Optical fiber and method of manufacturing the same

Abstract

An optical fiber comprising: a glass fiber including a core and a cladding; and a covering resin layer that is in contact with the glass fiber and covers the glass fiber, wherein the covering resin layer has a primary resin layer that is in contact with the glass fiber and covers the glass fiber, and a secondary layer that covers the primary resin layer, the primary resin layer contains a cured product of a first resin composition containing a photopolymerizable compound and a phosphine oxide-based photopolymerization initiator, the secondary resin layer contains a cured product of a second resin composition containing a photopolymerizable compound and a phosphine oxide-based photopolymerization initiator, and the amount of the unreacted phosphine oxide-based photopolymerization initiator in the covering resin layer is at most 0.5 mass%.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to optical fibers and methods for manufacturing optical fibers. This application claims priority to Japanese Application No. 2020-148903, filed on September 4, 2020, and incorporates by reference all of the contents of said Japanese application. [Background technology]

[0002] Generally, optical fibers are provided with a coating resin layer to protect the glass fiber that serves as the optical transmission medium. The coating resin layer is composed of two layers, for example, a primary resin layer that contacts the glass fiber and a secondary resin layer that is formed on the outer surface of the primary resin layer.

[0003] When connecting optical fibers, it is necessary to remove a part of the coating resin layer from the glass fiber. Patent Document 1 discloses that the removability of the coating resin layer is adjusted by focusing on the adhesion angle of mineral oil to the primary resin layer and the elastic modulus of the secondary resin layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-61157 Summary of the Invention

[0005] An optical fiber according to one embodiment of the present disclosure comprises a glass fiber including a core and a clad, and a coating resin layer that contacts and coats the glass fiber, the coating resin layer having a primary resin layer that contacts and coats the glass fiber and a secondary resin layer that coats the primary resin layer, the primary resin layer comprising a cured product of a first resin composition containing a photopolymerizable compound and a phosphine oxide-based photopolymerization initiator, the secondary resin layer comprising a cured product of a second resin composition containing a photopolymerizable compound and a phosphine oxide-based photopolymerization initiator, and the amount of unreacted phosphine oxide-based photopolymerization initiator in the coating resin layer is 0.5 mass% or less. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of an optical fiber according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] [Problem to be solved by this disclosure] When an optical fiber is exposed to light from a fluorescent lamp or the like, the curing reaction of the coating resin layer progresses over time, and the adhesive strength of the coating resin layer to the glass fiber may become too high. If the adhesive strength of the coating resin layer to the glass fiber is too high, a part of the coating resin layer may remain on the outer periphery of the glass fiber when the coating resin layer is removed from the glass fiber.

[0008] An object of the present disclosure is to provide an optical fiber and a method for manufacturing an optical fiber in which changes in coating strippability over time are reduced.

[0009] [Effects of this disclosure] According to the present disclosure, it is possible to provide an optical fiber and a method for manufacturing an optical fiber in which the change over time in coating removability is reduced.

[0010] [Description of the embodiments of the present disclosure] First, the contents of the embodiments of the present disclosure will be listed and described. An optical fiber according to one aspect of the present disclosure includes a glass fiber including a core and a cladding, and a coating resin layer that contacts the glass fiber and coats the glass fiber. The coating resin layer includes a primary resin layer that contacts the glass fiber and coats the glass fiber, and a secondary resin layer that coats the primary resin layer. The primary resin layer includes a cured product of a first resin composition containing a photopolymerizable compound and a phosphine oxide-based photopolymerization initiator, and the secondary resin layer includes a cured product of a second resin composition containing a photopolymerizable compound and a phosphine oxide-based photopolymerization initiator. The amount of unreacted phosphine oxide-based photopolymerization initiator in the coating resin layer is 0.5 mass% or less.

[0011] When an optical fiber is exposed to light from a fluorescent lamp or the like, the unreacted photopolymerization initiator contained in the coating resin layer is cleaved, which accelerates the curing of the coating resin layer, making it difficult to remove the coating resin layer from the glass fiber. Since phosphine oxide-based photopolymerization initiators are particularly highly reactive, it is important to reduce the amount of unreacted phosphine oxide-based photopolymerization initiator in the coating resin layer. The optical fiber according to this embodiment can reduce the change in coating removability over time.

