Spherical silver powder, method for producing spherical silver powder, device for producing spherical silver powder, and conductive paste

Abstract

The present invention provides a spherical silver powder capable of imparting excellent fine line printability when used in a conductive paste or the like. A spherical silver powder in which a cumulative 10% diameter D10, a cumulative 50% diameter D50, and a cumulative 90% diameter D90 on a volume basis by a laser diffraction method satisfy the formula: (D90-D10) / D50lt; and the ratio of the D50 to the BET diameter DBET (D50 / DBET) is from 0.90 to 1.20 (inclusive).

Description

Technical Field

[0001] The present invention relates to spherical silver powder, a method for producing spherical silver powder, a device for producing spherical silver powder and a conductive paste. Background Art

[0002] As a conductive paste used in the internal electrodes of multilayer capacitors, the conductor patterns of circuit boards, solar cells, or other electronic components, a conductive paste produced by adding silver powder and glass powder to an organic binder and kneading them is used. The silver powder for the conductive paste is required to have a moderately small particle size, uniform particle size, and high dispersibility in order to cope with the miniaturization of electronic components, the high density and thinning of conductor patterns, etc.

[0003] As a method for manufacturing silver powder for such a conductive paste, Patent Document 1 proposes a method for manufacturing microparticle silver powder, which is characterized in that an aqueous silver nitrate solution and an ammonia solution are mixed and reacted to obtain an aqueous silver ammonia complex solution, the aqueous solution is flowed into a certain flow path (first flow path), a second flow path is provided to merge with the first flow path in the middle, an organic reducing agent is flowed through the second flow path, and contact mixing is performed at the confluence point of the first flow path and the second flow path.

[0004] In addition, Patent Document 2 proposes a method for producing silver powder, characterized in that a silver solution containing a silver complex and a reducing agent solution are respectively quantitatively and continuously supplied into a flow path, and the silver complex is quantitatively and continuously reduced in a reaction solution formed by mixing the silver solution and the reducing agent solution in the flow path to obtain silver powder, wherein, when the silver solution and the reducing agent solution are mixed, the ratio of the flow rate of the reducing agent solution supplied from a coaxial pipe arranged in the pipe in the same direction as the supply direction of the silver solution to the flow rate of the silver solution in the pipe forming the flow path is set to be 1.5 or more.

[0005] In addition, Patent Document 3 proposes a method for producing spherical silver powder, which comprises mixing an aqueous silver nitrate solution and an ammonia solution and reacting them to obtain an aqueous silver ammonia complex solution, mixing the aqueous silver ammonia complex solution with an aqueous reducing agent solution in the presence of particles serving as seeds and an imide compound, and reducing and precipitating silver particles to produce a spherical silver powder, wherein the aqueous silver ammonia complex solution and the aqueous reducing agent solution are caused to flow into respective flow paths that merge at a confluence point, and at the confluence point, the aqueous silver ammonia complex solution and the aqueous reducing agent solution are contacted and mixed.

[0006] In addition, Patent Document 4 proposes a method for producing silver particles in which ammonia and a reducing agent are added to a silver ion solution to reduce and precipitate silver particles, and a reducing agent is added within 20 seconds after the addition of ammonia to precipitate fine silver particles, but the silver ion solution to which ammonia is added and the reducing solution are mixed on the outside of the pipeline.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2005-48236

[0010] Patent Document 2: Japanese Patent Application Publication No. 2015-45064

[0011] Patent Document 3: Japanese Patent Application Publication No. 2010-70793

[0012] Patent Document 4: Japanese Patent Application Publication No. 2008-255378 Summary of the invention

[0013] Problem that the invention aims to solve

[0014] When forming internal electrodes, conductor patterns, etc. using a conductive paste containing silver powder, it is required that the silver powder can be printed with a thinner line width than before when it is made into a paste, etc. The silver powder obtained by the production methods of Patent Documents 1 to 4 has room for improvement in these aspects.

[0015] An object of the present invention is to provide spherical silver powder that can provide excellent fine line printing properties when used in a conductive paste or the like, and a method and apparatus for producing the same.

[0016] Solutions for solving problems

[0017] The present inventors have conducted intensive research to solve the above problems. In order to obtain excellent fine line printing properties, the present inventors have found that the particle size distribution is controlled so that the cumulative 10% diameter D based on the volume basis of the laser diffraction method is 10 , cumulative 50% diameter D 50 and cumulative 90% diameter D 90 Satisfaction (D 90 -D 10 ) / D 50 <1, and the dispersion is controlled so that the cumulative 50% diameter D based on the volume basis of the laser diffraction method 50 Relative to BET diameter D BET The ratio (D 50 / D BET ) satisfies 0.9 or more and 1.2 or less, thereby completing the present invention.

[0018] BET diameter D BET The BET specific surface area SSA (unit: m) is determined by the BET single point method. 2 / g) and true density (in g / cm 3 ) is calculated by the following formula.

[0019] D BET =6 / (SSA) / true density

[0020] Here, D 10 , D 50 , D 90 , D BET , SSA and true density are values ​​measured by the method described in the Examples. They are measured values ​​before classification.

[0021] (D 90 -D 10 ) / D 50 It is an indicator of particle size distribution. A value less than 1 means that the particle size distribution of the spherical silver powder is sharp and the particle size is uniform.

[0022] However, in silver powder, individual particles are usually not completely separated, and sometimes a plurality of particles are aggregated. The particle size measurement based on the laser diffraction method calculates the particle size based on the diffraction pattern of the particles, and thus measures the particle size of the aggregated particles. On the other hand, the BET single point method is a method of measuring the specific surface area using the amount of gas adsorbed on the particles. The BET diameter converted from the specific surface area represents the particle size (particle diameter) of the particles when the measured particles are assumed to be true spheres. Ratio (D 50 / D BET ) close to 1 means that there is little aggregation and the state is close to monodisperse.

