Silver powder and resin-curable electroconductive paste

Abstract

To provide a silver powder that, when formed into an electroconductive paste, is capable of imparting low volume resistivity even if fired at a low temperature.SOLUTION: The present invention is a silver powder which contains a surface treatment agent, wherein the ratio of the oxygen level to the BET surface area is at least 0.11, and the crystal grain size is 30 nm to 38 nm, inclusive.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a silver powder and a resin-curing type conductive paste. [Background technology]

[0002] In recent years, heterojunction (HJT) type solar cells have been attracting attention. In HJT type solar cells, electrodes and conductor patterns are generally formed by baking a resin-curing conductive paste using silver powder at a relatively low temperature of around 200°C in an air atmosphere to harden it.

[0003] For example, in Patent Document 1, the average particle diameter (D SEM ) is 30-100 nm, and the tap density is 3.0 g / cm 3 The silver fine particles described above have been proposed, and it is described that the silver fine particles are used in a resin-curing type conductive paste or the like. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-159805 A Summary of the Invention [Problem to be solved by the invention]

[0005] Here, if the firing temperature is lowered when forming electrodes, conductor patterns, etc., a problem of increased resistance may occur. Therefore, it is desirable that the conductive paste containing silver powder suppresses the increase in volume resistivity even when the firing temperature is lowered, and has a low volume resistivity even when fired at a low temperature of 150°C to 200°C.

[0006] Therefore, an object of the present invention is to provide a silver powder that, when made into a conductive paste, can impart low volume resistivity even when fired at a low temperature. Another object of the present invention is to provide a resin-curing type conductive paste that can obtain a low volume resistivity even when fired at a low temperature. [Means for solving the problem]

[0007] As a result of extensive research by the inventors to solve the above problems, the inventors have completed the present invention described below.

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

[0009] [1] Contains a surface treatment agent, The ratio of the amount of oxygen to the BET specific surface area is 0.11 or more, Silver powder having a crystallite size of 30 nm or more and 38 nm or less.

[0010] [2] The silver powder according to [1], having an Ig-loss ratio to BET specific surface area of ​​0.51 or more.

[0011] [3] Cumulative 50% diameter D by volume using laser diffraction method 50 is 0.1 μm or more and 1.0 μm or less, Volume-based cumulative 90% diameter D by laser diffraction method 90 The silver powder according to claim [1] or [2], having a particle size of 1.2 μm or less.

[0012] [4] BET specific surface area is 0.90m 2 / g or more 2.50m 2 / g or less.

[0013] [5] The silver powder according to any one of [1] to [4], which is used in a resin-curing type conductive paste.

[0014] [6] A resin-curing conductive paste comprising the silver powder according to any one of [1] to [4]. Effect of the Invention

[0015] According to the present invention, when made into an electrical paste, silver powder capable of imparting a low volume resistivity even when fired at a low temperature can be provided. Further, according to the present invention, a resin-cured conductive paste capable of obtaining a low volume resistivity even when fired at a low temperature can be provided.

Brief Description of the Drawings

[0016] [Figure 1] It is an external perspective view of an example of a silver powder manufacturing apparatus. [Figure 2A] It is a cross-sectional view perpendicular to the flow path of the silver complex solution at the center position of the reducing agent supply pipe of the reducing agent addition member of the silver powder manufacturing apparatus. [Figure 2B] It is a cross-sectional view taken along line A-A of FIG. 2A in the horizontal direction of the flow path of the silver complex solution. [Figure 2C] It is a cross-sectional view taken along line B-B of FIG. 2A in the horizontal direction of the flow path of the silver complex solution. [Diagram 3] It is an SEM photograph (20,000 times) of the silver powder according to Example 1. [Figure 4] It is an SEM photograph (20,000 times) of the silver powder according to Example 2. [Diagram 5] It is an SEM photograph (20,000 times) of the silver powder according to Example 3. [Figure 6] It is an SEM photograph (20,000 times) of the silver powder according to Example 4. [Figure 7] It is an SEM photograph (20,000 times) of the silver powder according to Comparative Example 1. [Figure 8] It is an SEM photograph (20,000 times) of the silver powder according to Comparative Example 2.

Modes for Carrying Out the Invention

[0017] (Terms and Measurement Methods) First, prior to the description of the embodiments, terms and measurement methods in this specification will be described.

[0018] <BET Specific Surface Area> In this specification, the "BET specific surface area" was measured by a single-point BET method using nitrogen adsorption with a Macsorb HM-model 1210 (manufactured by MOUNTECH). The BET specific surface area was measured with a sample weight of 3.0 g, a N2 / He (30 / 70) mixed gas at a gas flow rate of 25 mL / min, and degassing conditions before the measurement were 60°C and 10 minutes.

[0019] <Crystallite diameter> The crystallite diameter Dx was calculated using an X-ray diffraction apparatus (Rigaku SmartLab) according to the Scherrer formula (D hkl =Kλ / βcosθ) where D hkl means the size of the crystallite diameter (size of the crystallite in the direction perpendicular to hkl) (unit: nm), λ means the wavelength of the measured X-ray (0.15405 nm when using a Cu target), β means the spread of the diffraction line due to the size of the crystallite (rad) (expressed using the half-width), θ means the Bragg angle of the diffraction angle (rad) (the angle when the angle of incidence and the angle of reflection are equal, and the angle of the peak top is used), and K means the Scherrer constant (K = 0.94). Note that the peak data of the Miller index (111) plane may also be used for the calculation.

[0020] <Carbon and oxygen content of silver powder> In this specification, the "carbon content of silver powder" was determined by measuring the CO and CO2 generated when 0.07 g of a sample (silver powder) was melted by heating it to 1,350°C in an oxygen stream using a carbon / sulfur analyzer (EMIA-810W manufactured by Horiba, Ltd.) using an infrared absorption method, and converting the measured value. In addition, the "oxygen content of silver powder" was measured using an oxygen, nitrogen, and hydrogen simultaneous analyzer (ONH836 manufactured by LECO) by infrared absorption method, with the power value of the impulse furnace set to 3500 W in an Ar gas atmosphere to measure the oxygen content in 0.05 g of sample (silver powder).

[0021] , <Quantitative analysis of surface treatment agents> In this specification, for example, when the surface treatment agent for the silver powder is a fatty acid such as stearic acid, the content of the fatty acid was measured according to the quantitative analysis method for fatty acids described in Japanese Patent No. 5622543. Specifically, first, silver powder was dissolved in nitric acid, and then an organic solvent (n-hexane) was mixed therein. The entire amount of the surface treatment agent was extracted into the organic solvent phase. A predetermined amount of the organic solvent phase was then taken out, and the organic solvent was evaporated and dried. The carbon content of the remaining solid matter was measured using a carbon-sulfur analyzer, and the carbon content was calculated.

