JPWO2008059789A1 - Silver-plated copper fine powder, conductive paste produced using silver-plated copper fine powder, and method for producing silver-plated copper fine powder - Google Patents

Abstract

The copper fine powder is washed with water in the alkaline solution to remove the organic matter on the surface of the copper fine powder, and the oxide on the surface of the copper fine powder is pickled and washed in the acidic solution, and then reduced in the acidic solution in which the copper fine powder is dispersed. A copper fine powder slurry is prepared by adding an agent, and after adjusting the pH, a silver ion solution complexed with a chelating agent is continuously added to the copper fine powder slurry, so that electroless displacement plating and reduction type plating are performed. A method for producing silver-plated copper fine powder, characterized in that a silver layer is formed on the surface of the copper fine powder. In conventional silver-plated copper fine powder, it solves problems such as variations in the color tone after silver plating reaction due to the oxidation state of copper fine powder before silver plating and reduction of tap density due to silver plating, etc., and conductivity and silver plating It aims at providing the silver plating copper fine powder which is excellent in the reproducibility at the time of reaction, and has the tap density like raw material copper fine powder, and its manufacturing method.

Description

  The present invention relates to a silver-plated copper fine powder, a conductive paste produced using the silver-plated copper fine powder, and a method for producing the silver-plated copper fine powder. It relates to the silver plating copper fine powder which has the tap density of.

  Conventionally, copper fine powder has been widely used as a raw material for conductive paste. Conductive pastes are widely used because of their ease of handling, from experimental purposes to applications in the electronics industry.

Among them, silver-plated copper fine powder with a silver layer coated on its surface is processed into a conductive paste and applied to the formation of printed wiring board circuits using screen printing, various electrical contact points, etc., to ensure electrical continuity. It has been used as a material.
This is because silver-plated copper fine powder is more excellent in electrical conductivity than copper fine powder when compared with normal copper fine powder that does not cover the surface with a silver layer. Moreover, although it will become expensive only by silver powder, if silver is plated on copper, it will become cheap as the whole electroconductive powder, and manufacturing cost can be reduced significantly. Therefore, a conductive paste made of copper fine powder plated with silver, which is superior in conductive properties, has a great merit that a low-resistance conductor can be manufactured at low cost.

By the way, the technique of manufacturing such a silver plating copper fine powder for electrically conductive paste by the electroless displacement plating method using the substitution reaction of copper and silver is generally known. Patent Document 1 describes a method of substituting and depositing silver on the surface of metallic copper powder using a silver complex solution of silver nitrate, ammonium carbonate, and ethylenediaminetetraacetate.
Patent Document 2 discloses a method of dispersing a copper powder in a chelating agent solution, adding a silver nitrate solution to the copper powder dispersion, and then adding a reducing agent to deposit a silver coating on the surface of the copper powder. ing.
Furthermore, in Patent Document 3, a chelating agent is added to a copper powder dispersion to prepare a copper powder slurry, a pH is adjusted by adding a buffer to the slurry, and silver ions are added thereto to perform substitution reaction. A technique for producing silver-coated copper powder is disclosed.

Silver-plated copper fine powder obtained by these production methods is excellent in conductivity and moisture resistance characteristics, and has been used as a suitable material as a conductive paste material. However, the silver-plated copper fine powder obtained by these manufacturing methods has problems such as variations in the color tone after the silver plating reaction due to the oxidation state of the copper fine powder before silver plating, and a decrease in tap density due to silver plating. Was holding.
JP-A-57-59283 JP-A-2-46641 JP 2004-52044 A

  The present invention aims to solve the above problems, and provides a silver-plated copper fine powder having excellent conductivity and reproducibility at the time of silver plating reaction and having a tap density similar to that of a raw material copper fine powder and a method for producing the same.

  As a result of intensive research to solve the above problems, the present inventors have introduced a surface treatment process before and after the silver plating reaction in conventional silver-plated copper fine powder, and copper fine powder by electroless displacement plating and reduction type plating. It has been found that by forming a silver layer on the surface, the silver-plated copper fine powder is excellent in reproducibility during silver plating production and has a tap density similar to that of the raw material copper fine powder.

