Spherical silver powder and method for producing spherical silver powder

Abstract

To provide a spherical silver powder that can impart excellent thin line printability to conductive pastes.SOLUTION: The present invention is a spherical silver powder in which a surface treatment agent is present; for which, in measurement of the thermal expansion coefficient, the maximum value of the thermal expansion coefficient with reference to the value at 50°C is 0.3% or less; for which the BET specific surface area is 0.1 m2 / g or more and 0.8 m2 / g or less; and for which the value of D90 is 2.0 μm or more and 4.0 μm or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a spherical silver powder and a method for producing the spherical silver powder. [Background technology]

[0002] A method of forming a conductive film for electrodes, electrical wiring, etc., by applying or printing a conductive paste containing a conductive metal powder onto a substrate such as a film, a board, or an electronic component, and then heating the paste to dry, harden, or bake it has been widely used in the past. However, with the recent increase in the performance of electronic devices, the conductive film formed using the conductive paste is required to have lower resistance, and this requirement is becoming stricter every year.

[0003] In response to the above demands, for example, Patent Document 1 proposes a silver powder containing a specified surface treatment agent and having a specified coefficient of thermal expansion, BET value (specific surface area), and ignition loss difference, for the purpose of suppressing swelling of a conductive coating film during firing of a sinterable conductive paste and reducing the electrical resistance value of the cured film (conductive film). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6174301 Summary of the Invention [Problem to be solved by the invention]

[0005] Here, in recent years, there has been a trend toward thinner conductive films, and there is a demand for conductive pastes that allow for fine line printing.

[0006] Conventional silver powders have room for further improvement in terms of imparting excellent fine line printability to conductive pastes.

[0007] Therefore, an object of the present invention is to provide a spherical silver powder that can impart excellent fine line printability to a conductive paste. Another object of the present invention is to provide a method for producing spherical silver powder that can impart excellent fine line printability to a conductive paste. [Means for solving the problem]

[0008] As a result of extensive research by the inventors to solve the above-mentioned problems, the inventors have completed the present invention described below.

[0009] That is, the gist of the present invention for solving the above-mentioned problems is as follows.

[0010] [1] A surface treatment agent is present, In thermal expansion measurements, the maximum thermal expansion coefficient is 0.3% or less based on the value at 50°C. BET specific surface area is 0.1m 2 / g or more 0.8m 2 / g or less, D 90 The spherical silver powder has a value of 2.0 μm or more and 4.0 μm or less.

[0011] [2]D 50 The spherical silver powder according to [1], wherein the value is 1.0 μm or more and 2.5 μm or less.

[0012] [3]D 10 The spherical silver powder according to [1] or [2], wherein the value is 0.5 μm or more and 1.2 μm or less.

[0013] [4] The spherical silver powder according to any one of [1] to [3], wherein the surface treatment agent is one or more surface treatment agents selected from the group consisting of fatty acids, compounds having an azole structure, and fatty acid salts.

[0014] [5] A method for producing spherical silver powder, comprising adding a reducing agent to an aqueous reaction system containing silver ions and a chelating agent made of a polymer to reduce and precipitate silver particles, comprising: a carbonic acid concentration adjustment step of adjusting a ratio of a total molar concentration of carbonic acid to a total molar concentration of silver in the aqueous reaction system to 0.004 or more and 0.051 or less before adding the reducing agent to the aqueous reaction system; a surface treatment agent addition step of adding a surface treatment agent to the aqueous reaction system after the silver particles have precipitated; A method for producing spherical silver powder, comprising:

[0015] [6] The method for producing spherical silver powder according to [5], wherein the surface treatment agent is one or more surface treatment agents selected from the group consisting of fatty acids, compounds having an azole structure, and fatty acid salts.

[0016] [7] The method for producing spherical silver powder described in [5] or [6], wherein the chelating agent is polyethyleneimine having a weight average molecular weight of 600 or less.

[0017] [8] The method for producing spherical silver powder according to any one of [5] to [7], wherein the reducing agent is hydrazine. Effect of the Invention

[0018] According to the present invention, it is possible to provide a spherical silver powder that can impart excellent fine line printability to a conductive paste. The present invention also provides a method for producing spherical silver powder that can impart excellent fine line printability to a conductive paste. [Brief description of the drawings]

[0019] [Figure 1] 1 is a graph showing the results of thermomechanical analysis of the spherical silver powder obtained in Example 1. [Diagram 2] 2 is an enlarged graph of a portion of the graph in FIG. 1. [Diagram 3] 1 is a graph showing the results of thermomechanical analysis of the spherical silver powder obtained in Example 2. [Figure 4] 4 is an enlarged graph of a portion of the graph in FIG. 3. [Diagram 5] 1 is a graph showing the results of thermomechanical analysis of the spherical silver powder obtained in Example 3. [Figure 6]6 is a graph showing an enlarged portion of the graph in FIG. 5. [Figure 7] 1 is a graph showing the results of thermomechanical analysis of the spherical silver powder obtained in Example 4. [Figure 8] 8 is a graph showing an enlarged portion of the graph in FIG. 7. [Figure 9] 1 is a graph showing the results of thermomechanical analysis of the spherical silver powder obtained in Example 5. [Figure 10] 10 is a graph showing an enlarged portion of the graph in FIG. 9. [Figure 11] 1 is a graph showing the results of thermomechanical analysis of the spherical silver powder obtained in Example 6. [Figure 12] 12 is a graph showing an enlarged portion of the graph in FIG. 11. [Figure 13] 1 is a graph showing the results of thermomechanical analysis of the spherical silver powder obtained in Example 7. [Figure 14] 14 is a graph showing an enlarged portion of the graph in FIG. 13. [Figure 15] 2 is a graph showing the results of thermomechanical analysis of the spherical silver powder obtained in Comparative Example 1. [Figure 16] FIG. 15 is an enlarged view of a portion of the graph. [Figure 17] 1 is a graph showing the results of thermomechanical analysis of the spherical silver powder obtained in Comparative Example 2. [Figure 18] 18 is a graph showing an enlarged portion of the graph in FIG. 17. [Figure 19] 1 is a graph showing the results of thermomechanical analysis of the spherical silver powder obtained in Comparative Example 3. [Figure 20] 20 is a graph showing an enlarged portion of the graph in FIG. 19. [Figure 21] 1 is a graph showing the results of thermomechanical analysis of the spherical silver powder obtained in Comparative Example 4. [Figure 22] 22 is a graph showing an enlarged portion of the graph in FIG. 21. [Figure 23] 1 is a 10,000x SEM image of the spherical silver powder obtained in Example 1. [Figure 24] 1 is a 10,000x SEM image of the spherical silver powder obtained in Example 2. [Diagram 25]1 is a 10,000x SEM image of the spherical silver powder obtained in Example 3. [Figure 26] 1 is a 10,000x SEM image of the spherical silver powder obtained in Example 4. [Figure 27] 1 is a 10,000x SEM image of the spherical silver powder obtained in Example 5. [Figure 28] 1 is a 10,000x SEM image of the spherical silver powder obtained in Example 6. [Figure 29] 1 is a 10,000x SEM image of the spherical silver powder obtained in Example 7. [Diagram 30] 1 is a 10,000x SEM image of the spherical silver powder obtained in Comparative Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The spherical silver powder of the present invention is suitable for use as a conductive filler for conductive paste. The conductive paste using the spherical silver powder of the present invention can be used to form a conductive pattern or an electrode on a substrate. The conductive paste using the spherical silver powder of the present invention can be printed on a substrate by, for example, screen printing, offset printing, photolithography, or the like to form a conductive film such as a conductive pattern or an electrode.

