JP2014001455A

JP2014001455A - Silver powder

Info

Publication number: JP2014001455A
Application number: JP2013135923A
Authority: JP
Inventors: Yoshihiro Okabe; 良宏岡部; Kenya Ito; 研哉伊藤; Shuji Okada; 修二岡田; Hiromu Nishimoto; 大夢西本; Akihiro Murakami; 明弘村上; Shintaro Ishikawa; 進太郎石川
Original assignee: Sumitomo Metal Mining Co Ltd
Current assignee: Sumitomo Metal Mining Co Ltd
Priority date: 2013-06-28
Filing date: 2013-06-28
Publication date: 2014-01-09

Abstract

PROBLEM TO BE SOLVED: To provide a silver powder having an appropriate particle size and narrow particle size distribution.SOLUTION: In a process of producing a silver powder that involves quantitatively and continuously feeding each of a silver solution containing a silver complex, and a reductant solution into a flow pass; and quantitatively and continuously reducing the silver complex in the reaction solution that includes the silver solution and the reductant solution mixed in the flow pass, a dispersant is incorporated into the reaction solution, the silver concentration of the reaction solution is adjusted to 5-75 g/L, and the amount of ascorbic acid to 1 mol of silver is adjusted to 0.25-0.50 mol.

Description

本発明は、銀粉に関するものであり、より詳しくは、電子機器の配線層や電極等の形成に利用される樹脂型銀ペーストや焼成型銀ペーストの主たる成分となる銀粉に関する。 The present invention relates to silver powder, and more particularly to silver powder that is a main component of resin-type silver paste and fired-type silver paste used for forming wiring layers and electrodes of electronic devices.

電子機器における配線層や電極等の形成には、樹脂型銀ペーストや焼成型銀ペーストのような銀ペーストが多用されている。これらの銀ペーストは、塗布又は印刷した後、加熱硬化あるいは加熱焼成されることによって、配線層や電極等となる導電膜を形成する。 Silver pastes such as resin-type silver paste and fired-type silver paste are frequently used for forming wiring layers, electrodes, and the like in electronic devices. These silver pastes are applied or printed and then heat-cured or fired to form a conductive film that becomes a wiring layer, an electrode, or the like.

例えば、樹脂型銀ペーストは、銀粉、樹脂、硬化剤、溶剤等からなり、導電体回路パターン又は端子の上に印刷し、１００℃〜２００℃で加熱硬化させて導電膜とし、配線や電極を形成する。また、焼成型銀ペーストは、銀粉、ガラス、溶剤などからなり、導電体回路パターン又は端子の上に印刷し、６００℃〜８００℃に加熱焼成して導電膜とし、配線や電極を形成する。これらの銀ペーストで形成された配線や電極では、銀粉が連なることで電気的に接続した電流パスが形成されている。 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.

銀ペーストに使用される銀粉は、粒径が０．１μｍから数μｍであり、形成する配線の太さや電極の厚さによって使用される銀粉の粒径が異なる。また、ペースト中に均一に銀粉を分散させることにより、均一な太さの配線、均一な厚さの電極を形成することができる。 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 and an electrode having a uniform thickness.

銀ペースト用の銀粉に求められる特性としては、用途及び使用条件により様々であるが、一般的で且つ重要なことは、粒径が均一で凝集が少なく、ペースト中への分散性が高いことである。粒径が均一で、且つペースト中への分散性が高いと、硬化あるいは焼成が均一に進み、低抵抗で強度の大きい導電膜を形成できるからである。逆に、粒径が不均一で分散性が悪いと、印刷膜中に銀粒子が均一に存在しないため、配線や電極の太さや厚さが不均一となるばかりか、硬化あるいは焼成が不均一となるため、導電膜の抵抗が大きくなったり、導電膜が脆く弱いものになったりしやすい。 The characteristics required for silver powder for silver paste vary depending on the application and use conditions, but the general and important point is that the particle size is uniform, there is little aggregation, and the dispersibility in the paste is high. is there. This is because if the particle size is uniform and the dispersibility in the paste is high, curing or firing proceeds uniformly, and a conductive film having low resistance and high strength can be formed. Conversely, if the particle size is uneven and the dispersibility is poor, the silver particles are not uniformly present in the printed film, so the thickness and thickness of the wiring and electrodes are not uniform, and the curing or firing is not uniform. Therefore, the resistance of the conductive film tends to increase, or the conductive film tends to be brittle and weak.

更に、銀ペースト用の銀粉に求められる事項として、製造コストが低いことも重要である。銀粉はペーストの主成分であるため、ペースト価格に占める割合が大きいためである。製造コストの低減のためには、生産性が高いことや、使用する原料や材料の単価が低いだけでなく、廃液や排気の処理コストが低いことも重要となる。 Further, as a matter required for silver powder for silver paste, it is also important that the manufacturing cost is low. This is because silver powder is the main component of the paste and therefore has a large proportion of the paste price. In order to reduce manufacturing costs, it is important not only to have high productivity and low unit cost of raw materials and materials to be used, but also to have low waste liquid and exhaust treatment costs.

ところで、上述した銀ペーストに使用される銀粉の製造は、硝酸銀等の銀塩のアンミン錯体を含む溶液が入った槽内に還元剤溶液を投入して還元するバッチ式で行われることが多かった。しかしながら、バッチ式では、還元剤溶液が投入された位置で局部的に還元反応が始まり、還元剤溶液の投入開始から終了までの間で銀粒子の核が随時発生していくため、均一な粒径の銀粉を得ることは難しい。 By the way, manufacture of the silver powder used for the silver paste mentioned above was performed by the batch type which introduce | transduces and reduces a reducing agent solution in the tank containing the solution containing silver salt ammine complexes, such as silver nitrate, in many cases. . However, in the batch method, the reduction reaction starts locally at the position where the reducing agent solution is charged, and the nuclei of silver particles are generated as needed from the start to the end of charging of the reducing agent solution. It is difficult to obtain silver powder with a diameter.

バッチ式による還元を用いた銀粉の製造方法においても、粒度分布を改善した提案がなされている。例えば、特許文献１には、銀塩のアンミン錯体及び還元反応の際に媒晶剤として機能する重金属塩のアンミン錯体を含むスラリーと、還元剤である亜硫酸カリ及び保護コロイドとしてのアラビアゴムを含有する溶液とを混合して銀塩のアンミン錯体を還元し、生成した銀粒子を回収する銀粉の製造方法が開示されている。 Proposals have also been made to improve the particle size distribution in the silver powder production method using batch reduction. For example, Patent Document 1 includes a slurry containing an ammine complex of silver salt and an ammine complex of heavy metal salt that functions as a crystallizing agent in the reduction reaction, potassium sulfite as a reducing agent, and gum arabic as a protective colloid. A silver powder production method is disclosed in which a silver salt ammine complex is reduced by mixing with a solution to be recovered, and the generated silver particles are recovered.

