CN110325303B

CN110325303B - Copper particles and method for producing same

Info

Publication number: CN110325303B
Application number: CN201880012738.6A
Authority: CN
Inventors: 松山敏和; 织田晃祐; 上住义明; 远藤安俊
Original assignee: Mitsui Mining and Smelting Co Ltd
Current assignee: Mitsui Mining and Smelting Co Ltd
Priority date: 2017-03-31
Filing date: 2018-03-28
Publication date: 2022-01-11
Anticipated expiration: 2038-03-28
Also published as: WO2018181482A1; TWI803486B; KR20190132351A; JPWO2018181482A1; TW201841702A; CN110325303A; KR102403998B1; JP7050756B2

Abstract

The copper particles of the present invention have a core containing copper and a copper layer formed on the coreThe surface of the core portion contains CuO and Cu₂A copper oxide layer of O. When the content ratio (mass%) of oxygen contained in the copper particles is X, Cu contained in the copper oxide layer₂When the crystallite size (nm) of O is Y, the condition that Y is not less than 36X-18 is satisfied. Crystallite size D of metallic copper contained in core_C(mum) and a volume cumulative particle diameter D at a cumulative volume of 50% by volume in the laser diffraction scattering particle size distribution measurement method₅₀Ratio of (μm) namely D_C/D₅₀The value of (c) is preferably 0.10 to 0.40. The oxygen content is preferably 0.80 to 1.80 mass%.

Description

Copper particles and method for producing same

Technical Field

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

Background

Copper has a resistivity value similar to that of silver and is lower in material cost than silver, and therefore is used as a raw material for a conductive paste or the like used for forming a printed wiring board, a circuit, and an electrode. In recent years, in the field of circuits and the like, the pitch has been made finer and the thickness of electrodes has been made thinner, and accordingly, it has been required to achieve both the fine granulation of copper particles for conductive paste and good sinterability. On the other hand, copper after microparticulation has a very large surface area, and therefore surface oxidation of the particles becomes remarkable when producing a conductive paste, which may result in poor conductivity.

Patent document 1 proposes a method for producing copper powder by a physical vapor deposition method (PVD method) using direct-current thermal plasma in order to secure micronization and electrical conductivity of copper powder.

Documents of the prior art

Patent document

Patent document 1: international publication No. 2015/122251 pamphlet

Disclosure of Invention

Fine particles produced by PVD or the like have a very large surface area of copper grains, and the grains are likely to agglomerate with each other. Therefore, in a wet dispersion process or the like which is a production process after the production of copper particles, a surface treatment is generally performed in which copper particles are mixed with a surface treatment agent such as a fatty acid to make the particles less likely to aggregate with each other. However, in the case of such copper particles, the primary particles are sometimes aggregated again with each other (hereinafter also referred to as re-aggregation) even if surface treatment is performed.

In addition, the coarse particles of copper particles produced by PVD or the like are also large in number, in addition to the particles being easily aggregated. Therefore, when a conductive paste is prepared using such copper particles, and the paste is applied to a substrate and fired, it is difficult to obtain good surface smoothness of the conductive film obtained by firing. Therefore, in the case of producing a conductive paste using copper particles produced by PVD or the like as a raw material, it is necessary to remove agglomerated particles and coarse particles in advance using a filter, but since the amount of agglomerated particles and coarse particles is large, the amount of particles removed by the filter is increased in the conventional copper particles, and the yield may be lowered.

Accordingly, the present invention relates to an improvement of copper particles and a method for producing the same, and more particularly to copper particles and a method for producing the same, in which the particles are less likely to reagglomerate with each other when a surface treatment agent is used in a wet dispersion step which is a production step after the production of copper particles.

The present inventors have conducted intensive studies to solve the above problems, and as a result, have found that: oxygen content ratio and Cu₂Copper grains in which the crystallite size of O satisfies a specific relationship have a reduced degree of re-aggregation of grains with each other after surface treatment. The present invention has been completed based on this finding.

That is, the present invention provides a copper particle having a core containing copper and a surface formed on the core containing CuO and Cu₂A copper oxide layer of O, which satisfies the relationship of the following formula (1).

Y≥36X-18 (1)

Wherein X is the content (mass%) of oxygen contained in the copper particles, and Y is Cu contained in the copper oxide layer₂Crystallite size (nm) of O.

Further, the present invention provides a method for producing copper particles, which comprises the steps of:

introducing raw material powder containing copper element into a plasma flame to form copper in a gas phase,

generating copper particles by cooling the copper in a gaseous state while exposing the generated copper particles to an oxygen-containing atmosphere,

oxidizing the surface of the copper particles exposed to the oxygen-containing atmosphere to form a composition containing CuO and Cu₂A copper oxide layer of O.

Drawings

FIG. 1 is a view showing an embodiment of an apparatus for producing copper particles according to the present invention.

FIG. 2 shows Cu in copper particles obtained in examples and comparative examples₂A graph of the relationship between the crystallite size of O and the content ratio of oxygen.

