WO2023074827A1

WO2023074827A1 - Copper particles and method for producing same

Info

Publication number: WO2023074827A1
Application number: PCT/JP2022/040269
Authority: WO
Inventors: 瑞樹秋澤; 仁彦井手; 隆史佐々木
Original assignee: 三井金属鉱業株式会社
Priority date: 2021-10-28
Filing date: 2022-10-27
Publication date: 2023-05-04
Also published as: TW202327757A

Abstract

In the copper particles of the present invention, when Ts represents the sintering start temperature measured by thermomechanical analysis, P1 represents the maximum peak in the temperature range below Ts obtained by measurement using a thermogravimetric-mass spectrometer, and P2 represents the maximum in the temperature range at and above Ts, the value of P2/P1 is less than 0.2. In addition, in the copper particles, the crystallite size is 30-80 nm (inclusive). Furthermore, in the copper particles, the median diameter by image analysis is 0.3-2.0 μm (inclusive). The copper particles are preferably obtained by adding a reducing agent to a liquid dispersion containing dry copper particles and a copper compound and causing copper to reduce and deposit onto the surface of the dry copper particles.

Description

Copper particles and method for producing the same

The present invention relates to copper particles and a method for producing the same.

　Copper is a highly conductive metal and a versatile material, so it is widely used industrially as a conductive material. For example, copper powder, which is an aggregate of copper particles, is widely used as a raw material for manufacturing various electronic components such as external electrodes and internal electrodes of multilayer ceramic capacitors (hereinafter also referred to as "MLCC").

When copper powder is used as an external electrode or an internal electrode of an MLCC, a step of sintering the copper particles to form a sintered body is performed. In this case, if impurities such as organic substances are present in the copper particles, the impurities are burned during the sintering process to generate gas, which causes defects such as voids in the sintered body. Therefore, for the purpose of suppressing gas generation, in Patent Document 1, copper chloride gas is generated by a reaction between metallic copper and a chlorine-containing gas, and copper chloride gas is generated by a reaction between the generated copper chloride gas and a reducing gas. It has been proposed to produce copper powder by producing a primary powder containing and treating the primary powder with a nitrogen-containing heteroaromatic compound.

JP 2021-80549 A

Patent Document 1 describes that a copper powder having a degassing peak temperature of 150° C. or higher and 300° C. or lower can be obtained. However, the firing temperature of the copper powder ranges from a relatively low temperature range to a high temperature range depending on the properties of the copper powder, and the technique described in the document cannot prevent gas generation when firing in a high temperature range.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a copper particle and a method for producing the same that can overcome the above-described drawbacks of the prior art.

In the present invention, the sintering start temperature measured by thermomechanical analysis is Ts,
When the maximum peak in the temperature range below Ts obtained by measurement using a thermogravimetric-mass spectrometer is P1, and the maximum peak in the temperature range above Ts is P2,
The value of P2/P1 is less than 0.2,
The crystallite size is 30 nm or more and 80 nm or less,
Provided are copper particles having a median diameter of 0.3 μm or more and 2.0 μm or less as determined by image analysis.

The present invention also provides a method for producing copper particles, comprising the step of adding a reducing agent to a dispersion containing dry copper particles and a copper compound, and depositing copper on the surfaces of the dry copper particles by wet reduction. is.

FIG. 1 is a schematic diagram showing a DC plasma apparatus suitable for producing dry copper particles. FIG. 2 is a graph showing the results of thermomechanical analysis of the copper particles obtained in Examples and Comparative Examples. FIG. 3 is a graph showing the measurement results of thermogravimetric-mass spectrometry on the copper particles obtained in Examples and Comparative Examples. 4 is a scanning electron microscope image of the copper particles obtained in Example 3. FIG. 5 is a scanning electron microscope image of the copper particles obtained in Comparative Example 1. FIG.

The present invention will be described below based on its preferred embodiments. First, the method for producing copper particles of the present invention will be described.
This production method is roughly divided into the following two steps.
(1) A step of preparing dry copper particles.
(2) A step of adding a reducing agent to a dispersion containing dry copper particles and a copper compound to deposit copper on the surface of the dry copper particles by wet reduction.
Each step will be described below.

<Preparation process for dry copper particles>
The dry copper particles prepared in this step are copper particles produced by a dry method. In the present specification, the term "copper particles" mainly refers to particles consisting of copper and the remainder being unavoidable impurities. Particles which are unavoidable impurities are also included.

Due to the production method, the copper particles produced by the dry method have a much lower content of organic substances that cause gas generation compared to the copper particles produced by the wet method. Therefore, by using the dry copper particles as cores for grain growth, the copper particles obtained by this production method are those in which the generation of gas during firing in a high temperature range is suppressed. As used herein, the term "high temperature range" preferably refers to a temperature range of 450°C, more preferably a temperature range of 500°C or higher, and even more preferably a temperature range of 550°C or higher.

