JP2008223101A - Method for producing metal grain - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of easily producing metal grains having low aggregativity. <P>SOLUTION: The method for producing metal grains is characterized in that, in a state where, to slurry comprising the grains of a metal and a component to dissolve the grains, the other metal having an ionization tendency higher than that of the above metal is added in the form of a solid, the form of a soluble salt or the form of ions, the above component is removed. In the case the above metal is, e.g., silver, the other metal is preferably nickel, copper, iron, tin or zinc. In the case the slurry is aqueous, it is also preferably that, before or after the addition of the other metal, a hydrophobizing agent is added to the slurry. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing metal particles. The metal particles produced according to the present invention are particularly preferably used as a raw material for conductive ink, for example.

  The present applicant firstly added a EDTA salt to a silver nitrate solution, prepared a complex slurry of silver and EDTA, and added a reducing agent such as formalin to this slurry to cause a slow reduction reaction to obtain a fine silver powder. Proposed (see Patent Document 1). The fine silver powder obtained by this method has low agglomeration. Apart from this method, a method of stirring a solution obtained by dissolving a polymer compound, a reducing agent, and a silver salt at a temperature of 25 ° C. or more and 60 ° C. or less is proposed as a method for producing silver fine particles. (See Patent Document 2). In this production method, polyethyleneimine or the like is used as the polymer compound, and ascorbic acid or the like is used as the reducing agent. Silver particles obtained by this production method are plate-shaped.

  Apart from the method described in Patent Document 1, the present applicant forms a coherent aggregate between particles by treating ultrafine particles as a slurry consistently from the process of reducing and precipitating metal ultrafine particles. A method for preventing this problem has also been proposed (see Patent Document 3). In this method, a first slurry in which ultrafine metal particles are reduced and deposited is prepared by irradiating microwaves to a mixed solution in which a metal compound, a solvent having a reducing ability, and a dispersant are mixed, and rapidly heating the first slurry. The supernatant liquid is discarded to form a second slurry, and a solvent is added to the second slurry to obtain a target ultrafine metal particle slurry.

JP 2004-100013 A JP-A-2005-105376 JP 2006-169557 A

  An object of the present invention is to provide a method capable of producing silver fine particles having further improved performance as compared with the silver fine particles obtained by the above-described conventional production method.

  The present invention provides a slurry containing metal particles and a component that dissolves the particles in a state in which another metal having a higher ionization tendency than the metal is added in the form of a solid, a soluble salt, or an ion. The present invention provides a method for producing metal particles, wherein the component is removed.

  The present invention also adds another metal having a higher ionization tendency than the metal in a solid form, a soluble salt form or an ionic form to a slurry containing metal particles and a component for dissolving the particles. Then, the present invention provides a method for producing a conductive ink in which the component and the other metal are removed and an ink medium is further added.

  According to the present invention, low-cohesive metal particles can be easily produced.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. In the production method of the present invention, first, a slurry containing metal particles is prepared. This slurry is aqueous based on water or non-aqueous based on organic solvent. In the case of an aqueous system, it may be a mixed medium of water and an organic solvent soluble in water, for example, alcohols, ethers, ketones and the like.

  There is no particular limitation on the type of metal particles contained in the slurry, and for example, a single noble metal can be used. The precious metal mentioned here includes gold, silver and platinum groups (ruthenium, rhodium, palladium, osmium, iridium, platinum). In addition to the noble metal, for example, a simple substance such as nickel, copper, or tin can be used. Among these metals, the effect of the present invention is remarkable when a noble metal is the target, and the effect of the present invention is even more remarkable when silver is the target among the noble metals. When a metal other than a noble metal is targeted, copper is preferable as the metal. In addition, when targeting a metal other than a noble metal, for example, when targeting nickel or tin particles, a substance (for example, a ligand such as EDTA) that promotes dissolution of the particles exists in the slurry, and the particles are If the environment is easy to dissolve, the effect of the present invention becomes remarkable.

