WO2024071303A1 - Copper powder, copper paste containing same, and method for producing conductive film - Google Patents

Copper powder, copper paste containing same, and method for producing conductive film Download PDF

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WO2024071303A1
WO2024071303A1 PCT/JP2023/035411 JP2023035411W WO2024071303A1 WO 2024071303 A1 WO2024071303 A1 WO 2024071303A1 JP 2023035411 W JP2023035411 W JP 2023035411W WO 2024071303 A1 WO2024071303 A1 WO 2024071303A1
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copper
particles
copper particles
less
mass
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PCT/JP2023/035411
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French (fr)
Japanese (ja)
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瑞樹 秋澤
裕樹 澤本
隆史 佐々木
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三井金属鉱業株式会社
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Publication of WO2024071303A1 publication Critical patent/WO2024071303A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B22F1/052—Metallic powder characterised by the size or surface area of the particles characterised by a mixture of particles of different sizes or by the particle size distribution
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/07—Metallic powder characterised by particles having a nanoscale microstructure
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
    • B22F1/102—Metallic powder coated with organic material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F7/00—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression
    • B22F7/02—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite layers
    • B22F7/04—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite layers with one or more layers not made from powder, e.g. made from solid metal
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C9/00—Alloys based on copper
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B13/00—Apparatus or processes specially adapted for manufacturing conductors or cables

Definitions

  • the present invention relates to copper powder and a copper paste containing the same.
  • the present invention also relates to a method for producing a conductive film.
  • Copper is a highly conductive metal and a versatile material, and is therefore widely used industrially as a conductive material.
  • copper powder which is an aggregate of copper particles, is widely used as a raw material for manufacturing various electronic components, such as the external and internal electrodes of multilayer ceramic capacitors (hereafter also referred to as "MLCC"), and wiring for various substrates.
  • MLCC multilayer ceramic capacitors
  • the present applicant has previously proposed a technology relating to spherical copper particles in which the average particle size of the primary particles is 0.1 ⁇ m or more and 0.6 ⁇ m or less, and the particle surfaces are treated with a surface treatment agent (see Patent Document 1).
  • This technology has the advantage of improving the low-temperature sintering properties of the copper particles.
  • the objective of the present invention is therefore to provide copper powder that can produce conductive films with high continuity and density, and that has a low sintering temperature.
  • the present invention includes the following copper particles A and copper particles B,
  • the copper powder has a content of copper particles A of 60% by mass or more and 99% by mass or less relative to the total content of copper particles A and copper particles B, and a content of copper particles B of 1% by mass or more and 40% by mass or less.
  • the present invention comprises a core particle made of copper and a coating layer that coats the surface of the core particle, the coating layer is formed from a copper salt of an aliphatic organic acid, Copper particles having a primary particle diameter of 0.1 ⁇ m or more and 0.6 ⁇ m or less.
  • [Copper particles B] a ratio (S1B) of a first crystallite size S1 calculated by the Scherrer formula from the half-width of a peak derived from the copper (111) plane in an X-ray diffraction measurement to a BET diameter B calculated from a 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 calculated by the Scherrer formula from the half-width of the peak derived from the (220) plane of copper in X-ray diffraction measurement is 1.35 or less; Copper particles having a primary particle diameter of 0.1 ⁇ m or more and 2.0 ⁇ m or less.
  • the present invention will be described below based on preferred embodiments.
  • the copper powder of the present invention includes copper particles A and copper particles B described below.
  • the present invention comprises a core particle made of copper and a coating layer that coats the surface of the core particle, the coating layer is formed from a copper salt of an aliphatic organic acid, Copper particles having a primary particle diameter of 0.1 ⁇ m or more and 0.6 ⁇ m or less.
  • [Copper particles B] a ratio (S1B) of a first crystallite size S1 calculated by the Scherrer formula from the half-width of a peak derived from the copper (111) plane in an X-ray diffraction measurement to a BET diameter B calculated from a 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 calculated by the Scherrer formula from the half-width of the peak derived from the (220) plane of copper in X-ray diffraction measurement is 1.35 or less; Copper particles having a primary particle size of 0.1 ⁇ m or more and 2.0 ⁇ m or less, except for those that fall under Copper Particles A.
  • copper particles A have a spherical shape.
  • copper particles B have a flat shape.
  • the average image analysis diameter of the primary particles of the copper particles A is preferably 0.1 ⁇ m or more and 0.6 ⁇ m or less, more preferably 0.12 ⁇ m or more and 0.4 ⁇ m or less, and even more preferably 0.15 ⁇ m or more and 0.3 ⁇ m or less.
  • the primary particle refers to an object that is recognized as the smallest unit of a particle, judging from the geometric shape of its outer shape.
  • the average image analysis diameter of the primary particles of copper particles B is preferably 0.1 ⁇ m or more and 2.0 ⁇ m or less, more preferably 0.15 ⁇ m or more and 1.0 ⁇ m or less, and even more preferably 0.2 ⁇ m or more and 0.6 ⁇ m or less.
  • the particle diameter of the copper particles A calculated from the BET specific surface area is preferably 0.1 ⁇ m or more and 0.6 ⁇ m or less, more preferably 0.12 ⁇ m or more and 0.4 ⁇ m or less, and even more preferably 0.15 ⁇ m or more and 0.3 ⁇ m or less.
  • the particle diameter of copper particles B calculated from the BET specific surface area is preferably 0.1 ⁇ m or more and 2.0 ⁇ m or less, more preferably 0.15 ⁇ m or more and 1.0 ⁇ m or less, and even more preferably 0.2 ⁇ m or more and 0.6 ⁇ m or less.
  • BET diameter B the thermal conductivity of the copper powder of the present invention can be increased, and the sintering temperature can be effectively reduced.
  • the BET diameter B is also referred to as the primary particle diameter of the copper particles B.
  • the average image analysis diameter of the primary particles of copper particles A and B can be determined, for example, by observing the copper particles at a magnification of 10,000 times or 30,000 times using a scanning electron microscope (JSM-6330F manufactured by JEOL Ltd.), measuring the maximum Feret's diameter in the horizontal direction for 200 particles in the field of view, and calculating the volume average particle diameter converted into a sphere from these measured values.
  • the average image analysis diameter of the primary particles of copper particles A calculated in this manner 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 under the following conditions based on the BET method. Specifically, the measurements can be performed by nitrogen adsorption using "Macsorb” manufactured by Mountech Co., Ltd. The amount of powder to be measured is 0.2 g, and the preliminary degassing conditions are under vacuum at 80°C for 30 minutes.
  • the BET diameters A and B are calculated from the measured BET specific surface area by the following formula (I).
  • d is the BET diameter A or B [ ⁇ m]
  • a BET is the specific surface area measured by the BET single point method [m 2 /g]
  • ⁇ is the density of copper [g/cm 3 ].
  • d 6 / (A BET ⁇ ⁇ ) ... (I)
  • preferred embodiments of the copper particles A and B will be described in detail.
  • the copper particles A have a surface treatment agent containing a copper salt of an aliphatic organic acid applied to the surface of the particles.
  • a coating layer made of the surface treatment agent is formed so as to cover the surface of the copper core particle continuously or discontinuously.
  • the surface treatment agent is used to suppress both the oxidation of copper and the aggregation of the particles.
  • the core particles preferably consist of only copper with the remainder being unavoidable impurities.
  • the surface treatment agent used in the present invention contains a copper salt of an aliphatic organic acid.
  • surface treatment agents such as fatty acids and fatty acid amines have been used to simultaneously inhibit the oxidation of copper in copper particles and inhibit the aggregation of the particles.
  • such treatment agents have a high decomposition temperature, and there are cases where they cannot be sufficiently removed during sintering of the copper particles. This can cause the sintering start temperature to rise and the resistance of the conductive film obtained after sintering the copper particles together to increase.
  • the inventors conducted extensive research to solve this problem and found that by using a copper salt of an aliphatic organic acid as a surface treatment agent, it is possible to lower the sintering start temperature while inhibiting both the oxidation of copper and the aggregation of the particles, and as a result, it is possible to improve the low-temperature sintering of the particles while lowering the resistance of the conductive film obtained after sintering.
  • the number of carbon atoms in the aliphatic organic acid constituting the copper salt of an aliphatic organic acid is preferably 6 to 18, more preferably 8 to 18, even more preferably 10 to 18, and even more preferably 12 to 18.
  • examples of such aliphatic organic acids include linear or branched, saturated or unsaturated carboxylic acids, and linear or branched, saturated or unsaturated hydrocarbon group-containing sulfonic acids, and the like, preferably linear, saturated or unsaturated carboxylic acids.
  • the valence of copper in the copper salt of an aliphatic organic acid is monovalent or divalent, and preferably divalent.
  • carboxylic acids include citric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, lauric acid, palmitic acid, oleic acid, stearic acid, etc., of which lauric acid, oleic acid, and stearic acid are preferred, and lauric acid and stearic acid are more preferred.
  • sulfonic acids include hexanesulfonic acid, heptanesulfonic acid, octanesulfonic acid, nonanesulfonic acid, decanesulfonic acid, laurinsulfonic acid, palmitic acid, oleinsulfonic acid, stearinsulfonic acid, etc. These aliphatic organic acids can be used alone or in combination of two or more kinds.
  • the surface treatment agent can be applied to the particle surface, for example, in a process after the production of core particles made of copper, by contacting the obtained core particles with a copper salt of an aliphatic organic acid, which is the surface treatment agent.
  • the amount of the surface treatment agent applied is expressed as the proportion (mass %) of the entire surface treatment agent in copper particles A in a state in which the surface treatment agent is applied, and is preferably 0.2 mass % or more and 2.0 mass % or less in carbon atom equivalent, and more preferably 0.3 mass % or more and 1.0 mass % or less.
  • the proportion (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 an aggregate of copper particles A to which a surface treatment agent has been applied, is heated in an oxygen stream using a carbon/sulfur analyzer (Horiba, Ltd., EMIA-320V), and the carbon content in the copper powder is decomposed into CO or CO2 , and the amount of the decomposed carbon or CO2 is quantified to calculate the proportion of the surface treatment agent.
  • a carbon/sulfur analyzer Horiba, Ltd., EMIA-320V
  • NMR nuclear magnetic resonance
  • Raman spectroscopy Raman spectroscopy
  • infrared spectroscopy liquid chromatography
  • TOF-SIMS time-of-flight secondary ion mass spectrometry
  • Copper particles A have a coating layer formed on the surface of a core particle using a copper salt of an aliphatic organic acid as a surface treatment agent, and whether or not the coating layer was formed using a copper salt of an aliphatic organic acid can be determined, for example, by the following method.
  • the copper particles A are diluted with KBr so that the mass of the copper particles A becomes 5 mass%, and the measurement sample is mixed in a mortar and measured by a diffuse reflectance method using an infrared spectrophotometer (model number: FT-IR4600) manufactured by JASCO Corporation under conditions of a resolution of 4 cm -1 and an accumulation number of 128 times, and a graph (spectrum) is obtained in which the vertical axis represents the value obtained by Kubelka-Munk conversion of absorbance and the horizontal axis represents wave numbers (500 to 4000 cm -1 ).
  • FT-IR4600 infrared spectrophotometer
  • the coating layer is formed using a copper salt of an aliphatic organic acid. That is, it is preferable that, in the measurement by infrared spectroscopy, the copper particles A have an infrared absorption peak in the range of 1504 cm -1 or more and 1514 cm -1 or less and no infrared absorption peak is observed in the range of 1584 cm -1 or more and 1596 cm -1 or less. "Having an infrared absorption peak" is defined according to the following method.
  • IR spectrum data normalized with the maximum value of the peak observed in the range of 2910 cm -1 to 2940 cm -1 is differentiated twice, and waveform separation is performed in the range of 1500 cm -1 to 1600 cm -1 based on the zero-up crossing method.
  • an arithmetic mean value is calculated from the absolute value of the amplitude from the reference line (zero) in each waveform obtained by waveform separation.
  • an infrared absorption peak is detected in the range of 1584 cm -1 or more and 1596 cm -1 or less, and in this respect, they can be distinguished from copper particles A.
  • infrared absorption when infrared absorption is observed in infrared spectroscopy, it indicates that some bonds exist in the molecule. In particular, when infrared absorption is observed at a high wave number position, it can be said that bonds with high bond energy exist in the molecule because infrared rays at high wave numbers have high energy.
  • copper particles A are compared with copper particles using a fatty acid or an aliphatic amine as a surface treatment agent, infrared absorption is observed in the low wave number region of 1504 cm ⁇ 1 or more and 1514 cm ⁇ 1 or less for both particles, and it is presumed that the absorption in this region means that a coating layer is bonded to the surface of the core particles.
  • the copper particles A do not show infrared absorption observed in the high wavenumber region, whereas the copper particles using fatty acids or aliphatic amines as surface treatment agents show infrared absorption in the high wavenumber region.
  • the copper particles of the present invention have fewer bonds with large bond energy in the molecule.
  • copper particles A can be analyzed, for example, by TOF-SIMS.
  • the temperature at which the ratio of the mass loss to the mass loss at 500°C is 10% is preferably 150°C or higher and 220°C or lower, and more preferably 180°C or higher and 220°C or lower.
  • thermogravimetric analysis can be carried out, for example, by the following method. That is, using a TG-DTA2000SA manufactured by Bruker AXS, a measurement sample of 50 mg is used, and the mass loss rate is measured when heated from 25°C to 1000°C. The atmosphere is nitrogen, and the heating rate is 10°C/min. The lower the temperature at which the mass loss rate reaches a predetermined rate, the lower the temperature at which the aliphatic organic acid that forms the coating layer can be removed, and this is a measure of the low-temperature sintering property of copper particle A.
  • the shape of the copper particles A is preferably spherical.
  • the shape of the core particles may be spherical.
  • the spherical shape of the particles means that the circularity coefficient measured by the following method is preferably 0.85 or more, more preferably 0.90 or more.
  • the circularity coefficient is calculated by the following method. A scanning electron microscope image of the metal particles is taken, and 1000 particles that do not overlap with each other are randomly selected. When the area of the two-dimensional projection image of the particle is S and the perimeter is L, the circularity coefficient of the particle is calculated from the formula 4 ⁇ S/ L2 . The arithmetic average value of the circularity coefficient of each particle is the above-mentioned circularity coefficient. When the two-dimensional projection image of the particle is a perfect circle, the circularity coefficient of the particle is 1.
  • Copper particles B have a predetermined relationship in terms of crystallite size on a specific crystal plane calculated by X-ray diffraction measurement. Specifically, when the particle diameter calculated from the BET specific surface area is the BET diameter B, and the crystallite size calculated from the diffraction peak derived from the (111) plane of copper in the X-ray diffraction measurement by the Scherrer formula is 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 even more preferably 0.05 or more and 0.23 or less.
  • the diffraction peak originating from the (111) plane of copper is the peak with the maximum height of the X-ray diffraction pattern obtained by X-ray diffraction measurement of copper particles B. From this, it is considered that the first crystallite size is larger than the crystallite size calculated from the diffraction peaks originating from other crystallite planes, and is also representative of crystallinity. Therefore, it is presumed that the first crystallite size S1 is small relative to the BET diameter B, so that there are many crystal grain boundaries in one particle. As a result, the thermal energy applied when the particles are heated makes the crystallite interface more unstable, which activates atomic diffusion, thereby increasing the fusion between particles at low temperatures and lowering the sintering temperature. Such copper particles can be obtained, for example, by the manufacturing method described below.
  • the first crystallite size S1 of copper particles B is preferably 10 nm or more and 80 nm or less, more preferably 20 nm or more and 75 nm or less, and even more preferably 25 nm or more and 70 nm or less.
  • the ratio (S1/S2) of the first crystallite size S1 to the second crystallite size S2 is a predetermined value or less.
  • the S1/S2 ratio is preferably 1.35 or less, more preferably 0.1 or more and 1.3 or less, and further preferably 0.1 or more and 1.2 or less.
  • copper particles B have a copper (111) plane on a specific surface of the particle surface, and a copper (220) plane on a surface intersecting the (111) plane.
  • the flat shape means a shape having a pair of main surfaces facing each other and side surfaces intersecting these main surfaces.
  • the fusion property between the particles at low temperatures can be improved, and the sintering temperature of the copper powder can be reduced.
  • This is advantageous in that the sinterability can be further improved compared to spherical particles and mechanically produced flat copper particles.
  • the contact between the copper particles B is likely to be face-to-face contact as described above, the contact area is larger than that of spherical copper particles, etc. Due to this, the conductive film produced from the copper powder of the present invention containing the copper particles B has high continuity.
  • Such copper particles can be obtained, for example, by the manufacturing method described below.
  • the second crystallite size S2 of copper particles B is preferably 10 nm or more and 80 nm or less, more preferably 20 nm or more and 75 nm or less, and even more preferably 30 nm or more and 70 nm or less.
  • the ratio (S1/S3) of the first crystallite size S1 to the third crystallite size S3 is a predetermined value or less.
  • the S1/S3 ratio is preferably 1.35 or less, more preferably 0.20 or more and 1.30 or less, and further preferably 0.50 or more and 1.25 or less.
  • copper particles B Since metallic copper is prone to have a face-centered cubic crystal structure, copper particles B have a copper (111) plane on a specific surface of the particle surface, and a copper (311) plane on a surface intersecting the (111) plane.
  • the S1/S3 ratio in the above-mentioned range when the copper particles B are arranged during sintering, the main surfaces of the copper particles B or the side surfaces of the copper particles B are likely to contact each other, and the contact parts of the copper particles B are likely to have the same crystal plane.
  • the copper powder of the present invention when the copper powder of the present invention is heated, atomic diffusion at the crystallite interface of the copper particles B is activated, the fusion property of the particles at low temperatures is improved, and the sintering temperature of the copper powder can be reduced. This is advantageous in that the sinterability can be further improved compared to spherical particles and mechanically produced flat copper particles.
  • Such copper particles can be obtained, for example, by the manufacturing method described below.
  • the third crystallite size S3 of the particles B is preferably 10 nm or more and 80 nm or less, more preferably 20 nm or more and 75 nm or less, and even more preferably 30 nm or more and 70 nm or less.
  • Copper particles B preferably contain copper element as a major component.
  • Containing copper element as a major component means that the copper element content in the copper particles is 97.0% by mass or more, preferably 97.5% by mass or more, more preferably 98.0% by mass or more, and even more preferably 98.5% by mass or more.
  • the copper element content can be measured, for example, by ICP atomic emission spectrometry.
  • the copper particles B contain, in addition to elemental copper, elements other than copper, or consist of elemental copper and contain no elements other than copper except for unavoidable impurities. Copper particles B are permitted to contain trace amounts of unavoidable impurity elements such as oxygen, as long as this does not impair the effects of the present invention. In either embodiment, the content of elements other than copper in the copper particles is preferably 1.5 mass% or less. The content of these elements can be measured, for example, by ICP atomic emission spectrometry.
  • the copper particles B have a low carbon element content.
  • the carbon element content in the copper particles B is preferably 5000 ppm or less, more preferably 4500 ppm or less, and even more preferably 4000 ppm or less. The lower the content, the better, but 100 ppm or more is realistic.
  • Such copper particles can be manufactured, for example, by the manufacturing method described below.
  • the carbon element content can be measured by, for example, gas analysis or combustion carbon analysis.
  • This confirmation method includes, for example, 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, either alone or in combination. If it is determined that the particle surface is coated by this method, the above-mentioned methods are used alone or in combination to qualitatively and quantitatively analyze the type and amount of elements contained in the coating layer formed by the coating process.
  • the physical properties of the organic material can be evaluated by thermogravimetry (TG) by measuring the mass change occurring before and after the firing temperature and the amount of carbon after heating to that temperature.
  • TG thermogravimetry
  • the content of phosphorus contained in the copper particles B is within a predetermined range.
  • the content of phosphorus in the copper particles is preferably 300 ppm or more, more preferably 300 ppm or more and 1500 ppm or less, and even more preferably 300 ppm or more and 1000 ppm or less.
  • Such copper particles can be manufactured, for example, by the manufacturing method described below.
  • the presence or absence of phosphorus in the copper particles B and its content can be measured, for example, by ICP atomic emission spectroscopy.
  • the lower the carbon content of copper particles B the less likely sintering inhibition occurs, and the copper powder can be sintered at a lower temperature.
  • the carbon content is within the range mentioned above, it is possible to relatively suppress sintering inhibition caused by organic matter present on the surface of copper particles B, so organic matter may be intentionally applied to the surface of copper particles B.
  • the organic matter applied to the surface of the copper particles B can be, for example, various copper salts of fatty acids or aliphatic organic acids, and aliphatic amines.
  • various copper salts of fatty acids or aliphatic organic acids, and aliphatic amines By applying such an organic matter to the surface of the copper particles B, it is possible to suppress aggregation between the copper particles.
  • fatty acids or aliphatic amines include benzoic acid, pentanoic acid, hexanoic acid, octanoic acid, nonanoic acid, decanoic acid, lauric acid, palmitic acid, oleic acid, stearic acid, pentylamine, hexylamine, octylamine, decylamine, laurylamine, oleylamine, and stearylamine.
  • These fatty acids or aliphatic amines can be used alone or in combination of two or more.
  • the shape of copper particles B is not particularly limited as long as the effects of the present invention are achieved, but when produced by the method described below, it is preferably flat. Such particles have a pair of nearly flat main surfaces facing each other and side surfaces intersecting both main surfaces, and are plate-like in shape with the maximum span of the main surfaces being greater than the thickness. In this case, it is also preferable that when the main surfaces of copper particles B are viewed in plan, their shape has an outline defined by a combination of straight lines or a combination of straight lines and curves.
  • the conductive film produced from the copper paste containing the copper powder of the present invention has high density and continuity.
  • the content ratio of copper particles A to the total of copper particles A and copper particles B is preferably 60% by mass or more and 99% by mass or less, more preferably 65% by mass or more and 88% by mass or less, and even more preferably 70% by mass or more and 85% by mass or less.
  • the content ratio of copper particles B to the total of copper particles A and copper particles B is preferably 1 mass% or more and 40 mass% or less, more preferably 12 mass% or more and 35 mass% or less, and even more preferably 15 mass% or more and 30 mass% or less.
  • the copper powder of the present invention is preferably produced by mixing copper particles A and copper particles B in the preferred ratio described above. Below, a preferred method for producing copper particles A and copper particles B, and a method for mixing copper particles A and copper particles B will be described in detail in order.
  • This production method involves contacting core particles made of copper with a solution containing a copper salt of an aliphatic organic acid to form a coating layer that coats the surfaces of the core particles.
  • core particles made of copper are prepared.
  • the copper core particles can be produced, for example, by the wet method described in JP 2015-168878 A. That is, a reaction liquid containing a monovalent or divalent copper source such as copper chloride, copper acetate, copper hydroxide, copper sulfate, copper oxide, or cuprous oxide is prepared in a liquid medium containing water and a monohydric alcohol preferably having 1 to 5 carbon atoms. This reaction liquid is mixed with hydrazine in a ratio of preferably 0.5 to 50 moles per mole of copper, and the copper source is reduced to obtain core particles made of copper.
  • the core particles obtained by this method do not have a surface treatment agent such as a copper salt of an aliphatic organic acid applied to their surfaces, and have a small particle size.
  • the core particles obtained in the above-mentioned process are preferably washed.
  • washing methods include decantation and rotary filter methods.
  • an aqueous slurry is prepared by dispersing the core particles in a solvent such as water, and washing is performed until the conductivity of the slurry is preferably 2.0 mS or less.
  • the washing conditions at this time can be, for example, a washing temperature of 15°C to 30°C and a washing time of 10 minutes to 60 minutes when water is used as the washing solvent.
  • the core particles to be washed can be uniformly dispersed without agglomeration, and the surface treatment described below can be performed efficiently.
  • the content of copper core particles in this slurry is preferably 5% by mass to 50% by mass from the viewpoint of improving both washing efficiency and particle dispersibility.
  • a direct current thermal plasma (DC plasma) method described in WO 2015/122251 may be used as another method for producing core particles made of copper.
  • copper mother powder can be subjected to a direct current thermal plasma method, which is a type of PVD method, to generate core particles from the mother powder.
  • the core particles obtained by this method also have no surface treatment agent such as a copper salt of an aliphatic organic acid on their surfaces, and have a small particle size. If necessary, the obtained core particles may be subjected to a crushing process or a classification process to separate or remove coarse particles and fine particles.
  • the core particles obtained by the above-mentioned method are surface-treated with a surface treatment agent to form a coating layer that covers the surface of the core particles.
  • a method of surface treatment for example, a method of contacting the core particles with a solution in which a copper salt of an aliphatic organic acid is dissolved in a solvent can be adopted.
  • the form of the core particles to be contacted with the copper salt of an aliphatic organic acid in this step may be an aqueous slurry in which the core particles are dispersed in a solvent such as water, or may be in a dry state in which the core particles are not dispersed in a solvent or the like.
  • one of the core particles and the copper salt solution of an aliphatic organic acid may be added to the other, or the core particles and the copper salt solution of an aliphatic organic acid may be contacted simultaneously.
  • a solution of the copper salt of an aliphatic organic acid is added to a slurry in which the core particles are dispersed.
