WO2017073057A1 - Silver powder and method for producing same - Google Patents

Abstract

Provided are a silver powder having a small average particle size and low thermal shrinkage, and a method for producing the silver powder. The silver powder of the present invention is produced by blowing high-pressure water (preferably at a pressure of 90–160 MPa) on molten silver, which has been heated to a temperature (1292–1692°C) 330–730°C higher than the melting point of silver (962°C), as the molten silver is dropped downards, causing rapid solidification, thereby powderizing the silver. The average particle size of the silver powder is 1–6 μm; the shrinkage at 500°C is not more than 8% (preferably not more than 7%); and the product of the average particle size and the shrinkage at 500°C is 1–11 μm·% (preferably 1.5–10.5 μm·%).

Description

Silver powder and method for producing the same

The present invention relates to silver powder and a method for producing the same, and particularly used for conductive pastes used for electronic components such as internal electrodes of multilayer capacitors and multilayer inductors, conductor patterns of circuit boards, and electrodes and circuits of display panel boards. The present invention relates to a silver powder suitable for the manufacturing process and a method for producing the same.

Conventionally, silver powder is added together with glass frit into an organic vehicle and kneaded as a conductive paste used for electronic components such as internal electrodes of multilayer capacitors and multilayer inductors, conductor patterns on circuit boards, and electrodes and circuits on display panel substrates. The conductive paste manufactured by this is used.

As a method for producing such silver powder for conductive paste, a method for producing silver powder by a wet reduction method or an atomizing method is known (see, for example, Patent Documents 1 to 3).

JP 2002-80901 (paragraph number 0007) Japanese Unexamined Patent Publication No. 2007-18884 (paragraph numbers 0007-0012) JP 11-163487 A (paragraph 0009)

In recent years, it has been desired that such silver powder for conductive paste has a small particle size in order to cope with downsizing of electronic parts, high density of conductive patterns, fine lines, and the like.

However, in the conventional method for producing silver powder, there is a problem that if the particle size of the silver powder is made small, when it is used as the silver powder for the conductive paste, the conductive paste is greatly shrunk when fired.

Therefore, in view of such conventional problems, an object of the present invention is to provide a silver powder having a small average particle size and a small thermal shrinkage and a method for producing the same.

As a result of diligent research to solve the above problems, the inventors of the present invention have made silver powder by rapidly solidifying by blowing high-pressure water while dropping a molten silver heated to 330 to 730 ° C. higher than the melting point of silver. As a result, it was found that a silver powder having a small average particle size and a small thermal shrinkage can be produced, and the present invention has been completed.

That is, the method for producing silver powder according to the present invention is characterized in that silver is powdered by rapidly cooling and solidifying by blowing high-pressure water while dropping a molten silver heated to a temperature 330 to 730 ° C. higher than the melting point of silver. . In this silver powder production method, high-pressure water is preferably sprayed at a water pressure of 90 to 160 MPa.

The silver powder according to the present invention has an average particle size of 1 to 6 μm, a shrinkage rate at 500 ° C. of 8% or less, and a product of the average particle size and the shrinkage rate at 500 ° C. of 1 to 11 μm ·%. And This silver powder has a BET specific surface area (m ² / g) × tap density (g / m ³ ) / crystallite diameter (m) of 1 × 10 ¹³ to 6 × 10 ¹³ (m ⁻² ). preferable. Moreover, it is preferable that the carbon content in silver powder is 0.1 mass% or less.

In the present specification, the “average particle diameter” means a volume-based average particle diameter (cumulative 50% particle diameter D ₅₀ ) determined by a laser diffraction method.

According to the present invention, silver powder having a small average particle size and a small heat shrinkage rate can be produced.

It is a figure which shows the shrinkage | contraction rate at the time of heating at a temperature increase rate of 10 degree-C / min from room temperature to 800 degreeC in air | atmosphere atmosphere by making silver powder of an Example and a comparative example into a cylindrical pellet form.