この製造方法によれば、１次粒子の平均粒径が０．１〜１μｍであり、低凝集で且つ粒度分布が狭い粒状銀粉が得られるとされている。しかしながら、この製造方法では、重金属のアンミン錯体の存在下で銀塩を還元するため、重金属が不純物として混入しやすく、得られる銀粉の純度が低下する可能性がある。また、具体的な粒度分布は開示されておらず、どの程度の粒度分布を有した銀粉であるか不明である。 According to this production method, it is said that a granular silver powder having an average primary particle diameter of 0.1 to 1 μm, low aggregation and a narrow particle size distribution can be obtained. However, in this production method, since the silver salt is reduced in the presence of the heavy metal ammine complex, the heavy metal is likely to be mixed as an impurity, and the purity of the resulting silver powder may be reduced. Further, the specific particle size distribution is not disclosed, and it is unclear how much the particle size distribution is silver powder.

一方、銀塩のアンミン錯体を含む溶液と還元剤溶液を連続的に混合して還元する連続方式による粒度分布改善の試みも提案されている。例えば、特許文献２は、銀アンミン錯体水溶液Ｓ_１が一定の第一流路ａを流れ、その第一流路ａの途中に合流する第二流路ｂを設け、この第二流路ｂを通じて有機還元剤及び必要に応じた添加剤Ｓ_２を流し、第一流路ａと第二流路ｂとの合流点ｍで接触混合して還元析出させる銀粉の製造方法が開示されている。 On the other hand, attempts have been made to improve the particle size distribution by a continuous method in which a solution containing a silver salt ammine complex and a reducing agent solution are continuously mixed and reduced. For example, Patent Document 2 provides a second flow path b in which a silver ammine complex aqueous solution S ₁ flows through a fixed first flow path a and joins in the middle of the first flow path a, and organic reduction is performed through the second flow path b. flow agents and additives S ₂ as needed, a manufacturing method of the first flow path a and silver powder contacting mixture to be reduced and deposited at the merging point m between the second flow path b is disclosed.

しかしながら、この方法で得られる銀粉は、走査型電子顕微鏡像の画像解析により得られる一次粒子の平均粒径Ｄ_ＩＡが０．６μｍ以下で、結晶子径が１０ｎｍ以下であり、微細粒子であるため、一般的な銀ペーストの用途には不向きであり、用途が限られたものとなってしまう。また、反応溶液中の銀濃度が低く、生産性に優れた製造方法とは言い難い。 However, silver powder obtained by this method, the average particle diameter D _IA of the primary particles obtained by image analysis of scanning electron microscope images at 0.6μm or less, the crystallite diameter is not more 10nm or less, a fine particle In general, the silver paste is not suitable for use, and the use is limited. Further, it is difficult to say that the production method has a low silver concentration in the reaction solution and excellent productivity.

ここで、上述した従来の製造方法を含めて、銀源として用いる原料は硝酸銀が一般的である。しかしながら、硝酸銀はアンモニア水等への溶解過程で有毒な亜硝酸ガスを発生し、これを回収する装置が必要となる。また、廃水中に硝酸系窒素やアンモニア系窒素が多量に含まれるので、その処理のための装置も必要となる。さらに、硝酸銀は危険物であり劇物でもあるため、取り扱いに注意を要する。このように、硝酸銀を銀粉の原料として用いる場合は、環境に及ぼす影響やリスクが他の銀化合物に比べて大きいという問題点を抱えている。 Here, the raw material used as the silver source, including the above-described conventional manufacturing method, is generally silver nitrate. However, silver nitrate generates toxic nitrous acid gas in the process of dissolution in aqueous ammonia, and a device for recovering this is required. Further, since a large amount of nitrate nitrogen and ammonia nitrogen is contained in the wastewater, an apparatus for the treatment is also required. In addition, silver nitrate is dangerous and deleterious, so it must be handled with care. As described above, when silver nitrate is used as a raw material for silver powder, there is a problem that the influence and risk on the environment are larger than those of other silver compounds.

そこで、硝酸銀を原料とせずに、塩化銀を還元して銀粉を製造する方法も提案されている。塩化銀は危険物にも劇物にも該当せず、遮光の必要はあるものの比較的取り扱いが容易な銀化合物であるという利点を有している。また、塩化銀は銀の精製プロセスの中間品としても存在し、電子工業用として十分な純度を有するものが提供されている。 Therefore, a method for producing silver powder by reducing silver chloride without using silver nitrate as a raw material has been proposed. Silver chloride is neither a dangerous substance nor a deleterious substance, and has the advantage that it is a silver compound that is relatively easy to handle although it needs to be shielded from light. Silver chloride is also present as an intermediate product in the silver refining process, and has a sufficient purity for use in the electronics industry.

例えば、特許文献３には、塩化銀をアンモニア水に銀濃度で１〜１００ｇ／ｌとなるように溶解した後、この溶液に保護コロイドの存在下で還元剤を加えて撹拌し、溶液中の銀アンミン錯体を液相還元して銀超微粒子を得る方法が開示されている。しかしながら、この方法で得られる銀粉の粒径は０．１μｍ以下と微細であるため、電子工業用としては用途が限られるものであった。 For example, in Patent Document 3, after silver chloride is dissolved in ammonia water so that the silver concentration is 1 to 100 g / l, a reducing agent is added to this solution in the presence of a protective colloid and stirred, A method for obtaining silver ultrafine particles by liquid phase reduction of a silver ammine complex is disclosed. However, since the particle size of the silver powder obtained by this method is as fine as 0.1 μm or less, the use for the electronics industry is limited.

以上のように、銀粉の製造方法についてはこれまで多くの提案がなされているが、平均粒径が０．１μｍから数μｍで均一な粒径を有した銀粉、すなわち粒度分布が狭い銀粉を得ることと、優れた生産性を有し低コストで銀粉を得ることが両立できていなかった。 As described above, many proposals have been made for the production method of silver powder, but silver powder having an average particle diameter of 0.1 μm to several μm and a uniform particle diameter, that is, silver powder having a narrow particle size distribution is obtained. In other words, it has not been possible to obtain silver powder at a low cost with excellent productivity.