Detailed Description

The present invention will be described below based on preferred embodiments thereof. The copper particle of the present invention has a core containing copper and a surface formed on the core containing CuO and Cu₂A copper oxide layer of O. The core is located in the central region of the copper particle of the present invention, which is a portion occupying a large half of the mass in the copper particle of the present invention. On the other hand, the copper oxide layer is located in a surface region in the copper particle of the present invention, which constitutes the outermost surface of the copper particle of the present invention. The copper oxide layer preferably covers the entire surface of the core, but may cover the surface of the core so that a part of the surface of the core is exposed to the outside, as long as the effect of the present invention is not impaired. In the case of the copper particles of the present invention, there is no layer containing a metal element on the outer side than the copper oxide layer. However, it is permissible to have a layer made of an organic compound on the outer side of the copper oxide layer.

The copper particles of the present invention are not particularly limited in shape, and various shapes can be adopted according to the specific use. For example, copper particles having various shapes such as spherical, flake, plate, and resin shapes can be used.

In the case where the copper particles of the present invention have any of the above shapes, the cumulative volume particle diameter D when the cumulative volume is 50% by volume in the laser diffraction scattering particle size distribution measurement method₅₀Each of them is preferably 0.2 to 0.6. mu.m, more preferably 0.2 to 0.5. mu.m. When the particle diameter of the copper particles is within this range, a conductive composition such as a conductive paste is prepared from the copper particles and a conductive film is formed using the conductive composition, the conductive film becomes dense and has high conductivity. In order to obtain copper particles having a particle diameter in this range, for example, the copper particles may be produced by a wet reduction method, a PVD method, or the like. In addition, the volume cumulative particle diameter D₅₀The measurement of (2) can be carried out by the method described in the examples below.

The core in the copper particle of the present invention is constituted by containing copper. The core containing copper includes (i) a case where the core is substantially composed of copper and (ii) a case where the core is composed of copper and other elements. In the case of (i), the proportion of copper in the core portion is preferably 99 mass% or more, more preferably 99.5 mass% or more, and the core portion is more preferably composed of only copper and unavoidable impurities.

In either case of (i) and (ii) above, the core portion is, as described above, a portion that occupies a large part of the mass in the copper particle of the present invention. The thickness of the copper oxide layer is preferably 1nm to 100nm, more preferably 1nm to 55 nm. By making the copper oxide layer exist in this thickness range, the conductivity of the copper particles of the present invention can be sufficiently improved. The ratio of the core portion in the copper particle of the present invention can be measured by, for example, performing line analysis of the surface portion of the copper particle by STEM-EDS (Scanning Transmission Electron Microscope-Energy-Dispersive X-ray Spectroscopy), and measuring the thickness of the copper oxide layer from the line profile of oxygen (O-K line).

As described above, the copper oxide layer located at the surface of the core portion contains CuO and Cu₂And O. The copper oxide layer (iii) consists of only CuO andCu₂(iii) copper oxide of O, or (iv) contains CuO and Cu₂The copper oxide of O contains other substances in addition to the above. In the case of (iii), the copper oxide layer is preferably composed of only CuO and Cu₂Copper oxide of O and inevitable impurities.

In any of the above cases (iii) and (iv), CuO and Cu in the copper oxide layer₂The presence state of O is not particularly limited. E.g. CuO and Cu₂O may be in any mixture, or a portion composed of CuO and Cu₂The sites of O may be present individually. In the portion composed of CuO and Cu₂When the sites consisting of O are present individually, for example, Cu is used₂The core has a structure in which a site composed of O is present on the surface of the core and a site composed of CuO is present on the surface of the site.

A particularly preferred embodiment of the copper particles of the present invention includes, for example, a copper-containing alloy in which the core portion is composed of only copper and unavoidable impurities and the copper oxide layer is composed of only CuO and Cu₂And O is copper oxide and inevitable impurities.

The inventors of the present application have found, as a result of their studies, that: when the content ratio of oxygen in the copper particles of the present invention to Cu in the copper oxide layer of the copper particles₂When the crystallite size of O is in a specific relationship, the dispersibility of copper particles after surface treatment in the production step is improved. Specifically, it was found that: when the oxygen content (unit: mass%) in the copper particles is X, Cu in the copper oxide layer₂When the crystallite size (unit: nm) of O is Y, the copper particles after the surface treatment in the production step are less likely to reagglomerate and the dispersibility is particularly improved when the relationship of the following formula (1) is satisfied.

