Carbon nanotube electric heating film and preparation method and application thereof

Abstract

The invention discloses a carbon nanotube electric heating film and a preparation method thereof. The carbon nanotube electric heating film comprises a substrate layer, a bonding layer and a conducting layer which are sequentially arranged, carbon nanotubes are distributed in the conducting layer and comprise a plurality of first carbon nanotubes distributed in the first direction and a plurality of second carbon nanotubes distributed in the second direction on the plane of the conducting layer, and the first direction is perpendicular to the second direction. The carbon nanotubes in the conductive layer are directionally arranged to form a more ordered structure, so that higher light transmission is achieved, meanwhile, the transmission efficiency of electrons can be further improved, defects and impurities in the electrons are reduced, and the conductivity and the mechanical strength are guaranteed; and the stable conductive performance and structural strength can ensure that good electronic performance can still be kept during bending and stretching. And finally, good optical, electrical and mechanical properties are kept in the heating process, so that the demisting speed is higher.

Description

Technical Field

[0001] The present application relates to the technical field of electric heating films, and in particular to carbon nanotube electric heating films and preparation methods and applications thereof. Background Art

[0002] Traditional defogger films mainly rely on electric heating wires for heating and defogger, but electric heating wires have disadvantages such as high energy consumption and easy damage. In recent years, carbon nanotubes (CNTs) have attracted widespread attention due to their excellent conductivity and stability. The conductive layer prepared using carbon nanotubes has low resistance, high light transmittance and good mechanical properties. Therefore, the near-infrared high-transmittance electric heating defogger film based on the carbon nanotube conductive layer has broad application prospects. For example, there is a thin-film defogger device with a carbon nanotube film on the internal transparent heating film. However, the light transmittance of this defogger device is poor and the defogger speed is slow. Summary of the invention

[0003] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application proposes a carbon nanotube electric heating film with good light transmittance and fast defogging speed and a preparation method thereof.

[0004] In a first aspect of the present application, a carbon nanotube electric heating film is provided, comprising:

[0005] a substrate layer, the substrate layer comprising a polymer film;

[0006] A bonding layer, the bonding layer comprising a metal material;

[0007] The conductive layer has carbon nanotubes distributed in it. The carbon nanotubes include a plurality of first carbon nanotubes distributed along a first direction on the plane of the conductive layer and a plurality of second carbon nanotubes distributed along a second direction. The angle between the first direction and the second direction is 45° to 90°.

[0008] The carbon nanotube electric heating film according to the embodiment of the present application has at least the following beneficial effects:

[0009] The carbon nanotubes in the conductive layer are arranged in a directional manner to form a more orderly structure, which has higher light transmittance. At the same time, it can further improve the transmission efficiency of electrons, reduce defects and impurities, and ensure conductivity and mechanical strength; and the stable conductivity and structural strength can ensure that good electronic performance can be maintained when bent and stretched. Ultimately, it maintains good optical, electrical, and mechanical properties during the heating process, thereby having a faster defogging speed.

[0010] In some embodiments of the present application, the material of the polymer film includes at least one of polycarbonate, polyethylene terephthalate, polyethylene naphthalate, polyimide, and polymethyl methacrylate.

[0011] In some embodiments of the present application, the polymer film is opaque to visible light and transparent to near infrared light.

[0012] In some embodiments of the present application, the metal material of the bonding layer includes at least one of copper, silver, gold, aluminum and nickel.

[0013] In some embodiments of the present application, an anti-reflection layer is further provided on the other side of the substrate layer relative to the conductive layer.

[0014] In a second aspect of the present application, a method for preparing a carbon nanotube electric heating film is provided, the method comprising the following steps:

[0015] magnetron sputtering a metal material on the substrate layer to form a bonding layer;

[0016] A carbon nanotube slurry is coated on the bonding layer, and an electric field is applied along a first direction and a second direction to orient the carbon nanotubes along the first direction and the second direction to form a conductive layer.

