JP2005146408A - Superfine silver particulate-stuck silver powder, and method for producing the superfine silver particulate-stuck silver powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide silver powder having low temperature sintering properties which have not been obtained heretofore, and further dispersibility closer to single dispersion in which the flocculation of particulate matters is hardly caused. <P>SOLUTION: Superfine silver particulate-stuck silver powder obtained by sticking superfine silver particles with a particle diameter in a nanoorder onto the surfaces of the particulate matters of silver powder is adopted. Further, in the superfine particulate-stuck silver powder, the particulate matters have high dispersibility which has not been obtained heretofore. In the method for producing the superfine silver particulate-stuck silver powder, silver powder slurry obtained by adding silver powder to a dispersion medium is admixed with silver nitrate and a neutralizer, they are stirred and dissolved to precipitate superfine silver oxide particles on the surfaces of the particulate matters of the silver powder, washing is performed, and ultraviolet irradiation is performed thereto, and the superfine silver oxide particles are reduced into superfine silver particles. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The invention according to the present application relates to fine silver particle-attached silver powder and a method for producing the fine silver particle-attached silver powder.

  Conventionally, silver ink (paste) is used for circuit formation by cofiring with a ceramic substrate, as well as for firing at a relatively high temperature. Applications exist such that they are mixed and cured with various resin components such as circuits, via hole filling, and component mounting adhesives. In applications such as the latter, it has been common to obtain electrical conductivity only by contact between the powder particles without sintering the powder particles of the silver powder as the conductive filler.

  However, in recent years, electrical resistance to conductors formed using silver powder and high connection reliability to achieve electrical resistance have been required. There has been an increasing demand for silver ink or silver paste that sinters certain silver powder itself to exhibit conductivity. In general, in order to meet such demands, it is natural that atomization of silver powder as a conductive filler is necessary in order to lower the sintering temperature.

  As described in Patent Document 2, a conventional silver powder is produced by a wet reduction process in which a silver ammine complex aqueous solution is produced with a silver nitrate solution and aqueous ammonia, and an organic reducing agent is added thereto. It has been used after being processed into a paste. And the silver ink containing a silver nanoparticle which is disclosed by patent document 3 has been advocated in order to ensure the low temperature sintering property more than this conventional silver powder.

JP 2001-107101 A JP 2002-334618 A JP 2002-324966 A

  However, with metal powders containing silver powder, it is generally said that it is difficult to achieve both the atomization of powder particles and the dispersibility in the sense that the powder particles are closer to monodispersion. For example, in the case of a silver ink containing silver nanoparticles as disclosed in Patent Document 1, a large amount of a dispersant is added as a protective colloid in order to stabilize the dispersibility of the nanoparticles. It is common. In such a case, the decomposition temperature of the dispersant is generally higher than the sintering temperature of the silver nanoparticles, and the low-temperature sintering characteristics of the silver nanoparticles themselves cannot be fully utilized.

  In addition, the silver nanoparticle silver ink has a much lower filler content than conventional pastes, so it is difficult to form a thick film even if it is easy to form a thin film. This makes it difficult to apply a wiring circuit having a large circuit cross section at a level that can be used for a simple power supply circuit or a low resistance circuit. Furthermore, in adhesive applications for mounting parts, there are strict requirements for conductivity and adhesive strength, and it is indispensable to add a certain amount or more of resin that exhibits strong adhesive strength by curing, so there are parts that can not be handled with silver nanoparticle ink There were many.

On the other hand, it goes without saying that the silver powder at the level that has been used in conventional general silver pastes has limited low-temperature sinterability due to its particle size. Because particulate silver powder obtained by the conventional manufacturing method is greater than the average particle diameter D _IA is typically 0.6μm of the primary particles, the average particle size D ₅₀ by laser diffraction scattering particle size distribution measurement method 1. The actual situation was that the degree of aggregation exceeded 0 μm and the D ₅₀ / D _IA exceeded 1.7. Therefore, it has been unsuitable for forming circuits with fine pitches in recent years.

  Also, in the circuit formation with silver paste when using conventional silver powder, there are many non-firing or low-temperature sintering type applications where the heating temperature is 300 ° C. or less, and in order to obtain high sintering performance at low temperature, Low crystalline silver powder has been preferred. However, in order to obtain a low crystalline silver powder, a reaction system having a high reduction must be employed in terms of production conditions, and as a result, only a silver powder with remarkable agglomeration was obtained although the crystallinity was low. Accordingly, there has been a demand in the market for the supply of silver powder that has low-temperature sinterability and has a fine dispersibility that is fine and unprecedented, and that has good dispersibility with little aggregation of the powder.

  On the other hand, the silver powder has been required to have a small amount of impurities. That is, the above-described wet reduction process is employed for the production of silver powder, and the reducing agent used in the process remains on the surface of the silver powder particles. Therefore, as long as the conventional manufacturing method is adopted, it is an inevitable problem. And if the impurity amount of silver powder increases, the electrical resistance of the conductor formed using the silver powder will increase.

  As a result, there has been a demand for silver powder that has an unprecedented low-temperature sinterability, is fine and highly dispersed, and has a low impurity content to achieve low resistance. It is.

  Thus, the present inventors have eagerly studied a new method for atomizing the conventional silver powder itself, but the current technical level has been limited. However, the inventors think that when the silver powder particles are sintered, it is sufficient that the surface vicinity of the powder particles is sintered and connected. In that case, if only the surface layer of the conventional silver powder particles could be easily sintered, it was thought that low-temperature sinterability could be obtained even with the conventional silver powder. Hereinafter, the present invention will be described by dividing into “fine silver particle-attached silver powder” and “manufacturing method of fine silver particle-attached silver powder”.

<Silver powder with fine silver particles>
The fine silver particle-attached silver powder according to the present invention is "fine silver particle-attached silver powder in which fine silver particles are attached to the surface of the silver powder." That is, as shown in FIG. 1, the surface of the silver powder 2 as the core material is covered with finer silver particles 3. Thus, the presence of the fine silver particles 3 on the surface of the silver powder 2 allows the fine silver particles 2 having a small particle diameter to exhibit low-temperature sintering properties without depending on the shape and size of the core powder. Therefore, sintering of the adjacent powder particles of the fine silver particle-attached silver powder 1 is facilitated.

  The “fine silver particles” referred to here are silver nanoparticles having a particle size of the order of nm, and are present only on the surface of the silver powder 2 as a core material. As described above, when silver nanoparticles themselves are used in silver ink, a large amount of dispersant having a decomposition temperature higher than the sintering temperature of silver nanoparticles is added to stabilize the dispersibility of the nanoparticles. In general, the low temperature sintering characteristics of the silver nanoparticles themselves cannot be fully utilized. However, by attaching finer fine silver particles 3 to the surface of the silver powder 2 as the core material, the silver nanoparticles can be sintered at a low temperature regardless of the size and shape of the silver powder particles in the core material. This makes it possible to fully extract the characteristics. Therefore, even if the particle shape of the silver powder of the core material is substantially spherical or flake powder having a powder particle diameter of several tens of μm, it can be used as the core material.

