Radiation curable composition and urethane (METH) acrylate for forming first coating of optical fiber

Abstract

The present invention relates to a radiation-curable composition for forming a first coating layer of an optical fiber, which is capable of forming a cured product having excellent flexibility and sufficient mechanical strength, and more particularly, to a radiation-curable composition for forming a first coating layer of an optical fiber, which is capable of forming a cured product having excellent flexibility and sufficient mechanical strength. The present invention relates to a curable resin composition containing (A) a urethane (meth) acrylate, (B) a (meth) acrylate compound other than component (A), and (C) a radiation polymerization initiator, the urethane (meth) acrylate (A) is obtained by reacting at least (a) a polyether diol having a number average molecular weight of 2000-5000, (b) a diisocyanate compound, (c) a hydroxyl group-containing (meth) acrylate compound, and (d) a diol having a molecular weight of 500 or less.

Description

Technical Field

[0001] The present invention relates to a radiation-curable composition for forming a primary coating of an optical fiber and a urethane (meth) acrylate suitable for the radiation-curable composition, and particularly relates to a radiation-curable composition for forming a primary coating of an optical fiber that can form a cured product having excellent flexibility and sufficient mechanical strength. Background Art

[0002] An optical fiber is composed of a glass fiber obtained by thermally melting and spinning glass and a coating (or also called a covering layer) provided on the glass fiber for the purpose of protection and reinforcement. For example, an optical fiber is manufactured by the following operations: First, a soft primary coating (hereinafter also referred to as "primary coating") is provided on the surface of the glass fiber, and then a highly rigid secondary coating (hereinafter also referred to as "secondary coating") is provided on the primary coating. A ribbon optical fiber and an optical cable obtained by fixing a plurality of optical fibers provided with coatings using a bundling material are also well-known. As a method for forming a coating on a glass fiber, for example, a method of applying a liquid curable resin composition to the glass fiber and curing it using heat or light, particularly ultraviolet light, is widely used.

[0003] Japanese Patent No. 6526012 (Patent Document 1) describes an invention related to a radiation-curable covering composition that generates a fiber covering layer having a low Young's modulus and a high tear strength. In particular, it describes the following fiber covering composition, which contains a polyether urethane acrylate compound (specifically, a polyether urethane acrylate compound formed by the reaction of a diisocyanate compound, a hydroxy acrylate compound, and a polyol compound) and a diadduct compound (specifically, a diacrylate compound formed by the reaction of a diisocyanate compound and a hydroxy acrylate compound), and the diadduct compound is present in an amount of 2.35% by mass to 4.82% by mass.

[0004] Japanese Unexamined Patent Application Publication No. 2017-141125 (Patent Document 2) describes an invention related to a radiation-curable resin composition having suitable properties as a raw material for an optical fiber. In particular, it describes the following radiation-curable resin composition for forming a primary covering layer of an optical fiber, which contains a urethane (meth) acrylate (A) and a radiation polymerization initiator (D), and the urethane (meth) acrylate (A) is a reaction product of (a) a diol having a number average molecular weight of 3,000 or less, (b) a diisocyanate, and (c) a hydroxy-containing (meth) acrylate, and has a number average molecular weight of 4,000 or more, and component (A) is contained in an amount of 60% by mass or more in the entire composition.

[0005] Japanese Patent Publication No. 5788672 (Patent Document 3) describes an invention related to a radiation-curable resin composition having suitable properties as a raw material for optical fibers. In particular, it describes a radiation-curable resin composition for forming the first coating layer of an optical fiber, which is characterized in that it contains (A) 50 to 90% by mass of a urethane oligomer, (B) 5 to 45% by mass of a monomer having one ethylenically unsaturated group, and (C) the content of a monomer having two or more ethylenically unsaturated groups is 2% by mass or less. The (A) urethane oligomer includes (a1) a urethane oligomer containing a reaction product of an aliphatic polyether diol, a diisocyanate, and a monohydric alcohol, or (a2) a urethane oligomer having an average of more than 1.0 structural units derived from a polyether diol and not having a (meth)acryloyl group. The (A) urethane oligomer is obtained by reacting a reaction product of an aliphatic polyether diol and a diisocyanate with a monohydric alcohol and then reacting a hydroxy group-containing (meth)acrylate.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Publication No. 6526012

[0009] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2017-141125

[0010] Patent Document 3: Japanese Patent Publication No. 5788672 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] When pressure is locally applied to the side surface of an optical fiber, the core of the glass fiber in the pressurized part may bend with a small curvature, resulting in light loss. From the viewpoint of suppressing such light loss (also called microbending loss), it is desired that the first coating be sufficiently soft. On the other hand, if the first coating is made soft, sufficient mechanical strength (breaking strength and elongation at break) may not be obtained. The radiation-curable compositions described in Patent Documents 1 to 3 are all radiation-curable compositions for forming the first coating layer of an optical fiber, and although their purpose is to balance softness and mechanical strength, there is still room for improvement.

[0013] Therefore, an object of the present invention is to provide a radiation-curable composition for forming the first coating layer of an optical fiber that can form a cured product having excellent softness and sufficient mechanical strength by a method different from the prior art. Another object of the present invention is to provide a urethane (meth)acrylate suitable for the radiation-curable composition for forming the first coating layer of an optical fiber.

[0014] Means for Solving the Problem

[0015] The inventor of the present invention conducted intensive studies to achieve the above object, and as a result, found that: by reacting at least (a) a polyether diol having a number average molecular weight of 2000 to 5000, (b) a diisocyanate compound, (c) a hydroxy group-containing (meth)acrylate compound, and (d) a diol having a molecular weight of 500 or less to obtain a urethane (meth)acrylate, a radiation-curable composition capable of forming a cured product having excellent flexibility and sufficient mechanical strength can be provided, and thus the present invention has been completed.

[0016] Therefore, the radiation-curable composition of the present invention is a radiation-curable composition for forming the first coating of an optical fiber, which contains (A) a urethane (meth)acrylate, (B) a (meth)acrylate compound other than the component (A), and (C) a radiation polymerization initiator, and the (A) urethane (meth)acrylate is obtained by reacting at least the following components (a), (b), (c), and (d):

[0017] (a) A polyether diol having a number average molecular weight of 2000 to 5000;

[0018] (b) A diisocyanate compound;

[0019] (c) A hydroxy group-containing (meth)acrylate compound; and

[0020] (d) A diol having a molecular weight of 500 or less.

[0021] In a preferred example of the radiation-curable composition of the present invention, the component (d) is a diol having a molecular weight of 200 or less.

[0022] In other preferred examples of the radiation-curable composition of the present invention, the component (b) is toluene diisocyanate (TDI) or isophorone diisocyanate (IPDI).

