FR2843673A1 - Heated blanket, for localized heating in building construction, has layer of conductive polymer between conductive surfaces - Google Patents

Abstract

The heated blanket for building use has at least one layer of conductive polymer, with automatically controlled resistance using a PTC effect, placed between two conductive surfaces. The layer of conductive polymer and the two conductive surfaces can provide a homogenous laminate. The laminate can have perforations.

Description

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HEATED SHEETS WITH RESISTANCE SELF-CONTROLLED BY THE
FIELD OF THE INVENTION PTC EFFECT AND THEIR APPLICATIONS Field of the Invention The present invention relates to heating coats comprising polymers with autocontrolled resistance by temperature, as well as the materials for domestic or industrial use which incorporate them and in particular the materials used in the fields construction and building, energy transport in the seabed, human or animal health, food industry or process control industry.

PRIOR ART AND TECHNICAL PROBLEM The known means of heating by electricity suppose the installation of systems of temperature measurement to limit the contributions of energy according to the temperature levels reached in such or such place of the whole considered. When the systems in question are heterogeneous, which is most often the case, it is quickly impossible to locate practically the zones where to put the so-called measurement systems intended to give instructions to the electric power supply stations.

Electrical heating cord materials have been known in the industry for a very long time, but they present great difficulties of installation, of electrical connections, of insertion into floor systems, ceilings, tubes. The heat transfer coefficients are very low, and any failure is very costly to repair.

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In the prior art there are numerous documents which describe the implementation of the heating techniques permitted by PTC effect ceramics, and certain plastic polymers in the molten state.

The basic principle is that the temperature of any set can be guaranteed without permanent measurement, and this reversibly according to a large number of hot and cold cycles.

According to this principle, the devices of the prior art are used for various applications such as: # instantaneous heating of the water without the need for storage, # guarantee of non-condensation of zones or electrical boxes where the products must remain dry, # controlled odor emissions by varying the temperature of the tanks containing the said odors, # heaters for anti-fog on mirrors, # glue guns, # heating blanket, # heating of food or hot plates or heating tanks for liquids to variable levels in the case of cups drunk gradually with risk of cooling or overheating in the absence of PTC performance, # temperature capture by PTC effect, or permanent deglazing of satellite dishes and various external antennas.

In US patent 5,714,096, original compositions or formulations are described such as polypropylenes modified by maleic grafts with the use of a solvent and of conductive carbon to modify the temperatures of the PTC switch and their use for manufacturing conductive pastes for low cost car mirror heaters.

Controlled heating where it is difficult to put and read thermometers has been described in US patent 6,121,585 with a PTC polymer deposited on a support for

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 an arrangement of heating surfaces intended to keep warm cups of beverages in cars.

In US Patents 6,084,206 and 6,730.28, there are described conductive meshes placed on either side of a layer of PTC effect elements. These are integrated into electric blankets comprising multiple layers of different materials. A layer of thermally conductive silicone has regularly distributed holes. The discrete elements of PTC ceramic material are inserted into the holes provided for this purpose.

These electric blankets due to their structure made up of multiple layers of different superimposed materials and comprising discrete PTC effect elements which it is necessary to adjust separately to be integrated into the electric blanket are difficult and complicated to manufacture. In addition, their structure does not allow them to design or prepare heating materials with adjustable shapes and powers as needed.

There is therefore a need to have an energy supply system in the form of a heating sheet such that their shape and their electrical performance is adaptable to the material to be heated under, on or in which the sheet will be incorporated and which is inexpensive and easier to manufacture than the systems of the prior art.

SUMMARY OF THE INVENTION The subject of the invention is a heating sheet comprising at least one layer of conductive polymer with resistance self-controlled by temperature by PTC effect placed between at least two electrically conductive surfaces, this sheet being adjustable in temperature, in power, in voltage, heating kinetics and number of stability cycles.

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According to one embodiment, the two electrically conductive surfaces have mesh structures.

According to another embodiment, the polymer layer covers the electrically conductive surfaces with a density between 10 and 500 g / m2.

