Radiation curable composition for forming optical fiber primary covering layer

Abstract

Provided is a radiation curable composition for forming an optical fiber primary covering layer in which coloring of the cured resin composition comprising an acylphosphine oxide-based photoinitiator is reduced.　The radiation curable composition for forming an optical fiber primary covering layer comprises an acylphosphine oxide-based initiator (A) and a urethane acrylate oligomer (B). A content of the initiator (A) is 0.15 to 0.9 mass% with respect to a total mass of the radiation curable composition, the initiator (A) contains one or more selected from the group consisting of compounds having a predetermined structure, the oligomer (B) is obtained by reacting at least a predetermined compound, and a content of the oligomer (B) is 71 mass% or more with respect to the total mass of the radiation curable composition.

Description

RADIATION CURABLE COMPOSITION FOR FORMING OPTICAL FIBER PRIMARY COVERING LAYER

[0001] The present invention relates to a radiation curable composition for forming a primary covering layer, a cured product thereof, and an optical fiber. Background Art

[0002] An optical fiber includes glass fiber obtained by heat-melting and spinning glass, a covering layer provided on the glass fiber for the purpose of protection and reinforcement, and the like. An optical fiber is produced by, for example, first providing a soft primary covering layer (hereinafter, also referred to as a “primary covering layer”) on a surface of glass fiber, and providing a highly rigidity secondary covering layer (hereinafter, also referred to as a “secondary covering layer”) on the primary covering layer.

[0003] For such a covering layer, a method is widely used in which a liquid curable resin composition is applied to glass fiber, and cured by heat or light. In addition, it has been heretofore known that an acylphosphine oxide-based photoinitiator is added for curing a curable resin composition at a high rate.

[0004] For example, JP 2001-114535 A (Patent Literature 1) discloses a covered optical fiber that has good internal curability, and good adhesion between a glass optical fiber and a low-Young's modulus layer, and can be reliably produced even at a high drawing rate, and a method for producing the covered optical fiber, where Lucirin TPO (brand name, manufactured by BASF) which is a type of acylphosphine oxide-based photoinitiator is used for a low-Young's modulus resin (primary layer).

[0005] JP 2022-506003 A (Patent Literature 2) discloses a radiation curable composition for coating an optical fiber, a method for coating an optical fiber under processing conditions of a high drawing rate and low helium and / or via an LED light source, and an optical fiber and a cable prepared by use thereof, where bisacylphosphine oxide (BAPO) or monoacylphosphine oxide (MAPO) can be used as an acylphosphine oxide-based photoinitiator.

[0006] In addition, JP 2013-512856 A (Patent Literature 3) discloses a radiation curable coating composition for an optical fiber which includes at least one urethane (meth)acrylate oligomer, at least one reactive diluent monomer, and at least one photoinitiator, where an acylphosphine oxide-based photoinitiator such as benzoylphosphine oxide or ethoxyphosphine oxide can be used.

[0007] JP 2002-220550 A (Patent Literature 4) discloses a curable resin composition which is excellent in jelly resistance and water resistance preferred as a covering material for an optical fiber wire, an optical fiber tape or the like, and a cured product thereof, where 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis- (2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide or the like can be used as an acylphosphine oxide-based photoinitiator.

[0008] JP 2004-211057 A (Patent Literature 5) discloses a radiation curable resin composition useful for covering an optical fiber ,which the composition itself has good storage stability, is excellent in durability and gives a cured product with little hydrogen gas generation, where 2,4,6-trimethylbenzoyldiphenylphosphine oxide or bis- (2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide can be used as an acylphosphine oxide-based photoinitiator.

[0009] JP 2013-501125 A (Patent Literature 6) discloses a radiation curable covering material used as a primary covering material for an optical fiber, an optical fiber covered with the covering material, and a method for producing a covered optical fiber, where 2,4,6-trimethylbenzoyl-diphenylphosphine oxide type (TPO), 2,4,6-trimethylbenzoylphenyl, ethoxyphosphine oxide (TPO-L), monoacylphosphine oxide (MAPO), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and a bisacylphosphine oxide type (BAPO) can be used. Citation List Patent Literature

[0010] Patent Literature 1: JP 2001-114535 A Patent Literature 2: JP 2022-506003 A Patent Literature 3: JP 2013-512856 A Patent Literature 4: JP 2002-220550 A Patent Literature 5: JP 2004-211057 A Patent Literature 6: JP 2013-501125 A Summary of Invention Technical Problem

[0011] Addition of such an acylphosphine oxide-based photoinitiator tends to lead to coloring of a cured resin composition (so-called primary material) under the influence of absorption of light. If the amount of the addition is increased (to, for example, 1 mass% or more) for obtaining a high-rate curing property, the degree of coloring increases. If the coloring occurs in resin composition, the color of a color ink applied to an optical fiber so as to develop a specified color may be mistakenly viewed as a color differing from that of the color ink, resulting in a wiring mix-up during the operations of laying the optical fiber. For this reason, a radiation curable composition for forming an optical fiber primary covering layer is desired in which coloring of the cured resin composition containing an acylphosphine oxide-based photoinitiator is reduced, while an optimal performance for high-rate curing property and an optimal performance for composition productivity can also be obtained. Solution to Problem

[0012] The present inventors have conducted intensive studies to solve the above-described problems, and resultantly found that a radiation curable composition for forming an optical fiber primary covering layer which comprises an acylphosphine oxide-based initiator (A), a urethane acrylate oligomer (B), an acrylate compound (C) having a molecular weight of less than 200 and a N-vinyl heterocyclic compound (D) having a molecular weight of less than 200, in which a content of the acylphosphine oxide-based initiator (A) is 0.15 to 0.9 mass% with respect to a total mass of the radiation curable composition, the acylphosphine oxide-based initiator (A) comprises one or more selected from the group consisting of compounds having a predetermined structure, the urethane acrylate oligomer (B) is obtained by reacting at least a predetermined compound, a content of the urethane acrylate oligomer (B) is 71 mass% or more and 83 mass% or less with respect to the total mass of the radiation curable composition, a total content of the acrylate compound (C) and the N-vinyl heterocyclic compound (D) is 10 mass% or more with respect to the total mass of the radiation curable composition, and a content of the N-vinyl heterocyclic compound (D) is 11 mass% or less with respect to the total mass of the radiation curable composition, solves the above-described problems. On the basis of these findings, the present invention has been completed.

[0013] That is, the present invention has following configuration.

[0014] [1]　　　　　　　　A radiation curable composition for forming an optical fiber primary covering layer, comprising an acylphosphine oxide-based initiator (A), a urethane acrylate oligomer (B), an acrylate compound (C) having a molecular weight of less than 200 and a N-vinyl heterocyclic compound (D) having a molecular weight of less than 200,wherein 　　　　a content of the acylphosphine oxide-based initiator (A) is 0.15 to 0.9 mass% with respect to a total mass of the radiation curable composition, 　　　　the acylphosphine oxide-based initiator (A) comprises one or more selected from the group consisting of a compound represented by the following formula (I), a compound represented by the following formula (II), and a compound containing the compounds of formulae (I) and (II) as constituent units: 　　　　wherein P represents a phosphorus atom, C represents a carbon atom, O represents an oxygen atom, and the oxygen (=O) bonded to the phosphorus atom may be replaced by S (sulfur atom), 　　　　R1, R2 and R3 are each independently a substituent, and each of which is the following i) or ii): 　　　　i) an alkyl group optionally having a heteroatom, a cycloalkyl group optionally having a heteroatom, or an aryl group optionally having a substituent; and 　　　　ii) an alkoxy group, a halogen, or a substituent represented by O-Z+, with Z+ being one of a quaternary ammonium cation, an alkali metal cation, and a phosphonium cation, 　　　　R1 in the compound containing the compounds of formulae (I) and (II) as constituent units may be bonded together, 　　　　the urethane acrylate oligomer (B) is obtained by reacting at least 　　　　(a) a polyether diol having a number average molecular weight of 2,000 to 11,000, 　　　　(b) a diisocyanate compound; and 　　　　(c) a hydroxyl group-containing acrylate compound, 　　　　a content of the urethane acrylate oligomer (B) is 71 mass% or more and 83 mass% or less with respect to a total mass of the radiation curable composition, 　　　　a total content of the acrylate compound (C) and the N-vinyl heterocyclic compound (D) is 10 mass% or more with respect to the total mass of the radiation curable composition, and 　　　　a content of the N-vinyl heterocyclic compound (D) is 11 mass% or less with respect to the total mass of the radiation curable composition. [2]　　　　　　　The radiation curable composition according to [1], comprising the acylphosphine oxide-based initiator (A) in an amount of 0.25 to 0.8 mass% with respect to the total mass of the radiation curable composition. [3]　　　　　　　The radiation curable composition according to [1] or [2], comprising the acylphosphine oxide-based initiator (A) in an amount of 0.25 to 0.7 mass% with respect to the total mass of the radiation curable composition. [4]　　　　　　　The radiation curable composition according to any one of [1] to [3], comprising the urethane acrylate oligomer (B) in an amount of 74 mass% or more with respect to the total mass of the radiation curable composition. [5]　　　　　　　The radiation curable composition according to any one of [1] to [3], comprising the urethane acrylate oligomer (B) in an amount of 77 mass% or more with respect to the total mass of the radiation curable composition. [6]　　　　　　　The radiation curable composition according to any one of [1] to [5], comprising the acrylate compound (C) and the N-vinyl heterocyclic compound (D) in an amount of 15 mass% or more with respect to the total mass of the radiation curable composition. [7]　　　　　　　The radiation curable composition according to any one of [1] to [5], comprising the acrylate compound (C) and the N-vinyl heterocyclic compound (D) in an amount of 18 mass% or more with respect to the total mass of the radiation curable composition. [8]　　　　　　　The radiation curable composition according to any one of [1] to [7], comprising the acrylate compound (C) and the N-vinyl heterocyclic compound (D) in an amount of 30 mass% or less with respect to the total mass of the radiation curable composition. [9]　　　　　　　The radiation curable composition according to any one of [1] to [7], comprising the acrylate compound (C) and the N-vinyl heterocyclic compound (D) in an amount of 25 mass% or less with respect to the total mass of the radiation curable composition.