[0017] In some embodiments of the present application, the method for forming a conductive layer includes coating a first carbon nanotube slurry and applying an electric field along a first direction; after the first carbon nanotube slurry is dried, coating a second carbon nanotube slurry and applying an electric field along a second direction to orient the first carbon nanotubes and the second carbon nanotubes, respectively.

[0018] In some embodiments of the present application, the voltage of the electric field is 20-100V.

[0019] In some embodiments of the present application, the frequency of the electric field is 100-1000 Hz.

[0020] In some embodiments of the present application, the electric field is applied for 3 to 30 minutes.

[0021] The third aspect of the present application provides an application of a carbon nanotube electric heating film in the field of demisting.

[0022] In a fourth aspect of the present application, a device is also provided, the device comprising any one of the aforementioned carbon nanotube electric heating films.

[0023] In a fourth aspect of the present application, a device is provided, which includes the aforementioned carbon nanotube electric heating film.

[0024] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the structure of a carbon nanotube electric heating film in one embodiment of the present application.

[0026] Figure 2 This is a schematic diagram of the principle of a carbon nanotube electric heating film in one embodiment of the present application.

[0027] Figure 3 This is a schematic diagram of the principle of the carbon nanotube electric heating film in Comparative Example 1 of the present application.

[0028] Figure 4 This is a schematic diagram of the principle of the carbon nanotube electric heating film in Comparative Example 2 of the present application.

[0029] Reference numerals: base layer 100 , bonding layer 200 , conductive layer 300 , carbon nanotube 301 , first carbon nanotube layer 310 , first carbon nanotube 311 , second carbon nanotube layer 320 , second carbon nanotube 321 , third carbon nanotube layer 330 , anti-reflection layer 400 . DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the concept of the present application and the technical effects produced in combination with the embodiments, so as to fully understand the purpose, features and effects of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of them. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present application.

[0031] The embodiments of the present application are described in detail below. The described embodiments are exemplary and are only used to explain the present application, and should not be understood as limiting the present application.

[0032] In the description of this application, "several" means more than one, "more" means more than two, "greater than", "less than", "exceed", etc. are understood to exclude the number itself, and "above", "below", "within", etc. are understood to include the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0033] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein are only for the purpose of describing the embodiments of this application and are not intended to limit this application.

[0034] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0035] The first aspect of the embodiments of the present application relates to a carbon nanotube electric heating film. The term "electric heating film" refers to a film that can quickly heat up to a set temperature and generate heat radiation to the outside when powered on. Figure 1 , shows the structure of the carbon nanotube electric heating film in the embodiment of the present application, including a base layer 100, a bonding layer 200 and a conductive layer 300 arranged in sequence. The base layer 100 includes a polymer film, the bonding layer 200 includes a metal material, and the conductive layer 300 is distributed with carbon nanotubes. Figure 2 The carbon nanotubes include a plurality of first carbon nanotubes 301 distributed along a first direction and a plurality of second carbon nanotubes 302 distributed along a second direction on the plane of the conductive layer, and the angle between the first direction and the second direction is 45° to 90°.

[0036] The carbon nanotubes in the conductive layer have excellent electrical conductivity and heating uniformity, which can significantly improve heating efficiency and service life. As a lightweight, high-strength nanomaterial, carbon nanotubes can improve the mechanical strength and corrosion resistance of the film, and the price is competitive. In addition, the preparation process of the carbon nanotube conductive layer is simple and easy to operate, which is suitable for large-scale industrial production.

[0037] The carbon nanotubes in the conductive layer are distributed along the first direction and the second direction respectively, thereby forming a directional rectangular array. This more ordered structure makes the conductive layer have higher light transmittance. In addition, the orderly arranged carbon nanotubes in the conductive layer can further improve the transmission efficiency of electrons, allowing electrons to move more smoothly in it, reducing obstacles and scattering in the transmission path. And the orderly arranged conductive layer can usually reduce the defects and impurities in the carbon nanotube layer that may affect the conductive performance and mechanical strength. This stable conductive performance and structural strength can ensure that the device can still maintain good electronic performance when bent and stretched. Therefore, by precisely controlling the arrangement structure of carbon nanotubes, the quality and consistency of the conductive layer can be improved, so as to ensure that it maintains good optical, electrical and mechanical properties during the heating process as a defogging film, and better meet the needs of specific application scenarios.

