Heating Elements

Abstract

Heater assembly that may be used for heating a surface such as the glass rear windscreen (or window) of a motor vehicle comprises a heater element having a continuous metal strip of sinuous form. The element is sandwiched between two paper backing sheets which are adhesively secured to opposed surfaces of the metal strip. A first backing sheet is for removal prior to the mounting of the element on an automobile rear windscreen, and the other backing sheet is to be removed after the element has been so mounted. The first backing sheet is coated with a silicone or wax to facilitate its ready removal from the element. The surface of the element covered by the other backing paper is provided with a layer of electrically insulating material.

Description

BACKGROUND OF THE INVENTION

This invention relates to heating elements and it is an object of this invention to provide a heating element that may be used for heating a surface such as the glass rear windscreen (or window) of a vehicle.

Heretofore to achieve this object it has been proposed that the heating elements be either embedded in the glass composition, an expensive arrangement, or be incorporated with a plastics material panel, the whole panel being affixed to the interior surface of the glass rear windscreen, an unsightly and rear-view restricting arrangement.

SUMMARY OF THE INVENTION

The disadvantages of the aforementioned prior art arrangements are minimized or largely overcome by the present invention, which, according to one aspect thereof, provides a heating element comprising a long, narrow strip of thin electrically resistive material having on one surface thereof a layer of adhesive, and having at the ends thereof an electric terminal. It will be appreciated that by means of the adhesive layer the heating element can be itself affixed directly to the interior surface of the glass windscreen so that an effective and aesthetically pleasing rear windscreen heater can be inexpensively installed.

Preferably the surface of the electrically resistive material opposite the adhesive is provided with a layer of electrically insulating material. The electrically resistive material is preferably a metal (e.g., aluminum) or metal alloy; the electrically insulating material is preferably enamel or plastics material (e.g., a polyester resin such as that sold in the United Kingdom under the Trade Mark "MELINEX"); and the adhesive is preferably thermo-setting.

The adhesive may be in surface contact with a readily removable, preferably fairly thick, backing layer which is conveniently constituted by a sheet of siliconized paper. Preferably the strip of electrically resistive material follows a path of sinuous form e.g., the outline of a thick "S."

The layer of electrically insulating material may be in surface contact with a wax compound whose melting temperature is of the order of the setting temperature of the adhesive, the wax compound conveniently being in surface contact with a rigid member, e.g., cardboard. Alternatively and preferably the layer of electrically insulating material is in surface contact with a low tack adhesive coating on one surface of a transfer layer which is conveniently constituted by another sheet of paper or cardboard.

The electric terminals may comprise width-wise enlargements of the ends of the strip. Preferably the enlarged ends are each sandwiched between two metal members, one of which is held captive by the upwardly and inwardly turned side edges of the other. Furthermore, one or the other of said two metal members may have sharp projections to dig into the enlarged end of the strip with which it is associated. One or other of said two metal members may be bowed convexly with respect to the strip and to the other or one of said two metal members so that the associated enlarged end is tightly compressed between the two metal members.

Preferably one or other of said two metal members is provided with a projecting blade, conveniently at an angle thereto, to mate with a female connector at one end of an electric wire. The metal member on the same side of the strip as said layer of adhesive may be in adhesion with one surface of a pad whose opposite surface has a pressure adhesive or contact adhesive thereon by means of which the terminal can be affixed to the interior surface of the windscreen.

According to another aspect of this invention there is provided a heating element, according to said one aspect of this invention, sandwiched between two supporting sheets. The sheets, conveniently of generally rectangular shape, may be of paper or cardboard.

Preferably the long, narrow strip of thin electrically resistive material is the residue of a die-stamping operation upon a sheet of such material adhesively mounted upon one of said supporting sheets, which one sheet constitutes a backing layer, prior to the application of the other of said supporting sheets.