[0010] The radiation curable composition according to any one of [1] to [8], comprising the acrylate compound (C) and the N-vinyl heterocyclic compound (D) in an amount of 22 mass% or less with respect to the total mass of the radiation curable composition.

[0011] The radiation curable composition according to any one of [1] to

[0010] , comprising the N-vinyl heterocyclic compound (D) in an amount of 10 mass% or less with respect to the total mass of the radiation curable composition.

[0012] The radiation curable composition according to any one of [1] to

[0011] , comprising the N-vinyl heterocyclic compound (D) in an amount of 3 mass% or more with respect to the total mass of the radiation curable composition.

[0013] The radiation curable composition according to any one of [1] to

[0011] , comprising the N-vinyl heterocyclic compound (D) in an amount of 5 mass% or more with respect to the total mass of the radiation curable composition.

[0014] The radiation curable composition according to any one of [1] to

[0013] , comprising the N-vinyl heterocyclic compound (D) and the acrylate compound (C) in a molar ratio of the N-vinyl heterocyclic compound (D) to the acrylate compound (C) [(D) / (C)] in the radiation curable composition of 0.1 or more and 0.5 or less.

[0015] The radiation curable composition according to any one of [1] to

[0013] , comprising the N-vinyl heterocyclic compound (D) and the acrylate compound (C) in a molar ratio of the N-vinyl heterocyclic compound (D) to the acrylate compound (C) [(D) / (C)] in the radiation curable composition of 0.2 or more and 0.5 or less.

[0016] The radiation curable composition according to any one of [1] to

[0013] , comprising the N-vinyl heterocyclic compound (D) and the acrylate compound (C) in a molar ratio of the N-vinyl heterocyclic compound (D) to the acrylate compound (C) [(D) / (C)] in the radiation curable composition of 0.3 or more and 0.5 or less.

[0017] The radiation curable composition according to any one of [1] to

[0016] , wherein the total content of the N-vinyl heterocyclic compound (D) and the urethane acrylate oligomer (B) is 75 mass% or more with respect to the total mass of the radiation curable composition.

[0018] The radiation curable composition according to any one of [1] to

[0017] , optionally comprising a photopolymerization initiator other than the acylphosphine oxide-based initiator (A) in an amount of 0.5 mass% or less with respect to the total mass of the radiation curable composition.

[0019] The radiation curable composition according to any one of [1] to

[0017] , optionally comprising a photopolymerization initiator other than the acylphosphine oxide-based initiator (A) in an amount of 0.3 mass% or less with respect to the total mass of the radiation curable composition.

[0020] The radiation curable composition according to any one of [1] to

[0017] , optionally comprising a photopolymerization initiator other than the acylphosphine oxide-based initiator (A) in an amount of 0.1 mass% or less with respect to the total mass of the radiation curable composition.

[0021] A cured product of the radiation curable composition of any one of [1] to

[0020] .

[0022] An optical fiber including glass fiber, and a primary covering layer including the cured product of

[0021] .

[0023] The optical fiber according to

[0022] , further comprising a secondary covering layer.

[0024] A method for producing an optical fiber, comprising the steps of: disposing the radiation curable composition of any one of [1] to

[0020] on glass fiber; and curing the radiation curable composition by irradiating with radiation. Advantageous Effects of Invention

[0015] According to the present invention, it is possible to provide a radiation curable composition for forming an optical fiber primary covering layer which has optimal performance for high-rate curing property and for composition productivity and in which coloring after curing is suppressed. Description of Embodiments

[0016] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments. The term “to” used herein to indicate a numerical range means that in the range, the numerical values written before and after the term “to” are a minimum value and a maximum value, respectively. The upper limit values and the lower limit values written in series herein may be arbitrarily combined.

[0017] The present invention provides a radiation curable composition for forming an optical fiber primary covering layer, comprising an acylphosphine oxide-based initiator (A), a urethane acrylate oligomer (B), an acrylate compound (C) having a molecular weight of less than 200 and a N-vinyl heterocyclic compound (D) having a molecular weight of less than 200, wherein 　　　　a content of the acylphosphine oxide-based initiator (A) is 0.15 to 0.9 mass% with respect to a total mass of the radiation curable composition, 　　　　the acylphosphine oxide-based initiator (A) comprises one or more selected from the group consisting of a compound represented by the following formula (I), a compound represented by the following formula (II), and a compound containing the compounds of formulae (I) and (II) as constituent units: 　　　　wherein P represents a phosphorus atom, C represents a carbon atom, O represents an oxygen atom, and the oxygen (=O) bonded to the phosphorus atom may be replaced by S (sulfur atom), 　　　　R1, R2 and R3 are each independently a substituent, and each of which is the following i) or ii): 　　　　i) an alkyl group optionally having a heteroatom, a cycloalkyl group optionally having a heteroatom, or an aryl group optionally having a substituent; and 　　　　ii) an alkoxy group, a halogen, or a substituent represented by O-Z+, with Z+ being one of a quaternary ammonium cation, an alkali metal cation, and a phosphonium cation, 　　　　R1 in the compound containing the compounds of formulae (I) and (II) as constituent units may be bonded together, 　　　　the urethane acrylate oligomer (B) is obtained by reacting at least 　　　　(a) a polyether diol having a number average molecular weight of 2,000 to 11,000, 　　　　(b) a diisocyanate compound; and 　　　　(c) a hydroxyl group-containing acrylate compound, 　　　　a content of the urethane acrylate oligomer (B) is 71 mass% or more and 83 mass% or less with respect to a total mass of the radiation curable composition, 　　　　a total content of the acrylate compound (C) and the N-vinyl heterocyclic compound (D) is 10 mass% or more with respect to the total mass of the radiation curable composition, and 　　　　a content of the N-vinyl heterocyclic compound (D) is 11 mass% or less with respect to the total mass of the radiation curable composition. 　　　　Hereinafter, the components of the radiation curable composition of the present invention will be described in detail.

[0018] In the present specification, the term “optical fiber primary covering layer” is understood to mean one of the covering layers provided on glass fiber, which is located closest to the glass fiber. The primary covering layer may be provided so as to cover at least a part of the surface of the glass fiber. The term “for forming an optical fiber primary covering layer” is understood to mean being usable for forming a primary covering layer of an optical fiber, or being intended for forming a primary covering layer of an optical fiber. The radiation curable composition of the present invention is particularly preferred as a material for forming an optical fiber primary covering layer (also referred to as a primary material).

[0019] As used herein, the term “radiation curable composition” is understood to mean a composition that can be cured by irradiation with radiation. Here, the radiation is an infrared ray, a visible ray, an ultraviolet ray, an X-ray, an electron beam, an α ray, a β ray, a γ ray, or the like, and in particular, an ultraviolet ray is preferable.

[0020] As used herein, the term “urethane acrylate” is understood to mean a compound containing one or more acryloyl groups in the molecule and a urethane bond (-NHCOO-) in the repeat unit of a main chain. The urethane acrylate can be formed typically by reaction of at least a diol compound, a diisocyanate compound, and a hydroxyl group-containing acrylate compound, which forms a urethane bond.

[0021] Acylphosphine oxide-based initiator (A) The radiation curable composition of the present invention comprises an acylphosphine oxide-based initiator. The “acylphosphine oxide-based initiator” is a component (A), which is also referred to as an acylphosphine oxide-based initiator (A). As used herein, the acylphosphine oxide-based initiator (A) comprises one or more selected from the group consisting of a compound represented by formula (I), a compound represented by formula (II), and a compound containing the compounds of formulae (I) and (II) as constituent units. In the compound containing the compounds of formulae (I) and (II) as constituent units, R1 in the formulae may be bonded together.

[0022] In each of the formulae (I) and (II), P represents a phosphorus atom, C represents a carbon atom, O represents an oxygen atom, and the oxygen (=O) bonded to the phosphorus atom may be replaced by S (sulfur atom).

[0023] R1, R2 and R3 are each independently a substituent, and each of which is the following i) or ii): i) an alkyl group optionally having a heteroatom, a cycloalkyl group optionally having a heteroatom, or an aryl group optionally having a substituent; and ii) an alkoxy group, a halogen, or a substituent represented by O-Z+, with Z+ being one of a quaternary ammonium cation, an alkali metal cation, and a phosphonium cation.

[0024] The term “alkyl group optionally having a heteroatom” means that one or more carbon atoms forming the alkyl group may be replaced by O (oxygen atom) or N (nitrogen atom). Here, the “alkyl group optionally having a heteroatom” may have a substituent, and examples of the substituent include a halogen, a hydroxyl group, and an alkoxy group. The alkyl group may be linear or branched, and the number of carbon atoms forming the alkyl group is not limited, and is, for example, 1 to 20, preferably 1 to 10.

[0025] The term “cycloalkyl group optionally having a heteroatom” means that one or more carbon atoms forming the cycloalkyl ring may be replaced by O (oxygen atom), N (nitrogen atom) or S (sulfur atom). The cycloalkyl group is preferably a 5- to 8-membered ring. The cycloalkyl group may have a substituent, and examples of the substituent include a halogen, a hydroxyl group, an alkyl group, and an alkoxy group.

[0026] The aryl group in the “aryl group optionally having a substituent” includes polycyclic aromatic hydrocarbon groups such as a phenyl group and a naphthyl group. Examples of the substituent with which the aryl group may have include a halogen, a hydroxyl group, an alkyl group (for example, a methyl group or an ethyl group), and an alkoxy group (for example, a methoxy group or an ethoxy group). The aryl group may have one or more substituent (preferably one to four) that are the same or different.

