Paper-based flexible material with both electric heating and thermochromism as well as preparation method and application of paper-based flexible material

Abstract

The invention provides a paper-based flexible material with both electric heating and thermochromism and a preparation method and application thereof.The paper-based flexible material comprises a paper-based substrate, an electric heating layer located on one face of the paper-based substrate and a thermochromism layer located on the other face of the paper-based substrate, the electric heating layer comprises the following components: carbon black, graphite nanosheets, silver nanowires, carboxymethyl cellulose and waterborne polyurethane. The paper-based flexible material can realize excellent electric heating performance and thermochromism function, and is simple to prepare and good in stability.

Description

Technical Field

[0001] The present invention relates to the field of flexible electronic materials, in particular to a paper-based flexible material with both electrothermal heating and thermochromic properties, and a preparation method and application thereof. Background Art

[0002] With the increasing demand for information security and public safety, smart materials with electrothermal and thermochromic functions have gradually become a research hotspot in the field of emerging technologies. These materials have shown great potential in many fields, especially in file encryption and decryption and fire safety, because they can provide intuitive feedback through temperature changes. In terms of information protection, thermochromic materials can achieve the confidentiality of information through temperature changes, thereby effectively preventing unauthorized personnel from viewing sensitive content; and in fire safety, the combination of electrothermal and thermochromic materials can trigger color changes through temperature changes at the early stage of a fire, and send out warning signals in time to help prevent fires or take timely countermeasures, especially providing effective safety warnings for personnel at the beginning of a fire.

[0003] Although some electrothermal materials have been developed, the technology that effectively combines electrothermal and thermochromic functions is still relatively limited. At present, many existing materials either rely only on a single conductive material such as silver nanowires, graphene or carbon black, or cannot find an ideal balance between conductivity and flexibility, which affects the electrothermal performance. In addition, the existing technology also faces challenges such as complex processing, high cost and poor stability. For example, CN115450055A is a preparation and application of a colorful reversible electrothermochromic film based on graphene. This scheme only uses graphene as a conductive material, and its conductivity is limited. Its preparation involves multi-step operations, which is relatively cumbersome, such as the use of screen printing technology, the synthesis of microcapsules, and the printing of conductive silver paste circuits; its cyclic stability fluctuates greatly with temperature, and the mechanical properties of the material are not mentioned.

[0004] Therefore, how to develop a composite flexible material that has both excellent electrothermal properties and can effectively combine with thermochromic functions while ensuring low cost and high stability remains a technical problem that needs to be solved urgently in this field. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a paper-based flexible material having both electrothermal and thermochromic properties, and a preparation method and application thereof. The paper-based flexible material can achieve excellent electrothermal performance and thermochromic function, and is simple to prepare and has good stability.

[0006] The present invention is achieved through the following technical solutions: In the first aspect, the present invention provides a paper-based flexible material having both electrothermal and thermochromic properties, comprising: a paper-based substrate, an electrothermal layer on one side of the paper-based substrate, and a thermochromic layer on the other side of the paper-based substrate, wherein components of the electrothermal layer include: carbon black, graphite nanosheets, silver nanowires, carboxymethyl cellulose, and waterborne polyurethane.

[0007] Preferably, the mass ratio of carbon black, graphite nanosheets, silver nanowires, carboxymethyl cellulose and aqueous polyurethane is (10-40): (30-60): (10-70): (3-15): (5-20).

[0008] Preferably, the components of the thermochromic layer include: polyoxymethyleneimine, styrene-maleic anhydride monomethyl-maleate polymer, ODB-II, Green DCF, methyl stearate and color-changing phosphor.

[0009] Preferably, the paper-based substrate is printing paper.

[0010] In a second aspect, the present invention provides a method for preparing the paper-based flexible material having both electrothermal and thermochromic properties, comprising: S1, mixing carbon black, graphite nanosheets, silver nanowires, carboxymethyl cellulose, water-based polyurethane and water to obtain an electrothermal conductive ink; S2, coating the electrothermal conductive ink on one side of a paper-based substrate, drying, and heat-pressing; S3, coating the thermochromic ink on the other side of the paper-based substrate, and drying, to obtain a paper-based flexible material having both electrothermal and thermochromic properties.

