Patent Publication Number: US-2021179762-A1

Title: Resin composition, optical fiber, and method for producing optical fiber

Description:
TECHNICAL FIELD 
     The present disclosure relates to a resin composition, an optical fiber, and a method for manufacturing the optical fiber. 
     This application claims priority based on Japanese Patent Application No. 2019-108597 filed on Jun. 11, 2019, and incorporates all the contents described in the Japanese application. 
     BACKGROUND ART 
     An optical fiber has generally a coating resin layer for protecting a glass fiber that is an optical transmission medium. In order to reduce an increase in transmission loss induced by micro-bend generated when lateral pressure is applied to the optical fiber, the optical fiber has been required to have excellent lateral pressure characteristics. 
     The coating resin layer can be formed by using an ultraviolet curable resin composition containing an oligomer, a monomer, a photopolymerization initiator and the like. For example, in Patent Literature 1, it is investigated to improve the lateral pressure characteristics of the optical fiber by forming a resin layer using an ultraviolet curable resin composition containing a filler made of synthetic silica as a raw material. 
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] JP 2014-219550 A 
     SUMMARY OF INVENTION 
     A resin composition according to an aspect of the present disclosure comprises a base resin containing an oligomer comprising a urethane (meth)acrylate oligomer, a monomer, and a photopolymerization initiator, and hydrophobic inorganic oxide particles, and the breaking elongation of a resin film obtained by curing the resin composition with an integrated light amount of 900 mJ/cm 2  or more and 1100 mJ/cm 2  or less is 2.5% or more and 50% or less at 23° C., and the Young&#39;s modulus of the resin film is 1150 MPa or more and 2700 MPa or less at 23° C. 
    
    
     