  • the method of adding core particles to a copper salt solution of an aliphatic organic acid and performing surface treatment will be described below as an example.
  • the solvent used in the copper salt solution of an aliphatic organic acid is heated to a temperature below the boiling point of the solvent used (for example, 25°C to 80°C), and under that condition, the copper salt of an aliphatic organic acid is added to the solvent to prepare a copper salt solution of an aliphatic organic acid.
  • the dry core particles or core particle-containing slurry are added to the copper salt solution of an aliphatic organic acid, and then stirred for one hour to perform surface treatment on the surfaces of the core particles.
  • the copper particles A obtained by this method are core particles made of copper and have a coating layer made of a copper salt of an aliphatic organic acid formed on the surface of the core particles.
  • the slurry is heated to a temperature above the melting point of the copper salt of the aliphatic organic acid in order to uniformly form a coating layer on the surfaces of the core particles.
  • the content of the copper salt of an aliphatic organic acid in the reaction solution containing the core particles is preferably 0.1 parts by mass or more and 3.0 parts by mass or less, more preferably 0.2 parts by mass or more and 2.0 parts by mass or less, per 100 parts by mass of core particles that have not been surface-treated.
  • Solvents for dissolving the copper salt of an aliphatic organic acid include organic solvents such as monohydric alcohols having 1 to 5 carbon atoms, polyhydric alcohols, esters of polyhydric alcohols, ketones, and ethers. Of these, from the viewpoints of compatibility with water, economy, ease of handling, and ease of removal, it is preferable to use monohydric alcohols having 1 to 5 carbon atoms, and it is even more preferable to use an aqueous methanol solution, ethanol, 1-propanol, or isopropyl alcohol.
  • the copper particles A obtained through the above steps may be washed or separated into solid and liquid as necessary, and then mixed with copper particles B in the form of a slurry in which the copper particles A are dispersed in a solvent such as water or an organic solvent, or the copper particles A may be dried and mixed with copper particles B in the form of a dry powder that is an aggregate of copper particles.
  • a solvent such as water or an organic solvent
  • the copper particles A may be dried and mixed with copper particles B in the form of a dry powder that is an aggregate of copper particles.
  • oxidation of the copper, which is a constituent metal, and aggregation of particles are suppressed, while at the same time providing an excellent copper powder with a low sintering temperature.
  • This production method includes two reduction steps: a first reduction step in which copper ions are reduced to produce cuprous oxide, and a second reduction step in which cuprous oxide is reduced in the presence of diphosphate or higher polyphosphoric acid or a salt thereof (hereinafter, also referred to as polyphosphoric acids) to produce copper particles.
  • the polyphosphoric acids are present in the reaction system either when the second reduction step is performed or before the second reduction step is performed.
  • the polyphosphoric acids may be present in the reaction system before or when the first reduction step is performed, and the second reduction step may be performed in that state.
  • the polyphosphoric acids may not be present in the reaction system in the first reduction step, but may be present in the reaction system after the completion of the first reduction step, or when the second reduction step is performed or immediately before the second reduction step.
  • a reaction solution containing a copper source and a reducing compound is prepared, and a first reduction step is carried out to reduce copper ions and generate cuprous oxide in the solution.
  • the reaction solution may be prepared by adding each raw material to a solvent at the same time to form the reaction solution, or each raw material may be added to the solvent in any order. From the viewpoint of making it easier to control the reduction reaction of copper ions and improving the ease of handling during production, it is preferable to premix the copper source with a solvent to prepare a copper-containing solution, and then add a solid reducing compound or a solution of the reducing compound predissolved in a solvent to the copper-containing solution.
  • the reducing compound may be added all at once or gradually.
  • the reaction solution may or may not contain polyphosphates.
  • polyphosphates When polyphosphates are present in the reaction solution, it is preferable to add the copper source, polyphosphates, and reducing compound in that order, since this allows the reduction of copper ions by the reducing compound and the control of crystal growth to be effectively achieved.
  • the solvent for the reaction solution can be water or a lower alcohol such as methanol, ethanol, or propanol. These can be used alone or in combination.
  • the copper source used in the first reduction step includes compounds that generate copper ions in the reaction solution, and water-soluble copper compounds are preferred.
  • Specific examples of such copper sources include various copper compounds such as organic copper salts, such as copper formate, copper acetate, and copper propionate, and inorganic copper salts, such as copper nitrate and copper sulfate. These copper compounds may be anhydrides or hydrates. These 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 or more and 2.0 mol/L or less, more preferably 0.1 mol/L or more and 1.5 mol/L or less, expressed as the molar concentration of copper element.
  • the reducing compound is a water-soluble compound.
  • reducing compounds include hydrazine-based compounds such as hydrazine, hydrazine hydrochloride, hydrazine sulfate, and hydrazine hydrate; boron compounds and salts thereof such as sodium borohydride and dimethylamine borane; sulfur oxoacid salts such as sodium sulfite, sodium hydrogen sulfite, and sodium thiosulfate; nitrogen oxoacid salts such as sodium nitrite and sodium hyponitrite; and phosphorus oxoacids and salts thereof such as phosphorous acid, sodium phosphite, hypophosphorous acid, and sodium hypophosphite.
  • These reducing compounds may be anhydrides or hydrates. These reducing compounds may be used alone or in combination of two or more.
  • a hydrazine-based compound as the reducing compound in the reducing solution, and it is even more preferable to use an anhydride or hydrate of hydrazine.
  • the content of the reducing compound in the reaction solution in the first reduction step is preferably 0.1 to 2 moles, more preferably 0.1 to 1 mole, per mole of copper element.
  • the reaction solution in the first reduction step is preferably in an acidic condition with a pH of 3 to 5 at 25°C, in that when a reducing compound, particularly a hydrazine-based compound, is used, the degree of reduction can be appropriately controlled so that reduction to cuprous oxide proceeds but not to metallic copper, while facilitating anisotropy in the copper crystal growth that proceeds in the second reduction step.
  • a reducing compound particularly a hydrazine-based compound
  • the pH can be adjusted using various acids or basic substances, or by adding polyphosphoric acids to the reaction solution.
  • the subsequent reaction can be carried out efficiently without adding other substances to the reaction system, which is advantageous in that it prevents the inclusion of unintended impurities and allows the desired copper particles to be obtained efficiently.
  • the reduction reaction in the first reduction step may be carried out with the reaction liquid in an unheated state or in a heated state.
  • the temperature of the reaction liquid is preferably 10°C or higher and 60°C or lower, more preferably 20°C or higher and 50°C or lower.
  • the reaction time in the first reduction step is preferably 0.1 hours or higher and 2 hours or lower, more preferably 0.2 hours or higher and 1 hour or lower, provided that the temperature is within the above-mentioned range. From the viewpoint of uniformity of the reduction reaction, it is also preferable to continue stirring the reaction liquid from the start of the reaction to the end of the reaction.
  • a second reduction step is carried out in which the cuprous oxide obtained in the first reduction step is reduced to produce metallic copper particles.
  • the second reduction step is also preferably carried out under wet conditions, as in the first reduction step, and it is more preferable that both reduction steps are carried out in the same reaction system.
  • polyphosphoric acids used in the present production method include polyphosphoric acids and their salts, such as 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 ), etc., each of which has preferably 2 to 8, more preferably 2 to 5, phosphoric acid monomer units in its structure.
  • the polyphosphate salts include alkali metal salts, alkaline earth metal salts, other metal salts, ammonium salts, etc. These can be used alone or in combination.
  • the content of polyphosphates in the second reduction step is preferably 0.1 millimole or more, more preferably 0.1 millimole or more and 1 mole or less, per mole of copper element.
  • concentration of polyphosphates in this range the crystal growth of copper resulting from the reduction reaction of cuprous oxide can be made anisotropic, and copper particles having a small particle size and a small crystallite size on a specific crystal plane can be obtained with high productivity.
  • the concentration of polyphosphates does not change substantially before and after the first reduction step. Therefore, by adding polyphosphates in the above-mentioned concentration range to the reaction system in the first reduction step, the amount of polyphosphates present that is suitable for reduction to metallic copper and grain growth in the second reduction step can be sufficiently achieved.
  • the above-mentioned reducing compound can be added to perform reduction to metallic copper.
  • the content of the reducing compound in the reaction solution in the second reduction step is preferably 1 mole or more and 8 moles or less, more preferably 2 moles or more and 6 moles or less, relative to 1 mole of copper element.
  • the reducing compound in the second reduction step may be added all at once or gradually. From the viewpoint of efficiently obtaining copper particles that satisfy the above-mentioned crystallite size ratio and particle diameter, it is preferable to adopt gradually adding the reducing compound.
  • the reaction solution in the second reduction step is preferably kept under non-acidic conditions (neutral or alkaline conditions) with a pH of 7.0 or more at 25° C., in that when a reducing compound, particularly a hydrazine-based compound, is used, the reduction of the copper ions and cuprous oxide remaining in the reaction solution to metallic copper can be efficiently promoted, and the crystal growth of copper can be easily made anisotropic.
  • the pH is preferably adjusted before the addition of the reducing compound in the second reduction step, in that the degree of reduction of the copper ions can be appropriately controlled.
  • Various acids and basic substances can be used for adjusting the pH.
  • the reaction solution after the first reduction step is in an acidic condition, it is preferable to adjust the pH of the reaction solution by adding a basic substance such as sodium hydroxide or potassium hydroxide.
  • a basic substance such as sodium hydroxide or potassium hydroxide.
  • the heating conditions for the reaction solution are preferably such that the temperature is maintained at 10°C or higher and 60°C or lower, particularly 20°C or higher and 50°C or lower, from the start of the second reduction step, i.e., the time when the reducing compound is added, until the end of the reaction.
  • the reaction time is preferably 30 minutes or longer and 720 minutes or shorter under the above temperature conditions.
  • the inventors speculate as follows about the reason why copper particles with a low sintering temperature can be obtained in this manufacturing method by performing a two-step reduction process in which copper ions are reduced to cuprous oxide and then to metallic copper, and by having polyphosphoric acids present during the second reduction process.
  • first reduction step copper ions are reduced by a reducing compound in the reaction solution, and very small particles of cuprous oxide are generated in the reaction solution.
  • second reduction step monovalent copper ions eluted from the cuprous oxide particles are reduced to form metallic copper nuclei. Since these nuclei are very unstable, they repeatedly combine with each other or redissolve in the reaction solution, and eventually the particles grow.
  • the polyphosphates are adsorbed to specific crystal faces of copper, and growth in the direction of the crystal faces is suppressed. On the other hand, growth is not suppressed on crystal faces to which polyphosphates are not adsorbed, and growth in the direction of the crystal faces proceeds.
  • metallic copper is likely to have a face-centered cubic crystal structure and the results of X-ray diffraction measurement of the obtained copper particles.
  • the crystal face to which polyphosphates are adsorbed is the (111) face of copper in the particles, and the crystal face to which polyphosphates are not adsorbed is the (220) face of copper located perpendicular to the (111) face of copper. For this reason, it is considered that anisotropic growth occurs in which the growth of the (111) face of copper is suppressed and the growth of the (220) face of copper progresses, resulting in flat copper particles with a low sintering temperature.
  • the reduction reaction is carried out under acidic conditions, particularly in the first reduction step, so that the reducing power can be controlled to a level where copper ions can be reduced to cuprous oxide but not to metallic copper. In addition, this also makes it easier to control the subsequent metallic copper production reaction. Then, by changing 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 reduction reaction rate to metallic copper can be adjusted to gentle conditions, which is particularly advantageous in that the nucleus growth rate can be controlled.
  • the copper particles B obtained through the above steps even if they do not contain organic components that control crystal growth, such as organic amines, amino alcohols, or reducing sugars, will satisfy the above-mentioned suitable crystallite sizes and ratios thereof, suitable particle diameter, and suitable contents of various elements such as carbon, and will have a flattened shape.
  • the copper particles B thus obtained have a crystal face of the crystal present on the main surface and grown in a direction perpendicular to the main surface, and a crystal face of the crystal present on the side surface and grown in a direction along the main surface, each of which has a specific orientation direction, and each crystal face is formed uniformly in one direction.
  • the copper particles B obtained through the above steps may be washed or separated into solid and liquid as necessary, and then mixed with the copper particles A in the form of a slurry in which the copper particles B are dispersed in a solvent such as water or an organic solvent, or the particles may be dried and mixed with the copper particles A in the form of a dry powder that is an aggregate of the copper particles B. In either case, the copper particles B have a low sintering temperature and are excellent. If necessary, the copper particles B may be further surface-coated with an organic substance such as a fatty acid or a salt thereof, or an inorganic substance such as a silicon-based compound, in order to improve the dispersibility of the particles. As long as the effects of the present invention are achieved, it is acceptable for the obtained copper particles B to contain elements other than the copper element, for example by unavoidably oxidizing the surface slightly.
  • the copper particles A and the copper particles B can be mixed in a dry or wet manner, but from the viewpoint of ease of mixing, it is preferable to mix them in a dry manner. Dry mixing can be performed using a known dry mixing device. Wet 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, a resin, or the like and used in the form of a conductive composition such as a conductive ink or a copper paste.
  • a conductive composition such as a conductive ink or a copper paste.
  • the conductive composition is composed of at least copper powder and an organic solvent.
  • organic solvent those similar to those used in the technical field of conductive compositions containing metal powders can be used without any particular limitation. Examples of such organic solvents include monohydric alcohols, polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, polyethers, esters, nitrogen-containing heterocyclic compounds, amides, amines, and saturated hydrocarbons.
  • organic solvents can be used alone or in combination of two or more.
  • polyethers such as polyethylene glycol and polypropylene glycol, which have a high reducing action and prevent unintended oxidation of copper particles during sintering.
  • polyethylene glycol when polyethylene glycol is used as the organic solvent, its number average molecular weight is preferably 120 to 400, and more preferably 180 to 400.
  • the conductive composition containing copper powder of the present invention may further contain at least one of a dispersant, an organic vehicle, and a glass frit, if necessary.
  • dispersants include dispersants such as nonionic surfactants that do not contain sodium, calcium, phosphorus, sulfur, or chlorine.
  • organic vehicles include mixtures containing resin components such as acrylic resins, epoxy resins, ethyl cellulose, and carboxyethyl cellulose, and solvents such as terpene-based solvents such as terpineol and dihydroterpineol, and ether-based solvents such as ethyl carbitol and butyl carbitol.
  • glass frits include borosilicate glass, barium borosilicate glass, and zinc borosilicate glass.
  • the conductive composition containing the copper powder of the present invention can be applied to a substrate to form a coating film, which can then be fired to form a conductive film containing copper.
  • the conductive film is preferably used, for example, to form circuits on printed wiring boards and to ensure electrical continuity of external electrodes of ceramic capacitors.
  • the substrate include printed circuit boards made of glass epoxy resins and flexible printed circuit boards made of polyimide.
  • the amounts of copper powder and organic solvent in the conductive composition containing copper powder of the present invention can be adjusted according to the specific use of the conductive composition and the coating method of the conductive composition, but the content of copper powder in the conductive composition is preferably 5% by mass or more and 95% by mass or less, and more preferably 80% by mass or more and 90% by mass or less.
  • Coating methods that can be used include, for example, the inkjet method, the dispenser method, the microdispenser method, the gravure printing method, the screen printing method, the dip coating method, the spin coating method, the spray coating method, the bar coating method, and the roll coating method.
  • the heating temperature when sintering the formed coating film may be equal to or higher than the sintering start temperature of the copper powder, and may be, for example, 150°C to 220°C.
  • the heating atmosphere may be, for example, an oxidizing atmosphere or a non-oxidizing atmosphere.
  • oxidizing atmospheres include oxygen-containing atmospheres.
  • non-oxidizing atmospheres include reducing atmospheres such as hydrogen and carbon monoxide, weakly reducing atmospheres such as a hydrogen-nitrogen mixed atmosphere, and inert atmospheres such as argon, neon, helium, and nitrogen.
  • the heating time is preferably 1 minute to 3 hours, more preferably 3 minutes to 2 hours, provided that heating is performed within the above-mentioned temperature range.
  • the conductive film thus obtained is obtained by sintering the copper powder of the present invention, so that sintering can proceed sufficiently even when sintering is performed under relatively low temperature conditions. Furthermore, during sintering, the copper particles that make up the copper powder melt even at low temperatures, so that the contact area between the copper particles or between the copper particles and the surface of the base material can be increased, resulting in a high degree of adhesion to the objects to be joined and an efficient formation of a dense sintered structure. Furthermore, the conductive film obtained has high continuity, density, and conductive reliability.
  • the present invention has been described above based on its preferred embodiments, but the present invention is not limited to the above embodiments.
  • the copper powder of the present invention may contain copper particles other than copper particles A and copper particles B as long as the desired effect is achieved.
  • the above-described embodiment of the present invention encompasses the following technical ideas.
  • [1] Contains the following copper particles A and copper particles B, A copper powder in which the content of copper particles A is 60% by mass or more and 99% by mass or less, and the content of copper particles B is 1% by mass or more and 40% by mass or less, relative to the total of copper particles A and copper particles B.
  • [Copper particles A] The present invention comprises a core particle made of copper and a coating layer that coats the surface of the core particle, the coating layer is formed from a copper salt of an aliphatic organic acid, Copper particles having a primary particle diameter of 0.1 ⁇ m or more and 0.6 ⁇ m or less.
  • [Copper particles B] a ratio (S1/B) of a first crystallite size S1 calculated by the Scherrer formula from the half-width of a peak derived from the copper (111) plane in an X-ray diffraction measurement to a BET diameter B calculated from a 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 calculated by the Scherrer formula from the half-width of the peak derived from the (220) plane of copper in X-ray diffraction measurement is 1.35 or less; Copper particles having a primary particle diameter of 0.1 ⁇ m or more and 2.0 ⁇ m or less.
  • the copper particles B have a ratio (S1/S3) of the first crystallite size S1 to the third crystallite size S3 calculated by the Scherrer equation from the half-width of the peak derived from the (311) plane of copper in an X-ray diffraction measurement, of 1.35 or less.
  • [3] The copper powder according to [1] or [2], wherein the copper particles B contain carbon element and the content of the carbon element is 5000 ppm or less.
  • the copper powder according to any one of [1] to [3], wherein the copper particles B contain phosphorus element and the content of the phosphorus element is 300 ppm or more.
  • [5] A copper paste containing the copper powder according to any one of [1] to [4].
  • [6] A method for producing a conductive film, comprising applying the copper paste according to [5] to a substrate to form a coating film, and firing the coating film.
  • copper particles A-1, A-2, and B-1 to B-3 were used as copper particles.
  • spherical copper particles described in JP 2015-168878 A were used as copper particles A-2.
  • Other copper particles were produced by the following method.
  • the slurry of the washed core particles was heated to 50° C., and under this condition, a solution in which 17 g of copper (II) laurate was dissolved in 4 L of isopropyl alcohol was instantly added as a surface treatment agent, and the mixture was stirred at 50° C. for 1 hour. Then, solid-liquid separation was performed by filtration, and copper particles having a coating layer of a copper salt of an aliphatic organic acid formed on the surface of the core particles were obtained as a solid content. The content of the surface treatment agent in the obtained copper particles was 0.7% by mass in terms of carbon atoms. Next, the copper particles A-1 and A-2 were subjected to the following evaluations.
  • ⁇ Second reduction step> a 25% NaOH aqueous solution was added to the reaction solution in the first reduction step to adjust the pH of the solution to 7.0.
  • the solution was then heated to 40° C., and 1900.0 g of hydrazine (molar ratio relative to 1 mole of copper: 3.0) was quantitatively and sequentially added to the solution over 10 minutes to perform the second reduction step.
  • the solution was then cooled to 30° C. and stirred for 150 minutes to obtain copper particles in which the cuprous oxide particles were reduced to metallic copper.
  • the aqueous slurry of copper particles thus obtained was subjected to decantation washing until the electrical conductivity reached 1.0 mS (washed slurry).
  • the slurry of the washed core particles was heated to 50°C, and under this condition, a solution in which 4 g of copper (II) laurate was dissolved in 1 L of isopropyl alcohol was instantly added as a surface treatment agent, and the mixture was stirred at 50°C for 1 hour. Then, solid-liquid separation was performed by filtration, and copper particles in which a coating layer of a copper salt of an aliphatic organic acid was formed on the surface of the core particles were obtained as a solid content. Then, the mixture was dried to obtain copper powder consisting of an aggregate of copper particles.
  • the obtained copper particles had a copper element content of more than 98% by mass and had a flat shape.
  • Copper particles B-2 were obtained in the same manner as in the production of copper particles B-1, except that the amount of sodium tripolyphosphate added was 24 g (molar ratio relative to 1 mole of copper: 0.006). The obtained copper particles had a copper content of more than 98% by mass and a flat shape.
  • the carbon element content in the copper particles of copper particles B-1 to B-3 was measured using a carbon/sulfur analyzer (CS844 manufactured by LECO Japan LLC) by placing 0.50 g of any of copper particles B-1 to B-3 in a magnetic crucible, using oxygen gas (purity: 99.5%) as the carrier gas, and setting the analysis time to 40 seconds.
  • the measurement results are shown in Table 2 below.
  • the content of phosphorus element in the copper particles was measured by dissolving 1.00 g of any of copper particles B-1 to B-3 in 50 mL of 15% aqueous nitric acid solution, and introducing the solution into an ICP emission spectrometer (PS3520VDDII manufactured by Hitachi High-Tech Science Co., Ltd.). The measurement results are shown in Table 2 below.
  • Measurements were performed on copper particles B-1 to B-3 by the following method. First, a 20% by mass aqueous slurry was prepared using the washed slurry of copper particles B-1 to B-3. Then, an isopropyl alcohol solution in which 12 g of copper laurate was dissolved as a surface coating treatment agent was added at once to the slurry heated to 50 ° C., and the mixture was stirred for 1 hour. Then, the solid content obtained by solid-liquid separation by filtration was vacuum dried, and the copper powder obtained by obtaining copper particles subjected to surface coating treatment was classified using a sieve with a mesh size of 75 ⁇ m, and the undersized portion was used as a sample.
  • This sample was filled into a sample holder, and measurements were performed under the following conditions using an X-ray diffractometer (Ultima IV manufactured by Rigaku Co., Ltd.). Then, among the diffraction peaks, the main peaks at the positions corresponding to the (220) plane, (111) plane or (311) plane of copper are used as the target, and based on the full width at half maximum of the peak, the above-mentioned Scherrer formula is used to calculate each crystallite size S1 to S3, as well as the S1/S2 and S1/S3 ratios.Furthermore, the S1/B ratio is calculated from each crystallite size obtained. The results are shown in the following Table 2.
  • the copper powder to be measured was spread on a measurement holder, and the copper powder was smoothed using a glass plate so that the thickness of the copper powder was 0.5 mm and the surface was smooth.
  • the X-ray diffraction pattern obtained under the above measurement conditions was analyzed using analysis software under the following conditions.
  • the peak width was corrected using the LaB6 value.
  • the crystallite size was calculated using the full width at half maximum of the peak and the Scherrer constant (0.94).
  • the peaks of the X-ray diffraction pattern used in the analysis are as follows:
  • the Miller indices shown below are synonymous with the above-mentioned copper crystal planes.
  • a peak indexed with Miller index (220) in the vicinity of 2 ⁇ 71° to 76°.
  • a peak indexed with Miller index (111) in the vicinity of 2 ⁇ 40° to 45°.
  • a peak indexed with Miller index (311) in the vicinity of 2 ⁇ 87.5° to 92.5°.
  • 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 Comparative Example. Specifically, each copper particle was added to a 100 mL container in the ratios 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 Comparative Example. Mixing was performed at 100 rpm for 1 hour. The copper powder obtained as described above and polyethylene glycol having a number average molecular weight of 200 were mixed using a three-roll kneader to obtain a copper paste containing 85% by mass of copper powder. The content of each copper particle component relative to 100 parts by mass of the total of the copper particles is shown in Table 3. The "solid content concentration" indicates the ratio of the mass of the copper powder to the mass of the entire copper paste.
  • the copper paste of each of the Examples and Comparative Examples was applied onto a glass substrate, and the substrate was baked at 190° C. for 10 minutes in a nitrogen atmosphere to form a conductive film on the glass substrate.
  • the obtained conductive film had a length of 2 cm, a width of 1 cm and a thickness of 30 ⁇ m, and was evaluated as follows.
  • the thickness of the fired film of the Cu paste was determined by measuring the thickness of the conductive film and glass substrate, and the thickness of the glass substrate alone using a digital length measuring machine (Nikon MFC-101), and calculating the difference between these thicknesses as the thickness of the conductive film.
  • the surface roughness (average roughness Ra) of each conductive film was measured at three points using a surface roughness/contour shape measuring instrument (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 viewpoint of electrical resistance, the surface roughness Ra is preferably 2.0 or less. Furthermore, a conductive film having a small surface roughness Ra means that the conductive film has high density.
