Spherical silver powder and method for producing spherical silver powder

Abstract

The present invention aims to provide a spherical silver powder capable of imparting excellent fine line printability to a conductive paste. The present invention is a spherical silver powder in which a surface treatment agent is present, the maximum value of the thermal expansion rate based on the value at 50°C in a thermal expansion rate measurement is 0.3% or less, the BET specific surface area is 0.1 m 2 / g or more and 0.8 m 2 / g or less, and the value of D 90 is 2.0 μm or more and 4.0 μm or less.

Description

Technical Field

[0001] This invention relates to spherical silver powder and a method for manufacturing spherical silver powder. Background Technology

[0002] The method of forming conductive films such as electrodes and / or electrical wiring by coating or printing a conductive paste containing conductive metal powder onto substrates such as thin films, substrates, and electronic components, and then heating and curing and / or firing them, has been widely used. However, with the increasing performance of electronic devices in recent years, there is a growing demand for lower resistance in conductive films formed using conductive pastes, and this demand is becoming more stringent year by year.

[0003] To address the above requirements, for example, in Patent Document 1, a silver powder with a specified surface treatment agent and a specified thermal expansion rate, BET value (specific surface area), and difference in weight loss on ignition was proposed, with the aim of suppressing the expansion of the conductive coating and reducing the resistance of the cured film (conductive film) during the firing of the sintered conductive paste.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 6174301 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] In recent years, the finer lines of conductive films have been continuously developed, and there is a desire for conductive pastes that can be printed with fine lines.

[0009] In previous silver powders, there is room for further improvement in imparting excellent fine-line printability to conductive pastes.

[0010] Therefore, the object of the present invention is to provide spherical silver powder that can impart excellent fine-line printability to conductive pastes.

[0011] In addition, the present invention aims to provide a method for manufacturing spherical silver powder that can impart excellent fine-line printability to conductive pastes.

[0012] Solution for solving the problem

[0013] In order to solve the above-mentioned problems, the inventors have repeatedly conducted in-depth research, and as a result, the inventors have completed the present invention described below.

[0014] That is, the main structure of the present invention for solving the above-mentioned problems is as follows.

[0015] [1] A spherical silver powder containing a surface treatment agent.

[0016] In the determination of thermal expansion coefficient, the maximum value of the thermal expansion coefficient, based on the value at 50℃, is less than 0.3%.

[0017] The specific surface area of ​​BET is 0.1 m². 2 / g or more and 0.8m 2 / g or less

[0018] D 90 The value is above 2.0 μm and below 4.0 μm.

[0019] [2] According to the spherical silver powder described in [1], wherein D 50 The value is above 1.0 μm and below 2.5 μm.

[0020] [3] According to the spherical silver powder described in [1] or [2], wherein D 10 The value is above 0.5μm and below 1.2μm.

[0021] [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.

[0022] [5] A method for manufacturing spherical silver powder, wherein a reducing agent is added to an aqueous reaction system containing silver ions and a chelating agent composed of a polymer to reduce and precipitate silver particles, the method comprising:

[0023] In the carbonic acid concentration adjustment step, before adding the reducing agent to the aqueous reaction system, the ratio of the total molar concentration of carbonic acid to the total molar concentration of silver in the aqueous reaction system is adjusted to be 0.004 or more and 0.051 or less; and

[0024] In the surface treatment agent addition step, after the silver particles precipitate, a surface treatment agent is added to the aqueous reaction system.

[0025] [6] According to the method for manufacturing spherical silver powder described in [5], 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.

[0026] [7] The method for manufacturing spherical silver powder according to [5] or [6], wherein the chelating agent is polyethyleneimine with a weight average molecular weight of less than 600.

[0027] [8] The method for manufacturing spherical silver powder according to any one of [5] to [7], wherein the reducing agent is hydrazine.

[0028] The effects of the invention

[0029] According to the present invention, spherical silver powder capable of imparting excellent fine-line printability to conductive pastes can be provided.

[0030] In addition, the present invention can provide a method for manufacturing spherical silver powder that can impart excellent fine-line printability to conductive pastes. Attached Figure Description

[0031] Figure 1 This is a graph representing the thermomechanical analysis results of the spherical silver powder obtained in Example 1.

[0032] Figure 2 It is Figure 1 A magnified portion of the curve graph.

[0033] Figure 3 This is a graph representing the thermomechanical analysis results of the spherical silver powder obtained in Example 2.

[0034] Figure 4 It is Figure 3 A magnified portion of the curve graph.

[0035] Figure 5 This is a graph representing the thermomechanical analysis results of the spherical silver powder obtained in Example 3.

[0036] Figure 6 It is Figure 5 A magnified portion of the curve graph.

[0037] Figure 7 This is a graph representing the thermomechanical analysis results of the spherical silver powder obtained in Example 4.

[0038] Figure 8 It is Figure 7 A magnified portion of the curve graph.

[0039] Figure 9 This is a graph representing the thermomechanical analysis results of the spherical silver powder obtained in Example 5.

[0040] Figure 10 It is Figure 9 A magnified portion of the curve graph.

[0041] Figure 11 This is a graph representing the thermomechanical analysis results of the spherical silver powder obtained in Example 6.

[0042] Figure 12 It is Figure 11 A magnified portion of the curve graph.

[0043] Figure 13 This is a graph representing the thermomechanical analysis results of the spherical silver powder obtained in Example 7.

[0044] Figure 14 It is Figure 13 A magnified portion of the curve graph.

[0045] Figure 15 This is a graph representing the thermomechanical analysis results of the spherical silver powder obtained in Comparative Example 1.

[0046] Figure 16 It is Figure 15 A magnified portion of the curve graph.

[0047] Figure 17 This is a graph representing the thermomechanical analysis results of the spherical silver powder obtained in Comparative Example 2.

[0048] Figure 18 It is Figure 17 A magnified portion of the curve graph.

[0049] Figure 19 This is a graph representing the thermomechanical analysis results of the spherical silver powder obtained in Comparative Example 3.

