WO2008105659A1

WO2008105659A1 - Radiation curable resin composition

Info

Publication number: WO2008105659A1
Application number: PCT/NL2008/050117
Authority: WO
Inventors: Hiroyuki Ishii; Hiroshi Miyazawa; Takahiko Kurosawa
Original assignee: Dsm Ip Assets B.V.; Jsr Corporation
Priority date: 2007-02-27
Filing date: 2008-02-27
Publication date: 2008-09-04
Also published as: JP2008208226A

Abstract

A polymer cladding layer which exhibits a low refractive index, transparency, excellent applicability, excellent adhesion to the core, and excellent strength and flexibility using a known resin material used for a cladding layer of a polymer-clad optical fiber is described and claimed. This polymer cladding layer exhibits stable transparency even when the polymer-clad optical fiber to is exposed to a high temperature.

Description

Title: RADIATION CURABLE RESIN COMPOSITION

FIELD OF THE INVENTION

The present invention relates to a radiation curable liquid resin composition for forming a cladding layer of a polymer-clad optical fiber.

BACKGROUND OF THE INVENTION

An optical fiber is suitable for high-capacity and high-speed digital signal communications and has been widely used for information communication cables instead of electric wires made of a metal. There are various types of optical fibers, classified depending on the structures and forms. An optical fiber having the most basic structure has a core formed of glass, quartz, or a transparent resin, a cladding layer provided in contact with the exterior of the core, and a polymer coating layer provided over the cladding layer and formed of a radiation-curable resin or the like. In particular, an all-silica optical fiber of which the core and the cladding layer are formed of quartz (silica) is widely used. Typically, the diameter of the core of an optical fiber is about 50 micrometers (hereinafter micrometers will be abbreviated "μm"), the total diameter of the core and the cladding layer is about 125 μm, and the total diameter of the core, the cladding layer, and the resin coating layer is about 250 to 500 μm.

Optical modules having optical signal transmission/reception/branch/switching functions and the like have been developed for optical information communications. It is important to connect an optical module and an optical fiber with their optical axes aligned in order to suppress attenuation of optical signals. Since the diameter of the core of an optical fiber is small, as described above, it is difficult to align the optical axes when connecting an optical fiber to an optical module. Therefore, an optical fiber is used of which the core diameter is increased to about 200 μm. Such a large -diameter optical fiber typically has a cladding layer formed of a curable transparent resin, and is called a polymer-clad optical fiber (or plastic-clad optical fiber or polymer-clad fiber). As the curable transparent resin for forming the cladding layer, a fluorine -containing UV-curable composition containing a fluorine-containing urethane (me th) aery late, a fluorine -containing (meth)acrylate oligomer, or the like is known, see Patent Document JP-A- 10- 10340;

Patent Document JP-A- 10- 160947 ; and Patent Document JP-A- 11- 119036. A polymer-clad optical fiber having a core formed of glass or quartz is called a hard polymer-clad optical fiber, and a polymer-clad optical fiber having a core formed of a transparent resin is called a plastic fiber. The hard plastic-clad optical fiber is used for communications over a relatively long distance due to high optical transmission efficiency, and the plastic fiber is used for communications over a relatively short distance.

A curable transparent resin material used for the cladding layer of a polymer-clad optical fiber is required to have a low refractive index and transparency which is stable with time; an appropriate viscosity which ensures an excellent applicability; excellent adhesion to the core; and strength and flexibility represented by the Young's modulus, breaking strength, breaking elongation, and the like, for example.

However, it is difficult to obtain a polymer cladding layer which exhibits a low refractive index, transparency, excellent applicability, excellent adhesion to the core, and excellent strength and flexibility using a known resin material used for a cladding layer of a polymer-clad optical fiber. In particular, it is difficult to obtain a polymer cladding layer which exhibits stable transparency even when allowing the polymer-clad optical fiber to stand at a high temperature.

It would be desirable to develop such products.

SUMMARY OF THE INVENTION

The first aspect of the instant claimed invention is a radiation-curable resin composition comprising:

(A) 20 to 65 mass% of an ethylenically unsaturated group -containing fluorocopolymer;

(B) 20 to 60 mass% of a compound of the following formula,

wherein R⁸ represents a hydrogen atom or a methyl group, X represents a hydrogen atom or a fluorine atom, x represents 1 or 2, and y represents an integer from 2 or 8; and (C) 10 to 35 mass% of a compound other than the components (A) and (B) which does not have an aromatic structure and a polar group and contains two or more ethylenically unsaturated groups.

The second aspect of the instant claimed invention is a cured film comprising a cured product of the radiation-curable liquid resin composition according to the first aspect of the instant claimed invention.

