Method for coating fine particles

Abstract

This invention provides a method for mass-producing composite particles by coating submicron-sized core particles, while also allowing control over the thickness of the coating layer. [Solution] A method for coating fine particles comprising step A, in which a solution of core particles and a coating component is mixed to bond the coating component to the surface of the core particles, and step B, in which composite particles with the coating component bonded to the surface of the core particles are obtained as a dried powder, wherein step A is performed in a wet pulverizer and step B is performed in a slurry dryer.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for coating fine particles, and particularly relates to a method for coating fine particles having a size of submicron or less. BACKGROUND ART

[0002] Composite particles prepared by coating primary particles of submicron size or less are expected to be used as new materials for battery materials, optical materials, magnetic materials, electrochemical catalyst materials, semiconductor materials, pharmaceuticals, and the like. In addition, among these materials, even composite particles formed of the same combination of materials exhibit different behaviors and functions when the particle diameter thereof is submicron or less, so that new application values can be expected.

[0003] Accordingly, coating techniques for such fine particles have been studied. For example, Patent Document 1 proposes a method of forming a film made of a perovskite-type composite oxide on the surface of fine particles. According to this method, a film made of a perovskite-type composite oxide can be formed on the surface of core particles having a particle diameter of 1000 nm or less.

[0004] The method disclosed in Patent Document 1 comprises: a step of mixing a composite oxide precursor alkoxide containing two or more metal elements with a core material, and forming, in the mixture, a core material-composite oxide alkoxide in which the composite oxide alkoxide is bonded to the surface of the core material (hereinafter referred to as "bonding step"); a step of adding water to the core material-composite oxide alkoxide to cause hydrolytic polycondensation of the composite oxide alkoxide, thereby forming a core material-composite oxide alkoxide polycondensate (hereinafter referred to as "polycondensation step"); and a step of calcining the core material-composite oxide alkoxide polycondensate (hereinafter referred to as "calcination step"). PRIOR ART DOCUMENTS PATENT DOCUMENTS

[0005] Patent Document 1 Japanese Patent Publication No. 2015-51913 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, the method for preparing composite particles disclosed in Patent Document 1 above was not a technology that could be developed for mass production, and was limited to laboratory-level preparation.

[0007] In other words, both the "bonding process" and the "polycondensation process" described above require that each core particle be dispersed, and therefore are carried out at an extremely low core particle concentration over a long period of time. Moreover, the equipment used in these processes consists of an Erlenmeyer flask and a magnetic stirrer. Furthermore, in order for the complex oxide alkoxides bonded to the surface of the core particles to undergo efficient hydrolysis and polycondensation in the "bonding process," it was necessary to remove the core particle-complex oxide alkoxide from the anhydrous solvent by centrifugation before proceeding to the "polycondensation process," and then place it in a fresh anhydrous solvent to remove any free complex oxide precursor alkoxides that were not bonded to the surface of the core particles. In addition, the "calcination process," which involves calcining the core material-complex oxide alkoxide polycondensate obtained in the "polycondensation process," actually requires a drying process as a prerequisite. In this process, a rotary evaporator was used to extract the material as a dry powder, which was then crushed with a mortar and pestle before calcination. Thus, the multi-step method described in Patent Document 1 could only be implemented at the laboratory level, and the amount of complex particles obtained per unit time was extremely small.

[0008] Furthermore, in the method described in Patent Document 1, the amount of complex oxide alkoxide coated onto the core particles is basically determined by the amount of complex oxide alkoxide covalently bonded to the surface of the core particles in the "bonding step," and it was not possible to control the coating ratio. Although Patent Document 1 also discloses a method to increase the amount of complex oxide alkoxide bonded to the surface of the core particles by using a core particle-complex oxide alkoxide polycondensate that has undergone the above-mentioned "polycondensation step" instead of core particles, and performing the "bonding step" and "polycondensation step," in this case the process becomes even more complex, and in any case, the method described in Patent Document 1 was not capable of industrially mass-producing composite particles with coating components coated on the surface of core particles.

[0009] Furthermore, as a method for obtaining a dried powder of a core particle-composite oxide alkoxide polycondensate, there is also a method that uses spray drying instead of the evaporator disclosed in Patent Document 1. However, spray drying generally involves heating air to create a drying medium, and then dispersing and spraying a liquid or a mixture of liquid and solid into a drying tower, which is continuously supplied with the drying medium, using a two-fluid spray nozzle or a rotating disk, to evaporate the solvent and obtain a powder. Therefore, the particle size of the obtained powder is determined by the size of the sprayed droplets, and is generally 10 to 500 μm. There is also a lab-scale dryer called a nano-spray dryer, but the powder obtained is at least about 2 μm. Thus, even if the particle size of the core particles is 1 μm or less, the particle size of the composite particles obtained will be several times larger even when using a nano-spray dryer, and the composite particles cannot be obtained as primary particles (single particles), but only as secondary particles formed by the aggregation of multiple particles.

[0010] The present invention has been made in view of the problems of the background art described above, and its objective is to provide a method that enables mass production of composite particles by coating core particles of submicron size or smaller, allows control of the thickness of the coating layer, and enables the formation of composite particles with excellent properties. [Means for solving the problem]

[0011] To achieve the above-mentioned objectives, the present invention provides a coating method for fine particles as described in [1] to [6] below. [1] A method for coating fine particles, comprising step A of mixing core particles and a solution of coating components to bond the coating components to the surface of the core particles, and step B of obtaining composite particles with the coating components bonded to the surface of the core particles as a dried powder, characterized in that step A is performed in a wet pulverizer and step B is performed in a slurry dryer. [2] The method for coating fine particles according to [1] above, characterized in that the core particles are submicron-sized or smaller particles having hydrophilic groups on their surface. [3] The method for coating fine particles according to [2] above, characterized in that the solution of the coating component is a solution having a component that can react with or electrostatically adhere to the hydrophilic groups on the surface of the core particles. [4] A method for coating fine particles according to any one of [1] to [3] above, characterized in that the wet pulverizer is a wet media pulverizer that pulverizes a slurry-like material by applying a pulverizing force generated by a pulverizing medium that is forcibly moved by mechanical action, thereby pulverizing the processed product into particles of several millimeters to submicrons. [5] The method for coating fine particles according to [4] above, characterized in that the wet media pulverizer has an external circulation path. [6] The method for coating fine particles according to any one of [1] to [5] above, characterized in that the slurry dryer is a medium-type dryer that adheres a slurry-like treatment to the surface of a vibrating or fluidizing medium, evaporates the solvent to dry it, and recovers the fine particles contained in the slurry-like treatment as a dried powder by detaching them from the medium particles due to collisions between the mediums. [Effects of the Invention]

