Method of producing carbon material

Abstract

To provide heat generating paint that can contribute to reducing CO2, can be produced from a plant feedstock as a carbon source, and can maintain its strength in a wide variety of temperature zones.SOLUTION: The heat generating paint is characterized in that a carbon material produced from a plant feedstock containing 5% or more of a silicon component and including 1 to 50 wt% of a silicon component, is used as a pigment. It becomes possible to feed not only a high voltage DC power but also a high voltage AC power by using a mixture of a carbonized product 19 including many functional groups with graphene 113 as a pigment for paint, while stabilizing the strength thereof.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for producing a carbon material such as graphene from a plant raw material. [Background technology]

[0002] Traditionally, plant-based raw materials have been used for battery materials, conductive materials, heating elements, tires, building materials, etc., from the viewpoint of carbon neutrality. In particular, carbon materials with a large specific surface area have been used as materials for batteries and capacitors. In addition, carbon materials with excellent electrical conductivity have been widely used as heating materials and shielding materials.

[0003] As described above, various inventions have been proposed as methods for producing carbon materials from plant raw materials. For example, Patent Document 1 describes a method for producing a carbon material, in which a carbonaceous raw material is activated with an alkali metal compound to obtain activated carbon or activated carbon fiber with a high specific surface area, by surrounding the reaction system (a composition containing the carbonaceous raw material and the alkali metal compound) with a carbon-based powder layer and, if necessary, including an inorganic compound layer in the carbon-based powder layer for activation. Also, a method for producing a carbon material, in which the heating rate during activation is set to 20°C / hr or less, thereby increasing the yield of the carbon material per container. An electric double layer capacitor in which the activated carbon or activated carbon fiber obtained by the method is used as an electrode material.

[0004] For example, Patent Document 2 discloses an invention comprising a pretreatment step (S1) of drying, drying and pulverizing a plant-based raw material to obtain a carbon source, a carbonization step (S2) of carbonizing the carbon source to obtain a carbonized material, and a purification step (S3) of removing impurities including silica from the carbonized material obtained in the carbonization step, wherein the carbonization step includes a heating step of supplying an inert gas into a chamber and heating the carbon source in the chamber in a plasma atmosphere. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-362915 A [Patent Document 2] JP 2020-55727 A DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0006] In the method of producing carbon materials from plant raw materials as in the patent documents, activation is performed by using various chemicals. Porous carbon materials are produced using chemicals such as strong alkalis, which causes severe metal corrosion during the calcination process such as carbonization, shortening the life of the device. In addition, a production method that can reduce production costs by reducing the number of production steps as much as possible is desired. In addition, when used as a battery material, it is necessary to remove silicon to increase the purity of the carbon material in order to improve the specific surface area.

[0007] The present invention has been made to solve the above-mentioned problems, and aims to provide a production method that can contribute to reducing CO2 emissions by using a carbon material produced from plant raw materials and that can reduce production costs, etc. [Means for solving the problem]

[0008] A method for producing a heat-generating paint, comprising mixing and dispersing a carbon material produced from plant-based raw materials into a synthetic resin emulsion. Effect of the Invention

[0009] Due to the above-mentioned features, the present invention can contribute to reducing CO2 emissions by using carbon materials produced from plant-based raw materials, and can provide a heat-generating paint that can maintain its strength even in a variety of temperature ranges. [Brief description of the drawings]

[0010] [Figure 1] 1 is a Raman spectrum of the graphene of the embodiment. [Diagram 2] 1 is a Raman spectrum of a carbide according to an embodiment. [Diagram 3] FIG. 1 is a schematic diagram showing the configuration of a heating element coated with a heat-generating paint according to an embodiment. [Figure 4] FIG. 4 is a schematic diagram showing temperature characteristics of a heating element according to an embodiment. [Diagram 5] FIG. 4 is a schematic diagram showing temperature characteristics of a heating element according to an embodiment. [Figure 6] 1 is a schematic diagram showing a configuration of a plasma device according to an embodiment. [Figure 7] FIG. 1 is a diagram showing a process flow illustrating a manufacturing process for manufacturing a carbon material according to an embodiment. [Figure 8] FIG. 1 is a diagram showing a process flow illustrating a manufacturing process for manufacturing a carbon material according to an embodiment. [Figure 9] FIG. 11 is a conceptual diagram of another example of the neutralization process according to the embodiment. [Figure 10] FIG. 13 is a conceptual diagram of another example of an apparatus used in the neutralization process of the embodiment. [Figure 11] FIG. 1 is a diagram showing a process flow illustrating a manufacturing process for manufacturing a carbon material according to an embodiment. [Figure 12] FIG. 11 is a schematic diagram showing the configuration of another example of a heating element coated with the heat-generating paint of the embodiment. [Figure 13] FIG. 11 is a schematic diagram showing the configuration of another example of a heating element coated with the heat-generating paint of the embodiment. [Figure 14] FIG. 1 is a diagram showing a process flow illustrating a manufacturing process for manufacturing a carbon material according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The heat-generating paint according to the present invention will be described in detail with reference to the drawings. Note that the embodiments and drawings described below are merely examples of some of the embodiments of the present invention, and are not intended to limit the present invention to these configurations, and may be modified as appropriate without departing from the scope of the present invention.