The third aspect of the instant claimed invention is polymer-clad optical fiber comprising a core formed of glass, quartz, or a transparent resin and a cladding layer comprising the cured film according to the second aspect of the instant claimed invention and provided in contact with the exterior of the core.

The fourth aspect of the instant claimed invention is a process of making a polymer-clad optical fiber comprising the steps of A) providing a core of glass, quartz or transparent resin;

B) providing the radiation-curable liquid resin composition of the first aspect of the instant claimed invention; and

C) coating the core of glass, quartz or transparent resin with the radiation-curable liquid resin composition of the first aspect of the instant claimed invention; and

D) applying radiation to said radiation-curable liquid resin composition so that the liquid cures to a solid film.

An object of the present invention is to provide a radiation-curable resin composition which has properties suitable as a cladding material for a polymer-clad optical fiber and exhibits a low refractive index, stable transparency, excellent applicability, excellent adhesion to the core, and excellent strength and flexibility.

DETAILED DESCRIPTION OF THE INVENTION

The instant claimed invention is a radiation-curable resin composition containing a specific fluorine -containing polymer, a specific fluorine -containing (me th) aery late monomer, and a fluorine-free

(meth)acrylate monomer having a specific structure as essential components. A polymer-clad layer obtained using the resin composition of the present invention has a low refractive index, stable transparency, excellent applicability, excellent adhesion to a core, high strength, and excellent flexibility.

The present invention provides a radiation-curable resin composition comprising: (A) 20 to 65 mass% of an ethylenically unsaturated group -containing fluorocopolymer;

(B) 20 to 60 mass% of a compound of the following formula,

CH₂=CR⁸COO(CH2)x(CF₂)yX

wherein R⁸ represents a hydrogen atom or a methyl group, X represents a hydrogen atom or a fluorine atom, x represents 1 or 2, and y represents an integer from 2 or 8; and

(C) 10 to 35 mass% of a compound other than the components (A) and (B) which does not have an aromatic structure and a polar group and contains two or more ethylenically unsaturated groups. (A) Ethylenically unsaturated group-containing fluoropolymer

The ethylenically unsaturated group -containing fluoropolymer (A) is not particularly limited insofar as the polymer has an ethylenically unsaturated group and a fluorine atom. A fluorine -containing olefin copolymer having an ethylenically unsaturated group in its side chain is preferable. The component (A) provides the composition of the present invention with basic properties necessary for a cladding material of a polymer-clad optical fiber, such as a low refractive index, high mechanical strength, and excellent adhesion to a core formed of glass, quartz, or the like.

The ethylenically unsaturated group -containing fluoropolymer is obtained by reacting a compound having an ethylenically unsaturated group and an isocyanate group with a hydroxyl group of a hydroxyl group -containing fluoropolymer.

(1) Compound having ethylenically unsaturated group and isocyanate group

There are no limitations to the compound having an ethylenically unsaturated group and an isocyanate group insofar as the compound has at least one ethylenically unsaturated group and at least one isocyanate group in the molecule. A compound having a (meth)acryloyl group as the ethylenically unsaturated group is preferable due to the capability of easily curing a curable resin composition described later. As such a compound, (me th) acrylic acid, (meth)acryloyl chloride, (meth)acrylic anhydride, 2-(meth)acryloyloxyethyl isocyanate, 2-(meth)acryloyloxypropyl isocyanate, and l,l-(bisacryloyloxymethyl)ethyl isocyanate may be used either individually or in combination of two or more. Commercially available products of (me th) aery late having an isocyanate group, include but are limited to, Karenz MOI, AOI, and BEI (manufactured by Showa Denko K.K.).

Such a component may be synthesized by reacting a diisocyanate compound and a hydroxyl group -containing (meth)acrylate. As the diisocyanate compound, 2,4-tolylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, methylene bis(4-cyclohexylisocyanate), and l,3-bis(isocyanatemethyl)cyclohexane are preferable, for example.

As the hydroxyl group -containing (me th) aery late, 2-hydroxyethyl (meth)acrylate and pentaerythritol tri(meth)acrylate are preferable, for example.

Hydroxyl group -containing polyfunctional (me th) aery late s are commercially available as HEA (manufactured by Osaka Organic Chemical Industry, Ltd.), KAYARAD DPHA and PET-30 (manufactured by Nippon Kayaku Co., Ltd.), and Aronix M-215, M-233, M-305, and M-400

(manufactured by Toagosei Co., Ltd.), for example.

(2) Hydroxyl group -containing fluoropolymer

The hydroxyl group -containing fluoropolymer preferably contains the

following structural units (a), (b), and (c¹).

