Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
1999-06-24
2001-03-06
Healy, Brian (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S123000, C385S141000, C427S487000, C427S489000, C427S163200
Reexamination Certificate
active
06198867
ABSTRACT:
This invention relates to a radiation-curable liquid resin composition which has a low viscosity and cures into a product having a low Young's modulus and suitable as a primary coating or buffer layer on optical fibers. It also relates to an optical fiber covered with a cured product of the composition.
BACKGROUND OF THE INVENTION
Optical fibers for data communication include a variety of fibers such as quartz glass, multi-component glass and plastic fibers. In practice, because of their light weight, low loss, durability, and high transmission capacity, quartz glass optical fibers are vastly used in a wide range of application. Since the quartz glass optical fibers, however, are very thin and susceptible to changes by external factors, quartz glass fibers as melt spun are generally provided with a primary coating and then with a secondary coating for protecting the primary coating. The primary coating is formed by applying a liquid curable resin of the type giving a soft cured product, followed by curing. The secondary coating is formed by applying a liquid curable resin of the type giving a hard cured product, followed by curing.
Properties required for the primary coating material include a low Young's modulus and low temperature dependency thereof for preventing microbending losses by external stresses or temperature changes, durability in terms of heat resistance and water resistance, low water absorption, low hydrogen generation, a high refractive index, and a fast-curing ability and low viscosity for allowing the drawing speed of optical fibers to be increased for improved productivity. To meet these requirements, UV-curable compositions based on urethane acrylate were proposed in the past. For example, JP-B 1-19694 and Japanese Patent Nos. 2,522,663 and 2,547,021 disclose liquid UV-curable compositions comprising a urethane acrylate oligomer, a reactive monomer, and a polymerization initiator. These compositions, however, fail to meet some of the above requirements, that is, a low Young's modulus and good low-temperature properties (minimized temperature dependency of Young's modulus), low water absorption, and low viscosity, because they are based on urethane acrylate oligomers of urethane bond-bearing polyethers or polyesters.
For reducing Young's modulus and improving low-temperature properties, JP-B 4-29619 corresponding to U.S. Pat. No. 4,496,210 and JP-A 61-21121 disclose liquid UV-curable compositions using a silicone urethane acrylate containing an organic polysiloxane. Urethane bonds are contained likewise. Because of the structural factors of urethane bonds (specifically, rigidity of the structure and the hydrogen bond in the urethane bond), these compositions are not satisfactory to some of the above requirements, that is, a low Young's modulus and a low viscosity. The embodiments described in these patents suggest that the organic polysiloxane is limited to a dimethylsiloxane skeleton, which has a low refractive index and is less compatible with reactive monomers. It is then difficult to design a liquid UV-curable composition capable of satisfying the required values.
SUMMARY OF THE INVENTION
An object of the invention is to provide a low-viscosity radiation-curable liquid resin composition which cures into a product having a low Young's modulus and experiencing a less change of Young's modulus at low temperature. Another object of the invention is to provide an optical fiber coated with a cured product of this composition.
The invention addresses a radiation-curable liquid resin composition comprising a (meth)acryl group-bearing oligomer or polymer as a main component. The inventor has found that an organopolysiloxane having a (meth)acryl group at each end of its molecular chain, containing at least 15 mol % of aromatic hydrocarbon groups based on the entire organic groups attached to silicon atoms, and being free of a urethane bond within the molecule is fully compatible with a reactive monomer and when it is used as the main component, the resulting radiation-curable liquid resin composition has a low viscosity and cures into a product having a low Young's modulus and a high refractive index. Especially when a monomer based on an organosiloxane skeleton and having an ethylenically unsaturated group is used as the reactive monomer, the cured product experiences a minimal change of Young's modulus at low temperatures.
The invention provides a radiation-curable liquid resin composition comprising (A) an organopolysiloxane having a (meth)acryl group at either end of its molecular chain, containing at least 15 mol % of aromatic hydrocarbon groups based on the entire organic groups attached to silicon atoms, and being free of a urethane bond within the molecule, (B) a compound having at least one ethylenically unsaturated group in a molecule, and (C) a photopolymerization catalyst.
This composition is effective for the coating of optical fibers. Therefore, an optical fiber covered with a cured product of the composition is also contemplated herein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(A) Urethane Bond-free, (meth)Acryl Group-bearing Organopolysiloxane
The first component of the radiation-curable liquid resin composition according to the invention is an organopolysiloxane which has a (meth)acryl group at either end of its molecular chain, contains at least 15 mol % of aromatic hydrocarbon groups based on the entire organic substituents attached to silicon atoms, and is free of a urethane bond within the molecule; especially a linear diorganopolysiloxane containing at least 15 mol % of aromatic hydrocarbon groups based on the entire organic substituents (that is, substituted or unsubstituted monovalent hydrocarbon groups) attached to silicon atoms, excluding the (meth)acryl group-bearing organic groups attached to the silicon atoms at both ends of the molecular chain. In the specification, (meth)acryl group means acryl group and/or methacryl group.
This organopolysiloxane is the base polymer of the liquid resin composition according to the invention and is basically a linear diorganopolysiloxane whose backbone consists of recurring diorganosiloxane units. The number of silicon atoms in the molecule (or the degree of the polymerization) is generally about 80 to about 1,200, preferably about 100 to about 1,000. Preferably the (meth)acryl group is attached to the silicon atom at each end of the molecular chain as a (meth)acryloxyalkyl group.
Typically, the organopolysiloxane is represented by the following general formula (1).
Herein R
1
is a hydrogen atom or a methyl group, R
2
, which may be the same or different, is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms, R
2
contains at least 15 mol % of aromatic hydrocarbon groups, m is an integer of 1 to 5, and n is an integer of 80 to 1,200, and preferably 100 to 1,000.
Formula (1) is described in detail. R
1
is a hydrogen atom or a methyl group, although the hydrogen atom is preferred when the curing rate of the composition upon exposure to radiation is taken into account. R
2
represents substituted or unsubstituted monovalent hydrocarbon groups having 1 to 10 carbon atoms, preferably substituted or unsubstituted monovalent hydrocarbon group having no aliphatic unsaturated bonds, for example, straight, branched or cyclic alkyl groups of 1 to 10 carbon atoms, especially 1 to 6 carbon atoms, aryl groups of 6 to 10 carbon atoms, and aralkyl groups of 7 to 10 carbon atoms. Exemplary groups of R
2
are alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, cyclohexyl, octyl, nonyl and decyl; aryl groups such as phenyl, tolyl, xylyl, and ethylphenyl; aralkyl groups such as benzyl, &bgr;-phenylethyl, and &agr;-methyl-&bgr;-phenylethyl; and substituted ones of these groups wherein some of the hydrogen atoms are replaced by halogen atoms (e.g., F, Cl and Br), typically halo-substituted alkyl groups such as chloromethyl, bromoethyl, and 3,3,3-trifluoropropyl. Methyl and phenyl group
Iwasaki Satoshi
Kozakai Shouhei
Yamamoto Akira
Healy Brian
Shin-Etsu Chemical Co. , Ltd.
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