Heating nonwoven mat

Abstract

The present invention relates to the field of flexible heating materials, incorporating a nonwoven layer. The nonwoven layer does not incorporate any conductive fibers. The conductivity is ensured by the application of a conductive coating paste comprising 0.5 to 20 weight % of particles of an allotropic form of carbon, 0.5 to 20 weight % of polyurethane, and Water. The paste is then dried to obtain a conductive layer to which are fixed electrodes.

Description

[0001] Heating nonwoven mat

[0002] Field of the invention

[0003] The present invention relates to the field of flexible heating materials , incorporating a nonwoven layer .

[0004] Background of the invention

[0005] There exist a number of thin and flexible heating materials which can be used in the field of construction for example as underfloor heating, or wall covers or in other fields like the automotive industry or healthcare .

[0006] Most solutions incorporating nonwoven layers rely on the incorporation of conductive fibers in the nonwoven, electrodes are disposed at the surface of the conductive nonwoven and heat is generated between the electrodes when a current is applied .

[0007] One of the main problem in such constructions is the connectivity between the conductive fibers spread within the nonwoven and the electrodes , especially when an adhesive has to be used to fix them onto the nonwoven . Moreover, metallic fibers become oxidated after a while and the conductivity of the material decreases with time .

[0008] The applicant has therefore j udged necessary to develop a flexible heating material , which can rely on a nonwoven structure devoid of conductive fibers . Furthermore , it is an obj ective of the invention to provide heating materials that also can function as an acoustic barrier .

[0009] EP1127356 and EP4093148 describe conductive coatings and slurries but not in the context of nonwoven materials .

[0010] Summary of the invention

[0011] The invention in involves the use of a conductive coating paste comprising : 0.5 to 20 weight ! of particles of an allotropic form of carbon,

[0012] 0.5 to 20 weight ! of polyurethane, and

[0013] - water.

[0014] The particles of an allotropic form of carbon, such as carbon nanotubes (CNT) , nanobuds, nanoribbons, fullerenes, or graphene, preferably carbon nanotubes (CNT) and / or graphene, will confer the conductive properties of the coating. The coating paste preferably comprises between 1 and 18 weight!, preferably between 1.5 and 15 weight!, preferably between 1.8 and 12 weight!, preferably between 2 and 10 weight!, preferably between 2.2 and 8 weight! of an allotropic form of carbon, such as for example carbon nanotubes (CNT) and / or graphene.

[0015] Carbon nanotubes exist under various subforms like sponges, single wall carbon nanotubes, double wall carbon nanotubes, multiwall carbon nanotubes, graphitized carboxylic carbon nanotubes, etc., which can all be used for the present application .

[0016] Carbon nanotubes are usually characterized using their external diameter, which is for example comprised between 0.5 and 10 nm, preferably between 2 and 4 nm for single or double walls carbon nanotubes, between 20 and 60 nm for graphitized carboxylic CNT or sponges CNT, preferably between, 30 and 50 nm.

[0017] Carbon nanotubes can also be characterized using their length, which is usually comprised between 0.5 and 60 pm, or between 5 and 30 pm.

[0018] Graphene particles can be used in the form of flakes, for example flakes having a lateral size of a few microns and / r an average number of atomic layers of carbon of less than 10. The particles of an allotropic form of carbon can have a density of between 1 mg / cm3and 5 g / cm3, depending on their form and shape .

[0019] When a mixture of species of allotropic forms of carbon is used, the ratio of these species can vary. For example, but not limited to, a mixture can comprise CNTs and graphene, in a ratio between 10:1 and 1:10, preferably between 5:1 and 1:5.

[0020] The polyurethane in the coating paste allows the formation of a film upon drying. When used herein, the terms "film" and "conductive film" refer to a layer of dried conductive coating paste. The film should have sufficient strength, stability, thermal and ageing resistance. It should also confer hydrolysis resistance, i.e. resistance to salts and / or alkaline substance coming from the direct environment where the mat is place, such as the concrete when the heating mat is for flooring applications. However, the coating composition should have a sufficiently low viscosity to be applied in a low amount per surface unit, using techniques like for example with a knife over roll. To this purpose, the polyurethane content in the coating paste should be comprised between 0.5 to 20 weight!, preferably between 1 and 17 weight!, preferably between 1.5 and 15 weight!, preferably between 2 and 12!, still preferably between 3 and 10 weight!. Other binders can be used, like for example phenolic resins, acrylic resins, styrene butadiene resins .

[0021] Water is preferably the main solvent. Water is even preferably the only solvent, i.e., the coating paste is preferably devoid of any organic solvent. In one embodiment, the conductive coating paste is devoid of polypropylene glycol and devoid of polyethylene glycol. In one embodiment, the conductive coating paste is devoid of an anti-adsorption compound. In one embodiment, the conductive coating paste is devoid of polypropylene glycol, devoid of polyethylene glycol and devoid of an anti-adsorption compound. Water typically represents between 75 and 96 weight! of the coating paste.

[0022] The coating paste can further comprise additives like dispersants, thickeners, pH adjusters, solubilizers, polymer forming agents, etc.