       BRIEF DESCRIPTION OF DRAWING 
         FIG. 1  is a schematic cross-section diagram showing an example of the optical fiber according to the present embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Problem to be Solved by the Present Disclosure 
     A coating resin layer generally includes a primary resin layer and a secondary resin layer. The resin composition forming the secondary resin layer is required to improve the lateral pressure characteristics of the optical fiber by increasing the Young&#39;s modulus. However, the toughness of the resin layer formed from the resin composition containing the filler is lowered, causing the coating resin layer to crack in bending the optical fiber, and as a result, the optical fiber may not withstand long-term use. 
     An object of the present disclosure is to provide a resin composition capable of forming a resin layer having excellent toughness and an optical fiber including the secondary resin layer formed from the resin composition. 
     Effects of the Present Disclosure 
     The present disclosure can provide a resin composition capable of forming a resin layer having excellent toughness and an optical fiber including the secondary resin layer formed from the resin composition. 
     Description of Embodiments of the Present Disclosure 
     First, the contents of the embodiment of the present disclosure will be described by listing them. A resin composition according to an aspect of the present disclosure comprises a base resin containing an oligomer comprising a urethane (meth)acrylate oligomer, a monomer, and a photopolymerization initiator, and hydrophobic inorganic oxide particles, and the breaking elongation of a resin film obtained by curing the resin composition with an integrated light amount of 900 mJ/cm2 or more and 1100 mJ/cm 2  or less is 2.5% or more and 50% or less at 23° C., and the Young&#39;s modulus of the resin film is 1150 MPa or more and 2700 MPa or less at 23° C. 
     Such resin composition can form a resin layer having excellent toughness. In addition, an optical fiber having excellent lateral pressure characteristics can be prepared by using the above resin composition as an ultraviolet curable resin composition for coating the optical fiber. 
     Since the resin layer has an excellent balance between Young&#39;s modulus and elongation, the content of the urethane (meth)acrylate oligomer may be 15% by mass or more and 70% by mass or less based on the total amount of the oligomer and the monomer. 
     Due to easy formation of a tough resin layer, the monomer may include a monomer having a phenoxy group. 
     Due to excellent dispersion properties in the resin composition and easy adjustment of Young&#39;s modulus, the inorganic oxide particles may be particles including at least one selected from the group consisting of silicon dioxide, zirconium dioxide, aluminum oxide, magnesium oxide, titanium oxide, tin oxide, and zinc oxide. Due to formation of a resin layer with a high Young&#39;s modulus, the average primary particle size of the inorganic oxide particles may be 5 nm or more and 800 nm or less. 
     Due to easy formation of a tougher resin layer, the breaking elongation of the resin film may be 5.0% or more and 45% or less at 23° C. 
     The optical fiber according to an aspect of the present disclosure comprises a glass fiber comprising a core and a cladding, a primary resin layer being in contact with a glass fiber and coating the glass fiber, and a secondary resin layer coating the primary resin layer, wherein the secondary resin layer includes a cured product of the resin composition. Accordingly, the lateral pressure characteristics of the optical fiber can be improved. 
     A method for manufacturing the optical fiber according to an aspect of the present disclosure comprises an application step of applying the above resin composition onto the outer periphery of a glass fiber composed of a core and a cladding and a curing step of curing the resin composition by irradiation with ultraviolet rays after the application step. 
     This can form a resin layer having excellent toughness, allowing production of an optical fiber capable of preventing external wound during rewinding work. 
     Detail of Embodiment of the Present Disclosure 
     Specific examples of a resin composition and an optical fiber according to the present embodiment will be described referring to the drawing as necessary. The present invention is not limited to these illustrations but is indicated by the claims and intended to include meanings equivalent to the claims and all modifications within the claims. In the following description, the same reference numerals are given to the same elements in the description of the drawing, and redundant explanations are omitted. 
     &lt;Resin Composition&gt; 
     The resin composition according to the present embodiment comprises a base resin containing an oligomer comprising a urethane (meth)acrylate oligomer, a monomer, and a photopolymerization initiator, and hydrophobic inorganic oxide particles. 
