JP2005060831A - Composite metal powder and its production method, and silver clay - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide composite metal powder in which metal nanoparticles are present on the surface, to provide its production method and its application. <P>SOLUTION: Metal powder is suspended in at least either a metal ion solution or a reducing agent solution, and both the solutions are mixed to reduce metal ions, so that composite metal powder in which metal fine particles are precipitated on the surface of the metal powder can be obtained. The composite metal powder has satisfactory filterability and can be recovered by an ordinary filtering means, and the metal nanoparticles and metal powder having a particle diameter larger than that of the same are simultaneously present, thus, the state where the metal fine particles are interposed in the gap between each metal powder is made and each metal lies in a sufficiently contacted state, so that the material excellent in electrical conductivity can be obtained. Further, its thermal conductivity is satisfactory, so that metal clay sintered at a relatively low temperature can be obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a composite metal powder in which metal fine particles are deposited on the surface of the metal powder and a method for producing the same. The composite metal powder of the present invention is suitable as an electronic material such as a conductive paste or a material such as metal clay, and according to the production method of the present invention, a relatively coarse metal powder and nano-level metal fine particles A composite metal powder containing can be easily obtained.

Conventionally, conductive paste has been used as a material for forming circuits and the like. In this conductive paste, metal powder such as silver powder is mixed as a conductive material, and in order to lower the firing temperature of the paste, together with ordinary metal powder, nano-sized metal fine particles (for example, 0.1 μm or less) Mixed metal powder mixed with metal nanoparticles). Conventionally, this mixed metal powder is generally a mixture of individually produced metal powder and metal nanoparticles. In order to improve electromagnetic wave shielding properties, a transparent conductive film is provided on the surface of a cathode ray tube or the like. As a coating material for forming the transparent conductive film, a colloidal solution of silver fine particles has been proposed.

As a method for producing a metal powder in which such metal coarse particles and metal fine particles are mixed, for example, silver fine particles having different particle diameters are produced by reacting a silver compound solution and a reducing material solution at a constant temperature and stirring speed. Is obtained by centrifuging and collecting the mixture so as to obtain a predetermined packing density and dispersing it in a medium to form a silver colloid solution (Patent Document 1: JP-A-10-66861). . In addition, as a method for producing a colloidal solution of silver fine particles used for a transparent conductive film forming material, a reducing agent is added to silver silver chloride solution in the presence of a protective colloid such as gelatin, and the particle size is reduced to 0 by liquid phase reduction. A method for producing silver fine particles of 0.1 μm or less is known (Patent Document 2: Japanese Patent Laid-Open No. 10-265812).

However, when the metal powder and the metal fine particles are separately manufactured and mixed, the metal nanoparticles are extremely fine powders, so it is necessary to handle them in a dispersed state in a solution such as a paste, which is complicated and costly. Get higher. On the other hand, according to the wet method, since metal nanoparticles are formed by a liquid phase reaction, it can be obtained in a solution state. However, when used in a paste or the like, the reaction solution must be separated and removed. Since the nanoparticles cannot be separated by a normal filtration method, the reaction solution is removed by centrifugation, and the metal nanoparticle dispersion solution in which the metal nanoparticles are concentrated is collected.
Japanese Patent Laid-Open No. 10-66861 JP-A-10-265812

The present invention solves the above problems in the conventional production method, and unlike the conventional mixed metal powder in which the metal powder and the metal nanoparticles are mixed, the composite metal powder in which the metal fine particles are deposited on the surface of the metal powder is provided. Furthermore, it aims at providing the method of manufacturing this composite metal powder easily.

According to the present invention, the following composite metal powder, a method for producing the same, and silver clay are provided.
(1) A composite metal powder, wherein metal fine particles having an average particle size of less than a micron size are deposited on the surface of a metal powder having an average particle size of a micron size or more.
(2) The composite metal powder according to (1) above, wherein metal fine particles having an average particle size of 20 nm or less are deposited on the surface of metal powder having an average particle size of 0.1 to 10 μm.
(3) Composite silver powder obtained by depositing silver fine particles having an average particle size of 20 nm or less on the surface of silver powder having an average particle size of 0.1 to 10 μm.
(4) The metal powder is suspended in at least one of the metal ion solution and the reducing agent solution, and both solutions are mixed to reduce the metal ions, thereby reducing the average particle diameter on the surface of the metal powder having a micron size. A method for producing a composite metal powder, comprising producing a composite metal powder in which nano-sized metal fine particles are deposited.
(5) 0.1 to 10 μm silver powder is suspended in an aqueous silver nitrate solution or a reducing agent solution, both solutions are mixed to reduce silver ions, and silver nanoparticles having an average particle size of 20 nm or less are deposited on the surface of the silver powder. (4) The manufacturing method of said (4) which manufactures silver powder.
(6) A silver clay for low-temperature firing using the composite silver powder of (3) above.