  There are no particular restrictions on the particle size and shape of the metal particles. Regarding the particle size, those having a primary particle size in the range of 0.001 to 100 μm can be suitably used. Regarding the shape of the particles, various shapes such as a spherical shape, a hexahedral shape, an octahedral shape, a flake shape, and an indefinite shape can be used. In particular, when the present invention is applied to particles whose primary particles have a particle size of 0.001 to 1 μm and are spherical or indeterminate, which are particles that are likely to aggregate, a remarkable effect is further conspicuous. The average particle diameter of the primary particles is obtained by measuring the maximum diameter of individual particles using a photograph of particles taken with a transmission electron microscope (TEM) and calculating the average value.

  The amount of metal particles in the slurry is not particularly critical in the present invention. Considering handleability, workability, etc., the amount of metal particles relative to the total amount of slurry is preferably 0.01 to 50% by weight, particularly 0.01 to 3% by weight.

  There is no restriction | limiting in particular in the manufacturing method of a metal particle, A suitable method can be employ | adopted according to the kind of metal to be used. The metal particles are preferably obtained by wet reduction of metal ions. When using silver as a metal, the method as described in Unexamined-Japanese-Patent No. 2004-100013 and Unexamined-Japanese-Patent No. 2006-124787 based on the previous application of this applicant can be used, for example. Moreover, the method as described in Unexamined-Japanese-Patent No. 2004-183090 and 2005-105376 can also be used. When nickel is used as the metal, for example, methods described in Japanese Patent Application Laid-Open Nos. 2004-308013, 2005-298927, and 2006-45648 can be used. When copper is used as the metal, for example, a method described in JP-A-2003-342621 can be used.

  As an example of a method for producing metal particles, a novel method for producing silver nanoparticles will be described below. In this method, silver nanoparticles are obtained by reducing silver ions with formalin in the presence of ethylenediaminetetraacetate (hereinafter also referred to as EDTA salt) and polyethyleneimine (hereinafter also referred to as PEI).

  A water-soluble salt can be used as the EDTA salt. For example, a sodium salt thereof can be used. It is preferable to use a polyethyleneimine having a weight average molecular weight of 400 to 100,000, particularly 1,000 to 10,000, from the viewpoint that the particle diameter of the silver nanoparticles can be made uniform and the dispersibility can be improved.

  The concentration of silver ions in the reaction solution is 0.01 to 8% by weight, particularly 0.5 to 3% by weight, to improve the dispersibility of the resulting silver nanoparticles and to improve industrial productivity. It is preferable from the viewpoint that both can be achieved. The reaction solution uses water as a medium. As the silver ion source, a water-soluble silver salt can be used without particular limitation. Examples thereof include silver nitrate, silver acetate, silver sulfate, silver perchlorate, and silver nitrite. Particularly preferably, silver nitrate is used.

  The amount of EDTA salt and PEI is determined in relation to the amount used with silver ions. With respect to the EDTA salt, the use of 100 to 500% by weight, particularly 150 to 300% by weight, based on the silver ions contained in the reaction solution can reduce the particle size of the silver nanoparticles and improve the dispersibility. It is preferable from the point of obtaining. For the same reason, PEI is preferably used in an amount of 10 to 200% by weight, particularly 20 to 100% by weight, based on silver ions contained in the reaction solution.

  In this production method, silver ions are reduced with formalin as a reducing agent in the presence of EDTA salt and PEI. The reaction temperature is preferably 40 to 80 ° C., particularly 50 to 70 ° C., from the viewpoint that aggregation of particles can be prevented while appropriately increasing the reduction rate. The reaction time is preferably 0.5 to 3 hours, particularly 1 to 2 hours.

