KR101327973B1 - Process for producing flaky silver powder and flaky silver powder produced by the process - Google Patents

Abstract

In the case where the conductor is formed using the conductive paste with excellent powder characteristics, a method for producing flake silver powder which can prevent the increase in the conductor resistance and reliably prevent the conductivity, and the provision of the flake silver powder produced by the production method For the purpose. In order to achieve this object, a dispersion step of dispersing fine silver powder composed of substantially spherical silver particles in a solvent to form a slurry, and the slurry and media beads having a particle diameter of 0.2 mm or less in a bead mill Adding and stirring the silver particles to plastically deform each silver particle to form a flake silver powder; a separation step of separating the slurry and the media beads to collect the flake silver powder; and the collected flake silver powder. A method of producing a flake silver powder is employed, which comprises a washing and drying step of removing impurities and water by washing and drying to obtain flake silver powder.

Description

Manufacturing method of flake silver powder and flake silver powder manufactured by the manufacturing method TECHNICAL FIELD [PROCESS FOR PRODUCING FLAKY SILVER POWDER AND FLAKY SILVER POWDER PRODUCED BY THE PROCESS}

This invention relates to the manufacturing method of the flake silver powder which consists of flake shaped particle | grains, and the flake silver powder manufactured by the manufacturing method.

Conventionally, flake silver powder is used as one of the electrically conductive paste raw materials used for die bonding, circuit formation of a printed wiring board, or the like. This flake silver powder consists of flake silver particles. In addition, the flake silver powder has a large specific surface area because each particle is flaky. Therefore, when the conductive paste is produced using the flake silver powder, the contact area between the particles increases in the conductive paste, so that the conductivity is higher than that of the conductive paste using silver powder in which the particles are not flake-like, which is advantageous for conductor formation.

Moreover, in the manufacturing method of a flake silver powder, a silver powder and a grinding | pulverization medium (in this specification, the term "media" is used) are put into a grinder and mixed, and it presses and deforms each spherical particle which is substantially spherical. The method of making is generally used. In this method, however, when the particles are deformed, it is difficult to control the particle size, and when flakes are formed, coarse and large flake particles in which adjacently deformed particles are connected or excessively deformed are produced. Therefore, even when this electrically conductive paste is manufactured using this flake silver powder and tries to form a microcircuit using this electrically conductive paste again, formation of a microcircuit is difficult and the use range of the flake silver powder was limited.

In the production of such flake silver powder, in order to obtain a product having a uniform particle shape and particle size, a method of adding a lubricant during mixing and stirring has been proposed (see Patent Documents 1 and 2). By using this method, a lubricant is interposed between the particles, thereby suppressing agglomeration due to the plastic deformation of the particles when flakes, and it is possible to prevent the formation of large and large flake particles.

In the case of producing the flake silver powder, if a lubricant is used as in the methods proposed in Patent Documents 1 and 2, the lubricant remains on the surface of the finally obtained flake silver powder. For this reason, even if this electrically conductive paste is manufactured using this flake silver powder, and a conductor is formed and baked with this electrically conductive paste, since a lubricant remains on the surface of the particle | grains, since conductor resistance rises, it is unpreferable. Therefore, the method of removing the lubricant which remains on the surface of a flake silver powder is proposed (refer patent document 3).

Patent Document 1: Japanese Patent Application Laid-Open No. 4-359069

Patent Document 2: Japanese Patent Application Laid-Open No. 2003-55701

Patent Document 3: Japanese Patent Application Laid-Open No. 2004-197030

<Problem that invention is going to solve>

However, even if the method proposed in Patent Document 3 is used, the lubricant cannot be completely removed from the flake silver powder unless the treatment conditions are strictly controlled. Therefore, even if the lubricating agent is removed after the same as in Patent Document 3, the lubricating agent remains slightly on the surface of each particle of the flake silver powder. Therefore, even when this electrically conductive paste was manufactured and this conductor was formed using this flake silver powder, there existed a fixed limit in reducing the conductor resistance.

In addition, although flake copper powder is generally known as a powder of flake-shaped particles, the mechanical strength of copper powder is relatively high, so that the processing conditions are not strictly controlled when plastically deforming the particles using the media. We could supply the product to the market. On the other hand, silver powder is a soft material with excellent ductility in physical properties compared to copper powder. For this reason, when processing conditions, such as copper powder, are employ | adopted, deformation of silver particle will become remarkable and it will become the aggregated flake silver powder, and the powder characteristic was remarkably deteriorated and it was not practical to use it at all.

This invention solves such a conventional problem, and is excellent in powder characteristics, when forming a conductor using it for an electrically conductive paste, the manufacturing method of the flake silver powder which can prevent a raise of conductor resistance and can reliably prevent the fall of electroconductivity. And flake silver powder produced by the production method thereof.

〈Means for solving the problem〉

Therefore, the inventors of the present invention have adopted the following means in order to solve the above problems as a result of intensive studies.

Method for producing flake silver powder according to the present invention: The method for producing flake silver powder according to the present invention is a method of producing a slurry having a silver concentration of 5 vol% or more by dispersing a silver powder composed of substantially spherical silver particles in a solvent. A dispersing step, a processing step of plastically deforming each silver particle in the slurry to produce flake silver powder by mixing and mixing the slurry and media beads having a particle diameter of 0.2 mm or less in a bead mill, and mixing and stirring A separation step of separating the slurry and the media beads to collect the flake silver powder, and a washing and drying step of removing the impurities and moisture by washing and drying the collected flake silver powder to obtain the flake silver powder. It is a manufacturing method characterized by the above-mentioned.

