Graphene electric heating film and preparation method and application thereof

Abstract

The invention provides a graphene electric heating film and a preparation method and application thereof, the graphene electric heating film comprises a pretreatment substrate and a graphene coating, the pretreatment substrate comprises a substrate and a pretreatment solution coated on the surface of the substrate, the pretreatment solution comprises aqueous PU resin and a PVP solution, and the aqueous PU resin and the PVP solution are uniformly mixed. The graphene coating is coated on the pretreated substrate. According to the graphene electric heating film, the surface of the substrate is pretreated, the wettability, ductility and adhesive force of the graphene coating are improved, stripping or falling is prevented, the flexibility of the substrate is kept, meanwhile, the mechanical performance of the graphene electric heating film is improved, meanwhile, the graphene electric heating film has low sheet resistance, and the graphene electric heating film can be applied to the field of electric heating devices. And in a low-pressure environment, rapid temperature rise and heating can be achieved, and the heating requirement is met.

Description

Technical Field

[0001] The present invention belongs to the field of graphene electrothermal heating, and in particular relates to a graphene electrothermal heating film, a preparation method thereof, and an application thereof. Background Art

[0002] Graphene has very good thermal conductivity, with a thermal conductivity coefficient as high as 5300 W / (m·K), far higher than that of gold, silver, copper, and aluminum, which have the highest thermal conductivity among metals. Moreover, it has good flexibility and is the carbon material with the highest thermal conductivity coefficient so far, making graphene the most attractive material in the field of electrothermal heating. When the graphene heating film is connected to a voltage, it will radiate far-infrared rays beneficial to the human body into the surrounding environment, playing a physiotherapy and health care role for the human body. Therefore, graphene electrothermal heating films are used in many physiotherapy and health care products. However, the existing products with graphene electrothermal heating films on the market have the following problems:

[0003] First, the graphene slurry is mainly based on a solvent-based system, and the smell is relatively large during the production process, accompanied by certain environmental pollution (for example, DMF has strong volatility and can be released into the air to form volatile organic compounds, affecting air quality and causing serious harm to the human body). For example, the invention patent with the publication number CN109951902A discloses a graphene heating slurry, a graphene heating film prepared by using the same, and a preparation method thereof. The solvents used in this method are at least one of DMF, DBE, and anti-white water, and the base film is any one of a PVC film, a PET film, and an EVA film;

[0004] Second, the substrates all adopt rigid materials such as PI films, PE films, PV films, and PET films, with low flexibility and poor bending properties, reducing the application scenarios of the products and making them unable to be applied in knee pads, physiotherapy mattresses, clothing, etc. For example, the invention patent with the publication number CN117545112A discloses a graphene heating slurry, a graphene heating film prepared by using the same, and a preparation method thereof. It is mentioned in this method that the substrate required for the prepared graphene heating film is one of a PVC film, a PET film, or an EVA film;

[0005] Thirdly, most graphene heating slurries require high-temperature curing, which can cause embrittlement of the substrate such as PET film and reduce the service life. For example, the invention patent with the publication number CN115785780A discloses a graphene electrothermal coating. The coating is an aqueous coating, which is environmentally friendly and can rapidly heat up under low voltage. However, it needs to be coated on a PET film and dried in an oven at 105°C. The invention patent with the publication number CN108684091A discloses a graphene heating film and its preparation method. This patent points out that the graphene aqueous conductive slurry is coated on a non-woven fabric substrate and dried to form a bare film. From this method, it can be seen that the graphene heating slurry has no volatile organic solvents and uses a flexible material as the substrate, but it needs to be dried by a dryer, that is, it needs to be heated to cure. The invention patent with the publication number CN112208166A discloses a one-step method for preparing a graphene heating film on a non-woven fabric substrate and its preparation method. The heating film obtained by this method includes a heating film layer, an insulating layer and a waterproof film, and it is clearly pointed out that the heating film layer needs to be heated (temperature is 100°C) to a semi-cured state during the preparation process. Summary of the Invention

[0006] In view of this, the present invention aims to provide a graphene electrothermal film, its preparation method and application, which can coat the graphene coating on a flexible substrate without high-temperature curing, and the prepared graphene electrothermal film has a low sheet resistance, so that it can rapidly heat up and generate heat under a low-voltage environment, meeting the market demand.

