JP6968543B2 - Copper particle structure and copper ink - Google Patents

Description

The present invention relates to a copper particle structure and copper ink.

Metal nanoparticles with a diameter of about 2 nm to 100 nm show different properties from bulk metals in optical properties, magnetic properties, thermal properties, electrical properties, etc., and are expected to be applied to various technical fields. Has been done. For example, taking advantage of the property that the surface area increases and the melting point decreases as the particle size decreases, an electronic circuit made of metal fine wiring is manufactured on a substrate using an ink for fine wiring printing containing metal nanoparticles. Research is underway.

Such fine wiring printing ink uses a dispersion liquid containing metal nanoparticles whose surface is protected with an organic substance as an ink material, prints a circuit pattern on a substrate using fine wiring printing technology, and heats it at a low temperature. , Organic substances are removed from the surface of the metal nanoparticles to form a metal bond between the metal nanoparticles. In particular, when metal nanoparticles having a diameter of 10 nm or less are used, the melting point is significantly lowered. This makes it possible to form metal fine wiring having high thermal conductivity and electrical conductivity.

Copper nanoparticles are disclosed as an ink material for fine wiring printing (see Patent Document 1). Patent Document 1 states that the oxidation of copper is suppressed, the average particle size is 10 nm, so that the melting point drops significantly, the dispersibility is high, low-temperature sintering is possible, and the protective layer is at 150 ° C. or lower. Disclosed is a technique relating to copper nanoparticles, which can be removed at low temperature sintering and can be suitably used for a conductive copper nanoink material. In order to solve this problem, Patent Document 1 is copper nanoparticles formed from a central portion made of a single crystal of copper and a protective layer around the central portion, and (1) average particles of the copper nanoparticles. The protective layer has a diameter of 10 nm or less, and (2) the protective layer contains at least one selected from a primary alcohol having 3 to 6 carbon atoms, a secondary alcohol having 3 to 6 carbon atoms and derivatives thereof (3). ) Disclosed are copper nanoparticles characterized in that the boiling point or thermal decomposition temperature of the protective layer is 150 ° C. or lower.

International Publication No. 2015/12946

However, even if the copper nanoparticles described in Patent Document 1 are used, there is a problem that the copper nanoparticles tend to aggregate with each other and the stability with respect to the passage of days is poor. Further, even if the ink is stored under freezing at −30 ° C., the dispersibility of the ink (dispersed in a solvent as a dispersoid of copper nanoparticles) is impaired in about 3 months. Further, there is a problem that the ink thickens in about 1 hour at room temperature in the state of an ink in which copper nanoparticles are dispersed in a solvent.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a copper particle structure and a copper ink capable of improving dispersion stability in ink and improving viscosity stability.

In order to achieve the above object, one aspect of the copper particle structure is that copper-based particles having an average particle size of primary particles of 0.1 μm or more and 10 μm or less and copper cations adhered to the surface of the copper-based particles are reduced. The copper nanoparticles have an average particle size of 10 nm or less, and the copper nanoparticles include a central portion made of a single crystal of copper and a protective layer around the copper nanoparticles, and are the center of the copper nanoparticles. The portion is metal-bonded to the copper-based particles, and the protective layer contains at least one selected from primary alcohols having 3 to 6 carbon atoms, secondary alcohols having 3 to 6 carbon atoms and derivatives thereof. The boiling point or thermal decomposition temperature of the protective layer is 150 ° C. or lower, and at least one of the protective layers has a group represented by the following formula (1) or (2).

Further, in order to achieve the above object, one aspect of the copper ink includes the above-mentioned copper particle structure and the dispersion solvent.

According to the present invention, it is possible to provide a copper particle structure and a copper ink capable of improving dispersion stability in ink and improving viscosity stability.

It is an image diagram before and after firing of the copper particle structure which concerns on this embodiment. It is an optical microscope observation photograph of copper ink after firing. It is a figure which shows the flow curve of the copper ink of a comparative example. It is a figure which shows the flow curve of the copper ink of an Example. It is a figure which shows the change of the sheet resistance value after refrigerating storage in the copper ink of an Example. It is a figure which shows the relationship of the sheet resistivity of an Example and a comparative example.

