JP2010174348A - Copper powder and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of producing copper powder which is narrow in the width of particle size and is extremely less in the number of fine particles for every target particle size. <P>SOLUTION: In the method for producing the copper powder, a liquid containing at least one of a copper compound, such as a solid copper oxide or copper hydroxide, and copper ions as a substance to be reduced is added into a liquid containing a copper powder having a 50% diameter (D<SB>50</SB>) of ≥0.5 μm in the volume-based particle size distribution measured with a particle size distribution measuring device of a wet laser diffraction type and a reducing agent of hydrazine or hydrous hydrazine, thereby reducing the substance to be reduced to metal copper. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a copper powder and a method for producing the same, and more particularly to a copper powder suitable for use as a conductive filler of a conductive paste and a method for producing the same.

  Many conductive pastes are used to form circuits and electrodes on the surface, inside or outside of various electric and electronic component substrates. Such conductive paste contains copper powder, silver powder, or the like as a conductive filler (metal powder), and metal powder having an average particle size of 0.1 to 20 μm is used.

  In order to form an electrode or the like with such a conductive paste, the conductive paste applied to the substrate is baked. In order to control the sinterability of the conductive paste by this firing and the adhesive strength with the substrate, or to reduce fluctuations thereof, it is necessary to use a conductive filler (metal powder) having a uniform particle size. In addition, in order to obtain a dense and thick conductor film or electrode by firing the conductive paste, two or three kinds of metal powders with uniform particle diameters are mixed and mixed when adjusting the rheology of the conductive paste. Is known to be effective. In order to mix and mix such metal powders, it is necessary to manufacture metal powders having a uniform particle size for each different particle size.

  Generally, methods such as an atomizing method, an electrolytic method, and a wet reduction method are known as methods for producing metal powder. When producing copper powder, the copper powder obtained by the atomization method has a very wide range of particle size distribution, and in order to obtain particles having a uniform particle size, classification must be repeated many times, yield. Becomes very bad. Moreover, the copper powder obtained by the electrolytic method not only has a wide particle size distribution, but also has a dendritic shape, so it is used as a conductive paste for forming dense and thick conductor films and electrodes. Not suitable for. On the other hand, the copper powder obtained by the wet reduction method is a copper powder having a relatively uniform particle size, and the shape of the particles is substantially spherical, and thus is most suitable for use in a conductive paste.

  As a method for producing copper powder by a wet reduction method, a primary reducing agent is added to a suspension obtained by reacting a copper salt aqueous solution and an alkali agent to precipitate copper hydroxide, and intermediate reduction to cuprous oxide is performed. A method of producing a copper powder by adding a secondary reducing agent to the cuprous oxide suspension and finally reducing it to metallic copper is known (for example, see Patent Document 1). Also known is a method for producing copper by adding a reducing agent to a mixture comprising a copper powder, a solid component comprising a copper compound, and a liquid medium, and reducing the solid component comprising the copper compound to metallic copper. (For example, refer to Patent Document 2).

JP 2001-240904 A (paragraph number 0009) JP 2004-307881 A (paragraph number 0009)

  However, with the method of Patent Document 1, copper powder having a relatively uniform particle size can be obtained, but the degree of uniform particle size is not always sufficient. Also, with this method, it is not possible to produce copper powder with a narrow particle size distribution and a sufficiently uniform particle size for each target particle size.

  Moreover, in the method of Patent Document 2, copper powder having a narrow particle size distribution and uniform particle diameter can be produced for each target particle size as compared with the method of Patent Document 1. However, in this method, there are some fine particles considerably smaller than the target particle size, and it is not possible to produce copper powder having a sufficiently uniform particle size.

  Therefore, in view of such conventional problems, the present invention is capable of producing copper powder having a narrow particle size distribution and a very small number of fine particles for each target particle size. It aims to provide a method.

As a result of intensive studies to solve the above problems, the present inventors have found that a liquid containing a copper powder having a 50% diameter (D ₅₀ ) in a volume-based particle size distribution of 0.5 μm or more and a reducing agent is to be reduced. And adding a liquid containing at least one of a copper compound and copper ions, and reducing the reduction target to metallic copper to produce copper powder, the width of the particle size distribution is narrow for each target particle size and The inventors have found that copper powder having a very small number of fine particles can be produced, and have completed the present invention.

That is, the copper powder manufacturing method according to the present invention includes a copper compound and a copper ion as a reductant in a liquid containing copper powder having a 50% diameter (D ₅₀ ) of 0.5 μm or more in a volume-based particle size distribution and a reducing agent. By adding a liquid containing at least one of the above, the material to be reduced is reduced to metallic copper to produce copper powder. In this method for producing copper powder, the copper compound is preferably a solid copper compound, and is preferably a copper oxide or hydroxide. The reducing agent is preferably hydrazine or hydrous hydrazine. Further, the total number of moles of copper other than the copper powder in the liquid containing the copper powder and the reducing agent and the liquid to be reduced is n ₀ (mol), and the 50% diameter (D ₅₀ ) in the volume-based particle size distribution of the copper powder. ) Is x ₀ (μm), the weight of the copper powder is w (g), and the atomic weight of copper is AW (g / mol), 50 in the number-based particle size distribution of copper powder produced by reduction to metallic copper. The% diameter (D ₅₀ ) is within ± 20% of x (μm) represented by the following formula 1.