     From the viewpoint of forming the resin layer having excellent toughness, the breaking elongation of the resin film obtained by curing the above resin composition with an integrated light amount of 900 mJ/cm 2  or more and 1100 mJ/cm 2  or less is 2.5% or more and 50% or less at 23° C. The lower limit of the breaking elongation of the resin film may be 2.6% or more, 2.8% or more, 5.0% or more, or 7.0% or more, and the upper limit of the breaking elongation of the resin film may be 48% or less, 45% or less, or 40% or less. The breaking elongation of the resin film is preferably 5.0% or more and 45% or less, and more preferably 7.0% or more and 45% or less at 23° C., because the effect of the present disclosure can be easily exhibited. 
     The Young&#39;s modulus of the above resin film is 1150 MPa or more and 2700 MPa or less at 23° C., preferably 1200 MPa or more and 2600 MPa or less, and more preferably 1200 MPa or more and 2500 MPa or less. The Young&#39;s modulus of the resin film of 1150 MPa or more is easy to improve the lateral pressure characteristics of the optical fiber. The Young&#39;s modulus of the resin film of 2700 MPa or less can provide proper toughness to the secondary resin layer so that crack or the like in the secondary resin layer is hard to occur. 
     (Base Resin) 
     The oligomer according to the present embodiment includes a urethane (meth)acrylate oligomer. As the urethane (meth)acrylate oligomer, an oligomer obtained by reacting a polyol compound, a polyisocyanate compound, and a hydroxyl group-containing (meth)acrylate compound can be used. (Meth)acrylate means an acrylate or a methacrylate corresponding to it. The same applies to (meth)acrylic acid. 
     Examples of the polyol compound include polytetramethylene glycol, polypropylene glycol, and bisphenol A-ethylene oxide addition diol. Examples of the polyisocyanate compound includes 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane  4 , 4 ′-diisocyanate. Examples of the hydroxyl group-containing (meth)acrylate compound 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. 
     From the viewpoint of adjusting the Young&#39;s modulus and elongation of the resin film, the number average molecular weight of the polyol compound is preferably 300 or more and 3000 or less, more preferably 400 or more and 2500 or less, and further preferably 500 or more and 2000 or less. 
     As a catalyst for synthesizing a urethane (meth)acrylate oligomer, an organotin compound is generally used. Examples of the organotin compound include dibutyltin dilaurate, dibutyltin diacetate, dibutyltin maleate, dibutyltin bis(2-ethylhexyl mercaptoacetate), dibutyltin bis(isooctyl mercaptoacetate), and dibutyltin oxide. From the view point of easy availability or catalyst performance, it is preferable that dibutyltin dilaurate or dibutyltin diacetate be used as catalyst. 
     When the urethane (meth)acrylate oligomer is synthesized, lower alcohols having 5 or less carbon atoms may be used. Examples of the 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. 
     From the viewpoint of increasing the toughness of the resin layer, the content of the urethane (meth)acrylate oligomer is preferably 15% by mass or more and 70% by mass or less, more preferably 16% by mass or more and 65% by mass or less, and further preferably 17% by mass or more and 60% by mass or less based on the total amount of the oligomer and the monomer. 
     From the viewpoint of increasing the Young&#39;s modulus of the resin film, the oligomer may further contain an epoxy (meth)acrylate oligomer. As an epoxy (meth)acrylate oligomer, an oligomer obtained by reacting a compound having a (meth)acryloyl group with an epoxy resin having two or more glycidyl groups can be used. 
     As the monomer, a monofunctional monomer having one polymerizable group or a multifunctional monomer having two or more polymerizable groups can be used. A monomer may be used by mixing two or more monomers. 
     Due to easy formation of a tough resin layer, a monomer having a phenoxy group may be used as a monomer. 
     A (meth)acrylate compound having a phenoxy group can be used as the monomer having a phenoxy group. Examples of the (meth)acrylate compound having a phenoxy group include phenol EO-modified (meth)acrylate, nonylphenol EO-modified (meth)acrylate, phenol PO-modified (meth)acrylate, nonylphenol PO-modified (meth)acrylate, phenoxyethyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, and 3-phenoxybenzyl (meth)acrylate. EO-modification means having an ethylene oxide group represented by (C 2 H 4 O) n , and PO-modification means having a propylene oxide group represented by (C 3 H 6 O) n . n is an integer of 1 or more. 
     From the viewpoint of adjusting the Young&#39;s modulus of the resin film, the monomer having a phenoxy group may be at least one selected from the group consisting of phenol EO-modified acrylate, nonylphenol EO-modified acrylate, phenoxyethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, and 3-phenoxybenzyl acrylate. The monomer having a phenoxy group may be used by mixing two or more. 
