CNT single-sided directional heating film and preparation method thereof

Abstract

The invention relates to a CNT single-sided directional heating film and a preparation method thereof, and belongs to the technical field of heating materials. Polyurethane containing carbon nanofibers is prepared to serve as a heating film, the heating performance is remarkably improved, in addition, melamine polyphosphate and tricresyl phosphate serve as flame retardants, modified nanosilicon dioxide serves as an insulating agent to be mixed with polyurethane and auxiliaries, a flame-retardant insulating layer is formed on the heating film in a curtain coating mode, and the heating performance is improved. The insulation flame-retardant performance is improved, and the comprehensive energy consumption is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of heating materials, and relates to a CNT single-sided directional heating film and a preparation method thereof. Background Art

[0002] As an emerging heating technology material, heating films have been widely used in many fields in recent years. The main types of heating films include graphene heating films and carbon fiber heating films. Graphene heating films have attracted attention due to their excellent electrical conductivity and thermal conductivity. However, their preparation cost is relatively high, and uneven heating is likely to occur in large-area applications. Carbon fiber heating films are known for their good thermal stability and mechanical properties. However, due to the lower electrical conductivity of carbon fiber compared to graphene, there are certain limitations in achieving rapid temperature rise and uniform heating. In addition, both of these heating films may have a relatively large energy consumption during use, especially in the case of long-term continuous heating, which poses higher requirements for energy conservation and environmental protection.

[0003] As a new type of heating material, nano-carbon fiber heating films have attracted much attention because they can generate far-infrared rays after being powered on. The wavelength band of far-infrared rays is close to that of the sun's far-infrared rays, which is beneficial to human health. However, nano-carbon fiber heating films still face some technical challenges in practical applications. First of all, due to the uneven distribution of nano-carbon fibers, the heating effect of the heating film is uneven, which not only affects the user experience but may also cause local overheating, thus shortening the service life of the product. Secondly, although the electrical conductivity and thermal conductivity of nano-carbon fibers are better than those of traditional carbon fibers, in large-area applications, there is still a problem of relatively large energy consumption, which is closely related to the resistivity and structural design of the material itself. Therefore, how to optimize the distribution and structural design of nano-carbon fibers to achieve efficient energy utilization has become the focus of current technology research and development.

[0004] To address the above problems, the present invention prepares a polyurethane film containing nano-carbon fibers, and uses modified silica as an insulating agent on its back, and combines materials such as flame retardants to cast a flame-retardant insulating layer. This design not only effectively improves the uniformity of the heating film, making the heating more uniform, but also reduces energy consumption. In addition, the addition of the flame-retardant insulating layer improves the safety of the heating film, making it more stable in high-temperature environments. Summary of the Invention

[0005] The present invention relates to a CNT single-sided directional heating film and a preparation method thereof, belonging to the technical field of heating materials. The present invention prepares a polyurethane containing nano-carbon fibers as the heating film, significantly improving the heating performance. In addition, melamine polyphosphate and tricresyl phosphate are used as flame retardants, and modified nano-silica is used as an insulating agent to mix with polyurethane and additives, and a flame-retardant insulating layer is formed by casting on the heating film to improve the insulation and flame-retardant performance and reduce the comprehensive energy consumption.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] A CNT single-sided directional heating film is composed of a front heating layer and a back flame-retardant insulating layer.

[0008] As a preferred technical solution of the present invention, the component of the front heating layer is polyurethane containing CNT.

[0009] As a preferred technical solution of the present invention, the preparation method of the polyurethane containing CNT is as follows: Add 25-45 parts by weight of polyether polyol and 5-15 parts by weight of modified CNT into a reaction kettle, heat to 80-100 °C, stir for 30-90 minutes, add 30-50 parts by weight of diisocyanate and 1-5 parts by weight of catalyst, continue to stir for 30-60 minutes, lower the temperature to 70-80 °C, add 10-20 parts by weight of chain extender and stir for 1-2 hours, after cooling, defoam in a vacuum device and then carry out curing treatment at 100-120 °C for 2-4 hours to obtain the polyurethane containing CNT.

