A flexible planar heating element and water-based conductive carbon slurry suitable for flexible heating products

Abstract

The present invention discloses a flexible planar heating element and an aqueous conductive carbon slurry suitable for use in flexible heating products such as heated seats, seat cushions, electric blankets, and yoga mats. The flexible planar heating element includes a flexible substrate, an electrode, and a carbon film. The carbon film is made of an aqueous conductive carbon slurry. The aqueous conductive carbon slurry contains carbon nanotubes and a film-forming resin. The film-forming resin is a combination of two or three aqueous resins with different glass transition temperatures but all above 45°C. The flexible planar heating element of the present invention is flexible and bendable, and at the same time has suitable temperature characteristics. Under the premise of ensuring safety and improving the service life of the flexible planar heating element, the heating efficiency of the flexible planar heating element is maximized. It is particularly suitable for use in flexible products such as heated seats, seat cushions, electric blankets, and yoga mats, and is suitable for industrial production and market promotion.

Description

Technical Field

[0001] The invention relates to a flexible planar heating element and water-based conductive carbon slurry suitable for use in flexible heating products such as heated seats, seat cushions, electric blankets, yoga mats, etc. Background Art

[0002] With the advancement of science and technology and the improvement of living standards, people have higher and higher requirements for the safety and comfort of heating products. In cold seasons, some flexible heating products such as heated seats, seat cushions, electric blankets, yoga mats, etc. are often used, which can fit the human body directly for heating, and are soft and comfortable. Common flexible heating products on the market still generally use metal heating wires or carbon fibers as heating sources, which have defects such as slow heating, high power consumption, and uneven heating. In addition, metal heating wires and carbon fibers are relatively hard, which not only affects the comfort of flexible heating products, but also easily breaks and loses the heating function. After breaking, there are also greater safety hazards such as ignition or fire, electric shock, etc. As an emerging planar conductive heating material, the application of carbon-based flexible planar heating elements in flexible heating products is also considered. After being energized, carbon-based flexible planar heating elements can radiate far infrared rays and directly heat the human body by radiation. They have the advantages of high heating efficiency, health and comfort, energy saving and environmental protection, safety and pollution-free. Compared with linear heating elements, planar heating elements are more evenly dispersed and less likely to cause low-temperature scalding accidents, and are favored by more and more consumers.

[0003] However, in the prior art, the main application scenario of carbon-based flexible planar heating elements is still relatively fixed and rigid heating systems such as floor heating, and they are rarely used in flexible heating products such as electric blankets, heated seats, seat cushions, yoga mats, etc. A major factor limiting the application of planar heating elements in flexible heating products is the poor bending resistance of existing planar heating elements. Figure 5 As shown, the commercially available planar heating element breaks and becomes light-transmissive after being bent 10 times, and has a short service life, and cannot be applied to flexible products such as heated seats, seat cushions, electric blankets, and yoga mats that need to be bent frequently. Although patents such as CN113630914 A point out that the heating material prepared therein has bending resistance, the examination of the bending resistance is limited to whether there are changes in the appearance such as creases and fractures, and does not examine the changes in the electrical properties of the heating material after bending. In addition, the formula and process disclosed in the patent are relatively vague, and the claimed bending resistance effect cannot be achieved directly based on the disclosed content.

[0004] In addition, the surface temperature of the existing planar heating element will increase significantly when it is covered, generally more than twice the set temperature (above 100°C), which poses a safety hazard. In addition to the safety hazard, the significant increase in temperature also greatly affects the product experience and limits its application in flexible heating products. Summary of the invention

[0005] The purpose of the present invention is to provide a flexible planar heating element suitable for use in flexible heating products such as heated seats, seat cushions, electric blankets, yoga mats, etc., which is resistant to bending, has a long service life and good safety in view of the shortcomings and deficiencies of the prior art.

[0006] The present invention also provides an aqueous conductive carbon slurry for preparing a flexible planar heating element. The flexible planar heating element prepared therefrom is resistant to bending and not prone to peeling. It has the advantages of long service life, high safety, and good use experience when used in flexible heating products such as heated seats, seat cushions, electric blankets, yoga mats, or similar occasions.

