Silver particle spherical aggregate and spherical silver particles obtained by crushing same

Abstract

[Problem] To provide a silver particle spherical aggregate which is a nano-silver particle spherical aggregate obtained by aggregating spherical nano-silver particles into a spherical shape and a silver particle spherical aggregate obtained by heat-treating the nano-silver particle spherical aggregate, wherein both of said silver particle spherical aggregates can be suitably used as a conductive filler, can be crushed to produce spherical silver particles, have excellent dispersibility and excellent handleability, and can be produced by a simple method. [Solution] A nano-silver particle spherical aggregate obtained by aggregating spherical nano-silver particles having a BET diameter of 20-100 nm, wherein the value of [D50% particle diameter according to a laser diffraction particle size measurement method] / [BET diameter] of the nano-silver particle spherical aggregate is at least 10.

Description

Spherical agglomerates of silver particles and spherical silver particles obtained by crushing the agglomerates

[0001] The present invention relates to silver particle spherical agglomerates, specifically to nanosilver particle spherical agglomerates formed by spherically agglomerating spherical nanosilver particles, and to silver particle spherical agglomerates obtained by heat-treating the nanosilver particle spherical agglomerates, both of which can be suitably used as conductive fillers and which can be crushed to form spherical silver particles, and which have excellent dispersibility and handleability.

[0002] Silver particles are increasingly being used as a filler for conductive pastes (hereinafter referred to as "conductive filler") used to form electrodes, circuits, and the like.

[0003] Furthermore, in recent years, as a result of the advancement of finer line widths for electrodes and circuits in the above-mentioned applications, there has been a demand for monodispersed spherical fine silver particles that have the properties of a small particle diameter, a sharp particle size distribution, and high dispersibility.

[0004] However, the production of monodispersed spherical fine silver particles having a small particle diameter, a sharp particle size distribution, and high dispersibility requires special processes such as two-stage reduction or the use of core particles, and also requires an apparatus for air collision.

[0005] Furthermore, the produced monodispersed spherical fine silver particles have problems in that they are difficult to separate and recover, and are difficult to handle.

[0006] Therefore, there is a demand for the development of monodispersed spherical fine silver particles that can be produced by a simple method and that are easy to handle.

[0007] JP 2005-048237 A JP 2015-129352 A JP 2006-225760 A

[0008] Patent Document 1 describes a method for producing fine silver particles with excellent dispersibility, in which an organic reducing agent is brought into contact with and mixed with an aqueous solution of a silver ammine complex, and the silver concentration and the organic reducing agent concentration in the mixed solution are maintained within a certain range to reduce and precipitate silver particles.

[0009] However, the production method described in Patent Document 1 requires reduction via two routes, and the produced silver particles are so fine that they are difficult to separate and recover, making them difficult to handle.

[0010] Patent Document 2 describes a method for producing silver particles having a small particle size, a sharp particle size distribution, and excellent dispersibility without generating aggregated silver particles, by contacting and mixing an aqueous solution of a silver ammine complex with an aqueous solution of a reducing agent in the air to reduce and precipitate silver particles, thereby avoiding the phenomenon in which the produced silver particles adhere to the walls of a flow path.

[0011] However, the method described in Patent Document 2 requires a special device for contact-mixing in the air, and the produced silver particles are so fine that they are difficult to separate and recover, making them difficult to handle.

[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 selected from the group consisting of an aliphatic unsaturated dicarboxylic acid, an anhydride thereof, and a salt thereof.

[0013] The method described in Patent Document 3 can produce spherical silver particles, but has the problem that the average particle size is large, at 0.5 μm to 5 μm, and it is not possible to produce fine silver particles.