(Copper particle structure)
The copper particle structure according to the present embodiment is obtained by reducing copper-based particles having an average particle size of primary particles of 0.1 μm or more and 10 μm or less and copper cations adhering to the surface of the copper-based particles. It is a copper particle structure having copper nanoparticles having a diameter of 10 nm or less. The copper nanoparticles include a central portion made of a single crystal of copper and a protective layer around the central portion, and the central portion of the copper nanoparticles is metal-bonded to the copper base particles. The protective layer contains at least one selected from primary alcohols having 3 to 6 carbon atoms, secondary alcohols having 3 to 6 carbon atoms and derivatives thereof, and the boiling point or thermal decomposition temperature of the protective layer is 150 ° C. or lower. At least one of the protective layers has a group represented by the following formula (1) or (2).

FIG. 1 is an image diagram of the copper particle structure according to the present embodiment before and after firing. As shown in FIG. 1, in the copper particle structure according to the present embodiment, copper-based particles having an average particle size of primary particles of 0.1 μm or more and 10 μm or less and copper cations fixed on the surface of the copper-based particles are reduced. It has copper nanoparticles having an average particle size of 10 nm or less. By heating the copper particle structure shown in FIG. 1, copper nanoparticles having a low melting point are fused to bond micron-sized copper-based particles to each other, and conductivity is exhibited (FIG. 1, right). The protective layer on the surface of the copper nanoparticles disappears by firing.

According to the copper particle structure of the present embodiment, the average particle size of the primary particles is 0.1 μm or more and 10 μm or less, and the average obtained by reducing the copper cations fixed on the surface of the copper base particles. By having the copper nanoparticles having a particle size of 10 nm or less, the amount of the copper nanoparticles used can be reduced and the dispersion stability of the ink is improved. Since the copper nanoparticles are uniformly supported on the copper-based particles as a carrier, direct aggregation of the copper nanoparticles can be suppressed and the viscosity stability can be improved.

In addition, the copper particle structure of the present embodiment also has the following effects. Since the average particle size of the copper nanoparticles is 10 nm or less, the melting point is remarkably lowered, the sintering temperature is low, and the metal fine wiring can be formed on a substrate such as paper or plastic which is sensitive to heat. Further, in the copper nanoparticles, the central portion made of a single crystal of copper is coated with a protective layer containing a primary and / or secondary alcohol having 3 to 6 carbon atoms. Therefore, the oxidation of copper is suppressed. Further, since the protective layer contains primary and / or secondary alcohol having 3 to 6 carbon atoms and the boiling point or thermal decomposition temperature of the protective layer is 150 ° C. or lower, the protective layer decomposes or evaporates at a low temperature. When the copper nanoparticles are sintered at a low temperature of 150 ° C. or lower, the protective layer can also be removed. Therefore, the copper particle structure of the present embodiment can be suitably used as an ink material. Further, in the copper particle structure of the present embodiment, since the primary and / or secondary alcohol having 3 to 6 carbon atoms forming the protective layer is volatile, it is possible to perform low temperature sintering under reduced pressure. It is also possible to form metal microwiring. Therefore, the copper ink in which the copper particle structure is dispersed can be suitably used for forming metal fine wiring.

Hereinafter, the components constituting the copper particle structure according to the present embodiment will be described.

(Copper-based particles)
The copper-based particles are copper particles that serve as a base for reducing and precipitating copper nanoparticles, and the average particle size of the primary particles is 0.1 μm or more and 10 μm or less. When the average particle size of the copper-based particles is smaller than 0.1 μm, the effect of reducing the content of the copper nanoparticles becomes small. Further, if the average particle size of the copper-based particles is larger than 10 μm, the electric resistance value of the circuit may not be sufficiently reduced when the circuit is formed by using the copper ink containing the copper nanoparticle structure.

(Copper nanoparticles)
The copper nanoparticles are obtained by reducing the copper cations fixed on the surface of the copper base particles, and the average particle size thereof is 10 nm or less. The copper nanoparticles include a central portion made of a single crystal of copper and a protective layer around the central portion, and the central portion of the copper nanoparticles is metal-bonded to the copper base particles.

The term "single crystal" as used herein means that any part of the crystal has the same crystal orientation, and the atoms constituting the single crystal have a spatially regular arrangement. That is, in the copper single crystal forming the central portion of the copper nanoparticles of the present invention, the entire particles are one crystal, the crystals grown in various directions are not mixed, and the copper particles are aggregated or the like. Means not. This can be confirmed by peak measurement of XRD analysis of copper nanoparticles and direct observation of the atomic arrangement by a high-resolution electron microscope.