[0038] In addition, in the structural design of the carbon nanotube electric heating film, a metal material is added as a bonding layer. Taking advantage of one or more aspects of the metal layer's electrical conductivity, thermal conductivity, and stability, and considering the property differences between the carbon nanotubes and the polymer substrate, a metal material is added as a bonding layer to improve the adhesion of the carbon nanotubes to the substrate, thereby further improving its optical, electrical, and mechanical properties.

[0039] In some embodiments, the angle between the first direction and the second direction is 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, 90°. The structure with a lower angle will cause stronger light scattering and reflection due to the difference in edges and angles, so the light transmittance is lower. When the angle gradually increases so that the two are perpendicular to each other, the grid spacing is more uniform and the shape is more regular, which makes the scattering and blocking effect of light passing through the grid smaller, and the light transmittance will be higher.

[0040] In some embodiments, reference Figure 1 Combined with Figure 2 , the conductive layer 300 includes a first carbon nanotube layer 310 and a second carbon nanotube layer 320, wherein the first carbon nanotube layer 310 includes a plurality of first carbon nanotubes 311 distributed along a first direction, and the second carbon nanotube layer 320 includes a plurality of second carbon nanotubes 321 distributed along a second direction, and the orientation directions of the carbon nanotubes in the first carbon nanotube layer 310 and the second carbon nanotube layer 320 are perpendicular to each other. In some other embodiments, the conductive layer further includes a third nanotube layer 330 along the direction of the first carbon nanotube layer 310 and the second carbon nanotube layer 320, and optional fourth nanotube layers, fifth nanotube layers, and other multiple carbon nanotube layers (not shown in the figure), and the orientation directions of the carbon nanotubes in adjacent nanotube layers are perpendicular to each other.

[0041] In some embodiments, the overall thickness of the carbon nanotube electric heating film can be, for example, 1 μm to 1 cm, for example, 1 μm, 2 μm, 3 μm, 5 μm, 10 μm, 20 μm, 30 μm, 50 μm, 100 μm, 200 μm, 300 μm, 500 μm, 1 mm, 2 mm, 3 mm, 5 mm, or 1 cm.

[0042] In some embodiments, the substrate layer is a flexible substrate layer. In some embodiments, the polymer material forming the polymer film includes but is not limited to at least one of polycarbonate, polyethylene terephthalate, polyethylene naphthalate, polyimide, polymethyl methacrylate, etc. In some embodiments, the thickness of the substrate layer is 1 μm to 1 mm, for example, 1 μm, 2 μm, 3 μm, 5 μm, 10 μm, 20 μm, 30 μm, 50 μm, 100 μm, 200 μm, 300 μm, 500 μm, 1 mm.

[0043] In some embodiments, the polymer film of the substrate layer is not transparent to visible light and is transparent to near-infrared light. Not transparent to visible light means that the transmittance of the polymer film to visible light is less than 50%, for example, it can be less than 40%, less than 30%, less than 20%, less than 10%, less than 8%, less than 6%, less than 5%, less than 4%, less than 3%, less than 2%, less than 1%. Transparent to near-infrared light means that the transmittance of the polymer film to near-infrared light is more than 50%, for example, it can be more than 55%, more than 60%, more than 65%, more than 70%, more than 75%, more than 80%, more than 85%, more than 86%, more than 87%, more than 88%, more than 89%, more than 90%, more than 91%, more than 92%, more than 93%, more than 94%. In some embodiments, the transmittance to near-infrared light refers to the transmittance to light in the 750-2500nm band. In some embodiments, the transmittance to near-infrared light refers to the transmittance of light of any wavelength within the wavelength range of 750 to 2500 nm.

