HK1092101B

HK1092101B - Fine-grain silver powder and process for producing the same

Info

Publication number: HK1092101B
Application number: HK06112769.8A
Authority: HK
Inventors: 佐佐木卓也; 加藤政志; 吉丸克彦
Original assignee: 三井金属矿业株式会社
Priority date: 2003-07-29
Filing date: 2004-07-15
Publication date: 2009-06-05

Description

Fine-particle silver powder and method for producing fine-particle silver powder

Technical Field

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

Background

As described in patent document 1, in conventional silver powder production, a wet reduction process has been employed in which a silver-ammonia complex aqueous solution is produced from a silver nitrate solution and ammonia water, and an organic reducing agent is added to the silver-ammonia complex aqueous solution. In recent years, these silver powders have been mainly used for forming electrodes or circuits of chip components, plasma display panels, and the like.

Patent document 1: japanese unexamined patent application publication No. 2001-107101

Therefore, the electrodes and circuits are required to be formed with a great miniaturization, and the circuits, electrodes, and the like are required to have high reliability while achieving high density and high accuracy of the wiring.

However, the particles of the silver powder obtained by the conventional production method have an average particle diameter D of the primary particles thereof_IAIn general, is superior toAverage particle diameter D measured by laser reverse-refraction scattering particle size distribution measurement method after passing through 0.6 μm₅₀More than 1.0 μm, with D₅₀/D_IAThe degree of agglomeration indicated is more than 1.7. Therefore, the method is not suitable for forming a circuit with a fine pitch in recent years, and causes a significant decrease in the yield of products.

On the other hand, there are the following problems from the viewpoint of the method of using the silver powder. Conventionally, in circuit formation using silver paste, non-firing or low-temperature firing type silver powder having a heating temperature of 300 ℃ or lower is used in many cases, and it is preferable to use silver powder having low caking property in order to obtain high sintering performance at low temperature. However, in order to obtain a silver powder having low caking property, a reaction system which is rapidly reduced has to be used under production conditions, and as a result, only a silver powder having a remarkable aggregation can be obtained although the crystallinity is low.

Thus, there is a demand in the market for providing a fine-particle silver powder which has a dispersibility closer to monodispersion with less aggregation of particles and is excellent in low-temperature sinterability, which has not been available in the past.

Disclosure of Invention

In view of the above problems, the present inventors have made extensive studies based on a production method in which a silver nitrate aqueous solution and an aqueous ammonia solution are mixed and reacted to obtain a silver-ammonia complex aqueous solution, a reducing agent is added to the silver-ammonia complex aqueous solution to reduce and precipitate silver particles, and the silver particles are filtered, washed, and dried. As a result, a fine-particle silver powder of a level that could not be obtained by the conventional production method can be obtained, and particularly, a production method for stably producing the fine-particle silver powder with a good yield has been studied. Hereinafter, the present invention will be described in terms of "fine-particle silver powder" and "production method".

Fine silver powder

First, the fine-particle silver powder of the present invention will be explained. The fine-particle silver powder according to the present invention is characterized by having the following powder characteristics a to c. These powder characteristics are the most prominent features of the fine-particle silver powder of the present invention among the conventional powder measurement techniques, and are also satisfied. Each characteristic is explained below.

a. Is characterized by the average particle diameter D of the primary particles obtained by image analysis of a scanning electron microscope image_IAIs 0.6 μm or less. Here, the "average particle diameter D of primary particles obtained by image analysis of scanning electron microscope image" is_IA"is an average particle diameter obtained by image analysis of an observation image of the silver powder obtained by observation with a Scanning Electron Microscope (SEM) (preferably, 10000 times in the case of observing the fine-particle silver powder of the present invention, and 3000 to 5000 times in the case of observing the conventional silver powder). Further, the image analysis of the fine-particle silver powder observed by a Scanning Electron Microscope (SEM) in the present specification means that the average particle diameter D is obtained by performing a circular particle analysis at a circularity threshold of 10 and a degree of overlap of 20 using IP-1000PC manufactured by Asahi works (エンジニアリング)_IAIn (1). Due to the average particle diameter D obtained by image processing of the observed image of the fine-particle silver powder_IASince the average particle size of the primary particles is directly obtained from the SEM observation image, the average particle size can be accurately captured. D of fine-particle silver powder in the invention_IAThe present inventors have observed that the diameter is almost always in the range of 0.01 μm to 0.6 μm, but in practice, the diameter can be confirmed to be still finer, and therefore the lower limit value is not particularly specified.

b. The fine-particle silver powder of the present invention exhibits high dispersibility which the conventional silver powder does not have, and therefore the "degree of agglomeration" is used as an index indicating the dispersibility.

