Planar Heating Element for Underfloor Heating

A heating element includes two flexible plastics layers connected in overlying relationship with first and second conductors each running along the element between the layers the side edges with a row of printed conductive strips at right angles to the conductors. A grounding layer comprising a sheet of foil laminated to a carrier is laminated to the heating element. A reinforcing layer in the form of a bitumen anti-fracture membrane is applied on one surface and a reinforcing layer of a fiber reinforced material is applied on the opposite surface for engagement into a tile adhesive layer. First and second strips of an electrically insulating material are applied over the first and second conductors to define slots allowing insertion into the slots of respective clamp type terminals.

DETAILED DESCRIPTION

Turning firstly toFIGS. 1,2and9particularly, one example of a composite heating element19according to the present invention comprises a heating element20comprising a first flexible electrically insulating plastics layer21defining a first surface; a second flexible electrically insulating plastics layer22defining a second surface, the layers being connected in overlying relationship to form an elongate sheet with inside surfaces and outside surfaces and overlying side edges as shown inFIG. 5.

First and second conductors are defined by respective ones of two continuous electrodes24each running along the element between the layers each along a respective one of the side edges and arranged for connection across a supply of a voltage.

A conductive material extends between the first and second conductors and located between the first and second surfaces such that the voltage causes a current through the conductive material which generates heat substantially across the full extent of the sheet. The material is defined by a row of conductive strips formed by printed ink layer26applied at right angles to the electrodes, contacting the electrodes24and25thereby setting up parallel electrical heating circuits across the elongate sheet such that the voltage generates a heating current in the strips. A silver layer27is applied over the top of the printed ink to generate better contact to the bus bar or electrode24.

A grounding layer28is laminated to the heating element by a laminating layer29and comprises a sheet of a conductive foil30pre-laminated to a covering layer31of an electrically insulating plastics material over the foil. The grounding layer30is laminated to the first surface22of the flat sheet defining the heating element20by the laminating layer29formed by a layer of plastics material carrying layers of laminating glue. Other laminating methods and materials can be used as known to persons skilled in this art.

The first and second conductors24and25comprise respective ones of two continuous copper electrodes each running along the element between the layers each along a respective one of the side edges and arranged for connection across a supply of a voltage. The first and second layers21,22are polyester. There can be provided a second sheet of a conductive foil (not shown) attached to the second surface21of the heating element for retarding fire.

There is provided a reinforcing layer31on one side21which is the lower side of the heating element20which comprises an anti-fracture membrane formed of a resilient elastomeric layer such as bitumen.

The anti-fracture membrane32defines a pressure sensitive adhesive surface33on an outer surface thereof which is covered by a release sheet34which can be peeled away at35to expose the adhesive.

In an alternative arrangement, the anti-fracture membrane is translucent or at least can be seen through so as to make visible the conductive ink strips26so that a user can cut the element to length in a transverse direction while avoiding cutting through the strips26.

A first strip36of an electrically insulating material is applied over the first conductor defining a first slot37therebetween allowing insertion into the first slot of an electrical contact (FIG. 3,4) of a first terminal38;

A second strip40of an electrically insulating material over the second conductor defining a second slot therebetween allows insertion into the second slot of an electrical contact of a second terminal39. The slots are formed simply by the expedient of providing no adhesive between the strip and the respective conductor. The contact is one jaw of a clamp which bites through the layers of insulating material to engage into the respective conductor.

The strip36is wider than the second strip40so as to provide a location to receive an electrical contact of a terminal41for connection to a grounding layer. The terminals are covered by an insulating cover as is required for electrical insulation of the installation.

Again the contact of the terminal41is one jaw of a clamp which bites through the layers of insulating material to engage the foil grounding layer30. As the contact of the terminals38and39engages downwardly away from the grounding layer, they do not engage the grounding layer. As the terminal41is spaced along the strip36away from the contact24, it does not engage the strip24.

A reinforcing layer45of a fiber reinforced material is laminated by a laminating layer46so as to define an outermost layer on the first or upper side of the heating element, the fiber reinforced material defining a fibrous bonding layer for engagement into a tile adhesive layer.

The metal foil layer30and covering layer31of a plastics material are a pre-formed laminate applied as a common laminate onto the sheet forming the heating element with a foil thickness is less than 0.001 inch and preferably of the order of 0.00035 inch.

Thus the arrangement uses a thin gage aluminium of thickness only enough to carry the current to keep the costs down. This thin aluminium itself does not have the structural strength (tears/deforms easily) to be easily processed into our laminate structure.

The aluminium is already laminated to a polyester carrier sheet that provides all the structural strength for processing. The aluminium is anchored to the polyester using a dry cross-linked polyester based laminating adhesive. This structure is commonly used for shielding telecommunication cables.

The polyester on top and the heating element below also act as a barrier films preventing the aluminium from exposure to corrosive elements in all applications.

Referring toFIG. 4, as shown the terminal clips38and39must be attached to the assembly before adding the anti-fracture layer32.

In an alternative arrangement (not shown) additional strips similar to the strips36and40are used to provide a similar non adhered spaces or slots similar to the slots previously described but located between the anti-fracture layer32and the bottom of the element26to attach the terminal clips38and39. This allows the manufacturer to add the anti-fracture layer in line at the same time as other layers like layer45.

The following examples of specific combinations of components are provided:

Nonwoven PET Scrim

25 um PET Film

0.6 um PET Based Adhesive

13 um PET

51 um PET

Copper Bus Bar

Conductive Ink

114 um PET

25 um PET Film

0.6 um PET Based Adhesive

13 um PET

51 um PET

Copper Bus Bar

Conductive Ink

114 um PET

25 um PET film

0.6 um PET Based Adhesive

23 um PET

51 um PET

Copper Bus Bar

Conductive Ink

114 um PET

The Heating Element comprises a flexible, electrically insulated polyester coated element. The element consists of two electrodes or bus bars running parallel the length of the element. A conductive ink strip is printed onto the polyester at right angles to the electrodes, crossing the electrodes thereby setting up an electrical circuit. The conductive ink is resistive as per desired watts required per square foot (meter). Each bar of ink is calculated in resistance (Ohms) and is part of the heater. The entire element is covered by another electrically insulated polyester film.

While a third bus bar can be used to carry ground current in the event of a fault, this can be omitted in most circumstances since the current values which generate roughly 10 to 12 watts per square foot which is typical are insufficient to require the additional conductive material and the foil will suffice. The foil may be coated on both sides with a plastics insulating material (not shown) and in the event that the bus bar is not used, it is only necessary to connect to the ground layer at a single point by stripping the plastic coating layer on one side. The bus bar can be located underneath or on top of the foil. The top reinforcing layer of a woven or non-woven scrim can be of the type known as Collbond.

In a further embodiment (not shown) the top reinforcing layer of woven or non-woven scrim and the bottom anti-fracture membrane can be used in relation to a wire element type construction where the element is grounded with a grounding sheet or not grounded. The wire of the element is contained in a scrim.

A further example (not shown) includes a grounding layer and includes a second foil layer on the opposed side to the grounding layer for purposes of fire retardance.

The anti-fracture membrane may incorporate the heating element as part of the membrane or it may be separately applied depending on the manufacturer.

The arrangement can be used in a tiled floor comprising a sub-floor; a layer of tiles applied over the sub-floor; and a heating element where the reinforcing layer of a fiber reinforced material is on the upper side of the heating element and fastened to the layer of tiles by a tile adhesive and the anti-fracture membrane is on the bottom side of the heating element and fastened to the sub-floor.