Further, the copper powder according to the present invention has a 50% diameter (D ₅₀ ) in the number-based particle size distribution of 0.5 to 20 μm, and a 90% diameter (D ₁₀ ) with respect to the 10% diameter (D ₁₀ ) in the number-based particle size distribution. the ratio of _{90) (D 90 / D 10} ) is equal to or more than 1.5. In this copper powder, the 50% diameter (D ₅₀ ) in the volume-based particle size distribution is 0.5 to 20 μm, and the ratio of the 90% diameter (D ₉₀ ) to the 10% diameter (D ₁₀ ) in the volume-based particle size distribution (D ₉₀ / D ₁₀ ) is preferably 1.5 or less.

In the present specification, “volume-based particle size distribution” refers to a volume-based particle size distribution obtained by a wet laser diffraction type particle size distribution measuring apparatus, and “10% diameter (D ₁₀ ) in the volume-based particle size distribution”. , 50% diameter (D ₅₀ ), 90% diameter (D ₉₀ ) ”is a volume-based particle size distribution graph drawn by a wet laser diffraction type particle size distribution measuring apparatus, that is, the particle diameter D (μm on the horizontal axis). ), In the cumulative particle size curve in which the vertical axis represents the volume Q (%) in which particles having a particle size D (μm) or less exist, the particle size D (μm when Q% is 10%, 50%, and 90%, respectively. ).

In the present specification, “number-based particle size distribution” refers to a number-based particle size distribution obtained from a scanning electron micrograph (SEM image), and “10% diameter (D ₁₀ in the number-based particle size distribution)”. ), 50% diameter (D ₅₀ ), 90% diameter (D ₉₀ ) ”is a graph of the number-based particle size distribution drawn based on the SEM image, that is, the particle diameter D (μm) on the horizontal axis and the vertical axis In the cumulative particle size curve taking the frequency F (%) in which particles having a particle diameter D (μm) or less exist, the particle diameter D (μm) when Q% is 10%, 50%, and 90%, respectively.

  According to the present invention, copper powder having a narrow particle size distribution and a very small number of fine particles can be produced for each target particle size.

It is a figure which shows the particle size distribution of the volume reference | standard of the copper powder obtained in Example 1. FIG. It is a figure which shows the particle size distribution of the volume reference | standard of the copper powder obtained in Example 2. FIG. It is a figure which shows the particle size distribution of the volume reference | standard of the copper powder obtained in Example 3. FIG. It is a figure which shows the particle size distribution of the volume reference | standard of the copper powder obtained in Example 4. FIG. It is a figure which shows the particle size distribution of the volume reference | standard of the copper powder obtained by the comparative example 1. It is a figure which shows the volume-based particle size distribution of the copper powder obtained by the comparative example 2. It is a figure which shows the particle size distribution based on the number measured by the scanning electron micrograph (SEM image) of the copper powder obtained in Example 1. FIG. It is a figure which shows the particle size distribution of the number reference | standard measured by the SEM image of the copper powder obtained in Example 2. FIG. It is a figure which shows the particle size distribution of the number reference | standard measured by the SEM image of the copper powder obtained in Example 3. FIG. It is a figure which shows the particle size distribution based on the number measured by the SEM image of the copper powder obtained in Example 4. FIG. It is a figure which shows the particle size distribution of the number reference | standard measured by the SEM image of the copper powder obtained by the comparative example 1. It is a figure which shows the particle size distribution based on the number measured by the SEM image of the copper powder obtained by the comparative example 2. 2 is a SEM image of 1000 times the copper powder obtained in Example 1. FIG. 4 is a 1000 times SEM image of the copper powder obtained in Example 2. FIG. 4 is a 1000 times SEM image of the copper powder obtained in Example 3. FIG. 4 is a 1000 times SEM image of the copper powder obtained in Example 4. FIG. 3 is a SEM image of 1000 times the copper powder obtained in Comparative Example 1. FIG. 3 is a SEM image of 1000 times the copper powder obtained in Comparative Example 2.

  A conventional method for producing copper powder by a wet reduction method can be divided into a nucleation stage and a grain growth stage. The nucleation stage involves adjusting the pH, adjusting the temperature (such as quenching), adding a reducing agent, adding copper ions, adding impurity ions, introducing reactive gases, or irradiating light, and forming metallic copper as the core of the copper particles. This is the stage of generating ultrafine particles. The number of nuclei generated at this stage affects the target particle size of the copper powder. When obtaining a copper powder having a large particle size, the number of nucleation is reduced, and when obtaining a copper powder having a small particle size, the number of nucleation may be increased. However, in reality, the number of nuclei is affected by the amount of impurities that are inevitably mixed and slight fluctuations in the manufacturing process. Induces fluctuations in the particle size of copper powder. In the next grain growth stage, the nuclei of the produced copper particles are gradually grown (copper ions, copper oxides, etc. are reduced to deposit copper metal on the surface of the copper particle nuclei). This is the stage of adjusting to copper powder. Even at this stage, if the reducing power is too strong or if the total surface area of the generated nuclei is small, new nuclei (secondary nuclei) are generated simultaneously with the growth of the copper particles, and the particle size distribution of the copper powder is broadened. And cause atomization. Therefore, in order to obtain a copper powder having a uniform particle size for each production lot without fluctuation, it is necessary to suppress such fluctuations in the nucleation stage and fluctuations in the grain growth stage.

