KR20140030091A - Silver powder and method for producing same - Google Patents

Abstract

Dispersibility in a solvent is good at the time of paste preparation, and coarse powder, such as a flake, is suppressed at the time of kneading | mixing.
In the present invention, the cohesive force is -0.2 N / cm 2 or more and 0.7 N / cm 2 or less, the compressibility in the powder layer shear force measurement is 20 to 50%, and the absorption amount of dibutyl phthalate measured by the JIS-K6217-4 method Silver powder having a characteristic of 3.0 to 9.0 ml / 100 g is used.

Description

Silver powder and its manufacturing method {SILVER POWDER AND METHOD FOR PRODUCING SAME}

This invention relates to silver powder and its manufacturing method, More specifically, it is related with the silver powder which becomes a main component of the silver paste used for formation of the wiring layer, an electrode, etc. of an electronic device, and its manufacturing method.

This application claims priority based on Japanese Patent Application No. 2011-128015 for which it applied on June 8, 2011 in Japan, and is incorporated in this application by referring to these applications.

Silver pastes, such as a resin type silver paste and a baking type silver paste, are widely used for formation of the wiring layer of an electronic device, an electrode, etc. Conductive films, such as a wiring layer and an electrode, are formed by apply | coating or printing a silver paste, and heat hardening or heat baking.

For example, resin type silver paste consists of silver powder, resin, hardening | curing agent, a solvent, etc., after printing this resin type silver paste on a conductor circuit pattern or a terminal, it heat-hardens at 100 degreeC-200 degreeC, and makes it a conductive film. To form wiring and electrodes. In addition, the calcined silver paste is made of silver powder, glass, a solvent, and the like, and after the sintered silver paste is printed on a conductor circuit pattern or a terminal, the calcined silver paste is heated and baked at 600 ° C to 800 ° C to form a conductive film. Form a wiring or an electrode. Filling and sinterability of silver powder are important for electroconductivity of these wirings and electrodes formed by heating a silver paste.

Although silver powder with a particle diameter of 0.1 micrometer-several micrometers is generally used for electroconductive silver paste, the particle size of the silver powder to be used is selected in detail according to the thickness of the target wiring and the thickness of an electrode. Moreover, high uniformity is calculated | required by the thickness of the formed wiring and the thickness of an electrode, and dispersibility in silver paste is important to it. The improvement of dispersibility also leads to the improvement of filling property.

Although the characteristic required for the silver powder for electroconductive silver paste is various according to a use and a use condition, generally, it is high dispersibility in a paste, and sinterability. When silver powder with low dispersibility in the paste is used, not only the thickness of the wiring and the thickness of the electrode become uneven, but also the curing and baking treatment become uneven, leading to an increase in the resistance of the conductive film and brittleness of the conductive film. In addition, deterioration of sinterability is directly linked to an increase in the resistance of the conductive film. However, these three characteristics are largely dependent on the stability of a silver powder manufacturing process and the surface treatment of silver powder.

By the way, when producing a silver paste, first, silver powder is knead | mixed and mixed with other structural components, such as a solvent, and after that, it manufactures by kneading, applying a predetermined pressure with a 3-roll mill etc. At this time, the silver powder is required to be able to knead efficiently with a roll, that is, to have good kneading property.

However, when a large lump of silver powder exists in a paste, as it knead | mixes with a roll, the lump of silver powder in a paste is broken and coarse powder, such as flaky powder (flake) of several millimeters, will generate | occur | produce. Since it is not desirable to leave the flakes in the paste as it is, it is sieved to remove them using a mesh or the like.However, if too much flakes are formed, problems such as coarse powder may be blocked between the meshes. Productivity is significantly impaired.

In addition, if flakes are generated in the paste as described above, when screen printing is performed using the paste, coarse flakes are blocked on the fine screen, and accurate printing of the pattern becomes difficult.

Thus, the occurrence of flakes greatly affects the kneading property during paste production and the printability when screen printing. Therefore, silver powder is required to have good dispersibility in the solvent at the time of paste production and to avoid coarse powder such as flakes.

[Patent Literature]

Patent Document 1: Japanese Patent Application Laid-Open No. 2004-197030

Patent Document 2: Japanese Patent Application Laid-Open No. 2000-129318

Accordingly, the present invention has been proposed in view of the above circumstances, and provides a silver powder having a good dispersibility in a solvent at the time of paste preparation and suppressing generation of coarse powders such as flakes during kneading, and a method for producing the same. For the purpose of

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to achieve the objective mentioned above, the silver powder which has the aggregate formed by connecting substantially spherical particle | grains to the predetermined | prescribed magnitude | size has favorable dispersibility in a paste, and it is a flake etc. in kneading | mixing. The present inventors have found that the generation of coarse powder can be suppressed, thereby completing the present invention.

That is, the silver powder which concerns on this invention has cohesion force of -0.2N / cm <2> or more and 0.7N / cm <2>, the compressibility in powder layer shear force measurement is 20-50%, and phthalic acid measured by JIS-K6217-4 method It is characterized by the absorption amount of dibutyl 3.0-9.0 ml / 100g.

Moreover, the manufacturing method of the silver powder which concerns on this invention is a manufacturing method of the silver powder which mixes the silver complex containing solution obtained by melt | dissolving with silver chloride and a complexing agent, and a reducing agent solution, and reduces a silver complex to produce silver powder. 0.1-15 mass% of water-soluble polymers are added to both a solution and the said reducing agent solution, or either one with respect to silver, It is characterized by the above-mentioned.

According to the present invention, the dispersibility of the paste in the solvent is excellent, and generation of coarse powder such as flakes can be effectively suppressed during kneading of the paste preparation.

1 is a diagram schematically showing a silver particle form.

EMBODIMENT OF THE INVENTION Hereinafter, the specific embodiment of the silver powder which concerns on this invention, and its manufacturing method is demonstrated in detail. In addition, this invention is not limited to the following embodiment, It can change suitably, unless the summary of this invention is changed.

In the description, the name for the silver particle form is defined as shown in FIG. 1. That is, as shown to FIG. 1 (A), the silver particle is judged from an external geometric shape, and what is considered a unit particle is called primary particle. In addition, as shown to FIG. 1 (B), the particle | grains which 2-3 or more connected with the primary particle by necking are called secondary particle. In addition, as shown in Fig. 1C, an aggregate of primary particles and secondary particles is called an aggregate.

Conventionally, in the production of silver paste, individual primary particles are dispersed as much as possible, and silver powder having an average particle diameter of 0.1 μm to 1.5 μm has been used, but fine silver particles in which such primary particles are dispersed are densely Since it is filled, there are many contacts with other particle | grains, and cohesion force becomes large, and silver particle | grains aggregate easily in a paste, and a big lump is formed. Then, for example, when kneading is carried out by a three-roll mill generally used in paste production, the aggregated mass enters the roll without breaking, and as a result, coarse powder of mm order such as flakes is formed. It was found to be.

On the other hand, in the case of a silver powder having a large particle size distribution having aggregates coarsely aggregated with primary particles and secondary particles at a predetermined ratio, there are sufficient voids between the aggregates and the number of contacts is small, so that a large mass in the paste It was confirmed that no flakes occurred, without forming a flake. In such silver powder, primary particles and secondary particles are aggregated and connected to a predetermined size, for example, to form an aggregate as shown in Fig. 1 (C) in the shape of grapes. This agglomerate is usually about 5 to 10 µm in size, and has a structure in which secondary particles are formed by relatively strong bonding of several primary particles, and the secondary particles and primary particles are connected by relatively weak bonding. I guess. From this, the inventors of the present invention found that aggregates in which primary particles or secondary particles are connected to each other at a predetermined size are appropriately formed, and the aggregates have a predetermined strength, so that the silver particles in the case of viewing the aggregates as one particle as well. It was found that cohesion force between them was reduced, was excellent in dispersibility, effectively suppressed generation of coarse powder such as flakes during kneading of paste production, and improved kneading property.