[0023] In addition, the urethane (meth)acrylate of the present invention is a urethane (meth)acrylate obtained by reacting at least the following components (a), (b), (c), and (d):

[0024] (a) A polyether diol having a number average molecular weight of 2000 to 5000;

[0025] (b) A diisocyanate compound;

[0026] (c) A hydroxy group-containing (meth)acrylate compound; and

[0027] (d) A diol having a molecular weight of 500 or less.

[0028] In a suitable example of the urethane (meth)acrylate of the present invention, the component (d) is a diol having a molecular weight of 200 or less.

[0029] In other suitable examples of the urethane (meth)acrylate of the present invention, the component (b) is toluene diisocyanate (TDI) or isophorone diisocyanate (IPDI).

[0030] Advantages of the Invention

[0031] The radiation-curable composition according to the present invention can provide a radiation-curable composition for forming a primary coating of an optical fiber, which can form a cured product having excellent flexibility and sufficient mechanical strength. In addition, the urethane (meth)acrylate according to the present invention can provide a urethane (meth)acrylate suitable for the radiation-curable composition for forming a primary coating of an optical fiber. Detailed Description of the Invention

[0032] Hereinafter, the present invention will be described in detail. The present invention relates to a radiation-curable composition and a urethane (meth)acrylate for forming a primary coating of an optical fiber.

[0033] In this specification, the "primary coating of an optical fiber" can be understood as a coating disposed at the position closest to the glass fiber among the coatings provided on the glass fiber. The primary coating can be provided so as to cover at least a part of the surface of the glass fiber. "For forming a primary coating of an optical fiber" can be understood as being capable of being used in the formation of the primary coating of an optical fiber or for forming the primary coating of an optical fiber. The radiation-curable composition of the present invention is particularly suitable as a material (also referred to as a raw material) for forming a primary coating of an optical fiber.

[0034] In this specification, the "radiation-curable composition" can be understood as a composition that can be cured by irradiation with radiation. Here, the "radiation" refers to infrared rays, visible light, ultraviolet rays, X-rays, electron rays, α-rays, β-rays, γ-rays, etc., and ultraviolet rays are particularly preferred.

[0035] In this specification, the "urethane (meth)acrylate" can be understood as a compound containing one or more (meth)acryloyl groups in the molecule and containing a urethane bond (-NHCOO-) in the repeating unit of the main chain. Here, the "(meth)acryloyl group" refers to a methacryloyl group or an acryloyl group. Among urethane (meth)acrylates, there are substances having a methacryloyl group, substances having an acryloyl group, and substances having both a methacryloyl group and an acryloyl group. Urethane (meth)acrylates can generally be formed by forming a urethane bond by reacting at least a diol compound, a diisocyanate compound, and a hydroxy group-containing (meth)acrylate compound.

[0036] The radiation curable composition of the present invention is a radiation curable composition for forming the first coating of an optical fiber, which contains the following components (A), (B) and (C).

[0037] (A) A urethane (meth) acrylate

[0038] (B) A (meth) acrylate compound other than the component (A)

[0039] (C) A radiation polymerization initiator

[0040] Hereinafter, the components (A), (B) and (C) used in the radiation curable composition of the present invention, and additional components used as required, etc. will be described.

[0041] (A) Component: urethane (meth)acrylate

[0042] (A) The urethane (meth) acrylate is a urethane (meth) acrylate obtained by reacting at least the following components (a), (b), (c) and (d).

[0043] (a) A polyether diol having a number average molecular weight of 2,000 to 5,000

[0044] (b) A diisocyanate compound

[0045] (c) A hydroxyl group-containing (meth) acrylate compound

[0046] (d) A diol having a molecular weight of 500 or less

[0047] In the present specification, the urethane (meth) acrylate described herein will also be referred to as "the urethane (meth) acrylate of the present invention".

[0048] (a) Component: polyether diol with a number average molecular weight of 2000 to 5000

[0049] The polyether diol having a number average molecular weight of 2,000 to 5,000 can impart excellent flexibility to the coating. Generally, when using such a polyether diol, there is a problem with the mechanical strength of the coating. However, in the radiation curable composition of the present invention, by using in combination the following (d) diol having a molecular weight of 500 or less, a coating excellent in flexibility and having sufficient mechanical strength can be formed. In addition, from the viewpoint of obtaining a viscosity suitable for high-speed coating of the radiation curable composition, a polyether diol in this molecular weight range is also preferred. As the component (a), a polyether diol having a number average molecular weight of 3,000 to 4,000 is preferred.

[0050] In this specification, the number-average molecular weight is a value determined by gel permeation chromatography and converted according to a standard polystyrene standard curve.

[0051] The polyether diol having a number-average molecular weight of 2,000 to 5,000 is not particularly limited, and an aliphatic polyether diol is preferred. For example, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, polyheptamethylene glycol, polydecamethylene glycol, and an aliphatic polyether diol obtained by ring-opening copolymerization of two or more ionically polymerizable cyclic compounds are preferred.

[0052] Examples of the ionically polymerizable cyclic compound include cyclic ethers such as ethylene oxide, propylene oxide, 1-epoxybutane, epoxyisobutane, 3,3-bis(chloromethyl)oxetane, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, dioxane, trioxane, tetraoxane, cyclohexene oxide, styrene oxide, epichlorohydrin, glycidyl methacrylate, allyl glycidyl ether, allyl glycidyl carbonate, butadiene monooxide, isoprene monooxide, vinyl oxetane, vinyltetrahydrofuran, vinylcyclohexene oxide, phenyl glycidyl ether, butyl glycidyl ether, and glycidyl benzoate.

[0053] Specific examples of the polyether diol obtained by ring-opening copolymerization of two or more of the ionically polymerizable cyclic compounds include binary copolymers obtained by combinations such as tetrahydrofuran and propylene oxide, tetrahydrofuran and 2-methyltetrahydrofuran, tetrahydrofuran and 3-methyltetrahydrofuran, tetrahydrofuran and ethylene oxide, propylene oxide and ethylene oxide, and 1-epoxybutane and ethylene oxide; and ternary polymers obtained by combinations such as tetrahydrofuran, 1-epoxybutane, and ethylene oxide. In addition, a polyether diol obtained by ring-opening copolymerization of the ionically polymerizable cyclic compound with cyclic imines such as ethyleneimine, cyclic lactone acids such as β-propiolactone and glycolide, or dimethylcyclosiloxanes can also be used.

[0054] The above-mentioned aliphatic polyether diol as the component (a) can also be obtained in the form of commercially available products such as PTMG2000, PTMG3000, PTMG4000 (manufactured by Mitsubishi Chemical Corporation), EXCENOL2020, EXCENOL3020, EXCENOL3030, EXCENOL4030, PREMINOL S3006 (manufactured by AGC Inc.), UNIOL D-2000, UNIOL D-4000 (manufactured by NOF Corporation), etc.