[0010] As a preferred technical solution of the present invention, the modified CNT is hydroxylated CNT, and the preparation method is: Configure a mixed acid solution with a volume ratio of concentrated nitric acid to concentrated sulfuric acid of 1:3-4, add CNT into the mixed acid solution, stir at 20-40 °C for 2-4 hours, and obtain the modified CNT through filtration, washing and drying.

[0011] As a preferred technical solution of the present invention, the raw materials of the back flame-retardant insulating layer include 65-80 parts by weight of polyether-type polyurethane, 1-3 parts by weight of dispersant, 0.5-1 part by weight of coupling agent, 1-2 parts by weight of softener, 15-25 parts by weight of flame retardant and 2-5 parts by weight of insulating agent.

[0012] As a preferred technical solution of the present invention, the dispersant is a polyether-type dispersant, the coupling agent is a silane coupling agent, the softener is a polysiloxane softener, the flame retardant is melamine polyphosphate and tricresyl phosphate, and the insulating agent is modified nano-silica.

[0013] As a preferred technical solution of the present invention, the specific preparation method of the modified silica is: Dry nano-silica at 110-130 °C for 2-6 hours, dissolve isocyanatopropyltriethoxysilane in absolute ethanol and then add the dried nano-silica, stir at 50-70 °C for 4-12 hours, and after filtration, wash with absolute ethanol and then vacuum dry at 60-80 °C for 3-5 hours.

[0014] As a preferred technical solution of the present invention, the mass ratio of isocyanatopropyltriethoxysilane to nano-silica is 1:10-100.

[0015] Furthermore, the preparation method of the CNT single-sided directional heating film includes the following steps:

[0016] (1) Stir and melt the polyurethane containing CNT at 180 - 200 °C under a pressure of 10 - 20 MPa, and coat it through a coater to form a film with a thickness of 0.01 - 0.1 mm as the front heating layer;

[0017] (2) Stir and melt the raw materials of the back flame-retardant insulating layer at 180 - 200 °C under a pressure of 10 - 20 MPa, and cast a film with a thickness of 0.01 - 0.1 mm on the front heating layer with a casting machine as the back flame-retardant insulating layer;

[0018] (3) Place the material in a heat treatment device, set the heating rate at 2 - 5 °C per minute, the maximum temperature at 80 - 120 °C, treat for 1 - 2 hours, and obtain the CNT single-sided directional heating film after cooling.

[0019] Advantages of the present invention:

[0020] (1) The present invention uses the polyurethane containing CNT prepared from polyether polyol, hydroxyl-modified CNT and diisocyanate as the heating film. Compared with the polymer film mixed with CNT, the CNT is evenly dispersed and has a strong binding force with the polymer. The heating of the heating film is more uniform and the energy consumption is less.

[0021] (2) The present invention modifies the insulating agent nano-silica with isocyanatopropyltriethoxysilane, making the nano-silica evenly distributed in the polyurethane material, achieving good insulation effect with less addition of nano-silica, and not affecting the softness and comfort of the heating material.

[0022] (3) The present invention uses polyether polyol when preparing the polyurethane containing CNT and polyether-type polyurethane when preparing the flame-retardant insulating layer. The obtained heating material has excellent flexibility and elasticity, is not easy to break or damage during use as a wearable warming product, and extends the service life; it has good hydrolysis resistance, can maintain its physical properties and structural integrity in a humid and water-containing environment, still maintains its complete function after washing, and is safer and more reliable; it can still maintain good flexibility and elasticity at low temperatures, will not become hard or brittle, enabling the heating film to still work reliably in a cold environment and having a wider scope of application.

[0023] (4) The present invention further heat-treats the cast heating film, which can promote the rearrangement of molecular chains inside the material, improve the crystallinity, thereby enhancing the mechanical strength and thermal stability of the film; the internal stress that may be introduced during the preparation process can be released through heat treatment, reducing the deformation and warping of the material and improving the stability. Specific embodiments

[0024] To further elaborate on the technical means and effects adopted by the present invention to achieve the intended invention purpose, the following, in conjunction with embodiments, details the specific implementation manners, structures, features and their effects according to the present invention as follows.