[0023] One challenge when using particles in a composition is to obtain an homogeneous repartition of these particles, during use but preferably also during storage. Additives can therefore be used to such purposes. Additives may also be used to other purposes, for example coloring species to allow clear distinction of the final article of the areas where the coating was applied.

[0024] Additives may also be used to confer other properties, like anti-fire properties, water and / or air impermeability, etc.

[0025] Additives may also be used to enhance conductivity, like for example metallic particles like silver or copper particles, conductive silicates, etc. Preferably, additives represent between 0 and 7 weight! of the coating paste, preferably between 0.1 and 5 weight!, preferably between 0.2 and 3 weight!.

[0026] Dispersants are preferably present in the coating paste in amounts between 0 and 5 weight!, preferably between 0.05 and 4 weight!, preferably between 0.1 and 3 weight!. Dispersant can be any suitable compound known to the person skilled in the art of particulate dispersion, like inks, pigments, nanoparticle. In the present coating, it is preferable a solvent free wetting and dispersing additives for water-borne coating, like for example modified styrene maleic anhydride copolymer. Thickeners are used to adjust the viscosity of the coating and participate to the stability of the coating paste. Thickeners are preferably present in the coating paste in amounts between 0 and 5 weight!, preferably 0.1 and 3.5 weight!, preferably 0.2 and 2 weight!. The thickener used in the present invention are preferably suitable for use in aqueous emulsions or suspensions. In a preferred embodiment, the thickeners comprise an acrylate species, like an acrylic polymer. Other thickeners based on other chemistry are also possible.

[0027] Solubilizers are compounds used to favor the suspension of particulate matter. To provide solubilization of particles in water-based compositions, the solubilizer can comprise glycol ethers, like for example propylene glycol methyl ether, which present the advantage of having a low boiling point of 120 °C and in consequence to be easily removed during the drying step of the coating. pH adjuster are the typical species to stabilize a composition at a predefined pH. For example, ammonia can be used. Preferably the paste has a pH comprised between 7 and 10, preferably between 7.5 and 9.5, still preferably between 8 and 9.

[0028] The paste of the invention preferably has a viscosity comprised between 10 000 and 30 000 mPa.s (cPs) , preferably between 15 000 and 25 000 mPa.s (cPs) , still preferably between 20 000 and 24 000 mPa.s.

[0029] The conductive paste of the invention can be prepared in one step, mixing all ingredients, or in sequential steps. It can for example be advantageous to use pre-dissolved carbon particles, for safety purpose, as these are very volatile and can be contaminant to the operators handling them, or create dust in the working environment .

[0030] The conductive coating paste of the invention, i . e . a paste comprising particles of an allotropic form of carbon and polyurethane is for use in the manufacturing of flexible heating materials , i . e . sheet materials based on nonwovens .

[0031] The term "nonwoven" as used herein has its usual meaning in the art and refers to an assembly of fibers — other than a traditional paper, woven, or knit — which has been engineered to some level of structural integrity by physical and / or chemical means . Nonwovens typically contain void volumes .

[0032] Nonwovens are designed for their speci fic application, ranging from thin, light weight nonwovens to strong and durable nonwovens . Nonwovens manufacturing starts by the arrangement of fibers in a sheet or web . The fibers can be staple fibers . Manufacturing of nonwovens may comprise carding . Carding is a mechanical process which starts from bales of fibers . These fibers are 'opened' and blended after which they are conveyed to the card by air transport .

[0033] Webs may have a limited initial strength right after the web formation ( depending on various bonding mechanisms ) . The web is therefore typically consolidated in one or the other way . The choice of the web consolidation method strongly depends on functional properties that are needed as well as on the type of fibers used . Machine parameters and fiber mix can be varied to produce a wide range of fabrics with di f ferent properties . Thermobonding uses the thermoplastic properties of certain synthetic fibers to form bonds under controlled heating . In some cases , the web fiber itsel f can be used, but more often a low melt fiber or bicomponent fiber is introduced at the web formation stage to perform the binding function later in the process. Calendaring uses heat and high pressure applied through rollers to weld the fibers, one-sided or both sides. In mechanical bonding, the strengthening of the web is achieved by inter-fiber friction as a result of the physical entanglement of the fibers. There are two main types of mechanical bonding, needlepunching or hydro-entanglement. The difference with woven or knitted fabrics is that they use yarns instead of staple fibers and the yarns are being assembled by interlacing into warp and weft, and by stitching / interloping when we talk about knitting .

[0034] In some embodiments, the nonwoven comprises or consists of hydrophobic fibers or comprises a hydrophobic surface layer, for example comprising silicone, siloxane, waxes, or combinations thereof. In some embodiments, the conductive coating is applied onto a hydrophobic nonwoven or onto a hydrophobic surface layer of the nonwoven. In some embodiments, the surface is sufficiently hydrophobic to delay penetration of a drop of water into the material for at least 15 min, e.g. for at least 60 min.