[0023] The present inventors have discovered that, in a method for producing spherical silver powder in which a silver complex solution is allowed to flow in a flow path, a reducing agent is added to the flow path at a reducing agent addition position in the middle of the flow path, and the silver powder is reduced and precipitated in the flow path, spherical silver powder having a uniform particle size and being in a state close to monodisperse can be obtained by adding the reducing agent from multiple directions relative to the flow path, thereby completing the present invention.

[0024] The gist of the present invention is as follows.

[0025] [1] A spherical silver powder having a cumulative 10% diameter D based on volume by laser diffraction method. 10 , cumulative 50% diameter D 50 and cumulative 90% diameter D 90 Satisfaction formula: (D 90 -D 10 ) / D 50 <1, and the D 50 Relative to BET diameter D BET The ratio is D 50 / D BET It is 0.90 or more and 1.20 or less.

[0026] [2] The spherical silver powder according to [1], wherein D 50It is not less than 0.2 μm and not more than 3.5 μm.

[0027] [3] The spherical silver powder of [1] or [2] above, having a BET specific surface area of ​​0.17 m 2 / g or more and 3.23m 2 / g or less.

[0028] [4] The spherical silver powder according to any one of [1] to [3] above, wherein the ratio (D 50 / D BET ) is greater than or equal to 0.95 and less than or equal to 1.05.

[0029] [5] The spherical silver powder according to any one of [1] to [4] above, wherein D BET It is not less than 0.18 μm and not more than 3.9 μm.

[0030] [6] A method for producing spherical silver powder, wherein a silver complex solution is caused to flow in a flow path, a reducing agent is added to the flow path at a reducing agent addition position in the middle of the flow path, and the silver powder is reduced and precipitated in the flow path, and the reducing agent is added from multiple directions relative to the flow path.

[0031] [7] The method for producing spherical silver powder according to [6] above, wherein the plurality of directions each form an angle of not less than 75 degrees and not more than 105 degrees with respect to the flow path.

[0032] [8] The method for producing spherical silver powder according to [6] or [7] above, wherein the reducing agent is added from all directions around the flow path.

[0033] [9] The method for producing spherical silver powder according to any one of [6] to [8] above, wherein the reducing agent is added to a silver complex solution containing a surface treatment agent.

[0034]

[10] A method for producing spherical silver powder as described in any one of [6] to [9] above, wherein the silver-containing solution and the complexing agent are mixed upstream of the reducing agent addition position in the flow path to generate the silver complex solution in the flow path.

[0035]

[11] A device for producing spherical silver powder, which is a device for producing spherical silver powder by adding a reducing agent to a silver complex solution to reduce and precipitate the silver powder, the device having a tube forming a flow path for the silver complex solution, a slit having an opening radially outward along its inner circumference provided on the tube, and a supply pipe for the reducing agent connected to the slit.

[0036]

[12] The spherical silver powder manufacturing device as described in

[11] above has a plurality of supply pipes for the reducing agent, and at least two supply pipes for the reducing agent are eccentrically connected to the slit.

[0037]

[13] A conductive paste comprising the spherical silver powder according to any one of [1] to [5] above, an organic binder and a solvent.

[0038]

[14] The conductive paste according to

[13] above, which is used for forming an electrode of a solar cell.

[0039] Effects of the Invention

[0040] According to the present invention, there are provided spherical silver powder capable of providing excellent printability when used in a conductive paste or the like, and a method and apparatus for producing the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a perspective view of the appearance of an example of the silver powder production device of the present invention.

[0042] Figure 2A This is a cross-sectional view perpendicular to the flow path of the silver complex solution at the center position of the reducing agent supply pipe of the reducing agent adding means of the silver powder production device of the present invention.

[0043] Figure 2B It is horizontal to the flow path of the silver complex solution. Figure 2A AA line cross-section diagram.

[0044] Figure 2C It is horizontal to the flow path of the silver complex solution. Figure 2A BB line cross-section diagram.

[0045] Figure 3 This is a perspective view of the appearance of another example of the silver powder production device of the present invention.

[0046] Figure 4 This is a SEM photograph of the silver powder of Example 1 (5000 times).

[0047] Figure 5 This is a SEM photograph of the silver powder of Example 2 (5000 times).

[0048] Figure 6 This is a SEM photograph of the silver powder of Example 3 (5000 times).

[0049] Figure 7 This is a SEM photograph of the silver powder of Example 4 (5000 times).

[0050] Figure 8 This is a SEM photograph of the silver powder of Comparative Example 1 (5000 times).

[0051] Fig. 9 The diagram shows the shape of an electrode pattern used for EL evaluation of fine line printability.

[0052] Fig.10 These are photographs showing the EL evaluation results of the conductive paste using the silver powder of Example 1.

[0053] Fig.11 These are photographs showing the EL evaluation results of the conductive paste using the silver powder of Example 2.

[0054] Fig.12 These are photographs showing the EL evaluation results of the conductive paste using the silver powder of Example 3.

[0055] Fig.13 These are photographs showing the EL evaluation results of the conductive paste using the silver powder of Example 4.

[0056] Fig.14 These are photographs showing the EL evaluation results of the conductive paste using the silver powder of Comparative Example 1. DETAILED DESCRIPTION

[0057] <Spherical silver powder>

[0058] The cumulative 10% diameter D of the spherical silver powder of the present invention based on the volume basis by the laser diffraction method is 10 , cumulative 50% diameter D 50 And the cumulative 90% diameter D90 satisfies the formula: (D 90 -D 10 ) / D 50 <1, and the D 50 Relative to BET diameter D BET The ratio (D 50 / D BET ) is 0.9 or more and 1.2 or less. Here, the spherical shape includes a substantially spherical shape and refers to a shape in which the average aspect ratio (average of the ratio of the major diameter / minor diameter) is 1.5 or less.

[0059] The spherical silver powder of the present invention has a (D 90 -D 10 ) / D 50 The value of is less than 1, preferably less than 0.96. The smaller the value, the sharper the width of the particle size distribution, the more uniform the particle size, and the better the printability. Theoretically, the lower limit is 0, but if it is greater than 0.75, a sufficient effect can be obtained.

