Method for producing slightly oxidized copper-containing particle, and copper particle coated with slightly oxidized copper

Abstract

A method for producing a slightly oxidized copper-containing particle having slightly oxidized copper, which is at least one among Cu64O and Cu8O, on the surface thereof, the method comprising: preparing a raw material particle having, at least on the surface thereof, copper oxide including at least one among CuO and Cu2O; and mixing the raw material particle with a solution containing an amine-based compound and a complex forming agent, and then adding a reductant to the resultant to allow a reaction in an oxygen-containing atmosphere.

Description

Method for producing fine copper oxide-containing particles and fine copper oxide-coated copper particles

[0001] The present disclosure relates to a method for producing fine copper oxide-containing particles and fine copper oxide-coated copper particles.

[0002] In recent years, a technology called printable electronics has been attracting attention in the manufacture of printed circuit boards. This technology does not require the conventional exposure and etching processes and does not emit harmful chemical substances, allowing fine wiring to be directly formed by inkjet or printing methods. This is a clean technology.

[0003] The above-mentioned fine wiring is mainly obtained by heating and sintering metal particles. From the viewpoint of the heat resistance of the substrate, the metal particles are required to be sintered at a low temperature, for example, 150°C or less. Currently, silver particles that can be sintered at low temperatures are widely used, but silver particles are expensive and there are concerns about the influence of wiring short circuits due to ion migration. As an alternative to silver particles, copper particles, which are inexpensive and highly resistant to ion migration, have attracted attention, but copper particles have the problem of being difficult to sinter at low temperatures.

[0004] To address the above-mentioned problems, the present inventors have attempted to obtain particles for low-temperature sintering using copper oxides. ２ O, Cu ４ O ３ , Cu ８ O and Cu ６４ Five types of Cu are known. ６４ O and Cu ８ O is a stable phase such as CuO or Cu ２ Compared to O, the proportion of oxygen atoms is smaller, the stability is low, and it can be reduced to metallic copper with low energy. ６４ O and Cu ８ It is thought that by using O, low-temperature sintering at 150°C or less can be realized. ６４ O and Cu ８ O is specifically called "fine copper oxide", and other oxides such as CuO and Cu ２ O, Cu ４ O ３ Distinguish from.

[0005] For example, Patent Document 1 discloses Cu ６４ O and Cu as needed ２ O and coated with a carboxylic acid, ６４ O and Cu ２ Cu relative to the total mass of O ６４ Oxide-containing copper fine particles having an O mass ratio of 0.5 to 2.0 mass % are disclosed.

[0006] In recent years, electrical components have been required to have better electrical conductivity. In addition to the submicron oxide-containing copper particles described in Patent Document 1, which have improved surface necking characteristics due to a carboxylic acid coating, the following Patent Documents 2 and 3 are cited as conductive material technologies that utilize a nano-sized melting point depression. Patent Document 2 describes Cu ６４ O particles and Cu ８ O particles, and the Cu ６４ O particles and the Cu ８ Patent Document 3 discloses a copper oxide particle composition containing copper clusters having an average particle size of 0.1 nm or more and 1 nm or less, and copper oxide particles having an average particle size of more than 1 nm and 20 nm or less, and the copper oxide particles are Cu ６４ O particles and the Cu ８ Furthermore, Patent Document 3 discloses a mixed particle containing at least one of copper clusters having an average particle size of 0.1 nm or more and 1 nm or less, copper oxide particles having an average particle size of more than 1 nm and 20 nm or less, and metallic copper particles having an average particle size of more than 20 nm and 1 μm or less, and the copper oxide particles are Cu ６４ O particles and the Cu ８ Mixed particles are shown, at least one of which is O particles.

[0007] International Publication No. 2022 / 045252 Japanese Patent Application Laid-Open No. 2020-29392 Japanese Patent Application Laid-Open No. 2020-100893

[0008] In Patent Documents 2 and 3, copper salts such as copper acetate are used as starting materials to produce the copper oxide particles contained in the mixed particles. However, copper salts are bulky and heavy, and the reaction process, including dissolving the copper salt in a solvent, requires a long time. Furthermore, although the concentration of copper ions is high at the beginning of reduction, the concentration changes during the reaction, making it difficult to control the reaction and the resulting particle size, especially in concentrated systems. Therefore, further investigation is considered necessary for industrial mass production. Furthermore, in the obtained mixed particles, the metallic copper particles and the fine copper oxide particles tend to aggregate, making it difficult to obtain a state in which they are dispersed together. The present disclosure has been made in consideration of the above circumstances, and one of its purposes is to provide a Cu ion sintering method that is useful for low-temperature sintering. ６４ O and Cu ８ The present invention aims to provide a method for mass-producing fine copper oxide-containing particles having one or more fine copper oxides selected from the group consisting of copper oxide, ...

[0009] Aspect 1 of the present invention is a composition comprising CuO and Cu ２ preparing raw material particles having copper oxide containing one or more of O on at least their surfaces; and mixing the raw material particles with a solution containing an amine compound and a complexing agent, adding a reducing agent, and reacting the raw material particles in an oxygen-containing atmosphere. ６４ O and Cu ８ The present invention provides a method for producing fine copper oxide-containing particles having one or more fine copper oxides selected from O at least on the surface thereof.

[0010] In a second aspect of the present invention, the raw material particles are CuO and Cu ２ 2. The method according to claim 1, wherein the raw material particles are made of copper oxide containing one or more of O.

[0011] In a third aspect of the present invention, the raw material particles have a copper raw material particle as a core, and are composed of CuO and Cu. ２ 2. The method for producing copper oxide-coated copper raw material particles according to claim 1, wherein the copper oxide-coated copper raw material particles have a shell made of a copper oxide coating film containing one or more of O.

[0012] In a fourth aspect of the present invention, the copper oxide contained in the raw material particles is Cu ２ 4. The method of any one of Aspects 1 to 3, wherein O is O.

[0013] A fifth aspect of the present invention is the production method according to any one of the first to fourth aspects, wherein the complexing agent is a carboxylic acid.

[0014] A sixth aspect of the present invention is the method according to any one of the first to fifth aspects, wherein the complexing agent is acetic acid.

[0015] A seventh aspect of the present invention is the production method according to any one of the first to sixth aspects, wherein the reaction is carried out at 50° C. or lower.

[0016] Aspect 8 of the present invention is the manufacturing method according to any one of Aspects 1 to 7, wherein the raw material particles have an average particle size of more than 20 nm and not more than 10 μm.

[0017] A ninth aspect of the present invention is a composite material comprising a copper particle as a core and a Cu ６４ O and Cu ８ and a shell containing one or more fine copper oxides selected from the group consisting of copper oxide, copper oxide, copper oxynitride ...

[0018] Aspect 10 of the present invention is the Cu ６４ O and Cu ８ The fine copper oxide-coated copper particles according to aspect 9, wherein the one or more fine copper oxides of O are fine copper oxide particles having an average particle size of more than 1 nm and not more than 20 nm.

[0019] An eleventh aspect of the present invention is the finely oxide-coated copper particle according to the ninth or tenth aspect, wherein the core copper particle has an average particle size of more than 20 nm and not more than 2 μm.

[0020] A twelfth aspect of the present invention is a bonding material comprising the fine copper oxide-coated copper particles according to any one of the ninth to eleventh aspects.

[0021] According to the present disclosure, Cu is useful for sintering at low temperatures. ６４ O and Cu ８ The present invention provides a method for mass-producing fine copper oxide-containing particles having one or more fine copper oxides selected from O at least on the surface thereof with good productivity.

