Method for producing inorganic fine powder

Abstract

This method for producing an inorganic fine powder is a method in which a cumulative 50% particle diameter D50 on a volume basis is within a range of 0.01-5.0 μm, the method being characterized by comprising: a sorted powder producing step for obtaining a sorted powder which is sorted by dispersing, in a gas phase, a carboxylic acid-adsorbed inorganic raw material powder, in which a carboxylic acid is adsorbed onto an inorganic raw material powder having D50 of 10 μm or less; and a dry-sorting step for dry-sorting the sorted powder. The present invention can provide a method for producing an inorganic fine powder, with which an inorganic fine powder, having an extremely small number of coarse particles and a cumulative 50% particle diameter D50 on a volume basis within a range of 0.01-5.0 μm, can be produced with high productivity.

Description

[Technical Field]

[0001] This invention relates to a method for producing inorganic fine powder. [Background technology]

[0002] Conventionally, conductive metal powders have been used as conductive materials for electronic components. In multilayer ceramic capacitors, both the ceramic layer and the internal electrode layer are rapidly becoming thinner. Therefore, when metal powder is used for internal electrodes, it is required that the average particle size is small, the particle size distribution of the powder be narrow in order to form an electrode layer of uniform thickness, and that it does not contain coarse particles that could come into contact with both adjacent internal electrodes on either side of the dielectric layer and cause a short circuit.

[0003] To date, various methods have been used to produce powders with a desired particle size distribution, which involve classifying powders produced by different manufacturing methods. One such classification method utilizes the difference in particle size by taking advantage of the difference in particle sedimentation velocity in the gas phase or liquid phase. Classification performed in the gas phase is called dry classification, and classification performed in the liquid phase is called wet classification. While wet classification offers superior classification accuracy, it requires the use of a liquid as a dispersion medium, and also necessitates drying and crushing after classification. Therefore, dry classification is overwhelmingly less expensive.

[0004] However, conventionally, this dry classification method has been problematic because the powder adheres to various parts of the classifier, blocking the powder supply port and piping, making long-term operation difficult, and also resulting in low yield due to low classification accuracy.

[0005] As a method aimed at solving such problems, Patent Document 1 discloses a method in which a powder is mixed with an auxiliary agent consisting of alcohols with a boiling point of less than 200°C, such as ethanol, and the powder is dry-classified while the auxiliary agent is vaporized.

[0006] Furthermore, Patent Document 2 discloses a method of dry classification of a powder by mixing it with an auxiliary agent consisting of an aqueous alcohol solution containing 10 to 50% by mass of an alcohol such as ethanol, and vaporizing the auxiliary agent.

[0007] Furthermore, Patent Document 3 discloses a method for dry classifying a powder made of nickel by mixing it with an auxiliary agent consisting of an organic solvent having a flash point of 80°C or higher, such as diethylene glycol, and vaporizing the auxiliary agent. It also discloses a method for dry classifying a powder made of nickel by mixing it with an auxiliary agent consisting of water, and vaporizing the auxiliary agent.

[0008] Furthermore, Patent Document 4 discloses a method for dry-classifying a powder by mixing it with a liquid additive, diethylene glycol monomethyl ether. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] International Publication No. 2010 / 047175 [Patent Document 2] International Publication No. 2010 / 057206 [Patent Document 3] International Publication No. 2010 / 106716 [Patent Document 4] International Publication No. 2012 / 124453 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] However, the inventors of this invention conducted research and found that, for example, by adsorbing an auxiliary agent such as ethanol onto the powder and performing dry classification, it is possible to operate the classifier for a long time, but the resulting powder contains a large number of coarse particles, and it is necessary to repeat the classification many times to reduce the number of these coarse particles. Furthermore, although it is sometimes possible to reduce the number of coarse particles by repeating the classification many times, it is time-consuming and costly, reducing productivity, and also significantly reducing the yield of the resulting powder.

[0011] Therefore, the objective of the present invention is to achieve a volume-based cumulative 50% particle size D with an extremely small number of coarse particles. 50 The objective is to provide a method for producing inorganic fine powder with high productivity, in which inorganic fine powder having a particle size within the range of 0.01 μm to 5.0 μm. [Means for solving the problem]

[0012] The purpose of this is as follows (1) ~ ( 7 This is achieved by the present invention as described in ). (1) Cumulative 50% particle size D based on volume 50 A method for producing inorganic fine powder having a particle size in the range of 0.01 μm or more and 5.0 μm or less, boiling point 110℃ or more and 200℃ or less That is mono In the gaseous state, D 50 This is adsorbed onto inorganic raw material powders of 10 μm or less. The aforementioned item A process for producing a classifiable powder involves dispersing a carboxylic acid-adsorbed inorganic raw material powder in the gas phase to obtain a classifiable powder to be classified, and The process includes a dry classification step for dry classifying the powder to be classified. death, The inorganic component of the inorganic raw material powder is at least one selected from the group consisting of metals, metal oxides, glass, and oxide-based ceramics. A method for producing inorganic fine powder characterized by the above.

[0013] (2) Cumulative 50% particle size D based on volume 50 A method for producing inorganic fine powder having a particle size in the range of 0.01 μm or more and 5.0 μm or less, D is dispersed in the gas phase when it is formed.50 In an inorganic raw material powder with a particle size of 10 μm or less, dispersed in the gas phase, the inorganic raw material powder has a boiling point 110℃ or more and 200℃ or less That is mono A process for producing a powder to be classified, in which a carboxylic acid is adsorbed in a gaseous state to obtain a powder to be classified, The process includes a dry classification step for dry classifying the powder to be classified. death, The inorganic component of the inorganic raw material powder is at least one selected from the group consisting of metals, metal oxides, glass, and oxide-based ceramics. A method for producing inorganic fine powder characterized by the above.

[0014] (3) Between the powder to be classified production step and the dry classification step, A recovery step for recovering the classified powder, A method for producing inorganic fine powder according to (2) above, comprising a dispersion step of dispersing the classified powder obtained in the recovery step in the gas phase.

[0015] (4) Volume-based cumulative 50% particle size D 50 A method for producing inorganic fine powder having a particle size in the range of 0.01 μm or more and 5.0 μm or less, D 50 A process for producing a classifiable powder by dispersing inorganic raw material powder of 10 μm or less to obtain a classifiable powder, The process includes a dry classification step for dry classifying the powder to be classified, The to-be-classified powder generation step, Its boiling point is between 110°C and 200°C. gaseous state mono The process is carried out in an atmosphere containing a carboxylic acid. stomach, The inorganic component of the inorganic raw material powder is at least one selected from the group consisting of metals, metal oxides, glass, and oxide-based ceramics. A method for producing inorganic fine powder characterized by the above.

[0016] (5) Volume of the inorganic raw material powder 1 m³ 3 In contrast, the above mono A method for producing inorganic fine powder according to any one of (2) to (4) above, using a carboxylic acid in a ratio of 30 mol to 960 mol.

[0018] (6) The above monoThe method for producing an inorganic fine powder according to any one of (1) to (5) above, wherein the carboxylic acid is at least one selected from acetic acid, propionic acid, and butyric acid.