When producing copper particles by a dry method, there are no particular restrictions on the method. One example is a vapor phase method such as a plasma method. As another example, the atomization method is used. The greatest advantage of producing copper particles by the dry method is that the produced copper particles are less contaminated with organic matter and the like. In contrast, when copper particles are produced by a wet method, organic substances derived from reducing agents, complexing agents, and/or surface treatment agents are likely to be mixed as impurities. Mixing of organic matter, as described above, is one of the causes of voids in the sintered body, and should be avoided as much as possible.

When producing copper particles by the atomization method, for example, a gas atomization method and a water atomization method can be used. In the atomization method, after the copper base metal is melted in an induction furnace or gas furnace, the molten metal flowing out from the nozzle at the bottom of the tundish is blown with a jet stream of gas such as air or inert gas, or water to melt the molten metal. Copper particles are produced by pulverizing and solidifying into droplets. Although the water atomization method uses liquid water, it is not included in the wet method because it can be regarded as a dry method from the principle of manufacturing copper particles.

When producing dry copper particles by a vapor phase method such as a plasma method, a method of heating and injecting raw copper powder using a DC plasma device, for example, can be adopted. When performing this method, a mixed gas of argon and nitrogen can be used as the plasma gas. In particular, by adjusting the plasma conditions so that the plasma flame becomes thick and long in a laminar flow state, fine dry copper particles having a uniform particle size can be easily obtained.

Whether or not the plasma flame is in a laminar flow state is determined when the aspect ratio of the frame length to the frame width (hereinafter referred to as the frame aspect ratio) is 3 when the plasma flame is observed from the side where the frame width is observed to be the widest. It can be judged by whether or not it is above. Specifically, if the frame aspect ratio is 3 or more, it can be determined that the flow is laminar, and if it is less than 3, it can be determined that the flow is turbulent.

As a DC plasma apparatus, for example, as shown in FIG. 1, a plasma apparatus equipped with a powder supply device 2, a chamber 3, a DC plasma torch 4, a recovery pot 5, a powder supply nozzle 6, a gas supply device 7 and a pressure adjustment device 8. 1 can be used. In this plasma device 1 , the raw material powder passes through the inside of the DC plasma torch 4 from the powder supply device 2 through the powder supply nozzle 6 . A mixed gas of argon and nitrogen is supplied to the DC plasma torch 4 from a gas supply device 7, thereby generating a plasma flame.
The raw material powder is gasified in the plasma flame generated by the DC plasma torch 4 , discharged into the chamber 3 , cooled to become fine powder, and accumulated and collected in the collection pot 5 .
The inside of the chamber 3 is controlled by the pressure regulator 8 so as to maintain a negative pressure relative to the powder supply nozzle 6, and has a structure for stably generating a plasma flame.

When heating and injecting raw material copper powder using a DC plasma apparatus, as described above, it is preferable to adjust the plasma conditions so that the plasma flame becomes thick and long in a laminar flow state. A mixed gas of argon and nitrogen is preferably used as the plasma gas. By adjusting in this way, the raw material copper powder that is put into the plasma flame can be instantly vaporized and vaporized, and sufficient energy can be supplied within the plasma flame. and condensation can occur to form fine particles, especially fine particles of submicron order.

It is preferable to adjust the plasma output and gas flow rate so that the plasma flame becomes thick and long in a laminar flow state. From this point of view, the plasma output of the DC thermal plasma apparatus is preferably 2 kW or more and 30 kW or less, more preferably 4 kW or more and 15 kW or less. From the above-described viewpoint, the gas flow rate of the plasma gas is preferably 0.1 L/min or more and 20 L/min or less, and more preferably 0.5 L/min or more and 18 L/min or less.

In order to stably maintain the plasma flame in a laminar flow state, the above ranges of plasma power and gas flow rate must be maintained, and the Ar gas flow rate (B) and N ₂ gas flow rate (C) with respect to the plasma power (A) , that is, the value calculated by the formula (B+C)/A (unit: L/(min·kW)) is preferably 0.50 or more and 2.00 or less. In particular, the value of (B + C)/A is preferably 0.50 or more in order to obtain the flow rate necessary for gasifying the raw material powder. The value of B+C)/A is preferably 2.00 or less. In particular, it is more preferable to adjust the value of (B+C)/A to 0.70 or more and 1.70 or less, particularly 0.75 or more and 1.50 or less.

From the viewpoint of obtaining copper particles with a sharp particle size distribution, the ratio of argon and nitrogen in the plasma gas is preferably 99:1 to 10:90, particularly 95:5 to 60:40, especially 95: A ratio of 5 to 80:20 is preferred.

Regardless of whether the gas phase method such as the plasma method or the atomization method is used, the particle diameter of the dry copper particles is determined by image analysis based on the image taken by electron microscope observation. It is preferable that the particle size is 0.05 μm or more and less than 0.5 μm from the point of successfully obtaining the desired copper particles. From the viewpoint of making this advantage more remarkable, the particle size of the dry copper particles is more preferably 0.1 μm or more and 0.4 μm or less, and even more preferably 0.1 μm or more and 0.3 μm or less. A method for measuring the median diameter will be described in Examples.

