JP2020176334A - Copper powder and conductive paste - Google Patents

Abstract

To provide a copper powder that has low TAP density and can be used suitably for conductive paste and a method of producing the same.SOLUTION: A copper powder has an average particle size of 0.05-5.0 μm, measured with a laser diffraction scattering type particle-size distribution measuring device, and has a TAP density of 3.0 g/cm3 or less.SELECTED DRAWING: None

Description

The present invention relates to a copper powder having a low TAP density, a method for producing the copper powder, and a conductive paste containing the copper powder.

With the technological development of electronic devices, the characteristics required for electronic components used for them have become diverse and high-level, and as a result, various characteristics are also required for electronic materials that are raw materials for electronic components at a high level. Has been done. For example, conductive pastes are widely used to form electrodes, circuits, electromagnetic wave shields, etc., and various metal powders such as copper powder and silver powder are used as the conductive powders that compose them. Has been made.

The required characteristics of these conductive powders vary depending on the application, but in general, with the miniaturization of electronic parts, it is required to make the conductive powders finer, and it is suitable as the workability of the conductive paste. There is a demand for high viscosity and coatability, and an appropriate metal composition of the conductive powder that gives them. Further, the conductor obtained from the conductive paste is generally required to have high conductivity, and naturally the cost is required to be low.

For example, Patent Document 1 defines shapes such as dendrites, spines, and rods, the amount of silver coating, and the BET value of silver-coated copper powder. Further, Patent Document 1 has an object of providing a metal powder that can be used for a conductive paste that exhibits sufficient conductivity even with a low metal powder content, and in conjunction with this, the silver-coated copper. The TAP density of the powder is defined as a range including a relatively low value of 1 to 5 g / cm ³ .

On the other hand, many copper powders specify a high TAP density in order to achieve high conductivity and the like (Patent Documents 2 to 4), but in Patent Document 5, the tap density of the copper powder used for electromagnetic wave shielding is specified. It is specified as 2.0 g / cm ³ or more. The copper powder used in the examples of Patent Document 5 has a tap density of 3.4 g / cm ³ or more.

As a method for producing copper powder, an aqueous solution containing copper hydroxide is treated with a reducing agent such as hydrazine to reduce the copper component in the solution, and a copper salt or copper oxide is heated in a reducing gas atmosphere. A method of reducing copper chloride, a method of treating copper chloride vapor with a reducing gas to reduce copper chloride, and the like are known.

Among these methods for producing copper powder, the so-called hydrazine reduction method, in which an aqueous solution containing copper hydroxide is treated with a reducing agent such as hydrazine, is a reaction in the aqueous solution and is produced because the production cost is relatively low. It is a method with excellent sex. For example, in Patent Document 6, copper hydroxide is precipitated by adding aqueous ammonia to a copper salt aqueous solution containing an organic acid, the copper hydroxide is reduced to copper hydroxide, and the cuprous oxide is converted to metallic copper. A method for producing copper powder is disclosed. Further, Patent Document 3 discloses a method for producing copper powder using alkali hydroxide in the hydrazine reduction method.

In addition, Patent Document 7 discloses a coated copper powder obtained by coating the copper powder with an inorganic coating film. In the examples of the same document, evaluations of TAP density and the like have been made ([0078]), but these evaluations have been made on coated copper powder obtained by coating copper powder with SiO ₂ ([00905]). ]). And in the comparative example, copper powder without inorganic coating is evaluated, and its TAP density is 3.96 g / cm ³ .

JP 2015-105406 Japanese Unexamined Patent Publication No. 2011-94236 JP-A-2009-84614 JP-A-2007-165326 Japanese Unexamined Patent Publication No. 3-20341 Japanese Patent Application No. 2007-204837 Japanese Unexamined Patent Publication No. 2009-79269

As described above, the required characteristics of the conductive powder vary depending on the application (for example, the type of electronic component to be formed, the forming method thereof, the material of the substrate to which the conductive paste is applied, and other coexisting components in the conductive paste). Is. For example, the TAP density may be about 2 g / cm ³ as in Patent Document 1, and it is desirable that the TAP density is low from the viewpoint of cost in applications where such high conductivity is not required. However, as described above, conventionally, conductive powder having a high TAP density, particularly copper powder, has been developed, and the current situation is that a copper powder having a low TAP density such as 3.0 g / cm ³ or less has not been developed.

Further, if it is possible to freely design various characteristics of the conductive powder in order to meet various required characteristics, the conductive powder can be applied to many applications and is useful. The design of such characteristics can be performed by mixing a plurality of types of conductive powders having different characteristics. For example, regarding the TAP density, conductive powders having different TAP densities are mixed. By mixing a conductive powder having a low TAP density with a conductive powder having a high TAP density that has been conventionally developed, it is possible to provide a conductive powder in a range of a lower TAP density, and the conventional conductive powder can be used. Expected to expand.

By the way, in a conductive paste, it is known that organic substances adhering to the conductive powder also affect the physical properties of the paste. Therefore, the conductive powder is required to have little influence on other components in the paste, and when the different conductive powders are mixed, it is required that they are less likely to affect each other. Since the organic substance can be grasped by using the amount of carbon in the conductive powder as an index, it can be said that a low carbon conductive powder is required.

From the above, an object of the present invention is to provide a copper powder having a low TAP density and which can be suitably used for a conductive paste and a method for producing the same. Furthermore, it is an object of the present invention to provide a preferably low carbon copper powder and a method for producing the same.

As a result of diligent studies to solve the above problems, the present inventors have made a copper powder suitable for a conductive paste, which has a low TAP density by adopting predetermined conditions in the reduction method, which is a method for producing copper powder. It has been found that a copper powder having a lower carbon content can be preferably produced, and the present invention has been completed.

That is, the present invention is a copper powder having an average particle size of 0.05 to 5.0 μm and a TAP density of 3.0 g / cm ³ or less as measured by a laser diffraction / scattering type particle size distribution measuring device.

The amount of element C contained in the copper powder is preferably 0.2% by mass or less. The TAP density of the copper powder is preferably 1.0 to 3.0 g / cm ³ .

