Heating membrane and preparation method thereof, heating tube and heating electric appliance

Abstract

The invention provides a heating membrane and a preparation method thereof, a heating tube and a heating electric appliance. The preparation raw materials of the heating membrane comprise natural graphite, graphene oxide or graphene microchips, the heating membrane has a critical temperature, and when the temperature of the heating membrane is lower than the critical temperature, the resistance of the heating membrane is reduced along with the temperature rise; and when the temperature of the heating membrane is higher than the critical temperature, the resistance of the heating membrane is increased along with the rise of the temperature. The heating membrane has the characteristic of self-limiting temperature, so that on one hand, the heating membrane can accelerate the temperature rising speed of a temperature zone below the critical temperature so as to enable the heating membrane to reach the target temperature as soon as possible, and on the other hand, when the temperature is higher than the critical temperature, the problem of fusing caused in the continuous heating temperature rising process can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical appliances, and specifically, to a heating film, a preparation method thereof, a heating tube, and a heating appliance. Background Art

[0002] Traditional electric ovens mainly heat the air in the cavity through heating tubes to heat food and directly heat the surface of food by means of thermal radiation. Currently, the heating components used in heating appliances such as electric ovens, microwave ovens, steam ovens, etc. mainly include metal heating tubes (the highest heating temperature range is between 550 and 750 °C), quartz heating tubes (the temperature range of the heating wire is between 660 and 800 °C), halogen heating tubes (the highest heating temperature is less than 1000 °C), and carbon fiber heating tubes (the highest heating temperature is less than 1000 °C), etc. However, the above-mentioned heating tubes have problems such as slow heating speed, insufficient temperature, or easy high-temperature fusing during the heating process, which prolongs the cooking time and makes it difficult to achieve the crispy outside and tender inside of food during the heating process, resulting in a poor user experience. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems in the related art to some extent. For this reason, an object of the present invention is to provide a heating film, which has the advantage of self-limiting temperature and can reduce the fusing problem caused by high temperature during the continuous rise of the heating temperature.

[0004] In one aspect of the present invention, the present invention provides a heating film. According to an embodiment of the present invention, the preparation raw materials of the heating film include natural graphite, graphene oxide, or graphene microflakes. The heating film has a critical temperature. When the temperature of the heating film is less than the critical temperature, the resistance of the heating film decreases with the increase of temperature; when the temperature of the heating film is greater than the critical temperature, the resistance of the heating film increases with the increase of temperature. It can be seen that the heating film of the present invention has the characteristic of self-limiting temperature. Specifically: in the initial stage of heating (that is, when the temperature of the heating film is less than the critical temperature), the resistance of the heating film decreases with the increase of temperature, and the current increases, so that the power of the heating film increases with the increase of temperature. Therefore, in this stage, the heating film can quickly heat up; when the heating temperature of the heating film reaches the critical temperature, the resistance of the heating film increases with the increase of temperature, and the current decreases, so that the power of the heating film decreases with the increase of temperature. Therefore, in this stage, the heating rate of the heating film begins to slow down. The self-limiting temperature characteristic of the above-mentioned heating film can enable the heating film to, on the one hand, accelerate the heating rate in the temperature range below the critical temperature and make the heating film reach the target temperature as soon as possible, and on the other hand, when the temperature is higher than the critical temperature, it can reduce the fusing problem caused by the continuous rise of the heating temperature.

[0005] According to an embodiment of the present invention, when the temperature of the heating film is lower than the critical temperature, the heating rate of the heating film is the first heating rate; when the temperature of the heating film is higher than the critical temperature, the heating rate of the heating film is the second heating rate, wherein the first heating rate is greater than the second heating rate.

[0006] According to an embodiment of the present invention, the critical temperature value of the heating film is 50°C - 500°C.

[0007] According to an embodiment of the present invention, the material of the heating film is graphite, or the material of the heating film is graphene, or the heating film comprises graphene and an auxiliary agent, the auxiliary agent comprises at least one of a reinforcing agent and a resistance regulator, the reinforcing agent comprises at least one of carbon nanotubes, fullerenes, carbon black and graphene microflakes, and the resistance regulator comprises at least one of silicon carbide, boron nitride and silicon nitride.

[0008] According to an embodiment of the present invention, the heating film is sheet-shaped.

[0009] According to an embodiment of the present invention, the heating film satisfies at least one of the following conditions: the thickness of the heating film is 0.04 mm - 2 mm; the density of the heating film is 0.6 g / cm 3 ~1.8 g / cm 3 。

[0010] According to an embodiment of the present invention, the weight of the heating film with a length of 1 decimeter is 0.03 - 2 g.

[0011] According to an embodiment of the present invention, the thermal diffusivity of the heating film is 50 mm 2 / s - 450 mm 2 / s.

[0012] According to an embodiment of the present invention, the power of the heating film is 15 W - 10000 W.

[0013] According to an embodiment of the present invention, the heating film comprises a plurality of heating units arranged sequentially along the length direction, and adjacent heating units are spaced apart and connected by a connecting section.

[0014] According to an embodiment of the present invention, each of the heating units is provided with a hollow hole.

[0015] In another aspect of the present invention, the present invention provides a method for preparing the aforementioned heating film. According to an embodiment of the present invention, the method for preparing the heating film includes: providing natural graphite, and subjecting the natural graphite to intercalation treatment to obtain expandable graphite; subjecting the expandable graphite to expansion treatment to obtain expanded graphite; subjecting the expanded graphite to rolling or rolling and first heat treatment and cutting to obtain the heating film.

[0016] Alternatively, the method for preparing the heating film includes: uniformly dispersing graphene oxide in a solvent, or uniformly dispersing the graphene oxide and an auxiliary agent in a solvent to obtain a first dispersion liquid, where the auxiliary agent includes at least one of a binder, a reinforcing agent, and a resistance regulator. Among them, the binder includes at least one of ammonia water, glucose, ethylene glycol, ethylenediamine, carboxymethyl cellulose, polyvinyl alcohol, polyethylene glycol, and chitin, the reinforcing agent includes at least one of carbon nanotubes, fullerenes, carbon black, and graphene microflakes, and the resistance regulator includes at least one of silicon carbide, boron nitride, and silicon nitride; coating and drying the first dispersion liquid to obtain a graphene oxide film layer; sequentially performing low-temperature treatment, carbonization treatment, and graphitization treatment on the graphene oxide film layer to obtain a graphene film layer; rolling and cutting the graphene film layer to obtain the heating film.

[0017] Alternatively, the method for preparing the heating film includes: mixing and uniformly dispersing graphene microflakes and an additive to obtain a second dispersion liquid; coating the second dispersion liquid to obtain a dispersion liquid film; performing a second heat treatment on the dispersion liquid film to obtain a carbon-based primary film; rolling and cutting the carbon-based primary film to obtain the heating film.

[0018] Thus, the heating film prepared from natural graphite, graphene microflakes or graphene oxide has the characteristic of self-limiting temperature. Specifically: in the initial stage of heating (i.e., when the temperature of the heating film is lower than the critical temperature), the resistance of the heating film decreases with the increase of temperature, and the current increases, so that the power of the heating film increases with the increase of temperature. Therefore, in this stage, the heating film can quickly heat up; when the heating temperature of the heating film reaches the critical temperature, the resistance of the heating film increases with the increase of temperature, and the current decreases, so that the power of the heating film decreases with the increase of temperature. Therefore, in this stage, the heating rate of the heating film begins to slow down. The self-limiting temperature characteristic of the above heating film can enable the heating film to accelerate the heating rate in the temperature range below the critical temperature on the one hand, so that the heating film can reach the target temperature as soon as possible, and on the other hand, when the temperature is higher than the critical temperature, it can reduce the fusing problem caused by the continuous increase of the heating temperature. In addition, the heating film prepared by using natural graphite, graphene oxide or graphene microflakes can effectively reduce the manufacturing cost. Natural graphite is the graphite existing in nature and does not need to be prepared, thus reducing the manufacturing process flow and cost. The sources of graphene oxide and graphene microflakes are also relatively wide, which also helps to reduce the manufacturing cost of the heating film.