[0012] <Biomass materials> The plant-based raw material 9 for producing graphene will be described. In the present invention, the final product graphene is produced using food residues or discarded plant-based raw material 9. Plants, wood, etc. are used as the plant-based raw material 9, but in particular, if discarded plant-based raw material 9 such as residues from harvesting plants is used as the raw material for producing graphene, it is possible to obtain the raw material at low cost. [Table 1]

[0013] Table 1 is a composition table of plant-based raw materials 9. In Table 1, the percentages of the components that make up the raw materials shown on the far left are shown on the right. For example, rice straw has 37.4% carbon (C), 0.53% nitrogen (N), 0.06% phosphorus (P), 0.14% phosphoric acid (P2O5), 1.75% potassium (K), 2.11% potash (K2O), 0.05% calcium (Ca), 0.19% magnesium (Mg), and 0.11% sodium (Na).

[0014] Here, the silicon-containing porous plant raw material 9 derived from plants does not change substantially even when carbonized at a low temperature (300°C or more and 1000°C or less), and the arrangement of the pores can be maintained by removing the silicon. Many plant raw materials 9 have a structure in which cells are regularly arranged along the axis, and the cell walls are thickened by deposition of silicic acid. Furthermore, there are narrow compressed cell rows between the silicified cell rows, and it is possible to obtain a carbon material with a high specific surface area by removing silicon and the like after carbonization. As described above, a plant raw material 9 containing a large amount of silicic acid, 13% or more and 35% or less, is suitable. If there is too much silicic acid, the amount of graphene obtained will be small, so a plant raw material 9 containing about 20% silicic acid is preferable.

[0015] Examples of plant-based raw materials9 that are rich in carbon are shown in Table 1, and include, in addition to rice straw, wheat straw, barley straw, wheat husk, barley husk, cocoa husk, rice bran, rice husk, buckwheat straw, soybean vines, sweet potato vines, turnip leaves, carrot leaves, corn stalks, sugarcane tops, sake lees, coconut shells, coconut meal, peanut shells, tangerine 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's cellulose is composed of cellulose, hemicellulose, and lignin, and its minerals are composed of iron, magnesium, calcium, manganese, copper, nickel, etc. In addition, when bamboo leaves are baked, silanol groups (Si-OH) are extracted and become SiO4 during the baking process.

[0017] [Table 2] [Table 3]

[0018] Tables 2 and 3 are tables showing the composition of the plant-based raw material 9 that is most suitable for the method of producing a carbon material among the plant-based raw materials 9 in Table 1 described above in the present invention. Table 2 shows the ratio of the components constituting 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 become silica ash 19 are lignin, hemicellulose, and cellulose.

[0019] Table 3 shows the chemical composition of the inorganic matter of the plant-based raw material 9 shown in Table 2. The plant-based raw material 9 shown in Table 2 is 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% K2O, 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> 6 and 7, a manufacturing process for a method for manufacturing graphene 113 and carbide 19 will be described. Fig. 7 is a diagram showing a process flow illustrating the manufacturing process of the embodiment. First, in the pre-treatment step S1, after drying the plant-based raw material 9 as described above, the plant-based raw material 9 is pulverized, and 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 a suitable size, kneaded, and 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. Here, examples of the pulverizing 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, about 0.8 g of the plant-based raw material 9 is placed in a crucible 5 and covered with a metal net or the like. The crucible 5 is placed in a predetermined heating position of the plasma device 10 described above. The pressure in the chamber 1 is reduced to 80 Pa by the vacuum pump 30, and an inert gas 6 is injected into the chamber 1 at a flow rate of 8 to 10 ml / min, and the pressure in the chamber 1 is maintained at 1300 to 1500 Pa. Note that the carbonization step S2 can also be used in Examples 1 and 3 to produce similar graphene.

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

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

[0024] Here, potassium hydroxide is used from the viewpoint of promoting the removal of silicon and improving 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. In addition, 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] Among the carbide 19 reacted with potassium hydroxide, silicic acid reacts with potassium hydroxide to become potassium silicate, and the remaining water-soluble potassium hydroxide (KOH) and potassium silicate are dissolved in water, and the 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 process S3, it was possible to produce graphene 113, which is the final product with a weight of about 1 / 8 to 1 / 10 compared to when the initial plant-based 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 mainly comprises an inert gas 6, a control device 20, a chamber 1, and a vacuum pump 30.

[0027] Argon is mainly used as the inert gas 6 stored in the gas cylinder, 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] The chamber 1 is connected to a control valve 22, and the pressure inside the chamber 1 can be reduced to a vacuum state by a vacuum pump 30. The chamber 1 is connected to the control valve 22, and an inert gas 6 is introduced into the chamber 1. A leak valve 23 that releases the vacuum state inside the chamber 1 to atmospheric pressure is provided between the control valve 22 and the chamber 1. In addition, a control valve 14 and a leak valve 15 that releases the vacuum state inside the chamber 1 to atmospheric pressure are provided between the vacuum pump 30 and an outlet pipe 8 that introduces air inside the chamber 1.