[0022] FIG. 1 shows XRD patterns during the reaction process in Examples 1 to 3. FIG. 2 shows XRD patterns during the reaction process in Comparative Examples 1 to 3. FIG. 3 shows XRD patterns during the reaction process in Comparative Examples 4 to 6. FIG. 4 shows TEM images of the particles obtained in Examples 1 to 3. FIG. 5 shows XRD patterns during the reaction process in Example 1 (starting material Cu２ FIG. 6 is a STEM image of particles obtained in Example 2 (starting material CuO). FIG. 7 is an XRD pattern during the reaction process in Examples 4 to 6. FIG. 8 is an XRD pattern during the reaction process in Examples 7 and 8 and Comparative Example 7. FIG. 9 is an SEM image of particles after 24 hours of reaction with the starting material in Example 4. FIG. 10 is a TEM image of particles obtained in Example 4. FIG. 11 is a STEM image of particles obtained in Example 4, and the STEM image on the right is an enlarged image of each lattice plane spacing shown in the STEM image on the left. FIG. 12 is a SEM image of particles after 24 hours of reaction with the starting material in Example 5. FIG. 13 is a TEM image of particles obtained in Example 5. FIG. 14 is a TEM image of particles obtained in Example 6. FIG. 15 is a SEM image of particles after 24 hours of reaction with the starting material in Example 7. FIG. 16 is a TEM image of particles obtained in Example 7. FIG. 17 shows SEM images of the starting material of Example 8 and particles after 24 hours of reaction. FIG. 18 shows the TG-DTA measurement results for Example 4A. FIG. 19 shows the procedure for preparing a sample for bonding and firing evaluation for Example 4A. FIG. 20A is a schematic diagram of a copper test piece used to prepare the sample for bonding and firing evaluation for Example 4A. FIG. 20B is a schematic diagram of a metal mask used to prepare the sample for bonding and firing evaluation for Example 4A. FIG. 20C is a schematic diagram illustrating the hot pressing used in the bonding and firing evaluation test for Example 4A. FIG. 20D is a schematic cross-sectional view illustrating the method for the bonding and firing evaluation test for Example 4A. FIG. 21 shows the results of the bonding and firing evaluation test for Example 4A. FIG. 22 is an SEM image of a fracture surface observed after the bonding and firing evaluation test for Example 4A. FIG. 23 shows the temperature profile during hot pressing when the bonding time for Example 4A is 1 minute. FIG. 24 shows the results of conductivity evaluation for Example 4A. Fig. 25 shows XRD patterns before and after firing of the paste in the conductivity evaluation of Example 4A. Fig. 26 shows an SEM image of the fired product in the conductivity evaluation of Example 4A. Fig. 27 shows an XRD pattern during the reaction process of Example 9. Fig. 28 shows an SEM image of the starting material of Example 9 and particles after 24 hours of reaction. Fig. 29 shows a TEM image of the particles obtained in Example 9.

[0023] The present inventors have discovered that Cu is useful for low-temperature sintering. ６４ O and Cu ８ The present inventors have conducted extensive research to realize a method for mass-producing fine copper oxide-containing particles having at least one fine copper oxide of CuO on the surface thereof. ２ The present inventors have found that it is important to prepare raw material particles having copper oxide containing one or more of the following on their surfaces, and to mix the raw material particles with a solution containing a complexing agent during the manufacturing process. ６４ O and Cu ８ The present inventors have found fine copper oxide-coated copper particles having a shell containing one or more fine copper oxides selected from the group consisting of copper oxide, copper monoxide, copper oxide, copper oxide, and copper oxide-containing fine copper oxide particles. First, the production method according to this embodiment will be described in detail below.

[0024] [Cu ６４ O and Cu ８ Method for producing fine copper oxide-containing particles having one or more fine copper oxides selected from Cu and O at least on the surface thereof] ６４ O and Cu ８ The method for producing fine copper oxide-containing particles having at least one fine copper oxide selected from CuO and CuO at least on the surface thereof is as follows: ２ preparing raw material particles having copper oxide containing one or more of O on at least their surfaces; and mixing the raw material particles with a solution containing an amine compound and a complexing agent, then adding a reducing agent and reacting them in an oxygen-containing atmosphere.

[0025] The manufacturing method according to this embodiment is divided into the following first and second manufacturing methods depending on the form of the raw material particles.

[0026] The first manufacturing method is CuO and Cu ２ The method includes using particles made of copper oxide containing one or more of O as raw material particles, mixing the raw material particles with a solution containing an amine compound and a complexing agent, and then adding a reducing agent to cause a reaction. ６４ O and Cu ８ The present invention relates to a method for producing fine copper oxide-containing particles containing one or more fine copper oxides selected from the group consisting of copper oxides of 1 to 2.

[0027] The second manufacturing method is a method in which a copper raw material particle is used as a core, and CuO and Cu ２The method comprises: using copper oxide-coated copper raw material particles as raw material particles, the raw material particles having a shell formed of a copper oxide coating containing one or more of O; mixing the raw material particles with a solution containing an amine compound and a complexing agent; and then adding a reducing agent to cause a reaction. ６４ O and Cu ８ and a shell containing one or more fine copper oxides selected from the group consisting of copper oxide, copper oxynitride ...

[0028] The conditions for the manufacturing method according to this embodiment will be described in detail below.

[0029] [Step of Preparing Raw Material Particles] First, CuO and Cu ２ In the first manufacturing method, raw material particles having copper oxide containing one or more of CuO and CuO on at least the surface are prepared. ２ The raw material particles are made of copper oxide containing one or more of CuO and CuO. ２ The raw material particles of the first production method may be copper oxide raw material particles consisting of one or more of Cu, O, ２ The copper oxide raw material particles are composed of O.

[0030] In the second manufacturing method, the raw material particles are composed of copper raw material particles as a core, CuO and Cu ２ The copper oxide-coated copper raw material particles are prepared, each having a copper oxide coating containing at least one of CuO and Cu as a shell. ２ Copper oxide consisting of one or more of O, more preferably Cu ２ Preferably, the copper raw material particles are core-shell type copper oxide-coated copper particles coated with copper oxide consisting of O.

[0031] As the copper oxide-coated copper raw material particles, which are raw material particles in the second production method, commercially available products may be used, or particles on which a surface oxide film is formed by natural oxidation of copper particles may be used, or particles on which a surface oxide film is formed by subjecting the surface of copper particles to an oxidation treatment may be used. Alternatively, copper raw material particles on which no or almost no copper oxide is formed on the surface may be coated with CuO and Cu. ２Alternatively, copper oxide-coated copper raw material particles may be used, which are obtained by adding copper oxide containing one or more of O (e.g., copper oxide in powder form) to a dispersion containing the copper raw material particles, applying the copper oxide to the dispersion, or the like. Note that the surface oxide film formed by natural oxidation is formed only when the metallic copper particles are in the atmosphere. Therefore, it is believed that commercially available metallic copper particles also undergo natural oxidation due to their presence in the atmosphere, and commercially available metallic copper particles are included in the raw material particles of the second production method, which are copper particles having a surface oxide film formed by natural oxidation.

[0032] In the manufacturing method of this embodiment, the size of the raw material particles is not limited. ２ The raw material particles made of copper oxide containing one or more of O may have an average particle size of, for example, 20 nm to 10 μm. ２ From the viewpoint of suppressing the remaining O, the average particle size of the raw material particles in the first production method is preferably 10 μm or less as described above. In the case of the second production method, the average particle size of the core copper raw material particles may be, for example, 20 nm to 2 μm. In addition, CuO and Cu present on the surface of the core copper raw material particles ２ The copper oxide coating containing one or more of O may have a coating thickness of 20 nm or less. In this specification, the term "particle size" refers to the primary particle size and the circle-equivalent diameter, and the term "average particle size" refers to the median diameter of 150 or more particles randomly selected from an SEM image or a TEM image.

