Graded adjustable resistance type composite electrothermal film material and preparation method and application thereof

Abstract

The invention relates to the technical field of electric heating materials, and discloses a graded adjustable resistance type composite electrothermal film material and a preparation method and application thereof. The electrothermal film adopts a multi-layer composite structure and comprises an electrode layer, a polymer-conductive carbon composite functional layer (forming an adjustable resistor R1), an inorganic glass powder-conductive carbon composite functional layer (forming a stable resistor R2) and an electrode layer from top to bottom. The core is that the total resistance R is equal to R1 + R2, constant power output and linear temperature control under fixed voltage are realized by presetting the R value in the preparation stage, and an external regulation and control circuit is not needed. The material fundamentally eliminates the risk of electrode short circuit, has the advantages of high temperature resistance, good flexibility, low driving voltage, fast response, high safety and the like, and is especially suitable for high-power-density flexible heating devices in the working environment of 40-120 DEG C. The preparation method comprises the steps of inorganic layer / polymer layer ink preparation, layer-by-layer forming sintering and composite packaging, and is easy and convenient to operate and suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention relates to the field of medium- and high-temperature electric heating thin film materials technology, specifically to a novel electric heating film material, its preparation method, and its application. Background Technology

[0002] Electric heating technology, due to its cleanliness, environmental friendliness, high controllability, and high energy conversion efficiency, has become an important alternative to direct heating using traditional fossil fuels, showing broad application prospects in industry, agriculture, and household appliances. Among various electrothermal materials, polymer-based composite electrothermal films using conductive carbon materials such as graphene, carbon black, and carbon nanotubes as fillers have become a current research hotspot and development direction due to their advantages such as light weight, good flexibility, low cost, and ease of processing and molding.

[0003] However, due to limitations in material systems and structural design, existing conductive carbon-based electrothermal films, especially for high-power-density applications, still face several technical bottlenecks that urgently need to be addressed: (1) Currently widely used electrothermal films suffer from insufficient intrinsic safety and a high risk of short circuits and failures. In flexible applications, repeated bending or external pressure can easily cause distortion of the conductive path between electrodes or even direct contact, leading to local short circuits, overheating and burnout, posing significant safety hazards. In addition, the polymer matrix is ​​prone to thermal degradation and aging under high-temperature conditions, resulting in irreversible drift in resistance values, which not only affects heating stability but may also cause fire risks.

[0004] (2) Existing technologies for regulating heat generation power mostly rely on complex external circuit systems (such as pulse width modulation PWM) to achieve average power control by frequently switching current on and off. This method directly leads to lag in thermal response, large temperature fluctuations, and a poor user experience. More importantly, there is significant energy loss during the switching process, resulting in low overall energy efficiency. From the perspective of the materials themselves, there is a lack of an intrinsic mechanism that can achieve linear, stepless power regulation.

[0005] (3) A single material system is difficult to meet multiple performance requirements. Pure inorganic electrothermal films (such as metal foil and carbon crystal film) are usually brittle and have poor bending resistance; while pure polymer electrothermal films have the disadvantages of large thermal expansion coefficient and insufficient temperature resistance. Under the condition of hot and cold cycling, due to the mismatch of interlayer thermal stress, multilayer composite materials are prone to problems such as interface delamination and cracking, which leads to a sharp change in resistance or even complete failure of function, making it difficult to work stably for a long time in a wide temperature range.

[0006] Therefore, existing technologies lack an electrothermal film solution that can intrinsically prevent electrode short circuits structurally, inherently achieve linear adjustability in principle, and synergistically balance flexibility and temperature resistance in terms of materials. Developing such a novel composite electrothermal film material that combines high safety, precise adjustability, and excellent structural reliability is of great significance for promoting the advancement and safety of this technology. Summary of the Invention

[0007] The purpose of this invention is to solve the aforementioned problems of the prior art and provide a novel electrothermal film material, its preparation method, and its applications, which feature good high-temperature resistance, strong safety, low driving voltage, fast response speed, high efficiency and energy saving, low cost, and simple preparation process. The composite electrothermal film material provided by this invention can be driven by low voltage, rapidly heat up, and operate stably. Furthermore, the operating temperature can be adjusted by regulating the film layer resistance. In addition, the inorganic filler ensures good mechanical properties, and the layered design isolates the electrodes, avoiding short circuits. It is suitable for medium- and high-temperature heating thin film applications.

[0008] The technical solution adopted by this invention to solve its technical problem is: This invention provides a graded adjustable resistance composite electrothermal film material, which has a multi-layer composite structure and includes, from top to bottom: a first electrode layer, a polymer-conductive carbon composite functional layer, an inorganic glass powder-conductive carbon composite functional layer, and a second electrode layer. The polymer-conductive carbon composite functional layer forms an adjustable resistance layer R1, and the inorganic glass powder-conductive carbon composite functional layer forms a stable resistance layer R2. The total resistance of the electrothermal film is R = R1 + R2.

[0009] By adopting the aforementioned technical solution, the core of this invention lies in the total resistance R = R1 + R2. By presetting the R value during the manufacturing stage, constant power output and linear temperature control under a fixed voltage are achieved without the need for external control circuitry. This material inherently eliminates the risk of electrode short circuits and possesses advantages such as high temperature resistance, good flexibility, low driving voltage, fast response, and high safety. It is particularly suitable for high power density flexible heating devices operating in environments ranging from 40 to 120°C.

[0010] Preferably, the thickness of the polymer-conductive carbon composite functional layer is 50~200μm, the thickness of the inorganic glass powder-conductive carbon composite functional layer is 50~100μm, and the overall thickness of the electrothermal film material is 400~1000μm.

[0011] Preferably, the raw materials of the electrothermal film material mainly include conductive carbon filler, inorganic glass powder and polymer.

[0012] Preferably, the conductive carbon filler is selected from at least one of acetylene black, conductive carbon black, carbon nanotubes, carbon fibers, activated carbon, and spherical graphite.

