WO2005009651A1

WO2005009651A1 - Fine-grain silver powder and process for producing the same

Info

Publication number: WO2005009651A1
Application number: PCT/JP2004/010099
Authority: WO
Inventors: Takuya Sasaki; Masashi Kato; Katsuhiko Yoshimaru
Original assignee: Mitsui Mining & Smelting Co., Ltd.
Priority date: 2003-07-29
Filing date: 2004-07-15
Publication date: 2005-02-03
Also published as: TW200504166A; CA2534107A1; CN100455382C; TWI304832B; KR101132282B1; JP4489388B2; KR20060035781A; US20080138238A1; JP2005048236A; HK1092101A1; CN1826197A; DE112004001399T5

Abstract

Fine-grain silver powder that has a grain size of minuteness not known in the prior art, exhibiting dispersion close to monodispersion with reduced grain aggregation. For obtaining the fine-grain silver powder, an aqueous solution of silver ammine complex (S1) is caused to flow through given flow channel (hereinafter referred to as “first flow channel”). Second flow channel (b) is disposed so as to join the middle of the first flow channel (a), and an organic reducing agent optionally together with an additive (S2) is caused to flow through the second flow channel (b). At confluence (m) of the first flow channel (a) and the second flow channel (b), contact and mixing is carried out so as to effect reduction deposition. Thus, there is obtained fine-grain silver powder of such powder characteristics not known in the prior art that the average diameter of primary grain (DIA) obtained by an image analysis of scanning electron microscope images is 0.6 µm or less (a), the crystallite diameter 10 nm or less (b) and the sintering initiation temperature 240°C or below.

Description

Specification

Fine silver powder and method for producing the fine silver powder

Technical field

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

Background art

[0002] Conventionally, silver powder has been produced by a wet reduction process in which a silver ammine complex aqueous solution is produced from a silver nitrate solution and aqueous ammonia and an organic reducing agent is added thereto, as described in Patent Document 1. Was. In recent years, these silver powders have been mainly used for forming electrodes and circuits of chip components, plasma display panels, and the like.

[0003] Patent Document 1: JP 2001-107101 A

[0004] Therefore, the electrodes and circuits are required to be significantly finer in the circuits and electrodes to be formed, and are required to have higher densities and higher precision as well as higher reliability. I have.

Disclosure of the invention

Problems to be solved by the invention

[0005] While pressing, the average particle size D of the primary particles of the silver powder obtained by the conventional production method usually exceeds 0.6 m, and the particle size is measured by a laser diffraction scattering particle size distribution method. Flat

IA

The average particle size D exceeds l.O / z m, and the cohesion degree represented by D ZD exceeds 1.7.

50 50 IA

Met. Therefore, it is unsuitable for forming a circuit with a fine pitch in recent years, and has been a major cause of a decrease in product yield.

[0006] On the other hand, the following problems have arisen from the viewpoint of using silver powder. Conventionally, in the circuit formation using a silver base, the non-fired or low-temperature sintering type with a heating temperature of 300 ° C or less has been used in many cases. Silver powder has been favored. However, in order to obtain silver powder with low crystallinity, it is necessary to adopt a reaction system with fast reduction due to the production conditions.As a result, although the crystallinity is low, it is not possible to obtain an extremely agglomerated LV and silver powder. Helped. [0007] From these facts, in the field, the supply of silver powder that is unprecedented fine powder, has a dispersibility closer to monodispersion with less aggregation of powder, and is excellent in low-temperature sinterability. Has been required.

Means for solving the problem

[0008] Accordingly, the present inventors mixed and reacted a conventional silver nitrate aqueous solution and aqueous ammonia to obtain a silver ammine complex aqueous solution, and added a reducing agent to the silver ammine complex aqueous solution to reduce and precipitate silver particles. Based on the manufacturing method of filtration, washing, and drying, the inventor devoted himself to the manufacturing method and conducted intensive research. As a result, it has become possible to obtain a fine silver powder at a level that cannot be obtained by the conventional manufacturing method, and has further conceived a manufacturing method capable of stably obtaining the fine silver powder at a high yield. Hereinafter, the present invention will be described by dividing into “fine silver powder” and “production method”.