[0033] In the second manufacturing method, CuO and Cu present on the surface of the raw material particles ２ Copper oxide (preferably Cu) containing one or more of O ２ The copper oxide coating of the raw material particles may be thicker than the natural oxide coating. For example, the copper oxide coating of the raw material particles may be thicker than the natural oxide coating. For example, the copper oxide coating of the raw material particles may be thicker than the natural oxide coating. ２ The proportion of copper oxide containing one or more of O can be 1 mass % or more. ６４ O and Cu ８When it is desired to form a thick shell containing one or more fine copper oxides of O, the raw material particles may be actively oxidized. In this case, if the amount of copper oxide on the surface of the raw material particles is too large, Cu may be present in the core copper particle. ６４ O and Cu ８ The shell containing one or more fine copper oxides of CuO is difficult to adhere. ６４ O and Cu ８ The shell containing one or more fine copper oxides of CuO has lower crystallinity when sintered at low temperatures compared to the core copper particles having high crystallinity, and therefore, if the shell is thick, there is a concern that the mechanical strength and electrical conductivity may decrease. ２ The proportion of copper oxide containing one or more of O is preferably 10 mass % or less.

[0034] [Reaction Step] The raw material particles are mixed with a solution containing an amine compound and a complexing agent, and then a reducing agent is added to cause a reaction. The complexing agent and other components required for the reaction will be described below as described above.

[0035] (Complexing Agent) In this embodiment, the copper oxide contained in the raw material particles is reacted with a complexing agent to form copper complex ions. By ionizing the copper in the raw material particles in this manner, the reduction rate by the reducing agent can be significantly faster than the reduction of solid copper oxide. Examples of the complexing agent include carboxylic acids. Examples of carboxylic acids include formic acid, saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, and terpene carboxylic acids. These may be monocarboxylic acids or dicarboxylic acids. These may be used alone or in combination of two or more. The aliphatic monocarboxylic acid may be either linear or branched, and may be either saturated or unsaturated. Examples of linear saturated aliphatic monocarboxylic acids include acetic acid (carbon number 2), propionic acid (carbon number 3), butyric acid (carbon number 4), valeric acid (carbon number 5), and caproic acid (carbon number 6).

[0036] The aliphatic dicarboxylic acid may be either linear or branched, and may be either saturated or unsaturated. The aliphatic dicarboxylic acids may be used alone or in combination of two or more. Examples of aliphatic dicarboxylic acids include adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,0-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, brassylic acid, 1,12-dodecanedicarboxylic acid, 1,13-tridecanedicarboxylic acid, thapsic acid, 1,15-pentadecanedicarboxylic acid, and 1,16-hexadecanedicarboxylic acid. Examples of aromatic carboxylic acids include benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, hemimellitic acid, trimellitic acid, and trimesic acid. Terpene carboxylic acids that can be used include those contained in rosin. Examples include abietic acid, neoabietic acid, palustric acid, pimaric acid, isopimaric acid, and desidroabietic acid.

[0037] Among these, it is preferable to use acetic acid, which is easy to handle and easy to treat after the reaction.

[0038] The amount of the complexing agent used in the reaction is not particularly limited. ６４ O and Cu ８ From the viewpoint of promoting the formation of copper complex ions to promote the generation of O, the molar ratio of the amount of copper contained in the starting material particles is preferably 2 to 15 times.

[0039] (Amine Compound) A compound having an amino group (hereinafter referred to as "amine compound") is added as a protective agent. The amine compound also contributes to the formation of copper complex ions. The amine compound is not particularly limited, and it is preferable to use, for example, alkanolamine, diamine, aminocarboxylic acid, etc. Among them, it is more preferable to use alkanolamine. Examples of alkanolamine include 2-amino-1-butanol, 1-amino-2-propanol, 2-amino-2-ethyl-1,3-propanediol, 2-amino-2-hydroxymethyl-1,3-propanediol, 1,3-diamino-2-propanol, 1-amino-2-butanol, and 2-aminoethanol.

[0040] The amount of the amine compound used in the reaction is not particularly limited. ６４ O and Cu ８ From the viewpoint of promoting the generation of O, the molar ratio of the amine compound to the copper contained in the raw material particles is preferably 5 times or more. The molar ratio may be, for example, 20 times or less.

[0041] (Solvent) The solvent is not particularly limited, and examples thereof include polyhydric alcohols such as ethylene glycol, lower alcohols such as methanol, ethanol, and 2-propanol, ketones such as acetone, and water.

[0042] (Reducing Agent) The reducing agent is not particularly limited, and examples thereof include hydrazine-based reducing agents such as hydrazine, hydrazine hydrochloride, hydrazine sulfate, and hydrazine hydrate, as well as citric acid, ascorbic acids, and borohydrides such as sodium borohydride. The reducing agent may be added after the raw materials containing the raw material particles, complexing agent, amine compound, and solvent are charged and mixed. After adding the reducing agent, in the first production method, stirring is carried out at least until the raw material particles disappear, and in the second production method, stirring is carried out until the formation of the desired fine copper oxide is confirmed. In either production method, stirring is preferably carried out until the reducing agent disappears, allowing the reaction to proceed sufficiently.

[0043] (Cooling during reaction) In the production method according to the present embodiment, for example, when hydrazine is used as a reducing agent, heat is generated by the addition of the reducing agent, such as a decomposition reaction of hydrazine, and the temperature of the reaction solution may rise. ６４ O and Cu ８ From the viewpoint of suppressing the reduction of O to metallic copper, it is preferable to provide a temperature control means, such as cooling the reaction solution, so that the reaction proceeds at 50° C. or less. For example, as shown in the examples described later, it is preferable to add the reducing agent while the reaction vessel is bathed in water.

[0044] (Atmosphere during reaction) In the manufacturing method according to this embodiment, the atmosphere during the reaction is limited to an oxygen-containing atmosphere such as the air, and it is necessary to always expose the reaction vessel to the oxygen-containing atmosphere during the reaction. When an inert gas atmosphere such as nitrogen gas or argon gas is used, or when the reaction vessel is sealed even in the air, Cu ６４ O or Cu ８ This is not preferable because the reaction of forming oxides to O does not proceed and metallic copper particles are formed.

[0045] (Other Steps) The manufacturing method of this embodiment may further include steps other than those described above. For example, Cu obtained by the reduction may be ６４ O and Cu ８ The method may include a step of recovering fine copper oxide-containing particles by, for example, centrifuging or filtering a slurry containing particles having one or more fine copper oxides selected from O, followed by a purification step, a drying step, etc. In the purification step, purification is preferably performed using a washing solvent. The washing solvent is not particularly limited, and organic solvents such as N,N-dimethylacetamide, toluene, and hexane can be used.

[0046] According to the first manufacturing method, Cu ６４ O and Cu ８ As the fine copper oxide-containing particles having one or more fine copper oxides of O, particularly Cu ６４ O and Cu ８ The fine copper oxide particles obtained by the first production method are composed of one or more of Cu, O, and Cu. ６４ O and Cu ８Fine copper oxide-containing particles having one or more fine copper oxides of O (preferably Cu ６４ O and Cu ８ The average particle size of the copper oxide particles (fine copper oxide particles consisting of one or more of copper oxide particles, ...

[0047] According to the first production method, a fine copper oxide-containing particle composition can be obtained in which copper clusters having an average particle size of 0.1 nm to 1 nm are present together with the fine copper oxide-containing particles. The average particle size of the copper clusters can be 0.15 nm to 0.7 nm, or even 0.17 nm to 0.5 nm. Such copper clusters are typically formed by aggregating approximately 3 to 6 copper atoms. As described above, copper clusters are aggregates of an extremely small number of atoms and have extremely small particle sizes, resulting in a low melting point due to the nanosize effect. Therefore, such copper clusters have high sinterability.