[0022] In addition, in the present specification, for example, when the surface treatment agent for silver powder is benzotriazole, the content of said benzotriazole was measured according to the quantitative analysis method for benzotriazole and benzotriazole salts described in Japanese Patent No. 5523153. Specifically, the silver powder was first washed with an aqueous hydrochloric acid solution, and the washing solution was quantitatively analyzed by absorptiometry to determine the content of said benzotriazole.

[0023] The type of surface treatment agent can be identified by qualitative analysis by gas chromatography of the surface treatment agent volatilized by heating the silver powder.

[0024] <True density> The true density was measured by filling a 10cc platinum crucible with silver powder, precisely measuring the mass of the filled silver powder, and then measuring the volume of the mass-measured silver powder by the constant volume expansion method (the "gas pycnometer method" in the Japanese Pharmacopoeia) using a dry automatic density meter (Micromeritics, Inc., device name: AccuPyc II 1340) to calculate the density. Note that the true density is measured in such a way that the density includes the voids closed inside the silver particles that are not connected to the outside.

[0025] <Average primary particle diameter D SEM > Average primary particle diameter D SEM (Hereafter, simply "D SEM The Heywood diameter was determined by measuring the equivalent circle diameter (Heywood diameter) of 100 or more random silver particles in an SEM image of silver powder and calculating the average value. SEMcan be determined, for example, by using an image taken at 10,000x magnification and using image shape measurement software such as Mac-View (manufactured by Mountec Co., Ltd.).

[0026] <Particle size distribution> In this specification, the cumulative 10% particle diameter D of the silver powder based on volume 10 , Cumulative 50% particle size D 50 , and cumulative 90% particle size D 90 was measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT-3300 EXII, manufactured by Microtrack Bell Co., Ltd.). For the measurement, 0.1 g of sample (silver powder) was added to 40 mL of isopropyl alcohol (IPA) and dispersed. An ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho, device name: US-150T; 19.5 kHz, tip diameter 18 mm) was used for dispersion. The dispersion time was 2 minutes. The dispersed sample was subjected to the above-mentioned device, and the particle size distribution was obtained using the attached analysis software. In the following, the cumulative 10% particle diameter D based on volume measured by laser diffraction method is 10 , Cumulative 50% particle size D 50 , and cumulative 90% particle size D 90 , respectively, simply "D 10 ", "D 50 " and "D 90 "It is sometimes referred to as ".

[0027] <Ignition loss value> In this specification, the term "ignition loss (Ig-loss) value" refers to the amount of change in mass when heated from room temperature to 800°C, and specifically refers to the amount of components other than silver contained in the silver powder, and is an index showing the amount of components remaining in the silver powder, such as processing agents and additives used in the manufacturing process of the silver powder. In this specification, the "ignition loss (Ig-loss) value" is calculated by precisely weighing a silver powder sample (weighing value: w1), placing it in a magnetic crucible, heating it to 800°C, and holding it at 800°C for 30 minutes, which is a sufficient time to reach a constant weight, then cooling it and reweighing it (weighing value: w2), and calculating the "ignition loss (Ig-loss) value (mass%) = (w1-w2) / w1×100".

[0028] (Silver powder) The silver powder of the present invention contains a surface treatment agent, has a ratio of the amount of oxygen to the BET specific surface area ("oxygen amount of silver powder" / "BET specific surface area") of 0.11 or more, and has a crystallite diameter of 30 nm or more and 38 nm or less. Here, the ratio of the amount of oxygen to the BET specific surface area is the value of the amount of oxygen in the silver powder when the unit is mass%, and is expressed in units of m 2 / g, divided by the value of the BET specific surface area of ​​the silver powder. Note that, although the units of "oxygen content of silver powder" / "BET specific surface area" are omitted in this specification, the units are "mass% g / m 2 " When the above silver powder is made into a conductive paste, it can be given a low volume resistivity even when fired at a low temperature. The reason for this is presumably that when firing a resin-curing type material at a low temperature such as 200°C, the amount of heat required to cause necking between silver particles is sometimes insufficient, and the large amount of oxygen per specific surface area can promote the combustion of surface treatment agents, etc. on the silver particle surfaces, thereby compensating for the required amount of heat.

[0029] The crystallite size is 30 nm or more, preferably 32 nm or more, and 38 nm or less. If the crystallite size is within the above range, necking between silver particles will easily proceed, and when made into a conductive paste, it is expected that the silver powder will be able to impart low volume resistivity even when fired at a low temperature.

[0030] The ratio of the amount of oxygen to the BET specific surface area is 0.11 or more, and preferably 0.12 or more. Here, the amount of oxygen to the BET specific surface area is expressed by the value of the amount of oxygen in mass% and the unit of m 2 This is the value obtained by dividing the specific surface area by the specific surface area (g). When the ratio of the amount of oxygen to the BET specific surface area is 0.11 or more, the combustion of the silver particle surface can be promoted. On the other hand, the ratio of the amount of oxygen to the BET specific surface area is preferably, for example, 0.60 or less, and more preferably 0.50 or less, because if it exceeds 0.60, there is a risk of adverse effects due to the generation of voids caused by gas or shrinkage.

[0031] The oxygen content of the silver powder is preferably 0.13% by mass or more, more preferably 0.14% by mass or more, and is preferably 0.80% by mass or less, more preferably 0.50% by mass or less.

[0032] The carbon content of the silver powder is preferably 0.38% by mass or more, more preferably 0.40% by mass or more, and is preferably 1.00% by mass or less, more preferably 0.70% by mass or less. If the carbon content of the silver powder is 0.38 mass % or more, it is possible to promote the combustion of the silver particle surface together with the oxygen described above. On the other hand, if the carbon content of the silver powder exceeds 1.00 mass %, there is a risk of adverse effects due to the generation of voids caused by gas or shrinkage.

[0033] The BET specific surface area is 0.90m 2 / g or more, and 1.00m 2 / g or more is more preferable, and 1.05m 2 / g or more, and more preferably 1.10m 2 / g or more, and more preferably 2.50m 2 / g or less, and 2.25m 2 / g or less is more preferable, and 2.00m 2 / g or less, and more preferably 1.80m 2 It is even more preferable that the molecular weight is not more than 1 / g. BET specific surface area is 0.90m 2 / g or more, appropriate particle activity is obtained, which is advantageous in terms of the volume resistivity of the wiring pattern formed using the conductive paste even when fired at a low temperature. In addition, it is easy to respond to high density, etc. On the other hand, the BET specific surface area is 2.50m 2 / g or less is advantageous in terms of ease of handling of the paste when made into a conductive paste.

[0034] D 50is 0.1 μm or more, preferably 0.25 μm or more, more preferably 0.30 μm or more, and even more preferably 0.35 μm or more, and is 1.0 μm or less, preferably 0.9 μm or less, and more preferably 0.8 μm or less. 50 Within the above range, when the silver powder is used in a conductive paste, printing with a narrow line width becomes possible, and the fine line printability of the conductive paste can be improved. In addition, when it is important to obtain high conductivity in a conductive film obtained by firing a resin-curing conductive paste using the silver powder of the present invention at a low temperature, the D 50 can be set to 0.1 μm or more and 0.55 μm or less, and further, can be set to 0.2 μm or more and 0.5 μm or less.