[0007] To achieve the above object, the technical solution of the present invention is realized as follows:

[0008] In a first aspect, the present invention provides a graphene electrothermal film, which includes:

[0009] A pretreated substrate, which includes a substrate and a pretreatment liquid coated on the surface of the substrate. The pretreatment liquid includes an aqueous PU resin and a PVP solution;

[0010] A graphene coating, which is coated on the pretreated substrate.

[0011] Further, after the graphene coating is coated on the pretreated substrate, it does not require high-temperature curing or heat curing.

[0012] Further, the sheet resistance of the graphene electrothermal film is ≤50 Ω / square.

[0013] Further, the concentration of the PVP solution is 0.5% to 10%, for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, and the mass of the aqueous PU resin is 0.1% to 15% of the mass of the PVP solution, for example, it can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%; preferably, the mass of the aqueous PU resin is 2% to 10% of the mass of the PVP solution, and the concentration of the PVP solution is 1% to 5%.

[0014] Further, the graphene coating includes a carbon nanotube aqueous slurry, graphene, and a film-forming agent. The mass percentage of carbon nanotubes in the carbon nanotube aqueous slurry is 0.5% to 10%, for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, and the mass of graphene is 0.1% to 5% of the mass of the carbon nanotube aqueous slurry, for example, it can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, and the mass of the film-forming agent is 0.5% to 25% of the sum of the mass of the carbon nanotube aqueous slurry and graphene, for example, it can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%.

[0015] Further, the film-forming agent is selected from one or more of hydroxy acrylic-amine resin, acrylic emulsion, SBR solution, and polyurethane solution; preferably, it is one or more of aqueous hydroxy acrylic-amine resin, aqueous acrylic emulsion, SBR solution, and aqueous polyurethane solution.

[0016] Further, the substrate is a flexible substrate, selected from one of non-woven fabric, knitted fabric, PU film, TPU film, PE film, and silicone film.

[0017] In a second aspect, the present invention provides a method for preparing the graphene electrothermal film as described in the first aspect, and the preparation method includes the following steps:

[0018] (1) Prepare a pretreatment solution, coat the pretreatment solution on the substrate to obtain a pretreated substrate;

[0019] (2) Prepare a graphene coating, coat the graphene coating on the pretreated substrate to obtain the graphene electrothermal film.

[0020] Further, in step (2), after the graphene coating is coated on the pretreated substrate, it is not subjected to high-temperature curing or heat curing; preferably, it is air-dried naturally.

[0021] Further, the preparation method of the pretreatment liquid includes the following steps: Prepare a PVP solution, mix the aqueous PU resin and the PVP solution evenly to obtain the pretreatment liquid; preferably, the concentration of the PVP solution is 1% - 5%, for example, it can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%.

[0022] Further, the PVP solution is an aqueous PVP solution.

[0023] Further, the coating thickness of the pretreatment liquid is 5 - 30 μm, for example, it can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm; preferably, it is 10 - 30 μm.

[0024] Further, the preparation method of the graphene coating includes the following steps: Prepare a carbon nanotube slurry, mix the graphene and the carbon nanotube slurry and disperse them evenly by ultrasonic treatment to obtain a graphene slurry, mix the film-forming agent and the graphene slurry evenly to obtain the graphene coating; preferably, the concentration of the carbon nanotube slurry is 0.5% - 10%.

[0025] Further, the carbon nanotube slurry is an aqueous carbon nanotube slurry.

[0026] Further, the coating thickness of the graphene coating is 50 - 100 μm, for example, it can be 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm; preferably, it is 60 - 80 μm.

[0027] In the third aspect, the present invention provides the application of the graphene electrothermal film as described in the first aspect or the preparation method as described in the second aspect in the preparation of products for physical therapy; preferably, the products for physical therapy are products for physical therapy by heating, including but not limited to physical therapy blankets, wrist guards, knee guards, physical therapy mattresses, and clothing.

[0028] In the fourth aspect, the present invention provides the application of substrate pretreatment in the preparation of graphene electrothermal films. The method of substrate pretreatment includes the following steps: Prepare a PVP solution, mix the aqueous PU resin and the PVP solution evenly to obtain the pretreatment liquid; coat the pretreatment liquid on the substrate to obtain a pretreated substrate.

