Method for producing fine particle powder containing calcium oxide or calcium hydroxide, and fine particle powder containing calcium oxide or calcium hydroxide

Abstract

Provided is a production method for a fine-particle powder containing a calcium oxide or calcium hydroxide, the method including: a step for preparing a pulverized powder of shells or eggshells; a step in which the pulverized powder of shells or eggshells is introduced into a controlled atmosphere, evaporated by thermal plasma, and then coagulated in a gas phase to generate fine particles containing a calcium oxide or calcium hydroxide; and a step for collecting a fine-particle powder containing a calcium oxide or calcium hydroxide processed by thermal plasma.

Description

[Technical Field]

[0001] The present invention relates to a microparticle powder containing calcium oxide or calcium hydroxide that has antibacterial properties and a method for producing the microparticle powder containing calcium oxide or calcium hydroxide. The microparticle powder containing calcium oxide or calcium hydroxide is useful as an antibacterial material to be incorporated into resin products used, for example, in splash prevention sheets such as face shields used to combat coronavirus, tableware such as chopsticks and spoons, and film materials for food packaging. Furthermore, a resin composition containing the microparticle powder containing calcium oxide or calcium hydroxide as an antibacterial material can be used in protective films for touch panels of electronic devices such as smartphones. [Background technology]

[0002] Japan's scallop catch volume was approximately 480,000 tons in fiscal year 2018, of which approximately 80% was shells, much of which was treated as waste. Various attempts have been made to effectively utilize shells, but it is said that they have only been used in the same way as limestone. Environmental problems such as foul odors and soil pollution caused by the mountains of shells that are discarded are becoming serious, so it is necessary to develop new ways to utilize shells.

[0003] The main component of scallop shells is calcium carbonate (CaCO3), which is used as a food additive to supplement calcium, a fluidity improver for printing inks, and a reinforcing agent for plastics and rubber. Heat-treating this shell powder at temperatures above 700°C for several hours converts calcium carbonate (CaCO3) into calcium oxide (CaO) through the desorption of carbon dioxide. Powders containing calcium oxide as the main component after this high-temperature sintering process are called calcined scallop shell powder and possess strong antibacterial activity. Furthermore, when calcined scallop shell powder is made into a slurry, the main component, calcium oxide (CaO), reacts with water to form calcium hydroxide (Ca(OH)2). This calcined scallop shell powder slurry also possesses strong antibacterial activity, and has been reported to demonstrate high antibacterial activity against Escherichia coli, Staphylococcus aureus, and durable Bacillus subtilis spores (see, for example, Non-Patent Document 1).

[0004] In other words, it becomes alkaline when slightly dissolved in water, and the high pH is thought to be the main factor in its bactericidal mechanism, as it has a bactericidal effect. It also exhibits antibacterial effects when sintered at high temperatures of 700°C or higher, but the effect becomes stronger as the firing temperature increases, and powder fired at 1000°C has been confirmed to have antibacterial activity roughly equivalent to commercially available calcium oxide powder slurry. To produce fired shell powder with strong antibacterial effects, high-temperature sintering at 1000°C or higher for several hours is required.

[0005] Calcined scallop shell powder has been confirmed to have a bactericidal effect against viruses such as influenza, and Non-Patent Document 2 reports that a powder with a relatively small particle size (average particle size 3.5 micrometers) had a bactericidal effect 1,000 times greater than a powder with a larger particle size (average particle size 18.4 micrometers). As such, generally, as the particle size of antibacterial materials becomes smaller, that is, as the specific surface area increases, the antibacterial effect tends to become stronger, so there is a demand for microparticulate antibacterial materials.

[0006] When creating plastic or resin products with antibacterial properties, antibacterial materials are mixed into the resin raw materials before molding. The color of the final molded resin product is also affected by the color of the antibacterial particle powder added. Therefore, to avoid affecting the color of the final molded resin product, it is best to add small antibacterial particles with a particle shape that is easy to disperse. In particular, when adding antibacterial properties to resin films coated or attached to touch panels, such as the transparent resin sheets used to prevent splashes as a countermeasure against the recent coronavirus and the transparent resin films used in food packaging, fine particles of the added antibacterial material are desirable to maintain the transparency of the final product.

