IL40453A - Rigid electrical area heating elements and method for their manufacture - Google Patents

Description

Rigid electrical area heating elements and method for their manufacture REUTER U GmbH 58423 40453 2 The present invention relates to a process for the manufacture of a rigid surface heating element heated by electricity of the type consisting of a thin rigid heat resistant electrical insulating layer emittin the which is connected by means of an electrically conducting provided with corresponding electrodes and electrical connections to a electrically insulating Prom German there are known electrically heated surface heating elements which consist of a heat resistant heat emitting connected by of an electrically conducting film provided with corresponding and with electrical with rigid heat insulatin According to Patent Specification the electrically conducting film for produced from an aqueous dispersion of silica containing carbon by applying this dispersion for formation of conductive film as a coating on a supporting and drying the On this dry film the electrodes corresponding electrical connections are then and the insulatin is Also known are electrically heatable area elements which are produced by using wires or other tissues which are rendered electrically By virtue of production problems and the fact that the heat irradiation does not correspond to the has not so far been possible for these area heating elements to become broadly it is desirable to use a mechanically readily material for the a material is for example advantageous if structures or of tubes have to be heated or are to be constructed as heating laminated materials would need to be glued if box structures are produced they have a not completely satisfactory mechanical stressability and resistance to The object of the invention is to provide rigid area heating elements which do not exhibit the disadvantages of the prior art and which in particular a high mechanical and electrical stability as well as reproduceable electrical values and improved properties during the heating A further object of the invention is to provide a per se rigid area heating element in which the heat transmitting coating consists of a mechanically readily mechanically heavily highly and ageing resistant material and which furthermore conveys heat particularl well and irradiates it to the ambient The present invention thus provides a rigid surface heating element having a heat insulating layer of rigid polyurethane which in formed directly on the electrically conductive The electric resistance of the conductive film remains practically constant during the formation of the foam layer also during the use Accordin to a particular form of embodiment of the area heating element according to the the layer consists of a metal while the side of the metal layer which is towards the electrically The object the present invention has been solved by a process in an aqueous dispersion of a plastics material containing particles and in potassium o sodium silicate is on to a thin to a heat conducting which is diied preferably at a temperature of approximately and at a drying time approximately and after application o electrodes and corresponding electrical a coating of rigid polyurethane foam is applied to this film by bringing the reaction mixture into direct contact In order to produce the aqueous electrically conducting particles containing plastics dispersion an aqueous dispersion of an acrylic is mixed with an aqueous solutio of or sodium silicate and with an aqueous dispersion of carbon the viscosity of the plastics dispersion being so adjusted that a readily mixture is obtained This mixture is then applied for to the patterned side of a The use of alkali silicates for such gical uses was not hitherto because potassium or sodium silicate solutions are not and could therefore be destroyed even atmospheric Only by virtue of the foaming of rigid polyurethane foams and the use of an front according to it bedome possible expedien to use a film containing For heating films without silicates are subject to marked attack from the rigid starting components of the so that upon foaming the electrical resistance value undergoes a The acrylic reain dispersion additionally stirred into the silicate solution and exactly like the silicates serves to bond the electrically conductive imparts a certain elasticity to the This elasticity is desired during heating up within 10 seconds from to substantial differences in temperature and mechanical stresses occur in the a It has been demonstrated system is particularly suitable for absorbing such jumps in so that particularly the conductivity of the heating film at the moment of starting is very favourably The film of black miature is resistant to the aggressive starting components from which the rigid polyurethane is obtained so that the foam components can be applied directly onto the heating The residual humidity the film to polar is absorbed by the foam components which contain In addition to acrylic resin polytetrafluoroethylenes are also very suitable as a synthetic plastic The invention is illustrated by the following drawings in 1 shows a through a rigid area element according to the consistin of thin layer the 5 and the thick layer 2 shows a thi heat irradiating layer 1 provided with electrodes and electric connection points 4 shows the same object as 2 but a subsequently applied film 4 shows the thin hea irradiating layer 1 provided heating 5 together with a 6 producing a layer of foam 5 is a perspective view of a area heating element 10 accordin to the in the form of a the layer being a metal 11 being sheet metal 12 the heating 13 a plastics layer and 14 an electrical and 6 and 7 show a through a 15 having a heating shell 11 which has been formed from two tubular of the type shown in 5 16 bein packing As the thin layer 1 any rigid heat resistant possibly provided with a special design eat irradiating may be In order to avoid any outside on heatin for example by atmospheric the thin layer 1 is preferably impervious to As an example of the thi layer there may be mentioned boards commercially available the material known under trade name The electrically conducting particles contained in the electricall conducting 5 may consist of a carbon for carbon black or or from a noble metal or other metals or non metals plated with a noble Preferably For the further construction of a heating element according the invention at least two electrodes are also The purpose of the electrodes is to establish between them a resistance value which is homogeneous over the entire conductive When an electric voltage is applied to electrodes by virtue of film a homogeneous voltage potential forms between the The may be flexible metal strips for plastics if electrodes are not subjected to mechanical Especially suitable for the purpose of the present invention are those electrodes produced in the manner described As a conductive available copper of a particle of approximately 180 microns is Other metal apart from those coated with rare cannot be used for this For producing the the copper powder a particle diameter as indicated is stirred for example into a aqueous acrylic resin Sufficien powder is added to mixture to be just Since the relatively large particles of metal powder along their tangential contact relatively large a aqueous carbon black dispersion is stirred into the carbon black dispersion with readily conductive acetylene black content millicrons fills the empty interstices completely with particles of carbon black once the carrier liquid has the interface of the metal particles thicker heat insulating layer 2 consists of polyurethane The manufacture of various types of polyurethane is known to a man skilled in the is made to the The area heating elements according to the invention which are lined on the a coating of polyurethane foam are universally usable because in addition to the ready conversion into rigid polyurethane materials are particularly characterised by excellent thermal insulating owing to their excellent mechanical properties the area heating elements according to the invention may be used for ceiling In the case of floor heating it is or after they are laid on the to apply on the hea irradiating a coating of floor finish in which upon suitable selection of the a heating is weight of a one square metre large and 20 mm thick heating panel with a coating of polyurethane foam is mately The consists of a material which can be supplied in the widely diverse order to eliminate risks caused for example by knocking nails into the heating these heating elements preferably operate on low According to the field of the heating elements are adjusted to a wide range of temperatures and can be designed for any working If by virtue of poor heat an upper temperature limit has be then or some other temperature limiting means can be connected directly in or to For heating elements according to the with low working the mixture has to be somewhat modified in that the resistance is reduced to the desired values by the addition of metal If the layer the heating element to the invention is a metal then it can consist of all manner of metal including galvanised or anodlsed the metal plates being of any The electrical insulating layer which this ease is found on that side of the metal coating which is towards the heating adhere very rigidly to the metal and exhibit a satisfactory bond with the heatin the insulating layer must consis of a material with a high electrical insulatin capacity and a high breakdown A metal plate is cleaned and then coated on both with an resin The coating can be applied for example by the sinter at the spraying method or the coating preference is given to the latter The coated plate is then heated in order to dry out epoxide electrodes are to one side of the low working of 12 to volts flow above 2 silver plated or copper strips a glued directly onto the layer of epoxide Glues are used whic contain no acetone or methyl ethyl For lower flow less than 2 the electrodes can be produced by application of silver The electrical resist ance along an electrode ought not to exceed 1 Once the electrodes have been the heating film as previously described is applied and dried out at elevated tem The heating film ought to overlap both the el ctrodes are connected to connecting wires by means of terminals or by the entire system is foamed with rigid polyurethan foam by one of the previously described The invention is illustrated but not limited by the following Examples Example 1 Manufacture of a heating element A Resopal panel is first provided with electrodes on the side on which there is no The electrodes are applied by means of a template mm 270 mm and are at a reciprocal spacing of 370 The electrode mixture consists of 80 parts by weight of a dispersion of a copolymer of butyl vinyl acetate and acrylic 100 parts by weight of copper powder and 100 parts by weight of a acetylene soot using a frame x 370 the actual heating film is In order to produce the heating to a mixture of 100 parts by weight of a potassium silicate solution dry substance water with a and 80 parts by weight of a aqueous carbon black are added 80 parts parts by weight of aqueous acrylic resin The readily brushable mixture is applied evenly to the side of the Resopal The electrodes are completely covered by the heating The film is then dried for approximately minutes at approximately A contact plate and a cable shoe are attached to each electrode in order to allow connection to a voltage The entire heating film may if necessary be sealed with an electrically insulating plasties The formation of a rigid polyurethane foam on the heating film is now The pol material is foamed on in known manner and need hot therefore be described in greater The mould frame with sides for example 40 is so placed on the heating foil that the inside of the mould is at a minimum distance of 15 from each side of the heating The reaction mixture the rigid foam is poured into the space in the A cover placed onto the and pressure applied to to avoid the up material After removal of the mould frame the heating element has on its reverse side a layer of rigid polyurethane The generated when a voltage is applied is now irradiated from the s of the Reaopal of elemen metal coating is heated to the epoxide f insufficientOCRQuality