[0011] Preferably, in S2, the drying temperature is 60-80° C. and the drying time is 20-25 minutes.

[0012] Preferably, in S2, the hot pressing conditions are: pressure of 2-10 MPa, temperature of 50-150° C., and time of 5-10 minutes.

[0013] Preferably, in S3, the drying temperature is 50°C to 80°C, and the time is 4 to 6 hours.

[0014] Preferably, in S2, the electrothermal conductive ink is coated on one side of the paper-based substrate by screen printing; in S3, the thermochromic ink is coated on the other side of the paper-based substrate by screen printing.

[0015] In a third aspect, the present invention provides the application of the paper-based flexible material having both electrothermal and thermochromic properties in the field of information security or fire warning.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The paper-based flexible material of the present invention has both electrothermal and thermochromic properties. It uses the synergistic effect of three conductive materials of different dimensions (zero-dimensional conductive carbon black (CB), one-dimensional silver nanowires (AgNWs), and two-dimensional graphite nanosheets) to construct a "mud-brick" structure, the formation of which depends on the size and shape differences of different conductive materials. Carbon black particles are filled between silver nanowires and graphite nanosheets like mud, while silver nanowires and graphite nanosheets form a stable framework structure in the material like bricks. Since conductive materials of different dimensions can provide various types of electron transmission paths, the conductivity, heating performance and flexibility of the material are effectively improved. Carboxymethyl cellulose can disperse carbon black, effectively prevent its agglomeration and ensure physical adsorption with the surface of graphite nanosheets. The addition of WPU (waterborne polyurethane) further enhances the film-forming property of the material and the bonding between the conductive materials, promotes the stability of the material, and ensures its excellent performance in multiple processing and use. At the same time, the present invention successfully integrates electrothermal heating and thermochromic functions, so that the paper-based flexible material generates heat under the action of voltage and changes color when a certain temperature is reached. It has dual functions and can be applied to fields such as information security (such as file encryption and decryption) and fire warning. The material of the present invention not only provides an indication of temperature changes, but also provides intuitive visual feedback, which enhances the reliability and practicality in security monitoring systems.

[0017] The present invention uses silver nanowires combined with conductive carbon black and graphite nanosheets to construct an electrothermal conductive ink, which is coated on one side of a paper-based substrate and subjected to hot pressing after drying to obtain a paper-based flexible material with an electrothermal function. The hot pressing treatment not only enhances the connectivity of the conductive path, but also improves the electrothermal performance of the material. At the same time, after the hot pressing treatment, the stability and stress resistance of the material are significantly improved, ensuring its reliability in long-term use and thermal cycles. Further, by coating thermochromic ink, a paper-based flexible material is prepared that has both an electrothermal function and can achieve fixed color changes from black to red, blue, green, etc.

[0018] Furthermore, the present invention adopts screen printing technology to prepare paper-based flexible materials, which has the advantages of simple process, low cost, and large-scale production. Compared with traditional methods, screen printing ensures the uniformity and stability of the material without affecting its flexibility, making it have broad application prospects in the fields of information security (such as file encryption and decryption) and fire warning. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 The cross-sectional scanning electron micrographs of the paper-based electrothermal material before and after heat pressing at different magnifications of Example 1 of the present invention are shown; (a) is the paper-based electrothermal material before heat pressing; (b) is the paper-based electrothermal material after heat pressing.

[0021] Figure 2 The surface scanning electron microscope images of the paper-based electrothermal material before and after heat pressing at different magnifications of Example 1 of the present invention are shown; a) the paper-based electrothermal material before heat pressing; (b) the paper-based electrothermal material after heat pressing.

[0022] Figure 3 The conductivity data of the paper-based electrothermal materials of Example 1 of the present invention and Comparative Example 1 before and after hot pressing are shown.

[0023] Figure 4 This is a temperature curve diagram of the paper-based electrothermal material without heat pressing treatment in Example 1 of the present invention when the voltage is 3V~9V.

[0024] Figure 5 This is a temperature curve diagram of the paper-based electrothermal material after heat pressing treatment in Example 1 of the present invention at a voltage of 3V~9V.

[0025] Figure 6 Thermal imaging of the paper-based flexible material with both electrothermal and thermochromic properties prepared in Example 1 of the present invention under deformation; a) is before deformation; b) to e) are bent by 10°, 30°, 60°, and 90°, respectively; f) to i) are twisted by 10°, 30°, 60°, and 90°, respectively.

