Heating element and method for producing heat-generating coating material

Abstract

[Problem] The present invention provides a heat-generating coating material, which uses a carbon material produced with a plant-based raw material as a carbon source and which can contribute to CO2 reduction, and a heat-generating coating material, which is capable of maintaining strength even in a variety of temperature zones. [Solution] The heat-generating coating material is characterized in that a carbon material, which is produced from a plant-based raw material containing 5% or more of silicon components and which contains 1-50 wt% of the silicon components, is used as a pigment. Moreover, by forming the pigment for the coating material by mixing carbide 19, which contains many functional groups, with graphene 113, it is also possible to supply not only direct current but also alternating current high-voltage power while stabilizing the strength of the material.

Description

Heat generating element and method for manufacturing heat generating paint

[0001] The present invention relates to a method for producing a heating element and a heat-generating paint that are manufactured using graphene or a carbon material produced from plant-derived raw materials and are used for heat generation or electrical conductivity.

[0002] Heating elements have traditionally been used in a variety of fields. For example, they are used as heat sources in heat presses, pipe heaters, heat sealing / laminating devices, drying devices, defrosting devices, snow melting devices, and copy machines. The advantage of turning a heating element into a paint is that it can be installed without being restricted by shape. Considering cost, turning it into a paint also offers significant cost benefits, as it can be applied only to the desired area or location.

[0003] As such, various inventions have been proposed for heat-generating paints with significant advantages. For example, Patent Document 1 describes a heat-generating sheet comprising a heat-generating layer having a thickness of 10 to 150 μm formed on a support, and a plurality of electrodes connected to the heat-generating layer at a distance from one another, with the electrodes sealed with an insulating coating except for the connection portions to an external circuit, and with a maximum overall thickness of 500 μm or less. One example of an invention is that the heat-generating layer of this sheet is formed by applying an aqueous composition containing a conductive material to a resin support that has been subjected to corona discharge treatment.

[0004] For example, Patent Document 2 discloses an invention for a heat-generating paint whose main components are a fine carbon material and an inorganic binder, with the aim of providing a heat-generating paint that has high heat generation even at low voltages and can form a paint film that can maintain its paint film even in high temperature ranges and is less likely to break.

[0005] JP 2021-163540 A JP 2020-26458 A

[0006] As in Patent Document 2, heat-generating paints are composed of inorganic binders and fine carbon materials. However, the problem is that many of these are manufactured from ores and do not contribute to CO2 reduction. Furthermore, it is necessary to improve the strength against breakage by uniformly dispersing the carbon material and inorganic material into a paint. Therefore, if the proportion of carbon material is too high in order to reduce the resistance value, it becomes difficult to increase the strength of the heat-generating paint.

[0007] The present invention has been made to solve the above problems, and aims to provide a heat-generating paint that can contribute to reducing CO2 emissions by using carbon materials produced from plant-based raw materials and that can maintain its strength even in various temperature ranges.

[0008] A method for producing a heat-generating paint, characterized in that a carbon material produced from plant-based raw materials is mixed and dispersed in a synthetic resin emulsion.

[0009] Due to the above features, the present invention can contribute to CO2 reduction by using carbon materials produced from plant-based raw materials, and can provide a heat-generating paint that can maintain its strength even in various temperature ranges.

[0010] 1 is a Raman spectrum of graphene according to an embodiment; 2 is a Raman spectrum of a carbide according to an embodiment; 3 is a schematic diagram showing the configuration of a heating element coated with a heat-generating paint according to an embodiment; 4 is a schematic diagram showing the temperature characteristics of a heating element according to an embodiment; 5 is a schematic diagram showing the temperature characteristics of a heating element according to an embodiment; 6 is a schematic diagram showing the configuration of a plasma device according to an embodiment; 7 is a diagram showing a process flow showing a manufacturing process for producing a carbon material according to an embodiment; 8 is a diagram showing a process flow showing a manufacturing process for producing a carbon material according to an embodiment; 9 is a conceptual diagram of another example of a neutralization treatment according to an embodiment; 10 is a conceptual diagram of another example of an apparatus used in the neutralization treatment according to an embodiment; 11 is a diagram showing a process flow showing a manufacturing process for producing a carbon material according to an embodiment; 12 is a schematic diagram showing the configuration of a heating element according to an embodiment;

[0011] The heat-generating paint of the present invention will be described in detail with reference to the drawings. Note that the embodiments and drawings described below are intended to exemplify some of the embodiments of the present invention, and are not intended to limit the present invention to these configurations, and can be modified as appropriate within the scope of the present invention.

[0012] <Biomass Material> The plant raw material 9 for producing graphene will be described. The present invention produces graphene, which is a final product, using food residues or discarded plant raw material 9. Plants, wood, etc. are used as the plant raw material 9, but in particular, if discarded plant raw material 9 such as residues after harvesting plants is used as the raw material for producing graphene, it is possible to obtain the raw material at low cost.

[0013] Table 1 is a table of ingredients for plant-based raw material 9. In Table 1, the proportions of the ingredients constituting the raw material shown on the far left are shown as percentages on the right. For example, rice straw contains 37.4% carbon (C), 0.53% nitrogen (N), 0.06% phosphorus (P), 0.14% phosphoric acid (PO), 1.75% potassium (K), 2.11% potash (KO), 0.05% calcium (Ca), 0.19% magnesium (Mg), and 0.11% sodium (Na).