The degree of agglomeration referred to in the present specification means the average particle diameter D of the primary particles_IAAnd an average particle diameter D measured by a laser-refraction scattering-type particle size distribution measuring method₅₀By D₅₀/D_IAThe values indicated. Here, D₅₀The average particle diameter D is a particle diameter at 50% by weight accumulation obtained by a laser refraction scattering particle size distribution measurement method₅₀The value of (d) is not a value obtained by directly observing the diameter of each particle, but means an average particle diameter calculated by using the agglomerated particles as one particle (agglomerated particle). That is, this is because it is considered that the fine particles of the silver powder are not actually completely separated for each particle, so-called monodispersed powder, but are generally in a state in which a plurality of particles are agglomerated. However, generally, the smaller the aggregation state of the particles, the closer to monodispersion, the average particle diameter D₅₀The smaller the value of (c). Average particle diameter D of fine-particle silver powder used in the present invention₅₀In the range of about 0.25 to 0.80 μm, the average particle diameter D is in a range which could not be obtained at all by the conventional production method₅₀The fine particulate silver powder of (3). The laser reverse-scattering particle size distribution measurement method in the present invention is a method in which 0.1g of fine-particle silver powder is mixed with ion-exchange water, dispersed for 5 minutes by an ultrasonic homogenizer (U.S. Pat. No. 300T, manufactured by Nippon Seiko Co., Ltd.), and then measured by a laser reverse-scattering particle size distribution measuring apparatus MicroTrac HRA 9320-X100 type (manufactured by Leeds + Northrup Co., Ltd.).

In contrast, the "average particle diameter D of primary particles obtained by image analysis of scanning electron microscope image_IA"means an average particle diameter obtained by image analysis of an observation image of the silver powder observed by a Scanning Electron Microscope (SEM), and is an average particle diameter of primary particles accurately captured without taking into account an aggregated state.

As a result, the present inventors determined the average particle diameter D by the laser diffraction scattering particle size distribution measurement method₅₀And D obtained by image analysis_IABy D₅₀/D_IAThe calculated value was taken as the degree of aggregation. That is, in the same lot of the fine-particle silver powder, it is assumed that D can be measured with the same accuracy₅₀And D_IAIf considered according to the above theory, the measured value D of the aggregation state is reflected₅₀Has a value of greater than D_IAThe value of (c). At this time, if the aggregation state of the particles of the fine-particle silver powder is smaller,D₅₀the value of (A) is infinitely close to D_IAValue of (b) as degree of agglomeration D₅₀/D_IAThe value of (d) is close to 1. When the degree of aggregation is 1, it can be said that the single-dispersed powder is in an aggregated state in which no powder particles are present at all.

Therefore, the present inventors investigated the correlation between the degree of aggregation and the viscosity of the fine silver powder paste produced from the fine silver powder of each degree of aggregation, the surface smoothness of the conductor obtained by sintering, and the like. As a result, it was found that a good correlation can be obtained. From this, it was found that, if the degree of aggregation of the fine-particle silver powder is adjusted, the viscosity of the fine-particle silver powder paste produced using the fine-particle silver powder can be arbitrarily adjusted. Further, it was found that when the degree of aggregation is adjusted to 1.5 or less, the change in the viscosity of the fine silver particle paste, the surface smoothness after firing, and the like can be controlled in a very narrow region. Further, the less the aggregation state, the higher the film density of the conductor obtained by sintering with the fine-particle silver oxide powder, and as a result, the resistance of the sintered conductor formed can be reduced.