According to yet another embodiment, the ply is covered by an electrically insulating and thermally conductive polymer.

The invention also provides a mono or multilayer heating structure comprising at least one heating sheet according to the invention.

The invention also provides the use of a heating mat or structure according to the invention in the fields of construction and building, energy transport in the seabed, human or animal health, the food industry or from the process control industry.

The invention also provides heating materials for domestic use or for industrial use comprising a heating mat or structure according to the invention, in particular heating systems of the pipe or instantaneous hot plate heat exchanger type.

The invention also provides heating materials for the construction of buildings for floors, walls, ceilings, or under layer of carpet comprising at least one layer or heating structure according to the invention.

The invention also provides heating systems comprising at least one heating mat or structure according to the invention.

The invention also relates to the use for the removal by heating of contamination by

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 pathogens of at least one heating mat or structure according to the invention.

DETAILED STATEMENT OF THE INVENTION The subject of the invention is a heating mat comprising at least one layer of conductive polymer with resistance self-controlled by temperature by PTC effect placed between at least two electrically conductive surfaces which can be regulated in temperature, in power, in voltage, in heating kinetics and number of stability cycles.

The sheets according to the invention can be adapted to all forms of heating materials. In addition, depending on the desired performance, very reactive systems are obtained which rise to more than 100 C in a few seconds and with powers of more than 10,000 watt / m2 in some cases, depending on the different compositions with PTC effect used and placed between the two conductive surfaces.

In the case of lower powers, with higher inertias which can be counted in minutes, and average temperatures, below 70/80 C, the preferred energy contributions are in the form of bands of meshes or nets between which are installed conductors for the current supply.

Thus, according to a particularly advantageous embodiment, the heating mat comprises a layer of conductive polymer with resistance self-controlled by temperature by PTC effect placed between 2 electrically conductive surfaces, the surfaces having mesh structures. The current is supplied by conductors regularly distributed between the meshes.

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 These energy supply systems in supported PCT-effect sheets have the advantage of simplifying the methods of electrical connection, while remaining reliable even in the event of mechanical damage to surfaces.

This possibility of heating zones of all sizes in sheets, and in a homogeneous manner, makes it possible to simplify the installation of the heating elements in the most varied industrial and domestic situations. With very different voltages (2.5 to 440 volts), for powers ranging from 30 to 10,000 watts per m2 and more, equilibrium temperatures ranging from 0 C to 120 or 150 C or more, an unlimited range use of conductive polymer compositions at controlled temperatures is thus defined.

According to another embodiment, the heating sheets are dosed, depending on the desired heating power, between 10 and 500 g / m2 of active substances distributed over the continuous or meshed surfaces of the support which ensure the mechanical stability and the operating time.

The current contributions are made between spaces of conductors spaced from 0.5 mm to 50 cm depending on the voltages, temperatures and wattages desired.

Depending on the subsequent uses of the heating sheets, these can advantageously be covered with an electrically insulating but thermally conductive polymer in order to ensure heat transfers.

This insulating layer comprises, for example, powders of the aluminum type embedded in polymer matrices of the PMMA type or any other insulating coating system.

The layer of conductive polymer with autocontrol resistance by temperature comprises in particular a polymeric composite material made conductive by incorporation of graphite in a polymer matrix.

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The application of sufficient voltage leads to heating by the Joule effect. In the absence of a circuit breaker mechanism, the temperature increases until the material is destroyed. The polymeric composite materials used show an increase in resistance as a function of temperature (PTC effect or "Positive Temperature Coefficient"), so that the intensity stabilizes at an equilibrium temperature. This PTC effect therefore allows thermal regulation of the intensity of the current, it has many advantages compared with traditional resistors: # Regulation of electric heating systems is conventionally obtained by inclusion in the circuit of a thermal circuit breaker. In the event of a fault in the latter, the circuit or the safety fuse is blown. The PTC material self-regulates without the need to include a circuit breaker or fuse.