特開平１１−１８９８１２号公報JP-A-11-189812 特開２００５−４８２３６号公報JP-A-2005-48236 特開平１０−２６５８１２号公報JP-A-10-265812

本発明は、このような従来の事情に鑑み、生産性が高く低コストで製造でき、適度な粒径を有するとともに粒度分布が狭い銀粉を提供することを目的とする。 In view of such conventional circumstances, an object of the present invention is to provide a silver powder that has high productivity and can be manufactured at low cost, has an appropriate particle size, and has a narrow particle size distribution.

本発明者らは、上記目的を達成するため、銀錯体を含む溶液に還元剤溶液を連続的に混合して還元する銀粉の製造方法において、得られる銀粒子の粒径制御について検討を重ねた結果、反応液中の銀濃度によって得られる銀粒子の粒径制御ができ、従来より高い銀濃度とすることによって粒径の均一化が可能であることを見出し、本発明に至ったものである。 In order to achieve the above object, the present inventors have repeatedly studied the particle size control of the obtained silver particles in a method for producing silver powder in which a reducing agent solution is continuously mixed in a solution containing a silver complex for reduction. As a result, it was found that the particle size of the silver particles obtained can be controlled by the silver concentration in the reaction solution, and that the particle size can be made uniform by making the silver concentration higher than before, and the present invention has been achieved. .

本発明に係る銀粉は、塩素含有量が４０質量ｐｐｍ未満であり、走査型電子顕微鏡観察によって測定される一次粒子の平均粒径が０．３〜２．０μｍであり、粒径の標準偏差をその平均値で除した値が０．３以下であることを特徴とする。 The silver powder according to the present invention has a chlorine content of less than 40 ppm by mass, the average particle size of primary particles measured by scanning electron microscope observation is 0.3 to 2.0 μm, and the standard deviation of the particle size is The value divided by the average value is 0.3 or less.

本発明に係る銀粉は、適度な粒径を有するとともに粒度分布が狭く、電子機器の配線層や電極等の形成に利用される樹脂型銀ペーストや焼成型銀ペースト等のペースト用銀粉として好適であり、その工業的価値は極めて大きいものである。 The silver powder according to the present invention has an appropriate particle size and a narrow particle size distribution, and is suitable as a silver powder for pastes such as resin-type silver paste and fired-type silver paste used for forming wiring layers and electrodes of electronic devices. Yes, its industrial value is extremely high.

銀溶液と還元剤溶液との混合し反応させる反応管の一例を示す概略模式図である。It is a schematic diagram which shows an example of the reaction tube which mixes and reacts a silver solution and a reducing agent solution. 銀溶液供給管内に還元剤溶液供給管の出口を配置させた反応管の一例を示す断面模式図である。It is a cross-sectional schematic diagram which shows an example of the reaction tube which has arrange | positioned the exit of the reducing agent solution supply pipe in the silver solution supply pipe.

以下、本発明に係る銀粉及びその製造方法の具体的な実施形態について詳細に説明する。なお、本発明は、以下の実施の形態に限定されるものではなく、本発明の要旨を逸脱しない限りにおいて適宜変更することができる。 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 modified as appropriate without departing from the gist of the present invention.

本実施の形態に係る銀粉の製造方法は、銀錯体を含む銀溶液と還元剤溶液とをそれぞれ定量的かつ連続的に流路内に供給し、銀溶液と還元剤溶液とを流路内で混合させた反応液中で銀錯体を定量的かつ連続的に還元するものであり、その反応液中の銀濃度を５〜７５ｇ／Ｌの範囲で調整することを特徴としている。 In the silver powder production method according to the present embodiment, a silver solution containing a silver complex and a reducing agent solution are quantitatively and continuously supplied into the flow path, and the silver solution and the reducing agent solution are supplied in the flow path. The silver complex is quantitatively and continuously reduced in the mixed reaction liquid, and the silver concentration in the reaction liquid is adjusted in the range of 5 to 75 g / L.

この銀粉の製造方法においては、銀溶液と還元剤溶液を定量的かつ連続的に一定の空間に供給し、これらを混合させた反応液中で還元反応を生じせしめ、還元反応が終了した還元後反応液、すなわち銀粒子スラリーを定量的かつ連続的に排出する。これにより、還元反応場の銀錯体の濃度と還元剤の濃度が一定に保たれ、核発生の速度とその濃度が一定になり、さらに一定の粒成長を図るものである。このような方法によれば、得られる銀粒子の大きさが揃い、粒度分布が狭い銀粉を得ることができる。さらに、銀溶液と還元剤溶液の供給と銀粒子スラリーの排出を連続的に行うことで、連続的に銀粉を得ることができ、高い生産性でもって銀粉を製造することができる。 In this method for producing silver powder, a silver solution and a reducing agent solution are quantitatively and continuously supplied to a certain space, and a reduction reaction is caused in a reaction solution in which these are mixed, after the reduction reaction is completed. The reaction solution, that is, the silver particle slurry is discharged quantitatively and continuously. As a result, the concentration of the silver complex and the concentration of the reducing agent in the reduction reaction field are kept constant, the rate of nucleation and the concentration thereof are kept constant, and a further constant grain growth is achieved. According to such a method, silver powder having a uniform particle size distribution and a narrow particle size distribution can be obtained. Further, by continuously supplying the silver solution and the reducing agent solution and discharging the silver particle slurry, the silver powder can be continuously obtained, and the silver powder can be produced with high productivity.

そして、本実施に形態に係る銀粉の製造方法においては、反応液中の銀濃度を５〜７５ｇ／Ｌの範囲で調整することが重要である。これにより、平均粒径が０．３〜２．０μｍで粒度分布が狭い銀粉を高い生産性で製造することが可能となる。すなわち、本実施の形態に係る銀粉の製造方法は、反応液中の銀濃度を５〜７５ｇ／Ｌの範囲で調整することにより、還元により生成される銀粒子の粒径及び粒度分布を制御する。上述のように、この製造方法においては、連続的に銀溶液と還元剤溶液を定量的に混合するため、混合後の還元反応場の銀錯体の濃度と還元剤の濃度が一定に保たれる。したがって、核発生の速度とその濃度が一定であるため、高い銀濃度であっても濃度の揺らぎによる異常な粒成長が抑制され、全体として粒子の成長速度を一定に保つことができ、粗大粒子の生成を抑制することができる。 And in the manufacturing method of the silver powder which concerns on this embodiment, it is important to adjust the silver density | concentration in a reaction liquid in the range of 5-75 g / L. This makes it possible to produce silver powder having an average particle size of 0.3 to 2.0 μm and a narrow particle size distribution with high productivity. That is, the method for producing silver powder according to the present embodiment controls the particle size and particle size distribution of silver particles produced by reduction by adjusting the silver concentration in the reaction solution in the range of 5 to 75 g / L. . As described above, in this production method, since the silver solution and the reducing agent solution are quantitatively mixed continuously, the concentration of the silver complex and the concentration of the reducing agent in the reduction reaction field after mixing are kept constant. . Therefore, since the rate of nucleation and its concentration are constant, abnormal grain growth due to concentration fluctuation is suppressed even at high silver concentration, and the growth rate of particles as a whole can be kept constant. Generation can be suppressed.