[0060] From the viewpoint of ease of paste handling when preparing a conductive paste, D 50 It is preferably 0.2 μm or more, and more preferably 0.5 μm or more. In addition, D is advantageous in terms of low-temperature sintering of a wiring pattern formed using a conductive paste or the like and in terms of ease of handling high density. 50 It is preferably 3.5 μm or less, and more preferably 3.0 μm or less.

[0061] The ratio of the spherical silver powder of the present invention (D 50 / D BET ) is 0.90 or more and 1.20 or less, and from the viewpoint of obtaining more excellent dispersibility, it is preferably 0.95 or more and 1.05 or less, and more preferably 1.04 or less.

[0062] The BET specific surface area (SSA) is a specific surface area measured by the BET single point method, and is preferably 0.17 m2 from the viewpoints of being advantageous in low temperature sintering of a wiring pattern formed using a conductive paste or the like and being easy to cope with high density. 2 / g or more, more preferably 0.20m 2 / g or more. In addition, from the viewpoint of ease of handling of the conductive paste when it is prepared, it is preferably 3.23 m 2 / g or less, more preferably 2.40m 2 / g or less.

[0063] From the viewpoint of easily coping with the high density of the wiring pattern, the true density is preferably more than 9.0 g / cm 3 , more preferably 9.4 g / cm 3 In addition, from the viewpoint of low temperature sintering performance, the true density is preferably less than 10.45 g / cm 3 , more preferably 10.0 g / cm 3 Below, more preferably 9.9 g / cm 3 the following.

[0064] D BET The specific surface area (m 2 / g) and true density (g / cm 3 ), and the BET diameter (μm) was calculated by the following formula.

[0065] BET diameter = 6 / specific surface area / true density

[0066] D BET The diameter is preferably 0.18 μm or more, more preferably 0.45 μm or more, and is preferably 3.9 μm or less, more preferably 3.2 μm or less.

[0067] From the viewpoint of being easy to handle high-precision patterns, the tap density of the spherical silver powder of the present invention is preferably 2.5 g / cm 3 More preferably 4.5 g / cm 3 On the other hand, if the true density of silver and the closest packing of uniform spherical powder are taken into consideration, the upper limit of the tap density is 7.8 g / cm 3 .

[0068] <Method for producing spherical silver powder>

[0069] The method for producing spherical silver powder of the present invention is a method for producing spherical silver powder, wherein a silver complex solution is made to flow in a flow path, a reducing agent is added to the flow path at a reducing agent adding position in the middle of the flow path, and silver powder is reduced and precipitated in the flow path, wherein the reducing agent is added from multiple directions relative to the flow path. In the production method of the present invention, the speed of reduction and precipitation of silver powder can be kept constant by continuously supplying the silver complex solution and the reducing agent and quantitatively mixing them, and spherical silver powder can be quantitatively and continuously obtained.

[0070] In the method for producing spherical silver powder of the present invention, the reducing agent is added to the flow path from multiple directions relative to the flow path at the reducing agent adding position, thereby mixing the reducing agent with the silver complex solution. By adding the reducing agent to the silver complex solution from multiple directions at the flow path where the reducing agent is added (reducing agent adding position), the mixing efficiency of the reducing agent and the silver complex solution is improved, and the unreacted silver ions are reduced, thereby suppressing the generation of secondary nuclei by the unreacted silver ions. Therefore, it is inferred that it can be controlled as (D 90 -D 10 ) / D 50 and ratio (D 50 / D BET ) falls within the prescribed range. Even without classification, silver powder with a sharp width of particle size distribution can be obtained, thus simplifying the manufacturing process.

[0071] When the reducing agent is added from one direction relative to the flow path, it takes time for the reducing agent to reach the side opposite to the adding point, and the concentration of the reducing agent at the reducing agent adding position is biased, so such an effect cannot be obtained. The same reason cannot be achieved when a Y-tube or a T-tube is used to contact and mix the silver complex solution and the reducing agent at the confluence.

[0072] In addition, when the reducing agent is added at the center of the flow path using a coaxial double tube, since the reducing agent is added in parallel with the flow of the silver complex solution, it takes time for the silver complex solution and the reducing agent to mix. In addition, in the coaxial double tube, the flow velocity in the center of the tube is relatively fast, and the flow velocity near the wall is relatively slow, so the growth of particles tends to become uneven.

[0073] The reducing agent is preferably added in two or more directions relative to the flow path, more preferably in four or more directions, and particularly preferably added from all directions of the periphery of the flow path. Depending on the number and shape of the openings described later, the reducing agent can be added from multiple directions relative to the flow path.

[0074] It is preferred that the plurality of directions form an angle of 75 degrees or more and 105 degrees or less relative to the flow path. From the viewpoint of rapid mixing of the silver complex solution and the reducing agent, it is advantageous to add the reducing agent to the flow path substantially vertically. The angle relative to the flow path is more preferably 80 degrees or more and 100 degrees or less. The "relative to the flow path" can be alternatively said as "relative to the axial direction of the tube in which the silver complex solution flows".

[0075] In the manufacturing method of the present invention, the silver complex solution is not particularly limited as long as it is a solution that is reduced by a reducing agent to precipitate silver, and a silver ammonia complex solution is preferred. The silver ammonia complex solution can be prepared, for example, by dissolving silver chloride in ammonia water or mixing a silver nitrate aqueous solution with ammonia water.