[0014] The inventors set solving the above-mentioned problems as a technical task and conducted extensive experiments. As a result, they made the remarkable discovery that a nanosilver particle spherical agglomerate formed by the aggregation of spherical nanosilver particles having a BET diameter of 20 nm or more and 100 nm or less, and in which the value of [D50% particle diameter as measured by laser diffraction particle size measurement method] / [BET diameter] of the nanosilver particle spherical agglomerate is 10 or more, has excellent dispersibility and handleability, and can be suitably used as a conductive filler. In addition, if the nanosilver particle spherical agglomerate is crushed, it can be converted into spherical nanosilver particles, and if it is heated, it becomes a silver particle spherical agglomerate formed by the aggregation of spherical submicron silver particles, and can be produced by a simple method, thereby solving the above-mentioned technical task.

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

[0016] The present invention relates to a nanosilver particle spherical agglomerate formed by agglomeration of spherical nanosilver particles having a BET diameter of 20 nm or more and 100 nm or less, wherein the value of [D50% particle diameter as measured by laser diffraction particle size measurement method] / [BET diameter] of the nanosilver particle spherical agglomerate is 10 or more.

[0017] The present invention also provides a granular material having a D50% particle size of 1.0 μm or more and 10.0 μm or less as measured by a laser diffraction particle size measurement method, and a BET specific surface area of ​​6.0 m ２ / g or more and 30.0m ２ The nanosilver particle spherical agglomerates have a particle size of 1 / g or less.

[0018] The present invention also relates to a spherical agglomerate of silver particles obtained by heat-treating the aforementioned spherical agglomerate of nanosilver particles.

[0019] The present invention also relates to a silver particle agglomerate comprising spherical submicron silver particles having a BET diameter of 120 nm or more and 400 nm or less, wherein the value of [D50% particle diameter as measured by laser diffraction particle size measurement method] / [BET diameter] of the silver particle agglomerate is 2 or more and 100 or less.

[0020] The present invention also provides a granular material having a D50% particle size measured by a laser diffraction particle size measurement method of 1.0 μm or more and 10.0 μm or less, and a BET specific surface area of ​​1.5 m ２ / g or more and 5.0m ２ / g or less.

[0021] The present invention also relates to the aforementioned spherical agglomerates of silver particles, wherein the weight loss upon reduction is 1.0% by mass or less.

[0022] The present invention also provides spherical silver particles obtained by crushing the aforementioned spherical agglomerates of silver particles.

[0023] The present invention also provides a method for producing the nanosilver particle spherical agglomerates, which is produced by adding at least one of phthalic acid, phthalic anhydride, and phthalate salts to a silver compound solution and a reducing agent solution.

[0024] The present invention relates to an agglomerate composed of spherical nanosilver particles having a BET diameter of 20 nm or more and 100 nm or less, and the value of [D50% particle diameter as measured by laser diffraction particle size measurement method] / [BET diameter] of the agglomerate is 10 or more, resulting in a spherical agglomerate of nanosilver particles that is excellent in both handleability and dispersibility.

[0025] Furthermore, the spherical nanoparticle agglomerates of the present invention can be handled in the same manner as spherical silver particle powder, and can be suitably used as a conductive filler.

[0026] In addition, the nanosilver particle spherical agglomerate of the present invention has a D50% particle size of 1.0 μm or more and 10.0 μm or less as measured by a laser diffraction particle size measurement method, and a BET specific surface area of ​​6.0 m ２ / g or more and 30.0m ２ If the particle size is 1 / g or less, the resulting nano-silver particle spherical agglomerates will have the handleability of micro-order silver particle powder.

[0027] Furthermore, when crushed, the resulting particles become spherical nano-silver particles, which have the properties of nano-order fine silver particle powder and can be suitably used as a conductive filler.

[0028] Furthermore, by heat treatment, the spherical nanosilver particles that make up the nanosilver particle spherical agglomerates grow into spherical submicron silver particles, making it possible to produce silver particle spherical agglomerates in which spherical submicron silver particles are aggregated.

[0029] Furthermore, additives and the like are decomposed by the heat treatment, resulting in highly pure spherical agglomerates of silver particles.