On the other hand, in the embodiment of the method for producing copper powder according to the present invention, the liquid containing 50% diameter (D ₅₀ ) in the volume-based particle size distribution (D ₅₀ ) of 0.5 μm or more (acting as a nucleus) and a reducing agent. By adding a liquid containing at least one of a solid copper compound and copper ions as a reduction target, the reduction target is reduced to metallic copper to produce copper powder. In this method, the nucleation stage is eliminated by introducing copper powder acting as a nucleus into the reaction system, thereby eliminating the fluctuation of the nucleation stage. In addition, since the particle size of the copper powder to be introduced is larger than the fine nuclei at the time of nucleation in the conventional copper powder production method by the general wet reduction method, the total surface area on which the metal copper produced by the reduction precipitates is large. Thus, since the grain growth is promoted and the generation of secondary nuclei is suppressed, fluctuations in the grain growth stage can be controlled.

Further, in the embodiment of the method for producing copper powder according to the present invention, almost all of the copper present in the liquid containing the copper powder and the reducing agent and the liquid containing the reductant can be used for grain growth. By adjusting the amount of copper components other than copper powder (total number of moles of copper other than copper powder), the particle size of copper powder, and the amount of copper powder added, the particle size of the produced copper powder can be adjusted extremely accurately. Can be controlled. That is, the total number of moles of copper other than the copper powder in the liquid containing the copper powder and the reducing agent and the liquid containing the reductant is n ₀ (mol), and the 50% diameter (D ₅₀ ) in the volume-based particle size distribution of the copper powder. X ₀ (μm), the weight of the copper powder is w (g), and the atomic weight of copper is AW (g / mol), the 50% diameter (D ₅₀ ) x in the volume-based particle size distribution of the produced copper powder (Μm) can be expressed by the following formula 2.

Α in Equation 2 is a correction coefficient. In this equation, the value of the particle size of the copper powder produced differs slightly depending on the particle size measurement method, or the shape factor changes depending on the particle shape, so that it matches the particle size measurement method and particle shape. Is corrected by the coefficient α. This coefficient α is usually in the range of 0.8 to 1.2. That is, the 50% diameter (D ₅₀ ) in the volume-based particle size distribution of the produced copper powder falls within ± 20% of x (μm) in Equation 1.

Further, in the embodiment of the method for producing copper powder according to the present invention, unlike the copper powder produced by the conventional method for producing copper powder by the wet reduction method, It may be replaced by the 50% size of the volume-based particle size distribution of _{(D 50)} 50% diameter of the number-based particle distribution _{(D 50).} The 50% diameter (D ₅₀ ) in the number-based particle size distribution of the copper powder produced by the embodiment of the method for producing copper powder according to the present invention is preferably 0.5 to 20 μm, and more preferably _{5 to 20} μm. Is more preferable, and it is most preferable that it is 8-15 micrometers.

  In embodiment of the manufacturing method of the copper powder by this invention, the quantity of the copper powder introduce | transduced by making copper components (copper compounds, such as a copper oxide and a hydroxide) other than copper powder exist in a liquid. The solubility of metal ions is not limited as in the conventional wet reduction method. Therefore, it is possible to increase the total amount of copper atoms serving as a copper supply source. That is, since there is no limit on the number of copper atoms that contribute to grain growth, it becomes easier to adjust the copper powder to a desired grain size, leading to an improvement in productivity. Moreover, without using a solid copper compound, an aqueous solution containing copper ions can be added to a solution containing copper powder and a reducing agent, and copper powder can be produced by reduction.

  Moreover, when using a copper compound, the one where the oxidation number (valence) of the copper is smaller is better. When the oxidation number is large, the reduction reaction has several stages, and a plurality of reduction reactions may proceed simultaneously, and secondary nuclei may be generated. In addition, solid copper compounds may be reduced on the surface of coexisting copper powder particles to contribute to grain growth, or may be eluted once in the reaction solution and then contribute to grain growth by dissolution precipitation type reaction. It may be possible. Copper compounds such as copper sulfate, nitric acid, carbonic acid, phosphoric acid and other oxoacid salts, copper halides and other salts, copper sulfide and other chalcogenides, copper amino acid salts and carboxylate and other organic acid salts, etc. Although various copper compounds can be used, it is preferable to use copper oxides or hydroxides.

