JPWO2012176831A1 - Silver powder and method for producing the same - Google Patents

Abstract

Provided are a silver powder having an appropriate viscosity range at the time of producing a paste, easy kneading and suppressing the generation of flakes, and a method for producing the same. The present invention is a paste in which at least silver powder, terpineol and resin are kneaded with a centrifugal revolution of 420 G using a self-revolving stirrer, and the volume-based particle size distribution is in the region of 0.3 μm to 14.0 μm, and the peak or In the relationship between the shoulder P1 and the peak or shoulder P2, P1> P2, P1 is in the range of 2.0 μm to 5.0 μm, and P2 is in the range of 0.5 μm to 3.0 μm.

Description

The present invention relates to silver powder and a method for producing the same, and more particularly to a silver powder that is a main component of a silver paste used for forming a wiring layer or an electrode of an electronic device and a method for producing the same.
This application claims priority on the basis of Japanese Patent Application No. 2011-137622 filed in Japan on June 21, 2011. By referring to these applications, the present application Incorporated.

  Silver pastes such as resin-type silver paste and fired-type silver paste are frequently used to form wiring layers and electrodes in electronic devices. That is, after applying or printing these silver pastes on various substrates, a conductive film to be a wiring layer, an electrode, or the like can be formed by heat curing or heat baking.

  For example, a resin-type silver paste is made of silver powder, resin, curing agent, solvent, etc., printed on a conductor circuit pattern or terminal, and cured by heating at 100 ° C. to 200 ° C. to form a conductive film. Form. The fired silver paste is made of silver powder, glass, solvent, etc., printed on a conductor circuit pattern or terminal, and heated and fired at 600 ° C. to 800 ° C. to form a conductive film to form wirings and electrodes. In wirings and electrodes formed of these silver pastes, electrically connected current paths are formed by continuous silver powder.

  The silver powder used in the silver paste has a particle size of 0.1 μm to several μm, and the particle size of the silver powder used varies depending on the thickness of the wiring to be formed and the thickness of the electrode. Further, by uniformly dispersing silver powder in the paste, it is possible to form a wiring having a uniform thickness or an electrode having a uniform thickness.

  In producing the silver paste, generally, for example, first, silver powder is preliminarily kneaded with other components such as a solvent, and then kneaded while applying a predetermined pressure with a three-roll mill or the like. To make. According to this method, since a large amount of silver paste can be produced at a time, the productivity is high and the effect of reducing the production cost can be expected. On the other hand, silver powder is required to be efficiently kneaded with a roll, that is, to have good kneading properties.

  If the viscosity of the paste is too high or too low, efficient kneading with a three-roll mill becomes difficult. When the silver powder has a low viscosity, the shear stress in the three-roll mill is reduced and the shearing force applied to the silver paste is reduced, so that the dispersion of the silver powder in the paste is insufficient. On the other hand, in the case of silver powder having a high viscosity, it becomes difficult to knead and blend with other components such as a solvent, and a paste that is insufficiently kneaded between silver powder and other components such as a solvent is put into a three-roll mill. It will be.

  When the dispersion of the silver powder in the paste is insufficient, or when the paste viscosity is lowered due to insufficient kneading of the silver powder and other components such as a solvent, there is an aggregate of silver particles in the paste. . When this paste is kneaded with a three-roll mill, agglomerated silver particles lump, and coarse powder such as flaky powder (flakes) of several mm is generated. Since it is not desirable to leave the generated flakes in the paste as they are, they are removed by sieving using a mesh or the like, but if too much flakes are formed, there is a problem such as coarse powder clogging between the meshes It is generated and cannot be removed efficiently, and productivity is significantly impaired.

  Further, when flakes are generated in the paste as described above, when screen printing is performed using the paste, coarse flakes are clogged on a fine screen, making it difficult to accurately print a pattern.

  Thus, the occurrence of flakes during paste production greatly affects the printability during screen printing. Therefore, it is desired that the silver powder has a viscosity that can be easily kneaded at the time of preparing the paste, has good dispersibility of the silver halide powder in the solvent, and does not generate coarse powder such as flakes.

In order to realize easy paste production, proposals have been made to control the particle size distribution and form of silver powder. For example, Patent Document 1 discloses a conductive adhesive in which silver powder as a conductive powder is blended in a conductive adhesive in an amount of 30 to 98% by weight in a binder resin, and the primary particles are made from flat silver powder as silver powder. A conductive adhesive containing 30% by weight or more of silver powder having a lump aggregate structure with a tap density of 1.5 g / cm ³ or less is proposed.

  According to this proposal, agglomerated silver powder can be easily deagglomerated into primary particles, so it is highly dispersible and can exhibit stable electrical conductivity without causing deterioration in conductivity due to poor dispersion of silver powder. It is said that a conductive adhesive that gives a cured product excellent in not only conductivity but also adhesiveness, heat resistance, moisture resistance, workability, thermal conductivity and the like is obtained.

  However, in this proposal, the viscosity change of the paste and the occurrence of coarse flakes due to reaggregation of silver particles dispersed in the paste are not taken into account, and the dispersibility in the finally obtained paste is ensured. It's hard to say.

In Patent Document 2, a nonionic surfactant having an HLB value of 6 to 17 is added to a solution containing a silver complex, and when a reducing agent is added thereto, aggregation of reduced silver particles is prevented. Therefore, by making the addition rate of the reducing agent-containing aqueous solution faster than 1 equivalent / minute, the tap density is 2.5 g / cm ³ or more, the average particle diameter is 1 to 6 μm, and the specific surface area is 5 m ² / g or less. There has been proposed a method for producing a silver powder to obtain a silver powder having excellent dispersibility.

  However, this proposal is to obtain a dispersed silver powder by preventing aggregation of the obtained silver powder, and does not take into consideration any dispersibility in the solvent and the occurrence of flakes during paste preparation.

Further, in Patent Document 3, conductive particles having an average particle size of 0.5 to 20 μm, a specific surface area of 0.07 to 1.7 m ² / g, and having at least two or more peaks in the particle size distribution, or There has been proposed a conductive paste comprising conductive particles formed by mixing at least two conductive particles having different particle size distributions and a binder mainly composed of a thermosetting resin. According to this proposal, a conductive paste with good fluidity and dispersibility can be obtained, the filling property to the via and the contact between the conductive particles inside the via hole are stable, and the high-quality via-hole conductor is stable with little variation. Can be formed.

  However, this proposal is aimed at the filling property of the paste into the via and the high connection reliability, and the dispersibility of the silver powder itself in the solvent and the generation of flakes are taken into consideration at the time of paste preparation. is not.

  As described above, although the dispersibility of silver powder in the paste and the improvement of the conductivity and reliability of the electrodes and wiring formed using the paste have been proposed, regarding the suppression of flake generation during paste production Not proposed.

Japanese Patent Application Laid-Open No. 2004-197030 JP 2000-129318 A JP 2004-265607 A

  In view of the above-described conventional circumstances, an object of the present invention is to provide a silver powder that has an appropriate viscosity range during paste production, is easy to knead, and suppresses the generation of flakes, and a method for producing the same.

  As a result of repeated investigations to achieve the above-mentioned object, the present inventor has an aggregate of silver particles and has a particle size distribution having two or more peaks or peaks and shoulders. The present inventors have found that it has a viscosity range, can be easily kneaded at the time of paste production, can suppress a change in viscosity, and can improve kneadability.

That is, the silver powder according to the present invention has a volume-based particle size distribution of 0.3 μm to 14.0 μm in a paste obtained by kneading at least silver powder, terpineol, and a resin with a centrifugal force of 420 G using a self-revolving stirrer. In the relationship between the peak or shoulder P ₁ and the peak or 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 0.5 μm to 3 It is characterized by being in the range of 0.0 μm.