[0013] Preferably, the inorganic glass powder is selected from at least one of the low-melting-point lead-free glass systems, with a melting point preferably not higher than 460°C; more preferably, it is selected from at least one of the Bi-Zn-B, VP-Sb, Zn-B-Si, and Sn-P-Zn systems.

[0014] Preferably, the polymer is a high-temperature resistant polymer material with a glass transition temperature that is at least 20°C higher than the working temperature of the composite electrothermal film material; more preferably, the polymer is selected from at least one of polyethersulfone resin, polyetheretherketone, polyimide, polyphenylene sulfide, and polyurethane.

[0015] The present invention also provides a method for preparing any of the above-mentioned graded adjustable resistance composite electrothermal film materials, comprising the following steps: (1) Preparation of inorganic glass powder-conductive carbon composite functional layer: By weight, 50-80 parts of inorganic glass powder, 40-90 parts of conductive carbon filler, 1-4 parts of surface modifier and 100-300 parts of liquid dispersant are mixed and dispersed by ball milling until the particle size D50≤1μm to obtain inorganic ink. (2) Molding and sintering: The inorganic ink is scraped onto the substrate and cured at 350~500℃ for 2~12h in an inert atmosphere. The resulting inorganic layer is separated from the substrate to form an inorganic glass powder-conductive carbon composite functional layer. (3) Preparation of polymer-conductive carbon composite functional layer: By weight, 30-50 parts of polymer, 40-90 parts of conductive carbon filler, 1-5 parts of antioxidant, 1-4 parts of surface modifier and 100-300 parts of liquid dispersant are mixed and dispersed to obtain polymer ink. (4) Interlayer composite: The polymer ink is spin-coated onto the surface of the inorganic glass powder-conductive carbon composite functional layer and cured at 80~300℃ for 2~12h in an inert atmosphere to form a dual-functional layer structure. (5) Install electrodes: Install electrodes at both ends of the dual-functional layer and heat-press to cure.

[0016] Preferably, the surface modifier in steps (1) and (3) is selected from at least one of paraffin wax, ethyl cellulose, stearic acid, polyvinyl butyral, and polyvinyl alcohol.

[0017] Preferably, the liquid dispersant in steps (1) and (3) is selected from at least one of dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, isopropanol, n-butanol, ethanol, glycerol, and distilled water.

[0018] Preferably, the inert atmosphere described in steps (2) and (4) is selected from at least one of nitrogen, helium, and argon.

[0019] Preferably, the ball milling speed in step (1) is 300~500 rpm and the ball milling time is 2~10 h.

[0020] Preferably, the substrate in step (2) is capable of separating the inorganic layer on it after sintering and curing, and is preferably selected from any one of metal foil, mica sheet, or rigid glass plate with a sacrificial layer on its surface.

[0021] Preferably, the scraping speed in step (2) is 5~50 mm / s.

[0022] Preferably, the antioxidant in step (3) is selected from at least one of hydrogenated rosin glycerol ester, L-ascorbic acid, and dilauryl thiodipropionate.

[0023] Preferably, the dispersion in step (3) is carried out by dispersing at a high-speed shear emulsifier at 2000~5000 rpm for 0.5~2h.

[0024] Preferably, the spin coating speed in step (4) is 1000~4000 rpm.

[0025] Preferably, the electrode installation method in step (5) is to attach a prefabricated metal electrode sheet by means of conductive adhesive, or to form an electrode by means of printing conductive ink.

[0026] Preferably, the hot pressing curing temperature in step (5) is 80~180℃, the pressure is 1~3 MPa, and the time is 3~12h.

[0027] The present invention also provides an application of any of the above-mentioned graded adjustable resistivity composite electrothermal film materials in high power density flexible heating devices.

[0028] Preferably, this electrothermal film material is suitable for long-term working environments of 40~120℃ and can achieve linear temperature control at low voltage of 1~12V.

[0029] Compared with the prior art, the novel electrothermal film material provided by this invention has the following advantages: (1) High intrinsic safety and structural reliability: This invention innovatively adopts a polymer / inorganic composite dual-functional layer structure. This design is not a simple material stacking, but solves the long-standing problems of weak interfacial bonding and thermal stress mismatch in existing composite technologies through layer sequence optimization and interface engineering. In the prior art, although there have been attempts at organic-inorganic composites, the large differences in the physicochemical properties of the two types of materials (such as polarity, coefficient of thermal expansion, molding temperature, etc.) often lead to problems such as poor interfacial compatibility and insufficient interlayer adhesion during the composite process, resulting in delamination and cracking during high and low temperature cycling or mechanical bending, which reduces the overall reliability. For example, simply mixing inorganic fillers into the polymer matrix can improve temperature resistance, but it will sacrifice flexibility; while physical layered composites are difficult to withstand long-term thermal stress due to weak interfacial bonding. This invention employs a process path of first preparing an independent inorganic layer and then composite it with a polymer layer, and precisely controls the sintering and curing conditions (such as staged hot pressing under an inert atmosphere) to achieve a strong interfacial bond between the inorganic layer (R2) and the polymer layer (R1). This retains the rigid isolation function of the inorganic layer while utilizing the flexibility and adhesiveness of the polymer layer. The inorganic glass powder-conductive carbon composite functional layer (R2), as a physical isolation layer, possesses high rigidity and stable electrical resistance. Even under external pressure, bending, interlayer misalignment, or high-temperature expansion, it effectively prevents direct contact between the upper and lower electrodes, fundamentally eliminating the risk of short circuits. Simultaneously, through material selection and thickness design, this composite structure achieves a near-matching of the thermal expansion coefficients of the two layers, significantly reducing interlayer stress caused by temperature changes, thereby improving the structural integrity and service life of the electrothermal film under high-temperature cycling.