[0026] Figure 7 This is a temperature curve diagram of the paper-based flexible material with both electrothermal heating and thermochromic properties prepared in Example 1 of the present invention when voltage is applied continuously and cyclically.

[0027] Figure 8 These are photos of the paper-based flexible material with both electrothermal and thermochromic properties connected to a voltage of 3.5 V in Example 1 of the present invention; a) to i).

[0028] Fig. 9 This is a picture of the application of paper-based flexible materials with both electrothermal and thermochromic properties in information protection according to Example 1 of the present invention; a) the pattern of the thermochromic layer is the QR code of the official website of Shaanxi University of Science and Technology, Invisible is before voltage is applied, and Visible is after voltage is applied; b) the pattern of the thermochromic layer is the Morse code of 0-9 and AZ, Invisible is before voltage is applied, and Visible is after voltage is applied.

[0029] Fig.10These are pictures of the application of the paper-based flexible material with both electrothermal heating and thermochromic properties in the early stage of a fire according to Example 1 of the present invention; a) before voltage is applied; b) after voltage is applied.

[0030] Fig.11 These are stress-strain curves of the paper-based electrothermal material of Example 1 of the present invention without hot pressing treatment, hot pressing treatment at 50°C and 10 MPa, and hot pressing treatment at 150°C and 10 MPa. DETAILED DESCRIPTION

[0031] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0032] It should be noted that the process equipment or devices not specifically specified in the following embodiments are all conventional equipment or devices in the art.

[0033] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0034] The paper-based flexible material with both electrothermal and thermochromic properties described in the present invention comprises: a paper-based substrate, an electrothermal layer located on one side of the paper-based substrate, and a thermochromic layer located on the other side of the paper-based substrate. Components of the electrothermal layer include: carbon black, graphite nanosheets, silver nanowires, carboxymethyl cellulose and waterborne polyurethane.

[0035] The paper-based flexible material of the present invention has both electrothermal and thermochromic properties. It uses the synergistic effect of three conductive materials of different dimensions (zero-dimensional conductive carbon black, one-dimensional silver nanowires, and two-dimensional graphite nanosheets) to construct a "mud-brick" structure, which effectively improves the conductivity and flexibility of the material. Carbon black is dispersed by carboxymethyl cellulose, which effectively prevents its agglomeration and ensures physical adsorption on the surface of graphite nanosheets. The combination of silver nanowires and graphite nanosheets further improves the conductivity and heating performance of the paper-based flexible material. At the same time, the present invention successfully integrates electrothermal and thermochromic functions, so that the material generates heat under the action of voltage and changes color when a certain temperature is reached. It has dual functions and can be applied to fields such as information security (such as file encryption and decryption) and fire warnings. The material not only provides an indication of temperature changes, but also provides intuitive visual feedback, which enhances the reliability and practicality in security monitoring systems.

[0036] In some embodiments of the present invention, the mass ratio of the carbon black, graphite nanosheets, silver nanowires, carboxymethyl cellulose and aqueous polyurethane is (10-40): (30-60): (10-70): (3-15): (5-20).

[0037] In some embodiments of the present invention, the components of the thermochromic layer include: polyoxymethyleneimine, styrene-maleic anhydride monomethyl-maleate polymer, ODB-II, Green DCF, methyl stearate and color-changing phosphor.

[0038] In some embodiments of the present invention, the paper-based substrate is one of printing paper, filter paper or other papers.

[0039] The method for preparing the paper-based flexible material having both electrothermal and thermochromic properties comprises: S1, mixing carbon black, graphite nanosheets, silver nanowires, carboxymethyl cellulose, water-based polyurethane and water to obtain an electrothermal conductive ink; S2, coating the electrothermal conductive ink on one side of a paper-based substrate, drying, and heat-pressing; S3, coating the thermochromic ink on the other side of the paper-based substrate, and drying, to obtain a paper-based flexible material having both electrothermal and thermochromic properties.