  The silver powder used as the core material can be of a substantially spherical shape, a flat shape such as a flake shape, etc., and by considering the manufacturing conditions in the existing manufacturing method, the particle size distribution is sharp to some extent It is possible to ensure dispersibility. As a result, even if the silver nanoparticles are poorly dispersible when viewed as a single substance, the silver nanoparticles are used as fine silver particle-attached silver powder that is attached to the surface of the core silver powder, so that the handleability is excellent and the paste When processing, a large amount of protective colloid is not required, and the same silver particle content as that of conventional silver paste can be achieved, and the coating film can be made thicker when the circuit shape is drawn. It becomes.

  The fine silver particle-attached silver powder as described above has a sinterable temperature of 170 ° C. or lower and exhibits extremely good sintering characteristics. As a result, a silver paste (ink) is manufactured using this fine silver particle-attached silver powder, and when this is used to draw the shape of a circuit, etc., a circuit that can be used with a large current is obtained by increasing the film pressure. I can do it. Moreover, since it is easy to sinter the powder particles, electrical resistance reduction and conduction reliability as a conductor are greatly improved.

  The fine silver particle-attached silver powder according to the present invention uses silver powder as a core material. Therefore, the particle diameter and dispersibility of the fine silver particle-attached silver powder tend to be very dependent on the silver powder as the core material. That is, it is preferable to use the silver powder used for the core material within a range in which the particle size distribution and dispersibility can be secured at a high level. And it can be said that it is still good if it also has the condition that the amount of impurities that inhibit electric resistance is small. Therefore, as a result of intensive studies by the present inventors in pursuit of atomization of the silver powder itself, silver powder having the following powder characteristics could be obtained. And it was conceived that a very good product can be obtained by using this as a core material to produce fine silver particle-attached silver powder.

Its silver powder essentially has "a. An average particle diameter D _IA of the primary particles obtained by image analysis of scanning electron microscope images 0.6μm or less." The average particle diameter D _IA of "b. The primary particles, The degree of aggregation represented by D ₅₀ / D _IA using the average particle diameter D ₅₀ by the laser diffraction / scattering particle size distribution measurement method is 1.5 or less, and “c. The crystallite diameter is 10 nm or less.” It also has powder characteristics. Another silver powder is a. ~ C. In addition to the above powder characteristics, the powder characteristics of “d. Organic impurity content is 0.25 wt% or less in terms of carbon amount” are also provided. These two types of silver powder appear as a difference in impurity content by changing the production conditions. The silver powder having such powder characteristics is a fine silver powder having a level of dispersibility that cannot be obtained by a conventional manufacturing method. Hereinafter, the powder characteristics of the silver powder as the core material will be described.

a. Characteristics of an average particle diameter D _IA of the primary particles obtained by image analysis of scanning electron microscope images is that 0.6μm or less. Here, “average particle diameter D _IA of primary particles obtained by image analysis of scanning electron microscope image” refers to an observation image of silver powder observed with a scanning electron microscope (SEM) (core material in the present invention) In the case of fine silver powder used in the above, it is preferably observed at a magnification of 10,000 times, and in the case of conventional silver powder, it is preferably observed at a magnification of 3000 to 5000 times. In addition, image analysis of fine silver powder observed using a scanning electron microscope (SEM) in the present specification uses an IP-1000PC manufactured by Asahi Engineering Co., Ltd. A circular particle analysis is performed to obtain an average particle diameter _DIA . Since the average particle diameter _DIA obtained by image processing the observation image of the fine silver powder is obtained directly from the SEM observation image, the average particle diameter of the primary particles is surely captured. D _IA of fine silver powder referred to in the present invention, mostly in the range of 0.01μm~0.6μm unless observing present inventors although incoming reality that can be confirmed even more of fine particle size There is also a lower limit that is not clearly stated.

b. Since the fine silver powder used for the core material in the present invention exhibits a high dispersibility that is not found in conventional silver powders, “aggregation” is used as an index indicating the dispersibility. The degree of aggregation referred to in the present invention is a value represented by D ₅₀ / D _IA using the average particle diameter D _IA of the primary particles and the average particle diameter D ₅₀ obtained by the laser diffraction / scattering particle size distribution measurement method. It is. Here, D ₅₀ is a particle size at a weight accumulation of 50% obtained by using a laser diffraction scattering type particle size distribution measuring method, and the value of this average particle size D ₅₀ is truly one of powder particles. It can be said that the average particle diameter is calculated by capturing the aggregated particles as one particle (aggregated particle) rather than directly observing one diameter. That is, it is considered that the actual silver powder is not a so-called monodispersed powder in which individual particles are completely separated, but a plurality of powders are usually aggregated. However, little aggregation state of granular, closer to monodisperse, the value of the average particle diameter D ₅₀ is becoming small things usually. D ₅₀ of the fine silver powder used in the present invention is in the range of about 0.25 μm to 0.80 μm, and becomes a fine silver powder having an average particle diameter D ₅₀ in a range that could not be obtained at all by the conventional production method. In this specification, the laser diffraction / scattering particle size distribution measurement method is performed by mixing 0.1 g of fine silver powder with ion-exchanged water and dispersing for 5 minutes with an ultrasonic homogenizer (US-300T manufactured by Nippon Seiki Seisakusho). It is measured using a laser diffraction / scattering particle size distribution measuring apparatus Micro Trac HRA 9320-X100 (Leeds + Northrup).

On the other hand, “the average particle diameter D _IA of primary particles obtained by image analysis of a scanning electron microscope image” is an image analysis of an observation image of silver powder observed using a scanning electron microscope (SEM). The average particle size of the primary particles is reliably captured without considering the aggregation state.

As a result, the present inventors have found that, by using the average particle diameter D _IA obtained by an average particle size D ₅₀ and the image analysis of a laser diffraction scattering particle size distribution measuring method, the value calculated by D _{50 /} D _IA It was taken as the degree of aggregation. That is, assuming that the values of D ₅₀ and D _IA can be measured with the same accuracy in fine silver powder of the same lot, the value of D ₅₀ that reflects the presence of an agglomerated state in the measured value is considered in the above theory. Is considered to be larger than the value of _DIA . At this time, the value of D ₅₀ approaches the value of D _IA as much as the aggregation state of the fine silver powder particles disappears, and the value of D ₅₀ / D _{IA as} the degree of aggregation approaches 1. Become. When the degree of aggregation becomes 1, it can be said to be a monodisperse powder having no agglomerated state of particles.

