Spherical silver powder, method for producing spherical silver powder, and conductive paste

Abstract

To provide a spherical silver powder that can impart an excellent low-temperature sinterability to conductive pastes.SOLUTION: The present invention is a spherical silver powder that has, in XRD analysis, a cubic Ag peak and a hexagonal Ag peak, and in which the ratio of the intensity of the hexagonal Ag peak to the intensity of the cubic Ag peak is at least 0.5%.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] A method of forming a conductive film such as an electrode or electrical wiring 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 it to dry, harden, or bake it has been widely used. However, with the recent increase in the performance of electronic devices, conductive films formed using conductive pastes are required to have lower resistance, and this requirement is becoming stricter every year.

[0003] In response to the above requirements, for example, Patent Document 1 discloses a silver powder having an apparent density of 8.2 g / cm3, which has a lower volume resistivity than conventional silver powders when used as a conductive paste. 3 More than 9.2g / cm 3 and a silver powder has been proposed in which the ratio of the line length of the outer periphery of the cross section of a silver particle to the line length circumscribing the periphery of the cross section of the particle is 1.1 or more and 1.4 or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2023 / 054405 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, in addition to lowering the resistance value of the conductive film, it has become desirable to sinter the conductive paste at a low temperature (for example, 200° C. or lower) in order to reduce damage to the substrate and the like.

[0006] Therefore, an object of the present invention is to provide a spherical silver powder that can impart excellent low-temperature sintering properties to a conductive paste. Another object of the present invention is to provide a method for producing spherical silver powder that can impart excellent low-temperature sintering properties to a conductive paste. Another object of the present invention is to provide a conductive paste that is excellent in low-temperature sintering properties. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have completed the present invention described below.

[0008] That is, the gist and configuration of the present invention for solving the above-mentioned problems is as follows.

[0009] [1] In XRD analysis, it has a cubic Ag peak and a hexagonal Ag peak, A spherical silver powder in which the ratio of the intensity of the hexagonal Ag peak to the intensity of the cubic Ag peak is 0.5% or more.

[0010] [2] The spherical silver powder according to [1], having a crystallite diameter of 28 nm or less.

[0011] [3] BET specific surface area is 0.1m 2 / g or more 1.8m 2 / g or less.

[0012] [4] Cumulative 10% particle size (D) based on volume using laser diffraction method 10 , Cumulative 50% particle size D 50 , and cumulative 90% particle diameter D 90 However, the following formula (1): 0.5≦(D 90 -D 10 ) / D 50 ≦2.5 (1) The spherical silver powder according to any one of [1] to [3], which satisfies the relationship:

[0013] [5] Cumulative 50% particle diameter D by volume using laser diffraction method 50 The spherical silver powder according to any one of [1] to [4], wherein the particle size is 0.5 μm or more and 6 μm or less.

[0014] [6] Cumulative 100% particle size (D) based on volume using laser diffraction method MAX The spherical silver powder according to any one of [1] to [5], wherein the diameter of the spherical silver powder is 15 μm or less.

[0015] [7] A method for producing the spherical silver powder according to any one of [1] to [6], a silver complex forming step of adding ammonia and a first chelating agent comprising ethylenediaminetetraacetic acid to the silver-containing aqueous solution to obtain an aqueous silver complex; a reduction step of adding a reducing agent to the aqueous silver complex solution to reduce and precipitate silver particles, A method for producing spherical silver powder, wherein the amount of the first chelating agent added is 3 parts by mass or more and 40 parts by mass or less per 100 parts by mass of silver in the silver-containing aqueous solution.

[0016] [8] The method for producing spherical silver powder according to [7], further comprising adding a second chelating agent made of a polymer to the silver-containing aqueous solution or the silver complex solution.

[0017] [9] The method for producing spherical silver powder according to [8], wherein the amount of the second chelating agent added is 0.1 parts by mass or more per 100 parts by mass of silver in the silver-containing aqueous solution.

[0018]

[10] The method for producing spherical silver powder according to any one of [7] to [9], wherein a surface treatment agent is added to a slurry containing the precipitated silver particles after the reduction step.

[0019]

[11] A conductive paste containing the spherical silver powder according to any one of [1] to [6] as a conductive filler. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a spherical silver powder that can impart excellent low-temperature sintering properties to a conductive paste. Furthermore, the present invention can provide a method for producing spherical silver powder that can impart excellent low-temperature sintering properties to a conductive paste. Furthermore, according to the present invention, a conductive paste having excellent low-temperature sintering properties can be provided. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 2 is an enlarged graph of an XRD analysis of the spherical silver powder according to Example 1. [Figure 2] FIG. 2 is an enlarged graph of an XRD analysis of the spherical silver powder according to Example 2. [Figure 3] FIG. 10 is an enlarged graph of an XRD analysis of the spherical silver powder according to Example 3. [Figure 4] FIG. 10 is an enlarged graph of an XRD analysis of the spherical silver powder according to Example 4. [Figure 5] FIG. 10 is an enlarged graph of an XRD analysis of the spherical silver powder according to Example 5. [Figure 6] FIG. 2 is an enlarged graph of an XRD analysis of the spherical silver powder according to Comparative Example 1. [Figure 7] FIG. 1 is an enlarged graph of an XRD analysis of the spherical silver powder according to Comparative Example 2. [Figure 8] FIG. 10 is an enlarged graph of an XRD analysis of the spherical silver powder according to Comparative Example 3. [Figure 9] FIG. 1 is a graph showing the XRD analysis results of the spherical silver powders according to Examples 1 to 5 and Comparative Examples 1 to 3. [Figure 10] 1 is a 50,000x SEM image of spherical silver powder after crushing in the separation step of Example 1. [Figure 11] 1 is a 50,000x SEM image of spherical silver powder after crushing in the separation step of Comparative Example 1. [Figure 12] 1 is a 50,000x SEM image of spherical silver powder after crushing in the separation step of Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0022] The spherical silver powder of the present invention is suitable as a conductive filler for a conductive paste. The conductive paste using the spherical silver powder of the present invention can be used for forming a conductive pattern on a substrate, forming or joining an electrode. The conductive paste using the spherical silver powder of the present invention can form a conductive film such as a conductive pattern or an electrode by printing on a substrate by, for example, screen printing, offset printing, photolithography, etc. Further, components etc. can be joined through the paste printed on the substrate.