[0035] In one aspect, the invention relates to a first method for manufacturing a flexible heating material (heating mat) wherein :

[0036] - a conductive coating paste comprising: a) 0.5 to 20 weight % of particles of an allotropic form of carbon, b) 0.5 to 20 weight % of polyurethane, and c) water is applied onto a carrier layer and dried to form a conductive film;

[0037] - the conductive film is transferred onto a nonwoven layer and; - at least two substantial ly parallel electrodes are fixed to the conductive film .

[0038] In some embodiments , the nonwoven :

[0039] - has at least one calendared surface , and / or

[0040] - is hydrophobic or has a hydrophobic surface layer .

[0041] In one embodiment , the conductive coating paste is applied directly onto the calendared and / or hydrophobic surface layer .

[0042] In this first method, it will be appreciated that the order of the steps can vary . The trans fer step involves that the nonwoven layer is applied to the surface of the conductive film opposite to the carrier layer .

[0043] In some case , the . The electrodes can be fixed onto the conductive film before the film is trans ferred to the nonwoven, meaning that the electrodes end up between the nonwoven and the conductive film . The carrier may or may not be released . When it is not released it can serve as a protecting layer . The electrodes can be applied to the carrier before coating by a hot melt technique , or to the coating after drying, or the electrodes can be embedded within the coating, before the drying step . In this latter case , there i s no need to glue or stitch the electrodes , thereby saving a step in the manufacturing process , the coating serving as fixation means to the electrodes .

[0044] Alternatively, the conductive film can be trans ferred onto the nonwoven, the carrier is then removed or released, and the electrodes are fixed on the face where the carrier was , meaning the opposite face to the nonwoven . Alternatively, still, a first electrode ca be applied on the conductive layer before the film is transferred to the nonwoven, and the second electrode can be applied to the conductive layer after the film is transferred to the nonwoven, resulting in the two electrodes being on opposite sides of the conductive film.

[0045] In some embodiments, all of the conductive coating paste is dried to form a conductive film prior to transfer onto the nonwoven layer, i.e. there is no wet paste present upon transfer onto the nonwoven layer.

[0046] In some embodiments, at least one, or all, of the electrodes are fixed to the conductive film after the transfer step.

[0047] In some embodiments, at least one, or all, of the electrodes are embedded into the conductive coating prior to the drying step or fixed to the film between the drying step and the transfer step.

[0048] In some embodiments, at least one, or all, of the electrodes are applied to the nonwoven layer prior to the transfer of the conductive film to the nonwoven layer. Thus, the electrodes may be applied to the nonwoven, preferably the calendared and / or hydrophobic surface of the nonwoven if present, for example using holt melt techniques or low-melt fiber. The conductive film is subsequently transferred onto the nonwoven thus fixing the electrodes to the film.

[0049] The carrier layer is preferably a thin layer which allows releasable adhesion of the film thereon. It is for example a transfer paper as is well known in the field. The conductive film is trans ferred onto a nonwoven layer by any suitable means known to a person skilled in the art and preferably by lamination .

[0050] The applicant also surprisingly identi fied that when the nonwoven layer is a spunbond layer, the trans fer step may be superfluous , and the coating paste can be applied directly on the spunbond nonwoven layer (which is then the carrier layer ) . This principle was further tested and extended to other types of nonwovens with a relatively closed surface ( for example nonwoven with calendared surfaces ) .

[0051] Accordingly, the invention also relates to a second method for manufacturing a flexible heating material (heating mat ) wherein :

[0052] - a conductive coating paste comprising : a ) 0 . 5 to 20 weight % of particles of an allotropic form of carbon, b ) 0 . 5 to 20 weight % of polyurethane , and c ) water is applied directly onto a nonwoven layer and dried to form a conductive film; and

[0053] - at least two substantial ly parallel electrodes are fixed to the conductive film .

[0054] In some embodiments , the nonwoven :

[0055] - has at least one calendared surface ; and / or

[0056] - is hydrophobic or has a hydrophobic surface layer .

[0057] In a further embodiment hereof , the conductive coating paste is applied directly onto the calendared and / or hydrophobic surface layer . Application of the conductive coating paste or film on a calendared and / or hydrophobic surface has the advantage that penetration into the nonwoven is avoided or at least reduced and thus a thin superficial conductive layer with good conductivity is obtained .

[0058] In the second method as well , the order of the steps can vary .

[0059] The electrodes can applied to the nonwoven layer before coating by a hot melt technique , or to the coating after drying, or the electrodes can be embedded within the coating, before the drying step . In this latter case , there i s no need to glue or stitch the electrodes , thereby saving a step in the manufacturing process , the coating serving as fixation means to the electrodes .

[0060] Accordingly, in some embodiments , at least one , or all , of the electrodes are fixed to the conductive film after the drying step .

[0061] In some embodiments , at least one , or all , of the electrodes are embedded into the conductive coating prior to the drying step .

