JP7208842B2 - Easily crushable copper powder and its production method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an easily crushable copper powder and a method for producing the same.

Copper powder paste has been widely used as an electronic material. Copper powder paste is used, for example, for forming electrodes of multilayer ceramic capacitors by sintering after application. As the electrode layers used become thinner and the wiring pitch becomes narrower, the copper powder used as the paste material is required to be finer. A method of synthesizing copper powder by a wet method using chemical reduction or disproportionation is used for the production of submicron-sized copper powder. Patent Document 1 discloses a method for producing a paste using copper powder. Patent Document 2 discloses a method for producing copper powder by a disproportionation method. Patent Document 3 discloses a method for producing copper powder by a chemical reduction method.

WO2013/125659 Japanese Patent No. 6297018 Japanese Patent No. 4164009

The copper powder obtained by the wet method is once in the form of a dry cake through a solid-liquid separation step. In this dry cake, the present inventors have found a phenomenon in which the copper powder particles aggregate together when the size of the copper powder particles is small. If this agglomeration is left unattended, the particles (secondary particles) formed by agglomeration of the copper powder (primary particles) remain in the paste, deteriorating the properties of the copper powder paste. For this reason, a dry cake in which fine copper powders have aggregated together requires a complicated process of crushing and classifying the cake. The processes from rough crushing required in this case to crushing by a jet mill and subsequent classification are complicated and at the same time cause a lot of loss, which imposes a heavy burden on the production.

Therefore, an object of the present invention is to provide a copper powder that can be produced by reducing the burden of crushing and classifying a dry cake, and in which residual secondary particles are sufficiently reduced. It is in.

As a result of intensive research, the inventors have found that the above object can be achieved by treating copper powder produced by a wet method under specific pH conditions, and have completed the present invention.

Therefore, the present invention includes the following (1).
(1)
A copper powder produced by a wet method and having a zeta potential absolute value of 20 mV or more.

According to the present invention, it is possible to obtain an easily crushable copper powder in which residual secondary particles are sufficiently reduced while reducing the burden of crushing and classifying the dried cake.

FIG. 1 is a graph showing the results of a viscosity measurement test.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to embodiments. The present invention is not limited to the specific embodiments given below.

[Easily crushable copper powder]
The copper powder according to the present invention is a copper powder produced by a wet method and has an absolute value of zeta potential of 20 mV or more.

By using such a copper powder, the dispersibility of the copper powder is improved due to repulsion between the copper powder (primary particles). In other words, such a copper powder can suppress the generation of copper powder aggregates (secondary particles). As a result, it is possible to obtain an easily crushable copper powder in which residual secondary particles are sufficiently reduced while reducing the load of the process of crushing and classifying the dried cake.

Such a copper powder is suitably used as a metal powder for additive manufacturing (AM). As a mode of additive manufacturing, after forming a powder bed by spreading metal powder, an ink containing an organic substance that functions as a binder is sprayed onto the powder bed with an inkjet to form a shape, and then sintered to create a modeled object. technology is known. Such layered manufacturing requires ink (binder) wettability with respect to the metal powder (powder bed). This is because if the ink wettability is poor, the metal powder repels the ink, resulting in a low modeling accuracy. In this respect, layered manufacturing using the easily crushable copper powder described above exhibits excellent dispersibility due to the repulsion of the copper powder (primary particles), so the ink is not dispersed between the copper powder. It flows easily, in other words, it has high ink wettability, and high modeling accuracy can be achieved.

[Easily crushable]
Easy crushability means that the dry cake can be easily crushed, and the remaining secondary particles are sufficiently reduced without performing the classification process. In the case of the paste prepared under the conditions described in Examples described later, when a dry coating film of the paste is formed on a slide glass, Ra is 0.2 μm or less and Rz is 2 μm or less.

[Zeta potential]
In a preferred embodiment, the copper powder according to the present invention can have an absolute value of zeta potential measured under pH 7 conditions of, for example, 20 mV or more, preferably in the range of 20 to 100 mV. The zeta potential can be measured by known means, and specifically by the means and conditions described later in Examples.