[0019] According to an embodiment of the present invention, the raw material for preparing the heating film is the natural graphite, and the critical temperature of the heating film is 50-300 °C.

[0020] According to an embodiment of the present invention, the raw material for preparing the heating film is the graphene oxide or graphene microflakes, and the critical temperature of the heating film is 100-500 °C.

[0021] According to an embodiment of the present invention, the dispersion satisfies at least one of the following conditions: based on the total mass of the first dispersion, the mass addition amount of the binder ≤ 10%; based on the total mass of the dispersion, the mass addition amount of the reinforcing agent ≤ 30%; based on the total mass of the dispersion, the mass addition amount of the resistance regulator ≤ 20%, the solid content of the first dispersion is 1% - 10%, and the second dispersion satisfies at least one of the following conditions: the additive includes at least one of carboxymethyl cellulose, polyvinyl alcohol, polyethylene glycol, polyacrylic acid and waterborne polyurethane, and based on the total mass of the second dispersion, by mass percentage, the mass fraction of the additive is less than or equal to 5%; the solid content of the second dispersion is 3-20%.

[0022] In another aspect of the present invention, the present invention provides a heating tube. According to an embodiment of the present invention, the heating tube includes the heating film described above. Thus, the heating tube has a relatively fast heating speed, a relatively high heating temperature, and has the characteristic of self-limiting temperature, which enables the heating tube to, on the one hand, accelerate the heating speed in the temperature range below the critical temperature so that the heating tube can reach the target temperature as soon as possible, and on the other hand, when the temperature is higher than the critical temperature, it can reduce the melting problem caused during the continuous increase of the heating temperature.

[0023] In another aspect of the present invention, the present invention provides a heating appliance. According to an embodiment of the present invention, the heating appliance includes the heating tube described above. Thus, the heating appliance has a relatively fast heating speed, a relatively high heating temperature, and has the characteristic of self-limiting temperature, which enables the heating appliance to, on the one hand, have a relatively fast heating speed so that the heating appliance can reach the target temperature as soon as possible, and on the other hand, it can reduce the melting problem caused during the continuous increase of the heating temperature.

[0024] According to an embodiment of the present invention, the heating appliance is an electric oven, a microwave oven, a steam oven, an electric kettle, an electric blanket, an electric warm air blower, an electric heater, a bathroom heater, an electric ceramic stove or a disinfection cabinet. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above and / or additional aspects and advantages of the present invention will become apparent and easy to understand from the description of the embodiments in conjunction with the following drawings, wherein:

[0026] Figure 1 is a schematic diagram of the thermal radiation of the heating film of the present invention;

[0027] Figure 2 is a schematic diagram of the thermal radiation of the heating tube in the prior art;

[0028] Figure 3 is a schematic structural diagram of the heating film in an embodiment of the present invention;

[0029] Figure 4 is a schematic structural diagram of the heating film in some other embodiments of the present invention;

[0030] Figure 5 is a schematic structural diagram of the heating film in some other embodiments of the present invention;

[0031] Figure 6 is a schematic structural diagram of the heating tube in some other embodiments of the present invention

[0032] Figure 7 is a schematic structural diagram of the heating tube in some other embodiments of the present invention;

[0033] Figure 8 is a schematic structural diagram of the heating tube in some other embodiments of the present invention;

[0034] Figure 9 It is a schematic structural diagram of the heating film in some other embodiments of the present invention.

[0035] Figure 10 It is a schematic diagram of the curve of the resistance of the heating film in Embodiment 1 of the present invention changing with temperature;

[0036] Figure 11 It is a scanning electron micrograph of the heating film in Embodiment 1;

[0037] Figure 12 It is a scanning electron micrograph of the heating film in Embodiment 4;

[0038] Figure 13 It is a schematic diagram of the curve of the resistance of the heating film in Embodiment 4 of the present invention changing with temperature. Detailed implementation manners

[0039] The solution of the present invention will be explained below in conjunction with the embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. For those reagents or instruments not specified with the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0040] The present invention will be described below with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0041] In one aspect of the present invention, the present invention provides a heating film. According to an embodiment of the present invention, the raw materials for preparing the heating film include natural graphite, graphene oxide or graphene microflakes. The heating film has a critical temperature. When the temperature of the heating film is lower than the critical temperature, the resistance of the heating film decreases as the temperature increases; when the temperature of the heating film is higher than the critical temperature, the resistance of the heating film increases as the temperature increases. It can be seen that the heating film of the present invention has the characteristic of self-limiting temperature. Specifically: in the initial stage of heating (that is, when the temperature of the heating film is lower than the critical temperature), the resistance of the heating film decreases as the temperature increases, and the current increases, so that the power of the heating film increases as the temperature increases. Therefore, in this stage, the heating film can quickly heat up; when the heating temperature of the heating film reaches the critical temperature, the resistance of the heating film increases as the temperature increases, and the current decreases, so that the power of the heating film decreases as the temperature increases. Therefore, in this stage, the heating rate of the heating film begins to slow down and gradually reaches the highest heating temperature of the heating film slowly. The above characteristic of the self-limiting temperature of the heating film can enable the heating film to, on the one hand, accelerate the heating rate in the temperature range below the critical temperature, so that the heating film can reach the target temperature as soon as possible, and on the other hand, when the temperature is higher than the critical temperature, it can reduce the melting problem caused during the continuous increase of the heating temperature, such as improving the reliability and stability of the heating film.

[0042] According to some embodiments of the present invention, when the temperature of the heating film is lower than the critical temperature, the heating rate of the heating film is the first heating rate, and when the temperature of the heating film is higher than the critical temperature, the heating rate of the heating film is the second heating rate, wherein the first heating rate is greater than the second heating rate. It can be seen that the heating film of the present invention has a relatively fast first heating rate, which can accelerate the heating speed of the heating film, enable it to reach the critical temperature in a relatively short time, and then continue to heat up at a relatively small second heating rate, thereby avoiding the melting problem caused during the continuous increase of the heating temperature, such as improving the reliability and stability of the heating film.

[0043] According to some embodiments of the present invention, the critical temperature value of the heating film is 50°C - 500°C. For example, the critical temperature of the heating film can be 50°C, 80°C, 100°C, 120°C, 150°C, 180°C, 200°C, 230°C, 250°C, 280°C, 300°C, 330°C, 350°C, 370°C, 400°C, 420°C, 450°C, 480°C, 500°C, etc. It can be seen that the heating film of the present invention can adjust the specific critical temperature value of the heating film within a relatively wide range. If the heating temperature of the heating film is relatively high, a higher critical temperature value can be selected; if the heating temperature of the heating film is relatively low, a lower critical temperature value can be selected. In this way, it can better ensure both the faster heating speed of the heating film and the problem of anti-fusing at the same time.