[0062] In some embodiments , at least one , or all , of the electrodes are applied to the nonwoven layer prior to application of the conductive coating paste to the nonwoven layer . Thus , the electrodes may be applied to the nonwoven, preferably the calendared and / or hydrophobic surface of the nonwoven i f present , for example using holt melt techniques or low-melt fiber . The conductive coating paste is then applied and subsequently dried thus fixing the electrodes to the conductive film . Whether using the first or the second method, a further protective layer can be applied, for example by lamination. The protective layer can be for example impermeable to liquids and / or gas, or can impart mechanical protection against scratches .

[0063] In all cases, the nonwoven is preferably devoid of any metallic and / or conductive fiber.

[0064] The conductive coating paste is applied onto the carrier or the nonwoven layer by any suitable means known to the person skilled in the art, allowing to spread a homogeneous thickness of paste over the carrier. Application of the paste can for example be performed using the reverse roll technique, the knife over roll technique, the blade over air technique (floating knife coating) , foaming technique. In some embodiments, application of the conductive coating paste does not involve extrusion.

[0065] If using the knife over roll coating technique, the distance between the carrier and the knife will determine the thickness of the layer of paste applied. This distance if preferably comprised between 0.1 and 1 mm, preferably between 0.2 and 0.75 mm, preferably between 0.3 and 0.5 mm.

[0066] Application of the conductive paste on the carrier or the nonwoven can be applied as one continuous zone along the width of the carrier or nonwoven (usually provided as a roll for continuous application) . Alternatively, the conductive paste can be applied along zones relative to the width of the carrier or nonwoven layer, i.e. bands of coating are applied along the machine direction, creating parallel conductive bands. This allows to create insulation zones between two conductive bands, thereby avoiding having to cut the carrier or nonwoven to obtain the desired breadth and reducing signi ficantly the loss of material .

[0067] After application, the conductive coating paste is dried in order to remove the water and possibly other volatile species . The drying temperature is preferably comprised between 120- 200 ° C, preferably 150- 175 ° C .

[0068] After drying, a conductive film is obtained . The conductive film weight per surface unit is preferably comprised between 15 and 50 g / m2, preferably between 20 and 40 g / m2, preferably between 30 and 35 g / m2. A too low thickness does not al low to obtain the desired conductive properties while a too high thickness has a negative impact on the flexibility of the overall material , without necessarily improving the conductive ef fectiveness .

[0069] The electrodes are fixed to the conductive film, meaning they are in direct contact with the conductive film . The electrodes are contact electrodes , preferably of the stripe-type or bandtype , meaning they are thin flexible electrodes , which can be applied on the conductive layer by lamination, adhesion, gluing, etc . Such electrodes are commercially available . However, any suitable type of electrode can be used, like for example classical wires or any other type known to the person skilled in the art . Stripes or bands electrode can typically comprise a number of metal wires or conductive fibers extending along the electrode , arranged in paral lel to each other, usually between 4 and 10 wires , preferably between 4 and 8 wires , preferably 7 wires . The wires are preferably (partially) embedded into a nonwoven band, for example the wires are interwoven, inwoven, weft inserted and / or entangled . The structure of embedment allows contact of the wires with the conductive layer when the electrodes are fixed thereon . The electrodes can be straight bands or wavy bands as well known by the person skilled in the art .

[0070] In some embodiments of the first or the second method of the invention, the method does not involve :

[0071] - forming,

[0072] - applying, and / or

[0073] - fixing an electrode on the nonwoven layer or the carrier layer prior to application of the coating .

[0074] Furthermore , in some embodiments of the first or the second method of the invention, the conductivity coating paste is applied directly on, or trans ferred to , a calendared and / or hydrophobic first surface of the nonwoven and said nonwoven comprises a second surface which is not calendared and not hydrophobic .

[0075] Thus , in a further embodiment , the first or second method of the invention further comprises :

[0076] - applying a conductive coating paste comprising :

[0077] • 0 . 5 to 20 weight % of particles of an allotropic form of carbon,

[0078] • 0 . 5 to 20 weight % of polyurethane , and

[0079] • water onto the second surface , allowing penetration of the conductive coating paste into the second surface , drying, and fixing at least two substantially parallel electrodes to the conductive film . The steps may be performed in the specified order or in a different order. Furthermore, the treatment of the second surface may be performed after or prior to the treatment of the first surface.

[0080] In a further embodiment, the first or second method of the invention further comprises the following step:

[0081] - a conductive coating paste comprising:

[0082] • 0.5 to 20 weight % of particles of an allotropic form of carbon,

[0083] • 0.5 to 20 weight % of polyurethane, and

[0084] • water is applied onto a carrier layer to form a conductive layer;

[0085] - the conductive layer is transferred onto the second surface of the nonwoven layer;

[0086] - a drying step is performed; and,

[0087] - at least two substantially parallel electrodes are fixed to the conductive film.

[0088] Again, the steps may be performed in the specified order or in a different order and the treatment of the second surface may be performed after or prior to the treatment of the first surface. Preferably, there is no drying step between the application of the paste to the carrier layer and the transfer to the second surface of the nonwoven layer. Alternatively, a drying step is performed, but followed by application of an additional layer of wet pasta prior to transfer to the second surface of the nonwoven layer.