  Formalin as a reducing agent is added to the reaction solution in a state diluted with water. The addition may be batch addition or sequential addition. The concentration of the diluted formalin solution is preferably 1 to 37% by weight, more preferably 30 to 37% by weight, from the viewpoint of efficiently producing silver nanoparticles industrially. The amount of formalin added is determined in relation to the amount of silver ions. In detail, it is preferable to add 40-100 weight%, especially 50-60 weight% of formalin with respect to the silver ion contained in a reaction liquid.

  Addition of formalin causes reduction of silver ions. In this case, since silver ions form a complex with the EDTA salt in the reaction solution, the silver nanoparticles generated by the reduction of silver ions are spherical. Further, since formalin is a reducing agent having a relatively low reducing property, the reduction of silver ions does not proceed rapidly, so that fine silver particles are generated. Furthermore, the presence of PEI in the reaction system reduces silver ions to silver nanoparticles having a uniform particle size.

  From the viewpoint of successfully producing silver nanoparticles having a more uniform particle size, polyvinyl pyrrolidone may also be present in the reaction solution in addition to the PEI described above, and silver ions can be reduced in the presence of PEI and polyvinyl pyrrolidone. preferable. The amount of polyvinyl pyrrolidone added is determined in relation to the amount of silver ions. Specifically, it is preferable to add 10 to 100% by weight, particularly 30 to 70% by weight of polyvinylpyrrolidone with respect to silver ions contained in the reaction solution.

  Polyvinylpyrrolidone having a weight average molecular weight of 10,000 to 500,000, particularly 30,000 to 100,000, prevents deterioration of the settling property of silver nanoparticles due to an increase in viscosity of the reaction solution, and maintains good dispersibility. It is preferable from the point of obtaining.

  By the above operation, an aqueous slurry in which silver ions are reduced and silver nanoparticles are generated is obtained. To this slurry, another metal having a higher ionization tendency than the metal constituting the particles contained in the slurry (in this method, silver) is added in a solid form, a soluble salt form, or an ionic form. By this operation, the dispersibility of the metal particles in the slurry can be improved. The reason for this is as follows.

  Some of the metal particles present in the slurry are dissolved in the solvent as metal ions, and the dissolved metal ions are precipitated again. The dissolution of the metal is caused by a component that dissolves the metal present in a minute amount in the slurry. Examples of such components include various salts added as raw materials for producing metal particles, and various salts generated as a result of producing metal particles. The reprecipitation of the dissolved metal ions is caused by, for example, a reducing agent remaining in a minute amount in the slurry. The dissolution / reprecipitation causes aggregation of metal particles, and the dispersibility of the metal particles during storage of the slurry tends to decrease. In contrast, by adding another metal having a higher ionization tendency than the metal in the form of a solid, a soluble salt, or an ion in the slurry of metal particles, Solids and / or ions coexist, whereby the dissolution of the metal particles is suppressed, and thus the reprecipitation of the metal ions is suppressed. As a result, the dispersibility of the metal particles during storage of the slurry can be improved. The other metal may be added to the slurry in at least one of a solid form, a soluble salt form, and an ionic form. A combination of at least two of these forms may be used.

  As said other metal, a suitable thing is selected according to the kind of metal particle contained in a slurry. Other metals can be used alone or in combination of two or more. For example, when the above-described silver nanoparticles are used as the metal particles, for example, nickel, copper, iron, tin, or zinc can be used as the other metal. Of these, nickel and copper are particularly preferred. When nickel particles are used as the metal particles, zinc, manganese, or aluminum can be used as the other metal.

  When the other metal is blended in the slurry in a solid form, it can be blended in a bulk form such as an ingot or in the form of particles. When blended in the form of particles, the particle size of the particles is not particularly limited. The particle size of the particles can be, for example, about 1 to 1000 μm. Considering the ease of separation from the metal particles contained in the slurry, it is preferable to use other metals in the form of soluble salts and / or ions rather than in the form of particles.