[BET specific surface area]
In a preferred embodiment, the copper powder according to the present invention has a BET specific surface area of, for example, 2 m ² g ⁻¹ or more, preferably 2 m ² g ⁻¹ or more and 100 m ² g ⁻¹ or less, more preferably 2.5 m ² g ⁻¹ or more and 20 m ² g ⁻¹ or less, more preferably 3 m ² g ⁻¹ or more and 15 m ² g ⁻¹ or less. The BET specific surface area can be measured by known means, and specifically by the means and conditions described later in Examples.

[Carbon deposit]
In a preferred embodiment, the copper powder according to the present invention has a carbon deposition amount with respect to the copper powder as measured by a combustion method, for example, in the range of 0.1 to 0.6% by mass, preferably 0 0.1 to 0.5 mass %, more preferably 0.2 to 0.5 mass %, more preferably 0.2 to 0.4 mass %. The amount of carbon deposited by the combustion method can be measured by known means, and specifically by the means and conditions described later in Examples. The carbon deposition amount measured from the copper powder originates from the process of producing the copper powder by the wet method. If the amount of additive containing carbon is the same, the smaller the copper powder (copper powder with a larger specific surface area), the larger the amount of carbon adhered. Moreover, the copper powder having a larger amount of carbon adhered is more likely to be affected by the zeta potential fluctuation due to the pH treatment described later. In a preferred embodiment, the present inventor believes that excellent crushability can be achieved by using a copper powder having a specific combination of carbon deposition amount and zeta potential.

[TMA 1% shrinkage temperature]
In a preferred embodiment, the copper powder according to the present invention can have a TMA 1% shrinkage temperature of, for example, 500°C or less, preferably 200 to 500°C, more preferably 200 to 400°C. The TMA 1% shrinkage temperature can be measured by known means, and specifically by the means and conditions described later in Examples. That is, it can be measured using a TMA4000 manufactured by Netsch Japan Co., Ltd., under the following conditions: green compact density: 4.7 g/cm ³ , measurement atmosphere: nitrogen, temperature rise. Speed: 5°C/min, load: 10 mN.

[Tap density]
In a preferred embodiment, the copper powder according to the present invention has a tap density (hardened bulk density) of, for example, 3 g/cm ³ or less, preferably 3.0 g/cm ³ or less, preferably 2.9 g/cm ³ or less. , preferably 2.5 g/cm ³ or less. By making the tap density (hardened bulk density) smaller than the above upper limit, the dispersibility of the copper powder in the paste can be improved. The tap density can be measured by known means, and specifically by the means and conditions described later in Examples. That is, it can be measured using a powder tester PT-X manufactured by Hosokawa Micron Corporation. Specifically, a guide is attached to a 10 cc cup, powder is put in, tapped 1000 times, the guide is removed, the portion exceeding the volume of 10 cc is scraped off, and the weight of the powder in the container is measured. can be measured to determine the compacted bulk density.

In a preferred embodiment, the copper powder according to the invention has good dispersibility in the paste. The present inventor presumes that this is related to the low tap density (firm bulk density). The reason is not clear, but if the tap density is low in the dry powder state, there are many gaps between the dry powder, and one of the factors may be that solvents and resins easily enter these spaces. The inventor thinks.

In a preferred embodiment, the copper powder according to the invention is sufficiently crushed and thus has a large surface area. Therefore, the present inventor believes that the interaction with the solvent and the vehicle is strengthened in the paste, and the copper powder obtained in the present invention behaves as a thickening agent in the paste. As will be described later, in a preferred embodiment, the paste using the copper powder according to the present invention has a high viscosity in the low shear rate range and a low viscosity in the high shear rate range. The present inventors presume that in the low shear rate region, the interaction between the copper powder, the solvent, the resin, etc. is strong, and thus the viscosity is high. On the other hand, in the high shear rate range, the copper powder itself is sufficiently pulverized, so the present inventors presume that the paste is easily deformed and has a low viscosity as the shear rate increases. Such a paste is expected to be excellent in printability due to its behavior in the low shear rate region and the retention of the shape of the printed pattern, and in the high shear rate region. In a preferred embodiment, the copper powder according to the present invention may be used alone as a paste material, or mixed with larger micron-sized copper powders to increase the viscosity of the paste and adjust printability. . In the latter case, since the copper powder according to the present invention itself has low-temperature sinterability, the paste as a whole is sintered and a high-density sintered body is obtained.