[0007] Furthermore, when manufacturing transparent plastic sheets or resin films containing antibacterial materials, the antibacterial materials must be produced in large quantities and at low cost. From the perspective of the resin mixing process, it is preferable to use dry particles rather than a slurry dispersed in a solution. When using a slurry, various additional processes such as waste liquid treatment and drying are required, and the process takes a long time. Furthermore, when using a slurry, the dispersant and slurry solvent introduced to prevent the particles from agglomerating become contaminants (impurities) during the resin mixing process, which can reduce the strength of the final resin molded product and reduce the antibacterial effect.

[0008] Common manufacturing methods for micronizing materials include jet mills, which use high-speed airflow to blow raw materials into fine particles, causing particles to collide with each other, and bead mills, which use ceramic or zirconia beads to mechanically pulverize the bulk raw material. However, Patent Document 1 states that mechanical pulverization using jet mills and other methods has a limit of an average particle size of 1.5 microns, and that even using wet pulverization methods such as ball mills, which have high pulverization efficiency and are capable of advanced pulverization, currently only produces calcium hydroxide with an average particle size of 3 microns. Therefore, these mechanical pulverization methods are limited to micron and submicron sizes, making it difficult to pulverize calcium oxide and calcium hydroxide from shell pulverized powder into nano-sized particles (100 nanometers or less).

[0009] Another method for atomizing materials is the atomization method, in which the material is melted and sprayed into air or water. However, calcium oxide, which is found in fired shell powder, has a high melting point of 2613°C, so maintaining the material in a molten state is energy inefficient. Furthermore, while atomization generally allows for the formation of submicron-sized particles, it is difficult to form particles smaller than 100 nanometers.

[0010] FIG. 6A shows a circulation flow diagram of the method for producing ultrafine particles of calcium hydroxide in Conventional Example 1.

[0011] In Conventional Example 1, a slurry of calcium hydroxide, the raw material, with an average particle size of 20 micrometers is introduced into a slurry tank 102. In the slurry tank 102, the slurry is stirred with an agitator 104 while being sent to a wet-milling device 101 using a circulation pump 103. Because the system is circulated, the grinding of calcium hydroxide progresses continuously over the grinding time, making it possible to control the particle size. In addition, additives that inhibit dispersion can be added from the slurry tank 102.

[0012] FIG. 6B shows an example of the configuration of a wet-milling apparatus 101. The wet-milling apparatus 101 has a disk-shaped agitator 108 with a rotating shaft at the center of the milling chamber 107. The milling chamber 107 is filled with microbeads with a diameter of 0.03 to 2 mm, approximately 60 to 95% of which is used as a milling medium. In this wet-milling apparatus 101, calcium hydroxide slurry is introduced through a slurry inlet 105, and the beads and calcium hydroxide slurry are agitated and milled in the agitator 108 and discharged from a slurry outlet 106. A gap separator 109 is installed just before the slurry outlet 106, separating the microbeads in the milling chamber 107 from the agitated and milled calcium hydroxide slurry, allowing only the slurry to circulate. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-31212 [Non-patent literature]

[0014] [Non-Patent Document 1] Jun Sawai: Agriculture and Horticulture, Vol. 94, No. 11, P956, 2019 [Non-patent document 2] Ayumi Murata et al.: Journal of the Toyama University Nursing Society, Vol. 7, No. 2, p. 39, 2008 Summary of the Invention

[0015] A method for producing a fine particle powder containing calcium oxide or calcium hydroxide according to one embodiment of the present invention includes the steps of preparing a crushed powder of seashells or eggshells, introducing the crushed seashell or eggshell powder into a controlled atmosphere, evaporating it under thermal plasma, and then solidifying it in the gas phase to produce fine particles containing calcium oxide or calcium hydroxide, and recovering the powder of fine particles containing calcium oxide or calcium hydroxide that has been treated with thermal plasma.