[0048] In this embodiment, the obtained fine copper oxide-containing particles contain Cu. ６４ O and Cu ８ The presence of one or more fine copper oxides of O can be confirmed by STEM observation, as will be shown in the examples described later. ６４ O and Cu ８ The same is true for O.

[0049] [Fine-Oxide Coated Copper Particles] The fine-oxide coated copper particles according to this embodiment comprise a copper particle as a core and a Cu ６４ O and Cu ８ and a shell containing one or more fine copper oxides of Cu. ６４ O particles and Cu ８ In the case of a composition containing at least one of fine copper oxide particles, metallic copper particles, and copper clusters, it has been difficult to uniformly disperse these. In particular, when the fine copper oxide particles are fine particles with an average particle size of 20 nm or less, the fine particles tend to aggregate and are difficult to disperse. In contrast, the fine copper oxide-coated copper particles according to this embodiment have a Cu ６４ O and Cu ８The copper oxide-coated copper particles according to this embodiment have a core-shell structure in which one or more fine copper oxides of O are attached to the surface of the metallic copper particle as, for example, a coating, thereby solving the above-mentioned dispersion problem. ６４ Sintering between fine copper oxide particles such as O is promoted, and a sintered body exhibiting high electrical conductivity can be easily produced.

[0050] In the fine copper oxide-coated copper particles according to this embodiment, the size of the copper particles constituting the core is not limited, and may have an average particle size of, for example, 20 nm to 2 μm. The average particle size may be greater than 20 nm. However, when used in printable electronics, for example, coarse particles may cause a decrease in print quality, so the average particle size is preferably 2 μm or less.

[0051] Cu forming the shell ６４ O and Cu ８ The fine copper oxide of one or more of O may be in the form of a film or a plurality of particles. When it is in the form of a plurality of particles, the average particle size of the particles may be, for example, 1 nm to 20 nm. The thickness of the shell (the thickness of the film or the thickness of the deposition of the plurality of particles) may be, for example, 1 to 20 nm. Cu ６４ O and Cu ８ The shell containing one or more fine copper oxides of O is reduced to copper by sintering, but since its crystallinity is not as high as that of the core copper particles, if the shell is too thick, there is a concern that the mechanical strength and electrical conductivity will decrease. From these points of view, it is preferable that the shell thickness is 20 nm or less as described above.

[0052] The shell contains Cu ６４ O and Cu ８ In addition to one or more fine copper oxides of O, for example, CuO, Cu ２ It is acceptable for copper oxides such as CuO and CuO to be contained in trace amounts at a level that does not impair sinterability or electrical conductivity. ２ The shell preferably does not contain copper oxide such as Cu. ６４ O and Cu ８ O, and more preferably Cu６４ O or Cu ６４ O and Cu ８ It is formed from copper oxide consisting of O.

[0053] The fine copper oxide-coated copper particles can be produced by the second production method described above, but are not limited thereto, and may be produced by a method different from the second production method.

[0054] The fine copper oxide-coated copper particles according to this embodiment contain Cu ６４ O and Cu ８ O on the surface, and has high sinterability. That is, by using the finely oxide-coated copper particles according to this embodiment, a sufficiently sintered body can be obtained under normal pressure (or a higher pressure) at 250°C or less, further 200°C or less, further 150°C or less, and even at a relatively low temperature of room temperature to 130°C. Furthermore, the finely oxide-coated copper particles according to this embodiment have a core made of metallic copper, and do not contain CuO or Cu. ２ Since the content of copper oxide, which can increase the resistance of O etc., is reduced, the fine copper oxide coated copper particles can be sintered to obtain a sintered body exhibiting high electrical conductivity.

[0055] The sintering material may be, for example, a paste or ink containing the fine copper oxide-coated copper particles according to this embodiment, intended for forming a conductive film, etc. Known materials may be used as the dispersion medium, binder, etc. contained in the paste or ink.

[0056] The present disclosure also includes a bonding material containing the finely oxide-coated copper particles according to this embodiment. Examples of the bonding material include a paste or ink containing the finely oxide-coated copper particles according to this embodiment. Known materials can be used as the dispersion medium, binder, and the like contained in the paste or ink. A bonding material containing the finely oxide-coated copper particles according to this embodiment can be applied to and bonded to bonding surfaces of multiple materials, such as metals (pure metals, alloys), ceramics, and the like, to obtain a bonded body with high adhesive strength.

[0057] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples, and can be practiced with appropriate modifications within the scope of the above-mentioned and below-mentioned aims, and all such modifications are included in the technical scope of the present invention.

[0058] [1] Production Examples According to First Production Method In Examples 1 to 3, copper oxide microparticles were produced using the starting materials shown in Table 1. Specifically, ethylene glycol (Kanto Chemical Co., Ltd.) as a solvent, 1-amino-2-propanol (AmIP, Kanto Chemical Co., Ltd.) as an amine compound, and acetic acid (Junsei Chemical Co., Ltd.) as a complexing agent were placed in a reaction vessel and thoroughly stirred. ２ Copper oxide II (CuO, manufactured by Nisshin Chemco, NB-2, particle size 0.1 to 1 μm) or copper oxide II (CuO, manufactured by Nisshin Chemco, NB-2, particle size 0.1 to 1 μm) was added.

[0059] With the reaction vessel in a water bath, hydrazine monohydrate (manufactured by Kanto Chemical) was added as a reducing agent, and the reaction was carried out while stirring at 1,100 rpm. The reaction was carried out in the air. To confirm the difference between lab-scale and mass production, the starting material was used at two levels: 1 g of copper equivalent (Examples 1 and 2) and 100 g of copper equivalent (Example 3). The obtained product was purified by multiple centrifugation using N,N-dimethylacetamide, toluene, and hexane, to obtain a slurry containing the product.

[0060] As comparative examples, in Comparative Examples 1 to 3, copper acetate II anhydride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as the starting material and the amount of the amine compound was changed; in Comparative Examples 4 and 5, copper oxide was used as the starting material and no complexing agent was added; and in Comparative Example 6, the reaction vessel was not cooled in a water bath. Except for this, a slurry containing a product was obtained by reaction in the same manner as in the Examples.

[0061] As shown in Table 1, the amount of the amine compound added is 5 times or more the molar ratio of the amine compound to copper to obtain the target Cu. ６４ O and Cu ８ The rapid production of O was confirmed separately, and in Examples 1 to 3, the amount was set to 10 times.

[0062]

[0063] (X-ray Diffraction Measurement) Using the slurry containing the product, X-ray diffraction measurement was performed using a powder X-ray diffractometer (XRD, Rigaku MiniFlex II, D / teX Ultra) to obtain the XRD measurement results of the reaction process. The measurement was performed using Cu-Kα radiation at a scan rate of 20° min －１ The results are shown in Figure 1 for Examples 1 to 3, Figure 2 for Comparative Examples 1 to 3, and Figure 3 for Comparative Examples 4 to 6. In the XRD measurement results for the reaction process, "0 h" indicates the time of addition of the reducing agent, and for example, "1 h" indicates the measurement result 1 hour after the addition of the reducing agent. Comparative Examples 1 to 3 in Figure 2 show the reaction of copper II acetate anhydride, which is the starting material, to Cu. ６４ O and Cu ８ In order to observe the reaction process to O, the results of XRD measurement at 2θ = 0 to 55°, including 2θ = 10°, which is the peak position of copper II acetate anhydride, are shown. In the examples other than Comparative Examples 1 to 3 in which the starting material is copper oxide, the results of XRD measurement at 2θ = 30 to 80° are shown.

