Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1998-06-18
2001-02-13
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...
C522S075000, C522S120000, C522S121000, C522S142000, C522S144000, C522S137000, C522S079000, C522S071000, C428S375000, C428S378000, C428S030000, C428S426000, C428S441000
Reexamination Certificate
active
06187835
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to radiation-curable optical fiber coating compositions. In particular, the invention relates to compositions which are both fast-curing and have, upon radiation-cure, reduced rates of yellowing upon accelerated aging.
DESCRIPTION OF THE RELATED ART
Optical fibers have become a medium of choice for transmitting information in the modern telecommunications era. Immediately after their manufacture, optical fibers are usually coated with a radiation-curable inner primary coating (or simply “primary coating”) which directly contacts the underlying optical fiber. After radiation-cure, this inner primary coating is relatively soft and susceptible to damage. Therefore, the fiber is also usually coated with a radiation-curable outer primary coating (or simply “secondary coating”) which overlays the inner primary coating and is stiffer than the soft inner primary coating. This dual coating structure maximizes fiber transmission efficiency and durability and preserves the desirable characteristics of freshly-prepared, pristine glass fiber. The two coatings must function together to maximize fiber performance. In many cases, radiation-curable inks are applied over the outer primary coatings before the coated fibers are further processed into ribbons and cables. Besides the two fiber coatings, other radiation-curable fiber optic materials include matrix and bundling materials which are used to construct ribbons and cables.
After their cure, the radiation-curable compositions used in optical fiber production should not substantially change color over time, and in particular, should not yellow. Non-yellowing has become a crucial coating parameter in the optical fiber industry. Discoloration and yellowing is particularly encouraged by photolytic aging (e.g., aging in the presence of UV or fluorescent light). Also, discoloration is a general problem with urethane acrylate-based compositions, now the industry standard, and tends to be a greater problem with the inner primary rather than outer primary coatings. Yellowing in either coating, however, is undesirable.
Fast cure speed also remains an important coating parameter. Fiber production is limited by the rate at which the coatings can be sufficiently cured. Inner primary coatings usually have slower cure speeds than outer primary coatings.
Although attempts have been made to solve the aforementioned yellowing problem, any solution should be arrived at without impairing other important properties such as fast cure speed. That combination of properties, however, can be difficult to achieve. In addition, coating design is complicated by the effects of the outer primary coating on the cure of the inner primary coating. Systemic approaches are needed to solve these problems and satisfy stringent demands made by producers of coated optical fibers, ribbons, and cables. These producers demand both fast cure speed and non-yellowing performance from the coating system which prior art coatings do not provide.
UV absorbing compounds (“UV absorbers”) have been added to optical fiber coatings, but with mixed results. It is generally recognized that they slow cure speed. For example, U.S. Pat. Nos. 5,146,531 and 5,527,835 teach optical fiber coatings which allegedly are suitably non-yellowing and have suitable cure speed. However, the use of UV absorbing compounds is not taught in these patents.
U.S. Pat. No. 4,482,204 to Blyler et al. discloses that optical loss in the fiber can be reduced if the radiation-curable fiber coatings comprise a UV-absorbing additive which functions to screen UV light (but, unlike a photoinitiator, does not generate substantial amounts of free radicals upon UV exposure). According to this patent, however, the UV absorbing material is preferably located in the inner primary coating, and is not used in the outer primary coating if a fully-cured outer primary coating is desired. This patent also does not suggest the preparation of fast cure speed outer primary coatings which reduce yellowing of the inner primary coating through use of a UV absorber. Rather, it teaches away from the use of a UV absorber in the outer primary coating if fast cure speed is desired.
Similarly, U.S. Pat. No. 4,935,455 teaches use of UV absorber in an inner primary coating. However, this patent also teaches that increasing the amount of UV absorber will slow cure speed. Hence, it exemplifies use of UV absorber only in low amounts.
Therefore, in general, UV absorbers are considered undesirable when fast cure is essential, and commercial optical fiber coatings today generally do not include them. Past commercial optical fiber coatings have employed them, but in very low concentrations. These coating systems are inadequate to meet present commercial demands.
In sum, a long-felt need exists for fast-curing inner and outer primary coatings which provide both enhanced protection against light-induced discoloration and fast cure speed.
SUMMARY OF THE INVENTION
The present invention recognizes that the aforementioned problems with optical fiber coatings can be resolved by tailoring the coating's photoinitiator system together with a UV absorbing system. In addition, inner and outer primary coating compositions can be designed to function together. As a result, this invention helps fulfill a long-felt need in the industry to provide optical fiber coating systems with both fast cure speed and non-yellowing properties.
The present invention provides a radiation-curable composition for an optical fiber coating comprising the combination of pre-mixture ingredients:
about 5 wt. % to about 95 wt. % of at least one radiation-curable oligomer,
about 5 wt. % to about 95 wt. % of at least one reactive diluent,
about 0.1 wt. % to about 20 wt. % of at least one photoinitiator, wherein the photoinitiator is selected to provide a fast cure speed,
about 0.1 wt. % to about 20 wt. % of at least one UV absorbing compound which does not substantially impair the fast cure speed.
The present invention also provides a coated optical fiber comprising the combination of:
an optical fiber,
a radiation-cured inner primary optical fiber coating, and
a radiation-cured outer primary optical fiber coating, wherein
said outer primary optical fiber coating comprises, before radiation-cure:
about 5 wt. % to about 95 wt. % of at least one radiation-curable oligomer,
about 5 wt. % to about 95 wt. % of at least one reactive diluent,
about 0.1 wt. % to about 20 wt. % of at least one photoinitiator, wherein the photoinitiator is selected to provide a fast cure speed,
about 0.1 wt. % to about 20 wt. % of at least one UV absorbing compound which does not substantially impair the fast cure speed of the inner or outer primary coating.
The present invention also provides a method for reducing the rate of color degradation in an inner primary optical fiber coating comprising the combination of steps of:
coating an optical fiber with a radiation-curable inner primary coating,
coating the inner primary coating with an outer primary coating which comprises a UV absorber which does not substantially impair the cure speed of the outer primary coating, and
curing the coatings.
In particular, the outer primary coating compositions of the invention advantageously exhibit good cure speed, and after curing, demonstrate non-yellowing, oxidative stability, good moisture resistance, and tough film properties.
REFERENCES:
patent: 4129667 (1978-12-01), Lorenz et al.
patent: 4263366 (1981-04-01), Lorenz et al.
patent: 4276136 (1981-06-01), Gruber et al.
patent: 4472019 (1984-09-01), Bishop et al.
patent: 4482204 (1984-11-01), Blyler, Jr. et al.
patent: 4528311 (1985-07-01), Beard et al.
patent: 4611061 (1986-09-01), Beard et al.
patent: 4935455 (1990-06-01), Huy et al.
patent: 5015068 (1991-05-01), Petisce
patent: 5141990 (1992-08-01), McKoy et al.
patent: 5384235 (1995-01-01), Chen et al.
patent: 5539014 (1996-07-01), Swedo et al.
patent: 5664041 (1997-09-01), Szum et al.
patent: 114 982 B1 (1984-08-01), None
patent: 114 982 (1987-06-01), None
patent: 84-03085 (1994-0
Bishop Timothy E.
Chawla Chander P.
Szum David M.
DSM N.V.
McClendon Sanza
Pillsbury Madison & Sutro LLP Intellectual Property Group
Seidleck James J.
LandOfFree
Radiation-curable optical fiber coatings having reduced... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Radiation-curable optical fiber coatings having reduced..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Radiation-curable optical fiber coatings having reduced... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2574929