[0023] (Terms and measurement methods) First, prior to the description of the embodiments, terms and measurement methods etc. in this specification will be described.

[0024] <Confirmation of spherical silver powder (particle shape)> In this specification, the spherical silver powder means silver powder in which the average of the shape factors of 100 or more particles observed by image analysis based on a scanning electron microscope (SEM) image is in the range of 1.0 or more and less than 1.7. Note that, in this specification, the shape factor is the ratio of the area of a virtual circle with the average maximum length as the diameter to the average particle area of the silver particles obtained by tracing the outer shape of the particles among 100 or more particles observed by the above image analysis, and is the value obtained by dividing the area of the virtual circle by the average particle area. The calculation formula of the shape factor is π(average maximum length / 2) 2 / average particle area. <..

[0025] <X-ray diffraction method (XRD) analysis> In this specification, X-ray diffraction (XRD) analysis was performed using an X-ray diffractometer (SmartLab manufactured by Rigaku Corporation). The measurement conditions are as follows. Target material: Cu Target voltage: 45 kV Target current: 200 mA Measurement method: θ-2θ Scan speed: 1 deg / min Scan step: 0.02 deg Scan range:​

[0026] <Cubic Ag peak> In this specification, the "cubic Ag peak" is an X-ray diffraction peak derived from the 3C(111) plane, and usually, a peak where the peak top (the point where the X-ray diffraction intensity profile reaches its maximum) appears around 2θ = 38.14°. Also, in this specification, the "intensity of the cubic Ag peak" means the numerical value (count number) of the intensity at the peak top of the cubic Ag peak. In this specification, the numerical value of the intensity at 38.14° is used.

[0027] <Hexagonal Ag peak> In this specification, the "hexagonal Ag peak" is an X-ray diffraction peak derived from the 4H(0004) plane, and usually, a peak where the peak top appears around 2θ = 36.00°. In this specification, considering the influence of the base of the above-mentioned cubic Ag peak, when the intensity at 35.60° and the intensity at 36.40° are connected by a straight line and this straight line is used as the baseline, if there is a point where the difference between the baseline and the X-ray diffraction intensity profile reaches its maximum, it is also considered a hexagonal Ag peak. Also, in this specification, the "intensity of the hexagonal Ag peak" means the difference between the numerical value (count number) of the intensity of the hexagonal Ag peak and the count number of the baseline at the 2θ position of the peak top of the hexagonal Ag peak when the intensity at 35.60° and the intensity at 36.40° are connected by a straight line and this straight line is used as the baseline. Here, specifically explaining the intensity of the hexagonal Ag peak using the enlarged graph (Figure 1) of the XRD analysis of the spherical silver powder according to Example 1 described later, the dotted line in Figure 1 is the straight line (baseline) connecting the intensity at 35.60° and the intensity at 36.40°, and the intensity of the hexagonal Ag peak is within the range of the arrow in Figure 1 where the value of 2θ is 36.00°. In this specification, for the calculation of the intensity of the hexagonal Ag peak in Examples 1 to 4, the 2θ position is calculated as 36.00°. Also, for the calculation of the intensity of the hexagonal Ag peak in Example 5, the 2θ position is calculated as 35.92°, and for the calculation of the intensity of the hexagonal Ag peak in Comparative Example 3, the 2θ position is calculated as 36.04°.

[0028] <BET specific surface area> The "BET specific surface area" was measured using a specific surface area analyzer (Macsorb HM-model 1210, manufactured by MOUNTECH) employing the BET method. 3 g of spherical silver powder was placed in a measurement cell, and a carrier gas mixture of 70 vol% He gas and 30 vol% nitrogen gas was passed through the measurement cell at 25 mL / min to degas the material at 60°C for 10 minutes, followed by measurement using the BET single-point method.

[0029] <Particle size distribution> In this specification, the cumulative 10% particle diameter D of the spherical silver powder based on volume 10 , Cumulative 50% particle size D 50 , Cumulative 90% particle size D 90 , and cumulative 100% particle diameter D MAX was measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT-3300 EXII, manufactured by Microtrac Bell Corporation). For the measurement, 0.1 g of sample (spherical 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 placed in the above-mentioned device, and the particle size distribution was calculated using the attached analysis software. During the measurement, an SDC device was used as the circulator of the laser diffraction / scattering particle size distribution analyzer, and the "flow rate (%)" setting of the circulator was set to 60. Furthermore, the post-measurement calculation mode of the MT-3300 EXII was HRA mode. In the following, the cumulative 10% particle diameter D on a volume basis determined by laser diffraction method is calculated. 10 , Cumulative 50% particle size D 50 , Cumulative 90% particle size D 90 , and cumulative 100% particle diameter D MAX , respectively, simply "D 10 "," "D 50 "," "D 90 " and "D MAX "It is sometimes referred to as ".

[0030] <Ig-loss> In this specification, the term "loss on ignition (Ig-loss) value" refers to the amount of change in mass when heated from room temperature to 800°C, and specifically serves as an index of the amount of components other than silver contained in the spherical silver powder, and indicates the amount of components remaining in the spherical silver powder, such as processing agents and additives used in the manufacturing process of the spherical silver powder. In this specification, the "loss on ignition (Ig-loss) value" was calculated by precisely weighing a spherical silver powder sample (weighing value: w1), placing it in a porcelain crucible, heating it to 800°C, and holding it at 800°C for 30 minutes, a time sufficient to reach constant weight, then cooling and reweighing it (weighing value: w2), and calculating the "loss on ignition (Ig-loss) value (mass%) = (w1 - w2) / w1 × 100."