[0014] Here, plant-derived silicon-containing porous plant material 9 undergoes no substantial change even when carbonized at low temperatures (300°C or higher and 1000°C or lower), and the arrangement of pores can be maintained by removing the silicon. Many plant materials 9 have a structure in which cells are regularly arranged along their axes, with thickened cell walls due to the deposition of silicic acid. Furthermore, there are compressed, narrow cell rows between the silicified cell rows, and by removing silicon and other components after carbonization, a carbon material with a high specific surface area can be obtained. As mentioned above, a plant material 9 containing a high amount of silicic acid, between 13% and 35%, is suitable. Too much silicic acid results in less graphene being obtained, so a plant material 9 with a silicic acid content of around 20% is preferable.

[0015] Examples of carbon-rich plant materials 9 are shown in Table 1, and include, in addition to rice straw, wheat straw, barley straw, wheat husks, barley husks, cocoa husks, rice bran, rice husks, buckwheat straw, soybean vines, sweet potato vines, turnip leaves, carrot leaves, corn stalks, sugarcane tops, sake lees, coconut shells, coconut meal, peanut shells, mandarin orange peels, coffee husks, coffee grounds, red cedar sawdust, larch bark, and fallen ginkgo leaves. Plants themselves may also be used instead of residues.

[0016] For example, bamboo is made up of cellulose, hemicellulose, and lignin as cellulose components, and minerals such as iron, magnesium, calcium, manganese, copper, and nickel. When bamboo leaves are burned, silanol groups (Si-OH) are extracted, and are converted into SiO4 during the burning process.

[0017]

[0018] Tables 2 and 3 are tables showing the composition of the plant raw material 9 that is most suitable for the method of producing a carbon material in the present invention, among the plant raw materials 9 in Table 1 described above. Table 2 shows the proportions of the components that make up the raw material in percentage. For example, moisture is 8% to 10%, ash is 10% to 18%, lipids are 0.1% to 0.5%, lignin is 18% to 25%, hemicellulose is 16% to 20%, cellulose is 30% to 35%, and others are 5% to 10%. Thus, the main components that make up silica ash 19 are lignin, hemicellulose, and cellulose.

[0019] Table 3 shows the chemical composition of the inorganic matter in the plant-based raw material 9 shown in Table 2. The plant-based raw material 9 shown in Table 2 contains 80 wt% organic matter such as cellulose and 20 wt% inorganic matter. The chemical composition of the inorganic matter in Table 3 is 92.14 wt% SiO2, 0.04 wt% Al2O3, 0.48 wt% CaO, 0.03 wt% Fe2O3, 3.2 wt% KO, 0.16 wt% MgO, 0.18 wt% MnO, and 0.09 wt% Na2O. The plant-based raw material 9 shown in Table 2 contains a large amount of silicon oxide (SiO2) in the inorganic matter.

[0020] (Example) <Process Flow 1> Referring to FIGS. 6 and 7 , the manufacturing steps of a method for producing graphene 113 and carbide 19 will be described. FIG. 7 is a diagram showing a process flow illustrating the manufacturing steps of an embodiment. First, in the pretreatment step S1, after drying the plant-based raw material 9 as described above, the plant-based raw material 9 is pulverized. The pulverized plant-based raw material 9 is mixed with a granulating agent such as PVA in a ratio of 10:1 and water to form the plant-based raw material 9 into particles of appropriate size, which are then kneaded together. The mixture is then heated to approximately 100°C on a drying device such as a hot plate to evaporate the water, thereby producing the plant-based raw material 9. Examples of the pulverization method include a mill, a mixer, a grinder, and the like. In particular, the granulating agent can prevent bumping of the plant-based raw material 9 due to steam during induction heating.

[0021] Next, the carbonization step S2 will be described. In the pretreatment step S1, approximately 0.8 g of plant-derived raw material 9 is placed in a crucible 5 and covered with a metal mesh or the like. The crucible 5 is placed in a predetermined heating position in the plasma device 10 described above. The pressure inside the chamber 1 is reduced to 80 Pa using a vacuum pump 30, and an inert gas 6 is injected into the chamber 1 at a flow rate of 8 to 10 ml / min, so that the pressure inside the chamber 1 is maintained at 1300 to 1500 Pa. Note that in the carbonization step S2, similar graphene can be produced using Examples 1 and 3.

[0022] The highest yield of 36% was measured at 500°C to 800°C, and relatively high yields were obtained at temperatures above 300°C and below 1000°C. In this measurement, rice straw, bran, coconut shells, rice husks, peanut shells, etc. were used, and similar results were obtained. In the carbonization step S2, the plant-derived raw material 9 is carbonized in about 10 to 30 minutes by heating at a temperature range of 300°C to 1000°C using thermal plasma generated by arc discharge while an inert gas 6 is being introduced.

[0023] Next, the activation step S3 will be described. The carbide 19 obtained above was mixed with potassium hydroxide in a weight ratio of 1 part to 5 parts, and the mixture was placed in a small crucible and covered with a lid. The small crucible was then placed inside a large crucible, and activated carbon was embedded around it. The activated carbon was embedded to prevent oxygen from entering the small crucible. The heating furnace was heated to a temperature of nearly 950°C, and the mixture was fired for approximately 2 to 3 hours.