[0064] (Electron Microscope Observation) In the electron microscope observation, the obtained product was observed with a scanning electron microscope (SEM, JEOL Ltd. JSM-6701F, accelerating voltage 15 kV) to obtain an SEM image, observed with a transmission electron microscope (TEM, JEOL Ltd. JEM-2000FX, accelerating voltage 200 kV) to obtain a TEM image, and further observed with a scanning transmission electron microscope (STEM, JEM-ARM200F, accelerating voltage 200 kV) to obtain a STEM image. The TEM and STEM observations were carried out in a state in which the fine particles were dispersed to prevent aggregation.

[0065] In this production example, as a result of the above-mentioned electron microscope observation, the TEM images of Examples 1 to 3 are shown in FIG. 4, and Example 1 (wherein the starting material is Cu) ２ FIG. 5 shows an STEM image of Example 1 (wherein the starting material is CuO), and FIG. 6 shows an STEM image of Example 2 (wherein the starting material is CuO).

[0066] The above results reveal the following: First, in Examples 1 and 2, in which the starting material was copper oxide raw material particles on a 1 g scale and acetic acid was added as a complexing agent, particles with a particle diameter of about 5 nm were formed from the TEM images in Figures 4A and 4B, and these particles were found to be Cu particles from the XRD patterns in Figure 1.６４ O and Cu ８ It can be seen that the particles contain O. From the STEM images in Figs. ６４ In Example 3, which is 100 times larger than Example 1, the TEM image in FIG. 4C and the XRD pattern in FIG. 1 show that particles with a diameter of about 10 nm are included, but they are generally similar to Cu. ６４ O and Cu ８ It was confirmed that particles containing O were obtained.

[0067] On the other hand, when copper acetate II was used as the starting material as in Comparative Examples 1 to 3, the XRD patterns shown in FIG. ６４ O and Cu ８ Although particles containing O were produced, the weight and bulk of the raw materials were large, and when dissolving the starting materials in a solvent, techniques such as ultrasonic dispersion while stirring manually were required, making mass production unsuitable. In these comparative examples, acetic acid was not added as a complexing agent, but water and acetic acid were released during the reaction process, so it is thought that the reaction proceeded in the same way as in the examples. On the other hand, in comparative examples 4 and 5, in which copper oxide raw material particles were used as the starting material and acetic acid was not added as a complexing agent, Cu was not produced, as shown in the XRD measurement results of the reaction process shown in Figure 3. ６４ O and Cu ８ No O was observed, and the main product was metallic copper. These results demonstrate that acetic acid is necessary as a complexing agent to produce copper particles containing fine copper oxide. Furthermore, the STEM dark-field images shown in Figures 5 and 6 confirm the presence of numerous white bright spots, indicating the presence of copper clusters of approximately 0.2 nm.

[0068] From the above, by using copper oxide particles as a starting material and adding acetic acid as a complexing agent, it is possible to obtain the desired Cu ６４ O and Cu ８ It was confirmed that particles containing O and copper clusters were obtained.

[0069] From the comparison between Example 1 and Example 2, it is preferable to use Cu as the starting material. ２ By using O, the reaction occurred quickly and the time required for the reaction was shortened. ２Compared with the prior art in which copper II acetate was used as the starting material, the method using O reduces the raw material weight by 0.4 times and the bulk by 0.125 times. Furthermore, it does not require the step of dissolving copper II acetate in a solvent as a pre-reaction step, making it easier to handle the raw materials, and therefore it can be said to be a production method that is particularly suitable for mass production.

[0070] In Comparative Example 6, in which the reaction solution was not cooled, the solution temperature rose to a maximum of 53.8°C in about 90 minutes after the start of the reaction. At 70 minutes after the start of the reaction, the solution temperature exceeded 50°C, and a copper luster color began to appear on the wall of the reaction vessel. As can be seen from the XRD pattern shown in Figure 3, at the beginning of the reaction after 1 hour, Cu ６４ Although a peak for O was observed, no peaks other than copper were observed after 2 hours had passed, which indicated that it was desirable to cool the reaction solution to 50° C. or less.

[0071] [2] Production Example According to Second Production Method (Preparation of Starting Material) As copper oxide-coated metallic copper raw material particles having different types of oxide coating, Taiyo Nippon Sanso copper particles TN-Cu100 (particle diameter 50-200 nm), acetate-coated copper particles (particle diameter 50-200 nm), and Kanto Chemical copper particles 07439-01 (particle diameter 1-10 μm) were used. These particles were used as the starting material either as is or after undergoing the oxidation treatment described below. The copper oxide formed on the surface of the starting material was quantitatively measured by the RIR method of XRD. The results are shown in Table 2. The Taiyo Nippon Sanso copper particles used as the starting material in Example 4 are commercially available products and contain Cu from the initial state. ２ It is characterized by having an O layer. ２ The O layer was confirmed to be 1.5 mass %.

[0072] The acetate-coated copper particles used as the starting material for Example 5 were produced by a liquid-phase reduction method using the following procedure. 1 mol of copper oxide II (NB-2 manufactured by Nisshin Chemco) was added as a raw material, 1 L of ethyl carbitol (manufactured by Sankyo Chemical) was added as a solvent, and 60 mmol of acetic acid was added as a protective agent. The mixture was heated to 70°C, and then 2 mol of hydrazine monohydrate (manufactured by Kanto Chemical) was added and reacted for 1 hour with stirring. After the reaction, the mixture was purified twice each using acetone and methanol, and then vacuum dried to obtain copper powder. The resulting copper powder was subjected to an oxidation treatment by exposure to air at room temperature for 44 hours, resulting in 2.2 mass% of Cu as the acetate-coated copper particles used as the starting material for Example 5. ２ Copper microparticles having an O layer were obtained. Note that, since oxidation of the copper on the surface of these acetic acid-coated copper particles was inhibited, it is believed that acetic acid was present on the surface.

[0073] The Kanto Chemical copper particles used as the starting material for Examples 6 to 8 were also commercially available. Initially, no oxides were detected by XRD, but the surface was thought to be slightly naturally oxidized. In Example 6, these copper raw material particles with slightly naturally oxidized surfaces were used as the starting material. In Example 7, as an oxidation treatment, the Kanto Chemical copper particles were placed in a thermo-hygrostat maintained at 80°C and 80% RH for 48 hours, and copper oxide-coated metallic copper raw material particles with a 1.1% by mass CuO layer were used as the starting material. Furthermore, in Example 8, as another oxidation treatment, 0.5 mol of the Kanto Chemical copper particles were added to 500 g of ultrapure water, heated to boiling at 100°C for 90 minutes, and 3.4% by mass CuO was formed. ２ The starting material was copper oxide-coated metallic copper raw material particles on which an O layer had been formed.

[0074] (Production of Core-Shell Microparticles) Using the above starting materials, a reaction was carried out using the solvents and other additives shown in Table 2 in the amounts shown. Specifically, ethylene glycol (Kanto Chemical) as a solvent, 1-amino-2-propanol (AmIP, Kanto Chemical) as an amine compound, and acetic acid (Junsei Chemical) as a complexing agent were placed in a reaction vessel, and after thorough stirring, the above starting materials were added. With the reaction vessel immersed in a water bath, hydrazine monohydrate (Kanto Chemical) was added as a reducing agent, and the reaction was carried out while stirring at 1100 rpm. The reaction was carried out in the air. After the reaction, purification was carried out by centrifugation multiple times using N,N-dimethylacetamide, toluene, and hexane, and a slurry containing the product was obtained. As a comparative example, in Comparative Example 7, a slurry containing the product was obtained in the same manner as in Example 4, except that no complexing agent was added.

[0075]

[0076] (X-ray Diffraction Measurement) Using the slurry containing the product, X-ray diffraction measurement of the reaction process was carried out in the same manner as in the Production Example relating to Production Method 1 above [1]. The results are shown in Figure 7 for Examples 4 to 6, and in Figure 8 for Examples 7, 8, and Comparative Example 7.