[0009] <fine silver powder>

First, the fine silver powder according to the present invention will be described. The major feature of the fine silver powder according to the present invention is that it has the following powder characteristics a.-c. Among these powder characteristics, the characteristics of the fine silver powder according to the present invention most clearly appear among the current powder measurement technologies, and the characteristics that are satisfied at the same time are listed. Hereinafter, each characteristic will be described.

[0010] The characteristic of a. Is that the average particle diameter D of the primary particles obtained by image analysis of a scanning electron microscope image is 0.6 m or less. Here, "Image analysis of scanning electron microscope image

IA

The average particle diameter D of the primary particles obtained by the above is defined by using a scanning electron microscope (SEM).

IA

Observed images of silver powder (observed at a magnification of 10,000 times in the case of fine silver powder which is useful in the present invention, and preferably at a magnification of 3000 to 5000 times in the case of conventional silver powder) are obtained by image analysis. Mean particle size. The image analysis of the fine silver powder observed using a scanning electron microscope (SEM) in the present specification was performed using an IP-1000PC manufactured by Asahi Engineering Co., Ltd. The circular particle analysis was performed as

IA was requested. The average particle size D obtained by image processing the observation image of this fine silver powder is obtained directly from the SEM observation image.

IA

This means that the average particle size of the primary particles is reliably captured. Fine silver powder referred to in the present invention D is almost in the range from 0.01 μm to 0.6 μm as observed by the present inventors.

IA

However, in reality, even finer particles can be confirmed in some cases, and the lower limit is not explicitly specified.

[0011] In the characteristic b., The fine silver powder according to the present invention has a higher dispersibility than the conventional silver powder, and therefore, "aggregation degree" was used as an index indicating the dispersibility.

[0012] The agglomeration degree referred to in the present specification means the average particle diameter D of the primary particles and the laser diffraction scatter.

IA

A value expressed as D / Ό using the average particle size D obtained by random particle size distribution measurement.

50 50 IA

is there. Here, D is the weight obtained using the laser diffraction scattering type particle size distribution measuring method.

50

This is the particle size at 50% of the cumulative value.

50

It can be said that the average particle size is calculated by directly observing the two diameters and treating the aggregated particles as a single particle (agglomerated particles). That is, it is generally considered that the actual silver powder particles are in a state where a plurality of particles are aggregated, unlike the so-called monodispersed powder, in which individual particles are completely separated. As the agglomeration state of the powder particles decreases and approaches monodispersion, the average particle diameter D increases.

50 values are usually small. The D of the fine silver powder used in the present invention is in the range of about 0.25 ^ πι-0.80 / zm.

50

With the conventional manufacturing method, it becomes a fine silver powder having an average particle size

50

It is. In the present specification, the laser diffraction scattering type particle size distribution measuring method is as follows: 0.1 g of fine silver powder is mixed with ion-exchanged water and dispersed with an ultrasonic homogenizer (US-SOOT manufactured by Nippon Seiki Seisakusho) for 5 minutes. Measured using a laser diffraction scattering type particle size distribution analyzer, Micro Trac HRA 9320-X100 (Leeds + Northrup)

[0013] In contrast, the "average particle diameter D of primary particles obtained by image analysis of a scanning electron microscope image" refers to an image of a silver powder observed using a scanning electron microscope (SEM).

IA

This is the average particle size obtained by precipitation, and the average particle size of the primary particles can be reliably grasped without considering the aggregation state.

[0014] As a result, the present inventors found that the average particle diameter D of the laser diffraction scattering

Aggregate the value calculated by D ZD using 50 and the average particle size D obtained by image analysis.

