KR20140024830A - Silver powder and method for producing same - Google Patents

Abstract

Provided are silver powder having a suitable viscosity range at the time of paste production, easy kneading and suppressing the occurrence of flakes, and a method for producing the paste.
The present invention relates to a paste in which at least silver powder, terpineol and resin are kneaded with a centrifugal force of 420 G using a magnetostatic stirrer, wherein the particle size distribution on a volume basis is in a region of 0.3 µm to 14.0 µm, and has a peak or shoulder P _1. and, in relation to the shoulder or peak P _2, P ₁ > P ₂ , P ₁ is in the range of 2.0 μm to 5.0 μm, and P ₂ is in the range of 0.5 μm to 3.0 μm.

Description

TECHNICAL FIELD [0001] The present invention relates to a silver powder,

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 of an electronic device, an electrode, etc., and its manufacturing method.

This application claims priority based on Japanese Patent Application No. 2011-137622 for which it applied on June 21, 2011 in Japan, and is incorporated in this application by referring to these applications.

Silver pastes, such as resin type silver paste and baked type silver paste, are used abundantly in formation of a wiring layer, an electrode, etc. in an electronic device. That is, after apply | coating or printing these silver pastes on various base materials, the electrically conductive film used as a wiring layer, an electrode, etc. can be formed by heat-hardening or heat baking.

For example, the resin-type silver paste is made of silver powder, resin, a curing agent, a solvent, or the like, printed on a conductor circuit pattern or a terminal, and cured by heating at 100 ° C to 200 ° C to form a wiring film or an electrode. . Moreover, the baking type silver paste consists of silver powder, glass, a solvent, etc., and it prints on a conductor circuit pattern or a terminal, heat-fires at 600 degreeC-800 degreeC, and forms wiring and an electrode as a conductive film. In the wirings and electrodes formed of these silver pastes, current paths electrically connected by silver powder are formed.

The silver powder used for silver paste has a particle diameter of 0.1 micrometer to several micrometers, and differs in the particle size of silver powder used according to the thickness of the wiring formed, the thickness of an electrode, etc. In addition, by uniformly dispersing the silver powder in the paste, wirings of uniform thickness or electrodes of uniform thickness can be formed.

When producing silver paste, generally, silver powder is first preliminarily knead | mixed and mixed with other structural components, such as a solvent, and is produced by kneading, then applying a predetermined pressure with a 3-roll mill etc. after that. According to this method, since a large amount of silver paste can be produced at one time, the productivity is high and the effect of reducing the manufacturing cost can be expected. On the other hand, about silver powder, what can be knead | mixed efficiently by a roll, ie, having favorable kneading property is calculated | required.

Even if the viscosity of the paste is too high or too low, efficient kneading with a three-roll mill becomes difficult. As silver powder with low viscosity, the shear stress to a three roll mill becomes small, and the shear force applied to silver paste becomes small, and dispersion of silver powder in a paste becomes inadequate. On the other hand, with silver powder with high viscosity, it becomes difficult to knead | mix and mix with other structural components, such as a solvent, and the paste which is insufficient in kneading with other structural components, such as silver powder and a solvent, is thrown into a three roll mill.

In the case where the dispersion of silver powder in the paste is insufficient, or when the kneading of silver powder and other constituents such as a solvent is insufficient and the paste viscosity decreases, agglomerates of silver particles exist in the paste. When the paste is kneaded with a three-roll mill, coarse powders such as flake powder (flakes) on the order of several millimeters are generated by breaking up agglomerates of aggregated silver particles. 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 using the paste, coarse flakes are blocked on the fine screen, making it difficult to accurately print the pattern.

In this manner, flakes generated during paste production greatly affect the printability at the time of screen printing. Therefore, silver powder is required to have a viscosity which can be easily kneaded at the time of paste preparation, the dispersibility of silver powder in a solvent is good, and coarse powder, such as a flake, does not generate | occur | produce.

In order to realize the ease of paste preparation, proposals for controlling the particle size distribution and the form of silver powder have been made. For example, Patent Literature 1 discloses a conductive adhesive obtained by mixing 30 to 98% by weight of silver powder in a conductive adhesive with a resin for a binder, and has a tap density of 1.5 g / cm 3 made of silver powder having primary particles as flat powder. The conductive adhesive which contains 30 weight% or more of silver powder which has the following mass aggregate structure in a conductive adhesive is proposed.

According to this proposal, since the silver powder having agglomerated structure can be easily deagglomerated into primary particles, it is highly dispersible and can exhibit stable electrical conductivity without causing deterioration of conductivity resulting from poor dispersion of silver powder. It is said that the conductive adhesive which gives not only electroconductivity but hardened | cured material excellent in adhesiveness, heat resistance, moisture resistance, workability, heat conductivity, etc. is obtained.

However, in this proposal, generation of coarse flakes due to the change in viscosity of the paste and the reaggregation of silver particles dispersed in the paste is not considered, and it is difficult to say that the dispersibility in the finally obtained paste is secured.

In addition, Patent Literature 2 adds a nonionic surfactant having a HLB value of 6 to 17 to a solution containing a silver complex, and when a reducing agent is added thereto, in order to prevent aggregation of the reduced silver particles, A method for producing silver powder, which obtains silver powder excellent in dispersibility with a tap density of 2.5 g / cm 3 or more, an average particle diameter of 1 to 6 µm, and a specific surface area of 5 m 2 / g or less by rapidly adding the addition rate to 1 equivalent / minute or more, is proposed. It is.

However, this proposal prevents aggregation of the silver powder obtained and obtains the dispersed silver powder. The dispersibility and flake generation in the solvent at the time of paste preparation are not considered at all.

In addition, in patent document 3, electroconductive particle which has an average particle diameter of 0.5-20 micrometers, specific surface area 0.07-1.7 m <2> / g, and has at least 2 or more peaks of a particle size distribution, or electroconductive particle of at least 2 or more different particle size distribution The electrically conductive paste characterized by consisting of the electroconductive particle formed by mixing and the binder which has a thermosetting resin as a main component is proposed. According to this proposal, a good fluidity and dispersibility conductive paste is obtained, the filling of the via and the contact between the conductive particles inside the via hole are stable, and a high quality via hole conductor can be formed with little variation and stability. Doing.

However, this proposal is aimed at the filling of the paste into buyers and high connection reliability, and no consideration has been given to the dispersibility of the silver powder itself in the solvent during the paste preparation and the occurrence of flakes.

As mentioned above, although the dispersibility of silver powder in a paste, and the improvement of the electroconductivity and reliability of the electrode and wiring formed using the paste are proposed, it is not proposed about suppression of the flake generation at the time of paste manufacture.

[Patent Literature]

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

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

Patent Document 3: Japanese Patent Application Laid-Open No. 2004-265607

An object of the present invention is to provide a silver powder having a suitable viscosity range at the time of paste production, easy kneading and suppressing the occurrence of flakes, and a method for producing the same, in view of the above conventional circumstances.

MEANS TO SOLVE THE PROBLEM As a result of repeated examination in order to achieve the objective mentioned above, it has a suitable viscosity range by setting it as the silver powder which has the aggregate of silver particle, and has the particle size distribution which has two or more peaks or a peak and a shoulder, and at the time of paste manufacture, It has been found that the kneading is easy, the viscosity change can be suppressed, and the kneading property can be improved, and the present invention has been reached.