  The liquid used for the reaction may be water, an organic liquid, or a mixed liquid of water and an organic liquid. When using water or a reducing agent that generates gas by reduction, an antifoaming agent or an organic solvent with low surface tension (for example, alcohols such as ethanol and isopropyl alcohol, ketones such as acetone) Coexisting with hydrocarbons such as hexane), the rise in liquid level due to gas such as nitrogen generated by reduction can be suppressed.

  When reducing to metallic copper by adding a liquid containing at least one of a copper compound and copper ions as a reductant to a liquid containing copper powder and a reducing agent, so as to suppress a rapid reaction, that is, secondary In order to suppress the generation of nuclei, it is preferable to gradually add a liquid containing a reductant to a liquid containing copper powder and a reducing agent, and it is preferable to add continuously over several hours.

If the particle size of the copper powder in the liquid containing the copper powder and the reducing agent is too small, aggregation may become intense and the width of the particle size distribution may be widened, or secondary nuclei may be generated. In addition, the growth rate of the particles does not depend on the particle size of the copper powder in the liquid containing the copper powder and the reducing agent, and depends on the reducing conditions (such as the reaction temperature, the amount of the reducing agent and the reductant), Since the particle size is maintained at a constant value of several μm per unit time, if the particle size is too large, the ratio of the grain growth to the initial particle size becomes small, resulting in poor production efficiency. Therefore, the 50% diameter (D ₅₀ ) in the volume-based particle size distribution of the copper powder to be introduced is preferably 0.5 to 10 μm.

  As the reducing agent, a reducing agent capable of reducing the substance to be reduced (at least one of solid copper compound and copper ion) to metallic copper, such as hydrazine, hydrous hydrazine, borohydride compound, dimethylamine borane, formalin, etc. is used. From the viewpoints of controllability, handleability and productivity, it is preferable to use hydrazine or hydrous hydrazine. The addition amount of the reducing agent needs to be equal to or more than an equivalent capable of reducing the reduction target (at least one of a solid copper compound and copper ions) to metallic copper. However, since there will be a cost disadvantage if there is too much addition amount of this reducing agent, it is preferable that it is 1-10 equivalent with respect to a to-be-reduced object (at least one of a solid copper compound and a copper ion).

In the embodiment of the method for producing copper powder according to the present invention, a copper compound and a reductant are contained in a liquid containing copper powder having a 50% diameter (D ₅₀ ) in a volume-based particle size distribution of 0.5 μm or more and a reducing agent. Although a liquid containing at least one of copper ions is added, it is preferable to add reversely (adding a reducing agent after adding copper powder to a liquid containing at least one of a copper compound and copper ions as a reduction target) Absent. When a reducing agent is added (continuously or batchwise) to a liquid in which at least one of a copper compound and copper ions is present as the reductant, the reductant (solid copper compound and copper ion) At least one) is reduced to produce metallic copper. In the initial stage of addition of the reducing agent (initial stage of the reduction reaction), the reduced product to be reduced (at least one of a copper compound and copper ions) is deposited on the surface of the added copper powder. However, from the middle to the second half of the reaction, the amount of the reducing agent added increases with respect to the substance to be reduced (at least one of the copper compound and the copper ion). As a result, the reduction reaction is promoted and not only precipitates on the surface of the added copper powder but also newly precipitates copper particles (secondary nuclei are generated). The reducing agent is consumed together with the reduction of the substance to be reduced (copper compound and / or copper ion). The consumption rate and the reduction rate are determined based on the addition amount of the reducing agent, the addition method, and the reduction conditions (temperature, pH, etc.). It is very difficult to control by. As a result, new copper particles precipitate (secondary nuclei are generated). Because this secondary nucleus is generated from the middle to the end of the reaction, unlike the copper powder added at the beginning of the reduction reaction, its growth opportunities are relatively small, and because it is a newly generated nucleus, Since the added copper powder is remarkably fine, the newly formed copper becomes fine. As a result, the produced copper powder becomes a copper powder partially containing fine particles.

  On the other hand, in the embodiment of the method for producing copper powder according to the present invention, since the substance to be reduced (at least one of a copper compound and copper ions) is added to the liquid containing copper powder and the reducing agent, the reducing agent is As a result, the introduced reductant (at least one of the copper compound and copper ion) is rapidly reduced to metallic copper and deposited on the surface of the introduced copper powder. I will do it. Since this state (relationship between the amount of the reducing agent and the substance to be reduced) does not change significantly until the end of the reaction, no new secondary nuclei are generated, and the produced copper powder does not contain fine particles, Copper powder with very uniform diameter.

The copper powder produced by the embodiment of the method for producing copper powder according to the present invention has a 90% diameter (D ₉₀ ) with respect to a 10% diameter (D ₁₀ ) in a volume-based particle size distribution by a wet laser diffraction type particle size distribution measuring device. ) Ratio (D ₉₀ / D ₁₀ ) is a copper powder having a narrow particle size distribution of 1.5 or less. In copper powder having D ₉₀ / D ₁₀ exceeding 1.5, since the particle diameters are not sufficiently uniform, when copper powders having different particle diameters are combined and used as a conductive filler of a conductive paste, the purpose is It becomes difficult to obtain copper powder having a particle size distribution.