[0024] Here, potassium hydroxide is used to promote the removal of silicon and therefore to improve the yield of the final product, graphene 113. Examples of bases include alkali metal hydroxides such as sodium hydroxide and lithium hydroxide, alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide, alkali metal oxides such as sodium oxide and potassium oxide, alkaline earth metal oxides such as magnesium oxide and calcium oxide, alkali metal sulfides such as sodium sulfide and potassium sulfide, and alkaline earth metal sulfides such as magnesium sulfide and calcium sulfide. Alternatively, it is also possible to remove lignin that has not been completely carbonized with one or more acids selected from the group consisting of hydrochloric acid, sulfuric acid, PTSA, and aluminum chloride.

[0025] Of the carbide 19 reacted with potassium hydroxide, silicic acid reacts with potassium hydroxide to form potassium silicate, and the remaining water-soluble potassium hydroxide (KOH) and potassium silicate are dissolved in water, and the resulting mixture is placed on filter paper and passed through a vacuum or reduced-pressure filter to remove silicon oxide (silicon). Then, in the drying activation step S3, it was possible to produce graphene 113, which is the final product, with a weight that is about 1 / 8 to 1 / 10 of that when the initial plant-derived raw material 9 was granulated.

[0026] The plasma device 10 of this embodiment will be described with reference to Fig. 6. Fig. 6 is a schematic diagram showing the configuration of the plasma device 10 of this embodiment. The plasma device 10 is mainly composed of an inert gas 6, a control device 20, a chamber 1, and a vacuum pump 30.

[0027] The inert gas 6 stored in the gas cylinder is mainly argon, but other examples include helium, neon, nitrogen, etc. The inert gas 6 can be filled into the chamber 1 via an inlet pipe 7 and a gas amount control device 21. The gas amount control device 21 can adjust the flow rate of the inert gas 6.

[0028] Chamber 1 is connected to control valve 22, and the pressure inside chamber 1 can be reduced to a vacuum state by vacuum pump 30. It is connected to chamber 1, and an inert gas 6 is introduced into chamber 1. A leak valve 23 that releases the vacuum state inside chamber 1 to atmospheric pressure is provided between control valve 22 and chamber 1. In addition, a control valve 14 and a leak valve 15 that releases the vacuum state inside chamber 1 to atmospheric pressure are also provided between outlet pipe 8 that introduces air inside chamber 1 and vacuum pump 30.

[0029] The temperature control device 24 also controls the high-frequency power supply 4, managing the temperature maintenance and maintenance time within the chamber 1. The plasma device 10 of this embodiment uses an inert gas (argon gas) 6 as a working gas under a low pressure close to a vacuum, and a high current is passed between the electrodes (cathode 2 and anode 3) to generate thermal plasma by arc discharge. A carbon crucible 5 is placed between the cathode 2 and anode 3, and the crucible 5 contains a plant-derived raw material 9 (described below). The plant-derived raw material 9 is heated to a temperature range of 300°C to 1000°C by the thermal plasma generated by the arc discharge, and is carbonized in approximately 10 to 30 minutes. In addition to the plasma device described above, other methods of generating thermal plasma include barrier discharge, corona discharge, pulse discharge, and DC discharge.

[0030] In the above manufacturing method, a gas phase reaction occurs, and by mixing a small amount of reactive gas such as inert gas 6, functional groups such as -OH (hydroxyl group), -CHO, -C=O (carbonyl group), and -COOH (carboxyl group) are generated, imparting hydrophilicity. The manufacturing method is not limited to the above. The heat source may be induction heating, gas, or an electric furnace, in addition to the plasma device.

[0031] In the case of induction heating, even if there is an insulator such as silicon dioxide (SiO2) in the plant-derived raw material 9, the magnetic flux passes through, making the plant-derived raw material 9 conductive, and the plant-derived raw material 9 itself is heated, accelerating the heating and allowing for carbonization in a short period of time. Furthermore, because the insulator such as silicon dioxide (SiO2) itself is penetrated by the alternating magnetic flux, the silicon dioxide (SiO2) itself remains as it is because it is only heated from the storage box 205 and is not at a temperature that melts it, and much of the insulator such as silicon dioxide (SiO2) remains.

[0032] <Process Flow 2> Fig. 8 shows a main flow of a manufacturing method for manufacturing the carbon material 100. In this example, a method for manufacturing the carbon material 100 to be converted into graphene will be described based on the flow from S11 to S16.

[0033] First, the plant-derived raw material 9 is pulverized in a pulverizer, but since the plant-derived raw material 9 is held in a dehydration container 15 with slits, holes, or a mesh, as described below, for dehydration, a carbon-origin pulverization process (S11) is performed to pulverize the plant-derived raw material to a degree that does not result in an excessively fine powder. The carbon-origin pulverization process (S11) may be performed to a degree that allows the plant-derived raw material 9 to be easily soaked in the alkaline solution in the next process. Note that S11 does not necessarily have to be performed first, and may be performed last.

[0034] Next, the crushed plant raw material 9 is subjected to an aqueous solution infiltration treatment (S12) in which the plant raw material 9 is reacted with an alkaline aqueous solution 20 at a temperature of 60° C. or higher for 1 to 10 hours. The most efficient production is achieved by providing a reaction step for about 4 hours.

[0035] In addition, this step (S12) may be a method of immersing the plant-derived raw material 9 in the aqueous solution 20 at room temperature for about one week. In this case, it is possible to adjust the pH of the aqueous solution 20 and use a weakly alkaline aqueous solution 20 with a pH of about 9.

[0036] The concentration of the alkali in the aqueous solution 20 is set to 10 to 50% by weight, and the plant-derived raw material 9 is reacted in this aqueous solution 20, thereby mainly removing the silica component contained in the plant-derived raw material 9 and extracting the silica component into the aqueous solution 20.