[0019] ( 7 ) The method for producing an inorganic fine powder according to any one of (1) to ( 6 ) above, wherein the dry classification step is performed in a gas phase at 60°C or higher and 300°C or lower. [Advantages of the Invention]

[0021] According to the present invention, there is provided a method for producing an inorganic fine powder capable of producing, with high productivity, an inorganic fine powder in which the number of coarse particles is extremely small and the volume-based cumulative 50% particle diameter D 50 is in the range of 0.01 μm or more and 5.0 μm or less. [Brief Description of the Drawings]

[0022] [Figure 1] FIG. 1 is a diagram showing one configuration example of a classifier used in the method for producing an inorganic fine powder of the present invention. [Embodiments for Carrying Out the Invention]

[0023] Hereinafter, preferred embodiments of the present invention will be described in detail. [Method for Producing Inorganic Fine Powder] 1. First Embodiment

[0024] The method for producing an inorganic fine powder according to the first embodiment of the present invention is a method for producing an inorganic fine powder in which the volume-based cumulative 50% particle diameter D 50 is in the range of 0.01 μm or more and 5.0 μm or less, and comprises a classified powder generation step of dispersing a carboxylic acid-adsorbed inorganic raw material powder in which a carboxylic acid is adsorbed on an inorganic raw material powder having a D 50 of 10 μm or less in a gas phase to obtain a classified powder to be classified, and a dry classification step of dry-classifying the classified powder.

[0025] Thereby, the number of coarse particles is extremely small, and the volume-based cumulative 50% particle diameter D 50This invention provides a method for producing inorganic fine powders with high productivity, where the particle size of the inorganic fine powder is within the range of 0.01 μm to 5.0 μm.

[0026] The excellent effects obtained are thought to be due to the following reasons. Specifically, compared to cases where an auxiliary agent such as ethanol is adsorbed onto the powder and dry classification is performed, dispersing carboxylic acid-adsorbed inorganic raw material powder (in which carboxylic acid is adsorbed onto inorganic raw material powder) in the gas phase improves the dispersibility of the powder to be classified in the gas phase, thereby increasing the classification accuracy. As a result, the number of coarse particles contained in the manufactured inorganic fine powder can be reduced to an extremely small amount. Furthermore, this reduces the number of classification cycles, improving productivity.

[0027] Furthermore, adsorbing carboxylic acids onto inorganic raw material powders increases the fluidity of the powder to be classified, reducing adhesion of the powder to the classifier and improving the yield. In addition, reduced adhesion to the classifier makes it less likely for the powder supply port and piping inside the classifier to become clogged, thus extending the operating time of the classifier and improving productivity.

[0028] Furthermore, in this embodiment, since carboxylic acid-adsorbed inorganic raw material powder, in which carboxylic acid has been adsorbed onto the inorganic raw material powder in advance, is used, it is advantageous in simplifying and miniaturizing the configuration of the apparatus used for manufacturing inorganic fine powder compared to other embodiments which will be described in detail later. In addition, because carboxylic acid-adsorbed inorganic raw material powder, in which carboxylic acid has been adsorbed on in advance, is used, the fluidity of the powder is higher compared to when inorganic raw material powder without adsorbed carboxylic acid is put into the disperser, adhesion within the disperser is less likely to occur, and the movement of the powder within the disperser is smoother.

[0029] In this specification, the cumulative 50% particle size (D) is defined as the volume-based cumulative 50% particle size. 50 Unless otherwise specified, ) refers to the 50% cumulative fraction of the volume-based particle size distribution measured using a laser particle size distribution analyzer, which can be obtained, for example, by measurement using a laser diffraction / scattering particle size distribution analyzer LA-960 (manufactured by HORIBA Corporation).

[0030] Furthermore, in this specification, classification refers to the operation of separating powder into a group of relatively large particles (in other words, coarse powder) and a group of relatively small particles (in other words, fine powder) according to their size. Specifically, in this specification, fine powder is defined as the cumulative 50% particle size by volume D 50 This refers to a group of particles whose size is within the range of 0.01 μm to 5.0 μm, and coarse powder is D 50 This refers to a group of particles larger than fine powder. Of these, fine powder is defined as the inorganic fine powder produced in this invention.

[0031] Furthermore, coarse particles refer to the D of the inorganic fine powder to be manufactured. 50 In contrast, this refers to particles with a sufficiently large particle size, for example, the particle size of the inorganic fine powder to be manufactured is D 50 This can be defined as particles that are 1.5 times or more in size, and also, for example, the D of the powder in question. 50 The particles can be made to be 2.0 times or more in size, and for example, the D of the target powder 50 The particles can be made to be 2.5 times or more in size.

[0032] 2. Second Embodiment Furthermore, the method for producing inorganic fine powder according to the second embodiment of the present invention is a volume-based cumulative 50% particle size D 50 A method for producing inorganic fine powder having a particle size in the range of 0.01 μm to 5.0 μm, wherein the particle is dispersed in the gas phase at the time of production, D 50 The apparatus comprises a powder to be classified step, in which inorganic raw material powder with particles of 10 μm or less is dispersed in the gas phase, and a carboxylic acid is adsorbed onto the inorganic raw material powder to obtain a powder to be classified, and a dry classification step, in which the powder to be classified is dry classified.

[0033] This results in an extremely low number of coarse particles, with a volume-based cumulative 50% particle size D 50 This invention provides a method for producing inorganic fine powders with high productivity, where the particle size of the inorganic fine powder is within the range of 0.01 μm to 5.0 μm.

[0034] The excellent effects obtained are thought to be due to the following reasons. In other words, compared to methods such as mixing powder with an auxiliary agent such as ethanol and dry classifying the powder while vaporizing the auxiliary agent, adsorbing carboxylic acid onto the inorganic raw material powder, which is dispersed in the gas phase at the time of production, improves the dispersibility of the powder to be classified in the gas phase and increases the classification accuracy. As a result, the number of coarse particles contained in the manufactured inorganic fine powder can be made extremely small. Furthermore, this reduces the number of classification cycles, improving productivity.

[0035] Furthermore, adsorbing carboxylic acids onto inorganic raw material powders increases the fluidity of the powder to be classified, reducing adhesion of the powder to the classifier and improving the yield. In addition, reduced adhesion to the classifier makes it less likely for the powder supply port and piping inside the classifier to become clogged, thus extending the operating time of the classifier and improving productivity.

[0036] Furthermore, in this embodiment, since the inorganic raw material powder, which is dispersed in the gas phase during production, is adsorbed with carboxylic acid while dispersed in the gas phase to obtain the powder to be classified, the number of steps can be reduced compared to the previously described embodiment, which is advantageous from the viewpoint of further improving productivity. In addition, variations in the amount of carboxylic acid adsorbed at each part of the inorganic raw material powder can be suppressed more effectively, and the final inorganic fine powder has an extremely small number of coarse particles and a more ideal particle size distribution. Moreover, since the amount of carboxylic acid adsorbed in the powder to be classified can be easily controlled by controlling the supply amount of carboxylic acid, the final inorganic fine powder has an extremely small number of coarse particles and a more ideal particle size distribution.

[0037] 3. Third Embodiment Furthermore, the method for producing inorganic fine powder according to the third embodiment of the present invention is a volume-based cumulative 50% particle size D 50 A method for producing inorganic fine powder having a particle size of 0.01 μm or more and 5.0 μm or less, D 50The system comprises a classifiable powder generation step of dispersing inorganic raw material powder of 10 μm or less to obtain a classifiable powder to be classified, and a dry classification step of dry classifying the classifiable powder, wherein the classifiable powder generation step is carried out in an atmosphere containing a gaseous carboxylic acid.

[0038] This results in an extremely low number of coarse particles, with a volume-based cumulative 50% particle size D 50 This invention provides a method for producing inorganic fine powders with high productivity, where the particle size of the inorganic fine powder is within the range of 0.01 μm to 5.0 μm.