[0089] The products obtained by any of the processes described above are also an object of the invention. The product is a flexible heating material comprising a nonwoven layer in direct contact with a conductive film, wherein at least two substantially parallel electrodes are fixed to the conductive film, the nonwoven being devoid of conductive fibers , wherein the conductive film comprises particles of an allotropic form of carbon and polyurethane .

[0090] The conductive film covers at least part of the nonwoven surface , preferably between 50% and 95% of the nonwoven surface , preferably between 60% and 90% of the surface of the nonwoven .

[0091] Preferably, the electrodes are each positioned close to an opposite edge of the conductive fi lm, i . e . at opposite edges . Each electrode is meant to be connected to an external electrical circuit comprising a current source . The electrical circuit is closed by the sequence comprising the first electrode , the conductive layer and the second electrode . To this purpose , the two electrodes are preferably connected to the external electrical circuit at opposite extremities : each electrode represent a segment extending along a length of the conductive layer on the nonwoven layer, said length having an extremity . The two electrodes being parallel , they both have an extremity positioned at a first side of the material and another extremity at the other side of the material ; the first electrode is arranged to be connected to the external circuit at one side of the material and the second electrode is arranged to be connected to the external circuit at the other side of the heating material . This allows to maximi ze the electrical path between both electrodes , thereby maximizing the heating surface which covers substantially the entirety of the conductive film .

[0092] The flexible heating material of the invention functions following the electric resistance heating principle or Joule heating principle . Upon application of a current between the electrodes , the current flows through the conductive film, which has a defined resistance and generates heat .

[0093] Such an arrangement is suitable to be connected to any type of electrical source , direct current and / or alternative current , at a broad range of voltages . For example , the flexible heating material of the invention can be directly connected to solar panels , providing direct current at 12V, 24V or 48V . An inverter is not necessary . The flexible heating material of the invention can also be connected to a battery, like a car battery or a domestic battery, or can be connected to the domestic electric circuit . Preferably, the electric power output of the flexible heating material is comprised between 50 and 500W, when suppl ied with 48V, preferably between 75 and 350 W, still preferably between 75-200 W 100 and 150 W . The heat generation typically depends on the concentration of the particles of allotropic carbon and the thickness of the conductive layer .

[0094] Though higher temperatures can be reached with the heating mat of the invention, the flexible heating material is preferably arranged to reach temperatures comprised between 28 ° C and 50 ° C, preferably between 30 ° C and 40 ° C .

[0095] The type of nonwoven layer depends on the final applications of the flexible heating material . Such applications comprise construction applications such as for example underfloor heating, wall heating, carpet heating, domestic or healthcare applications like bedcover heating, automotive applications like car seat heating, car roof heating, etc . Depending on the final application, the nonwoven layer may comprise one or more sublayers , of various nature and / or thickness .

[0096] For example , for construction applications , the nonwoven layer can have acoustic and / or thermal isolation properties .

[0097] In a preferred embodiment , the nonwoven is a spunbond nonwoven . When the nonwoven is a spunbond nonwoven, it preferably comprises polypropylene fibers and / or PET fibers , but it can also comprise PLA and / or viscose fibers or any plant-based fibers .

[0098] When the nonwoven is a spunbond nonwoven, it preferably has a weight per surface unit of 30-70 g / m2and up to 150 g / m2.

[0099] The flexible heating material of the invention is preferably provided as a coil or roll , in particular for applications in the construction sector .

[0100] The invention further relates to the following listed embodiments :

[0101] 1 . Conductive coating paste comprising :

[0102] 0 . 5 to 20 weight % of particles of an allotropic form of carbon,

[0103] 0 . 5 to 20 weight % of polyurethane , and Water .

[0104] 2 . Conductive coating paste according to embodiment 1 , further comprising between 0 and 5 weight! of a dispersant . 3 . Conductive coating paste according to one of embodiment 1 or 2 , further comprising between 0 and 5 weight! of a thickener .

[0105] 4 . Conductive coating paste according to one of embodiment 1 to 3 , devoid of any organic solvent .

[0106] 5 . Method for manufacturing a flexible heating material wherein : the conductive coating paste of any of embodiments 1 to 4 is applied onto a carrier layer and dried to form a conductive film; the conductive film is trans ferred onto a nonwoven layer and; at least two substantially parallel electrodes are fixed to the conductive film .

[0107] 6 . Method for manufacturing a flexible heating material wherein : the conductive coating paste of any of embodiments 1 to 4 is applied directly onto a nonwoven layer and dried to form a conductive film; at least two substantially parallel electrodes are fixed to the conductive film .

[0108] 7 . Method according to embodiment 6 , wherein the nonwoven is a spunbond nonwoven and / or a nonwoven having a calendared surface .

[0109] 8 . Method according to one of embodiment 5 or 7 , further comprising applying a protective layer on the conductive layer . 9 . Method according to any of embodiment 5 to 8 , wherein the conductive film has a weight per surface unit comprised between 15 and 50 g / m2.

[0110] 10 . Method according to any of embodiment 5 to 9 , wherein the conductive coating paste is applied on between 50% and 95% of the surface of the carrier layer or of the nonwoven layer .