[Production of easily crushable copper powder]
In a preferred embodiment, the easily crushable copper powder of the present invention is produced by a pH treatment step of contacting copper powder produced by a wet method with an alkaline aqueous solution of pH 8 to 14 or an acid aqueous solution of pH 0 to 4, It can be manufactured by a method comprising

[pH treatment step]
In a preferred embodiment, the pH treatment step is carried out by contacting with an alkaline aqueous solution or an acid aqueous solution having the above pH. In a preferred embodiment, the contact can be carried out, for example, by stirring copper powder produced by a wet method in the aqueous solution. Stirring can be performed, for example, by known means, and the stirring time can be, for example, using a rotating blade, a mixer, and a stirrer, for example, 5 minutes or more and 48 hours or less, preferably 10 minutes or more, It can be within 24 hours. In a preferred embodiment, the contact can be carried out, for example, by passing the aqueous solution through a copper powder produced by a wet method. The contact with the alkaline aqueous solution or the acid aqueous solution may be carried out, for example, batchwise once or multiple times. The copper powder after being brought into contact with the alkaline aqueous solution or the acid aqueous solution can be solid-liquid separated by a known means to obtain a cake. In a preferred embodiment, the copper powder that has been brought into contact with the alkaline aqueous solution or acid aqueous solution can be washed with pure water.

In a preferred embodiment, washing with pure water can be carried out by known means, for example, by passing pure water through the cake obtained by solid-liquid separation.

[Aqueous alkaline solution]
In a preferred embodiment, the pH of the alkaline aqueous solution to be brought into contact with the copper powder produced by the wet method can be, for example, pH 8-14, preferably pH 8-13, preferably pH 9-13. As the alkaline aqueous solution adjusted to the above pH, for example, ammonia water, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, organic substance aqueous solution containing an amino group at the molecular end, or a mixed aqueous solution thereof can be used.

[Aqueous acid solution]
In a preferred embodiment, the pH of the acid aqueous solution that is brought into contact with the copper powder produced by the wet method can be, for example, pH 0-4, preferably pH 1-4, preferably pH 1-3. As the acid aqueous solution adjusted to the above pH, for example, an aqueous solution of an organic acid such as dilute sulfuric acid or methanesulfonic acid, or a mixed aqueous solution thereof can be used.

[Drying]
In a preferred embodiment, the pH treated copper powder is then dried. Drying can be performed by known means, for example, at 60 to 300° C., preferably 60 to 150° C., in a nitrogen atmosphere or a vacuum atmosphere. The copper powder thus obtained is often obtained in the form of a dry cake.

[Crushing]
In a preferred embodiment, the pH treated and then dried copper powder is then ground. Crushing can be performed by known means, for example, a pestle, mortar, or mixer can be used. According to the present invention, the coarse crushing by such a simple means is sufficiently crushed and the secondary particles are sufficiently reduced. The process of crushing by a powerful crushing means and the process of classification are not required. In addition, since it does not require a powerful crushing means such as a bead mill crushing using ceramic beads, the natural shape of the copper powder produced by the wet method can be maintained, and the mechanically deformed shape can be preserved. can be avoided. According to the present invention, it is sufficiently crushed by rough crushing by such a simple means, but if desired, mechanical crushing such as a Henschel mixer or jet mill crushing may be performed thereafter. However, it does not exclude performing a classification step afterwards, if desired. The copper powder according to the present invention achieves easy crushability by pH treatment, and can be easily crushed. For example, it can be sufficiently crushed with a pestle, mortar, or mixer. However, as a crushing means for easily crushable copper powder, it is not excluded to adopt a more powerful crushing means, for example, mechanical crushing such as Henschel mixer, jet mill crushing may be performed.