[0012] According to the method for coating fine particles according to the present invention described above, composite particles in which the surface of core particles of submicron size or smaller are coated with a coating component can be mass-produced, and the thickness of the coating layer can be controlled. Furthermore, the formed coating layer makes it possible to improve the properties of core particles having functionalities such as optical properties, catalytic properties, and battery properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] [Figure 1] FIG. 1 is a longitudinal sectional view showing an example of a wet medium fine pulverizer used in step A of the present invention. [Figure 2] FIG. 2 is a transverse cross-sectional view of the wet medium fine pulverizer shown in FIG. 1. [Figure 3] FIG. 3 is a front view conceptually showing an example of an external circulation type wet medium fine pulverizer used in step A of the present invention. [Figure 4] FIG. 4 is a front view conceptually showing an example of a medium fluidized dryer used in step B of the present invention, together with front and rear incidental devices. [Figure 5] FIG. 5 is a conceptual diagram for evaluating the homogeneity of a coating layer using XPS and XRF values. [Figure 6] FIG. 6 is an FE-SEM image of "Kitami Institute of Technology SiO₂" before treatment in Example A. [Figure 7] FIG. 7 is an FE-SEM image of "Kitami Institute of Technology SiO₂" ("RE") after treatment according to a conventional technique. [Figure 8] FIG. 8 is a TEM image of "T-2" after step A of the present invention for "Kitami Institute of Technology SiO₂". [Figure 9] FIG. 9 is a TEM image of "T-4-2" after step A and step B of the present invention for "Kitami Institute of Technology SiO₂". [Figure 10] FIG. 10 is a TEM image of "T-5-2" after step A and step B of the present invention for "Kitami Institute of Technology SiO₂". [Figure 11] FIG. 11 is a TEM image of "T-6-2" after step A and step B of the present invention for "commercially available SiO₂". [Figure 12]This is a TEM image of "T-7-2" obtained after step A and step B of the present invention for "commercially available SiO₂". [Figure 13] This figure is obtained by calculating the Ti detection ratio "Ti / (Ti+Si)" from the Ti and Si components quantitatively detected respectively from the XPS and XRF analysis results of the sample of each test number, and plotting the ratio with the vertical axis and the horizontal axis set respectively. [Figure 14] This figure is plotted, based on the XPS and XRF analysis results of the sample of each test number, with the core particle mass concentration taken on the horizontal axis and XPS / XRF taken on the vertical axis. [Figure 15] It is a conceptual exploded perspective view showing the structure of the cell used when verifying the cycle stability of the battery material in Example B. [Figure 16] This is an FE-SEM image of "NCM particles" before treatment in Example B. [Figure 17] This is an FE-SEM image of "T-10-2" obtained after step A and step B of the present invention for "NCM particles". [Figure 18] This is an FE-SEM image of "T-11-2" obtained after step A and step B of the present invention for "NCM particles". [Figure 19] This is an FE-SEM image of "T-12-2" obtained after step A and step B of the present invention for "NCM particles". [Figure 20] This is an FE-SEM image of "T-13-2" prepared only through step B of the present invention for "NCM particles". [Figure 21] This is a comparison diagram of XRF values of samples of each test number. [Figure 22] This figure shows a STEM-HAADF image of "T-11-2" after treatment according to the present invention, and the spectral analysis results of the coating film and the interior of the core particle. [Figure 23] This figure shows the charge-discharge characteristics of cells respectively prepared with samples of each test number, untreated "NCM particles", and "RE(B)" which is a product prepared by the prior art. [Figure 24] This figure shows the configuration of a three-electrode electrochemical measurement apparatus used for evaluating an oxygen evolution catalyst in Example C. [Figure 25]This is a conceptual diagram illustrating the evaluation and performance enhancement of oxygen evolution catalysts. [Figure 26] This is an SEM image of the "NiO particles" before treatment in Example C. [Figure 27] This is an SEM image of "T-14-2" after steps A and B of the present invention for "NiO particles". [Figure 28] This is an SEM image of "T-15-2" after steps A and B of the present invention for "NiO particles". [Figure 29] These are SEM images of "T-16-2" after steps A and B of the present invention for "NiO particles". [Figure 30] This figure shows a STEM-HAADF image of "T-14-2" after processing according to the present invention, as well as the spectral analysis results of the coating film and the inside of the core particle. [Figure 31] This figure shows a STEM-HAADF image of "T-15-2" after processing according to the present invention, as well as the spectral analysis results of the coating film and the inside of the core particle. [Figure 32] This figure shows a STEM-HAADF image of "T-16-2" after processing according to the present invention, as well as the spectral analysis results of the coating film and the inside of the core particle. [Figure 33] This figure shows the evaluation results of the oxygen evolution activity of untreated "NiO particles" and "T-15-2," the treated product of the present invention. [Figure 34] This figure shows the cycle characteristics of current density when the applied voltage to the electrodes of untreated "NiO particles" (without coating) and "T-15-2" (proposed technical material), which is the treated product of the present invention, is 1.75V. [Figure 35] This is an SEM image of the "Fe3O4 particles" before treatment in Example D. [Figure 36] These are SEM images of "T-24-2" after steps A and B of the present invention for "Fe3O4 particles". [Figure 37] This is an SEM image of "T-26-2" after steps A and B of the present invention for "Fe3O4 particles". [Figure 38]This is an SEM image of "T-27-2" after steps A and B of the present invention for "Fe3O4 particles". [Figure 39] This figure shows a STEM-HAADF image of "T-24-2" after processing according to the present invention, as well as the spectral analysis results of the coating film and the inside of the core particle. [Figure 40] This figure shows a STEM-HAADF image of "T-26-2" after processing according to the present invention, as well as the spectral analysis results of the coating film and the inside of the core particle. [Figure 41] This figure shows a STEM-HAADF image of "T-27-2" after processing according to the present invention, as well as the spectral analysis results of the coating film and the inside of the core particle. [Figure 42] This is a conceptual diagram of the reflectance measurement device used to evaluate the performance of the optical material in Example E. [Figure 43] This is an SEM image of the "Ag particles" before treatment in Example E. [Figure 44] This is an SEM image of "T-32-2" after steps A and B of the present invention for "Ag particles". [Figure 45] This is an SEM image of "T-33-2" after steps A and B of the present invention for "Ag particles". [Figure 46] This is an SEM image of "T-34-2" after steps A and B of the present invention for "Ag particles". [Figure 47] This figure shows a STEM-HAADF image of "T-33-1," which is a product treated only in step A of the present invention, as well as the spectral analysis results of the coating film and the inside of the core particles. [Figure 48] This figure shows a STEM-HAADF image of "T-33-2" after processing according to the present invention, as well as the spectral analysis results of the coating film and the inside of the core particle. [Figure 49] This is a comparative chart showing the visible light absorption rates of "Ag particles" in the untreated sample for each test number. [Figure 50]The left figure shows the absorption rate in the visible light range of Ag-TiO2 prepared using a similar combination and previously published in a paper, while the right figure shows the absorption rate of "T-33-2" after treatment according to the present invention. [Modes for carrying out the invention]

[0014] The following describes in detail embodiments of the coating method for fine particles according to the present invention.

[0015] The present invention relates to a method for coating fine particles, comprising: step A, mixing core particles and a coating component solution to bond the coating component to the surface of the core particles; and step B, obtaining composite particles with the coating component bonded to the surface of the core particles as a dried powder, wherein step A is performed using a wet pulverizer and step B is performed using a slurry dryer.

[0016] The core particles to be processed in the present invention described above are fine particles having hydrophilic groups, such as hydroxyl groups and carboxyl groups, on their surface. For example, inorganic oxide particles, metal particles, polymer particles, carbon material particles, etc., of submicron size or smaller can be targeted. Specifically, examples include inorganic materials such as silicon dioxide, barium titanate, magnesium oxide, zinc oxide, titanium dioxide, zirconium oxide, iron oxide, aluminum oxide, nickel oxide, NCM, and metals (nickel, silver, etc.); organic materials such as polystyrene, polypropylene, polymethyl methacrylate, polytetrafluoroethylene, and polyacrylonitrile; and carbon materials such as hydrophilically treated carbon black, graphite, and carbon nanotubes. Furthermore, the core particles are preferably nanoscale particles. In the case of substantially spherical core particles, their particle size is preferably 50 nm to 1000 nm, more preferably 50 nm to 500 nm, and particularly preferably 50 nm to 100 nm. In the case of core particles of other shapes, their minimum diameter is preferably 50 nm or more, more preferably 100 nm or more. It is possible to process core particles with a maximum diameter of up to 10,000 nm. These core particles may be powders used as functional materials such as optical materials, catalytic materials, and battery materials, and are applicable even if they are amorphous particles with particle sizes ranging from submicrons to several tens of micrometers.

[0017] Furthermore, in the present invention, the coating component solution, i.e., the coating precursor solution, is a solution having a component that can react with or electrostatically adhere to the hydrophilic groups on the surface of the core particles. Examples include metal complex solutions having hydroxyl groups, metal alkoxide precursor solutions, and metal cation solutions. Specifically, examples include silicon alkoxide precursor solutions, titanium alkoxide precursor solutions, lithium silicate complex metal alkoxide precursor solutions, and barium titanate complex metal alkoxide precursor solutions. Furthermore, the composition of the precursor solution can be designed using combinations of multiple metal ions and alkoxides as appropriate to control the thickness and uniformity of the coating film.

[0018] In the present invention, first, step A, in which the core particles and the coating component solution are mixed to bond the coating component to the surface of the core particles, is performed using a wet pulverizer. Step A, using this wet pulverizer, involves preparing a mixture in which core particles are dispersed in a coating precursor solution, introducing this mixture into the container of the wet pulverizer, and using the pulverizing force of the wet pulverizer to forcibly bring the coating precursor solution into contact with the surface of the core particles in a dispersed state, thereby bonding the coating precursor to the surface of the core particles. Examples of bonding modes for the coating precursor to the surface of the core particles include covalent bonds, electrostatic bonds, hydrogen bonds, and van der Waals bonds. The coating precursor layer that is formed may be a continuous film or may be formed in a discontinuous distribution on the particle surface.

[0019] As the above-mentioned wet-type fine grinder, a wet-media fine grinder is preferably used, which grinds a slurry-like material by applying grinding force (shear stress, friction force, compressive force, impact force) generated by a grinding medium that is forcibly moved by mechanical action, thereby finely grinding the processed product to particles of several millimeters to submicrons. When step A is performed using this wet media pulverizer, the powerful pulverizing force of the pulverizing medium can be used as the dispersion force for core particles of submicron size or smaller. Even in high-concentration systems, the core particles can be dispersed in the mixture at the primary particle level, and the coating precursor can be efficiently brought into contact with and bonded to the surface of each dispersed core particle. Therefore, in step A, which uses the wet media pulverizer, a mixture with a coating precursor solution with a high core particle mass concentration can be used as the raw material, and the processing time is also short, making it possible to mass-produce treated products in which the coating component is bonded to the surface of the core particles. According to tests conducted by the inventors, it was confirmed that, even when using raw materials with a core particle mass concentration exceeding 10%, a processed product with a good coating component bonded to the surface of the core particles can be obtained in approximately 90 minutes using this wet media pulverizer in step A. Furthermore, it was confirmed that setting the molar ratio of core particles to coating component in step A is important for optimizing the homogeneity and film thickness of the coating, and that a molar ratio range of 0.005 to 0.5 is preferable. Moreover, it was confirmed that step A using this wet media pulverizer distributes the coating component to the surface of the core particles and functions as a pretreatment for efficient drying and film formation in the subsequent step B.