[0012] The second resin composition may further contain an acetophenone-based photopolymerization initiator from the viewpoint of improving surface curability. The first resin composition and the second resin composition may not contain any photopolymerization initiator other than the phosphine oxide-based photopolymerization initiator from the viewpoint of reducing the cost of the resin composition.

[0013] In order to further reduce the change in coating removability over time, at least one of the first resin composition and the second resin composition may contain nonylphenol polyethylene glycol acrylate as a photopolymerizable compound, and the amount of unreacted nonylphenol polyethylene glycol acrylate in the coating resin layer may be less than 1.0 mass%.

[0014] The method for manufacturing an optical fiber according to this embodiment includes a coating step of coating a glass fiber having a temperature of 80°C or less with a first resin composition and a second resin composition, in that order, in a manner that increases the distance from the glass fiber, and a curing step of curing the resin compositions by irradiating them with ultraviolet light after the coating step. By keeping the temperature of the glass fiber at 80°C or less immediately before coating the resin compositions on the glass fiber, it becomes easier to reduce the proportion of unreacted phosphine oxide-based photopolymerization initiator, and it is possible to suppress the progress of curing of the coating resin layer over time.

[0015] In the curing step, ultraviolet light emitted by an ultraviolet light emitting diode (ultraviolet LED) may be irradiated, which can further reduce the proportion of unreacted phosphine oxide photopolymerization initiator.

[0016] The wavelength of the ultraviolet light may be in the range of 350 nm to 405 nm, from the viewpoint of hardening the coating resin layer to the inside in the hardening step.

[0017] [Details of the embodiments of the present disclosure] Specific examples of optical fibers and methods for manufacturing the same according to the present embodiments will be described with reference to the drawings as necessary. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. In the following description, identical elements in the drawings will be designated by the same reference numerals, and duplicated explanations will be omitted.

[0018] (optical fiber) Fig. 1 is a cross-sectional view showing the configuration of an optical fiber according to one embodiment. Fig. 1 shows a cross section perpendicular to the central axis direction (optical axis direction) of the optical fiber 1. As shown in Fig. 1, the optical fiber 1 of this embodiment includes a glass fiber 10, which is an optical transmission body, and a coating resin layer 20 that contacts the glass fiber 10 and coats the glass fiber 10.

[0019] The glass fiber 10 includes a core 12 and a cladding 14 that covers the core 12. The glass fiber 10 is a glass member made of, for example, silica (SiO2) glass. The glass fiber 10 transmits light introduced into the optical fiber 1. The core 12 is provided, for example, in a region that includes the central axis of the glass fiber 10. The core 12 is made, for example, of pure SiO2 glass, or SiO2 glass containing GeO2 and / or fluorine. The cladding 14 is provided in a region that surrounds the core 12. The cladding 14 has a refractive index lower than that of the core 12. The cladding 14 is made, for example, of pure SiO2 glass, or SiO2 glass doped with fluorine.

[0020] The coating resin layer 20 is an ultraviolet-curable resin layer that covers the clad 14. The coating resin layer 20 includes a primary resin layer 22 that coats the outer periphery of the glass fiber 10, and a secondary resin layer 24 that coats the outer periphery of the primary resin layer 22. The primary resin layer 22 is in contact with the outer periphery of the clad 14 and coats the entire clad 14. The secondary resin layer 24 is in contact with the outer periphery of the primary resin layer 22 and coats the entire primary resin layer 22. The thickness of the primary resin layer 22 is, for example, 10 μm or more and 50 μm or less. The thickness of the secondary resin layer 24 is, for example, 10 μm or more and 40 μm or less. The coating resin layer 20 may further include a colored resin layer that coats the outer periphery of the secondary resin layer 24.

