WO2007111231A1

WO2007111231A1 - Process for production of copper powder and copper powder obtained by the process

Info

Publication number: WO2007111231A1
Application number: PCT/JP2007/055956
Authority: WO
Inventors: Takahiko Sakaue; Katsuhiko Yoshimaru; Yoshinobu Nakamura
Original assignee: Mitsui Mining & Smelting Co., Ltd.
Priority date: 2006-03-24
Filing date: 2007-03-23
Publication date: 2007-10-04
Also published as: KR20080104020A; JP5144022B2; CN101394961A; JP2007254846A; TW200744954A

Abstract

The invention aims at providing a process for producing copper powder composed of uniform fine particles by a wet reduction method efficiently and high-quality copper powder excellent in particle size distribution. In order to attain the aim, a process for the production of copper powder is employed, which comprises reacting an aqueous solution of copper ions with an alkali solution to form a copper hydroxide slurry, adding a reducing agent to the slurry to conduct the first reduction treatment of the slurry and thereby form a copper suboxide slurry, allowing the copper suboxide slurry to stand to precipitate copper suboxide particles, removing the formed supernatant, washing the copper suboxide particles by the addition of water to form a washed copper suboxide slurry, and adding a reducing agent to the suboxide slurry to conduct the second reduction treatment of the slurry and thereby form copper powder, characterized in that in the first reduction treatment, both a hydrazine as a reducing agent and aqueous ammonia as a pH regulator are added to the copper hydroxide slurry.

Description

Specification

Copper powder manufacturing method and copper powder obtained by the manufacturing method

Technical field

TECHNICAL FIELD [0001] The present invention relates to a method for producing copper powder by a wet reduction method, and particularly relates to a method for efficiently producing copper powder that is uniform in fine particles and has high conductivity, and copper powder produced by this production method.

Background art

Conventionally, copper powder has been widely used as a raw material for copper paste and copper ink. Because of its ease of handling, copper paste is applied to circuit formation of printed wiring boards using screen printing, various electrical contacts, etc., and is used as a means of ensuring electrical continuity. In order to control the viscosity of the copper paste according to the field of use, it is necessary to consider various characteristics of the copper powder.

[0003] For example, a copper paste is obtained by appropriately blending a resin component with a copper powder having a fine particle size of several μm, and is used for forming a circuit shape and the like, and is fired or solidified to form a conductor film. As such, it exhibits conductivity. In response to miniaturization of printed wiring boards and the like, the copper powder used in the copper paste is required to have higher properties in terms of the conductivity and reliability of the circuit formed by the paste.

[0004] The copper powder used for the copper paste has been desired to reduce the paste viscosity, facilitate the handling as a paste, and improve the via hole filling property of the printed wiring board. In order to meet this demand, various solutions such as optimization of the particle size and specific surface area of the copper powder and surface treatment with an organic agent on the surface of the powder are adopted to reduce the viscosity of the copper paste. I have been.

[0005] The wet reduction method is generally used as a method for producing such copper powder. Patent Document 1 discloses a method for producing a fine copper powder controlled to have a good particle size using a wet reduction method. On the other hand, Patent Document 2 discloses a method for efficiently producing copper powder having a fine particle diameter and a smooth surface in order to cope with fine wiring by using the atomizing method. [0006] Patent Document 1: Japanese Patent Publication No. 5-57324

Patent Document 2: JP 2002-343135 A

Disclosure of the invention

Problems to be solved by the invention

[0007] Recently, as the utilization technology has advanced, further improvement of the powder characteristics of copper powder has been demanded from the factory. That is, a method for producing a copper powder having a smooth surface, a fine surface and a uniform particle size and high conductivity at a low cost is desired. Here, in the case of fine copper powder produced by the atomizing method, it is possible to produce copper powder that is excellent in terms of particle size distribution and dispersibility with low carbon content. And tends to contain impurities, and the yield tends to be low. In addition, there is a problem that if the classification is strengthened to eliminate coarse grains, the manufacturing cost increases. On the other hand, copper powder by the conventional wet reduction method, which makes it easy to obtain uniform and fine particles, is due to the dispersing agent contained in the reducing system, which often uses organic reducing agents, although the primary particles themselves are fine and uniform. As the amount of adsorbed organic agent becomes high, the gas generated due to the diffusion of the organic matter adsorbed during firing causes the surface of the fired film to become rough, causes internal defects, and is immediately problematic in terms of conductivity. It was.

[0008] In addition, as in Patent Document 1, in the case of a wet reduction method using an inorganic reducing agent, the above problem is solved, but there is a problem that the particle size and yield of the obtained copper powder are likely to vary. I

[0009] Here, the result of manufacturing copper powder using the manufacturing method disclosed in Patent Document 1 is shown.

That is, 80 kg (320 mol) of copper sulfate was dissolved in water, ammonia water was added while maintaining the temperature at 40 ° C., the pH of the aqueous solution was adjusted to 4.0, a copper hydroxide slurry was formed, and then water was added. The total liquid volume was 160 liters by addition. While maintaining this solution at a temperature of 50 ° C. and a pH of 4.0, 6.01 kg (120. lmol) of hydrazine hydrate was added and reacted for 60 minutes to form a copper oxide slurry. After completion of the reaction, the mixture was allowed to stand for 60 minutes, the supernatant was removed, and water was also added to make the total liquid volume 160 liters.