Comparing the vapor phase method such as the plasma method with the atomization method, dry copper particles produced by the vapor phase method have the advantage that the content of organic substances that cause gas generation is less.
It is also conceivable to use dry copper particles themselves produced by a vapor phase method such as a plasma method as copper particles for sintering. However, since it is difficult to produce dry copper particles with a large particle size by a vapor phase method such as a plasma method, it is not easy to produce copper particles with a particle size suitable for sintering. Therefore, in this production method, dry copper particles produced by a gas phase method such as a plasma method are used as cores for grain growth because the content of organic substances that cause gas generation is small, although the particle size is small. , the dry copper particles were subjected to the next step of reducing and depositing copper ions.
It is also not advantageous to use the dry copper particles themselves produced by the atomization method as the copper particles for sintering. The reason for this is that it is not easy to produce copper particles of a size required for sintering copper particles used in small electronic devices by the atomization method.

<Reduction deposition step>
In this step, a reducing agent is added to the dispersion containing the dry copper particles and the copper compound prepared in the preparation step, and copper is precipitated on the surface of the dry copper particles by wet reduction.
A compound containing monovalent or divalent copper can be used as the copper compound.
Compounds containing monovalent copper include, for example, cuprous oxide (Cu ₂ O).
Compounds containing divalent copper include, for example, copper hydroxide (Cu(OH) ₂ ) and copper sulfate (CuSO ₄ ).
From the viewpoint of reducing the amount of gas generated from the produced copper particles, cuprous oxide or cuprous hydroxide is preferably used, and cuprous oxide is more preferably used. The use of cuprous oxide is also preferable because the amount of reducing agent used can be reduced. This is because the reducing agent can also be one of the causative substances for gas generation.

From the viewpoint of successfully obtaining copper particles with suppressed gas generation, it is preferable to use a compound that does not contain a carbon element as a reducing agent that reduces the copper compound. From this point of view, it is preferable to use hydrazine, which is a compound consisting only of hydrogen and nitrogen, as the reducing agent.

In this step, the ratio of the dry copper particles to the copper compound used is determined from the viewpoint of the desired particle size of the copper particles and the uniformity of the particle size. Theoretically, the desired particle size of the copper particles can be estimated from the amount of dry copper particles to be added and the amount of copper deposited by wet reduction. However, it is not easy to produce copper particles with a uniform particle size by the dry method, and the particle size distribution tends to be wide and the distribution shape varies, so there may be a deviation between the theoretical value and the actual particle size. There is
The particle size of the copper particles produced by wet reduction converges to the particle size of the dry copper particles as the amount of the dry copper particles added increases with respect to the amount of the copper compound added. However, when the ratio of the dry copper particles to the amount of the copper compound to be added increases, the particle size distribution of the generated copper particles tends to widen. Therefore, from the viewpoint of obtaining copper particles with high particle size uniformity, the amount of the dry copper particles added is preferably 80 atomic % or less with respect to the total copper atoms of the dry copper particles and the copper compound. It is preferably 60 atomic % or less, more preferably 40 atomic % or less. The lower limit of this value is preferably 0.1 atomic % or more as a realistic value.

In this process, copper ions are reduced while the dry copper particles and copper compound are dispersed in water. The ratio of the dry copper particles and water is preferably 10 parts by mass or more and 20000 parts by mass or less, preferably 50 parts by mass or more, relative to 1 part by mass of the dry copper particles, from the viewpoint of successful reduction deposition of copper ions. It is more preferable to use 10000 parts by mass or less, and it is even more preferable to use 100 parts by mass or more and 1000 parts by mass or less. By using water in an amount of 20000 parts by mass or less with respect to 1 part by mass of the dry copper particles, the dispersibility of the dry copper particles can be sufficiently enhanced. Further, by using water in an amount of 10 parts by mass or more with respect to 1 part by mass of the dry copper particles, production efficiency can be enhanced.

When the dry copper particles and water are mixed, (a) prior to mixing the two, the copper compound and water are mixed, and the resulting dispersion and the dry copper particles can be mixed. Alternatively, (b) the dry copper particles and water can be mixed first, and the resulting dispersion can be mixed with the copper compound. Which of (a) and (b) is adopted can be appropriately determined according to the type of copper compound.

When the method (b) is employed, the dry copper particles and water are first mixed, and the resulting dispersion and reducing agent are mixed, and then the copper compound can be added. The reason for adding the reducing agent to the dispersion containing the dry copper particles and water is to remove the oxide film that may exist on the surface of the dry copper particles, so that the subsequent reduction deposition of copper ions can be performed successfully. That's what it is. Therefore, when the reducing agent is added to the dispersion containing the dry copper particles and water, no copper compound is present in the dispersion, and no copper ions are precipitated by reduction.

A reducing agent is added to the dispersion while the dry copper particles and the copper compound are present in the dispersion. As a result, copper ions derived from the copper compound present in the dispersion are reduced, and copper is deposited on the surface of the dry copper particles as cores.