  Moreover, the manufacturing method of the silver powder which concerns on this invention obtains silver powder through each process of washing | cleaning and drying, after reducing the solution containing the silver complex which melt | dissolved the silver compound with a reducing agent solution, and obtaining the slurry of silver particles. A method for producing silver powder, in which 1.0 to 15.0% by mass of a water-soluble polymer is added to the reducing agent solution for reduction, and the dried silver particles are rotated at a peripheral speed using a rolling stirrer. The crushing process is performed at 5 to 40 m / sec.

  According to the silver powder of the present invention, it is possible to control the aggregation state of silver particles, to have an appropriate viscosity range at the time of paste production, to prevent kneading by suppressing the viscosity change, and to suppress the occurrence of flakes. Thus, kneadability and printability can be improved.

  Furthermore, 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 and the fired-type silver paste using the paste are uniform and It has excellent electrical conductivity, and has extremely high industrial value as a silver paste used for forming wiring layers and electrodes of electronic devices.

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

Hereinafter, specific embodiments of the silver powder and the production method thereof according to the present invention will be described in detail. Note that the present invention is not limited to the following embodiments, and can be appropriately changed without changing the gist of the present invention.

  In the description, the name for the silver particle morphology is defined as shown in FIG. That is, as shown in FIG. 1 (A), silver particles are judged from the apparent geometric form, and those considered as unit particles are called primary particles. Further, as shown in FIG. 1B, particles in which two to three or more primary particles are connected by necking are called secondary particles. Further, as shown in FIG. 1C, an aggregate of primary particles and secondary particles is called an aggregate. The primary particles, secondary particles, and aggregates may be collectively referred to as silver particles.

As an evaluation test, the silver powder according to this embodiment has a volume-based particle size distribution of 0.3 μm in a paste obtained by kneading at least the silver powder, tarpioneel, and resin with a centrifugal force of 420 G using a self-revolving stirrer. In the relationship between the particle diameters of the peak or shoulder P ₁ and the peak or shoulder P ₂ , P ₁ > P ₂ , and P ₁ is in the range of 2.0 μm to 5.0 μm. ₂ exists in the range of 0.5 μm to 3.0 μm.

  The present inventor has found that it is important that the silver powder has a specific particle size distribution at least in the initial stage of the paste production in order to have an appropriate viscosity for the silver powder paste and good kneadability. That is, as the presence state of silver powder in the paste at the initial stage of paste production, silver powder composed of primary particles, secondary particles in which a plurality of the primary particles are connected, and aggregates (hereinafter referred to as aggregates) in which they are aggregated are: The silver powder and the organic solvent in the paste are difficult to separate, the formation of coarse aggregates excessively aggregated in the paste is suppressed, the viscosity of the paste is easily adjusted, and the kneadability is improved.

  Conventionally, in the production of silver paste, silver powder having an individual primary particle dispersed as much as possible and an average particle diameter of 0.1 μm to 1.5 μm has been used. Fine silver in which such primary particles are dispersed is used. In the case of particles, they tend to agglomerate during paste production to form a coarse mass. In such agglomerates, the primary particles have many points of contact with other particles and voids are reduced, so that the solvent component of the paste does not easily enter between the primary particles, and the apparent amount of solvent that flows freely in the paste is small. Become more. Then, 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 shearing force is small and the kneading becomes insufficient. As a result, it was found that the agglomerated mass entered the roll as it was without breaking, and as a result, a 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 of loosely aggregated primary or secondary particles, the paste solvent component penetrates into the gaps between the aggregates during paste production, and the paste The apparent amount of solvent that flows freely through the inside is reduced. Then, since the viscosity of the paste becomes high, it becomes difficult to mix and blend silver powder and other components such as a solvent. At this time, for example, when kneading is performed by a three-roll mill generally used in the manufacture of paste, the agglomerated lump in the paste enters the roll as it is, and as a result, coarse powder of mm order such as flakes is formed. I found out.

  On the other hand, in the case of silver powder in which the agglomerates and primary particles and secondary particles described above are mixed, the amount of the solvent component that freely flows in the paste is appropriate at the time of manufacturing the paste, so that it has an appropriate viscosity range. Therefore, it was confirmed that kneading of silver powder with other constituents such as a solvent and kneading with a three-roll mill were facilitated and coarse flakes were not generated.

  The above-mentioned aggregate has, for example, a tuft shape of grapes, and has a size of about 5 to 10 μm. Silver powder in which particles containing such aggregates are mixed is a general paste production stage in which paste is mixed, that is, a stage in which silver powder and a solvent component are mixed, for example, preliminary kneading with a kneader or the like and main kneading with a three-roll mill or the like. In the pre-kneading stage of the method, fine primary particles are not aggregated, and the solvent component wraps around each particle constituting the silver powder and has an appropriate viscosity (hereinafter, distinguished from the finally obtained paste) Therefore, it may be called a kneaded product). When such a kneaded material is kneaded by main kneading, a sufficient shearing force can be applied between the silver particles, and the silver particles can be dispersed in the paste without agglomeration. In addition, since the sufficiently dispersed silver particles hardly reaggregate, it is possible to suppress the generation of flakes caused by coarse agglomerates.

  Conventional silver powder in which primary particles are dispersed, or silver powder mainly composed of aggregates, can be kneaded to adjust the kneaded product to an appropriate viscosity and finally become a paste. When the viscosity is adjusted with the kneaded product, the subsequent viscosity change is large, and it becomes difficult to adjust the viscosity of the final paste to an appropriate value.

  If the viscosity of the paste is too high or too low, good paste printability cannot be obtained, but silver powder in which aggregates, primary particles and secondary particles are mixed, that is, two or more peaks as described above Alternatively, it can be adjusted to an appropriate viscosity by being a silver powder having a particle size distribution having a peak and a shoulder. And the paste which has the outstanding printability can be obtained by using such silver powder.

  The particle size distribution of the silver powder described above is in the paste prepared as an evaluation test, but in order to further improve the kneadability of the silver powder, the particle size distribution in the state of the silver powder before the paste preparation is also described above. It is preferable to have a form similar to that of the particle size distribution in the paste after kneading.

  For the silver powder according to the present embodiment, a paste prepared as an evaluation test is, for example, a vehicle in which the weight ratio of epoxy resin (viscosity 2 to 6 Pa · s, for example, JER819 manufactured by Mitsubishi Chemical Corporation) and terpineol is 1: 7. The silver powder can be produced by kneading the vehicle with 8.0% by mass and 92.0% by mass of silver powder with respect to the paste, and using a self-revolving stirrer with a centrifugal force of 420 G.

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

  In the above-mentioned particle size range, the cumulative volume is less than 95%, and when the volume-based particle size distribution is present up to an area of less than 0.3 μm, fine particles are present in the silver powder, and the silver particles are contained in the paste. Dispersibility is reduced, resulting in a non-uniform paste. On the other hand, when the particle size distribution is present up to a region exceeding 14.0 μm, coarse particles exist in the silver powder, and the conductive film becomes non-uniform when fine wiring or electrodes are formed.

The silver powder in the paste is P ₁ > P ₂ in the relationship between the particle sizes of P ₁ and 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 μm. It exists in the range of 0.0 μm.

In the particle size distribution described above, the peak or shoulder P ₁ (hereinafter sometimes simply referred to as P ₁ ) is a secondary particle formed by connecting primary particles, and a plurality of primary particles are further connected to the secondary particles. On the other hand, the peak or shoulder P ₂ (hereinafter sometimes simply referred to as P ₂ ) is considered to be derived from the primary particles or the secondary particles. When a plurality of peaks or shoulders appear in the particle size range where P ₁ and P ₂ exist, the highest peaks may be P ₁ and P ₂ , respectively. When P ₁ or P ₂ appears as a shoulder, the position where the increase rate of the differential value of the change rate of the appearance frequency indicating the particle size distribution in the vicinity of P ₁ or P ₂ is the lowest as P ₁ or P ₂ do it. P ₁ and P ₂ can also be specified by performing peak separation using, for example, peak separation software, Origin 8.5 (manufactured by Lightstone).

