WO2005009652A1

WO2005009652A1 - Fine-grain silver powder and process for producing the same

Info

Publication number: WO2005009652A1
Application number: PCT/JP2004/010102
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: CA2534108A1; KR101132283B1; US20070079665A1; JP4489389B2; KR20060040712A; TWI295666B; DE112004001403T5; JP2005048237A; CN1826198A; TW200503961A; CN100500333C

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 and exhibiting a low impurity content. 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, followed by washing with excess alcohol. 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 (D1A) 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), the sintering initiation temperature 240°C or below (c), and the carbon content 0.25 wt.% or less (d).

Description

Specification

Fine silver powder and method for producing the fine silver powder

Technical field

The invention according to the present application relates to fine silver powder and a method for producing the fine silver powder. In particular, the present invention relates to fine silver powder having a low impurity content.

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.

[0008] On the other hand, it has been demanded that silver powder has a small amount of impurities. That is, the production of silver powder employs the above-described wet reduction process, and the reducing agent and the like used in the process remain on the surface of silver powder particles. Therefore, this is an unavoidable problem as far as the conventional manufacturing method is adopted. When the amount of impurities in the silver powder increases, the electrical resistance of a conductor formed using the silver powder increases.

[0009] As a result, there has been a demand in the market for silver powder to be fine, highly dispersed, and to have a low impurity content. Means for solving the problem

[0010] Therefore, 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 cause precipitation and precipitation of 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 is possible to obtain a fine silver powder at a level that cannot be obtained by the conventional manufacturing method, and it is possible to obtain an unprecedented fine silver powder by significantly reducing the amount of impurities in the fine silver powder. It became possible. Furthermore, the production method according to the present invention has conceived a production method capable of stably obtaining the fine silver powder in a yield. Hereinafter, the present invention will be described by dividing into “fine silver powder” and “production method”.

[0011] <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. Among these powder characteristics, the characteristics of the fine silver powder according to the present invention, which are most remarkable among the current powder measurement technologies, and which are simultaneously established are listed. The following describes each characteristic

The characteristic of a. Is that the average particle diameter D of 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 average particle diameter D was obtained by performing a circular particle analysis. Image processing of the observation image of this fine silver powder

IA

Is obtained directly from the SEM observation image.

IA

This means that the average particle size of the primary particles is reliably captured. Most of the D of the fine silver powder referred to in the present invention falls within the range of 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.

[0013] In the characteristic b., Since the fine silver powder according to the present invention has a higher dispersibility than the conventional silver powder, the "aggregation degree" is used as an index indicating the dispersibility.

[0014] The agglomeration degree referred to in the present specification refers to the average particle diameter D of the primary particles and the laser diffraction scatter.

IA

A value expressed as D ZD 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 observing the aggregated particles rather than directly observing one diameter as one 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. Generally, the smaller the agglomeration state of the powder particles and the closer to the monodispersion, the smaller the value of the average particle diameter D.

50

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. Laser diffraction scattering particle size distribution analyzer Micro T rac HRA 9320—measured using XIOO (Leeds + Northrup)

[0015] 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.

[0016] As a result, the present inventors found that the average particle diameter D of the laser diffraction / scattering particle size distribution measurement method was large.

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 50 IA value can be measured with the same accuracy, considering the above theory, 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, the particles are completely agglomerated and can be said to be monodisperse powder.

[0017] 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, the surface smoothness of a conductor obtained by sintering, and the like. 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.

[0018] Also, 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 has a very close relationship with the sintering start temperature. 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. I believe that.

[0020] The characteristic of d. 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 a measure of the amount of impurities attached to the silver powder particles. The carbon content at this time was measured using EMIA-320V manufactured by Horiba Seisakusho, using 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. Combustion was measured by infrared absorption method. The carbon content of the silver powder obtained by the conventional production method is such that the carbon content exceeds 0.25 wt%, no matter how the cleaning is enhanced.

[0021] The fine silver powder according to the present invention has the powder characteristics a. To d. Described above, and thus can be regarded as an unprecedented silver powder. From the viewpoint of the sintering start temperature, the fine silver powder according to the present invention can be said to be a fine silver powder capable of starting sintering at a low temperature of 240 ° C or less. Also, the lower limit of the sintering start temperature is not particularly specified, but in consideration of the research conducted by the present inventors and general technical common sense, a sintering start temperature lower than 170 ° C is obtained. It is almost impossible to do so, and we believe that the temperature is equivalent to the lower limit.