[0030] Furthermore, the heat treatment can convert the constituent particles into spherical submicron silver particles of the desired size.

[0031] In particular, agglomerates composed of spherical submicron silver particles with a BET diameter of 120 nm or more and 400 nm or less are spherical, and the reduction weight loss can be reduced to 1.0 mass% or less, resulting in silver particle spherical agglomerates with excellent conductivity, which can be suitably used as a conductive filler.

[0032] Furthermore, if crushed, the silver particles become spherical submicron particles, which can be suitably used as a conductive filler.

[0033] 1 is an SEM photograph (5000x magnification) of a spherical agglomerate of nanosilver particles according to the present invention (Example 1). 2 is an SEM photograph (5000x magnification) of a spherical agglomerate of silver particles according to the present invention (Reference Example 3). 3 is an SEM photograph (20000x magnification) of a spherical agglomerate of nanosilver particles according to the present invention that has been heat-treated and then crushed (Reference Example 10). 4 is an SEM photograph (5000x magnification) of Comparative Example 8. 5 is an SEM photograph (10000x magnification) of Comparative Example 8 after heat treatment.

[0034] The present invention relates to a nanosilver particle spherical agglomerate in which spherical nanoparticles having a BET diameter of 20 nm or more and 100 nm or less are spherically agglomerated.

[0035] If the BET diameter is less than 20 nm or more than 100 nm, spherical aggregates will not form, and there is a risk that the particles will not grow even if they are subjected to heat treatment.

[0036] In the present invention, the nanosilver particle spherical agglomerates preferably have a value of [D50% particle diameter by laser diffraction particle size measurement method] / [BET diameter] of 10 or more, more preferably 10 or more and 300 or less, and even more preferably 20 or more and 200 or less.

[0037] The value of [D50% particle size] / [BET size] indicates the degree of aggregation of the aggregates, and if it is less than 10, the degree of aggregation will be low, resulting in poor handling, and there is a risk that the constituent silver particles will not grow into spherical submicron silver particles even after heat treatment.

[0038] The nanosilver particle spherical agglomerates in the present invention preferably have a D50% particle size measured by laser diffraction particle size measurement method 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.

[0039] If the particle size is less than 1.0 μm, handling becomes difficult, and if it exceeds 10.0 μm, there is a risk of generating coarse powder, making it unsuitable as a fine conductive filler.

[0040] The nanosilver particle spherical agglomerates of the present invention have a BET specific surface area of ​​6.0 m ２ / g to 30.0m ２ / g is preferred, and 6.0 m ２ / g to 20.0m ２ / g.

[0041] BET specific surface area is 6.0m ２ If the silver particle density is less than 30 m / g, the silver particles may not grow into spherical submicron silver particles even after heat treatment, or may not become spherical nano silver particles after crushing treatment. ２ This is because it is difficult to produce aggregates having a particle size of 1 / g or more.

[0042] The nanosilver particle spherical agglomerates of the present invention can be produced by adding at least one of phthalic acid, phthalic anhydride, and phthalate to a silver compound solution and a reducing agent solution.

[0043] (Silver Compound Solution) The silver compound in the present invention is not particularly limited as long as it can react with a reducing agent to produce silver particles.

[0044] Examples of silver compounds include silver nitrate, silver carbonate, and silver acetate, but from the standpoint of cost, it is preferable to use silver nitrate.

[0045] As the solvent for dissolving the silver compound, it is preferable to use water and / or alcohol.

[0046] (Reducing Agent Solution) The reducing agent used in the present invention is not limited as long as it can reduce the silver compound by mixing with the silver compound solution to precipitate silver particles.

[0047] Examples of reducing agents include L-ascorbic acid, D-erythorbic acid, salts of L-ascorbic acid or D-erythorbic acid, hydrazine, hydrazine compounds, formaldehyde, formic acid, and glucose.