The protective layer contains at least one selected from primary alcohols having 3 to 6 carbon atoms, secondary alcohols having 3 to 6 carbon atoms and derivatives thereof.

As the secondary alcohol having 3 to 6 carbon atoms and its derivative, an amino group, a carboxyl group, a hydroxyl group and the like are added to the secondary alcohol having 3 to 6 carbon atoms and the secondary alcohol having 3 to 6 carbon atoms. Specific examples thereof include 1-amino-2-propanol, 2-hydroxybutyric acid, 3-hydroxybutyric acid, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, and the like. Examples include 2,3-butanediol. These secondary alcohols and the like may be used alone or in combination.

The hydroxy group of the secondary alcohol has a high affinity for both the solvent and the copper surface, and contributes to the improvement of dispersibility. Since the hydroxy group of the secondary alcohol has a reducing ability, it suppresses the oxidation of copper, and the oxide produced during low-temperature sintering is a ketone compound, so that it easily volatilizes and decomposes.

The secondary alcohol having 3 to 6 carbon atoms and a derivative thereof are preferably monoalcohols. By using monoalcohol, it becomes easy to adjust the boiling point or the thermal decomposition temperature of the protective layer to 150 ° C. or lower.

The secondary alcohol having 3 to 6 carbon atoms and its derivative preferably have a group represented by the following formula (1). In the following formulas (1) to (5), * indicates a bond.

The group represented by the above formula (1) is oxidized to a ketone to form a group represented by the following formula (3).

The groups represented by the above formulas (1) and (3) show high coordination force and form a 5-membered ring with a copper atom on the surface of the central portion composed of a copper single crystal, and the following formulas (4) and It becomes a base having the metallacycle structure shown in (5) and stabilizes.

As the primary alcohol having 3 to 6 carbon atoms and its derivative, an amino group, a carboxyl group, a hydroxyl group and the like are added to the primary alcohol having 3 to 6 carbon atoms and the primary alcohol having 3 to 6 carbon atoms. Examples thereof include 2-amino-2ethyl-1,3-propanediol and 2-amino-1-butanol. These primary alcohols and the like may be used alone or in combination.

The primary alcohol having 3 to 6 carbon atoms and its derivative thereof are preferably monoalcohols. By using monoalcohol, it becomes easy to adjust the boiling point or the thermal decomposition temperature of the protective layer to 150 ° C. or lower.

The primary alcohol having 3 to 6 carbon atoms and its derivative preferably have a group represented by the following formula (2).

The group represented by the above formula (2) also forms a 5-membered ring with a copper atom on the surface of the central portion made of a single crystal of copper to become a group having a metallacycle structure and is stabilized.

The boiling point or thermal decomposition temperature of the protective layer is 150 ° C. or lower. Here, the thermal decomposition temperature of the protective layer is a temperature at which the substance constituting the protective layer is desorbed from the central portion composed of a single crystal of copper by heat, and the desorption includes the substance constituting the protective layer. Includes a form that evaporates by heat. As a result, the protective layer can be removed by heating at a low temperature of 150 ° C. or lower, and copper nanoparticles can be sintered at a low temperature.

The boiling point or the thermal decomposition temperature of the protective layer of the copper nanoparticles can be measured by performing a thermal analysis by TG-DTA in a nitrogen atmosphere using the dry powder of the copper nanoparticles.

At least one of the protective layers has a group represented by the above formula (1) or (2). The other one of the protective layers contains other components other than at least one selected from the above-mentioned primary alcohols having 3 to 6 carbon atoms, secondary alcohols having 3 to 6 carbon atoms and derivatives thereof. However, the protective layer may be a primary alcohol having 3 to 6 carbon atoms, a secondary alcohol having 3 to 6 carbon atoms, and derivatives thereof, in that the protective layer can facilitate low-temperature sintering of copper nanoparticles. It is preferable that it consists of at least one selected from.

The mass ratio of the protective layer in the copper nanoparticles is preferably 10 to 30% by mass, with the mass of the copper nanoparticles being 100% by mass. If the mass ratio of the protective layer is too high, the protective layer may not be sufficiently removed even when heated at a low temperature of 150 ° C. or lower when sintering copper nanoparticles. If the mass ratio of the protective layer is too low, the copper single crystal may not be sufficiently protected.