[0044] In some embodiments, the metal material of the bonding layer includes at least one of copper, silver, gold, aluminum and nickel. Due to the non-reactivity of carbon nanotubes (i.e., it is not easy to react with other substances such as oxidation, corrosion, etc.) and low surface energy (it is not easy for other substances to adhere to the surface of the object), some metals have insufficient wettability (referring to the degree of penetration of the liquid contact surface) to carbon nanotubes, which affects the bonding of the substrate layer and the conductive layer. Wettability is related to many factors. Among the above-mentioned metal materials, nickel and copper have good wettability with carbon nanotubes due to their special electronic structure; gold and silver also have good wettability with carbon nanotubes due to their higher surface energy. In some specific embodiments, the metal material of the bonding layer includes copper, which takes into account stability, electrical conductivity, thermal conductivity and cost, so that the electric heating film has a higher demisting efficiency. Silver and gold have good electrical conductivity and thermal conductivity, but the cost is much higher than copper; aluminum and nickel have lower costs, but their electrical conductivity and thermal conductivity are relatively poor compared to copper.

[0045] In some embodiments, the thickness of the bonding layer is 1 nm to 5 nm, for example, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm. When the bonding layer is controlled to have the above thickness, the light transmittance is little affected because the metal is extremely thin.

[0046] In some embodiments, reference Figure 1, the other side of the substrate layer 100 relative to the conductive layer 300 is also provided with an anti-reflection layer 400. The other side of the substrate layer 100 is subjected to an anti-reflection treatment, so that the light transmittance of the electric heating film is further increased. In some embodiments, the material of the anti-reflection layer 400 includes but is not limited to at least one of nitrides, oxides, and fluorides, for example, but not limited to at least one of silicon oxide, silicon nitride, silicon oxynitride, titanium dioxide, titanium pentoxide, magnesium oxide, magnesium fluoride, aluminum oxide, zirconium oxide, and tantalum oxide. In some embodiments, the thickness of the anti-reflection layer is 1nm to 500nm, for example, it can be 1nm, 2nm, 3nm, 5nm, 10nm, 20nm, 30nm, 50nm, 100nm, 200nm, 300nm, 500nm.

[0047] In some embodiments, the conductive layer of the carbon nanotube electric heating film is also connected to an electrode, so that the carbon nanotube electric heating film can be electrically heated. In some embodiments, the electrode is provided with an insulating layer.

[0048] The second aspect of the embodiments of the present application relates to a method for preparing a carbon nanotube electric heating film, which comprises the following steps: magnetron sputtering a metal material on a base layer to form a bonding layer; coating a carbon nanotube slurry on the bonding layer, and applying an electric field along a first direction and a second direction to orient the carbon nanotubes to form a conductive layer.

[0049] Chemical vapor deposition has high purity and good crystallization, but the process temperature is relatively high, and the base layer of some polymer materials has intolerance problems. Therefore, magnetron sputtering is used in this scheme to prepare the bonding layer.

[0050] In some embodiments, the method for forming a conductive layer includes applying a first carbon nanotube slurry and applying an electric field along a first direction; after the first carbon nanotube slurry is dried, applying a second carbon nanotube slurry and applying an electric field along a second direction to orient the first carbon nanotube and the second carbon nanotube, respectively, to form a first carbon nanotube layer and a second carbon nanotube layer. In some other embodiments, it also includes applying a third carbon nanotube slurry after the second carbon nanotube slurry is dried, and applying an electric field along the first direction to form a third carbon nanotube layer. In some other embodiments, it also includes applying a fourth carbon nanotube slurry after the third carbon nanotube slurry is dried, and applying an electric field along the second direction to form a fourth carbon nanotube layer. In some other embodiments, it also includes applying a fifth carbon nanotube slurry after the fourth carbon nanotube slurry is dried, and applying an electric field along the first direction to form a fifth carbon nanotube layer. In some other embodiments, it also includes applying a sixth carbon nanotube slurry after the fifth carbon nanotube slurry is dried, and applying an electric field along the second direction to form a sixth carbon nanotube layer. By switching the two pairs of electrodes back and forth three times to apply the electric field during the coating of the carbon nanotube slurry, the oriented rectangular distribution of the carbon nanotubes can be effectively controlled. The oriented rectangular arrangement of the carbon nanotubes can form an orderly distribution to reduce light scattering and increase light transmittance, forming an effective conductive network to make electron transmission smoother and improve conductivity.