Based on these findings, the present invention is as follows: 1) Silver-plated copper fine powder having an average particle diameter of 1 to 30 μm, a tap density of 2.4 g / cm ³ or more, and a specific surface area of 0.9 m ² / g or less 2) Average grains Silver-plated copper fine powder having a diameter of 3 to 20 μm, a tap density of 3.0 g / cm ³ or more, and a specific surface area of 0.6 m ² / g or less 3) Silver-plated copper fine powder is further 0.01 to 5.0 weight The silver-plated copper fine powder according to 1 or 2 above, which is coated with 1% of fatty acid 4) The silver according to 1 or 2 above, wherein the silver-plated copper fine powder is further coated with 0.1 to 1.0% by weight of fatty acid Plating copper fine powder 5) Provided is a conductive paste produced using the silver-plated copper fine powder according to any one of 1 to 4 above.

The present invention also relates to 6) a method for producing a silver-plated copper fine powder in which a silver layer is formed on the surface of the copper fine powder. In the alkaline solution, the copper fine powder is removed in an alkaline solution, washed with water, and then washed in an acidic solution After pickling and washing the oxide on the surface of the copper fine powder, a reducing agent is added to the acidic solution in which the copper fine powder is dispersed to adjust the pH to create a copper fine powder slurry, and a silver ion solution is added to the copper fine powder slurry. A method for producing silver-plated copper fine powder in which a silver layer is formed on the surface of copper fine powder by electroless displacement plating and reduction-type electroless plating. 7) An acidic solution using potassium hydroxide as the alkaline solution 8. A method for producing a silver-plated copper fine powder as described in 6 above, wherein sulfuric acid is used as the reducing agent. 8) One or more selected from polyvalent carboxylic acids or salts thereof or formaldehyde are used as the reducing agent. Method for producing silver-plated copper fine powder according to 6 or 7 9) Method for producing silver-plated copper fine powder according to any one of 6 to 8 above, wherein the pH at the start of addition of the silver ion solution is adjusted to 3.0 to 5.0 10) The method for producing silver-plated copper fine powder according to any one of 6 to 8 above, wherein the pH at the start of addition of the silver ion solution is adjusted to 3.5 to 4.5. 11) The silver ion solution is a transparent ammoniacal silver nitrate. The method for producing a silver-plated copper fine powder according to any one of the above 6 to 10 as a solution 12) The silver-plated copper fine powder is heat-treated in a reducing atmosphere under a hydrogen stream at 150 to 220 ° C for 20 to 90 minutes. The manufacturing method of the silver plating copper fine powder in any one of said 6-11 13) Said 6-6 which heat-processes silver plating copper fine powder in 180-210 degreeC and 20-40 minutes in the reducing atmosphere under hydrogen stream. Of the silver-plated copper fine powder according to any one of 11 Production method 14) The silver-plated copper fine powder is immersed in an alcohol solution containing a fatty acid, and the surface of the silver-plated copper fine powder is coated with 0.01 to 5.0% by weight of a fatty acid. 15) Silver-plated copper fine powder 15) The silver-plated copper fine powder is immersed in an alcohol solution containing a fatty acid, and the surface of the silver-plated copper fine powder is coated with 0.1 to 1.0% by weight of fatty acid. The manufacturing method of the silver plating copper fine powder in any one of 13 is provided.

  By introducing a surface treatment process before and after the silver plating reaction and forming a silver layer on the surface of the copper fine powder by electroless displacement plating and reduction plating, it becomes possible to uniformly coat the silver layer on the surface of the copper fine powder. As a result, it has excellent conductivity and reproducibility at the time of silver plating reaction, resulting in silver-plated copper fine powder with tap density similar to that of raw copper fine powder, and stable and high filling when used in conductive paste It has an excellent effect that it can be achieved.