  • a copper paste was screen-printed on the polished side of a 5 mm square copper chip with one side polished with a #800 polishing sheet in the form of 2 mm x 2 mm x 30 ⁇ m, and a 3 mm square copper chip with one side polished with a #800 polishing sheet was placed so that the polished surface was the bonding surface. Thereafter, the chip was bonded by firing at 200 ° C. for 30 minutes under a nitrogen atmosphere while applying pressure of 5 MPa using a pressure firing machine (IMC-1AB6 manufactured by Imoto Seisakusho). The bond strength of the resulting bonded body was measured using a bond tester (Condor Sigma manufactured by XYZTEC Corporation).
  • Example 8 Comparative Example 8 and Comparative Example 9
  • Table 4 As shown in Table 4 below, when copper powder and polyethylene glycol having 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 copper pastes containing 90 mass% copper powder. Except for this, the copper pastes and conductive films thereof of Example 8, Comparative Example 8, and Comparative Example 9 were prepared in the same manner as in Example 2, Comparative Example 3, and Comparative Example 5. These copper pastes and conductive films thereof 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.
  • the copper powders of Examples 2 and 8, which contain both copper particles A-1 and B-1 are less likely to be adversely affected in the resistivity and surface roughness Ra of the conductive film, even when the content of the organic solvent in the copper paste is changed.
  • Comparative Examples 8 and 9 when copper powder containing only either copper particles A-1 or B-1 is used, if the content of the organic solvent in the copper paste is 10 mass%, it can be seen that the resistivity of the conductive film in particular increases significantly.
  • a copper powder is provided that can produce a conductive film having high continuity and density and can be sintered at a low temperature.

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 μm 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 μm, 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

銅粉及びこれを含む銅ペースト並びに導電膜の製造方法Method for producing copper powder, copper paste containing the same, and conductive film
　本発明は、銅粉及びこれを含む銅ペーストに関する。また本発明は、導電膜の製造方法に関する。 The present invention relates to copper powder and a copper paste containing the same. The present invention also relates to a method for producing a conductive film.
　銅は導電性の高い金属であり、また汎用性が高い材料であることから、導電材料として工業的に広く用いられている。例えば銅粒子の集合体である銅粉は、積層セラミックコンデンサ（以下「ＭＬＣＣ」ともいう。）の外部電極及び内部電極、並びに各種基板への配線など、各種電子部品を製造するための原材料として幅広く利用されている。 Copper is a highly conductive metal and a versatile material, and is therefore widely used industrially as a conductive material. For example, copper powder, which is an aggregate of copper particles, is widely used as a raw material for manufacturing various electronic components, such as the external and internal electrodes of multilayer ceramic capacitors (hereafter also referred to as "MLCC"), and wiring for various substrates.
　そのような銅粉の一つとして、本出願人は先に、一次粒子の平均粒径が０．１μｍ以上０．６μｍ以下であり、粒子表面に表面処理剤が施されている球状銅粒子に関する技術を提案した（特許文献１参照）。この技術によれば、銅粒子の低温焼結性が良好になるという利点がある。 As one such copper powder, the present applicant has previously proposed a technology relating to spherical copper particles in which the average particle size of the primary particles is 0.1 μm or more and 0.6 μm or less, and the particle surfaces are treated with a surface treatment agent (see Patent Document 1). This technology has the advantage of improving the low-temperature sintering properties of the copper particles.
特開２０１５－１６８８７８号公報JP 2015-168878 A
　しかし、球状銅粒子を用いてペーストを調製し、該ペーストから各種の導電膜を製造する場合、その粒子形状に起因して、導電膜の連続性が担保しづらいことがある。
　一方、銅粒子として扁平状の銅粒子も知られている。しかし、扁平状銅粒子を用いてペーストを調製し、該ペーストから各種の導電膜を製造する場合、その粒子形状に起因して、導電膜の緻密性を向上させづらいことがある。
　そこで現在では、お互いの短所を補うことを目的として、球状銅粒子と扁平状銅粒子とを混合して用いる場合が多い。しかし、昨今では、導電膜の連続性及び緻密性に加えて、導電膜を製造するときの銅粒子の低温焼結性も求められている。球状銅粒子と扁平状銅粒子とを単に混合して用いただけでは混合銅粒子の低温焼結性は高まらない。 However, when a paste is prepared using spherical copper particles and various conductive films are produced from the paste, it may be difficult to ensure the continuity of the conductive film due to the particle shape.
On the other hand, flat copper particles are also known as copper particles. However, when a paste is prepared using the flat copper particles and various conductive films are produced from the paste, it may be difficult to improve the density of the conductive film due to the particle shape.
Therefore, in order to compensate for each other's shortcomings, spherical copper particles and flat copper particles are often used in combination. However, in recent years, 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. Simply mixing spherical copper particles and flat copper particles does not improve the low-temperature sintering property of the mixed copper particles.
　したがって本発明の課題は、連続性及び緻密性が高い導電膜を製造でき、且つ、焼結温度が低い銅粉を提供することにある。 The objective of the present invention is therefore to provide copper powder that can produce conductive films with high continuity and density, and that has a low sintering temperature.
　本発明は、以下の銅粒子Ａ及び銅粒子Ｂを含み、
　銅粒子Ａと銅粒子Ｂの合計に対する銅粒子Ａの含有割合が６０質量％以上９９質量％以下であり、銅粒子Ｂの含有割合が１質量％以上４０質量％以下である、銅粉を提供するものである。
〔銅粒子Ａ〕
　銅からなるコア粒子と、該コア粒子の表面を被覆する被覆層とを備え、
　前記被覆層は脂肪族有機酸の銅塩によって形成されており、
　一次粒子径が０．１μｍ以上０．６μｍ以下である銅粒子。
〔銅粒子Ｂ〕
　ＢＥＴ比表面積から算出されたＢＥＴ径Ｂに対する、Ｘ線回折測定において銅の（１１１）面に由来するピークの半値幅からシェラーの式によって求められる第１結晶子サイズＳ１の比（Ｓ１Ｂ）が０．２３以下であり、
　Ｘ線回折測定において銅の（２２０）面に由来するピークの半値幅からシェラーの式によって求められる第２結晶子サイズＳ２に対する、前記第１結晶子サイズＳ１の比（Ｓ１／Ｓ２）が１．３５以下であり、
　一次粒子径が０．１μｍ以上２．０μｍ以下である銅粒子。 The present invention includes the following copper particles A and copper particles B,
The copper powder has a content of copper particles A of 60% by mass or more and 99% by mass or less relative to the total content of copper particles A and copper particles B, and a content of copper particles B of 1% by mass or more and 40% by mass or less.
[Copper particles A]
The present invention comprises a core particle made of copper and a coating layer that coats the surface of the core particle,
the coating layer is formed from a copper salt of an aliphatic organic acid,
Copper particles having a primary particle diameter of 0.1 μm or more and 0.6 μm or less.
[Copper particles B]
a ratio (S1B) of a first crystallite size S1 calculated by the Scherrer formula from the half-width of a peak derived from the copper (111) plane in an X-ray diffraction measurement to a BET diameter B calculated from a 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 calculated by the Scherrer formula from the half-width of the peak derived from the (220) plane of copper in X-ray diffraction measurement is 1.35 or less;
Copper particles having a primary particle diameter of 0.1 μm or more and 2.0 μm or less.
　以下本発明を、その好ましい実施形態に基づき説明する。本発明の銅粉は、以下の銅粒子Ａ及び銅粒子Ｂを含む。
〔銅粒子Ａ〕
　銅からなるコア粒子と、該コア粒子の表面を被覆する被覆層とを備え、
　前記被覆層は脂肪族有機酸の銅塩によって形成されており、
　一次粒子径が０．１μｍ以上０．６μｍ以下である銅粒子。
〔銅粒子Ｂ〕
　ＢＥＴ比表面積から算出されたＢＥＴ径Ｂに対する、Ｘ線回折測定において銅の（１１１）面に由来するピークの半値幅からシェラーの式によって求められる第１結晶子サイズＳ１の比（Ｓ１Ｂ）が０．２３以下であり、
　Ｘ線回折測定において銅の（２２０）面に由来するピークの半値幅からシェラーの式によって求められる第２結晶子サイズＳ２に対する、前記第１結晶子サイズＳ１の比（Ｓ１／Ｓ２）が１．３５以下であり、
　一次粒子径が０．１μｍ以上２．０μｍ以下である銅粒子。ただし、銅粒子Ａに該当するものは除く。 The present invention will be described below based on preferred embodiments. The copper powder of the present invention includes copper particles A and copper particles B described below.
[Copper particles A]
The present invention comprises a core particle made of copper and a coating layer that coats the surface of the core particle,
the coating layer is formed from a copper salt of an aliphatic organic acid,
Copper particles having a primary particle diameter of 0.1 μm or more and 0.6 μm or less.
[Copper particles B]
a ratio (S1B) of a first crystallite size S1 calculated by the Scherrer formula from the half-width of a peak derived from the copper (111) plane in an X-ray diffraction measurement to a BET diameter B calculated from a 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 calculated by the Scherrer formula from the half-width of the peak derived from the (220) plane of copper in X-ray diffraction measurement is 1.35 or less;
Copper particles having a primary particle size of 0.1 μm or more and 2.0 μm or less, except for those that fall under Copper Particles A.
　本発明者らが鋭意検討したところ、驚くべきことに、前記の銅粒子Ａ及びＢを含む銅粉は焼結温度が低く、また該銅粉を含む銅ペーストから製造された導電膜は高い連続性及び緻密性を有することを見いだした。 The inventors conducted extensive research and surprisingly found that the copper powder containing the copper particles A and B has a low sintering temperature, and that the conductive film produced from the copper paste containing the copper powder has high continuity and density.
　上述の効果をより一層高める観点から、銅粒子Ａは球状の形状を有することが好ましい。一方、銅粒子Ｂは扁平状の形状を有することが好ましい。 In order to further enhance the above-mentioned effects, it is preferable that copper particles A have a spherical shape. On the other hand, it is preferable that copper particles B have a flat shape.
　本発明の銅粉の低温での焼結性の向上と、該粒子の焼結によって得られる導電膜の導電性の向上を両立する観点から、銅粒子Ａは、その一次粒子の平均画像解析径が好ましくは０．１μｍ以上０．６μｍ以下、より好ましくは０．１２μｍ以上０．４μｍ以下、更に好ましくは０．１５μｍ以上０．３μｍ以下である。一次粒子とは、外形上の幾何学的形態から判断して、粒子としての最小単位と認められる物体のことをいう。
　同様の観点から、銅粒子Ｂは、その一次粒子の平均画像解析径が、好ましくは０．１μｍ以上２．０μｍ以下、より好ましくは０．１５μｍ以上１．０μｍ以下、更に好ましくは０．２μｍ以上０．６μｍ以下である。 From the viewpoint of achieving both improved sinterability at low temperatures of the copper powder of the present invention and improved electrical conductivity of the conductive film obtained by sintering the particles, the average image analysis diameter of the primary particles of the copper particles A is preferably 0.1 μm or more and 0.6 μm or less, more preferably 0.12 μm or more and 0.4 μm or less, and even more preferably 0.15 μm or more and 0.3 μm or less. The primary particle refers to an object that is recognized as the smallest unit of a particle, judging from the geometric shape of its outer shape.
From the same viewpoint, the average image analysis diameter of the primary particles of copper particles B is preferably 0.1 μm or more and 2.0 μm or less, more preferably 0.15 μm or more and 1.0 μm or less, and even more preferably 0.2 μm or more and 0.6 μm or less.
　また、ＢＥＴ比表面積から算出された銅粒子Ａの粒子径（以下、ＢＥＴ径Ａともいう。）は、好ましくは０．１μｍ以上０．６μｍ以下、より好ましくは０．１２μｍ以上０．４μｍ以下、更に好ましくは０．１５μｍ以上０．３μｍ以下である。ＢＥＴ径Ａがこのような範囲となっていることによって、本発明の銅粉の熱伝導性を高めて、焼結温度を効果的に低下させることができる。
　同様の観点から、ＢＥＴ比表面積から算出された銅粒子Ｂの粒子径（以下、ＢＥＴ径Ｂともいう。）は、好ましくは０．１μｍ以上２．０μｍ以下、より好ましくは０.１５μｍ以上１．０μｍ以下、更に好ましくは０．２μｍ以上０．６μｍ以下である。ＢＥＴ径Ｂがこのような範囲となっていることによって、本発明の銅粉の熱伝導性を高めて、焼結温度を効果的に低下させることができる。
　本明細書においては、ＢＥＴ径Ｂのことを銅粒子Ｂの一次粒子径ともいう。 The particle diameter of the copper particles A calculated from the BET specific surface area (hereinafter also referred to as BET diameter A) is preferably 0.1 μm or more and 0.6 μm or less, more preferably 0.12 μm or more and 0.4 μm or less, and even more preferably 0.15 μm or more and 0.3 μm or less. By having the BET diameter A in such a range, the thermal conductivity of the copper powder of the present invention can be increased and the sintering temperature can be effectively reduced.
From the same viewpoint, the particle diameter of copper particles B calculated from the BET specific surface area (hereinafter also referred to as BET diameter B) is preferably 0.1 μm or more and 2.0 μm or less, more preferably 0.15 μm or more and 1.0 μm or less, and even more preferably 0.2 μm or more and 0.6 μm or less. By having the BET diameter B in such a range, the thermal conductivity of the copper powder of the present invention can be increased, and the sintering temperature can be effectively reduced.
In this specification, the BET diameter B is also referred to as the primary particle diameter of the copper particles B.
　銅粒子Ａ及びＢの一次粒子の平均画像解析径は、例えば走査型電子顕微鏡（日本電子（株）製ＪＳＭ－６３３０Ｆ）を用い、倍率１００００倍又は３００００倍で銅粒子を観察し、視野中の粒子２００個について水平方向における最大フェレ径を測定し、これらの測定値から、球に換算した体積平均粒径を算出することができる。
　本明細書においては、このように算出された銅粒子Ａの一次粒子の平均画像解析径のことを銅粒子Ａの一次粒子径ともいう。 The average image analysis diameter of the primary particles of copper particles A and B can be determined, for example, by observing the copper particles at a magnification of 10,000 times or 30,000 times using a scanning electron microscope (JSM-6330F manufactured by JEOL Ltd.), measuring the maximum Feret's diameter in the horizontal direction for 200 particles in the field of view, and calculating the volume average particle diameter converted into a sphere from these measured values.
In this specification, the average image analysis diameter of the primary particles of copper particles A calculated in this manner is also referred to as the primary particle diameter of copper particles A.
　ＢＥＴ比表面積から算出されたＢＥＴ径Ａ及びＢは、ＢＥＴ法に基づいて、以下の条件で測定できる。具体的には、株式会社マウンテック製の「Ｍａｃｓｏｒｂ」を用い、窒素吸着法で測定することができる。測定粉末の量は０．２ｇとし、予備脱気条件は真空下、８０℃で３０分間とする。そして、ＢＥＴ径Ａ及びＢは、測定されたＢＥＴ比表面積から、以下の式（Ｉ）にて算出される。
　式（Ｉ）中、ｄはＢＥＴ径Ａ又はＢ［μｍ］、ＡＢＥＴはＢＥＴ一点法で測定される比表面積［ｍ２／ｇ］、ρは銅の密度［ｇ／ｃｍ３］である。
　　ｄ＝６／（ＡＢＥＴ×ρ）　　・・・（Ｉ）
　以下、銅粒子Ａ及びＢについて、その好ましい実施形態をそれぞれ詳述する。 The BET diameters A and B calculated from the BET specific surface area can be measured under the following conditions based on the BET method. Specifically, the measurements can be performed by nitrogen adsorption using "Macsorb" manufactured by Mountech Co., Ltd. The amount of powder to be measured is 0.2 g, and the preliminary degassing conditions are under vacuum at 80°C for 30 minutes. The BET diameters A and B are calculated from the measured BET specific surface area by the following formula (I).
In formula (I), d is the BET diameter A or B [μm], A BET is the specific surface area measured by the BET single point method [m 2 /g], and ρ is the density of copper [g/cm 3 ].
d = 6 / (A BET × ρ) ... (I)
Hereinafter, preferred embodiments of the copper particles A and B will be described in detail.
＜銅粒子Ａの好ましい実施形態＞
　銅粒子Ａは、該粒子の表面に脂肪族有機酸の銅塩を含む表面処理剤が施されているものである。これによって、表面処理剤からなる被覆層が、銅からなるコア粒子の表面を連続的に又は不連続的に覆うように形成されている。表面処理剤は、銅の酸化と、粒子の凝集との双方を抑制するために用いられる。
　またコア粒子は、好ましくは銅及び残部不可避不純物のみからなる。 <Preferable embodiment of copper particles A>
The copper particles A have a surface treatment agent containing a copper salt of an aliphatic organic acid applied to the surface of the particles. As a result, a coating layer made of the surface treatment agent is formed so as to cover the surface of the copper core particle continuously or discontinuously. The surface treatment agent is used to suppress both the oxidation of copper and the aggregation of the particles.
The core particles preferably consist of only copper with the remainder being unavoidable impurities.
　上述のとおり、本発明に用いられる表面処理剤は、脂肪族有機酸の銅塩を含んでいる。 As mentioned above, the surface treatment agent used in the present invention contains a copper salt of an aliphatic organic acid.
　本技術分野においては、銅粒子における銅の酸化の抑制と、粒子どうしの凝集の抑制とを両立するために、脂肪酸や脂肪酸アミン等の表面処理剤が用いられてきた。しかし、このような処理剤は、該処理剤の分解温度が高く、銅粒子の焼結時に十分に除去できない場合があった。このことに起因して、焼結開始温度が上昇したり、銅粒子どうしの焼結後に得られる導電膜の抵抗が高くなったりすることがあった。この問題点を解決すべく本発明者が鋭意検討したところ、表面処理剤として、脂肪族有機酸の銅塩を用いることによって、銅の酸化及び粒子どうしの凝集の双方を抑制しつつ、焼結開始温度を低くすることができ、その結果、粒子どうしの低温焼結性を向上しつつ、焼結後に得られる導電膜の抵抗を低くすることができることを見出した。 In this technical field, surface treatment agents such as fatty acids and fatty acid amines have been used to simultaneously inhibit the oxidation of copper in copper particles and inhibit the aggregation of the particles. However, such treatment agents have a high decomposition temperature, and there are cases where they cannot be sufficiently removed during sintering of the copper particles. This can cause the sintering start temperature to rise and the resistance of the conductive film obtained after sintering the copper particles together to increase. The inventors conducted extensive research to solve this problem and found that by using a copper salt of an aliphatic organic acid as a surface treatment agent, it is possible to lower the sintering start temperature while inhibiting both the oxidation of copper and the aggregation of the particles, and as a result, it is possible to improve the low-temperature sintering of the particles while lowering the resistance of the conductive film obtained after sintering.
　本発明の銅粉の焼結温度を低下させつつ、銅の酸化抑制と粒子どうしの凝集抑制とを兼ね備える観点から、脂肪族有機酸の銅塩を構成する脂肪族有機酸の炭素原子数は、６以上１８以下であることが好ましく、８以上１８以下であることがより好ましく、１０以上１８以下であることが更に好ましく、１２以上１８以下であることが一層好ましい。このような脂肪族有機酸としては、例えば、直鎖又は分枝鎖であり且つ飽和又は不飽和であるカルボン酸、あるいは直鎖又は分枝鎖であり且つ飽和又は不飽和である炭化水素基を有するスルホン酸等が挙げられ、好ましくは直鎖であり、且つ飽和又は不飽和のカルボン酸である。また、脂肪族有機酸の銅塩における銅の価数は一価又は二価であり、好ましくは二価である。 From the viewpoint of lowering the sintering temperature of the copper powder of the present invention while simultaneously suppressing oxidation of copper and agglomeration between particles, the number of carbon atoms in the aliphatic organic acid constituting the copper salt of an aliphatic organic acid is preferably 6 to 18, more preferably 8 to 18, even more preferably 10 to 18, and even more preferably 12 to 18. Examples of such aliphatic organic acids include linear or branched, saturated or unsaturated carboxylic acids, and linear or branched, saturated or unsaturated hydrocarbon group-containing sulfonic acids, and the like, preferably linear, saturated or unsaturated carboxylic acids. The valence of copper in the copper salt of an aliphatic organic acid is monovalent or divalent, and preferably divalent.
　カルボン酸の具体例としては、クエン酸、ヘキサン酸、ヘプタン酸、オクタン酸、ノナン酸、デカン酸、ラウリン酸、パルミチン酸、オレイン酸、ステアリン酸等が挙げられ、好ましくはラウリン酸、オレイン酸及びステアリン酸であり、更に好ましくはラウリン酸及びステアリン酸である。
　スルホン酸の具体例としては、ヘキサンスルホン酸、ヘプタンスルホン酸、オクタンスルホン酸、ノナンスルホン酸、デカンスルホン酸、ラウリンスルホン酸、パルミチンスルホン酸、オレインスルホン酸、ステアリンスルホン酸等が挙げられる。これらの脂肪族有機酸は、単独で又は二種以上を組み合わせて用いることができる。 Specific examples of carboxylic acids include citric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, lauric acid, palmitic acid, oleic acid, stearic acid, etc., of which lauric acid, oleic acid, and stearic acid are preferred, and lauric acid and stearic acid are more preferred.
Specific examples of sulfonic acids include hexanesulfonic acid, heptanesulfonic acid, octanesulfonic acid, nonanesulfonic acid, decanesulfonic acid, laurinsulfonic acid, palmitic acid, oleinsulfonic acid, stearinsulfonic acid, etc. These aliphatic organic acids can be used alone or in combination of two or more kinds.
　表面処理剤は、例えば、銅からなるコア粒子を製造した後の工程において、得られたコア粒子と、表面処理剤である脂肪族有機酸の銅塩とを接触させることによって、粒子表面に施すことができる。表面処理剤を施す量は、該表面処理剤が施された状態での銅粒子Ａに占める該表面処理剤全体の割合（質量％）で表して、炭素原子換算で０．２質量％以上２．０質量％以下とすることが好ましく、０．３質量％以上１．０質量％以下とすることが更に好ましい。このような範囲にあることで、表面処理剤による銅粒子表面の酸化被膜の除去や、共融解による効果によって、銅粒子どうしの融解温度を低温化することができ、その結果、焼結温度を低下させることができる。 The surface treatment agent can be applied to the particle surface, for example, in a process after the production of core particles made of copper, by contacting the obtained core particles with a copper salt of an aliphatic organic acid, which is the surface treatment agent. The amount of the surface treatment agent applied is expressed as the proportion (mass %) of the entire surface treatment agent in copper particles A in a state in which the surface treatment agent is applied, and is preferably 0.2 mass % or more and 2.0 mass % or less in carbon atom equivalent, and more preferably 0.3 mass % or more and 1.0 mass % or less. By being in such a range, the melting temperature between the copper particles can be lowered by the effect of removing the oxide film on the copper particle surface by the surface treatment agent and co-melting, and as a result, the sintering temperature can be lowered.
　銅粒子Ａの表面に施された表面処理剤の割合（質量％）は、次のようにして測定することができる。表面処理剤が施された銅粒子Ａの集合体である銅粉０．５ｇを、炭素・硫黄分析装置（堀場製作所製、ＥＭＩＡ－３２０Ｖ）にて酸素気流中で加熱し、銅粉中の炭素分をＣＯあるいはＣＯ２に分解させてその量を定量することで表面処理剤の割合を算出する。 The proportion (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 an aggregate of copper particles A to which a surface treatment agent has been applied, is heated in an oxygen stream using a carbon/sulfur analyzer (Horiba, Ltd., EMIA-320V), and the carbon content in the copper powder is decomposed into CO or CO2 , and the amount of the decomposed carbon or CO2 is quantified to calculate the proportion of the surface treatment agent.
　表面処理剤の定性及び定量は、例えば核磁気共鳴（ＮＭＲ）法、ラマン分光法、赤外分光法、液体クロマトグラフィー法、飛行時間型二次イオン質量分析法（ＴＯＦ－ＳＩＭＳ）等の方法を単独で又は組み合わせて用いて行うことができる。 Qualitative and quantitative analysis of surface treatment agents can be performed using methods such as nuclear magnetic resonance (NMR) spectroscopy, Raman spectroscopy, infrared spectroscopy, liquid chromatography, and time-of-flight secondary ion mass spectrometry (TOF-SIMS), either alone or in combination.
