JP7619967B2 - Radiation-curable resin composition, cured product thereof, and optical fiber - Google Patents

Description

The present invention relates to a radiation-curable resin composition and a cured product thereof, as well as an optical fiber.

Optical fiber is composed of glass fiber obtained by hot melt spinning of glass, and a coating layer provided on the glass fiber for the purpose of protection and reinforcement. For example, optical fiber is manufactured by first providing a flexible primary coating layer (hereinafter also referred to as the "primary coating layer") on the surface of the glass fiber, and then providing a rigid secondary coating layer (hereinafter also referred to as the "secondary coating layer") on the primary coating layer. Tape-shaped optical fiber and optical fiber cables, in which multiple optical fibers with coating layers are bound together with a bundling material, are also well known.

A widely used method for forming a coating layer on a glass fiber is, for example, to apply a liquid curable resin composition to the glass fiber and cure it with heat or light, especially ultraviolet light. For example, Patent Document 1 discloses a radiation-curable composition that combines a urethane oligomer produced by a specific production method and a compound having one ethylenically unsaturated group as a resin composition for forming a primary coating layer.

JP 2012-111674 A

When pressure is applied locally to the side of an optical fiber, the core of the glass fiber in the area where pressure is applied can bend with a small curvature, resulting in optical loss. From the perspective of suppressing such optical loss (also known as microbending loss), it is desirable for the primary coating layer to be sufficiently flexible. Furthermore, in recent years, from the perspective of increasing the density, reducing weight, and improving the handleability of optical fiber cables, there has been a demand for the primary coating layer to have high mechanical strength (breaking strength and breaking elongation).

However, when the primary coating layer is made flexible, sufficient mechanical strength (breaking strength and breaking elongation) may not be obtained. In particular, it is difficult to achieve both excellent mechanical strength and excellent flexibility at low temperatures (e.g., -40°C).

The present invention aims to provide a radiation-curable resin composition for forming a primary coating layer that is capable of forming a cured product having excellent flexibility and mechanical strength, a cured product thereof, and an optical fiber.

As a result of various investigations conducted to achieve the above object, the inventors discovered that by using a urethane oligomer with a specific structure, it is possible to obtain a radiation-curable resin composition capable of forming a cured product having excellent flexibility and mechanical strength, and thus completed the present invention.

That is, one aspect of the present invention relates to a radiation-curable resin composition for forming a primary coating layer of an optical fiber, which contains a urethane oligomer having an ethylenically unsaturated group, a free-radically polymerizable non-urethane monomer, and a polymerization initiator, and the urethane oligomer contains 30% by mass or more of a reaction product of a polyether polyol having a weight average molecular weight of 9,000 or more, a polyisocyanate, and an isocyanate-reactive compound containing one active hydrogen group (excluding polyether polyol) relative to the total amount of the radiation-curable resin composition (100% by mass), and the isocyanate-reactive compound contains an isocyanate-reactive compound containing an ethylenically unsaturated group.

The radiation-curable resin composition of the above aspect can form a cured product that is excellent in flexibility and mechanical strength, and can provide an optical fiber having a primary coating layer made of the cured product.

The polyether polyol may be a polyether diol or a polyether triol.

The polyether polyol is preferably an aliphatic polyether polyol.

The above reactant contained in the urethane oligomer may be a reactant of a polyether polyol and a polyisocyanate with an isocyanate-reactive compound, or a reactant of a polyisocyanate and an isocyanate-reactive compound with a polyether polyol.

The isocyanate-reactive compound preferably further comprises an aliphatic alcohol.

Another aspect of the present invention relates to a cured product of the above-mentioned radiation-curable resin composition.

Another aspect of the present invention relates to an optical fiber having a primary coating layer made of the above-mentioned cured product.

The present invention provides a radiation-curable resin composition for forming a primary coating layer, which is capable of forming a cured product having excellent flexibility and mechanical strength, a cured product thereof, and an optical fiber.

Preferred embodiments of the present invention are described in detail below. However, the present invention is not limited to the following embodiments. In this specification, a numerical range indicated using "~" indicates a range that includes the numerical values before and after "~" as the minimum and maximum values, respectively. The upper and lower limit values described in stages in this specification may be combined in any combination.

The radiation-curable resin composition of the embodiment is a radiation-curable resin composition for forming a primary coating layer of an optical fiber, which contains a urethane oligomer having an ethylenically unsaturated group (hereinafter, also simply referred to as "urethane oligomer"), a radically polymerizable non-urethane monomer, and a polymerization initiator. The composition for forming a primary coating layer of an optical fiber can also be called a primary material.

Here, radiation refers to infrared rays, visible light, ultraviolet rays, X-rays, electron beams, alpha rays, beta rays, gamma rays, etc., with ultraviolet rays being particularly preferred.

The urethane oligomer contains a reaction product (hereinafter also referred to as "urethane oligomer A") between a polyether polyol having a weight average molecular weight of 9000 or more (hereinafter also referred to simply as "polyether polyol"), a polyisocyanate, and an isocyanate-reactive compound containing one active hydrogen group (hereinafter also referred to simply as "isocyanate-reactive compound"), in which the isocyanate-reactive compound contains an ethylenically unsaturated group-containing isocyanate-reactive compound. That is, the urethane oligomer contains components derived from polyether polyol, polyisocyanate, and isocyanate-reactive compound. Urethane oligomer A contains structural units derived from polyether polyol, structural units derived from polyisocyanate, and structural units derived from isocyanate-reactive compound, and contains urethane bonds derived from the reaction between polyether polyol and polyisocyanate, and bonds (e.g., urethane bonds) derived from the reaction between polyisocyanate and isocyanate-reactive compound.

