TW202423573A - Copper powder, copper paste containing same, and method for producing conductive film - Google Patents

Abstract

A copper powder comprising copper particle A and copper particle B, wherein the content of copper particle A is 60-99 mass% and the content of copper particle B is 1-40 mass% on the basis of the total amount of copper particle A and copper particle B. [Copper particle A] A copper particle having a primary particle size of 0.1-0.6 [mu]m and comprising a core particle made of copper and a coating layer covering the surface of the core particle, wherein the coating layer is formed of a copper salt of an aliphatic organic acid. [Copper particle B] A copper particle having a primary particle size of 0.1-2.0 [mu]m, wherein the ratio (S1/B) of first crystallite size S1 determined from the half width of a peak originating from (111) plane of copper in an X-ray diffraction measurement to BET diameter B is 0.23 or less, and the ratio (S1/S2) of S1 to second crystallite size S2 determined from the half width of a peak originating from (220) plane is 1.35 or less.

Description

Copper powder, copper slurry containing the same, and method for producing conductive film

The present invention relates to a copper powder and a copper slurry containing the same. In addition, the present invention relates to a method for manufacturing a conductive film.

Copper is a metal with high electrical conductivity and is a highly versatile material, so it is widely used as a conductive material in industry. For example, copper powder, which is a collection of copper particles, is widely used as a raw material for various electronic parts such as external electrodes and internal electrodes of multilayer ceramic capacitors (hereinafter also referred to as "MLCC"), and wiring on various substrates.

As one of such copper powders, the applicant first proposed a technology for spherical copper particles, the average particle size of the primary particles of the spherical copper particles is 0.1 μm or more and 0.6 μm or less, and a surface treatment agent is applied to the particle surface (see patent document 1). According to this technology, the copper particles have the advantage of good low-temperature sintering properties. Prior art documents Patent document

Patent document 1: Japanese Patent Publication No. 2015-168878

However, when spherical copper particles are used to prepare a slurry and various conductive films are manufactured from the slurry, it is sometimes difficult to ensure the continuity of the conductive film due to the shape of the particles. On the other hand, flat copper particles are also known as copper particles. However, when flat copper particles are used to prepare a slurry and various conductive films are manufactured from the slurry, it is sometimes difficult to improve the density of the conductive film due to the shape of the particles. Therefore, in order to compensate for each other's shortcomings, spherical copper particles and flat copper particles are often used in combination. However, recently, in addition to the continuity and density of the conductive film, the low-temperature sintering property of the copper particles when manufacturing the conductive film is also required. If spherical copper particles and flat copper particles are simply mixed and used, the low-temperature sintering properties of the mixed copper particles will not be improved.

Therefore, the subject of the present invention is to provide a copper powder capable of manufacturing a conductive film with higher continuity and density and having a lower sintering temperature.

The present invention provides a copper powder comprising the following copper particles A and copper particles B, and relative to the total of copper particles A and copper particles B, the content ratio of copper particles A is 60 mass% or more and 99 mass% or less, and the content ratio of copper particles B is 1 mass% or more and 40 mass% or less. [Copper particles A] The copper particles have a core particle containing copper and a coating layer covering the surface of the core particle, the coating layer is formed of a copper salt of an aliphatic organic acid, and the primary particle size of the copper particles is 0.1 μm or more and 0.6 μm or less. [Copper particles B] The ratio (S1B) of the first crystallite size S1 obtained by the Sherlock formula based on the half-value width of the peak originating from the (111) plane of copper in the X-ray diffraction measurement to the BET diameter B calculated based on the BET specific surface area is 0.23 or less, The ratio (S1/S2) of the first crystallite size S1 to the second crystallite size S2 obtained by the Sherlock formula based on the half-value width of the peak originating from the (220) plane of copper in the X-ray diffraction measurement is 1.35 or less, and The primary particle size of the copper particles is 0.1 μm or more and 2.0 μm or less.

The present invention is described below based on its preferred embodiment. The copper powder of the present invention comprises the following copper particles A and copper particles B. [Copper particles A] The copper particles have a core particle comprising copper and a coating layer covering the surface of the core particle, the coating layer is formed of a copper salt of an aliphatic organic acid, and the primary particle size of the copper particles is 0.1 μm or more and 0.6 μm or less. [Copper particles B] The ratio (S1B) of the first crystallite size S1 obtained by the Sherlock formula based on the half-value width of the peak originating from the (111) plane of copper in X-ray diffraction measurement to the BET diameter B calculated based on the BET specific surface area is 0.23 or less, The ratio (S1/S2) of the first crystallite size S1 to the second crystallite size S2 obtained by the Sherlock formula based on the half-value width of the peak originating from the (220) plane of copper in X-ray diffraction measurement is 1.35 or less, and The primary particle size of the copper particles is 0.1 μm or more and 2.0 μm or less. Among them, those meeting the requirements of copper particles A are excluded.

The inventors of the present invention have conducted intensive research and surprisingly found that the sintering temperature of the copper powder containing copper particles A and B is relatively low, and the conductive film made from the copper slurry containing the copper powder has higher continuity and density.

From the viewpoint of further improving the above-mentioned effect, the copper particles A are preferably spherical in shape. On the other hand, the copper particles B are preferably flat in shape.

From the perspective of improving the sinterability of the copper powder of the present invention at low temperatures and improving the conductivity of the conductive film obtained by sintering the particles, the average image resolution diameter of the primary particles of the copper particles A is preferably 0.1 μm to 0.6 μm, more preferably 0.12 μm to 0.4 μm, and further preferably 0.15 μm to 0.3 μm. The so-called primary particle refers to an object that is identified as the smallest unit of a particle based on its geometric shape. From the same point of view, the average image resolution diameter of the primary particles of copper particles B is preferably 0.1 μm to 2.0 μm, more preferably 0.15 μm to 1.0 μm, and further preferably 0.2 μm to 0.6 μm.

Furthermore, the particle size of copper particles A calculated based on the BET specific surface area (hereinafter, also referred to as BET diameter A) is preferably 0.1 μm to 0.6 μm, more preferably 0.12 μm to 0.4 μm, and further preferably 0.15 μm to 0.3 μm. By making the BET diameter A in such a range, the thermal conductivity of the copper powder of the present invention can be improved and the sintering temperature can be effectively reduced. From the same point of view, the particle size of copper particles B calculated based on the BET specific surface area (hereinafter, also referred to as BET diameter B) is preferably 0.1 μm to 2.0 μm, more preferably 0.15 μm to 1.0 μm, and further preferably 0.2 μm to 0.6 μm. By making the BET diameter B in this range, the thermal conductivity of the copper powder of the present invention can be improved and the sintering temperature can be effectively reduced. In this specification, the BET diameter B is also referred to as the primary particle size of the copper particle B.

Regarding the average image resolution diameter of the primary particles of copper particles A and B, for example, a scanning electron microscope (JSM-6330F manufactured by JEOL Ltd.) can be used to observe the copper particles at a magnification of 10,000 or 30,000 times, and the maximum Feret diameter in the horizontal direction of 200 particles in the field of view is measured. Based on these measured values, the volume average particle diameter converted into a sphere is calculated. In this specification, the average image resolution diameter of the primary particles of copper particles A calculated in this way is also referred to as the primary particle diameter of copper particles A.

The BET diameters A and B calculated from the BET specific surface area can be measured based on the BET method under the following conditions. Specifically, the measurement can be performed using the nitrogen adsorption method using "Macsorb" manufactured by Mountech Co., Ltd. The amount of powder to be measured is set to 0.2 g, and the pre-degassing conditions are set to 30 minutes at 80°C under vacuum. In addition, the BET diameters A and B are calculated based on the measured BET specific surface area using the following formula (I). In formula (I), d is the BET diameter A or B [μm], A _BET is the specific surface area measured using the BET single point method [m ² /g], and ρ is the density of copper [g/cm ³ ]. d=6/( _ABET ×ρ) (I) Hereinafter, preferred embodiments of the copper particles A and B are described in detail.

<Preferred embodiment of copper particle A> Copper particle A is a particle having a surface treatment agent containing a copper salt of an aliphatic organic acid applied to the surface of the particle. Thus, a coating layer containing the surface treatment agent is formed in a manner that continuously or discontinuously covers the surface of a core particle containing copper. The surface treatment agent is used to inhibit both oxidation of copper and aggregation of particles. In addition, the core particle is preferably composed only of copper and remaining inevitable impurities.

As mentioned above, the surface treatment agent used in the present invention comprises a copper salt of an aliphatic organic acid.

In the present technical field, in order to take into account both the inhibition of copper oxidation in copper particles and the inhibition of agglomeration between particles, surface treatment agents such as fatty acids or fatty acid amines are used. However, such treatment agents have a high decomposition temperature and cannot be fully removed during sintering of copper particles. Therefore, there is a situation where the sintering starting temperature rises or the resistance of the conductive film obtained after the copper particles are sintered with each other increases. In order to solve this problem, the inventors conducted intensive research and found that by using a copper salt of an aliphatic organic acid as a surface treatment agent, both the oxidation of copper and the agglomeration of particles can be suppressed, and the sintering starting temperature can be lowered. As a result, the low-temperature sintering property of the particles can be improved, and the resistance of the conductive film obtained after sintering can be reduced.