When P ₁ is present in a range of less than 2.0 μm, formation of the above-mentioned aggregate is not sufficient, voids between silver particles become small, and the apparent amount of solvent component in the kneaded product increases, thereby kneading. Since the viscosity of the product is low, the shearing force is small during kneading during paste production, and kneading becomes insufficient. For this reason, it reagglomerates in the paste and coarse agglomerates are formed, and flakes are easily generated. On the other hand, when P ₁ is present in a range exceeding 5.0 μm, the above-mentioned aggregate becomes coarse, and the solvent component that enters the voids of the aggregate increases, so that the solvent component that freely flows in the paste Since the amount decreases and the viscosity of the kneaded product increases, it becomes difficult to form a paste.

Further, when P ₂ is present in the range of less than 0.5μm is increased fine primary particles, coarse agglomerates kneaded material occurs, flake occurs in the paste preparation. On the other hand, if P ₂ is present in the range exceeding the range of 3.0μm, the overall particle size of the silver powder increases, the conductive film becomes uneven in the case of forming a fine wiring or electrodes.

In the particle size distribution of the silver powder in the paste, the relationship between the heights (appearance frequencies) of P ₁ and P ₂ is not particularly limited, but it is more preferable that P ₂ has a height of 25% or more of P ₁ . When P ₂ is less than 25% of P ₁ , the above-described aggregates are large, and the solvent component that enters the voids of the aggregates increases, which may make it difficult to form a paste. In addition, P ₂ is preferably 150% or less of P ₁ in height. When P ₂ is more than 150% of P _1, will exist many fine particles in the silver powder, the dispersibility of the silver particles may become uneven paste decreases in the paste. Also, flakes are likely to occur. Thus, the height of the relationship between P ₂ and P ₁ is within the range described above, with silver powder has excellent kneading properties, can be those obtained paste also have good printability, low Resistance wiring, electrodes, and the like can be formed.

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

  Moreover, according to the silver powder according to the present embodiment, not only is it excellent in dispersibility in the paste, but the wiring layer and the electrode formed by the resin-type silver paste and the fired-type silver paste using the same are uniform. It is excellent in properties and conductivity.

Here, silver powder in the paste described above, when the calculated cumulative curve of the total volume as 100%, the cumulative curve is the particle diameter _{D 50} of the point at which 50% was 2.0Myuemu～5.0Myuemu, following The standard deviation SD of the volume-based particle size distribution represented by the formula (1) is preferably 0.8 μm to 3.0 μm. Further, the particle diameter _{D 50} is 2.0Myuemu～3.5Myuemu, and more preferably the standard deviation SD is 1.0Myuemu～2.0Myuemu.
_{SD = (D 84 -D 16)} / 2 (1)
In the formula (1), D ₈₄ represents the particle diameter of the point where the cumulative volume curve becomes 84%, D ₁₆ represents the particle diameter of the point where the cumulative volume curve becomes 16%.

The silver powder according to the present embodiment preferably has two or more peaks or peaks and shoulders as described above, and has a broad particle size distribution. The particle diameter D ₅₀ and the standard deviation SD indicate the degree of broadness of the particle size distribution in absolute values.

When the particle diameter D ₅₀ is less than 2.0 μm, a sufficient amount of aggregates is not formed, and the paste viscosity is lowered, so that the shearing force during kneading is reduced and the aggregates are coarsened by reaggregation in the paste. Agglomerates are likely to be generated, and flake generation may not be sufficiently suppressed. On the other hand, when D ₅₀ exceeds 5.0 μm, a large amount of coarse aggregates are present, the apparent amount of solvent is reduced, and paste formation may be difficult. In addition, coarse silver particles remain after pasting, and the conductive film may be non-uniform when fine wiring or electrodes are formed.

  Further, when the standard deviation SD is less than 0.8 μm, the formation of aggregates is not sufficient, and reaggregation in the paste tends to generate coarse aggregates. On the other hand, when the standard deviation SD exceeds 3.0 μm, fine primary particles and coarse agglomerates are relatively increased, and the apparent amount of solvent is reduced. When the electrode is formed, the conductive film may be non-uniform.

Furthermore, when this broad particle size distribution is seen in relation to the particle size, the silver powder in the paste described above has a variation coefficient CV of the volume-based particle size distribution represented by the following formula (2) of 40 to 70. preferable.
CV = (SD / D ₅₀ ) × 100 (2)

  The coefficient of variation CV indicates the degree of broadness with respect to the particle size. If the coefficient of variation CV is less than 40, the formation of aggregates is not sufficient, and reaggregation in the paste tends to generate coarse aggregates. On the other hand, when the coefficient of variation CV exceeds 70, fine silver particles and coarse agglomerates are relatively increased, and the apparent amount of solvent is reduced. When formed, the conductive film may be non-uniform.

  In addition, the silver powder according to the present embodiment preferably has the following relationship when viewed in terms of the particle content in a predetermined particle size range. That is, it is preferable that the silver powder in the paste described above contains 40 to 80% of particles in a particle size range of 1.5 μm to 5.0 μm with a volume-based particle size distribution.

As described above, at two or more peaks or peaks and shoulders, P ₁ is a secondary particle formed by connecting primary particles, and an aggregate formed by connecting a plurality of primary particles to the secondary particles. And P ₁ exists in the range of 2.0 μm to 5.0 μm. Therefore, the content of particles present in the particle size range of 1.5 μm to 5.0 μm indicates the formation ratio of moderately sized aggregates.

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

As described above, the silver powder according to the present embodiment is, as a test evaluation, in a kneaded material obtained by kneading at least silver powder, tarpioneel, and resin with a centrifugal force of 420 G using a self-revolving stirrer. The volume-based particle size distribution of silver powder is in the range of 0.3 μm to 14.0 μm, and in the relationship between the particle sizes of the peak or shoulder P ₁ and the peak or shoulder P ₂ , P ₁ > P ₂ , and P ₁ is in the range of 2.0μm~5.0μm, _{P 2} is present in the range of 0.5μm~3.0μm. According to the silver powder having such a particle size distribution, when the silver paste is produced using this silver powder, it becomes difficult to separate the silver powder from the organic solvent in the paste, and the coarse agglomeration excessively aggregated in the paste. Generation of lumps is suppressed, and generation of flakes is suppressed. Moreover, the viscosity change during paste manufacture is small, and the viscosity adjustment of the paste becomes easy.

  The silver powder according to the present embodiment is not limited to the above-described silver paste for evaluation tests, but is applied to all commonly used silver pastes. When the conductive silver paste is produced using the silver powder according to the above, the viscosity of the paste at a shear rate of 4.0 (1 / sec) measured with, for example, a cone plate viscometer is 50 to 150 Pa · s. Can do. The viscosity at a shear rate of 20.0 (1 / sec) can be 20 to 50 Pa · s.

  In silver powder in which the viscosity of the paste is lower than the above-described range, the wiring formed by printing the paste may bleed or sag, and the shape may not be maintained. On the other hand, in the case of silver powder in which the viscosity of the paste is higher than the above-described range, it may be difficult to print the paste.

  Moreover, in the silver powder which concerns on this Embodiment which has the outstanding paste characteristic as mentioned above, formation of the coarse aggregate by excessive aggregation can be effectively suppressed also in the silver paste generally used. It can be said. That is, in the silver powder in which excessive agglomeration occurs in the paste and coarse agglomerates are formed, flakes in which the agglomerates are crushed are generated. In addition, when the silver powder has excessive aggregates, the viscosity at the time of paste production becomes too large, and kneading becomes difficult, resulting in a problem in paste production. In addition, the manufactured paste has poor paste characteristics such as printability. Since the silver powder according to the present embodiment can produce the paste having an appropriate viscosity as described above, it effectively suppresses the occurrence of defects due to the formation of coarse aggregates by suppressing excessive aggregation. It can be said that it can be done.