  Therefore, the present inventors examined the correlation between the degree of aggregation and the viscosity of the fine silver powder paste produced using the fine silver powder of each aggregation degree, the surface smoothness of the conductor obtained by sintering, and the like. As a result, it was found that a very good correlation was obtained. As can be seen from this, it can be determined that if the degree of aggregation of the fine silver powder is controlled, the viscosity of the fine silver powder paste produced using the fine silver powder can be freely controlled. Moreover, it has been found that if the degree of aggregation is 1.5 or less, it is possible to keep fluctuations in the viscosity of the fine silver powder paste, the surface smoothness after the sintering process, etc. in a very narrow region. In addition, the more the aggregated state is resolved, the higher the film density of the conductor obtained by sintering with the fine silver powder, and the lower the electrical resistance of the resulting sintered conductor. It becomes.

Further, when the degree of aggregation is actually calculated, a value less than 1 may be indicated. This makes the D _IA used for calculating the degree of aggregation is considered because it is assumed that true sphere, but in theory is not become a value less than 1, in reality, since not a true sphere It appears that a cohesion value of less than 1 is obtained.

  c. The characteristic is that the crystallite diameter is 10 nm or less, and the crystallite diameter and the sinterable temperature have a very close relationship. In other words, if silver powders having the same average particle diameter are compared with each other, the smaller the crystallite diameter, the lower the sintering possible. Therefore, the surface energy is large because it is fine like the fine silver powder according to the present invention, and it has a small crystallite diameter of 10 nm or less, thereby lowering the sinterable temperature of the fine silver powder itself as the core material. It can be done. Here, although no lower limit is set for the crystallite diameter, it is because a certain measurement error occurs depending on the measurement apparatus, measurement conditions, and the like. In addition, it is difficult to obtain high reliability for the measurement value in the range where the crystallite diameter is less than 10 nm. If the lower limit value is deliberately determined, it is about 2 nm obtained as a result of the present inventors' research. I think there is.

  d. The characteristic is that the organic impurity content is 0.25 wt% or less in terms of carbon amount. Here, the carbon content is used as an index of the organic impurity content, and is used as a measure of the amount of impurities adhering to the fine silver powder. The carbon content at this time is measured by mixing EMIA-320V manufactured by Horiba Seisakusho, mixing 0.5 g of fine silver powder, 1.5 g of tungsten powder, and 0.3 g of tin powder, and placing this in a magnetic crucible and burning. -Measured by infrared absorption method. The carbon content of the silver powder obtained by the conventional manufacturing method includes a carbon amount exceeding 0.25 wt%, no matter how strong the cleaning is.

  The fine silver powder according to the present invention has the a. ~ C. Or a. ~ D. Therefore, it can be understood that it is an unprecedented fine silver powder. Moreover, even if the fine silver powder used for the core material in the present invention is seen from the property of the sinterable temperature, it can be said that the fine silver powder can start sintering at a low temperature of 240 ° C. or lower. The sinterable temperature in the present invention is the lowest temperature at which a silver paste is produced using each silver powder, a circuit is drawn on an alumina substrate, and sintering is possible to the extent that resistance can be measured. Further, although there is no particular lower limit for the sinterable temperature, considering the research conducted by the present inventors and general technical common sense, 170 ° C. is considered when considering the fine silver powder itself as the core material. It is almost impossible to obtain a sinterable temperature lower than 1, and is considered to be a temperature corresponding to the lower limit.

Furthermore, as an effect having the above-described powder characteristics, the tap filling density of the fine silver powder according to the present invention is as high as 4.0 g / cm ³ or more. The tap packing density here is measured by a method in which 200 g of fine silver powder is precisely weighed, placed in a 150 cm ³ graduated cylinder, repeatedly tapped 1000 times with a stroke of 40 mm, and then the volume of the fine silver powder is measured. It is. The tap filling density has a theoretically fine particle size, and the higher the dispersibility without aggregation of powder particles, the higher the value obtained. Considering that the tap packing density of the conventional silver powder is less than 4.0 g / cm ³ , the fine-grained silver powder according to the present invention also supports that it is very fine and has excellent dispersibility. It is.

  The fine silver powder used as the core material described above is fine and has excellent dispersibility, and the fine silver powder itself has a low-temperature sinterability of 240 ° C. or lower. Then, by attaching silver nanoparticles to the surface of the fine silver powder, it is finer and more dispersible than conventional silver powder. It becomes a fine silver particle-attached silver powder having performance.

<Method for producing fine silver particle-attached silver powder>
The method for producing the fine silver particle-attached silver powder according to the present invention will be described below, roughly divided into two methods, ie, production method 1 and production method 2. The fine silver powder suitable for use in each of the production method 1 and the production method 2 will be described as a production method of the fine silver powder.

Production method 1: This production method is “contacting a silver powder and a solution containing a silver complex obtained by mixing and dissolving silver nitrate and a complexing agent, and adding a reducing agent to the fine silver particles. Is a method for producing fine silver particle-attached silver powder, characterized by being deposited on the surface of the powder grains of

There is no limitation in particular about the silver powder amount in a slurry when it is set as a silver powder slurry here. However, unless the amount of silver powder in the slurry is clarified, the amount of chemical used in the production cannot be clearly indicated. Therefore, this production method 1 will be described as a method for obtaining fine silver particle-attached silver powder by attaching silver nanoparticles to the powder grain surface in a silver powder slurry in which 50 g of silver powder is dispersed in 1 liter of pure water. In addition, this silver powder presupposes using the silver powder whose average particle diameter _DIA of the primary particle obtained by the image analysis of a scanning electron microscope image is 1 micrometer or less.

  First, “a solution containing a silver complex obtained by mixing and dissolving silver nitrate and a complexing agent” will be described. In order to process the amount of silver powder under the above conditions, 8 to 26 g of silver nitrate is used. This is because, when silver nitrate is less than 8 g, a practically sufficient coverage with fine silver cannot be obtained, and even when silver nitrate exceeds 26 g, the coverage is not further improved. The complexing agents used here are sulfites and ammonium salts. When potassium sulfite is used, it is used in the range of 50 g to 150 g. When the amount of potassium sulfite added is less than 50 g, the complexation of silver cannot be performed completely and a silver complex cannot be completely formed. Even if the amount of potassium sulfite added exceeds 150 g, the amount of complexing agent sufficient to form a silver complex is already exceeded, and the reaction rate for obtaining a silver complex is not increased, which is uneconomical. Because it becomes. This silver nitrate is dissolved in 1 liter of pure water, a complexing agent is added thereto, and the mixture is sufficiently stirred to obtain a solution containing a silver complex.