　銅粒子Ａは、表面処理剤として脂肪族有機酸の銅塩を用いて形成された被覆層をコア粒子の表面に有するものであるところ、被覆層が脂肪族有機酸の銅塩を用いて形成されたものであるか否かは、例えば以下の方法によって判定することができる。詳細には、銅粒子Ａの質量が５質量％となるようにＫＢｒにて希釈し、乳鉢混合した測定試料を、日本分光社製の赤外分光光度計（型番：ＦＴ－ＩＲ４６００）を用い、拡散反射法にて、分解能４ｃｍ－１、積算回数１２８回の条件で測定して、縦軸に吸光度をクベルカ－ムンク変換した値をとり、横軸に波数（５００～４０００ｃｍ－１）をとったグラフ（スペクトル）を得る。このとき、赤外線吸収ピークが１５０４ｃｍ－１以上１５１４ｃｍ－１以下の範囲に観察され、且つ１５８４ｃｍ－１以上１５９６ｃｍ－１以下の範囲に観察されなければ、被覆層が脂肪族有機酸の銅塩を用いて形成されたものと判断することができる。すなわち、銅粒子Ａは、赤外分光法による測定において、１５０４ｃｍ－１以上１５１４ｃｍ－１以下の範囲に赤外線吸収ピークが観察され、１５８４ｃｍ－１以上１５９６ｃｍ－１以下の範囲に赤外線吸収ピークが観察されないことが好ましい。
　「赤外線吸収ピークを有する」とは、以下の方法に従い定義される。まず、２９１０ｃｍ－１以上２９４０ｃｍ－１以下の範囲に観測されるピークの最大値で規格化したＩＲスペクトルデータに対して二回微分を行い、１５００ｃｍ－１以上１６００ｃｍ－１以下の範囲においてゼロアップクロス法に基づいて波形分離する。次いで、波形分離した各波形における基準線（ゼロ）からの振幅の絶対値から、算術平均値を算出する。そして、当該算術平均値の半分の値よりも、ピーク高さの絶対値が大きい場合に「赤外線吸収ピークを有する」とする。
　なお、脂肪酸や脂肪族アミンを表面処理剤として用いた銅粒子の場合、１５８４ｃｍ－１以上１５９６ｃｍ－１以下の範囲に赤外線吸収ピークが検出されるので、この点で銅粒子Ａと区別することができる。 Copper particles A have a coating layer formed on the surface of a core particle using a copper salt of an aliphatic organic acid as a surface treatment agent, and whether or not the coating layer was formed using a copper salt of an aliphatic organic acid can be determined, for example, by the following method. In detail, the copper particles A are diluted with KBr so that the mass of the copper particles A becomes 5 mass%, and the measurement sample is mixed in a mortar and measured by a diffuse reflectance method using an infrared spectrophotometer (model number: FT-IR4600) manufactured by JASCO Corporation under conditions of a resolution of 4 cm -1 and an accumulation number of 128 times, and a graph (spectrum) is obtained in which the vertical axis represents the value obtained by Kubelka-Munk conversion of absorbance and the horizontal axis represents wave numbers (500 to 4000 cm -1 ). In this case, if an infrared absorption peak is observed in the range of 1504 cm -1 or more and 1514 cm -1 or less and not in the range of 1584 cm -1 or more and 1596 cm -1 or less, it can be determined that the coating layer is formed using a copper salt of an aliphatic organic acid. That is, it is preferable that, in the measurement by infrared spectroscopy, the copper particles A have an infrared absorption peak in the range of 1504 cm -1 or more and 1514 cm -1 or less and no infrared absorption peak is observed in the range of 1584 cm -1 or more and 1596 cm -1 or less.
"Having an infrared absorption peak" is defined according to the following method. First, IR spectrum data normalized with the maximum value of the peak observed in the range of 2910 cm -1 to 2940 cm -1 is differentiated twice, and waveform separation is performed in the range of 1500 cm -1 to 1600 cm -1 based on the zero-up crossing method. Next, an arithmetic mean value is calculated from the absolute value of the amplitude from the reference line (zero) in each waveform obtained by waveform separation. Then, when the absolute value of the peak height is greater than half the value of the arithmetic mean value, it is deemed to "have an infrared absorption peak."
In addition, in the case of copper particles using a fatty acid or an aliphatic amine as a 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 in this respect, they can be distinguished from copper particles A.
　脂肪族有機酸の銅塩を用いることによって、銅の酸化及び粒子どうしの凝集の双方を抑制しつつ、本発明の銅粉の焼結温度を低下させることができる銅粒子が得られる理由は明らかでないが、本発明者は以下のように推測している。
　上述のように、本発明の銅粒子と、脂肪酸や脂肪族アミンを表面処理剤として用いた銅粒子とでは、特定の波数における赤外線吸収ピークの有無に違いを有している。
　赤外分光法は、赤外線を測定対象の物質又は分子に照射することによって、分子中の結合の運動エネルギーに相当する光エネルギーの吸収を測定することを測定原理としている。一般に、赤外分光法において赤外吸収が観察される場合には、分子中に何らかの結合が存在していることを示している。特に、高波数位置に赤外吸収が観察される場合、高波数の赤外線はエネルギーが高いので、結合エネルギーが大きい結合が分子中に存在するといえる。
　銅粒子Ａと、脂肪酸や脂肪族アミンを表面処理剤として用いた銅粒子とを比較すると、いずれの粒子も１５０４ｃｍ－１以上１５１４ｃｍ－１以下の範囲の低波数領域に赤外吸収が観測されるので、当該領域の吸収は、コア粒子表面に被覆層が結合して存在していることを意味すると推測される。このため、コア粒子の銅の酸化及び粒子どうしの凝集の双方を抑制することができると考えられる。
　一方、１５８４ｃｍ－１以上１５９６ｃｍ－１以下の範囲の高波数領域に着目すると、銅粒子Ａは、前記高波数領域に観測される赤外吸収が観察されないのに対し、脂肪酸や脂肪族アミンを表面処理剤として用いた銅粒子は、赤外吸収が前記高波数領域に観測される。つまり、脂肪酸や脂肪族アミンを表面処理剤として用いた銅粒子と比較して、本発明の銅粒子は、結合エネルギーが大きい結合が分子中に少ないことを意味している。このことは、本発明の銅粒子において、表面処理剤とコア粒子との結合が比較的弱くなっていると考えられるので、表面処理剤が低温で脱離しやすくなり、粒子どうしの焼結が低温で達成できると考えられる。
　以上の理由から、銅粒子Ａの表面に脂肪族有機酸の銅塩を含む表面処理剤を施すことによって、銅の酸化及び粒子どうしの凝集の双方を抑制しつつ、焼結温度の低下が達成できると考えられる。 The reason why the use of a copper salt of an aliphatic organic acid can produce copper particles that can lower the sintering temperature of the copper powder of the present invention while suppressing both copper oxidation and aggregation between particles is unclear, but the inventors speculate as follows.
As described above, there is a difference between the copper particles of the present invention and copper particles using a fatty acid or an aliphatic amine as a surface treatment agent in terms of the presence or absence of an infrared absorption peak at a specific wave number.
The principle of infrared spectroscopy is to measure the absorption of light energy equivalent to the kinetic energy of bonds in a molecule by irradiating infrared rays to a substance or molecule to be measured. In general, when infrared absorption is observed in infrared spectroscopy, it indicates that some bonds exist in the molecule. In particular, when infrared absorption is observed at a high wave number position, it can be said that bonds with high bond energy exist in the molecule because infrared rays at high wave numbers have high energy.
When copper particles A are compared with copper particles using a fatty acid or an aliphatic amine as a surface treatment agent, infrared absorption is observed in the low wave number region of 1504 cm −1 or more and 1514 cm −1 or less for both particles, and it is presumed that the absorption in this region means that a coating layer is bonded to the surface of the core particles. For this reason, it is considered that both the oxidation of the copper of the core particles and the aggregation of the particles can be suppressed.
On the other hand, when focusing on the high wavenumber region in the range of 1584 cm -1 to 1596 cm -1 , the copper particles A do not show infrared absorption observed in the high wavenumber region, whereas the copper particles using fatty acids or aliphatic amines as surface treatment agents show infrared absorption in the high wavenumber region. In other words, 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 large bond energy in the molecule. This is thought to be because the bond between the surface treatment agent and the core particles in the copper particles of the present invention is relatively weak, so that the surface treatment agent is easily detached at low temperatures, and sintering between the particles can be achieved at low temperatures.
For the above reasons, it is believed that by applying a surface treatment agent containing a copper salt of an aliphatic organic acid to the surface of copper particles A, it is possible to suppress both copper oxidation and aggregation between particles while achieving a reduction in the sintering temperature.
　また銅粒子Ａについて、脂肪族有機酸の銅塩を構成する脂肪族有機酸がどの有機酸であるかを特定するためには、例えばＴＯＦ－ＳＩＭＳによって分析することができる。 In addition, to identify which aliphatic organic acid constitutes the copper salt of an aliphatic organic acid, copper particles A can be analyzed, for example, by TOF-SIMS.
　本発明の銅粉の焼結温度を更に低下させる観点から、銅粒子Ａを２５℃から１０００℃まで加熱したときの熱重量分析において、５００℃における質量減少値に対する質量減少値の割合が１０％となる温度が、好ましくは１５０℃以上２２０℃以下、更に好ましくは１８０℃以上２２０℃以下である。 In order to further reduce the sintering temperature of the copper powder of the present invention, in a thermogravimetric analysis when copper particles A are heated from 25°C to 1000°C, the temperature at which the ratio of the mass loss to the mass loss at 500°C is 10% is preferably 150°C or higher and 220°C or lower, and more preferably 180°C or higher and 220°C or lower.
　上述した熱重量分析は、例えば以下の方法で行うことができる。すなわち、ブルカー・エイエックスエス社製のＴＧ－ＤＴＡ２０００ＳＡを用いて、測定サンプルを５０ｍｇとし、２５℃から１０００℃まで加熱したときの質量減少率を測定する。雰囲気は窒素とし、昇温速度は１０℃／ｍｉｎとする。質量減少率が所定の割合となる温度が低いほど、被覆層を形成する脂肪族有機酸を除去できる温度が低いことを示すので、銅粒子Ａの低温焼結性の尺度となるものである。 The above-mentioned thermogravimetric analysis can be carried out, for example, by the following method. That is, using a TG-DTA2000SA manufactured by Bruker AXS, a measurement sample of 50 mg is used, and the mass loss rate is measured when heated from 25°C to 1000°C. The atmosphere is nitrogen, and the heating rate is 10°C/min. The lower the temperature at which the mass loss rate reaches a predetermined rate, the lower the temperature at which the aliphatic organic acid that forms the coating layer can be removed, and this is a measure of the low-temperature sintering property of copper particle A.
　上述のとおり、銅粒子Ａの形状は球状であることが好ましい。球状の銅粒子Ａを得るためには、例えばコア粒子の形状を球状とすればよい。なお、粒子が球状であるとは、以下の方法で測定した円形度係数が好ましくは０．８５以上、更に好ましくは０．９０以上であることをいう。円形度係数は、次の方法で算出される。金属粒子の走査型電子顕微鏡像を撮影し、粒子どうしが重なり合っていないものを無作為に１０００個選び出す。粒子の二次元投影像の面積をＳとし、周囲長をＬとしたときに、粒子の円形度係数を４πＳ／Ｌ２の式から算出する。各粒子の円形度係数の算術平均値を上述した円形度係数とする。粒子の二次元投影像が真円である場合は、粒子の円形度係数は１となる。 As described above, the shape of the copper particles A is preferably spherical. In order to obtain spherical copper particles A, for example, the shape of the core particles may be spherical. In addition, the spherical shape of the particles means that the circularity coefficient measured by the following method is preferably 0.85 or more, more preferably 0.90 or more. The circularity coefficient is calculated by the following method. A scanning electron microscope image of the metal particles is taken, and 1000 particles that do not overlap with each other are randomly selected. When the area of the two-dimensional projection image of the particle is S and the perimeter is L, the circularity coefficient of the particle is calculated from the formula 4πS/ L2 . The arithmetic average value of the circularity coefficient of each particle is the above-mentioned circularity coefficient. When the two-dimensional projection image of the particle is a perfect circle, the circularity coefficient of the particle is 1.
＜銅粒子Ｂの好ましい実施形態＞
　銅粒子Ｂは、Ｘ線回折測定によって算出された特定の結晶面における結晶子サイズが所定の関係にある。具体的には、ＢＥＴ比表面積から算出された粒子径をＢＥＴ径Ｂとし、Ｘ線回折測定において銅の（１１１）面に由来する回折ピークからシェラーの式によって求められる結晶子サイズを第１結晶子サイズＳ１としたときに、ＢＥＴ径Ｂに対する第１結晶子サイズＳ１の比（Ｓ１／Ｂ）が、好ましくは０．２３以下、より好ましくは０．０２以上０．２３以下、更に好ましくは０．０５以上０．２３以下である。 <Preferable embodiment of copper particles B>
Copper particles B have a predetermined relationship in terms of crystallite size on a specific crystal plane calculated by X-ray diffraction measurement. Specifically, when the particle diameter calculated from the BET specific surface area is the BET diameter B, and the crystallite size calculated from the diffraction peak derived from the (111) plane of copper in the X-ray diffraction measurement by the Scherrer formula is 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 even more preferably 0.05 or more and 0.23 or less.
　銅の（１１１）面に由来する回折ピークは、銅粒子ＢをＸ線回折測定したと得られるＸ線回折パターンの最大の高さを有するピークである。このことから、第１結晶子サイズは他の結晶面に由来する回折ピークから算出された結晶子サイズよりも大きく、結晶性も代表していると考えられる。したがって、第１結晶子サイズＳ１がＢＥＴ径Ｂに対して小さい構成となっていることによって、結晶粒界が一粒子中に多いと推測される。その結果、粒子を加熱したときに印加される熱エネルギーによって、結晶子界面が不安定化しやすくなって原子拡散が活発になり、低温での粒子どうしの融着性を高め、焼結温度を低下させることができる。
　このような銅粒子は、例えば後述する製造方法にて得ることができる。 The diffraction peak originating from the (111) plane of copper is the peak with the maximum height of the X-ray diffraction pattern obtained by X-ray diffraction measurement of copper particles B. From this, it is considered that the first crystallite size is larger than the crystallite size calculated from the diffraction peaks originating from other crystallite planes, and is also representative of crystallinity. Therefore, it is presumed that the first crystallite size S1 is small relative to the BET diameter B, so that there are many crystal grain boundaries in one particle. As a result, the thermal energy applied when the particles are heated makes the crystallite interface more unstable, which activates atomic diffusion, thereby increasing the fusion between particles at low temperatures and lowering the sintering temperature.
Such copper particles can be obtained, for example, by the manufacturing method described below.
　銅粒子Ｂの第１結晶子サイズＳ１は、好ましくは１０ｎｍ以上８０ｎｍ以下、より好ましくは２０ｎｍ以上７５ｎｍ以下、更に好ましくは２５ｎｍ以上７０ｎｍ以下である。結晶子サイズＳ１がこのような範囲となっていることによって、結晶粒界を一粒子中に更に多く形成しやすくして、加熱時の粒子の融着性を更に高めて、焼結温度を効果的に低下させることができる。 The first crystallite size S1 of copper particles B is preferably 10 nm or more and 80 nm or less, more preferably 20 nm or more and 75 nm or less, and even more preferably 25 nm or more and 70 nm or less. By having the crystallite size S1 in this range, it becomes easier to form more crystal grain boundaries in each particle, further increasing the fusion properties of the particles when heated, and effectively lowering the sintering temperature.
　また銅粒子Ｂは、Ｘ線回折測定において銅の（２２０）面に由来するピークの半値幅からシェラーの式によって求められる結晶子サイズを第２結晶子サイズＳ２としたときに、第２結晶子サイズＳ２に対する第１結晶子サイズＳ１の比（Ｓ１／Ｓ２）が所定の値以下であることも好ましい。
　具体的には、Ｓ１／Ｓ２比は、好ましくは１．３５以下、より好ましくは０．１以上１．３以下、更に好ましくは０．１以上１．２以下である。 In addition, when the second crystallite size S2 is the crystallite size calculated by the Scherrer formula from the half-width of the peak derived from the (220) plane of copper in X-ray diffraction measurement, it is also preferable that the ratio (S1/S2) of the first crystallite size S1 to the second crystallite size S2 is a predetermined value or less.
Specifically, the S1/S2 ratio is preferably 1.35 or less, more preferably 0.1 or more and 1.3 or less, and further preferably 0.1 or more and 1.2 or less.
　金属銅は面心立方構造の結晶構造をとりやすいことから、銅粒子Ｂは、粒子表面の特定の面に銅の（１１１）面が存在し、（１１１）面と交差する面に銅の（２２０）面が存在する。そして、Ｓ１／Ｓ２比が小さいほど、銅粒子が、（１１１）面方向に成長していないか、又は、（２２０）面方向に成長していることを示している。したがって、Ｓ１／Ｓ２が上述した所定の範囲であることは、銅粒子Ｂが扁平形状であることなどの粒子形状に異方性を有することと概ね相関する。扁平形状とは、互いに対向する一対の主面と、これらの主面に交差する側面とを有する形状を意味する。銅粒子Ｂが扁平形状である場合、銅粒子Ｂの主面に銅の（１１１）面が存在し、銅粒子Ｂの側面に銅の（２２０）面が存在すると推測される。
　したがって、Ｓ１／Ｓ２比が上述の範囲となっていることによって、焼結する際に銅粒子Ｂどうしが配列したときに、銅粒子Ｂの主面どうし、又は粒子の側面どうしが接触しやすく、銅粒子Ｂどうしの接触部が同じ結晶面となりやすい。熱エネルギーが印加された粒子は、異なる結晶面どうしで接触する場合よりも、同じ結晶面どうしで接触する場合のほうが熱エネルギーの利用効率が高く、結晶子界面の原子が拡散されやすくなる。その結果、低温での粒子どうしの融着性を高め、銅粉の焼結温度を低下させることができる。このことは、球状粒子や、機械的に製造された扁平状の銅粒子と比較して、焼結性が更に向上できる点で有利である。
　また、銅粒子Ｂどうしの接触は上述のように面どうしの接触となりやすいため、球状銅粒子等と比較して接触面積が大きくなる。このことに起因して、銅粒子Ｂを含む本発明の銅粉から製造される導電膜は高い連続性を有する。
　このような銅粒子は、例えば後述する製造方法にて得ることができる。 Since metallic copper is prone to have a face-centered cubic crystal structure, copper particles B have a copper (111) plane on a specific surface of the particle surface, and a copper (220) plane on a surface intersecting the (111) plane. The smaller the S1/S2 ratio, the more the copper particles do not grow in the (111) plane direction, or grow in the (220) plane direction. Therefore, the fact that S1/S2 is in the above-mentioned predetermined range generally correlates with the copper particles B having anisotropy in particle shape, such as a flat shape. The flat shape means a shape having a pair of main surfaces facing each other and side surfaces intersecting these main surfaces. When copper particles B have a flat shape, it is presumed that the copper (111) plane is present on the main surface of copper particles B, and the copper (220) plane is present on the side surface of copper particles B.
Therefore, by having the S1/S2 ratio in the above-mentioned range, when the copper particles B are arranged during sintering, the main surfaces of the copper particles B or the side surfaces of the particles are likely to contact each other, and the contact parts of the copper particles B are likely to be the same crystal plane. When the particles to which thermal energy is applied are in contact with each other on the same crystal plane, the utilization efficiency of the thermal energy is higher than when the particles are in contact with each other on different crystal planes, and the atoms at the crystallite interface are more likely to diffuse. As a result, the fusion property between the particles at low temperatures can be improved, and the sintering temperature of the copper powder can be reduced. This is advantageous in that the sinterability can be further improved compared to spherical particles and mechanically produced flat copper particles.
In addition, since the contact between the copper particles B is likely to be face-to-face contact as described above, the contact area is larger than that of spherical copper particles, etc. Due to this, the conductive film produced from the copper powder of the present invention containing the copper particles B has high continuity.
Such copper particles can be obtained, for example, by the manufacturing method described below.
　銅粒子Ｂの第２結晶子サイズＳ２は、好ましくは１０ｎｍ以上８０ｎｍ以下、より好ましくは２０ｎｍ以上７５ｎｍ以下、更に好ましくは３０ｎｍ以上７０ｎｍ以下である。結晶子サイズＳ２がこのような範囲となっていることによって、結晶子サイズが比較的小さいことに起因する低温焼結性を高めつつ、銅粒子の形状に由来する導電路を多く形成でき、焼結後に低抵抗な導電膜を形成することができる。 The second crystallite size S2 of copper particles B is preferably 10 nm or more and 80 nm or less, more preferably 20 nm or more and 75 nm or less, and even more preferably 30 nm or more and 70 nm or less. By having the crystallite size S2 in this range, it is possible to form many conductive paths due to the shape of the copper particles while improving the low-temperature sintering property due to the relatively small crystallite size, and it is possible to form a conductive film with low resistance after sintering.
　銅粒子Ｂは、Ｘ線回折測定において銅の（３１１）面に由来するピークの半値幅からシェラーの式によって求められる結晶子サイズを第３結晶子サイズＳ３としたときに、第３結晶子サイズＳ３に対する第１結晶子サイズＳ１の比（Ｓ１／Ｓ３）が、所定の値以下であることが好ましい。
　具体的には、Ｓ１／Ｓ３比は、好ましくは１．３５以下、より好ましくは０．２０以上１．３０以下、更に好ましくは０．５０以上１．２５以下である。 In copper particles B, when the third crystallite size S3 is determined by the Scherrer formula from the half-width of the peak derived from the (311) plane of copper in X-ray diffraction measurement, it is preferable that the ratio (S1/S3) of the first crystallite size S1 to the third crystallite size S3 is a predetermined value or less.
Specifically, the S1/S3 ratio is preferably 1.35 or less, more preferably 0.20 or more and 1.30 or less, and further preferably 0.50 or more and 1.25 or less.
　金属銅は面心立方構造の結晶構造をとりやすいことから、銅粒子Ｂは、粒子表面の特定の面に銅の（１１１）面が存在し、（１１１）面と交差する面に銅の（３１１）面が存在する。そして、Ｓ１／Ｓ３比が小さいほど、銅粒子Ｂが、（１１１）面方向に成長していないか、又は、（３１１）面方向に成長していることを示している。したがって、Ｓ１／Ｓ３が上述した所定の範囲であることは、銅粒子Ｂが扁平形状であることなどの粒子形状に異方性を有することと概ね相関する。この場合、銅粒子Ｂの主面に銅の（１１１）面が存在し、銅粒子の側面に銅の（３１１）面が存在すると推測される。
　したがって、Ｓ１／Ｓ３比が上述の範囲となっていることによって、焼結する際に銅粒子Ｂどうしが配列したときに、銅粒子Ｂの主面どうし、又は銅粒子Ｂの側面どうしが接触しやすく、銅粒子Ｂどうしの接触部が同じ結晶面となりやすい。その結果、本発明の銅粉を加熱したときに銅粒子Ｂの結晶子界面の原子拡散を活発にして、低温での粒子の融着性を高め、銅粉の焼結温度を低下させることができる。このことは、球状粒子や、機械的に製造された扁平状の銅粒子と比較して、焼結性が更に向上できる点で有利である。
　このような銅粒子は、例えば後述する製造方法にて得ることができる。 Since metallic copper is prone to have a face-centered cubic crystal structure, copper particles B have a copper (111) plane on a specific surface of the particle surface, and a copper (311) plane on a surface intersecting the (111) plane. The smaller the S1/S3 ratio, the more copper particles B do not grow in the (111) plane direction, or grow in the (311) plane direction. Therefore, the fact that S1/S3 is in the above-mentioned predetermined range generally correlates with the copper particles B having anisotropy in particle shape, such as being flat. In this case, it is presumed that the copper (111) plane is present on the main surface of the copper particles B, and the copper (311) plane is present on the side surface of the copper particles.
Therefore, by having the S1/S3 ratio in the above-mentioned range, when the copper particles B are arranged during sintering, the main surfaces of the copper particles B or the side surfaces of the copper particles B are likely to contact each other, and the contact parts of the copper particles B are likely to have the same crystal plane. As a result, when the copper powder of the present invention is heated, atomic diffusion at the crystallite interface of the copper particles B is activated, the fusion property of the particles at low temperatures is improved, and the sintering temperature of the copper powder can be reduced. This is advantageous in that the sinterability can be further improved compared to spherical particles and mechanically produced flat copper particles.
Such copper particles can be obtained, for example, by the manufacturing method described below.
　粒子Ｂの第３結晶子サイズＳ３は、好ましくは１０ｎｍ以上８０ｎｍ以下、より好ましくは２０ｎｍ以上７５ｎｍ以下、更に好ましくは３０ｎｍ以上７０ｎｍ以下である。結晶子サイズＳ３がこのような範囲となっていることによって、結晶子サイズが比較的小さいことに起因する低温焼結性を高めつつ、銅粒子Ｂの形状に由来する導電路を多く形成でき、焼結後に低抵抗な導電膜を形成することができる。 The third crystallite size S3 of the particles B is preferably 10 nm or more and 80 nm or less, more preferably 20 nm or more and 75 nm or less, and even more preferably 30 nm or more and 70 nm or less. By having the crystallite size S3 in this range, it is possible to form many conductive paths due to the shape of the copper particles B while improving the low-temperature sintering property due to the relatively small crystallite size, and it is possible to form a conductive film with low resistance after sintering.
　第１結晶子サイズＳ１、第２結晶子サイズＳ２及び第３結晶子サイズＳ３はそれぞれ、Ｘ線回折測定によって得られる銅の（１１０）面、（２２０）面又は（３１１）面に由来する回折ピークの半値幅の全幅から、以下に示すシェラーの式を用いて算出することができる。Ｘ線回折測定の条件は、後述する実施例にて詳述する。ＰＤＦ番号は００－００４－０８３６を用いる。
　・シェラーの式：Ｄ＝Ｋλ／βｃｏｓθ
　・Ｄ：結晶子サイズ
　・Ｋ：シェラー定数（０．９４）
　・λ：Ｘ線の波長
　・β：半値幅［ｒａｄ］
　・θ：回折角 The first crystallite size S1, the second crystallite size S2, and the third crystallite size S3 can be calculated from the full width at half maximum of the diffraction peak derived from the (110), (220) or (311) plane of copper obtained by X-ray diffraction measurement, using the Scherrer formula shown below. The conditions of the X-ray diffraction measurement will be described in detail in the Examples described later. The PDF number used is 00-004-0836.