Moreover, when the copper powder manufactured by embodiment of the manufacturing method of the copper powder by this invention is observed with a scanning electron microscope (SEM), it can confirm that it is a copper powder with a very uniform particle size. In general, a wet laser diffraction type particle size distribution measuring apparatus has a particle size distribution based on the volume of particles, and it may be difficult to detect fine particles present in copper powder having a certain particle size. For example, if the ratio of the minimum particle size / maximum particle size is 1/10, the volume ratio will be 1/1000. For this reason, particles smaller than a certain particle size may not be detected or ignored in the volume-based particle size distribution because they are too small. Therefore, even when the particle size distribution by the wet laser diffraction type particle size distribution measuring device becomes sharp, there may be countless fine particles that are not actually detected. On the other hand, the true particle size distribution can be obtained by directly observing particles by SEM and the number-based particle size distribution obtained from the observation. It can be confirmed that the copper powder produced by the embodiment of the method for producing copper powder according to the present invention is a copper powder having a very uniform particle size without fine particles even by observation with an SEM. The copper powder is, in the graph of the particle size distribution of number-based by SEM image, a ratio of 90% diameter to 10% diameter _{(D 10) (D 90)} (D 90 / D 10) is 1.5 or less of particle size distribution It is a narrow copper powder. In copper powder having D ₉₀ / D ₁₀ exceeding 1.5, since the particle diameters are not sufficiently uniform, when copper powders having different particle diameters are combined and used as a conductive filler of a conductive paste, the purpose is It becomes difficult to obtain copper powder having a particle size distribution.

  The reduction reaction is preferably carried out in a reaction vessel that can be controlled in atmosphere and temperature and has a stirring function. As an atmosphere during the reaction, in order to suppress the progress of side reactions such as oxidation by oxygen in the air, it is basically preferable to carry out under an inert gas atmosphere throughout. However, if necessary, the liquidity may be controlled by introducing a reactive gas such as ammonia, oxygen, or the like, and oxidation or reduction potential of copper or a complexing agent may be adjusted. As an inert gas, it is optimal to use nitrogen from the viewpoint of cost, but a rare gas such as argon may be used.

  A liquid containing at least one of a copper compound and copper ions as a reductant is prepared by dissolving or suspending copper salts, copper hydroxide, copper oxide, etc. in pure water or a mixture of pure water and an organic solvent. Adjust by turbidity. As copper salts, it is preferable to use inexpensive copper sulfate or copper chloride, but copper oxoacid salts such as nitric acid, carbonic acid and phosphoric acid, copper halide salts, copper chalcogenides such as copper sulfide, copper, and the like. Organic acid salts such as carboxylic acid salts or copper amino acid salts may be used. Moreover, when using at least one of a copper hydroxide and an oxide as a solid copper compound, a solution obtained by precipitating a dissolved copper salt by neutralization or the like may be used. The produced cuprous oxide powder may be used. In addition, there is no restriction | limiting of the particle size and particle size distribution of the solid copper compound to be used.

  In this way, a liquid containing at least one of a solid copper compound and copper ions is prepared as a substance to be reduced, and a complexing agent, a pH adjusting agent, a reducing agent, etc. are added to this liquid as necessary. As a result, the liquidity, the amount of solid components, the particle size, the oxidation number of copper, and the like can be adjusted. Moreover, when using carboxylate as copper salt, the carboxylic acid contained in the salt can also be utilized as a complexing agent.

  If a substance capable of forming a complex with copper ions (complexing agent) is added, the rapid reaction is suppressed to suppress the generation of secondary nuclei, the ion solubility is improved, and the surface property is good (surface (Smooth) particles can be obtained. Complexing agents include organic acids such as tartaric acid, succinic acid, citric acid, succinic acid, ethylenediaminetetraacetic acid, amines such as ammonia and ethylenediamine, alcohols such as glycerol and mannitol, amino acids, cyanogen (cyanic acid) or these The salt can be used. Further, without adding a complexing agent, solid metal salts (for example, carboxylates) as raw materials and by-products during the reaction may be used as a complexing agent.

  As the copper powder to be introduced, the particle diameter is uniform to some extent, and copper powder produced by an atomizing method or a wet reduction method can be used as long as the copper powder is nearly spherical. The correction coefficient α in the equation for calculating x in Equation 2 can be uniquely determined when the reaction system and the measuring apparatus are determined, has a desired particle size, and a width of the particle size distribution with good reproducibility. Can produce a narrow copper powder.

  The liquid containing the copper powder and the reducing agent is repulped in an inert gas for an appropriate period of time, and then a liquid containing at least one of a copper compound and copper ions is gradually added as a substance to be reduced, and the reduction reaction is performed while stirring. Make it progress. In addition, the liquid used as the solvent of the liquid containing the copper powder and the reducing agent may be a component that remarkably inhibits the reduction (for example, an oxidizing agent), and contains at least one of a copper compound and copper ions as a reduction target. Although it may be the same liquid as the liquid used as the solvent, it must be a liquid that does not contain the substance to be reduced (at least one of a copper compound and copper ions).

