EP1053658B1 - Flat heating element and use of flat heating elements - Google Patents

Abstract

The invention relates to uses of a flat heating element in a heatable pipe, a heatable transportation device and a heat roller, and to a flat heating element comprising a thin resistance layer containing an intrinsically electroconductive polymer and at least two flat electrodes arranged on one side of the resistance layer at a distance from each other.

Description

The invention relates to a surface heating element, in particular a resistance heating element, and applications of surface heating element.

Resistance heating elements are used in various areas to generate heat. These heating elements generally require high voltages in the heating element in order to generate a sufficient temperature. However, these high voltages can pose safety risks, particularly when used to heat media or when in contact with the human body. In addition, conventional resistance heating elements are mostly only suitable for low temperatures due to the materials used therein, particularly in long-term operation. Other proposals of the prior art require a complex structure of the resistance heating element and thus restrict the possible uses of the resistance heating element.

From the patent application DE 35 02 838 A1 a heating element with a centimeter-thick, thermally insulating resistance layer is known, which is made of granular and / or spherical insulating materials, e.g. pre-expanded polystyrene or the like. The insulating materials are in turn connected to one another by a binding agent - optionally an intrinsically electrically conductive plastic.

From the patent specification AT 313 588 three exemplary lists of the ingredients for the production of a polymer are known, which is converted into an intrinsically electrically conductive plastic by doping with metal or semimetal atoms, in a ratio of one to one to the number of polymer molecules.

A flat heating element is known from patent specification FR 1 347 047, in which a plurality of electrodes are arranged on both sides of the resistance layer, offset from one another. Through this arrangement of the electrodes, the voltage prevailing at the respective zones of the resistance layer is correspondingly reduced by series connection in a manner known per se.

The object of the present invention is to provide a heating element with which high area outputs and thus high temperatures can be generated even in long-term operation and at the same time low voltages prevail in the heating element. Furthermore, the heating element should be versatile and easy to contact.

Further objects of the invention result from applications of the heating element, as can be gathered from the exemplary embodiments below.

The invention thus further relates to a heatable tube in which a resistance heating element is used.

Pipes become versatile, e.g. used for media forwarding. If these pipes are e.g. laid underground or in cold regions outdoors, there is a risk that the medium in the pipe will solidify due to the low temperature and blockage of the pipe will occur.

It is therefore a further object of the invention to provide a tube which can be heated with simple means and is versatile.

The invention further relates to a heatable transport device for media.

Media such as gases or liquids are often transported in tanks that are attached to railroad cars or trucks. At low ambient temperatures, the medium in the tank can freeze and the tank may even be damaged. The Attaching heating elements to such wagons places high demands on the heating element, as well as on the possible heat transfer between the heating element and the wagon. Hazardous substances are sometimes transported in such tanks. It is important that the heating element does not cause local temperature increases. Failure of the heating element due to, for example, detachment from the tank must also be avoided in order to prevent the medium from freezing.

It is therefore an object of the present invention to provide a transport device for media, with which a medium can be kept at a predetermined temperature during transport, without security risks such as e.g. Freezing, causing an explosion or fire.

The invention further relates to a heating roller, in particular for use as a copying or foiling roller.

In many areas of thermal engineering it is necessary to provide a roller that can be heated to a certain temperature. So far, such heating rollers have been produced by heating elements in which resistance wires are embedded in an insulating mass. Another variant, heating rollers, which e.g. can be used in copiers, is to provide a halogen lamp in the roller. Both variants have the disadvantage that they are either very expensive to manufacture or have poor heat transfer efficiency.

The present invention has for its object to provide a heating roller that has a simple construction, can be operated with low voltage and at the same time a high efficiency Has heat transfer. Furthermore, the heating roller should be versatile.

The invention is based on the knowledge that these objects can be achieved by a resistance heating element in which a suitable resistance mass is optimally flowed through by the heating current.

The invention is also based on the knowledge that the further objects can be achieved in particular by a tube, a transport device and a heating roller which are provided with a resistance heating element, the resistance heating element having a suitable resistance mass, the heating current flowing through it being optimally flat and a ensures uniform heat emission over the surface.

The objects are achieved according to the invention by a surface heating element.

The first of the further objects of the invention is achieved by a heatable tube in which an inner tube is at least partially covered on the outside thereof directly or via an intermediate layer with a thin resistance layer, which comprises an intrinsically electrically conductive polymer, and at least two on the outside of the resistance layer , the resistance layer at least partially covering, flat electrodes are arranged spaced apart.

The second of the further objects of the invention is achieved by a heatable transport device for media, which comprises a container for receiving the medium, the container at least partially on its outside directly or via an intermediate layer is covered with a thin resistance layer, which comprises an intrinsically electrically conductive polymer, and on the outside of the resistance layer at least two flat electrodes, which at least partially cover the resistance layer, are arranged spaced apart from one another.

The container can be easily and reliably heated by the transport device according to the invention.

The third of the further objects of the invention is achieved by a heating roller which comprises a roller shell and at least one flat resistance heating element arranged on the inside of the roller shell, the resistance heating element comprising at least two flat electrodes and a thin resistance layer which comprises an intrinsically electrically conductive polymer, consists.

In the heating element according to the invention, in the pipe according to the invention, in the transport device according to the invention and in the roller according to the invention, the resistance layer comprises an intrinsically electrically conductive polymer.

These polymers used in the resistance layer according to the invention are designed so that the current flows along the polymer molecules. Due to the polymer structure, the heating current is conducted along the polymers through the resistance layer. Due to the electrical resistance of the polymers, heat is generated which can be given off to an object to be heated, to the inner tube to be heated, to the container to be heated or to the roller jacket to be heated. The heating current cannot take the shortest path between the two electrodes, but follows the structure of the polymer structure. The length of the current path is thus predetermined by the polymers, so that even with thin layers, relatively high voltages can be applied without the voltage breaking through. Burning out is not to be feared even at high currents, for example inrush currents.

Furthermore, by distributing the current in the first electrode and then conducting it through the resistance layer along the polymer structure, a homogeneous temperature distribution in the resistance layer is achieved. This occurs immediately after the voltage is applied to the electrodes.

Due to the polymers used according to the invention, it is possible to use the resistance heating element, the tube, the transport device and the heating roller even at high voltages, e.g. To operate mains voltage. Since the achievable heating power increases with the square of the operating voltage, it is possible to achieve high heating powers and thus high temperatures with the resistance heating element according to the invention, the tube, the transport device or the heating roller. The current density is minimized according to the invention by providing a relatively long current path along the electrically conductive polymers or by creating at least two zones which are electrically connected in series and have the intrinsically electrically conductive polymer used according to the invention.

Furthermore, the electrically conductive polymers used according to the invention are long-term stable. This stability is mainly due to the fact that the polymers are stretchable, so that when the temperature rises, the polymer chains do not tear off and the current path is not interrupted. Even with repeated temperature fluctuations, the polymer chains are not damaged. In contrast, with conventional resistance heating elements, or when using them for heatable pipes, for heatable transport devices or heating rollers, in which the conductivity, For example, generated by soot structures, such thermal expansion would result in a break in the current path and thus in a. Cause overheating. This would result in strong oxidation and lead to the resistance layer burning out. The intrinsically electrically conductive polymer used according to the invention is not subject to such signs of aging.

The intrinsically conductive polymers used according to the invention are also resistant to aging in a reactive environment, for example atmospheric oxygen. Furthermore, the type of conduction of the current through the resistance mass is an electron conduction. Self-destruction of the resistance layer by electrolysis reactions under the influence of electrical currents does not occur in the resistance heating element according to the invention, the tube, the transport device or the heating roller. In the resistance heating element according to the invention, the pipe, the transport device or the heating roller, the losses in the surface heating power over time are very low even at high temperatures of, for example, 500 ° C. and high surface heating powers of, for example, 50 kW / m ² , and are approximately zero.

This long-term resistance or aging resistance is of particular importance for the pipe according to the invention, since heatable pipes, e.g. in the ground or in other hard to reach places and frequent repairs are undesirable, if not impossible.

Overall, the resistance layer used according to the invention has a homogeneous structure due to the use of intrinsically electrically conductive polymers, which allows uniform heating over the entire layer.