Y≥36X-18 (1)

The reason why the dispersibility of the copper particles after the surface treatment in the production step is particularly improved when the relationship of the formula (1) is satisfied is not clear, but the inventors of the present invention presume as follows. In the case of copper particles produced by wet reduction, PVD method or the like, Cu at the surface of the particles₂The degree of exposure of O increases. When such copper particles are mixed with a surface treatment agent such as fatty acid in a production step such as a wet dispersion step, the fatty acid and Cu are mixed₂Reaction of O to Cu₂O is dissolved, and the metal copper contained in the core of the copper particle is exposed to the outside. Copper particles in a state where metal copper is exposed to the outside are easily bonded to copper particles in the same state, and thus re-agglomeration of the particles is easily caused. In contrast, the copper particles satisfying formula (1) are formed by Cu contained in the copper oxide layer₂Since O has high crystallinity, CuO is considered to be uniformly generated on the outermost surface of the copper particle. CuO is greater than Cu₂O is stable and thus hardly reacts with a surface treatment agent such as fatty acid, and Cu₂O is less soluble than O. Therefore, the metal copper contained in the core portion is less likely to be exposed to the outside of the copper particles. As a result, the copper particles are less likely to re-agglomerate with each other.

The content of oxygen in the copper particles of the present invention is preferably 0.8 to 1.80% by mass, more preferably 0.8 to 1.6% by mass, and still more preferably 0.8 to 1.5% by mass, on condition that the relationship of the above formula (1) is satisfied. When the oxygen content is in this range, the copper particles are less likely to reagglomerate after the surface treatment in the production step. The oxygen content in the copper particles of the present invention can be measured, for example, by the method described in the examples below.

Similarly, the copper particles of the present invention are Cu contained in the copper oxide layer on condition that the relationship of the above formula (1) is satisfied₂The crystallite size of O is preferably 15nm to 60nm, more preferably 20nm to 60nm, and still more preferably 20nm to 55 nm. By making Cu₂The crystallite size of O is in this range, and copper particles are less likely to re-agglomerate after surface treatment in the production step. Cu₂The crystallite size of O is calculated from the diffraction peak obtained by powder X-ray diffraction according to Scherrer formula. The measurement based on powder X-ray diffraction can be carried out by the method described in the examples described later.

In order to satisfy the conditions of formula (1) for the copper particles of the present invention, for example, the copper particles can be produced by a method described below.

The above description mentions Cu in the copper particles of the invention₂Crystallite size of O, but in addition to the crystallite size, in the copper particles of the present invention, crystallite size D of metallic copper contained in the core portion_CPreferably 0.060 to 0.090 μm, more preferably 0.065 to 0.085 μm, and still more preferably 0.070 to 0.085. mu.m. By making the crystallite size D of the metallic copper_CIn this range, Cu can be increased₂The crystallite size of O further enables CuO to be uniformly formed on the outermost surface of the copper oxide layer. The crystallite size of metallic copper was calculated from the diffraction peak obtained by powder X-ray diffraction according to Scherrer formula. The measurement based on powder X-ray diffraction can be carried out by the method described in the examples described later.

From the viewpoint of more effectively preventing the copper particles from reagglomerating with each other, with the copper particles of the present invention, the crystallite size D of the metallic copper in the core portion_C(mum) and a volume cumulative particle diameter D at a cumulative volume of 50% by volume in the laser diffraction scattering particle size distribution measurement method₅₀Ratio of (μm) namely D_C/D₅₀The value of (b) is preferably 0.10 to 0.40, more preferably 0.10 to 0.30, and further preferably 0.20 to 0.30. To make D_C/D₅₀The value of (b) satisfies this range, and for example, copper particles are produced by the method described later.

As described above, the copper particles of the present invention contain metallic copper as 0-valent copper, Cu as monovalent copper₂O and CuO as divalent copper. The presence ratio of these three at the surface of the copper particle can be measured using X-ray photoelectron spectroscopy (XPS). By XPS measurement, X-ray photoelectron spectra of various elements can be obtained, and the elemental composition of the copper particles up to a depth of about ten nanometers on the surface can be quantitatively analyzed. In the X-ray photoelectron spectroscopy obtained by measuring the surface state of the copper particles of the present invention by XPS, the ratio of the peak area P2 of Cu (ii) as divalent copper to the peak area P1 of Cu (i) as monovalent copper and the peak area P0 of Cu (0) as 0-valent copper, that is, the value of P2/(P1+ P0) is preferably 0.30 to 2.50, more preferably 0.40 to 2.50. By saturating the copper particles of the inventionWith this ratio range, the total amount of Cu (0) and Cu (i) present on the surface of the copper particles and the amount of Cu (ii) can be appropriately set to suppress reagglomeration of the copper particles with each other. The measurement using XPS can be performed by the method described in the examples described later.

Hereinafter, a preferred method for producing the copper particles of the present invention will be described.

< step 1. Synthesis of copper particles >

As the heretofore known method for producing copper particles, there are generally cited a wet reduction method, an atomization method, a physical vapor deposition method (PVD method), and the like. In these production methods, the oxygen content in the copper particles and Cu are adjusted₂Crystallite size of O and metallic copper and D of copper particles₅₀The above range is easily satisfied, and it is preferable to produce copper particles by PVD method. Thus, a method for producing copper particles by PVD method will be described below.