That is, the silver powder which concerns on this embodiment has a cohesion force of -0.2 N / cm <2> or more and 0.7 N / cm <2>, the compressibility in powder layer shear force measurement is 20 to 50%, and is measured by JIS-K6217-4 method. The amount of dibutyl phthalate absorbed is 3.0 to 9.0 ml / 100 g. Silver powder having such characteristics has good dispersibility in a solvent at the time of paste preparation and can effectively suppress the generation of coarse powder such as flakes at the time of kneading.

It is preferable that primary particle | grains are the range whose average particle diameter is 0.1-1.5 micrometers in the silver particle used in this embodiment. When the average particle diameter of primary particle | grains is 0.1 micrometer or more, when electroconductive paste is used, electroconductivity becomes favorable without generating big resistance. Moreover, by making the average particle diameter of a primary particle into 1.5 micrometers or less, even when a primary particle connects to a predetermined | prescribed size and forms an aggregate as mentioned later, good kneading | mixing property and printability are made without degrading dispersibility. It becomes.

Cohesion force shows the easiness of aggregation of silver powder itself, and becomes an index which silver particle aggregates in a paste. This cohesion force can be defined as the shear stress in the state without the weight of silver powder. Therefore, for example, using a powder layer shear force measuring device, it is possible to obtain from the graph of the shear stress and the vertical stress, and in the graph of the shear stress with respect to the vertical stress, the shear stress value of the Y segment becomes the cohesive force. That is, as the Y-intercept rises, it means that the cohesion force is large. Moreover, the inclination of the graph of the shear stress with respect to the vertical stress becomes the internal frictional force of silver powder, and becomes an index of the ease of sliding of powder.

The silver powder which concerns on this embodiment has the cohesion force of -0.2N / cm <2> or more and 0.7N / cm <2> or less. By the cohesion force being in the above-mentioned range, generation of coarse flakes is suppressed without excessive aggregation of silver particles in a paste.

The absorption amount of dibutyl phthalate can be measured based on JIS-K6217-4 method. The silver powder which concerns on this embodiment is 3.0-9.0 ml / 100g of water absorption of the dibutyl phthalate. Silver powder whose absorption amount of dibutyl phthalate is 3.0-9.0 ml / 100 g shows that silver particle is connected by the predetermined magnitude | size, and for example, it forms the aggregate of grape cluster shape suitably.

That is, in silver powder having an aggregate formed by connecting silver particles to a predetermined size, the voids increase, and when dibutyl phthalate is added dropwise, dibutyl phthalate is absorbed (oil absorption) between the silver particles forming the aggregate. do. In silver powder with few aggregates, the amount of absorption also decreases because there are few voids between silver particles. Therefore, by measuring the absorption amount of this dibutyl phthalate, it can be judged how much the aggregate is formed. Moreover, by having a predetermined | prescribed absorption amount, components, such as a solvent of a paste, and silver particle become easy to mix, and it can knead well.

Moreover, the viscosity of the paste produced using this silver powder can also be judged based on the absorption amount of this dibutyl phthalate. As described above, the silver powder having the aggregates in which the silver particles are connected receives the solvent component of the paste between the particles constituting the aggregate, so that the amount of the solvent component in the paste other than the aggregate is relatively decreased, so that the viscosity of the paste is reduced. Increases. As the viscosity becomes high, the shear force generated between the rolls at the time of kneading is efficiently propagated to the paste as a dispersing force for dispersing the silver powder, and the silver powders are easily dispersed without aggregation.

Moreover, when the absorption amount of dibutyl phthalate is less than 3.0 ml / 100 g, it shows that the number of the aggregates formed above is small, and a flake is produced at the time of paste preparation. On the other hand, when there is more water absorption than 9.0 ml / 100g, it shows that silver particle is aggregated too much, dispersibility deteriorates and flakes generate | occur | produce.

A compression ratio is a volume reduction rate of silver powder from the set load zero to the state which loaded the set load, and becomes an index which shows the structural strength of the amount of voids between silver particles, and the aggregate of silver powder. This compressibility is measured from the volume (the apparent volume) measured by filling a predetermined amount of silver powder in the cell and using a powder layer shear force measuring device, and the volume (volume) when the set load (60 N) is loaded. can do. When a load is applied to the silver powder by the powder layer shear force measuring device, the powder layer is compressed. However, when the silver particles are separated into primary particles, the amount of voids between the particles after compression decreases and the compression ratio is large. On the other hand, when the silver particles form the agglomerates described above, the compression ratio is small because the voids are also included in the agglomerates to increase the voids after compression. However, even when the aggregate is formed, when the compressibility becomes too large in a state where a set load is applied, the aggregate does not have sufficient strength and is easily disintegrated into primary particles during kneading.

As mentioned above, the silver powder which concerns on this embodiment contains the aggregate formed by connecting silver particle to the predetermined magnitude | size. Since the presence of this aggregate can effectively suppress generation of flakes, it is preferable that the aggregate does not easily change its structure but has structural strength.

For example, the aggregate contained in silver powder is not preferable to be easily broken by the hands of the operator of paste production. In addition, when preparing a paste using silver powder, the preliminary kneading | mixing by the autorotation mixer etc. and this kneading | mixing by a 3-roll mill etc. are generally performed. At this time, in the case of silver powder having agglomerates having low structural strength, the agglomerates are broken into primary particles or secondary particles in the initial stage of kneading, so that they are densely filled in the paste and the contact points with other particles increase, resulting in cohesive force. Since it becomes large, it becomes easy to aggregate in a paste and produces flakes. Accordingly, the kneading property is significantly impaired.

Therefore, it is preferable that the formed aggregate has structural strength, and structural changes do not occur easily. Thereby, the state which the aggregate exists in silver powder is maintained, generation | occurrence | production of coarse powder, such as a flake, can be suppressed without a viscosity fall, and favorable kneading property can be exhibited.

The silver powder which concerns on this embodiment is 20 to 50% in the compression rate. When the compressibility is less than 20%, the structure of the agglomerates described above is strong, indicating that the agglomeration structure is hard to be broken, and flakes are generated during paste production. On the other hand, when the compressibility is greater than 50%, the mechanical strength of the agglomerates is weak and the agglomeration structure is easily broken, and the silver particles are densely filled at the time of paste production, and the contact points with other particles are increased so that the cohesive force is increased. Since it becomes large, it becomes easy to aggregate in a paste and produces a flake.

Thus, the cohesion force is -0.2 N / cm 2 or more and 0.7 N / cm 2 or less, the compressibility in the powder layer shear force measurement is 20 to 50%, and the absorption amount of dibutyl phthalate measured by the JIS-K6217-4 method is 3.0. As for the silver powder of -9.0 ml / 100g, the aggregate with many voids with which silver particle was connected by the predetermined size exists, and the aggregate maintains the predetermined intensity | strength. According to such silver powder, dispersibility in a solvent is good at the time of paste preparation, and coarse powder, such as flakes, can be suppressed effectively at the time of kneading | mixing.

The presence of the aggregate contained in silver powder as mentioned above can also be judged by comparing an average particle diameter as follows. Specifically, it can judge by comparing the average particle diameter D50 of the volume cumulative total measured using the laser diffraction scattering method, and the average particle diameter DS obtained by the image analysis of a scanning electron microscope (SEM).

The particle size measurement by the laser diffraction scattering method includes not only the primary particles dispersed alone but also aggregates or secondary particles when the particle diameters of the particles dispersed in the solvent, that is, aggregated particles are included. The particle size is shown. On the other hand, the average particle diameter obtained by SEM image analysis is an average value of the particle diameter of a primary particle. Therefore, as the ratio determined by D50 / DS is larger than 1, it indicates that secondary particles or aggregates in which primary particles are connected at a predetermined ratio are formed.

