Foil-based heating device

Abstract

Foil-based heating device (10), comprising: A) a base sheet (12) having an inner (12b) and an outer surface (12a), wherein the base sheet (12) comprises: a) an aromatic polyimide in an amount of 55 to 90 wt. %, based on the total weight of the base film (12), b) an electrically conductive filler (14) in an amount of 10 to 45 wt. %, based on the total weight of the base film (12), B) a first laminate comprising: a) an adhesive layer (16) comprising an inner surface (16a) bonded to the inner surface (12b) of the base film (12) and an outer surface (16b), wherein the adhesive layer (16) comprises: i. 55 to 90 wt. %, based on the total weight of the adhesive layer (16), of a thermoplastic polyimide in which 70 to 100 mol. % of the thermoplastic polyimide are derived from at least one aromatic diamine and at least one aromatic dianhydride, ii. 10 to 45 wt. %, based on the total weight of the adhesive layer (16), of an electrically conductive filler (18), b) a metal foil (20) which has: i. an inner surface (20a) bonded to the outer surface (16b) of the adhesive layer (16) as well as ii. an exterior surface, wherein the metal foil (20) of the first laminate is 5 to 200 µm thick, C) a second laminate comprising: a) an adhesive layer (22) having an inner surface (22a) bonded to the inner surface (12b) of the base film (12) and an outer surface (22b), wherein the adhesive layer (22) contains: i. 55 to 90 wt. %, based on the total weight of the adhesive layer (22), of a thermoplastic polyimide in which 70 to 100 mol. % of the thermoplastic polyimide are derived from at least one aromatic diamine and at least one aromatic dianhydride, ii. 10 to 45 wt. %, based on the total weight of the adhesive layer (22), of an electrically conductive filler (24), b) a metal foil (26) which has: i. an inner surface (26a) bonded to the outer surface (22b) of the adhesive layer (22) as well as ii. an exterior surface, wherein the metal foil (26) of the second laminate is 5 to 200 µm thick, wherein at least a part of the first laminate and a part of the second laminate are arranged at a certain distance from each other and are connected to each other over at least a part of the base film (12).

Description

FIELD OF INVENTION

[0001] The field of the present invention is that of foil-based heating devices in which heat is generated along the surface of a foil. BACKGROUND OF THE INVENTION

[0002] Metal pastes are used to manufacture durable heating elements supported by temperature-resistant films. However, such compositions can be problematic because metal paste-based heating elements can suffer from kinking fractures, flaking, and other age-related deterioration. Furthermore, such heating elements can exhibit undesirable stress drift (sagging) along their length. There is a need for a film-based heating technology that offers advantages compared to such metal paste-based film heating systems. US 2008 / 0213605 A1 discloses polyimide metal laminates that can be used in flexible heating elements. Heating elements are also described in US 3,359,525 and JP 2007109640A. US 5,298,331 discloses flexible polyimide multilayer laminates. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] The invention is illustrated by way of example with reference to the accompanying drawings. Fig. Figure 1 is a cross-sectional view of part of a foil-based heating device comprising a base foil, a first laminate and a second laminate. Fig. Figure 2 is a cross-sectional view of another embodiment of a foil-based heating device comprising a base foil, a first laminate, a second laminate and a second base foil. Fig. Figures 3 to 5 are cross-sectional views of various embodiments of a foil-based heating device comprising a base foil, a first laminate, a second laminate, a second base foil and a top layer. Fig. Figure 6 is a drawing that indicates the position of the thermal coupling in the first example. SUMMARY

[0004] The present invention relates to a foil-based heating device. The heating device according to the invention comprises a base film having an inner and outer surface. The base film comprises a base film consisting of aromatic polyimide for 55 to 90 wt. % of its total weight, and an electrically conductive filler comprising 10 to 45 wt. % of its total weight.

[0005] The foil-based heating device according to the invention comprises a first laminate, which includes an adhesive layer bonded to the inner surface of the base film and an outer surface. The adhesive layer of the first laminate contains, based on the total weight of the adhesive layer, 55 to 90 wt.% of a thermoplastic polyimide, in which 70 to 100 mol.% of the thermoplastic polyimide is derived from at least one aromatic diamine and at least one aromatic dianhydride. The adhesive layer contains an electrically conductive filler comprising 10 to 45 wt.% of the total weight of the adhesive layer. The first laminate comprises a metal foil having an inner surface bonded to the outer surface of the adhesive layer of the first laminate and an outer surface. The metal foil of the first laminate is 5 to 200 µm thick.

[0006] The foil-based heating device according to the invention comprises a second laminate, which includes an adhesive layer bonded to the inner surface of the base film and an outer surface. The adhesive layer of the second laminate contains, based on the total weight of the adhesive layer, 55 to 90 wt.% of a thermoplastic polyimide, in which 70 to 100 mol.% of the thermoplastic polyimide is derived from at least one aromatic diamine and at least one aromatic dianhydride. The adhesive layer contains an electrically conductive filler comprising 10 to 45 wt.% of the total weight of the adhesive layer. The second laminate comprises a metal foil having an inner surface bonded to the outer surface of the adhesive layer of the second laminate and an outer surface. The metal foil of the second laminate is 5 to 200 µm thick.At least a part of the first laminate and a part of the second laminate are arranged at a certain distance from each other and connected to each other via at least a part of the base film. DETAILED DESCRIPTION Definitions

[0007] In this context, the terms "comprise," "include," "exhibit," and their variants are to be understood as non-exclusive inclusion. A procedure, object, or apparatus that, for example, comprises a series of elements is not necessarily limited to these elements but may exhibit other elements that are not explicitly listed or that, by definition, belong to the procedure, object, or apparatus in question. Furthermore, unless explicitly stated otherwise, "or" is to be interpreted in an inclusive, not an exclusive, sense. A condition A or B is satisfied, for example, by any of the following variants: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

[0008] The indefinite article is also used to describe elements and components of the invention. This is purely for convenience and is intended only to provide a general outline of the invention. This description is to be interpreted as encompassing 1 or at least 1; furthermore, the singular also includes the plural, unless otherwise obviously intended.

[0009] In this context, the term "dianhydride" also includes precursors, derivatives and analogues thereof which are not technically dianhydrides, but would nevertheless react with a diamine to produce a polyamic acid which could in turn be converted into a polyimide.

[0010] In this context, the term "diamine" also includes precursors, derivatives and analogs thereof which are not technically diamines, but would nevertheless react with a dianhydride to produce a polyamic acid which could in turn be converted into a polyimide.

[0011] In this context, "polyamic acid" refers to any polyimide precursor (prepolymer) derived from a combination of dianhydride and diamine that can be converted into a polyimide via a chemical or thermal conversion process.

[0012] In this context, "high temperature" means temperatures of at least 200 °C.

[0013] In this context, "long-term" means a total duration of at least 50 hours. This minimum of 50 hours can be cumulative (e.g., a few hours at once, which, after repeated use, result in a total of at least 50 hours) or continuous. "Adhesion," "adherence," or any variant thereof are synonymous with "bonding" and can be used interchangeably. "Direct adhesion" refers to two layers (films) that are bonded directly to each other without any intervening layers, unless otherwise specified.

[0014] Where a quantity, concentration, or other value or parameter is specified as a range, preferred range, or list of preferred maximum or minimum values, this shall be construed as expressly disclosing all of any pair of maximum or preferred values, irrespective of whether ranges are disclosed separately. Where a numerical range is specified herein, that range shall also include the endpoints and all integers and fractions within the range, unless otherwise specified.

[0015] The materials, methods, and examples presented here serve only for illustration and are not to be construed as limiting unless expressly stated otherwise. Although methods and materials similar to or corresponding to those described herein may be used in the implementation or investigation of the present invention, suitable methods and materials are described herein.

[0016] The present invention relates to a foil-based heating device. The heating device is a high-temperature foil-based heating device that heats uniformly during long-term or repeated use.

[0017] Regarding the characters: Fig.Figure 1 shows the foil-based heating device 10 according to the invention. The foil-based heating device 10 comprises a base film 12 having an inner surface 12b and an outer surface 12a. The base film 12 comprises an electrically conductive filler 14. The foil-based heating device 10 also comprises at least one first laminate and a second laminate. The first laminate comprises an adhesive layer 16 having an inner surface 16a and an outer surface 16b. The adhesive layer 16 comprises an electrically conductive filler 18. The first laminate also comprises a metal foil 20 having an inner surface 20a and an outer surface. The inner surface of the metal foil 20a adheres directly to the outer surface of the adhesive layer of the first laminate 16b. The second laminate comprises an adhesive layer 22 having an inner surface 22a and an outer surface 22b. The adhesive layer 22 comprises an electrically conductive filler 24.The second laminate also comprises a metal foil 26, which has an inner surface 26a and an outer surface. The inner surface of the metal foil 26a adheres directly to the outer surface of the adhesive layer of the second laminate 22b. The inner surface of the adhesive layer of the first laminate 16a adheres directly to a portion of the inner surface of the base foil 12b. The inner surface of the adhesive layer of the second laminate 22a adheres directly to a different portion of the inner surface of the base foil 12b than the inner surface of the adhesive layer of the first laminate 16a.