Urethane oligomer A is, for example, a reaction product between a polyether-based urethane prepolymer and an isocyanate-reactive compound. The polyether-based urethane prepolymer is a reaction product between a polyether polyol and a polyisocyanate, and has an isocyanate group.

Urethane oligomer A is, for example, a reaction product of polyether polyol and an isocyanate group-containing end-capping compound. The isocyanate group-containing end-capping compound is a reaction product of polyisocyanate and an isocyanate-reactive compound, and has an isocyanate group.

The weight average molecular weight (Mw) of the polyether polyol is 9,000 or more, preferably 9,500 or more, more preferably 9,800 or more, and even more preferably 10,000 or more. The weight average molecular weight (Mw) of the polyether polyol may be 20,000 or less, 15,000 or less, or 12,000 or less. When the weight average molecular weight (Mw) of the polyether polyol is 20,000 or less, excellent compatibility with radically polymerizable non-urethane monomers tends to be obtained. The weight average molecular weight is a value measured by gel permeation chromatography and converted based on a standard polystyrene calibration curve.

The polyether polyol is preferably a polyether diol or a polyether triol. That is, the number of hydroxyl groups (-OH) in the polyether polyol is preferably 2 or 3.

The polyether polyol is preferably an aliphatic polyether polyol, more preferably an aliphatic polyether diol or an aliphatic polyether triol.

Preferred examples of the aliphatic polyether diol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, polyheptamethylene glycol, polydecamethylene glycol, and aliphatic polyether diols obtained by ring-opening copolymerization of two or more ionically polymerizable cyclic compounds.

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 methacrylate, allyl glycidyl ether, allyl glycidyl carbonate, butadiene monoxide, isoprene monoxide, vinyl oxetane, vinyltetrahydrofuran, vinylcyclohexene oxide, phenyl glycidyl ether, butyl glycidyl ether, and benzoic acid glycidyl ester.

Specific examples of polyether diols obtained by ring-opening copolymerization of two or more of the above ionically polymerizable cyclic compounds include binary copolymers obtained by combinations of tetrahydrofuran and propylene oxide, tetrahydrofuran and 2-methyltetrahydrofuran, tetrahydrofuran and 3-methyltetrahydrofuran, tetrahydrofuran and ethylene oxide, propylene oxide and ethylene oxide, butene-1-oxide and ethylene oxide, etc.; and terpolymers obtained by combinations of tetrahydrofuran, butene-1-oxide, and ethylene oxide.

It is also possible to use polyether diols obtained by ring-opening copolymerization of the above ionically polymerizable cyclic compounds with cyclic imines such as ethyleneimine; cyclic lactone acids such as β-propiolactone and glycolic acid lactide; or dimethylcyclopolysiloxanes.

Among these aliphatic polyether diols, it is preferable to use one or more ring-opening polymers of ionically polymerizable cyclic compounds having 2 to 4 carbon atoms, from the viewpoint of achieving both high-speed application of the resin liquid and flexibility of the coating material. Such preferred aliphatic polyether diols include ring-opening polymers of one or more oxides selected from ethylene oxide, propylene oxide, butene-1-oxide, and isobutene oxide. As the aliphatic polyether diol, polypropylene glycol diol (ring-opening polymer of propylene oxide) is particularly preferable.

As the aliphatic polyether triol, aliphatic polyether triols obtained by addition polymerization of an ionically polymerizable cyclic compound to a triol such as glycerin or trimethylolpropane are preferred. The ionically polymerizable cyclic compound may be the ionically polymerizable cyclic compound described above. Among the aliphatic polyether triols, it is preferred to use an addition polymer of a triol and one or more ionically polymerizable cyclic compounds having 2 to 4 carbon atoms in terms of both high-speed application of the resin liquid and flexibility of the coating material. Such a preferred aliphatic polyether triol includes an addition polymer of a triol and one or more oxides selected from ethylene oxide, propylene oxide, butene-1-oxide, and isobutene oxide. As the aliphatic polyether triol, polypropylene glycol triol (addition polymer of glycerin and propylene oxide) is particularly preferred.

The above aliphatic polyether diols and aliphatic polyether triols are also available as commercially available products such as PREMINOL S 3011, PREMINOL S 4011, PREMINOL S-X3015, PREMINOL 4016, and PREMINOL 7012 manufactured by AGC Inc., and Acclaim Polyol 12200 N and Acclaim Polyol 18200 N manufactured by Sumika Covestro Urethane Co., Ltd.

Polyisocyanates are compounds that have two or more isocyanate groups. Examples of polyisocyanates include aromatic polyisocyanates, alicyclic polyisocyanates, and aliphatic polyisocyanates.

The polyisocyanate is preferably a diisocyanate. Examples of diisocyanates include aromatic diisocyanates, alicyclic diisocyanates, and aliphatic diisocyanates. Examples of aromatic diisocyanates 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-isocyanateethyl)fumarate, 6-isopropyl-1,3-phenyl diisocyanate, 4-diphenylpropane diisocyanate, and tetramethylxylylene diisocyanate. Examples of alicyclic diisocyanates include isophorone diisocyanate, methylene bis(4-cyclohexyl isocyanate), hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, 2,5-bis(isocyanatemethyl)-bicyclo[2.2.1]heptane, 2,6-bis(isocyanatemethyl)-bicyclo[2.2.1]heptane, etc. Examples of aliphatic diisocyanates include 1,6-hexane diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, etc.