  The reaction is terminated when the presence of a copper ion, a copper complex or a solid component of the copper compound cannot be detected in the reaction solution. After completion of the reaction, solid-liquid separation is performed by filtration, and the filtered fraction is washed with pure water or a water-soluble organic solvent. In addition, you may perform other solid-liquid separations, such as centrifugation and spray drying, instead of filtration. The cake obtained by solid-liquid separation can be dried for several hours to several tens of hours at a temperature of 50 to 300 ° C. in an inert gas or a reducing atmosphere to obtain copper powder having a uniform particle size. it can. Nitrogen or a rare gas can be used as the inert gas, but a reducing gas such as hydrogen or carbon monoxide may be mixed and used.

  In the embodiment of the method for producing copper powder according to the present invention, copper powder having a uniform particle size can be produced while increasing the particle size of the copper powder. That is, in the embodiment of the method for producing copper powder according to the present invention, a liquid containing at least one of a compound and copper ions is added as a copper reductant to a liquid containing copper powder and a reducing agent, Is reduced to metallic copper, thereby producing a copper powder with a narrow particle size distribution and very few fine particles.

  Hereinafter, examples of the copper powder and the method for producing the same according to the present invention will be described in detail.

[Example 1]
First, 2.5 kg of copper sulfate pentahydrate (number of moles of copper = 10 mol) was dissolved in 6.1 kg of pure water at room temperature in a nitrogen atmosphere to obtain a copper sulfate solution. This copper sulfate solution was added to 9.6 kg of a 10% by mass sodium hydroxide solution and neutralized by stirring to produce copper hydroxide.

  Next, 6.5 kg of a 42 mass% glucose aqueous solution is added as a reducing agent capable of reducing the produced copper hydroxide to cuprous oxide, and the temperature is raised to 70 ° C. to promote the production of cuprous oxide. The reaction was carried out at 30 ° C. for 30 minutes. Thereafter, while maintaining the liquid temperature at 70 ° C., air was introduced at 4 L / min for 150 minutes to stabilize the liquid property, and then returned to a nitrogen atmosphere and cooled to room temperature. The solution was continuously stirred from the addition of the reducing agent to the end of cooling. After cooling to room temperature, stirring was stopped and the produced cuprous oxide was allowed to settle by decantation. After confirming that the cuprous oxide had sufficiently settled, the supernatant was removed to obtain 2.5 kg of wet cuprous oxide (cuprous oxide in which the supernatant that could not be removed remained). If the yield of the obtained copper is 100%, cuprous oxide (715 g) corresponding to 10 mol of copper will be obtained in the cuprous oxide in a wet state.

  Next, 700 g of the supernatant was further taken from the cuprous oxide in a wet state, and this supernatant and 2400 g of pure water were placed in a 5 L beaker. Meanwhile, 1800 g of the wet cuprous oxide slurry from which 700 g of the supernatant was removed (including 715 g of cuprous oxide) was transferred to a 2 L beaker, and stirring was started so that the cuprous oxide did not settle.

Next, in a 5 L beaker containing 700 g of the supernatant and 2400 g of pure water, 50% diameter (D ₅₀ ) = 5.30 μm in the volume-based particle size distribution (to obtain copper powder with a final target particle size of 10.0 μm). After adding 111 g of copper powder (acting as a nucleus), 373 g of 80% hydrous hydrazine was added as a reducing agent, sufficiently dispersed while stirring at 630 rpm, and heated to 60 ° C. in a nitrogen atmosphere. To this solution, a cuprous oxide slurry stirred in a 2 L beaker was continuously added by a tube pump in 360 minutes. After 60 minutes from the end of this addition, cuprous oxide was not confirmed, so the reaction was terminated.

  After completion of the reaction, the mixture was cooled to room temperature, and then the cake obtained by solid-liquid separation by suction filtration was washed with 8 L of pure water. The cake after washing was put into a dryer capable of controlling the atmosphere, and dried at 120 ° C. for 11 hours in a nitrogen atmosphere to obtain a target copper powder.

The volume-based particle size distribution of the obtained copper powder was measured by a wet laser diffraction particle size distribution measuring device (LS230 manufactured by Beckman Coulter, Inc.). As a result, the volume-based particle size distribution of the obtained copper powder was D ₁₀ = 8.62 μm, D ₂₅ = 9.31 μm, D ₅₀ = 10.18 μm, D ₇₅ = 11.07 μm, D ₉₀ = 11.76 μm. D ₉₀ / D ₁₀ = 1.36, and the coefficient of variation was 11.4%.