[0016] The fine particle powder according to one embodiment of the present invention is composed of particles having a primary particle diameter of 5 nanometers or more and 300 nanometers or less, and the specific surface area of ​​the entire particle powder is 18 m 2 / g or more of calcium oxide or calcium hydroxide. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a flow diagram of a method for producing a fine particle powder containing calcium oxide or calcium hydroxide according to a first embodiment. [Figure 2] 1 is a schematic cross-sectional view showing the cross-sectional configuration of a fine particle manufacturing apparatus according to a first embodiment. [Figure 3] 1 is an SEM image of a fine-particle powder produced by a method for producing a fine-particle powder containing calcium oxide or calcium hydroxide according to the first embodiment. [Figure 4]FIG. 1 is a diagram showing X-ray diffraction spectra of a material used in the method for producing a fine particle powder containing calcium oxide or calcium hydroxide according to the first embodiment and a fine particle powder produced by thermal plasma. [Figure 5] 1 is Table 1 showing the results of an antibacterial test of the fine particle powder produced by the method for producing a fine particle powder containing calcium oxide or calcium hydroxide according to the first embodiment. [Figure 6A] FIG. 1 is a circulation flow diagram of the method for producing ultrafine calcium hydroxide particles described in Conventional Example 1. [Figure 6B] FIG. 1 is a schematic diagram showing an example of the configuration of a wet-grinding device described in Conventional Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0018] In the above-mentioned conventional example 1, calcium hydroxide slurry is used and a wet mechanical grinding method with high grinding power is used to achieve fine particles of calcium hydroxide with an average particle size of 0.5 micrometers or less. In addition, a carboxylate-based polymer compound or a nonionic wetting agent is added as a dispersant to produce a calcium hydroxide slurry with stable dispersibility for more than 1,400 hours.

[0019] However, the particle size of the above-mentioned microparticle production method is still too large to maintain transparency when blended into transparent resin sheets for splash prevention or transparent resin films used in food packaging. To maintain transparency when blending resins or coating films, it is necessary to disperse microparticles of 100 nanometers or less. Even if mechanical grinding is performed for extended periods to further refine the particles, there is a risk of contamination (impurities) from the microbeads used as the grinding medium or compositional deviations due to mechanical grinding, which can result in a deterioration of the antibacterial effect. Furthermore, the use of a slurry increases the number of processes required when blending resins, such as drying and waste liquid treatment, which increases manufacturing costs and raises concerns about a deterioration of the antibacterial effect due to residual solvents and dispersants.

[0020] In consideration of the above-mentioned conventional problems, one aspect of the present invention aims to provide a method for producing a fine particle powder containing calcium oxide or calcium hydroxide, which can efficiently produce a fine particle powder containing calcium oxide or calcium hydroxide having high antibacterial activity in a dry environment using crushed shell material, and the fine particle powder.

[0021] The method for producing a fine particle powder containing calcium oxide or calcium hydroxide according to the first aspect includes the steps of preparing a crushed powder of seashells or eggshells, introducing the crushed seashell or eggshell powder into a controlled atmosphere, evaporating it under thermal plasma, and then solidifying it in the gas phase to produce fine particles containing calcium oxide or calcium hydroxide, and recovering the powder of fine particles containing calcium oxide or calcium hydroxide that has been treated with thermal plasma.

[0022] A second aspect of the present invention relates to a method for producing a fine particle powder containing calcium oxide or calcium hydroxide, wherein the controlled atmosphere in the first aspect contains argon gas and may further contain at least one gas selected from the group consisting of oxygen gas, hydrogen gas, and water vapor.

[0023] A third aspect of the method for producing a fine particle powder containing calcium oxide or calcium hydroxide is the same as the first aspect, except that water may be used when introducing the crushed shell or eggshell powder into the controlled atmosphere.

[0024] The fine particle powder containing calcium oxide or calcium hydroxide according to the fourth aspect is composed of particles having a primary particle diameter of 5 nanometers or more and 300 nanometers or less, and the specific surface area of ​​the entire particle powder is 18 m 2 / g or more.

[0025] A resin composition according to a fifth aspect contains a fine particle powder containing calcium oxide or calcium hydroxide according to the fourth aspect in a resin.

[0026] A resin molded article according to a sixth aspect contains the fine particle powder containing calcium oxide or calcium hydroxide according to the fourth aspect in a resin.

[0027] A resin sheet-like molding according to a seventh aspect contains the fine particle powder containing calcium oxide or calcium hydroxide according to the fourth aspect in a resin.

[0028] According to one embodiment of the present invention, a method for producing a fine particle powder containing calcium oxide or calcium hydroxide can be used to produce calcined shell fine particle powder (primarily calcium carbonate) containing calcium oxide or calcium hydroxide as its primary component and having high antibacterial activity and an average particle size of 100 nanometers or less from ground shell powder (primarily calcium carbonate) without using a solution. By using thermal plasma in the calcination process of ground shell powder, etc., the conventional high-temperature calcination at 1000°C in an electric furnace, which requires 1 to 3 hours, can be eliminated. Thermal plasma enables high-temperature (approximately 10,000°C) calcination in a very short time (a few milliseconds), resulting in the production of a fine particle powder with high antibacterial activity. Because no slurry or solution is used, there are no drying or waste liquid treatment steps, and the resin kneading process can be simplified. As a result, material processing time is significantly reduced and large quantities of material can be processed, increasing the amount of fine particles produced and providing a low-cost method for producing a fine particle powder of antibacterial material.

