Copper powder and method for producing same

Abstract

This copper powder comprises an aggregate of copper particles containing a phosphorus (P) element. In an X-ray photoelectron spectrum obtained by measuring the surface of the copper particle by using an X-ray photoelectron spectrometer, a value of P1 / PP, which is the ratio of the peak intensity P1 of Cu (I) to the peak intensity PP of P is between 15.5 and 250.0 (both inclusive). The phosphorus element is preferably present from the center to the surface of the copper particle. The copper particles are suitably produced by a method including a step of mixing a raw material powder comprising the aggregate of copper particles containing the phosphorus (P) element and an aqueous solution containing a complexing agent of Cu (II) ions.

Description

Copper powder and method for producing the same 【0001】 The present invention relates to copper powder and a method for producing the same. 【0002】 Copper powder is suitably used as a raw material for conductive compositions such as conductive pastes. Conductive compositions are made by dispersing copper powder in a vehicle containing a binder resin and an organic solvent. Conductive compositions are used, for example, in the formation of electrical circuits and the formation of external electrodes for multilayer ceramic capacitors (hereinafter also referred to as "MLCCs"). 【0003】 For example, Patent Document 1 proposes a phosphorus-containing copper powder in which the surface phosphorus content, as measured by X-ray photoelectron spectroscopy, is 2.5 atom% or more. This copper powder is obtained by processing phosphorus-containing copper powder produced by atomization using a bead mill to reduce the surface phosphorus content. The same document states that copper powder produced by this method can suppress surface oxidation even when stored in the atmosphere. 【0004】 Japanese Patent Publication No. 2016-176133 【0005】 Incidentally, when forming the external electrodes of an MLCC using copper powder, a process is carried out in which copper particles are sintered together by firing to form a sintered body. In this case, if organic matter is present in the copper powder, it burns during the sintering process, generating gas, which can cause defects such as voids and cracks in the sintered body. From this viewpoint, copper powder in which sintering begins after the combustion of organic matter is desirable. Therefore, the object of the present invention is to provide copper powder with a higher sintering start temperature than conventional methods and a method for producing the same. 【0006】 The present invention relates to a copper powder consisting of an aggregate of copper particles containing the element P (phosphorus), wherein the concentration of P on the surface of the copper particles is measured by X-ray photoelectron spectroscopy. Ｐ The Cu(I) concentration P １ P is the ratio of １ / P Ｐ The present invention provides copper powder in which the value of is between 15.5 and 250.0. 【0007】The present invention also provides a method for producing copper powder, comprising the step of mixing a raw material powder consisting of an aggregate of copper particles containing the element P (phosphorus) with an aqueous solution containing a Cu(II) ion complexing agent. 【0008】 Figure 1 is a graph showing the distribution of phosphorus in the surface region of copper particles in the copper powder obtained in Example 1 and Comparative Example 1. 【0009】 The present invention will be described below based on its preferred embodiments. The present invention relates to copper powder. Copper powder consists of aggregates of copper particles. It is permissible for copper powder to contain trace amounts of unavoidable impurities other than copper particles. When unavoidable impurities are present in copper powder, it is preferable that their amount be 0.01% by mass or less, in order to avoid impairing the inherent properties of the copper powder of the present invention. Copper particles are composed of copper (Cu), phosphorus (P), and oxygen (O). It is preferable that copper particles consist only of copper, phosphorus, and oxygen. It is permissible for copper particles to contain copper, phosphorus, and oxygen, with the remainder being unavoidable impurity elements. It is preferable that the amount of impurity elements contained in copper particles be 0.01% by mass or less, in order to avoid impairing the inherent properties of the copper powder of the present invention. 【0010】 Phosphorus is included in copper particles from the viewpoint of improving the oxidation resistance of copper powder. From this viewpoint, the phosphorus content is preferably 50 ppm by mass or more, more preferably 60 ppm by mass or more, and even more preferably 70 ppm by mass or more. Furthermore, from the viewpoint of not impairing the inherent properties of copper powder such as conductivity, the phosphorus content in copper powder is preferably 300 ppm by mass or less, more preferably 260 ppm by mass or less, and even more preferably 230 ppm by mass or less. The method for measuring the phosphorus content in copper powder will be explained in the examples described later. 【0011】 From the viewpoint of improving the oxidation resistance of copper powder, it is preferable for the phosphorus element to be present from the center to the surface of the copper particles. The distribution of the phosphorus element in copper particles can be confirmed, for example, by semi-quantitative analysis using Auger electron spectroscopy after exposing the center of the particles by ion milling. 【0012】 When copper particles are divided into a central region and a surface region located outside the central region and including the outermost surface of the particles, it is preferable that phosphorus is present at a generally constant concentration in the central region. On the other hand, from the viewpoint of enhancing the oxidation resistance of the copper powder, it is preferable that the concentration of phosphorus in the surface region is higher than that in the central region. In order to increase the concentration of phosphorus in the surface region, for example, a method of producing copper powder by atomization using a molten copper containing phosphorus can be adopted. This method has an advantage that when droplets generated from the molten metal solidify, phosphorus is likely to concentrate on the surface of the droplets. In this specification, the surface region refers to the region up to 200 nm from the surface in terms of SiO ２ conversion when the copper particles are ion sputtered with argon. The central region refers to the region located inside the particles rather than the surface region. 