Dry fiber optic cable

Details Dry fiber optic cable Dry fiber optic cable

1998-03-27

2001-10-16

Healy, Brian (Department: 2874)

Optical waveguides

Optical transmission cable

Tightly confined

C385S100000, C385S103000

Reexamination Certificate

active

06304701

ABSTRACT:

The present invention relates to fiber optic cables and, more particularly, to water blocking features of fiber optic cables.
Fiber optic cables include optical fibers which transmit information in cable television, computer, power, and telephone systems. A fiber optic cable may be installed in an environment where the cable is exposed to water. The migration of water in a fiber optic cable may occur where the cable jacket has been breached and water enters the cable. The migration of water in a cable may cause the flooding of a cable passageway or enclosure, and/or it may negatively affect the performance of the optical fibers. As a typical maximum optical fiber packing factor in a buffer or a core tube is about 30%, the tubes present potential water migration paths. Moreover, the grooves of slotted rods present potential water migration paths.
To block the flow of water in a cable, known fiber optic cables may include a hard to remove and messy flooding or filling compound, and/or a more craft-friendly, dry water absorbent chemical. A typical water absorbent chemical includes a polymer chain with reaction sites that react with water, thereby transforming the water absorbent chemical into an expanded mass of viscous gel. The viscous gel acts as a physical barrier to the migration of water.
A fiber optic cable has been developed by the assignee hereof which eliminates the necessity for a flooding compound. U.S. Pat. No. 5,649,041 discloses buffer tubes that include exterior surfaces treated with a water absorptive adhesive which bonds a water swellable powder to the exterior surfaces of the tubes. Although the water swellable powder and water absorptive adhesive block the flow of water outside of the buffer tubes, a filling compound may be needed inside the buffer tubes to block the flow of water therein.
U.S. Pat. No. 5,179,611 discloses a slotted rod type fiber optic cable that includes a water absorptive tape wrapped around the slotted rod. The tape is a non-woven fabric, a paper or other sheet-like material, which is topically coated or impregnated with a combination of a thermoplastic elastomer binding agent, and a water absorptive resin combined with a water soluble resin. The water soluble resin is described as having a high rate of dissolution so that it will dissolve and thereby free the water absorptive resin for enhancing the effectiveness of the water absorptive resin. However, the water absorptive tape is limited in its application and in its water blocking effectiveness. For example, the water absorptive tape is not suited for use inside a buffer tube, and the tape may not be effective to block the flow of water in small interstices of the cable. Moreover, application of the water absorptive tape requires special manufacturing equipment for wrapping the tape about the slotted core and then applying binders to hold the tape in place. Further, the water absorptive tape adds to the cost, size, and weight of the cable. Additionally, a craftsman will be obliged to perform the time consuming task of cutting and removing the binders and water absorptive tape in order to gain access to optical fibers in the cable.
The assignee hereof has developed a fiber optic cable which eliminates the necessity for a flooding or filling compound, and may eliminate the need for a water absorptive tape. U.S. Pat. No. 5,684,904 discloses a fiber optic cable having buffer tubes that include inner and/or outer coatings of a moisture-absorptive polymer. The moisture-absorptive polymer may be a mixture of a moisture-absorptive powder and a carrier resin. The carrier resin may be a thermoplastic, a thermally cross linked polymer, or a cured ultraviolet light curable resin. The moisture-absorptive polymer is described as one that has a rapid swelling speed; however, all of the moisture absorptive polymer may not swell when water enters the tube, as some of the moisture absorptive powder may be encapsulated in the carrier resin and therefore insulated from the water.
The water swellable materials as described in the foregoing disclosures may disadvantageously have a relatively low gel strength. Gel strength is indicative of the strength of the cross linking of the water absorptive polymer after the polymer has been exposed to water and gelation has occurred. A low gel strength may result in a flow of water around the gelled material, termed wicking. Wicking is especially likely to occur where the gel is resisting a head of water. Moreover, if the swell rate of the swellable material is too low, a substantial amount of water may migrate in the cable before the swellable material gels enough to block the flow of water.
OBJECTS OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide a fiber optic cable that includes a mixture of at least two distinct superabsorbent substances, one superabsorbent substance having a high gel strength and the other superabsorbent substance having a very fast swell rate.
It is a further object of the invention to provide a fiber optic cable having dry water blocking features which obviate the necessity for flooding and/or filling compounds.


REFERENCES:
patent: 4401366 (1983-08-01), Hope
patent: 4587308 (1986-05-01), Makita et al.
patent: 4758617 (1988-07-01), Tanioku et al.
patent: 4815813 (1989-03-01), Arroyo et al.
patent: 4947679 (1990-08-01), McGee et al.
patent: 5179611 (1993-01-01), Umeda et al.
patent: 5213893 (1993-05-01), Kobayashi et al.
patent: 5306641 (1994-04-01), Saccocio
patent: 5321788 (1994-06-01), Arroyo et al.
patent: 5322896 (1994-06-01), Ueda et al.
patent: 5373100 (1994-12-01), Arroyo et al.
patent: 5389442 (1995-02-01), Arroyo et al.
patent: 5399591 (1995-03-01), Smith et al.
patent: 5410629 (1995-04-01), Arroyo
patent: 5422973 (1995-06-01), Ferguson et al.
patent: 5462972 (1995-10-01), Smith et al.
patent: 5561729 (1996-10-01), Parris
patent: 5563218 (1996-10-01), Rebre et al.
patent: 5630003 (1997-05-01), Arroyo
patent: 5635569 (1997-06-01), Sackmann et al.
patent: 5642452 (1997-06-01), Gravely et al.
patent: 5649041 (1997-07-01), Clyburn, III et al.
patent: 5684904 (1997-11-01), Bringuier et al.
patent: 5689601 (1997-11-01), Hager et al.
patent: 5698615 (1997-12-01), Polle
Swift adhesives Product Data; Swift's 2H547 Hot Melt Coating with MSDS (pp.1-4) Apr. 1997.
Technical Information, Thermoplastic Non-ionic Water-Absorbent Polymer “AQUA CAULK”; Sumitomo Seika Chemical Co., Ltd., May 17, 1995.
Product Literature, Water Swellable Coated Yarns, Fiberline, TB-004, 10-31-96/04.

Affiliated with

Also associated with

Rating

Dry fiber optic cable does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Dry fiber optic cable, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dry fiber optic cable will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2599963