[0037] This increases the concentration of organic components and the carbon content of the final carbon material 100. The best alkaline concentration is 30% wt, with a pH of about 9 to 14. An aqueous solution 20 produced with potassium hydroxide at a pH of 13 is best. The best amount of plant-derived raw material 9 to be added is in the range of 80% wtm to 200% wtm relative to the potassium hydroxide before dissolving it in water.

[0038] Examples of alkaline materials include sodium hydroxide, potassium carbonate, and alkalis such as potassium hydroxide and sodium carbonate. The best is potassium hydroxide with a pH of 13, which is the same component as potassium contained in the plant-derived raw material 9, and is effective for converting the carbon material 100 into graphene.

[0039] This is a photograph taken through a scanning transmission electron microscope after carbonization at 300 to 500°C without alkali treatment. When checking the element distribution, Al (aluminum) is scattered in the form of fine particles, and K (potassium) is present as large particles.

[0040] Therefore, removing potassium and aluminum improves the purity of the carbon, which also leads to improved electrical conductivity. Aluminum, in particular, is easily soluble in alkali, so it can be removed more easily by carbonizing at high temperatures. Potassium also dissolves easily in alkali, so it is better to use potassium hydroxide.

[0041] Therefore, examples of alkaline materials include sodium hydroxide, potassium carbonate, and alkalis such as potassium hydroxide and sodium carbonate. The best is potassium hydroxide with a pH of 13, which is the same component as potassium contained in the plant-derived raw material 9, and is effective for converting the carbon material 100 into graphene.

[0042] Next, the alkaline plant-derived raw material 9 is subjected to a dehydration treatment (S13) to remove the water content from the aqueous solution 20, and is left in an alkaline atmosphere without being subjected to a neutralization treatment or being washed with water (S13). Because the water content can be removed in this step, it is possible to minimize damage to the apparatus or containers such as crucibles caused by alkaline water due to evaporation of water during carbonization.

[0043] In the dehydration treatment (S13), the plant-derived raw material 9 that has been subjected to the aqueous solution permeation treatment (S12) is placed in a metal, cloth, or plastic dehydration container 15 that has a mesh, slits, or holes, or a combination thereof, and is then dehydrated in a centrifugal dehydrator, similar to laundry. The dehydration container 15 may be any container that allows water to escape by centrifugation, and may be in the shape of a bag, box, cylinder, or the like.

[0044] Another method of dehydration is to place the plant material 9 in a bag-shaped dehydration container 15 and squeeze the bag with a squeezer to remove the water.

[0045] The plant raw material 9 is centrifuged for dehydration in a rotary dehydrator, typically a washing machine (S13). The rotation speed during dehydration is preferably 300 to 3000 rpm, and most preferably 500 to 1500 rpm. This centrifugation can promote the destruction of plant cells and the discharge of impurities such as silica contained in the plant raw material 9.

[0046] Next, a drying process (S14) is performed to remove the water content of the aqueous solution 20 using a drying device or drying in the shade. The aqueous solution 20 is left in an alkaline atmosphere without undergoing a neutralization process or washing with water (S14). Because the water content can be removed in this process, it is possible to minimize damage to the apparatus or containers such as crucibles caused by alkaline water due to evaporation of water during carbonization. It should be noted that, as long as the alkaline water content is removed, the drying process (S14) is not necessarily required as long as the water content can be removed in the dehydration process (S13) described above, although it is preferable to have it.

[0047] Next, a carbonization process is carried out in which the plant-based raw material 9 is carbonized in an alkaline atmosphere by flowing gas such as nitrogen or argon gas or sealing it with carbon felt or the like, and maintaining a combustion temperature of 1100°C for 5 hours in an oxygen-free environment (S15).

[0048] In the carbonization step (S15), the higher the temperature, the more the graphene formation and graphitization progress. A combustion temperature of approximately 1000°C to 2200°C is best, and it is sufficient to maintain the above temperature for a carbonization time of 2 to 10 hours.

[0049] In addition, while metal is often used for the manufacturing equipment to store the plant-derived raw materials 9, it is preferable to use a rotary kiln-type carbonization device, induction heating furnace, electric furnace, or the like that can withstand alkalinity, such as spraying alumina or using a storage container for storing the plant-derived raw materials 9 made of alumina material to make it resistant to alkalinity.

[0050] Compared to the conventional process of activating the plant-derived raw material 9 by reacting it with a solid alkaline material, the plant-derived raw material 9 in the state of S13 is less likely to cause direct alkali corrosion of metals, which makes it possible to improve the durability of the manufacturing equipment.

[0051] Finally, after the carbonization treatment (S15), the carbon material 100 is subjected to a neutralization treatment (S16) by exposing it to water or an acidic aqueous solution such as hydrochloric acid, sulfuric acid, or citric acid, and further removing any remaining silica, etc. (S16). Furthermore, if the carbon material 100 is then dried and stored in a vacuum, it can be shipped in a state where its physical properties, such as electrical conductivity, are maintained.

[0052] In the neutralization treatment (S16), it is desirable to neutralize by washing using only water such as pure water in order to improve purity. Neutralization using an acid or the like is also good, but it is necessary to wash away the acid and also to remove solids such as silica, so the neutralization treatment (S16) using water is the most cost-effective option.