Next, while maintaining this at a temperature of 50 ° C., 8. Olkg (160. Omol) of hydrazine hydrate was added and allowed to react for 60 minutes. Thereby, cuprous oxide is reduced to become metallic copper powder.

[0011] Next, this was filtered with a natural gravity filter, washed with water, and then glued with a glue concentration of 0.5gZl. 40 liters of solution through filtration (water washing filtration with water, filtration with 9 liters of methanol solution with oleic acid concentration of 0.2% by volume), and normal atmosphere at a temperature of 80 ° C And dried to obtain 20 kg of copper fine powder.

[0012] For the 10 lots of copper powder obtained above, D, D, D, standard deviation (SD

10 50 90

), D ZD, specific surface area, tap packing density are evaluated using current analyzers,

90 10

For each powder property, the average value for 10 lots and the standard deviation σ were calculated.

[0013] The average value of the powder properties of the copper powder obtained through the above process for 10 lots is D = 1.03 m

Ten

, D = 3. 42 μ τ, Ό = 7. 46; z m, standard deviation (SD) = 2. 85; z m, D / Ό = 7.

50 90 90 10

29, specific surface area (SSA) O. 89m ² Zg, tap packing density (TD) 3.4g Zcc, average yield was 85.8%. The results are shown in Table 1. The yield was calculated by the amount of copper powder actually obtained relative to the theoretical amount of copper powder calculated from the amount of copper salt used.

[0014] [Table 1] Results of Patent Document 1

[0015] From Table 1, the copper powder disclosed in Patent Document 1 has an average yield of 85.8% and a standard deviation σ of yield of 8.5, which varies greatly between lots. In addition, it can be seen that the characteristics related to grain size vary considerably from lot to lot. In other words, although the invention disclosed in Patent Document 1 may show good powder characteristics, it can be said that it is a technique for which further improvement is desired in terms of stable production. [0016] Therefore, the present inventor verified the above-mentioned Patent Document 1. As a result, in Patent Document 1, hydrazine hydrate is added and reacted while maintaining the pH of a solution obtained by adding water to a copper hydroxide slurry, and a cuprous oxide slurry is produced. Although it can be maintained within a certain range, it is difficult to maintain the reaction slurry at a constant pH throughout the reduction reaction. Therefore, there was always a pH fluctuation during the reduction, and it was considered that this pH fluctuation state had a negative effect on stable yield inhibition and copper powder characteristics.

[0017] In response to the above problems, the present invention is a method for producing fine and uniform copper powder by a wet reduction method, which increases the electrical conductivity and makes a homogeneous and high-quality copper powder stable and high. The present invention provides a method for producing copper powder obtained in a yield and a copper powder obtained by this production method. Means for solving the problem

[0018] Therefore, as a result of earnest research, the present inventor has adopted the following means in order to solve the above problems.

[0019] A method for producing a copper powder according to the present invention: Obtaining a copper hydroxide slurry obtained by reacting a copper ion-containing aqueous solution with an alkaline solution (step 1), and adding a reducing agent to the copper hydroxide slurry. The first reduction treatment is performed as a cuprous oxide slurry (step 2), the cuprous oxide slurry is allowed to stand to precipitate cuprous oxide particles, the supernatant is removed, and water is added to add cuprous oxide. The particles are washed to form a washed cuprous oxide slurry, and a reducing agent is added to the washed cuprous oxide slurry to perform a second reduction treatment to obtain copper powder (step 3) in the copper powder production method by wet reduction! Thus, the first reduction treatment is a production method characterized in that hydrazines as a reducing agent and an aqueous ammonia solution as a pH adjusting agent are added to a copper hydroxide slurry in combination.

[0020] Here, the process 2 is characterized in that hydrazines as a reducing agent and an aqueous ammonia solution as a pH adjuster are added to the copper hydroxide slurry in combination. The above manufacturing methods can be classified into steps 1 to 3 as described above if the steps are roughly classified. Details will be described in an embodiment described later.

[0021] In Step 2 (first reduction treatment), hydrazines as a reducing agent and an aqueous ammonia solution as a pH adjusting agent are added to the copper hydroxide slurry in combination with a pH of 3.0. It is preferable to control the fluctuation of pH in the range of ~ pH 7.0.

[0022] It should be noted that the fluctuation control of the pH is based on the starting point pH at the start of the addition of the reducing agent and the pH adjusting agent. It is preferable to control the difference from the end point pH at the end of the addition to 3.0 or less.

[0023] Here, the "starting pH" is the pH of a solution before the combined addition of a hydrazine as a reducing agent and an aqueous ammonia solution as a pH adjusting agent is started. On the other hand, “end-point pH” is defined as reducing agent and p

This is the pH of the solution at the end of the addition of the H modifier.

[0024] Further, in step 2 (first reduction treatment), the pH is changed by adding to the copper hydroxide slurry a combination of hydrazines as a reducing agent and an aqueous ammonia solution as a pH adjuster. Preferably, the minimum pH of 2.8 or higher.

[0025] Furthermore, in the method for producing copper powder according to the present invention, it is preferable that the alkaline solution to be reacted with the copper ion-containing aqueous solution is an aqueous ammonia solution when producing the copper hydroxide slurry.

[0026] In the method for producing copper powder according to the present invention, the washed cuprous oxide slurry has a pH of

4. It is preferably 1 to ρ〜6.0.

[0027] Copper powder obtained by the production method according to the present invention: The copper powder production method according to the invention is used.

