JPH0676609B2 - Method for producing fine copper powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing fine copper powder having an average particle size in the range of 0.1 μm to several μm, and these powders are substantially single crystals. Therefore, it is stable and can be highly purified, so that it is suitable as a filler for conductive paste.

[Conventional technology]

Copper powder is conventionally produced by an electrolytic method and a spraying method.

The electrolytic method has high purity, but is dendritic and has a particle size of 10
It has a size of several μm or more and is suitable for them (for powder metallurgy,
(For shielding paints, etc.), but is not suitable as a filler for conductive paste of high temperature baking type.

In the spraying method, impurities are likely to be mixed in when dissolved, and they are also oxidized during spraying, and the shape is spherical or a tuft of grapes, and the particle size is 10μ.
Since this powder also has a large particle size and is oxidized, it cannot be said to be preferable as a filler powder.

There is also a method of reducing and precipitating copper ions in a liquid phase with a reducing agent (for example, Japanese Patent Publication No. 57-155302), and a particle size and shape suitable for a conductive paste can be obtained, but impurities from the liquid phase are easily mixed and reoxidized. However, the batch type method has drawbacks such as high manufacturing cost.

An example of producing a granular copper component by a method by a gas phase chemical reaction is disclosed (Japanese Patent Publication No. 59-7765), but the reaction temperature is 1100 ° C., and it is a polycrystalline granular powder. This powder is also preferable. It can not be said.

[Problems to be Solved by the Invention]

The present invention is suitable for high-temperature firing type copper conductive paste filler powder of 0.1 to several μm (preferably 1 to several μm for high conductive paste).
It is intended to provide a powder having a high purity of several μm and which is hard to oxidize, and to solve the problem that it is difficult to obtain a copper powder satisfying a fine particle size and stability at the same time by the conventional method.

[Means for Solving the Problems]

The present invention, in order to solve the above problems, when producing copper fine powder by the reaction of cuprous chloride vapor and reducing gas, by limiting the reaction temperature to 700 ℃ or more and less than 900 ℃, substantially Since it is a single crystal, it is stable and high-purity fine copper powder is obtained.

[Action]

In order to solve the above problems, the present inventors have
As a result of repeated research on the reaction temperature when producing fine copper powder having an average particle size of 1 by the vapor phase chemical reaction method using cuprous chloride as a raw material, the reaction rate decreases when reacted below 900 ° C. , The powder had a crystal habit, and the reaction rate was close to 100% at higher temperatures, but polycrystalline spherical particles were obtained.

The powder generation mechanism has a high reaction rate in high temperature reactions,
The aggregation process is described as rate limiting. This theory can be applied in this case as well, and it is considered that the spherical shape is caused by the growth at a temperature close to the melting point of copper.

Since the reaction rate is slow at low temperature and the precipitation on the already formed particles continues (CVD reaction), it is considered that a substantially single-crystal powder having a crystal habit with sufficient grain growth can be formed.

The present invention has been made possible by the discovery of this phenomenon.

Therefore, the requirement for producing a substantially single-crystal copper powder of 1 to several μm (surface stability and difficult to oxidize due to good crystallinity) is at a reaction temperature of less than 900 ° C. in the vapor phase reduction of cuprous chloride. It is to manufacture. However, if the temperature is too low, the reaction rate decreases and copper is less likely to precipitate. Therefore, 700 ° C or higher is required. However, this condition defines the temperature in the reaction part, not the temperature in the evaporation part of cuprous chloride.

The residence time of the cuprous chloride vapor in the reaction section is 0.05 to 5
Seconds are preferable, and if it is less than 0.05 seconds, it tends to be amorphous, and if it is more than 5 seconds, the particle size distribution of the obtained copper fine powder becomes large.

An apparatus for suitably implementing the present invention is, for example, as shown in FIG.