  When the other metal is used in the form of a soluble salt, a water-soluble salt is used when the slurry is aqueous. When the slurry is non-aqueous, a salt that is soluble in a non-aqueous solvent is used. Similarly, when the other metal is used in the form of ions, an aqueous solution containing the ions is used when the slurry is aqueous. When the slurry is non-aqueous, a non-aqueous solution containing the ions is used.

  The compounding amount of the other metal is 1 equivalent of the metal constituting the particles contained in the slurry regardless of whether it is in the form of a solid, a soluble salt, or an ion. The amount is preferably 0.01 to 10 equivalents, particularly 0.5 to 2 equivalents, from the viewpoint of effectively preventing dissolution of the metal particles in the slurry. When silver particles are used as the metal particles and copper is used as the other metal, 1 equivalent of copper per 1 equivalent of silver means that 0.5 mol of copper is used per 1 mol of silver.

  In order to remove the other metal and the component that dissolves the metal particles separately from the metal particles, for example, when the other metal is used in the form of a soluble salt and / or ion, the component in the slurry is used. The decantation may be repeated using water or a non-aqueous solvent until the concentration of other metal ions becomes a predetermined value or less. When the other metal is used in a solid form, particles or ingots that are 100 times larger than the particles to be produced are separated and removed by filtration or the like, and then decanted.

  As is apparent from the above description, the above operation is carried out in the form of a solid salt or a soluble salt in a slurry containing metal particles and a component that dissolves the particles, and other metals having a higher ionization tendency than the metal. Alternatively, it can be said to be a method for stabilizing metal particles, in which the component is removed under the condition of being added in the form of ions.

  By the above operation, impurities in the slurry are removed, and low-cohesive metal particles are obtained in a slurry state. The slurry may be left still or centrifuged to settle the metal particles, and the liquid component may be separated and removed. This further removes the component that dissolves the metal particles present in the slurry. When the slurry is aqueous, it is preferable to subject the metal particles to a hydrophobization treatment from the viewpoint of promoting sedimentation. In particular, when the metal particles are fine particles such as nanoparticles, it takes a long time to settle in a normal state because of the fine particles. On the other hand, the settling time can be shortened by hydrophobizing the metal particles.

  What is necessary is just to add a hydrophobizing agent in a slurry for the hydrophobization process of a metal particle. As the hydrophobizing agent, a compound having a good affinity for the surface of the metal particles and having a hydrophobic group is used. Examples of such compounds include aliphatic amines having hydrocarbon groups such as oleylamine, trioctylamine, octylamine, decylamine, dodecylamine, stearylamine, oleic acid, stearic acid, decanoic acid, palmitic acid, linoleic acid, etc. Of fatty acids. Of these hydrophobizing agents, it is preferable to use an aliphatic amine such as oleylamine and a fatty acid such as palmitic acid or linoleic acid from the viewpoint of aggregation and precipitation while maintaining the dispersibility of the particles.

  When the metal particles are hydrophobized with a hydrophobizing agent, it is preferable that a compatibilizing agent for the hydrophobizing agent coexists in the slurry. This is because the action of the compatibilizing agent makes it easier for the hydrophobizing agent to bind to the surface of the metal particles, and the hydrophobization can be performed more successfully. Examples of the compatibilizer include lower alcohols (1 to 4 carbon atoms) such as ethanol, ketones such as acetone, esters such as ethyl acetate, and the like. The addition amount of the compatibilizer is preferably 100 to 10,000% by weight, particularly 500 to 2000% by weight, based on the hydrophobizing agent.

  The metal particles that have been hydrophobized by the hydrophobizing agent and settled are discarded, for example, by decantation. Then, solvent substitution and concentration are performed as necessary. Furthermore, for example, a conductive ink or a conductive paste can be obtained by blending a predetermined component such as an ink medium into the metal particles. According to this method, the steps from the production of the metal particles to the preparation of the ink can be performed consistently and without making the metal particles dry, so the metal particles contained in the obtained ink are aggregated. This can be prevented even more effectively.

