Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1997-05-06
2001-04-10
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...
C522S085000, C522S096000, C522S172000, C528S025000, C528S026000
Reexamination Certificate
active
06214899
ABSTRACT:
FIELD OF THE INVENTION
This invention provides a method for making radiation-curable fiber optic materials having an extended shelf-life, and in particular, materials which comprise hydrolyzable glass coupling agent and which have reduced moisture content.
DESCRIPTION OF RELATED ART
Optical glass fibers are frequently coated with two or more superposed radiation-curable coatings, which together form a primary coating. The coating which contacts the optical glass fiber is called the “inner primary” coating and the overlaying coating is called the “outer primary” coating. Alternatively, the inner primary coating may simply be called the “primary” coating and the outer primary coating the “secondary” coating. Other optical fiber materials include matrix materials, inks, and bundling materials. All of these fiber optic materials are preferably radiation-curable and are within the scope of the present invention. Coated optical fibers can be incorporated into ribbon and cable structures.
The inner primary coating is usually a soft coating providing resistance to microbending. Microbending is associated with attenuation of the signal transmission capability of the coated optical glass fiber and is therefore undesirable. The outer primary coating is typically a harder coating providing desired resistance to handling forces such as those encountered when the fiber is cabled.
Inner primary coatings are a particular focus for the present invention. Coating compositions for making inner primary coatings generally comprise a polyethylenically unsaturated monomer or oligomer dissolved or dispersed in a liquid ethylenically unsaturated medium. These coating compositions also generally include a glass adhesion promoter which provides a link between the polymer inner primary coating and the surface of the optical glass fiber. Silane coupling agents, which are hydrolyzable, have been used as glass adhesion promoters. Silane coupling agents can also be used in so-called single coatings as disclosed in, for example, U.S. Pat. No. 4,932,750. Hydrolyzable silane compounds may also be found in other fiber optic materials besides inner primary and single coatings which directly contact the glass fiber. In this case, the adhesion promoter or coupling agent may not directly function to induce bonding to glass, but nevertheless, it may improve adhesion in general to other components in the optical fiber ribbon or cable structure.
In general, optical glass fibers are weakened upon exposure to water. For example, moisture in air can cause weakening and the eventual breakage of optical glass fibers. It is therefore desirable that the coating system in general and the inner primary coating in particular prevent moisture from attacking the optical glass fiber.
In addition to causing the weakening of the optical glass fibers, moisture can also cause the inner primary coating layer to delaminate from the optical glass fiber. The delamination of the inner primary coating from the optical glass fiber further results in a weakened optical glass fiber, because the inner primary coating can no longer protect the optical glass fiber from attack from moisture. Delamination may also cause attenuation of the signal transmission capability of the coated optical glass fiber.
Hence, it is desirable to use a radiation-curable, inner primary optical glass fiber coating composition that when suitably cured provides a reliable and consistent resistance to delamination from optical glass fibers. However, for certain applications, conventional radiation-curable, optical glass fiber coating compositions may not provide cured inner primary coatings having sufficient reliability and consistency in resistance to delamination caused by moisture. Moreover, when suitable compositions have been formulated, erratic and inconsistent performance on the glass fiber has been observed. For example, when coated optical glass fibers are soaked in water (“water-soak”), different strands of optical glass fiber can show different delamination behavior even though the fiber may have been coated with what was intended to be the same coating.
It has also been found that the resistance to delamination of the cured inner primary coating from an optical fiber decreases with the age or shelf-life of the radiation-curable, optical glass fiber coating composition, and this decrease may be erratic from one batch of composition to another. Such inconsistency can have severe repercussions in optical fiber technology.
Hence, there is a need for a solution to the above performance problems and to provide improved radiation-curable fiber optic materials with better, more consistent characteristics. In particular, improved shelf-life is needed so that, for example, materials can be stored for greater lengths of time. Materials with insufficient shelf life may need to be discarded.
SUMMARY OF THE INVENTION
An objective of the present invention is to provide a process of making radiation-curable fiber optic materials having extended shelf-life and which when suitably cured provide materials having reliable and consistent characteristics, and in particular, adhesion characteristics.
Another objective of the present invention is to provide a radiation-curable, inner primary, optical glass fiber coating composition having extended-shelf life, which when suitably cured provides consistent and reliable adhesion and delamination characteristics to optical glass fibers.
Surprisingly, after extensive testing of the many components in radiation-curable, inner primary, optical glass fiber coating compositions, it has been found that the shelf-life of the uncured coating composition, and the final adhesion characteristics of the cured inner primary coating to the optical glass fiber, are dependent upon the amount of water present in the uncured coating composition.
The present invention is therefore based on the discovery that the amount of water can be carefully controlled when making the radiation-curable, inner primary, optical glass fiber coating composition to provide an extended shelf-life for the uncured composition and to provide a cured inner primary coating having reliable and predictable adhesion characteristics.
In particular, the present invention provides a process for extending the useful shelf-life of radiation-curable resin coating compositions, adapted for use in forming inner primary coatings on optical glass fibers for signal transmission, and which contain a coupling agent having a functionally-effective glass binding group for promoting adhesion to glass fibers and which group is susceptible to hydrolysis under normal shelf storage conditions for the coating composition. The cured coating provides reliable and consistent resistance to delamination from the optical glass fiber.
The process of this invention consists essentially in the steps of establishing and controlling the water content for each component utilized in the preparation of the coating composition such that the ratio of total molar equivalent water content of the final coating composition to the total molar content of the functionally-effective glass binding groups is maintained at a level of less than one.
The invention also provides a process for extending the shelf-life of radiation-curable coating compositions adapted for use in forming inner primary coatings on optical glass fibers for signal transmission and containing a coupling agent having a functional group which bonds with the glass fiber and which is susceptible to hydrolysis under normal shelf storage conditions for the coating composition. The cured coating provides reliable and consistent adhesion to the optical glass fiber. The process consists essentially in the steps of formulating the coating composition from components having sufficiently low respective water contents such that after formulation the ratio of total molar equivalent water content of the formulated coating composition to the total molar equivalent content of the functional groups is less than one.
In known processes for the formulation or production of ra
Chawla Chander P.
Julian James M.
Schmid Steven R.
Zimmerman John M.
DSM N.V.
Gorr Rachel
Pillsbury & Winthrop LLP
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