 # The PTC heating system presents a lower risk of combustion and short circuit.

 # In the event of an unintentional earthing of a PTC heating element zone, a short circuit does not occur.

 # The PTC effect generates a moderate temperature, which has 2 benefits compared to traditional systems: # The specifications imposed on insulating materials must be less strict; # The heat is supplied by a larger surface.

 # The composite material can be transformed by methods used in the plastics industry (co-extrusion, molding, etc.). It can also be applied as a paint on insulating substrates of any geometry.

Several types of composite polymer systems can be used which exhibit the PTC effect.

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According to a first type, the PTC effect is based on the phenomenon of the expansion of polymer crystals disturbing the network of the conductive charge. The resistance of the composite slowly decreases as the amount of carbon black in a semi-crystalline polymer matrix is increased, to a concentration where the resistance drops. The latter represents a geometric transition called the percolation threshold. It has been found that the maximum of the PTC effect corresponds to a critical concentration which is in the vicinity of the percolation threshold. When the temperature of the material approaches the melting of the matrix, an expansion of the crystalline zone triggers the PTC effect. However, high energy of the carbon black particles and a low shear modulus of the matrix cause a drop in resistance, known as the NTC (Negative Temperature Coefficient) effect.

This first type is described in the following references (CA designates the Chemical Abstracts): 131: 243891 CA Tl Organic PTC thermistor materials with high transitive temperature AU Yang, Fubiao; Li, Yongqin; Li, Xiaojun CS Department 5, National University of Defense Technology, Changsha, 410073, Peop. Rep. China SO Gongneng Cailiao (1998), 29 (Suppl.), 724-725 CODEN: GOCAEA; ISSN: 1001- 9731 PB Gongneng Cailiao Bianjibu 129: 331461 CA TI Effect of thermal treatment on crystallization and PTC properties of conductive PVDF / CB composite AU Wang, Jikui; Wang, Gengchao; Zhang Bingyu; Fang, Bin; Zhiping CS Inst. Mater. Sci. Eng., East China Univ. Sci.

Technol., Shanghai, 200237, Peop. Rep. China SO Gaofenzi Cailiao Kexue Yu Gongcheng (1998), 14 (5), 93-95 CODEN: GCKGEI; ISSN: 1000-7555 PB "Gaofenzi Cailiao Kexue Yu Gongcheng" Bianjibu 125: 277325 CA Tl Influences of crystallization histories on PTC / NTC effects of PVDF / CB composites AU Zhang, Mingyin; Jia,

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 Wentao; Chen, Xinfang CS Dep. Materials Science, Jilin Univ., Changchun, 130023, Peop. Rep. China SO J. Appl.

Polym. Sci. (1996), 62 (5), 743-747 CODEN: JAPNAB; ISSN: 0021-8995 104: 121274 CA TI Heaters IN Shibata, Tsuneo; Nishida, Takeo; Terakado, Masayuki; Nitta, Isao PA Matsushita Electric Industrial Co., Ltd., Japan SO Jpn. Tokkyo Koho, 5 pp. CODEN: According to a second type, the PTC effect is based on the presence of two immiscible polymers. Among such materials, the PVDF / HDPE systems loaded with carbon black are the best known. The PVDF and HDPE phases are immiscible, so the PTC effect in this case depends very much on the morphology and the distribution of carbon black between these two phases. The carbon black is preferably dispersed in the HDPE phase which becomes the conductive phase. If the PVDF is in good balance compared to the HDPE, the PVDF phase forms a particular structure favorable for the PTC effect. A singular distribution of the conductive PE phase in the PVDF phase is the condition for counteracting the NTC effect which occurs at the melting of HDPE which is less than that of PVDF.