[0031] <Crystallite diameter Dx> The crystallite diameter Dx was determined using an X-ray diffractometer (SmartLab manufactured by Rigaku Corporation) from the half-width of the (111) peak appearing around 2θ = 38.14° according to the Scherrer formula (D hkl =Kλ / βcosθ) where, in Scherrer's formula, D hkl denotes the crystallite diameter (size of the crystallite in the direction perpendicular to hkl) (unit: nm), λ denotes the wavelength of the measured X-rays (0.15405 nm when a Cu target is used), β denotes the broadening (rad) of the diffraction line due to the size of the crystallite (expressed using the half-width), θ denotes the Bragg angle (rad) of the diffraction angle (the angle when the angle of incidence and the angle of reflection are equal, and the angle at the peak top is used), and K denotes the Scherrer constant (K = 0.94).

[0032] (spherical silver powder) In XRD analysis, the spherical silver powder of the present invention has a cubic Ag peak at 2θ of approximately 38.14° and a hexagonal Ag peak at 2θ of approximately 36.00°, and the ratio of the intensity of the hexagonal Ag peak to the intensity of the cubic Ag peak (hexagonal Ag peak intensity / cubic Ag peak intensity × 100[%]) is 0.5% or more. The spherical silver powder described above can impart excellent low-temperature sinterability to a conductive paste. The reason for this is presumably due to the possibility of a transition from a hexagonal crystal structure to a cubic crystal structure occurring during sintering at low temperatures, but the reason for this is not entirely clear. However, the results of the following examples and comparative examples clearly show that spherical silver powders that satisfy the above requirements can impart excellent low-temperature sinterability to a conductive paste. The spherical silver powder of the present invention can be obtained by the method for producing the spherical silver powder of the present invention described below.

[0033] The ratio of the intensity of the hexagonal Ag peak to the intensity of the cubic Ag peak is 0.5% or more, preferably 0.8% or more, and more preferably 1% or more. The ratio of the hexagonal Ag peak intensity to the cubic Ag peak intensity may be, for example, 30% or less, 15% or less, or 9% or less.

[0034] The BET specific surface area of ​​spherical silver powder is 0.1m 2 / g or more, and 0.2m 2 / g or more is more preferable, and 1.8m 2 / g or less, and 1.5m 2 It is more preferable that the saturation coefficient is 1 / g or less. The BET specific surface area of ​​the spherical silver powder is 0.1m 2 If it is / g or more, the low-temperature sintering property can be improved. On the other hand, the BET specific surface area of ​​spherical silver powder is 1.8m 2 If the spherical silver powder has a viscosity of 1 / 2 g or less, when the spherical silver powder is used in a conductive paste or the like, the viscosity of the resulting conductive paste or the like can be effectively reduced.

[0035] Spherical silver powder D 10 is preferably 0.2 μm or more, more preferably 0.5 μm or more, and is preferably 3 μm or less, more preferably 2 μm or less.

[0036] Spherical silver powder D 50is preferably 0.5 μm or more, more preferably 0.8 μm or more, and is preferably 6 μm or less, more preferably 3 μm or less.

[0037] Spherical silver powder D 90 is preferably 1 μm or more, more preferably 2 μm or more, and is preferably 8 μm or less, more preferably 5 μm or less.

[0038] Spherical silver powder D MAX is preferably 2 μm or more, more preferably 3 μm or more, and is preferably 15 μm or less, more preferably 10 μm or less.

[0039] Spherical silver powder D 10、 D 50、 D 90、 D MAX When the spherical silver powder is used in a conductive paste or the like, the viscosity of the resulting conductive paste or the like can be effectively reduced if each of the above is equal to or greater than the above lower limit. On the other hand, spherical silver powder D 10 D 50、 D 90、 D MAX When each of these is equal to or less than the above upper limit, the particle size of the spherical silver powder becomes favorable, and low-temperature sintering properties can be improved.

[0040] For spherical silver powder, the cumulative 10% particle diameter D on a volume basis measured by laser diffraction method 10 , Cumulative 50% particle size D 50 , and cumulative 90% particle diameter D 90 is expressed by the following formula (1): 0.5≦(D 90 -D 10 ) / D 50 ≦2.5 (1) It is preferable that the following relationship is satisfied. (D 90 -D 10 ) / D 50 If the particle diameter is within the above range, when the spherical silver powder is used in a conductive paste or the like, the stability of the resulting conductive paste can be improved. Here, the spherical silver powder (D 90 -D 10 ) / D 50 is more preferably 2.0 or less, and even more preferably 1.5 or less. (D 90 -D 10 ) / D 50 If the value is 2.5 or less, the uniformity of the silver particles is high, and when a conductive paste is prepared using the spherical silver powder, the conductive paste can be easily prepared.

[0041] The ignition loss (Ig-loss) value of the spherical silver powder is preferably 0.05% by mass or more, more preferably 0.2% by mass or more, and is preferably 10% by mass or less, more preferably 5% by mass or less. If the ignition loss value of the spherical silver powder is 0.05% by mass or more, when the spherical silver powder is used in a conductive paste or the like, aggregation of the spherical silver powder in the conductive paste can be effectively suppressed. On the other hand, if the ignition loss value of the spherical silver powder is 10 mass% or less, the impurities are low, so when a conductive film is obtained using a conductive paste containing the spherical silver powder, an increase in the resistance value of the obtained conductive film can be effectively suppressed.

[0042] The crystallite diameter Dx of the spherical silver powder is preferably 28 nm or less, and more preferably 20 nm or less. If the crystallite diameter Dx of the spherical silver powder is 28 nm or less, the low-temperature sintering property can be improved. The crystallite diameter Dx of the spherical silver powder may be, for example, 1 nm or more, or 10 nm or more.

[0043] In one embodiment, the spherical silver powder of the present invention preferably contains a surface treatment agent. The surface treatment agent is not particularly limited as long as the spherical silver powder satisfies the above-mentioned predetermined requirements, but examples thereof include fatty acids, compounds having an azole structure, fatty acid salts, surfactants, organometallic chelating agents, protective colloids, etc. Here, 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, from the viewpoint of being able to adhere uniformly to the surface of the spherical silver powder and achieving high dispersibility.