Claims (10)

'CIAIMS

1. A process for the manufacture of a rigid surface heating element heated by electricity and consisting of a thin, rigid, heat-resistant, electrically insulating layer emitting the heat, which is connected by means of an electrically conducting film provided with corresponding electrodes and electrical connections to a thicker, rigid, electrically insulating layer, characterized in that an aqueo plastic dispersion containing electrically conducting particles is deposited on the thin, heat-emitting layer in order to form the electrically conducting film, said dispersion containing a potassium or sodium silicate, and in ' that following drying of the film and after mounting the electrodes and corresponding electrical junctions a polyurethane resin layer as the thicker, heat-insulating layer is deposited "by bringing the foam-forming reaction mixture into direct contact with the previously deposited electrically conducting film.

2. The process of Claim 1, characterized in that precious metals, or other metals or substances coated with precious metals, or carbon are used as electrically conducting particles.

3. A process as defined in Claim 1, characterized in that an acrylic resin is used as the plastic contributing to the forma-tion of the electrically conducting film,

4. A process as defined in Claim 1, characterized in that an airtight plastic layer is used as the thin, heat-emitting layer. 40453-3

5. A process as defined in Claim 1, characterized in that the thin, rigid, heat-resistant and heat-emitting layer consists of a metal layer provided with an electrically insulating layer, the electrically conducting film being deposited on the electrically insulating layer.

6. A process as defined in Claims 1 through 4 / characterized in that the electrically insulating layer is heat-resistant up to temperatures of 150 °C. and lacks softening or otherwise rheological disadvantageous properties when exposed to heat, consisting of a plastic which does not generate gases under such circumstances.

7. An electrical heating element manufactured in accordance with the process of Claim 1.

8. The process of Claim 2 wherein the carbon is lampblack, carbon black or graphite.

9. · . The process of Claim 4 wherein the plastic layer is formica.

10. The process of Claim 6 wherein the electrically insulatin layer is an epoxy resin. For 'he App//ca„ts