TWI777182B - Silver powder and method for producing same - Google Patents

Abstract

There are provided a silver powder, which is able to form an electrically conductive film having a lower resistance value than that of conventional electrically conductive films when the silver powder is used as the material of an electrically conductive paste which is fired to form the electrically conductive film, and a method for producing the same. A first silver powder, wherein the number of peak(s) having the maximum frequency in a volume-based particle size distribution obtained by measuring the first silver powder in a dry process by means of a laser diffraction particle size analyzer is one or more, is mixed with a second silver powder, wherein the number of peaks having the maximum frequency in a volume-based particle size distribution obtained by measuring the second silver powder in a dry process by means of a laser diffraction particle size analyzer is two or more, to produce a silver powder wherein the number of peaks having the maximum frequency in a volume-based particle size distribution obtained by measuring the silver powder in a dry process by means of a laser diffraction particle size analyzer is three or more and wherein the number of peak(s) having the maximum frequency in a volume-based particle size distribution obtained by measuring the silver powder in a wet process by means of a laser diffraction particle size analyzer is one or more.

Description

Silver powder and method for producing the same

The present invention relates to silver powder and a manufacturing method thereof, in particular to silver powder suitable for a material of conductive paste and a manufacturing method thereof.

Conventionally, it has been used as an electrode for forming a solar cell, an electronic component using a low temperature firing ceramic (LTCC), an internal electrode for a multilayer ceramic electronic component such as a multilayer ceramic inductor (MLCI), and an external electrode for a multilayer ceramic capacitor or a multilayer ceramic inductor. The material of the paste is metal powder such as silver powder.

As a material for this conductive paste, a mixed conductive powder has been proposed in the literature, which contains particles composed of silver, palladium, or a combination of two of these alloys with a generally monodispersed particle size and a generally spherical shape, and relatively The packing density is 68 to 80%, and the average particle size of one of the two types of silver, palladium, or these alloys is 5 to 25 times the average particle size of the other (for example, refer to Patent Document 1).

In addition, regarding the use of mixed metal particles obtained by mixing two kinds of metal particles, a conductive paint in which mixed metal particles are dispersed has been proposed. A mixture of small-diameter metal particles having an average particle diameter of 0.1 to 1 µm (the particle size distribution has two or more peaks) (for example, refer to Patent Document 2). prior art literature Patent Literature

Patent Document 1: Japanese Patent Laid-Open No. 2011-204688 (paragraph number 0012) Patent Document 2: Japanese Patent Application Laid-Open No. 1-295170 (page 2)

The problem to be solved by the invention

However, when the mixed conductive powder of Patent Document 1 or the mixed metal particles of Patent Document 2 are used as a material for a conductive paste, and the conductive paste is fired to form an electrode of a solar cell, the resistance value of the electrode may change. In the higher case, in order to improve the conversion efficiency of the solar cell, it is desirable to reduce the resistance value of the electrode.

Therefore, in view of the above-mentioned conventional problems, an object of the present invention is to provide a silver powder and a method for producing the same, which can form a resistance value when a conductive film is formed using the silver powder as a material of a conductive paste and firing the conductive paste. A lower conductive film than before. means of solving problems

The inventors of the present invention have made intensive studies in order to solve the above-mentioned problems, and as a result, they have found that if silver powder is produced by mixing the following first silver powder and the following second silver powder, it can be produced and used as a material for a conductive paste, and the conductive paste can be fired. When the conductive film is formed by paste, a silver powder with a lower resistance value than the conventional conductive film can be formed, and the present invention is completed; the first silver powder is based on the volume obtained by dry measurement using a laser diffraction particle size distribution measuring device. In the particle size distribution, there is one or more peaks with a maximum frequency; the second silver powder is a particle size distribution based on a volume obtained by dry measurement using a laser diffraction particle size distribution measuring device, and the peak frequency becomes a maximum of 2 The silver powder produced by mixing the first silver powder and the second silver powder has three or more peaks whose frequency becomes the maximum in the volume-based particle size distribution obtained by dry measurement with a laser diffraction particle size distribution analyzer. , and in the particle size distribution on a volume basis obtained by wet measurement with a laser diffraction scattering particle size distribution analyzer, there is one peak whose frequency becomes the maximum.

That is, the method for producing silver powder according to the present invention is characterized in that the silver powder is produced by mixing a first silver powder and a second silver powder, the first silver powder being on a volume basis obtained by dry measurement using a laser diffraction particle size distribution analyzer. In the particle size distribution of , the frequency of which becomes the maximum peak is one or more; the second silver powder is in the volume-based particle size distribution obtained by dry measurement using a laser diffraction particle size distribution measuring device, and the frequency becomes the maximum peak of Two or more; the silver powder produced by mixing the first silver powder and the second silver powder has three peaks whose frequency becomes the maximum in the volume-based particle size distribution obtained by dry measurement with a laser diffraction particle size distribution measuring device As mentioned above, in the particle size distribution on a volume basis obtained by wet measurement with a laser diffraction scattering particle size distribution measuring apparatus, one peak whose frequency becomes the maximum is one.