And in the said dispersion | distribution process of the manufacturing method of the flake silver powder which concerns on this invention, it is preferable to set the compounding quantity of the said silver powder and the said solvent so that the said silver powder concentration in the said slurry may be 5 to 90 volume%. .

In addition, in the said processing process of the manufacturing method of the flake silver powder which concerns on this invention, the compounding ratio of the said media beads with respect to the said silver powder in the said slurry is [the amount of silver powder in a slurry (vol%)]: [the amount of media beads] (Volume%)] is preferably set in the range of 1: 1: 1 to 1: 110.

Moreover, in the manufacturing method of the flake silver powder which concerns on this invention, the dissolution process is provided before the said dispersing process, It is preferable that the said silver powder used at the said dispersing process uses the silver powder processed by this disassembly process. Do.

Flake silver powder obtained by the manufacturing method which concerns on this invention: The flake silver powder which consists of flake silver powders manufactured using the manufacturing method which concerns on this invention.

<Effects of the Invention>

The method for producing flake silver powder according to the present invention facilitates contact between media particles and media beads when plastically deforming the silver powder particles to form a flake shape, and furthermore, by using media beads having a small particle size. And plastic deformation stress at the time of the collision of silver particle and a media bead were considered appropriate. This enables proper flake formation without deforming to coarse particle levels in a state in which coagulation is not caused from the soft and fine raw silver powder. Therefore, the flake silver powder excellent in the powder characteristic can be manufactured.

In addition, since the lubricating silver powder manufacturing method which concerns on this invention does not need to use a lubricating agent like flakes in a dry method, it does not generate | occur | produce a strong contamination like flake particle surface contamination by a lubricating agent. Therefore, even when the conductor is formed by using the flake silver powder obtained by this manufacturing method in the conductive paste forming a fine circuit, the electrical resistance due to the incorporation of impurities is prevented, so that the increase in the conductor resistance is prevented and the conductivity is lowered. You can definitely stop it.

As mentioned above, the powder characteristic of the flake silver powder obtained by the manufacturing method of the flake silver powder which concerns on this invention is the outstanding thing which has not existed conventionally. In addition, the flake silver powder is excellent in particle dispersibility and has little organic contamination on the surface of its constituent particles, and is therefore suitable as a high quality conductive paste material. Therefore, in the case where the conductor is formed using the flake silver powder for the conductive paste, the increase in the conductor resistance can be prevented and the drop in the conductivity can be reliably prevented, so that it can be used in a wide range of fields.

1 is a scanning electron microscope observation image of flake silver powder obtained by the method described in the first embodiment.

Fig. 2 is a scanning electron microscope observation image of flake silver powder obtained by the method described in the second embodiment.

3 is a scanning electron microscope observation image of the flake silver powder obtained by the method described in Example 3. FIG.

Fig. 4 is a scanning electron microscope observation image of flake silver powder obtained by the method described in the fourth embodiment.

Fig. 5 is a scanning electron microscope observation image of flake silver powder obtained by the method described in the first comparative example.

6 is a scanning electron microscope observation image of the flake silver powder obtained by the method described in Comparative Example 2. FIG.

Production form of flake silver powder according to the present invention: The method for producing the flake silver powder according to the present invention includes the following steps. It explains by process.

Dispersion process: In this process, the silver powder which consists of substantially spherical silver particle is disperse | distributed in a solvent, and the slurry of 5 volume% or more of silver concentration is produced. The raw material powder for obtaining a flake silver powder here is "silver powder which consists of roughly spherical silver particle." The reason for this is that the silver powder composed of substantially spherical silver particles is obtained by the wet neutralization reduction method and is excellent in economic efficiency, and is also very suitable for producing the flake silver powder according to the present invention. And the powder characteristic of the flake silver powder which can be obtained largely depends on the powder characteristic which the silver powder which consists of this substantially spherical silver particle has originally. The silver powder which consists of this substantially spherical silver particle is mentioned later.

And as a solvent which disperse | distributes the silver powder which consists of said substantially spherical silver particle, the mixed solvent of water, an organic solvent, water, and an organic solvent can be used. Considering the residual of the solvent component as a contaminant on the particle surface, it is preferable to employ a solvent having a composition as close to water as possible.

However, it is preferable to use an organic solvent independently from a viewpoint of improving the dispersibility of silver particles in a slurry and aiming at quality stabilization at the time of flaking. In such a case, it is preferable to use alcohols, such as methanol, ethanol, ethylene glycol, as an organic solvent. The reason for this is that volatilization is easy, the acid efficiency during drying of the flake silver powder is high, and there is little residue on the surface of the particles.

In addition, when using a mixed solvent of water and an organic solvent, it is preferable to use a mixed solvent in the range of [organic solvent (% by volume)] / [water (% by volume)] = 0.05 to 0.5. When [organic solvent (% by volume)] / [water (% by volume)] is less than 0.05, the amount of organic solvent is small and the effect of improving the dispersibility of silver particles cannot be obtained. On the other hand, if the amount of organic solvent is set to exceed [organic solvent (vol%)] / [water (vol%)] = 0.5, the residual amount of the organic solvent component in the particles can be obtained even if it is possible to carry out post drying. It becomes remarkable, and when the drying conditions are weak, as a result, the residual amount of carbon on the surface of the flake silver powder particles increases.