In terms of economy and the ability to obtain a composition of stable quality, the diisocyanate is preferably an aromatic diisocyanate, more preferably 2,4-tolylene diisocyanate or 2,6-tolylene diisocyanate. The diisocyanates may be used alone or in combination of two or more kinds.

An isocyanate-reactive compound is a compound containing one active hydrogen group. However, the above-mentioned polyether polyol is not included in the isocyanate-reactive compound. Examples of the active hydrogen group include a mercapto group (-SH), a hydroxyl group (-OH), and an amino group (-NH ₂ ).

The ethylenically unsaturated group-containing isocyanate-reactive compound is a compound having one active hydrogen group. Examples of the ethylenically unsaturated group include a (meth)acryloyl group, a vinyl group, a vinylene group, and a vinylidene group. In this specification, the term "(meth)acryloyl group" means an "acryloyl group" or the corresponding "methacryloyl group". The same applies to similar expressions such as "(meth)acrylate".

The ethylenically unsaturated group in the ethylenically unsaturated group-containing isocyanate-reactive compound is preferably a (meth)acryloyl group. The active hydrogen group in the ethylenically unsaturated group-containing isocyanate-reactive compound is preferably a hydroxy group. That is, the ethylenically unsaturated group-containing isocyanate-reactive compound may be a compound having a (meth)acryloyl group and an active hydrogen group (active hydrogen group-containing (meth)acrylate), or may be a compound having a (meth)acryloyl group and a hydroxy group (hydroxy group-containing (meth)acrylate).

Examples of hydroxyl group-containing (meth)acrylates include hydroxyl group-containing (meth)acrylates in which the hydroxyl group is bonded to a primary carbon atom (also referred to as first hydroxyl group-containing (meth)acrylates), hydroxyl group-containing (meth)acrylates in which the hydroxyl group is bonded to a secondary carbon atom (also referred to as second hydroxyl group-containing (meth)acrylates), and hydroxyl group-containing (meth)acrylates in which the hydroxyl group is bonded to a tertiary carbon atom (also referred to as tertiary hydroxyl group-containing (meth)acrylates). From the viewpoint of reactivity with isocyanate groups, the hydroxyl group-containing (meth)acrylates may be first hydroxyl group-containing (meth)acrylates or second hydroxyl group-containing (meth)acrylates.

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

Examples of secondary hydroxyl group-containing (meth)acrylates include 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenyloxypropyl (meth)acrylate, 4-hydroxycyclohexyl (meth)acrylate, and the like. Also included are compounds obtained by addition reaction of glycidyl group-containing compounds, such as alkyl glycidyl ether, allyl glycidyl ether, and glycidyl (meth)acrylate, with (meth)acrylic acid.

From the viewpoint of more significantly achieving the effects of the present invention, the content of the ethylenically unsaturated group-containing isocyanate-reactive compound in the isocyanate-reactive compound may be 40 mol% or more, 45 mol% or more, or 50 mol% or more, and may be 60 mol% or less, or 55 mol% or less.

The isocyanate-reactive compound preferably further contains an aliphatic alcohol. When the isocyanate-reactive compound further contains an aliphatic alcohol, the flexibility of the cured product can be further improved. The aliphatic alcohol has a hydroxyl group as an active hydrogen group. The number of carbon atoms in the aliphatic alcohol may be 1 to 15, 5 to 12, or 6 to 10. The carbon chain in the aliphatic alcohol may be linear or branched. Examples of the aliphatic alcohol include methanol, ethanol, propanol, butanol, and 2-ethyl-1-hexanol. From the viewpoint of more prominently exhibiting the effects of the present invention, the aliphatic alcohol may be methanol or 2-ethyl-1-hexanol.

From the viewpoint of more significantly achieving the effects of the present invention, the content of the aliphatic alcohol in the isocyanate-reactive compound may be 24 mol% or more, 30 mol% or more, 35 mol% or more, or 40 mol% or more, and may be 60 mol% or less, 55 mol% or less, 50 mol% or less, or 45 mol% or less.

The urethane oligomer A may contain, for example, an oligomer (oligomers a1 to a5) having a structure represented by the following formula (a1), (a2), (a3), (a4) or (a5).
A-(ICN-POD)n-ICN-A (a1)
A-(ICN-POD)n-ICN-R ¹ (a2)
A-(ICN-POT)n-(ICN-A)(ICN-R ¹ ) (a3)
A-(ICN-POT)n-(ICN-R ¹ ) ₂ (a4)
A-(ICN-POT)n-(ICN-A) ₂ (a5)
In these formulas, n each independently represents a number of 1.0 or more, ICN each independently represents a structure derived from a diisocyanate, POD each independently represents a structure derived from an aliphatic polyether diol having a weight average molecular weight of 9000 or more, POT each independently represents a structure derived from an aliphatic polyether triol having a weight average molecular weight of 9000 or more, A each independently represents a structure derived from an ethylenically unsaturated group-containing isocyanate-reactive compound, and ^R1 each independently represents a structure derived from an aliphatic alcohol.

n is 1.0 or more, and may be greater 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. n may be, for example, 1.1 to 3.0, 1.3 to 2.5, or 1.5 to 2.0.