[0050] Figure 20 It is Figure 19 A magnified portion of the curve graph.

[0051] Figure 21 This is a graph representing the thermomechanical analysis results of the spherical silver powder obtained in Comparative Example 4.

[0052] Figure 22 It is Figure 21 A magnified portion of the curve graph.

[0053] Figure 23 This is a 10,000x SEM image of the spherical silver powder obtained in Example 1.

[0054] Figure 24 This is a 10,000x SEM image of the spherical silver powder obtained in Example 2.

[0055] Figure 25 This is a 10,000x SEM image of the spherical silver powder obtained in Example 3.

[0056] Figure 26 This is a 10,000x SEM image of the spherical silver powder obtained in Example 4.

[0057] Figure 27 This is a 10,000x SEM image of the spherical silver powder obtained in Example 5.

[0058] Figure 28This is a 10,000x SEM image of the spherical silver powder obtained in Example 6.

[0059] Figure 29 This is a 10,000x SEM image of the spherical silver powder obtained in Example 7.

[0060] Figure 30 This is a 10,000x SEM image of the spherical silver powder obtained in Comparative Example 3. Detailed Implementation

[0061] The spherical silver powder of the present invention is suitable for use as a conductive filler in conductive pastes. Conductive pastes using the spherical silver powder of the present invention can be used to form conductive patterns and / or electrodes on a substrate. Conductive pastes using the spherical silver powder of the present invention can be printed on a substrate, for example, by screen printing, offset printing, photolithography, etc., thereby forming conductive films such as conductive patterns and / or electrodes.

[0062] (Terminology and Measurement Methods)

[0063] First, before describing the implementation method, the terminology and measurement methods used in this specification will be explained.

[0064] <Confirmation of spherical silver powder (particle shape)>

[0065] In this specification, spherical silver powder refers to silver powder in which the average shape factor of 400 or more particles observed through image analysis based on scanning electron microscopy (SEM) images is in the range of 1.0 or higher and less than 1.7. There are no particular limitations on the scanning electron microscope; for example, JSM-6100 and / or JSM-IT300L manufactured by Nippon Egis Corporation can be used. It should be noted that in this invention, the silver powder of Examples 1 and 5 was observed using the JSM-IT300L, and the silver powder of Examples 2, 3, 4, 6, 7, and Comparative Example 3 was observed using the JSM-6100. It should be noted that the shape factor in this specification refers to the ratio of the area of ​​an imaginary circle with an average maximum length as its diameter for 400 or more particles observed through the above image analysis to the average particle area obtained by depicting the shape of the particles; it is the value obtained by dividing the area of ​​the imaginary circle by the average particle area. The shape factor is calculated using the formula π(average maximum length / 2). 2 It is expressed as average particle area.

[0066] <Determination of the thermal expansion coefficient of spherical silver powder>

[0067] The thermal expansion coefficient of spherical silver powder was determined as follows.

[0068] First, weigh 0.3 g of spherical silver powder. Then, put the spherical silver powder into a specified mold with a diameter of 5 mmφ, and compact it with a press under a load of 50 kg for 1 minute to make a cylindrical test sample. Place the test sample on the sample holder of the thermomechanical analysis (TMA) device (Thermo plus EVO 2 series TMA8311), apply a test load of 98 mN using the test probe, and heat the sample from room temperature to 900 °C at a heating rate of 10 °C / min. Perform thermomechanical analysis (TMA) on the test sample, and calculate the coefficient of thermal expansion at each temperature with the value at 50 °C as the reference using the following formula (1).

[0069] The thermal expansion coefficient (%) when the temperature rises from 50℃ to T℃ = (L T -L 50 ) / L 50 ×100…(1),

[0070] Here, L 50 It measures the axial length (mm) of a cylindrical specimen at a sample temperature of 50℃.

[0071] L T It is the axial length (mm) of a cylindrical specimen measured at a specimen temperature T℃.

[0072] <BET specific surface area>

[0073] In this specification, the "BET specific surface area" was determined using a Macsorb HM-model 1210 (manufactured by MOUNTECH) via the nitrogen adsorption-based BET one-point method. It should be noted that in the determination of the BET specific surface area, the sample weight was set to 3.0 g, an N2 / He (30 / 70) mixed gas was used, the gas flow rate was set to 25 mL / min, and the degassing conditions before measurement were set to 60 °C for 10 minutes.

[0074] <Quantitative determination of surface treatment agents>

[0075] In this specification, for example, when the surface treatment agent for the spherical silver powder is a fatty acid, the content of the fatty acid is determined according to the quantitative analysis method for fatty acids described in Japanese Patent No. 5622543.

[0076] Specifically, firstly, the spherical silver powder is dissolved in acid and then mixed with an organic solvent to extract all the surface treatment agent into the organic solvent phase. Then, a specified amount of the organic solvent phase is separated, evaporated and dried, and the carbon content of the remaining solids is determined using a carbon-sulfur analysis device. The carbon content is then calculated from this result.

[0077] For example, if the surface treatment agent is determined to be stearic acid, and the spherical silver powder does not contain any carbon source other than stearic acid, the method for determining stearic acid is as follows.

[0078] When determining the carbon content (intensity) of standard solutions with different stearic acid contents (mg) using a carbon-sulfur analysis device to obtain a standard curve, its slope is set as A (intensity / mg). Furthermore, regarding the mass X (mg) and concentration Y (%) of stearic acid in spherical silver powder, a specified amount b (mL) is taken from the substance obtained by extracting the treatment agent to the total organic solvent volume a (mL) through the above-mentioned treatment of spherical silver powder, the carbon content determined by the determination of its residual solids is set as C (intensity), and the amount of spherical silver powder dissolved in acid is set as M (g), the mass X and concentration Y of stearic acid are calculated by the following formulas (A) and (B), respectively.