[0007] In order to achieve the above object, a technical solution adopted by the present invention is as follows:

[0008] A flexible planar heating element comprises a flexible substrate, an electrode and a carbon film. The carbon film is made of an aqueous conductive carbon slurry. The aqueous conductive carbon slurry contains carbon nanotubes and a film-forming resin. The film-forming resin is a combination of two or three aqueous resins with different glass transition temperatures but all above 45°C.

[0009] Preferably, the glass transition temperatures of different types of waterborne resins differ by 10 to 30°C.

[0010] Furthermore, the flexible substrate described in the present invention includes but is not limited to polyethylene terephthalate (PET), polyimide (PI) and the like.

[0011] In a further preferred embodiment of the present invention, the aqueous conductive carbon paste of the present invention further comprises a polyolefin dispersion. Further preferably, the polyolefin dispersion is a combination of two or three aqueous polyolefin dispersions having a melting point of more than 70°C, and the melting points of the different aqueous polyolefin dispersions differ by 10 to 30°C.

[0012] Preferably, the peel strength between the carbon film and the substrate in the flexible planar heating element is greater than or equal to 20 N·m -1 .

[0013] Preferably, the temperature of the flexible planar heating element after being covered for 180 minutes does not exceed 100%, preferably does not exceed 95%, and more preferably does not exceed 90% of the set heating temperature. For example, when the set heating temperature is 45°C, the temperature of the flexible planar heating element after being covered for 180 minutes does not exceed 90°C.

[0014] Further preferably, the temperature of the flexible planar heating element after being covered for 180 minutes increases by no less than 50% compared to the set heating temperature.

[0015] In some preferred embodiments, the temperature of the flexible planar heating element after being covered for 180 minutes increases by 60% to 100% compared to the set heating temperature. In some more specific embodiments, the temperature of the flexible planar heating element after being covered for 180 minutes increases by 80% to 100% compared to the set heating temperature.

[0016] Furthermore, the "flexible planar heating element is covered" in the present invention means that the flexible planar heating element is covered with a 2 cm thick polystyrene extruded board (with a thermal conductivity of 0.03 W / (m·K) and a density of 35 kg / m 3 ) is covered.

[0017] Preferably, the melting points of different types of aqueous polyolefin dispersions differ by 10 to 30°C.

[0018] Furthermore, the carbon nanotubes are a combination of one or more of single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, carboxylated carbon nanotubes, and hydroxylated carbon nanotubes; the diameter of the carbon nanotubes may be 2 to 150 nm; the length of the carbon nanotubes may be 5 to 100 μm.

[0019] According to some specific preferred aspects of the present invention, the film-forming resin is composed of two or three aqueous resins selected from the group consisting of aqueous resins having glass transition temperatures of 45-55°C, 55-65°C, and 65-80°C, and the mass proportion of various aqueous resins in the film-forming resin is not less than 5%.

[0020] According to some preferred aspects of the present invention, the aqueous resin is a polyurethane resin and / or a polyester resin.

[0021] In some embodiments, the film-forming resin is composed of an aqueous resin with a glass transition temperature of 45 to 55° C. and an aqueous resin with a glass transition temperature of 55 to 65° C. in a mass ratio of 0.2 to 5:1. Preferably, the mass ratio of the two resins is 0.5 to 2:1.

[0022] In other embodiments, the film-forming resin is composed of an aqueous resin with a glass transition temperature of 45 to 55° C. and an aqueous resin with a glass transition temperature of 65 to 80° C. in a mass ratio of 0.2 to 5:1. Preferably, the mass ratio of the two resins is 0.5 to 2:1.

[0023] In some other embodiments, the film-forming resin is composed of an aqueous resin with a glass transition temperature of 55 to 65° C. and an aqueous resin with a glass transition temperature of 65 to 80° C. in a mass ratio of 0.2 to 5:1. Preferably, the mass ratio of the two resins is 0.5 to 2:1.

[0024] According to other specific preferred aspects of the present invention, the polyolefin dispersion is composed of two or three selected from aqueous polyolefin dispersions with melting points of 70-80°C, 80-90°C, and 90-115°C, and the mass proportion of various aqueous polyolefin dispersions in the polyolefin dispersion is not less than 10%.