[0027] The quaternary ammonium cation can be represented by -N+(Ra)3, and the Ragroups may be the same or different, and are each independently selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, and an aryl group optionally having a substituent. The aryl group optionally having a substituent is as described in detail for i).

[0028] The alkali metal cation is preferably selected from Li+, Na+and K+.

[0029] The phosphonium cation can be represented by -P+(Rb)3, and the Rbgroups may be the same or different, and are each independently selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, and an aryl group optionally having a substituent. The aryl group optionally having a substituent is as described in detail for i).

[0030] The compound whose constituent units are a compound represented by formula (I) and a compound represented by formula (II) comprises various compounds so long as which comprise a compound represented by formula (I) and / or a compound represented by formula (II) as constituent units. Examples include compounds containing a compound represented by formula (I) and / or a compound represented by formula (II) as a unit of a side chain of an oligomer or a polymer chain.

[0031] In the compound containing a compound represented by formula (I) and a compound represented by formula (II) as constituent units, R1 may be bonded together. Such a compound means a compound in which each R1 in Formula (1) and / or Formula (2) is bonded together.

[0032] Examples of the compounds include such case, when a compound whose constituent units is a compound represented by formula (I) or formula (II), the number of the constituent units is 2 for example, and R1 in the formula is an alkyl group (-(CH2)n-CH3, where n is 0 or more) for example, each terminal -CH3group of the compound is bonded together to form the connected chain of -(CH2)n-CH2-CH2-(CH2)n-. In addition, those cases can be included, where when a compound whose constituent unit is a compound represented by formula (I) or formula (II), the number of the constituent units is 3 for example, and R1 in the formula is a methoxy group-terminated polyethylene glycol chain (-(O-CH2-CH2)m-OCH3, where m is 1 or more) for example, as an alkyl group optionally having a heteroatom, the three of each terminal OCH3group of the compound is bonded together to form the connected chain of -(O-CH2-CH2)m-OCH2-CH[-O-(CH2-CH2-O)m-]-CH2O-(CH2-CH2-O)m-. Here, the moiety of [-O-(CH2-CH2-O)m-] means that the oxygen atom at the left end is bonded to C (carbon atom) written on the left side in the above formula. Examples of the compound forming the connected chain include a compound represented by formula (VIII).

[0033] While examples are shown above, the compounds containing compounds of formulae (I) and (II) as constituent units include those in which various R1 in compounds contained as the constituent units are bonded together.

[0034] The compound whose constituent units is a compounds represented by formula (I) and formula (II) may include compounds containing one or more constituent units of the compounds of formula (I) and formula (II) in addition to compounds containing a plurality of constituent units of the compound represented by formula (I) and compounds containing a plurality of constituent units of the compound represented by formula (II). In these compounds, the constituent units of the compounds of formula (I) and formula (II) may be the same or different.

[0035] Examples of the component (A) in`clude diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, (2,6-dimethoxyphenyl)(diphenylphosphinyl)methanone, (diphenylphosphinyl)(2,3,5,6-tetramethylphenyl)methanone, ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, phenyl(2,4,6-trimethylbenzoyl)phosphinic acid glycerol ethoxylate triester, [bis(4-methylphenyl)phosphinyl](2,4,6-trimethylphenyl)methanone, bis(2,6,dimethoxybenzoyl)2,4,4 trimethylpentylphosphine oxide and lithium phenyl(2,4,6-trimethylbenzoyl)phosphinate, which are compounds of the following formulae (III) to (XI), respectively. From the viewpoint of economic efficiency, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate are preferable. Examples of the commercially available product include Omnirad 403, Omnipol TP, Omnirad TPO, Omnirad TPO-L, and Omnirad 819 (all manufactured by IGM Resins). Preferred components (A) are compounds according to formula (III), (IV), (V), (VI), (VII), (VIII), (IX), (X) and / or (XI).

[0036]

[0037]

[0038]

[0039]

[0040]

[0041] (Here, a, b, and c in formula (VIII) each represent a natural number, and a+b+c is an integer of 1 to 20.)

[0042]

[0043]

[0044]

[0045] The radiation curable composition of the present invention may contain a photopolymerization initiator other than the acylphosphine oxide-based initiator (A) described above. Examples thereof 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 dimethylketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one, 2-hydroxy-2-methyl-1-phenylpropane-1-one, thioxanthone, diethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propane-1-one. Examples of the commercially available product include Omnirads 184, 369, 651, 500, 907, 1700, 1870 and 1173(all manufactured by IGM Resins); CGI1700, CGI1750, CGI1850, CG24-61, DAROCUR1116 and 1173 (all manufactured by Ciba Specialty Chemicals); and EBECRYL P36 (manufactured by UCB S.A.).

[0046] The radiation curable composition of the present invention may contain a photosensitizer in addition to the component (A). Examples of the photosensitizer include triethylamine, diethylamine, N-methyldiethanolamine, ethanolamine, 4-dimethylaminobenzoic acid, methyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, and isoamyl 4-dimethylaminobenzoate. Examples of commercially available products of the photosensitizer include ANTHRACUREs UVS-1101, 581, 2171 and 1331 (all manufactured by AIR WATER PERFORMANCE CHEMICAL INC.). The content of the photopolymerization initiator other than the acylphosphine oxide-based initiator (A) in the radiation curable composition of the present invention is preferably 0.5 mass% or less, more preferably 0.3 mass% or less, particularly preferably 0.1 mass% or less with respect to the total mass of the radiation curable composition.

[0047] The content of the acylphosphine oxide-based initiator (A) in the radiation curable composition of the present invention is preferably 0.15 mass% or more, more preferably 0.20 mass% or more, and still more preferably 0.25 mass% or more, with respect to the total mass of the radiation curable composition. The content of the acylphosphine oxide-based initiator (A) is preferably 0.9 mass% or less, more preferably 0.8 mass% or less, and particularly preferably 0.7 mass% or less. If the content of the acylphosphine oxide-based initiator (A) is less than 0.15 mass% with respect to the total mass of the radiation curable composition, the curing rate may decrease, resulting in poor productivity of the fiber. If the content is more than 0.9 mass%, the degree of coloring of the resin composition increases.

[0048] When a photosensitizer is also used, the total amount of the radiation polymerization initiator and the photosensitizer is preferably 0.3 mass% or more and 1 mass% or less, and particularly preferably 0.4 mass% or more and 0.8 mass% or less with respect to the total mass of the radiation curable composition.

[0049] The acylphosphine oxide-based initiators (A) may be used alone, or may be used in combination of two or more thereof. When the composition contains the photosensitizer, the photosensitizers may be used alone, or may be used in combination of two or more thereof.

[0050] Component (B): Urethane acrylate oligomer (B) The radiation curable composition of the present invention comprises a urethane acrylate oligomer. The “urethane acrylate oligomer” is a component (B), which is also referred to as a “urethane acrylate oligomer (B)”. As used herein, the urethane acrylate oligomer (B) is obtained by reacting at least: 　　　　(a) a polyether diol having a number average molecular weight of 2,000 to 11,000, 　　　　(b) a diisocyanate compound; and 　　　　(c) a hydroxyl group-containing acrylate compound.

[0051] The urethane acrylate oligomer (B) contains a structural unit derived from a polyether diol, a structural unit derived from a diisocyanate, and a structural unit of a hydroxyl group-containing acrylate, and contains a urethane bond derived from a reaction between a polyether diol and a diisocyanate, and a urethane bond derived from a reaction between a diisocyanate and a hydroxyl group-containing acrylate.

[0052] The urethane acrylate oligomer (B) may comprise a reaction product of a polyether-based prepolymer and a hydroxyl group-containing acrylate compound. Here, the polyether-based prepolymer is a reaction product of a polyether diol and a diisocyanate, and has an isocyanate group.

[0053] The urethane acrylate oligomer (B) may comprise a reaction product of a polyether diol and an isocyanate group-containing end-capping compound. Here, the isocyanate group-containing end-capping compound is a reaction product of a diisocyanate and a hydroxyl group-containing acrylate, and has an isocyanate group.

[0054] Component (a): polyether diol having a numberaverage molecular weight of 2,000 to 11,000 The urethane acrylate oligomer (B) according to the present invention comprises a polyether diol, and the polyether diol preferably has a number average molecular weight of 2,000 to 11,000. As used herein, a polyether diol having a number average molecular weight of 2,000 to 11,000 is a component (a), which is also referred to as “(a) a polyether diol having a number average molecular weight of 2,000 to 11,000” or “(a) a polyether diol”.

[0055] The number average molecular weight (Mn) of the (a) polyether diol is more preferably 3,000 to 10,000, and particularly preferably 3,000 to 5,000. When the number average molecular weight (Mn) of the (a) polyether diol is in the above-mentioned range, it is possible to obtain a viscosity suitable as a resin composition and physical properties suitable as a cured product. The number average molecular weight (Mn) is a value obtained by measurement using a gel permeation chromatography method, followed by calculation based on a standard polystyrene calibration curve.

[0056] The (a) polyether diol is preferably an aliphatic polyether diol. As the aliphatic polyether diol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, polyheptamethylene glycol, polydecamethylene glycol, an aliphatic polyether diol obtained by ring-opening copolymerization of two or more ionically polymerizable cyclic compounds, and the like are preferable.

[0057] Examples of the ionically polymerizable cyclic compound include cyclic ethers such as ethylene oxide, propylene oxide, butene-1-oxide, isobutene oxide, 3,3-bischloromethyloxetane, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, dioxane, trioxane, tetraoxane, cyclohexene oxide, styrene oxide, epichlorohydrin, glycidyl acrylate, allyl glycidyl ether, allyl glycidyl carbonate, butadiene monooxide, isoprene monooxide, vinyl oxetane, vinyl tetrahydrofuran, vinyl cyclohexene oxide, phenyl glycidyl ether, butyl glycidyl ether, and benzoic acid glycidyl ester.