【0013】 In the copper powder of the present invention, it has been found as a result of the study by the present inventors that controlling the abundance ratio of monovalent copper element Cu(I) and phosphorus element on the surface of the copper particles constituting the same is advantageous from the viewpoint of increasing the sintering start temperature of the copper powder. Specifically, when the amount of phosphorus, an element that easily causes sintering, is reduced on the surface of the copper particles, it is considered that necking at the site where the copper particles are in contact is less likely to occur and the sintering start temperature increases. Also, when the amount of Cu(I), a chemical species with high thermal stability, increases on the surface of the copper particles, it is also considered that necking is less likely to occur and the sintering start temperature increases. 【0014】 From the above viewpoints, the ratio of the Cu(I) concentration P Ｐ to the P concentration P １ on the surface of the copper particles measured by an X-ray photoelectron spectrometer (hereinafter also referred to as "XPS"), which is the ratio of P １ / P Ｐ is preferably 15.5 or more, more preferably 15.7 or more, and still more preferably 16.0 or more. There is no particular limitation on the upper limit value of P １ / P Ｐ , and the higher this value, the more advantageous it is for increasing the sintering start temperature. However, P １ / P ＰIf the value of becomes excessively large, the effect of increasing the sintering start temperature saturates, P １ / P Ｐ The value of is preferably 250.0 or less, more preferably 235.0 or less, even more preferably 225.0 or less, and even more preferably 35.0 or less. Note that monovalent copper element Cu(I) is generally called cuprous oxide (Cu ２ It is thought to exist in state O), and the XPS peak of Cu(I) is mainly Cu ２ It originates from O. 【0015】 The above explanation concerns the relative abundance of monovalent copper and phosphorus on the surface of copper particles. However, divalent copper (Cu(II)) may also be present on the surface of copper particles in addition to monovalent copper. Regarding the relationship between divalent copper and phosphorus, the phosphorus concentration (P) on the surface of copper particles is measured by XPS. Ｐ The Cu(II) concentration P ２ P is the ratio of ２ / P Ｐ The value of P is preferably 8.0 or higher, more preferably 8.2 or higher, and even more preferably 8.4 or higher. ２ / P Ｐ Setting the value in this way has the advantage that the proportion of P compounds contained in divalent copper is reduced, thereby suppressing sintering at low temperatures. ２ / P Ｐ The value of is preferably 100.0 or less, more preferably 80.0 or less, even more preferably 70.0 or less, even more preferably 60.0 or less, and particularly preferably 20.0 or less, because if it becomes excessively large, the effect of increasing the sintering start temperature saturates. In the X-ray photoelectron spectroscopy spectrum, the Cu(II) peak is mainly CuO and Cu(OH) ２ It originates from and is observed in the range of 934.0 eV to 936.0 eV. 【0016】In the present invention, controlling the ratio of monovalent to divalent copper elements on the surface of the copper particles is also advantageous from the viewpoint of raising the sintering start temperature of the copper powder of the present invention. Specifically, the Cu(I) concentration P on the surface of the copper particles as measured by XPS. １ The Cu(II) concentration P ２ P is the ratio of ２ / P １ The value of P is preferably 0.70 or less, more preferably 0.60 or less, and even more preferably 0.58 or less. ２ / P １ Setting the value in this way has the advantage of suppressing sintering at low temperatures by reducing the ratio of divalent copper to monovalent copper. ２ / P １ The value of is preferably 0.20 or higher, more preferably 0.24 or higher, and even more preferably 0.28 or higher, because if it becomes too small, the effect of increasing the sintering start temperature saturates. 【0017】 The relative proportions of Cu(I) and Cu(II) on the surface of copper particles can be controlled by adjusting the oxidation state of the raw material powder used in the copper powder manufacturing method described later. １ / P Ｐ and P ２ / P Ｐ The value of P can be controlled by the copper powder manufacturing method described later. １ / P Ｐ , P ２ / P Ｐ and P ２ / P １ Details of the method for measuring the value by XPS will be explained in the examples described later. In this specification, the peak intensity of the XPS spectrum refers to the height of the peak. 【0018】The copper powder of the present invention contains oxygen elements bonded to Cu(I) and Cu(II). From the viewpoint of improving the oxidation resistance of the copper powder, the amount of oxygen elements contained in the copper powder is preferably 1000 ppm or more, more preferably 1200 ppm or more, and even more preferably 1400 ppm or more. Furthermore, from the viewpoint of improving the conductivity of the sintered body obtained by sintering the copper powder, the amount of oxygen elements contained in the copper powder is preferably 4800 ppm or less, more preferably 4600 ppm or less, and even more preferably 4300 ppm or less. The proportion of oxygen elements contained in the copper powder can be controlled by adjusting the oxidation state of the raw material powder used in the copper powder manufacturing method described later. It can also be controlled by the copper powder manufacturing method described later. The method for measuring the proportion of oxygen elements contained in the copper powder will be explained in the examples described later. 