The copper powder of the present invention has a mixing step of adding an organic acid that complexes copper to a copper (II) salt aqueous solution to obtain a copper / organic acid mixed solution, and the copper / organic acid mixed solution is used as an alkali metal hydroxide salt. A copper hydroxide slurry forming step of mixing to form a copper hydroxide slurry, a copper slurry forming step of adding a reducing agent to the copper hydroxide slurry to form a copper slurry, and recovering copper powder from the copper slurry. It can be produced by a method for producing copper powder, which has a recovery step and has a concentration of copper (II) salt in the copper (II) salt aqueous solution of 11.5-14.0% by mass in terms of copper. it can.

As the alkali metal hydroxide salt, sodium hydroxide and potassium hydroxide are preferable. In the copper slurry forming step, a reducing agent is added to the copper hydroxide slurry and the slurry is held at a temperature of 50 ° C. or lower for a predetermined time to generate cuprous oxide in the slurry, and then the cuprous oxide is formed. It is preferable to add a reducing agent to the slurry to be contained and hold the slurry at a temperature of 50 ° C. or lower for a predetermined time, and then hold the slurry at 60 to 90 ° C. for a predetermined time to form copper in the slurry.

The low TAP density copper powder of the present invention can be used to provide conductive pastes suitable for various uses.

According to the present invention, a copper powder having a low TAP density, which can be suitably used for a conductive paste, and preferably a low carbon powder can be provided. The present invention also provides a method for producing such copper powder.

Hereinafter, the present invention will be described in detail.
[Copper powder]
The copper powder of the present invention is a generally spherical particle having an average particle diameter of 0.05 to 5.0 μm and a TAP density of 3.0 g / cm ³ or less as measured by a laser diffraction / scattering type particle size distribution measuring device. is there.

When the average particle size is within the above range, it is possible to meet the recent demand for miniaturization of electronic components, and further, there is an advantage that the viscosity of the conductive paste using the copper powder of the present invention can be easily adjusted. is there.

Since the TAP density of the copper powder of the present invention is as low as 3.0 g / cm ³ or less, it can be suitably used for applications requiring a constant low TAP density. Further, by mixing the copper powder of the present invention with the conventionally developed conductive powder having a high TAP density, the TAP density as a whole can be lowered while maintaining the excellent characteristics of the conductive powder. That is, it is expected that the copper powder of the present invention will widen the design range of the TAP density of the conductive powder and expand the application applications of the conductive powder. Further, if the conductive powder is expensive, the copper powder of the present invention may significantly reduce the cost of the entire conductive paste.

In the present invention, the TAP density is measured according to the method described in JP-A-2007-263860. That is, a copper powder sample is filled in a bottomed cylindrical container having an inner diameter of 6 mm to form a copper powder sample layer, and a pressure of 0.16 N / m ² is applied to this layer from above, and then the copper powder sample layer is formed. The height is measured, and the density of the copper powder sample is obtained from the measured value of the height of the copper powder sample layer and the weight of the filled copper powder sample. This is defined as the TAP density of copper powder in the present invention.

In preparing the above conductive paste, there is a problem that the organic substance attached to the copper powder of the present invention affects other components in the paste. There is also a problem when the copper powder of the present invention is mixed with another conductive powder and the TAP density thereof is adjusted. In response to such a problem, the amount of element C contained in the copper powder of the present invention is preferably 0.2% by mass or less, more preferably 0.01 to 0.1% by mass. The amount of element C is an index of the amount of organic matter adhering to the surface of the copper powder of the present invention. As described above, since the amount of C element in the copper powder of the present invention is small, the copper powder has almost no problem of affecting other components in the paste. In this specification, the amount of C element in the copper powder is measured by the melting-infrared absorption method.

The BET specific surface area of the copper powder of the present invention is usually 0.1 to 5.0 m ² / g, and is preferably 0.5 to 4.0 m ² / g from the viewpoint of viscosity when formed into a paste.

The copper powder of the present invention has the characteristics described above, and can be suitably used as a conductive paste for applications requiring particularly low TAP density. Further, by mixing with the conventionally developed conductive powder having a high TAP density to reduce the TAP density as a whole, it becomes possible to freely design the TAP density of the conventional product, and its applicable applications are expanded. .. In these cases, the influence of the copper powder of the present invention on other components in the paste and the conductive powder having a high TAP density becomes a problem, but the copper powder of the present invention preferably has a low C element content and contains organic substances. Since it hardly adheres to the surface, it does not deteriorate the characteristics of the conductive paste due to the above-mentioned effects.

The conductive paste of the present invention contains the copper powder and binder of the present invention, and optionally contains other additives. The desired conductive film is formed by applying the conductive paste onto a substrate by various printing methods or the like, drying and sintering the substrate. The conductor film can be used for various electronic components depending on the characteristics such as the TAP density of the conductive powder contained in the paste.

[Copper powder manufacturing method]
Subsequently, the method for producing the copper powder of the present invention described above will be described. The copper powder of the present invention has a mixing step of adding an organic acid that complexes copper to a copper (II) salt aqueous solution to obtain a copper / organic acid mixed solution, and an alkali metal hydroxide salt added to the copper / organic acid mixed solution. A copper hydroxide slurry forming step of adding and forming a copper hydroxide slurry, a copper slurry forming step of adding a reducing agent to the copper hydroxide slurry to form a copper slurry, and recovering copper powder from the copper slurry. It can be produced by carrying out a recovery step, and the concentration of the copper (II) salt in the copper (II) salt aqueous solution is 11.5 to 14.0% by mass in terms of copper.

The present inventor diligently studied a method for producing copper powder in order to solve the above-mentioned problems, and found that it was used for the concentration of copper in an aqueous solution of copper (II) salt in the reduction method and for neutralizing the copper (II) salt. It has been found that a copper powder having a low TAP density can be produced by appropriately setting and selecting a neutralizing agent. Hereinafter, each step of the method for producing copper powder of the present invention will be described.