[0044] In some embodiments, different heating films can have different critical temperature values, and the specific size of this critical temperature value can be adjusted by adjusting factors such as the crystallinity, density, thickness, or carbon content of the heating film material. In some embodiments, the higher the crystallinity of the heating film, the lower its critical temperature; in some other embodiments, the greater the density of the heating film, the lower its critical temperature; in some other embodiments, the greater the thickness of the heating film, the lower its critical temperature; in some other embodiments, the greater the carbon content of the heating film, the lower its critical temperature. It can be seen that in the present invention, the critical temperature value of the heating film can be adjusted by flexibly adjusting factors such as the density, crystallinity, or carbon content of the heating film.

[0045] According to some embodiments of the present invention, the time for the heating film to reach the highest heating temperature is 0.5 s - 2 s, such as 0.5 s, 0.6 s, 0.7 s, 0.8 s, 0.9 s, 1 s, 1.1 s, 1.2 s, 1.3 s, 1.4 s, 1.5 s, 1.6 s, 1.7 s, 1.8 s, 1.9 s, 2.0 s, etc. It can be seen that the heating film of the present invention has a relatively fast heating speed and can reach the highest heating temperature within a relatively short time, thereby greatly improving the heating efficiency of the heating film.

[0046] According to some embodiments of the present invention, the highest heating temperature of the heating film is 500°C - 1700°C. For example, the highest heating temperature of the heating film can be 500°C, 550°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, 1600°C, 1700°C, etc. It can be seen that the heating film of the present invention has a relatively high highest heating temperature, even up to 1700°C, so it can meet more application heating requirements of the heating film and obtain heating films with various different powers, such as ultra-low power heating films or ultra-high power heating films.

[0047] According to some embodiments of the present invention, the heating film is in a sheet structure, and the raw materials for preparing the heating film, natural graphite, graphene microflakes or graphene oxide, are in a sheet structure, and the sheet extension plane of the heating film is the same as the sheet extension plane of natural graphite, graphene microflakes or graphene oxide. Thus, as Figure 1 shown, when the sheet-structured heating film generates heat, the heat is mainly radiated in the vertical direction of the heating surface (i.e., the plane of the film), with strong directivity and more concentrated radiated heat, thereby being able to better improve the heating efficiency and reduce heat loss. In the current prior art, referring to Figure 2 , the heat radiation of the heating tube core 1 (such as a metal heating tube core or a quartz tube core) is uniformly emitted in all directions and cannot emit heat concentratedly, which usually causes waste of heat and reduces the heating efficiency. Thus, through comparison, it can be seen that the heat radiation direction of the heating film of the present invention is more concentrated, and it can better heat the object to be heated directionally and improve the heating efficiency. Among them, it should be noted that the above "same" means that the sheet extension plane of the heating film is substantially the same as the sheet extension plane of natural graphite and / or graphene oxide, and it is not required that the two are completely the same or completely parallel.

[0048] According to some embodiments of the present invention, as described above, the material of the heating film prepared from the raw material natural graphite is graphite, which enables the heating film of the present invention to have a relatively high heating temperature and a relatively fast heating rate. Among them, the prepared graphite is still in a sheet structure, and the plane extension direction of this sheet structure is basically the same as the plane extension direction of the raw material natural graphite. Therefore, it can be said that the sheet extension plane of the heating film is basically the same as the sheet extension plane of its material graphite.

[0049] According to some embodiments of the present invention, the material of the heating film is graphene. Thus, graphene as the heating material of the heating film can enable the heating film to have better heating temperature, a relatively fast heating rate, and a relatively high emission coefficient; moreover, both graphene and the heating film are in a sheet structure. When the heating film generates heat, the heat is mainly radiated in the vertical direction of the heating surface, with strong directivity and more concentrated radiated heat, thereby being able to better improve the heating efficiency.

[0050] According to some embodiments of the present invention, the heating film includes graphene and an additive. The additive includes at least one of a reinforcing agent and a resistance regulator. The reinforcing agent includes at least one of carbon nanotubes, fullerenes, carbon black, and graphene microflakes. The resistance regulator includes at least one of silicon carbide, boron nitride, and silicon nitride. Thus, graphene as the heating material of the heating film can endow the heating film with better heating temperature, faster heating rate, and higher emissivity. Moreover, both graphene and the heating film are in sheet structures. When the heating film generates heat, the heat is mainly radiated in the vertical direction of the heating surface, with strong directivity and more concentrated radiated heat, thereby better improving the heating efficiency. Additionally, by adding additives to adjust the resistance and strength of the heating film, heating films with different performances can be obtained, which is easy to expand its applicable requirements.

[0051] According to some embodiments of the present invention, based on the total mass of the heating film, by mass percentage, the heating film includes 70% - 80% (such as 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, etc.) of the graphene and 20% - 30% (such as 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc.) of the reinforcing agent. That is, when preparing the heating film, a certain amount of the reinforcing agent is added to the graphene. The reinforcing agent in the above proportion can, while ensuring the relatively high thermal radiation power, good mechanical strength, and bending resistance of the heating film, further increase the maximum heating temperature of the heating film.

[0052] According to some embodiments of the present invention, based on the total mass of the heating film, by mass percentage, the heating film includes 90% - 99% (such as 90%, 91%, 92%, 93%, 94%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, etc.) of the graphene and 1% - 10% (such as 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, etc.) of the resistance regulator. That is, when preparing the heating film, a certain amount of the resistance regulator is added to the graphene. The resistance regulator in the above proportion can adjust the resistance of the heating film to adapt to different powers, especially the requirements of ultra-low power heating films.

[0053] According to some embodiments of the present invention, based on the total mass of the heating film, by mass percentage, the heating film comprises 70% - 79% (such as 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, etc.) of graphene, 20% - 29% (such as 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc.) of reinforcing agent, and 1% - 10% (such as 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, etc.) of resistance regulator. That is, when preparing the heating film, a certain amount of reinforcing agent and resistance regulator are added to the graphene. The reinforcing agent and resistance regulator in the above proportions can, while ensuring a relatively high heating temperature, relatively high heat radiation power, and good bending resistance of the heating film, further improve the strength of the heating film and adjust the resistance of the heating film to adapt to different powers, especially the requirements of ultra-low power heating films.

[0054] According to some embodiments of the present invention, for a heating film with a length of 1 decimeter, the weight is 0.03 - 2 g, such as 0.03 g, 0.04 g, 0.05 g, 0.06 g, 0.07 g, 0.08 g, 0.09 g, 0.1 g, 0.5 g, 0.7 g, 0.9 g, 1.0 g, 1.2 g, 1.4 g, 1.5 g, 1.6 g, 1.8 g, 2.0 g, etc. It can be seen that the heating film material of the present invention is graphite with a relatively light mass, which can make the heating film have a relatively small weight, far less than the weight of heating tubes such as metal heating tubes or quartz tubes, thus contributing to the lightweight design of the heating film of the present invention and further contributing to obtaining a relatively lightweight heating tube.

[0055] According to some embodiments of the present invention, the carbon content of the heating film is greater than or equal to 85%. Thus, the heating film has a relatively high carbon content, that is, a relatively high purity, which is conducive to obtaining a heating film with better performance. Moreover, in the present invention, the critical temperature value of the heating film can also be adjusted by adjusting the carbon content to meet its various different adaptation requirements.