The method of adding the reducing agent is preferably determined according to the valence of copper ions contained in the copper compound.
For example, when the copper ion contained in the copper compound is divalent (for example, when copper hydroxide or copper sulfate is used as the copper compound), it is preferable to add the reducing agent in two steps. By carrying out like this, there exists an advantage that it is easy to control the particle size of the copper particle finally obtained. Specifically, the first addition of the reducing agent reduces the divalent copper ions to monovalent copper ions, and then, upon completion of the reduction of the divalent copper ions in the system, the second addition of the reducing agent. An addition is made to reduce the monovalent copper ions to metallic copper, which is deposited on the surface of the dry copper particles. Both the first addition of the reducing agent and the second addition of the reducing agent may be performed sequentially over a predetermined period of time, or the entire amount may be added at once.

On the other hand, when the copper ions contained in the copper compound are monovalent (for example, when cuprous oxide is used as the copper compound), the reduction reaction of the copper ions is only one step from monovalent to zero valent, so the reducing agent is added all at once. be able to. In this case, adding the reducing agent in multiple times is not prevented, but adding the reducing agent in multiple times has no particular practical advantage.

By adding a reducing agent to the dispersion liquid, the copper contained in the copper compound is reduced, and the reduced copper is deposited on the surface of the dry copper particles. The reduced copper grows pseudoepitaxially on the surface of the dry copper particles. Epitaxial growth is a method in which the crystal planes of the material grown on top are aligned with the crystal planes of the underlying material when the same or different material is grown on the crystal of the underlying material. is. Strictly speaking, the reduction deposition of copper in the present production method is not epitaxial growth. It is called pseudo epitaxial growth in this specification.
The copper produced by the reduction undergoes pseudoepitaxial growth on the surface of the dry copper particles, so that the finally obtained copper particles radially extend from the central area of the particles toward the surface area, and have a plurality of crystal grains exposed on the surface. It becomes a structure with Copper grains having such a structure are less likely to retain impurities at the grain boundaries, so that the content of impurities is small. Due to this also, the copper particles obtained by this production method are those in which the generation of gas during firing in a high temperature range is suppressed. In particular, when the grain boundaries are shaped so as to radially extend from the surface of the dry copper particles toward the surface of the copper particles, gas can easily escape to the outside during the sintering process of the copper particles. Voids are less likely to occur in the

It is advantageous to use dry copper particles produced by a vapor phase method such as a plasma method in order to allow the copper produced by reduction to grow pseudo-epitaxially on the surface of the dry copper particles. This is because dry copper particles produced by a vapor phase method such as a plasma method have very high crystallinity compared to dry copper particles produced by other methods.

When reducing the copper contained in the copper compound by adding a reducing agent to the dispersion, the dispersion may be heated or may be reduced without heating. Moreover, the dispersion may be stirred, or the reduction may be carried out while standing still.

By depositing copper on the surface of the dry copper particles, copper particles having the desired particle size can be obtained. Hereinafter, these copper particles are referred to as "copper particles of the present invention". The copper particles of the present invention are subjected to washing and drying processes as necessary. Copper particles obtained by adding a reducing agent to the copper particles of the present invention thus obtained, i.e., the dispersion containing the dry copper particles and the copper compound, and reducing and depositing copper on the surface of the dry copper particles. Owing to its manufacturing method, it combines the starting points of dry copper particles with the advantages of wet copper particles. Specifically, due to the advantage of dry copper particles, that is, the content of impurities, especially organic matter, in the interior of the particles is small, when producing a sintered body using the copper particles, it is possible to use the copper particles in a high temperature range. Generation of gas during firing is suppressed. In addition, due to the advantages of wet copper particles, namely sharp particle size distribution and small particle size, the surface smoothness of a coating film produced from a paste containing copper particles is enhanced.

The degree of suppression of gas generation in firing in a high temperature range can be evaluated by measurement using a thermogravimetric-mass spectrometer (hereinafter also referred to as “TG-MS”). Specifically, when the copper particles of the present invention are subjected to TG-MS measurement, preferably at temperatures above the sintering start temperature, peaks of a certain size or more are not observed. In this specification, the sintering start temperature is the temperature at which the displacement rate changes by 2% when measured by thermomechanical analysis (hereinafter also referred to as "TMA"). Note that "a peak of a certain size or more is not observed at temperatures above the sintering start temperature" does not mean that no peaks are observed in a temperature range below the sintering start temperature. In other words, the copper particles of the present invention preferably show no peak in the temperature range above the sintering start temperature, and may have a peak in the temperature range below the sintering start temperature.
In the present specification, "a peak of a certain size or more is not observed above the sintering start temperature" means that the sintering start temperature measured by TMA is Ts, and is obtained by measurement using TG-MS. The value of P2/P1 is less than 0.2, where P1 is the maximum peak in the temperature range below Ts and P2 is the maximum peak in the temperature range above Ts. From the viewpoint of further suppressing gas generation, the value of P2/P1 is preferably 0.18 or less, more preferably 0.15 or less.
The TMA and TG-MS measurement methods for the copper particles of the present invention will be described in Examples.

