Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2001-12-26
2003-07-29
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...
C522S097000, C528S049000, C528S075000, C560S025000, C428S375000, C428S378000
Reexamination Certificate
active
06599956
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to optical fiber coating compositions, and, more particularly, to fiber optic coating compositions that include a non-crystal-forming oligomer, and to optical fibers coated with such compositions.
2. Description of Related Art
Optical glass fibers are frequently coated with two or more superposed radiation-curable coatings which together form a primary coating immediately after the glass fiber is produced by drawing in a furnace. The coating which directly contacts the optical glass fiber is called the “inner primary coating” and an overlaying coating is called the “outer primary coating.” In some references, the inner primary coating is also called simply the “primary coating” and the outer primary coating is called a “secondary coating.” Inner primary coatings are softer than outer primary coatings.
Single-layered coatings (“single coatings”) can also be used to coat optical fibers. Single coatings generally have properties (e.g., hardness) which are intermediate to the properties of the softer inner primary and harder outer primary coatings.
The relatively soft inner primary coating provides resistance to microbending which results in attenuation of the signal transmission capability of the coated optical fiber and is therefore undesirable. The harder outer primary coating provides resistance to handling forces such as those encountered when the coated fiber is ribboned and/or cabled.
Optical fiber coating compositions, whether they are inner primary coatings, outer primary coatings, or single coatings, generally comprise, before cure, a mixture of ethylenically-unsaturated compounds, often consisting of one or more oligomers dissolved or dispersed in liquid ethylenically-unsaturated diluents and photoinitiators. The coating composition is typically applied to the optical fiber in liquid form and then exposed to actinic radiation to effect cure.
For the purpose of multi-channel transmission, optical fiber assemblies containing a plurality of coated optical fibers have been used. Examples of optical fiber assemblies include ribbon assemblies and cables. A typical ribbon assembly is made by bonding together a plurality of parallel oriented, individually coated optical fibers with a matrix material. The matrix material has the function of holding the individual optical fibers in alignment and protecting the fibers during handling and installation. Often, the fibers are arranged in “tape-like” ribbon structures, having a generally flat, strand-like structure containing generally from about 2 to 24 fibers. Depending upon the application, a plurality of ribbon assemblies can be combined into a cable which has from several up to about one thousand individually coated optical fibers. An example of a ribbon assembly is described in published European patent application No. 194891. A plurality of ribbon assemblies may be combined together in a cable, as disclosed, for example, in U.S. Pat. No. 4,906,067.
The term “ribbon assembly” includes not only the tape-like ribbon assembly described above, but optical fiber bundles as well. Optical fiber bundles can be, for example, a substantially circular array having at least one central fiber surrounded by a plurality of other optical fibers. Alternatively, the bundle may have other cross-sectional shapes such as square, trapezoid, and the like.
Coated optical fibers whether glass, or as has come into use more recently, plastic, for use in optical fiber assemblies can be subject to low temperature, and thus the coating must be stable at low temperature to avoid attenuation of the signal in the fiber optic. Moreover, coating compositions that are not stable at low temperatures are prone to crystallize or solidify when transported or stored at low temperatures. Before the coatings can be applied to a fiber they must be warmed sufficiently, as for example, by standing at room temperature, to melt the solids in order to avoid attenuation problems or the like when the coating is applied. Coatings for optical fibers heretofore known have not been entirely satisfactory in terms of their low temperature stability.
Despite the efforts of the prior art to provide materials and methods to impart low temperature stability optical fibers, there remains a need for coatings which are stable at low temperature while satisfying the many diverse requirements desired, such as, improved curing and enhanced cure speeds, and versatility in application while still achieving the desired physical characteristics of the various coatings employed. More particularly, there remains a need for a fiber-optic coating composition generally, and in particular, for an inner primary coating composition, which is stable at low temperature and which freezes below 0° C., or melts below 0° C. or both.
SUMMARY OF THE INVENTION
The present invention provides an improved radiation-curable coating composition having a freezing temperature below about 0° C. for coating optical fiber. The coating composition of the present invention comprises a reactive functionality-terminated urethane oligomer which comprises the reaction product of (i) a semi-crystalline polyol, (ii) a non-crystalline polyol, (iii) at least one isocyanate, and (iv) an endcapping compound capable of supplying the reactive functionality terminus. The oligomer is formed by reacting the semi-crystalline polyol and the non-crystalline polyol in the presence of isocyanate. In one embodiment of the invention, the mole ratio of the semi-crystalline polyol to the non-crystalline polyol is between 1:10 and 10:1, preferably between 3:1 and 1:6, more preferably between 2:1 and 1:3. Preferably, the stoichiometry of the respective components is chosen such that, on average, at least 50% of the oligomers contains a non-crystalline polyol. In another embodiment of the invention, the mole ratio of semi-crystalline polyol to non-crystalline polyol is at least 1:1 in the reaction process used to form the oligomer. The mole ratio of semi-crystalline polyol to non-crystalline polyol is also desirably at least 1:1 in the resulting oligomer.
In some embodiments of the invention, the composition has a freezing temperature below about 0° C., a melting temperature below 0° C., or it has both a freezing and melting temperature below 0° C. In other embodiments, the composition has no observable freezing temperature or melting temperature, above about −60° C.
The coating composition of the present invention is more versatile than previously known compositions because of its low freezing temperature and/or low melting temperature, despite the fact that the oligomer contains a polyol that is prone to crystallization. The coating composition is particularly useful in applications where optical fiber and ribbon assemblies made using such fiber are subjected to cold weather and freezing. Advantageously, the coating compositions of the present invention also can be handled more efficiently prior to use if they have been subjected to cold weather because they do not have to be thawed before use. The coating composition of the present invention can be used for an inner primary coating, an outer primary coating, single coatings, buffering coatings, a matrix material or the base for an ink (or colored) coating. Use of the coating composition of the present invention as an inner primary coating, outer primary coating, single coating or ink coating will minimize or even avoid adverse attenuation effects.
These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention. The invention may be best understood with reference to the detailed description of the preferred embodiments.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In accordance with the present invention, there is provided an improved radiation-curable coating composition for coating optical fiber which has a freezing temperature below about 0° C., or a melting temperature below about 0° C., or which has both a freez
Clark Michael R.
Montgomery Eva I.
Ward Jeanette L.
DSM N.V.
Gorr Rachel
Leydig , Voit & Mayer, Ltd.
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