[0021] The primary resin layer 22 contains a cured product of a first resin composition containing a photopolymerizable compound and a phosphine oxide-based photopolymerization initiator. The secondary resin layer 24 contains a cured product of a second resin composition containing a photopolymerizable compound and a phosphine oxide-based photopolymerization initiator. The amount of unreacted phosphine oxide-based photopolymerization initiator in the coating resin layer 20 is 0.5% by mass or less. This reduces the change over time in coating strippability of the optical fiber. The amount of unreacted phosphine oxide-based photopolymerization initiator is preferably 0.49% by mass or less, more preferably 0.48% by mass or less, and even more preferably 0.45% by mass or less. The lower limit of the amount of unreacted phosphine oxide-based photopolymerization initiator is not particularly limited and may be 0.01% by mass or more, 0.03% by mass or more, or 0.05% by mass or more.

[0022] Examples of phosphine oxide photopolymerization initiators include 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Omnirad TPO, manufactured by IGM Resins), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (Omnirad 819, manufactured by IGM Resins), and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

[0023] The first resin composition contains only a phosphine oxide-based photopolymerization initiator as a photopolymerization initiator. From the viewpoint of reducing the cost of the resin compositions, the first resin composition and the second resin composition may contain only a phosphine oxide-based photopolymerization initiator as a photopolymerization initiator.

[0024] The second resin composition may further contain an acetophenone-based photopolymerization initiator from the viewpoint of improving surface curability.

[0025] Examples of acetophenone-based photopolymerization initiators include 1-hydroxycyclohexyl phenyl ketone (Omnirad 184, manufactured by IGM Resins), 2,2-dimethoxy-2-phenylacetophenone (Omnirad 651, manufactured by 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, manufactured by IGM Resins).

[0026] The photopolymerizable compound according to this embodiment may include an oligomer and a monomer. Examples of the oligomer include urethane (meth)acrylate and epoxy (meth)acrylate.

[0027] The urethane (meth)acrylate may be a compound obtained by reacting a polyol compound, a polyisocyanate compound, and a hydroxyl group-containing (meth)acrylate compound.

[0028] Examples of polyol compounds include polytetramethylene glycol, polypropylene glycol, and bisphenol A-ethylene oxide adduct diol. The number average molecular weight (Mn) of the polyol compound may be 300 or more and 8000 or less in order to adjust the Young's modulus of the coating resin layer. The Mn of the polyol compound constituting the urethane (meth)acrylate contained in the first resin composition may be 1200 or more and 8000 or less, 2000 or more and 7000 or less, or 3000 or more and 6000 or less in order to reduce the Young's modulus of the primary resin layer. The Mn of the polyol compound constituting the urethane (meth)acrylate contained in the second resin composition may be 300 or more and less than 1200, 400 or more and 1100 or less, or 500 or more and 1000 or less in order to increase the Young's modulus of the secondary resin layer.

[0029] 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 (meth)acrylate.

[0030] Organotin compounds are generally used as catalysts for synthesizing 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. From the viewpoints of easy availability and catalytic performance, it is preferable to use dibutyltin dilaurate or dibutyltin diacetate as the catalyst.

[0031] A lower alcohol having 5 or less carbon atoms may be used during synthesis of the urethane (meth)acrylate. 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.

[0032] As the epoxy (meth)acrylate, a compound obtained by reacting an epoxy resin having two or more glycidyl groups with a compound having a (meth)acryloyl group can be used.

[0033] The monomer may be a monofunctional monomer having one polymerizable group or a polyfunctional monomer having two or more polymerizable groups. Two or more types of monomers may be used in combination.