[0035] D 10 is preferably 0.05 μm or more, more preferably 0.10 μm or more, and is preferably 0.40 μm or less, more preferably 0.35 μm or less. D 10 If it is within the above range, the fine line printability of the conductive paste can be improved.

[0036] D 90 is preferably 0.5 μm or more, more preferably 0.6 μm or more, and is preferably 1.2 μm or less, more preferably 1.1 μm or less. D 90 If it is within the above range, the fine line printability of the conductive paste can be improved.

[0037] In one embodiment, the silver powder is 50 is 0.1 μm or more and 1.0 μm or less, and D 90 It is preferable that the thickness is 1.2 μm or less. The above-mentioned silver powder can effectively improve the fine line printability of the conductive paste.

[0038] Here, the true density of silver is 10.49 g / cm 3 However, the true density of the silver powder of the present invention is, for example, 9.8 g / cm 3More than 10.49g / cm 3 Less than or equal to 9.9 g / cm 3 More than that is fine.

[0039] D SEM is preferably 0.10 μm or more, more preferably 0.20 μm or more, even more preferably 0.25 μm or more, even more preferably 0.35 μm or more, and is preferably 1.00 μm or less, more preferably 0.90 μm or less, even more preferably 0.80 μm or less. SEM Within the above range, the fine line printability of the conductive paste can be effectively improved. In addition, when it is important to obtain high conductivity in a conductive film obtained by firing the resin-curing conductive paste using the silver powder of the present invention at a low temperature, the D SEM can be 0.10 μm or more and 0.4 μm or less, and further, can be 0.20 μm or more and 0.35 μm or less.

[0040] The ignition loss (Ig-loss) value is preferably 0.3% by mass or more, more preferably 0.35% by mass or more, more preferably 1.2% by mass or less, more preferably 1.1% by mass or less, even more preferably 0.95% by mass or less, and even more preferably 0.8% by mass or less. If the ignition loss value is 0.3% by mass or more, the aggregation of the silver powder particles can be suppressed and the dispersibility can be improved. On the other hand, if the ignition loss value is less than 1.2% by mass, the deterioration of the resistance value due to excess impurities can be prevented. In addition, when it is important to obtain high conductivity for the conductive film obtained by firing the resin-type conductive paste using the silver powder of the present invention at a low temperature, the ignition loss value of the silver powder of the present invention can be 0.65% by mass or more and 1.2% by mass or less, and further, can be 0.7% by mass or more and 1.2% by mass or less.

[0041] The ratio of the ignition loss (Ig-loss) value to the BET specific surface area ("Ig-loss" / "BET specific surface area") is preferably 0.51 or more, and more preferably 0.52 or more. Also, it is preferably 1.0 or less, and more preferably 0.8 or less. Here, the ratio of the ignition loss (Ig-loss) to the BET specific surface area is the value of the ignition loss (Ig-loss) in the silver powder when the unit is mass%, and is expressed in units of m 2 / g, divided by the value of the BET specific surface area of ​​the silver powder. Note that, although the units of "Ig-loss" / "BET specific surface area" are omitted in this specification, the units are "mass% g / m 2 " If the "Ig-loss" / "BET specific surface area" is 0.51 or more, the combustion of the silver particle surface can be promoted. On the other hand, if the "Ig-loss" / "BET specific surface area" ratio exceeds 1.0, there is a risk of the opposite effect occurring due to the generation of voids caused by gas or shrinkage.

[0042] Here, the silver powder of the present invention contains a surface treatment agent. Specific examples of the surface treatment agent will be described later in the section entitled "Method of producing silver powder."

[0043] The silver powder of the present invention can be used in conductive pastes such as resin-curing conductive pastes and sintered conductive pastes without any particular limitations. However, since the silver powder of the present invention can obtain a low volume resistivity even when fired at a low temperature, it can be suitably used in resin-curing conductive pastes.

[0044] (Silver powder manufacturing method) The silver powder of the present invention can be produced by a method including, but not limited to, flowing a silver-containing solution through a flow path, adding a pH adjuster to the flow path at a pH adjuster addition position midway through the flow path, adding a complexing agent to the flow path at a complexing agent addition position downstream of the pH adjuster addition position, adding hydrazine to the flow path at a reducing agent addition position downstream of the complexing agent addition position, and reducing and precipitating silver powder within the flow path. In addition, in the above-mentioned method for producing silver powder, the silver-containing solution, pH adjuster, complexing agent, and hydrazine-based reducing agent are continuously supplied in this order and mixed quantitatively, thereby maintaining constant the rate of formation of the silver complex and the rate of reductive precipitation of silver powder, and thus enabling the specified silver powder to be obtained quantitatively and continuously.

[0045] The silver-containing solution is a solution that reacts with a complexing agent to form a silver complex, and a solution containing a silver salt can be used. Examples of the solution include aqueous solutions of silver nitrate, silver chloride, silver formate, silver oxalate, and silver sulfate, and an aqueous solution of silver nitrate is preferred from the viewpoint of availability.

[0046] From an economical viewpoint, the silver concentration of the silver-containing solution is preferably 0.01 mol / L or more, and more preferably 0.05 mol / L or more. On the other hand, the silver concentration of the silver-containing solution is preferably 0.5 mol / L or less, and more preferably 0.3 mol / L or less, from the viewpoints of ensuring the interparticle distance of the particles after reduction precipitation and suppressing aggregation.

[0047] The flow rate in this embodiment is a value obtained by dividing the flow rate of the solution by the cross-sectional area of ​​the tube, assuming that the tube is filled with liquid. The time elapsed between specific positions is obtained by dividing the length between positions by the flow rate. From the viewpoints of productivity and monodisperse particle formation, the flow rate of the silver-containing solution is preferably 0.45 m / s or more, more preferably 0.65 m / s or more, and even more preferably 1.00 m / s or more. From the viewpoints of aggregation suppression and monodisperse particle formation, the flow rate is preferably 3.20 m / s or less, more preferably 2.70 m / s or less, and even more preferably 2.00 m / s or less.

[0048] In the above-mentioned method for producing silver powder, the silver-containing solution is passed through a flow path, and a pH adjuster is added to the flow path at a pH adjuster addition position in the flow path, thereby adjusting the pH of the silver-containing solution. This makes it possible to effectively adjust the particle size of the silver powder. As the pH adjuster, general alkaline or acidic pH adjusters such as sodium hydroxide, potassium hydroxide, sodium carbonate, and nitric acid can be used. The pH adjuster is usually added to the flow path in the form of an aqueous solution of the pH adjuster. The amount of pH adjuster added is appropriately adjusted according to the particle size of the silver powder to be produced.

[0049] In the above-mentioned method for producing silver powder, a complexing agent is added to the flow path at a complexing agent addition position downstream of the pH adjuster addition position to form a silver complex. The complexing agent is usually added to the flow path in the form of an aqueous solution of the complexing agent.