[0058] Specific examples of the polyether diol obtained by ring-opening copolymerization of two or more ionically polymerizable cyclic compounds include binary copolymers obtained by combination of, for example, tetrahydrofuran and propylene oxide, tetrahydrofuran and 2-methyltetrahydrofuran, tetrahydrofuran and 3-methyltetrahydrofuran, tetrahydrofuran and ethylene oxide, propylene oxide and ethylene oxide, and butene-1-oxide and ethylene oxide; and terpolymers obtained by combination of tetrahydrofuran, butene -1 oxide and ethylene oxide.

[0059] It is also possible to use polyether diols obtained by ring-opening copolymerization of the above ionically polymerizable cyclic compound and a cyclic imine such as ethyleneimine; a cyclic lactone acid such as β-propiolactone or lactide glycolate; or a dimethylcyclopolysiloxane.

[0060] The aliphatic polyether diol can also be obtained as a commercially available product, for example, PTMG 2000, PTMG 3000 and PTMG 4000 (all manufactured by Mitsubishi Chemical Corporation), EXCENOL 2020, EXCENOL 3020, EXCENOL 3030, EXCENOL 4030 and PREMINOL S3006(all manufactured by AGC Corporation), and UNIOL D-2000 and UNIOL D-4000 (all from NOF CORPORATION).

[0061] Of these aliphatic polyether diols, diols having a number average molecular weight of 2,000 to 5,000 and obtained by ring-opening polymerization of one or more ionically polymerizable cyclic compounds having 2 to 4 carbon atoms are preferably used from the viewpoint of securing both abilities to apply a covering layer at a high rate and softness. The preferred aliphatic polyether diol is a diol having a number average molecular weight of 3,000 to 4,000 and obtained by ring-opening polymerization of one or more oxides selected from ethylene oxide, propylene oxide, butene-1-oxide and isobutene oxide, with polypropylene glycol diol (obtained by ring-opening polymerization of propylene oxide) being particularly preferable.

[0062] The amount of structural moieties derived from the component (a) in the component (B) is preferably 83 mass% or more and less than 95 mass%, and more preferably 86 mass% or more and less than 92 mass%.

[0063] The (a) polyether diols having a number average molecular weight of 2,000 to 11,000 may be used alone, or may be used in combination of two or more thereof.

[0064] Component (b): Diisocyanate compound As used herein, the diisocyanate compound is a component (b), which is also referred to as “(b) a diisocyanate compound” or “(b) a diisocyanate”.

[0065] The urethane acrylate oligomer (B) according to the present invention comprises the (b) diisocyanate compound. The diisocyanate compound can form a urethane bond by reacting with hydroxyl groups of the component (a), and a component (c) and a component (d) that will be described later.

[0066] Examples of the (b) diisocyanate compound include aromatic diisocyanates, alicyclic diisocyanates, and aliphatic diisocyanates.

[0067] Examples of the aromatic diisocyanate compound include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, 1,5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3,3'-dimethyl-4,4' -diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethylphenylene diisocyanate, 4,4'-biphenylene diisocyanate, bis(2-isocyanatoethyl) fumarate, 6-isopropyl-1,3-phenyl diisocyanate, 4-diphenylpropane diisocyanate, and tetramethylxylylene diisocyanate. Examples of the alicyclic diisocyanate include isophorone diisocyanate, methylenebis(4-cyclohexyl isocyanate), hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, 2,5-bis(isocyanatomethyl)-bicyclo[2.2.1] heptane, and 2,6-bis (isocyanatomethyl)-bicyclo[2.2.1] heptane. Examples of the aliphatic diisocyanate include 1,6-hexane diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate.

[0068] In particular, from the viewpoint of economic efficiency and quality stability, the (b) diisocyanate compound is preferably an aromatic diisocyanate, and particularly preferably tolylene diisocyanate (TDI) such as 2,4-tolylene diisocyanate or 2,6-tolylene diisocyanate.

[0069] From the viewpoint of increasing the concentration of urethane groups in the component (B), it is preferable to use a diisocyanate compound having a molecular weight that is not very large, and preferred examples thereof include tolylene diisocyanate (TDI) and isophorone diisocyanate (IPDI).

[0070] The amount of structural moieties derived from the component (b) in the component (B) is preferably 3 mass% or more and less than 10 mass%, and more preferably 5 mass% or more and less than 8 mass%.

[0071] The (b) diisocyanate compounds may be used alone, or may be used in combination of two or more thereof.

[0072] Component (c): Hydroxyl group-containing acrylate compound The urethane acrylate oligomer (B) according to the present invention comprises a hydroxyl group-containing acrylate compound. As used herein, the hydroxyl group-containing acrylate compound is a component (c), which is also referred to as “(c) a hydroxyl group-containing acrylate compound” or “(c) a hydroxyl group-containing acrylate”.

[0073] As the hydroxyl group-containing acrylate compound for use in the synthesis of the urethane acrylate oligomer (B), a hydroxyl group-containing acrylate in which a hydroxyl group is bonded to a primary carbon atom (referred to as a first hydroxyl group-containing acrylate) and a hydroxyl group-containing acrylate in which a hydroxyl group is bonded to a secondary carbon atom (referred to as a second hydroxyl group-containing acrylate) are preferable, with a first hydroxyl group-containing acrylate being particularly preferable. A hydroxyl group-containing acrylate in which a hydroxyl group is bonded to a tertiary carbon atom (referred to as a tertiary hydroxyl group-containing acrylate) is not preferable because it is poor in reactivity with an isocyanate group (hereinafter, also referred to as “NCO”).

[0074] Examples of the first hydroxyl group-containing acrylate include 2-hydroxyethyl acrylate, 3-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 1,6-hexanediol mono acrylate, pentaerythritol triacrylate, dipentaerythritol pentaacrylate, neopentyl glycol monoacrylate, trimethylolpropane diacrylate, and trimethylolethane diacrylate.

[0075] Examples of the second hydroxyl group-containing acrylate include 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 2-hydroxy-3-phenyloxypropyl acrylate, and 4-hydroxycyclohexyl acrylate, as well as compounds obtained by addition reaction of a glycidyl group-containing compound such as alkyl glycidyl ether, allyl glycidyl ether or glycidyl acrylate and acrylic acid.

[0076] The amount of structural moieties derived from the component (c) in the component (B) is preferably 2 mass% or more and less than 8 mass%, and more preferably 3 mass% or more and less than 7 mass%.

[0077] The (c) hydroxyl group-containing acrylates may be used alone, or may be used in combination of two or more thereof.

[0078] Component (d): additional component In the synthesis of the urethane acrylate oligomer (B), an additional component may be used in addition to the components (a) to (c). As used herein, a component that does not correspond to any of the components (a) to (c) is also referred to as a “component (d)”. Examples of the component (d) include monohydric alcohols or polyhydric alcohols which do not correspond to any of (a) and (c), mercaptosilane, and aminosilane. By using the component (d), the acryloyl group bonded to an end of the component (B) can be replaced to obtain the component (B) having one acryloyl group.

[0079] For example, the monohydric alcohol as the component (d) is preferably a lower alcohol having 1 to 8 carbon atoms, and more preferably an aliphatic alcohol such as methanol, n-octanol or 2-ethylhexanol. Examples of the polyhydric alcohol as the component (d) include glycerin, 1,2,3-propylenetriol, and saccharides. Mercaptosilane and the aminosilane as the component (d) include, for example, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, and 3-aminopropyltrimethoxysilane can be preferably used. When the component (d) is used, two or more components (d) may be used.

[0080] The amount of structural moieties derived from the component (d) in the component (B) is preferably less than 6 mass%, more preferably less than 5 mass%, and particularly less than 4 mass%.

[0081] It is preferable that the urethane acrylate oligomer (B) is synthesized by reacting a diol [component (a)] and a diisocyanate [component (b)] in the presence of dibutyltin dilaurate or the like as a urethane synthesis catalyst, and then reacting a hydroxyl group-containing acrylate [component (c)]. In the reaction of the diol and the diisocyanate, the order in which the diol and the diisocyanate are reacted is not limited, and for example, the component (b) may be reacted with the component (a), or the component (a) and a part of the component (b) may be reacted, followed by reaction of the remaining part of the component (b). When the component (d) is used, the component (d) can be reacted after the reaction of the diol and the diisocyanate, and in parallel to, or before or after the reaction of the hydroxyl group-containing acrylate (c). Here, when a monohydric alcohol and / or an aminosilane are used as the component (d), the reaction of the diol and the diisocyanate may be followed by reaction of the product with the (c) hydroxyl group-containing acrylate and the component (d) in the stated order, or with the component (d) and the (c) hydroxyl group-containing acrylate in the stated order, or with the component (d) accompanied by the (c) hydroxyl group-containing acrylate, where it is preferable that the product of the reaction of the diol and the diisocyanate is reacted with the (c) hydroxyl group-containing acrylate and the component (d) in the stated order. When mercaptosilane is used as the component (d), the reaction of the diol and the diisocyanate may be followed by reaction of the product with the (c) hydroxyl group-containing acrylate and the component (d) in the stated order, or with the component (d) and the (c) hydroxyl group-containing acrylate in the stated order, or with the component (d) accompanied by the (c) hydroxyl group-containing acrylate, wherein is preferable that the product of the reaction of the diol and the diisocyanate is reacted with the component (d) and the (c) hydroxyl group-containing acrylate in the stated order.