[0034] 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, 2 ... Octyl (meth)acrylate, isooctyl (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, (Meth)acrylate monomers such as dicyclopentenyloxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, nonylphenol polyethylene glycol (meth)acrylate, nonylphenol EO-modified acrylate, nonylphenoxy polyethylene glycol (meth)acrylate, and isobornyl (meth)acrylate; (meth)acrylic acid, (meth)acrylic acid dimer, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, and ω-carboxy -Carboxyl group-containing monomers such as polycaprolactone (meth)acrylate; heterocycle-containing (meth)acrylates such as N-acryloylmorpholine, N-vinylpyrrolidone, N-vinylcaprolactam, N-acryloylpiperidine, N-methacryloylpiperidine, N-acryloylpyrrolidine, 3-(3-pyridyl)propyl (meth)acrylate, and cyclic trimethylolpropane formal acrylate; maleimide-based monomers such as maleimide, N-cyclohexylmaleimide, and N-phenylmaleimide;Examples of such N-substituted amide monomers include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-hexyl(meth)acrylamide, N-methyl(meth)acrylamide, N-butyl(meth)acrylamide, N-butyl(meth)acrylamide, N-methylol(meth)acrylamide, and N-methylolpropane(meth)acrylamide; aminoalkyl(meth)acrylate monomers include aminoethyl(meth)acrylate, aminopropyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, and tert-butylaminoethyl(meth)acrylate; and succinimide monomers include N-(meth)acryloyloxymethylene succinimide, N-(meth)acryloyl-6-oxyhexamethylene succinimide, and N-(meth)acryloyl-8-oxyoctamethylene succinimide.

[0035] Examples of polyfunctional monomers include ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, di(meth)acrylate of alkylene oxide adduct of bisphenol A, tetraethylene glycol di(meth)acrylate, hydroxypivalic acid 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, isopentyldiol di(meth)acrylate, 3-ethyl-1,8-octanediol di(meth)acrylate, bisphenol A EO adduct di(meth)acrylate of Nol A, trimethylolpropane tri(meth)acrylate, trimethyloloctane tri(meth)acrylate, trimethylolpropane polyethoxytri(meth)acrylate, trimethylolpropane polypropoxytri(meth)acrylate, trimethylolpropane polyethoxypolypropoxytri(meth)acrylate, tris[(meth)acryloyloxyethyl]isocyanurate, pentaerythritol tri(meth)acrylate, pentaerythritol Examples of the acrylate copolymer include dipentaerythritol polyethoxytetra(meth)acrylate, pentaerythritol polypropoxytetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and caprolactone-modified tris[(meth)acryloyloxyethyl]isocyanurate.

[0036] From the viewpoint of adjusting the viscosity of the resin composition to improve its applicability to glass fiber or optimizing the Young's modulus of the cured product, at least one of the first resin composition and the second resin composition may contain nonylphenol polyethylene glycol acrylate as a monofunctional monomer, and it is preferable that the first resin composition contains nonylphenol polyethylene glycol acrylate. Examples of nonylphenol polyethylene glycol acrylate include nonylphenol ethylene oxide-modified (8-mol adduct) acrylate, nonylphenol ethylene oxide-modified (1-mol adduct) acrylate, and nonylphenol ethylene oxide-modified (4-mol adduct) acrylate.

[0037] From the viewpoint of suppressing deterioration of coating removability over time, the amount of unreacted nonylphenol polyethylene glycol acrylate in the coating resin layer may be less than 1.0% by mass, preferably 0.95% by mass or less, more preferably 0.93% by mass or less, and even more preferably 0.90% by mass or less. The lower limit of the amount of unreacted nonylphenol polyethylene glycol acrylate is not particularly limited, and may be 0.1% by mass or more, 0.3% by mass or more, or 0.5% by mass or more.

[0038] The resin composition may further contain a silane coupling agent, a leveling agent, an antifoaming agent, an antioxidant, a sensitizer, and the like.

[0039] The silane coupling agent is not particularly limited as long as it does not interfere with the curing of the resin composition. Examples of the silane coupling agent 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, N-(β-aminoethyl)-γ β-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-trimethoxysilylpropyldimethylthiocarbamyltetrasulfide, and γ-trimethoxysilylpropylbenzothiazyltetrasulfide.

[0040] (Optical fiber manufacturing method) The method for manufacturing an optical fiber according to this embodiment includes a coating step of coating a first resin composition and a second resin composition onto the outer circumference of a glass fiber whose temperature is 80°C or less, and a curing step of curing the resin compositions by irradiating them with ultraviolet light after the coating step.