[0018] Fig. Figure 2 shows an embodiment of the present invention. The foil-based heating device 10 optionally comprises a secondary base foil 28. The secondary base foil 28 has an inner surface 28a and an outer surface 28b. The inner surface of the secondary base foil 28a adheres directly to the outer surface of the base foil 12a.

[0019] Fig.Figure 3 shows an embodiment of the present invention. The foil-based heating device can optionally have a cover layer 30. The cover layer 30 is bonded to the outer surface of the base foil 12a.

[0020] Fig. Figure 4 shows a further embodiment of the present invention. The foil-based heating device can optionally have a cover layer 30. The cover layer 30 is bonded to the exposed areas of the inner surface of the base foil 12b and the exposed areas of the adhesive layer of the first laminate 16, the metal foil of the first laminate 20, the adhesive layer of the second laminate 22, and the metal foil of the second laminate 26.

[0021] Fig.Figure 5 shows a further embodiment of the present invention. The foil-based heating device optionally comprises a cover layer 30 that encapsulates the base film 12, the adhesive layer of the first laminate 16, the metal foil of the first laminate 20, the adhesive layer of the second laminate 22, and the metal foil of the second laminate 26. BASE SLIDE

[0022] The base film comprises an aromatic polyimide in an amount between two of the following values, selectively comprising: 55, 60, 65, 70, 75, 80, 85, and 90 wt.% based on the total weight of the base film. In some embodiments, the aromatic polyimide is present at 55 to 90 wt.% based on the total weight of the base film. In some embodiments, the aromatic polyimide is present at 60 to 85 wt.% based on the total weight of the base film. In some embodiments, the aromatic polyimide is present at 65 to 80 wt.% based on the total weight of the base film. In one embodiment, the aromatic polyimide according to the invention is derived from at least one aromatic dianhydride and at least one aromatic diamine.

[0023] In some embodiments, the aromatic diamine is selected from the group comprising 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenylmethane, benzidine, 2,2'-bis(trifluoromethyl)benzidine, 2,2'-bis(4-aminophenyl)hexafluoropropane, 3,5-diaminobenzotrifluoride; diaminodures, 3,3',5,5'-tetramethylbenzidine, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 1,5-diaminonaphthalene; 1,4-diaminonaphthalene, 4,4'-diaminodiphenylsilane, 4,4'-diaminodiphenyl(phenylphosphine oxide), 4,4'-diaminodiphenyl-N-phenylamine, 3,4'-diaminophenyl ether; 1,4-Bis(4-aminophenoxy)benzene, 1,3-Bis(4-aminophenoxy)benzene; 4,4'-Diaminobenzanilide, 4,4'-Bis(4-aminophenoxy)biphenyl, 9,9'-Bis(4-aminophenyl)fluorine, m-Tolidine, o-Tolidine, 3,3'Dihydroxy-4,4'-diaminobiphenyl, 1,4-diaminobenzene (p-phenylenediamine), 1,3-Diaminobenzene (p-phenylenediamine), 1,2-Diaminobenzene and mixtures thereof.

[0024] In some embodiments, the aromatic dianhydride is selected from the group comprising 2,3,6,7-naphthalene tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride, 2,2',3,3'-biphenyl tetracarboxylic dianhydride, 2,3',3,4'-biphenyl tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, bis(3,4-dicarboxyphenyl)sulfonic dianhydride, 3,4,9,10-perylene tetracarboxylic dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 4,4'-oxydiphthalic dianhydride, bis(3,4-dicarboxyphenyl) Sulfonedianhydride, 2,2-bis(3,4-dicarboxyphenyl), hexafluoropropanedianhydride; bis(3,4-dicarboxyphenyl)sulfide; hydroquinone, diphthalene anhydride and mixtures thereof. In some embodiments, at least 70 mol.% of the aromatic polyimide is derived from pyromellite dianhydride and 4,4'-diaminodiphenyl ether.In some embodiments, the aromatic polyimide is derived from pyromellite dianhydride and 4,4'-diaminodiphenyl ether.

[0025] The base film comprises an electrically conductive filler in an amount between two of the following values, optionally comprising: 10, 15, 20, 25, 30, 35, 40, and 45 wt.% based on the total weight of the base film. In some embodiments, the electrically conductive filler is present at 10 to 45 wt.% based on the total weight of the base film. In some embodiments, the electrically conductive filler is present at 15 to 40 wt.% based on the total weight of the base film. In some embodiments, the electrically conductive filler is present at 20 to 35 wt.% based on the total weight of the base film. In some embodiments, the electrically conductive filler is carbon black.In some embodiments, the electrically conductive filler is selected from the group comprising: acetylene carbon blacks, highly abrasion-resistant furnace carbon blacks, conductive furnace carbon blacks, conductive trough furnace carbon blacks, and fine thermal carbon blacks and their mixtures. The surface oxidation of the carbon black, usually measured by the proportion of volatile components, refers to various oxygenated species (such as carboxyl, hydroxyl, and quinone) located on the surface of the aggregates. Although these species are present to some extent in all carbon blacks, some carbon blacks are post-treated to intentionally increase the surface oxidation level. The oxygen complexes on the surface act as an electrical insulating layer. Thus, a low proportion of volatile components is desirable to ensure high conductivity. However, it is also necessary to take into account the dispersion difficulties associated with the carbon black.Uniform dispersion of the electrically conductive filler enables the foil-based heater to heat uniformly. Surface oxidation enhances the deglomeration and dispersion of the carbon black. In some embodiments, the carbon black has a volatile content of less than or equal to 1% when the electrically conductive filler is carbon black. In one embodiment, the carbon black is RAVEN® 16 (available from Columbian Chemicals Company); in another, it is CDX 7055U (available from Columbian Chemicals Company). In some embodiments, the electrically conductive filler of the base foil has an electrical resistance of at least 100 ohms per square millimeter. In some embodiments, the electrically conductive filler of the base foil has an electrical resistance of at least 1000 ohms per square millimeter.In another embodiment, the electrically conductive filler of the base film has an electrical resistance of at least 10,000 ohms per square meter. In some embodiments, the electrically conductive filler is a metal or metal alloy. In some embodiments, the electrically conductive filler is a mixture of electrically conductive fillers. In some embodiments, the electrically conductive filler is milled to achieve the desired agglomerate size (particle size). In some embodiments, the average particle size of the electrically conductive filler lies between two of the following values, and optionally includes: 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1 µm. The average particle size can be determined using a Horiba Scattering Light Particle Analyzer.In some embodiments, the average particle size of the electrically conductive filler is between 0.05 and 1 µm. In other embodiments, the average particle size of the electrically conductive filler is between 0.1 and 0.5 µm. Generally, the occurrence of electrical short circuits and / or hot spots is more likely with an average particle size greater than 1 µm. In another embodiment, the particle size of the electrically conductive filler is less than or equal to 1 µm. Common sense and experimentation may be required to adjust the type and amount of electrically conductive filler to achieve the desired resistance for the specific application. In some embodiments, the desired resistance of the base film is between 10 ohms / square and 1,000,000 ohms / square; this is measured using a four-point probe from Veeco Instruments Inc., model FPP5000.

[0026] In some embodiments, the thickness of the base film is between two of the following values, and optionally includes: 8, 10, 20, 40, 60, 80, 100, 120, 140, 160, 180, and 200 µm. In some embodiments, the thickness of the base film is between 8 and 200 µm. In some embodiments, the thickness of the base film is between 8 and 100 µm. In some embodiments, the thickness of the base film is between 8 and 50 µm. In some embodiments, the thickness of the base film is between 8 and 25 µm.

[0027] In some embodiments, the base film optionally comprises a non-electrically conductive filler. In some embodiments, the non-electrically conductive filler is present in an amount between two of the following numbers and optionally includes: 1, 2, 4, 6, 8, 10, 12, 14, and 15 wt.% based on the total weight of the base film. In some embodiments, the base film comprises 1 to 15 wt.% of a non-electrically conductive filler. In some embodiments, the non-electrically conductive filler is selected from the group comprising metal oxides, carbides, borides, and nitrides. In some embodiments, the non-electrically conductive filler is selected from the group comprising, but not limited to, aluminum oxide, titanium dioxide, silicon dioxide, mica, talc, barium titanate, barium sulfate, dicalcium phosphate, and mixtures thereof. PRODUCTION OF THE BASE FILM

[0028] The base film can be produced using any method known from the prior art. In some embodiments, a slurry is generated to produce the electrically conductive filler. In one embodiment, the electrically conductive filler can be added to a solution of polyamic acid in a solvent (e.g., DMAC), or a solution of the electrically conductive filler in a solvent can be mixed with a solution of polyamic acid in a solvent. The slurry is then mixed. In some embodiments, the slurry is mixed in a rotor-stator high-speed dispersion mill. In some embodiments, the slurry is milled until the desired particle size of the electrically conductive filler is achieved. In some embodiments, a ball mill is used.In some embodiments, the ground slurry is filtered to remove any remaining large particles. The slurry can be stored in a tank equipped with a stirrer to maintain its dispersion until it is ready for use, or it can be used immediately after grinding.