The cuprous chloride is accommodated in a quartz boat 3, heated in an independent evaporation section 2 and evaporated, and sent to a reaction section 5 as an inert gas such as argon as a carrier gas 4. So nozzle 6
When mixed with the reducing gas 7 such as hydrogen gas that has been fed in, a gas phase reaction occurs and copper fine powder is generated. The reaction temperature is 70
By setting the temperature to 0 ° C. or higher and lower than 900 ° C., a fine copper powder of 0.1 to several μm that is substantially a single crystal is obtained. However, since the reaction rate is slow at this reaction temperature, a considerable part of the evaporated cuprous chloride does not react and is mixed in the copper fine powder. However, since it does not exist inside one particle of the copper fine powder, the cuprous chloride can be removed by washing or the like, so that copper fine powder of sufficiently high purity can be obtained.

When the reaction temperature is 900 ° C or higher, the presence of spherical particles becomes remarkable. When the temperature is below 700 ° C, unreacted first chloride
Since a large amount of copper is deposited in the cooling section 8 and the collection section (not shown), the efficiency of producing fine copper powder is reduced.

As an apparatus for carrying out the present invention, in addition to the apparatus of the type shown in FIG. 1, various types such as a vertical furnace can be considered.

〔Example〕

Example 1 Using the apparatus shown in FIG. 1, about 5 g of cuprous chloride was put into a quartz boat, both the evaporation part and the reaction part were kept at 850 ° C., argon was used as a carrier gas at 4 l / min, and the reducing gas was Hydrogen
Flowing at 2 l / min, the fine copper powder generated by the gas phase reaction was collected.

A transmission electron micrograph of the obtained copper fine powder is shown in FIG. It can be seen that it is a truncated polyhedron, single crystal or twin crystal of face-centered cubic metal. That is, since it has few grain boundaries, it can be said to be substantially a single crystal grain.

The collected copper fine powder contains cuprous chloride and has a chlorine content of 5.0.
Although the content was weight% (hereinafter simply referred to as%), the chlorine content after cleaning and removal was 0.002%. The oxygen content is 0.05%
So, even if left in a dry atmosphere for several days, the oxygen content is
The surface remained extremely stable at 0.05%.

Example 2 Copper fine powder was produced under the same conditions as in Example 1 except that both the evaporation section and the reaction section were set to 750 ° C.

A fine copper powder having a high chlorine content of 12.5% was obtained, but after cleaning, the fine copper powder was almost the same as in Example 1.

Example 3 A fine copper powder was produced under exactly the same conditions as in Example 1 except that the evaporation part was set to 925 ° C. and the reaction part was set to 800 ° C., and copper fine powder similar to those in Examples 1 and 2 had higher productivity (evaporation). Part temperature is high and the supply rate of cuprous chloride is high).

Comparative Example 1 Copper fine powder was manufactured under the same conditions as in Example 1 except that the evaporation part and the reaction part were both set to 900 ° C., and the copper fine powder shown in the transmission electron microscope photograph in FIG. And these particles were polycrystalline.

The X-ray diffraction result of the fine copper powder obtained in Comparative Example 1 is shown in FIG.

Comparative Example 2 Copper fine powder was produced under exactly the same conditions as in Example 1 except that the evaporation part was 750 ° C. and the reaction part was 675 ° C. However, the reaction rate was extremely poor and the amount of chlorine in the copper fine powder produced was 20%. Beyond.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY According to the present invention, a fine copper powder that is substantially single crystal, has high purity, and is suitable for a stable high-temperature firing type conductive paste was obtained.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a reactor which can be suitably used for carrying out the present invention, FIG. 2 is a transmission electron micrograph of copper fine powder in an example of the present invention, and FIG. 3 is a transmission of copper fine powder in a comparative example. An electron micrograph, FIG. 4 is an X-ray diffraction diagram of the fine copper powder whose transmission electron micrograph is shown in FIG. DESCRIPTION OF SYMBOLS 1 ... Reactor, 2 ... Evaporation part 3 ... Quartz boat, 4 ... Carrier gas 5 ... Reaction part, 6 ... Nozzle 7 ... Reducing gas, 8 ... Cooling part 9 ... Copper fine powder

Claims (1)

[Claims] 1. A method for producing a copper metal powder by a vapor phase reaction between cuprous chloride vapor and a reducing gas, wherein the reaction temperature is
A method for producing a copper fine powder, which comprises producing a single crystal copper fine powder by setting the temperature to 700 ° C or higher and lower than 900 ° C.