JPH05214063A - Polymerizable unsaturated polyurethane and ultra-violet-curable resin composition containing same - Google Patents

Abstract

PURPOSE:To obtain the title polyurethane excellent in curability, heat resistance, etc., by reacting a specified polyether polyol with a polyisocyanate and a compound containing an active hydrogen atom and a polymerizable unsaturated group. CONSTITUTION:A mixture containing at least two alkylene oxides and containing 1,2-butylene oxide as an essential component and other alkylene oxides (e.g. propylene oxide) as optional components is subjected to ring-opening polymerization to produce a polyether polyol. This polyol is reacted with a polyisocyanate (e.g. tolylene diisocyanate) and a compound containing an isocyanate-reactive active hydrogen atom and a polymerizable unsaturated group (e.g. 2-hydroxypropyl acrylate) to produce a polymerizable unsaturated polyurethane. This polyurethane can desirably be used in the production of an ultraviolet-curable resin composition for cladding optical fibers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel polymerizable unsaturated polyurethane and an ultraviolet curable resin composition using the same, which is particularly suitable for optical fiber coating applications.

[0002]

2. Description of the Prior Art Optical fibers are very fragile and easily damaged.
Moreover, it is well known that optical transmission loss increases due to contamination. Therefore, conventionally, immediately after spinning an optical fiber, the glass surface is primarily coated with a material having a low elastic modulus, and then secondary coated with a material having a high elastic modulus.

In recent years, ultraviolet curable resins have been used as these materials in terms of productivity. Further, an ultraviolet curable resin is also used when bundling optical fibers having a primary coating and a secondary coating into a tape.

Polyether urethane acrylate is widely used as a polymerizable unsaturated polyurethane used in the ultraviolet curable resin. Examples of the polyether polyol component constituting the known polyether urethane acrylate include, for example, polyethylene glycol, polypropylene glycol, polybutylene glycol, polytetramethylene glycol, a copolymer of propylene oxide and ethylene oxide, a copolymer of tetrahydrofuran and propylene oxide. Examples thereof include a polymer, a copolymer of tetrahydrofuran and ethylene oxide, an ethylene oxide adduct of bisphenol A, and a propylene oxide adduct of bisphenol A.

Among these, the ultraviolet curable resin for coating the optical fiber is polypropylene glycol (PP).
G), a polyether urethane acrylate using polytetramethylene glycol (PTG) as a polyether polyol component is widely used.

[0006]

The properties required for an ultraviolet curable resin for optical fiber coating are (1) low viscosity, excellent workability at room temperature liquid, and (2) sufficient curing even at low UV irradiation dose. Excellent productivity, and (3) excellent long-term reliability such as heat resistance, jelly resistance, and hydrolysis resistance of the cured coating film.

When polypropylene glycol is used as the polyether polyol component of the polyether urethane acrylate, it has a low viscosity and excellent workability, but has the drawback of poor curability and heat resistance. On the other hand, when polytetramethylene glycol is used, it has excellent curability and heat resistance, but has the disadvantage of poor workability because it has high crystallinity and becomes a solid at room temperature. A copolymer of tetrahydrofuran and propylene oxide has been studied to improve this drawback, but the fact is that the curability and heat resistance are insufficient. Further, when polytetramethylene glycol is used, the Young's modulus of the cured coating film becomes high, so that the use thereof is limited when a low Young's modulus is required.

As described in Japanese Patent Application No. 2-184139, the present inventors have used polybutylene glycol as a polyether polyol component to improve curability, heat resistance and hydrolysis resistance. We have found an excellent UV curable resin for optical fiber coating. Furthermore, a coating film having a low Young's modulus can be obtained with this material. However, while this material has excellent hydrolysis resistance due to its strong hydrophobicity, when the cable is filled with petroleum jelly as a waterproof material, the problem of swelling due to jelly and low jelly resistance is apparent. Became.

The present invention has been made in view of such circumstances, and an object thereof is to obtain a coating film having excellent curability, heat resistance, hydrolysis resistance, and low Young's modulus. An optical fiber that exhibits the properties of polybutylene glycol, improves jelly resistance, has excellent long-term reliability such as curability, heat resistance, and jelly resistance, and has low viscosity and good workability, and has an excellent total balance. It is to provide an ultraviolet curable resin composition for coating.