[Copper powder paste]
In a preferred embodiment, the easily crushable copper powder of the present invention can be suitably used as a copper powder paste containing this copper powder. The copper powder paste can be prepared, for example, by kneading easily crushable copper powder with a binder resin and an organic solvent. and/or antifoaming agents may be added. The easily crushable copper powder of the present invention is sufficiently crushed by simple means, and the primary particles repel each other, so the risk of subsequent reaggregation is reduced. , becomes highly dispersed in the paste. Therefore, the copper powder paste according to the present invention has a smooth surface on the electrode obtained by printing and firing the paste, and the risk of disconnection of the wiring is reduced.
Such a copper powder paste is suitably used as a metal ink for inkjet printing. The reason for this is that metal inks for inkjet printing are required to have properties that do not clog nozzles, and the above-mentioned easily crushable copper powder is less likely to clog nozzles. This is because the readily crushable copper powder has excellent dispersibility and is less likely to form secondary particles.

In a preferred embodiment, binder resins used in the paste include, for example, cellulose resins, acrylic resins, alkyd resins, polyvinyl alcohol resins, polyvinyl acetals, ketone resins, urea resins, melamine resins, polyesters, polyamides, polyurethanes. can give The binder resin in the copper powder paste can be contained at a ratio of, for example, 0.1 to 10% with respect to the mass of the copper powder. In a preferred embodiment, the organic solvent includes an alcohol solvent (eg, one or more selected from the group consisting of terpineol, dihydroterpineol, isopropyl alcohol, butyl carbitol, terpineloxyethanol, and dihydroterpineloxyethanol), One or more selected from the group consisting of glycol ether solvents (e.g. butyl carbitol), acetate solvents (e.g. butyl carbitol acetate, dihydroterpineol acetate, dihydrocarbitol acetate, carbitol acetate, linaryl acetate, terpinyl acetate) ), ketone solvents (e.g. methyl ethyl ketone), hydrocarbon solvents (e.g. one or more selected from the group consisting of toluene and cyclohexane), cellosolves (e.g. one or more selected from the group consisting of ethyl cellosolve and butyl cellosolve), diethyl Phthalate or propineate-based solvents (for example, one or more selected from the group consisting of dihydroterpinylpropineate, dihydrocarbylpropineate, and isobornylpropineate) can be mentioned. In a preferred embodiment, a glass frit having a diameter of, for example, 0.1 to 10 μm, preferably 0.1 to 5.0 μm can be used as the glass frit. In preferred embodiments, dispersants include, for example, oleic acid, stearic acid and oleylamine. In a preferred embodiment, antifoaming agents include, for example, organically modified polysiloxanes and polyacrylates. In a preferred embodiment, the copper powder paste has a copper powder mass ratio of 30 to 90%, a glass frit mass ratio of 0 to 5%, and a binder resin. The mass ratio is set as above, and the balance can be contained as an organic solvent, dispersant, or the like. Kneading can be performed using known means. In a preferred embodiment, a copper powder paste can be prepared from easily crushable copper powder according to the paste preparation disclosed in Patent Document 1 (WO2013/125659), for example.

[Sintered body]
In a preferred embodiment, the copper powder paste containing the easily crushable copper powder of the present invention can be printed or coated, if desired, and then sintered to form a sintered body. In a preferred embodiment, the sintered body obtained has a smooth surface.

In a preferred embodiment, after printing the copper powder paste containing the easily crushable copper powder of the present invention, the surface roughness Ra of the dried coating film is, for example, in the range of 0.01 to 0.4 μm, preferably can range from 0.01 to 0.3 μm. The roughness of the sintered body is actually affected not only by the dispersibility of the copper powder in the paste, but also by the printing conditions. bottom. The surface roughness Ra of the dry coating film can be measured by known means, and specifically by the means and conditions described later in Examples. A sintered body formed by sintering such a coating film can be suitably used as an electrode layer, a conductive layer, and the like in electronic circuits and electronic parts. In a preferred embodiment, the easily crushable copper powder of the present invention can be sintered to form a sintered body.