From the viewpoint of lowering the sintering temperature of the copper powder of the present invention and taking into account both the inhibition of copper oxidation and the inhibition of aggregation of particles, the carbon number of the aliphatic organic acid constituting the copper salt of the aliphatic organic acid is preferably 6 to 18, more preferably 8 to 18, further preferably 10 to 18, further preferably 12 to 18. Examples of such aliphatic organic acids include linear or branched saturated or unsaturated carboxylic acids, or sulfonic acids having linear or branched saturated or unsaturated alkyl groups, preferably linear saturated or unsaturated carboxylic acids. The valence of copper in the copper salt of an aliphatic organic acid is monovalent or divalent, preferably divalent.

Specific examples of carboxylic acids include citric acid, caproic acid, heptanoic acid, caprylic acid, nonanoic acid, capric acid, lauric acid, palmitic acid, oleic acid, stearic acid, etc., preferably lauric acid, oleic acid and stearic acid, and more preferably lauric acid and stearic acid. Specific examples of sulfonic acids include hexanesulfonic acid, heptanesulfonic acid, octanesulfonic acid, nonanesulfonic acid, decanesulfonic acid, lauric sulfonic acid, palmitic acid, oleic acid, stearic acid, etc. These aliphatic organic acids can be used alone or in combination of two or more.

The surface treatment agent can be applied to the particle surface by bringing the obtained core particles into contact with a copper salt of an aliphatic organic acid as a surface treatment agent, for example, in a step after manufacturing the core particles containing copper. The amount of the surface treatment agent applied is expressed as the ratio (mass %) of the surface treatment agent as a whole in the copper particles A in the state where the surface treatment agent is applied, and is preferably set to 0.2 mass % or more and 2.0 mass % or less, and further preferably set to 0.3 mass % or more and 1.0 mass % or less in terms of carbon atoms. By being in this range, the oxide film on the surface of the copper particles can be removed by the surface treatment agent or the effect obtained by eutectic dissolution, thereby lowering the melting temperature of the copper particles, and as a result, the sintering temperature can be lowered.

The ratio (mass %) of the surface treatment agent applied to the surface of the copper particles A can be measured as follows. 0.5 g of copper powder, which is a collection of copper particles A to which the surface treatment agent is applied, is heated in an oxygen flow using a carbon-sulfur analyzer (EMIA-320V manufactured by Horiba, Ltd.) to decompose the carbon component in the copper powder into CO or CO ₂ and measure its amount, thereby calculating the ratio of the surface treatment agent.

The qualitative and quantitative analysis of the surface treatment agent can be performed using, for example, nuclear magnetic resonance (NMR), Raman spectroscopy, infrared spectroscopy, liquid chromatography, time-of-flight secondary ion mass spectrometry (TOF-SIMS), etc., alone or in combination.

The copper particles A have a coating layer formed on the surface of the core particles using a copper salt of an aliphatic organic acid as a surface treatment agent. Whether the coating layer is formed using a copper salt of an aliphatic organic acid can be determined, for example, by the following method. Specifically, the copper particles A are diluted with KBr so that the mass of the copper particles A becomes 5 mass %, and the emulsified and mixed test sample is measured using an infrared spectrophotometer (model: FT-IR4600) manufactured by JASCO Corporation by diffuse reflectance method at a resolution of 4 cm ^-1 and a cumulative number of 128 times, and a curve (spectrum) is obtained with the value obtained by Kubeka-Munk conversion of the absorbance on the vertical axis and the wave number (500 to 4000 cm ^-1 ) on the horizontal axis. At this time, if an infrared absorption peak is observed in the range of 1504 cm ^-1 to 1514 cm ^-1 , and is not observed in the range of 1584 cm ^-1 to 1596 cm ^-1 , it can be determined that the coating layer is formed using a copper salt of an aliphatic organic acid. That is, the copper particle A preferably has an infrared absorption peak observed in the range of 1504 cm ^-1 to 1514 cm ^-1 , and no infrared absorption peak is observed in the range of 1584 cm ^-1 to 1596 cm ^-1 in the measurement based on infrared spectroscopy. "Having an infrared absorption peak" is defined as follows. First, the IR (Infrared Ray) spectrum data normalized by the maximum value of the peak observed in the range of 2910 cm ^-1 to 2940 cm ^-1 is subjected to secondary differentiation, and waveform separation is performed based on the zero-up cut method in the range of 1500 cm ^-1 to 1600 cm ^-1 . Then, the arithmetic mean is calculated from the absolute value of the amplitude derived from the reference line (zero) in each waveform separated by waveform. And, when the absolute value of the peak height is greater than half of the arithmetic mean, it is regarded as "having an infrared absorption peak". Furthermore, in the case of copper particles using fatty acids or aliphatic amines as the surface treatment agent, an infrared absorption peak is detected in the range of 1584 cm ^-1 or more and 1596 cm ^-1 or less, and thus it can be distinguished from copper particles A in this respect.

The reason why copper particles that can inhibit both copper oxidation and particle aggregation and reduce the sintering temperature of the copper powder of the present invention can be obtained by using copper salts of aliphatic organic acids is not clear, but the inventors speculate as follows. As described above, the copper particles of the present invention and the copper particles using fatty acids or aliphatic amines as surface treatment agents differ in the presence or absence of infrared absorption peaks at specific wave numbers. The measurement principle of infrared spectroscopy is to measure the absorption of light energy equivalent to the kinetic energy of the bonds in the molecules by irradiating the substance or molecules of the measurement object with infrared rays. Generally speaking, when infrared absorption is observed in infrared spectroscopy, it indicates that certain bonds exist in the molecules. In particular, when infrared absorption is observed at a high wave number position, since the energy of infrared rays at high wave numbers is higher, it can be said that a bond with a larger bond energy exists in the molecule. When comparing copper particles A and copper particles using fatty acids or aliphatic amines as surface treatment agents, infrared absorption is observed in the low wave number region of 1504 cm ^-1 to 1514 cm ^-1 for both particles, so it is inferred that the absorption in this region means that the coating exists by bonding to the surface of the core particles. Therefore, it is believed that both oxidation of copper in the core particles and aggregation of particles can be suppressed. On the other hand, if we focus on the high wave number region in the range of 1584 cm ^-1 to 1596 cm ^-1 , the infrared absorption observed in the high wave number region is not observed in copper particle A. In contrast, the copper particles using fatty acids or aliphatic amines as surface treatment agents observe infrared absorption in the high wave number region. That is, compared with the copper particles using fatty acids or aliphatic amines as surface treatment agents, the copper particles of the present invention have fewer bonds with greater bonding energy in the molecules. It is believed that in the copper particles of the present invention, the bonding between the surface treatment agent and the core particles is relatively weak, so it is believed that the surface treatment agent is easily detached at low temperatures, and the particles can be sintered at low temperatures. Based on the above reasons, it is considered that by applying a surface treatment agent containing a copper salt of an aliphatic organic acid to the surface of the copper particles A, both oxidation of copper and aggregation of particles can be suppressed, and the sintering temperature can be lowered.

Furthermore, in order to identify the type of aliphatic organic acid constituting the copper salt of an aliphatic organic acid, the copper particles A can be analyzed by, for example, TOF-SIMS.

From the perspective of further lowering the sintering temperature of the copper powder of the present invention, in the thermogravimetric analysis when the copper particles A are heated from 25°C to 1000°C, the temperature at which the ratio of the mass loss value to the mass loss value at 500°C becomes 10% is preferably 150°C to 220°C, and further preferably 180°C to 220°C.

The above-mentioned thermogravimetric analysis can be performed, for example, by the following method. That is, using TG-DTA2000SA manufactured by Bruker AXS, the sample to be measured is set to 50 mg, and the mass reduction rate when heated from 25°C to 1000°C is measured. The atmosphere is set to nitrogen, and the heating rate is set to 10°C/min. The lower the temperature at which the mass reduction rate becomes a specified ratio, the lower the temperature at which the aliphatic organic acid forming the coating layer can be removed, and thus becomes the evaluation standard of the low-temperature sintering property of the copper particles A.

As mentioned above, the shape of the copper particle A is preferably spherical. In order to obtain a spherical copper particle A, for example, the shape of the core particle can be set to be spherical. Furthermore, the particle is spherical when the roundness coefficient measured by the following method is preferably 0.85 or more, and further preferably 0.90 or more. The roundness coefficient is calculated by the following method. Take a scanning electron microscope image of metal particles, and randomly select 1000 particles that do not overlap with each other. When the area of the two-dimensional projection image of the particle is set to S and the circumference is set to L, the roundness coefficient of the particle is calculated according to the formula 4πS/L ^2. The arithmetic mean of the roundness coefficients of each particle is taken as the above-mentioned roundness coefficient. When the two-dimensional projection image of the particle is a true circle, the roundness coefficient of the particle is 1.

<Preferred implementation method of copper particles B> The crystallite size of a specific crystal plane of copper particles B calculated by X-ray diffraction measurement is in a prescribed relationship. Specifically, when the particle size calculated based on the BET specific surface area is set as the BET diameter B, and the crystallite size obtained by the Scherrer formula based on the diffraction peak originating from the (111) plane of copper in the X-ray diffraction measurement is set as the first crystallite size S1, the ratio (S1/B) of the first crystallite size S1 to the BET diameter B is preferably 0.23 or less, more preferably 0.02 or more and 0.23 or less, and further preferably 0.05 or more and 0.23 or less.

The diffraction peak originating from the (111) plane of copper is a peak with the maximum height of the X-ray diffraction pattern obtained by X-ray diffraction measurement of copper particle B. It is therefore considered that the first crystallite size is larger than the crystallite size calculated from the diffraction peaks originating from other crystal planes, and also represents crystallinity. Therefore, it is inferred that by forming a structure in which the first crystallite size S1 is smaller than the BET diameter B, there are more grain boundaries in one particle. As a result, by the heat energy applied when heating the particles, the crystallite interface is easily unstable, and atomic diffusion becomes active, which can improve the fusion of particles at low temperatures and reduce the sintering temperature. Such copper particles can be obtained, for example, by the following manufacturing method.