[0077] (Electron Microscope Observation) The obtained product was subjected to SEM observation, TEM observation, and STEM observation in the same manner as in the above-mentioned [1] Production Example according to the first production method.

[0078] From the X-ray diffraction measurements and electron microscope observations, the following was confirmed for each example. First, for Example 4, from the XRD pattern of the reaction process in FIG. 7, it was found that in this example, Taiyo Nippon Sanso copper particles with a particle size of 50 to 200 nm and an oxide film of 1.5 mass % were used as the starting material, and acetic acid was used, Cu was also added in addition to the copper of the starting material. ６４ O and Cu ８The generation of O was confirmed. SEM images of the starting material in Example 4 and the particles after 24 hours of reaction are shown in Figure 9. A in Figure 9 shows the starting material, and B in Figure 9 shows the particles after 24 hours of reaction. Comparing these photographs, it was confirmed that what is thought to be fine oxides formed by the reaction were attached to the periphery of the copper raw material particles of the starting material. Figure 10 shows a TEM image of the particles obtained in Example 4. Figure 11 shows a STEM image of the particles obtained in Example 4. From the TEM image in Figure 10, it can be seen that the particles produced are core-shell shaped, and from the lattice spacing confirmed in the STEM image in Figure 11, the core portion is copper, and the surface of the core is Cu with a particle diameter of about 3 nm. ６４ O and Cu ８ It was confirmed that the nanoparticles were covered with a shell of O-containing nanoparticles.

[0079] On the other hand, in Comparative Example 7, the reaction was carried out under the same conditions as in Example 4 except that acetic acid was not added. ６４ O and Cu ８ No O was detected and the only product was metallic copper. This confirmed that acetic acid as a complexing agent was necessary for producing the oxide-containing particles according to this embodiment.

[0080] Next, in Example 5, from the XRD pattern of the reaction process in FIG. 7, when copper oxide-coated metallic copper raw material particles having an oxide film of 2.2 mass % were used as the starting material, Cu was also produced in addition to the copper of the starting material, as in Example 4. ６４ O and Cu ８ It was confirmed that O was produced. SEM images of the starting material of Example 5 and the particles after 24 hours of reaction are shown in Figure 12. A in Figure 12 shows the starting material, and B in Figure 12 shows the particles after 24 hours of reaction. A TEM image of the particles obtained in Example 5 is shown in Figure 13. These SEM and TEM images also show that the surface of the core copper particles is covered with Cu. ６４ O and Cu ８ It was confirmed that the nanoparticles were covered with a shell of O-containing nanoparticles.

[0081] Examples 6 to 8 are examples using copper particles manufactured by Kanto Chemical. From the XRD patterns of the reaction process shown in FIGS. 7 and 8, it can be seen that regardless of whether or not the copper particles manufactured by Kanto Chemical were subjected to oxidation treatment, Cu ６４ O and Cu ８It was confirmed that O was produced. A TEM image of the particles obtained in Example 6 is shown in Figure 14. SEM images of the particles obtained in Example 7 after 24 hours of reaction with the starting material are shown in Figure 15. A in Figure 15 shows the starting material, and B in Figure 15 shows the particles after 24 hours of reaction. A TEM image of the particles obtained in Example 7 is shown in Figure 16. Furthermore, a SEM image of the particles obtained in Example 8 after 24 hours of reaction with the starting material is shown in Figure 17. A in Figure 17 shows the starting material, and B in Figure 17 shows the particles after 24 hours of reaction. As shown in Figures 14 to 17, the surface of the core copper particles is covered with Cu. ６４ O and Cu ８ It was confirmed that the nanoparticles were covered with a shell of O-containing nanoparticles.

[0082] From the above confirmation, the following can be said: In the above-mentioned Examples 1 to 3, Cu was efficiently produced from copper oxide. ６４ O and Cu ８ Considering that CuO and CuO were generated on the surface of the starting material, it is preferable that the starting material be copper oxide-coated metallic copper raw material particles having a surface oxide layer in order to efficiently generate core-shell particles having a shell containing fine copper oxide. Even in Example 6, which had a surface oxide layer of natural oxidation that could not be detected by XRD, sufficient shell formation was confirmed from the TEM image shown in Figure 14. This indicates that CuO and CuO present on the surface of the starting material ２ The copper oxide coating containing one or more of O is sufficient if it is an oxide coating at a natural oxidation level that is undetectable by X-ray diffraction. ６４ O and Cu ８ When it is desired to form a thick shell containing one or more fine copper oxides of O, by using starting material particles whose surfaces have been actively oxidized as in Examples 5, 7 and 8, fine copper oxide-coated copper particles with a thick shell can be formed.

[0083] In addition, the results of RIR quantitative measurement of the particles obtained in Examples 4 to 8 showed that Cu ６４ O and Cu ８ Since the quantitative value of O is greater than the amount calculated from the amount of oxide contained in the starting material, oxidation and complex formation of the metallic copper particles, which are the starting material, occurs in the reaction solution, resulting in Cu ６４ O and Cu ８ It was also revealed that a reaction producing O occurred.

[0084] When it is desired to form core-shell particles having a shell of fine copper oxide with a small core particle diameter and a large surface area ratio, and to form a thick shell, the starting material must have a larger surface oxide layer, and it is desirable to have a surface oxide layer of 1.5% by mass to 2.2% by mass, as in Examples 4 and 5.

[0085] From the above, when producing core-shell particles having a shell of fine copper oxide, Cu ２ The starting material is copper particles having a copper oxide coating of one or more of O and CuO, and by adding acetic acid as a complexing agent, the copper particles as cores and Cu particles with a diameter of 20 nm or less are separated. ６４ O and Cu ８ It has been confirmed that core-shell type fine copper oxide-coated copper microparticles can be obtained, which have a shell composed of nanoparticles containing O. According to this method, it is possible to easily obtain core-shell type fine copper oxide-coated copper microparticles in which the surfaces of copper particles of submicron to micron size are covered with nanoparticles containing fine copper oxide, which was not possible with conventional mixing methods.

[0086] The method according to this embodiment can be used not only for submicron copper particles but also for micron-order copper particles, i.e., core-shell type fine copper oxide-coated copper microparticles in which the surfaces of micron-order copper particles are covered with nanoparticles containing fine copper oxide can be obtained. Furthermore, the fine copper oxide-coated copper particles according to this embodiment have the advantage that the fine copper oxide particles are easily settled, and the particles can be easily recovered during purification, since the fine copper oxide particles are attached to the core copper particles.

[0087] In the firing of the copper paste containing the copper particles coated with fine copper oxide according to this embodiment, Cu ６４ O and Cu ８ The shell composed of O nanoparticles is easily reduced to metallic copper, and adjacent copper particle cores are densely connected, dramatically accelerating sintering between core particles. The resulting sintered body has a structure in which highly crystalline copper particle cores are densely connected, and is expected to exhibit excellent mechanical strength and high electrical conductivity.

[0088] [3] Another Production Example According to the Second Production Method (Example 4A) Example 4A is an example in which the synthesis scale of Example 4 was changed.