[0039] The excellent effects obtained are thought to be due to the following reasons. Specifically, compared to methods such as mixing powder with an auxiliary agent such as ethanol and dry classifying the powder while vaporizing the auxiliary agent, dispersing the inorganic raw material powder in an atmosphere containing a gaseous carboxylic acid to obtain the powder to be classified improves the dispersibility of the powder in the gas phase and increases the classification accuracy. As a result, the number of coarse particles contained in the manufactured inorganic fine powder can be made extremely small. Furthermore, this reduces the number of classification cycles, improving productivity.

[0040] Furthermore, adsorbing carboxylic acids onto inorganic raw material powders increases the fluidity of the powder to be classified, reducing adhesion of the powder to the classifier and improving the yield. In addition, reduced adhesion to the classifier makes it less likely for the powder supply port and piping inside the classifier to become clogged, thus extending the operating time of the classifier and improving productivity.

[0041] Furthermore, in this embodiment, since the inorganic raw material powder is dispersed in an atmosphere containing gaseous carboxylic acid to obtain the powder to be classified, considering the step of adsorbing carboxylic acid, the number of steps can be reduced compared to the first embodiment described above, which is advantageous from the viewpoint of further improving productivity. In addition, variations in the amount of carboxylic acid adsorbed at each part of the inorganic raw material powder can be suppressed more effectively, and the final inorganic fine powder has an extremely small number of coarse particles and a more ideal particle size distribution. Moreover, since the amount of carboxylic acid adsorbed in the powder to be classified can be easily controlled by controlling the supply amount of carboxylic acid, the final inorganic fine powder has an extremely small number of coarse particles and a more ideal particle size distribution.

[0042] Furthermore, although it is not clear why obtaining a classified powder in which carboxylic acid is adsorbed onto an inorganic raw material powder in each of the above embodiments improves the dispersibility of the classified powder, the inventors speculate as follows: Inorganic raw material powders generally have functional groups on the surface of their constituent particles that can interact with carboxyl groups, such as hydroxyl groups. By adsorbing carboxylic acid onto the inorganic raw material powder, the functional groups such as hydroxyl groups on the surface of the constituent particles of the inorganic raw material powder interact with the carboxyl groups (-COOH) of the carboxylic acid, causing the parts of the carboxylic acid other than the carboxyl groups, such as the hydrocarbon portion, to be located on the outside of the metal powder particles. This is thought to suppress aggregation of the inorganic raw material powder due to polar groups such as hydroxyl groups, thereby improving dispersibility. In addition, in the case of the inorganic raw material powder, for example, a metal powder, even in parts where there are no functional groups that interact with carboxyl groups such as hydroxyl groups, the carboxylic acid can be adsorbed by reacting with the metal to produce a carboxylic acid metal salt, or by the carboxyl groups forming coordination bonds with metal atoms on the surface of the metal powder, so that the carboxylic acid can be adsorbed more uniformly and in a suitable amount on the particle surface. Furthermore, by allowing a suitable amount of carboxylic acid to be uniformly adsorbed onto the particle surface, the generation of polar groups such as hydroxyl groups can be suppressed. As described above, the adsorption in this invention can be either physical or chemical.

[0043] If the above configuration is not met, satisfactory results cannot be obtained. For example, in each of the above embodiments, if carboxylic acid is not adsorbed onto the powder to be classified, the dispersibility of the powder in the gas phase cannot be sufficiently improved in the dry classification process. As a result, the classification accuracy cannot be sufficiently improved, and the number of coarse particles contained in the manufactured inorganic fine powder increases. In addition, the number of classification cycles required increases, reducing productivity. Furthermore, because the fluidity of the powder to be classified cannot be sufficiently improved, the adhesion of the powder to be classified to the classifier increases, reducing the yield. Moreover, the increased adhesion to the classifier makes the powder supply port and the inside of the piping of the classifier more prone to clogging, shortening the operating time of the classifier and reducing productivity.

[0044] <Classifier> Figure 1 shows an example of the configuration of a classifier used in the inorganic fine powder production method of the present invention. In the following explanation, the upper side of Figure 1 will be referred to as "upper" and the lower side as "lower".

[0045] Classifier 1 is an airflow type classifier that performs classification using centrifugal force acting on powder, and is equipped with a casing 3 that forms a classification chamber 10.

[0046] Upstream from the classification chamber (classification zone) 10, a dispersion zone 11 is provided for dispersing inorganic raw material powder prior to classification. The classification chamber 10 is the region where the dispersed inorganic raw material powder is classified.

[0047] Furthermore, the classifier 1 includes an inlet 4 for introducing inorganic raw material powder into the dispersion zone 11, an air nozzle 5 for injecting high-pressure air (primary air) into the dispersion zone 11, a guide vane 6 for introducing secondary air into the classification chamber 10 to form a swirling airflow within the classification chamber 10, a fine powder discharge port 7 opening in the upper center of the classification chamber 10, and a coarse powder discharge port 8 opening along the lower outer circumference of the classification chamber 10.

[0048] Next, we will explain a method for dispersing and classifying inorganic raw material powders using such a classifier 1.

[0049] The inorganic raw material powder is introduced into the dispersion zone 11 from the inlet 4. The inorganic raw material powder is dispersed by the primary air sprayed into the dispersion zone 11. The dispersed inorganic raw material powder is then introduced into the classification chamber 10.

[0050] In the classification chamber 10, secondary air is introduced into the classification chamber 10 from the guide vane 6, causing the airflow to swirl within the classification chamber 10 and be exhausted from the upper center of the classification chamber 10. The outward centrifugal force acting due to this swirling airflow and the gas flow moving towards the center separate the inorganic raw material powder in the solid-gas mixed fluid into coarse and fine powders.

[0051] Specifically, the coarse powder moves radially outward within the classification chamber 10 due to the outward centrifugal force caused by the swirling airflow and is collected from the coarse powder discharge port 8 on the lower outer circumference of the classification chamber 10. On the other hand, the fine powder moves radially inward within the classification chamber 10 due to the gas flow moving towards the center and is collected from the fine powder discharge port 7 in the upper center of the classification chamber 10.

[0052] A suction pump (not shown) is connected to the fine powder discharge port 7, and the fine powder is discharged and collected together with the air (exhaust) in the classification chamber 10.

[0053] The powder to be classified process corresponds to the process carried out in the dispersion zone 11, and the dry classification process corresponds to the process carried out in the classification chamber (classification zone) 10. In other words, the inorganic raw material powder dispersed in the dispersion zone 11, or to put it another way, the powder introduced into the classification chamber 10, is referred to as the powder to be classified in this specification.

[0054] In the explanation above, an airflow classifier that uses centrifugal force from a swirling airflow for classification was used as an example, but the classification method of the classifier is not particularly limited. For example, a method that uses centrifugal force from the rotation of a rotor for classification, a method that uses gravity for classification, or a method that uses inertial force for classification may also be used.

[0055] Furthermore, in the present invention, the process of generating the powder to be classified and the dry classification process are not limited to being carried out using the same apparatus, but may be carried out using separate apparatuses. That is, inorganic raw material powder may be dispersed in a disperser to obtain the powder to be classified, and then the powder to be classified may be classified in a dry classifier.

[0056] <Classified powder generation process> In the process of producing the classified powder, a classified powder is obtained in which carboxylic acid is adsorbed onto inorganic raw material powder and dispersed in the gas phase.

[0057] (Inorganic raw material powder) The inorganic raw material powder is the raw material for the inorganic fine powder produced in the present invention, and is the cumulative 50% particle size D by volume. 50 The particle size is 10 μm or less.