In the manufacturing method of the silver powder, the cumulative 50% particle size (D ₅₀ ) of the first silver powder in the volume-based particle size distribution obtained by wet measurement is preferably larger than the volume-based particle size distribution of the second silver powder by wet measurement. Cumulative 50% particle size (D ₅₀ ). In addition, the cumulative 50% particle size (D ₅₀ ) of the second silver powder in the volume-based particle size distribution obtained by wet measurement is preferably 0.3 to 1 µm. In addition, it is preferable that the cumulative 50% particle size (D ₅₀ ) of the first silver powder in the particle size distribution based on the volume obtained by the wet measurement is 1 to 4 μm, and the second silver powder is preferably the volume standard obtained by the wet measurement. 4 times or less of the cumulative 50% particle diameter (D ₅₀ ) in the particle size distribution. In addition, the wet measurement by a laser diffraction scattering particle size distribution analyzer is preferably performed by dispersing silver powder in isopropyl alcohol.

In addition, the silver powder of the present invention is characterized in that in the particle size distribution on a volume basis obtained by dry measurement using a laser diffraction particle size distribution measuring device, there are three or more peaks whose frequency becomes the maximum, and in the particle size distribution using the laser diffraction particle size distribution In the volume-based particle size distribution obtained by the wet measurement of the radiation scattering particle size distribution analyzer, there is one peak whose frequency becomes the maximum.

For the silver powder, the cumulative 50% particle size (D ₅₀ ) of the silver powder in the volume-based particle size distribution obtained by wet measurement is preferably 1.2 to 3.0 μm. In addition, the ratio of the cumulative 90% particle size (D ₉₀ ) to the cumulative 10% particle size (D ₁₀ ) of the silver powder is preferably 2.0 to 8.0. In addition, the wet measurement by a laser diffraction scattering particle size distribution analyzer is preferably performed by dispersing silver powder in isopropyl alcohol.

Furthermore, the conductive paste of the present invention is characterized in that the above-mentioned silver powder is dispersed in an organic component.

In this specification, "the peak whose frequency becomes the maximum in the particle size distribution based on volume" means that the particle size distribution based on volume with the particle size (µm) as the horizontal axis and the frequency (%) as the vertical axis is represented as a frequency distribution When the ratio of the particle diameters of the adjacent measurement points showing the particle size distribution is 1.2 in the dry measurement (1.09 in the wet measurement), the measurement point of the maximum value is shown in the histogram of the frequency distribution. In addition, if there are multiple peaks, when the peak with the highest frequency is the main peak and the other peaks are the secondary peaks, "the peak whose frequency becomes the maximum in the particle size distribution based on the volume" does not include: the frequency is very small to A secondary peak that cannot be distinguished from the background (a secondary peak with a frequency below 15% of the frequency of the primary peak), or a secondary peak with a very small difference between the particle size of the primary peak and the secondary peak (the particle size of the primary peak is The difference in particle size of the secondary peak is less than 30% of the particle size of the main peak (secondary peak). Also, in the relationship between the sub-peaks, the sub-peaks whose frequency is very small, or the sub-peaks whose particle diameters differ from other sub-peaks are very small are also not included in "the frequency becomes the largest in the particle size distribution based on volume". crest". Invention effect

According to the present invention, when used as a material of a conductive paste, and when the conductive paste is fired to form a conductive film, a silver powder that can form a conductive film with a lower resistance value than conventional ones can be produced.

The manufacturing method of the embodiment of the silver powder of the present invention is to manufacture the silver powder by mixing the first silver powder and the second silver powder, and the first silver powder is on the volume basis obtained by dry measurement using a laser diffraction particle size distribution measuring device. In the particle size distribution, there is one or more peaks with a maximum frequency; the second silver powder is a particle size distribution based on a volume obtained by dry measurement using a laser diffraction particle size distribution measuring device, and the peak frequency becomes a maximum of 2 The silver powder produced by mixing the first silver powder and the second silver powder has three or more peaks whose frequency becomes the maximum in the volume-based particle size distribution obtained by dry measurement with a laser diffraction particle size distribution analyzer. , and in the particle size distribution on a volume basis obtained by wet measurement with a laser diffraction scattering particle size distribution analyzer, there is one peak whose frequency becomes the maximum.

The first silver powder and the second silver powder used in the embodiment of the method for producing silver powder are silver powders with different agglutination properties, and the silver powder with the different agglomeration properties is prepared by mixing the silver powders with different agglomeration properties. Under the condition that the dispersing force can be exerted, the agglomeration will be eliminated, and the peak frequency becomes one in the particle size distribution based on the volume, and under the condition that the dispersing force cannot be exerted (such as the dry state), the agglomeration will be caused. In the particle size distribution based on volume, there are three or more wave peaks where the frequency becomes the maximum, and the filling property becomes high. As long as this silver powder is used as the material of the conductive paste, by coating the conductive paste and drying it, a uniform highly filled film with few defects or scratches can be formed. By firing such a high-filling film, a conductive film with a low resistance value can be formed. When the cross-section of the conductive film formed as described above is observed, compared with the cross-section of the conductive film formed using conventional silver powder as a material for the conductive paste, voids (formed when silver particles are agglomerated by firing) The ratio of the area occupied or the size of the voids decreases, and we think that the resistance value of the conductive film becomes lower due to the reduction in the ratio of the area occupied by the voids or the size of the voids.