     The content of the monomer having a phenoxy group is preferably 1% by mass or more and 30% by mass or less, more preferably 2% by mass or more and 25% by mass or less, and further preferably 4% by mass or more and 20% by mass or less based on the total amount of the oligomer and the monomer. The resin composition includes a monomer having a phenoxy group in such a range, allowing a resin layer having an appropriate Young&#39;s modulus as a secondary coating material for an optical fiber to be formed. 
     A monomer having no phenoxy group may be used as the monomer, a. The monomer having no phenoxy group may be a monofunctional monomer or a multifunctional monomer. 
     Examples of the monofunctional monomer having no phenoxy group include (meth)acrylate monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, sec-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, isooctyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, 4-tert-butylcyclohexanol (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, benzyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, nonylphenol polyethylene glycol (meth)acrylate, and isobornyl (meth)acrylate; carboxyl group containing monomers such as (meth)acrylic acid, (meth)acrylic acid dimer, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, and co-carboxy-polycaprolactone (meth)acrylate; heterocycle containing (meth)acrylates such as N-acryloyl morpholine, N-vinyl pyrrolidone, N-vinyl caprolactam, N-acryloylpiperidine, N-methacryloylpiperidine, N-acryloylpyrrolidine, 3-(3-pyridine) propyl (meth)acrylate, and cyclic trimethylolpropane formal acrylate; maleimide monomers such as maleimide, N-cyclohexyl maleimide, and N-phenyl maleimide; N-substituted 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-isopropyl (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)acryloyloxymethylene succinimide, N-(meth)acryloyl-6-oxyhexamethylene succinimide, and N-(meth)acryloyl-8-oxyoctamethylene succinimide. 
     Examples of the multifunctional monomer having no phenoxy group 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, isopentyl diol di(meth)acrylate, 3-ethyl-1,8-octanediol di(meth)acrylate, EO adduct of bisphenol A di(meth)acrylate, trimethylol propane tri(meth)acrylate, trimethylol octane tri(meth)acrylate, trimethylol propane polyethoxy tri(meth)acrylate, trimethylol propane polypropoxy tri(meth)acrylate, trimethylol propane polyethoxy polypropoxy tri(meth)acrylate, tris[(meth)acryloyloxyethyl] isocyanurate, pentaerythritol tri(meth)acrylate, pentaerythritol polyethoxy tetra(meth)acrylate, pentaerythritol polypropoxy tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylol propane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and caprolactone-modified tris[(meth)acryloyloxyethyl]isocyanurate. 
     The photopolymerization initiator can be appropriately selected from known radical photopolymerization initiators and used. Examples of the photopolymerization initiator include 1-hydroxycyclohexyl phenyl ketone (Omnirad 184 manufactured by IGM Resins), 2,2-dimethoxy-2-phenylacetophenone, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one (Omnirad 907 manufactured by IGM Resins), 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Omnirad TPO manufactured by IGM Resins), and bis(2,4,6-trimethylbenzoyl) phenylphosphine oxide (Omnirad 819, manufactured by IGM Resins). 
     The resin composition may further contain a silane coupling agent, a leveling agent, an antifoaming agent, an antioxidant, and a sensitizer. 
     The silane coupling agent is not particularly limited as long as it does not disturb curing of the resin composition. Examples of the silane coupling agent include tetramethyl silicate, tetraethyl silicate, mercaptopropyl trimethoxysilane, vinyltrichlorosilane, vinyltriethoxysilane, vinyltris(β-methoxy-ethoxy)silane, β-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane, dimethoxydimethylsilane, diethoxydimethylsilane, 3-acryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-methacryloxypropyltrimethoxysilane, N-(β-aminoethyl)-γ-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-trimethoxysilylpropyldimethylthiocarbamyl tetrasulfide, and γ-trimethoxysilylpropyl benzothiazyl tetrasulfide. 
     (Inorganic Oxide Particles) 
     The inorganic oxide particles according to the present embodiment have a surface subjected to hydrophobic treatment. The hydrophobic treatment according to the present embodiment is introduction of a hydrophobic group onto the surface of the inorganic oxide particles. The inorganic oxide particles having a hydrophobic group introduced have excellent dispersibility in the resin composition. The hydrophobic group may be a reactive group such as a (meth)acryloyl group or a vinyl group, or may be a non-reactive group such as an aliphatic hydrocarbon group (for example, an alkyl group) or an aromatic hydrocarbon group (for example, a phenyl group). In the case of the inorganic oxide particles having a reactive group, the resin layer having high Young&#39;s modulus is easy to form. 