[0030] (2) Precise built-in regulation of heating power and intelligent temperature self-stabilization: This invention achieves precise built-in regulation of heating power and intelligent temperature self-stabilization through a unique “R1 + R2” series resistor design. Among them, the inorganic glass powder-conductive carbon composite functional layer (R2) serves as a stable resistance layer. Its resistance value forms a stable three-dimensional conductive network after high-temperature sintering, exhibiting high stability and a low temperature coefficient of resistance. The polymer-conductive carbon composite functional layer (R1) serves as an adjustable resistance layer, exhibiting a significant positive temperature coefficient (PTC) effect. During normal operation, the conductive filler forms a stable conductive path in the polymer matrix. When the material temperature rises abnormally and exceeds a specific transition point (usually close to the glass transition temperature Tg of the polymer matrix) due to external factors (such as heat dissipation obstruction, sudden changes in ambient temperature, or heat accumulation caused by external pressure), the volume of the polymer matrix expands significantly, causing the internal conductive network to be stretched and destroyed, and the number of conductive paths to decrease sharply, thereby causing the resistivity of the R1 layer to increase by orders of magnitude. Since R1 is an adjustable resistance layer and dominates the total resistance R, its sharp increase in resistance directly leads to a significant increase in the total resistance R. According to P = U 2Under a fixed voltage U, the heating power P will automatically and rapidly decrease, forcing the material surface temperature to drop. Once the temperature drops, the polymer matrix shrinks, the conductive network is rebuilt, the resistance decreases, the power recovers, and the temperature rises again. Through this autonomous negative feedback loop of "temperature rise → resistance increase → power decrease → temperature drop", this invention endows the electrothermal film with intrinsic temperature self-limiting capability, enabling it to automatically stabilize the operating temperature within the design range. Furthermore, the resistance (R2) of the inorganic glass powder-conductive carbon composite functional layer is low in sensitivity to fluctuations in process parameters and possesses inherent high stability, making it suitable as a reference resistor in circuits. Conversely, the resistance (R1) of the polymer-conductive carbon composite functional layer is more sensitive to the content, morphology, and dispersion state of the conductive filler. Therefore, by precisely controlling the composition and structure of the polymer-conductive carbon composite functional layer to set the target value of R1, a precise, flexible, and efficient preset of the total resistance R = R1 + R2 can be achieved. According to Joule's law, the heating power of the electrothermal film is P = U. 2 When a fixed driving voltage is applied during operation, the heating film will output a constant heating power, thereby achieving intrinsic linear temperature control without external regulation, with fast response speed and high energy utilization.

[0031] (3) Wide temperature range applicability and superior overall performance: This invention achieves a breakthrough in performance through the optimized combination of material systems. The matrix is ​​constructed using high-molecular polymers (such as polyetheretherketone) with a temperature resistance of over 200℃ and low-melting-point inorganic glass powder, ensuring that the electrothermal film can operate stably for a long time at 40~120℃ and withstand higher instantaneous temperatures. This material system, combined with low-resistance silver-based conductive adhesive and conductive carbon filler, can be driven at a safe low voltage of 1~12V, rapidly heating up and achieving linear temperature control. Furthermore, this preparation process has strong compatibility and advantages of low cost and simple process. Attached Figure Description

[0032] Figure 1 A schematic diagram and equivalent circuit diagram of a novel electrothermal film material; Figure 2 The heating curves of the electrothermal film material prepared in Example 1 under driving voltages of 2V, 3V, and 4V are shown. Detailed Implementation

[0033] To better clarify and understand the objectives, process solutions, and advantages of this invention, the technical solutions and implementation methods of this invention will be further described clearly, completely, and in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the embodiments described in this invention are implemented under the premise of the technical solutions of this invention, providing detailed implementation methods and specific operating procedures, but are only some embodiments of this invention, not all embodiments. The specific implementation methods described are limited to illustrating and explaining this invention and do not limit this invention. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0034] Unless otherwise specified, the experimental methods and conditions used in the embodiments of this invention are conventional methods and conditions. The materials, reagents, instruments, and equipment used in the embodiments, unless otherwise specified, are all conventional substances or equipment known to those skilled in the art and can be obtained commercially or prepared by conventional methods. The reaction conditions described in the invention's content can all achieve the stated reactions and obtain the desired products. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of this invention.

[0035] Example 1

[0036] The specific material composition and implementation steps of a novel electrothermal film material are as follows: (1) Inorganic layer preparation: Weigh 6.2g of VP-Sb system glass powder (Shijiazhuang Lomat Glass Technology Co., Ltd., brand name LMT-V390), 8.5g of conductive carbon black (particle size of 50nm, Dongguan Kelude Innovation Technology Co., Ltd., model name Super PLi), and 0.25g of paraffin (Xi'an Tianmao Baoding Biotechnology Co., Ltd.). After mixing, add it to 10.5g of dimethylformamide and ball mill at 300rpm for 2h to disperse it to a particle size D50≈0.6μm to obtain inorganic ink; (2) Molding and sintering: Take a 0.1 mm thick 304 stainless steel foil (10 cm × 10 cm), ultrasonically clean it with anhydrous ethanol and acetone, and dry it. Apply inorganic ink to the stainless steel foil at 5 mm / s and cure it at 400°C in a nitrogen atmosphere for 5 h. After cooling, the inorganic layer can be peeled off naturally or by slight external force; (3) Preparation of polymer layer: Weigh 3.5g of thermoplastic polyurethane (Shenzhen Baoan District Xingwang Plastic Raw Material Factory), 6.8g of multi-walled carbon nanotubes (length-to-diameter ratio > 200, Suzhou Carbon Graphene Technology Co., Ltd.), 0.35g of hydrogenated rosin glycerol ester, and 0.25g of ethyl cellulose. Mix them and add them to 15g of dimethylformamide. Disperse the mixture for 0.5 h at 2000 rpm using a high-speed shear emulsifier to obtain polymer ink. (4) Interlayer composite: The polymer ink is spin-coated onto the surface of the inorganic layer at 1000 rpm and cured at 130°C in a nitrogen atmosphere for 2 hours to form a dual-functional layer structure. (5) Electrode installation and encapsulation: Silver-based conductive adhesive is coated on both ends of the dual-functional layer and copper foil is attached. The mixture is then hot-pressed and cured for 6 hours at 80°C and 1MPa.

