JPWO2009001710A1 - Spherical copper fine powder and method for producing the same - Google Patents

Abstract

A spherical copper fine powder, wherein the copper fine powder has an average particle size of 0.05 μm or more and 0.25 μm or less. In an aqueous medium containing an additive of a natural resin, a polysaccharide or a derivative thereof, cuprous oxide is added to make a slurry, and a 5-50% aqueous acid solution is added to the slurry at once within 15 minutes, A method for producing spherical copper fine powder by disproportionation reaction, characterized by carrying out a disproportionation reaction. It is an object of the present invention to provide a copper fine powder production method capable of producing metal copper particles having a controlled particle shape or particle size, particularly finer copper fine powder, quickly, efficiently and stably.

Description

  The present invention relates to a method for producing a spherical copper fine powder capable of quickly and efficiently producing a spherical metal copper particle having a controlled particle shape or particle size, particularly finer spherical copper fine powder, and a spherical copper obtained thereby. Concerning fine powder.

There are an electrolytic method and an atomizing method for a long time in the manufacturing method of copper powder. Copper powder produced by these methods is good for powder metallurgy applications such as oil-impregnated bearings and electrobrushes, but finer particles for conductive fillers such as paints, pastes and resins, for which demand is expected to increase in recent years. Therefore, a controlled particle size and particle shape is desired.
As a manufacturing method of finer metal copper particles suitable for these applications,
(1) Hydrogen pressure reduction method of copper salt aqueous solution (2) Chemical addition reduction method of copper salt aqueous solution (3) Thermal decomposition method of organic copper salt, etc., but there is a problem that equipment cost and operation cost are expensive In addition, there is no satisfactory method for controlling the particle size to a predetermined particle size because there are disadvantages such as poor yield, easy surface oxidation, and high chemical costs.

Therefore, the method of reacting the cuprous oxide particles with the acid can suitably control the particle shape and particle size of the metal copper particles to be produced, and the reaction conditions such as pH, temperature, and average residence time can be controlled. It has been found that, by controlling, a predetermined particle size can be adjusted and high-purity metallic copper fine particles can be produced.
Moreover, it became possible to obtain aggregated and linked powders such as chains by selecting the reaction conditions (see, for example, Patent Document 1).

This patent document was published in 1985, and was the highest level technology as copper powder manufacturing technology at that time.
The contents of this technology are as follows: 1) A copper salt aqueous solution and metal copper particles are produced by reacting cuprous oxide particles with an acid, and a solution containing metal copper particles is recovered by solid-liquid separation. Addition of cuprous oxide particles to maintain the pH of the reaction vessel at a predetermined value while continuously flowing in at a flow rate to obtain a predetermined average residence time corresponding to the target particle size of the metal copper particles to be produced Added at a rate, reacted at a liquid temperature of 50 ° C. or less, and generated metal copper particle slurry is discharged at a rate corresponding to the amount of the solution inflow, and the metal copper particle slurry thus discharged is subjected to solid-liquid separation means through metal-liquid separation means A method for producing metallic copper particles characterized by producing metallic copper particles having a controlled particle size by collecting copper particles, 2) a copper salt aqueous solution and metallic copper by reacting cuprous oxide particles with an acid grain A process for recovering metallic copper particles by solid-liquid separation, wherein the reaction is carried out while maintaining the liquid temperature to obtain a predetermined particle shape and particle size. It is.

However, recently, it has been demanded to make the copper powder finer and more uniform, and a rapid manufacturing technique is required. For this reason, the present inventor conducted a disproportionation reaction with acid in an aqueous medium containing additives of natural resins, polysaccharides or derivatives thereof to produce copper fine powder. In addition, a method for producing a copper fine powder characterized by setting the disproportionation reaction start temperature to 10 ° C. or less has been proposed (see Patent Document 2).
This method is a very effective method for rapidly producing fine copper fine powder. However, the average particle diameter of the copper fine powder is at a level of 0.5 μm to 3.0 μm, and a method for further refinement has been searched.
JP-A-60-33304 Japanese Patent Laid-Open No. 2005-256012

  The present invention relates to a method of producing spherical copper fine powder capable of producing spherical metal copper particles having a controlled particle shape or particle size, particularly finer copper fine powder, quickly and efficiently and stably, and the spherical copper obtained thereby. The purpose is to provide fine powder.