[0058] Volume-based cumulative 50% particle size D of inorganic raw material powder 50 The particle size should be 10 μm or less, but preferably greater than 0.01 μm. In particular, the cumulative 50% particle size D of the inorganic raw material powder by volume. 50 D is an inorganic fine powder. 50 Preferably, the particle size is greater than 0.03 μm and less than or equal to 2.5 μm; more preferably, greater than 0.05 μm and less than or equal to 1.2 μm; and even more preferably, greater than 0.10 μm and less than or equal to 0.80 μm.

[0059] The inorganic components of the inorganic raw material powder are not particularly limited, but include various metals, various metal oxides, various glasses, various ceramics, and various semiconductors.

[0060] Examples of metals that make up inorganic raw material powders include silver, gold, platinum, copper, palladium, nickel, tungsten, zinc, tin, iron, cobalt, and alloys containing one or more of these selected metals.

[0061] Furthermore, examples of metal oxides (metal oxides other than ceramics) that constitute the inorganic raw material powder include nickel oxide, copper oxide, silver oxide, and iron oxide.

[0062] Furthermore, examples of glass that constitutes the inorganic raw material powder include bismuth-based glass, tellurium-based glass, and silicate glass.

[0063] Furthermore, examples of ceramics that constitute inorganic raw material powders include oxide-based ceramics, nitride-based ceramics, and boride-based ceramics. More specifically, examples include alumina, silica, zirconia, barium titanate, calcium zirconate, alumina nitride, silicon nitride, and boron nitride. In addition, ceramics include functional ceramics such as phosphors.

[0064] Furthermore, examples of semiconductors that constitute inorganic raw material powders include InP, GaP, InAs, GaAs, InGaP, InZnP, ZnSe, CdSe, and CdS.

[0065] In particular, it is preferable that the inorganic component of the inorganic raw material powder is at least one selected from the group consisting of metals, metal oxides, glass, ceramics, and semiconductors.

[0066] This allows the carboxylic acid to act more favorably, further improving the dispersibility of the inorganic raw material powder.

[0067] Furthermore, when the inorganic component of the inorganic raw material powder is a metal, metal oxide, glass, or oxide-based ceramic, the effects described above are exhibited more significantly. The reason for this is not entirely clear, but the inventors speculate that it is because there are many hydroxyl groups on the particle surface of the inorganic raw material powder. In particular, when the inorganic component of the inorganic raw material powder is a metal, the inventors speculate that there are many hydroxyl groups in the parts of the powder surface that have been oxidized to form metal oxides, and in the parts that have not been oxidized, the carboxylic acid can be adsorbed more uniformly and in a suitable amount through the formation of carboxylic acid metal salts by the reaction of metal and carboxylic acid, or through the formation of coordination bonds between carboxyl groups and metal atoms on the powder surface, thus exhibiting the above effects more significantly. These effects are exhibited more significantly when the inorganic component of the inorganic raw material powder is nickel.

[0068] The shape of the inorganic raw material powder is not particularly limited, but various shapes can be used, such as spherical, flake-shaped, or granular, and one or more of these shapes can be selected and used in combination.

[0069] In this specification, "spherical" refers to a particle shape where the ratio of the major axis to the minor axis is 2 or less. "Flake-like" refers to a shape where the ratio of the major axis to the minor axis is greater than 2.

[0070] The method for producing inorganic raw material powder is not particularly limited, but examples include electrolysis, atomization, mechanical grinding, wet reduction, spray pyrolysis, chemical vapor deposition, and physical vapor deposition.

[0071] Furthermore, the multiple particles of the inorganic raw material powder may have the same composition as each other, or they may contain particles with different compositions.

[0072] (Carboxylic acid) In the classified powder, the carboxylic acid is adsorbed onto the inorganic raw material powder. In this invention, the adsorption can be either physical or chemical. This results in good dispersibility of the classified powder in the gas phase, making it possible to easily and efficiently obtain inorganic fine powder with the desired particle size distribution in high yield, and to minimize the number of coarse particles in the resulting inorganic fine powder.

[0073] The carboxylic acid is not particularly limited as long as it is a compound having a carboxyl group, but examples include formic acid, acetic acid, propionic acid, isobutyric acid, butyric acid, crotonic acid, isovaleric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, lactic acid, oxalic acid, succinic acid, oleic acid, acrylic acid, methacrylic acid, etc., and one or more selected from these can be used in combination.

[0074] Among these, the carboxylic acid is preferably one with a boiling point of 100°C to 400°C, more preferably one with a boiling point of 105°C to 250°C, and even more preferably one with a boiling point of 110°C to 200°C.

[0075] This allows the carboxylic acid to be handled suitably in a liquid state during the powder classification process, improving handling efficiency. Furthermore, it more effectively prevents the inorganic raw material powder from sintering when the carboxylic acid is adsorbed onto the powder in a vaporized state, enabling the carboxylic acid to be adsorbed onto the inorganic raw material powder with greater uniformity.

[0076] In this specification, unless otherwise specified, "boiling point" refers to the boiling point at 1 atmosphere.

[0077] Furthermore, the carboxylic acid is preferably a monocarboxylic acid. This results in better dispersibility of the powder to be classified, and the effects of the present invention are more pronounced.

[0078] The carboxylic acid is preferably at least one selected from acetic acid, propionic acid, butyric acid, and oleic acid, and more preferably acetic acid.

[0079] This further improves the dispersibility of the classified powder, and the effects of the present invention are exhibited even more significantly.

[0080] In the first embodiment described above, the cumulative 50% particle diameter D is based on volume. 50 A carboxylic acid-adsorbed inorganic raw material powder, in which carboxylic acid is adsorbed onto an inorganic raw material powder with a particle size of 10 μm or less, is dispersed in the gas phase to obtain a powder to be classified.

[0081] First, the cumulative 50% particle size D based on volume 50 Prepare a carboxylic acid-adsorbed inorganic raw material powder in which carboxylic acid is adsorbed onto an inorganic raw material powder with a particle size of 10 μm or less.

[0082] The method for producing carboxylic acid-adsorbed inorganic raw material powder is not particularly limited, but it is preferable to use a method in which a carboxylic acid in a gaseous state is adsorbed onto the inorganic raw material powder.

[0083] By adsorbing gaseous carboxylic acids onto inorganic raw material powder, the carboxylic acids can be uniformly adsorbed by the inorganic raw material powder. This allows the effects of the present invention to be exhibited more significantly.

[0084] The method for adsorbing gaseous carboxylic acid onto inorganic raw material powder is not particularly limited, but examples include leaving the inorganic raw material powder standing in an atmosphere containing gaseous carboxylic acid, or blowing a gas containing vaporized carboxylic acid onto the inorganic raw material powder.

[0085] Then, by dispersing the carboxylic acid-adsorbed inorganic raw material powder in the gas phase, the powder to be classified is obtained.

[0086] In the second embodiment described above, the cumulative 50% particle size D, based on volume, is dispersed in the gas phase during generation. 50 In an inorganic raw material powder with a particle size of 10 μm or less, a carboxylic acid is adsorbed onto the inorganic raw material powder while it is dispersed in the gas phase to obtain a powder to be classified.

[0087] Methods for producing inorganic raw material powder that is dispersed in the gas phase during production include, for example, gas-phase methods such as chemical vapor deposition and physical vapor deposition, as well as atomization and spray pyrolysis. In particular, by producing inorganic raw material powder using gas-phase methods or spray pyrolysis, the inorganic raw material powder can be more easily adjusted to the particle size range of the present invention.

