Method for manufacturing copper powder

Abstract

To provide a method capable of producing copper powder that has superior oxidation resistance while containing sulfur.SOLUTION: A method for producing copper powder includes an anticorrosion step for subjecting untreated copper powder to anticorrosive treatment with an anticorrosive agent including at least one selected from the group consisting of 2-mercaptobenzothiazole sodium salt and a hydrate thereof, 3-(2-benzothiazylthio) propionic acid, and (2-benzothiazylthio) acetic acid.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a method for producing copper powder. [Background technology]

[0002] Copper powder is sometimes incorporated into an organic binder to form a metal powder paste, which is then used in the manufacture of electronic components such as wiring or terminals for low-temperature co-fired ceramic (LTCC) substrates, or as electrode materials for multilayer ceramic chip capacitors (MLCCs). Copper powder has high conductivity and is considered promising as a raw material for the above-mentioned electronic components because it has the potential to enable thinning or miniaturization of electrode materials and improvement of frequency characteristics.

[0003] To manufacture copper powder, liquid-phase or gas-phase methods can be used. In particular, the gas-phase reduction method involves contacting copper chloride gas with a reducing gas to reduce the copper chloride back into copper, thereby producing copper powder. This method allows for easy control of particle size and efficient production of spherical particles. An example of this type of technology is described in Patent Document 1.

[0004] Patent Document 1 proposes a method for producing copper powder, comprising: generating copper chloride gas by reaction of metallic copper with a chlorine-containing gas; generating a plurality of copper particles by reaction of the copper chloride gas with a reducing gas; reducing the chlorine content of the plurality of copper particles by treating them with a cleaning solution containing an alkali metal hydroxide; reducing the oxygen content of the plurality of copper particles by treating them with a cleaning solution containing ascorbic acid, hydrazine, or citric acid; and treating the plurality of copper particles obtained by the reduction of the oxygen content with a treatment solution containing a nitrogen-containing heteroaromatic compound. Here, the above-mentioned "nitrogen-containing heteroaromatic compounds" include "benzotriazole and its derivatives, triazole and its derivatives, thiazole and its derivatives, benzothiazole and its derivatives, imidazole and its derivatives, and benzimidazole and its derivatives." Furthermore, Patent Document 1 describes the use of "an aqueous solution (approximately 300 mL) containing 0.33% by mass of benzotriazole at room temperature" for rust prevention treatment. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6738460 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Incidentally, copper powder containing sulfur is sometimes required to improve conductivity after sintering. In this case, it is desirable that sulfur can be added during the rust prevention treatment, as this eliminates the need for a separate process for sulfur addition.

[0007] However, rust prevention treatment also requires the addition of sulfur to the copper powder to provide high oxidation resistance. In particular, copper powder is sometimes required to have sufficient oxidation suppression even under harsh conditions with higher-than-usual temperature and humidity.

[0008] While Patent Document 1 provides several examples of rust inhibitors, only benzotriazole was actually used. Sulfur cannot be added to benzotriazole. Furthermore, Patent Document 1 does not address the inclusion of sulfur in copper powder during rust prevention treatment.

[0009] The object of this invention is to address the problems described above, and its purpose is to provide a method for producing copper powder that contains sulfur while having excellent oxidation resistance. [Means for solving the problem]

[0010] The present invention provides a method for producing copper powder, which includes a rust prevention step in which the copper powder is subjected to rust prevention treatment using a rust inhibitor containing at least one selected from the group consisting of 2-mercaptobenzothiazole sodium salt and its hydrate, 3-(2-benzothiadilthio)propionic acid, and (2-benzothiadilthio)acetic acid.

[0011] The sulfur content relative to the specific surface area of ​​the copper powder obtained after the aforementioned rust prevention process is 0.005 mass%·g / m². 2 ~0.4 mass% g / m 2 It is preferable that this be the case.

[0012] The carbon content relative to the specific surface area of ​​the copper powder obtained after the aforementioned rust prevention process is 0.01 mass%·g / m². 2 ~0.4 mass% g / m 2 It is preferable that this be the case.

[0013] In the rust prevention process, it is preferable to perform the rust prevention treatment on the copper powder before treatment, followed by washing with water.

