JPH11264001A - Flake copper powder and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce flake copper powder whose surface is uniformly coated with an oxidation inhibitor and excellent in oxidation resistance, particularly in heat resistance and moisture resistance by a dry method. SOLUTION: This flake copper powder having <=0.5% oxygen concn. is coated with an organic compd. having <=200 deg.C m.p. and formed into the shape of solid powder at an ordinary temp. In the flake copper powder, the coating weight of the solid powder-shaped organic compd. is regulated to 0.01 to 5.0% to the weight of the copper powder, preferably to 0.05 to 3.0%. The solid powder- shaped organic compd. is composed of one or >= two kinds selected from stearic acid, myristic acid, citric acid, glutaric acid, palmitic acid and maleic acid. Furthermore, as for the method for producing the flake copper powder, copper powder obtd. from an atomizing method, an electrolyzing method or a chemical reducing method and an solid powder shaped organic compd. are subjected to dry blending and pulverizing, and after that, size regulation is executed by a pneumatic classifier having certain screen meshes. The dry blending and pulverizing at this time are executed by using a ball mill or a vibrating mill, and the size distribution of the raw material copper powder is the one which passes all of 63 μm in JIS standard meshes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flake copper powder and a method for producing the same, and more particularly to a flake copper powder suitable as a conductive filler for a conductive paste or a conductive adhesive and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, conductive pastes used in the field of chip parts, contact materials and the like in electronic component mounting techniques for OA equipment, portable communication equipment, etc. include:
There is a conductive metal powder or flake containing silver or silver-palladium as a main component mixed with a resin binder or a glass frit. These pastes are mainly baked, and are used for through holes in printed wiring boards, wiring crossovers, electrodes, and the like.
Conductive pastes using conductive metal powders or flakes containing silver or silver-palladium as a main component are excellent in conductivity and oxidation resistance, but metal powders such as silver and palladium are expensive. In addition, stable acquisition is difficult, and there is a problem in migration resistance. Therefore, inexpensive copper powder having excellent conductivity in place of expensive silver and palladium has been increasingly demanded as a conductive filler, especially in combination with the surface treatment which has been significantly improved in recent years.

[0003] The copper powder used for the copper paste as described above is inexpensive compared to silver powder, is easily available, and has high productivity. On the other hand, surface oxidation is liable to occur. Oxidation resistance, especially heat resistance and moisture resistance of the used thick film conductors and contact portions are degraded, leading to a situation in which the quality of various parts becomes problematic. For this reason, it is conceivable to coat the surface of the copper powder used for the above applications with an antioxidant. There are two methods of coating the antioxidant on the copper powder surface, a wet method and a dry method, but the wet method involves washing, water separation, drying, etc. in the process, and it is difficult to obtain an excellent oxidation resistance. Since the treatment requires a long time and is inferior in productivity, it can be said that the dry method is suitable for actual operation.

Japanese Patent Application Laid-Open No. 7-278614 discloses a method of adding a fatty acid (stearic acid) to the surface of copper powder and performing dry pulverization to produce spherical copper powder having excellent appearance and solderability. However, in the conventional copper powders including the publication, the degree of oxidation was used as an index based on the weight loss of hydrogen reduction and the like, but the surface treatment agent or the like attached or coated on the copper powder surface was also determined. Therefore, the degree of oxidation of the copper powder itself has not been measured, and is an unreliable absolute index of the degree of oxidation when used as an actual conductive filler, etc. It was ambiguous and could only take indirect judgments based on the appearance and solderability, and the superiority of oxidation resistance based on specific oxygen concentration was not expected. Further, the copper powder described in the publication has a spherical shape, and is mainly referred to as a method for producing copper powder for maintaining the spherical diameter within a predetermined range.

In view of the above circumstances, the present invention provides a flake copper powder excellent in acid resistance, particularly heat resistance and moisture resistance, the copper powder of which surface is coated with an antioxidant by a dry method. Aim. The present inventors have made intensive efforts to achieve these objects, and as a result, the oxygen concentration itself of the flake copper powder has a great effect on the oxidation resistance. For copper powder having an oxygen concentration exceeding a predetermined amount, conductive fillers such as As an antioxidant, an organic compound that is in the form of a solid powder at room temperature as an antioxidant, and when its melting point is below a predetermined value, these organic compounds are uniformly coated on the surface of the flake copper powder. Was obtained. The present invention is based on these findings.