[0111] 11 . Method according to any of embodiment 5 to 10 , wherein the electrodes are embedded into the conductive coating .

[0112] 12 . Flexible heating material comprising a nonwoven layer in direct contact with a conductive film, wherein at least two substantially parallel electrodes are fixed to the conductive film, the nonwoven being devoid of conductive fibers , wherein the conductive film comprises particles of an allotropic form of carbon and polyurethane .

[0113] 13 . Flexible heating material according to embodiment 12 , wherein the electrodes are each positioned close to an opposite edge of the conductive film .

[0114] 14 . Flexible heating material according to one of embodiment 12 and 13 , wherein the first electrode is arranged to be connected to the external circuit at one side of the material and the second electrode is arranged to be connected to the external circuit at the other side of the heating material .

[0115] 15 . Flexible heating material according to one of embodiment 12 to 14 , having an electric power output comprised between 50 and 500W, when supplied with 48V .

[0116] 16 . Use of the flexible heating material according to anyone of embodiment 12 to 15 for construction applications such as for example underfloor heating, wal l heating, carpet heating, domestic or healthcare applications like bedcover heating or automotive applications like car seat heating, car roof heating .

[0117] Examples

[0118] The invention will be better understood with the following description of several examples , referring to the accompanying drawings :

[0119] Figure 1 is a scheme of a production line of a flexible heating material according to the invention, illustrating a method of manufacturing .

[0120] Figure 2 is a scheme of another production line of a flexible heating material according to the invention, illustrating another method of manufacturing .

[0121] Figure 3 is a scheme of still another production line of a flexible heating material according to the invention, illustrating a further method of manufacturing .

[0122] Example 1 - preparation of a coating paste .

[0123] ACS Material Graphiti zed Carboxylic Multi-Walled Carbon Nanotubes ( Graphiti zed MWNTs-COOH, 30-50 nm) , ACS Material Double-Walled Carbon Nanotubes ( DWCNTs ) , ACS Material Highly Puri fied Single-Walled Carbon Nanotubes ( SWCNTs , Length = 5-30 pm) and ACS Material Carbon Nanotube Sponges were purchased from ACS Material , LLC . Pasadena, CA, USA. Few layers graphene ( CNul OL ) was purchased from nanoemi .

[0124] A coating paste comprising 1 to 25 weight % of particles of an allotropic form of carbon, such as carbon nanotubes ( CNT ) and / or graphene , 0 . 1 to 15 weight % of polyurethane , and water was prepared in two steps . In a first step, the materials listed in Table 1 were combined under stirring to give a pre-dispersion of carbon particles :

[0125] Table 1 .

[0126] The obtained pre-dispersion was further combined with the materials in table 2 , under stirring to give a conductive coating paste .

[0127] Table 2.

[0128] The resulting paste has a total dry content of 12.5 weight!, including 7 weight! of polyurethan, 4.9 weight! of carbon particles and 0.6weight! additives.

[0129] It has a viscosity of 22.000 mPa.s (cPs) .

[0130] Example 2 - Use of the paste of example 1 to manufacture a nonwoven with a conductive film thereon

[0131] With reference to figure 1, a manufacturing line with a number of stations is used to prepare nonwoven having a conductive coating thereon. The line is handing rolls of materials in order to provide a continuous manufacturing.

[0132] A carrier paper 1 (transfer or release paper) having a breadth of 160 cm is first passing into a knife-over-roll coating station 2 where the paste 10 is applied on a blade 20 arranged over a roll 21 with a gap of 0.30 mm between the roll and the blade. The paste is applied over 100 cm of the breadth of the paper, leaving about 30 cm free of paste on each side of the paper .

[0133] The coated paper then passes through a oven for drying. The paste is there converted into a film having a weight per surface unit of 20 to 30 g / m2.

[0134] The paper with the conductive film passes then here through a second knife-over-roll station 4, where a hot melt adhesive is spread over the conductive film . This step is however optional as will be explained below .

[0135] The conductive film on released paper is then laminated in station 6 to a nonwoven 5 , and the laminated assembly is passing through an oven drying and curing station 7 to ensure fixation of the nonwoven to the conductive film .

[0136] Lastly, the carrier paper 1 is released ( delaminated) from the nonwoven onto which the conductive film is fixed .

[0137] The breadth of the nonwoven is typically the same as the release paper (here 160 cm) , but can be di f ferent . The important aspect is that it is a least as broad as the conductive film .

[0138] In the example above , an adhesive paste is used to fix the conductive film onto the nonwoven after curing . However, there can be several other methods to ensure adhesion of both layers . For example , the adhesive paste could be spread on the nonwoven instead of on the conductive film . The adhesive could be in a spray form instead of a paste , and the kni fe-over-roll station would then be replaced by a spraying station .

[0139] Alternatively, there could be no adhesive substance , but the nonwoven could comprise low melt fibers and / or a binder that would ensure adhesion to the conductive film by heating .

[0140] The nonwoven can be any type of nonwoven, that is suited for the final application of the product .

