An electrothermal film with pressure-sensitive characteristics and a preparation method thereof

Abstract

The present invention discloses a pressure-sensitive electrothermal film and a preparation method thereof. The pressure-sensitive electrothermal film structurally comprises a lower protective layer, a heating layer, an upper protective layer, and electrodes attached to the heating layer and lead wires led out. The heating layer comprises the following components: 95-98 wt% of polyurethane resin, 2-5 wt% of graphene, and 0.01-0.5 wt% of black phosphorus / metal oxide nanocomposite. In the present invention, graphene fillers slightly lower than the conductive percolation threshold range are filled in the polyurethane film, and a small amount of black phosphorus / metal oxide nanocomposite is added to enhance the pressure-sensitive property of the film. After the electrothermal film is powered on, when there is no external pressure, since the content of graphene in the heating layer is slightly lower than the percolation threshold, the resistance of the heating layer is large at this time and it does not generate heat; when a certain pressure is applied to the electrothermal film from the outside, the graphene sheets in the heating layer approach each other to form a conductive path, and the electrothermal film starts to generate heat. When the external force disappears, the heating layer returns to its original state and stops generating heat.

Description

Technical Field

[0001] The present invention belongs to the technical field of new materials, relates to an electrothermal film, and particularly relates to an electrothermal film with pressure-sensitive characteristics and a preparation method thereof. Background Art

[0002] Black phosphorus is an inorganic semiconductor material with a layer-stacked honeycomb structure, which is a direct-bandgap P-type semiconductor with a bandgap value between 0.33 - 0.39 eV. Few-layer black phosphorus has a current on-off ratio of 10 3 -10 5 . Research shows that applying compressive stress in the direction perpendicular to the phosphorene plane can cause the transition of phosphorene from a direct-bandgap semiconductor to an indirect-bandgap semiconductor. The strain along the normal direction of phosphorene can reduce its bandgap width, realizing the transition of the physical properties from a semiconductor to a metal. When the strain is 3.32%, black phosphorus changes from a direct-bandgap semiconductor to an indirect-bandgap semiconductor; when the strain is 13.35%, black phosphorus changes from a semiconductor to a conductor. Based on the first-principles calculation, researchers found that the bandgap of black phosphorus can be adjusted by external stress. Therefore, various properties related to the bandgap, such as the conductivity and static dielectric constant of black phosphorus, will change with the variation of external stress. This characteristic indicates that black phosphorus has excellent piezoresistive properties. In addition, black phosphorus also has a high thermal resistance value, a relatively high Seebeck coefficient, an extremely low thermal conductivity and resistivity, making it have excellent thermoelectric properties, which helps to design high-performance thermoelectric devices.

[0003] Nanometal oxides are a kind of multifunctional new materials with excellent non-ohmic characteristics, fast response time, large current-carrying capacity, and small leakage current, and possess excellent piezoresistive characteristics. Graphene has excellent electrical conductivity and can endow originally insulating materials with electrical conductivity, but this often requires a high graphene filling rate, and graphene itself has weak piezoresistivity and is not sensitive enough to external pressure.

[0004] Currently, electrothermal films are increasingly popular among people due to their fast heating speed, uniform heating temperature, convenient use, and high energy utilization efficiency. Especially in the southern regions without heating in winter, they have become a widespread demand. However, currently, the electrothermal films on the market are for overall heating controlled by a switch. After the switch is turned on, the entire heating surface of the electrothermal film starts to heat, and even the areas not in contact with the human body are in a heating state. However, the heat generated in these areas is not transferred to the human body but wasted in the form of thermal radiation, resulting in increased energy consumption. Especially for electrothermal films such as seat cushions and mattresses, there are a large number of areas not in contact with the human body, and more heat is wasted. Therefore, how to prepare an electrothermal film using new materials that can accurately transfer heat to the human body and reduce ineffective heating is of great significance for improving heat utilization efficiency and reducing energy consumption. Summary of the Invention

[0005] The main object of the present invention is to provide a pressure-sensitive electrothermal film and its preparation method, so as to overcome the deficiencies in the prior art.

