Electric heating – Heating devices – With heating unit structure
Reexamination Certificate
1998-10-02
2001-02-27
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
With heating unit structure
C219S528000
Reexamination Certificate
active
06194692
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electric heating sheets and, in particular, to flexible electric heating sheets of the type used to heat articles such as seats in automobiles, trucks, other vehicles, aircraft and the like.
2. Related Art
Planar heating elements have been used for such applications as automobile seat heating, ceiling heating, underfloor heating, wood/panel heating, motor vehicle mirror and personal cushion heating. Automobile seats have been heated, for example, by flexible elements which are fabricated by bonding an insulated resistor wire to the internal surface of a fabric or leather covering of the seat. The wire is typically made of nickel/chromium or another suitable high-resistance metal. Heat is generated by power dissipated during the passing of current through the wire. The power dissipated is given by the expression: P=I
2
R=VI where P is the power dissipated (watts), R is the resistance of the heating element (ohms), I is the current running through the element (amperes) and V is a voltage drop in the heating element (volts). A problem arises in that the heating surface of the wire occupies generally only one to five percent of the surface area required to be heated. Because of the high power required to heat the entire surface from the narrow wire, hot spots are created on the surface which may cause premature deterioration of the fabric or leather covering.
Attempts have been made to ameliorate the aforementioned problem. For example, U.S. Pat. No. 5,229,582 to Graham, issued Jul. 20, 1993, discloses a flexible heating element constructed by securing a flexible layer of conductive material constituting an electric heater to a flexible sheet. The layer of conductive material is connected to an electrical supply means by at least one copper strip (column 2, line 22) electrode that has an embossed surface with protuberances which are said to enhance direct contact of the electrode with the layer of conductive material. A thermoplastic polymer-based adhesive at the interface between the embossed surface and the conductive layer secures the latter to the electrode. The protuberances are provided to penetrate the adhesive layer to provide an improved electrical contact between the electrode and the conductive material.
U.S. Pat. No. 5,629,073 to Lovell, issued May 13, 1997, which discloses a medium-temperature conductive resistive article made from a composition including graphite suspended in a high-temperature polymer base activator with water. The conductive resistive composition can be applied as a layer to a fabric-like substrate in order to provide a resistive temperature adjustable heating element for the fabric. Conductive strips of copper foil “as well as many other types of electrodes” (column 3, line 15) are connected to the heating element as electrodes.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided an electric heating sheet comprising the following components. A heating element comprises a first cured conductive coating. At least a pair of electrodes comprised of a second cured conductive coating are spaced apart from each other and disposed in electrical contact with the first cured conductive coating of the heating element. A substrate on which the heating element and the electrodes are disposed and a first insulating layer may be provided which substantially covers the electrodes and the heating element.
In accordance with another aspect of the present invention there is provided an electric heating sheet comprising the following components. A heating element comprising a first cured conductive coating. At least a pair of electrodes spaced apart from each other and disposed in electrical contact with the first cured conductive coating of the heating element. One or more current distributing elements of greater conductivity than the first cured conductive coating are disposed in electrical contact with the first cured conductive coating of the heating element, the current distributing elements being dimensioned and configured to influence the pattern of current distribution through the heating element. A substrate may be provided, on which the heating element, the electrodes and the current distributing elements are disposed. A first insulating layer substantially covers the heating element, the electrodes and the current distributing elements.
The following additional aspects of the invention may apply singly or in combination of any two or more thereof. The current distributing elements may optionally comprise a third cured conductive coating; the current distributing elements may be dimensioned and configured to enhance the uniformity of current distribution through the heating element and may be located on the heating element; the electrodes may, and preferably do, have a higher conductivity than that of the heating element; and the electrodes may be disposed at respective opposite ends of the heating element and be located on the heating element. Further, the substrate may be formed of thermoplastic adhesive and may further comprise a backing material on which the substrate is supported. Still further, the electrodes may be of elongate configuration and extend longitudinally substantially parallel to each other, with the current distributing elements comprising a pair of elongate balance bars spaced apart from and substantially parallel to both each other and to the electrodes, with the balance bars being disposed between the electrodes.
Another aspect of the present invention includes providing a second insulating layer which cooperates with the first insulating layer to sandwich therebetween and cover the conductive coatings, and wherein at least one of the first and second insulating layers comprises a thermoplastic adhesive.
Yet another aspect of the present invention includes the sheet being sufficiently flexible to allow it to conform to an irregular surface in the manner in which a woven fabric conforms to an irregular surface.
Still other aspects of the invention include one or more of the following, alone or in any combination of two or more thereof. At least one of the cured conductive coatings may comprise a coating containing at least one particulate conductive material selected from the group consisting of copper, nickel, graphite, tin oxide doped with indium, and silver suspended in a layer of one or more cured polymers selected from the group consisting of polyamides, polyesters, natural rubbers, synthetic rubbers, polyimides and elastomers; the particulate conductive material may comprise from about 20% to about 50% by volume of the coating; the particulate conductive material may comprise silver; and the particulate conductive material may comprise from about 33% to about 50% by volume of the coating.
In accordance with a method aspect of the present invention, there is provided a method of making an electric heating sheet comprising the following steps. A first conductive ink comprising a suspension of first particulate conductive material in a first curable liquid is deposited onto a substrate and is cured on the substrate to form a first cured conductive coating comprising a heating element. A second conductive ink comprising a suspension of second particulate conductive materials in a second curable liquid is deposited in contact with the first cured conductive coating in a pattern defining at least a pair of spaced-apart areas coated with the second conductive ink. The second conductive ink is cured in contact with the cured first conductive ink to provide a second cured conductive coating comprising disposed electrodes in electrical contact with the first conductive coating. A first layer of an electrically insulating material is deposited over the first and the second cured conductive coatings to substantially cover the same to form a layered electric heating sheet.
In accordance with another method aspect of the present invention there is further provided a method of making an electric heating sheet com
Engelhard Corporation
Miller Stephen I.
Van Quang
Walberg Teresa
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