[0041] In the coating step, a first resin composition is applied to the surface of the glass fiber 10 to form a first resin layer (a layer corresponding to the primary resin layer 22 after curing) made of the first resin composition on the surface of the glass fiber 10, and a second resin composition is applied to the surface of the first resin layer to form a second resin layer (a layer corresponding to the secondary resin layer 24 after curing) made of the second resin composition on the surface of the first resin layer. That is, in the coating step, the first resin composition and the second resin composition are applied to the glass fiber 10 at a temperature of 80°C or less, in that order, from the glass fiber 10 to the next.

[0042] Controlling the temperature of the glass fiber in the coating step facilitates reducing the proportion of unreacted phosphine oxide-based photopolymerization initiator. The temperature of the glass fiber is preferably 75°C or less, more preferably 70°C or less. The lower limit of the temperature of the glass fiber is not particularly limited, and may be 30°C or more, 40°C or more, or 45°C or more.

[0043] In the curing step, the first resin layer and the second resin layer are cured by ultraviolet irradiation, thereby forming a primary resin layer 22 from the first resin layer and a secondary resin layer 24 from the second resin layer.

[0044] Examples of ultraviolet light sources include ultraviolet LEDs and ultraviolet lamps. The wavelength of ultraviolet light emitted from ultraviolet LEDs is, for example, in the range of 300 nm to 450 nm, and the wavelength range of ultraviolet light emitted from ultraviolet lamps is, for example, 200 nm to 450 nm. It is preferable to use ultraviolet LEDs because they have high illuminance and can reduce power consumption, and it is more preferable to use ultraviolet LEDs whose ultraviolet wavelengths are in the range of 350 nm to 405 nm. The irradiation time of ultraviolet light from ultraviolet LEDs is, for example, 4×10 -3 The ultraviolet light is irradiated in an inert gas atmosphere such as a nitrogen atmosphere. [Example]

[0045] The present disclosure will be described in more detail below by showing the results of evaluation tests using examples and comparative examples according to the present disclosure. Note that the present disclosure is not limited to these examples.

[0046] [First resin composition] (Resin composition P1) Urethane acrylate a was prepared as an oligomer by reacting polypropylene glycol with a molecular weight of 4000, 2,4-tolylene diisocyanate, and hydroxyethyl acrylate. Resin composition P1 was prepared by mixing 78 parts by mass of urethane acrylate a, 9 parts by mass of nonylphenol polyethylene glycol acrylate (product name "SR504" manufactured by Sartomer), 7 parts by mass of N-vinyl caprolactam, 5 parts by mass of 1,6-hexanediol diacrylate, and 1 part by mass of 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Omnirad TPO).

[0047] [Second resin composition] (Resin composition S1) Urethane acrylate b was prepared as an oligomer by reacting polypropylene glycol with a molecular weight of 600, 2,4-tolylene diisocyanate, and hydroxyethyl acrylate. Resin composition S1 was prepared by mixing 27 parts by mass of urethane acrylate b, 30 parts by mass of tripropylene glycol diacrylate (trade name "TPGDA" from Daicel-Allnex Corporation), 40 parts by mass of 2-phenoxyethyl acrylate (trade name "Light Acrylate PO-A" from Kyoeisha Chemical Co., Ltd.), 1 part by mass of TPO, and 2 parts by mass of 1-hydroxycyclohexyl phenyl ketone (Omnirad 184).

[0048] (Resin composition S2) Resin composition S2 was prepared by mixing 29 parts by mass of urethane acrylate b, 30 parts by mass of TPGDA, 40 parts by mass of PO-A, and 1 part by mass of TPO.

[0049] [Fabrication of optical fiber] Example 1 In the coating process, the temperature 50 A first resin layer having a thickness of 32.5 μm was formed on the outer periphery of a glass fiber having a diameter of 125 μm and temperature of 0°C using resin composition P1, and a second resin layer having a thickness of 27.5 μm was further formed on the outer periphery of the first resin layer using resin composition S1.

[0050] In the curing process, ultraviolet LED (emission wavelength λ = 385 nm) is used, and the ultraviolet irradiation dose (illuminance x irradiation time) is 29 mW / cm 2 The first and second layers were cured by irradiation under the condition of 1 / 4 sec, and an optical fiber having a coating resin layer consisting of a primary resin layer and a secondary resin layer was fabricated.