[0006] To achieve the foregoing object of the invention, the technical solutions adopted by the present invention include:

[0007] An embodiment of the present invention provides a pressure-sensitive electrothermal film, including the following structure: a lower protective layer, a heating layer, an upper protective layer, and electrodes attached to the heating layer and lead wires led out.

[0008] In some more specific embodiments, the heating layer includes the following components: 95-98 wt% of polyurethane resin, 2-5 wt% of graphene, and 0.01-0.5 wt% of black phosphorus / metal oxide nanocomposite.

[0009] Further, the thickness of the graphene is 1-10 nm, the sheet diameter is 0.5-10 μm, and the oxygen content is less than 0.1 wt%.

[0010] Further, the mass ratio of black phosphorus to metal oxide in the black phosphorus / metal oxide nanocomposite is 0.1-10, and the particle size range of the composite material is 10-100 nm.

[0011] Further, the preparation method of the black phosphorus / metal oxide nanocomposite is the high-energy ball milling method, the ball milling atmosphere is argon, the ball milling speed is 500-1000 r / min, and the ball milling time is 5-15 h.

[0012] Further, the metal oxide is one or more mixtures of nano zinc oxide, nano aluminum oxide, nano titanium dioxide or nano zirconium oxide.

[0013] In some more specific embodiments, the preparation method of the pressure-sensitive electrothermal film includes the following steps: 1) uniformly disperse the black phosphorus / metal oxide nanocomposite in deionized water after removing oxygen to obtain a black phosphorus / metal oxide nanocomposite dispersion, and the concentration of the dispersion is 1-10 mg / ml;

[0014] 2) Disperse the required mass of graphene in the above-mentioned nanocomposite dispersion to obtain a dispersion with a graphene concentration of 50-100 mg / ml;

[0015] 3) Add the required mass of aqueous polyurethane emulsion to the dispersion prepared in 2) and further disperse it evenly to obtain an aqueous slurry; the solid content of the aqueous polyurethane is 30-60%;

[0016] 4) The aqueous slurry is applied by doctor blading to scrape a wet film with a specific thickness on the release film, and the wet film is dried under heating conditions to obtain a dry film; the thickness of the wet film is 200 - 800 μm; the drying temperature of the wet film is 60 - 100 °C;

[0017] Steps 1) - 4) are all carried out in a glove box filled with inert gas;

[0018] 5) On the upper and lower surfaces of the dry film prepared in 4), complete metal conductive paste layers are respectively printed, and after drying, they are used as heating electrodes, and wires are led out on the upper and lower layers respectively for connecting the power supply; the dry film with metal electrodes and wires on the surface is the heating layer of the electrothermal film; the metal conductive paste is any one of conductive silver paste, conductive copper paste, and conductive aluminum paste; the drying temperature is 100 - 150 °C.

[0019] In some more specific embodiments, the lower protective layer, the heating layer, and the upper protective layer are laminated by hot pressing to obtain the described heating film.

[0020] Further, both the upper protective layer and the lower protective layer are PET films, PI films, acrylic fiber cloths, and nylon fiber cloths with hot melt adhesive on one side; the lamination temperature is 120 - 160 °C.

[0021] The idea of the present invention is to utilize the excellent piezoresistivity of nano black phosphorus and metal oxides, so that the black phosphorus / metal oxide nanocomposite can combine the characteristics of the two, further improving the piezoresistive performance. Then, combining the black phosphorus / metal oxide nanocomposite with graphene can simultaneously exert the conductivity of graphene and the piezoresistivity of the composite material, while greatly reducing the graphene filling rate and endowing it with piezoresistivity.

[0022] Compared with the prior art, the advantages of the present invention include:

[0023] 1) The content of graphene in the heating layer of the heating film of the present invention is slightly lower than its percolation threshold in polyurethane. Under normal conditions, the graphene sheets do not form a complete conductive path, and at this time, the heating film is in an insulating state and does not heat up when powered on. When a certain external pressure is applied, the heating layer is elastically deformed under pressure, the graphene sheets approach each other, forming a complete conductive network, so that the resistance of the heating layer drops sharply, and the current can flow through the heating layer when powered on, causing the heating layer to heat up. When the external pressure disappears, the heating layer rebounds, and the graphene sheets in the layer return to their original state, the conductive path breaks, and the resistance of the heating layer rises, stopping heating. The heating film provided by the present invention can heat in real time according to the change of external pressure, the part with external pressure heats up, and the part without external pressure does not heat up, which can greatly reduce energy consumption and save electricity.