[0021] (Terminology and Measurement Methods) Prior to describing the embodiments, the terms and measurement methods used in this specification will be described.

[0022] <Confirmation of spherical silver powder (particle shape)> In this specification, spherical silver powder means silver powder in which the average shape factor of 400 or more particles observed by image analysis based on scanning electron microscope (SEM) images is in the range of 1.0 to less than 1.7. The scanning electron microscope is not particularly limited, but for example, JSM-6100 or JSM-IT300L manufactured by JEOL Ltd. can be used. In the present invention, the silver powders of Examples 1 and 5 were observed using JSM-IT300L, and the silver powders of Examples 2, 3, 4, 6, 7, and Comparative Example 3 were observed using JSM-6100. In this specification, the shape factor is the ratio of the area of ​​a virtual circle having the average maximum length as the diameter of 400 or more particles observed by the image analysis to the average particle area of ​​the silver particles obtained by tracing the outer shape of the particles, and is the value obtained by dividing the area of ​​the virtual circle by the average particle area. The shape factor is calculated by π(average maximum length / 2) 2 / average particle area.

[0023] <Measurement of thermal expansion coefficient of spherical silver powder> The thermal expansion coefficient of the spherical silver powder was measured as follows. First, 0.3 g of spherical silver powder was weighed. Next, the spherical silver powder was put into a specified mold with a diameter of 5 mmφ, and pressed with a press machine for 1 minute under a load of 50 kg to prepare a cylindrical measurement sample. This measurement sample was set in the sample holder of a thermomechanical analysis (TMA) device (Thermo plus EVO 2 series TMA8311), and a measurement load of 98 mN was applied by the measurement probe, and the temperature was raised from room temperature to 900°C at a heating rate of 10°C / min to perform a thermomechanical analysis (TMA) of the measurement sample, and the thermal expansion coefficient at each temperature was calculated based on the value at 50°C using the following formula (1). Thermal expansion coefficient (%) when heated from 50℃ to T℃ = (L T -L 50 ) / L 50 ×100 (1) Here, L 50 is the axial length (mm) of the cylindrical measurement sample at a sample temperature of 50°C, L T is the axial length (mm) of the cylindrical measurement sample at sample temperature T°C.

[0024] <BET Specific Surface Area> In this specification, the "BET specific surface area" was measured by the BET one-point method using nitrogen adsorption with a Macsorb HM-model 1210 (manufactured by MOUNTECH). For the measurement of the BET specific surface area, the sample weight was 3.0 g, and N 2 / He (30 / 70) mixed gas was used, the gas flow rate was 25 mL / min, and the degassing conditions before measurement were 60 °C for 10 minutes.

[0025] <Quantification of Surface Treatment Agent> In this specification, for example, when the surface treatment agent of spherical silver powder is a fatty acid, the content of the fatty acid was measured according to the quantitative analysis method of fatty acids described in Japanese Patent No. 5622543. Specifically, first, after dissolving the spherical silver powder in an acid, an organic solvent was mixed, and after extracting the entire amount of the surface treatment agent into the organic solvent phase, a predetermined amount of the organic solvent phase was taken, evaporated to dryness, and the remaining solid was determined by measuring the carbon content with a carbon-sulfur analyzer and calculated.

[0026] For example, when the surface treatment agent is identified as stearic acid and no carbon source other than stearic acid is contained in the spherical silver powder, the measurement method of stearic acid is as follows.

[0027] When calibration curves were obtained by measuring the respective carbon amounts (intensities) with a carbon-sulfur analyzer in standard solutions with different contents (mg) of stearic acid, the slope was designated as A (intensity / mg). And for the stearic acid mass X (mg) and concentration Y (%) in the spherical silver powder, from the extraction of the treatment agent into the total amount of organic solvent a (mL) by the above treatment of the spherical silver powder, a predetermined amount b (mL) was taken, and when the carbon amount C (intensity) obtained by measuring the remaining solid and the amount of spherical silver powder dissolved in the acid was M (g), the stearic acid mass X and concentration Y were calculated by the following formulas (A) and (B), respectively. X (mg) = (C / A × a / b) ··· (A) Y (%) = X / (M × 1000) × 100 ··· (B)

[0028] Even when oleic acid was used as the surface treatment agent, the carbon content was measured and calculated in the same manner as above. The oleic acid concentration was also calculated using the calibration curve of stearic acid. The molecular weight of stearic acid is 284.48, with a carbon content of 216.19, and the molecular weight of oleic acid is 282.46, with a carbon content of 216.19, so the oleic acid concentration Y' was calculated using the following formula (C). Oleic acid concentration Y' (%) = Y × (216.19 / 284.48) × (282.46 / 216.19) (C)

[0029] In addition, in the present specification, for example, when the surface treatment agent of the spherical silver powder is benzotriazole, the content of the benzotriazole was measured according to the quantitative analysis method for benzotriazole and benzotriazole salts described in Japanese Patent No. 5,523,153. Specifically, the spherical silver powder was first washed with an aqueous hydrochloric acid solution, and the washings were quantitatively analyzed by absorptiometry.