[0076] A silver complex solution prepared separately may be allowed to flow in the flow path, or a silver-containing solution (e.g., silver nitrate aqueous solution, etc.) may be reacted with a complexing agent (e.g., ammonia water) upstream of the position where the reducing agent is added in the flow path to form a silver complex solution in the flow path. In the case where a silver complex solution is prepared outside the flow path, the stability of the complex at the time of reduction may vary depending on the time until the silver complex solution is supplied to the flow path. That is, when the time from the mixing of the silver-containing solution and the complexing agent to the addition of the reducing agent is too short, sometimes the complex is not fully complexed, and when it is too long, byproducts may be generated in the silver complex solution, so it is unstable. On the other hand, in the case of a silver complex solution prepared in the flow path, since the reducing agent is added after a certain period of time, the state of the complex at the time of reduction is constant, which is advantageous in controlling the shape of the spherical silver powder. For example, a silver-containing solution (e.g., silver nitrate aqueous solution, etc.) may be allowed to flow in the flow path, a complexing agent (e.g., ammonia water) may be supplied using a coaxial double-layer tube, and the two may be mixed and reacted to form a silver complex solution.

[0077] In the production method of the present invention, the reducing agent is not particularly limited, and hydrazine, ascorbic acid, hydroquinone, formalin (aqueous formaldehyde solution), etc. can be used. Formalin, hydrazine, etc. are preferred from the viewpoint of easy control of the reduction reaction.

[0078] From the viewpoint of ensuring sufficient reaction efficiency and leaving no unreacted silver complex, the amount of reducing agent added is preferably 1.1 equivalents or more, more preferably 1.2 equivalents or more, relative to silver. From the viewpoint of economic efficiency, it is preferably 25.0 equivalents or less, more preferably 20.0 equivalents or less, relative to silver.

[0079] Regarding the silver concentration of the silver complex solution, from the viewpoint of ensuring sufficient reaction efficiency, the silver concentration after mixing with the reducing agent is preferably 0.01 mol / L or more, more preferably 0.05 mol / L or more. In addition, from the viewpoint of strictly adjusting the particle size and particle size distribution of the silver powder precipitated by reduction, it is preferably 0.5 mol / L or less, more preferably 0.3 mol / L or less.

[0080] In the manufacturing method of the present invention, from the viewpoint of productivity, the flow rate of the silver complex solution before adding the reducing agent to the flow path is preferably 8 L / min or more, more preferably 12 L / min or more, and from the viewpoint of suppressing aggregation and forming monodisperse particles, it is preferably 275 L / min or less, more preferably 230 L / min or less.

[0081] The flow rate of the reducing agent when adding the reducing agent to the flow path is 0.5 times or more relative to the flow rate of the silver complex solution immediately before the reducing agent is added, and is preferably 2.5 times or less, more preferably 1.3 times or less, and further preferably 0.9 times or more and 1.1 times or less, from the viewpoint of suppressing the increase of the liquid flow to the pipe wall surface and the decrease of the mixing efficiency.

[0082] In the manufacturing method of the present invention, the reaction of the silver complex solution and the reducing agent in the presence of a surface treatment agent is advantageous in suppressing the aggregation of the silver powder precipitated by reduction. The surface treatment agent may be either pre-coated with the silver complex solution or pre-mixed with the reducing agent. Alternatively, in the case of forming the silver complex solution in the flow path using a silver-containing solution and a complexing agent, the surface treatment agent may be co-coated with the silver-containing solution or the like. The surface treatment agent may be added to the flow path upstream or downstream of the reducing agent addition position, and is preferably added upstream of the reducing agent addition position from the viewpoint of suppressing aggregation and forming monodisperse particles.

[0083] Examples of the surface treatment agent include fatty acids, fatty acid salts, surfactants, organic metals, chelate forming agents, protective colloids, etc. The surface treatment agent can be used in an amount of 0.03 mass % to 1.0 mass % based on the silver in the silver-containing solution.

[0084] (1) Fatty acids

[0085] Examples of the fatty acid include propionic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, acrylic acid, oleic acid, linoleic acid, arachidonic acid, ricinoleic acid, etc. The surface treatment agent can be used in the form of an emulsion, a solution, or the like.

[0086] (2) Fatty acid salts

[0087] Examples of the fatty acid salt include metal salts of the fatty acid described in (1) above, and examples of the metal include lithium, sodium, potassium, barium, magnesium, calcium, aluminum, iron, cobalt, manganese, lead, zinc, tin, strontium, zirconium, silver, and copper.

[0088] (3) Surfactants

[0089] Examples of the surfactant include anionic surfactants such as alkylbenzene sulfonates and polyoxyethylene alkyl ether phosphates, cationic surfactants such as aliphatic quaternary ammonium salts, amphoteric surfactants such as imidazoline betaine, and nonionic surfactants such as polyoxyethylene alkyl ethers and polyoxyethylene fatty acid esters.

[0090] (4) Organic metals

[0091] Examples of the organic metal include tributoxyzirconium acetylacetonate, magnesium citrate, diethyl zinc, dibutyl tin oxide, dimethyl zinc, tetra-n-butoxy zirconium, triethyl indium, triethyl gallium, trimethyl indium, trimethyl gallium, monobutyl tin oxide, tetraisocyanate silane, tetramethylsilane, tetramethoxysilane, monomethyl triisocyanate silane, silane coupling agents, titanate-based coupling agents, and aluminum-based coupling agents.

[0092] (5) Chelate Forming Agent

[0093] Examples of the chelate forming agent include imidazole, oxazole, thiazole, selenazole, pyrazole, isoxazole, isothiazole, 1H-1,2,3-triazole, 2H-1,2,3-triazole, 1H-1,2,4-triazole, 4H-1,2,4-triazole, 1,2,3-oxadiazole, 1,2,4-oxadiazole, 1,2,5-oxadiazole, 1,3,4-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiadiazole, 1,2,5 -thiadiazole, 1,3,4-thiadiazole, 1H-1,2,3,4-tetrazole, 1,2,3,4-oxatriazole, 1,2,3,4-thiatriazole, 2H-1,2,3,4-tetrazole, 1,2,3,5-oxatriazole, 1,2,3,5-thiatriazole, indazole, benzimidazole, benzotriazole, etc., and salts of these chelate formers, polycarboxylic acids represented by dicarboxylic acids such as succinic acid, malonic acid, glutaric acid, and adipic acid, etc.