[0029] Hereinafter, a method for producing a fine particle powder containing calcium oxide or calcium hydroxide according to an embodiment and a fine particle powder containing calcium oxide or calcium hydroxide obtained by the method will be described in detail with reference to the drawings.

[0030] (First embodiment) 1 is a flow diagram of a method for producing a fine particle powder containing calcium oxide or calcium hydroxide according to the first embodiment. The main production flow includes a step of preparing a crushed powder of seashells or eggshells, a step of performing a thermal plasma treatment, and a step of collecting the produced fine particle powder.

[0031] The method for producing a fine particle powder containing calcium oxide or calcium hydroxide according to the first embodiment consists of a very simple dry process, but by passing it through a thermal plasma treatment process, it is possible to produce nanometer-sized fired shell fine particle powder (fine particle powder mainly containing calcium oxide) or fine particle powder containing calcium hydroxide from shell powder (calcium carbonate) with a particle diameter of several micrometers.

[0032] <Fine particle production equipment> 2 is a schematic cross-sectional view showing the cross-sectional configuration of the particle production apparatus 20 according to the first embodiment. For convenience, the Z direction is defined as the vertically upward direction, the X direction is defined as the horizontal direction from left to right on the page, and the Y direction is defined as the front to back on the page. Using FIG. 1, we will explain a multiphase AC arc plasma process as an example of thermal plasma processing for producing nanometer-order particles of baked shell particle powder.

[0033] The particle manufacturing apparatus 20 used in the first embodiment includes at least a reaction chamber 1 as an example of a reaction chamber, a material supply device 10, six electrodes 4 that generate an arc discharge (thermal plasma) 16, and a particle collection section 3 that collects the generated particles 18, and is configured to generate an arc discharge 16 within the reaction chamber 1 and manufacture the particles 18 from material particles 17.

[0034] Furthermore, in the microparticle manufacturing apparatus 20 of the first embodiment, in addition to the above-mentioned configuration, a material supply pipe 11, and discharge gas supply pipes 14 for controlling the flow of the vaporized raw material gas and a cooling gas supply pipe 15 for cooling the vaporized raw material gas are installed above and below the heat insulating member 2. Furthermore, a pressure adjustment valve 6 and an exhaust pump 7 are installed downstream of the microparticle collection section 3, so that the pressure inside the reaction chamber 1 can be adjusted.

[0035] Furthermore, in the microparticle manufacturing apparatus 20 of the first embodiment, in addition to the above configuration, the opening of each discharge gas supply pipe 14 is arranged on the lower side (-Z direction) of the reaction chamber 1 relative to the material supply port 12, and discharge gas is supplied from a gas supply device 30 via a gas flow regulator 31. Each electrode 4 is connected to AC power sources 5-1 to 5-6 that apply AC power, and is configured to be movable so that it can be moved back and forth in a radial direction (radial direction) relative to the center of the reaction chamber 1 by an electrode drive device 8 configured by a motor or the like.

[0036] <Method of producing fine particle powder containing calcium oxide or calcium hydroxide> The method for producing a fine particle powder containing calcium oxide or calcium hydroxide using the fine particle production apparatus according to the above configuration includes the steps of preparing a crushed powder of shells or eggshells, subjecting the shells to a thermal plasma treatment, and recovering the produced fine particle powder. i) generating a thermal plasma 16; ii) supplying material particles 17 to the thermal plasma 16; iii) generating microparticles 18; It consists of at least three steps:

[0037] i) First, in the step of generating the thermal plasma 16, AC powers of different phases are applied to the electrodes 4 arranged in the direction in which the material particles 17 flow (Z direction) within the reaction chamber 1, thereby generating a vertically elongated thermal plasma 16 in the direction in which the material particles 17 flow (i.e., from bottom to top: Z direction).

[0038] ii) Next, in the step of supplying the material particles 17 to the thermal plasma 16, the material particles 17 are supplied into the region of the thermal plasma 16 from the material supply port 12 of the material supply device .