[0048] As the solvent for dissolving the reducing agent, water and / or alcohol is preferably used.

[0049] In the present invention, one or more of phthalic acid, phthalic anhydride, and phthalate salts (hereinafter referred to as "phthalic acid, etc.") are used as additives.

[0050] Phthalic acid and the like are thought to have the effect of reducing the primary particle size of spherical nanosilver particles and also of arranging the agglomerated state of the spherical nanosilver particles into particle shapes that are close to perfect spheres.

[0051] By forming a spherical aggregate, the contact area is reduced, preventing further aggregation and improving dispersibility.

[0052] The amount of phthalic acid or the like added varies depending on the type of phthalic acid or the like used, but is preferably 3.0 parts by weight or more and 25.0 parts by weight or less per 100 parts by weight of silver (metal equivalent) contained in the silver compound solution.

[0053] If the amount of phthalic acid added is less than 3.0 parts by weight, the primary particle size will not be sufficiently small, and there is a risk that spherical aggregates will not be obtained.

[0054] If the amount of phthalic acid added is more than 25.0 parts by weight, it becomes difficult to dissolve it in the silver nitrate solution, which may result in the formation of spherical agglomerates of nanosilver particles containing impurities. Also, in order to dissolve it, the overall concentration must be significantly reduced, which increases costs.

[0055] It is preferable to produce the silver compound solution by mixing phthalic acid or the like with at least one of a silver compound solution and a reducing agent solution, and then mixing the silver compound solution with the reducing agent solution.

[0056] The mixing method is not particularly limited, and may be any of a method of adding the silver compound solution and the reducing agent solution to a reaction vessel at the same time, a method of adding the reducing agent solution to the silver compound solution, and a method of adding the silver compound solution to the reducing agent solution.

[0057] 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.

[0058] If the temperature is higher than 50° C., the primary particle size of the spherical silver particles may become too large, and if the temperature is lower than 15° C., it may become difficult to dissolve the additives, resulting in the generation of silver particle powder containing impurities. Also, in order to dissolve the additives, the overall concentration must be significantly reduced, which increases costs.

[0059] The pH of the mixed solution may be any value within the range of the chemicals used.

[0060] The precipitated silver particles can be easily separated from the reaction solution by filtration, etc. After separation, they are washed with water or alcohol and then dried to produce spherical agglomerates of nanosilver particles.

[0061] In the present invention, the spherical agglomerates of nanosilver particles can be grown by heat treatment, thereby producing spherical agglomerates of silver particles composed of grown spherical submicron silver particles.

[0062] The heat treatment temperature is preferably 200 to 250°C, more preferably 230 to 250°C.

[0063] If the heat treatment temperature is less than 200°C, the organic matter on the surface is not decomposed and particle growth does not proceed, and if the temperature exceeds 250°C, rapid particle growth occurs, making it difficult to obtain the desired particle diameter.

[0064] The heat treatment time depends on the temperature, but is preferably 1 to 3 hours.

[0065] If the time is less than one hour, the organic matter on the surface will not be sufficiently decomposed and particle growth will not proceed, and if the time is more than three hours, aggregation will proceed and dispersibility may be lost.

[0066] The apparatus used for the heat treatment is not particularly limited, and any apparatus can be used as long as it can heat up to about 300° C. and can maintain the inside of the heating chamber at a predetermined temperature uniformly for a certain period of time.

[0067] If the heating chamber cannot be heated and maintained uniformly, the nanosilver particles that make up the nanosilver particle aggregates will grow unevenly, resulting in large variations in the particle diameters of the spherical submicron silver particles that make up the silver particle aggregates obtained by heating treatment.

[0068] The atmosphere for the heat treatment is not particularly limited, and the heat treatment may be performed in any atmosphere such as air, nitrogen, or hydrogen.

[0069] The silver particle spherical agglomerates of the present invention become high-purity silver particle spherical agglomerates by heat treatment, since impurities are decomposed by the heat treatment.