ここで、銀濃度が低い場合には、粒子の成長速度は一定に保たれるものの、粒子成長が十分でなく、得られる銀粒子は微細なものとなる。このような微細な銀粒子では、洗浄後の乾燥処理において、銀粒子間で過度凝集が起こり易くなる。一方、銀濃度が高い場合には、核発生の濃度が一定に保たれても核発生が多過ぎるため、粒子の凝集が発生して粗大粒子が生成されてしまう。したがって、連続的に銀溶液と還元剤溶液を定量的に混合し、かつ混合後の反応液中の銀濃度を５〜７５ｇ／Ｌの範囲で調整することにより、上記粒径の範囲で粒度分布が狭い銀粉を高い生産性で得ることができる。 Here, when the silver concentration is low, the growth rate of the particles is kept constant, but the particle growth is not sufficient, and the resulting silver particles are fine. In such fine silver particles, excessive aggregation easily occurs between the silver particles in the drying treatment after washing. On the other hand, when the silver concentration is high, too much nucleation occurs even if the concentration of nucleation is kept constant, so that aggregation of particles occurs and coarse particles are generated. Therefore, by continuously mixing the silver solution and the reducing agent solution quantitatively, and adjusting the silver concentration in the reaction solution after mixing in the range of 5 to 75 g / L, the particle size distribution in the above particle size range. Narrow silver powder can be obtained with high productivity.

より具体的に、銀粒子の粒径は、反応液中の銀錯体を低濃度とすれば小さくなり、高濃度すれば大きくなる傾向にあり、反応液中の銀濃度の調整により粒径を制御することができる。しかしながら、銀濃度が５ｇ／Ｌ未満では、粒径が小さくなり過ぎるとともに十分な生産性が得られない。また、得られる銀粉のタップ密度も低くなってしまう。一方、銀濃度が７５ｇ／Ｌを超えると、粒子の凝集による粗大粒子が生成するため、粒度分布が広くなってしまう。 More specifically, the particle size of silver particles tends to decrease when the silver complex in the reaction solution is low, and increases when the concentration is high. The particle size is controlled by adjusting the silver concentration in the reaction solution. can do. However, when the silver concentration is less than 5 g / L, the particle size becomes too small and sufficient productivity cannot be obtained. Moreover, the tap density of the silver powder obtained will also become low. On the other hand, when the silver concentration exceeds 75 g / L, coarse particles due to the aggregation of particles are generated, so that the particle size distribution becomes wide.

本実施の形態に係る銀粉の製造方法において用いる還元剤としては、一般的なヒドラジンやホルマリン等を用いることもできるが、アスコルビン酸を用いることが特に好ましい。アスコルビン酸は、その還元作用が緩やかであるため、銀粒子中の結晶粒が成長しやすく、また銀濃度が高濃度の反応液中でも粒径制御が容易であることも好ましい理由となっている。また、反応の均一性あるいは反応速度を制御するために、還元剤を純水等で溶解又は希釈して濃度調整した水溶液として用いることもできる。 As the reducing agent used in the method for producing silver powder according to the present embodiment, general hydrazine, formalin and the like can be used, but it is particularly preferable to use ascorbic acid. Ascorbic acid has a moderate reducing action, so that the crystal grains in the silver particles are likely to grow, and it is also preferable that the particle diameter can be easily controlled even in a reaction solution having a high silver concentration. 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.

還元剤としてアスコルビン酸を用いた場合、化学量論的にはアスコルビン酸０．２５モルで銀１モルを還元することができる。銀溶液と還元剤溶液との混合時における混合比は、化学量論による混合比より多くすることが好ましく、具体的には銀１モルに対して還元剤を０．２５〜０．５０モルとすることが好ましく、０．３０〜０．４０モルとすることがより好ましい。０．２５モル未満の場合は、廃液に未還元の銀錯体が残留し、銀粉の収率が低下する。一方、０．５０モルを超えると、還元に利用されないアスコルビン酸が多く残留することになり、コスト的に不利となる。 When ascorbic acid is used as the reducing agent, 1 mol of silver can be reduced stoichiometrically with 0.25 mol of ascorbic acid. The mixing ratio at the time of mixing the silver solution and the reducing agent solution is preferably larger than the mixing ratio based on the stoichiometry, specifically, the reducing agent is 0.25 to 0.50 mol per 1 mol of silver. It is preferable to use 0.30 to 0.40 mol. When the amount is less than 0.25 mol, unreduced silver complex remains in the waste liquid, and the yield of silver powder decreases. On the other hand, if it exceeds 0.50 mol, a large amount of ascorbic acid that is not used for reduction remains, which is disadvantageous in terms of cost.

さらに、本発明者は、銀粉の原料として塩化銀を用いた場合、反応液中の銀濃度に対する還元剤添加量が、銀粉の残留塩素濃度に影響することを見出した。塩化銀をアンモニア水で溶解した銀溶液を還元剤で還元する従来の方法によって得られる銀粒子は、原料由来の塩素を多く含む。しかしながら、還元剤添加量を、銀溶液と還元剤溶液との混合時における混合比で銀１モルに対して０．５０モル以下とすることによって、銀粉の塩素濃度を大幅に低減させることができる。これにより、塩化銀を原料としながら塩素濃度が４０ｐｐｍ未満となる銀粉を得ることができる。 Furthermore, the present inventors have found that when silver chloride is used as a raw material for silver powder, the amount of reducing agent added to the silver concentration in the reaction solution affects the residual chlorine concentration of the silver powder. Silver particles obtained by a conventional method in which a silver solution obtained by dissolving silver chloride with aqueous ammonia is reduced with a reducing agent contains a large amount of chlorine derived from the raw material. However, the chlorine concentration of the silver powder can be greatly reduced by setting the addition amount of the reducing agent to 0.50 mol or less with respect to 1 mol of silver in the mixing ratio when the silver solution and the reducing agent solution are mixed. . Thereby, silver powder with a chlorine concentration of less than 40 ppm can be obtained using silver chloride as a raw material.