The copper particles of the present invention may contain carbon in an amount suitable for preventing oxidation or agglomeration of the particle surface. From this point of view, the copper particles of the present invention preferably have a carbon content of 10 ppm or more and 7000 ppm or less, more preferably 10 ppm or more and 5000 ppm or less, even more preferably 100 ppm or more and 2000 ppm or less, and 150 ppm or more and 1000 ppm or less. The following are even more preferred. The carbon contained in the copper particles of the present invention is an organic substance derived from raw materials, or a carbonate derived from adsorption of carbon dioxide. In addition, organic substances such as fatty acids and aliphatic amines may be intentionally applied to the surface of the copper particles for the purpose of preventing oxidation and aggregation. By setting the carbon content to 7000 ppm or less, carbon hardly remains after sintering, and gas generation is effectively suppressed.
The amount of carbon contained in the copper particles of the present invention is measured by placing 0.50 g of copper particles in a magnetic crucible using a carbon/sulfur analyzer (CS844 manufactured by LECO Japan LLC). The carrier gas is oxygen gas (purity: 99.5%), and the analysis time is 40 seconds.

Since the copper particles of the present invention are preferably produced by the method described above, the crystallite size is larger than that of conventionally known dry copper particles, such as dry copper particles produced by an atomizing method. becomes small. Specifically, the copper particles of the present invention preferably have a crystallite size of 30 nm or more and 80 nm or less, more preferably 35 nm or more and 75 nm or less, and still more preferably 40 nm or more and 65 nm or less. The copper particles produced by the production method described above and having such a small crystallite size can more effectively suppress gas generation. A method for measuring the crystallite size of copper particles will be described in Examples.

The copper particles of the present invention preferably have a particle size suitable for forming a sintered body by firing. From this point of view, the copper particles of the present invention preferably have a median diameter of 0.3 μm or more and 2.0 μm or less by image analysis, more preferably 0.4 μm or more and 1.8 μm or less, and 0.4 μm or more. It is more preferably 1.5 μm or less. Copper particles having a particle size within this range and having suppressed gas generation during firing in a high-temperature range cannot be easily obtained by a gas phase method such as a plasma method, and can be obtained by adopting this production method. It is obtained for the first time. A method for measuring the median diameter will be described in Examples.

In relation to the median diameter described above, the copper particles of the present invention are measured by the image analysis particle size distribution measurement method, with the volume cumulative particle diameter at 50 volume % of the cumulative volume measured by the image analysis particle size distribution measurement method as D50. When the standard deviation of the particle size distribution is SD, the value of SD/D50 is 0.9 or less. is preferable from the viewpoint of improvement. The value of SD/D50 is an index of the sharpness of the particle size distribution of copper particles, and the closer this value is to 0, the sharper the particle size distribution of copper particles. From the viewpoint of further enhancing the surface smoothness of the coating film, the SD/D50 value is more preferably 0.7 or less, and even more preferably 0.6 or less. Methods for measuring SD and D50 are described in the Examples. Note that D50 has the same meaning as the median diameter described above.

In relation to the SD/D50 described above, the copper particles of the present invention have a volume cumulative particle diameter measured by image analysis particle size distribution measurement method at 10% by volume and 90% by volume respectively. It is preferable that the value of D90/D10, which is the ratio of D90 to D10, is small. D90/D10, like SD/D50 described above, is a value that is an index indicating the sharpness of the particle size distribution of copper particles, and the closer the value is to 1, the sharper the particle size distribution of copper particles is. do. From this viewpoint, the copper particles of the present invention preferably have a D90/D10 value of 20.0 or less, more preferably 10.0 or less, and even more preferably 5.0 or less. The closer the lower limit of the D90/D10 value is to 1, the better from the point of view of sharpness of the particle size distribution. .
Methods for measuring D10 and D90 are described in Examples.

The present invention discloses the following copper particles and a method for producing copper particles.
[1]
Let the sintering start temperature measured by thermomechanical analysis be Ts,
When the maximum peak in the temperature range below Ts obtained by measurement using a thermogravimetric-mass spectrometer is P1, and the maximum peak in the temperature range above Ts is P2,
The value of P2/P1 is less than 0.2,
The crystallite size is 30 nm or more and 80 nm or less,
Copper particles having a median diameter of 0.3 μm or more and 2.0 μm or less as determined by image analysis.
[2]
The volume cumulative particle size measured by image analysis particle size distribution measurement is defined as D50,
When the standard deviation of the particle size distribution measured by the image analysis particle size distribution measurement method is SD,
The copper particles according to [1], having an SD/D50 value of 0.9 or less.
[3]
The copper particles according to [1] or [2], wherein the amount of carbon is 10 ppm or more and 7000 ppm or less.
[4]
Any one of [1] to [3], which is obtained by adding a reducing agent to a dispersion containing dry copper particles and a copper compound to reduce and deposit copper on the surface of the dry copper particles. Copper particles as described.
[5]
A method for producing copper particles, comprising a step of adding a reducing agent to a dispersion containing dry copper particles and a copper compound, and depositing copper on the surfaces of the dry copper particles by wet reduction.
[6]
The production method according to [5], wherein the dry copper particles are produced by a vapor phase method.
[7]
The production method according to [5] or [6], wherein the dry copper particles are produced by an atomizing method.
[8]
the copper compound is a divalent copper compound,
The production method according to any one of [5] to [7], wherein the reducing agent is added in multiple batches.
[9]
the copper compound is a monovalent copper compound,
The production method according to any one of [5] to [7], wherein the reducing agent is added all at once.

