenol polyethylene glycol(meth)acrylate, nonylphenoxy polyethylene glycol(meth)acrylate, 2-hydroxyethyl(meth)acrylate, nonylphenol ethylene oxide modified(meth)acrylate, tricyclodecanyl(meth)acrylate, polypropylene glycol mono(meth)acrylate, isobornyl(meth)acrylate, etc.; (meth)acrylic acid, (meth)acrylic acid dimer, carboxyethyl(meth)acrylate, Carboxy group-containing monomers such as carboxypentyl (meth)acrylate and ω-carboxy-polycaprolactone (meth)acrylate; heterocyclic monomers such as N-vinylpyrrolidone, N-vinylcaprolactam, N-(meth)acryloylmorpholine, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, 3-(3-pyridine)propyl (meth)acrylate, and cyclic trimethylolpropane formal acrylate; maleimide monomers such as maleimide, N-cyclohexylmaleimide, and N-phenylmaleimide;Examples include amide monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-hexyl(meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-butyl(meth)acrylamide, N-methylol(meth)acrylamide, and N-methylolpropane(meth)acrylamide; aminoalkyl (meth)acrylate monomers such as aminoethyl (meth)acrylate, aminopropyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and tert-butylaminoethyl (meth)acrylate; and succinimide monomers such as N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, and N-(meth)acryloyl-8-oxyoctamethylenesuccinimide.

[0039] From the viewpoint of excellent copolymerization with other monomers and improved curing speed, a cyclic N-vinyl monomer may be used as the monofunctional monomer. The content of the N-vinyl monomer may be 1 to 15 parts by mass or 2 to 10 parts by mass per 100 parts by mass of the total amount of the resin composition.

[0040] Examples of polyfunctional monomers include polyethylene glycol di(meth)acrylate, tricyclodecanediyl dimethylene di(meth)acrylate, isocyanurate ethylene oxide-modified di(meth)acrylate, ethylene oxide-modified bisphenol F di(meth)acrylate, ethylene oxide-modified bisphenol A di(meth)acrylate, polypropylene glycol di(meth)acrylate, propylene oxide-modified bisphenol A di(meth)acrylate, and propylene oxide-modified neopentyl glycol di(meth)acrylate. Polytetraethylene glycol di(meth)acrylate, hydroxypivalate neopentyl glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, 1,14-tetradecanediol di(meth)acrylate, 1,16-hexadecanediol di(meth)acrylate, 1,20-eicosanediol di(meth)acrylate, neopentyl glycol di (meth)acrylate, isopentyldiol di(meth)acrylate, 3-ethyl-1,8-octanediol di(meth)acrylate; trimethylolpropane tri(meth)acrylate, trimethyloloctan tri(meth)acrylate, trimethylolpropane polyethoxytri(meth)acrylate, trimethylolpropane polypropoxytri(meth)acrylate, trimethylolpropane polyethoxypolypropoxytri(meth)acrylate, trimethylolpropane polyethoxytri(meth)acrylate, tris[(meth)acryloyloxyethyl]isocyanurate, pentaerythritol Examples include tri(meth)acrylate, pentaerythritol polyethoxytetra(meth)acrylate, pentaerythritol polypropoxytetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropanetetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and caprolactone-modified tris[(meth)acryloyloxyethyl]isocyanurate.

[0041] The photopolymerizable compound may include an alkylene oxide-modified polyfunctional monomer from the viewpoint of adjusting the Young's modulus of the primary resin layer. The alkylene oxide-modified polyfunctional monomer may have at least one selected from the group consisting of ethylene oxide (EO) chains and propylene oxide (PO) chains. The ethylene oxide chain can be represented as "(EO)n" and the propylene oxide chain as "(PO)n". n is an integer of 1 or more, and may be 2 or more, or 3 or more, and may be 30 or less, 25 or less, or 20 or less.