This second type is described in the following references: 131: 287163 CA Tl Carbon black-filled immiscible blends of poly (vinylidene fluoride) and high density polyethylene: the relationship between morphology and positive and negative temperature coefficient effects AU Feng, Jiyun; Chan, Chi-Ming CS Department of Chemical Engineering Advanced Engineering Materials Facility, The Hong Kong University of Science and Technology, Kowloon, Hong Kong SO Polym. Eng. Sci. (1999), 39 (7), 1207-1215 CODEN: PYESAZ; ISSN: 0032-3888 PB Society of Plastics Engineers

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 130: 96227 CA Tl Carbon black-filled immiscible blends of poly (vinylidene fluoride) and high density polyethylene: electrical properties and morphology AU Feng, Jeng; Chan, Chi-Ming CS Dep. of Chemical Engineering, Advanced Engineering Materials Facility, The Hong Kong University of Science and Technology, Kowloon, Hong Kong SO Polym. Eng. Sci. (1998), 38 (10), 1649-1657 CODEN: PYESAZ; ISSN: 0032-3888 PB Society of Plastics Engineers 130: 52964 CA Tl Carbon black-filled immiscible blend of poly (vinylidene fluoride) and high-density polyethylene: electrical properties and morphology AU Feng, Jiyun; Chan, Chi-Ming CS Department of Chemical Engineering, The Hong Kong University of Science and Technology, Kowloon, Hong Kong SO Annu. Tech. Conf. - Soc. Plast. Eng. (1998), 56th (Vol.

2), 2476-2480 CODEN: ACPED4; ISSN: 0272-5223 PB Society of Plastics Engineers and finally patent application WO 9805503 It is advantageous to use compositions with a PTC effect containing fluorinated polymers, for example those disclosed in application EP-A-1205514 (to which it is referred for the description of the polymer blends in question) which describes compositions based on PVDF polymers combined with liquid solvents and compatible diluents or compositions containing PMMA polymers in suspension and in well-dispersed mixture with suitable conductive particles.

According to one embodiment, having latexes with dispersed particles allows them to be implemented between two conductive surfaces, by soaking, impregnation, drying or extrusion on different

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 continuous supports, or on wires of different natures depending on the media chosen, the desired energy input densities and the foreseeable mechanical stresses. The supports or the wires may be made of any material whose melting points are in particular greater than 220 ° C. to allow the resistance to heat treatment at 180 ° C. for 30 minutes and for example, either polyester or polyamide 6 or polyamide 6 6.

The electrically conductive surfaces which are according to the invention in the form of a continuous support or in the form of a comb, meshes or nets or cords are made of any electrically conductive material comprising for example a metal such as iron, aluminum , copper, nickel, brass and their alloys The tablecloths are generally in the form of rolls with a length of at least 1 meter up to about 50 meters long and a width of at least 0.5 meters up to at 5 meters with conductive meshes of size between 0.5 by 0.5 mm to 50 by 50 cm according to the required powers.

According to a particular embodiment and in the case of low powers required for example from 30 to 1500 W / m2 and 15 minutes of inertia the meshes of the sheets have sizes between 10 by 10 cm to 50 by 50 cm.

According to another particular embodiment and in the case of high powers required for example from 2000 to 15000 W / m2 and an inertia of a few seconds, the meshes of the sheets have sizes between 0.5 by 0.5 mm to 2 by 2 mm. In the case of very small spacings, the current contributions can be made with continuous conductive electrical surfaces between which the PTC polymer material in the form of grain is inserted by hot sintering.

The network of electrical conductors is preferably integrated in the form of sealed modules.

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 Once the desired type of performance has been identified, the products with autocontrolled temperature resistance (PTC) available can be used according to the following choice parameters: # Voltage from 9 to 440 v.

 # Power density from 30 to 15,000 w / m2.

 # Temperatures from +2 c to +150 c or more depending on the polymer compositions used.

 # Longevity adapted to situations according to the formulas.

 # Frequency of hot / cold changes.

 # Temperature rise rate.

 # Regulation mode around the set point.

 # Economic limits and surface criteria.

According to another object, the invention relates to single or multi-layer structures for insulation and / or protection, for example from corrosion, comprising the heating layers described above.

By monolayer heating structures is meant the integration of the heating mat into a single thickness of insulating material, for example concrete slabs or acrylic floor plates, plasterboard, polymer plates, etc.