  The above-mentioned 50 g of silver powder is added to the solution containing the silver complex obtained as described above, and sufficiently stirred. Then, a reducing agent is added thereto to cause a reduction reaction, and fine silver powder having a nano-order particle diameter is uniformly deposited on the surface of the silver powder. The reducing agent used at this time is hydrazine, DMAB, SBH, formalin, or hypophosphorous acid. In the case of using hydrazine, 5 g to 50 g of hydrazine is dissolved in 200 ml or less (including 0 ml) of pure water, and this is added within 60 minutes (including the case where it is added all at once). If the amount of hydrazine is less than 5 g, the reduction is not successful and the fine silver powder cannot uniformly coat the surface of the silver powder. And even if the amount of hydrazine exceeds 50 g, it does not say that the reduction rate is particularly fast, and it only impairs the economy.

  And the liquid temperature at the time of performing a reductive reaction is the range of room temperature-45 degreeC. When the liquid temperature exceeds 45 ° C., the reduction reaction becomes too fast, and the precipitation of the fine silver powder on the surface of the silver powder tends to be nonuniform, and the particle size distribution of the resulting fine silver particle-attached silver powder is deteriorated. And in the range of the said reducing agent density | concentration, it is preferable to employ | adopt the range for about 5 minutes-40 minutes for addition time. When the reaction time is less than 5 minutes, there is a tendency for the aggregation of the produced particles to become strong. On the other hand, if an addition time of 40 minutes is employed, a sufficiently uniform coating can be achieved.

  When the fine silver powder is reduced and deposited on the surface of the silver powder as described above, the fine silver particle-attached silver powder according to the present invention is obtained by filtering, washing, dehydrating and drying. Various methods can be used for the filtering, washing, dehydration, and drying referred to here, and there is no particular limitation on the method and conditions.

Manufacturing method 2: This manufacturing method is “adding silver nitrate and a neutralizing agent to a silver powder slurry in which silver powder is added to a dispersion medium, stirring and dissolving it, and precipitating fine silver oxide particles on the surface of the silver powder and washing. "A method for producing fine silver particle-attached silver powder, characterized by reducing the fine silver oxide particles to fine silver particles by ultraviolet irradiation."

There is no limitation in particular about the amount of silver powder in a slurry when it is set as a silver powder slurry here. However, unless the amount of silver powder in the slurry is clarified, the amount of chemical used in the production cannot be clearly indicated. Therefore, a method for obtaining fine silver particle-attached silver powder by attaching silver nanoparticles to the powder grain surface of a silver powder slurry in which 50 g of silver powder is dispersed in 1500 g of a dispersion medium will be described. In addition, this silver powder presupposes using the silver powder whose average particle diameter _DIA of the primary particle obtained by the image analysis of a scanning electron microscope image is 1 micrometer or less.

  The “silver powder slurry in which silver powder is added to a dispersion medium” will be described. The dispersion medium used here is ethylene glycol (including monoethylene glycol, diethylene glycol, triethylene glycol), butanediol (including 1,4-butanediol, 1,2-butanediol, 2,3-butanediol), Glycerin. Here, the case where ethylene glycol is used as the dispersion medium will be described. Therefore, the silver powder slurry is obtained by adding 50 g of the silver powder to 1500 g of ethylene glycol and stirring.

  To the silver powder slurry obtained as described above, silver nitrate and a neutralizing agent are added and dissolved by stirring to precipitate fine silver oxide particles on the surface of the silver powder. The silver nitrate and the neutralizing agent at this time are preferably used in an aqueous solution in which silver nitrate or the neutralizing agent is dissolved. This is to prevent the drug from being unevenly distributed in the silver powder slurry so that the neutralization reaction occurs uniformly in the silver powder slurry. The silver nitrate aqueous solution used at this time is preferably a silver nitrate aqueous solution in which 2.50 g to 33.34 g (silver nitrate concentration corresponds to 3 wt% to 40 wt%) of silver nitrate is dissolved in 500 g of pure water. When the amount of silver nitrate is less than 2.50 g, the amount of silver oxide that uniformly coats the surface of the silver powder does not precipitate. Even if the amount of silver nitrate exceeds 33.34 g, the amount of silver oxide adhering to the surface of the silver powder does not change significantly, but rather the particle size distribution and dispersibility of the powder are deteriorated.

  An alkali metal salt such as sodium hydroxide or potassium hydroxide can be used as the neutralizing agent. The amount of the neutralizing agent added is naturally dependent on the amount of silver nitrate to be neutralized. When sodium hydroxide is used, it is used in a range of 0.588 g to 7.840 g corresponding to the amount of silver nitrate. Will be. Since sodium hydroxide at this time is also preferably used as an aqueous solution, it is used as an aqueous sodium hydroxide solution dissolved in 500 g of pure water.

  When the fine silver oxide powder is adhered to the surface of the silver powder as described above, the silver powder with the fine silver oxide powder is then washed. This washing must remove the solution used in the reaction and remove water sufficiently. Therefore, it is most preferable to use a combination of water washing and alcohol washing. Washing with water is preferably performed by washing with as much water as possible at least 500 g or more with respect to the silver powder with fine silver oxide powder obtained under the conditions described above. This is to remove the impurity amount as much as possible. And in order to remove a water | moisture content more reliably, alcohol washing is performed. For this alcohol cleaning, ethyl alcohol, methyl alcohol, isopropyl alcohol or the like can be used, and there is no particular limitation on the amount of use, and it is sufficient to use an amount capable of sufficiently removing water.

  When the above washing is completed, ultraviolet irradiation is performed immediately without drying, and the fine silver oxide particles on the surface of the fine particles are reduced to fine silver particles, thereby obtaining fine silver particle-attached silver powder. Here, by performing ultraviolet irradiation, rapid conversion of fine silver oxide to fine silver is promoted, and non-uniform reduction does not occur. The wavelength of ultraviolet rays used here is not particularly limited in a strict sense, and for example, an ultraviolet lamp used for sterilization can be used. When this ultraviolet irradiation is completed, it is sufficiently dried to obtain the fine silver particle-attached silver powder according to the present invention.

Preferred production method of silver powder as core material : Here, production of silver powder suitable for use as the core material of the fine silver particle-attached silver powder according to the present invention described above (in which the powder particles are substantially spherical) will be described. To do. Wherein the manufacturing method of the silver powder to be described, the above-described "a. An average particle diameter D _IA of the primary particles obtained by image analysis of scanning electron microscope images 0.6μm or less.", Mean "b. The primary particles The degree of aggregation represented by D ₅₀ / D _IA is 1.5 or less using the particle size D _IA and the average particle size D ₅₀ obtained by the laser diffraction scattering particle size distribution measurement method. ”,“ C. The silver powder described here can be referred to as a finely divided silver powder as compared with the silver powder produced using a conventional silver nitrate aqueous solution.

