WO2002074849A2

WO2002074849A2 - Liquid curable resin composition

Info

Publication number: WO2002074849A2
Application number: PCT/NL2002/000182
Authority: WO
Inventors: Masanobu Sugimoto; Hideki Sugimoto; Hiroshi Miyazawa; Zen Komiya; Takashi Ukachi
Original assignee: JSR Corp; DSM NV
Current assignee: JSR Corp; Koninklijke DSM NV
Priority date: 2001-03-21
Filing date: 2002-03-21
Publication date: 2002-09-26
Anticipated expiration: 2003-09-21
Also published as: WO2002074849A3; AU2002241395A1

Abstract

A liquid curable resin composition comprising an urethane (meth)acrylate which comprises at least one diol component selected from the group consisting of polypropylene glycol with a number average molecular weight of 300-5,000, a copolymer of propylene oxide and ethylene oxide with a number average molecular weight of 300-5,000 and a copolymer of ethylene oxide and butylene oxide with a number average molecular weight of 300-5000. The liquid curable resin composition of the present invention produces a cured product which exhibits improved stability against the influence of heat and moisture and is useful as a secondary material, a ribbon matrix material and an encapsulating matrix material.

Description

LIQUID CURABLE RESIN COMPOSITION

Field of the invention

The present invention relates to a liquid curable resin composition. More particularly, the present invention relates to a liquid curable resin composition suitable as a coating material for a secondary material, a ribbon matrix material or an encapsulating matrix material for optical fibers.

Description of background art

In the fabrication of optical fibers, a resin coating is applied for protection and reinforcement immediately after spinning molten glass fibers. A resin coating having a structure in which a flexible primary coating layer is formed on the surface of optical fiber and a rigid secondary coating layer is formed over the primary coating layer is known. Before subjecting optical fibers provided with a resin coating to practical application, a number of optical fibers, for example four or eight, are arranged side by side, e.g. on a plane, and secured using a bundling material, thereby forming a ribbon structure which may have a rectangular cross section. Several ribbons may be encapsulated within a radiation cured encapsulating matrix material to form optical fiber ribbon assembly. A resin composition for forming the primary coating layer is called a primary material, a resin composition for forming the secondary coating layer is called a secondary material, and a material for binding several optical fibers is called a ribbon matrix material. A material for encapsulating several ribbons is called an encapsulating matrix material.

One of the features of the secondary material and the ribbon matrix material is that these materials form strong protective films in order to protect the primary material in the lower layer and quartz fibers. Since these materials and encapsulating matrix materials are located in the outer layer of fibers, these materials tend to be affected by heat and humidity under various environments. Therefore, these materials are required to exhibit only a small change in characteristics over time.

Object of the invention Accordingly, an object of the present invention is to provide a liquid curable resin composition suitable for a secondary material, a ribbon matrix material or an encapsulating matrix material and capable of producing cured products exhibiting an improved resistance to heat and humidity.

Summary of the invention

The present inventors have found that a liquid curable resin composition suitable for a secondary material, a ribbon matrix material or an encapsulating matrix material which are affected by heat and humidity to only a small degree can be obtained by using a urethane (meth)acrylate obtained using a specific diol as a diol component. This finding has led to the completion of the present invention. Specifically, the present invention provides a liquid curable resin composition comprising an urethane (meth)acrylate which comprises at least one diol component (A1) selected from the group consisting of polypropylene glycol with a number average molecular weight of 300-5,000, a copolymer of propylene oxide and ethylene oxide with a number average molecular weight of 300-5,000 and a copolymer of ethylene oxide and butylene oxide with a number average molecular weight of 300- 5000.

Detailed description of the invention

In a preferred embodiment the composition after cure results in a material having a Youngs modulus higher than 50 MPa. A preferred range for the

Youngs modulus, after cure, of the composition according to the invention if used as a secondary material, is between about 100 and about 1000 MPa. If the composition after cure is used as a matrix material, a preferred range for the Youngs modulus is between about 50 and about 1500 MPa. If the composition after cure is used as a soft ribbon matrix material, the Youngs modulus preferably has a value in the range of between about 50 and about 200 MPa, and if it is used as a hard ribbon matrix material it preferably has a Youngs modulus in the range of about 200 to about 1500 MPa. In the examples it is described how the Youngs modulus was determined.

The glass transition temperature (Tg) measured as the peak tan-delta determined by dynamic mechanical analysis (DMA), can be optimized depending on the use of the composition. Preferably, the composition according to the invention, after cure, has a Tg of at least 10°C, more preferably the Tg has a value between 10 and 120°C, even more preferred between 20 and 100°C, particularly preferred between 23 and 80°C. The feature of a urethane (meth)acrylate used in the liquid curable resin composition of the present invention is that the urethane (meth)acrylate is obtained by using at least one diol component (A1) selected from the group consisting of polypropylene glycol with a number average molecular weight of 300-5,000, a copolymer of propylene oxide and ethylene oxide with a number average molecular weight of 300-5,000 or a copolymer of ethylene oxide and butylene oxide with a number average molecular weight of 300-5000. Other components, specifically, (B) a diisocyanate and (C) a (meth)acrylate containing a hydroxyl group are not limited.

The urethane (meth)acrylate used in the present invention is produced by reacting the diol (A1), the diisocyanate (B), and the (meth)acrylate (C) containing a hydroxyl group. Specifically, the urethane (meth)acrylate is produced by reacting isocyanate groups of the diisocyanate with hydroxyl groups of the diol and the (meth)acrylate containing a hydroxyl group.

As a method of reacting these compounds, a method of reacting a diol, diisocyanate, and (meth)acrylate containing a hydroxyl group all together; a method of reacting a diol with a diisocyanate, and reacting the resulting product with a (meth)acrylate containing a hydroxyl group; a method of reacting a diisocyanate with a (meth)acrylate containing a hydroxyl group, and reacting the resulting product with a diol; a method of reacting a diisocyanate with a (meth)acrylate containing a hydroxyl group, reacting the resulting product with a diol, and further reacting the resulting product with a (meth)acrylate containing a hydroxyl group; and the like can be given.

The proportion of the diol, diisocyanate, and (meth)acrylate containing a hydroxyl group is preferably determined so that isocyanate groups included in the diisocyanate and hydroxyl groups included in the (meth)acrylate containing a hydroxyl group are respectively 1.1-3 equivalents and 0.2-1.5 equivalents for one equivalent of hydroxyl groups included in the diol.