[0056] According to some embodiments of the present invention, the heating film satisfies at least one of the following conditions: the thickness of the heating film is 0.04 mm - 2 mm, such as the thickness of the heating film is 0.04 mm, 0.06 mm, 0.08 mm, 0.1 mm, 0.2 mm, 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2.0 mm, etc.; the density of the heating film is 0.6 g / cm 3 ~1.8 g / cm 3 ,such as the density of the heating film is 0.6 g / cm 3, 0.8 g / cm 3 , 1.0 g / cm 3 , 1.2 g / cm 3 , 1.4 g / cm 3 , 1.5 g / cm 3 , 1.6 g / cm 3 , 1.8 g / cm 3 etc. The heating film sheets with the above densities and thicknesses can meet the requirements for different power levels of the heating film sheets; moreover, the heating film sheets of the present invention have high manufacturability, that is, a high production yield, and a long service life. In some specific embodiments of the present invention, the resistance characteristics of the heating film sheet (under the condition of equal density) are: the resistance gradually decreases as the thickness increases; the greater the thickness, the closer the resistance approaches 0, and the smaller the thickness, the greater the resistance. Based on this, in the present invention, heating film sheets with various different power levels can be obtained under the above density and thickness conditions.

[0057] According to some embodiments of the present invention, the power of the heating film sheet is 15 W to 10,000 W, such as 15 W, 20 W, 40 W, 50 W, 70 W, 100 W, 150 W, 300 W, 500 W, 800 W, 1000 W, 1500 W, 3000 W, 4500 W, 5000 W, 6000 W, 7000 W, 8000 W, 9000 W, 10,000 W, etc. Thus, the heating film sheets of the present invention can effectively achieve heating film sheets with a large span of different powers, that is, the present invention can achieve heating film sheets with ultra-low power as well as heating film sheets with ultra-high power, meeting the power usage requirements of the heating film sheets under various different application conditions.

[0058] According to some embodiments of the present invention, the thermal diffusivity of the heating film sheet is 50 mm 2 / s to 450 mm 2 / s, such as 50 mm 2 / s, 80 mm 2 / s, 100 mm 2 / s, 130 mm 2 / s, 150 mm 2 / s, 280 mm 2 / s, 300 mm 2 / s, 320 mm 2 / s, 350 mm 2 / s, 370 mm 2 / s, 400 mm 2 / s, etc. The above thermal diffusivity allows the heat of the heating film to be transferred to the heating cavity at a relatively appropriate rate, so that the heat generated by the heating film is mainly concentrated on the object to be heated. In this way, it can not only ensure a better heating rate, but also prevent the heat from being transferred out too quickly, resulting in a large amount of heat loss. Moreover, the above thermal diffusivity also helps to extend the service life of the heating film and improve the manufacturability of the heating film. Moreover, the above thermal diffusivity also helps to extend the service life of the heating film, and the thermal diffusivity is less than 50mm 2 / s. Too little heat is transferred by the heating film in the form of heat conduction, resulting in too high a temperature of the heating film and the service life not meeting the requirements; the thermal diffusivity is greater than 450m 2 / s. More heat is conducted out and less radiant energy, resulting in a low heating efficiency of the heating film. Moreover, a higher thermal diffusivity requires a greater density of the heating film to be fabricated. The density corresponding to a thermal diffusivity greater than 450mm 2 / s is relatively large and difficult to fabricate in terms of process.

[0059] According to an embodiment of the present invention, the method for testing the thermal diffusivity of the heating film is as follows: Take a piece of graphite film with a flat and smooth surface, and cut out a circular sample with a diameter of about 25.4mm using a tool; Measure the thickness of the sample using a micrometer or a digital display thickness gauge; Place the sample in a bracket, then place the bracket in a circular standard bracket, and place it in a flash method thermal conductivity meter for testing. Instrument test parameter settings: test temperature 25°C, more than 5 flash points, pulse width 50μs, detection diameter 14mm, sampling time about 30ms. After the test is completed, import the data into analysis software for calculation to obtain the thermal diffusivity value.

[0060] In an embodiment of the present invention, the specific cutting pattern of the heating film can be diversified, and those skilled in the art can flexibly design the cutting pattern of the heating film according to the actual requirements such as the resistance and power of the heating film. The following introduces some cutting patterns of the heating film according to some specific embodiments of the present invention:

[0061] In some embodiments of the present invention, referring to Figure 3 , the heating film includes a plurality of heating units 01 arranged in sequence along the length direction, and adjacent heating units 01 are spaced apart and connected by a connecting section 02. It can be seen that the heating film of the present invention can be cut into various structures with different cutting patterns to meet different usage requirements. Among them, in some embodiments of the present invention, referring to Figure 3 , the outer peripheral wall of the heating unit is formed into an oval or a polygon.

[0062] In some embodiments of the present invention, referring to Figure 3In (b), (c), and (i) thereof, each heating unit 01 is provided with a hollow hole 03. Thus, the setting of the hollow hole can accelerate the heat dissipation rate of the heating film and the heating rate of the object to be heated.

[0063] In some embodiments of the present invention, referring to Figure 4 , the heating film includes a first heating section S2 and a second heating section S1 adjacent in the length direction. The first heating section S2 includes a plurality of connected heating units 01, and the second heating section S2 includes a plurality of adjacent heating units 01. The size of the heating unit 01 corresponding to the first heating section S2 is smaller than the size of the heating unit 10 corresponding to the second heating section S1. For example, Figure 4 in (a) thereof, the length of the heating unit 01 corresponding to the first heating section S2 is the same as the length of the heating unit 10 corresponding to the second heating section S1, but the widths d1 and d2 thereof are not equal. For example, Figure 4 in (b) and (c) thereof, the width of the heating unit 01 corresponding to the first heating section S2 is the same as the width of the heating unit 10 corresponding to the second heating section S1, but the lengths d1 and d2 thereof are not equal. Thus, the diversification of the structure of the heating film can be realized.

[0064] In some embodiments of the present invention, referring to Figure 5 , the first heating section S2 and the second heating section S1 are arranged offset in the width direction of the heating film. Thus, the diversification of the structure of the heating film can be realized.

[0065] In some embodiments of the present invention, referring to Figure 3 in (d), (e), (f), (h), (i), and (j) thereof, the heating film includes a plurality of notches arranged at intervals in the length direction. Thus, the diversification of the structure of the heating film can be realized. Further, in some embodiments of the present invention, referring to Figure 3 in (i) thereof, each notch is obtained by bending a part of the heating film after separating it from the rest.

[0066] In some embodiments, as Figure 9 shown, the same heating film may also include multiple different cutting patterns or the same cutting pattern with uneven density distribution.

[0067] In another aspect of the present invention, the present invention provides a method for preparing the aforementioned heating film. According to an embodiment of the present invention, the raw materials for preparing the heating film include natural graphite, graphene oxide, or graphene nanoplatelets. Thus, the heating film prepared from natural graphite, graphene oxide, or graphene nanoplatelets has the characteristic of self-limiting temperature. Specifically: in the initial stage of heating (i.e., when the temperature of the heating film is lower than the critical temperature), the resistance of the heating film decreases with the increase in temperature, and the current increases, so that the power of the heating film increases with the increase in temperature. Therefore, in this stage, the heating film can rapidly heat up; when the heating temperature of the heating film reaches the critical temperature, the resistance of the heating film increases with the increase in temperature, and the current decreases, so that the power of the heating film decreases with the increase in temperature. Therefore, in this stage, the heating rate of the heating film begins to slow down. The self-limiting temperature characteristic of the above-mentioned heating film can enable the heating film to, on the one hand, accelerate the heating rate in the temperature range below the critical temperature, so that the heating film can reach the target temperature as soon as possible, and on the other hand, when the temperature is higher than the critical temperature, it can reduce the melting problem caused during the continuous increase in the heating temperature. In addition, the heating film prepared by using natural graphite, graphene oxide, or graphene nanoplatelets can effectively reduce the production cost. Natural graphite is the graphite existing in nature and does not need to be prepared, thus reducing the preparation process flow and cost. The sources of graphene oxide or graphene nanoplatelets are also relatively wide, which also helps to reduce the preparation cost of the heating film.