In the silver powder according to the present embodiment, when the average particle diameter of the cumulative volume measured by the laser diffraction scattering method is D50, and the average particle diameter obtained by SEM image analysis is DS, the ratio determined by D50 / DS is used. It becomes 1.5-5.0.

Moreover, when the ratio calculated | required by D50 / DS is smaller than 1.5, there are few aggregates mentioned above, and there exists a possibility that flakes may be produced at the time of paste preparation. On the other hand, when the ratio determined by D50 / DS is larger than 5.0, silver particles are agglomerated too much to form large aggregates, and the dispersion stability in the solvent of the paste deteriorates and may cause flakes. There is this.

In addition, the intensity | strength of an aggregate can also be judged by comparing a specific surface area as follows. Specifically, it can judge by comparing the specific surface area calculated | required by the BET method, and the specific surface area calculated | required from the average particle diameter obtained by the image analysis of SEM.

Here, the BET method is a method of measuring the surface area of the powder by vapor phase adsorption and is a method of determining the total surface area, that is, the specific surface area, of the 1 g sample from the adsorption isotherm. As adsorption gas, nitrogen gas is used abundantly and the method of measuring an adsorption amount from the pressure of a to-be-adsorbed gas, or a volume change is used abundantly. A specific surface area can be calculated | required by obtaining an adsorption amount based on BET formula, and multiplying the area which one adsorption molecule occupies on a surface.

The strength of the aggregate relates to the strength of the connection between the silver particles. In the measurement by the BET method, when the connection between the particles is weak, for example, when the spherical primary particles seem to be connected only at the contact point, the surface area decreases because only the contact part to which the particles are connected decreases. The reduction of the specific surface area to be measured is slightly smaller than the sum of the specific surface areas in the state where the particles are completely dispersed, that is, the specific surface area of the primary particles. On the other hand, when the connection between the particles is strong, for example, when the primary particles are strongly connected so that the secondary particles become a foil shape or a snowman shape, the specific surface area of the thick connection portion decreases, and as a result, the BET method The specific surface area, measured by, decreases more than the specific surface area of the primary particles. In addition, as mentioned above, the average particle diameter obtained by SEM image analysis is an average value of the particle diameter of a primary particle, and the specific surface area calculated | required from this average particle diameter becomes the total of the surface area which used the individual particle | grains, It is close to the specific surface area.

Therefore, the ratio (SSA ₁ / SSA ₂ ) between the specific surface area SSA ₁ obtained by the BET method and the specific surface area SSA ₂ obtained from the average particle diameter obtained by SEM image analysis becomes a cohesive index or a spherical index of silver powder, Thereby, it can be determined how firmly the above-mentioned connection particle | grains are connected, and the intensity | strength of an aggregate can be judged.

Silver powder according to the present embodiment has a specific surface area determined by the BET method to the SSA _1, and when the specific surface area determined from the average particle diameter obtained by the image analysis of the SEM to SSA _2, as determined by SSA ₁ / SSA ₂ The ratio becomes less than 1.0. In this way, the silver powder having a ratio of less than 1.0 obtained by SSA ₁ / SSA ₂ means that the formed aggregate has a predetermined strength, and the aggregation structure is maintained even by kneading, for example, to generate flakes during paste production. Can be suppressed more effectively. On the other hand, the ratio is preferably not less than 0.7 as determined by SSA ₁ / SSA _2. In the case of less than 0.7, aggregation progresses and it shows that the coarse and high intensity aggregate is contained in silver powder. If such agglomerates are contained in the silver powder, it may cause clogging during screen printing, and there is a fear of impairing the uniformity of the wiring layer and the electrode formed of silver paste.

In addition, when the ratio determined by SSA ₁ / SSA ₂ is 1.0 or more, the aggregate is not formed or the connection of the connecting particles is weak, for example, when the mixture is kneaded at a predetermined pressure or more, the aggregate structure is easily broken and flakes. There is a possibility to generate.

By the way, generally, when manufacturing a baking type paste etc. using silver powder, each component is weighed and put into a predetermined container, it preliminarily knead | mixes using a revolving mixer etc., and is produced by main-kneading with 3 rolls. As described above, it is important to maintain the aggregated structure of the aggregate formed by connecting silver particles to a predetermined size, and the aggregated structure to a high level even when pre-kneading and kneading of the present kneading are performed during paste production. Is preferably maintained. That is, it is preferable that the aggregate has appropriate stability of the structure.

Therefore, the silver powder and the epoxy resin were kneaded experimentally by centrifugal force of 420 G to prepare a paste, and the silver powder in the paste was measured using a laser diffraction scattering method to obtain an average particle diameter D1 of the cumulative total volume, and then a three roll mill. The stability of the aggregate structure can be judged by comparing the average particle diameter D2 of the cumulative total volume of silver powder in the paste obtained by kneading with the laser diffraction scattering method. That is, in general, the structure of the aggregate collapses with kneading, and the average particle diameter of silver powder is shifted so as to be small. Thus, the stability of the structure of the aggregate is compared by comparing the average particle diameter D1 after preliminary kneading with the average particle diameter D2 after the main kneading. You can judge.

The silver powder which concerns on this embodiment is an average particle diameter of the volume cumulative which measured the silver powder in the paste obtained by kneading this silver powder and an epoxy resin by the centrifugal force of 420G as evaluation of the structural stability of the aggregate mentioned above using the laser diffraction scattering method. Is D1, and the ratio obtained by D2 / D1 is 0.5-1.5 when the average particle diameter of the volume cumulative value measured by the laser diffraction scattering method is used for the silver powder in the paste obtained by kneading with a 3-roll mill again after that. Becomes

When the ratio determined by D2 / D1 is 0.5 to 1.5, it can be judged that the structure of the aggregate is stable even by preliminary kneading and the main kneading. Moreover, when the ratio calculated | required by D2 / D1 is smaller than 0.5, there is no stability of the structure of an aggregate, the structure may be broken by kneading | mixing, and a sudden viscosity fall may occur, and a flake may be generated.

In the case of obtaining D1, the device for kneading (preliminary kneading) the silver powder and the epoxy resin at a centrifugal force of 420G is not particularly limited as long as it can be kneaded at the centrifugal force of 420G. Can be. In the case of obtaining D2, kneading by the three-roll mill (main kneading) is performed under conditions of, for example, a roll diameter of 150 mm and a roll pressure of 10 bar.

In addition, the stability of the structure of the aggregate can be evaluated by not only comparing the average particle diameter after kneading as mentioned above but also measuring the viscosity of the paste after kneading.

That is, as mentioned above, the silver powder which concerns on this embodiment has the aggregate with many voids which the silver particle (primary particle and secondary particle) aggregated by predetermined size. Therefore, as mentioned above, although the viscosity rises in the initial stage of paste preparation, when the intensity | strength of an aggregate is weak, it shifts so that a viscosity may become small gradually with kneading | mixing. Therefore, a paste is produced by silver powder and an epoxy resin experimentally, and the stability of the structure of the aggregate can be judged by comparing the viscosity η 1 of the paste after preliminary kneading with the viscosity η 2 of the paste after the main kneading.

The silver powder which concerns on this embodiment is an evaluation of the structural stability of the aggregate mentioned above, The shear powder which measured the paste obtained by kneading this silver powder and an epoxy resin by the centrifugal force of 420G by the viscoelasticity measuring apparatus in 4 sec <^-1> When the viscosity was made into (eta) 1 and the paste obtained by kneading | mixing again by the 3-roll mill after that was made into the viscosity in the shear rate 4 sec ^-1 measured by the viscoelasticity measuring apparatus as (eta) 2, the ratio calculated | required by (eta) 2 / (eta) 1 is 0.5. It becomes -1.5.

When the ratio determined by η2 / η1 is 0.5 to 1.5, it can be judged that the structure of the aggregate is stable even by preliminary kneading and the main kneading. Moreover, when the ratio calculated by (eta) 2 / (eta) 1 is smaller than 0.5, there is no stability of the structure of an aggregate, the structure may be broken by kneading | mixing, and a sudden viscosity fall may occur, and a flake may be generated.