[0053] 9, pure water 81 is placed in a container 80, and the carbon material 100 and pure water are placed in a bag-shaped permeation membrane 82 that allows only water molecules to pass through, and both ends 83 are submerged in the pure water. A pressure balance occurs from the aqueous solution containing impurities including the carbon material 100, and the water containing alkaline components flows through the membrane into the pure water 81. In this way, the use of the permeation membrane 82 enables rapid treatment.

[0054] Another example of the neutralization treatment (S16) will be described with reference to Fig. 10. An aqueous solution (L1) containing carbon material 100 is forced up by pump 61 from a bathtub 64 containing carbon material 100 and pure water, and passed through tube 62 equipped with a plurality of tubular reverse osmosis membranes 67.

[0055] The aqueous solution (L2) containing the alkaline component is collected from the tube 62 into the collection container 63, and the aqueous solution (L3) containing the carbon material 100 is returned to the bath 64. The bath 64 is replenished with the same amount of pure water as collected in the collection container 63. In this way, the aqueous solution containing the alkaline component is gradually neutralized by circulation.

[0056] <Process Flow 3> A method for producing a carbon material 100 using rice husks, which are one of the plant raw materials 9 of the present embodiment, in Example 2 will be described with reference to Fig. 11. This production method is particularly suitable for carbon material 100 used as a conductive material.

[0057] The plant-based raw material 9 is pulverized. Since the microparticulation is performed in the pulverization step (S21), the pulverization step is sufficient to allow the particles to penetrate the interior of the plant-based raw material when immersed in water. Furthermore, since the dehydration step is performed, the particles should be small enough to not slip through the slits or holes. The optimal size after pulverization is approximately 5 mm to 10 mm. Examples of pulverization methods include mills, mixers, grinders, etc. Furthermore, a pulverization step is not necessary; it is sufficient if water or the like penetrates the raw material during washing.

[0058] Next, the crushed plant-based raw material 9 is washed with water (S22). For example, the rice husks are soaked in pure water. After soaking the rice husks for about one hour to one day, stones, mud, etc. are washed away. The liquid temperature is preferably between room temperature and 80°C. The water washing (S22) may be carried out by pouring water and then stirring with a stirrer. Alternatively, washing may be carried out by pouring water little by little while stirring. For stirring, a vortex device or a device that stirs by rotating blades may be used, or a stirrer device may be used.

[0059] Next, the washed plant-based raw material 9 is placed in the dehydration vessel 15 and dehydrated in a rotary dehydrator such as a washing machine (S23). The rotation speed during dehydration is preferably 300 to 3000 rpm, and most preferably 500 to 1500 rpm. The gravitational acceleration during centrifugation in the dehydrator is preferably about 2 to 5 G.

[0060] Dehydration removes impurities along with the water. It is then possible to proceed directly to the next baking process without going through a drying process. It was confirmed that the dehydration process by rotation also promotes the decomposition of the plant-derived raw material 9's tissue, allowing the plant-derived raw material 9 to proceed to the next process without a drying process. This reduction in process steps makes it possible to shorten the manufacturing time. Furthermore, when water is removed by centrifugation during dehydration, the destruction of the cell walls of the plant-derived raw material 9 is promoted, leading to further destruction.

[0061] Therefore, in the first embodiment, if rotary dewatering is performed, it is not necessarily necessary to carry out a drying step, but drying will reduce the effects of rust and the like on the machinery.

[0062] Next, in the firing step (S24), the plant-derived raw material 9 is placed in a furnace, which is filled with argon gas or nitrogen gas to create an oxygen-free state, and the temperature inside the furnace is raised to 1100°C and maintained at 1100°C for a fixed period of time of about 1 to 10 hours. Thereafter, the plant-derived raw material 9 is naturally fired for a total firing time of 1 day. This produces the carbon material 10.

[0063] Furthermore, in the calcination step (S24), the plant-derived raw material 9 after the dehydration step (S23) is not completely dried, but rather remains somewhat moist when it is transferred to the calcination step (S24), which causes so-called steam activation in the initial stage, which promotes the destruction and decomposition of cell walls. Furthermore, steam activation generates micropores, which facilitates the formation of a porous material similar to activated carbon.

[0064] Furthermore, during the water washing (S22), the plant-derived raw materials 9 are placed in a container such as a pressure cooker, and pressure is applied to the plant-derived raw materials 9 together with water at 2 to 2.45 atmospheres, and a temperature of 120 to 128°C is applied, which quickly destroys the cell walls of the plant-derived raw materials 9, leading to the removal of impurities and an improvement in purity.

[0065] (Graphene and carbide) The carbide 19 obtained in the carbonization step S2 and the graphene 113, which is the carbon material 100 obtained in the activation step S3, produced in the examples will be described below.

[0066] Fig. 1 shows the Raman spectrum of graphene 113 obtained by the production apparatus of the present invention. Fig. 2 shows the Raman spectrum of carbide 19 obtained by the production apparatus of the present invention. These figures were analyzed using a Raman spectrometer, and the obtained data are Raman spectra with the horizontal axis representing wavelength (wave number (Raman shift (cm-1))) and the vertical axis representing intensity.

[0067] Also, as shown in Table 4, the peak values ​​I G and I D of the G band (2850 cm −1 ) and 2D band (1650 cm −1 ), which are wavelength peaks according to Raman spectroscopy, are given.

[0068] As shown in Table 4, the value obtained by dividing IG by ID is 1.68 for graphene 113, which indicates that it has fewer layers than the plant-derived raw material 9. In particular, it was confirmed that carbide 19 contains a large amount of silicon, and that oxygen functional groups containing -OH, -CHO, -COOH, etc. are generated.