The urethane oligomer A may contain a urethane (meth)acrylate oligomer having a (meth)acryloyl group as an ethylenically unsaturated group. The urethane oligomer A may contain at least two or more selected from the group consisting of a monofunctional urethane (meth)acrylate oligomer having one (meth)acryloyl group as an ethylenically unsaturated group (corresponding to oligomers a2 and a4), a bifunctional urethane (meth)acrylate oligomer having two (meth)acryloyl groups as an ethylenically unsaturated group (corresponding to oligomers a1 and a3), and a trifunctional urethane (meth)acrylate oligomer having three (meth)acryloyl groups as an ethylenically unsaturated group (corresponding to oligomer a5). The urethane oligomer A preferably contains a monofunctional urethane (meth)acrylate oligomer and a bifunctional urethane (meth)acrylate oligomer.

The ratio of the number of moles of monofunctional urethane (meth)acrylate oligomer to the number of moles of difunctional urethane (meth)acrylate oligomer may be 3/1 or more and 100/1 or less, 5/1 or more and 75/1 or less, 7/1 or more and 50/1 or less, or 10/1 or more and 35/1 or less.

The weight average molecular weight (Mw) of the urethane oligomer A may be 9,000 or more, 16,000 or more, 19,500 or more, or 23,000 or more, and may be 40,000 or less, 37,000 or less, or 33,000 or less. The weight average molecular weight is a value measured by gel permeation chromatography and converted based on a standard polystyrene calibration curve.

The content of urethane oligomer A may be 30% by mass or more, 35% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, based on 100% by mass of the total amount of the radiation-curable resin composition, from the viewpoint of being able to further improve the flexibility and mechanical strength of the cured product, and may be 90% by mass or less, 85% by mass or less, or 83% by mass or less, based on the viewpoint of being able to easily obtain a radiation-curable resin composition having an appropriate viscosity.

The urethane oligomer having an ethylenically unsaturated group may further contain a urethane oligomer other than urethane oligomer A, or may consist only of urethane oligomer A. For example, the urethane oligomer having an ethylenically unsaturated group may contain a reaction product of a polyether polyol having a weight average molecular weight of less than 9000, a polyisocyanate, and an isocyanate-reactive compound. The proportion of urethane oligomer A in the total mass of the urethane oligomer having an ethylenically unsaturated group may be, for example, 90% by mass or more, 95% by mass or more, or 100% by mass.

The urethane oligomer A may be produced by reacting a polyether-based urethane prepolymer with an isocyanate-reactive compound. For example, the urethane oligomer can be produced by reacting a polyether-based urethane prepolymer with an ethylenically unsaturated group-containing isocyanate-reactive compound, and then adding and reacting an aliphatic alcohol.

In the production of urethane oligomer A, a urethane catalyst may be used as necessary. Examples of urethane catalysts include copper naphthenate, cobalt naphthenate, zinc naphthenate, dibutyltin dilaurate, dioctyltin dilaurate, triethylamine, 1,4-diazabicyclo[2.2.2]octane, and 2,6,7-trimethyl-1,4-diazabicyclo[2.2.2]octane. The amount of the urethane catalyst used may be 0.01 to 1 mass% based on the total amount of reactants. In the production of urethane oligomer A, a radical polymerization inhibitor such as 2,6-di-t-butyl-p-cresol may be used as necessary. The reaction temperature is usually 5 to 90°C, and preferably 10 to 80°C.

The radiation-curable resin composition may further contain a urethane oligomer other than the urethane oligomer having an ethylenically unsaturated group, i.e., a urethane oligomer not having an ethylenically unsaturated group. For example, the urethane oligomer may further contain an oligomer having a structure represented by the following formula (a6) or (a7) (oligomers a6 to a7).
R ¹ -(ICN-POD)n-ICN-R ¹ (a6)
R ¹ -(ICN-POT)n-(ICN-R ¹ ) ₂ (a7)
In the formula, ICN, POD, POT, n and ^R1 are defined as above.

The proportion of the urethane oligomer not having an ethylenically unsaturated group in the total mass of the radiation-curable resin composition may be, for example, 10% by mass or less, 5% by mass or less, or 1% by mass or less.

The radiation curable resin composition further contains a radically polymerizable non-urethane monomer. As the radically polymerizable non-urethane monomer, a monomer containing an ethylenically unsaturated group can be used. The ethylenically unsaturated group may be any of the groups exemplified above. The radically polymerizable non-urethane monomer may be used alone or in combination of two or more kinds.

The radically polymerizable non-urethane monomer may contain a vinyl group-containing compound (which may also be called a vinyl monomer, except for monomers that fall under the category of (meth)acrylate monomers described below), and may contain a (meth)acrylate monomer having a (meth)acryloyl group. The radically polymerizable non-urethane monomer may contain a vinyl group-containing compound and a (meth)acrylate monomer.

The vinyl group-containing compound may be at least one selected from the group consisting of vinyl ester compounds and vinyl amide compounds. In other words, the radically polymerizable non-urethane monomer may contain at least one vinyl group-containing compound selected from the group consisting of vinyl ester compounds and vinyl amide compounds. The number of vinyl groups in the vinyl group-containing compound may be one or two or more.

