Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Utility Patent
1999-01-04
2001-01-02
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S272000, C528S288000, C528S292000, C528S322000, C528S324000, C528S326000, C528S332000, C528S339300, C528S345000, C528S397000, C524S600000, C524S606000, C385S066000, C385S084000, C385S100000, C523S173000, C174S019000, C174S076000, C174S07700S, C439S275000
Utility Patent
active
06169160
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention generally relates to protecting moisture and/or corrosion sensitive substrates from moisture and/or corrosion, to articles that contain a moisture and/or corrosion sensitive component as well as a protectant composition; and to compositions that may be used to protect substrates from moisture and/or corrosion.
BACKGROUND OF THE INVENTION
Transmission cables (e.g., service or power wires/cables) as well as telecommunication devices (e.g., fiber optic cables, telephone cables, terminal blocks, junctions and connections) are often exposed to harsh environmental conditions. Yet, both are required to maintain uninterrupted mechanical and electrical characteristics despite the surrounding environmental conditions. In the past, transmission cables were strung above ground between poles, and occasionally, placed under water. Increasingly, these cables are being buried beneath the ground for aesthetic reasons and to protect them from extremes of temperature, rain, snow, ice, high winds, falling tree limbs and the like. However, even when placed underground, these cables are subject to many environmental stresses including mechanical shock during back filling, moisture, the possibility of water immersion, attack from rodents and exposure to salt and other corrosive materials.
Transmission cables typically contain either a bundle of individually insulated copper wires, or a bundle of fiber optic cables. The copper wires, in particular, are protected by an inner metal shield, which covers the bundle of wires, and an outer sheath made from plastic or other insulating material. Likewise, a communication cable is generally constructed of an outer plastic jacket and an inner metal core wrap with an annular space therebetween. See, e.g., U.S. Pat. No. 3,745,321 to Eager, Jr. et al. The core wrap enwraps a plurality of twisted insulated conductors with a filler material, such as petroleum, wax, or other hydrocarbons, located between the conductors. The filler material typically functions as an insulator.
Even though wires and cables are normally well protected, if the protective outer sheath is cut or otherwise broken, water can seep into the wire or cable. Whenever moisture is present in the interior of a cable or wire, it tends, over a period of time, to migrate or flow longitudinally into connections at the splice closures, terminals, or the like. In the special case of optical fibers, passage of the water to connection points or terminals and associated equipment can not only result in damage to such equipment, especially to any metal parts thereof, but can cause problems at low temperature or freezing environments due to fiber microbending. This is particularly true when an immersed wire is cut.
In an inadequately unprotected device, corrosion of the contacts or short circuits caused by moisture or other outside elements will eventually interrupt service. Replacement or repair of the cables, whether strung along the ground or buried, can be particularly difficult and/or expensive, and the interruption of service may be particularly irritating to the customer. Because of this, much attention has focused on the protection of these cables from both physical damage and from chemical attack. As a result, various techniques have been disclosed to prevent or restrict migration of moisture along cable internal passages.
In one such technique, cable passages may be filled by a pressurized gas. Upon an escape of gas through a ruptured cable jacket, an alarm provides notice of cable damage. However, the gas does not prevent the flow of water into and along the cable internal passages before the repair is effected.
U.S. Pat. Nos. 4,867,526, 5,082,719 and 5,163,115 disclose a super-absorbent polymer or tape which is impregnated with a superabsorbent material for preventing water migration through cables. It has been found that, for a number of reasons, the production and/or installation of these materials is often impractical and/or uneconomical.
Silicone grease lubricant, elastomeric seals, or mastic sealing strips have been used in an attempt to seal out moisture. While these sealants offer some protection, moisture can often seep into the enclosure and cause a short circuit, which will interrupt telecommunications service, particularly when the terminal block is buried underground.
It is also known that insulating materials, such as mineral oil, protect the conductor from moisture and corrosive materials. Such insulating materials, however, drip when the cable is being serviced (i.e., cut). To overcome this “dripping” problem, various gelling agents are know to be added to the insulator, to thereby provide a gelled, non-dripping protectant composition.
The requirements imposed on gelled protectant compositions for transmission cables and telecommunication devices are numerous. A gelled protectant composition must remain stable throughout the temperature range of use of the cable or device, which is typically from about −40° to +70° C. If the maximum working temperature of the gelled protectant composition is not at least as high as about +70° C., then during operation of the cable or device, the insulating material may be subjected to a temperature sufficient to reduce its viscosity to the point that it runs out of the enclosure, exposing the component to moisture and/or other environmental conditions that may induce corrosion. In addition, the gelled protectant composition must be sufficiently fluid over the temperature range experienced during installation, for the composition to completely fill the enclosure without the risk of breaking or over-stressing the components.
A gelled protectant composition should also be sufficiently cohesive to ensure that compression of the enclosure will not result in the formation of voids in either the interior or on the surface of the composition. Also, the gelled protectant composition should be soft enough to allow such compression without subjecting the protected components to any significant strain, and yet be resistant to flow under gravitational forces as well as the hydrostatic pressures likely to be applied to the protected components if the end of a service wire is exposed in a flooded manhole. Moreover, the gelling agent must not chemically attack the components of the service wire or the enclosure of the terminal block.
Due to the relatively long lengths of cable that are typically installed, certain cable components are made from inexpensive plastic components such as polypropylene in an attempt to reduce the cost of the cable as well as obtain multiple supply sources for such components. This presents a problem to the supplier of protectant compositions in that many such compositions are not compatible with materials such as polypropylene and can cause deterioration of those materials.
Hydrophobic fumed silica has been used as a gelling agent, particularly for fiber optic cables, however, hydrophobic fumed silica is expensive and relatively large amounts of fumed silica must be used to provide useful gels. Use of hydrophobic fumed silicas, moreover, can cause the resulting gels to be abrasive.
A need therefore exists for suitable protectant compositions to be used in transmission cables and telecommunication devices. More specifically, there exists a need for gelled cable filling) compositions having improved properties against moisture and corrosive materials, and which avoid the abrasiveness of silica-based gel formulations. The gelled compositions should be compatible with the insulating material, the cable wire and the cable components. The present invention fulfills these needs and further provides related advantages.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides an article that includes a moisture-sensitive or corrosion-sensitive substrate in contact with a protectant composition. The protectant composition includes a polyamide gelling agent and a gelled solvent. The protectant composition is preferably shear thinning and/or non-dripping at the operating
Jackson Marc
MacQueen Richard C.
Pavlin Mark S.
Hampton-Hightower P.
Seed Intellectual Property Law Group PLLC
Union Camp Corporation
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