[0069] The value obtained by dividing IG of the graphene 113 by ID is preferably 0.9 or more, and exhibits a value of about 0.9 to 2.0.

[0070] According to thermogravimetry, the ash content of the carbide 19 obtained in the carbonization step S2 is as high as 37.1 wt%, excluding carbon, and silicon (Si) of that ash content accounts for 24 wt% to 50 wt% of the entire carbide 19. In addition, K is 0.51 wt% to 7 wt%, Al is 0.1 wt% to 1.6 wt%, Ca is 0.17 wt% to 0.5 wt%, Fe is 0.4 wt%, and Cr, Ni, Mn, Mg, P, S, and Na are 0.1 wt% or less.

[0071] The carbonized material 19 obtained in the carbonization step S2 without the activation step S3, which is a so-called activation treatment, contains a lot of silicon, and when carbonized in an inert gas, it is not strongly reduced and becomes SiO2-x, which bonds with aromatic -OH groups and the like in the form of -O-Si-O-R to form a lignin polysaccharide complex, which is thought to be likely to take the form of C / SiOx.

[0072] Furthermore, the graphene 113 obtained in the activation step S3 described below has a high ash content excluding carbon, ranging from 1% to 24 wt% according to thermogravimetry, of which silicon (Si) accounts for 1 wt to 20 wt% of the entire graphene 113. In addition, K is 4.3 wt%, Al is 1.5 wt%, Ca is 1.3 wt%, Fe is 0.4 wt%, and P, Mn, Cl, S, and Mg are 0.1 wt% or less.

[0073] As described above, the amount of silicon in the graphene 113 and the carbide 19 that are the carbon material 100 is large, ranging from 1 wt % to 50 wt %.

[0074] As shown in Table 4, the results of the CO 2 adsorption / desorption measurement confirmed that the graphene 113 and the carbide 19 had fine pores with pore diameters mainly ranging from 0.8 nm to 2 nm.

[0075] Therefore, it is considered that they easily adsorb metal ions, etc. Furthermore, as shown in Table 4, the mesopore volumes measured by gas adsorption measurement and water vapor adsorption measurement were 0.487 ml / g for Graphene 113 and 0.259 ml / g for Carbide 19. Furthermore, the micropore volumes were 0.46 ml / g for Graphene 113 and 0.27 ml / g for Carbide 19.

[0076] Furthermore, as shown in Table 4, the particles of graphene 113 or carbide 19 have a diameter distribution of 15 μm to 229 μm, and the median diameter, which is the median value of the integrated value of the distribution, is approximately 110 μm.

[0077] Thus, a mesopore volume of 0.2 ml / g to 0.6 ml / g is formed. In particular, graphene 113 after the activation treatment to remove impurities, which will be described later, shows a higher value, and it is thought that mesopores and micropores grow due to the removal of silicon.

[0078] Furthermore, as shown in Table 4, the specific surface area measured by the water vapor adsorption measurement method, according to the BET method, is 1792 m / g for graphene 113, with a range of 890 m / g to 2000 m / g. Carbide 19 is 726.4 m / g, with a range of 890 m / g to 1500 m / g. Both have large specific surface areas, and graphene 113 after removal of the silicon component (Si) has an even larger specific surface area. Therefore, graphene 113 has a high adsorption effect.

[0079] Similarly, carbide 19 may exist in two states: one in which Si (silicon), an elemental component, is contained as minute particles on the surface or inside of carbide 19 in the form of Si (silicon) or silicon dioxide (SiO2), and the other in which Si (silicon) or silicon dioxide (SiO2) is aggregated on the surface or inside of carbide 19. By subjecting carbide 19 to activation treatment, the purity of carbon increases and the specific surface area increases.

[0080] As shown in Table 4, the true densities measured by a gas displacement density measurement device were 2.56 g / cm for graphene 113 and 2.27 g / cm for carbide 19. The bulk density of graphene 113 was 0.21 to 0.29 g / cm.

[0081] Furthermore, the powder resistivity measured by the double ring method and the four-terminal method was 1.27×10 to 5 Ω cm for carbide 19, and 1.0×10 Ω cm for graphene 113 by removing silicon, improving conductivity. Note that the lower the resistance, the better, and the optimum value for graphene 113 is 1.0×10 Ω cm to 3.8×10 Ω cm. Furthermore, by leaving a large amount of silicon in carbide 19, it becomes easier for carbide 19 to dissolve in substances that are easily adsorbed by silicon, and at the same time, its insulating performance is improved.

[0082] (Heat-generating Paint) Hereinafter, a heat-generating paint produced using the above-described carbon material 100 (carbide 19 and graphene 113) as a pigment will be described. The applicant has conducted tests on various types of paint to find the optimal conditions. As the types of paint mentioned in this example, tests were conducted on a solvent-based two-component type, a solvent-based one-component type, and a water-based one-component type.

[0083] As shown in Table 5, the two-component solvent paint uses acrylic urethane as the binder and is diluted with xylene as the solvent. The above-mentioned carbon material 100 (carbide 19 and graphene 113) was used as the pigment. This two-component solvent paint is a type that is cured using a curing agent.

[0084] The solvent-based one-component adhesive used silicone as the binder, xylene as the solvent, and the above-mentioned carbon material 100 (carbide 19 and graphene 113) as the pigment. This solvent-based one-component adhesive is heat-curable and has excellent heat resistance, withstanding temperatures up to 150°C.