[0029] Further, the graphene electrothermal film includes:

[0030] A pretreated substrate, which includes a substrate and a pretreatment solution coated on the surface of the substrate. The pretreatment solution includes an aqueous PU resin and a PVP solution;

[0031] Graphene coating, which is coated on the pretreated substrate.

[0032] Compared with the prior art, the graphene electrothermal film, its preparation method and application of the present invention have the following advantages:

[0033] (1) By pretreating the surface of the substrate, the graphene coating of the graphene electrothermal film of the present invention has improved wettability, ductility and adhesion, preventing peeling or falling off, and while maintaining the flexibility of the substrate, improving the mechanical properties of the graphene electrothermal film.

[0034] (2) The graphene electrothermal film of the present invention has a low sheet resistance and can quickly heat up and generate heat under a low-voltage environment to meet the heating requirements.

[0035] (3) The preparation method of the graphene electrothermal film of the present invention uses an environmentally friendly aqueous graphene coating. After being coated on the substrate, it does not need to be heated or cured at high temperature, which can reduce the damage to the substrate and extend the service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0037] Figure 1 It is a schematic diagram of the heating temperature of the graphene electrothermal film prepared in the embodiment and comparative example of the present invention under a 5V voltage. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0039] The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0040] Example 1

[0041] The preparation method of the graphene electrothermal film in this embodiment includes the following steps:

[0042] 1. Substrate pretreatment

[0043] (1) Prepare a 2% aqueous PVP solution;

[0044] (2) Weigh 1 g of waterborne PU resin and pour it into 10 g of 2% PVP aqueous solution. After stirring evenly, coat it on the non-woven fabric with a PU film, and the coating thickness is 20 μm to obtain a pretreated substrate.

[0045] 2. Prepare the graphene coating

[0046] (1) Prepare the aqueous carbon nanotube slurry, and the mass percentage of carbon nanotubes is 1%;

[0047] (2) Disperse graphene in the aqueous carbon nanotube slurry by ultrasonic wave to prepare the graphene aqueous slurry, where the mass percentage of graphene in the aqueous carbon nanotube slurry is 0.1%;

[0048] (3) Weigh 0.5 g of waterborne hydroxy acrylic-amine resin, SBR solution, and waterborne polyurethane solution respectively, add them to 30 g of the graphene aqueous slurry, stir evenly to obtain the graphene aqueous coating.

[0049] 3. Use an 80-μm wire bar coater to evenly coat the graphene aqueous coating on the pretreated substrate, air dry it naturally, and paste the electrodes.

[0050] Example 2

[0051] The preparation method of the graphene electrothermal film in this example includes the following steps:

[0052] 1. Substrate pretreatment

[0053] (1) Prepare 2% PVP aqueous solution;

[0054] (2) Weigh 1 g of waterborne PU resin and pour it into 10 g of 2% PVP aqueous solution. After stirring evenly, coat it on the non-woven fabric with a PU film, and the coating thickness is 20 μm to obtain a pretreated substrate.

[0055] 2. Prepare the graphene coating

[0056] (1) Prepare the aqueous carbon nanotube slurry, and the mass percentage of carbon nanotubes is 1%;

[0057] (2) Disperse graphene in the aqueous carbon nanotube slurry by ultrasonic wave to prepare the graphene aqueous slurry, where the mass percentage of graphene in the aqueous carbon nanotube slurry is 0.1%;

[0058] (3) Weigh 0.5 g, 0.75 g, and 0.65 g of waterborne hydroxy acrylic-amine resin, SBR solution, and waterborne polyurethane solution respectively, add them to 30 g of the graphene aqueous slurry, stir evenly to obtain the graphene aqueous coating.

[0059] 3. Use an 80-μm wire bar coater to evenly coat the graphene aqueous coating on the pretreated substrate, air dry it naturally, and paste the electrodes.

[0060] Example 3

[0061] The preparation method of the graphene electrothermal film in this example includes the following steps:

[0062] 1. Substrate pretreatment

[0063] (1) Prepare a 2% PVP aqueous solution;

[0064] (2) Weigh 1 g of aqueous PU resin and pour it into 10 g of the 2% PVP aqueous solution. After stirring evenly, coat it on the silicone film with a coating thickness of 20 μm to obtain a pretreated substrate.