[0037] Example 2

[0038] The specific material composition and implementation steps of a novel electrothermal film material are as follows: (1) Inorganic layer preparation: Weigh 7g of Sn-P-Zn system glass powder (Hunyuan Junhong New Material Co., Ltd., brand name D02), 8g of spherical graphite (particle size of 5μm, Bohuas Nanotechnology (Ningbo) Co., Ltd.), and 0.35g of ethyl cellulose. After mixing, add to 12.5g of N-methyl-2-pyrrolidone and ball mill at 350rpm for 3h to disperse to a particle size of D50≈0.8μm to obtain inorganic ink; (2) Molding and sintering: A piece of borosilicate glass (10cm×10cm) was used as a substrate. A 5wt% sodium chloride aqueous solution was spin-coated onto its surface at 1000 rpm and dried at 80°C to form a sacrificial layer. Inorganic ink was then scraped onto the sacrificial layer at 10mm / s and cured at 380°C in a nitrogen atmosphere for 5 hours. After the sample cooled, it was immersed in deionized water, and the inorganic layer automatically detached from the glass substrate. The sample was then gently rinsed with deionized water to remove residual salts on the surface and finally dried in an oven at 80°C to obtain an independent inorganic layer. (3) Preparation of polymer layer: Weigh 4 g of thermoplastic polyurethane (Shenzhen Baoan District Xingwang Plastic Raw Material Factory), 7.5 g of multi-walled carbon nanotubes (length-to-diameter ratio > 200, Suzhou Carbon Graphene Technology Co., Ltd.), 0.3 g of hydrogenated rosin glycerol ester, and 0.15 g of ethyl cellulose. Mix them and add them to 18 g of N-methyl-2-pyrrolidone. Disperse the mixture for 1 h at 2500 rpm using a high-speed shear emulsifier to obtain polymer ink. (4) Interlayer composite: The polymer ink is spin-coated onto the surface of the inorganic layer at 1500 rpm and cured at 150°C in a nitrogen atmosphere for 4 hours to form a dual-functional layer structure. (5) Electrode installation and encapsulation: Silver-based conductive adhesive is coated on both ends of the dual-functional layer and aluminum foil is attached. The mixture is then hot-pressed and cured for 12 hours at 100°C and 1.5MPa.

[0039] Example 3

[0040] The specific material composition and implementation steps of a novel electrothermal film material are as follows: (1) Inorganic layer preparation: Weigh 7.6g of Bi-Zn-B system glass powder (Shijiazhuang Lomat Glass Technology Co., Ltd., brand name LMT-B440), 7.2g of conductive carbon black (particle size of 50nm, Dongguan Kelude Innovation Technology Co., Ltd., model name Super PLi), 1.4g of carbon fiber (diameter of 7μm, Carbonene Technology (Shenzhen) Co., Ltd.), and 0.3g of stearic acid. After mixing, add to 18.5g of glycerol and ball mill at 400rpm for 3h to disperse to a particle size D50≈0.9μm to obtain inorganic ink; (2) Molding and Sintering: A smooth ordinary float glass (10cm × 10cm) was selected as the substrate. The glass substrate was ultrasonically cleaned with acetone and deionized water for 15 minutes in sequence and then dried. Graphene oxide (GO) dispersion was spin-coated onto the substrate at 1000 rpm, and then dried on a hot table at 80℃ for 10 minutes to form a GO sacrificial layer film. Inorganic ink was scraped onto the surface of the GO sacrificial layer film at 15 mm / s and cured at 450℃ in an argon atmosphere for 6 hours. Since the GO sacrificial layer had been reduced and deactivated at high temperature, the bonding force between the formed inorganic glass layer and the glass substrate was extremely weak. The complete inorganic layer could be peeled off from the glass substrate by gently lifting it from the corner with tweezers. (3) Preparation of polymer layer: Weigh 4.3 g of polyimide (Shenzhen Baoan District Xingwang Plastic Raw Material Factory), 8 g of conductive carbon black (particle size of 50 nm, Dongguan Kelude Innovation Technology Co., Ltd., model Super P Li), 0.35 g of L-ascorbic acid, and 0.35 g of stearic acid. Mix them and add them to 22 g of glycerol. Disperse the mixture for 1 h at 3000 rpm using a high-speed shear emulsifier to obtain polymer ink. (4) Interlayer composite: The polymer ink is spin-coated onto the surface of the inorganic layer at 2000 rpm and cured in an argon atmosphere at 80℃, 120℃ and 150℃ for 4 hours respectively to form a dual-functional layer structure. (5) Electrode installation and encapsulation: Silver-based conductive adhesive is coated on both ends of the dual-functional layer and copper foil is attached. The mixture is then hot-pressed and cured for 6 hours at 120°C and 1.5MPa.

[0041] Example 4

[0042] The specific material composition and implementation steps of a novel electrothermal film material are as follows: (1) Inorganic layer preparation: Weigh 8g of Bi-Zn-B system glass powder (Shijiazhuang Lomat Glass Technology Co., Ltd., brand name LIT-B490), 8.5g of activated carbon (particle size of 1μm, Bohuas Nanotechnology (Ningbo) Co., Ltd.), and 0.4g of stearic acid. After mixing, add to 30g of n-butanol and ball mill at 400rpm for 5h to disperse until the particle size D50≈0.95μm, to obtain inorganic ink; (2) Molding and Sintering: A high-quality mica sheet (10cm × 10cm) with a thickness of 0.1 mm was selected as the substrate. The mica sheet was ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for 15 minutes each, and then dried with nitrogen. Inorganic ink was applied to the substrate at 20mm / s and cured at 500℃ in an argon atmosphere for 2 hours. After sintering, the furnace temperature was allowed to cool naturally to below 60℃. The sample was removed, and a thin blade was inserted into the interface between the inorganic layer and the mica substrate from one corner of the sample. The blade was gently pried and pushed forward. Then, the entire inorganic layer was peeled off from the mica substrate with tweezers. (3) Preparation of polymer layer: Weigh 5 g of polyethersulfone resin (Dongguan Qimei Plastic Raw Material Co., Ltd.), 6.8 g of conductive carbon black (particle size of 40 nm, Guangdong Luwei New Material Co., Ltd., model Super P Li), 2.2 g of carbon fiber (diameter of 7 μm, Carbonene Technology (Shenzhen) Co., Ltd.), 0.5 g of L-ascorbic acid, and 0.35 g of stearic acid. Mix them and add them to 27 g of n-butanol. Disperse the mixture for 1.5 h at 3500 rpm using a high-speed shear emulsifier to obtain polymer ink. (4) Interlayer composite: The polymer ink is spin-coated onto the surface of the inorganic layer at 2500 rpm and cured at 280°C in an argon atmosphere for 6 hours to form a bifunctional layer structure. (5) Electrode installation and encapsulation: The conductive silver paste is directly printed onto both ends of the electrothermal film by dispensing, and then hot-pressed and cured for 6 hours at 150°C and 1.5 MPa.