<Mixing process>
First, an organic acid that complexes copper is added to a copper (II) salt aqueous solution to obtain a copper / organic acid mixed solution. The copper (II) salt is not particularly limited, and copper (II) salts conventionally used in the production of copper powder, for example, divalent copper nitrates, sulfates, carbonates, chlorides and the like can be used. is there. These may be used alone or in combination of two or more. The salt that complexes copper is not particularly limited, and for example, hydroxycarboxylic acids such as citric acid, tartaric acid, and malic acid can be used. Among these, citric acid is used from the viewpoint of obtaining copper powder having a low TAP density. Is preferable. These complexing agents may be used alone or in combination of two or more. Since the complexing agent is a water-soluble solid, it can be used by dissolving it in pure water. The amount of the complexing agent added is preferably 0.1 or more, and usually 0.5 or less, in terms of the molar ratio to copper. Further, when the complexing agent is added to the copper (II) salt aqueous solution and mixed, the liquid temperature of the copper (II) aqueous solution (and the complexing agent aqueous solution) is maintained at 10 to 50 ° C. It is preferable that the solution is completely dissolved.

In the example of Patent Document 3, 220 kg of copper nitrate (trihydrate) having a concentration of about 100% and 17 kg of citric acid are dissolved in pure water to prepare a 480 L aqueous solution. The concentration of copper nitrate in the portion obtained by removing citric acid from this aqueous solution is 8.3% by mass in terms of copper. On the other hand, in the present invention, the concentration of the copper (II) salt in the aqueous solution of the copper (II) salt used in the mixing step is set to 11.5-14.0% by mass in terms of copper. If it is out of this range, copper powder having a low TAP density cannot be obtained. From the viewpoint of efficiently obtaining copper powder having a low TAP density, the concentration of the copper (II) salt is 11.6 to 13.5% by mass in terms of copper.

<Copper hydroxide slurry forming process>
The copper / organic acid mixed solution obtained in the mixing step is mixed with an alkali metal hydroxide salt to neutralize the copper (II) salt, thereby forming a copper hydroxide slurry. Conventionally, ammonia and alkali metal hydroxide salts have been used as neutralizers. For example, in the examples of Patent Document 6, ammonia is used as a neutralizing agent. As a result of examination, the present inventors used an alkali metal hydroxide salt instead of ammonia as a neutralizing agent, and determined the concentration of the copper (II) salt in the copper (II) salt aqueous solution used in the mixing step as described above. It has been found that a copper powder having a low TAP density can be obtained by setting it in a predetermined limited range.

From the viewpoint of the production cost of copper powder, sodium hydroxide and potassium hydroxide are preferable as the alkali metal hydroxide salt as a neutralizing agent, and sodium hydroxide is particularly preferable. Ammonia is usually used as ammonia water, but since ammonia water is highly volatile and the gas is harmful to the human body, the space of the storage tank is always sucked and sucked gas. Large-scale equipment is required in addition to the tank that carries out the neutralization reaction, such as the equipment that removes the ammonia gas inside. According to the present invention, copper powder can be produced without using ammonia water, which requires a large-scale storage facility for industrial mass production.

Further, when carrying out the neutralization reaction, the alkali metal hydroxide salt may be added as it is to the copper / organic acid mixed solution or as an aqueous solution (forward neutralization), or copper / alkali metal hydroxide aqueous solution may be added with copper. An organic acid mixture may be added (reverse neutralization). The liquid temperature at this time is not particularly limited, but is usually in the range of about 10 to 50 ° C. In the mixing of the copper / organic acid mixed solution and the alkali metal hydroxide salt, it is preferable to blow nitrogen gas while stirring to reduce the oxygen concentration in the aqueous solution. Further, it is preferable that the blowing of the nitrogen gas into the reaction vessel is continued until immediately before the recovery step described later.

<Copper slurry forming process>
A reducing agent is added to the copper hydroxide slurry obtained in the copper hydroxide slurry forming step to form metallic copper to obtain a copper slurry. As the reducing agent, hydrazine compounds such as hydrazine, hydrated hydrazine, hydrazine carbonate, and hydrazine hydrochloride can be used. The amount of the reducing agent used is usually 3.0 to 8.0 eq, which is the reaction equivalent, preferably 3.0 to 5.0 eq. Regarding the reaction equivalent, the amount of reducing agent required to reduce divalent copper to monovalent copper or monovalent copper to zero-valent metallic copper is defined as 1 equivalent. As described below, the copper slurry forming step is preferably carried out in two steps.

(Primary reduction process)
First, as a primary reduction step, a reducing agent is added to the copper hydroxide slurry. The amount of the reducing agent used is usually 0.5 to 2.5 eq, preferably 0.5 to 1.5 eq, which is the reaction equivalent required to reduce copper hydroxide to cuprous oxide. The temperature of the copper hydroxide slurry when the reducing agent is added is usually 50 ° C. or lower, preferably 20 to 50 ° C., and after the reducing agent is added and the reaction solution is mixed, the temperature in the above range is about 60 to 180 minutes. It is retained and aged, and cuprous oxide is produced from copper hydroxide. In the aging reaction, in order to allow the reaction to proceed, the temperature may be raised from the temperature at which the reducing agent is added within the above temperature range.

(Secondary reduction process)
Subsequently, as a secondary reduction step, a reducing agent is further added to the slurry in which cuprous oxide is produced. The amount of the reducing agent used is usually 1.0 to 4.0 eq of the reaction equivalent required to reduce copper hydroxide (assuming that all copper hydroxide has been converted to copper hydroxide by the primary reduction step) to copper. , Preferably 2.0 to 3.5 eq. The temperature of the slurry when the reducing agent is added is usually 50 ° C. or lower, preferably 25 to 50 ° C., and after adding the reducing agent and mixing the reaction solution, the temperature is maintained in the above range for about 10 to 180 minutes. And perform the aging reaction.

Metallic copper is produced by this aging reaction, but in order to complete the metallic copper production reaction, it is preferable to raise the temperature to 60 to 90 ° C. and hold it for about 40 to 360 minutes. Metallic copper is produced by the above reaction. The purpose of the primary reduction step is to produce cuprous oxide, but unreacted copper hydroxide may be present at the end of the step, and cuprous oxide is further reduced to present metallic copper. There is a possibility. In any case, by completing the secondary reduction step, metallic copper is produced.