[0079] X(mg) = (C / A × a / b) …(A)

[0080] Y(%)=X / (M×1000)×100…(B)

[0081] When oleic acid is used as a surface treatment agent, the carbon content is determined in the same manner as described above. For oleic acid, the standard curve of stearic acid is also used for calculation. The molecular weight of stearic acid is 284.48, and the carbon content is 216.19. The molecular weight of oleic acid is 282.46, and the carbon content is 216.19. Therefore, the oleic acid concentration Y' is calculated using the following formula (C).

[0082] Oleic acid concentration Y' (%) = Y × (216.19 / 284.48) × (282.46 / 216.19) … (C)

[0083] Furthermore, in this specification, for example, when the surface treatment agent for the spherical silver powder is benzotriazole, the content of benzotriazole is determined according to the quantitative analysis method for benzotriazole and benzotriazole salts described in Japanese Patent No. 5523153.

[0084] Specifically, firstly, the spherical silver powder is cleaned with hydrochloric acid aqueous solution, and the cleaning solution is quantitatively analyzed based on spectrophotometry to determine the amount of silver powder.

[0085] For example, weigh 0.2 g of spherical silver powder, and follow the steps below to wash with hydrochloric acid aqueous solution and perform quantitative analysis based on spectrophotometry to determine the content of benzotriazole. First, dilute concentrated hydrochloric acid (manufactured by Kanto Scientific Co., Ltd., premium grade) with pure water to prepare an 18% (w / w) hydrochloric acid aqueous solution. Next, place 0.2 g of silver powder and 20 mL of hydrochloric acid aqueous solution into a 100 mL glass beaker and heat to boiling. After boiling begins, continue heating for 15 minutes, maintaining the boiling state. During heating, to prevent the solution from evaporating and drying out, add 18% (w / w) hydrochloric acid aqueous solution within the range not exceeding the original volume before heating. After heating, cool the solution to 25°C, filter, and add 18% (w / w) hydrochloric acid aqueous solution to make the filtrate 20 mL, then make up to volume to prepare the sample solution for spectrophotometric determination.

[0086] Furthermore, to determine the absorbance of the sample solution, a spectrophotometer (Hitachi, U-3210) was used to measure the absorbance of the peak with a peak wavelength of 272.8 nm ± 0.5 nm. For the relationship between the concentration of benzotriazole and absorbance, a standard curve was pre-determined. The concentration of benzotriazole in the filtrate was calculated using this standard curve and the absorbance value of the sample solution. Based on this concentration, the volume of the filtrate, and the weighing value of the silver powder, the amount (mass %) of the spherical silver powder was determined.

[0087] It should be noted that the type of surface treatment agent can be determined by qualitative analysis using gas chromatography of the surface treatment agent that volatilizes after heating the spherical silver powder.

[0088] <Particle Size Distribution>

[0089] In this specification, the cumulative 10% particle size (D) of the spherical silver powder is defined on a volume basis. 10 ), cumulative 50% particle size (D 50 ), cumulative 90% particle size (D 90 The particle size distribution was measured using a laser diffraction-scattering particle size analyzer (Microtrac BEL Co., Ltd., Microtrac MT-3300 EXII). During the measurement, 0.1 g of the sample (silver powder) was dispersed in 40 mL of isopropanol (IPA). Dispersion was performed using an ultrasonic homogenizer (Nippon Seiki Co., Ltd., device name: US-150T; 19.5 kHz, front end diameter 18 mm). The dispersion time was set to 2 minutes. The dispersed sample was then fed into the aforementioned apparatus, and the particle size distribution was determined using the accompanying analytical software.

[0090] (Spherical silver powder)

[0091] The spherical silver powder of this invention contains a surface treatment agent, and in the measurement of thermal expansion coefficient, the maximum value of the thermal expansion coefficient based on a value at 50°C is less than 0.3%, and the BET specific surface area is 0.1 m². 2 / g or more and 0.8m 2 / g or less, D 90 The value is above 2.0 μm and below 4.0 μm. It should be noted that, in the following, "the thermal expansion rate based on the value at 50 °C in the thermal expansion rate determination" is sometimes simply referred to as "thermal expansion rate". As described above, the thermal expansion rate determination can be performed by heating from room temperature to 900 °C at a heating rate of 10 °C / min to measure the axial expansion rate of a cylindrical test sample.

[0092] If the silver powder is spherical as described above, it can impart excellent fine-line printability to the conductive paste and reduce the resistivity of the conductive film. The reason for this is presumably that, compared to flake-shaped powders, it is less likely to form large particles that clog the printing nozzles during gelatinization, thus reducing the specific surface area relative to the particle size. This suppresses viscosity increase and inhibits expansion of the conductive coating during firing.

[0093] Examples of surface treatment agents include fatty acids, compounds with azole structures, fatty acid salts, surfactants, organometallic chelate forming agents, and protective colloids.

[0094] From the viewpoint of being able to uniformly adhere to the surface of silver powder and obtain high dispersibility, the surface treatment agent is preferably one or more selected from the group consisting of fatty acids, compounds having an azole structure and fatty acid salts.

[0095] Examples of fatty acids include benzyl acid, stearic acid, palmitic acid, myristic acid, lauric acid, ricinoleic acid, oleic acid, linoleic acid, and linolenic acid. They can be used individually or in combination of two or more. Stearic acid and oleic acid are preferred.

[0096] As fatty acid salts, examples include salts of the fatty acids listed above. Examples of salts include sodium salts and potassium salts.

[0097] Examples of compounds having an azole structure include benzotriazole, sodium salts of benzotriazole, and potassium salts of benzotriazole. They can be used alone or in combination of two or more. Benzotriazole and sodium benzotriazole are preferred.

[0098] The content of surface treatment agent in the spherical silver powder is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, 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.

[0099] If the content of surface treatment agent in spherical silver powder is 0.01% by mass or more, the dispersibility of silver powder can be improved.

[0100] On the other hand, if the content of the surface treatment agent in the spherical silver powder is less than 1.00% by mass, the dispersibility of the silver powder will be maintained without hindering sintering, thus improving the conductivity.

[0101] 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.

[0102] If the maximum thermal expansion rate of the spherical silver powder is below 0.30%, it will not expand during firing, will not cause short circuits in the resulting cured film, and will maintain a low resistance value.