[0025] In some embodiments, the polyolefin dispersion is composed of an aqueous polyolefin dispersion with a melting point of 70 to 80° C. and an aqueous polyolefin dispersion with a melting point of 80 to 90° C. in a mass ratio of 0.2 to 5:1. Preferably, the mass ratio of the two dispersions is 0.5 to 2:1.

[0026] In other embodiments, the polyolefin dispersion is composed of an aqueous polyolefin dispersion with a melting point of 70-80°C and an aqueous polyolefin dispersion with a melting point of 90-115°C in a mass ratio of 0.2-5:1. Preferably, the mass ratio of the two dispersions is 0.5-2:1.

[0027] In some other embodiments, the polyolefin dispersion is composed of an aqueous polyolefin dispersion with a melting point of 80-90°C and an aqueous polyolefin dispersion with a melting point of 90-115°C in a mass ratio of 0.2-5:1. Preferably, the mass ratio of the two dispersions is 0.5-2:1.

[0028] According to some preferred aspects of the present invention, the mass ratio of the film-forming resin to the polyolefin dispersion is 0.5 to 2:1, and more preferably, the mass ratio of the two is 0.5 to 1:1.

[0029] Furthermore, the aqueous conductive carbon slurry of the present invention is preferably prepared by the following steps:

[0030] First, the carbon nanotubes are dispersed in water in the presence of a dispersant and a defoamer to obtain a carbon nanotube dispersion having a uniform flow dynamic as a whole, wherein the mass content of the carbon nanotubes is 5% to 15%, the mass content of the dispersant is 5% to 15%, and the mass content of the defoamer is 0.1% to 1%;

[0031] Secondly, the carbon nanotube dispersion is mixed with the film-forming resin and polyolefin dispersion, and auxiliary agents are selectively added to obtain water-based conductive carbon slurry, wherein the mass content of the polyolefin dispersion in the water-based conductive carbon slurry is 10% to 50%.

[0032] In some preferred embodiments, the mass content of the polyolefin dispersion in the aqueous conductive carbon slurry is 20% to 30%.

[0033] In some preferred embodiments, the water-based resins are all single-component water-based resins, which can not only improve the storage stability of the water-based conductive carbon paste, but also avoid resistance fluctuations caused by insufficient cross-linking, thereby ensuring the resistance stability after film formation.

[0034] In some preferred embodiments, the defoaming agent includes a silicone defoaming agent and / or a polymer defoaming agent; preferably, the silicone defoaming agent includes polydimethylsiloxane and / or ethylene glycol siloxane; the polymer defoaming agent includes one or more of high carbon alcohols, polyoxyethylene oxypropylene glycerol, and copolymers of ethylene oxide and propylene oxide.

[0035] In some embodiments, the auxiliary agent includes one or more of an anti-settling agent, a thickener, a leveling agent, a rheological agent, and a film-forming aid. The thickener may be one or more of urea-modified polyurethane, polyurea, and water-based bentonite. The anti-settling agent may be one or more of a modified urea solution, a modified polyamide solution, and a urea-modified polyurethane solution. The film-forming aid may be one or more of propylene glycol methyl ether, diethylene glycol butyl ether, dipropylene glycol methyl ether, and N-ethyl pyrrolidone.

[0036] According to a specific embodiment of the present invention, the carbon nanotube dispersion, aqueous resin, aqueous polyolefin dispersion and film-forming aid are stirred and mixed at a stirring speed of 600 to 1200 rpm for 30 to 60 min, and then the aid is added and stirred and mixed at a stirring speed of 200 to 400 rpm for 10 to 30 min to obtain the aqueous conductive carbon slurry.

[0037] Compared with the prior art, the present invention has the following technical effects:

[0038] The flexible planar heating element of the present invention is specially designed for application in flexible heating products such as heated seats, seat cushions, electric blankets, yoga mats, etc. (but not limited to such occasions). g The components can delay overheating and ensure that no safety accidents will occur even if the product is partially covered within a few hours of power-on. When connected to a thermostat with a time limit function, safety accidents can be greatly reduced. The flexible surface heating element has significantly better bending resistance, which can extend the service life of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a SEM image of the dispersion of carbon nanotubes prepared in Example 1;

[0040] Figure 2 is a SEM image of the dispersion of carbon black prepared in Comparative Example 3;