[0141] For example here , for a flooring application, it can be an acoustic nonwoven, made of polyester fibers and having a weight per surface unit of 150 to 200 g / m2, with a thickness of 1 . 5 to 2 mm . Such nonwoven can allow for acoustic attenuation as well as correction of floor irregularities .

[0142] Another example of suitable nonwoven is a needle punched nonwoven made of diverse fibers like polyester and / or polypropylene, excluding conductive fibers, having a width of 55 m, a thickness of 3.0 mm and a weight per surface unit of 170 g / m2.

[0143] Example 3 - Use of the paste of example 1 to manufacture another nonwoven with a conductive film thereon

[0144] With reference to figure 2, in this example, the application of the conductive coating paste was performed in the same way as for example 2. The difference is that it is not applied onto a carrier paper but directly on a spunbond nonwoven.

[0145] A spunbond nonwoven 100, for example a polyester spunbond [30 g / m2, 0.15 mm thick, with a tensile strength of 60 and 35 N / 5 cm in Machine Direction (MD) and Cross Direction (CD) respectively and an elongation to break of 17 and 24 % in MD and CD respectively, as measured according to NWSP110.4 R0 (15) , and a tear strength of 20 and 25N in MD and CD respectively as measured according to NWSP100.2 Rl (15) ] passes through a knife- over roll station 2 where the coating paste 10 is applied as in example 1. It is then dried in the oven drying station 3 to convert the paste into a conductive film in order to form the nonwoven 110 having, on at least part of its surface, a conductive film.

[0146] Example 4 - fixation of electrodes on the conductive film

[0147] The fixation method of electrodes depends on the type of electrode. For example, two parallel electrodes are fixed parallelly at a distance of 40 cm, meaning that, on a conductive film 50 cm broad, the electrodes are placed at about 5 cm from the edges of the conductive film, preferably in the machine direction of the manufacturing line. Two parallel strips of conductive tapes or strips of wires can be laminated onto the conductive film, for example using thermal calendaring or a hot plate .

[0148] Alternatively, the electrodes comprise an adhesive layer allowing them to stick to the conductive layer without thermal treatment , only application of a slight pressure .

[0149] Needled stitched electrodes were adhered to the material of example 3 . A coupon of 0 . 62 m2of conductive film disposed between the electrodes was characteri zed . A current of 1 . 33 A / m2with a voltage of 48 V were measured, which leads to an electrical power (heat output ) up to 64 W / m2to achieve radiant heat of up to 35 ° C .

[0150] Example 5 - Direct coating on a nonwoven ( through air bonded) with a relatively closed calendared surface and embedded electrodes .

[0151] With reference to figure 3 , a manufacturing line with a number of stations is used to prepare nonwoven having a conductive coating thereon . The line is handing rolls of materials in order to provide a continuous manufacturing .

[0152] A nonwoven material 30 ( a viscose or PET based nonwoven for example ) having for example a breadth of 120 cm, is first passing under a calendaring roll which smoothen the nonwoven surface and partially closes openings at the surface . The calendared nonwoven then passes into a kni fe-over-roll coating station 4 where the conductive paste as disclosed in figures 1 and 2 . The paste is for example applied over two parallel zones of 50 cm of the breadth of the paper with two lateral zones of 5 cm and one central zone of 10 cm devoid of paste .

[0153] Electrodes 35 , here four parallel electrodes , are then applied onto the paste appl ied on the nonwoven, one at each side of the two coating bands. The electrodes are laminated against the coating and pressed by rolls 36 to ensure adhesion of the electrodes to the coating paste.

[0154] The coated nonwoven with the electrodes then passes through a oven 37 for drying to give the final heating material 31.

[0155] A protective film may be further applied over the coated surface of the material, by means known to the person skilled in the art. It can for example be applied online or offline. More than one layer can be applied if needed.

Claims

Claims1. Method for manufacturing a flexible heating material wherein:- a conductive coating paste comprising: a) 0.5 to 20 weight % of particles of an allotropic form of carbon, b) 0.5 to 20 weight % of polyurethane, and c) water is applied directly onto a nonwoven layer and dried to form a conductive film; and,- at least two substantially parallel electrodes are fixed to the conductive film.

2. Method according to claim 1, wherein the nonwoven- has at least one calendared surface; and / or- is hydrophobic or has a hydrophobic surface layer.

3. Method according to claim 2, wherein the conductive coating paste is applied directly onto the calendared and / or hydrophobic surface layer.

4. Method according to any one of claims 1 to 3, wherein at least one, or all, of the electrodes are fixed to the conductive film after the drying step.

5. Method according to any one of claims 1 to 3, wherein at least one, or all, of the electrodes are embedded into the conductive coating prior to the drying step.

6. Method according to any one of claims 1 to 3, wherein at least one, or all, of the electrodes are applied to the nonwoven layer prior to application of the conductive coating paste to the nonwoven layer.

7. Method for manufacturing a flexible heating material wherein:- a conductive coating paste comprising: a) 0.5 to 20 weight % of particles of an allotropic form of carbon, b) 0.5 to 20 weight % of polyurethane, and c) water is applied onto a carrier layer and dried to form a conductive film;- the conductive film is transferred onto a nonwoven layer; and,- at least two substantially parallel electrodes are fixed to the conductive film.

