Flake copper powder and method for producing flake copper powder

Abstract

The present invention provides a method for producing flake copper powder, and flake copper powder, which allows for lowering the temperature when forming a conductive layer by applying a conductive paste containing flake-shaped copper particles as a filler and then firing it. [Solution] The present invention provides flake copper powder having a flake shape, a cumulative 50% particle diameter value based on volume measured by a laser diffraction particle size distribution analyzer being 0.3 μm or more and less than 2 μm, and a phosphorus content exceeding 200 ppm.

Description

Technical Field

[0001] The present invention relates to flaky copper powder suitable for use in conductive pastes and a method for producing the flaky copper powder.

Background Art

[0002] Conventionally, metal powders such as copper powder and silver powder have been used as materials for conductive pastes that form internal electrodes and the like of multilayer ceramic electronic components such as multilayer ceramic capacitors (MLCCs) and multilayer ceramic inductors (MLCIs).

[0003] A conductive paste is a dispersion of metal powder in an organic vehicle such as a resin or a solvent. After applying the conductive paste to form a coating film and subjecting it to a firing process or the like, multilayer ceramic electronic components are manufactured.

[0004] Patent Document 1 describes copper powder for a conductive paste, which contains flat particles. When copper powder composed of flat copper particles is used as a material for a conductive paste, when a conductive layer is formed by firing after applying the conductive paste, it is described that the packing density of the conductive layer can be increased and the conductivity of the conductive layer can be enhanced (paragraph 0006). Further, in the examples, it is described that when applying a conductive paste to form a coating film and firing the coating film to obtain a conductor, firing was performed at 845°C (paragraph 0047).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] When forming a conductive layer by firing after applying a conductive paste, the firing is typically performed at around 800°C. However, to improve productivity and reduce energy costs by shortening the heating time, it is necessary to lower the temperature at which the conductive layer is formed during firing. The object of the present invention is to provide a flake copper powder that allows for a lower temperature when forming a conductive layer by applying a conductive paste containing flake-shaped copper particles (sometimes referred to as "flake copper powder" in the present invention) as a filler and then firing it, and a method for producing flake copper powder. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the inventors conducted intensive research and concluded that the problems could be solved by controlling the particle size and phosphorus content of the flake copper powder within a predetermined range, thereby completing the present invention.

[0008] In other words, the first invention that solves the above-mentioned problem is, This is a flake copper powder having a flake shape, with a cumulative 50% particle diameter based on volume measured by a laser diffraction particle size distribution analyzer being between 0.3 μm and 2 μm, and a phosphorus content exceeding 200 ppm. The second invention is, When thermomechanical analysis (TMA) was performed to raise the temperature from 25°C to 900°C at a rate of 10°C / min, the shrinkage rate data measured at 10°C intervals starting from 400°C was defined as T. A The shrinkage rate at a temperature of (A+10)°C is T A+10 When this is the case, the change in contraction rate (T A+10 -T A The flake copper powder according to the first invention is defined as having a sintering start temperature of 600°C or less, which is the lowest temperature among the temperatures A°C in which the value of ) exceeds 0.3%. The third invention is, This is a flake copper powder according to the first or second invention, wherein the carbon content after firing at 400°C in air for 1 hour is 0.1% by mass or less. The fourth invention is, A reduction step is performed by mixing an aqueous solution of copper ammine complex with a first hydrazine compound, adding phosphoric acid or a water-soluble phosphate to the resulting mixture, and then adding a second hydrazine compound to obtain copper powder containing phosphorus. A method for producing flake copper powder, comprising a flakeization step of flaking the obtained copper powder to obtain flake copper powder, The method for producing flake copper powder is to set the amount of the hydrazine compound in the first step to a molar ratio of 0.15 or more relative to the amount of copper contained in the copper ammine complex, and to set the amount of phosphorus contained in the phosphoric acid or water-soluble phosphate to a mass ratio of 0.045 or more relative to the amount of copper contained in the copper ammine complex. The fifth invention is, The fourth invention relates to a method for producing flake copper powder, wherein the second addition of the hydrazine compound is divided into two stages: an early addition and a late addition, with a gap between the early and late additions while continuing to stir, and the amount of hydrazine compound added in the later stage is greater than the amount added in the early stage. The sixth invention is, A method for producing flake copper powder according to the fourth or fifth invention, wherein the cumulative 50% particle size on a volume basis, measured by a laser diffraction particle size distribution analyzer for the phosphorus-containing copper powder, is 0.3 μm or more and less than 1.7 μm. The seventh invention is, The method for producing flake copper powder according to any one of the fourth to sixth inventions, wherein the first and second hydrazine compounds are hydrazine, and the phosphoric acid or water-soluble phosphate is an alkali metal salt of pyrophosphate. [Effects of the Invention]