Copper nanoparticles have an average particle size of 10 nm or less. If the average particle size of the copper nanoparticles exceeds 10 nm, the copper nanoparticles cannot be sintered at a low temperature. The average particle size is preferably 3 to 8 nm, more preferably 3 to 6 nm. If the average particle size of the copper nanoparticles is smaller than 3 nm, the copper nanoparticles may aggregate.

The average particle size in the present specification is an arithmetic mean value of the particle size of any 100 particles in the TEM observation image.

The copper nanoparticles of the present invention preferably have a standard deviation based on the particle size distribution of 20% or less of the average particle size of the copper nanoparticles. That is, it is preferable that the standard deviation based on the particle size distribution of the copper nanoparticles is divided by the average particle size of the copper nanoparticles and the value expressed as a percentage is 20% or less. By setting the standard deviation based on the particle size distribution of the copper nanoparticles in the above range, the average particle size of the copper nanoparticles can be made uniform, and the copper nanoparticles suitable for sintering at a low temperature can be obtained.

(Copper ink)
The copper ink according to this embodiment contains the above-mentioned copper particle structure and a dispersion solvent (dispersion medium).

Examples of the dispersion medium include alcohols such as methanol, ethanol, propylene glycol and glycerol, and polar solvents such as toluene, alkanolamines and N, N-dimethylformiamides. These dispersion media may be used alone or in combination of two or more. For example, propylene glycol and glycerol may be mixed and used at a volume ratio of 1: 1. Among these, it is preferable to use an alkanolamine, which has the same number of carbon atoms as the primary and / or secondary alcohol having 3 to 6 carbon atoms forming the protective layer of the copper nanoparticles in that high dispersion stability can be maintained. It is more preferable to use 3 to 6 alkanolamines. These dispersion media can be appropriately selected depending on the printing method to which the copper nanoink is applied, the desired viscosity, the type of copper circuit to be formed, and the like.

The copper particle structure according to the present embodiment can be suitably used as an ink material for forming metal fine wiring, but is not limited to this application and is also used as a catalyst material (catalyst or catalyst carrier). It can also be used as a transparent conductive film or an antireflection coating material instead of ITO.

(Example)
Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. However, the present invention is not limited to the examples.

<Example 1>
(Preparation of copper particle structure)
Isopropanolamine (Wako Pure Chemical Industries, 3.75 g) was dissolved in ethylene glycol (Wako Pure Chemical Industries, 46.75 g) to prepare a mixed solution. Copper (II) acetate (Wako Pure Chemical Industries, Ltd., 0.91 g) was dissolved in a mixed solution to prepare a 0.1 M copper acetate solution. The solution turned deep blue with complex formation. Copper micropowder (High Purity Chemical Laboratory, D ₅₀ 1 μm, 1 g), which is a spherical copper-based particle, was dissolved therein. With the addition of copper micropowder, the solution turned brown. Hereinafter, this is referred to as a “raw material solution”.

The raw material solution was left at 25 ° C. for one day under atmospheric pressure (under a nitrogen atmosphere) while stirring at 1100 rpm. Then, about 15 times the amount of hydrazine (Wako Pure Chemical Industries, Ltd., 2.43 ml) was added in terms of copper molars. Immediately after the addition of hydrazine, a large amount of bubbles were generated from the raw material solution, and the color instantly changed to reddish black. Then, it was left for a day in an air atmosphere. As a result of this reaction, a copper particle structure in which copper nanoparticles were precipitated and supported on the surface of copper-based particles was obtained in solution. The separation, purification, and recovery of the copper particle structure from the solution in which the copper particle structure was dispersed were carried out by the following operations.