The first crystallite size S1 of the copper particle B is preferably 10 nm to 80 nm, more preferably 20 nm to 75 nm, and further preferably 25 nm to 70 nm. By making the crystallite size S1 within such a range, it is easy to form more grain boundaries in one particle, which can further improve the weldability of the particle during heating and effectively reduce the sintering temperature.

In addition, the copper particles B are also preferably such that when the crystallite size obtained by the Scherrer formula based on the half-value width of the peak originating from the (220) plane of copper in the X-ray diffraction measurement is set as the second crystallite size S2, the ratio (S1/S2) of the first crystallite size S1 to the second crystallite size S2 is less than a specified value. Specifically, the S1/S2 ratio is preferably less than 1.35, more preferably greater than 0.1 and less than 1.3, and further preferably greater than 0.1 and less than 1.2.

Metallic copper easily adopts a face-centered cubic crystal structure, so copper particle B has a copper (111) plane on a specific surface of the particle surface, and a copper (220) plane on a surface intersecting the (111) plane. Furthermore, the smaller the S1/S2 ratio is, the less likely the copper particle will grow in the (111) plane direction, or the more likely it will grow in the (220) plane direction. Therefore, the S1/S2 being within the above-specified range is roughly related to the anisotropy of the particle shape, such as the copper particle B being flat. The so-called flat shape refers to a shape having a pair of main surfaces facing each other and side surfaces intersecting the main surfaces. When the copper particle B is flat, it is estimated that there is a copper (111) plane on the main surface of the copper particle B and a copper (220) plane on the side surface of the copper particle B. Therefore, by making the S1/S2 ratio within the above range, when the copper particles B are arranged with each other during sintering, the main surfaces of the copper particles B or the side surfaces of the particles are easy to contact each other, and the contact parts of the copper particles B are easy to become the same crystal plane. Compared with the case where the particles to which heat energy is applied are in contact with each other with different crystal planes, the utilization efficiency of heat energy is higher when the particles are in contact with each other with the same crystal plane, and the atoms at the microcrystalline interface are easier to diffuse. As a result, the welding property between the particles at low temperature can be improved, and the sintering temperature of the copper powder can be reduced. Compared with spherical particles or mechanically manufactured flat copper particles, this is advantageous in that the sintering performance can be further improved. In addition, the contact between the copper particles B is easily made into surface contact as described above, so the contact area is larger than that of spherical copper particles. Therefore, the conductive film made of the copper powder of the present invention containing the copper particles B has higher continuity. Such copper particles can be obtained, for example, by the following manufacturing method.

The second crystallite size S2 of the copper particles B is preferably 10 nm to 80 nm, more preferably 20 nm to 75 nm, and further preferably 30 nm to 70 nm. By making the crystallite size S2 within such a range, the low-temperature sintering property obtained due to the relatively small crystallite size can be improved, and more conductive paths derived from the shape of the copper particles can be formed, so that a low-resistance conductive film can be formed after sintering.

The copper particles B preferably have a ratio (S1/S3) of the first crystallite size S1 to the third crystallite size S3 of less than a specified value when the crystallite size obtained by the Scherrer formula based on the half-value width of the peak originating from the (311) plane of copper in X-ray diffraction measurement is set as the third crystallite size S3. Specifically, the S1/S3 ratio is preferably less than 1.35, more preferably greater than 0.20 and less than 1.30, and further preferably greater than 0.50 and less than 1.25.

Metallic copper tends to adopt a face-centered cubic crystal structure, so copper particle B has a copper (111) plane on a specific surface of the particle surface, and a copper (311) plane on a surface intersecting the (111) plane. Furthermore, the smaller the S1/S3 ratio is, the less likely copper particle B will grow in the (111) plane direction, or the more likely it will grow in the (311) plane direction. Therefore, the fact that S1/S3 is in the above-specified range is roughly related to the fact that the copper particle B is flat and has anisotropy in particle shape. In this case, it is estimated that the copper (111) plane exists on the main surface of copper particle B, and the copper (311) plane exists on the side surface of the copper particle. Therefore, by making the S1/S3 ratio within the above range, when the copper particles B are arranged with each other during sintering, the main surfaces of the copper particles B or the side surfaces of the copper particles B are easily in contact with each other, and the contact parts of the copper particles B are easy to become the same crystal plane. As a result, when the copper powder of the present invention is heated, the atomic diffusion of the microcrystalline interface of the copper particles B can be activated, the welding property of the particles at low temperature can be improved, and the sintering temperature of the copper powder can be reduced. Compared with spherical particles or mechanically manufactured flat copper particles, this is advantageous in that the sintering performance can be further improved. Such copper particles can be obtained, for example, by the following manufacturing method.

The third crystallite size S3 of the particle B is preferably 10 nm to 80 nm, more preferably 20 nm to 75 nm, and further preferably 30 nm to 70 nm. By making the crystallite size S3 within such a range, the low-temperature sintering property obtained due to the relatively small crystallite size can be improved, and more conductive paths derived from the shape of the copper particle B can be formed, so that a low-resistance conductive film can be formed after sintering.

The first crystallite size S1, the second crystallite size S2, and the third crystallite size S3 can be calculated using the Sherer formula shown below based on the full width of the half-value width of the diffraction peak originating from the (110) plane, (220) plane, or (311) plane of copper obtained by X-ray diffraction measurement. The conditions of the X-ray diffraction measurement are described in detail in the following examples. The PDF number is 00-004-0836. ･ Sherer formula: D = Kλ/βcosθ ･D: crystallite size ･K: Sherer constant (0.94) ･λ: wavelength of X-ray ･β: half-value width [rad] ･θ: diffraction angle

The copper particles B preferably contain copper elements as a main component. The copper elements as a main component means that the copper content in the copper particles is 97.0 mass % or more, preferably 97.5 mass % or more, more preferably 98.0 mass % or more, and further preferably 98.5 mass % or more. The copper content can be measured, for example, by ICP (Inductively Coupled Plasma) emission spectrometry.

The copper particles B contain not only the copper element but also other elements other than the copper element, or contain the copper element and do not contain other elements other than the copper element except for inevitable impurities. The copper particles B are allowed to contain trace amounts of inevitable impurity elements such as oxygen elements as long as the effect of the present invention is not impaired. In any embodiment, the content of other elements other than the copper element in the copper particles is preferably less than 1.5 mass %. The content of these elements can be measured, for example, by ICP emission spectrometry.

The copper particle B also preferably has a lower carbon content. Specifically, the carbon content in the copper particle B is preferably 5000 ppm or less, more preferably 4500 ppm or less, and further preferably 4000 ppm or less, the less the better, and in practice it is 100 ppm or more. By making the carbon content within this range, the sintering barrier caused by the organic matter present on the surface of the copper particle can be relatively suppressed. Such copper particles can be manufactured, for example, by the following manufacturing method.

The carbon content can be measured, for example, by gas analysis or combustion carbon deposition. When measuring the carbon content, first determine whether the surface of the copper particle B has been coated. Regarding the confirmation method, for example, there can be cited methods of confirmation using X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), Raman spectroscopy, infrared spectroscopy, liquid chromatography, time-of-flight secondary ion mass spectrometry (TOF-SIMS) and other methods alone or in combination. If it is determined by this method that the particle surface has been coated, the above methods are used alone or in combination to perform qualitative and quantitative analysis on the types and amounts of elements contained in the coating layer formed by the coating treatment. In addition, by using thermogravimetric measurement (TG), the physical properties of organic matter can be evaluated by measuring the mass change before and after the calcination temperature and the amount of carbon after heating to that temperature. When it is determined that the particle surface is not coated, the copper particle B as the measurement object is directly used for measurement, and the quantitative value obtained is used as the carbon content contained in the copper particle B.

The copper particle B also preferably has a phosphorus content within a specified range. Specifically, the phosphorus content in the copper particle is preferably 300 ppm or more, more preferably 300 ppm or more and 1500 ppm or less, and further preferably 300 ppm or more and 1000 ppm or more. By making the phosphorus content within such a range, the electrical conductivity of copper can be fully maintained, and the melting point is lowered, further reducing the sintering temperature. Such copper particles can be manufactured, for example, by the following manufacturing method. The presence and content of phosphorus in the copper particle B can be measured, for example, by ICP emission spectrometry.

As described above, the less carbon content of copper particles B, the less likely it is to cause sintering resistance, and the copper powder can be sintered at a lower temperature. However, if the carbon content is within the above range, the sintering resistance caused by the organic matter on the surface of copper particles B can be relatively suppressed, so the organic matter can be intentionally applied to the surface of copper particles B.

As the organic substance applied to the surface of the copper particle B, for example, copper salts of various fatty acids or aliphatic organic acids, and aliphatic amines can be cited. By applying such an organic substance to the surface of the copper particle B, the aggregation between the copper particles can be suppressed. In terms of improving the low-temperature sintering property of the copper powder, it is particularly preferred to use a saturated or unsaturated fatty acid or aliphatic amine with a carbon number of 6 to 18, especially a carbon number of 10 to 18. As specific examples of such fatty acids or aliphatic amines, benzoic acid, valeric acid, caproic acid, caprylic acid, nonanoic acid, capric acid, lauric acid, palmitic acid, oleic acid, stearic acid, amylamine, hexylamine, octylamine, decylamine, laurylamine, oleylamine, stearylamine, etc. These fatty acids or aliphatic amines can be used alone or in combination of two or more.