(a) Structural unit shown by the following formula (1)

(b) Structural unit shown by the following formula (2)

(c') Structural unit shown by the following formula (6)

Structural unit (a):

H R¹ I I

-C-C — I I

H C=O I (1) O

^Cm^H2m

(CF₂)_nF

wherein R¹ represents a hydrogen atom or a methyl group, m represents an integer from 1 to 8, and n represents an integer from 1 to 20. Structural unit (b): H R²

I I

— C-C —

H C=O ^W

I O i> wherein R² represents a hydrogen atom or a methyl group, and R³ represents a monovalent organic group having an alicyclic structure. Structural unit (c'):

H R⁷

I I — C-C —

I I H C=O _(β)

O

I

C_yH₂₇

OH

wherein R⁷ represents a hydrogen atom or a methyl group, and v represents an integer from 1 to 20. (i) Structural unit (a):

In the formula (1), m represents 1 to 8, preferably 1 to 4, and more

preferably 2. n represents 1 to 20, preferably 3 to 12, more preferably 4 to 8,

and most preferably 8.

The structural unit (a) may be introduced using a compound shown by

the following formula (7) as a polymerization component. Suitable

examples of such a compound, include, but are not limited to, perfluorooctylethyl (meth)acrylate and the like.

wherein R¹, m, and n are the same as R¹, m, and n in the formula (1). The content of the structural unit (a) in the hydroxyl group-containing fluoropolymer is 20 to 70 mol%, preferably 30 to 60 mol%, and more preferably 35 to 60 mol% based on 100 mol% of the structural units (a), (b), and (c¹) in total. If the content of the structural unit (a) exceeds 70 mol%, the solubility of the hydroxyl group -containing fluoropolymer decreases, whereby the polymer may precipitate during a polymerization reaction or may become insoluble in a solvent. If the content of the structural unit (a) is less than 20 mol%, the fluorine content (i.e., the weight ratio of fluorine atoms contained in the polymer) in the hydroxyl group -containing fluoropolymer decreases, whereby the refractive index of the hydroxyl group -containing fluoropolymer increases, (ii) Structural unit (b): R³ in the formula (2) represents a monovalent organic group having an alicyclic structure. When R³ has an aliphatic structure, the Young's modulus of the cured product obtained by curing the composition of the present invention becomes too small. When R³ has an aromatic structure, the Young's modulus of the cured product obtained by curing the composition of the present invention becomes too large. In each case, the cured product exhibits properties inappropriate for a cladding layer. When R³ is a monovalent organic group having an alicyclic structure, the Young's modulus and the refractive index of the cured product are well-balanced. Note that the alicyclic structure used herein includes a heterocyclic structure.

The structural unit (b) may be introduced using a compound shown by the following formula (8) as a polymerization component. Suitable examples of such compounds, include, but are not limited to, cyclohexyl (meth) aery late, dicy elope ntanyl (meth)acrylate, isobornyl (meth) aery late, dicyclopentenyl (meth) aery late, and the like. H₂C=C

C=O (8) O

R'

wherein R² and R³ are the same as R² and R³ in the formula (2).

The content of the structural unit (b) in the hydroxyl group-containing fluoropolymer is 10 to 70 mol%, preferably 20 to 60 mol%, and more preferably 20 to 55 mol% based on 100 mol% of the structural units (a), (b), and (c') in total. If the content of the structural unit (b) exceeds 70 mol%, the refractive index of the fluoropolymer increases. If the content of the structural unit (b) is less than 20 mol%, the solubility of the fluoropolymer decreases.

(iii) Structural unit (c'):

The structural unit (c') may be introduced using a compound shown by the following formula (9) as a polymerization component. Suitable examples of such compounds, include, but are not limited to, 2-hydroxyethyl (meth)acrylate, 2-hydroxybutyl (meth) aery late, 2-hydroxypropyl (me th) aery late, caprolactone (meth)acrylate, polyethylene glycol (meth)acrylate, polypropylene glycol (meth) aery late, and the like.

wherein R⁷ and v are the same as R⁷ and v in the formula (6).

The content of the structural unit (c') in the hydroxyl group -containing fluoropolymer is 5 to 70 mol%, preferably 10 to 40 mol%, and more preferablyl to 20 mol% based on 100 mol% of the structural units (a), (b), and

(c') in total. If the content of the structural unit (c¹) exceeds 70 mol%, the refractive index of the fluoropolymer increases. If the content of the structural unit (c') is less than 5 mol%, a sufficient number of ethylenically unsaturated groups may not be introduced. (3) Ethylenically unsaturated group -containing fluoropolymer

The ethylenically unsaturated group -containing fluoropolymer (the component (A)) is obtained by reacting a hydroxyl group of the structural unit (c') of the hydroxyl group -containing fluoropolymer with a reactive group such as an isocyanate group of the compound having an ethylenically unsaturated group and the isocyanate group. In this case, the number of moles of the isocyanate groups of the compound having an ethylenically unsaturated group and the isocyanate group is preferably 0.5 to 1.0 times the number of moles of the hydroxyl groups of the hydroxyl group -containing fluoropolymer.