In a preferred embodiment, sintering can be performed under known conditions, for example, by heating at a temperature in the range of 200 to 1000° C. in a non-oxidizing atmosphere for 0.1 to 10 hours. can do.

[Copper powder produced by wet method]
In a preferred embodiment, the copper powder to be subjected to the pH treatment step is copper powder produced by a wet method. Wet methods include so-called disproportionation methods and so-called chemical reduction methods.

In a preferred embodiment, for example, the method disclosed in Patent Document 2 (Japanese Patent No. 6297018) can be used as a method for producing copper powder by a disproportionation method. In a preferred embodiment, the method for producing copper powder by a disproportionation method includes, for example, a step of adding cuprous oxide to an aqueous solvent containing an additive of gum arabic to prepare a slurry, adding dilute sulfuric acid to the slurry, and adding dilute sulfuric acid to the slurry. A production method including a step of performing a disproportionation reaction by adding them all at once within 5 seconds can be mentioned. In a preferred embodiment, the slurry is maintained at room temperature (20 to 25° C.) or lower, and dilute sulfuric acid similarly maintained at room temperature or lower is added to carry out the disproportionation reaction. In a preferred embodiment, the slurry is maintained at 7° C. or lower, and dilute sulfuric acid similarly maintained at 7° C. or lower is added to carry out the disproportionation reaction. In a preferred embodiment, dilute sulfuric acid can be added so that the pH is 2.5 or less, preferably 2.0 or less, and more preferably 1.5 or less. In a preferred embodiment, the dilute sulfuric acid is added to the slurry within 5 minutes, preferably within 1 minute, more preferably within 30 seconds, more preferably within 10 seconds, and more preferably within 5 seconds. , can be added. In a preferred embodiment, the disproportionation reaction can be completed in 10 minutes. In a preferred embodiment, the concentration of gum arabic in the slurry can be 0.229-1.143 g/L. As the cuprous oxide, cuprous oxide used by a known method, preferably cuprous oxide particles can be used. Coarse cuprous oxide particles can be used because they are not directly related to the particle size of the particles. The principle of this disproportionation reaction is as follows:
_{Cu2O +} H2SO4→Cu↓+ _{CuSO4 + H2O}

The copper powder thus obtained may be subjected to the pH treatment step in the form of a slurry after being washed, or may be subjected to the pH treatment step after being dried once in the form of copper powder. .

In a preferred embodiment, for example, the method disclosed in Patent Document 3 (Japanese Patent No. 4164009) can be used as a method for producing copper powder by chemical reduction. In a preferred embodiment, as a method for producing copper powder by a chemical reduction method, for example, after adding 2 g of gum arabic to 2900 mL of pure water, 125 g of copper sulfate is added and stirred while adding 80% hydrazine monohydrate. is added, the temperature is raised from room temperature to 60 ° C. over 3 hours after the addition of hydrazine monohydrate, copper oxide is reacted over 3 hours, and after the reaction is completed, the resulting slurry is and then washed with pure water and methanol and dried to obtain copper powder. The dried copper powder thus obtained may be subjected to the above pH treatment step, or may be subjected to the above pH treatment step in the form of a slurry.

[Preferred embodiment]
The present invention includes the following (1) embodiments.
(1)
A copper powder produced by a wet method and having a zeta potential absolute value of 20 mV or more.
(2)
The copper powder according to (1), which has a BET specific surface area of 2 m ² g ⁻¹ or more.
(3)
The copper powder according to any one of (1) to (2), having a carbon deposition amount in the range of 0.1 to 0.6%.
(4)
The copper powder according to any one of (1) to (3), having a TMA 1% shrinkage temperature in the range of 200 to 500°C.
(5)
The copper powder according to any one of (1) to (4), which has a tap density of less than 3 gcm ^-3 .
(6)
The copper powder according to any one of (1) to (5), which is an easily crushable copper powder.
(7)
The copper powder according to any one of (1) to (6), which is a copper powder for additive manufacturing.
(8)
A copper powder paste containing the copper powder according to any one of (1) to (7).
(9)
The copper powder paste according to (8), wherein the copper powder paste is ink for inkjet printing.
(10)
A sintered body obtained by sintering the copper powder according to any one of (1) to (7) or the copper powder paste according to any one of (8) to (9).
(11)
A pH treatment step of contacting the copper powder produced by the wet method with an alkaline aqueous solution of pH 8 to 14 or an acid aqueous solution of pH 0 to 4,
A method for imparting easy crushability to copper powder.
(12)
A pH treatment step of contacting the copper powder produced by the wet method with an alkaline aqueous solution of pH 8 to 14 or an acid aqueous solution of pH 0 to 4,
A method for producing an easily crushable copper powder, comprising:

Accordingly, the present invention includes external electrodes provided on a ceramic laminate, laminated ceramic products in which external electrodes are provided on a ceramic laminate, laminated ceramic capacitors, and laminated ceramic inductors.

The present invention will be described in more detail with reference to the following examples. The invention is not limited to the following examples.

[Example 1]
[Production of copper powder by disproportionation method (milling method A)]
2.5 L of 25 vol % dilute sulfuric acid was instantaneously added to a slurry consisting of 1 kg of cuprous oxide, 4 g of gum arabic, and 7 L of pure water, and stirred at 500 rpm for 10 minutes. After the copper powder obtained by this operation settled sufficiently, the supernatant was removed, 7 L of pure water was added, and the mixture was stirred at 500 rpm for 10 minutes. This operation was repeated until the concentration of Cu derived from Cu ²⁺ in the supernatant fell below 1 g/L. After that, decantation was performed to obtain a copper powder slurry by a disproportionation method. The copper powder produced by the disproportionation method is described as "A" as the production method in Table 1.

[pH treatment]
The supernatant liquid obtained by decantation was removed, and 500 g (wet mass) of the precipitated copper powder slurry was poured into 1 L of ammonia water adjusted to pH 8 and stirred. Stirring was carried out at 25° C. for 1 hour. Thereafter, solid-liquid separation was performed by suction filtration to obtain a pH-treated copper powder cake. The resulting cake was washed with pure water when the pH of the pure water after filtration was below 8 as a guideline.

[Drying and crushing]
The washed copper powder cake was dried at 100° C. under a nitrogen atmosphere to obtain a pH-treated copper powder dry cake.
The resulting dry cake was coarsely crushed with a pestle and mortar. Thus, a copper powder according to Example 1 was obtained.

[Tap density]
The tap density of the copper powder according to Example 1 was measured under the following conditions.
It was measured using Hosokawa Micron Corporation Powder Tester PT-X. Attach a guide to a 10 cc cup and put the powder in it, tap it 1000 times, remove the guide, scrape off the part exceeding the 10 cc volume, measure the weight of the powder in the container, tap Density (firm bulk density) was determined.

[BET specific surface area]
The BET specific surface area of the copper powder according to Example 1 was measured after pretreatment by heating in vacuum at 200° C. for 5 hours using BELSORP-miniII manufactured by Microtrac Bell.

[Carbon deposit]
For the copper powder of Example 1, the carbon deposition amount was measured by a combustion method using LECO's CS600.

[TMA 1% shrinkage temperature]
The TMA 1% shrinkage temperature of the copper powder according to Example 1 was measured under the following conditions.
It was measured using a TMA4000 manufactured by Netch Japan Co., Ltd. The conditions were:
Green compact density: 4.7 g/cm ³
Measurement atmosphere: Nitrogen Heating rate: 5°C/min
Load: 10mN

[Zeta potential]
The zeta potential of the copper powder according to Example 1 was measured at pH 7 as follows.
The zeta potential of the powder was measured using a Zetasizer Nano ZS from Malvern Panalytical. More specifically, about 50 mg of a sample was collected in a 50 mL sample bottle, a 0.1 wt % sodium hexametaphosphate aqueous solution was injected so that the total amount was 50 g, and ultrasonic waves were applied for 3 minutes. At that time, US-4R manufactured by AS ONE was used as an ultrasonic irradiation device, and the output was set to 180 W and the frequency was set to 40 kHz. After that, 100 μL of the above dispersion was diluted with 900 μL of 0.1% sodium hexametaphosphate aqueous solution, and 900 μL of the diluted solution was injected into the measurement cell with a micropipette. The liquid temperature was adjusted to 25°C.