Examples of vinyl group-containing compounds include vinyl amide compounds (vinyl group-containing lactams) such as N-vinylpyrrolidone and N-vinylcaprolactam, vinyl imidazole, and vinyl pyridine. From the viewpoint of further improving the curing speed, the vinyl group-containing compound may be a vinyl amide compound. From the same viewpoint, the vinyl amide compound may be N-vinylcaprolactam.

The content of the vinyl group-containing compound in the radiation-curable resin composition may be 3 to 20% by mass, or 5 to 12% by mass, based on 100% by mass of the total amount of the radiation-curable resin composition.

The radically polymerizable non-urethane monomer may contain, as the (meth)acrylate monomer, a monofunctional (meth)acrylate monomer having one (meth)acryloyl group and a polyfunctional (meth)acrylate monomer having two or more (meth)acryloyl groups.

Examples of monofunctional (meth)acrylate monomers include alicyclic structure-containing (meth)acrylates such as 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, bornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, 4-butylcyclohexyl (meth)acrylate, and acryloylmorpholine. Further examples include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, methoxyethylene glycol (meth)acrylate, ethoxyethyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, etc. Also, the above-mentioned hydroxyl group-containing (meth)acrylate may be used as the monofunctional (meth)acrylate monomer.

The content of the monofunctional (meth)acrylate monomer in the radiation curable resin composition may be 3 to 30% by mass, or 8 to 15% by mass, relative to 100% by mass of the total amount of the radiation curable resin composition.

The radically polymerizable non-urethane monomer may contain a polyfunctional (meth)acrylate monomer. In this case, the crosslink density in the cured product is increased, and the mechanical strength of the cured product can be further improved.

Examples of polyfunctional (meth)acrylate monomers include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, ethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane trioxyethyl (meth)acrylate, and tris(2-hydroxyethyl)isocyanate. di(meth)acrylate of a diol of an adduct of bisphenol A with ethylene oxide or propylene oxide, di(meth)acrylate of a diol of an adduct of hydrogenated bisphenol A with ethylene oxide or propylene oxide, epoxy (meth)acrylate in which a (meth)acrylate is added to a diglycidyl ether of bisphenol A, and triethylene glycol divinyl ether are examples thereof. Commercially available products include, for example, Iupimer UV SA1002, SA2007 (manufactured by Mitsubishi Chemical Corporation); Viscoat 700 (manufactured by Osaka Organic Chemical Industry Co., Ltd.); KAYARAD R-604, DPCA-20, -30, -60, -120, HX-620, D-310, D-330 (manufactured by Nippon Kayaku Co., Ltd.); Aronix M-210, M-215, M-315, M-325 (manufactured by Toagosei Co., Ltd.), etc.

The content of the polyfunctional (meth)acrylate monomer in the radiation curable resin composition may be 2% by mass or less, 1.5% by mass or less, or 1.0% by mass or less, relative to 100% by mass of the total amount of the radiation curable resin composition, or may be more than 0% by mass.

The radiation curable resin composition contains a polymerization initiator. As the polymerization initiator, a typical polymerization initiator used as a photopolymerization initiator can be used. Examples of the polymerization initiator include 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole, 3-methylacetophenone, 4-chlorobenzophenone, 4,4'-dimethoxybenzophenone, 4,4'-diaminobenzophenone, Michler's ketone, benzoin propyl ether, benzoin ethyl ether, benzyl dimethyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropanone, and the like. thioxanthone, diethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide; IRGACURE 184, 369, 651, 500, 907, CGI 1700, CGI 1750, CGI 1850, CG24-61, DAROCUR 1116, 1173 (all manufactured by Ciba Specialty Chemicals); LUCIRIN TPO (manufactured by BASF); and Ubecryl P36 (manufactured by UCB). Examples of photosensitizers include triethylamine, diethylamine, N-methyldiethanolamine, ethanolamine, 4-dimethylaminobenzoic acid, methyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate; Ubecryl P102, 103, 104, and 105 (all manufactured by UCB).

The content of the polymerization initiator in the radiation curable resin composition may be 0.1 to 10% by mass, or 0.3 to 7% by mass, relative to 100% by mass of the total amount of the radiation curable resin composition.

The radiation curable resin composition may further contain additives other than the above-mentioned components. Examples of additives include Irganox 245.

In a radiation-curable resin composition in which the urethane oligomer and/or the radically polymerizable non-urethane monomer contains a (meth)acryloyl group-containing compound (e.g., the above-mentioned urethane (meth)acrylate oligomer, (meth)acrylate monomer) and the radically polymerizable non-urethane monomer contains a vinyl group-containing compound (vinyl monomer), the ratio of the number of moles of the (meth)acryloyl group-containing compound to the number of moles of the vinyl group-containing compound may be 1/1 or more and 10/1 or less, 1/1 or more and 5/1 or less, 1/1 or more and 3/1 or less, 1/1 or more and 2/1 or less, or 1/1 or more and 1.5/1 or less.

In a radiation-curable resin composition in which the urethane oligomer and the radically polymerizable non-urethane monomer have an ethylenically unsaturated group, the ratio of the number of moles of the monofunctional compound having one ethylenically unsaturated group to the number of moles of the polyfunctional compound having two or more ethylenically unsaturated groups may be 2/1 or more and 100/1 or less, 5/1 or more and 75/1 or less, 10/1 or more and 50/1 or less, or 15/1 or more and 30/1 or less.