[0070] The BET diameter of the spherical silver particles grown by heat treatment is preferably 120 nm or more and 400 nm or less.

[0071] This is because if the BET diameter is less than 120 nm or exceeds 400 nm, the aggregates may not become spherical.

[0072] The value of [D50% particle size measured by laser diffraction particle size measurement method] / [BET diameter] of the spherical agglomerates of silver particles in the present invention is preferably 2 or more and 100 or less, and more preferably 5 or more and 30 or less.

[0073] If the [D50% particle size] / [BET size] is less than 2, the degree of aggregation will be low and handling will be poor, and if it exceeds 100, there is a risk that spherical submicron silver particles will not be obtained even after crushing treatment.

[0074] The silver particle spherical agglomerates in the present invention preferably have a D50% particle size measured by laser diffraction particle size measurement method of 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.

[0075] If the particle size is less than 1.0 μm, handling becomes difficult, and if it exceeds 10.0 μm, there is a risk of generating coarse powder, making it unsuitable as a fine conductive filler.

[0076] The silver particle spherical agglomerates of the present invention have a BET specific surface area of ​​1.5 m ２ / g to 5.0m ２ / g, more preferably 2.0 m２ / g to 4.0m ２ / g.

[0077] BET specific surface area is 1.5m ２ If the heat treatment is too much, there is a risk of excessive aggregation. ２ If the solubility is greater than 1 / g, the heat treatment may not have progressed sufficiently, and the particles may not have grown to spherical submicron silver particles.

[0078] The weight loss upon reduction of the silver particle spherical agglomerates in the present invention is preferably 1.0% by mass or less, more preferably 0.8% by mass or less, and even more preferably 0.5% by mass or less.

[0079] When the weight loss due to reduction is 1.0 mass % or less, the electrical conductivity is excellent, and the material can be suitably used as a conductive filler.

[0080] The nanosilver particle spherical agglomerates and silver particle spherical agglomerates of the present invention can be subjected to a crushing treatment to produce spherical nanosilver particles and spherical submicron silver particles.

[0081] The crushing method may be either a dry method or a wet method, and is not particularly limited. Known crushing methods and devices can be used.

[0082] As a crushing treatment method, a crushing treatment using a roll mixer and a jet mill will be exemplified.

[0083] 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 5.

[0084] Example 1 A silver compound solution was prepared by dissolving 50.0 g of silver nitrate and 4.0 g of phthalic acid in 1000 mL of pure water and adjusting the solution temperature to 26°C.

[0085] A reducing agent solution was prepared by dissolving 26.8 g of ascorbic acid in 1000 mL of pure water and adjusting the solution temperature to 26°C.

[0086] The reducing agent solution was added to the prepared silver compound solution, and the mixture was stirred for 10 minutes to react with the silver compound solution. The resulting precipitate was filtered, washed, and then dried at 40° C. for 3 hours.

[0087] The nanosilver particle aggregates of Example 1 are shown in Figure 1. As shown in Figure 1, it can be seen that the nanosilver particle aggregates of Example 1 are nearly spherical and monodispersed.

[0088] Each comparative example was produced in the same manner as in Example 1, except that the additives were changed as shown in Table 1.

[0089]

[0090] When additives other than phthalic acid were used, the shape of the aggregates did not become spherical, or even if the shape of the aggregates was spherical, the silver particles (constituent particles) that constituted the aggregates did not become spherical.

[0091] Next, nanosilver particle aggregates were produced in the same manner as in Example 1, except that the amount of phthalic acid added was changed as shown in Table 2.

[0092]

[0093] When the amount of phthalic acid added was small, the aggregates did not become spherical, or even if they were spherical, the silver particles (constituent particles) that made them up were not spherical. The silver particle aggregate of Comparative Example 8 is shown in Figure 4.