[0065] 2. Prepare the graphene coating

[0066] (1) Prepare a carbon nanotube aqueous slurry with a mass percentage of carbon nanotubes of 1%;

[0067] (2) Disperse graphene in the carbon nanotube aqueous slurry by ultrasonic treatment to prepare a graphene aqueous slurry, where the mass percentage of graphene in the carbon nanotube aqueous slurry is 0.1%;

[0068] (3) Weigh 0.5 g, 0.75 g, and 0.65 g of aqueous hydroxy acrylic - amino resin, SBR solution, and aqueous polyurethane solution respectively, and add them to 30 g of the graphene aqueous slurry. Stir evenly to obtain the graphene aqueous coating.

[0069] 3. Use an 80-μm wire bar coater to evenly coat the graphene aqueous coating on the pretreated substrate, air dry it naturally, and paste the electrodes.

[0070] Example 4

[0071] The preparation method of the graphene electrothermal film in this example includes the following steps:

[0072] 1. Substrate pretreatment

[0073] (1) Prepare a 1% PVP aqueous solution;

[0074] (2) Weigh 0.1 g of aqueous PU resin and pour it into 10 g of the 1% PVP aqueous solution. After stirring evenly, coat it on the knitted fabric with a PU film with a coating thickness of 20 μm to obtain a pretreated substrate.

[0075] 2. Prepare the graphene coating

[0076] (1) Prepare a carbon nanotube aqueous slurry with a mass percentage of carbon nanotubes of 0.5%;

[0077] (2) Disperse graphene in the aqueous carbon nanotube slurry by ultrasonic treatment to prepare an aqueous graphene slurry, where the mass percentage of graphene in the aqueous carbon nanotube slurry is 0.1%.

[0078] (3) Weigh 0.1 g each of the aqueous hydroxy acrylic-amine resin, SBR solution, and aqueous polyurethane solution, add them to 30 g of the aqueous graphene slurry, and stir evenly to obtain an aqueous graphene coating.

[0079] 3. Use an 80-μm wire bar coater to evenly coat the aqueous graphene coating on the pretreated substrate, air dry naturally, and paste the electrodes.

[0080] Example 5

[0081] The preparation method of the graphene electrothermal film in this example includes the following steps:

[0082] 1. Substrate pretreatment

[0083] (1) Prepare a 5% aqueous PVP solution;

[0084] (2) Weigh 1 g of the aqueous PU resin and pour it into 10 g of the 5% aqueous PVP solution. After stirring evenly, coat it on the TPU film with a coating thickness of 20 μm to obtain a pretreated substrate.

[0085] 2. Preparation of the graphene coating

[0086] (1) Prepare an aqueous carbon nanotube slurry with a mass percentage of carbon nanotubes of 10%;

[0087] (2) Disperse graphene in the aqueous carbon nanotube slurry by ultrasonic treatment to prepare an aqueous graphene slurry, where the mass percentage of graphene in the aqueous carbon nanotube slurry is 5%;

[0088] (3) Weigh 2.5 g each of the aqueous hydroxy acrylic-amine resin, SBR solution, and aqueous polyurethane solution, add them to 30 g of the aqueous graphene slurry, and stir evenly to obtain an aqueous graphene coating.

[0089] 3. Use an 80-μm wire bar coater to evenly coat the aqueous graphene coating on the pretreated substrate, air dry naturally, and paste the electrodes.

[0090] Example 6

[0091] The preparation method of the graphene electrothermal film in this example includes the following steps:

[0092] 1. Substrate pretreatment

[0093] (1) Prepare a 5% aqueous PVP solution;

[0094] (2) Weigh 0.1 g of waterborne PU resin and pour it into 10 g of 5% PVP aqueous solution. After stirring evenly, coat it on the PE film with a coating thickness of 20 μm to obtain a pretreated substrate.

[0095] 2. Preparation of graphene coating

[0096] (1) Prepare an aqueous carbon nanotube slurry with a mass percentage of carbon nanotubes of 5%.

[0097] (2) Disperse graphene in the aqueous carbon nanotube slurry by ultrasonic treatment to prepare an aqueous graphene slurry, where the mass percentage of graphene in the aqueous carbon nanotube slurry is 2%.