8. Method according to claim 7, wherein the nonwoven- has at least one calendared surface; and / or- is hydrophobic or has a hydrophobic surface layer.

9. Method according to claim 8, wherein the conductive film is transferred onto the calendared and / or hydrophobic surface layer .

10. Method according to any one of claims 7 to 9, wherein all of the conductive coating paste is dried to form a conductive film prior to transfer onto the nonwoven layer.

11. Method according to any one of claims 7 to 9, wherein at least one, or all, of the electrodes are fixed to the conductive film after the transfer step.

12. Method according to any one of claims 7 to 9, wherein at least one, or all, of the electrodes are embedded into the conductive coating prior to the drying step or fixed to the film between the drying step and the transfer step.

13. Method according to any one of claims 7 to 9, wherein at least one, or all, of the electrodes are applied to the nonwoven layer prior to the transfer of the conductive film to the nonwoven layer.

14. Method according to any one of claims 1 to 5 or 7 to 12, wherein the method does not involve forming, does not involve applying and / or does not involve fixing an electrode on the nonwoven layer or the carrier layer prior to application of the coating.

15. Method according to any one of claims 1 to 13, wherein the conductivity coating paste is applied directly on, or transferred to, a calendared and / or hydrophobic first surface of the nonwoven and wherein the nonwoven comprises a second surface which is not calendared and not hydrophobic.

16. Method according to claim 15, comprising- applying a conductive coating paste comprising: a) 0.5 to 20 weight % of particles of an allotropic form of carbon, b) 0.5 to 20 weight % of polyurethane, and c) water onto the second surface, allowing penetration of the conductive coating paste into the second surface, drying, and fixing at least two substantially parallel electrodes to the conductive film.

17. Method according to claim 15, wherein- a conductive coating paste comprising: a) 0.5 to 20 weight % of particles of an allotropic form of carbon, b) 0.5 to 20 weight % of polyurethane, and c) water is applied onto a carrier layer to form a conductive layer;- the conductive layer is transferred onto the second surface of the nonwoven layer;- a drying step is performed; and,- at least two substantially parallel electrodes are fixed to the conductive film.

18. Method according to any one of claims 1 to 17, wherein the nonwoven is a spunbond nonwoven.

19. Method according to any one of claims 1 to 18, wherein the conductive coating paste is devoid of any organic solvent.

20. Method according to any one of claims 1 to 19, wherein the conductive coating paste is devoid of polypropylene glycol and devoid of polyethylene glycol, preferably wherein the conductive coating pasta is devoid of an anti-adsorption compound .

21. Method according to any one of claims 1 or 20, further comprising applying a protective layer on the conductive layer .

22. Method according to any of claims 1 to 21, wherein the conductive film has a weight per surface unit comprised between 15 and 50 g / m2.

23. Method according to any of claims 1 to 22, wherein the conductive coating paste is applied on between 50% and 95% of the surface of the carrier layer or of the nonwoven layer.

24. Conductive coating paste comprising:0.5 to 20 weight % of particles of an allotropic form of carbon,0.5 to 20 weight % of polyurethane, and- Water .25 . Conductive coating paste according to claim 24 , further comprising between 0 and 5 weight! of a dispersant .26 . Conductive coating paste according to any one of claims 24 or 25 , further compri sing between 0 and 5 weight! of a thickener .27 . Conductive coating paste according to any one of claims 24 to 26 , devoid of any organic solvent .28 . Flexible heating material comprising a nonwoven layer in direct contact with a conductive fi lm, wherein at least two substantially parallel electrodes are fixed to the conductive film, the nonwoven being devoid of conductive fibers , wherein the conductive film comprises particles of an allotropic form of carbon and polyurethane , such as a conductive fi lm obtained by drying a conductive coating paste according to any one of claims 25 to 27 .29 . Flexible heating material according to claim 28 , wherein the electrodes are each positioned close to an opposite edge of the conductive film .30 . Flexible heating material according to any one of claims 28 and 29 , wherein the first electrode is arranged to be connected to the external circuit at one side of the material and the second electrode is arranged to be connected to the external circuit at the other side of the heating material .31 . Flexible heating material according to any one of claims 28 to 30 , having an electric power output comprised between 50 and 500W, when supplied with 48V .32 . Flexible heating material according to any one of claims 28 to 31 , wherein the nonwoven :- has at least one calendared surface in direct contact with the conductive film; and / or- is hydrophobic or has a hydrophobic surface layer in direct contact with a conductive film .33 . Flexible heating material according claim 32 , wherein the wherein the nonwoven comprises a second surface which is not calendared and not hydrophobic, wherein said second surface pre ferably i s coated with a conductive layer which has been allowed to penetrate into the second surface .34 . Use of the flexible heating material according to any one of claims 28 to 32 for construction applications such as for example underfloor heating, wal l heating, carpet heating, domestic or healthcare applications like bedcover heating or automotive applications like car seat heating, car roo f heating .

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