  In the above method, another metal having a higher ionization tendency than the metal is added to the slurry containing the metal particles in the form of a solid, a soluble salt or an ion, and then the metal particles are added to the slurry. The above hydrophobization treatment was performed. Instead, the above-described hydrophobization treatment is performed on the metal particles in the slurry containing metal particles, and then another metal having a higher ionization tendency than the metal is added to the slurry in the form of solid, soluble You may add in the form of a salt or an ion. That is, the hydrophobizing agent may be added before or after the addition of another metal.

  The metal particles obtained by the above operation are suitably used as a raw material for conductive ink or conductive paste, for example. Wiring circuits and electrodes of electronic devices such as plasma display panels, chip parts, glass ceramic packages, and ceramic filters can be formed using such inks and pastes. In order to form fine circuits and electrodes, it is required that the metal particles have a low agglomeration property, but the silver nanoparticles produced according to the present invention have a low agglomeration property as described above. Matched.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[Example 1]
In a 1 liter beaker, 10.0 g of silver nitrate, 15.0 g of EDTA4Na salt, PEI having a weight average molecular weight of 1800 and 300 ml of pure water were added and sufficiently stirred. While maintaining the liquid temperature at 50 ° C., 100.0 g of a 37 wt% formalin aqueous solution was added all at once to carry out a silver ion reduction reaction. The reaction was carried out for 1.5 hours while maintaining the liquid temperature at 50 ° C. In this way, a slurry of silver nanoparticles was obtained. The average particle diameter of primary particles of silver nanoparticles by TEM was 28 nm.

An aqueous solution in which 4.0 g of nickel nitrate hexahydrate (Ni (NO ₃ ) ₂ .6H ₂ O) was dissolved in 100 ml of pure water was added to the silver nanoparticle slurry and stirred for 1 minute. The temperature of the slurry was maintained at 50 ° C.

  Next, a solution in which 0.3 g of oleylamine was dissolved in 100 ml of ethanol was added to the slurry and stirred for 30 minutes to hydrophobize the silver nanoparticles. The temperature of the slurry was maintained at 50 ° C.

Finally, the slurry was decanted repeatedly with pure water to remove nickel ions in the slurry. A TEM image of the silver nanoparticles thus obtained is shown in FIG. As is apparent from the results shown in FIG. 1, it can be seen that almost no aggregation is observed in the silver nanoparticles. It can also be seen that the silver nanoparticles have a very uniform particle size. Apart from the TEM observation, was subjected to laser diffraction scattering particle size distribution measurement for silver _{nanoparticles, D 10 = 0.227μm, D 50} = 0.358μm, D 90 = 0.923μm , and the particle size distribution is sharp I found out. From this result, the result of TEM observation was supported. In measuring the particle size distribution, ultrasonic dispersion was performed for 5 minutes in a 1% -weight sodium hexametaphosphate aqueous solution as a pre-dispersion.

[Example 2]
In the same manner as in Example 1, a slurry of silver nanoparticles having an average particle size of 28 nm was obtained. To this silver nanoparticle slurry, an aqueous solution in which 10.9 g of copper nitrate trihydrate was dissolved in 100 mL of pure water was added and stirred for 1 minute. The temperature of the slurry was maintained at 50 ° C.

Next, a solution in which 0.3 g of oleylamine was dissolved in 100 mL of ethanol was added to the slurry and stirred for 30 minutes to hydrophobize the silver nanoparticles. The temperature of the slurry was maintained at 50 ° C.

Finally, decantation was repeated with pure water to remove copper ions in the slurry. A TEM image of the silver nanoparticles thus obtained is shown in FIG. As is clear from the results shown in FIG. 2, it can be seen that almost no aggregation is observed in the silver nanoparticles. When the laser diffraction scattering particle size distribution measurement was performed on the silver nanoparticles in the same manner as in Example 1, D ₁₀ = 0.192 μm, D ₅₀ = 0.256 μm, D ₉₀ = 0.357 μm, and the particle size distribution was sharp. I found out. From this result, the result of TEM observation was supported.