And it is preferable to set the compounding quantity of the said silver powder and the said solvent so that the said silver powder concentration in the said slurry may be 5 volume% or more of silver concentration, More preferably, it is 5 volume%-90 volume%. Here, if the silver powder concentration in the slurry is set to less than 5% by volume, that is, if the amount of silver powder blended is too small for the solvent, the amount of flake silver powder obtained in one step is extremely small, so that Production efficiency is not good. On the other hand, when the silver powder concentration in the slurry is set to more than 90% by volume, that is, when the amount of the silver powder blended is too large with respect to the solvent, there is a high probability that the particles are connected at the time of flake formation, and the occurrence frequency of the coarse and large flake particles rapidly increases. To rise. Therefore, by setting the blending amount of the silver powder and the solvent so that the silver powder concentration in the slurry is optimal, not only the connection between the particles can be reliably prevented but also the production efficiency can be increased.

And when disperse | distributing in a solvent, you may perform simple stirring. However, when agitation and dispersing means capable of releasing the aggregated state of particles such as a fluid mill or TK Philmix as a means for dispersing the silver powder into a solvent, dissociation of the agglomerated particles in the preparation step of the slurry containing the silver powder can be achieved. It is possible to improve particle dispersibility.

In addition, when a remarkable aggregation state is recognized by the silver powder which consists of substantially spherical silver particles used at a dispersion process, or when it is desired to improve the particle dispersibility as a raw material powder, it is preferable to provide a disassembly process before a dispersion process. Disassembly means releasing the aggregation state of a particle | grain, and making it approach the state of a primary particle. In other words, the raw silver powder is preferably in a separated state as close to the primary particles as possible. When the dispersibility of each particle is increased by this dissociation step, the particle dispersibility into the slurry prepared in the dispersing step is also improved. In the processing step described later, contact with the media beads becomes possible in a state where the particle dispersibility is high. Even if the particle size is small, the flake silver powder can be reliably manufactured without using a lubricant. In particular, the silver powder produced by the wet method forms a uniform aggregated state as it is atomized. Therefore, it is preferable to perform the dissociation process in this invention before a dispersion process.

For the purpose of simply dismantling, various means such as high-energy ball mill, high-speed conductor impingement airflow pulverizer, impact crusher, cage mill, medium stirring mill, high hydraulic pulverizer, etc. Can be used. By the way, in consideration of reducing the viscosity of the electrically conductive paste using flake silver powder as much as possible, it is preferable to make the specific surface area of the silver powder which consists of substantially spherical silver particle which is raw material powder as small as possible. Therefore, disassembly should not be a disassembly method, such as damaging the surface of the particle at the time of disassembly and increasing its specific surface area. In particular, silver powder, which is softer than copper powder, is an important problem.

Therefore, a method of minimizing the contact of silver powder particles with parts of the inner wall of the apparatus, the stirring blades, the pulverizing medium, etc., and agglomerated particles collide with each other, and furthermore, a method capable of sufficiently dissolving should be adopted. And a method which raises the particle | grains in the aggregation state by causing sufficient particle collision, and simultaneously improves the smoothness of the particle surface by collision of particle | grains is employ | adopted.

As a method of performing such a disassembly process, the wind circulator which used the centrifugal force with respect to the dry silver powder which is agglomerated state is used. The "wind circulator using centrifugal force" as used herein refers to a pulverized silver powder blown with air to circulate in a circumferential orbit, and the particles are collided with each other in the airflow by the centrifugal force generated at this time to perform the dissociation work. It is to. At this time, it is also possible to use a commercially available wind classifier using centrifugal force. In such a case, it is not aimed at the classification to the last, but a circular wind power blower blows up the aggregated silver powder to draw a circumferential orbit, and the circle which collides the aggregated particle | grains in the atypical state is carried out. It acts as a rater.

As another method of performing the disintegration treatment, a fluid mill using centrifugal force may be used for the silver powder slurry containing the silver powder in the aggregated state. The "fluid mill using centrifugal force" referred to herein means that the silver powder slurry is flowed at high speed so as to draw a circumferential trajectory, and the particles agglomerated by the centrifugal force generated at this time collide with each other in a solvent to perform the dissociation work.

The above-mentioned disassembly process may be repeated several times as needed, and arbitrary selection of a disassembly process level is possible according to quality required. The silver powder subjected to the disintegration treatment is released from the aggregated state and has new powder characteristics. When the dissociation level at this time is expressed as a numerical value, the value of the cohesiveness represented by D ₅₀ / D _IA is 1.5 using the volume cumulative particle diameter D ₅₀ obtained by laser diffraction scattering particle size distribution measurement method and the average particle diameter D _IA obtained by image analysis. It is preferable to set it as follows. It is because the particle dispersibility close to monodispersion is ensured when the aggregation degree here is 1.5 or less.

The aggregation degree used here was employ | adopted for the following reasons. That is, the value of the volume cumulative particle diameter D ₅₀ obtained using the laser diffraction scattering particle size distribution measurement method does not actually observe the diameter of each particle directly. Particles constituting most of the silver powder are in a state where a plurality of particles aggregate and aggregate. The laser diffraction scattering particle size distribution measuring method calculates the volume cumulative particle diameter by grasping aggregated particles as one particle (aggregated particle). On the other hand, since the average particle diameter D _IA obtained by image-processing the observation image of the silver powder observed using the scanning electron microscope (SEM) is directly obtained from the SEM observation image, the primary particle can be grasped reliably, It does not reflect the presence of particle agglomeration at all.

