JP3245965B2 - Production method of copper powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing fine copper powder used for copper paste and the like.

[0002]

2. Description of the Related Art Copper powder used for copper paste is 1 μm.
Copper particles with a particle size of 1 μm or less have high activity, and when baked on a substrate using a copper paste, the bonding strength is improved by chemical bonding at the interface with the substrate, The feature is that a dense and high-quality copper electrode can be formed. In order to produce such fine copper powder, various production methods such as an electrolysis method, a spray method, a gas reduction method, and a mechanical pulverization method are conventionally known. However, these methods require time and effort for production. In addition, there are problems that impurities are easily mixed therein, and that the particles of the produced copper powder are large and irregular in particle size.

[0003] In order to solve such a problem, the present applicant has proposed a method of mixing a copper-containing solution containing copper pyrophosphate, cupric chloride or copper formate with hydrazine or a hydrazine compound and heating the mixed solution. A method for producing copper powder by reducing and precipitating copper powder by the method described in Japanese Patent Application Laid-Open No. 3-28.
No. 7707).

[0004]

According to this, when copper pyrophosphate is used as a starting material, the average particle size of the obtained copper powder is 0.6 μm, and when copper (II) chloride is used, the average particle size is 0.6 μm. It was 3 μm. However, when copper formate was used as a starting material, a uniform copper powder having a small particle size distribution width was obtained, but the average particle size was as large as 5 μm. Therefore, an object of the present invention is to provide a method for producing a copper powder that can obtain ultrafine particles having an average particle diameter of 1 μm or less and a uniform copper powder having a small particle diameter distribution width using copper formate. is there.

[0005]

In order to achieve the above object, a method for producing a copper powder according to the present invention comprises adding a pH adjusting solution to a copper-containing solution containing copper formate to adjust the solution pH to 6 or less.
To 14, a step of mixing the pH-adjusted copper-containing solution with hydrazine or a hydrazine compound, and a step of heating the mixed solution to cause the copper powder to undergo reductive precipitation.

[0006]

According to the present invention, copper formate is used as a starting material, and a pH adjusting solution is added to the aqueous solution to adjust the solution pH to 6 to 14.
Adjust to Next, when a hydrazine or a hydrazine compound as a reducing agent is mixed with this copper-containing solution and heat-treated, copper in the copper salt is reduced and precipitated, the average particle size is 1 μm or less, and the particle size distribution width is small and uniform. Copper powder is obtained.

[0007] The appropriate temperature of the heat treatment is 20 ° C to 100 ° C.
Is desirable. The reason is that when the temperature is lower than 20 ° C., the reductive precipitation of the copper powder is insufficient, and when the temperature exceeds 100 ° C., the particle size of the reductively precipitated copper powder is large and the variation in the particle size is large. The heating time is not particularly limited. 1
Deposition of copper powder occurs even for 0 minutes, but unreacted substances remain, so that 30 minutes to 3 hours are preferable. If the time exceeds 3 hours, aggregation of the precipitated copper powder occurs. As the pH adjusting solution, an aqueous solution of sodium hydroxide, potassium hydroxide, ammonia or the like can be used. Examples of the hydrazine or hydrazine compound include hydrazine itself, hydrazine hydrate, hydrazine hydrate, hydrazine sulfate, hydrazonium sulfate, hydrazonium chloride and the like. The mixing ratio of copper formate to hydrazine or a hydrazine compound is not particularly limited, but 1 to 15 moles of hydrazine is suitable for 1 mole of copper formate. If the amount is less than 1 mol, the reaction rate is low and unreacted materials remain. If the amount exceeds 15 mol, the yield is poor, and fine-particle copper powder cannot be obtained with a particle size.

[0008]

EXAMPLES Copper formic acid _{[Cu (HCOO) 2 · 4H 2} O ] 3
An aqueous solution (pH adjusting solution) in which sodium hydroxide was dissolved was added to a solution in which 50 g was dissolved in 2500 cc of water, and the solution pH was adjusted to 6 to 14. This solution and hydrazine hydrate were mixed, and this mixed solution was heated to 80 ° C. (heating time was 2 hours) to obtain a precipitated powder. This was allowed to cool for 1 hour, filtered at room temperature using a glass filter, washed with water of pH 7, washed with acetone, and dried. The average particle size and particle size distribution of the copper powder thus obtained are shown in the following table together with comparative examples. The particle size and the particle size distribution were determined from a scanning electron micrograph.

[0009]

[Table 1] In Table 1, in Comparative Example, no pH adjusting solution (sodium hydroxide) was added, and the solution pH represents the pH of the copper formate solution itself.

As is apparent from Table 1, the p of copper formate solution
The larger H is, the smaller the average particle size is,
Conversely, if the pH is too high, the particle size distribution ratio tends to be relatively large. For example, in Example A, the particle size distribution ratio is in the range of 0.5 to 2, in Example B, the particle size distribution ratio is in the range of 0.4 to 1.6, and in Example C, the particle size distribution ratio is 0. 0.3 to 2.3. In addition, when the copper powder finally obtained was observed by an electron micrograph, it was a spherical powder having a small aggregation and a good dispersibility and a high purity containing almost no impurities.

This copper powder is mixed with a glass frit and an organic varnish to form a copper paste, and is also used as a fine powder additive to the paste. Since the copper powder had good dispersibility, it was uniformly mixed with the glass frit and the organic varnish to obtain a homogeneous paste. This paste is printed and applied on a ceramic substrate or the like, and then baked in a non-oxidizing atmosphere such as nitrogen. The thus obtained electrodes and circuit patterns had good solderability and sufficient adhesive strength, and a highly reliable thick film circuit could be obtained.

[0012]

As is apparent from the above description, according to the present invention, the pH of the copper formate solution is previously adjusted to 6 to 14, that is, almost neutral or alkaline, by a pH adjusting solution, and the hydrazine is added thereto. Alternatively, by adding a hydrazine compound and precipitating copper powder by a wet reduction method, a homogeneous copper powder having an average particle size of 1 μm or less and a small particle size distribution width can be obtained.

Claims (1)

(57) [Claims] A step of adjusting the solution pH to 6 to 14 by adding a pH adjusting solution to a copper-containing solution containing copper formate; and mixing the pH-adjusted copper-containing solution with hydrazine or a hydrazine compound. A method for producing a copper powder, comprising: a step of reducing and precipitating a copper powder by heating the mixed solution.