IA 50 IA

I decided to take it as a degree. That is, in the fine silver powder of the same lot, Assuming that the values can be measured with the same precision, the above-mentioned theory suggests that the value of D, which reflects the presence of aggregation in the measured value, will be larger than the value of D.

50 IA

At this time, the value of D is infinitely large as the agglomerated state of the fine silver powder particles disappears.

As it approaches 50 IA, the value of the cohesion, D ZD, will approach 1. Cohesion degree is 1

50 IA

At this stage, it can be said that the powder is a monodispersed powder having no aggregation state of the powder particles.

[0015] The present inventors have determined the correlation between the degree of agglomeration, the viscosity of the fine silver powder paste produced using the fine silver powder of each degree of agglomeration, and the surface smoothness of a conductor obtained by sintering. I checked it. As a result, it was found that an extremely good correlation was obtained. From this fact, it can be concluded that by controlling the degree of aggregation of the fine silver powder as a component, it is possible to freely control the viscosity of the fine silver powder paste produced using the fine silver powder. Also, if the agglomeration degree is set to 1.5 or less, fluctuations in the viscosity of the fine silver powder paste, surface smoothness after sintering, etc. will be extremely narrow, and it will be possible to fit in the range. It is. In addition, the more the cohesion state is eliminated, the higher the film density of the conductor obtained by sintering using the fine silver oxide powder, and the lower the electrical resistance of the resulting sintered conductor. It becomes possible.

[0016] In addition, when actually calculating the cohesion degree, it may show a value less than 1. This is thought to be due to the assumption that D used for calculating the degree of agglomeration is a true sphere.

IA

In reality, however, it seems that a cohesion value of less than 1 can be obtained because it is not a true sphere.

The characteristic of c is that the crystallite diameter is lOnm or less, and the crystallite diameter and the sintering start temperature have a very close relationship. In other words, when silver powders having the same average particle diameter are compared, the smaller the crystallite diameter, the lower the sintering temperature. Therefore, the sintering start temperature can be reduced by using a small crystallite diameter of lOnm or less, because the surface energy is large because the particles are fine particles like the fine silver powder that works in the present invention. . This is because a certain measurement error occurs depending on a force measuring device, a measurement condition, and the like for which a lower limit is not provided for the crystallite diameter. In addition, it is difficult to obtain high reliability for the measured values in the range where the crystallite diameter is less than lOnm, and if the lower limit is determined, it is about 2 nm obtained as a result of the research by the present inventors. In I think that.

The fine silver powder according to the present invention has the powder characteristics a. To c. Described above, and when the fine silver powder according to the present invention is characterized by the characteristic power of the sintering start temperature, it can be sintered at a low temperature of 240 ° C. or less. This makes it possible to capture it as fine silver powder with binding properties. Although no lower limit is specified for the sintering start temperature, a sintering start temperature lower than 170 ° C can be obtained in consideration of the research conducted by the present inventors and general technical common sense. It is almost impossible, and it is considered to be a temperature corresponding to the lower limit.

[0019] Furthermore, as an effect with the to have powder characteristics, power strips packing density of the force mowing fine silver powder to the present invention will become one as high as 4. OgZcm ³ or more. The tap filling density here is determined by precisely weighing 200 g of fine silver powder, placing it in a 150 cm ³ measuring cylinder, tapping repeatedly 1000 times with a stroke of 40 mm, and measuring the volume of fine silver powder! Measured by the method. The higher the tap filling density, the higher the theoretically fine particle size and the higher the dispersibility without aggregation of the particles, the higher the value obtained. Considering that the tap filling density of conventional silver powder is less than 4.Og / cm ³ , the fine silver powder according to the present invention is also very fine and has excellent dispersibility. It becomes.