【0019】 The copper powder of the present invention has a cumulative volume particle size D at 50% of the cumulative volume, as measured by laser diffraction scattering particle size distribution analysis. ５０ The particle size D is preferably 0.3 μm or larger, more preferably 0.7 μm or larger, and even more preferably 1.0 μm or larger. ５０ The particle size is preferably 15.0 μm or less, more preferably 12.0 μm or less, and even more preferably 10.0 μm or less. Having the copper particle size within this range improves the sinterability of the copper powder. D ５０ For similar reasons, the copper powder of the present invention has a volume cumulative particle size D at 10% cumulative volume as measured by laser diffraction scattering particle size distribution analysis. １０ It is preferable that the particle size is 0.4 μm or more and 6.0 μm or less, more preferably 0.6 μm or more and 5.6 μm or less, and preferably 0.65 μm or more and 5.2 μm or less. Also, D ５０ For similar reasons, the copper powder of the present invention has a volume cumulative particle size D at 90% of the cumulative volume as measured by laser diffraction scattering particle size distribution analysis. ９０ The particle size is preferably 1.3 μm to 20.0 μm, more preferably 1.5 μm to 18.0 μm, and preferably 1.8 μm to 16.0 μm.１０ , D ５０ and D ９０ The measurement method will be explained in the examples described later. 【0020】 The copper powder of the present invention may be used in an unsintered powder state, but it is preferably used after sintering. When the copper powder of the present invention is used after sintering, it is preferable that the sintering start temperature of the copper powder is 480°C or higher and 780°C or lower. It is particularly preferable that it is 500°C or higher and 750°C or lower, and especially preferable that it is 520°C or higher and 730°C or lower. When a composition containing organic matter such as a binder is prepared using the copper powder of the present invention, which has a sintering start temperature within this range, and a sintered body is manufactured from the composition, the sintering of the copper particles begins after the combustion of organic matter such as the binder contained in the composition and the resulting gas generation, which has the advantage of making it less likely for defects such as voids and cracks to occur in the sintered body. In this specification, the sintering start temperature is the temperature at which the degree of shrinkage of the copper powder due to sintering reaches 2 volume%, and is measured by thermomechanical analysis. 【0021】 The copper particles constituting the copper powder of the present invention are not particularly limited in shape and can be used in various forms, such as spherical, flake, plate-like, or dendritic. The shape of the copper particles used should be appropriately selected according to the specific application of the copper powder of the present invention. The shape of the copper particles generally depends on the manufacturing method. Spherical copper particles can be manufactured, for example, by atomization or wet reduction. Flake-like particles can be manufactured, for example, by mechanically deforming spherical particles. Plate-like particles can be manufactured, for example, by wet reduction. Dendritic copper particles can be manufactured, for example, by electrolysis. The copper powder of the present invention may also be a mixture of copper particles of various shapes. 【0022】 Furthermore, when we say that the copper particles constituting the copper powder of the present invention exhibit the aforementioned shapes, we mean that when the copper powder of the present invention is observed under an electron microscope (for example, at 1000x magnification), particles exhibiting the aforementioned shapes account for 80% or more of the total number of particles. 【0023】Next, a preferred method for producing the copper powder of the present invention will be described. The copper powder of the present invention is broadly divided into a raw material preparation step and a treatment step of the raw material powder with a complexing agent. The copper powder obtained through these steps has an appropriately adjusted ratio of phosphorus elements and monovalent and divalent copper elements on the surface of the copper particles. Each step will be described below. 【0024】 In the raw material preparation step, the raw copper powder used to manufacture the copper powder of the present invention is prepared. The raw copper powder contains copper and phosphorus elements, with the remainder being unavoidable impurities. Examples of methods for manufacturing the raw copper powder include atomization, wet reduction, and electrolysis. Of these methods, atomization is preferred from the viewpoint of successfully incorporating phosphorus elements into the copper particles. 【0025】 As atomization methods, gas atomization and water atomization can be preferably employed. When aiming to equalize the particle shape, gas atomization is preferable. On the other hand, when aiming to make the particles finer, water atomization is preferable. Among gas atomization and water atomization, high-pressure atomization is particularly preferable because it can produce fine and uniform particles. In the case of water atomization, high-pressure atomization is a method of atomizing with a water pressure of about 50 MPa to 150 MPa. In the case of gas atomization, it is a method of atomizing with a gas pressure of about 0.5 MPa to 3 MPa. 【0026】 When producing raw material powder by atomization, a melting process is first carried out to obtain molten copper. In the melting process, the copper ingot, which will be the raw material for the molten metal, is heated to a predetermined temperature under atmospheric pressure and melted. Any copper ingot known in the relevant art can be used without particular restriction. For example, electrolytic copper can be used as the copper ingot. Various heating furnaces can be used as heating means to obtain molten metal using copper ingot as a raw material. Examples of heating furnaces include induction furnaces and combustion furnaces. 