As described above, as an apparatus for kneading the silver powder and the epoxy resin with a centrifugal force of 420 G (preliminary kneading), for example, a revolving mixer or the like can be used. In addition, kneading | mixing (main kneading) by a 3-roll mill is performed on conditions of a roll diameter of 150 mm and a roll pressure of 10 bar, for example. Moreover, also about a viscoelasticity measuring apparatus, if a viscosity measurement in a desired shear rate is possible, it will not specifically limit.

In addition, the composition of the evaluation paste prepared in this viscosity measurement is 80 mass% of silver powder, epoxy resin (100-200 P (10-20 Pa.s) / 25 degreeC, Preferably it is 120-150 P ( It is preferable to make 12-15 Pa.s) / 25 degreeC) 20 mass%.

As described above, the silver powder according to the present embodiment has a cohesive force of -0.2 N / cm 2 or more and 0.7 N / cm 2 or less, a compressibility in the powder layer shear force measurement is 20 to 50%, and the JIS-K6217-4 method. It has the characteristic that the water absorption amount of dibutyl phthalate measured by 3.0-9.0 ml / 100g. That is, this silver powder has an aggregate with many voids with which silver particle was connected by the predetermined magnitude | size, and this aggregate has predetermined intensity | strength. According to such silver powder, dispersibility in a solvent at the time of paste preparation becomes favorable, it can suppress that silver powder aggregates in a paste and becomes agglomerate, and it can suppress that coarse powder, such as a flake, generate | occur | produce.

According to the silver powder capable of suppressing the occurrence of such flakes, clogging can be prevented even when screen printing is performed without impairing the kneading property during kneading of paste production, and excellent printability can be realized.

Next, the above-mentioned manufacturing method of silver powder is demonstrated. The manufacturing method of the silver powder which concerns on this embodiment uses silver chloride and silver nitrate as starting materials, for example, The solution (silver complex containing solution) containing the silver complex obtained by melt | dissolving silver chloride etc. with a complexing agent basically The silver particle slurry is obtained by mixing a reducing agent solution, reducing a silver complex, and depositing silver particle. In the case of using silver chloride as a starting material, it is not necessary to provide a nitrite gas recovery device or a treatment device for nitrate-based nitrogen in wastewater, which is required by the method of using silver nitrate as a starting material, and has a low impact on the environment. For this reason, manufacturing cost can be reduced.

And in the manufacturing method of the silver powder which concerns on this embodiment, 0.1-15 mass% of water-soluble polymer is added with respect to silver either or both of a silver complex containing solution and a reducing agent solution. Moreover, More preferably, more than 3.0 mass% and 10 mass% or less of water-soluble polymer is added with respect to silver. Thus, cohesion force is -0.2 N / cm <2> or more and 0.7 N / cm <2> or less by adding 0.1-15 mass% water-soluble polymer with respect to silver to both, or one of a silver complex containing solution and a reducing agent solution, and a powder layer shear force The silver powder whose compressibility in a measurement is 20 to 50%, and the absorption amount of dibutyl phthalate measured by JIS-K6217-4 method 3.0-9.0 ml / 100g can be manufactured.

In production of silver powder which concerns on this embodiment, selecting a water-soluble polymer as an aggregation inhibitor, and the addition amount become important. The silver particles (primary particles) produced by reduction by the reducing agent solution are active on the surface and are easily connected with other silver particles to form secondary particles. Secondary particles also aggregate to form aggregates. At this time, when an anti-agglomeration agent having a high anti-aggregation effect, for example, a surfactant or a fatty acid is used, secondary particles or aggregates are not sufficiently formed, and primary particles are increased, so that an appropriate aggregate is not formed. On the other hand, when a coagulation inhibitor having a low coagulation prevention effect is used, the formation of secondary particles or aggregates becomes excessive, resulting in silver powder containing coarse aggregated aggregates that are excessively aggregated. Since the water-soluble polymer has an appropriate agglomeration preventing effect, it is possible to easily control the formation of secondary particles or aggregates by adjusting the amount of addition, so that aggregates of appropriate size can be formed in the silver-containing solution after addition of the reducing agent solution. have.

Although it does not specifically limit as water-soluble polymer to add, It is preferable that it is at least 1 sort (s) of polyethyleneglycol, polyethylene oxide, polyvinyl alcohol, and polyvinylpyrrolidone. According to these water-soluble polymers, in particular, it is possible to prevent excessive aggregation, to prevent insufficient aggregation of the grown nucleus, and to prevent fine silver particles (primary particles), thereby easily forming silver powder having aggregates of a predetermined size. Can be.

Here, the following mechanism is considered as a mechanism by which silver particles are connected to a predetermined size by adding a water-soluble polymer to form aggregates. In other words, by adding the water-soluble polymer, the water-soluble polymer is adsorbed on the surface of the silver particles. At this time, if almost all of the surface of the silver particles is covered with the water-soluble polymer, the silver particles are present as a single body, but by adding 0.1 to 15% by weight of the water-soluble polymer relative to the silver, a surface where some water-soluble polymers do not exist remains, It is thought that silver particles are connected through the surface and form aggregates.

From this, 0.1-15 mass% is added with respect to silver with respect to the addition amount of a water-soluble polymer. When the amount of the water-soluble polymer added is less than 0.1% by mass with respect to silver, the dispersibility in the silver particle slurry becomes poor, and the silver powder aggregates excessively and generates many coarse aggregated flakes. On the other hand, when the addition amount with respect to silver is more than 15 mass%, almost all silver particle surfaces are covered with water-soluble polymer, and silver particles cannot connect, and aggregates cannot be formed. As a result, it becomes silver powder which consists of primary particles, and also in this case, a flake is produced at the time of paste preparation. Therefore, by adding 0.1-15 mass% of water-soluble polymers with respect to silver, it is possible to connect the silver particles with an appropriate cohesive force and to form a structurally stable aggregate, thereby improving the dispersibility in the paste and improving the generation of flakes. It can be effectively suppressed.

In addition, a water-soluble polymer is added to both or either one of a silver complex containing solution and a reducing agent solution. The addition of the water-soluble polymer to both or both of the silver complex-containing solution and the reducing agent solution may be added to the solution to be added beforehand before the reduction treatment, and at the time of mixing the silver complex-containing solution and the reducing agent solution for the reduction treatment. It may be added to.

More preferably, the water-soluble polymer may be added to the reducing agent solution in advance. In this way, by adding the water-soluble polymer to the reducing agent solution in advance, the water-soluble polymer exists in the place of nucleation or nuclear growth, and quickly adsorbs the water-soluble polymer on the surface of the generated nucleus or silver particles, thereby agglomeration of silver particles. It can be controlled efficiently. And, more preferably, by adding the concentration so that the concentration is more than 3.0% by mass and 10% by mass or less, the silver particles can be more suitably connected to a predetermined size to form agglomerates having high stability, and the generation of flakes more effectively. It can be suppressed.

In addition, when the water-soluble polymer is added to the silver complex-containing solution in advance, it is difficult to supply the water-soluble polymer to the place of nucleation or nuclear growth, and there is a possibility that the water-soluble polymer cannot be adsorbed on the surface of the silver particles properly. Therefore, when adding to a silver complex containing solution previously, it is preferable to make the addition amount of a water-soluble polymer into the quantity exceeding 3.0 mass%.

Next, the manufacturing method of silver powder is demonstrated more concretely for every process. First, in a reduction process, the starting material of silver chloride is melt | dissolved using a complexing agent, and the solution containing a silver complex is prepared. Although it does not specifically limit as a complexing agent, It is preferable to use ammonia water which is easy to form a complex with silver chloride and does not contain the component which remains as an impurity. In addition, when using silver chloride, it is preferable to use the thing of high purity.