In the manufacturing method of the silver powder, the cumulative 50% particle size (D ₅₀ ) of the first silver powder in the volume-based particle size distribution obtained by wet measurement is preferably larger than the volume-based particle size distribution of the second silver powder by wet measurement. Cumulative 50% particle size (D ₅₀ ). In addition, the cumulative 50% particle size (D ₅₀ ) of the second silver powder in the volume-based particle size distribution obtained by wet measurement is preferably 0.3 to 1 µm, more preferably 0.5 to 0.9 µm. Furthermore, the cumulative 50% particle size (D ₅₀ ) of the first silver powder in the volume-based particle size distribution obtained by wet measurement is preferably 1 to 4 μm, more preferably 1.5 to 3.3 μm. In addition, the cumulative 50% particle size (D ₅₀ ) of the first silver powder in the volume-based particle size distribution obtained by wet measurement is preferably the cumulative 50% of the second silver powder in the volume-based particle size distribution obtained by wet measurement. The particle size (D ₅₀ ) is 5 times or less, preferably 4 times or less. In addition, in the silver powder (mixed silver powder), the mass ratio of the first silver powder to the second silver powder is preferably 95:5~50:50, more preferably 90:10~65:35. In addition, the wet measurement by a laser diffraction scattering particle size distribution measuring apparatus is preferably performed by dispersing silver powder in a solvent such as isopropyl alcohol.

In addition, in the embodiment of the silver powder of the present invention, in the particle size distribution on a volume basis obtained by dry measurement with a laser diffraction particle size distribution measuring device, there are three or more peaks with a maximum frequency, and in the particle size distribution using a laser diffraction particle size distribution In the volume-based particle size distribution obtained by the wet measurement of the radiation-scattering particle size distribution analyzer, there is one or more peaks at which the frequency becomes the maximum.

In the silver powder, the cumulative 50% particle size (D ₅₀ ) of the silver powder in the volume-based particle size distribution obtained by wet measurement is preferably 1.2-3.0 μm, more preferably 1.5-2.8 μm. In addition, the ratio of the cumulative 90% particle size (D ₉₀ ) to the cumulative 10% particle size (D ₁₀ ) of the silver powder is preferably 2.0 to 8.0, more preferably 2.5 to 7.0. In addition, the wet measurement by a laser diffraction scattering particle size distribution analyzer is preferably performed by dispersing silver powder in a solvent such as isopropyl alcohol.

In addition, the shape of the said 1st silver powder and the 2nd silver powder may be any shape among various granular shapes, such as spherical shape and a small flake shape, and may be an indefinite shape in which the shape does not match.

When the embodiment of the silver powder of the present invention is used as a material of a conductive paste (such as a fired conductive paste), the components of the conductive paste include: silver powder and (saturated aliphatic hydrocarbons, unsaturated aliphatic hydrocarbons) , ketones, aromatic hydrocarbons, glycol ethers, esters, alcohols, etc.) organic solvents. In addition, if necessary, a vehicle, glass frit, inorganic oxide, dispersant, etc., in which a binder resin (such as an ethyl cellulose or an acrylic resin) has been dissolved in an organic solvent may also be included.

The content of the silver powder in the conductive paste is preferably 5 to 98% by mass, and more preferably 70 to 95% by mass, from the viewpoints of the conductivity of the conductive paste and the production cost. In addition, the content of the binder resin in the conductive paste is preferably 0.1 to 10 mass %, more preferably 0.1 to 6 mass %, from the viewpoints of the dispersibility of the silver powder in the conductive paste and the electrical conductivity of the conductive paste. . It is also possible to mix and use two or more types of the vehicle in which the binder resin has been dissolved in an organic solvent. In addition, the content of the glass frit in the conductive paste is from the viewpoint of securing the conduction between the electrode and the substrate and the conductivity of the electrode by firing through the conductive paste when the conductive paste is applied to the substrate to form the electrode. In view of this, it is preferably 0.1 to 20 mass %, more preferably 0.1 to 10 mass %. The glass frit may be used by mixing two or more types. In addition, considering the dispersibility of the silver powder in the conductive paste and the appropriate viscosity of the conductive paste, the content of the organic solvent in the conductive paste (when the conductive paste contains a vehicle, it is the total of the organic solvents including the vehicle). The content of the organic solvent) is preferably 0.8 to 20% by mass, more preferably 0.8 to 15% by mass. This organic solvent can also be used in mixture of 2 or more types.

Such a conductive paste can be produced by, for example, measuring each component, placing it in a predetermined container, pre-kneading using a beater, an all-purpose mixer, a kneader, etc., and then performing full-scale kneading with three rolls. In addition, an organic solvent may be added thereafter to adjust the viscosity as required. In addition, after only main-kneading the glass frit or inorganic oxide and the vehicle liquid to reduce the particle size, silver powder may be added to perform main-kneading at the end. Example

Hereinafter, embodiments of the silver powder of the present invention and its manufacturing method will be described in detail.