[0043] Example 5

[0044] The specific material composition and implementation steps of a novel electrothermal film material are as follows: (1) Inorganic layer preparation: Weigh 5g of Sn-P-Zn system glass powder, 4g of acetylene black (particle size 45nm), and 0.1g of stearic acid. The Sn-P-Zn system glass powder was purchased from Hunyuan Junhong New Material Co., Ltd. (brand name D06), and the acetylene black was purchased from Dongguan Kelude Innovation Technology Co., Ltd. After mixing, add it to 10g of glycerol and ball mill at 500rpm for 10h to disperse it to a particle size D50≈0.5μm to obtain inorganic ink; (2) Molding and Sintering: A smooth quartz glass (10cm×10cm) was used as a substrate. The quartz glass substrate was ultrasonically cleaned for 15 minutes in sequence with acetone, anhydrous ethanol and deionized water, and then dried with nitrogen. A 10wt% sodium sulfate aqueous solution was spin-coated onto its surface at 1000 rpm and dried at 120℃ to form a sacrificial layer. Inorganic ink was then scraped onto the sacrificial layer at 50 mm / s and cured at 420℃ in a nitrogen atmosphere for 4 hours. After the sample cooled, it was immersed in deionized water at 30℃. The inorganic layer naturally separated from the quartz glass substrate. It was then gently rinsed with deionized water to remove residual salt on the surface and finally dried in an oven at 80℃ to obtain an independent inorganic layer. (3) Preparation of polymer layer: Weigh 3 g of thermoplastic polyurethane (Shenzhen Baoan District Xingwang Plastic Raw Material Factory), 4 g of N330 carbon black (particle size of 10 μm, Kelepu Chemical Products Co., Ltd.), 0.1 g of L-ascorbic acid, and 0.1 g of stearic acid. Mix them and add them to 10 g of glycerol. Disperse the mixture for 2 h at 5000 rpm using a high-speed shear emulsifier to obtain polymer ink. (4) Interlayer composite: The polymer ink is spin-coated onto the surface of the inorganic layer at 4000 rpm and cured at 180°C in a nitrogen atmosphere for 10 hours to form a dual-functional layer structure. (5) Electrode installation and encapsulation: Conductive copper paste is screen printed onto both ends of the electrothermal film and then hot-pressed and cured at 180℃ and 3MPa for 4 hours.

[0045] Comparative Example 1

[0046] An inorganic electrothermal film material, the specific material composition and steps of its implementation are as follows: (1) Inorganic layer preparation: Weigh 6.2g of VP-Sb system glass powder (Shijiazhuang Lomat Glass Technology Co., Ltd., brand name LMT-V390), 8.5g of conductive carbon black (particle size of 50nm, Dongguan Kelude Innovation Technology Co., Ltd., model name Super PLi), and 0.25g of paraffin (Xi'an Tianmao Baoding Biotechnology Co., Ltd.). After mixing, add it to 10.5g of dimethylformamide and ball mill at 300rpm for 2h to disperse it to a particle size D50≈0.6μm to obtain inorganic ink; (2) Molding and sintering: Take a 0.1 mm thick 304 stainless steel foil (10 cm × 10 cm), ultrasonically clean it with anhydrous ethanol and acetone, and dry it. Apply inorganic ink to the stainless steel foil at 5 mm / s and cure it at 400°C in a nitrogen atmosphere for 5 h. After cooling, the inorganic layer can be peeled off naturally or by slight external force; (3) Electrode installation and encapsulation: Silver-based conductive adhesive is coated on both ends of the inorganic electrothermal film and copper foil is attached. The film is then hot-pressed and cured for 6 hours at 80°C and 1MPa.

[0047] Comparative Example 2

[0048] A polymer-based electrothermal film material, the specific material composition and steps of its implementation are as follows: (1) Preparation of polymer layer: Weigh 3.5g of thermoplastic polyurethane (Shenzhen Baoan District Xingwang Plastic Raw Material Factory), 6.8g of multi-walled carbon nanotubes (length-to-diameter ratio > 200, Suzhou Carbon Graphene Technology Co., Ltd.), 0.35g of hydrogenated rosin glycerol ester, and 0.25g of ethyl cellulose. After mixing, add to 15g of dimethylformamide. Disperse the mixture for 0.5 h at 2000 rpm using a high-speed shear emulsifier to obtain polymer ink. (2) Molding and sintering: Take a 0.1 mm thick 304 stainless steel foil (10 cm × 10 cm), ultrasonically clean it with anhydrous ethanol and acetone and dry it. Spin-coat the polymer ink onto the surface of the stainless steel foil at 1000 rpm, cure it at 130 °C in a nitrogen atmosphere for 2 h, and after cooling, peel the polymer layer off the stainless steel foil to obtain a polymer-based electrothermal film; (3) Electrode installation and encapsulation: Silver-based conductive adhesive is coated on both ends of the polymer-based electrothermal film and copper foil is attached. The film is then hot-pressed and cured for 6 hours at 80°C and 1 MPa.