In a heating roller according to the invention, the choice of an electrically intrinsically electrically conductive polymer as the material of the resistance layer the heating roller on the one hand ensures sufficient flexibility of the heating element, as a result of which it can be placed well on the inner surface of a roller, and on the other hand heat is generated uniformly over a large area. By providing the resistance heating element on the inside of the roll shell, it is protected against mechanical stress during operation.

In addition, the resistance heating element with electrically conductive polymer can serve as a "black body". This body can emit radiation of all wavelengths. As the temperature decreases, the wavelength of the emitted radiation shifts more and more towards the infrared. If the roller is made of a material that transmits this radiation, e.g. Glass or plastic, the infrared radiation from the roller can affect the material to be heated. Due to the depth effect, no high temperatures are required in the resistance layer itself.

According to one embodiment, the resistance layer is arranged between the electrodes connected to a current source, which at least partially cover the resistance layer. In this embodiment e.g. the roll shell itself serve as an electrode. The resistance layer with a predetermined thickness is applied directly to the inside of the roller. A counter electrode is then arranged on the side of the resistance layer facing away from the roll shell. The heating current applied to the electrode and the roller jacket serving as the electrode essentially flows through the resistance mass in its thickness. This construction ensures good heat transfer to the material to be heated, because the roller jacket is in direct contact with the resistance layer.

According to this embodiment, however, a flat electrode can also be arranged on the inside of the roll shell, the electrode on the roller shell opposite side is covered with a resistance layer. The further electrode is then arranged on this resistance layer. In this case the heating current flows between the two electrodes and the roller surface can be kept free of tension. This embodiment is particularly advantageous in applications in which direct contact between the heating roller and, for example, the user of the device can occur.

According to a further embodiment, the at least two flat electrodes are arranged spaced apart from one another on the side of the resistance layer facing away from the roller shell.

According to the invention, the resistance heating element, the tube, the transport device and the roller are contacted by two electrodes, which are preferably made of a material with high electrical conductivity and are arranged on one side of the resistance layer. This type of contacting allows the mode of action of the intrinsically conductive polymers used according to the invention to be used particularly advantageously. The applied current is initially distributed in the first electrode, then flows through the thickness of the resistance layer along the polymer structure, in order then to be conducted to the second contacted electrode. The current path is therefore longer compared to a structure in which the two electrodes enclose the resistance layer between them. Due to this current flow, the thickness of the resistance layer can be kept small - particularly small in the case of the roller.

The heating element according to the invention, the tube, the transport device or this embodiment of the heating roller also has the advantage that it or it is versatile. The electrodes are contacted via one side of the resistance layer. This is facing away from the inner tube, the container or the roller jacket and thus for contacting easily accessible. The opposite side of the resistance layer is thus free of contact connections and can therefore be pronounced. Such a flat surface allows direct application to the body to be heated, to the inner tube, to the container or to the roller jacket. Since the contact surface between the resistance heating element and the body to be heated, the inner tube, the container or the roller jacket is not interrupted by contact connections, an ideal heat transfer is possible, with the roller jacket up to 98%. In addition, uniform heat transfer from the resistance heating element to the roller jacket and thus to the material to be heated can take place reliably.

This construction according to the invention enables pipes to be easily heated. The inner tube can already be provided with the resistance layer and the electrodes as well as, if necessary, the intermediate layer at the place of manufacture and can be installed in the pipeline on site in this finished state.

According to a preferred embodiment of the heating element, a flat floating electrode is arranged on the side of the resistance layer opposite the two flat electrodes. According to one embodiment of the tube or the transport device according to the invention, this or this has an intermediate layer of material that has a high electrical conductivity between the inner tube or the container and the resistance layer. This intermediate layer serves as a floating electrode. On the side of the resistance layer of the roller facing away from the electrodes, an intermediate layer made of a material with high electrical conductivity can be provided between the resistance layer and the roller shell. This intermediate layer also serves as a floating electrode. But it is also within the scope of the invention, the resistance layer in this embodiment of the Apply the roller directly to the roller jacket. Electrical insulation of the intermediate layer or the resistance layer from the roll shell can also be achieved by simple means, for example by a film.

For the purposes of the invention, a floating electrode is an electrode that is not contacted with the current source. This can have insulation that prevents electrical contact with a power source.

This floating electrode supports the flow of current through the resistance layer. In this embodiment, the current is distributed in the first electrode, flows from it through the thickness of the resistance layer to the opposite floating electrode, is passed on in this, and then through the thickness of the resistance layer to the further electrode which is on the side of the resistance layer where the first electrode is arranged or which is facing away from the tube or container. The intermediate layer or can be isolated from the inner tube or the container by foils. The non-contacted intermediate layer can be insulated using known films made of polyimide, polyester and silicone rubber.

In this embodiment of the heating element, the heatable tube, the heatable transport device or the heating roller, the current flows essentially perpendicular to the surface of the resistance layer through its thickness. Essentially two zones are formed in the resistance layer. In the first zone, the current flows essentially perpendicularly from the first contacted electrode to the floating electrode and in the second zone essentially perpendicularly from the floating electrode to the second contacted electrode. With this arrangement, a series connection of several resistors is achieved. Has this phenomenon as a result, the partial voltage that prevails in the individual zones is reduced compared to the applied voltage. In this embodiment of the invention, the voltage prevailing in the individual zones is therefore half of the voltage applied. Safety risks can be avoided in the heating element, tube, transport device or heating roller according to the invention due to the low voltage prevailing in the resistance layer, and the possible uses are therefore diverse. Thus, the heating element can also be used for devices in which it comes into direct contact with a medium to be heated, or must be touched by the people who operate or use the device. The pipe according to the invention can be used in wet areas or, for example, in moist soil, or can be used in which people have to touch the pipe. The transport device according to the invention can thus also be used in which people have to touch the container. When transporting media, the device according to the invention is exposed to the weather conditions. The device can therefore come into contact with water, in particular in the event of rain or snow. As a result of the extremely low voltage that is present in the resistance layer in the device according to the invention, there is no safety risk as a result. Furthermore, it is possible to operate the device according to the invention by means of a conventional voltage source, for example a battery. This can be easily attached to the railway wagon or truck. In the latter case, the device according to the invention can also be supplied with voltage by the battery of the truck, which represents an additional design simplification.

Furthermore, the intermediate space between the contacted electrodes acts as an additional parallel resistor. If air is chosen as insulation in this space, the resistance becomes determined by the distance between the electrodes and thus by the surface resistance of the resistance layer. The distance is preferably greater than the thickness of the resistance layer and is, for example, twice the thickness of the resistance layer.

The electrodes and the floating electrode preferably have good thermal conductivity. This can be greater than 200 W / m · K, preferably greater than 250 W / m · K. Local overheating can be quickly dissipated thanks to this good thermal conductivity in the electrodes. Overheating can therefore only occur in the direction of the layer thickness and does not have a negative effect due to the small layer thickness that can be achieved with the resistance heating element according to the invention, the transport device, the heating roller or the tube. Another advantage of the resistance heating element, the transport device, the heating roller or the tube is that one from the outside or from the inside, e.g. from the body to be heated, from the environment by solar radiation, from the material to be heated or from the inner tube to be heated, local temperature increase caused by the resistance heating element can be compensated for in an ideal manner. Such temperature increases can also take place from the inside, e.g. occur with only partially filled containers, since the heat transfer from the container to the air is lower in the areas filled with air. They can also be caused from the inside, e.g. if there is a build-up of heat in the roller. For this reason, an insulating material can be provided inside the roller. They can also e.g. occur with pipes that are only partially filled, since the heat transfer from the pipe to the air is lower in the areas filled with air.

The heatable tube, the heatable transport device or the heatable heating roller also has the advantage that the resistance layer is arranged on the inner tube, the container or the roller shell is able to withstand heavy loads without causing local temperature increases. The mechanical loads that can act on a pipe in the installed state, in particular under the ground, on the container or on the roller shell, generally occur in the radial direction. This direction corresponds to the direction of the current flow in the resistance layer of the resistance heating element. With such a load, there is therefore no increase in the resistance at the points where the pressure occurs, as would be the case with a resistance heating element in which the current would flow perpendicular to the pressure load.

In a further embodiment of the heatable tube according to the invention or the heatable transport device according to the invention, the resistance layer is arranged directly on the inner tube or container, which consists of an electrically conductive material.