[0029] A polyamic acid solution is prepared. The polyamic acid solution can be prepared using methods known from the prior art. Generally, the polyamic acid solutions can be prepared by dissolving the aromatic diamine in a dry (anhydrous) solvent and slowly adding the dianhydride under stirring conditions and controlled temperature in an inert atmosphere. The organic solvent should dissolve one or both of the polymerizing reactants. The organic solvent will dissolve the polyamic acid formed. The solvent should exhibit essentially no reaction with any of the polymerizing reactants or with the polyamic acid polymerization product. Suitable solvents for the purposes of the present invention include, in particular, low molecular weight carboxylamides, especially N,N-dimethylformamide and N,N-dimethylacetamide.Other suitable solvents include N,N-dimethylformamide, N,N-diethylacetamide, N-methyl-2-pyrrolidone, tetramethylurea, dimethyl sulfone, and the like. These solvents can be used alone or in combination. The polyamic acid solution can be filtered or left unfiltered.

[0030] In some embodiments, the polyamic acid solution is mixed in a high-shear-energy stirrer with the slurry of the electrically conductive filler and optionally a slurry of a non-electrically conductive filler. In some embodiments, the dispersions may include one or more suitable dispersing agents known to those skilled in the art to promote the formation of a stable dispersion.

[0031] Regardless of how the dispersions are prepared, the dispersion of the electrically conductive filler in the base film is carried out in such a way as to avoid undesired agglomeration. In some embodiments, the solution can be poured or applied onto a support such as an endless metal surface (belt) or a rotating drum. In some embodiments, a small amount of a release agent can be added to facilitate easy separation of the cast film from the mold surface. In some embodiments, the aromatic polyimide in the base film is chemically converted. In some embodiments, the aromatic polyimide in the base film is thermally converted. In some embodiments, the amounts of polyamic acid and the slurry of electrically conductive filler are adjusted to achieve the desired dosage level of the electrically conductive filler and the desired viscosity of the casting solution. FIRST LAMINATE

[0032] The first laminate comprises an adhesive layer and a metal foil. The adhesive layer of the first laminate contains a thermoplastic polyimide and an electrically conductive filler. The thermoplastic polyimide of the adhesive layer of the first laminate is derived from at least one aromatic diamine and at least one aromatic dianhydride. Thermoplastic polyimides are generally polyimides with glass transition temperatures below 280 °C or preferably 250 °C. Under suitable heat and pressure, they exhibit sufficient flux to form a reliable bond (greater than or equal to 2 pli) between the metal foil and the base foil. The use of aromatic diamines and aromatic dianhydride groups enables high temperature resistance.In some embodiments, small amounts of aliphatic diamines or cycloaliphatic diamines may be used, provided that the amount does not adversely affect the high temperature resistance of the adhesive layers. Typically, thermoplastic polyimides according to the invention are produced using at least some flexible aromatic diamines and / or dianhydrides. In some embodiments, the aromatic dianhydride of the thermoplastic polyimide is selected in particular from the group comprising: 4,4-oxydiphthalanhydride, 2,3',3,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, hydroquinone diphthalanhydride, bis-(3,4-dicarboxyphenyl)bisphenyl A dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, and mixtures thereof.In some embodiments, the aromatic diamine of the thermoplastic polyimide is selected in particular from the group comprising: 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 2,2-bis(4-[4-aminophenoxy]phenyl)propane, 2,2-bis(4-[4-aminophenoxy]phenyl)hexafluoropropane, bis-4-[3-aminophenoxy]phenylsulphone, bis-4-[4-aminophenoxy]phenylsulphone, 4,4'-bis(4-aminophenoxy)biphenyl, 3,4'-diaminophenyl ethers and mixtures thereof. In some embodiments, the thermoplastic polyimide is derived at least partially from 4,4'-oxydiphthalenhydride (ODPA), pyromellite dianhydride (PMDA), and 1,3-bis(4-aminophenoxy)benzene (RODA). The thermoplastic polyimide is present in an amount between two of the following values, optionally including either of them: 55, 65, 70, 75, 80, 85, and 90 wt.% based on the total weight of the adhesive layer of the first laminate.In some embodiments, the aromatic polyimide is present at 55 to 90 wt.% based on the total weight of the base film. In some embodiments, the thermoplastic polyimide of the adhesive layer of the first laminate is derived from 70 to 95 mol.% oxydiphthalic dianhydride, 5 to 30 mol.% pyromellite dianhydride, and at least 70 mol.% 1,3-bis(4-aminophenoxy)benzene. In some embodiments, at least 80 mol.% 1,3-bis(4-aminophenoxy)benzene is present.

[0033] In some embodiments, the thermoplastic polyimide of the adhesive layer of the first laminate is derived from at least one aromatic diamine and at least one aromatic dianhydride to a concentration of 70 to 100 mol.%. In some embodiments, the amount lies between two of the following numbers and may optionally include: 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 99, and 100 mol.% of the thermoplastic polyimide is derived from at least one aromatic diamine and at least one aromatic dianhydride. In some embodiments, the thermoplastic polyimide of the adhesive layer of the first laminate is derived from at least one aromatic diamine and at least one aromatic dianhydride to a concentration of 80 to 100 mol.%. In another embodiment, the thermoplastic polyimide of the adhesive layer of the first laminate is derived from at least one aromatic diamine and at least one aromatic dianhydride to a concentration of 90 to 100 mol. %.In yet another embodiment, the thermoplastic polyimide of the adhesive layer of the first laminate is derived from at least one aromatic diamine and at least one aromatic dianhydride to a concentration of 70 to 99 mol.%. In yet another embodiment, the thermoplastic polyimide of the adhesive layer of the first laminate is derived from at least one aromatic diamine and at least one aromatic dianhydride to a concentration of 80 to 99 mol.%. In yet another embodiment, the thermoplastic polyimide of the adhesive layer of the first laminate is derived from at least one aromatic diamine and at least one aromatic dianhydride to a concentration of 80 to 99 mol.%.

[0034] The electrically conductive filler in the adhesive layer of the first laminate is present in an amount between two of the following values, optionally including either of them: 10, 15, 20, 25, 30, 35, 40, and 45 wt.% based on the total weight of the adhesive layer. In some embodiments, the electrically conductive filler is present at 10 to 45 wt.% based on the total weight of the base film. In some embodiments, the electrically conductive filler is present at 15 to 40 wt.% based on the total weight of the base film. In some embodiments, the electrically conductive filler is present at 20 to 35 wt.% based on the total weight of the base film.

[0035] In some embodiments, the thickness of the adhesive layer of the first laminate is between two of the following values, and optionally includes: 5, 12, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, and 80 µm. In some embodiments, the thickness of the adhesive layer is between 5 and 80 µm. The adhesive layer of the first laminate should be thick enough to allow the metal foil of the first laminate to adhere to the base film, but not so thick as to cause a voltage drop or undesirable resistance of the metal foil against the base film.

[0036] The thickness of the metal foil lies between two of the following values ​​and optionally includes: 5, 10, 20, 40, 60, 80, 100, 120, 140, 160, 180, and 200 µm. In some embodiments, the thickness of the metal foil is between 5 and 200 µm. The metal foil of the first laminate can consist of any suitable conductive material. In some embodiments, the metal foil of the first laminate is selected, in particular, from the group comprising gold, silver, platinum, nickel, palladium, stainless steel, titanium, Inconel®, Invar, and aluminum. In some embodiments, the metal foil of the first laminate is copper. SECOND LAMINATE

[0037] The second laminate comprises an adhesive layer and a metal foil. The adhesive layer of the second laminate contains a thermoplastic polyimide and an electrically conductive filler. The thermoplastic polyimide of the adhesive layer of the second laminate is derived from at least one aromatic diamine and one aromatic dianhydride. In some embodiments, aliphatic diamine or cycloaliphatic diamine may be used in small amounts, provided that the amount does not adversely affect the high temperature resistance of the adhesive layers. Typically, thermoplastic polyimides according to the invention are produced using at least some flexible aromatic diamines and / or dianhydrides.In some embodiments, the aromatic dianhydride of the thermoplastic polyimide is selected in particular from the group comprising: 4,4-oxydiphthalanhydride, 2,3',3,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, hydroquinone diphthalanhydride, bis-(3,4-dicarboxyphenyl)bisphenyl A dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride and mixtures thereof. In some embodiments, the aromatic diamine of the thermoplastic polyimide is selected in particular from the group comprising: 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, bis-4-[3-aminophenoxy]phenylsulfone, bis-4-[4-aminophenoxy]phenylsulfone, 3,4'-diaminophenyl ethers, and mixtures thereof. In some embodiments, the thermoplastic polyimide is derived at least partially from 4,4'-oxydiphthalenhydride (ODPA), pyromellite dianhydride (PMDA), and 1,3-bis(4-aminophenoxy)benzene (RODA).In another embodiment, the thermoplastic polyimides of the adhesive layers of the first and second laminates are partially derived from 4,4'-oxyphthalenhydride, pyromellite dianhydride, and 1,3-bis(4-aminophenoxy)benzene. The thermoplastic polyimide is present in an amount between two of the following values, optionally including either: 55, 65, 70, 75, 80, 85, and 90 wt.% based on the total weight of the adhesive layer of the second laminate. In some embodiments, the aromatic polyimide is present in amounts ranging from 55 to 90 wt.% based on the total weight of the base film. In some embodiments, the thermoplastic polyimide of the adhesive layer of the second laminate is derived from 70 to 95 mol.% oxydiphthalic dianhydride, 5 to 30 mol.% pyromellite dianhydride, and at least 70 mol.% 1,3-bis(4-aminophenoxy)benzene. In some embodiments, at least 80 mol.% 1,3-bis(4-aminophenoxy)benzene is present.