[0088] The method for adsorbing carboxylic acid onto inorganic raw material powder is not particularly limited, but it is preferable to adsorb carboxylic acid in a gaseous state onto the inorganic raw material powder. Specifically, for example, one method is to blow vaporized carboxylic acid onto the inorganic raw material powder during the cooling process of inorganic raw material powder that is generated at a predetermined temperature and is dispersed in the gas phase at the time of generation.

[0089] This allows carboxylic acids to be adsorbed onto inorganic raw material powders with greater uniformity. As a result, particle aggregation can be more effectively suppressed, and dispersibility can be further improved. This allows the effects of the present invention to be exhibited more significantly.

[0090] Furthermore, by adsorbing carboxylic acid onto the inorganic raw material powder, which is dispersed in the gas phase during production, to obtain the powder to be classified, the number of steps can be reduced, and productivity can be further improved.

[0091] Furthermore, in the second embodiment, it is preferable to further include a recovery step for recovering the powder to be classified and a dispersion step for dispersing the powder to be classified obtained in the recovery step into the gas phase, between the powder to be classified generation step and the dry classification step.

[0092] This makes it easier to combine more suitable classifiers, further improving the accuracy of classification in the subsequent dry classification process and resulting in better productivity of inorganic fine powders.

[0093] In the third embodiment of the present invention, the cumulative 50% particle size D is determined by volume. 50 A powder of inorganic raw materials with a particle size of 10 μm or less is dispersed in an atmosphere containing a gaseous carboxylic acid to obtain a powder to be classified.

[0094] First, the cumulative 50% particle size D based on volume 50 An inorganic raw material powder with a particle size of 10 μm or less is prepared. Then, the powder to be classified is obtained by dispersing this inorganic raw material powder in an atmosphere containing a gaseous carboxylic acid.

[0095] By dispersing inorganic raw material powder in an atmosphere containing gaseous carboxylic acid, the carboxylic acid can be adsorbed onto the inorganic raw material powder with greater uniformity. As a result, particle aggregation can be more effectively suppressed, and dispersibility can be further improved. In addition, the amount of carboxylic acid adsorbed onto the inorganic raw material powder can be easily controlled. This allows the effects of the present invention to be exhibited more significantly. Furthermore, by dispersing the inorganic raw material powder in an atmosphere containing gaseous carboxylic acid, the number of steps can be reduced, further improving productivity.

[0096] Furthermore, in the second and third embodiments, the amount of carboxylic acid used is not particularly limited, but the volume of inorganic raw material powder is 1 m³. 3 It is preferable to use it in a ratio of 30 mol to 960 mol, more preferably in a ratio of 60 mol to 480 mol, and even more preferably in a ratio of 120 mol to 240 mol.

[0097] This allows for more uniform adsorption of a suitable amount of carboxylic acid onto the inorganic raw material powder, resulting in improved dispersibility of the classified powder. Furthermore, it prevents excessive adsorption of carboxylic acid onto the inorganic raw material powder, leading to better physical properties when the resulting inorganic fine powder is formed into a paste.

[0098] In this invention, the volume of the inorganic raw material powder refers to the volume calculated from the weight and true density of the powder.

[0099] The supply rate of inorganic raw material powder to the classifier, that is, for example, in the classifier 1 shown in Figure 1, the supply rate of inorganic raw material powder from the inlet 4 into the dispersion zone 11, depends on the size (capacity) of the classifier, but is preferably 1 kg / hour or more and 20 kg / hour or less, more preferably 3 kg / hour or more and 15 kg / hour or less, and even more preferably 5 kg / hour or more and 12 kg / hour or less.

[0100] This makes it possible to improve the dispersibility of inorganic raw material powders while also improving the productivity of inorganic fine powders.

[0101] The supply dispersion pressure during dispersion, that is, for example, the pressure of the dispersion air injected from the air nozzle 5 into the dispersion zone 11 in the classifier 1 shown in Figure 1, is not particularly limited, but is preferably 0.2 MPa or more and 1.0 MPa or less, more preferably 0.4 MPa or more and 0.8 MPa or less, and even more preferably 0.5 MPa or more and 0.7 MPa or less.

[0102] This makes it possible to improve the dispersibility of inorganic raw material powders while also improving the productivity of inorganic fine powders.

[0103] <Dry classification process> In the dry classification process, the powder to be classified obtained in the powder to be classified generation process is subjected to dry classification.

[0104] Since the powder to be classified with adsorbed carboxylic acid is suitably dispersed in the gas phase, the classification accuracy in the dry classification process is improved. Therefore, the number of coarse particles contained in the manufactured inorganic fine powder can be drastically reduced. Furthermore, the improved classification accuracy allows for a reduction in the number of classification cycles, thus improving productivity.

[0105] Furthermore, increased fluidity of the powder to be classified reduces its adhesion to the inside of the classifier, improving the yield. Reduced adhesion also makes it less likely for the powder supply port and piping of the classifier to become clogged, thus extending the operating time of the classifier and improving productivity.

[0106] This makes it possible to manufacture inorganic fine powder with an extremely low number of coarse particles with high productivity.

[0107] The gas phase temperature used in the dry classification process is not particularly limited, but is preferably 60°C to 300°C, more preferably 100°C to 250°C, and even more preferably 150°C to 200°C.

[0108] This allows for more effective prevention of problems such as particle deformation due to heat and alteration of the constituent materials of the particles. Furthermore, the increased airflow velocity enhances centrifugal force, prevents water vapor from adhering to the particles, and further improves classification accuracy. It also allows for increased productivity. Additionally, it significantly reduces the number of coarse particles in the inorganic fine powder.

[0109] The suction airflow rate during the dry classification process, that is, for example, the suction airflow rate from the suction pump connected to the fine powder discharge port 7 in the classifier 1 shown in Figure 1, is not particularly limited, but is approximately 5.0 m³. 3 / min more than 30m 3 Preferably, it should be less than / minute, and 6.0m 3 Over 20m / minute 3 It is more preferable to be less than or equal to / min, and 7.0m 3 Over 9.0m / minute 3 It is even more preferable if it is less than / minute. This allows for more efficient classification of the powder to be classified.

[0110] The suction pressure used for dry classification, that is, for example, the suction pressure from the suction pump connected to the fine powder discharge port 7 in the classifier 1 shown in Figure 1, is not particularly limited, but is preferably -60kPa or more and -5kPa or less, more preferably -50kPa or more and -10kPa or less, and even more preferably -40kPa or more and -15kPa or less. This allows for more favorable classification of the powder to be classified.

[0111] By dry classification of the powder to be classified, the powder is separated into fine powder and coarse powder. The powder to be classified is, for example, based on the cumulative 50% particle size D by volume. 50 Fine powders that are in the range of 0.01 μm to 5.0 μm, and D 50 The material is classified into coarse and fine powders. Of these, the fine powder is recovered as the inorganic fine powder produced by this invention.

[0112] As described above, the cumulative 50% particle size D based on volume is determined. 50Inorganic fine powders with a particle size between 0.01 μm and 5.0 μm are produced.

[0113] The inorganic fine powder produced in this way contains an extremely small number of coarse particles. Furthermore, secondary aggregation is prevented because carboxylic acids are adsorbed onto the inorganic fine powder.

[0114] Furthermore, the methods described above improve classification accuracy, thus reducing the number of classification cycles. Additionally, the adhesion of the powder to be classified to the inside of the classifier is reduced, leading to improved yield. Moreover, reduced adhesion to the inside of the classifier reduces the likelihood of blockages in the powder supply port and piping, allowing for longer operating times and increased productivity.