なお、銀粉の粒径及び残留塩素濃度低減のみであれば、バッチ式による銀の還元において銀濃度と還元剤添加量を上述した範囲に制御すことで達成できるが、さらに上述のように銀溶液と還元剤溶液とを定量的かつ連続的に流路内に供給して銀錯体を還元する連続式により銀粉を製造することにより、優れた粒度分布を有する銀粉を、高い生産性でもって製造することができる。 If only the particle size of silver powder and the residual chlorine concentration are reduced, it can be achieved by controlling the silver concentration and the amount of the reducing agent added to the above-mentioned range in the batch reduction of silver. Silver powder with an excellent particle size distribution is produced with high productivity by producing silver powder by a continuous method in which a silver complex is reduced by supplying a reducing agent solution and a reducing agent solution quantitatively and continuously. be able to.

銀溶液は、還元されて銀となる銀錯体を含む溶液であり、各種銀塩を銀の原料として用いることができるが、塩化銀をアンモニア水に溶解することにより得たものであることが好ましい。このように、塩化銀を原料とすることにより、硝酸銀を出発原料とする方法で必要とされた亜硝酸ガスの回収装置や廃水中の硝酸系窒素の処理装置を設置する必要がなく、環境への影響も少ないプロセスとなり、製造コストの低減を図ることができる。また、粒径制御と反応液中の銀の高濃度化を両立することにおいて、塩化銀を用いることで他の銀塩より容易に行えることが実験的に確認された。 The silver solution is a solution containing a silver complex that is reduced to silver, and various silver salts can be used as a raw material for silver, but it is preferably obtained by dissolving silver chloride in aqueous ammonia. . Thus, by using silver chloride as a raw material, there is no need to install a nitrite gas recovery device and a treatment system for nitrate nitrogen in wastewater, which are required in the method using silver nitrate as a starting material. Therefore, the manufacturing cost can be reduced. It has also been experimentally confirmed that the use of silver chloride makes it easier than other silver salts to achieve both particle size control and higher silver concentration in the reaction solution.

塩化銀は高純度のものを用いることが好ましく、このような塩化銀としては、純度９９．９９９９質量％の高純度塩化銀が工業用に安定的に製造されている。塩化銀を溶解するアンモニア水は、工業的に用いられる通常のものでよいが、不純物混入を防止するため可能な限り高純度のものが好ましい。 High-purity silver chloride is preferably used, and as such silver chloride, high-purity silver chloride having a purity of 99.9999% by mass is stably produced for industrial use. Ammonia water that dissolves silver chloride may be a normal one that is used industrially, but is preferably as highly pure as possible in order to prevent contamination with impurities.

以下では、塩化銀を用いた場合を具体例として、本実施の形態に係る銀粉の製造方法について、より詳細に説明する。 Below, the case where silver chloride is used is taken as a specific example, and the manufacturing method of the silver powder which concerns on this Embodiment is demonstrated in detail.

銀溶液と還元剤溶液とをそれぞれ定量的かつ連続的に流路内に供給して銀錯体を還元させるに際して、銀溶液及び還元剤溶液のそれぞれの濃度と供給速度は、銀溶液と還元剤溶液とが混合された反応液中の銀濃度が５〜７５ｇ／Ｌの範囲で所望の濃度となるように適宜調整すればよい。供給速度が過度に低い場合には、流速が低下して流路内における銀の堆積や生産性が低下する問題が生じる。また、供給速度が高過ぎる場合には、銀溶液と還元剤溶液の混合不足や銀の還元反応の不足が生じる場合がある。これらは流路の大きさにも影響されるため、流路の大きさを考慮しながら適正な供給速度を決めればよい。 When the silver complex and the reducing agent solution are supplied quantitatively and continuously into the flow path to reduce the silver complex, the concentration and the supply rate of the silver solution and the reducing agent solution are determined depending on the silver solution and the reducing agent solution. And the silver concentration in the reaction solution in which is mixed may be suitably adjusted so as to be a desired concentration in the range of 5 to 75 g / L. When the supply rate is excessively low, there arises a problem that the flow rate is lowered and silver deposition or productivity in the flow path is lowered. Further, when the supply rate is too high, insufficient mixing of the silver solution and the reducing agent solution or insufficient silver reduction reaction may occur. Since these are also affected by the size of the flow path, an appropriate supply speed may be determined in consideration of the size of the flow path.

また、銀の還元反応時の反応液の温度は、２５〜４０℃とすることが好ましい。２５℃未満では、塩化銀のアンモニア水に対する溶解度が小さくなり、反応液中の銀濃度を高められないことにより所望の粒径が得られない可能性がある。一方、４０℃を超えると、アンモニアの揮発が激しくなり、溶解度が低下して核発生速度が大きくなり粒径が変動する可能性があり、さらの塩化銀の析出が起きることがある。 Moreover, it is preferable that the temperature of the reaction liquid at the time of silver reduction reaction shall be 25-40 degreeC. If it is less than 25 degreeC, the solubility with respect to the ammonia water of silver chloride will become small, and since the silver concentration in a reaction liquid cannot be raised, a desired particle size may not be obtained. On the other hand, when the temperature exceeds 40 ° C., the volatilization of ammonia becomes violent, the solubility decreases, the nucleation rate increases and the particle size may fluctuate, and further silver chloride precipitation may occur.

この製造方法においては、流路内で銀の還元反応を完了させることが好ましい。このため、流路内で銀溶液と還元剤溶液とが混合されてからその流路内を流下して出口に出るまでの時間（流下時間）が１５秒以上６０秒以下となるような流路長に流路を構成することが好ましい。その流下時間が１５秒以下では還元反応が終了せず、未還元の銀錯体が反応液中に残留し、粒子が連結して粗大粒となることや、凝集して分散性が悪くなることがある。一方、６０秒以上では、装置を無用に大きくするだけである。また、流路の長さは、銀溶液と還元剤溶液とを混合させる混合管に軟質チューブを接続し、そのチューブを螺旋状に巻くようにして調整してもよい。これにより、スペースを要せずに流路の長さを調整することができる。 In this production method, it is preferable to complete the silver reduction reaction in the flow path. For this reason, a flow path in which the time (flow time) from when the silver solution and the reducing agent solution are mixed in the flow path to when flowing down the flow path to the outlet is 15 seconds or more and 60 seconds or less. It is preferable to configure the flow path long. When the flow-down time is 15 seconds or less, the reduction reaction is not completed, and the unreduced silver complex remains in the reaction solution, and the particles may be connected to become coarse particles, or may be aggregated and dispersibility may be deteriorated. is there. On the other hand, in the case of 60 seconds or more, the device is simply enlarged unnecessarily. The length of the flow path may be adjusted by connecting a soft tube to a mixing tube for mixing the silver solution and the reducing agent solution, and winding the tube in a spiral shape. Thereby, the length of the flow path can be adjusted without requiring a space.