[0029] The temperature control device 24 controls the high frequency power source 4 to manage the temperature maintenance and the maintenance time in the chamber 1. The plasma device 10 of this embodiment is a method in which argon gas, which is an inert gas 6, is flowed as a working gas under a low pressure close to a vacuum state, a high current is flowed between the electrodes, the cathode 2 and the anode 3, and thermal plasma is obtained by arc discharge. A carbon crucible 5 is placed between the cathode 2 and the anode 3, and the crucible 5 contains a vegetable raw material 9 described later. The vegetable raw material 9 is carbonized in about 10 to 30 minutes by heating to a temperature range of 300°C to 1000°C by the thermal plasma generated by the arc discharge. In addition to the above-mentioned plasma device, there are methods of obtaining thermal plasma by barrier discharge, corona discharge, pulse discharge, and direct current discharge.

[0030] In the above-mentioned production method, a gas phase reaction occurs, and in particular, 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, thereby imparting hydrophilicity. The manufacturing method is not limited to the above. The heat source may be induction heating, gas, or an electric furnace other than the plasma device.

[0031] In the case of induction heating, even if there is an insulator such as silicon dioxide (SiO2) in the plant-based raw material 9, the magnetic flux penetrates and the plant-based raw material 9 becomes conductive, so that the plant-based raw material 9 itself is heated and the heating is accelerated, allowing the plant-based raw material 9 to be carbonized in a short period of time.

[0032] In addition, since the insulating material such as silicon dioxide (SiO2) itself allows the alternating magnetic flux to penetrate, the silicon dioxide (SiO2) itself is only heated from the storage box 205, and the temperature is not high enough to melt it, so it remains as it is, and many insulating materials such as silicon dioxide (SiO2) remain.

[0033] <Process flow 2> 8 shows a main flow of the method for producing the carbon material 100. In this example, the method for producing the carbon material 100 to be graphened will be described based on the flow from S11 to S16.

[0034] First, the above-mentioned plant-derived raw material 9 is pulverized by a pulverizer, and a carbon raw material pulverization process (S11) is performed to pulverize the plant-derived raw material 9 to a degree that does not result in too fine a powder, since the plant-derived raw material 9 is held in a dehydration container 15 having slits, holes, or a mesh, which will be described later, and is then dehydrated. The carbon raw material pulverization process (S11) may be performed to a degree that allows the plant-derived raw material 9 to be easily permeated with an alkaline aqueous solution in the next process. It is not necessary to perform the process S11 first, and the plant-derived raw material 9 may be pulverized last.

[0035] Next, the crushed plant raw material 9 is subjected to an aqueous solution soaking treatment (S12) in which the raw material 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.

[0036] Incidentally, this step (S12) may be a method of soaking the plant-derived raw material 9 in the aqueous solution 20 at room temperature for about one week. In this case, it is also possible to adjust the pH of the aqueous solution 20 to use a weakly alkaline aqueous solution 20 having a pH of about 9.

[0037] 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 to mainly remove the silica components contained in the plant-derived raw material 9, and the silica components are extracted into the aqueous solution 20.

[0038] This increases the concentration of organic components and the carbon ratio in the final product, the carbon material 100. The concentration of the alkaline aqueous solution 20 is best at 30% wt, with a pH of about 9 to 14. An aqueous solution 20 produced with potassium hydroxide at pH 13 is best. The amount of plant-derived raw material 9 added is best in the range of 80% wtm to 200% wtm, relative to the potassium hydroxide before dissolving in water.

[0039] Examples of alkaline materials include alkalis such as sodium hydroxide, potassium carbonate, 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 in converting the carbon material 100 into graphene.

[0040] This is a photograph taken through a scanning transmission electron microscope after carbonization at 300℃ to 500℃ without alkali treatment. When checking the element distribution, Al (aluminum) is scattered as fine particles, and K (potassium) is present as large particles.

[0041] Therefore, removing potassium and aluminum improves the purity of carbon, which also leads to improved electrical conductivity. It is also ideal for forming porous carbon materials. Aluminum in particular dissolves easily 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 the same potassium hydroxide.

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

[0043] In the dehydration process (S13), the plant-based raw material 9 that has been subjected to the aqueous solution permeation process (S12) is placed in a metal, cloth or plastic dehydration container 15 that has a structure of mesh, slits and / or holes, and is then dehydrated in a centrifugal spin-drying machine, as in 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] As another method for dehydration, the plant-based raw material 9 may be placed in a bag-shaped dehydration container 15 and the bag may be squeezed with a squeezer to remove the water.

[0045] The plant material 9 is dehydrated by centrifugation in a rotary dehydrator such as 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 material 9.

[0046] Next, a drying process (S14) is performed to remove the moisture from the aqueous solution 20 using a drying device or drying in the shade in the same manner. The aqueous solution 20 is left in an alkaline atmosphere without being neutralized or washed with water (S14). Since the moisture can be removed in this process, it is possible to minimize damage caused by alkaline moisture to the apparatus or containers such as crucibles due to evaporation of moisture during carbonization. Note that since it is only necessary to remove alkaline moisture, it is not necessarily necessary to provide the drying process (S14) as long as the moisture can be removed in the above-mentioned dehydration process (S13), and the aqueous solution 20 may be in a wet state.