[0039] iii) Next, in the step of generating microparticles 18, the material particles 17 evaporate or vaporize to become material gas as they pass through the region of the thermal plasma 16, and the moment the material gas leaves the region of the thermal plasma 16, the material gas is rapidly cooled and microparticles 18 are generated.

[0040] The thermal plasma treatment step in the method for producing a fine particle powder containing calcium oxide or calcium hydroxide will be described in detail below along with the actual procedure for producing a calcined shell fine particle powder.

[0041] (1) First, the reaction chamber 1, the particle collection unit 3, and the material supply device 10 are evacuated to several tens of Pa by the exhaust pump 7, thereby reducing the influence of oxygen and moisture in the atmosphere.

[0042] (2) Next, gas is supplied from gas supply device 30 to material supply device 10, discharge gas supply pipe 14, and cooling gas supply pipe 15 via gas flow regulator 31, and the pressure inside reaction chamber 1 is adjusted by pressure adjustment valve 6 attached upstream of exhaust pump 7. Gas is supplied from multiple supply ports in discharge gas supply pipe 14 at the bottom of reaction chamber 1.

[0043] (3) The cooling gas supply pipe 15 above the reaction chamber 1 supplies gas into the reaction chamber 1 from multiple supply ports, and ejects the cooling gas in a direction normal to the horizontal plane at an angle of 30° vertically upward from the horizontal plane, thereby efficiently cooling the gas evaporated and vaporized by the arc discharge 16 and controlling the particle size of the microparticles 18 to be produced.

[0044] (4) In one example of this first embodiment, in order to produce shell calcined microparticle powder, argon gas was supplied into the reaction chamber 1 from the gas supply device 30 via the discharge gas supply pipe 14 and the cooling gas supply pipe 15, respectively, and the reaction chamber 1 was maintained at a desired pressure of 0.3 atmospheres or more and 1.0 atmospheres (atmospheric pressure) or less in an inert gas atmosphere containing argon, and the following microparticle production process was carried out.

[0045] Here, argon, an inert gas, is used as the discharge gas and cooling gas. To promote carbon removal from the shell material and carbon dioxide desorption, hydrogen gas, oxygen gas, or water may be introduced into the reaction chamber 1 in mist form from the gas supply device 30 via the discharge gas supply pipe 14 and the cooling gas supply pipe 15. This allows for efficient removal of carbon impurities, increasing the purity of the resulting microparticles and enhancing their antibacterial effects. A small amount of a carbonizing gas, such as methane gas, may also be mixed into the argon gas atmosphere. This results in a carbon film coating on the surface, which is expected to improve the compatibility of the resulting fired shell microparticles with resin and extend the life of the antibacterial material.

[0046] (5) Next, arc discharge 16 (in other words, thermal plasma) is generated. As shown in FIG. 2, six metal electrodes 4 that generate arc discharge 16 are radially arranged at 60° intervals on the circumferential wall of reaction chamber 1 with their tips protruding laterally into reaction chamber 1 (for example, electrodes 4 are at an angle of 30° vertically upward from the horizontal). The number of electrodes is not limited to six, but may be eight or twelve. Furthermore, the number of electrodes is not limited to one as shown in FIG. 2, but may be two.

[0047] Adjacent electrodes of these electrodes 4 are applied with phase-shifted AC power from AC power supply 5. As an example, 60 Hz AC power with a phase shift of 60° is applied to each of the six electrodes 4 from AC power supply 5, generating a vertically elongated arc discharge 16 that is thermal plasma at approximately 10,000°C.

[0048] When arc discharge 16 is to be ignited after the AC power is applied, any two electrodes 4 are moved toward the center of reaction chamber 1 by electrode driving device 8. After arc discharge 16 is ignited, the current applied to each electrode 4 is adjusted to be constant, and each electrode 4 is moved by electrode driving device 8 in a radial direction (a direction from the center of the circle formed by the tips of each radially arranged electrode 4 toward the outside) to position each electrode 4 at the desired position.

[0049] (6) Next, the supply of the material to be processed is initiated. As an example, the material particles 17 used as the raw material for the microparticles 18 are crushed scallop shell powder with a particle diameter of approximately 5.4 micrometers, which is placed in the material supply device 10. The average particle diameter of the material was determined by measuring the particle diameter distribution using a laser diffraction / scattering method, and the median diameter was used as the average particle diameter. In the first example, particles with a particle diameter of 5.4 micrometers were used. However, although this depends on the thermal plasma conditions, particles with a particle diameter of 100 micrometers or less can be vaporized in the thermal plasma 16 to produce nanometer-order microparticles 18. If a material with a particle diameter larger than 100 micrometers is used, the material cannot be completely vaporized, and the generated microparticles may become large, on the order of micrometers.