[0038] In some embodiments, the thermoplastic polyimide of the adhesive layer of the second laminate is derived from at least one aromatic diamine and at least one aromatic dianhydride to a concentration of 70 to 100 mol.%. In some embodiments, the amount lies between two of the following numbers and may optionally include: 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 99, and 100 mol.% of the thermoplastic polyimide is derived from at least one aromatic diamine and at least one aromatic dianhydride. In some embodiments, the thermoplastic polyimide of the adhesive layer of the second laminate is derived from at least one aromatic diamine and at least one aromatic dianhydride to a concentration of 80 to 100 mol.%. In another embodiment, the thermoplastic polyimide of the adhesive layer of the 2nd laminate is derived from at least one aromatic diamine and at least one aromatic dianhydride to a concentration of 90 to 100 mol. %.In yet another embodiment, the thermoplastic polyimide of the adhesive layer of the second laminate is derived from at least one aromatic diamine and at least one aromatic dianhydride to a composition of 70 to 99 mol.%. In yet another embodiment, the thermoplastic polyimide of the adhesive layer of the second laminate is derived from at least one aromatic diamine and at least one aromatic dianhydride to a composition of 80 to 99 mol.%. In yet another embodiment, the thermoplastic polyimide of the adhesive layer of the second laminate is derived from at least one aromatic diamine and at least one aromatic dianhydride to a composition of 90 to 99 mol.%.

[0039] The electrically conductive filler of the adhesive layer of the second laminate is present in an amount between two of the following values, optionally including: 10, 15, 20, 25, 30, 35, 40, and 45 wt.% based on the total weight of the adhesive layer. In some embodiments, the electrically conductive filler is present at 10 to 45 wt.% based on the total weight of the base film. In some embodiments, the electrically conductive filler is present at 15 to 40 wt.% based on the total weight of the base film. In some embodiments, the electrically conductive filler is present at 20 to 35 wt.% based on the total weight of the base film. In some embodiments, the electrically conductive filler of the adhesive layer of the first laminate and the electrically conductive filler of the adhesive layer of the second laminate are different. In some embodiments, the electrically conductive filler of the adhesive layer of the first laminate is different.In a further embodiment, the electrically conductive filler of the base film, the electrically conductive filler of the adhesive layer of the first laminate, and the electrically conductive filler of the second laminate are identical. In yet another embodiment, the electrically conductive filler of the base film, the electrically conductive filler of the adhesive layer of the first laminate, and the electrically conductive filler of the second laminate are identical.

[0040] In some embodiments, the electrically conductive filler of the base film, the electrically conductive filler of the adhesive layer of the first laminate, and the electrically conductive filler of the second laminate each comprise carbon black. In some embodiments, the electrically conductive filler of the adhesive layer of the first laminate and the electrically conductive filler of the adhesive layer of the second laminate are selected from the group comprising: acetylene carbon blacks, highly abrasion-resistant furnace carbon blacks, conductive furnace carbon blacks, conductive flue furnace carbon blacks, and fine thermal carbon blacks and mixtures thereof. In some embodiments, the carbon black has a volatile content of less than or equal to 2% when the electrically conductive filler of the first or second or both laminates is carbon black. In another embodiment, the carbon black has a volatile content of less than or equal to 1%.In one embodiment, the carbon black is RAVEN® 16 (available from Columbian Chemicals Company); in another, it is CDX 7055U (available from Columbian Chemicals Company). In some embodiments, the electrically conductive filler of the base film, the electrically conductive filler of the adhesive layer of the first laminate, and the electrically conductive filler of the second laminate are all carbon black. In some embodiments, the electrically conductive filler of the adhesive layer of the first laminate and the electrically conductive filler of the adhesive layer of the second laminate have an electrical resistance of at least 100 ohms squared. In some embodiments, the electrically conductive filler of the adhesive layer of the first laminate, the electrically conductive filler of the adhesive layer of the second laminate, or both, have an electrical resistance of at least 1000 ohms squared.In a further embodiment, the electrically conductive filler of the adhesive layer of the first laminate, the electrically conductive filler of the adhesive layer of the second laminate, or both, have an electrical resistance of at least 10,000 ohms per square meter. The electrically conductive filler of the adhesive layer of the first laminate can be an electrically conductive filler mixture. The electrically conductive filler of the adhesive layer of the second laminate can also be an electrically conductive filler mixture.

[0041] The electrically conductive filler in the adhesive layers of the first and second laminates facilitates the transfer of current to the base film. If no electrically conductive filler is used in the adhesive layer of the first or second laminate, the adhesive layers are non-conductive and act as a dielectric barrier. If the electrically conductive fillers in the adhesive layers of the first and second laminates have low electrical conductivity, more current is required to overcome the desired resistance of the base film. The adhesive layers of the first and second laminates should have the same or higher conductivity than the base film. If the conductivity of the adhesive layers of the first and second laminates is lower than that of the base film, unwanted heating of the metal foil of the first or second laminate, or of both metal foils, may occur.Common sense and experimentation may be required to adjust the type and quantity of electrically conductive filler to achieve a balanced relationship between adhesion strength and physical properties.

[0042] In some embodiments, the electrically conductive filler of the adhesive layer of the first laminate and the electrically conductive filler of the adhesive layer of the second laminate, or both, are milled to achieve the desired particle size. In some embodiments, the average particle size of the electrically conductive filler of the adhesive layer of the first or second laminate lies between two of the following values, optionally including: 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1 µm. The average particle size can be determined using a Horiba Scattering Light Particle Analyzer. In some embodiments, the average particle size of the electrically conductive filler in the adhesive layer of the 1st or 2nd laminate is between 0.05 and 1 µm: In some embodiments, the average particle size of the electrically conductive filler in the adhesive layer of the 0.5th or 2nd laminate is between 0.05 and 1 µm.Laminates between 0.1 and 0.5 µm: In a further embodiment, the electrically conductive filler of the adhesive layer of the 1st or 2nd laminate is less than or equal to 1 µm.

[0043] In some embodiments, the thickness of the adhesive layer of the second laminate is between two of the following values, and optionally includes: 5, 12, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, and 80 µm. In some embodiments, the thickness of the adhesive layer is between 5 and 80 µm. The adhesive layer of the second laminate should be thick enough to allow the metal foil of the second laminate to adhere to the base film, but not so thick as to cause a voltage drop or undesirable resistance of the metal foil against the base film.

[0044] Acrylic and epoxy adhesives cannot withstand the high lamination temperatures (290 °C or higher to bond the metal foil to the base film). Acrylic and epoxy adhesives cannot withstand high temperatures (200 °C or higher) during long-term use. The thermoplastic polyimide adhesive layer of the first and second laminations can withstand the high lamination temperatures exceeding 290 °C and can be used at high temperatures long-term.

[0045] The thickness of the metal foil of the second laminate lies between two of the following values ​​and optionally includes: 5, 10, 20, 40, 60, 80, 100, 120, 140, 160, 180, and 200 µm. In some embodiments, the thickness of the metal foil lies between 5 and 200 µm. Typically, for applications in the lower voltage range (less than 48 volts), a thinner metal foil can be used for the first and second laminates without risk of failure. For applications in the upper voltage range, thicker metal foils are typically required. The thickness of the metal foil can be tailored to the application or the voltage range. The adhesive layers of the first and second laminates according to the invention provide good adhesion of the metal foils of the first and second laminates to the base film. The adhesive strength must be sufficient to prevent air holes or cavities from forming, which could lead to arcing and possibly also to the failure of the device (the heating unit).Furthermore, the good adhesive strength must be maintained during long-term use. The metal foil of the second laminate can consist of any suitable conductive material. In some embodiments, the metal foil of the second laminate is specifically selected from the group comprising gold, silver, platinum, nickel, palladium, stainless steel, titanium, Inconel®, Invar, and aluminum. In some embodiments, the metal foil of the second laminate is copper.

[0046] In some embodiments, the metal foil of the first laminate and that of the second laminate are different. In some embodiments, the metal foil of the first laminate and that of the second laminate are the same. In one embodiment, the metal foil of the first laminate and that of the second laminate comprise copper. In one embodiment, the metal foil of the first laminate and that of the second laminate are copper. Copper exhibits little to no stress drop over long lengths. This is particularly advantageous because uniform heating over long lengths is desired.