[0050] Examples of the complexing agent include ammonia, ammonium salts, citric acid, acetic acid, etc., and among these, ammonia is preferred. Ammonia can be added as aqueous ammonia. For example, when aqueous ammonia is added as a complexing agent, a silver ammine complex is formed, which is preferable because it can be easily reduced by hydrazine.

[0051] From an economical viewpoint, the concentration of the aqueous ammonia is preferably 0.35 mol / L or more, more preferably 0.50 mol / L or more, and is preferably 16.2 mol / L or less, more preferably 15.1 mol / L or less, and even more preferably 10.0 mol / L or less.

[0052] The amount of ammonia added per mole of silver is preferably 2.10 moles or more, and more preferably 2.20 moles or more. On the other hand, the amount of ammonia added per mole of silver is preferably 10.00 moles or less, and more preferably 8.00 moles or less.

[0053] The flow velocity of the complexing agent added at the complexing agent addition position is preferably 0.40 m / sec or more, more preferably 0.60 m / sec or more, even more preferably 1.00 m / sec or more, and is preferably 3.20 m / sec or less, more preferably 2.70 m / sec or less, even more preferably 2.00 m / sec or less.

[0054] When a complexing agent other than ammonia is used, the concentration, amount added and flow rate can be similar to those described above, taking into consideration the amount of complexing agent relative to the amount of silver required to form a complex.

[0055] In the above-mentioned method for producing silver powder, a hydrazine-based reducing agent is added to the flow path at a reducing agent addition position downstream of the complexing agent addition position, thereby reducing and precipitating the silver powder. The hydrazine-based reducing agent includes hydrazine, hydrazine hydrate, hydrazine carbonate, hydrazine sulfate, phenylhydrazine, etc., and is preferably hydrazine or hydrazine carbonate, and more preferably hydrazine. By using hydrazine, silver powder having a desired particle size can be stably obtained. Usually, the hydrazine-based reducing agent is added to the flow path in the form of an aqueous solution.

[0056] From the viewpoint of a uniform reduction reaction, the concentration of hydrazine in the aqueous hydrazine solution is preferably 0.025 mol / L or more, more preferably 0.05 mol / L or more, even more preferably 0.10 mol / L or more, and is preferably 3.3 mol / L or less, more preferably 2.0 mol / L or less, and even more preferably 1.0 mol / L or less. From the viewpoint of a uniform reduction reaction, the concentration of the hydrazine-based reducing agent in the aqueous hydrazine-based reducing agent solution is preferably 0.025 mol / L or more, more preferably 0.05 mol / L or more, even more preferably 0.10 mol / L or more, and is preferably 3.3 mol / L or less, more preferably 2.0 mol / L or less, and even more preferably 1.0 mol / L or less.

[0057] The amount of hydrazine added per mole of silver is preferably such that substantially no unreacted silver is generated, and is preferably 0.26 moles or more, and more preferably 0.28 moles or more. On the other hand, the amount of hydrazine added per mole of silver is preferably 0.88 moles or less, more preferably 0.75 moles or less, and even more preferably 0.50 moles or less, in order not to add more reducing agent than necessary. The amount of the hydrazine reducing agent added per mole of silver is preferably 0.26 moles or more, and more preferably 0.28 moles or more, so that substantially no unreacted silver is generated. On the other hand, the amount of hydrazine-based reducing agent added per mole of silver is preferably 0.88 moles or less, more preferably 0.75 moles or less, and even more preferably 0.50 moles or less, in order not to add more reducing agent than necessary.

[0058] In the production method of the present invention, the flow velocity of the silver complex solution immediately before adding the reducing agent to the flow path is preferably 0.50 m / sec or more, more preferably 0.75 m / sec or more, and even more preferably 1.0 m / sec or more from the viewpoint of productivity, and is preferably 3.5 m / sec or less, more preferably 3.0 m / sec or less, and even more preferably 2.0 m / sec or less from the viewpoint of suppressing aggregation and forming monodisperse particles.

[0059] The flow rate of the reducing agent when it is added to the flow path is preferably 0.5 times or more, more preferably 0.8 times or more, the flow rate of the silver complex solution immediately before the reducing agent. Also, in order to prevent the liquid flow toward the wall surface of the pipe from increasing and the mixing efficiency from decreasing, the flow rate is preferably 2.5 times or less, more preferably 2.0 times or less, and even more preferably 1.5 times or less.

[0060] In the above-mentioned method for producing silver powder, a hydrazine-based reducing agent is added to the site where the silver complex has been formed, so the time required for the silver-containing solution to flow from the complexing agent addition position to the reducing agent addition position (the elapsed time obtained by dividing the length from the complexing agent addition position to the reducing agent addition position by the flow rate of the silver complex solution immediately before the reducing agent is added) is preferably 0.1 seconds or more, and more preferably 0.5 seconds or more. On the other hand, if the time that has elapsed since the formation of the complex is long, the stability of the silver complex increases and the reduction reaction may not proceed as easily. Therefore, in order to ensure the freshness of the silver complex when the reducing agent is added, the elapsed time is preferably within 10.0 seconds, and more preferably within 5.0 seconds.

[0061] In the above-mentioned method for producing silver powder, a surface treatment agent can be added to the flow path between the complexing agent addition position and the reducing agent addition position, or downstream of the reducing agent addition position. The addition of the surface treatment agent is advantageous in that it suppresses the aggregation of the reduced and precipitated silver powder. The addition is preferably carried out at a point between the complexing agent addition position and the reducing agent addition position.

[0062] Examples of the surface treatment agent include fatty acids, fatty acid salts, surfactants, organic metals, chelating agents, protective colloids, etc. The surface treatment agent can be used in an amount of 0.3% by mass or more and 1.3% by mass or less based on the silver in the silver-containing solution. The surface treatment agent may be used in the form of an emulsion, solution, etc.

[0063] (1)Fatty acid Examples of fatty acids include propionic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, acrylic acid, oleic acid, linoleic acid, arachidonic acid, and ricinoleic acid.

[0064] (2) Fatty acid salts Examples of fatty acid salts include metal salts of the fatty acids described above in (1). Examples of metals include lithium, sodium, potassium, barium, magnesium, calcium, aluminum, iron, cobalt, manganese, lead, zinc, tin, strontium, zirconium, silver, and copper.

[0065] (3) Surfactants Examples of the surfactant include anionic surfactants such as alkylbenzene sulfonates and polyoxyethylene alkyl ether phosphates, cationic surfactants such as aliphatic quaternary ammonium salts, amphoteric surfactants such as imidazolinium betaine, and nonionic surfactants such as polyoxyethylene alkyl ethers and polyoxyethylene fatty acid esters.