[0010]

In order to solve the above problems, the present invention provides a ring-opening copolymer of (a) a mixture containing two or more alkylene oxide compounds containing 1,2-butylene oxide as an essential component. Polyether polyol obtained by polymerization, (b) polyisocyanate and (c)
Provided is a polymerizable unsaturated polyurethane (hereinafter, referred to as the polymerizable unsaturated polyurethane of the present invention) obtained by reacting a compound having an active hydrogen which reacts with an isocyanate group and a polymerizable unsaturated group, and further, of the present invention. Provided is an ultraviolet-curable resin composition containing a polymerizable unsaturated polyurethane, (2) a monomer having an ethylenically unsaturated bond, and (3) a photopolymerization initiator.

The polymerizable unsaturated polyurethane used in the present invention contains 1,2-butylene oxide as an essential component.
It can be obtained by reacting a polyether polyol obtained by ring-opening copolymerization of a mixture of one or more alkylene oxide compounds, a polyisocyanate and a hydroxy compound having an acryloyl group.

Examples of alkylene oxide compounds other than 1,2-butylene oxide used in the present invention include ethylene oxide, propylene oxide, isobutylene oxide, 2,3-butylene oxide, trimethylethylene oxide, tetramethylethylene oxide and butadiene. Monooxide, styrene oxide, α-methylstyrene oxide, 1,1-diphenylethylene oxide, epifluorohydrin, epichlorohydrin, epibromohydrin, glycidol,
Butyl glycidyl ether, hexyl glycidyl ether, allyl glycidyl ether, phenyl glycidyl ether, 2-chloroethyl glycidyl ether, cyclohexene oxide, dihydronaphthalene oxide,
Vinylcyclohexene monooxide, oxetane, tetrahydrofuran, tetrahydropyran and the like can be mentioned.

Of these, polyether polyols obtained by the combination of 1,2-butylene oxide and propylene oxide and the combination of 1,2-butylene oxide and tetrahydrofuran constitute a polymerizable unsaturated polyurethane for coating an optical fiber. It is particularly suitable as a material. Examples of commercially available polyether polyols composed of 1,2-butylene oxide and propylene oxide include "Z-3" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.
004 ”, a commercially available product of a polyether polyol composed of 1,2-butylene oxide and tetrahydrofuran is, for example,“ Unisafe DDC-30 ”manufactured by NOF Corporation.
00 "," THF / BO copolymer "manufactured by Hodogaya Chemical Co., Ltd., and the like.

1,2-butylene oxide and 1,2-butylene oxide
The weight ratio of the alkylene oxide compound other than butylene oxide used is preferably 20:80 to 90:10.

Examples of the polyisocyanate compound include tolylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, tetramethylxylylene diisocyanate, trimethylhexamethylene diisocyanate. , 1,5-naphthalene diisocyanate, tolidine diisocyanate, p-phenylene diisocyanate,
Examples include lysine diisocyanate.

Examples of the hydroxy compound having an acryloyl group include hydroxyethyl acrylate and 2
-Hydroxypropyl acrylate, 2-hydroxybutyl acrylate, phenoxyhydroxypropyl acrylate, butoxyhydroxypropyl acrylate,
Pentaerythritol triacrylate, dipentaerythritol monohydroxypentaacrylate, trimethylolpropane diacrylate, dipropylene glycol monoacrylate, 1,6-hexanediol monoacrylate, glycerin diacrylate, caprolactone modified 2-hydroxyethyl acrylate, stearic acid modified pentaerythritol Diacrylate etc. are mentioned.

As the monomer having an ethylenically unsaturated bond used in the present invention, an acrylate compound is mainly used. When the cured film is required to have softness, a monofunctional (meth) acrylic acid ester compound is used. When the cured film is required to have hardness, a bifunctional or higher polyfunctional acrylic acid ester compound is used. Is commonly used.