[0049] Comparative Example 3

[0050] The specific material composition and implementation steps of a novel electrothermal film material are as follows: (1) Inorganic layer preparation: Weigh 6.2g of VP-Sb system glass powder (Shijiazhuang Lomat Glass Technology Co., Ltd., brand name LMT-V390), 8.5g of conductive carbon black (particle size of 50nm, Dongguan Kelude Innovation Technology Co., Ltd., model name Super PLi), and 0.25g of paraffin (Xi'an Tianmao Baoding Biotechnology Co., Ltd.). After mixing, add it to 10.5g of dimethylformamide and ball mill at 300rpm for 2h to disperse it to a particle size D50≈0.6μm to obtain inorganic ink; (2) Inorganic layer forming and sintering: Take a 0.1 mm thick 304 stainless steel foil (10 cm × 10 cm), ultrasonically clean it with anhydrous ethanol and acetone, and dry it. Apply inorganic ink to the stainless steel foil at 5 mm / s and cure it at 400 °C in a nitrogen atmosphere for 5 h. After cooling, the inorganic layer can be peeled off naturally or by slight external force; (3) Preparation of polymer layer: Weigh 3.5g of thermoplastic polyurethane (Shenzhen Baoan District Xingwang Plastic Raw Material Factory), 6.8g of multi-walled carbon nanotubes (length-to-diameter ratio > 200, Suzhou Carbon Graphene Technology Co., Ltd.), 0.35g of hydrogenated rosin glycerol ester, and 0.25g of ethyl cellulose. Mix them and add them to 15g of dimethylformamide. Disperse the mixture for 0.5 h at 2000 rpm using a high-speed shear emulsifier to obtain polymer ink. (4) Polymer layer molding and sintering: The polymer ink was spin-coated onto the cleaned surface of 304 stainless steel foil (10cm×10cm) at 1000 rpm and cured at 130℃ in a nitrogen atmosphere for 2 hours. After cooling, the polymer layer was peeled off from the stainless steel foil, and the inorganic layer electrothermal film and the polymer layer electrothermal film were simply physically bonded together to obtain a double-layer film; (5) Electrode installation and encapsulation: Silver-based conductive adhesive is coated on both ends of the double-layer film and copper foil is attached. The film is then hot-pressed and cured for 6 hours at 80°C and 1 MPa.

[0051] Comparative Example 4

[0052] An inorganic-polymer composite electrothermal film material, the specific material composition and steps of its implementation are as follows: (1) Ink preparation: Weigh 6.2g of VP-Sb system glass powder (Shijiazhuang Lomat Glass Technology Co., Ltd., brand name LMT-V390), 8.5g of conductive carbon black (particle size of 50nm, Dongguan Kelude Innovation Technology Co., Ltd., model name Super PLi), and 0.25g of paraffin (Xi'an Tianmao Baoding Biotechnology Co., Ltd.). After mixing, add it to 10.5g of dimethylformamide and ball mill at 300rpm for 2h to disperse it to a particle size D50≈0.6μm to obtain inorganic slurry. Weigh out 3.5g of thermoplastic polyurethane (Shenzhen Baoan District Xingwang Plastic Raw Material Factory), 6.8g of multi-walled carbon nanotubes (aspect ratio > 200, Suzhou Carbonfeng Graphene Technology Co., Ltd.), 0.35g of hydrogenated rosin glycerol ester, 0.25g of ethyl cellulose, and 15g of dimethylformamide. Mix them and add them to the inorganic slurry. Disperse the mixture for 0.5 h at 2000 rpm using a high-speed shear emulsifier to obtain the inorganic-polymer composite electrothermal film ink. (2) Molding and sintering: Take a 0.1 mm thick 304 stainless steel foil (10 cm × 10 cm), ultrasonically clean it with anhydrous ethanol and acetone, and dry it. Apply ink to the stainless steel foil at 5 mm / s and cure it at 400 °C in a nitrogen atmosphere for 5 h. After cooling, an inorganic-polymer composite electrothermal film material is obtained; (3) Electrode installation and encapsulation: Silver-based conductive adhesive is coated on both ends of the inorganic-polymer composite electrothermal film material and copper foil is attached. The material is then hot-pressed and cured for 6 hours at 80°C and 1 MPa.

[0053] Comparative Example 5

[0054] The specific material composition and implementation steps of a novel electrothermal film material are as follows: (1) Inorganic layer preparation: Weigh 6.2g of VP-Sb system glass powder (Shijiazhuang Lomat Glass Technology Co., Ltd., brand name LMT-V390), 8.5g of conductive carbon black (particle size of 50nm, Dongguan Kelude Innovation Technology Co., Ltd., model name Super PLi), and 0.25g of paraffin (Xi'an Tianmao Baoding Biotechnology Co., Ltd.). After mixing, add it to 10.5g of dimethylformamide and ball mill at 300rpm for 2h to disperse it to a particle size D50≈0.6μm to obtain inorganic ink; (2) Molding and sintering: Take a 0.1 mm thick 304 stainless steel foil (10 cm × 10 cm), ultrasonically clean it with anhydrous ethanol and acetone, and dry it. Apply inorganic ink to the stainless steel foil at 5 mm / s and cure it at 400°C in a nitrogen atmosphere for 5 h. After cooling, the inorganic layer can be peeled off naturally or by slight external force; (3) Preparation of polymer layer: Weigh 3.5g of thermoplastic polyurethane (Shenzhen Baoan District Xingwang Plastic Raw Material Factory), 8.5g of multi-walled carbon nanotubes (length-to-diameter ratio > 200, Suzhou Carbon Graphene Technology Co., Ltd.), 0.35g of hydrogenated rosin glycerol ester, and 0.25g of ethyl cellulose. Mix them and add them to 15g of dimethylformamide. Disperse the mixture for 0.5 h at 2000 rpm using a high-speed shear emulsifier to obtain polymer ink. (4) Interlayer composite: The polymer ink is spin-coated onto the surface of the inorganic layer at 1000 rpm and cured at 130°C in a nitrogen atmosphere for 2 hours to form a dual-functional layer structure. (5) Electrode installation and encapsulation: Silver-based conductive adhesive is coated on both ends of the dual-functional layer and copper foil is attached. The mixture is then hot-pressed and cured for 6 hours at 80°C and 1MPa.