[0098] (3) Weigh 1 g each of waterborne hydroxy acrylic - amino resin, SBR solution, and waterborne polyurethane solution, add them to 30 g of the aqueous graphene slurry, stir evenly to obtain an aqueous graphene coating.

[0099] 3. Use an 80 - μm wire bar coater to evenly coat the aqueous graphene coating on the pretreated substrate, air - dry it naturally, and paste the electrodes.

[0100] Example 7

[0101] The preparation method of the graphene electro - heating film in this example includes the following steps:

[0102] 1. Substrate pretreatment

[0103] (1) Prepare a 1% PVP aqueous solution.

[0104] (2) Weigh 1 g of waterborne PU resin and pour it into 10 g of 1% PVP aqueous solution. After stirring evenly, coat it on the non - woven fabric with a coating thickness of 20 μm to obtain a pretreated substrate.

[0105] 2. Preparation of graphene coating

[0106] (1) Prepare an aqueous carbon nanotube slurry with a mass percentage of carbon nanotubes of 8%.

[0107] (2) Disperse graphene in the aqueous carbon nanotube slurry by ultrasonic treatment to prepare an aqueous graphene slurry, where the mass percentage of graphene in the aqueous carbon nanotube slurry is 4%.

[0108] (3) Weigh 1.5 g each of waterborne hydroxy acrylic - amino resin, SBR solution, and waterborne polyurethane solution, add them to 30 g of the aqueous graphene slurry, stir evenly to obtain an aqueous graphene coating.

[0109] 3. Use an 80-μm wire bar coater to evenly coat the graphene aqueous coating on the pretreated substrate, air dry it naturally, and paste the electrodes.

[0110] Comparative Example 1

[0111] The difference between the preparation method of the graphene electrothermal film in this comparative example and that in Example 1 is only that the non-woven fabric substrate with a PU film in this comparative example is not pretreated and the graphene aqueous coating is directly coated, and the other steps are the same as those in Example 1.

[0112] Comparative Example 2

[0113] The difference between the preparation method of the graphene electrothermal film in this comparative example and that in Example 1 is only that the substrate pretreatment in this comparative example includes the following steps:

[0114] Weigh 1 g of aqueous PU resin and pour it into 10 g of water. After stirring evenly, coat it on the non-woven fabric with a PU film to obtain a pretreated substrate.

[0115] The other steps are the same as those in Example 1.

[0116] Comparative Example 3

[0117] The difference between the preparation method of the graphene electrothermal film in this comparative example and that in Example 1 is only that the substrate pretreatment in this comparative example includes the following steps:

[0118] Prepare a 2% PVP aqueous solution, weigh 10 g of the 2% PVP aqueous solution and coat it on the non-woven fabric with a PU film to obtain a pretreated substrate.

[0119] The other steps are the same as those in Example 1.

[0120] Comparative Example 4

[0121] The difference between the preparation method of the graphene electrothermal film in this comparative example and that in Example 1 is only that the substrate pretreatment in this comparative example includes the following steps:

[0122] (1) Prepare a 10% PVP aqueous solution

[0123] (2) Weigh 1 g of aqueous PU resin and pour it into 10 g of the 10% PVP aqueous solution. After stirring evenly, coat it on the non-woven fabric with a PU film to obtain a pretreated substrate.

[0124] The other steps are the same as those in Example 1.

[0125] Comparative Example 5

[0126] The difference between the preparation method of the graphene electrothermal film in this comparative example and that in Example 1 is only that the substrate pretreatment in this comparative example includes the following steps:

[0127] (1) Prepare a 2% aqueous PVP solution.

[0128] (2) Weigh 1.5 g of aqueous PU resin and pour it into 10 g of the 2% aqueous PVP solution. After stirring evenly, coat it on the non-woven fabric with a PU film to obtain a pretreated substrate.

[0129] Other steps are the same as those in Example 1.

[0130] Comparative Example 6

[0131] The difference between the preparation method of the graphene electrothermal film in this comparative example and that in Example 1 is only that the method for preparing the coating of graphene in this comparative example includes the following steps:

[0132] (1) Prepare an aqueous carbon nanotube slurry with a mass percentage of carbon nanotubes of 1%.