That is, the silver powder which concerns on this invention is the paste which knead | mixed at least silver powder, terpineol, and resin by the centrifugal force of 420G using the self-rotating stirrer, The particle size distribution on a volume basis exists in the range of 0.3 micrometer-14.0 micrometers, a peak or shoulder P ₁ and a peak or shoulder in relation P _2, P ₁ > P ₂ , P ₁ is in the range of 2.0 μm to 5.0 μm, and P ₂ is in the range of 0.5 μm to 3.0 μm.

Moreover, the manufacturing method of the silver powder which concerns on this invention reduces the solution containing the silver complex which melt | dissolved a silver compound with the reducing agent solution, obtains the slurry of silver particle, and produces silver powder through each process of washing and drying. As a method, 1.0-15.0 mass% of water-soluble polymers are put into the reducing agent solution, and reduced, and the silver particles after drying are subjected to pulverization treatment at a circumferential speed of 5 to 40 m / sec using an electric stirrer. It is done.

According to the silver powder according to the present invention, it is possible to control the aggregation state of the silver particles, have a suitable viscosity range at the time of paste production, the viscosity change is suppressed, kneading is easy, and the occurrence of flakes is suppressed, Can improve sex.

According to the silver powder according to the present invention, not only the dispersibility in the paste is excellent, but also the wiring layer and the electrode formed by the resin type silver paste or the calcined silver paste using the same have excellent uniformity and conductivity, Industrial value is very large for silver paste used for formation of a wiring layer, an electrode, etc.

1 is a diagram schematically illustrating a silver particle form.
FIG. 2 is a diagram showing a particle size distribution of cumulative volume of silver powder in Example 1. FIG.
3 is a diagram showing a particle size distribution of cumulative volume of silver powder in the evaluation paste in Example 1. FIG.
4 is a diagram showing a particle size distribution of cumulative volume of silver powder in Example 2. FIG.
FIG. 5 is a diagram showing a particle size distribution of cumulative volume of silver powder in the evaluation paste in Example 2. FIG.
FIG. 6 is a diagram showing a particle size distribution of cumulative volume of silver powder in Example 3. FIG.
FIG. 7 is a diagram showing a particle size distribution of the cumulative volume of silver powder in the evaluation paste in Example 3. FIG.
FIG. 8 is a diagram illustrating a particle size distribution of cumulative volume of silver powder in Comparative Example 1. FIG.
9 is a diagram showing a particle size distribution of cumulative volume of silver powder in the evaluation paste in Comparative Example 1. FIG.
FIG. 10 is a diagram showing a particle size distribution of cumulative volume of silver powder in Comparative Example 2. FIG.

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. In addition, primary particles, secondary particles, and aggregates may be collectively called silver particles.

The silver powder which concerns on this embodiment is an evaluation test, In the paste which knead | mixed at least this silver powder, terpineol, and resin by the centrifugal force of 420G using the self-rotating stirrer, the particle size distribution of a volume reference is 0.3 micrometer-14.0 micrometers. in the range of, in relation to the shoulder or peak P ₁ and P ₂ peak or shoulder diameter, P ₁ > P ₂ , P ₁ is in the range of 2.0 μm to 5.0 μm, and P ₂ is in the range of 0.5 μm to 3.0 μm.

MEANS TO SOLVE THE PROBLEM This inventor acquired the knowledge that it is important for silver powder to have specific particle size distribution at least in the initial stage of paste manufacture, in order to have a suitable viscosity for silver powder paste, and to have favorable kneading property. That is, as a state of silver powder in a paste at the beginning of paste manufacture, the silver powder comprised from the secondary particle in which the primary particle and the primary particle were connected in multiple numbers, and the aggregate which aggregated these (henceforth an aggregate) is silver silver and The organic solvent in the paste is in a difficult state to separate, and the formation of coarse aggregates aggregated excessively in the paste is suppressed, the viscosity of the paste is easily adjusted, and the kneading property is improved.

Conventionally, in the production of silver paste, silver powder having individual primary particles dispersed as much as possible and having an average particle diameter of 0.1 µm to 1.5 µm has been used, but in the case of fine silver particles having such primary particles dispersed therein, paste It is easy to aggregate and form a coarse mass at the time of manufacture. In such agglomerated masses, since the primary particles have more contacts with other particles and the voids decrease, the solvent component of the paste hardly penetrates between the primary particles, and the amount of free solvent flowing freely in the paste increases. In this case, since the viscosity of the paste is lowered, for example, when kneading is performed by a three-roll mill generally used in the manufacture of paste, the shear force is small and the kneading is insufficient. As a result, it was found that the aggregated mass remained in the roll without breaking, and as a result, coarse powder of mm order such as flakes was formed.

On the other hand, in the case of silver powder having a large particle size distribution composed mostly of aggregates coarsely aggregated with primary particles or secondary particles, the solvent component of the paste penetrates into the pores between the aggregates during paste production, and the paste is freely released. The amount of free solvent that flows decreases. In this case, since the viscosity of the paste is increased, it becomes difficult to knead and mix other components such as silver powder and a solvent. At this time, for example, when kneading is carried out by a three-roll mill generally used in the manufacture of paste, the aggregated mass in the paste enters the roll as it is, and as a result, coarse powder of mm order such as flakes is formed. there was.

On the other hand, in the case of the silver powder in which the above-mentioned aggregate, the primary particles and the secondary particles are mixed, the solvent component which freely flows in the paste at the time of paste production becomes appropriate and has an appropriate viscosity range, It was confirmed that kneading with other constituents, such as silver powder and a solvent, and kneading by a three-roll mill became easy and coarse flakes did not generate | occur | produce.

The agglomerates described above have a grape cluster shape, for example, and have a size of about 5 to 10 m. The silver powder in which the particles containing such aggregates are mixed is used in a general paste production method in which the initial stage of paste production, that is, the silver powder and the solvent component are mixed, for example, preliminary kneading by kneader or the like and main kneading by 3-roll mill or the like. In the preliminary kneading step, the fine primary particles do not agglomerate, and a solvent component is returned between the particles constituting the silver powder to have a suitable viscosity (hereinafter, referred to as a kneaded material in order to distinguish it from the finally obtained paste). I may do it). When the kneaded material is kneaded by the present kneading, sufficient shear force can be applied between the silver particles, and the silver particles can be dispersed in the paste without agglomerating the silver particles. In addition, since the silver particles sufficiently dispersed rarely reaggregate, it becomes possible to suppress the generation of flakes due to coarse aggregated mass.

Conventionally, even silver powder in which primary particles are dispersed or silver powder composed mostly of agglomerates can be kneaded to adjust the kneaded product to an appropriate viscosity and finally to a paste, but if the viscosity is adjusted in the kneaded product, Since the subsequent viscosity change is large, it becomes difficult to adjust the viscosity in the final paste to an appropriate value.

Even if the viscosity of the paste is too high or too low, good printability of the paste is not obtained, but the silver powder in which the aggregate and the primary particles and the secondary particles are mixed, that is, the particle size having two or more peaks or peaks and shoulders as described above. It can adjust to an appropriate viscosity by being silver powder which has a distribution. And by using such silver powder, the paste which has the outstanding printability can be obtained.