[0009] The conductive paste using flake copper powder as a filler according to the present invention allows for a lower temperature when forming the conductive layer by firing after application. [Modes for carrying out the invention]

[0010] 1. Shape and particle size of particles contained in flake copper powder (1) Particle shape In this invention, the flake shape refers to a particle shape having two flat plate surfaces and a thickness between these two plate surfaces. The flake copper powder according to this invention contains copper particles having a flake shape, and the ratio of the length of the longest side of the flat plate surface (the length of the longest side on the flat plate surface) to the thickness is the aspect ratio of the flake copper particles. Since particles having a flake shape have a higher specific surface area and a larger contact area with other particles than spherical particles, a conductive layer with excellent conductivity can be formed when flake copper powder is sintered.

[0011] When the flake copper powder according to the present invention, in a dry state, is photographed using a scanning electron microscope (SEM) at an acceleration voltage of 5kV and a magnification of 5000x, the image shows the flattened plate-like surfaces of many of the particles constituting the flake copper powder. On the other hand, the flake copper powder according to the present invention is mixed with a thermosetting resin to form a mixture, and the cured product obtained by heating and curing the mixture is processed by cutting out a predetermined cross section using a cross-section polisher. When the obtained cross section is photographed using a SEM at an acceleration voltage of 5kV and a magnification of 5000x, an image is obtained in which a large number of particles show a cross section perpendicular to the plate surface.

[0012] Thus, in the image in which a cross-section perpendicular to the plate surface is observed, the particles of the flake copper powder are oriented such that a cross-section perpendicular to the plate surface of the flake copper powder is visible. Therefore, in the image of the particles in which the cross-section can be observed, the minor axis diameter can be considered as the thickness of the flake copper powder particles, and the major axis diameter can be considered as the length of the long side of the flake copper powder particles.

[0013] Furthermore, in the flake copper powder according to the present invention, an image is obtained showing the cross-section perpendicular to the plate surface for 100 or more particles, and the major axis diameter and minor axis diameter are determined. When the average value of the major axis diameter / minor axis diameter is calculated as the aspect ratio, it is preferable that the aspect ratio value is 2.0 or higher, and more preferably 4.0 or higher.

[0014] (2) Particle size The volume-based cumulative 50% particle size (which may be referred to as "D50" in the present invention) measured by the laser diffraction particle size distribution measuring apparatus for the flake copper powder according to the present invention is 0.3 μm or more and less than 2 μm. Since the value of D50 is 0.3 μm or more, it is possible to suppress the increase in the viscosity of the conductive paste due to excessive fine particle formation. On the other hand, since the value of D50 is less than 2 μm, the temperature at the time of firing after applying the conductive paste using the flake copper powder according to the present invention to form a conductor layer becomes low. From this viewpoint, the value of D50 of the flake copper powder according to the present invention is more preferably 0.5 μm or more and 1.7 μm or less.