[Surface roughness of coating film Ra]
A vehicle obtained by passing terpineol and ethyl cellulose through a rotation-revolution mixer and three rolls and sufficiently kneading them in advance, oleic acid, and the copper powder of Example 1 were mixed in a ratio of copper powder:ethyl cellulose:oleic acid:terpineol=80:2. The mixture was mixed so as to have a weight ratio of 3:1.6:16.1, preliminarily kneaded with a rotation/revolution mixer, passed through three rolls (finishing roll gap: 5 μm), and defoamed using a rotation/revolution mixer. . The resulting paste was applied onto a slide glass using an applicator with a 25 μm gap and dried at 120° C. for 10 minutes. The Ra of the coating film obtained in the coating direction was measured with a stylus type roughness meter according to JIS B 0601-2001, and the average of 5 points was calculated.

[result]
Table 1 summarizes the results of the above measurements for the copper powder of Example 1.

[Examples 2 to 6]
[Production of copper powder by disproportionation method (milling method A)]
In the same manner as in Example 1, a copper powder slurry was obtained by a disproportionation method.

[pH treatment]
The pH of the ammonia water used for the treatment was changed from that in Example 1 (Examples 2 to 4), or instead of the ammonia water, dilute sulfuric acid adjusted to pH 1 (Example 5) or hydroxylation adjusted to pH 13 After stirring with an aqueous potassium solution for 1 hour, solid-liquid separation was performed by suction filtration, the collected cake was filtered with 5 L of diluted sulfuric acid having a pH of 1, and the cake was washed with pure water until the pH of the filtrate exceeded 5 (Example 6). ), the pH treatment was carried out in the same manner as in Example 1 to obtain a slurry of pH-treated copper powder.
Thereafter, solid-liquid separation was performed by suction filtration to obtain a pH-treated copper powder cake. The cake thus obtained was washed with pure water when the pH of the pure water after filtration exceeded 5 as a guideline.
However, in Example 6, instead of washing the obtained cake with pure water, the cake was washed by suction filtration using 1250 mL of pH 1 dilute sulfuric acid per 100 g of copper powder.
The pH values used in Examples 2-6 are summarized in Table 1, respectively. Incidentally, the pH was adjusted by appropriately adding ammonia and dilute sulfuric acid. Further, Table 2 summarizes the treatment method of the pH treatment.

[Drying and crushing]
The copper powder cake was treated in the same manner as in Example 1 to obtain a dry cake, which was coarsely pulverized to obtain copper powders of Examples 2-6.

[Measurements and results]
The copper powders of Examples 2 to 6 were measured in the same manner as in Example 1, and Table 1 summarizes the results.

[Example 7]
[Production of copper powder by reduction method (milling method B)]
Copper powder was obtained by a chemical reduction method according to Patent Document 3 (Patent No. 4164009). That is, after adding 2 g of gum arabic to 2900 mL of pure water, 125 g of copper sulfate was added and 360 mL of 80% hydrazine monohydrate was added while stirring. After adding hydrazine monohydrate, the temperature was raised from room temperature to 60° C. over 3 hours, and copper oxide was allowed to react over 3 hours. After completion of the reaction, the resulting slurry was filtered with a Nutsche, and pure water filtration was repeated until the pH of the filtrate reached the level of 7 to obtain a copper powder slurry. Thus, a copper powder slurry was obtained by the reduction method. The copper powder produced by the reduction method is described as "B" as the production method in Table 1.

[pH treatment]
The obtained copper powder slurry was subjected to pH treatment in the same manner as in Example 1, except that the pH of the aqueous ammonia used for the treatment was changed from that in Example 1. A cake of copper powder was obtained. The resulting cake was washed with pure water in the same manner as in Example 1. The pH values used in Example 7 are shown in Table 1.