Fig. 1 shows a thermal plasma-generating device 1 suitable for producing copper particles on the basis of a PVD method. The thermal plasma generating apparatus 1 includes a raw material powder supply device 2, a raw material powder supply path 3, a plasma flame generating section 4, a plasma gas supply device 5, a chamber 6, a recovery tank 7, an oxygen supply device 8, a pressure adjusting device 9, and an exhaust device 10.

A raw powder containing copper element (hereinafter also simply referred to as a raw powder) is introduced into the plasma flame generation section 4 from the raw powder supply device 2 via the raw powder supply path 3. In the plasma flame generating section 4, a plasma gas is supplied from the plasma gas supply device 5, thereby generating a plasma flame. The raw material powder introduced into the plasma flame is evaporated and gasified to become copper in a gas phase, and then discharged into the chamber 6 existing on the terminal end side of the plasma flame. The copper in the gas phase is cooled as it is separated from the plasma flame, and copper particles are produced by nuclear generation and grain growth. The generated copper particles are exposed to the atmosphere within the chamber 6. The copper particles exposed to the atmosphere in the chamber 6 adhere to the wall surface inside the chamber 6 or are accumulated in the recovery tank 7. The chamber 6 is controlled by the pressure adjusting means 9 and the exhaust means 10 so as to maintain a negative pressure relative to the raw powder supply path 3, and is configured to stably generate a plasma flame and to introduce the raw powder into the plasma flame generating section 4. Details of the atmosphere in the chamber 6 will be described later.

The particle diameter of the raw material powder for producing the copper particles of the present invention is not particularly limited. The volume cumulative particle diameter D of the raw material powder from the viewpoint of the efficiency of supply to the thermal plasma generating apparatus₅₀Preferably 3 to 30 μm. The shape of the particles of the raw material powder is not particularly limited, and particles having various shapes such as spherical, flaky, plate-like, and dendritic shapes can be used. The oxidation state of the copper element in the raw material powder is not particularly limited, and for example, copper metal powder or copper oxide powder (for example, CuO or Cu) can be used₂O) or mixtures thereof, and the like. The method for producing the raw material powder is also not particularly limited.

In the present production method, the amount of raw material powder to be supplied is preferably 0.1 g/min to 100 g/min from the viewpoint of stably producing copper particles having a large crystallite size of metallic copper.

The plasma gas for generating the plasma flame is preferably a mixed gas of argon and nitrogen. By using the mixed gas, a larger amount of energy can be supplied to the raw powder, and thereby a powder having a particle diameter and a crystallite size (Cu) preferable for exerting the effects of the present invention can be obtained₂O and metallic copper). In particular, from the viewpoint of obtaining spherical or approximately spherical copper particles, it is preferable to use a mixed gas of argon and nitrogen as the plasma gas and to adjust the plasma flame to be laminar, and to make it coarse and long. "approximately spherical" refers to a shape that is not completely spherical but can be recognized as a ball. Whether or not the plasma flame is in a laminar state can be determined by the ratio of the length of the plasma flame to the width of the plasma flame when observed from the side where the width of the plasma flame is observed to be the thickest. The laminar state can be determined when the ratio of the length of the plasma flame to the width of the plasma flame is 3 or more, and the turbulent state can be determined when the ratio of the length of the plasma flame to the width of the plasma flame is less than 3.

From stably maintaining plasmaFrom the viewpoint of the laminar state of the flame, the gas flow rate of the plasma gas is preferably 1L/min to 35L/min, and more preferably 5L/min to 30L/min at room temperature. By adopting the gas flow rate in this range, the generated particles are brought into contact with an oxygen-containing atmosphere in the chamber 6 described later while maintaining an appropriate temperature. As a result, CuO and Cu can be formed on the surface of the core smoothly₂A copper oxide layer of O. The plasma output power of the thermal plasma generation device is preferably 2kW to 50kW, and more preferably 5kW to 35 kW. From the same viewpoint, the ratio of the flow rate (L/min) of argon to nitrogen in the plasma gas is preferably argon at room temperature: nitrogen 99: 1-10: 90, more preferably 95: 5-70: 30.

in the present manufacturing method, the atmosphere in the chamber 6 is preferably an oxygen-containing atmosphere. This is because, by exposing the copper in the gas phase to an oxygen-containing atmosphere during the process of cooling to form copper particles, the content of oxygen in the copper particles can be maintained in the above range, and Cu having high crystallinity can be formed on the surface of the core portion₂A copper oxide layer of O. In this case, by setting the produced core portion to an appropriate temperature, Cu having high crystallinity can be easily formed₂A copper oxide layer of O. The temperature setting can be controlled by, for example, adjusting the gas flow rate of the plasma gas and adjusting the flow rate of oxygen to be supplied into the chamber 6 (as described later). As the oxygen-containing atmosphere, oxygen itself, a mixed gas of oxygen and another gas, or the like can be used. When a mixed gas is used, various inert gases such as argon and nitrogen can be used as the other gas. In the embodiment shown in fig. 1, the oxygen supply device 8 is connected to the side surface of the chamber to supply oxygen into the chamber, and the connection position of the oxygen supply device is not particularly limited as long as oxygen can be stably supplied into the chamber 6.