[0015] 2. Composition of particles contained in the flake copper powder (1) Phosphorus content The flake copper powder according to the present invention contains more than 200 ppm of phosphorus. When the flake copper powder contains more than 200 ppm of phosphorus, it becomes easier to sinter, and the temperature at the time of firing after applying the conductive paste using the flake copper powder according to the present invention to form a conductor layer becomes low. On the other hand, although the upper limit of the phosphorus content of the flake copper powder according to the present invention is not particularly defined, even if the phosphorus content exceeds 1000 ppm, the effect of lowering the temperature at the time of firing after applying the conductive paste to form a conductor layer saturates. Therefore, the phosphorus content may be 1000 ppm or less.

[0016] (2) Carbon content after firing in air The flake copper powder according to the present invention preferably has a carbon content of 0.1 mass% or less after firing at 4**00**° C. for 1 hour in air. When the carbon content after firing at 4**00**° C. for 1 hour in air is 0.1 mass% or less, when the conductive paste using the flake copper powder according to the present invention is fired after application, the risk of gas being released from the coating film and a defect called a blister occurring can be reduced. From this viewpoint, the carbon content after firing at 4**00**° C. for 1 hour in air is more preferably 0.05 mass% or less, and even more preferably 0.02 mass% or less.

[0017] 3. Sintering start temperature of the flake copper powder The flake copper powder according to the present invention preferably has a sintering start temperature of 600°C or lower, as measured by the procedure described later. By having a sintering start temperature of 600°C or lower for the flake copper powder, it is possible to obtain a conductive paste that can be fired at a lower temperature when forming a conductive layer by firing after coating, that is, a conductive paste that can be produced that significantly reduces the energy cost required for conductive film formation. Although there is no particular lower limit to the sintering start temperature of the flake copper powder according to the present invention, the manufacturing method of the present invention makes it possible to obtain flake copper powder with a sintering start temperature of 500°C or higher.

[0018] 4. Method for producing copper powder and copper flake powder The flake copper powder according to the present invention is produced by a reduction step in which phosphoric acid or a water-soluble phosphate is added to a mixture obtained by mixing an aqueous solution of copper ammine complex with a first hydrazine compound, and then a second hydrazine compound is added to obtain a copper powder containing phosphorus, and a flakeization step in which the obtained copper powder is flaked to obtain flake copper powder.

[0019] (1) Reduction process An aqueous solution of copper ammine complex is mixed with a first hydrazine compound, phosphoric acid or a water-soluble phosphate is added to the resulting mixture, and then a second hydrazine compound is added to obtain a copper powder containing phosphorus. An aqueous solution of copper ammine complex can be produced by mixing a water-soluble copper salt such as copper sulfate with ammonia and water in a molar ratio of 1 or more relative to the amount of copper contained in the water-soluble copper salt.

[0020] As the water-soluble phosphate, pyrophosphate (H4P2O7) or its alkali metal salt, orthophosphate (H3PO4) or its alkali metal salt, or metaphosphate (HPO3) or its alkali metal salt can be used, with pyrophosphate or its alkali metal salt being preferred. The amount of phosphoric acid or water-soluble phosphate added should be such that the mass ratio of the amount of phosphorus in the water-soluble phosphate to the amount of copper in the copper ammine complex is 0.045 or more, in order to obtain flake copper powder with a final phosphorus content of more than 200 ppm.

[0021] For the first and second hydrazine compounds, one or more of hydrazine, hydrazine carbonate, and hydrazine sulfate can be used. In order to reduce the particle size of the copper powder obtained in the reduction step, the amount of the first hydrazine compound should be set to a molar ratio of 0.15 or more, preferably 0.20 or more, relative to the amount of copper contained in the copper ammine complex. Furthermore, it is preferable that the total amount of hydrazine compounds added in the first and second steps be added to a molar ratio of approximately 0.6 relative to the amount of copper contained in the copper ammine complex.

[0022] The temperature of the mixture after the first addition of hydrazine is preferably between 40°C and 90°C to promote the reduction reaction of copper. It is preferable to continue stirring the mixture after the first addition of hydrazine for at least 10 minutes, and then begin adding the second hydrazine compound to the mixture.