[Example 1] A commercially available silver powder (AG-5-54F manufactured by DOWA HIGHTECH CO., LTD.) was prepared as silver powder 1, and a dry laser diffraction particle size distribution analyzer (Sympatec manufactured by Nippon Laser Co., Ltd.) was used. Particle size distribution measuring device (HELOS & RODOS)), measure the particle size distribution on the volume basis of the silver powder under the measuring lens R1, the focal distance 20mm, the dispersion pressure 2.0bar, and the suction pressure 100mbar, and obtain (using a dry laser diffraction particle size distribution) The volume-based particle size distribution of the obtained silver powder 1 was measured, and the cumulative 10% particle size (D ₁₀ diameter) was 1.4 μm, the cumulative 50% particle size (D ₅₀ diameter) was 2.8 μm, and the volume-based cumulative 90% particle size (D ₉₀ diameter) was 4.2 μm. In addition, in this particle size distribution, there is one peak where the frequency becomes the maximum, and when the particle size with the highest frequency is the peak particle size A, the peak particle size A is 3.6 µm at a frequency of 19.6%. The measurement results are shown in Fig. 1A.

In addition, 0.1 g of the above-mentioned silver powder (silver powder 1) was added to 40 mL of isopropyl alcohol (IPA), and dispersed by an ultrasonic homogenizer (US-150T, 19.5 kHz, manufactured by Nippon Seiki Co., Ltd., Japan Seiki Co., Ltd.) with a diameter of 18 mm at the front end of the wafer. A sample was obtained for 2 minutes, and the obtained sample was determined in the total reflection mode using a laser diffraction scattering particle size distribution analyzer (MICROTRAC MT3300EXII manufactured by MicrotracBEL Co., Ltd.) (particle size distribution measurement by wet laser diffraction scattering). The obtained) volume-based particle size distribution of the silver powder 1 shows that the cumulative 10% particle size (D ₁₀ ) is 1.7 μm, the cumulative 50% particle size (D ₅₀ ) is 2.5 μm, and the cumulative 90% particle size (D ₉₀ ) is 3.9 μm. In addition, in this particle size distribution, there is one peak with a maximum frequency, and when the particle size with the highest frequency is the peak particle size A, the peak particle size A is 2.8 µm at a frequency of 11.2%. The measurement results are shown in FIG. 1B . A scanning electron microscope photograph (SEM image) of 10,000 times the above-mentioned silver powder (silver powder 1) is shown in FIG. 1C . Using this SEM image, the (circle-equivalent) diameter of any 100 or more particles was measured, and the average value (SEM particle diameter) was calculated to be 1.32 µm.

Further, another commercially available silver powder (AG-2-1C manufactured by DOWA HIGHTECH CO., LTD.) was prepared as silver powder 2, and was obtained by the same method as above (by dry laser diffraction particle size distribution measurement). ) Volume-based particle size distribution of silver powder 1, the cumulative 10% particle diameter (D ₁₀ diameter) is 0.5 μm, the cumulative 50% particle diameter (D ₅₀ diameter) is 0.9 μm, and the cumulative 90% particle diameter (D ₉₀ diameter) is 0.9 μm 1.9 μm. In addition, in this particle size distribution, there are two peaks whose frequency becomes the maximum, when let the particle size with the highest frequency among these two peaks be the peak particle size A, and let the particle size with a lower frequency be the peak particle size B. , the peak particle size A of frequency 13.1% is 1.5µm, and the peak particle size B of frequency 11.4% is 0.7µm. The measurement results are shown in Fig. 2A.

In addition, with respect to the above-mentioned silver powder (silver powder 2), the volume-based particle size distribution of the silver powder 2 (obtained by wet laser diffraction scattering particle size distribution measurement) was obtained by the same method as described above, and the cumulative 10% particle size ( D ₁₀ ) was 0.4 μm, the cumulative 50% particle diameter (D ₅₀ ) was 0.9 μm, and the cumulative 90% particle diameter (D ₉₀ ) was 1.7 μm. In addition, in this particle size distribution, there is one peak where the frequency becomes the maximum, and when the particle size with the highest frequency is the peak particle size A, the peak particle size A is 1.1 µm at a frequency of 6.6%. The measurement results are shown in Fig. 2B. A 10,000-fold SEM image of the above-mentioned silver powder (silver powder 2) is shown in FIG. 2C . Using this SEM image, the (circle-equivalent) diameter of 100 or more arbitrary particles was measured, and the average value (SEM particle diameter) was calculated to be 0.46 µm.

Next, 42.5 g (85 mass %) of silver powder 1 and 7.5 g (15 mass %) of silver powder 2 were placed in an electric coffee mill (ECG-62 manufactured by Melitta Ltd.), and mixed for 4 minutes.

For the silver powder (mixed silver powder) obtained as described above, the volume-based particle size distribution of the silver powder (obtained by the dry laser diffraction particle size distribution measurement) was obtained by the same method as above, and the cumulative 10% particle size (D ₁₀ diameter) was 0.7 μm, the volume-based cumulative 50% particle diameter (D ₅₀ diameter) was 2.3 μm, and the volume-based cumulative 90% particle diameter (D ₉₀ diameter) was 4.5 μm. Also, in this particle size distribution, there are 3 peaks whose frequency becomes the maximum, when let the particle diameter with the highest frequency among these 3 peaks be the peak particle diameter A, and let the particle diameter with a lower frequency be the peak particle diameter B, And let the particle size of the lower frequency be the peak particle size C, the peak particle size A of the frequency 11.6% is 3.6µm, the peak particle size B of the frequency 7.1% is 1.8µm, and the peak particle size of the frequency 3.9% is 1.8µm. C is 0.7µm. The measurement results are shown in Fig. 3A.

