JP2018119187A - Copper particle structure and copper ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper particle structure that can improve dispersion stability in an ink and can improve viscosity stability and to provide a copper ink.SOLUTION: The copper particle structure has a copper base particle having an average primary particle size of 0.1 μm to 10 μm and a copper nanoparticle produced by allowing a copper cation fixed to the copper base particle surface to be reduced and having an average particle size of 10 nm or less. The copper nanoparticle comprises a central part composed of a single crystal of copper and a protective layer formed around the central part in which the central part of the copper nanoparticle forms a metallic bond with the copper base particle; and the protective layer includes at least one kind selected from a 3-6C primary alcohol, a 3-6C secondary alcohol and a derivative thereof and has a boiling point or a thermal decomposition temperature of 150°C or lower.SELECTED DRAWING: Figure 1

Description

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

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

  Such a fine wiring printing ink uses a dispersion containing metal nanoparticles whose surface is protected by an organic material as an ink material, prints a circuit pattern on a substrate using a fine wiring printing technique, and heats at a low temperature. Then, the organic substance is removed from the surface of the metal nanoparticle 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 remarkably lowered. Thereby, metal fine wiring with high thermal conductivity and high electrical conductivity can be formed.

  Copper nanoparticles are disclosed as an ink material for fine wiring printing (see Patent Document 1). In Patent Document 1, the oxidation of copper is suppressed, and since the average particle diameter is 10 nm, the melting point drop is remarkably high, the dispersibility is high, the low temperature sintering is possible, and the protective layer is 150 ° C. or less. A technique relating to copper nanoparticles that can be removed during low-temperature sintering and can be suitably used for a conductive copper nano-ink material has been disclosed. In order to solve this problem, Patent Document 1 discloses copper nanoparticles formed from a central portion made of a single crystal of copper and a protective layer around the center, and (1) an average particle of the copper nanoparticles (2) 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; ) Disclosed is a copper nanoparticle characterized in that the protective layer has a boiling point or thermal decomposition temperature of 150 ° C. or lower.

International Publication No. 2015/129466

  However, even if it uses the copper nanoparticle of patent document 1, there exists a problem that copper nanoparticles are easy to aggregate and stability with respect to passage of days is bad. Further, even when stored under refrigeration at −30 ° C., the dispersibility of the ink (copper nanoparticles dispersed in a solvent as a dispersoid) is impaired in about 3 months. Furthermore, there is a problem that the viscosity increases in about 1 hour at room temperature in the state of ink in which copper nanoparticles are dispersed in a solvent.

  This invention is made | formed in view of such a situation, and it aims at providing the copper particle structure and copper ink which can improve the dispersion stability in an ink, and can improve viscosity stability.

In order to achieve the above object, one aspect of the copper particle structure is that copper base particles having an average primary particle size of 0.1 μm or more and 10 μm or less and copper cations fixed on the surface of the copper base particles are reduced. Copper nanoparticles having an average particle diameter of 10 nm or less obtained, the copper nanoparticles comprising a central portion made of a single crystal of copper and a protective layer around the center, the center of the copper nanoparticles Part is metal-bonded to the copper base particles, and the protective layer includes 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).

  Moreover, in order to achieve said objective, one aspect | mode of copper ink contains the copper particle structure mentioned above and a dispersion | distribution solvent.

  ADVANTAGE OF THE INVENTION According to this invention, the dispersion stability in an ink can be improved and the copper particle structure and copper ink which can improve viscosity stability can be provided.

It is an image figure before and behind baking of the copper particle structure which concerns on this embodiment. It is an optical microscope observation photograph of the copper ink after baking. 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 refrigerated storage in the copper ink of an Example. It is a figure which shows the relationship between 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 base particles having an average primary particle size of 0.1 μm or more and 10 μm or less and copper cations fixed on the surface of the copper base particles. 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 particle. The protective layer includes 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. In addition, at least one of the protective layers has a group represented by the following formula (1) or (2).

  Drawing 1 is an image figure before and behind baking of a copper particle structure concerning this embodiment. As shown in FIG. 1, the copper particle structure according to the present embodiment is obtained by reducing copper base particles having an average primary particle diameter of 0.1 μm or more and 10 μm or less and copper cations fixed on the surface of the copper base particles. The obtained copper nanoparticles have an average particle size of 10 nm or less. When the copper particle structure shown in FIG. 1 is heated, the copper nanoparticles having a low melting point are fused to join the micron-sized copper base particles to each other, and conductivity is developed (right side of FIG. 1). The protective layer on the surface of the copper nanoparticles disappears upon firing.