The secondary reduction step described above may be further divided into two. Specifically, a reducing agent is added to the slurry obtained through the primary reduction step to produce cuprous oxide, and the slurry is held at 25 to 50 ° C. for about 5 to 120 minutes, and further the reducing agent is added to 25 to 120. Hold at 90 ° C. for about 5 to 120 minutes. The total amount of the reducing agent used is the same as the amount used when the secondary reduction step is carried out by adding the reducing agent once. The aging reaction temperature when the second reducing agent is added is usually higher than the temperature of the aging reaction when the first reducing agent is added. This is to allow the reduction reaction to proceed appropriately. Finally, similarly to the above, it is preferable to raise the temperature to 60 to 90 ° C. and hold it for about 40 to 360 minutes in order to complete the reaction for producing metallic copper.

<Recovery process>
Copper powder is recovered from the slurry containing metallic copper obtained through the copper slurry forming step. Specifically, for example, the slurry is solid-liquid separated, the solid content is washed with pure water, and the slurry is dried in a nitrogen atmosphere to obtain a substantially spherical copper powder. The recovery means is not limited to this method, and the obtained copper powder may be crushed or pulverized as necessary.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples. The evaluation of the copper powder obtained in the following Examples and Comparative Examples was carried out as follows.

[Average particle size D50]
The cumulative volume of 50% particle size (D50) was determined by measurement with a laser diffraction / scattering type particle size distribution device (Heros particle size distribution measuring device (HELOS & RODOS) manufactured by SYMPATEC).

[BET specific surface area]
It was determined by the BET one-point method using a BET specific surface area measuring device (4 Sorb US manufactured by Your Sionics Co., Ltd.).

[TAP density measurement]
The measurement was performed according to the method described in JP-A-2007-263860. That is, a copper powder sample is filled in a bottomed cylindrical container having an inner diameter of 6 mm to form a copper powder sample layer, and a pressure of 0.16 N / m ² is applied to this layer from above, and then the copper powder sample layer is formed. The height was measured, and the density of the copper powder sample was determined from the measured value of the height of the copper powder sample layer and the weight of the filled copper powder sample. This was defined as the TAP density of copper powder.

[Amount of C element in copper powder]
The amount of C element in the copper powder was measured by a carbon / sulfur analyzer (manufactured by HORIBA, Ltd .: EMIA-220V).

<< Example 1 >>
[Preparation of aqueous copper (II) salt solution]
1172.3 g of copper (II) nitrate aqueous solution manufactured by Ensho Sangyo Co., Ltd., 156.9 g of pure water, and citric acid monohydration manufactured by Fuso Chemical Industry Co., Ltd. with a copper nitrate trihydrate concentration of 50.3% by mass. An aqueous citric acid solution prepared by dissolving 92.3 g of a product in 531.2 g of pure water was stirred and mixed at room temperature to prepare a copper (II) nitrate / citric acid mixed solution. Further, a sodium hydroxide diluted aqueous solution was prepared by mixing 448.3 g of a 48.8 mass% sodium hydroxide aqueous solution and 453.3 g of pure water.

[Production of copper (II) hydroxide]
Next, the above-mentioned copper (II) nitrate / citric acid mixed solution was put into a 4 L reaction vessel, and stirring was started. The rotation speed was 350 rpm. After that, the stirring operation was continued under these conditions until immediately before the solid-liquid separation described later. Next, the copper (II) nitrate / citric acid mixed solution was maintained at 27 ° C. After that, nitrogen gas is blown onto the mixed solution of the 4L reaction tank, and the blowing is continued until the oxygen concentration in the exhausted gas becomes 0% by volume, and thereafter, this nitrogen is continued until just before the solid-liquid separation described later. Continued gas blowing. When the oxygen concentration in the exhausted gas reached 0% by volume, the above sodium hydroxide diluted aqueous solution was added to the copper (II) nitrate / citric acid mixed solution to generate copper (II) hydroxide. ..

[Primary reduction process]
Next, after raising the temperature of this reaction solution to 35 ° C., 26.6 g of 80 mass% hydrazine monohydrate, which is a hydrated hydrazine manufactured by MGC Otsuka Chemical Co., Ltd., was dissolved in 546.3 g of pure water. An aqueous hydrazine solution was added. Hereinafter, this hydrazine aqueous solution will be referred to as a "primary reduced hydrazine aqueous solution". Then, after raising the temperature of the reaction solution to 50 ° C. and holding it for 120 minutes, primary reduction was carried out to generate cuprous oxide. Hereinafter, the held temperature is referred to as "primary reduction holding temperature", and the holding time is referred to as "primary reduction holding time".

[Secondary reduction process]
Next, the reaction solution was cooled to 50 ° C., 114.0 g of 80% by mass hydrazine monohydrate, which is a hydrated hydrazine manufactured by MG Otsuka Chemical Co., Ltd., was added and held for 10 minutes for secondary reduction. went. Then, in order to complete the reaction, the reaction solution was heated to 90 ° C. and held for 180 minutes to generate metallic copper.

In the comparative example described later, the secondary reduction step may be divided into two steps. In that case, the temperature when the reducing agent is added for the first time is called the "secondary reduction early stage holding temperature", this reducing agent is called the "secondary reduction early stage hydrazine", and the time held at the secondary reduction early stage temperature is called. "Secondary reduction first half retention time". The temperature at which the reducing agent is added for the second time after that is called the "secondary reduction late holding temperature", and the added reducing agent is called "secondary reduction late hydrazine", and the time held at the secondary reduction late temperature. Is called the "secondary reduction late retention time". For the hydrazine monohydrate of Example 1, the secondary reduction early stage holding temperature, the secondary reduction early stage hydrazine, and the secondary reduction early stage holding time are set.

After that, the temperature was raised to a predetermined temperature and held for the completion of the reaction as in Example 1, but the temperature at this time was called the "final holding temperature" and the time held at the final holding temperature was "final holding". Call it "time".

[Recovery process]
Next, the reaction solution was solid-liquid separated, the solid content was washed with pure water, and dried in a nitrogen atmosphere at 110 ° C. for 9 hours to obtain a spherical copper powder according to Example 1. With respect to the copper powder according to Example 1, the average particle size D50 was measured, the BET specific surface area was measured, the TAP density was measured, and the amount of C element was measured.