[0103] On the other hand, the minimum thermal expansion rate of spherical silver powder can be 0% (no expansion) or more than 0.01%.

[0104] The BET specific surface area of ​​spherical silver powder is 0.10 m². 2 / g or more, preferably 0.25m 2 / g or more, more preferably 0.30m 2 / g or above, is 0.80m 2 / g or less, preferably 0.65m 2 / g or less, more preferably 0.60m 2 / g or less.

[0105] The BET specific surface area of ​​spherical silver powder is less than 0.10 m². 2 At a density of / g, the particle size becomes too large, making it unsuitable for fine-line printing.

[0106] On the other hand, the BET specific surface area of ​​spherical silver powder is greater than 0.80 m². 2 At a density of / g, the particle size becomes too small, and the viscosity of the paste becomes high, making it unsuitable for fine-line printing.

[0107] D of spherical silver powder 90 The value is 2.0 μm or more, preferably 2.1 μm or more, and 4.0 μm or less, preferably 3.7 μm or less.

[0108] In D 90 When the particle size is greater than 4.0 μm, the particles are prone to clogging the printing plate, making printing difficult, and therefore it is not suitable.

[0109] D of spherical silver powder 50 The value is preferably 1.0 μm or more, more preferably 1.3 μm or more, more preferably 2.5 μm or less, and more preferably 2.2 μm or less.

[0110] D of spherical silver powder 10 The value is preferably 0.5 μm or more, more preferably 0.7 μm or more, and more preferably 1.2 μm or less.

[0111] In the D of spherical silver powder 90 D 50 D 10 If the value exceeds the upper limit, the particle size is too large and therefore unsuitable for fine line printing. If it is less than the lower limit, the viscosity of the paste becomes too high and it is also unsuitable for fine line printing.

[0112] (Method for manufacturing spherical silver powder)

[0113] The method for manufacturing spherical silver powder of the present invention (hereinafter sometimes simply referred to as the "manufacturing method") is a method of reducing and precipitating silver particles by adding a reducing agent to an aqueous reaction system containing silver ions and a chelating agent composed of a polymer. Furthermore, the manufacturing method of the present invention includes: a carbonic acid concentration adjustment step, wherein the ratio of the total molar concentration of carbonic acid (CO3) to the total molar concentration of silver (Ag) in the aqueous reaction system (hereinafter sometimes referred to as "CO3 / Ag") is adjusted to 0.004 or more and 0.051 or less before adding the reducing agent to the aqueous reaction system; and a surface treatment agent addition step, wherein a surface treatment agent is added to the aqueous reaction system after the silver particles have precipitated.

[0114] If the manufacturing method described above is used, spherical silver powder with excellent fine-line printability can be obtained. This is presumably because by setting the CO3 / Ag ratio in the aqueous reaction system to a specified ratio or higher, the rapid reduction of silver ions caused by the reducing agent is mitigated. In other words, by moderating the reducing effect of the reducing agent, the formation of irregularly shaped particles such as confetti-like particles is effectively suppressed. Furthermore, it is presumably because by setting the CO3 / Ag ratio in the aqueous reaction system to a specified ratio or lower, the particle size of the obtained silver particles can be effectively prevented from becoming too small, and the viscosity of the conductive paste can be effectively prevented from becoming too high when used in a conductive paste.

[0115] It should be noted that, in this specification, confetti-like particles refer to particles with multiple protrusions radiating from the center of the particle.

[0116] The aqueous reaction system contains silver ions and a chelating agent composed of polymers (hereinafter sometimes simply referred to as "chelating agent"). An aqueous reaction system can be obtained, for example, by adding a chelating agent to an aqueous solution containing silver ions.

[0117] Here, there are no particular limitations on the use of aqueous solutions containing silver ions; for example, silver nitrate aqueous solutions can be used.

[0118] In one embodiment, from the viewpoint of effectively adjusting the shape and particle size distribution of the obtained spherical silver powder, it is preferable to add ammonia or an ammonium salt to an aqueous solution containing silver ions to obtain a silver-ammonia complex. It should be noted that the ammonia or ammonium salt is preferably added in an amount equal to or greater than 1 mol of ammonia per mol of silver.

[0119] Specific examples of preferred chelating agents of the present invention include amino compounds and imine compounds. Among them, polyethyleneimine (PEI) is preferred. In particular, PEI, as an imine compound, has a network structure in which both primary amine (-NH2) and secondary amine (=NH) are present in the molecule, which provides preferred results in the present invention.

[0120] The weight-average molecular weight of the chelating agent of the present invention is preferably less than 600, and more preferably 145 or more and 600 or less. This is because when the weight-average molecular weight of the chelating agent is 145 or more, it is possible to obtain silver particles with high dispersibility. On the other hand, it is believed that by making the weight-average molecular weight of the polymeric amine less than 600, the water solubility of the polymeric amine can be ensured, and the polymeric amine will hardly remain on the surface and inside the generated silver particles.

[0121] It should be noted that the weight-average molecular weight of the chelating agent can be determined by the GPC-MALS method.

[0122] 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 more preferably 1.000% by mass or less.

[0123] The reducing agent added to the aqueous reaction system (after the carbonic acid concentration adjustment step described later) is not particularly limited, but a reducing agent that does not contain carbonic acid is preferred. Specific reducing agents include, for example, hydrazine, formalin, sodium borohydride, glucose, and hypophosphorous acid. Among these, hydrazine is particularly preferred from the viewpoint of its reactivity stability and ability to rapidly reduce silver ions.

[0124] The following describes the carbonic acid concentration adjustment step and the surface treatment agent addition step included in the manufacturing method of the present invention, but the manufacturing method of the present invention is not limited to including only these steps. For example, the manufacturing method of the present invention may optionally include steps other than the carbonic acid concentration adjustment step and the surface treatment agent addition step (hereinafter sometimes referred to as "other steps"). Examples of other steps include, for example, a separation step that separates and dries the reduced silver particles from the aqueous reaction system.