Therefore, this matter inventors, by using the average grain size D _IA obtained by a volume cumulative particle diameter D ₅₀ and an image analyzer of a laser diffraction scattering type particle size distribution measuring method, and determine the value calculated by D ₅₀ / D _IA as the degree of compaction. That is, in the same lot of silver powder, assuming that the values of D ₅₀ and D _IA can be measured with the same accuracy, and considering the above theory, the value of D ₅₀ reflecting the agglomeration state in the measured value is D. It is considered normal to be larger than the value of _IA . At this time, the value of D ₅₀ becomes closer to the value of D _IA as the aggregation state of the silver powder particles disappears, and the value of D ₅₀ / D _{IA which} is the degree of aggregation becomes close to one. In the stage where the degree of aggregation became 1, it can be judged that the monodisperse powder has completely lost the aggregation state of the particles. In reality, however, the degree of aggregation may be less than 1. In theory, in the case of a perfect spherical form, the value is not less than 1, but in practice, a value of a cohesiveness of less than 1 may be obtained instead of a perfect spherical form. In addition, image analysis of the silver powder observed using the scanning electron microscope (SEM) in this specification makes roundness threshold value 10 and superposition degree 20 using IP-1000PC of Asahi Engineering Co., Ltd. product. Circular particle analysis was performed to obtain an average particle diameter D _IA .

Processing step: In this step, the silver particles in the slurry are plastically deformed by mixing the slurry and media beads having a particle diameter of 0.2 mm or less into a bead mill, followed by mixing and stirring to obtain a flake silver powder.

Here, it is characterized by using fine-grained media beads having a particle diameter of 0.2 mm or less. Production method of the flake silver powder according to the matter application, it is intended for the production of flake silver powder of the minute particle diameter, weird kind of way may be made of a silver powder of the raw material powder is substantially spherical particles, D ₅₀ is less than the 2㎛, D _IA 1.0 The premise is to use fine silver powder at a level of not more than m. Therefore, the fine silver powder should be plastically deformed to form a flake, and the production of coarse and large flake particles must be prevented so that the particles are not connected without the use of a lubricant. In order to obtain such an effect, it is necessary to satisfy the condition that the weight of the media beads is not too heavy and that the size of the media beads is appropriate for the raw material powder size.

In this case, when media beads having a particle diameter of more than 0.2 mm are used, that is, when the particle diameter of the media beads to be used is too large, the weight of the media beads is heavy and the pressing force on the particles becomes very large. For this reason, the particle size as flake silver powder becomes coarse, and particle | grains become easy to connect, and the formation frequency of a thick and large flake particle rises dramatically. The lower limit of the particle size range of the media beads is 0.03 mm in reality. The reason for this is that the smaller the particle diameter is, the longer the processing time of the flake shape becomes and the industrial productivity is not satisfied.

On the other hand, in considering the weight of the media beads, the material constituting the media beads is also an important factor. As the media bead material, it is preferable to selectively use any one of zirconia beads, alumina beads, and glass beads. In the case of glass beads, it is necessary to selectively employ processing conditions that do not cause the glass beads themselves to break during physical processing.However, the components of the glass beads themselves are less likely to remain on the surface of the particles of the flake silver powder. It is preferable to consider in order to obtain the flake silver powder with few components. In addition, alumina beads are the most particulate media beads in terms of particle size. As in the case of glass beads, it is necessary to employ | adopt alumina beads selectively the processing conditions which do not cause destruction of the alumina beads itself at the time of physical processing. On the other hand, zirconia beads can select a wide range of processing conditions without the zirconia beads themselves being destroyed under the conditions of physical processing generally conceivable.

In addition, in the said processing process, the mixing ratio of the said media beads with respect to the said silver powder in the said slurry is [the amount of silver powder in a slurry (vol%)]: [the amount of media beads (vol%)] = 1: 1-1 It is preferable to set in the range of: 110. Here, when the blending ratio of the media beads to the silver powder in the slurry is smaller than 1: 1, that is, when the blending amount of the media beads is too small for the silver powder, the media beads are not evenly spread evenly over an area of a size such as a container. It becomes difficult to uniformly flake the substantially spherical silver particles, which takes a long time to flake. In addition, when a long processing time is adopted, the connection between particles once flaked easily occurs, and the frequency of generation of coarse and large particles increases. On the other hand, when the blending ratio of the media beads to the silver powder is larger than 1: 110, that is, when the blending amount of the media beads is too large for the silver powder, the pressurization points of the media beads to the particles become large and coarse and large particles In addition, the particle size distribution of the obtained flake silver powder is bad and becomes wide. Therefore, by setting the mixing ratio of the media beads to the silver powder in the slurry in an optimum range, it is possible to reliably produce a flake silver powder having a small particle size and a good particle size distribution in the absence of a lubricant.

Preparative step: In this step, the flake silver powder is collected by separating the mixed and stirred slurry and the media beads. There is no particular restriction regarding the means for collecting the flake silver powder at this time, and any technique can be adopted. For example, when an example is shown, since the media beads have a larger particle size than the flake silver powder, the media beads can be easily separated by filtering the slurry in a state containing the media beads. The flake silver powder can be collected by allowing the slurry from which the media beads are removed to stand still for a predetermined time to settle the flake silver powder, discard the supernatant, and then filter it. Moreover, SAM-1 (Super Apex Mill), Dyno mil, etc. are equipped with the separator of media beads, and it has a structure which does not leak media beads. Therefore, in the case of using the apparatus provided with such a media beads separator from the beginning, it is unnecessary to separate the media beads afterwards.