Although the particle size distribution of the silver powder mentioned above is in the paste produced as an evaluation test, in order to make the kneading property of silver powder more suitable, the particle size distribution degree in the state of silver powder before paste preparation, and in the paste after kneading mentioned above It is preferable to have the same form as that of the particle size distribution.

For the silver powder according to the present embodiment, the paste prepared as the evaluation test has, for example, a weight ratio of epoxy resin (viscosity 2 to 6 Pa · s, for example, Mitsubishi Chemical Co., Ltd. JER819) and terpineol. The vehicle and silver powder which are: 7 can be prepared by mixing 8.0 mass% of vehicles and 92.0 mass% of silver powder with respect to a paste, and knead | mixing by the centrifugal force of 420G using a magnetoelectric stirrer.

As described above, the silver powder in the paste has a particle size distribution on a volume basis of 0.3 µm to 14.0 µm. Here, the particle size distribution on a volume basis can be obtained by, for example, measuring using a laser diffraction scattering method or the like. The range of the particle size distribution based on the volume means that 95% or more of silver particles are included in the particle size range by volume accumulation, but it is preferable that all silver particles are included in the range.

In the above-mentioned particle size range, when the volume accumulation is less than 95% and the volume-based particle size distribution is present in an area of less than 0.3 µm, fine particles are present in the silver powder, and the dispersibility of silver particles in the paste It falls and it becomes a nonuniform paste. On the other hand, when a particle size distribution exists even in the area | region exceeding 14.0 micrometers, coarse particle exists in silver powder, and when a fine wiring or an electrode is formed, a conductive film will become nonuniform.

In addition, the paste of silver powder is characterized in that: in the relationship between the particle size of the P ₁ and P _2, P ₁ > P ₂ , P ₁ is in the range of 2.0 μm to 5.0 μm, and P ₂ is in the range of 0.5 μm to 3.0 μm.

In the above-described particle size distribution, the peak or shoulder P ₁ (hereinafter sometimes referred to simply as P ₁ ) is a secondary particle formed by connecting primary particles and a plurality of primary particles connected to the secondary particles. derived from the aggregates formed, and, on the other hand (which is hereinafter simply described to be P _2, d) the peak or shoulder P ₂ is thought to be derived from the primary particles or secondary particles. P ₁ And in the particle size range where P ₂ exists, when a plurality of peaks or shoulders appear, the highest peaks may be P ₁ and P ₂ , respectively. In addition, P ₁ Or when P ₂ is appearing as a shoulder, P ₁ or P ₂ The position where the increase rate of the derivative value of the change rate of the appearance frequency which shows particle size distribution in the vicinity is the lowest is P ₁ Or P ₂ . In addition, P _1, P ₂ is, may for example, by using the peak separation software, Origin 8.5 ((state) Light stone, Ltd.) to be specific by isolating the peak.

When P ₁ exists in the range of less than 2.0 micrometers, since formation of the aggregate mentioned above is not enough, the space | gap between silver particles becomes small, the amount of free solvent components in a kneaded material increases, and since the viscosity of a kneaded material becomes low, a paste At the time of kneading at the time of manufacture, the shear force is small and kneading is insufficient. For this reason, it re-aggregates in a paste, and coarse aggregated mass arises, and it becomes easy to produce a flake. On the other hand, when P ₁ exists in the range exceeding 5.0 micrometers, since the above-mentioned aggregate becomes coarse and the solvent component which penetrates into the space | gap of an aggregate increases, the amount of the solvent component which flows freely in a paste decreases, Since the viscosity becomes high, it becomes difficult to form a paste.

In addition, P is a _divalent flakes occurs while the blossomed paste prepared from the coarse agglomerates, the increase in the fine primary particles, if present in the range of less than 0.5 ㎛, and kneaded. On the other hand, when P ₂ exists in the range exceeding the range of 3.0 micrometers, the whole particle diameter of silver powder becomes large, and when a fine wiring or an electrode is formed, a conductive film will become nonuniform.

In the particle size distribution of silver powder in this paste, the relationship between the height (appearance frequency) of P ₁ and P ₂ is not particularly limited, but P ₂ preferably has a height of 25% or more of P ₁ . When P ₂ is less than 25% of P ₁ , many of the aggregates described above are increased, and the solvent component that penetrates into the pores of the aggregates increases, which makes it difficult to paste. In addition, P ₂ is preferably 150% or less of P ₁ . If P ₂ is greater than 150% of P _1, and the fine particles are present much in the silver powder, paste in the paste is something that a non-uniform dispersion of the particles is reduced. In addition, flakes also tend to occur. Therefore, when the relationship between the heights of P ₂ and P ₁ is in the above-described range, the silver powder has excellent kneading property, and the obtained paste can also have good printability. Can be formed.

As described above, the silver powder according to the present embodiment is derived from primary particles and aggregates in a paste obtained by kneading at least silver powder, terpineol, and resin with a centrifugal force of 420 G using a self-rotating stirrer. It has a particle size distribution with two or more peaks or peaks and shoulders. According to the silver powder having such a particle size distribution, the formation of coarse aggregates aggregated excessively in the paste is suppressed, the viscosity of the paste can be easily adjusted, the occurrence of flakes during paste production is suppressed, and a paste having excellent printability can be obtained. It can manufacture.

Moreover, according to the silver powder which concerns on this embodiment, not only the dispersibility in a paste is excellent but the wiring layer and the electrode formed by the resin type silver paste and the baking type silver paste using this are excellent in uniformity and electroconductivity.

Here, the silver powder in the paste mentioned above has a particle size D ₅₀ of 2.0 µm to 5.0 µm at the point where the cumulative curve is 50% when the total volume is 100% and the cumulative curve is obtained. It is preferable that the standard deviation SD of the particle size distribution on the volume basis expressed by is 0.8 m to 3.0 m. In addition, the particle size and D ₅₀ is 2.0 ㎛~3.5 ㎛, it is more preferable that the standard deviation SD is 1.0 ㎛~2.0 ㎛.

SD = (D ₈₄ -D ₁₆ ) / 2 (1)

In formula (1), D ₈₄ represents the particle diameter of the point at which the volume accumulation curve is 84%, and D ₁₆ represents the particle diameter at the point at which the volume accumulation curve is 16%.

As described above, the silver powder according to the present embodiment preferably has two or more peaks or peaks and shoulders, and has a broad particle size distribution. This particle size D ₅₀ And the standard deviation SD are absolute values of the degree of broadness of the particle size distribution.

When the particle size D ₅₀ is less than 2.0 µm, a sufficient amount of aggregates are not formed, and the paste viscosity is lowered, so that the shear force at the time of kneading becomes small, and it is easy to reaggregate in the paste to produce coarse aggregated masses, thereby generating flakes. It may not be fully suppressed. On the one hand, when the D ₅₀ exceeds 5.0 ㎛ include, but might be present in a large amount becomes coarse aggregates, and becomes less the amount of free solvent, the paste is difficult. In addition, coarse silver particles remain after the paste formation, and the conductive film may become uneven when fine wiring or electrodes are formed.

Moreover, when standard deviation SD is less than 0.8 micrometer, formation of aggregate is not enough and it becomes easy to reaggregate in a paste and produce coarse aggregated mass. On the other hand, if the standard deviation SD exceeds 3.0 µm, the fine primary particles and coarse aggregates are relatively large, and the amount of free solvent decreases, which makes it difficult to paste and to form a conductive film when a fine wiring or electrode is formed. It may become uneven.