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

  Moreover, the copper particle structure of this embodiment also has the following effects. Since the average particle diameter of the copper nanoparticles is 10 nm or less, the melting point is remarkably lowered, the sintering temperature is low, and metal fine wiring can be formed on a substrate such as paper or plastic that is weak against heat. Moreover, the center part which consists of a copper single crystal of copper nanoparticles is coat | covered with the protective layer containing C3-C6 primary and / or secondary alcohol. For this reason, the oxidation of copper is suppressed. Furthermore, since the protective layer contains primary and / or secondary alcohols having 3 to 6 carbon atoms and the protective layer has a boiling point or thermal decomposition temperature of 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. For this reason, the copper particle structure of this embodiment can be used suitably as an ink material. In addition, since the primary and / or secondary alcohol having 3 to 6 carbon atoms forming the protective layer is volatile in the copper particle structure of the present embodiment, the low-temperature sintering under reduced pressure, It is also possible to form metal fine wiring. For this reason, the copper ink in which the said copper particle structure is disperse | distributed can be used suitably for forming metal fine wiring.

  Below, the component which comprises the copper particle structure which concerns on this embodiment is demonstrated.

(Copper base particles)
A copper base particle is a copper particle used as the base for carrying out reduction | restoration precipitation of the copper nanoparticle, The average particle diameter of the primary particle is 0.1 micrometer or more and 10 micrometers or less. When the average particle diameter of the copper base particles is smaller than 0.1 μm, the content reduction effect of the copper nanoparticles is reduced. Moreover, when the average particle diameter of the copper base particles is larger than 10 μm, there is a possibility that the electric resistance value of the circuit cannot be sufficiently reduced when the circuit is formed using the copper ink containing the copper nanoparticle structure.

(Copper nanoparticles)
The copper nanoparticles are obtained by reducing a copper cation fixed on the surface of the copper base particles, and the average particle size 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 particle.

  Note that a single crystal in this specification refers to a crystal having the same crystal orientation in any part of the crystal and in which atoms constituting the crystal are spatially ordered. That is, the single crystal of copper forming the central part of the copper nanoparticles of the present invention is a single crystal as a whole, crystals grown in various directions are not mixed, and the copper particles are aggregated. Means no. This can be confirmed by peak measurement of XRD analysis of copper nanoparticles and direct observation of 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 derivatives thereof, 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. Specifically, 1-amino-2-propanol, 2-hydroxybutyric acid, 3-hydroxybutyric acid, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol is mentioned. These secondary alcohols may be used alone or in combination.

  The hydroxy group of the secondary alcohol has 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, the oxidation of copper is suppressed, and the oxide generated during low-temperature sintering is a ketone compound, so that it is easily volatile and decomposed.

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

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

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

The groups represented by the above formulas (1) and (3) exhibit a high coordinating power, and form a five-membered ring with a copper atom on the surface of the central portion made of a single crystal of copper. It becomes a group having a metallacycle structure represented by (5) and is stabilized.

  As said C3-C6 primary alcohol and its derivative (s), an amino group, a carboxyl group, a hydroxyl group etc. are added to C3-C6 primary alcohol and the said C3-C6 primary alcohol. Specific examples include 2-amino-2ethyl-1,3-propanediol and 2-amino-1-butanol. These primary alcohols may be used alone or in combination.

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

  The primary alcohol having 3 to 6 carbon atoms and the derivative thereof 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, becomes 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 a substance constituting the protective layer is desorbed from the central portion made of copper single crystal by heat, and the substance constituting the protective layer includes the above desorption. Includes forms that evaporate with heat. This makes it possible to remove the protective layer by low-temperature heating at 150 ° C. or lower, and enables low-temperature sintering of copper nanoparticles.

  The boiling point or thermal decomposition temperature of the protective layer of copper nanoparticles can be measured by performing thermal analysis with TG-DTA in a nitrogen atmosphere using a dry powder of 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 facilitate the low-temperature sintering of the copper nanoparticles, so that the primary alcohol having 3 to 6 carbon atoms, the secondary alcohol having 3 to 6 carbon atoms, and derivatives thereof. It is preferable that it consists only of at least 1 sort (s) selected from these.

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

  The copper nanoparticles have an average particle size of 10 nm or less. If the average particle diameter 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, and more preferably 3 to 6 nm. If the average particle diameter of the copper nanoparticles is smaller than 3 nm, the copper nanoparticles may be aggregated.

  In addition, the average particle diameter in this specification is an arithmetic average value of the particle diameters of arbitrary 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 diameter 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 diameter 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 within the above range, the average particle diameter of the copper nanoparticles is made uniform, and copper nanoparticles suitable for sintering at a low temperature can be obtained.

(Copper ink)
The copper ink according to the present embodiment includes the above-described 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, alkanolamine, and N, N-dimethylformamide. 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, and the same carbon number as the primary and / or secondary alcohol having 3 to 6 carbon atoms that forms the protective layer of the copper nanoparticles in that high dispersion stability can be maintained. It is more preferable to use 3 to 6 alkanolamine. These dispersion media can be appropriately selected depending on the printing technique to which the copper nano ink is applied, the desired viscosity, the type of copper circuit to be formed, and the like.