[0022] Further, as an effect of providing the above-mentioned powder characteristics, the tap filling density of the fine silver powder which is effective in the present invention is 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.

[0023] <Method for producing fine silver powder>

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.

[0024] The first 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. In addition, it is possible to reduce the amount of organic reducing material taken into the inside of the particles during the growth process of the particles. Therefore, it is most preferable to maintain the silver concentration of lgZl-l6gZl and the organic reducing agent concentration of lgZl-3gZl in the mixed solution.

Here, the silver concentration and the amount of the reducing agent 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. [0026] The most suitable condition for obtaining the fine silver powder according to the present invention with a high yield is to maintain the silver concentration at lgZl-6gZl and maintain the organic reducing agent concentration at lgZl-3gZl. Here, the reason why the concentration of the organic reducing agent is lgZl-3gZl 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. If the concentration of the organic reducing agent exceeds 3 gZl, the amount of the reducing agent added to the silver ammine complex aqueous solution is reduced, but the aggregation of the silver particles that are precipitated by reduction starts to progress remarkably, and the impurities contained in the particles are started. The amount (in this specification, the amount of impurities is regarded as the carbon content) begins to increase sharply. On the other hand, if the concentration of the organic reducing agent is less than lgZi, the total amount of the reducing agent used increases, the amount of wastewater treatment increases, and the industrial economics is not satisfied.

[0027] 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.

[0028] Then, other additives can be used in combination with the organic reducing agent. The additives mentioned here are glues such as gelatin, amine-based polymer agents, celluloses, etc., which stabilize the reduction and precipitation process of silver powder and also function as a certain dispersant. It is desirable to use it selectively as appropriate according to the organic reducing agent, the type of the process, and the like.

[0029] 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, the present invention employs, 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”). ,

[0030] By employing such a combined mixing method, the mixing time of the two liquids is completed in the shortest time. However, since the reaction proceeds in a uniform state in the system, 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 nitrate aqueous solution is contacted with an aqueous ammonia solution to obtain a silver ammine complex aqueous solution, 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.

[0032] The second feature of the manufacturing method according to the present invention is the final cleaning, which is very important. The washing at this time may be performed by combining the water washing and the alcohol washing, or only the alcohol washing may be used, but the washing at the time of washing with the alcohol is strengthened. That is, about 40 g of the fine silver powder precipitated by reduction is usually washed with about 100 ml of pure water and then with about 50 ml of alcohol. On the other hand, in the present invention, when performing alcohol washing, 200 ml or more, or 1 kg of fine silver powder is washed with 5 L or more of excess alcohol.

[0033] Impurities can be reduced by such enhanced washing because, in the contact reaction between the silver amine complex aqueous solution and the reducing agent when obtaining fine silver powder, a reaction system having a dilute concentration is used and the solution after mixing is used. This is because we have adopted a method to reduce the amount of organic reducing agent when viewed as a whole.

The invention's effect

[0034] The fine silver powder according to the present invention is finer than ever before, and has a high dispersibility. This is because the fine powder having a small amount of pure material and not found in the conventional silver powder is a component. 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 embodiment 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 was dissolved in 9.7 liter of pure water to prepare a silver nitrate aqueous solution, and 235 ml of 25 wt% ammonia water was added thereto all at once, followed by stirring and stirring. Thus, an aqueous amine complex solution was obtained.

[0038] 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. 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.

[0039] In order to collect 40g of the fine silver powder obtained as described above, the mixture was filtered using Nutsche, washed with 100ml of water and 600ml of methanol, and further dried at 70 ° C for 5 hours. Row V, fine silver powder was obtained. FIG. 2 shows a scanning electron micrograph of the obtained fine silver powder.

The powder properties of the fine silver powder obtained as described above are shown in Table 1 together with the powder properties 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 as follows: 0.5 g of fine silver powder was precisely weighed with a balance, and pressed at a pressure of ² t / cm ² for 1 minute to form pellets, and a thermomechanical analyzer manufactured by Seiko Instruments Inc. (TMA equipment) TMA Using the ZSS6000, the measurement was performed in the range of room temperature to 900 ° C under the conditions of an air flow rate of 200 ccZ, a heating rate of 2 ° CZ, and a holding time of 0 minutes. The copper body resistance listed in Table 1 was obtained by producing a silver paste using each silver powder, laying a circuit on a ceramic substrate, and sintering at a temperature of 180-250 ° C. It was measured using a circuit. The silver paste was composed of 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.