【0027】 When heating copper ingots to obtain molten metal, additionally Cu ３It is preferable to add P (copper(I) phosphide). Cu ３ The addition of phosphorus (P) has the advantage of suppressing the formation of copper oxides because phosphorus is oxidized before copper in the molten metal (sacrificial oxidation). From this perspective, Cu ３ The amount of P added is Cu ３ It is preferable that the amount of phosphorus in the molten metal after the addition of P be 50 ppm by mass or more, more preferably 60 ppm by mass or more, and even more preferably 70 ppm by mass or more. ３ The amount of P added is determined from the viewpoint of sufficiently increasing the electrical conductivity of copper particles, Cu ３ The amount of phosphorus in the molten metal after the addition of P is preferably 300 ppm by mass or less, more preferably 260 ppm by mass or less, and even more preferably 220 ppm by mass or less. ３ The mass of phosphorus in copper particles obtained after the addition of P is equal to the mass of added Cu ３ The amount of phosphorus may be less than the amount of phosphorus in P. This is presumably because the phosphorus may sublimate during the manufacturing of the particles. Therefore, the amount of Cu converted to phosphorus is... ３ The amount of phosphorus (P) added may differ from the phosphorus content in the copper particles. 【0028】 Raw material powders obtained by atomization are generally spherical. By subjecting such shaped raw material powders to a flattening treatment, raw material powders consisting of flake-shaped particles can be obtained. Flattening treatment can be achieved, for example, by subjecting spherical particle-based raw material powders to a bead mill treatment. 【0029】 The raw material powder obtained in this way can be subjected to grinding and classification as needed. This allows for adjustment of particle size and the oxidation state of the particle surface. The oxidation state of the particle surface can also be adjusted by oxidizing or reducing the raw material powder. 【0030】Next, the raw material powder is subjected to a processing step with a complexing agent. In this step, the raw material powder is mixed with an aqueous solution containing the complexing agent. As the complexing agent, a compound that can form a complex with Cu(II) ions is used. Examples of such complexing agents include ammonia. Furthermore, examples include ethylenediaminetetraacetic acid, triethylenediamine, iminodiacetic acid, citric acid, tartaric acid, and their salts. Furthermore, examples include amino acids such as glycine, aminoacetic acid, alanine, and glutamic acid, and methylglyoxime. Among these complexing agents, ammonia is preferred from the viewpoint that complex formation with copper(II) ions is easily achieved and the relative abundance of phosphorus elements and monovalent and divalent copper elements on the surface of the copper particles can be successfully adjusted. 【0031】 When using ammonia as a complexing agent, it is preferable from the viewpoint of ease of handling to use ammonia water, which is ammonia dissolved in water. When using ammonia water, its concentration is preferably 10% by mass or more and 30% by mass or less. 【0032】 To form a copper ion complex, the raw material powder is dispersed in water to prepare a dispersion, and this dispersion is mixed with ammonia water. The mixing ratio should be such that the mass ratio of ammonia to the raw material powder is preferably 0.007 to 0.150, more preferably 0.009 to 0.130, and even more preferably 0.010 to 0.120. This successfully generates a copper ion complex (i.e., a copper ammine complex) in the liquid. 【0033】In raw material powders consisting of copper particles containing phosphorus, it is thought that copper pyrophosphate, a compound of phosphorus, is present on the surface of the copper particles. When these copper particles come into contact with a complexing agent such as ammonia, it is thought that the copper pyrophosphate dissolves and a copper ion complex is formed. In other words, the phosphorus present on the surface of the copper particles is removed. Since copper pyrophosphate is considered to be a substance that promotes low-temperature sintering of copper particles, it is thought that the removal of copper pyrophosphate from the surface of the copper particles increases the sintering start temperature of the copper particles. Since the valence of copper in copper pyrophosphate is divalent, the removal of copper pyrophosphate from the surface of the copper particles causes a change in the ratio of valences of copper elements on the surface of the copper particles (the atomic ratio of monovalent copper to divalent copper). Furthermore, it is thought that the removal of copper pyrophosphate from the surface of the copper particles promotes oxidation of the surface of the copper particles, which also increases the sintering start temperature of the copper particles. However, the present invention is not bound by these theories. 【0034】The copper powder of the present invention can be dispersed in an organic solvent and a resin, etc., and used in the form of a conductive resin composition such as a paste composition. This conductive resin composition may contain only the copper powder of the present invention as the metal component, or it may contain the copper powder of the present invention and other metal powders. The conductive resin composition is composed of at least the copper powder of the present invention and an organic solvent. As the organic solvent, those that have been used in the art of conductive resin compositions containing metal powders can be used without particular limitation. Examples of such organic solvents include monohydric alcohols such as terpineol; polyhydric alcohols; polyhydric alcohol alkyl ethers such as ethyl carbitol; polyhydric alcohol aryl ethers; polyethers; esters such as carbitol acetate, butyl cellosolve acetate and butyl carbitol acetate; nitrogen-containing heterocyclic compounds; amides; amines and saturated hydrocarbons. These organic solvents can be used individually or in combination of two or more. From the viewpoint of having a high reducing effect and suppressing unintended oxidation of the copper powder during sintering, it is preferable to use polyethers such as polyethylene glycol and polypropylene glycol. From a similar viewpoint, when polyethylene glycol is used as an organic solvent, its number-average molecular weight is preferably 120 or more and 400 or less, and more preferably 180 or more and 400 or less. 