Cleaning and drying step: In this step, the flake silver powder collected is washed and dried to remove impurities and water to obtain the brake silver powder. There is no special limitation regarding the method of washing and drying a flake silver powder here. In addition, in this process, it was said that the said flake silver powder collected was wash | cleaned. Even if the flake silver powder collected at the said preparative process used for washing | cleaning is undried state, the slurry which remove | eliminated media beads as mentioned above stills for a fixed time. The flakes may be in a state where the powder is settled and the supernatant is discarded. These are washed using alcohols such as water, ethanol and methanol. And, more preferably, by washing with water and then repeatedly washing with two or more alcohols to enhance washing, contaminants adhering to the particle surface of the flake silver powder can be efficiently removed. Moreover, it is common to perform drying for 3 hours-8 hours in the temperature atmosphere of about 50 degreeC-80 degreeC.

Flake silver powder obtained by the manufacturing method which concerns on this invention: The flake silver powder manufactured using the manufacturing method which concerns on this invention described above has the following powder characteristics.

A silver powder composed of substantially spherical silver particles, which is a raw material powder, has a primary particle diameter D _IA of 1.2 µm or less, and a volume cumulative particle diameter D ₅₀ obtained by laser diffraction scattering particle size distribution measurement and an average particle diameter D _IA obtained by image analysis. If the value of the degree of compaction is represented by D ₅₀ / D _IA using 1.5 or less using a particulate silver powder, the silver powder having a flake is obtained horse powder properties as described below. On the other hand, the powder properties described below _{assume that the} particle size (D _IA ) is 3 μm or less, and satisfies at least one of the other powder property items:

Average particle diameter (D _IA ): greater than 0 and less than 3 μm

Volume cumulative particle diameter (D ₅₀ ): greater than 0 and less than 4.5 μm

Standard deviation (SD): 0.143 μm to 3.265 μm

Coefficient of variation (SD / D ₅₀ ): 0.15 to 0.40

Maximum particle diameter (D _max ): greater than 0 and less than 10.0 μm

Average aspect ratio ([thickness] / [D ₅₀ ]): 0.3 to 0.7

Carbon content: 0.3 weight% or less.

One or more powder properties, and the "grain size 3㎛ below", and the value of the "laser diffraction scattering type particle size D ₅₀ by volume cumulative particle size distribution measurement by the" small, and can easily grasp the horse flake silver powder of the level of fine particles that are not in the prior have. The flake silver powder which exists conventionally is generally more than 7 micrometers although these particle diameters vary slightly.

And pay attention to the value of D _max . This is the value of D _max, represents the largest particle size obtained using a laser diffraction scattering type particle size distribution measuring method. When flake silver powder is manufactured by the conventional method, it is common that large coarse particle | grains exceeding 100 micrometers are contained. On the other hand, the process for producing a flake silver powder prepared by using the matter according to the invention, D _max is not more than 10.0 ㎛, the existence probability of the coarse particles is decreased dramatically.

In terms of standard deviation alone, in the case of flake silver powder obtained by a conventional manufacturing method, the value of standard deviation SD is dispersed in a range of 0.321 µm to 14.155 µm, indicating that the variation in particle size distribution between lots is very large. have. On the other hand, the standard deviation of the flake silver powder manufactured using the manufacturing method which concerns on this invention becomes the range of 0.143 micrometers-3.265 micrometers, and it turns out that the variation of the particle size distribution between lots is extremely small.

Next, let's focus on the value of SD / D ₅₀ . It can be judged that the larger the deviation of this value, the less stable the particle size distribution as a product is. The flake silver powder produced using the manufacturing method according to the present invention has a value of SD / D _{50 in} the range of 0.15 to 0.40. On the other hand, in the case of the flake silver powder obtained by the conventional manufacturing method, it becomes 0.55-0.87 in the range recognized by this inventor.

And let's focus on aspect ratio. A control value of an aspect ratio ([thickness] / [D _50]) of the flake silver powder prepared matter with the production process according to the invention is 0.3 to 0.7. This aspect ratio shows the workability of a flake silver powder. Therefore, when the value of the aspect ratio is less than 0.3, it is considered that the thickness of the particles becomes too thin and the dislocation density inside the particles rapidly rises, leading to miniaturization of crystal grains and causing an increase in resistance. On the other hand, when the value of the aspect ratio exceeds 0.7, since the workability is low and the flatness is low, the sufficient contact interface area required for the flake silver powder cannot be obtained, and the resistance cannot be lowered.

On the other hand, in the laser diffraction scattering particle size distribution measurement method, 0.1 g of flake silver powder is mixed with a 0.1% aqueous solution of SN-dispercent 5468 (manufactured by Sanofko Co., Ltd.) to produce an ultrasonic homogenizer (Nihonseki Sesakusho Co., Ltd.). US-300T) was dispersed for 5 minutes, and a laser diffraction scattering particle size distribution analyzer Micro Trac HRA 9320-X100 type (manufactured by Leeds + Northrup) was used.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is concretely demonstrated to an Example and a comparative example. In addition, this invention is not limited to a following example.

1st Example

Preparation of silver powder consisting of approximately spherical silver particles: First, 9.0 kg of silver nitrate was dissolved in 475 L of pure water to prepare an aqueous solution of silver nitrate, and then, 20 kg of 25 wt% aqueous ammonia water was added to this solution in a batch, followed by stirring. Got.

The silver ammine complex aqueous solution was introduced into the first flow path at a flow rate of 1500 ml / sec, and the second flow path was introduced with a reducing agent at a flow rate of 1500 ml / sec, and the temperature was 20 ° C. at the confluence of the first flow path and the second flow path. The fine silver powder was reduced by precipitation in contact with As a reducing agent used at this time, an aqueous hydroquinone solution in which 3 kg of hydroquinone was dissolved in 475 L of pure water was used.

