JPH0593214A - Production of fine copper powder - Google Patents

Abstract

PURPOSE:To stably and industrially produce a fine copper powder consisting of the uniform grains having a narrow grain size distribution and having sufficient oxidation resistance. CONSTITUTION:A fine copper powder is produced utilizing disproportionation reaction. In this case, a first aq. acidic soln. contg. cuprous ion and kept at <=pH2.5 and a second aq. acidic soln. kept at <=pH2.5 and having the temp. lower than that of the first soln. are mixed to cause a reaction.

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 which has a narrow particle size distribution and is excellent in oxidation resistance and is suitable for conductive paste and the like.

[0002]

2. Description of the Related Art In recent years, there is an increasing demand for fine copper powder for use in conductive fillers such as paints, pastes, and resin molded products. It is required that the shapes are uniform, b) the specific surface area is not so large, c) the dispersibility is good, d) the width of the particle size distribution is narrow, and e) the oxidation resistance is excellent. In particular, in the case of fine copper powder for conductive paste, the requirements for the above characteristics are very strict, and there has been a strong demand for a means capable of mass-producing copper fine powder having a particle size of 0.2 to 5 μm, which satisfies these requirements, on an industrial scale. Under such circumstances, recently, as a suitable means for producing fine copper powder having a narrow width of particle size distribution, by rapidly cooling an aqueous solution of cuprous sulfate in a high temperature state, Cu ⁺ in the aqueous solution becomes unstable. A method for producing copper powder by a so-called "disproportionation reaction", which causes a rightward reaction (cooling reaction) to precipitate fine copper powder, has been proposed (Japanese Patent Laid-Open No. 63-310910).

However, the fine copper powder obtained by this method is surely a uniform particle having a remarkably small particle size variation as compared with the conventionally used method such as "a method of hydrogen pressure reduction of an aqueous solution of copper sulfate". However, there is a problem in that the oxidation resistance is not sufficient and the color tends to change when left in the air for a certain period of time. In addition, in this kind of fine copper powder, "excellent oxidation resistance" is also a required characteristic in order to secure a stable effect related to conductivity, etc., and improvement of oxidation resistance is necessary for practical use. Needless to say, it was necessary.

In view of the above, the object of the present invention is to prepare a fine copper powder having uniform particle size distribution with a narrow width and having sufficient oxidation resistance, in a particularly large-scale equipment and It was to establish an industrial means capable of stable production without requiring expensive chemicals.

[0005]

In order to achieve the above-mentioned object, the inventors of the present invention firstly explained the reason why the fine copper powder obtained by the method proposed in JP-A-63-310910 is inferior in oxidation resistance. As a result of an examination, "the method is characterized in that a disproportionation reaction is caused by transferring a high temperature cuprous sulfate aqueous solution to a cooling tank and rapidly cooling it. Fine copper powder tends to have an irregular shape with a rough surface, which leads to poor oxidation resistance. "

Therefore, the present inventors have further studied the possibility of depositing fine copper powder having a smooth surface by a disproportionation reaction, and as a result, "a high-temperature acidic aqueous solution containing cuprous ions is prepared. Prepared and mixed with a lower temperature acidic aqueous solution, The reaction in the right direction of "No.1" progresses relatively smoothly, and unlike the case where the high temperature cuprous ion-containing acidic aqueous solution is rapidly cooled as it is, "fine copper powder with a narrow grain size distribution and a smooth crystal surface"
Will be stably deposited, and it is possible to control the average particle size of the fine copper powder to be deposited by adjusting the cooling conditions after the above-mentioned mixing operation. "

The present invention has been completed on the basis of the above-mentioned findings and the like. "When producing fine copper powder by utilizing a disproportionation reaction, the temperature containing the prepared cuprous ion: 50 ° C As described above, by mixing a first acidic aqueous solution having a pH of 2.5 or less and a second acidic aqueous solution having a pH of 2.5 or less and having a temperature lower than that of the first acidic aqueous solution to cause a reaction, oxidation resistance is improved. The point is that stable and fine copper powder with a uniform particle size can be obtained ”.

[0008]

Despite the method for producing fine copper powder using the same disproportionation reaction, the method of "high-temperature cuprous sulfate aqueous solution to a cooling tank proposed in JP-A-63-310910 is used. In the method of "transferring and rapidly cooling", the following is considered as the reason why the precipitated copper powder does not have a rough and irregular surface and does not have a smooth crystal surface. That is, when the high temperature Cu ⁺ ion-containing acidic aqueous solution is cooled, nucleus generation and nucleus growth (crystal growth) occur to form fine copper powder.
It is desirable to slow down the copper deposition rate in order to make the crystal plane that leads to a smooth surface beautiful, and a state where a considerable amount of Cu ⁺ ions remain after the nucleation at a low temperature (with a certain degree of supersaturation). While it is important to carry out crystal growth while suppressing new nucleation in the above condition), in the above proposed method, cooling was simply “quick cooling” with a focus on “fine grain size”. The growth proceeded rapidly and only amorphous fine powder with a rough surface was obtained.