[0041] Figure 3The DSC spectrum of the aqueous conductive carbon slurry prepared in Example 1 after film formation;

[0042] Figure 4 This is the DSC spectrum of the water-based conductive carbon slurry without adding polyolefin dispersion after film formation;

[0043] Figure 5 These are illumination photographs of the planar heating element after bending, where a is a commercially available planar heating element; b is a flexible planar heating element prepared based on the carbon film of Experimental Example 1. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with the examples. However, the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0045] This invention studies the characteristics and requirements of flexible heating products such as heated seats, seat cushions, electric blankets, yoga mats, etc. in application scenarios, and develops corresponding flexible planar heating elements based on the characteristics of flexible products, so as to maximize the satisfaction of user needs, extend product service life, and reduce product safety risks. According to our research:

[0046] 1) Compared with floor heating, heated seats, seat cushions, electric blankets, and yoga mats have different requirements for the mechanical properties of planar heating elements. The planar heating elements are required to be soft and resistant to bending, especially that the heating performance of the planar heating elements will not be affected after repeated bending;

[0047] 2) Safety is the most basic requirement for all heating products, which requires that the flexible planar heating elements of heated seats, seat cushions, electric blankets, and yoga mats can generate heat evenly and limit the temperature within a safe range to avoid local overheating of the flexible planar heating elements, which may cause burns, fires, and other safety issues. At the same time, according to our research, flexible products such as heated seats, seat cushions, electric blankets, and yoga mats generally do not overheat when the entire surface is covered due to the temperature sensing device. Avoiding partial coverage of the temperature sensing device is the core issue of safety risks. Taking into account safety, heating and heat dissipation effects, and user experience, it is appropriate for the flexible planar heating element to have a properly controlled heating characteristic after being partially covered.

[0048] In order to obtain the above-mentioned performance products, the present invention has comprehensively designed the overall formula of the carbon film, which is the core part of the flexible planar heating element. The carbon film used in the flexible planar heating element of the present invention is formed by water-based conductive carbon slurry. In terms of the formula composition, the conductive component uses carbon nanotubes, and the film-forming resin uses a variety of different glass transition temperatures T gIn addition to the conductive component and the film-forming resin, a polyolefin dispersion with a specific melting point is preferably added. Through the overall formula design, the prepared flexible planar heating element has excellent bending resistance and safety performance, and a long service life. This product is very suitable for use in flexible heating products such as heated seats, seat cushions, electric blankets, yoga mats, etc., and the product comfort and safety of use are further improved.

[0049] According to the water-based conductive carbon slurry of the present invention, the carbon nanotubes have a special linear structure and can be interwoven with the resin into a mesh connection structure, so that the flexible planar heating element prepared by using the carbon nanotubes has good bending resistance. In addition, the use of carbon nanotubes has significantly higher peel strength than other conductive materials. Figure 1 and Figure 2 It can be seen that the carbon nanotubes are distributed linearly after forming the film, and can form a more compact and reliable network connection structure with the resin compared to the point-like distribution of carbon black. Some experiments have proved that the peel strength between the carbon film made of carbon nanotubes and the flexible substrate is twice or more than the peel strength of the carbon film made of carbon black.

[0050] According to the aqueous conductive carbon slurry of the present invention, the combination of multiple aqueous resins, or the combination of multiple aqueous resins and aqueous polyolefin dispersions, in combination with carbon nanotubes, makes the formed carbon film have excellent flexibility, bending resistance and good bonding with the substrate. Among them, the combination of multiple aqueous resins in the formula helps to regulate the hardness of the carbon film. When an aqueous polyolefin dispersion is added, especially a polyolefin dispersion with a certain melting point, in addition to helping to improve the flexibility and bending resistance of the carbon film, it can also slow down and suppress the increase in temperature after the flexible planar heating element is covered. Figure 3 The DSC spectrum of the carbon film based on the formulation of Example 1 is shown (measured using a TA model Q-2000 differential calorimeter). It can be seen that the carbon film has obvious endothermic peaks and crystallization peaks in the range of 40 to 90°C. Accordingly, when covered, its surface temperature will increase rapidly in the initial stage, but after reaching a certain level, there will be no significant increase. Figure 4 It shows that no polyolefin dispersion is added and the waterborne resin contains only polyurethane dispersion DSC spectrum of carbon film made of UH 2606 water-based conductive carbon slurry. It can be seen that when no polyolefin dispersion is added and the glass transition temperature of the water-based resin is T g The carbon film prepared at low temperature has no endothermic peak and crystallization peak during the entire heating and cooling process. Accordingly, when covered, its surface temperature will continue to rise rapidly, generally exceeding the set temperature by more than twice (above 100°C), posing a safety hazard.