Therefore, the ethylenically unsaturated group -containing fluoropolymer (A) possesses, in addition to the structural unit (a) and the structural unit (b) originating from the hydroxyl group -containing fluoropolymer, the following structural unit (c) which is produced by the reaction of the structural unit (c') of the hydroxyl group -containing fluoropolymer with the compound having an ethylenically unsaturated group and an isocyanate group. Structural unit (c):

wherein R⁴ represents a hydrogen atom or a methyl group, R⁵ represents a group shown by the following formula (4) or (5), and v represents an integer from 1 to 20.

wherein R⁶ represents a hydrogen atom or a methyl group.

The content of the structural unit (a) in the ethylenically unsaturated

group -containing fluorocopolymer is 20 to 70 mol%, preferably 30 to 60 mol%,

and more preferably 35 to 60 mol% based on 100 mol% of the structural units

(a), (b), and (c) in total for the same reasons as the hydroxyl group -containing

fluorine -containing copolymer. The content of the structural unit (b) in the ethylenieally unsaturated group -containing fluorocopolymer is 10 to 70 mol%, preferably 20 to 60 mol%, and more preferably 20 to 55 mol% based on 100 mol% of the structural units

(a), (b), and (c) in total for the same reasons as the hydroxyl group -containing fluorine -containing copolymer.

The content of the structural unit (c) in the ethylenieally unsaturated group-containing fluorocopolymer is 25 to 70 mol%, preferably 5 to 40 mol%, and more preferably 5 to 20 mol% based on 100 mol% of the structural units (a), (b), and (c) in total for the same reasons as the hydroxyl group-containing fluorine -containing copolymer. If the content of the structural unit (c) exceeds 70 mol%, the refractive index of the fluoropolymer increases. If the content of the structural unit (c) is less than 5 mol%, the physical strength of the cured product decreases.

The molecular weight of the ethylenieally unsaturated group-containing fluorocopolymer, in terms of a polystyrene-reduced number average molecular weight determined by gel-permeation chromatography (GPC) using tetrahydrofuran as a solvent, is preferably 5000 to 500,000. If the number average molecular weight is less than 5000, the cured product may have reduced mechanical strength. If the number average molecular weight is more than 500,000, the composition may have such a high viscosity that a coating operation is difficult.

The polystyrene -reduced number average molecular weight of the ethylenically unsaturated group -containing fluorocopolymer is more preferably 10,000 to 300,000, and still more preferably 10,000 to 100,000.

The ethylenically unsaturated group -containing fluorocopolymer (component (A)) is added to the composition in an amount of usually 20 to 65 mass%, preferably 20 to 50 mass%, and particularly preferably 30 to 40 mass%. If the amount of the ethylenically unsaturated group-containing fluorocopolymer is less than 20 mass%, the viscosity of the composition becomes too low, whereby the applicability may decrease when producing optical fibers. If the amount of the ethylenically unsaturated group -containing fluorocopolymer exceeds 65 mass%, the amounts of the components (B) and (C) are reduced, resulting in reduced solubility of the component (A) and difficulty in obtaining a cured product with high transparency. Component (B): The component (B) is a compound shown by the following formula (10).

wherein R⁸ represents a hydrogen atom or a methyl group, X represents a hydrogen atom or a fluorine atom, x represents 1 or 2, and y represents an integer from 2 or 8.

The component (B) is added to ensure the solubility of the component (A) together with the component (C) and to reduce the refractive index of the cured product. The component (B) is not particularly limited insofar as the component (B) is a compound shown by the formula (10). Specific examples of the component (B) include 2-perfluorooctylethyl (meth) aery late, 2,2,3,3-tetrafluoropropyl (meth) aery late, IH, lH,5H-octafluoropentyl (meth)acrylate, and the like. Suitable commercially available products include, but are not limited to, Viscoat 17F, 4F, 8F (manufactured by Osaka Organic Chemical Industry, Ltd.) and the like. Of these, 2-perfluorooctylethyl (meth)acrylate is preferable due to excellent capability of dissolving the component (A) and easy availability.

The component (B) is added to the composition in an amount of usually 20 to 60 mass%, preferably 20 to 50 mass%, and particularly preferably 20 to 45 mass%. If the amount of the component (B) is less than 20 mass%, the solubility of the component (A) may be impaired, and the refractive index of the cured product may increase. If the amount of the component (B) exceeds 70 mass%, the viscosity of the composition decreases, whereby applicability is impaired.