In a radiation-curable resin composition in which the urethane oligomer or the radically polymerizable non-urethane monomer contains a monofunctional (meth)acrylate (a (meth)acryloyl group-containing compound having one (meth)acryloyl group) and a polyfunctional (meth)acrylate (a (meth)acryloyl group-containing compound having two or more (meth)acryloyl groups), the ratio of the number of moles of the monofunctional (meth)acrylate in the radiation-curable resin composition to the number of moles of the polyfunctional (meth)acrylate in the radiation-curable resin composition may be 1/1 or more and 75/1 or less, 2/1 or more and 50/1 or less, or 5/1 or more and 25/1 or less.

The radiation curable resin composition may be in a liquid state. That is, the radiation curable resin composition granules may be a liquid radiation curable resin composition.

The radiation-curable resin composition may contain other oligomers, polymers, and other additives, if necessary.

The viscosity of the radiation curable resin composition may be 0.1 to 10 Pa·s or 1 to 8 Pa·s at 25°C from the viewpoints of handleability and coatability. The viscosity of the radiation curable resin composition is measured by the method described in the examples below.

The radiation-curable resin composition of the embodiment described above can form a cured product (e.g., a cured layer) that has excellent flexibility and mechanical strength. Specifically, the radiation-curable resin composition of the embodiment described above can form a cured product that has a sufficiently low Young's modulus at 23°C and at -40°C, and is excellent in breaking strength and breaking elongation.

The cured product of the radiation curable composition is used for the primary coating layer of an optical fiber. In other words, one embodiment of the present invention relates to a cured product of the radiation curable resin composition used for the primary coating layer of an optical fiber. Also, one embodiment of the present invention relates to an optical fiber having a primary coating layer made of the cured product of the radiation curable resin composition. This optical fiber further has, for example, a secondary coating layer in contact with the outside of the primary coating layer. The Young's modulus of the secondary coating layer is, for example, 1,000 MPa or more, preferably 1,000 to 2,000 MPa. Optical fibers can be manufactured by known methods, but are generally manufactured by applying a primary material and a secondary material to a molten quartz base material while thermally melting and drawing the material, and then curing the material with radiation to form a primary coating layer and a secondary coating layer. In this case, the optical fiber of the embodiment is obtained by using the radiation curable resin composition of the above embodiment as the primary material.

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

(Examples 1 to 5)
[Synthesis of urethane oligomer]
In a reaction vessel equipped with a stirrer, 68.87 g of polypropylene glycol triol having a weight average molecular weight of 10,000 (manufactured by AGC Corporation, trade name PREMINOL S 3011), 3.60 g of 2,4-tolylene diisocyanate, and 0.018 g of 2,6-di-t-butyl-p-cresol were charged, and these were heated with stirring until the liquid temperature reached 40°C. Then, 0.020 g of dibutyltin dilaurate was added, and the liquid temperature was raised to 60°C over 20 minutes with stirring. After that, the mixture was stirred for 60 minutes, and after the residual isocyanate group concentration became 1.20 mass% (ratio to the charged amount) or less, 1.33 g of 2-hydroxyethyl acrylate was added, and the mixture was reacted at a liquid temperature of 70°C for 60 minutes. After the residual isocyanate group concentration reached 0.52% by mass or less (ratio to the charged amount), 1.20 g of 2-ethyl-1-hexanol was added and the mixture was allowed to react for 60 minutes at a liquid temperature of 70° C. The reaction was terminated when the residual isocyanate group concentration reached 0.05% by mass or less. The obtained urethane oligomer was a mixture mainly composed of a urethane oligomer (I) represented by the following formula (I) and a urethane oligomer (II) represented by the following formula (II).
HEA-TDI-PPT10000-(TDI-HEA)(TDI-EH) (I)
HEA-TDI-PPT10000-(TDI-EH) ₂ (II)
(In the formula, PPT10000 is a structural unit derived from polypropylene glycol triol having a weight average molecular weight of 10,000, TDI is a structural unit derived from 2,4-tolylene diisocyanate, HEA is a structural unit derived from 2-hydroxyethyl acrylate, and EH is a structural unit derived from 2-ethyl-1-hexanol. All bonds "-" are urethane bonds.)

The obtained urethane oligomer was used to produce liquid curable resin compositions of Examples 1 to 5 having the compositions shown in Table 1. The abbreviations shown in Table 1 represent the following compounds. In addition, (I) and (II) in Table 1 represent urethane oligomers (I) and (II), respectively.
ACMO: Acryloyl morpholine
ENPA: Ethoxylated nonylphenol acrylate
IBOA: Isobornyl acrylate
2-EHA: 2-ethylhexylacrylate
NVC: N-Vinylcaprolactam
HDDA: 1,6-Hexanediol diacrylate
TPO: 2,4,6-Trimethylbenzoyl diphenylphosphineoxide