(Operation 1: Separation of copper particle structure)
The solution in which the copper particle structure was dispersed was centrifuged at 7000 rpm for 5 minutes to obtain a solution in which the copper particle structure was precipitated. Dimethylacetamide (DMA, Wako Pure Chemical Industries, Ltd.) was added to the copper particle structure precipitated by removing the solution, and dispersed in dimethylacetamide. Then, centrifugation was performed at 7000 rpm for 5 minutes to obtain a solution in which the copper particle structure was precipitated. Toluene (Wako Pure Chemical Industries, Ltd.) was added to the copper particle structure precipitated by removing the solution, and the mixture was dispersed in toluene (Wako Pure Chemical Industries, Ltd.). Then, centrifugation was performed at 7000 rpm for 5 minutes to obtain a solution in which the copper particle structure was precipitated. Hexane (Wako Pure Chemical Industries, Ltd.) was added to the precipitated copper particle structure after removing the solution, and the mixture was dispersed in hexane. Then, centrifugation was performed at 7000 rpm for 5 minutes to obtain a solution in which the copper particle structure was precipitated. The copper particle structure was separated and recovered by removing the solution.

(Operation 2: Preparation of copper ink)
A mixed solvent was prepared in which propylene glycol (Wako Pure Chemical Industries, Ltd.) and glycerol (Wako Pure Chemical Industries, Ltd.) each had a 50 volume ratio (1: 1). The mixed solvent was added to the copper particle structure obtained in operation 1 so that the solid content concentration was 80% by weight to obtain a copper ink in which the copper particle structure was uniformly dispersed.

(Operation 3: Electrical resistance measurement)
The copper ink (content of about 80 weight-weight-supported powder) obtained in operation 2 was formed into a film on a polyimide substrate to form a coating film. When this coating film was heated at a low temperature of 150 ° C. for 30 minutes in a nitrogen atmosphere, the copper nanoparticles melted to form a conductive path with the copper base particles, and a crack-free reddish brown copper foil film was obtained. (See the optical microscope observation photograph in FIG. 2). The obtained copper foil film was measured for electrical resistance by the four-probe method using Mitsubishi Chemical Analytic Loresta. The sheet resistivity of the copper foil film was 12 m (/ sq).

(Operation 4: Flow curve measurement)
Using a rotational viscometer, the flow curves of the copper ink at room temperature were measured every 0,1,2,3,4,5 hours (hr) with a shear rate in the range of ^{0 to 1000 s -1.} The copper ink of the comparative example in which the copper nanoparticles were dispersed was also measured under the same conditions. FIG. 3 shows the flow curve of the copper ink of the comparative example, and FIG. 4 shows the flow curve of the copper ink of the example. Comparing the flow curves of the copper ink of the example and the copper ink of the comparative example, the viscosity of the copper ink of the example remained low even after 7.5 hours (FIG. 4). The copper ink of the comparative example thickened in 1 hour (Fig. 3).

(Operation 5: Measurement of changes in electrical resistance over time)
The ink of the supported powder was refrigerated at -4 ° C for one week to form a copper foil film in the same manner as in operation 3, and the electrical resistance of the copper foil film was measured. As a result, the sheet resistivity was hardly changed. (Fig. 5).

<Comparison example>
As a comparative example, a copper ink in which copper microparticles and copper nanoparticles were separately dispersed in a dispersion medium was prepared. The copper ink of the comparative example is different from the copper ink of the present embodiment in that the copper nanoparticles are not adhered to the copper nanoparticles and the central portion of the copper nanoparticles is not metal-bonded to the copper nanoparticles. Hereinafter, a method for manufacturing the copper ink of the comparative example will be described.

(Operation 1: Preparation of copper nanoparticles)
Isopropanolamine (Wako Pure Chemical Industries, 3.75 g) was dissolved in ethylene glycol (Wako Pure Chemical Industries, 46.75 g) to prepare a mixed solution. Copper (II) acetate (Wako Pure Chemical Industries, Ltd., 0.91 g) was dissolved in a mixed solution to prepare a 0.1 M copper acetate solution. The solution turned deep blue with complex formation. Then, hydrazine was added to the obtained solution in the same manner as in Examples, and the mixture was left to stand in an air atmosphere for one day. As a result of this reaction, a dispersion liquid in which copper nanoparticles were dispersed was obtained.

(Operation 2: Separation of copper nanoparticles)
N, N-dimethylacetamide (DMA), which is three times the volume of the dispersion, was prepared separately. Twenty-four hours after the addition of hydrazine, a copper nanoparticle dispersion was slowly added dropwise to the prepared DMA so that the droplets could be seen, and the mixed solution was prepared. DMA was able to remove excess hydrazine, isopropanolamine, and ethylene glycol. The mixed solution was left in the air for a few minutes and exposed to the air. By the above operation, the mixed solution began to suspend, and the particles could be recovered by centrifugation.