[0020] An example of the wet media pulverizer described above is the apparatus 100 shown in Figures 1 and 2, in which a supply port 2 for slurry-like processed material is provided at the bottom of a container 1, a rotating main shaft 3 is erected inside, a plurality of sub-shafts 4 are supported around the main shaft 3 at intervals, a plurality of ring-shaped members (pulverizing media) 5 are fitted onto the sub-shafts 4 with gaps between them, the ring-shaped members 5 are arranged to abut against the inner wall of the container 1, and an outlet 6 for slurry-like processed material is provided at the top. This apparatus 100 can be configured such that the outer circumference of the container 1 is covered with a jacket 7, and a supply port 8 and an outlet 9 for a heat transfer medium are provided on the jacket 7. An example of a wet media pulverizer with the above configuration is the Micros (batch type) manufactured by Nara Machine Works Co., Ltd.

[0021] The wet media pulverizer 100 described above has a motor that controls the rotational speed of the main shaft 3, and the pulverizing force applied to the processed material by the ring-shaped member 5 increases in proportion to the increase in rotational speed, and this large pulverizing force has the function of pulverizing the processed material to micron size. However, when the processed material is submicron-sized or smaller core particles (primary particles), which is the target of the present invention, the pulverizing force acts as a dispersion force on the processed material, preventing aggregation of core particles even at high concentrations, and allowing the surface of the core particles to come into efficient contact with the coating precursor solution, thereby bonding coating components to the surface of each individual core particle. Furthermore, the outer circumference of the container 1 has a jacket structure, and by supplying hot or cold water to heat or cool it, the processed material can be set to the optimal temperature for the coating reaction.

[0022] Furthermore, as a wet media pulverizer, an external circulation type of the wet media pulverizer described above can be used. As shown in Figure 3, this external circulation type wet media fine grinder 100 is a device in which a supply port 2 located at the bottom of the container 1 of the grinder 100 and an outlet port 6 located at the top of the container 1 are connected by an external circulation path 10, an external tank 11 is provided on the outlet side of the external circulation path 10, and a slurry-like material supply device 12 is provided on the supply port side of the external circulation path 10. In the external circulation type wet media pulverizer 100, the external tank 11 can be configured to include an agitator 13, and its outer circumference can be covered with a jacket 14, with a heat transfer medium supply port 15 and an outlet 16 provided in the jacket 14. An example of a wet media pulverizer with the above configuration is the Micros (external circulation type) manufactured by Nara Machine Works Co., Ltd.

[0023] According to the external circulation type wet media pulverizer 100 described above, first, only the coating precursor solution (or a mixed solution in which a small amount of core particles are dispersed in the coating precursor solution) is put into the external tank 11, the coating precursor solution is sent into the container 1 from the supply port 2 by the supply device 12, and an external circulation circuit is formed by discharging it from the discharge port 6 and returning it to the external tank 11, after which the main shaft 1 is rotated, and then core particles are added to the external tank 11, thereby further suppressing the aggregation of core particles and allowing coating components to bond to the surface of individual core particles. In addition, since core particles do not stagnate at the bottom of the pulverizer container 1, homogeneous composite particles can be prepared. Furthermore, by adding and supplying precursor solutions or dilution solutions containing coating components to the external tank 11, it becomes possible to perform layered coating and composite processing of coating components, which was difficult with batch type systems. Moreover, by making the external tank 11 a jacket structure in addition to the outer circumference of the pulverizer container 1 and heating it by supplying hot water, it is possible to promote the chemical reaction of the processed product and promote the nucleation (precipitation) of precursor components in the mixed solution by evaporating the solvent and concentrating the processed product. Furthermore, since the processed product can be directly transferred and supplied from the external tank 11 during processing to the next process (process B, in which composite particles with coating components bonded to the surface of core particles are obtained as a dried powder), the re-aggregation of core particles is prevented, and composite particles in which the coating components are coated while maintaining a high dispersion state and the core particles remain in a primary particle state are more easily obtained. In addition, by providing the external tank 11, the processing volume per batch can be significantly increased compared to the processing volume of the batch method.

[0024] In addition to the wet media pulverizers described above (micros (batch type) and (external circulation type) manufactured by Nara Machine Works Co., Ltd.), the process may also be carried out using wet media pulverizers such as a planetary ball mill, which imparts stronger pulverizing energy to the processed material than a normal ball mill by rotating and revolving a container containing hard balls and the processed material, or a bead mill, which pulverizes the processed material using beads that are subjected to strong centrifugal force generated by rotating a stirring mechanism such as a disc at high speed, to mix the core particles and the coating component solution and bond the coating component to the surface of the core particles.

[0025] In the present invention, following step A using the wet pulverizer described above, step B is performed using a slurry dryer to obtain composite particles in which a coating component is bonded to the surface of core particles as a dried powder. Step B, which uses this slurry dryer, involves supplying the mixed liquid processed in Step A to the slurry dryer and evaporating the solvent using the drying function of the slurry dryer (direct heating by hot air, indirect heating by conduction from the container wall, a combination thereof, as well as radiant heat such as infrared rays, direct heating of the solvent by high frequency or microwaves, etc.) to obtain composite particles in which the coating component is bonded to the surface of the core particles as a dried powder. This dried powder may be any of the following: composite particles in which the coating component is homogeneously coated on the surface of the core particles in the primary particle state, composite particles in which the coating component is heterogeneously coated on the surface of the core particles in the primary particle state, or composite particles in which the coating component is coated on the surface of each core particle in the secondary particle (aggregate of primary particles) state.

[0026] Preferably, the slurry dryer used is a media-type dryer that adheres the slurry-like material to the surface of a vibrating or fluidizing medium, evaporates the solvent to dry it, and recovers the fine particles contained in the slurry-like material as a dried powder by separating them from the medium particles through collisions between the media. When step B is performed using this media-type dryer, the mixed liquid processed in step A (which includes composite particles with coating components bonded to the surface of core particles and coating components that did not bond to the surface of core particles) is supplied to the media-type dryer. The mixed liquid is dried while adhering to the surface of the vibrating or fluidized media particles. Furthermore, the uniformly nucleated coating components that did not bond to the surface of the core particles in step A (which precipitated due to solvent volatilization during drying) are bonded to the composite particles with coating components bonded to the surface of core particles. After this, the composite particles are detached from the media particles by repeated collisions with each other, and finely granulated composite particles can be obtained as a dried powder that is close to primary particles. In other words, step B can include not only a simple drying step, but also a precipitation step and a crushing step. According to tests conducted by the inventors, the solid content concentration of the core particles in step B using this media-type dryer and step A using the wet media pulverizer described above can be set in each step. However, in order to improve the homogeneity of the coating, it is preferable to set the solid content concentration in step B to be less than or equal to the solid content concentration in step A. In this case, it was confirmed that a solid content concentration of 0.5 to 25% for the core particles in step B is preferable. Furthermore, even if step A is omitted, it is possible to obtain a dried powder with a coating layer using only step B with this media-type dryer, but it was confirmed that the uniformity and film thickness of the coating layer will decrease.

[0027] Specifically, an example of the above-mentioned media-type dryer is the media slurry dryer, a fluidized media dryer manufactured by Nara Machinery Works Co., Ltd. This media slurry dryer, along with its preceding and succeeding equipment, is shown in Figure 4. In Figure 4, 200 is a media slurry dryer, and its interior is divided into a hot air chamber 52 below a perforated dispersion plate 51 and a fluidization chamber 53 above it. An inlet 55 for introducing air heated by an air heater 54 is connected to the hot air chamber 52, and an outlet 56 for discharging the dried powder after processing is provided above the fluidization chamber 53, and a powder separation device such as a cyclone 57 and / or a bag collector 58 is connected to the outlet 56 via piping. 59 are numerous media particles contained in the fluidization chamber 53 on the dispersion plate 51 and made into a fluid state by blowing hot air upwards. 60 is a supply nozzle for liquid substance inserted into the fluidization chamber 53, and the liquid substance to be dried is continuously supplied to the layer of fluidized media particles 59 through the supply nozzle 60. Note that 61 is a supply tank for the mixed liquid, and 62 is a stirrer.