Moreover, when this broad particle size distribution is seen from the relationship with a particle size, it is preferable that the silver powder in the paste mentioned above is 40-70 with the variation coefficient CV of the particle size distribution of the volume reference represented by following formula (2). .

CV = (SD / D ₅₀ ) × 100 (2)

This variation coefficient CV shows the degree of broad with respect to a particle diameter. When the variation coefficient CV is less than 40, formation of aggregates is not enough and it becomes easy to reaggregate in a paste and produce coarse aggregate. On the other hand, when the coefficient of variation CV exceeds 70, fine silver particles and coarse aggregates become relatively large, and the amount of free solvent decreases, which makes it difficult to paste and to form non-uniform conductive films when fine wirings or electrodes are formed. There is a thing.

In addition, it is preferable that the silver powder which concerns on this embodiment has the following relationship, when seen from the relationship of particle content in a predetermined particle diameter range. That is, it is preferable that the silver powder in the paste mentioned above contains 40 to 80% of particles in the particle size range of 1.5 µm to 5.0 µm of the particle size distribution on a volume basis.

As described above, in two or more peaks or peaks and shoulders, P ₁ is derived from a secondary particle formed by connecting primary particles and an aggregate formed by connecting a plurality of primary particles to the secondary particle again, and P ₁ exists in the range of 2.0 micrometers-5.0 micrometers. Therefore, the particle content present in the particle size range 1.5 µm to 5.0 µm, that is, exhibits the formation rate of aggregates of appropriate size.

When the particle content is less than 40%, the formation of aggregates is not sufficient. On the other hand, when the particle content exceeds 80%, it indicates that coarse aggregates are excessively present, and when the kneading is carried out by a three-roll mill, flakes in which the aggregates are crushed are easily generated.

As described above, the silver powder according to the present embodiment has a particle size distribution based on the volume of silver powder in the kneaded product obtained by kneading at least silver powder, terpineol and resin with a centrifugal force of 420 G using a self-rotating stirrer. in the range of 0.3 ㎛~14.0 ㎛, in relation to the shoulder or peak P ₁ and P ₂ peak or shoulder diameter, P ₁ > P ₂ , P ₁ is in the range of 2.0 μm to 5.0 μm, and P ₂ is in the range of 0.5 μm to 3.0 μm. According to the silver powder which has such a particle size distribution, when silver paste is manufactured using this silver powder, silver powder and the organic solvent in a paste will become difficult to separate, and generation | occurrence | production of the coarse aggregate which aggregated excessively in the paste is suppressed. The occurrence of flakes is suppressed. Moreover, the viscosity change during paste manufacture is small, and the viscosity adjustment of a paste becomes easy.

Although the silver powder which concerns on this embodiment is not limited to the silver paste for evaluation test mentioned above, and is applicable to all the silver pastes generally used, Specifically, electroconductive silver paste using the silver powder which concerns on this embodiment In the case of producing a, the viscosity of the paste at a shear rate of 4.0 (1 / sec) measured by, for example, a corn plate viscometer or the like can be 50 to 150 Pa · s. Moreover, the shear rate can be 20-50 Pa.s in the viscosity in 20.0 (1 / sec).

In the silver powder in which the viscosity of the paste is lower than the above-mentioned ranges, bleeding, sagging, etc. may occur in wirings formed by printing of the paste, and the shape thereof may not be maintained. On the other hand, in silver powder whose viscosity of a paste becomes higher than the range mentioned above, printing of a paste may become difficult.

In addition, in the silver powder which concerns on this embodiment which has the outstanding paste characteristic as mentioned above, it can be said that formation of coarse aggregated mass by excessive aggregation can be effectively suppressed also in the silver paste generally used. In other words, flakes in which the aggregates are crushed are produced from silver powder in which the excessive aggregates occur in the paste and the coarse aggregates are formed. In addition, in the silver powder in which the aggregate is excessive, the viscosity at the time of paste manufacture becomes too large, kneading | mixing etc. become difficult and a problem arises in paste manufacture. In addition, the manufactured paste also has poor paste characteristics such as printability. Since the silver powder which concerns on this embodiment can manufacture the paste which has the above-mentioned suitable viscosity, it can suppress suppression of excessive aggregation and can effectively suppress generation | occurrence | production of the problem by which coarse aggregated mass is formed.

Moreover, in producing a silver paste using the silver powder which concerns on this embodiment which has the above-mentioned characteristic, it does not specifically limit about a paste forming method, A well-known method can be used. For example, as the vehicle to be used, those obtained by dissolving various celluloses, phenol resins, acrylic resins, and the like in solvents such as alcohols, ethers, and esters can be used.

Next, the manufacturing method of silver powder which has the above-mentioned characteristic is demonstrated.

The manufacturing method of the silver powder which concerns on this embodiment uses silver chloride, silver nitrate, etc. as a starting raw material, and basically contains the solution and reducing agent solution containing the silver complex obtained by melt | dissolving starting raw materials, such as silver chloride, with a complexing agent. The mixture was mixed with the silver complex to reduce the silver particles to precipitate the silver particles to obtain a silver particle slurry, and silver powder was obtained by going through each step of washing, drying and crushing.

And in the manufacturing method of the silver powder which concerns on this embodiment, with respect to the reducing agent solution which reduces a silver complex, 1.0-15.0 mass% with respect to silver, More preferably, it is 1.0-10.0 mass%, Especially preferably, it is 3.0 mass More than 10.0 mass% of water-soluble polymer is added.

In addition, in the manufacturing method of the silver powder which concerns on this embodiment, after reducing a silver complex with the above-mentioned reducing agent solution, and obtaining a silver particle slurry, when performing each process of washing, drying, and pulverization, after vacuum drying, vacuum pressure reduction is carried out. Disintegrate while stirring gently using an atmosphere electric stirrer or the like.

Thus, 1.0-15.0 mass% with respect to silver, More preferably, 1.0-10.0 mass%, Especially preferably, more than 3.0 mass% 10.0 mass% of water-soluble polymers are added to a reducing agent solution, and a silver complex is reduced, After drying of the obtained silver particle slurry, it disintegrates with mild stirring, and can control the aggregation state of silver particle, and 2 originates from the aggregate which the primary particle and the primary particle aggregated in the paste at the time of paste manufacture. Silver powder having a particle size distribution having more than one peak or peak and shoulder can be produced.

Hereinafter, the manufacturing method of this silver powder is demonstrated more concretely for every process, taking the case where silver chloride is used as a starting material as an example as a preferable aspect. In the case where silver chloride is used as a starting material, silver powder can be obtained by the same method. However, when silver nitrate is used, a recovery device for nitrous acid gas and a treatment device for nitrogen nitrate in wastewater are required.

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, it is preferable to use silver chloride which is high purity.

As a dissolution method of 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 complex concentration and increase productivity, it is preferable to add silver chloride in 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. Since hydrazine or formalin has stronger reducing power than ascorbic acid, crystals in silver particles can be made 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 the silver powder which concerns on this embodiment, it is 1.0-15.0 mass% with respect to silver, More preferably, it is 1.0-10.0 mass% with respect to silver, Especially preferably, it is more than 3.0 mass% 10.0. Up to mass% water-soluble polymer is added.