[0082] The urethane acrylate oligomer (B) obtained by the above method has, for example, a structure represented by the following formula (U1). 　　　　 [c]-([b]-[a])n-[b]-[c] formula (U1) In formula (U1), [a], [b] and [c] are structural moieties derived from the component (a), the component (b) and the component (c), respectively. Each of points of attachment represented by “-” is a urethane bond.

[0083] When the component (d) is used in the synthesis of the urethane acrylate oligomer (B), the urethane acrylate oligomer (B) has, for example, any of structures of the following formulae (U2) and (U3) in addition to the structure represented by the above formula (U1). [c]-([b]-[a])n-[b]-[d] formula (U2) [d]-([b]-[a])n-[b]-[d] formula (U3) In formula (U2) and formula (U3), [a], [b], [c] and [d] are structural moieties derived from the component (a), the component (b), the component (c) and the component (d), respectively. The point of attachment represented by “-” is a urethane bond, a thiourethane bond or a urea bond depending on the chemical species of the component (d). Each of other points of attachment “-” is a urethane bond.

[0084] In formulae (U1) to (U3), “n” represents a numerical value of 1.0 or more, and may be, for example, more than 1.0, 1.1 or more, 1.3 or more, or 1.5 or more, or 3.0 or less, 2.5 or less, or 2.0 or less. The subscript n may be, for example, 1.1 to 3.0, 1.3 to 2.5, or 1.5 to 2.0.

[0085] When the component (d) is used in the synthesis of the urethane acrylate oligomer (B), 　　　　(i) a compound having both an acryloyl group and a structure derived from the component (d), and containing a urethane bond (-NHCOO-) in a repeat unit of a main chain, for example, a compound represented by formula (U2), which has one acryloyl group and one structure derived from the component (d), and contains a urethane bond (-NHCOO-) in a repeat unit of a main chain can be formed, and 　　　　(ii) a compound having a structure derived from the component (d) without acryloyl group, and containing a urethane bond (-NHCOO-) in a repeat unit of the main chain, for example, a compound represented by formula (U3), which has two structures derived from the component (d), and contains a urethane bond (-NHCOO-) in the repeat unit of the main chain can be formed.

[0086] The (ii) compound having a structure derived from the component (d) without acryloyl group, and containing a urethane bond (-NHCOO-) in a repeat unit of a main chain does not correspond to the urethane acrylate oligomer (B) and corresponds to a component (E) that will be described later.

[0087] The urethane acrylate oligomer (B) may be a monofunctional urethane acrylate oligomer having one acryloyl group derived from the (c) hydroxyl group-containing acrylate, or may be a bifunctional urethane acrylate oligomer having two acryloyl groups. Preferably, the urethane acrylate oligomer (B) contains a monofunctional urethane acrylate oligomer and a bifunctional urethane acrylate oligomer.

[0088] The ratio of the number of moles of the monofunctional urethane acrylate oligomer to the bifunctional urethane acrylate oligomer may be 0 / 100 or more and 95 / 5 or less, 20 / 80 or more and 95 / 5 or less, 40 / 60 or more and 95 / 5 or less, or 50 / 50 or more and 95 / 5 or less.

[0089] The content of the urethane acrylate oligomer (B) in the radiation curable resin composition of the present invention is 71 mass% or more, preferably 74 mass% or more, and particularly preferably 77 mass% or more with respect to the total mass of the radiation curable composition. The content of the urethane acrylate oligomer (B) is 83 mass% or less. If the content of the urethane acrylate oligomer (B) in the total mass of the radiation curable composition is less than 71 mass%, the curing rate decreases. If the content of the urethane acrylate oligomer (B) is more than 83 mass%, the viscosity of a resin composition may increase.

[0090] The urethane acrylate oligomers (B) may be used alone, or may be used in combination of two or more thereof.

[0091] Component (C): acrylate compound (C) having a molecular weight of less than 200 The radiation curable composition of the present invention further comprises an acrylate compound having a molecular weight of less than 200. The “acrylate compound having a molecular weight of less than 200” is a component (C), which is also referred to as a “acrylate compound (C) having a molecular weight of less than 200” or a “acrylate compound (C)”. As used herein, the acrylate compound (C) is distinguished from the hydroxyl group-containing acrylate compound (c) [component (c)] and the component (B).

[0092] The component (C) is typically a monomer having one or more acryloyl groups in the molecule, preferably a polymerizable non-urethane monomer having one acryloyl group in the molecule. When the component (C) is a monomer, the component (C) is also referred to as a “reactive diluent monomer” because it is often used for the purpose of diluting a composition containing the urethane acrylate oligomer (B). Examples of the component (C) include aliphatic acrylates having an aliphatic structure, acrylates having a (hetero)alicyclic structure, and acrylates having an aromatic structure. The component (C) also includes acrylate compounds having a functional group differing from an acryloyl group, such as hydroxyl group-containing acrylates. Further, as used herein, compounds in which an acryloyl group is bonded to a nitrogen atom, such as acrylamide and acryloylmorpholine, also correspond to the acrylate compound, and is encompassed by the component (C). The component (C) also includes oligomers and polymers that do not correspond to the component (B).

[0093] The molecular weight of the component (C) is less than 200, and preferably 190 or less.

[0094] Examples of the component (C), in particular, the acrylate having an aliphatic structure and having one acryloyl group in the molecule include butyl acrylate, isobutyl acrylate, t-butyl acrylate, amyl acrylate, isoamyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, nonyl acrylate, isononyl acrylate, methoxyethylene glycol acrylate, ethoxyethyl acrylate, and 2-[2-(ethoxy)ethoxy]ethyl acrylate.

[0095] Examples of the acrylate having a (hetero)alicyclic structure and having one acryloyl group in the molecule include cyclohexyl acrylate, tetrahydrofurfuryl acrylate, (3-ethyloxetane-3-yl) methyl acrylate, and 3,3,5-trimethylcyclohexyl acrylate.

[0096] Examples of the acrylate having an aromatic structure and having one acryloyl group in the molecule include benzyl acrylate and phenoxyethyl acrylate.

[0097] Examples of the hydroxyl group-containing acrylate having one acryloyl group in the molecule include a hydroxyl group-containing acrylate compound used for the synthesis of the urethane acrylate oligomer (B), with 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate and 4-hydroxybutyl acrylate being preferable.

[0098] Examples of the compound which has one acryloyl group in the molecule and in which an acryloyl group is bonded to a nitrogen atom include acryloylmorpholine, N,N-dimethyl acrylamide, N,- (2-hydroxyethyl) acrylamide, N-isopropyl acrylamide, N-isobutoxymethyl acrylamide, N,N-diethyl acrylamide, N-[3-(dimethylamino) propyl] acrylamide, and t-octyl acrylamide.

[0099] Examples of the component (C), in particular, the acrylate compound having two or more acryloyl groups in the molecule include ethylene glycol diacrylate and 1,4-butanediol diacrylate.

[0100] Examples of commercially available product of the component (C) include PHOTOMER 4211 (manufactured by IGM Resins B.V.), ACMO (manufactured by KJ Chemicals Corporation), 2-ethylhexyl acrylate, isobutyl acrylate and 2-methoxyethyl acrylate (all manufactured by Nippon Shokubai Co., Ltd.), 4HBA (manufactured by Mitsubishi Chemical Group Corporation), isoamyl acrylate (manufactured by FUJIFILM Wako Pure Chemical Corporation), and TBA, NOAA, Viscoat #150, Viscoat #155, Viscoat #160 and OXE-10 (all manufactured by Osaka Organic Chemical Industry Ltd.).

[0101] Among the components (C), acrylates such as 2-[2-(ethoxy)ethoxy]ethyl acrylate, acryloylmorpholine, and 2-ethylhexyl acrylate are particularly preferable.

[0102] The content of the component (C) in the radiation curable composition of the present invention is preferably 4 mass% or more, more preferably 6 mass% or more, and particularly preferably 8 mass% or more, with respect to the total mass of the radiation curable composition. The content of the component (C) is preferably 25 mass% or less, more preferably 20 mass% or less, and particularly preferably 15 mass% or less.

[0103] The components (C) may be used alone, or may be used in combination of two or more thereof.

[0104] When the component (C) having one acryloyl group in the molecule is a [monofunctional component (C)] and the component (C) having two or more acryloyl groups in the molecule is a [polyfunctional component (C)], the ratio of the number of moles of the [monofunctional component (C)] to the [polyfunctional component (C)] may be 30 / 70 or more and 99 / 1 or less, 40 / 60 or more and 98 / 2 or less, or 50 / 50 or more and 95 / 5 or less.

[0105] Component (C)’: Monomer having monofunctional acryloyl group having a molecular weight of 200 or moreComponent (C)’’: Monomer having polyfunctional acryloyl group having a molecular weight of 200 or more The radiation curable composition of the present invention may comprise a monomer having an acryloyl group other than the component (C); a monomer having a monofunctional acryloyl group having a molecular weight of 200 or more and / or a monomer having a polyfunctional acryloyl group having a molecular weight of 200 or more. As used herein, a monomer having a monofunctional acryloyl group having a molecular weight of 200 or more is a component (C)’, which is referred to as an "acrylic monomer (C)’ ". A monomer having a polyfunctional acryloyl group having a molecular weight of 200 or more is a component (C)”, which is referred to as an "acrylic monomer (C)” ". The component (C)' and the component (C)” are each distinguished from the hydroxyl group-containing acrylate compound (c) [component (c)], the component (B) and the component (C).