[0125] <Carbon Dioxide Concentration Adjustment Process>

[0126] In the carbonic acid concentration adjustment process, before adding the reducing agent to the aqueous reaction system, the ratio of the total molar concentration of carbonic acid to the total molar concentration of silver in the aqueous reaction system is adjusted to be above 0.004 and below 0.051.

[0127] The CO3 / Ag ratio in the aqueous reaction system is above 0.004 and below 0.051, preferably below 0.031.

[0128] Here, the adjustment of CO3 / Ag is not particularly limited. For example, it can be done by adding a specified amount of carbonated water and / or carbonate to the aqueous reaction system, or by blowing carbon dioxide into the aqueous reaction system (so-called bubbling). It should be noted that, from an operational point of view, the method of adding a specified amount of carbonate to the aqueous reaction system is preferred.

[0129] When using carbonates to adjust the CO3 / Ag ratio, the carbonates can be used in the form of an aqueous solution. The concentration of the aqueous carbonate solution is, for example, 1% by mass or more and 30% by mass or less.

[0130] It should be noted that there are no particular limitations as a carbonate; for example, sodium carbonate, potassium carbonate, etc., can be used.

[0131] <Surface treatment agent addition process>

[0132] In the surface treatment agent addition process, after the silver particles precipitate, a surface treatment agent is added to the aqueous reaction system. This yields surface-treated silver particles.

[0133] It should be noted that aqueous reaction systems containing silver particles are usually suspensions (so-called slurries) or dispersions in which silver particles are dispersed.

[0134] Examples of surface treatment agents include fatty acids, compounds with azole structures, fatty acid salts, surfactants, organometallic chelate forming agents, and protective colloids.

[0135] From the viewpoint of easily and uniformly adhering to the surface of silver powder, the surface treatment agent is preferably one or more selected from the group consisting of fatty acids, compounds having an azole structure, and fatty acid salts.

[0136] Examples of fatty acids include benzyl acid, stearic acid, palmitic acid, myristic acid, lauric acid, ricinoleic acid, oleic acid, linoleic acid, and linolenic acid. They can be used individually or in combination of two or more. Stearic acid and oleic acid are preferred.

[0137] As fatty acid salts, salts of the fatty acids listed above can be included. Examples of salts include sodium salts and potassium salts.

[0138] Examples of compounds having an azole structure include benzotriazole, sodium salts of benzotriazole, and potassium salts of benzotriazole. They can be used alone or in combination of two or more. Benzotriazole and sodium benzotriazole are preferred.

[0139] The amount of surface treatment agent added in the surface treatment agent addition process is usually more than 0.01% by mass and less than 1.00% by mass relative to the mass of silver contained in the aqueous reaction system.

[0140] <Separation Process>

[0141] In any separation process, the reduced silver particles are separated from the aqueous reaction system and dried.

[0142] It should be noted that during the separation process, a cleaning and recycling process can be carried out to recover and clean the separated silver particles, etc.

[0143] In the cleaning and recovery process, for example, the separated silver particles are aggregated into a cake shape, and the filter cake of the silver particle aggregate is then cleaned. The cleaning in the cleaning and recovery process can be performed, for example, using pure water. Dewatering in the cleaning and recovery process can be performed, for example, by decantation and / or a filter press. The end point of cleaning can be determined using the conductivity of the cleaning water. Specifically, cleaning can be considered complete when the conductivity of the cleaning water falls below a predetermined value. The cleaned silver particles can then be supplied to the drying process in an aggregated state such as a cake shape.

[0144] In the drying process, aggregates of silver particles, etc., containing moisture and in an aggregated state are dried. Vacuum drying and / or airflow drying machines can be used in the drying process. In the drying process, a high-pressure airflow can be blown onto the aggregates of silver particles, etc., or the filter cake and / or spherical silver powder from the drying process can be fed into a mixer equipped with a stirring rotor for stirring, thereby imparting a dispersing force to the filter cake and / or the spherical silver powder from the drying process, promoting dispersion and / or drying.

[0145] During the drying process, the temperature of the spherical silver powder is usually below 100°C. If the temperature of the spherical silver powder is below 100°C, it can effectively prevent the silver particles in the spherical silver powder from burning together.

[0146] Since dried spherical silver powder sometimes forms lumps, dry crushing or grading operations can be performed simultaneously with or after the drying process to improve its workability. Improving the workability of spherical silver powder refers, for example, appropriately loosening the powder to ensure sufficient flowability for feeding into the processing unit, or enabling efficient processing within the unit.

[0147] There are no particular restrictions on the dry crushing process; it can be selected appropriately according to the purpose. It is preferable to use a crusher that uses rotating stirring blades to crush and flow the spherical silver powder, such as a sample mill, blender, or coffee mill.

[0148] Example

[0149] The present invention will be further described in detail below using examples, but the present invention is by no means limited to the following examples.

[0150] It should be noted that the confirmation of spherical silver powder (particle shape), the thermomechanical analysis of spherical silver powder (calculation of the maximum value of thermal expansion coefficient), the determination of BET specific surface area, the quantification of surface treatment agent, and the determination of particle size distribution are performed by the methods described above.

[0151] <Evaluation of the printability of fine lines>

[0152] First, the silver powder, aluminum powder (SEM average diameter 2.0 μm) obtained in the examples and comparative examples, glass powder (containing PbO as the main component, and containing B2O3, SiO2 and other oxides), ethyl cellulose, dodecayl alcohol ester, butyl carbitol acetate, tributyl citrate, 1-octanol, oleic acid, triacetin, methylphenyl polysiloxane, hydrogenated castor oil and fatty acid amide were mixed according to the composition shown in Table 1 to obtain a mixture.

[0153] Next, the mixture was premixed in a rotary mixer (1000 rpm) and then kneaded in a three-roll mill (EXAKT) to obtain a conductive paste.

