US2961522A - Heating panel - Google Patents

Description

T. HAMMER HEATING PANEL Nov. 22, 1960 2 Sheets-Sheet 1 Filed July 50, 1957 ATTORNEK Nov. 22, 1960 "r. HAMMER 2,961,522

HEATING PANEL Filed July 30, 1957 2 Sheets-Sheet 2 IN VE N TOR WON/25 H/VMMEPI ATTORNEYE HEATING PANEL Thomas Hammer, Princeton, N.J., assignor, by mesn'e assignments, to Mayflower Eiectronics Corporation, Wilmington, Del, a corporation of Delaware Filed July 30, E57, Ser. No. 675,186

4 Claims. 01. 219-19 This invention relates to heating panels, and more par ticularly to a flexible web form of panel that is adapted to be suspended like a shade, or located as a covering over walls, ceilings, or other interior surfaces, including vehicles, homes, oflices, and other buildings for heating thereof. The nature of this heating panel is such that it may be rolled up upon itself for ease of storing and shipping and may be produced in any desired lengths and in varying widths. V

The heating panel of this invention is electricallyoperated and is of the radiant heat type but is characteristically different, in its physical form and adaptability for various uses, from the usual rigid form of radiant heating device, whether it be of the resistant wire, or metal covered glass or other known form of radiant heater.

One of the important features of the heating panel of this invention comprises an extremely thin deposit of suitable metals, such as, for example, aluminum, copper, gold, etc., on a heat resistant, thin, flexible sheet or web having a suitable smooth continuous surface adapted for depositing the thin film of metal thereon. Examples of the flexible sheet or web base are heat resistant paper sheets, plastic films, and fabrics, including non-woven fabrics, having. a suitably smooth surface. In the usual case, plastic films may advantageously be used for supporting the thin metallic deposit and examples of suitable plastics are cellophane, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polyethylene, vinyl polymers, and polymerized ethylene glycol terephthalate, which is commonly known as Mylar. The Mylar film offers certain practical advantages over mostof the other plastic films from the standpoint of mechanical strength, electrical resistance and adaptability for depositing the thin coating of metal thereon. Similarly, with respect to the metal to be used, there are economic and other practical advantages in the use of aluminum.

In accordance with this invention, it is important to have the metal coating on the plastic or other flexible base material sufficiently thin to provide the necessary electrical resistance properties required for reliable and efiicient heating of the panel upon the passage of an electric current through the thin metal deposit. I have discovered, in accordance with this invention, that the thinness of this metal deposit or metallic layer on the base material is of promiary importance and that it should be many times thinner than the thinnest available metal foil, this extremely thin aluminum or other metal deposit is best obtained by metalizing the base material, that is, by evaporating the aluminum or other metal and causing it to condense on and adhere, as a thin metallic layer, to the base material. As a result of many tests that I have made, I am bale to predict and thereby control the depth of metallic deposit, and also to assure a uniformity of metallic deposit on the plastic film or other base material. This metalizing process produces a metallic film of only a few millionths of an inch in thickness, as determined by electrical resistance measurements.

The metalizing process may be carried out in accordance with known practices which use thermal evaporation or cathodic sputtering. Inaccordance with one illustra- United grates Patent 0 Patented New". 22,

tive example of procedure, a base sheet of the plastic film such as Mylar may be passed through a high vacuum chamber in apposition to a grid, coil, powder, sheeting or other form of the metal, such as, for example, aluminum, to be employed in the coating. The metal to be deposited is heated by suitable heating grids, trays, coils or other heating apparatus to volatilize the metal in such a way that it will condense on the plastic film or other base material to be coated.

As illustrative of the thinness of the metalized deposit which I use in the panel of my invention, and a comparison thereof with the thinnest available foil, commercial examples of the latter are approximately one hundred and fifty millionths of an inch, 0.000150, in thickness. Although this foil for most purposes would be considered extremely thin, it is nevertheless substantially thicker than the metallic layer resulting from the metalizing' treatment that I use and which produces aluminum deposits of the order of 0.000001" to 0.000100 in thickness. In a typical panel of my invention' I have obtained good results with a metallic deposit of 0.000005 to 0.000050" thickness. I have found that deposits of this order of thickness make it possible to produce a highly efiective and etficient electrical radiant heating panel such as could not be obtained from the use of metallic foil or the like having a minimum thickness of about .000150. In the usual case I have found it advantageous to employ metallic deposits of less than 0.000100 in thickness. The selected thickness of the metallic deposit will depend upon the available voltage and the amount of heat to be dissipated by the panel per square foot of space. For example in the heating of an automobile, by covering the ceiling and interior walls thereof with the flexible web ty e panel, the available voltage usually does not exceed 24 volts, and the heat per square foot for this type of panel would require about 48 watts with a current of 2 amperes. To produce the same amount of heat using -volt supply, the current required would be only 0.436 ampere.