また、還元反応が終了しても余剰の還元剤の活性により、銀粒子の連結や凝集を起こすことがある。そのため、流路末端の反応液の出口に受槽を配置するようにし、流路内で混合し還元反応させた反応液を、その受槽に保持して攪拌することが好ましい。 Even when the reduction reaction is completed, the silver particles may be linked or aggregated due to the activity of the excess reducing agent. Therefore, it is preferable to arrange a receiving tank at the outlet of the reaction liquid at the end of the flow path, and hold and stir the reaction liquid mixed and reduced in the flow path in the receiving tank.

ここで、受槽内では、還元により生成した銀粒子が沈降しないように十分に攪拌することが必要になる。沈降すると、銀粒子が凝集体を形成して分散性が悪くなってしまうため好ましくない。攪拌は、銀粒子が沈降しない程度の力で行えばよく、一般的な攪拌機を用いることができる。受槽に入って余剰の還元剤が失活した反応液は、ポンプでフィルタープレス等の濾過機に送液することで、連続的に次の工程へと移送することができる。 Here, in the receiving tank, it is necessary to sufficiently stir the silver particles generated by the reduction so as not to settle. When settled, silver particles form aggregates and dispersibility deteriorates, which is not preferable. Stirring may be performed with such a force that silver particles do not settle, and a general stirrer can be used. The reaction liquid that has entered the receiving tank and the excess reducing agent has been deactivated can be continuously transferred to the next step by sending the reaction liquid to a filter such as a filter press with a pump.

銀溶液と還元剤溶液との混合においては、流路内における銀溶液の供給方向に対する還元剤溶液の供給方向を、両液の供給方向を含む平面内において０°以上、９０°以下として混合することができる。銀溶液の供給方向に対する還元剤溶液の供給方向を０°以上、９０°以下とすることにより、銀溶液を供給する銀溶液供給管内への還元剤溶液の逆流、あるいは還元剤溶液を供給する還元剤供給管内への銀溶液の逆流を防ぎ、いずれかの供給管出口付近で銀粉の堆積が発生することを防止することができる。なお、このような堆積銀粉が生成されると、その堆積銀粉が剥離して銀粉中に粗大粒子として混入することがあり、また堆積が進むといずれかの供給管が閉塞することがある。 In the mixing of the silver solution and the reducing agent solution, the reducing agent solution supply direction with respect to the silver solution supplying direction in the flow path is set to 0 ° or more and 90 ° or less in a plane including the supply directions of both solutions. be able to. By making the supply direction of the reducing agent solution with respect to the supply direction of the silver solution 0 ° or more and 90 ° or less, the reducing agent solution flows backward into the silver solution supply pipe for supplying the silver solution, or the reducing agent solution is supplied. The backflow of the silver solution into the agent supply pipe can be prevented, and the accumulation of silver powder can be prevented near one of the supply pipe outlets. When such deposited silver powder is generated, the deposited silver powder may be peeled off and mixed as coarse particles in the silver powder, and any of the supply pipes may be blocked as the deposition proceeds.

上述した銀溶液と還元剤溶液との混合に用いられる装置、すなわち反応管としては、特に限定されるものではないが、流路が銀溶液を供給する銀溶液供給管と、還元剤溶液を供給する還元剤溶液供給管と、銀溶液と還元剤とを混合させる２液混合管とからなり、銀溶液と還元剤溶液とを混合管内で混合する構造を有するものが用いられ、例えばＹ字管が挙げられる。なお、後でも述べるが、ここで言う「反応管」、「混合管」との用語は、筒状やパイプ状等の外周囲が閉塞され空洞を形成するものに限定解釈されるものではなく、例えば樋のような、その外周囲の一部が開口した形状のものも含む意味であり、形状は何れであっても供給される銀溶液と還元剤溶液とが混合して反応する場となるものを意味する。 The apparatus used for mixing the silver solution and the reducing agent solution described above, that is, the reaction tube is not particularly limited, but the silver solution supply pipe for supplying the silver solution through the flow path and the reducing agent solution are supplied. A reducing agent solution supply pipe and a two-liquid mixing pipe that mixes the silver solution and the reducing agent, and has a structure in which the silver solution and the reducing agent solution are mixed in the mixing pipe. Is mentioned. As will be described later, the terms “reaction tube” and “mixing tube” used herein are not construed as being limited to those in which the outer periphery of a cylindrical shape or pipe shape is closed to form a cavity, For example, it is meant to include a shape having a part of its outer periphery opened, such as a candy, and it is a place where the supplied silver solution and the reducing agent solution are mixed and reacted regardless of the shape. Means things.

より具体的に、図１に反応管の一具体例としてのＹ字管（Ｙ字反応管）１０の模式図を示す。図１に示すように、銀溶液と還元剤溶液との混合に用いるＹ字管１０は、銀錯体を含む銀溶液を供給する銀溶液供給管１１と、還元剤溶液を供給する還元剤溶液供給管１２と、銀溶液と還元剤溶液とを混合させる混合管１３とから構成されている。 More specifically, FIG. 1 shows a schematic diagram of a Y-shaped tube (Y-shaped reaction tube) 10 as a specific example of the reaction tube. As shown in FIG. 1, a Y-shaped tube 10 used for mixing a silver solution and a reducing agent solution includes a silver solution supply tube 11 that supplies a silver solution containing a silver complex, and a reducing agent solution supply that supplies a reducing agent solution. It is comprised from the pipe | tube 12 and the mixing pipe | tube 13 which mixes a silver solution and a reducing agent solution.

このようなＹ字管１０を用いることにより、銀溶液と還元剤溶液とを定量的かつ連続的に供給し、混合管１３内で混合させて反応液とし、銀錯体を定量的かつ連続的に還元することができる。 By using such a Y-shaped tube 10, the silver solution and the reducing agent solution are supplied quantitatively and continuously, mixed in the mixing tube 13 to obtain a reaction solution, and the silver complex is quantitatively and continuously supplied. Can be reduced.