From the viewpoint of stably exposing the copper particles formed from the copper in the gas phase to the oxygen-containing atmosphere, the flow rate of oxygen supplied into the chamber 6 is preferably 0.002L/min to 0.75L/min, and more preferably 0.004L/min to 0.70L/min. In addition, from forming a bagContaining Cu of high crystallinity₂From the viewpoint of the copper oxide layer of O, the oxygen concentration in the chamber is preferably 100ppm to 2000ppm, more preferably 200ppm to 1000 ppm.

< step 2. Oxidation treatment >

From the above<Step 1>The resulting copper particles are preferably further subjected to an oxidation treatment. By performing this step, the method can be used in<Step 1>In the surface of unreacted copper particles₂O is slowly oxidized to CuO, and Cu can be generated to be contained in a thicker layer without any gap on the whole surface₂Copper oxide layers of O and CuO can provide copper particles that are less prone to reagglomeration after surface treatment.

The oxidation in this step proceeds as follows. Stopping the supply of the raw material powder and the generation of the plasma flame to return the chamber 6 to the normal pressure, and then returning the raw material powder to the normal pressure<Step 1>The produced copper particles are accumulated in a recovery tank 7 and recovered, and the copper particles are placed in an atmospheric atmosphere to contain Cu on the surfaces of the copper particles₂The O is oxidized to CuO to form a copper oxide layer.

In this step, when the copper particles are allowed to stand in the atmosphere, the copper oxide layer can be formed without causing a rapid oxidation reaction of the copper particles. However, from the viewpoint of industrial productivity, it is preferable that the produced copper particles are placed in an atmosphere while crushing the agglomerated particles using a sieve or the like.

In this step, from the viewpoint of uniformity of the oxidation treatment of the copper particles, it is preferable to place the copper particles in an atmosphere having a relative humidity of 30% to 60% and a temperature of 15 ℃ to 30 ℃. By performing the oxidation reaction under such conditions, Cu of the copper oxide layer can be oxidized by moisture contained in the atmospheric atmosphere₂O is slowly oxidized to CuO, and a stable copper oxide layer can be formed on the surface.

In addition, the treatment time in this step is preferably 5 to 60 minutes, more preferably 5 to 30 minutes, under the condition of the atmospheric atmosphere in the above range, from the viewpoint of preventing a rapid oxidation reaction during recovery of copper particles.

The copper particles of the present invention can be produced smoothly by the above production method. The copper particles thus obtained are preferably sealed in a container made of a moisture-impermeable material and stored at room temperature (25 ℃) or lower for the purpose of maintaining the oxidized state of the surface of the copper particles.

In addition, in the copper particles of the present invention produced by the above production method, when the surface treatment agent is used in the wet dispersion step which is a production step after the production of the copper particles, the copper particles are less likely to undergo reagglomeration than conventional copper particles. Further, by using the copper particles of the present invention, a conductive composition such as a conductive paste can be produced without impairing the sinterability at low temperatures.

Examples

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 the embodiments. Unless otherwise specified, "%" means "% by mass".

[ example 1]

The above-described < step 1> and < step 2> were performed under the following production conditions, and copper particles were produced.

< step 1>

Copper particles (particle diameter D) as a raw material powder obtained by an atomization method₅₀: 12 μm, particle shape: spherical) was introduced into a plasma flame of the thermal plasma generation apparatus shown in fig. 1 at a supply rate of 5 g/min, and copper in a vapor phase was formed. As conditions for generating the plasma flame, a mixed gas of argon and nitrogen was used as a plasma gas, and the flow rate of the plasma gas was set to 19.0L/min, and the ratio of the flow rate (L/min) of argon and nitrogen in the plasma gas was set to 82: 18. the plasma output power was set to 19 kW.

Copper particles are generated from copper in a gas phase by cooling in a chamber while exposing the copper particles to an oxygen-containing atmosphere, thereby forming copper particles having a core and a copper oxide layer. The flow rate of an oxygen-nitrogen mixture gas (containing 5 vol% of oxygen) into the chamber was set to 0.20L/min (the flow rate of oxygen was 0.01L/min), and the oxygen concentration in the chamber was set to 440 ppm. After that, the generation of the plasma flame was stopped in a state where the copper particles were present in the chamber, and nitrogen gas was supplied into the chamber having a negative pressure (-0.05MPa) at a flow rate of 30L/min, and the pressure was returned from the negative pressure to the normal pressure for 15 minutes.

< step 2>

After < step 1> is performed, copper particles are recovered. The copper particles were crushed by a sieve in an atmospheric atmosphere having a relative humidity of 50% and a temperature of 25 ℃, and a copper oxide layer was formed on the surfaces of the copper particles. The time for placing under the atmospheric atmosphere was set to 30 minutes.