[0085] The aqueous one-component type used an acrylic emulsion as the binder, water as the solvent, and the above-mentioned carbon material 100 (carbonized material 19 and graphene 113) as the pigment. The binder was gradually added to the carbon material while stirring with a disperser, and the limiting amount at which the stirred solution remained liquid was determined. The pigment weight concentration (PWC value) at this time was also calculated.

[0086] As shown in Table 6, each carbon material and each coating film with different PWC values ​​were evaluated. First, 10 g of each limit solution was placed on a tin plate, and the binder, hardener, etc. were mixed so that the PWC value within the set < > was achieved. The mixture was then stirred with a spatula to form a coating. The dry film thickness was then measured. The coating film was also visually inspected for irregularities, cracks, color, and gloss spots. ◯ indicates no defects, △ indicates the presence of any of these, and × indicates the presence of noticeable defects.

[0087] The film-forming property is the result of a test in which the coating surface is scratched with a fingernail or the like to see if the coating peels off. ◯ indicates no peeling, and × indicates peeling. The gloss is the result of measuring the 60-degree gloss value. <1 indicates a value less than 1.

[0088] Furthermore, film properties are the results of a test to see if the coating peels off when the coating surface is scratched with a fingernail, etc. A circle indicates no peeling, and an x ​​indicates peeling.

[0089] Flexibility was evaluated by forming a coating film on paper, bending the paper into a mountain fold, and checking whether cracks or breaks occurred in the coating film at the peaks of the folds. ○ indicates that no cracks or breaks occurred, and × indicates that cracks or breaks occurred.

[0090] Next, we will explain its performance as a heat-generating paint. Figure 3 shows the above-mentioned one-component solvent heat-generating paint 50 applied to an insulator 51 such as paper, cloth, or plastic resin. A positive electrode 52 and a negative electrode 53 are provided at the ends of the center of the heat-generating paint 50, and by supplying power to these electrodes, heat is generated from the area where the heat-generating paint 50 is applied. The distance H between the electrodes is 4.5 cm, and the area where the paint is applied is 22.5 cm2.

[0091] 4 and 5 are diagrams showing the heat-generating characteristics of the heat-generating paint 50. Fig. 4 is a graph of time (seconds) and temperature (°C) for a heating element 40 with a coating thickness of 160 μm to 175 μm. V1 is a temperature graph measured at point P in Fig. 3 when DC 20 V is supplied. The power value is 4 to 4.8 W, and the temperature rises from room temperature of 22.1°C to a maximum of approximately 62°C in about 300 seconds.

[0092] V2 is a temperature graph measured at point P in Figure 3 when DC 12V is supplied. The power value is 2 to 2.4W, and the temperature rises from room temperature of 26.3°C to a maximum of approximately 43.4°C in about 300 seconds.

[0093] Figure 5 is a graph of time (seconds) and temperature (°C) for heating element 40 with a coating thickness of 60 μm to 75 μm. V1 is a temperature graph measured at point P in Figure 3 when DC 20 V was supplied. The power value was 1.6 W to 2.0 W, and the temperature rose from room temperature of 25.4°C to a maximum of approximately 44.1°C in approximately 280 seconds.

[0094] V2 is a temperature graph measured at point P in Figure 3 when DC 12V is supplied. The power value is 0.6W, and the temperature rises from room temperature of 25.4°C to a maximum of approximately 32.6°C in about 240 seconds.

[0095] Because the carbon material 100 contains a large amount of silicon, it is possible to improve the strength and electrical resistance of the paint without the need to add an inorganic material later. In particular, a heat-generating paint containing silicon in a carbon material can maintain the continuity of the paint film even when heated to high temperatures, making it possible to produce a planar heater with high heat resistance.

[0096] Furthermore, by mixing the carbide 19 containing many functional groups with the graphene 113 to form a pigment for the paint, it is possible to supply high voltage power such as AC as well as DC while stabilizing the strength.

[0097] Furthermore, the carbide 19 containing many functional groups facilitates dispersion and mixing in the adjustment of the resistance value. The ratio of the carbide 19 to the graphene 113 is preferably about 0.5:9.5 to 3:7. Furthermore, the carbon material 100 having a powder resistance in the range of 1.0×10 Ω cm to 3.8×10 Ω cm may be used alone or in combination with other carbon materials 100.

[0098] Next, another example of the heating element 40 is shown in Figures 12 and 13. Figure 12(A) is a front view of the heating element 40. Figure 12(B) is a cross-sectional view of the heating element 40 taken along line A-B in the front view. The heating paint 50 is made by mixing and kneading a carbon material 100 at a ratio of 10% to 75% by weight into a synthetic resin emulsion, typically vinyl chloride, vinyl acetate, or acrylic. The best ratio is a carbon ratio of 20% to 60% by weight. It may also be dispersed using water.

[0099] The thickness t of the coating film was formed to be 500 μm to 1000 μm. The ideal thickness of the coating film is 100 μm to 1500 μm, and can be changed appropriately depending on the resistance value and the location of use. When an acrylic emulsion was used, it was possible to coat the film with a thick film thickness.

[0100] 12, a heating element 40 has a + electrode 52 and a - electrode 53 formed on wiring 41 using copper foil, silver foil, copper or silver paste, or conductive wire on a substrate 42. The substrate 42 may be glass, ceramic, concrete, cement, cloth (glass fiber, cotton polyester), plastic, etc. Heat-generating paint 50 is applied to the substrate and electrodes and allowed to dry.