【0035】 The conductive resin composition may contain, in addition to copper powder, at least one of a dispersant, an organic vehicle, and glass frit. Examples of dispersants include nonionic surfactants that do not contain sodium, calcium, phosphorus, sulfur, and chlorine. Examples of organic vehicles include mixtures containing resin components such as acrylic resin, epoxy resin, ethylcellulose, and carboxyethylcellulose, and solvents such as terpene solvents such as terpineol and dihydroterpineol, or ether solvents such as ethyl carbitol and butyl carbitol. Examples of glass frit include borosilicate glass, barium borosilicate glass, and zinc borosilicate glass. These can be used individually or in combination of two or more. 【0036】 A sintered body can be formed by applying the above-described conductive resin composition onto a substrate to form a coating film, and then sintering it. The sintered body is suitably used, for example, for circuit formation in printed circuit boards or for ensuring electrical conductivity of external electrodes in multilayer ceramic capacitors. When the sintered body is used as an external electrode in a multilayer ceramic capacitor, the sintered body may be a sintered body of metal powder containing the copper powder of the present invention. When the sintered body is used as wiring in a printed circuit board, the printed circuit board may be made of glass epoxy resin or the like, or a flexible printed circuit board made of polyimide or the like, depending on the type of electronic circuit in which the metal powder containing the copper powder of the present invention is used. 【0037】 The total content of copper powder and organic solvent in the conductive resin composition can be appropriately set according to the specific application and application method of the conductive resin composition, but it 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. 【0038】 The conductive resin composition can be applied by methods such as inkjet printing, dispenser printing, microdispenser printing, gravure printing, screen printing, dip coating, spin coating, spray coating, bar coating, and roll coating. 【0039】Sintering can be carried out, for example, under an oxidizing atmosphere or a non-oxidizing atmosphere. An oxidizing atmosphere is, for example, an oxygen-containing atmosphere. A non-oxidizing atmosphere is, for example, a reducing atmosphere such as hydrogen and carbon monoxide, a weakly reducing atmosphere such as a hydrogen-nitrogen mixed atmosphere, and an inert atmosphere such as argon, neon, helium, and nitrogen. In any atmosphere, the sintering time is preferably 0.1 hours to 5 hours, and more preferably 0.2 hours to 3 hours, provided that the temperature is within the above-mentioned temperature range. During the process of sintering the coating film, the resin components in the coating film are thermally decomposed (binder removal step). The heating temperature at which the resin components are thermally decomposed varies depending on the type of resin component, but is generally 300°C to 500°C under a nitrogen atmosphere. When the heating temperature of the coating film containing copper powder of the present invention reaches this range, the sintering of the copper powder has not yet started, so the decomposed resin components effectively escape to the outside of the coating film through the voids between the copper particles. As a result, the resulting sintered body is less prone to the formation of bubbles caused by the decomposition products of the resin components, thus achieving high density. In the binder removal process, a constant temperature may be maintained for a predetermined time, or the temperature may be increased over time. 【0040】 Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments. For example, in the above embodiments, when the raw material powder is flake-shaped copper particles, a raw material powder consisting of spherical copper particles is manufactured, flattened, and then treated with a complexing agent. Alternatively, the raw material copper powder consisting of spherical copper particles may be treated with a complexing agent, and then the raw material powder may be subjected to a flattening treatment. 【0041】 Further disclosure relating to the above embodiments is provided for copper powder and a method for producing the same. [1] Copper powder comprising an aggregate of copper particles containing the element P (phosphorus), wherein the concentration of P on the surface of the copper particles is measured by X-ray photoelectron spectroscopy. Ｐ The Cu(I) concentration P １ P is the ratio of １ / P Ｐ Copper powder having a value of 15.5 or more and 250.0 or less. [2] P concentration on the surface of the copper particles measured by X-ray photoelectron spectroscopy. ＰThe Cu(II) concentration P ２ P is the ratio of ２ / P Ｐ The copper powder described in [1], wherein the value of is 8.0 or greater. [3] The Cu(I) concentration P on the surface of the copper particles as measured by X-ray photoelectron spectroscopy. １ The Cu(II) concentration P ２ P is the ratio of ２ / P １ Copper powder according to [1] or [2], wherein the value of is 0.20 or more and 0.70 or less. [4] Copper powder according to any one of [1] to [3], wherein the phosphorus element is present from the center to the surface of the copper particles. [5] Copper powder according to any one of [1] to [4], wherein the phosphorus element content is 50 ppm by mass or more and 300 ppm by mass or less. [6] Volume cumulative particle size D at 50% cumulative volume measured by laser diffraction scattering particle size distribution method. ５０ Copper powder according to any one of [1] to [5], wherein the particle size is 0.3 μm or more and 15.0 μm or less. 【0042】 [7] Copper powder according to any one of [1] to [6], wherein the copper particles are spherical or flake-shaped. [8] A method for producing copper powder, comprising the step of mixing a raw material powder consisting of aggregates of copper particles containing the element P (phosphorus) with an aqueous solution containing a complexing agent for Cu(II) ions. [9] The method for producing the raw material powder according to [8], wherein molten copper containing copper(I) phosphide is subjected to an atomization method.