The suspended mixed solution was centrifuged at 6000 rpm for 2 minutes to obtain a solution in which a precipitate of copper nanoparticles was precipitated. The clear supernatant was removed from the solution, a precipitate of copper nanoparticles was collected and further DMA was added. Then, the precipitate of copper nanoparticles was dispersed in DMA and rewashed.

Immediately after confirming that the precipitate of copper nanoparticles was dispersed in DMA, centrifugation was performed under the conditions of 6000 rpm for 3 minutes. The supernatant was removed, toluene was added to the remaining precipitate, and the residue was redispersed for washing. After confirming that the precipitate of copper nanoparticles was dispersed in toluene, centrifugation was performed at 6000 rpm for 1 minute to separate the precipitate of copper nanoparticles. The clear supernatant was removed, hexane was added to the remaining precipitate, redispersed and washed. After confirming that the precipitate of copper nanoparticles was dispersed in hexane, centrifugation was performed under the condition of 6000 rpm for 5 minutes to remove the transparent supernatant and separate the precipitate of copper nanoparticles, and the washing was completed. .. The average particle size of the obtained copper nanoparticles was 3 nm.

(Operation 3: Preparation of ink containing copper nanoparticles)
Similar to operation 2 of Example 1, a mixed solvent was prepared in which propylene glycol and glycerol were each in a 50 volume ratio (1: 1). The above mixed solvent was added to the copper nanoparticles obtained in (Operation 2) so that the solid content concentration was 40% by weight to obtain copper nanoinks.

(Operation 4: Preparation of ink for comparative example)
Similar to (Operation 3), a copper microparticle dispersion liquid (hereinafter, “copper microink”) in which copper microparticles having an average particle diameter of 1 (m) were dispersed was obtained. This copper microink and (Operation 3) were obtained. The ink was prepared by mixing the copper nano-inks with the copper nano-inks at the mixing ratios shown in Table 1. The ink of this comparative example is a copper ink in which copper nanoparticles and copper microparticles are dispersed.

In the same manner as in Example 1 (Operation 3), a copper thin film having a thickness of 80 μm was prepared using an ink in which copper micro ink and copper nano ink were mixed. FIG. 6 shows the results of the electrical resistance of the copper conductive film formed by the copper inks of Comparative Examples 2 to 6 and this example. FIG. 6 shows the relative value of the electric resistance of the copper conductive film according to the addition amount of the copper nanoink, when the electric resistance when the copper nanoink is 100 weight ratio is 1. When the copper ink of this example was used, an electric resistance value equivalent to that when the copper nanoink was used at a weight ratio of 100 was obtained, and no bubbles or cracks were observed on the surface of the conductive film. In the copper ink of the comparative example, the electric resistance of the conductive film decreased as the weight ratio of the copper nanoink increased. However, at the same time, the formation of bubbles and cracks was also observed on the surface of the conductive film. In addition, continuity could not be confirmed with the ink having a copper micro ink 100 weight ratio.

<Example 2>
Example 2 is different from Example 1 in that flat copper micropowder is used as the copper base particles, and is the same as Example 1 in other points.

That is, isopropanolamine (Wako Pure Chemical Industries, 3.75 g) was dissolved in ethylene glycol (Wako Pure Chemical Industries, 46.75 g) to prepare a mixed solution. Copper (II) acetate (Wako Pure Chemical Industries, Ltd., 0.91 g) was dissolved in a mixed solution to prepare a 0.1 M copper acetate solution. The solution turned deep blue with complex formation. Flat copper micropowder (Mitsui Mining & Smelting, 1050YP, 1g) was dissolved in this as copper-based particles. With the addition of copper micropowder, the solution turned brown. Hereinafter, this is referred to as a “raw material solution”.

The raw material solution was left at 25 ° C. for one day under atmospheric pressure (under a nitrogen atmosphere) while stirring at 1100 rpm. Then, about 15 times the amount of hydrazine (Wako Pure Chemical Industries, Ltd., 2.43 mL) was added in terms of copper molars. Immediately after the addition of hydrazine, a large amount of bubbles were generated from the raw material solution, and the color instantly changed to reddish black. Then, it was left for a day in an air atmosphere. As a result of this reaction, a copper particle structure in which copper nanoparticles were precipitated and supported on the surface of copper-based particles was obtained in solution.