[0025] In the following examples and comparative examples, the polypropylene glycol was purchased from Wuhan Jushun Chemical Co., Ltd.; the carbon nanotubes were purchased from Turing New Materials Co., Ltd., with the model number TL300; the polyether-type polyurethane was purchased from Jinshu Teng Plastics Co., Ltd., with the product number 95A; the polyether-type dispersant was purchased from Hai'an Petrochemical Factory, with the model number OP-10; the silane coupling agent was purchased from Bosheng Chemical Co., Ltd., with the product number KH570; the polysiloxane softener was purchased from Zhonghe Shengtai Chemical Co., Ltd., with the product number PMX-200; the melamine polyphosphate was purchased from Quzhou Weikai Chemical Co., Ltd.; the nano-silica was purchased from Huifu Nano Materials Co., Ltd., with the product number HB139.

[0026] Example 1

[0027] A CNT single-sided directional heating film is composed of a front heating layer and a back flame-retardant insulating layer.

[0028] The component of the front heating layer is polyurethane containing CNT.

[0029] The preparation method of the polyurethane containing CNT is as follows: Add 35 parts by weight of polyether polyol (polypropylene glycol) and 10 parts by weight of modified CNT into a reaction kettle, heat to 90 °C, stir for 60 minutes, add 40 parts by weight of toluene diisocyanate and 2 parts by weight of catalyst stannous octoate, continue to stir for 40 minutes, lower the temperature to 70 °C, add 15 parts by weight of chain extender (1,4-butanediol) and stir for 2 hours, cool and then defoam in a vacuum device to improve the quality of the polyurethane, and then carry out a 3-hour curing treatment at 110 °C to further crosslink and cure the polyurethane to obtain the polyurethane containing CNT.

[0030] The modified CNT is hydroxylated CNT, and the preparation method is: Prepare a mixed acid solution with a volume ratio of 65% concentrated nitric acid and 98% concentrated sulfuric acid of 1:3, add the CNT into the mixed acid solution, stir at 30 °C for 3 hours, and obtain the modified CNT through washing, filtering and drying.

[0031] The mass ratio of the CNT to the mixed acid is 1:10.

[0032] The raw materials of the back flame-retardant insulating layer include 70 parts by weight of polyether-type polyurethane, 2 parts by weight of dispersant, 1 part by weight of coupling agent, 2 parts by weight of softener, 20 parts by weight of flame retardant and 3 parts by weight of insulating agent.

[0033] The dispersant is a polyether-type dispersant, the coupling agent is a silane coupling agent, the softener is a polysiloxane softener, the flame retardant is a mixture of melamine polyphosphate and tricresyl phosphate in a mass ratio of 1:1, and the insulating agent is modified nano-silica.

[0034] The preparation method of the modified silica is as follows: The nano-silica is dried at 120 °C for 4 hours to remove the adsorbed moisture on the surface, which helps the subsequent attachment of the silane coupling agent; isocyanatopropyltriethoxysilane is dissolved in absolute ethanol and then added to the dried nano-silica, and stirred at 60 °C for 8 hours to cause the ethoxy groups of the silane coupling agent to undergo hydrolysis condensation reaction with the hydroxyl groups on the surface of the nano-silica to form silicon-oxygen bonds; after filtration and washing with absolute ethanol, it is vacuum dried at 70 °C for 4 hours.

[0035] The mass ratio of the isocyanatopropyltriethoxysilane to the nano-silica is 1:50.

[0036] The preparation method of a CNT single-sided directional heating film includes the following steps:

[0037] (1) The polyurethane containing CNT is stirred and melted at 190 °C under a pressure of 15 MPa, and coated by a coater to form a film with a thickness of 0.05 mm as the front heating layer;

[0038] (2) The raw materials of the back flame-retardant insulating layer are stirred and melted at 190 °C under a pressure of 15 MPa, and cast on the front heating layer by a casting machine to form a film with a thickness of 0.03 mm as the back flame-retardant insulating layer;

[0039] (3) The material is placed in a heat treatment device, the heating rate is set at 3 °C per minute, the maximum temperature is 100 °C, and it is treated for 2 hours. After cooling, the CNT single-sided directional heating film is obtained.

[0040] Example 2

[0041] A CNT single-sided directional heating film is composed of a front heating layer and a back flame-retardant insulating layer.