Specific examples of the monomer having an ethylenically unsaturated bond used in the present invention include aromatic vinyl monomers such as styrene, chlorostyrene and divinylbenzene; methyl, ethyl, propyl, butyl and amyl as substituents. , 2-ethylhexyl, octyl, nonyl,
Dodecyl, hexadecyl, octadecyl, cyclohexyl, benzyl, methoxyethyl, butoxyethyl, phenoxyethyl, nonylphenoxyethyl, tetrahydrofurfuryl, allyl, methallyl, glycidyl, 2-hydroxyethyl, 2-hydroxypropyl, 3-chloro-2-hydroxy. Acrylate, methacrylate or fumarate having groups such as propyl, dimethylaminoethyl, diethylaminoethyl, etc .; ethylene glycol, polyethylene glycol, propylene glycol,
Mono (meth) acrylates or poly (meth) acrylates such as polypropylene glycol, 1,3-butylene glycol, tetramethylene glycol, hexamethylene glycol, trimethylolpropane, glycerin and pentaerythritol; vinyl acetate, vinyl butyrate or vinyl benzoate, Acrylonitrile, cetyl vinyl ether, limonene, cyclohexene, diallyl phthalate,
2-, 3- or 4-vinyl pyridine, acrylic acid, methacrylic acid, acrylamide, methacrylamide, N-hydroxymethyl acrylamide or N-hydroxyethyl acrylamide and their alkyl ether compounds, and 2 mol or more per 1 mol of neopentyl glycol Di (meth) acrylate of diol obtained by adding ethylene oxide or propylene oxide, di- or tri (meth) acrylate of triol obtained by adding 3 mol or more of ethylene oxide or propylene oxide to 1 mol of trimethylolpropane, Di (meth) acrylate of diol obtained by adding 2 moles or more of ethylene oxide or propylene oxide to 1 mole of bisphenol A, 1 mole of 2-hydroxyethyl (meth) acrylate and phenol. Le isocyanate or n-
The reaction product with 1 mol of butyl isocyanate, poly (meth) acrylate of dipentaerythritol and the like can be mentioned.

Further, N-vinyl-2-pyrrolidone, N-
Acryloylmorpholine, N-vinylimidazole,
At least one monomer selected from the group consisting of N-vinylcaprolactam, vinyl-p-tert-butylbenzoate, cyclohexyl acrylate, isobornyl acrylate, dicyclopentanyl acrylate and dicyclopentenyl acrylate can also be used, and is bifunctional or more. When used in combination with the above (meth) acrylate, the curability is improved, the gel fraction becomes high after curing, and a highly reliable material can be provided.

The photopolymerization initiator used in the present invention includes:
What is necessary is that a radical is generated by light and the radical efficiently reacts with the polymerizable unsaturated compound. There are a type in which a molecule is cleaved to generate a radical and a type in which a compound is used such as a combination of an aromatic ketone and a hydrogen donor.

Examples of the former include, for example, benzoin ethyl ether, benzoin isobutyl ether,
Benzyl dimethyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1
-Phenyl-propan-1-one, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 1-
(4-Isopropylphenyl) -2-hydroxy-2-
Methylpropan-1-one and 2-methyl-1- [4-
(Methylthio) phenyl] -2-morpholinopropanone-1 and the like.

Examples of the aromatic ketone of the latter example include benzophenone, 4-phenylbenzophenone, isophthalophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, 2,4-diethylthioxanthone and 2-isopropyl. Examples thereof include thioxanthone and 2-chlorothioxanthone, and examples of the hydrogen donor to be combined therewith include mercapto compounds and amine compounds, but amine compounds are generally preferable.

Examples of amine compounds include triethylamine, methyldiethanolamine, triethanolamine, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, p-dimethylaminoacetophenone, p-dimethylaminobenzoate ethyl, p
-Isoamyl dimethylaminobenzoate, N, N-dimethylbenzylamine, 4,4'-bis (diethylamino) benzophenone and the like can be mentioned.

These photopolymerization initiators may be used alone or in combination of two or more kinds.

Further, as other components, a thermal polymerization inhibitor, an antioxidant, a plasticizer, a silane coupling agent, a surfactant, a polymerizable unsaturated polyurethane other than the present invention, etc. are added for the purpose of improving various characteristics. You can also do it.