BRIEF DESCRIPTION OF THE DRAWINGS

Three embodiments of this invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 shows the third embodiment in partly broken away plan view; and

FIG. 2 is a fragmentary diagrammatic sectional view on the Line II--II of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a first exemplary embodiment of this invention, there is provided a long length of metal strip approximately 1.8 m (2 yards) long, 150 .mu.m (0.006 in) thick, and 1.6 mm (a sixteenth of an inch) wide. Preferably this strip is integrally provided with enlarged ends, e.g., twice as wide, to constitute electrical terminals therefor. One side surface of the metal strip is coated with a pressure-sensitive Use of resin adhesive that cures at 69 effeciive demsting 70.degree. centigrade. The other side surface of the metal strip is insulated by a clear plastics material coating or by an enamel coating. The metal is chosen to have a resistance over its total length within the approximate range of 1 to 2 ohms.

The exemplary heating element so formed as applied in one test to the inner surface of a vehicle rear glass windscreen by contacting the adhesive layer directly to the glass while disposing the strip in a sinuous pattern over the glass. On the application of the vehicle's battery voltage of some 12 volts across the heating element, its temperature rise was sufficient to cure the adhesive and provide a permanent bond to the glass. Subsequent use of the permanently fixed heating element provided effective demisting and defrosting of the rear glass windscreeen.

In a second exemplary embodiment of this invention, a rectangular sheet of aluminum foil having side lengths approximately 20 cm (8 in) and 46 cm (18 in) long, has one surface bonded to a film of "MELINEX," and its opposite surface coated with a thermo-setting adhesive having a setting or curing temperature of the order of 70.degree. C. A sheet of siliconized brown paper is in surface contact with the adhesive to form a backing member or supporting layer for the laminate. The siliconizing provides the paper with a low-cohesion surface. The surface of the "MELINEX" film opposite to that which is bonded to the aluminum foil is coated with polymeric wax whose melting temperature is somewhat less than 70.degree. C and the wax serves to bond the laminate to a sheet of cardboard which provides a rigid mounting and further supporting layer for the laminate.

The six layer composite laminated rectangular structure so formed may be stamped or cut into a desired pattern which preferably comprises a thin strip following a sinuous snake-like path. The straight long sides of this sinuous strip lie parallel to the 8 inch long sides of the rectangular structure. The sinuous strip so formed may provide a heating element for heating a surface such as the glass rear windscreen of a vehicle. To achieve this the siliconized brown paper backing is peeled away from the strip which is then pressed against the interior surface of the glass rear windscreen. When electric current is applied to the aluminum foil via terminals provided at its ends, the heat produced by the current (which may be of the order of 10 to 15 amps) raises the temperature of the adhesive to thereby initiate curing or setting of the adhesive and also raises the temperature of the polymeric wax causing it to melt. As the polymeric wax melts, the cardboard providing a rigid support for the laminate falls away to leave the aluminum foil in strip form bonded by one surface to the glass rear windscreen with its opposite surface electrically insulated by the "MELINEX" film in corresponding strip form. Subsequent electric current passage through the heater so formed provided effective demisting and defrosting of the rear glass windscreen.

In a third exemplary embodiment of this invention, illustrated in the accompanying drawings, there is provided a rectangular laminated sheet, approximately 47 cm (18.5 in) long by 21 cm (8.5 in) wide and approximately 38 .mu.m (0.0015 in) thick, comprising a layer of aluminum foil bonded to a layer of plastics material film e.g., a polyester such as that sold in the United Kingdom under the Trade Mark "MELINEX." Preferably the metal foil layer and plastics film layer have similar thicknesses. The exposed surface of the aluminum foil layer is coated with a thermo-setting adhesive, and a fairly thick sheet of backing paper having similar rectangular dimensions is then applied to this adhesive-coated surface to provide a supporting layer and covering for the laminated sheet. The backing paper, which is pre-treated with a low cohesion material such as silicone or wax, has a polished or smooth surface which is therefore a low-cohesion surface and is readily separable from the aluminum foil/MELINEX film sheet.