[0030] For example, 0.2 g of spherical silver powder was weighed, washed with an aqueous hydrochloric acid solution and quantitatively analyzed by spectrophotometry according to the following procedure to determine the content of benzotriazole. First, concentrated hydrochloric acid (Kanto Scientific Co., Ltd., special grade) was diluted with pure water to prepare an 18% by mass aqueous hydrochloric acid solution. Next, 0.2 g of silver powder and 20 mL of the aqueous hydrochloric acid solution were placed in a 100 mL glass beaker and heated to boiling. After the start of boiling, heating was continued for 15 minutes to maintain the boiling state. During heating, an 18% by mass aqueous hydrochloric acid solution was added within a range not exceeding the amount of liquid before heating so that the solution would not evaporate to dryness. After heating, the solution was cooled to 25°C and filtered, and an 18% by mass aqueous hydrochloric acid solution was added so that the volume of the filtrate was 20 mL to make a constant volume, and a measurement sample solution by spectrophotometry was prepared. Furthermore, the absorbance of the measurement sample solution was measured using a spectrophotometer (Hitachi, U-3210) to measure the absorbance of the peak at a wavelength of 272.8 nm ± 0.5 nm. A calibration curve was previously prepared for the relationship between the concentration of benzotriazole and the absorbance, and the concentration of benzotriazole in the filtrate was calculated from this calibration curve and the absorbance value of the measurement sample solution. The amount (mass%) of the spherical silver powder was calculated based on this concentration, the volume of the filtrate, and the weighed value of the silver powder.

[0031] The type of surface treatment agent can be identified by qualitative analysis by gas chromatography of the surface treatment agent volatilized by heating the spherical silver powder.

[0032] <Particle size distribution> In this specification, the cumulative 10% particle diameter (D 10 ), cumulative 50% particle diameter (D 50 ), cumulative 90% particle diameter (D 90 ) was measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT-3300 EXII, manufactured by Microtrack Bell Co., Ltd.). For the measurement, 0.1 g of sample (silver powder) was added to 40 mL of isopropyl alcohol (IPA) and dispersed. An ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho, device name: US-150T; 19.5 kHz, tip diameter 18 mm) was used for dispersion. The dispersion time was 2 minutes. The dispersed sample was subjected to the above-mentioned device, and the particle size distribution was determined using the attached analysis software.

[0033] (spherical silver powder) The spherical silver powder of the present invention has a surface treatment agent, and in thermal expansion coefficient measurements, the maximum thermal expansion coefficient is 0.3% or less based on the value at 50°C, and the BET specific surface area is 0.1 m 2 / g or more 0.8m 2 / g or less, D 90is 2.0 μm or more and 4.0 μm or less. Hereinafter, "thermal expansion coefficient based on the value at 50° C. in thermal expansion coefficient measurement" may be simply referred to as "thermal expansion coefficient." As described above, the thermal expansion coefficient measurement may be performed by increasing the temperature from room temperature to 900° C. at a heating rate of 10° C. / min to measure the expansion coefficient in the axial direction of a cylindrical measurement sample. The spherical silver powder described above can impart excellent fine line printability to the conductive paste and can reduce the electrical resistance of the conductive film. This is presumably because, compared to flake powder, coarse particles that clog printing nozzles are less likely to form when the powder is made into a paste, and the specific surface area can be made smaller relative to the particle diameter, suppressing an increase in viscosity and suppressing swelling of the conductive coating film during firing.

[0034] Examples of the surface treatment agent include fatty acids, compounds having an azole structure, fatty acid salts, surfactants, organometallic chelating agents, and protective colloids. Here, from the viewpoint of being able to uniformly adhere to the surface of the silver powder and obtain high dispersibility, it is preferable that the surface treatment agent be one or more surface treatment agents selected from the group consisting of fatty acids, compounds having an azole structure, and fatty acids.

[0035] Examples of fatty acids include behenic acid, stearic acid, palmitic acid, myristic acid, lauric acid, ricinoleic acid, oleic acid, linoleic acid, linolenic acid, etc. These may be used alone or in combination of two or more. Among these, stearic acid and oleic acid are preferred. Examples of the fatty acid salt include salts of the fatty acids listed above, such as sodium salts and potassium salts.

[0036] Examples of compounds having an azole structure include benzotriazole, sodium salt of benzotriazole, potassium salt of benzotriazole, etc. These may be used alone or in combination of two or more. Among these, benzotriazole and sodium benzotriazole are preferred.

[0037] The content of the surface treatment agent in the spherical silver powder is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and is preferably 1.00% by mass or less, more preferably 0.60% by mass or less, and even more preferably 0.40% by mass or less. When the content of the surface treatment agent in the spherical silver powder is 0.01% by mass or more, the dispersibility of the silver powder can be improved. On the other hand, if the content of the surface treatment agent in the spherical silver powder is 1.00% by mass or less, the dispersibility of the silver powder is maintained while not impeding sintering, thereby improving the electrical conductivity.

[0038] The maximum value of the thermal expansion coefficient of the spherical silver powder is 0.30% or less, preferably 0.25% or less, and more preferably 0.20% or less. If the maximum thermal expansion coefficient of the spherical silver powder is 0.30% or less, the powder will not blister during firing, the resulting cured film will not develop short circuits, and the electrical resistance will be kept low. On the other hand, the minimum value of the thermal expansion coefficient of the spherical silver powder may be 0% (no expansion) or may be 0.01% or more.