[0055] Among these aliphatic polyether diols, from the viewpoint of achieving both the softness of the coating and the high-speed coatability of the radiation-curable composition, it is preferable to use one or more ring-opening polymers of ionic polymerizable cyclic compounds having 2 to 4 carbon atoms, and the diol has a number-average molecular weight of 2,000 to 5,000. As such an aliphatic polyether diol, it is more preferable to use a ring-opening polymer of one or more oxides selected from ethylene oxide, propylene oxide, 1,2-epoxybutane, and 2,2-dimethyloxirane, especially a diol having a number-average molecular weight of 3,000 to 4,000.

[0056] The amount of the structural part derived from the component (a) in the component (A) is preferably 74% by mass or more and less than 91% by mass, more preferably 78% by mass or more and less than 87% by mass.

[0057] (a) The polyether diol having a number-average molecular weight of 2,000 to 5,000 can be used alone or in combination of two or more.

[0058] (b) Component: diisocyanate compound

[0059] The diisocyanate compound can react with the hydroxyl groups of the components (a), (c), and (d) to form urethane bonds.

[0060] Examples of the diisocyanate compound include aromatic diisocyanates, alicyclic diisocyanates, aliphatic diisocyanates, etc. Examples of the aromatic diisocyanate include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 1,3-benzenedimethylene diisocyanate, 1,4-benzenedimethylene diisocyanate, 1,5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethylbenzene diisocyanate, 4,4'-biphenyl diisocyanate, bis(2-isocyanatoethyl) fumarate, 6-isopropyl-1,3-phenylene diisocyanate, 4,4'-diphenylpropane diisocyanate, tetramethylbenzene dimethylene diisocyanate, etc. Examples of the alicyclic diisocyanate include isophorone diisocyanate, methylene bis(4-cyclohexyl isocyanate), hydrogenated diphenylmethane diisocyanate, hydrogenated benzene dimethylene diisocyanate, 2,5-bis(isocyanatomethyl)-bicyclo[2.2.1]heptane, 2,6-bis(isocyanatomethyl)-bicyclo[2.2.1]heptane, etc. Examples of the aliphatic diisocyanate include 1,6-hexane diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, etc.

[0061] Among these isocyanate compounds, from the viewpoints of economy and the ability to obtain a composition with stable quality, aromatic diisocyanates are more preferred, and tolylene diisocyanates (TDI) such as 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate are particularly preferred.

[0062] In addition, from the viewpoint of increasing the concentration of the urethane group in (A) urethane (meth)acrylate, a diisocyanate compound with a relatively low molecular weight is preferably used. In a preferred embodiment, component (d) is tolylene diisocyanate (TDI) or isophorone diisocyanate (IPDI).

[0063] The amount of the structural part derived from component (b) in component (A) is preferably 5% by mass or more and less than 17% by mass, more preferably 8% by mass or more and less than 14% by mass.

[0064] Component (b), the diisocyanate compound, can be used alone as one kind, or two or more kinds can be used in combination.

[0065] (c) Component: hydroxy group-containing (meth)acrylate compound

[0066] As the hydroxy group-containing (meth)acrylate compound used in the synthesis of (A) urethane (meth)acrylate, a hydroxy group-containing (meth)acrylate obtained by bonding a hydroxy group to a primary carbon atom (referred to as a primary hydroxy group-containing (meth)acrylate) and a hydroxy group-containing (meth)acrylate obtained by bonding a hydroxy group to a secondary carbon atom (referred to as a secondary hydroxy group-containing (meth)acrylate) are preferred, and a primary hydroxy group-containing (meth)acrylate is particularly preferred. A hydroxy group-containing (meth)acrylate in which the hydroxy group is bonded to a tertiary carbon atom (referred to as a tertiary hydroxy group-containing (meth)acrylate) has poor reactivity with an isocyanate group (hereinafter also referred to as "NCO"), so it is not preferred.

[0067] Examples of the primary hydroxy group-containing (meth)acrylate include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 1,6-hexanediol mono(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, neopentyl glycol mono(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolethane di(meth)acrylate, and the like.

[0068] Examples of the (meth)acrylate containing a secondary hydroxyl group include 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenyloxypropyl (meth)acrylate, 4-hydroxycyclohexyl (meth)acrylate, etc. In addition, compounds obtained by the addition reaction of a compound containing a glycidyl group such as an alkyl glycidyl ether, allyl glycidyl ether, glycidyl (meth)acrylate, etc. with (meth)acrylic acid can also be cited.

[0069] The amount of the structural part derived from the component (c) in the component (A) is preferably 2% by mass or more and less than 8% by mass, more preferably 3% by mass or more and less than 7% by mass.

[0070] (c) The hydroxyl group-containing (meth)acrylate can be used alone or in combination of two or more.

[0071] (d) Component: diol with a molecular weight of 500 or less

[0072] The diol having a molecular weight of 500 or less is a low molecular weight diol as the diol used in the synthesis of (A) urethane (meth)acrylate. By using such a low molecular weight diol, the mechanical strength of the coating can be significantly improved without reducing the softness of the coating. By using a urethane (meth)acrylate having a number average molecular weight of 2000 to 5000 as described above as a raw material in the radiation curable composition, a coating having a low Young's modulus and excellent softness can be formed, but there is a problem with mechanical strength. The present inventors found that by using the above-mentioned polyether diol having a number average molecular weight of 2000 to 5000 and a diol having a molecular weight of 500 or less in the radiation curable composition of the present invention, a coating having excellent softness and sufficient mechanical strength can be formed. As the component (d), a diol having a molecular weight of 200 or less is preferred, and a diol having a molecular weight of 100 or less is particularly preferred.

[0073] As the diol having a molecular weight of 500 or less, there is no particular limitation, and examples thereof include 1,2-ethanediol, 1,2-propanediol (also known as propylene glycol), 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,2-pentanediol, 1,3-pentanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, 1,2-hexanediol, 1,6-hexanediol, 2,5-hexanediol, 3-methyl-1,5-pentanediol, 1,4-cyclohexanediol, 2-methyl-2-propyl-1,3-propanediol, 2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-benzenedimethanol, 2,4-diethyl-1,5-pentanediol, 1,2-indanedimethanol, 2-butyl-2-ethyl-1,3-propanediol, 1,9-nonanediol, 1,2-decanediol, 1,10-decanediol, 3-hydroxy-2,2-dimethylpropyl 3-hydroxy-2,2-dimethylpropionate, 3-(2-ethylhexyloxy)-1,2-propanediol, 1,2-dodecanediol, 5,6-dodecanediol, 1,12-dodecanediol, 2,2-diisopentyl-1,3-propanediol, 1,2-tetradecanediol, 1,2-hexadecanediol, 1,16-hexanediol, 1,18-octadecanediol, 2,2-dinonyl-1,3-propanediol, and aliphatic polyether diols within the range satisfying the condition of having a molecular weight of 500 or less. Particularly preferred are 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, and aliphatic polyether diols. As the aliphatic polyether diols, for example, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, polyheptamethylene glycol, polydecamethylene glycol, and aliphatic polyether diols obtained by ring-opening copolymerization of two or more ion-polymerizable cyclic compounds are preferred.