By multilayer heating structures means the insertion of the heating mat between different layers of identical or different materials having insulating and / or protective properties, for example corrosion. The meshes which are empty between two conductors, allow the complete integration of the heating elements in the insulation and / or corrosion protection structures.

The subject of the invention is also the heating materials produced from such heating layers.

In particular, it is possible to use the heating sheets covered with an electrically insulating but thermally conductive polymer, to produce an instant heat exchanger with lighter and more compact than current systems which limit their

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 installations at dispersed sites but under strong technical control.

This instantaneous heating plate exchanger is designed according to the known model in aluminum or steel. The corresponding modules are produced here in PMMA sheets or other plastic binder system loaded with aluminum powder with well distributed particle sizes and already used to make rapid molds for limited series. In doing so, the plates which surround the PTC elements are made electrically insulating, while having very good properties of desired electrical conductivity, with 1 to 5 mm thickness instead of the 20 mm imposed for the moment by the heating elements. at 800 C and the problems associated with reducing these temperatures to less than 100 C without loss of tightness and without deformation of the metal plates.

The elements obtained are much more compact than the models known to date for the same service.

The applications of these heating materials are now specified in all known human and industrial fields with the establishment, on a case-by-case basis, of the most effective PTC-effect polymer compositions.

The studied systems of self-limited energy supply in groundwater can cover the following activities; # buildings heated in frost protection to +2 C on the ground, or
15 C for a first heating on the ground, or sheets on the ceiling around 40 C according to the limits imposed by the stability of the materials (plasters, polymers ...).

 # The under layers of carpet to dry and avoid the proliferation of mites and ensure immediate contact comfort.

# Domestic uses in gastronomy between 30 and
70/80 C and more to improve the tastes of products under controlled cooking, and the temperature maintenance of prepared foods, or even their rapid reheating

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 no other equipment than a heating plate without thermostat required.

 # Details of contact heaters in bathrooms.

 # Energy transport on the seabed, in water at +4 C from a depth of 500 meters, with the possibility of heating 12 inch tubes% in addition to the precautions of insulating the tubes by insulating elements.

 # Defrosting of means of transport by rapid supply of energy at a temperature fixed in advance, and with changing power; it can be both boat decks and airplane wings and the interiors of cars or commercial vehicles.

 # The fields of health, the breeding of all domestic animals as well as for the food industry, with the possibility of heating at any time all surfaces to the desired temperature, from 35 C to the pasteurization temperature / 70 C during the period considered optimal after validation tests.

 # The industry in general with temperature sensitive products for storage, transport lines, reactors, molds for various materials.

 # Also, the surfaces under the roots of the plants to allow controlled growth at each optimal determined temperature level. Heat transfers to plants take place much more quickly and economically through root contact than through the air.

According to another object, the invention relates to materials for household or industrial use in the fields of construction and building, energy transport in the seabed, human or animal health, the food industry or from the process control industry which includes the devices (heating sheets or structures) as described above.

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For the construction materials of buildings for industrial or domestic use such as materials for floors, ceiling walls or under layer of carpet for industrial or domestic use, this practical concept of heating sheets is used more particularly to maintain the temperatures at the targeted thresholds: frost-free at +2 C, comfort at 15/25 C, drying at 30/40 C, heating by low-temperature radiation.

Application transfers are made between the industrial sector and the domestic sector by reducing the size of the heated areas to the usual 10 to 100 m2 in urban or rural housing.

According to another embodiment, the invention relates to heating pipes and in particular heating pipes for the transport of oil or gas in off shore or on shore production which include the heating layers.

The problem of maintaining the temperature of oil flows underwater at more than 500 meters deep is very important, because the water is at 4 C due to the pressure, while the fluids are pumpable at more than 50 C It is imperative to maintain minimum temperatures so as not to block the circuits. This is achieved with thermal insulations which allow stops limited to a certain number of hours, but without possible energy supply to date.

PTC heating meshes allow the power required to compensate for heat losses of the order of 60 W / m2 to be measured for 12 3/4 inch tubes which offer loss areas of 1 m2 / linear meter. The power required is therefore 480 KW for an 8 km deep-sea tube, which is typical in offshore production. The powers of a few MW on platforms allow this kind of extra power.