[0050] In this example, scallop shell powder was used as the shell powder, but the present invention is not limited to this, and shell powders containing calcium carbonate as the main component, such as oyster, clam, surf clam, etc., may also be used. In addition to shell powder, egg shells and snail shells, which are also mainly composed of calcium carbonate, can also be used.

[0051] A fixed-volume powder feeder was used as an example of the material supply device 10. This fixed-volume powder feeder controls the supply amount by supplying a fixed amount of powder material to a groove such as a hopper and sucking it in with the carrier gas according to the flow rate of the carrier gas and the rotation speed of the container into which the material is introduced, and can send the powder material to the material supply pipe 11 at a constant rate.

[0052] In the first embodiment, a fixed-volume powder feeder was used as the material supply device 10. However, it is also possible to stir the raw material, crushed shell powder, into water and use a liquid pump to supply the crushed shell powder dispersed in the liquid to the thermal plasma 16. In this case, the material supply port 12 is changed to a one-fluid nozzle or a two-fluid nozzle. By using crushed shell powder dispersed in water, the water and shells are simultaneously evaporated by the thermal plasma, and a calcined shell microparticle powder mainly composed of calcium hydroxide can be obtained in the gas phase. Depending on the antibacterial application, it is possible to select either calcium oxide or calcium hydroxide-based calcined shell microparticle powder.

[0053] In this case, water is used as a transport medium for the raw materials and as a reactant for calcium hydroxide, but since the water evaporates the moment it is supplied to the thermal plasma, the reaction occurs in a gas phase with few impurities.

[0054] Furthermore, by using water, additional processes such as drying or waste liquid disposal are not required, so resin kneading can be done at low cost, just like when gas is used.

[0055] (7) As shown in FIG. 2, material particles 17 are sent from a material supply device 10 to a material supply pipe 11 and introduced into the reaction chamber 1 through a material supply port 12 .

[0056] (8) When the material particles 17 introduced into the reaction chamber 1 pass through the arc discharge 16, they are evaporated and vaporized, and the material particles 17 are gasified.

[0057] (9) Finally, as shown in Fig. 2, the fine particles 18 generated by the arc discharge 16 are carried to the fine particle collection section 3 by the gas flow from the discharge gas supply pipe 14, the updraft caused by the arc discharge 16, or the flow caused by the exhaust gas. Although not shown, the fine particle collection section 3 is equipped with a bag filter capable of collecting fine particle powder within a desired particle size range.

[0058] By using the above-described process, it is possible to recover from the bag filter a powder of baked shell fine particles having a particle size of, for example, 5 nanometers or more and 300 nanometers or less.

[0059] Figure 3 shows a scanning electron microscope (SEM) image of microparticles produced from crushed scallop shell powder using the method for producing a microparticle powder containing calcium oxide or calcium hydroxide according to the first embodiment. While the average particle diameter of the raw material crushed shell powder was 5.4 micrometers, it can be seen that most of the produced particles were nanoparticles with diameters of 100 nanometers or less. Furthermore, the microparticles constituting the obtained microparticle powder were spherical particles with a smooth surface, and no cracks, angular shapes, or irregular shapes typical of mechanically crushed particles were observed. Due to this smooth surface shape, it can be assumed that the obtained microparticle powder has higher dispersibility during the resin kneading process than mechanically crushed particle powder. The specific surface area of ​​this sample, analyzed using the BET method by gas adsorption with nitrogen gas, was 23.7 m. 2 / g. The average particle size of the primary particles calculated from this specific surface area was approximately 76 nanometers, and it was confirmed that there was no significant difference with the number-average particle size calculated from the SEM image shown in Figure 3. Furthermore, when the specific surface area was measured by changing the conditions of the thermal plasma treatment, the specific surface area was found to be 55.7 m under some conditions. 2 / g, and the calculated average particle size of the primary particles was reduced to approximately 32 nanometers.

[0060] <Fine particle powder containing calcium oxide or calcium hydroxide> The primary particles of the fine particles containing calcium oxide or calcium hydroxide according to the first embodiment are 5 nanometers or more and 300 nanometers or less, and the specific surface area of ​​the entire powder is 18 m 2 This means that the average particle size of the primary particles is 100 nanometers or less, and this size allows the transparency to be maintained even when mixed with a transparent resin.