[0074] Examples of the ion-polymerizable cyclic compounds include cyclic ethers such as ethylene oxide, propylene oxide, 1-epoxybutane, epoxyisobutane, 3,3-bischloromethyloxetane, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, dioxane, trioxane, tetraoxane, epoxycyclohexane, styrene oxide, epichlorohydrin, glycidyl methacrylate, allyl glycidyl ether, allyl glycidyl carbonate, butadiene monooxide, isoprene monooxide, vinyl oxetane, vinyl tetrahydrofuran, vinyl epoxycyclohexane, phenyl glycidyl ether, butyl glycidyl ether, and glycidyl benzoate.

[0075] As specific examples of the polyether diol obtained by ring-opening copolymerization of two or more of the above-mentioned ion-polymerizable cyclic compounds, binary copolymers obtained from combinations such as tetrahydrofuran and propylene oxide, tetrahydrofuran and 2-methyltetrahydrofuran, tetrahydrofuran and 3-methyltetrahydrofuran, tetrahydrofuran and ethylene oxide, propylene oxide and ethylene oxide, 1-epoxybutane and ethylene oxide, etc. can be cited; ternary polymers obtained from combinations of tetrahydrofuran, 1-epoxybutane and ethylene oxide, etc. In addition, polyether diols obtained by ring-opening copolymerization of the above-mentioned ion-polymerizable cyclic compounds with cyclic imines such as ethyleneimine, cyclic lactone acids such as β-propiolactone and glycolide, or dimethylcyclopolysiloxanes can also be used.

[0076] Regarding the diol of a polymer such as an aliphatic polyether diol, the diol having a number-average molecular weight of 500 or less is defined as the "diol having a molecular weight of 500 or less" of the component (d).

[0077] The above-mentioned aliphatic polyether diol as the component (d) can also be obtained in the form of commercially available products such as PTMG250 (manufactured by Mitsubishi Chemical Corporation), EXCENOL420, EXCENOL430 (both manufactured by AGC), PEG200, PEG300, PEG400, UNIOX G-450, UNIOLD-250, UNIOL D-400G, UNIOL TG-330 (all manufactured by NOF Corporation), etc.

[0078] Among these aliphatic polyether diols, from the viewpoint of improving the mechanical strength of the coating, it is preferable to use a ring-opening polymer of one or more ion-polymerizable cyclic compounds having 2 to 4 carbon atoms, and it is a diol having a number-average molecular weight of 500 or less. As such an aliphatic polyether diol, it is further preferably a ring-opening polymer of one or more oxides selected from ethylene oxide, propylene oxide, 1-epoxybutane, and epoxyisobutane, and it is a diol having a number-average molecular weight of 200 or less, and particularly preferably a ring-opening polymer of propylene oxide having a number-average molecular weight of less than 100.

[0079] Even when using the component (a) as a sufficiently high molecular weight component, the component (d) can increase the urethane group concentration of the component (A). Therefore, by using the composition of the present invention, a cured product having a low Young's modulus and high mechanical strength (breaking strength, elongation at break) can be obtained. In addition, regarding compounds other than diols that generate urea and thiourea by reacting with compounds having both an amino group and a hydroxyl group, diamines, and isocyanates such as dithiols, there is also a possibility of substituting for the component (d) or using it together with the component (d). Among them, from the viewpoint of controlling reactivity, the component (d) is preferably a diol.

[0080] The amount of the structural part derived from the component (d) in the component (A) is preferably 0.5% by mass or more and less than 4% by mass, more preferably 0.5% by mass or more and less than 3% by mass, and particularly preferably 0.7% by mass or more and less than 2% by mass.

[0081] The diol having a molecular weight of 500 or less of the component (d) may be used alone or in combination of two or more.

[0082] (e) Component: further component

[0083] In the synthesis of the urethane (meth)acrylate of the component (A), on the basis of using the above components (a) to (d), further components may be used. In this specification, the components that do not conform to the above components (a) to (d) are also referred to as "(e) components". Examples of the (e) component include monohydric alcohols or polyhydric alcohols, mercapto silanes, and amino silanes that do not conform to the above (a), (c), or (d). By using the (e) component, it bonds to the terminal of the component (A) instead of the (meth)acryloyl group, and thus a component (A) having one (meth)acryloyl group can be obtained.

[0084] Regarding the monohydric alcohol as the (e) component, for example, a lower alcohol having 1 to 8 carbon atoms is preferred, and aliphatic alcohols such as methanol, n-octanol, and 2-ethylhexanol are more preferred. Examples of the polyhydric alcohol as the (e) component include glycerol, 1,2,3-propanetriol, and saccharides. When using the component (d), two or more kinds of the component (d) can be used. In addition, regarding the mercapto silane and amino silane as the (e) component, for example, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, and 3-aminopropyltrimethoxysilane can be suitably used respectively. When using the (e) component, two or more kinds of the (e) component can be used.

[0085] The amount of the structural part derived from the component (e) in the component (A) is preferably less than 4% by mass, more preferably less than 3% by mass, and particularly preferably less than 2% by mass.

[0086] Regarding the synthesis of (A) urethane (meth)acrylate, preferably: in the presence of dibutyltin dilaurate or the like as a urethane synthesis catalyst, a diol [(a) component, (d) component] is reacted with a diisocyanate [(b) component], and thereafter, a hydroxy group-containing (meth)acrylate [(c) component] is reacted to proceed. In addition, when reacting the aforementioned diol with the diisocyanate, the reaction order of the diol and the diisocyanate is not particularly limited. For example, a mixture of the (a) component and the (d) component can be reacted with the (b) component, or the following order can be used: after reacting the (a) component with a part of the (b) component, then reacting the (d) component with the remainder of the (b) component, or after reacting the (d) component with a part of the (b) component, then reacting the (a) component with the remaining (b) component. Considering productivity, it is suitable to use the operation of reacting the aforementioned mixture of the (a) component and the (d) component with the (b) component. In addition, when using the (e) component, it can be reacted after the reaction of the diol and the diisocyanate, either simultaneously with or before or after the reaction with the hydroxy group-containing (meth)acrylate. Here, when using a monohydric alcohol and / or an aminosilane as the (e) component, after the reaction of the diol and the diisocyanate, the product thereof can be reacted successively with the hydroxy group-containing (meth)acrylate and the (e) component, or it can be reacted successively with the (e) component and the hydroxy group-containing (meth)acrylate, or it can be reacted simultaneously with the hydroxy group-containing (meth)acrylate and the (e) component. Preferably, the product obtained by the reaction of the diol and the diisocyanate is reacted successively with the hydroxy group-containing (meth)acrylate and the (e) component. On the other hand, when using a mercapto silane as the (e) component, after the reaction of the diol and the diisocyanate, the product thereof can be reacted successively with the hydroxy group-containing (meth)acrylate and the (e) component, or it can be reacted successively with the (e) component and the hydroxy group-containing (meth)acrylate, or it can be reacted simultaneously with the hydroxy group-containing (meth)acrylate and the (e) component. Preferably, the product obtained by the reaction of the diol and the diisocyanate is reacted successively with the (e) component and the hydroxy group-containing (meth)acrylate.