2-propanol was added so that the obtained copper particles were 30 mass%, and then 5 mass% of lauric acid as a dispersant was added to the copper particles to prepare a slurry. The slurry was crushed by NanomizermarkII (Wet crusher, product name: NM2-2000AR, manufactured by Guitian machinery K.K.) (crushing conditions: 50MPa, five passes). The crushed slurry was filtered through a filter (ROKI TECHNO Co., LTD., product name: SBP010) having a mesh size of 1 μm, and then the filtrate was removed, and the remaining solid matter was dried at 40 ℃ by a vacuum dryer (manufactured by ADVANTEC). Thereafter, the copper particles were sieved through a sieve having a mesh size of 150 μm under a nitrogen atmosphere to obtain copper particles.

[ example 2]

Copper pellets were produced in the same manner as in example 1, except that in example 1, the flow rate of the oxygen-nitrogen mixture gas into the chamber was set to 0.29L/min (the flow rate of oxygen was 0.0145L/min), and the oxygen concentration in the chamber was set to 640 ppm.

[ example 3]

Copper pellets were produced in the same manner as in example 1, except that in example 1, the flow rate of the oxygen-nitrogen mixture gas into the chamber was set to 0.11L/min (the flow rate of oxygen was 0.0055L/min), and the oxygen concentration in the chamber was set to 240 ppm.

[ example 4]

Copper pellets were produced in the same manner as in example 1, except that in example 1, the flow rate of the oxygen-nitrogen mixture gas into the chamber was set to 0.34L/min (the flow rate of oxygen was 0.017L/min), and the oxygen concentration in the chamber was set to 750 ppm.

[ example 5]

Copper pellets were produced in the same manner as in example 1, except that in example 1, the flow rate of the oxygen-nitrogen mixture gas into the chamber was set to 0.09L/min (the flow rate of oxygen was set to 0.0045L/min), and the oxygen concentration in the chamber was set to 200 ppm.

[ example 6]

Copper pellets were produced in the same manner as in example 1, except that in example 1, the flow rate of the oxygen-nitrogen mixture gas into the chamber was set to 0.39L/min (the flow rate of oxygen was 0.0195L/min), and the oxygen concentration in the chamber was set to 850 ppm.

[ example 7]

Copper particles were produced in the same manner as in example 1, except that in example 1, the flow rate of the oxygen-nitrogen mixture gas into the chamber was set to 0.33L/min (the flow rate of oxygen was 0.0165L/min), and the oxygen concentration in the chamber was set to 730 ppm.

[ example 8]

Copper pellets were produced in the same manner as in example 1, except that in example 1, the flow rate of the oxygen-nitrogen mixture gas into the chamber was set to 0.18L/min (the flow rate of oxygen was 0.009L/min), and the oxygen concentration in the chamber was set to 400 ppm.

[ example 9]

Copper pellets were produced in the same manner as in example 1, except that in example 1, the flow rate of the oxygen-nitrogen mixture gas into the chamber was set to 0.26L/min (the flow rate of oxygen was 0.013L/min), and the oxygen concentration in the chamber was set to 570 ppm.

[ example 10]

Copper pellets were produced in the same manner as in example 1, except that in example 1, the flow rate of the oxygen-nitrogen mixture gas into the chamber was set to 0.24L/min (the flow rate of oxygen was 0.012L/min), and the oxygen concentration in the chamber was set to 540 ppm.

Comparative example 1

Copper particles were produced in the same manner as in example 1, except that in example 1, the flow rate of the plasma gas was set to 36L/min, the flow rate of the oxygen-nitrogen mixture gas into the chamber was set to 0.74L/min (the flow rate of oxygen was 0.037L/min), and the oxygen concentration in the chamber was set to 860 ppm.

Comparative example 2

Copper particles were produced in the same manner as in example 1, except that in example 1, the flow rate of the plasma gas was set to 36L/min, the flow rate of the oxygen-nitrogen mixture gas into the chamber was set to 0.35L/min (the flow rate of oxygen was 0.0175L/min), and the oxygen concentration in the chamber was set to 410 ppm.

Comparative example 3

Copper particles were produced in the same manner as in example 1, except that in example 1, the flow rate of the plasma gas was set to 36L/min, the flow rate of the oxygen-nitrogen mixture gas into the chamber was set to 0.79L/min (the flow rate of oxygen was 0.0395L/min), and the oxygen concentration in the chamber was set to 910 ppm.

Comparative example 4

Copper particles were produced in the same manner as in example 1, except that the flow rate of the plasma gas was set to 36L/min in example 1 and the oxygen-nitrogen mixed gas was not introduced into the chamber.

Comparative example 5

Copper particles were produced in the same manner as in example 1, except that in example 1, the flow rate of the plasma gas was set to 36L/min, the flow rate of the oxygen-nitrogen mixture gas into the chamber was set to 0.44L/min (the flow rate of oxygen was 0.022L/min), the oxygen concentration in the chamber was set to 510ppm, and the < step 2> was not performed.