  In addition, when producing silver paste using the silver powder which concerns on this Embodiment which has the characteristics mentioned above, it does not specifically limit about the pasting method, A well-known method can be used. For example, as a vehicle to be used, a solution in which various celluloses, phenol resins, acrylic resins, etc. are dissolved in alcohol-based, ether-based, ester-based solvents or the like can be used.

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

  The silver powder production method according to the present embodiment uses, for example, silver chloride or silver nitrate as a starting material. Basically, silver obtained by dissolving a starting material such as silver chloride with a complexing agent is used. A solution containing the complex and a reducing agent solution are mixed, the silver complex is reduced to precipitate silver particles, a silver particle slurry is obtained, and silver powder is obtained through the washing, drying, and crushing steps.

  And in the manufacturing method of the silver powder concerning this Embodiment, it is 1.0-15.0 mass% with respect to silver with respect to the reducing agent solution which reduces a silver complex, More preferably, it is 1.0-10.0. The water-soluble polymer is added in an amount of mass%, particularly preferably more than 3.0 mass% and 10.0 mass% or less.

  And in the manufacturing method of silver powder concerning this embodiment, after carrying out each process of washing, drying, and crushing, after reducing a silver complex with the reducing agent solution mentioned above and obtaining silver particle slurry, After drying, the mixture is crushed with weak stirring using a vacuum reduced pressure atmosphere rolling stirrer or the like.

  Thus, 1.0 to 15.0 mass%, more preferably 1.0 to 10.0 mass%, particularly preferably more than 3.0 mass% and 10.0 mass% or less of water based on silver. Aggregation state of silver particles can be controlled by adding a functional polymer to the reducing agent solution to reduce the silver complex and crushing the resulting silver particle slurry with weak agitation after drying. Silver powder having a particle size distribution having two or more peaks or peaks and shoulders derived from an aggregate in which a plurality of primary particles and primary particles aggregate in the paste at the time of paste production can be produced.

  Hereinafter, this silver powder production method will be described more specifically for each step, taking a case where silver chloride is used as a starting material as a preferred embodiment. Silver powder can be obtained by the same method when starting materials other than silver chloride. However, when silver nitrate is used, the above-described nitrite gas recovery device and the treatment device for nitrate nitrogen in wastewater are used. Necessary.

  First, in the reduction step, a silver chloride starting material is dissolved using a complexing agent to prepare a solution containing a silver complex. Although it does not specifically limit as a complexing agent, It is preferable to use the ammonia water which is easy to form a complex with silver chloride and does not contain the component which remains as an impurity. Moreover, it is preferable to use a high purity silver chloride.

  As a method for dissolving silver chloride, for example, when ammonia water is used as a complexing agent, a slurry such as silver chloride may be prepared and ammonia water may be added. However, in order to increase the complex concentration and increase the productivity, It is preferable to add and dissolve silver chloride in ammonia water. The aqueous ammonia used for the dissolution may be a normal one used industrially, but preferably has a purity as high as possible in order to prevent contamination with impurities.

  Next, a reducing agent solution to be mixed with the silver complex solution is prepared. As the reducing agent, it is preferable to use a strong reducing power such as ascorbic acid, hydrazine, formalin and the like. Ascorbic acid is particularly preferred because the crystal grains in the silver particles are easy to grow. Since hydrazine or formalin has a reducing power stronger than ascorbic acid, crystals in silver particles can be reduced. Moreover, in order to control the uniformity of reaction or reaction rate, it can also be used as an aqueous solution whose concentration is adjusted by dissolving or diluting a reducing agent with pure water or the like.

  As described above, in the method for producing silver powder according to the present embodiment, the reducing agent solution is 1.0 to 15.0 mass%, more preferably 1.0 to 10.0 mass%, based on silver. Particularly preferably, more than 3.0% by mass and 10.0% by mass or less of the water-soluble polymer is added.

  Thus, in the production of the silver powder according to the present embodiment, it is important to select a water-soluble polymer as an anti-aggregation agent and to add it. Silver particles (primary particles) produced by reduction with a reducing agent solution have an active surface, and are easily connected to other silver particles to form secondary particles. Further, the secondary particles aggregate to form an aggregate. At this time, when an anti-aggregation agent having a high anti-aggregation effect, for example, a surfactant or a fatty acid is used, secondary particles and aggregates are not sufficiently formed, primary particles increase, and appropriate aggregates are not formed. On the other hand, when an anti-agglomeration agent having a low anti-agglomeration effect is used, the formation of secondary particles and aggregates becomes excessive, resulting in a silver powder containing excessively aggregated coarse aggregates. The water-soluble polymer has an appropriate anti-aggregation effect, so it is possible to easily control the formation of secondary particles and aggregates by adjusting the addition amount, and the silver complex containing after the addition of the reducing agent solution Aggregates of an appropriate size can be formed in the solution.

  The water-soluble polymer to be added is not particularly limited, but is preferably at least one of polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide, gelatin and the like, and at least one of polyethylene glycol, polyvinyl alcohol, and polyvinyl pyrrolidone. It is more preferable that According to these water-soluble polymers, in particular, excessive aggregation is prevented and aggregation of the grown nuclei is insufficient to prevent the silver particles (primary particles) from becoming fine. Silver powder having aggregates can be easily formed.

  Here, the mechanism by which silver particles are connected to a predetermined size by adding a water-soluble polymer to form an aggregate is considered as follows. That is, by adding a water-soluble polymer, the water-soluble polymer is adsorbed on the surface of silver particles. At this time, when almost all of the surface of the silver particles is covered with the water-soluble polymer, the silver particles will be present alone, but by adding the water-soluble polymer at a predetermined ratio to the silver, It is considered that a surface where no partly water-soluble polymer exists remains, and silver particles are connected to each other through the surface to form an aggregate.

  From this, about the addition amount of water-soluble polymer, it adds in the ratio of 1.0-15.0 mass% with respect to silver. When the addition amount of the water-soluble polymer is less than 1.0% by mass with respect to silver, the dispersibility in the silver particle slurry is deteriorated, the silver powder is excessively aggregated, and many coarse aggregates Will be generated. On the other hand, when the addition amount with respect to silver is more than 15.0% by mass, almost all silver particle surfaces are covered with the water-soluble polymer, the silver particles cannot be connected to each other, and the aggregate It cannot be formed. As a result, silver powder composed of primary particles is formed, and even in this case, flakes are generated during paste production.

  Therefore, by adding 1.0 to 15.0% by mass of the water-soluble polymer with respect to silver as described above, the silver particles are appropriately connected through the surface where the water-soluble polymer is not present. Stable aggregates can be formed, the dispersibility during paste production can be improved, and the occurrence of flakes can be effectively suppressed. Moreover, it is more preferable to add the water-soluble polymer at a ratio of 1.0 to 10.0% by mass with respect to silver. By making the addition amount 1.0 to 10.0% by mass or less, the water-soluble polymer can be adsorbed more appropriately on the surface of the silver particles, and the silver particles are connected to a predetermined size and have high stability. Aggregates can be formed, and the formation of flakes can be more effectively suppressed.

  Furthermore, this water-soluble polymer is added to the reducing agent solution. By adding the water-soluble polymer to the reducing agent solution, the water-soluble polymer is present at the nucleation or growth stage, and the water-soluble polymer is quickly adsorbed on the surface of the generated nucleus or silver particle. Thus, the aggregation of silver particles can be controlled efficiently. Therefore, in addition to the adjustment of the concentration of the water-soluble polymer described above, by adding the water-soluble polymer to the reducing agent solution in advance, the formation of coarse aggregates due to excessive aggregation of silver particles is suppressed. The silver particles can be more appropriately connected to a predetermined size to form a highly stable aggregate.