[0051] In some embodiments, the method for forming the conductive layer further comprises drying and curing after the slurry coating is completed, for example, when there are two carbon nanotube layers, the second carbon nanotube slurry is dried and cured after coating; when there are three carbon nanotube layers, the third carbon nanotube slurry is dried and cured after coating; when there are four carbon nanotube layers, the fourth carbon nanotube slurry is dried and cured after coating; when there are five carbon nanotube layers, the fifth carbon nanotube slurry is dried and cured after coating; when there are six carbon nanotube layers, the sixth carbon nanotube slurry is dried and cured after coating. In some embodiments, the drying and curing treatment conditions are 80-120°C for 30-60 minutes.

[0052] In some embodiments, the voltage of the applied electric field is 20 to 100 V. In some embodiments, the frequency of the applied electric field is 100 to 1000 Hz. In some embodiments, the duration of each applied electric field is 3 to 30 minutes.

[0053] The third aspect of the embodiments of the present application relates to an application of the aforementioned carbon nanotube electric heating film in the field of defogging. Specifically, the carbon nanotube electric heating film accelerates the volatilization of water vapor on the surface of the device, thereby preventing fogging or removing the fog beads that have already formed. Therefore, the embodiments of the present application also relate to a method for heating or defogging the surface of a device, which includes attaching the carbon nanotube electric heating film to the surface of the device and electrically heating the conductive layer.

[0054] In some of the embodiments, the device may be any material having a certain surface, such as a medical device, a camera, a sensor, a window glass, etc.

[0055] In a fourth aspect of the embodiments of the present application, a device is provided, the device comprising any of the above-mentioned electric heating films. The device may be, for example, a medical device, a camera, a sensor, a window glass, or at least one of the devices that requires heating.

[0056] Example 1

[0057] This embodiment provides an electric heating film, and the preparation process thereof is as follows:

[0058] (1) Substrate preparation: A polyethylene terephthalate (PET) film (purchased from Dongguan Haiyue Plastic Chemical Co., Ltd., model HYM-HS) that is opaque to visible light, has high near-infrared transparency, and has good thermal stability is selected as the substrate layer.

[0059] (2) Preparation of carbon nanotube (CNTs) dispersion: Single-walled carbon nanotubes (SWCNTs) with a diameter of less than 4 nm were mixed with a 0.2 g / L sodium dodecyl sulfate aqueous solution, stirred and then ultrasonically dispersed for 6 hours to uniformly disperse the CNTs in the solvent to form a stable CNT dispersion with a concentration of 0.2 mg / mL.

[0060] (3) Preparation of bonding layer: The PET substrate layer was ultrasonically cleaned and dried and then placed in a magnetron sputtering device. Metal copper was used as the sputtering source. The sputtering power was 200 W, the working gas pressure was 2 Pa, the sputtering time was 3 min, and the substrate temperature was controlled at 60 °C. Finally, a 5 μm thick copper metal layer was deposited on the PET surface to provide good conductivity and adhesion.

[0061] (4) Preparation of conductive layer: The carbon nanotube dispersion is evenly coated on the surface of a substrate such as PET with a copper film by coating to form a carbon nanotube conductive layer. Specifically, a layer of carbon nanotube slurry is first coated, and during the coating process, a transverse electric field is applied in one direction of the plane of the base layer to control the orientation of the carbon nanotubes laterally, and then the carbon nanotubes are dried; then a layer of carbon nanotube slurry is coated, and during the coating process, a longitudinal electric field is applied in the plane of the base layer perpendicular to the previous direction to control the orientation of the carbon nanotubes longitudinally, and then the carbon nanotubes are dried; then a layer of carbon nanotube slurry is coated again, and during the coating process, a transverse electric field is applied in the plane of the base layer parallel to the first direction to control the orientation of the carbon nanotubes laterally. Each switching of the electric field is performed after the coated slurry is completely dried, which effectively controls the directional distribution of the carbon nanotubes. In the three electric fields, the electrode spacing is 0.5m, the electric field strength is 200V / m, the voltage of each electric field is 100V, the frequency is 1000Hz, and the processing time is 3 to 30min. The two pairs of electrodes are switched back and forth 3 times to apply the electric field.