The ultraviolet resin composition for coating an optical fiber of the present invention comprises (1) 10 to 80% by weight of a polymerizable unsaturated polyurethane, (2) 10 to 80% by weight of a monomer having an ethylenically unsaturated bond, and an optical resin. Polymerization initiator 0.1-10% by weight
It is preferable that it is blended from the range.

[0027]

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

First, a synthetic example of the polymerizable unsaturated polyurethane of the present invention will be shown.

Synthesis Example 1 Copolymer of 1,2-butylene oxide (hereinafter abbreviated as BO) and propylene oxide (hereinafter abbreviated as PO) (BO: PO =)
8: 2 (weight ratio), 2 mol of number average molecular weight of 5,000) and 3 mol of 2,4-tolylene diisocyanate were charged into a reaction vessel equipped with a nitrogen gas introducing pipe, a stirrer and a cooling pipe, and 7
The reaction was carried out at 0 ° C for 2 hours.

Next, 2 mol of 2-hydroxypropyl acrylate, a small amount of t-butylhydroquinone as a polymerization inhibitor and a small amount of dibutyltin dilaurate as a catalyst were gradually added, and the mixture was further reacted at 70 ° C. for 15 hours to form an acryloyl group. Having a polymerizable unsaturated polyurethane (A-
1) was obtained.

(Synthesis Example 2) 1 mol of a copolymer of 1,2-butylene oxide and tetrahydrofuran (hereinafter referred to as THF) (BO: THF = 3: 7 (weight ratio), number average molecular weight 3,000), 2 mol of 2,4-tolylene diisocyanate was charged into a reaction vessel equipped with a nitrogen gas introduction tube, a stirrer and a cooling tube, and reacted at 70 ° C for 2 hours.

Next, 2-mol of 2-hydroxypropyl acrylate, a small amount of t-butylhydroquinone as a polymerization inhibitor and a small amount of dibutyltin dilaurate as a catalyst were gradually added, and the mixture was further reacted at 70 ° C. for 15 hours to form an acryloyl group. Having a polymerizable unsaturated polyurethane (A-
2) was obtained.

Next, a synthetic example of a polymerizable unsaturated polyurethane as a comparative control will be shown.

(Synthesis Example 3) 2 mol of polybutylene glycol (number average molecular weight of 5,000) and 3 mol of 2,4-tolylene diisocyanate were charged into a reaction vessel equipped with a nitrogen gas introducing pipe, a stirrer and a cooling pipe. The reaction was carried out at 0 ° C for 2 hours.

Next, 2-mol of 2-hydroxypropyl acrylate, a small amount of t-butylhydroquinone as a polymerization inhibitor and a small amount of dibutyltin dilaurate as a catalyst were gradually added, and the mixture was further reacted at 70 ° C. for 15 hours to form an acryloyl group. Having a polymerizable unsaturated polyurethane (A-
3) was obtained.

(Synthesis Example 4) 1 mol of a copolymer of propylene oxide and tetrahydrofuran (PO: THF = 3: 7 (weight ratio), number average molecular weight of 3,000), and 2 mol of 2,4-tolylene diisocyanate were replaced with nitrogen. A reaction vessel equipped with a gas introduction tube, a stirrer and a cooling tube was charged and reacted at 70 ° C. for 2 hours.

Next, 2 mol of 2-hydroxypropyl acrylate, a small amount of t-butylhydroquinone as a polymerization inhibitor and a small amount of dibutyltin dilaurate as a catalyst were gradually added, and the mixture was further reacted at 70 ° C. for 15 hours to form an acryloyl group. Having a polymerizable unsaturated polyurethane (A-
4) was obtained.

(Synthesis Example 5) 1 mol of polypropylene glycol (number average molecular weight 3,000) and 2 mol of 2,4-tolylene diisocyanate were charged into a reaction vessel equipped with a nitrogen gas introducing pipe, a stirrer and a cooling pipe, and 70 The reaction was carried out at 0 ° C for 2 hours.

Next, 2-mol of 2-hydroxypropyl acrylate, a small amount of t-butylhydroquinone as a polymerization inhibitor and a small amount of dibutyltin dilaurate as a catalyst were gradually added, and the mixture was further reacted at 70 ° C. for 15 hours to form an acryloyl group. Having a polymerizable unsaturated polyurethane (A-
5) was obtained.