On the other hand, in the method according to the present invention,
In order to cause and proceed the disproportionation reaction by cooling the “high-temperature acidic aqueous solution containing cuprous ion” with the “lower-temperature acidic aqueous solution”, it is possible to After nucleation occurred from a state where the cooling was relatively slow and the supersaturation was sufficient, the copper deposition rate slowed down during the crystal growth stage, forming a smooth fine copper powder with a well-defined crystal surface. To be done. Moreover, since there is a room to adjust the cooling conditions after mixing the two liquids, it is possible to control the grain growth, and thus it is possible to easily control the average grain size of the fine copper powder.

In the present invention, the acid concentrations of the "first acidic aqueous solution" and the "second acidic aqueous solution" are p in order to avoid formation of cuprous oxide and precipitation of impurities other than copper.
H is 2.5 or less (more strongly acidic than 2.5), but the pH is adjusted to 1.0 or less to ensure the above action even when the "first acidic aqueous solution" is at a higher temperature. Is desirable. Also, "first acidic aqueous solution containing Cu ⁺ ions" and "second acidic aqueous solution" may be all inorganic acid acidic aqueous solutions, but from the viewpoint of industrial use and ease of repeated use. Both are preferably "sulfuric acid-acidified copper sulfate aqueous solution". However, in this case, if the temperature of the “first acidic aqueous solution” is lower than 50 ° C., the Cu ⁺ ion concentration is not stable and a high concentration cannot be secured even if the supersaturation degree is taken into consideration. The liquid temperature should be 50 ° C. or higher because the amount of fines collected will not be sufficient. However, in the above-mentioned disproportionation reaction, the Cu ⁺ ion concentration is more stable and the concentration becomes higher as the temperature becomes higher.
It is preferable to keep the liquid temperature of the "first acidic aqueous solution" at 0 ° C or higher). Even if the temperature is 100 ° C. or less, a fine copper powder can be obtained by adding a stabilizer for Cu ⁺ ions, such as hydrochloric acid or acetonitrile, with a simplified apparatus and without significantly reducing the recovery amount.

By the way, in an acidic aqueous solution containing Cu ⁺ ions, it is considered that nucleation and crystal growth may occur due to temperature elapse after adjustment. When such a phenomenon occurs in the acidic aqueous solution to be used, there arises a problem that the particle size distribution of the recovered fine copper powder becomes broad. Therefore, when such a problem is concerned, Cu
It is desirable that the ⁺ ion-containing acidic aqueous solution (in the present invention, at least the “first acidic aqueous solution” is a Cu ⁺ ion-containing acidic aqueous solution, so at least the “first acidic aqueous solution”) is used after filtering. Further, in order to suppress the coagulation of the fine powders and to make them monodisperse, to cause a disproportionation reaction in the presence of a protective colloid as disclosed in JP-A-63-310911, the particle size distribution is sharpened. It is effective in doing.

Regarding the solution temperature when the "first acidic aqueous solution" and the "second acidic aqueous solution" are mixed (this is determined by the temperature difference between the two solutions and the amount of the solution), what is the average particle size of copper? Although various adjustments can be made depending on whether the fine powder is collected, it is preferably 100 ° C. or lower from the viewpoint of simplifying the apparatus. The atmosphere for mixing the above two liquids is not particularly limited when the liquid temperature is low, but when the liquid temperature is high, the reoxidation of Cu ⁺ ions cannot be ignored. In such cases, it is desirable to use a non-oxidizing atmosphere. However, it was confirmed that even if such reoxidation occurs, the recovery rate of the obtained copper fine powder only decreases and does not affect the particle size and shape.

Next, the present invention will be described more specifically by way of examples.

EXAMPLES Example 1 1 L (liter) of sulfuric acid acidic copper sulfate aqueous solution (Cu: 48 g / L, FreeH ₂ SO ₄ : 50 g / L) was put into an autoclave filled with a thin copper wire, and the atmosphere was changed to N. After replacing with ₂ gas, raise the temperature to 220 ° C The leftward disproportionation reaction was allowed to proceed and held for 30 minutes to prepare an acidic aqueous solution having a Cu ⁺ ion concentration of 28 g / L.

On the other hand, a large stainless steel pot was also prepared, and 4 L of an aqueous copper sulfate solution at room temperature (20 ° C.) having the same composition as that in the autoclave was stored in the pot and the atmosphere was set to N 2. _It was replaced with ₂ gases.

Next, the high temperature aqueous solution (220 ° C.) in the autoclave is jetted into the stainless steel pot at normal pressure and room temperature to obtain a 4 L copper sulfate aqueous solution contained in the pot. Mixed. The temperature of the high-temperature aqueous solution, which became normal pressure by this injection, was 104 ° C, and the liquid temperature was 7 by mixing.
It has reached 0 ° C. Subsequently, this mixed solution was held for 12 hours while being gently stirred.