[0042] Examples of alkylene oxide-modified di(meth)acrylates include polyethylene glycol di(meth)acrylate, isocyanurate ethylene oxide-modified di(meth)acrylate, ethylene oxide-modified bisphenol F di(meth)acrylate, ethylene oxide-modified bisphenol A di(meth)acrylate, polypropylene glycol di(meth)acrylate, propylene oxide-modified bisphenol A di(meth)acrylate, and propylene oxide-modified neopentyl glycol di(meth)acrylate.

[0043] The primary resin layer 14 can be formed using an ultraviolet-curable resin composition containing a photopolymerizable compound including urethane (meth)acrylate, an acylphosphine oxide-based photopolymerization initiator, a silane coupling agent, and an organic base.

[0044] From the viewpoint of adjusting the Young's modulus of the primary resin layer, the content of urethane (meth)acrylate may be 15 parts by mass or more and 80 parts by mass or less, 20 parts by mass or more and 70 parts by mass or less, or 30 parts by mass or more and 60 parts by mass or less, per 100 parts by mass of the total amount of the resin composition.

[0045] Resin compositions may contain trace amounts of acidic components, such as acrylic acid, derived from photopolymerizable compounds. These acidic components can hydrolyze and deactivate the silane coupling agent, causing the resin composition to change over time. In contrast, the resin composition according to this embodiment contains an organic base, which neutralizes the acidic components and suppresses the deactivation of the silane coupling agent. Therefore, it is possible to produce optical fibers with excellent resistance to hot water even after a certain period of time has elapsed since resin production. This effect is particularly pronounced when the Young's modulus of the primary resin layer is low.

[0046] As the organic base, amine compounds or amide compounds can be used. Examples of amine compounds include aromatic amines such as aniline, aliphatic amines having an aromatic ring such as benzylamine, and heterocyclic amines such as pyrrolidine, piperidine, and pyridine. Examples of amide compounds include cyclic amides such as δ-valerolactam and ε-caprolactam.

[0047] Basic components are generally known to corrode glass. Because the large molecular structure of basic components hinders the corrosion reaction of glass due to steric hindrance, the organic base may be an aromatic amine, an aliphatic amine with an aromatic ring, a heterocyclic amine, or a cyclic amide. From the viewpoint of suppressing the deactivation of the silane coupling agent in the resin composition, a heterocyclic amine or cyclic amide may be used as the organic base. From the viewpoint of further improving resistance to hot water, δ-valerolactam or ε-caprolactam may be used as the organic base.

[0048] The content of organic bases may be 5 ppm or more and 9000 ppm or less based on the total amount of the coating resin layer, from the viewpoint of improving resistance to hot water. The content of organic bases may be 8 ppm or more, 10 ppm or more, 100 ppm or more, 500 ppm or more, 800 ppm or more, or 1000 ppm or more based on the total amount of the coating resin layer, from the viewpoint of suppressing the deactivation of the silane coupling agent, and may be 8500 ppm or less, 8000 ppm or less, 7000 ppm or less, 6000 ppm or less, or 5000 ppm or less, from the viewpoint of suppressing corrosion of glass.

[0049] The silane coupling agent is not particularly limited as long as it does not interfere with the curing of the resin composition. Examples of silane coupling agents include tetramethyl silicate, tetraethyl silicate, mercaptopropyltrimethoxysilane, vinyltrichlorosilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, β-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane, dimethoxydimethylsilane, diethoxydimethylsilane, 3-acryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-methacryloxypropyltrimethoxysilane, and N-(β-aminoethyl)-γ Examples include aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, bis-[3-(triethoxysilyl)propyl]tetrasulfide, bis-[3-(triethoxysilyl)propyl]disulfide, γ-trimethoxysilylpropyldimethylthiocarbamoyltetrasulfide, and γ-trimethoxysilylpropylbenzothiazyltetrasulfide. The resin composition according to this embodiment may contain two or more silane coupling agents from the viewpoint of improving adhesion of the primary resin layer to the glass fibers.