[0042] The component of the front heating layer is polyurethane containing CNT.

[0043] The preparation method of the polyurethane containing CNT is as follows: 40 parts by weight of polyether polyol (polypropylene glycol) and 10 parts by weight of modified CNT are added to a reaction kettle, heated to 100 °C, stirred for 30 minutes, 40 parts by weight of diphenylmethane diisocyanate and 2 parts by weight of catalyst stannous octoate are added, and stirring is continued for 40 minutes. The temperature is lowered to 80 °C, 10 parts by weight of chain extender (1,4-butanediol) is added and stirred for 1 hour. After cooling, it is defoamed in a vacuum device to improve the quality of the polyurethane, and then subjected to a curing treatment at 120 °C for 2 hours to further crosslink and cure the polyurethane, and the polyurethane containing CNT is obtained.

[0044] The modified CNT is hydroxylated CNT, and the preparation method is as follows: Prepare a mixed acid solution with a volume ratio of 65% concentrated nitric acid to 98% concentrated sulfuric acid of 1:4. Add CNT to the mixed acid solution, stir at 40 °C for 2 hours, and obtain the modified CNT through washing, filtration, and drying.

[0045] The mass ratio of the CNT to the mixed acid is 1:10.

[0046] The raw materials of the back flame-retardant insulating layer include 80 parts by weight of polyether-type polyurethane, 2 parts by weight of dispersant, 1 part by weight of coupling agent, 2 parts by weight of softener, 25 parts by weight of flame retardant, and 5 parts by weight of insulating agent.

[0047] The dispersant is a polyether-type dispersant, the coupling agent is a silane coupling agent, the softener is a polysiloxane softener, the flame retardant is a mixture of melamine polyphosphate and tricresyl phosphate in a mass ratio of 1:2, and the insulating agent is modified nano-silica.

[0048] The specific preparation method of the modified silica is as follows: Dry the nano-silica at 120 °C for 4 hours to remove the adsorbed moisture on the surface, which helps the subsequent attachment of the silane coupling agent; Dissolve isocyanatopropyltriethoxysilane in absolute ethanol and then add the dried nano-silica, stir at 50 °C for 12 hours to cause the ethoxy groups of the silane coupling agent to undergo hydrolysis and condensation reaction with the hydroxyl groups on the surface of the nano-silica to form silicon-oxygen bonds; Through filtration, wash with absolute ethanol and then vacuum dry at 70 °C for 4 hours.

[0049] The mass ratio of the isocyanatopropyltriethoxysilane to the nano-silica is 1:40.

[0050] The preparation method of a CNT single-sided directional heating film includes the following steps:

[0051] (1) Stir and melt the polyurethane containing CNT at 190 °C under a pressure of 15 MPa, and form a film with a thickness of 0.05 mm by coating with a coater as the front heating layer;

[0052] (2) Stir and melt the raw materials of the back flame-retardant insulating layer at 190 °C under a pressure of 15 MPa, and cast a film with a thickness of 0.03 mm on the front heating layer with a casting machine as the back flame-retardant insulating layer;

[0053] (3) Place the material in a heat treatment device, set the heating rate at 3 °C per minute, the maximum temperature at 120 °C, process for 2 hours, and obtain the CNT single-sided directional heating film after cooling.

[0054] Comparative Example 1

[0055] A CNT single-sided directional heating film is composed of a front heating layer and a back flame-retardant insulating layer.

[0056] The raw materials of the front heating layer include: 85 parts by weight of polyether-type polyurethane, 3 parts by weight of dispersant, 2 parts by weight of coupling agent, and 10 parts by weight of CNT.

[0057] The raw materials of the back flame-retardant insulating layer include 70 parts by weight of polyether-type polyurethane, 2 parts by weight of dispersant, 1 part by weight of coupling agent, 2 parts by weight of softening agent, 20 parts by weight of flame retardant, and 3 parts by weight of insulating agent.

[0058] The dispersant is a polyether-type dispersant, the coupling agent is a silane coupling agent, the softening agent is a polysiloxane softening agent, the flame retardant is a mixture of melamine polyphosphate and tricresyl phosphate in a mass ratio of 1:1, and the insulating agent is modified nano-silica.