[10] The method for producing the raw material powder according to [8] or [9], wherein the complexing agent is ammonia.

[11] The method for producing the raw material powder according to

[10] , wherein the mass ratio of ammonia to the raw material powder is 0.007 or more and 0.150 or less.

[12] A conductive resin composition comprising copper powder and resin according to any one of [1] to [7].

[13] A multilayer ceramic capacitor having an external electrode made of a sintered metal powder containing copper powder according to any one of [1] to [7]. 【0043】 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 these examples. Unless otherwise specified, "%" means "mass%". 【0044】[Example 1] (1) Production of raw material powder Electrolytic copper (copper purity: Cu 99.95%) was heated in a gas furnace to produce molten metal. Copper(I) phosphide (Cu) was present in the molten metal. ３ P) was added. Copper(I) phosphide was atomized, and the copper powder was processed with TC-25 to a particle size D ５０ After classifying the molten metal to a particle size of 2 μm, phosphorus was added to achieve an elemental phosphorus content of 200 ppm by ICP analysis. The molten metal was poured into a tundish in a water atomizing apparatus, and while the molten metal was allowed to fall from a nozzle at the bottom of the tundish, water was jet-injected onto the molten metal from the injection holes of a full-cone type nozzle to create an inverted cone-shaped water flow, thereby producing copper powder by water atomization. The obtained copper powder was classified using a classification apparatus ("Turbo Classifier (product name) TC-25 (model number)" manufactured by Nisshin Engineering Co., Ltd.), and the classified powder was used as the raw material powder. The raw material powder was a spherical dry powder with a particle size of D ５０ It was 2.28 μm. 【0045】 (2) Treatment with a complexing agent 100 g of raw material powder was dispersed in 500 mL of pure water to make a dispersion. 25% aqueous ammonia (density: approximately 0.91 g / cm³) was added to this dispersion. ３ The following was done by adding ammonia water. The amount of ammonia water added was as shown in Table 3 below. The mass ratio of ammonia to raw material powder was 0.011. The liquid temperature was kept at 20°C, and the dispersion was stirred for 30 minutes with a stirring bar (rotation speed 400 rpm) to obtain the target copper powder. Thereafter, suction filtration and washing with pure water were repeated six times, and then it was dried at 80°C for 1 hour. The dried copper powder was crushed and classified, and the copper powder that passed through a 45 μm sieve was recovered. 【0046】 [Examples 2 to 4] Copper powder was obtained by performing the same procedure as in Example 1, except that the amount of ammonia water added was changed to the value shown in Table 3. 【0047】 [Comparative Example 1] Copper powder was obtained by performing the same procedure as in Example 1, except that ammonia water was not added. 【0048】 [Example 5] In Example 1, the classification conditions during the production of the raw material powder were changed, D ５０A raw material powder with a particle size of 1.18 μm was obtained. Using this raw material powder, copper powder was obtained by performing the same procedure as in the previous example, except that the amount of ammonia water added was changed to the value shown in Table 4 below. 【0049】 [Comparative Example 2] Copper powder was obtained by performing the same procedure as in Example 5, except that ammonia water was not added. 【0050】 [Example 6] In Example 1, the classification conditions during the production of the raw material powder were changed, D ５０ A raw material powder with a particle size of 8.10 μm was obtained. Using this raw material powder, copper powder was obtained by performing the same procedure as in the previous example, except that the amount of ammonia water added was changed to the value shown in Table 4 below. 【0051】 [Comparative Example 3] Copper powder was obtained by performing the same procedure as in Example 6, except that ammonia water was not added. 【0052】 [Example 7] In Example 1, the raw material powder was subjected to a flattening treatment using a bead mill, D ５０ A flake-like raw material powder with a particle size of 3.86 μm was obtained. Using this raw material powder, copper powder was obtained by performing the same procedure as in the previous example, except that the amount of ammonia water added was changed to the value shown in Table 4 below. 【0053】 [Comparative Example 4] Copper powder was obtained by performing the same procedure as in Example 7, except that ammonia water was not added. 【0054】 [Evaluation] Quantitative analysis of each element was performed on the copper powder obtained in the examples and comparative examples using the following methods. In addition, BET specific surface area, particle size distribution, and P were also analyzed. １ / P Ｐ , P ２ / P Ｐ and P ２ / P １ The values ​​of and the sintering start temperature were measured. The results are shown in Tables 3 and 4. 【0055】[Elemental analysis] The content ratio of phosphorus was measured by ICP emission spectrometry for a sample solution obtained by dissolving copper powder in an acid such as hydrochloric acid. The ratio of oxygen contained in the copper powder was measured by the following method. 0.1 g of copper powder was weighed, placed in a nickel capsule, and then burned in a graphite crucible. The oxygen content ratio was determined using an oxygen / nitrogen analyzer (EMGA-920 manufactured by Horiba, Ltd.). 【0056】 [BET specific surface area] It was measured by the one-point method using macsorb manufactured by Mountech Co., Ltd. The amount of the measurement powder was 4.0 g, and the preliminary degassing conditions were 75 °C for 10 minutes. 【0057】 [Particle size distribution] 0.1 g of copper powder was mixed with 100 mL of an aqueous solution of sodium hexametaphosphate at 20 mg / L and dispersed for 3 minutes using an ultrasonic homogenizer (US-300T manufactured by Nippon Seiki Co., Ltd.). Subsequently, the particle size distribution was measured using a laser diffraction scattering type particle size distribution measuring device (Microtrac MT3300EX-II manufactured by Microtrac Bell Co., Ltd.), and the volume cumulative particle size D １０ at a cumulative volume of 10% by volume, the volume cumulative particle size D ５０ at a cumulative volume of 50% by volume, and the volume cumulative particle size D ９０ at a cumulative volume of 90% by volume were determined. 