  In addition, a part or all of the water-soluble polymer can be added to the silver complex-containing solution, but in this case, it is difficult to supply the water-soluble polymer to the site of nucleation or growth. There is a possibility that the water-soluble polymer cannot be adsorbed to the surface of the particles appropriately. 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. Accordingly, when the water-soluble polymer can be added to any of the reducing agent solution and the silver complex-containing solution, the amount is more than 3.0% by mass and not more than 10.0% by mass with respect to silver. It is particularly preferable to do this.

  In addition, since addition of a water-soluble polymer may cause foaming during the reduction reaction, an antifoaming agent can be added to the silver complex-containing solution or the reducing agent mixed solution. The antifoaming agent is not particularly limited, and may be one usually used during reduction. However, in order not to inhibit the reduction reaction, the addition amount of the antifoaming agent is preferably set to a minimum level at which an antifoaming effect can be obtained.

  In addition, about the water used when preparing a silver complex containing solution and a reducing agent solution, in order to prevent mixing of an impurity, it is preferable to use the water from which the impurity was removed, and it is especially preferable to use a pure water.

  Next, the silver complex-containing solution prepared as described above and the reducing agent solution are mixed, and the silver complex is reduced to precipitate silver particles. This reduction reaction may be performed by a batch method or a continuous reduction method such as a tube reactor method or an overflow method. In order to obtain primary particles having a uniform particle diameter, it is preferable to use a tube reactor method in which the grain growth time can be easily controlled. The particle size of the silver particles can be controlled by the mixing rate of the silver complex-containing solution and the reducing agent solution and the reduction rate of the silver complex, and can be easily controlled to the target particle size.

  Silver particles obtained in the reduction process have a large amount of chloride ions and water-soluble polymers adsorbed on the surface. Therefore, in order to make the conductivity of the wiring layer and the electrode formed using the silver paste sufficient, the obtained silver particle slurry is washed in the next washing step, and the surface adsorbate is removed by washing. It is preferable. As will be described later, in order to suppress the occurrence of excessive aggregation by removing the water-soluble polymer adsorbed on the surface of the silver particles, the washing step may be performed after the surface treatment step on the silver particles. preferable.

  The washing method is not particularly limited, but the silver particles solid-liquid separated from the slurry by a filter press or the like are put into the washing liquid, stirred using an agitator or an ultrasonic washing machine, and then again solid-liquid. A method of separating and collecting silver particles is generally used. Further, in order to sufficiently remove the surface adsorbate, it is preferable to repeat the operations consisting of charging into the cleaning liquid, stirring cleaning, and solid-liquid separation several times.

  The cleaning liquid may use water, but an alkaline aqueous solution may be used in order to efficiently remove chlorine. Although it does not specifically limit as an alkaline solution, It is preferable to use the sodium hydroxide aqueous solution with few remaining impurities and cheap. In the case of using a sodium hydroxide aqueous solution as the cleaning liquid, it is desirable to further wash the silver particles or the slurry thereof with water in order to remove sodium after washing with the sodium hydroxide aqueous solution.

  Moreover, it is preferable that the density | concentration of sodium hydroxide aqueous solution shall be 0.01-1.00 mol / l. When the concentration is less than 0.01 mol / l, the cleaning effect is insufficient. On the other hand, when the concentration exceeds 1.00 mol / l, sodium may remain in silver particles more than allowable. The water used for the cleaning liquid is preferably water that does not contain an impurity element harmful to silver particles, and pure water is particularly preferable.

  In the production of the silver powder according to the present embodiment, before the aggregate formed by reduction in the silver complex-containing solution further aggregates to form a coarse aggregate, the surface of the formed aggregate is aggregated. It is more preferable to perform surface treatment with a treatment agent having a high prevention effect to prevent excessive aggregation. That is, after the above-described aggregates are formed and before excessive aggregation proceeds, the silver particles are treated with a surfactant, or more preferably a surface treatment on silver particles treated with a surfactant and a dispersant. Perform the process. Thereby, it can prevent that excessive aggregation arises, maintains the structural stability of the desired aggregate, and can suppress effectively that a coarse aggregate is formed.

  Since excessive agglomeration is particularly advanced by drying, the effect of 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 process, before the above-described cleaning process, simultaneously with the cleaning process, or after the cleaning process.

  Among these, it is particularly preferable to carry out after the reduction step and before the washing step or after one washing step. As a result, aggregates formed through a reduction treatment and aggregated to a predetermined size can be maintained, and the surface treatment is performed on the silver particles including the aggregates. Can be manufactured.

  More specifically, in the present embodiment, a water-soluble polymer is added to the reducing agent solution at a predetermined ratio with respect to silver to reduce the amount, and the water-soluble polymer is appropriately added to the surface of the silver particles. Aggregates in which silver particles are linked to a predetermined size are formed by adsorption. However, since the water-soluble polymer adsorbed on the surface of the silver particles is relatively easily washed by the washing treatment, the water-soluble polymer on the surface of the silver particles is removed when the washing step is performed prior to the surface treatment. The silver particles are excessively aggregated with each other, and a coarse aggregate larger than the formed aggregate may be formed. Further, when such a coarse aggregate is formed, uniform surface treatment on the surface of the silver particles becomes difficult.

  Therefore, by performing after the reduction step, before the washing step, or after one washing step, excessive aggregation of silver particles due to removal of the water-soluble polymer is suppressed and formed. The silver particles including the desired aggregate can be efficiently subjected to surface treatment, and a silver powder having no coarse aggregate and good dispersibility can be produced. The surface treatment after the reduction treatment and before the washing step is preferably performed after solid-liquid separation of the slurry containing silver particles with a filter press or the like after the reduction step. By performing the surface treatment after the solid-liquid separation in this way, it is possible to directly actuate a surfactant or dispersant as a surface treatment agent on the generated silver particles including aggregates of a predetermined size. Thus, it is possible to more effectively suppress the surface treatment agent from adsorbing to the formed aggregates and forming aggregates that are excessively aggregated.

  In this surface treatment step, it is more preferable to treat the surface with both a surfactant and a dispersant. When the surface treatment is performed with both the surfactant and the dispersant as described above, a strong surface treatment layer can be formed on the surface of the silver particles due to the interaction. It is effective to maintain the aggregate. As a specific method of preferable surface treatment using a surfactant and a dispersant, the silver particles are put into water added with a surfactant and a dispersant and stirred, or put into water added with a surfactant. After stirring, a dispersant may be further added and stirred. Moreover, when performing surface treatment simultaneously with a washing | cleaning process, a surfactant and a dispersing agent should be added simultaneously to a washing | cleaning liquid, or a dispersing agent should just be added after addition of surfactant. In order to improve the adsorptivity of the surfactant and the dispersant to the silver particles, the silver particles are added to the water or the cleaning liquid to which the surfactant is added and stirred, and then the dispersant is further added and stirred. It is preferable.

  As another form, a surfactant may be added to a reducing agent solution, and a dispersing agent may be added to a slurry of silver particles obtained by mixing a silver complex-containing solution and a reducing agent solution, followed by stirring. . A surface active agent is present in the nucleation or growth stage, and the surface is rapidly adsorbed on the surface of the generated nucleus or silver particle, and then a dispersant is adsorbed to provide a stable and uniform surface treatment. be able to.

  Here, the surfactant is not particularly limited, but a cationic surfactant is preferably used. Since the cationic surfactant is ionized into positive ions without being affected by pH, for example, an effect of improving the adsorptivity to silver powder using silver chloride as a starting material can be obtained.