As described above, in the production of silver powder according to the present embodiment, the water-soluble polymer is selected as the aggregation inhibitor and the amount of addition thereof becomes 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 a coagulation inhibitor having a high anticoagulation effect, such as a surfactant or a fatty acid, is used, secondary particles or aggregates are not sufficiently formed, the primary particles are increased, and appropriate aggregates are 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, and thus silver powder containing coarse aggregated aggregates that are excessively aggregated. Since the water-soluble polymer has an appropriate aggregation preventing effect, it is possible to easily control the formation of secondary particles or aggregates by adjusting the amount of addition, and to form aggregates of appropriate size in the silver-containing solution after addition of the reducing agent solution. have.

Although it does not specifically limit as a water-soluble polymer to add, It is preferable that it is at least 1 sort (s), such as polyethyleneglycol, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, gelatin, and the like of polyethyleneglycol, polyvinyl alcohol, polyvinylpyrrolidone It is more preferable that it is at least 1 sort. According to these water-soluble polymers, in particular, excessive aggregation is prevented and silver nuclei (primary particles) are prevented from becoming fine due to insufficient aggregation of the grown nuclei, 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. That is, by adding a water-soluble polymer, the water-soluble polymer adsorbs on the surface of 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 will be present as a single body, but by adding the water-soluble polymer at a predetermined ratio with respect to the silver, a surface free from some water-soluble polymer remains. It is thought that silver particles are connected through the surface and form aggregates.

From this, about the addition amount of a water-soluble polymer, it adds in the ratio of 1.0-15.0 mass% with respect to silver. When the amount of the water-soluble polymer added is less than 1.0% by mass with respect to silver, the dispersibility in the silver particle slurry is poor, and the silver powder is excessively aggregated to generate many coarse aggregates. On the other hand, when the addition amount to silver is more than 15.0 mass%, almost all silver particle surfaces are covered with a water-soluble polymer, and silver particles cannot connect and aggregates cannot be formed. As a result, it becomes the silver powder which consists of primary particles, and also in this case, a flake is produced at the time of paste manufacture.

Therefore, by adding 1.0-15.0 mass% of water-soluble polymer with respect to silver in this way, silver particles can be suitably connected through the surface where a water-soluble polymer does not exist, and can form a structurally stable aggregate, and at the time of paste manufacture, The dispersibility of can be improved, and the occurrence of flakes can be effectively suppressed. Moreover, it is more preferable to add a water-soluble polymer in the ratio of 1.0-10.0 mass% with respect to silver. By setting the addition amount to 1.0 to 10.0% by mass or less, the water-soluble polymer can be adsorbed on the surface of the silver particles more appropriately, the silver particles can be linked to a predetermined size to form a highly stable aggregate, and the formation of flakes more effectively. Can be suppressed.

In addition, this water-soluble polymer is added to a reducing agent solution. By adding the water-soluble polymer to the reducing agent solution, the water-soluble polymer exists in the place of nucleation or nuclear growth, and the water-soluble polymer is rapidly adsorbed on the surface of the generated nucleus or silver particles to efficiently control the aggregation of the silver particles. Can be. Therefore, by adjusting the concentration of the water-soluble polymer described above and adding the water-soluble polymer to the reducing agent solution in advance, formation of coarse aggregates due to excessive aggregation of silver particles is suppressed, and silver particles are more appropriately selected. It can be connected to the size of to form a highly stable aggregate.

In addition, the water-soluble polymer may be added part or all of the added amount to the solution containing the silver complex, but in this case, it is difficult to supply the water-soluble polymer to the place of nucleation or nucleus growth. There is a possibility that it cannot be adsorbed. 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% with respect to silver. Therefore, when it is possible to add the water-soluble polymer to either the solution of the reducing agent solution or the silver complex-containing solution, it is particularly preferable to set it as an amount of more than 3.0% by mass and 10.0% by mass or less with respect to silver.

Moreover, since adding a water-soluble polymer may foam at the time of a reduction reaction, an antifoamer can also be added to a silver complex containing solution or a reducing agent mixed liquid. 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-containing 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 order to obtain primary particles having a uniform particle size, it is preferable to use a tube reactor method in which particle growth time can be easily controlled. In addition, the particle size of silver particle can be controlled by the mixing rate of a silver complex containing solution and a reducing agent solution, or the reduction rate of silver complex, and can be easily controlled to a target particle size.

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 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. Moreover, the water used for a washing | cleaning liquid is preferable the water which does not contain the impurity element harmful to silver particle, and especially pure water is preferable.

In the production of silver powder according to the present embodiment, before the aggregate formed by reduction in the silver complex-containing solution aggregates again 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. It is more preferable to prevent excessive aggregation. 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 formation of coarse aggregated mass can be effectively suppressed.

Excessive aggregation proceeds in particular by drying, so that the surface treatment can be obtained 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, before a washing process, or after a washing process once. 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 present embodiment, the water-soluble polymer is added to the reducing agent solution at a predetermined ratio to silver to reduce the silver, and the water-soluble polymer is suitably adsorbed on the surface of the silver particles to connect the silver particles to a predetermined size. Aggregates are formed. However, since the water-soluble polymer adsorbed on the surface of the silver particles is relatively easily washed by the washing treatment, when the washing step is performed prior to the surface treatment, the water-soluble polymer on the surface of the silver particles is washed away and the silver particles are separated. Excessive agglomeration may start with each other, and coarse aggregated mass larger than the formed aggregate may be formed. Moreover, when coarse aggregated mass is formed in this way, uniform surface treatment to the silver particle surface becomes difficult.

Therefore, from this, after the reduction process and before the washing process or after one washing process, excessive aggregation of the silver particles due to the removal of the water-soluble polymer can be suppressed and the silver particles containing the desired aggregates formed can be efficiently removed. Can be surface-treated, and there is no coarse aggregate, and silver powder with good dispersibility can be manufactured. Moreover, it is preferable to perform the surface treatment after a reduction process and before a washing | cleaning process, after solid-liquid separation of the slurry containing silver particle by the filter press etc. after completion | finish of a reduction process. In this way, the surface treatment agent or the dispersant, which is a surface treatment agent, can be directly acted on the silver particles containing the aggregates of the predetermined size generated by performing the surface treatment after the solid-liquid separation. The formation of aggregated aggregates can be suppressed more 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, a strong surface treatment layer can be formed on the surface of the silver particles by the interaction thereof, so that the effect of preventing excessive aggregation is high and the desired aggregate is maintained. Valid. 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 cleaning liquid to which the surfactant has been added and stirred, and then add the dispersant and stir again.

Moreover, as another aspect, you may add surfactant to a reducing agent solution, and may add a dispersing agent to the slurry of the silver particle obtained by mixing a silver complex containing solution and a reducing agent solution, and stirring. A surfactant exists in the place of nucleation or nucleation, and a surfactant can be quickly adsorbed on the surface of the nucleus or silver particle which was produced, and a dispersant can be adsorbed again, and a stable and uniform surface treatment can be performed.

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, butyl group, 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, a protective colloid such as a fatty acid, an organometallic or gelatin can be used. However, in consideration of the possibility of impurity incorporation and in view of adsorption with a surfactant, it is preferable to use a fatty acid or a salt 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 addition amount of a dispersing agent has the preferable range of 0.01-3.00 mass% 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.