[0066] Examples of the organic metal include acetylacetone tributoxyzirconium, magnesium citrate, diethyl zinc, dibutyl tin oxide, dimethyl zinc, tetra-n-butoxyzirconium, triethyl indium, triethyl gallium, trimethyl indium, trimethyl gallium, monobutyl tin oxide, tetraisocyanate silane, tetramethyl silane, tetramethoxy silane, monomethyl triisocyanate silane, silane coupling agents, titanate-based coupling agents, and aluminum-based coupling agents.

[0067] (5) Chelating agents Chelating agents include imidazole, oxazole, thiazole, selenazole, pyrazole, isoxazole, isothiazole, 1H-1,2,3-triazole, 2H-1,2,3-triazole, 1H-1,2,4-triazole, 4H-1,2,4-triazole, 1,2,3-oxadiazole, 1,2,4-oxadiazole, 1,2,5-oxadiazole, 1,3,4-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiadiazole, 1,2,5-thiadiazole, Examples of the chelating agent include diazole, 1,3,4-thiadiazole, 1H-1,2,3,4-tetrazole, 1,2,3,4-oxatriazole, 1,2,3,4-thiatriazole, 2H-1,2,3,4-tetrazole, 1,2,3,5-oxatriazole, 1,2,3,5-thiatriazole, indazole, benzimidazole, benzotriazole, and the like, as well as salts of these chelating agents, and polycarboxylic acids including dicarboxylic acids such as succinic acid, malonic acid, glutaric acid, and adipic acid.

[0068] (6) Protective colloids Examples of protective colloids include peptides, gelatin, albumin, gum arabic, prothalbic acid, risalbic acid, glue, and the like.

[0069] As the surface treatment agent, from the viewpoint of ease of modification of the silver particle surface, (1) fatty acids are preferred, and among them, stearic acid is preferred. (1) The fatty acid is preferably in the form of an emulsion, such as a stearic acid emulsion.

[0070] In the above-mentioned method for producing silver powder, the temperature of the silver complex solution immediately before the addition of the reducing agent is preferably 20° C. or higher, and more preferably 30° C. or higher, from the viewpoint of the reactivity of the reduction reaction. On the other hand, the temperature of the liquid flowing through the flow path is preferably 65° C. or less, and more preferably 60° C. or less, from the viewpoint of operability.

[0071] In the above-mentioned method for producing silver powder, a mixer may be used to apply spiral rotation in the axial direction of the flow path to mix the liquids.

[0072] In the above-mentioned method for producing silver powder, the liquid containing the reduced and precipitated silver powder (hereinafter also referred to as "silver powder-containing liquid") is discharged outside the flow path and recovered, thereby obtaining the silver powder. The silver powder-containing liquid is usually obtained in the form of a slurry or a dispersion.

[0073] The time from the addition of the reducing agent to the release of the silver powder-containing liquid outside the flow path is preferably 1 second or more, and more preferably 2 seconds or more, so that the completion of the reduction reaction can be anticipated. On the other hand, the time from the addition of the reducing agent to the release of the silver powder-containing liquid outside the flow path is preferably 10 seconds or less, and more preferably 5 seconds or less, in order to prevent the silver powder-containing liquid from remaining in the piping.

[0074] The silver powder-containing liquid discharged outside the flow path is filtered and washed with water to obtain a lumpy cake that contains silver powder and water and has almost no fluidity. The desired silver powder can be obtained by drying this cake in a dryer such as a forced circulation air dryer, a vacuum dryer, or an airflow dryer. The drying can be accelerated by replacing the water in the cake with a lower alcohol or the like. The cake can be subjected to a dry crushing treatment, a surface smoothing treatment, etc. The dry crushing treatment can be carried out using, for example, a sample mill, a blender, a coffee mill, a multipurpose mixer, etc. The surface smoothing treatment can be carried out by mechanically colliding particles with each other using a high-speed stirrer. Thereafter, a classification process may be performed to remove aggregates of silver powder larger than a predetermined particle size. Furthermore, the cake may be dried, crushed and classified using an integrated device capable of performing drying, crushing and classification (such as Dry Meister or Micron Dryer manufactured by Hosokawa Micron Corp.).

[0075] Below, an example of a silver powder manufacturing apparatus that can be used in the above-mentioned silver powder manufacturing method is described with reference to the drawings, but the method for manufacturing the above-mentioned silver powder is not limited to the method using this silver powder manufacturing apparatus. Below, an example of a silver powder manufacturing apparatus that can be used in the manufacturing method of the present invention is described with reference to the drawings.

[0076] FIG. 1 is an external perspective view of an example of a silver powder manufacturing apparatus. In FIG. 1, the silver powder manufacturing apparatus 1 has a pipe 2 for flowing a silver-containing solution, a pH adjuster supply pipe 7 for supplying a pH adjuster, a complexing agent supply pipe 6 located downstream of the pH adjuster supply pipe 7 and supplying a complexing agent, a surface treatment agent supply pipe 5 located downstream of the complexing agent supply pipe 6 and supplying a surface treatment agent, and a reducing agent adding member 10 located downstream of the surface treatment agent supply pipe 5 and supplying a hydrazine-based reducing agent as a reducing agent. The reducing agent adding member 10 is eccentrically connected to the reducing agent supply pipes 4a and 4b. The silver powder manufacturing apparatus 1 in FIG. 1 is provided with a surface treatment agent supply pipe 5 between the complexing agent supply pipe 6 and the reducing agent adding member 10, but the surface treatment agent supply pipe 5 may be arranged downstream of the reducing agent adding member 10.

[0077] Fig. 2A is a cross-sectional view perpendicular to the flow path of the silver complex solution at the center positions of the reducing agent supply pipes 4a and 4b of the reducing agent addition member 10 in Fig. 1. Fig. 2B is a cross-sectional view in the horizontal direction and the flow path of the silver complex solution, and is a cross-sectional view taken along line AA in Fig. 2A. Fig. 2C is a cross-sectional view in the horizontal direction and the flow path of the silver complex solution, and is a cross-sectional view taken along line BB in Fig. 2A.

[0078] In FIG. 2A, a gap 13 is provided along the outer periphery of the tube 2 which serves as a flow path for the silver complex solution, and the gap 13 is connected to the inside of the tubes of the reducing agent supply pipes 4a and 4b. As shown in FIG. 2C, which is a cross-sectional view of line BB in FIG. 2A, the downstream side of the flow path for the silver complex solution in the gap 13 is connected to a slit section 12 having an opening 11 facing radially outward along the inner circumference of the tube 2. Then, as shown in FIG. 2B, which is a cross-sectional view of line AA in FIG. 2A, when the reducing agent is poured into the gap 13 from the inside of the reducing agent supply pipes 4a and 4b, the reducing agent reaches the slit section 12 through the gap 13, and the reducing agent enters the tube 2 from the opening 11 of the slit section 12 approximately perpendicularly (for example, 75 degrees or more and 105 degrees or less) from the entire circumference of the tube 2, and is added to the silver complex solution. Here, the angle at which the reducing agent enters the flow path for the silver complex solution is the angle at which the axial direction of the tube 2 intersects with the opening direction of the opening 11 through which the reducing agent enters the tube 2. The opening direction can be considered to be the direction along the wall surface near the opening of slit portion 12 as shown in FIG. 2B.