[0051] In summary, the flexible planar heating element in the present invention is flexible and bendable, and its temperature characteristics are suitable for use in flexible heating products such as heated seats, seat cushions, electric blankets, yoga mats, etc., and the heating efficiency of the flexible planar heating element is maximized under the premise of ensuring safety and improving the service life of the flexible planar heating element. The flexible planar heating element of the present invention has a fast temperature response speed at low temperature, rapid temperature rise, high energy utilization efficiency, and is suitable for industrial production and market promotion.

[0052] The present invention is further described in detail below with reference to specific embodiments.

[0053] The water-based resins used in the following examples and comparative examples are from Covestro Polymers Co., Ltd. (water-based polyurethane UH 2606, glass transition temperature of about 45°C) and Toyobo Co., Ltd. (aqueous polyester dispersion MD-1500, glass transition temperature of about 77°C), and the polyolefin dispersion was from Japan Unitika Co., Ltd. (SB-1010, melting point of about 83°C; SE-1010, melting point of about 93°C).

[0054] Example 1

[0055] This embodiment provides a carbon film for preparing a flexible planar heating element, which is prepared by the following method:

[0056] (1) Preparation of a dispersion of carbon nanotubes

[0057] After mechanically stirring water and dispersant at 400 rpm for 10 minutes, carbon nanotube powder was added thereto, stirred at a low speed of 600 rpm for 20 minutes in a high-speed disperser, then adjusted to a high speed of 1200 rpm for 30 minutes, and during the high-speed stirring process, a defoamer (polyether-modified organic silicone emulsion BYK1724) was added dropwise at a rate of 50 g / min, and then introduced into a sand mill for turbine grinding at 2000 rpm for 90 minutes, and then the sand milling was stopped to obtain a uniform dispersion; after standing for defoaming, a dispersion of carbon nanotubes was obtained and set aside.

[0058] Based on the total mass percentage of 100%, the composition of the carbon nanotube dispersion is: 10% carbon nanotubes, 10% dispersant DISPERBYK 2012, 0.3% defoaming agent and the balance water.

[0059] (2) Preparation of water-based conductive carbon slurry

[0060] 30 g of the carbon nanotube dispersion prepared in step (1) and the polyurethane dispersion 7 g of UH 2606, 8 g of aqueous polyester dispersion MD-1500, 15 g of polyolefin dispersion SB-1010, 15 g of polyolefin dispersion SE-1010, and 0.25 g of diethylene glycol butyl ether were mixed and dispersed at 600 rpm in a high-speed disperser for 30 min. Subsequently, 0.03 g of thickener BYK425 was added, and mechanical stirring was carried out at 300 rpm for 10 min. After standing for defoaming, an aqueous conductive carbon slurry was obtained.

[0061] (3) The aqueous conductive carbon slurry was coated on the carrier PET film by a doctor blade coating process and maintained at 140° C. for 3 min to solidify and form a carbon film.

[0062] Example 2

[0063] This embodiment provides a carbon film for preparing a flexible planar heating element. The preparation method of the carbon film is basically the same as that of Example 1. The main difference is that the polyolefin dispersion used in the aqueous conductive carbon slurry in this embodiment is a combination of SB-1010 and SE-1010 in a mass ratio of 0.5:1.

[0064] Example 3

[0065] This example provides a carbon film. The preparation method of the carbon film is basically the same as that of Example 1, except that in this example, the aqueous conductive carbon slurry does not contain a polyolefin dispersion. Specifically, the aqueous conductive carbon slurry is prepared by the following steps:

[0066] 30 g of the carbon nanotube dispersion prepared in step (1) of Example 1 and a polyurethane dispersion were added. 22 g of UH 2606, 23 g of aqueous polyester dispersion MD-1500, and 0.25 g of diethylene glycol butyl ether were mixed, dispersed at 600 rpm in a high-speed disperser for 30 min, and then 0.03 g of thickener BYK425 was added, mechanically stirred at 300 rpm for 10 min, and allowed to stand for defoaming to obtain an aqueous conductive carbon slurry.

