Method for producing spherical aggregates of silver particles

Abstract

This invention provides a method for producing spherical aggregates of nanosilver particles using a simple method. The produced spherical aggregates of nanosilver particles exhibit excellent dispersibility and handling properties, and exhibit conductivity upon sintering at low temperatures, making them suitable for use as conductive fillers. [Solution] 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

Description

Technical Field

[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.

Background Art

[0002] The use of silver particles as a filler for conductive pastes (hereinafter referred to as "conductive fillers") used to form electrodes, circuits, etc. is expanding.

[0003] Furthermore, in recent years, as a result of the progress of fine-lining 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 the need for special processes such as two-stage reduction or the use of core particles, or the need for a device for air collision.

[0005] In addition, the produced monodisperse spherical fine silver particles have problems that they 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.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

[0008] Patent Document 1 describes a method for producing fine silver particles with excellent dispersibility, which involves contacting and mixing an organic reducing agent with an aqueous solution of silver ammine complex, and then reducing and precipitating silver particles by maintaining the silver concentration and organic reducing agent concentration within a certain range in the mixed solution.

[0009] However, the manufacturing method described in Patent Document 1 requires reduction in two pathways, and the resulting silver particles are very fine, making separation and recovery difficult 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. The process requires specialized equipment, and the resulting silver particles are extremely fine, making separation and recovery difficult 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, with the resolution of the aforementioned problems as their technical challenge, conducted numerous experiments and, as a result, discovered 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 exhibit excellent dispersibility and handling properties, and exhibit conductivity upon sintering at low temperatures, making them suitable for use as conductive fillers. This discovery thus solves the aforementioned technical challenges. [Means for solving the problem]

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

[0016] The present invention is 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] The present invention also 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] In addition, in the present invention, the silver particle spherical aggregates have a D50% particle diameter of 1.0 μm or more and 10.0 μm or less by laser diffraction particle size measurement method, and a specific surface area of 2.0 m 2 / g or more and 6.0 m 2 / g or less by the BET method. It is a method for producing the silver particle spherical aggregates described above.

Advantages of the Invention

[0020] According to the present invention, a monodisperse silver particle spherical aggregate in which silver particles are spherically aggregated as shown in FIG. 1 can be produced by a simple method of adding and mixing an additive of Group A to a silver compound solution and a reducing agent solution.

[0021] Further, if the addition amount of the additive of Group A is 3.0 parts by weight or more and 25.0 parts by weight or less with respect to 100 parts by weight of the silver amount contained in the silver compound solution, a silver particle spherical aggregate in which nano silver particles with little variation in particle diameter are aggregated can be produced.

[0022] In addition, when the BET diameter of the silver particles constituting the silver particle spherical aggregates is 100 nm or more and 285 nm or less, the silver particle spherical aggregates have excellent sinterability and exhibit conductivity at low-temperature sintering.

[0023] In addition, the silver particle spherical aggregates have a D50% particle diameter of 1.0 μm or more and 10.0 μm or less by laser diffraction particle size measurement method, and a specific surface area of 2.0 m 2 / g or more and 6.0 m 2 / g or less, they have excellent handling properties and filling properties, and moreover, they become silver particle spherical aggregates that exhibit conductivity at low-temperature sintering, so they can be suitably used as conductive fillers.

Brief Description of the Drawings

[0024] [Figure 1] SEM photograph (5000 times) of the silver particle spherical aggregates in the present invention produced by adding citric acid (Example 1). [Figure 2]This is an SEM image (5000x magnification) of the silver particle spherical aggregates produced by adding trimellitic acid in the present invention (Example 2). [Figure 3] This is an SEM image (5000x magnification) of a comparative example of silver particle aggregates produced by adding maleic acid (Comparative Example 1). [Figure 4] This is an SEM image (5000x magnification) of the silver particle aggregate of the comparative example prepared by adding oxalic acid (Comparative Example 2). [Modes for carrying out the invention]

[0025] The present invention is 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 the silver compound.

[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, thereby precipitating 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, citrate anhydride, citrate salt, trimellitic acid, trimellitic anhydride, trimellitic salt) are used as additives.

[0033] Additives in group A have the effect of reducing the primary particle size of nanosilver particles and also have the effect of arranging the aggregated state of nanosilver particles into a shape close to a sphere.

[0034] By forming a spherical aggregate state, the contact area is reduced, thus preventing further aggregation. It can improve dispersion.

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

[0036] If the amount added is less than 3.0 parts by weight, the primary particle size may not become sufficiently small, and spherical aggregates may not form.

[0037] If the amount added exceeds 25.0 parts by weight, it may become difficult to dissolve in the silver nitrate solution, potentially resulting in a powder of silver particle aggregates containing impurities. Furthermore, dissolving it would require significantly reducing the overall concentration, which increases costs.

[0038] It is preferable to produce the additives of Group A by adding them to at least one of the silver compound solution or the reducing agent solution, and then mixing the silver compound solution and the reducing agent solution.

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

[0040] The temperature of the silver compound solution and the reducing agent solution in 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] This is because temperatures above 50°C may increase the primary particle size of the silver particles, and temperatures below 15°C may make it difficult to dissolve the additives, potentially resulting in the formation of powdered silver particle aggregates containing impurities. Furthermore, dissolving it would require significantly reducing the overall concentration, which increases costs.

[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 other means.

[0044] After separation, the material can be washed with water or alcohol and then dried to produce spherical aggregates of silver particles.

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

[0046] This is because if the wavelength is less than 100 nm or greater than 285 nm, there is a risk that spherical aggregates will not form.

[0047] In the present invention, the spherical aggregates of silver particles preferably have a D50% particle size of 1.0 μm to 10.0 μm or less, more preferably 1.0 μm to 6.0 μm, and even more preferably 2.0 μm to 4.0 μm, as determined by laser diffraction particle size measurement.

[0048] This is because if the particle size is less than 1.0 μm, handling becomes difficult, and if it exceeds 10.0 μm, the packing of conductive filler becomes poor.

[0049] The spherical aggregate of silver particles in this invention has a BET specific surface area of ​​2.0 m². 2 / g~6.0m 2 It is preferable that it be / g.

[0050] BET specific surface area is 2.0m 2 If the value is less than 6.0 m, there is a risk that the primary particle size of the silver particles constituting the spherical aggregate of silver particles will be large, and also, 6.0 m 2 This is because it is difficult to make it larger than / g. [Examples]

[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] Except for the changes in the additives shown in Table 1, Example 2 and Example 3 were carried out in the same manner as Example 1. Each comparative example was manufactured.

[0056] [Table 1]

[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] [Table 2] [Industrial applicability]

[0061] The method for producing spherical aggregates of silver particles according to the present invention makes it possible to produce 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 is highly applicable to industry.

Claims

1. A method for producing spherical aggregates of silver particles by adding one or more additives selected from group A below 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 aforementioned spherical aggregate of silver particles has a particle size of 1.0 μm at D50% as determined by laser diffraction particle size measurement. The above, and less than or equal to 10.0 μm, and the specific surface area by the BET method is 2.0 m². 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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