[0047] Next, a carbonization process is performed 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 in an oxygen-free state and maintaining a combustion temperature of 1100°C for 5 hours (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 optimal, 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 advisable to use a rotary kiln-type carbonization device, induction heating furnace, electric furnace, or the like that is resistant to alkali, such as spraying with alumina or using a storage container for the plant-derived raw materials 9 made of alumina material to make it resistant to alkali.

[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 susceptible to direct alkali corrosion of metals, which makes it possible to improve the durability of the manufacturing equipment.

[0051] Finally, after the carbonization process (S15), the carbon material 100 is neutralized (S16) by exposing it to water or an acidic aqueous solution such as hydrochloric acid, sulfuric acid, or citric acid, and the like, and the remaining silica and the like are removed (S16). If the carbon material 100 is then dried and stored in a vacuum, it can be shipped while maintaining its physical properties, such as its electrical conductivity.

[0052] In the neutralization process (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 to remove solids such as silica, so neutralization using water (S16) is the most cost-effective option.

[0053] 9, pure water 81 is placed in a container 80, and carbon material 100 and pure water are placed in a bag-shaped permeation membrane 82 that only allows water molecules to pass through, and both ends 83 are submerged in the pure water, and a pressure balance is generated from the aqueous solution containing impurities including carbon material 100, causing the water containing alkaline components to pass through the membrane and flow into the pure water 81. In this way, the use of 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 the carbon material 100 is forced up from a bath 64 containing carbon material 100 and pure water by a pump 61 and passed through a 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 amount of pure water collected in the collection container 63. In this manner, the aqueous solution containing the alkaline component is gradually neutralized by circulation.

[0056] <Process flow 3> A method for producing the carbon material 100 using rice husks as the plant raw material 9 of this embodiment will be described in the examples with reference to Fig. 11. The method is particularly suitable for producing the carbon material 100 used as a conductive material.

[0057] The plant-based raw material 9 is pulverized, but since the microparticulation is performed at the end, it is sufficient to pulverize the raw material so that the particles penetrate the inside of the raw material when immersed in water. Also, since the raw material will go through a dehydration process, it is sufficient that the particles are small enough not to slip through the slits or holes. The size after pulverization is preferably about 5 mm to 10 mm. Here, examples of the pulverization method include a mill, mixer, grinder, etc. Also, a pulverization process is not necessary, and it is sufficient that water or the like penetrates the raw material when 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 from room temperature to 80°C. The water washing (S22) may be performed by pouring water and then stirring with a stirrer. Alternatively, washing may be performed by pouring water little by little while stirring. For stirring, a vortex device or a device that rotates blades may be used, or a stirrer device or the like may be used.

[0059] Next, the washed vegetable raw material 9 is placed in the above-mentioned dehydration container 15 and dehydrated in a rotary dehydration device such as a washing machine (S23). The rotation speed during dehydration is preferably 300 to 3000 rpm, and most preferably 500 to 1500 rpm.

[0060] Moreover, the gravitational acceleration during centrifugation by the dehydrator is preferably about 2 G to 5 G. The dehydrator may be the same device from washing to rinsing and dehydration (S22 to S23), or may be a structure in which dehydration container 15 is stored or built-in.

[0061] By dehydration, impurities are removed along with the moisture. It is possible to move the plant-based raw material 9 to the next firing step while it is still wet, without going through a drying step. It was confirmed that the dehydration step by rotation also promotes the decomposition of the plant-based raw material 9's tissue, making it possible to proceed to the next step without a drying step.

[0062] Therefore, it became possible to shorten the manufacturing time by eliminating the drying process. In addition, when the water is removed by centrifugation during dehydration, the destruction of the cell walls of the plant-derived raw material 9 is promoted, and the destruction progresses to the inside.

[0063] Therefore, if rotary dehydration is performed in the embodiment, it is not necessary to carry out the drying process, but drying further reduces the impact of rust, etc. on the combustion device. Also, compared to the process of activating the material together with a solid alkaline material, the impact on the combustion device is even less.

[0064] Next, in the firing step (S24), the plant-based raw material 9 is placed in a furnace, the furnace is filled with argon gas or nitrogen gas to create an oxygen-free state, the temperature inside the furnace is raised to 1100°C, and the temperature is maintained at 1100°C for a certain period of time, about 1 to 10 hours. Thereafter, the plant-based raw material 9 is naturally fired for a total firing time of 1 day. As a result, the carbon material 10 is produced.

[0065] Furthermore, in the calcination step (S24), the plant-derived raw material 9 after the dehydration step (S23) is not completely dried, but rather remains slightly moist when it is transferred to the calcination step (S24). This causes so-called steam activation to occur in the initial stage, which leads to the destruction and decomposition of cell walls.

[0066] In addition, the steam activation generates micropores, which makes it easier to form a porous material similar to activated carbon. In the calcination step (S24), it is preferable to use a rotary kiln-type carbonization device, an induction heating furnace, an electric furnace, a continuous carbonization furnace, or the like.