[0055] Comparative Example 6

[0056] The specific material composition and implementation steps of a novel electrothermal film material are as follows: (1) Inorganic layer preparation: Weigh 6.2g of VP-Sb system glass powder (Shijiazhuang Lomat Glass Technology Co., Ltd., brand name LMT-V390), 8.5g of conductive carbon black (particle size of 50nm, Dongguan Kelude Innovation Technology Co., Ltd., model name Super PLi), and 0.25g of paraffin (Xi'an Tianmao Baoding Biotechnology Co., Ltd.). After mixing, add it to 10.5g of dimethylformamide and ball mill at 300rpm for 2h to disperse it to a particle size D50≈0.6μm to obtain inorganic ink; (2) Molding and sintering: Take a 0.1 mm thick 304 stainless steel foil (10 cm × 10 cm), ultrasonically clean it with anhydrous ethanol and acetone, and dry it. Apply inorganic ink to the stainless steel foil at 5 mm / s and cure it at 400°C in a nitrogen atmosphere for 5 h. After cooling, the inorganic layer can be peeled off naturally or by slight external force; (3) Preparation of polymer layer: Weigh 3.5g of thermoplastic polyurethane (Shenzhen Baoan District Xingwang Plastic Raw Material Factory), 5.1g of multi-walled carbon nanotubes (length-to-diameter ratio > 200, Suzhou Carbon Graphene Technology Co., Ltd.), 0.35g of hydrogenated rosin glycerol ester, and 0.25g of ethyl cellulose. Mix them and add them to 15g of dimethylformamide. Disperse the mixture for 0.5 h at 2000 rpm using a high-speed shear emulsifier to obtain polymer ink. (4) Interlayer composite: The polymer ink is spin-coated onto the surface of the inorganic layer at 1000 rpm and cured at 130°C in a nitrogen atmosphere for 2 hours to form a dual-functional layer structure. (5) Electrode installation and encapsulation: Silver-based conductive adhesive is coated on both ends of the dual-functional layer and copper foil is attached. The mixture is then hot-pressed and cured for 6 hours at 80°C and 1MPa.

[0057] Test case

[0058] The electrothermal film materials obtained in the above embodiments and comparative examples, when voltages of 2V, 3V, and 4V are applied to their two ends respectively, can rapidly heat up to the equilibrium temperature within 200 seconds from a starting temperature of 30°C, exhibiting excellent heating performance. Specific data are shown in Table 1 below:

[0059] The following tests were performed on the electrothermal film materials obtained in Example 1 and Comparative Examples 1-6 above: 1) Bending resistance test: Measure the initial resistance R0 of the sample in a flat state without bending, connect the electrodes, apply a 3V voltage, and start a periodic 180° "bending-recovery" cycle at a frequency of 20 times per minute. After 150 bends, measure the final resistance R and calculate the resistance change rate (ΔR / R0). 2) Compression resistance test: Place the sample between two parallel plates of the press, connect the electrodes, apply a 3V voltage, apply pressure at 1 mm / min, increase from 0 MPa to 3 MPa, measure the initial current I0 and the final current I, and calculate the resistance change rate (ΔR / R0 = I0 / I - 1).

[0060] The obtained data is shown in Table 2 below:

[0061] The electrothermal film samples prepared in Example 1 and Comparative Examples 1-4 were placed in a high and low temperature test chamber and subjected to temperature cycling tests at -40℃ (30 min) and 120℃ (30 min), with a temperature transition time of less than 1 minute. After 200 cycles, the resistance change rate (ΔR / R0) of the samples under a 2V DC voltage was measured at room temperature. The test results are shown in Table 3.

[0062] Comparative Example 1 is an entirely inorganic material with typically low resistivity. To achieve suitable operating power, it requires a high driving voltage, resulting in poor safety. It also has a large heat capacity and slow thermal response. Furthermore, as a single material, it is prone to cracking due to thermal shock.

[0063] Comparative Example 2 is an all-polymer material. The polymer matrix is ​​easily deformed under bending or pressure, leading to distortion of the conductive path between the upper and lower electrodes or direct contact, resulting in an extremely high risk of short circuit. Under long-term thermal aging, the polymer's molecular chains break and oxidize, causing significant drift in resistance, short lifespan, and inability to operate at high temperatures for extended periods.

[0064] Comparative Example 3 shows only physical contact between the layers, resulting in weak interfacial bonding. Under stress, interfacial misalignment is prone to occur, leading to electrode isolation failure and a high risk of short circuits. While flexibility is acceptable, poor interfacial bonding causes stress concentration at the interface during bending or thermal cycling, making delamination and peeling highly likely. High and unstable interfacial contact resistance leads to high and fluctuating total resistance, increased energy consumption, poor linear temperature control accuracy, and response characteristics affected by the interface.

[0065] In Comparative Example 4, the electrodes are made of a homogeneous composite material without an inherent physical insulating layer, still posing a risk of short circuits under localized damage or high voltage. The brittle inorganic particles have poor compatibility with the flexible polymer matrix, leading to increased material brittleness, decreased flexibility, and a tendency to develop microcracks during bending. The conductive path is blocked by the polymer phase, requiring a higher filler content to achieve conductivity, resulting in a higher driving voltage. Poor material homogeneity leads to poor temperature control linearity. The interface between the inorganic filler and the polymer matrix is ​​prone to debonding and microcracks under thermal stress, resulting in significant performance degradation after multiple cycles.