[0089] (Production of Core-Shell Microparticles) The core-shell type copper oxide-coated copper microparticles used in this production example were synthesized in the same manner as in Example 4, except that the starting materials, 1-amino-2-propanol (AmIP), acetic acid, hydrazine monohydrate, and ethylene glycol (EG) were each added in 100-fold amounts, to obtain a slurry containing copper oxide-coated copper microparticles as a product in hexane. The weight of the copper oxide-coated copper microparticles in the slurry was calculated in advance using the following formula (1):

[0090]

[0091] In formula (1), Y: weight of particles in the slurry (g) M ｓ V: Slurry weight (g) ｓ : Slurry volume (cm ３ ) ρ ｍ : Solvent density (g / cm ３ ) ρ Ｃｕ : Copper density (g / cm ３ )

[0092] (Production of paste containing core-shell microparticles) The solvent of the slurry containing the synthesized finely oxide-coated copper microparticles was replaced from hexane to ethanol by centrifugation. This was further centrifuged to remove the ethanol supernatant, yielding a wet cake of finely oxide-coated copper microparticles. 7.5 parts by weight of triethanolamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to 92.5 parts by weight of the finely oxide-coated copper microparticles in the wet cake (the value calculated by formula (1)). After addition, the mixture was stirred for 4 minutes using a planetary mixer (AR-100 manufactured by Thinky), and then dispersed intermittently for 3 minutes using a thin film gyration high-speed mixer (Filmix 56-L manufactured by Primix) to obtain a paste after dispersion treatment. The obtained paste after dispersion treatment was divided into small portions, and different amounts of triethanolamine were further added to each portion to adjust the concentration, followed by stirring for 8 minutes using a planetary mixer. The mixture was then held at room temperature in a vacuum until no weight change was observed, and the ethanol was removed, yielding five levels of paste with different concentrations of finely oxide-coated copper microparticles.

[0093] The obtained pastes were subjected to thermogravimetry and differential thermal analysis (TG-DTA) at a heating rate of 5°C / min in a 3% hydrogen / nitrogen mixed gas using a Shimadzu TG / DTA simultaneous measurement device. The results are shown in Figure 18. From the weight loss shown by the TGA in Figure 18, it was confirmed that the five levels of paste obtained contained 91.3 wt%, 89.8 wt%, 87.6 wt%, 84.4 wt%, and 83.0 wt% of finely oxide-coated copper microparticles, respectively. Hereinafter, the concentration of the finely oxide-coated copper microparticles contained in the paste may be referred to as the "paste concentration."

[0094] (Bonding and Firing Evaluation) Two copper test pieces were bonded together using the paste, and a bonded and sintered bonding evaluation sample was prepared by sintering the paste, and the adhesive strength was measured.

[0095] 1. Preparation of Samples for Bonding and Sintering Evaluation The preparation procedure for the samples for bonding and sintering evaluation is as shown in Figure 19. First, circular copper test pieces, Copper Test Piece 1 with a diameter of 12 mm and Copper Test Piece 2 with a diameter of 5 mm, were cut out from a 5 mm thick oxygen-free copper plate (C1020P), as shown in Figure 20A. The surface of each copper test piece was polished with waterproof abrasive paper (SiC paper) P4000, then mirror-finished (buffed) with a polishing cloth soaked in a suspension of 0.5 μm alumina powder, and degreased. Before applying the paste, each copper test piece was immersed in 2.5 M hydrochloric acid to remove the copper oxide film on the surface, thoroughly washed with pure water and methanol, and dried.

[0096] Next, metal mask printing was performed. Specifically, a metal mask having an opening size of 5 mm in diameter x 0.15 mm in thickness, as shown in FIG. 20B, was used. As shown in FIG. 20C, the paste (paste containing 91.3 wt% finely oxidized copper-coated copper fine particles) 3 was applied to the center of a 12 mm diameter copper test piece 1, and then bonded to a 5 mm diameter copper test piece 2. Then, a load of 15 MPa was applied to the two bonded copper test pieces in the direction of the arrow in FIG. 20C using a hot press, and the temperature was rapidly increased to 200 ° C. at 90 ° C. / min. The temperature was maintained at 200 ° C. after the paste was fired. The holding time from reaching 200 ° C. was set to four levels: 1 minute, 5 minutes, 10 minutes, or 15 minutes. After holding at 200 ° C., the test pieces were removed from the hot press and rapidly cooled to room temperature. The copper test pieces were bonded together by the sintered product formed by firing the paste. A sample for bonded firing evaluation was obtained. The entire process from printing the metal mask to firing and rapid cooling to room temperature was carried out in a nitrogen atmosphere.

[0097] 2. Bonding and Sintering Evaluation Test (Adhesive Strength Measurement) The adhesive strength of the bonding and sintering evaluation sample was evaluated using a 5 kN materials testing machine (Shimadzu Corporation). Specifically, as shown in the schematic cross-sectional view in FIG. 20D , a load was applied parallel to the coated surface of the bonding and sintering evaluation sample fixed to the fixture 4 of the testing machine at a rate of 1 mm / min, and the breaking load of the copper test piece was measured as adhesive strength. The results are shown in FIG. 21 as a graph illustrating the relationship between the holding time (bonding time) from reaching 200°C and the breaking load (adhesive strength). The vertical width of each measurement in FIG. 21 indicates the variation between two and four measurements. As shown in FIG. 21 , extremely high adhesive strengths of 66 MPa or more were obtained with a bonding time of 5 minutes or more, and sufficient adhesive strength of 47 MPa was obtained even with a bonding time of 1 minute.

[0098] Figure 22 shows an SEM image of the fracture surface of a sample for evaluation of bonding and sintering after a bonding time of 1 minute. From Figure 22, it was confirmed that the particles were densely sintered. Figure 23 shows the temperature profile in hot pressing when the bonding time was 1 minute. As shown in Figure 23, when the bonding time was 1 minute, the bonding process was a short process, with the time from the start of heating to cooling being approximately 8 minutes. It was proven that a paste containing the finely oxide-coated copper microparticles of this embodiment could produce a firmly sintered fired product even in such an extremely short time.

[0099] (Evaluation of Conductivity (Electrical Conductivity)) A 1 mm thick alumina plate (AO-5050 manufactured by Furuuchi Chemical) was cut into a size of 5 cm x 2.5 cm to serve as the substrate for evaluation. The five levels of paste with different concentrations (paste concentrations) of the finely oxide-coated copper microparticles were applied to the surface of the substrate using a doctor blade (manufactured by Imoto Manufacturing Co., Ltd.) with a coating width of 2 cm and a coating thickness of 10 μm. The paste was then placed in a tubular furnace, and nitrogen gas or a 3% hydrogen / nitrogen mixed gas was supplied into the tube at a flow rate of 1 L / min, followed by gas replacement at room temperature for 30 minutes or more. Thereafter, nitrogen gas or a 3% hydrogen / nitrogen mixed gas was supplied into the tube at a flow rate of 1 L / min, and the temperature was raised to an evaluation temperature of 200 ° C. in about 20 minutes. After maintaining the evaluation temperature at 200 ° C. for 1 hour, the paste was naturally cooled to room temperature to obtain a fired substrate of the paste. When the paste concentration was 91.3 wt%, the evaluation temperatures were set to three levels: 150°C, 200°C, and 250°C. The paste, which was dark brown when applied, turned reddish brown after firing. The entire process from applying the paste to holding it at the evaluation temperature and allowing it to cool naturally to room temperature was carried out in a nitrogen atmosphere.

[0100] The conductivity of the fired product was measured using a resistivity meter (Loresta GP, ASP Probe, manufactured by Mitsubishi Chemical Analytic). Figure 24 shows a graph showing the relationship between paste concentration and volume resistivity at each evaluation temperature, along with the volume resistivity of bulk copper. From Figure 24, it can be seen that the volume resistivity of the fired product using 91.3 wt% paste was 6 × 10 －６ Ωcm and the resistivity of bulk copper at 0°C (1.55 × 10 －６The resistivity was measured using a resistivity correction factor (RCF) calculated using a Loresta GP, which corrects for the shape factor of the coating film, and the film thickness of the fired product was calculated from an image of a cross section of a broken fired substrate observed under a microscope (Keyence Digital Microscope VHX-7000).