[0094] In Comparative Example 8, the amount of phthalic acid added was small, so the BET diameter of the silver particles constituting the silver particle aggregates increased, and even after heat treatment at 230°C for 1.5 hours, the constituent silver particles partially aggregated to form coarse powder (shown by the arrow in Figure 5), and did not become spherical submicron silver particles (Figure 5).

[0095] The nanosilver particle aggregate obtained in Example 1 was placed in a container, heat-treated at the temperature shown in Table 3, and then removed from the oven and cooled to obtain spherical silver particle aggregates. All of these operations were carried out in an air atmosphere.

[0096]

[0097] It can be seen from Table 3 that the desired spherical agglomerate of silver particles, in which spherical submicron silver particles are aggregated, can be produced by adjusting the heating temperature and heating time. The spherical agglomerate of silver particles of Reference Example 3 is shown in Figure 2.

[0098] The spherical agglomerates of silver particles obtained by the heat treatment were kneaded and disintegrated using a three-roll mill (manufactured by Imex Co., Ltd.) at a weight ratio of silver:solvent of 8:2, with a clearance of 0.03 mm and a rotation speed of 30 Hz (loading 23, intermediate 63.5, finishing 175 rpm) for 5 passes.

[0099] Electrical resistivity of submicron silver particles after crushing treatment (10 －６ The values ​​of the surface tension (Ω·cm) are shown in Table 4.

[0100] Table 4 shows that submicron silver particles having a BET diameter in the range of 120 nm to 400 nm (Reference Example 10 / FIG. 3), which were obtained by crushing spherical agglomerates of silver particles obtained by heat treatment, have low electrical resistivity and can be suitably used as a conductive filler.

[0101] The present invention relates to nanosilver particle spherical agglomerates in which spherical nanosilver particles are spherically agglomerated, and to silver particle spherical agglomerates obtained by heat-treating the nanosilver particle spherical agglomerates. Either of the silver particle spherical agglomerates can be suitably used as a conductive filler, and spherical silver particles can be produced by crushing the agglomerates. Moreover, the silver particle spherical agglomerates are monodispersed and have excellent handleability. Therefore, the present invention is an invention with high industrial applicability.

Claims

1. A spherical nano-silver particle aggregate formed by aggregation of spherical nano-silver particles having a BET diameter of 20 nm or more and 100 nm or less, wherein the value of [D50% particle diameter by laser diffraction particle size measurement method] / [BET diameter] of the spherical nano-silver particle aggregate is 10 or more.

2. The D50% particle size by the laser diffraction particle size measurement method is 1.0 μm or more and 10.0 μm or less, and the BET specific surface area is 6.0 m ２ / g or more and 30.0 m ２ / g or less, and the spherical aggregate of silver nanoparticles according to claim 1.

3. A spherical silver particle aggregate obtained by heat-treating the spherical nano-silver particle aggregate according to claim 1 or 2.

4. A silver particle aggregate formed by aggregation of spherical submicron silver particles having a BET diameter of 120 nm or more and 400 nm or less, wherein the value of [D50% particle diameter by laser diffraction particle size measurement method] / [BET diameter] of the silver particle aggregate is 2 or more and 100 or less, which is the spherical silver particle aggregate according to claim 3.

5. The silver particle spherical aggregate according to claim 3, wherein the D50% particle size by the laser diffraction particle size measurement method is 1.0 μm or more and 10.0 μm or less, and the BET specific surface area is 1.5 m ２ / g or more and 5.0 m ２ / g or less.

6. The spherical silver particle aggregate according to claim 3, wherein the reduction loss is 1.0 mass% or less.

7. Spherical silver particles obtained by crushing the spherical silver particle aggregate of claim 1 or claim 3.

8. A method for producing the spherical nano-silver particle aggregate according to claim 1 or 2, which is produced by adding at least one of phthalic acid, phthalic anhydride or phthalate to a silver compound solution and a reducing agent solution.

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