[0047] In some embodiments, the adhesive layers of the first laminate, the second laminate, or both the first and second laminates optionally comprise 1 to 15 wt.% of a non-electrically conductive filler. In some embodiments, the non-electrically conductive filler is selected from the group comprising metal oxides, carbides, borides, and nitrides. In some embodiments, the non-electrically conductive filler is selected from the group comprising, but not limited to, aluminum oxide, titanium dioxide, silicon dioxide, mica, talc, barium titanate, barium sulfate, dicalcium phosphate, and mixtures thereof.

[0048] In one embodiment, the adhesive layer of the first or second laminate can optionally comprise an aliphatic diamine, a cycloaliphatic diamine, or any combination thereof. With increasing molar percentage of the aliphatic diamine (or cycloaliphatic diamine) in the aromatic diamine, the glass transition temperature (Tg) of the polyimide and the lamination temperature generally decrease. In some embodiments, the thermoplastic polyimide of the adhesive layer of the first laminate comprises 1 to 30 mol% of a non-aromatic diamine selected from the group consisting of aliphatic diamine, cycloaliphatic diamine, and a combination thereof. In some embodiments, the thermoplastic polyimide of the adhesive layer of the second laminate comprises 1 to 30 mol% of a non-aromatic diamine selected from the group consisting of aliphatic diamine, cycloaliphatic diamine, and a combination thereof.In some embodiments, the thermoplastic polyimide of the adhesive layer of the first laminate and that of the adhesive layer of the second laminate comprises 1 to 30 mol% of a non-aromatic diamine selected from the group consisting of aliphatic diamine, cycloaliphatic diamine, and a combination thereof. In some embodiments, the thermoplastic polyimides of the adhesive layers of the first and second laminates, or of both, comprise a mol% between any two of the following numbers, optionally including: 1, 2, 4, 6, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, and 30 mol% of a non-aromatic diamine selected from the group consisting of aliphatic diamine, cycloaliphatic diamine, or a combination thereof. If the proportion of aliphatic diamine, cycloaliphatic diamine or a combination thereof exceeds 30 mol. %, the high temperature resistance of the adhesive layers decreases.In some embodiments, the thermoplastic polyimide of the adhesive layer of the first laminate and that of the adhesive layer of the second laminate, or both, comprises 1 to 20 mol% of a non-aromatic diamine selected from the group consisting of aliphatic diamine, cycloaliphatic diamine, and combinations thereof. In another embodiment, the thermoplastic polyimide of the adhesive layer of the first laminate and that of the adhesive layer of the second laminate, or both, comprises 1 to 10 mol% of a non-aromatic diamine selected from the group consisting of aliphatic diamine, cycloaliphatic diamine, and combinations thereof. In one embodiment, the lamination temperature is typically about 25°C higher than the glass transition temperature of the polyimide adhesive to facilitate adequate bonding to metal.In some embodiments, suitable aliphatic diamines are selected from the group comprising 1,4-tetramethylenediamine, 1,5-pentamethylenediamine (PMD), 1,7-heptamethylenediamine, 1,8-octamethylenediamine, 1,9-nonamethylenediamine, 1,10-decamethylenediamine (DMD), 1,11-undecamethylenediamine, 1,12-dodecamethylenediamine (DDD), 1,16-hexadecamethylenediamine, and mixtures thereof. In some embodiments, the aliphatic diamine is hexamethylenediamine. In some embodiments, the thermoplastic polyimides of the adhesive layers of the 1st and 2nd laminates are derived from 4,4'-oxyphthalenhydride, pyromellite dianhydride, 1,3-bis(4-aminophenoxy)benzene and hexamethylenediamine, respectively. PRODUCTION OF THE FIRST AND SECOND LAMINATE

[0049] The adhesive layers of the first and second laminates can be produced using any method known in the art. In one embodiment, polyamic acid is produced by reacting anhydrides with amines with a slight excess of diamine in DMAC solvent. The suspension of the electrically conductive filler in DMAC is prepared by adding the desired amount of electrically conductive filler to a DMAC solvent using a Silverson L4RT high-shear stirrer at 4000 to 6000 rpm for 5 to 10 minutes, or until the electrically conductive filler is dispersed. The suspension of the electrically conductive filler is then added to the polyamic acid solution and stirred again with the Silverson L4RT-A high-shear stirrer at 4000 to 6000 rpm until the desired amount of electrically conductive filler in the polyamic acid, e.g., 30 wt%, is achieved.A finishing solution of dianhydride monomer in DMAC is added stepwise to increase the molecular weight until a target viscosity of 500 to 1000 poise is reached. The slurry is degassed to remove any air bubbles before the film is poured. In some embodiments, the filled, finished polymer solution is poured directly onto exposed copper foils approximately 14 inches long x 10 inches wide x 0.001 inches thick. The sample is then placed on a hot plate at approximately 80 to 100 °C for about 30 minutes to dry the solvent or until the film has solidified to at least 70% (green film state). The poured green polyimide film on copper is then placed on a film curing frame.The complete polyimide adhesive film on copper is then placed in a nitrogen-purged Blue M high-temperature oven under the following ramp-up conditions: 10 minutes at 50°C, 60 minutes at 100 to 400°C, and subsequently cooled back to room temperature in a nitrogen environment for 60 minutes. In some embodiments, the thermoplastic polyimide of the adhesive layer of the first or second laminate is thermally converted from a polyamic acid to a polyimide. In some embodiments, the thermoplastic polyimide of the adhesive layer of the first or second laminate, or both, is converted using suitable imidizing agents in conjunction with heat. In some embodiments, the first and second laminates can be produced according to prior art methods such as double-belt pressing or slit lamination. HEATER

[0050] The foil-based heating device according to the invention is intended for high-temperature applications and long-term use. The heating device according to the invention also heats uniformly. A known method for promoting uniform heating involves the use of nodes to facilitate control or migration of localized heating. The foil-based heating device according to the invention does not require any additional means, such as nodes arranged throughout the entire heating device, to enable uniform heating. Furthermore, the adhesive layers of the first and second laminates according to the invention can withstand the high temperatures required for the adhesion of the metal foil of the first laminate and the second laminate to the base film. Lamination temperatures of more than 290 °C are typically required.

[0051] The temperature of the foil-based heating device depends on the voltage and the position or spacing of the metal foil (busbar). With a fixed busbar position, the temperature increases with increasing voltage. With a constant voltage, the temperature can be increased by reducing the spacing between the metal foils. In some embodiments, more than two metal foils are used. The number of metal foils used depends on the size of the area to be heated and the desired temperature. This allows the heating device to be tailored to the intended use. The foil-based heating device according to the invention can be used for flexible and rigid applications. Examples of high-temperature applications include hair straighteners, hair curling irons, and industrial heaters. The foil-based heating device according to the invention is also suitable as a wall heater, floor heater, roof heater, or seat heater.The foil-based heating device according to the invention is also suitable for heating windmill blades, the leading edges of aircraft and helicopters to prevent the accumulation of snow or ice, or for any application where little or no voltage drop over long distances is desired. While the applications listed above are particularly suitable for the foil-based heating device according to the invention, those skilled in the art could also consider using the foil-based heating device for other applications, such as low-voltage and low-temperature applications, low-voltage high-temperature applications, high-voltage low-temperature applications, and high-voltage high-temperature applications.

[0052] The base film has an inner and an outer surface. The adhesive layer of the first laminate has an inner and an outer surface. The metal foil of the first laminate has an inner and an outer surface. The inner surface of the metal foil of the first laminate adheres directly to the outer surface of the adhesive layer of the first laminate. The inner surface of the adhesive layer of the first laminate adheres directly to a portion of the inner surface of the base film.

[0053] The adhesive layer of the second laminate has an inner and an outer surface. The metal foil of the second laminate also has an inner and an outer surface. The inner surface of the metal foil of the second laminate adheres directly to the outer surface of the adhesive layer of the second laminate. The inner surface of the adhesive layer of the second laminate adheres directly to a different part of the inner surface of the base foil than the inner surface of the adhesive layer of the first laminate. In one embodiment, the current flows between the first and second laminates via the base foil, which bridges both laminates, thereby generating a resistant heating of the base foil.

[0054] In some embodiments, the foil-based heating device according to the invention can also have a secondary base film with an inner and outer surface, wherein the inner surface of the secondary base film adheres directly to the outer surface of the base film. In one embodiment, the secondary base film comprises an aromatic polyimide. The secondary base film constitutes a dielectric barrier. The use of a secondary base film makes it possible to attach the heating device to adjacent, electrically conductive surfaces without disturbing the conductive heating film surface. Therefore, it is undesirable for the secondary base film to contain electrically conductive fillers. The aromatic polyimide of the secondary base film can be the same as, or different from, the aromatic polyimide of the base film. In some embodiments, the aromatic polyimide of the secondary base film is derived from pyromellite dianhydride and 4,4'-diaminodiphenyl ether.