The present invention will be described in more detail below with reference to examples. However, the scope of the invention is not limited to such examples. "%" means "% by mass" unless otherwise specified.

[Example 1]
(1) Production of Dry Copper Particles Using the apparatus shown in FIG. 1, dry copper particles were produced by a vapor-phase DC plasma method.
A raw material copper powder (particle size: 10 μm, spherical particles) was introduced into the powder supply device 2 and supplied into the chamber 3 from the powder supply nozzle 6 at a supply rate of 10 g/min.
A mixed gas of argon and nitrogen was used as the plasma gas, and the mixed gas was supplied to the inside of the plasma flame at an argon flow rate of 13.0 L/min and a nitrogen flow rate of 0.7 L/min. The ratio of argon flow (B) to nitrogen flow (C) was 95:5. The plasma power was 10.0 kW.
The produced plasma flame was photographed from the side where the frame width was observed to be the widest, the photographed image was binarized, and the aspect ratio of the frame length to the frame width (frame aspect ratio) was measured. As a result, the flame aspect ratio of the plasma flame was 4, confirming that the flow was laminar.
The median diameter of the dry copper particles thus obtained was 150 nm.

(2) Preparation of Copper Compound Powder of copper hydroxide (Cu(OH) ₂ ) was prepared as a copper compound.
(3) Preparation of reducing agent Hydrazine was prepared as a reducing agent.
(4) Production of Copper Particles After mixing 200 g of copper hydroxide and 2000 mL of water, 13 g of the dry copper particles were added. 200 g of 25% aqueous ammonia was added to the dispersion thus obtained. The reaction activity was adjusted by adding aqueous ammonia.
Furthermore, a mixed solution of 30 g of hydrazine and 60 g of water was added at an addition rate of 2 ml/min to perform the first reduction at 25°C. The dispersion was kept under stirring.
Thirty minutes after the addition of hydrazine, the liquid was heated to 35° C., and 50 g of hydrazine was added at an addition rate of 2 ml/min to carry out the second reduction. The dispersion was kept under stirring. The resulting dispersion of copper particles was washed with decantation using pure water to reduce the electrical conductivity to 2 mS/cm or less and prepare a dispersion having a solid concentration of 10%. A solution obtained by dissolving 0.48 g of lauric acid in 300 mL of methanol was added all at once to this dispersion for surface treatment. After that, a cake of copper particles was collected by filtration and vacuum-dried at 70° C. to obtain copper powder.

[Example 2]
The same dry copper particles and reducing agent as used in Example 1 were used. Cuprous oxide (Cu ₂ O) having a specific surface area of 5.4 m ² /g was used as the copper compound. Copper particles were produced according to the following (4).
(4) Production of Copper Particles 7 g of dry copper particles and 2000 mL of water were mixed to obtain a dispersion. 7 g of hydrazine was added to this dispersion without heating to remove the oxide film present on the surface of the dry copper particles.
100 g of cuprous oxide was then added to the dispersion. After the temperature was raised to 40° C., 70 g of hydrazine was added to the dispersion at an addition rate of 10 ml/min for reduction. The dispersion was kept under stirring.
The copper particles thus obtained were washed with water, surface-treated and dried in the same manner as in Example 1, except that the amount of lauric acid added was changed to 0.26 g.

[Example 3]
The same dry copper particles and reducing agent as used in Example 1 were used. Copper sulfate pentahydrate (CuSO ₄ .5H ₂ O) was used as the copper compound. Copper particles were produced according to the following (4).
(4) Production of Copper Particles 600 g of copper sulfate pentahydrate and 700 mL of water were mixed and stirred at 40° C. to obtain a copper raw material solution. To this solution, 180 g of 25% aqueous ammonia was added at an addition rate of 18 ml/min to adjust the pH.
An additional 7.5 g of dry copper particles were added. Next, a mixed solution of 25 g of hydrazine and 100 g of 25% aqueous ammonia was added at an addition rate of 4 ml/min to carry out the first reduction. The dispersion was kept under stirring.
Thirty minutes after hydrazine addition, 150 g of a 25% sodium hydroxide aqueous solution was added at an addition rate of 40 ml/min to adjust the pH. Furthermore, a mixed solution of 110 g of hydrazine and 110 g of water was added at an addition rate of 15 ml/min to carry out the second reduction. The dispersion was kept under stirring.
The copper particles thus obtained were washed with water, surface-treated and dried in the same manner as in Example 1 except that the amount of lauric acid added was changed to 0.75 g.

[Example 4]
The same dry copper particles and reducing agent as used in Example 1 were used. Cuprous oxide (Cu ₂ O) having a specific surface area of 6.8 m ² /g was used as the copper compound. Copper particles were produced according to the following (4).
(4) Production of Copper Particles 10 g of dry copper particles and 2000 mL of water were mixed to obtain a dispersion liquid. To this dispersion was added 0.4 g of sodium diphosphate decahydrate. 7 g of hydrazine was added to this dispersion without heating to remove the oxide film present on the surface of the dry copper particles.
100 g of cuprous oxide was then added to the dispersion. After heating to 40° C., 50 g of hydrazine was added to the dispersion at an addition rate of 10 ml/min for reduction. The dispersion was kept under stirring.
Water washing, surface treatment and drying treatment were carried out in the same manner as in Example 2 except that the amount of lauric acid for surface treatment of the copper particles thus obtained was changed to 0.3 g to obtain copper particles. rice field.