反応管における各管の径は、銀溶液と還元剤溶液の供給に対する抵抗が過度にならず、かつ十分な攪拌が得られるように各溶液の供給量に基づいて決めることができる。 The diameter of each tube in the reaction tube can be determined based on the supply amount of each solution so that the resistance to the supply of the silver solution and the reducing agent solution does not become excessive and sufficient stirring is obtained.

また、反応管における各管は、パイプ状となっており、またその形状は、特に限定されるものではないが、円柱状であることが銀溶液と還元剤溶液を供給する配管と接続しやすいという点で好ましい。また、反応管の材質としては、銀溶液や還元剤溶液と反応しないことと、還元反応後の銀が付着しないことが選択上重要であり、これらの条件を満たす材質であればよい。例えば、ガラス、塩化ビニル、ポリプロピレン、ポリエチレン、テフロン等から選択することができ、その中でもガラスを用いることが特に好ましい。 In addition, each tube in the reaction tube has a pipe shape, and the shape thereof is not particularly limited, but a cylindrical shape is easy to connect to a pipe for supplying a silver solution and a reducing agent solution. This is preferable. In addition, as a material of the reaction tube, it is important for selection that it does not react with the silver solution or the reducing agent solution and that the silver after the reduction reaction does not adhere, and any material satisfying these conditions may be used. For example, it can be selected from glass, vinyl chloride, polypropylene, polyethylene, Teflon, etc. Among them, it is particularly preferable to use glass.

さらに、銀溶液と還元剤溶液を、それぞれ銀溶液供給管１１と還元剤溶液供給管１２を介して供給するに際しては、一般的な定量ポンプを用いることができる。このとき、定量ポンプとしては、脈動の小さいものを用いることが好ましい。また、例えば、還元剤溶液の供給量が銀溶液の供給量より少ない場合には、その合流点でこれら２液が十分に混合されるように還元剤溶液の流速を大きくするように供給することが好ましい。 Furthermore, when supplying the silver solution and the reducing agent solution through the silver solution supply pipe 11 and the reducing agent solution supply pipe 12, respectively, a general metering pump can be used. At this time, it is preferable to use a metering pump having a small pulsation. Also, for example, when the supply amount of the reducing agent solution is smaller than the supply amount of the silver solution, supply the reducing agent solution so that the flow rate of the reducing agent solution is increased so that these two liquids are sufficiently mixed at the junction. Is preferred.

また、図１（及び図１中の一部拡大図）に示すように、Ｙ字管１０を構成する混合管１３内には、スタティックミキサー（ＳＭ）１４を設けることができる。銀溶液と還元剤溶液をそれぞれ供給すると、混合管１３内での乱流や拡散等により各溶液が混合されて反応液となる。このとき、それぞれの溶液が均一に混合されない場合や混合が終わるまでに時間がかかる場合には、銀溶液と還元剤溶液の合流点の下流側にスタティックミキサー１４を設置することにより、反応液を均質化させることができる。 Further, as shown in FIG. 1 (and a partially enlarged view in FIG. 1), a static mixer (SM) 14 can be provided in the mixing tube 13 constituting the Y-shaped tube 10. When the silver solution and the reducing agent solution are respectively supplied, the solutions are mixed by turbulent flow or diffusion in the mixing tube 13 to become a reaction solution. At this time, when the respective solutions are not uniformly mixed or when it takes time until the mixing is completed, the reaction solution is prepared by installing the static mixer 14 on the downstream side of the confluence of the silver solution and the reducing agent solution. It can be homogenized.

スタティックミキサー１４としては、衝突板型、捻り翼型等のものがあるが、混合管１３内に設置するという観点からすると捻り翼型のものが好ましい。図１中の一部拡大図に示すように、捻り翼型のスタティックミキサーは、９０°捻った捻り翼（固定スクリュー）を１エレメントとして捻り方向を変えた捻り翼を交互に数エレメント配置したものである。なお、図１中の一部拡大図では、左側から順に、右エレメントと左エレメントが交互に配置されている様子を示している。 The static mixer 14 includes a collision plate type, a twisted wing type, and the like, but a twisted wing type is preferable from the viewpoint of being installed in the mixing tube 13. As shown in the partially enlarged view of FIG. 1, the twisted wing type static mixer has a twisted wing (fixed screw) twisted by 90 ° as one element and several twisted wings with different twist directions arranged alternately. It is. Note that the partially enlarged view in FIG. 1 shows a state in which the right element and the left element are alternately arranged in order from the left side.

また、そのスタティックミキサー１４のエレメントの数については、特に限定されないが、エレメント数が少な過ぎると、銀溶液と還元剤溶液が十分に混合されず還元反応が不均一となり、微粒が発生することがある。一方で、エレメント数が多過ぎても、無用に混合管を長くすることになるばかりか銀の付着が発生することがある。このエレメント数については、各溶液の供給量と流速により、溶液の混合が十分にできる程度に適宜決めればよい。また、その材質は、銀の付着や反応性の観点から、ガラスとすることが好ましい。 Further, the number of elements of the static mixer 14 is not particularly limited. However, if the number of elements is too small, the silver solution and the reducing agent solution are not sufficiently mixed and the reduction reaction becomes non-uniform and fine particles are generated. is there. On the other hand, if the number of elements is too large, the mixing tube is unnecessarily lengthened and silver adhesion may occur. The number of elements may be appropriately determined depending on the supply amount and flow rate of each solution to such an extent that the solution can be sufficiently mixed. The material is preferably glass from the viewpoint of adhesion of silver and reactivity.

また、混合管１３の水平面に対する角度は、任意に決定することができるが、混合管１３内面と反応液の間に空隙が多くなるような場合、例えば混合管の断面で８０％以上の空隙が生じる場合や、後述するような樋状の混合管を用いる場合には、混合管の水平面に対する角度を２０°〜４０°とすることが好ましい。これにより、混合管内の反応液の流速を適度に抑制することができ、十分な反応時間を得ることができる。 In addition, the angle of the mixing tube 13 with respect to the horizontal plane can be arbitrarily determined. However, when there are many voids between the inner surface of the mixing tube 13 and the reaction solution, for example, 80% or more of the voids in the cross section of the mixing tube When it occurs, or when a bowl-shaped mixing tube as described later is used, the angle of the mixing tube with respect to the horizontal plane is preferably 20 ° to 40 °. Thereby, the flow rate of the reaction liquid in the mixing tube can be moderately suppressed, and a sufficient reaction time can be obtained.