The two bonded sheets of backing paper and aluminum/MELINEX are subjected to a die-stamping operation from the MELINEX side. The pattern die-stamped is one of long, narrow strip form such that the strip follows a sinuous path, for example the border outline of a thick "S" (see the accompanying drawing). The width of the strip is approximately 3,200 .mu.m (an eighth of an inch) except for its ends which have a large width of approximately 1.4 cm (nine-sixteenths of an inch). The depth of cut of the die-stamping operation is sufficient to pass wholly through the aluminum/MELINEX sheet but not through the backing paper. Thus, as illustrated in the accompanying drawing, the sheet of backing paper 2 supports by means of the thermo-setting adhesive 3 only the long narrow strip 4 of aluminum 6 bonded to MELINEX 8 after the remaining residue (not shown) of the aluminum/MELINEX sheet has been peeled away from the backing paper 2. Another paper sheet 10 (only part of which is shown), having similar rectangular dimensions to sheet 2, is coated on one surface with a low tack adhesive 11 and this surface is applied to the sheet 2 supporting the aluminum/MELINEX strip 4. The thickness of paper sheet 10 is not very important, although the thicker it is the more rigid support it will give to the strip 4 during installation (see below).

The rectangular laminate of strip 4 adhesively sandwiched between sheets 2 and 10 is formed with an L-shaped cut-out adjacent one corner in the vicinity of the strip's enlarged width ends 14. To each of these ends an electric terminal connector 15 is affixed making electrical connection with the aluminum part 6 of the strip end 14. Each terminal connector 15 comprises a flat metal plate 16 formed with an integral blade 18, extending at an angle to the plane of plate 16, and a shallow channel-shaped metal member 20 formed with a convex base having a plurality of upstanding sharp projections. Each plate 16 is placed on sheet 10 above its associated strip end 14 and placed within the metal member 20 whose upstanding edges project past the side edges of both strip end 14 and plate 16. Plate 16 and member 20 are clamped so that the projections of the convex base of member 20 pass through the backing paper sheet 2 and on into the aluminum. The electrical connection thus made is maintained by turning in the upstanding edges of member 20 to thereby maintain the clamping pressure. If desired the plate 16 may be convex to the sheet 10 as an alternative or in addition to the base of member 20 being convex to the sheet 2, and/or may have the sharp projections. A pad having a contact adhesive or pressure adhesive on both major surfaces is affixed to the base of each member 20.

The heating element constituted by the aluminum part 6 of the strip 4 is installed in a vehicle in the following manner for use as a rear glass windscreen (or window) heater. The interior glass surface is first cleaned with methylated spirits and allowed to dry. The backing paper 2 is readily peeled away from the strip 4 (adhesively mounted on the sheet 10) starting at the corner remote from the terminal connectors 15, and at the terminal connectors the backing paper is torn, using the edge of these terminal connectors as cutters. The strip 4 supported by sheet 10 is placed to the screen so that the thermo-setting adhesive 3 of the strip and the low tack adhesive 11 of the sheet 10 contact the clean surface of the glass. The strip 4 and terminal connectors 15 are pressed firmly to the glass, a check for good adhesion being obtained by viewing from outside of the glass (i.e., outside of the vehicle) -- the strip 4 being visible as the outline of a thick "S." The supporting sheet 10 is then stripped off starting at the corner furthest from the terminal connectors 15, and torn off at the terminal connectors in a similar manner to that used before with the backing paper 2. A short electrical lead or wire having a female tag connector at one end connects one blade 18 to a ground point on the car body and another, long, electrical lead or wire similarly connects the other blade 18, via an electric on/off switch mounted on the dashboard, to a battery voltage point that is only energized when the vehicle ignition is on. If desired, a warning light can be fitted by wiring between the aluminum element side of the switch and ground. Such a warning light can be incorporated in the apparatus sold by Smiths Industries Limited in the United Kingdom under the Trade Mark "WARNALITE." Furthermore the electric on/off switch may be such as that described in United Kingdom Application No. 43478/70.

The laminate comprising sheet 2 in the form of a polythene coated, silicone release, heavy Kraft paper, and the sheet of aluminum bonded to MELINEX, which sheets are attached to one another by a cross-linked, acrylic based, thermosetting adhesive 3, may be obtained from Coated Specialities Limited, of Chester Hall Lane, Basildon, Essex, England. The sheet 10 coated with a low tack adhesive 11 may be one of the Butterfly Brand of Samuel Jones & Company Limited, Letchworth Mill, Pixmore Avenue, Letchworth, Hertfordshire, England.