[0115] The dry classification process may be performed only once, or it may be repeated multiple times. This can further improve the classification accuracy.

[0116] The yield of inorganic fine powder in the dry classification process is not particularly limited, but is preferably 80% or more, more preferably 85% or more, and even more preferably 88% or more. This further enhances the effects of the present invention.

[0117] In this specification, the yield of inorganic fine powder in the dry classification process is calculated using the following formula, based on the weight of the powder before classification (i.e., the weight of the powder to be classified) and the weight of the powder after classification (i.e., the weight of the inorganic fine powder): Yield (%) = (Weight of powder after classification / Weight of powder before classification) × 100 This is the value obtained by [the specified method].

[0118] The inorganic fine powder produced by the method of the present invention described above has a volume-based cumulative 50% particle size D 50 It is acceptable if the particle size is within the range of 0.01 μm to 5.0 μm, but the inorganic fine powder D 50The particle size is preferably 0.03 μm or more and 2.0 μm or less, more preferably 0.05 μm or more and 1.0 μm or less, and even more preferably 0.10 μm or more and 0.60 μm or less.

[0119] This makes it possible to obtain inorganic fine powder with a more ideal particle size distribution. In addition, conventionally, D 50 When the value is within this range, coarse particles tend to be a problem, and adverse effects from coarse particles are particularly likely to occur. In contrast, in the present invention, D 50 Even if the value is within this range, the occurrence of the above-mentioned problems can be prevented more effectively. That is, the D of inorganic fine powder 50 The effects of the present invention are more pronounced when the value falls within the aforementioned range.

[0120] The inorganic fine powder produced by the method of the present invention described above has a volume-based cumulative fraction 10% value of the particle size distribution measured using a laser particle size distribution analyzer, which is D 10 Let [μm] be the unit, and the 50th percentile of the cumulative fraction is D 50 Let [μm] be the unit, and the 90th percentile value of the cumulative fraction is D 90 (D when set to [μm]) 90 -D 10 ) / D 50 The value of is preferably 0.30 or more and 0.90 or less, more preferably 0.35 or more and 0.80 or less, and even more preferably 0.40 or more and 0.75 or less.

[0121] (D 90 -D 10 ) / D 50 This is an index that represents the uniformity of the particle size distribution, (D 90 -D 10 ) / D 50 A smaller value indicates a narrower particle size distribution, i.e., a more uniform particle size distribution.

[0122] As a result, the inorganic fine powder has a more uniform particle size, making it suitable for use in various applications.

[0123] Furthermore, in the method for producing inorganic fine powder according to the present invention, the number of coarse particles determined by the following measurements is preferably 30 or less, more preferably 15 or less, and even more preferably 5 or less.

[0124] This makes it possible to more effectively prevent various problems caused by the inclusion of coarse particles in inorganic fine powder.

[0125] The number of the above-mentioned coarse particles can be measured, for example, as follows. First, 1.0 g of inorganic fine powder is mixed with 20 mL of ethanol, and then treated for 1 minute using an ultrasonic cleaner (e.g., Honda Electronics Co., Ltd., W-113) to prepare a dispersion. 30 μL of this dispersion is weighed out and dropped onto an aluminum sample stage, and the dispersion medium is removed by drying to prepare a sample for measurement. This sample for measurement is observed using a scanning electron microscope (e.g., Hitachi High-Technologies Corporation, SU-1510) at 10,000x magnification for 50 fields of view. The volume-based cumulative 50% particle size D of the inorganic fine powder is then measured. 50 Determine the total number of particles with a particle size 1.5 times or larger, and define this number as the number of coarse particles.

[0126] [Uses of inorganic fine powders] The applications of the inorganic fine powder produced by the method of the present invention are not particularly limited, but for example, inorganic fine powder produced using conductive metal powder as the inorganic raw material powder can be used as a conductive powder.

[0127] Examples of constituent materials for conductive metal powder include silver, gold, platinum, copper, palladium, nickel, tungsten, zinc, tin, iron, cobalt, and alloys containing at least one of these materials. Two or more of the above materials may be used in combination as the conductive powder.

[0128] Conductive powders can be suitably used as conductive materials for electronic components. As conductive materials for electronic components, they are used to form conductive parts. While their applications are not particularly limited, they are especially suitable for forming internal conductors (internal electrodes) and terminal electrodes of multilayer ceramic electronic components such as multilayer ceramic capacitors, multilayer ceramic inductors, and multilayer piezoelectric actuators. Conductive powders used in such applications require particularly high reliability.

[0129] The conductive powder produced by the method of the present invention has a small average particle size, a narrow particle size distribution, and contains almost no coarse particles. Therefore, when the conductive powder is used as an internal electrode, an electrode layer of uniform thickness can be formed, and short circuits caused by the conductive powder particles contacting both sides of the internal electrode are effectively prevented. Thus, even in applications where particularly high reliability is required, a sufficiently satisfactory effect can be obtained. Accordingly, the effects of the present invention are more pronounced when the conductive powder produced by the method of the present invention is used to form internal conductors (internal electrodes) or terminal electrodes of multilayer ceramic electronic components such as multilayer ceramic capacitors, multilayer ceramic inductors, and multilayer piezoelectric actuators.

[0130] The conductive powder may be used, for example, as a conductive paste by mixing it with glass frit and an organic vehicle, for forming conductive parts of electronic components.

[0131] Although preferred embodiments of the present invention have been described above, the present invention is not limited to these.

[0132] For example, the apparatus used for the method of producing inorganic fine powder according to the present invention is not limited to those described in the embodiments above.

[0133] Furthermore, in the method for producing inorganic fine powder of the present invention, two or more methods from the first to third embodiments described above may be combined.

[0134] More specifically, for example, a carboxylic acid-adsorbed inorganic raw material powder, in which carboxylic acid is adsorbed onto an inorganic raw material powder beforehand, may be dispersed in the gas phase, and then carboxylic acid may be further added to the powder and adsorbed to obtain the powder to be classified. In other words, the method described in the first embodiment and the method described in the third embodiment may be combined.

[0135] Also, for example, D is in a dispersed state in the gas phase when it is formed. 50 In this method, an inorganic raw material powder of 10 μm or less is produced, and while the inorganic raw material powder is dispersed in the gas phase, a carboxylic acid is adsorbed onto the inorganic raw material powder to obtain a powder to be classified. After that, the classified powder is recovered, and additional carboxylic acid may be adsorbed onto the recovered powder. In this case, when additional carboxylic acid is adsorbed, the powder may be in a state where it is not dispersed in the gas phase, or it may be in a state where it is dispersed in the gas phase. That is, the method described in the second embodiment may be combined with the method described in the first embodiment, or the second embodiment and the third embodiment may be combined.

[0136] Furthermore, for example, the method described in the first embodiment, the method described in the second embodiment, and the method described in the third embodiment may be combined.

[0137] In these cases, the order of the corresponding combinations of methods in each embodiment (in particular, the order of the methods for adsorbing the carboxylic acid) is not particularly limited. [Examples]

[0138] The present invention will be described in more detail below with specific examples, but the present invention is not limited to the following examples. In the following description, processes for which temperature and humidity conditions are not specifically stated were performed at room temperature (25°C) and relative humidity 50%. Similarly, for various measurement conditions, unless specifically stated, the values ​​are for room temperature (25°C) and relative humidity 50%. Furthermore, the 10% cumulative fraction D value based on volume for inorganic raw material powder and inorganic fine powder is also included. 10 , cumulative fraction 50th percentile D 50, cumulative fraction 90th percentile D 90 This was determined by measurement using a laser diffraction / scattering particle size distribution analyzer LA-960 (manufactured by HORIBA Corporation). Furthermore, Table 1 summarizes the boiling points of the carboxylic acids used in each of the examples described below.