[0059] The specific preparation method of the modified silica is as follows: The nano-silica is dried at 120 °C for 4 hours to remove the adsorbed moisture on the surface, which helps the subsequent attachment of the silane coupling agent; The isocyanatopropyltriethoxysilane is dissolved in anhydrous ethanol and then added to the dried nano-silica, and stirred at 60 °C for 8 hours to cause the ethoxy group of the silane coupling agent to undergo hydrolysis and condensation reaction with the hydroxyl group on the surface of the nano-silica to form a silicon-oxygen bond; After filtration and washing with anhydrous ethanol, it is vacuum dried at 70 °C for 4 hours.

[0060] The mass ratio of the isocyanatopropyltriethoxysilane to the nano-silica is 1:50.

[0061] The preparation method of the CNT single-sided directional heating film includes the following steps:

[0062] (1) The raw materials of the heating layer are stirred and melted at 190 °C under a pressure of 15 MPa, and formed into a film with a thickness of 0.05 mm by a coater as the front heating layer;

[0063] (2) The raw materials of the back flame-retardant insulating layer are stirred and melted at 190 °C under a pressure of 15 MPa, and cast on the front heating layer by a casting machine to form a film with a thickness of 0.03 mm as the back flame-retardant insulating layer;

[0064] (3) The material is placed in a heat treatment device, the heating rate is set at 3 °C per minute, the highest temperature is 100 °C, and it is treated for 2 hours, and then cooled to obtain the CNT single-sided directional heating film.

[0065] Comparative Example 2

[0066] A CNT single-sided directional heating film is composed of a front heating layer and a back flame-retardant insulating layer.

[0067] The composition of the front heating layer is polyurethane containing CNT.

[0068] The preparation method of the CNT-containing polyurethane is as follows: Add 35 parts by weight of polyether polyol (polypropylene glycol) and 10 parts by weight of modified CNT into a reaction kettle, heat to 90 °C, stir for 60 minutes, add 40 parts by weight of toluene diisocyanate and 2 parts by weight of catalyst stannous octoate, continue to stir for 40 minutes, lower the temperature to 70 °C, add 15 parts by weight of chain extender (1,4-butanediol) and stir for 2 hours. After cooling, defoam in a vacuum device to improve the quality of the polyurethane, and then carry out a curing treatment at 110 °C for 3 hours to further crosslink and cure the polyurethane, thereby obtaining the CNT-containing polyurethane.

[0069] The modified CNT is hydroxylated CNT, and the preparation method is as follows: Prepare a mixed acid solution with a volume ratio of 65% concentrated nitric acid to 98% concentrated sulfuric acid of 1:3. Add CNT into the mixed acid solution, stir at 30 °C for 3 hours, and obtain the modified CNT through washing, filtration, and drying.

[0070] The mass ratio of the CNT to the mixed acid is 1:10.

[0071] The raw materials of the back flame-retardant insulation layer include 70 parts by weight of polyether-type polyurethane, 2 parts by weight of dispersant, 1 part by weight of coupling agent, 2 parts by weight of softener, 20 parts by weight of flame retardant, and 3 parts by weight of insulating agent.

[0072] The dispersant is a polyether-type dispersant, the coupling agent is a silane coupling agent, the softener is a polysiloxane softener, the flame retardant is a mixture of melamine polyphosphate and tricresyl phosphate with a mass ratio of 1:1, and the insulating agent is nano-silica.

[0073] The preparation method of a CNT single-sided directional heating film includes the following steps:

[0074] (1) Stir and melt the CNT-containing polyurethane at 190 °C under a pressure of 15 MPa, and form a film with a thickness of 0.05 mm by coating with a coater as the front heating layer;

[0075] (2) Stir and melt the raw materials of the back flame-retardant insulation layer at 190 °C under a pressure of 15 MPa, and cast a film with a thickness of 0.03 mm on the front heating layer with a casting machine as the back flame-retardant insulation layer;

[0076] (3) Place the material in a heat treatment device, set the heating rate to 3 °C per minute, the maximum temperature to 100 °C, treat for 2 hours, and obtain the CNT single-sided directional heating film after cooling.

