Method for producing spherical aggregates of silver particles

Abstract

[Problem] To provide a method for producing spherical aggregates of silver particles, the method enabling easy production of aggregates in which silver nanoparticles are spherically aggregated. The produced spherical aggregates of the silver nanoparticles have excellent dispersibility and excellent handling properties, exhibit electrical conductivity when sintered at low temperatures, and are suitable for use as a conductive filler. [Solution] A method for producing spherical aggregates of silver particles by adding one or more additives selected from the group A described below to a silver compound solution and a reducing agent solution. Group A: citric acid, citric acid anhydride, a citrate, trimellitic acid, trimellitic acid anhydride, and a trimellitate.

Description

Method for Producing Spherical Aggregates of Silver Particles

[0001] The present invention relates to a method for producing spherical aggregates of silver particles. Specifically, according to the production method of the present invention, aggregates in which nano silver particles are aggregated into spherical shapes can be produced by a simple method. The spherical aggregates of silver particles produced by the present invention are excellent in dispersibility, have excellent handling properties, sinter at low temperatures to exhibit conductivity, and are a method for producing spherical aggregates of silver particles that can be suitably used as a conductive filler.

[0002] Silver particles are increasingly being used as fillers for conductive pastes (hereinafter referred to as "conductive fillers") used to form electrodes, circuits, etc.

[0003] In recent years, as a result of the progress of fine line formation of electrodes and circuits in the above applications, monodisperse spherical fine silver particles having the characteristics of a small particle diameter, a sharp particle size distribution, and high dispersibility have been demanded.

[0004] However, the production of monodisperse spherical fine silver particles having a small particle diameter, a sharp particle size distribution, and high dispersibility has problems such as requiring special processes such as two-stage reduction or using nuclear particles, or requiring a device for causing air collisions.

[0005] In addition, there is a problem that the produced monodisperse spherical fine silver particles are difficult to separate and recover and have poor handling properties.

[0006] Therefore, the development of monodisperse spherical fine silver particles that can be produced by a simple method and have excellent handling properties is desired.

[0007] Japanese Patent Application Laid-Open No. 2005-048237, Japanese Patent Application Laid-Open No. 2015-129352, Japanese Patent Application Laid-Open No. 2006-225760

[0008] Patent Document 1 describes a method for producing silver particles that are fine particles and have excellent dispersibility by bringing an organic reducing agent into contact and mixing with an aqueous solution of a silver ammine complex and maintaining the silver concentration and the organic reducing agent concentration within a certain range in the mixed solution to reduce and precipitate the silver particles.

[0009] However, the manufacturing method described in Patent Document 1 requires reduction in two paths, and the resulting silver particles are very fine, making them difficult to separate and recover, and resulting in poor handling.

[0010] Patent Document 2 describes a method for producing silver particles that have a small particle size, a sharp particle size distribution, and excellent dispersibility, without generating aggregated silver particles, by bringing an aqueous solution of silver ammine complex and an aqueous solution of a reducing agent into contact and mixing them in air to reduce and precipitate silver particles, thereby avoiding the phenomenon of the produced silver particles adhering to the flow channel wall.

[0011] However, the method described in Patent Document 2 requires special equipment for contact mixing in the air, and the manufactured silver particles are very fine, making them difficult to separate and recover, and resulting in poor handling.

[0012] Patent Document 3 describes a method for producing silver particles by reacting a silver compound solution with a reducing agent solution in the presence of at least one of the group consisting of aliphatic unsaturated dicarboxylic acids, their anhydrides, and their salts.

[0013] The method described in Patent Document 3 can produce spherical silver particles, but it has the problem that the average particle size is large, ranging from 0.5 μm to 5 μm, making it impossible to produce fine silver particles.

[0014] The inventors of the present invention considered solving the aforementioned problems as a technical challenge and, as a result of diligent experiments, have found a remarkable finding that a method for producing spherical aggregates of silver particles by adding one or more additives selected from citric acid, citrate anhydride, citrate salt, trimellitic acid, trimellitic anhydride, and trimellitic salt is a simple method for producing aggregates in which nano-silver particles are aggregated into a spherical shape. Furthermore, the produced spherical aggregates have excellent dispersibility and handling properties, and since conductivity is exhibited upon sintering at low temperatures, spherical aggregates of silver particles can be produced that are suitable for use as conductive fillers. This has thus solved the aforementioned technical challenges.

[0015] The aforementioned technical problems can be solved by the present invention as follows.

[0016] The present invention relates to a method for producing spherical aggregates of silver particles by adding one or more additives selected from the following group A to a silver compound solution and a reducing agent solution. Group A: citric acid, citrate anhydride, citrate salt, trimellitic acid, trimellitic anhydride, trimellitic salt

[0017] Furthermore, the present invention relates to a method for producing the aforementioned spherical aggregate of silver particles, wherein the amount of the additive added is 3.0 parts by weight or more and 25.0 parts by weight or less, relative to 100 parts by weight of silver contained in the silver compound solution.