[0139] [Table 1]

[0140] [1] Production of inorganic fine powder

[0141] (Example 1) In this example, the method of the first embodiment described above was used to obtain a classifiable powder by dispersing the carboxylic acid-adsorbed inorganic raw material powder in the gas phase, thereby producing an inorganic fine powder. More details are as follows.

[0142] First, as an inorganic raw material powder, the cumulative 50% particle size D by volume 50 Nickel powder with a particle size of 0.31 μm was prepared.

[0143] This nickel powder was left to stand in an atmosphere containing acetic acid as a carboxylic acid to obtain acetic acid-adsorbed nickel powder. The acetic acid used was close to 100% purity (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade 99.7+%).

[0144] The obtained acetic acid-adsorbed nickel powder was fed at a rate of 10 kg per hour into the dry classifier shown in Figure 1, and the supply dispersion pressure was set to 0.6 MPa to disperse the acetic acid-adsorbed nickel powder and obtain the powder to be classified.

[0145] Next, the dispersed acetic acid-adsorbed nickel powder (the powder to be classified) is introduced into the classification chamber, and the temperature inside the classifier is set to 25°C and the suction airflow to 8.5 m³. 3 Dry classification was performed with a suction pressure set to -35kPa at a rate of / min to produce inorganic fine powder.

[0146] (Examples 2-5) Inorganic fine powder was produced in the same manner as in Example 1, except that a carboxylic acid shown in Table 2 was used instead of acetic acid.

[0147] (Example 6) In this example, the method of the second embodiment described above was used to obtain a classifiable powder by adsorbing carboxylic acid onto an inorganic raw material powder that was dispersed in the gas phase during production, thereby producing an inorganic fine powder. More details are as follows.

[0148] First, we prepared nickel acetate tetrahydrate powder. This nickel acetate tetrahydrate powder was sprayed and heated to 1500°C to obtain nickel powder as an inorganic raw material powder dispersed in the gas phase. With this nickel powder as an inorganic raw material powder dispersed in the gas phase, the gas phase was cooled to 500°C, and in this state, gaseous acetic acid was supplied to the gas phase to obtain acetic acid-adsorbed nickel powder as the powder to be classified. The amount of acetic acid added (used) was equal to the volume of the nickel raw material powder (1 m³). 3 120 mol was used for that.

[0149] The resulting nickel powder adsorbed with acetate, as the powder to be classified, was introduced into the dry classifier shown in Figure 1 at a rate of 10 kg per hour, with the internal temperature of the classifier set to 25°C and the suction airflow rate to 8.5 m³. 3 Dry classification was performed with a suction pressure of -35kPa at a rate of / min to produce inorganic fine powder.

[0150] (Example 7) In this example, the method of the third embodiment described above was used to obtain a classifiable powder by dispersing the inorganic raw material powder in an atmosphere containing a gaseous carboxylic acid, thereby producing an inorganic fine powder. More details are as follows.

[0151] First, as an inorganic raw material powder, the cumulative 50% particle size D by volume 50 A nickel powder of 0.48 μm was prepared.

[0152] While feeding 10 kg of nickel powder per hour into the dry classifier shown in Figure 1, acetic acid gas is also introduced into the dispersion zone of the nickel powder at a rate of 1 m³. 3 The nickel powder was supplied in an amount of 15 mol per unit, and the supply dispersion pressure was set to 0.6 MPa. Acetic acid was adsorbed onto the nickel powder while it was dispersed, and acetic acid-adsorbed nickel powder was obtained as the powder to be classified.

[0153] Next, the powder to be classified is introduced into the classification chamber, and the temperature inside the classifier is set to 25°C and the suction airflow to 8.0 m³. 3 Dry classification was performed with a suction pressure of -25kPa at a rate of / min to produce inorganic fine powder.

[0154] (Examples 8-14) Inorganic fine powder was produced in the same manner as in Example 7, except that the amount of acetic acid added was as shown in Table 4.

[0155] (Examples 15-18) Inorganic fine powder was produced in the same manner as in Example 10, except that the particle size of the inorganic raw material powder was as shown in Table 4, and the conditions for the dry classification process were as shown in Table 4.

[0156] (Example 19) As an inorganic raw material powder, the cumulative 50% particle size D is determined by volume. 50 Inorganic fine powder was produced in the same manner as in Example 1, except that 2.45 μm Cu powder was used and the conditions for the dry classification process were as shown in Table 5.

[0157] (Example 20) As an inorganic raw material powder, the cumulative 50% particle size D is determined by volume. 50 Inorganic fine powder was produced in the same manner as in Example 1, except that a 1.30 μm Ag-Pd alloy (Ag:Pd=7:3 (weight ratio)) powder was used and the conditions for the dry classification process were as shown in Table 5.

[0158] (Example 21) As an inorganic raw material powder, the cumulative 50% particle size D is determined by volume. 50Inorganic fine powder was produced in the same manner as in Example 1, except that a 2.24 μm BaO-SiO2 glass powder was used and the conditions for the dry classification process were as shown in Table 5.

[0159] (Example 22) As an inorganic raw material powder, the cumulative 50% particle size D is determined by volume. 50 Inorganic fine powder was produced in the same manner as in Example 1, except that 0.92 μm silica powder was used and the conditions for the dry classification process were as shown in Table 5.

[0160] (Comparative Example 1) An inorganic fine powder was produced in the same manner as in Example 1, except that a carboxylic acid was not used.

[0161] (Comparative Examples 2 and 3) Inorganic fine powder was produced in the same manner as in Example 1, except that the compounds shown in Table 2 were used instead of carboxylic acids.

[0162] (Comparative Example 4) Inorganic fine powder was produced in the same manner as in Example 7, except that a carboxylic acid was not used.

[0163] (Comparative Example 5) Inorganic fine powder was produced in the same manner as in Example 10, except that the compounds shown in Table 4 were used instead of carboxylic acids.

[0164] (Comparative Example 6) An inorganic fine powder was produced in the same manner as in Example 15, except that a carboxylic acid was not used.

[0165] (Comparative Example 7) An inorganic fine powder was produced in the same manner as in Example 19, except that a carboxylic acid was not used.

[0166] (Comparative Example 8) Inorganic fine powder was produced in the same manner as in Example 20, except that a carboxylic acid was not used.

[0167] (Comparative Example 9) Inorganic fine powder was produced in the same manner as in Example 21, except that a carboxylic acid was not used.

[0168] (Comparative Example 10) Inorganic fine powder was produced in the same manner as in Example 22, except that a carboxylic acid was not used.

[0169] [2] Evaluation [2-1] Yield For each of the above examples and comparative examples, the weight of the powder before classification (i.e., the weight of the powder to be classified) and the weight of the powder after classification (i.e., the weight of the inorganic fine powder) were measured, and the yield was calculated using the following formula. Yield (%) = (Weight of powder after classification / Weight of powder before classification) × 100

[0170] Furthermore, the inorganic fine powders of each of the above examples and comparative examples were subjected to further dry classification in the same manner as described above, that is, dry classification was performed a total of two times, and the yields at each stage were also determined.