[0106] The component (C)’ is typically a monomer having one or more acryloyl groups in the molecule, preferably a radically polymerizable non-urethane monofunctional monomer having one acryloyl group in the molecule. The component (C)” is typically a radically polymerizable non-urethane polyfunctional monomer having two or more acryloyl groups in the molecule. Like the component (C), the component (C)’ and the component (C)” have an aliphatic structure; a (hetero)alicyclic structure; an aromatic structure; a hydroxyl group-containing structure; or a structure in which an acryloyl group is bonded to a nitrogen atom, or the like. It is preferred that the radiation curable composition of the present invention further comprises the component (C)’ and / or the component (C)” from the viewpoint of adjusting the viscosity of a curable composition and improving the curing rate in the case of the former, and from the viewpoint of improving the curing rate in the case of the latter.

[0107] Examples of the component (C)’, which has an aliphatic structure, include decyl acrylate, isodecyl acrylate, undecyl acrylate, lauryl acrylate, stearyl acrylate, isostearyl acrylate, polyethylene glycol monoacrylate, polypropylene glycol monoacrylate, methoxypolyethylene glycol acrylate, and methoxypolypropylene glycol acrylate. Examples of the component (C)’, which has a (hetero)alicyclic structure, include isobornyl acrylate, bornyl acrylate, tricyclodecanyl acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate, and 4-butylcyclohexyl acrylate. Examples of the component (C)’, which has an aromatic structure, include benzophenone acrylate, and nonylphenol EO-modified acrylate. Examples of the component (C)’, which has a hydroxyl group-containing structure, include 12-hydroxystearic acrylate, caprolactone-modified hydroxyethyl acrylate, and polyethylene glycol monoacrylate. Examples of the component (C)’, in which an acryloyl group is bonded to a nitrogen atom, include N-acryloyl-11-aminoundecanoic acid, N-acryloyl-L-phenylalanine, N-acryloyl-N’-phenylpiperazine, N-acryloyl-4-amino-1,8-naphthalimide, and N-acryloyl-N’-stearoylhydrazine.

[0108] Among the (C)' components described above, methoxypolyethylene glycol acrylate, and the like are preferred from the viewpoint of improving the curing rate. Examples of the commercially available product include ARONIX M-113 (manufactured by Toagosei Co., Ltd.), and M-90G and M-130G (all manufactured by Shin-Nakamura Chemical Co., Ltd.).

[0109] Examples of the component (C)” include glycerin diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, glycerin triacrylate, ethoxylated glycerin triacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, 1,9-nonanediol diacrylate, 1,10-decanediol diacrylate, trimethylolpropanetrioxyethyl acrylate, tris(2-hydroxyethyl)isocyanurate triacrylate, tris(2-hydroxyethyl)isocyanurate diacrylate, tricyclodecanedimethanol diacrylate, diacrylates of a diol as an ethylene oxide or propylene oxide adduct of bisphenol A, diacrylates of a diol as an ethylene oxide or propylene oxide adduct of hydrogenated bisphenol A, and epoxy acrylates obtained by adding acrylate to diglycidyl ether of bisphenol A.

[0110] Among the components (C)” described above, 1,6-hexanediol diacrylate, polyethylene glycol diacrylate, and the like are preferred from the viewpoint of improving the curing rate. Examples of the commercially available product include LIGHT ESTER 1.6HX (manufactured by Kyoeisha Chemical Co., Ltd.), and A-200 and A-400 (manufactured by Shin Nakamura Chemical Co., Ltd.).

[0111] The content of the component (C)’ in the radiation curable composition of the present invention is preferably 1 mass% or more, and more preferably 2 mass% or more, with respect to the total mass of the radiation curable composition. The content of the component (C)’ is preferably 10 mass% or less, and more preferably 8 mass% or less.

[0112] The components (C)’ may be used alone, or may be used in combination of two or more thereof.

[0113] The content of the component (C)” in the radiation curable composition of the present invention is preferably 0.5 mass% or more, and more preferably 0.8 mass% or more, with respect to the total mass of the radiation curable composition. The content of the component (C)” is preferably 3 mass% or less, and more preferably 2 mass% or less.

[0114] The components (C)” may be used alone, or may be used in combination of two or more thereof.

[0115] Component (D): N-vinyl heterocyclic compound (D) having a molecular weight of less than 200 The radiation curable composition of the present invention comprises a N-vinyl heterocyclic compound having a molecular weight of less than 200. The “N-vinyl heterocyclic compound having a molecular weight of less than 200” is a component (D), which is also referred to as a “N-vinyl heterocyclic compound (D) having a molecular weight of less than 200” or a “N-vinyl heterocyclic compound (D)”. As used herein, the N-vinyl heterocyclic compound (D) is distinguished from the hydroxyl group-containing acrylate compound (c) [component (c)], the component (B), the component (C), and the components (C)’ and (C)”.

[0116] The component (D) is typically a polymerizable monomer which has one or more vinyl groups in the molecule and in which a carbon atom of the vinyl group is bonded to a nitrogen atom forming a heterocyclic structure. It is advantageous that the radiation curable composition of the present invention further comprises the component (D) from the viewpoint of improving the curing rate. From the viewpoint of adjusting the viscosity of the curable composition, the molecular weight of the component (D) is preferably less than 200, and more preferably 100 to 190.

[0117] Examples of the N-vinyl heterocyclic compound (D) include N-vinylcarbazole, N-vinylpyrrolidone, N-vinylethylacetamide, N-vinylpyrrole, N-vinylacetanilide, N-vinylsuccinimide, N-vinylphthalimide, N-vinylcaprolactam, N-vinylimidazole, N-vinylpyridine, 3-ethenyl-2-oxazolidinone, and 3-ethenyl-5-methyl-2-oxazolidinone.

[0118] Examples of commercially available products of the component (D) include Vinyl caprolactam HO-Tempo (manufactured by BASF) and VMOX (manufactured by BASF).

[0119] Among the components (D) described above, N-vinylcaprolactam and / or 3-ethenyl-5-methyl-2-oxazolidinone are preferable from the viewpoint of improvement of curing rate, production efficiency, economic efficiency, and the like.

[0120] The content of the component (D) in the radiation curable composition of the present invention is preferably 1 mass% or more, more preferably 3 mass% or more, and particularly preferably 5 mass% or more, with respect to the total mass of the radiation curable composition. The content of the component (D) is 11 mass% or less, and particularly preferably 10 mass% or less, resulting in reduced emissions of volatile compounds during application of the radiation curable composition on the optical fiber. If the content of the component (D) is more than 11 mass%, the emissions of volatile compounds during application of the radiation curable composition on the optical fiber increase. A too high amount of N-vinyl heterocyclic compound (D) is not desired since it remains largely unreacted during the initial stages of application and therefore retains its volatility, making it prone to evaporation from the radiation curable composition when applying the radiation curable composition to the glass fiber. During optical fiber manufacturing, the radiation curable composition is applied to glass fiber at elevated temperatures. The glass fiber emerges from the drawing furnace at temperatures typically ranging from 1000-2000°C and, while it cools rapidly, it remains significantly hot during the coating application process. This thermal environment creates a unique technical challenge where slow-reacting volatile components in the coating composition are prone to rapid evaporation. The evaporation of volatile components from the coating composition may create harmful vapor concentrations in the workplace atmosphere, and therefore may require enhanced ventilation systems and personal protective equipment. Furthermore, volatile compounds that evaporate during application may deposit on UV curing lamps and / or compromise curing uniformity and / or may alter the intended stoichiometry of the coating composition, potentially affecting its curing characteristics and final properties and leading to unpredictable coating performance.

[0121] The components (D) may be used alone, or may be used in combination of two or more thereof.

[0122] The total content of the acrylate compound (C) and the N-vinyl heterocyclic compound (D) is 10 mass% or more, preferably 15 mass% or more, and particularly preferably 18 mass% or more, with respect to the total mass of the radiation curable composition. The total content of the acrylate compound (C) and the N-vinyl heterocyclic compound (D) is preferably 30 mass% or less, more preferably 25 mass% or less, and particularly preferably 22 mass% or less.

[0123] The molar ratio of the N-vinyl heterocyclic compound (D) to the acrylate compound (C) [(D) / (C)] in the radiation curable composition is preferably 0.1 or more and 0.5 or less, preferably 0.2 or more and 0.5 or less, and particularly preferably 0.3 or more and 0.5 or less.

[0124] The total content of the N-vinyl heterocyclic compound (D) and the urethane acrylate oligomer (B) is preferably 75 mass% or more, more preferably 80 mass% or more, and particularly preferably 82 mass% or more, with respect to the total mass of the radiation curable composition. The total content of the component (D) and the urethane acrylate oligomer (B) is preferably 92 mass% or less, more preferably 90 mass% or less, and particularly preferably 87 mass% or less.

[0125] Component (E): Oligomer or polymer that does not correspond to component (B)

[0126] The radiation curable resin composition of the present invention may further comprise an oligomer or polymer that does not correspond to the component (B). The oligomer or polymer is a component (E), which is referred to as an “oligomer or polymer (E) which does not correspond to the component (B)”.

[0127] Examples of the component (E) include polyether triol, urethane acrylate oligomers containing the component (b) and the component (c), and oligomers which have a structure derived from the component (d) without acryloyl group and which contain a urethane bond (-NHCOO-) in a repeat unit of a main chain.

[0128] The radiation curable resin composition may contain one or more components (E), and the content of the component (E) in the radiation curable composition of the present invention may be, for example, less than 5 mass% with respect to the total mass of the radiation curable composition.

[0129] Component (F): Monomer having one or more ethylenically unsaturated groups that do not correspond to constituents of component (B) [components (a) to (d)], component (C), component (C)’, component (C)”, or component (D)

[0130] The radiation curable resin composition of the present invention may further comprise a monomer having one or more ethylenically unsaturated groups that do not correspond to the constituents of the component (B) [components (a) to (d)], the component (C), the component (C)’, the component (C)”, or the component (D). The monomer is a “monomer (F)”, which is referred to as a “monomer (F)”.