In addition, for the above-mentioned silver powder (mixed silver powder), the volume-based particle size distribution of the silver powder (obtained by wet laser diffraction scattering particle size distribution measurement) was obtained by the same method as above, and the cumulative 10% particle size (D ₁₀ ) was 0.8 μm, the cumulative 50% particle diameter (D ₅₀ ) was 2.1 μm, and the cumulative 90% particle diameter (D ₉₀ ) was 4.1 μm. In addition, in this particle size distribution, there is one peak where the frequency becomes the maximum, and when the particle size with the highest frequency is the peak particle size A, the peak particle size A is 2.5 µm at a frequency of 6.5%. The measurement results are shown in Fig. 3B. 10,000 times the SEM image of the above-mentioned silver powder (mixed silver powder) is shown in FIG. 3C .

Further, 89.8% by mass of the obtained silver powder (mixed silver powder), 2.0% by mass of glass frit (FSGCO2 manufactured by Okamoto Glass Co., Ltd.), 0.4% by mass of oleic acid as a dispersant, ethyl cellulose and hydroxypropyl fiber as resins 0.2 mass % of a mixture of vegans, a mixture of terpineol and Texanol (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate) and tetracarbitol acetate as a solvent 6.2 % by mass, 1.1% by mass of hydrogenated sesame oil as a thixotropic agent, and 0.4% by mass of dimethylpolysiloxane as a linear maintenance agent, using a propellerless rotating revolution type stirring and defoaming device (AR250 manufactured by Thinky Co., Ltd. ) was kneaded and kneaded with three rolls (80S manufactured by EXAKT Corporation), and passed through a mesh of 500 μm to obtain a conductive paste.

Next, a silicon substrate (100Ω/□) for solar cells was prepared, and aluminum paste (ALSOLAR 14- manufactured by Toyo Aluminium Co., Ltd.) was applied to the back surface of the silicon substrate by a screen printing machine (MT-320T manufactured by Micro-tec Co., Ltd.). 7021) was printed into a 154mm square rectangular pattern, and dried at 200 ° C for 10 minutes by a hot air dryer, and at the same time on the surface of the silicon substrate by a screen printing machine (MT-320T manufactured by Micro-tec Co., Ltd.) The above conductive paste was printed into 110 finger electrodes with a width of 27µm and 4 busbar electrodes with a width of 1.1mm, dried at 200°C for 10 minutes by a hot air dryer, and then fired in a high-speed IR furnace. (High-speed firing test 4-chamber furnace manufactured by NGK Co., Ltd.) The solar cell was produced by firing at 770° C. with in-out for 21 seconds in the atmosphere to form a conductive film.

The solar cell was irradiated with simulated sunlight having a light irradiation energy of 100 mW/cm ² using a xenon lamp of a solar simulator (manufactured by WACOM ELECTRIC CO., LTD.). As a result, when the output terminal of the solar cell was short-circuited, the current (short-circuit current) Isc flowing between the two terminals was 8.78 A, the voltage (open-circuit voltage) Voc between the two terminals when the output terminal of the solar cell was opened was 0.63 V, and the current density Jsc ( The short-circuit current Isc) per 1 cm ² is 3.7×10 ^-2 A/cm ² , the value obtained by dividing the maximum power Pmax (=Imax·Vmax) by the product of the open circuit voltage Voc and the current density Jsc (fill factor) FF (=Pmax /Voc・Isc) was 79.66, and the conversion efficiency (power generation efficiency) Eff (the value obtained by dividing the maximum power Pmax by the amount of irradiated light (W) per 1 cm ² and multiplying it by 100) was 18.27%, which was considered good. The series resistance Rs was 6.4×10 ^-3 Ω/□.

[Example 2] 5525 g (85 mass %) of silver powder 1 and 975 g (15 mass %) of silver powder 2 were put into a V-type mixer (DV-1-10 manufactured by DULTON COMPANY LIMITED), and mixed at 60 rpm for 360 minutes , except that by the same method as in Example 1 for the obtained silver powder (mixed silver powder), the particle size distribution on the volume basis of the silver powder (obtained by dry laser diffraction particle size distribution measurement) was obtained, and the result accumulated 10% particles The diameter (D ₁₀ diameter) was 0.6 μm, the cumulative 50% particle diameter (D ₅₀ diameter) was 2.1 μm, and the cumulative 90% particle diameter (D ₉₀ diameter) was 4.2 μm. Also, in this particle size distribution, there are 3 peaks whose frequency becomes the maximum, when let the particle diameter with the highest frequency among these 3 peaks be the peak particle diameter A, and let the particle diameter with a lower frequency be the peak particle diameter B, And let the particle size of the lower frequency be the peak particle size C, the peak particle size A of the frequency 11.1% is 3.0µm, the peak particle size B of the frequency 8.4% is 1.8µm, and the peak particle size of the frequency 3.8% is 1.8µm. C is 0.7µm. The measurement results are shown in Fig. 4A.

