CH719597A1 - Self-regulated multilayer electrothermal structure. - Google Patents

Abstract

The invention relates to a flexible, substantially planar, multilayer electrothermal structure (100) having a front face intended to allow infrared rays to pass through and a rear face opposite the front face. The structure has a width and a length, i.e. a surface, the structure comprises at least one electrical input terminal (131), at least one electrical output terminal (132), a substrate for receiving a plurality of layers of the structure . The substrate comprises at least one polymeric substrate layer (110), at least one electrothermal layer comprising a resistive element (149) having an input and an output. The resistive element (149) has a substantially rectangular shape with a width substantially equal to the width of the structure and at least one conductive layer (140) for connecting the input terminal (131) of the structure to the input of the resistive element, and the output terminal (132) of the structure at the output of the resistive element. The structure is covered with a passivation (120) comprising at least one polymeric passivation layer. The electrothermal layer comprises a first type of graphene (140) and the conductive layer comprises hybrid graphene with a content greater than 50% of graphene (130), the remainder is composed in particular of resin and solvents, the hybrid graphene having a particle size of the order of 0.5 to 1 micron making it possible to obtain a particle size of nano particles between 30 and 50 nanos to promote electrical conductivity.

Description

TECHNICAL AREA

The present invention relates to films heated by ohmic resistance. More particularly, the invention relates to heating elements having a surface extending essentially in two dimensions in which the conductor is mounted on an insulating base and covered with an insulating material.

STATE OF THE TECHNIQUE

[0002] The international patent application, published under number 2013/179341A1, describes a heating film comprising a planar heating element which has a pair of terminals, a pair of conductive wires welded to the terminals and two sheets of thermoplastic polyamide film which are respectively laminated on the surfaces of the planar heating element by thermal welding and which maintain said planar heating element in a sealed state. In the heating film, the thermoplastic polyamide films can be hermetically welded by thermal welding to the planar heating element so as to seal it.

[0003] We also know, for example, the Chinese patent application, publication number 110913515A, which describes a heating film comprising graphene, which heats by emitting infrared rays, as well as the Chinese patent, published under number 102083246B, which describes an electric heating film comprising a conductive carbon paste as a heating element. European patent, publication number 3251468B1 describes a heating film comprising a base substrate and a heating layer, carried by the substrate, the heating layer comprising metal nanowires and graphene nanotubes.

[0004] The main problems with these solutions are complicated implementations and high consumption for primary use, namely heating. Another problem is heat management in existing heating films.

SUMMARY OF THE INVENTION

[0005] An aim of the present invention is to propose a heating solution which is quicker to implement. Another goal is to propose a simplified solution of a self-regulated heating film. It is also an aim of the present invention to propose heating films which are simpler to produce in factories, with more efficient manufacturing processes.

[0006] According to a first aspect, a heating film is presented. It is a multilayer electrothermal structure, which is flexible and which is substantially planar. In at least one embodiment the structure can be rolled up on itself. The structure has a front face intended to allow infrared rays to pass through and a rear face opposite the front face. The structure has a certain width and a certain length, i.e. a surface. In at least one embodiment, the structure is significantly wider than it is long and can be deployed in large rolls. According to one embodiment, the structure comprises: at least one electrical input terminal; at least one electrical output terminal; a substrate for receiving a plurality of layers of the structure, the substrate comprising at least one polymeric substrate layer; at least one electrothermal layer comprising a resistive element having an input and an output; and at least one conductive layer for connecting: the input terminal of the structure to the input of the resistive element; and the output terminal of the structure at the output of the resistive element; the structure being covered with a passivation comprising at least one polymeric passivation layer. Advantageously, the electrothermal layer comprises a first type of graphene; and the conductive layer comprises hybrid graphene.

[0007] In a preferred embodiment, the substrate comprises two layers of insulator and the passivation also comprises two layers of insulator. The heating layer is encapsulated between the passivation and the substrate, preferably by a hot lamination process, thus making the multilayer electrothermal structures proposed by the present invention watertight and airtight. At the same time, these structures provide great protection against possible damage by mechanical action, such as scratches and/or cuts. Multilayer electrothermal structures also provide good electrical insulation.