[0131] Examples of the component (F) include N-vinyl heterocyclic compounds having a molecular weight of 200 or more (for example, poly N-vinylcarbazole, N-vinyl-2-pyrrolidone dimer, and N-vinyl-3,6-dibromocarbazole).

[0132] The content of the component (F) in the radiation curable composition of the present invention is, for example, 1 mass% or more and 5 mass% or less per 100 mass% of the composition. When the composition contains the component (F), the components (F) may be used alone, or may be used in combination of two or more thereof.

[0133] The radiation curable composition of the present invention may contain a silane coupling agent as long as it does not interfere with the effect of the present invention. Examples of the silane coupling agent include tetraethoxysilane, vinyltrichlorosilane, vinyltriethoxysilane, vinyltris(β-methoxy-ethoxy)silane, β-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane, 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, and, γ-trimethoxysilylpropyldimethylthiocarbamyl tetrasulfide, and γ-trimethoxysilylpropylbenzothiazyl tetrasulfide. Examples of the commercially available product include DOWSIL Z-6062 and SZ6030 (all manufactured by Dow Toray Co., Ltd.), and KBEs 903, 603 and 403 (all manufactured by Shin-Etsu Chemical Co., Ltd.). The silane coupling agent is preferably γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, or γ-aminopropyltrimethoxysilane from the viewpoint of adhesion between the cover and the glass.

[0134] The content of the silane coupling agent in the radiation curable composition of the present invention is preferably 0.01 mass% or more and 2 mass% or less, more preferably 0.1 mass% or more and 1.5 mass% or less, and particularly preferably 0.3 mass% or more and 1.5 mass% or less per 100 mass% of the composition, from the viewpoint of maintaining adhesion between the cured product of the radiation curable composition of the present invention and the glass fiber. When the composition comprises the silane coupling agent, the silane coupling agents may be used alone, or may be used in combination of two or more thereof.

[0135] In addition to the above-described components, various additives such as an antioxidant, a colorant, an ultraviolet absorber, a light stabilizer, a thermal polymerization inhibitor, a leveling agent, a surfactant, a storage stabilizer, a plasticizer, a slipping agent, a solvent, a filler, an anti-aging agent, a wettability improver, a coated surface improver, and the like can be blended in the radiation curable composition of the present invention as necessary.

[0136] Examples of the antioxidant include IRGANOXs 245, 1010, 1035, 1076 and 1222 (all manufactured by BASF Japan Ltd.), ANTIGENE P, 3C, Sumilizer GA-80, and GP (manufactured by Sumitomo Chemical Company, Limited.). Examples of the ultraviolet absorber include TINUVINs P, 234, 320, 326, 327, 328, 329 and 213 (all manufactured by BASF Japan Ltd.), and Seesorbs 102, 103, 501, 202, 712 and 704 (all manufactured by Shipro Kasei Kaisha, Ltd.). Examples of the light stabilizer include TINUVINs 292, 144 and 622LD, and Sanols LS-770 and 765 (all manufactured by BASF Japan Ltd.).

[0137] The surfactant is not particularly limited. A fatty acid ester type nonionic surfactant is preferable because it effectively suppresses the occurrence of defects resulting from immersion of the optical fiber wire in warm water. Nonionic surfactants such as glycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, and polyoxysorbitol fatty acid ester are particularly preferable.

[0138] Other oligomers, polymers and / or silane compounds, other additives, and the like as components that do not correspond to any of the components described above, can be optionally blended in the radiation curable composition of the present invention as long as they do not interfere with the effect of the present invention.

[0139] The method for producing the radiation curable composition is not particularly limited, and may include, for example, melt-blending in a heretofore known reaction vessel equipped with a stirrer.

[0140] The radiation curable composition of the present invention enables the obtainment of a cured product of the composition which has a reduced level of coloring. The level of coloring can be determined by measuring the transmitted light yellowness index YI of a film-shaped cured product of the composition which has a predetermined thickness. A specific measurement method is described in examples below.

[0141] The cured product of the radiation curable composition of the present invention has a high-rate curing property suitable for an optical fiber primary covering layer. The high-rate curing property can be determined by comparing Young's moduli of cured products obtained by irradiation with different intensities of energy. A specific measurement method is described in examples below.

[0142] 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 at 25°C. When the Young's modulus of the optical fiber primary covering layer is 0.1 to 1.3 MPa at 25°C, so-called microbending losses caused by bending of glass fiber upon localized application of pressure 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.

[0143] Typically, an optical fiber including a cured product of the radiation curable composition of the present invention as an optical fiber primary covering layer further includes an optical fiber secondary covering layer that is in contact with the outside of the optical fiber primary covering layer. The Young's modulus of the optical fiber secondary covering layer is preferably 500 MPa, and more preferably 500 to 1,500 MPa. The Young's modulus of the optical fiber secondary covering layer can be measured by a method similarly to the method for measuring the Young's modulus of the cured product of the radiation curable composition which will be described in examples below. Glass fiber, whose surface is provided with an optical fiber primary covering layer and an optical fiber secondary covering layer in the stated order, can be used as an optical fiber wire.

[0144] The viscosity of the radiation curable composition of the present invention is preferably 0.1 to 10 Pa・s, and more preferably 1 to 8 Pa・s at 25°C from the viewpoint of productivity that depends on, for example, the time required for a filtration step during production of the composition. As used herein, the viscosity of the composition is a viscosity measured by a Brookfield viscometer (for example, model TVB-10H manufactured by TOKISANGYO).

[0145] An embodiment of a method for producing an optical fiber comprises the steps of disposing the radiation curable composition of the present invention on a surface of at least a part of glass fiber, and curing the radiation curable composition by irradiation with radiation to form an optical fiber primary covering layer. Preferably, the method further comprises the step of disposing a radiation curable composition for an optical fiber secondary covering layer is disposed on the surface of the optical fiber primary covering layer, and curing the composition to form an optical fiber secondary covering layer. Another embodiment comprises a method for producing an optical fiber, comprising the step of disposing the radiation curable composition of the present invention and a radiation curable composition for an optical fiber secondary covering layer in the stated order on a surface of at least a part of glass fiber, and curing them by irradiation with radiation to form an optical fiber primary covering layer and an optical fiber secondary covering layer.

[0146] The method for disposing the radiation curable composition on the surface of glass fiber is not particularly limited, and a heretofore known method can be used. Examples thereof include a method in which the radiation curable composition is applied to the surface, and a method in which the surface is immersed in the radiation curable composition.

[0147] The method for curing the radiation curable composition is not particularly limited, and examples thereof include a method in which the radiation curable composition is irradiated with one or more selected from an infrared ray, a visible ray, an ultraviolet ray, an X-ray, an electron beam, an α ray, a β ray, a γ ray, and the like.

[0148] Examples of the common method for producing an optical fiber include drawing a molten quartz base material, which is being heat-melted, applying the radiation curable composition of the present invention and a radiation curable composition for an optical fiber secondary covering layer in the stated order, and then curing with radiation to form an optical fiber primary covering layer and an optical fiber secondary covering layer.

[0149] An optical fiber assembly such as an optical fiber ribbon or an optical fiber cable is an assembly including two or more of the optical fibers described above. A tape-shaped optical fiber or an optical fiber cable can be obtained in which the optical fibers are integrated using a binding material. Examples

[0150] Hereinafter, the present disclosure will be described in detail with examples and comparative examples, but the present disclosure is not limited to these examples.Synthesis of urethane acrylate oligomer and preparation of radiation curable composition (primary material)

[0151] (Synthesis Example 1) A reaction vessel equipped with a stirrer was charged with 8,869 g of polypropylene glycol having a number average molecular weight of 3,000 (EXCENOL 3020 manufactured by AGC Inc.), 772.3 g of 2,4-toluene diisocyanate (COSMONATE T-100 manufactured by Mitsui Chemicals, Inc.), and 2.4 g of 2,6-di-t-butyl-p-cresol (manufactured by Honshu Chemical Industry Co., Ltd.) were added, and the mixture was heated to 30°C with stirring. To this, 2.7 g of dibutyltin dilaurate (manufactured by Sakai Chemical Industry Co., Ltd.) was added, and the mixture was heated to 60°C with stirring, and allowed to react for 1 hour. Subsequently, 257.6 g of 2-hydroxyethyl acrylate (manufactured by Nippon Shokubai Co., Ltd.) was added, the mixture was allowed to react at 70°C for 1 hour, 96.2 g of 2-ethylhexanol (manufactured by Mitsubishi Chemical Corporation) was added, and the mixture was allowed to react at 70°C for 1 hour, thereby obtaining a urethane acrylate oligomer 1.

[0152] (Example 1) A vessel equipped with a stirrer was charged with 75.0 g of the urethane acrylate oligomer 1 obtained in Synthesis Example 1, 19.0 g of 2-[2-(ethoxy)ethoxy]ethyl acrylate (manufactured by IGM Resins), 5.0 g N-vinylcaprolactam (manufactured by BASF), 1.0 g of 1,6-hexanediol diacrylate (manufactured by Kyoeisha Chemical Co., Ltd.), 0.6 g of Omnirad 403 (manufactured by IGM Resins), and 0.3 g of Irganox 245, and the mixture was stirred at 60°C for 1 hour to obtain a radiation curable composition 1.

[0153] Examples 2 to 14 and Comparative Examples 1 to 37 Raw materials were added to containers with a stirrer at weight ratios shown in Tables 1-7, and stirred at 60°C for 1 hour as in Example 1 to obtain radiation curable compositions 2 to 14 and radiation curable compositions R1 to R37, respectively. The raw materials used in Example 2 to 14 and Comparative Example 1 to 37 are as follows.

[0154]

[0155]

[0156]

[0157]

[0158]

[0159]

[0160]

[0161] Chemical names and brand names of components used in Examples and Comparative Examples are as shown in Table 8.