[0101] (X-ray Diffraction Measurement) (XRD Measurement Results Before and After Firing) Using a powder X-ray diffractometer (XRD, Rigaku MiniFlex II, D / teX Ultra), X-ray diffraction measurements were performed on the paste before and after firing, and the XRD measurement results for the reaction process when fired at 250°C under a 3% hydrogen / nitrogen mixed gas were obtained. The results are shown in Figure 25. As shown in Figure 25, Cu, which was found in the coating paste before firing, was ６４ O and Cu ８ The broad peak of O disappeared after firing due to reduction, and only the sharp peak derived from copper was confirmed. Figure 26 is an SEM image of the fired material fired at 250°C under a 3% hydrogen / nitrogen mixed gas. From the photograph in Figure 26, it was confirmed that a fired material with densely sintered particles was obtained. Cu ６４ O and Cu ８ Since O is a nano-sized particle and is formed in a shell shape on the surface of the copper particle, it is suggested that in the process of reduction, adjacent copper particles are efficiently sintered due to a drop in melting point, and it has been proven that the fine copper oxide-coated copper microparticles of this embodiment have high sinterability.

[0102] [4] Another Production Example Related to the Second Production Method (Example 9) (Preparation of Copper Powder) Hexanoic acid-coated copper particles (particle diameter 30 to 100 nm) were used as the starting metallic copper particles. The hexanoic acid-coated copper particles were produced by a liquid-phase reduction method using the following procedure. 1 mol of copper oxide II (NB-2 manufactured by Nisshin Chemco) was added as the raw material, 1 L of ethanol (manufactured by Nippon Alcohol Sales) as the solvent, and 60 mmol of hexanoic acid as the protective agent. The mixture was heated to 70°C, and then 2 mol of hydrazine monohydrate (manufactured by Kanto Chemical) was added and reacted for 1 hour with stirring. After the reaction, the mixture was purified twice each with acetone and methanol, and then vacuum dried to obtain copper powder.

[0103] (Addition of copper oxide powder and production of core-shell microparticles) The addition of copper oxide powder to copper powder and the production of core-shell microparticles were carried out by the following procedure. 222.9 mmol of ethylene glycol (manufactured by Kanto Chemical) as a solvent, 157 mmol of 1-amino-2-propanol (AmIP, manufactured by Kanto Chemical) as an amine compound, and 78.5 mmol of acetic acid (manufactured by Junsei Chemical) as a complexing agent were placed in a reaction vessel and stirred thoroughly. After that, 15.7 mmol (0.998 g) of hexanoic acid-coated copper particles as a starting material and copper oxide I (Cu ２ To the reaction mixture, 0.367 mmol (0.0525 g) of copper oxide I (Furukawa Chemicals, particle size 0.5-10 μm) was added. The amount of copper oxide I added relative to the starting materials (total amount of metallic copper and copper oxide) was 5% by mass. With the reaction vessel immersed in a water bath, hydrazine monohydrate (Kanto Chemical) was added as a reducing agent, and the reaction was carried out while stirring at 1100 rpm. The reaction was carried out in the air. After the reaction, purification was carried out by centrifugation multiple times using N,N-dimethylacetamide, toluene, and hexane, and a slurry containing the product was obtained.

[0104] (X-ray Diffraction Measurement) Using the obtained product, X-ray diffraction measurement was carried out in the same manner as in the above-mentioned [1] Production Example according to the first production method. The results are shown in FIG.

[0105] (Electron microscope observation) Using the obtained product, SEM observation and TEM observation were carried out in the same manner as in the above-mentioned [1] Production Example relating to the first production method. The resulting SEM image is shown in Figure 28. Figure 28A shows the starting material, and Figure 28B shows the product after 24 hours of reaction. Figure 29 also shows the TEM image.

[0106] From the XRD pattern of the reaction process shown in FIG. 27, in addition to copper, Cu ６４ O and Cu ８ From the comparison of the SEM images of A (starting material) and B (after 24 hours of reaction) shown in FIG. 28, it was found that CuO was generated around the copper particles of the starting material due to the reaction. ６４ O, Cu ８ It was confirmed that the surface of the core copper particle was covered with what appeared to be fine oxides such as Cu and O. ６４ O and Cu ８It was confirmed that the nanoparticles were covered with a shell of O-containing nanoparticles.

[0107] In the production example according to the second production method [2], copper particles having a surface oxide layer were used as the starting material. From the above results, it can be seen that even when copper oxide particles are separately added to the core copper particles as the starting material, the copper particles as the core and the Cu particles having a particle size of 20 nm or less can be mixed. ６４ O and Cu ８ It was confirmed that core-shell type fine copper oxide-coated copper microparticles having a shell composed of nanoparticles containing O were obtained. In Example 9, copper oxide particles were used as the additive, but any additive that forms copper complex ions in the reaction solution can be used. ６４ O, Cu ８ It is believed that the reaction to O proceeds. Therefore, the same effect can be obtained by adding copper complex salts, etc. to the core particles in addition to copper oxide.

[0108] The copper oxide-containing particles according to this embodiment can be sufficiently sintered at a relatively low temperature of 200°C or less under normal pressure (or higher pressure), and a sintered body exhibiting sufficient electrical conductivity can be obtained. Therefore, the copper oxide-containing particles according to this embodiment can be used, for example, as a circuit forming material for printed circuit boards (especially flexible boards) and other microwiring materials, as well as a die bonding material for power semiconductors for heat conduction. They can also be used as an antistatic material, an electromagnetic wave blocking material, an infrared blocking material, etc.

[0109] This application claims priority from Japanese Patent Applications Nos. 2022-140366 and 2023-018736, both of which are incorporated herein by reference.

[0110] 1, 2 Copper test piece 3 Paste containing copper fine particles coated with copper oxide 4 Fixing jig for testing machine

Claims

1. CuO and Cu ２ preparing raw material particles having copper oxide on at least the surface thereof, the copper oxide including one or more of O; The raw material particles are mixed with a solution containing an amine compound and a complexing agent, and then a reducing agent is added to the solution, followed by reaction in an oxygen-containing atmosphere. Including Cu ６４ O and Cu ８ A method for producing fine copper oxide-containing particles having one or more fine copper oxides selected from O on at least the surface thereof.

2. The raw material particles are CuO and Cu ２ The method according to claim 1 , wherein the raw material particles are made of copper oxide containing one or more of O.

3. The raw material particles have a copper raw material particle as a core, and are composed of CuO and Cu ２ 2. The method according to claim 1, wherein the copper oxide-coated copper raw material particles have a shell made of a copper oxide coating containing one or more of O.

4. The copper oxide contained in the raw material particles is Cu ２ The method according to claim 2 or 3, wherein the formula (I) is O.

5. The method according to claim 2 or 3, wherein the complexing agent is a carboxylic acid.

6. The process according to claim 2 or 3, wherein the complexing agent is acetic acid.

7. The method according to claim 2 or 3, wherein the reaction is carried out at 50° C. or lower.

8. The method according to claim 2 or 3, wherein the average particle size of the raw material particles is more than 20 nm and not more than 10 μm.

9. A copper particle as a core and Cu ６４ O and Cu ８ and a shell containing one or more fine copper oxides of Cu. ６４ O and Cu ８ The fine copper oxide-coated copper particles, wherein one or more of the fine copper oxides of O are fine copper oxide particles having an average particle size of more than 1 nm and not more than 20 nm.

10. The fine copper oxide-coated copper particle according to claim 9, wherein the core copper particle has an average particle size of more than 20 nm and not more than 2 μm.

11. A bonding material comprising the fine copper oxide-coated copper particles according to claim 9 or 10.

12. A paste comprising the fine copper oxide-coated copper particles according to claim 9 or 10.

13. An ink comprising the fine copper oxide-coated copper particles according to claim 9 or 10.

14. A method for producing a bonded body using the fine copper oxide-coated copper particle according to claim 9 or 10.

15. A method for producing a sintered body using the fine copper oxide-coated copper particles according to claim 9 or 10.