(Synthesis Example 6) 1 mol of polytetramethylene glycol (number average molecular weight of 3,000) and 2 mol of 2,4-tolylene diisocyanate were charged into a reaction vessel equipped with a nitrogen gas introducing tube, a stirrer and a cooling tube. The mixture was reacted at 70 ° C for 2 hours.

Next, 2 mol of 2-hydroxypropyl acrylate, a small amount of t-butylhydroquinone as a polymerization inhibitor and a small amount of dibutyltin dilaurate as a catalyst were gradually added, and the mixture was further reacted at 70 ° C. for 15 hours to form an acryloyl group. Having a polymerizable unsaturated polyurethane (A-
6) was obtained.

(Synthesis Example 7) 1 mol of polybutylene glycol (number average molecular weight of 3,000) and 2 mol of 2,4-tolylene diisocyanate were charged into a reaction vessel equipped with a nitrogen gas introducing tube, a stirrer and a cooling tube. The reaction was carried out at 70 ° C for 2 hours.

Next, 2-mol of 2-hydroxypropyl acrylate, a small amount of t-butylhydroquinone as a polymerization inhibitor and a small amount of dibutyltin dilaurate as a catalyst were gradually added, and the mixture was further reacted at 70 ° C. for 15 hours to form an acryloyl group. Having a polymerizable unsaturated polyurethane (A-
7) was obtained.

Examples and comparative examples of the ultraviolet-curable resin composition for coating an optical fiber of the present invention are shown below.

Example 1 50 parts by weight of the polymerizable unsaturated polyurethane (A-1) obtained in Synthesis Example 1, 50 parts by weight of nonylphenoxy polyethylene glycol monoacrylate and 2,4,6-trimethylbenzoyldiphenylphosphine oxide. Two parts by weight were mixed and dissolved at 60 ° C. for 1 hour to obtain a liquid ultraviolet curable resin composition having a viscosity of 55.5 poise (25 ° C.).

(Comparative Example 1) The procedure of Example 2 was repeated, except that the polymerizable unsaturated polyurethane (A-1) was replaced by the polymerizable unsaturated polyurethane (A-3). A liquid ultraviolet curable resin composition having a viscosity of 118.6 poise (25 ° C.) was obtained.

(Example 2) 50 parts by weight of the polymerizable unsaturated polyurethane (A-2) obtained in Synthesis Example 2, 50 parts by weight of nonylphenoxy polypropylene glycol monoacrylate and 2,4,6-trimethylbenzoyldiphenylphosphine oxide 2 By mixing and dissolving 1 part by weight at 60 ° C. for 1 hour, a liquid ultraviolet curable resin composition having a viscosity of 57.3 poise (25 ° C.) was obtained.

(Comparative Example 2) In the same manner as in Example 1 except that the polymerizable unsaturated polyurethane (A-4) was used in place of the polymerizable unsaturated polyurethane (A-2) in Example 2. A liquid ultraviolet curable resin composition having a viscosity of 57.6 poise (25 ° C.) was obtained.

(Comparative Example 3) In the same manner as in Example 1 except that the polymerizable unsaturated polyurethane (A-5) was used in place of the polymerizable unsaturated polyurethane (A-2) in Example 2. A liquid ultraviolet curable resin composition having a viscosity of 26.0 poise (25 ° C.) was obtained.

(Comparative Example 4) The procedure of Example 1 was repeated, except that the polymerizable unsaturated polyurethane (A-6) was replaced by the polymerizable unsaturated polyurethane (A-6). A liquid ultraviolet curable resin composition having a viscosity of 154.4 poise (25 ° C.) was obtained.

(Comparative Example 5) In the same manner as in Example 2 except that the polymerizable unsaturated polyurethane (A-7) was used in place of the polymerizable unsaturated polyurethane (A-2) in Example 2. A liquid UV curable resin composition having a viscosity of 29.0 poise (25 ° C.) was obtained.

The following evaluations were performed using each of the ultraviolet curable resin compositions obtained in Examples 1 and 2 and Comparative Examples 1 to 5, and the results are shown in Table 1. Based on this data, Table 2 shows a relative comparison of properties depending on the type of polyether.