     The inorganic oxide particles according to the present embodiment are dispersed in a dispersion medium. Using the inorganic oxide particles dispersed in the dispersion medium allows for uniform dispersion of the inorganic oxide particles in the resin composition and then improvement of the storage stability of the resin composition. The dispersion medium is not particularly limited as long as curing of the resin composition is not obstructed. The dispersion medium may be reactive or non-reactive. 
     A monomer such as a (meth)acryloyl compound and an epoxy compound can be used as the reactive dispersion medium. Examples of the (meth)acryloyl compound include 1,6-hexanediol di(meth)acrylate, EO-modified bisphenol A di(meth)acrylate, polyethylene glycol di(meth)acrylate, PO-modified bisphenol A di(meth)acrylate, polypropylene glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate. Compounds exemplified by monomers described above may be used as the (meth)acryloyl compound. 
     A ketone solvent such as methyl ethyl ketone (MEK), an alcohol solvent such as methanol (MeOH), or an ester solvent such as propylene glycol monomethyl ether acetate (PGMEA) may be used as a non-reactive dispersion medium. In the case of the non-reactive dispersion medium, the resin composition may be prepared by mixing the base resin and the inorganic oxide particles dispersed in the dispersion medium and removing a part of the dispersion medium. 
     The inorganic oxide particles dispersed in the dispersion medium remain to be dispersed in the resin layer after curing of the resin composition. When a reactive dispersion medium is used, the inorganic oxide particles are mixed with the dispersion medium in the resin composition and are incorporated in the resin layer with the dispersion condition maintained. When a non-reactive dispersion medium is used, at least a part of the dispersion medium evaporates and disappears from the resin composition, but the inorganic oxide particles remain in the resin composition with the dispersion condition remained and are also present in the cured resin layer with the dispersion condition remained. Electron microscope observation shows that the inorganic oxide particles present in the resin layer are in the condition of dispersion of the primary particle. 
     Due to excellent dispersion properties in the resin composition and easy formation of tough resin layer, it is preferable that the inorganic oxide particles are at least one selected from the group consisting of silicon dioxide (silica), zirconium dioxide (zirconia), aluminum oxide (alumina), magnesium oxide (magnesia), titanium oxide (titania), tin oxide, and zinc oxide. From the view point of excellent inexpensiveness, easy surface treatment, permeability to ultraviolet ray, easy provision of a resin layer with appropriate hardness, and the like, it is more preferable that the hydrophobic silica particles be used as the inorganic oxide particles according to the present embodiment. 
     From the viewpoint of increasing the Young&#39;s modulus of the resin film, the average primary particle size of the inorganic oxide particles is preferably 5 nm or more and 800 nm or less, more preferably 10 nm or more and 700 nm or less, and further preferably 10 nm or more and 650 nm or less. The average primary particle diameter can be measured with image analysis of electron microscope pictures, a light scattering method or a BET method, for example. The dispersion medium in which the primary particle of the inorganic oxide is dispersed appears to be visually transparent when the diameter of the primary particle is small. When the diameter of the primary particle diameter is relatively large (40 nm or more), the dispersion medium in which the primary particle is dispersed appears to be clouded, but the precipitate is not observed. 
     The content of the inorganic oxide particles is preferably 1% by mass or more and 60% by mass or less, more preferably 10% by mass or more and 50% by mass or less, and further preferably 15% by mass or more and 40% by mass or less based on the total amount of the oligomer, the monomer, and the inorganic oxide particles. The content of the inorganic oxide particles of 1% by mass or more allows for easy formation of the resin layer with excellent lateral pressure characteristics. The content of the inorganic oxide particles of 60% by mass or less allows for easy improvement in the application properties of the resin composition. 
     The resin composition according to the present embodiment is preferably used as the secondary coating material for the optical fiber. Using the resin composition according to the present embodiment for the secondary resin layer, the coating resin layer having excellent toughness can be formed and the lateral pressure characteristics of the optical fiber can be improved. 
     &lt;Optical Fiber&gt; 
       FIG. 1  is a schematic cross-section diagram showing an example of the optical fiber according to the present embodiment. The optical fiber  10  comprises the glass fiber  13  including the core  11  and the cladding  12 , and the coating resin layer  16  including the primary resin layer  14  provided on the outer periphery of the glass fiber  13  and the secondary resin layer  15 . 