[0062] (5) Drying and curing: The PET film coated with the carbon nanotube conductive layer was dried and cured at 100° C. for 60 min to remove the solvent and enhance the bonding force between the conductive layer and the substrate layer.

[0063] (6) Post-processing: Anti-reflection film (Shanghai Juanrou New Technology Co., Ltd., surface anti-reflection coating, model: JR-AR-965) is applied on the side of the substrate without the conductive layer to increase the transmittance and reduce the reflectivity in the near-infrared spectrum. Silver paste electrodes are screen-printed on both ends of the carbon nanotube conductive film, an overheat protection switch is added, and an insulating layer is encapsulated on top to make an electric heating defogging film.

[0064] refer to Figure 3 When the carbon nanotubes 301 are conventionally coated, the carbon nanotubes 301 are chaotically and disorderly arranged on the base layer 100. However, in the above-mentioned preparation process of the embodiment of the present application, the carbon nanotubes have high polarizability and unevenly distributed charges on the surface. When placed in an electric field, these charges will be affected by the electric field force, thereby causing the carbon nanotubes to rearrange along the direction of the electric field. When an electric field perpendicular or horizontal to the coating direction (i.e., longitudinal and transverse) is applied during coating, the carbon nanotubes are induced by the strong electric field and become highly polarized, and a pair of dipoles will be generated at both ends. When there is an angle between the carbon nanotubes and the direction of the electric field, a torsional force will be generated, causing the carbon nanotubes to be oriented along the direction of the electric field, and the two are superimposed to form a structure such as Figure 2 In this way, the carbon nanotubes can be arranged vertically in an orderly manner to reduce light scattering and improve light transmittance, and form an effective conductive network to make electron transmission smoother and improve conductivity.

[0065] Example 2: Performance Test

[0066] Comparative Example 1: This comparative example provides a carbon nanotube electric heating film, which is different from Example 1 in that the application of the electric field is omitted during the coating process of the carbon nanotube slurry.

[0067] Comparative Example 2: This comparative example provides a carbon nanotube electric heating film, which is different from Example 1 in that only a unidirectional electric field is applied during the coating process of the carbon nanotube slurry.

[0068] The carbon nanotube electric heating films prepared in Example 1 and Comparative Examples 1-2 were tested respectively, and the specific methods are as follows:

[0069] 1. Transmittance: Turn on the power of the transmittance tester and perform automatic calibration; place the sample in the measuring area of ​​the instrument, ensure that the sample is flat and fits tightly with the measuring area; start the test program, test the transmittance of the sample through the instrument, and record the transmittance test value at a wavelength of 950nm. Measure the transmittance of Example 1 and Comparative Examples 1-2 with and without anti-reflection film.

[0070] 2. Sheet resistance: Use the four-probe method to measure. Turn on the four-probe tester, preheat for 30 minutes, and select the "sheet resistance test" mode. Place the sample on the test table, hold the tester, and gently press the four probe heads on the sample surface to make good contact between the probes and the sample. Wait for a while, and the device will automatically calculate and display the sheet resistance value.

[0071] 3. Heating time: Connect the sample to a DC power supply (15V) and place it under an infrared thermal imager. Observe and record the temperature changes of the sample during the heating stage, and record the time required to heat up to 60°C.

[0072] 4. Demisting time: Turn on the power supply and operate at a rated working voltage of 15V and reach a stable state, then spray water on the surface of the sample to form water mist. The time it takes for the mist on the sample surface to dissipate is the demisting time.