The present invention
1) A spherical copper fine powder characterized in that the average particle diameter of the copper fine powder is 0.05 μm or more and 0.25 μm or less. 2) The specific surface area (BET) of the copper fine powder is 2.5 m ² / g or more, 15.0 m. The spherical copper fine powder according to 1) above, which is ² / g or less.
Here, the spherical shape means that the ratio of the short diameter to the long diameter of each copper particle is 150% or less, particularly 120% or less. Therefore, those having a ratio of the minor axis to the major axis exceeding 150% have a flat shape and are not called spherical.
In the present invention, even when flat copper fine powder is mixed, the amount is 20% or less of the whole, preferably 10% or less, and further 5% or less. It is preferable that substantially no flat copper fine powder is contained.

The present invention also provides:
3) A slurry is prepared by adding cuprous oxide into an aqueous medium containing an additive of a natural resin, polysaccharide or derivative thereof, and a 5-50% aqueous acid solution is added to the slurry at once within 15 minutes. Thus, a method for producing fine copper powder by a disproportionation reaction for carrying out a disproportionation reaction is provided.
As additives, natural rubbers or gelatins can be used. Specific examples of the additive include rosin, gelatin, glue, carboxymethyl cellulose (CMC), starch, dextrin, gum arabic and casein.
The slurry concentration of the cuprous oxide is suitably 500 g / L or less, but is usually 300 g / L or less. The slurry concentration can be appropriately selected and is not particularly limited. If the slurry concentration of cuprous oxide is extremely low, the reaction does not proceed, and only the cost is increased.
The molar ratio (specified number of acids / number of moles of slurry) is preferably 1.00 to 2.00. If the molar ratio is equal (1.0) or more, there is no problem in the reaction. Adding too much does not mean that it will be effective. Conversely, if the acid concentration is too high, the amount of heat generated when adding acid to the cuprous oxide slurry will increase, the temperature of the reaction system will rise, and it will be disadvantageous for pulverization. There may be a disadvantage.
On the other hand, when the acid concentration is low, the reaction rate is consequently reduced, which is disadvantageous for pulverization. From the above, it can be said that the molar ratio (specified number of acids / number of moles of slurry) is preferably 1.00 to 2.00.

When producing a copper fine powder by performing a disproportionation reaction with an acid in an aqueous medium, it is desirable to set the disproportionation reaction start temperature to 10 ° C or lower. This is effective for forming fine copper fine powder.
Furthermore, it is very important that the acid aqueous solution is added all at once. That is, add all at once within 15 minutes. Thereby, spherical copper fine powder having an average particle size of 0.25 μm or less can be obtained. The disproportionation reaction by this rapid addition can achieve a fine spherical copper powder. The reason why this short-time addition is effective for the production of copper fine powder is not necessarily clear.
However, this short-term disproportionation reaction is considered to have an effect of suppressing the growth of copper particles. Therefore, short-time batch addition is effective for miniaturization. The addition time of the acid aqueous solution is preferably a short time of 3 minutes or less, particularly preferably 1 minute or less.

Furthermore, the present invention provides
4) Solid-liquid separation of the copper fine powder slurry obtained after the disproportionation reaction and washing with water, reduction treatment with an alkaline solution, and repeated solid-liquid separation and water washing of the obtained fine powder slurry were repeated. The method for producing a copper fine powder as described in 3) above, wherein a powder is obtained. This reduction treatment with an alkaline solution is effective in homogenizing the chemical composition of the copper particles by reducing the oxide remaining in the obtained copper fine powder and unreacted cuprous oxide.
5) The method for producing copper fine powder according to 3) or 4), wherein acidification treatment with an acid is performed in the middle of repeating solid-liquid separation and water washing of the fine powder slurry.
This acidification treatment with an acid can further enhance the rust prevention effect when performing the rust prevention treatment.
6) After finally washing with water, the copper powder is filtered and further dried under vacuum to obtain a copper powder 7) The copper fine powder production method according to any one of 3) to 5) above. The method for producing copper fine powder according to any one of 3) to 6), wherein the average particle size is 0.05 μm or more and 0.25 μm or less 8) The specific surface area (BET) of the copper fine powder is 2.5 m ² / g or more. The method for producing a copper fine powder according to any one of 3) to 7), which is 15 m ² / g or less.

  The method for producing copper fine powder of the present invention has an excellent effect that the particle shape can be made spherical and the particle size can be controlled arbitrarily, and finer copper fine powder can be produced quickly, efficiently and stably.

It is a figure which shows the outline | summary of the manufacturing flow of spherical copper fine powder. It is a FE-SEM photograph of spherical copper fine powder.