[0067] Comparative Example 1

[0068] This comparative example provides a carbon film. The preparation method of the carbon film is basically the same as that of Example 1. The main difference is that the aqueous resin in the aqueous conductive carbon slurry in this comparative example is only one kind. Specifically, in step (2):

[0069] 30 g of carbon nanotube dispersion and polyurethane dispersion 15 g of UH 2606, 15 g of polyolefin dispersion SB-1010, 15 g of polyolefin dispersion SE-1010, and 0.18 g of diethylene glycol butyl ether were mixed and dispersed at 600 rpm in a high-speed disperser for 30 min. Subsequently, 0.03 g of thickener BYK425 was added, and mechanical stirring was carried out at 300 rpm for 10 min. After standing and defoaming, an aqueous conductive carbon slurry was obtained.

[0070] Comparative Example 2

[0071] This comparative example provides a carbon film, and the preparation method of the carbon film is basically the same as that of Example 1, except that in this example, there is only one polyolefin dispersion. Specifically, in step (2):

[0072] 30 g of the carbon nanotube dispersion prepared in step (1) and the polyurethane dispersion 7 g of UH 2606, 8 g of aqueous polyester dispersion MD-1500, 30 g of polyolefin dispersion SE-1010, and 0.25 g of diethylene glycol butyl ether were mixed and dispersed at 600 rpm in a high-speed disperser for 30 min. Subsequently, 0.03 g of thickener BYK425 was added, and mechanical stirring was carried out at 300 rpm for 10 min. After standing for defoaming, an aqueous conductive carbon slurry was obtained.

[0073] Comparative Example 3

[0074] This comparative example provides a carbon film, and the preparation method of the carbon film is as follows:

[0075] (1) Preparation of conductive carbon black dispersion

[0076] After mechanically stirring water and dispersant at 400 rpm for 10 min, carbon black was added and stirred at a low speed of 600 rpm for 20 min in a high-speed disperser and then adjusted to a high speed of 1200 rpm for 30 min. During the high-speed stirring, a defoamer (polyether-modified organosiloxane emulsion BYK1724) was added dropwise at a rate of 50 g / min. The mixture was then introduced into a sand mill and ground at 2000 rpm for 90 min, and then the sand mill was stopped to obtain a uniform dispersion. The carbon black dispersion was obtained after standing for defoaming and was set aside.

[0077] The composition of the conductive carbon black dispersion is 100% by weight: 25% conductive carbon black, 25% dispersant DISPERBYK 2012, 0.3% defoamer and the balance water.

[0078] (2) 30 g of the conductive carbon black dispersion prepared in step (1) and the polyurethane dispersion UH 26067g, aqueous polyester dispersion MD-1500 8g, polyolefin dispersion SB-1010 15g, polyolefin dispersion SE-1010 15g, and diethylene glycol butyl ether 0.25g were mixed and dispersed at 600 rpm in a high-speed disperser for 30 min, and then 0.03g of thickener BYK425 was added, mechanically stirred at 300 rpm for 10 min, and the aqueous conductive carbon slurry was obtained after standing and defoaming.

[0079] (3) The aqueous conductive carbon slurry was coated on the carrier PET film by a doctor blade coating process and maintained at 140° C. for 3 min to solidify and form a carbon film.

[0080] Example 4

[0081] This embodiment provides a flexible planar heating element suitable for flexible heating products such as heated seats, seat cushions, electric blankets, yoga mats, etc., which is prepared by the following method:

[0082] The silver paste prepared from the nano silver material is coated on the edge of the PET substrate with a polyurethane resin coating at both ends 55mm away by the gravure process, and the width is 15mm. Then, the water-based conductive paste is prepared according to the method described in Example 1 or 3 by the micro-dimpled technology and coated on the polyurethane resin coating (coated between 62.5mm from the edge of the first substrate on both sides, and part of the silver paste is covered on both sides), and kept at 140°C for 10min to solidify to form a carbon film and a silver electrode. The solidified silver electrode is partially exposed to the carbon film on both sides, and the nickel-plated copper foil electrode material is continued to be covered on the exposed silver electrode (12mm wide is covered on both sides at 47.5mm from the edge of the first substrate), and the electrode is made, and then the adhesive material is further coated on one side of the other PET substrate, and it is laid on the PET substrate with the electrode and carbon film made, and the substrate is bonded to the first substrate, the carbon film and the electrode by the adhesive material to obtain the flexible planar heating element. At this time, the peel strength of the flexible planar heating element can be tested, and accelerated life tests can be performed.