In the reaction of these compounds, it is preferable to use a urethanization catalyst such as copper naphthenate, cobalt naphthenate, zinc naphthenate, di-n-butyltin dilaurate, triethylamine, 1 ,4-diazabicyclo[2.2.2]octane, or 2,6J-trimethyl-1 ,4-diazabicyclo[2.2.2]octane in an amount of 0.01-1 part by weight for 100 parts by weight of the total reactant. The reaction is carried out preferably at 10- 90°C, and particularly preferably at 30-80°C.

According to one preferred embodiment of the present invention, the diol used as the component (A1) is polypropylene glycol or a copolymer of propylene oxide and ethylene oxide. The number average molecular weight of polypropylene glycol or a copolymer of propylene oxide and ethylene oxide used as the component (A1) is 300- 5000, and preferably 400-4000, more preferred 500-3000 and most preferred 700- 2,500.Examples of commercially available polypropylene glycol suitable for the preparation of a urethane(meth)acrylate as used in the composition according to the invention are PPG400, PPG1000, PPG2000, PPG3000, EXCENOL 720, 1020, 2020 (manufactured by Asahi Glass Urethane Co., Ltd.), and the like.

It is an advantage of liquid curable resin compositions according to the invention comprise an urethane (meth)acrylate which comprises at least one diol component selected from the group consisting of polypropylene glycol with a number average molecular weight of 300-5,000 and a copolymer of propylene oxide and ethylene oxide with a number average molecular weight of 300-5,000 said compositions after having been suitably cured having a relatively short stress relaxation time. The stress relaxation time is defined as the period of time in which the stress is reduced to 37% of the initial stress. In the examples it is described how the stress relaxation time is determined.

In a preferred embodiment the liquid curable resin composition according to the invention comprises an urethane (meth)acrylate which comprises at least one diol component selected from the group consisting of polypropylene glycol with a number average molecular weight of 300-5,000 and a copolymer of propylene oxide and ethylene oxide with a number average molecular weight of 300-5,000, and the composition after cure exhibits a stress relaxation time of 30 minutes or less when subjected to a tensile strain of 5% at 23°C and 50% relative humidity (RH). More preferably, the composition after cure exhibits a stress relaxation time of less than 20, and most preferably of less than 10 minutes. A short stress relaxation time is advantageous because it is undesirable that the secondary material, the ribbon matrix material or the encapsulating matrix material cause an external load to the primary material in the lower layer and quartz fibers. Therefore, secondary materials, ribbon matrix materials and encapsulating matrix materials are often designed so as to have a glass transition temperature of more than room temperature and a high modulus of rigidity. However, when the composition according to the invention is cured during the production process, a residual stress may occur in the cured film due to cooling or cure shrinkage which results in a load being applied to the primary material in the lower layer. One of the phenomena caused by the load is occurrence of voids due to damage to the primary material. This is considered to be one of the causes for transmission loss. In another preferred embodiment, the diol (A1) is a copolymer of ethylene oxide and butylene oxide. The number average molecular weight of the copolymer diol (A1) of ethylene oxide and butylene oxide is 300-5000, and preferably 400-4000, more preferred 500-3000 and most preferred 700-2,500.. The copolymerization ratio (weight ratio) of ethylene oxide to butylene oxide which make up the copolymer is 5:95-50:50, preferably 7:93-40:60, and still more preferably 10:90- 35:65. If the amount of ethylene oxide exceeds 50 wt%, viscosity of the liquid curable resin composition may be increased.

Examples of copolymer diols of ethylene oxide and butylene oxide that are commercially available are EO/BO500, EO/BO1000, EO/BO2000,

EO/BO3000, EO/BO4000 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and the like.

Preferably, the liquid curable composition according to the present invention wherein the diol (A1) is a copolymer of ethylene oxide and butylene oxide with a number average molecular weight of 300-5000 and wherein the weight ratio of ethylene oxide to butylene oxide which makes up the polymer is 5:95 to 50:50, after being cured, shows an "absolute" change in breaking strength (as defined under the test method section) when allowed to stand at a temperature of 120°C for 30 days or when allowed to stand in hot water at 80°C for 30 days or less than about 6, more preferably about 5 or less, even more preferred about 4 or less and most preferred about 3 or less. With "absolute" change in breaking strength is meant to refer to the positive value of the difference in breaking strength after and before the durability test. In addition to the diol (A1), other polyols (A2) or a mixture of (A1) and (A2)at least one polyol may optionally be used. Urethane (meth)acrylates comprising (A2) polyols may be prepared in the same way as described above for urethane (meth)acrylates comprising (A1) diol components. When one diol is selected from the group consisting of polypropylene glycol with a number average molecular weight of 300-5,000, a copolymer of propylene oxide and ethylene oxide with a number average molecular weight of 300-5,000 is used copolymer of ethylene oxide and butylene oxide with a number average molecular weight of 300-5000 is used to prepare a urethane (meth)acrylate in accordance with the invention, the other di- or polyol components are regarded as (A2) polyols.

As examples of polyols used as the component (A2), a polyether polyol, polyester polyol, polycarbonate polyol, polycaprolactone polyol, and the like can be given. There are no specific limitations to the manner of polymerization of the structural units of these polyols, which may be any of random polymerization, block polymerization, or graft polymerization. As examples of polyether polyols, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, polyheptamethylene glycol, polydecamethylene glycol, polyether diols obtained by ring- opening copolymerization of two or more ion-polymerizable cyclic compounds, and the like can be given. As examples of ion-polymerizable cyclic compounds, 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, vinyloxetane, vinyltetrahydrofuran, vinylcyclohexene oxide, phenyl glycidyl ether, butyl glycidyl ether, and glycidyl benzoate can be given. Polyether diols obtained by the ring-opening copolymerization of these ion-polymerizable cyclic compounds and cyclic imines such as ethyleneimine, cyclic lactonic acids such as β-propyolactone and glycolic acid lactide, or dimethylcyclopolysiloxanes may be used. As examples of specific combinations of two or more ion-polymerizable cyclic compounds, combinations of tetrahydrofuran and propylene oxide, tetrahydrofuran and 2-methyltetrahydrofuran, tetrahydrofuran and 3-methyltetrahydrofuran, tetrahydrofuran and ethylene oxide, propylene oxide and ethylene oxide, a ternary copolymer of tetrahydrofuran, butene-1 - oxide, and ethylene oxide, and the like can be given. The ring-opening copolymer of these ion-polymerizable cyclic compounds may be either a random copolymer or a block copolymer.