[0094] (6) Protective colloid

[0095] Examples of the protective colloid include peptides, gelatin, albumin, gum arabic, ovalbumin, gelatin, and glue.

[0096] As the surface treatment agent, from the viewpoint of the ease of modifying the silver particle surface, (1) fatty acids are preferred, and among them, stearic acid is preferred. (1) The fatty acid is preferably in the form of an emulsion, and examples thereof include stearic acid emulsions.

[0097] In the production method of the present invention, the temperature of the liquid flowing in the flow path is preferably 5°C or higher, more preferably 15°C or higher from the viewpoint of the reduction reaction, and is preferably 60°C or lower, more preferably 50°C or lower in terms of operation.

[0098] In the production method of the present invention, a mixer may be used to impart a spiral rotation in the axial direction of the flow path to mix the liquids.

[0099] In the production method of the present invention, spherical silver powder can be obtained by releasing the liquid containing the silver powder precipitated by reduction (hereinafter also referred to as "silver powder containing liquid") to the outside of the flow path and recovering it. From the viewpoint of being able to predict the end of the reduction reaction, the time from the reducing agent addition position to the outlet of the silver powder containing liquid is preferably 1 second or more, more preferably 2 seconds or more, and from the viewpoint of suppressing retention in the piping, it is preferably 10 seconds or less, more preferably 5 seconds or less.

[0100] The silver powder-containing liquid discharged to the outside of the flow channel was filtered and washed with water to obtain a block-like filter cake containing silver powder and water and having almost no fluidity.

[0101] The filter cake is dried using a forced circulation air dryer, a vacuum dryer, an airflow dryer, or the like to obtain the spherical silver powder of the present invention. Drying can be accelerated by replacing the water in the filter cake with a lower alcohol or the like.

[0102] The filter cake may be subjected to dry crushing treatment, surface smoothing treatment, etc. The surface smoothing treatment may be performed by mechanically colliding particles with each other using a high-speed stirrer.

[0103] Then, aggregates of silver powder having a particle size larger than a predetermined size may be removed by classification treatment.

[0104] Furthermore, the cake may be dried, crushed, and classified using an integrated device capable of drying, crushing, and classifying (DryMysta and MICRON dryers manufactured by HosokawaMicron Corporation, etc.).

[0105] <Silver powder manufacturing device>

[0106] In the production method of the present invention, the device used is not particularly limited as long as the reducing agent can be added from multiple directions relative to the flow path. For example, it is advantageous to use the following silver powder production device: a tube having a flow path for forming a silver complex solution, with openings provided at two or more locations on the tube or around the entire circumference of the tube, and the openings are connected to a supply pipe for the reducing agent. Figure 1 and Figure 2A to Figure 2C , an example of such a silver powder manufacturing apparatus is described.

[0107] Figure 1This is an external perspective view of an example of the silver powder production device of the present invention, which includes a pipe 2 for flowing a silver complex solution, reducing agent supply pipes 4a and 4b for supplying a reducing agent, and a reducing agent adding member 10.

[0108] Figure 2A yes Figure 1 A cross-sectional view perpendicular to the flow path of the silver complex solution at the center position of the reducing agent supply pipes 4a and 4b of the reducing agent adding member 10. Figure 2B is a cross-sectional view in the horizontal direction of the flow path of the silver complex solution, Figure 2A AA line cross-section diagram. Figure 2C is a cross-sectional view in the horizontal direction of the flow path of the silver complex solution, Figure 2A BB line cross-section diagram.

[0109] Figure 2A In the embodiment, there is a gap 13 along the outer periphery of the tube 2 which becomes the flow path of the silver complex solution, and the gap 13 is connected to the inside of the reducing agent supply tubes 4a and 4b. Figure 2A BB line cross section Figure 2C As shown, the downstream side of the flow path of the silver complex solution in the gap 13 is connected to the slit portion 12 having an opening 11 extending radially outward along the inner circumference of the tube 2. Figure 2A AA line cross section Figure 2B As shown, when the reducing agent flows into the gap 13 from the reducing agent supply pipes 4a and 4b, the reducing agent reaches the slit portion 12 through the gap 13, and the reducing agent enters the tube 2 from the opening 11 of the slit portion 12 substantially perpendicularly (for example, 75 degrees or more and 105 degrees or less) to the entire circumference of the tube 2, and is added to the silver complex solution. Here, the angle at which the reducing agent enters the flow path of the silver complex solution is the angle at which the axial direction of the tube 2 intersects with the opening direction of the opening 11 into the reducing agent entering the tube 2. Figure 2B As shown, the opening direction can be regarded as a direction along the wall surface near the opening of the slit portion 12 .

[0110] The flow rate of the reducing agent when adding the reducing agent to the flow path of the silver complex solution can be controlled by the flow rate of the reducing agent flowing into the reducing agent supply pipes 4a and 4b and the size of the total area of ​​the openings 11. By controlling the flow rate of the reducing agent within the above range, the reaction between the silver complex and the reducing agent can be rapidly performed, thereby obtaining a silver powder with a sharp width of particle size distribution.

[0111] Will Figure 2B and Figure 2CThe width of the opening 11 of the slit portion 12 in the embodiment is referred to as the slit width. In order to reduce the total area of ​​the opening 11, the slit width is preferably narrower than the diameter of the reducing agent supply pipe. The shape of the gap 13 and the slit portion 12 that can add the reducing agent from multiple directions relative to the flow path and can form a slit width narrower than the diameter of the reducing agent supply pipe are not limited to Figure 2A to Figure 2C In addition, the opening 11 of the slit portion 12 is not provided on the entire circumference of the tube 2 but is provided as a plurality of through holes, etc., which can also be modified.