In addition, the degree of aggregation actually calculated may not have a value of 1. This is because D is used for the calculation of the degree of aggregation_IAAssuming true spherical balls, a value of 1 should not be obtained theoretically, but actually, since true spherical balls are not obtained, a value of 1 degree of aggregation is obtained.

c. Has a crystallite diameter of 10nm or less, and the crystallite diameter is very closely related to the sintering initiation temperature. That is, when silver powders having the same average particle size are compared with each other, the smaller the crystallite diameter is, the more likely sintering is to occur at a low temperature. Therefore, the fine particles such as the fine particle silver powder of the present invention have a large surface energy and a small crystallite diameter of 10nm or less, and thus the sintering initiation temperature can be lowered. Here, the crystallite diameter is not limited to a lower limit because a certain measurement error occurs depending on a measurement apparatus, measurement conditions, and the like. In addition, it is difficult to require high reliability for the measured value in the range of the crystallite diameter of 10nm or less, and if the lower limit value is not specified, the measured value is about 2nm according to the results of the study by the present inventors.

The fine-particle silver powder of the present invention has the powder characteristics of a to c as described above, and is a fine-particle silver powder having a low-temperature sinterability of 240 ℃ or lower in view of the characteristic of the sintering initiation temperature of the fine-particle silver powder of the present invention. The lower limit of the sintering initiation temperature is not particularly limited, but if the study by the inventors and the general technical knowledge are taken into consideration, it is almost impossible to obtain the sintering initiation temperature of 170 ℃ or lower, and the temperature is considered to be a temperature corresponding to the lower limit.

In particular, as an effect of having the above powder characteristics, the fine-particle silver powder of the present invention has a tap filling density of 4.0g/cm³The above high density. The tap filling density referred to herein is obtained by accurately weighing 200g of fine-particle silver powder in a 150cm container³The silver powder volume was measured by repeating the falling impact 1000 times with a stroke of 40mm in the measuring cylinder of (1). The tap filling density is theoretically a higher value as the particle size is fine and the dispersibility of the particles is high without aggregation, and the higher value is obtained. Considering that the tap density of the conventional silver powder is less than 4.0g/cm³It was confirmed that the fine-particle silver powder of the present invention is a very fine-particle silver powder having excellent dispersibility.

Method for producing fine-particle silver powder

The method for producing a silver powder is characterized by using a reducing agent amount, a silver nitrate amount and an ammonia amount which are added to a silver nitrate aqueous solution to be a thin concentration, and performing a mixing reaction of the silver nitrate aqueous solution and ammonia water to obtain a silver-ammonia complex aqueous solution, subjecting the silver-ammonia complex aqueous solution to a contact reaction with an organic reducing agent to reduce and precipitate silver particles, and performing filtration, washing and drying. Conventionally, since a reducing agent solution and a silver ammine complex aqueous solution are generally mixed in a batch in a tank, it is not possible to ensure productivity on a plant scale without adding a large amount of silver nitrate, reducing agent, and ammonia water in order to adjust the silver concentration to a concentration of 10g/l or more.

The most important feature of the production method of the present invention is that the concentration of the organic reducing agent after the contact reaction between the aqueous solution of silver-ammonia complex and the organic reducing agent is low, and the organic reducing material remaining on the surface of the particles of the silver powder to be produced or entering the interior of the particles during the growth of the particles can be reduced. Therefore, it is most preferable to maintain the silver concentration in the mixed solution at 1g/l to 6g/l and the organic reducing agent concentration at 1g/l to 3 g/l.

Here, there is a proportional relationship between the silver concentration and the amount of the organic reducing agent, and it is needless to say that a larger amount of the silver powder can be obtained as the silver concentration is higher. However, if the silver concentration exceeds 6g/l, the deposited silver particles tend to be coarse, and the particle diameter is not different from that of the conventional silver powder, and thus the fine-particle silver powder having high dispersibility according to the present invention cannot be obtained. On the other hand, if the silver concentration is less than 1g/l, the silver powder is obtained as fine particles, but if it is too fine, the oil absorption increases, which increases the tackiness, and the amount of the organic vehicle needs to be increased, which eventually decreases the film density of the sintered conductor to be formed, and tends to increase the electric resistance. In addition, the necessary industrial productivity cannot be satisfied.