In addition, with respect to the above-mentioned silver powder (mixed silver powder), the volume-based particle size distribution of the silver powder (obtained by wet laser diffraction scattering particle size distribution measurement) was obtained by the same method as in Example 1, and the result was a cumulative 10% particle size. (D ₁₀ ) was 0.9 μm, the cumulative 50% particle diameter (D ₅₀ ) was 2.2 μm, and the cumulative 90% particle diameter (D ₉₀ ) was 4.0 μm. In addition, in this particle size distribution, there is one peak with a maximum frequency, and when the particle size with the highest frequency is the peak particle size A, the peak particle size A is 2.5 µm at a frequency of 7.1%. The measurement results are shown in Fig. 4B. The SEM image of 10,000 times the above-mentioned silver powder (mixed silver powder) is shown in FIG. 4C .

Moreover, after obtaining a conductive paste by the same method as Example 1 using the obtained silver powder (mixed silver powder), the solar cell was produced, and the series resistance was calculated|required, and 6.4×10 ^-3 Ω/□ was obtained.

[Comparative Example 1] Put 3670.1 g of an aqueous silver nitrate solution with a silver concentration of 1.4 mass % into a glass beaker, add 161.8 g of ammonia water with a concentration of 28 mass % to the silver nitrate aqueous solution (2.67 molar equivalent of ammonia with respect to 1 molar of silver), and put it in a glass beaker. 30 seconds after the addition of the ammonia water, 7.5 g of an aqueous sodium hydroxide solution having a concentration of 20 mass % was added to obtain a silver ammonia complex aqueous solution. After the silver-ammine complex aqueous solution was stirred for 3 minutes, 357.6 g (relative to silver) of 21.0 mass % formaldehyde aqueous solution (formalin was diluted with pure water) was mixed with the stirred silver-ammine complex aqueous solution. 1 mol is 12.4 mol equivalent), 15 seconds after the start of the mixing, 6.01 g of an ethanol solution of stearic acid with a concentration of 1.55 mass % (as a reducing agent) was added to complete the reduction reaction, and a silver-containing particle was obtained. slurry. The slurry was filtered and washed with water until the conductivity of the filtrate became 0.2 mS. After drying at 73° C. for 10 hours with a vacuum dryer, the resulting dried powder was put into a disintegrator (SK-M10, manufactured by Kyoritsu Kogyo Co., Ltd.) In the process, the disintegration for 30 seconds was repeated twice to obtain silver powder.

The silver powder obtained in the above manner was used as silver powder 1, and the particle size distribution on the volume basis of the silver powder (obtained by dry laser diffraction particle size distribution measurement) was obtained by the same method as in Example 1, and the result was a cumulative 10% particle size ( D ₁₀ diameter) was 1.0 μm, cumulative 50% particle diameter (D ₅₀ diameter) was 2.1 μm, and volume-based cumulative 90% particle diameter (D ₉₀ diameter) was 3.4 μm. In addition, in this particle size distribution, there is one peak with a maximum frequency, and when the particle size with the highest frequency is the peak particle size A, the peak particle size A is 2.3 µm at a frequency of 17.4%. The measurement results are shown in Fig. 5A.

Moreover, with respect to the obtained silver powder (silver powder 1), the volume-based particle size distribution of the silver powder (obtained by wet laser diffraction scattering particle size distribution measurement) was obtained by the same method as in Example 1, and the result was a cumulative 10% particle size. (D ₁₀ ) was 1.1 μm, the cumulative 50% particle diameter (D ₅₀ ) was 1.8 μm, and the cumulative 90% particle diameter (D ₉₀ ) was 2.8 μm. In addition, in this particle size distribution, there is one peak with a maximum frequency, and when the particle size with the highest frequency is the peak particle size A, the peak particle size A is 2.1 µm at a frequency of 10.2%. The measurement results are shown in Fig. 5B. The 10,000-fold SEM image of the above-mentioned silver powder is shown in FIG. 5C . Using this SEM image, the (circle equivalent) diameter of 100 or more arbitrary particles was measured, and the average value (SEM particle diameter) was calculated to be 1.29 µm.

In addition, the obtained silver powder (silver powder 1) was used as it was (not mixed silver powder), and a conductive paste was obtained in the same manner as in Example 1, and then a solar cell was fabricated and the series resistance was determined to obtain 6.8×10 ^-3 Ω/□ .

[Comparative Example 2] In addition, the silver powder 1 of Example 1 (AG-5-54F manufactured by DOWA HIGHTECH CO., LTD.) was used as it was (without mixed silver powder), and conductivity was obtained by the same method as in Example 1. After pasting, a solar cell was fabricated and the series resistance was determined to be 6.8×10 ^-3 Ω/□.