[Drying and crushing]
The copper powder cake was treated in the same manner as in Example 1 to obtain a dry cake, which was coarsely pulverized to obtain the copper powder of Example 7.

[Measurements and results]
The copper powder of Example 7 was measured in the same manner as in Example 1, and the results are shown in Table 1.

[Examples 8-9]
[Production of copper powder by reduction method (milling method B)]
In the same manner as in Example 7, a copper powder slurry was obtained by a reduction method.

[pH treatment]
pH treatment was performed in the same manner as in Example 1, except that dilute sulfuric acid adjusted to pH 3 or pH 1 (Examples 8 to 9) was used instead of aqueous ammonia to obtain a pH-treated copper powder cake. got The resulting cake was washed with pure water until the pH of the filtrate exceeded 5. The pH values used in Examples 8-9 are summarized in Table 1, respectively.

[Drying and crushing]
A dry cake was obtained from the pH-treated copper powder slurry in the same manner as in Example 1, and this was coarsely pulverized to obtain copper powders of Examples 8 and 9.

[Measurements and results]
The copper powders of Examples 8 and 9 were measured in the same manner as in Example 1, and Table 1 summarizes the results.

[Comparative Example 1]
[Production of copper powder by disproportionation method (milling method A)]
In the same manner as in Example 1, a copper powder slurry was obtained by a disproportionation method.

[Drying and crushing]
A dry cake was obtained in the same manner as in Example 1 without performing a pH treatment on the copper powder slurry, which was coarsely pulverized to obtain a copper powder of Comparative Example 1.
The copper powder of Comparative Example 1 was measured in the same manner as in Example 1, and the results are summarized in Table 1.

[Comparative Example 2]
[Production of copper powder by reduction method (milling method B)]
In the same manner as in Example 7, a copper powder slurry was obtained by a reduction method.

[Drying and crushing]
A dry cake was obtained in the same manner as in Example 1 without performing a pH treatment on the slurry of the copper powder, and this was coarsely pulverized to obtain the copper powder of Comparative Example 2.
The copper powder of Comparative Example 2 was measured in the same manner as in Example 1, and the results are summarized in Table 1.

[Viscosity measurement test]
A paste was prepared in the same manner as in Example 1 using the copper powders of Example 3 and Comparative Example 1. The viscosity of the resulting paste was measured using an E-type viscometer MCR102 (2° cone plate, 25° C., shear rate range 0.01-1000 s ⁻¹ ). The results are shown in FIG. As shown in FIG. 1, the viscosity of the paste using the copper powder of Example 3 is high in the low shear rate range of 0.2 s ^-1 or less, and the copper powder of Example 3 is used in the shear rate range of over 10 s ^-1 . The paste used is less viscous. Thus, the copper powder paste according to the present invention was excellent in shape retention from the behavior in the low shear rate region and excellent in printability from the behavior in the high shear rate region.

The present invention provides an easily crushable copper powder. The present invention is an industrially useful invention.

Claims (9)

The absolute value of the zeta potential is 20 mV or more ,
A copper powder having a tapped density of less than 3 gcm ⁻³ . The copper powder according to claim 1, which has a BET specific surface area of 2 m ² g ^-1 or more. The copper powder according to any one of claims 1 and 2, having a carbon deposition amount in the range of 0.1 to 0.6%. The copper powder according to any one of claims 1 to 3, having a TMA 1% shrinkage temperature in the range of 200 to 500°C. The copper powder according to any one of claims 1 to 4 , which is an easily crushable copper powder. The copper powder according to any one of claims 1 to 5 , which is a copper powder for additive manufacturing. A copper powder paste containing the copper powder according to any one of claims 1 to 6 . The copper powder paste according to claim 7 , wherein the copper powder paste is ink for inkjet printing. A sintered body obtained by sintering the copper powder according to any one of claims 1 to 7 or the copper powder paste according to any one of claims 7 to 8 .

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