As a result, the average particle size D50 is 0.67 μm, the BET specific surface area is 2.44 m ² / g, the TAP density is 2.77 g / cm ³ , and the amount of C element in the copper powder is 0.03. It was% by mass.

Regarding Example 1 described above, the concentration of the copper (II) nitrate aqueous solution, the amount of the aqueous solution used, the amount of pure water added to the aqueous solution, the mass of copper in the copper (II) nitrate aqueous solution, and the copper (II) nitrate aqueous solution. Copper (II) nitrate concentration in copper equivalent, amount of citrate monohydrate used, molar ratio to copper, amount of pure water in which citrate monohydrate is dissolved; 48.8% by mass hydroxide Amount of sodium aqueous solution used, amount of pure water mixed with it, order of neutralization, equivalent of sodium hydroxide to copper (II) nitrate, rotation speed; type of reducing agent used for primary reduction, amount thereof, dissolved Amount of pure water, equivalent of reducing agent to copper hydroxide, type of reducing agent used in the first and second stages of secondary reduction, amount thereof, copper nitrate (assuming that all were converted to copper nitrate by primary reduction) Equivalent to; primary reduction agent addition temperature, primary reduction holding temperature, primary reduction holding time, secondary reduction early holding temperature, secondary reduction early holding time, secondary reduction late holding temperature, secondary reduction late holding time, final holding temperature , Final retention time; and average particle size D50, BET specific surface area, TAP density and C element amount of copper powder are shown in Tables 1 to 5 below. The same applies to Examples 2 and 3 and Comparative Examples 1 to 30 below.

<< Example 2 >>
[Preparation of aqueous copper (II) salt solution]
1312.9 g of copper (II) nitrate aqueous solution manufactured by Ensho Sangyo Co., Ltd., 16.3 g of pure water, and citric acid monohydration manufactured by Fuso Chemical Industry Co., Ltd. with a copper nitrate trihydrate concentration of 50.3% by mass. A citric acid aqueous solution prepared by dissolving 103.4 g of the product in 520.1 g of pure water was stirred and mixed to prepare a copper (II) nitrate / citric acid mixed solution. Further, a diluted sodium hydroxide aqueous solution was prepared by mixing 502.1 g of a 48.8 mass% sodium hydroxide aqueous solution and 399.5 g of pure water.

[Production of copper (II) hydroxide]
Next, as in Example 1, the above-mentioned copper (II) nitrate / citric acid mixed solution was put into a 4 L reaction vessel, stirred, and nitrogen gas was blown onto the mixed solution in the reaction vessel, and copper (II) nitrate was blown into the mixed solution. -Copper (II) hydroxide was produced by mixing a citric acid mixed solution and a diluted aqueous solution of sodium hydroxide.

[Primary reduction process]
Next, after raising the temperature of this reaction solution to 35 ° C., 29.8 g of 80 mass% hydrazine monohydrate, which is a hydrated hydrazine manufactured by MGC Otsuka Chemical Co., Ltd., was dissolved in 543.1 g of pure water. An aqueous hydrazine solution was added. After that, it was held at a predetermined temperature in the same manner as in Example 1 to generate cuprous oxide.

[Secondary reduction process]
Next, the reaction solution was cooled to 50 ° C., 127.7 g of 80% by mass hydrazine monohydrate, which is a hydrated hydrazine manufactured by MGC Otsuka Chemical Co., Ltd., was added and held for 10 minutes for secondary reduction. went. Then, in order to complete the reaction, the reaction solution was heated to 90 ° C. and held for 180 minutes to generate metallic copper.

[Recovery process]
Next, the recovery step was carried out in the same manner as in Example 1 to obtain spherical copper powder according to Example 2. With respect to the copper powder according to Example 2, the average particle size D50 was measured, the BET specific surface area was measured, the TAP density was measured, and the amount of C element was measured.

As a result, the average particle size D50 is 0.76 μm, the BET specific surface area is 2.39 m ² / g, the TAP density is 2.58 g / cm ³ , and the amount of C element in the copper powder is 0.05. It was% by mass.

<< Example 3 >>
[Preparation of aqueous copper (II) salt solution]
Pure water of copper (II) nitrate aqueous solution 1412.3 manufactured by Ensho Sangyo Co., Ltd. and 110.8 g of citric acid monohydrate manufactured by Fuso Chemical Industry Co., Ltd. with a concentration of copper nitrate trihydrate of 50.1% by mass. A citric acid aqueous solution dissolved in 512.7 g was stirred and mixed to prepare a copper (II) nitrate / citric acid mixed solution. Further, a sodium hydroxide diluted aqueous solution was prepared by mixing 538.0 g of a 48.8 mass% sodium hydroxide aqueous solution and 363.6 g of pure water.

[Production of copper (II) hydroxide]
Next, as in Example 1, the above-mentioned copper (II) nitrate / citric acid mixed solution was put into a 4 L reaction vessel, stirred, and nitrogen gas was blown onto the mixed solution in the reaction vessel, and copper (II) nitrate was blown into the mixed solution. -Copper (II) hydroxide was produced by mixing a citric acid mixed solution and a diluted aqueous solution of sodium hydroxide.

[Primary reduction process]
Next, after raising the temperature of this reaction solution to 35 ° C., 31.9 g of 80 mass% hydrazine monohydrate, which is a hydrated hydrazine manufactured by MGC Otsuka Chemical Co., Ltd., was dissolved in 541.0 g of pure water. An aqueous hydrazine solution was added. After that, it was held at a predetermined temperature in the same manner as in Example 1 to generate cuprous oxide.

[Secondary reduction process]
Next, the reaction solution was cooled to 50 ° C., 136.8 g of 80% by mass hydrazine monohydrate, which is a hydrated hydrazine manufactured by MG Otsuka Chemical Co., Ltd., was added and held for 10 minutes for secondary reduction. went. Then, in order to complete the reaction, the reaction solution was heated to 90 ° C. and held for 180 minutes to generate metallic copper.

[Recovery process]
Next, the recovery step was carried out in the same manner as in Example 1 to obtain spherical copper powder according to Example 3. With respect to the copper powder according to Example 3, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured.