[0101] The heating element 40 had a total length of 56 cm, a width of 4 cm, and an electrode width of 1 cm, and the overall resistance between the electrodes was 1 Ω to 20 Ω. When DC 12 V was applied, a temperature rise of 20°C to 80°C from room temperature was confirmed at a power of around 24 W. Here, the carbon material 100 most suitable for heat-generating paint was found to be one in which cocoa husks, barley husks, wheat husks, or the like from among the plant-derived raw materials 9 were burned at a combustion temperature of 900°C to 1500°C.

[0102] 13 has a positive electrode and a negative electrode formed on wiring 41 using copper foil, silver foil, aluminum foil, copper or silver paste, or conductive wire on a substrate 42. The substrate 42 may be glass, ceramic, concrete, cement, cloth (glass fiber, cotton polyester), aluminum tape, plastic, or the like.

[0103] A nonwoven fabric 43 was laid on the substrate 42 and the wiring 41, and then the heat-generating paint 50 was applied thereon and dried. The nonwoven fabric 43 was thin enough to be transparent, and was made of a material that allowed the heat-generating paint 50 to pass through. The thickness of the nonwoven fabric 43 was 10 g / m ２ to 30 g / m ２ is good.

[0104] Various materials such as polyester, polypropylene, polyethylene, rayon, nylon, wool, etc. can be used for the nonwoven fabric 43. The heat-generating paint 50 can pass through the nonwoven fabric 43, so when viewed from the cross section, the nonwoven fabric 43 and the heat-generating paint are mixed together.

[0105] The heating element 40 had a total length of 50 cm, a width of 4 cm, and an electrode width of 1 cm, and the overall resistance between the electrodes was 1 Ω to 20 Ω. When DC 12 V was applied, a temperature rise of 20°C to 90°C from room temperature was confirmed at a power of around 24 W. Here, the carbon material 100 most suitable for heat-generating paint was found to be one in which plant-based raw materials 9 such as cocoa husks, barley husks, and wheat husks were burned at a combustion temperature of 900°C to 1500°C.

[0106] Alternatively, the heat-generating paint 50 may be a paint in which the carbon material 100 is mixed into an aqueous solution in which sodium silicate is diluted with water. This is particularly suitable for carbon materials 100 obtained by carbonizing plant-derived raw materials 9 containing 5% to 20% silicon. The silicon contained in the carbon material 100 dissolves in the sodium silicate, improving conductivity and strength. It is also suitable as a fire-resistant paint, so that when used as a heat-generating paint, it is possible to reduce the risk of fire, etc.

[0107] Wheat and barley husks, cocoa husks, and sake lees were burned in an oxygen-free environment at temperatures between 1000 and 1500°C. The specific surface area was also measured using the BET adsorption isotherm based on the amount of nitrogen adsorbed at liquid nitrogen temperature.

[0108] As a result, wheat and barley husks, cocoa husks, and sake lees were 15m ２ / g to 80m ２ / g. This small specific surface area improves dispersibility in emulsions such as acrylic, allowing the carbon material to mix evenly and improve conductivity. In addition, the improved dispersibility improves the dispersibility of the coating film, making it possible to ensure strength.

[0109] Regarding industrial applications of the heat-generating coating material of the present invention, in addition to heat-generating coating materials for construction such as concrete, it can also be used as a conductive coating material for batteries, circuit boards, heat-dissipating materials, etc.

[0110] REFERENCE SIGNS LIST 1 chamber 2 cathode 3 anode 4 high frequency power supply 5 crucible 6 inert gas 7 inlet pipe 8 outlet pipe 9 plant-derived raw material 10 plasma device 14 control valve 15 leak valve 19 carbide 20 control device 21 gas amount control device 30 vacuum pump 40 heating element 42 substrate 50 heat-generating paint 51 insulator 52, 53 electrode 100 carbon material 113 graphene S1 pretreatment process S2 carbonization process S3 activation process.

Claims

1. A method for producing heat-generating paint, characterized in that carbon materials produced from plant-based raw materials are mixed and dispersed in a synthetic resin emulsion.

2. The method for producing heat generating paint according to claim 1, characterized in that the weight ratio of the carbon material is 10 to 75 wt %.

3. The method for producing the heat generating paint according to claim 1, in which a carbon material containing a functional group is used as a pigment.

4. A method for producing a heat-generating paint as described in claim 1, characterized in that it includes a washing process in which the plant-based raw material is immersed in water, stirred and washed with water, a dehydration process in which the plant-based raw material is stored in a container after the washing process and rotated using a rotary dehydrator to remove water contained in the plant-based raw material, and a firing process in which the plant-based raw material is fired after the dehydration process.

5. The method for producing a heat generating paint according to claim 4, characterized in that the rotation speed of said dehydration device is 300 rpm to 3000 rpm.

6. Powder resistance is 1.0 x 10 －３ Ω cm to 3.8 x 10 －２ The method for producing a heat generating paint according to claim 1, further comprising the step of:

7. The method for producing a heat generating paint according to claim 4, characterized in that the baking process involves burning the material in an oxygen-free state at a temperature of 1000°C or higher.

8. The plant-based raw material is wheat or barley husk, cocoa husk, or sake lees. The carbon material is burned in an oxygen-free environment at a temperature of 1000°C to 1500°C and has a specific surface area of ​​15 m. ２ / g to 80m ２ The method for producing a heat generating paint according to claim 1, characterized in that the heat generating paint has a molecular weight of 1000 to 10000.

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