[0023] Furthermore, it is also preferable to divide the second addition of the hydrazine compound into two stages: an early addition and a late addition. In this case, it is preferable to leave an interval of 10 minutes or more between the early and late additions while continuing to stir. By dividing the second addition of the hydrazine compound into two stages, an early addition and a late addition, and leaving an interval of 10 minutes or more between the early and late additions while continuing to stir, it is possible to obtain copper powder with a narrow particle size distribution, and as a result, flake copper powder with a narrow particle size distribution can be obtained. It is also preferable to increase the amount of the late addition compared to the amount of the hydrazine compound added. For example, the amount of the early addition is set to 12% to 20% by mass of the total amount of the second addition of the hydrazine compound. As a result, it is possible to obtain phosphorus-containing copper powder with uniform particle sizes, where the cumulative 50% particle diameter value based on volume, as measured by a laser diffraction particle size distribution analyzer, is 0.3 μm or more and less than 1.7 μm.

[0024] The obtained phosphorus-containing copper powder can be subjected to solid-liquid separation to recover the solid components, followed by washing with water and drying to obtain phosphorus-containing copper powder from which impurities such as hydrazine compounds and moisture have been removed. Using this phosphorus-containing copper powder, after a subsequent flakeping process, flake copper powder can be obtained in which the cumulative 50% particle size by volume, as measured by a laser diffraction particle size distribution analyzer, is between 0.3 μm and less than 2 μm.

[0025] (2) Flake formation process In this invention, flake copper powder is obtained by using media beads to plastically deform the copper powder in a mixed slurry of phosphorus-containing copper powder obtained in the reduction process and a liquid medium by mechanical energy (this may be referred to as "flaking" in this invention). The liquid medium can be water, alcohol, or a mixed solvent of water and alcohol. Examples of alcohols include alcohols having 1 to 5 carbon atoms, preferably alcohols having 1 to 3 carbon atoms.

[0026] The proportion of liquid medium in the mixed slurry is preferably 20 to 95% by mass, and more preferably 45 to 90% by mass, from the viewpoint of achieving efficient flake formation. The diameter of the media beads is preferably 0.8 mm or less, and more preferably 0.1 to 0.7 mm, in order to obtain flake copper powder of uniform thickness. The material of the media beads is preferably yttria-stabilized zirconia. Furthermore, from the viewpoint of achieving sufficient and efficient flake formation, the mass ratio of the amount of media beads to the amount of copper powder is preferably 4 to 15.

[0027] In this process, it is preferable to carry out the flake formation described above using a stirring device, such as an attritor, which has a container for holding the mixed slurry and media beads, and stirring blades for stirring the mixed slurry and media beads. In this case, in order to obtain flake copper powder of uniform thickness, it is preferable to remove the mixed slurry from the stirring device and put it back into the stirring device for circulation.

[0028] After flake formation, the obtained slurry is subjected to solid-liquid separation, and the resulting solid content is dried to obtain flake copper powder according to the present invention, which has a flake shape, a cumulative 50% particle diameter value based on volume measured by a laser diffraction particle size distribution analyzer of 0.3 μm or more and less than 2 μm, and a phosphorus content exceeding 200 ppm. A conductive paste obtained by mixing the flake copper powder according to the present invention with an organic vehicle such as a resin or solvent allows for a lower firing temperature when applying and firing the conductive paste to form a conductive layer.

[0029] 5. Evaluation Methods for Copper Powder and Flake Copper Powder (1) Cumulative 50% particle size (D50) based on volume The volume-based cumulative 50% particle size (D50) of the copper powder produced in the reduction process according to the present invention and the flake copper powder according to the present invention is determined by dispersing the copper powder and flake copper powder in nitrogen gas at a dispersion pressure of 5 bar using a laser diffraction particle size distribution analyzer (SYMPATEC HELOS particle size distribution analyzer (HELOS&RODOS (airflow-type dispersion module))) and evaluating the particle size distribution to determine the volume-based cumulative 50% particle size (D50).