In order to be able to heat by controlling the temperature, the sheets are for example inserted in the

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 multilayer corrosion protection of the tubes, between the epoxy layer and the polyolefin layer. The meshes which are possibly empty between two conductors, allow the complete integration of the heating elements in the insulation and corrosion protection structures.

According to another mode of application, the invention relates to the use for the removal by heating of the contamination by pathogenic agents of the heating sheets or structures as described above.

The physical cleaning of technical surfaces is more or less crucial at the micro biological level depending on the destination of these work plans. Whether in the food industry, pharmacy, surgery, various biological laboratories, it is often essential to have clean surfaces which we are also certain to be decontaminated from any external microbial pollution at a time given.

Usually, this goal is presumed to be achieved when surface cleaners are said to be antibacterial under the prescribed conditions of use. But it is clear that surface checks are not carried out routinely, with each antimicrobial cleaning.

The PTC heating option for surfaces allows you to proceed in two stages, the first of which consists in mechanically cleaning the surfaces. Then, the second step is to heat the target surface for the time counted from 1 to 15 minutes to the required temperature and obtain the desired sanitation.

In a particular mode of application of the removal by heating of contamination by pathogenic agents, the heating layers covered with insulating polymer make it possible to set up instant hot water generation systems which heat the water only tap opening times, which are lighter and more compact than the systems

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 that offer an enhanced warranty and performance option.

Regarding the various process controls in the industry for the entire temperature range between +5 C and +150 C, it is often very difficult to regulate around the required levels due to the heterogeneity of the systems studied. We are witnessing overheating phenomena on the surface, for insufficient core temperatures.

In the implementation of delicate food systems, of organic fermentations, for example lactic and / or cheese, of maturation of meats, creams, chocolates, glucoses and others, compliance with strict maximum temperatures requires very strict regulation systems. complex.

The installation of heating pads with adjustable shapes and powers as needed makes it possible to simplify the design of these materials. These plies can be adapted in all forms, with the heating conductive surfaces or meshes described above.

In the field of aviation, airplanes have very sensitive points to temperatures outside of -50 C. The current protections are made with constant power inputs, which leads to overheating or too low temperatures. It is therefore desirable to be able to heat at various points in a controlled delocalized manner by integrating, for example, heating layers in the airplane wings for surface antifreeze protections as well as for maintaining the temperature of various evacuation members and circuits. exposed out of the cabin.

This performance is made possible by the uniform and regular heating properties of the sheets of the invention.

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The invention will be better understood with regard to the following examples, which are given by way of illustration and not limitation.

Examples Preparation of the heating pads Example 1 A roll of 1 meter wide is impregnated by soaking in a suspension of a mixture of PTC polymers (30% Graphite, 40% PVDF, 30% PMMA) with a density of 100 g / m2 on a support material either polyester or polyamide 6 or polyamide 6.6 of 1 cm2 (1 cm by 1 cm). Drying is then carried out, then conditioning at 180 ° C. or by continuous printing roller with the following suitable heat treatments. The network of electrical conductors for current control is woven into the mesh with a distribution of 15 cm wide for the polarities of the current. Redistributions are made using a comb of conductors (110 V or 42 V connections).

The conductive meshes give off a power of 100 W / m2 at 12 C at 110 V and 50 W / m2 at 3 C at 42 V.

Example 1b The heating sheets obtained according to example 1a are electrically insulated by application of a PMMA type polymer.

Preparation of monolayer or multilayer structure and applications.

Example 2 An electrically insulated heating sheet with 2 mm thick mesh obtained as described in Example 1b is integrated into a thickness of 10 mm of self-leveling cement above the ground concrete and in strips 10 meters long.

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The current is connected, giving the indicated temperatures in 20 minutes. The current consumption records show the alternations of power required between day and night, as well as the power changes as a function of temperature during the day.