[0112] There may be at least one reducing agent supply pipe for flowing reducing agent into the reducing agent adding member 10, and preferably at least two reducing agent supply pipes. When there are at least two reducing agent supply pipes, the flow paths of reducing agent connected from the reducing agent supply pipes to the opening 11 may be opposite or eccentric. Figure 2A to Figure 2C In the embodiment, the reducing agent supply pipes 4a and 4b are connected eccentrically with respect to the center of the pipe 2, and the flow paths of the reducing agent supply pipes 4a and 4b are connected to the slit portion 12 having the opening 11. When a plurality of reducing agent supply pipes are connected, if at least two reducing agent supply pipes are eccentric to each other, the reducing agent can be flowed into the opening 11 of the slit portion 12 while the outer circumference of the flow path (pipe 2) of the silver complex solution is rotated in one direction.

[0113] When the reducing agent rotates on the periphery of the flow path of the silver complex solution, the flow rate of the reducing agent toward the opening 11 can be adjusted by changing the cross-sectional area of ​​the flow path of the reducing agent (the gap 13 or the slit portion 12 ).

[0114] exist Figure 1 In the embodiment, the silver complex solution is supplied to tube 2, but it is also possible to replace it, such as Figure 3 As shown, a coaxial double-layer tube is provided with a coaxial complexing agent supply tube 6 for supplying a complexing agent to the inner side of the tube 2 on the upstream side of the reducing agent adding member 10 of the tube 2, a silver-containing solution is supplied from the tube 2 as the outer pipeline, and a complexing agent is supplied from the complexing agent supply tube 6 as the inner pipeline, and the two are mixed and reacted to form a silver complex solution.

[0115] In addition, Figure 1 and 3 In the embodiment, a surface treatment agent supply pipe 5 for an arbitrary surface treatment agent is provided on the upstream side of the reducing agent adding member 10 of the pipe 2. The surface treatment agent supply pipe 5 is preferably provided on the upstream side rather than being provided on the downstream side of the reducing agent adding member 10. By providing it on the upstream side, the reducing agent can be added to the silver complex solution containing the surface treatment agent. As a result, the width of the particle size distribution of the obtained silver powder can be made sharper.

[0116] <Conductive paste>

[0117] The spherical silver powder of the present invention can provide a conductive paste having excellent printability and low-temperature sintering properties, and is suitable as a conductive paste used for internal electrodes of multilayer capacitors, conductor patterns of circuit boards, solar cells, electrodes of other electronic components, circuits, and the like.

[0118] The conductive paste of the present invention may contain the spherical silver powder of the present invention, an organic binder, and a solvent.

[0119] The organic binder is not particularly limited, and examples thereof include silicone resins, epoxy resins, acrylic resins, polyester resins, polyimide resins, polyurethane resins, phenoxy resins, cellulose resins (ethyl cellulose, hydroxypropyl cellulose, etc.), etc. They may be used alone or in combination of two or more in any ratio.

[0120] The solvent is not particularly limited, and examples thereof include alcohol solvents such as terpineol, butyl carbitol, Texanol, ethylene glycol, diethylene glycol, and glycerol; ester solvents such as butyl carbitol acetate and ethyl acetate; hydrocarbon solvents such as toluene, xylene, and cyclohexane, etc. These may be used alone or in combination of two or more in any ratio.

[0121] The content of the spherical silver powder of the present invention in the conductive paste can be 80% by mass or more, preferably 85% by mass or more, and can be 95% by mass or less, preferably 90% by mass or less.

[0122] The content of the organic binder in the conductive paste can be 0.1% by mass or more, preferably 0.2% by mass or more, and can be 0.4% by mass or less, preferably 0.3% by mass or less.

[0123] The content of the solvent in the conductive paste can be 6% by mass or more, preferably 7% by mass or more, and can be less than 20% by mass, preferably 15% by mass or less.

[0124] The conductive paste may contain glass powder, a dispersant, a surfactant, a viscosity modifier, a lubricant, etc. as optional components. The conductive paste used in the manufacture of the electrode of the solar cell preferably contains glass powder, for example, glass powders of Pb-Te-Bi system, Pb-Si-B system, etc. are mentioned.

[0125] The method for producing the conductive paste is not particularly limited, and examples thereof include a method of mixing the spherical silver powder of the present invention, an organic binder, a solvent, and optional components as appropriate. The mixing method is not particularly limited, and examples thereof include a self-rotating revolution mixer, an ultrasonic disperser, a disperser, a three-roll mill, a ball mill, a bead mill, a biaxial kneader, and the like.

[0126] The conductive paste of the present invention can be coated on a substrate, for example, by printing such as screen printing, offset printing, photolithography, or dipping such as impregnation, to form a coating film. The coating film can also be made into a specified pattern shape by photolithography using a resist or the like.

[0127] The coating film can be fired to form a conductive film. The firing can be carried out in an atmospheric atmosphere or in a non-oxidizing atmosphere such as nitrogen.

[0128] The firing temperature of the coating film can be set to 600 °C or higher and 800 °C or lower, preferably 690 °C or higher and 760 °C or lower. The firing time can be set to 20 seconds or longer and 1 hour or shorter. It is preferably 40 seconds or longer, and preferably 20 minutes or shorter, more preferably 2 minutes or shorter.

[0129] The conductive paste of the present invention can be suitably used for forming internal electrodes of multilayer capacitors, conductor patterns of circuit boards, solar cells, electrodes of other electronic components, and circuits.

[0130] Examples

[0131] Hereinafter, examples of the present invention will be described, but the present invention is not limited by the examples.

[0132] [Evaluation of silver powder]

[0133] The silver powder in the examples and comparative examples was evaluated as follows.

[0134] <True density>

[0135] Using a dry automatic densitometer (manufactured by Micromeritics, device name: Occupy (Accupyc) II 1340), the true density was measured by the constant volume expansion method ("gas pycnometer method" in the Japanese Pharmacopoeia).

[0136] <BET specific surface area>

[0137] The BET specific surface area was measured using a fully automatic specific surface area measuring device (manufactured by Mountech, device name: Macsorb HM-model 1210). The silver powder was placed in the device, and a He-N 2 mixed gas (30% nitrogen) was circulated at 60 °C for 10 minutes. After degassing, the measurement was carried out by the BET single-point method.