[Composite metal powder]
The composite metal powder of the present invention is characterized in that metal fine particles having an average particle size of less than a micron size are deposited on the surface of a metal powder having an average particle size of a micron size or more. Here, the metal powder having an average particle size of micron size or more is, for example, a metal powder having an average particle size of 0.1 μm or more, and the metal particle having an average particle size of less than micron size has an average particle size of 0.5. Metal fine particles of less than 1 μm. The metal species is not limited.

Specifically, the particle size of the metal powder is determined according to the application. For example, a composite metal powder formed by depositing metal nanoparticles having an average particle size of 20 nm or less on the surface of metal powder having an average particle size of 0.1 to 10 μm is a conductive material such as a conductive paste, metal clay, or transparent conductive material. It is suitable as a material such as a film.

In the composite metal powder of the present invention, for example, micron-sized metal powder and nano-sized metal fine particles are present at the same time, so that it is not necessary to individually manufacture and mix metal particles of each particle size. Therefore, it is suitable as a material such as a conductive material or metal clay containing coarse metal powder and metal fine particles, or other materials. Further, since it is a composite metal powder based on a metal powder, it can be handled as a solid even if it contains metal fine particles. Therefore, it is not necessary to make a colloidal dispersion even when stored.

〔Production method〕
The composite metal powder of the present invention is obtained by suspending metal powder in at least one of a metal ion solution and a reducing agent solution, mixing both solutions to reduce metal ions, and depositing metal nanoparticles on the metal powder surface. Can be manufactured by. The metal species, reaction conditions, and the like are not limited, and may be any conditions and metal species in which metal fine particles are precipitated by reduction of metal ions. The metal ion solution is a solution containing metal ions such as an aqueous silver nitrate solution or an aqueous silver chloride solution. The concentration of metal ions and the type of reducing agent are not limited, and metal nanoparticles may be deposited on the surface of the metal powder. The amount of precipitation can be controlled by the concentration of the metal ion solution. The kind of metal powder may be the same as the metal ion or a different metal kind.

According to this production method, a composite metal powder based on a metal powder is formed in a solution, so that the filterability is good, centrifugation is not necessary, and the composite metal powder can be easily recovered by ordinary filtration means. it can.

For example, to produce composite silver powder, silver powder is suspended in either a silver nitrate aqueous solution or a reducing agent solution such as ferrous citrate solution, and both solutions are mixed to reduce silver ions. It can be obtained by depositing silver nanoparticles. Incidentally, 10 mL of a silver nitrate aqueous solution with a concentration of 8.0 wt% adjusted to pH 1.5 and 50 mL of a ferrous citrate solution with a concentration of 18 wt% were used, and silver powder with an average particle diameter of 0.5 to 1.0 μm was used in any of the solutions. When 1.0 g is suspended and both solutions are mixed to reduce silver ions, silver nanoparticles having an average particle size of 20 nm or less are deposited on the surface of the silver powder to produce a composite silver powder. The solution is suction filtered to separate and recover the solid content, and this is washed and dried, whereby a silver powder having silver nanoparticles having an average particle size of 20 nm or less deposited on the surface can be easily obtained.

The composite metal powder of the present invention is obtained by depositing metal fine particles having an average particle size of less than micron size on the surface of metal powder having an average particle size of micron or larger. Since metal particles (metal nanoparticles) are present at the same time, nano-sized metal particles are interposed between micron-sized metal powders, and the metal powder and metal particles are in sufficient contact with each other. A material having excellent conductivity can be obtained. Moreover, since the thermal conductivity is good, a metal clay that can be sintered at a relatively low temperature can be obtained.

Further, when this is used for an electronic material such as a conductive paste, a conductive material such as a transparent conductive film, or metal clay, it is not necessary to mix metal nanoparticles with micron-sized metal powder. Moreover, since it is a composite powder based on a metal powder, it can be handled as a solid even if it contains fine particles.

Specifically, for example, a composite silver powder obtained by depositing silver nanoparticles having an average particle diameter of 20 nm (nanometer) or less on the surface of silver powder having an average particle diameter of 0.1 to 10 μm is suitable as a conductive material such as a conductive paste. In addition, it can be used as silver clay that can be sintered at a relatively low temperature. Incidentally, the sintering temperature of silver clay obtained by mixing silver powder having an average particle diameter of 0.8 μm with no silver nanoparticles on the surface into the paste is about 650 ° C. The composite silver powder of the present invention was used. The sintering temperature of silver clay is 300 to 40 ° C., and it is sintered at a lower temperature than the conventional one.