The cuprous oxide particles may be produced by a known method such as passing through cuprous chloride from an aqueous copper salt solution. That is, since there is no direct relationship between the particle size of the cuprous oxide particles used and the particle size of the metallic copper particles obtained by the method of the present invention, coarse cuprous oxide particles can also be used.
As the acid, sulfuric acid is usually used, but nitric acid, phosphoric acid, and acetic acid can also be used. It is not particularly necessary to specify the type of acid. When sulfuric acid is used, the disproportionation reaction generates an aqueous copper sulfate solution and metallic copper particles according to the following reaction formula.
Cu ₂ O + H ₂ SO ₄ = Cu ↓ + CuSO ₄ + H ₂ O

If the addition ratio of the acid to the cuprous oxide is increased, the pH of the reaction system is lowered, and in the opposite case, the pH is increased. Therefore, the pH can be controlled by the addition ratio of the acid or the cuprous oxide.
In order to avoid the formation of impurity precipitates during the reaction and to allow the cuprous oxide to remain without causing the reaction to proceed rapidly, the pH is maintained at 2.5 or lower, preferably around 1.0.
In the production of copper fine powder by such a disproportionation reaction of cuprous oxide, an acid disproportionation reaction is performed in an aqueous medium containing an additive (protective colloid) of a natural resin, a polysaccharide or a derivative thereof. This is one of the major features of the present invention.
This additive (protective colloid) has a function of suppressing particle growth and an effect of reducing the contact frequency between particles. Therefore, it is effective for producing fine particles.

As the additive, natural rubbers or gelatins are particularly effective. More specifically, pine resin, gelatin, glue, carboxymethyl cellulose (CMC), starch, dextrin, gum arabic, and casein can be used as additives. In particular, when glue is used, it can be pulverized with an average particle size of 0.25 μm or less, and has an aggregation suppressing effect.
The liquid temperature during the reaction is 30 ° C. or lower, preferably 10 ° C. or lower, in the case of producing metallic copper fine particles. This is because when the liquid temperature exceeds 30 ° C., metal copper fine particles tend to aggregate and connect. In particular, in order to achieve miniaturization, it is desirable to set the disproportionation reaction start temperature to 10 ° C. or less. By lowering the reaction temperature, particle growth can be effectively suppressed, and finer pulverization becomes possible.

  This temperature of 10 ° C. or lower is more effective if it is maintained until the end of the reaction if possible. The reaction temperature may be higher than 30 ° C. In this case, focusing on the fact that the metal copper particles are coherently connected, a special particle shape is to be obtained. Thus, the particle shape and particle size of the produced metal copper particles can be controlled by the reaction temperature. The present invention encompasses all such temperature controls.

In addition, in the present invention, it is very important that the acid aqueous solution is added all at once when a copper fine powder is produced by performing a disproportionation reaction of cuprous oxide with an acid. That is, it is added at once within 15 minutes, preferably within 3 minutes, more preferably within 1 minute. Thereby, spherical copper fine powder having an average particle size of 0.25 μm or less can be obtained.
The disproportionation reaction by this rapid addition can achieve a fine spherical copper powder. That is, by increasing the acid addition rate, nucleation is more dominant than particle growth, and the copper powder is made finer.
This short-time disproportionation reaction is considered to have an effect of suppressing the growth of copper particles. For miniaturization, short-time batch addition is indispensable.

The average particle diameter of the present invention is desirably a smaller value, but the actual value of D ₁₀ that is smaller than the average particle diameter (D ₅₀ ) is 0.06 μm, and D is the minimum value of the particle size distribution. _min becomes even smaller. However, in the disproportionation method which is a wet reaction, since 0.05 μm is the lower limit value that can be produced, the average particle size was set to 0.05 μm.
Since D _min which is the minimum value of the particle size distribution is even smaller, finer copper fine powder is included. From this, it is estimated that in the disproportionation method, which is a wet reaction, about 0.05 μm is the lower limit for production, so the lower limit of the average particle size was set to 0.05 μm.