[0083] Performance test of the prepared carbon film and flexible planar heating element

[0084] The carbon films of the above examples were tested for thickness, square resistance, adhesion, hardness, and bending resistance, among which:

[0085] The thickness of the carbon film was measured using a height gauge;

[0086] The sheet resistance of the carbon film was measured by a four-probe sheet resistance meter at different locations at room temperature (25°C);

[0087] The adhesion test method of carbon film refers to ASTM D3359 standard method test;

[0088] The pencil hardness of carbon film is tested according to GB / T6031-1998 standard method.

[0089] Testing method for the bending resistance of carbon film: Make the carbon film into a standard thin strip with a length of 10 cm, a width of 0.6 mm, and a thickness of 5 μm. Use a digital ohmmeter or multimeter to measure the two ends of the carbon film to obtain the initial resistance value. Bend the carbon film outward 180 degrees, and press a 3kg weight on the crease for 1 minute; then bend the carbon film 180 degrees in the opposite direction at the crease, and press a 3kg weight on the crease for 1 minute; then unfold the carbon film, press the crease flat, and place a 3kg weight on the crease for 30 seconds; use an ohmmeter or multimeter to measure the resistance of the two ends of the standard carbon film again to obtain the resistance value after one bend. Repeat the above steps 10 times, use an ohmmeter or multimeter to measure the resistance value after each bend and calculate the resistance change rate.

[0090] The peel strength performance test of the flexible planar heating element is tested according to the JG / T286-2010 standard method.

[0091] The accelerated life test of flexible planar heating elements is based on the JG / T 286-2010 standard method test.

[0092] The above performance test results are shown in Table 1.

[0093] Table 1 Performance test results

[0094]

[0095] In addition, the flexible planar heating element made of the carbon paste of Example 1 and the commercially available heating film were folded 180 degrees. After being bent about 10 times, the commercially available heating film was creased / broken, while the heating film made of the carbon film of Example 1 was not broken or creased at all. The pictures of the samples after being bent and illuminated are as follows: Figure 5 shown.

[0096] From Table 1 and Figure 5 It can be seen that the flexible planar heating element according to the present invention has excellent bending resistance, suitable hardness, and long service life. Not only will no creases or breaks occur after bending, but the resistance value changes little after multiple bending, that is, the heating effect is less affected by bending.

[0097] In addition, the covering effect of the flexible planar heating element made of the conductive carbon paste based on the embodiment and the comparative example was tested. The testing method is as follows: through electrode design, the power density is 200W / m 2For heating, the heating temperature was set to 40°C, and an extruded board with good thermal insulation (made of polystyrene and 1.5 cm thick) was used for covering, with a covering area of ​​10 cm×10 cm. The temperature change of the flexible planar heating element after covering was tested by a thermocouple, and the results are shown in Table 2.

[0098] Table 2 Coverage performance test results of flexible planar heating element

[0099] project Example 1 Example 2 Comparative Example 1 Comparative Example 2 Initial temperature 40℃ 40℃ 40℃ 40℃ Cover 10min 69℃ 69℃ 69℃ 70℃ Cover 30min 71℃ 73℃ 75℃ 79℃ Cover 90min 80℃ 82℃ 83℃ 90℃ Coverage 180min 84℃ 85℃ 86℃ 93℃

[0100] It can be seen from Table 2 that the temperature of the flexible planar heating element of the present invention rises rapidly in the initial stage of being covered, but when the covering temperature rises to a higher temperature, the further heating rate decreases significantly, the heating element is safer and has a better product usage experience.