[0040] In some embodiments of the present invention, S1 specifically comprises: grinding, filtering and screening carbon black particles; adding carbon black, graphite nanosheets, silver nanowires, carboxymethyl cellulose, water-based polyurethane and water into a ball mill for ball milling to obtain an electrothermal conductive ink. The mass ratio of carbon black, graphite nanosheets, silver nanowires, carboxymethyl cellulose, water-based polyurethane and water in the electrothermal conductive ink is (10-40): (30-60): (10-70): (3-15): (5-20): (1000-1600). The addition of carboxymethyl cellulose can disperse carbon black, effectively prevent its agglomeration and ensure physical adsorption with the surface of graphite nanosheets; the addition of water-based polyurethane further enhances the film-forming property of the ink and the bonding property between the conductive materials, promotes the stability of the material, and ensures its excellent performance in multiple processing and use.

[0041] In some embodiments of the present invention, in S2, the drying temperature is 60-80° C. and the drying time is 20-25 minutes.

[0042] In some embodiments of the present invention, the hot pressing conditions are: pressure of 2-10 MPa, temperature of 50-150° C., and time of 5-10 minutes. Hot pressing can significantly reduce the cross-section of the conductive layer, and form node welding between AgNWs, thereby improving the conductivity of the material.

[0043] In some embodiments of the present invention, in S3, the drying temperature is 50°C-80°C, and the drying time is 4-6 hours.

[0044] In some embodiments of the present invention, in S2, the electrothermal conductive ink is coated on one side of the paper-based substrate by screen printing; in S3, the thermochromic ink is coated on the other side of the paper-based substrate by screen printing; the mesh number of the screen printing screen is preferably 80 meshes.

[0045] The present invention adopts screen printing process to prepare paper-based flexible materials with both electrothermal and thermochromic properties, which has the advantages of simple process, low cost, and large-scale production. Compared with traditional methods, screen printing ensures the uniformity and stability of the material without affecting its flexibility, making it have broad application prospects in the fields of wearable devices, flexible electronic devices, etc.

[0046] The paper-based flexible material with both electrothermal and thermochromic properties prepared by the above preparation method can achieve a maximum temperature of about 77±5°C after 1 minute under a low applied voltage of 3V in an electrothermal test; maintain about 108±4°C when bent 10°~90° or twisted 10°~90° under a low applied voltage of 4.5V; and reach a saturation temperature of about 235°C±7°C after 1 minute under a low applied voltage of 9V.

[0047] Example 1 Step 1, grinding and filtering the carbon black particles, sieving them with a 100-mesh grading sieve, and ball-milling the carbon black, graphite nanosheets, silver nanowires, carboxymethyl cellulose, water-based polyurethane and deionized water in a ball mill at a mass ratio of 30:40:70:10:10:1000 at a rotation speed of 550 rpm for 6 hours to obtain an electrothermal conductive ink.

[0048] Step 2, using screen printing with a screen mesh of 80 meshes, print a pattern of 6 cm in length and 1 cm in width on one side of A4 printing paper.

[0049] Step 3, placing in an electric hot air drying oven at 80° C., pre-drying for 20 minutes to obtain a paper-based electrothermal material.

[0050] Step 4, placing the obtained paper-based electrothermal material between two iron plates, and treating it with a small hot press at 150° C. and 10 MPa for 10 min to form an electrothermal layer, thereby obtaining a paper-based flexible electrothermal material.

[0051] Step 5, on the other side of the printing paper, continue to print three different thermochromic inks, namely black to red ink, black to green ink, and black to blue ink, and dry them in an electric hot air drying oven at 80°C for 4 hours to form a thermochromic layer, thereby obtaining a paper-based flexible material with both electrothermal and thermochromic properties.

[0052] The paper-based flexible material with both electrothermal and thermochromic properties obtained in this embodiment has an electrical conductivity of 183.2 S / cm. In the electrothermal test, it can be achieved under a low voltage of 4.5V, and maintain about 108±4°C when bent 10°~90° or twisted 10°~90°; under a low applied voltage of 9V, it reaches a saturation temperature of about 235°C±7°C after 1min. When the thermochromic layer pattern is a screen-printed Shaanxi University of Science and Technology official website QR code, the QR code pattern is invisible under natural visual observation. When a 4V voltage is connected, the QR code is blue and can be observed by the naked eye. Similarly, when printing the Morse code of 0-9 and AZ, it is also invisible under visual observation. When a voltage is connected, electrothermal heating, thermochromic, and Morse code appears blue. The electrothermal conductive ink is printed on one side of the printing paper, and the thermochromic ink is printed on the other side of the printing paper. The pattern of the thermochromic layer is "Caution Hot, EXIT, DO not touch". After the voltage is connected, it will change color thermochromically to help prevent fire or take timely countermeasures.