Example 2

In the present example, fine silver powder was manufactured using manufacturing conditions different from those in Example 1, 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.

[0042] First, 63.3 g of silver nitrate is dissolved in 3.1 liter 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 solution was 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. 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.

[0044] 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 methanol, and further heated 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 listed in Table 1 together with the powder characteristics of the silver powder obtained in Example 1 and Comparative Example.

Comparative Example 1

In this comparative example, only the cleaning conditions of Example 1 were changed, and only the cleaning conditions will be described to avoid redundant description. [0046] 40 g of the fine silver powder obtained in Example 1 was filtered using a Nutsche, washed with 100 ml of water and 50 ml of methanol, and further dried at 70 ° C for 5 hours to obtain fine silver powder. I got it. A scanning electron micrograph of the obtained fine silver powder is similar to that shown in FIG. 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 other examples and comparative examples.

Comparative Example 2

In this comparative example, only the cleaning conditions of Example 2 were changed, and only the cleaning conditions will be described to avoid redundant description.

[0048] 40 g of the fine silver powder obtained in Example 2 was 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 fine silver powder. I got it. A scanning electron micrograph of the obtained fine silver powder is similar to that shown in FIG. 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 other examples and comparative examples.

Comparative Example 3

[0049] In this comparative example, the fine silver powder was produced using the production method described below, 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.

[0050] 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, followed by stirring and stirring. Thus, an aqueous amine complex solution was obtained.

[0051] 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 liters 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.

[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. Fig. 4 shows a scanning electron micrograph of the obtained silver powder. Table 1 shows the powder characteristics of the fine silver powder obtained as described above. It is shown together with the powder characteristics of the silver powder obtained in the example and the second comparative example. Comparative Example 4

[0053] 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 a silver nitrate aqueous solution, and 235 ml of 25 wt% ammonia water was added thereto all at once, followed by stirring and stirring. An aqueous solution was obtained.

[0055] 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 in which 21 g of hydroquinone was dissolved in 700 ml of pure water was added. 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. The hydroquinone concentration at the end of this mixing is approximately 14.5 gZ1, which is a high concentration.

[0056] 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. 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 5

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.

[0058] First, 20 g of polybutylpyrrolidone is dissolved in 260 ml of pure water, and then 50 g of silver nitrate is dissolved to prepare an aqueous silver nitrate solution. 25 g of nitric acid is added thereto all at once and the mixture is stirred to contain silver. A nitric acid solution was obtained. At the end of this mixing, the ascorbic acid concentration is approximately 36. OgZl.

On the other hand, 35.8 g of ascorbic acid as a reducing agent was added to and dissolved in 500 ml of pure water to prepare a reducing solution. [0060] Then, the silver-containing nitric acid-based solution is put into a reaction vessel, and the above-mentioned reducing solution is added thereto all at once. The solution is kept at a temperature of 25 ° C and stirred to cause a reaction, whereby silver powder is reduced and precipitated. I let it.

[0061] 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!

<Study of Comparison between Examples and Comparative Examples> [0062] Each of the above examples and comparative examples 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.

[0063] [Table 1]

[0064] 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 component that has a high dispersibility and a low impurity amount and is not present in the conventional silver powder. 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 amount of impurities is small, so that the electric resistance is low. In the case of each comparative example, it is a component that the conductor resistance is too high to be measured.

Industrial applicability

[0065] 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. And However, it shows very excellent 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 obtained fine silver powder 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.

d. The content of organic impurities is 0.25 wt% or less in terms of carbon.

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

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

An organic reducing agent is contact-mixed with the aqueous silver ammine complex solution, and silver particles are reduced and precipitated while maintaining the silver concentration of lgZl-6 gZl and the organic reducing agent concentration of lgZl-3 gZl in the mixed solution. A method for producing fine silver powder, comprising filtering particles, washing with water, and washing with an excess alcohol solution.

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

When the 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 in 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;

[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 any one of claims 3 to 6, wherein the organic reducing agent uses hydroquinone.

[8] The method for producing fine silver powder according to any one of claims 3 to 7, wherein the alcohol uses an amount of 5 L or more per 1 kg of the obtained silver particles. Manufacturing method.