Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-07-14
2003-06-17
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S007000, C522S025000, C522S028000, C522S090000, C522S096000, C522S100000, C522S101000, C522S103000, C522S111000, C522S113000, C522S122000, C522S134000, C522S143000, C428S378000, C428S426000, C428S441000
Reexamination Certificate
active
06579914
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to compositions for coating glass surfaces and, more specifically, coating compositions for optical waveguides such as optical fibers, the coating compositions having improved mechanical characteristics and adhesion to the glass.
2. Description of the Related Prior Art
Optical fiber waveguides have been coated with plastic compositions of various materials in order to protect the fiber and increase its tensile strength. The coating materials that have been utilized include polyvinylidene fluoride, polymethylsiloxane, polyesters, polyimides, polyester imides, epoxides and polyurethanes.
For example, U.S. Pat. No. 4,099,837 discloses a coating composition for an optical fiber waveguide, the coating composition is a prepolymer made by mixing certain epoxy resins and reacting the mixture with acrylic and/or methacrylic acid. The mixture contains an aliphatic-type glycidyl ether and an aromatic-type glycidyl ether, such as a mixture of 1,4-butanediol diglycidyl ether and a diglycidyl ether of bisphenol A or substituted, e.g., halogenated, bisphenol A, such as brominated bisphenol A. The proportion of aliphatic diglycidyl ether to aromatic diglycidyl ether is 0.4 to 1.0 on a weight ratio basis. The epoxy resin mixture is reacted with acrylic and/or methacrylic acid on an equivalent basis with between 0.5 to 1.0 mol of acid per epoxy equivalent weight, and preferably 0.8-0.95 mol of acid per equivalent weight.
U.S. Pat. No. 4,311,726 discloses a method for manufacturing an optical waveguide with a plastic layer of the epoxy-acrylate type located on the lightguide fiber. A radiation-hardenable prepolymer composition is applied to the lightguide fiber immediately after the fiber-drawing process. The prepolymer is hardened by actinic radiation and includes an acylated hydroxy ester of acrylic and/or methacrylic acid and an epoxide.
U.S. Pat. No. 5,229,433 discloses a liquid, radiation-curable coating composition for the coating of glass surfaces. The coating composition includes 56 to 89% by weight of one or more diethylenically unsaturated polyurethanes optionally containing urea groups, 3 to 30% by weight of one or more ethylenically unsaturated monomers, 0.5 to 8% by weight of one or more photoinitiators and 0.05 to 6% by weight of an alkoxysilane. The ethylenically unsaturated monomers include one or more ethylenically unsaturated monomers containing carboxyl groups, optionally together with other ethylenically unsaturated monomers, and the alkoxysilane contains epoxide groups. The coating compositions are used for the coating of optical glass fibers.
U.S. Pat. No. 5,985,952 discloses a radiation curable primary coating composition for coating an optical fiber composed of a component having a first end and a second end, a sauturated aliphatic backbone based upon a polyethylene/butylene structure, and at least one epoxide group at the first end of the component and at least one reactive functional group at the second end. The composition described also contains a mixture of acrylate monomers, one being monofunctional and one being at least difunctional. The patent also teaches the use of vinyl ether monomers in conjunction with the aliphatic backbone/epoxide moiety to form an IPN.
While the conventional coating compositions have been adequate for most applications, it would be desirable to be able to tailor the properties of a coating formulation for improved stress relaxation properties and still maintain good mechanical characteristics and adhesion to glass.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide a new coating composition for optical fibers, whereby the characteristics of the cured coating can surprisingly be tailored to achieve a desired optical fiber coating specification or specifications.
Another object of the invention is to provide optical fibers coated with the coating composition in accordance with the present application.
These objectives and other objectives are achieved by providing a liquid, radiation curable composition for coating an optical fiber, and a optical fiber coated therewith. The coating composition includes an aliphatic epoxide, a urethane acrylate oligomer, a cationic photoinitiator, a free radical photoinitiator, and a reactive diluent. The cationic photoinitiator is present in the composition in an amount effective to initiate polymerization of the aliphatic epoxide, and the free radical photoinitiator is present in the composition in an amount effective to initiate polymerization of the urethane diacrylate oligomer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides an improved optical fiber coating composition that can be tailored by adjusting the molecular weight and polydispersity of the components of the composition to meet a particular set of optical fiber coating specifications for both primary and secondary coatings. As one skilled in the art would readily recognize, the properties of the coating compositions in accordance with the present invention can also be tailored by controlling the cure conditions, such as temperature, and level of oxygen present in the cure environment.
Compositions in accordance with the present invention include an aliphatic epoxide, a urethane acrylate oligomer, a reactive diluent, and suitable photoinitiators for the aliphatic epoxide and the urethane acrylate oligomer. While not wishing to be bound by theory, it is believed that the composition in accordance with the present invention forms an interpenetrated polymer network. In any event, the photocured composition while relatively hard, has some flexibility between the polymer chains, and can advantageously be tailored to meet the desired characteristic or characteristics of the coating.
Again, while not wishing to be bound by theory, it is believed that the aliphatic epoxide polymerizes under the influence of the cationic photoinitiator. Also, the urethane acrylate polymerizes under the influence of the free radical photoinitiator with some copolymerization with the reactive diluent. However, there is no or substantially no copolymerization between the aliphatic epoxide and the urethane acrylate.
Coating compositions in accordance with the present invention may advantageously be utilized for both primary and secondary coatings for optical fibers. As used herein, the term “primary coating” is defined as that coating which directly contacts the glass portion of the optical fiber. The primary coating should be liquid at room temperature. The primary coating should have a viscosity suitable for high speed processing, and the primary coating should have a high cure speed. The primary coating should exhibit good adhesion to glass to prevent premature delamination of the coating from the glass portion of the optical fiber. The primary coating should have a low modulus at lower temperatures to minimize the effects of microbend attenuation due to small stresses on the optical fiber itself. The primary coating should have a refractive index high enough to ensure that errant signals escaping from the glass core are refracted back to the core of the optical fiber.
As used herein, the term “secondary coating” is defined as the coating which covers the primary coating on the optical fiber. The secondary coating should have sufficient modulus to give impact resistance and to provide a protective barrier, and give tensile strength to the optical fiber. The secondary coating should exhibit little physical change over a wide temperature range, good resistance to water and solvent absorption and have good color stability. Both primary and secondary coatings should exhibit good characteristics of adhesion, but should still be strippable, such as for field splicing, etc.
When used as primary coatings, cured coatings in accordance with the present invention preferably have a glass transition temperature (T
g
) of from about −60 C. to about 0° C., more preferably from about −50 to about −30° C., and most preferably about &mi
Gantt Todd W.
Khudyakov Igor V.
Overton Bob J.
Purvis Michael B
Alcatel
McClendon Sanza L.
Seidleck James J.
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