[0008] Meeting the requirements of construction standards such as RT2020 standards, MOPEC in Switzerland or NF EN 60335-1 and NF EN 60335-2-96 in relation to domestic electrical appliances and radiant films, these structures can be used in the field of domestic heating.

SUMMARY DESCRIPTION OF THE DRAWINGS

[0009] The characteristics of the invention will appear more clearly on reading the description of several embodiments given solely by way of example, in no way limiting with reference to the schematic figures, in which: – Figure 1 shows the different layers present in an electrothermal structure according to an embodiment described in this document; – Figure 2 illustrates an equivalent electrical diagram representing an electrothermal layer which can be deployed in one embodiment of the electrothermal structure; – Figure 3 shows the layers present in an electrothermal structure according to another embodiment; and – Figure 4 shows the layers present in an electrothermal structure according to yet another embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a multilayer electrothermal structure which comprises a heating element by the Joule effect. The heating element includes an electrothermal material, which heats when it conducts an electric current. According to one embodiment, the electrothermal material has a positive temperature coefficient (PTC). According to one embodiment, the material has an emissivity such that when heated, it begins to emit infrared radiation, preferably far infrared. Thus, the electrothermal structure of the present invention heats by the effect of infrared radiation rather than by convection. The choice of far infrared radiation is made to promote the sensation of heat felt by a human being, because the human body favors the absorption of radiation in this spectrum.

Preferably, the electrothermal structure of the present invention is substantially planar, extending in two dimensions. The structure is preferably elongated, having a length several times greater than its width. According to one embodiment, the electrothermal structure has a certain flexibility such that it is sufficiently flexible to be rolled up on itself. The structures of the present invention are therefore easy to handle and transport.

[0012] The materials chosen for the encapsulation of the structure, namely the substrate and the passivation, are chosen to allow infrared rays to pass through. Preferably, at least one of the two surfaces allows infrared rays to pass through. In one embodiment, a reflective layer is used to promote the passage of infrared rays through a single side of the structure, i.e. the side called the front side, rather than through the rear side. In other embodiments, the infrared rays can pass through the front face and the rear face of the structure.

[0013] Figure 1 shows the layers which may be present in an electrothermal structure 100 according to one embodiment of the invention. The structure is built on a base, namely the substrate 110. According to one embodiment, the substrate is made of a layer of flexible polymer material, for example polyethylene terephthalate (PET). A conductive layer 130 comes next. According to one embodiment of the invention, the conductive layer is a conductive ink, deposited by a “slot dies” process then dried by infrared radiation, which promotes rapid drying. Optionally, to facilitate adhesion of the ink to the polymeric layer of the substrate, the substrate undergoes plasma treatment. In another embodiment, a primer layer can be applied to the substrate instead of using plasma treatment to ensure adhesion of the conductive layer to the substrate.

[0014] On the conductive layer is drawn, in conductive ink, a certain number of current conductors to bring a current which arrives at a pair of terminals 131 132, input/output, preferably located towards one edge of the structure, at least towards the heating element of the structure. Figure 2 shows an electrical diagram which represents the heating element 149 of the structure 100, with its input 131 and output 132 terminals. The heating element is represented by a resistor 149.

According to the embodiment described above, the heating element is located in the electrothermal layer, which is denoted 140 in Figure 1. The heating element can have any shape as long as it presents sufficient resistance to produce the desired Joule effect. Thanks to the emissivity properties of the electrothermal material chosen as the heating element, its dimensions will dictate the temperature, depending on the current, and the quantity of infrared radiation produced. The electrothermal material of the heating element can be deposited by a screen printing process, like the conductive layer, preferably by a slot die process. Contacts between the electrothermal material of the electrothermal layer and the conductive material of the conductive layer are made at the places where the two materials touch, thus creating the resistance, shown schematically in Figure 2. The resistance at an input and an output. In one embodiment, the input of the resistor is connected to the input terminal of the structure and the output of the resistor is connected to the output terminal of the structure.