V, a copper powder characterized by being manufactured.

The invention's effect

[0028] The method for producing copper powder according to the present invention employs a two-stage reduction process in which copper particles are precipitated and reduced through cuprous oxide, and in particular as a reducing agent during reduction from copper ions to cuprous oxide. By using both hydrazines and an aqueous ammonia solution as a pH adjuster in combination, the reaction slurry can be brought into a good reduced state by controlling the fluctuation of the pH of the reaction solution as small as possible. This improves the process stability of the copper powder manufacturing process, suppresses the occurrence of agglomeration, and makes it possible to obtain a copper powder with a sharp particle size distribution with little particle variation. It can be made more homogeneous and the yield is improved.

[0029] By adopting the above-described method for producing copper powder, it becomes possible to stably produce copper powder, which not only suppresses the production cost but also sharpens the particle size distribution with less particle variation. This makes it possible to provide high-quality copper powder.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the best embodiment of the method for producing copper powder according to the present invention will be described.

[0031] Method for producing copper powder according to the present invention: The method for producing copper powder according to the present invention comprises the following steps: This can be classified into steps 1 to 3. Hereinafter, it demonstrates for every process.

[0032] Step 1: In Step 1, a copper hydroxide slurry obtained by reacting a copper ion-containing aqueous solution with an alkaline solution is obtained. The said copper hydroxide slurry means the slurry containing copper hydroxide, and may contain other components other than copper hydroxide. Here, “copper ion-containing aqueous solution” and “al strength solution” will be described.

[0033] The copper ion-containing aqueous solution here is a solution obtained by adding a water-soluble copper salt to water and dissolving it, and contains a divalent copper ion. The copper salt here means copper sulfate, copper nitrate, copper acetate, copper chloride, etc., with copper sulfate and copper nitrate being particularly preferred. The copper salt content in the copper ion-containing aqueous solution is 2.2 mol / l to 3. Omol / 1, more preferably 2.5 molZl to 3. OmolZl. . When the copper concentration in the copper ion-containing aqueous solution is less than 2.2 molZl, the copper concentration in the solution is too low, and the particle diameter of the copper powder particles is difficult to be uniform. On the other hand, if the copper concentration in the copper ion-containing aqueous solution exceeds 3. OmolZl, the copper concentration becomes too high, and the aggregation of the copper powder particles that are reduced and precipitated becomes remarkable.

[0034] The alkaline solution used here includes potassium hydroxide, sodium hydroxide, an aqueous ammonia solution, and the like. Most preferably, it is an aqueous ammonia solution. This is because it is easy to control the variation in pH during the reduction reaction in Step 2 described later, and there are few residual components on the surface of the obtained copper powder particles. The added amount of the alkaline solution is 1.4 mol to 1.8 mol with respect to 1 mol of copper. When the alkali is less than 1.4 mol with respect to 1 mol of copper, a copper hydroxide slurry suitable for copper powder production cannot be obtained, a good yield cannot be achieved, and the powder characteristics of the obtained copper powder vary. Also grows. On the other hand, when the alkali concentration in the copper hydroxide slurry exceeds 1.8 mol with respect to 1 mol of copper, the pH of the hydroxide and copper slurry becomes strong alkali, and the control port is adjusted to an appropriate pH range in the reduction process. It becomes difficult.

In the preparation of the copper hydroxide slurry, the liquid temperature of the copper ion-containing aqueous solution is set to 30 ° C. to 70 ° C. (more preferably 40 ° C. to 60 ° C.). It is preferable to neutralize the solution so that the pH becomes 3.0 to 7.0. Here, the liquid temperature of the copper ion-containing aqueous solution was set to 30 ° C to 70 ° C when the liquid temperature was lower than 30 ° C. This is because the salt cannot be dissolved properly and a solution with an appropriate copper concentration cannot be obtained. On the other hand, if the liquid temperature of the copper ion-containing aqueous solution exceeds 70 ° C, it is likely to be highly crystalline copper hydroxide. As a result, the dissolution rate of copper hydroxide is slowed down in the next step 2 and the obtained cuprous oxide particles become large, so that uniform copper can be obtained in the subsequent step, and the process and quality are unstable. Become.

[0036] The pH of the copper hydroxide slurry is preferably controlled in the range of 3.0 to 7.0. Outside this range, it becomes difficult to bring the solution pH in Step 2 described below closer to the neutral region. This pH range is a range that can be controlled when the copper concentration in the above-described copper hydroxide slurry is set to 2.2 molZl to 3. OmolZl and the amount of alkali relative to copper lmol is set to 1.4 mol to 1.8 mol.

[0037] Step 2: In Step 2, a first reducing treatment is performed by adding a reducing agent to the copper hydroxide slurry to obtain a cuprous oxide slurry. The copper powder production method according to the present invention is characterized in that, in Step 2, hydrazines as a reducing agent and an aqueous ammonia solution as a pH adjuster are added to the copper hydroxide slurry in combination.