As a result, the average particle size D50 is 0.75 μm, the BET specific surface area is 2.39 m ² / g, the TAP density is 2.69 g / cm ³ , and the amount of C element in the copper powder is 0.03. It was% by mass.

<< Comparative Example 1 >>
[Preparation of aqueous copper (II) salt solution]
941.6 g of copper (II) nitrate aqueous solution manufactured by Ensho Sangyo Co., Ltd., 387.6 g of pure water, and citric acid monohydration manufactured by Fuso Chemical Industry Co., Ltd. with a copper nitrate trihydrate concentration of 50.1% by mass. A citric acid aqueous solution prepared by dissolving 73.9 g of the product in 549.6 g of pure water was stirred and mixed to prepare a copper (II) nitrate / citric acid mixed solution. Further, a sodium hydroxide diluted aqueous solution was prepared by mixing 358.6 g of a 48.8 mass% sodium hydroxide aqueous solution and 543.0 g of pure water.

[Production of copper (II) hydroxide]
Next, the above-mentioned diluted sodium hydroxide aqueous solution was placed in a 4 L reaction vessel, and the aqueous solution was stirred and nitrogen gas was blown onto the aqueous solution in the reaction vessel under the same conditions as in Example 1. The rotation speed was 350 rpm. After that, the stirring operation was continued under these conditions until immediately before the addition of the copper (II) nitrate / citric acid mixed solution described later. When the oxygen concentration of the exhausted gas reaches 0% by volume, the stirring is stopped, the above-mentioned copper (II) nitrate / citric acid mixed solution is added to the sodium hydroxide diluted aqueous solution, and then the same as before the stirring is stopped. Stirring under the conditions was resumed, thereby producing copper (II) hydroxide. After that, the stirring operation was continued under these conditions until immediately before the solid-liquid separation described later.

[Primary reduction process]
Next, after raising the temperature of this reaction solution to 35 ° C., 21.3 g of 80 mass% hydrazine monohydrate, which is a hydrated hydrazine manufactured by MGC Otsuka Chemical Co., Ltd., was dissolved in 551.6 g of pure water. An aqueous hydrazine solution was added. Then, after raising the temperature of the reaction solution to 70 ° C. and holding it for 120 minutes, primary reduction was performed to generate cuprous oxide.

[Secondary reduction process]
Next, the reaction solution was cooled to 50 ° C., 40.5 g of 80% by mass hydrazine monohydrate, which is a hydrated hydrazine manufactured by MGC Otsuka Chemical Co., Ltd., was added and held for 60 minutes. Subsequently, while maintaining the liquid temperature at 50 ° C., 50.7 g of the same hydrazine monohydrate as described above was added and held for 60 minutes. Then, in order to complete the reaction, the reaction solution was heated to 90 ° C. and held for 180 minutes to generate metallic copper.

[Recovery process]
Next, a recovery step was carried out in the same manner as in Example 1 to obtain a spherical copper powder according to Comparative Example 1. With respect to the copper powder according to Comparative Example 1, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured.

As a result, the average particle size D50 is 0.60 μm, the BET specific surface area is 1.99 m ² / g, the TAP density is 3.47 g / cm ³ , and the amount of C element in the copper powder is 0.06. It was% by mass.

<< Comparative Example 2 >>
Spherical copper powder according to Comparative Example 2 was obtained by the same method as in Comparative Example 1 except that the holding temperature in the late secondary reduction was set to 70 ° C. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 is 0.84 μm, the BET specific surface area is 1.13 m ² / g, the TAP density is 3.81 g / cm ³ , and the amount of C element in the copper powder is 0.04. It was% by mass.

<< Comparative Example 3 >>
A spherical copper powder according to Comparative Example 3 was obtained by the same method as in Comparative Example 2 except that the holding temperature in the latter stage of the secondary reduction was set to 90 ° C. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 is 0.61 μm, the BET specific surface area is 2.38 m ² / g, the TAP density is 3.43 g / cm ³ , and the amount of C element in the copper powder is 0.07. It was% by mass.

<< Comparative Example 4 >>
939.7 g of a copper (II) nitrate aqueous solution having a concentration of 50.2 mass% was used, 389.5 g of pure water was added thereto, and 358.9 g of a 48.8 mass% sodium hydroxide aqueous solution was used, which was pure. By the same method as in Comparative Example 1, 542.7 g of water was mixed and 47.4 g of hydrazine monohydrate was used in the first stage of secondary reduction and 59.2 g of hydrazine monohydrate was used in the second stage of secondary reduction. A spherical copper powder according to Comparative Example 4 was obtained. The obtained copper powder was measured for an average particle size D50, a BET specific surface area, and a TAP density by the same method as in Example 1. As a result, the average particle size D50 was 0.69 μm, the BET specific surface area was 1.96 m ² / g, and the TAP density was 3.35 g / cm ³ .

<< Comparative Example 5 >>
Spherical copper according to Comparative Example 5 by the same method as in Comparative Example 4 except that 33.8 g of hydrazine monohydrate was used in the first half of the secondary reduction and 42.2 g of hydrazine monohydrate was used in the second half of the secondary reduction. I got the powder. The obtained copper powder was measured for an average particle size D50, a BET specific surface area, and a TAP density by the same method as in Example 1. As a result, the average particle size D50 was 0.68 μm, the BET specific surface area was 1.77 m ² / g, and the TAP density was 3.71 g / cm ³ .

<< Comparative Example 6 >>
In the primary reduction, 33.5 g of hydrazine monohydrate was used, and the spherical copper powder according to Comparative Example 6 was obtained by the same method as in Comparative Example 4 except that it was dissolved in 539.4 g of pure water. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.74 μm, the BET specific surface area was 1.53 m ² / g, the TAP density was 3.58 g / cm ³ , and the C element content was 0.04 mass%. It was.

<< Comparative Example 7 >>
In the primary reduction, 24.4 g of hydrazine monohydrate was used, and the spherical copper powder according to Comparative Example 7 was obtained by the same method as in Comparative Example 4 except that it was dissolved in 548.5 g of pure water. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.63 μm, the BET specific surface area was 2.12 m ² / g, the TAP density was 3.55 g / cm ³ , and the C element content was 0.05 mass%. It was.