[0039] The BET specific surface area of ​​spherical silver powder is 0.10m 2 / g or more, and 0.25m 2 / g or more, and 0.30m 2 / g or more is more preferable, and 0.80m 2 / g or less, and 0.65m 2 / g or less, and 0.60m 2 It is more preferable that the molecular weight is not more than 1 / g. The BET specific surface area of ​​spherical silver powder is 0.10m 2 If it is less than 1 / g, the particle size becomes too large, making it unsuitable for fine line printing. On the other hand, the BET specific surface area of ​​spherical silver powder is 0.80m 2 If it is greater than 1 / g, the particle size becomes too small and the viscosity of the paste becomes too high, making it unsuitable for fine line printing.

[0040] Spherical silver powder D 90 The value of is 2.0 μm or more, preferably 2.1 μm or more, and is 4.0 μm or less, preferably 3.7 μm or less. D 90 If the value is greater than 4.0 μm, the particles tend to clog the printing plate, making printing difficult, and is therefore unsuitable.

[0041] Spherical silver powder D 50 The value of is preferably 1.0 μm or more, more preferably 1.3 μm or more, and is preferably 2.5 μm or less, more preferably 2.2 μm or less.

[0042] Spherical silver powder D 10 The value of is preferably 0.5 μm or more, more preferably 0.7 μm or more, and is preferably 1.2 μm or less. Spherical silver powder D 90 , D 50 , D 10 If the value exceeds the upper limit, the particle size is too large and the particle is not suitable for fine line printing. If the value is below the lower limit, the viscosity of the paste becomes too high and the paste is not suitable for fine line printing.

[0043] (Method of manufacturing spherical silver powder) The method for producing spherical silver powder of the present invention (hereinafter sometimes simply referred to as the "production method") is a method for reducing and precipitating silver particles by adding a reducing agent to an aqueous reaction system containing silver ions and a chelating agent made of a polymer. The production method of the present invention further comprises the steps of: before adding the reducing agent to the aqueous reaction system, reducing the ratio of carbon dioxide (CO) to the total molar concentration of silver (Ag) in the aqueous reaction system; 3 ) total molar concentration ratio (hereafter referred to as "CO 3 / Ag). The carbon dioxide concentration is adjusted to 0.004 or more and 0.051 or less, and a surface treatment agent is added to the aqueous reaction system after the silver particles have precipitated.

[0044] The above-mentioned manufacturing method can provide spherical silver powder that can impart excellent fine line printability to conductive paste. The reason is that CO 3 It is presumed that this is because by setting the ratio of CO to Ag at a certain level or higher, the rapid reduction of silver ions by the reducing agent, in other words, the reducing action of the reducing agent is mitigated, and the formation of irregularly shaped particles such as confetti-like particles is effectively suppressed. 3 It is presumed that this is because by keeping / Ag at a specified ratio or less, the particle size of the resulting silver particles is effectively prevented from becoming too small, and the viscosity of the conductive paste when used in a conductive paste is effectively prevented from becoming too high. In this specification, confetti-like particles refer to particles having numerous protrusions radially from the center of the particle.

[0045] The aqueous reaction system contains silver ions and a chelating agent made of a polymer (hereinafter, may be simply referred to as a "chelating agent.") The aqueous reaction system can be obtained, for example, by adding the chelating agent to an aqueous solution containing silver ions.

[0046] Here, the aqueous solution containing silver ions is not particularly limited, but an aqueous silver nitrate solution or the like can be used. In one embodiment, it is preferable to obtain a silver ammine complex by adding ammonia water or an ammonium salt to an aqueous solution containing silver ions, since this allows effective adjustment of the shape and particle size distribution of the obtained spherical silver powder. Note that it is preferable to add ammonia water or an ammonium salt in an amount of at least one mole of ammonia per mole of silver.

[0047] Specific examples of preferred chelating agents according to the present invention include amino compounds and imine compounds. Among them, polyethyleneimine (PEI) is preferred. In particular, the imine compound PEI has a structure in which a primary amine (-NH 2 ) and secondary amine (=NH), which gives the preferred results in the present invention.

[0048] The chelating agent according to the present invention preferably has a weight-average molecular weight of less than 600, and more preferably 145 or more and 600 or less. This is because a chelating agent having a weight-average molecular weight of 145 or more has the effect of producing highly dispersible silver particles. On the other hand, a polymeric amine having a weight-average molecular weight of 600 or less is believed to ensure the water solubility of the polymeric amine, and therefore the polymeric amine is unlikely to remain on the surface or inside of the produced silver particles. The weight average molecular weight of the chelating agent can be measured by a GPC-MALS method.

[0049] In the aqueous reaction system, the ratio of the chelating agent to the total mass of silver is preferably 0.001% by mass or more, more preferably 0.040% by mass or more, and is preferably 1.000% by mass or less.

[0050] The reducing agent to be added to the aqueous reaction system (after the carbon dioxide concentration adjustment step described later) is not particularly limited, but is preferably a reducing agent that does not contain carbon dioxide. Specific reducing agents that can be used include, for example, hydrazine, formalin, sodium borohydride, glucose, hypophosphorous acid, etc. Among these, hydrazine is particularly preferred from the viewpoints of stable reactivity and rapid reduction of silver ions.

[0051] The carbonation concentration adjustment step and the surface treatment agent addition step included in the production method of the present invention will be described below, but the production method of the present invention is not limited to a method including only these steps. For example, the production method of the present invention may optionally include steps other than the carbonation concentration adjustment step and the surface treatment agent addition step (hereinafter, these steps may be referred to as "other steps"). Examples of other steps include a separation step in which the reduced and precipitated silver particles are separated from the aqueous reaction system and dried.

[0052] <Carbonation concentration adjustment process> In the carbon dioxide concentration adjustment step, the ratio of the total molar concentration of carbon dioxide to the total molar concentration of silver in the aqueous reaction system is adjusted to 0.004 or more and 0.051 or less before adding a reducing agent to the aqueous reaction system. CO in aqueous reaction systems 3 / Ag is 0.004 or more and 0.051 or less, and preferably 0.031 or less.

[0053] Where CO 3 The adjustment of / Ag is not particularly limited, and can be performed, for example, by a method of adding a predetermined amount of carbonated water and / or carbonate to the aqueous reaction system, a method of blowing carbon dioxide gas into the aqueous reaction system (so-called bubbling), etc. From the viewpoint of operability, the method of adding a predetermined amount of carbonate to the aqueous reaction system is preferred.