[0067] In addition, during the water washing (S22), the plant-derived raw materials 9 are stored 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, whereby the cell walls of the plant-derived raw materials 9 are quickly destroyed, leading to the removal of impurities and the improvement of purity.

[0068] As another example, wheat or barley husks, cocoa husks, and sake lees are burned in an oxygen-free state at a temperature of 1000°C to 1500°C using a rotary kiln-type carbonizer, induction heating furnace, electric furnace, continuous carbonizer, etc. Also, firing may be performed after steps S21 to S23.

[0069] In addition, the specific surface area was measured using the BET adsorption isotherm based on the amount of nitrogen adsorbed at liquid nitrogen temperature.

[0070] As a result, wheat and barley husks, cocoa husks, and sake lees were recycled at a rate of 15m 2 / g to 80m 2 / g. This small specific surface area improves the dispersibility of the carbon material in emulsions such as acrylic, resulting in a uniform mix of the carbon material and improved conductivity. In addition, the improved dispersibility of the coating film improves its dispersibility, making it possible to ensure strength.

[0071] <Process flow 4> A method for producing the carbon material 100 using rice husks as the plant raw material 9 of this embodiment will be described in the examples with reference to Fig. 13. The method is particularly suitable for producing the carbon material 100 used as a conductive material.

[0072] The plant-based raw material 9 is pulverized, but since the microparticulation is performed in the last step, it is sufficient to pulverize the raw material so that the particles penetrate the inside when immersed in water. Also, since the dehydration step is performed, it is sufficient that the particles are small enough not to slip through the slits or holes. The size after pulverization is preferably about 5 mm to 10 mm. Here, examples of the pulverization method include a mill, mixer, grinder, etc. Also, a pulverization step is not necessary, and it is sufficient if the aqueous solution penetrates the raw material during washing, etc.

[0073] Next, the plant-derived raw material 9 is carbonized at a temperature of 500° C. to 800° C. for about 3 minutes to 3 hours (S32). The carbonized carbide 19 is immersed in acid (S33). At this time, hydrofluoric acid is preferable, and any solution that dissolves silicon components in the acid solution is acceptable.

[0074] Next, after acid washing (S33), the silicon component is removed from the carbide 19 by washing with water or the like. At this time, it is best to neutralize the carbide by washing with water or the like. Thereafter, the carbide is immersed in an alkaline aqueous solution as in the above-mentioned process flow 1 or 2 (S34).

[0075] Next, the carbonized material 19 is placed in the above-mentioned dehydration vessel 15, and dehydration is performed in a rotary dehydration device such as a washing machine (S35). The rotation speed during dehydration is preferably 300 to 3000 rpm, and most preferably 500 to 1500 rpm. In terms of gravitational acceleration, about 2G to 5G is preferable.

[0076] The dehydrated carbide 19 can be moved to the next firing step in a wet state without going through a drying step. The silicon component contained in the carbide 19 is removed by this dehydration step (S35) using rotation.

[0077] Therefore, it has become possible to shorten the manufacturing time by eliminating the steps of drying, etc. In addition, when the water is removed by centrifugation during dehydration, the destruction of the cell walls of the plant-derived raw materials 9 is promoted, and the alkaline aqueous solution can penetrate deeper into the cell walls.

[0078] Therefore, if rotary dehydration is performed in the embodiment, it is not necessary to carry out the drying process, but drying further reduces the impact of rust, etc. on the combustion device. Also, compared to the process of activating the material together with a solid alkaline material, the impact on the combustion device is even less.

[0079] Next, in the firing process (S35), the plant-based raw material 9 is placed in a furnace, the furnace is filled with argon gas or nitrogen gas to create an oxygen-free state, the temperature inside the furnace is raised to 1100°C, and the temperature is maintained at 1100°C for a certain period of time, about 1 to 10 hours, after which the carbon material 100 is produced.

[0080] Furthermore, in the calcination step (S36), the plant-derived raw material 9 after the dehydration step (S35) is not completely dried, but rather remains slightly moist when it is transferred to the calcination step (S36). This causes so-called steam activation to occur in the initial stage, which leads to the destruction of cell walls and the promotion of the formation of porous pores.

[0081] In addition to steam activation, activation in an alkaline atmosphere can also generate micropores, making it easier to form a porous material similar to activated carbon. In the calcination step (S36), it is recommended to use a rotary kiln-type carbonization device, an induction heating furnace, an electric furnace, a continuous carbonization furnace, or the like. Finally, the neutralization treatment (S16) of process flow 2 may be performed.

[0082] (Graphene and Carbides) The carbonized material 19 obtained in the carbonization step S2 and the firing step (S24, S32) and the graphene 113, which is the carbon material 100 obtained in the activation step S3, produced in the above-mentioned Example will be described below.

[0083] Fig. 1 shows a Raman spectrum of graphene 113 obtained by the production apparatus of the present invention. Fig. 2 shows a Raman spectrum of carbide 19 obtained by the production apparatus of the present invention. These figures were analyzed using a Raman spectrometer, and the data obtained is a Raman spectrum with the horizontal axis representing wavelength (wave number (Raman shift (cm-1))) and the vertical axis representing intensity.