[0014] The above manufacturing method preferably includes a deoxidation step, prior to the rust prevention step, in which the untreated copper powder is brought into contact with an oxygen scavenger containing at least one selected from the group consisting of ascorbic acid, hydrazine, and citric acid, thereby reducing the oxygen content of the untreated copper powder.

[0015] The oxygen content with respect to the specific surface area of the copper powder obtained after the rust prevention step is 0.03 mass%·g / m 2 ~1.0 mass%·g / m 2 and it is preferably this.

[0016] The above manufacturing method may include a reduction step of bringing copper chloride gas into contact with a reducing gas to obtain the pre-treatment copper powder, and a dechlorination step of bringing the pre-treatment copper powder into contact with a dechlorinating agent containing a hydroxide of an alkali metal after the reduction step and before the rust prevention step to reduce the chlorine content of the pre-treatment copper powder.

Advantages of the Invention

[0017] According to the method for producing copper powder of this invention, it is possible to produce copper powder having excellent oxidation resistance while containing sulfur.

Brief Description of the Drawings

[0018] [Figure 1] It is a flowchart showing a method for producing copper powder according to an embodiment of this invention. [Figure 2] It is a flowchart showing an example of a method for producing pre-treatment copper powder that can be used in the method for producing copper powder of FIG. 1.

Modes for Carrying Out the Invention

[0019] Hereinafter, embodiments of this invention will be described in detail. The method for producing copper powder according to an embodiment of this invention includes a rust prevention step of performing rust prevention treatment on the pre-treatment copper powder using a predetermined rust prevention agent.

[0020] Here, the specified rust inhibitor is one selected from the group consisting of 2-mercaptobenzothiazole sodium salt and its hydrate, 3-(2-benzothiadylthio)propionic acid, and (2-benzothiadylthio)acetic acid. By using the above rust inhibitor in the rust prevention process, it is possible to produce copper powder that contains sulfur and has high oxidation resistance, making it less susceptible to oxidation even under harsh conditions.

[0021] If necessary, a deoxygenation step may be performed before the rust prevention step, as shown in Figure 1. However, such a deoxygenation step may be omitted.

[0022] (Untreated copper powder) In this context, "pre-processed copper powder" refers to copper powder before the rust prevention treatment is applied in the rust prevention process, and is a term used to distinguish it from the final manufactured copper powder.

[0023] The copper powder to be prepared can be a commercially available or pre-fabricated product, or it may be prepared by a gas-phase method such as gas-phase reduction, or by a liquid-phase method. Here, we will explain in detail the case of preparing the copper powder to be prepared by gas-phase reduction as an example, but this is not the only method.

[0024] In the gas-phase reduction method, as shown in Figure 2, a solid copper raw material consisting mainly of elemental copper is brought into contact with chlorine gas in a chlorination step to obtain copper chloride gas, and a reduction step is performed in which the copper chloride gas is brought into contact with a reducing gas and reacted. More specifically, copper chloride gas can be generated in the chlorination step and supplied to the reduction step to come into contact with a reducing gas, thereby continuously reducing the copper chloride gas.

[0025] In the chlorination process, the copper raw material is heated to a temperature below its melting point, for example, 800°C to 1000°C, while chlorine gas is supplied to bring the high-temperature copper raw material into contact with the chlorine gas. At this time, an inert gas for dilution may be supplied along with the chlorine gas to adjust the amount of chlorine that comes into contact with the copper raw material. In this way, the copper in the copper raw material is chlorinated to produce gaseous copper chloride, i.e., copper chloride gas. However, if copper chloride gas is already available or obtained by another method, the chlorination process may be omitted.

[0026] In the reduction process, the copper chloride gas is brought into contact with a reducing gas at a temperature of, for example, 1000°C to 1300°C to reduce the copper chloride in the copper chloride gas to copper. Examples of reducing gases include hydrogen, hydrazine, ammonia, and methane. In addition to the reducing gas, chlorine gas or an inert gas for dilution may also be supplied. When the copper chloride gas comes into contact with the reducing gas, copper atoms are generated at that moment, and ultrafine particles are generated and grow as the copper atoms collide with each other to form copper particles.