In this embodiment, the current flow from one electrode to the next is conducted via the resistance mass and the inner tube or container. Due to the low voltages prevailing in the resistance layer in the tube or transport device according to the invention, the inclusion of the inner tube, which in this case acts as a floating electrode, can be used to conduct the current without safety risks. At the same time, the heat generated in this embodiment can be given off well to the medium located in the pipe or container. In this embodiment, the inner tube or container can be completely covered with the resistance layer and the electrodes can cover it essentially completely. The distance between the electrodes to be provided for electrical reasons is also present in this embodiment.

According to a further embodiment, the resistance layer and the electrodes arranged thereon extend longitudinally in the axial direction and the electrodes are arranged on the resistance layer at a distance from one another in the circumferential direction.

Due to the longitudinal extent of the resistance layer and the electrodes as well as, if necessary, the resistance heating element formed, a certain length or area of the tube or the container can be heated, the current supply only having to take place at one point of the two electrodes.

According to a preferred embodiment, the resistance layer covers only a partial area of the circumference of the inner tube or the container and extends longitudinally in the axial direction. The length of the resistance layer and the electrodes preferably corresponds to the length of the tube or the container.

In this embodiment, heat can be emitted to the tube or the container over a defined area in which the resistance layer or, if appropriate, the intermediate layer is applied to the inner tube or container. In the case of pipes or in transport devices in which the inner pipe or the container has good thermal conductivity, the heat given off by the resistance layer is distributed over the entire circumference of the inner pipe or the container and can thus the medium located in the pipe or in the container heat completely. With this structure, the medium is heated well with little construction effort. However, this embodiment is only possible with a construction of the heatable pipe or transport device according to the invention. Only with such a structure can a high area performance be achieved without the resistance layer being used over a longer period of time and under the influence of reactive substances such as Operating time and under the influence of reactive substances such as water or atmospheric oxygen.

The resistance layer preferably covers a partial area of the circumference, which lies on the lower side of the tube in the installed state. This ensures that the medium to be heated is in contact with this subarea even in the case of a pipe which is not completely filled, and is thus heated reliably and quickly.

According to the invention, the electrodes, which are attached to the side of the resistance layer facing away from the roll shell, can extend essentially over the entire circumference and are arranged axially spaced from one another.

This arrangement is advantageous because, in the case of a heating roller which is rotating in use, current can be supplied from the two roller ends.

The electrodes and the floating electrode of the resistance heating element or the intermediate layer of the tube, the transport device or the roller are preferably formed from a material with a high electrical conductivity. The specific electrical resistance of the electrodes can be less than 10 ^-4 Ω · cm, preferably less than 10 ^-5 Ω · cm. Suitable materials are, for example, aluminum or copper. The choice of such an electrode material ensures that the current applied is passed on in the flat electrode, that is to say it is distributed in the latter before it flows through the resistance layer. In this way, a uniform flow through the resistance layer through the heating current and thus a uniform and essentially complete heating of the resistance layer is achieved. With such a resistance heating element, heat can therefore be generated and emitted evenly. In particular, by choosing one Such electrode material makes it possible to produce large resistance heating elements without the electrodes having to be subjected to voltage at several points along their length or width.

This is also of particular importance in the case of the tube, the transport device or the roller according to the invention. Pipes are usually used to manufacture pipes, e.g. Pipelines used. Since the resistance layer and the electrodes in such a pipeline, which consists of pipes according to the invention, have long lengths, it is advantageous if the electrical resistance of the electrodes is low. Containers for transport devices are usually made in a long length. Since the resistance heating element in such a transport device has long lengths, it is advantageous if the electrical resistance of the electrodes is low. Heating rollers, e.g. used as a copying or foiling roller must heat up quickly and have a uniform temperature over the entire length.

With an electrode material with such a specific resistance, a voltage drop across the surface of the electrode, which would lead to a total power drop and to different temperatures over the surface, can be avoided. In addition, the conductivity ensures a rapid distribution of the current in the electrode, which permits rapid, uniform heating of essentially the entire resistance layer and thus the length of the tube, the container or the roller, without the electrodes over their length or Width must be applied to voltage in several places.

A routing of power supply lines along the surface of the resistance heating element is therefore unnecessary, or a routing along the tube or the container may therefore be unnecessary. Such multiple contacting is selected according to the invention only in embodiments in which the resistance heating element covers a large area or length, for example in areas of more than 60 cm ² , preferably more than 80 cm ² . The size of the resistance heating element from which a multiple contact makes sense depends not only on the choice of the electrode material but also on the location of the contact. Such pipes or containers can have a length of up to 1 m. Such multiple contacting is selected according to the invention only in embodiments in which the container has a great length. The length from which a multiple contact makes sense depends not only on the choice of the electrode material but also on the location of the contact. Thus, multiple contacting can also be dispensed with in the case of larger areas than those mentioned above, if the electrode is accessible in the middle of its area and can be contacted there.

Furthermore, the size of the resistance heating element which can be operated with a simple contact, the length of the tube which can be operated with a simple contact, the length of the transport device which can be operated with a simple contact or the heating speed and temperature generation over the surface in the roller depend on the thickness of the electrodes selected , According to one embodiment, the electrodes and the floating electrode or the intermediate layer each have a thickness in the range from 50 to 150 μm, preferably from 75 to 100 μm. These small layer thicknesses are further advantageous in that the heat generated by the resistance layer can be easily released by this or the intermediate layer to the body to be heated, the tube, the container or the roller jacket. In addition, thin electrodes are more flexible, which prevents the electrodes from flaking off the resistance layer and thereby breaking the electrical contact when the resistance layer is thermally expanded.

In the case of pipelines or containers of great length, multiple contacting of the electrodes may still be necessary. However, this can easily be provided in the case of a pipe or a transport device according to the invention. The electrodes are only contacted from the outside, so that they are easily accessible. In the case of a pipeline or a container, a power line can thus be provided which extends along the tube or the container and connects the electrodes at intervals to the voltage source. As a result, pipe or transport devices according to the invention can be operated as long as desired.

The resistance layer is thin according to the invention. It is limited at the bottom only by the breakdown voltage and has a thickness of 0.1 to 2 mm, preferably 1 mm. The advantage of a low layer thickness of the resistance layer is the short heating-up time, rapid heat emission and high surface heating capacity. Such a layer thickness is, however, only possible with a resistance heating element according to the invention or only with the intrinsically conductive polymer used and can be further improved by the type of contacting. On the one hand, the current path in the resistance layer is predetermined by the polymers used according to the invention and, even with small layer thicknesses, can have a sufficient length to prevent the voltage from breaking through. On the other hand, the one-sided contacting of the resistance heating element allows the resistance layer to be divided into zones with a lower voltage, which further reduces the risk of breakdown.

The advantages of the resistance heating element according to the invention, the tube, the transport device or the roller are further increased if the resistance layer has a positive temperature coefficient of electrical resistance (PTC). A self-regulating effect with regard to the maximum achievable temperature is hereby achieved. Through this effect local overheating of the container, the pipe or the roller jacket can be prevented. This effect is due to the fact that, due to the PTC of the resistance layer, the current flow through the resistance mass is regulated as a function of the temperature. The higher the temperature rises, the lower the current intensity until it is finally immeasurably small at a certain thermal equilibrium. Local overheating and melting of the resistance mass can therefore be reliably prevented. This self-regulating effect is of great importance for the heating element according to the invention, since local temperature increases can occur, for example, if the heating element according to the invention does not come into sufficient contact with a body to be heated and the resultant low heat transfer. This effect is also of particular importance in the present invention of the tube, the transport device or the roller. If, for example, the inner tube or the container is only half full with a liquid medium, the heat can be dissipated better in this area of the tube or the container than in the area in which air is in the tube or the container. Due to the lack of heat dissipation, a conventional resistance heating element would heat up and possibly melt. In the heatable pipe or container according to the invention, however, this melting is avoided by the self-regulating effect.

The choice of a PTC material as the material for the resistance layer thus also has the consequence that the entire resistance layer is heated to substantially the same temperature. This enables a uniform heat emission, which can be essential for individual areas of application of the resistance heating element, the tube, the container or the roller, for example when temperature-sensitive media are passed or transported through the tube or in the container or because some of them are otherwise Place, for example, the film to be applied by the roller not adhering to the substrate, since it has not been heated sufficiently.