[0024] 2) The present invention adds a black phosphorus / metal oxide nanocomposite into a polyurethane / graphene conductive film. Black phosphorus is a typical semiconductor material with an extremely high current on-off ratio. When under pressure, black phosphorus can quickly transform from a semiconductor to a conductor, and this property can greatly enhance the pressure sensitivity of the heating layer in the present invention. After adding black phosphorus, its pressure sensitivity is greatly improved compared with traditional pressure-sensitive conductive materials. In addition, black phosphorus has excellent thermoelectric effects and can effectively convert electrical energy into heat energy, thus improving the heating efficiency. Nano metal oxides have strong pressure-sensitive characteristics. The combination of nano black phosphorus and nano metal oxides can fully utilize the unique properties of both, and the prepared composite material has extremely strong semiconductor properties, thermoelectric properties, and pressure-sensitive characteristics. Adding it into related materials can effectively improve the thermoelectric and pressure-sensitive properties of pressure-sensitive materials and products.

[0025] 3) The black phosphorus / metal oxide nanocomposite has a strong nano effect, which helps to improve the dispersion of graphene in polyurethane resin. In addition, the surface effect and nano-size effect of nano materials can significantly improve the toughness, heat resistance, and anti-aging properties of the polyurethane / graphene film, increasing the service life of the heating film. Description of the Drawings

[0026] Figure 1 is a schematic structural diagram of the heating film according to an embodiment of the present invention;

[0027] Among them, 101 is the upper protective layer, 102 is the heating layer, 103 is the lower protective layer, 201 is the metal paste electrode, 202 is the pressure-sensitive layer, and 203 is the wire connected to the electrode.

[0028] Figure 2 is a graph showing the relationship between the resistance and pressure of the specimens prepared in Examples 1-4 and Comparative Example 1 of the present invention. Detailed Embodiments

[0029] In view of the deficiencies in the prior art, the inventors of this case have, through long-term research and a large number of practices, proposed the technical solution of the present invention. The following will further explain the technical solution, its implementation process, principles, etc.

[0030] An embodiment of the present invention provides a pressure-sensitive electrothermal film, including the following structure: a lower protective layer, a heating layer, an upper protective layer, and an electrode attached to the heating layer and a lead wire led out; the heating layer includes the following components: 95-98 wt% of polyurethane resin, 2-5 wt% of graphene, and 0.01-0.5 wt% of black phosphorus / metal oxide nanocomposite.

[0031] In some more specific implementation schemes, the preparation method of the pressure-sensitive electrothermal film includes the following steps:

[0032] (1) Take two substances with a mass ratio of black phosphorus to metal oxide of 0.1 - 10 and place them in a ball milling tank filled with argon. Ball mill at a speed of 500 - 1000 r / min for 5 - 15 h to obtain a black phosphorus / metal oxide composite material with a particle size range of 10 - 100 nm;

[0033] (2) In a glove box filled with inert gas, uniformly disperse the black phosphorus / metal oxide nanocomposite material in deionized water after removing oxygen to obtain a dispersion with a concentration of 1 - 10 mg / ml; Subsequently, disperse the required mass of graphene in the above nanocomposite material dispersion to obtain a graphene dispersion with a concentration of 50 - 100 mg / ml; Add an appropriate amount of aqueous polyurethane emulsion with a solid content of 30 - 60% to the above dispersion and further disperse it evenly to obtain an aqueous slurry; Use the doctor blade coating method to scrape a wet film with a thickness of 200 - 800 μm on a release film, and dry the wet film at 60 - 100 °C to obtain a dry film;

[0034] (3) Print complete metal conductive paste layers on the upper and lower surfaces of the dry film respectively, dry them at 100 - 150 °C, and use them as heating electrodes. Lead out wires on the upper and lower layers for connecting the power supply; The dry film with metal electrodes and wires on the surface is the heating layer of the electrothermal film; Adopt a hot pressing lamination method at 120 - 160 °C to laminate the lower protective layer, the heating layer, and the upper protective layer to obtain the heating film.