[0038] In step 2, hydrazines (reducing agent) are added to the copper hydroxide slurry, and mainly a process of reducing the copper hydroxide to cuprous oxide to produce a cuprous oxide slurry is performed. . The said cuprous oxide slurry means the slurry containing cuprous oxide, and may contain components other than cuprous oxide. The same applies to the washed cuprous oxide slurry in Step 3 described later. The reason why hydrazines are used as a reducing agent in this step is that they are less likely to be adsorbed on the surface of the cuprous oxide particles and are unlikely to become pollutants. The hydrazines have various abilities such as hydrazine hydrate, hydrazine sulfate, and hydrazine anhydride, and most preferably hydrazine hydrate. These hydrazines can be used alone or in combination. And it is preferable to use for reaction as a solution. This is because it diffuses rapidly into the reaction system solution and does not cause a heterogeneous reaction.

[0039] The amount of added hydrazines is 0.3 mol to 0.00 mol with respect to 1 mol of copper in the copper hydroxide slurry.

5 mol is preferable. Addition capacity of hydrazines Less than 0.3 mol with respect to lmol of copper is not preferable because a large amount of unreacted copper hydroxide remains. On the other hand, when the addition amount of hydrazine exceeds 0.5 mol with respect to lmol of copper, The reduction reaction cannot be stopped at the cuprous oxide stage, and as a result, it becomes difficult to produce copper powder having good powder characteristics that easily cause aggregation and the like.

[0040] In the process of reducing the copper hydroxide slurry to the cuprous oxide slurry in step 2, an aqueous ammonia solution as a pH adjuster is added while adding hydrazines as the reducing agent. Addition and reduction treatment while controlling pH fluctuation. The reason why the aqueous ammonia solution is used here is that when ammonia is used as the neutralizing agent in the formation of the copper hydroxide slurry, the consistency between the type of the neutralizing agent and the pH adjusting agent is improved, and different components are used. As much as possible, the adsorption of foreign elements to the particle surface is avoided as much as possible, and the purity of the resulting copper powder can be easily controlled. Further, in order to bring the solution pH shifted to the acidic side due to the addition of hydrazines close to neutrality with high accuracy, it is preferable to use the characteristics of ammonia as a neutralizing agent.

[0041] Here, FIG. 1 shows the pH fluctuation state of the solution from the start of the addition of hydrazines to the copper hydroxide slurry until the end of the step 2 in the step 2. FIG. 1 shows the pH fluctuation curve of Example 1 in which hydrazine and an aqueous ammonia solution were used in combination, and the pH fluctuation curve of a comparative example in which hydrazine was used alone. As is clear from the comparison, in both Example 1 and Comparative Example, when the addition of hydrazine is started, the pH of the copper hydroxide slurry changes to the acidic side abruptly. Thereafter, the pH is shifted to the alkali side by a certain width, and a steady state is obtained. The following contents are explained on the assumption that there is such pH fluctuation.

[0042] By adding hydrazines and an aqueous ammonia solution in combination to the copper hydroxide slurry, the pH is adjusted to the acidic side so that it falls within the range of pH 3.0 to 7.0 compared to the case where the aqueous ammonia solution is not used. It is preferable to control the shift width to be small. As a result, copper powder obtained with less influence of particle aggregation and the like can produce copper powder with higher dispersibility and sharp particle size distribution in high yield.

[0043] The addition of the hydrazines and the aqueous ammonia solution to the copper hydroxide slurry is more preferably performed as follows in order to control the pH within the range of pH 3.0 to 7.0. . That is, the hydrazines and the aqueous ammonia solution are 0.3 mol to 0.5 mol of hydrazine and 0.5 mol of ammonia aqueous solution (as ammonia) at the end of the addition with respect to 1 mol of copper in the copper hydroxide slurry. It is preferable to add continuously so that the ratio is ~ 0.4mol. The pH of the slurry thus added may be adjusted so that the difference between the starting pH at the start of the addition of the reducing agent and the pH adjusting agent and the end pH at the end of the addition is 3.0 or less. Further, it is more preferable to control the fluctuation of the pH within the range of pH 3.5 to 5.0. The total amount of alkali used in step 1 and step 2 is preferably 1.85 mol to 2.0 mol of the alkali component with respect to 1 mol of copper.

[0044] Here, when hydrazines are added alone, the pH of the solution fluctuates from time to time depending on the amount of addition, resulting in a fluctuation exceeding 3 from the initial pH. If the solution pH fluctuates, the particle size variation of the obtained cuprous oxide copper particles will increase, and the particle size distribution of the final product copper powder particles will deteriorate. Therefore, hydrazines and aqueous ammonia are used in combination, and these are added continuously to minimize the fluctuation of the solution pH during the reduction operation and maintain a constant pH.

[0045] Here, when the addition amount of the hydrazines and the aqueous ammonia solution is less than the lower limit, it is not possible to satisfactorily reduce hydroxide to cuprous oxide. On the other hand, if the addition amount of the hydrazines and aqueous ammonia solution exceeds the upper limit, the reduction operation cannot be stopped with cuprous oxide. Further, if the addition range is out of the above range, the pH of the addition solution cannot be controlled to vary between 3.0 and 7.0, and as a result, copper powder with good powder characteristics cannot be obtained. Yes.