The mutual solubility of the ethylenically unsaturated group -containing fluorocopolymer (component (A)) and a (meth) aery late monomer is generally poor. However, the solubility of the component (A) is improved using the component (B) in combination with the component (C), whereby a homogeneous composition can be obtained. In particular, the mass ratio of the components (B) and (C) is preferably 2:3 to 5:1, and more preferably 2:3 to 4:1. (C) Compound which does not have aromatic structure and polar group and contains two or more ethylenically unsaturated groups

The component (C) added to the composition of the present invention is a compound other than the components (A) and (B) which does not have an aromatic structure and a polar group and contains two or more ethylenically unsaturated groups. Since the component (C) does not have a polar group, the component (C) can increase the solubility of the component (A) to produce a homogeneous composition by using the component (C) in combination with the component (B). Since the component (C) does not have an aromatic structure, the resulting cured product has a low refractive index.

The term "polar group" used herein includes dissociable groups such as a carboxyl group and an amino group, polarizable groups such as a carbonyl group and an alkylene oxide group having three or less carbon atoms, but excludes a hydroxyl group. There are no specific limitations to the component (C) insofar as the above conditions are satisfied. Specific examples of the component (C) include aliphatic structure -containing (me th) aery late s such as neopentyl glycol di(meth)acrylate, neopentyl glycol hydroxypivalate di(meth) aery late, trimethylolprop ane tri(meth) aery late , trimethylolprop anetrioxyethyl (meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, polyester di(meth)acrylate, 1,4-butanediol di(meth)acrylate, and 1,6-hexanediol di(meth)acrylate, and the like.

As the component (C), a monofunctional or polyfunctional aliphatic structure -containing (meth)acrylate is preferable, with neopentyl glycol di(meth) aery late or neopentyl glycol hydroxypivalate di(meth)acrylate being particularly preferable. The component (C) may be used either individually or in combination of two or more. The component (C) is added to the composition in an amount of usually 10 to 35 mass%, preferably 15 to 35 mass%, and particularly preferably 15 to 30 mass%. If the amount of the component (C) is less than 10 mass%, the solubility of the component (A) may be impaired. If the amount of the component (C) exceeds 35 mass%, the amounts of the components (A) and (B) are reduced, resulting in an increased refractive index of the cured product and poor adhesion to a core.

The composition of the present invention may further contain (D) a (meth)acrylic acid or a (meth)acrylic acid dimer. The addition of the component (D) improves adhesion between a cladding layer and a core formed of glass or quartz.

The component (D) is added to the composition in an amount of usually 0 to 10 mass%, and preferably 1 to 7 mass%. If the amount of the component (D) exceeds 10 mass%, the storage stability of the composition may be impaired.

When curing the composition of the present invention by applying light such as ultraviolet rays, it is preferable to add a photoinitiator (E).

Specific examples of the photoinitiator (E) include 1 -hydroxy cyclohexyl 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, l-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-l-one, 2-hydroxy-2-methyl-l-phenylpropan-l-one, thioxanethone, diethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl-l-[4-(methylthio)phenyl]-2-morpholino-propan-l-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, CG 24-61, Darocure 1116, 1173 (all manufactured by Ciba Specialty Chemicals Co.); Lucirin TPO (manufactured by BASF); Ubecryl P36 (manufactured by UCB); and the like. A photosensitizer may be added when using the photoinitiator (E). Suitable examples of photosensitizers, include, but are not limited to, the photosensitizer, triethylamine, diethylamine, N-methyldiethanoleamine, ethanolamine, 4-dimethylaminobenzoic acid, 4-methyl dimethylaminobenzoate, 4-ethyl dimethylaminobenzoate, 4-isoamyl dimethylaminobenzoate; Ubecryl P102, 103, 104, 105 (all manufactured by UCB); and the like. If both heat and ultraviolet rays are used to cure the curable liquid resin composition of the present invention, the photoinitiator may be used in combination with a heat polymerization initiator. The initiator (E) is added to the composition in an amount of preferably 0.1 to 10 mass%, and particularly preferably 0.3 to 7 mass%.

A compound (F) other than the components (A), (B), and (C) which does not have an aromatic structure and a polar group and contains one ethylenically unsaturated group may be added to the composition of the present invention insofar as the effects of the present invention are not impaired.

Specific examples of a compound which does not have an aromatic structure and a polar group and contains one ethylenically unsaturated group include vinyl group -containing lactams such as N-vinylpyrrolidone and N-vinylcaprolactam; vinyl ethers such as hydroxybutyl vinyl ether, lauryl vinyl ether, cetyl vinyl ether, and 2-ethylhexyl vinyl ether; acrylamides such as diacetone(meth)acrylamide, isobutoxymethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide,

N,N-dimethylaminopropyl(meth)acrylamide, and t-octyl(meth) aery lamide; alicyclic structure-containing (meth)acrylates such as isobornyl (meth)acrylate, bornyl (meth)acrylate, tricyclodecanyl (me th) aery late, dicyclopentanyl (meth)acrylate, and 4-butylcyclohexyl (meth)acrylate; aliphatic structure-containing (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth) aery late, 2-hydroxybutyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth) aery late, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth) aery late, amyl (meth) aery late, isobutyl (meth) aery late, t-butyl (meth)acrylate, pentyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth) aery late, heptyl

(meth)acrylate, octyl (meth)acrylate, isooctyl (meth) aery late, 2-ethylhexyl (meth) aery late, nonyl (meth)acrylate, decyl (meth) aery late, isodecyl (meth)acrylate, undecyl (meth) aery late, dodecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (me th) aery late, isostearyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, butoxyethyl (meth)acrylate, and ethoxydiethylene glycol (me th) aery late; and the like.