As indicated in Figure 1, the last layer is a passivation layer 120. The passivation layer can be made of the same material as the substrate layer, i.e. a flexible polymer, preferably allowing infrared rays to pass through. According to one embodiment, the passivation layer is made of polyethylene terephthalate (PET). According to one embodiment, a layer of glue is used to fix the passivation layer on the electrothermal layer. Thus a structure called a “sarcophagus” ensures airtightness and watertightness to protect the heating element and the electrical conductors.

[0017] According to one embodiment, the glue is a heat-treated polyurethane glue. Polyurethane glue can be deposited in the liquid phase. According to another embodiment, the glue is solid, for example a “PSA” glue (pressure sensitive adhesive), the adhesion functioning by applying mechanical pressure.

[0018] Figure 1 shows the order of the layers starting from bottom to top with the substrate layer 110, the conductive layer 130, the electrothermal layer 140 and the passivation layer 120. In other embodiments, it is possible to change the order, for example: substrate 110, electrothermal 140, conductive 130, passivation 120; or passivation 120, conductive 130, electrothermal 140, substrate 110; or even passivation 120, electrothermal 140, conductive 130, substrate 110.

According to one embodiment, the radiation passes through one face of the structure, either through passivation or through the substrate. In this embodiment, the structure includes a reflective layer to reflect far infrared rays towards one of the two surfaces, i.e. the front face. The other side is the back side. The reflective layer is made of aluminum according to a preferred embodiment and is placed towards the rear face.

According to a preferred embodiment, the substrate comprises two polymeric layers of substrate, glued together. The passivation can also include two polymeric passivation layers glued together. Thus, the structure provides good electrical insulation as well as mechanical protection against scratches or other surface damage. Having two layers glued together provides better mechanical protection than a single layer having double the thickness, because the glue layer provides a barrier to stop the propagation of a possible cut or tear in a polymeric layer. Figure 3 and Figure 4 show examples of structures having double polymer layers of substrate and passivation.

[0021] The polymeric layers (substrate or passivation) can be made of PET according to a preferred embodiment but can also be made of polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), flexible PVC ( PVC-P), polystyrene (PS), polycarbonate (PC), polymethyl methacrylate (PMMA), polyoxymethylene (POM), polyethylene terephthalate (PET), polyester, co-polyester, polyetheretherketone (PEEK), polyamide, in particular polyamide 6 (PA6), polyamide 12 (PA12), polyamide 10, polyamide 610, polyamide 66, polyamide based on aliphatic and cycloaliphatic constituents such as in particular MACM12 or amorphous co-polyamide, preferably based on PA12, or copolymers or mixtures thereof.

The resistive element may contain carbon, preferably graphene. Graphene can be a form of graphene called graphene microparticles, preferably in a form of nanoparticles (for example 1nm - 100nm) of graphene, either nanotubes, or nano-spheres, or graphene nano-wires. This form of graphene is preferred for screen printing processes, in particular slot dies so as not to block the ink outlet nozzles. Sintering can be done at temperatures low enough not to damage the polymer layers. Conductors can be made of silver, copper or graphene.

The conductive layer comprises hybrid graphene, which has advantageous conductive properties.

Claims (15)