Example 3
1 g of copper acetate and 1 g of oleylamine were dissolved in 20 mL of methanol. This is A liquid. Separately, 1 g of hydrazine hydrate was added to 20 mL of methanol. This is B liquid. The A liquid was added to the B liquid at once, and copper ions were reduced to obtain copper nanoparticles having an average particle diameter of about 80 nm. To this slurry containing copper nanoparticles, 0.1 g of iron (II) sulfate was added and stirred for 1 minute. Finally, decantation was repeated with pure water to remove iron ions in the slurry. An FE-SEM image of the copper nanoparticles thus obtained is shown in FIG. As is clear from the results shown in FIG. 3, it can be seen that almost no aggregation is observed in the copper nanoparticles. Was subjected to laser diffraction scattering particle size distribution measurement in the same manner as in Example 1 copper _{nanoparticles, D 10 = 0.257μm, D 50} = 0.385μm, D 90 = 0.661μm , and the particle size distribution is sharp I found out. From this result, the result of FE-SEM observation was supported.

[Comparative Example 1]
Based on Example 1 of Unexamined-Japanese-Patent No. 2005-105376 (above-mentioned patent document 2), the silver particle was prepared in the following procedures. In 100 parts by weight of water, 0.3 part by weight of PEI having a weight average molecular weight of 1800 was dissolved, and 0.024 part by weight of silver nitrate was added and dissolved in the obtained aqueous solution. The liquid temperature was kept at 60 ° C., 0.03 part by weight of ascorbic acid was added as a reducing agent, and the reaction was completed while stirring for 2 hours. The average particle diameter of primary particles of silver particles by TEM was 120 nm. The shape of the particles was indefinite. Further, when the particle size distribution measurement of the laser diffraction scattering type was performed on the silver particles in the same manner as in Example 1, D ₁₀ = 0.358 μm, D ₅₀ = 0.711 μm, D ₉₀ = 1.306 μm, and aggregation of the particles was observed. It was.

[Comparative Example 2]
In Example 3, copper nanoparticles were obtained in the same manner as in Example 3 except that the operation of adding iron (II) sulfate to the slurry of copper nanoparticles was not performed. An FE-SEM image of the obtained copper nanoparticles is shown in FIG. As is apparent from the results shown in FIG. 4, it can be seen that the copper nanoparticles are aggregated. When copper diffraction particles were subjected to laser diffraction / scattering particle size distribution measurement in the same manner as in Example 3, D ₁₀ = 0.469 μm, D ₅₀ = 1.068 μm, D ₉₀ = 1.980 μm, and the particle size distribution was broad. I found out. From this result, the result of FE-SEM observation was supported.

2 is a TEM image of silver nanoparticles obtained in Example 1. FIG. 3 is a TEM image of silver nanoparticles obtained in Example 2. FIG. 4 is an FE-SEM image of copper nanoparticles obtained in Example 3. FIG. 3 is an FE-SEM image of copper nanoparticles obtained in Comparative Example 2. FIG.

Claims (5)

  This component is removed under the condition that a metal particle and another metal having a higher ionization tendency than that of the metal are added in a solid form, soluble salt form, or ion form to a slurry containing the metal particle and a component that dissolves the particle. A method for producing metal particles, comprising:   The method according to claim 1, wherein the metal is silver or copper, and the other metal is nickel, copper, iron, tin, or zinc.   The production method according to claim 1 or 2, wherein a hydrophobizing agent is added to the slurry before or after the addition of the other metal.   The process according to claim 3, wherein the hydrophobizing agent is an aliphatic amine.   To a slurry containing metal particles and a component that dissolves the particles, another metal having a higher ionization tendency than the metal is added in the form of a solid, a soluble salt, or an ion, and then the component is added. And a method for producing a conductive ink in which the other metal is removed and an ink medium is further added.