[0084] As shown in Table 4, the peak values ​​IG and ID of the G band (2850 cm-1) and 2D band (1650 cm-1), which are wavelength peaks according to the Raman spectroscopy, are also shown.

[0085] 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-based raw material 9. In particular, it was confirmed that carbide 19 contains a lot of silicon, and that oxygen functional groups including -OH, -CHO, and -COOH are generated.

[0086] The value obtained by dividing IG of graphene 113 by ID is preferably 0.9 or more, and shows a value of about 0.9 to 2.0.

[0087] The ash content of the carbide 19 obtained in the carbonization step S2 was 37.1 wt% according to thermogravimetry, excluding carbon, and of that ash content, silicon (Si) was 24 wt% to 50 wt% of the entire carbide 19. In addition, K was 0.51 wt% to 7 wt%, Al was 0.1 wt% to 1.6 wt%, Ca was 0.17 wt% to 0.5 wt%, Fe was 0.4 wt%, and Cr, Ni, Mn, Mg, P, S, and Na were 0.1 wt% or less.

[0088] 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, etc. in the form of -O-Si-OR to become a lignin-polysaccharide complex, and is thought to be likely to take the form of C / SiOx.

[0089] In addition, the graphene 113 obtained in the activation step S3 described below has a high ash content excluding carbon, ranging from 1% to 24wt%, according to thermogravimetry, of which silicon (Si) accounts for 1wt to 20wt% of the entire graphene 113. In addition, K is 4.3wt%, Al is 1.5wt%, Ca is 1.3wt%, Fe is 0.4w%, and P, Mn, Cl, S, and Mg are 0.1wt% or less.

[0090] As described above, the amount of silicon in the graphene 113 and the carbide 19, which are the carbon material 100, is high, ranging from 1 wt % to 50 wt %.

[0091] [Table 4] As shown in Table 4, the results of the CO2 adsorption / desorption measurements confirmed that graphene 113 and carbide 19 had fine pores with diameters mainly ranging from 0.8 nm to 2 nm.

[0092] Therefore, it is considered that metal ions and the like are easily adsorbed. 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. The micropore volumes were 0.46 ml / g for Graphene 113 and 0.27 ml / g for Carbide 19.

[0093] Moreover, as shown in Table 4, the particles of graphene 113 or carbide 19 have a diameter distribution ranging from 15 μm to 229 μm, and the median diameter, which is the median value of the integrated value of the distribution, is about 110 μm.

[0094] Thus, a mesopore volume of 0.2 ml / g to 0.6 ml / g is formed. In particular, the graphene 113 after the activation treatment to remove impurities (described later) shows a higher value, and it is considered that the mesopores and micropores grow due to the removal of silicon.

[0095] In addition, as shown in Table 4, the specific surface area of ​​graphene 113 measured by water vapor adsorption measurement method and the BET equation was 1792 m 2 / g, and the width is 890m 2 / g~2500m 2 / g. Carbon 19 shows 726.4 m2 / g, and this width is 890 m 2 / g~1500m 2 / g. All of them have a large specific surface area, and after removing the silicon component (Si), graphene 113 has an even larger specific surface area.

[0096] Therefore, the graphene 113 has a high adsorption effect. In particular, the carbon material 100 produced by using rice husk as the plant raw material 9 in the process flow 4 has a high adsorption effect of 2000 m 2 / g from 2600m 2 / g value.

[0097] Similarly, carbide 19 may contain minute amounts of Si (silicon) as Si (silicon) or silicon dioxide (SiO2) on the surface or inside of carbide 19, or may be formed as Si (silicon) or silicon dioxide (SiO2) by agglomeration on the surface or inside of carbide 19. By subjecting carbide 19 to activation treatment, the carbon purity increases and the specific surface area increases.

[0098] As shown in Table 4, the true density measured by a gas displacement density measurement device was 2.56 g / cm3 for graphene 113 and 2.27 g / cm3 for carbide 19. In addition, the bulk density of graphene 113 was 0.21 to 0.29 g / cm3.

[0099] In addition, the powder resistance measured by the double ring method and the four-terminal method was 1.27×103 to 5 Ω·cm for carbide 19, and 1.0×10-2 Ω·cm for graphene 113 by removing silicon, improving conductivity. The lower the resistance, the better, and the optimum resistance for graphene 113 is 1.0×10-3 Ω·cm to 3.8×10-2 Ω·cm. Furthermore, by leaving a large amount of silicon behind, the carbide 19 becomes more easily dissolved in substances that are easily adsorbed by silicon, and at the same time, the insulating performance is improved.

[0100] (heat-generating paint) Hereinafter, a heat-generating paint produced using the above-mentioned carbon material 100 (the carbide 19 and the graphene 113) as a pigment will be described. The applicant has conducted tests on various types of paint to find the optimal conditions. In this embodiment, tests were conducted on two-component solvent-based paints, one-component solvent-based paints, and one-component water-based paints. [Table 5]

[0101] As shown in Table 5, the solvent-based two-component paint uses acrylic urethane as the binder and is diluted with xylene as the solvent. The above-mentioned carbon material 100 (carbonized material 19 and graphene 113) is used as the pigment. This solvent-based two-component paint is a type that is hardened using a hardener.

