Electric heating mat

Abstract

To provide an electric surface heater in which energy is saved in comparison with a full-area heater and local heat generation functions without any external electronic control or regulation.SOLUTION: An electric surface heater comprises an electrically-conductive plastic body 1, and an upper electrode 2 and a lower electrode 3 to which an electric voltage is applied. At least one of the two electrodes is flexible. Between the upper electrode and the plastic body and / or between the lower electrode and the plastic body, a plurality of thin spacers 4 of very limited dimensions are attached at predetermined distances from one another, so that no current flows in an unloaded state. When a load is applied, the flexible electrode sags, and a material-bonded contact to the electrically-conductive plastic body develops, thereby realizing a local flow of current and heating.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electric surface heater or an electric heating mat based on a conductive polymer foil or a conductive polymer foam that locally heats only the location on the mat where a person, animal, or object is located. Thereby, energy can be saved compared to a full-area heater. Ideally, this local heat generation functions without external electronic control or adjustment.

Background Art

[0002] Electric surface heaters have many applications, such as wall heaters, floor heaters, mirror heaters, terrarium heaters, water bed heaters, heatable foot mats, etc. For example, for heating a room, a large-area heat output is desired, but in the case of a heatable foot mat or a heating blanket for a household pet such as a dog, heat is only required at the points of direct contact.

[0003] Known electric surface heating systems generate heat by converting electrical energy (Joule heat). They are made of a conductive plastic that is contacted over the entire area or partially contacted by electrodes that can be implemented as conductive wiring. Alternatively, the metal conductive wiring itself on the heating surface, which is produced by etching or pressing on an insulating holding material, can be used for resistive heating.

[0004] A common feature of all these electric surface heaters is that the local current flow and thus the local heat generation are ultimately fixed by the position and fastening of the electrodes. Local selective control is only possible when the individual sectors of the heating surface are actively controlled.

[0005] An alternative is disclosed in Patent Document 1. Patent Document 1 describes a partial and selective supply of current by a piezoresistor. The drawback of this invention is that a plurality of pressure sensors have to be implemented according to the desired local resolution. This drawback is overcome in Patent Document 2. In Patent Document 2, the conductive heating layer itself is implemented in a pressure-sensitive manner, and electrical heating occurs only at the location where force or pressure acts. However, the drawback of this solution is that, due to the still existing finite resistance, a residual current flows even in the absence of a load, and as a result, a small amount of energy is permanently consumed. This drawback is also overcome in the present invention because no idle current flows in the unloaded case. In the present invention, the absence of an idle current means that the magnitude of the current is less than 1 mA.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

[0007] The object of the present invention is to disclose a technical solution for an electric surface heater or heating mat based on a conductive polymer foil or a conductive polymer foam. In this technical solution, local heating is generated only at the location where a person, animal or object is located on the surface / mat, and no current flows in the unloaded state. Thereby, thermal energy can be reduced. In this technical solution, neither a sensor nor an electrical controller is required.

[0008] Specifically, the object is achieved by a substance (1) containing a conductive plastic coming into contact with the upper and lower electrodes (2) and (3). A spacer (4) made of a non-conductive material is also disposed on the upper side and / or the lower side of the conductive plastic (see FIGS. 1 and 2). As a result, there is no material locking contact or frictional locking contact between the electrodes. A close contact between the electrode and the heating element is established only as a result of an increase in pressure following a local load on the surface, whereby an electric current can flow and heat can be generated in this region.

[0009] The conductive plastic may be either a plastic that is inherently conductive or a plastic that has become conductive by including an additive.

[0010] As the inherently conductive plastic, doped poly-3,4-ethylenedioxythiophene, polyaniline, polypyrrole, or polythiophene may be used.

[0011] A plastic that is not inherently conductive may become conductive by containing a conductive additive. Suitable additives include, for example, carbon black, graphite, graphene, metal particles, and carbon nanotubes. Plastics include, for example, polymers having a main chain consisting only of carbon such as polyethylene and polypropylene, as well as polyamides, polyurethanes, polyesters, and silicones.

[0012] The conductive plastic may exist in either a solid form or a porous or foamed form. Depending on the underlying polymer, it can become hard or flexible.

[0013] A conductive plastic having a positive temperature coefficient (PTC) of electrical resistance, which automatically reduces the current and thereby automatically reduces heat generation as the temperature rises, is particularly preferred.

[0014] The conductivity of the plastic is between 10 2 ~10 5 S / m, preferably 102 ~10 4 is between S / m.

[0015] The planar electrode preferably has a certain degree of mechanical flexibility, thereby enabling reversible pressing and releasing of the contact in the heating element under pressure. Suitable planar electrodes can be, for example, metal foils, metal-coated polymer foils, metal wire meshes, metallized meshes or conductive foams that ensure a sufficiently low electrical supply resistance. The material of the surface heating element (1) is preferably a conductive plastic in the form of a foil or a plate or a conductive foam.

[0016] In order to prevent the flow of current in the unloaded state, non-conductive spacers (4) need to be attached between the electrodes (2), (3) and the conductive surface heating element (1) at intervals from each other in a dot or linear arrangement. The spacers prevent limited, random, local contact from occurring between the electrodes and the surface heating element. By applying the invention of the spacers, the magnitude of the current is reduced completely to zero. The spacer (4) may be a thin flexible foam with foil or fine textile fibers. It is necessary to ensure that the surface covered by the spacer (4) is very small compared to the total area of the heating mat, preferably less than 10% if possible.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0018] In the first embodiment, the conductive plastic (1) comprises a conductive foam panel, electrodes (2), (3) of a metal wire mesh, and spacers (4) of fine polyester fibers arranged at a distance of several centimeters from each other between the foam panel and the electrodes.