[0044] 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. Examples of fatty acid salts include salts of the fatty acids listed above, such as sodium salts and potassium salts.

[0045] Examples of compounds having an azole structure include benzotriazole, sodium salts of benzotriazole, potassium salts of benzotriazole, etc. These may be used alone or in combination of two or more.

[0046] (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") comprises a silver complex formation step in which ammonia and a first chelating agent consisting of ethylenediaminetetraacetic acid are added to a silver-containing aqueous solution to obtain a silver complex aqueous solution, and a reduction step in which a reducing agent is added to the silver complex aqueous solution to reduce and precipitate silver particles, wherein the amount of the first chelating agent added is 3 parts by mass or more and 40 parts by mass or less per 100 parts by mass of silver (Ag) in the silver-containing aqueous solution. The above-described production method makes it possible to obtain the spherical silver powder of the present invention, which can impart excellent low-temperature sintering properties to a conductive paste. The production method of the present invention may optionally include steps other than the silver complex formation step and the reduction step (hereinafter, these steps may be referred to as "other steps"). Examples of other steps include a pH adjuster addition step of adding a pH adjuster to the aqueous silver complex solution before reduction, a surface treatment agent addition step of adding a surface treatment agent to a mixed solution containing precipitated silver particles, and a separation step of separating and drying the silver particles or the surface treatment agent-coated silver particles (silver particles coated with a surface treatment agent) obtained in the surface treatment agent addition step.

[0047] <Silver complex formation process> In the silver complex formation step, ammonia and a first chelating agent consisting of ethylenediaminetetraacetic acid are added to a silver-containing aqueous solution to obtain a silver complex aqueous solution. The order of adding ammonia and the first chelating agent to the silver-containing aqueous solution may be ammonia first, or the first chelating agent may be added first, or ammonia and the first chelating agent may be added simultaneously to the silver-containing aqueous solution. Both ammonia and the first chelating agent can form a complex with silver, but it is preferable to stir and mix them until they are complexed.

[0048] In the silver complex formation step, a second chelating agent consisting of a polymer may be further added to the silver-containing aqueous solution or the silver complex aqueous solution. The timing of adding the second chelating agent is not particularly limited, and the second chelating agent may be added before the addition of ammonia, before the addition of the first chelating agent, after the addition of ammonia, or after the addition of the first chelating agent, or may be added simultaneously with the ammonia and the first chelating agent.

[0049] The silver-containing aqueous solution is not particularly limited, but may be a silver nitrate aqueous solution, a silver oxide-containing aqueous solution, etc. Among these, a silver nitrate aqueous solution is preferred.

[0050] Examples of the ammonia to be added to the silver-containing aqueous solution include aqueous ammonia and ammonium salts.

[0051] The amount of ammonia added is not particularly limited as long as a silver ammine complex is obtained as a complex constituting the silver complex aqueous solution, but it is preferably 38 parts by mass or more, more preferably 47 parts by mass or more, and preferably 78 parts by mass or less, more preferably 62 parts by mass or less, per 100 parts by mass of silver in the silver-containing aqueous solution.

[0052] The first chelating agent added to the silver-containing aqueous solution is ethylenediaminetetraacetic acid. Ethylenediaminetetraacetic acid may be in the form of an alkali metal salt. That is, some or all of the four carboxylic acids in ethylenediaminetetraacetic acid may be in the form of an alkali metal salt. From the viewpoint of solubility in the silver-containing aqueous solution, it is preferable to use ethylenediaminetetraacetic acid in the form of an alkali metal salt. The ethylenediaminetetraacetic acid in the form of an alkali metal salt may be in the form of a hydrate.

[0053] Examples of ethylenediaminetetraacetic acid in the form of an alkali metal salt include disodium ethylenediaminetetraacetic acid, trisodium ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetic acid, dipotassium ethylenediaminetetraacetic acid, tripotassium ethylenediaminetetraacetic acid, and tetrapotassium ethylenediaminetetraacetic acid. Among these, disodium ethylenediaminetetraacetic acid is preferred. The ethylenediaminetetraacetic acid may be used alone or in combination of two or more.

[0054] The amount of the first chelating agent added is 3 parts by mass or more, preferably 3.5 parts by mass or more, and 40 parts by mass or less, preferably 36 parts by mass or less, per 100 parts by mass of silver in the silver-containing aqueous solution. If the amount of the first chelating agent added is less than 3 parts by mass, the resulting silver powder will have a very low proportion of hexagonal Ag, which may not achieve the effects of the present invention. However, if the amount is within the above range, it is easy to effectively obtain silver powder in which the ratio of the hexagonal Ag peak intensity to the cubic Ag peak intensity falls within the range of the present invention. Although the reason for this is unclear, it is thought that the coexistence of the first chelating agent and ammonia, which can form a complex with silver, affects the anisotropy of silver deposition. In the present invention, the amount of the first chelating agent added is preferably 5 parts by mass or more, more preferably 6 parts by mass or more, and is preferably 70 parts by mass or less, more preferably 65 parts by mass or less, per 100 parts by mass of ammonia in the silver-containing aqueous solution.

[0055] The second chelating agent added to the silver-containing aqueous solution is composed of a polymer. The use of a second chelating agent composed of a polymer can effectively suppress aggregation of silver particles obtained in the reduction step.

[0056] Specific examples of preferred second chelating agents include amino compounds and imine compounds. Among these, polyethyleneimine (PEI) is preferred. In particular, the imine compound PEI has a network structure containing both a primary amine (-NH) and a secondary amine (=NH) in the molecule, and provides preferred results in the present invention.

[0057] The second chelating agent preferably has a weight-average molecular weight of 600 or less, and more preferably 145 or more, and 600 or less. This is because a weight-average molecular weight of 145 or more of the second chelating agent has the effect of producing highly dispersible silver particles. On the other hand, a weight-average molecular weight of 600 or less of the polymeric amine ensures the water solubility of the polymeric amine, and it is believed that the polymeric amine hardly remains on the surface or inside of the produced silver particles. The weight average molecular weight of the second chelating agent can be measured by the GPC-MALS method.