[0055] The foil-based heating device can be manufactured by vacuum pressure lamination. Sufficient heat and pressure are required to ensure that the first and second laminates (or more) adhere to the base foil.

[0056] In one embodiment, the film-based heating device also includes a cover layer. In one embodiment, the cover layer adheres directly to the outer surface of the base film. In another embodiment, the cover layer adheres directly to the outer surface of the secondary base film. In some embodiments, there may be further layers between the cover layer and the base film. In another embodiment, the cover layer adheres to the exposed areas of the inner surface of the base film (areas not directly adjacent to the adhesive layer of the first or second laminate) and to the exposed areas of the first and second laminates. In yet another embodiment, the cover layer encapsulates the film-based heating device, as shown in Fig. Figure 5 shows. In a further embodiment, the top layer can adhere to both the outer surface of the base film (or the outer surface of the secondary base film 28b) and the exposed areas of the first and second laminates and the inner surface of the base film that does not adhere directly to the adhesive layer of the first or second laminate. In some embodiments, the top layer encapsulates at least the base film, the first laminate, and the second laminate. In some embodiments, the top layer encapsulates at least the base film, the adhesive layer of the first laminate, the metal foil of the first laminate, the adhesive layer of the second laminate, and the metal foil of the second laminate.

[0057] In some embodiments, the top layer is selected from the group comprising tetrafluoroethylene-hexyfluoropropylene copolymer (FEP), perfluoroalkoxy polymer (PFA), and mixtures thereof. PFA is a poly(tetrafluoroethylene copolymer) alkyl vinyl ether, comprising its variants and derivatives, including the following group, which constitutes at least 50, 60, 70, 80, 85, 90, 95, 96, 97, 99, 99, or about 100 wt.% of the total polymer, where R1 is CnF2n+1, where n is any natural number greater than or equal to 1, in particular up to 20 or more. Typically, n is equal to 1 to 3, where x and y are mole fractions, with x in the range between 0.95 and 0.99, typically 0.97, and with y in the range between 0.01 and 0.05, typically 0.03, and with the melt flowability described in ASTM D 1238 in the range between 1 and 100 (g / 10 min), preferably 1 and 50 (g / 10 min), rather 2 and 30 (g / 10 min) and most preferably 5 and 25 (g / 10 min).

[0058] FEP is a poly(tetrafluoroethylene-co-hexaperfluoro]alkyl vinyl ether [also known as poly(tetrafluoroethylene-co-hexafluoropropylene) copolymer], composed wholly or partially of tetrafluoroethylene and hexafluoropropylene, comprising its variants and derivatives, including the following group, which constitutes at least 50, 60, 70, 80, 85, 90, 95, 96, 97, 99, or about 100 wt.% of the total polymer, where x and y are mole fractions, with x being in the range of 0.85 to 0.95, typically 0.92, and with y being in the range of 0.05 to 0.15, typically 0.08, and where the melt flowability described in ASTM D 1238 is in the range of 1 to 100 (g / 10 min), preferably 1 to 50 (g / 10 min), more preferably 2 and 30 (g / 10 min) and preferably 5 and 25 (g / 10 min).

[0059] The FEP copolymer can be derived directly or indirectly from (i.) 50, 55, 60, 65, 70, or 75% to approximately 75, 80, 85, 90, or 95% tetrafluoroethylene; and (ii.) 5, 10, 15, 20, or 25% to approximately 25, 30, 35, 40, 45, or 50% (generally 7 to 27%) hexafluoropropylene. In some embodiments, the top layer is selected from the group consisting of Teflon® FEP film (available from DuPont), Teflon® PFA film (available from DuPont), and mixtures thereof. In some embodiments, the top layer is surface-treated to promote better adhesion to the film-based heating device. Any known surface treatment, such as corona or plasma treatment, may be used.

[0060] The top layer is intended to prevent environmental damage and the leakage of electricity from the heated surface to adjacent material surfaces. In some embodiments, the thickness of the top layer lies between two of the following values, and optionally includes: 12, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, and 130 µm. In some embodiments, the thickness of the top layer lies between 12 and 130 µm. The top layer according to the invention can be directly slit-laminated or press-laminated onto the foil-based heating device.

[0061] All publications, patent applications, patent specifications, and other works mentioned herein are considered to be fully integral parts of this patent specification. Unless otherwise defined, all technical and scientific terms used herein have the meaning that corresponds to the general understanding of a person skilled in the art in the field relevant to the invention. In case of conflict, the content of this patent specification, in particular its definitions, shall prevail.

[0062] Although methods and materials similar to or corresponding to those described herein may be used in the execution or investigation of the present invention, suitable methods and materials are described herein.

[0063] The term "approximately" in relation to a value or a limit of a range is to be understood as including the specific value or limit. EXAMPLES

[0064] The advantages are illustrated in the following examples, which do not restrict the scope of the patent claims. 5025 Silver Conductor Conductive silver paste, available from EI du Pont de Nemours and Company, Wilmington, DE. Kapton® 200RS100 Two-layer electrically conductive polyimide film available from EI duPont de Nemours and Company, Wilmington, DE. 200CLP20 2 MIL (0.002 in) thick PFA Teflon film with double-sided surface treatment to improve adhesion during heat lamination. Surface treatment is achieved through either corona or plasma treatment. Available from E.I. du Pont de Nemours and Company, Wilmington, DE. 100EKJ 1MIL (0.001 in) thick three-layer Kapton film structure in which the outer two Kapton layers are an adhesive polyimide formulation and the core layer is a high-modulus polyimide film, available from E.I. DuPont de Nemours and Company, Wilmington, DE. Raven® 16 Carbon black, available from Columbian Chemicals Company CDX 7055U Carbon black, available from Columbian Chemicals Company Example 1:

[0065] Example 1 illustrates the uniform heating of the foil heater. Heating layer structure (Aluminium sheet / 100EKJ (top layer) / Kapton® 200RS100 (Heating unit / base film) / PMDA / ODPA / RODA, filled with 30 wt. % Raven 16 (adhesive layer) / copper (metal foil( / 200CLP20 (top layer)) Production of the polyimide adhesive film filled with PMDA / ODPA / RODA

[0066] A 19 to 20% solids content in polyamic acid was prepared by reacting anhydrides and amines with each other in DMAC solvent. The formulation used for the polyamic acid was PMDA / ODPA / RODA at 20 / 80 / 100, mixed in DMAC solvent.

[0067] Raven® in DMAC slurry was prepared by mixing 12 grams of Raven® 16 carbon black with 50 grams of DMAC solvent using a Silverson L4RT-A high-shear stirrer at 4000 to 6000 rpm for 5 to 10 minutes, or until the carbon-containing filler was wet and dispersed. The carbon slurry was then added to the polyamic acid and again stirred using a Silverson L4RT-A high-shear stirrer at approximately 400 to 6000 rpm until 30 wt% carbon was achieved in the polyamic acid. A finishing solution of 6 wt% PMDA monomer in DMAC was added stepwise using a 3 mL syringe until a target viscosity of 500 to 1000 poise was reached.

[0068] The slurry was degassed to remove any air bubbles before casting the film. The filled, finished PMDA / ODPA / / RODA polymer was immediately cast onto exposed copper foils approximately 14 inches long x 10 inches wide x 0.001 inches thick. The sample was then placed on a hot plate at approximately 80 to 100 °C for about 30 minutes to dry the solvent or until the film was at least 70% solid (green film state). The cast green polyimide film on copper was then peeled off and placed on a film curing frame. The fully cast polyimide adhesive film on copper was then placed in a nitrogen-purged Blue M high-temperature oven under the following ramp-up conditions: 10 minutes at 50 °C, 60 minutes at 100 to 400 °C, and then cooled to room temperature in a nitrogen environment for 60 minutes.The cured, full polyimide adhesive layer on copper is then cut into desired busbar strips of approximately 0.125 to 0.75 inches in width for lamination.

[0069] A prototype hair straightener is fabricated by vacuum laminating an aluminum sheet together with a multilayer stack of 100 EKJ foil, 200RS100 foil, copper busbars with 30 wt% full polyimide (described above), and 200CLP20 Teflon. A tetrahedral vacuum lamination press is used to bond the conductive polyimide and copper busbars to the 200RS100 foil surface and the surrounding layer stack. The vacuum lamination conditions applied were 680°F (360°C), pressure 20 to 25 tons (40,000 to 50,000 lbs), and a residence time of 30 minutes. 100 EKJ is used as a dielectric barrier. 200CLP20 is used as a top layer (moisture barrier). The samples were suspended in air at a room temperature of 23°C. The voltage was measured using an Extech Instruments True RMS Industrial Multimeter, model EX520.Positive and negative electrical leads with mechanical clamps were used as the power connection for the copper busbars. Alternating current was applied using a Powerstat variable AC autotransformer, type 3PN116C, power: 0-280 VAC & 4 amp.