The component (F) is added to the composition in an amount of usually 0 to 30 mass%, preferably 0 to 25 mass%, and particularly preferably 0 to 20 mass%. If the amount of the component (F) exceeds 30 mass%, the transparency of the composition and its cured product may be impaired.

An ethylenically unsaturated group-containing compound (G) other than the components (A), (B), (C), and (F) may be added to the composition of the present invention insofar as the effects of the present invention are not impaired. Suitable examples of the component (G), an aromatic structure-containing (meth) aery late, a polar group -containing (meth) aery late such as a carboxyl group -containing (meth)acrylate and an alkylene oxide structure -containing (meth)acrylate, and the like. Since the component (G) not only tends to increase the refractive index of the cured product in the same manner as an aromatic structure -containing (meth)acrylate, but also tends to decrease the solubility of the component (A) in the same manner as a polar group -containing (meth) aery late, the amount of the component (G) is preferably 5 mass% or less based on 100 mass% of the composition.

Suitable commercially available products of the component (G), Yupimer UV, SA-1002 (manufactured by Mitsubishi Chemical Corp.), Aronix M-215, M-315, M-325 (manufactured by Toagosei Co., Ltd.), Sartomer CN4000 (manufactured by Sartomer Co., Inc.), Aronix TO-1210 (manufactured by Toagosei Co., Ltd.), and the like.

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 improvers, and coating surface improvers may optionally be added to the composition of the present invention insofar as the characteristics of the present invention are not adversely affected. The viscosity, at 25⁰C, of the composition of the present invention is preferably from about 0.8 to about 6.0 Pa s, and particularly preferably from about 1.5 to about 5.0 Pa s.

After the radiation curable composition is prepared it may be applied to the core of an optical fiber by following the steps of the following process:

A) providing a core of glass, quartz or transparent resin;

In step D), the curable liquid resin composition of the present invention is cured by applying radiation. It is possible to cure the curable liquid resin composition by applying radiation and heat in combination. The term "radiation" used herein refers to infrared rays, visible rays, ultraviolet rays, X-rays, electron beams, α-rays, B-rays, γ-rays, and the like.

The cured product of the curable liquid resin composition of the present invention preferably has a Young's modulus from about 200 MPa to about 500 MPa. When forming an upjacket layer, the composition is preferably applied to a thickness of from about 100 μm to about 350 μm. A cable layer formed of a thermoplastic resin may be provided on the outer surface of an optical fiber upjacket layer.

Examples

The following examples further illustrate the invention but, of course, should not be construed as in any way limiting its scope.

Preparation Example 1 (synthesis of hydroxyl group -containing fluoropolymer)

A 500-mL separable flask was charged with 66 g of

2-perfluorooctylethyl acrylate, 28 g of isobornyl acrylate, 6 g of hydroxyethyl acrylate, and 150 g of 2-butanone (methyl ethyl ketone) as a solvent. After the addition of 1 g of azobisisobutyronitrile, the mixture was heated in an oil bath. The mixture was reacted at 8O⁰C with stirring under reflux. After six hours, the oil bath was removed to terminate the reaction to obtain a polymer solution with a solid content of about 40%. The resulting polymer solution was poured into methanol to precipitate the polymer. The precipitate was washed with methanol and dried at 5O⁰C under vacuum to obtain 80 g of a hydroxyl group-containing fluoropolymer. The conversion rate of the monomer was 95% or more. This polymer is referred to as "hydroxyl group -containing fluoropolymer 1". Preparation Example 2 (synthesis 2 to 5 of hydroxyl group -containing fluoropolymer)

Hydroxyl group -containing fluoropolymers were obtained in the same manner as in Preparation Example 1 according to Table 1. The conversion rate of the monomer was 95% or more in each case. Table 2 shows the amounts (mol%) of the components (a), Qo), and (c) provided that the total amount of the components (a), (b), and (c) is 100 mol%. In Tables 1 and 2, the component (a) is 2-perfluorooctylethyl acrylate, the component (b) is isobornyl acrylate, and the component (c) is hydroxyethyl acrylate.