As a dissolution method such as silver chloride, for example, when ammonia water is used as a complexing agent, a slurry such as silver chloride may be prepared to add ammonia water. However, in order to increase the concentration of the complex and increase productivity, it is preferable to add silver chloride in the ammonia water to dissolve it. The aqueous ammonia used for dissolution may be a conventional one used industrially. However, in order to prevent impurity mixing, the ammonia water is preferably as high as possible.

Next, a reducing agent solution to be mixed with the silver complex solution is prepared. As a reducing agent, it is preferable to use what has strong reducing power, such as ascorbic acid, hydrazine, and formalin. Ascorbic acid is particularly preferable because crystal grains in the silver particles easily grow. Hydrazine or formalin can make the crystal | crystallization in a silver particle small. Further, in order to control the uniformity of the reaction or the reaction rate, the reducing agent may be used as an aqueous solution adjusted to a concentration by dissolving or diluting the reducing agent with pure water or the like.

As mentioned above, in the manufacturing method of this silver powder, 0.1-15 mass% of water-soluble polymers are added to both or one of a silver complex containing solution and a reducing agent, but at this time, by addition of a water-soluble polymer Since it may foam at the time of a reduction reaction, an antifoamer can also be added to a silver complex solution or a reducing agent liquid mixture. The antifoaming agent is not particularly limited and may be usually used at the time of reduction. However, in order not to inhibit a reduction reaction, it is preferable to make the addition amount of a defoaming agent into the minimum at which a defoaming effect is acquired.

In addition, as for the water used when preparing the silver complex solution and the reducing agent solution, in order to prevent the incorporation of impurities, it is preferable to use water from which impurities have been removed, and it is particularly preferable to use pure water.

Next, the silver complex-containing solution and the reducing agent solution prepared as described above are mixed, and the silver complex is reduced to precipitate silver particles. This reduction reaction may be carried out by a batch method or by a continuous reduction method such as a tube reactor method or an overflow method. In addition, the particle diameter of silver particle can be controlled by the mixing rate of a silver complex solution and a reducing agent solution, or the reduction rate of a silver complex, and can be easily controlled by the target particle diameter.

The silver particle obtained by the reduction process adsorb | sucks a large amount of chlorine ion and water-soluble polymer on the surface. Therefore, in order to make sufficient the electroconductivity of the wiring layer and electrode formed using silver paste, it is preferable to wash | clean the obtained slurry of silver particle in the next washing | cleaning process, and to remove a surface adsorbate by washing | cleaning. Moreover, although mentioned later, in order to suppress that excessive aggregation arises by removing the water-soluble polymer which adsorb | sucked on the silver particle surface, it is preferable to perform a washing | cleaning process after a surface treatment process to silver particle, etc.

The washing method is not particularly limited, but a method of injecting silver particles, which have been solid-liquid separated from the slurry by a filter press or the like into a washing liquid, stirring using a stirrer or an ultrasonic cleaner, and then solid-liquid separation again, recovers the silver particles. Used as In addition, in order to fully remove a surface adsorbate, it is preferable to repeat operation | movement which consists of input to a washing | cleaning liquid, stirring washing | cleaning, and solid-liquid separation several times.

Although the washing | cleaning liquid may use water, in order to remove chlorine efficiently, you may use aqueous alkali solution. Although it does not specifically limit as alkaline solution, It is preferable to use the sodium hydroxide aqueous solution which has few residual impurities and is inexpensive. In the case of using an aqueous sodium hydroxide solution as the washing liquid, it is preferable to wash the silver particles or the slurry again with water in order to remove sodium after washing in the aqueous sodium hydroxide solution.

Moreover, it is preferable to make the density | concentration of the sodium hydroxide aqueous solution into 0.01-1.00 mol / l. If the concentration is less than 0.01 mol / l, the cleaning effect is insufficient. On the other hand, if the concentration exceeds 1.00 mol / l, sodium may remain in the silver particles more than acceptable. The water used for the cleaning liquid is preferably water containing no impurity element harmful to silver particles, and particularly preferably pure water.

In the production of silver powder according to the present embodiment, before the aggregate formed by reduction in the silver complex-containing solution further aggregates to form coarse aggregates, the surface of the formed aggregate is subjected to a surface treatment with a treatment agent having a high anti-aggregation effect. Preventing excessive aggregation is a second important factor. That is, after the above-mentioned aggregate is formed, before the excessive aggregation progresses, the silver particles are treated with a surfactant or, more preferably, a surface treatment step is performed on the silver particles treated with the surfactant and the dispersant. As a result, excessive aggregation can be prevented, the structural stability of the desired aggregate can be maintained, and generation of flakes can be more effectively suppressed.

Excessive aggregation proceeds in particular by drying, so that the surface treatment can be effected at any stage as long as the silver particles are dried. For example, it can be performed after the reduction step, before the above-described cleaning step, at the same time as the cleaning step, or after the cleaning step.

Especially, it is preferable to perform after a reduction process and before a washing process especially. Or it is preferable to carry out after one washing process. Thereby, the aggregate which aggregated to the predetermined | prescribed magnitude | size which was formed through the reduction process can be hold | maintained, and since the surface treatment is given to the silver particle containing this aggregate, silver powder with good dispersibility can be manufactured.

More specifically, in the manufacturing method of silver powder which concerns on this embodiment, as mentioned above, by adding 0.1-15 mass% water-soluble polymer with respect to silver, water-soluble polymer is made to adsorb | suck suitably on the surface of silver particle, Agglomerates in which silver particles are connected at a predetermined size are formed. However, the water-soluble polymer adsorbed on the surface of the silver particles is relatively easily washed by the washing step. Therefore, when the washing step is performed prior to the surface treatment, the water-soluble polymer on the surface of the silver particles is washed, and the silver particles start to excessively aggregate with each other, whereby a large amount of aggregates may be formed larger than the formed aggregates. As a result, there is a possibility of causing flakes.

Therefore, from this, it is preferable to perform surface treatment process before the washing | cleaning process or after one washing process, ie, in the state in which the water-soluble polymer of the quantity which can suppress aggregation of silver particle at least on the surface of silver particle remains. Do. The surface treatment after the reduction treatment and before the washing step may be performed after the liquid-liquid separation of the slurry containing silver particles after the completion of the reduction step by a filter press or the like. In this way, the surface treatment agent or dispersant, which is a surface treatment agent, can be directly acted on the silver particles produced by performing surface treatment after solid-liquid separation. Therefore, the surface treatment agent is adsorbed to the formed aggregates accurately, and the aggregated structure is formed by excessive aggregation. It becomes large, and it can suppress that a flake generate | occur | produces effectively.

In this surface treatment process, it is more preferable to surface-treat with both surfactant and a dispersing agent. When surface treatment is performed with both the surfactant and the dispersant in this manner, the surface treatment layer can be formed on the surface of the silver particles by the interaction thereof, and thus the effect of preventing excessive aggregation is high and is effective for maintaining the desired aggregate. As a specific method of the preferable surface treatment using a surfactant and a dispersing agent, silver particle is thrown in the water which added surfactant and a dispersing agent, and it stirred, or it stirred in the water which added surfactant, and then adds a dispersing agent and stirred. Do it. In addition, when surface-treating simultaneously with a washing | cleaning process, surfactant and a dispersing agent are added simultaneously to a washing | cleaning liquid, or what is necessary is just to add a dispersing agent after addition of surfactant. In order to improve the adsorption property of the surfactant and the dispersant to the silver particles, it is preferable to add the silver particles to the water or the washing liquid to which the surfactant is added and to stir, and then to add and disperse the dispersant again.

Although it does not specifically limit as surfactant here, It is preferable to use a cationic surfactant. Since cationic surfactants are ionized with cations without being affected by pH, for example, an effect of improving the adsorption property to silver powder using silver chloride as a starting material is obtained.