     The cladding  12  surrounds the core  11 . The core  11  and the cladding  12  mainly include glass such as silica glass, germanium-added silica glass or pure silica glass can be used, for example, in the core  11 , and pure silica glass or fluorine-added silica glass can be used in the cladding  12 . 
     In  FIG. 1 , for example, the outside diameter (D 2 ) of the glass fiber  13  is about 100 μm to 125 μm, and the diameter (D 1 ) of the core  11  constituting the glass fiber  13  is about 7 μm to 15 μm. The thickness of the coating resin layer  16  is typically about 22 μm to 70 μm. The thickness of each of the primary resin layer  14  and the secondary resin layer  15  may be about 5 μm to 50 μm. 
     When the outside diameter (D 2 ) of the glass fiber  13  is about 125 μm and the thickness of the coating resin layer  16  is 60 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 about 10 μm to 50 μm, for example, the thickness of the primary resin layer  14  may be 35 μm and the thickness of the secondary resin layer  15  may be 25 μm. The outside diameter of the optical fiber  10  may be about 245 μm to 265 μm. 
     When the outer diameter (D 2 ) of the glass fiber  13  is about 125 μm and the thickness of the coating resin layer  16  is 27 μm or more and 48 μm or less, the thickness of each of the primary resin layer  14  and the secondary resin layer  15  may be about 10 μm to 38 μm, for example, the thickness of the primary resin layer  14  may be 25 μm and the thickness of the secondary resin layer  15  may be 10 μm. The outside diameter of the optical fiber  10  may be about 179 μm to 221 μm. 
     When the outside diameter (D 2 ) of the glass fiber  13  is about 100 μm and the thickness of the coating resin layer  16  is 22 μm or more and 37 μm or less, the thickness of each of the primary resin layer  14  and the secondary resin layer  15  may be about 5 μm to 32 μm, for example, the thickness of the primary resin layer  14  may be 25 μm and the thickness of the secondary resin layer  15  may be 10 μm. The outside diameter of the optical fiber  10  may be about 144 μm to 174 μm. 
     The resin composition according to the present embodiment can be applied to the secondary resin layer. The secondary resin layer can be formed by curing a resin composition comprising the above base resin and inorganic oxide particles. This can form the resin layer having excellent toughness. 
     A method for manufacturing the optical fiber according to the present embodiment comprises an application step of applying the above resin composition onto the outer periphery of a glass fiber composed of a core and a cladding; and a curing step of curing the resin composition by irradiation with ultraviolet rays after the application step. 
     The primary resin layer  14  can be formed by curing a resin composition including a urethane (meth)acrylate oligomer, a monomer, a photopolymerization initiator and a silane coupling agent. Prior art techniques can be used for a resin composition for the primary resin layer. A urethane (meth)acrylate oligomer, a monomer, a photopolymerization initiator and a silane coupling agent may be appropriately selected from compounds exemplified in the above base resin. The resin composition constituting the primary resin layer has composition different from the base resin forming the secondary resin layer. 
     Examples 
     Hereinafter, the results of evaluation test using Examples and Comparative Examples according to the present disclosure will be shown, and the present disclosure is described in more detail. The present invention is not limited to these examples. 
     [Resin Composition for a Secondary Resin Layer] 
     (Oligomer) 
     A urethane acrylate oligomer (UA-1) obtained by reacting polypropylene glycol having a molecular weight of 2000, 2,4-tolylene diisocyanate, and hydroxyethyl acrylate, a urethane acrylate oligomer (UA-2) obtained by reacting polypropylene glycol having a molecular weight of 600, 2,4-tolylene diisocyanate, and hydroxyethyl acrylate, and an epoxy acrylate oligomer (EA) were prepared as the oligomers. 
     (Monomer) 
     2-phenoxyethyl acrylate (POA, trade name “Light Acrylate PO-A” of Kyoeisha Chemical Co., Ltd.) and tripropylene glycol diacrylate (TPGDA, trade name “Viscoat #310HP” of Osaka Organic Chemical Industry Co., Ltd.) were prepared as the monomers. 
     (Photopolymerization Initiator) 
     As the photopolymerization initiator, 1-hydroxycyclohexyl phenyl ketone and 2,4,6-trimethylbenzoyldiphenylphosphine oxide were prepared. 
     (Inorganic Oxide Particles) 
     Silica sol including silica particles (Si-1 to Si-6) having the surface condition and the average primary particle size shown in Table 1 was prepared as the inorganic oxide particles. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Silica particles 
                 Si-1 
                 Si-2 
                 Si-3 
                 Si-4 
                 Si-5 
                 Si-6 
               