[0087] The (A) urethane (meth)acrylate obtained by the above method has, for example, the structure shown by the following formula (1).

[0088] [c]-[b]-[a]-[b]-[d]-[b]-[c] Formula (1)

[0089] In formula (1), [a], [b], [c], and [d] are structural moieties derived from the (a) component, (b) component, (c) component, and (d) component, respectively. The connecting bonds represented by "-" are all urethane bonds.

[0090] When component (e) is used in the synthesis of (A) urethane (meth) acrylate, a compound (i) having both a (meth) acryloyl group and a structure derived from component (e) and containing a urethane bond (-NHCOO-) in the repeating unit of the main chain can be formed, for example, a compound having one (meth) acryloyl group and a structure derived from component (e) and containing a urethane bond (-NHCOO-) in the repeating unit of the main chain; (ii) a compound having a structure derived from component (e) but not having a (meth) acryloyl group and containing a urethane bond (-NHCOO-) in the repeating unit of the main chain, for example, a compound having two structures derived from component (e) and containing a urethane bond (-NHCOO-) in the repeating unit of the main chain.

[0091] When component (e) is used, the resulting (A) urethane (meth) acrylate has, on the basis of the structure shown in the above formula (1) or on the basis of the structure shown in the above formula (1), a structure shown in, for example, the following formula (2).

[0092] [c]-[b]-[a]-[b]-[d]-[b]-[e] Formula (2)

[0093] In formula (2), the linking bond "-" connected to [e] is a urethane bond, a thiocarbamate bond, or a urea bond depending on the chemical species of component (e). The other linking bonds "-" are urethane bonds.

[0094] The concentration of the urethane group contained in (A) urethane (meth) acrylate is preferably 1.0 mmol / g or more, more preferably 1.1 mmol / g or more, still more preferably 1.15 mmol / g or more, and particularly preferably 1.2 mmol / g or more. In addition, the concentration of the urethane group contained in (A) urethane (meth) acrylate is preferably less than 1.7 mmol / g. When the urethane group concentration is within the above specific range, an increase in the Young's modulus can be suppressed and high strength can be obtained for the cured product of the radiation-curable composition of the present invention. The urethane group concentration can be increased by using a low molecular weight diol [(d) component] and a low molecular weight diisocyanate [preferably toluene diisocyanate (TDI) or isophorone diisocyanate (IPDI)].

[0095] In this specification, the "carbamate group concentration" means the amount of bonds formed by the reaction of the isocyanate group with an isocyanate group-reactive group in the urethane (meth)acrylate. The representative of the bonds that can be formed by this reaction is the urethane bond, so it is called the "carbamate group concentration". However, the bonds formed by the reaction of the isocyanate group with an isocyanate group-reactive group are not limited to the urethane bond (-NH-COO-), and examples thereof include a thiocarbamate bond (-NH-COS-), a urea bond (-NH-CO-NH-), etc. Therefore, the "carbamate group concentration" can also be expressed as the "concentration of bonds formed by the reaction of the isocyanate group with an isocyanate group-reactive group". Examples of the isocyanate group-reactive group include a hydroxyl group (-OH), a mercapto group (-SH), an amino group (-NH2), etc. When a mercapto silane or an amino silane is used as the aforementioned component (e), a thiocarbamate group or a urea group is formed, respectively.

[0096] The content of the (A) urethane (meth)acrylate in the radiation-curable composition of the present invention is preferably 50 parts by mass or more and less than 95 parts by mass, more preferably 60 parts by mass or more and less than 95 parts by mass, and particularly preferably 70 parts by mass or more and less than 90 parts by mass with respect to 100 parts by mass of the composition. By making the content of the (A) urethane (meth)acrylate within the above specific range, high-speed coatability of the radiation-curable composition of the present invention and appropriate softness as the first coating of an optical fiber can be obtained.

[0097] (A) The urethane (meth)acrylate may be used alone as one kind, or two or more kinds may be used in combination.

[0098] (B) Component: (meth)acrylate compound other than (A) component

[0099] The radiation-curable composition of the present invention contains a (meth)acrylate compound that does not conform to (A) urethane (meth)acrylate. In this specification, this (meth)acrylate compound is referred to as the "(meth)acrylate compound other than component (A)" or "component (B)". Typically, component (B) is a monomer having one or more (meth)acryloyl groups in the molecule, and preferably a monomer having one (meth)acryloyl group in the molecule. When component (B) is a monomer, it is often used for the purpose of diluting the composition containing (A) urethane (meth)acrylate, and thus is sometimes also referred to as a reactive diluent monomer. As component (B), examples include (meth)acrylates containing an aliphatic structure, (meth)acrylates containing an alicyclic structure, (meth)acrylates containing an aromatic structure, and the like. In addition, component (B) also includes (meth)acrylate compounds having a functional group different from the (meth)acryloyl group, such as (meth)acrylates containing a hydroxyl group. Furthermore, in this specification, compounds in which a (meth)acryloyl group is bonded to a nitrogen atom, such as (meth)acrylamide and acryloylmorpholine, also conform to the (meth)acrylate compound and are included in component (B). It should be noted that component (B) also includes oligomers and polymers that do not conform to component (A).

[0100] Among component (B), as the (meth)acrylate containing an aliphatic structure and having one (meth)acryloyl group in the molecule, examples include butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, methoxyethylene glycol (meth)acrylate, ethoxyethyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, and the like.

[0101] As the (meth)acrylate containing an alicyclic structure and having one (meth)acryloyl group in the molecule, examples include isobornyl (meth)acrylate, bornyl (meth)acrylate, tricyclodecyl (meth)acrylate, dicyclopentyl (meth)acrylate, dicyclopentenyl (meth)acrylate, cyclohexyl (meth)acrylate, 4-butylcyclohexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and the like.

[0102] Examples of the (meth)acrylate having an aromatic structure and having 1 (meth)acryloyl group in the molecule include benzyl (meth)acrylate and the like.

[0103] In addition, as the hydroxy group-containing (meth)acrylate having 1 (meth)acryloyl group in the molecule, the hydroxy group-containing (meth)acrylate compound used in the synthesis of (A) urethane (meth)acrylate can be used, and 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl acrylate, etc. are preferably exemplified.

[0104] In addition, examples of the (meth)acrylate compound having 1 (meth)acryloyl group in the molecule also include (meth)acrylamides such as diacetone (meth)acrylamide, isobutoxymethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, tert-octyl (meth)acrylamide, and acryloylmorpholine.

[0105] Among the component (B) having 1 (meth)acryloyl group in the above molecule, (meth)acrylates having an aliphatic structure such as 2-ethylhexyl (meth)acrylate are preferred.