Conventionally, since an alkaline solution is used instead of an acidic solution, the copper hydroxide may be reprecipitated when taken out as a powder. In addition, since the silver ion solution was put together during the substitution reaction, it was considered that the silver ion concentration became non-uniform around the copper powder, and silver-plated copper fine powder having a poor silver coating state was formed.
In contrast, the present invention removes organic substances on the surface of copper fine powder by dispersing copper fine powder in an alkaline solution, and removes oxides on the surface of copper fine powder by dispersing copper fine powder in an acidic solution. Since the pH is adjusted so that the copper ions complexed by the agent can be maintained in a stable state, and the silver ion solution is continuously added so that the substitution reaction with the silver ions proceeds uniformly, the copper fine powder The silver layer can be coated on the surface very uniformly.

As the alkaline solution, sodium hydroxide, potassium hydroxide or the like is used. Any alkaline solution that can reliably remove the organic matter on the surface of the copper fine powder before the substitution reaction may be used, but potassium hydroxide is preferred.
In an acidic solution, sulfuric acid, hydrochloric acid, phosphoric acid or the like is used. It is preferable to use sulfuric acid, and any acidic solution that can reliably remove the copper oxide on the surface of the copper fine powder before the substitution reaction is performed. However, the type and concentration to be selected should not excessively dissolve the copper fine copper itself. There is a need to.
The pH of this acidic solution is desirably in the acidic range of 2.0 to 5.0. If the pH exceeds 5.0, the oxide of the copper fine powder cannot be sufficiently dissolved and removed, and if the pH is lower than 2.0, the copper powder is dissolved and the aggregation of the copper fine powder itself easily proceeds. More preferably, it is an acidic region having a pH of 3.5 to 4.5.

In the production method of the present invention, EDTA, ammonia or the like can be used as the chelating agent. The chelating agent used in the present invention is not particularly limited as long as the effects of the present invention are exhibited, but is preferably ammonia.
When ammonia water is added to the silver nitrate solution, precipitation occurs, but when excess ammonia water is added, a clear ammoniacal silver nitrate solution (containing [Ag (NH ₃ ) ₂ ] ⁺ therein) is obtained. When a reducing agent such as sodium potassium tartrate is added thereto, silver is deposited on the surface of the copper fine powder, and silver-plated copper fine powder is formed.

In the present invention, polyvalent carboxylic acids, polyvalent carboxylates, formaldehyde and the like can be used as the reducing agent. Examples include sodium potassium tartrate (Rochelle salt) and glucose (glucose). Preferably, potassium sodium tartrate (Rochelle salt), this reducing agent exhibits weak reducing power, and reduces only oxides (CuO, Cu ₂ O, AgO, Ag ₂ O) produced as a by-product of the substitution reaction, Copper complex ions are not reduced.

And the silver ion solution in this invention uses a silver nitrate solution. The silver ion solution used in the present invention is not particularly limited as long as the effects of the present invention are exhibited. This silver nitrate solution has a silver nitrate concentration of 20 to 300 g / L, preferably 50 to 100 g / L.
Moreover, the speed | rate of the silver ion solution added to a copper fine powder slurry shall be 200 mL / min or less, Preferably you may be 100 mL / min or less. By adding a silver nitrate solution in the above concentration range at a relatively slow addition rate, practically at 20 to 200 mL / min, it is possible to reliably coat a uniform silver layer on the copper fine powder surface.

  Furthermore, in the production method of the present invention, it is preferable to carry out a decantation treatment after copper fine powder is dispersed in an acidic solution. The decantation process is also called a gradient method. After copper fine powder is dispersed in an acidic solution, the solution is allowed to stand to settle copper fine powder or silver-plated copper fine powder, and then the supernatant is gently inclined. An operation to separate and collect. According to this, since copper fine powder or silver plating copper fine powder does not contact air | atmosphere, it becomes possible to transfer to the following process in the state which prevented reoxidation of copper fine powder or silver plating copper fine powder.

One method of post-treatment used in the production method of the present invention is to perform heat treatment at 150 to 220 ° C. for 30 to 90 minutes in a reducing atmosphere under a hydrogen stream. Preferably, the heat treatment is performed at 180 to 210 ° C. for 20 to 40 minutes, and the interface between the copper fine powder and the silver layer is partially alloyed by this heat treatment, whereby the bonding force at the interface can be increased.
Silver-plated copper fine powder is mixed with a resin or solvent and kneaded when making a conductive paste, but if the bonding force at the interface is weak, the silver layer will be peeled off when subjected to mechanical friction. Therefore, heat treatment at low temperature and short time is effective. However, if the heat treatment is performed at a very high temperature or for a long time, silver may be completely diffused into copper.