In order to collect 5.7 kg of fine silver powder obtained as described above, the mixture was filtered using Nutsche, washed with 10 L of water and 40 L of methanol, and dried at 70 ° C. for 5 hours to obtain fine silver powder. . Fine powder characteristics of the silver powder obtained as described above is, was the primary particle size D _IA is 0.5㎛, the value of the degree of compaction is represented by D ₅₀ / D _IA 1.02. In this example, the surface of the particles of the fine silver powder was further surface treated with oleic acid.

Dispersion step: Into a mixed solvent of 4.0 kg of methanol and 4.0 kg of ethylene glycol, 4.0 kg of the surface-treated fine silver powder was added and stirred well to obtain a slurry having a concentration of 13 volume% (33 wt%) of silver powder in the slurry.

Processing process: 2.5 kg of zirconia beads having a diameter of 0.1 mm were prepared, and the amount of silver powder in the slurry (volume%): [the amount of zirconia beads (vol%)] was set to 1:94, and Kotobuki Kogyo was manufactured. It was charged in SAM-1 (Super Apex Mill) of the Corporation. And the slurry flow rate was set to 0.6 L / min and the rotational speed of the disperser to 2400 rpm, and flake was made by the mechanical impact by the pass system. This flake processing was performed in three passes.

Preparative step: After completion of the flake treatment, the zirconia beads were removed with a separator of SAM-1, after which the slurry was left for a certain time to settle the flake silver powder and discard the supernatant.

Washing and drying process: After washing twice by adding water while discarding the supernatant and discarding the supernatant, washing three times with ethanol to enhance the washing, and then removing contaminants on the particle surface. Removed as much as possible. And it dried at 70 degreeC for 5 hours, and obtained fine flake silver powder. The scanning electron microscope observation image of the fine particle silver powder obtained at this time is shown in FIG.

The characteristics of the flake silver powder obtained as described above were D ₁₀ 0.32 μm, D ₅₀ 0.72 μm, D ₉₀ 1.06 μm, maximum particle size D _max 2.2 μm, and standard deviation by laser diffraction scattering particle size distribution measurement. and SD are 0.22㎛, the standard deviation SD is represented by using the SD / D value of ₅₀ is 0.31, the carbon content was 0.24% by weight.

On the other hand, measurement of carbon content was carried out using EMIA-320V manufactured by Horiba Seisakusho, 0.5 g of flake silver powder, 1.5 g of tungsten powder, and 0.3 g of tin powder were put in a magnetic crucible and burned. It is measured by the infrared absorption method. The carbon content of the silver powder obtained by the conventional manufacturing method was carbon amount exceeding 0.20 weight%, even if washing | cleaning was strengthened.

Second Example

Production of silver powder composed of substantially spherical silver particles: A fine silver powder prepared in the same manner as in Example 1 was used. However, unlike the case of the first embodiment, the surface treatment with oleic acid was not performed.

Dispersion step: To 4.0 kg of methanol, 2.0 kg of the fine silver powder was added and stirred well to obtain a slurry having a silver powder concentration of 14 vol% (33 wt%) in the slurry.

Processing process: 2.5 kg of zirconia beads having a diameter of 0.1 mm were prepared, and [the amount of silver powder in the slurry (% by volume)]: [amount of zirconia beads (% by volume)] = 1: 105, manufactured by Kotobuki Kogyo Co., Ltd. Charged to SAM-1 (Super Apex Mill). And the slurry flow rate was set to 0.6 L / min and the rotational speed of the disperser to 2400 rpm, and the solution was circulated for 30 minutes to physically flake.

Hereinafter, the fine flake silver powder was obtained through the preparative process similar to the 1st Example, and the washing drying process. The scanning electron microscope observation image of the fine particle silver powder obtained at this time is shown in FIG.

The characteristics of the flake silver powder obtained as described above were D ₁₀ 0.41 μm, D ₅₀ 0.88 μm, D ₉₀ 1.26 μm, D _max 2.5 μm, and standard deviation by laser diffraction scattering particle size distribution measurement. and SD are 0.34㎛, the standard deviation SD is represented by using the SD / D value of ₅₀ is 0.39, the carbon content was 0.18% by weight.

Third Example

Production of silver powder composed of substantially spherical silver particles: A fine silver powder obtained by treating the surface with oleic acid prepared in the same manner as in Example 1 was used.

Dispersion step: To 8.0 kg of methanol, 4.0 kg of the surface-treated fine silver powder was added and stirred well to obtain a slurry having a silver powder concentration of 14% by volume (33% by weight) in the slurry.

Processing process: 2.5 kg of zirconia beads having a diameter of 0.2 mm were prepared, and [the amount of silver powder in the slurry (% by volume)]: [the amount of the zirconia beads (% by volume)] = 1: 105 was used. Charged to SAM-1 (Super Apex Mill). Then, the slurry flow rate was set to 0.6 L / min, the rotation speed of the disperser to 2400 rpm, and the solution was circulated for 40 minutes to physically flake.

Hereinafter, the fine flake silver powder was obtained through the preparative process similar to the 1st Example, and the washing drying process. The scanning electron microscope observation image of the fine particle silver powder obtained at this time is shown in FIG.

Characteristics of the flake silver powder obtained as described above, the laser diffraction scattering type particle size distribution measurement by the D ₁₀ 0.28㎛, D ₅₀ is 0.68㎛, D ₉₀ is 0.92㎛, the maximum grain size D _max is 1.95㎛, standard deviation and SD are 0.25㎛, the standard deviation SD is represented by using the SD / D ₅₀ value of 0.36, carbon content was 0.26% by weight.