The number-based particle size distribution of the copper powder was evaluated by a field emission scanning electron microscope (FE-SEM) (S-4700 manufactured by Hitachi, Ltd.). The number-based particle size distribution of the copper powder observed by SEM was calculated from the Heywood diameter of 500 particles present in the SEM image. Further, in this example and the examples and comparative examples described later, the particle size was calculated using a 1000 × field of view, but when the number of 500 particles could not be measured, a plurality of 1000 × field of view was used. Calculated. As a result, the number-based particle size distribution of the copper powder is as follows: D ₁₀ = 8.51 μm, D ₂₅ = 8.85 μm, D ₅₀ = 9.45 μm, D ₇₅ = 10.37 μm, D ₉₀ = 11.28 μm, D It was ₉₀ / _D 10 = 1.33. Incidentally, the deviation from the final target particle size of 50% diameter of the number-based particle distribution of the resulting copper powder (D _50), (50% diameter of the number-based particle distribution (D ₅₀₎ - final target particle size ) × 100 / calculated from the final target particle size, it was −5.5%.

[Example 2]
D ₅₀ = using copper powder 0.09g of _D 50 = 0.52 .mu.m in place of copper powder 111g of 5.30Myuemu, except that the addition time of the cuprous oxide slurry is stirred at 2L beaker 480 minutes By the same method as Example 1, copper powder was obtained. When the volume-based particle size distribution of the copper powder was measured by the same method as in Example 1, D ₁₀ = 8.08 μm, D ₂₅ = 8.96 μm, D ₅₀ = 10.12 μm, D ₇₅ = 11.44 μm, D ₉₀ = _12.06μm, a D ₉₀ / D 10 = 1.49, coefficient of variation was 19.4%. Further, the number-based particle size distribution of the copper powder was measured by the same method as in Example 1. As a result, D ₁₀ = 8.76 μm, D ₂₅ = 9.43 μm, D ₅₀ = 10.61 μm, D ₇₅ = 11. _88μm, D 90 = _13.16μm, was D ₉₀ / D 10 = 1.50. The deviation from the final target particle size of 50% diameter (D ₅₀ ) in the number-based particle size distribution of the obtained copper powder was 6.1%.

[Example 3]
Except for using D ₅₀ = 5.30μm instead of copper powder 111g of (in order to obtain a copper powder final target particle size 5.8 [mu] _m) copper powder 82.5g of D 50 = 2.82μm is Example 1 By the same method, copper powder was obtained. When the volume-based particle size distribution of this copper powder was measured by the same method as in Example 1, D ₁₀ = 4.60 μm, D ₂₅ = 4.99 μm, D ₅₀ = 5.50 μm, D ₇₅ = 6.05 μm, D ₉₀ = 6.56 μm, D ₉₀ / D ₁₀ = 1.43, and the coefficient of variation was 13.0%. Further, the number-based particle size distribution of the copper powder was measured by the same method as in Example 1. As a result, D ₁₀ = 4.20 μm, D ₂₅ = 4.53 μm, D ₅₀ = 5.07 μm, D ₇₅ = 5. _55μm, D 90 = _5.86μm, was D ₉₀ / D 10 = 1.39. The deviation of the 50% diameter (D ₅₀ ) from the final target particle diameter in the number-based particle size distribution of the obtained copper powder was −12.6%.

[Example 4]
Example 1 with the exception of using 29.33 g of D ₅₀ = 5.30 μm copper powder (in order to obtain copper powder with a final target particle size of 15.0 μm) instead of 111 g of D ₅₀ = 5.30 μm copper powder. By the same method, copper powder was obtained. When the volume-based particle size distribution of the copper powder was measured by the same method as in Example 1, D ₁₀ = 12.87 μm, D ₂₅ = 13.75 μm, D ₅₀ = 15.55 μm, D ₇₅ = 17.45 μm, D ₉₀ = 19.04 μm, D ₉₀ / D ₁₀ = 1.48, and the coefficient of variation was 18.5%. Further, the number-based particle size distribution of the copper powder was measured by the same method as in Example 1. As a result, D ₁₀ = 11.63 μm, D ₂₅ = 13.21 μm, D ₅₀ = 14.99 μm, D ₇₅ = 16. They were 42 μm, D ₉₀ = 17.36 μm, and D ₉₀ / D ₁₀ = 1.49. The deviation of the 50% diameter (D ₅₀ ) from the final target particle diameter in the number-based particle size distribution of the obtained copper powder was −0.1%.

[Comparative Example 1]
First, 2.5 kg of wet cuprous oxide (cuprous oxide in which the supernatant liquid that could not be completely removed) was obtained in the same manner as in Example 1. Next, after 2.5 kg of wet cuprous oxide was transferred to a 5 L beaker, 2400 g of pure water was added and D ₅₀ = 5.30 μm (to obtain copper powder with a final target particle size of 10.0 μm). Of copper powder was added and sufficiently dispersed while stirring at 630 rpm, and the temperature was raised to 60 ° C. in a nitrogen atmosphere. To this solution, 373 g of 80% hydrous hydrazine as a reducing agent was continuously added by a tube pump for 360 minutes. After 60 minutes from the end of this addition, cuprous oxide was not confirmed, so the reaction was terminated. After completion of the reaction, the intended copper powder was obtained by the same method as in Example 1.