The shape of the copper particle B is not particularly limited as long as it can exert the effect of the present invention. When produced by the following method, it is preferably flat. Such particles have a pair of substantially flat main surfaces facing each other, and side surfaces intersecting the two main surfaces, and are plate-shaped with the maximum diameter of the main surface being greater than the thickness. In this case, it is also preferred that when the main surface of the copper particle B is viewed from above, its shape has a contour defined by a combination of straight lines, or a combination of straight lines and curves.

The conductive film made of the copper slurry containing the copper powder of the present invention has high density and continuity. From the perspective of further improving the density and continuity of the conductive film, the content ratio of copper particles A is preferably 60 mass% to 99 mass%, more preferably 65 mass% to 88 mass%, and further preferably 70 mass% to 85 mass%. From the same perspective, the content ratio of copper particles B is preferably 1 mass% to 40 mass%, more preferably 12 mass% to 35 mass%, and further preferably 15 mass% to 30 mass%.

Next, the preferred method for producing the copper powder of the present invention is described. The copper powder of the present invention is preferably produced by mixing copper particles A and copper particles B at the above-mentioned preferred ratio. The preferred method for producing copper particles A and copper particles B, and the method for mixing copper particles A and copper particles B are described in detail below.

<Method for producing copper particles A> First, a preferred method for producing copper particles A is described. This method is to bring a core particle containing copper into contact with a solution containing a copper salt of an aliphatic organic acid to form a coating layer that covers the surface of the core particle.

First, before surface treatment with a copper salt of an aliphatic organic acid, core particles containing copper are prepared. The method for producing the copper core particles can be produced, for example, by a wet method described in Japanese Patent Publication No. 2015-168878. That is, a reaction solution containing a monovalent or divalent copper source such as copper chloride, copper acetate, copper hydroxide, copper sulfate, copper oxide or cuprous oxide in a liquid medium containing water and preferably a monohydric alcohol having 1 to 5 carbon atoms is prepared. The reaction solution is mixed with hydrazine in a ratio of preferably 0.5 to 50 mol relative to 1 mol of copper, and the copper source is reduced to obtain core particles containing copper. The core particles obtained by the method are not treated with a surface treatment agent such as copper salt of aliphatic organic acid, and have a smaller particle size.

The core particles obtained by the above steps are preferably washed. As a washing method, for example, decanting or rotary filtration can be cited. When the core particles are washed by rotary filtration, for example, an aqueous slurry is prepared in which the core particles are dispersed in a solvent such as water, and the slurry is washed until the conductivity of the slurry is preferably less than 2.0 mS. Regarding the washing conditions at this time, for example, when water is used as a washing solvent, the washing temperature can be set to be greater than 15°C and less than 30°C, and the washing time can be set to be greater than 10 minutes and less than 60 minutes. By making the conductivity of the slurry within the above range, the core particles of the cleaning object can be efficiently subjected to the following surface treatment in a uniformly dispersed state without agglomeration. From the perspective of improving both cleaning efficiency and particle dispersibility, the content ratio of the core particles containing copper in the slurry is preferably 5 mass % or more and 50 mass % or less.

In addition, as another method for manufacturing core particles containing copper, for example, the direct current thermal plasma (DC plasma) method described in the specification of International Publication No. 2015/122251 can also be used instead of the above method. In detail, the direct current thermal plasma method, which is a type of PVD (Physical Vapor Deposition) method, can be performed on the copper mother powder to generate core particles from the mother powder. The core particles obtained by this method also do not have a surface treatment agent such as copper salt of aliphatic organic acid applied to their surface, and the particle size is relatively small. The obtained core particles can be crushed or graded as needed to separate or remove coarse particles or fine particles.

Next, the core particles obtained by the above method are surface treated with a surface treatment agent to form a coating layer covering the surface of the core particles. As a surface treatment method, for example, a method of contacting the core particles with a solution obtained by dissolving a copper salt of an aliphatic organic acid in a solvent can be adopted. In this step, the form of the core particles contacting the copper salt of an aliphatic organic acid can be an aqueous slurry in which the core particles are dispersed in a solvent such as water, or can be a dry state in which the core particles are not dispersed in a solvent, etc. In addition, regarding the contact sequence in this step, one of the core particles and the copper salt solution of an aliphatic organic acid can be added to the other, or the core particles and the copper salt solution of an aliphatic organic acid can be contacted at the same time. From the perspective of uniformly treating the surface of the core particles with the copper salt of an aliphatic organic acid, it is preferable to adopt a method of adding a solution of the copper salt of an aliphatic organic acid to the slurry in which the core particles are dispersed.

The following is an example of a method for surface treatment by adding core particles to a copper salt solution of an aliphatic organic acid. First, the solvent used for the copper salt solution of an aliphatic organic acid is heated to a temperature below the boiling point of the solvent used (for example, above 25°C and below 80°C), and in this state, the copper salt of an aliphatic organic acid is added to the solvent to prepare the copper salt solution of an aliphatic organic acid. Then, the temperature of the copper salt solution is maintained above the melting point of the copper salt of an aliphatic organic acid, and in this state, the dried core particles or the slurry containing the core particles are added to the copper salt solution of an aliphatic organic acid, and then stirred for 1 hour to perform surface treatment on the surface of the core particles. The copper particles A obtained by the method are formed with a coating layer containing a copper salt of an aliphatic organic acid formed on the surface of a core particle containing copper. When a slurry containing core particles is used for surface treatment, it is preferred to heat the slurry to a temperature above the melting point of the copper salt of an aliphatic organic acid in order to uniformly form the coating layer on the surface of the core particles.

In the surface treatment using a solution of a copper salt of an aliphatic organic acid, the content of the copper salt of an aliphatic organic acid in the reaction solution containing the core particles is preferably set to 0.1 mass part or more and 3.0 mass parts or less, and more preferably set to 0.2 mass part or more and 2.0 mass parts or less, relative to 100 mass parts of the core particles that have not been surface treated. By performing the surface treatment with such an amount, copper particles A that have been surface treated with the above carbon atomic ratio can be obtained.

Solvents for dissolving copper salts of aliphatic organic acids include organic solvents such as monohydric alcohols having 1 to 5 carbon atoms, polyhydric alcohols, esters of polyhydric alcohols, ketones, and ethers. Among these, monohydric alcohols having 1 to 5 carbon atoms are preferably used from the viewpoints of compatibility with water, economy, handling properties, and ease of removal, and more preferably, aqueous methanol solutions, ethanol, 1-propanol, or isopropanol are used.

The copper particles A obtained through the above steps can be washed or solid-liquid separated as needed, and then dispersed in water or an organic solvent to form a slurry and mixed with the copper particles B. Alternatively, the copper particles A can be dried and mixed with the copper particles B in the form of a dry powder of a collection of copper particles. In either case, the copper powder of the present invention can contain the copper particles A to obtain an excellent copper powder that suppresses oxidation of copper as a constituent metal, suppresses aggregation of particles, and has a lower sintering temperature.

<Method for producing copper particles B> Next, a preferred method for producing copper particles B is described. This production method has the following two reduction steps: a first reduction step, reducing copper ions to produce cuprous oxide; and a second reduction step, reducing cuprous oxide to produce copper particles in the presence of polyphosphoric acid or salts thereof of diphosphoric acid or higher (hereinafter also referred to as polyphosphoric acids). The polyphosphoric acid may be present in the reaction system at any stage during or before the second reduction step. That is, the polyphosphoric acid may be present in the reaction system before or during the first reduction step, and the second reduction step may be performed in this state. Alternatively, the polyphosphoric acid may not be present in the reaction system in the first reduction step, but may be present in the reaction system after the first reduction step and during or just before the second reduction step.

From the perspective of uniform control of the reduction reaction, improved productivity of the copper particles obtained thereby, and reduced manufacturing costs, it is preferred that any reduction step of the present production method is carried out under wet conditions in an aqueous liquid, and it is also preferred that any reduction step is carried out in the same reaction system. The following is an example of a production method under wet conditions and in the same reaction system.

First, a reaction solution containing a copper source and a reducing compound is prepared, and the first reduction step is performed to reduce copper ions and generate cuprous oxide in the solution. Regarding the preparation of the reaction solution, each raw material can be added to a solvent at the same time to prepare the reaction solution, or each raw material can be added to the solvent in any order. From the perspective of easily controlling the reduction reaction of copper ions and improving the handling properties during manufacturing, it is better to pre-mix the copper source with a solvent to prepare a copper-containing solution, and then add a solid reducing compound or a reducing compound solution pre-dissolved in a solvent to the copper-containing solution. The reducing compound can be added all at once or successively.

In the first reduction step, as described above, polyphosphoric acid may or may not be contained in the reaction solution. When polyphosphoric acid is present in the reaction solution, it is possible to effectively control the reduction of copper ions and crystal growth by the reducing compound, and it is preferred to add the copper source, polyphosphoric acid, and reducing compound in sequence.

The solvent in the reaction solution may be water or a lower alcohol such as methanol, ethanol, propanol, etc. These may be used alone or in combination.

The copper source used in the first reduction step may be a compound that generates copper ions in the reaction solution, preferably a water-soluble copper compound. Specific examples of such a copper source include copper compounds such as copper formate, copper acetate, copper propionate, and copper inorganic salts such as copper nitrate and copper sulfate. The copper compounds may be anhydrous or hydrated. The copper compounds may be used alone or in combination.

The content of the copper source in the reaction system in the first reduction step is preferably 0.01 mol/L to 2.0 mol/L, more preferably 0.1 mol/L to 1.5 mol/L, expressed as the molar concentration of the copper element. By being within this range, copper particles with a smaller particle size and a smaller crystallite size on a specific crystal plane can be produced with high productivity.