               
                   
               
             
            
               
                 Dispersion medium 
                 MEK 
                 MEK 
                 MEK 
                 MEK 
                 MEK 
                 MEK 
               
               
                 Surface condition 
                 Hydrophobic 
                 Hydrophobic 
                 Hydrophobic 
                 Hydrophobic 
                 Hydrophobic 
                 Hydrophilic 
               
               
                 Average primary 
                 10-20 
                 30-60 
                 80-110 
                 250-350 
                 450-640 
                 250-350 
               
               
                 particle size (nm) 
               
               
                   
               
            
           
         
       
     
     (Resin Composition) 
     First, a base resin was prepared by mixing the above oligomer, monomer, and photopolymerization initiator. Next, the silica sol was mixed with the base resin so as to have the content of the silica particles shown in Table 2 or Table 3, and then most of MEK (methyl ethyl ketone) as a dispersion medium was removed under reduced pressure to produce resin compositions of Examples and Comparative Examples, respectively. The content of remaining MEK in the resin composition was 5% by mass or less. 
     In Tables 2 and 3, the value of the oligomer and the monomer is the content based on the total amount of the oligomer and the monomer, and the value of the silica particles is the content based on the total amount of the monomer, the oligomer, and the silica particles. 
     (Young&#39;s Modulus) 
     The resin composition was applied onto a polyethylene terephthalate (PET) film by using a spin coater, and then cured by using an electrodeless UV lamp system (“VPS600 (D valve)” manufactured by Heraeus) at an integrated light amount of 900 mJ/cm 2  or more and 110 mJ/cm 2  or less to form a resin layer having a thickness of 200±20 μm on the PET film. The resin layer was peeled off from the PET film to obtain a resin film. The resin film was punched into a dumbbell shape of JIS K 7127 type 5 to prepare a test piece for measuring Young&#39;s modulus. A stress-strain curve was obtained by pulling the test piece under the conditions of 23±2° C. and 50±10% RH, a tensile speed of 1 mm/min, and a distance between marked lines of 25 mm using a tensile tester. Young&#39;s modulus was determined by 2.5% secant line. 
     (Breaking Elongation) 
     A resin layer having a thickness of 50±5 μm was formed on the PET film by the same operation as in the preparation of the above resin film. The resin layer was peeled off from the PET film to obtain a resin film. The resin film was punched into a dumbbell shape of JIS Z6251 type 3 to prepare a test piece for measuring the breaking elongation. Under the conditions of 23±2° C. and 50±10% RH, the test piece was pulled at a speed of 1 mm/min using a material testing machine 5985 manufactured by INSTRON, and the elongation was measured with a high-precision video elongation meter AVE manufactured by INSTRON. 
     [Production of Optical Fiber] 
     A urethane acrylate oligomer obtained by reacting polypropylene glycol having a molecular weight of 4000, isophorone diisocyanate, hydroxyethyl acrylate, and methanol was prepared. 75 parts by mass of the urethane acrylate oligomer, 12 parts by mass of a nonylphenol EO-modified acrylate, 6 parts by mass of N-vinylcaprolactam, 2 parts by mass of 1,6-hexanediol diacrylate, 1 part by mass of 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and 1 part by mass of 3-mercaptopropyltrimethoxysilane were mixed to obtain a resin composition for the primary resin layer. 
     The resin composition for the primary resin layer and the resin composition of Examples or Comparative Examples for the secondary resin layer were applied onto the outer periphery of a 125 μm diameter glass fiber composed of a core and a cladding, and then the resin composition was cured by irradiation with ultraviolet rays and a primary resin layer having a thickness of 35 μm and a secondary resin layer having a thickness of 25 μm around the outer periphery thereof were formed to produce an optical fiber. A linear speed was 1500 m/min. 
     (Bending Test) 
     An optical fiber having a length of 1 m was wound around a mandrel having a diameter of 3 mm once, both ends were fixed, and the mandrel was reciprocated three times in the longitudinal direction, and the presence or absence of disconnection was confirmed. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Example 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
                 10 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Silica 
                 Si-1 
                 38 
                 30 
                 20 
                 — 
                 — 
                 — 
                 — 
                 20 
                 1 
                 20 
               