[0028] According to the media slurry dryer 200 described above, when a mixed liquid containing the coating fine particles obtained in step A is supplied to the fluidization chamber 53 via the supply nozzle 60, the mixed liquid is uniformly dispersed and adheres to the surface of the individual fluidized media particles 59 in a film-like state, and the solvent evaporates uniformly on the media surface as the entire coating film is uniformly exposed to hot air. The evaporation of the solvent uniformly nucleates the coating components, which are uniformly fixed to the surface of the core particles. Then, due to contact, collision and friction between the media particles 59, the coating fine particles are detached from the surface of the media particles 59, broken down and dispersed to a size close to that of the core particles (primary particles), and discharged outside the machine from the outlet 56 accompanied by the hot air, and recovered by the cyclone 57 and bag collector 58.

[0029] The media-type dryer used for step B is not limited to the above-mentioned fluidized media dryer (media slurry dryer manufactured by Nara Machine Works Co., Ltd.), but any known media-type dryer capable of performing a similar function can be widely used to carry out step B, which yields composite particles in which a coating component is bonded to the surface of the core particles as a dried powder.

[0030] The inventors focused on the fact that X-ray photoelectron spectroscopy (XPS) allows for quantitative analysis of the surface of a sample (a few nanometers in the surface layer), while X-ray fluorescence analysis (XRF) allows for quantitative analysis of entire particles on the micrometer order. They believed that by integrating the quantitative analysis results from these different regions, the homogeneity of the coating layer could be comprehensively discussed. Therefore, they performed two types of quantitative analysis, XPS and XRF, to evaluate the coating state of the coating material on the core material.

[0031] Figure 5 is a conceptual diagram for evaluating the homogeneity of the coating layer. If the homogeneity of the coating layer is constant, the amount of coating measured by XPS is expected to increase linearly as the amount of coating increases, as seen from the quantitative analysis results by X-ray fluorescence. If the core particles are completely coated, the quantitative analysis results of the coating components by XPS are expected to be constant. Conversely to this linear correlation, if the quantitative analysis results by XRF are low and the quantitative analysis results by XPS are high, it is thought that a highly homogeneous coating layer has been formed because the ratio of coating components on the surface is high despite the small amount of coating. Conversely, if the quantitative analysis results by XRF are high and the quantitative analysis results by XPS are low, it is suggested that the coating layer has an island-like structure. In addition, the XPS / XRF value indicates the homogeneity of the coating layer, and a higher value indicates higher homogeneity. Therefore, by using this method to evaluate all coated particles under different coating conditions, it is possible to distinguish between samples with high and low coating layer homogeneity.

[0032] Based on the findings described above, the inventors confirmed the coating film using electron microscope images and measured the XPS, XRF, and XPS / XRF values ​​of the sample. As a result, they confirmed that the composite particles prepared by the present invention have a much more homogeneous coating film than composite particles prepared using a laboratory-level rotary evaporator. Furthermore, they confirmed that the homogeneously formed coating film can improve the properties of the core particles, which have functional properties such as optical properties, catalytic properties, and battery properties. [Examples]

[0033] The present invention will be specifically described below with reference to examples. Example A is an example to confirm the feasibility and versatility of the coating method for fine particles of the present invention, while Examples B to E, described later, are examples in which the method of the present invention is applied to various materials with different properties. However, the present invention is not limited in any way to these embodiments.

[0034] -Example A- [Processed raw materials] -Core Particles- • SiO2 particles prepared by the sol-gel method at Kitami Institute of Technology, a national university corporation in Hokkaido. (D50 ≈ 378 nm; hereinafter referred to as "Kitami Institute of Technology SiO2"). • Seahostar S30 manufactured by Nippon Shokubai Co., Ltd. (D50 ≈ 259 nm, hereinafter referred to as "commercially available SiO2"). -Coating precursor solution- A mixture of titanium tetraisopropoxide ([(CH3)2CHO]4Ti, CAS RN 546-68-9) and the diluent 2-propanol ((CH3)2CHOH).

[0035] [Coating treatment] -A process- Step A, in which core particles and a coating precursor solution are mixed to bond the coating component to the surface of the core particles, was performed using Micros (MIC-0 and MIC-2 models) manufactured by Nara Machine Works Co., Ltd., with the configurations shown in Figures 1 and 2. • Specifications of Micros MIC-0 Maximum rotational speed: 2400 min⁻¹ -1 Motor power: 2.2kW inverter control Rated current value: 8.6A Vessel effective volume: 0.4 liters Vessel contact part material: SUS304 + zirconia ceramics (ZrO2) Grinding medium material: Zirconia ceramics (ZrO2) Specifications of Micros MIC-2 Maximum rotational speed: 1400 min⁻¹ -1 Motor power: 5.5kW inverter control Rated current: 22A Vessel effective volume: 1.4 liters Vessel contact part material: SUS404 + zirconia ceramics (ZrO2) Grinding medium material: Zirconia ceramics (ZrO2) • Processing steps (1) Pass the heat transfer fluid through the Micros jacket and preheat until the temperature inside the container stabilizes (approximately 1 hour). (2) The core particles and the coating precursor solution are weighed separately. (3) The core particles and precursor solution are each placed into the microvessel, and the main shaft is rotated to start the processing of step A. (4) After the processing time required for the coating agent to bond has elapsed, the rotation of the main shaft is stopped to terminate step A. (5) Measure the amount of coated particle slurry recovered in the prepared microvessel. (6) Dilution solvent is added to the recovered micros and diluted to the specified concentration to prepare the raw material for the subsequent B step.

[0036] Table 1 shows the processed products and processing conditions for process A, which was carried out using the Micros manufactured by Nara Machine Works Co., Ltd. as described above. [Table 1] As shown in Table 1, coated particles were prepared in step A using the Micros MIC-0 type and the Micros MIC-2 type, which has a larger vessel effective capacity. In addition, the presence or absence of the coating layer was confirmed using the Micros MIC-0 type by changing the Ti / Si mol ratio in "T-1" and "T-2". From "T-3-1" onward, coated particles were prepared using the Micros MIC-2 type, with the purpose of creating the raw material for step B, by changing the Ti / Si mol ratio and core particle mass concentration.

[0037] -B process- Step B, which involves obtaining composite particles in which a coating component is bonded to the surface of core particles as a dried powder, was performed using a media slurry dryer MSD-100 manufactured by Nara Machine Works Co., Ltd., with the configuration shown in Figure 4. Specifications of the Media Slurry Dryer MSD-100 Fluidization column diameter: φ108.3mm Medium: φ2mm zirconia beads (4.0kg batch) Sky tower speed: 5.5m / sec Heater: 10kW • Processing steps (1) Bring hot air (air) through the media slurry dryer and preheat it until the exhaust temperature stabilizes (approximately 1 hour). (2) The diluted raw material slurry that has gone through step A is put into the supply tank and stirred with a stirrer. (3) Switch the hot air from the media slurry dryer to nitrogen gas and confirm that the exhaust temperature stabilizes. (4) The raw material slurry is continuously supplied from the tank to the fluidization chamber of the media slurry dryer using a feeder. (5) Adjust the slurry supply flow rate from the feeder so that the exhaust temperature does not fall below a predetermined temperature. This is to prevent the moisture content of the recovered coating particles from becoming unstable due to excessive supply. (6) After processing the entire raw material slurry, the dried powder of the coated particles is recovered from the recovery tank.

[0038] Table 2 shows the processed products and processing conditions for process B, which was carried out using the media slurry dryer manufactured by Nara Machinery Works Co., Ltd. as described above. [Table 2] As shown in Table 2, the preparation obtained through step A was used as the raw material, and the coated particles were prepared in step B using a media slurry dryer. The raw material was diluted with 2-propanol for processing in order to confirm the effect of the core particle mass concentration. Dilution does not change the Ti / Si molar ratio, but it does change the molar concentration. The supply amount of the raw material was adjusted with the hot air temperature of the media slurry dryer as a guideline of 200°C and the exhaust temperature of 130°C or higher.

[0039] [Preparation of comparative samples] For comparison, coated particles were prepared on a laboratory scale. Using "Kitami Institute of Technology SiO2" as the processing material, a coating precursor solution was prepared in an Erlenmeyer flask using a magnetic stirrer. Step A involved mixing the core particles with the coating precursor solution (Ti / Si molar ratio: 0.02, core particle mass concentration: 3.82%) to bond the coating component to the surface of the core particles. Step B involved obtaining composite particles with the coating component bonded to the surface of the core particles as a dry powder. These steps were carried out using a rotary evaporator (REV202M manufactured by Yamato Scientific Co., Ltd.). The resulting dry powder was then manually crushed using a mortar and pestle to a state close to primary particles to prepare the comparative coated particles ("RE"). The operating conditions for steps A and B using this rotary evaporator are shown in Table 3. [Table 3]

[0040] [Evaluation of coatings] The presence and shape of the coating film on each prepared test sample were confirmed using electron microscope images, and the homogeneity of the coating was compared and evaluated using XPS, XRF, and XPS / XRF values.