The above polyether polyols are commercially available as PTMG650, PTMG1000, PTMG2000 (manufactured by Mitsubishi Chemical Corp.),

PEG1000, Unisafe DC1100, DC1800 (manufactured by Nippon Oil and Fats Co., Ltd.), PPTG2000, PPTG1000, PTG400, PTGL2000 (manufactured by Hodogaya Chemical Co., Ltd.), Z-3001-4, Z-3001-5, PBG2000A, PBG2000B (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and the like. As examples of polyether polyols having a cyclic structure, alkylene oxide addition diol of bisphenol A, alkylene oxide addition diol of bisphenol F, hydrogenated bisphenol A, hydrogenated bisphenol F, alkylene oxide addition diol of hydrogenated bisphenol A, alkylene oxide addition diol of hydrogenated bisphenol F, alkylene oxide addition diol of hydroquinone, alkylene oxide addition diol of naphthohydroquinone, alkylene oxide addition diol of anthrahydroquinone, 1 ,4- cyclohexanediol and alkylene oxide addition diol thereof, tricyclodecanediol, tricyclodecanedimethanol, pentacyclopentadecanediol, pentacyclopentadecanedimethanol, and the like can be given. Of these, alkylene oxide addition diol of bisphenol A and tricyclodecanedimethanol are preferable. These polyols are commercially available as Uniol DA400, DA700, DA1000, DB400 (manufactured by Nippon Oil and Fats Co., Ltd.), tricyclodecanedimethanol (manufactured by Mitsubishi Chemical Corp.), and the like.

As examples of polyester polyols, polyester polyols obtained by reacting a polyhydric alcohol and a polybasic acid and the like can be given. As examples of polyhydric alcohols, ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, tetramethylene glycol, polytetramethylene glycol, 1,6-hexanediol, neopentyl glycol, 1 ,4-cyclohexanedimethanol, 3-methyl-1 ,5-pentanediol, 1 ,9- nonanediol, 2-methyl-1 ,8-octanediol, and the like can be given. As examples of polybasic acids, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, adipic acid, sebacic acid, and the like can be given. These polyester polyols are commercially available as Kurapol P-2010, PMIPA, PKA-A, PKA-A2, PNA-2000 (manufactured by Kuraray Co., Ltd.), and the like.

As examples of polycarbonate polyols, polycarbonate of polytetrahydrofuran, polycarbonate of 1 ,6-hexanediol, and the like can be given. As commercially available products of polycarbonate polyols, DN-980, 981 , 982, 983

(manufactured by Nippon Polyurethane Industry Co., Ltd.), PC-8000 (manufactured by PPG), PC-THF-CD (manufactured by BASF), and the like can be given.

As examples of polycaprolactone polyols, polycaprolactonediols obtained by reacting ε-caprolactone with a diol such as ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, tetramethylene glycol, polytetramethylene glycol, 1 ,2-polybutylene glycol, 1 ,6-hexanediol, neopentyl glycol, 1 ,4-cyclohexanedimethanol, or 1 ,4-butanediol, and the like can be given. These diols are commercially available as PLACCEL 205, 205AL, 212, 212AL, 220, 220AL (manufactured by Daicel Chemical Industries, Ltd.), and the like. Polyols other than those illustrated above may be used. As examples of other polyols, ethylene glycol, 1 ,4-butanediol, 1 ,5-pentanediol, 1 ,6-hexanediol, neopentyl glycol, 1 ,4-cyclohexanedimethanol, dimethylol compound of dicyclopentadiene, tricyclodecanedimethanol, β-methyl-δ-valerolactone, hydroxy- terminated polybutadiene, hydroxy-terminated hydrogenated polybutadiene, castor oil- modified polyol, diol-terminated compound of polydimethylsiloxane, polydimethylsiloxanecarbitol-modified polyol, and the like can be given.

Diamines may be used in combination with the above polyols. As examples of diamines, ethylenediamine, tetramethylenediamine, hexamethylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, diamines containing a hetero atom, polyether diamine, and the like can be given.

Of these polyols, polyether polyols and alkylene oxide addition diol of bisphenol A are preferable. These polyols are commercially available as PTMG650, PTMG1000, PTMG2000 (manufactured by Mitsubishi Chemical Corp.), Uniol DA400, DA700, DA1000, and DB400 (manufactured by Nippon Oil and Fats Co., Ltd.).

As examples of the diisocyanate (B), 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, 1 ,6-hexane diisocyanate, isophorone diisocyanate, methylenebis(4-cyclohexylisocyanate), 2,2,4- trimethylhexamethylene diisocyanate, bis(2-isocyanate ethyl)fumarate, 6-isopropyl-1 ,3- phenyl diisocyanate, 4-diphenylpropane diisocyanate, lysine diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, tetramethylxylylene diisocyanate, 2,5(or 6)-bis(isocyanatemethyl)- bicyclo[2.2.1]heptane, and the like can be given. Of these, 2,4-tolylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, and methylenebis(4- cyclohexylisocyanate) are preferable.

These diisocyanates can be used either individually or in combinations of two or more.

As examples of the (meth)acrylate (C) containing a hydroxyl group, 2- hydroxyethyl(meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenyloxypropyl (meth)acrylate, 1 ,4-butanediol mono(meth)acrylate, 2-hydroxyalkyl(meth)acryloyl phosphate, 4-hydroxycyclohexyl (meth)acrylate, 1 ,6-hexanediol mono(meth)acrylate, neopentyl glycol mono(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolethane di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, and (meth)acrylates shown by the following formulas (1) and (2) can be given: CH₂=CR¹ — COOCH₂CH₂— OCOCH₂CH₂CH₂CH₂CH₂-^ — OH (i)

CH₂=CR¹ — COOCH₂CH(OH)CH₂ — 0— "ζ (2)

wherein R¹ represents a hydrogen atom or a methyl group and n is an integer from 1 to 15. Compounds obtained by the addition reaction of (meth)acrylic acid and a compound containing a glycidyl group such as alkyl glycidyl ether, allyl glycidyl ether, and glycidyl (meth)acrylate may be used. Of these (meth)acrylates containing a hydroxyl group, 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate are particularly preferable.