[0050] The silane coupling agent content may be 0.1 parts by mass or more and 5.0 parts by mass or 0.2 parts by mass or more and 4.0 parts by mass or 0.3 parts by mass or more and 3.0 parts by mass or less, per 100 parts by mass of the total amount of the resin composition.

[0051] The Young's modulus of the primary resin layer may be 0.6 MPa or less, 0.55 MPa or less, 0.5 MPa or less, or 0.4 MPa or less at 23°C, from the viewpoint of improving the glass strength of the optical fiber. The lower limit of the Young's modulus of the primary resin layer is not particularly limited, but may be 0.05 MPa or more, 0.1 MPa or more, or 0.2 MPa or more. The Young's modulus of the primary resin layer can be measured by the Pullout Modulus (POM) method at 23°C. The Young's modulus of the primary resin layer can be adjusted by the type of urethane (meth)acrylate, the molecular weight of the urethane (meth)acrylate, the type of monomer, the amount of monomer blended, etc.

[0052] The secondary resin layer 15 may be formed using a conventionally known resin composition for secondary resin layers. For example, the secondary resin layer 15 can be formed by curing a resin composition containing a urethane (meth)acrylate, a monomer, and an acylphosphine oxide-based photopolymerization initiator.

[0053] The Young's modulus of the secondary resin layer 15 may be 800 MPa or higher, 1000 MPa or higher, or 1200 MPa or higher at 23°C, from the viewpoint of further improving the hot water resistance of the optical fiber. The Young's modulus of the secondary resin layer 15 may be 2000 MPa or lower, 1800 MPa or lower, or 1500 MPa or lower at 23°C, from the viewpoint of forming a resin layer with excellent toughness. The Young's modulus of the secondary resin layer can be measured by a tensile test of the coating resin layer. The Young's modulus of the secondary resin layer can be adjusted by the type of urethane (meth)acrylate, the molecular weight of the urethane (meth)acrylate, the type of monomer, the amount of monomer blended, etc. [Examples]

[0054] The following describes the results of evaluation tests using the examples and comparative examples related to this disclosure, and further explains this disclosure in detail. However, this disclosure is not limited to these examples.

[0055] [Resin composition for primary resin layer] As a photopolymerizable compound, a urethane acrylate was prepared by reacting polypropylene glycol with a molecular weight of 4000, isophorone diisocyanate, and hydroxyethyl acrylate. A resin composition P for the primary resin layer was prepared by mixing 60 parts by mass of this urethane acrylate with 30 parts by mass of nonylphenol EO-modified acrylate, 7.5 parts by mass of 1,6-hexanediol diacrylate, 1.5 parts by mass of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO₄N), 0.5 parts by mass of mercaptotrimethoxysilane, and 0.5 parts by mass of ε-caprolactam.

[0056] [Resin composition for secondary resin layer] A urethane (meth)acrylate was prepared by reacting polypropylene glycol with a molecular weight of 1000, isophorone diisocyanate, and 2-hydroxyethyl acrylate. A resin composition S for the secondary resin layer was prepared by mixing 60 parts by mass of this urethane (meth)acrylate, 19 parts by mass of isobornyl acrylate, 20 parts by mass of trimethylolpropane triacrylate, and 1 part by mass of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO N).

[0057] [Glass fiber] Glass fibers with a diameter of 125 μm were prepared, consisting of a core and a cladding. The cladding had an inner cladding, trenches, and an outer cladding, and glass fibers with different average chlorine mass concentrations in the outer cladding were prepared. The average chlorine mass concentration could be measured by elemental analysis.

[0058] [Fabrication of optical fibers] Optical fibers were fabricated by forming a primary resin layer with a thickness of 17.5 μm on the outer circumference of a glass fiber using resin composition P, and then forming a secondary resin layer with a thickness of 15 μm on the outer circumference of the primary resin layer using resin composition S. Test Examples 1 to 5 correspond to examples, and Test Example 6 corresponds to a comparative example. The optical fibers were evaluated as follows. The results are shown in Table 1.