[0041] -Electron microscope image- FE-SEM images of each test number sample were taken using a JSM-6701F manufactured by JEOL Ltd. TEM images of each test number sample were also taken using a JEM-F200 manufactured by JEOL Ltd. -XPS value measurement- X-ray photoelectron spectroscopy measurements were performed at room temperature using AI-Kα rays with a PHI 5000 Versa Probe manufactured by ULVAC-PHI. The sample was pressed onto a Sn sheet and then compressed into a tablet approximately 2 mm wide using a single-shot tablet press. During measurement, the device was operated with a power of 20 W, and the measurement spot size was 100 μm in diameter. From the quantitatively detected Ti and Si components in each of the obtained XPS analysis results, the detection ratio of Ti, "Ti / (Ti+Si)", was calculated and used as the XPS value. -XRF value measurement- The measurement was performed using a Bruker S8 TIGER. Approximately 400 mg of the prepared dry sample powder was uniaxially pressed at 15 MPa to form pellets approximately 1 cm in diameter and 2 mm thick, which were then set in a dedicated circular sample holder for measurement. The effective measurement area was approximately 8 mm in diameter. From the quantitatively detected Ti and Si components in each of the obtained XRF analysis results, the detection ratio of Ti, "Ti / (Ti+Si)", was calculated and used as the XRF value.

[0042] Figure 6 shows the FE-SEM image of "Kitami Institute of Technology SiO2" before treatment, and Figure 7 shows the FE-SEM image of "RE" after treatment. Figure 8 shows the TEM image of "T-2". Figures 9 and 10 show the TEM images of "T-4-2" and "T-5-2", respectively. Furthermore, Figures 11 and 12 show the TEM images of "T-6-2" and "T-7-2", respectively. In addition, the XPS and XRF measurements for each test number sample are listed in Table 4, and the XPS / XRF values ​​for each test number sample are also listed in Table 4. [Table 4]

[0043] -Regarding "RE" coated particles at lab scale- From the FE-SEM images in Figures 6 and 7, it can be seen that the particle surface shape of the core SiO2 particles ("Kitami Institute of Technology SiO2") differs before and after treatment, and a coating film with an uneven surface can be observed on the treated product. The XPS / XRF value of the prepared coated particles was 2.935, as shown in Table 4.

[0044] -Regarding the coating particles "T-1" and "T-2"- Figure 8 shows a TEM image of the prepared "T-2" sample, which revealed a coating film of several nanometers in size. Furthermore, the quantitative analysis results of XPS and XRP shown in Table 4 indicated that both the "T-1" and "T-2" preparations had a Ti component coating layer on the surface of the core particles.

[0045] -Regarding the coating particles "T-3-2", "T-4-2", "T-5-2", and "T-5-3"- A coating layer of Ti was present on the surface of the particles, and all of these coating layers showed higher homogeneity than "RE". From the TEM images of "T-4-2" and "T-5-2" in Figures 9 and 10, a coating layer of several nanometers can be observed in both cases, confirming the difference in particle surface shape. Furthermore, from Table 4, it can be seen that in process B, the XPS / XRF value tends to increase as the core particle mass concentration decreases.

[0046] -Regarding the coating particles "T-6-2" and "T-7-2" of "commercially available SiO2"- From the TEM images of "T-6-2" and "T-7-2" in Figures 11 and 12, a coating layer of several nanometers can be confirmed in both cases, and differences in the shape of the particle surface can also be seen. Furthermore, "T-6-2" has a thinner, more uniform Ti coating film thickness and a smoother surface shape. "T-7-2" has a thicker, but more uneven, coating film, and some lumpy film with a particle shape was also observed. This is because the Ti / Si mol ratio was increased in "T-7-2," which increased the amount of nucleation due to the precipitation of the Ti component. It was confirmed that increasing the Ti / Si mol ratio (concentration of the coating material) tends to result in a thicker coating film. Furthermore, when the Ti / Si molar ratio was increased to 0.4 in additional experiments, a large amount of solid material consisting only of Ti components that were not coated on the core particles was observed, which was not a desirable state for a dry powder.

[0047] -Regarding the homogeneity of the coating layer- Figure 13 shows a plot of the Ti detection ratio "Ti / (Ti+Si)" calculated from the quantitatively detected Ti and Si components from the XPS and XRF analysis results of each preparation, with these values ​​plotted on the vertical and horizontal axes, respectively. Figure 14 shows a plot of the core particle mass concentration on the horizontal axis and XPS / XRF on the vertical axis. As shown in Figure 13, and based on the trends explained in Figure 5, the immobilized and coated particles produced by the mass-production machine all exhibit higher homogeneity than the "RE" prepared samples. Furthermore, lower core particle mass concentrations are associated with higher homogeneity. Furthermore, the results for "T-1" and "T-2" show that the coating thickness is thin (less coating amount). In other words, the difference between the coating layers of process A and process B is clearly demonstrated. Figure 14 also shows that the lower the core particle mass concentration, the higher the homogeneity of the coating, and that the homogeneity is higher than that of the "RE" prepared sample.

[0048] Based on the above, it is possible to prepare coated particles by performing step A, in which core particles and a coating precursor solution are mixed and the coating component is bonded to the surface of the core particles, using a wet pulverizer, and then performing step B, in which the composite particles with the coating component bonded to the surface of the core particles are obtained as a dry powder, using a slurry dryer. These particles showed higher homogeneity than coated particles produced on a laboratory scale using a rotary evaporator.

[0049] Next, we will describe Example B, in which the coating method for fine particles of the present invention is applied to a battery material.

[0050] -Example B- [Processed raw materials] -Core Particles- • Positive electrode active material particles of lithium-ion secondary batteries containing Ni, Co, and Mn (D50 ≈ 10 μm, hereinafter referred to as "NCM particles"). These NCM particles were prepared by holding commercially available positive electrode active material powder at 300°C for 1 hour in an oxygen-purged atmosphere, followed by natural cooling. -Coating precursor solution- • A mixture of lithium silicate (Li4SiO4) solution and the diluent 2-methoxyethanol (C3H8O2).

[0051] [Coating treatment] -A process- Step A, which involves bonding the coating component to the surface of the core particles, was performed as a wet pulverization process similar to that in Example A. Specifically, the core particles, which are NCM particles, were mixed with the coating precursor solution and processed using a wet-type fine grinding machine, Micros MIC-2, manufactured by Nara Machine Works Co., Ltd. The specifications of the Micros MIC-2 device and the processing operations using the device are the same as those described in section

[0035] of Embodiment A above.

[0052] Table 5 shows the processed products and processing conditions for process A, which was carried out using the Micros MIC-2 model manufactured by Nara Machine Works Co., Ltd. as described above. [Table 5] As shown in Table 5, coated particles were prepared using the Micros MIC-2 type in step A. In all cases, the molar ratio and core particle mass concentration were changed to prepare the coated particles for the purpose of creating the raw materials for step B. For "T-13-1", the coating particles were prepared using only step B, without processing with Micros. The core particles and precursor solution were placed in a beaker in the same formulation amount as for "T-11-1", and while stirring with a propeller-type stirrer, the process proceeded to step B, which will be described later. "T-13-1" is a comparative processed product used to compare and verify the effect of the presence or absence of step A on the coating state and performance.

[0053] -B process- Step B, which involves obtaining composite particles in which a coating component is bonded to the surface of core particles as a dried powder, was carried out using a media slurry dryer MSD-100 manufactured by Nara Machine Works Co., Ltd., in the same manner as in Example A. The specifications of the media slurry dryer MSD-100 and the processing operation using the device are the same as those described in section

[0037] of the above embodiment A.

[0054] Table 6 shows the processed products and processing conditions for process B, which was carried out using the MSD-100 media slurry dryer manufactured by Nara Machinery Works Co., Ltd. as described above. [Table 6] As shown in Table 6, the preparation obtained through step A and "T-13-1," which is simply a stirred product, were used as raw materials, and coating particles were prepared in step B using a media slurry dryer MSD-100. The raw materials were diluted with 2-methoxyethanol for processing in order to confirm the effect of core particle mass concentration. Dilution does not change the molar ratio, but it does change the molar concentration. The supply amount of raw materials was adjusted with the hot air temperature of the media slurry dryer as a guideline of 200°C and the exhaust temperature of 130°C or higher.

[0055] [Comparison product] For comparison, uncoated NCM particles (the core particle raw material used in Example B) and coated particles prepared by the conventional rotary evaporator method using the coating precursor solution used in Example B were used. The coated particles obtained by this conventional method will be referred to as "RE(B)" below. The preparation conditions for this RE(B) product are shown in Table 7. [Table 7]

[0056] [Evaluation of coatings] For each test number, the presence or absence of a coating film, its thickness, and its homogeneity were evaluated. The evaluation was performed using electron microscopy observation, XPS analysis, XRF analysis, and calculation of XPS / XRF values. Furthermore, EDS mapping and spectral analysis were performed using a scanning transmission electron microscope (STEM) to confirm the elemental distribution of the coating layer. In addition, evaluation cells were fabricated using each prepared product, and the stability of the battery characteristics was evaluated by charge-discharge cycle testing at 4.55V. The structure of the evaluation cells was as shown in Figure 15.