[0068] The method for preparing the heating film will be described in detail below according to different raw materials:

[0069] According to some embodiments of the present invention, the method for preparing the aforementioned heating film using natural graphite includes:

[0070] S110: Provide natural graphite and perform intercalation treatment on it to obtain expandable graphite.

[0071] In the present invention, natural graphite is used. Natural graphite ore has a large reserve in the earth's minerals. At the same time, during the preparation of carbon-based film materials, high-temperature graphitization is not required, and it does not need to be prepared by other processes and can be continuously produced, reducing costs. Generally speaking, carbon-based film materials have the advantages of wide raw material sources, simple preparation processes, good product stability, and easy adjustment of performance parameters according to requirements. They have great advantages in reducing product costs, enhancing product reliability, and enriching product types. If artificial graphite is used, further process flows for making artificial graphite need to be set up, which will greatly increase the production cost and duration of the heating film and reduce production efficiency; moreover, natural flake graphite can be further used. The graphite monolayer structure is a layered structure, which can make the graphite in the prepared heating film also in a layered structure, improving the concentrated heating effect of the heating film.

[0072] In some embodiments of the present invention, the method for treating natural graphite to obtain expandable graphite is to uniformly mix natural graphite (such as natural flake graphite) with an appropriate amount of oxidant and intercalating agent, control a certain temperature, continuously stir, and obtain expandable graphite after washing with water, filtering, and drying. Commonly used oxidants include at least one of potassium permanganate, potassium dichromate, chromium trioxide, potassium chlorate, hydrogen peroxide, etc., and the intercalating agent can be at least one of sulfuric acid, nitric acid, phosphoric acid, etc.

[0073] S120: Perform an expansion treatment on the expandable graphite to obtain expanded graphite.

[0074] In some embodiments, after the expandable graphite enters the puffing furnace, it undergoes instant high temperature and rapid expansion to form graphite worms, that is, expanded graphite. Through the expansion treatment, the expansion multiple of the expandable graphite can be 30 to 400 times. Among them, during the expansion treatment, the expansion temperature is 850 - 1200 °C, and the expansion time is 0.7 - 1.3 s.

[0075] S130: Perform calendering and cutting on the expanded graphite to obtain a heating film sheet, or perform calendering, first heat treatment, and cutting on the expanded graphite to obtain a heating film sheet. A heating film sheet with a certain cut shape is obtained through cutting, and the specific cut shape can refer to Figure 3 、 Figure 4 and Figure 5 , and the characteristics of the specific cut shape are consistent with the requirements described above, and will not be elaborated here too much.

[0076] In some embodiments, after the expanded graphite is cloth-covered and then calendered, the calendering is carried out in a multi-stage roll pressing manner, and the expanded graphite is calendered into a graphite film with a certain thickness and density through 3 - 7 rubber rollers and steel rollers. Among them, heating film sheets with different densities can be obtained by changing the calendering conditions, and heating film sheets with different thicknesses can be obtained by changing the cloth-covered thickness.

[0077] In some embodiments, the first heat treatment can be vacuum heat treatment, with a temperature of 800 - 1200 °C and a time of 8 - 30 min. The first heat treatment can reduce the gas in the graphite film, avoid the film from foaming during the heating process, and at the same time remove volatile substances such as amorphous carbon in the expanded graphite.

[0078] In some embodiments, the critical temperature of the heating film sheet prepared from the above natural graphite is 50 - 200 °C. Thus, it can be seen that a heating film sheet with a lower critical temperature can be prepared through the above method.

[0079] According to other embodiments of the present invention, the method for preparing the above-mentioned heating film sheet includes:

[0080] S210: Uniformly disperse graphene oxide in a solvent, or uniformly disperse graphene oxide and an auxiliary agent in a solvent to obtain a first dispersion liquid.

[0081] According to some embodiments of the present invention, the auxiliary agent includes at least one of a binder, a reinforcing agent, and a resistance regulator. Among them, the solvent can be water. In some embodiments, the binder includes at least one of ammonia water, glucose, ethylene glycol, ethylenediamine, carboxymethyl cellulose, polyvinyl alcohol, polyethylene glycol, and chitin; the reinforcing agent includes at least one of carbon nanotubes, fullerenes, carbon black, and graphene microflakes; and the resistance regulator includes at least one of silicon carbide, boron nitride, and silicon nitride.

[0082] According to some embodiments of the present invention, based on the total mass of the first dispersion liquid, the mass addition amount of the binder ≤ 10%. Thus, by adding a certain amount of the binder, the adhesiveness of the dispersion liquid can be adjusted, which is convenient for coating the dispersion liquid, and graphene oxide can be adhered together to avoid the occurrence of faults in graphene oxide, which helps to obtain a graphene oxide film layer with good structure. In this way, the adhesion between the graphene layers in the prepared heating film sheet is enhanced, and the adhesion of the prepared heating film sheet can be further improved, that is, it has a high peeling force.

[0083] According to some embodiments of the present invention, based on the total mass of the first dispersion liquid, the mass addition amount of the reinforcing agent ≤ 30%. The addition of the reinforcing agent in the above proportion can not only improve the mechanical properties of the film material but also effectively prevent the secondary graphitization of the graphite material at high temperatures and reduce fusing.

[0084] According to some embodiments of the present invention, based on the total mass of the first dispersion liquid, the mass addition amount of the resistance regulator ≤ 20%. The resistance regulator in the above proportion can effectively adjust the resistance of the heating film sheet, and the resistance regulator is non-conductive and high-temperature resistant (the temperature resistance is greater than or equal to 1300 °C). The resistance of the heating film sheet can be adjusted by adjusting the dosage of the resistance regulator. The higher the content used, the greater the resistance of the heating film sheet, which is convenient for adjusting the resistance of the heating tube and power matching.

[0085] According to some embodiments of the present invention, the first dispersion liquid includes graphene oxide, ammonia water, and a solvent.

[0086] According to some embodiments of the present invention, the first dispersion liquid includes graphene oxide, ammonia water, glucose, and a solvent.

[0087] According to some embodiments of the present invention, the first dispersion liquid includes graphene oxide, ammonia water, carbon nanotubes, and a solvent.

[0088] According to some embodiments of the present invention, the first dispersion liquid includes graphene oxide, ammonia water, graphene microflakes, and the solvent.

[0089] According to some embodiments of the present invention, the first dispersion liquid includes graphene oxide, ammonia water, glucose, carbon nanotubes, and a solvent.

[0090] According to some embodiments of the present invention, the first dispersion liquid includes graphene oxide, ammonia water, boron nitride and a solvent.

[0091] According to some embodiments of the present invention, the solid content of the first dispersion liquid is 1% to 10%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc. In the first dispersion liquid with the above solid content, solutes such as graphene are relatively evenly dispersed and convenient for uniform coating; if the solid content is less than 1%, the first dispersion liquid is relatively dilute and has relatively large fluidity, which is not conducive to the coating of the first dispersion liquid and will also affect the uniformity of the obtained graphene oxide film; if the solid content of the first dispersion liquid is greater than 10%, the first dispersion liquid is relatively difficult to disperse evenly. In some specific embodiments, the solid content of the first dispersion liquid is 3% to 7%.

[0092] S220: Coat and dry the first dispersion liquid to obtain a graphene oxide film layer.