[0053] Example 2 The method is basically the same as Example 1, except that the mass ratio of carbon black, graphite nanosheets, silver nanowires, carboxymethyl cellulose, aqueous polyurethane and deionized water is 30:40:50:10:10:1000.

[0054] The paper-based flexible material with both electrothermal and thermochromic properties obtained in this embodiment has an electrical conductivity of 133.3 S / cm. In an electrothermal test, it can maintain a temperature of about 73°C±3°C when bent by 10°~90° or twisted by 10°~90° under a low applied voltage of 4.5V; and reach a saturation temperature of about 176±5°C after 1 minute under a low applied voltage of 9V.

[0055] Example 3 The method is basically the same as Example 1, except that the mass ratio of carbon black, graphite nanosheets, silver nanowires, carboxymethyl cellulose, aqueous polyurethane and deionized water is 30:40:30:10:10:1000.

[0056] The paper-based flexible material with both electrothermal and thermochromic properties obtained in this embodiment has an electrical conductivity of 116.3 S / cm. In an electrothermal test, it can maintain a temperature of about 56°C±3°C when bent by 10°~90° or twisted by 10°~90° under a low applied voltage of 4.5V; and reach a saturation temperature of about 154°C±5°C after 1 minute under a low applied voltage of 9V.

[0057] Example 4 The method is basically the same as Example 1, except that the mass ratio of carbon black, graphite nanosheets, silver nanowires, carboxymethyl cellulose, aqueous polyurethane and deionized water is 30:40:10:10:10:1000.

[0058] The paper-based flexible material with both electrothermal and thermochromic properties obtained in this embodiment has an electrical conductivity of 113.6 S / cm. In an electrothermal test, it can maintain a temperature of about 49°C±4°C when bent by 10°~90° or twisted by 10°~90° under a low applied voltage of 4.5V; and reach a saturation temperature of about 138°C±5°C after 1 minute under a low applied voltage of 9V.

[0059] Comparative Example 1 The method is basically the same as Example 1, except that no silver nanowires are added.

[0060] The paper-based flexible material with both electrothermal and thermochromic properties obtained in this comparative example has an electrical conductivity of 103S / cm. In an electrothermal test, it can maintain a temperature of about 46°C±4°C when bent by 10°~90° or twisted by 10°~90° under a low applied voltage of 4.5V; and reach a saturation temperature of about 103°C±6°C after 1 minute under a low applied voltage of 9V.

[0061] Figure 1 The cross-sectional SEM images of the paper-based electrothermal material before and after hot pressing under different magnifications in Example 1 of the present invention are shown. Figure 1As can be seen in a), the cross section of the paper-based electrothermal material that has not been heat-pressed forms a conductive layer in which graphite nanosheets, carbon black, and AgNWs overlap with each other. Figure 1 As can be seen in b), the cross-section of the paper-based electrothermal material after heat pressing is significantly smaller than the cross-section of the conductive layer without heat pressing, which improves the conductivity of the material and thus achieves excellent conductivity.

[0062] Figure 2 The surface scanning electron microscope of the paper-based electrothermal material before and after hot pressing at different magnifications in Example 1 of the present invention. Figure 2 It can be seen from a) that the conductive layer is formed on the plane of the paper-based electrothermal material that has not been heat-pressed. Figure 2 As can be seen in b), there will be node welding between the AgNWs in the paper-based electrothermal material after hot pressing treatment, which improves the conductivity of the material and thus achieves excellent conductivity.

[0063] like Figure 3 As shown, the conductivity of the paper-based electrothermal material before and after hot pressing in Example 1 of the present invention and Comparative Example 1 can be seen. It can be seen that when silver nanowires are added, the conductivity can be improved. As the content of silver nanowires increases, the conductivity gradually increases. When the content of silver nanowires is increased to 100% of the total mass of graphite nanosheets and carbon black, the conductivity reaches 183.2 S / cm. Therefore, the conductivity of the paper-based flexible material with both electrothermal and thermochromic properties finally prepared is 183.2 S / cm. At the same time, it can also be seen that compared with the paper-based electrothermal material without hot pressing, the conductivity of the paper-based electrothermal material after hot pressing is improved.