[0057] -Electron microscope image- FE-SEM images of each test number sample were taken using a JEOL Ltd. JSM-6701F. In addition, STEM-HAADF images of each test number sample were taken using a JEOL Ltd. JEM-2100F, and film thickness was confirmed, and elemental mapping and quantitative analysis were performed using EDS. This allowed us to evaluate the presence or absence of a coating film, its thickness, and the distribution of the coating components. -XPS value measurement- To evaluate the amount of Si component near the surface, X-ray photoelectron spectroscopy (XPS) was performed. Measurements were performed using a PHI 5000 Versa Probe manufactured by ULVAC-PHI, employing Al-Kα radiation at room temperature. The sample was pressed onto a Sn sheet and then compressed into a tablet approximately 2 mm wide using a single-shot tablet press. The measurement conditions were an applied power of 20 W and a measurement spot diameter of 100 μm. From the obtained XPS analysis results, the detected Si component (Si / (Si+Ni+Co+Mn)) was used to calculate the Si detection ratio, and this was defined as the XPS value. Note that this XPS value generally reflects surface information from the particle surface down to about 10-20 nm. -XRF value measurement- To quantitatively evaluate the Si component contained in the entire preparation, X-ray fluorescence analysis (XRF) was performed. A Bruker S8 TIGER was used for the measurements. Approximately 400 mg of the prepared dry sample powder was uniaxially compressed at 15 MPa to create pellets with a diameter of approximately 1 cm and a thickness of approximately 2 mm. These pellets were then placed in a dedicated circular sample holder for measurement. The effective measurement area was approximately 8 mm in diameter. From the obtained analysis results, the detection ratio of Si, "Si / (Si+Ni+Co+Mn)", was calculated using the quantitative values ​​of Si, Ni, Co, and Mn components, and this was defined as the XRF value. This XRF value accurately reflects the average composition of the entire sample.

[0058] Figure 16 shows an FE-SEM image of the core particle raw material, "NCM particles," before processing. Figures 17 to 20 show FE-SEM images of "T-10-2," "T-11-2," and "T-12-2," which were prepared through steps A and B of the present invention, as well as "T-13-2," which was prepared using only step B without step A. Furthermore, Figure 21 shows a comparison of the XRF values ​​measured for each test number preparation, and Figure 22 shows the STEM-HAADF image and spectral analysis results of the coating layer and core particle interior of the "T-11-2" preparation. In addition, Figure 23 shows the charge-discharge characteristics of evaluation cells prepared using each preparation, untreated "NCM particles," and "RE(B)," a preparation made using conventional technology. Table 8 shows the XPS value, XRF value, and their ratio (XPS / XRF value) obtained for each test number of the prepared product. [Table 8]

[0059] -Evaluation of particle surface shape and coating state- From the FE-SEM images shown in Figures 16 to 20, it was confirmed that the preparations "T-10-2," "T-11-2," and "T-12-2," prepared by the method of the present invention through steps A and B, had reduced surface irregularities and a smoother surface shape compared to untreated "NCM particles." On the other hand, "T-13-2," prepared by step B only without step A, was clearly different from the other preparations and showed a surface shape close to that of untreated "NCM particles." This suggests that in step A, the mechanical energy applied by the wet pulverizer causes the finely pulverized coating component particles to adhere to and become fixed on the core particle surface, contributing to the formation of the coating layer.

[0060] -Quantitative determination of Si component and homogeneity of the coating layer- As shown in Figure 21 and Table 8, the results obtained through steps A and B of the present invention showed a tendency for the XRF value and XPS / XRF value to increase as the core particle mass concentration decreased and the molar ratio of the Si component was within an appropriate range. This indicates that processing in a slurry state with low particle concentration and high dispersibility results in a more uniform distribution of the Si component on the particle surface. On the other hand, "T-13-2," which did not undergo process A, showed the lowest XRF value, confirming that a homogeneous coating layer had not been formed.

[0061] -Confirmation of the coating film using STEM-HAADFSTEM imaging- STEM-HAADF images and EDS mapping results of the "T-11-2" preparation shown in Figure 22 revealed a layered structure in which the Si component is continuously distributed along the particle surface. The thickness of this coating layer was approximately 40-50 nm, and a clear Si spectral peak was observed. On the other hand, peaks of Ni, Co, and Mn were detected from within the core particles, confirming that the coating components are mainly located on the particle surface. From these results, it was confirmed that a clear Si-based coating layer was formed on the surface of the NCM particles.

[0062] -Charge / discharge characteristics using evaluation cells- As shown in Figure 23, the charge-discharge test results indicate that the "T-11-2" compound exhibited cycle stability equal to or better than that of the conventional compound "RE(B)". On the other hand, "T-10-2," which was prepared under conditions of high core particle concentration, and "T-13-2," which did not undergo process A, were found to have inferior characteristics. Furthermore, a decrease in volume was observed in the early stages of the cycle for "T-12-2," which has a low molar ratio of Si (0.01), and for untreated "NCM particles."

[0063] The results above demonstrate that by applying the method of the present invention to NCM particles with a particle size of approximately 10 μm, it is possible to obtain coated particles with performance equivalent to or better than those produced by conventional rotary evaporator-based laboratory-scale preparations. Furthermore, it was revealed that setting appropriate molar ratios of Si components and core particle concentrations, and combining steps A and B, is effective in forming a homogeneous coating layer and improving battery characteristics. This embodiment B demonstrates the applicability of the liquid-phase coating method to mass production of battery materials.

[0064] Next, Example C, in which the coating method for fine particles of the present invention is applied to a catalyst material, will be described.

[0065] -Example C- [Processed raw materials] -Core Particles- Nickel oxide (CAS RN 1313-99-1, nominal particle size: approximately 1 μm, hereinafter referred to as "NiO particles"). -Coating precursor solution- A mixture of cobalt acetate tetrahydrate (CAS RN 6147-53-1) and ethanol 99.5% reagent grade (CAS RN 64-17-5).

[0066] [Coating treatment] -A process- Step A, which involves bonding the coating component to the surface of the core particles, was performed as a wet pulverization process similar to that in Example A. Specifically, the core particles, which are NiO particles, were mixed with the coating precursor solution, and the mixture was processed using a wet-type fine grinding machine, Micros MIC-2, manufactured by Nara Machine Works Co., Ltd. The specifications of the Micros MIC-2 device and the processing operations using the device are the same as those described in section

[0035] of Embodiment A above.

[0067] Table 9 shows the processed products and processing conditions for process A, which was carried out using the Micros MIC-2 model manufactured by Nara Machine Works Co., Ltd. as described above. [Table 9] As shown in Table 9, coated particles were prepared using the Micros MIC-2 type in step A. The core particle mass concentration was kept constant at 9.6% for each test number, and the coated particles were prepared by changing the Co / Ni molar ratio.

[0068] -B process- The composite particle slurry obtained through step A was subjected to step B, in which the composite particles were dried into powder. Step B was carried out using a media slurry dryer MSD-100 manufactured by Nara Machine Works Co., Ltd., as in Example A. The specifications of the media slurry dryer MSD-100 and the processing operation using the device are the same as those described in section

[0037] of the above embodiment A.

[0069] Table 10 shows the processed products and processing conditions for process B, which was carried out using the MSD-100 media slurry dryer manufactured by Nara Machinery Works Co., Ltd. as described above. [Table 10] As shown in Table 10, the prepared product after step A was used as the raw material, and coating particles were prepared in step B using a media slurry dryer MSD-100. The amount of ethanol lost due to evaporation during step A was corrected by adding ethanol before step B, so that the core particle mass concentration was kept constant for each test number. For drying conditions, the supply amount of raw material slurry was adjusted to maintain the hot air temperature at 110°C and the exhaust temperature at 70°C or higher.

[0070] [Performance evaluation as an electrochemical catalyst] The preparation obtained in this Example C is an electrochemical catalyst in which a Co-based coating component is formed on the surface of NiO particles, with the aim of improving the oxygen-evolving catalytic function of nickel oxide. To evaluate this performance, working electrodes were prepared using each prepared product, and the oxygen evolution activity was evaluated using an electrochemical measuring device. The electrochemical measuring device used and the structure of the prepared working electrodes are shown in Figure 24.

[0071] In electrochemical measurements, a voltage was applied to a working electrode coated with a catalyst, and the resulting current density was measured. The catalytic performance of the preparation was evaluated by utilizing the characteristic that catalysts with higher oxygen evolution activity exhibit higher current density at the same voltage. In this embodiment, the current density is 10 mA / cm² at an operating voltage of 1.75 V. 3 The above criteria were used as practical indicators of oxygen-evolving activity. These evaluation criteria are shown in Figure 25.