With respect to the current density used in this type of heating panel, there are practical limits as to the density of current permitted to flow through a unit width of the material. Within the range of variables, I have found as a typical but non-limiting example, that using a metalized surface of such a thickness that it has a resistance of one ohm per square foot, a current density of /2 ampere per linear inch of cross-section, gives good erformance. It is contemplated that this current density might be increased to ampere or as much as one ampere per linear inch. For higher resistance surfaces, the permissible current densities will usually be lower than these respective amounts.

For lower resistance surfaces the permissible current densities have been found to be higher. For instance, I have designed and built a strip heating unit /4 inch wide by 224 inches long which yields a heat output of 300 watts per square foot of surface. The metal film in this case was copper and the current density for volts is 3.34 amperes per inch of web.

For operating this type of electric panel, a simple series circuit rs satisfactory,

and with the single panel unit would involve electrical connections at opposite ends of the panel. Where more than one panel is used, which would normally be the case for heating walls, ceilings, or other areas of appreciable size, the several panels would be connected elctrically in parallel and suitable connections provided on the panels at opposite ends of the area heated.

Where it is desired to increase the electrical resistance of the heating panel, the metallic layer may be de posited on the plastic or other film base in the form of spaced strips, leaving non-conductive strips of plastic film inbetween, and these metalized strips connected electrically in series to provide maximum resistance and higher heating capacity of the panel.

To increase the B.t.u. output per square foot of heating surface, both sides of the plastic base sheet may be covered with the thin metallic layer and, the panel would be electrically connected with the two sides in parallel.

As above indicated, the two primary components of the heating panel comprise a plastic or other flexible web base material, and the extremely thin metalized coating deposited on the base material. While these are the two principal components from the electrical and operation standpoint, it is important, of course, to provide in addition, a suitable electrically insulating cover over the metalized deposit to prevent electrical shock or other injury where high voltages are used, and also to protect the extremely thin metalized deposit from becoming damaged in use. This protective cover or layer may consist of any suitable flexible sheet material in the form of a cellulose sheet or a plastic sheet such as illustrated by the examples given hereinabove. Because of its high strength characteristics as well as the electrical resistance characteristics, polymerized ethylene glycol terephthalate (Mylar), plastic film, is advantageous. This Mylar or other film may be secured to the metalized coating and base sheet by means of a suitable thermoplastic adhesive, such as, for example the type of adhesive disclosed in Patent No. 2,673,826, issued on March 30, 1954, to Arthur Ness. A particular form of this adhesive, which we have found very satisfactory for laminating the Mylar sheets, is disclosed in Example 1 of said Patent No. 2,673,826.

For the purpose of improving the tear strength of the metalized plastic member, I have found it desirable to cover the untreated or non-metalized face of the plastic film, e.g., Mylar, with another plastic film, such as, for example, polyethylene. This latter film may be laminated to the Mylar film on the face opposite to the above described metalized deposit, and the two laminated films bonded together by means of a suitable thermoplastic adhesive, such as disclosed in the above Patent No. 2,673,826.

Also, in instances where it is desired to provide increased strength or stability to the heating panel consisting of the components described above, a suitable backing material may be secured either directly to the Mylar base film on the side opposite to the metallic coating or secured to the additional plastic film, such as, for example, the above mentioned polyethylene film where it is used to improve the tear strength of the Mylar. This backing material may be a plastic film, e.g., vinyl plastic of suitable thickness.

In most uses of the radiant heating panel of this invention it is desirable to have the heat radiated substantially in one direction, that is, outward from one face of the panel and to prevent or minimize the radiation of heat from the other face of the panel, this being particularly true where the flexible web panel is applied to a wall or ceiling structure for heating a room or other space enclosed thereby. To effect such unilateral heating by the panel, a heat reflective surface or layer may be provided on the side opposite the above-described metalized heat radiating surface. Any suitable form of heat reflective material may be used for this purpose, such as, for example, aluminum foil which could be laminated by means of adhesive to the Mylar or other flexible base material used in the main heating unit, and on the side opposite to the heat radiating, metalized surface. Alternatively, plastic film metalized on one face thereof to provide a heat reflective surface could be bonded by adhesive to the plastic film or other base sheet on which the current conducting, heat radiating, metalized surface is located.

Regarding the electrical connections for the heating panel, it is important not to damage the extremely thin metallic deposit. It is necessary, of course, to connect current conducting wires between the ends of the panel and the current supply source, and it is difficult to provide a reliable permanent connection between such wires and aluminum surfaces using ordinary solder. The oxide that forms on exposed aluminum surfaces prevents ordinary solder from wetting the aluminum, and it is not practical to make direct contact between the current conducting wire and the extremely thin metallic deposit on the thin flexible backing material. Furthermore, the usual type of copper clamps cannot be attached directly to the metalized surface because they would scratch or damage this surface.