1. Multilayer electrothermal structure (100), flexible, substantially planar, having a front face intended to allow infrared rays to pass through and a rear face opposite the front face, the structure having a width and a length, i.e. a surface, the structure (100) comprising: at least one electrical input terminal (131); at least one electrical output terminal (132); a substrate for receiving a plurality of layers of the structure, the substrate comprising at least one polymeric substrate layer (110); at least one electrothermal layer (140) comprising a resistive element (149) having an input and an output, the resistive element having a substantially rectangular shape with a width substantially equal to the width of the structure; And at least one conductive layer (130) to connect: the input terminal (131) of the structure at the input of the resistive element (149); And the output terminal (132) of the structure at the output of the resistive element (149); the structure (100) being covered with a passivation comprising at least one polymeric passivation layer (120); characterized in that: the electrothermal layer (140) comprises a first type of graphene; And the conductive layer (130) comprises hybrid graphene with a content greater than 50% of graphene, the remainder being composed in particular of resin and solvents, the hybrid graphene having a particle size of the order of 0.5 to 1 micron allowing obtain a particle size of nano particles between 30 and 50 nanos to promote electrical conductivity. 2. Structure (100) according to claim 1, in which the entry points (138) of the resistive element (149) are interposed with the output points (139) of the resistive element (149) along the length of each of the electrothermal bands (145). 3. Structure (400, 500) according to any one of claims 1 or 2, in which the substrate comprises a plurality of polymeric substrate layers (110, 111) bonded together and/or the passivation comprises a plurality of polymeric layers passivation (120, 121) stuck together. 4. Structure (400, 500) according to any one of claims 1 to 3, in which the structure further comprises a reflective layer of far infrared waves (170) to reflect at least the far infrared waves from the rear face towards the front face of the structure. 5. Structure (400, 500) according to claim 4, in which the reflective layer (170) is located between the electrothermal layer (140) and the rear face of the structure, the reflective layer (170) being glued to a polymeric layer (110, 120) or between two polymeric layers (110, 111, 120, 121). 6. Structure (100, 400. 500) according to any one of the preceding claims, in which the conductive layer (130) is located between the electrothermal layer (140) and the substrate (110, 111), said conductive layer (130 ) being bonded to the substrate (110, 111) and said electrothermal layer being bonded to the passivation (120, 121). 7. Structure (100, 400, 500) according to any one of claims 1 to 5, in which the conductive layer (130) is located between the electrothermal layer (140) and the passivation (120, 121), said conductive layer being bonded to the passivation (120, 121) and said electrothermal layer (140) being bonded to the substrate (110, 111). 8. Structure (100, 400, 500) according to one of claims 6 or 7, in which a primer layer is interposed between the conductive layer (130) and the substrate (110, 111) or between the conductive layer ( 130) and passivation (120, 121). 9. Structure (100, 400, 500) according to any one of the preceding claims, in which said bonding between layers is made using a polyurethane glue. 10. Structure (100, 400, 500) according to any one of the preceding claims, in which the length of the electrothermal strips (145) is equal to, or less than, the length of the structure (100, 400, 500), the plurality of electrothermal strips (145) covering substantially the entire surface of the structure (100, 400, 500). 11. Structure (100, 400, 500) according to any one of the preceding claims, in which the resistive element (149) comprises carbon, preferably graphene, preferably in a form of graphene microparticles, preferably in a form of graphene nanoparticles, either nanotubes, nano-spheres, or graphene nano-wires. 12. Structure (100, 400, 500) according to any one of the preceding claims, in which the conductive layer (130) comprises, as conductive material, copper, gold, silver, nickel or platinum. 13. Structure (400, 500) according to any one of claims 4 to 12, in which the reflective layer (170) comprises aluminum which covers substantially the entire surface of the structure. 14. Structure (100, 400, 500) according to any one of the preceding claims, in which the polymeric layers (110, 111, 120, 121) are made of polyethylene terephthalate (PET) (polyethylene (PE), polypropylene (PP ), polyvinyl chloride (PVC), flexible PVC (PVC-P), polystyrene (PS), polycarbonate (PC), polymethyl methacrylate (PMMA), polyoxymethylene (POM), polyethylene terephthalate (PET), polyester, co-polyester, polyetheretherketone (PEEK), polyamide, in particular polyamide 6 (PA6), polyamide 12 (PA12), polyamide 10, polyamide 610, polyamide 66, polyamide based on aliphatic and cycloaliphatic constituents such as in particular MACM12 or amorphous co-polyamide, preferably based on PA12, or copolymers or mixtures thereof. 15. Structure (100, 400, 500) according to any one of the preceding claims, the structure being rollable.