[0030] (2) Carbon and phosphorus content The carbon content of the flake copper powder according to the present invention is measured using a carbon-sulfur analyzer (EMIA-920V2, manufactured by Horiba, Ltd.). The phosphorus content is measured using an ICP emission spectrometer (SPS3520V, manufactured by Hitachi High-Tech Science Corporation).

[0031] (3) Carbon content of flake copper powder after firing in air The flake copper powder according to the present invention is calcined in air at 400°C for 1 hour, and then the amount of carbon in the generated gas is measured using a carbon-sulfur analyzer (EMIA-920V2, manufactured by Horiba, Ltd.).

[0032] (4) Sintering start temperature in flake copper powder 0.5 g of the flake copper powder according to the present invention is mixed with a vehicle (a mixture of Mitsubishi Plastics BR-105 (manufactured by Mitsubishi Plastics, Inc.) and terpineol in a mass ratio of 3:7 (BR-105:terpineol)) at a mass ratio of 2% to the powder, and pressed with a press machine under a load of 360 N for 20 seconds to prepare a 5 mmφ measurement sample. This measurement sample is packed into an alumina pan with a diameter of 5 mm and a height of 3 mm, and set in the sample holder (cylinder) of a thermomechanical analyzer (TMA) (TMA / SS6200 manufactured by Seiko Instruments Inc.). Under a nitrogen gas atmosphere, a measurement load of 49 mN is applied using a measurement probe, and the temperature is raised from room temperature (25 °C) to 900 °C at a heating rate of 10 °C / min to measure the amount of shrinkage and shrinkage rate (%) of the measurement sample relative to room temperature. In the shrinkage rate data measured at 10 °C intervals from 400 °C, the shrinkage rate at temperature A °C is set to T A The shrinkage rate at a temperature of (A+10)°C is T A+10 When this is the case, the change in contraction rate (T A+10 -T A The lowest temperature A°C at which the value of ) exceeds 0.3% is defined as the sintering start temperature. [Examples]

[0033] (Example 1) To 6256 g of copper sulfate pentahydrate, 6288 g of 25.7% ammonia and 1076 g of pure water were added, and the mixture was heated to 80°C and stirred to obtain an aqueous solution of the copper ammine complex. After adding 392.1 g of 80% by mass hydrazine monohydrate (the first hydrazine compound), 559.0 g of sodium pyrophosphate decahydrate was added, and the mixture was stirred for 10 minutes. Here, the molar ratio of the amount of the first hydrazine compound to the amount of copper in the copper ammine complex was 0.25, and the mass ratio of the amount of phosphorus in sodium pyrophosphate to the amount of copper in the copper ammine complex was 0.049.

[0034] Next, 78.4 g of 80% by mass hydrazine monohydrate (second addition, the hydrazine compound from the first stage) was added and the mixture was allowed to mature for 10 minutes. Then, while continuing to stir, 470.5 g of 80% by mass hydrazine monohydrate (second addition, the hydrazine compound from the second stage) was added and the mixture was allowed to mature for 60 minutes, after which stirring was stopped to obtain the matured liquid. The molar ratio of the amount of the second hydrazine compound to the amount of copper contained in the copper ammine complex was 0.35, and the amount added in the first stage was 14% by mass of the total amount of the second hydrazine compound added. The resulting aged liquid was subjected to solid-liquid separation using a filtration device, and the solid components were washed with water and dried to obtain copper powder. The D50, carbon, and phosphorus content of the obtained copper powder was measured, and it was found that the D50 was 0.9 μm, the carbon content was 80 ppm, and the phosphorus content was 220 ppm.

[0035] 4.20 g of stearic acid was mixed and dissolved with 1056 g of industrial alcohol (Solmix AP7, manufactured by Nippon Alcohol Sales Co., Ltd.). This mixture, along with 1400 g of the resulting copper powder and 11 kg of φ0.5 mm zirconia beads, was loaded into an attritor and stirred for 3 hours while circulating the slurry. The stirred material was separated into solid and liquid components using a filtration device, and the solid components were dried to obtain flake copper powder. The D50, carbon and phosphorus content, carbon content after firing in air, and sintering start temperature of the obtained flake copper powder were measured. The results showed a D50 of 1.4 μm, a carbon content of 0.20 mass%, a phosphorus content of 210 ppm, a carbon content of 90 ppm after firing in air, and a sintering start temperature of 570°C. Table 1 shows the manufacturing conditions for the copper powder and the evaluation results of the copper powder and flake copper powder (the same applies to the following examples and comparative examples).