[0162] Evaluation Method

[0163] (1) Level of coloring As described below, the transmitted light yellowness index YI of a cured layer (layered cured product) of the compositions obtained in each of examples and comparative examples was measured to determine the level of coloring.

[0164] A liquid radiation curable composition was applied onto a glass plate with a 381 μm-thick applicator bar, cured by irradiation with an ultraviolet ray at an energy of 0.02 J / cm2in the air, and peeled from the glass plate to obtain a test film. The transmitted light yellowness index YI of the cured test film was measured with a colorimeter Colour Cute i manufactured by Suga Test Instruments Co., Ltd., and the coloring property was determined on the basis of the following criteria. Tables 1 to 7 show the results. 　　　　○: The transmitted light yellowness index YI of the cured film, obtained by application with 381 μm-thick applicator bar and curing, is less than 0.7. 　　　　×: The transmitted light yellowness index YI of the cured film, obtained by application with 381 μm-thick applicator bar and curing, is 0.7 or more.

[0165] (2) High-rate curing property As described below, the Young's modulus of a cured layer (layered cured product) of the compositions obtained in each of examples and comparative examples was measured to determine the high-rate curing property.

[0166] A liquid radiation curable composition was applied onto a glass plate with a 381 μm-thick applicator bar, cured by irradiation with an ultraviolet ray at an energy of 0.02 J / cm2and 1 J / cm2in the air, and peeled from the glass plate to obtain a test film. The cured test film was allowed to stand at a temperature of 23°C and a relative humidity of 50% for 24 hours, and a strip-shaped sample was then prepared such that the stretched portion had a width of 6 mm and a length of 25 mm. A tensile test was conducted on the strip-shaped sample was according to JISK7161-1 under the above-mentioned temperature and relative humidity conditions using a tensile tester 5542 C4600 (manufactured by Instron Japan Co., Ltd.). The tension rate was 1 mm / min, and the Young's modulus was determined from the tensile strength at 2.5% strain. The ratio of the Young's modulus of the film cured at 0.02 J / cm2to the Young's modulus of the film cured at 1 J / cm2was used as an index for determining the high-rate curing property, and the high-rate curing property was determined on the basis of the following criteria. Tables 1 to 6 show the results.

[0167] (3) Composition productivity From the results of measuring the viscosity of the compositions obtained in examples and comparative examples, the time required for the filtration step during production as a composition was estimated, and the composition productivity was determined on the basis of following criteria. Tables 1 to 7 show the results. Synthesis of urethane acrylate oligomer and preparation of radiation curable composition (secondary material)

[0168] (Preparation Example 1) A reaction vessel equipped with a stirrer was charged with 2,910 g of polypropylene glycol having a number average molecular weight of 1,000 (EXCENOL 1020 manufactured by Asahi Glass Co., Ltd.), 2,949 g of 2,4-toluene diisocyanate, 2.5 g of 2,6-di-t-butyl-p-cresol, and 820 g of isobornyl acrylate (manufactured by Osaka Organic Chemical Industry Ltd.), and the mixture was cooled to 15°C with stirring. While the liquid was cooled, 7.5 g of dibutyltin dilaurate was added, 509 g of 2-hydroxypropyl acrylate was then added, and the mixture was allowed to react at 35°C for 1 hour after the temperature rise stopped. Subsequently, 2,801 g of 2-hydroxyethyl acrylate was gradually added to the extent that the liquid temperature did not exceed 70°C. After the end of the addition, the mixture was allowed to react at a liquid temperature of 70°C for 1 hour, thereby obtaining a urethane acrylate oligomer 2. A reaction vessel equipped with a stirrer was charged with 56.0 g of the urethane acrylate oligomer 2, 5.0 g of isobornyl acrylate, 26.0 g of tripropylene glycol diacrylate (TPGDA manufactured by Nippon Kayaku Co., Ltd.), 14.0 g of bisphenol A-type epoxy diacrylate (CN-120Z manufactured by Sartomer), 0.50 g of 1-hydroxycyclohexyl phenyl ketone (Omnirad 184 manufactured by IGM Resins), and 0.70 g of 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Omnirad TPO manufactured by IGM Resins), and the mixture was stirred at 60°C for 1 hour to obtain a radiation curable composition for a secondary material.

[0169] (Example 15) An optical fiber drawing apparatus (manufactured by Yoshida Industries Co., Ltd.) was used. The composition of Example 1 was used as a primary covering material, and the liquid curable resin composition for a secondary material which had obtained in Preparation Example 1 was used as a secondary covering material. Two covering layers including a primary covering material and a secondary covering material were applied onto glass fiber under the following conditions to prepare an optical fiber wire. The optical fiber drawing conditions were as follows. The diameter of the optical fiber was adjusted so that the optical fiber had a diameter of 150 μm in a naked state, 200 μm when covered with the primary covering material, and 260 μm when further covered with the secondary covering material. The optical fiber drawing rate was 120 m / min. An UV lamp SMX 3.5kw manufactured by ORC Manufacturing Co., Ltd. was used as an ultraviolet irradiation apparatus for curing the composition applied to the optical fiber. The quartz tube for the optical fiber to pass through in the ultraviolet curing apparatus was purged with nitrogen gas flowing at a rate of 10l / min.

Claims

1. A radiation curable composition for forming an optical fiber primary covering layer, comprising an acylphosphine oxide-based initiator (A), a urethane acrylate oligomer (B), an acrylate compound (C) having a molecular weight of less than 200 and a N-vinyl heterocyclic compound (D) having a molecular weight of less than 200, wherein 　　　　a content of the acylphosphine oxide-based initiator (A) is 0.15 to 0.9 mass% with respect to a total mass of the radiation curable composition, 　　　　the acylphosphine oxide-based initiator (A) comprises one or more selected from the group consisting of a compound represented by the following formula (I), a compound represented by the following formula (II), and a compound containing the compounds of formulae (I) and (II) as constituent units: 　　　　wherein P represents a phosphorus atom, C represents a carbon atom, O represents an oxygen atom, and the oxygen (=O) bonded to the phosphorus atom may be replaced by S (sulfur atom), 　　　　R1, R2 and R3 are each independently a substituent, and each of which is the following i) or ii): 　　　　i) an alkyl group optionally having a heteroatom, a cycloalkyl group optionally having a heteroatom, or an aryl group optionally having a substituent; and 　　　　ii) an alkoxy group, a halogen, or a substituent represented by O-Z+, with Z+ being one of a quaternary ammonium cation, an alkali metal cation, and a phosphonium cation, 　　　　R1 in the compound containing the compounds of formulae (I) and (II) as constituent units may be bonded together, 　　　　the urethane acrylate oligomer (B) is obtained by reacting at least 　　　　(a) a polyether diol having a number average molecular weight of 2,000 to 11,000, 　　　　(b) a diisocyanate compound; and 　　　　(c) a hydroxyl group-containing acrylate compound, 　　　　a content of the urethane acrylate oligomer (B) is 71 mass% or more and 83 mass% or less with respect to a total mass of the radiation curable composition, 　　　　a total content of the acrylate compound (C) and the N-vinyl heterocyclic compound (D) is 10 mass% or more with respect to the total mass of the radiation curable composition, and 　　　　a content of the N-vinyl heterocyclic compound (D) is 11 mass% or less with respect to the total mass of the radiation curable composition.

2. The radiation curable composition according to claim 1, wherein the urethane acrylate oligomer (B) is present in an amount of 77 mass% or more with respect to the total mass of the radiation curable composition.

3. The radiation curable composition according to claim 1 or 2, wherein the acrylate compound (C) and the N-vinyl heterocyclic compound (D) is present in an amount of 15 mass% or more, preferably in an amount of 18 mass% or more, with respect to the total mass of the radiation curable composition.

4. The radiation curable composition according to any one of claims 1 to 3, wherein the total content of the acrylate compound (C) and the N-vinyl heterocyclic compound (D) is 30 mass% or less, preferably 25 mass% or less, more preferably 22 mass% or less, with respect to the total mass of the radiation curable composition.

5. The radiation curable composition according to any one of claims 1 to 4, wherein the N-vinyl heterocyclic compound (D) in present in an amount of 10 mass% or less with respect to the total mass of the radiation curable composition.

6. The radiation curable composition according to any one of claims 1 to 5, wherein the N-vinyl heterocyclic compound (D) is present in an amount of 3 mass% or more, preferably in an amount of 5 mass% or more, with respect to the total mass of the radiation curable composition.

7. The radiation curable composition according to any one of claims 1 to 6, wherein the N-vinyl heterocyclic compound (D) and the acrylate compound (C) are present in the radiation curable composition in a molar ratio of the N-vinyl heterocyclic compound (D) to the acrylate compound (C) [(D) / (C)] of 0.1 or more and 0.5 or less, preferably in a molar ratio of 0.2 or more and 0.5 or less, more preferably in a molar ratio of 0.3 or more and 0.5 or less.

8. The radiation curable composition according to any one of claims 1 to 7, optionally comprising a photopolymerization initiator other than the acylphosphine oxide-based initiator (A) in an amount of 0.5 mass% or less, preferably in an amount of 0.3 mass% or less, preferably in an amount of 0.1 mass% or less, with respect to the total mass of the radiation curable composition.

9. The radiation curable composition according to claim 1 to 8, wherein the total content of the N-vinyl heterocyclic compound (D) and the urethane acrylate oligomer (B) is 75 mass% or more with respect to the total mass of the radiation curable composition.

10. A cured product of the radiation curable composition of any of claims 1 to 9.

11. An optical fiber comprising glass fiber, and a primary covering layer including the cured product of claim 10.

12. The optical fiber according to claim 11, further comprising a secondary covering layer.

13. A method for producing an optical fiber, comprising the steps of: disposing the radiation curable composition of any of claims 1 to 9 on glass fiber; and curing the radiation curable composition by irradiating with radiation.

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