Therefore, maintaining the silver concentration at 1g/l to 6g/l and the organic reducing agent concentration at 1g/l to 3g/l is the most suitable condition for obtaining the fine-particle silver powder of the present invention with a good yield. Here, the organic reducing agent concentration is set to 1g/l to 3g/l, which is selected as the most suitable range for obtaining the fine-particle silver powder in relation to the silver concentration of the silver-ammonia complex aqueous solution. If the concentration of the organic reducing agent exceeds 3g/l, the amount of the reducing agent added to the silver-ammonia complex aqueous solution can be reduced, but the aggregation of the silver powder particles precipitated by reduction starts to progress significantly, and the amount of impurities contained in the particles (in this specification, the content of impurities is represented by the carbon content) starts to increase rapidly. On the other hand, if the concentration of the organic reducing agent is less than 1g/l, the total amount of the reducing agent used increases, and the amount of wastewater to be treated also increases, and thus the industrial economy cannot be satisfied.

As used herein, the term "organic reducing agent" refers to hydroquinone, ascorbic acid, glucose, and the like. Among them, hydroquinone is preferably used as the organic reducing agent. In the present invention, hydroquinone has the most suitable reaction rate necessary to obtain a silver powder having low crystallinity, which has relatively excellent reactivity and a small crystallite diameter, as compared with other organic reducing agents.

In addition, other additives may be used in combination with the organic reducing agent. The additive mentioned here is a gum such as gelatin, an amine-based polymer agent, cellulose, or the like, and preferably an additive that can stabilize the reduction and precipitation process of silver powder and also function as a dispersant, and may be appropriately selected and used depending on the type of the organic reducing agent, the process, and the like.

Further, as for the method of reducing and precipitating the fine-particle silver powder by bringing the silver-ammonia complex aqueous solution obtained by the above-mentioned method into contact with a reducing agent, in the present invention, as shown in FIG. 1, it is preferable to use a silver-ammonia complex aqueous solution S₁Flows through a predetermined flow path (hereinafter referred to as a "first flow path" as well as above), a second flow path b provided in the first flow path a and joining the first flow path a, and an organic reducing agent and an additive S as required are fed through the second flow path b₂A method of flowing into the first channel a, mixing the first channel a and the second channel b at the confluence point m, and reducing the deposited silver particles (hereinafter, this method is referred to as "confluence mixing method").

By adopting the confluence mixing method as described above, the mixing of the two liquids is completed in a minimum time, and the reaction proceeds in a uniform state in the system, so that particles in a uniform state can be formed. In addition, the small amount of the organic reducing agent as viewed in the entire mixed solution means that the amount of the organic reducing agent adsorbed and remaining on the particle surfaces of the fine-particle silver powder reduced and precipitated is small. As a result, the amount of impurities adhering to the fine-particle silver powder obtained by filtering and drying can be reduced. By reducing the amount of impurities attached to the fine silver powder, the resistance of the sintered conductor formed of the silver paste can also be reduced.

Particularly, when the silver nitrate aqueous solution and the ammonia water are subjected to contact reaction to obtain the silver-ammonia complex aqueous solution, the silver nitrate aqueous solution with the silver nitrate concentration of 2.6g/l to 48g/l is preferably used to obtain the silver-ammonia complex aqueous solution with the silver concentration of 2g/l to 12 g/l. The concentration of the silver nitrate aqueous solution defined herein has the same meaning as the liquid amount of the silver nitrate aqueous solution defined herein, and the concentration and liquid amount of the aqueous ammonia solution added thereto are necessarily defined amounts so that the silver concentration of the silver-ammonia complex aqueous solution is 2g/l to 12 g/l. At this stage, although the clear technical reason has not been clarified, the fine silver powder having more excellent production stability and stable quality can be obtained by using the silver nitrate aqueous solution having the silver nitrate concentration of 2.6g/l to 48 g/l.

Effects of the invention

It was confirmed that the fine-particle silver powder of the present invention has a degree of fineness that has not been found in the past, and has high dispersibility. In addition, by adopting the production method as described above, the fine-particle silver powder of the present invention can be efficiently produced.

Drawings

Fig. 1 is a diagram showing a concept of mixing a silver-ammonia complex aqueous solution and a reducing agent.