[Example 5]
The same dry copper particles and reducing agent as used in Example 1 were used. Cuprous oxide (Cu ₂ O) having a specific surface area of 1.9 m ² /g was used as the copper compound. Copper particles were produced according to the following (4).
(4) Production of Copper Particles 3 g of dry copper particles and 2000 mL of water were mixed to obtain a dispersion. 7 g of hydrazine was added to this dispersion without heating to remove the oxide film present on the surface of the dry copper particles.
100 g of cuprous oxide was then added to the dispersion. After heating to 35° C., 70 g of hydrazine was added to the dispersion liquid at an addition rate of 10 ml/min for reduction. The dispersion was kept under stirring.
The copper particles thus obtained were washed with water, surface-treated and dried in the same manner as in Example 2.

[Comparative Example 1]
In this comparative example, copper particles were produced by wet reduction without using dry copper particles.
An aqueous solution was obtained by mixing 4000 g of copper sulfate pentahydrate and 4400 mL of water at 45°C. 2.17 g of sodium pyrophosphate was added to this aqueous solution. Further, 874 g of 25% aqueous ammonia was added, and 2836 g of 25% aqueous sodium hydroxide solution was added.
Further, 300 g of hydrazine was added together with 393 g of 25% aqueous ammonia at a constant rate over 60 minutes to carry out the first reduction. The dispersion was kept under stirring.
After 15 minutes from the addition of hydrazine, 200 g of hydrazine was added at a constant rate over 10 minutes for the second reduction. The dispersion was kept under stirring.
The copper particles thus obtained were washed with water, surface-treated and dried in the same manner as in Example 1 except that the amount of lauric acid added was changed to 3.0 g.

〔evaluation〕
The median diameter of the copper particles obtained in Examples and Comparative Examples was measured by the following method. Also, TMA measurement was performed by the following method to obtain the sintering start temperature. Furthermore, TG-MS measurement was performed by the following method, and the above P2/P1 value was calculated. Furthermore, the presence or absence of a peak in the temperature range above the sintering start temperature Ts was observed. Furthermore, the crystallite size of the copper particles and SD, D10, D50 and D90 by image analysis particle size distribution measurement were measured by the following methods. Furthermore, the amount of carbon (C value) was measured by the method described above. The results are shown in Table 1 below. FIG. 2 shows the TMA measurement results, and FIG. 3 shows the results normalized by the maximum peak height of P1 using the TG-MS measurement results. FIG. 3 also shows the results of TG-MS measurement of the dry copper particles themselves. Furthermore, the SEM image of the copper particles obtained in Example 3 is shown in FIG. 4, and the SEM image of the copper particles obtained in Comparative Example 1 is shown in FIG.

[Median diameter]
The median diameter of the copper particles was measured using image analysis type particle size distribution measurement software Mac-View manufactured by MOUNTECH. For the measurement, 1000 particles are measured using an SEM image observed at a magnification of 5000 times, and the median value obtained from the obtained particle size distribution is defined as the median diameter of the copper particles.

[TMA measurement]
The sintering start temperature Ts was measured using EXSTAR 6000 manufactured by Seiko Instruments. Pellets were produced by putting 500 mg of copper particles into an aluminum cup of φ4.0 mm and pressing at 1.0 MPa. This pellet was heated at a rate of 10° C./min in a nitrogen atmosphere, measurement was started from room temperature (25° C.), and a graph showing the relationship between temperature and displacement rate (%) was obtained. The relationship between the two shows a flat graph with no change in the displacement rate in the low temperature range, and the displacement rate becomes negative (shrinkage) as it reaches the high temperature range. In some cases, due to variations in pellet production, the displacement rate once rises to the positive (expansion) side in the low temperature range, and then the displacement turns downward as the high temperature range is reached, and finally became negative (shrinkage). Therefore, the sintering start temperature in this specification is the temperature at which the displacement rate decreases by 2.0% from the flat state when the graph of the displacement rate changes from a flat state to a negative value as the temperature rises. defined as the initiation temperature. In addition, when the graph of the displacement rate once rises in the positive direction as the temperature rises and then falls in the negative direction, the displacement rate decreases by 2.0% from the time when the rise turns to the decline. This temperature is defined as the sintering start temperature.
The displacement rate (%) is defined as (T1−T0)/T0×100, where T0 is the initial height of the pellet before heating and T1 is the height of the pellet at a certain temperature after heating. be.