[0006]

Means for Solving the Problems The flake copper powder according to the present invention is a flake copper powder having an oxygen concentration of 0.5% or less,
This problem has been solved by a flake copper powder coated with an organic compound having a melting point of 200 ° C. or less and forming a solid powder at room temperature. In the flake copper powder of the present invention, the coating amount of the solid powdery organic compound is 0.01 to 5.0%, preferably 0.05 to 3.0% based on the weight of the copper powder. The solid powdery organic compound is stearic acid, myristic acid,
Any one or two or more selected from citric acid, glutaric acid, palmitic acid, and maleic acid. Further, the method for producing flake copper powder according to the present invention is a method of dry-mixing and pulverizing copper powder and a solid powdery organic compound obtained from an atomizing method, an electrolytic method, and a chemical reduction method, and then wind classification having a certain sieve mesh. The particle size is adjusted by a machine. The dry mixing and pulverization at this time is performed using a ball mill or a vibration mill, and the particle size distribution of the raw material copper powder passes through all 63 μm of the JIS standard sieve.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The copper powder used in the present invention is generally obtained by a production method such as an atomizing method, an electrolytic method, and a chemical reduction method. Preferably, the copper powder has a fine particle size distribution and is not oxidized as much as possible, and the shape is not particularly limited, such as spheres, grains, and dendrites. The degree of oxidation is important as a raw material powder, and as an example of an analysis method, the degree of oxidation of copper powder itself can be quantified with good reproducibility by an inert gas-impulse heating melting method (non-dispersive infrared absorption method). .
The oxygen content of the copper powder used in the present invention is 0.5% or less, preferably 0.3%
Or less, more preferably 0.1% or less. In addition,
The particle size distribution of the copper powder raw material should pass through all the 63 μm nets of the JIS standard sieve, and preferably be fine copper powder which further passes 50% or more through the 45 μm net.

Next, the solid powdery organic compound used together with the above-mentioned copper powder raw material has a melting point of 200 ° C. or lower, preferably 150 ° C. or lower, and is solid at room temperature. Specific compounds include stearic acid, myristic acid, citric acid, glutaric acid, palmitic acid, maleic acid and the like. It is preferable that these solid powdery organic compounds are sufficiently pulverized before being mixed with the copper powder, and the finer the finer the better the compatibility with the raw material copper powder. The coating amount of the solid powdery organic compound with respect to the raw material copper powder is 0.01 to 5.0% by weight, preferably 0.05 to 3.0% by weight. When the coating amount is less than 0.05 wt%, the oxidation resistance starts to gradually decrease, and when the coating amount is less than 0.01 wt%, the tendency becomes remarkable. The coating amount is 3.0wt%
If the amount exceeds 5.0%, the oxidation resistance starts to decrease gradually. If the amount exceeds 5.0% by weight, the tendency becomes remarkable.

The method for producing flake copper powder obtained from the above-mentioned copper powder raw material and solid powdery organic compound will be described.
First, copper powder and a treating agent are charged into a container such as a ball mill. In this case, a ball for flakes is put in the container in advance. Then, while the container is closed and the container is kept in a sealed state, the container is horizontally rotated or vibrated for a predetermined time to form flakes. At this time, the copper powder is beaten by the filled ball to be flaked, and the surface is uniformly coated with the solid powdery organic compound to be coated. In addition, frictional heat is generated at the time of flakes, whereby the solid powdery organic compound having a melting point of 200 ° C. or lower, preferably 150 ° C. or lower reaches the melting point and smoothly promotes surface treatment. In the flake state, the aspect ratio tends to increase in proportion to the vibration time or the like, but it is preferable to appropriately adjust the processing time in consideration of economical aspects. The flaked copper powder is then adjusted in particle size distribution by an air classifier having a certain mesh. This air classification is a method of obtaining a powder having a desired particle size by interposing a screen having a certain aperture in a carrier fluid. A typical example of such a classifier is a flow-through type high-bolter classifier. At the time of flake formation, it is preferable that the inside of the container is replaced with a vacuum or an inert gas to prevent the oxidation from further progressing.

In general, copper powder has a very high stretchability, and when mixed and pulverized using a ball mill or the like, the copper powder agglomerates with each other to form a large flake. And, the melting point is 200 ℃ or less, preferably to mix and pulverize the solid powdery organic compound having a temperature of 150 ℃ or less together with copper powder, the organic compound is dissolved by frictional heat in a ball mill and adsorbed on the copper powder surface, Acts like a kind of inclusion that suppresses agglomeration between copper powders, prevents the flake copper powder from agglomerating and coarsening, and can obtain uniform and fine flake copper powder. The flake copper powder obtained by the present invention can be used for various applications, and can be suitably used as a conductive filler such as a conductive paste and a conductive adhesive.

