Electric heating – Heating devices – With heating unit structure
Reexamination Certificate
2002-02-15
2003-05-13
Hoang, Tu Ba (Department: 3742)
Electric heating
Heating devices
With heating unit structure
C219S529000
Reexamination Certificate
active
06563094
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
This invention relates to soft and flexible electrical heaters, and particularly to heating elements, which have soft and strong metal or carbon containing electrically conductive textile threads/fibers.
2. Description of the Prior Art
Heating elements have extremely wide applications in household items, construction, industrial processes, etc. Their physical characteristics, such as thickness, shape, size, strength, flexibility and other characteristics affect their usability in various applications.
Numerous types of thin and flexible heating elements have been proposed. For example, U.S. Pat. No. 4,764,665 to Orban et al. discloses an electrically heated fabric for use in gloves, airfoils and aircraft parts. In this patent the fabric is metallized after being formed in a glove structure, following weaving or arranging in a non-woven format. Copper bus bars are utilized for introduction of electrical current to the metallized textile. Having been made of a solid piece of fabric with metallized coating, this heating element does not allow for flexibility in selection of desired power density.
Furthermore, the metallizing of the formed heating element results in a loss of significant economies of scale; only a small number of embodiments can be achieved, thus severely limiting the potential application of this invention. The '665 design is also not conducive to tight hermetic sealing throughout the heater areas (no gaps inside), which can increase the possibility of a short circuit through puncture and admission of liquid into the body of the heating element. In addition, this element cannot be used with higher temperatures due to the damage that would be caused to the polyaramid, polyester or cotton metallized fabric, described in the invention.
Another prior art example is U.S. Pat. No. 4,713,531 to Fennekels et al. Fennekels et al. discloses a sheet textile structure having resistance elements combined with it. These resistance elements comprise metallic fibers or filaments with a denier like that of natural or synthetic textile fibers, and with overall cross sectional thickness of 8 to 24 microns. The '531 design suffers from the following drawbacks: (a) being a sheet product, it is not conducive to hermetic sealing throughout the body of the heater (no gaps inside); only perimeter sealing is possible, which can increase the possibility of a short circuit due to puncture and admission of liquid into the body of the heating element; (b) yarns, comprising metal fibers, lack consistency of electrical resistance per given length, and their stretching, compression, or both, will result in very wide fluctuations in resistance, thus limiting the use of this technology for embodiments controlled by strict design and where uncontrollable power output and temperature variability are unacceptable; (c) yams are very heavy: from 1 to 7 grams per 1 meter of yarn; (d) the use of silver fibers makes these yams very expensive; (e) individual conductors have a large cross sectional thickness, each having an outer sheath of braided textile or elastomer.
Another prior art example is U.S. Pat. No. 4,538,054 to de la Bretoniere. The heating element of de la Bretoniere '054 suffers from the following drawbacks: its manufacturing is complex requiring weaving of metal or carbon fibers into non-conductive fabric in a strictly controlled pattern; the use of the metal wire can result in breakage due to folding and crushing and the use of metal wires affects the softness, weight and flexibility of the finished heater; it can not be manufactured in various shapes, only a rectangular shape is available; only perimeter sealing is possible (no gaps inside), which can result in a short circuit due to puncture and admission of a liquid into the body of the heating element; the method of interweaving of wires and fibers does not result in a strong heating element, the individual wires can easily shift adversely affecting the heater durability; the fabric base of the heating element is flammable and may ignite as a result of a short circuit; it is not suitable for high temperature applications due to destruction of the insulating weaving fibers at temperatures exceeding 120° C.
A heating element proposed by Ohgushi (U.S. Pat. No. 4,983,814) is based on a proprietary electro conductive fibrous heating element produced by coating an electrically nonconductive core fiber with electro conductive polyurethane resin containing the carbonatious particles dispersed therein. Ohgushi's manufacturing process appears to be complex; it utilizes solvents, cyanides and other toxic substances. The resulting heating element has a temperature limit of 100° C. and results in a pliable but not soft heating element. In addition, polyurethane, used in Ohgushi's invention, when heated to high temperature, will decompose, releasing very toxic substances, such as products of isocyanides. As a consequence, such heating element must be hermetically sealed in order to prevent human exposure to toxic off gassing. Ohgushi claims temperature self limiting quality for his invention, however “activation” of this feature results in the destruction of the heater. He proposes the use of the low melting point non-conductive polymer core for his conductive fabric-heating element, which should melt prior to melting of the conductive layer, which uses the polyurethane binder with the melting point of 100° C. Thus, the heating element of Ohgushi's invention operates as Thermal Cut Off (TCO) unit, having low temperature of self destruction, which limits its application.
U.S. Pat. No. 4,149,066 to Niibe et al. describes a sheet-like thin flexible heater made with an electro-conductive paint on a sheet of fabric. This method has the following disadvantages: the paint has a cracking potential as a result of sharp folding, crushing or punching; the element is hermetically sealed only around its perimeter, therefore lacking adequate wear and moisture resistance; such an element can't be used with high temperatures due to destruction of the underlying fabric and thermal decomposition of the polymerized binder in the paint; the assembly has 7 layers resulting in loss of flexibility and lack of softness.
The present invention seeks to alleviate the drawbacks of the prior art and describes the fabrication of a heater comprising metal fibers, metal wires, metal coated, carbon containing or carbon coated threads/fibers, which is economical to manufacture; does not pose environmental hazards; results in a soft, flexible, strong, thin, and light heating element core, suitable for even small and complex assemblies, such as hand wear. A significant advantage of the proposed invention is that it provides for fabrication of heaters of various shapes and sizes with predetermined electrical characteristics; allows for a durable heater, resistant to kinks and abrasion, and with electro-physical properties that are almost unaffected by application of pressure, sharp folding, small perforations, punctures and crushing. A preferred embodiment of the invention consists of utilizing electrically conductive textile threads/fibers having a Thermal Cut Off (TCO) function to prevent overheating and/or fire hazard. The heaters described in this invention may also comprise a continuous temperature sensor to control heating power output in the heating product.
SUMMARY OF THE INVENTION
The first objective of the invention is to provide a significantly safe and reliable heater which can function properly after it has been subjected to sharp folding, kinks, small perforations, punctures or crushing, thereby solving problems associated with conventional flexible metal wire heaters. In order to achieve the first objective, the heater of the present invention may comprise (A) electrically conductive threads/fibers and (B) multi-layer insulation of the conductive threads/fibers. The conductive threads/fibers may be comprised of carbon, metal fibers, textile threads coated with one or combination of the follo
Kochman Arkady
Kochman Dmitry
Hoang Tu Ba
Liniak Berenato & White
Thermosoft International Corporation
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