[0019] In the second embodiment, as the spacer (4), thin foam pads having a size of several millimeters in the lateral direction are adhered onto the foam panel at a distance of several centimeters from each other.

[0020] In the third embodiment, the electrodes (2), (3) are realized by a metallized mesh. The important advantages of these electrodes over the metal wire meshes of the first and second embodiments are greater flexibility and lighter weight.

Example

[0021] Example 1 This example shows the operating principle of the present invention. A conductive PE foam (ELS-M) having dimensions of 470×320 mm and a thickness of 6 mm has stainless steel wire mesh electrodes on both sides. The wire mesh electrodes include stainless steel wires having a mesh width of 1.4 mm and are loosely fixed to the edges of the foam. PET plastic filaments with a diameter of 0.5 mm and spaced at intervals of about 6 cm are woven into the wire mesh as spacers between the lower wire mesh electrode and the conductive foam. Twenty-eight small foam plates (2 mm thick) are adhered as spacers between the upper wire mesh electrode and the conductive foam at intervals of about 8 cm from each other. In principle, other materials and body shapes arranged so as not to prevent wide-area contact between the electrodes and the conductive foam during loading can be used as spacers.

[0022] When no load is applied, even when a voltage of 60 V is applied to the electrodes, no measurable current flows through the heating mat. When a local load is applied to the mat, a significantly high current begins to flow at this location. In one example, the load, which is determined by the shape of the applied load, is applied to an annular region with an inner diameter of 3.5 cm and an outer diameter of 6.6 cm. This corresponds to a load area of 24.6 cm 2 corresponding. When a mass of 9.4 kg is loaded in this region, a current of 140 mA flows. This is 5.7 mA / cm 2corresponds to the local current density. When the load increases to 13.3 kg, the current increases to 160 mA or 6.5 mA / cm 2 and the temperature rises by 30 - 35 K compared to the unloaded part of the mat.

[0023] In the second modification, the central part of the mat receives a weight of 80 kg in a rectangular area of 31×20 cm. The current density becomes 1.3 A and the local current density becomes 2.1 mA / cm 2 .

[0024] When a person weighing about 75 kg steps on the mat, a current of 1.34 A flows. Assuming the sole area is about 500 cm 2 , the current density becomes 2.7 mA / cm 2 . The 80 W of power thus generated rapidly heats the mat under the foot, and a temperature rise of 15 - 25 degrees corresponding to the contact of the foot is shown by thermography after about 10 seconds (Figure 3).

[0025] Example 2 This example shows the importance of the spacer for reducing the idle current under no load as a result of not using the spacer. A conductive foam having dimensions of 21×21 cm and a thickness of 7 mm has stainless steel wire mesh electrodes attached to both sides. The wire mesh electrodes include stainless steel wires with a mesh width of 1.4 mm and are loosely fixed to the edges of the foam. There is no spacer. When a voltage of 60 V is applied to the electrodes, a small but easily measurable current of 10 mA caused by random punctiform contacts flows through the heating mat under no load. When a local load is applied to the mat, a higher current comparable to that in Example 1 begins to flow through this location.

Explanation of Symbols

[0026] 1 Conductive plastic 2 Upper electrode 3 Lower electrode 4 Spacer 5 Heating mat

Claims

1. An electric surface heater comprising a conductive plastic body, an upper electrode and a lower electrode to which a voltage is applied, at least one of the two electrodes is flexible, a plurality of small spacers of extremely limited dimensions are attached at a predetermined distance from each other between the upper electrode and the plastic body and / or between the lower electrode and the plastic body so that no current flows in the unloaded state, An electric surface heater in which, when a load is applied, the flexible electrode bends and material bonding contact with the conductive plastic body progresses, thereby realizing a local flow and heating of current.

2. The electric surface heater according to claim 1, wherein the conductive plastic body is essentially conductive.

3. The electric surface heater according to claim 2, wherein the conductive plastic body contains doped poly-3,4-ethylenedioxythiophene, polyaniline, polypyrrole or polythiophene, or contains doped poly-3,4-ethylenedioxythiophene, polyaniline, polypyrrole or polythiophene.

4. The electric surface heater according to claim 1, wherein the conductive plastic body has become conductive by containing an additive.

5. The electric surface heater according to claim 4, wherein the conductive plastic body has become conductive by containing carbon black, graphite, graphene, metal particles and / or carbon nanotubes.

6. The conductive plastic body according to claim 4 or 5, wherein the plastic is selected from polymers having a main chain consisting only of carbon.

7. The conductive plastic body according to claim 1, wherein the body exists in either a solid form or a porous or foamed form.

8. The conductive plastic body according to claim 1, having a positive temperature coefficient (PTC) of its electrical resistance.

9. The conductivity of the plastic is 10 ２ to 10 ５ S / m, and the conductive plastic body according to claim 1.

10. The electric surface heater according to claim 1, wherein the planar electrode is a metal foil, a metal-coated polymer foil, a metal wire mesh, a metallized mesh or a conductive foam.

11. The electric surface heater according to claim 1, wherein the spacer is non-conductive and is attached on the upper side and / or the lower side of the conductive plastic body in a dot or parallel arrangement with a certain interval from each other.

12. Including foamed material with foil or textile fibers, The surface area covered by the spacer is less than 10% of the total surface area of the conductive plastic body, the spacer according to claim 11.

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