[Comparative Example 3] A commercially available silver powder (FA-S-16 manufactured by DOWA HIGHTECH CO., LTD.) was prepared as silver powder 1, and was obtained by the same method as in Example 1 (using a dry laser diffraction particle size distribution The particle size distribution on the volume basis of the obtained silver powder was measured, and the cumulative 10% particle diameter (D ₁₀ diameter) was 0.5 μm, the cumulative 50% particle diameter (D ₅₀ diameter) was 1.5 μm, and the cumulative 90% particle diameter (D ₉₀ diameter) was 1.5 μm. ) is 9.5 μm. Also, in this particle size distribution, there are 3 peaks whose frequency becomes the maximum, when let the particle diameter with the highest frequency among these 3 peaks be the peak particle diameter A, and let the particle diameter with a higher frequency be the peak particle diameter B, And let the particle size of the higher frequency be the peak particle size C, the peak particle size A of the frequency 8.0% is 1.5µm, the peak particle size B of the frequency 6.3% is 0.7µm, and the peak particle size of the frequency 5.3% is 0.7µm. C is 8.6 µm. The measurement results are shown in Fig. 6A.

In addition, with respect to the above-mentioned silver powder (silver powder 1), the volume-based particle size distribution of the silver powder (obtained by wet laser diffraction scattering particle size distribution measurement) was obtained by the same method as in Example 1, and the result was a cumulative 10% particle size. (D ₁₀ ) was 0.5 μm, the cumulative 50% particle diameter (D ₅₀ ) was 1.9 μm, and the cumulative 90% particle diameter (D ₉₀ ) was 9.8 μm. In addition, in this particle size distribution, there are two peaks whose frequency becomes the maximum, when the particle size with the highest frequency among these two peaks is the peak particle size A, and the particle size with a higher frequency is the peak particle size B. , the peak particle size A is 1.4 µm at a frequency of 3.2%, and the peak particle size B is 7.1 µm at a frequency of 2.6%. The measurement results are shown in Fig. 6B. The 10,000-fold SEM image of the above-mentioned silver powder is shown in FIG. 6C .

In addition, the above-mentioned silver powder (silver powder 1) was used as it was (not mixed silver powder), and a conductive paste was obtained by the same method as in Example 1, and then a conductive film was formed to try to produce a solar cell, but the conductive film was disconnected and the series connection could not be measured. resistance. As can be seen from this comparative example, when the conductive paste using the following silver powder is printed on the substrate, defects and scratches will increase, and it is difficult to form a uniform high-fill film. There are 3 peaks with a maximum frequency in the volume-based particle size distribution obtained by the distribution measurement, and there are 3 peaks with a maximum frequency in the volume-based particle size distribution (obtained by the wet laser diffraction scattering particle size distribution measurement). 2.

The properties of the silver powders of these examples and comparative examples are listed in Tables 1 to 2.

[Table 1]

[Table 2]

In addition, each solar cell obtained in Examples 1 to 2 and Comparative Examples 1 to 2 was cut in a direction perpendicular to the surface thereof, and the cross section was subjected to an ion milling apparatus (ArBlade 500 manufactured by Hitachi High-Technologies Co., Ltd.), At a beam current of 180 µA, ON-OFF (20 seconds ON and 10 seconds OFF) was intermittently repeated, and polishing was performed for 3 hours. Scanning electron microscope photographs (SEM images) of the cross-sections of the conductive films of the solar cells polished as described above are shown in FIGS. 7 to 10 .

The SEM images shown in FIGS. 7 to 10 were analyzed using image analysis software (Mac-View manufactured by Mounttech Co., Ltd.), and the ratio of the void area to the conductive film area was obtained. In addition, the image analysis software used can calculate the area of the conductive film and the void area by tracing the outline of the conductive film and the void in the SEM image with a stylus. As a result, the ratio of the void area to the conductive film area was 14.4% in Example 1, 13.8% in Example 2, 18.7% in Comparative Example 1, and 22.8% in Comparative Example 2. From these results, compared with Comparative Examples 1 and 2, the ratio of the void area to the conductive film area of Examples 1 to 2 is small, so we think that the resistance value of the conductive film is low. industrial availability

The silver powder of the present invention can be used to form electrodes for solar cells, electronic components using low temperature firing ceramics (LTCC), internal electrodes for multilayer ceramic electronic components such as multilayer ceramic inductors, and external electrodes for multilayer ceramic capacitors or multilayer ceramic inductors. It is used as a material for sintered conductive paste to obtain a conductive film with high conductivity.