[0054] CO 3 When a carbonate is used to adjust / Ag, the carbonate may be used in the form of an aqueous solution. The concentration of the aqueous solution of the carbonate is, for example, 1% by mass or more and 30% by mass or less. The carbonate is not particularly limited, and for example, sodium carbonate, potassium carbonate, etc. can be used.

[0055] <Surface treatment agent addition process> In the surface treatment agent addition step, after the silver particles are precipitated, a surface treatment agent is added to the aqueous reaction system, thereby obtaining surface-treated silver particles. The aqueous reaction system containing silver particles is usually a suspension (so-called slurry) or a dispersion in which the silver particles are dispersed.

[0056] Examples of the surface treatment agent include fatty acids, compounds having an azole structure, fatty acid salts, surfactants, organometallic chelating agents, and protective colloids. Here, from the viewpoint of being easily and uniformly attached to the silver powder surface, the surface treatment agent is preferably one or more surface treatment agents selected from the group consisting of fatty acids, compounds having an azole structure, and fatty acid salts.

[0057] Examples of fatty acids include behenic acid, stearic acid, palmitic acid, myristic acid, lauric acid, ricinoleic acid, oleic acid, linoleic acid, linolenic acid, etc. These may be used alone or in combination of two or more. Among these, stearic acid and oleic acid are preferred. Examples of the fatty acid salt include salts of the fatty acids listed above, such as sodium salts and potassium salts.

[0058] Examples of compounds having an azole structure include benzotriazole, sodium salt of benzotriazole, potassium salt of benzotriazole, etc. These may be used alone or in combination of two or more. Among these, benzotriazole and sodium benzotriazole are preferred.

[0059] The amount of the surface treatment agent added in the surface treatment agent addition step is usually 0.01% by mass or more and 1.00% by mass or less based on the mass of silver contained in the aqueous reaction system.

[0060] <Separation process> In an optional separation step, the reduced and precipitated silver particles are separated from the aqueous reaction system and dried. In addition, the separation step may optionally include a washing and recovery step of recovering and washing the separated silver particles and the like.

[0061] In the washing and recovery step, for example, an aggregate of the separated silver particles, etc. is formed into a cake-like form, and the cake of the aggregate of the silver particles, etc. is washed. Washing in the washing and recovery step may be performed using, for example, pure water. Dehydration in the washing and recovery step may be performed by, for example, decantation or a filter press. The end point of washing may be determined using the electrical conductivity of the washing water. Specifically, the end of washing may be determined when the electrical conductivity of the washing water becomes a predetermined value or less. The silver particles, etc. after washing may be subjected to a drying step in an aggregated state such as a cake-like form.

[0062] In the drying step, aggregates of silver particles and the like that contain moisture and are in an agglomerated state are dried. The drying step may be performed by vacuum drying or using an airflow type dryer. In the drying step, a high-pressure air flow may be blown onto the aggregates of silver particles and the like, or the cake or the spherical silver powder in the drying process may be put into a stirrer having a stirring rotor and stirred to apply a dispersing force to the cake or the spherical silver powder in the drying process, thereby promoting dispersion or drying.

[0063] In the drying step, the temperature of the spherical silver powder is usually 100° C. or less. If the temperature of the spherical silver powder is 100° C. or less, the silver particles in the spherical silver powder can be effectively prevented from sintering with each other.

[0064] Since the spherical silver powder after drying may be in the form of lumps, a dry crushing treatment or classification operation may be carried out simultaneously with or after the drying step in order to improve the handleability of the spherical silver powder, etc. Here, improving the handleability of the spherical silver powder means, for example, ensuring a degree of fluidity that does not interfere with the supply operation into an apparatus, or moderately loosening the spherical silver powder so that the processing in the apparatus proceeds efficiently.

[0065] The method of the dry crushing treatment is not particularly limited and can be appropriately selected depending on the purpose. However, it is preferable to use a crusher that rotates a stirring blade to crush the silver powder and fluidize the spherical silver powder. For example, a sample mill, a blender, a coffee mill, etc. can be used. EXAMPLES

[0066] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples in any way. The confirmation of the spherical silver powder (particle shape), thermomechanical analysis of the spherical silver powder (calculation of the maximum thermal expansion coefficient), measurement of the BET specific surface area, quantification of the surface treatment agent, and measurement of the particle size distribution were performed using the methods described above.

[0067] <Evaluation of fine line printability> First, the silver powder and aluminum powder (SEM average diameter 2.0 μm) obtained in the examples and comparative examples and the glass powder (containing PbO as the main component and B 2 O 3 , SiO 2 and other oxides), ethyl cellulose, texanol, butyl carbitol acetate, tributyl citrate, 1-octanol, oleic acid, triacetin, methylphenylpolysiloxane, hydrogenated castor oil, and fatty acid amide were mixed to obtain the composition shown in Table 1 to obtain a mixture. Next, the obtained mixture was premixed under conditions of a planetary centrifugal mixer (revolution 1000 rpm) and then kneaded with a three-roll mill (manufactured by EXAKT) to obtain a conductive paste. Using the conductive paste obtained above, a straight line shape was printed by screen printing. The straight line had a design line width of 12 μm and a straight line length of 150 mm. A Microtec printer was used for printing, and printing was performed at a squeegee speed of 350 mm / s. A silicon substrate (for solar cell use, textured and SiNx film formed) with a thickness of about 170 μm was used for printing. After printing, the substrate was dried for 5 minutes in a dryer set at 200 degrees, and then baked in a solar cell baking furnace (NGK) under conditions where the peak temperature of the wafer's upper surface was 750 degrees Celsius to produce a sample. The obtained sample was observed with a digital microscope (Keyence, VHX-5000) to check for the presence or absence of breaks, and the fine line printability was evaluated according to the following criteria. A: No disconnection was confirmed. B: A break was confirmed. C: Printing was not possible because the paste viscosity was too high.