<< Comparative Example 8 >>
In the primary reduction, 18.3 g of hydrazine monohydrate was used, and the spherical copper powder according to Comparative Example 8 was obtained by the same method as in Comparative Example 4 except that it was dissolved in 554.6 g of pure water. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.83 μm, the BET specific surface area was 1.35 m ² / g, the TAP density was 3.81 g / cm ³ , and the C element amount was 0.03 mass%. It was.

<< Comparative Example 9 >>
In the primary reduction, 27.4 g of hydrazine monohydrate was used, and the spherical copper powder according to Comparative Example 9 was obtained by the same method as in Comparative Example 4 except that it was dissolved in 545.5 g of pure water. The obtained copper powder was measured for an average particle size D50, a BET specific surface area, and a TAP density by the same method as in Example 1. As a result, the average particle size D50 was 0.60 μm, the BET specific surface area was 2.18 m ² / g, and the TAP density was 3.70 g / cm ³ .

<< Comparative Example 10 >>
A spherical copper powder according to Comparative Example 10 was obtained by the same method as in Comparative Example 6 except that 383.7 g of an aqueous sodium hydroxide solution was used and 517.9 g of pure water was mixed thereto. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.76 μm, the BET specific surface area was 1.39 m ² / g, the TAP density was 3.65 g / cm ³ , and the C element content was 0.04 mass%. It was.

<< Comparative Example 11 >>
937.8 g of an aqueous solution of copper (II) nitrate having a concentration of 50.3% by mass was used, and 391.4 g of pure water was added thereto to produce a mixture of copper (II) nitrate and citric acid in the production of copper (II) hydroxide. A spherical copper powder according to Comparative Example 11 was obtained by the same method as in Comparative Example 1 except that a diluted aqueous solution of sodium hydroxide was added to the solution. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.63 μm, the BET specific surface area was 1.97 m ² / g, the TAP density was 3.59 g / cm ³ , and the C element content was 0.06 mass%. It was.

<< Comparative Example 12 >>
Stirring is continued until just before solid-liquid separation without stopping stirring when the oxygen concentration of the exhausted gas reaches 0% by volume, and secondary reduction is performed in one step, at which time hydrazine monohydrate A spherical copper powder according to Comparative Example 12 was obtained by the same method as in Comparative Example 11 except that 91.2 g was used and the retention time in the first half of the secondary reduction was set to 10 minutes. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.61 μm, the BET specific surface area was 2.00 m ² / g, the TAP density was 3.73 g / cm ³ , and the C element amount was 0.06 mass%. It was.

<< Comparative Example 13 >>
Spherical copper powder according to Comparative Example 13 was obtained by the same method as in Comparative Example 12 except that 27.4 g of primary reduced hydrazine was used and this was dissolved in 545.5 g of pure water. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.62 μm, the BET specific surface area was 2.16 m ² / g, the TAP density was 3.57 g / cm ³ , and the C element content was 0.06 mass%. It was.

<< Comparative Example 14 >>
Spherical copper powder according to Comparative Example 14 was obtained by the same method as in Comparative Example 12 except that 15.2 g of primary reduced hydrazine was used and this was dissolved in 557.7 g of pure water. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.67 μm, the BET specific surface area was 2.56 m ² / g, the TAP density was 3.35 g / cm ³ , and the C element content was 0.06 mass%. It was.

<< Comparative Example 15 >>
A spherical copper powder according to Comparative Example 15 was obtained by the same method as in Comparative Example 13 except that 85.1 g of secondary reduced hydrazine was used. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle diameter D50 was 0.61 μm, the BET specific surface area was 1.98 m ² / g, the TAP density was 3.83 g / cm ³ , and the amount of C element was 0.06 mass%. It was.

<< Comparative Example 16 >>
A spherical copper powder according to Comparative Example 16 was obtained by the same method as in Comparative Example 14 except that 97.3 g of secondary reduced hydrazine was used. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.62 μm, the BET specific surface area was 2.05 m ² / g, the TAP density was 3.59 g / cm ³ , and the C element content was 0.05 mass%. It was.

<< Comparative Example 17 >>
A spherical copper powder according to Comparative Example 17 was obtained by the same method as in Comparative Example 12 except that 374.6 g of an aqueous sodium hydroxide solution was used and this was mixed with 527.0 g of pure water. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.85 μm, the BET specific surface area was 1.13 m ² / g, the TAP density was 3.82 g / cm ³ , and the C element amount was 0.03 mass%. It was.

<< Comparative Example 18 >>
Comparative Example 12 except that 102.6 g of citric acid monohydrate was used, this was dissolved in 520.9 g of pure water, 358.7 g of an aqueous sodium hydroxide solution was used, and this was mixed with 542.9 g of pure water. A spherical copper powder according to Comparative Example 18 was obtained by the same method as in the above. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.64 μm, the BET specific surface area was 2.58 m ² / g, the TAP density was 3.40 g / cm ³ , and the C element content was 0.08 mass%. It was.

<< Comparative Example 19 >>
844 g of an aqueous solution of copper (II) nitrate was used, 485.2 g of pure water was added thereto, 66.5 g of citrate monohydrate was used, this was dissolved in 557 g of pure water, and an aqueous solution of sodium hydroxide was 322. Compared except that 0.8 g was used, this was mixed with 578.8 g of pure water, 19.2 g of primary reduced hydrazine was used, this was dissolved in 553.7 g of pure water, and 82.1 g of secondary reduced hydrazine was used. A spherical copper powder according to Comparative Example 19 was obtained by the same method as in Example 12. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.65 μm, the BET specific surface area was 1.75 m ² / g, the TAP density was 3.52 g / cm ³ , and the C element content was 0.06 mass%. It was.

<< Comparative Example 20 >>
1078.5 g of an aqueous solution of copper (II) nitrate was used, 250.7 g of pure water was added thereto, 84.9 g of citrate monohydrate was used, and this was dissolved in 538.6 g of pure water, and hydroxide was added. 412.4 g of aqueous sodium solution was used, this was mixed with 489.2 g of pure water, 24.5 g of primary reduced hydrazine was used, this was dissolved in 548.4 g of pure water, and 104.9 g of secondary reduced hydrazine was used. A spherical copper powder according to Comparative Example 20 was obtained by the same method as in Comparative Example 12 except for the above. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.60 μm, the BET specific surface area was 2.28 m ² / g, the TAP density was 3.28 g / cm ³ , and the C element amount was 0.06 mass%. It was.