[0093] Among them, there are no special requirements for the specific coating method. Those skilled in the art can flexibly select a suitable coating method according to the actual situation. For example, it can be a spin coating method, a doctor blade coating method, etc., as long as it is conducive to obtaining a graphene oxide film with a uniform thickness.

[0094] S230: Perform low-temperature treatment, carbonization treatment and graphitization treatment on the graphene oxide film layer in sequence to obtain a graphene film layer.

[0095] In the above steps, the deoxidation treatment of graphene oxide is realized through low-temperature treatment, carbonization treatment and graphitization treatment to obtain a graphene film layer.

[0096] In some embodiments, the maximum temperature of the low-temperature treatment is 250°C to 400°C, such as 250°C, 280°C, 300°C, 320°C, 350°C, 380°C, 400°C, etc. The holding time at the maximum temperature is 5 min - 3 h (such as 5 min, 10 min, 30 min, 45 min, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, etc.). Under the above conditions, graphene oxide starts to deoxygenate, and its oxygen content can be controlled within 10%. The maximum temperature of the carbonization treatment is 900°C to 1300°C, such as 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, etc. The holding time at the maximum temperature is 5 min - 3 h (such as 5 min, 10 min, 30 min, 45 min, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, etc.). Under the above carbonization conditions, graphene oxide continues to deoxygenate, and its oxygen content can be controlled within 5%. The maximum temperature of the graphitization treatment is 1800°C to 3150°C, such as 1800°C, 1900°C, 2000°C, 2100°C, 2200°C, 2300°C, 2400°C, 2500°C, 2600°C, 2700°C, 2800°C, 2900°C, 3000°C, 3100°C, 3150°C, etc. The holding time at the maximum temperature is 5 min - 3 h (such as 5 min, 10 min, 30 min, 45 min, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, etc.). Under the above conditions, the deoxygenation treatment of graphene oxide can be effectively completed to obtain a graphene film layer.

[0097] According to some embodiments of the present invention, the heating film is prepared from graphene oxide, a binder, and a solvent as raw materials. Since the binder used includes at least one of ammonia water, glucose, ethylene glycol, ethylenediamine, carboxymethyl cellulose, polyvinyl alcohol, polyethylene glycol, and chitin, the above organic binder is decomposed after a series of subsequent heat treatments. Therefore, the prepared heating film is basically a heating film made of graphene (of course, due to process reasons, it may include some inevitable impurities), and it basically does not contain or contains a very small amount of binder. Thus, the heating film has a relatively high heating temperature, a relatively high thermal radiation power, and good bending resistance, which is conducive to various different cutting designs of the heating film.

[0098] According to some embodiments of the present invention, the heating film only includes graphene, and no additives such as binders, reinforcing agents, and resistance regulators are added to the heating film. The carbon content of the graphene film layer prepared by the above method is greater than or equal to 99%. Thus, the purity of graphene in the prepared graphene film layer is relatively high, which is conducive to obtaining a heating film with better performance.

[0099] S240: Calender and cut the graphene film layer to obtain a heating film sheet. The cutting pattern of the heating film sheet obtained after cutting can refer to Figures 3 to 5 .

[0100] In some embodiments, after cloth-making the graphene film layer, calendering is carried out. The calendering adopts a multi-stage roll pressing method, and the expanded graphite is calendered into a heating film sheet with a certain thickness and density through 3 to 7 rubber rollers and steel rollers. Among them, heating film sheets with different densities can be obtained by changing the calendering conditions, and heating film sheets with different thicknesses can be obtained by changing the cloth-making thickness.

[0101] According to the embodiments of the present invention, using graphene as the heating material of the heating film sheet can enable the heating film sheet to have better heating temperature, faster heating rate and higher thermal radiation power; moreover, both graphene and the heating film sheet are in a sheet structure. When the heating film sheet generates heat, the heat is mainly radiated in the vertical direction of the heating surface, with strong directivity and more concentrated radiated heat, thereby further improving the heating efficiency. Further, in the present invention, graphene is used. Graphene has a sheet structure, and the single-layer graphene is relatively close, and the thickness of a single graphene sheet is relatively thin, so that the graphene film can have good bending resistance, that is, it helps to improve the bending resistance of the heating film sheet. When designing the cutting pattern of the heating film sheet, it is not affected by easy bending, the operation control is large, and it is convenient for assembly, thereby improving the production yield. Further, the inventor found that under the condition of a certain density, the resistance of the graphene film decreases as the thickness increases.

[0102] S310: Mix and disperse the graphene microparticles and the additive evenly to obtain a second dispersion liquid.

[0103] In some embodiments, graphene nanoplatelets refer to ultrathin graphene layered stacks with 3 to 10 carbon layers and a thickness in the range of 5 - 100 nanometers. In some specific embodiments, the planar size of the graphene nanoplatelets is 1 - 100 μm, and the specific surface area is 30 - 800 m 2 / g. The graphene nanoplatelets meeting the above requirements are convenient for uniform dispersion.

[0104] In some embodiments, the additive includes at least one of carboxymethyl cellulose, polyvinyl alcohol, polyethylene glycol, polyacrylic acid, and waterborne polyurethane. The addition of the above additives can effectively improve the film-forming property of graphene microflakes. It should be noted that the above additives decompose during the subsequent second heat treatment. Therefore, the prepared heating film sheet is basically a heating film sheet made of graphene (of course, due to process reasons, it may include some inevitable impurities), and it basically does not contain or contains a very small amount of additives. Thus, the heating film sheet has a high heating temperature, a high thermal radiation power, and good bending resistance, which is conducive to various different cutting designs of the heating film sheet.

[0105] Furthermore, based on the total mass of the second dispersion liquid, by mass percentage, the mass fraction of the additive is less than or equal to 5%, such as 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc. The low dosage of the additive can not only make the second dispersion liquid have good film-forming property, but also help to reduce the production cost.

[0106] Furthermore, the solid content of the second dispersion liquid is 3 - 20%, such as the solid content of the second dispersion liquid is 3%, 5%, 7%, 9%, 10%, 12%, 15%, 18%, 20%, etc.

[0107] S320: Coating the second dispersion liquid to obtain a dispersion liquid film.

[0108] In some embodiments, there are no special requirements for the specific coating method. Those skilled in the art can flexibly select a suitable coating method according to actual needs. For example, spin coating, spraying, etc. can be used.

[0109] S430: Performing a second heat treatment on the second dispersion liquid film to obtain a carbon-based primary film.

[0110] In this step, the second heat treatment can be carried out in a vacuum or an inert atmosphere, and the second heat treatment temperature is 1500 - 3000 °C. Through the above method, graphene with a high carbon content can be obtained. For example, the carbon content can reach more than 99%.

[0111] S540: Calendering and cutting the carbon-based primary film to obtain the heating film sheet. By cutting, a heating film sheet with a certain cutting shape is obtained. The specific cutting shape can refer to Figure 3 、 Figure 4 and Figure 5 , and the characteristics of the specific cutting shape are the same as the requirements described above, and will not be elaborated here too much.

[0112] In some embodiments, after the graphene film layer is cloth-covered, calendering is carried out. The calendering adopts a multi-stage roll pressing method, and expanded graphite is calendered into a heating film sheet with a certain thickness and density through 3 to 7 rubber rollers and steel rollers. Among them, heating film sheets with different densities can be obtained by changing the calendering conditions, and heating film sheets with different thicknesses can be obtained by changing the cloth-covered thickness.

[0113] In some embodiments, the critical temperature of the heating film sheet prepared from graphene micropieces or graphene oxide is 150 - 500 °C. Thus, it can be seen that heating film sheets with a higher critical temperature can be prepared through the above method.