According to the invention, the resistance layer can be metallized on its surfaces facing the electrodes and optionally the floating electrode or the intermediate layer. Due to the metallization, metal is deposited on the surface of the resistance layer and thus improves the current flow between the electrodes or the floating electrode and the resistance layer. In addition, in this embodiment, the heat transfer from the resistance layer to the floating electrode and thus to the body or object to be heated, the inner tube, the container or the roller jacket is also improved. The surface can be metallized by spraying metal. Such metallization is only possible with the material of the resistance layer used according to the invention. A complex metallization step by e.g. Electroplating is therefore unnecessary and considerably reduces the manufacturing costs.

The intrinsically electrically conductive polymer is preferably produced by doping a polymer. The doping can be a metal or semi-metal doping. With these polymers, the interfering conductor is chemically bound to the polymer chain and creates an interfering point. The doping atoms and the matrix molecule form a so-called charge transfer complex. When doping, electrons are transferred from filled bands of the polymer to the doping material. The electron holes created in this way give the polymer semiconductor-like electrical properties. In this embodiment, a metal or semimetal atom is incorporated or attached to the polymer structure by chemical reaction in such a way that free charges are generated thereby, which enable current to flow along the polymer structure. The free charges are in the form of free electrons or holes. An electron conductor is thus created.

The doping material was preferably added to the polymer in such an amount that the ratio of atoms of the doping material to the number of polymer molecules is at least 1: 1, preferably between 2: 1 and 10: 1. This ratio ensures that essentially all polymer molecules are doped with at least one atom of the doping material. By choosing the ratio, the conductance of the polymers and thus the resistance layer, as well as the temperature coefficient of the resistance of the resistance layer can be adjusted.

Although the intrinsically electrically conductive polymer used according to the invention can also be used as material for the resistance layer without adding graphite in the resistance heating element according to the invention, the tube, the transport device and the roller, according to a further embodiment the resistance layer can additionally have graphite particles. These particles can contribute to the conductivity of the entire resistance layer and preferably do not touch and in particular do not form a lattice or skeleton structure. The graphite particles are not firmly integrated into the polymer structure, but are freely movable. If a graphite particle is in contact with two polymer molecules, the current can jump from one chain over the graphite to the next chain. The conductivity of the resistance layer can be increased in this way. At the same time, due to their free mobility in the resistance layer, the graphite particles can reach their surface and there improve the contact with the electrodes or the floating electrode, the intermediate layer, the inner tube, the container or the roller jacket.

The graphite particles are preferably present in an amount of at most 20 vol%, particularly preferably at most 5 vol%, based on the total volume of the resistance layer and have an average diameter of at most 0.1 μm. Due to this small amount of graphite and the small diameter, the formation of a graphite grid, which would lead to a conduction of the current through these grids, can be avoided. It is thus ensured that the current continues to flow essentially via the polymer molecules through electron conduction and the above-mentioned advantages can thus be achieved. In particular, the line does not have to be made via a graphite grid or skeleton in which the graphite particles have to touch and which is easily destroyed under mechanical and thermal stress, but takes place along the stretchable and aging-resistant polymer.

Intrinsically electrically conductive polymers which can be used are both electrically conductive polymers such as polystyrene, polyvinyl resins, polyacrylic acid derivatives and copolymers thereof, and also electrically conductive polyamides and their derivatives, polyfluorocarbons, epoxy resins and polyurethanes. Polyamides, polymethyl methacrylates, epoxies, polyurethanes and polystyrene or mixtures thereof can preferably be used. Here, polyamides additionally have good adhesive properties which are necessary for the production of the resistance heating element according to the invention, the tube, the transport device or the roller of. The advantage is that this makes it easier to apply to the inner tube, the container, the roller jacket or the intermediate layer. Some polymers, such as polyacetylenes, are ruled out for use in accordance with the invention due to their low aging resistance due to their reactivity with oxygen.

The length of the polymer molecules used varies in large ranges depending on the type and structure of the polymer, but is preferably at least 500, particularly preferably at least 4000 Å.

In one embodiment, the resistance layer of the resistance heating element, the tube, the transport device or the heating roller has a support material. This support material can serve on the one hand as a carrier material of the intrinsically conductive polymer and on the other hand acts as a spacer, in particular between the electrodes and the floating electrode, the intermediate layer, the electronically conductive inner tube, the container or the roller jacket. The support material also gives the resistance layer a stiffness on the basis of which it can withstand mechanical loads. Such can e.g. by pressing devices, e.g. Clamping rings, for pressing the heating element against the roller jacket. Furthermore, when using a support material, the layer thickness of the resistance layer can be set precisely. The support material can be glass balls, glass fibers, rock wool, ceramics, e.g. Barium titanate or plastics. If the support material is in the form of a fabric or mat, for example made of glass fibers, it can be immersed in a mass consisting of the intrinsically electrically conductive polymer, i.e. are soaked with the intrinsically electrically conductive polymer. The layer thickness is determined by the thickness of the grid or mat. Methods such as racking, spreading or known screen printing methods can also be used.

The support material is preferably a flat, porous, electrically insulating material. Such a material can additionally prevent the heating current from flowing through the support material instead of through the polymer structure.

The possibility of producing layers that only have minimal tolerances, e.g. 1% deviate from the desired layer thickness, is particularly important in the case of the layer thicknesses according to the invention, since otherwise there is fear of direct contact between the contacted electrode and the floating electrode, intermediate layer, inner tube, container or roller shell. A fluctuation in the layer thickness over the surface can also affect the temperature generated and lead to an uneven temperature distribution.

The support material also has the effect that the current flow cannot take the shortest path between the electrodes and the floating electrode, the intermediate layer, the inner tube, the container or the roller jacket, but is deflected or split up on the filling material. This ensures optimal use of the energy supplied.

The subject matter of the invention - the heating element according to the invention, the tube according to the invention, the transport device according to the invention and the roller according to the invention - is explained below with reference to the accompanying drawings.

Figur 1

einen Teilschnitt durch eine Ausführungsform des erfindungsgemäßen Heizelementes;

Figur 2

schematische Seitenansicht einer Ausführungsform mit mehreren schwimmenden Elektroden.

Figur 3

Prinzipskizze der sich bei einer Ausführungsform gemäß Figur 2 ausbildenden Zonen.

Fig. 4

Schnittansicht einer Ausführungsform eines erfindungsgemäßen Rohres ohne Wärmedämmschicht

Fig. 5

Schnittansicht einer Ausführungsform eines erfindungsgemäßen Rohres mit einer Wärmedämmschicht;

Fig. 6

Schnittansicht einer Ausführungsform einer erfindungsgemäßen Vorrichtung ohne Wärmedämmschicht;

Fig. 7

Schnittansicht einer Ausführungsform einer erfindungsgemäßen Vorrichtung mit einem in die Wärmedämmschicht eingebrachten Widerstandsheizelement;

Fig. 8

perspektivische Ansicht der in Figur 7 gezeigten Ausführungsform einer erfindungsgemäßen Vorrichtung;

Figur 9

eine Ausführungsform der erfindungsgemäßen Heizwalze mit einer zwischen den Elektroden eingeschlossenen Widerstandsschicht;

Figur 10

einen Längsschnitt durch eine erfindungsgemäße Heizwalze mit zwei nebeneinander angeordneten Elektroden auf einer Seite der Widerstandsschicht;

Show it:

Figure 1

a partial section through an embodiment of the heating element according to the invention;

Figure 2

schematic side view of an embodiment with several floating electrodes.

Figure 3

Schematic diagram of the zones forming in an embodiment according to FIG. 2.

Fig. 4

Sectional view of an embodiment of a pipe according to the invention without a thermal barrier coating

Fig. 5

Sectional view of an embodiment of a pipe according to the invention with a thermal barrier coating;

Fig. 6

Sectional view of an embodiment of a device according to the invention without a thermal barrier coating;

Fig. 7

Sectional view of an embodiment of a device according to the invention with a resistance heating element introduced into the thermal insulation layer;

Fig. 8

perspective view of the embodiment of a device according to the invention shown in FIG. 7;

Figure 9

an embodiment of the heating roller according to the invention with a resistance layer enclosed between the electrodes;

Figure 10

a longitudinal section through a heating roller according to the invention with two electrodes arranged side by side on one side of the resistance layer;

The heating element 1 has a thin resistance layer 2 and two flat electrodes 3 and 4, which are arranged next to one another at a distance and essentially completely cover the resistance layer. A floating electrode 5 is arranged on the opposite side of the resistance layer 2 and covers the resistance layer over the entire area formed by the electrodes 3 and 4 and the distance between them. If the electrodes 3 and 4 are contacted with a current source (not shown), the current is initially distributed in the Electrode 3 then flows through the resistance layer 2 substantially perpendicular to its surface to the floating electrode 5, is passed on in this and flows through the resistance layer 2 to the electrode 4 and is removed from there. Depending on the contacting of the electrodes 3 and 4, the current flow can also take place in the opposite direction. In the embodiment shown, the insulation between the electrodes 3 and 4 is formed by an air gap.