[0018] Furthermore, the present invention relates to a method for producing the aforementioned spherical aggregate of silver particles, wherein the BET diameter of the silver particles constituting the spherical aggregate of silver particles is 100 nm or more and 285 nm or less.

[0019] Furthermore, the present invention provides that the silver particle spherical aggregate has a particle diameter of 1.0 μm or more and 10.0 μm or less at D50% as measured by laser diffraction particle size measurement, and a specific surface area of ​​2.0 m² as measured by BET. ２ / g or more, and 6.0m ２ This is a method for producing the aforementioned spherical aggregates of silver particles, which are less than or equal to / g.

[0020] According to the present invention, a monodisperse spherical aggregate of silver particles, as shown in Figure 1, can be produced by a simple method of adding and mixing additives from group A to a silver compound solution and a reducing agent solution.

[0021] Furthermore, if the amount of additives in group A is 3.0 parts by weight or more and 25.0 parts by weight or less per 100 parts by weight of silver contained in the silver compound solution, it is possible to produce spherical aggregates of silver particles in which nano-silver particles with little variation in particle size are aggregated.

[0022] Furthermore, if the BET diameter of the silver particles constituting the silver particle spherical aggregate is 100 nm or more and 285 nm or less, the sinterability is excellent, and the silver particle spherical aggregate exhibits conductivity through low-temperature sintering.

[0023] Furthermore, the spherical aggregates of silver particles have a particle size of 1.0 μm or more and 10.0 μm or less at D50% as measured by laser diffraction particle size measurement, and a specific surface area of ​​2.0 m² as measured by BET. ２ / g or more, and 6.0m ２If the concentration is less than / g, the resulting spherical aggregate of silver particles exhibits excellent handling and packing properties, and also exhibits conductivity through low-temperature sintering, making it suitable for use as a conductive filler.

[0024] This is an SEM image (5000x magnification) of the silver particle spherical aggregates produced by the present invention with the addition of citric acid (Example 1). This is an SEM image (5000x magnification) of the silver particle spherical aggregates produced by the present invention with the addition of trimellitic acid (Example 2). This is an SEM image (5000x magnification) of the comparative example silver particle aggregates produced by the addition of maleic acid (Comparative Example 1). This is an SEM image (5000x magnification) of the comparative example silver particle aggregates produced by the addition of oxalic acid (Comparative Example 2).

[0025] The present invention relates to a method for producing spherical aggregates of silver particles by adding one or more additives selected from the following group A to a silver compound solution and a reducing agent solution. Group A: citric acid, citrate anhydride, citrate salt, trimellitic acid, trimellitic anhydride, trimellitic salt

[0026] (Silver compound solution) The silver compound used in this invention is not particularly limited as long as it can react with a reducing agent to produce silver particles.

[0027] Examples of silver compounds include silver nitrate, silver carbonate, and silver acetate, but from a cost perspective, silver nitrate is preferred.

[0028] Water and / or alcohol are preferred as solvents for dissolving silver compounds.

[0029] (Reducing agent solution) The reducing agent solution in the present invention is not limited as long as it reduces the silver compound when mixed with the silver compound solution and precipitates silver particles.

[0030] Examples of reducing agents used in the reducing agent solution include L-ascorbic acid, D-erythorbic acid, salts of L-ascorbic acid or D-erythorbic acid, hydrazine, hydrazine compounds, formaldehyde, formic acid, and glucose.

[0031] Water and / or alcohol are preferred as the solvent for dissolving the reducing agent.

[0032] In the present invention, one or more additives selected from Group A (citric acid, citric anhydride, citrate, trimellitic acid, trimellitic anhydride, trimellitate) are used as additives.

[0033] The additives in Group A have the effect of reducing the primary particle size of the silver nanoparticles and the effect of adjusting the aggregated state of the silver nanoparticles to a shape close to a sphere.

[0034] By forming a spherical aggregated state, the contact area is reduced, further aggregation can be prevented, and the dispersibility can be enhanced.

[0035] The addition amount of the additives in Group A varies depending on the type of additive used, but it is preferably 3.0 parts by weight to 25.0 parts by weight, more preferably 6.0 parts by weight to 25.0 parts by weight, based on 100 parts by weight of the amount of silver (in terms of metal) contained in the silver compound solution.

[0036] When the addition amount is less than 3.0 parts by weight, the primary particle size may not be sufficiently small, and there is a possibility that a spherical aggregate may not be formed.

[0037] When the addition amount is more than 25.0 parts by weight, it becomes difficult to dissolve it in the silver nitrate solution, and there is a possibility that it may become a powder of silver particle aggregates containing impurities. Also, in order to dissolve it, it is necessary to significantly reduce the overall concentration, resulting in an increase in cost.

[0038] It is preferable that the additives in Group A are added to at least one of the silver compound solution or the reducing agent solution, and then the silver compound solution and the reducing agent solution are mixed for production.