[ evaluation ]

Regarding the copper particles obtained in examples and comparative examples, the oxygen content ratio and Cu were measured by the following methods₂The crystallite size of O was determined. Further, when the oxygen content (unit: mass%) in the copper particles is X, Cu contained in the copper oxide layer₂When the crystallite size (unit: nm) of O was set to Y, it was confirmed whether or not the relation of the above formula (1) was satisfied in each of the examples and comparative examples. The results are shown inTable 1. Fig. 2 is a graph showing the relationship between X and Y.

Further, with respect to the copper particles obtained in examples and comparative examples, the volume cumulative particle diameter D was measured by the following method₅₀And crystallite size D of metallic copper_CThe measurement was carried out. And, the crystallite size D of the metal copper_CDivided by the cumulative volume particle diameter D of the copper particles₅₀From which D is calculated_C/D₅₀The value of (c). The results are shown in table 1.

Further, the existence ratio of copper in each valence number in XPS was measured for the copper particles obtained in examples and comparative examples by the following method. The results are shown in table 1.

Further, in order to evaluate the degree of agglomeration of the copper particles obtained in examples and comparative examples, the recovery rate of the copper particles based on filter filtration and the surface roughness of the coating film of the composition containing the copper particles were measured by the following methods. The results are shown in table 1.

[ method for measuring oxygen content ]

An oxygen and nitrogen analysis apparatus TC-500 manufactured by LECO Japan treaty was used. 0.05g of the measurement sample was weighed and filled in a nickel capsule, and then heated in a graphite crucible. During heating, carbon monoxide and carbon dioxide generated by reaction of oxygen in the sample with the crucible were detected by an infrared absorption method, and the oxygen content (% by mass) was calculated.

[Cu₂Determination of crystallite size of O]

Cu contained in copper oxide layer of copper particle₂The crystallite size of O is calculated as follows: the X-ray diffraction intensity of copper particles was measured in a measurement range of 2 θ to 20 ° to 100 ° using CuK α 1 rays by SmartLab manufactured by japan ltd₂The integral width of the X-ray diffraction peak at the crystal plane (111) of O is calculated according to the scherrer equation described below.

The Xile formula: k λ/β cos θ

D: crystallite size

K: xi le constant (1.333)

λ: wavelength of X-ray

Beta: integration Width [ rad ]

θ: angle of diffraction

[ volume cumulative particle diameter D of copper particles₅₀Measurement of (2)]

A few drops of a 0.1% aqueous solution of polyoxyethylene (10) octylphenyl ether (Wako pure chemical industries, Ltd.) was added to 0.1g of the measurement sample by a syringe and fused, and then mixed with 80ml of a 0.1% aqueous solution of an anionic surfactant (product name: SN-DISPERSANT 5468, manufactured by Sannopo Co., Ltd.) and dispersed for 5 minutes by an ultrasonic homogenizer (US-300T, manufactured by Nippon Seiko Seisaku-Sho Ltd.). Then, the volume cumulative particle diameter D was measured by using a Microtrac HRA manufactured by Micke Bayer corporation as a laser diffraction scattering particle size distribution measuring apparatus₅₀The measurement was carried out.

[ measurement of crystallite size of metallic copper ]

The crystallite size of the metallic copper contained in the core of the copper particle is calculated as follows: the X-ray diffraction intensity of the copper particles was measured in a measurement range of 20 ° to 100 ° using CuK α 1 rays by SmartLab manufactured by kyowski corporation, and the integrated width of the X-ray diffraction peak at the crystal plane (200) of the metallic copper at that time was calculated from the following scherrer equation.

The Xile formula: k λ/β cos θ

D: crystallite size

K: xi le constant (1.333)

λ: wavelength of X-ray

Beta: integration Width [ rad ]

θ: angle of diffraction

[ measurement of the proportion of copper present for each valence based on XPS ]

Versa Probe II manufactured by ULVAC-PHI corporation was used. The measurement conditions are as follows.

An X-ray source: Mg-Kalpha ray (1253.6eV)

Conditions of the X-ray source: 400W

Energy application: 23eV

Energy step length: 0.1eV

Angle of detector to sample stage: 90 degree

And (3) charge neutralization: using low-velocity ions and electrons

For the analysis, MultiPak9.0 analysis software manufactured by ULVAC-PHI corporation was used. Peak separation Using Curve Fit of MultiPak9.0, the main peak of Cu 2p3/2 is the peak indicated at 930eV to 940 eV. The background mode used was Shirley. The charging correction set the binding energy of C1s to 234.8 eV.

The peak areas P0, P1 and P2 were calculated from the peak area ratios obtained by waveform separation of Cu 2P3/2 peaks for Cu (I) in the range of 930.0eV to 933.0 eV.