  This silver powder is produced by mixing an aqueous silver nitrate solution with a complexing agent to obtain a silver complex aqueous solution, which is contacted with an organic reducing agent to cause silver particles to be reduced and precipitated, filtered, washed, and dried. In the method for producing silver powder, the feature is that the amount of reducing agent, the amount of silver nitrate, and the amount of complexing agent, which are diluted after addition, are used. Conventionally, the reducing agent solution and the silver complex aqueous solution are generally mixed together in a tank. Therefore, in order to generally set the silver concentration to 10 g / l or more, a large amount of silver nitrate, reduction If the amount of the agent and the amount of the complexing agent were not added, productivity for the scale of the equipment could not be ensured. In the following description, a method using ammonia water as a complexing agent will be described as an example in order to express the specificity more clearly.

  The most important feature in the production method according to the present invention is that the concentration of the organic reducing agent after the silver ammine complex aqueous solution and the organic reducing agent are contact-reacted is low, and remains adsorbed on the surface of the generated silver powder, It is in the point which can reduce the organic reduction material taken in the inside of a powder grain in the growth process of a grain. Therefore, it is most preferable to maintain the organic reducing agent concentration at 1 g / l to 3 g / l while the silver concentration in the mixed solution is 1 g / l to 6 g / l.

  Here, there is a proportional relationship between the silver concentration and the amount of the reducing agent, and it is natural that a higher amount of silver powder can be obtained as the silver concentration is higher. However, if the silver concentration here exceeds 6 g / l, the precipitated silver particles tend to be coarse, and the particle size is not different from that of conventional silver powder, and has high dispersibility as referred to in the present invention. It becomes impossible to obtain fine silver powder. On the other hand, when the silver concentration here is less than 1 g / l, an extremely fine powder can be obtained as a fine silver powder, but it becomes too fine and the oil absorption increases, resulting in an increase in paste viscosity. It is necessary to increase the amount, and the film density of the finally formed sintered conductor is low, and the electric resistance tends to increase. In addition, the required industrial productivity is not satisfied.

  And in order to obtain the fine silver powder according to the present invention with a good yield, maintaining the organic reducing agent concentration at 1 g / l to 3 g / l while the silver concentration is set to 1 g / l to 6 g / l. This is the most suitable condition. Here, the organic reducing agent concentration of 1 g / l to 3 g / l is selected as the most suitable range for obtaining fine silver powder in relation to the silver concentration of the silver ammine complex aqueous solution. When the concentration of the organic reducing agent exceeds 3 g / l, the amount of the reducing agent added to the silver ammine complex aqueous solution decreases, but the progress of aggregation of silver powder particles that are reduced and precipitated begins to become remarkable and is contained in the powder particles. The amount of impurities (in this specification, the amount of impurities is regarded as the carbon content) begins to increase rapidly. On the other hand, when the concentration of the organic reducing agent is less than 1 g / l, the total amount of reducing agent to be used increases, the amount of wastewater treatment increases, and industrial economic efficiency is not satisfied.

  The “organic reducing agent” mentioned here is hydroquinone, ascorbic acid, glucose and the like. Among these, it is desirable to selectively use hydroquinone as the organic reducing agent. In the present invention, hydroquinone is relatively excellent in reactivity as compared with other organic reducing agents, and can be said to have a reaction rate most suitable for obtaining a low crystalline silver powder having a small crystallite size.

  And it is also possible to use another additive in combination with the said organic reducing agent. The additives mentioned here are glues such as gelatin, amine-based polymer agents, celluloses, etc., which stabilize the reduction precipitation process of silver powder and at the same time serve as a certain dispersant. It is desirable to use it appropriately and selectively depending on the organic reducing agent, the type of process, and the like.

Then, a method of precipitating the above manner was silver ammine complex solution thus obtained fine silver powder and a reducing agent are contacted reacting reduction, in the present invention, as shown in FIG. 2, silver ammine complex solution S ₁ is flow constant And a second flow path b that joins in the middle of the first flow path a, and the organic reducing agent passes through the second flow path b. and flowing the additive S ₂ as needed in the first flow path a, in contact mixed at the merging point m between the first flow path a and the second channel b, a method of reducing precipitation of silver particles (hereinafter, this It is desirable to adopt a method called “joint mixing method”.

  By adopting such a merging and mixing method, the mixing time of the two liquids is completed in the shortest time, and the reaction proceeds in a uniform state in the system, so that uniform-shaped powder particles are formed. Moreover, when the amount of the organic reducing agent when viewed as the whole solution after mixing is low, the amount of the organic reducing agent adsorbed and retained on the surface of the fine silver powder to be reduced and precipitated is reduced. As a result, it becomes possible to reduce the amount of impurities deposited on the fine silver powder obtained by filtration and drying. By reducing the amount of impurities deposited on the fine silver powder, the electrical resistance of the sintered conductor formed through the silver paste can be reduced.

  Furthermore, when silver nitrate aqueous solution and ammonia water are contact-reacted to obtain a silver ammine complex aqueous solution, a silver nitrate aqueous solution having a silver nitrate concentration of 2.6 g / l to 48 g / l is used, and a silver concentration of 2 g / l to 12 g. It is desirable to obtain a silver ammine complex aqueous solution of / l. Here, prescribing the concentration of the silver nitrate aqueous solution is synonymous with prescribing the amount of the silver nitrate aqueous solution, and it is considered that the silver concentration of the silver ammine complex aqueous solution is 2 g / l to 12 g / l. In addition, the concentration and amount of ammonia water added thereto are inevitably determined. At the present stage, a clear technical reason is not known, but by using a silver nitrate aqueous solution having a silver nitrate concentration of 2.6 g / l to 48 g / l, the best production stability is shown and the quality is improved. Stable fine-grained silver powder can be obtained.

  And the silver powder used as a core material is obtained by washing and drying. The cleaning here may be performed in combination with water cleaning and alcohol cleaning, or only alcohol cleaning may be used, and the cleaning method is not particularly limited. Also, there is no particular limitation on the drying method.

  And said a. Obtained by the said manufacturing method. ~ C. In order to have the powder characteristics of “d. Organic impurity content is 0.25 wt% or less in terms of carbon amount” at the same time, the cleaning method must be changed. Don't be. The cleaning method will be described below.

  In order to reduce the impurity content, cleaning is finally performed, which is very important. The cleaning at this time may be performed in combination with water cleaning and alcohol cleaning, or only alcohol cleaning may be used, but the cleaning at the time of cleaning with alcohol is strengthened. That is, 40 g of finely precipitated fine silver powder is usually washed with about 100 ml of pure water, and then washed with about 50 ml of alcohol. On the other hand, in the present invention, 200 kg or more per 1 kg of fine silver powder is washed with 5 L or more of excess alcohol when performing alcohol washing.

  Impurities can be reduced by such cleaning strengthening when the reaction solution between the silver ammine complex aqueous solution and the reducing agent in obtaining fine silver powder is used as a whole solution after mixing using a dilute concentration reaction system. This is because a technique for keeping the amount of the organic reducing agent low is employed.