In the embodiment of the method for producing silver powder according to the present invention, when silver powder is produced by the water atomization method in which high-pressure water is sprayed and rapidly solidified while dropping the molten silver, 330 to 730 ° C. from the melting point of silver (962 ° C.). While dropping a molten silver heated to a high temperature (1292 to 1692 ° C.) (preferably at a water pressure of 90 to 160 MPa and a water amount of 80 to 190 L / min), silver is pulverized by rapid cooling and solidification.

In the embodiment of the silver powder according to the present invention, the average particle size is 1 to 6 μm, the shrinkage at 500 ° C. is 8% or less (preferably 7% or less), and the product of the average particle size and the shrinkage at 500 ° C. Is 1 to 11 μm ·% (preferably 1.5 to 10.5 μm ·%). As the average particle size of silver powder decreases, the shrinkage rate of silver powder at 500 ° C tends to increase, but the average particle size of silver powder is 1 to 6 µm, the shrinkage rate at 500 ° C is 8% or less, and the average particle size and shrinkage at 500 ° C. When the product of the rates is 1 to 11 μm ·%, silver powder having a small average particle size and a small heat shrinkage rate can be produced. The silver powder has a BET specific surface area of preferably 0.1 to 3 m ² / g so that a highly conductive conductive film can be formed by using the silver powder as a conductive paste. More preferably, it is 1 m ² / g. Further, the tap density of the silver powder is preferably 1 to 7 g / cm ³ so that a high conductive film can be formed by using the conductive paste by increasing the packing density. More preferably, it is ˜6 g / cm ³ . The crystallite diameter of the silver powder is preferably 10 to 200 nm, and preferably 30 to 150 nm, so that a highly conductive conductive film can be formed by reducing the number of grain boundaries of the silver powder. Further preferred. Further, this silver powder has a surface area per unit volume (= BET specific surface area (m ² / g) × tap density (g / m ³ )) and the number of crystallites in the unit range (= 1 / crystallite diameter (m). ) Is preferably 1 × 10 ¹³ to 6 × 10 ¹³ (m ⁻² ). When the surface area per unit volume of silver powder increases, it is considered that it is easily affected by heating and heat shrinks easily, and when the number of crystallites in the unit range of silver powder increases, the number of crystal grains that can be heat shrunk also increases. However, if these products are within the above range, it is considered that silver powder can be used for the conductive paste to form a highly conductive conductive film. The carbon content in the silver powder is preferably 0.1% by mass or less in order to use the silver powder as a conductive paste to form a conductive film having high adhesion to the substrate. More preferably, it is mass%.

In addition, a conductive paste is prepared by mixing the above silver powder as a conductive powder with a resin, a solvent, glass frit or the like (mixing a dispersant or the like as necessary) and kneading. If a conductive film is produced by firing the film, a conductive film having a low linear shrinkage rate by firing can be obtained.

Hereinafter, examples of the silver powder and the production method thereof according to the present invention will be described in detail.

[Example 1]
While dropping 12 kg of silver to 1600 ° C (temperature higher by 638 ° C than the melting point of silver (962 ° C)) and dropping the molten metal from the bottom of the tundish, high pressure water is sprayed at a water pressure of 150 MPa and a water volume of 160 L / min. The obtained powder was filtered, washed with water, dried and crushed, and coarse particles were removed by an air classifier (Classeal N-01 type manufactured by Seishin Enterprise Co., Ltd.) to obtain silver powder.

The particle size distribution, shrinkage rate, crystallite diameter, BET specific surface area, tap density, and carbon content of the silver powder produced by such a water atomization method were determined.

The particle size distribution of the silver powder was measured at a dispersion pressure of 5 bar using a laser diffraction type particle size distribution measuring device (Heros particle size distribution measuring device (HELOS & RODOS (airflow type drying module) manufactured by SYMPATEC)). As a result, the cumulative 10% particle diameter (D ₁₀ ) was 0.6 μm, the cumulative 50% particle diameter (D ₅₀ ) was 1.6 μm, and the cumulative 90% particle diameter (D ₉₀ ) was 2.7 μm.