And the manufacturing method of the silver powder which concerns on this embodiment controls the aggregation of silver particle by a reduction process, Preferably, it controls by crushing conditions with mild crushing conditions with respect to the silver powder after drying which stabilized the aggregation degree by surface treatment. The process is performed. Although the silver powder after surface treatment mentioned above is aggregated again between aggregates by subsequent drying etc., since the binding force is weak, even the aggregate of predetermined size at the time of paste preparation is easily isolate | separated. However, in order to stabilize a paste, it is preferable to disintegrate and to classify.

In the disintegration method, specifically, as the disintegration conditions, the silver particles after drying are disintegrated while stirring at, for example, a circumferential speed of 5 to 40 m / s of the stirring blade by using a device having a weak disintegration force such as a vacuum reduced pressure atmosphere electric stirrer. Thus, by weakly pulverizing the silver powder after drying, it is possible to prevent the aggregates of the predetermined size formed by connecting the silver particles from being crushed, and the two originating from the aggregates in which a plurality of primary particles and primary particles are connected in the paste. Silver powder having a particle size distribution having two peaks or shoulders can be produced. When the circumferential speed is 5 m / s or less, the aggregate energy remains because of the weak disintegration energy, while on the other hand, when the circumferential speed is larger than 40 m / s, the disintegration energy is increased and the aggregate is too small, and in either case, Silver powder having a particle size distribution is not obtained.

After the above-mentioned disintegration treatment, silver fraction having a desired particle size can be obtained by performing a classification treatment. As a classification apparatus used at the time of classification processing, it is not specifically limited, An airflow classifier, a sieve, etc. 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.) maintained at a liquid temperature of 36 ° C. in a 38 ° C. hot bath were added with stirring to prepare a silver solution. Antifoaming agent (made by Adeka Co., Ltd., Adecanol LG-126) was diluted 100-fold by volume ratio, 24.4 ml of this antifoamer diluent was added to the said silver complex solution, and the obtained silver complex solution was kept at 36 degreeC in the warm bath. .

On the other hand, 1068 g of ascorbic acid (56.9 mass% relative to Kanto Chemical Co., Ltd., reagents and silver particles) of the reducing agent was dissolved in 13.56 L of pure water at 36 ° C to obtain a reducing agent solution. Next, 159.5 g of polyvinyl alcohol (8.5 mass% based on Kuraray Co., Ltd., PVA205, silver) of the water-soluble polymer was aliquoted, and a solution dissolved in 1 L of pure water at 36 ° C was mixed with a reducing agent solution.

The produced silver complex solution and reducing agent solution were sent to a gutter at 2.7 L / min of a silver complex solution and 0.9 L / min of a reducing agent solution using the mono pump (made by Heishin Sowbi Co., Ltd.), and the silver complex was reduced. 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. In addition, a vinyl chloride pipe having an inner diameter of 25 mm and a length of 725 mm was used for the trough. The slurry containing the silver particle obtained by reduction of a silver complex was taken in the water tank, stirring.

Thereafter, the silver particle slurry obtained by reduction is subjected to solid-liquid separation, 0.75 g of polyoxyethylene-added quaternary ammonium salt which is a commercially available cationic surfactant as a surface-treating agent and the silver particles before drying are recovered (Kuroda Japan Co., Ltd.) 0.04 mass% of silasol and silver particles) and 14.08 g of stearic acid emulsion (Junkyo Yushi Co., Ltd., Cellosol 920, 0.76 mass% of silver particles) were added to 15.4 L of pure water, followed by stirring for 60 minutes. Surface treatment was performed. After surface treatment, the silver particle slurry was filtered using the filter press, and silver particle was solid-liquid separated.

Subsequently, before the recovered silver particles were dried, the silver particles were charged in 15.4 L of 0.05 mol / L sodium hydroxide (NaOH) aqueous solution, stirred for 15 minutes, washed, and then filtered through a filter press to recover the silver particles. .

Next, the collected silver particles were poured into 23 L of pure water maintained at 40 degrees, stirred and filtered, and then the silver particles were transferred to a stainless pad and dried at 60 ° C. for 10 hours with a vacuum dryer. 1.75 kg of dried silver powder was taken, and it put into the 5 L Henschel mixer (made by Nippon Coke Co., Ltd. product, FM5C). In the Henschel mixer, silver powder was obtained by depressurizing and depressurizing with a vacuum pump, stirring at 2000 revolutions per minute (18.2 m / s of stirring blades) for 30 minutes.

The particle size distribution of the obtained silver powder was measured using the laser diffraction scattering type particle size distribution measuring apparatus (The Nikiso Co., Ltd. make, MICROTRAC HRA 9320X-100). In addition, the dispersion medium was measured by putting silver powder in the state which circulated the inside of the apparatus using isopropyl alcohol. The particle size distribution of the measured total volume is shown in FIG. 2, and the obtained value is shown in following Table 1. FIG.

2, the obtained silver powder is characterized in that in the particle size distribution in the region of 0.3 ㎛~14.0 ㎛, and the peak P ₁ and the relationship of the shoulder P _2, P ₁ > P ₂ , P ₁ was in the range of 2.0 μm to 5.0 μm, and P ₂ was in the range of 0.5 μm to 3.0 μm.

In addition, as shown in Table 1, the particle size (D ₅₀ ) of the particle size distribution on the volume basis obtained by the laser diffraction scattering method is 2.3 μm, and the standard deviation (SD) of the particle size distribution on the volume basis is 1.14 μm, and the variation coefficient ( CV) was 49.7%, and the ratio of the particle | grains of the particle size range of 1.5 micrometers-5.0 micrometers of the particle size distribution on a volume basis was 68.9%. In addition, the _{SD = (D 84 -D 16)} / 2, and _{CV = (SD / D 50)} × 100, below is the same.

Next, the paste was produced using the obtained silver powder, the particle size distribution of the silver powder in a paste was measured, and the paste characteristic was evaluated by measuring the viscosity of the paste.

First, 9.2 g of silver powder obtained in a stainless steel dish and 0.8 g of a vehicle having a weight ratio of 1: 7 of epoxy resin (JER819 manufactured by Mitsubishi Chemical Co., Ltd.) and terpineol were weighed, and using a metallic spatula After mixing, the mixture was kneaded at 2000 rpm (420 G as centrifugal force) for 5 minutes using a revolving kneading machine (Type ARE-250 manufactured by Thinkki Co., Ltd.) to avoid confusion with a uniform evaluation paste (hereinafter, referred to as a general paste). In order to obtain a mixture).

About the obtained kneaded material, silver powder was disperse | distributed in isopropyl alcohol, and the particle size distribution of the silver powder in paste was measured using the laser diffraction scattering method. The particle size distribution of the silver powder in the measured paste is shown in FIG. 3, and the obtained value is shown in following Table 1. FIG.

3, the silver powder in the kneaded product is, according to the particle size distribution in the region of 0.3 ㎛~14.0 ㎛, and the peak P ₁ and the relationship of the shoulder P _2, P ₁ > P ₂ , P ₁ was in the range of 2.0 μm to 5.0 μm, and P ₂ was in the range of 0.5 μm to 3.0 μm.

In addition, as shown in Table 1, the particle size (D ₅₀ ) of the particle size distribution on the volume basis obtained by the laser diffraction scattering method is 2.3 μm, and the standard deviation (SD) of the particle size distribution on the volume basis is 1.13 μm, and the variation coefficient ( CV) was 49.7%, and the ratio of the particle | grains whose particle size ranges from 1.5 micrometers to 5.0 micrometers of the particle size distribution on a volume basis was 68.7%.