[0064] Figure 4 This is a temperature curve of the paper-based electrothermal material that has not been heat-pressed in Example 1 of the present invention, at 3V to 9V. Figure 4 It can be seen that the paper-based electrothermal material that has not been heat-pressed can heat to 158.7°C within 1 minute under an applied voltage of 9V.

[0065] Figure 5 The temperature curve of the paper-based electrothermal material after heat pressing treatment in Example 1 of the present invention under the voltage of 3V~9V is shown. It can be seen that the paper-based electrothermal material after heat pressing treatment of the present invention has excellent electrothermal performance. Under the external voltage of 9V, it can heat up to 242℃ within 1min and maintain a stable heating temperature. After the applied voltage is turned off, it returns to room temperature within 50s. Figure 4 By comparison, it can be seen that the electrothermal performance of the paper-based electrothermal material is significantly improved after hot pressing treatment, which should be due to the improvement of the conductivity of the paper-based electrothermal material after hot pressing treatment.

[0066] Figure 6 The paper-based flexible material having both electrothermal heating and thermochromic properties according to Example 1 of the present invention maintains about 108±4° C. when bent by 10° to 90° or twisted by 10° to 90° at a voltage of 4.5V.

[0067] Figure 7 This is a temperature curve diagram of the paper-based flexible material with both electrothermal and thermochromic properties under a voltage of 4.5 V when voltage is continuously applied and voltage is cyclically applied. It can be seen that the material has good long-term and cyclic stability.

[0068] Figure 8 The paper-based flexible material with both electrothermal heating and thermal color change prepared in Example 1 of the present invention changes from black to red, green and blue respectively after being connected to an external voltage of 3.5V.

[0069] Fig. 9 The thermochromic layer patterns prepared for Example 1 of the present invention are the two-dimensional code of the official website of Shaanxi University of Science and Technology and the Morse code, which are both electrothermal and thermochromic paper-based flexible material images. Under natural visual observation, the two-dimensional code pattern is invisible. When a 4V voltage is connected, the two-dimensional code pattern is blue and can be observed by the naked eye. Similarly, when the Morse code of 0-9 and AZ is printed, it is also invisible under visual observation. When a voltage is connected, electrothermal heating and thermochromic change occur, and the Morse code appears blue.

[0070] Fig.10 The thermochromic layer pattern prepared in Example 1 of the present invention is "Caution Hot, EXIT, DO nottouch" and the paper-based flexible material with both electrothermal and thermochromic properties can be observed with the naked eye after voltage is connected, which helps prevent fire or take timely countermeasures.

[0071] Fig.11 The stress-strain curves of the paper-based electrothermal material without hot pressing treatment, hot pressing treatment at 50°C and 10MPa, and hot pressing treatment at 150°C and 10MPa are shown in Example 1 of the present invention. It can be seen that the stability and stress resistance of the paper-based electrothermal material are significantly improved after hot pressing treatment.

[0072] Example 5 Step 1, the carbon black particles are ground and filtered, and sieved using a 100-mesh grading sieve, and the carbon black, graphite nanosheets, carboxymethyl cellulose, water-based polyurethane, silver nanowires and deionized water are ball-milled in a ball mill at a mass ratio of 10:60:35:3:20:1250 at a rotation speed of 550 rpm for 6 hours to obtain an electrothermal conductive ink.

[0073] Step 2, using screen printing with a screen mesh of 80 meshes, print a pattern of 6 cm in length and 1 cm in width on one side of A4 printing paper.

[0074] Step 3, placing in an electric hot air drying oven at 80° C., pre-drying for 20 minutes to obtain a paper-based electrothermal material.

[0075] Step 4: Place the obtained paper-based electrothermal material between two iron plates, and process it with a small hot press at 100° C. and 10 MPa for 10 min to form an electrothermal layer, thereby obtaining a paper-based flexible electrothermal material.