Fourth Example

Production of silver powder composed of substantially spherical silver particles: A fine silver powder obtained by treating the surface with oleic acid prepared in the same manner as in Example 1 was used.

Dispersion step: For 4.0 kg of methanol and 4.0 kg of ethylene glycol, 4.0 kg of the surface-treated fine silver powder was added and stirred well to obtain a slurry having a silver powder concentration of 13% by volume (33% by weight) in the slurry.

Processing step: 2.5 kg of zirconia beads having a diameter of 0.05 mm were prepared, and [the amount of silver powder in the slurry (% by volume)]: [the amount of the zirconia beads (% by volume)] = 1:94 was used. Charged to SAM-1 (Super Apex Mill). And the slurry flow rate was set to 0.6 L / min and the rotational speed of the disperser to 2400 rpm, and flake was made by the mechanical impact by the pass system. This flake processing was performed in three passes.

Hereinafter, the fine flake silver powder was obtained through the preparative process similar to the 1st Example, and the washing drying process. The scanning electron microscope observation image of the fine particle silver powder obtained at this time is shown in FIG.

Characteristics of the flake silver powder obtained as described above, the laser diffraction scattering type particle size distribution measurement by the D ₁₀ 0.27㎛, D ₅₀ is 0.42㎛, D ₉₀ is 0.71㎛, the maximum grain size D _max is 1.64㎛, standard deviation and SD are 0.16㎛, the standard deviation SD is represented by using the SD / D ₅₀ value of 0.38, carbon content was 0.29% by weight.

Comparative Example

[First Comparative Example]

Production of silver powder composed of substantially spherical silver particles: A fine silver powder prepared in the same manner as in Example 1 was used. However, unlike the case of the first embodiment, the surface treatment with oleic acid was not performed.

Dispersion step: To 4.0 kg of methanol, 2.0 kg of the fine silver powder was added and stirred well to obtain a slurry having a silver powder concentration of 14 vol% (33 wt%) in the slurry.

Processing step: A zirconia beads having a diameter of 1.0 mm having a larger particle size than that of the zirconia beads used in the Example was prepared, and [the amount of silver powder in the slurry (% by volume)]: [amount of the zirconia beads (% by volume)] = 1: 105 480 cc of the mixing ratio was added to a 0.6 L Dinomil machine manufactured by Shinmaru Enterprise. Then, the slurry was circulated for 10 minutes by the circulation system at a flow rate of 3.0 L / min, and flake was formed by mechanical impact. On the other hand, a device different from the above embodiment was used because zirconia beads having a large particle diameter of 1.0 mm, which were not used in the examples, were used, and the zirconia beads of the size were SAM-1 manufactured by Tobu-Kiko Co., Ltd. Because it is not available in. On the other hand, in SAM-1 manufactured by Tobu-Kikokyo Co., Ltd., a large media beads having a particle diameter of about 1.0 mm cannot be used. Therefore, there is a necessity of changing the device.

Preparative process: After completion | finish of a flake process, the method similar to Example 1 was employ | adopted.

Washing drying process: The washing | cleaning operation which adds water, wash | cleans, and discards a supernatant liquid in the state which discarded the supernatant liquid was repeated twice, and the normal washing method which wash | cleans once with ethanol was employ | adopted. And it dried at 70 degreeC for 5 hours, and obtained fine flake silver powder. The scanning electron microscope observation image of the fine particle silver powder obtained at this time is shown in FIG.

The characteristics of the flake silver powder obtained as described above were D ₁₀ of 6.71 μm, D ₅₀ of 14.1 μm, D ₉₀ of 26.0 μm, maximum particle diameter D _max of 104.7 μm, and standard deviation by laser diffraction scattering particle size distribution measurement. and SD are 6.93㎛, the standard deviation SD is represented by using the SD / D value of ₅₀ is 0.49, the carbon content was 0.54% by weight.

Second Comparative Example

Production of silver powder composed of substantially spherical silver particles: A fine silver powder obtained by treating the surface with oleic acid prepared in the same manner as in Example 1 was used.

Dispersion process: With respect to 8.0 kg of methanol and 4.0 kg of ethylene glycol, 1.5 kg of the surface-treated fine silver powder was added and stirred well to obtain a slurry having a silver powder concentration of 4.0% by volume (11% by weight) in the slurry.

Processing process: 0.5 kg of zirconia beads having a diameter of 0.1 mm are prepared, and a balance between the amount of silver powder (vol%) and the amount of zirconia beads (vol%) in the slurry is released from the conditions according to the present invention. %)]: [Zirconia beads amount (% by volume)] = 3: 1, and filled in SAM-1 manufactured by Tobuki Kogyo Co., Ltd. And the slurry flow rate was set to 0.6 L / min and the rotational speed of the disperser to 2400 rpm, and flaking was performed by the mechanical impact by the pass system. This flake processing was performed in three passes.

Hereinafter, the fine flake silver powder was obtained through the preparative process similar to the 1st comparative example, and the washing drying process. The scanning electron microscope observation image of the fine particle silver powder obtained at this time is shown in FIG.

Characteristics of the flake silver powder obtained as described above, the laser diffraction scattering type particle size distribution measurement by the D ₁₀ 0.59㎛, D ₅₀ is 1.07㎛, D ₉₀ is 1.81㎛, the maximum grain size D _max is 4.63㎛, standard deviation and SD are 0.45㎛, the standard deviation SD is represented by using the SD / D value of ₅₀ is 0.42, the carbon content was 0.62% by weight.