[0133] (2) Disperse graphene in the aqueous carbon nanotube slurry by ultrasonic waves to prepare an aqueous graphene slurry, wherein the mass percentage of graphene in the aqueous carbon nanotube slurry is 0.1%.

[0134] (3) Weigh 2.5 g each of aqueous hydroxyl acrylic-amine resin, SBR solution, and aqueous polyurethane solution, add them to 30 g of the aqueous graphene slurry, and stir evenly to obtain an aqueous graphene coating.

[0135] Other steps are the same as those in Example 1.

[0136] Performance Test Example

[0137] I. Sheet Resistance Test

[0138] Use a handheld four-probe tester to measure the sheet resistance of the graphene electrothermal films prepared in Examples 1-3 and Comparative Examples 1-6 respectively. The results are shown in Table 1.

[0139] Table 1 Sheet Resistance Test Results

[0140]

[0141] As can be seen from Table 1, the sheet resistance of Example 1 is 50 Ω / square, and that of Comparative Example 1 is 75 Ω / square, which proves that the substrate pretreatment method in the present invention can reduce the sheet resistance by 33%. The sheet resistance of Comparative Example 2 is 67 Ω / square, which is 34% higher than that of Example 1 and 10.6% lower than that of Comparative Example 1. It can be seen that when only aqueous PU resin is used as the substrate pretreatment liquid, the sheet resistance increases significantly. The sheet resistance of Comparative Example 3 is 72 Ω / square, which is 44% higher than that of Example 1 and 4% lower than that of Comparative Example 1. The sheet resistance of Comparative Example 4 is 66 Ω / square, which is 32% higher than that of Example 1 and 12% lower than that of Comparative Example 1. The sheet resistance of Comparative Example 5 is 58 Ω / square, which is 16% higher than that of Example 1 and 22.7% lower than that of Comparative Example 1. Through the comparison of Example 1 and Comparative Examples 1-5, it can be seen that mixing aqueous PU resin and PVP aqueous solution as the substrate pretreatment liquid and controlling it within a suitable concentration range can effectively reduce the sheet resistance. Excessive addition of aqueous PU resin or PVP aqueous solution will cause the sheet resistance to increase.

[0142] The sheet resistance of Example 2 is 32 Ω / square, which is 36% lower than that of Example 1. The sheet resistance of Comparative Example 6 is 70 Ω / square, indicating that after substrate pretreatment, the proportion of film-forming substances in the graphene coating formula also has a greater impact on the sheet resistance. Within a certain range, as the content of film-forming substances increases, the resistance of the electrothermal film will decrease significantly, while excessive addition of film-forming substances will also cause the sheet resistance to increase.

[0143] II. Heating Test

[0144] Connect the graphene electrothermal films prepared in Examples 1-3 and Comparative Examples 1-6 to a 5V voltage, and measure the temperature of the graphene electrothermal films after 10S. The results are as Figure 1 shown.

[0145] From Figure 1 it can be seen that at a 5V voltage, the temperatures of the graphene electrothermal films in Examples 1-3 and Comparative Examples 1-6 are 57°C, 64°C, 69°C, 45°C, 48°C, 46°C, 48.5°C, 50°C, and 47°C respectively. The heating test results are consistent with the sheet resistance test results. The graphene electrothermal film with a lower sheet resistance can heat up more quickly under a low-voltage environment.

[0146] III. Adhesion Test

[0147] According to GB / T 9286-1998, use a QFH-type cross cutter to test the coating adhesion of the graphene electrothermal films prepared in Examples 1-3 and Comparative Examples 1-6. The results are shown in Table 2.

[0148] Table 2 Adhesion Test Results

[0149]

[0150] As can be seen from Table 2, the graphene electrothermal films obtained by substrate pretreatment in Examples 1-3 and Comparative Examples 4-6 have better coating adhesion than the graphene electrothermal films obtained without substrate pretreatment in Comparative Examples 1-3, which fully demonstrates that after substrate pretreatment, the adhesion between the graphene slurry and the substrate is increased, making its coating more firm. The test results of Comparative Example 6 are similar to those of Example 2, indicating that excessive increase in the content of film-forming substances has basically no effect on the adhesion. The test result of Example 3 is 1.0. Comparing with Example 2, it can be seen that after substrate pretreatment, when different substrates are used, the adhesion difference is not significant.