These (meth)acrylate compounds containing a hydroxyl group can be used either individually or in combinations of two or more.

A urethane (meth)acrylate obtained by reacting 1 mol of diisocyanate with 2 mols of (meth)acrylate containing a hydroxyl group may be added to the liquid curable resin composition of the present invention. As examples of such a urethane (meth)acrylate, a reaction product of hydroxyethyl (meth)acrylate and 2,4-tolylene diisocyanate, a reaction product of hydroxyethyl (meth)acrylate and 2,5(or 6)- bis(isocyanatemethyl)-bicyclo[2.2.1]heptane, a reaction product of hydroxyethyl (meth)acrylate and isophorone diisocyanate, a reaction product of hydroxypropyl (meth)acrylate and 2,4-tolylene diisocyanate, and a reaction product of hydroxypropyl (meth)acrylate and isophorone diisocyanate can be given. The urethane (meth)acrylate obtained using the specific diol (A1 is added in an amount of preferably 1-95 wt%, and still more preferably 5-80 wt% of the composition. Even more preferred amounts are between 10-70 wt%. If the amount is less than 1 wt% or exceeds 95 wt%, applicability may be impaired.The proportion of (A1) - diol according to the present invention to (A2) - diol in the urethane (meth)acrylate [(A1):(A2)] preferably is ranging from 95:5 to 50:50, preferably from 90:10 to 40:60, even more preferred from 85:15 to 35:65.

A polymerizable monofunctional_compound or a polymerizable polyfunctional compound may be added to the liquid curable resin composition of the present invention. A polymerizable monofunctional compound is defined herein as a compound that has one functional group capable of polymerization and a polymerizable polyfunctional compound is defined herein as a compound that has more than one functional group capable of polymerization. As examples of monofunctional compounds, vinyl group-containing lactams such as N-vinylpyrrolidone and N- vinylcaprolactam, (meth)acrylates having an alicyclic structure such as isobornyl (meth)acrylate, bornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, and dicyclopentanyl (meth)acrylate, benzyl (meth)acrylate, 4-butylcyclohexyl (meth)acrylate, acryloylmorpholine, vinylimidazole, vinylpyridine, and the like can be given. Further examples include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, amyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl

(meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (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, diacetone (meth)acrylamide, isobutoxymethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, t-octyl (meth)acrylamide, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, 7-amino-3J-dimethyloctyl (meth)acrylate, N,N-diethyl (meth)acrylamide, N,N-dimethylaminopropyl (meth)acrylamide, hydroxybutyl vinyl ether, lauryl vinyl ether, cetyl vinyl ether, 2- ethylhexyl vinyl ether, and compounds shown by the following formulas (3) to (6):

wherein R² represents a hydrogen atom or a methyl group, R³ represents an alkylene group having 2-6, and preferably 2-4 carbon atoms, R⁴ represents a hydrogen atom or an alkyl group having 1-12, and preferably 1-9 carbon atoms, and m is an integer from 0 to 12, and preferably from 1 to 8;

wherein R⁵ represents a hydrogen atom or a methyl group, R⁶ represents an alkylene group having 2-8, and preferably 2-5 carbon atoms, R⁷ represents a hydrogen atom or a methyl group, and p is preferably an integer from 1 to 4;

wherein R⁸, R⁹, R¹⁰, and R¹¹ individually represent a hydrogen atom or a methyl group, and q is an integer from 1 to 5.

Of these monofunctional compounds, N-vinylpyrrolidone, lactams containing a vinyl group such as N-vinylcaprolactam, isobomyl (meth)acrylate, and lauryl acrylate are prefeable.

As examples of commercially available products of these monofunctional compounds, IBXA (manufactured by Osaka Organic Chemical Industry

Co., Ltd.), Aronix M-111 , M-113, M-114, M-117, and TO-1210 (manufactured by

Toagosei Co., Ltd.) can be given.

As examples of polyfunctional compounds, trimethylolpropane tri(meth)acrylate, trimethylolpropanetrioxyethyl (meth)acrylate, pentaerythritol tri(meth)acrylate, ethylene glycol di(meth)acrylate, triethylene glycol diacrylate, tetraethylene glycol di(meth)acrylate, tricyclodecanediyldimethylene 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, tripropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, both terminal (meth)acrylic acid addition compound of bisphenol A diglycidyl ether, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, polyester di(meth)acrylate, tris(2- hydroxyethyl)isocyanurate tri(meth)acrylate, tris(2-hydroxyethyl)isocyanurate di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, di(meth)acrylate of ethylene oxide or propylene oxide addition diol of bisphenol A, di(meth)acrylate of ethylene oxide or propylene oxide addition diol of hydrogenated bisphenol A, epoxy(meth)acrylate prepared by the addition of (meth)acrylate to diglycidyl ether of bisphenol A , triethylene glycol divinyl ether, and the like can be given.

Of these polyfunctional compounds, tricyclodecanediyldimethylene di(meth)acrylate, di(meth)acrylate of ethylene oxide addition product of bisphenol A , and tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate are preferable.

As commercially available products of these polyfunctional compounds, Yupimer UV, SA1002 (manufactured by Mitsubishi Chemical Corp.), Aronix M-215, M-315, M-325, TO-1210 (manufactured by Toagosei Co., Ltd.), and the like can be given. These polymerizable compounds are added to the composition in an amount of preferably 5-90 wt%, and particularly preferably 10-80 wt%. If the amount is less than 5 wt% or exceeds 90 wt%, application may become uneven due to changes in the application form.

The liquid curable resin composition of the present invention may comprise a polymerization initiator. As the polymerization initiator, a heat polymerization initiator or a photoinitiator may be used.

In the case of curing the liquid curable resin composition of the present invention using heat, a heat polymerization initiator such as peroxides or azo compounds is used. Specific examples include benzoyl peroxide, t-butyloxybenzoate, azobisisobutyronitrile, and the like.