[0073] The results are shown in Table 1. It can be seen from the results in the table that the near-infrared transmittance of the electric heating film provided in Example 1 can reach 91% when no anti-reflection film is added. After adding the anti-reflection film, the near-infrared transmittance is above 96%. In addition, the electric heating film has high heating efficiency (it can reach the set temperature in 35 seconds), fast defogging speed (the surface fog is removed within 70 seconds), and uniform heating of the entire surface (the infrared thermal imager shows that the surface temperature difference is less than 8%).

[0074] Table 1. Performance test comparison

[0075] structure Transmittance / 950nm Transmittance after anti-reflection / 950nm Square resistance / Ω Heating time / s Defogging time / s Comparative Example 1 90％ 94％ 100 55 100 Comparative Example 2 90％ 94％ 93 50 90 Example 1 91％ 96％ 70 35 70

[0076] As can be seen from the table above, the CNTs conductive layer arranged in a directional manner in Example 1 has a higher transmittance and a smaller sheet resistance, so that after applying the same 15V voltage, the time to reach the set temperature is shorter and the defogging time is also shorter. Coating an anti-reflection film on the side of the substrate PET without a conductive layer can further increase the transmittance of the heated defogging film device.

[0077] Among them, the transmittance of comparative examples 1 and 2 is 90%, but the near infrared transmittance in Example 1 can reach 91%. This is due to the different arrangement of the conductive material CNTs rather than errors. Figure 2 , the spacing between the orderly arranged first carbon nanotubes 311 and the second carbon nanotubes 321 is relatively large, which helps to reduce the shielding of light by the metal lines, thereby improving the light transmittance. Similarly, after the transmittance is increased, the light transmittance of the disordered or unidirectional CNTs in Comparative Examples 1 and 2 is only increased by 4%, while in Example 1, the orderly distribution of CNTs helps to evenly distribute the light, further reducing light scattering and loss, so the light transmittance can be further improved, and the light transmittance is increased by 5%.

[0078] Comparative Example 1: No electric field was applied when coating CNTs. Figure 3 , the carbon nanotubes 301 are randomly distributed on the substrate layer 100; the light transmittance is low, the in-plane square resistance is large, and the defogging time is long. Comparative Example 2 applies a unidirectional electric field, reference Figure 4 The carbon nanotubes 301 are arranged in a "one" shape on the substrate 100 horizontally or vertically. The arrangement distance between the carbon nanotubes 301 is not easy to control. There is no significant difference in transmittance compared with the disordered CNTs in Comparative Example 1, and the change in the in-plane square resistance is small; the defogging time is not significantly shortened. In Example 1, a staggered electric field is applied when coating CNTs, and the CNTs are orderly and directional arranged parallel to the coating direction. Due to the switching of the electric field, the CNTs will form a mutually perpendicular rectangular distribution pattern.

[0079] Example 3: Binding Layer Comparison

[0080] With reference to Example 1, copper was replaced with other metals during the preparation process, and the various properties of the carbon nanotube heating film were tested according to the method in Example 2. The results are shown in Table 2.

[0081] Table 2. Effects of different bonding layers on electric heating films

[0082] Bonding layer Transmittance / 950nm Transmittance after anti-reflection / 950nm Heating uniformity Time to reach set temperature / s Defogging time / s copper 91％ 96％ OK 35 70 silver 91％ 96％ OK 33 65 gold 91％ 96％ OK 36 72 nickel 91％ 95％ OK 40 88 aluminum 91％ 95％ NG 50 100

[0083] In the structural design of electric heating film, adhesion is affected by many factors, such as material thermal conductivity, surface wettability, chemical compatibility, etc. Therefore, when selecting materials and designing interfaces, the following factors need to be considered comprehensively to achieve optimal adhesion:

[0084] Thermal stability: When heat is generated between the carbon nanotubes and the substrate layer due to the passage of electric current or other heat sources, if the interface has good thermal conductivity, the heat can be effectively conducted and dissipated, which helps prevent thermal stress or thermal deformation caused by heat accumulation at the interface, maintains the stability of the interface, and thus helps to enhance adhesion.