  The fine silver particle-attached silver powder according to the present invention has a structure in which fine silver powder (silver nanoparticles) is further adhered to the surface of the silver powder, so that it has a low temperature sintering characteristic not seen in conventional silver powder. Will be demonstrated. In addition, the silver powder used for the core material of the fine silver particle-attached silver powder is particularly excellent by using a fine powder that is finer than ever, excellent in dispersibility, has a small amount of impurities, and is not found in conventional silver powder. In addition, it exhibits low temperature sintering characteristics.

  On the other hand, the method for producing fine silver particle-attached silver powder according to the present invention is excellent in operational stability of the process, and can produce the fine silver particle-attached silver powder very efficiently. Moreover, the silver powder used as a core material can be efficiently obtained by adopting the method for producing silver powder using the above-described dilute solution.

  Hereinafter, the best mode of the present invention will be described in detail while comparing with a comparative example. In the following examples, silver powder used as a core material was first manufactured. Further, fine silver particle-attached silver powder was produced, a silver paste was produced using this, a test circuit was formed, and specific resistance and sinterable temperature were measured.

Manufacturing method of silver powder used as core material : In this example, silver powder (having a substantially spherical shape) was first used as a core material. The manufacturing method is as follows.

  First, 63.3 g of silver nitrate was dissolved in 9.7 liters of pure water to prepare an aqueous silver nitrate solution. To this, 235 ml of 25 wt% aqueous ammonia was added all at once and stirred to obtain an aqueous silver ammine complex solution. It is.

  Then, this silver ammine complex aqueous solution is introduced into the first flow path a having an inner diameter of 13 mm shown in FIG. 2 at a flow rate of 1500 ml / sec, and the reducing agent is allowed to flow from the second flow path b at a flow rate of 1500 ml / sec. The fine silver powder was reduced and precipitated by contacting the mixture at a temperature of 0 ° C. As the reducing agent used at this time, an aqueous hydroquinone solution in which 21 g of hydroquinone was dissolved in 10 liters of pure water was used. Accordingly, the hydroquinone concentration at the end of mixing is about 1.04 g / l, which is a very dilute concentration.

  In order to fractionate 40 g of the fine silver powder obtained as described above, it is filtered using a Nutsche, washed with 100 ml of water and 600 ml of methanol, and further dried at 70 ° C. for 5 hours. I got.

  The powder characteristics of the silver powder obtained as described above correspond to Comparative Example 1 shown in Table 1, and are listed together with the powder characteristics of other Examples and Comparative Examples. Here, the measurement method and the like that are unknown in the above description will be described. The sinterable temperature in Table 1 is the lowest temperature at which a silver paste is produced using each silver powder, a circuit is drawn on an alumina substrate, and sintering is possible to the extent that resistance measurement is possible. The specific resistance was measured using a 1 mm wide circuit obtained by selecting and sintering in the range of ° C. Note that the observation of the sintering state with a scanning electron microscope was also used in determining whether the sintering was performed satisfactorily. In addition, the composition of the silver paste was 85% by weight of fine silver powder and 15% by weight of terpineol. In FIB analysis, the size of the precipitated crystal grains was measured and used to measure the crystallite diameter.

Production of fine silver particle-attached silver powder: Here, fine silver particle-attached silver powder was produced according to the above-described production method 1 using the silver powder obtained as described above as a core material.

  First, in order to attach fine silver particles to the surface of 50 g of the above silver powder, a “solution containing a silver complex obtained by adding silver nitrate and a complexing agent and dissolving by stirring” was prepared. Here, 17 g of silver nitrate was dissolved in 1 liter of pure water, and 86 g of potassium sulfite was added thereto as a complexing agent to form a silver complex, thereby preparing a solution containing the silver complex.

  The above-described 50 g of silver powder was added to the solution containing the silver complex obtained as described above and stirred for 1 minute. Then, a reducing agent was added thereto to cause a reduction reaction, and fine silver powder having a nano-order particle size was uniformly deposited on the surface of the silver powder. To this reducing agent, 10 g of hydrazine hydrazine was dissolved in 90 ml of pure water, added all at once, and a reduction reaction was performed at a liquid temperature of 40 ° C. for 10 minutes. When the fine silver powder was reduced and deposited on the surface of the silver powder as described above, the fine silver particle-attached silver powder according to the present invention was obtained by filtration, washing, dehydration and drying according to a conventional method.

  Using the fine silver particle-attached silver powder thus obtained, measurement of the same powder characteristics as that performed on the silver powder as the core material, and manufacturing a silver paste, forming a test circuit, the specific resistance and The sinterable temperature was measured. The results are shown in Table 1 as Example 1.

Manufacturing method of silver powder used as core material : In this example, silver powder (having a substantially spherical shape) was first used as a core material. The manufacturing conditions are as follows.

  In this example, the powder characteristics of fine silver powder obtained by producing fine silver powder using production conditions different from those of Example 1 were measured. Further, a silver paste was produced using fine silver powder, a test circuit was formed, and the conductor resistance and the sinterable temperature were measured.

  First, 63.3 g of silver nitrate was dissolved in 3.1 liters of pure water to prepare an aqueous silver nitrate solution. To this, 235 ml of 25 wt% aqueous ammonia was added all at once and stirred to obtain an aqueous silver ammine complex solution. It is.

  Then, this silver ammine complex solution is introduced into the first flow path a having an inner diameter of 13 mm shown in FIG. 2 at a flow rate of 1500 ml / sec, and the reducing agent is flowed from the second flow path b at a flow rate of 1500 ml / sec. The fine silver powder was reduced and precipitated by contacting the mixture at a temperature of 0 ° C. As the reducing agent used at this time, an aqueous hydroquinone solution in which 21 g of hydroquinone was dissolved in 3.4 liters of pure water was used. Therefore, the hydroquinone concentration at the end of mixing is about 3.0 g / l, which is a very dilute concentration.

  In the same manner as in Example 1, 40 g of the fine silver powder obtained as described above was filtered using Nutsche, washed with 100 ml of water and 600 ml of a large volume of methanol, and further 70 ° C. × 5 hours. Was dried to obtain a silver powder as a core material. The powder characteristics of the silver powder obtained as described above correspond to Comparative Example 2 shown in Table 1, and are listed together with the powder characteristics of other Examples and Comparative Examples.

Production of fine silver particle-attached silver powder: Here, fine silver particle-attached silver powder was produced according to the above-described production method 2 using the silver powder obtained as described above as a core material. Therefore, first, 1500 g of ethylene glycol was used as a dispersion medium, and 50 g of the above-described silver powder was added thereto and sufficiently stirred and dispersed to prepare a silver powder slurry.