The shrinkage rate of silver powder is 0.5 g of silver powder mixed with 30 μL of butyl carbitol acetate as a solvent, placed in a cylindrical mold with an inner diameter of 5 mm, and a cylindrical pellet-shaped silver powder sample formed by applying a load of 1623 N. Using a thermomechanical analyzer (TMA / SS6200, manufactured by Hitachi High-Tech Science Co., Ltd.), the length of the sample when heated from room temperature to 800 ° C. at a heating rate of 10 ° C./min in an air atmosphere is measured. Asked. The result is shown in FIG. As shown in FIG. 1, in this example, when a cylindrical pellet-shaped silver powder sample is heated from room temperature to 800 ° C. in the air atmosphere at a heating rate of 10 ° C./min, it shrinks without expanding. I understand. The shrinkage rate at 500 ° C. was 6.2%, and the value of the shrinkage rate at a cumulative 50% particle size (D ₅₀ ) × 500 ° C. was 9.9 μm ·%.

The crystallite diameter of silver powder was determined by the Scherrer equation (Dhkl = Kλ / βcos θ). In this equation, Dhkl is the crystallite size (crystallite size perpendicular to hkl) (angstrom), λ is the wavelength of the measured X-ray (angstrom) (1.78989 angstrom when using the Co target), β is the diffraction line spread (rad) depending on the crystallite size (expressed by using the half width), θ is the Bragg angle (rad) of the diffraction angle (the angle when the incident angle and the reflection angle are equal, and the peak K is a Scherrer constant (depending on the definition of D or β, and K = 0.9 when a half-value width is used for β). Note that a powder X-ray diffractometer was used for the measurement, and peak data on the (111) plane was used for the calculation. As a result, the crystallite diameter (Dx) of the silver powder was 50.9 nm.

The BET specific surface area was degassed by flowing nitrogen gas at 105 ° C. for 20 minutes in a measuring instrument using a BET specific surface area measuring instrument (4 Sorb US made by Yuasa Ionics Co., Ltd.), While flowing a mixed gas (N ₂ : 30% by volume, He: 70% by volume), the BET one-point method was used for measurement. As a result, the BET specific surface area of the silver powder was 0.62 m ² / g.

The tap density (TAP) of the silver powder is the same as the method described in Japanese Patent Application Laid-Open No. 2007-263860. The silver powder is filled into a bottomed cylindrical die having an inner diameter of 6 mm to form a silver powder layer. After uniformly applying a pressure of 0.160 N / m ^{2 on} the upper surface, the height of the silver powder layer is measured, and the density of the silver powder is determined from the measured value of the height of the silver powder layer and the weight of the filled silver powder. It calculated | required and it was set as the tap density of silver powder. As a result, the tap density of the silver powder was 4.9 g / cm ³ .

In addition, when obtaining the product of the surface area per unit volume = BET specific surface area (m ² / g) × tap density (g / m ³ ) and the number of crystallites in the unit range = 1 / crystallite diameter (m), It becomes 5.97 × 10 ¹³ (m ⁻² ).

The carbon content in the silver powder was measured with a carbon / sulfur analyzer (EMIA-220V manufactured by Horiba, Ltd.). As a result, the carbon content in the silver powder was 0.012% by mass.

[Example 2]
The particle size distribution and shrinkage ratio of the silver powder obtained by the same method as in Example 1 except that the particle size was adjusted by removing silver aggregates larger than 10 μm when coarse particles were removed by an air classifier. The crystallite diameter, the BET specific surface area, the tap density, and the carbon content were determined.