In addition, the paste was evaluated using the obtained silver powder. After weighing 9.2 g of silver powder and 0.8 g of a vehicle having a weight ratio of 1: 7 of epoxy resin (Mitsubishi Chemical Co., Ltd.) and terpineol in a small dish made of stainless steel, and mixing using a metallic spatula And kneading were carried out using a three-roll mill (manufactured by Kodaira Seisakusho Co., Ltd., a desk-type three-roll mill, type RIII-1 CR-2). During kneading with a three-roll mill, no flakes were found by the naked eye, and the kneading property was good.

With respect to the obtained paste, using a viscoelasticity measuring device (Anton Paar, MCR-301), the shear rate is 4 (1 / sec), the viscosity at 20 (1 / sec) and the shear rate is 4 (1 / The viscosity ratio obtained by dividing the viscosity in sec) by the viscosity in shear rate 2.0 (1 / sec) was measured. Table 1 shows the measurement results.

As shown in Table 1, the obtained paste had a viscosity of 4 (1 / sec) of 93.0 Pa.s and a shear rate of 20 (1 / sec) of 39.1 Pa.s. In addition, the viscosity ratio was 2.4. From this result, it was confirmed that it has a favorable paste characteristic. That is, by using the silver powder obtained in Example 1, it can be known that a paste having an appropriate viscosity can be produced, and that a paste having good printability can be produced by suppressing the occurrence of bleeding or sagging at the time of application to wiring or the like. Could.

[Example 2]

Silver powder was manufactured in the same manner as in Example 1 except that the amount of the polyvinyl alcohol used for the water-soluble polymer was 65.7 g (3.5 mass% based on Kuraray Co., Ltd. product, PVA205, silver particles).

As a result of evaluating the obtained silver powder in the same manner as in Example 1, the obtained particle size distribution is shown in FIG. 4, and each value is shown in Table 1 below.

In addition, using the obtained silver powder, the particle size distribution obtained by evaluating the uniform kneaded material produced with the revolving kneading machine (type ARE-250 made by Thinkki Co., Ltd.) similarly to Example 1 is shown in FIG. The obtained values are shown in Table 1 below.

4, Fig. 5, in the particle size distribution in the region of 0.3 ㎛~14.0 ㎛, and the peak P ₁ and the relationship of the shoulder P _2, P ₁ > P ₂ , P ₁ was in the range of 2.0 μm to 5.0 μm, and P ₂ was in the range of 0.5 μm to 3.0 μm.

As shown in Table 1, the particle size (D ₅₀ ) of the particle size distribution on the basis of volume obtained by laser diffraction scattering method of the obtained silver powder is 2.5 μm, and the standard deviation (SD) of the particle size distribution on the basis of volume is 1.32 μm, the coefficient of variation (CV) was 52.4%, and the ratio of the particle | grains of the particle size range whose 1.5-5.0 micrometers of the particle size distribution by volume was 71.4%.

In addition, as shown in Table 1, the particle size (D ₅₀ ) of the particle size distribution on a volume basis obtained by the laser diffraction scattering method of the obtained kneaded product is 2.4 μm, and the standard deviation (SD) of the particle size distribution on a volume basis is 1.20 μm, The coefficient of variation (CV) was 50.9%, and the proportion of particles having a particle size range of 1.5 µm to 5.0 µm in the volume-based particle size distribution was 69.7%.

In addition, a viscoelasticity measuring device (Anton Paar, MCR) was produced with respect to the paste obtained by kneading the obtained silver powder with a three-roll mill (manufactured by Kodaira Seisakusho Co., Ltd., a table-type three-roll mill, RIII-1 CR-2 type). -301), the shear rate is 4 (1 / sec), the viscosity at 20 (1 / sec), and the shear rate is 4 (1 / sec), the shear rate is 2.0 (1 / sec) The viscosity ratio divided by the viscosity in () was measured.

As a result, as shown in Table 1, the viscosity at the shear rate of 4 (1 / sec) was 97.2 Pa.s, the shear rate at 20 (1 / sec) was 37.4 Pa.s, and the viscosity ratio was 2.6 and the viscosity was in the preferable range. From this result, it was confirmed that paste characteristics are also favorable. In addition, during the kneading by the three-roll mill, the occurrence of flakes was not found by the naked eye, and the kneading property was also good.

[Example 3]

The polyvinyl alcohol used as the water-soluble polymer is 262.8 g (manufactured by Kuraray Co., Ltd., PVA205, 14.0 mass% based on silver particles), and the disintegration condition is 5 L of a high speed stirrer (manufactured by Nippon Coke Co., Ltd., FM5C). In the same manner as in Example 1, silver powder was produced except that the mixture was decomposed by depressurizing with a vacuum pump while stirring at 33 m / s at a circumferential speed for 30 minutes.

As a result of evaluating the obtained silver powder in the same manner as in Example 1, the obtained particle size distribution is shown in FIG. 6, and each value is shown in Table 1 below.

In addition, the particle size distribution obtained by evaluating the uniform kneaded material produced with the revolving kneading machine (type ARE-250 by Thinkki Co., Ltd.) using the obtained silver powder similarly to Example 1 is shown in FIG. The obtained values are shown in Table 1 below.

As Figure 6, shown in Figure 7, according to the particle size distribution in the region of 0.3 ㎛~14.0 ㎛, and the peak P ₁ and the relationship of the shoulder P _2, P ₁ > P ₂ , P ₁ was in the range of 2.0 μm to 5.0 μm, and P ₂ was in the range of 0.5 μm to 3.0 μm.

As shown in Table 1, the particle size (D ₅₀ ) of the particle size distribution on the basis of volume obtained by laser diffraction scattering method of the obtained silver powder is 2.5 μm, and the standard deviation (SD) of the particle size distribution on the basis of volume is 1.15 μm, and the coefficient of variation (CV) was 45.6%, and the ratio of the particle | grains of the particle size range of 1.5 micrometers-5.0 micrometers of the particle size distribution on a volume basis was 75.7%.

In addition, as shown in Table 1, the particle size (D ₅₀ ) of the particle size distribution on the volume basis obtained by the laser diffraction scattering method of the obtained kneaded product is 2.5 μm, and the standard deviation (SD) of the particle size distribution on the volume basis is 1.11 μm, The coefficient of variation (CV) was 44.6%, and the proportion of particles having a particle size range of 1.5 µm to 5.0 µm in the volume-based particle size distribution was 75.9%.

In addition, a viscoelasticity measuring device (Anton Paar, MCR) was produced with respect to the paste obtained by kneading the obtained silver powder with a three-roll mill (manufactured by Kodaira Seisakusho Co., Ltd., a table-type three-roll mill, RIII-1 CR-2 type). -301), the shear rate is 4 (1 / sec), the viscosity at 20 (1 / sec), and the shear rate is 4 (1 / sec), the shear rate is 2.0 (1 / sec) The viscosity ratio divided by the viscosity in () was measured.

As a result, as shown in Table 1, the viscosity at a shear rate of 4 (1 / sec) is 73.1 Pa.s, the viscosity at 20 (1 / sec) is 28.7 Pa.s, and the viscosity ratio is 2.5, and the viscosity was in the preferable range. From this result, it was confirmed that paste characteristics are also favorable. In addition, during the kneading by the three-roll mill, the occurrence of flakes was not found by the naked eye, and the kneading property was good.