In the case of curing the liquid curable resin composition of the present invention using light, a photoinitiator is used. In addition, a photosensitizer is preferably added as required. As examples of photoinitiators, 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 methyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2- methylpropan-1-one, 2- hydroxy-2-methyl-1-phenylpropan-1-one, thioxanethone, diethylthioxanthone, 2- isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl-1 -[4-(methylthio)phenyl]-2- morpholino-propan-1-one, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, bis-(2,6- dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide; IRGACURE 184, 369, 651, 500, 907, CGI 1700, CGI 1750, CGI 1850, CG24-61 (manufactured by Ciba Specialty Chemicals Co.); Lucirin LR8728 (manufactured by BASF); Darocure 1116, 1173 (manufactured by Merck), Ubecryl P36 (manufactured by UCB), and the like can be given. As examples of photosensitizers, triethylamine, diethylamine, N- methyldiethanoleamine, ethanolamine, 4-dimethylaminobenzoic acid, methyl 4- dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, isoamyl 4- dimethylaminobenzoate; Ubecryl P102, 103, 104, 105 (manufactured by UCB); and the like can be given.

In the case of curing the liquid curable resin composition of the present invention using both heat and ultraviolet rays, the heat polymerization initiator and the photoinitiator may be used in combination. The polymerization initiators are added to the composition in an amount of preferably between 0.1-10 wt%, and more preferably between 0.5-8 wt%, even more preferably between 1-7 wt% and most preferably between 2-5 wt%.

Various additives such as antioxidants, coloring agents, UV absorbers, light stabilizers, silane coupling agents, heat polymerization inhibitors, leveling agents, surfactants, preservatives, plasticizers, lubricants, solvents, fillers, aging preventives, wettability importers, and coating surface improvers may be optionally added to the liquid curable resin composition of the present invention insofar as the characteristics of the composition are not adversely affected.

The liquid curable resin composition of the present invention is cured using heat and/or radiation. Radiation used herein includes infrared rays, visible rays, ultraviolet rays, X-rays, electron beams, α-rays, β-rays, γ-rays, and the like.

A cured product of the liquid curable resin composition of the present invention is affected by heat and humidity to only a small degree. Therefore, the cured product is useful as a coating material for optical fibers, in particular, as a secondary material, a ribbon matrix material or an encapsulating matrix material for optical fibers. When the composition of the present invention is used as a secondary material, the composition is applied to optical fiber provided with a primary coating in an appropriate amount and cured. When the composition is used as a ribbon matrix material, the composition is applied over several bundled optical fibers provided with a secondary coating and cured. When the composition is used as an encapsulating matrix material, the composition is applied over several bundled ribbons provided with a matrix material and cured.

The present invention is described below in more detail by examples, which should not be construed as limiting the scope of the present invention.

EXAMPLES AND COMPARATIVE EXPERIMENTS

In the examples, "part(s)" refers to "part(s) by weight".

Example 1. Preparation of a composition comprising urethane (meth)acrylate prepared from polypropylene glycol

A reaction vessel equipped with a stirrerwas charged with 16.98 g of 2,4-tolylene diisocyanate, 0.015 g of 2,6-di-t-butyl-p-cresol, 0.05 g of dibutyltin dilaurate, and 0.005 g of phenothiazine. The mixture was cooled with ice to 10°C or less while stirring. After the addition of 11.32 g of hydroxyethyl acrylate dropwise while controlling the temperature at 20°C or less, the mixture was allowed to react for one hour while stirring. After the addition of 25.40 g of polypropylene glycol with a number average molecular weight of 1000 and 9.36 g of alkylene oxide addition diol of bisphenol A with a number average molecular weight of 400, the mixture was stirred at 70-75°C for three hours. The reaction was terminated when the residual isocyanate concentration was 0.1 wt% or less. The mixture was then cooled to 50-60°C. After the addition of 9.70 g of isobornyl acrylate, 14.55 g of tricyclodecanediyldimethyl (meth)acrylate, 9J0 g of N-vinylcaprolactam, 2.91 g of Irgacure 184 (manufactured by Ciba Specialty Chemicals Co., Ltd.), and 0.3 g of Sumilizer GA-80 (manufactured by Sumitomo Chemical Industries Co., Ltd.), the mixture was stirred until a homogeneous liquid resin was obtained to obtain a liquid curable resin composition of the present invention.

Example 2. Preparation of a composition comprising urethane (meth)acrylate prepared from polypropylene glycol

A reaction vessel equipped with a stirrer was charged with 16.49 g of 2,4-tolylene diisocyanate, 0.015 g of 2,6-di-t-butyl-p-cresol, 0.05 g of dibutyltin dilaurate, and 0.005 g of phenothiazine. The mixture was cooled with ice to 10°C or less while stirring. After the addition of 14.59 g of hydroxyethyl acrylate dropwise while controlling the temperature at 20°C or less, the mixture was allowed to react for one hour while stirring. After the addition of 30.64 g of polypropylene glycol with a number average molecular weight of 1000, the mixture was stirred at 70-75°C for three hours. The reaction was terminated when the residual isocyanate concentration was 0.1 wt% or less. The mixture was then cooled to 50-60°C. After the addition of 13.56 g of isobornyl acrylate, 12.59 g of tricyclodecanediyldimethyl (meth)acrylate, 9.68 g of N- vinylcaprolactam, 2.91 g of Irgacure 184 (manufactured by Ciba Specialty Chemicals Co., Ltd.), and 0.3 g of Sumilizer GA-80 (manufactured by Sumitomo Chemical Industries Co., Ltd.), the mixture was stirred until a homogeneous liquid resin was obtained to obtain a liquid curable resin composition of the present invention.

Comparative Experiment A. Preparation of a composition comprising urethane (meth)acrylate prepared from polytetramethylene glycol

A reaction vessel equipped with a stirrer was charged with 16.98 g of 2,4-tolylene diisocyanate, 0.015 g of 2,6-di-t-butyl-p-cresol, 0.05 g of dibutyltin dilaurate, and 0.005 g of phenothiazine. The mixture was cooled with ice to 10°C or less while stirring. After the addition of 11.32 g of hydroxyethyl acrylate dropwise while controlling the temperature at 20°C or less, the mixture was allowed to react for one hour while stirring. After the addition of 25.40 g of polytetramethylene glycol with a number average molecular weight of 1000 and 9.36 g of alkylene oxide addition diol of bisphenol A with a number average molecular weight of 400, the mixture was stirred at 70-75°C for three hours. The reaction was terminated when the the residual isocyanate concentration was 0.1 wt% or less. The mixture was then cooled to 50-60°C. After the addition of 9J0 g of isobornyl acrylate, 14.55 g of tricyclodecanediyldimethyl (meth)acrylate, 9.70 g of N-vinylcaprolactam, 2.91 g of Irgacure 184 (manufactured by Ciba Specialty Chemicals Co., Ltd.), and 0.3 g of Sumilizer GA-80 (manufactured by Sumitomo Chemical Industries Co., Ltd.), the mixture was stirred until a homogeneous liquid resin was obtained to obtain a liquid curable resin composition.