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

(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, 0.91 g) was dissolved in the mixed solution to prepare a 0.1 M copper acetate solution. The solution turned dark blue with complexation. Copper micropowder (High Purity Chemical Laboratory, D ₅₀ 1 μm, 1 g) serving as a spherical copper base particle was dissolved therein. With the addition of copper micropowder, the solution turned brown. This is hereinafter referred to as “raw material solution”.

  The raw material solution was allowed to stand at 25 ° C. for one day under atmospheric pressure (nitrogen atmosphere) while stirring at 1100 rpm. Subsequently, about 15 times the amount of hydrazine (Wako Pure Chemical Industries, 2.43 ml) in terms of copper mole was added. Immediately after the addition of hydrazine, a large amount of bubbles was generated from the raw material solution and instantly changed to a reddish black color. Then, it was left for one day under an air atmosphere. As a result of this reaction, a copper particle structure in which copper nanoparticles were deposited and supported on the surface of the copper base particles was obtained in the solution. Separation / purification and recovery of the copper particle structure from the solution in which the copper particle structure was dispersed were performed 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) was added to the copper particle structure precipitated by removing the solution and dispersed in dimethylacetamide. Next, 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) was added to the copper particle structure precipitated by removing the solution and dispersed in toluene (Wako Pure Chemical Industries). Next, 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) was added to the copper particle structure precipitated by removing the solution and dispersed in hexane. Next, 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 in which propylene glycol (Wako Pure Chemical Industries) and glycerol (Wako Pure Chemical Industries) were each 50 volume ratio (1: 1) was prepared. The above mixed solvent was added to the copper particle structure obtained in Operation 1 so that the solid content concentration would be 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 (about 80 weight ratio supported powder content) obtained in operation 2 was formed on a polyimide substrate to form a coating film. When this coating film was heated at a low temperature for 30 minutes at 150 ° C. in a nitrogen atmosphere, the copper nanoparticles melted to form a conductive path with the copper base particles, and a red-brown copper foil film without cracks was obtained. (Refer to the optical microscope observation photograph in FIG. 2). The obtained copper foil film was subjected to electric resistance measurement by a four-point 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 curve of the copper ink at room temperature was measured every 0, 1, 2, 3, 4, 7.5 hours (hr) in the range of a shear rate of 0 to 1000 s ⁻¹ . A comparative copper ink in which 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 electrical resistance over time)
The ink of the supported powder was refrigerated for one week at −4 ° C., a copper foil film was formed 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).

<Comparative example>
As a comparative example, a copper ink was prepared in which copper microparticles and copper nanoparticles were separately dispersed in a dispersion medium. The copper ink of the comparative example is different from the copper ink of this example in that the copper nanoparticles are not fixed to the copper microparticles, and the central part of the copper nanoparticles is not metal-bonded to the copper microparticles. Hereinafter, the manufacturing method of the copper ink of a comparative example is demonstrated.

(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, 0.91 g) was dissolved in the mixed solution to prepare a 0.1 M copper acetate solution. The solution turned dark blue with complexation. Subsequently, hydrazine was added to the resulting solution in the same manner as in the Examples, and the mixture was allowed to stand for one day in an air atmosphere. As a result of this reaction, a dispersion in which copper nanoparticles were dispersed was obtained.

(Operation 2: Separation of copper nanoparticles)
Separately, N, N-dimethylacetamide (DMA) having a volume ratio of 3 times that of the dispersion was prepared. 24 hours after the addition of hydrazine, the mixed solution was prepared by slowly dropping the copper nanoparticle dispersion into the prepared DMA so that the liquid droplets could be seen. Excess hydrazine, isopropanolamine, and ethylene glycol could be removed by DMA. The mixed solution was left in the atmosphere for several minutes and exposed to air. As a result of the above operation, the mixed solution started to be suspended, and particles could be collected 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 more DMA was added. Next, the precipitate of copper nanoparticles was dispersed in DMA and rewashed.

  After confirming that the precipitate of copper nanoparticles was dispersed in DMA, the precipitate was immediately centrifuged at 6000 rpm for 3 minutes. The supernatant was removed, and toluene was added to the remaining precipitate and redispersed for washing. After confirming that the precipitate of copper nanoparticles was dispersed in toluene, the precipitate of copper nanoparticles was separated by centrifugation at 6000 rpm for 1 minute. The clear supernatant was removed, and hexane was added to the remaining precipitate and redispersed for washing. After confirming that the precipitate of copper nanoparticles was dispersed in hexane, centrifugation was performed at 6000 rpm for 5 minutes, the transparent supernatant was removed to separate the precipitate of copper nanoparticles, and washing was completed. . The average particle diameter of the obtained copper nanoparticles was 3 nm.