【0058】 [P １ / P Ｐ , P ２ / P Ｐ and P ２ / P １Value (Apparatus and Conditions): Analysis was performed using a PHI Quantess manufactured by ULVAC-PHI, Inc. as an XPS measurement apparatus. The conditions used for the measurement were as follows: - Excitation X-ray: Monochromated Al-Kα ray (1486.7 eV) - Output: 50 W - Acceleration voltage: 15 kV - X-ray irradiation diameter: φ200 μm - X-ray scanning area: 1000 μm × 300 μm - Detection angle: 45° - Pass energy: 26.0 eV - Energy step: 0.1 eV / step - Measured elements: C1s, O1s, P2s, Cu2p, CuLMM Note that since it is generally known that the states of copper hydroxide and copper oxide change under vacuum, it is necessary to quickly complete the measurement preparation and measurement before the state changes significantly during the introduction into the apparatus and the measurement. 【0059】 (Analysis): Semi-quantitative analysis of XPS data and waveform separation analysis of Cu2p ３／２ and CuLMM were performed using data analysis software (MultiPak Ver9.9 manufactured by ULVAC-PHI, Inc.). The Shirley background mode was used. Charge correction was performed with the binding energies of the C-C peak and C-H peak derived from atmospheric contamination carbon set to 284.8 eV. 【0060】 The Cu(I) concentration P １ and the Cu(II) concentration P ２ and the P concentration P Ｐ were calculated by the following method. 【0061】 (Calculation of Total Cu Concentration P Ｃｕ　ｔｏｔａｌ and P Concentration P Ｐ ): For the spectra of C1s, O1s, P2s, and Cu2p ３／２ , the background (BG) range was set to the conditions shown in Table 1 below, and the total Cu concentration P Ｃｕ　ｔｏｔａｌ and the P concentration P Ｐ were calculated. 【0062】 【0063】 (Calculation of Cu(I) Concentration P １ and Cu(II) Concentration P ２ ): The Cu(I) concentration P １ and the Cu(II) concentration P２ This refers to the total Cu concentration P mentioned above. Ｃｕ　ｔｏｔａｌ And Cu2p ３／２ The ratio of Cu(I) states to total Cu, calculated from waveform separation analysis of spectra and CuLMM spectra. １ and the ratio of Cu(II) states I ２ It was calculated using the following. First, Cu2p ３／２ Regarding the spectrum, waveform separation analysis was performed using the curve-fit mode of the analysis software, and Cu2p ３／２ "metal + Cu" ２ Area ratio I of state O 金属＋Ｃｕ２Ｏ Area ratio I of the "CuO" state ＣｕＯ and "Cu(OH) ２ Area ratio I of the state Ｃｕ（ＯＨ）２ The following was calculated: Cu2p ３／２ The background range for spectral waveform separation analysis was the same as that for semi-quantitative analysis, and the waveform separation parameters were set according to the conditions shown in Table 2 below. In the table, items marked "Fix" indicate that the parameters were fixed to the values ​​listed in the table for the analysis. 【0064】 【0065】 Next, the CuLMM spectrum was subjected to waveform separation analysis using the target factor analysis (TFA) mode of the analysis software, and the area ratio of the "metallic" state of CuLMM I was determined. 金属 The following was calculated. The number of spectral components was set to 3. Cu metal foil, Cu ２ For the O powder and CuO powder, the CuLMM spectra obtained under the aforementioned measurement conditions were used as external standard spectra for waveform separation analysis, and the area ratio of the obtained Cu metal foil component was determined to be I 金属 The Cu metal foil is manufactured by Alfa Aesar. ２ The O powder and CuO powder were manufactured by Mitsuwa Chemical Co., Ltd., and had a purity of 99.9% or higher. ２ O powder and CuO powder were pelletized using a press machine. For the Cu metal foil, the following settings were applied beforehand: acceleration voltage: 2kV, raster area: 2mm square, sputtering rate: 5.1nm / min (SiO₂ ２Ar ion sputtering was performed under the conditions (conversion) until the O1s peak was no longer detected. Cu ２ For the O reagent, the following settings were used in advance: acceleration voltage: 1 kV, raster area: 3 mm square, sputtering rate: 1.0 nm / min (SiO ２ Under the conditions of conversion, Cu2p ３／２ CuO state or Cu(OH) in the spectrum ２ Sputtering was performed using an Ar ion beam irradiation time at which the 933.5–935.5 eV peaks originating from the state and the 567.1–568.9 eV and 564.3–566.1 eV peaks originating from the metallic state in the CuLMM spectrum were not detected. After removing the surface oxide layer, the CuLMM spectrum was measured. 【0066】 The obtained area ratio I 金属＋Ｃｕ２Ｏ , I ＣｕＯ , I Ｃｕ（ＯＨ）２ and I 金属 Regarding this, use the following equations 1 and 2 to determine the ratio of Cu(I) state to total Cu. １ and the ratio of Cu(II) states I ２ The following was calculated: (Equation 1) I １ = I 金属＋Ｃｕ２Ｏ - I 金属 (Equation 2) I ２ = I ＣｕＯ + I Ｃｕ（ＯＨ）２ 【0067】 Next, the obtained I １ , I ２ and total Cu concentration P Ｃｕ　ｔｏｔａｌ Regarding this, use the following equations 3 and 4 to determine the Cu(I) concentration P １ and Cu(II) concentration P ２ P was calculated. (Equation 3) １ = P Ｃｕ　ｔｏｔａｌ × I １ ÷ 100 (Formula 4) P ２ = P Ｃｕ　ｔｏｔａｌ × I ２ ÷ 100 Finally, P obtained by the above procedure １ , P ２ , P Ｐ Regarding P １ / P Ｐ , P２ / P Ｐ and P ２ / P １ The ratio was calculated. Figure 1 shows the distribution of phosphorus in the surface region of copper particles in the copper powder obtained in Example 1 and Comparative Example 1. 【0068】 [Sintering Initiation Temperature] A thermomechanical analyzer (TMA / EXSTAR 6000, manufactured by Hitachi High-Tech Science Co., Ltd.) was used. 0.2 g of copper powder was placed in a φ4.0 mm aluminum mold container. Pellet was prepared by pressure molding the copper powder under a pressure of 4.0 MPa for 5 minutes. The pellet length of the obtained pellet was measured and used as the sample. This sample was set in the thermomechanical analyzer. The sample was heated at a rate of 10°C / min under a load of 49 mN and a nitrogen atmosphere. Measurement was started from room temperature (25°C), and a graph showing the relationship between temperature and shrinkage rate (%) was obtained. The temperature at which the shrinkage rate was 2% was defined as the sintering initiation temperature. In this manner, the sintering start temperatures of the copper powders in the examples and comparative examples were measured. For Examples 1 to 4, the ratio to the sintering start temperature of Comparative Example 1 was calculated; for Example 5, the ratio to the sintering start temperature of Comparative Example 2 was calculated; for Example 6, the ratio to the sintering start temperature of Comparative Example 3 was calculated; and for Example 7, the ratio to the sintering start temperature of Comparative Example 7 was calculated. These ratios were used as a measure of the sintering start temperature. 【0069】 【0070】 【0071】 As is clear from the results shown in Tables 3 and 4, the copper powder obtained in each example showed a higher sintering start temperature compared to the copper powder of the comparative example. Furthermore, as is clear from the graph shown in Figure 1, the copper powder obtained in Example 1 showed a concentration of phosphorus elements in the surface region of the particles. 【0072】 As described in detail above, according to the present invention, since the sintering of copper powder can be initiated after the combustion of organic matter, it is possible to form a dense sintered body.