  To the silver powder slurry obtained as described above, silver nitrate and a neutralizing agent are added and dissolved by stirring to precipitate fine silver oxide particles on the surface of the silver powder. First, silver nitrate is added. At this time, silver nitrate was added using a silver nitrate aqueous solution in which 16.67 g (silver nitrate concentration corresponding to 30 wt%) of silver nitrate was dissolved in 500 g of pure water. Then, a neutralizing agent is added and stirred sufficiently. For this neutralizing agent addition, a sodium hydroxide aqueous solution in which 3.92 g of sodium hydroxide was dissolved in 500 g of pure water was used. As described above, the fine silver oxide powder was adhered to the surface of the silver powder.

  Thereafter, the silver powder with fine silver oxide powder was separated by filtration and washed. This washing was performed using a combination of water washing and alcohol washing. First, it was washed with water. The washing with water at this time was performed by washing the silver powder with fine silver oxide powder obtained under the above conditions with an amount of water of 500 g, removing the impurity amount as much as possible, and dehydrating. Then, in order to remove moisture more reliably, alcohol cleaning was performed using 500 g of isopropyl alcohol.

  When the above washing was completed, ultraviolet irradiation was performed immediately without drying, and the fine silver oxide particles on the powder surface were reduced to fine silver particles. For UV irradiation, CL15-A, which is normally used as a sterilization lamp by Toshiba Corporation, is irradiated for 3 hours to promote rapid conversion of fine silver oxide to fine silver, and to prevent uneven reduction. It was. Thereafter, drying was performed according to a conventional method to obtain a fine silver particle-attached silver powder with a small amount of impurities according to the present invention.

  Using the fine silver particle-attached silver powder thus obtained, measurement of the same powder characteristics as that performed on the silver powder as the core material, and manufacturing a silver paste, forming a test circuit, the specific resistance and The sinterable temperature was measured. The results are shown in Table 1 as Example 2.

Production method of silver powder as a core material: In this example, the powder characteristics of silver powder obtained by producing silver powder having a large crystallite diameter (having a substantially spherical shape) using the production method shown below. It was measured. Further, a silver paste was produced using fine silver powder, a test circuit was formed, and the conductor resistance and the sinterable temperature were measured.

  First, 20 g of polyvinyl pyrrolidone is dissolved in 260 ml of pure water, 50 g of silver nitrate is further dissolved to prepare an aqueous silver nitrate solution, and 25 g of nitric acid is added all at once and stirred to obtain a silver-containing nitric acid solution. It was. The ascorbic acid concentration at the end of this mixing is about 36.0 g / l.

  On the other hand, 35.8 g of ascorbic acid as a reducing agent was added to 500 ml of pure water and dissolved to prepare a reducing solution.

  Then, the silver-containing nitric acid solution was put into a reaction vessel, and the reducing solution was added all at once, and the liquid temperature was maintained at 25 ° C., followed by stirring and reacting, whereby silver powder was reduced and precipitated.

  The fine silver powder obtained as described above is filtered using Nutsche, washed with 100 ml of water and 50 ml of methanol, and further dried at 70 ° C. for 5 hours to obtain a silver powder used as a core material. It was. The powder characteristics of this silver powder are listed as Comparative Example 3 in Table 1.

Production of fine silver particle-attached silver powder: Here, fine silver particle-attached silver powder was produced in the same manner as in Example 2 above, using the silver powder obtained as described above as a core material. Therefore, in order to avoid redundant description, a detailed description of the steps here is omitted.

  Using the fine silver particle-attached silver powder thus obtained, measurement of the same powder characteristics as that performed on the silver powder as the core material, and manufacturing a silver paste, forming a test circuit, the specific resistance and The sinterable temperature was measured. The results are shown in Table 1 as Example 3.

Method for producing flake silver powder as core material: In this example, flake-shaped silver powder was obtained by physically processing a substantially spherical silver powder, and this was used as the core material. The powder characteristics of this flake silver powder are shown in Table 2 as Comparative Example 4.

Production of fine silver particle-attached flake silver powder: Here, using the flake silver powder obtained as described above as a core material, fine silver particle-attached flake silver powder was produced according to the production method 1 described above. The manufacturing conditions at this time are the same as those in the first embodiment, and the description is omitted because they are duplicated.

  Using the obtained fine silver particle-attached flake silver powder, measurement of powder characteristics similar to that performed on the flake silver powder as a core material, and manufacturing a silver paste, forming a test circuit, Resistance and sintering temperature were measured. The results are shown in Table 2 as Example 4.

Comparative example

(Comparative Example 1)
The silver powder used as the core material described in Example 1 was used as it was as a comparative example. The powder characteristics and the like are shown as Comparative Example 1 shown in Table 1.

(Comparative Example 2)
The silver powder used as the core material described in Example 2 was used as it was as a comparative example. The powder characteristics and the like are shown as Comparative Example 2 shown in Table 1.

(Comparative Example 3)
The silver powder used as the core material described in Example 3 was used as it was as a comparative example. The powder characteristics and the like are shown as Comparative Example 3 shown in Table 1.

(Comparative Example 4)
The flake silver powder used as the core material described in Example 4 was used as it was as a comparative example. The powder characteristics and the like are shown as Comparative Example 4 shown in Table 1.

<Contrast Study between Examples and Comparative Examples> The above-described Examples 1 to 3 and Comparative Examples 1 to 3 will be compared with reference to Table 1.

In Table 1, the powder characteristics of each core material silver powder and fine silver particle-attached silver powder of Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, and Example 3 and Comparative Example 3 are compared. Then, even if fine silver particles are adhered, it can be seen that the powder characteristics of the core material hardly change. In particular, since the value of D _max hardly fluctuates before and after adhesion of the fine silver particles, it can be seen that the dispersibility of the silver powder of the core material is maintained even as the fine silver particle-attached silver powder. Therefore, it can be seen that it is very advantageous to use silver powder that is as fine and highly dispersed as possible for the silver powder used as the core material. In addition, in Table 1, although the crystallite diameter of fine silver particle adhesion silver powder is not described, it is because the crystallite diameter of the silver powder of a core material is maintained as it is.

  Next, when the sintered conductor characteristics of Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, and Example 3 and Comparative Example 3 are compared, the fine silver powder is adhered, whereby the sinterable temperature is increased. The temperature is so low that it cannot be considered by conventional common sense. In particular, in Examples 1 to 3, the sinterable temperature is 150 ° C. even though the powder characteristics of the core material and the fine silver particle-attached silver powder are different. On the other hand, in Comparative Examples 1 to 3, since there is no fine silver particle layer, it is greatly affected by powder characteristics, and in Comparative Example 3, it is impossible to measure specific resistance. . From the above, it can be said that the fine silver particle-attached silver powder according to the present invention can be sintered at low temperature without being affected by the powder characteristics of the core material by providing fine silver particles on the surface of the silver powder. is there.