[0085] Reduce thermal stress: When the temperature changes, the thermal expansion coefficients of different materials are different, which may cause thermal stress at the interface. If the bonding layer has good thermal conductivity, it can conduct heat faster and reduce the temperature difference, reducing the thermal stress at the interface, then the integrity of the interface can be maintained and the adhesion can be enhanced.

[0086] Improve interface strength: Studies have shown that heat treatment and cooling can change the microstructure and chemical bonding state at the interface, affecting adhesion. Materials with good thermal conductivity are more likely to form a microstructure or chemical bonding that is conducive to adhesion at the interface.

[0087] Prevent local overheating: Local overheating may cause material performance degradation or failure. If the interface between the carbon nanotubes and the substrate layer has good thermal conductivity, it can quickly transfer heat to a wider area to prevent local overheating, thereby maintaining the performance and stability of the material and indirectly enhancing adhesion.

[0088] Combined with the results in the above table, the transmittance of the carbon nanotube electric heating film prepared by depositing different metal layers on the substrate is almost the same. This is because the metal bonding layer is extremely thin and has little effect on the transmittance. Among them, gold and silver are more expensive, nickel and aluminum have slightly poor thermal conductivity, and aluminum has insufficient adhesion to carbon nanotubes, and the heating surface is unevenly heated after long-term heating. Copper has better stability under general environmental conditions, is not easy to react with other substances, has better electrical conductivity, better thermal conductivity, and lower cost, so copper material is preferred as the bonding layer.

[0089] The present application is described in detail above in conjunction with the embodiments, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present application. In addition, the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

Claims

1. Carbon nanotube electric heating film, characterized in that, Including the following settings: a substrate layer comprising a polymer film; a bonding layer comprising a metal material; A conductive layer is provided with carbon nanotubes, wherein the carbon nanotubes include a plurality of first carbon nanotubes distributed along a first direction on the plane of the conductive layer and a plurality of second carbon nanotubes distributed along a second direction, wherein the angle between the first direction and the second direction is 45° to 90°.

2. The carbon nanotube electric heating film according to claim 1, characterized in that: The material of the polymer film includes at least one of polycarbonate, polyethylene terephthalate, polyethylene naphthalate, polyimide, and polymethyl methacrylate.

3. The carbon nanotube electric heating film according to claim 1, characterized in that: The polymer film is opaque to visible light but transparent to near-infrared light.

4. The carbon nanotube electric heating film according to claim 1, characterized in that: The metal material of the bonding layer includes at least one of copper, silver, gold, aluminum and nickel.

5. The carbon nanotube electric heating film according to claim 1, characterized in that: An anti-reflection layer is further provided on the other side of the base layer relative to the conductive layer.

6. The method for preparing the carbon nanotube electric heating film according to any one of claims 1 to 5, characterized in that: The following steps are involved: magnetron sputtering a metal material on the substrate layer to form a bonding layer; A carbon nanotube slurry is coated on the bonding layer, and an electric field is applied along a first direction and a second direction to align the carbon nanotubes along the first direction and the second direction to form the conductive layer.

7. The preparation method according to claim 6, characterized in that The method for forming the conductive layer includes coating a first carbon nanotube slurry and applying an electric field along a first direction; After the first carbon nanotube slurry is dried, the second carbon nanotube slurry is applied, and an electric field along a second direction is applied to align the first carbon nanotubes and the second carbon nanotubes.

8. The preparation method according to claim 6, characterized in that The voltage of the electric field is 20 to 100 V, and / or the frequency of the electric field is 100 to 1000 Hz, and / or the action time of the electric field is 3 to 30 minutes.

9. Use of the carbon nanotube electric heating film according to any one of claims 1 to 5 in the field of defogging.

10. The device, characterized in that The carbon nanotube electric heating film comprises the carbon nanotube electric heating film according to any one of claims 1 to 5.

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