As a result, the cumulative 10% particle diameter (D ₁₀ ) was 0.7 μm, the cumulative 50% particle diameter (D ₅₀ ) was 2.0 μm, the cumulative 90% particle diameter (D ₉₀ ) was 4.1 μm, and the shrinkage at 500 ° C. Was 1.0%, and the value of shrinkage at a cumulative 50% particle size (D ₅₀ ) × 500 ° C. was 2.0 μm ·%. The crystallite diameter (Dx) is 84.4 nm, the BET specific surface area is 0.48 m ² / g, the tap density is 5.2 g / cm ³ , and the surface area per unit volume = BET specific surface area (m ² / g) × The product of the tap density (g / m ³ ) and the number of crystallites in the unit range = 1 / crystallite diameter (m) was 2.96 × 10 ¹³ (m ⁻² ). Moreover, carbon content was 0.010 mass%.

[Example 3]
The silver powder obtained by the same method as in Example 1 except that the heating temperature was 1400 ° C. and the water pressure was 100 MPa, particle size distribution, shrinkage rate, crystallite diameter, BET specific surface area, tap density, carbon content Asked.

As a result, the cumulative 10% particle diameter (D ₁₀ ) was 1.0 μm, the cumulative 50% particle diameter (D ₅₀ ) was 3.0 μm, the cumulative 90% particle diameter (D ₉₀ ) was 6.1 μm, and the shrinkage at 500 ° C. Was 3.4%, and the value of shrinkage at 50% cumulative particle size (D ₅₀ ) × 500 ° C. was 10.2 μm ·%. The crystallite diameter (Dx) is 80.3 nm, the BET specific surface area is 0.36 m ² / g, the tap density is 5.4 g / cm ³ , and the surface area per unit volume = BET specific surface area (m ² / g) × The product of the tap density (g / m ³ ) and the number of crystallites in the unit range = 1 / crystallite diameter (m) was 2.42 × 10 ¹³ (m ⁻² ). Moreover, carbon content was 0.017 mass%.

[Example 4]
The silver powder obtained by the same method as in Example 1 except that the heating temperature was 1400 ° C. and the water pressure was 70 MPa, the particle size distribution, shrinkage rate, crystallite diameter, BET specific surface area, tap density, carbon content Asked.

As a result, the cumulative 10% particle size (D ₁₀ ) was 1.7 μm, the cumulative 50% particle size (D ₅₀ ) was 4.9 μm, the cumulative 90% particle size (D ₉₀ ) was 9.5 μm, and the shrinkage at 500 ° C. Was 1.5%, and the value of shrinkage at a cumulative 50% particle size (D ₅₀ ) × 500 ° C. was 7.4 μm ·%. The crystallite diameter (Dx) is 131.6 nm, the BET specific surface area is 0.26 m ² / g, the tap density is 5.6 g / cm ³ , and the surface area per unit volume = BET specific surface area (m ² / g) × The product of the tap density (g / m ³ ) and the number of crystallites in the unit range = 1 / crystallite diameter (m) was 1.11 × 10 ¹³ (m ⁻² ). Moreover, carbon content was 0.008 mass%.

[Example 5]
Except that the heating temperature was 1500 ° C., the particle size distribution, shrinkage rate, crystallite diameter, BET specific surface area, tap density, and carbon content were determined for the obtained silver powder by the same method as in Example 1.

As a result, the cumulative 10% particle diameter (D ₁₀ ) was 0.7 μm, the cumulative 50% particle diameter (D ₅₀ ) was 1.8 μm, the cumulative 90% particle diameter (D ₉₀ ) was 2.9 μm, and the shrinkage at 500 ° C. Was 3.4%, and the value of shrinkage at a cumulative 50% particle size (D ₅₀ ) × 500 ° C. was 6.1 μm ·%. The crystallite diameter (Dx) is 45.4 nm, the BET specific surface area is 0.60 m ² / g, the tap density is 4.5 g / cm ³ , and the surface area per unit volume = BET specific surface area (m ² / g) × The product of the tap density (g / m ³ ) and the number of crystallites in the unit range = 1 / crystallite diameter (m) was 5.92 × 10 ¹³ (m ⁻² ). Moreover, carbon content was 0.008 mass%.