[0051] (Examples 2-5 and Comparative Examples 1-2) An optical fiber was produced in the same manner as in Example 1, except that the temperature of the glass fiber and the ultraviolet irradiation conditions were changed to the values ​​shown in Table 1.

[0052] Example 6 In the coating process, a first resin layer having a thickness of 32.5 μm was formed on the outer periphery of a glass fiber having a diameter of 125 μm and a temperature of 60°C using resin composition P1, and a second resin layer having a thickness of 27.5 μm was further formed on the outer periphery of the first resin layer using resin composition S2.

[0053] In the curing process, ultraviolet LEDs are used, and the ultraviolet light with an emission wavelength of 385 nm is irradiated at a dose of 21 mW / cm. 2 The first and second layers were cured by irradiation under the condition of 1 / 4 sec, and an optical fiber having a coating resin layer consisting of a primary resin layer and a secondary resin layer was fabricated.

[0054] (Examples 7-9 and Comparative Example 3) An optical fiber was produced in the same manner as in Example 6, except that the temperature of the glass fiber and the ultraviolet irradiation conditions were changed to the values ​​shown in Table 2.

[0055] (Measurement of unreacted amount) After immersing 1 g of optical fiber in acetone, the unreacted TPO and nonylphenol polyethylene glycol acrylate extracted into the acetone were measured by GC-FPD analysis using a Frontier Lab UA-1 column.

[0056] (Coating removal) The optical fiber plate was placed 30 cm from a 30 W fluorescent lamp and left to stand at room temperature for 14 days. The resin coating layer was then removed from the optical fiber at 23°C using a Sumitomo Electric Industries, Ltd. "JR-6" jacket remover. Residue from the resin layer remaining on the glass fiber was wiped off with a Kimwipe (Nippon Paper Crecia) moistened with ethanol. The results were rated as "A" if the coating residue was removed in one try, "B" if it was removed in two or three tries, and "C" if it was removed in four or more tries or if the coating residue could not be removed.

[0057] [Table 1]

[0058] [Table 2] [Explanation of symbols]

[0059] 1. Optical fiber 10 Glass Fiber 20 Coating resin layer 22 Primary resin layer 24 Secondary resin layer

Claims

1. a glass fiber including a core and a clad; and a coating resin layer that is in contact with the glass fiber and coats the glass fiber; the coating resin layer includes a primary resin layer that is in contact with the glass fiber and coats the glass fiber, and a secondary resin layer that coats the primary resin layer, the primary resin layer includes a cured product of a first resin composition containing a photopolymerizable compound and a phosphine oxide-based photopolymerization initiator; the secondary resin layer includes a cured product of a second resin composition containing a photopolymerizable compound and a phosphine oxide-based photopolymerization initiator; the amount of unreacted phosphine oxide photopolymerization initiator in the coating resin layer is 0.5% by mass or less, the first resin composition and the second resin composition do not contain any photopolymerization initiator other than the phosphine oxide-based photopolymerization initiator; At least one of the first resin composition and the second resin composition contains nonylphenol polyethylene glycol acrylate as the photopolymerizable compound, An optical fiber, wherein the amount of unreacted nonylphenol polyethylene glycol acrylate in the coating resin layer is less than 1.0 mass %.

2. 2. The method of claim 1, further comprising the steps of: a coating step of coating the first resin composition and the second resin composition in this order on a glass fiber having a temperature of 80°C or less, in such a manner that the first resin composition and the second resin composition are applied in that order from the glass fiber; a curing step of curing the resin composition by irradiating it with ultraviolet light after the coating step, In the curing step, ultraviolet light emitted by an ultraviolet light emitting diode is irradiated.

3. 3. The method for producing an optical fiber according to claim 2, wherein the wavelength of the ultraviolet light is in the range of 350 nm to 405 nm.

4. The irradiation amount of the ultraviolet light is 14 mW / cm ２ ・Seconds or more 29mW / cm ２ The method for producing an optical fiber according to claim 3, wherein the irradiation is carried out for 1 second or less.

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