As the reducing compound, water-soluble compounds are preferably exemplified. Specific examples of the reducing compound include: hydrazine compounds such as hydrazine, hydrazine hydrochloride, hydrazine sulfate and hydrazine hydrate; boron compounds such as sodium borohydride or dimethylamine borane and their salts; sulfuric acid salts such as sodium sulfite, sodium hydrogen sulfite and sodium thiosulfate; nitrogen acid salts such as sodium nitrite and sodium hyponitrite; phosphorous acid salts such as phosphorous acid, sodium phosphite, hypophosphorous acid and sodium hypophosphite and their salts. These reducing compounds may be anhydrous or hydrated. These reducing compounds may be used alone or in combination of two or more.

From the viewpoint of easily controlling the reduction product in the first reduction step to become cuprous oxide, easily controlling the grain growth of copper in the subsequent reduction step and easily obtaining particles with a specified crystallite size, and reducing the accidental mixing of impurities such as carbon after reduction, the reducing compound in the reducing solution is preferably a hydrazine compound, and more preferably an anhydrate or a hydrate of hydrazine.

The content of the reducing compound in the reaction solution in the first reduction step is preferably set to 0.1 mol or more and 2 mol or less, and more preferably set to 0.1 mol or more and 1 mol or less, relative to 1 mol of the copper element. By controlling the concentration of the reducing compound within this range, the reduction reaction of copper ions and the progress of grain growth can be appropriately controlled, and copper particles with smaller particle size and smaller crystallite size on a specific crystal plane can be obtained with high productivity.

When a reducing compound, particularly a hydrazine compound, is used, the degree of reducing property can be appropriately controlled to the extent that reduction to cuprous oxide is performed and reduction to metallic copper is not performed, and the crystal growth of copper in the second reduction step can be easily made anisotropic. The reaction solution in the first reduction step is preferably under an acidic condition with a pH value of 3 or more and 5 or less at 25° C. In order to appropriately control the degree of reduction of copper ions, it is preferred to add the reducing compound after the pH value is adjusted in the first reduction step.

Regarding the adjustment of pH value, as long as the effect of the present invention is exerted, various acids or alkaline substances can be used, or polyphosphoric acid can be present in the reaction solution. In particular, when adjusting the pH value, by using polyphosphoric acid, the subsequent reaction can be efficiently carried out even without adding other substances to the reaction system, which is advantageous in preventing accidental mixing of impurities and efficiently obtaining the target copper particles.

The reduction reaction in the first reduction step can be carried out without heating the reaction solution or in a heated state. In either case, the temperature of the reaction solution is preferably set to 10°C to 60°C, more preferably 20°C to 50°C. The reaction time in the first reduction step is preferably set to 0.1 hour to 2 hours, more preferably 0.2 hour to 1 hour, under the above temperature range. In addition, from the perspective of uniformity of the reduction reaction, it is also preferred to continuously stir the reaction solution from the reaction start time point to the reaction end time point.

Then, a second reduction step is performed to reduce the cuprous oxide obtained in the first reduction step to generate metal copper particles. The second reduction step is also preferably performed under wet conditions like the first reduction step, and more preferably, the two reduction steps are performed in the same reaction system.

As described above, it is preferred that polyphosphoric acids are present in the reaction system during or before the second reduction step. Examples of polyphosphoric acids used in the present production method include diphosphoric acid (H ₄ P ₂ O ₇ ), triphosphoric acid (tripolyphosphoric acid, H ₅ P ₃ O ₁₀ ), tetrapolyphosphoric acid (H ₆ P ₄ O ₁₃ ), and polyphosphoric acids having preferably 2 to 8, more preferably 2 to 5, phosphate monomer units in the structure, and salts thereof. Examples of polyphosphate salts include alkali metal salts, alkali earth metal salts, other metal salts, ammonium salts, and the like. These can be used alone or in combination.

The content of the polyphosphoric acid in the second reduction step is preferably set to 0.1 millimole or more, and more preferably set to 0.1 millimole or more and 1 mole or less, relative to 1 mole of the copper element. By making the concentration of the polyphosphoric acid in such a range, the crystal growth of copper due to the reduction reaction of cuprous oxide can be performed in an anisotropic manner, and copper particles with a smaller particle size and a smaller crystallite size on a specific crystal plane can be obtained with high productivity. Furthermore, when polyphosphoric acid is present at the time point of the first reduction step, the polyphosphoric acid is not consumed in the reaction of the first reduction step, and the concentration of the polyphosphoric acid does not substantially change before and after the first reduction step. Therefore, by adding polyphosphoric acid to the reaction system in the first reduction step within the above concentration range, the amount of polyphosphoric acid present that is suitable for reduction to metallic copper and grain growth in the second reduction step can be sufficiently achieved.

In the second reduction step, the above-mentioned reducing compound can be added to reduce to metallic copper. The content of the reducing compound in the reaction solution in the second reduction step is preferably set to 1 mol or more and 8 mol or less, and more preferably set to 2 mol or more and 6 mol or less, relative to 1 mol of the copper element. When the second reduction step is carried out in the same reaction system as the first reduction step, from the perspective of both improving the reducing property and controlling the reduction of impurities, it is preferred to further add the reducing compound to the solution in a manner to achieve the above-mentioned content. In addition, the type of reducing compound is preferably the same compound used in each reduction step. By controlling the concentration of the reducing compound within this range, the reduction reaction to metallic copper can be fully carried out, and copper particles with smaller particle size and smaller crystallite size on specific crystal planes can be obtained with high productivity.

The reducing compound in the second reduction step may be added all at once or in succession. From the perspective of efficiently obtaining copper particles satisfying the above-mentioned crystallite size ratio or particle size, successive addition is preferred.

When using reducing compounds, especially hydrazine compounds, the residual copper ions and cuprous oxide in the reaction solution can be efficiently reduced to metallic copper, so that the crystal growth of copper is anisotropic. The reaction solution in the second reduction step is preferably under non-acidic conditions (neutral or alkaline conditions) with a pH value of 7.0 or above at 25°C. In order to properly control the degree of reduction of copper ions, the pH value is preferably adjusted before adding the reducing compound in the second reduction step. Various acids or alkaline substances can be used to adjust the pH value. When the second reduction step is performed in the same reaction system as the first reduction step, the reaction solution after the first reduction step becomes acidic, so it is preferred to adjust the pH of the reaction solution by adding alkaline substances such as sodium hydroxide or potassium hydroxide. In order to efficiently reduce copper ions and cuprous oxide, it is preferred to add a reducing compound after adjusting the pH in the second reduction step.

From the viewpoint of efficiently reducing the copper ions and cuprous oxide in the reaction solution and obtaining copper particles with a predetermined crystallite size with high productivity, it is preferred to heat the reaction solution in the second reduction step. Regarding the heating conditions of the reaction solution, it is preferred to heat the reaction solution in a manner that the temperature is maintained at 10°C to 60°C, especially 20°C to 50°C, from the start time point of the second reduction step, i.e., the time point of adding the reducing compound, to the end time point of the reaction. The reaction time is preferably set to 30 minutes to 720 minutes under the above temperature conditions. Furthermore, from the viewpoint of uniformly causing the reduction reaction and obtaining copper particles with smaller particle size differences, it is also preferred to continuously stir the reaction solution from the reaction start time point to the reaction end time point.

The inventors speculate as follows as to why copper particles with a lower sintering temperature can be obtained by performing a two-stage reduction step in which copper ions are reduced to metallic copper via cuprous oxide and by the presence of polyphosphoric acid during the second reduction step in the present manufacturing method. First, in the first reduction step, copper ions are reduced by a reducing compound in the reaction solution to generate very fine particles of cuprous oxide in the reaction solution. Then, in the second reduction step, monovalent copper ions dissolved from the cuprous oxide particles are reduced to form metallic copper cores. The cores are very unstable, so the cores repeatedly combine with each other or redissolve in the reaction solution, and finally the particles grow. If polyphosphate is present during the growth of the particle, the polyphosphate is adsorbed on a specific crystal face of copper, inhibiting the growth in the direction of the crystal face. On the other hand, the growth of the crystal face that does not adsorb polyphosphate is not inhibited, and the growth in the direction of the crystal face proceeds. Based on the fact that metallic copper easily adopts a face-centered cubic structure and the results of X-ray diffraction measurement of the obtained copper particles, it is inferred that the crystal face that adsorbs polyphosphate is the (111) face of copper in the particle, and the crystal face that does not adsorb polyphosphate is inferred to be the (220) face of copper located in the perpendicular direction to the (111) face of copper. It is believed that the growth of the copper (111) plane is suppressed, and the growth of the copper (220) plane is anisotropic, resulting in flat copper particles with a lower sintering temperature.

In addition, regarding the preferred method for producing copper particles B, in particular, by carrying out the reduction reaction under acidic conditions in the first reduction step, it is possible to control the reducing force to a degree that copper ions can be reduced to cuprous oxide and cannot be reduced to metallic copper. In addition, it is also easy to control the subsequent metallic copper generation reaction. Thereafter, by setting the conditions to non-acidic conditions, the dissolution rate of cuprous oxide can be reduced and the supply of monovalent copper ions can be controlled. By carrying out the second reduction in this environment, the reaction rate of reduction to metallic copper can be adjusted to a slow condition, which is particularly advantageous in terms of being able to control the nuclear growth rate.