The production method that is effective in the present invention is that a silver nitrate aqueous solution and ammonia water are mixed and reacted to obtain a silver ammine complex aqueous solution, and this is contacted with an organic reducing agent to reduce and precipitate silver particles. The method of producing silver powder by washing and drying is characterized by using an amount of a reducing agent, an amount of silver nitrate, and an amount of aqueous ammonia which become diluted after addition. Conventionally, the reducing agent solution and the silver ammine complex aqueous solution are generally mixed together in a tank, and therefore, in general, to increase the silver concentration to lOgZi or more, a large amount of silver nitrate and reducing Unless the amount of the agent and the amount of aqueous ammonia were added, it was impossible to secure the productivity for the scale of the equipment.

[0021] The most important feature of the production method according to the present invention is that the concentration of the organic reducing agent after the contact reaction between the aqueous solution of silver ammine complex and the organic reducing agent is low, and the residual silver adsorbed on the surface of the generated silver powder particles. Or the organic reducing material taken into the inside of the powder during the growth of the powder The point is that it can be reduced. Therefore, it is most preferable to maintain the organic reducing agent concentration at lgZl-3 gZl while the silver concentration of the mixed solution is lgZl-6 gZ1.

Here, the silver concentration and the reducing agent amount are in a proportional relationship, and it is natural that the higher the silver concentration, the more quantitatively the silver powder can be obtained. However, if the silver concentration here exceeds 6 g / l, the precipitated silver particles tend to be coarse and have a particle size that is no different from that of conventional silver powder. This makes it impossible to obtain fine silver powder with good properties. On the other hand, if the silver concentration here is less than lg / 1, very fine silver powder can be obtained, but it becomes too fine and the oil absorption increases, leading to an increase in paste viscosity. It is necessary to increase the amount of the organic vehicle, which tends to lower the film density of the finally formed sintered conductor and increase the electric resistance. It is not enough to satisfy the required industrial productivity.

[0023] While the silver concentration is lgZl-6gZl, maintaining the organic reducing agent concentration at lgZl-3gZl is the most suitable condition for obtaining the fine silver powder according to the present invention with high yield. Become. Here, the reason why the concentration of the organic reducing agent is set to lgZl to 13gZl is selected as a range most suitable 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 gZl, the amount of the reducing agent added to the aqueous solution of silver ammine complex decreases, but the aggregation of the silver powder particles that are precipitated by reduction begins to become remarkable, and the impurities contained in the powder particles become large. The amount (in this specification, the amount of impurities is regarded as the carbon content) begins to increase sharply. On the other hand, the organic reducing agent

If it is less than Zi, the total amount of the reducing agent used increases, the wastewater treatment amount also increases, and the industrial economic efficiency is not satisfied.

[0024] The "organic reducing agent" mentioned here is hydroquinone, ascorbic acid, glucose, or the like. Among them, it is desirable to selectively use hydroquinone as the organic reducing agent. In the present invention, hydroquinone has relatively high reactivity compared to other organic reducing agents, and can be said to have the most suitable reaction rate for obtaining low-crystalline silver powder having a small crystallite diameter S. It is.

[0025] Other additives can be used in combination with the organic reducing agent. This The additives referred to here are glues such as gelatin, amine-based polymer agents, celluloses, etc., which stabilize the reductive precipitation process of silver powder and simultaneously function as a certain dispersant. Is preferred, and it may be appropriately selected according to the organic reducing agent, the type of the process, and the like.

[0026] In the method of contacting and reacting the aqueous silver ammine complex solution obtained as described above with a reducing agent to reduce and precipitate fine silver powder, in the present invention, as shown in FIG. A second flow path b that flows through a certain flow path through which S flows (hereinafter referred to as “first flow path”) and joins in the middle of the first flow path a is provided. Flow the organic reducing agent and optional additive S through the first channel a through the second channel b.