[TG-MS measurement]
Gas generation was measured using Rigaku's ThermoMassPhoto. 50 mg of copper particles were weighed in an alumina pan, and the temperature was raised from 25° C. to 900° C. at a rate of 50° C./min under a He atmosphere and measured. Thermo plus EVO2 software was used for the measurement, and measurement conditions were set. The He gas flow rate was set to 300 ml/min, the ionization mode was selected to be electron ionization, the emission was set to 1.0 mA, and the SEM was set to 1000V. The data acquisition interval was 1 second. Measurement sensitivity, scan speed, and filters were measured with AUTO settings. The obtained MS data were analyzed by QuadVision. As for the analysis method, the TIC data was converted into data relating to m/z=44. Generally, m/z=44 is considered to be carbon dioxide produced by decomposition of organic matter.

[Crystallite size]
The copper particles were classified using a sieve with an opening of 75 μm, and the fraction under the sieve was used as a sample. This sample was filled in a sample holder and measured under the following conditions using an X-ray diffractometer (Ultima IV manufactured by Rigaku Co., Ltd.).
Then, among the diffraction peaks, the crystallite size was calculated using Scherrer's formula based on the full width of the half-width of the main peak corresponding to the (111) plane of copper. The results are shown in Table 1 below.

<X-ray diffraction measurement conditions>
・Tube: CuKα ray ・Tube voltage: 40 kV
・Tube current: 50mA
・Measurement diffraction angle: 2θ = 20 to 100°
・Measurement step width: 0.01°
・Collection time: 3 sec/step ・Light receiving slit width: 0.3 mm
・Vertical divergence limiting slit width: 10 mm
・Detector: High-speed one-dimensional X-ray detector D/teX Ultra250

<Method for preparing sample for X-ray diffraction>
The copper powder to be measured was spread over a measurement holder and smoothed using a glass plate so that the copper powder had a thickness of 0.5 mm and was smooth.

Using the X-ray diffraction pattern obtained under the above measurement conditions, analysis was performed using analysis software under the following conditions. LaB ₆ was used for peak width correction. Crystallite size was calculated using the full width at half maximum of the peak and the Scherrer constant (0.94).

<Measurement data analysis conditions>
・ Analysis software: Rigaku PDXL2
・Smoothing: Gaussian function, smoothing parameter=10
・Background removal: fitting method ・Kα2 removal: intensity ratio 0.497
・Peak search: second derivative method ・Profile fitting: FP method ・Crystallite size distribution type: Lorentz model ・Scherrer constant: 0.9400

The peaks of the X-ray diffraction pattern used for analysis are as follows. The Miller indices shown below are synonymous with the crystal planes of copper described above.
A peak indexed by the Miller index (111) around 2θ=40°-45°.

[SD and D10, D50 and D90]
D10, D50, D90 and SD of the copper particles were measured using image analysis type particle size distribution measurement software Mac-View manufactured by MOUNTECH. For the measurement, 1000 particles were measured using an SEM image observed at a magnification of 5000, and volume cumulative particle diameters D10, D50, D90 and SD of the particle size distribution were obtained.

As is clear from the results shown in Table 1 and FIG. 3, the copper particles obtained in each example had a particle size similar to that of the copper particles of the comparative examples, and were sintered in a temperature range equal to or higher than the sintering start temperature. It can be seen that the generation of gas is suppressed.
In addition, in Example 1-3 shown in FIG. 3, the peak observed below the sintering start temperature is considered to be derived from impurities existing on the particle surface. In addition, in FIG. 3, noise is magnified in the case of copper particles that are less likely to generate gas, such as in Example 1-3, due to the fact that the graph is normalized by the height of the maximum peak in the entire temperature range. tend to

As described in detail above, according to the present invention, copper particles in which the generation of gas during firing in a high temperature range is suppressed, and a method for producing the same are provided.

Claims

Let the sintering start temperature measured by thermomechanical analysis be Ts,
When the maximum peak in the temperature range below Ts obtained by measurement using a thermogravimetric-mass spectrometer is P1, and the maximum peak in the temperature range above Ts is P2,
The value of P2/P1 is less than 0.2,
The crystallite size is 30 nm or more and 80 nm or less,
Copper particles having a median diameter of 0.3 μm or more and 2.0 μm or less as determined by image analysis.
The volume cumulative particle size measured by image analysis particle size distribution measurement is defined as D50,
When the standard deviation of the particle size distribution measured by the image analysis particle size distribution measurement method is SD,
The copper particles according to claim 1, having an SD/D50 value of 0.9 or less.
The copper particles according to claim 1, wherein the amount of carbon is 10 ppm or more and 7000 ppm or less.
The copper particles according to claim 1, which are obtained by adding a reducing agent to a dispersion containing dry copper particles and a copper compound, and reducing and depositing copper on the surfaces of the dry copper particles.
A method for producing copper particles, comprising a step of adding a reducing agent to a dispersion containing dry copper particles and a copper compound, and depositing copper on the surface of the dry copper particles by wet reduction.
The manufacturing method according to claim 5, wherein the dry copper particles are manufactured by a vapor phase method.
The manufacturing method according to claim 5, wherein the dry copper particles are manufactured by an atomizing method.
the copper compound is a divalent copper compound,
The production method according to any one of claims 5 to 7, wherein the reducing agent is added in multiple batches.
the copper compound is a monovalent copper compound,
The production method according to any one of claims 5 to 7, wherein the reducing agent is added all at once.