[0061] Figure 4 shows the X-ray diffraction spectra of the materials used in the method for producing a fine particle powder containing calcium oxide or calcium hydroxide according to the first embodiment, and of particles produced using thermal plasma. The X-ray diffraction spectrum of the raw material, crushed shell powder, showed a large peak at a diffraction angle 2θ of 29.6°. Investigation of the other peaks revealed that the crushed shell powder had a calcite structure, a stable structure of calcium carbonate. The X-ray diffraction spectrum of the nanoparticles produced was completely different, with the main component being calcium oxide, with a peak at 2θ of 37.6°. A slight broad calcium hydroxide peak was also observed near 2θ of 34.4°. We speculate that this is due to the calcium oxide's small particle size and high surface activity, which led to its reaction with atmospheric moisture during sample recovery, resulting in calcium hydroxide.

[0062] These results show that nano-order calcined shell fine particle powder (mainly calcium oxide) can be produced from crushed shell powder (calcium carbonate) using thermal plasma.

[0063] The results of the antibacterial test of the nano-order baked shell microparticles produced by the method for producing a microparticle powder of the first embodiment are shown in Table 1 of FIG. 5. The antibacterial test of the nano-order baked shell microparticles produced was carried out as follows. Escherichia coli was suspended in 0.85% physiological saline and about 10 9 A bacterial suspension of 0.5 mg / mL was prepared. 200 mL of sterilized pure water was placed in a beaker, and 0.5 mg / mL of the baked shell microparticle powder was added while stirring. After the pH stabilized, the bacterial suspension was added, and samples were taken at 0, 20, 60, and 180 seconds, and the number of viable bacteria per mL was measured after one day of incubation. The results of the antibacterial test showed that the pH was 12.1, which was very alkaline, and the number of viable bacteria was 1.3 x 10 180 seconds after the addition of the bacterial suspension. 2cfu / mL. This confirmed that the calcined shell microparticles produced from shells using thermal plasma have a very strong bactericidal effect in a short time. In addition, calcined shell particle powder of a few micrometers in size, which has almost the same antibacterial activity as the calcined shell microparticles produced this time, was used to carry out an antibacterial test by mixing it with a polypropylene-based resin at a concentration of 3 wt%. As a result, the number of live bacteria after 6 hours was measured at a detection limit of 1.6 x 10 0 cfu / mL or less, and a high antibacterial effect was confirmed even when the baked shell microparticle powder was kneaded into resin.

[0064] Therefore, the desired antibacterial effect can be obtained from resin compositions and resin moldings containing the fired shell microparticle powder produced by thermal plasma. Furthermore, when kneaded into resin, sufficient antibacterial effect can be obtained by mixing in 3 wt% or less. In particular, even when mixed into transparent resin, it is possible to maintain transparency by mixing in 3 wt% or less.

[0065] In this case, the resin used was a mixture of polypropylene-based resin and fired shell microparticle powder, but any resin based on polyethylene, polystyrene, acrylic, methacrylic, polyethylene terephthalate (PET), polycarbonate, etc. would also be acceptable.

[0066] (First Example) In the first example, multiphase AC arc plasma was used as the thermal plasma. Calcium oxide, the main component of the resulting fine shell powder, has a high melting point of 2613°C and a high boiling point of 2850°C. Therefore, multiphase AC arc plasma, which has a relatively high plasma temperature and a wide high-temperature range among thermal plasmas, was adopted to improve productivity and reduce production costs. Furthermore, since the raw material used is crushed shell powder, which is industrial waste, the powder can contain many impurities and the raw material composition can vary greatly. Even in such cases, the use of multiphase AC arc plasma is advantageous because it is easy to maintain the discharge of the thermal plasma and is resistant to disturbances caused by gases and impurities.

[0067] Although multiphase AC arc plasma was used in this study, DC arc discharge, high-frequency inductively coupled plasma (ICP), etc. may also be used as thermal plasma. When DC arc discharge is used, thermal plasma can be generated using simpler equipment, which may further reduce production costs. Furthermore, when high-frequency inductively coupled plasma is used, the discharge part is covered with a quartz tube, which may enable the production of high-quality fine particles with fewer impurities than multiphase AC arc plasma.