FIG. 2 shows a heating element in which there is a thin resistance layer 2. Two flat electrodes 3 and 4 and a plurality of floating electrodes 5 arranged between them are provided on one side of the resistance layer 2. The electrodes 3, 4 and the floating electrodes 5 are spaced apart and offset from the floating electrodes 5 arranged on the opposite side of the resistance layer 2. In this construction, the current applied to the electrodes 3, 4 flows through the resistance layer 2 and the floating electrodes 5 in the direction indicated by arrows in the drawing. With this current flow, the resistance layer 2 serves as a series connection of a plurality of electrical resistors, as a result of which high performance can be achieved and at the same time a low voltage prevails in the individual regions or zones of the resistance layer. Here, both the resistance in the thickness of the resistance layer 2 and the surface resistance in the distances between the floating electrodes 5 or the floating electrode 5 and the electrodes 3 or 4 are used. In addition, the large spatial distance between the contacted electrodes has the advantage that direct contact between them can be avoided.

FIG. 3 shows a schematic diagram on the basis of which the electrotechnical dimensioning of an embodiment of the resistance heating element according to the invention is to be explained. Based on the desired in individual cases The surface heating power of the entire resistance heating element is first determined from the quotient of the total voltage to be applied to the contacted electrodes and the uniform maximum partial voltage applied to the individual partial zones which are always connected in series. The number of heating zones required in the width of the resistance heating element. The length of the heating zone is designated S, the width Z of the individual zones themselves is calculated using the following approach: $$\text{Z =}\frac{\text{BnA / 2 - 2K}}{\text{n}}$$

B =

Gesamtbreite des Flächenheizelementes (mm)

A =

Abstand zwischen den schwimmenden Elektroden bzw. der schwimmende Elektrode und der Elektrode auf einer Seite der Widerstandsschicht (mm)

K =

Breite des Randstreifens (mm)

n =

Anzahl der einzelnen in Serie geschalteten Heizzonen

In which:

B =

Total width of the surface heating element (mm)

A =

Distance between the floating electrodes or the floating electrode and the electrode on one side of the resistance layer (mm)

K =

Edge strip width (mm)

n =

Number of individual heating zones connected in series

The width of the individual electrodes or floating electrodes arranged alternately on one and the other surface of the resistance layer results from the sum of two zone widths and the distance A of the electrodes arranged on one side of the resistance layer.

The heating power N _{z of} an individual zone of the resistance heating element results from: $${\text{N}}_{\text{Z}}{\text{= U}}_{\text{Z}}{\text{· I}}_{\text{G}}{\text{= U}}_{\text{Z}}{}^{\text{2}}{\text{· L = U}}_{\text{Z}}{}^{\text{2}}\text{· S · Z / ρ · D}$$

U =

aufgrund der im einzelnen Anwendungsfall erforderlichen elektrische Isolation (Durchschlagfestigkeit) der Widerstandsheizschicht am Teilwiderstand anliegende, zulässige maximale elektrische Zonenspannung (V)

I =

Stromstärke, die aufgrund der Serienschaltung an allen Teilwiderständen konstant und gleich dem Gesamtstrom ist (A)

L =

elektrischer Leitwert der intrinsisch leitenden Polymer-Widerstandsschicht (S)

ρ =

spezifischer Widerstand der Polymerschicht (Ω · mm)

S =

Länge der Elektrode des Widerstandsheizelementes (mm)

Z =

Breite der einzelnen Heizzonen (mm)

D =

Dicke der Widerstandsschicht (mm)

In which

U =

due to the required electrical insulation (dielectric strength) of the resistance heating layer at the partial resistor, permissible maximum electrical zone voltage (V)

I =

Amperage that is constant due to the series connection of all partial resistors and equal to the total current (A)

L =

electrical conductivity of the intrinsically conductive polymer resistance layer (S)

ρ =

specific resistance of the polymer layer (Ω · mm)

S =

Length of the electrode of the resistance heating element (mm)

Z =

Width of the individual heating zones (mm)

D =

Resistance layer thickness (mm)

The electrodes and the floating electrode can be used in the heating element according to the invention e.g. consist of metal foils or metal sheets. Furthermore, the electrically conductive layer can be coated with a black plastic on the side facing away from the resistance layer. Through this additional layer, the heating element according to the invention can assume the function of a black radiator and produce a depth effect of the radiation generated.

In the heating element according to the invention, a plurality of electrodes can be provided on one side of the resistance layer. By providing a plurality of electrodes which are separated from one another by insulations and are arranged next to one another and each serve as pairs of electrodes which can be subjected to voltages, zone-by-zone heating of the heating element can be achieved.

It is also within the scope of the invention to realize the insulation between the electrodes by means of an insulating material which is introduced into the gap existing between the electrodes. Conventional dielectrics, in particular plastics, can be used as the insulating material.

If the surface of the heating element facing the body to be heated is to be kept stress-free, the resistance layer can be used or the floating electrode can be coated with polyester, PTFE, polyimide and other foils. The use of these conventional insulating materials and the simple shape, for example a film, is possible in the heating element according to the invention in that the floating electrode is not provided with contacts and thus has a smooth surface.

By using the resistance layer used according to the invention, the heating element can have a wide variety of shapes. The resistance heating element can be in the form of a band, the length of which is greater than its width and in which the electrodes represent strips which extend over the entire length of the band and which are arranged next to one another in the width direction of the resistance heating element. Square shapes are also possible with the heating element according to the invention.

The resistance heating element can e.g. be attached inside or outside on a pipe. The one-sided contacting of the heating element is of particular advantage here, since the heat transfer from the resistance heating element to the body to be heated, e.g. a pipe, not hindered by contacts. The electrical insulation between the body to be heated and the resistance heating element is also simplified by the elimination of contact points on the electrically conductive layer.

4, the heatable tube 10 consists of an inner tube 11 and a resistance layer 12 arranged thereon, which completely covers the inner tube 11. Two electrodes 13 and 14 are arranged on the resistance layer 12, which are flat and are separated from one another by electrical insulation 16. If current is applied to the electrodes 13, 14 from a current source (not shown), it flows through the resistance layer 12 and passes from the one electrode 13 to the inner tube 11. In this embodiment, the inner tube 11 is preferably made of an electrically conductive material. The current is passed on in the wall of the inner tube 11 and flows through the resistance layer 12 to the second electrode 14. The entire resistance layer 12 is heated by this heating current and can release this heat to the inside of the tube via the inner tube 11.

5, a resistance heating element 12, 13, 14, 15, 16 is applied to part of the circumference of the inner tube 11. This has an electrically conductive layer 15 facing the inner tube 11. This layer 15 is flat and is covered with a resistance layer 12 on the side facing away from the inner tube 11. Two electrodes 13 and 14 are spaced apart from one another on the resistive layer 12. The inner tube 11 is covered with a heat insulation layer 17 over the area that is not in contact with the resistance heating element. An insulating shell 18 is arranged around this thermal insulation layer 17, which encloses both the thermal insulation layer 17 and the resistance heating element 12, 13, 14, 15, 16. The tube also has power supply devices 19. The power supply devices 19 are connected to feed lines 19 a, which run parallel to the axis of the inner tube 11 through the insulating shell 18. These leads 19a extend through the entire length of the tube and can be connected to a power source (not shown) at the end of the tube or can be contacted with the leads 19a of the next tube. Materials for improving the heat transfer can be provided between the electrically conductive layer 12 facing the inner tube 11 and the inner tube 11. These can be: thermal paste, pillows with heat-conducting material, silicone rubber and others. The resistance heating element 12, 13, 14, 15, 16 in this embodiment can also be applied to the curvature of the inner tube 11 be adapted, whereby an immediate heat transfer is guaranteed.

In the embodiments shown, the electrodes 13, 14 extend in the longitudinal direction of the tube and are arranged circumferentially next to one another. However, it is also within the scope of the invention to arrange the electrodes 13, 14 on the resistance layer 12 such that they extend in the direction of the circumference of the tube and are arranged axially next to one another.