Claims

1. Copper powder consisting of an aggregate of copper particles containing element P (phosphorus), wherein the concentration of P on the surface of the copper particles is measured by X-ray photoelectron spectroscopy. Ｐ The Cu(I) concentration P １ P is the ratio of １ / P Ｐ Copper powder in which the value is between 15.5 and 250.

0.

2. P concentration on the surface of the copper particles as measured by X-ray photoelectron spectroscopy. Ｐ The Cu(II) concentration P ２ P is the ratio of ２ / P Ｐ The copper powder according to claim 1, wherein the value of is 8.0 or greater.

3. The concentration P of Cu(I) on the surface of the copper particles measured by X-ray photoelectron spectroscopy １ relative to the concentration P of Cu(II) ２ is the ratio P ２ / P １ of which the value is 0.20 or more and 0.70 or less, the copper powder according to claim 1.

4. The copper powder according to claim 1, wherein the phosphorus element is present from the center to the surface of the copper particles.

5. The copper powder according to claim 1, wherein the phosphorus element content is 50 ppm by mass or more and 300 ppm by mass or less.

6. Volume cumulative particle size D at 50% cumulative volume, measured by laser diffraction scattering particle size distribution analysis. ５０ The copper powder according to claim 1, wherein the particle size is 0.3 μm or more and 15.0 μm or less.

7. The copper powder according to claim 1, wherein the copper particles are spherical or flake-shaped.

8. A method for producing copper powder, comprising the step of mixing a raw material powder consisting of an aggregate of copper particles containing the element P (phosphorus) with an aqueous solution containing a Cu(II) ion complexing agent.

9. The manufacturing method according to claim 8, wherein molten copper containing copper(I) phosphide is subjected to an atomization method to obtain the raw material powder.

10. The manufacturing method according to claim 8 or 9, wherein the complexing agent is ammonia.

11. The manufacturing method according to claim 10, wherein the mass ratio of ammonia to the raw material powder is 0.007 or more and 0.150 or less.

12. A conductive resin composition comprising copper powder and resin according to any one of claims 1 to 7.

13. A multilayer ceramic capacitor having an external electrode made of a sintered body of metal powder containing copper powder as described in any one of claims 1 to 7.

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