Scherrer's formula: D = Kλ/βcosθ
D: crystallite size K: Scherrer constant (0.94)
・λ: X-ray wavelength ・β: Half-width [rad]
θ: Diffraction angle
　銅粒子Ｂは、銅元素を主体として含むことが好ましい。銅元素を主体として含むとは、銅粒子中の銅元素含有量が９７.０質量％以上であることをいい、好ましくは９７．５質量％以上、より好ましくは９８.０質量％以上、更に好ましくは９８．５質量％以上である。銅元素の含有量は、例えばＩＣＰ発光分光分析法で測定することができる。 Copper particles B preferably contain copper element as a major component. "Containing copper element as a major component" means that the copper element content in the copper particles is 97.0% by mass or more, preferably 97.5% by mass or more, more preferably 98.0% by mass or more, and even more preferably 98.5% by mass or more. The copper element content can be measured, for example, by ICP atomic emission spectrometry.
　銅粒子Ｂは、銅元素に加えて、銅元素以外の他の元素を含むものであるか、又は、銅元素からなり、不可避不純物を除いて銅元素以外の他の元素を含まないものである。銅粒子Ｂは、本発明の効果を損なわない限りにおいて、酸素元素等の微量の不可避不純物元素が含まれることが許容される。いずれの態様であっても、銅粒子における銅元素以外の他の元素の含有量は、好ましくは１．５質量％以下である。これらの元素の含有量は、例えばＩＣＰ発光分光分析法で測定することができる。 The copper particles B contain, in addition to elemental copper, elements other than copper, or consist of elemental copper and contain no elements other than copper except for unavoidable impurities. Copper particles B are permitted to contain trace amounts of unavoidable impurity elements such as oxygen, as long as this does not impair the effects of the present invention. In either embodiment, the content of elements other than copper in the copper particles is preferably 1.5 mass% or less. The content of these elements can be measured, for example, by ICP atomic emission spectrometry.
　銅粒子Ｂは、該粒子に含まれる炭素元素の含有量が少ないことも好ましい。詳細には、銅粒子Ｂにおける炭素元素の含有量は、好ましくは５０００ｐｐｍ以下であり、より好ましくは４５００ｐｐｍ以下であり、更に好ましくは４０００ｐｐｍ以下であり、少なければ少ないほど好ましいが、１００ｐｐｍ以上が現実的である。炭素元素の含有量がこのような範囲であることによって、銅粒子表面に存在する有機物による焼結阻害を比較的抑えることが可能である。このような銅粒子は、例えば後述する製造方法によって製造することができる。 It is also preferable that the copper particles B have a low carbon element content. In detail, the carbon element content in the copper particles B is preferably 5000 ppm or less, more preferably 4500 ppm or less, and even more preferably 4000 ppm or less. The lower the content, the better, but 100 ppm or more is realistic. By having the carbon element content in this range, it is possible to relatively suppress sintering inhibition caused by organic matter present on the copper particle surface. Such copper particles can be manufactured, for example, by the manufacturing method described below.
　炭素元素の含有量は、例えば、ガス分析や燃焼式炭素分析などの方法で測定することができる。炭素元素の含有量の測定にあたっては、まず銅粒子Ｂ表面に被覆処理が行われているか否かを判断する。この確認方法は、例えばＸ線光電子分光（ＸＰＳ）法、核磁気共鳴（ＮＭＲ）法、ラマン分光法、赤外分光法、液体クロマトグラフィー法、飛行時間型二次イオン質量分析法（ＴＯＦ－ＳＩＭＳ）等の方法を単独で又は組み合わせて行う方法が挙げられる。この方法によって粒子表面に被覆処理が行われていると判断されれば、上述の方法を単独で又は複数組み合わせて、被覆処理によって形成された被覆層に含まれる元素の種類及びその量を定性分析及び定量分析を行う。これに加えて、熱重量測定（ＴＧ）によって、焼成温度前後で生じる質量変化とその温度まで加熱したあとの炭素量の測定とによって、有機物の物性を評価可能である。
　粒子表面に被覆処理が行われていないと判断された場合には、測定対象となる銅粒子Ｂをそのまま測定に供して、得られた定量値を銅粒子Ｂに含まれる炭素元素含有量とする。 The carbon element content can be measured by, for example, gas analysis or combustion carbon analysis. In measuring the carbon element content, first, it is determined whether the copper particle B surface is coated. This confirmation method includes, for example, 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, either alone or in combination. If it is determined that the particle surface is coated by this method, the above-mentioned methods are used alone or in combination to qualitatively and quantitatively analyze the type and amount of elements contained in the coating layer formed by the coating process. In addition, the physical properties of the organic material can be evaluated by thermogravimetry (TG) by measuring the mass change occurring before and after the firing temperature and the amount of carbon after heating to that temperature.
When it is determined that no coating treatment has been applied to the particle surface, the copper particles B to be measured are directly subjected to the measurement, and the quantitative value obtained is regarded as the carbon element content contained in the copper particles B.
　銅粒子Ｂは、該粒子に含まれるリン元素の含有量が所定の範囲であることも好ましい。詳細には、銅粒子におけるリン元素の含有量は、好ましくは３００ｐｐｍ以上、より好ましくは３００ｐｐｍ以上１５００ｐｐｍ以下、更に好ましくは３００ｐｐｍ以上１０００ｐｐｍである。リン元素の含有量をこのような範囲にすることによって、銅が有する導電性を十分に維持しつつ、融点降下を発生させて、焼結温度更に低下させることができる。このような銅粒子は、例えば後述する製造方法によって製造することができる。銅粒子Ｂ中のリン元素の有無及びその含有量は、例えば、ＩＣＰ発光分光分析法で測定することができる。 It is also preferable that the content of phosphorus contained in the copper particles B is within a predetermined range. In detail, the content of phosphorus in the copper particles is preferably 300 ppm or more, more preferably 300 ppm or more and 1500 ppm or less, and even more preferably 300 ppm or more and 1000 ppm or less. By setting the content of phosphorus in such a range, it is possible to cause a drop in the melting point while fully maintaining the electrical conductivity of copper, thereby further lowering the sintering temperature. Such copper particles can be manufactured, for example, by the manufacturing method described below. The presence or absence of phosphorus in the copper particles B and its content can be measured, for example, by ICP atomic emission spectroscopy.
　上述のとおり、銅粒子Ｂの炭素含有量が少ないほど、焼結阻害が起こりにくく、銅粉の低温での焼結が可能となる。尤も、上述した炭素元素の含有量の範囲であれば、銅粒子Ｂの表面に存在する有機物による焼結阻害を比較的抑えることが可能であるため、銅粒子Ｂの表面に有機物を意図的に施してもよい。 As mentioned above, the lower the carbon content of copper particles B, the less likely sintering inhibition occurs, and the copper powder can be sintered at a lower temperature. However, as long as the carbon content is within the range mentioned above, it is possible to relatively suppress sintering inhibition caused by organic matter present on the surface of copper particles B, so organic matter may be intentionally applied to the surface of copper particles B.
　銅粒子Ｂの表面に施す有機物としては、例えば各種の脂肪酸や脂肪族有機酸の銅塩、及び脂肪族アミンを挙げることができる。このような有機物を銅粒子Ｂの表面に施すことによって、銅粒子間での凝集を抑制することができる。特に炭素数６以上１８以下、とりわけ炭素数１０以上１８以下である飽和又は不飽和脂肪酸あるいは脂肪族アミンを用いることが、銅粉の低温焼結性の向上の点から好ましい。そのような脂肪酸あるいは脂肪族アミンの具体例としては、安息香酸、ペンタン酸、ヘキサン酸、オクタン酸、ノナン酸、デカン酸、ラウリン酸、パルミチン酸、オレイン酸、ステアリン酸、ペンチルアミン、ヘキシルアミン、オクチルアミン、デシルアミン、ラウリルアミン、オレイルアミン、ステアリルアミンなどが挙げられる。これらの脂肪酸あるいは脂肪族アミンは、１種を単独で、又は２種以上を組み合わせて用いることができる。 The organic matter applied to the surface of the copper particles B can be, for example, various copper salts of fatty acids or aliphatic organic acids, and aliphatic amines. By applying such an organic matter to the surface of the copper particles B, it is possible to suppress aggregation between the copper particles. In particular, it is preferable to use a saturated or unsaturated fatty acid or aliphatic amine having 6 to 18 carbon atoms, particularly 10 to 18 carbon atoms, from the viewpoint of improving the low-temperature sintering property of the copper powder. Specific examples of such fatty acids or aliphatic amines include benzoic acid, pentanoic acid, hexanoic acid, octanoic acid, nonanoic acid, decanoic acid, lauric acid, palmitic acid, oleic acid, stearic acid, pentylamine, hexylamine, octylamine, decylamine, laurylamine, oleylamine, and stearylamine. These fatty acids or aliphatic amines can be used alone or in combination of two or more.
　銅粒子Ｂは、本発明の効果が奏される限りにおいて、その形状は特に制限されないが、後述する方法によって製造される場合には、好ましくは扁平形状である。このような粒子は、互いに対向するほぼ平坦な一対の主面と、両主面に交差する側面とを有し、該主面の最大差し渡し長さが厚みに比べて大きい板状のものである。この場合、銅粒子Ｂにおける主面を平面視したときに、その形状は、直線どうしの組み合わせ、又は直線及び曲線の組み合わせによって画定される輪郭を有することも好ましい。 The shape of copper particles B is not particularly limited as long as the effects of the present invention are achieved, but when produced by the method described below, it is preferably flat. Such particles have a pair of nearly flat main surfaces facing each other and side surfaces intersecting both main surfaces, and are plate-like in shape with the maximum span of the main surfaces being greater than the thickness. In this case, it is also preferable that when the main surfaces of copper particles B are viewed in plan, their shape has an outline defined by a combination of straight lines or a combination of straight lines and curves.
　本発明の銅粉を含む銅ペーストから製造された導電膜は高い緻密性及び連続性を有する。該導電膜の緻密性及び連続性をより一層高める観点から、銅粒子Ａと銅粒子Ｂの合計に対する銅粒子Ａの含有割合は６０質量％以上９９質量％以下であることが好ましく、６５質量％以上８８質量％以下であることがより好ましく、７０質量％以上８５質量％以下であることが更に好ましい。
　同様の観点から、銅粒子Ａと銅粒子Ｂの合計に対する銅粒子Ｂの含有割合は１質量％以上４０質量％以下であることが好ましく、１２質量％以上３５質量％以下であることがより好ましく、１５質量％以上３０質量％以下であることが更に好ましい。 The conductive film produced from the copper paste containing the copper powder of the present invention has high density and continuity. From the viewpoint of further increasing the density and continuity of the conductive film, the content ratio of copper particles A to the total of copper particles A and copper particles B is preferably 60% by mass or more and 99% by mass or less, more preferably 65% by mass or more and 88% by mass or less, and even more preferably 70% by mass or more and 85% by mass or less.
From the same viewpoint, the content ratio of copper particles B to the total of copper particles A and copper particles B is preferably 1 mass% or more and 40 mass% or less, more preferably 12 mass% or more and 35 mass% or less, and even more preferably 15 mass% or more and 30 mass% or less.
　次に、本発明の銅粉の好適な製造方法について説明する。本発明の銅粉は、好適には、銅粒子Ａ及び銅粒子Ｂを上述の好ましい割合で混合することによって製造される。以下、銅粒子Ａ及び銅粒子Ｂの好適な製造方法、並びに銅粒子Ａ及び銅粒子Ｂの混合方法について順に詳述する。 Next, a preferred method for producing the copper powder of the present invention will be described. The copper powder of the present invention is preferably produced by mixing copper particles A and copper particles B in the preferred ratio described above. Below, a preferred method for producing copper particles A and copper particles B, and a method for mixing copper particles A and copper particles B will be described in detail in order.
＜銅粒子Ａの製造方法＞
　まず、銅粒子Ａの好適な製造方法について説明する。本製造方法は、銅からなるコア粒子と、脂肪族有機酸の銅塩を含む溶液とを接触させて、コア粒子の表面を被覆する被覆層を形成するものである。 <Method of producing copper particles A>
First, we will explain a suitable method for producing copper particles A. This production method involves contacting core particles made of copper with a solution containing a copper salt of an aliphatic organic acid to form a coating layer that coats the surfaces of the core particles.
　まず、脂肪族有機酸の銅塩による表面処理に先立ち、銅からなるコア粒子を用意する。銅のコア粒子の製造方法としては、例えば特開２０１５－１６８８７８号公報に記載の湿式による方法で製造することできる。すなわち、水と、好ましくは炭素原子数が１以上５以下の一価アルコールとを含む液媒体に、塩化銅、酢酸銅、水酸化銅、硫酸銅、酸化銅又は亜酸化銅等の一価又は二価の銅源を含む反応液を調製する。この反応液とヒドラジンとを、銅１モルに対して好ましくは０．５モル以上５０モル以下の割合となるように混合し、該銅源を還元して、銅からなるコア粒子を得る。本方法で得られるコア粒子は、その表面に脂肪族有機酸の銅塩等の表面処理剤が施されていないものであり、且つ粒径が小さいものである。 First, prior to the surface treatment with a copper salt of an aliphatic organic acid, core particles made of copper are prepared. The copper core particles can be produced, for example, by the wet method described in JP 2015-168878 A. That is, a reaction liquid containing a monovalent or divalent copper source such as copper chloride, copper acetate, copper hydroxide, copper sulfate, copper oxide, or cuprous oxide is prepared in a liquid medium containing water and a monohydric alcohol preferably having 1 to 5 carbon atoms. This reaction liquid is mixed with hydrazine in a ratio of preferably 0.5 to 50 moles per mole of copper, and the copper source is reduced to obtain core particles made of copper. The core particles obtained by this method do not have a surface treatment agent such as a copper salt of an aliphatic organic acid applied to their surfaces, and have a small particle size.
　上述の工程で得られたコア粒子は、洗浄処理することが好ましい。洗浄方法としては、例えばデカンテーション法や、ロータリーフィルター法等が挙げられる。ロータリーフィルター法でコア粒子を洗浄する場合、例えばコア粒子を水等の溶媒に分散させた水性スラリーを調製し、該スラリーの導電率が好ましくは２．０ｍＳ以下となるまで洗浄を行う。このときの洗浄条件は、例えば、洗浄溶媒として水を用いた場合、洗浄温度を１５℃以上３０℃以下、洗浄時間を１０分以上６０分以下とすることができる。スラリーの導電率を上述の範囲とすることによって、洗浄対象のコア粒子が凝集することなく均一に分散したままで、後述する表面処理を効率よく行うことができる。このスラリー中の銅からなるコア粒子の含有割合は、洗浄効率の向上と粒子の分散性の向上とを両立する観点から、好ましくは５質量％以上５０質量％以下である。 The core particles obtained in the above-mentioned process are preferably washed. Examples of washing methods include decantation and rotary filter methods. When washing the core particles by the rotary filter method, for example, an aqueous slurry is prepared by dispersing the core particles in a solvent such as water, and washing is performed until the conductivity of the slurry is preferably 2.0 mS or less. The washing conditions at this time can be, for example, a washing temperature of 15°C to 30°C and a washing time of 10 minutes to 60 minutes when water is used as the washing solvent. By setting the conductivity of the slurry within the above-mentioned range, the core particles to be washed can be uniformly dispersed without agglomeration, and the surface treatment described below can be performed efficiently. The content of copper core particles in this slurry is preferably 5% by mass to 50% by mass from the viewpoint of improving both washing efficiency and particle dispersibility.
　また、上述の方法に代えて、銅からなるコア粒子の別の製造方法として、例えば国際公開第２０１５／１２２２５１号パンフレットに記載の直流熱プラズマ（ＤＣプラズマ）法を採用してもよい。詳細には、銅の母粉をＰＶＤ法の一種である直流熱プラズマ法に付して、該母粉からコア粒子を生成させることができる。本方法で得られるコア粒子も、その表面に脂肪族有機酸の銅塩等の表面処理剤が施されていないものであり、且つ粒径が小さいものである。必要に応じて、得られたコア粒子に対して、解砕処理や分級処理を行って、粗大粒子や微粒子を分離又は除去してもよい。 In place of the above-mentioned method, a direct current thermal plasma (DC plasma) method described in WO 2015/122251 may be used as another method for producing core particles made of copper. In detail, copper mother powder can be subjected to a direct current thermal plasma method, which is a type of PVD method, to generate core particles from the mother powder. The core particles obtained by this method also have no surface treatment agent such as a copper salt of an aliphatic organic acid on their surfaces, and have a small particle size. If necessary, the obtained core particles may be subjected to a crushing process or a classification process to separate or remove coarse particles and fine particles.
　次いで、上述した方法で得られたコア粒子に対して、表面処理剤による表面処理を行って、コア粒子の表面を被覆する被覆層を形成する。表面処理の方法としては、例えばコア粒子と、脂肪族有機酸の銅塩を溶媒に溶解させた溶液とを接触させる方法を採用することができる。本工程において脂肪族有機酸の銅塩と接触させるコア粒子の形態は、コア粒子を水等の溶媒に分散させた水性スラリーであってもよく、溶媒等に分散させていない乾燥状態のものであってもよい。また本工程における接触順序としては、コア粒子及び脂肪族有機酸の銅塩溶液のうち一方を他方に添加してもよく、コア粒子及び脂肪族有機酸の銅塩の溶液を同時に接触させてもよい。
　コア粒子に対して脂肪族有機酸の銅塩による表面処理を均一に行う観点から、コア粒子が分散したスラリー中に脂肪族有機酸の銅塩の溶液を添加する方法を採用することが好ましい。 Next, the core particles obtained by the above-mentioned method are surface-treated with a surface treatment agent to form a coating layer that covers the surface of the core particles. As a method of surface treatment, for example, a method of contacting the core particles with a solution in which a copper salt of an aliphatic organic acid is dissolved in a solvent can be adopted. The form of the core particles to be contacted with the copper salt of an aliphatic organic acid in this step may be an aqueous slurry in which the core particles are dispersed in a solvent such as water, or may be in a dry state in which the core particles are not dispersed in a solvent or the like. In addition, as the order of contact in this step, one of the core particles and the copper salt solution of an aliphatic organic acid may be added to the other, or the core particles and the copper salt solution of an aliphatic organic acid may be contacted simultaneously.
From the viewpoint of uniformly treating the surface of the core particles with the copper salt of an aliphatic organic acid, it is preferable to employ a method in which a solution of the copper salt of an aliphatic organic acid is added to a slurry in which the core particles are dispersed.
　脂肪族有機酸の銅塩溶液にコア粒子を添加して、表面処理を行う方法を例にとり以下に説明する。まず、脂肪族有機酸の銅塩溶液に用いられる溶媒を、使用する溶媒の沸点以下の温度（例えば２５℃以上８０℃以下）に加熱し、その状態下で、該溶媒に脂肪族有機酸の銅塩を添加し、脂肪族有機酸の銅塩溶液を調製する。次いで、銅塩溶液の温度を脂肪族有機酸の銅塩の融点以上に維持したまま、乾燥状態のコア粒子又はコア粒子含有スラリーを脂肪族有機酸の銅塩溶液に添加して、その後１時間撹拌し、コア粒子の表面に表面処理を施す。この方法によって得られた銅粒子Ａは、銅からなるコア粒子の表面に脂肪族有機酸の銅塩からなる被覆層が形成されたものとなる。コア粒子含有スラリーを用いて表面処理を行う場合、該スラリーは脂肪族有機酸の銅塩の融点以上の温度に加熱されていることが、被覆層をコア粒子の表面に均一に形成させる観点から好ましい。 The method of adding core particles to a copper salt solution of an aliphatic organic acid and performing surface treatment will be described below as an example. First, the solvent used in the copper salt solution of an aliphatic organic acid is heated to a temperature below the boiling point of the solvent used (for example, 25°C to 80°C), and under that condition, the copper salt of an aliphatic organic acid is added to the solvent to prepare a copper salt solution of an aliphatic organic acid. Next, while maintaining the temperature of the copper salt solution above the melting point of the copper salt of the aliphatic organic acid, the dry core particles or core particle-containing slurry are added to the copper salt solution of an aliphatic organic acid, and then stirred for one hour to perform surface treatment on the surfaces of the core particles. The copper particles A obtained by this method are core particles made of copper and have a coating layer made of a copper salt of an aliphatic organic acid formed on the surface of the core particles. When performing surface treatment using a core particle-containing slurry, it is preferable that the slurry is heated to a temperature above the melting point of the copper salt of the aliphatic organic acid in order to uniformly form a coating layer on the surfaces of the core particles.
　脂肪族有機酸の銅塩の溶液を用いた表面処理において、コア粒子を含む反応溶液中の脂肪族有機酸の銅塩の含有量は、表面処理が施されていないコア粒子１００質量部に対して、好ましくは０．１質量部以上３．０質量部以下、より好ましくは０．２質量部以上２．０質量部以下とする。このような量で表面処理を行うことによって、上述した炭素原子割合で表面処理された銅粒子Ａを得ることができる。 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 0.1 parts by mass or more and 3.0 parts by mass or less, more preferably 0.2 parts by mass or more and 2.0 parts by mass or less, per 100 parts by mass of core particles that have not been surface-treated. By carrying out the surface treatment in such an amount, copper particles A that have been surface-treated with the above-mentioned carbon atom ratio can be obtained.
　脂肪族有機酸の銅塩を溶解させる溶媒は、炭素原子数が１以上５以下である一価アルコール、多価アルコール、多価アルコールのエステル、ケトン、エーテル等の有機溶媒を挙げることができる。これらのうち、水との相溶性、経済性、取扱い性及び除去の容易性の観点から、炭素原子数が１以上５以下の一価アルコールを用いることが好ましく、メタノール水溶液、エタノール、１－プロパノール、又はイソプロピルアルコールを用いることが更に好ましい。 Solvents for dissolving the copper salt of an aliphatic organic acid include organic solvents such as monohydric alcohols having 1 to 5 carbon atoms, polyhydric alcohols, esters of polyhydric alcohols, ketones, and ethers. Of these, from the viewpoints of compatibility with water, economy, ease of handling, and ease of removal, it is preferable to use monohydric alcohols having 1 to 5 carbon atoms, and it is even more preferable to use an aqueous methanol solution, ethanol, 1-propanol, or isopropyl alcohol.
　以上の工程を経て得られた銅粒子Ａは、必要に応じて洗浄や固液分離を行った後、銅粒子Ａを水や有機溶媒等の溶媒に分散させたスラリーの形態で銅粒子Ｂと混合させてもよく、銅粒子Ａを乾燥させて、銅粒子の集合体である乾燥粉の形態で銅粒子Ｂと混合させることもできる。いずれの場合であっても、本発明の銅粉に銅粒子Ａを含ませることによって、構成金属である銅の酸化が抑制され、且つ粒子の凝集が抑制されたものでありながら、焼結温度の低い優れた銅粉となる。 The copper particles A obtained through the above steps may be washed or separated into solid and liquid as necessary, and then mixed with copper particles B in the form of a slurry in which the copper particles A are dispersed in a solvent such as water or an organic solvent, or the copper particles A may be dried and mixed with copper particles B in the form of a dry powder that is an aggregate of copper particles. In either case, by including copper particles A in the copper powder of the present invention, oxidation of the copper, which is a constituent metal, and aggregation of particles are suppressed, while at the same time providing an excellent copper powder with a low sintering temperature.
＜銅粒子Ｂの製造方法＞
　次に、銅粒子Ｂの好適な製造方法を説明する。本製造方法は、銅イオンを還元して亜酸化銅を生成させる第１還元工程と、二リン酸以上のポリリン酸又はそれらの塩（以下、これをポリリン酸類ともいう）の存在下で亜酸化銅を還元して銅粒子を生成させる第２還元工程との２つの還元工程を備える。
　ポリリン酸類は、第２還元工程を行うときに、又は第２還元工程を行う前のいずれかの段階において、反応系に存在させる。つまり、ポリリン酸類は、第１還元工程を行う前に又は第１還元工程を行うときに反応系に存在させて、その状態で第２還元工程を行ってもよい。これに代えて、第１還元工程ではポリリン酸類を反応系に存在させずに、第１還元工程の終了後、第２還元工程を行うときに又はその直前にポリリン酸類を反応系に存在させてもよい。 <Method of producing copper particles B>
Next, a description will be given of a preferred method for producing copper particles B. This production method includes two reduction steps: a first reduction step in which copper ions are reduced to produce cuprous oxide, and a second reduction step in which cuprous oxide is reduced in the presence of diphosphate or higher polyphosphoric acid or a salt thereof (hereinafter, also referred to as polyphosphoric acids) to produce copper particles.