[0068] In the method for producing a fine particle powder containing calcium oxide or calcium hydroxide according to Example 1, the use of thermal plasma treatment allows high-temperature firing at temperatures above 1000°C to be completed in a short time, while simultaneously achieving fine particle size of 100 nanometers or less. Furthermore, because evaporation and chemical reactions occur in the gas phase, impurity contamination is minimized, resulting in high material properties, such as a high antibacterial effect. Another major advantage is the ability to design various materials, such as oxidation, reduction, nitridation, carbonization, and surface coating, depending on the type of gas. Furthermore, the nanoparticle powder can be produced using a dry process that does not require solutions, eliminating the need for lengthy processes such as drying when embedding in resin. Furthermore, excess organic components (impurities) adhering to the shells are volatilized by the thermal plasma treatment, simplifying the pre-cleaning of the crushed shell powder.

[0069] Furthermore, by using highly effective particles of 100 nanometers or less as an antibacterial agent for resin filling, it is possible to achieve the same level of antibacterial effect with a smaller amount than conventional antibacterial materials. Therefore, even when the antibacterial material is added to transparent sheets or films, transparency can be maintained, making it possible to add antibacterial effects to transparent splash-proof resin sheets, food packaging materials, transparent protective films for touch panels, etc., which are currently in high demand.

[0070] It should be noted that any of the various embodiments or modifications described above can be appropriately combined to achieve the effects of each. In addition, combinations of embodiments, combinations of examples, or combinations of embodiments and examples are possible, and combinations of features from different embodiments or examples are also possible. [Industrial Applicability]

[0071] According to the method for producing a fine particle powder containing calcium oxide or calcium hydroxide of the present invention, it is possible to produce a high-quality fine particle powder containing calcium oxide or calcium hydroxide without using a solution or through a complicated dry process. Furthermore, it is possible to produce a fine particle powder containing calcium oxide or calcium hydroxide having a high antibacterial effect at low cost. Therefore, the fine particle powder containing calcium oxide or calcium hydroxide obtained by the method for producing a fine particle powder containing calcium oxide or calcium hydroxide of the present invention is useful as an antibacterial material that is kneaded into resins such as transparent resin sheets and films to impart antibacterial effects while maintaining transparency. [Explanation of symbols]

[0072] 1. Reaction chamber 2. Heat insulating materials 3. Particle collection section 4 electrodes 5, 5-1~5-6 AC power supply 6 Pressure Regulating Valve 7. Exhaust pump 8 Electrode drive unit 10 Material feeding device 11 Material supply pipe 12 Material supply port 14 Discharge gas supply pipe 15 Cooling gas supply pipe 16 Arc discharge (thermal plasma) 17 Material particles 18 Fine particles 20 Fine particle production equipment 101 Wet grinding equipment 102 Slurry tank (circulation tank) 103 Circulation Pump 104 Mixer 105 Slurry inlet 106 Slurry outlet 107 Crushing Chamber 108 Mixing section 109 Gap Separator

Claims

1. Providing a crushed shell or eggshell powder; introducing the crushed shell or eggshell powder into a controlled atmosphere, evaporating it under thermal plasma, and then solidifying it in the gas phase to produce fine particles comprising calcium oxide or calcium hydroxide; a step of recovering a powder of fine particles containing calcium oxide or calcium hydroxide treated with the thermal plasma; A method for producing a fine particle powder containing calcium oxide or calcium hydroxide, comprising:

2. 2. The method for producing a fine particle powder containing calcium oxide or calcium hydroxide according to claim 1, wherein the controlled atmosphere contains argon gas and further contains at least one gas selected from the group consisting of oxygen gas, hydrogen gas, and water vapor.

3. 2. The method for producing a fine particle powder containing calcium oxide or calcium hydroxide according to claim 1, wherein water is used when introducing the crushed shell or eggshell powder into the controlled atmosphere.

4. A step of preparing a fine particle powder obtained by the method for producing a fine particle powder according to claim 1; a step of kneading the fine particle powder into a resin to form a resin composition; A method for producing a resin composition, comprising:

5. A step of preparing a resin composition obtained by the method for producing a resin composition according to claim 4; a step of molding the resin composition into a molded article; A method for producing a resin molded article, comprising:

6. A step of preparing a fine particle powder obtained by the method for producing a fine particle powder according to claim 1; a step of kneading the fine particle powder into a transparent resin to obtain a transparent resin composition; a step of forming the transparent resin composition into a sheet-like molded product; A method for producing a transparent resin sheet-shaped molded product, comprising:

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