[0066] Comparative Example 5 (with a 25% increase in CNT content in the polymer layer) had an equilibrium temperature higher than Example 1 at all voltages, reaching 75.3°C at 4V; Comparative Example 6 (with a 25% decrease in CNT content in the polymer layer) had an equilibrium temperature lower than Example 1 at all voltages, reaching 51.9°C at 4V. The filler content and equilibrium temperature showed a good linear relationship, demonstrating that precise temperature presets can be achieved by adjusting the polymer layer composition.

[0067] The heating film in Example 1 was first operated at 12V for 3 minutes, and then the operating temperature was gradually increased to 120°C. After stabilizing for 5 minutes, the voltage was increased again to raise the temperature to 150°C within 10 seconds. Then the voltage was adjusted back to 12V. At this time, the heating film could still work normally, while the heating films of Comparative Examples 1-3, which were operated in the same way, had already been damaged. This shows that the present invention can be used for long-term stable operation at 40°C to 120°C and can withstand higher instantaneous temperatures.

[0068] Furthermore, a control experiment was conducted by setting the film thickness in Example 1 outside the range defined by this invention. The results showed that the electrothermal film material in control group 1 had many defects and could not function properly; the electrothermal film material in control group 2 could function, but due to its excessive rigidity, the film was prone to bending, reducing safety. Specific conditions and results are shown in Table 4 below:

[0069] This invention creatively and successfully constructs an organic-inorganic synergistic system with a robust interface and clear functional division. This structure not only combines rigidity and flexibility, but also fundamentally overcomes the shortcomings of the aforementioned comparative model, meeting the stringent requirements of high-end flexible heating devices for comprehensive performance.

[0070] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications may be made without departing from the technical solutions described in the claims.

Claims

1. A graded adjustable resistance composite electrothermal film material, characterized in that, The electrothermal film has a multi-layer composite structure, which includes, from top to bottom: a first electrode layer, a polymer-conductive carbon composite functional layer, an inorganic glass powder-conductive carbon composite functional layer, and a second electrode layer. The polymer-conductive carbon composite functional layer forms an adjustable resistance layer R1, and the inorganic glass powder-conductive carbon composite functional layer forms a stable resistance layer R2. The total resistance of the electrothermal film is R = R1 + R2.

2. The graded adjustable resistance composite electrothermal film material according to claim 1, characterized in that, The thickness of the polymer-conductive carbon composite functional layer is 50~200μm, the thickness of the inorganic glass powder-conductive carbon composite functional layer is 50~100μm, and the overall thickness of the electrothermal film material is 400~1000μm.

3. The graded adjustable resistance composite electrothermal film material according to claim 1, characterized in that, The raw materials for the electrothermal film material include conductive carbon filler, inorganic glass powder, and polymer.

4. The graded adjustable resistance composite electrothermal film material according to claim 3, characterized in that, The conductive carbon filler is selected from at least one of acetylene black, conductive carbon black, carbon nanotubes, carbon fibers, activated carbon, and spherical graphite.

5. The graded adjustable resistance composite electrothermal film material according to claim 3, characterized in that, The inorganic glass powder is selected from at least one of the low-melting-point lead-free glass systems, with a melting point not exceeding 460°C; And / or, the inorganic glass powder is selected from at least one of the Bi-Zn-B, VP-Sb, Zn-B-Si, and Sn-P-Zn systems.

6. The graded adjustable resistance composite electrothermal film material according to claim 3, characterized in that, The polymer is a high-temperature resistant polymer material, and its glass transition temperature is not less than 20°C higher than the working temperature of the composite electrothermal film material. And / or, the polymer is selected from at least one of polyethersulfone resin, polyetheretherketone, polyimide, polyphenylene sulfide, and polyurethane.

7. A method for preparing a graded adjustable resistance composite electrothermal film material as described in any one of claims 1 to 6, characterized in that, Includes the following steps: (1) Preparation of inorganic glass powder-conductive carbon composite functional layer: Mix 50-80 parts of inorganic glass powder, 40-90 parts of conductive carbon filler, 1-4 parts of surface modifier and 100-300 parts of liquid dispersant, and disperse by ball milling until the particle size D50≤1μm to obtain inorganic ink; (2) Molding and sintering: The inorganic ink is scraped onto the substrate and cured at 350~500℃ for 2~12h in an inert atmosphere. The resulting inorganic layer is separated from the substrate to form an inorganic glass powder-conductive carbon composite functional layer. (3) Preparation of polymer-conductive carbon composite functional layer: Mix 30-50 parts of polymer, 40-90 parts of conductive carbon filler, 1-5 parts of antioxidant, 1-4 parts of surface modifier and 100-300 parts of liquid dispersant, and disperse to obtain polymer ink; (4) Interlayer composite: The polymer ink is spin-coated onto the surface of the inorganic glass powder-conductive carbon composite functional layer and cured at 80~300℃ for 2~12h in an inert atmosphere to form a dual-functional layer structure. (5) Install electrodes: Install electrodes at both ends of the dual-functional layer and heat-press to cure.

8. The method for preparing a graded adjustable resistance composite electrothermal film material according to claim 7, characterized in that, The surface modifier mentioned in steps (1) and (3) is selected from at least one of paraffin wax, ethyl cellulose, stearic acid, polyvinyl butyral, and polyvinyl alcohol; the liquid dispersant mentioned in steps (1) and (3) is selected from at least one of dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, isopropanol, n-butanol, ethanol, glycerol, and distilled water; the antioxidant mentioned in step (3) is selected from at least one of hydrogenated rosin glycerol ester, L-ascorbic acid, and dilauryl thiodipropionate.

9. The method for preparing a graded adjustable resistance composite electrothermal film material according to claim 7, characterized in that, The substrate in step (2) is capable of separating the inorganic layer on it after sintering and curing; the hot pressing curing temperature in step (5) is 80~180℃, the pressure is 1~3 MPa, and the time is 3~12h.

10. The application of the graded adjustable resistance composite electrothermal film material according to any one of claims 1 to 6 or the graded adjustable resistance composite electrothermal film material prepared by any one of claims 7 to 9 in a high power density flexible heating device.

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