[0072] [Evaluation of coatings] For each sample prepared for each test number, the presence, thickness, and distribution of the coating film were evaluated in the same manner as in the examples described above. The evaluation was performed by surface observation using an electron microscope (SEM), and elemental mapping and EDS spectral analysis using a scanning transmission electron microscope (STEM-HAADF). For SEM observation, we used the JSM-IT200 manufactured by JEOL Ltd., and for STEM-HAADF observation and EDS analysis, we used the JSM-2100F manufactured by JEOL Ltd.

[0073] Figure 26 shows an SEM image of the core particle raw material, "NiO particles," and Figures 27 to 29 show SEM images of "T-14-2," "T-15-2," and "T-16-2" prepared through steps A and B of the present invention. Furthermore, Figures 30 to 32 show the STEM-HAADF images and EDS spectral analysis results obtained for each preparation product, "T-14-2," "T-15-2," and "T-16-2."

[0074] - Observation results of particle surface morphology - As shown in the SEM images in Figures 26 to 29, the "T-14-2", "T-15-2", and "T-16-2" samples prepared by the method of the present invention all maintained an irregular shape containing submicron particles, similar to the raw material "NiO particles," and no significant particle breakage or excessive aggregation was observed. This confirms that the coating treatment of the present invention can form a coating layer without significantly impairing the morphology of the catalyst particles.

[0075] -Formation state of the coating film- From the STEM-HAADF images and EDS analysis results shown in Figures 30 to 32, a grayish-white dot-like distribution originating from the Co component was observed on the surface of the core particles of each preparation. Based on the thickness of the layer in which these dots are aggregated, the thickness of the coating film is estimated to be approximately 20 to 50 nm. Furthermore, in all three test numbers, spectral peaks of Co, which are not present inside the core particles, were detected from the particle surface. From these results, it was confirmed that a Co-based coating layer was formed on the surface of the NiO particles under each condition in which the Co / Ni molar ratio was changed.

[0076] -Evaluation of oxygen-evolving activity- Figure 33 shows the relationship between applied voltage and current density for electrodes using uncoated "NiO particles" and "T-15-2," a preparation of the present invention. Based on these results, the "T-15-2" formulation has a current density of 10 mA / cm². 3 The potential reached at this point was 1.72V, which was confirmed to be below 1.75V, a practical indicator of oxygen-evolving activity. On the other hand, the uncoated "NiO particles" did not reach the same current density under the same conditions. This indicates that the coating catalyst prepared by the method of the present invention exhibits significantly improved oxygen evolution activity.

[0077] -Cyclical characteristics of catalytic activity- Figure 34 shows the cycle characteristics of the current density when the applied voltage is fixed at 1.75V. These results show that "T-15-2," the preparation of the present invention, exhibits higher durability compared to uncoated "NiO particles," and maintains a current density of 10 mA / cm² even after more than 100 cycles. 3 It was confirmed that the above conditions could be maintained.

[0078] From the above results, it has been shown that the method of the present invention is also applicable to amorphous catalyst materials with a particle size of about 1 μm, and that by forming a Co-based coating layer on the surface of NiO particles, an electrochemical catalyst with excellent oxygen evolution activity and durability can be obtained. In other words, this embodiment C demonstrates the applicability of the liquid-phase coating method for mass production of catalyst materials.

[0079] Next, we will describe Example D, in which the coating method for fine particles of the present invention is applied to a magnetic material.

[0080] -Example D- [Processed raw materials] -Core Particles- Magnetite (CAS RN 1317-61-9, nominal particle size: approximately 1 μm, hereinafter referred to as "Fe3O4 particles"). -Coating precursor solution- A mixture of titanium tetraisopropoxide (CAS RN 546-68-9) and the diluent 2-methoxyethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.).

[0081] [Coating treatment] -A process- Step A, which involves bonding the coating component to the surface of the core particles, was performed as a wet pulverization process similar to that in Example A. Specifically, the core particles, which are Fe3O4 particles, were mixed with the coating precursor solution and processed using a wet-type fine grinding machine, Micros MIC-2, manufactured by Nara Machine Works Co., Ltd. The specifications of the Micros MIC-2 device and the processing operations using the device are the same as those described in section

[0035] of Embodiment A above.

[0082] Table 11 shows the processed products and processing conditions for process A, which was carried out using the Micros MIC-2 model manufactured by Nara Machine Works Co., Ltd. as described above. [Table 11] As shown in Table 11, coated particles were prepared using the Micros MIC-2 type in step A. The core particle mass concentration and Ti / Fe molar ratio were optimized in advance, and each coated particle was prepared under the processing conditions shown in Table 11.

[0083] -B process- Step B, which involves obtaining composite particles in which a coating component is bonded to the surface of core particles as a dried powder, was carried out using a media slurry dryer MSD-100 manufactured by Nara Machine Works Co., Ltd., in the same manner as in Example A above. The specifications of the media slurry dryer MSD-100 and the processing operation using the device are the same as those described in section

[0037] of the above embodiment A.

[0084] Table 12 shows the processed products and processing conditions for process B, which was carried out using the MSD-100 media slurry dryer manufactured by Nara Machinery Works Co., Ltd. as described above. [Table 12] As shown in Table 12, the prepared product from step A was used as the raw material, and coating particles were prepared in step B using a media slurry dryer MSD-100. The amount of 2-methoxyethanol lost due to evaporation in step A was added to the raw material and processed, and the molar ratio of Ti / Fe was kept constant for each test number. The hot air temperature of the media slurry dryer MSD-100 was set to 120°C and the exhaust temperature to 80°C or higher, and the amount of raw material supplied was adjusted accordingly.

[0085] [Evaluation of coatings] For each sample prepared for each test number, the presence, thickness, and distribution of the coating film were evaluated in the same manner as in the examples described above. The evaluation was performed by surface observation using an electron microscope (SEM), and elemental mapping and EDS spectral analysis using a scanning transmission electron microscope (STEM-HAADF). For SEM observation, we used the JSM-IT200 manufactured by JEOL Ltd., and for STEM-HAADF observation and EDS analysis, we used the JSM-2100F manufactured by JEOL Ltd.

[0086] Figure 35 shows an SEM image of the core particle raw material, "Fe3O4 particles," and Figures 36 to 38 show SEM images of "T-24-2," "T-26-2," and "T-27-2" after undergoing steps A and B of the present invention. Furthermore, Figure 39 shows the STEM-HAADF image and spectral analysis results for "T-24-2," Figure 40 shows the STEM-HAADF image and spectral analysis results for "T-26-2," and Figure 41 shows the STEM-HAADF image and spectral analysis results for "T-27-2." In addition, the STEM-HAADF image observations focused on particles of approximately 100-500 nm in size.

[0087] - Observation results of particle surface morphology - From the SEM images shown in Figures 35 to 38, it was confirmed that the particles in each sample of the preparation according to the present invention, "T-24-2," "T-26-2," and "T-27-2," were amorphous and contained submicron-sized particles. Furthermore, in the case of "T-26-2," processing was performed with the maximum rotation speed of the Micros MIC-2 type in step A, but no significant particle breakage was observed. Some areas of aggregation due to TiO2 precipitation were observed, but it was not a strong aggregation, indicating that the processing steps of the present invention contribute to the dispersion of particles.

[0088] -Formation state of the coating film- From the STEM-HAADF images and spectral analysis results shown in Figures 39 to 41, it was observed that grayish-white dots, indicating Ti, were clustered on the surface of core particles around 200-400 nm in size. Based on the thickness of the areas where these grayish-white dots were clustered in a band-like pattern, the thickness of the coating film could be estimated to be approximately 10-30 nm. Furthermore, in all three test numbers, a Ti spectral peak, which is not present inside the particles, was observed on the particle surface. This confirms that a TiO2 coating layer was formed on the core particle surface in each of the samples prepared in this study.

[0089] From the above results, it was confirmed that composite particles coated with TiO2 can be prepared using the method of the present invention, which involves non-spherical, amorphous magnetic core particles Fe3O4 ranging in size from approximately 1 μm to submicron size. In other words, the method of the present invention is also applicable to magnetic materials, demonstrating the possibility of mass production.

[0090] Next, Example E, in which the coating method for fine particles of the present invention is applied to an optical material, will be described.

[0091] -Example E- [Processed raw materials] -Core Particles- Silver particles (CAS RN 7440-22-4, nominal particle size: D50 = 100-300 nm, hereinafter referred to as "Ag particles"). -Coating precursor solution- A mixture of titanium tetraisopropoxide ([(CH3)2CHO]4Ti, CAS RN 546-68-9) and the diluent 2-methoxyethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.).

[0092] [Coating treatment] -A process- Step A, which involves bonding the coating component to the surface of the core particles, was performed as a wet pulverization process similar to that in Example A. Specifically, the core particles, which are Ag particles, were mixed with the coating precursor solution, and the mixture was processed using a wet-type fine grinding machine, Micros MIC-2, manufactured by Nara Machine Works Co., Ltd. The specifications of the Micros MIC-2 device and the processing operations using the device are the same as those described in section

[0035] of Embodiment A above.