[0046] In addition, in step 2, when the addition of hydrazines to the copper hydroxide slurry is started, the pH of the solution changes suddenly to the acidic side as shown in the comparative example of FIG. The fluctuation range varies depending on the amount of addition, but if an aqueous ammonia solution is not used, the copper hydroxide slurry in which the addition of hydrazine has started becomes strongly acidic below pH 2.8. In such a strongly acidic region, the powder characteristics of the obtained copper powder deteriorate, and the variation in production yield increases. Therefore, as shown in Example 1 of FIG. 1, by adding hydrazines as a reducing agent and an aqueous ammonia solution as a pH adjuster in combination, as in the method for producing copper powder according to the present invention. Immediately after the start of the addition of hydrazines, the pH shift to the acidic side should be on the alkali side at pH 2.8 or higher, and the shift to the strongly acidic side of the pH fluctuation curve should be reduced in total. Thus, the powder characteristics of the obtained copper powder are improved, and a high production yield is stably obtained. Above and below, this abrupt acid The pH that varies to the sex side and is on the most acidic side is referred to as the “minimum pH”.

[0047] The temperature of the solution in Step 2 is preferably a temperature range of 40 ° C to 60 ° C. At temperatures below 40 ° C, industrial productivity is not satisfactory because the reduction reaction rate is slow. On the other hand, when the reduction temperature exceeds 60 ° C, the reduction reaction becomes too fast and a non-uniform reduction reaction occurs, so that the powder characteristics of the obtained copper powder deteriorate. In general, in the above temperature range, the obtained cuprous oxide has a fine particle size, if it is kept constant at a low temperature, and if it has a larger particle size, it should be kept constant at a higher temperature. Favored ,.

[0048] Step 3: In Step 3, the cuprous oxide slurry is allowed to stand to precipitate the cuprous oxide particles, and the supernatant is removed and water is added to wash the cuprous oxide particles and to wash the cuprous oxide particles. As a copper oxide slurry, copper powder is obtained by adding a reducing agent to the washed cuprous oxide slurry and performing a reduction treatment.

[0049] In step 3, the cuprous oxide slurry is allowed to stand to precipitate cuprous oxide particles. The solution pH at this stage is approximately 3.9. Then, the supernatant is removed and the cuprous oxide particles are washed by adding water and calcining. As for the cleaning method at this time, it is possible to adopt any cleaning method without any particular limitation. However, the recuperation cleaning is adopted as follows, and the cleaning level of the cuprous oxide slurry ( The pH value of the “washed cuprous oxide slurry” described below) is preferably controlled. Here, the slurry state when the wash water is poured when the supernatant is discarded and the wash water is added several times during the washing is referred to as a washed cuprous oxide slurry.

[0050] In the repulp washing, it is preferable that the washing cuprous oxide slurry is repeatedly washed until the pH becomes any constant between pH 4.1 and 6.0. If the pH of the washed cuprous oxide slurry is more acidic than 4.1, the powder properties such as agglomeration of copper powder obtained when adding a reducing agent to make copper powder become stronger, and the dispersibility is poor. Deteriorate. On the other hand, when the pH of the washed cuprous oxide slurry is more alkaline than 6.0, the amount of ions is small and the electron transfer reaction becomes worse, and when a reducing agent is added to form a copper powder, agglomeration occurs and particles are generated. The uniformity of the powder is reduced, and the powder properties are also bad, and the reduction efficiency is poor. In other words, it can be said that the pH between 4.1 and 6.0 is an appropriate range to avoid particle aggregation.

[0051] And, more preferably, the washed cuprous oxide slurry is any one between pH 4.3 and 4.7. Wash until constant pH. By setting the pH of the washed cuprous oxide slurry to 4.3 to 4.7, it is possible to obtain high-quality copper powder with less coarse particles and less variation in addition to suppressing aggregation, at a low cost. However, it is most excellent in process stability for obtaining fine particles and high dispersibility.

[0052] Then, a reducing agent is added to the washed cuprous oxide slurry obtained as described above. At this time, the pH at the end of the addition may be adjusted to 7.0 to 9.0. That is, in the case of hydrazines, the reducing agent to be added is preferably added at a ratio of 0.4 mol to 0.7 mol with respect to 1 mol of copper contained in the washed cuprous oxide slurry at the end of the addition. More preferably, the total amount of hydrazines added in step 2 and step 3 is 0.885 mol to l.2 mol relative to 1 mol of copper. If this pH is on the alkaline side of 9.0, there will be a large amount of reducing agent, which tends to form fine particles and easily aggregate. On the other hand, if the pH is on the acidic side from 7.0, coarse particles increase and aggregate, and dispersibility soon deteriorates. Therefore, when the pH at the end of addition is out of the range of 7.0 to 9.0, the resulting powder characteristics of the copper powder are significantly deteriorated, and a broad particle size distribution is exhibited.

[0053] The temperature of the reducing agent is preferably maintained at a constant level between 40 ° C and 55 ° C. If the temperature of the reducing agent is lower than 40 ° C, the reduction reaction becomes dull and the industrially desirable productivity is not satisfied. On the other hand, if the temperature is higher than 55 ° C, the reduction rate becomes too fast and the particle size tends to be uneven. Further, as the reducing agent in Step 3, it is preferable to use the hydrazines used in Step 2 described above. The reason is that the reducing ability of hydrazine as a reducing agent is suitable for obtaining copper powder with good powder characteristics. Also, by adopting the same reducing agent as the reducing agent used in step 2, the amount of foreign components related to the reduction of copper powder is reduced as much as possible, and the amount of contaminating components adhering to the copper powder particle surface is reduced. This is to make it happen.