  Although it does not specifically limit as a cationic surfactant, Alkylmonoamine salt type represented by the monoalkylamine salt, Alkyldiamine represented by N-alkyl (C14-C18) propylenediamine dioleate Salt type, alkyltrimethylammonium salt type represented by alkyltrimethylammonium chloride, alkyldimethylbenzylammonium salt type represented by alkyldimethylbenzylammonium chloride, quaternary ammonium salt type represented by alkyldipolyoxyethylenemethylammonium chloride , Alkylpyridinium salt type, tertiary amine type typified by dimethylstearylamine, polyoxyethylene alkylamine type typified by polyoxypropylene / polyoxyethylene alkylamine N, N ′, N′-tris (2-hydroxyethyl) -N-alkyl (C14-18) at least one selected from oxyethylene addition types of diamines represented by 1,3-diaminopropane is preferable, A quaternary ammonium salt type, a tertiary amine salt type, or a mixture thereof is more preferable.

  In addition, the surfactant preferably has at least one alkyl group having a carbon number of C4 to C36 typified by methyl group, butyl group, cetyl group, stearyl group, beef tallow, hard beef tallow, and plant stearyl. The alkyl group is preferably a group to which at least one selected from polyoxyethylene, polyoxypropylene, polyoxyethylene polyoxypropylene, polyacrylic acid, and polycarboxylic acid is added. Since these alkyl groups are strongly adsorbed with a fatty acid used as a dispersant described later, the fatty acid can be strongly adsorbed when the dispersant is adsorbed to the silver particles via the surfactant.

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

  As the dispersant, for example, protective colloids such as fatty acids, organometallics, and gelatins can be used. However, in view of adsorbability with a surfactant without the possibility of contamination with impurities, it is preferable to use fatty acids or salts thereof. . In addition, you may add a fatty acid or its salt as an emulsion.

  The fatty acid used as the dispersant is not particularly limited, but is preferably at least one selected from stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid, and 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 electrodes formed 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. The amount of adsorption on the silver particles varies depending on the type of the dispersant, but when the added amount is less than 0.01% by mass, the amount of the dispersant is sufficient to sufficiently suppress the aggregation of the silver particles or improve the adsorptivity of the dispersant. May not be adsorbed by silver powder. On the other hand, when the added amount of the dispersant exceeds 3.00% by mass, the dispersant adsorbed on the silver particles increases, and the conductivity of the wiring layer and the electrode formed using the silver paste cannot be sufficiently obtained. Sometimes.

  After washing and surface treatment, the silver particles are recovered by solid-liquid separation. In addition, the apparatus used for washing | cleaning and surface treatment may be used normally, For example, the reaction tank with a stirrer etc. can be used. Moreover, the apparatus used for solid-liquid separation may also be a normally used apparatus, for example, a centrifuge, a suction filter, a filter press, etc. can be used.

  The silver particles that have been washed and surface-treated are dried by evaporating moisture in the drying step. As a drying method, for example, silver powder collected after completion of cleaning and surface treatment is placed on a stainless steel pad and heated at a temperature of 40 to 80 ° C. using a commercially available drying apparatus such as an atmospheric oven or a vacuum dryer. Good.

  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 is weak crushing conditions with respect to the silver powder after drying which stabilized the degree of aggregation by surface treatment. The crushing process is performed under control. Even if the silver powder after the surface treatment described above is further aggregated between the aggregates by subsequent drying or the like, since the binding force is weak, it is easily separated into aggregates of a predetermined size at the time of preparing the paste. However, in order to stabilize the paste, it is preferable to crush and classify.

  The pulverization method specifically stirs the silver particles after drying at a peripheral speed of 5 to 40 m / s of a stirring blade, for example, using a device having a low pulverization force such as a vacuum decompression atmosphere rolling stirrer as the pulverization condition. While disintegrating. Thus, by weakly crushing the silver powder after drying, it is possible to prevent agglomerates of a predetermined size formed by connecting silver particles to be crushed, and in the paste Silver powder having a particle size distribution having two peaks or shoulders derived from an aggregate in which a plurality of particles and primary particles are linked can be produced. When the peripheral speed is 5 m / s or less, the pulverization energy is weak, so that a large amount of aggregate remains. On the other hand, when the peripheral speed is higher than 40 m / s, the pulverization energy becomes strong and the aggregate becomes too small. Even in this case, the silver powder having the above-mentioned particle size distribution cannot be obtained.

  After the pulverization process described above, a silver powder having a particle size equal to or less than a desired particle diameter can be obtained by performing a classification process. The classifying apparatus used in the classification process is not particularly limited, and an airflow classifier, a sieve, or the like can be used.

Specific examples of the present invention will be described below. However, the present invention is not limited to the following examples.

[Example 1]
A silver complex solution was prepared by adding, while stirring, 36 L of 25% aqueous ammonia and 2492 g of silver chloride (manufactured by Sumitomo Metal Mining Co., Ltd.) maintained in a 38 ° C. warm bath at a liquid temperature of 36 ° C. An antifoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times in volume ratio, 24.4 ml of this antifoaming agent dilution was added to the silver complex solution, and the resulting silver complex solution was Maintained at 36 ° C. in a warm bath.

  On the other hand, ascorbic acid 1068g (56.9 mass% with respect to the reagent and silver particle) of a reducing agent ascorbic acid was melt | dissolved in 13.56 L of 36 degreeC pure water, and it was set as the reducing agent solution. Next, 159.5 g of water-soluble polymer polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA205, 8.5% by mass with respect to silver) was collected, and a solution dissolved in 1 L of 36 ° C. pure water was used as a reducing agent. Mixed into solution.

  The prepared silver complex solution and the reducing agent solution are fed into the basket 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 Hyojin Equipment Co., Ltd.). The silver complex was reduced. The reduction rate at this time is 127 g / min in terms of silver. The ratio of the reducing agent supply rate to the silver supply rate was 1.4. Note that a PVC pipe having an inner diameter of 25 mm and a length of 725 mm was used for the rod. The slurry containing silver particles obtained by reduction of the silver complex was received in a receiving tank with stirring.

  Thereafter, the silver particle slurry obtained by reduction is subjected to solid-liquid separation, and the recovered silver particles before drying and 0.75 g of a polyoxyethylene-added quaternary ammonium salt which is a commercially available cationic surfactant as a surface treatment agent. (0.04% by mass with respect to silasol and silver particles, manufactured by Croda Japan Co., Ltd.) and 14.08 g of stearic acid emulsion as a dispersant (manufactured by Chukyo Yushi Co., Ltd., cellosol 920, and 0.08% with respect to silver particles) 76 mass%) was put into 15.4 L of pure water and stirred for 60 minutes for surface treatment. After the surface treatment, the silver particle slurry was filtered using a filter press, and the silver particles were solid-liquid separated.

  Subsequently, before the recovered silver particles are dried, the silver particles are put into 15.4 L of a 0.05 mol / L aqueous sodium hydroxide (NaOH) solution, stirred for 15 minutes, washed, and then filtered with a filter press. The silver particles were recovered.

  Next, the collected silver particles were put into 23 L of pure water maintained at 40 degrees, stirred and filtered, then transferred to a stainless steel pad, and dried at 60 ° C. for 10 hours in a vacuum dryer. 1.75 kg of dried silver powder was taken and charged into a 5 L Henschel mixer (manufactured by Nippon Coke Industries, Ltd., FM5C). In a Henschel mixer, silver powder was obtained by reducing the pressure with a vacuum pump while stirring at 2000 rpm for 30 minutes (the peripheral speed of the stirring blade was 18.2 m / s).

  The particle size distribution of the obtained silver powder was measured using a laser diffraction / scattering particle size distribution measuring apparatus (MICROTRAC HRA 9320X-100, manufactured by Nikkiso Co., Ltd.). Note that isopropyl alcohol was used as a dispersion medium, and the measurement was performed by adding silver powder in a state where the dispersion medium was circulated. FIG. 2 shows the measured volume-integrated particle size distribution, and Table 1 below shows the obtained values.