[0171] [2-2] Evaluation of particle size distribution Using a laser diffraction / scattering particle size distribution analyzer LA-960 (manufactured by HORIBA), the particle size distribution of the inorganic raw material powder and the obtained inorganic fine powder was determined for each of the above examples and comparative examples, and from the results, the 10% cumulative fraction of the volume-based particle size distribution (D 10 )[μm], cumulative fraction 50th percentile (D 50 )[μm], cumulative fraction 90th percentile (D 90 The values ​​[μm] were calculated for each.

[0172] Furthermore, D obtained as described above 10 [μm], D 50 [μm], D 90 From the value of [μm], (D 90 -D 10 ) / D 50 The result was calculated.

[0173] [2-3] Evaluation of the number of coarse particles For each of the above examples and comparative examples, 20 mL of ethanol as a dispersion medium was mixed with 1 g of the powder after two-stage classification, and the mixture was treated for 1 minute using an ultrasonic cleaner (manufactured by Honda Electronics Co., Ltd., W-113) to prepare a dispersion liquid. 30 μL was weighed out from the prepared dispersion liquid, dropped onto an aluminum sample stage, and dried to remove the dispersion medium, thereby preparing a measurement sample. The above sample was magnified 10,000 times using a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, SU-1510), and 50 fields of view were observed. Particles having a particle size of 2.0 times or more of D 50 of the target inorganic fine powder obtained in the above [2-2] were regarded as coarse particles, and the number of coarse particles was determined.

[0174] These results are summarized in Tables 2 to 5 together with the manufacturing conditions of the inorganic fine powder and the like. In the tables, acetic acid is indicated as "AA", propionic acid as "PA", butyric acid as "BA", isobutyric acid as "IBA", oleic acid as "OA", ethanol as "EtOH", and isopropanol as "IPA". Also, in the tables, the unit of the numerical value of the suction air volume is [m 3 / min], and the unit of the numerical value of the suction pressure is [kPa]. Also, in Tables 3 and 4, the unit of the numerical value of the addition amount of carboxylic acid is [mol / 1 m 3 Ni]. Also, regarding the inorganic fine powder obtained in each of the above examples, by the method shown in the above [2-3], when the number of particles having a particle size of 3.0 times or more of the volume-based cumulative 50% particle size D 50 of each inorganic fine powder was determined, such particles were not contained in any of the examples.

[0175]

Table 2

[0176]

Table 3

[0177]

Table 4

[0178]

Table 5

[0179] As is clear from Tables 2 to 5, in each of the above embodiments, D 50 is in the range of 0.01 μm or more and 5.0 μm or less, and metal fine powder with an extremely small number of coarse particles could be suitably produced at a high yield.

Industrial Applicability

[0180] The method for producing inorganic fine powder of the present invention is a method for producing inorganic fine powder in which the volume-based cumulative 50% particle diameter D 50 is in the range of 0.01 μm or more and 5.0 μm or less. In the method, a carboxylic acid-adsorbed inorganic raw material powder in which carboxylic acid is adsorbed on an inorganic raw material powder with D 50 of 10 μm or less is dispersed in a gas phase to obtain a classified powder to be classified, and a dry classification step of dry-classifying the classified powder. Further, the method for producing inorganic fine powder of the present invention is a method for producing inorganic fine powder in which the volume-based cumulative 50% particle diameter D 50 is in the range of 0.01 μm or more and 5.0 μm or less. In the method, in a state where an inorganic raw material powder with D 50 of 10 μm or less that is in a dispersed state in a gas phase during generation is dispersed in the gas phase, carboxylic acid is adsorbed on the inorganic raw material powder to obtain a classified powder to be classified, and a dry classification step of dry-classifying the classified powder. Further, the method for producing inorganic fine powder of the present invention is a method for producing inorganic fine powder in which the volume-based cumulative 50% particle diameter D 50 is in the range of 0.01 μm or more and 5.0 μm or less. In the method, D 50The process comprises a gradable powder generation step of dispersing inorganic raw material powder of 10 μm or less to obtain a gradable powder to be classified, and a dry classification step of dry classifying the gradable powder, wherein the gradable powder generation step is carried out in an atmosphere containing a gaseous carboxylic acid. As a result, the number of coarse particles is extremely small, and the volume-based cumulative 50% particle size D 50 The present invention provides a method for producing inorganic fine powder with high productivity, in which inorganic fine powder having a particle size within the range of 0.01 μm to 5.0 μm. Therefore, the present invention has industrial applicability. [Explanation of Symbols]

[0181] 1...Classifier 3…Casing 4…Inlet 5...Air nozzle 6… Guide vanes 7…Fine powder outlet 8…Coarse powder outlet 10...Classification room (classification zone) 11…Distributed Zones

Claims

1. Volume-based cumulative 50% particle size D ５０ A method for producing inorganic fine powder having a particle size in the range of 0.01 μm or more and 5.0 μm or less, A monocarboxylic acid with a boiling point between 110°C and 200°C is in a gaseous state, D ５０ A process to produce a classifiable powder, in which the monocarboxylic acid is adsorbed onto an inorganic raw material powder of 10 μm or less, and the carboxylic acid-adsorbed inorganic raw material powder on which the monocarboxylic acid is adsorbed is dispersed in the gas phase to obtain a classifiable powder to be classified, The process includes a dry classification step for dry classifying the powder to be classified, A method for producing inorganic fine powder, characterized in that the inorganic component of the inorganic raw material powder is at least one selected from the group consisting of metals, metal oxides, glass, and oxide ceramics.

2. Volume-based cumulative 50% particle size D ５０ A method for producing inorganic fine powder having a particle size in the range of 0.01 μm or more and 5.0 μm or less, D is in a dispersed state in the gas phase when it is formed. ５０ A classifiable powder production step to obtain a classifiable powder to be classified, wherein an inorganic raw material powder with a particle size of 10 μm or less is dispersed in the gas phase, and a monocarboxylic acid having a boiling point of 110°C or more and 200°C or less is adsorbed onto the inorganic raw material powder in a gaseous state, The process includes a dry classification step for dry classifying the powder to be classified, A method for producing inorganic fine powder, characterized in that the inorganic component of the inorganic raw material powder is at least one selected from the group consisting of metals, metal oxides, glass, and oxide ceramics.

3. Between the powder to be classified generation step and the dry classification step, A recovery step for recovering the classified powder, A method for producing inorganic fine powder according to claim 2, comprising a dispersion step of dispersing the classified powder obtained in the recovery step in the gas phase.

4. Volume-based cumulative 50% particle size D ５０ A method for producing inorganic fine powder having a particle size in the range of 0.01 μm or more and 5.0 μm or less, D ５０ A process for producing a classifiable powder by dispersing inorganic raw material powder of 10 μm or less to obtain a classifiable powder, The process includes a dry classification step for dry classifying the powder to be classified, The aforementioned powder classification step is carried out in an atmosphere containing a gaseous monocarboxylic acid having a boiling point of 110°C or higher and 200°C or lower. A method for producing inorganic fine powder, characterized in that the inorganic component of the inorganic raw material powder is at least one selected from the group consisting of metals, metal oxides, glass, and oxide ceramics.

5. Volume of the inorganic raw material powder: 1 m³ ３ A method for producing inorganic fine powder according to any one of claims 2 to 4, wherein the monocarboxylic acid is used in a ratio of 30 mol to 960 mol.

6. A method for producing inorganic fine powder according to any one of claims 1 to 5, wherein the monocarboxylic acid is at least one selected from acetic acid, propionic acid, and butyric acid.

7. A method for producing inorganic fine powder according to any one of claims 1 to 6, wherein the dry classification step is performed in a gas phase at a temperature of 60°C or higher and 300°C or lower.

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