In the post-treatment method 2 used in the production method of the present invention, silver-plated copper fine powder is immersed in an alcohol solution containing 0.01 to 5.0% by weight of a fatty acid, filtered and dried after stirring for about 30 minutes. . Preferably, the silver-plated copper fine powder is immersed in an alcohol solution containing 0.1 to 1.0% by weight of a fatty acid, filtered and dried after stirring for about 30 minutes. As the fatty acid, stearic acid is used. Fatty acid coating is an excellent effect that the surface is smoothed by the fatty acid being coated on the irregularities of the silver-plated copper fine powder surface, and that the fatty acid itself acts as a lubricant and the filling property of the silver-plated copper fine powder is increased. Have
By these post-treatments, the tap density of the silver-plated copper fine powder lowered by the silver plating reaction can be increased to the same level as the raw material copper fine powder, which is advantageous for via hole applications that require high filling properties.

The copper fine powder used in the silver-plated copper fine powder and the production method thereof shown above is not particularly limited in the type, production method, etc., and is obtained from a normal electrolytic method, reduction method, atomizing method, mechanical grinding, etc. Can be used. Moreover, the shape of the copper powder is not specified, and a spherical shape, a flake shape, a needle shape, or a resin shape can be used.
As described above, silver-plated copper fine powder having an average particle diameter of 1 to 30 μm, a tap density of 2.4 g / cm ³ or more, and a specific surface area of 0.9 m ² / g or less can be obtained. The silver-plated copper fine powder can further achieve an average particle size of 3 to 20 μm, a tap density of 3.0 g / cm ³ or more, and a specific surface area of 0.6 m ² / g or less.
Moreover, this silver plating copper fine powder can be made into the silver plating copper fine powder of the structure coat | covered with 0.01 to 5.0 weight% of fatty acid by said process. Furthermore, this silver plating copper fine powder can also be made into the structure coat | covered with 0.1-1.0 weight% of fatty acid. These silver-plated copper fine powders are useful as a conductive paste. The present invention includes a conductive paste manufactured using these copper powders.

  Next, this invention is demonstrated based on an Example. The following examples are for facilitating the understanding of the present invention, and the present invention is not limited by these examples. That is, modifications and other examples based on the technical idea of the present invention are included in the present invention.

Example 1
In the present Example 1, the copper fine powder obtained by further pulverizing the electrolytic copper powder obtained by the so-called electrolysis method with a jet mill was used. This copper fine powder had a weight cumulative particle diameter D ₅₀ of 6.2 μm as measured by a laser diffraction / scattering particle size distribution measurement method.
500 g of this copper fine powder was added to 1000 ml of 1% aqueous potassium hydroxide solution and stirred for 20 minutes, followed by primary decantation treatment, and further 1000 ml of pure water was added and stirred for several minutes.
Then, the secondary decantation process was performed, 2500 ml of sulfuric acid aqueous solution with a sulfuric acid concentration of 15 g / L was added, and it stirred for 30 minutes. Further, tertiary decantation treatment was performed, 2500 ml of pure water was added, and the mixture was stirred for several minutes.
Next, quaternary decantation treatment was performed, and 2500 ml of 1% sodium potassium tartrate solution was added and stirred for several minutes to form a copper slurry.
A dilute sulfuric acid or potassium hydroxide solution was added to the copper slurry to adjust the pH of the copper slurry to 3.5 to 4.5.

Substitution reaction treatment while adding silver nitrate ammonia solution 1000ml (added 887.5g silver nitrate to water and adding ammonia water to 1000ml) to pH adjusted copper slurry slowly over 30 minutes Then, a reduction reaction treatment was performed, and the mixture was further stirred for 30 minutes to obtain silver-plated copper fine powder.
Then, the fifth decantation process was performed, 3500 ml of pure water was added, and it stirred for several minutes. Further, a sixth decantation treatment was performed, 3500 ml of pure water was added, and the mixture was stirred for several minutes. Then, the silver-plated copper fine powder and the solution were separated by filtration, washing and dehydrating, and the silver-plated copper fine powder was dried at a temperature of 90 ° C. for 2 hours.