[0154] Using the conductive paste obtained above, straight lines were printed via screen printing. The designed linewidth of the lines was 12 μm, and the length of the lines was 150 mm. Printing was performed using a Microtec printer at a squeegee speed of 350 mm / s. A silicon substrate with a thickness of approximately 170 μm (for solar cell applications, textured SiN) was used. x (Film formation). After printing, the wafer is dried in a dryer at 200°C for 5 minutes, and then fired in a solar cell firing furnace (NGK) at a peak temperature of 750°C on the wafer surface to produce samples. The samples are observed using a digital microscope (KEYENCE, VHX-5000) to check for broken lines, and the printability of fine lines is evaluated according to the following criteria.

[0155] A: No disconnection confirmed.

[0156] B: The connection has been confirmed to be broken.

[0157] C: The paste viscosity is too high, therefore it cannot be printed.

[0158] (Example 1)

[0159] Prepare 87410g of silver nitrate aqueous solution containing 1260g (11.7mol) Ag, and add 2560g of ammonia water with a concentration of 28% by mass to prepare an aqueous solution containing silver ions. Set the liquid temperature to 35℃.

[0160] Add 63g of a 10% by mass sodium carbonate aqueous solution to the above-mentioned aqueous solution containing silver ions, adjusting the ratio of the total molar concentration of carbonic acid to the total molar concentration of silver (CO3 / Ag) in the aqueous reaction system to 0.005. Next, add 13g of an aqueous solution containing polyethyleneimine (PEI) with a weight average molecular weight of 600 (5% by mass, relative to Ag) as a chelating agent to the adjusted CO3 / Ag aqueous reaction system to prepare an aqueous reaction system containing silver ions and a chelating agent. Then, add 2684g of a 6.2% by mass hydrazine aqueous solution as a reducing agent to this aqueous reaction system and stir thoroughly to obtain a slurry containing silver powder. Further, add 65g of a 3.5% by mass oleic acid (surface treatment agent) Neoethanol solution to the obtained slurry, stir thoroughly, and allow it to mature. Filter the matured slurry and wash the filtrate with water. Then, the filtered material after washing was dried, and 150g of silver powder was added to a sample mill (manufactured by Kyoritsu Riko Co., Ltd., SK-M10) and crushed twice for 90 seconds to obtain the silver powder of Example 1.

[0161] The obtained silver powder was used to confirm spherical shape (particle shape), perform thermomechanical analysis (calculation of the maximum thermal expansion coefficient), determine BET specific surface area, determine surface treatment agent content and particle size distribution, and evaluate fine-line printability. The results are shown in Table 3. Additionally, the thermomechanical analysis curves of the silver powder are plotted in... Figure 1 and 2 The SEM image of the silver powder at 10,000x magnification is shown below. Figure 23 .

[0162] (Example 2)

[0163] Prepare 96690g of silver nitrate aqueous solution containing 1620g (15.0mol) Ag, and add 3280g of ammonia water with a concentration of 28% by mass to prepare an aqueous solution containing silver ions. Set the liquid temperature to 35℃.

[0164] Add 65g of a 10% by mass sodium carbonate aqueous solution to the above-mentioned aqueous solution containing silver ions, adjusting the ratio of the total molar concentration of carbonic acid to the total molar concentration of silver (CO3 / Ag) in the aqueous reaction system to 0.004. Next, add 16g of an aqueous solution containing polyethyleneimine (PEI) with a weight average molecular weight of 600 (5% by mass, relative to the mass of Ag) as a chelating agent to the aqueous reaction system after adjusting the CO3 / Ag ratio, to prepare an aqueous reaction system containing silver ions and a chelating agent. Then, add 3441g of a 6.2% by mass hydrazine aqueous solution as a reducing agent to this aqueous reaction system and stir thoroughly to obtain a slurry containing silver powder. Next, 138.8 g of a Solmix solution containing 4.0% benzotriazole (surface treatment agent) was added to the obtained slurry (a solution prepared by adding 133.3 g of Solmix (manufactured by Nippon Kokusai Co., Ltd., Solmix AP-7) relative to 5.5 g of benzotriazole, and the mixture was stirred thoroughly and allowed to mature. The matured slurry was filtered, and the filtrate was washed with water. Then, the washed filtrate was dried, and 150 g of silver powder was added to a sample mill (manufactured by Kyoritsu Riko Co., Ltd., SK-M10), and the mixture was crushed twice for 90 seconds to obtain the silver powder of Example 2.

[0165] The obtained silver powder was used to confirm spherical shape (particle shape), perform thermomechanical analysis (calculation of the maximum thermal expansion coefficient), determine BET specific surface area, determine surface treatment agent content and particle size distribution, and evaluate fine-line printability. The results are shown in Table 3. Additionally, the thermomechanical analysis curves of the silver powder are plotted in... Figure 3 and 4 The SEM image of the silver powder at 10,000x magnification is shown below. Figure 24 .

[0166] (Example 3)

[0167] Prepare 96190g of silver nitrate aqueous solution containing 1620g (15.0mol) Ag, and add 3280g of ammonia water with a concentration of 28% by mass to prepare an aqueous solution containing silver ions. Set the liquid temperature to 35℃.

[0168] Add 324 g of a 5% (w / w) sodium carbonate aqueous solution to the above-mentioned aqueous solution containing silver ions to adjust the ratio of the total molar concentration of carbonic acid to the total molar concentration of silver (CO3 / Ag) in the aqueous reaction system to 0.010. Next, add 202 g of an aqueous solution containing polyethyleneimine (PEI) with a weight average molecular weight of 600 (0.4% (w / w) as a chelating agent) as a chelating agent to the adjusted aqueous reaction system to prepare an aqueous reaction system containing silver ions and a chelating agent. Then, add 3512 g of a 6.2% (w / w) hydrazine aqueous solution as a reducing agent to this aqueous reaction system and stir thoroughly to obtain a slurry containing silver powder. Then, add 340 g of a 0.86% (w / w) stearic acid (surface treatment agent) emulsion to the obtained slurry, stir thoroughly, and allow it to mature. Filter the matured slurry and wash the filtrate with water. Then, the filtered material after washing was dried, and 150g of silver powder was added to a sample mill (manufactured by Kyoritsu Riko Co., Ltd., SK-M10) and crushed twice for 90 seconds to obtain the silver powder of Example 3.