The pipe according to the invention can be any length of pipe. Such pipe sections can optionally be connected to further pipes according to the invention or with conventional non-heatable pipe sections to form a pipeline. It is therefore possible to heat only those areas of the line where a certain temperature has to be set, e.g. to avoid freezing. This selective heating allows the costs for a pipeline to be optimized. Pipes according to the invention can be produced in lengths of 10 cm, but also up to 2 m.

If direct current is applied to the electrodes of the heating element and the inner tube is made of an electrically conductive material, then a cathodic protective voltage can be generated on the inner tube, which prevents corrosion of the tube.

With a pipe according to the present invention e.g. Pipelines will also be installed in areas where there is a risk of pipe freezing.

6, the device 20 consists of a tubular container 21 and a resistance layer 22 arranged thereon, which completely covers the container 21. There are two electrodes on the resistance layer 22 24 and 24 are arranged, which are flat and are separated from one another by electrical insulation 26. If current is applied to the electrodes 23, 24 from a current source (not shown), it flows through the resistance layer 22 and reaches the container 21 from one electrode 23. The container 21 in this embodiment preferably consists of an electrically conductive material. The current is passed on in the wall of the container 21 and flows through the resistance layer 22 to the second electrode 24. This heating current heats the entire resistance layer 22 and can release this heat to the interior of the container via the container 21.

In Fig. 7, a resistance heating element is applied to a part of the circumference of a tubular container 21. This has an electrically conductive layer 25 facing the container 21. This layer 25 is flat and is covered on the side facing away from the container 21 with a resistance layer 22. Two electrodes 23 and 24 are arranged at a distance from one another on the resistance layer 22. The container 21 is covered with a thermal insulation layer 27 over the area that is not in contact with the resistance heating element. An insulation shell 28 is arranged around this heat insulation layer 27, which encloses both the heat insulation layer 27 and the resistance heating element 22, 23, 24, 25, 26. The device also has power supply devices 29. The power supply devices 29 are connected to feed lines 29a which run through the insulating shell 28 parallel to the axis of the tubular container 21. These feed lines 29a extend through the entire length of the insulation shell 28 and can be connected at the end to a power source (not shown) or can be contacted with the feed lines 29a of a further insulation shell 28 with resistance heating element and heat insulation layer 27 arranged on the container 21. Between the electrically conductive layer 25 facing the container 21 and the container 21 may be provided materials to improve heat transfer. These can be: thermal paste, pillows with heat-conducting material, silicone rubber and others. In this embodiment, the resistance heating element 22, 23, 24, 25, 26 can also be adapted to the curvature of the container 21, whereby an immediate heat transfer is ensured.

In the embodiments shown, the electrodes 23, 24 extend in the longitudinal direction of the container 21 and are arranged next to one another in the circumferential direction. However, it is also within the scope of the invention to arrange the electrodes 23, 24 on the resistance layer 22 such that they extend in the direction of the circumference of the container 21 and are arranged axially next to one another.

8, the container 21 is surrounded over most of its length with an insulating shell 28. The resistance heating element 22, 23, 24, 25, 26 as well as the feed lines 29a and the power supply devices 29 are arranged in the insulation shell 28. The resistance heating element extends over a wide range of the length of the insulating shell 28 and ends in the insulating shell 28. The feed lines 29a emerge at the end of the insulating shell and can be connected to a power source (not shown). The fastening devices with which the transport device according to the invention can be arranged on a wagon or a truck are shown schematically in FIG. 8. These fastening devices are preferably arranged such that neither the insulating shell nor the resistance heating element is exposed to pressure loads due to the container resting on the fastening devices.

In the case of a pipe according to the invention and a transport device according to the invention, a plurality of pipe sections which have a structure according to the invention or a plurality of insulating shells with a resistance heating element and a thermal insulation layer can be arranged one behind the other or one behind the other on the container through the feed lines running parallel to the pipe axis or to the container axis and the power supply of the individual resistance heating elements are connected in parallel. The supply lines are protected from damage or contact with e.g. Water protected.

In a transport device according to the invention, the resistance heating element is preferably arranged in the insulating shell in such a way that it rests against the container at the bottom. This position of the heating element has the advantage that even with a container that is only filled to a small extent, the heat can be dissipated well from the heating element.

In a pipe according to the invention and a transport device according to the invention, a resistance heating element as shown in FIG. 2 can also be used. This resistance heating element is used in the tube according to the invention or in the transport device according to the invention such that the side of the resistance heating element on which the contacted electrodes are arranged faces away from the inner tube or the container. The electrical. Dimensioning takes place when using such a resistance heating element according to the schematic diagram 3 and the associated calculation formulas. This resistance heating element is used in the device according to the invention so that the side of the resistance heating element on which the electrodes are arranged faces away from the container. The electrodes and floating electrodes are preferably arranged in a tube or in a cylindrical container so that they are apart from one another over the circumference of the container are spaced and extend in the axial direction. As a result, several zones are formed over the circumference, each of which has a lower voltage than the applied voltage.

The heat insulation layer serves to avoid heat losses due to radiation in the direction facing away from the inner tube or the container and to direct the heat generated by the resistance heating element predominantly in the direction of the inner tube or the container. The heat insulation layer can consist of insulation materials and, if appropriate, an additional reflection layer.

It is also possible that the entire inner tube or the entire container is surrounded by the thermal insulation layer and the resistance layer as well as the flat electrodes and the intermediate layer are arranged in a longitudinal groove of the thermal insulation layer facing the inner tube or container. In the case of the pipe, the heat insulation layer prevents the release of heat over the remaining area of the circumference of the inner pipe, which is not covered by the resistance layer or the intermediate layer. In this embodiment of the transport device, heat can be emitted to the container over a defined area in which the heating element rests on the container. At the same time, heat loss through the remaining area of the container through the thermal insulation layer is avoided. The arrangement of the resistance heating element in the insulation layer ensures good contact of the insulation layer over the remaining area with the inner tube or container.

Such an embodiment of the transport device can also be used for devices in which the container has good thermal conductivity. With these containers, the heat generated by the resistance heating element is distributed over the entire surface of the container wall and can thus additionally heat the medium in the container. With this construction, the medium is heated on the one hand by infrared radiation from the resistance heating element and on the other hand is heated directly by the resistance heating element and the container wall.

The embodiments of the tube or the transport device shown in FIGS. 5 to 8 can additionally be provided with pressing devices. These pressing devices can optionally be applied externally to the heatable pipes or devices according to the invention shown in each case, e.g. by adhesive tapes or tension rings, or in the embodiment shown in FIG. 5 or in FIGS. 7 and 8 also be arranged directly on the outside of the resistance heating element. In the latter case, the devices can be made of foam rubber. In particular in the case of containers or large tubes, inflatable or foamable chambers can also be provided on the side of the resistance heating element facing away from the container or inner tube. The pressing devices ensure a constant contact pressure and thus good heat transfer from the resistance heating element to the container or inner tube.

The container is preferably tubular. But it can also have other forms, e.g. be rectangular.

The inner tube or the container in the heatable tube according to the invention or the transport device according to the invention can consist, for example, of metal or plastic, in particular or preferably polycarbenate. If a material is selected for the inner tube or the container that has no electrical conductivity, the resistance heating element can have an intermediate layer between the inner tube or container and the resistance layer. But it is also within the scope of the invention to provide such an inner tube or container a resistance heating element which only comprises the electrodes and the resistance layer. In this embodiment, the heating current is conducted from one electrode via the resistance mass of the resistance layer, ie via the electrically conductive polymer, to the other electrode. Such a flow of current is possible with the tube or device according to the invention, since the structure of the polymers causes a sufficient current flow through the resistance mass and thus sufficient heat generation.

It is within the scope of the invention to lead the leads, which are connected to the electrodes of the resistance heating element via the power supply devices, on the outer surface of the insulating shell.

As an insulation piece between the electrodes contacted with current, conventional electrically insulating materials can also be used in the transport device, e.g. Air or conventional dielectrics, in particular plastics, are used in the tube according to the invention.

The connections for supplying the heating element with current are made as required by any length of insulated strands, but also firmly glued contacts, whereby known contacting systems can be used.