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

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

Fig. 4 is a scanning electron microscope observation image of the fine-particle silver powder according to the conventional production method.

Fig. 5 is a scanning electron microscope observation image of the fine-particle silver powder according to the conventional production method.

Detailed Description

Hereinafter, preferred examples of the present invention will be described in detail with reference to comparative examples.

Example 1

In this example, the fine-particle silver powder was produced by the above-described production method, and the powder characteristics of the obtained fine-particle silver powder were measured. Further, silver paste was prepared using fine-particle silver powder to form a test circuit, and the conductor resistance and the sintering initiation temperature were measured.

First, 63.3g of silver nitrate was dissolved in 9.7 liters of pure water to prepare a silver nitrate aqueous solution, and 235ml of 25 wt% aqueous ammonia was added to the silver nitrate aqueous solution at once, followed by stirring to obtain a silver-ammonia complex aqueous solution.

The silver-ammonia complex aqueous solution was introduced into a first channel a having an inner diameter of 13mm as shown in FIG. 1 at a flow rate of 1500ml/sec, and a reducing agent was introduced from a second channel b at a flow rate of 1500ml/sec, and contacted at a temperature of 20 ℃ in the confluence point m, thereby reducing and depositing a fine-particle silver powder. The reducing agent used in this case was an aqueous hydroquinone solution prepared by dissolving 21g of hydroquinone in 10 liters of purified water. Therefore, the hydroquinone concentration at the end of the mixing was about 1.04g/l, which is a very dilute concentration.

To separate the thus obtained fine particulate silver powder, filtration was performed using a filter, washing was performed with 100ml of water and 50ml of methanol, and further drying was performed at 70 ℃ for 5 hours to obtain a fine particulate silver powder. Fig. 2 shows a scanning electron microscope image of the fine-particle silver powder thus obtained.

The powder characteristics of the fine-particle silver powder thus obtained are shown in table 1 together with the powder characteristics of the silver powders obtained in example 2 and comparative example. Here, a measurement method and the like which are not clear from the above description will be described. The sintering initiation temperature in Table 1 was set such that 0.5g of the fine-particle silver powder was accurately weighed out by a balance and used at 2t/cm²The pressure of (3) was increased for 1 minute to prepare pellets, which were then subjected to a thermomechanical analyzer (TMA device) TMA/SS6000 manufactured by セイコ - インスツルメンツ to prepareThe air flow rate was 200 cc/min, the temperature rise rate was 2 ℃/min, and the holding time was 0 min, and the measurement was carried out at a temperature ranging from room temperature to 900 ℃. The conductor resistance shown in Table 1 is a value measured by using a circuit having a width of 1mm which is obtained by preparing a silver paste using each silver powder, forming a circuit on a ceramic substrate, and sintering the circuit at a temperature of 180 to 250 ℃ until the resistance can be measured. The silver paste consisted of 85 wt% of fine silver powder, 0.75 wt% of ethyl cellulose, and 14.25 wt% of terpineol. FIB analysis is used to measure the size of precipitated crystal grains and to measure the crystallite diameter. The carbon content was an index for measuring the content of impurities adhering to the particles of the silver powder, and was measured by a combustion-infrared absorption method using ENMIA-320V manufactured by horiba, mixing 0.5g of fine-particle silver powder, 1.5g of tungsten powder, and 0.3g of tin powder, placing them in a magnetic crucible.

Example 2

In this example, a fine-particle silver powder was produced under production conditions different from those of example 1, and the powder characteristics of the obtained fine-particle silver powder were measured. Further, silver paste was prepared using fine-particle silver powder to form a test circuit, and the conductor resistance and the sintering initiation temperature were measured.

First, 63.3g of silver nitrate was dissolved in 3.1 liters of pure water to prepare a silver nitrate aqueous solution, and 235ml of 25 wt% aqueous ammonia was added to the silver nitrate aqueous solution at a time, followed by stirring to obtain a silver-ammonia complex aqueous solution.