The copper particles B obtained through the above steps satisfy the above-mentioned preferred crystallite size and ratio, preferred particle size, preferred content of various elements such as carbon, and have a flat shape even when they do not contain organic components such as organic amines or amino alcohols, reducing sugars, etc. that control crystal growth. In addition, the crystal planes of the copper particles B obtained in this way that exist on the main surface and grow in a direction perpendicular to the main surface, and the crystal planes of the crystals that exist on the side surface and grow in a direction along the main surface have specific orientation directions, and each crystal plane is uniformly formed in one direction. Therefore, when copper powder containing copper particles B is used and sintered in a state where the main surfaces of the copper particles B are in contact with each other or the side surfaces of the copper particles B are in contact with each other, since the evenly arranged identical crystal planes are in contact with each other, the energy required for welding is not excessively required and sintering can be performed at a low temperature.

The copper particles B obtained through the above steps can be washed or solid-liquid separated as needed, and then dispersed in water or an organic solvent to form a slurry and mixed with copper particles A. The particles can also be dried to form a dry powder of a collection of copper particles B and mixed with copper particles A. In either case, copper particles B are excellent copper particles with a lower sintering temperature. Copper particles B can be further surface coated with organic substances such as fatty acids or their salts, or inorganic substances such as silicon compounds, in order to improve the dispersibility of the particles. Furthermore, as long as the effect of the present invention is exerted, it is permitted that the surface of the obtained copper particle B is inevitably oxidized in a small amount and contains elements other than copper.

<Method for mixing copper particles A and copper particles B> Copper particles A and copper particles B can be mixed in a dry or wet manner. From the perspective of the ease of mixing, it is preferred to mix in a dry manner. Dry mixing can be performed using a known dry mixing device. Regarding wet mixing, specifically, mixing can be performed in an organic solvent or an aqueous solvent.

The copper powder of the present invention can also be further dispersed in an organic solvent or resin, etc., and used in the form of a conductive composition such as conductive ink or copper paste. When the copper powder of the present invention is made into a conductive composition, the conductive composition at least contains copper powder and an organic solvent. As an organic solvent, the same solvent as that used in the past in the technical field of conductive compositions containing metal powder can be used without particular restrictions. As such an organic solvent, for example: monohydric alcohol, polyhydric alcohol, polyhydric alcohol alkyl ether, polyhydric alcohol aryl ether, polyether, ester, nitrogen-containing heterocyclic compound, amide, amine and saturated hydrocarbon can be cited. These organic solvents can be used alone or in combination of two or more. Among them, polyethers such as polyethylene glycol and polypropylene glycol are preferred from the viewpoint of having a higher reduction effect and preventing accidental oxidation of copper particles during sintering. From the same viewpoint, when polyethylene glycol is used as an organic solvent, its number average molecular weight is preferably greater than 120 and less than 400, and more preferably greater than 180 and less than 400.

If necessary, at least one of a dispersant, an organic medium and a glass frit may be further added to the conductive composition containing the copper powder of the present invention. Examples of the dispersant include: a dispersant such as a non-ionic surfactant that does not contain sodium, calcium, phosphorus, sulfur and chlorine. Examples of the organic medium include: a mixture of a resin component such as an acrylic resin, an epoxy resin, ethyl cellulose, and carboxyethyl cellulose, and a terpene solvent such as terpineol and dihydroterpineol, and an ether solvent such as ethyl carbitol and butyl carbitol. Examples of the glass frit include: borosilicate glass, barium borosilicate glass, zinc borosilicate glass, etc.

The conductive composition containing the copper powder of the present invention can be formed into a conductive film containing copper by coating it on a substrate to form a coating and firing the coating. The conductive film is suitable for forming a circuit of a printed wiring board or ensuring electrical conduction of an external electrode of a ceramic capacitor. As a substrate, depending on the type of electronic circuit using copper particles, examples include a printed circuit board containing glass epoxy resin or a flexible printed circuit board containing polyimide or the like.

The amount of copper powder and organic solvent in the conductive composition containing the copper powder of the present invention can be adjusted according to the specific use of the conductive composition or the coating method of the conductive composition. The content of copper powder in the conductive composition is preferably 5 mass % to 95 mass %, and more preferably 80 mass % to 90 mass %. As the coating method, for example, inkjet method, dispensing method, microdispensing method, gravure printing method, screen printing method, dip coating method, rotary coating method, spray coating method, rod coating method, roller coating method, etc. can be used.

The heating temperature when sintering the formed coating film can be above the sintering starting temperature of the copper powder, for example, it can be set to be above 150°C and below 220°C. Regarding the atmosphere during heating, for example, it can be carried out in an oxidizing atmosphere or a non-oxidizing atmosphere. As an oxidizing atmosphere, for example, an oxygen-containing atmosphere can be cited. As a non-oxidizing atmosphere, for example, reducing atmospheres such as hydrogen or carbon monoxide, weakly reducing atmospheres such as a hydrogen-nitrogen mixed atmosphere, and inert atmospheres such as argon, neon, helium and nitrogen can be cited. When using any atmosphere, the heating time is preferably set to be above 1 minute and below 3 hours, and more preferably to be set to be above 3 minutes and below 2 hours, with heating being carried out within the above-mentioned temperature range.

The conductive film obtained in this way is obtained by sintering the copper powder of the present invention, so it can be fully sintered even when sintering is performed under relatively low temperature conditions. In addition, during sintering, the copper particles constituting the copper powder will also melt at low temperatures, so the contact area between the copper particles or between the copper particles and the surface of the substrate can be increased, resulting in a higher adhesion with the bonding object and a dense sintered structure can be formed efficiently. Furthermore, the continuity, density and conductive reliability of the obtained conductive film are higher.

The present invention has been described above based on its preferred embodiments, but the present invention is not limited to the above embodiments. For example, the copper powder of the present invention may also contain copper particles other than copper particles A and copper particles B within the range of exerting the expected effect.

The above-mentioned implementation method of the present invention includes the following technical ideas. [1] A copper powder, which includes the following copper particles A and copper particles B, and relative to the total of copper particles A and copper particles B, the content ratio of copper particles A is 60 mass% or more and 99 mass% or less, and the content ratio of copper particles B is 1 mass% or more and 40 mass% or less, [Copper particles A] The copper particles have a core particle containing copper and a coating layer covering the surface of the core particle, the coating layer is formed by a copper salt of an aliphatic organic acid, and the primary particle size of the copper particles is 0.1 μm or more and 0.6 μm or less; [Copper particles B] The ratio (S1/B) of the first crystallite size S1 of the copper particle obtained by the Sherlock formula based on the half-value width of the peak originating from the (111) plane of copper in the X-ray diffraction measurement to the BET diameter B calculated based on the BET specific surface area is 0.23 or less, the ratio (S1/S2) of the first crystallite size S1 to the second crystallite size S2 obtained by the Sherlock formula based on the half-value width of the peak originating from the (220) plane of copper in the X-ray diffraction measurement is 1.35 or less, and the primary particle size of the copper particle is 0.1 μm or more and 2.0 μm or less. [2] The copper powder as described in [1], wherein the ratio (S1/S3) of the first crystallite size S1 of the copper particle B to the third crystallite size S3 calculated by the Scherrer equation based on the half width of the peak originating from the (311) plane of copper in X-ray diffraction measurement is 1.35 or less. [3] The copper powder as described in [1] or [2], wherein the copper particle B contains carbon element, and the content of the carbon element is 5000 ppm or less. [4] The copper powder as described in any one of [1] to [3], wherein the copper particle B contains phosphorus element, and the content of the phosphorus element is 300 ppm or more. [5] A copper slurry comprising the copper powder as described in any one of [1] to [4]. [6] A method for manufacturing a conductive film, comprising applying the copper slurry described in [5] to a substrate to form a coating, and then firing the coating. Example

The present invention is described in more detail below by way of examples. However, the scope of the present invention is not limited to the examples. Unless otherwise specified, "%" means "mass %".

In the following embodiments and comparative examples, copper particles A-1, copper particles A-2, and copper particles B-1 to B-3 are used as copper particles. Among them, copper particles A-2 use spherical copper particles described in Japanese Patent Publication No. 2015-168878. Other copper particles are manufactured by the following method.

[Manufacturing of copper particles A-1] According to the method described in Example 1 of Japanese Patent Publication No. 2015-168878, a slurry was prepared by dispersing spherical core particles (copper: 100 mass%) without applying a surface treatment agent in water. The slurry was washed at 25°C for 30 minutes by a rotary filter to obtain a slurry of washed core particles. The conductivity after washing was 1.0 mS, and the shape was spherical. In addition, the content of the core particles containing copper in the slurry was 1000 g (10 mass%).

Next, the slurry of the washed core particles was heated to 50°C, and in this state, a solution of 17 g of copper laurate (II) dissolved in 4 L of isopropanol was instantly added as a surface treatment agent, and stirred at 50°C for 1 hour. Thereafter, solid-liquid separation was performed by filtration, and copper particles having a coating layer of copper salt of an aliphatic organic acid formed on the surface of the core particles were obtained as solid components. The content of the surface treatment agent of the obtained copper particles was 0.7% by mass in terms of carbon atoms. Next, the following evaluations were performed on copper particles A-1 and A-2.

[Measurement of the average image resolution diameter of primary particles] The average image resolution diameter of primary particles of copper particles was measured by the above method. The results are shown in Table 1 below.

[Calculation of BET diameter A based on BET specific surface area] First, the specific surface areas of copper particles A-1 and A-2 were measured by the BET single point method using the above-mentioned measurement method, and the BET diameter A was calculated based on the specific surface areas. The results are shown in Table 1.