As described above, in the composite metal powder of the present invention, nano-sized metal particles are present, for example, on the surface of micron-sized metal powder, and since these are included at the same time, when obtaining a mixture of metal particles having different particle sizes, There is no need to manufacture them individually. Moreover, even if it contains fine particles, it can be handled as a solid. The composite metal powder can be widely used as a conductive material such as a conductive paste, or a material such as metal clay.

Further, according to the production method of the present invention, the composite metal powder can be produced by depositing metal nanoparticles on the surface of the metal powder in a solution, and the composite metal powder has good filterability, Since it can be easily recovered by ordinary filtration means, a composite metal powder containing metal nanoparticles can be produced at low cost.

Hereinafter, the present invention will be specifically described by way of examples.
[Example 1]
50 mL of a ferrous citrate solution having a concentration of 18 wt% was prepared by mixing 30 mL of a 10 wt% ferrous sulfate aqueous solution with 20 mL of a 27 wt% sodium citrate aqueous solution. To this solution, 1.0 g of spherical silver powder having an average particle diameter of 0.5 μm was added and stirred to be suspended. To this suspension was added 10 mL of a silver nitrate aqueous solution having a concentration of 8.0 wt% adjusted to pH 1.5 with an aqueous sodium hydroxide solution at a rate of 10 mL per minute, and the temperature was maintained at around 20 ° C. while stirring at a rotation speed of 300 rpm. The composite powder containing liquid which made it react and made silver nanoparticle precipitate on the spherical silver powder surface was obtained. Next, this silver composite powder-containing liquid was suction filtered to separate it into a solid part and a solution part, and water was added to the resulting solid part to wash away iron. The solid part after washing was dried to recover the composite powder in which silver nanoparticles were deposited on the surface of the spherical silver powder. The average particle diameter of the silver nanoparticles on the surface of the silver composite powder was 20 nm and the amount of precipitation was 0.9 g. It was confirmed that the silver nanoparticles covered the powder surface almost uniformly.

[Example 2]
Using 10 mL of an aqueous silver nitrate solution having a concentration of 8.0 wt% adjusted to pH 1.5 with an aqueous sodium hydroxide solution, 1.0 g of spherical silver powder having an average particle size of 0.5 μm was added and stirred and suspended. This suspension solution is added to a mixed solution of 30 mL of a 10 wt% ferrous sulfate aqueous solution and 20 mL of a 27 wt% sodium citrate aqueous solution, and the temperature is maintained at around 20 ° C. while stirring at a rotation speed of 300 rpm. Thus, a composite powder-containing liquid in which silver nanoparticles were deposited on the surface of the spherical silver powder was obtained. Next, this silver composite powder-containing liquid was suction filtered to separate it into a solid part and a solution part, and water was added to the resulting solid part to wash away iron. The solid part after washing was dried to recover the composite powder in which silver nanoparticles were precipitated on the surface of the spherical silver powder. The average particle diameter of the silver nanoparticles on the surface of the silver composite powder was 20 nm and the amount of precipitation was 0.9 g. It was confirmed that the silver nanoparticles covered the powder surface almost uniformly.

Claims (6)

A composite metal powder, wherein metal fine particles having an average particle size of less than a micron size are deposited on the surface of a metal powder having an average particle size of a micron size or more.
The composite metal powder according to claim 1, wherein metal fine particles having an average particle diameter of 20 nm or less are deposited on the surface of a metal powder having an average particle diameter of 0.1 to 10 µm.
A composite silver powder obtained by depositing silver fine particles having an average particle diameter of 20 nm or less on the surface of silver powder having an average particle diameter of 0.1 to 10 μm.
The metal powder is suspended in at least one of the metal ion solution and the reducing agent solution, and both solutions are mixed to reduce the metal ions. A method for producing a composite metal powder, comprising producing a composite metal powder in which metal fine particles are deposited.
Silver powder in which 0.1 to 10 μm silver powder is suspended in a silver nitrate aqueous solution or a reducing agent solution, both solutions are mixed to reduce silver ions, and silver nanoparticles having an average particle size of 20 nm or less are deposited on the surface of the silver powder. The manufacturing method of Claim 4 which manufactures.
A silver clay for low-temperature firing using the composite silver powder of claim 3.