[0114] According to the embodiments of the present invention, the above three process methods for preparing heating film sheets are simple, the formula is adjustable, and heating film sheets with different critical temperature values can be obtained, so as to meet various heating temperature requirements for heating film sheets.

[0115] On the other hand of the present invention, the present invention provides a heating tube. According to the embodiments of the present invention, the heating tube includes the above-mentioned heating film sheet. Thus, the heating tube has a faster heating speed, a higher heating temperature, and has the characteristic of self-limiting temperature, which can enable the heating tube to, on the one hand, accelerate the heating speed in the temperature range below the critical temperature so that the heating tube can reach the target temperature as soon as possible, and on the other hand, when the temperature is higher than the critical temperature, it can also reduce the fusing problem caused during the continuous increase of the heating temperature. Those skilled in the art can understand that the heating tube has all the features and advantages of the above-mentioned heating film sheet, and will not be elaborated here too much.

[0116] In some embodiments, referring to Figure 6 (the S area in the figure refers to the partial cross-sectional view of the sleeve), Figure 7 and Figure 8 , the heating tube further includes a sleeve 10, the heating film sheet 20 is placed in the sleeve 10, and terminals 21 are arranged at both ends of the heating film sheet 20. Among them, the sleeve can be a quartz glass tube, etc.

[0117] On the other hand of the present invention, the present invention provides a heating appliance. According to the embodiments of the present invention, the heating appliance includes the above-mentioned heating tube. Thus, the heating appliance has a faster heating speed, a higher heating temperature, and has the characteristic of self-limiting temperature, which can enable the heating appliance to, on the one hand, have a faster heating speed so that the heating appliance can reach the target temperature as soon as possible, and on the other hand, it can also reduce the fusing problem caused during the continuous increase of the heating temperature.

[0118] According to the embodiments of the present invention, the heating appliance is an electric oven, a microwave oven, a steam oven, an electric kettle, an electric blanket, an electric heater, an electric warmer, a bathroom heater, an electric ceramic stove, or a disinfection cabinet.

[0119] Those skilled in the art can understand that in addition to the above-mentioned heating tubes, heating appliances also include the necessary structures or components. Taking an electric oven as an example, in addition to the above-mentioned heating tubes, it also includes necessary structures or components such as a housing, a heating space, a base, and a plug.

[0120] Embodiment

[0121] Embodiment 1

[0122] A heating film is prepared using natural graphite, and the preparation method includes:

[0123] Provide 5 g of natural graphite, uniformly mix it with 1 g of potassium permanganate and 15 g of concentrated sulfuric acid, continuously stir, and then obtain expandable graphite through water washing, filtration, and drying.

[0124] Place the expandable graphite in an expansion furnace at 1000 °C for 1 s of expansion treatment.

[0125] Perform cloth laying and multi-stage calendering on the expanded graphite. Through multi-stage calendering by a belt roller, a rubber roller, and a steel roller, calender the expanded graphite to obtain a graphite film with a specified thickness and density, and cut the graphite film to obtain the heating film.

[0126] The scanning electron microscope image of the heating film can be referred to Figure 11 , through Figure 11 It can be seen that the heating film of the present invention has a lamellar structure.

[0127] The structural schematic diagram of the heating film can be referred to Figure 3 in (c), the density of the heating film is 1.5 g / cm 3 , the thickness is 1 mm, the length is 300 mm, the width is 8 mm. Test the temperature, current, resistance, power, maximum heating temperature, and the time required to reach the maximum heating temperature of the heating film under a voltage of 50 v. The test results are shown in Table 1. The curve of the resistance of the heating film changing with temperature can be referred to Figure 10 . From Figure 10 and Table 1, it can be seen that the critical temperature value of the heating film is 200 °C. Among them, the maximum heating temperature refers to the highest temperature at which the heating film can maintain for at least 800 hours without fusing or deteriorating.

[0128] Table 1

[0129]

[0130] Embodiment 2

[0131] The difference from Example 1 is that natural graphite is used to prepare the heating film sheet, the rolling conditions are changed to obtain graphite films with different densities, and then the graphite films are subjected to the first vacuum heat treatment at a heat treatment temperature of 1200 °C and a holding time of 5 min to obtain the heat-treated graphite films. The schematic structural diagram of the cut heating film sheet can be referred to Figure 3 in (c). The thickness of the heating film sheet is 0.7 mm, the length is 270 mm, and the width is 10 mm. The critical temperature of the heating film sheet at different densities is tested under a voltage of 50 v, and the test results are shown in Table 2. It can be seen that as the density of the heating film sheet increases, its critical temperature value gradually decreases.

[0132] Table 2

[0133] <![CDATA[Density / g / cm 3 > 0.6 0.8 1.1 1.5 Power / W 91.03 150.24 180.43 201.84 Resistance / Ω 27.46 16.64 13.86 12.39 Critical Temperature / °C 199 189 181 179

[0134] Example 3

[0135] The difference from Example 1 is that natural graphite is used to prepare the heating film sheet, different amounts of expanded graphite are cloth and rolled to obtain graphite films with different thicknesses, and then the graphite films are subjected to the first vacuum heat treatment at a heat treatment temperature of 1000 °C and a holding time of 15 min. Finally, the heat-treated graphite films are obtained. The schematic structural diagram of the cut heating film sheet can be referred to Figure 3 in (c). The density of the heating film sheet is 1.3 g / cm 3 , the length is 420 mm, and the width is 10 mm. The critical temperature of the heating film sheet is tested under a voltage of 100 v, and the test results are shown in Table 3. It can be seen that as the thickness of the heating film sheet increases, its critical temperature value gradually decreases.

[0136] Table 3

[0137] Thickness / mm 0.08 0.15 0.3 0.7 1.0 Power / W 209.5 310.4 420.5 551.4 632.3 Resistance / Ω 47.7 32.32 23.78 15.14 15.81 Critical Temperature / °C 195 162 139 121 115

[0138] Example 4

[0139] Graphene oxide is used to prepare the heating film sheet. The preparation method includes: uniformly dispersing graphene oxide in water to obtain a uniform graphene oxide dispersion liquid with a solid content of 6%. Then, the dispersion liquid is coated and dried, and then successively subjected to low-temperature treatment (temperature: 300 °C, holding time: 0.5 h), carbonization treatment (temperature: 1100 °C, holding time: 1 h), and graphitization treatment (temperature: 2000 °C, holding time: 2 h) to obtain a graphene film layer. Finally, the graphene film layer is rolled to a specified thickness to obtain the heating film sheet. The scanning electron micrograph of the heating film sheet can be referred to Figure 12 , and it can be seen through Figure 12 that the heating film sheet of the present invention has a sheet layer structure.

[0140] The schematic structural diagram of the heating film sheet can be referred toFigure 3 In (c), the thickness of the heating film is 0.2 mm and the density is 0.54 g / cm 3 , the length is 350 mm, the width is 9.5 mm. Under a voltage of 65 v, test the temperature, current, resistance, power, maximum heating temperature of the heating film and the time required to reach the maximum heating temperature. The test results are shown in Table 4. The curve of the resistance of the heating film changing with temperature can be referred to Figure 13 . From Figure 13 and Table 4, it can be seen that the critical temperature value of the heating film is 173 °C.