[Comparative Example 1]
The silver powder obtained by the same method as in Example 1 except that the heating temperature was 1250 ° C. and the water pressure was 150 MPa, particle size distribution, shrinkage rate, crystallite diameter, BET specific surface area, tap density, carbon content Asked.

As a result, the cumulative 10% particle diameter (D ₁₀ ) was 0.5 μm, the cumulative 50% particle diameter (D ₅₀ ) was 1.3 μm, the cumulative 90% particle diameter (D ₉₀ ) was 2.4 μm, and the shrinkage at 500 ° C. Was 9.7%, and the value of the shrinkage at a cumulative 50% particle size (D ₅₀ ) × 500 ° C. was 12.6 μm ·%. The crystallite diameter (Dx) is 61.9 nm, the BET specific surface area is 0.90 m ² / g, the tap density is 4.2 g / cm ³ , and the surface area per unit volume = BET specific surface area (m ² / g) × The product of the tap density (g / m ³ ) and the number of crystallites in the unit range = 1 / crystallite diameter (m) was 6.11 × 10 ¹³ (m ⁻² ). Moreover, carbon content was 0.020 mass%.

[Comparative Example 2]
To 4500 kg of an aqueous silver nitrate solution containing 54 kg of silver, 203 kg of 25 mass% ammonia water was added to obtain an aqueous silver ammine complex salt solution. The liquid temperature of this silver ammine complex salt aqueous solution was 40 degreeC, 240 kg of 37 mass% formalin aqueous solution was added, silver particles were deposited, and the silver containing slurry was obtained. A stearic acid emulsion containing 0.2% by mass of stearic acid with respect to silver was added to the silver-containing slurry, followed by filtration and washing with water to obtain 15.0 kg of a cake. This cake was put into a dryer to obtain 13.6 kg of dried powder. The dried powder was crushed and classified to remove silver aggregates larger than 10 μm.

The particle size distribution, shrinkage rate, crystallite diameter, BET specific surface area, tap density, and carbon content were determined for the silver powder produced by such a wet reduction method.

As a result, the cumulative 10% particle diameter (D ₁₀ ) was 0.9 μm, the cumulative 50% particle diameter (D ₅₀ ) was 1.9 μm, the cumulative 90% particle diameter (D ₉₀ ) was 3.0 μm, and the shrinkage at 500 ° C. Was 14.1%, and the value of the shrinkage at a cumulative 50% particle size (D ₅₀ ) × 500 ° C. was 26.8 μm ·%. The crystallite diameter (Dx) is 40.7 nm, the BET specific surface area is 0.43 m ² / g, the tap density is 6.5 g / cm ³ , and the surface area per unit volume = BET specific surface area (m ² / g) × The product of the tap density (g / m ³ ) and the number of crystallites in the unit range = 1 / crystallite diameter (m) was 6.87 × 10 ¹³ (m ⁻² ). Moreover, carbon content was 0.196 mass%.

Tables 1 to 3 show the production conditions and characteristics of the silver powders of these examples and comparative examples, and FIG. 1 shows the change in shrinkage with temperature.

Claims (6)

A method for producing silver powder, characterized in that silver is pulverized by spraying high-pressure water and rapidly solidifying it while dropping a molten silver heated to 330 to 730 ° C. higher than the melting point of silver. The method for producing silver powder according to claim 1, wherein the high-pressure water is sprayed at a water pressure of 90 to 160 MPa. A silver powder characterized by having an average particle size of 1 to 6 μm, a shrinkage rate at 500 ° C. of 8% or less, and a product of the average particle size and the shrinkage rate at 500 ° C. of 1 to 11 μm ·%. BET specific surface area (m ² / g) × tap density (g / m ³ ) / crystallite diameter (m) is 1 × 10 ¹³ to 6 × 10 ¹³ (m ⁻² ), The silver powder according to claim 3. The silver powder according to claim 3, wherein the carbon content is 0.1 mass% or less. A conductive paste comprising a solvent and a resin, and containing the silver powder according to claim 3 as a conductive powder.

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