As shown in FIG. 2, the obtained silver powder has a particle size distribution in the region of 0.3 μm to 14.0 μm, and P ₁ > P ₂ in the relationship between the peak P ₁ and the shoulder P _{2. 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 volume-based particle size distribution obtained by the laser diffraction scattering method is 2.3 μm, and the standard deviation (SD) of the volume-based particle size distribution is 1. It was 14 μm, the coefficient of variation (CV) was 49.7%, and the proportion of particles in the particle size range of 1.5 μm to 5.0 μm in the volume-based particle size distribution was 68.9%. Note that SD = (D ₈₄ −D ₁₆ ) / 2, CV = (SD / D ₅₀ ) × 100, and so on.

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

  First, weighed 9.2 g of silver powder obtained in a small stainless steel plate, 0.8 g of a 1: 7 weight ratio of epoxy resin (JER819 manufactured by Mitsubishi Chemical Co., Ltd.) and terpineol and weighed a metallic spatula. And then kneading for 5 minutes at 2000 rpm (420 G as centrifugal force) using a self-revolving kneading machine (ARE-250 type, manufactured by Shinky Co., Ltd.). In order to avoid confusion with the paste, it was described as a kneaded product).

  About the obtained kneaded material, silver powder was disperse | distributed in isopropyl alcohol, and the particle size distribution of the silver powder in a paste was measured using the laser diffraction scattering method. FIG. 3 shows the measured particle size distribution of the silver powder in the paste, and Table 1 below shows the obtained values.

As shown in FIG. 3, the silver powder in the kneaded material has a particle size distribution in the region of 0.3 μm to 14.0 μm, and P ₁ > P ₂ in the relationship between the peak P ₁ and the shoulder 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 volume-based particle size distribution obtained by the laser diffraction scattering method is 2.3 μm, and the standard deviation (SD) of the volume-based particle size distribution is 1. It was 13 μm, the coefficient of variation (CV) was 49.7%, and the proportion of particles in the particle size range of 1.5 μm to 5.0 μm in the volume-based particle size distribution was 68.7%.

  Moreover, the paste was evaluated using the obtained silver powder. After weighing 9.2 g of silver powder, 0.8 g of a 1: 7 weight ratio of epoxy resin (Mitsubishi Chemical Co., Ltd. JER819) and terpineol in a stainless steel dish and mixing with a metal spatula In addition, the evaluation was carried out by kneading using a three-roll mill (manufactured by Kodaira Seisakusho Co., Ltd., desktop three-roll mill, RIII-1CR-2 type). During the kneading by the three roll mill, the occurrence of flakes by visual observation was not recognized, and the kneading property was good.

  About the obtained paste, using a viscoelasticity measuring apparatus (Anton Paar, MCR-301), the shear rate is 4 (1 / sec), the viscosity at 20 (1 / sec), and the shear rate is 4 (1 / sec) was measured by dividing the viscosity by the viscosity at a shear rate of 2.0 (1 / sec). Table 1 shows the measurement results.

  As shown in Table 1, the obtained paste had a viscosity of 93.0 Pa · s at a shear rate of 4 (1 / sec) and a viscosity of 39.1 Pa · s at a shear rate of 20 (1 / sec). s. The viscosity ratio was 2.4. From this result, it was confirmed that it has a good paste characteristic. That is, by using the silver powder obtained in Example 1, it is possible to produce a paste having an appropriate viscosity and to suppress the occurrence of bleeding or dripping at the time of application to a wiring or the like and have good printability. It was found that a paste could be made.

[Example 2]
Silver powder was prepared in the same manner as in Example 1 except that the amount of water-soluble polymer polyvinyl alcohol used was 65.7 g (manufactured by Kuraray Co., Ltd., PVA205, 3.5% by mass with respect to silver particles). Manufactured.

  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.

  Further, using the obtained silver powder, the particle size distribution obtained by evaluating a uniform kneaded material produced by a self-revolving kneading machine (ARE-250 type, manufactured by Shinky Co., Ltd.) in the same manner as in Example 1 was obtained. The values shown in FIG. 5 are shown in Table 1 below.

4, as shown in FIG. 5, there is a particle size distribution in the region of 0.3Myuemu～14.0Myuemu, the peak P _1, in the context of the shoulder _{P 2,} a _{P 1>} P _2, P ₁ is 2 It was in the range of 0.0 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 volume-based particle size distribution obtained by the laser diffraction scattering method of the obtained silver powder is 2.5 μm, and the standard deviation (SD) of the volume-based particle size distribution Was 1.32 μm, the coefficient of variation (CV) was 52.4%, and the ratio of particles having a particle size range of 1.5 μm to 5.0 μm in the volume-based particle size distribution was 71.4%.

Moreover, as shown in Table 1, the particle diameter (D ₅₀ ) of the volume-based particle size distribution obtained by the laser diffraction scattering method of the obtained kneaded product is 2.4 μm, and the standard deviation of the volume-based particle size distribution (SD) is 1.20 μm, coefficient of variation (CV) is 50.9%, and the proportion of particles in the particle size range of 1.5 μm to 5.0 μm in the volume-based particle size distribution is 69.7%. there were.

  Moreover, about the paste produced by kneading the obtained silver powder with a three roll mill (manufactured by Kodaira Manufacturing Co., Ltd., desktop type three roll mill, RIII-1CR-2 type), a viscoelasticity measuring device (Anton Paar, MCR) -301), the viscosity at a shear rate of 4 (1 / sec) and 20 (1 / sec) and the viscosity at a shear rate of 4 (1 / sec) at a shear rate of 2.0 (1 / sec) The viscosity ratio divided by the viscosity was measured.

  As a result, as shown in Table 1, the viscosity at a shear rate of 4 (1 / sec) is 97.2 Pa · s, the viscosity at a shear rate of 20 (1 / sec) is 37.4 Pa · s, and the viscosity ratio Was 2.6 and the viscosity was in the preferred range. From this result, it was confirmed that the paste characteristics were also good. Further, during the kneading by the three-roll mill, the occurrence of flakes by visual observation was not recognized, and the kneadability was good.

[Example 3]
The amount of water-soluble polymer polyvinyl alcohol used was 262.8 g (manufactured by Kuraray Co., Ltd., PVA205, 14.0% by mass with respect to silver particles), and the pulverization condition was a 5 L high-speed stirrer (Nippon Coke Industries, Ltd.) Silver powder was produced in the same manner as in Example 1 except that the powder was decompressed with a vacuum pump while being stirred for 30 minutes at a peripheral speed of 33 m / s.

  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.

  Further, using the obtained silver powder, the particle size distribution obtained by evaluating a uniform kneaded material produced by a self-revolving kneading machine (ARE-250 type, manufactured by Shinky Co., Ltd.) in the same manner as in Example 1 was obtained. The values shown in FIG. 7 are shown in Table 1 below.

As shown in FIG. 6 and FIG. 7, there is a particle size distribution in the region of 0.3 μm to 14.0 μm, and in the relationship between the peak P ₁ and the shoulder P ₂ , P ₁ > P ₂ and P ₁ is 2 It was in the range of 0.0 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 volume-based particle size distribution obtained by the laser diffraction scattering method of the obtained silver powder is 2.5 μm, and the standard deviation (SD) of the volume-based particle size distribution Was 1.15 μm, the coefficient of variation (CV) was 45.6%, and the proportion of particles in the particle size range of 1.5 μm to 5.0 μm in the volume-based particle size distribution was 75.7%.

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

  Moreover, about the paste produced by kneading the obtained silver powder with a three roll mill (manufactured by Kodaira Manufacturing Co., Ltd., desktop type three roll mill, RIII-1CR-2 type), a viscoelasticity measuring device (Anton Paar, MCR) -301), the viscosity at a shear rate of 4 (1 / sec) and 20 (1 / sec) and the viscosity at a shear rate of 4 (1 / sec) at a shear rate of 2.0 (1 / sec) The viscosity ratio divided by the viscosity was measured.