[Evaluation of the temperature at which the mass decreases by 10%] In the thermogravimetric analysis conducted under the above conditions when heating from 25°C to 1000°C, the temperature at which the mass decrease becomes 10% relative to the mass decrease at 500°C is determined. The results are shown in Table 1.

[Evaluation of infrared absorption peak] Copper particles A-1 and A-2 were measured by infrared spectroscopy using the above method. The ranges from 1504 cm ^-1 to 1514 cm ^-1 and from 1584 cm ^-1 to 1596 cm ^-1 were taken as the objects, and those with infrared absorption peaks were evaluated as "yes", and those without infrared absorption peaks were evaluated as "no". The results are shown in Table 1.

[Table 1] Copper particles Copper particles A-1 Copper particles A-2 Surface treatment agent Type Copper(II) laurate Lauric acid Added amount based on carbon atom conversion [%] 1.7 1.3 BET diameter A[μm] 0.21 0.22 Average image resolution diameter of primary particles (primary particle size) [μm] 0.18 0.19 Is there an infrared absorption peak? 1504～1514 cm ^-1 have have 1584～1596 cm ^-1 without have 10% mass reduction temperature [℃] 187 246

[Production of copper particles B-1] <First reduction step> 2.5 kg of copper acetate monohydrate as a copper source and 8.0 g of sodium tripolyphosphate (molar ratio relative to 1 mol of copper element: 0.002) as a polyphosphoric acid were added to a stainless steel tank containing 5.0 liters of warm pure water and 5.0 liters of methanol, and stirred for 30 minutes at a liquid temperature of 25°C to dissolve both. Next, 235.0 g of hydrazine (molar ratio relative to 1 mol of copper element: 1.55) was added to the solution, and the solution was stirred for 30 minutes without heating at a liquid temperature of 25°C to generate microparticles of cuprous oxide in the solution. After the generation of cuprous oxide, the reaction solution was stirred for 30 minutes.

<Second reduction step> Then, a 25% NaOH aqueous solution was added to the reaction solution in the first reduction step to adjust the pH value of the solution to 7.0. Thereafter, the liquid temperature was heated to 40°C, and 1900.0 g of hydrazine (molar ratio relative to 1 mole of copper element: 3.0) was quantitatively added to the solution over 10 minutes to perform the second reduction step. Thereafter, the solution was cooled to a liquid temperature of 30°C, and stirring was continued for 150 minutes to obtain copper particles in which the cuprous oxide microparticles were reduced to metallic copper.

The aqueous slurry of the copper particles obtained in this way was washed by decanting until the conductivity reached 1.0 mS (washed slurry). The washed core particle slurry was heated to 50°C, and in this state, a solution prepared by dissolving 4 g of copper laurate (II) in 1 L of isopropanol was instantly added as a surface treatment agent, and stirred at 50°C for 1 hour. Thereafter, solid-liquid separation was performed by filtration, and copper particles having a coating layer of copper salt of an aliphatic organic acid formed on the surface of the core particles were obtained as solid components. Thereafter, drying was performed to obtain copper powder containing aggregates of copper particles. The copper content of the obtained copper particles exceeds 98% by mass and they are flat in shape.

[Manufacturing of copper particles B-2] Copper particles B-2 were manufactured in the same manner as copper particles B-1, except that the amount of sodium tripolyphosphate added was set to 24 g (molar ratio relative to 1 mole of copper element: 0.006). The copper particles obtained had a copper element content of more than 98% by mass and had a flat shape.

[Production of copper particles B-3] 4 kg of copper sulfate pentahydrate and 120 g of aminoacetic acid were dissolved in water to prepare 8 L of copper salt aqueous solution at a liquid temperature of 70°C. Then, while stirring the aqueous solution, 6.6 kg of 25 mass% sodium hydroxide solution was added at a constant rate over a period of about 5 minutes. Then, the solution was stirred at a liquid temperature of 70°C for 60 minutes and aged until the solution color completely turned black to generate copper oxide. Thereafter, the solution was allowed to stand for 30 minutes, 1.5 kg of glucose was added, and the solution was aged for 1 hour to reduce the copper oxide to cuprous oxide. Furthermore, 1 kg of hydrazine hydrate was quantitatively added over a period of 5 minutes to reduce the cuprous oxide to produce metallic copper and generate copper powder slurry. The obtained copper powder slurry is filtered, washed thoroughly with pure water, filtered again, and then dried. The obtained Cu powder is plastically deformed using the flattening method described in Japanese Patent No. 4227373, thereby converting the roughly spherical copper powder into a flat copper powder. At this time, the particle diameter used is not 0.7 mm, but changed to 0.2 mm.

Next, the copper particles B-1 to B-3 were subjected to the following evaluations.

[Measurement of the average image resolution diameter of primary particles] Regarding copper particles B-1 to B-3, the average image resolution diameter of primary particles of each copper particle was measured by the above method. The results are shown in Table 2.

[Calculation of BET diameter B based on BET specific surface area] The BET diameter B of copper particles B-1 to B-3 was measured using the same method as the BET diameter A of copper particle A. The results are shown in Table 2 below.

[Determination of the content of carbon and phosphorus] Regarding the content of carbon in copper particles B-1 to B-3, 0.50 g of any one of copper particles B-1 to B-3 was added to a magnetic crucible using a carbon-sulfur analyzer (CS844 manufactured by LECO Japan Co., Ltd.), and the analysis time was 40 seconds with oxygen (purity: 99.5%) as carrier gas. The measurement results are shown in Table 2 below. Regarding the content of phosphorus in copper particles, 1.00 g of any one of copper particles B-1 to B-3 was dissolved in 50 mL of 15% nitric acid aqueous solution and the solution was introduced into an ICP emission spectrometer (PS3520VDDII manufactured by Hitachi High-Tech Science Co., Ltd.) for measurement. The measurement results are shown in Table 2 below.

[Determination of crystallite size] The copper particles B-1 to B-3 were measured using the following method. First, a 20 mass% aqueous slurry was prepared using the washed slurry of the copper particles B-1 to B-3. Then, an isopropyl alcohol solution containing 12 g of copper laurate was added to the slurry heated to 50°C as a surface coating treatment agent, and stirred for 1 hour. Thereafter, the solid-liquid separation was performed by filtration to obtain a solid component, which was vacuum dried, and the copper powder of the copper particles subjected to the surface coating treatment was graded using a sieve with a mesh size of 75 μm, and the sieved component was used as a sample. The sample was placed in a sample holder and measured using an X-ray diffraction device (Ultima IV manufactured by Rigaku Co., Ltd.) under the following conditions. Thereafter, the main peak corresponding to the position of the (220) plane, (111) plane or (311) plane of copper in the diffraction peak was taken as the object, and based on the full width at half maximum of the peak, the above-mentioned Scherrer formula was used to calculate the crystallite sizes S1 to S3, as well as the S1/S2 and S1/S3 ratios. In addition, the S1/B ratio was calculated based on the obtained crystallite sizes. The results are shown in Table 2 below.

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

<Preparation method of samples for X-ray diffraction> The copper powder to be measured is spread all over the measuring frame, and smoothed using a glass plate until the copper powder thickness is 0.5 mm and becomes smooth.

The X-ray diffraction pattern obtained under the above measurement conditions was analyzed using the analysis software under the following conditions. During the analysis, the peak width was corrected using the LaB6 value. The crystallite size was calculated using the full width of the peak half-value width and the Scherrer constant (0.94).

<Measurement data analysis conditions> ･Analysis software: PDXL2 manufactured by Rigaku ･Smoothing: Gaussian function, smoothing parameter = 10 ･Background removal: Fitting method ･Kα2 removal: Intensity ratio is 0.497 ･Peak search: Secondary differential method ･Profile fitting: FP (Fundamental Parameter) method ･Crystalline size distribution type: Lorenz model ･Scherrer constant: 0.9400

Furthermore, the peaks of the X-ray diffraction pattern used for the analysis are shown below. The Miller indices shown below are synonymous with the above-mentioned copper crystal planes. ･The peak indexed by the Miller index (220) located near 2θ=71°～76°. ･The peak indexed by the Miller index (111) located near 2θ=40°～45°. ･The peak indexed by the Miller index (311) located near 2θ=87.5°～92.5°.

[Table 2] Copper particles Copper particles B-1 Copper particles B-2 Copper particles B-3 BET diameter B[μm] 0.24 0.35 0.28 Average image resolution diameter of primary particles [μm] 0.32 0.44 0.42 (111) plane crystallite size S1[nm] 35 32.8 28.8 (220) plane crystallite size S2[nm] 34.3 29.6 18 (311) plane crystallite size S3[nm] 30.4 30.4 12.9 S1/B ratio 0.14 0.09 0.10 S1/S2 Ratio 1.02 1.11 1.60 S1/S3 Ratio 1.15 1.08 2.23 Carbon content [ppm] 4000 2700 2000 Phosphorus content [ppm] 335 360 ＜10

[Examples 1 to 7 and 9 and Comparative Examples 1 to 7] Copper particles A-1, A-2 and B-1 to B-3 were mixed in the ratios shown in Table 3 below to obtain copper powders of each example and each comparative example. Specifically, each copper particle was added to a 100 mL container in the ratio shown in Table 3, and then mixed using a small ball mill (AV-1 manufactured by Asahi Rika) to obtain copper powders of each example and each comparative example. The mixing was performed at 100 rpm for 1 hour. The copper powder obtained in the above manner and polyethylene glycol having a number average molecular weight of 200 were mixed using a three-roll mixer to obtain a copper slurry containing 85% by mass of copper powder. Furthermore, Table 3 shows the content of each copper particle component relative to the total mass of 100 parts by mass of copper particles. In addition, "solid content concentration" represents the ratio of the mass of copper powder to the mass of the entire copper slurry.