Although it does not specifically limit as cationic surfactant, It is represented by the alkyl monoamine salt type represented by the monoalkyl amine salt, the alkyldiamine salt type represented by N-alkyl (C14-C18) propylene diamine dioleate, and the alkyl trimethyl ammonium chloride. Tertiary represented by alkyltrimethylammonium salt type, alkyldimethylbenzylammonium chloride type represented by alkyldimethylbenzylammonium chloride, quaternary ammonium salt type represented by alkyldipolyoxyethylenemethylammonium chloride type, alkylpyridinium salt type, and dimethylstearylamine Polyoxyethylene alkylamine type represented by amine type, polyoxypropylene polyoxyethylene alkylamine, N, N ', N'-tris (2-hydroxyethyl) -N-alkyl (C14-18) 1,3 At least 1 sort (s) chosen from the oxyethylene addition type of the diamine represented by -diaminopropane is preferable, and among a quaternary ammonium salt type and a tertiary amine salt type, Either one or mixtures thereof is more preferred.

Moreover, it is preferable that surfactant has at least 1 alkyl group which has C4-C36 carbon number represented by methyl group, a butyl group, a cetyl group, stearyl group, tallow, hardened tallow, and plant type stearyl. As an alkyl group, what added at least 1 sort (s) chosen from polyoxyethylene, polyoxypropylene, polyoxyethylene polyoxypropylene, polyacrylic acid, and polycarboxylic acid is preferable. Since these alkyl groups adsorb | suck strongly with the fatty acid used as a dispersing agent mentioned later, when adsorbing a dispersing agent to silver particle through surfactant, a fatty acid can be strongly adsorbed.

In addition, the amount of the surfactant added is preferably in the range of 0.002 to 1.000 mass% with respect to the silver particles. Since almost all of the surfactant is adsorbed by the silver particles, the amount of the surfactant added and the amount of the adsorption are almost the same. When the amount of the surfactant added is less than 0.002% by mass, the effect of suppressing aggregation of silver particles or improving adsorbability of the dispersant may not be obtained. On the other hand, when the added amount exceeds 1.000% by mass, the conductivity of the wiring layer and the electrode formed by using the silver paste decreases, which is not preferable.

As the dispersant, for example, protective colloids such as fatty acids, organometallics, gelatin and the like can be used. However, in consideration of the possibility of impurity incorporation and in view of adsorption with surfactants, it is preferable to use fatty acids or salts thereof. Moreover, you may add a fatty acid or its salt as an emulsion.

Although it does not specifically limit as a fatty acid used as a dispersing agent, It is preferable that it is at least 1 sort (s) chosen from stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, linolenic acid. This is because these fatty acids have a relatively low boiling point, and thus have little adverse effect on the wiring layer and the electrode formed by using the silver paste.

Moreover, the range of 0.01-3.00 mass% is preferable with respect to silver particle, and, as for the addition amount of a dispersing agent, the range of 0.01-1.00 mass% is more preferable with respect to silver particle. Although the amount of adsorption to silver particles varies depending on the type of dispersing agent, when the amount of addition is less than 0.01% by mass, the amount of dispersing agent that sufficiently satisfies the effect of suppressing aggregation of silver particles or improving adsorbability of the dispersing agent may not be adsorbed onto silver powder. have. On the other hand, when the addition amount of a dispersing agent exceeds 3.00 mass%, the dispersing agent adsorb | sucked by silver particle may increase, and the electrical conductivity of the wiring layer and electrode formed using silver paste may not be obtained sufficiently.

After washing and surface treatment, the solid solution is separated to recover the silver particles. Moreover, the apparatus used for washing | cleaning and surface treatment is good to be used normally, For example, the reaction tank etc. with a stirrer can be used. Moreover, the apparatus used for solid-liquid separation may also be used normally, For example, a centrifuge, a suction filter, a filter press, etc. can be used.

In the drying step, the silver particles having finished washing and surface treatment are evaporated and dried. As a drying method, the silver powder collect | recovered after completion | finish of washing | cleaning and surface treatment may be put on a stainless pad, for example, and it may heat at 40-80 degreeC using commercially available drying apparatuses, such as an atmospheric oven or a vacuum dryer.

In addition, the silver powder after drying is pulverized and classified. Although the silver powder after surface treatment mentioned above is further aggregated between aggregates by subsequent drying etc., since the bonding force is weak, it isolate | separates easily even the aggregate of predetermined size at the time of paste preparation. However, in order to stabilize a paste, it is preferable to disintegrate and to classify. Although a disintegration method is not specifically limited, It is preferable to use apparatuses with weak disintegration force, such as a jet mill and a high speed stirrer. In the apparatus with strong disintegration force, even the aggregates described above may be disintegrated or the silver powder may be deformed, which is not preferable. In addition, as disintegration conditions, it may adjust to the extent to which the formed aggregate is maintained. The classifier is not particularly limited, and an air classifier, a sieve, or the like can be used.

Example

EMBODIMENT OF THE INVENTION Below, the specific Example of this invention is described. However, this invention is not limited to the following example at all.

Example 1

36 L of 25% ammonia water and 2492 g of silver chloride (manufactured by Sumitomo Kinzoku Co., Ltd.) while stirring at a liquid temperature of 36 ° C. were prepared while stirring at 38 ° C. to prepare a silver complex solution, and the obtained silver complex solution was 36 in a warm bath. Maintained at ° C.

On the other hand, 1068 g of ascorbic acid (Kanto Chemical Co., Ltd. make, reagent) of a reducing agent was melt | dissolved in 14 L of pure water of 36 degreeC, and it was set as the reducing agent solution. Subsequently, 64.1 g of polyvinyl alcohol (3.5 mass% based on PURA205, manufactured by Kuraray Co., Ltd.) as a water-soluble polymer was dissolved in 550 ml of pure water at 36 ° C., and then mixed in a reducing agent solution.

The produced silver complex solution and reducing agent solution were sent to a mixing tube with a silver complex solution of 2.7 L / min and a reducing agent solution of 0.9 L / min using a mono pump (manufactured by Heishin Sowbi Co., Ltd.) to reduce the silver complex. . The reduction rate at this time is 127 g / min in silver. In addition, the ratio of the feed rate of the reducing agent to the feed rate of silver was 1.4. As the mixing pipe, a pipe made of vinyl chloride having an inner diameter of 25 mm and a length of 725 mm was used. The slurry containing the silver particle obtained by reduction of a silver complex was taken in the water tank, stirring.

Then, 0.88 g of polyoxyethylene addition quaternary ammonium salt which is a commercial cationic surfactant as surface treatment agent to the silver particle slurry obtained by reduction (about Kuroda Japan Co., Ltd. make, brand name Syrahsol G-265, silver particle) 0.048 mass%) and 16.47 g of stearic acid emulsion (Junkyo Yushi Co., Ltd., cellosol 920, 0.90 mass% with respect to silver particle) were added, and it stirred for 60 minutes and surface-treated. After surface treatment, the silver particle slurry was filtered using the filter press, and silver particle was solid-liquid separated.

Subsequently, before the collected silver particles are dried, the silver particles are poured into 23 L of a 0.2 mass% sodium hydroxide (NaOH) aqueous solution held at 40 ° C, stirred for 15 minutes, washed, and then filtered through a filter press to obtain silver. Particles were recovered.

Next, the collect | recovered silver particle was thrown in 23L pure water maintained at 40 degreeC, and after stirring and filtration, the silver particle was moved to the stainless pad and dried at 60 degreeC by the vacuum dryer for 10 hours. Subsequently, the dried silver particles were pulverized at a circumferential speed of 22.7 m / sec using a 5 L high speed stirrer (manufactured by Nippon Coke Co., Ltd., FM5C). After the pulverization treatment, the coarse particles were removed using a air flow classifier (Nihon Kogyo Co., Ltd., EJ-3) at a classification point of 7 µm to obtain silver particles.