[0036] (Example 2) Except for using 439.2g of the hydrazine compound in the first application and 423.4g of the hydrazine compound in the second application, the copper powder and flake copper powder according to Example 2 were obtained using the same procedure as in Example 1. The molar ratio of the amount of hydrazine compound added in the first dose to the amount of copper in the copper ammine complex is 0.28. The molar ratio of the amount of hydrazine compound added in the second dose to the amount of copper in the copper ammine complex is 0.32, and the amount added in the first dose is 16% by mass of the total amount of hydrazine compound added in the second dose.

[0037] When the D50, carbon, and phosphorus content of the obtained copper powder was measured, the D50 content was 0.7 μm, the carbon content was 80 ppm, and the phosphorus content was 230 ppm. The D50, carbon, and phosphorus content of the obtained flake copper powder, the carbon content after firing in air, and the sintering start temperature were measured. The results showed that the D50 was 1.1 μm, the carbon content was 0.21 mass%, the phosphorus content was 220 ppm, the carbon content after firing in air was 80 ppm, and the sintering start temperature was 560°C.

[0038] (Comparative Example 1) The copper powder and flake copper powder of Comparative Example 1 were obtained using the same procedure as in Example 1, except that the amount of hydrazine compound added in the first step was 188.2 g, the amount of sodium pyrophosphate decahydrate added was 329.9 g, and the amount of hydrazine compound added in the second step (late stage) was 674.4 g. Here, the molar ratio of the amount of hydrazine compound in the first dose to the amount of copper in the copper ammine complex is 0.12, and the mass ratio of the amount of phosphorus in sodium pyrophosphate to the amount of copper in the copper ammine complex is 0.029. The molar ratio of the amount of hydrazine compound in the second dose to the amount of copper in the copper ammine complex is 0.48, and the amount added in the first dose is 10% by mass of the total amount of hydrazine compound added in the second dose.

[0039] When the volume-based D50, carbon, and phosphorus content of the obtained copper powder was measured, the D50 was 1.7 μm, the carbon content was 60 ppm, and the phosphorus content was 130 ppm. The volume-based D50, carbon and phosphorus content, carbon content after firing in air, and sintering start temperature of the obtained flake copper powder were measured. The results showed a D50 of 2.0 μm, a carbon content of 0.20 mass%, a phosphorus content of 120 ppm, a carbon content of 100 ppm after firing in air, and a sintering start temperature of 720°C.

[0040] (Comparative Example 2) Copper powder and flake copper powder according to Comparative Example 2 were obtained using the same procedure as in Example 1, except that the amount of the hydrazine compound added in the first stage was 188.2 g and the amount of the hydrazine compound added in the second stage was 674.4 g. Here, the molar ratio of the amount of the hydrazine compound added in the first stage to the amount of copper contained in the copper ammine complex was 0.12. The molar ratio of the amount of the hydrazine compound added in the second stage to the amount of copper contained in the copper ammine complex was 0.48, and the amount added in the first stage was 10% by mass of the total amount of the hydrazine compound added in the second stage.

[0041] When the volume-based D50, carbon, and phosphorus content of the obtained copper powder was measured, the D50 was 1.8 μm, the carbon content was 90 ppm, and the phosphorus content was 220 ppm. The volume-based D50, carbon and phosphorus content, carbon content after firing in air, and sintering start temperature of the obtained flake copper powder were measured. The results showed a D50 of 2.2 μm, a carbon content of 0.23 mass%, a phosphorus content of 210 ppm, a carbon content of 90 ppm after firing in air, and a sintering start temperature of 690°C.