[0035] The following will further explain the technical solution, its implementation process, principle, etc. in combination with specific embodiments.

[0036] Example 1

[0037] A preparation method of an electrothermal film with pressure-sensitive characteristics includes the following steps:

[0038] (1) Take two substances with a mass ratio of black phosphorus to nano-zinc oxide of 0.1 and place them in a ball milling tank filled with argon. Ball mill at a speed of 1000 r / min for 5 h to obtain a black phosphorus / zinc oxide composite material with a particle size range of 80 nm;

[0039] (2) In a glove box filled with inert gas, uniformly disperse the black phosphorus / zinc oxide nanocomposite material in 100 ml of deionized water after removing oxygen to obtain a dispersion with a concentration of 1 mg / ml; Subsequently, disperse the required mass of graphene in the above nanocomposite material dispersion to obtain a graphene dispersion with a concentration of 50 mg / ml; Add 200 g of aqueous polyurethane emulsion with a solid content of 60% to the above dispersion and further disperse it evenly to obtain an aqueous slurry; Use the doctor blade coating method to scrape a wet film with a thickness of 200 μm on a release film, and dry the wet film at 100 °C to obtain a dry film;

[0040] (3) On the upper and lower surfaces of the dry film, complete conductive silver paste layers are printed respectively. After drying at 100 °C, they serve as heating electrodes, and wires are led out on the upper and lower layers respectively for connecting the power supply; the dry film with metal electrodes and wires on its surface is the heating layer of the electrothermal film; by using a hot pressing lamination method at 120 °C, the PET film with hot melt adhesive on its upper surface is used as the lower protective layer, the heating layer, and the PET film with hot melt adhesive on its lower surface is used as the upper protective layer for lamination, and the said heating film can be obtained.

[0041] Comparative Example 1

[0042] (1) In a glove box filled with inert gas, the required mass of graphene is dispersed in 100 ml of deionized water after removing oxygen to obtain a graphene dispersion with a concentration of 50 mg / ml; 200 g of an aqueous polyurethane emulsion with a solid content of 60% is added to the above dispersion and further dispersed evenly to obtain an aqueous slurry; the aqueous slurry is scraped onto a release film to form a wet film with a thickness of 200 μm, and the wet film is dried at 100 °C to obtain a dry film.

[0043] (2) On the upper and lower surfaces of the dry film, complete conductive silver paste layers are printed respectively. After drying at 100 °C, they serve as heating electrodes, and wires are led out on the upper and lower layers respectively for connecting the power supply; the dry film with metal electrodes and wires on its surface is the heating layer of the electrothermal film; by using a hot pressing lamination method at 120 °C, the PET film with hot melt adhesive on its upper surface is used as the lower protective layer, the heating layer, and the PET film with hot melt adhesive on its lower surface is used as the upper protective layer for lamination, and the said heating film can be obtained.

[0044] Example 2

[0045] (1) Two substances with a mass ratio of black phosphorus to nano-aluminum oxide of 1 are placed in a ball milling tank filled with argon and ball milled at a speed of 600 r / min for 7 h to obtain a black phosphorus / aluminum oxide composite material with a particle size range of 100 nm.

[0046] (2) In a glove box filled with inert gas, the black phosphorus / aluminum oxide nano-composite material is evenly dispersed in 100 ml of deionized water after removing oxygen to obtain a dispersion with a concentration of 2 mg / ml; subsequently, the required mass of graphene is dispersed in the above nano-composite material dispersion to obtain a graphene dispersion with a concentration of 60 mg / ml; 260 g of an aqueous polyurethane emulsion with a solid content of 50% is added to the above dispersion and further dispersed evenly to obtain an aqueous slurry; the aqueous slurry is scraped onto a release film to form a wet film with a thickness of 400 μm, and the wet film is dried at 80 °C to obtain a dry film.

[0047] (3) On the upper and lower surfaces of the dry film, complete conductive copper paste layers are printed respectively. After drying at 120 °C, they serve as heating electrodes, and wires are led out on the upper and lower layers respectively for connecting the power supply; the dry film with metal electrodes and wires on its surface is the heating layer of the electrothermal film; by using a hot pressing lamination method at 180 °C, the PI film with hot melt adhesive on its upper surface is used as the lower protective layer, the heating layer, and the PI film with hot melt adhesive on its lower surface is used as the upper protective layer for lamination, and the heating film can be obtained.