[Evaluation of slurry printability] The slurry printability of each embodiment and each comparative example was evaluated based on the following evaluation criteria. <Evaluation criteria of slurry printability> Acceptable: Can be applied to a glass plate shielded with a size of 2 cm in length and 1 cm in width. Unacceptable: Cannot form a continuous coating film under the above conditions.

[Manufacturing of conductive film] The copper slurry of each embodiment and each comparative example was coated on a glass substrate, and the substrate was fired at 190°C for 10 minutes in a nitrogen atmosphere to form a conductive film on the glass substrate. The obtained conductive film was 2 cm in length, 1 cm in width, and 30 μm in thickness, and the following evaluation was performed on it.

[Evaluation of film strength] The film strength of each conductive film was evaluated based on the following evaluation criteria. ＜Evaluation criteria of film strength＞ High: No powder will be attached to the hand when the conductive film surface is scratched. Low: Powder will be attached to the hand when the conductive film surface is scratched.

[Measurement of the resistivity of the conductive film] The resistivity of each conductive film was measured using a resistivity meter (Loresta-GP MCP-T610 manufactured by Mitsubishi Chemical Analytech Co., Ltd.). The conductive film to be measured was measured three times, and the arithmetic average was taken as the resistivity (μΩ･cm). The lower the resistivity, the smaller the resistance of the conductive film, preferably less than 50 μΩ･cm. The results are shown in Table 3 below.

[Evaluation of the thickness of the conductive film] Regarding the thickness of the film formed by the calcination of the Cu slurry, a digital length measuring machine (MFC-101 manufactured by Nikon) was used to measure the thickness of the conductive film and the glass substrate and the thickness of the glass substrate alone, and the difference between these thicknesses was calculated as the thickness of the conductive film.

[Measurement of surface roughness Ra of conductive film] The surface roughness (average roughness Ra) of each conductive film was measured at 3 locations using a surface roughness and profile shape measuring machine (SURFCOM 130A manufactured by Tokyo Seimitsu Co., Ltd.), and the average value of the obtained values was calculated. The results are shown in Table 3. From the perspective of resistance, the surface roughness Ra is preferably 2.0 or less. In addition, a smaller surface roughness Ra of a conductive film means that the conductive film has a higher density.

[Measurement of bonding strength] For a 5 mm square copper sheet polished on one side with a #800 polishing sheet, a copper paste was screen-printed on the polished side in a shape of 2 mm×2 mm×30 μm, and a 3 mm square copper sheet polished on one side with a #800 polishing sheet was placed so that the polished surface became the bonding surface. Thereafter, a pressurized sintering machine (IMC-1AB6 manufactured by Imoto Seisakusho) was used to pressurize at 5 MPa while sintering at 200°C for 30 minutes in a nitrogen atmosphere to bond the obtained bonded body. The bonding strength of the obtained bonded body was measured using a bonding strength tester (Condor Sigma manufactured by XYZTEC). The above measurement was performed 3 times, and the maximum and average values of the bonding strength were calculated. They are shown in Table 3. In Table 3, the bonding strength is a value standardized in such a way that the bonding strength of Comparative Example 3 is 1.0. In Table 3, "-" means not measured.

[table 3] Copper slurry composition Evaluation results Copper particles A-1 [parts by mass] Copper particles A-2 [parts by mass] Copper particles B-1 [mass parts] Copper particles B-2 [mass parts] Copper particles B-3 [mass parts] Solid content concentration [%] Slurry printability Film strength Conductive film thickness [μm] Resistivity [μΩ･cm] Surface roughness Ra[μm] Bond strength (normalized value) Maximum average value Embodiment 1 85 0 0 15 0 85 qualified high 31 37 1.5 - Embodiment 2 80 0 0 20 0 85 qualified high 29 36 1.8 1.6 1.3 Embodiment 3 75 0 0 25 0 85 qualified high 33 44 1.4 - - Embodiment 4 70 0 0 30 0 85 qualified high 26 34 0.8 - - Embodiment 5 60 0 0 40 0 85 qualified high twenty four 32 1.9 - - Embodiment 6 80 0 20 0 0 85 qualified high 30 38 0.7 - - Embodiment 7 60 0 40 0 0 85 qualified high twenty four 42 0.8 - - Embodiment 9 95 0 0 5 0 85 qualified high 27 20 - 1.5 1.5 Comparison Example 1 80 0 0 0 20 85 qualified high 43 73917 0.9 - - Comparison Example 2 0 80 0 20 0 85 qualified Low 29 Exceeding the upper limit of measurement Unable to determine - - Comparison Example 3 100 0 0 0 0 85 qualified high 35 58 4.0 1.0 1.0 Comparison Example 4 0 100 0 0 0 85 qualified Low 35 Exceeding the upper limit of measurement Unable to determine - - Comparison Example 5 0 0 100 0 0 85 qualified high 25 170 1.1 - - Comparative Example 6 0 0 0 100 0 85 qualified high 26 384 1.8 0.7 0.5 Comparison Example 7 0 0 0 0 100 85 qualified Low 42 Exceeding the upper limit of measurement Unable to determine - -

As shown in Table 3, although the conductive films of each embodiment are manufactured by sintering at a relatively low temperature of 190°C, they still have a relatively low resistivity. It can be seen that the copper powder used in each embodiment has a relatively low sintering temperature. In addition, it can be seen that the conductive films of each embodiment have good continuity and density due to excellent slurry printing properties and low surface roughness Ra. In addition, from the comparison between Example 2 and Comparative Example 1, it can be seen that even if the same flat copper particles are used, when mechanically flattened copper particles such as copper particles B-3 are used, the sintering temperature of the copper powder also increases, and the resistivity of the conductive film also becomes higher.

[Example 8, Comparative Example 8 and Comparative Example 9] As shown in Table 4 below, when copper powder and polyethylene glycol with a number average molecular weight of 200 were mixed using a three-roll mixer, the mixing ratio of copper powder and polyethylene glycol was changed to prepare a copper slurry containing 90% by mass of copper powder. In addition, the copper slurries of Example 8, Comparative Example 8 and Comparative Example 9 and their conductive films were prepared in the same manner as in Example 2, Comparative Example 3 and Comparative Example 5. The copper slurries and their conductive films were evaluated in the same manner as in Examples 1 to 7 and Comparative Examples 1 to 7. The results are shown in Table 4.

[Table 4] Copper slurry composition Evaluation results Copper particles A-1 [parts by mass] Copper particles B-1 [mass parts] Solid content concentration [%] Slurry printability Film strength Resistivity [μΩ･cm] Surface roughness Ra[μm] Embodiment 2 80 20 85 qualified high 36 1.8 Embodiment 8 80 20 90 qualified high 33 2.6 Comparison Example 3 100 0 85 qualified high 58 4.0 Comparative Example 8 100 0 90 qualified high 825 3.5 Comparison Example 5 0 100 85 qualified high 170 1.1 Comparative Example 9 0 100 90 qualified high Exceeding the upper limit of measurement 3.1

As shown in Table 4, for the copper powders of Examples 2 and 8 containing both copper particles A-1 and B-1, even when the content of the organic solvent in the copper slurry is changed, the resistivity and surface roughness Ra of the conductive film are not easily adversely affected. On the other hand, as shown in Comparative Examples 8 and 9, when using copper powder containing only one of copper particles A-1 and B-1, if the content of the organic solvent in the copper slurry is set to 10 mass%, the resistivity of the conductive film in particular will increase significantly. [Industrial Applicability]

According to the present invention, a copper powder is provided which can be used to manufacture a conductive film with high continuity and density and has a low sintering temperature.

Claims (6)

A copper powder comprising the following copper particles A and copper particles B, and relative to the total of copper particles A and copper particles B, the content ratio of copper particles A is 60 mass% or more and 99 mass% or less, and the content ratio of copper particles B is 1 mass% or more and 40 mass% or less, [Copper particles A] The copper particles have a core particle containing copper and a coating layer covering the surface of the core particle, the coating layer is formed by a copper salt of an aliphatic organic acid, and the primary particle size of the copper particles is 0.1 μm or more and 0.6 μm or less; [Copper particles B] The ratio (S1/B) of the first crystallite size S1 of the copper particle obtained by the Sherlock formula based on the half-value width of the peak originating from the (111) plane of copper in the X-ray diffraction measurement to the BET diameter B calculated based on the BET specific surface area is 0.23 or less, the ratio (S1/S2) of the first crystallite size S1 to the second crystallite size S2 obtained by the Sherlock formula based on the half-value width of the peak originating from the (220) plane of copper in the X-ray diffraction measurement is 1.35 or less, and the primary particle size of the copper particle is 0.1 μm or more and 2.0 μm or less. The copper powder of claim 1, wherein the ratio (S1/S3) of the first crystallite size S1 of the copper particles B to the third crystallite size S3 obtained by the Sherlock formula based on the half width of the peak originating from the (311) plane of copper in X-ray diffraction measurement is less than 1.35. The copper powder of claim 1, wherein the copper particles B contain carbon element, and the content of the carbon element is less than 5000 ppm. The copper powder of claim 1, wherein the copper particles B contain phosphorus, and the content of the phosphorus is greater than 300 ppm. A copper slurry comprising the copper powder as claimed in any one of claims 1 to 4. A method for manufacturing a conductive film comprises applying the copper slurry as claimed in claim 5 on a substrate to form a coating, and then firing the coating.