[0077] Comparative Example 3

[0078] A CNT single-sided directional heating film is composed of a front heating layer and a back flame-retardant insulation layer.

[0079] The composition of the front heat - generating layer is polyurethane containing CNT.

[0080] The preparation method of the polyurethane containing CNT is as follows: Add 35 parts by weight of polyether polyol (polypropylene glycol) and 10 parts by weight of modified CNT into a reaction kettle, heat to 90 °C, stir for 60 minutes, add 40 parts by weight of toluene diisocyanate and 2 parts by weight of stannous octoate catalyst, continue to stir for 40 minutes, lower the temperature to 70 °C, add 15 parts by weight of chain extender (1,4 - butanediol) and stir for 2 hours. After cooling, defoam in a vacuum device to improve the quality of the polyurethane, and then carry out a curing treatment at 110 °C for 3 hours to further cross - link and cure the polyurethane to obtain the polyurethane containing CNT.

[0081] The modified CNT is hydroxylated CNT, and the preparation method is: Prepare a mixed acid solution with a volume ratio of 65% concentrated nitric acid to 98% concentrated sulfuric acid of 1:3. Add CNT into the mixed acid solution, stir at 30 °C for 3 hours, and obtain the modified CNT through washing, filtering, and drying.

[0082] The mass ratio of the CNT to the mixed acid is 1:10.

[0083] The raw materials of the back flame - retardant insulating layer include 70 parts by weight of polyether - type polyurethane, 2 parts by weight of dispersant, 1 part by weight of coupling agent, 2 parts by weight of softener, 20 parts by weight of flame retardant, and 3 parts by weight of insulating agent.

[0084] The dispersant is a polyether - type dispersant, the coupling agent is a silane coupling agent, the softener is a polysiloxane softener, the flame retardant is a mixture of melamine polyphosphate and tricresyl phosphate in a mass ratio of 1:1, and the insulating agent is modified nano - silica.

[0085] The specific preparation method of the modified silica is as follows: Dry the nano - silica at 120 °C for 4 hours to remove the adsorbed moisture on the surface, which helps the subsequent attachment of the silane coupling agent; Dissolve isocyanatopropyltriethoxysilane in absolute ethanol and then add the dried nano - silica, stir at 60 °C for 8 hours to cause the ethoxy group of the silane coupling agent to undergo hydrolysis and condensation reaction with the hydroxyl group on the surface of the nano - silica to form a silicon - oxygen bond; Filter, wash with absolute ethanol, and then dry in a vacuum at 70 °C for 4 hours.

[0086] The mass ratio of isocyanatopropyltriethoxysilane to nano - silica is 1:50.

[0087] The preparation method of a kind of CNT single - sided directional heating film includes the following steps:

[0088] (1) Stir and melt the polyurethane containing CNT at 190 °C and a pressure of 15 MPa, and coat it through a coater to form a film with a thickness of 0.05 mm as the front heat - generating layer;

[0089] (2) Stir and melt the raw materials of the back flame-retardant insulating layer at 190 °C and a pressure of 15 MPa, and use a casting machine to cast a 0.03-mm-thick film on the front heating layer as the back flame-retardant insulating layer;

[0090] Performance testing

[0091] Resistance measurement: Use a four-probe square resistance to measure the surface resistance of the film;

[0092] Heating uniformity test: Measured by infrared thermal imaging method. Specifically, the heating temperature uniformity of the heating film can be judged from the mottling degree in the infrared thermal imaging picture;

[0093] Aging resistance test: Represented by the power attenuation ratio after continuous power-on at 220 V for 360 h. Among them, the lower the power attenuation ratio, the longer the service life of the heating film.