(Example 2)
500 g of the silver-plated copper fine powder produced in Example 1 was dispersed in 750 ml of 0.5% stearic acid ethanol solution and stirred for 30 minutes. Then, the stearic acid-coated silver-plated copper fine powder and the solution were separated by filtration, washing and dehydrating, and the stearic acid-coated silver-plated copper fine powder was dried at a temperature of 90 ° C. for 2 hours.

(Example 3)
500 g of the silver-plated copper fine powder produced in Example 1 was placed in a tubular furnace and heat-treated at 200 ° C. for 30 minutes in a reducing atmosphere under a hydrogen stream (3.0 to 3.5 l / min). The heat-treated silver-plated copper fine powder was pulverized in a mortar.

Example 4
500 g of the silver-plated copper fine powder prepared in Example 3 was dispersed in 750 ml of 0.5% stearic acid ethanol solution and stirred for 30 minutes. Then, the stearic acid-coated silver-plated copper fine powder and the solution were separated by filtration, washing and dehydrating, and the stearic acid-coated silver-plated copper fine powder was dried at a temperature of 90 ° C. for 2 hours.

(Comparative Example 1)
To 2500 ml of 1% sodium potassium tartrate solution, 500 g of the copper fine powder used in Example 1 was added and stirred for several minutes. Next, dilute sulfuric acid or potassium hydroxide solution was added to the copper slurry to adjust the pH of the copper slurry to 3.5 to 4.5.
The copper slurry adjusted to pH in this way was replaced with 1000 ml of silver nitrate ammonia solution (87.5 g of silver nitrate added to water and adjusted to 1000 ml) and slowly added over 30 minutes. Reaction treatment and reduction reaction treatment were performed, and stirring was further performed for 30 minutes to obtain silver-plated copper fine powder.
Subsequently, decantation was performed, 3500 ml of pure water was added, and the mixture was stirred for several minutes. Further, decantation treatment was performed, 3500 ml of pure water was added, and the mixture was stirred for several minutes. Then, the silver-plated copper fine powder and the solution were separated by filtration, washing and dehydrating, and the silver-plated copper fine powder was dried at a temperature of 90 ° C. for 2 hours.

The average particle diameter, specific surface area, apparent density, and tap density of the silver-plated copper fine powder according to the above-described example were measured. The average particle diameter was determined by a laser diffraction / scattering particle size distribution measurement method, and the value of weight cumulative particle diameter D ₅₀ was adopted. The specific surface area was measured by the BET method. The apparent density was measured according to JISZ2504. The tap density was measured according to JISZ2512. The results are shown in Table 1.
As shown in Table 1, the raw material powder has an average particle size of 6.2 μm, a specific surface area of 0.48 m ² / g, a tap density of 4.98 g / cm ³ , and a specific resistance of 2.9 × 10 ⁻⁴ Ω · cm. In Example 1, the average particle size was 9.4 μm, the specific surface area was 0.33 m ² / g, the tap density was 3.92 g / cm ³ , and the specific resistance was 1.3 × 10 ⁻⁴ Ω · cm. . In Example 2, the average particle size was 11.7 μm, the specific surface area was 0.24 m ² / g, the tap density was 4.76 g / cm ³ , and the specific resistance was 7.1 × 10 ⁻⁵ Ω · cm. In Example 3, the average particle size was 13.8 μm, the specific surface area was 0.19 m ² / g, the tap density was 3.99 g / cm ³ , and the specific resistance was 1.1 × 10 ⁻⁴ Ω · cm. In Example 4, the average particle size was 13.3 μm, the specific surface area was 0.16 m ² / g, the tap density was 4.95 g / cm ³ , and the specific resistance was 6.5 × 10 ⁻⁵ Ω · cm.
These are all within the range of the silver-plated copper fine powder of the present invention having an average particle diameter of 1 to 30 μm, a tap density of 2.4 g / cm ³ or more and a specific surface area of 0.9 m ² / g or less, It was a suitable silver-plated copper fine powder. In addition, in all of Examples 1 to 4, the specific resistance was 1.5 × 10 ⁻⁴ Ω · cm or less, which showed better conductivity than the raw material powder and the comparative example described later.