About the obtained silver particle, cohesion force was measured using the powder layer shear force measuring apparatus (manufactured by Nanoseeds Co., Ltd., NS-S300). The measurement was put into the measuring container of 15 mm of internal diameters using the silver powder 18g, and it measured continuously in the state which put silver powder in setting the applied load of 20N, 40N, 60N. At this time, the indentation rate to silver powder is 0.2 mm / sec, and if it reaches up to a predetermined applied load, the indentation is stopped, and after waiting 100 seconds thereafter, the side sliding is started at a rate of 10 μm / sec to measure the shear force and the shear force is measured. It was. In addition, the sampling frequency of the shear force was 10 Hz. From the maximum value of the shear force and the vertical load just before the start of side sliding, the shear stress and the vertical stress at each set applied load of 20 N, 40 N, and 60 N are obtained, and a graph of the shear stress against the vertical stress is produced, and these The relation of the straight line using the least square method was calculated for three points. As a result, the cohesion force corresponding to the Y fragment was 0.37 N / cm 2. In addition, the compression ratio was a value when the applied load was 60 N and was 30.1%. In addition, the absorption amount of the dibutyl phthalate measured by JIS-K6217-4 method using the absorption amount measuring apparatus (made by Asahi Soken Co., Ltd.) was 6.9 ml / 100 g.

In addition, the average particle diameter DS of the silver powder measured by SEM observation was 1.12 micrometers. In addition, the average particle diameter D50 of the cumulative total volume measured by the laser diffraction scattering method by disperse | distributing silver powder in isopropyl alcohol was 2.37 micrometers. Therefore, the ratio determined by D50 / DS was 2.12. In addition, the specific surface area SSA ₁ measured by the BET method is 0.42 m 2 / g, the specific surface area SSA ₂ obtained from the average particle diameter DS obtained by SEM observation is 0.51 m 2 / g, and the ratio determined by SSA ₁ / SSA ₂ is 0.82.

Next, 80 mass% of silver powder obtained and epoxy resin (Mitsubishi Chemical Co., Ltd. product 819) are weighed so that it may be 20 mass%, and it uses the magnetoelectric mixer (Thinkki Co., Ltd. product, ARE-250), After kneading with a centrifugal force of 420 G and pasting, the resultant was kneaded again using a three-roll mill (manufactured by Burer Co., Ltd., three-roll mill SDY-300) and evaluated. During the kneading by the three-roll mill, the occurrence of flakes by the naked eye was not found, and the kneading property was good.

About the obtained paste, the viscosity in shear rate 4 sec <^-1> was calculated | required using the viscoelasticity measuring apparatus (Anton Paar company, MCR-301). Viscosity (eta) 1 after kneading with an autorotation mixer was 62.7 (Pa * s), the viscosity (eta) 2 after kneading with a 3-roll mill was 56.3 (Pa * s), and ratio calculated by (eta2 / eta1) was 0.90.

In addition, 2 g of the paste kneaded with a three-roll mill was introduced into 40 ml of isopropyl alcohol, followed by ultrasonic dispersion, followed by suction filtration using a 20 µm aperture sieve. The number was measured on the SEM. As a result, there were two particles of 20 µm or more. In addition, the paste was dispersed in isopropyl alcohol, and the average particle diameter of the cumulative volume was measured using a laser diffraction scattering method. As a result, the average particle diameter D1 of the paste after kneading by the mixer was 2.35 µm and the average particle diameter after 3 roll milling. D2 was 2.10 mu m, and the ratio found D2 / D1 was 0.89.

As mentioned above, in Example 1, when the aggregate which silver particle was connected to the predetermined size is formed, it was confirmed that hardly a flake generate | occur | produces in a paste. In addition, it was found that the viscosity and the average particle diameter were little changed after kneading with an autorotation mixer and after kneading with a three-roll mill, and the aggregated structure of the aggregate was maintained.

[Example 2]

In Example 2, silver powder was manufactured like Example 1 except having set the quantity of polyvinyl alcohol which is a water-soluble polymer to 183g (10 mass% with respect to silver).

The silver powder obtained was evaluated in the same manner as in Example 1, and the cohesive force was 0.14 N / cm 2, and the compressibility was 35.0%. In addition, the absorption amount of butyl phthalate measured by the JIS-K6217-4 method was 7.0 ml / 100 g.

In addition, the average particle diameter DS of the silver powder measured by SEM observation was 1.05 micrometer. In addition, the average particle diameter D50 of the volume cumulative total which measured silver powder in the isopropyl alcohol and measured using the laser diffraction scattering method was 2.16 micrometers. Therefore, the ratio determined by D50 / DS was 2.06. In addition, the specific surface area SSA ₁ measured by the BET method is 0.46 m 2 / g, the specific surface area SSA ₂ obtained from the average particle diameter DS obtained by SEM observation is 0.55 m 2 / g, and the ratio determined by SSA ₁ / SSA ₂ is 0.84.

Next, a paste was produced in the same manner as in Example 1 using the obtained silver powder. Also in Example 2, when the paste was formed using a three-roll mill, no flakes were produced by the naked eye, and the kneading property was good.

About the obtained paste, the viscosity in shear rate 4 sec ^-1 was calculated | required using the viscoelasticity measuring apparatus (Anton Paar Co., MCR-301), The viscosity (eta) 1 after kneading with an autorotation mixer is 58.6 (Pa * s). The viscosity (eta) 2 after kneading with a 3-roll mill was 46.4 (Pa * s), and the ratio calculated | required by (eta) 2 / (eta) 1 was 0.79.

Moreover, it was confirmed that the number of flakes on the opening 20 micrometer sieve after 6 micrograms of paste paste 2g kneaded with a 3-roll mill in 40 ml of isopropyl alcohols, and ultrasonically disperse | distributed. In addition, the paste was dispersed in isopropyl alcohol and the average particle diameter of the cumulative volume was measured using a laser diffraction scattering method. Was 2.13 µm and the ratio determined by D2 / D1 was 0.99.

As described above, in Example 2, it was confirmed that, in the same manner as in Example 1, almost no flakes were generated in the paste by forming an aggregate in which silver particles were connected at a predetermined size. In addition, after kneading with an autorotation mixer and after kneading with a three-roll mill, it was found that the change in viscosity and average particle diameter was small, and the aggregated structure of the aggregate was maintained.

Comparative Example 1

In Comparative Example 1, a silver powder was prepared in the same manner as in Example 1 except that the amount of polyvinyl alcohol which was a water-soluble polymer was 329.4 g (18 mass% relative to silver).

The obtained silver powder was evaluated similarly to Examples 1 and 2, and the cohesion force was 0.80 N / cm <2>, and the compression ratio was 38.1%. In addition, the absorption amount of butyl phthalate measured by JIS-K6217-4 method was 2.5 ml / 100 g.

In addition, the average particle diameter DS of the silver powder measured by SEM observation was 1.04 micrometer. In addition, the average particle diameter D50 of the cumulative total volume measured by using the laser diffraction scattering method by dispersing silver powder in isopropyl alcohol was 1.51 micrometers. Therefore, the ratio determined by D50 / DS was 1.45. In addition, the specific surface area SSA ₁ measured by the BET method is 0.62 m 2 / g, the specific surface area SSA ₂ obtained from the average particle diameter DS obtained by SEM observation is 0.55 m 2 / g, and the ratio determined by SSA ₁ / SSA ₂ is 1.13.

Next, the paste was produced similarly to Example 1 and 2 using the obtained silver powder. As a result, when the paste was formed using a three-roll mill, flakes were generated by the naked eye.

About the obtained paste, the viscosity at shear rate 4 sec ^-1 was calculated | required using the viscoelasticity measuring apparatus (Anton Paar company, MCR-301), The viscosity (eta) 1 after kneading with an autorotation mixer is 42.8 (Pa * s) The viscosity eta 2 after kneading with a three-roll mill was 38.1 (Pa · s), the ratio determined by eta 2 / η 1 was 0.89, and the change in viscosity was small.