The polyphosphoric acids are present in the reaction system either when the second reduction step is performed or before the second reduction step is performed. In other words, the polyphosphoric acids may be present in the reaction system before or when the first reduction step is performed, and the second reduction step may be performed in that state. Alternatively, the polyphosphoric acids may not be present in the reaction system in the first reduction step, but may be present in the reaction system after the completion of the first reduction step, or when the second reduction step is performed or immediately before the second reduction step.
　本製造方法は、還元反応の均一な制御、及びこれに起因して得られる銅粒子の生産性向上、並びに製造コストの低減を兼ね備える観点から、いずれの還元工程も水性液中での還元を行う湿式条件下で行うことが好ましく、またいずれの還元工程も同一の反応系で行うことが好ましい。以下に、湿式条件で且つ同一の反応系での製造方法を例にとり説明する。 In order to achieve uniform control of the reduction reaction, improve the productivity of the resulting copper particles, and reduce production costs, it is preferable that all reduction steps are carried out under wet conditions in an aqueous liquid, and that all reduction steps are carried out in the same reaction system. Below, we will explain the production method under wet conditions and in the same reaction system as an example.
　まず、銅源及び還元性化合物を含む反応液を調製して第１還元工程を行って、銅イオンを還元して亜酸化銅を液中に生成させる。反応液の調製は、溶媒に各原料を同時に添加して反応液としてもよく、各原料を任意の順序で溶媒に添加してもよい。
　銅イオンの還元反応を制御しやすくして、製造時の取扱い性を高める観点から、銅源と溶媒とを予め混合して銅含有溶液とした後、固体の還元性化合物、又は溶媒に予め溶解した還元性化合物溶液を銅含有溶液に添加することが好ましい。還元性化合物は一括添加でもよく、逐次添加でもよい。 First, a reaction solution containing a copper source and a reducing compound is prepared, and a first reduction step is carried out to reduce copper ions and generate cuprous oxide in the solution. The reaction solution may be prepared by adding each raw material to a solvent at the same time to form the reaction solution, or each raw material may be added to the solvent in any order.
From the viewpoint of making it easier to control the reduction reaction of copper ions and improving the ease of handling during production, it is preferable to premix the copper source with a solvent to prepare a copper-containing solution, and then add a solid reducing compound or a solution of the reducing compound predissolved in a solvent to the copper-containing solution. The reducing compound may be added all at once or gradually.
　第１還元工程においては、上述のとおり、ポリリン酸類が反応液中に含まれていてもよく、非含有としてもよい。ポリリン酸類を反応液中に存在させる場合、銅源、ポリリン酸類及び還元性化合物の順に添加することが、還元性化合物による銅イオンの還元及び結晶成長の制御を効果的に行える点で好ましい。 In the first reduction step, as described above, the reaction solution may or may not contain polyphosphates. When polyphosphates are present in the reaction solution, it is preferable to add the copper source, polyphosphates, and reducing compound in that order, since this allows the reduction of copper ions by the reducing compound and the control of crystal growth to be effectively achieved.
　反応液における溶媒は、水や、メタノール、エタノール、プロパノール等の低級アルコールを用いることができる。これらは単独で又は複数組み合わせて用いることができる。 The solvent for the reaction solution can be water or a lower alcohol such as methanol, ethanol, or propanol. These can be used alone or in combination.
　第１還元工程に用いる銅源としては、反応液中で銅イオンを生成する化合物が挙げられ、水溶性の銅化合物が好ましく挙げられる。このような銅源の具体例としては、ギ酸銅、酢酸銅、プロピオン酸銅等の銅有機酸塩や、硝酸銅、硫酸銅等の銅無機酸塩等の各種の銅化合物が挙げられる。これらの銅化合物は、無水物であってもよく、水和物であってもよい。これらの銅化合物は単独で又は複数組み合わせて用いることができる。 The copper source used in the first reduction step includes compounds that generate copper ions in the reaction solution, and water-soluble copper compounds are preferred. Specific examples of such copper sources include various copper compounds such as organic copper salts, such as copper formate, copper acetate, and copper propionate, and inorganic copper salts, such as copper nitrate and copper sulfate. These copper compounds may be anhydrides or hydrates. These copper compounds may be used alone or in combination.
　第１還元工程における反応系中の銅源の含有量は、銅元素のモル濃度で表して、好ましくは０．０１ｍｏｌ／Ｌ以上２.０ｍｏｌ／Ｌ以下、より好ましくは０．１ｍｏｌ／Ｌ以上１．５ｍｏｌ／Ｌ以下である。このような範囲であることによって、粒径が小さく且つ特定の結晶面での結晶子サイズが小さい銅粒子を生産性高く製造することができる。 The content of the copper source in the reaction system in the first reduction step is preferably 0.01 mol/L or more and 2.0 mol/L or less, more preferably 0.1 mol/L or more and 1.5 mol/L or less, expressed as the molar concentration of copper element. By keeping it in such a range, copper particles having a small particle size and a small crystallite size on a specific crystal plane can be produced with high productivity.
　還元性化合物としては、水溶性の化合物が好ましく挙げられる。還元性化合物の具体例としては、ヒドラジン、塩酸ヒドラジン、硫酸ヒドラジン及び抱水ヒドラジン等のヒドラジン系化合物、水素化ホウ素ナトリウムやジメチルアミンボラン等のホウ素化合物及びその塩、亜硫酸ナトリウム、亜硫酸水素ナトリウム及びチオ硫酸ナトリウム等の硫黄オキソ酸塩、亜硝酸ナトリウム及び次亜硝酸ナトリウム等の窒素オキソ酸塩、亜リン酸、亜リン酸ナトリウム、次亜リン酸及び次亜リン酸ナトリウム等のリンオキソ酸及びその塩が挙げられる。これらの還元性化合物は、無水物であってもよく、水和物であってもよい。これらの還元性化合物は１種を単独で、又は２種以上を組み合わせて用いることができる。 Preferably, the reducing compound is a water-soluble compound. Specific examples of reducing compounds include hydrazine-based compounds such as hydrazine, hydrazine hydrochloride, hydrazine sulfate, and hydrazine hydrate; boron compounds and salts thereof such as sodium borohydride and dimethylamine borane; sulfur oxoacid salts such as sodium sulfite, sodium hydrogen sulfite, and sodium thiosulfate; nitrogen oxoacid salts such as sodium nitrite and sodium hyponitrite; and phosphorus oxoacids and salts thereof such as phosphorous acid, sodium phosphite, hypophosphorous acid, and sodium hypophosphite. These reducing compounds may be anhydrides or hydrates. These reducing compounds may be used alone or in combination of two or more.
　第１還元工程における還元生成物が亜酸化銅となるように制御しやすくして、以後の還元工程における銅の粒成長を制御しやすくして所定の結晶子サイズを有する粒子を得やすくする観点、及び還元後における炭素元素等の不純物の意図しない混入を低減する観点から、還元性溶液中の還元性化合物としてヒドラジン系化合物を用いることが好ましく、ヒドラジンの無水物又は水和物を用いることが更に好ましい。 From the viewpoint of easily controlling the reduction product in the first reduction step to be cuprous oxide, easily controlling the grain growth of copper in the subsequent reduction steps, and easily obtaining particles having a predetermined crystallite size, and from the viewpoint of reducing the unintended incorporation of impurities such as carbon element after reduction, it is preferable to use a hydrazine-based compound as the reducing compound in the reducing solution, and it is even more preferable to use an anhydride or hydrate of hydrazine.
　第１還元工程における反応液中の還元性化合物の含有量は、銅元素１モルに対して、好ましくは０．１モル以上２モル以下、より好ましくは０．１モル以上１モル以下とする。還元性化合物の濃度をこのような範囲に制御することによって、銅イオンの還元反応及び粒成長の進行を適度に制御して、粒径が小さく且つ特定の結晶面での結晶子サイズが小さい銅粒子を生産性高く得ることができる。 The content of the reducing compound in the reaction solution in the first reduction step is preferably 0.1 to 2 moles, more preferably 0.1 to 1 mole, per mole of copper element. By controlling the concentration of the reducing compound within this range, the progress of the reduction reaction of the copper ions and the grain growth can be appropriately controlled, and copper particles having small grain sizes and small crystallite sizes on specific crystal planes can be obtained with high productivity.
　第１還元工程における反応液は、その２５℃におけるｐＨが３以上５以下の酸性条件にすることが、還元性化合物、特にヒドラジン系化合物を用いた場合に、亜酸化銅への還元が進行し、且つ金属銅への還元には進行しない程度に還元性の度合いを適度に制御しつつ、第２還元工程において進行する銅の結晶成長に異方性を持たせやすくすることができる点で好ましい。第１還元工程においては、ｐＨの調整を行ったあと、還元性化合物を添加することが、銅イオンの還元の度合いを適切に制御できる点で好ましい。 The reaction solution in the first reduction step is preferably in an acidic condition with a pH of 3 to 5 at 25°C, in that when a reducing compound, particularly a hydrazine-based compound, is used, the degree of reduction can be appropriately controlled so that reduction to cuprous oxide proceeds but not to metallic copper, while facilitating anisotropy in the copper crystal growth that proceeds in the second reduction step. In the first reduction step, it is preferable to add a reducing compound after adjusting the pH, in that the degree of reduction of the copper ions can be appropriately controlled.
　ｐＨの調整は、本発明の効果が奏される限りにおいて、各種の酸や塩基性物質を用いたり、あるいはポリリン酸類を反応液中に存在させたりすることができる。特に、ｐＨの調整において、ポリリン酸類を用いることによって、他の物質を反応系中に添加しなくとも以後の反応を効率的に行えるので、意図しない不純物の混入を防ぎ、目的とする銅粒子を効率的に得られる点で有利である。 As long as the effects of the present invention are achieved, the pH can be adjusted using various acids or basic substances, or by adding polyphosphoric acids to the reaction solution. In particular, by using polyphosphoric acids to adjust the pH, the subsequent reaction can be carried out efficiently without adding other substances to the reaction system, which is advantageous in that it prevents the inclusion of unintended impurities and allows the desired copper particles to be obtained efficiently.
　第１還元工程における還元反応は、反応液を非加熱状態で行ってもよく、加熱状態で行ってもよい。いずれの場合であっても、反応液の温度は、好ましくは１０℃以上６０℃以下、より好ましくは２０℃以上５０℃以下とする。第１還元工程における反応時間は、上述の温度範囲であることを条件として、好ましくは０．１時間以上２時間以下、より好ましくは０．２時間以上１時間以下とする。また還元反応の均一性の観点から、反応開始時点から反応終了時点にわたって、反応液の撹拌を継続することも好ましい。 The reduction reaction in the first reduction step may be carried out with the reaction liquid in an unheated state or in a heated state. In either case, the temperature of the reaction liquid is preferably 10°C or higher and 60°C or lower, more preferably 20°C or higher and 50°C or lower. The reaction time in the first reduction step is preferably 0.1 hours or higher and 2 hours or lower, more preferably 0.2 hours or higher and 1 hour or lower, provided that the temperature is within the above-mentioned range. From the viewpoint of uniformity of the reduction reaction, it is also preferable to continue stirring the reaction liquid from the start of the reaction to the end of the reaction.
　続いて、第１還元工程において得られた亜酸化銅を還元して、金属銅の粒子を生成させる第２還元工程を行う。第２還元工程についても、第１還元工程と同様に湿式条件で行うことが好ましく、また両還元工程は同一の反応系で行うことがより好ましい。 Subsequently, a second reduction step is carried out in which the cuprous oxide obtained in the first reduction step is reduced to produce metallic copper particles. The second reduction step is also preferably carried out under wet conditions, as in the first reduction step, and it is more preferable that both reduction steps are carried out in the same reaction system.
　上述のとおり、第２還元工程を行うときに、又は第２還元工程を行う前のいずれかの段階において、反応系にポリリン酸類を存在させることが好ましい。本製造方法に用いられるポリリン酸類としては、二リン酸（Ｈ４Ｐ２Ｏ７）、三リン酸（トリポリリン酸、Ｈ５Ｐ３Ｏ１０）、テトラポリリン酸（Ｈ６Ｐ４Ｏ１３）等といった、構造中にリン酸モノマー単位を好ましくは２つ以上８つ以下、より好ましくは２つ以上５つ以下有するポリリン酸及びこれらの塩が挙げられる。ポリリン酸塩としては、アルカリ金属塩や、アルカリ土類金属塩、他の金属塩、アンモニウム塩等が挙げられる。これらは単独で又は複数組み合わせて用いることができる。 As described above, it is preferable to have polyphosphoric acids present in the reaction system when the second reduction step is performed or at any stage before the second reduction step is performed. The polyphosphoric acids used in the present production method include polyphosphoric acids and their salts, such as 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 ), etc., each of which has preferably 2 to 8, more preferably 2 to 5, phosphoric acid monomer units in its structure. The polyphosphate salts include alkali metal salts, alkaline earth metal salts, other metal salts, ammonium salts, etc. These can be used alone or in combination.
　第２還元工程におけるポリリン酸類の含有量は、銅元素１モルに対して、好ましくは０．１ミリモル以上、より好ましくは０．１ミリモル以上１モル以下とする。ポリリン酸類の濃度をこのような範囲とすることによって、亜酸化銅の還元反応に起因する銅の結晶成長に異方性を持たせるように行うことができ、粒径が小さく且つ特定の結晶面での結晶子サイズが小さい銅粒子を生産性高く得ることができる。なお、ポリリン酸類を第１還元工程の時点で含有させる場合、ポリリン酸類は第１還元工程での反応では消費されず、ポリリン酸類の濃度は第１還元工程の前後で実質的に変化しないので、第１還元工程において上述の濃度範囲でポリリン酸類を反応系に添加することによって、第２還元工程における金属銅への還元及び粒成長に好適なポリリン酸類の存在量は十分に達成できる。 The content of polyphosphates in the second reduction step is preferably 0.1 millimole or more, more preferably 0.1 millimole or more and 1 mole or less, per mole of copper element. By setting the concentration of polyphosphates in this range, the crystal growth of copper resulting from the reduction reaction of cuprous oxide can be made anisotropic, and copper particles having a small particle size and a small crystallite size on a specific crystal plane can be obtained with high productivity. Note that when polyphosphates are added at the time of the first reduction step, the polyphosphates are not consumed in the reaction in the first reduction step, and the concentration of polyphosphates does not change substantially before and after the first reduction step. Therefore, by adding polyphosphates in the above-mentioned concentration range to the reaction system in the first reduction step, the amount of polyphosphates present that is suitable for reduction to metallic copper and grain growth in the second reduction step can be sufficiently achieved.
　第２還元工程においては、上述した還元性化合物を添加して、金属銅への還元を行うことができる。第２還元工程における反応液中の還元性化合物の含有量は、銅元素１モルに対して、好ましくは１モル以上８モル以下、より好ましくは２モル以上６モル以下とする。第２還元工程を第１還元工程と同一の反応系で行う場合、還元性向上と不純物低減の制御とを両立する観点から、還元性化合物を上述の含有量となるように液中に更に添加することが好ましい。また還元性化合物の種類は各還元工程で同一のものを用いることも好ましい。
　還元性化合物の濃度をこのような範囲に制御することによって、金属銅への還元反応を十分に進行させて、粒径が小さく且つ特定の結晶面での結晶子サイズが小さい銅粒子を生産性高く得ることができる。 In the second reduction step, the above-mentioned reducing compound can be added to perform reduction to metallic copper. The content of the reducing compound in the reaction solution in the second reduction step is preferably 1 mole or more and 8 moles or less, more preferably 2 moles or more and 6 moles or less, relative to 1 mole of copper element. When the second reduction step is performed in the same reaction system as the first reduction step, it is preferable to further add the reducing compound to the solution so as to have the above-mentioned content, from the viewpoint of achieving both improvement of reduction and control of impurity reduction. It is also preferable to use the same type of reducing compound in each reduction step.
By controlling the concentration of the reducing compound within this range, the reduction reaction to metallic copper can be sufficiently progressed, and copper particles having a small particle size and a small crystallite size on a specific crystal plane can be obtained with high productivity.
　第２還元工程における還元性化合物は、一括添加でもよく、逐次添加でもよい。上述した結晶子サイズの比や粒子径を満たす銅粒子を効率よく得る観点から、逐次添加を採用することが好ましい。 The reducing compound in the second reduction step may be added all at once or gradually. From the viewpoint of efficiently obtaining copper particles that satisfy the above-mentioned crystallite size ratio and particle diameter, it is preferable to adopt gradually adding the reducing compound.
　第２還元工程における反応液は、その２５℃におけるｐＨが７．０以上の非酸性条件（中性又はアルカリ性条件）にすることが、還元性化合物、特にヒドラジン系化合物を用いた場合に、反応液中に残存する銅イオン及び亜酸化銅の金属銅への還元を効率的に進行させ、銅の結晶成長に異方性を持たせやすくすることができる点で好ましい。ｐＨの調整は、第２還元工程において還元性化合物を添加する前に行うことが、銅イオンの還元の度合いを適切に制御できる点で好ましい。ｐＨの調整は、各種の酸や塩基性物質を用いることができる。
　第２還元工程を第１還元工程と同一の反応系で行う場合、第１還元工程後の反応液は酸性条件となっているので、水酸化ナトリウムや水酸化カリウムなどの塩基性物質を添加することによって、反応液のｐＨを調整することが好ましい。第２還元工程においては、ｐＨの調整を行ったあと、還元性化合物を添加することが、銅イオン及び亜酸化銅を金属銅に効率的に還元できる点で好ましい。 The reaction solution in the second reduction step is preferably kept under non-acidic conditions (neutral or alkaline conditions) with a pH of 7.0 or more at 25° C., in that when a reducing compound, particularly a hydrazine-based compound, is used, the reduction of the copper ions and cuprous oxide remaining in the reaction solution to metallic copper can be efficiently promoted, and the crystal growth of copper can be easily made anisotropic. The pH is preferably adjusted before the addition of the reducing compound in the second reduction step, in that the degree of reduction of the copper ions can be appropriately controlled. Various acids and basic substances can be used for adjusting the pH.
When the second reduction step is carried out in the same reaction system as the first reduction step, since the reaction solution after the first reduction step is in an acidic condition, it is preferable to adjust the pH of the reaction solution by adding a basic substance such as sodium hydroxide or potassium hydroxide. In the second reduction step, it is preferable to add a reducing compound after adjusting the pH, since this allows copper ions and cuprous oxide to be efficiently reduced to metallic copper.
　反応液中の銅イオン及び亜酸化銅の還元を効率よく進行させ、所定の結晶子サイズを有する銅粒子を生産性高く得る観点から、第２還元工程においては、反応液を加熱することが好ましい。反応液の加熱条件は、第２還元工程の開始時点、すなわち還元性化合物の添加時点から、反応終了時点にわたって、１０℃以上６０℃以下、特に２０℃以上５０℃以下に維持するように加熱することが好ましい。反応時間は、上述の温度条件において、３０分以上７２０分以下とすることが好ましい。また、還元反応を均一に生じさせて、粒径のばらつきが少ない銅粒子を得る観点から、反応開始時点から反応終了時点にわたって、反応液の撹拌を継続することも好ましい。 In order to efficiently reduce the copper ions and cuprous oxide in the reaction solution and to obtain copper particles having a predetermined crystallite size with high productivity, it is preferable to heat the reaction solution in the second reduction step. The heating conditions for the reaction solution are preferably such that the temperature is maintained at 10°C or higher and 60°C or lower, particularly 20°C or higher and 50°C or lower, from the start of the second reduction step, i.e., the time when the reducing compound is added, until the end of the reaction. The reaction time is preferably 30 minutes or longer and 720 minutes or shorter under the above temperature conditions. In order to uniformly cause the reduction reaction to occur and obtain copper particles with little variation in particle size, it is also preferable to continue stirring the reaction solution from the start of the reaction until the end of the reaction.
　本製造方法において、銅イオンが亜酸化銅を経て金属銅に還元するという二段階の還元工程を行うこと、及び第２還元工程を行う際にポリリン酸類を存在させることで、焼結温度の低い銅粒子が得られる理由について、本発明者は以下のように推測している。
　まず第１還元工程において、反応液中の還元性化合物によって銅イオンが還元され、亜酸化銅の非常に微小な粒子が反応液中に生成する。続いて、第２還元工程において、亜酸化銅粒子から溶出した一価の銅イオンが還元され金属銅の核を形成する。この核は非常に不安定であるため、核どうしの合体、又は反応液中への再溶解を繰り返し、最終的に粒子が成長していく。この粒子成長時にポリリン酸類が存在すると、銅の特定の結晶面にポリリン酸類が吸着し、当該結晶面方向の成長が抑制される。一方、ポリリン酸類が吸着しない結晶面は、成長が抑制されず、当該結晶面方向の成長が進行する。
　金属銅が面心立方構造の結晶構造をとりやすい点と、得られた銅粒子のＸ線回折測定による結果とに基づくと、ポリリン酸類が吸着する結晶面は、当該粒子における銅の（１１１）面と推定され、ポリリン酸類が吸着しない結晶面は、銅の（１１１）面の垂直方向に位置する銅の（２２０）面であると推定される。このことから、銅の（１１１）面の成長が抑制され、かつ銅の（２２０）面の成長が進行するという異方的な成長となり、その結果、焼結温度の低い扁平状の銅粒子となると考えられる。 The inventors speculate as follows about the reason why copper particles with a low sintering temperature can be obtained in this manufacturing method by performing a two-step reduction process in which copper ions are reduced to cuprous oxide and then to metallic copper, and by having polyphosphoric acids present during the second reduction process.
First, in the first reduction step, copper ions are reduced by a reducing compound in the reaction solution, and very small particles of cuprous oxide are generated in the reaction solution. Then, in the second reduction step, monovalent copper ions eluted from the cuprous oxide particles are reduced to form metallic copper nuclei. Since these nuclei are very unstable, they repeatedly combine with each other or redissolve in the reaction solution, and eventually the particles grow. If polyphosphates are present during this particle growth, the polyphosphates are adsorbed to specific crystal faces of copper, and growth in the direction of the crystal faces is suppressed. On the other hand, growth is not suppressed on crystal faces to which polyphosphates are not adsorbed, and growth in the direction of the crystal faces proceeds.
Based on the fact that metallic copper is likely to have a face-centered cubic crystal structure and the results of X-ray diffraction measurement of the obtained copper particles, it is estimated that the crystal face to which polyphosphates are adsorbed is the (111) face of copper in the particles, and the crystal face to which polyphosphates are not adsorbed is the (220) face of copper located perpendicular to the (111) face of copper. For this reason, it is considered that anisotropic growth occurs in which the growth of the (111) face of copper is suppressed and the growth of the (220) face of copper progresses, resulting in flat copper particles with a low sintering temperature.
　また銅粒子Ｂの好適な製造方法として、特に第１還元工程では酸性条件で還元反応を行うことによって、銅イオンを亜酸化銅に還元できる程度であり且つ金属銅までは還元できない程度の還元力に制御できる。これに加えて、以後の金属銅生成反応の制御も容易になる。その後、非酸性条件とすることで、亜酸化銅の溶出速度を低下させ、一価の銅イオン供給を制御することができる。その環境下で第２還元を行うことで、金属銅への還元反応速度を緩やかな条件に調整することができるので、核成長速度を制御できる点で特に有利である。 As a preferred method for producing copper particles B, the reduction reaction is carried out under acidic conditions, particularly in the first reduction step, so that the reducing power can be controlled to a level where copper ions can be reduced to cuprous oxide but not to metallic copper. In addition, this also makes it easier to control the subsequent metallic copper production reaction. Then, by changing 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 reduction reaction rate to metallic copper can be adjusted to gentle conditions, which is particularly advantageous in that the nucleus growth rate can be controlled.
　以上の工程を経て得られた銅粒子Ｂは、有機アミンやアミノアルコール、還元糖などの結晶成長を制御する有機成分を非含有とした場合であっても、上述した好適な結晶子サイズ及びその比、好適な粒子径、炭素元素等の各種元素の好適な含有量を満たすものとなり、また、扁平状の形状を有するものとなる。
　またこのようにして得られた銅粒子Ｂは、主面に存在し且つ主面に直交する方向に成長した結晶の結晶面と、側面に存在し且つ主面に沿う方向に成長した結晶の結晶面とがそれぞれ特定の配向方向を有し、各結晶面が一方向に均一に形成されたものとなる。したがって、銅粒子Ｂを含む銅粉を用いて、銅粒子Ｂの主面どうしが接触した状態、あるいは銅粒子Ｂの側面どうしが接触した状態で焼成した場合には、均等に整列した同一の結晶面どうしが接触することに起因して、融着に要するエネルギーを過度に必要とせず、低温での焼結が可能となる。 The copper particles B obtained through the above steps, even if they do not contain organic components that control crystal growth, such as organic amines, amino alcohols, or reducing sugars, will satisfy the above-mentioned suitable crystallite sizes and ratios thereof, suitable particle diameter, and suitable contents of various elements such as carbon, and will have a flattened shape.
In addition, the copper particles B thus obtained have a crystal face of the crystal present on the main surface and grown in a direction perpendicular to the main surface, and a crystal face of the crystal present on the side surface and grown in a direction along the main surface, each of which has a specific orientation direction, and each crystal face is formed uniformly in one direction. Therefore, when copper powder containing copper particles B is used and sintered in a state where the main surfaces of copper particles B are in contact with each other or the side surfaces of copper particles B are in contact with each other, sintering at a low temperature is possible without excessive energy required for fusion due to the contact of the same evenly aligned crystal faces.