2

It is desirable to employ a method in which silver particles are reduced and precipitated by contact mixing at the confluence m of the flow path and the second flow path b (hereinafter, this method will be referred to as a “merge-mixing method”). ,

[0027] By adopting such a combined 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 powder particles having a uniform shape are formed. . In addition, the fact that the amount of the organic reducing agent as a whole as a whole after mixing is low means that the amount of the organic reducing agent adsorbed and remaining on the surface of the fine silver powder that is reduced and precipitated is reduced. As a result, it becomes possible to reduce the amount of impurities adhering to the fine silver powder obtained by filtering and drying. Due to the reduction in the amount of impurities adhering to the fine silver powder, the electrical resistance of the sintered conductor formed via the silver paste can be reduced.

Further, when a silver ammine complex aqueous solution is obtained by contacting and reacting an aqueous silver nitrate solution with aqueous ammonia, a silver nitrate concentration of 2.6 gZl to 48 gZl is used, and a silver concentration of 2 g / 1 to 12 g / It is desirable to obtain an aqueous solution of the silver ammine complex. Here, defining the concentration of the silver nitrate aqueous solution is synonymous with defining the liquid volume of the silver nitrate aqueous solution.Considering that the silver concentration of the silver ammine complex aqueous solution is 2 gZl-12 gZl, there is The concentration and amount of the ammonia water to be added are inevitably determined. At this stage, a clear technical reason has not been clarified, but the use of an aqueous solution of silver nitrate with a silver nitrate concentration of 2.6 gZl-48 gZl indicates the best production stability and stable quality. Fine silver powder can be obtained.

The invention's effect [0029] The fine silver powder according to the present invention is finer than ever before, and it is a component that the fine silver powder that does not exist in the conventional silver powder having high dispersibility is present. Further, by employing the above-described production method, the fine silver powder according to the present invention can be efficiently obtained.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the best mode of the present invention will be described in detail while comparing with a comparative example.

Example 1

In this example, fine silver powder was manufactured using the above-described manufacturing method, and the powder characteristics of the fine silver powder obtained were measured. Further, a silver paste was produced using fine silver powder, a test circuit was formed, and the conductor resistance and the sintering start temperature were measured.

First, 63.3 g of silver nitrate is dissolved in 9.7 liters of pure water to prepare an aqueous silver nitrate solution, and 235 ml of 25 wt% ammonia water is added thereto all at once, followed by stirring and stirring. Thus, an aqueous amine complex solution was obtained.

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. 1 at a flow rate of 1500 mlZsec, and the reducing agent is flowed through the second flow path b at a flow rate of 1500 mlZsec, and at the junction point m The temperature was brought to a temperature of ° C, and the fine silver powder was reduced and precipitated. As the reducing agent used at this time, an aqueous solution of hydroquinone in which 21 g of hydroquinone was dissolved in 10 liters of pure water was used. Therefore, the hydroquinone concentration at the end of the mixing is about 1.04 g / l, which is a very dilute concentration.

[0034] In order to separate the fine silver powder obtained as described above, the mixture is filtered using a nutsche, washed with 100 ml of water and 50 ml of methanol, and further dried at 70 ° C for 5 hours. Then, fine silver powder was obtained. Fig. 2 shows a scanning electron micrograph of the obtained fine silver powder.

The powder characteristics of the fine silver powder obtained as described above are listed in Table 1 together with the powder characteristics of the silver powder obtained in Example 2 and Comparative Example. Therefore, here we will explain the ones whose measurement method etc. is unknown in the above explanation. The sintering start temperature in Table 1 was determined by precisely weighing 0.5 g of fine silver powder with a balance, pressing it at a pressure of ² t / cm ² for 1 minute, Using a TMA ZSS6000, a thermomechanical analyzer (TMA) manufactured by Seiko Instruments, Inc., at an air flow rate of 200 ccZ, a heating rate of 2 ° CZ, and a holding time of 0 min. It was measured in the range up to 900 ° C. The conductor resistances listed in Table 1 were obtained by producing silver paste using each silver powder, laying out circuits on a ceramic substrate, and sintering to the extent that resistance could be measured in a temperature range of 180-250 ° C. It was measured using the lmm width circuit provided. The composition of the silver paste was 85% by weight of fine silver powder, 0.75% by weight of ethyl cellulose, and 14.25% by weight of terbineol. FIB analysis measured the size of the precipitated crystal grains and used it to measure the crystallite diameter. The carbon content is used as a measure of the amount of impurities attached to the silver powder particles. Using EMIA-320V manufactured by Horiba, 0.5 g of fine silver powder, 1.5 g of tungsten powder, and 0 g of tin powder are used. 3 g was mixed, placed in a magnetic crucible, and measured by a combustion infrared absorption method.