[ recovery of copper particles based on Filter ]

In the production of the copper particles obtained in each of examples and comparative examples, a filter having a mesh size of 1 μm after filtering a slurry containing copper particles was dried at 40 ℃ by a vacuum dryer (manufactured by ADVANTEC), and the mass of the copper particles and the filter remaining on the filter was measured. The mass of the filter before filtration was subtracted from the measured mass to calculate the mass of copper particles remaining on the filter. In addition, the mass of the copper particles obtained by the methods of the respective examples and comparative examples was measured. From these masses, the ratio of the mass of the produced copper particles to the total mass of the copper particles remaining on the filter and the produced copper particles (mass of the produced copper particles/(mass of the copper particles remaining on the filter + mass of the produced copper particles) × 100) was calculated, and this value was taken as the recovery rate (%). When the recovery rate was 60% or more, the mark was "O", and when the recovery rate was less than 60%, the mark was "X".

[ surface roughness of coating film of composition containing copper particles ]

10g of copper particles obtained from the copper particles obtained in each of examples and comparative examples and 1.5g of a terpineol (product name: ETHOCEL STD100, manufactured by Anthoku corporation) carrier containing 10 mass% of a thermoplastic cellulose ester (manufactured by Takara chemical Co., Ltd.) were weighed, premixed and kneaded with a spatula, and then treated in two cycles of a stirring mode (1000 rpm. times.1 min) and a defoaming mode (2000 rpm. times.30 sec.) for gelatinization by using a rotation and revolution vacuum mixer ARE-500, manufactured by Kabushiki Kaisha, as one cycle. Further, the paste was subjected to five treatments in total using a three-roll mill, and thereby further subjected to dispersion mixing to prepare a paste. The paste thus prepared was applied to a glass slide substrate using a spatula with the gap set to 35 μm. Thereafter, the film was dried by heating at 150 ℃ for 10 minutes in a nitrogen oven to produce a coating film. The surface roughness of the coating film was measured by using a surface roughness meter (SURFCM 480B-12, made by Tokyo Seiko Seikagaku Kogyo Co., Ltd.).

From the results shown in table 1, it can be seen that: the filter recovery rate of the copper particles of each example was increased, while the filter recovery rate of the copper particles of the comparative example was decreased. The reason for this is because the copper particles of the examples inhibit the particles from re-agglomerating with each other.

In addition, it is known that: the surface roughness of the coating film obtained from the copper particles of each example having a high recovery rate was equal to the surface roughness of the coating film obtained from the copper particles of the comparative example, although the filter recovery rate was increased. The reason for this is also because the copper particles of the examples inhibit the particles from agglomerating with each other.

Industrial applicability

According to the present invention, there is provided copper particles which are less likely to undergo reagglomeration with each other when a surface treatment agent is used in a wet dispersion step which is a production step after copper particle production.

Claims

1. A copper particle having a core containing copper and a surface formed on the core containing CuO and Cu₂A copper oxide layer of O satisfying the following formula (1),

Y≥36X-18 (1)

wherein X is the content of oxygen in mass% contained in the copper particles and is 0.80 to 1.80 mass%, and Y is Cu contained in the copper oxide layer₂Crystallite size in nm of O.

2. Copper granules according to claim 1, wherein the crystallite size D of the metallic copper contained in the core is_CAnd a volume cumulative particle diameter D at a cumulative volume of 50% by volume in a laser diffraction scattering particle size distribution measurement method₅₀Ratio of (1) namely D_C/D₅₀Has a value of 0.10 to 0.40, D₅₀And D_CIn μm.

3. The copper particle according to claim 1 or 2, wherein a ratio of a peak area P2 of Cu (II) to peak areas P1 of Cu (I) and P0 of Cu (0), i.e., a value of P2/(P1+ P0), in an X-ray photoelectron spectrum obtained by measuring the surface of the copper particle is 0.30 to 2.50.

4. A method for producing copper particles, comprising the steps of:

raw material powder containing copper element is introduced into a plasma flame to form copper in a gas phase state, the gas flow rate of the plasma gas is 1L/min to 35L/min at room temperature,

generating copper particles by cooling the copper in the gas phase while exposing the generated copper particles to an oxygen-containing atmosphere,

oxidizing the surface of the copper particles after exposure to an oxygen-containing atmosphere to form a composition comprising CuO and Cu₂A copper oxide layer of O, and a copper oxide layer of,

the copper particles satisfy the following relation of formula (1),

Y≥36X-18 (1)

5. The method for producing copper particles according to claim 4, wherein the copper particles exposed to an oxygen-containing atmosphere are left in an atmospheric atmosphere having a relative humidity of 30% to 60% and a temperature of 15 ℃ to 30 ℃ for 5 minutes to 60 minutes to oxidize the surface of the copper particles and thereby form the copper oxide layer.

6. The method for producing copper particles according to claim 4 or 5, wherein a gas flow rate of the plasma gas is 1L/min to 30L/min at room temperature.

7. The method for producing copper particles according to claim 6, wherein a gas flow rate of the plasma gas is 5L/min to 30L/min at room temperature.