Example 6
In a reaction vessel equipped with a stirrer, 70.84 g of polypropylene glycol diol having a weight average molecular weight of 10,000 (manufactured by AGC Corporation, trade name PREMINOL S 4011), 3.29 g of 2,4-tolylene diisocyanate, and 0.018 g of 2,6-di-t-butyl-p-cresol were charged, and these were heated with stirring until the liquid temperature reached 40°C. Then, 0.020 g of dibutyltin dilaurate was added, and the liquid temperature was raised to 60°C over 20 minutes with stirring. After that, the mixture was stirred for 60 minutes, and after the residual isocyanate group concentration became 0.81 mass% (ratio to the charged amount) or less, 1.23 g of 2-hydroxyethyl acrylate was added, and the mixture was reacted at a liquid temperature of 70°C for 60 minutes. After the residual isocyanate group concentration reached 0.20% by mass or less (ratio to the charged amount), 0.47 g of 2-ethyl-1-hexanol was added and the mixture was allowed to react for 60 minutes at a liquid temperature of 70° C. The reaction was terminated when the residual isocyanate group concentration reached 0.05% by mass or less. The obtained urethane oligomer was a mixture mainly composed of a urethane oligomer (III) represented by the following formula (III) and a urethane oligomer (IV) represented by the following formula (IV).
HEA-TDI-PPG10000-TDI-HEA (III)
HEA-TDI-PPG10000-TDI-EH (IV)
(In the formula, PPG10000 is a structural unit derived from polypropylene glycol diol having a weight average molecular weight of 10,000, and TDI, HEA, EH and the bond "-" are defined as above.)

The obtained urethane oligomer was used to produce the liquid curable resin composition of Example 6 having the composition shown in Table 1. In addition, (III) and (IV) in Table 1 indicate urethane oligomers (III) and (IV), respectively.

(Example 7)
A urethane oligomer was obtained in the same manner as in Example 6, except that the ratio of the amounts of the various components charged was changed. The obtained urethane oligomer was a mixture mainly composed of a urethane oligomer (III) represented by formula (III) and a urethane oligomer (IV) represented by formula (IV). The obtained urethane oligomer was used to produce the liquid curable resin composition of Example 7 having the composition shown in Table 1.

(Comparative Example 1)
Except for using a polypropylene glycol diol having a weight average molecular weight of 3000 instead of the polypropylene glycol diol having a weight average molecular weight of 10000, and changing the ratio of the amounts of the various components charged, a urethane oligomer was obtained in the same manner as in Example 6. The obtained urethane oligomer was a mixture mainly composed of a urethane oligomer (V) represented by the following formula (V) and a urethane oligomer (VI) represented by the following formula (VI).
HEA-(TDI-PPG3000) _2.0 -TDI-HEA (V)
HEA-(TDI-PPG3000) _2.0 -TDI-EH (VI)
(In the formula, PPG3000 is a structural unit derived from polypropylene glycol diol having a weight average molecular weight of 3000, and TDI, HEA, EH and the bond "-" are as defined above.)

The obtained urethane oligomer was used to produce a liquid curable resin composition of Comparative Example 1 having the composition shown in Table 1. In Table 1, (V) and (VI) represent urethane oligomers (V) and (VI), respectively.

(Examples 8 and 9)
In a reaction vessel equipped with a stirrer, 70.86 g of polypropylene glycol diol having a weight average molecular weight of 10,000 (manufactured by AGC Corporation, trade name PREMINOL S 4011), 2.49 g of 2,4-tolylene diisocyanate, and 0.018 g of 2,6-di-t-butyl-p-cresol were charged, and these were heated while stirring until the liquid temperature reached 40°C. Subsequently, 0.020 g of dibutyltin dilaurate was added, and the liquid temperature was raised to 60°C over 20 minutes while stirring. After that, stirring was continued for 60 minutes, and after the residual isocyanate group concentration became 0.82 mass% (ratio to the charged amount) or less, 1.66 g of 2-hydroxyethyl acrylate was added, and the reaction was carried out for 60 minutes at a liquid temperature of 70°C. The reaction was terminated when the residual isocyanate group concentration became 0.05 mass% or less. The obtained urethane oligomer was the urethane oligomer (III) represented by the above formula (III). Using the obtained urethane oligomer (III), curable liquid resin compositions of Examples 8 and 9 having the formulations shown in Table 2 were produced.

(Example 10)
A urethane oligomer was obtained in the same manner as in Example 6, except that a polypropylene glycol triol having a weight average molecular weight of 10,000 was used instead of a polypropylene glycol diol having a weight average molecular weight of 10,000, and the ratio of the amounts of various components charged was changed. The obtained urethane oligomer was a urethane oligomer (I) represented by the above formula (I). The obtained urethane oligomer (I) was used to produce the liquid curable resin composition of Example 10 having the composition shown in Table 2.

(Comparative Example 2)
A urethane oligomer was obtained in the same manner as in Examples 8 and 9, except that a polypropylene glycol triol having a weight average molecular weight of 5000 was used instead of the polypropylene glycol diol having a weight average molecular weight of 10000, and the ratio of the amounts of various components charged was changed. The obtained urethane oligomer was a urethane oligomer (VII) represented by the following formula (VII).
HEA-TDI-PPT5000-(TDI-HEA) ₂ (VII)
(In the formula, PPT5000 is a structural unit derived from polypropylene glycol triol having a weight average molecular weight of 5000, and TDI, HEA and the bond "-" are defined as above.)
Using the obtained urethane oligomer (VII), a liquid curable resin composition of Comparative Example 2 having the composition shown in Table 2 was produced.

(Comparative Example 3)
A urethane oligomer was obtained in the same manner as in Examples 8 and 9, except that a polypropylene glycol diol having a weight average molecular weight of 3000 was used instead of the polypropylene glycol diol having a weight average molecular weight of 10000, and the ratio of the amounts of various components charged was changed. The obtained urethane oligomer was a urethane oligomer (VIII) represented by the following formula (VIII).
HEA-(TDI-PPG3000) _3.0 -TDI-HEA (VIII)
(In the formula, PPG3000, TDI, HEA and the bond "-" are defined as above.)
Using the obtained urethane oligomer (VIII), a liquid curable resin composition of Comparative Example 3 having the composition shown in Table 2 was produced.