               
                 particles 
                 Si-2 
                 — 
                 — 
                 — 
                 30 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 (% by 
                 Si-3 
                 — 
                 — 
                 — 
                 — 
                 30 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 mass) 
                 Si-4 
                 — 
                 — 
                 — 
                 — 
                 — 
                 30 
                 — 
                 — 
                 — 
                 — 
               
               
                   
                 Si-5 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 30 
                 — 
                 — 
                 — 
               
               
                 Oligomer 
                 UA-1 
                 18.0 
                 18.0 
                 18.0 
                 18.0 
                 18.0 
                 18.0 
                 18.0 
                 — 
                 — 
                 — 
               
               
                 (% by 
                 UA-2 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 50.0 
                 50.0 
                 60.0 
               
               
                 mass) 
                 EA 
                 45.0 
                 45.0 
                 45.0 
                 45.0 
                 45.0 
                 45.0 
                 45.0 
                 27.4 
                 27.4 
                 22.0 
               
               
                 Monomer 
                 POA 
                 10.0 
                 10.0 
                 10.0 
                 10.0 
                 10.0 
                 10.0 
                 10.0 
                 6.1 
                 6.1 
                 4.9 
               
               
                 (% by 
                 TPGDA 
                 27.0 
                 27.0 
                 27.0 
                 27.0 
                 27.0 
                 27.0 
                 27.0 
                 16.5 
                 16.5 
                 13.2 
               
               
                 mass) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Young&#39;s modulus 
                 2100 
                 1800 
                 1500 
                 1750 
                 1700 
                 1700 
                 1600 
                 1500 
                 1200 
                 1400 
               
               
                 (MPa) 
               
               
                 Breaking 
                 3 
                 8 
                 14 
                 7.5 
                 7 
                 6 
                 5 
                 30 
                 40 
                 35 
               
               
                 elongation (%) 
               
               
                 Disconnection 
                 Absence 
                 Absence 
                 Absence 
                 Absence 
                 Absence 
                 Absence 
                 Absence 
                 Absence 
                 Absence 
                 Absence 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Comparative Example 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Silica particles 
                 Si-1 
                 30 
                 38 
                 — 
                 38 
                 20 
                 — 
               
               
                 (% by mass) 
                 Si-6 
                 — 
                 — 
                 38 
                 — 
                 — 
                 — 
               
               
                 Oligomer (% 
                 UA-1 
                 18.0 
                 18.0 
                 18.0 
                 14.0 
                 — 
                 18.0 
               
               
                 by mass) 
                 UA-2 
                 — 
                 — 
                 — 
                 — 
                 75.0 
                 — 
               
               
                   
                 EA 
                 45.0 
                 45.0 
                 45.0 
                 47.2 
                 13.7 
                 45.0 
               
               
                 Monomer (% 
                 POA 
                 — 
                 — 
                 10.0 
                 10.5 
                 3.1 
                 — 
               
               
                 by mass) 
                 TPGDA 
                 37.0 
                 37.0 
                 27.0 
                 28.3 
                 8.2 
                 37.0 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Young&#39;s modulus (MPa) 
                 — 
                 — 
                 — 
                 — 
                 — 
                 1100 
               
               
                 Breaking elongation (%) 
                 1 
                 &lt;1 
                 1 
                 2 
                 — 
                 18 
               
               
                 Disconnection 
                 Presence 
                 — 
                 Presence 
                 Presence 
                 — 
                 Absence 
               
               
                   
               
            
           
         
       
     
     REFERENCE SIGNS LIST 
       10 : Optical fiber,  11 : Core,  12 : Cladding,  13 : Glass fiber,  14 : Primary resin layer,  15 : Secondary resin layer,  16 : Coating resin layer.