[0058] The addition amount of the second chelating agent is preferably 0.1 part by mass or more, and more preferably 0.3 part by mass or more, based on 100 parts by mass of silver in the silver-containing aqueous solution. If the addition amount of the second chelating agent is 0.1 part by mass or more based on 100 parts by mass of silver in the silver-containing aqueous solution, it is presumed that silver particles grow uniformly and spherically, and aggregation can be effectively suppressed. Although the upper limit of the addition amount is not particularly limited, when added excessively, the growth of silver is significantly inhibited, so it is, for example, 10 parts by mass or less, and preferably 3 parts by mass or less.

[0059] The temperature of the silver complex aqueous solution is preferably 5°C or higher, more preferably 20°C or higher, and preferably 50°C or lower, more preferably 40°C or lower. If the temperature of the silver complex aqueous solution is 5°C or higher, the reduction reaction can proceed effectively. On the other hand, if the temperature of the silver complex aqueous solution is 50°C or lower, it can effectively suppress the excessive reaction rate of the reduction reaction described later, and effectively suppress the variation in the particle diameter of silver particles. Also, if the temperature of the silver complex aqueous solution is within the above range, it can effectively suppress the increase in energy cost.

[0060] <pH Adjusting Agent Addition Step> As the pH adjusting agent addition step, a pH adjusting agent may be added to the silver complex aqueous solution before adding the reducing agent. Adding a pH adjusting agent to the silver complex aqueous solution before reduction can easily adjust the particle diameter of the obtained silver powder. As the pH adjusting agent, general acids or bases may be used, for example, nitric acid, sodium hydroxide, etc. The amount of the pH adjusting agent to be added can be appropriately adjusted according to the amount of the silver nitrate aqueous solution used and the particle diameter of the silver powder to be obtained. As the adjustment method, for example, a method of adjusting the addition amount by conducting a level test of the particle diameter of silver powder according to the addition amount of the pH adjusting agent can be mentioned.

[0061] <Reduction Step> In the reduction step, a reducing agent is added to the stirred aqueous silver complex solution to reduce and precipitate silver particles, thereby obtaining a slurry in which silver particles are dispersed, which is a mixture containing silver particles.

[0062] The reducing agent to be added to the aqueous silver complex solution is not particularly limited, but examples thereof include hydrazine, formalin, sodium borohydride, glucose, hypophosphorous acid, etc. Among these, hydrazine is preferred.

[0063] To increase the silver reaction yield, the amount of reducing agent added is preferably at least one equivalent relative to the silver of the reducing agent being reacted. The term "equivalent" here refers to the molar equivalent, which represents the quantitative relationship in the chemical reaction between silver and the reducing agent. For example, in the case of hydrazine reduction, 1 equivalent of hydrazine per mole of silver is 0.25 moles. When using a reducing agent with weak reducing power, such as formalin or glucose, an amount of at least 2 equivalents relative to the silver is preferred, with 10 to 20 equivalents being more preferred.

[0064] <Surface treatment agent addition process> When the surface treatment agent addition step is performed, the surface treatment agent is added to the mixture containing the silver particles precipitated in the reduction step, thereby obtaining silver particles coated with the surface treatment agent. The mixed liquid containing silver particles coated with a surface treatment agent is usually a slurry in which silver particles coated with a surface treatment agent are dispersed.

[0065] Examples of surface treatment agents that can be added to the mixture containing precipitated silver particles include fatty acids, compounds having an azole structure, fatty acid salts, surfactants, organometallic chelating agents, and protective colloids. Here, 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, from the viewpoint of being easily and uniformly attached to the silver powder surface.

[0066] 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. Examples of fatty acid salts include salts of the fatty acids listed above, such as sodium salts and potassium salts.

[0067] Examples of compounds having an azole structure include benzotriazole, sodium salts of benzotriazole, potassium salts of benzotriazole, etc. These may be used alone or in combination of two or more.

[0068] The amount of the surface treatment agent added to the mixed solution containing silver particles is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, per 100 parts by mass of silver in the silver-containing aqueous solution, and is preferably 3 parts by mass or less, more preferably 1 part by mass or less. When the amount of the surface treatment agent added is 0.05 parts by mass or more per 100 parts by mass of silver in the silver-containing aqueous solution, the dispersibility of the silver particles can be improved. On the other hand, if the amount of the surface treatment agent added is 3 parts by mass or less per 100 parts by mass of silver in the silver-containing aqueous solution, the risk of a decrease in low-temperature sinterability can be effectively suppressed.

[0069] The surface treatment agent is preferably added to the mixed solution containing silver particles after a specific time has elapsed since the addition of the reducing agent to the aqueous silver complex solution. In the present invention, the addition of the surface treatment agent stops the particle growth of the silver particles, so the timing of addition can be determined as long as it allows the silver in the mixed solution to be sufficiently precipitated as silver particles.

[0070] <Separation process> In the separation step, the silver particles are separated from the mixed solution containing the silver particles or the silver particles coated with the surface treatment agent. After the separation step, a washing and recovery step can be carried out, or the drying step can be carried out without going through the washing and recovery step.

[0071] In the washing and recovery step, for example, a cake-like aggregate of separated silver particles or silver particles coated with a surface treatment agent 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. After washing, the silver particles or silver particles coated with a surface treatment agent may be subjected to a drying step in an aggregated state such as a cake.

[0072] In the drying step, aggregates of silver particles containing moisture and in an agglomerated state or silver particles coated with a surface treatment agent are dried. The drying step may be performed by vacuum drying or using an airflow dryer. In the drying step, a high-pressure air flow may be blown onto the aggregates of silver particles or silver particles coated with a surface treatment agent, or the cake or spherical silver powder in the drying process may be placed in a mixer having a stirring rotor and stirred, thereby applying a dispersing force to the cake or spherical silver powder in the drying process and promoting dispersion and drying.