[0059] (Remaining amount of acylphosphine oxide-based photopolymerization initiator) The amount of acylphosphine oxide-based photopolymerization initiator remaining in the optical fiber was adjusted by the amount of light irradiation during optical fiber fabrication. The optical fiber was immersed in acetone for extraction. The amount (mass %) of acylphosphine oxide-based photopolymerization initiator was determined by measuring the extract using gas chromatography (Shimadzu Corporation, product name "GC2030").

[0060] (Young's modulus of the primary resin layer) The Young's modulus of the primary resin layer was measured using the POM method at 23°C. Two points on the optical fiber were fixed with two chuck devices, and the portion of the coating resin layer (primary resin layer and secondary resin layer) between the two chuck devices was removed. Then, one chuck device was fixed, and the other chuck device was slowly moved in the opposite direction to the fixed chuck device. When L is the length of the portion of the optical fiber held between the moving chuck devices, Z is the amount of movement of the chuck devices, Dp is the outer diameter of the primary resin layer, Df is the outer diameter of the glass fiber, n is the Poisson's ratio of the primary resin layer, and W is the load during the movement of the chuck devices, the Young's modulus of the primary resin layer was calculated using the following formula. Young's modulus (MPa) = ((1+n)W / πLZ) × ln(Dp / Df)

[0061] (Glass strength) A bundle of optical fibers was immersed in 85°C hot water for 60 days, and the glass strength before and after immersion was evaluated. The quality of the glass strength was determined by measuring the 50% strength. The 50% strength is the strength at which half of the optical fibers tested break in a tensile test. In this test example, a tensile test was performed on each optical fiber at a tensile speed of 25 mm / min. The 50% strength of the glass strength after immersion was evaluated as follows: if it was less than 80% of the 50% strength of the glass strength before immersion, it was evaluated as "C"; if it was between 80% and 90%, it was evaluated as "B"; and if it was greater than 90%, it was evaluated as "A".

[0062] [Table 1] [Explanation of Symbols]

[0063] 10A… Optical fiber 11... Core 12... Clad 13…Glass fiber 14…Primary resin layer 15…Secondary resin layer 16…Coating resin layer 121...Inner cladding 122... Trench 123... Outer cladding D1...Outer diameter of glass fiber 13 D2...Diameter of Core 11

Claims

1. The device comprises a glass fiber including a core and a cladding, and a coating resin layer that is in contact with and covers the glass fiber, The cladding includes an inner cladding covering the outer circumference of the core, a trench covering the outer circumference of the inner cladding, and an outer cladding covering the outer circumference of the trench. The coating resin layer comprises a primary resin layer that covers the glass fiber and a secondary resin layer that covers the primary resin layer. An optical fiber in which the outer cladding contains quartz glass to which chlorine has been added, and the average mass concentration of chlorine in the outer cladding is 100 ppm or more and 6000 ppm or less.

2. The optical fiber according to claim 1, wherein the coating resin layer comprises a cured product of a resin composition containing a photopolymerizable compound and an acylphosphine oxide-based photopolymerization initiator, and the amount of the acylphosphine oxide-based photopolymerization initiator remaining in the coating resin layer is 0.3% by mass or less based on the total amount of the optical fiber.

3. The optical fiber according to claim 1, wherein the primary resin layer comprises a cured product of a resin composition containing a photopolymerizable compound including urethane (meth)acrylate, an acylphosphine oxide-based photopolymerization initiator, a silane coupling agent, and an organic base.

4. The optical fiber according to claim 3, wherein the organic base is δ-valerolactam or ε-caprolactam.

5. The optical fiber according to any one of claims 1 to 4, wherein the Young's modulus of the primary resin layer is 0.6 MPa or less at 23°C.

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