When the volume-based particle size distribution of the obtained copper powder was measured by the same method as in Example 1, D ₁₀ = 5.55 μm, D ₂₅ = 7.62 μm, D ₅₀ = 8.66 μm, D ₇₅ = 9. _63μm, D 90 = _10.46μm, a D ₉₀ / D 10 = 1.89, coefficient of variation was 21.1%. Further, the number-based particle size distribution of the copper powder was measured by the same method as in Example 1. As a result, D ₁₀ = 1.36 μm, D ₂₅ = 1.92 μm, D ₅₀ = 4.01 μm, D ₇₅ = 7. It was 72 μm, D ₉₀ = 9.14 μm, and D ₉₀ / D ₁₀ = 6.70. The deviation of the 50% diameter (D ₅₀ ) from the final target particle diameter in the number-based particle size distribution of the obtained copper powder was −59.9%.

[Comparative Example 2]
Comparative Example 1 except that D ₅₀ = 5.30 μm copper powder 111 g (in order to obtain a final target particle size of 8.0 μm copper powder) D ₅₀ = 5.30 μm copper powder 260.5 g was used instead of D ₅₀ = 5.30 μm copper powder 111 g By the same method, copper powder was obtained. When the volume-based particle size distribution of the copper powder was measured by the same method as in Example 1, D ₁₀ = 5.57 μm, D ₂₅ = 6.43 μm, D ₅₀ = 7.29 μm, D ₇₅ = 8.12 μm, D ₉₀ = 8.85 μm, D ₉₀ / D ₁₀ = 1.59, and the coefficient of variation was 21.1%. Moreover, as measured by the same method the particle size distribution of number-based copper powder as in Example _{1, D 10 = 2.13μm, D} 25 = 2.59μm, D 50 = 3.44μm, D 75 = 6. It was 61 μm, D ₉₀ = 7.69 μm, and D ₉₀ / D ₁₀ = 3.61. The deviation of the 50% diameter (D ₅₀ ) from the final target particle diameter in the number-based particle size distribution of the obtained copper powder was −57%.

  Table 1 shows the volume-based particle size distribution of the copper powders obtained in Examples 1 to 4 and Comparative Examples 1 and 2, and Table 2 shows the number-based particle size distribution. Further, the volume-based particle size distributions of the copper powders obtained in Examples 1 to 4 and Comparative Examples 1 and 2 are shown in FIGS. 1A to 1F, respectively, and the number-based particle size distributions are shown in FIGS. 2A to 2F, respectively. Furthermore, the SEM image of the copper powder obtained in Examples 1-4 and Comparative Examples 1-2 is shown to FIG. 3A-FIG. 3F, respectively.

From the results of Table 1, Table 2, FIGS. 1A to 1F, FIGS. 2A to 2F, and FIGS. 3A to 3F, as in Examples 1 to 4, the 50% diameter (D ₅₀ ) in the volume-based particle size distribution is A liquid containing at least one of a copper compound and a copper ion as a reductant is added to a liquid containing copper powder of 0.5 μm or more and a reducing agent, and the reductant is reduced to metallic copper to produce copper powder. Thus, it can be seen that copper powder having a narrow particle size distribution and a very small number of fine particles can be produced for each target particle size.

Claims (7)

In a liquid containing a copper powder having a 50% diameter (D ₅₀ ) of 0.5 μm or more and a reducing agent in a volume-based particle size distribution by a wet laser diffraction type particle size distribution measuring device, at least a copper compound and copper ions are to be reduced. A method for producing a copper powder, characterized in that a copper powder is produced by adding a liquid containing one of the reduced substances to metallic copper. The said copper compound is a solid copper compound, The manufacturing method of the copper powder of Claim 1 characterized by the above-mentioned. The method for producing a copper powder according to claim 1 or 2, wherein the copper compound is a copper oxide or hydroxide. The method for producing copper powder according to any one of claims 1 to 3, wherein the reducing agent is hydrazine or hydrous hydrazine. The total mole number of copper other than the copper powder in the liquid containing the copper powder and the reducing agent and the liquid to be reduced is n ₀ (mol), and the 50% diameter in the volume-based particle size distribution of the copper powder ( When D ₅₀ ) is x ₀ (μm), the weight of the copper powder is w (g), and the atomic weight of copper is AW (g / mol), a scanning electron microscope of copper powder produced by reduction to the metallic copper 5. The 50% diameter (D ₅₀ ) in the number-based particle size distribution determined from the photograph is within ± 20% of x (μm) represented by the following equation (1): The manufacturing method of the copper powder in any one.

The 50% diameter (D ₅₀ ) in the number-based particle size distribution determined from the scanning electron micrograph is 0.5 to 20 μm, and the 90% diameter (D ₉₀ ) with respect to the 10% diameter (D ₁₀ ) in the number-based particle size distribution. ratio) _(D 90 _/ D ₁₀₎ is equal to or more than 1.5, copper powder. The 50% diameter (D ₅₀ ) in the volume-based particle size distribution by a wet laser diffraction type particle size distribution measuring apparatus is 0.5 to 20 μm, and the 90% diameter with respect to the 10% diameter (D ₁₀ ) in the volume-based particle size distribution wherein the ratio of _{(D 90) (D 90 /} D 10) is 1.5 or less, copper powder of claim 6.

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