It is also possible to provide only part of the length of the inner tube or of the container with the structure according to the invention with the insulating shell with a resistance heating element and a thermal barrier coating. Furthermore, at least one resistance heating element can be arranged in the thermal insulation layer of the tube or the size of the resistance heating element can be selected depending on the application so that one or more resistance heating elements are arranged in the thermal insulation layer of the container can. In the case of a tube or tubular container, these can extend in the radial or axial direction. The resistance heating elements can be arranged, for example, in a plurality of longitudinal grooves in an insulation layer.

The tube or the device can also have a structure in which the inner tube or the container is formed by a conventional tube or a conventional container and this is surrounded by two shell halves, at least one of the shell halves comprising a resistance heating element. The shell halves are preferably made of insulating material such as Glass fibers or foam formed.

FIG. 9 shows a heating roller 30 in which the inside of the roller jacket 31 is covered by a flat electrode 33. The resistance layer 32 is arranged on this electrode 33 and has a further electrode 34 on the side facing away from the electrode 33. A thermal insulation material 37 is arranged in the interior of the roller, which completely fills the interior of the heating roller and bears against the inner electrode 34. In the illustrated embodiment, electrodes 33 and 34 are connected to a power source (not shown). The current flowing through the resistance layer 32 heats it up and thereby leads to a heating of the roll shell 31.

FIG. 10 shows an embodiment of the heating roller 30 according to the invention. In this embodiment, the resistance layer 32 is arranged directly on the roller shell 31 and is essentially completely covered on its side facing away from the roller shell 31 by two electrodes 33 and 34. The electrodes 33 and 34 are electrically separated from one another by insulation 36.

Conventional dielectrics such as air or plastic can be used as the material for the insulation 36.

The electrode 34 can be connected to the power source (not shown) from the left side and the electrode 33 from the right side of the copying roller. In this embodiment, the heating current flows from the first electrode 33 to the roller shell, which is preferably made of a material which is a good electrical conductor, and from there through the resistance mass 32 back to the further electrode 34, or vice versa.

If the at least two electrodes are arranged on one side of the resistance layer and an intermediate layer made of material with high conductivity is provided on the opposite side, the heating current flows from an electrode through the resistance layer to the intermediate layer, is passed on in this and flows through the resistance layer to the another electrode. Due to the choice of the resistance material, it is also possible to work without an intermediate layer, even if the roller jacket is made of a non-conductive material. In this case, the heating current flows through the resistance layer, the entire resistance mass being heated due to the polymer structure. Finally, the roll shell can also consist of conductive material and can be used to conduct the current. In this case, the current applied to the electrodes flows from one electrode through the resistance mass and is passed on in the roller jacket, in order then to reach the further electrode through the resistance mass.

In all of these embodiments, in which the current is supplied to the resistance mass from one side, the voltage prevailing in the zones is reduced by half in contrast to the two-sided current supply.

The distance provided between the electrodes acts as an additional parallel resistor. If air is selected as the insulation 36, the resistance is determined by the distance between the electrodes and thus by the surface resistance.

A resistance heating element as shown in FIG. 2 can also be used. This resistance heating element is used in the heating roller according to the invention so that the side of the resistance heating element on which the contacted electrodes are arranged faces away from the roller shell. The electrical dimensioning takes place when using such a resistance heating element in accordance with the schematic diagram 3 and the associated calculation formulas.

If the surface of the heating roller is to be kept free of tension, known insulation in the form of polyester, polyimide and other foils can be provided between the resistance heating element and the roller shell. The electrodes are preferably supplied with current via known contacting techniques for flat heating elements or slip rings or via bearings serving as electrical contacts.

Depending on the intended use, metal foils or sheets can be used as electrodes. It is also within the scope of the invention to press the resistance heating element onto the roll shell by pressing devices. For example, clamping rings can be used as the pressing device, which can simultaneously serve as electrodes. To improve the heat transfer between the resistance heating element and the roller shell, thermoplastic materials in the form of foils or heat-conducting pastes can be provided between the resistance heating element and the roller shell.

In the roller according to the invention, several resistance heating elements can be provided separately from one another in the interior of the roller over the length of the roller. However, it is also within the scope of the invention to provide a continuous resistance layer in the interior of the roll, to which a plurality of electrodes are applied in the form of segments. These segments extend over the entire inner circumference of the roll shell covered with the resistance layer and can be easily inserted into the roll. They therefore allow quick assembly. Furthermore, by providing a plurality of electrodes in the heating roller according to the invention, each of which functions as an electrode pair and is optionally supplied with current, heating of individual regions of the roller can be achieved. These electrodes also preferably extend over the entire circumference and are spaced apart from one another in the axial direction. When using the heating roller as a film roller, for example, the edge regions of the roller can be additionally heated. With this additional supply of heat, a uniform temperature distribution over the area which comes into contact with the material to be heated can be achieved, since lower temperatures in the edge area are compensated for by the additional heating.

In the interior of the roller, on the side of the electrodes facing away from the resistance layer, a thermal insulation material can be provided which, if necessary, can completely fill the interior of the roller. This thermal insulation material prevents radiation of the heat from the resistance heating element in the direction of the interior of the roller and thus prevents heat accumulation in the roller.

The heating roller according to the invention is particularly suitable for use as a copying roller in a photocopier or as a foil roller for sealing materials with foils.

It is also within the scope of the invention to use a material for the resistance layer of the resistance heating element, the tube, the transport device and the heating roller, the temperature coefficient of the electrical resistance of which is negative.

With a negative temperature coefficient of electrical resistance, a very low inrush current is required. In addition, the material of the resistance layer can be selected so that the resistance mass used in accordance with the invention at a certain temperature, e.g. 80 ° C regulates back, so that from this temperature the temperature coefficient of the electrical resistance becomes positive.

The resistance layer of the resistance heating element, the tube, the transport device or the heating roller can have a structure in which different resistance materials with different specific electrical resistances are present in layers.

This embodiment of the resistance heating element, the tube or the transport device has the advantage that the side of the resistance layer is to be released from the heat to the body to be heated, the inner tube or the container by the appropriate choice of materials in the resistance layer Can have temperatures without having to conduct different heating currents separately, for example through heating wires in individual layers of the resistance layer. This effect is achieved in that the specific electrical resistance of the polymer used is selected to be ever higher from the layer which lies against the electrodes to the side facing the body, tube or container to be heated. In this embodiment of the heating roller, the side of the resistance layer facing the interior of the roller can consist of a material which has a low resistance. On this layer, other materials are applied in layers, their specific resistance increases from layer to layer. In this arrangement, the side facing the roll shell has the highest specific resistance of the resistance layer, so that this surface is heated more, since the greater voltage drop occurs here.

The resistance heating element, the tube, the transport device or the roller according to the invention can be operated with low voltages of, for example, 24V and also with very high voltages of, for example, 240, 400 and up to 1000V due to the resistance layer used and the contacting.

In the resistance heating element, the pipe, the transport device or the roller according to the invention, surface heating outputs of greater than 10 kW / m ² , preferably greater than 30 kW / m ² can be achieved. With the heating roller, outputs of up to 60 kW / m ^{2 can be} achieved. This heating output of up to 60 kW / m ² can also be achieved with a layer thickness of the resistance layer of 1 mm. The drop in performance over time can be less than 0.01% per year with a continuous exposure to a voltage of 240 V.

The temperature that can be achieved with the resistance heating element, the tube, the transport device or the roller is limited by the thermal properties of the polymer selected, but can be more than 240 ° C. and up to 500 ° C. In particular, the polymer should be selected so that the conduction continues to be carried out by electron conduction, even at the desired temperatures.

According to the invention, the electrically conductive polymer used in the resistance layers of the resistance heating element, the heatable tube and the heating roller are, in particular, those polymers which are conductive through metal or semimetal atoms which are attached to the polymers. These polymers have a specific one Volume resistance in the range of values achieved by semiconductors. It can be up to 10 ² but at most 10 ⁵ Ω · cm. Such polymers can be obtained by a process in which polymer dispersions, polymer solutions or polymers are mixed with metal or semimetal compounds or their solution in an amount so that there is approximately one metal or semimetal atom on a polymer molecule. A small excess of a reducing agent is added to this mixture or metal or semimetal atoms are formed by known thermal decomposition. The ions formed or still present are then washed out and the dispersion solution or the granules can optionally be mixed with graphite or soot.