[0094] The test results are shown in the table:

[0095] Resistance Uniformity of heat generation Power attenuation ratio Example 1 2.1 Ω 96％ 1.5％ Example 2 2.2 Ω 95％ 2.1％ Comparative example 1 8.7 Ω 64％ 16.4％ Comparative example 2 3.6 Ω 78％ 12.9％ Comparative example 3 2.6 Ω 83％ 15.1％

[0096] It can be seen from the test results that the prepared polyurethane containing CNT as the heating film has more uniform CNT dispersion and stronger binding force with the polymer than the polyether-based polyurethane film mixed with CNT. The heating of the heating film is more uniform and the energy consumption is less; by modifying the insulating agent nano-silica with isocyanatopropyltriethoxysilane, the nano-silica is evenly distributed in the polyurethane material, achieving good insulation effect with less addition of nano-silica; further heat treatment of the cast heating film can promote the rearrangement of molecular chains inside the material, improve the crystallinity, and thus enhance the mechanical strength, thermal stability and aging resistance of the film.

[0097] The above is only a preferred embodiment of the present invention, and it does not impose any form of limitation on the present invention. Although the present invention has been disclosed as above with a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the equivalent embodiments with equivalent changes within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any indirect modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A CNT single-sided directional heating film, characterized in that: The heating film consists of a front heating layer and a back flame-retardant insulating layer.

2. A CNT single-sided oriented heating film according to claim 1, characterized in that: The component of the front heating layer is polyurethane containing CNT.

3. A CNT single-sided oriented heating film according to claim 2, characterized in that: The preparation method of the polyurethane containing CNT is as follows: 25-45 parts by weight of polyether polyol and 5-15 parts by weight of modified CNT are added into a reaction kettle, heated to 80-100° C., stirred for 30-90 minutes, 30-50 parts by weight of diisocyanate and 1-5 parts by weight of catalyst are added, stirring is continued for 30-60 minutes, the temperature is lowered to 70-80° C., 10-20 parts by weight of chain extender are added, stirred for 1-2 hours, cooled, degassed in a vacuum device, and then aged at 100-120° C. for 2-4 hours to obtain the polyurethane containing CNT.

4. A CNT single-sided oriented heating film according to any one of claims 2 and 3, characterized in that: The modified CNT is hydroxylated CNT, and the preparation method is as follows: a mixed acid solution of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:3-4 is prepared, CNT is added to the mixed acid solution, stirred at 20-40° C. for 2-4 hours, and the modified CNT is obtained by filtering, washing and drying.

5. The CNT single-sided oriented heating film according to claim 2, characterized in that: The raw materials of the back flame retardant insulating layer include 65-80 parts by weight of polyether polyurethane, 1-3 parts by weight of dispersant, 0.5-1 parts by weight of coupling agent, 1-2 parts by weight of softener, 15-25 parts by weight of flame retardant and 2-5 parts by weight of insulating agent.

6. The CNT single-sided oriented heating film according to claim 5, characterized in that: The dispersant is a polyether dispersant, the coupling agent is a silane coupling agent, the softener is a polysiloxane softener, the flame retardant is melamine polyphosphate and tricresyl phosphate, and the insulating agent is modified nano silicon dioxide.

7. A CNT single-sided oriented heating film according to any one of claim 6, characterized in that: The modified silicon dioxide is specifically prepared by drying the nano silicon dioxide at 110-130° C. for 2-6 hours, dissolving isocyanate propyl triethoxysilane in anhydrous ethanol and adding the dried nano silicon dioxide, stirring at 50-70° C. for 4-12 hours, filtering, washing with anhydrous ethanol and then drying at 60-80° C. in a vacuum oven for 3-5 hours.

8. The CNT single-sided oriented heating film according to claim 7, characterized in that: The mass ratio of the isocyanatepropyltriethoxysilane to the nano-silicon dioxide is 1:10-100.

9. A method for preparing a CNT single-sided oriented heating film according to any one of claims 2 to 8, characterized in that: The following steps are involved: (1) Stirring and melting the CNT-containing polyurethane at 180-200° C. and a pressure of 10-20 MPa, and coating the polyurethane with a thickness of 0.01-0.1 mm using a coating machine as a front heating layer; (2) stirring and melting the raw material of the back flame-retardant insulating layer at 180-200° C. and a pressure of 10-20 MPa, and casting the raw material on the front heating layer with a casting machine to form a 0.01-0.1 mm film as the back flame-retardant insulating layer; (3) placing the material in a heat treatment device, setting the heating rate to 2-5°C per minute, the maximum temperature to 80-120°C, treating for 1-2 hours, and obtaining a CNT single-sided oriented heating film after cooling.