[0076] Step 5, on the other side of the paper-based electrothermal material, continue to print thermochromic ink (black turns to red, green, and blue), dry it in an electric hot air drying oven at 80° C. for 4 hours to form a thermochromic layer, and obtain a paper-based flexible material with both electrothermal and thermochromic properties.

[0077] The flexible material with both electrothermal and thermochromic properties obtained in this embodiment has an electrical conductivity of 148 S / cm. In the electrothermal test, it can be achieved that under a low voltage of 4.5V, it can maintain about 83°C when bent 10°~90° or twisted 10°~90°; under a low applied voltage of 9V, it reaches a saturation temperature of about 142°C after 1min. When the thermochromic layer pattern is the screen-printed Shaanxi University of Science and Technology official website QR code, the QR code pattern is invisible under natural visual observation. When a 4V voltage is connected, the QR code is blue and can be observed by the naked eye. Similarly, when the Morse code of 0-9 and AZ is printed, it is also invisible under visual observation. When a voltage is connected, electrothermal heating, thermochromic, and Morse code appears blue. The electrothermal conductive ink is printed on one side of the printing paper, and the thermochromic ink is printed on the other side of the printing paper. The thermochromic layer pattern is "Caution Hot, EXIT, DO nottouch". After the voltage is connected, it is thermochromic, which helps prevent fires or take timely countermeasures.

[0078] Example 6 Step 1, the carbon black particles are ground and filtered, and sieved using a 100-mesh grading sieve, and the carbon black, graphite nanosheets, carboxymethyl cellulose, water-based polyurethane, silver nanowires and deionized water are ball-milled in a ball mill at a mass ratio of 20:50:20:15:5:1500 at a rotation speed of 550 rpm for 6 hours to obtain an electrothermal conductive ink.

[0079] Step 2, using screen printing with a screen mesh of 80 meshes, print a pattern of 6 cm in length and 1 cm in width on one side of A4 printing paper.

[0080] Step 3, placing in an electric hot air drying oven at 80° C., pre-drying for 25 minutes to obtain a paper-based electrothermal material.

[0081] Step 4, placing the obtained paper-based electrothermal material between two iron plates, and processing it with a small hot press at 75° C. and 10 MPa for 10 min to form an electrothermal layer, thereby obtaining a paper-based flexible electrothermal material.

[0082] Step 5, on the other side of the printing paper, continue to print the thermochromic ink (black turns to red, green, and blue), dry it in an electric hot air drying oven at 50° C. for 6 hours to form a thermochromic layer, and obtain a paper-based flexible material with both electrothermal and thermochromic properties.

[0083] The paper-based flexible material with both electrothermal and thermochromic properties obtained in this embodiment has an electrical conductivity of 125 S / cm. In the electrothermal test, it can be achieved that under a low voltage of 4.5V, it can be bent 10°~90° or twisted 10°~90° to maintain about 82°C; under a low applied voltage of 9V, it reaches a saturation temperature of about 136°C after 1min. When the thermochromic layer pattern is the Shaanxi University of Science and Technology official website QR code, the QR code pattern is invisible under natural visual observation. When a 4V voltage is connected, the QR code is blue and can be observed by the naked eye. Similarly, when the Morse code of 0-9 and AZ is printed, it is also invisible under visual observation. When a voltage is connected, electrothermal heating, thermochromic, and Morse code appears blue. The electrothermal conductive ink is printed on one side of the printing paper, and the thermochromic ink is printed on the other side of the printing paper. The thermochromic layer pattern is "Caution Hot, EXIT, DO nottouch". After the voltage is connected, it is thermochromic, which helps prevent fires or take timely countermeasures.

[0084] Example 7 Step 1, the carbon black particles are ground and filtered, and sieved using a 100-mesh grading sieve, and the carbon black, graphite nanosheets, carboxymethyl cellulose, water-based polyurethane, silver nanowires and deionized water are ball-milled in a ball mill at a mass ratio of 40:30:10:5:15:1600 at a rotation speed of 550 rpm for 6 hours to obtain an electrothermal conductive ink.

[0085] Step 2, using screen printing with a screen mesh of 80 meshes, print a pattern of 6 cm in length and 1 cm in width on one side of A4 printing paper.

[0086] Step 3, placing in an electric hot air drying oven at 80° C., pre-drying for 25 minutes to obtain a paper-based electrothermal material.