Separation / purification of the copper particle structure from the solution in which the copper particle structure is dispersed, preparation of ink, and measurement of electrical resistance are the same as those of (Operation 1) to (Operation 3) of Example 1 described above.

It was confirmed that the copper ink containing the copper particle structure of Example 2 also had the same effect as that of Example 1.

<Example 3>
Example 3 is different from Example 1 in that copper submicron powder is used as the copper base particles, and is the same as Example 1 in other points.

That is, isopropanolamine (Wako Pure Chemical Industries, 3.75 g) was dissolved in ethylene glycol (Wako Pure Chemical Industries, 46.75 g) to prepare a mixed solution. Copper (II) acetate (Wako Pure Chemical Industries, Ltd., 0.91 g) was dissolved in a mixed solution to prepare a 0.1 M copper acetate solution. The solution turned deep blue with complex formation. Copper submicron powder (SSN, 0811XX, 1 g) having a _{particle size of D 50} : 300 nm was dissolved therein as copper-based particles. With the addition of copper micropowder, the solution turned brown. Hereinafter, this is referred to as a “raw material solution”.

The raw material solution was left at 25 ° C. for one day under atmospheric pressure (under a nitrogen atmosphere) while stirring at 1100 rpm. Then, about 15 times the amount of hydrazine (Wako Pure Chemical Industries, Ltd., 2.43 mL) was added in terms of copper molars. Immediately after the addition of hydrazine, a large amount of bubbles were generated from the raw material solution, and the color instantly changed to reddish black. Then, it was left for a day in an air atmosphere. As a result of this reaction, a copper particle structure in which copper nanoparticles were precipitated and supported on the surface of copper-based particles was obtained in solution.

Separation / purification of the copper particle structure from the solution in which the copper particle structure is dispersed, preparation of ink, and measurement of electrical resistance are the same as those of (Operation 1) to (Operation 3) of Example 1 described above.

It was confirmed that the copper ink containing the copper particle structure of Example 3 also had the same effect as that of Example 1.

From the results of the above Examples and Comparative Examples, the following can be said.
Since the copper nanoparticles are fixed to the copper-based particles, it is possible to prevent the copper nanoparticles from coming into direct contact with each other, so that an ink with high dispersion stability can be produced.
Since the copper nanoparticles melt and spread wet during firing to form a conductive path in the coating film, it is possible to produce a conductive film having a low electrical resistance equivalent to that when the copper nanoparticles are used alone.
Even if time elapses from the adjustment of the copper ink to the film formation of the conductive film, it is possible to handle the ink having a low viscosity.

It should be noted that each of the embodiments described above is for facilitating the understanding of the present invention, and is not for limiting the interpretation of the present invention. The present invention can be modified / improved without departing from the spirit thereof, and the present invention also includes an equivalent thereof. That is, those skilled in the art with appropriate design changes to each embodiment are also included in the scope of the present invention as long as they have the features of the present invention. For example, each element included in each embodiment and its arrangement, material, condition, shape, size, and the like are not limited to those exemplified, and can be appropriately changed. Furthermore, the dimensional ratios in the drawings are not limited to the ratios shown. Further, each embodiment is an example, and it goes without saying that partial substitution or combination of the configurations shown in different embodiments is possible, and these are also included in the scope of the present invention as long as the features of the present invention are included. ..

Claims (1)

Copper-based particles having an average particle size of 0.1 μm or more and 10 μm or less of the primary particles, and
It has copper nanoparticles having an average particle size of 10 nm or less obtained by reducing copper cations fixed on the surface of the copper base particles.
The copper nanoparticles include a central portion made of a single crystal of copper and a protective layer around the central portion.
The central portion of the copper nanoparticles is metal-bonded to the copper-based particles.
The standard deviation of the copper nanoparticles based on the particle size distribution is 20% or less of the average particle size of the copper nanoparticles.
The protective layer contains at least one selected from primary alcohols having 3 to 6 carbon atoms, secondary alcohols having 3 to 6 carbon atoms and derivatives thereof, and the boiling point or thermal decomposition temperature of the protective layer is 150 ° C. Below,
At least one of the protective layers is a method for producing a copper particle structure having a group represented by the following formula (1) or (2).

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