Comparative Experiment B. Preparation of a composition comprising urethane (meth)acrylate prepared from polytetramethylene glycol

A reaction vessel equipped with a stirrer was charged with 16.49 g of 2,4-tolylene diisocyanate, 0.015 g of 2,6-di-t-butyl-p-cresol, 0.05 g of dibutyltin dilaurate, and 0.005 g of phenothiazine. The mixture was cooled with ice to 10°C or less while stirring. After the addition of 14.59 g of hydroxyethyl acrylate dropwise while controlling the temperature at 20°C or less, the mixture was allowed to react for one hour while stirring. After the addition of 30.64 g of polytetramethylene glycol with a number average molecular weight of 1000, the mixture was stirred at 70-75°C for three hours. The reaction was terminated when the residual isocyanate concentration was 0.1 wt% or less. The mixture was then cooled to 50-60°C. After the addition of 13.56 g of isobornyl acrylate, 12.59 g of tricyclodecanediyldimethyl (meth)acrylate, 9.68 g of N- vinylcaprolactam, 2.91 g of Irgacure 184 (manufactured by Ciba Specialty Chemicals Co., Ltd.), and 0.3 g of Sumilizer GA-80 (manufactured by Sumitomo Chemical Industries Co., Ltd.), the mixture was stirred until a homogeneous liquid resin was obtained to obtain a liquid curable resin composition.

Tests

Preparation of test film:

The liquid curable resin composition was applied to a glass plate using an applicator bar for a thickness of 250 Dm. The composition was cured by irradiation of ultraviolet rays at a dose of 1 J/cm² in air to obtain a test film.

1. Measurement of Young's modulus:

The above film was cut into a sample in the shape of a strip with a width of 6 mm and a length of 25 mm (portion to be tensed). The sample was subjected to a tensile test at a temperature of 23°C and a humidity of 50%. The Young's modulus was calculated from the tensile strength at a strain of 2.5% and a tensile rate of 1 mm/min.

2. Measurement of stress relaxation:

The above film was cut into a sample in the shape of a strip with a width of 6 mm and a length of 25 mm. A strain of 5% was applied to the sample at a rate of 1000 mm/minute at a temperature of 23°C and a humidity of 50%. Changes in the stress was monitored with a cross head of a tensile tester being suspended. A period of time in which the stress was reduced to 37% of the initial stress was determined as the stress relaxation time.

3. Observation of occurrence of void in primary material: 3-1. Preparation of primary material:

A reaction vessel equipped with a stirrer was charged with 6.6 parts of 2,4-tolylene diisocyanate, 0.015 part of 2,6-di-t-butyl-p-cresol, 0.48 part of dibutyltin dilaurate, 0.005 part of phenothiazine, and 16.2 parts of IBXA (manufactured by Osaka Organic Chemical Industry, Ltd.). The mixture was cooled with ice to 10°C or less while stirring. After the addition of 2.9 parts of hydroxyethyl acrylate dropwise while controlling the temperature at 20°C or less, the mixture was allowed to react for one hour while stirring. After the addition of 50.0 parts of polytetramethylene glycol with a number average molecular weight of 2000 (manufactured by Mitsubishi Chemical

Corp.), the mixture was stirred at 50-60°C for four hours. The reaction was terminated when the residual isocyanate concentration was 0.1 wt% or less. After the addition of 10.8 parts of isobornyl acrylate (manufactured by Rohm and Haas Japan K.K.), 4.8 parts of vinylcaprolactam, 5.6 parts of lauryl acrylate, and 0.2 part of Irganox 1035 (manufactured by Ciba Geigy), the mixture was stirred at 40-50°C for 30 minutes. After the addition of 0.1 part of diethylamine while controlling the temperature at 30-40°C, the mixture was stirred for 30 minutes. After the addition of 1 part of bis-(2,6- methoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide and 1 part of Darocure 1173 (manufactured by Merck) while controlling the temperature at 50-60°C, the mixture was stirred until a homogeneous transparent solution was obtained. The primary material was thus obtained.

3-2. Drawing:

The primary material was applied to a metal wire and cured using an optical fiber drawing equipment (manufactured by Yoshida Kogyo Co., Ltd.). The compositions of the Examples and Comparative Examples were applied to the cured primary material.

The drawing conditions for the wire were as follows. The diameter of the metal wire was 125 μm. The diameter of the coated wire was adjusted to 200 μm after the primary coating material was cured. The composition of the Example or Comparative Example was applied to the primary material thus formed so that the diameter was 250 μm after curing. A UV lamp ("SMX 3.5 kW" manufactured by ORC Manufacturing Co., Ltd.) was used as a UV irradiation equipment. Applicability was evaluated at a wire drawing rate of 1000 m/min.

3-3. Observation of occurrence of void

After immersing the above wire in hot water at a temperature of 60°C for 72 hours, occurrence of void in the primary material was observed using a microscope.

Table 1. Stress relaxation times

As is clear from Table 1 , for the resin compositions of the Examples 1 and 2 no voids occured in the primary material after immersing the wire in hot water as indicated above. Further, the compositions of the Examples have a high stress relaxation rate.