[0101] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

[0102] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

Claims

1. A flexible planar heating element, comprising a flexible substrate, an electrode and a carbon film, wherein the carbon film is made of an aqueous conductive carbon slurry. Features: The aqueous conductive carbon paste contains carbon nanotubes and a film-forming resin, wherein the film-forming resin is a combination of two or three aqueous resins with different glass transition temperatures but all above 45°C; the film-forming resin is composed of two or three aqueous resins selected from aqueous resins with glass transition temperatures of 45-55°C, 55-65°C, and 65-80°C, and the mass proportion of various aqueous resins in the film-forming resin is not less than 5%; the aqueous resin is a polyurethane resin and / or a polyester resin; the aqueous conductive carbon paste also includes a polyolefin dispersion, which is a combination of two or three aqueous polyolefin dispersions with melting points all above 70°C, and the melting points of different aqueous polyolefin dispersions differ by 10-30°C.

2. The flexible planar heating element according to claim 1, Features: The glass transition temperatures of different types of the waterborne resins differ by 10 to 30°C.

3. The flexible planar heating element according to claim 1, Features: The carbon nanotubes are a combination of one or more of single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, carboxylated carbon nanotubes, and hydroxylated carbon nanotubes.

4. The flexible planar heating element according to claim 1, Features: The diameter of the carbon nanotubes is 2-150 nm.

5. The flexible planar heating element according to claim 1, Features: The film-forming resin is composed of an aqueous resin with a glass transition temperature of 45 to 55°C and an aqueous resin with a glass transition temperature of 55 to 65°C in a mass ratio of 0.2 to 5:1; or an aqueous resin with a glass transition temperature of 45 to 55°C and an aqueous resin with a glass transition temperature of 65 to 80°C in a mass ratio of 0.2 to 5:1; or an aqueous resin with a glass transition temperature of 55 to 65°C and an aqueous resin with a glass transition temperature of 65 to 80°C in a mass ratio of 0.2 to 5:

1.

6. The flexible planar heating element according to claim 1, Features: The length of the carbon nanotubes is 5 to 100 μm.

7. The flexible planar heating element according to claim 1, Features: The polyolefin dispersion is composed of two or three selected from aqueous polyolefin dispersions with melting points of 70-80° C., 80-90° C., and 90-115° C., and the mass proportion of various aqueous polyolefin dispersions in the polyolefin dispersion is not less than 10%.

8. The flexible planar heating element according to claim 7, Features: The polyolefin dispersion is composed of an aqueous polyolefin dispersion with a melting point of 70 to 80°C and an aqueous polyolefin dispersion with a melting point of 80 to 90°C in a mass ratio of 0.2 to 5:1; or, the polyolefin dispersion is composed of an aqueous polyolefin dispersion with a melting point of 70 to 80°C and an aqueous polyolefin dispersion with a melting point of 90 to 115°C in a mass ratio of 0.2 to 5:1; or, the polyolefin dispersion is composed of an aqueous polyolefin dispersion with a melting point of 80 to 90°C and an aqueous polyolefin dispersion with a melting point of 90 to 115°C in a mass ratio of 0.2 to 5:

1.

9. The flexible planar heating element according to claim 1, Features: The mass ratio of the film-forming resin to the polyolefin dispersion is 0.5 to 2:

1.

10. The flexible planar heating element according to claim 1, Features: The aqueous conductive carbon slurry is prepared by the following steps: The first step is to disperse the carbon nanotubes in water in the presence of a dispersant and a defoamer to obtain a dispersion of carbon nanotubes that is uniform and dynamic as a whole, wherein the mass content of the carbon nanotubes, the mass content of the dispersant, and the mass content of the defoamer are 5% to 15%, 5% to 15%, and 0.1% to 1% respectively; The second step is to mix the carbon nanotube dispersion with the film-forming resin and the polyolefin dispersion, and selectively add an auxiliary agent to obtain the aqueous conductive carbon slurry, wherein the mass content of the polyolefin dispersion in the aqueous conductive carbon slurry is 10% to 50%.

11. An aqueous conductive carbon slurry as claimed in any one of claims 1 to 10.

12. Use of the flexible planar heating element according to any one of claims 1 to 10 in a flexible heating product.

13. Application of the flexible planar heating element according to claim 12 in a flexible heating product, Features: The flexible heating product is a heated seat, a seat cushion, an electric blanket or a yoga mat.

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