In addition, 2 g of the paste kneaded with a three-roll mill was introduced into 40 ml of isopropyl alcohol, and the number of flakes on the opening 20 µm sieve after ultrasonic dispersion was 36, and it was confirmed that a large number of flakes occurred. Furthermore, when the paste was dispersed in isopropyl alcohol and the average particle diameter of the cumulative volume was measured using a laser diffraction scattering method, the average particle diameter D1 after the mixer was 1.62 µm and the average particle diameter D2 after 3 roll mill was 1.56 µm. The ratio determined by D2 / D1 was 0.96, and D1 and D2 were almost the same, and silver powder was dispersed by the kneading of the autorotation mixer.

As described above, in Comparative Example 1, although there was no sudden drop in viscosity or deterioration in dispersibility, a large amount of flakes occurred, resulting in a decrease in kneading property. This is considered to have caused excessive aggregation because the formation of aggregates was not sufficient, and the strength of the aggregate structure was also weak and easily decomposed by kneading.

[Comparative Example 2]

In Comparative Example 2, a silver powder was prepared in the same manner as in Example 1 except that the amount of polyvinyl alcohol which was a water-soluble polymer was 0.92 g (0.05 mass% with respect to silver).

The silver powder obtained was evaluated in the same manner as in Examples 1 and 2, and the cohesive force was -0.82 N / cm 2, and the compressibility was 18.4%. In addition, the absorption amount of butyl phthalate measured by JIS-K6217-4 method was 14.8 ml / 100 g.

In addition, the average particle diameter DS of the silver powder measured by SEM observation was 1.02 micrometer. In addition, the average particle diameter D50 of the cumulative total volume measured by the laser diffraction scattering method by disperse | distributing silver powder in isopropyl alcohol was 5.92 micrometers. Therefore, the ratio determined by D50 / DS was 5.80. In addition, the specific surface area SSA ₁ measured by the BET method is 0.12 m 2 / g, the specific surface area SSA ₂ obtained from the average particle diameter DS obtained by SEM observation is 0.56 m 2 / g, and the ratio determined by SSA ₁ / SSA ₂ is 0.21.

Next, the paste was produced similarly to Example 1 and 2 using the obtained silver powder. In that case, it became a very hard paste by kneading with an autorotation mixer. Further, when kneaded using a three roll mill, occurrence of flakes was observed during kneading.

About the obtained paste, the viscosity at shear rate 4 sec ^-1 was calculated | required using the viscoelasticity measuring apparatus (Anton Paar company, MCR-301), The viscosity (eta) 1 after kneading with a self-rotating mixer is 211.3 (Pa * s) And the viscosity (eta) 2 after kneading with a 3-roll mill was 95.1 (Pa * s), and the ratio calculated | required by (eta) 2 / (eta) 1 was 0.45.

In addition, 2 g of the paste kneaded with a three-roll mill was poured into 40 ml of isopropyl alcohol, and the number of flakes on the opening 20 µm sieve after ultrasonic dispersion was 134, particularly large flakes exceeding 50 µm occurred. It was confirmed. In addition, the paste was dispersed in isopropyl alcohol and the average particle diameter of the cumulative volume was measured using a laser diffraction scattering method. The average particle diameter D1 after the mixer was 5.94 µm, and the average particle diameter D2 after 3 roll milling was 2.49 µm. The ratio calculated by D2 / D1 was 0.42.

As mentioned above, in the comparative example 2, a large amount of flakes generate | occur | produced in a paste, and also the rapid viscosity fall and dispersibility fall, and it was difficult to paste and brought about the remarkable fall of kneading property. This is considered to be because the large aggregated aggregate which excessively aggregated was formed in large quantity, and became silver powder which is hard to decompose.

Table 1 below summarizes the evaluation results in each of Examples and Comparative Examples.

Using Examples 1 and 2 and the silver powder of Comparative Example 1, an epoxy resin, a curing agent (phenol resin) and a solvent (trimethylene glycol, dipropylene glycol) were kneaded to produce a commercially available general silver paste. Kneading was confirmed. In the kneading, preliminary kneading and main kneading were performed using mass production type kneader and 3 rolls.

As a result, the paste produced using the silver powder of Examples 1 and 2 showed favorable kneading property with little generation of flakes. On the other hand, in the paste produced using the silver powder of Comparative Example 1, there were many flakes and poor kneading property.

As can be seen from the above results, the silver powder has a cohesive force of -0.2 or more and 0.7 N / cm 2 or less, the compressibility in the powder layer shear force measurement is 20 to 50%, and dibutyl phthalate measured by the JIS-K6217-4 method. By the absorption amount of 3.0-9.0 ml / 100g, it turned out that generation | occurrence | production of a flake can be suppressed effectively at the time of paste preparation, and favorable kneading property can be exhibited. In addition, it has been found that an appropriate viscosity can be maintained and excellent printability can be realized.

Claims (11)

Cohesion force is -0.2 N / cm 2 or more and 0.7 N / cm 2 or less, the compressibility in powder layer shear force measurement is 20 to 50%, and the absorption amount of dibutyl phthalate measured by JIS-K6217-4 method is 3.0 to 9.0 ml. Silver powder characterized in that it is / 100g. The ratio obtained by D50 / DS according to claim 1, wherein the average particle diameter of the cumulative total volume measured by the laser diffraction scattering method is D50, and the average particle diameter obtained by SEM image analysis is DS. Silver powder characterized in that the. The method of claim 1 or claim 2 wherein the specific surface area obtained by the BET method to the SSA _1, and when the specific surface area determined from the average particle diameter obtained by the image analysis of the SEM to SSA _2, obtained with SSA ₁ / SSA ₂ Silver powder, characterized in that the losing ratio is less than 1.0. The average particle diameter of the volume cumulative value of any one of Claims 1-3 whose silver powder in the paste obtained by kneading the said silver powder and an epoxy resin by the centrifugal force of 420 G was measured using the laser diffraction scattering method, When the silver powder in the paste obtained by kneading with a three roll mill after that was measured using the laser diffraction scattering method and the average particle diameter of the cumulative total volume was set to D2, the ratio determined by D2 / D1 was 0.5 to 1.5. Silver powder. The viscosity at the shear rate of 4 sec ^-1 of the paste obtained by kneading the silver powder and the epoxy resin at a centrifugal force of 420 G by a viscoelasticity measuring device is set to η1 according to any one of claims ¹ to ³ . When the paste obtained by kneading with a three-roll mill after that is made into (eta) 2 at the shear rate of 4 sec <^-1> measured with the viscoelasticity measuring device as (eta) 2, the ratio calculated by (eta2 / eta1) is 0.5-1.5, It is characterized by the above-mentioned. Silver powder to be. In the manufacturing method of the silver powder which mixes the silver complex containing solution and the reducing agent solution obtained by melt | dissolving with silver chloride and a complexing agent, and reducing a silver complex,
To both or either of the silver complex-containing solution and the reducing agent solution, 0.1 to 15% by mass of a water-soluble polymer is added to silver, and the surface treatment is performed with a surfactant or a surfactant and a dispersant before reduction after reduction. The manufacturing method of silver powder characterized by the above-mentioned. The silver powder according to claim 6, wherein the surface treatment is performed in a state in which water-soluble polymers capable of inhibiting aggregation of at least silver particles remain on the surface of silver particles before or after one time of cleaning. Manufacturing method. 8. The method for producing silver powder according to claim 7, wherein the washing is performed using an aqueous 0.01 to 1.00 mol / l sodium hydroxide solution. The method for producing silver powder according to any one of claims 6 to 8, wherein the water-soluble polymer is at least one selected from polyethylene glycol, polyvinyl alcohol, polyethylene oxide, and polyvinylpyrrolidone. The method for producing silver powder according to any one of claims 6 to 9, wherein the water-soluble polymer is added to the reducing agent solution in advance. The method for producing silver powder according to any one of claims 6 to 10, wherein the reducing agent solution is a solution containing at least one selected from ascorbic acid, hydrazine and formalin.

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