Example 3. Preparation of a composition comprising urethane (meth)acrylate prepared from a copolymer of ethylene oxide and butylenes oxide A reaction vessel equipped with a stirrer was charged with 11.835 g of 2,4-tolylene diisocyanate, 0.011 g of 2,6-di-t-butyl-p-cresol, 0.036 g of dibutyltin dilaurate, and 0.004 g of phenothiazine. The mixture was cooled with ice to 10°C or less while stirring. After the addition of 10.709 g of hydroxyethyl acrylate dropwise while controlling the temperature at 20°C or less, the mixture was allowed to react for one hour while stirring. After the addition of 21.857 g of EO/BO1000 with a number average molecular weight of 1000 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and 4.107 g of ethylene oxide addition diol of bisphenol A with a number average molecular weight of 400, the mixture was stirred at 70-75°C for three hours. The reaction was terminated when the residual isocyanate concentration was 0.1 wt% or less. The mixture was cooled to 50-60°C. After the addition of 9.866 g of tricyclodecanediyldimethyl (meth)acrylate, 4.736 g of N-vinylcaprolactam, 27.627 g of triacylate of ethylene oxide addition product of trimethylenepropane, 2.91 g of Irgacure 184 (manufactured by Ciba Specialty Chemicals Co., Ltd.), and 0.3 g of Sumilizer GA- 80 (manufactured by Sumitomo Chemical Industries Co., Ltd.), the mixture was stirred into a homogeneous liquid resin to obtain a liquid curable resin composition of the present invention.

Example 4. Preparation of a composition comprising urethane (meth)acrylate prepared from a copolymer of ethylene oxide and butylene oxide A reaction vessel equipped with a stirrer was charged with 11.835 g of 2,4-tolylene diisocyanate, 0.011 g of 2,6-di-t-butyl-p-cresol, 0.036 g of dibutyltin dilaurate, and 0.004 g of phenothiazine. The mixture was cooled with ice to 10°C or less while stirring. After the addition of 10.709 g of hydroxyethyl acrylate dropwise while controlling the temperature at 20°C or less, the mixture was allowed to react for one hour while stirring. After the addition of 21.857 g of EO/BO1000 with a number average molecular weight of 1000 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), the mixture was stirred at 70-75°C for three hours. The reaction was terminated when the residual isocyanate concentration was 0.1 wt% or less. The mixture was cooled to 50- 60°C. After the addition of 9.866 g of tricyclodecanediyldimethyl (meth)acrylate, 4.933 g of diacrylate of EO addition product of bisphenol A, 9.867 g of N-vinylcaprolactam, 27.627 g of triacylate of ethylene oxide addition product of trimethylenepropane, 2.91 g of Irgacure 184 (manufactured by Ciba Specialty Chemicals Co., Ltd.), and 0.3 g of Sumilizer GA-80 (manufactured by Sumitomo Chemical Industries Co., Ltd.), the mixture was stirred into a homogeneous liquid resin to obtain a liquid curable resin composition of the present invention.

Example 5. Preparation of a composition comprising urethane (meth)acrylate prepared from a copolymer of ethylene oxide and butylene oxide

A reaction vessel equipped with a stirrerwas charged with 9.9 g of tricyclodecanediyldimethyl diacrylate, 15.4 g of 2,4-tolylene diisocyanate, 0.013 g of 2,6-di-t-butyl-p-cresol, 0.044 g of dibutylin dilaurate, and 0.004 g of phenothiazine. The mixture was cooled with ice to 10°C or below while stirring. After the addition of 13.1 g of hydroxyethyl acrylate dropwise while controlling the temperature at 20°C or less, the mixture was allowed to react for one hour while stirring. Next, 21.9 g of a ring-opening polymer of the ethylene oxide and butylene oxide with a number average molecular weight of 1000 ("H-3988" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and 4.1 g of ethylene oxide addition diol of bisphenol A with a number average molecular weight of 400 ("Uniol DA 400" manufactured by Nippon Oil and Fats Co., Ltd.) were added, and the mixture was stirred at 70-75°C for three hours. The reaction was terminated when the residual isocyanate concentration became 0.1 wt% or less. The mixture was then cooled to 50-60°C. After the addition of 27.6 g of Viscoat #360 (manufactured by Osaka Organic Chemical Industry Co., Ltd), 4J g of N-vinylcaprolactam, 3.0 g of Irgacure 184 (manufactured by Ciba Specialty Chemicals Co., Ltd), and 0.3 g of Irganox 1035 (manufactured by Ciba Specialty Chemicals Co., Ltd), the mixture was stirred until it became a homogeneous liquid resin, thereby obtaining a composition.

Example 6 Preparation of a composition comprising urethane (meth)acrylate prepared from a copolymer of ethylene oxide and butylene oxide

A reaction vessel equipped with a stirrerwas charged with 14.5 g of 2,4-tolylene diisocyanate, 0.012 g of 2,6-di-t-butyl-p-cresol, 0.040 g of dibutyltindilaurate, and 0.004 g of phenothiazine. The mixture was cooled with ice to 10°C or below while stirring. After the addition of 12.5 g of hydroxyethyl acrylate dropwise while controlling the temperature at 20°C or less, the mixture was allowed to react for one hour while stirring. Next, 19.4 g of a ring-opening polymer of the ethylene oxide and butlylene oxide with a number average molecular weight of 1000 ("H-3988" manufactured by Daiichi Kogyo Seiyaku Co., Ldt.) and 4.1 g of alkylene oxide addition diol of bisphenol A with a number average molecular weight of 400 ("Uniol DA400" manufactured by Nippon Oil and Fats Co., Ltd) were added, and the mixture was stirred at 70-75°C for three hours. The reaction was terminated when the residual isocyanate concentration became 0.1 wt% or less. The mixture was then cooled to 50- 60°C. After the addition of 30.0 g of Viscoat #360 (manufactured by Osaka Organic Chemical Industry Co., Ltd.), 4J g of N-vinylpyrrolidone, 11.8 g of tricyclodecanediyldimethyl diacrylate, 1.5 g of LUCIRIN TPO (manufactured by BASF), and Irganox 1035 (manufactured by Ciba Specialty Chemicals Co., Ltd.), the mixture was stirred until it became a homogeneous liquid resin, thereby obtaining a composition.