[0042] (Comparative Example 3) Except for adding 406.6 g of sodium pyrophosphate decahydrate, the copper powder and flake copper powder according to Comparative Example 3 were obtained using the same procedure as in Example 1. The mass ratio of the amount of phosphorus in sodium pyrophosphate to the amount of copper in the copper ammine complex was 0.036. The molar ratio of the amount of hydrazine compound added in the second dose to the amount of copper in the copper ammine complex was 0.35, and the amount added in the first dose was 14% by mass of the total amount of hydrazine compound added in the second dose.

[0043] When the volume-based D50, carbon, and phosphorus content of the obtained copper powder was measured, the D50 was 1.0 μm, the carbon content was 80 ppm, and the phosphorus content was 160 ppm. The volume-based D50, carbon and phosphorus content, carbon content after firing in air, and sintering start temperature of the obtained flake copper powder were measured. The results showed that the D50 was 1.5 μm, the carbon content was 0.21 mass%, the phosphorus content was 150 ppm, the carbon content after firing in air was 90 ppm, and the sintering start temperature was 700°C.

[0044] (summary) From the results of the above examples and comparative examples, it was found that the sintering start temperature can be reduced to 600°C or below by setting the D50 of the flake copper powder to 0.3 μm or more and less than 2 μm, and the phosphorus content to more than 200 ppm. On the other hand, it was found that when the D50 of the flake copper powder is 2 μm or more, or the phosphorus content is 200 ppm or less, the sintering start temperature exceeds 600°C, and the effects of the present invention cannot be obtained.

[0045] [Table 1]

Claims

1. Flake copper powder having a flake shape, with a cumulative 50% particle diameter by volume measured by a laser diffraction particle size distribution analyzer being 0.3 μm or more and less than 2 μm, and a phosphorus content exceeding 200 ppm.

2. When thermomechanical analysis (TMA) was performed to raise the temperature from 25°C to 900°C at a rate of 10°C / min, the shrinkage rate data measured at 10°C intervals starting from 400°C was defined as T. Ａ The shrinkage rate at a temperature of (A + 10)°C is T Ａ＋１０ When this is the case, the change in contraction rate (T Ａ＋１０ -T Ａ The flake copper powder according to claim 1, wherein the sintering start temperature, defined as the lowest temperature among the temperatures A°C in which the value of ) exceeds 0.3%, is 600°C or less.

3. The flake copper powder according to claim 1 or 2, wherein the carbon content after firing at 400°C in air for 1 hour is 0.1% by mass or less.

4. A reduction step is performed by mixing an aqueous solution of copper ammine complex with a first hydrazine compound, adding phosphoric acid or a water-soluble phosphate to the resulting mixture, and then adding a second hydrazine compound to obtain copper powder containing phosphorus. A method for producing flake copper powder, comprising a flakeization step of flaking the obtained copper powder to obtain flake copper powder, A method for producing flake copper powder, wherein the amount of the first hydrazine compound is set to 0.15 or more in molar ratio to the amount of copper contained in the copper ammine complex, and the amount of phosphorus contained in the phosphoric acid or water-soluble phosphate is set to 0.045 or more in mass ratio to the amount of copper contained in the copper ammine complex.

5. The method for producing flake copper powder according to claim 4, wherein the second addition of the hydrazine compound is divided into two stages: an early addition and a late addition, with a gap between the early and late additions while continuing stirring, and the amount of the hydrazine compound added in the later stage is greater than the amount added in the early stage.

6. A method for producing flake copper powder according to claim 4 or 5, wherein the cumulative 50% particle size by volume measured by a laser diffraction particle size distribution analyzer of the phosphorus-containing copper powder is 0.3 μm or more and less than 1.7 μm.

7. The method for producing flake copper powder according to claim 4 or 5, wherein the first and second hydrazine compounds are hydrazine, and the phosphoric acid or water-soluble phosphate is an alkali metal salt of pyrophosphate.

Images