[0073] In the drying step, the temperature of the spherical silver powder is not particularly limited as long as the conditions are such that the aggregates of silver particles are sufficiently dried, but it is preferably 40°C or higher, more preferably 70°C or higher, and is preferably 120°C or lower, and more preferably 100°C or lower. If the temperature of the spherical silver powder is 40°C or higher, the drying efficiency can be improved. On the other hand, if the temperature of the spherical silver powder is 120°C or less, the transition from the hexagonal crystal structure to the cubic crystal structure in the silver particles or silver particles coated with a surface treatment agent can be effectively suppressed.

[0074] Since the spherical silver powder after drying may be in the form of lumps, it is preferable to carry out a dry crushing treatment or classification operation 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 fluidity to the extent that it does not interfere with the supply operation into the apparatus, or loosening the spherical silver powder to an appropriate extent so that processing in the apparatus proceeds efficiently.

[0075] The method for 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 particles and fluidize the spherical silver powder, and for example, a sample mill, a blender, a coffee mill, or the like can be used.

[0076] (Conductive paste) The conductive paste of the present invention contains the spherical silver powder of the present invention as a conductive filler. In addition to the spherical silver powder, the conductive paste preferably contains a solvent and a binder, and may further contain other components as necessary. The solvent, binder, etc. may be selected appropriately depending on the application mode. [Example]

[0077] 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 XRD analysis, cubic Ag peak intensity, hexagonal Ag peak intensity, BET specific surface area, particle size distribution, ignition loss (Ig-loss), and crystallite diameter Dx were measured or calculated by the methods described above.

[0078] Example 1 <Silver complex formation process> First, 3436 g of a silver nitrate solution containing 50.84 g of silver was stirred at 174 rpm, and 103.2 g of 28% by weight aqueous ammonia (Junsei Chemical Co., Ltd.) was added. Then, with continued stirring, 30 seconds after the addition of the aqueous ammonia, 4.17 g of a 43% by weight aqueous EDTA solution (Chelest OD-50, manufactured by Chelest) was added as a first chelating agent (3.53 parts by weight of EDTA per 100 parts by weight of silver), yielding an aqueous silver complex. 60 seconds after the addition of the aqueous ammonia, 10.17 g of a 5% by weight aqueous PEI solution (Nippon Shokubai Co., Ltd., weight-average molecular weight 600) was added as a second chelating agent (1.00 parts by weight of PEI per 100 parts by weight of silver), and the liquid temperature was adjusted to 35°C.

[0079] <Reduction process> 180 seconds after adding the ammonia water, 302.8 g of a 2.43 mass% aqueous solution of hydrazine (manufactured by Mitsubishi Gas Chemical Company, Inc.) (amount of hydrazine added per 100 mass parts of silver: 14.47 mass parts) was added all at once to the obtained aqueous solution of silver complex, thereby obtaining a slurry containing silver particles.

[0080] <Surface treatment agent addition process> Next, the resulting slurry containing silver particles was stirred for 5 seconds after the addition of hydrazine, and then stirring was stopped. 130 seconds after the addition of hydrazine, stirring was resumed. At the same time, 5.12 g of a 1.55% stearic acid emulsion (amount of stearic acid added per 100 parts by mass of silver: 0.16 parts by mass) was added as a surface treatment agent, and stirring was continued for an additional 75 seconds to obtain a slurry containing silver particles coated with a surface treatment agent. A baffled reaction chamber and a two-stage turbine blade were used for the reaction.

[0081] <Separation process> Thereafter, stirring was stopped to allow the silver particles coated with the surface treatment agent to settle, and the liquid in which the silver particles coated with the surface treatment agent had precipitated was filtered and washed with water until the electrical conductivity of the liquid after passing through the water was 0.5 mS / m or less, and then vacuum dried at 73° C. The dried silver powder obtained was put into a sample mill (SK-M10, manufactured by Kyoritsu Riko Co., Ltd.) and crushed twice for 30 seconds using a dial scale of 100, to obtain the spherical silver powder of Example 1.

[0082] The spherical silver powder thus obtained was used to measure or calculate the following: XRD analysis, cubic Ag peak intensity, hexagonal Ag peak intensity, ratio of hexagonal Ag peak intensity to cubic Ag peak intensity, BET specific surface area, particle size distribution, loss on ignition (Ig-loss), and crystallite diameter Dx. The results are shown in Table 2. An enlarged graph of the XRD analysis of the spherical silver powder according to Example 1 in the 2θ range of 35.00° to 37.00° is shown in Figure 1, a graph of the XRD analysis in the 2θ range of 35.00 to 40.00° is shown in Figure 9, and an SEM image of the spherical silver powder after crushing in the separation step at 50,000x magnification is shown in Figure 10. Note that the cubic Ag peak intensity, hexagonal Ag peak intensity, and ratio of the hexagonal Ag peak intensity to the cubic Ag peak intensity of the spherical silver powder after vacuum drying in the separation step (before crushing) are shown in Table 2 as a reference example.

[0083] <Resistance measurement> A mixture was obtained by mixing 93.01 parts by weight of the spherical silver powder obtained above, 0.25 parts by weight of ethyl cellulose, 1.59 parts by weight of Texanol, 3.86 parts by weight of butyl carbitol acetate, 0.26 parts by weight of tributyl citrate, 0.25 parts by weight of oleic acid, 0.26 parts by weight of triacetin, and 0.51 parts by weight of methylphenylpolysiloxane (KF96-100). The mixture was then premixed using a planetary mixer (revolution 1000 rpm) and kneaded using a three-roll mill (manufactured by EXAKT) with a roll gap varying from 100 μm to 20 μm to obtain a conductive paste. The conductive paste obtained above was used to print a linear shape by screen printing. The linear shape had a designed line width of 500 μm and a linear length of 128 mm. A Microtec printer was used for printing, and the printing was performed at a squeegee speed of 80 mm / sec. A silicon substrate (for solar cell applications, texture formation, SiN) with a thickness of approximately 170 μm was used for printing. x Pre-formed film) was used. After printing, the conductive paste was dried for 10 minutes in a dryer set at 100°C to form a conductive film. The conductive film was measured for its resistance (unit: Ω) over time from room temperature to 300°C at a heating rate of 10°C / min using a high-temperature microscope (manufactured by Yonekura Seisakusho Co., Ltd.). The resistance values ​​at 100°C, 140°C, 160°C, 180°C, 190°C, 195°C, and 200°C are shown in Table 3. The lower the resistance value shown in Table 3, the better the conductive paste's low-temperature sintering properties.