[0106] The content of the component (B) having 1 (meth)acryloyl group in the radiation-curable composition of the present invention is preferably 5 parts by mass or more and 45 parts by mass or less, particularly preferably 10 parts by mass or more and 30 parts by mass or less, relative to 100 parts by mass of the composition.

[0107] Among the component (B), examples of the (meth)acrylate compound having 2 or more (meth)acryloyl groups in the molecule include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, ethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane triethoxyethyl (meth)acrylate, tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, tris(2-hydroxyethyl)isocyanurate di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, di(meth)acrylate of a diol obtained by adding ethylene oxide or propylene oxide to bisphenol A, di(meth)acrylate of a diol obtained by adding ethylene oxide or propylene oxide to hydrogenated bisphenol A, and epoxy (meth)acrylate obtained by adding (meth)acrylate to bisphenol A diglycidyl ether.

[0108] From the viewpoint of easily adjusting the Young's modulus of the cured product as the first coating of the optical fiber to the preferred range, the content of the component (B) having two or more (meth)acryloyl groups in the molecule in the radiation-curable composition of the present invention is preferably 2 parts by mass or less (0 to 2 parts by mass), more preferably 1.5 parts by mass or less (0 to 1.5 parts by mass) relative to 100 parts by mass of the composition.

[0109] Examples of commercially available products of the component (B) include ARONIX M-111, M-113, M-114, M-117 (manufactured by Toagosei Co., Ltd.); KAYARAD, TC110S, R629, R644 (manufactured by Nippon Kayaku Co., Ltd.); IBXA, Viscoat 3700 (manufactured by Osaka Organic Chemical Industry Co., Ltd.); Upimer UV SA1002, SA2007 (manufactured by Mitsubishi Chemical Corporation); Viscoat 700 (manufactured by Osaka Organic Chemical Industry Co., Ltd.); KAYARAD R-604, DPCA-20, -30, -60, -10, HX-620, D-310, D-330 (manufactured by Nippon Kayaku Co., Ltd.); ARONIX M-210, M-215, M-315, M-325 (manufactured by Toagosei Co., Ltd.), etc.

[0110] The total amount of the component (B) in the radiation-curable composition of the present invention is preferably 5 parts by mass or more and 45 parts by mass or less, particularly preferably 10 parts by mass or more and 30 parts by mass or less relative to 100 parts by mass of the composition.

[0111] The (meth)acrylate compound as the component (B) may be used alone or in combination of two or more.

[0112] (C) Component: radiation polymerization initiator

[0113] The radiation curable composition of the present invention contains a radiation polymerization initiator. The radiation polymerization initiator can also be referred to as a photoinitiator. Additionally, the radiation curable composition of the present invention may, as needed, further contain a photosensitizer on the basis of containing a radiation polymerization initiator as the component (C). Examples of the radiation polymerization initiator include 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole, 3-methylacetophenone, 4-chlorobenzophenone, 4,4'-dimethoxybenzophenone, 4,4'-diaminobenzophenone, Michler's ketone, benzoin propyl ether, benzoin ethyl ether, benzyl dimethyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone, diethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, etc. Commercially available products of the radiation polymerization initiator include Omnirad 184, 369, 651, 500, 907, 1700, 1870, 1173, TPO H (manufactured by IGM Resins B.V., etc.). Additionally, examples of the photosensitizer include triethylamine, diethylamine, N-methyldiethanolamine, ethanolamine, 4-dimethylaminobenzoic acid, methyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, isopentyl 4-dimethylaminobenzoate, etc. Commercially available products of the photosensitizer include ANTHRACURE UVS-1101, 581, 2171, 1331 (manufactured by Air Water Performance Chemical, etc.).

[0114] The content of the component (C) radiation polymerization initiator in the radiation curable composition of the present invention is preferably 0.1 part by mass or more and 10 parts by mass or less, particularly preferably 0.3 part by mass or more and 7 parts by mass or less, relative to 100 parts by mass of the composition. Additionally, in the case of using a photosensitizer in combination, the total amount of the radiation polymerization initiator and the photosensitizer is preferably 0.1 part by mass or more and 10 parts by mass or less, particularly preferably 0.3 part by mass or more and 7 parts by mass or less, relative to 100 parts by mass of the composition.

[0115] (C) The radiation polymerization initiator can be used singly or in combination of two or more. In the case where the composition contains a photosensitizer, the photosensitizer can be used singly or in combination of two or more.

[0116] (D) Component: monomer having one or more ethylenically unsaturated groups not conforming to (A) component or (B) component

[0117] The radiation curable composition of the present invention may contain a monomer having one or more ethylenically unsaturated groups that do not conform to component (A) or component (B). In the present specification, this compound is also referred to as "(D) component". Examples of the (D) component include lactams containing vinyl, vinylimidazole, vinylpyridine, triethylene glycol divinyl ether, etc. Examples of the lactam containing vinyl include N-vinylpyrrolidone, N-vinylcaprolactam, etc.

[0118] The content of the (D) component in the radiation curable composition of the present invention is, for example, 1 part by mass or more and 15 parts by mass or less relative to 100 parts by mass of the composition. When the (D) component is contained in the composition, one kind of the (D) component can be used alone, or two or more kinds can be used in combination.

[0119] (E) Component: oligomer or polymer not conforming to (A) component or (B) component

[0120] The radiation curable composition of the present invention may contain an oligomer or polymer that does not conform to component (A) or component (B). In the present specification, this compound is also referred to as "(E) component". Examples of the (E) component include, for example, a compound having a structure derived from component (e) but not having a (meth)acryloyl group and containing a urethane bond (-NHCOO-) in the repeating unit of the main chain, which may be generated when component (e) is used in the synthesis of (A) urethane (meth)acrylate as described above, for example, a compound having two structures derived from component (e) and containing a urethane bond (-NHCOO-) in the repeating unit of the main chain.

[0121] The content of the (E) component in the radiation curable composition of the present invention is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, relative to 100 parts by mass of the composition. When the (E) component is contained in the composition, one kind of the (E) component can be used alone, or two or more kinds can be used in combination.

[0122] In the radiation curable composition of the present invention, a silane coupling agent may be included within a range not impairing the effects of the invention. Examples of the silane coupling agent include vinyltrichlorosilane, vinyltriethoxysilane, vinyltri(β-methoxy-ethoxy)silane, β-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-methacryloxypropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, bis-[3-(triethoxysilyl)propyl]tetrasulfide, bis-[3-(triethoxysilyl)propyl]disulfide, γ-trimethoxysilylpropyldimethylthiocarbamyltetrasulfide, γ-trimethoxysilylpropylbenzothiazolyltetrasulfide, etc. Examples of commercially available products thereof include DOWSIL Z-6062, SZ6030 (manufactured by Dow Toray Co., Ltd.), KBE903, 603, 403 (manufactured by Shin-Etsu Chemical Co., Ltd.), etc. From the viewpoint of the adhesion between the coating layer and the glass, the silane coupling agent is preferably γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, or γ-aminopropyltrimethoxysilane.