[0070] The in Fig. 6. Displayed position of the thermal coupling (temperature values ​​in Celsius) Table 1 Gradual increase# Voltage (alternating current) 1 2 3 4 Time (min) current 1 60 69 61 62 61 2 0,91 2 70 95 85 84 83 2 1,07 3 80 118 104 105 105 2 1,24 4 90 143 124 127 127 2 1,40 5 100 161 139 142 143 2 1,55 6 110 170 152 155 156 2 1,72 7 120 186 161 163 163 2 1,88 8 120 190 165 164 164 10 1,88 Example 2:

[0071] Example 2 illustrates the constant voltage versus fluctuating busbar length (metal foil length).

[0072] The PMDA / OPDA / RODA-filled polyimide was produced as described in Example 1. The laminated copper (metal foil) / solid polyimide (adhesive) / Kapton® 200RS100 (heater / base foil) sample intended for the heater was produced using the vacuum lamination process described in Example 1, with a spacing of 0.75 inches between the approximately 0.5-inch wide x 40-inch long x 0.001-inch thick copper busbars.

[0073] 1 MIL (0.001 in) thick standard copper was used to transmit DC and AC voltage for voltage drop measurement. 0.001 in thick copper strips, cut to 40 in length, were used for current transmission. Positive and negative electrical leads with mechanical clamps were used to connect the copper busbars. DC current was applied using an HC Protek DC Power Supply Transformer, Model 3003, rated at 0-30 VAC & 3 amps. AC current was applied using a Powerstat Variable AC Autotransformer, Type 3PN116C, rated at 0-280 VAC & 4 amps. Voltage was measured using an Extech Instruments True RMS Industrial Multimeter, Model EX520. The results are shown in Table 2. Table 2 Sample type Applied voltage Measured voltage Measured voltage Measured voltage Measured voltage Measured voltage (Direct current) at terminals (Direct current) at 1.0 inch (Direct current) at 10 inches (Direct current) at 20 inches (Direct current) at 30 inches (Direct current) at 40 inches copper 5,062 5,062 5,062 5,062 5,062 5,062 copper 10,08 10,08 10,08 10,08 10,08 10,08 (Alternating current) at terminals (Alternating current) at 1.0 inch (Alternating current) at 10 inches (Alternating current) at 20 inches (Alternating current) at 30 inches (Alternating current) at 40 inches copper 5,07 5,07 5,07 5,07 5,07 5,07 copper 10,20 10,20 10,20 10,20 10,20 10,20 copper 20,40 20,40 20,40 20,40 20,40 20,40 Comparative example 1

[0074] Comparison example 1 illustrates the current drop of the 5025 paste over the length of the busbar.

[0075] 5025 silver conductive paste was screen-printed onto the surface of Kapton® 200RS100 foil. The paste thickness was printed to a target thickness of 0.001 in, 0.5 in wide, 40 in long, and with a busbar spacing of 0.75 in (as described in Example 2). The 200RS100 5025 silver paste was then dried / cured on a laboratory hot plate at 120°C for 15 minutes. Power was supplied from a variable-amp DC power supply and a variable-amp AC power supply. Positive and negative electrical leads with mechanical clamps were used to connect the 5025 silver busbars. DC power was applied using an HC Protek DC Power Supply Transformer, Model 3003, rated at 0-30 VAC & 3 amp. Alternating current was applied using a Powerstat Variable AC Autotransformer, type 3PN116C, power: 0-280 VAC & 4 amp. The voltage was measured with an Extech Instruments True RMS Industrial Multimeter, model EX520.Measurements were taken as with the copper busbars shown in Example 2. The results are shown in Table 3. Table 3 Sample type Applied voltage Measured voltage Measured voltage Measured voltage Measured voltage Measured voltage (Direct current) at terminals (Direct current) at 1.0 inch (Direct current) at 10 inches (Direct current) at 20 inches (Direct current) at 30 inches (Direct current) at 40 inches 5025 Paste 5,062 4,688 3,581 2,809 2,369 2,225 5025 Paste 10,08 9,20 7,01 5,436 4,563 4,282 (Alternating current) at terminals (Alternating current) at 1.0 inch (Alternating current) at 10 inches (Alternating current) at 20 inches (Alternating current) at 30 inches (Alternating current) at 40 inches 5025 Paste 5,07 4,34 3,33 2,57 2,11 2,04 5025 Paste 10,20 8,48 6,47 5,03 4,20 3,97 5025 Paste 20,40 16,68 12,25 9,39 7,79 7,35 Example 3:

[0076] Example 3 illustrates the high temperature resistance of carbon-filled polyimides.

[0077] The sample, consisting of solid polyimide and the heating device, was prepared as in Example 1. After bonding, a PFA-Teflon coating temperature of 310°C, a pressure of 10 tons, and a residence time of 15 minutes were used. Electrical leads with mechanical clamps were connected directly to the copper busbars (only one end) using conductive KJ wire and subsequently connected to a variable-ampere DC or AC power supply.

[0078] Direct current was applied using an HC Protek DC Power Supply Transformer, model 3003, rated at 0-30 VDC & 3 amps. Alternating current was applied using a Powerstat Variable AC Autotransformer, type 3PN116C, rated at 0-280 VAC & 4 amps. Voltage was measured using an Extech Instruments True RMS Industrial Multimeter, model EX520.

[0079] The results can be found in Table 4. Comparative example 2

[0080] Comparison example 2 shows that the 5025 paste does not have high temperature resistance.

[0081] Heater devices constructed with 5025 silver paste are assembled by screen printing or lab masking to achieve the desired busbar length, width, and thickness. In the following example, the Kapton® 200RS 100 (heater) sample used to measure voltage fluctuation was fabricated by lab masking. The samples were created by assembling three parallel busbars measuring 40.0 inches long x 0.5 inches wide x 0.001 inches thick. The paste was applied with a foam doctor blade and then cured for 15 minutes at 120°C using a Thermolyne Type 2200 remote-controlled heating plate. Electrical leads with mechanical clamps were connected directly to the 5025 silver busbars (one end only) and then connected to a variable-ampere DC or AC power supply.Direct current was applied using an HC Protek DC Power Supply Transformer, model 3003, rated at 0-30 VAC & 3 amps. Alternating current was applied using a Powerstat Variable AC Autotransformer, type 3PN116C, rated at 0-280 VAC & 4 amps. Voltage was measured using an Extech Instruments True RMS Industrial Multimeter, model EX520. The results are shown in Table 4. Table 4 Example 3: PMDA / OPDA / RODA with filler Comparison example: 25025 paste 180°C No charring No visible charring in the short term. 200°C Some copper oxidation without a top layer Oxidation and discoloration of the paste surface, browning 250°C Increased oxidation and browning of copper at +250°C Severe discoloration and deterioration of the silver paste rails 300 °C Copper oxidation, but no electrical problems Cracks, peeling, oxidation / browning, paste begins to degrade 400°C Cu oxidation, KJ begins to delaminate and peels off from the 200RS 100 surface. No data - paste fails at 300°C Example 4:

[0082] Example 4 illustrates the variable adhesive strength in relation to the dosage level of the filler.

[0083] A CDX 7055U carbon slurry was prepared by adding the following substances in the following ratios: 73.25% DMAC / 9.5% CDX 7055U carbon black filler / 13.06% PMDA / ODA prepolymer / 4.19% PMDA / BPDA / ODA / PPD prepolymer. This CDX 7055U slurry was added to a polyamic acid prepolymer to achieve filler concentrations of 10, 20, and 30 wt.%. To ensure complete and uniform particle dispersion, the slurry was milled and stirred with high shear energy. Particle size analysis data were targeted for a particle size of approximately 1 µm in diameter. A Horiba particle size analyzer with light scattering was used to measure the particle size.

[0084] Approximately 800 grams of a second adhesive were prepared similarly to Example 1, yielding a PMDA / ODPA / RODA / HMD polyamic acid mixture with the following ratios of 20 / 80 / 70 / 30 in DMAC solvent. The PMDA / ODPA / RODA / HMD anhydrides and amides contained 20 wt% solids in DMAC.

[0085] Two types of prepolymer adhesive formulations, PMDA / ODPA / / RODA / HMD and PMDA / ODPA / / RODA (prepared as in Example 1), were injected at target doses of 0%, 10%, 20%, and 30% to investigate adhesion strength. Samples were processed to achieve viscosities of 400 to 600 poise with 6 wt% PMDA in DMAC solvent (finishing solution). All sample slurries and combination mixtures were prepared in a dry-box environment (nitrogen-purged). All samples were degassed in a vacuum chamber and poured onto approximately 8 in x 11 in x 0.001 in foil molds (for pouring foil onto glass, see Example 1). Filled polyimide samples were dried on a Thermolyne Type 2200 hotplate with remote temperature control at 80 to 100°C for approximately 30 minutes until about 70% solids remained (green foil state). The foil samples were then peeled from the glass plate surface and placed on foil frames for high-temperature curing.Each film and frame was placed in a Blue M oven and cured for approximately 45 minutes at an initial temperature of 120 to 320°C, increasing at about 5°C / min. PMDA / OPDA / RODA-filled polyimide samples were then placed in another Blue M oven at 400°C for five minutes for high-temperature final curing. PMDA / OPDA / RODA-filled polyimide samples were then placed in a further Blue M oven at 350°C for five minutes for ultra-high-temperature curing.