(Comparative Example 4)
A urethane oligomer was obtained in the same manner as in Example 6, except that a polypropylene glycol triol having a weight average molecular weight of 5000 was used instead of the polypropylene glycol diol having a weight average molecular weight of 10000, and the ratio of the amounts of various components charged was changed. The obtained urethane oligomer was urethane oligomer (IX) represented by the following formula (IX).
HEA-TDI-PPT5000-(TDI-HEA)(TDI-EH) (IX)
(In the formula, PPT5000, TDI, HEA, EH and the bond "-" are as defined above.)
Using the obtained urethane oligomer (IX), a liquid curable resin composition of Comparative Example 4 having the composition shown in Table 2 was produced.

(evaluation)
(1) Viscosity:
The viscosity at 25° C. of the compositions obtained in the examples and comparative examples was measured using a viscometer TV-10H (manufactured by Toki Sangyo Co., Ltd.).

(2) Young's modulus:
The Young's modulus of the cured product of the composition obtained in the examples and comparative examples at 23 ° C. and -40 ° C. was measured. A liquid curable resin composition was applied to a glass plate using a 354 μm thick applicator bar, and the liquid curable resin composition was cured in air by irradiating it with ultraviolet light with an energy of 1 J / cm ² to obtain a test film. A rectangular sample was prepared from the cured film so that the stretched part had a width of 6 mm and a length of 25 mm. A tensile test was performed in accordance with JIS K7127 using a tensile tester 5542C4600 (manufactured by Instron Japan) under conditions of a temperature of 23 ° C. and a humidity of 50%. The Young's modulus at 23 ° C. was obtained from the tensile strength at 2.5% strain at a tensile speed of 1 mm / min. In addition, a tensile test was performed in the same manner as above to obtain the Young's modulus at -40 ° C., except that the tensile tester was changed to a 5567P5961 (manufactured by Instron Japan) and the temperature was changed to -40 ° C. When the Young's modulus at -40°C was 30 MPa or less, it was evaluated as having excellent flexibility at low temperatures.

(3) Breaking strength and breaking elongation:
A liquid curable resin composition was applied onto a glass plate using a 354 μm thick applicator bar, and cured by irradiating the composition with ultraviolet light in air with an energy of 1 J/ ^cm2 to obtain a test film. The breaking strength and breaking elongation of the test piece were measured under the following measurement conditions using a tensile tester (Shimadzu Corporation, AG-IS). Note that a breaking strength of 4.0 MPa or more and a breaking elongation of 220% or more were evaluated as having excellent mechanical strength.
Tensile speed: 50 mm/min. Marked line distance (measurement distance): 25 mm
Measurement temperature: 23°C
Relative humidity: 50%

Claims (5)

A radiation-curable resin composition for forming a primary coating layer of an optical fiber, comprising a urethane oligomer having an ethylenically unsaturated group, a radical-polymerizable non-urethane monomer, and a polymerization initiator,
the urethane oligomer contains 30% by mass or more of a reaction product of a polyether triol having a weight average molecular weight of 9,000 or more, a polyisocyanate, and an isocyanate-reactive compound containing one active hydrogen group, relative to 100% by mass of the total amount of the radiation-curable resin composition;
the urethane oligomer contains a monofunctional urethane (meth)acrylate oligomer having one (meth)acryloyl group as an ethylenically unsaturated group, and a bifunctional urethane (meth)acrylate oligomer having two (meth)acryloyl groups as ethylenically unsaturated groups,
the radical polymerizable non-urethane monomer contains, as an ethylenically unsaturated group, a (meth)acrylate monomer and a vinyl monomer, and, as the (meth)acrylate monomer, contains a monofunctional (meth)acrylate monomer having one (meth)acryloyl group and a polyfunctional (meth)acrylate monomer having two or more (meth)acryloyl groups;
the isocyanate-reactive compound includes an ethylenically unsaturated group-containing isocyanate-reactive compound and an aliphatic alcohol , the content of the ethylenically unsaturated group-containing isocyanate-reactive compound in the isocyanate-reactive compound is 40 mol % or more and 60 mol % or less, and the content of the aliphatic alcohol in the isocyanate-reactive compound is 24 mol % or more and 60 mol % or less,
in the radiation curable resin composition, a ratio of a total number of moles of the monofunctional urethane (meth)acrylate oligomer, the monofunctional (meth)acrylate monomer, and a vinyl monomer, as monofunctional compounds having one ethylenically unsaturated group, to a total number of moles of the bifunctional urethane (meth)acrylate oligomer and the polyfunctional (meth)acrylate monomer, as polyfunctional compounds having two or more ethylenically unsaturated groups, is 15/1 or more and 30/1 or less;
Radiation curable resin composition. 2. The radiation curable resin composition according to claim 1, wherein the polyether triol is an aliphatic polyether polyol. The reactants are
a reaction product of the polyether triol and the polyisocyanate with the isocyanate-reactive compound; or
3. The radiation-curable resin composition according to claim 1, which is a reaction product of the polyisocyanate, the isocyanate-reactive compound, and the polyether triol . A cured product of the radiation-curable resin composition according to any one of claims 1 to 3 . An optical fiber comprising a primary coating layer comprising the cured product according to claim 4 .