[Table 1]

[Table 2]

Preparation Example 3 (synthesis of ethylenically unsaturated group -containing fluorocopolymer (A))

A separable flask (1 L) equipped with an electromagnetic stirrer, a glass condensers, and a thermometer was charged with 41.0 g of the hydroxyl group -containing fluoropolymer 1, 0.01 g of

2,6-di-t-butylmethylphenol as a polymerization inhibitor, 41.0 g of

2-perfluorooctylethyl (meth) acrylate as a dilution solvent, and 17.0 g of neopentyl glycol di(meth)acrylate. The hydroxyl group -containing fluoropolymer 1 dissolved at 5O⁰C. The mixture was stirred until a transparent and homogeneous solution was obtained.

After the addition of 0.2 g of 2-methacryloyloxyethyl isocyanate to the system, the mixture was stirred until a homogeneous solution was obtained.

0.030 g of dibutyltin dilaurate was then added to the mixture to initiate a reaction. The mixture was stirred at 55 to 65⁰C for five hours to obtain an ethylenically unsaturated group -containing fluoropolymer. The resulting polymer is referred to as "ethylenically unsaturated group -containing fluoropolymer 1". The diluent used in the synthesis may be used as a component of the UV curable resin. Preparation Example 4

Ethylenically unsaturated group -containing fluoropolymers 2 to 5 were obtained in the same manner as described above using the hydroxyl group-containing fluoropolymers 2 to 5, respectively.

Examples 1 to 7 and Comparative Examples 1 to 5 A reaction vessel equipped with a stirrer was charged with components shown in Table 3. The mixture was stirred for one hour while controlling the liquid temperature at 5O⁰C to obtain a curable liquid resin composition. Test Example 1

The curable liquid resin compositions obtained in the examples and comparative examples were cured using the following method to prepare specimens. The specimens were evaluated as described below. The results are shown in Table 3.

1. Viscosity

The viscosity at 25⁰C of the compositions obtained in the examples and comparative examples was measured using a B-type viscometer.

2. Young's modulus The curable liquid resin composition was applied to a glass plate using an applicator bar with a gap size of 250 μm. The composition was cured in nitrogen by applying ultraviolet rays at a dose of 1 J/cm² to obtain a Young's modulus measurement film. The 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 23⁰C and a humidity of 50%. The Young's modulus was calculated from the tensile strength at a tensile rate of 1 mm/min. and a strain of 2.5%.

3. Breaking strength and elongation at break The breaking strength and the elongation at break of the specimen were measured using a tensile tester ("AGS-50G" manufactured by Shimadzu Corp.). Treating rate: 50 mm/min Benchmark distance (measurement distance): 25 mm Measurement temperature: 23⁰C Relative humidity (abbreviated "RH"): 50% RH

4. Refractive index

The resin composition was applied to a glass plate to a thickness of 200 μm using an applicator bar. Ultraviolet rays were applied to the composition in nitrogen at a dose of 1.0 J/cm² to obtain a specimen. The refractive index at 25⁰C of the specimen was measured using an Abbe refractometer (manufactured by Atago Co., Ltd.) in accordance with JIS K7105. In the Examples of the instant claimed invention the Refractive Index is reported to be from about 1.400 to about 1.430.

5. Transparency (Haze value)

The total light transmittance of the cured film was measured in accordance with JIS K7105 using a color haze meter (manufactured by Suga Test Instruments Co., Ltd.). The measurement was carried out using a cured film immediately after preparation and a cured film after allowed to stand at 12O⁰C for 72 hours. In Table 3, "whitening" indicates that each component of the composition was not completely dissolved so that the composition was cloudy when observed with the naked eye. 6. Adhesion

The adhesion stability of the cured products of the compositions obtained in the examples and comparative examples was evaluated. The liquid composition was applied to a sliding glass plate using an applicator with a gap size of 381 μm. The applied liquid composition was irradiated with ultraviolet rays at a dose of 0.1 J/cm² in a nitrogen atmosphere to obtain a cured film with a thickness of about 200 μm. The cured film on a slide was allowed to stand at a temperature of 23⁰C and a relative humidity of 50% for 24 hours. A sample in the shape of a strip was prepared from the cured film so that the portion to be tensed had a width of 10 mm. The sample was subjected to an adhesion test in accordance with JIS Z0237 using a tensile tester. The adhesion was calculated from the tensile strength at a tensile rate of 50 mm/min. In Table 3, "broke" indicates that the cured film and the slide were not separated and the cured film broke due to high adhesion.