Example 2

In the present example, fine silver powder was manufactured under manufacturing conditions different from those in Example 1, and the powder characteristics of the obtained fine silver powder were measured. Further, a silver paste was produced using the fine silver powder, a test circuit was formed, and the conductor resistance and the sintering start temperature were measured.

First, 63.3 g of silver nitrate was dissolved in 3.1 liter of pure water to prepare an aqueous silver nitrate solution, and 235 ml of 25 wt% aqueous ammonia was added thereto all at once, followed by stirring and stirring. Thus, an aqueous amine complex solution was obtained.

Then, this silver ammine complex solution is introduced into the first flow path a having an inner diameter of 13 mm shown in FIG. 1 at a flow rate of 1,500 mlZsec, and the reducing agent is flowed through the second flow path b at a flow rate of 1,500 mlZsec. The temperature was brought to a temperature of ° C, and the fine silver powder was reduced and precipitated. The reducing agent used at this time was a hydroquinone aqueous solution in which 21 g of hydroquinone was dissolved in 3.4 liters of pure water. Therefore, the concentration of hydroquinone at the end of mixing is about 3. OgZl, a very dilute concentration.

[0039] The fine silver powder obtained as described above was filtered using Nutch II in the same manner as in Example 1, washed with 100 ml of water and 50 ml of methanol, and further treated at 70 ° C for 5 hours. After drying, fine silver powder was obtained. Fig. 3 shows a scanning electron micrograph of the obtained fine silver powder. The powder characteristics of the fine silver powder obtained as described above are shown in Table 1. It is shown together with the powder characteristics of the silver powder obtained in Example 1 and Comparative Example. Comparative Example 1

In this comparative example, the fine silver powder was produced by the following production method, and the powder characteristics of the obtained fine silver powder were measured. Further, a silver paste was produced using the fine silver powder, a test circuit was formed, and the conductor resistance and the sintering start temperature were measured.

First, 63.3 g of silver nitrate was dissolved in 1.0 liter of pure water to prepare an aqueous silver nitrate solution, and 235 ml of 25 wt% ammonia water was added thereto all at once and stirred, followed by stirring. Thus, an aqueous amine complex solution was obtained.

[0042] Then, the silver ammine complex solution was put into a reaction vessel, and a hydroquinone aqueous solution in which 21 g of hydroquinone was dissolved as a reducing agent in 1.3 liter of pure water was added thereto all at once. The silver powder was reduced and precipitated by maintaining the temperature at 20 ° C. and stirring and reacting. The hydroquinone concentration at the end of this mixing is approximately 8.23 gZl, which is a high concentration.

[0043] The fine silver powder obtained as described above was filtered using Nutch II in the same manner as in Example 1, washed with 100 ml of water and 50 ml of methanol, and further treated at 70 ° C for 5 hours. After drying, fine silver powder was obtained. Fig. 4 shows a scanning electron micrograph of the obtained silver powder. The powder characteristics of the fine silver powder obtained as described above are listed in Table 1 together with the powder characteristics of the silver powder obtained in the above Examples and the second comparative example.