The silver-ammonia complex aqueous solution was introduced into a first channel a having an inner diameter of 13mm as shown in FIG. 1 at a flow rate of 1500ml/sec, and a reducing agent was introduced from a second channel b at a flow rate of 1500ml/sec, and contacted at a temperature of 20 ℃ in the confluence point m, thereby reducing and depositing a fine-particle silver powder. The reducing agent used at this time was an aqueous hydroquinone solution prepared by dissolving 21g of hydroquinone in 3.4L of pure water. Therefore, the hydroquinone concentration at the end of the mixing was about 3.0g/l, which was a very dilute concentration.

The thus-obtained fine-particle silver powder was filtered using a filter, washed with 100ml of water and 50ml of methanol, and further dried at 70 ℃ for 5 hours in the same manner as in example 1 to obtain a fine-particle silver powder. Fig. 3 shows a scanning electron microscope image of the fine-particle silver powder thus obtained. The powder characteristics of the fine-particle silver powder thus obtained are shown in table 1 together with the powder characteristics of the silver powders obtained in example 1 and comparative example.

Comparative example 1

In this comparative example, the fine-particle silver powder was produced by the production method shown below, and the powder characteristics of the obtained fine-particle silver powder were measured. Further, silver paste was prepared using fine-particle silver powder to form a test circuit, and the conductor resistance and the sintering initiation temperature were measured.

First, 63.3g of silver nitrate was dissolved in 1.0 liter of pure water to prepare a silver nitrate aqueous solution, and 235ml of 25 wt% aqueous ammonia was added to the silver nitrate aqueous solution at a time, followed by stirring to obtain a silver-ammonia complex aqueous solution.

The silver-ammonia complex solution was charged into a reaction tank, an aqueous hydroquinone solution prepared by dissolving 21g of hydroquinone in 1.3 l of purified water was added to the reaction tank as a reducing agent at a time, and the solution temperature was maintained at 20 ℃ to reduce and precipitate silver powder by stirring reaction. The hydroquinone concentration at the end of the mixing was about 8.23g/l, a high concentration.

The thus-obtained fine-particle silver powder was filtered through a filter in the same manner as in example 1, washed with 100ml of water and 50ml of methanol, and further dried at 70 ℃ for 5 hours to obtain a fine-particle silver powder. Fig. 4 shows a scanning electron microscope image of the fine-particle silver powder thus obtained. The powder characteristics of the fine-particle silver powder thus obtained are shown in table 1 together with the powder characteristics of the silver powder obtained in the above examples and comparative example 2.

Comparative example 2

First, 63.3g of silver nitrate was dissolved in 300ml of pure water to prepare a silver nitrate aqueous solution, and 235ml of 25 wt% aqueous ammonia was added to the silver nitrate aqueous solution at a time, followed by stirring to obtain a silver-ammonia complex aqueous solution.

The silver-ammonia complex solution was charged into a reaction vessel, and a solution of gelatin (3 g) in pure water (200 ml) and an aqueous hydroquinone solution (21 g) in which hydroquinone (21 g) was dissolved in pure water (700 ml) were placed in the reaction vessel at once, and silver powder was reduced and precipitated by stirring reaction while maintaining the temperature at 20 ℃. The hydroquinone concentration at the end of the mixing was about 14.5g/l, a high concentration.

The thus-obtained fine-particle silver powder was filtered through a filter in the same manner as in example 1, washed with 100ml of water and 50ml of methanol, and further dried at 70 ℃ for 5 hours to obtain a fine-particle silver powder. Fig. 5 shows a scanning electron microscope image of the silver powder thus obtained. The powder characteristics of the fine-particle silver powder thus obtained are shown in table 1 together with the powder characteristics of the silver powder obtained in the above examples and comparative example 2.

Comparative example 3

First, 20g of polyvinylpyrrolidone and 50g of silver nitrate were dissolved in 260ml of pure water to prepare a silver nitrate aqueous solution, and 25g of nitric acid was added to the silver nitrate aqueous solution at a time and stirred to obtain a silver-containing nitric acid solution. The ascorbic acid concentration at the end of this mixing was about 36.0 g/l.

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

The silver-containing nitric acid-based solution was placed in a reaction tank, the reducing solution was added to the reaction tank at once, and the silver powder was reduced and precipitated by stirring reaction while maintaining the liquid temperature at 25 ℃.