Example 3 Plates comprising a tablecloth according to example la or 1b of size 0.5 x 0.5 meters are fixed to the ceilings by adapting to the dimensions of the unit elements of different removable models. The powers are of the order of 100 to 120 W / m2 with about 45 C maximum in the case of plaster-type surfaces.

These heating surfaces are suitable for heating houses by radiations under the ceiling or under layers of carpets or in submerged concrete floors.

In the case of floors and carpet mats, the heating layers are immersed in the target environments, with the appropriate temperature thresholds for the required power and the voltage accepted by safety standards.

Example 4 In the case of acrylic floors loaded with glass beads, the heating and conductive layers obtained according to Example 1b are immersed as they are without the need for insulation since the PMMA is waterproof and electrically insulating.

The electrical connections are made from one unrolled strip to the other to allow the installation of homogeneous heating of an area 5 meters wide by 10 meters long.

When thermal insulation is installed on the floor, we see that we ultimately keep the same set temperature which is 12 C for 110 V.

The temperature cycles were tested over periods of 5 days, then 30 and 90 days without significant change in performance. Ground markings are provided

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 to indicate the limits of electrical connections by modules of suitable sizes, for example 50 m2 in a set of 500 m2 or more.

EXAMPLE 5 For the frost protection of industrial surface, use is made of netting plies according to example la of 1 meter wide in rolls of 20 to 50 meters with conductive meshes of size 0.5 by 0.5. 2 cm according to the required powers and a network of conductors integrated in the form of waterproof modules.

The temperatures reached are +5 C minimum and +28 C maximum in less than 15 minutes on the floor, and 45 C maximum on ceilings and walls.

In the case of permanent human habitat, presence detections by IR make it possible to trigger localized heaters only when there is a need to heat, and to stop according to selected time delays.

Example 6 To prepare heating tubes used in offshore and onshore oil and gas installations, a banner of fixed width is used as a function of the power to be transmitted and the diameter of the tubes. This banner is continuously wound around the tube to be treated.

The heating strip is prepared by inserting the heating sheet in the multilayer corrosion protection of the tubes, between the epoxy layer and the polyolefin layer.

The thermal balances are established for example at a height of 60 W / m2 at 60 C for a 12 inch tube to be immersed under 1500 meters of water in a medium at 4 C. The power consumed is 480 KW for a line of 8 km which is typical in offshore installation.

Example 7

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 When using sensitive surfaces, it is possible to guarantee microbiological cleanliness at all times without the need for immediate prior control.

Heating tests at 70 C minimum, and 80 C maximum, have shown that conventional germs are eliminated while the control surface remains contaminated.

This also applies for the guarantee of maintaining the temperature of the water in the hot water reserves without the risk of going below 50 C as well as for the systems of generation of instantaneous hot water with exchanger with instantaneous hot plates .

Claims (10)

CLAIMS 1. Heating mat comprising at least one layer of conductive polymer with self-temperature controlled resistance by PTC effect placed between at least two electrically conductive surfaces. 2. Heating mat according to claim 1 wherein the two electrically conductive surfaces have mesh structures. 3. Heating mat according to claims 1 or 2 wherein the polymer layer covers the electrically conductive surfaces with a density between 10 and 500g / m2. 4. Heating mat according to any one of the preceding claims covered by an electrically insulating and thermally conductive polymer. 5. Mono or multilayer heating structure comprising at least one heating sheet according to one of claims 1 to 4. 6. Use of a heating cloth or structure according to claims 1 to 5 in the fields of construction and building, energy transport in the seabed, human or animal health, the food industry or the process control industry. 7. Heating materials for household use or for industrial use comprising the heating layers or structures according to claims 1 to 5. 8. Heating materials for building construction for floors, walls, ceilings or under carpet <Desc / Clms Page number 23>  comprising at least one heating mat or structure according to one of claims 1 to 5. 9. Heating systems comprising at least one heating mat or structure according to one of the claims 1 to 5. 10. Use for the removal by heating of the contamination by pathogenic agents of at least one heating sheet or structure according to one of claims 1 to 5.