[0048] Example 3

[0049] (1) Take two substances with a mass ratio of black phosphorus to nano-titanium dioxide of 5 and place them in a ball milling tank filled with argon. Ball mill at a rotation speed of 800 r / min for 10 h to obtain a black phosphorus / titanium dioxide composite material with a particle size range of 30 nm;

[0050] (2) In a glove box filled with inert gas, uniformly disperse the black phosphorus / titanium dioxide nano-composite material in 100 ml of deionized water after removing oxygen to obtain a dispersion with a concentration of 5 mg / ml; subsequently, disperse the required mass of graphene in the above nano-composite material dispersion to obtain a graphene dispersion with a concentration of 70 mg / ml; add 350 g of an aqueous polyurethane emulsion with a solid content of 40% to the above dispersion and further disperse it evenly to obtain an aqueous slurry; use the aqueous slurry in a doctor blade coating method to scrape a wet film with a thickness of 500 μm on a release film, and dry the wet film at 80 °C to obtain a dry film;

[0051] (3) On the upper and lower surfaces of the dry film, complete conductive aluminum paste layers are printed respectively. After drying at 150 °C, they serve as heating electrodes, and wires are led out on the upper and lower layers respectively for connecting the power supply; the dry film with metal electrodes and wires on its surface is the heating layer of the electrothermal film; by using a hot pressing lamination method at 140 °C, the acrylic fiber cloth with hot melt adhesive on its upper surface is used as the lower protective layer, the heating layer, and the nylon fiber cloth with hot melt adhesive on its lower surface is used as the upper protective layer for lamination, and the heating film can be obtained.

[0052] Example 4

[0053] Take two substances with a mass ratio of black phosphorus to nano-zirconium oxide of 10 and place them in a ball milling tank filled with argon. Ball mill at a rotation speed of 500 r / min for 15 h to obtain a black phosphorus / zirconium oxide composite material with a particle size range of 10 nm;

[0054] (2) In a glove box filled with inert gas, uniformly disperse the black phosphorus / zirconium oxide nanocomposite in 100 ml of deionized water after removing oxygen to obtain a dispersion with a concentration of 10 mg / ml; subsequently, disperse the required mass of graphene in the above nanocomposite dispersion to obtain a graphene dispersion with a concentration of 100 mg / ml; add 600 g of an aqueous polyurethane emulsion with a solid content of 30% to the above dispersion and further disperse it evenly to obtain an aqueous slurry; use the scraping method to scrape a wet film with a thickness of 800 μm on a release film, and dry the wet film at 60 °C to obtain a dry film;

[0055] (3) Print complete conductive aluminum paste layers on the upper and lower surfaces of the dry film respectively. After drying at 130 °C, use them as heating electrodes, and lead out wires on the upper and lower layers for connecting the power supply; the dry film with metal electrodes and wires on its surface is the heating layer of the electrothermal film; use a hot pressing method at 160 °C to bond the acrylic fiber cloth with hot melt adhesive on the upper surface as the lower protective layer, the heating layer, and the nylon fiber cloth with hot melt adhesive on the lower surface as the upper protective layer, and then the heating film can be obtained.

[0056] Table 1 Test results of elongation at break of specimens prepared in examples and comparative examples

[0057] specimen Example 1 Comparative Example 1 Example 2 Example 3 Example 4 Elongation at break (%) 1180 950 1230 1290 1410

[0058] Table 2 Test results of working life of specimens prepared in examples and comparative examples

[0059] (Test method: Simulated life test method in Chapter 22 of GB / T 7287-2008, test time 60 hours)

[0060]

[0061] From Figure 2 the results, it can be seen that as the external pressure increases, the resistance of the specimens in the examples and comparative examples all decreases to varying degrees, but the decrease amplitude of Comparative Example 1 is the smallest. When the pressure is 40 N, the resistance drops from 550 Ω to about 300 Ω. When the pressure is further increased, the resistance only shows a slight decrease; while the specimens of Examples 1-4 show an obvious decrease in resistance under a smaller pressure, and the decrease amplitude of the resistance is larger, dropping from above 500 Ω to about 60 Ω, showing a more obvious pressure-sensitive characteristic, and showing the pressure-sensitive characteristic under a smaller pressure compared with the comparative examples, which indicates that the black phosphorus / metal oxide nanocomposite effectively improves the pressure-sensitive characteristic of the electrothermal film.