[0079] The flow rate of the reducing agent when it is added to the flow path of the silver complex solution can be controlled by the flow rate of the reducing agent flowing through the reducing agent supply pipes 4a and 4b and the total area of ​​the openings 11. By controlling the flow rate of the reducing agent within the above-mentioned range, the reaction between the silver complex and the reducing agent can be carried out quickly, thereby making it possible to obtain silver powder with a narrow particle size distribution.

[0080] The width of the opening 11 of the slit portion 12 in Fig. 2B and Fig. 2C is referred to as the slit width. The slit width is preferably narrower than the diameter of the reducing agent supply pipe in order to reduce the total area of ​​the opening 11. The shape of the gap 13 and the slit portion 12 that allows the addition of the reducing agent to the flow path from multiple directions and that can form a slit width narrower than the diameter of the reducing agent supply pipe is not limited to the structure of Fig. 2A to C, and various modifications are possible. In addition, the opening 11 of the slit portion 12 can be modified to be a plurality of through holes instead of being provided around the entire circumference of the pipe 2.

[0081] The number of reducing agent supply pipes for feeding the reducing agent into the reducing agent adding member 10 may be one or more, and it is also preferable that there are two or more. When there are two or more reducing agent supply pipes, the flow paths of the reducing agent connecting the reducing agent supply pipes to the opening 11 may be opposed to each other or eccentric. In Figs. 2A to 2C, the reducing agent supply pipes 4a and 4b are connected eccentrically to each other with respect to the center of the pipe 2, and the flow paths of the reducing agent supply pipes 4a and 4b are connected to a slit portion 12 having an opening 11. When connecting a plurality of reducing agent supply pipes, if at least two reducing agent supply pipes are eccentric to each other, the reducing agent can be caused to flow into the opening 11 of the slit portion 12 while rotating the outer periphery of the flow path (pipe 2) of the silver complex solution in one direction. When the reducing agent rotates around the outer periphery of the flow path of the silver complex solution, the flow rate of the reducing agent toward the opening 11 may be adjusted by changing the cross-sectional area of ​​the flow path of the reducing agent (gap 13 or slit portion 12).

[0082] (Resin curing conductive paste) The resin-curing conductive paste of the present invention contains the silver powder of the present invention described above. In the metal powder contained in the resin-curing conductive paste, the proportion of the silver powder of the present invention in the total amount of metal powder may be 20 to 100%. It is also preferable that the metal powder other than the silver powder of the present invention contains silver powder having a particle size (D50) larger than that of the silver powder of the present invention. Since the resin-curing conductive paste of the present invention contains the silver powder of the present invention, a low volume resistivity can be obtained even when fired at a low temperature. The resin-curing conductive paste of the present invention usually contains the silver powder of the present invention, a resin, and a solvent. The resin-curing conductive paste of the present invention may further contain optional components other than the silver powder, the resin, and the solvent (hereinafter, sometimes referred to as "other components").

[0083] The resin is not particularly limited, and examples thereof include silicone resin, epoxy resin, acrylic resin, polyester resin, polyimide resin, polyurethane resin, phenoxy resin, cellulose resin (ethyl cellulose, hydroxypropyl cellulose, etc.), etc. These may be used alone or in any combination of two or more kinds in any ratio.

[0084] The solvent is not particularly limited, and examples thereof include alcohol-based solvents such as terpineol, butyl carbitol, texanol, ethylene glycol, diethylene glycol, and glycerin, ester-based solvents such as butyl carbitol acetate and ethyl acetate, and hydrocarbon-based solvents such as toluene, xylene, and cyclohexane. These may be used alone or in any combination of two or more kinds in any ratio.

[0085] Examples of other components include dispersants, surfactants, viscosity modifiers, slip agents, and the like.

[0086] The method for producing the resin-curing conductive paste is not particularly limited, and may be a method of mixing the silver powder of the present invention, an organic binder, a solvent, and any other components. The mixing method is not particularly limited, and may be, for example, a self-revolving mixer, ultrasonic dispersion, a disperser, a three-roll mill, a ball mill, a bead mill, a two-axis kneader, or the like.

[0087] The resin curing type conductive paste of the present invention can be applied to a substrate to form a coating film by, for example, screen printing, offset printing, printing such as photolithography, dipping, etc. The coating film may be formed into a predetermined pattern shape by photolithography using a resist.

[0088] The conductive film can be formed by heating the coating film to cure it. Heat curing may be performed in air or in a non-oxidizing atmosphere such as nitrogen.

[0089] The resin-curing conductive paste of the present invention can obtain a low volume resistivity even when fired at a low temperature, and therefore can be suitably used in the manufacture of heterojunction (HJT) solar cells and the like in which electrodes and conductor patterns are formed by heating at a relatively low temperature. EXAMPLES

[0090] 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. In addition, the BET specific surface area, true density, and average primary particle diameter D SEM The particle size distribution, ignition loss (Ig-loss), quantitative amount of the surface treatment agent, oxygen amount and carbon amount of the silver powder, carbon amount derived from the surface treatment agent, and crystallite size were measured or calculated by the methods described above.

[0091] Example 1 Silver powder was produced using a silver powder production apparatus 1 shown in FIG. 1 and FIGS. 2A to 2C. A 0.160 mol / L aqueous silver nitrate solution was introduced into tube 2 (inner diameter 20 mm) at a flow rate of 23.35 L / min at a liquid temperature of 50°C, and a 0.024 mol / L aqueous nitric acid solution was introduced into the coaxial double tube pH adjuster supply tube 7 (inner diameter 6 mm) at a flow rate of 2.13 L / min to adjust the pH, and 4.500 mol / L aqueous ammonia as a complexing agent was introduced into the coaxial double tube complexing agent supply tube 6 (inner diameter 6 mm) at a flow rate of 2.33 L / min to generate a silver ammine complex in tube 2. A surface treatment agent (0.10 mass% Cellosol 920 (manufactured by Chukyo Yushi Co., Ltd., containing 15.5 wt% stearic acid) was introduced at a flow rate of 2.19 L / min from a surface treatment agent supply pipe 5 (inner diameter 6 mm) upstream of the reducing agent addition member 10. The amount of the silver nitrate aqueous solution was such that the silver concentration in the total liquid volume after adding the pH adjuster, complexing agent, reducing agent, and surface treatment agent was 0.115 mol / L. A 0.500 mol / L aqueous hydrazine solution was introduced as a reducing agent from the entire circumference of the slit portion 12 (slit width 0.44 mm, tube inner diameter 20.6 mm) of the reducing agent addition member 10 at a flow rate of 2.55 L / min to precipitate silver powder. The flow rate of the reducing agent entering from the slit portion with a slit width of 0.44 mm was 1.49 m / sec, the flow rate of the silver ammine complex just before the addition of the reducing agent in the tube 2 with an inner diameter of 20.6 mm where the reducing agent enters was 1.50 m / sec, and the ratio of the flow rate of the complex to the flow rate of the reducing agent (complex flow rate / reducing agent flow rate) was 1.01. The operating time of the silver powder production apparatus (the time from the start to the stop of introduction of the reducing agent to the silver ammine complex after the flow of the silver ammine complex into which the surface treatment agent was introduced stabilizes) was 616 seconds. Note that the slurry generated before the flow of the silver ammine complex stabilized was received in a separate container and separated from the silver powder of the present invention. In the above, it took 0.5 seconds from the silver nitrate aqueous solution flow path inlet to the nitric acid aqueous solution addition position, 0.5 seconds from the nitric acid aqueous solution addition position to the ammonia water addition position, 2.12 seconds (2.1 m) from the ammonia water addition position to the hydrazine aqueous solution addition position, and 0.12 seconds from the surface treatment agent addition position to the hydrazine aqueous solution addition position. The temperature of the silver ammine complex aqueous solution immediately before the hydrazine aqueous solution addition position was 47.2°C.