[0086] Extruded foil samples were then removed from the frames and mounted between approximately 10-inch x 12-inch copper foils. The copper foils with the filled polyimide samples were then placed in a tetrahedral vacuum lamination press for copper lamination. The vacuum pressing conditions applied to all PMDA / OPDA / / RODA-filled copper-clad polyimide samples were a temperature of 680°F (360°C) at 25 tons of pressure and a residence time of 30 minutes. The vacuum pressing conditions applied to all copper-clad PMDA / OPDA / / RODA / MD samples were a temperature of 572°F (300°C) at 25 tons of pressure and a residence time of 30 minutes. The samples were cut to a width of 0.5 inches using a Thwing-Albert Instruments JDC Precision Cutter. Bond strength was measured using an Instron Model 3345 single-beam column with an attached Rhönrad and Instron Bluehill PC software. The results can be found in Table 5. Table 5 Sample carbon dose (%) Sample type Average adhesion strength (lb / in) 0 PMDA / OPDA / / RODA 10,306 10 PMDA / OPDA / / RODA 8,948 20 PMDA / OPDA / / RODA 8,197 30 PMDA / OPDA / / RODA 2,466 0 PMDA / OPDA / / RODA / HMD 5,507 10 PMDA / OPDA / / RODA / HMD 4,323 20 PMDA / OPDA / / RODA / HMD 1,852

[0087] It should be noted that not all activities described in the general description or the examples are necessary; indeed, part of a specific activity may be unnecessary. Furthermore, additional activities may be performed besides those described above. Moreover, the sequence of activities described above does not necessarily correspond to the actual sequence in which they should be carried out. After reading this patent specification, a person skilled in the art will be able to determine which activities are necessary to meet specific needs or requirements.

[0088] The invention has been described in the above patent specification with reference to specific embodiments. However, the person skilled in the art will recognize that various modifications and changes are possible without exceeding the scope of the invention as described in the patent claims. All features disclosed in the present patent specification can be replaced by alternative features that pursue the same, a corresponding, or a similar purpose. Consequently, the patent specification and drawings are to be interpreted as illustrations and not as limitations, and all modifications of the type described above are considered to be part of the invention.

[0089] Advantages and solutions to problems have been described with reference to specific embodiments. The advantages, solutions to problems, and other elements that lead to the realization or enhancement of an advantage or solution are not to be interpreted as critical, necessary, or essential features or elements of any or all of the claims.

Claims

[1] Foil-based heating device (10), comprising: A) a base sheet (12) having an inner (12b) and an outer surface (12a), wherein the base sheet (12) comprises: a) an aromatic polyimide in an amount of 55 to 90 wt. %, based on the total weight of the base film (12), b) an electrically conductive filler (14) in an amount of 10 to 45 wt. %, based on the total weight of the base film (12), B) a first laminate comprising: a) an adhesive layer (16) comprising an inner surface (16a) bonded to the inner surface (12b) of the base film (12) and an outer surface (16b), wherein the adhesive layer (16) comprises: i. 55 to 90 wt. %, based on the total weight of the adhesive layer (16), of a thermoplastic polyimide in which 70 to 100 mol. % of the thermoplastic polyimide are derived from at least one aromatic diamine and at least one aromatic dianhydride, ii. 10 to 45 wt. %, based on the total weight of the adhesive layer (16), of an electrically conductive filler (18), b) a metal foil (20) which has: i. an inner surface (20a) bonded to the outer surface (16b) of the adhesive layer (16) as well as ii. an exterior surface, wherein the metal foil (20) of the first laminate is 5 to 200 µm thick, C) a second laminate comprising: a) an adhesive layer (22) having an inner surface (22a) bonded to the inner surface (12b) of the base film (12) and an outer surface (22b), wherein the adhesive layer (22) contains: i. 55 to 90 wt. %, based on the total weight of the adhesive layer (22), of a thermoplastic polyimide in which 70 to 100 mol. % of the thermoplastic polyimide are derived from at least one aromatic diamine and at least one aromatic dianhydride, ii. 10 to 45 wt. %, based on the total weight of the adhesive layer (22), of an electrically conductive filler (24), b) a metal foil (26) which has: i. an inner surface (26a) bonded to the outer surface (22b) of the adhesive layer (22) as well as ii. an exterior surface, wherein the metal foil (26) of the second laminate is 5 to 200 µm thick, wherein at least a part of the first laminate and a part of the second laminate are arranged at a certain distance from each other and are connected to each other over at least a part of the base film (12). [2] Film-based heating device (10) according to claim 1, further comprising a secondary base film (28) having an outer (28b) and an inner surface (28a), wherein the inner surface (28a) adheres directly to the outer surface (12a) of the base film (12) and the secondary base film (28) comprises an aromatic polyimide. [3] Foil-based heating device (10) according to claim 2, wherein the aromatic polyimide of the secondary base film (28) is derived from pyromellite dianhydride and 4,4'-diaminodiphenyl ether. [4] Foil-based heating device (10) according to claim 1, comprising a cover layer (30) selected from the group consisting of: tetrafluoroethylenehexafluoropropylene copolymer (FEP), perfluoroalkoxy polymer (PFA) and mixtures thereof. [5] Foil-based heating device (10) according to claim 4, in which the cover layer (30) encapsulates at least the base film (12), the adhesive layer (16) of the 1st laminate, the metal foil (20) of the 1st laminate, the adhesive layer (22) of the 2nd laminate and the metal foil (26) of the 2nd laminate. [6] Heating device on a foil basis (10) according to claim 1, wherein at least 70 mol % of the aromatic polyimide of the base foil (12) are derived from pyromellite dianhydride and 4,4'-diaminodiphenyl ether. [7] Heating device on a film basis (10) according to claim 1, in which the thermoplastic polyimide of the adhesive layer (16) of the 1st laminate is also derived to 1 to 30 mol. % from a non-aromatic diamine selected from the group consisting of aliphatic diamine, cycloaliphatic diamine and any combination thereof. [8] Heating device on a film basis (10) according to claim 1, in which the thermoplastic polyimide of the adhesive layer (22) of the 2nd laminate is also derived to 1 to 30 mol. % from a non-aromatic diamine selected from the group consisting of aliphatic diamine, cycloaliphatic diamine and any combination thereof. [9] Film-based heating device (10) according to claim 1, in which the thermoplastic polyimide of the adhesive layer (16) of the 1st laminate and the thermoplastic polyimide of the adhesive layer (22) of the 2nd laminate are also derived to 1 to 30 mol. % from a non-aromatic diamine selected from the group consisting of aliphatic diamine, cycloaliphatic diamine and any combination thereof. [10] Foil-based heating device (10) according to claim 9, in which the aliphatic diamine is hexamethylenediamine. [11] Foil-based heating device (10) according to claim 1, in which the electrically conductive filler (18) of the adhesive layer (16) of the 1st laminate and the electrically conductive filler (24) of the adhesive layer (22) of the 2nd laminate are the same. [12] Foil-based heating device (10) according to claim 1, in which the electrically conductive filler (14) of the base film (12), the electrically conductive filler (18) of the adhesive layer (16) of the 1st laminate and the electrically conductive filler (24) of the adhesive layer (22) of the 2nd laminate are the same. [13] Foil-based heating device (10) according to claim 1, in which the electrically conductive filler (14) of the base film (12), the electrically conductive filler (18) of the adhesive layer (16) of the 1st laminate, and the electrically conductive filler (24) of the adhesive layer (22) of the 2nd laminate each comprise carbon black. [14] Foil-based heating device (10) according to claim 1, in which the metal foil (20) of the 1st laminate and the metal foil (26) of the 2nd laminate are the same. [15] Foil-based heating device (10) according to claim 1, in which the metal foil (20) of the 1st laminate and the metal foil (26) of the 2nd laminate comprise copper. [16] Heating device on a foil base (10) according to claim 1, in which the base foil (12) comprises 1 to 15 wt. % of a non-electrically conductive filler. [17] Foil-based heating device (10) according to claim 1, in which the adhesive layer (16) of the 1st laminate, the adhesive layer (22) of the 2nd laminate or both adhesive layers (16, 22) comprise 1 to 15 wt. % of a non-electrically conductive filler. [18] Film-based heating device (10) according to claim 1, in which the thermoplastic polyimide of the adhesive layer (16) of the 1st laminate and the thermoplastic polyimide of the adhesive layer (22) of the 2nd laminate are partly derived from 4,4'-oxydiphthalenhydride, pyromellite dianhydride and 1,3-bis(4-aminophenoxy)benzene. [19] Film-based heating device (10) according to claim 1, in which the thermoplastic polyimide of the adhesive layer (16) of the 1st laminate and the thermoplastic polyimide of the adhesive layer (22) of the 2nd laminate are each derived from 4,4'-oxydiphthalanhydride, pyromellite dianhydride and 1,3-bis(4-aminophenoxy)benzene and hexamethylenediamine.

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