The thus-obtained fine-particle silver powder was filtered through a filter in the same manner as in example 1, washed with 100ml of water and 50ml of methanol, and further dried at 70 ℃ for 5 hours to obtain a fine-particle silver powder. The powder characteristics of the fine-particle silver powder thus obtained are shown in table 1 together with the powder characteristics of the silver powders obtained in the above examples and comparative examples.

Comparative analysis of examples and comparative examples

The above examples and comparative examples are compared with each other with reference to table 1. The particle size of the primary particles can be clearly understood from the scanning electron microscope images shown in fig. 2 to 5.

TABLE 1

As is clear from table 1, even when the characteristic values of the respective powders are compared, the fine-particle silver powders obtained in the above examples are fine-particle silver powders having high dispersibility with respect to the silver powders produced by the conventional production methods, and are not present in the conventional silver powders. Further, regarding the sintered conductor characteristics, the fine silver particles of the present invention have high film density and low electrical resistance when used to form a circuit. In each comparative example, it was found that the conductor resistance was high, and the measurement was impossible in some cases.

Possibility of industrial utilization

The fine-particle silver powder of the present invention is composed of fine particles which are not imaginable in the conventional silver powder, and the fine particles have a low degree of aggregation, and exhibit very excellent dispersibility even when compared with the conventional silver powder. Further, according to the method for producing fine-particle silver powder of the present invention, the organic matter remaining in the obtained fine-particle silver powder can be reduced to cause an overlapping action with a high film density due to the fine-particle silver powder, and as a result, the method contributes to reduction in the electric resistance of the obtained conductor.

Claims

1. A fine-particle silver powder having low particle cohesion, characterized by having the following powder characteristics a to c:

a. average particle diameter D of primary particles obtained by image analysis of scanning electron microscope image_IAIs less than 0.6 μm;

b. using the average particle diameter D of the primary particles_IAAnd an average particle diameter D measured by a laser-refraction scattering-type particle size distribution measuring method₅₀By D₅₀/D_IAThe degree of aggregation is 1.5 or less;

c. the crystallite diameter is less than 10 nm.

2. The particulate silver powder according to claim 1, wherein the sintering initiation temperature is 240 ℃ or lower.

3. A process for producing a fine-particle silver powder, which comprises mixing a silver nitrate aqueous solution and an aqueous ammonia solution to react and obtain a silver-ammonia complex aqueous solution, adding a reducing agent to the silver-ammonia complex aqueous solution to reduce and precipitate silver particles, and filtering, washing and drying the silver-ammonia complex aqueous solution to obtain a fine-particle silver powder, characterized in that the silver-ammonia complex aqueous solution is mixed in contact with an organic reducing agent, and the silver concentration is maintained at 1 to 6g/l and the organic reducing agent concentration is maintained at 1 to 3g/l in the mixed solution to reduce and precipitate the silver particles.

4. The method for producing the particulate silver powder according to claim 3, wherein the silver-ammonia complex aqueous solution is mixed by contacting the silver-ammonia complex aqueous solution with the organic reducing agent, the silver-ammonia complex aqueous solution is caused to flow through a predetermined first channel, a second channel merged in the first channel is provided, the organic reducing agent is caused to flow through the second channel, and the contact mixing is carried out at a merging point of the first channel and the second channel.

5. The method for producing the fine-particle silver powder according to claim 3, wherein an aqueous silver-ammonia complex solution having a silver concentration of 2 to 12g/l is used, in which an aqueous silver nitrate solution having a silver nitrate concentration of 2.6 to 48g/l and aqueous ammonia are mixed and reacted.

6. The method for producing the fine-particle silver powder according to claim 4, wherein an aqueous solution of a silver-ammonia complex having a silver concentration of 2 to 12g/l is used, in which an aqueous solution of silver nitrate having a silver nitrate concentration of 2.6 to 48g/l and aqueous ammonia are mixed and reacted.

7. The method for producing the particulate silver powder according to any one of claims 3 to 6, wherein the organic reducing agent used contains a dispersant.

8. The method for producing the particulate silver powder according to any one of claims 3 to 6, wherein hydroquinone is used as the organic reducing agent.

9. The method for producing a particulate silver powder according to claim 7, wherein hydroquinone is used as the organic reducing agent.