[0123] From the viewpoint of maintaining the adhesion between the cured product of the radiation curable composition of the present invention and the glass fiber, the content of the silane coupling agent in the radiation curable composition of the present invention is preferably 0.01 part by mass or more and 2 parts by mass or less, more preferably 0.1 part by mass or more and 1.5 parts by mass or less, and particularly preferably 0.3 part by mass or more and 1.5 parts by mass or less, based on 100 parts by mass of the composition. When the silane coupling agent is included in the composition, one kind of the silane coupling agent may be used alone, or two or more kinds may be used in combination.

[0124] In the radiation curable composition of the present invention, in addition to blending the above components, various additives may be blended as needed, such as antioxidants, colorants, ultraviolet absorbers, light stabilizers, thermal polymerization inhibitors, leveling agents, surfactants, storage stabilizers, plasticizers, lubricants, solvents, fillers, anti-aging agents, wettability improvers, coating surface improvers, etc.

[0125] Examples of the antioxidant include IRGANOX 245, 1010, 1035, 1076, 1222 (manufactured by BASF JAPAN Co., Ltd.), ANTIGENE P, 3C, Sumilizer GA-80, GP (manufactured by Sumitomo Chemical Co., Ltd.), and the like. Examples of the ultraviolet absorber include TINUVIN P, 234, 320, 326, 327, 328, 329, 213 (manufactured by BASF JAPAN Co., Ltd.), Seesorb 102, 103, 501, 202, 712, 704 (manufactured by SHIPRO KASEI Co., Ltd.), and the like. Examples of the light stabilizer include TINUVIN 292, 144, 622LD, SANOL LS-770, 765 (manufactured by BASF JAPAN Co., Ltd.), and the like.

[0126] In addition, the surfactant is not particularly limited, and fatty acid ester type nonionic surfactants are effective in suppressing defects that occur when the optical fiber core is immersed in warm water, and thus are preferred. Particularly preferred are nonionic surfactants such as glycerol fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and polyoxy sorbitol fatty acid esters.

[0127] In addition, in the radiation curable composition of the present invention, other oligomers, polymers, and / or silane compounds (such as tetraethoxysilane) and other additives can be optionally blended within the range that does not impair the effects of the invention as components that do not conform to any of the above components.

[0128] The method for producing the radiation curable composition is not particularly limited, and it can be carried out, for example, by melt blending in a conventionally known reaction vessel equipped with a stirrer.

[0129] From the viewpoints of operability and coatability, the viscosity of the radiation curable composition of the present invention is preferably 0.1 to 10 Pa·s at 25°C, more preferably 1 to 8 Pa·s. In this specification, the viscosity of the composition is the viscosity measured using a B-type viscometer (such as the TVB-10H type manufactured by Toki Sangyo Co., Ltd.).

[0130] The cured product of the radiation-curable composition of the present invention has a low Young's modulus suitable as the primary coating of an optical fiber. From the viewpoint of being preferably usable as the primary coating of an optical fiber, the Young's modulus of the cured product of the radiation-curable composition of the present invention is preferably 0.1 MPa or more and 1.3 MPa or less (0.1 to 1.3 MPa) at 25°C. When the Young's modulus of the primary coating of an optical fiber is 0.1 to 1.3 MPa at 25°C, so-called microbending loss caused by the bending of glass fibers when pressure is locally applied to the optical fiber can be prevented. The Young's modulus of the cured product of the radiation-curable composition of the present invention is more preferably 0.2 MPa or more and 1 MPa or less (0.2 to 1 MPa). The Young's modulus of the cured product of the radiation-curable composition of the present invention is measured by the method described in the following examples.

[0131] An optical fiber having the cured product of the radiation-curable composition of the present invention as the primary coating of an optical fiber usually further has a secondary coating of an optical fiber that contacts the outside of the primary coating of the optical fiber. The Young's modulus of the secondary coating of an optical fiber is preferably 1,000 MPa or more, and more preferably 1,000 to 2,000 MPa. The Young's modulus of the secondary coating of an optical fiber can also be measured by the same method as the method for measuring the Young's modulus of the cured product of the radiation-curable composition described in the following examples. A substance having a primary coating of an optical fiber and a secondary coating of an optical fiber sequentially provided on the surface of a glass fiber can be used as an optical fiber core wire.

[0132] One embodiment of a method for manufacturing an optical fiber includes: a step of disposing the radiation-curable composition of the present invention on at least a part of the surface of a glass fiber and curing the radiation-curable composition to form a primary coating of an optical fiber; and then, a step of disposing and curing a radiation-curable composition for a secondary coating of an optical fiber on the surface of the primary coating of an optical fiber to form a secondary coating of an optical fiber. As another embodiment, there can be mentioned, for example, the following method for manufacturing an optical fiber, etc., which includes: a step of sequentially disposing the radiation-curable composition of the present invention and a radiation-curable composition for a secondary coating of an optical fiber on at least a part of the surface of a glass fiber and curing them to form a primary coating of an optical fiber and a secondary coating of an optical fiber.

[0133] The method for disposing the radiation-curable composition on the surface of the glass fiber is not particularly limited, and known methods can be used. For example, there can be mentioned a method of coating the surface with the radiation-curable composition, a method of immersing the surface in the radiation-curable composition, etc.

[0134] The method for curing the radiation-curable composition is not particularly limited. For example, there can be mentioned a method of irradiating the radiation-curable composition with one or more types of radiation selected from infrared rays, visible rays, ultraviolet rays, X-rays, electron rays, α-rays, β-rays, and γ-rays, etc.

[0135] As a general method for manufacturing an optical fiber, the following method can be cited: The molten quartz base material is heat-melted and drawn into a wire, and at the same time, the radiation-curable composition of the present invention and the radiation-curable composition for the second coating of the optical fiber are sequentially coated, and radiation curing is performed to form the first coating of the optical fiber and the second coating of the optical fiber, thereby manufacturing an optical fiber.

[0136] An optical fiber assembly such as an optical fiber ribbon or an optical cable is an assembly containing two or more of the above optical fibers, and the optical fibers can be fixed using a bundling material to form a ribbon optical fiber or an optical cable.

[0137] Examples

[0138] Hereinafter, examples are shown to more specifically explain the present invention, but the interpretation of the present invention is not limited by these examples.

[0139] [Synthesis of urethane acrylate and preparation of radiation-curable composition]

[0140] (Example 1)

[0141] 613.7 g of polypropylene glycol (UNIOL D-4000, manufactured by NOF Corporation) having a number average molecular weight of 4,000, 80.2 g of 2,4-toluene diisocyanate (TOLDY-100, manufactured by Mitsui Chemicals, Inc.), and 11.7 g of propylene glycol (manufactured by Tokyo Chemical Industry Co., Ltd.) were added to a reaction vessel equipped with a stirrer, and 0.2 g of 2,6-di-tert-butyl-p-cresol (manufactured by Honshu Chemical Industry Co., Ltd.) was added.