[0084] Examples 2 to 4 Spherical silver powders according to Examples 2 to 4 were obtained in the same manner as in Example 1, except that the amounts of the first chelating agent and the second chelating agent added were as shown in Table 1. The spherical silver powder thus obtained was subjected to XRD analysis, and the BET specific surface area, particle size distribution, ignition loss (Ig-loss), and crystallite diameter Dx were measured or calculated. The results are shown in Table 2. The spherical silver powder was then subjected to resistance measurement, and the results are shown in Table 3. Further, enlarged graphs of XRD analysis of the spherical silver powders according to Examples 2 to 4 in the 2θ range of 35.00° to 37.00° are shown in FIGS. 2 to 4, and a graph of XRD analysis in the 2θ range of 35.00° to 40.00° is shown in FIG.

[0085] Example 5 The spherical silver powder of Example 5 was obtained in the same manner as Example 1, except that 50 g of silver was added to the dried silver powder obtained and crushed twice for 30 seconds using a coffee mill (manufactured by Melitta Japan Co., Ltd.). The spherical silver powder thus obtained was subjected to XRD analysis, and the BET specific surface area, particle size distribution, ignition loss (Ig-loss), and crystallite diameter Dx were measured or calculated. The results are shown in Table 2. The spherical silver powder was also used to measure the resistance, and the results are shown in Table 3. Furthermore, an enlarged graph of the XRD analysis of the spherical silver powder according to Example 5 in the 2θ range of 35.00° to 37.00° is shown in FIG. 5, and a graph of the XRD analysis in the 2θ range of 35.00° to 40.00° is shown in FIG.

[0086] (Comparative Example 1) <Silver complex formation process> First, 113.2 g of 28% by mass aqueous ammonia (manufactured by Junsei Chemical Co., Ltd.) was added to 3489 g of an aqueous silver nitrate solution containing 53.71 g of silver while stirring at 332 rpm to obtain an aqueous silver complex solution. Next, while continuing to stir, 4.98 g of a 20% by mass aqueous solution of sodium hydroxide as a pH adjuster was added to the obtained aqueous silver complex solution, and the liquid temperature was adjusted to 28°C.

[0087] <Reduction process> After 180 seconds from the addition of the ammonia water to the pH-adjusted solution, 251.3 g of a 26% by mass formaldehyde aqueous solution (formalin) (amount of formaldehyde added per 100 mass parts of silver: 121.11 mass parts) was added all at once to obtain a slurry containing silver particles.

[0088] <Surface treatment agent addition process> Next, 15 seconds after the addition of the reducing agent, 6.13 g of a 1.55% stearic acid emulsion (0.18 parts by mass of stearic acid per 100 parts by mass of silver) was added as a surface treatment agent to the resulting slurry containing silver particles, and the mixture was stirred for an additional 180 seconds to obtain a slurry containing silver particles coated with the surface treatment agent. Note that a baffled reaction chamber and a two-stage turbine blade were used for the reaction.

[0089] <Separation process> Thereafter, stirring was stopped to allow the silver particles coated with the surface treatment agent to settle, and the liquid in which the silver particles coated with the surface treatment agent had precipitated was filtered and washed with water until the electrical conductivity of the liquid after passing through the water was 0.5 mS / m or less, and then vacuum dried at 73° C. The dried silver powder obtained was placed in a sample mill (SK-M10, manufactured by Kyoritsu Riko Co., Ltd.) and crushed twice for 30 seconds using a dial scale of 100, to obtain spherical silver powder according to Comparative Example 1.

[0090] The spherical silver powder thus obtained was subjected to XRD analysis, and the BET specific surface area, particle size distribution, ignition loss (Ig-loss), and crystallite diameter Dx were measured or calculated. The results are shown in Table 2. The spherical silver powder thus obtained was used to measure the resistance value, and the results are shown in Table 3. Furthermore, an enlarged graph of the XRD analysis of the spherical silver powder according to Comparative Example 1 in the 2θ range of 35.00° to 37.00° is shown in FIG. 6, a graph of the XRD analysis in the 2θ range of 35.00° to 40.00° is shown in FIG. 9, and a 50,000x SEM image of the spherical silver powder after crushing in the separation step is shown in FIG. 11.

[0091] (Comparative Example 2) <Silver complex formation process> First, 103.2 g of 28% by mass aqueous ammonia (manufactured by Junsei Chemical Co., Ltd.) was added to 3448 g of an aqueous silver nitrate solution containing 50.84 g of silver while stirring at 174 rpm to obtain an aqueous silver complex solution. Next, while continuing to stir, 1.02 g of a 5% by mass aqueous solution of sodium carbonate was added to the resulting aqueous silver complex solution as a pH adjuster, and 60 seconds after the addition of the ammonia water, 0.508 g (amount of PEI added per 100 parts by mass of silver: 0.05 parts by mass) of a 5% by mass aqueous solution of PEI (manufactured by Nippon Shokubai Co., Ltd., weight-average molecular weight 600) was added, and the liquid temperature was adjusted to 35°C.

[0092] <Reduction process> 180 seconds after adding the ammonia water, 302.8 g of a 2.43 mass% aqueous solution of hydrazine (manufactured by Mitsubishi Gas Chemical Company, Inc.) (amount of hydrazine added per 100 mass parts of silver: 14.47 mass parts) was added all at once to the obtained aqueous solution of silver complex, thereby obtaining a slurry containing silver particles.