7. Curing speed The composition was applied to a quartz glass plate using an applicator with a gap size of 200 μm. The applied composition was irradiated with ultraviolet rays by using a 3.5 kW metal halide lamp ("SMX-3500/F-OS" manufactured by ORC Co., Ltd.) at doses of 20 mJ/cm² and 1.0 J/cm² in air to form a cured film. After allowing the cured film to stand at a temperature of 23⁰C and a relative humidity of 50% for 24 hours, a sample in the shape of a strip was prepared from the cured film so that the portion to be tensed had a width of 6 mm and a length of 25 mm. The Young's modulus (MPa) of the specimen was measured using a tensile tester. A value obtained by dividing the Young's modulus at a UV dose of 20 mJ/cm² by the Young's modulus at a UV dose of U/cm2 was taken as the curing speed. [Table 3]

Viscoat 17F: 2-perfluorooctylethyl (meth)acrylate (manufactured by Osaka

Organic Chemical Industry, Ltd.)

Irgacure 184: 1 -hydroxy cyclohexyl phenyl ketone (manufactured by Ciba Specialty Chemicals Co., Ltd.)

Lucirin: 2,4,6-trimethylbenzoyldiphenylphosphine oxide (manufactured by

BASF Japan)

Kynar ADS: copolymer of VDF/TFE/HFP (vinylidene fluoride, tetrafluoroethylene, and hexafiuoropropylene) (manufactured by Arkema Co.)

As is clear from Table 3, the product of each example was excellent in the composition viscosity and the Young's modulus, mechanical strength

(breaking strength and elongation at break), refractive index, and transparency (haze) of the cured product. The cured product maintained excellent transparency even after having been exposed to a high temperature.

The composition also exhibited excellent adhesion to quartz as a core material.

The cured product of Comparative Example 1, which contained an excessive amount of the component (C), showed poor transparency due to a decrease in solubility of the component (A) caused by an imbalance proportion of the components (B) and (C).

In Comparative Example 2 using the hydroxyl group -containing fluoropolymer which does not contain an ethylenically unsaturated group instead of the component (A), the composition had a low viscosity and poor transparency due to the inability of the fluoropolymer to dissolve in the composition.

In Comparative Example 3 using a fluoropolymer which does not fall under the component (A), the composition had poor transparency due to the inability of the fluoropolymer to dissolve in the composition.

In Comparative Examples 4 and 5 in which the component (C) was not used, since the solubility of the hydroxyl group-containing fluoropolymer in the polymerization solvent decreased, a resin composition could not be obtained. All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms "comprising," "having," "including," and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to,") unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

What is Claimed:

1. A radiation-curable resin composition comprising:

(A) 20 to 65 mass% of an ethylenically unsaturated group-containing

fluorocopolymer;

(B) 20 to 60 mass% of a compound of the following formula,

CH₂=CR⁸COO(CH₂)_x(CF2)_yX

(C) 10 to 35 mass% of a compound other than the components (A) and (B) which does not have an aromatic structure and a polar group and contains two or more ethylenically unsaturated groups.

2, The radiation-curable resin composition of claim 1, wherein the component (A) is an ethylenically unsaturated group -containing fluorocopolymer having a structural unit (a) shown by the following formula

(D, structural unit (a): H R¹

I I

-c—c —

I I H C=O ₍₁₎

O

^Cm^H2m (CFjOnF

wherein R¹ represents a hydrogen atom or a methyl group, m represents an integer from 1 to 8, and n represents an integer from 1 to 20, a structural unit (b) shown by the following formula (2), structural unit (b):

H ir

I I

I I H C=O (2)

O

R-

wherein R² represents a hydrogen atom or a methyl group, and R³ represents a monovalent organic group having an alicyclic structure, and a structural unit (c) shown by the following formula (3), structural unit (c):

wherein R⁴ represents a hydrogen atom or a methyl group, R⁵ represents a group shown by the following formula (4) or (5), and v represents an integer from 1 to 20,

R⁶

H

-C-N- (CH₂)₂ 0-C-C=CH_{2 (4})

O O

wherein R⁶ represents a hydrogen atom or a methyl group.

3. The radiation-curable resin composition of claim 1 or 2, further

comprising (D) (meth) acrylic acid or a (meth)acrylic acid dimer.

4. The radiation-curable resin composition of any one of claims 1,

2 or 3, further comprising (E) a photoinitiator.

5. The radiation-curable resin composition of any one of claims 1,

2, 3 or 4, which is used to form an optical fiber cladding layer.

6. A cured film comprising a cured product of the

radiation-curable liquid resin composition of any one of claims 1, 2, 3, 4 or 5.

7. A polymer-clad optical fiber comprising a core formed of glass, quartz, or a transparent resin and a cladding layer comprising the cured film of claim 6 and provided in contact with the exterior of the core.

8. A process of making a polymer-clad optical fiber comprising the steps of A) providing a core of glass, quartz or transparent resin;

9. A radiation-curable composition of Claim 1, wherein the refractive index is from about 1.400 to about 1.430.