Beispiel 1:

1470 Gew.Teile Dispersion von Fluorkohlenwasserpolymers (55 % Feststoff in Wasser), 1 Gew.-Teil Netzmittel, 28 Gew.-Teile Silbernitratlösung 10 %, 6 Gew.-Teile Kreide, 8 Gew.-Teile Ammoniak, 20 Gew.-Teile Ruß, 214 Gew.-Teile Graphit, 11 Gew.-Teile Hydrazinhydrat.

Beispiel 2:

1380 Gew.-Teile Acrylharzdispersion 60 Gew.-% in Wasser, 1 Gew.-Teil Netzmittel, 32 Gew.-Teile Silbernitratlösung 10 %ig, 10 Gew.-Teile Kreide, 12 Gew.-Teile Ammoniak, 6 Gew.-Teile Ruß, 310 Gew.-Teile Graphit, 14 Gew.-Teile Hy drazinhydrat.

Beispiel 3:

2200 Gew.-Teile dest. Wasser, 1000 Gew.-Teile Styrol (monomer), 600 Gew.-Teile Ampholytseife (15 %ig), 2 Gew.-Teile Natriumpyrophosphat, 2 Gew.-Teile Kaliumpersulfat, 60 Gew.-Teile Nickelsuflat, 60 Gew.-Teile Natriumhypophospit, 30 Gew.-Teile Adipinsäure, 240 Gew.-Teile Graphit.

The electrically conductive polymers used according to the invention are preferably free of ions. The maximum amount of free ions is 1% by weight based on the total weight of the resistance layer. The ions are either washed out as described above or a suitable reducing agent is added. The reducing agent is added in such a ratio that the ions can be completely reduced. The low proportion of ions, preferably the absence of ions, of the electrically conductive polymers used according to the invention brings about a long resistance of the resistance layer under the action of electrical currents. It has been shown that polymers which contain ions to a higher percentage have only a low resistance to aging under the action of electrical currents, since the resistance layer self-destructs as a result of electroysis reactions. The electrically conductive polymer used according to the invention, however, is resistant to aging due to the low ion concentration even when exposed to current for a long time. As reducing agents for the process described above for producing an electrically conductive polymer used according to the invention, those reducing agents are used which either do not form ions because they are thermally decomposed during processing, such as hydrazine, or react chemically with the polymer itself, such as formaldehyde or those whose excess or reaction products are easily washed out, such as hypophosphites. Silver, arsenic, nickel, graphite or molybdenum are preferably used as metal or semimetals. Those metal or semimetal compounds which form the metal or semimetal without disruptive reaction products by pure thermal decomposition are particularly preferred. In particular, arsine or nickel carbonyl have proven to be particularly advantageous. The electrically conductive polymers used according to the invention can be produced, for example, by adding 1-10% by weight (based on the polymer) of a premix which has been prepared according to one of the following recipes to the polymer.

Example 1:

1470 parts by weight dispersion of fluorocarbon polymer (55% solids in water), 1 part by weight of wetting agent, 28 parts by weight of silver nitrate solution 10%, 6 parts by weight of chalk, 8 parts by weight of ammonia, 20 parts by weight Carbon black, 214 parts by weight of graphite, 11 parts by weight of hydrazine hydrate.

Example 2:

1380 parts by weight of acrylic resin dispersion 60% by weight in water, 1 part by weight of wetting agent, 32 parts by weight of silver nitrate solution 10%, 10 parts by weight of chalk, 12 parts by weight of ammonia, 6 parts by weight Carbon black, 310 parts by weight of graphite, 14 parts by weight of hydrazine hydrate.

Example 3:

2200 parts by weight of dist. Water, 1000 parts by weight of styrene (monomeric), 600 parts by weight of ampholyte soap (15%), 2 parts by weight of sodium pyrophosphate, 2 parts by weight of potassium persulfate, 60 parts by weight of nickel sulfate, 60 parts by weight Sodium hypophosphite, 30 parts by weight of adipic acid, 240 parts by weight of graphite.

Claims (20)

1. Flat heating element (1) comprising at least two flat electrodes (3, 4) and a resistance layer (2) containing an intrinsically electroconductive polymer having a metal or semimetal doping,
      characterized in that

   - the resistance layer (2) consists to at least 80 percent by volume of the intrinsically conductive polymer that has a specific resistance in the range of values achieved with semiconductors, but at most 10⁵ Ω·cm, preferably at most 10² Ω·cm,

   - the resistance layer (2) has a thickness of 0.1 to 2 mm, preferably 1 mm,

   - the at least two flat electrodes (3, 4) are arranged on one side of the resistance layer (2) at a distance from each other.
2. Heating element according to claim 1, characterized in that a flat floating electrode (5) is arranged on the side of the resistance layer (2) that is opposite to the two flat electrodes.
3. Heating element according to claim 2, characterized in that the electrodes (3, 4, 5) consist of a material with a specific electric resistance of less than 10^-4 Ω·cm, preferably of less than 10^-5 Ω·cm.
4. Heating element according to one of the preceding claims, characterized in that the electrodes (3, 4, 5) have a thickness in the range of 50 to 150 µm, preferably of 75 to 100 µm.
5. Heating element according to one of the preceding claims, characterized in that the resistance layer (2) has a positive temperature coefficient of electric resistance.
6. Heating element according to one of the preceding claims, characterized in that the resistance layer (2) is metallized on its surfaces facing the electrodes (3, 4) and/or the floating electrode (5).
7. Heating element according to one of the preceding claims, characterized in that the distance between the electrodes (3, 4) on one side of the resistance layer (2) amounts to approximately twice the thickness of resistance layer (2).
8. Heating element according to one of the preceding claims, characterized in that the ratio of doping atoms to the number of polymer molecules is at least 2 : 1, and at most 10 : 1.
9. Heating element according to one of the preceding claims, characterized in that the resistance layer (2) in addition contains graphite particles in an amount of preferably at most 20, more particularly of at most 5 percent by volume relative to the total volume of the resistance layer, the graphite particles having a mean diameter of at most 0.1 µm.
10. Heating element according to one of the preceding claims, characterized in that the content of free ions in the resistance layer is at most 1 percent by weight relative to the total weight of the resistance layer.
11. Heating element according to one of the preceding claims, characterized in that the polymer is selected from the group consisting of polyamides, acrylic resins, epoxides, and polyurethanes.
12. Heating element according to one of the preceding claims, characterized in that the resistance layer (2) comprises a support material that preferably is a flat porous, electrically insulating material.
13. Heating element according to one of the preceding claims, characterized in that the resistance layer (12, 22, 32) is a multilayer structure where each individual layer comprises at least one resistive material that differs from that of the neighbouring layer and has a different specific electric resistance.
14. Heating element according to one of the preceding claims, characterized in that the resistance layer (12, 22, 32) is applied to the surface of a hollow body that has an axis and is selected from the group consisting of a pipe (10), a container (21), and a heat roller shell (31).
15. Heating element according to claim 14, characterized in that between the hollow body and the resistance layer (12, 22, 32) an intermediate layer (15, 25, 35) is arranged that consists of a material of high electric conductivity and the resistance layer (12, 22, 32) preferably is metallized at its surfaces facing the electrodes (13, 14; 23, 24; 33, 34) and/or the intermediate layer (15, 25, 35).
16. Heating element according to claim 14 or 15, characterized in that the resistance layer (12, 22, 32) is arranged directly on the surface of the hollow body that consists of a material of high electric conductivity.
17. Heating element according to one of claims 14 to 16, characterized in that the resistance layer (12, 22) and the electrodes (13, 14; 23, 24) arranged on it extend in an axial direction along the outer surface of the pipe (10) or container (21), and the electrodes (13, 14; 23, 24) are arranged on the resistance layer (12, 22) in a peripherally spaced apart relationship.
18. Heating element according to one of claims 14 to 17, characterized in that it comprises a current feeder device (29) extending in an axial direction over the entire length of the hollow body on the outside of the hollow body, and contacting each of the electrodes (23, 24) in at least two points.
19. Heating element according to one of claims 14 to 16, characterized in that the resistance layer (32) and the electrodes (33, 34) arranged on it extend in an axial direction along the inner surface of a heat roller shell (31), the electrodes (33, 34) being arranged in a peripherally spaced apart relationship on the side of the resistance layer (32) facing away from the heat roller shell (31).
20. Heating element according to one of claims 14 to 16, characterized in that the resistance layer (32) and the electrodes (33, 34) arranged on it extend along the inner surface of a heat roller shell (31), the electrodes (33, 34) being arranged in an axially spaced apart relationship and extending over essentially the entire circumference.