[0093] <Surface treatment agent addition process> Next, 15 seconds after the addition of the reducing agent, 5.12 g of a 1.55% stearic acid emulsion (0.16 parts by mass of stearic acid per 100 parts by mass of silver) was added as a surface treatment agent to the resulting slurry containing silver particles, and the mixture was stirred for an additional 180 seconds to obtain a slurry containing silver particles coated with the surface treatment agent. Note that a baffled reaction chamber and a two-stage turbine blade were used for the reaction.

[0094] <Separation process> Thereafter, stirring was stopped to allow the silver particles coated with the surface treatment agent to settle, and the liquid in which the silver particles coated with the surface treatment agent had precipitated was filtered and washed with water until the electrical conductivity of the liquid after passing through the water was 0.5 mS / m or less, and then vacuum dried at 73° C. The dried silver powder obtained was milled using a sample mill (SK-M10, manufactured by Kyoritsu Riko Co., Ltd.) with 50 g of silver added, and crushed twice for 30 seconds using a dial scale of 100, to obtain spherical silver powder according to Comparative Example 2.

[0095] The spherical silver powder thus obtained was subjected to XRD analysis, and the BET specific surface area, particle size distribution, ignition loss (Ig-loss), and crystallite diameter Dx were measured or calculated. The results are shown in Table 2. The spherical silver powder thus obtained was used to measure the resistance value, and the results are shown in Table 3. Furthermore, an enlarged graph of the XRD analysis of the spherical silver powder according to Comparative Example 2 in the 2θ range of 35.00° to 37.00° is shown in FIG. 7, a graph of the XRD analysis in the 2θ range of 35.00° to 40.00° is shown in FIG. 9, and a 50,000x SEM image of the spherical silver powder after crushing in the separation step is shown in FIG. 12.

[0096] (Comparative Example 3) A spherical silver powder according to Comparative Example 3 was obtained in the same manner as in Example 1, except that the amounts of the first chelating agent and the second chelating agent added were as shown in Table 1. The spherical silver powder thus obtained was subjected to XRD analysis, and the BET specific surface area, particle size distribution, ignition loss (Ig-loss), and crystallite diameter Dx were measured or calculated. The results are shown in Table 2. The spherical silver powder was then subjected to resistance measurement, and the results are shown in Table 3. Furthermore, an enlarged graph of XRD analysis of the spherical silver powder according to Comparative Example 3 in the 2θ range of 35.00° to 37.00° is shown in FIG. 8, and a graph of XRD analysis in the 2θ range of 35.00° to 40.00° is shown in FIG.

[0097] [Table 1]

[0098] [Table 2]

[0099] [Table 3]

[0100] As is clear from the results in Table 3, the spherical silver powders of Examples 1 to 5 can impart excellent low-temperature sintering properties to the conductive pastes. It is clear that the conductive pastes using spherical silver powders in which the ratio of the hexagonal Ag peak intensity to the cubic Ag peak intensity is less than 0.5%, as in Comparative Examples 1 to 3, have poor low-temperature sintering properties. Furthermore, as is clear from the results in Table 3, it is possible to impart excellent low-temperature sintering properties to conductive pastes using spherical silver powders obtained by the manufacturing methods of Examples 1 to 5. It is also clear that conductive pastes using spherical silver powders obtained without adding a predetermined amount of the first chelating agent, as in Comparative Examples 1 to 3, have poor low-temperature sintering properties. [Industrial Applicability]

[0101] According to the present invention, it is possible to provide a spherical silver powder that can impart excellent low-temperature sintering properties to a conductive paste. Furthermore, the present invention can provide a method for producing spherical silver powder that can impart excellent low-temperature sintering properties to a conductive paste. Furthermore, according to the present invention, a conductive paste having excellent low-temperature sintering properties can be provided.

Claims

1. In XRD analysis, it has a cubic Ag peak and a hexagonal Ag peak, A spherical silver powder in which the ratio of the intensity of the hexagonal Ag peak to the intensity of the cubic Ag peak is 0.5% or more.

2. 2. The spherical silver powder according to claim 1, wherein the crystallite diameter is 28 nm or less.

3. BET specific surface area is 0.1m ２ / g or more 1.8m ２ 2. The spherical silver powder according to claim 1, wherein the silver content is 0.1 / g or less.

4. Volume-based cumulative 10% particle diameter D measured by laser diffraction method １０ , cumulative 50% particle diameter D ５０ , and cumulative 90% particle diameter D ９０ is expressed by the following formula (1): 0.5≦(D ９０ -D １０ ) / D ５０ ≦2.5・・・(1) The spherical silver powder according to claim 1 , which satisfies the relationship:

5. Cumulative 50% particle diameter D on a volume basis measured by laser diffraction method ５０ The spherical silver powder according to claim 1, wherein the particle size is 0.5 μm or more and 6 μm or less.

6. Volume-based cumulative 100% particle diameter D measured by laser diffraction method ＭＡＸ The spherical silver powder according to claim 1, wherein the particle size is 15 μm or less.

7. A method for producing the spherical silver powder according to claim 1, comprising: a silver complex forming step of adding ammonia and a first chelating agent comprising ethylenediaminetetraacetic acid to the silver-containing aqueous solution to obtain an aqueous silver complex; a reduction step of adding a reducing agent to the aqueous silver complex solution to reduce and precipitate silver particles, A method for producing spherical silver powder, wherein the amount of the first chelating agent added is 3 parts by mass or more and 40 parts by mass or less per 100 parts by mass of silver in the silver-containing aqueous solution.

8. 8. The method for producing spherical silver powder according to claim 7, further comprising adding a second chelating agent made of a polymer to the silver-containing aqueous solution or the silver complex aqueous solution.

9. 9. The method for producing spherical silver powder according to claim 8, wherein the amount of the second chelating agent added is 0.1 parts by mass or more per 100 parts by mass of silver in the silver-containing aqueous solution.

10. 10. The method for producing spherical silver powder according to claim 7, wherein a surface treatment agent is added to a slurry containing the precipitated silver particles after the reduction step.

11. A conductive paste comprising the spherical silver powder according to any one of claims 1 to 6 as a conductive filler.

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