[0027] The copper particles obtained in the reduction process are rapidly cooled to a predetermined temperature while blowing in an inert gas such as nitrogen as needed to suppress aggregation. The copper particles are then separated and recovered using a bag filter or the like. This yields untreated copper powder, which is an aggregate of copper particles.

[0028] (Dechlorination process) As described above, the untreated copper powder obtained in the reduction process tends to contain chlorine, for example, as copper chloride formed on the surface of the copper particles through a reaction with hydrogen chloride. Chlorine can cause metal degradation and other adverse effects in multilayer ceramic chip capacitors and the like that can be manufactured using copper powder. The dechlorination process removes this chlorine from the untreated copper powder and can therefore be performed after the reduction process and before the rust prevention process described later (or before the deoxygenation process if one is performed).

[0029] In the dechlorination process, the untreated copper powder obtained in the reduction process is brought into contact with a dechlorinating agent containing alkali metal hydroxides. Typically, the untreated copper powder can be added to the dechlorinating agent to form a slurry, which can then be stirred. This removes the chlorine from the untreated copper powder.

[0030] Specifically, as a dechlorinating agent, alkaline aqueous solutions such as sodium hydroxide or potassium hydroxide with a concentration of approximately 0.1 ml to 1.5 ml can be used. Among these, aqueous sodium hydroxide solution is preferred because it is inexpensive.

[0031] The dechlorination process reduces the chlorine content of the copper powder before treatment. The chlorine (Cl) content of the copper powder obtained after the dechlorination and rust prevention process is preferably 100 ppm by mass or less, and may be, for example, 30 ppm by mass or less. The chlorine content of the copper powder is measured by coulometric titration using a chlorine analyzer TOX2100H (manufactured by Mitsubishi Chemical Corporation).

[0032] (Deoxygenation process) It is desirable to deoxygenate the copper powder before subjecting it to the rust prevention process described below to reduce its oxygen content. This allows for the copper powder to maintain a relatively low oxygen content while being given oxidation resistance during the rust prevention process.

[0033] Furthermore, copper powder with a high oxygen content and advanced oxidation forms an uneven copper oxide surface, resulting in reduced circularity. This deteriorates the flatness of electrodes manufactured using such powder, leading to increased electrical resistance and poor contact. To prevent such problems, it is preferable to reduce the oxygen content through a deoxygenation process and to enhance oxidation resistance through a rust prevention process, as described here.

[0034] In the deoxygenation process, the untreated copper powder is brought into contact with the deoxygenating agent by adding it to the deoxygenating agent and stirring. This removes the oxygen from the untreated copper powder, thereby reducing its oxygen content.

[0035] The oxygen absorber may be an aqueous solution containing at least one selected from the group consisting of ascorbic acid, hydrazine, and citric acid. When using an oxygen absorber containing ascorbic acid, the ascorbic acid concentration of the oxygen absorber may be 5% by mass or more, more specifically 10% by mass, 25% by mass or less, and more specifically 20% by mass or less. The oxygen absorber may contain water, alcohols such as ethanol or isopropyl alcohol, or ketones such as acetone or methyl ethyl ketone as a solvent.

[0036] By performing a deoxygenation process, the oxygen content relative to the specific surface area of ​​the copper powder obtained after the rust prevention process can be reduced to, for example, 0.03 mass%·g / m². 2 ~1.0 mass% g / m 2 This can be reduced to a suitable degree.

[0037] (Rust prevention process) The copper powder before treatment is subjected to the deoxygenation process described above, if necessary, before being subjected to the rust prevention process.

[0038] In the rust prevention process, sulfur is added to the copper powder while applying a rust prevention treatment. As a result, the copper powder produced in this embodiment contains sulfur. It is generally known that copper sulfide has higher conductivity than copper oxide. Sulfur-containing copper powder is more readily formed into copper sulfide than copper oxide and is expected to be suitably used in applications such as the aforementioned electronic components.

[0039] While sulfur is added in rust prevention treatment, it is also necessary to effectively impart oxidation resistance, which is the original purpose. The inventor diligently studied rust inhibitors that could add sulfur while suppressing the oxidation of copper powder even under harsh conditions of high temperature and high humidity, and as a result found that using the following sulfur-containing rust inhibitor is effective.