Comparative Example 1

In Comparative Example 1, the disintegration conditions were carried out in the same manner as in Example 1 except that the disintegration was carried out by decompression with a vacuum pump while stirring at 4600 revolutions per minute (the circumferential speed of the stirring blade was 42 m / s) for 30 minutes using a Henschel mixer. To prepare a silver powder. That is, compared with Example 1, pulverization was performed on strong disintegration conditions.

The particle size distribution of the silver powder obtained was measured in the same manner as in Example 1. The particle size distribution of the measured total volume is shown in FIG. 8, and the obtained value is shown in following Table 1. FIG.

In addition, similarly to Example 1, using the obtained silver powder, the particle size distribution of the silver powder in the uniform kneaded material produced with the revolving kneading machine (type ARE-250 by Thinkki Co., Ltd.) was measured. The particle size distribution of the silver powder in the measured kneaded material is shown in FIG. 9, and the obtained value is shown in following Table 1. FIG.

As shown in FIGS. 8 and 9, the particle size distribution of the silver powder obtained and the particle size distribution of the silver powder in the kneaded material produced using the silver powder have only one peak and have two or more peaks or peaks and shoulders. It was not a particle size distribution. As shown in Table 1, the silver powder in the kneaded product has a particle size (D ₅₀ ) of the particle size distribution on the basis of volume obtained by laser diffraction scattering method, which is 1.4 μm in the range of 2.0 μm to 5.0 μm, and the particle size on the basis of volume The standard deviation (SD) of distribution was 0.57 micrometer which is not in the range of 0.8 micrometer-3.0 micrometers. Moreover, the ratio of the particle | grains which are the particle size range of 1.5 micrometers-5.0 micrometers of the particle size distribution on a volume basis was 33.8% which is not in the range of 40 to 80%.

In addition, as shown in Table 1, the silver powder before producing the uniform kneaded product has only one peak in its particle size distribution, and the ratio of particles having a particle size range of D ₅₀ , SD, and 1.5 μm to 5.0 μm is also included. , It was not in the above-mentioned range, and they were 1.4 µm, 0.55 µm and 32.9%, respectively.

In the case of such silver powder, in the paste manufactured by kneading the silver powder with a 3-roll mill (made by Kodaira Seisakusho Co., Ltd., a table-type 3-roll mill, type RIII-1 CR-2), the viscosity measurement result of Table 1 As can be seen from the above, the viscosity at a shear rate of 4 (1 / sec) is 28.7 Pa.s, the shear rate at 20 (1 / sec) is 8.1 Pa.s, and the viscosity ratio is 3.5, and the viscosity is very high. It turns out that sufficient paste characteristics are not obtained. In the case of the paste of such a viscosity, bleeding and sagging occur at the time of application | coating to wiring etc., and the shape cannot be maintained. In addition, in this silver powder, flakes were produced by visual observation during the kneading by a three-roll mill, and it was confirmed that kneading property is inadequate.

[Comparative Example 2]

Silver powder was manufactured in the same manner as in Example 1, except that the amount of the polyvinyl alcohol used in the water-soluble polymer was 1.9 g (0.1 mass% based on Kuraray Co., Ltd., PVA205, silver particles).

As a result of evaluating the obtained silver powder in the same manner as in Example 1, the obtained particle size distribution is shown in FIG. 10, and each value is shown in Table 1 below.

As shown in FIG. 10, the particle size distribution of the obtained silver powder had only one peak and was not a particle size distribution having two peaks or shoulders. In addition, as shown in Table 1, the particle size (D ₅₀ ) of the particle size distribution on the volume basis obtained by the laser diffraction scattering method is 7.7 μm, which is not in the range of 2.0 μm to 5.0 μm, and the standard deviation of the particle size distribution on the volume basis (SD). ) Was 6.84 µm which was not in the range of 0.8 µm to 3.0 µm. In addition, the coefficient of variation (CV) was 88.5% which is not in the range of 40 to 70%, and the proportion of particles having a particle size range of 1.5 µm to 5.0 µm in the volume-based particle size distribution was 33.1% which was not in the range of 50 to 80%. .

Using the obtained silver powder, a uniform kneaded product was prepared by using a self-rotating kneader (type ARE-250 manufactured by Thinkki Co., Ltd.), and the silver powder was 3 roll mill (manufactured by Kodaira Seisakusho Co., Ltd., tabletop 3-roll mill, RIII). -1 CR-2 type), each of the pastes was intended to be produced. Since the silver powder absorbed the vehicle and did not have fluidity, the particle size distribution of the silver powder in the kneaded product and the viscosity of the paste could not be evaluated. In addition, during the kneading by the three-roll mill, the occurrence of flakes with the naked eye was found, and it was confirmed that the kneading property was insufficient.

Claims (6)

In a paste in which at least silver powder, terpineol and resin are kneaded with a centrifugal force of 420 G using a magnetic resonator, the particle size distribution on a volume basis is in the region of 0.3 µm to 14.0 µm, and the peak or shoulder P ₁ and the peak or In the relationship of the shoulder P ₂ , P ₁ > P ₂ , P ₁ is in the range of 2.0 μm to 5.0 μm, and P ₂ is in the range of 0.5 μm to 3.0 μm. The paste according to claim 1, wherein in the paste obtained by kneading at least silver powder, terpineol, and resin with a centrifugal force of 420 G using a self-rotating stirrer, the cumulative curve is obtained when the cumulative curve is obtained with 100% of the total volume of each group. The particle size D ₅₀ of the point at which 50% is 50% is 2.0 µm to 5.0 µm, and the standard deviation SD of the particle size distribution on the volume basis expressed by the following formula (1) is 0.8 µm to 3.0 µm.
SD = (D ₈₄ -D ₁₆ ) / 2 (1)
[In Formula (1), D ₈₄ represents the particle diameter of the point at which the volume cumulative curve becomes 84%, and D ₁₆ represents the particle diameter of the point at which the volume cumulative curve becomes 16%. The paste according to claim 2, wherein at least the silver powder, the terpineol, and the resin are kneaded with a centrifugal force of 420 G using a self-rotating stirrer, the coefficient of variation CV of the particle size distribution on the volume basis expressed by the following formula (2) is 40. Silver powder characterized by being -70.
CV = (SD / D ₅₀ ) × 100 (2) The paste according to any one of claims 1 to 3, wherein at least the silver powder, the terpineol, and the resin are kneaded with a centrifugal force of 420 G using a self-rotating stirrer, wherein the particle size distribution is 1.5 µm to 5.0 µm. The silver powder characterized by containing 40 to 80% of particles in the particle size range of. The silver powder according to any one of claims 1 to 4, wherein the particle size distribution of the silver powder before the kneading has the same form as that of the particle size distribution in the paste after the kneading. In the manufacturing method of the silver powder which reduces the solution containing the silver complex which melt | dissolved a silver compound to the reducing agent solution, obtains the slurry of silver particle, and obtains silver powder through each process of washing and drying,
1.0-15.0 mass% of water-soluble polymers are added to the reducing agent solution, and the silver particles after drying are subjected to a pulverization treatment at a circumferential speed of 5 to 40 m / sec using an electric stirrer.

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