[0138] <D 10 、D 50 、D 90 >

[0139] D 10 、D 50 、D 90The measurement was performed by laser diffraction wet sample measurement using a Microtrac particle size distribution measuring device (manufactured by Microtrac BEL Co., Ltd., device name: MT-3300EXII). During the measurement, 0.1 g of the sample (silver powder) was added to 40 mL of isopropyl alcohol (IPA) for dispersion. An ultrasonic homogenizer (manufactured by Nippon Seiki Manufacturing Co., Ltd., device name: US-150T; 19.5 kHz, tip diameter 18 mm) was used for dispersion. The dispersion time was set to 2 minutes. The dispersed sample was supplied to the above-mentioned device, and the particle size distribution was obtained using the attached analysis software.

[0140] <Tap density>

[0141] The tap density (TAP) is the value obtained using a tap density measuring device (manufactured by Shibayama Scientific Co., Ltd., Casa specific gravity measuring device SS-DA-2). The tap density is measured as follows. 30 g of silver powder is weighed and placed in a 20 mL test tube, and tapped 1000 times with a drop of 20 mm. Then, the sample volume (cm 3 ). Tap density (g / cm 3 ) is obtained by the following formula.

[0142] Tap density (g / cm 3 )=30(g) / volume of sample after impact(cm 3 )

[0143] [Production of silver powder]

[0144] The silver powders of Examples and Comparative Examples were prepared as follows.

[0145] <Example 1>

[0146] use Figure 3 and Figure 2A to Figure 2C The apparatus shown produces silver powder.

[0147] A 0.13 mol / L silver nitrate aqueous solution is introduced into tube 2 (inner diameter 20 mm) at a liquid temperature of 22°C at a flow rate of 25.1 L / min, and a 9.2 mass % ammonia aqueous solution is introduced from supply tube 6 (inner diameter 6 mm) which is a coaxial double-layer tube at a flow rate of 2.69 L / min to generate a silver-ammine complex in tube 2.

[0148] A surface treatment agent (0.18 mass % SELOSOL 920 (manufactured by Chukyo Yushi Co., Ltd., containing 15.5 wt % stearic acid) was introduced from the supply pipe 5 (inner diameter 6 mm) upstream of the reducing agent adding means 10 at a flow rate of 2.19 L / min. The amount of the silver nitrate aqueous solution was such that the silver concentration in the total liquid volume after adding the complexing agent / formalin / surface treatment agent became 0.1 mol / L. The amount of stearic acid added relative to silver (target value) was 0.18 mass %.

[0149] Formalin (19.8 mass % formaldehyde aqueous solution) was introduced at a flow rate of 2.55 L / min from the entire circumference of the slit portion (slit width 0.44 mm, tube inner diameter 20.6 mm) of the reducing agent adding member 10 to precipitate silver powder. The flow rate of the reducing agent entering from the slit portion with a slit width of 0.44 mm was 1.49 m / s, the flow rate of the silver ammonia complex immediately before the reducing agent was added at the position where the reducing agent entered at the inner diameter of the tube 2 of 20.6 mm was 1.50 m / s, and the ratio of the flow rate of the complex to the flow rate of the reducing agent (complex flow rate / reducing agent flow rate) was 1.01.

[0150] The operation time of the silver powder production apparatus (the time from the start to the stop of introduction of the reducing agent into the silver ammine complex after the flow of the silver ammine complex into which the surface treatment agent was introduced became stable) was set to 37 seconds.

[0151] In the above, the time from the flow path inlet of the silver nitrate aqueous solution to the ammonia aqueous solution addition position is 1 second, the time from the ammonia aqueous solution addition position to the formalin addition position is 2.12 seconds (2.1m), the time from the surface treatment agent addition position to the formalin addition position is 0.123 seconds, and the temperature of the silver ammonia complex solution immediately before the formalin addition position is 27.8°C.

[0152] The slurry containing silver powder was discharged from tube 2. The time from the formalin addition position to the discharge was about 2 seconds. The slurry containing silver powder after the reduction reaction was stabilized was recovered, and the solid obtained by solid-liquid separation was washed with pure water to remove impurities in the solid. The end point of the washing can be judged by the conductivity of the water after washing. The washing was carried out until the conductivity reached 0.5mS / m or less, and 217g of silver powder was obtained.

[0153] Other preparation conditions and evaluation results are shown in Tables 1 and 2. SEM photographs (5000 times) are shown in Figure 4 .

[0154] <Examples 2 to 4>

[0155] Silver powder was prepared in the same manner as in Example 1 except that the conditions were changed to those shown in Table 1. In Examples 3 and 4, a mixer was used. The operation time of the silver powder production apparatus in Examples 2, 3, and 4 was set to 33 seconds, 43 seconds, and 870 seconds, respectively. The silver powders obtained were 193 g, 126 g, and 5091 g, respectively.

[0156] The evaluation results of Examples 2 to 4 are shown in Table 2. In addition, SEM photographs (5000 times) of the silver powders of Examples 2 to 4 are shown in Figures 5 to 7 .

[0157] <Comparative Example 1>

[0158] replace Figure 3 The reducing agent adding member 10 of the silver powder manufacturing device is arranged on the inner side of the tube 2 and is provided with a coaxial double-layer tube having a coaxial supply tube (inner diameter 6 mm) for supplying formalin. Formalin (19.8% by mass formaldehyde aqueous solution) is introduced at a flow rate of 2.55 L / min to precipitate the silver powder. The operation time of the silver powder manufacturing device is 47 seconds. Other than this, it is the same as in Example 1, or as shown in Table 1. The obtained silver powder is 275 g. The evaluation results are shown in Table 2. The SEM photograph (5000 times) of the silver powder of Comparative Example 1 is shown in Figure 8 .