On the other hand, the average particle diameter of Comparative Example 1 is 8.7 μm and the tap density is 4.00 gg / cm ³ , but the specific surface area is 0.44 m ² / g, which is a higher numerical value than the other examples. Thus, the surface of the silver-plated copper fine powder has many irregularities, the color tone of the silver-plated surface is poor, and the conductivity is lowered, so that the object of the present invention cannot be achieved, resulting in an undesirable result.

  The silver-plated copper fine powder in which the silver layer is uniformly coated on the surface of the copper fine powder according to the present invention has excellent conductivity and excellent reproducibility during the silver plating reaction, and has a tap density similar to that of the raw copper powder. Ideal for materials that ensure electrical continuity, such as paste.

Claims (15)

A silver-plated copper fine powder having an average particle size of 1 to 30 μm, a tap density of 2.4 g / cm ³ or more, and a specific surface area of 0.9 m ² / g or less. A silver-plated copper fine powder having an average particle size of 3 to 20 μm, a tap density of 3.0 g / cm ³ or more, and a specific surface area of 0.6 m ² / g or less.   The silver-plated copper fine powder according to claim 1 or 2, wherein the silver-plated copper fine powder is further coated with 0.01 to 5.0% by weight of a fatty acid.   The silver-plated copper fine powder according to claim 1 or 2, wherein the silver-plated copper fine powder is further coated with 0.1 to 1.0% by weight of a fatty acid.   The electrically conductive paste manufactured using the silver plating copper fine powder in any one of Claims 1-4.   In the method for producing silver-plated copper fine powder that forms a silver layer on the surface of copper fine powder, the copper fine powder is washed with water in the alkaline solution to remove the organic matter on the surface of the copper fine powder, and then the oxide on the surface of the copper fine powder in the acidic solution. After pickling and washing with water, a reducing agent is added to the acidic solution in which the copper fine powder is dispersed to adjust the pH to create a copper fine powder slurry, and a silver ion solution is continuously added to the copper fine powder slurry. A method for producing silver-plated copper fine powder, comprising forming a silver layer on the surface of the copper fine powder by electroless displacement plating and reduction-type electroless plating.   The method for producing a silver-plated copper fine powder according to claim 6, wherein potassium hydroxide is used as the alkaline solution and sulfuric acid is used as the acidic solution.   The method for producing silver-plated copper fine powder according to claim 6 or 7, wherein one or more selected from polyvalent carboxylic acids or salts thereof or formaldehyde is used as the reducing agent.   The method for producing silver-plated copper fine powder according to any one of claims 6 to 8, wherein the pH at the start of addition of the silver ion solution is adjusted to 3.0 to 5.0.   The method for producing silver-plated copper fine powder according to any one of claims 6 to 8, wherein the pH at the start of addition of the silver ion solution is adjusted to 3.5 to 4.5.   The method for producing a silver-plated copper fine powder according to any one of claims 6 to 10, wherein the silver ion solution is a transparent ammoniacal silver nitrate solution.   The silver-plated copper fine powder according to any one of claims 6 to 11, wherein the silver-plated copper fine powder is heat-treated in a reducing atmosphere under a hydrogen stream at 150 to 220 ° C for 20 to 90 minutes. Method.   The silver-plated copper fine powder according to any one of claims 6 to 11, wherein the silver-plated copper fine powder is heat-treated in a reducing atmosphere under a hydrogen stream at 180 to 210 ° C for 20 to 40 minutes. Method.   The silver-plated copper fine powder is immersed in an alcohol solution containing a fatty acid, and the surface of the silver-plated copper fine powder is coated with 0.01 to 5.0% by weight of a fatty acid. The manufacturing method of the silver plating copper fine powder of description.   The silver-plated copper fine powder is immersed in an alcohol solution containing a fatty acid, and the surface of the silver-plated copper fine powder is coated with 0.1 to 1.0% by weight of a fatty acid. The manufacturing method of the silver plating copper fine powder of description.