Comparative Example 2

[0044] In this comparative example, fine silver powder was manufactured using the manufacturing method described below, and the powder characteristics of the fine silver powder obtained were measured. Further, a silver paste was produced using the fine silver powder, a test circuit was formed, and the conductor resistance and the sintering start temperature were measured.

First, 63.3 g of silver nitrate was dissolved in 300 ml of pure water to prepare an aqueous silver nitrate solution, and 235 ml of 25 wt% aqueous ammonia was added thereto all at once, followed by stirring and stirring. An aqueous solution was obtained.

[0046] Then, the silver ammine complex solution was put into a reaction vessel, 3 g of gelatin was added to 200 ml of pure water, and hydroquinone as a reducing agent was dissolved in 700 g of pure water. The aqueous solution was added all at once, and the silver powder was reduced and precipitated by maintaining the liquid temperature at 20 ° C and stirring and reacting. At the end of this mixing, the hydroquinone concentration is approximately 14.5 gZ 1, which is a high concentration.

[0047] The fine silver powder obtained as described above was filtered using Nutch II in the same manner as in Example 1, washed with 100 ml of water and 50 ml of methanol, and further treated at 70 ° C for 5 hours. After drying, fine silver powder was obtained. Fig. 5 shows a scanning electron micrograph of the obtained silver powder. The powder characteristics of the fine silver powder obtained as described above are listed in Table 1 together with the powder characteristics of the silver powder obtained in the above Examples and the second comparative example.

Comparative Example 3

[0048] In this comparative example, the fine silver powder was manufactured using the following manufacturing method, and the powder characteristics of the obtained fine silver powder were measured. Further, a silver paste was produced using the fine silver powder, a test circuit was formed, and the conductor resistance and the sintering start temperature were measured.

[0049] First, 20 g of polybutylpyrrolidone is dissolved in 260 ml of pure water, and further, 50 g of silver nitrate is dissolved to prepare an aqueous silver nitrate solution. A nitric acid solution was obtained. At the end of this mixing, the ascorbic acid concentration is approximately 36. OgZl.

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

[0051] Then, the silver-containing nitric acid-based solution is put into a reaction tank, and the above-mentioned reducing solution is added thereto all at once. The liquid temperature is kept at 25 ° C, and the mixture is stirred and reacted, whereby silver powder is reduced and precipitated. I let it.

[0052] The fine silver powder obtained as described above was filtered using Nutsche, washed with 100 ml of water and 50 ml of methanol in the same manner as in Example 1, and further treated at 70 ° C for 5 hours. After drying, fine silver powder was obtained. The powder properties of the fine silver powder obtained as described above are listed in Table 1 together with the powder properties of the silver powder obtained in the above Examples and Comparative Examples!

<Examination of Comparison between Example and Comparative Example> The above-described examples and the comparative example will be compared with reference to Table 1. From the scanning electron micrographs shown in Figs. 2 to 5, it is considered that the particle size of the primary particles can be clearly understood.

[Table 1] Powder characteristics sintered conductor properties specimen SSA tap DD, D _S. ZD, _A crystal Carbon content Conductor resistance Sintering Starting packing density Dish size £ κ.m Vg g / cm ³ μmn in% ΜΩ cm cm ° C Example 1 2.5 4 4 .2 0.3 10 0.3 0 1 .0 3 7 0 .2 8 4 .6 1 .6 0 Example 2 1.6 .8 4 .7 0 .5 5 0 .9 1 .1 .2 7 0 .3 2 5 .9 1 9 0 Comparative example 1 1 .1 8 4 .3 1 .7 8 1 .0 2 1 .7 .5 9 0 .8 8 Unmeasurable 2 5 0 Comparative example 2 .5 5 4 .0 3 .9 0 2. 2 0 1 .77 7 δ 0.89 Unmeasurable 2 5 0 Comparative example 3 0.6 2 4 .0 3.0 3 1 .2 0 2 .5 3 3 8 0 .3 0 Unmeasurable 3 5 0

[0055] As is clear from Table 1, even when comparing each of the powder characteristic values, the fine silver powder obtained in the above example is extremely fine compared to the silver powder manufactured using the conventional manufacturing method. It is a fine powder that does not exist in conventional silver powder, which has high dispersibility. Regarding the characteristics of the sintered conductor, when a circuit is formed using the fine silver powder according to the present invention, the film density is high and the electric resistance is low. In the case of each comparative example, it is a component that the conductor resistance is high and measurement becomes impossible.