On the other hand, the smaller the average particle diameter, the larger the specific surface area tends to be, but it is not necessarily proportional. Moreover, the measured value and the theoretical value of the specific surface area are different.
Assuming that the copper fine powder is a spherical shape, the specific surface area is calculated from the volume, surface area, and mass with the true density of copper being 8.93 g / cm ³ and the average particle diameter (D ₅₀ ) as the diameter, and D ₅₀ = 0.05 μm. The theoretical specific surface area is 13.44 m ² / g.
However, regarding the relationship between the average particle size (D ₅₀ ) and the specific surface area, the smaller the average particle size, the more the difference between the theoretical value and the measured value tends to disappear. If the average particle size is large, the surface condition (such as irregularities on the outermost surface) has a large effect on the specific surface area. However, if the average particle size is small, the influence of the size itself is greater than the surface condition, and there is a difference between the theoretical value and the actual measurement value. Because it is thought that it will disappear.
Combining the above, when the lower limit value of D ₅₀ is 0.05 μm, the upper limit of the specific surface area can be expected to be about 15.0 m ² / g. Therefore, the upper limit of the BET specific surface area is 15.0 m ² / g.

The ultrafine spherical copper powder obtained in this way may aggregate in the air or liquid. However, this aggregate can be dispersed again by means such as applying ultrasonic waves in an aqueous solution. It should be understood that the initial particles are premised on spherical copper fine powder having an average particle size of 0.25 μm or less. This is because a spherical fine copper powder cannot be obtained by miniaturization by means of pulverization.
When the reaction is carried out batchwise, an acid may be added to the cuprous oxide particle slurry, and conversely, the cuprous oxide particles or the cuprous oxide particle slurry may be added to the acid solution.
In any case, the obtained metallic copper particles are highly pure and rich in surface activity. Therefore, the metal copper particles obtained by solid-liquid separation are dried after being subjected to an appropriate rust prevention treatment. FIG. 1 shows an outline of the manufacturing flow of spherical copper fine powder.
As shown in FIG. 1, dissolution of an additive → slurry (a step of making a slurry by adding cuprous oxide into an aqueous medium containing the additive) → disproportionation reaction (addition of an acid aqueous solution) → washing → Produced through rust prevention → filtration → drying → crushing → classification process.

  Next, examples of the present invention will be described. In addition, a present Example is an example to the last, and is not restrict | limited to this example. That is, all aspects or modifications other than the embodiments are included within the scope of the technical idea of the present invention.

Example 1
8 g of glue was dissolved in 7 liters of pure water, 1000 g of cuprous oxide was added and suspended while stirring, and the cuprous oxide slurry was cooled to 7 ° C. The amount of cuprous oxide in the slurry is about 143 g / L.
Next, 2000 cc of dilute sulfuric acid (concentration 24%: 9 N, molar ratio (acid aqueous solution / slurry): 1.5) cooled to 7 ° C. was added in 1 minute. The produced copper fine powder was washed and rust-proofed and then dried to obtain 420 g of copper fine powder.
The reaction was completed in about 1 minute after the addition. An FE-SEM photograph of the spherical copper fine powder thus obtained is shown in FIG. As shown in FIG. 2, the average particle diameter of the copper fine powder was 0.09 μm. It can be seen that the addition of cooled dilute sulfuric acid in 1 minute is extremely effective for copper fines. The specific surface area BET was 6.66 m ² / g. This Example 1 is a particularly preferable example among the conditions of other Examples.

(Examples 2 to 8)
Examples when rosin, gelatin, carboxymethylcellulose (CMC), starch, dextrin, gum arabic, and casein are used as additives are shown. In this case, copper powder was produced under the same conditions as in Example 1 except that the additive was changed. As a result, all of the above additives were effective, but the addition of “Niwa” in Example 1 gave the best results.

(Comparative Examples 1-2)
Copper polyethylene pulverization was investigated when polyethylene glycol (PEG) was selected as an additive and when it was not added. The results are shown in Comparative Examples 1-2. In this case, copper powder was generated under the same conditions as in Example 1 for all other conditions. As a result, the additive of Comparative Example 1 was not effective, and when it was not added, a copper powder having a large particle size and a low BET specific surface area was obtained, resulting in a bad result.
The average particle diameter and specific surface area of the spherical copper fine powder according to the above-described Examples and Comparative Examples were measured. The average particle size is due to a laser diffraction scattering particle size distribution measuring method was adopted the value of the weight-cumulative particle diameter D _50. The specific surface area was measured by the BET method.
The results of Examples 1 to 8 and Comparative Examples 1 and 2 are shown in Table 1.