[0068] Example 1 87,410 g of an aqueous silver nitrate solution containing 1,260 g (11.7 mol) of Ag was prepared, and 2,560 g of ammonia water with a concentration of 28% by mass was added thereto to prepare an aqueous solution containing silver ions. The liquid temperature was set to 35°C. To the aqueous solution containing silver ions, 63 g of a 10% by mass aqueous sodium carbonate solution was added, and the ratio of the total molar concentration of carbon dioxide to the total molar concentration of silver in the aqueous reaction system (CO 3The ratio of Ag / Ag was adjusted to 0.005. 3 To the aqueous reaction system after the adjustment of / Ag, 13 g of an aqueous solution containing polyethyleneimine (PEI) with a weight average molecular weight of 600 at a ratio of 5 mass% as a chelating agent (0.052 mass% relative to Ag mass) was added, and an aqueous reaction system containing silver ions and a chelating agent was prepared. Then, 2684 g of a 6.2 mass% aqueous hydrazine solution was added to the aqueous reaction system as a reducing agent and thoroughly stirred to obtain a slurry containing silver powder. Furthermore, 65 g of a neoethanol solution of oleic acid (surface treatment agent) with a concentration of 3.5 mass% was added to the obtained slurry, thoroughly stirred, and then aged. The aged slurry was filtered, and the filtered product was washed with water. Then, the filtered product after washing was dried, and 150 g of silver powder was charged using a sample mill (manufactured by Kyoritsu Riko Co., Ltd., SK-M10) and crushed twice for 90 seconds, to obtain the silver powder according to Example 1. Using the obtained silver powder, the spherical silver powder (particle shape) was confirmed, the thermomechanical analysis of the spherical silver powder (calculation of the maximum thermal expansion coefficient), the BET specific surface area was measured, the content of the surface treatment agent was measured, the particle size distribution was measured, and the fine line printability was evaluated. The results are shown in Table 3. In addition, graphs of the thermomechanical analysis of the silver powder are shown in Figures 1 and 2, and a SEM image of the silver powder at 10,000 times magnification is shown in Figure 23.

[0069] Example 2 96,690 g of an aqueous silver nitrate solution containing 1,620 g (15.0 mol) of Ag was prepared, and 3,280 g of ammonia water with a concentration of 28 mass % was added thereto to prepare an aqueous solution containing silver ions. The liquid temperature was set to 35°C. To the aqueous solution containing silver ions, 65 g of a 10% by mass aqueous sodium carbonate solution was added, and the ratio of the total molar concentration of carbon dioxide to the total molar concentration of silver in the aqueous reaction system (CO 3 The ratio of Ag / Ag was adjusted to 0.004. 3To the aqueous reaction system after the adjustment of / Ag, 16 g of an aqueous solution containing polyethyleneimine (PEI) with a weight average molecular weight of 600 as a chelating agent at a ratio of 5 mass% (0.049 mass% relative to Ag mass) was added to prepare an aqueous reaction system containing silver ions and a chelating agent. Then, 3441 g of a hydrazine aqueous solution with a concentration of 6.2 mass% was added as a reducing agent to the aqueous reaction system and thoroughly stirred to obtain a slurry containing silver powder. Furthermore, 138.8 g of a Solmix solution of benzotriazole (surface treatment agent) with a concentration of 4.0 mass% (133.3 g of Solmix (Solmix AP-7, manufactured by Japan Alcohol Sales Co., Ltd.) was added to the obtained slurry, thoroughly stirred, and then aged. The aged slurry was filtered, and the filtered residue was washed with water. The residue after washing was dried, and 150 g of silver powder was added to a sample mill (SK-M10, manufactured by Kyoritsu Riko Co., Ltd.) and crushed twice for 90 seconds to obtain the silver powder according to Example 2. Using the obtained silver powder, the spherical silver powder (particle shape) was confirmed, the thermomechanical analysis of the spherical silver powder (calculation of the maximum thermal expansion coefficient), the BET specific surface area was measured, the content of the surface treatment agent was measured, the particle size distribution was measured, and the fine line printability was evaluated. The results are shown in Table 3. In addition, graphs of the thermomechanical analysis of the silver powder are shown in Figures 3 and 4, and a SEM image of the silver powder at 10,000 times magnification is shown in Figure 24.

[0070] Example 3 96,190 g of an aqueous silver nitrate solution containing 1,620 g (15.0 mol) of Ag was prepared, and 3,280 g of ammonia water with a concentration of 28 mass % was added thereto to prepare an aqueous solution containing silver ions. The liquid temperature was set to 35°C. To the aqueous solution containing silver ions, 324 g of a 5% aqueous sodium carbonate solution was added, and the ratio of the total molar concentration of carbon dioxide to the total molar concentration of silver in the aqueous reaction system (CO 3 The ratio of Ag / Ag was adjusted to 0.010. 3To the aqueous reaction system after the adjustment of Ag / Ag, 202 g of an aqueous solution containing 0.4 mass% polyethyleneimine (PEI) with a weight average molecular weight of 600 as a chelating agent (0.050 mass% relative to Ag mass) was added, and an aqueous reaction system containing silver ions and a chelating agent was prepared. Then, 3512 g of a hydrazine aqueous solution with a concentration of 6.2 mass% as a reducing agent was added to the aqueous reaction system and thoroughly stirred to obtain a slurry containing silver powder. Furthermore, 340 g of a stearic acid (surface treatment agent) emulsion with a concentration of 0.86 mass% was added to the obtained slurry, thoroughly stirred, and then aged. The aged slurry was filtered, and the filter cake was washed with water. Then, the filter cake after washing was dried, and 150 g of silver powder was charged using a sample mill (SK-M10 manufactured by Kyoritsu Riko Co., Ltd.) and crushed twice for 90 seconds, to obtain the silver powder according to Example 3. Using the obtained silver powder, the spherical silver powder (particle shape) was confirmed, the thermomechanical analysis of the spherical silver powder (calculation of the maximum thermal expansion coefficient), the BET specific surface area was measured, the content of the surface treatment agent was measured, the particle size distribution was measured, and the fine line printability was evaluated. The results are shown in Table 3. In addition, graphs of the thermomechanical analysis of the silver powder are shown in Figures 5 and 6, and a SEM image of the silver powder at 10,000 times magnification is shown in Figure 25.

