JPH0353092A - Production of copper fine powder - Google Patents

Abstract

PURPOSE:To efficiently produce the copper fine powder to be used for a conductive paste, an electrically conductive coating, etc., by specifying the time interval for scraping the copper powder deposited on a cathode plate in the electrolytic production of copper powder. CONSTITUTION:Electrolytic copper is ordinarily used as the anode and a copper sheet or a Ti sheet as the cathode, when copper powder is electrolytically produced. The electrodes are alternately arranged at regular intervals. An electrolyte acidified with sulfuric acid and contg. about 2.5-10g/l of copper is used, and the current density is controlled to about 10-30A/dm<2>. In this case, the time interval for scraping the copper powder deposited on the cathode plate is adjusted to <=60sec. Consequently, copper fine powder having <=10mum, or preferably 2-5mum, average particle diameter is obtained.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for producing fine copper powder using an electrolytic method.

[Prior Art] In recent years, various regulations have been put in place to prevent erroneous movements of electronic components and the like due to electromagnetic waves, and various methods have been proposed in response. Among these, conductive pastes, conductive paints, etc. using fine copper powder have come to be used in large numbers because they have a high electromagnetic shielding effect and are inexpensive.

The average particle size of fine copper powder used for these purposes is 10μ.
m or less, preferably 2 to 5 μm,
Currently, the demand for copper fine powder of less than 10 μm is being produced as follows: (1) Adding sodium borohydride or dimethylamine borane as a reducing agent to an aqueous solution containing copper ions (2) ) A method in which bismuth is added to an aqueous copper sulfate solution and reduced under pressure with hydrogen. (3) A method in which copper oxide is reduced with hydrazine and/or a hydrazine compound in an aqueous medium containing a protective colloid. (4) A method in which the copper compound is reduced to a temperature below its melting point. Methods of reducing copper with C○, H, etc. at high temperatures (5) Methods of evaporating and condensing copper in a vacuum or inert gas (6) Methods of atomizing molten copper using a high-pressure spray device are known. .

However, these methods: (1) require chemicals as raw materials and auxiliary raw materials, resulting in high costs ((1), (2) above);

■ Special equipment is required and costs are high ((2)
), (4), (5), (6)).

■ Difficult to control particle size and low yield.

It has the following drawbacks.

Furthermore, in the production of copper powder by conventional electrolytic methods, the present situation is that only powder having an average particle size of 20 to 40 μm can be obtained.

[Means for Solving the Problems] In order to solve the above problems, the inventors of the present invention have conducted intensive studies on a method for producing copper powder using an electrolytic method, which is considered to be especially suitable for continuous and mass production. The inventors have discovered that by setting the scraping interval to 60 seconds or less under the electrolytic conditions described above, fine copper powder having an average particle size of 10 μm or less can be obtained in good yield, leading to the present invention.

Therefore, it is an object of the present invention that the average particle size used for conductive pastes, conductive paints, etc. be less than 10 μm, preferably 2 to 5 μm.
It is an object of the present invention to provide a method for producing fine copper powder using an electrolytic method that can efficiently produce fine copper powder of μm size.

[Structure of the Invention] That is, the present invention provides a method for producing copper powder by electrolytic method, in which the average particle size of the fine copper powder is reduced by scraping the copper powder electrodeposited on the cathode plate at a scraping interval of 60 seconds or less. IOμ
Provided is a method for producing fine copper powder, characterized in that the particle diameter is less than or equal to m.

[Specific Description of the Invention] Next, the present invention will be described in detail in order to facilitate understanding of the present invention.

When producing copper powder by an electrolytic method, electrolytic copper is usually used as an anode, and a copper plate or a Ti plate is used as a cathode. Then alternate these at appropriate intervals (approximately 20
~50n/m).

The electrolyte used is acidic with sulfuric acid and has a copper concentration of 2.5 to 10 gi. When the copper concentration is less than 2.5 g/Q, it is difficult to control the copper concentration in the electrolyte;
If it exceeds this, the particle size of the copper powder obtained will become coarse, making it impossible to obtain the target fine copper powder.

The liquid temperature is 10-35°C, preferably 20-25°C. 1
If it is less than 0°C, special equipment will be required for liquid temperature control, which is impractical, and if it exceeds 35°C, the particle size of the resulting copper powder will become coarse.