[0039] The mixing method is not particularly limited, and any of the methods of simultaneously adding the silver compound solution and the reducing agent solution to the reaction vessel, adding the reducing agent solution to the silver compound solution, or adding the silver compound solution to the reducing agent solution may be used.

[0040] The temperature of the silver compound solution and the reducing agent solution of the mixture is preferably 50°C or lower, more preferably 15°C to 35°C, and even more preferably 20°C to 30°C.

[0041] If the temperature is higher than 50°C, the primary particle diameter of the silver particles may increase. If the temperature is lower than 15°C, it may be difficult to dissolve the additive, and there is a risk of generating a powder of silver particle aggregates containing impurities. Also, in order to dissolve it, it is necessary to significantly reduce the overall concentration, which increases the cost.

[0042] The pH of the mixed solution can be any value within the range of the chemicals used.

[0043] The precipitated silver particles can be easily separated from the reaction solution by filtration or the like.

[0044] After separation, after washing with water or alcohol and then drying, spherical aggregates of silver particles can be produced.

[0045] The BET diameter of the silver particles constituting the spherical aggregates of silver particles is preferably 100 nm to 285 nm.

[0046] If it is less than 100 nm or exceeds 285 nm, there is a risk that it will not form a spherical aggregate.

[0047] In the spherical aggregates of silver particles in the present invention, the particle diameter of D50% by the laser diffraction particle size measurement method is preferably 1.0 μm to 10.0 μm, more preferably 1.0 μm to 6.0 μm, and even more preferably 2.0 μm to 4.0 μm.

[0048] If the particle diameter is less than 1.0 μm, the handling property deteriorates. If it exceeds 10.0 μm, the filling property of the conductive filler deteriorates.

[0049] The spherical aggregates of silver particles in the present invention have a BET specific surface area of 2.0 m ２ / g to 6.0 m ２ / g is preferred.

[0050] If the BET specific surface area is less than 2.0 m ２ / g, there is a risk that the primary particle diameter of the silver particles constituting the spherical aggregates of silver particles is large. Also, it is difficult to make it larger than 6.0 m ２ / g.

[0051] The present invention will be described with reference to examples and comparative examples, but the present invention is not limited to these. The evaluation methods for the examples and comparative examples are shown in Table 2.

[0052] (Example 1) As a silver compound solution, 50.0 g of silver nitrate and 4.0 g of citric acid were dissolved in 1000 mL of pure water, and the solution temperature was adjusted to 26°C.

[0053] As a reducing agent solution, 26.8 g of ascorbic acid was dissolved in 1000 mL of pure water, and the solution temperature was adjusted to 26°C.

[0054] The prepared silver compound solution and reducing agent solution were mixed and stirred for 10 minutes to allow the reaction to occur. The resulting precipitate was filtered, washed, and then dried at 40°C for 3 hours.

[0055] As shown in Table 1, Example 2 and each comparative example were prepared in the same manner as Example 1, except that the additives were changed.

[0056]

[0057] When additives other than citric acid and trimellitic acid were used, the resulting silver particle aggregates did not form a spherical shape, or the sintering temperature of the silver particle aggregates was higher than that of the present invention.

[0058] SEM images of the silver particle spherical aggregates of Example 1 and Example 2 are shown in Figures 1 and 2, and SEM images of the silver particle aggregates of Comparative Example 1 and Comparative Example 2 are shown in Figures 3 and 4.

[0059] As shown in Figures 1 and 2, the silver particle aggregates produced by the manufacturing method of the present invention are spherical and monodisperse.

[0060]

[0061] The method for producing spherical aggregates of silver particles according to the present invention allows for the production of aggregates in which nano-silver particles are aggregated into a spherical shape. The produced spherical aggregates of nano-silver particles have excellent dispersibility and handling properties, and since they exhibit conductivity upon sintering at low temperatures, they are suitable for use as conductive fillers. Therefore, the present invention has high industrial applicability.

Claims

1. A method for producing spherical aggregates of silver particles by adding one or more additives selected from the following group A to a silver compound solution and a reducing agent solution. Group A: citric acid, citrate anhydride, citrate salt, trimellitic acid, trimellitic anhydride, trimellitic salt 2. The method for producing spherical aggregates of silver particles according to claim 1, wherein the amount of the additive added is 3.0 parts by weight or more and 25.0 parts by weight or less, based on 100 parts by weight of silver contained in the silver compound solution.

3. A method for producing a spherical aggregate of silver particles according to claim 1 or 2, wherein the BET diameter of the silver particles constituting the spherical aggregate of silver particles is 100 nm or more and 285 nm or less.

4. The silver particle spherical aggregate has a particle diameter of 1.0 μm or more and 10.0 μm or less at D50% as measured by laser diffraction particle size measurement, and a specific surface area of ​​2.0 m² as measured by BET. ２ / g or more, and 6.0m ２ A method for producing a spherical aggregate of silver particles according to claim 1 or 2, wherein the amount is less than or equal to / g.

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