Next, the above-described Example 4 and Comparative Example 4 will be compared with reference to Table 2. Regarding the powder characteristics of the core material flake silver powder and the fine silver particle-attached flake silver powder, powder characteristics different from those having the substantially spherical powder grains shown in Table 1 are extracted. The flake powder was changed in crystallite size by physical processing and was subjected to surface contamination by a lubricant used during physical processing, so measurement of the crystallite size and carbon content was omitted. Furthermore, the value of _DIA observed with a scanning electron microscope was also excluded from the measurement items because of the large fluctuation in one field of view, and the measured value by the laser diffraction scattering particle size distribution measurement method was mainly used.

In Table 2, when comparing the powder characteristics of each core material flake silver powder of Example 4 and Comparative Example 4 with fine silver particle-attached flake silver powder, even if fine silver particles are attached, the powder characteristics of the core material It is the same as in the case of the substantially spherical powder in Table 1 that there is no significant change. However, although it seems that the value of D _max is increased after the fine silver particles are adhered, it cannot be asserted that there is a very large variation in consideration of measurement errors.

  Next, when the sintered conductor characteristics of Example 4 and Comparative Example 4 are compared, the sinterable temperature is lowered by attaching fine silver powder. This is the same as in the first to third embodiments. From the above, the fine silver particle-attached flake silver powder according to the present invention can be sintered at a low temperature without causing a significant change in the powder characteristics of the core material by providing the fine silver particles on the surface of the flake silver powder. It can be said that a simple flake powder can be obtained.

  The fine silver particle-attached silver powder according to the present invention has a structure in which fine silver powder (silver nanoparticles) is further adhered to the surface of the silver powder, so that it has a low temperature sintering characteristic not seen in conventional silver powder. Will be demonstrated. Since it exhibits stable low-temperature sinterability as never before, it is expected to greatly expand the application field of silver powder, and the energy cost of the sintering process can be greatly reduced. In addition, the silver powder used for the core material of the fine silver particle-attached silver powder is particularly excellent by using a fine powder that is finer than ever, excellent in dispersibility, has a small amount of impurities, and is not found in conventional silver powder. In addition, low temperature sintering characteristics and low resistance sintered conductors can be formed.

  On the other hand, the method for producing fine silver particle-attached silver powder according to the present invention is excellent in operational stability of the process, and can produce the fine silver particle-attached silver powder very efficiently, enabling the supply of inexpensive and high-quality silver powder to the market. As such, it contributes to the expansion of the field of use of the silver powder with fine silver particles according to the present invention.

The schematic cross section of the powder grain of fine silver particle adhesion silver powder. The figure showing the mixing concept of silver ammine complex aqueous solution and a reducing agent.

Explanation of symbols

1 Fine silver particle-attached silver powder 2 Silver powder (core material)
3 Fine silver particles a First flow path b Second flow path m Merge point S ₁ Silver ammine complex aqueous solution S ₂ Organic reducing agent and additives as required

Claims (12)

Fine silver particle-attached silver powder in which fine silver particles are attached to the surface of silver powder. 2. The fine silver particle-attached silver powder according to claim 1, wherein the silver powder has a substantially spherical shape. Silver powder has the following a. ~ C. The fine silver particle-attached silver powder according to claim 2, comprising the following powder characteristics.
a. The average particle diameter D _IA of the primary particles obtained by image analysis of scanning electron microscope images 0.6μm or less.
b. The degree of aggregation represented by D ₅₀ / D _IA using the average particle diameter D _IA of the primary particles and the average particle diameter D ₅₀ obtained by a laser diffraction / scattering particle size distribution measurement method is 1.5 or less.
c. The crystallite diameter is 10 nm or less. Silver powder has the following a. ~ D. The fine silver particle-attached silver powder according to claim 2, comprising the following powder characteristics.
a. The average particle diameter D _IA of the primary particles obtained by image analysis of scanning electron microscope images 0.6μm or less.
b. The degree of aggregation represented by D ₅₀ / D _IA using the average particle diameter D _IA of the primary particles and the average particle diameter D ₅₀ obtained by a laser diffraction / scattering particle size distribution measurement method is 1.5 or less.
c. The crystallite diameter is 10 nm or less.
d. Organic impurity content is 0.25 wt% or less in terms of carbon content. The fine silver particle-attached silver powder according to claim 1, wherein the silver powder has a flat shape. Sinterable temperature is 170 degrees C or less, The fine silver particle adhesion silver powder in any one of Claims 1-5. A method for producing fine silver particle-attached silver powder according to any one of claims 1 to 6,
It is characterized by bringing silver powder into contact with a solution containing a silver complex obtained by mixing and dissolving silver nitrate and a complexing agent, and adding a reducing agent to precipitate fine silver particles on the surface of the silver powder. A method for producing fine silver particle-attached silver powder. The method for producing fine silver particle-attached silver powder according to claim 7, wherein the complexing agent is a sulfite or an ammonium salt. A method for producing fine silver particle-attached silver powder according to any one of claims 1 to 6,
Add silver nitrate and neutralizing agent to a silver powder slurry with silver powder added to the dispersion medium, stir and dissolve to precipitate fine silver oxide particles on the surface of the silver powder powder, wash, and then irradiate with ultraviolet rays to remove the fine silver oxide particles. A method for producing fine silver particle-attached silver powder, characterized in that it is reduced to fine silver particles. The method for producing fine silver particle-attached silver powder according to claim 9, wherein the neutralizing agent is one kind or two or more kinds of sodium hydroxide, potassium hydroxide, and ammonia water. In the manufacturing method of the fine silver particle adhesion silver powder in any one of Claims 1-4,
Silver powder is obtained by mixing a silver nitrate aqueous solution and a complexing agent to react to obtain a silver complex aqueous solution, contacting and mixing an organic reducing agent with the silver complex aqueous solution, and a silver concentration of 1 g / l in the mixed solution. Approx. 6 g / l, an organic reducing agent concentration maintained at 1 g / l to 3 g / l, silver particles are reduced and precipitated, the silver particles are separated by filtration, washed with water, and washed with an alcohol solution. A method for producing fine silver particle-attached silver powder, characterized by using spherical powder particles. In the manufacturing method of the fine silver particle adhesion silver powder in any one of Claims 1-4,
Silver powder is obtained by mixing a silver nitrate aqueous solution and a complexing agent to react to obtain a silver complex aqueous solution, contacting and mixing an organic reducing agent with the silver complex aqueous solution, and a silver concentration of 1 g / l in the mixed solution. It is obtained by maintaining the organic reducing agent concentration at ˜6 g / l and the organic reducing agent concentration at 1 g / l-3 g / l, reducing and precipitating silver particles, filtering the silver particles, washing with water, and washing with an excess alcohol solution. A method for producing fine silver particle-attached silver powder, characterized by using substantially spherical powder particles.

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