[0142] The mixture was heated to 30°C with stirring. After adding 0.2 g of dibutyltin dilaurate (manufactured by Sakai Chemical Industry Co., Ltd.), the mixture was slowly heated to 65°C with stirring over 15 minutes. Then, the mixture was stirred at 60°C for 1 hour to react. Thereafter, 26.1 g of 2-hydroxyethyl acrylate (manufactured by Nippon Shokubai Co., Ltd.) was added, and after reacting at 70°C for 1 hour, 10.6 g of 2-ethylhexanol was added, and the reaction was carried out at 70°C for 1 hour to obtain urethane acrylate 1.

[0143] 99.0 g of 4-acryloylmorpholine (manufactured by KJ Chemical Co., Ltd.), 148.5 g of 2-ethylhexyl acrylate, and 9.9 g of 2,4,6-trimethylbenzoyl diphenylphosphine oxide (manufactured by Tokyo Chemical Industry Co., Ltd.) were added to the obtained urethane acrylate 1, and the mixture was stirred at 60°C for 1 hour to obtain radiation-curable composition 1.

[0144] (Examples 2 to 8 and Comparative Examples 9 to 10)

[0145] The raw materials were respectively charged according to the weight ratios shown in Table 1, and the same operations as in Example 1 were carried out to obtain urethane acrylates 2 to 10. The radiation-curable compositions 2 to 10 were obtained by carrying out the same operations as in Example 1 using the obtained urethane acrylates 2 to 10 respectively. In Table 1, urethane acrylates 1 to 10 were denoted as UA1 to UA10 respectively. In Table 2, the radiation-curable compositions formulated with UA1 to UA10 were denoted as Compositions 1 to 10 respectively. It should be noted that in Example 5 and Comparative Example 10, polypropylene glycol with a number-average molecular weight of 3,000 (polypropylene glycol, diol type, 3000, manufactured by Fujifilm Wako Pure Chemical Corporation) was used instead of polypropylene glycol with a number-average molecular weight of 4,000 (UNIOL D-4000, manufactured by NOF Corporation).

[0146] The synthesis results of the urethane acrylate as the component (A) are shown in Table 1. The values attached to the respective raw materials shown in Table 1 represent the weight ratios of the raw materials used. In addition, the results obtained by adjusting the radiation-curable composition using the obtained urethane acrylate are shown in Table 2.

[0147] [Evaluation method]

[0148] (1) Viscosity

[0149] The viscosities of the compositions obtained in the examples and comparative examples at 25 °C were measured using a viscometer B8H-BII (manufactured by Tokimec Inc.). The results are shown in Table 2.

[0150] (2) Young's modulus

[0151] The Young's modulus of the cured layer (layered cured product) of the compositions obtained in the examples and comparative examples was measured as follows. The results are shown in Table 2.

[0152] A liquid radiation-curable composition was coated on a glass plate using a 381 μm thick applicator bar, and it was cured by irradiating ultraviolet rays with an energy of 1 J / cm 2 in the air, and then peeled off from the glass plate to obtain a test film. After the cured test film was allowed to stand at a temperature of 23 °C and a relative humidity of 50% for 24 hours, a short strip sample was prepared with a width of 6 mm and a length of 25 mm in the stretching part. For this short strip sample, under the same temperature and relative humidity conditions, a tensile test was carried out in accordance with JIS K7161-1 using a tensile testing machine 5542C4600 (manufactured by Instron Japan Co., Ltd.). Under the condition of a tensile speed of 1 mm / min, the Young's modulus was calculated based on the tensile strength at a deformation of 2.5%.

[0153] (3) Tensile strength and elongation at break

[0154] Using a 354-μm thick applicator bar, a liquid radiation-curable composition was coated on a glass plate, and it was irradiated with ultraviolet rays having an energy of 1 J / cm 2 in air to cure it, obtaining a test film. Using a tensile tester (manufactured by Shimadzu Corporation, AGS-50G), the breaking strength and elongation at break of the test film were measured under the following measurement conditions. The results are shown in Table 2.

[0155] <Measurement conditions>

[0156] Tensile speed: 50 mm / min

[0157] Distance between gauge marks (measurement distance): 25 mm

[0158] Measurement temperature: 23 °C

[0159] Relative humidity: 50%

[0160] (4) Concentration of urethane groups in urethane acrylate

[0161] Calculated based on the raw material feeding amounts used for synthesizing urethane acrylate. The calculated values are shown in Table 1.

[0162] [Table 1]

[0163] Table 1. Synthesis results of urethane acrylate

[0164]

[0165] [Table 2]

[0166] Table 2. Preparation results of radiation-curable composition and measurement results of test film

[0167]

[0168] Compared with the radiation-curable compositions obtained in Comparative Examples 9 to 10, the radiation-curable compositions obtained in Examples 1 to 8 showed equivalent viscosities. In addition, compared with the cured layers of the radiation-curable compositions obtained in Comparative Examples 9 to 10, the cured layers of the radiation-curable compositions obtained in Examples 1 to 8 showed higher breaking strength and elongation at break under equivalent Young's moduli.

[0169] Therefore, it can be known that: compared with the radiation-curable compositions obtained in Comparative Examples 9 to 10, the radiation-curable compositions obtained in Examples 1 to 8 are more suitable as radiation-curable compositions for forming the primary coating of optical fibers.

Claims

1. A radiation-curable composition for forming a primary coating of an optical fiber, which contains (A) urethane (meth)acrylate, (B) a (meth)acrylate compound other than the component (A), and (C) a radiation polymerization initiator. The (A) urethane (meth)acrylate is obtained by reacting at least the following components (a), (b), (c), and (d): (a) a polyether diol having a number average molecular weight of 2000 to 5000; (b) a diisocyanate compound; (c) a hydroxy group-containing (meth)acrylate compound; and (d) a diol having a molecular weight of 500 or less.

2. The radiation-curable composition according to claim 1, wherein, The component (d) is a diol having a molecular weight of 200 or less.

3. The radiation curable composition according to claim 1 or 2, wherein The component (b) is toluene diisocyanate (TDI) or isophorone diisocyanate (IPDI).

4. A urethane (meth)acrylate obtained by reacting at least the following components (a), (b), (c), and (d): (a) a polyether diol having a number average molecular weight of 2000 to 5000; (b) a diisocyanate compound; (c) a hydroxy group-containing (meth)acrylate compound; and (d) a diol having a molecular weight of 500 or less.

5. The urethane (meth) acrylate according to claim 4, wherein, The component (d) is a diol having a molecular weight of 200 or less.

6. The urethane (meth) acrylate according to claim 4 or 5, wherein, The component (b) is toluene diisocyanate (TDI) or isophorone diisocyanate (IPDI).

Images