[0054] In addition, the agglomerated particles can be rapidly separated from each other by using a fluid mill method (such as a fin flow mill) or a laminar flow mixing method (such as TK fill mix) while the slurry is in a state of being reduced to copper powder. It is also preferable to improve the particle dispersibility by colliding with a centrifugally flowing slurry in order to break up the agglomerated state and bring it closer to the primary particles, and at the same time smoothing the particle surface.

[0055] The copper powder obtained as described above is subjected to general steps such as filtration, washing, and drying to obtain copper powder. And commercialized. In order to improve the oxidation resistance, the copper powder is preferably subjected to a surface treatment with fatty acid diamines such as oleic acid and stearic acid, if necessary. Even in this dried copper powder state, if necessary, the particles can be dispersed using a device capable of colliding the agglomerated particles, such as a classifier, a high pretizer, and a turbo classifier. It is also possible to improve.

[0056] As described above, the copper powder obtained by the production method according to the present invention can stably produce a copper powder having fine powder characteristics and uniform powder characteristics. Further, since adsorption of foreign elements to the particle surface is suppressed, it is possible to suppress the gas diffusion during baking, to avoid internal defects of the fired film as much as possible, and to produce copper powder with good conductivity.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The present invention is not limited to the following examples. In order to make it easier to understand the copper powder production conditions in the following examples and comparative examples, Table 2 lists the outline of the production conditions.

[0058] [Table 2]

Note) Copper sulfate: As copper sulfate pentahydrate

Ammonia: Aqueous ammonia solution with a concentration of 25 w t%

Reducing agent: hydrazine monohydrate

PH adjusting agent: Aqueous ammonia solution with a concentration of 25 w t% Example 1

[0059] Step 1: 50. Add 6000 g (24. Omol) of copper sulfate pentahydrate to 6.5 liters of pure water of C to prepare a copper ion-containing aqueous solution containing divalent copper ions. Then, an aqueous ammonia solution (concentration: 25 wt%) 2500 ml (36.7 mol) was added to the copper ion-containing aqueous solution kept at a temperature of 50 ° C. in 30 minutes for neutralization to obtain a copper hydroxide slurry. After that, pure water was added to the copper hydroxide slurry to make the copper concentration 2 molZl and ρΗ6.3.

[0060] Step 2: Hydrazine monohydrate and a pH adjuster as a reducing agent are added to the copper hydroxide slurry. The ammonia solution was added to control pH fluctuation. That is, the liquid temperature of the copper hydroxide slurry at pH 6.3 was kept at 50 ° C, and hydrazine monohydrate 450g (9. Omol) and ammonia aqueous solution (concentration 25wt%) 590ml (8.7 mol) The solution was continuously added over a period of minutes, and the pH at the end of the addition was 3.9. As for the pH fluctuation, the starting point pH was 6.3, the end point pH was 3.9, the minimum pH was 3.5, and the difference between the starting point pH and the end point pH was 2.4. Stirring was continued for another 30 minutes in order to complete the reduction reaction.

[0061] Thereafter, repulp washing was performed. That is, add pure water to the slurry after step 2 and adjust to 18 liters, leave it to stand, and remove 14 liters of the supernatant after standing until the pH after washing with repulp reaches 4.7. This was used as a washed cuprous oxide slurry.

[0062] Step 3: Next, water was added to the washed cuprous oxide slurry, the liquid temperature was maintained at 50 ° C, and the copper concentration was adjusted to 2 molZl. Thereafter, 600 g (12. Omol) of hydrazine monohydrate was added over 30 minutes. The solution pH at the end of the addition was 8.2. The mixture was further stirred for 60 minutes to complete the reduction reaction to reduce and precipitate copper powder (second reduction treatment).

[0063] The copper powder thus obtained was collected by filtration. Then, the copper powder was put into 5 liters of a methanol solution in which 1.5 g of dodecylamine was dissolved, subjected to surface treatment, stirred for 30 minutes, and heated and dried at 80 ° C. for 5 hours to obtain a powder.

[0064] In order to verify the dispersion of the powder characteristics and yield of the copper powder obtained in Example 1, D, D, D for each lot of the 10 lots of copper powder obtained in Example 1 above. , Standard deviation (SD

10 50 90

), D ZD, specific surface area, tap fill density

90 10

Table 3 shows the results of calculating the average value and standard deviation σ for the lot. The standard deviation for each lot is expressed as SD, and the standard deviation for 10 lots of data is expressed as σ to distinguish the two.

[0065] Powder characteristics of copper powder: The average value of 10 lots of powder characteristics of copper powder obtained through the above process is D = 0. ΊΊ μ ι, Ό = 1. 75, um, D = 3. 68 m, standard deviation (SD) = 1.1

10 50 90

ZD = 4.77, specific surface area (SSA) O. 54m ² Zg, tap packing density (TD) 4.

90 10

7gZ cc and te.

[0066] When the yield of copper powder for each lot was calculated, all were 97% or more, and the standard deviation σ of yield was 0.8, and a stable yield could be obtained. The yield is calculated from the amount of copper salt used. It calculated with the quantity of the copper powder actually obtained with respect to the theoretical copper powder quantity taken out.

[0067] [Table 3]

Example 2

Step 1: A copper hydroxide slurry was obtained in the same manner as in Example 1.