[0071] Example 4 The amount of sodium carbonate solution with a concentration of 10% by mass was changed from 65 g to 275 g. 3 A silver powder according to Example 4 was obtained in the same manner as in Example 2, except that / Ag was adjusted to 0.017 and the amount of the aqueous solution of 3.7 mass % benzotriazole sodium (surface treatment agent) was changed to 147 g. Using the obtained silver powder, the spherical silver powder (particle shape) was confirmed, the thermomechanical analysis of the spherical silver powder (calculation of the maximum thermal expansion coefficient), the BET specific surface area was measured, the content of the surface treatment agent was measured, the particle size distribution was measured, and the fine line printability was evaluated. The results are shown in Table 3. In addition, graphs of the thermomechanical analysis of the silver powder are shown in Figures 7 and 8, and a SEM image of the silver powder at 10,000 times magnification is shown in Figure 26.

[0072] Example 5 The amount of sodium carbonate solution with a concentration of 10% by mass was changed from 63 g to 189 g. 3A silver powder according to Example 5 was obtained in the same manner as in Example 1, except that / Ag was adjusted to 0.015. Using the obtained silver powder, the spherical silver powder (particle shape) was confirmed, the thermomechanical analysis of the spherical silver powder (calculation of the maximum thermal expansion coefficient), the BET specific surface area was measured, the content of the surface treatment agent was measured, the particle size distribution was measured, and the fine line printability was evaluated. The results are shown in Table 3. In addition, graphs of the thermomechanical analysis of the silver powder are shown in Figures 9 and 10, and a SEM image of the silver powder at 10,000 times magnification is shown in Figure 27.

[0073] Example 6 The amount of sodium carbonate solution with a concentration of 5% by mass was changed from 324 g to 971 g. 3 The silver powder of Example 6 was obtained in the same manner as in Example 3, except that / Ag was adjusted to 0.031 and 340 g of stearic acid (surface treatment agent) emulsion with a concentration of 0.86 mass% was changed to 327 g of a stearic acid emulsion aqueous solution with a concentration of 1.3 mass%. Using the obtained silver powder, the spherical silver powder (particle shape) was confirmed, the thermomechanical analysis of the spherical silver powder (calculation of the maximum thermal expansion coefficient), the BET specific surface area was measured, the content of the surface treatment agent was measured, the particle size distribution was measured, and the fine line printability was evaluated. The results are shown in Table 3. In addition, graphs of the thermomechanical analysis of the silver powder are shown in Figures 11 and 12, and a SEM image of the silver powder at 10,000 times magnification is shown in Figure 28.

[0074] Example 7 Add 421 g of 15% sodium carbonate aqueous solution and CO 3 The silver powder of Example 7 was obtained in the same manner as in Example 1, except that / Ag was adjusted to 0.051 and the amount of 3.5 mass % oleic acid (surface treatment agent) neoethanol solution was changed from 65 g to 126 g. Using the obtained silver powder, the spherical silver powder (particle shape) was confirmed, the thermomechanical analysis of the spherical silver powder (calculation of the maximum thermal expansion coefficient), the BET specific surface area was measured, the content of the surface treatment agent was measured, the particle size distribution was measured, and the fine line printability was evaluated. The results are shown in Table 3. In addition, graphs of the thermomechanical analysis of the silver powder are shown in Figures 13 and 14, and a SEM image of the silver powder at 10,000 times magnification is shown in Figure 29.

[0075] Comparative Example 1 3887 g of an aqueous silver nitrate solution containing 43.16 g (0.40 mol) of Ag was prepared, and 97.1 g of ammonia water with a concentration of 28 mass % was added thereto to prepare an aqueous solution containing silver ions. The liquid temperature was set to 34.5°C. To the aqueous solution containing silver ions, 0.043 g (0.100% by mass relative to the Ag mass) of polyethyleneimine (PEI) having a weight average molecular weight of 300 was added as a chelating agent to prepare an aqueous reaction system containing silver ions and a chelating agent. Next, 7.5 g of an aqueous hydrazine solution was added as a reducing agent to the aqueous reaction system and thoroughly stirred to obtain a slurry containing silver powder. To the obtained slurry, 0.12% by mass of stearic acid relative to the silver mass was added, thoroughly stirred, and then aged. The aged slurry was filtered, and the residue was washed with water. Then, the residue after washing was crushed and dried to obtain the silver powder according to Comparative Example 1. Using the obtained silver powder, the spherical silver powder (particle shape) was confirmed, the thermomechanical analysis of the spherical silver powder (calculation of the maximum thermal expansion coefficient), the BET specific surface area was measured, the content of the surface treatment agent was measured, the particle size distribution was measured, and the fine line printability was evaluated. The results are shown in Table 3. Graphs of the thermomechanical analysis of the silver powder are shown in Figures 15 and 16.

[0076] Comparative Example 2 The silver powder of Comparative Example 2 was obtained in the same manner as Comparative Example 1, except that the chelating agent, polyethyleneimine (PEI) having a weight-average molecular weight of 300, was changed to polyethyleneimine (PEI) having a weight-average molecular weight of 600, and the surface treatment agent, stearic acid, was changed to benzotriazole. Using the obtained silver powder, the spherical silver powder (particle shape) was confirmed, the thermomechanical analysis of the spherical silver powder (calculation of the maximum thermal expansion coefficient), the BET specific surface area was measured, the content of the surface treatment agent was measured, the particle size distribution was measured, and the fine line printability was evaluated. The results are shown in Table 3. Graphs of the thermomechanical analysis of the silver powder are shown in Figures 17 and 18.