[0062] Table 1 results show that the elongation at break of the example specimens with the addition of black phosphorus / metal oxide nanocomposites is higher than that of the comparative examples, and the toughness of the example specimens is significantly enhanced compared to the comparative examples. The test results in Table 2 show that after the simulated aging test, the electro-thermal conversion efficiency of the example specimens is more than 90% of that before the test, while this value for the comparative examples is 89.2%, lower than 90%, which reflects that the aging life of the example specimens is significantly improved compared to the comparative examples.

[0063] It should be understood that the above examples are only for illustrating the technical concept and features of the present invention, and the purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. An electrothermal film with pressure-sensitive characteristics, characterized in that, It includes the following structures: a lower protective layer, a heating layer, an upper protective layer, and electrodes attached to the heating layer and the lead wires led out. The heating layer includes the following components: 95-98 wt% of polyurethane resin, 2-5 wt% of graphene, and 0.01-0.5 wt% of black phosphorus / metal oxide nanocomposite; the mass ratio of black phosphorus to metal oxide in the black phosphorus / metal oxide nanocomposite is 0.1-10, and the particle size range of the composite is 10-100 nm; the preparation method of the black phosphorus / metal oxide nanocomposite is the high-energy ball milling method, the ball milling atmosphere is argon, the rotation speed of the ball mill is 500-1000 r / min, and the ball milling time is 5-15 h; the metal oxide in the black phosphorus / metal oxide nanocomposite is one or more of nano-zinc oxide, nano-aluminum oxide, nano-titanium dioxide, or nano-zirconium oxide.

2. The electrothermal film with pressure-sensitive characteristics according to claim 1, wherein: The thickness of the graphene is 1-10 nm, the sheet diameter is 0.5-10 μm, and the oxygen content is less than 0.1 wt%.

3. The preparation method of the electrothermal film with pressure-sensitive characteristics according to any one of claims 1 to 2, characterized by including: 1) Uniformly disperse the black phosphorus / metal oxide nanocomposite in deionized water after removing oxygen to obtain a black phosphorus / metal oxide nanocomposite dispersion, and the concentration of the dispersion is 1-10 mg / ml; 2) Disperse the required mass of graphene powder in the above-mentioned nanocomposite dispersion to obtain a dispersion with a graphene concentration of 50-100 mg / ml; 3) Add the required mass of aqueous polyurethane emulsion to the dispersion prepared in 2) and further disperse it evenly to obtain an aqueous slurry, and the solid content of the aqueous polyurethane is 30-60%; 4) Use the aqueous slurry by the doctor blade method to scrape a wet film with a specific thickness on the release film, and dry the wet film under heating conditions to obtain a dry film; the thickness of the wet film is 200-800 μm, and the drying temperature of the wet film is 60-100 °C; steps 1)-4) are all carried out in a glove box filled with inert gas; 5) Print a complete metal conductive paste layer on the upper and lower surfaces of the dry film prepared in step 4), and after drying, it is used as a heating electrode, and lead wires are led out on the upper and lower layers for connecting the power supply; the dry film with metal electrodes and lead wires on the surface is the heating layer of the electrothermal film; the metal conductive paste is any one of conductive silver paste, conductive copper paste, and conductive aluminum paste; the drying temperature is 100-150 °C.

4. The preparation method of the electrothermal film with pressure-sensitive characteristics according to claim 3, wherein: The lower protective layer, the heating layer, and the upper protective layer are laminated by hot pressing to obtain the electrothermal film.

5. The preparation method of the electrothermal film with pressure-sensitive characteristics according to claim 4, characterized in that: The upper protective layer and the lower protective layer are one or two of PET film, PI film, acrylic fiber cloth, and nylon fiber cloth with hot melt adhesive on one side; the lamination temperature is 120-160 °C.

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