[0102] The solvent-based one-component type uses 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 type is a type that hardens when heated, and has excellent heat resistance, withstanding temperatures up to 150°C.

[0103] The water-based one-component type used an acrylic emulsion as the binder, water as the solvent, and the above-mentioned carbon material 100 (carbide 19 and graphene 113) as the pigment. In addition, the binder was gradually added to the carbon material while stirring with a disperser, and the limit of the amount of binder added at which the mixture remained liquid was determined. The pigment weight concentration (PWC value) at that time was also calculated.

[0104] [Table 6] As shown in Table 6, each carbon material and each coating film with different PWC values ​​were evaluated. First, 10 g of each limit liquid was placed on a tin plate, and the binder, hardener, etc. were mixed so that the PWC value was within the set range, and the mixture was coated by stirring with a spatula. The dry film thickness was then measured. The coating film was also visually judged for unevenness, cracks, color and gloss spots, with ○ indicating no defects, △ indicating the presence of any of these defects, and × indicating the presence of noticeable defects.

[0105] The film-forming property is the result of a test to see whether the coating peels off when the coating surface is scratched with a fingernail, etc. A circle indicates no peeling, and an x ​​indicates peeling. The gloss is the result of measuring the gloss value at 60 degrees. <1 indicates that it is less than 1.

[0106] Furthermore, the film properties are the results of a test to see whether the coating peels off when the coating surface is scratched with a fingernail, etc. A circle indicates no peeling, and an x ​​indicates peeling.

[0107] Flexibility was evaluated by forming a coating film on paper, folding the paper in a mountain fold, and determining whether or not cracks or breaks occurred in the coating film at the peaks of the folds. A mark of ◯ indicates that no cracks or breaks occurred, and a mark of × indicates that cracks or breaks occurred.

[0108] Next, the performance of the heat-generating paint will be explained. Figure 3 shows the above-mentioned solvent-based one-liquid heat-generating paint 50 applied to an insulator 51 such as paper, cloth, or plastic resin. The heat-generating paint 50 is provided with a positive electrode 52 and a negative electrode 53 at the end of the center, and heat is generated from the place where the heat-generating paint 50 is applied by supplying power to the electrodes. The distance H between the electrodes is 4.5 cm, and the area where the paint is applied is 22.5 cm2.

[0109] 4 and 5 are diagrams showing the heat generating characteristics of the heat generating paint 50. In FIG. Figure 4 is a graph of time (seconds) and temperature (°C) for heating element 40 with a coating thickness of 160 μm to 175 μm. V1 is a temperature graph measured at point P in Figure 3 when DC 20 V was supplied. The power value was 4 to 4.8 W, and the temperature rose from room temperature 22.1°C to a maximum of about 62°C in about 300 seconds.

[0110] V2 is a graph showing the temperature measured at point P in Figure 3 when DC12V was supplied. The power value was 2 to 2.4W, and the temperature rose from room temperature of 26.3°C to a maximum of about 43.4°C in about 300 seconds.

[0111] 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 25.4°C to a maximum of about 44.1°C in about 280 seconds.

[0112] V2 is a graph showing the temperature measured at point P in Figure 3 when DC12V was supplied. The power value was 0.6W, and the temperature rose from room temperature of 25.4°C to a maximum of about 32.6°C in about 240 seconds.

[0113] Since 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 inorganic materials later. In particular, heat-generating paint containing silicon in the carbon material can maintain the continuity of the paint film even when heated to high temperatures, making it possible to produce a highly heat-resistant sheet heater.

[0114] In addition, by mixing the carbide 19 containing many functional groups with the graphene 113 to form a pigment for paint, it is possible to supply high voltage power such as AC as well as DC while stabilizing the strength.

[0115] In addition, the carbide 19 containing many functional groups can be easily dispersed and mixed in to adjust the resistance value. The ratio of the carbide 19 to the graphene 113 is preferably about 0.5:9.5 to 3:7. The carbon material 100 having a powder resistance in the range of 1.0×10-3 Ω·cm to 3.8×10-2 Ω·cm may be used alone or in combination.

[0116] Next, Figures 12 and 13 show another example of the heat generating element 40. Figure 12(A) is a front view of the heat generating element 40. Figure 12(B) is a cross-sectional view of the heat generating element 40 taken along line AB in the front view. Heat generating paint 50 is made by mixing and kneading carbon material 100 in a synthetic resin emulsion, typically vinyl chloride, vinyl acetate, or acrylic, at a ratio of 10% to 75% by weight. The best ratio is a carbon ratio of 20% to 60% by weight. It may also be dispersed using water.

[0117] The thickness t of the coating film was 500μm to 1000μm. The ideal thickness of the coating film is 100μm to 1500μm, and can be changed appropriately depending on the resistance value and the place of use. When an acrylic emulsion was used, it was possible to apply a thick coating.