To overcome these difficulties and to provide a type of connection that will assure uniform even distribution of the current along the length of the end connection and thereby avoid local heating or excessive resistance, a strip of thin copper foil may be bonded to the metallic layer by an electrically conductive adhesive, such as, for example, a silver paste, and suitable current conducting clamps attached to the copper foil strip. A silver paste that I have found to work satisfactorily is manufactured by the E. I. du Pont de Nemours & Co., and identified as No. 4922. This paste has the advantage of remaining in a permanently wet state which effects high electrical conductivity. Paste using other low melting metals such as indium ir gallium may be used in lieu of the silver paste. A cold pressed clamp formed of a soft metal such as copper may be clamped to the two outer surfaces of the heating panel adjacent the copper foil and the copper foil extended into the clamp to complete the electrical circuit. Suitable electrical leads may be attached to the outer surface of the clamp or squeezed inbetween the clamp and the copper foil, as desired. Alternatively, the conducting clamps may be attached directly to the copper foil strip without the use of an adhesive between the copper strip and the metallic layer.

Further details of the heating panel of this invention will be understood from the following more specific description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a fragmentary exploded view in perspective showing several of the component parts of one form of the heating panel of my invention;

Fig. 2 is a fragmentary cross sectional view of the panel shown in Fig. 1, taken along lines 22;

Fig. 3 is a fragmentary sectional view of another embodiment of the panel of my invention;

Fig. 4 is a cross sectional view showing one form of electrical end connection for the panel;

Fig. 5 is a cross sectional view of a further embodiment of electric..l end connection for the panel;

Fig. 6 is a plan view illustrating an arrangement of several of the panels connected electrically in series;

Fig. 7 is a plan view of a single panel using spaced, metalized strips to increase the electrical resistance; and

Fig. 8 is a perspective view of an application of the heating panel for heating ducts or space heaters.

Referring to Figs. 1 and 2, the form of panel illustrated therein consists of the base sheet of plastic 10 having a thin deposit of aluminum 12 adhering thereto, and a protective plastic sheet 14 covering the metallic deposit 12. The plastic covering sheet 14 is substantially coextensive with the metalized sheet 10 and protects and electrically insulates the metallic layer 12.

The several components for forming the end connection as illustrated in FEgs. 1 and 2 comprise a strip of thin copper foil 18 bonded to the metallic layer 12 by means of an electrically conductive paste 20 such as silver paste. Conductive plates 22 and 24 further support the end connection and all of the components are clamped together by means of rivets or bolts 26.

The form of panel illustrated in Fig. 3 is like that of Figs. 1 and 2, omitting the end electrical connecting members for sake of simplicity, and modified to include two additional components, namely, a backing or reinforcing sheet 28, which may be a vinyl plastic sheet, or aluminum foil, or other suitable supporting or heat reflectng material, and another plastic sheet 29, such as polyethylene for increasing the tear strength and crease resistance of the plastic base sheet 10. For sake of simplicity the adhesive or other means used for bonding or laminating the several sheets together are omitted in these illustrations.

An end connection that has been found to work very satisfactorily is illustrated in Fig. 4. It comprises a protective sheet 14 secured to the metalized layer 12 of plastic base sheet by a suitable adhesive and having an electrically conductive paste 20 applied to the metallic layer 12 at one edge thereof. A thin copper foil strip 18 is arranged on the paste 20 and preferably extends outwardly from the edge of the heating panel. A soft metal clamp 31 formed from an electrical conduct'ng material such as copper, is cold pressed in a U-shape at the edge of the heating panel adjacent the foil strip 18 and in contact with the two outer surfaces of the heating panel. Suitable electric leads (not shown) may be attached directly to the clamp 31 or between the foil strip 18 and clamp 31, as desired. By extending the copper strip 18 outwardly from the edge of the heating panel to contact clamp 31, the electrical c'rcuit is completed.

Another form of end connection that has been employed satisfactorily is shown in Fig. 5 and is similar to the end connection shown in Fig. 1. It comprises a copper strip 18 having an electrically conductive paste 20 thereon, in contact w'th the metallic layer 12. The copper strip 18 is upturned at one edge thereof so that an electrical conductor may be easily aflixed thereto by solder or otherwise.

Figs. 6 and 7 illustrate circuit layouts that can be used to vary the electrical heating parameters such as current density, voltage, resistance, and B.t:u. per square foot output. In Fig. 6, a plurality of metalized strips 30 are connected in seres by being joined in serpentine configuration through the use of end connections 32. Conductors 34 are connected to the appropriate electrical end connections 32.