[0040] That is, in this embodiment, in the rust prevention step, among benzothiazoles, at least one rust preventive agent selected from the group consisting of sodium 2-mercaptobenzothiazole and its hydrate, 3-(2-benzothiazylthio)propionic acid, and (2-benzothiazylthio)acetic acid is used. Here, the hydrate of sodium 2-mercaptobenzothiazole includes sodium 2-mercaptobenzothiazole monohydrate. The above rust preventive agent may include at least one selected from the group consisting of sodium 2-mercaptobenzothiazole (C6H4(NCS)-SNa), sodium 2-mercaptobenzothiazole monohydrate (C6H4(NCS)-SNa·H2O), 3-(2-benzothiazylthio)propionic acid (C6H4(NCS)-S-C3H5O2), and (2-benzothiazylthio)acetic acid (C6H4(NCS)-S-C2H3O2). Note that other rust preventive agents containing thiourea and the like cannot impart such high oxidation resistance.

[0041] Typically, the above rust preventive agent is dissolved in a solvent to form an aqueous solution, and the rust prevention treatment can be performed on the copper powder before treatment by adding the copper powder before treatment into this aqueous solution. Examples of the solvent used here include water, alcohols such as ethanol and isopropyl alcohol, ketones such as acetone and methyl ethyl ketone, amides such as N,N-dimethylacetamide and N,N-dimethylformamide, and aromatic compounds such as toluene and xylene. When water is used as the solvent, rust preventive agents such as 3-(2-benzothiazylthio)propionic acid and (2-benzothiazylthio)acetic acid, which are insoluble in water, can be dissolved after being neutralized with a neutralizing agent such as sodium hydroxide.

[0042] The usage amount of the rust preventive agent can be appropriately determined according to the target values such as the sulfur content and carbon content of the copper powder obtained after the rust prevention step.

[0043] The specific surface area of the copper powder obtained after the rust prevention step depends on the particle size, but is 2 m 2 / g to 30 m 2It is preferable that the concentration is / g. The specific surface area of ​​the copper powder is measured by the BET method (gas adsorption method) using a fully automatic specific surface area measuring device Macsorb® (manufactured by Mountec Co., Ltd.). The adsorption gas can be, for example, nitrogen gas.

[0044] The sulfur content relative to the specific surface area of ​​the copper powder obtained after the rust prevention process is 0.005 mass%·g / m², from the viewpoint of improving conductivity after sintering. 2 ~0.4 mass% g / m 2 This is preferable. However, if the sulfur content of the copper powder is too high, a large amount of sulfur-derived gas will be generated, which may cause cracks and delamination. The sulfur content of the copper powder is measured by ICP emission spectroscopy using an ICP emission spectrometer SPS3100 (manufactured by SII Nanotechnology Co., Ltd.).

[0045] Furthermore, the carbon content relative to the specific surface area of ​​the copper powder obtained after the rust prevention process is 0.01 mass%·g / m². 2 ~0.4 mass% g / m 2 This is preferable. If the carbon content of the copper powder is high, there is a concern that a large amount of gas derived from the carbon will be generated during sintering. The carbon content of the copper powder is measured by combustion infrared absorption spectroscopy using a carbon-sulfur analyzer EMIA-920V2 (manufactured by Horiba, Ltd.).

[0046] After the rust prevention treatment, it is preferable to wash with water such as pure water. This effectively removes sodium that may adhere due to the rust inhibitors and neutralizing agents mentioned above. The sodium content of the copper powder obtained after the rust prevention process is preferably less than 10 ppm by mass. The sodium content of the copper powder is measured by atomic absorption spectrometry using a polarized Zeeman atomic absorption spectrophotometer ZA3300 (manufactured by Hitachi High-Tech Corporation).

[0047] After the rust prevention process is complete, if necessary, dry or wet classification, crushing using a jet mill, sieving, etc. are performed to obtain copper powder with a 50% particle size of approximately 100 nm to 500 nm. The 50% particle size refers to the particle size at which the cumulative frequency in the volume-based particle size histogram reaches 50%. The copper powder produced in this way contains sulfur and is resistant to oxidation even under harsh conditions, exhibiting excellent oxidation resistance. [Examples]

[0048] Next, the copper powder manufacturing method of this invention was experimentally implemented and its effects were confirmed, which are described below. However, this description is for illustrative purposes only and is not limited to this.