[0169] The obtained silver powder was used to confirm spherical shape (particle shape), perform thermomechanical analysis (calculation of the maximum thermal expansion coefficient), determine BET specific surface area, determine surface treatment agent content and particle size distribution, and evaluate fine-line printability. The results are shown in Table 3. Additionally, the thermomechanical analysis curves of the silver powder are plotted in... Figure 5 and 6 The SEM image of the silver powder at 10,000x magnification is shown below. Figure 25 .

[0170] (Example 4)

[0171] The concentration of 10% sodium carbonate aqueous solution was changed from 65g to 275g, the CO3 / Ag ratio was adjusted to 0.017, and the concentration of 3.7% sodium benzotriazole (surface treatment agent) aqueous solution was changed to 147g. Otherwise, the silver powder of Example 4 was obtained in the same manner as in Example 2.

[0172] The obtained silver powder was used to confirm spherical shape (particle shape), perform thermomechanical analysis (calculation of the maximum thermal expansion coefficient), determine BET specific surface area, determine surface treatment agent content and particle size distribution, and evaluate fine-line printability. The results are shown in Table 3. Additionally, the thermomechanical analysis curves of the silver powder are plotted in... Figure 7 and 8 The SEM image of the silver powder at 10,000x magnification is shown below. Figure 26 .

[0173] (Example 5)

[0174] The concentration of 10% sodium carbonate aqueous solution was changed from 63g to 189g, and the CO3 / Ag ratio was adjusted to 0.015. Otherwise, the silver powder of Example 5 was obtained in the same manner as in Example 1.

[0175] The obtained silver powder was used to confirm spherical shape (particle shape), perform thermomechanical analysis (calculation of the maximum thermal expansion coefficient), determine BET specific surface area, determine surface treatment agent content and particle size distribution, and evaluate fine-line printability. The results are shown in Table 3. Additionally, the thermomechanical analysis curves of the silver powder are plotted in... Figure 9 and 10 The SEM image of the silver powder at 10,000x magnification is shown below. Figure 27 .

[0176] (Example 6)

[0177] The concentration of 5% sodium carbonate aqueous solution was changed from 324g to 971g, the CO3 / Ag ratio was adjusted to 0.031, and the concentration of 0.86% stearic acid (surface treatment agent) emulsion was changed from 340g to 1.3% stearic acid emulsion aqueous solution. Otherwise, the silver powder of Example 6 was obtained in the same manner as in Example 3.

[0178] The obtained silver powder was used to confirm spherical shape (particle shape), perform thermomechanical analysis (calculation of the maximum thermal expansion coefficient), determine BET specific surface area, determine surface treatment agent content and particle size distribution, and evaluate fine-line printability. The results are shown in Table 3. Additionally, the thermomechanical analysis curves of the silver powder are plotted in... Figure 11 and 12 The SEM image of the silver powder at 10,000x magnification is shown below. Figure 28 .

[0179] (Example 7)

[0180] Add 421g of a 15% by mass sodium carbonate aqueous solution to adjust the CO3 / Ag ratio to 0.051, and change the 3.5% by mass oleic acid (surface treatment agent) Neoethanol solution from 65g to 126g. Otherwise, the silver powder of Example 7 was obtained in the same manner as in Example 1.

[0181] The obtained silver powder was used to confirm spherical shape (particle shape), perform thermomechanical analysis (calculation of the maximum thermal expansion coefficient), determine BET specific surface area, determine surface treatment agent content and particle size distribution, and evaluate fine-line printability. The results are shown in Table 3. Additionally, the thermomechanical analysis curves of the silver powder are plotted in... Figure 13 and 14 The SEM image of the silver powder at 10,000x magnification is shown below. Figure 29 .

[0182] (Comparative Example 1)

[0183] Prepare 3887g of silver nitrate aqueous solution containing 43.16g (0.40mol) Ag, and add 97.1g of ammonia water with a concentration of 28% by mass to prepare an aqueous solution containing silver ions. Set the liquid temperature to 34.5℃.

[0184] 0.043 g (0.100% by mass relative to Ag) of polyethyleneimine (PEI) with a weight average molecular weight of 300 was added as a chelating agent to the above-mentioned aqueous solution containing silver ions to prepare an aqueous reaction system containing silver ions and a chelating agent. Next, 7.5 g of an aqueous solution of hydrazine as a reducing agent was added to this aqueous reaction system and stirred thoroughly to obtain a slurry containing silver powder. Stearic acid at 0.12% by mass relative to silver was added to the obtained slurry, and the mixture was stirred thoroughly and allowed to mature. The matured slurry was filtered, and the filtrate was washed with water. Then, the washed filtrate was pulverized and dried to obtain the silver powder of Comparative Example 1.

[0185] The obtained silver powder was used to confirm spherical shape (particle shape), perform thermomechanical analysis (calculation of the maximum thermal expansion coefficient), determine BET specific surface area, determine surface treatment agent content and particle size distribution, and evaluate fine-line printability. The results are shown in Table 3. Additionally, the thermomechanical analysis curves of the silver powder are plotted in... Figure 15 and 16 .

[0186] (Comparative Example 2)

[0187] The chelating agent, polyethyleneimine (PEI) with a weight average molecular weight of 300, was changed to polyethyleneimine (PEI) with a weight average molecular weight of 600, and the surface treatment agent, stearic acid, was changed to benzotriazole. Otherwise, the silver powder of Comparative Example 2 was obtained in the same manner as Comparative Example 1.

[0188] The obtained silver powder was used to confirm spherical shape (particle shape), perform thermomechanical analysis (calculation of the maximum thermal expansion coefficient), determine BET specific surface area, determine surface treatment agent content and particle size distribution, and evaluate fine-line printability. The results are shown in Table 3. Additionally, the thermomechanical analysis curves of the silver powder are plotted in... Figure 17 and 18 .