In the form of the invention illustrated in Fig. 7 a single sheet of base material 38 has the metallic layer 40 disposed thereon in serpentine configuration. This particular form of the invention lends itself quite Well to the vacuum deposition of aluminum on the sheet 38. In that process, the areas 42, on which no metal is to be deposited, are masked with tape, and after metalization, the tapes are removed, leaving the non-metalized areas 42. End connections as described above are made at 44 for the application of current to the panel. It should be noted that the embod ment of the invention shown in Fig. 6 can also be formed with non-metalized areas that are masked during metalization.

In Fig. 8 there is illustrated a convective panel formed by corrugating a metalized lamination 50 and disposing the lamination in a passageway 52 formed by wall members 54. Electrical connections are made at 56. This convective panel will heat air by a natural chimney effeet and, at the same time, will emit some head by radiation.

Representative but non-limiting uses of the panel of this invention are as follows: wall ceiling and floor panels or covers for offices, rooms and automobiles; window shades and draperies; de-icers for airplane wings and props; toasters; flexible hoses; heating pads; heated blankets, pilloys, sheets and mattresses; floor mats; automobile seat and seat back warmer; heating tape; ironing board covers; folding screens; hair dryers; therapeutic heaters for throat, shoulders, ears, head, etc.; toilet seat warmer; heaters for laboratory apparatus such as beakers, flasks, retorts, etc.; windshield defrosters; refrigerator and freezer defrosters; heated silos, infant incubator and bassinet liners; vehicle cover (outdoor heated garage), windshield wipers, hot water heaters, piping systems, tents, pressure-sensitive heating panels and strips.

Various changes may be made in the foregoing without departing from the princ'ples of the present invention as comprehended within the scope of the accompanying claims.

I claim:

1. An electrical heating panel comprising a flexible sheet of dielectric material, an electrically conductive heating element, sa'd element being a very thin continuous film of metal deposited directly on said sheet and providing a relatively high electrical resistance over a. relatively large heat transfer area, said film being sufficiently thin to avoid cracking when flexed and sufficiently thin so as not to reduce substant'ally the flexibility of the dielectric sheet, connector strips on the surface of said film along opposite end portions of said film in continuous surface contact with the entire width of said end portions, and clamping means clamping the sheet, film and connector strips together along the entire w'dth of the ends and in a direction normal to the surface of the film to provide an uninterrupted electrical connection between the film and strip.

2. An electrical heating panel comprising a flexible sheet of dielectric material, an electrically conduct've heating element, said element being a thin continuous film of metal deposited directly on said sheet and providing a relatively high electrical resistance over a relatively large heat transfer area, sa'd film being sufficiently thin to avoid cracking when flexed and sufliciently th'n so as not to reduce substantially the flexibility of the dielectric sheet, and connecting means on the surface of said film along opposed end portions of said film in continuous contact with the entire width of sad end portions, said connecting means including an elongated U-shaped clamping member extending the width of the ends and clamping the film and sheet therebetween so as to maintain electrical contact between the film and connecting means.

3. An electrical heating panel comprising a flexible sheet of d'electric material, an electrically conductive heating element, said element being a very thin continuous film of metal deposited directly on said sheet and providing a relatively high electrical resistance over a relatively large heat transfer area, said film being sufficiently thin to avo'd cracking when flexed and sufficiently thin so as not to reduce substantially the flexibility of the dielectric sheet, connector strips on the surface of said film along opposite end portions of said film and extending the entire width of said end portions, a l'quid conductor between the connector strips and thin film, and clamping means clamping the sheet, film, liquid conductor and connector strips together in a direction normal to the surface of the film and along the entire width of the film ends to provide an electrical connect on between the film and strip, the liquid conductor insuring a continuous connection along the entire width of said film ends.

4. The electrical heating panel of claim 3 wherein the liquid conductor is silver paste.

References Cited in the file of this patent UNITED STATES PATENTS 2,507,036 McCrumm et al. May 9, 1950 2,511,378 Robertson June 13, 1950 2,572,163 Lamb Oct. 23, 1951 2,590,944 Cowdrey et al. Apr. 1, 1952 2,600,486 Cox June 17, 1952 2,600,913 Olson June 17, 1952 2,680,800 Chandler June 8, 1954 2,683,673 Silversher July 13, 1954 2,715,668 Booker et al. Aug. 16, 1955 2,739,083 Brown et al. Mar. 20, 1956 2,761,945 Colbert et al. Sept. 4, 1956 2,799,764 Chandler July 16, 1957 2,808,351 Colbert et al. Oct. 1, 1957

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