<< Comparative Example 21 >>
1125.4 g of an aqueous solution of copper (II) nitrate was used, 203.8 g of pure water was added thereto, 88.6 g of citric acid monohydrate was used, and this was dissolved in 534.9 g of pure water, and hydroxide was added. 430.4 g of aqueous sodium solution was used, this was mixed with 471.2 g of pure water, 25.5 g of primary reduced hydrazine was used, this was dissolved in 547.4 g of pure water, and 109.5 g of secondary reduced hydrazine was used. A spherical copper powder according to Comparative Example 21 was obtained by the same method as in Comparative Example 12 except for the above. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.62 μm, the BET specific surface area was 2.39 m ² / g, the TAP density was 3.57 g / cm ³ , and the C element content was 0.06 mass%. It was.

<< Comparative Example 22 >>
A spherical copper powder according to Comparative Example 22 was obtained by the same method as in Comparative Example 21 except that 418.8 g of an aqueous sodium hydroxide solution was used and this was mixed with 482.8 g of pure water. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.59 μm, the BET specific surface area was 2.39 m ² / g, the TAP density was 3.36 g / cm ³ , and the C element amount was 0.06 mass%. It was.

<< Comparative Example 23 >>
1129.9 g of an aqueous solution of copper (II) nitrate having a concentration of 50.1 mass% was used, 199.3 g of pure water was added thereto, 80.3 g of primary reduced hydrazine was used, and this was dissolved in 492.6 g of pure water. Then, a spherical copper powder according to Comparative Example 23 was obtained by the same method as in Comparative Example 21 except that 54.7 g of the secondary reduced hydrazine was used. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.64 μm, the BET specific surface area was 2.01 m ² / g, the TAP density was 3.34 g / cm ³ , and the C element content was 0.04 mass%. It was.

<< Comparative Example 24 >>
25.5 g of primary reduced hydrazine was used, this was dissolved in 547.4 g of pure water, the primary reduction holding temperature was set to 40 ° C., and 109.5 g of secondary reduced hydrazine was used by the same method as in Comparative Example 23. , A spherical copper powder according to Comparative Example 24 was obtained. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.63 μm, the BET specific surface area was 2.28 m ² / g, the TAP density was 3.41 g / cm ³ , and the C element content was 0.05 mass%. It was.

<< Comparative Example 25 >>
1125.4 g of an aqueous solution of copper (II) nitrate having a concentration of 50.3 mass% was used, and 203.8 g of pure water and 123.1 g of citric acid monohydrate were dissolved in 500.4 g of pure water. The mixture was mixed to obtain a spherical copper powder according to Comparative Example 25 by the same method as in Comparative Example 24 except that the primary reduction holding temperature was set to 50 ° C. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.60 μm, the BET specific surface area was 2.74 m ² / g, the TAP density was 3.80 g / cm ³ , and the C element amount was 0.09 mass%. It was.

<< Comparative Example 26 >>
Using 1129.9 g of a copper (II) nitrate aqueous solution having a concentration of 50.1% by mass, 199.3 g of pure water was added thereto, and the primary reduction holding time was set to 60 minutes by the same method as in Comparative Example 25. , A spherical copper powder according to Comparative Example 26 was obtained. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.58 μm, the BET specific surface area was 1.96 m ² / g, the TAP density was 3.41 g / cm ³ , and the C element amount was 0.10 mass%. It was.

<< Comparative Example 27 >>
A spherical copper powder according to Comparative Example 27 was obtained by the same method as in Comparative Example 26 except that the rotation speed of stirring during the formation of copper (II) hydroxide was 250 rpm and the primary reduction holding time was 120 minutes. It was. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.64 μm, the BET specific surface area was 2.12 m ² / g, the TAP density was 3.30 g / cm ³ , and the C element content was 0.05 mass%. It was.

<< Comparative Example 28 >>
A spherical copper powder according to Comparative Example 28 was obtained by the same method as in Comparative Example 26 except that the rotation speed of stirring during the formation of copper (II) hydroxide was 450 rpm and the primary reduction holding time was 120 minutes. It was. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 0.63 μm, the BET specific surface area was 2.36 m ² / g, the TAP density was 3.36 g / cm ³ , and the C element amount was 0.05 mass%. It was.

<< Comparative Example 29 >>
Stirring is continued until just before the solid-liquid separation without stopping the stirring when the oxygen concentration of the exhausted gas reaches 0% by volume, and the holding temperature in the first half of the secondary reduction is set to 90 ° C. The spherical copper powder according to Comparative Example 29 was obtained by the same method as in Comparative Example 2 except that the temperature was 90 ° C. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 1.26 μm, the BET specific surface area was 0.79 m ² / g, the TAP density was 4.03 g / cm ³ , and the C element content was 0.03 mass%. It was.

<< Comparative Example 30 >>
The spherical copper powder according to Comparative Example 30 was obtained by the same method as in Comparative Example 23 except that the holding temperature in the first half of the secondary reduction was set to 90 ° C. With respect to the obtained copper powder, the average particle size D50, the BET specific surface area, the TAP density, and the amount of C element were measured by the same method as in Example 1. As a result, the average particle size D50 was 1.52 μm, the BET specific surface area was 0.69 m ² / g, the TAP density was 4.24 g / cm ³ , and the C element content was 0.02 mass%. It was.

The above results are summarized in Tables 1 to 5 below.

Claims (4)

A generally spherical copper powder having an average particle size of 0.67 to 5.0 μm and a TAP density of 2.77 g / cm ³ or less as measured by a laser diffraction / scattering type particle size distribution measuring device. The copper powder according to claim 1, wherein the amount of element C contained in the copper powder is 0.2% by mass or less. The copper powder according to claim 1 or 2, wherein the TAP density is 1.0 to 2.77 g / cm ³ . A conductive paste containing the copper powder according to any one of claims 1 to 3.