　以上の工程を経て得られた銅粒子Ｂは、必要に応じて洗浄や固液分離を行った後、銅粒子Ｂを水や有機溶媒等の溶媒に分散させたスラリーの形態で銅粒子Ａと混合させてもよく、該粒子を乾燥させて、銅粒子Ｂの集合体である乾燥粉の形態で銅粒子Ａと混合することもできる。いずれの場合であっても、銅粒子Ｂは、焼結温度の低い優れたものとなる。銅粒子Ｂは、必要に応じて、粒子同士の分散性の向上を目的として、脂肪酸又はその塩等の有機物や、ケイ素系化合物等の無機物による表面被覆処理を更に施してもよい。なお、本発明の効果が奏される限りにおいて、得られた銅粒子Ｂは、その表面が不可避的に微量酸化されるなどして、銅元素以外の他の元素を含むことは許容される。 The copper particles B obtained through the above steps may be washed or separated into solid and liquid as necessary, and then mixed with the copper particles A in the form of a slurry in which the copper particles B are dispersed in a solvent such as water or an organic solvent, or the particles may be dried and mixed with the copper particles A in the form of a dry powder that is an aggregate of the copper particles B. In either case, the copper particles B have a low sintering temperature and are excellent. If necessary, the copper particles B may be further surface-coated with an organic substance such as a fatty acid or a salt thereof, or an inorganic substance such as a silicon-based compound, in order to improve the dispersibility of the particles. As long as the effects of the present invention are achieved, it is acceptable for the obtained copper particles B to contain elements other than the copper element, for example by unavoidably oxidizing the surface slightly.
＜銅粒子Ａ及び銅粒子Ｂの混合方法＞
　銅粒子Ａ及び銅粒子Ｂは、乾式又は湿式で混合することができるが、混合の簡便性の観点から、乾式で混合することが好ましい。乾式での混合は、公知の乾式混合装置を用いて行うことができる。湿式での混合は、具体的には有機溶媒や水溶媒中で混合することができる。 <Method of mixing copper particles A and copper particles B>
The copper particles A and the copper particles B can be mixed in a dry or wet manner, but from the viewpoint of ease of mixing, it is preferable to mix them in a dry manner. Dry mixing can be performed using a known dry mixing device. Wet mixing can be performed in an organic solvent or an aqueous solvent.
　本発明の銅粉は、有機溶媒や樹脂等に更に分散させて、導電性インクや銅ペースト等の導電性組成物の形態で用いることもできる。
　本発明の銅粉を導電性組成物の形態とする場合、導電性組成物は、銅粉及び有機溶媒を少なくとも含んで構成される。有機溶媒としては、金属粉を含む導電性組成物の技術分野においてこれまで用いられてきたものと同様のものを特に制限なく用いることができる。そのような有機溶媒としては、例えば一価アルコール、多価アルコール、多価アルコールアルキルエーテル、多価アルコールアリールエーテル、ポリエーテル、エステル類、含窒素複素環化合物、アミド類、アミン類、及び飽和炭化水素などが挙げられる。これらの有機溶媒は、単独で又は二種以上を組み合わせて用いることができる。これらのうち、高い還元作用を有し、焼結時における銅粒子の意図しない酸化を防ぐ観点から、ポリエチレングリコール及びポリプロピレングリコールなどのポリエーテルを用いることが好ましい。同様の観点から、有機溶媒としてポリエチレングリコールを用いる場合、その数平均分子量は、１２０以上４００以下であることが好ましく、１８０以上４００以下であることが更に好ましい。 The copper powder of the present invention can also be further dispersed in an organic solvent, a resin, or the like and used in the form of a conductive composition such as a conductive ink or a copper paste.
When the copper powder of the present invention is in the form of a conductive composition, the conductive composition is composed of at least copper powder and an organic solvent. As the organic solvent, those similar to those used in the technical field of conductive compositions containing metal powders can be used without any particular limitation. Examples of such organic solvents include monohydric alcohols, polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, polyethers, esters, nitrogen-containing heterocyclic compounds, amides, amines, and saturated hydrocarbons. These organic solvents can be used alone or in combination of two or more. Among these, it is preferable to use polyethers such as polyethylene glycol and polypropylene glycol, which have a high reducing action and prevent unintended oxidation of copper particles during sintering. From the same viewpoint, when polyethylene glycol is used as the organic solvent, its number average molecular weight is preferably 120 to 400, and more preferably 180 to 400.
　本発明の銅粉を含む導電性組成物には、必要に応じて、分散剤、有機ビヒクル及びガラスフリットの少なくとも一種を更に添加してもよい。分散剤としては、ナトリウム、カルシウム、リン、硫黄及び塩素等を含有しない非イオン性界面活性剤等の分散剤等が挙げられる。有機ビヒクルとしては、例えば、アクリル樹脂、エポキシ樹脂、エチルセルロース、カルボキシエチルセルロース等の樹脂成分と、ターピネオール及びジヒドロターピネオール等のテルペン系溶剤、エチルカルビトール及びブチルカルビトール等のエーテル系溶剤等の溶剤とを含む混合物が挙げられる。ガラスフリットとしては、例えばホウケイ酸ガラス、ホウケイ酸バリウムガラス、ホウケイ酸亜鉛ガラス等が挙げられる。 The conductive composition containing copper powder of the present invention may further contain at least one of a dispersant, an organic vehicle, and a glass frit, if necessary. Examples of dispersants include dispersants such as nonionic surfactants that do not contain sodium, calcium, phosphorus, sulfur, or chlorine. Examples of organic vehicles include mixtures containing resin components such as acrylic resins, epoxy resins, ethyl cellulose, and carboxyethyl cellulose, and solvents such as terpene-based solvents such as terpineol and dihydroterpineol, and ether-based solvents such as ethyl carbitol and butyl carbitol. Examples of glass frits include borosilicate glass, barium borosilicate glass, and zinc borosilicate glass.
　本発明の銅粉を含む導電性組成物は、これを基板上に塗布して塗膜を形成し、この塗膜を焼成することによって、銅を含む導電膜を形成することができる。導電膜は、例えばプリント配線板の回路形成や、セラミックコンデンサの外部電極の電気的導通確保のために好適に用いられる。基板としては、銅粒子が用いられる電子回路の種類に応じて、ガラスエポキシ樹脂等からなるプリント基板や、ポリイミド等からなるフレキシブルプリント基板が挙げられる。 The conductive composition containing the copper powder of the present invention can be applied to a substrate to form a coating film, which can then be fired to form a conductive film containing copper. The conductive film is preferably used, for example, to form circuits on printed wiring boards and to ensure electrical continuity of external electrodes of ceramic capacitors. Depending on the type of electronic circuit in which the copper particles are used, examples of the substrate include printed circuit boards made of glass epoxy resins and flexible printed circuit boards made of polyimide.
　本発明の銅粉を含む導電性組成物における銅粉及び有機溶媒の配合量は、該導電性組成物の具体的な用途や該導電性組成物の塗布方法に応じて調整可能であるが、導電性組成物における銅粉の含有割合は、好ましくは５質量％以上９５質量％以下、より好ましくは８０質量％以上９０質量％以下である。塗布方法としては、例えばインクジェット法、ディスペンサ法、マイクロディスペンサ法、グラビア印刷法、スクリーン印刷法、ディップコーティング法、スピンコーティング法、スプレー塗布法、バーコーティング法、ロールコーティング法などを用いることができる。 The amounts of copper powder and organic solvent in the conductive composition containing copper powder of the present invention can be adjusted according to the specific use of the conductive composition and the coating method of the conductive composition, but the content of copper powder in the conductive composition is preferably 5% by mass or more and 95% by mass or less, and more preferably 80% by mass or more and 90% by mass or less. Coating methods that can be used include, for example, the inkjet method, the dispenser method, the microdispenser method, the gravure printing method, the screen printing method, the dip coating method, the spin coating method, the spray coating method, the bar coating method, and the roll coating method.
　形成された塗膜を焼結させる際の加熱温度は、銅粉の焼結開始温度以上であればよく、例えば１５０℃以上２２０℃以下とすることができる。加熱時における雰囲気は、例えば酸化性雰囲気下、又は非酸化性雰囲気下で行うことができる。酸化性雰囲気としては、例えば酸素含有雰囲気が挙げられる。非酸化性雰囲気としては、例えば水素や一酸化炭素等の還元性雰囲気、水素－窒素混合雰囲気等の弱還元性雰囲気、アルゴン、ネオン、ヘリウム及び窒素等の不活性雰囲気が挙げられる。いずれの雰囲気を用いる場合であっても、加熱時間は、上述の温度範囲で加熱することを条件として、好ましくは１分以上３時間以下、更に好ましくは３分以上２時間以下とする。 The heating temperature when sintering the formed coating film may be equal to or higher than the sintering start temperature of the copper powder, and may be, for example, 150°C to 220°C. The heating atmosphere may be, for example, an oxidizing atmosphere or a non-oxidizing atmosphere. Examples of oxidizing atmospheres include oxygen-containing atmospheres. Examples of non-oxidizing atmospheres include reducing atmospheres such as hydrogen and carbon monoxide, weakly reducing atmospheres such as a hydrogen-nitrogen mixed atmosphere, and inert atmospheres such as argon, neon, helium, and nitrogen. Regardless of which atmosphere is used, the heating time is preferably 1 minute to 3 hours, more preferably 3 minutes to 2 hours, provided that heating is performed within the above-mentioned temperature range.
　このようにして得られた導電膜は、本発明の銅粉の焼結によって得られたものであるので、比較的低温の条件で焼結を行った場合でも、十分に焼結を進行させることができる。また焼結時には、銅粉を構成する銅粒子が低温でも溶融するので、銅粒子どうし、あるいは銅粒子と基材の表面との接触面積を大きくすることができ、その結果、接合対象物との密着性が高く、且つ密な焼結構造を効率よく形成することができる。更に、得られた導電膜は、連続性、緻密性及び導電信頼性が高いものとなる。 The conductive film thus obtained is obtained by sintering the copper powder of the present invention, so that sintering can proceed sufficiently even when sintering is performed under relatively low temperature conditions. Furthermore, during sintering, the copper particles that make up the copper powder melt even at low temperatures, so that the contact area between the copper particles or between the copper particles and the surface of the base material can be increased, resulting in a high degree of adhesion to the objects to be joined and an efficient formation of a dense sintered structure. Furthermore, the conductive film obtained has high continuity, density, and conductive reliability.
　以上、本発明をその好ましい実施形態に基づき説明したが、本発明は前記実施形態に制限されない。例えば、本発明の銅粉は、所期の効果が奏される範囲において、銅粒子Ａ及び銅粒子Ｂ以外の銅粒子を含んでもよい。 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 contain copper particles other than copper particles A and copper particles B as long as the desired effect is achieved.
　本発明の上記の実施形態は、以下の技術思想を包含するものである。
［１］　以下の銅粒子Ａ及び銅粒子Ｂを含み、
　銅粒子Ａと銅粒子Ｂの合計に対する銅粒子Ａの含有割合が６０質量％以上９９質量％以下であり、銅粒子Ｂの含有割合が１質量％以上４０質量％以下である、銅粉。
〔銅粒子Ａ〕
　銅からなるコア粒子と、該コア粒子の表面を被覆する被覆層とを備え、
　前記被覆層は脂肪族有機酸の銅塩によって形成されており、
　一次粒子径が０．１μｍ以上０．６μｍ以下である銅粒子。
〔銅粒子Ｂ〕
　ＢＥＴ比表面積から算出されたＢＥＴ径Ｂに対する、Ｘ線回折測定において銅の（１１１）面に由来するピークの半値幅からシェラーの式によって求められる第１結晶子サイズＳ１の比（Ｓ１／Ｂ）が０．２３以下であり、
　Ｘ線回折測定において銅の（２２０）面に由来するピークの半値幅からシェラーの式によって求められる第２結晶子サイズＳ２に対する、前記第１結晶子サイズＳ１の比（Ｓ１／Ｓ２）が１．３５以下であり、
　一次粒子径が０．１μｍ以上２．０μｍ以下である銅粒子。
［２］　銅粒子Ｂは、Ｘ線回折測定において銅の（３１１）面に由来するピークの半値幅からシェラーの式によって求められる第３結晶子サイズＳ３に対する、前記第１結晶子サイズＳ１の比（Ｓ１／Ｓ３）が１．３５以下である、［１］に記載の銅粉。
［３］　銅粒子Ｂは炭素元素を含み、且つ該炭素元素の含有量が５０００ｐｐｍ以下である、［１］又は［２］に記載の銅粉。
［４］　銅粒子Ｂはリン元素を含み、且つ該リン元素の含有量が３００ｐｐｍ以上である、［１］ないし［３］のいずれか一項に記載の銅粉。
［５］　［１］ないし［４］のいずれか一項に記載の銅粉を含む銅ペースト。
［６］　［５］に記載の銅ペーストを基材に塗布して塗膜を形成し、該塗膜を焼成する、導電膜の製造方法。 The above-described embodiment of the present invention encompasses the following technical ideas.
[1] Contains the following copper particles A and copper particles B,
A copper powder in which the content of copper particles A is 60% by mass or more and 99% by mass or less, and the content of copper particles B is 1% by mass or more and 40% by mass or less, relative to the total of copper particles A and copper particles B.
[Copper particles A]
The present invention comprises a core particle made of copper and a coating layer that coats the surface of the core particle,
the coating layer is formed from a copper salt of an aliphatic organic acid,
Copper particles having a primary particle diameter of 0.1 μm or more and 0.6 μm or less.
[Copper particles B]
a ratio (S1/B) of a first crystallite size S1 calculated by the Scherrer formula from the half-width of a peak derived from the copper (111) plane in an X-ray diffraction measurement to a BET diameter B calculated from a 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 calculated by the Scherrer formula from the half-width of the peak derived from the (220) plane of copper in X-ray diffraction measurement is 1.35 or less;
Copper particles having a primary particle diameter of 0.1 μm or more and 2.0 μm or less.
[2] The copper particles B have a ratio (S1/S3) of the first crystallite size S1 to the third crystallite size S3 calculated by the Scherrer equation from the half-width of the peak derived from the (311) plane of copper in an X-ray diffraction measurement, of 1.35 or less. The copper powder according to [1].
[3] The copper powder according to [1] or [2], wherein the copper particles B contain carbon element and the content of the carbon element is 5000 ppm or less.
[4] The copper powder according to any one of [1] to [3], wherein the copper particles B contain phosphorus element and the content of the phosphorus element is 300 ppm or more.
[5] A copper paste containing the copper powder according to any one of [1] to [4].
[6] A method for producing a conductive film, comprising applying the copper paste according to [5] to a substrate to form a coating film, and firing the coating film.
　以下、実施例により本発明を更に詳細に説明する。しかしながら本発明の範囲は、かかる実施例に制限されない。特に断らない限り、「％」は「質量％」を意味する。 The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."
　以下の実施例及び比較例では、銅粒子として銅粒子Ａ－１、銅粒子Ａ－２及び銅粒子Ｂ－１ないしＢ－３を用いた。これらのうち、銅粒子Ａ－２としては特開２０１５－１６８８７８号公報に記載されている球状の銅粒子を用いた。
　その他の銅粒子は、以下の方法によって製造した。 In the following examples and comparative examples, copper particles A-1, A-2, and B-1 to B-3 were used as copper particles. Of these, spherical copper particles described in JP 2015-168878 A were used as copper particles A-2.
Other copper particles were produced by the following method.
〔銅粒子Ａ－１の製造〕
　特開２０１５－１６８８７８号公報の実施例１に記載の方法に準じて、表面処理剤が施されていない球状のコア粒子（銅：１００質量％）が水に分散したスラリーを製造した。このスラリーをロータリーフィルターによって２５℃で３０分間洗浄して、洗浄処理されたコア粒子のスラリーを得た。洗浄後の導電率は１．０ｍＳであり、球状の形状を有していた。またスラリー中の銅からなるコア粒子の含有量は、１０００ｇ（１０質量％）であった。 [Production of copper particles A-1]
According to the method described in Example 1 of JP 2015-168878 A, a slurry was produced in which spherical core particles (copper: 100% by mass) not treated with a surface treatment agent were dispersed in water. This slurry was washed with a rotary filter at 25°C for 30 minutes to obtain a slurry of washed core particles. The conductivity after washing was 1.0 mS and the core particles had a spherical shape. The content of the copper core particles in the slurry was 1000 g (10% by mass).
　次いで、洗浄処理されたコア粒子のスラリーを５０℃に加熱し、この状態下で、ラウリン酸銅（II）１７ｇをイソプロピルアルコール４Ｌに溶解させた溶液を表面処理剤として瞬時に添加し、５０℃で１時間撹拌した。その後、ろ過により固液分離を行い、脂肪族有機酸の銅塩の被覆層がコア粒子の表面に形成された銅粒子を固形分として得た。得られた銅粒子の表面処理剤の含有量は、炭素原子換算で０．７質量％であった。
　次に、銅粒子Ａ－１及びＡ－２について、以下の評価を行った。 Next, the slurry of the washed core particles was heated to 50° C., and under this condition, a solution in which 17 g of copper (II) laurate was dissolved in 4 L of isopropyl alcohol was instantly added as a surface treatment agent, and the mixture was stirred at 50° C. for 1 hour. Then, solid-liquid separation was performed by filtration, and copper particles having a coating layer of a copper salt of an aliphatic organic acid formed on the surface of the core particles were obtained as a solid content. The content of the surface treatment agent in the obtained copper particles was 0.7% by mass in terms of carbon atoms.
Next, the copper particles A-1 and A-2 were subjected to the following evaluations.
〔一次粒子の平均画像解析径の測定〕
　銅粒子の一次粒子の平均画像解析径は上述の方法によって測定した。結果を以下の表１に示す。 [Measurement of the average image analysis diameter of primary particles]
The average image analysis diameter of the primary particles of the copper particles was measured by the method described above, and the results are shown in Table 1 below.
〔ＢＥＴ比表面積に基づくＢＥＴ径Ａの算出〕
　まず、上述した測定方法によって、ＢＥＴ一点法に基づいて銅粒子Ａ－１及びＡ－２の比表面積を測定し、当該比表面積に基づいてＢＥＴ径Ａを算出した。結果を表１に示す。 [Calculation of BET diameter A based on BET specific surface area]
First, the specific surface areas of the copper particles A-1 and A-2 were measured based on the BET single point method by 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.
〔１０％質量減少時の温度の評価〕
　２５℃から１０００℃まで加熱したときの熱重量分析において、５００℃における質量減少値に対する質量減少値の割合が１０％となる温度を、上述した条件で測定した。結果を表１に示す。 [Evaluation of temperature at 10% mass loss]
In the thermogravimetric analysis when heated from 25° C. to 1000° C., the temperature at which the ratio of the mass loss to the mass loss at 500° C. was 10% was measured under the above-mentioned conditions. The results are shown in Table 1.
　〔赤外線吸収ピークの評価〕
　銅粒子Ａ－１及びＡ－２について、上述の方法で赤外分光法による測定を行った。１５０４ｃｍ－１以上１５１４ｃｍ－１以下、及び１５８４ｃｍ－１以上１５９６ｃｍ－１以下の各範囲を対象として、それぞれ独立に、赤外線吸収ピークを有するものを「あり」と評価し、赤外線吸収ピークを有しないものを「なし」と評価した。結果を表１に示す。 [Evaluation of infrared absorption peaks]
Copper particles A-1 and A-2 were subjected to infrared spectroscopy measurement by the above-mentioned method. For each range of 1504 cm -1 or more and 1514 cm -1 or less, and 1584 cm -1 or more and 1596 cm -1 or less, those having an infrared absorption peak were evaluated as "present", and those not having an infrared absorption peak were evaluated as "absent". The results are shown in Table 1.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
〔銅粒子Ｂ－１の製造〕
＜第１還元工程＞
　温純水５．０リットル及びメタノール５．０リットルを入れたステンレス製タンク中に、銅源として２．５ｋｇの酢酸銅一水和物と、ポリリン酸類として８．０ｇのトリポリリン酸ナトリウム（銅元素１モルに対するモル割合：０．００２）を入れ、液温２５℃にて３０分間撹拌し、両者を溶解させた。
　次いで、２３５．０ｇのヒドラジン（銅元素１モルに対するモル割合：１．５５）を液中に添加した後、液温２５℃の非加熱条件にて３０分間にわたって撹拌を継続して、液中に亜酸化銅の微粒子を生成させた。亜酸化銅を生成させたあと、反応液を３０分間攪拌した。 [Production of copper particles B-1]
<First reduction step>
Into a stainless steel tank containing 5.0 L of warm pure water and 5.0 L of methanol, 2.5 kg of copper acetate monohydrate as a copper source and 8.0 g of sodium tripolyphosphate (molar ratio relative to 1 mole of copper element: 0.002) as a polyphosphate were placed, and the mixture was stirred at a liquid temperature of 25° C. for 30 minutes to dissolve both components.
Next, 235.0 g of hydrazine (molar ratio relative to 1 mole of copper: 1.55) was added to the liquid, and stirring was continued for 30 minutes under non-heating conditions with a liquid temperature of 25° C. to generate cuprous oxide fine particles in the liquid. After the cuprous oxide was generated, the reaction liquid was stirred for 30 minutes.
＜第２還元工程＞
　続いて、第１還元工程における反応液に対して、２５％ＮａＯＨ水溶液を添加して、液のｐＨを７．０に調整した。その後、液温を４０℃に加熱し、１９００．０ｇのヒドラジン（銅元素１モルに対するモル割合：３．０）を液中に１０分間かけて定量的に逐次添加して、第２還元工程を行った。その後、液温が３０℃となるように冷却し、１５０分間にわたって撹拌を継続し、亜酸化銅の微粒子が金属銅に還元された銅粒子を得た。 <Second reduction step>
Next, a 25% NaOH aqueous solution was added to the reaction solution in the first reduction step to adjust the pH of the solution to 7.0. The solution was then heated to 40° C., and 1900.0 g of hydrazine (molar ratio relative to 1 mole of copper: 3.0) was quantitatively and sequentially added to the solution over 10 minutes to perform the second reduction step. The solution was then cooled to 30° C. and stirred for 150 minutes to obtain copper particles in which the cuprous oxide particles were reduced to metallic copper.
　このようにして得られた銅粒子の水性スラリーに対してデカンテーション洗浄を行って、電導度が１．０ｍＳになるまで洗浄を行った（洗浄スラリー）。
　洗浄処理されたコア粒子のスラリーを５０℃に加熱し、この状態下で、ラウリン酸銅（II）４ｇをイソプロピルアルコール１Ｌに溶解させた溶液を表面処理剤として瞬時に添加し、５０℃で１時間撹拌した。その後、ろ過により固液分離を行い、脂肪族有機酸の銅塩の被覆層がコア粒子の表面に形成された銅粒子を固形分として得た。その後乾燥して、銅粒子の集合体からなる銅粉を得た。得られた銅粒子は、銅元素含有量が９８質量％超であり、扁平状の形状を有していた。 The aqueous slurry of copper particles thus obtained was subjected to decantation washing until the electrical conductivity reached 1.0 mS (washed slurry).
The slurry of the washed core particles was heated to 50°C, and under this condition, a solution in which 4 g of copper (II) laurate was dissolved in 1 L of isopropyl alcohol was instantly added as a surface treatment agent, and the mixture was stirred at 50°C for 1 hour. Then, solid-liquid separation was performed by filtration, and copper particles in which a coating layer of a copper salt of an aliphatic organic acid was formed on the surface of the core particles were obtained as a solid content. Then, the mixture was dried to obtain copper powder consisting of an aggregate of copper particles. The obtained copper particles had a copper element content of more than 98% by mass and had a flat shape.
〔銅粒子Ｂ－２の製造〕
　トリポリリン酸ナトリウムの添加量を２４ｇ（銅元素１モルに対するモル割合：０．００６）とした以外は銅粒子Ｂ－１と同様に製造して、銅粒子Ｂ－２を得た。得られた銅粒子は、銅元素含有量が９８質量％超であり、扁平状の形状を有していた。 [Production of copper particles B-2]
Copper particles B-2 were obtained in the same manner as in the production of copper particles B-1, except that the amount of sodium tripolyphosphate added was 24 g (molar ratio relative to 1 mole of copper: 0.006). The obtained copper particles had a copper content of more than 98% by mass and a flat shape.