[0151] IV. Flexural resistance test

[0152] The graphene electrothermal films prepared in Examples 1-3 and Comparative Examples 1-6 were bent inward by 180°, pressed with a 1 kg weight for 1 min, then the coating was bent outward by 180°, and pressed with a 1 kg weight for 1 min. Each bending and pressing was recorded as 1 time. The flexural resistance of the electrothermal film was investigated by the degree of deviation of the resistance of the electrothermal film after testing from the original resistance (△R / R), where △R = Ra - R, Ra is the resistance of the electrothermal film after testing, and R is the original resistance. The final value of △R / R is expressed as a percentage. The results are shown in Table 3.

[0153] Table 3 Flexural resistance test results

[0154]

[0155] As can be seen from Table 3, the graphene electrothermal films obtained by substrate pretreatment in Examples 1-3 and Comparative Examples 4-6 have better flexural resistance than the graphene electrothermal films obtained without substrate pretreatment in Comparative Examples 1-3. Substrate pretreatment increases the flexural resistance of the graphene electrothermal film by more than 200%.

[0156] In summary, by pretreating the substrate and then coating the graphene coating, the present invention increases the wettability, ductility and adhesion of the graphene coating. The prepared graphene electrothermal film has a low sheet resistance, fast heating rate, and significantly improved flexural resistance, and has broad application prospects in physiotherapy products.

[0157] The above-described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts shall fall within the scope of protection of the present invention.

Claims

1. A graphene electrothermal film, characterized in that, The graphene electrothermal film includes: A pretreated substrate, which includes a substrate and a pretreatment liquid coated on the surface of the substrate. The pretreatment liquid includes a water-based PU resin and a PVP solution; A graphene coating, which is coated on the pretreated substrate.

2. The graphene electrothermal film according to claim 1, wherein: The sheet resistance of the graphene electrothermal film is ≤50 Ω / square.

3. The graphene electrothermal film according to claim 1, characterized in that: The concentration of the PVP solution is 0.5% - 10%, and the mass of the water-based PU resin is 0.1% - 15% of the mass of the PVP solution.

4. The graphene electrothermal film according to claim 1, wherein: The graphene coating includes a carbon nanotube aqueous slurry, graphene, and a film-forming agent. The mass percentage of carbon nanotubes in the carbon nanotube aqueous slurry is 0.5% - 10%, the mass of the graphene is 0.1% - 5% of the mass of the carbon nanotube aqueous slurry, and the mass of the film-forming agent is 0.5% - 25% of the sum of the masses of the carbon nanotube aqueous slurry and the graphene.

5. The graphene electrothermal film according to claim 4, wherein: The film-forming agent is selected from one or more of hydroxyacrylic acid - amino resin, acrylic emulsion, SBR solution, and polyurethane solution.

6. The preparation method of the graphene electrothermal film according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: (1) Prepare a pretreatment liquid, coat the pretreatment liquid on the substrate to obtain a pretreated substrate; (2) Prepare a graphene coating, coat the graphene coating on the pretreated substrate to obtain the graphene electrothermal film.

7. The preparation method according to claim 6, characterized in that, The preparation method of the pretreatment liquid includes the following steps: Configure a PVP solution, mix the water-based PU resin and the PVP solution evenly to obtain a pretreatment liquid; preferably, the concentration of the PVP solution is 1% - 5%.

8. The preparation method according to claim 6, characterized in that, The preparation method of the graphene coating includes the following steps: Prepare a carbon nanotube slurry, mix the graphene and the carbon nanotube slurry and disperse them evenly by ultrasonic to obtain a graphene slurry, mix the film-forming agent and the graphene slurry evenly to obtain a graphene coating; preferably, the concentration of the carbon nanotube slurry is 0.5% - 5%.

9. The application of the graphene electrothermal film according to any one of claims 1 - 5 or the preparation method according to any one of claims 6 - 8 in the preparation of products for physical therapy.

10. Application of substrate pretreatment in the preparation of graphene electrothermal film, the method of the substrate pretreatment comprising the following steps: Configure a PVP solution, mix the water-based PU resin and the PVP solution evenly to obtain a pretreatment liquid; Coat the pretreatment liquid on the substrate to obtain a pretreated substrate.

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