[Comparison of Examples and Comparative Examples]

Scanning electron microscope observation image: FIG. 1 thru | or FIG. 4, and FIG. 5 and FIG. 6 are compared. As can be seen from Figs. 1 to 4, it can be said that the particles of the flake silver powder obtained by the production method according to the present invention are referred to as fine nuggets or microplates rather than flake shapes. On the other hand, in the case of FIG. 5, it can confirm from the particulate particle to the particle | grain of the coarse particle level, and it turns out that particle size distribution is very wide. In addition, in the case of FIG. 6, silver concentration (silver powder content) in a slurry is sparse, and flake formation is not performed favorably, and most particle | grains remain | surviving substantially spherical. As is apparent from the above, since the surface shape is smooth compared to the shape of the conventional flake silver powder, and the particle size is constant, the dispersibility of the flake silver powder when processed into a conductive paste can be improved, resulting in It is thought that this contributes to the reduction of paste viscosity.

Average primary particle diameters (D ₁₀ , D ₅₀ , D ₉₀ , D _max and D _IA ): The above examples and comparative examples differ in whether or not the surface is treated with oleic acid as a raw material powder, but are substantially the same fine grains. Silver powder is used. On the premise of this, when the first to fourth embodiments are compared with the first comparative example, all values of D ₁₀ , D ₅₀ , D ₉₀ , D _max and D _IA are small in size, so that fine flake silver powder is obtained. It can be seen that. In particular, the value of D _max is smaller than that of the first comparative example, and it can be understood that flake silver powder having no coarse particles and a narrow particle size distribution is obtained therefrom. On the other hand, since the 2nd comparative example did not form appropriate flake, it was not made into the comparison object here.

Standard Deviation SD and Coefficient of Variation SD / D ₅₀ : In addition, when the values of the standard deviation SD of each example and the first comparative example are compared, the value of the standard deviation of each example is overwhelmingly small. Therefore, even if the numerical value of a standard deviation is seen, it can be understood that compared with a 1st comparative example, each Example is a flake silver powder with few coarse particles and having a narrow particle size distribution.

In addition, it is clear that each of the examples is fine compared to the first comparative example and has a small deviation from the standard deviation. Therefore, also regarding the coefficient of variation, it can be understood that, in comparison with the first comparative example, each of the examples is smaller and the flake silver powder having less unbalance between lots can be produced.

Carbon content: This carbon content is employ | adopted in order to estimate the amount of contaminants (remaining organic component amount) of the particle | grain surface of flake silver powder. In the above embodiment, the flake silver powder is obtained by enhancing the cleaning. On the other hand, in the comparative example, the usual washing | cleaning generally adopted is employ | adopted. As a result, carbon content of each Example is few compared with the carbon content of a comparative example. Therefore, the flake silver powder obtained in the above example has a smaller adhesion amount of contaminants than the conventional flake silver powder, and can be said to be a flake silver powder suitable for low conductor resistance formation.

As described above, in the manufacturing method of the flake silver powder of this invention, and the flake silver powder manufactured by the manufacturing method, it is excellent in powder characteristics, and when a conductor is formed using an electrically conductive paste, the raise of conductor resistance is prevented, Since the fall of electroconductivity can be prevented reliably, it can fully utilize in the technical field regarding manufacture of flake silver powder.

Claims (5)

In the manufacturing method of flake silver powder which consists of flake silver particles, By using the volume cumulative particle diameter D ₅₀ by the laser diffraction scattering particle size distribution measurement method and the average particle diameter D _IA obtained by image analysis, the coherence degree represented by D ₅₀ / D _IA is approximately spherical silver particles of 1.5 or less. Dissolution process of silver powder  A dispersing process of dispersing the granulated silver powder in a solvent to produce a slurry having a silver concentration of 5 vol% or more; A processing step in which the silver particles in the slurry are plastically deformed to form a flake silver powder by mixing the slurry and media beads having a particle diameter of 0.2 mm or less in a bead mill and stirring the mixture; A preparative step of separating the mixed and stirred slurry and the media beads to collect the flake silver powder; And a washing and drying step of removing the impurities and water by washing and drying the collected flake silver powder to obtain the flake silver powder. The method of claim 1, In the said dispersing process, the compounding quantity of the said silver powder and the said solvent was set so that the said silver powder concentration in the said slurry might be 5 to 90 volume%, The manufacturing method of the flake silver powder characterized by the above-mentioned. The method of claim 1, In the processing step, the blending ratio of the media beads to the silver powder in the slurry is determined by [the amount of silver powder in the slurry (vol%)]: [the amount of media beads (vol%)] = 1: 1 to 1: 110. It is set to the range, The manufacturing method of the flake silver powder. delete In the flake silver powder which consists of flake shaped silver particles manufactured using the manufacturing method in any one of Claims 1-3, The average particle diameter (D _IA ) is larger than 0 and 3 µm or less, the average aspect ratio ([thickness] / [D ₅₀ ]) is 0.3 or more and 0.7 or less, and at least one of the following powder characteristics (1) to (5) Flake silver powder characterized by: (1) Volume cumulative particle diameter (D ₅₀ ): greater than 0 and less than 4.5 ㎛ (2) standard deviation (SD): 0.143 µm to 3.265 µm (3) Coefficient of variation (SD / D ₅₀ ): 0.15 ~ 0.40 (4) Maximum particle diameter (D _max ): greater than 0 and less than 10.0㎛ (5) Carbon content: 0.3 weight% or less.

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