Industrial applicability

[0056] The fine silver powder according to the present invention is composed of fine particles that are hardly considered in conventional silver powder, and has a lower force than conventional silver powder in which the degree of aggregation of the powder is low. Even so, it shows very good dispersibility. In addition, by employing the method for producing fine silver powder according to the present invention, the amount of residual organic matter in the fine silver powder obtained is reduced, and the fine silver powder acts in combination with the high film density due to the fine silver powder. This contributes to reducing the electrical resistance of the obtained conductor.

Brief Description of Drawings

FIG. 1 is a diagram showing the concept of mixing an aqueous silver ammine complex solution and a reducing agent.

FIG. 2 is a scanning electron microscope observation image of the fine silver powder according to the present invention.

FIG. 3 is a scanning electron microscope observation image of the fine silver powder according to the present invention.

[Fig. 4] Scanning electron microscope observation image of fine silver powder that works in a conventional manufacturing method.

FIG. 5 is a scanning electron microscope observation image of fine silver powder according to a conventional production method.

Claims

The scope of the claims

[1] A fine silver powder, which is a fine silver powder having a low cohesiveness of the powder and which has the following powder characteristics of a.

a. Average particle size of primary particles obtained by image analysis of scanning electron microscope images D Force SO

IA

• 6 μm or less "ho

b. The average particle diameter D of the primary particles and the laser diffraction scattering type particle size distribution measurement method

IA

The cohesion degree represented by D / Ό using the average particle diameter D is 1.5 or less.

50 50 IA

c. Crystallite diameter is 10nm or less.

[2] The fine silver powder according to claim 1, wherein the sintering temperature is 240 ° C or lower.

[3] An aqueous silver nitrate solution and aqueous ammonia are mixed and reacted to obtain an aqueous silver ammine complex solution, and a reducing agent is added thereto to precipitate and precipitate silver particles, which is filtered, washed and dried to obtain fine particles. Regarding the production method of silver powder,

Contacting and mixing an organic reducing agent with the aqueous solution of silver ammine complex, and reducing and precipitating silver particles while maintaining a silver concentration of lgZl-6 gZl and an organic reducing agent concentration of lgZl-3 gZl in the mixed solution. A unique method of producing fine silver powder.

[4] The method for producing fine silver powder according to claim 3,

When an organic reducing agent is brought into contact with and mixed with the aqueous silver ammine complex solution, the aqueous silver ammine complex solution flows through a certain flow path (hereinafter, referred to as a “first flow path”) and joins the middle of the first flow path. A method for producing fine silver powder, comprising: providing a second flow path, flowing an organic reducing agent through the second flow path, and contacting and mixing the organic reducing agent at a junction of the first flow path and the second flow path.

[5] In the method for producing fine silver powder according to claim 3 or claim 4,

A method for producing fine silver powder, characterized by using a silver ammine complex aqueous solution having a silver concentration of 2 to 12 g / l, which is obtained by mixing and reacting an aqueous solution of silver nitrate having a silver nitrate concentration of 2.6 gZl to 48 gZl and aqueous ammonia.

[6] The method for producing fine silver powder according to claim 3-claim 5, wherein

A method for producing fine silver powder in which a dispersant is contained in an organic reducing agent to be used.

[7] The method for producing fine silver powder according to claim 3 or claim 6, wherein

A method for producing fine silver powder, wherein the organic reducing agent uses hydroquinone.