[0093] Table 13 shows the processed products and processing conditions for process A, which was carried out using the Micros MIC-2 model manufactured by Nara Machine Works Co., Ltd. as described above. [Table 13] As shown in Table 13, the core particle mass concentration was kept constant, and the Ti / Ag molar ratio was changed, and coated particles were prepared using the Micros MIC-2 type in step A.

[0094] -B process- Step B, which involves obtaining composite particles in which a coating component is bonded to the surface of core particles as a dried powder, was carried out using a media slurry dryer MSD-100 manufactured by Nara Machine Works Co., Ltd., in the same manner as in Example A above. The specifications of the media slurry dryer MSD-100 and the processing operation using the device are the same as those described in section

[0037] of the above embodiment A.

[0095] Table 14 shows the processed products and processing conditions for process B, which was carried out using the MSD-100 media slurry dryer manufactured by Nara Machine Works Co., Ltd. as described above. [Table 14] As shown in Table 14, the amount of 2-methoxyethanol lost due to evaporation in step A was added to the raw material and processed to maintain a constant core particle mass concentration for each test number. The hot air temperature of the media slurry dryer MSD-100 was set to 90-70°C, and the exhaust temperature to 70-55°C or higher, and the amount of raw material supplied was adjusted accordingly.

[0096] [Evaluation of coatings] For each sample prepared for each test number, the presence, thickness, and distribution of the coating film were evaluated in the same manner as in the examples described above. The evaluation was performed by surface observation using an electron microscope (SEM), and elemental mapping and EDS spectral analysis using a scanning transmission electron microscope (STEM-HAADF). For SEM observation, we used the JSM-IT200 manufactured by JEOL Ltd., and for STEM-HAADF observation and EDS analysis, we used the JSM-2100F manufactured by JEOL Ltd. Furthermore, to evaluate the results using the obtained Ag-TiO2 composite particles, the electromagnetic wave absorption characteristics in the visible light range were measured using the UV-VIS-NIR reflectance analyzer shown in Figure 42, and compared with literature values.

[0097] As SEM images, Figure 43 shows the core particle raw material, "Ag particles," Figure 44 shows "T-32-2" after going through steps A and B, Figure 45 shows "T-33-2," and Figure 46 shows "T-34-2." Furthermore, Figure 47 shows the STEM-HAADF image and spectral analysis results for "T-33-1" after undergoing only step A, and Figure 48 shows the STEM-HAADF image and spectral analysis results for "T-33-2" after undergoing both steps A and B. In addition, the STEM-HAADF image observations focused on particles of approximately 100-500 nm in size. Furthermore, Figure 49 shows the visible light absorption rates of each prepared sample measured with the measuring device shown in Figure 42.

[0098] - Observation results of particle surface morphology - SEM images shown in Figures 43 to 46 confirm that the particles in each sample of the preparations "T-32-2," "T-33-2," and "T-34-2" according to the present invention were irregular in shape and submicron in size. Furthermore, no significant particle fracture was observed in any of the preparations. Although some aggregation due to TiO2 precipitation was observed, it was not a strong aggregation, and it was found that the processing with the wet pulverizer Micros MIC-2 and the slurry dryer Media Slurry Dryer MSD-100 contributed to the dispersion of the particles. Furthermore, due to the thinness of the coating film, it was difficult to clearly determine the formation of the coating film on the particle surface from the SEM images.

[0099] -Formation state of the coating film- From the STEM-HAADF images and mapping data shown in Figures 47 and 48, it was confirmed that grayish-white dots indicating Ti were aggregated on the surface of the core particles. In the "T-33-1" product, which underwent only step A, the thickness of the coating film was determined to be approximately 5-10 nm based on the grayish-white dots aggregated in a band-like manner on the particle surface. On the other hand, in the "T-33-2" product, the final product prepared after undergoing both steps A and B of the present invention, the aggregate width of the grayish-white dots indicating the presence of Ti on the particle surface increased, reaching a maximum of approximately 100 nm. Furthermore, since a Ti spectral peak, which is not present inside the particles, was observed on the particle surface in both samples, it was confirmed that a coating layer was formed in both process A and process B.

[0100] - Absorption rate in the visible light range - As shown in Figure 49, the absorption rate in the visible light range was higher for all prepared products than for the uncoated product, and it was confirmed that the absorption rate tended to increase with a higher Ti / Ag molar ratio. The left panel of Figure 50 shows the absorption rates in the visible light range for Ag-TiO2 previously prepared using similar combinations and reported in the literature, while the right panel shows the absorption rate of the "T-33-2" product prepared in this study. Literature data indicates that the maximum absorption value is observed around 470 nm, which is believed to be a peak that appears due to the compounding of Ag and TiO2. Similarly, in the preparation used in this study, the maximum absorption value was observed around 450 nm. Furthermore, as shown in Figure 49, a similar tendency for maximum values ​​to appear was observed in other samples with altered molar ratios.

[0101] From these results, it has been demonstrated that, as an example of the present invention, it is possible to coat submicron-sized, non-spherical, amorphous Ag core particles with TiO2. Furthermore, it was confirmed that the Ag-TiO2 composite particles obtained by the method of the present invention exhibit a maximum value in electromagnetic wave absorption characteristics in the visible light range.

[0102] From the results of Examples A to E described above, it was confirmed that the coating method for fine particles of the present invention can stably prepare composite particles in which a coating component is attached to core particles of submicron size or smaller. In other words, it was shown that step A, using a wet pulverizer, can efficiently bond coating components that can react with or electrostatically adhere to the hydrophilic groups on the surface of the core particles, and that step B, using a slurry dryer, can recover the composite particles to which the coating components are bonded as a dried powder. Furthermore, it was confirmed that the formation of the coating layer and its thickness can be controlled by adjusting the supply amount of the coating component and the processing conditions, demonstrating that the method of the present invention is applicable to various core particles such as inorganic materials, magnetic materials, and optical materials. Furthermore, it was confirmed that the composite particles obtained by the method of the present invention exhibit excellent dispersibility while suppressing particle fracture, and contribute to the expression of functions such as magnetic properties and electromagnetic wave absorption properties in the visible light range. These results confirm that the present invention is useful as a method for mass-producing composite particles by coating core particles of submicron size or smaller, and for controlling the thickness of the coating layer to form composite particles with excellent properties. [Industrial applicability]

[0103] The present invention's method for coating fine particles allows for the mass production of composite particles in which a coating component is coated on the surface of submicron-sized or smaller core particles, and also allows for control of the thickness of the coating layer. Therefore, it is expected to be widely used in the manufacture of new materials such as battery materials, optical materials, magnetic materials, electrochemical catalyst materials, semiconductor materials, and pharmaceuticals. [Explanation of Symbols]

[0104] 100 wet media pulverizer 1 container 2. Supply port for slurry-like material 3 Main shaft 4 Sub-shaft 5. Ring-shaped member (crushing medium) 6. Discharge port for processed materials 7 Jacket 8. Heat transfer medium supply port 9 Heat transfer medium outlet 10 External circulation path section 11 External tank 12. Supply device for slurry-like processed material 13. Agitator 14 Jackets 15 Heat transfer medium supply port 16 Heat transfer medium outlet 200 Media dryer 51 Perforated plate-like dispersion plate 52 Hot air room 53 Fluidization Room 54 Air heater 55 Inlet for heated air 56 Discharge port for dried powder etc. after processing 57 Cyclone 58 Bag Collectors 59 Media particles 60. Supply nozzle for slurry-like material 61 Mixture supply tank 62 Agitator

Claims

1. A method for coating fine particles comprising: step A, mixing a core particle with a coating component solution to bond the coating component to the surface of the core particle; and step B, obtaining composite particles with the coating component bonded to the surface of the core particle as a dried powder, wherein A method for coating fine particles, characterized in that step A is performed using a wet pulverizer and step B is performed using a slurry dryer.

2. The method for coating fine particles according to claim 1, characterized in that the core particles are submicron-sized or smaller particles having hydrophilic groups on their surface.

3. The method for coating fine particles according to claim 2, characterized in that the solution of the coating component is a solution having a component that can react with or electrostatically adhere to the hydrophilic groups on the surface of the core particles.

4. The method for coating fine particles according to claim 1 or 2, characterized in that the above-mentioned wet micro-pulverizer is a wet-media micro-pulverizer that pulverizes a slurry-like material by applying a pulverizing force generated by a pulverizing medium that is forcibly moved by mechanical action, thereby pulverizing the processed product into particles of several millimeters to submicrons.

5. The method for coating fine particles according to claim 4, characterized in that the wet media pulverizer has an external circulation path.

6. The method for coating fine particles according to claim 1 or 2, characterized in that the slurry dryer is a media-type dryer that adheres a slurry-like treatment to the surface of a vibrating or fluidizing medium, evaporates the solvent to dry it, and separates the fine particles contained in the slurry-like treatment from the medium particles by collisions between the mediums, and recovers the fine particles as a dried powder.

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