(Operation 3: Preparation of ink containing copper nanoparticles)
In the same manner as in Operation 2 of Example 1, a mixed solvent in which propylene glycol and glycerol were each 50 volume ratio (1: 1) was prepared. 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 a copper nano ink.

(Operation 4: Preparation of Comparative Example Ink)
As in (Operation 3), a copper microparticle dispersion (hereinafter referred to as “copper microink”) in which copper microparticles having an average particle size of 1 (m) were dispersed was obtained. An ink was prepared by mixing copper nanoinks at a mixing ratio 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 electrical resistance of copper conductive films formed with the copper inks of Comparative Examples 2 to 6 and this example. FIG. 6 shows the relative value of the electrical resistance of the copper conductive film according to the amount of copper nanoink added when the electrical resistance when the copper nanoink is 100 weight ratio is 1. When the copper ink of this example was used, an electrical resistance value equivalent to that obtained when the copper nano ink was 100 weight ratio 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 electrical resistance of the conductive film decreased as the weight ratio of the copper nano ink increased. However, at the same time, generation of bubbles and cracks has been observed on the surface of the conductive film. In addition, conduction was not able to be confirmed with the ink made into the 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 the other points are the same as Example 1.

  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, 0.91 g) was dissolved in the mixed solution to prepare a 0.1 M copper acetate solution. The solution turned dark blue with complexation. To this, flat copper micropowder (Mitsui Metal Mining, 1050YP, 1 g) was dissolved as copper base particles. With the addition of copper micropowder, the solution turned brown. This is hereinafter referred to as “raw material solution”.

  The raw material solution was allowed to stand at 25 ° C. for one day under atmospheric pressure (nitrogen atmosphere) while stirring at 1100 rpm. Subsequently, about 15 times the amount of hydrazine (Wako Pure Chemical Industries, 2.43 mL) was added in terms of copper mole. Immediately after the addition of hydrazine, a large amount of bubbles was generated from the raw material solution and instantly changed to a reddish black color. Then, it was left for one day under an air atmosphere. As a result of this reaction, a copper particle structure in which copper nanoparticles were deposited and supported on the surface of the copper base particles was obtained in the 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 electric resistance are the same as (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 exhibited the same effect as Example 1.

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

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, 0.91 g) was dissolved in the mixed solution to prepare a 0.1 M copper acetate solution. The solution turned dark blue with complexation. A copper submicron powder (SSN, 0811XX, 1 g) having a particle diameter D _{50 of} 300 nm was dissolved as copper base particles. With the addition of copper micropowder, the solution turned brown. This is hereinafter referred to as “raw material solution”.

  The raw material solution was allowed to stand at 25 ° C. for one day under atmospheric pressure (nitrogen atmosphere) while stirring at 1100 rpm. Subsequently, about 15 times the amount of hydrazine (Wako Pure Chemical Industries, 2.43 mL) was added in terms of copper mole. Immediately after the addition of hydrazine, a large amount of bubbles was generated from the raw material solution and instantly changed to a reddish black color. Then, it was left for one day under an air atmosphere. As a result of this reaction, a copper particle structure in which copper nanoparticles were deposited and supported on the surface of the copper base particles was obtained in the 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 electric resistance are the same as (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 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 base particles, the copper nanoparticles can be prevented from coming into direct contact with each other, so that an ink having high dispersion stability can be produced.
Since the copper nanoparticles melt and wet during firing and form a conductive path in the coating film, a conductive film having a low electrical resistance equivalent to that obtained when the copper nanoparticles are used alone can be produced.
Even if time elapses after the copper ink adjustment until the formation of the conductive film, it is possible to handle an ink having a low viscosity.

  Each embodiment described above is for facilitating the understanding of the present invention, and is not intended to limit the present invention. The present invention can be changed / improved without departing from the spirit thereof, and the present invention includes equivalents thereof. In other words, those obtained by appropriately modifying the design of each embodiment by those skilled in the art are also included in the scope of the present invention as long as they include 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 illustrated, and can be changed as appropriate. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios. Each embodiment is an exemplification, and it is needless to say that a partial replacement or combination of configurations shown in different embodiments is possible, and these are also included in the scope of the present invention as long as they include the features of the present invention. .

Claims (2)

Copper base particles having an average primary particle size of 0.1 μm or more and 10 μm or less;
Copper nanoparticles having an average particle size of 10 nm or less obtained by reduction of the copper cation 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 it.
The center of the copper nanoparticles is metal bonded to the copper base particles;
The protective layer includes 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 a boiling point or a thermal decomposition temperature of the protective layer is 150 ° C. And
At least one of the protective layers is a copper particle structure having a group represented by the following formula (1) or (2).
  A copper ink comprising the copper particle structure according to claim 1 and a dispersion solvent.