[0159] [Table 1]

[0160]

[0161] [Table 2]

[0162]

[0163] [Preparation of conductive paste]

[0164] Conductive pastes were prepared as follows using the silver powders of Examples and Comparative Examples.

[0165] The following treatments were performed to obtain conductive pastes using the silver powder of Examples and Comparative Examples at the composition ratios shown in Table 3. The mixture was stirred and mixed at 1400 rpm for 30 seconds using a propeller-free self-rotating and revolving stirring and degassing device (AR310 manufactured by THINKY), and then kneaded using a three-roll mill (80S manufactured by EXAKT) to pass through the roll gap from 100 μm to 20 μm.

[0166] [Table 3]

[0167]

[0168] * NAMLON206T manufactured by Kusumoto Chemicals Co., Ltd.

[0169] ** Shin-Etsu Chemical Co., Ltd. KF96-10C

[0170] [Evaluation of thin line printability]

[0171] The thin line evaluation (EL) is performed by forming a conductive pattern. The conductive pattern is formed as follows. First, a screen printer (Microtec, MT-320TV) is used on a silicon substrate for solar cells (100Ω / □) to form a 154mm solid pattern on the back of the substrate using aluminum paste (Rutech, 28D22G-2). Next, the conductive paste prepared using the silver powder of the embodiment and the comparative example is filtered through 500 mesh and then filtered on the surface of the substrate. Fig. 9 The pattern shown is printed (coated) with electrodes (finger electrodes) with a line width of 14μm-26μm and electrodes (busbar electrodes) with a width of 1mm at a scraper speed of 350mm / sec. After hot air drying at 200°C for 10 minutes, a high-speed sintering furnace IR furnace (manufactured by Nippon Insulator Co., Ltd., high-speed sintering test 4-chamber furnace) is used to perform sintering at a peak temperature of 750°C and an in-and-out time of 41 seconds to obtain a conductive pattern.

[0172] After obtaining the conductive pattern, an EL / PL evaluation device (PVX330+POPLI-3C manufactured by ITES Co., Ltd.) was used to check whether the electrode was broken. It should be noted that in the EL / PL evaluation device, a current was passed through the busbar electrode to perform EL (electroluminescence) evaluation. If there is a break in the electrode (finger electrode) between the busbar electrodes, the position where the break occurs does not emit light and appears black. Figure 10 to Figure 14 The EL evaluation results of the conductive paste using the silver powder of Examples 1 to 4 and Comparative Example 1 are shown. In the conductive paste using the silver powder of the comparative example, the results showed that the thinner the line width, the more black parts that did not emit light due to broken lines, and it was found that the conductive paste using the silver powder of the example can be printed with fine lines. Even when the peak temperature during firing was reduced from 750°C to 710°C and 690°C, light emission was observed in the thin line width parts as at 750°C, and luminous fine line printing was possible.

[0173] Industrial Applicability

[0174] According to the present invention, there are provided spherical silver powder capable of providing excellent printability when used in a conductive paste or the like, and a method and apparatus for producing the same.

[0175] Description of Reference Numerals

[0176] 1 Silver powder manufacturing device

[0177] 2 tubes

[0178] 4a Reducing agent supply pipe

[0179] 4b Reducing agent supply pipe

[0180] 5 Surface treatment agent supply pipe

[0181] 6 Complexing agent supply pipe

[0182] 10 Reducing agent adding component

[0183] 11 Opening

[0184] 12 Slit

[0185] 13 Gap

Claims

1. A spherical silver powder having a cumulative 10% diameter D based on volume by laser diffraction method. 10 , cumulative 50% diameter D 50 and cumulative 90% diameter D 90 Satisfaction formula: (D 90 -D 10 ) / D 50 <1, And the D 50 Relative to BET diameter D BET The ratio is D 50 / D BET It is 0.90 or more and 1.20 or less.

2. The spherical silver powder according to claim 1, wherein The D 50 It is not less than 0.2 μm and not more than 3.5 μm.

3. The spherical silver powder according to claim 1, wherein the BET specific surface area is 0.17 m 2 / g or more and 3.23m 2 / g or less.

4. The spherical silver powder according to claim 1, wherein The ratio D 50 / D BET It is 0.95 or more and 1.05 or less.

5. The spherical silver powder according to claim 1, wherein The D BET It is not less than 0.18 μm and not more than 3.9 μm.

6. A method for producing spherical silver powder, wherein: The silver complex solution is made to flow in the flow channel, and the reducing agent is added to the flow channel at a reducing agent adding position in the middle of the flow channel to reduce and precipitate the silver powder in the flow channel, and the reducing agent is added from multiple directions relative to the flow channel.

7. The method for producing spherical silver powder according to claim 6, wherein: The plurality of directions each form an angle of not less than 75 degrees and not more than 105 degrees with respect to the flow path.

8. The method for producing spherical silver powder according to claim 6, wherein: The reducing agent is added from all directions of the periphery of the flow path.

9. The method for producing spherical silver powder according to claim 6, wherein: The reducing agent is added to the silver complex solution containing the surface treating agent.

10. The method for producing spherical silver powder according to any one of claims 6 to 9, wherein: The silver-containing solution and the complexing agent are mixed upstream of the reducing agent addition location in the flow path to generate the silver complex solution in the flow path.

11. A device for producing spherical silver powder, which is a device for producing spherical silver powder, wherein a reducing agent is added to a silver complex solution to reduce and precipitate the silver powder, the device having a tube forming a flow path for the silver complex solution, a slit having an opening radially outward along its inner circumference provided on the tube, and a supply pipe for the reducing agent connected to the slit.

12. The spherical silver powder manufacturing device according to claim 11, comprising a plurality of supply pipes for the reducing agent, wherein at least two supply pipes for the reducing agent are connected to the slit eccentrically to each other. 13 . A conductive paste comprising the spherical silver powder according to claim 1 , an organic binder, and a solvent. The conductive paste according to claim 13 , which is used to form an electrode of a solar cell.

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