Comparative Experiment C. Preparation of a composition comprising urethane (meth)acrylate prepared from polytetramethylene glycol A reaction vessel equipped with a stirrer was charged with 11.835 g of 2,4-tolylene diisocyanate, 0.011 g of 2,6-di-t-butyl-p-cresol, 0.036 g of dibutyltin dilaurate, and 0.004 g of phenothiazine. The mixture was cooled with ice to 0°C or less while stirring. After the addition of 10.709 g of hydroxyethyl acrylate dropwise while controlling the temperature at 20°C or less, the mixture was allowed to react for one hour while stirring. After the addition of 21.857 g of polytetramethylene glycol with a number average molecular weight of 1000 and 4.107 g of ethylene oxide addition diol of bisphenol A with a number average molecular weight 400, the mixture was stirred at 70-75°C for three hours. The reaction was terminated when the residual isocyanate concentration was 0.1 wt% or less. The mixture was cooled to 50-60°C. After the addition of 9.866 g of tricyclodecanediyldimethyl (meth)acrylate, 4J36 g of N- vinylcaprolactam, 27.627 g of triacylate of ethylene oxide addition product of trimethylenepropane, 2.91 g of Irgacure 184 (manufactured by Ciba Specialty Chemicals Co., Ltd.), and 0.3 g of Sumilizer GA-80 (manufactured by Sumitomo Chemical Industries Co., Ltd.), the mixture was stirred into a homogeneous liquid resin to obtain a liquid curable resin composition.

Comparative Experiment P. Preparation of a composition comprising urethane (meth)acrylate prepared from polytetramethylene glycol

A reaction vessel equipped with a stirrer was charged with 11.835 g of 2,4-tolylene diisocyanate, 0.011 g of 2,6-di-t-butyl-p-cresol, 0.036 g of dibutyltin dilaurate, and 0.004 g of phenothiazine. The mixture was cooled with ice to 10°C or less while stirring. After the addition of 10.709 g of hydroxyethyl acrylate dropwise while controlling the temperature at 20°C or less, the mixture was allowed to react for one hour while stirring. After the addition of 21.857 g of polytetramethylene glycol with a number average molecular weight of 1000, the mixture was stirred at 70-75°C for three hours. The reaction was terminated when the residual isocyanate concentration was 0.1 wt% or less. The mixture was cooled to 50-60°C. After the addition of 9.866 g of tricyclodecanediyldimethyl (meth)acrylate, 4.933 g of diacrylate of EO addition product of bisphenol A, 9.867 g of N-vinylcaprolactam, 27.627 g of triacylate of ethylene oxide addition product of trimethylenepropane, 2.91 g of Irgacure 184 (manufactured by Ciba Specialty Chemicals Co., Ltd.), and 0.3 g of Sumilizer GA-80 (manufactured by Sumitomo Chemical Industries Co., Ltd.), the mixture was stirred into a homogeneous liquid resin to obtain a liquid curable resin composition.

Tests

Preparation of test film:

The liquid curable resin composition was applied to a glass plate using an applicator bar for a thickness of 250 μm. The composition was cured by irradiation of ultraviolet rays at a dose of 1 J/cm² in air to obtain a test film.

1. Durability test:

The above film was allowed to stand at a temperature of 120°C and in hot water at 80°C for 30 days.

2. Measurement of Young's modulus:

The cured film was cut into a sample in the shape of a strip with a width of 6 mm and a length of 25 mm. The sample was subjected to a tensile test at a temperature of 23°C and a humidity of 50%. The Young's modulus was calculated from the tensile strength at 2.5% strain and a tensile rate of 1 mm/min.

3. Measurement of breaking strength:

The cured film was cut into a sample in the shape of a strip with a width of 6 mm and a length of 25 mm. The sample was subjected to a tensile test at a temperature of 23°C and a humidity of 50% to measure the stress at the time of breaking. The tensile rate was 50 mm/min. 4. Evaluation of change in breaking strength over time as a result of exposure to heat and humidity:

A change in breaking strength before and after the durability test was calculated according to the equation given below. A sample which showed a change of -5 or more was judged as good.

Change = ((breaking strength after durability test - breaking strength before durability test)/ breaking strength before durability test) x 100

Test results

Table 3. Hot water test at 80°C

As is clear from Tables 2 and 3, each cured product shown in the tables had a Young's modulus before the test within the range of 700-1500 MPa, which is acceptable as a secondary material, a ribbon matrix material or an encapsulating matrix material. The cured products in the Examples 3-6 were stable for a long period of time, under the different aging/durability conditions used due to a small change in the breaking strength over time.

Claims

1. A liquid curable resin composition comprising an urethane (meth)acrylate which comprises at least one diol component (A1) selected from the group consisting of polypropylene glycol with a number average molecular weight of

300-5,000, a copolymer of propylene oxide and ethylene oxide with a number average molecular weight of 300-5,000 and a copolymer of ethylene oxide and butylene oxide with a number average molecular weight of 300-5000.

2. A liquid curable resin composition according to claim 1 which composition after cure has a Youngs modulus higher than 50 MPa.

3. A liquid curable resin composition according to any one of claims 1-2 wherein the diol is a copolymer of ethylene oxide and butylene oxide with a number average molecular weight of 300-5000 and wherein the copolymer of ethylene oxide and butylene oxide is a copolymer in which the the weight ratio of ethylene oxide to butylene oxide is 5:95 to 50:50.

4. A liquid curable resin composition according to claims 1-2 wherein the diol component is a copolymer of propylene oxide and ethylene oxide with a number average molecular weight of 300-5,000 and wherein the copolymer of propylene oxide and ethylene oxide is a copolymer in which the weight ratio of propylene oxide to ethylene oxide is from 100:0 to 20:70.

5. A liquid curable resin composition according to claims 1-2 and 4, wherein the the diol component is a copolymer of propylene oxide and ethylene oxide with a number average molecular weight of 300-5,000 or polypropylene glycol with a number average molecular weight of 300-5,000, and which composition after cure exhibits a stress relaxation time of 30 minutes or less when subjected to a tensile strain of 5% at 23°C and 50% relative humidity (RH).

6. A coated optical fiber comprising a glass fiber and a primary coating applied onto at least part of the glass fiber and a secondary coating applied onto at least part of the primary coating wherein the secondary coating is a cured composition, said composition being a composition according to any one of claims 1-5, after cure.

7. A ribbon comprising at least two optical fibers, said optical fibers being coated with at least a primary coating, and said fibers being encapsulated within a ribbon matrix material to form the ribbon, wherein the ribbon matrix material is a cured composition, said composition being a composition according to any one of claims 1-5 after cure.

8. An optical fiber ribbon assembly comprising at least two ribbons and an encapsulating matrix material, and wherein the encapsulating matrix material is a cured composition, said composition being a composition according to any one of claims 1-5 after cure.

9. Use of a composition according to any one of claims 1-5 as a secondary coating material, a ribbon matrix material or an encapsulating matrix material.