Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-08-10
2003-08-05
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C385S128000
Reexamination Certificate
active
06602929
ABSTRACT:
BACKGROUND OF THE INVENTION
Optical communications fibers include a variety of types such as quartz glass, multi-component glass and plastic fibers. In reality, quartz glass fibers are vastly used in a wide variety of applications because of their light weight, low loss, high durability and high transmission capacity. Since quartz glass fibers are very thin and sensitive to external factors, quartz glass fibers for optical communications are generally of the construction that a quartz glass fiber which is spun from a melt is coated with a liquid curable resin capable of curing to a soft state, the coating is cured to form a primary coating, and the primary coating is protected with a secondary coating using a liquid curable resin capable of curing to a hard state.
The primary coating material is required to have a low Young's modulus and low temperature dependence thereof for preventing microbend losses from being induced by external stresses or temperature changes. Other requirements on the primary coating material are durability (heat and water resistance), low water absorption, low hydrogen release, and a high refractive index. The secondary coating material is required to have a sufficient hardness, flexibility, resistance to acid and alkali attacks, and low water absorption.
For productivity improvement, the drawing rate of optical fiber is increased in the recent years. In this regard, both the primary and secondary coating materials are required to be fast curing and low viscous. To meet such requirements, UV-curable resin compositions based on urethane acrylate resins were proposed. JP-B 1-19694 and Japanese Patent Nos. 2,522,663 and 2,547,021 disclose liquid UV-curable resin compositions comprising a urethane acrylate oligomer, a reactive monomer, and a polymerization initiator. These compositions, however, encounter a limit in reducing water absorption or viscosity since acrylic groups are introduced into a straight chain polyether or polyester at its molecular chain ends through urethane bonds so that the concentration of urethane bonds is high.
SUMMARY OF THE INVENTION
An object of the invention is to provide a liquid radiation-curbable resin composition having a low viscosity to accommodate for high-speed coating and curing into a film with improved properties, especially a minimized water absorption. Another object is to provide a coating composition for optical fibers, and an optical fiber having a cured coating layer thereof.
It has been found that a liquid radiation-curable resin composition mainly comprising the reaction product obtained by reacting a polyether of the following general formula (1):
CH
2
═CRCOO(C
m
H
2m
O)
n
H (1)
wherein R is hydrogen or methyl, m is a number of 2 to 6, and n is a number of 6 to 100, with a diisocyanate having two isocyanate groups in a molecule, or the reaction product obtained by reacting a polyether of formula (1) and a (meth)acrylate compound containing a hydroxyl group and having a molecular weight of up to 300 with a diisocyanate having two isocyanate groups in a molecule is effectively curable. Since the reaction product has a low concentration of urethane bonds within a molecule, the composition can be reduced in both water absorption and viscosity.
In one aspect, the invention provides a liquid radiation-curable resin composition comprising the reaction product obtained by reacting (A) a polyether of the following general formula (1):
CH
2
═CRCOO(C
m
H
2m
O)
n
H (1)
wherein R is hydrogen or methyl, m is a number of 2 to 6, and n is a number of 6 to 100, with (B) a diisocyanate having two isocyanate groups in a molecule, in a molar ratio from 1.8/1 to 2.2/1.
In another aspect, the invention provides a liquid radiation-curable resin composition comprising the reaction product obtained by reacting the components (A) and (B) and (C) a (meth)acrylate compound containing a hydroxyl group and having a molecular weight of up to 300, in a molar ratio of (A)/(B)/(C) of (1.8-1.2)/1/(0.8-1.2).
In a further aspect, the invention provides a coating composition for optical fibers comprising the liquid radiation-curable resin composition defined above.
An optical fiber having a coating layer of the coating composition in cured stated is also contemplated herein.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Component (A) is a polyether having a (meth)acryloyl group at one end of a molecular chain and a hydroxyl group at the other end, represented by the general formula (1).
CH
2
═CRCOO(C
m
H
2m
O)
n
H (1)
Herein R is hydrogen or methyl. It desired from the curing standpoint that R be hydrogen. Letter m is a number of 2 to 6, and desirably 3 to 5 while the polyether may be either a homopolymer or a copolymer. Letter n is a number of 6 to 100, and may be suitably selected in this range depending on the desired properties of a cured film. The polyether may be prepared by adding an alkylene oxide (e.g., propylene oxide, butylene oxide or tetrahydrofuran) to (meth)acrylic acid. The polyethers having a (meth)acryloyl group and a hydroxyl group at opposite ends of a molecular chain may be used alone or in admixture of two or more.
Component (B) is a diisocyanate having two isocyanate groups in a molecule, which may be selected from organic diisocyanates such as aromatic, aliphatic and alicyclic diisocyanates. Illustrative examples include tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, hydrogenated 4,4′-diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate. Of these, tolylene diisocyanate and isophorone diisocyanate are preferred.
Component (C) is a (meth)acrylate compound containing a hydroxyl group and having a molecular weight of up to 300, examples of which include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2- or 3-hydroxypropyl (meth)acrylate, 2- or 4-hydroxybutyl (meth)acrylate, and neopentyl glycol mono(meth)acrylate, and 4-hydroxycyclohexyl (meth)acrylate, cyclohexane-1,4-dimethanol mono(meth)acrylate, trimethylol propane di(meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalic acid, 3-acryloyloxyglycerin mono(meth)acrylate, and 2-hydroxy-1-(meth)acryloxy-3-(meth)acryloxypropane. These hydroxyl-containing (meth)acrylate compounds may be used alone or in admixture of two or more. The preferred hydroxyl-containing (meth)acrylate compounds are hydroxy C
2-4
alkyl (meth)acrylates, especially 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate.
The liquid radiation-curable resin composition of the invention contains as a main ingredient the reaction product obtained by reacting the above-described components (A) and (B) or components (A), (B) and (C). The reaction is based on reaction between terminal hydroxyl groups in component (A) and isocyanate groups in component (B) and in the latter case, further reaction between hydroxyl groups in component (C) and isocyanate groups in component (B), both of which may be effected in a conventional manner. The reaction product of components (A), (B) and (C) may be obtained by first reacting a polyether having a (meth)acryloyl group at one end of a molecular chain and a hydroxyl group at the other end with an isocyanate group to form a urethane and then reacting the remaining isocyanate group with a hydroxyl-containing (meth)acrylate compound. For the urethane-forming reaction, an amine catalyst or a metal catalyst such as a tin or lead catalyst may be used.
In the reaction of components (A) and (B), they are used in a molar ratio (A)/(B) of from 1.8/1 to 2.2/1. In the reaction of components (A), (B) and (C), they are used in a molar ratio (A)/(B)/(C) of (0.8-1.2)/1/(0.8-1.2).
These reaction products preferably have a viscosity of about 1,000 to 30,000 mPa·s at 25° C., and especially about 3,000 to 20,000 mPa·s at 25° C.
In addition to the reaction products, the liquid radiation-curable resin compositions of the invention may further contain ethyleni
Kondo Kazunori
Kozakai Shouhei
Ohba Toshio
Birch & Stewart Kolasch & Birch, LLP
Gorr Rachel
Shin-Etsu Chemical Co. , Ltd.
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