[0141] Table 4

[0142]

[0143] Example 5

[0144] Manufacture the heating film according to the steps in Example 4, the difference is that boron nitride as a resistance regulator is added to the graphene oxide dispersion liquid, and the addition amounts of the resistance regulator boron nitride are changed to 1%, 3%, 7%, 15% respectively to obtain heating films with different carbon contents (85%, 93%, 97%, 99%). The structural schematic diagram of the heating film can be referred to Figure 3 in (c), the thickness of the heating film is 0.2 mm and the density is 0.54 g / cm 3 , the length is 350 mm, the width is 9.5 mm. Under a voltage of 65 v, test the critical temperature of the heating film under different carbon contents. The test results are shown in Table 5. It can be seen that as the carbon content of the heating film increases, its critical temperature value gradually decreases.

[0145] Table 5

[0146] Carbon Content / % 85 93 97 99 Power / W 230.9 300.7 340.1 350.2 Resistance / Ω 18.30 14.05 12.42 12.06 Critical Temperature / °C 486 341 288 253

[0147] Example 6

[0148] Make a heating tube from the heating film in Example 1, and apply this heating tube, halogen tube, quartz tube and metal tube in the same oven (volume 10 L) respectively. Test that the power of all heating tubes is 600 W, and test the time required for each heating tube when the oven reaches 200 °C. The test results can be seen in Table 6. From the data, it can be seen that the heating rate of the heating tube in this Example 6 is increased by 48.6% compared with the quartz tube, 46.6% compared with the metal tube, and 31.7% compared with the halogen tube.

[0149] Table 6

[0150] Heating Tube Heating Tube of Example 1 Halogen Tube Quartz Tube Metal Tube Heating Temperature / °C 279 235 204 209 Time / s 149 218 290 279

[0151] Comparative Example 1

[0152] Test the maximum heating temperature of the quartz tube and the metal tube, as well as the time to reach the maximum heating temperature. The test results can be seen in Table 7.

[0153] Table 7

[0154] Quartz Tube Metal Tube Highest Heating Temperature / °C 800 750 Time / s 60 70

[0155] From the above Example 1 and Comparative Example 1, it can be seen that the heating film of Example 1 of the present invention has a relatively high heating temperature and a rapid heating rate, and there is no adverse phenomenon of fusing during the heating process of the heating film in the above examples.

[0156] The terms "first" and "second" in the text are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, "a plurality" means two or more, unless otherwise specifically defined.

[0157] In the description of this specification, the descriptions with reference to the terms "an embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0158] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A heating film, characterized in that, The raw materials for preparing the heating film include natural graphite, graphene oxide or graphene microflakes. The heating film has a critical temperature. When the temperature of the heating film is lower than the critical temperature, the resistance of the heating film decreases as the temperature increases; when the temperature of the heating film is higher than the critical temperature, the resistance of the heating film increases as the temperature increases.

2. The heating film sheet according to claim 1, characterized in that, When the temperature of the heating film is lower than the critical temperature, the heating rate of the heating film is the first heating rate. When the temperature of the heating film is higher than the critical temperature, the heating rate of the heating film is the second heating rate, where the first heating rate is greater than the second heating rate.

3. The heating film according to claim 1, wherein The critical temperature value of the heating film is 50°C - 500°C.

4. The heating film according to any one of claims 1 to 3, characterized in that The material of the heating film is graphite. Alternatively, the material of the heating film is graphene. Alternatively, the heating film includes graphene and additives, and the additives include at least one of a reinforcing agent and a resistance regulator. The reinforcing agent includes at least one of carbon nanotubes, fullerenes, carbon black and graphene microflakes, and the resistance regulator includes at least one of silicon carbide, boron nitride and silicon nitride.

5. The heating film according to claim 4, wherein The heating film is in a sheet shape.

6. The heating film according to any one of claims 1 to 3, characterized in that, The heating film satisfies at least one of the following conditions: The thickness of the heating film is 0.04 mm - 2 mm. The density of the heating film is 0.6 g / cm 3 ~1.8 g / cm 3 .

7. The heating film according to claim 6, characterized in that, For a 1 - decimeter - long heating film, the weight is 0.03 - 2 g.

8. The heating film according to any one of claims 1 to 3, characterized in that, The thermal diffusivity of the heating film is 50 mm 2 / s to 450 mm 2 / s.

9. The heating film according to any one of claims 1 to 3, characterized in that, The power of the heating film is 15 W - 10000 W.

10. The heating film according to any one of claims 1 to 3, characterized in that The heating film includes a plurality of heating units arranged in sequence along the length direction. Adjacent heating units are spaced apart and connected by connecting sections.

11. The heating film according to claim 10, characterized in that, Each heating unit is provided with a hollow hole.

12. A method for preparing the heating diaphragm according to any one of claims 1 to 11, characterized in that, The method for preparing the heating film includes: Providing natural graphite and subjecting the natural graphite to intercalation treatment to obtain expandable graphite. Performing an expansion treatment on the expandable graphite to obtain expanded graphite. Performing rolling or rolling, first heat treatment and cutting on the expanded graphite to obtain the heating film. Alternatively, the method for preparing the heating film includes: Uniformly dispersing graphene oxide in a solvent, or uniformly dispersing the graphene oxide and additives in a solvent to obtain a first dispersion. The additives include at least one of a binder, a reinforcing agent and a resistance regulator. The binder includes at least one of ammonia water, glucose, ethylene glycol, ethylenediamine, carboxymethyl cellulose, polyvinyl alcohol, polyethylene glycol and chitin. The reinforcing agent includes at least one of carbon nanotubes, fullerenes, carbon black and graphene microflakes, and the resistance regulator includes at least one of silicon carbide, boron nitride and silicon nitride. Coating and drying the first dispersion to obtain a graphene oxide film layer. Successively performing a low - temperature treatment, a carbonization treatment and a graphitization treatment on the graphene oxide film layer to obtain a graphene film layer. Performing rolling and cutting on the graphene film layer to obtain the heating film. Alternatively, the method for preparing the heating film includes: Mixing and uniformly dispersing graphene microflakes and additives to obtain a second dispersion. Coating the second dispersion to obtain a dispersion film. Performing a second heat treatment on the dispersion film to obtain a carbon - based primary film. The carbon-based primary film is calendered and cut to obtain the heating film sheet.

13. The method according to claim 12, wherein The raw material for preparing the heating film sheet is the natural graphite, and the critical temperature of the heating film sheet is 50 - 300 °C.

14. The method according to claim 12, wherein The raw material for preparing the heating film sheet is the graphene oxide or graphene microplate, and the critical temperature of the heating film sheet is 100 - 500 °C.

15. The method according to claim 12, wherein The first dispersion satisfies at least one of the following conditions: Based on the total mass of the dispersion, the mass addition amount of the binder ≤ 10%; Based on the total mass of the dispersion, the mass addition amount of the reinforcing agent ≤ 30%; Based on the total mass of the dispersion, the mass addition amount of the resistance regulator ≤ 20%; The solid content of the first dispersion is 1% - 10%, The second dispersion satisfies at least one of the following conditions: The additive includes at least one of carboxymethyl cellulose, polyvinyl alcohol, polyethylene glycol, polyacrylic acid, and waterborne polyurethane; Based on the total mass of the second dispersion, by mass percentage, the mass fraction of the additive is less than or equal to 5%; The solid content of the second dispersion is 3% - 20%.

16. A heating tube, characterized in that, It includes the heating film sheet according to any one of claims 1 to 11.

17. A heating appliance, characterized in that, It includes the heating tube according to claim 16.

18. The heating appliance according to claim 17, wherein, The heating appliance is an electric oven, a microwave oven, a steam oven, an electric kettle, an electric blanket, an electric heater, an electric radiator, a bathroom heater, an electric ceramic stove, or a disinfection cabinet.

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