[0092] The silver powder-containing slurry was discharged from tube 2. The time from the addition of the hydrazine aqueous solution to the release was approximately 2 seconds. After the reduction reaction had stabilized, the silver powder-containing slurry was recovered, and the solid matter obtained by solid-liquid separation was washed with pure water to remove impurities in the solid matter. The end point of this washing could be determined by the electrical conductivity of the water after washing, and washing was continued until this electrical conductivity was 0.5 mS / m or less. After that, it was dried to obtain 3.8 kg of silver powder.

[0093] The silver powder obtained above was milled twice for 90 seconds in a sample mill (SK-M10, manufactured by Kyoritsu Riko Co., Ltd.) using 120 g of the silver powder, to obtain the silver powder according to Example 1.

[0094] The measurement results and the like for the silver powder according to Example 1 are shown in Table 3. Also, an SEM photograph (20,000 times magnification) of the silver powder according to Example 1 is shown in FIG.

[0095] (Example 2 and Example 3) Silver powders of Examples 2 and 3 were produced in the same manner as Example 1, except that the conditions were changed as shown in Tables 1 and 2. Measurement results and the like for the silver powders of Examples 2 and 3 are shown in Table 3. SEM photographs (20,000x magnification) of the silver powders of Examples 2 and 3 are shown in Figs. 4 and 5.

[0096] Example 4 A 0.070 mol / L aqueous silver nitrate solution was introduced into tube 2 (inner diameter 20 mm) at a flow rate of 23.35 L / min at a liquid temperature of 50°C, and a 0.016 mol / L aqueous sodium carbonate solution was introduced through the coaxial double tube pH adjuster supply tube 7 (inner diameter 6 mm) at a flow rate of 2.13 L / min to adjust the pH, and 3.773 mol / L aqueous ammonia as a complexing agent was introduced through the coaxial double tube complexing agent supply tube 6 (inner diameter 6 mm) at a flow rate of 2.33 L / min to produce a silver ammine complex in tube 2. From the surface treatment agent supply pipe 5 (inner diameter 6 mm) upstream of the reducing agent adding member 10, 0.08 mass % of the surface treatment agent (Cellosol 920 (manufactured by Chukyo Yushi Co., Ltd., containing 15.5 wt % stearic acid) was introduced at a flow rate of 2.19 L / min. The amount of the silver nitrate aqueous solution was such that the silver concentration in the total liquid volume after the addition of the pH adjuster, complexing agent, reducing agent, and surface treatment agent was 0.050 mol / L. A 0.240 mol / L aqueous solution of hydrazine carbonate as a reducing agent was introduced at a flow rate of 2.55 L / min from the entire circumference of the slit portion 12 (slit width 0.44 mm, tube inner diameter 20.6 mm) of the reducing agent addition member 10 to precipitate silver powder. The flow rate of the reducing agent entering from the slit portion with a slit width of 0.44 mm was 1.49 m / sec, the flow rate of the silver ammine complex just before the addition of the reducing agent in the tube 2 with an inner diameter of 20.6 mm at the position where the reducing agent enters was 1.50 m / sec, and the ratio of the flow rate of the complex to the flow rate of the reducing agent (complex flow rate / reducing agent flow rate) was 1.01. The operating time of the silver powder production apparatus (the time from the start to the stop of introduction of the reducing agent to the silver ammine complex after the flow of the silver ammine complex into which the surface treatment agent was introduced stabilizes) was 83 seconds. Note that the slurry generated before the flow of the silver ammine complex stabilizes was received in a separate container and separated from the silver powder of the present invention. In the above, it took 0.5 seconds from the silver nitrate aqueous solution inlet to the position where the sodium carbonate aqueous solution was added, 0.5 seconds from the sodium carbonate aqueous solution addition position to the position where the ammonia water was added, 2.12 seconds (2.1 m) from the ammonia water addition position to the position where the hydrazine carbonate aqueous solution was added, and 0.12 seconds from the surface treatment agent addition position to the position where the hydrazine carbonate aqueous solution was added. The temperature of the silver ammine complex aqueous solution immediately before the position where the hydrazine carbonate aqueous solution was added was 46.5°C.

[0097] The silver powder-containing slurry was discharged from tube 2. The time from the addition of the aqueous hydrazine carbonate solution to the release was approximately 2 seconds. After the reduction reaction had stabilized, the silver powder-containing slurry was collected, and the solid matter obtained by solid-liquid separation was washed with pure water to remove impurities in the solid matter. The end point of this washing can be determined by the electrical conductivity of the water after washing. The washing was continued until the electrical conductivity was 0.5 mS / m or less, and then the slurry was dried to obtain 0.24 kg of silver powder.

[0098] The silver powder obtained in Example 4 was subjected to the same pulverization treatment as in Example 1. The measurement results and the like for the silver powder according to Example 4 are shown in Table 3. Moreover, an SEM photograph (20,000 times magnification) of the silver powder according to Example 4 is shown in FIG.

[0099] Comparative Example 1 To 3233.4 g of an aqueous silver nitrate solution containing 40.99 g (0.38 mol) of silver, 124.65 g of industrial ammonia water having a concentration of 28% by mass (corresponding to 5.4 molar equivalents of ammonia per mol of silver) was added to obtain an aqueous silver ammine complex solution. 2.28g of a 20% by mass aqueous sodium hydroxide solution was added to this silver ammine complex aqueous solution, and the liquid temperature was adjusted to 25°C. Then, 111.17g of a 7.3% by mass aqueous hydrazine solution was added while stirring to obtain a slurry containing silver particles. Furthermore, 12.69g of a 1.55% by mass stearic acid emulsion was added to the obtained slurry containing silver particles and stirred. Then, stirring was stopped to allow the silver particles to settle, and the liquid in which the silver particles had settled was filtered, washed with water until the electrical conductivity of the liquid after passing water was 0.5mS / m or less, and dried in a vacuum at 73°C.