[0189] (Comparative Example 3)

[0190] Prepare 3637g of silver nitrate aqueous solution containing 43.16g (0.40mol) Ag, and add 87.6g of ammonia water with a concentration of 28% by mass to prepare an aqueous solution containing silver ions. Set the liquid temperature to 35℃.

[0191] 80 g of a 20% by mass sodium hydroxide aqueous solution was added to the above-mentioned aqueous solution containing silver ions. Next, 0.86 g (0.100% by mass relative to Ag) of an aqueous solution containing 0.043 g of polyethyleneimine (PEI) with a weight average molecular weight of 600 as a chelating agent was added to the aqueous reaction system after adding the sodium hydroxide aqueous solution, thus preparing an aqueous reaction system containing silver ions and a chelating agent. Then, 243 g of a 2.5% by mass hydrazine aqueous solution as a reducing agent was added to this aqueous reaction system and stirred thoroughly to obtain a slurry containing silver powder. 3.34 g of a 1.5% stearic acid (surface treatment agent) emulsion was added to the obtained slurry, and after thorough stirring, it was allowed to mature. The matured slurry was filtered, and the filtrate was washed with water. Then, the washed filtrate was dried, and 150 g of silver powder was added to a sample mill (manufactured by Kyoritsu Riko Co., Ltd., SK-M10) and crushed twice for 90 seconds to obtain the silver powder of Comparative Example 3.

[0192] The obtained silver powder was used to confirm spherical shape (particle shape), perform thermomechanical analysis (calculation of the maximum thermal expansion coefficient), determine BET specific surface area, determine surface treatment agent content and particle size distribution, and evaluate fine-line printability. The results are shown in Table 3. Additionally, the thermomechanical analysis curves of the silver powder are plotted in... Figure 19 and 20 The SEM image of the silver powder at 10,000x magnification is shown below. Figure 30 It should be noted that, in Figure 30 Particles resembling konpeito were confirmed near the center of the SEM image.

[0193] (Comparative Example 4)

[0194] Prepare 3572g of silver nitrate aqueous solution containing 56.11g (0.52mol) Ag, and add 113.9g of ammonia water with a concentration of 28% by mass to prepare an aqueous solution containing silver ions. Set the liquid temperature to 35℃.

[0195] 78.55 g of a 5% (w / w) sodium carbonate aqueous solution was added to the above-mentioned aqueous solution containing silver ions, adjusting the ratio of the total molar concentration of carbonic acid to the total molar concentration of silver (CO3 / Ag) in the aqueous reaction system to 0.071. Next, 0.561 g (0.028 g / w) of an aqueous solution containing 0.028 g of polyethyleneimine (PEI) as a chelating agent (weight average molecular weight 600) was added to the aqueous reaction system containing the adjusted CO3 / Ag and the added sodium hydroxide aqueous solution to prepare an aqueous reaction system containing silver ions and a chelating agent. Then, 300 g of a 2.5% (w / w) hydrazine aqueous solution as a reducing agent was added to this aqueous reaction system and stirred thoroughly to obtain a slurry containing silver powder. Subsequently, 1.964 g of a 10% (w / w) oleic acid (surface treatment agent) Neoethanol solution was added to the obtained slurry, stirred thoroughly, and allowed to mature. The matured slurry was filtered, and the filtrate was washed with water. Then, the filtered material after washing was dried, and 150g 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 of Comparative Example 4.

[0196] The obtained silver powder was used to confirm spherical shape (particle shape), perform thermomechanical analysis (calculation of the maximum thermal expansion coefficient), determine BET specific surface area, determine surface treatment agent content and particle size distribution, and evaluate fine-line printability. The results are shown in Table 3. Additionally, the thermomechanical analysis curves of the silver powder are plotted in... Figure 21 and 22 .

[0197] [Table 1]

[0198]

[0199] [Table 2]

[0200]

[0201] [Table 3]

[0202]

[0203] The results in Tables 2 and 3 clearly show that the spherical silver powders of Examples 1-7 can impart excellent fine-line printability to conductive pastes. It is also evident that if the CO3 / Ag ratio exceeds 0.051, the particle size becomes too small to print, as in Comparative Example 4.

[0204] Furthermore, the results in Tables 2 and 3 clearly show that spherical silver powder obtained by the manufacturing methods of Examples 1 to 7 can impart excellent fine-line printability to conductive pastes.

[0205] Industrial availability

[0206] According to the present invention, spherical silver powder capable of imparting excellent fine-line printability to conductive pastes can be provided.

[0207] In addition, the present invention can provide a method for manufacturing spherical silver powder that can impart excellent fine-line printability to conductive pastes.

Claims

1. A spherical silver powder containing a surface treatment agent, In the determination of thermal expansion coefficient, the maximum value of the thermal expansion coefficient based on the value at 50℃ is less than 0.3%. The specific surface area of ​​BET is 0.1 m². 2 / g or more and 0.8m 2 / g or less D 90 The value is above 2.0 μm and below 4.0 μm.

2. The spherical silver powder according to claim 1, wherein, D 50 The value is above 1.0 μm and below 2.5 μm.

3. The spherical silver powder according to claim 1, wherein, D 10 The value is above 0.5μm and below 1.2μm.

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

5. A method for manufacturing spherical silver powder, comprising adding a reducing agent to an aqueous reaction system containing silver ions and a chelating agent composed of a polymer to reduce and precipitate silver particles, wherein the method for manufacturing spherical silver powder includes: In the carbonic acid concentration adjustment step, before adding the reducing agent to the aqueous reaction system, the ratio of the total molar concentration of carbonic acid to the total molar concentration of silver in the aqueous reaction system is adjusted to be 0.004 or higher and 0.051 or lower; and In the surface treatment agent addition step, after the silver particles precipitate, a surface treatment agent is added to the aqueous reaction system.

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

7. The method for manufacturing spherical silver powder according to claim 5, wherein, The chelating agent is polyethyleneimine with a weight average molecular weight of less than 600.

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

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