[0011]

EXAMPLE A raw material copper powder obtained by the production method shown in Table 1 and a copper powder having an oxygen concentration and an average particle diameter thereof were used. 1.5 kg was charged into a 10-liter pot container together with copper powder in the amount shown, in which a 5.0 mmφ (14 kg) ball was placed.
Flaking and surface coating were performed by mixing and grinding for an hour. The oxygen content was measured by an inert gas-impulse heating melting method (non-dispersive infrared absorption method), and the average particle size was measured by a laser diffraction method.

The obtained flake copper powder was subjected to particle size adjustment using an air classifier having a mesh size of 25 μm, the oxygen content of the flake copper powder was measured, and the oxidation resistance was tested. The oxidation resistance test was conducted on heat resistance and moisture resistance.The heat resistance was measured after keeping the flake copper powder at 85 ° C for 240 hours, and the moisture resistance was maintained at 45 ° C and 95% RH for 240 hours, and the oxygen content was changed. The rate was measured. In all of the examples, the product recovery rate exceeded 97%. Table 1 shows the results. FIG. 1 shows a photograph of the flake copper powder obtained in Example 7 taken with a scanning electron microscope at a magnification of 3000.

[0013]

[Table 1]

[0014]

Comparative Example A comparative test was performed using the same copper powder as in Examples 1 to 4. Comparative Example 1 was mixed and pulverized for 24 hours using 5 liters of water and stearic acid together at the time of flake formation, and then dewatered
Drying was performed. The product recovery in this case was 85%.
Comparative Example 2 was treated in the same manner as in Example 1 except that the amount of stearic acid as a solid powdery organic compound was increased. Comparative Example 3 was treated in the same manner as in Example 2 except that oleic acid that was liquid at room temperature was used. Comparative Example 4 was treated in the same manner as in Example 2 except that sodium stearate having a melting point of 288 ° C. was used. Table 2 shows these results.
Shown in

[0015]

[Table 2]

From the above Examples of the present invention and Comparative Examples, it can be seen that when the oxygen content of the flake copper powder is 0.5% or less, a product excellent in oxidation resistance can be obtained. In addition, organic compounds cannot be flaked unless they are in the form of solid powder. When the amount of the organic compounds in the form of solid powder is 5.0 wt% or less, and even less than 3.0 wt%, the oxidation resistance becomes poor. It can be seen that when a compound having a melting point of the organic compound exceeding 200 ° C. is used, heat resistance becomes poor.

[0017]

According to the present invention as described above, flake copper powder can be obtained by a dry method without using a wet method, thereby improving productivity and greatly improving yield. Accordingly, silver or silver-palladium or the like can be used instead of silver or silver-palladium as a conductive filler such as a conductive paste in an electronic component mounting technique, and flake copper powder which is extremely inexpensive, uniform and excellent in oxidation resistance can be obtained.

[Brief description of the drawings]

FIG. 1 shows a flake copper powder obtained in Example 7 of the present invention of 3000
It is a scanning electron microscope photograph shown by the magnification.

Claims (7)

[Claims] 1. A flake copper powder obtained by coating a flake copper powder having an oxygen concentration of 0.5% or less with an organic compound having a melting point of 200 ° C. or less and forming a solid powder at room temperature. 2. The flake copper powder according to claim 1, wherein the coating amount of the solid powdery organic compound is 0.01 to 5.0% based on the weight of the copper powder. 3. The flake copper powder according to claim 1, wherein the coating amount of the solid powdery organic compound is 0.05 to 3.0% based on the weight of the copper powder. 4. The solid powdery organic compound is one or more selected from stearic acid, myristic acid, citric acid, glutaric acid, palmitic acid, and maleic acid. The flake copper powder according to the above. 5. A flake copper powder obtained by dry mixing and pulverizing a copper powder obtained by an atomizing method, an electrolytic method, and a chemical reduction method and a solid powdery organic compound, and then adjusting the particle size by an air classifier having a predetermined sieve mesh. Production method. 6. The copper powder raw material has a particle size distribution of 63 according to JIS standard sieve.
The method for producing flaked copper powder according to claim 5, wherein all of the flaked copper powder passes through μm. 7. The method for producing flake copper powder according to claim 5, wherein the dry mixing and pulverization is performed using a ball mill or a vibration mill.