Preferably, a diaphragm is used to prevent contamination by anode slime generated from the anode during electrolysis;
Further, the electrolytic solution is circulated in the same manner as in normal electrolytic refining to make the concentration of the electrolytic solution uniform in the electrolytic cell.

In addition, copper powder electrolysis is not necessarily 100% efficient, so
As electrolysis continues, the copper concentration increases and the sulfuric acid concentration decreases. Therefore, it is necessary to appropriately perform copper removal electrolysis (acid-forming electrolysis) during the liquid circulation process to control the copper concentration and sulfuric acid concentration to appropriate values.

On the other hand, trace amounts of organic additives eluted from the anode can be removed by passing the solution through a column filled with activated carbon or the like, if necessary.

The current density is 10 to 30 A/dm.1
If it is less than 0 A/dm', copper powder with the target particle size cannot be obtained, and if it exceeds 30 A/dm', the anode becomes passivated, which is not preferable.

The scraping interval must be 60 seconds or less.

If it exceeds 60 seconds, the particle size of the copper powder becomes coarse, and the yield of copper powder with the target particle size of 10 μm or less, preferably 2 to 5 μm becomes poor.

The scraping method involves using acid-resistant rubber, Teflon (trade name), soft PVC, etc., and mechanically moving the cathode surface where copper powder is generated up and down at the same time as the front and back sides so that the cathode does not move. etc., it is possible to attain the precepts.

The thus obtained fine copper powder having an average particle size of 10 μm, preferably 2 to 5 μm, is separated by natural sedimentation in a hopper at the bottom of the electrolytic cell or, in some cases, by providing a thickener in the liquid circulation process. After extraction, washing with water, rust prevention, dehydration, drying, and sieving, the product is made into a product. In the rust prevention process, the copper powder handled is very fine and easily causes surface oxidation during drying, so sufficient rust prevention treatment is required. It is necessary to select according to the copper powder that can obtain the copper powder and its concentration.

At this time, reduction may be carried out using sodium borohydride if necessary, or reduction may be carried out using H or gas after drying.

Examples will be described below.

[Example] 100mmWX 120+nmHX I as anode
3 pieces of Ommt electric steel, 100mm WX as a cathode
Using two Ti plates of 120 mm HX5 + nn + t, anodes and cathodes were alternately arranged with a distance of 35 mm, and electrolysis was performed for 48 r under various electrolytic conditions. The obtained copper powder was washed with water until the pH of the washing water became 6 to 7, stirred for 5 minutes in a rust preventive solution of Colomin (trade name) 3 mQ/Q, and then washed in an ethanol solution. After immersion in water for 2 minutes, vacuum drying was performed at room temperature. The copper powder thus obtained was crushed in an automatic mortar for 10 minutes, and then sieved using a 350 mesh sieve.

Table 1 shows the electrolysis conditions and test results.

Table 1: Average particle size was measured using a Shimadzu CP-50 centrifugal sedimentation particle size analyzer.

Zero 2: Passivated and cannot be electrolyzed.

As can be seen from Table 1, fine copper powder having an average particle size of 10 μm or less was obtained in Inventive Examples Na1 to 10, and the yield was 90% or more in all cases.

On the other hand, in the comparative example Seed 1 1, the copper concentration force v15g/
In Nll2, the current density is as low as 5 A/dm, and in l'hl4 and l5, the scraping interval is 90 seconds,
(2) Because it takes 20 seconds, the average particle size exceeds 10 μm.

On the other hand, in P&Ll4, the current density is as high as 35 A/di'', so the anode becomes inactive and copper powder cannot be obtained.

〔Effect of the invention〕

As shown above, according to the present invention, copper fine powder with an average particle size of 10 μm or less, preferably 2 to 5 μm, which is suitably used for conductive pastes, conductive paints, etc., can be efficiently produced by an electrolytic method. I was able to establish a method.

Claims (1)

[Claims] (1) A method for producing copper powder by electrolytic method, characterized in that the average particle size of the copper powder is made 10 μm or less by scraping off the copper powder electrodeposited on the cathode plate at 60 seconds or less. A method for producing fine copper powder.