[0049] Copper powder was produced by sequentially subjecting untreated copper powder, prepared by a gas-phase reduction method, to dechlorination treatment using an aqueous sodium hydroxide solution and deoxygenation treatment using ascorbic acid, followed by rust prevention treatment.

[0050] For rust prevention treatment, as shown in Table 1, (2-benzothiadylthio)acetic acid (Sunbit ABT manufactured by Sanshin Chemical Industry Co., Ltd.) was used as the rust inhibitor in Example 1, and thiourea (manufactured by Kanto Chemical Co., Ltd.) was used in Comparative Example 1.

[0051] In Example 1, (2-benzothiadylthio)acetic acid was used, and since it is insoluble in water as a solvent, it was neutralized with sodium hydroxide before being dissolved. In both Example 1 and Comparative Example 1, washing with pure water was performed after the rust prevention treatment.

[0052] The sulfur content, carbon content, and sodium content of the copper powder obtained in Example 1 and Comparative Example 1 were measured using the method described above, and are shown in Table 1. The sulfur content and carbon content of the copper powder are expressed as ratios to the specific surface area of ​​the copper powder.

[0053] Furthermore, for each copper powder, the oxygen content immediately after manufacturing following the completion of rust prevention treatment, and the oxygen content after being left to stand for 7 days in a harsh environment of 40°C and 70% humidity from immediately after manufacturing, were measured using the method described above. The results are also shown in Table 1. The oxygen content here is also expressed as a ratio to the specific surface area.

[0054] [Table 1]

[0055] Table 1 shows that in Example 1, the increase in the oxygen content of the copper powder was small, indicating that copper powder was obtained in which oxidation was effectively suppressed even under harsh conditions. Furthermore, the copper powder in Example 1 contained an appropriate amount of sulfur. In Comparative Example 1, the increase in the oxygen content of the copper powder was large, and the sulfur content was somewhat high.

[0056] Based on the above, it is suggested that the copper powder manufacturing method of this invention has the potential to produce copper powder that contains sulfur while having excellent oxidation resistance.

Claims

1. A method for producing copper powder, A method for producing copper powder, comprising a rust prevention step of applying a rust prevention treatment to copper powder before treatment using a rust inhibitor comprising at least one selected from the group consisting of 2-mercaptobenzothiazole sodium salt and its hydrate, 3-(2-benzothiadilthio)propionic acid, and (2-benzothiadilthio)acetic acid.

2. The sulfur content relative to the specific surface area of ​​the copper powder obtained after the aforementioned rust prevention process is 0.005% by mass / g / m². 2 ~0.4 mass%・g / m 2 The method for producing copper powder according to claim 1.

3. The carbon content relative to the specific surface area of ​​the copper powder obtained after the aforementioned rust prevention process is 0.01% by mass / g / m². 2 ~0.4 mass%・g / m 2 The method for producing copper powder according to claim 1 or 2.

4. A method for producing copper powder according to claim 1 or 2, wherein, in the rust prevention step, the rust prevention treatment is applied to the copper powder before treatment, and then washed with water.

5. A method for producing copper powder according to claim 1 or 2, comprising a deoxidation step in which, prior to the rust prevention step, the copper powder before treatment is contacted with an oxygen scavenger containing at least one selected from the group consisting of ascorbic acid, hydrazine, and citric acid, thereby reducing the oxygen content of the copper powder before treatment.

6. The oxygen content relative to the specific surface area of ​​the copper powder obtained after the aforementioned rust prevention process is 0.03 mass%·g / m². 2 ~1.0 mass%・g / m 2 The method for producing copper powder according to claim 5.

7. A reduction step involves contacting copper chloride gas with a reducing gas to obtain the copper powder before treatment, A dechlorination step is performed after the reduction step and before the rust prevention step, in which the untreated copper powder is brought into contact with a dechlorinating agent containing an alkali metal hydroxide to reduce the chlorine content of the untreated copper powder. A method for producing copper powder according to claim 1 or 2, including the method described in claim 1 or 2.

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