Raychem Limited

Joseph H Evans

Lee M Middleman

Richard B Wolfe

Donald F Pettengill

Clyde A Lofdahl

Arthur Edward Blake

Dave D Nyberg

Victor A Scheff

Conductive polymer compositions comprise carbon black or graphite dispersed in a polymer and further comprise an arc-controlling additive such as alumina hydrate. Such compositions have improved performance when subjected to electrical stress and are, therefore, particularly useful in circuit protection devices.

Conductive polymer compositions having improved properties under

Electrically conductive device having improved properties under

Circuit protection devices which comprise two columnar electrodes and a conductive polymer element, at least a part of which is a PTC element. The device is so constructed that if a hot zone forms in the PTC element when current is passed through the device, it forms at a location away from the electrodes, thus increasing the useful life of the device. In one preferred embodiment, the conductive polymer element has an intermediate portion of increased resistance, thus causing the hot zone to be located at or near the intermediate portion. The intermediate portion may be of reduced size and/or be composed of conductive polymer of relatively high resistivity.

Circuit protection devices

Circuit protection devices comprising PTC elements, and circuits containing such devices. The devices, which are particularly useful in circuits carrying a steady state current of 0.5 amp or more, can protect the circuit against excessive current, e.g. as a result of a short or a voltage surge, or against excessive temperature, or both. The PTC element is composed of a material, preferably a conductive polymer, having a resistivity less than 10 ohm. cm in the normal operating condition of the circuit, and the device comprises electrodes such that current flows through the PTC element over an area of equivalent diameter d with an average path length t such that d/t is at least 2. The circuit has a normal operating condition in which the device has a low resistance and is in stable thermal equilibrium with its surroundings; however, when a fault condition occurs, the device generates heat by I.sup.2 R heating at a rate which exceeds the rate at which heat can be lost from the device, thus causing the temperature and resistance of the device to rise until the device reaches a new, high temperature, stable thermal equilibrium state. In order to ensure that the circuit current is reduced to a sufficiently low level, the ratio of (a) the power in the circuit in the normal operating condition to (b) the power in the circuit when the device is in the high temperature equilibrium state, is at least 8, preferably at least 40.

Circuit protection devices comprising PTC elements

Electrical devices which comprise two planar electrodes and a conductive polymer element, at least a part of which is a PTC element. The conductive polymer element has an intermediate portion of increased resistance, resulting from the presence of insulating or high resistance portions within the conductive polymer element, so that when a hot zone is formed in the PTC element, it is located at or near the intermediate portion, away from the electrodes.

Circuit protection devices comprising PTC elements, and circuits containing such devices. The devices, which are particularly useful in circuits carrying a steady state current of 0.5 amp or more, can protect the circuit against excessive current, e.g. as a result of a short or a voltage surge, or against excessive temperature, or both. The PTC element is composed of a material, preferably a conductive polymer, having a resistivity less than 10 ohm. cm in the normal operating condition of the circuit, and the device comprises electrodes such that current flows through the PTC element over an area of equivalent diameter d with an average path length t such that d/t is at least 2. The circuit has a normal operating condition in which the device has a low resistance and is in stable thermal equilibrium with its surroundings; however, when a fault condition occurs, the device generates heat by I.sup.2 R heating at a rate which exceeds the rate at which heat can be lost from the device, thus causing the temperature and resistance of the device to rise until the device reaches a new, high temperature, stable thermal equilibrium state. In order to ensure that the circuit current is reduced to a sufficiently low level, the ratio of (a) the power in the circuit in the normal operating condition to (b) the power in the circuit when the device is in the high temperature equilibrium state, is at least 10, preferably at least 40.

A recoverable tubular article comprising an elastomeric sleeve held in a radially expanded or extended condition and capable of recovering to its pre-expanded condition of smaller diameter upon the removal of an outer restraint, an outer restraint, essentially tubular in configuration, bonded to said elastomeric sleeve, said bond between the sleeve and the restraint being sufficiently strong to retain the elastomeric sleeve in its expanded condition under ordinary conditions of storage and susceptible to attack by solvents weakening the bond sufficiently to allow the elastomeric sleeve to peel away from the restraint and recover to its original state. The article may be made by injection molding a rigid plastic material around an elastomeric sleeve, insuring that a suitable bond is formed between the sleeve and restraint, expanding said elastomeric sleeve when the plastic material is heated to softness and is formable and allowing the plastic material to cool and harden while the sleeve is held in the expanded state.

Recoverable sleeve

Method for covering an article with a recoverable sleeve

A carrier having substantially flat projections which extend from the carrier to snugly and slidably bear heat recovered sleeves thereby conforming to the flattened configuration of the projections. After positioning generally tubular heat recoverable sleeves over the projections and partial recovery of the same, printed information may be easily imparted to the sleeves on a modified typewriter or the like. The sleeves may then be removed from the projections and employed as identifying markers for electrical wire or other like articles to be marked. The sleeves may be further heat recovered in position on the marked article to snugly fit thereon.

Marker assembly

An apparatus for lubricating and/or cleaning a heated fuser roller in a heat-pressure fusing system for electrophotographic copying. The apparatus includes a lubricating and/or cleaning means in contact with the heated fuser roll, the means including a cross-linked polymeric material on its outer surface. The polymeric material may have a leachable lubricating material dispersed therein, for controlled lubrication of the fuser roller. After depletion of the lubricating material, the cross-linked polymeric material then functions to remove and collect the toner particles from the surface of the toner fuser roller. The apparatus is preferably mounted in contact with the fuser roller by a means which permits easy removal and replacement in the field, after the lubricant has been depleted or the polymeric material has become saturated with toner particles.

Cleaning and lubricating system for fusing apparatus

Described herein are articles which are heat recoverable in involute fashion to an overlapping, generally cylindrical configuration and which are useful as wrap-around sleeves for wires, cables, cable splices and the like. Also described are articles initially heat recoverable to an elongate S-shaped configuration, which latter can be wrapped about an elongate substrate, the edge portions thereof interlocked, and heat recovered to form a protective closure. The articles of the invention comprise a molecularly oriented unitary polymeric layer which has been differentially annealed while restrained against dimensional change and cross-linked to provide an anisotropic gradient from a first to a second primary face of the layer through the thickness thereof. Subsequently, when the article is heated to recovery temperature, regions of high anisotropy adjacent one primary face of the layer shrink. Because of the annealing process, regions adjacent the opposite primary face of the layer tend to resist linear shrinkage, whereupon the article heat recovers in involute fashion to form a wrap-around sleeve.

Heat recoverable articles and methods therefor

Method of making marker assemblies comprising an elongate denticule whose flat, pendent tines bear in snug and slidable relation heat recovered sleeves which conform to the flattened configuration of the tines. After positioning generally tubular heat recoverable sleeves over the pendent tines and recovery of the same, printed information may be imparted to the tine-borne sleeves, which thereafter may be removed from the denticular support and employed as identifying markers for electrical wire and the like.

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Palo Alto, CA, United States of America

Joseph H Evans