(Examples 9-12, 16)
Next, the results when the acid addition time is changed based on the representative Example 1 are shown in Examples 9 to 12. In this case, the acid addition time was changed from 5 seconds to 15 minutes. In this case, copper powder was produced under the same conditions as in Example 1 except that the acid addition time was changed. As a result, a copper powder having a smaller particle size and a lower BET specific surface area was obtained when the acid addition time was shortened. Since the acid addition time also affects the size of the particle size and the BET specific surface area, the acid addition time is preferably as short as possible. It is not added over time, but it is desirable to add it within approximately 15 minutes. This result was the same even when additives of pine resin, gelatin, carboxymethylcellulose (CMC), starch, dextrin, gum arabic, and casein were used.

(Comparative Examples 3-4)
Next, Comparative Examples 3 and 4 show examples in which the acid addition time is 16 minutes and 80 minutes outside the conditions of the present invention. In this case, copper powder was produced under the same conditions as in Example 1 except that the acid addition time was changed. In any case, copper powder having a large particle size and a low BET specific surface area was obtained, resulting in poor results.
Table 2 shows the results of Examples 9 to 12 and Comparative Examples 3 to 4.

(Examples 13 to 17)
Next, the results when the reaction start temperature is changed based on the representative Example 1 are shown in Examples 13 to 17. In this case, the reaction start temperature was changed by 0 to 30 ° C. In this case, copper powder was produced under the same conditions as in Example 1 except that the reaction start temperature was changed.
As a result, a copper powder having a smaller particle size and a larger BET specific surface area was obtained when the reaction start temperature was lowered. This result was the same even when additives of pine resin, gelatin, carboxymethylcellulose (CMC), starch, dextrin, gum arabic, and casein were used.

(Comparative Example 5)
Next, Comparative Example 5 shows an example in which the reaction start temperature is 50 ° C. outside the conditions of the present invention. In this case, copper powder was produced under the same conditions as in Example 1 except that the reaction start temperature was changed. As a result, a copper powder having a large particle diameter and a copper powder having a low BET specific surface area was obtained, resulting in a bad result.
The results of Examples 13 to 17 and Comparative Example 5 are shown in Table 3.

As shown above, the conditions of the present invention, that is, a slurry containing 10 to 300 g / L of cuprous oxide by adding cuprous oxide in an aqueous medium containing additives of natural resins, polysaccharides or derivatives thereof. Then, a 5-50% aqueous acid solution was added to the slurry at a molar ratio (specified number of acids / number of moles of slurry) of 1.00 to 2.00 within 3 minutes to carry out a disproportionation reaction. By performing, it becomes possible to obtain a suitable spherical copper fine powder.
And the spherical copper fine powder whose average particle diameter of fine powder is 0.25 micrometer or less can be obtained. Furthermore, these spherical copper fine powders can achieve a specific surface area (BET) of the copper fine powders of 4.0 m ² / g or more.

  The spherical copper fine powder produced according to the present invention has a small and uniform powder particle size, and is useful not only as a powder for oil-impregnated bearings and electric brushes but also as a conductive filler for paints, pastes, resins, and the like.

Claims (8)

  A spherical copper fine powder, wherein the copper fine powder has an average particle size of 0.05 μm or more and 0.25 μm or less. ^2. The spherical copper fine powder according to claim 1, wherein the copper fine powder has a specific surface area (BET) of 2.5 m ² / g or more and 15.0 m ² / g or less.   In an aqueous medium containing an additive of a natural resin, a polysaccharide or a derivative thereof, cuprous oxide is added to make a slurry, and a 5-50% aqueous acid solution is added to the slurry at once within 15 minutes, A method for producing spherical copper fine powder by disproportionation reaction, characterized by carrying out a disproportionation reaction.   The copper fine powder slurry obtained after the disproportionation reaction is subjected to solid-liquid separation and water washing, and this is subjected to a reduction treatment with an alkaline solution. Further, solid-liquid separation and water washing of the obtained fine powder slurry are repeated to obtain copper powder. The method for producing spherical copper fine powder according to claim 3, which is obtained.   The method for producing spherical copper fine powder according to claim 3 or 4, wherein acidification treatment with an acid is performed in the middle of repeating solid-liquid separation and water washing of the fine powder slurry.   6. The method of producing spherical copper fine powder according to claim 3, wherein after finally washing with water, the copper powder is filtered and further dried under vacuum to obtain copper powder.   The average particle diameter of copper fine powder is 0.05 micrometer or more and 0.25 micrometer or less, The manufacturing method of the spherical copper fine powder in any one of Claims 3-6 characterized by the above-mentioned. The method for producing a spherical copper fine powder according to any one of claims 3 to 7, wherein the specific surface area (BET) of the copper fine powder is 2.5 m ² / g or more and 15.0 m ² / g or less.