(Evaluation of Curing Property) An ultraviolet curable resin composition was applied on a glass plate so that the dry coating film thickness was 200 ± 20 μm, and then a nitrogen atmosphere was applied using a 80 W / cm metal halide lamp. The amount of irradiation light was changed below to cure. The tensile modulus of elasticity (Young's modulus) of the cured film was measured to evaluate the curability.

The tensile modulus of elasticity is measured according to JIS K7.
It carried out according to 113. Further, as an index of curability, the ratio of tensile elastic moduli upon irradiation with 20 mJ / cm ² and 1000 mJ / cm ² was taken. The larger the value, the better the curability.

(Evaluation of heat resistance) An ultraviolet-curable resin composition was applied onto a glass plate so that the dry coating film thickness was 200 ± 20 μm, and then in a nitrogen atmosphere using a 80 W / cm metal halide lamp. It was cured with an irradiation light amount of 200 mJ / cm ² . This cured film was stored in air at 120 ° C. for 1 week, and then the tensile modulus was measured in the same manner as in the above method. The ratio of this measured value to the initial value was used as an index of heat resistance.
The closer the value is to 1, the better the heat resistance.

(Evaluation of Jelly Resistance) The ultraviolet curable resin composition was applied onto a glass plate to give a dry coating film thickness of 200 ± 20 μm.
After coating, the amount of irradiation light is 200 mJ / in a nitrogen atmosphere using an 80 W / cm metal halide lamp.
It was cured at cm ² . The cured film is conditioned at 23 ° C. and 50% RH, and the weight M1 is measured. Then Jerry SY
After immersing in NCOLT (SYNCO Chemical Co.) for 7 days at 85 ° C., it is taken out, the jelly on the surface is wiped off, and the weight M2 is measured. Weight change = M2 / M1 × 100
(%) Was used as an index of jelly resistance. The closer the value is to 100, the better the jelly resistance.

[0057]

[Table 1]

(In Table 1, the irradiation light amount is mJ / cm ² unit,
The value of Young's modulus is expressed in units of Kg / mm ² , and the curing rate is expressed by the ratio of Young's modulus at the time of irradiation of 20 mJ / cm ² and 1000 mJ / cm ² . )

[0059]

[Table 2]

Evaluation method: Relative comparison based on the data in Table 1 ◎: Excellent (meaning that there is no crystallinity item) ○: Normal Δ: Inferior (however, there is a crystallinity item) ) PPG: Polypropylene glycol PTG: Polytetramethylene glycol PPT: Copolymer of propylene oxide and THF PBG: Polybutylene glycol

[0061]

The jelly resistance is improved by the copolymer of butylene oxide and propylene oxide from Example 1 and Comparative Example 1 in Table 1, and from Example 2, Comparative Examples 2 to 5 and Table 2, butylene oxide. With the copolymer of tetrahydrofuran and tetrahydrofuran, it is possible to obtain an excellent total balance that cannot be obtained with existing products. Therefore, the ultraviolet curable resin composition for optical fiber coating using the polymerizable unsaturated polyurethane of the present invention is excellent in workability and productivity, and further using the ultraviolet curable resin composition for optical fiber coating of the present invention The coated optical fiber can obtain high reliability even in long-term use.

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Claims (4)

[Claims] 1. A polyether polyol obtained by (a) ring-opening copolymerization of a mixture of two or more alkylene oxide compounds containing 1,2-butylene oxide as an essential component, (b) polyisocyanate and (c) isocyanate. A polymerizable unsaturated polyurethane obtained by reacting active hydrogen that reacts with a group and a compound having a polymerizable unsaturated group. 2. The polymerizable unsaturated polyurethane according to claim 1, wherein the alkylene oxide other than 1,2-butylene oxide is propylene oxide or tetrahydrofuran. 3. A polymerizable unsaturated polyurethane according to claim 1 or 2, containing (2) a monomer having an ethylenically unsaturated bond and (3) a photopolymerization initiator. UV curable resin composition. 4. The ultraviolet curable resin composition according to claim 3, which is used for coating an optical fiber.