[0077] Comparative Example 3 3637 g of an aqueous silver nitrate solution containing 43.16 g (0.40 mol) of Ag was prepared, and 87.6 g of an aqueous ammonia solution with a concentration of 28 mass % was added thereto to prepare an aqueous solution containing silver ions. The liquid temperature was set to 35°C. 80g of sodium hydroxide solution with a concentration of 20% by mass was added to the aqueous solution containing silver ions. Next, 0.86g (0.100% by mass relative to Ag mass) of an aqueous solution containing 0.043g of polyethyleneimine (PEI) with a weight average molecular weight of 600 as a chelating agent was added to the aqueous reaction system after the addition of the sodium hydroxide aqueous solution, to prepare an aqueous reaction system containing silver ions and a chelating agent. Then, 243g of hydrazine aqueous solution with a concentration of 2.5% by mass was added as a reducing agent to the aqueous reaction system and thoroughly stirred to obtain a slurry containing silver powder. 3.34g of stearic acid (surface treatment agent) emulsion with a concentration of 1.5% was added to the obtained slurry, thoroughly stirred, and then aged. The aged slurry was filtered, and the filter cake was washed with water. Then, the filter cake after washing was dried, and 150g of silver powder was charged using a sample mill (SK-M10 manufactured by Kyoritsu Riko Co., Ltd.) and crushed twice for 90 seconds to obtain silver powder according to Comparative Example 3. Using the obtained silver powder, confirmation of the spherical silver powder (particle shape), thermomechanical analysis of the spherical silver powder (calculation of the maximum thermal expansion coefficient), measurement of the BET specific surface area, measurement of the content of the surface treatment agent, measurement of the particle size distribution, and evaluation of the fine line printability were performed. The results are shown in Table 3. Graphs of the thermomechanical analysis of the silver powder are shown in Figures 19 and 20, and a 10,000x SEM image of the silver powder is shown in Figure 30. Note that confetti-like particles were confirmed near the center of the SEM image in Figure 30.

[0078] Comparative Example 4 3572 g of an aqueous silver nitrate solution containing 56.11 g (0.52 mol) of Ag was prepared, and 113.9 g of an aqueous ammonia solution with a concentration of 28 mass % was added thereto to prepare an aqueous solution containing silver ions. The liquid temperature was set to 35°C. To the aqueous solution containing silver ions, 78.55 g of a 5% by mass aqueous sodium carbonate solution was added, and the ratio of the total molar concentration of carbon dioxide to the total molar concentration of silver in the aqueous reaction system (CO 3 The ratio of Ag / Ag was adjusted to 0.071. 30.561g (0.050% by mass relative to Ag mass) of an aqueous solution containing 0.028g of polyethyleneimine (PEI) having a weight average molecular weight of 600 as a chelating agent was added to the aqueous reaction system after the sodium hydroxide aqueous solution was added after the adjustment of Ag / Ag, to prepare an aqueous reaction system containing silver ions and a chelating agent. Then, 300g of a hydrazine aqueous solution having a concentration of 2.5% by mass was added as a reducing agent to the aqueous reaction system and thoroughly stirred to obtain a slurry containing silver powder. Furthermore, 1.964g of a neoethanol solution of oleic acid (surface treatment agent) having a concentration of 10% by mass was added to the obtained slurry, thoroughly stirred, and then aged. The aged slurry was filtered, and the filtered product was washed with water. Then, the filtered product after washing was dried, and 150g of silver powder was charged using a sample mill (SK-M10 manufactured by Kyoritsu Riko Co., Ltd.) and crushed twice for 90 seconds to obtain the silver powder according to Comparative Example 4. Using the obtained silver powder, the spherical silver powder (particle shape) was confirmed, the thermomechanical analysis of the spherical silver powder (calculation of the maximum thermal expansion coefficient), the BET specific surface area was measured, the content of the surface treatment agent was measured, the particle size distribution was measured, and the fine line printability was evaluated. The results are shown in Table 3. Graphs of the thermomechanical analysis of the silver powder are shown in Figures 21 and 22.

[0079] [Table 1]

[0080] [Table 2]

[0081] [Table 3]

[0082] As is clear from the results in Tables 2 and 3, the spherical silver powders of Examples 1 to 7 can impart excellent fine line printability to the conductive paste. 3 It can be seen that when the ratio of / Ag exceeds 0.051, the particle size becomes too small to print, as in Comparative Example 4. Furthermore, as is clear from the results in Tables 2 and 3, the spherical silver powders obtained by the manufacturing methods of Examples 1 to 7 can impart excellent fine line printability to the conductive paste. [Industrial Applicability]

[0083] According to the present invention, it is possible to provide a spherical silver powder that can impart excellent fine line printability to a conductive paste. The present invention also provides a method for producing spherical silver powder that can impart excellent fine line printability to a conductive paste.

Claims

1. A surface treatment agent is present, In the thermal expansion coefficient measurement, the maximum value of the thermal expansion coefficient based on the value at 50°C is 0.3% or less, BET specific surface area is 0.1m ２ / g or more 0.8m ２ / g or less, D ９０ The spherical silver powder has a value of 2.0 μm or more and 4.0 μm or less.

2. D ５０ 2. The spherical silver powder according to claim 1, wherein the value of is 1.0 μm or more and 2.5 μm or less.

3. D １０ 2. The spherical silver powder according to claim 1, wherein the value of is 0.5 μm or more and 1.2 μm or less.

4. 4. The spherical silver powder according to claim 1, wherein the surface treatment agent is one or more surface treatment agents selected from the group consisting of fatty acids, compounds having an azole structure, and fatty acid salts.

5. A method for producing spherical silver powder, comprising adding a reducing agent to an aqueous reaction system containing silver ions and a chelating agent made of a polymer to reduce and precipitate silver particles, comprising: a carbonic acid concentration adjusting step of adjusting a ratio of a total molar concentration of carbonic acid to a total molar concentration of silver in the aqueous reaction system to 0.004 or more and 0.051 or less before adding the reducing agent to the aqueous reaction system; a surface treatment agent addition step of adding a surface treatment agent to the aqueous reaction system after the silver particles have precipitated; A method for producing spherical silver powder, comprising:

6. 6. The method for producing spherical silver powder according to claim 5, wherein the surface treatment agent is one or more surface treatment agents selected from the group consisting of fatty acids, compounds having an azole structure, and fatty acid salts.

7. The method for producing spherical silver powder according to claim 5, wherein the chelating agent is polyethyleneimine having a weight average molecular weight of 600 or less.

8. The method for producing spherical silver powder according to any one of claims 5 to 7, wherein the reducing agent is hydrazine.

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