Claims

I claim:

1. A heater assembly comprising a deformable electrical heating element which is to be adhesively secured to a surface to be heated and which has a plurality of limbs planarly disposed in spaced array, the heating element array having a continuous strip of electrically resistive material, two ends, and first and second opposed surfaces; two terminals electrically connected to said two ends of the heating element array respectively; a detachable covering layer; a first adhesive coating on the first surface of said strip for detachably adhering said covering layer to said first surface of the heating element array, the said covering layer being detachable from the heating element array prior to the mounting of said array on said surface; a detachable supporting layer; and a second adhesive coating in direct contact with said second surface for detachably adhering said supporting layer to said second surface of the heating element array to provide a predetermined level of adhesion therebetween, the said supporting layer being the sole support for maintaining the spatial relationship between the limbs of said heating element array after said covering layer has been detached, and said supporting layer being detachable from the heating element array after its mounting on said surface; the surface of said covering layer facing said first surface of the heating element array being a low-cohesion surface cooperating with said first adhesive coating to provide a level of adhesion between said covering layer and the first adhesive coating which is substantially less than the said predetermined level of adhesion between the said supporting layer and the second surface of the heating element array to enable the said covering layer to be detached from said heating element array more readily than the said supporting layer, whereby said first adhesive coating is exposed thereby to permit the heating element array, while supported by said supporting layer, to be adhesively secured to said surface by said first adhesive coating.

2. The heater assembly of claim 1 wherein the said limbs of the heating element array extend parallel to one another, the spacing between said limbs being substantially greater than the width of each said limb.

3. The heater assembly of claim 1 wherein said heating element array includes a strip of electrically insulating material bonded in surface contact and covering only said continuous strip of electrically resistive material, said insulating strip forming said second surface of said heating element array.

4. The heater assembly of claim 1 wherein said heating element array follows a path of sinuous form.

5. The heater assembly of claim 1 wherein said first adhesive coating comprises a thermo-setting adhesive.

6. The heater assembly of claim 1 wherein the low-cohesion surface of said covering layer is a polished surface.

7. The heater assembly of claim 1 wherein said low-cohesion surface of said covering layer comprises a low-cohesion coating on the surface of said covering layer facing said first surface of the heating element.

8. A heater assembly comprising an electrical heating element which is to be adhesively secured to a surface to be heated, said heating element comprising a continuous strip of electrically resistive metallic foil material having a plurality of spaced foil portions electrically connected to one another and arranged in a predetermined pattern, said heating element pattern having first and second opposed surfaces; electrical terminal means connected to said heating element pattern; a detachable covering layer; a first coating of bonding material on the first surface of said heating element pattern for detachably adhering the said covering layer to said first surface of the heating element pattern, the said covering layer being detachable from the heating element pattern prior to its mounting on said surface; a detachable supporting layer; a second coating of bonding material in direct contact with the second surface of said pattern for detachably adhering the supporting layer to said second surface of the heating element pattern, the said supporting layer comprising the sole support for maintaining the configuration of said heating element pattern after said covering layer has been detached, and said supporting layer being detachable from the heating element pattern after its mounting on said surface; the surface of said covering layer facing said first surface of the heating element pattern cooperating with said first coating of bonding material to provide a level of adhesion therebetween which is lower than the level of adhesion between said supporting layer and the second coating of bonding material.

9. The heater assembly of claim 8 wherein said heating element pattern includes a plurality of limbs disposed in spaced parallel relation to one another, the spacing between said limbs being greater than the width of each of said limbs.

10. The heater assembly of claim 8 including a strip of electrically insulating material bonded to said strip of electrically resistive foil material in a pattern which corresponds to said predetermined pattern to form said second surface of the heating element pattern.

11. The heater assembly of claim 9 wherein said electrical terminal means comprises a pair of spaced electrical terminals connected to spaced portions of said metallic foil material, each of said terminal means comprising two metallic members having one of said spaced portions of metallic foil material sandwiched therebetween, one of said metallic members having a pair of side edges which are turned inwardly to retain the other of said metallic members in place.

12. The heater assembly of claim 8 wherein at least one of said detachable layers is in the form of a strip which is essentially coextensive with said strip of electrically resistive metallic foil material.