　〔銅粒子Ｂ－３の製造〕
　硫酸銅五水和物４ｋｇ及びアミノ酢酸１２０ｇを水に溶解させて、液温７０℃の銅塩水溶液８Ｌを作製した。そして、この水溶液を撹拌しながら、６．６ｋｇの２５質量％水酸化ナトリウム溶液を約５分間かけて一定速度で添加した。次いで、液温７０℃で６０分間の撹拌を行い、液色が完全に黒色になるまで熟成させて酸化第二銅を生成した。その後３０分間放置し、グルコース１．５ｋｇ添加して、１時間熟成することで酸化第二銅を酸化第一銅に還元した。更に、水和ヒドラジン１ｋｇを５分間かけて定量的に添加して酸化第一銅を還元することで金属銅にして、銅粉スラリーを生成した。得られた銅粉スラリーをろ過し、純水で十分に洗浄し、再度ろ過した後、乾燥した。得られたＣｕ粉を特許４２２７３７３号記載の扁平化方法を用いて塑性変形させることで、略球形の銅粉を扁平状の銅粉にした。このとき、使用したビーズ径は０．７ｍｍではなく、０．２ｍｍに変更した。 [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 this aqueous solution, 6.6 kg of 25% by mass sodium hydroxide solution was added at a constant rate over about 5 minutes. Next, the solution was stirred at a liquid temperature of 70 ° C. for 60 minutes, and the solution was aged until the liquid color became completely black to generate cupric oxide. After that, the solution was left for 30 minutes, 1.5 kg of glucose was added, and the solution was aged for 1 hour to reduce cupric oxide to cuprous oxide. Furthermore, 1 kg of hydrazine hydrate was quantitatively added over 5 minutes to reduce cuprous oxide to metallic copper, thereby generating a copper powder slurry. The obtained copper powder slurry was filtered, thoroughly washed with pure water, filtered again, and then dried. The obtained Cu powder was plastically deformed using the flattening method described in Patent No. 4227373 to convert the approximately spherical copper powder into flat copper powder. At this time, the bead diameter used was changed from 0.7 mm to 0.2 mm.
　次に、銅粒子Ｂ－１ないしＢ－３について、以下の評価を行った。 Next, the following evaluations were carried out on copper particles B-1 to B-3.
〔一次粒子の平均画像解析径の測定〕
　銅粒子Ｂ－１ないしＢ－３について、各銅粒子の一次粒子の平均画像解析径は上述の方法によって測定した。結果を表２に示す。 [Measurement of the average image analysis diameter of primary particles]
For copper particles B-1 to B-3, the average image analysis diameter of the primary particles of each copper particle was measured by the above-mentioned method. The results are shown in Table 2.
〔ＢＥＴ比表面積に基づくＢＥＴ径Ｂの算出〕
　銅粒子Ｂ－１ないしＢ－３のＢＥＴ径Ｂを銅粒子ＡのＢＥＴ径Ａと同様の方法で測定した。結果を以下の表２に示す。 [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 in the same manner as the BET diameter A of copper particles A. The results are shown in Table 2 below.
〔炭素元素及びリン元素の含有量の測定〕
　銅粒子Ｂ－１ないしＢ－３における銅粒子中の炭素元素の含有量は、炭素・硫黄分析装置（ＬＥＣＯジャパン合同会社製ＣＳ８４４）を用いて、銅粒子Ｂ－１ないしＢ－３のいずれか０．５０ｇを磁性坩堝に入れて、キャリアガスは酸素ガス（純度：９９．５％）とし、分析時間は４０秒として測定した。測定結果を以下の表２に示す。
　銅粒子中のリン元素の含有量は、銅粒子Ｂ－１ないしＢ－３のいずれか１．００ｇを１５％硝酸水溶液５０ｍＬに溶解させた溶解液を、ＩＣＰ発光分光分析装置（株式会社　日立ハイテクサイエンス製ＰＳ３５２０ＶＤＤII）に導入して測定した。測定結果を以下の表２に示す。 [Measurement of Carbon and Phosphorus Content]
The carbon element content in the copper particles of copper particles B-1 to B-3 was measured using a carbon/sulfur analyzer (CS844 manufactured by LECO Japan LLC) by placing 0.50 g of any of copper particles B-1 to B-3 in a magnetic crucible, using oxygen gas (purity: 99.5%) as the carrier gas, and setting the analysis time to 40 seconds. The measurement results are shown in Table 2 below.
The content of phosphorus element in the copper particles was measured by dissolving 1.00 g of any of copper particles B-1 to B-3 in 50 mL of 15% aqueous nitric acid solution, and introducing the solution into an ICP emission spectrometer (PS3520VDDII manufactured by Hitachi High-Tech Science Co., Ltd.). The measurement results are shown in Table 2 below.
〔結晶子サイズの測定〕
　銅粒子Ｂ－１ないしＢ－３について、以下の方法で測定を行った。まず、銅粒子Ｂ－１ないしＢ－３の洗浄スラリーを用いて、２０質量％水性スラリーを調製した。その後、５０℃に加熱した該スラリーに表面被覆処理剤としてラウリン酸銅１２ｇを溶解させたイソプロピルアルコール溶液を一度に添加し、１時間撹拌した。その後、ろ過により固液分離して得られた固形分を真空乾燥させて、表面被覆処理が施された銅粒子を得た銅粉を７５μｍの目開きの篩を用いて分級し、その篩下分をサンプルとした。このサンプルをサンプルホルダーに充填し、Ｘ線回折装置（株式会社Ｒｉｇａｋｕ製　Ｕｌｔｉｍａ　IV）を使用し、以下の条件で測定を行った。
　その後、回折ピークのうち、銅の（２２０）面、（１１１）面又は（３１１）面に相当する位置のメインピークを対象として、該ピークの半値幅の全幅に基づいて、上述したシェラーの式を用いて、各結晶子サイズＳ１ないしＳ３、並びにＳ１／Ｓ２及びＳ１／Ｓ３比を算出した。また得られた各結晶子サイズから、Ｓ１／Ｂ比を算出した。結果を以下の表２に示す。 [Measurement of crystallite size]
Measurements were performed on copper particles B-1 to B-3 by the following method. First, a 20% by mass aqueous slurry was prepared using the washed slurry of copper particles B-1 to B-3. Then, an isopropyl alcohol solution in which 12 g of copper laurate was dissolved as a surface coating treatment agent was added at once to the slurry heated to 50 ° C., and the mixture was stirred for 1 hour. Then, the solid content obtained by solid-liquid separation by filtration was vacuum dried, and the copper powder obtained by obtaining copper particles subjected to surface coating treatment was classified using a sieve with a mesh size of 75 μm, and the undersized portion was used as a sample. This sample was filled into a sample holder, and measurements were performed under the following conditions using an X-ray diffractometer (Ultima IV manufactured by Rigaku Co., Ltd.).
Then, among the diffraction peaks, the main peaks at the positions corresponding to the (220) plane, (111) plane or (311) plane of copper are used as the target, and based on the full width at half maximum of the peak, the above-mentioned Scherrer formula is used to calculate each crystallite size S1 to S3, as well as the S1/S2 and S1/S3 ratios.Furthermore, the S1/B ratio is calculated from each crystallite size obtained.The results are shown in the following Table 2.
＜Ｘ線回折測定条件＞
　・管球：ＣｕＫα線
　・管電圧：４０ｋＶ
　・管電流：５０ｍＡ
　・測定回折角：２θ＝２０～１００°
　・測定ステップ幅：０．０１°
　・収集時間：３ｓｅｃ／ステップ
　・受光スリット幅：０．３ｍｍ
　・発散縦制限スリット幅：１０ｍｍ
　・検出器：高速１次元Ｘ線検出器　Ｄ／ｔｅＸ　Ｕｌｔｒａ２５０ <X-ray diffraction measurement conditions>
Tube: CuKα ray Tube voltage: 40 kV
Tube current: 50mA
Measurement diffraction angle: 2θ = 20 to 100°
Measurement step width: 0.01°
Acquisition time: 3 sec/step Receiving slit width: 0.3 mm
Divergence vertical limit slit width: 10 mm
・Detector: High-speed one-dimensional X-ray detector D/teX Ultra250
＜Ｘ線回折用試料の調製方法＞
　測定対象の銅粉を測定ホルダに敷き詰め、銅粉の厚さが０．５ｍｍで且つ平滑になるように、ガラスプレートを用いて平滑化した。 <Method of preparing samples for X-ray diffraction>
The copper powder to be measured was spread on a measurement holder, and the copper powder was smoothed using a glass plate so that the thickness of the copper powder was 0.5 mm and the surface was smooth.
　上述の測定条件にて得られたＸ線回折パターンを用いて、以下の条件にて、解析用ソフトウェアで解析した。解析には、ピーク幅の補正にＬａＢ６値を用いて補正した。結晶子サイズは、ピークの半値幅の全幅とシェラー定数（０．９４）とを用いて算出した。 The X-ray diffraction pattern obtained under the above measurement conditions was analyzed using analysis software under the following conditions. The peak width was corrected using the LaB6 value. The crystallite size was calculated using the full width at half maximum of the peak and the Scherrer constant (0.94).
＜測定データ解析条件＞
　・解析ソフトウェア：Ｒｉｇａｋｕ製ＰＤＸＬ２
　・平滑処理：ガウス関数、平滑化パラメータ＝１０
　・バックグラウンド除去：フィッティング方式
　・Ｋα２除去：強度比０．４９７
　・ピークサーチ：二次微分法
　・プロファイルフィッティング：ＦＰ法
　・結晶子サイズ分布タイプ：ローレンツモデル
　・シェラー定数：０．９４００ <Measurement data analysis conditions>
Analysis software: Rigaku PDXL2
Smoothing process: Gaussian function, smoothing parameter = 10
Background removal: Fitting method Kα2 removal: Intensity ratio 0.497
Peak search: Second derivative method Profile fitting: FP method Crystallite size distribution type: Lorentz model Scherrer constant: 0.9400
　なお、解析を行う際に使用したＸ線回折パターンのピークは、以下のとおりである。以下に示すミラー指数は、上述した銅の結晶面と同義である。
　・２θ＝７１°～７６°付近にあるミラー指数（２２０）で指数付けされるピーク。
　・２θ＝４０°～４５°付近にあるミラー指数（１１１）で指数付けされるピーク。
　・２θ＝８７.5°～９２.５°付近にあるミラー指数（３１１）で指数付けされるピーク。 The peaks of the X-ray diffraction pattern used in the analysis are as follows: The Miller indices shown below are synonymous with the above-mentioned copper crystal planes.
A peak indexed with Miller index (220) in the vicinity of 2θ=71° to 76°.
A peak indexed with Miller index (111) in the vicinity of 2θ=40° to 45°.
A peak indexed with Miller index (311) in the vicinity of 2θ=87.5° to 92.5°.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　〔実施例１ないし７及び９並びに比較例１ないし７〕
　銅粒子Ａ－１、Ａ－２、及びＢ－１ないしＢ－３を以下の表３に示す割合で混合し、各実施例及び各比較例の銅粉を得た。具体的には、１００ｍＬ容器に各銅粒子を表３に示す割合で加え、次いで小型ボールミル（アサヒ理化製ＡＶ－１）を用いて混合することで各実施例及び各比較例の銅粉を得た。混合は、１００ｒｐｍで1時間行った。
　上述のようにして得た銅粉と、数平均分子量が２００のポリエチレングリコールとを３本ロール混練機を用いて混合し、銅粉を８５質量％含む銅ペーストを得た。
　なお、表３には銅粒子の合計１００質量部に対する各銅粒子成分の含有量が示されている。また「固形分濃度」とは、銅ペースト全体の質量に対する銅粉の質量の割合を示す。 [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 Comparative Example. Specifically, each copper particle was added to a 100 mL container in the ratios 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 Comparative Example. Mixing was performed at 100 rpm for 1 hour.
The copper powder obtained as described above and polyethylene glycol having a number average molecular weight of 200 were mixed using a three-roll kneader to obtain a copper paste containing 85% by mass of copper powder.
The content of each copper particle component relative to 100 parts by mass of the total of the copper particles is shown in Table 3. The "solid content concentration" indicates the ratio of the mass of the copper powder to the mass of the entire copper paste.
〔ペースト印刷性の評価〕
　各実施例及び各比較例のペースト印刷性を、以下の評価基準に基づいて評価した。
＜ペースト印刷性の評価基準＞
　可：縦２ｃｍ、横１ｃｍの大きさでマスキングしたガラス板上に塗工可能。
　不可：上記条件において連続性のある塗膜を形成できない。 [Evaluation of Paste Printability]
The paste printability of each of the Examples and Comparative Examples was evaluated based on the following evaluation criteria.
<Evaluation Criteria for Paste Printability>
Possible: Can be applied to a masked glass plate measuring 2 cm in length and 1 cm in width.
Unacceptable: A continuous coating film cannot be formed under the above conditions.
〔導電膜の製造〕
　各実施例及び各比較例の銅ペーストをガラス基板上に塗布し、該基板を窒素雰囲気下、１９０℃で１０分間焼成し、導電膜をガラス基板上に形成させた。
　得られた導電膜は、縦２ｃｍ、横１ｃｍ、厚さ３０μｍであり、それらについて、以下の評価を行った。 [Production of Conductive Film]
The copper paste of each of the Examples and Comparative Examples was applied onto a glass substrate, and the substrate was baked at 190° C. for 10 minutes in a nitrogen atmosphere to form a conductive film on the glass substrate.
The obtained conductive film had a length of 2 cm, a width of 1 cm and a thickness of 30 μm, and was evaluated as follows.
〔製膜強度の評価〕
　各導電膜の製膜強度を、以下の評価基準に基づいて評価した。
＜製膜強度の評価基準＞
　高：導電膜表面をスクラッチして、粉が手につかない。
　低：導電膜表面をスクラッチして、粉が手につく。 [Evaluation of film strength]
The film strength of each conductive film was evaluated based on the following evaluation criteria.
<Evaluation criteria for film strength>
High: When the conductive film surface is scratched, no powder remains on the hands.
Low: The conductive film surface is scratched and powder comes off onto your hands.
〔導電膜の抵抗率の測定〕
　各導電膜の抵抗率を、抵抗率計（三菱ケミカルアナリテック株式会社製、Ｌｏｒｅｓｔａ－ＧＰ　ＭＣＰ－Ｔ６１０）を用いて測定した。測定対象の導電膜について３回測定し、その算術平均値を抵抗率（μΩ・ｃｍ）とした。抵抗率は低ければ低いほど導電膜の抵抗が小さいことを示し、５０μΩ・ｃｍ以下であることが好ましい。結果を以下の表３に示す。 [Measurement of resistivity of 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 value was taken as the resistivity (μΩ·cm). The lower the resistivity, the smaller the resistance of the conductive film, and it is preferable that the resistivity is 50 μΩ·cm or less. The results are shown in Table 3 below.
〔導電膜の厚さ評価〕
　Ｃｕペーストの焼成膜の厚さは、デジタル測長機（ニコン社製　ＭＦＣ－１０１）を用いて, 導電膜及びガラス基板の厚さと、ガラス基板のみの厚さとを測定し、これらの厚さの差分を導電膜の厚さとして求めた。 [Evaluation of Conductive Film Thickness]
The thickness of the fired film of the Cu paste was determined by measuring the thickness of the conductive film and glass substrate, and the thickness of the glass substrate alone using a digital length measuring machine (Nikon MFC-101), and calculating the difference between these thicknesses as the thickness of the conductive film.
〔導電膜の表面粗さＲａの測定〕
　各導電膜の表面粗さ（平均粗さＲａ）は、表面粗さ・輪郭形状測定機（東京精密社製　ＳＵＲＦＣＯＭ　１３０Ａ）を使用し、各導電膜に対し、３か所測定し、得られた値の平均値を求めた。結果を表３に示す。
　表面粗さＲａは、電気的抵抗の観点から、２．０以下であることが好ましい。また、導電膜の表面粗さＲａが小さいことは、該導電膜の緻密性が高いことを意味する。 [Measurement of Surface Roughness Ra of Conductive Film]
The surface roughness (average roughness Ra) of each conductive film was measured at three points using a surface roughness/contour shape measuring instrument (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 viewpoint of electrical resistance, the surface roughness Ra is preferably 2.0 or less. Furthermore, a conductive film having a small surface roughness Ra means that the conductive film has high density.
〔接合強度の測定〕
　片面が＃８００の研磨シートで研磨された５ｍｍ角の銅チップに対し、研磨側に２ｍｍ×２ｍｍ×３０μｍの形で銅ペーストをスクリーン印刷し、片面が＃８００の研磨シートで研磨された３ｍｍ角の銅チップを研磨面が接合面となるように載せた。その後、加圧焼成機（井元製作所製ＩＭＣ－１ＡＢ６）を用いて、５ＭＰａで加圧しながら、窒素雰囲気下、２００℃、３０分間焼成し、接合させた。得られた接合体をボンドテスター（ＸＹＺＴＥＣ社製　Ｃｏｎｄｏｒ　Ｓｉｇｍａ）を用いて、接合強度を測定した。
　上述した測定を３回実施し、接合強度の最大値と平均値を算出した。これを表３に示す。表３において、接合強度は比較例３の接合強度が１．０になるように規格化した値である。また表３において、「－」は未測定を示す。 [Measurement of Bonding Strength]
A copper paste was screen-printed on the polished side of a 5 mm square copper chip with one side polished with a #800 polishing sheet in the form of 2 mm x 2 mm x 30 μm, and a 3 mm square copper chip with one side polished with a #800 polishing sheet was placed so that the polished surface was the bonding surface. Thereafter, the chip was bonded by firing at 200 ° C. for 30 minutes under a nitrogen atmosphere while applying pressure of 5 MPa using a pressure firing machine (IMC-1AB6 manufactured by Imoto Seisakusho). The bond strength of the resulting bonded body was measured using a bond tester (Condor Sigma manufactured by XYZTEC Corporation).
The above-mentioned measurement was carried out three times, and the maximum and average values of the bonding strength were calculated. These are shown in Table 3. In Table 3, the bonding strength is a standardized value such that the bonding strength of Comparative Example 3 is 1.0. In Table 3, "-" indicates that the measurement was not performed.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　表３に示すとおり、各実施例の導電膜はいずれも、１９０℃という比較的低温での焼成によって製造したにもかかわらず、低い抵抗率を有していた。このことから、各実施例で用いた銅粉は低い焼結温度を有していることが分かる。また、各実施例の導電膜はペースト印刷性に優れ、且つ表面粗さＲａが低いことから、良好な連続性及び緻密性を有していることも分かる。
　また、実施例２と比較例１との比較から分かるように、同じ扁平状銅粒子でも、銅粒子Ｂ－３等の機械的に扁平化させた銅粒子を用いた場合には銅粉の焼結温度が上昇し、導電膜の抵抗率が高くなる。 As shown in Table 3, all of the conductive films of the examples had low resistivity even though they were produced by firing at a relatively low temperature of 190° C. This shows that the copper powder used in each example has a low sintering temperature. In addition, the conductive films of each example have excellent paste printability and low surface roughness Ra, which shows that they have good continuity and denseness.
Furthermore, as can be seen from a comparison between Example 2 and Comparative Example 1, even when 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 increases and the resistivity of the conductive film increases.
〔実施例８、比較例８及び比較例９〕
　以下の表４に示すように、銅粉と数平均分子量が２００のポリエチレングリコールとを３本ロール混練機を用いて混合する際、銅粉とポリエチレングリコールとの混合割合を変更し、銅粉を９０質量％含む銅ペーストを作成した以外は実施例２、比較例３、及び比較例５と同様にして、実施例８、比較例８、及び比較例９の銅ペースト及びその導電膜を作成した。これらの銅ペースト及びその導電膜について、実施例１ないし７及び比較例１ないし７と同様の評価を行った。結果を表４に示す。 [Example 8, Comparative Example 8 and Comparative Example 9]
As shown in Table 4 below, when copper powder and polyethylene glycol having 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 copper pastes containing 90 mass% copper powder. Except for this, the copper pastes and conductive films thereof of Example 8, Comparative Example 8, and Comparative Example 9 were prepared in the same manner as in Example 2, Comparative Example 3, and Comparative Example 5. These copper pastes and conductive films thereof 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.
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
　表４に示すとおり、銅粒子Ａ－１及びＢ－１の両方を含む、実施例２及び８の銅粉は、銅ペースト中の有機溶媒の含有量を変更した場合でも、導電膜の抵抗率及び表面粗さＲａが悪影響を受けにくい。一方、比較例８及び比較例９に示すように、銅粒子Ａ－１及びＢ－１のいずれか一方しか含まない銅粉を用いた場合に銅ペースト中の有機溶媒の含有量を１０質量％とすると、特に導電膜の抵抗率が大きく上昇することが分かる。 As shown in Table 4, the copper powders of Examples 2 and 8, which contain both copper particles A-1 and B-1, are less likely to be adversely affected in the resistivity and surface roughness Ra of the conductive film, even when the content of the organic solvent in the copper paste is changed. On the other hand, as shown in Comparative Examples 8 and 9, when copper powder containing only either copper particles A-1 or B-1 is used, if the content of the organic solvent in the copper paste is 10 mass%, it can be seen that the resistivity of the conductive film in particular increases significantly.
　本発明によれば、連続性及び緻密性が高い導電膜を製造でき、且つ、焼結温度が低い銅粉が提供される。
  According to the present invention, a copper powder is provided that can produce a conductive film having high continuity and density and can be sintered at a low temperature.

Claims (6)

  1. 　以下の銅粒子Ａ及び銅粒子Ｂを含み、
    　銅粒子Ａと銅粒子Ｂの合計に対する銅粒子Ａの含有割合が６０質量％以上９９質量％以下であり、銅粒子Ｂの含有割合が１質量％以上４０質量％以下である、銅粉。
    〔銅粒子Ａ〕
    　銅からなるコア粒子と、該コア粒子の表面を被覆する被覆層とを備え、
    　前記被覆層は脂肪族有機酸の銅塩によって形成されており、
    　一次粒子径が０．１μｍ以上０．６μｍ以下である銅粒子。
    〔銅粒子Ｂ〕
    　ＢＥＴ比表面積から算出されたＢＥＴ径Ｂに対する、Ｘ線回折測定において銅の（１１１）面に由来するピークの半値幅からシェラーの式によって求められる第１結晶子サイズＳ１の比（Ｓ１／Ｂ）が０．２３以下であり、
    　Ｘ線回折測定において銅の（２２０）面に由来するピークの半値幅からシェラーの式によって求められる第２結晶子サイズＳ２に対する、前記第１結晶子サイズＳ１の比（Ｓ１／Ｓ２）が１．３５以下であり、
    　一次粒子径が０．１μｍ以上２．０μｍ以下である銅粒子。     The copper particles A and B include:
    A copper powder in which the content of copper particles A is 60% by mass or more and 99% by mass or less, and the content of copper particles B is 1% by mass or more and 40% by mass or less, relative to the total of copper particles A and copper particles B.
    [Copper particles A]
    The present invention comprises a core particle made of copper and a coating layer that coats the surface of the core particle,
    the coating layer is formed from a copper salt of an aliphatic organic acid,
    Copper particles having a primary particle diameter of 0.1 μm or more and 0.6 μm or less.
    [Copper particles B]
    a ratio (S1/B) of a first crystallite size S1 calculated by the Scherrer formula from the half-width of a peak derived from the copper (111) plane in an X-ray diffraction measurement to a BET diameter B calculated from a 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 calculated by the Scherrer formula from the half-width of the peak derived from the (220) plane of copper in X-ray diffraction measurement is 1.35 or less;
    Copper particles having a primary particle diameter of 0.1 μm or more and 2.0 μm or less.
  2. 　銅粒子Ｂは、Ｘ線回折測定において銅の（３１１）面に由来するピークの半値幅からシェラーの式によって求められる第３結晶子サイズＳ３に対する、前記第１結晶子サイズＳ１の比（Ｓ１／Ｓ３）が１．３５以下である、請求項１に記載の銅粉。 The copper powder according to claim 1, wherein the ratio (S1/S3) of the first crystallite size S1 to the third crystallite size S3, calculated by the Scherrer formula from the half-width of the peak derived from the (311) plane of copper in an X-ray diffraction measurement, is 1.35 or less.
  3. 　銅粒子Ｂは炭素元素を含み、且つ該炭素元素の含有量が５０００ｐｐｍ以下である、請求項１に記載の銅粉。 The copper powder according to claim 1, wherein copper particles B contain carbon elements and the carbon element content is 5000 ppm or less.
  4. 　銅粒子Ｂはリン元素を含み、且つ該リン元素の含有量が３００ｐｐｍ以上である、請求項１に記載の銅粉。 The copper powder according to claim 1, wherein copper particles B contain phosphorus element and the content of said phosphorus element is 300 ppm or more.
  5. 　請求項１ないし４のいずれか一項に記載の銅粉を含む銅ペースト。 A copper paste containing the copper powder according to any one of claims 1 to 4.
  6. 　請求項５に記載の銅ペーストを基材に塗布して塗膜を形成し、該塗膜を焼成する、導電膜の製造方法。 A method for producing a conductive film, comprising applying the copper paste according to claim 5 to a substrate to form a coating film, and then firing the coating film.
PCT/JP2023/035411 2022-09-29 2023-09-28 Copper powder, copper paste containing same, and method for producing conductive film WO2024071303A1 (en)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2015168878A (en) * 2014-03-10 2015-09-28 三井金属鉱業株式会社 copper powder
JP2021025115A (en) * 2019-08-08 2021-02-22 三井金属鉱業株式会社 Copper particle

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2015168878A (en) * 2014-03-10 2015-09-28 三井金属鉱業株式会社 copper powder
JP2021025115A (en) * 2019-08-08 2021-02-22 三井金属鉱業株式会社 Copper particle

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