[0118] Heating element 40 shown in Fig. 12 has wiring 41 using copper foil, silver foil, copper or silver paste, or conductive wire formed on substrate 42, with + electrode 52 and - electrode 53. 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.

[0119] The heating element 40 was formed with a total length of 56 cm, a width of 4 cm, and an electrode width of 1 cm, and the total 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 about 24 W. Here, the carbon material 100 most suitable for the heat-generating paint was one in which cacao shells, barley husks, wheat husks, etc., among the plant-based raw materials 9, were burned at a combustion temperature of 900°C to 1500°C.

[0120] 13, a heating element 40 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, pottery, concrete, cement, cloth (glass fiber, cotton polyester), aluminum tape, plastic, or the like.

[0121] 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 made of a material through which the heat-generating paint 50 could pass. The thickness of the nonwoven fabric 43 was 10 g / m 2 From 30 g / m 2 is good.

[0122] Various materials can be used for the nonwoven fabric 43, such as polyester, polypropylene, polyethylene, rayon, nylon, wool, etc. Since the heat-generating paint 50 can pass through the nonwoven fabric 43, the nonwoven fabric 43 and the heat-generating paint are mixed together when viewed from the cross section.

[0123] The heating element 40 was formed with a total length of 50 cm, a width of 4 cm, and an electrode width of 1 cm, and the total 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 about 24 W. Here, the carbon material 100 most suitable for heat-generating paint was one in which vegetable raw materials 9 such as cacao shells, barley husks, and wheat husks were burned at a combustion temperature of 900°C to 1500°C.

[0124] Alternatively, the heat-generating paint 50 may be a paint in which the carbon material 100 is mixed into an aqueous solution of sodium silicate diluted with water. It is particularly suitable for the carbon material 100 obtained by carbonizing plant-derived raw material 9 containing 5% to 20% silicon. The silicon contained in the carbon material 100 dissolves into the sodium silicate, improving electrical conductivity and strength. It is also suitable as a fire-resistant paint, so it is possible to reduce the risk of fire, etc., when used as a heat-generating paint.

[0125] (Technical features) Below, examples of the technical features of this embodiment are shown in parentheses, but these are not particularly limiting and are merely examples, and the effects that can be expected from these features will also be described.

[0126] <Feature 1> The method includes a washing step in which the plant-based raw materials are immersed in an aqueous solution and washed with water while being stirred; a dehydration step in which the plant-based raw materials are stored in a container after the washing step and rotated by a rotary dehydrator to remove water contained in the plant-based raw materials; and a baking step in which the plant-based raw materials are baked after the dehydration step.

[0127] The aqueous solution may be an alkaline aqueous solution, pure water, treated water, or tap water. The temperature of the aqueous solution is preferably from room temperature (20°C) to 100°C. The dehydration container and the washing container may be the same container. The washing process and the dehydration process may be performed in the same device, such as a washing machine.

[0128] The above features reduce the time required for drying after immersion in a solution or washing with water, as was previously the case, improving production efficiency, while also accelerating the decomposition of cellulose and other substances and making it possible to remove impurities. [Industrial Applicability]

[0129] Regarding industrial applications of the carbon material of the present invention, in addition to heat-generating paints for construction such as concrete, heat-generating paints, it can also be used as conductive paints for battery materials, circuit boards, heat-dissipating materials, etc. [Explanation of symbols]

[0130] 1 Chamber 2 Cathode 3 Anode 4 High frequency power supply 5. Crucible 6. Inert Gas 7 Introductory tube 8 Outlet pipe 9 Plant-based raw materials 10 Plasma equipment 14 Control valve 15 Leak valve 19 Carbide 20 Control Device 21 Gas volume control device 30 Vacuum Pump 40 Heating element 42 Base material 50 Heat-generating paint 51 Insulators 52, 53 electrode 100 Carbon Materials 113 Graphene S1 Pretreatment process S2 Carbonization process S3 Activation step.

Claims

1. a washing step of immersing the plant-based raw material in an aqueous solution and washing it by stirring; a dehydration step in which the plant-based raw material is stored in a container after the washing step and rotated by a rotary dehydrator to remove water from the plant-based raw material; A baking step of baking the wet plant-based raw material without drying it after the dehydration step; A method for producing a carbon material, comprising:

2. 2. The method for producing a carbon material according to claim 1, wherein the rotation speed of the dehydration device is 300 rpm to 3000 rpm.

3. Powder resistance is 1.0 x 10 －３ Ω cm to 3.8 x 10 －２ The method for producing a carbon material according to claim 1, comprising the step of producing a carbon material having a viscosity of Ω·cm.

4. The plant-based raw materials used are wheat and barley husks, cocoa husks, 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 / g.

5. a carbonization step of carbonizing the plant-based raw material; an acid washing step of washing the carbonized material with an acid solution after the carbonization step; an alkaline aqueous solution immersion step of immersing the carbonized material in an alkaline aqueous solution after the acid washing step; a dehydration step of storing the carbonized plant material in a container and rotating the container with a rotary dehydrator to remove water contained in the plant raw material; a baking step of baking the plant-based raw material in a wet state without drying it after the dehydration step; A method for producing a carbon material, comprising:

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