[0069] Step 2: To the copper hydroxide slurry, an aqueous ammonia solution as hydrazine monohydrate and _P H adjusting agent as a reducing agent was added to control pH fluctuation. That is, the temperature of the copper hydroxide slurry at pH 6.3 was kept at 40 ° C, and 450 _g (9. OmolZl) of hydrazine monohydrate and 350 ml (5. Continuous addition over 15 minutes, the pH at the end of the addition was 4.8. The pH variation here was a starting point pH of 6.3, an ending point pH of 4.8, a minimum pH of 3.8, and a difference between the starting point pH and the ending point pH of 1.5. Stirring was continued for another 30 minutes in order to complete the reduction reaction. Then, repulp washing was performed in the same manner as in Example 1 to obtain a washed cuprous oxide slurry.

Step 3: Next, copper powder was reduced and deposited in the same manner as in Step 3 of Example 1 except that the temperature of the reaction slurry during the reduction was maintained at 45 ° C.

[0071] The copper powder thus obtained was subjected to the same post treatment as in Example 1 to obtain a powder.

[0072] About 10 lots of copper powder obtained in Example 2, as in Example 1, D and D for each lot.

Ten

, D, standard deviation (SD), D ZD, specific surface area, tap packing density measurement results

50 90 90 10

For each characteristic, the average value for 10 lots and the standard deviation σ were calculated. That The results are shown in Table 4.

[0073] Powder characteristics of copper powder: The average value of 10 lots of the powder characteristics of copper powder obtained through the above process is D = 0.63 ^ πι, D = 1.49μι, D = 3. 08 m, standard deviation (SD) = 0.9

10 50 90

l ^ mD ZD = 4.89, specific surface area 0.62m ² Zg, tap packing density 4. lgZcc

90 10

I got it. Moreover, when the yield of copper powder for each lot was calculated, all were 97% or more, and the standard deviation σ of yield was 0.9, and a stable yield could be obtained.

[0074] [Table 4]

Example 3

In Example 3, copper powder was obtained in the same manner as in Example 1, except that the liquid temperature during the reduction in Step 3 was changed to 45 ° C. As for the pH fluctuation in step 2, the starting point pH was 6.3, the end point pH was 3.9, the minimum pH was 3.5, and the difference between the starting point pH and the end point pH was 2.4.

[0076] About 10 lots of the copper powder obtained in Example 3, as in Example 1, D,

Ten

Combined with measurement results of D, D, standard deviation (SD), D ZD, specific surface area, and tap packing density

50 90 90 10

The average value for 10 lots and the standard deviation σ were calculated for each characteristic. The results are shown in Table 5. When the yield of copper powder for each lot was calculated, all were 97% or more, and the standard deviation σ of yield was 0.9, and a stable yield could be obtained.

[0077] Powder characteristics of copper powder: The average value of 10 lots of the powder characteristics of copper powder obtained through the above process is D = 0.85 ^ πι, D = 1.99 ^ πι, D = 4. 05 m, standard deviation (SD) = 1.2 O ^ m, D ZD = 4. 79, specific surface area 0.46 m ² Zg, tap packing density 5. OgZcc

90 10

I

[0078] [Table 5]

Comparative example

[0079] In step 2, an ammonia aqueous solution as a pH adjuster is used as a comparative example. Therefore, description of other processes is omitted.

Step 2: The liquid temperature of the copper hydroxide slurry was kept at 50 ° C., and 450 g (9.0 mol) of hydrazine monohydrate was continuously added over 30 minutes. The minimum pH was 2.4, and the pH at the end of the addition was 3.2. That is, since the pH after the copper hydroxide slurry adjustment step was 6.3, the difference between the starting point pH and the ending point pH was 3.1. Thereafter, stirring was continued for another 30 minutes in order to complete the reduction reaction.

[0081] Thereafter, repulp washing was performed. That is, add pure water to the slurry after step 2 and adjust to 18 liters, leave it to stand, and remove 14 liters of supernatant after standing until the pH after repulping is 4.5. This was used as a washed cuprous oxide slurry. At this time, compared with the number of repeated washings in the above-mentioned example (average of 2 times), the number of repeated washings in this comparative example is pH 4.5 when the number of repulp washings is 4 times, and the washing is costly. I understand.

[0082] About 10 lots of copper powder obtained in the comparative example, as in Example 1, D and D for each lot.

10 50

, D, standard deviation (SD), D ZD, tap packing density, and specific surface area measurement results For each characteristic, the average value for 10 lots and the standard deviation σ were calculated. The results are shown in Table 6. As can be seen from this result, the average yield was as low as 84.5%.

[Table 6]

[0084] Powder characteristics of copper powder: The average value of 10 lots of the powder characteristics of copper powder obtained in the comparative example is D

Ten

= 0. 63 ^ πι, D = 1. 71 ^ πι, D = 5.13 m, standard deviation (SD) = 1. m, D

50 90

ZD = 8.63, Specific surface area (SSA) 1. 51m ² Zg, Tap packing density (TD) 3. Og / cc

90 10

Met.

[0085] Here, the evaluation method and the evaluation apparatus for each characteristic in this specification will be described. Measurement of volume cumulative particle size and particle size distribution (D, D, D, SD)

10 50 90

After mixing with a 0.1% aqueous solution of Spar Santo 5468 (San Nopco) and dispersing with an ultrasonic homogenizer (US—300T, manufactured by Nippon Seiki Seisakusho) for 5 minutes, the laser diffraction scattering particle size distribution analyzer Micro Trac HRA 9320 — 100 type (1 ^ 6 (15 +? ^ 0 111: 1 ^ company)) was used, and “tap packing density” was measured using Powder Star PT—E (Hosoka Micron Corporation). Specific surface area was measured by BET 1-point method using monosoap (manufactured by Kantachrome Co., Ltd.) after deaeration treatment of Sample 2. OOg at 75 ° C for 10 minutes.