[0087] Step 4, placing the obtained paper-based electrothermal material between two iron plates, and processing it with a small hot press at 50° C. and 10 MPa for 10 min to form an electrothermal layer, thereby obtaining a paper-based flexible electrothermal material.

[0088] Step 5, on the other side of the printing paper, continue to print the thermochromic ink (black turns to red, green, and blue), dry it in an electric hot air drying oven at 50° C. for 6 hours to form a thermochromic layer, and obtain a paper-based flexible material with both electrothermal and thermochromic properties.

[0089] The flexible material with both electrothermal heating and thermochromic properties obtained in this embodiment has an electrical conductivity of 162S / cm. In the electrothermal test, it can be achieved that under a low voltage of 4.5V, it can maintain about 95°C when bent 10°~90° or twisted 10°~90°; under a low applied voltage of 9V, it reaches a saturation temperature of about 168°C after 1min. When the thermochromic layer pattern is the QR code of the official website of Shaanxi University of Science and Technology, the QR code pattern is invisible under natural visual observation. When a 4V voltage is connected, the QR code is blue and can be observed by the naked eye. Similarly, when the Morse code of 0-9 and AZ is printed, it is also invisible under visual observation. When a voltage is connected, electrothermal heating, thermochromic, and Morse code appears blue. The electrothermal conductive ink is printed on one side of the printing paper, and the thermochromic ink is printed on the other side of the printing paper. The thermochromic layer pattern is "Caution Hot, EXIT, DO not touch". After the voltage is connected, it is thermochromic, which helps prevent fires or take timely countermeasures.

Claims

1. A paper-based flexible material with both electrothermal and thermochromic properties, characterized in that: include: A paper-based substrate, an electrothermal layer on one side of the paper-based substrate, and a thermochromic layer on the other side of the paper-based substrate. The components of the electrothermal layer include carbon black, graphite nanosheets, silver nanowires, carboxymethyl cellulose and waterborne polyurethane.

2. The paper-based flexible material with both electrothermal and thermochromic properties according to claim 1, characterized in that: The mass ratio of carbon black, graphite nanosheets, silver nanowires, carboxymethyl cellulose and waterborne polyurethane is (10~40):(30~60):(10~70):(3~15):(5~20).

3. The paper-based flexible material with both electrothermal and thermochromic properties according to claim 1, characterized in that: The components of the thermochromic layer include: polyoxymethylene aminomethane, styrene-maleic anhydride monomethyl-maleate polymer, ODB-II, Green DCF, methyl stearate and color-changing fluorescent powder.

4. The paper-based flexible material with both electrothermal and thermochromic properties according to claim 1, characterized in that: The paper-based substrate is printing paper.

5. The method for preparing the paper-based flexible material having both electrothermal and thermochromic properties according to any one of claims 1 to 4, characterized in that: include: S1, mixing carbon black, graphite nanosheets, silver nanowires, carboxymethyl cellulose, water-based polyurethane and water to obtain an electrothermal conductive ink; S2, coating the electrothermal conductive ink on one side of a paper-based substrate, drying, and heat-pressing; S3, coating the thermochromic ink on the other side of the paper-based substrate, and drying, to obtain a paper-based flexible material having both electrothermal and thermochromic properties.

6. The method for preparing the paper-based flexible material having both electrothermal and thermochromic properties according to claim 5, characterized in that: In S2, the drying temperature is 60-80°C and the drying time is 20-25 minutes.

7. The method for preparing the paper-based flexible material having both electrothermal and thermochromic properties according to claim 5, characterized in that: In S2, the hot pressing conditions are: pressure of 2-10 MPa, temperature of 50-150°C, and time of 5-10 minutes.

8. The method for preparing the paper-based flexible material having both electrothermal and thermochromic properties according to claim 5, characterized in that: In S3, the drying temperature is 50°C~80 and the time is 4~6h.

9. The method for preparing the paper-based flexible material having both electrothermal and thermochromic properties according to claim 5, characterized in that: In S2, the electrothermal conductive ink is coated on one side of the paper-based substrate by screen printing; in S3, the thermochromic ink is coated on the other side of the paper-based substrate by screen printing.

10. Application of the paper-based flexible material having both electrothermal and thermochromic properties as claimed in any one of claims 1 to 4 in the field of information security or fire warning.

Images