Then, the mixed solution in which the copper powder was deposited and suspended was filtered and washed, and 11 g of fine copper powder having a very narrow particle size distribution with an average particle size of about 0.7 μm was recovered.

When the surface of this copper fine powder was observed with an electron microscope, it was confirmed that it was surrounded by smooth crystal faces as shown in the electron microscope photograph of FIG. Even when the obtained fine copper powder was left in the air for 3 months, no discoloration was observed.

Example 2 Example 1 was repeated except that the liquid temperature of 4 L of the copper sulfate aqueous solution contained in the stainless steel pot was preheated to 70 ° C.
Using the same equipment as above, a production test of fine copper powder was conducted under substantially the same conditions.

In this case, when the high temperature aqueous solution in the autoclave was jetted and mixed with the copper sulfate aqueous solution in the stainless steel pot, the liquid temperature in the pot rose to 95 ° C. Then, after cooling to 70 ° C., the temperature was maintained for 2 hours and allowed to cool. By this test, crystalline copper fine powder having an average particle size of about 5 μm was recovered.

The fine copper powder recovered was surrounded by a smooth crystal plane as in the case of Example 1 and was excellent in oxidation resistance, and was left in the air for 3 months. It did not discolor.

Example 3 As in Example 1, a high temperature acidic aqueous solution (220 ° C.) adjusted with an autoclave was transferred, and 2.5 L of a heated copper sulfate aqueous solution having the same composition was filled with N ₂ gas. When the two liquids were mixed by spraying into another autoclave, the liquid temperature near the liquid surface was 130 ° C, but the liquid temperature was maintained as it was until the temperature near the liquid surface reached 70 ° C. After that, when the mixed solution in which copper powder was precipitated and suspended was extracted, filtered, and washed,
Crystalline copper fine powder having an average particle size of about 10 μm was recovered.

The fine copper powder collected was surrounded by a smooth crystal surface and was excellent in oxidation resistance as in the case of those obtained in Examples 1 and 2, and it was kept in the air for 3 months. It did not discolor when left to stand.

Comparative Example A high temperature acidic aqueous solution (220 ° C.) prepared by an autoclave as in Example 1 was transferred to a cooling tank kept at −15 ° C. and rapidly cooled. And the temperature of the solution is 20 ℃
When the acidic solution in which the copper powder had precipitated and was suspended was filtered and washed, fine copper powder with an average particle size of about 0.8 μm was recovered, but oxidative discoloration was immediately observed after filtration and washing. .. Also, the copper powder suspension was held for 12 hours while being gently stirred, but again, oxidative discoloration was observed immediately after filtration and washing.

When the surface of this copper fine powder was observed with an electron microscope, as shown in the electron microscope photograph of FIG. 2, the surface was rough and irregular, and did not have a smooth crystal face.

[0025]

[Summary of Effects] As described above, according to the present invention, it becomes possible to stably produce fine copper powder having a narrow particle size distribution and excellent oxidation resistance, with controllable particle size. It has an extremely useful effect on the industry.

[Brief description of drawings]

FIG. 1 is an electron micrograph of the surface of fine copper powder obtained in an example.

FIG. 2 is an electron micrograph of the surface of a copper fine powder obtained in a comparative example.

[Procedure amendment]

[Submission date] September 29, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief explanation of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is an electron micrograph showing a particle structure of copper fine powder obtained in an example.

FIG. 2 is an electron micrograph showing a particle structure of copper fine powder obtained in a comparative example.

Claims (6)

[Claims] 1. A method for producing fine copper powder by a disproportionation reaction, wherein the temperature containing prepared cuprous ions: 50 ° C. or higher,
pH: 2.5 or less first acidic aqueous solution, pH: 2.5 or less and a second acidic aqueous solution having a lower temperature than the first acidic aqueous solution are mixed to cause a reaction, copper fine powder Production method. 2. The method for producing fine copper powder according to claim 1, wherein the first acidic aqueous solution and the second acidic aqueous solution are sulfuric acid acidic copper sulfate aqueous solutions. 3. The method for producing fine copper powder according to claim 1, wherein the first acidic aqueous solution is maintained at a temperature of 150 ° C. or higher and a pH of 1.0 or lower. 4. The copper fine powder according to claim 1, wherein the solution temperature when the first acidic aqueous solution and the second acidic aqueous solution are mixed is adjusted to 100 ° C. or lower. Manufacturing method. 5. The copper fine powder according to claim 1, wherein the atmosphere when mixing the first acidic aqueous solution and the second acidic aqueous solution is a non-oxidizing atmosphere. Production method. 6. The method according to claim 1, wherein when the first acidic aqueous solution and the second acidic aqueous solution are mixed, at least the first acidic aqueous solution is used after being filtered. A method for producing the copper fine powder described.