[0086] [Contrast between Example and Comparative Example] Hereinafter, referring to Table 7 showing the average values and standard deviations σ of the examples and comparative examples, the examples and comparative examples are compared for each evaluation item.

[0087] [Table 7]

[0088] Volume cumulative particle size and particle size distribution: In the particle size distribution, the comparative example D is slightly larger.

90

The power that proves to be strong The average value of the particle size distribution is not much different. However, focusing on the standard deviation of the particle size distribution, the standard deviation σ of Examples 1 to 3 is smaller than that of the comparative example. That is, it can be understood that Examples 1 to 3 have a good particle size distribution and sharp powder characteristics as compared with the comparative example.

[0089] Tap packing density (TD): As shown in Table 7, Examples 1 to 3 are clearly higher than Comparative Examples. Therefore, when the conductor is formed by pasting the copper powder of the example, and when the conductor is formed by pasting the copper powder of the comparative example, the conductor density is higher in the example. Will be possible.

[0090] Specific surface area (SSA): In Examples 1 to 3, it is considered that the smoothness of the particle surface is improved if the particle size of the primary particles is lower than that of the comparative example. .

[0091] Results for each lot: standard deviation σ of each characteristic is smaller in Examples 1 to 3 than in Comparative Examples Examples 1 to 3 are smaller in powder characteristics than in Comparative Examples It can be said that it is homogeneous with little noise. In particular, with regard to the yield, Examples 1 to 3 can be manufactured with high yield and less yield fluctuation and stable productivity compared to the comparative example, and as a result, it can be said to be a method for producing copper powder that leads to cost reduction. .

[0092] Considering the above as a whole, in the example, in Step 2, by adding a combination of hydrazines and aqueous ammonia solution, the pH fluctuation can be controlled within a certain range. Aggregation due to fluctuations in the particle size can be suppressed, and a stable production process and copper powder with little noise and a sharp particle size distribution can be produced with high yield. On the other hand, the copper powder of the comparative example has a large variation in powder characteristics, a low yield, and a poor yield stability. This is thought to be due to the reducing agent addition method in Step 2.

Industrial applicability

[0093] The production method of copper powder according to the present invention makes it possible to improve the production efficiency of copper powder having excellent powder characteristics. As a result, high quality copper powder can be provided to the market at a low cost. In addition, the copper powder production method according to the present invention does not require the use of special additives, nor does it require special production equipment, so that existing facilities can be used effectively and capital investment is not required. Since it becomes a thing, it is excellent in cost merit.

[0094] Further, in the production method according to the present invention, since the same reducing agent as that used in step 2 can be used in step 3, it is possible to reduce different components involved in the reduction of copper powder. Is possible. As a result, it is possible to produce copper powder in which the amount of contaminating components adhering to the particle surface of the obtained copper powder is reduced, and it is possible to provide high-quality fine copper powder with excellent conductivity. Effective for use in fine wiring.

Brief Description of Drawings

[0095] FIG. 1 is a view showing a pH variation state of a solution from the start of addition of hydrazines to a copper hydroxide slurry in step 2 until the end of step 2.

Claims

The scope of the claims

[1] Obtain a copper hydroxide slurry obtained by reacting a copper ion-containing aqueous solution with an alkaline solution, add a reducing agent to the hydrous copper oxide slurry, and perform a first reduction treatment to obtain a cuprous oxide slurry. The cuprous oxide slurry is allowed to stand to precipitate the cuprous oxide particles, and the supernatant is removed and water is added to wash the cuprous oxide particles to form a washed cuprous oxide slurry. In the copper powder manufacturing method by wet reduction to obtain a copper powder by adding a reducing agent to the copper slurry,

The first reduction treatment is a method for producing copper powder, characterized in that hydrazines as a reducing agent and an aqueous ammonia solution as a pH adjusting agent are added to a copper hydroxide slurry in combination.

[2] In the first reduction treatment, hydrazines as a reducing agent and an aqueous ammonia solution as a pH adjusting agent are added to the copper hydroxide slurry in combination with a pH in the range of ρpH3.0 to pH 7.0. 2. The method for producing copper powder according to claim 1, wherein fluctuation control is performed.

[3] The variation control of the pH is characterized in that the difference between the starting pH at the start of the addition of the reducing agent and the pH adjusting agent and the end pH at the end of the addition is controlled to 3.0 or less. The manufacturing method of the copper powder of Claim 1 or Claim 2.

[4] In the first reduction treatment, a minimum pH of 2.8 or more that fluctuates by adding hydrazine as a reducing agent and an aqueous ammonia solution as a pH adjuster to the copper hydroxide slurry in combination. The method for producing a copper powder according to any one of claims 1 to 3, wherein:

[5] The method for producing copper powder according to any one of claims 1 to 4, wherein the alkaline solution is an aqueous ammonia solution.

[6] The method for producing copper powder according to any one of claims 1 to 5, wherein the washed cuprous oxide slurry is ρΗ4.1 to ρΗ6.0.

[7] A copper powder obtained by the method for producing a copper powder according to any one of claims 1 to 6.