  As a result, as shown in Table 1, the viscosity at a shear rate of 4 (1 / sec) was 73.1 Pa · s, the viscosity at a shear rate of 20 (1 / sec) was 28.7 Pa · s, and the viscosity ratio Was 2.5 and the viscosity was in the preferred range. From this result, it was confirmed that the paste characteristics were also good. Further, during the kneading with the three roll mill, no flakes were visually observed, and the kneadability was good.

[Comparative Example 1]
In Comparative Example 1, as a crushing condition, except that the crushing was performed by reducing the pressure with a vacuum pump while stirring at 4600 rpm for 30 minutes (the peripheral speed of the stirring blade was 42 m / s) using a Henschel mixer. Produced silver powder in the same manner as in Example 1. That is, crushing was performed under a stronger crushing condition than in Example 1.

  The particle size distribution of the obtained silver powder was measured in the same manner as in Example 1. FIG. 8 shows the measured volume-integrated particle size distribution, and Table 1 below shows the obtained values.

  Similarly to Example 1, the obtained silver powder was used to measure the particle size distribution of the silver powder in a uniform kneaded material produced by a self-revolving kneading machine (ARE-250 manufactured by Sinky Corporation). FIG. 9 shows the measured particle size distribution of the silver powder in the kneaded material, and Table 1 below shows the obtained values.

As shown in FIGS. 8 and 9, the particle size distribution of the obtained silver powder and the particle size distribution of the silver powder in the kneaded material prepared using the silver powder have only one peak, and two or more peaks. Or it was not a particle size distribution with peaks and shoulders. Further, as shown in Table 1, the silver powder in the kneaded product does not have a volume-based particle size distribution particle size (D ₅₀ ) obtained by the laser diffraction scattering method in the range of 2.0 μm to 5.0 μm. The standard deviation (SD) of the volume-based particle size distribution was 0.57 μm which was not in the range of 0.8 μm to 3.0 μm. Further, the ratio of the particles in the particle size range of 1.5 μm to 5.0 μm in the volume basis particle size distribution was 33.8% which is not in the range of 40 to 80%.

In addition, as shown in Table 1, the silver powder before the preparation of the uniform kneaded product also has only one peak in the particle size distribution, and D ₅₀ , SD, and grains of 1.5 μm to 5.0 μm. The ratio of the particles in the diameter range was not in the above-described range, and was 1.4 μm, 0.55 μm, and 32.9%, respectively.

  In the case of such silver powder, from the viscosity measurement results in Table 1, the paste was prepared by kneading the silver powder with a three roll mill (manufactured by Kodaira Seisakusho, desktop type three roll mill, RIII-1CR-2 type). As can be seen, the viscosity at a shear rate of 4 (1 / sec) is 28.7 Pa · s, the viscosity at a shear rate of 20 (1 / sec) is 8.1 Pa · s, and the viscosity ratio is 3.5. It becomes very low, and it can be seen that sufficient paste characteristics cannot be obtained. In the case of a paste having such a viscosity, bleeding or sagging occurs when applied to a wiring or the like, and the shape cannot be maintained. Further, in this silver powder, flakes were visually observed during kneading with a three-roll mill, and it was confirmed that kneadability was insufficient.

[Comparative Example 2]
The silver powder was prepared in the same manner as in Example 1 except that the amount of the water-soluble polymer polyvinyl alcohol used was 1.9 g (manufactured by Kuraray Co., Ltd., PVA205, 0.1% by mass based on silver particles). Manufactured.

  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 with two peaks or shoulders. Further, as shown in Table 1, the particle size (D ₅₀ ) of the volume-based particle size distribution 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, The standard deviation (SD) of the particle size distribution was 6.84 μm not in the range of 0.8 μm to 3.0 μm. Further, the coefficient of variation (CV) is 88.5% which is not in the range of 40 to 70%, and the ratio of particles having a particle size range of 1.5 μm to 5.0 μm in the volume-based particle size distribution is 50 to 80% It was 33.1% which was not in the range.

  Using the obtained silver powder, a uniform kneaded product with a self-revolving kneading machine (ARE-250 type, manufactured by Shinky Co., Ltd.), a silver powder three roll mill (manufactured by Kodaira Seisakusho Co., Ltd., desktop type three roll mill, RIII-1CR-2 type) was used to produce pastes, and the silver powder absorbed the vehicle and did not have fluidity, so 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, visual flakes were observed, and it was confirmed that the kneading property was insufficient.

That is, the silver powder according to the present invention is a paste in which at least silver powder, terpineol and resin are kneaded with a centrifugal force of 420 G using a self-revolving stirrer, and aggregates, primary particles and secondary particles are mixed, and volume The standard particle size distribution is in the region of 0.3 μm to 14.0 μm, and in the relationship between the peak or shoulder P ₁ and the peak or shoulder P ₂ , P ₁ > P ₂ and P ₁ is 2.0 μm to 5. It is in the range of 0 μm, and P ₂ is in the range of 0.5 μm to 3.0 μm.

A method of manufacturing a silver powder according to the present invention, after obtaining the slurry of silver particles with a solution containing a silver complex dissolved silver compound is reduced with a reducing agent solution, washed, through the steps of drying, agglomerate Is a method for producing silver powder in which primary particles and secondary particles are mixed, and 1.0 to 15.0 mass% of water-soluble polymer is added to the reducing agent solution, and the water-soluble polymer is charged. The silver complex in the solution containing the silver complex in which the silver compound is dissolved is reduced with the reduced reducing agent solution, and the silver particles after drying are rotated at a peripheral speed of 5 to 40 m / sec using a rolling stirrer. A crushing process is performed.

Claims (6)

In a paste obtained by kneading at least silver powder, terpineol and resin with a centrifugal force of 420 G using a self-revolving stirrer, the volume-based particle size distribution is in the region of 0.3 μm to 14.0 μm, and the peak or shoulder P ₁ In the relationship of peak or 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. And silver powder. In a paste obtained by kneading at least silver powder, terpineol and resin with a centrifugal revolution of 420 G using a self-revolving stirrer, when the total curve of each group is 100%, the cumulative curve is 50%. The point particle size D ₅₀ is 2.0 μm to 5.0 μm, and the standard deviation SD of the volume-based particle size distribution represented by the following formula (1) is 0.8 μm to 3.0 μm. Item 2. The silver powder according to item 1.
_{SD = (D 84 -D 16)} / 2 (1)
[In the above formula (1), D ₈₄ represents the particle diameter of the point where the cumulative volume curve becomes 84%, D ₁₆ represents the particle diameter of the point where the cumulative volume curve becomes 16%. ] In a paste obtained by kneading at least silver powder, terpineol and resin with a centrifugal force of 420 G using a self-revolving stirrer, the variation coefficient CV of the volume-based particle size distribution represented by the following formula (2) is 40 to 70 The silver powder according to claim 2.
CV = (SD / D ₅₀ ) × 100 (2)   In a paste obtained by kneading at least silver powder, terpineol, and resin with a centrifugal force of 420 G using a self-revolving stirrer, 40-80% of the particles are in a particle size range of 1.5 μm to 5.0 μm of the volume-based particle size distribution The silver powder according to claim 1, wherein the silver powder is contained.   The silver powder according to any one of claims 1 to 4, wherein the particle size distribution of the silver powder before kneading has the same form as the particle size distribution in the paste after kneading. In a method for producing silver powder, after obtaining a silver particle slurry by reducing a solution containing a silver complex in which a silver compound is dissolved with a reducing agent solution, the silver powder is obtained through each step of washing and drying.
1.0-15.0% by mass of a water-soluble polymer is added to the reducing agent solution for reduction, and the dried silver particles are crushed at a peripheral speed of 5-40 m / sec using a rolling stirrer. A method for producing silver powder, characterized by applying a treatment.

Images