1A is a graph showing the particle size distribution on a volume basis obtained by dry measurement of the silver powder 1 used in the examples using a laser diffraction particle size distribution analyzer. 1B is a graph showing the particle size distribution on a volume basis obtained by wet measurement of the silver powder 1 used in the examples using a laser diffraction scattering particle size distribution analyzer. FIG. 1C is a scanning electron microscope photograph (SEM image) of 10,000 times the silver powder used in the example. FIG. 2A is a graph showing the particle size distribution on a volume basis obtained by dry measurement of the silver powder 2 used in the examples using a laser diffraction particle size distribution analyzer. 2B is a graph showing the particle size distribution on a volume basis obtained by wet measurement of the silver powder 2 used in the examples using a laser diffraction scattering particle size distribution measuring apparatus. FIG. 2C is an SEM image of 10,000 times the silver powder 2 used in the example. 3A is a graph showing the volume-based particle size distribution of the silver powder obtained in Example 1 by dry measurement using a laser diffraction particle size distribution analyzer. 3B is a graph showing the particle size distribution on a volume basis of the silver powder obtained in Example 1 by wet measurement with a laser diffraction scattering particle size distribution analyzer. FIG. 3C is an SEM image of 10,000 times the silver powder obtained in Example 1. FIG. 4A is a graph showing the particle size distribution on a volume basis of the silver powder obtained in Example 2 by dry measurement using a laser diffraction particle size distribution measuring device. 4B is a graph showing the volume-based particle size distribution of the silver powder obtained in Example 2 by wet measurement with a laser diffraction scattering particle size distribution analyzer. 4C is an SEM image of 10,000 times the silver powder obtained in Example 2. 5A is a graph showing the particle size distribution on a volume basis of the silver powder obtained in Comparative Example 1 by dry measurement with a laser diffraction particle size distribution analyzer. 5B is a graph showing the volume-based particle size distribution of the silver powder obtained in Comparative Example 1 by wet measurement with a laser diffraction scattering particle size distribution analyzer. FIG. 5C is an SEM image of the silver powder obtained in Comparative Example 1 at a magnification of 10,000 times. 6A is a graph showing the particle size distribution on a volume basis of the silver powder obtained in Comparative Example 3 by dry measurement using a laser diffraction particle size distribution analyzer. 6B is a graph showing the particle size distribution on a volume basis of the silver powder obtained in Comparative Example 3 by wet measurement with a laser diffraction scattering particle size distribution analyzer. FIG. 6C is an SEM image of 10,000 times the silver powder obtained in Comparative Example 3. FIG. 7 is a scanning electron microscope photograph (SEM image) of a cross-section of the conductive film after firing the conductive paste obtained in Example 1. FIG. FIG. 8 is an SEM image of a cross-section of the conductive film after firing the conductive paste obtained in Example 2. FIG. 9 is an SEM image of a cross-section of the conductive film after firing the conductive paste obtained in Comparative Example 1. FIG. 10 is an SEM image of a cross-section of the conductive film after firing the conductive paste obtained in Comparative Example 2. FIG.

Claims (10)

A method for producing silver powder, characterized in that: producing silver powder by mixing a first silver powder and a second silver powder, the first silver powder being in the volume-based particle size distribution obtained by dry measurement using a laser diffraction particle size distribution measuring device , the frequency becomes the maximum peak is 1 or more; the second silver powder is the particle size distribution based on the volume obtained by dry measurement using a laser diffraction particle size distribution measuring device, and the frequency becomes the maximum peak is 2 or more. ; The silver powder produced by mixing the first silver powder and the second silver powder is in the particle size distribution on the volume basis obtained by dry measurement using a laser diffraction particle size distribution measuring device, and there are three or more peaks whose frequency becomes the maximum, and in In the particle size distribution on a volume basis obtained by wet measurement with a laser diffraction scattering particle size distribution analyzer, one peak whose frequency becomes the maximum is one. The method for producing silver powder according to claim 1, wherein the cumulative 50% particle size (D ₅₀ ) of the first silver powder in the volume-based particle size distribution obtained by wet measurement is larger than that of the second silver powder obtained by wet measurement. Cumulative 50% particle size (D ₅₀ ) in the particle size distribution on a volume basis. The method for producing silver powder according to claim 1, wherein the cumulative 50% particle size (D ₅₀ ) of the second silver powder in the volume-based particle size distribution obtained by wet measurement is 0.3 to 1 µm. The method for producing silver powder according to claim 1, wherein the cumulative 50% particle size (D ₅₀ ) of the first silver powder in the volume-based particle size distribution obtained by wet measurement is 1 to 4 μm, and the second silver powder is in the range of 1 to 4 μm. Four times or less of the cumulative 50% particle diameter (D ₅₀ ) in the volume-based particle size distribution obtained by wet measurement. The method for producing silver powder according to claim 1, wherein the wet measurement using a laser diffraction scattering particle size distribution measuring device is performed by dispersing the silver powder in isopropyl alcohol. A silver powder, characterized in that: in the particle size distribution on the volume basis obtained by dry measurement by using a laser diffraction particle size distribution measuring device, there are more than 3 peaks whose frequency becomes the maximum, and when using a laser diffraction scattering particle size distribution In the volume-based particle size distribution obtained by the wet measurement of the distribution measuring apparatus, there is one peak whose frequency becomes the maximum. The silver powder of claim 6, wherein the cumulative 50% particle size (D50) of the aforementioned silver powder in the volume-based particle size distribution obtained by wet measurement is 1.2-3.0 μm. The silver powder of claim 6, wherein the ratio of the cumulative 90% particle size (D ₉₀ ) to the cumulative 10% particle size (D ₁₀ ) of the aforementioned silver powder is 2.0 to 8.0. The silver powder according to claim 6, wherein the wet measurement using a laser diffraction scattering particle size distribution analyzer is performed by dispersing the silver powder in isopropyl alcohol. A conductive paste characterized in that the silver powder according to claim 6 is dispersed in an organic component.

Images