[0100] The silver powder obtained by repeating the above silver powder production three times was milled twice for 90 seconds using a sample mill (SK-M10, manufactured by Kyoritsu Riko Co., Ltd.) with 120 g of silver charged, to obtain the silver powder of Comparative Example 1.

[0101] The measurement results and the like for the silver powder according to Comparative Example 1 are shown in Table 3. Also, an SEM photograph (20,000 times magnification) of the silver powder according to Comparative Example 1 is shown in FIG.

[0102] Comparative Example 2 To 3,374.7 g of an aqueous silver nitrate solution containing 45.32 g (0.42 moles) of silver, 3.3 g of a 60% by mass aqueous nitric acid solution was added, and then 76.5 g of industrial ammonia water with a concentration of 28% by mass (corresponding to 3 molar equivalents of ammonia per mole of silver) was added to obtain an aqueous silver ammine complex solution. The temperature of this silver ammine complex aqueous solution was adjusted to 35°C. Then, while stirring, 20.57 g of a 1.1 mass% aqueous solution of benzotriazole sodium was added as an azole (0.5 mass% of benzotriazole sodium was added relative to silver) to obtain a first liquid. Then, 142.7 g of a 5.6 mass% aqueous solution of hydrazine containing water was added as a reducing agent to the first liquid to obtain a slurry containing silver fine particles as a second liquid. Furthermore, 1.55 mass% The stearic acid emulsion (17.54 g) was added and stirred. After that, the stirring was stopped to allow the silver particles to settle, and the liquid in which the silver particles had settled was filtered, 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.

[0103] The silver powder obtained by repeating the above silver powder production three times was milled twice for 90 seconds in a sample mill (SK-M10, manufactured by Kyoritsu Riko Co., Ltd.) using 120 g of silver powder, to obtain the silver powder of Comparative Example 2.

[0104] The measurement results for the silver powder of Comparative Example 2 are shown in Table 3. Moreover, an SEM photograph (magnification: 20,000) of the silver powder according to Comparative Example 1 is shown in FIG.

[0105] [Table 1]

[0106] [Table 2]

[0107] [Table 3]

[0108] (Paste Evaluation) <Volume resistivity> First, a resin-curing conductive paste was prepared using the silver powders obtained in Examples 1 and 4 and Comparative Examples 1 and 2. Specifically, the silver powder to be evaluated and AG-5-54F (D 50 :2.9μm, BET:0.21m 2 / g, TAP: 6.1g / cm 3 ) were mixed in a mass ratio of 5:5 to obtain a mixed silver powder. Then, 91.92 parts by mass of the mixed silver powder, 3.87 parts by mass of the first epoxy resin (EP4901E manufactured by ADEKA), 0.97 parts by mass of the second epoxy resin (JER1009 manufactured by Mitsubishi Chemical), 0.24 parts by mass of the curing agent (boron trifluoride monoethylamine complex manufactured by Wako Pure Chemical Industries), and 3.00 parts by mass of the solvent (BCA: butyl carbitol acetate) were taken out and put into a propellerless self-rotating type stirring and degassing device (VMX-N360 manufactured by EME Co., Ltd.), stirred and mixed at 1200 rpm for 30 seconds, and then the mixture was kneaded by passing it through a three-roll (80S manufactured by EXAKT Co., Ltd.) with a roll gap of 100 μm to 20 μm to obtain a resin-cured conductive paste before viscosity adjustment. Furthermore, the required amount of BCA was added to the resin-curing conductive paste before viscosity adjustment to obtain a conductive paste after viscosity adjustment with a viscosity of 300 Pa s. The viscosity of the resin-curing conductive paste was adjusted by adding small amounts of BCA to the resin-curing conductive paste before viscosity adjustment and successively measuring the viscosity. Using the obtained resin-curing conductive paste, 10 lines each with line widths (design widths) of 15 μm and 19 μm were produced on a screen printing plate (#480 mesh) for evaluation. The squeegee speed during printing was 350 mm / sec, and printing was performed twice. Next, the coating was dried at 150° C. for 10 minutes using an air circulation dryer, and then cured by heating at 200° C. for 30 minutes to form a line-shaped conductive film (wiring). The volume resistivity of the resulting conductive film was measured. The line resistance (Ω) was measured using a digital multimeter (manufactured by ADC Corporation) with measuring terminals attached to both ends of the conductive film. The line resistance value was the average value of 20 line patterns (10 lines printed twice) (excluding those deemed to be broken, as described below). When measuring the line resistance, a measurement value of 100 kΩ or higher was deemed to be a break. In addition, a laser microscope (Keyence Corporation, VK-X1000) was used to measure the shape of the wiring in the line width direction at 10 locations (5 locations printed twice) and calculate the average cross-sectional area of ​​the wiring. From the measured line resistance and the above cross-sectional area, the volume resistivity was calculated according to the following formula (1). Volume resistivity [Ω cm] = line resistance [Ω] × cross-sectional area [cm 2 ]÷Line length [cm]···(1) In addition, the line length (design length) was set to 150 mm in the measurement of the line resistance. The measurement results of the volume resistivity are shown in Table 4.

[0109] [Table 4]

[0110] As is clear from Table 4, if the silver powder contains a surface treatment agent, has a ratio of oxygen to BET specific surface area of ​​0.11 or more, and has a crystallite size of 30 nm or more and 38 nm or less, when made into a conductive paste, it is possible to impart a low volume resistivity even when fired at a low temperature. [Industrial Applicability]

[0111] According to the present invention, it is possible to provide a silver powder that, when made into a conductive paste, can impart a low volume resistivity even when fired at a low temperature. Furthermore, according to the present invention, it is possible to provide a resin-curing type conductive paste that can obtain a low volume resistivity even when fired at a low temperature. [Explanation of symbols]

[0112] 1 Silver powder manufacturing equipment 2 tubes 4a Reducing agent supply pipe 4b Reducing agent supply pipe 5 Surface treatment agent supply pipe 6 Complexing agent supply pipe 7 pH adjuster supply pipe 10 Reducing agent additive material 11 Aperture 12 Slit section 13. Gap

Claims

1. Contains a surface treatment agent, The ratio of the amount of oxygen to the BET specific surface area is 0.11 or more, A silver powder having a crystallite size of 30 nm or more and 38 nm or less.

2. The silver powder according to claim 1, having a ratio of Ig-loss to BET specific surface area of ​​0.51 or more.

3. Cumulative 50% diameter D based on volume by laser diffraction method ５０ is 0.1 μm or more and 1.0 μm or less, Volume-based cumulative 90% diameter D by laser diffraction method ９０ The silver powder according to claim 1, wherein the average particle size is 1.2 μm or less.

4. BET specific surface area is 0.90m ２ / g or more 2.50m ２ The silver powder according to claim 1, wherein the silver content is 0.01 to 0.15 wt %.

5. The silver powder according to any one of claims 1 to 4, which is used in a resin-curing type conductive paste.

6. A resin-curing conductive paste comprising the silver powder according to any one of claims 1 to 4.

Images