上述したＹ字管１０は、用いられる反応管の一例を示したものであって、当然これに限定されるものではない。例えば、混合管は必ずしもパイプ状のものを用いる必要はなく、樋状、すなわち上部に開口部を有するものでもよい。そして、その桶状の混合管の断面形状としては、円や楕円、多角形等の一部を切断したものを用いることができ、特に断面形状として円弧状のものが好ましい。 The Y-shaped tube 10 described above is an example of a reaction tube to be used, and is not limited to this. For example, the mixing tube does not necessarily need to be pipe-shaped, and may be bowl-shaped, that is, having an opening at the top. As the cross-sectional shape of the bowl-shaped mixing tube, a part of a circle, an ellipse, a polygon or the like cut can be used, and an arc-shaped one is particularly preferable.

このような樋状の混合管を用いる場合、銀溶液の供給方向と還元剤溶液の供給方向が交差するように銀溶液供給管と還元剤供給管を混合管にそれぞれ接続する。例えば、銀溶液を混合管の上端から混合管と平行に流し込ませるように銀溶液供給管を接続し、還元剤溶液を混合管の上端から数ｃｍ下流側で混合管に直角に流し込ませるように還元剤供給管を接続する。これにより、各供給管から供給されたそれぞれの溶液を、その混合管の交差位置において衝突させることによって混合することができ、十分な混合を行うことができる。なお、混合管の内径は、銀溶液と還元剤溶液の流れに対して抵抗が大きくなるような細いものより、流れに対して直角な断面を見たときに上部に空間が残るものが好ましい。 When such a bowl-shaped mixing tube is used, the silver solution supply tube and the reducing agent supply tube are connected to the mixing tube so that the supply direction of the silver solution and the supply direction of the reducing agent solution intersect each other. For example, the silver solution supply pipe is connected so that the silver solution flows in parallel to the mixing pipe from the upper end of the mixing pipe, and the reducing agent solution is allowed to flow perpendicularly to the mixing pipe several cm downstream from the upper end of the mixing pipe. Connect the reducing agent supply pipe. Thereby, each solution supplied from each supply pipe | tube can be mixed by making it collide in the crossing position of the mixing pipe | tube, and sufficient mixing can be performed. In addition, it is preferable that the inner diameter of the mixing tube is such that a space remains in the upper part when a cross section perpendicular to the flow is viewed, rather than a thin tube having resistance to the flow of the silver solution and the reducing agent solution.

ところで、上述したように、銀溶液と還元剤溶液とを混合するに際しては、銀溶液供給管内への還元剤溶液の逆流や還元剤供給管内への銀溶液の逆流を防ぎ、いずれかの供給管出口付近での銀粉の堆積を防止することができるという点において、銀溶液の供給方向に対する還元剤溶液の供給方向を、両液の供給方向を含む平面内において０°以上、９０°以下として混合することが好ましい。しかしながら、銀溶液の供給方向に対する還元剤溶液の供給方向が１５°以下の場合には、各溶液の流れのみでは十分に混合されない場合がある。 By the way, as described above, when mixing the silver solution and the reducing agent solution, the backflow of the reducing agent solution into the silver solution supply pipe and the backflow of the silver solution into the reducing agent supply pipe are prevented, In terms of preventing the accumulation of silver powder in the vicinity of the outlet, the reducing agent solution supply direction relative to the silver solution supply direction is set to 0 ° or more and 90 ° or less in a plane including the supply directions of both solutions. It is preferable to do. However, when the supply direction of the reducing agent solution with respect to the supply direction of the silver solution is 15 ° or less, the flow may not be sufficiently mixed only by the flow of each solution.

したがって、そのため、銀溶液の供給方向に対する還元剤溶液の供給方向が１５°以下とする場合においては、いずれかの供給管内に他方の供給管出口を配置することが好ましい。すなわち、銀溶液の供給方向に対する還元剤溶液の供給方向を両液の供給方向を含む平面内において０°として、銀溶液と還元剤溶液の２液を同方向に流すようにすることが好ましい。 Therefore, when the supply direction of the reducing agent solution with respect to the supply direction of the silver solution is 15 ° or less, it is preferable to arrange the other supply pipe outlet in one of the supply pipes. That is, it is preferable that the supply direction of the reducing agent solution with respect to the supply direction of the silver solution is 0 ° in a plane including the supply directions of both solutions, and the two solutions of the silver solution and the reducing agent solution are allowed to flow in the same direction.

その具体的な態様としては、いずれかの供給管の中心に他方の供給管出口を配置することにより、銀溶液と還元剤溶液とを同方向に流すようにする。通常は、銀溶液の流量が還元剤溶液より多いため、還元剤供給管より銀溶液供給管が大径となる。このため、銀溶液供給管内に還元剤供給管出口を配置することが好ましく、銀溶液を供給する配管内に還元剤溶液を供給する配管を同軸上に設けることが好ましい。これにより、各溶液が十分に混合されるようになるとともに、還元反応が反応管の中心近傍で起こり反応管内壁付近での還元反応が少なくなるため、反応管内壁への銀の付着を減少させ、粗大粒子の生成を抑制することができる。 As a specific mode, the other supply pipe outlet is arranged at the center of one of the supply pipes so that the silver solution and the reducing agent solution flow in the same direction. Usually, since the flow rate of the silver solution is larger than that of the reducing agent solution, the silver solution supply pipe has a larger diameter than the reducing agent supply pipe. For this reason, it is preferable to arrange | position a reducing agent supply pipe | tube exit in a silver solution supply pipe, and it is preferable to provide the piping which supplies a reducing agent solution coaxially in the piping which supplies silver solution. As a result, each solution is sufficiently mixed, and the reduction reaction takes place near the center of the reaction tube and the reduction reaction near the inner wall of the reaction tube is reduced, thereby reducing the adhesion of silver to the inner wall of the reaction tube. The generation of coarse particles can be suppressed.

ここで、図２に、銀溶液を供給する銀溶液供給管内に還元剤溶液を供給する還元剤溶液供給管の出口を配置させた反応管２０の一例を示す。この図２は、反応管のＡＡ’断面を模式的に示した図である。図２に示すように、この反応管２０は、銀錯体を含む銀溶液を供給する銀溶液供給管２１と、還元剤溶液を供給する還元剤溶液供給管２２と、銀溶液供給管２１と還元剤溶液供給管２２が接合され銀溶液と還元剤溶液とを混合する混合管２３とから構成されている。なお、この反応管２０においても、混合管２３内の銀溶液と還元剤溶液の合流位置より下流側にスタティックミキサーを設けるようにしてもよい。 Here, FIG. 2 shows an example of the reaction tube 20 in which the outlet of the reducing agent solution supply pipe for supplying the reducing agent solution is arranged in the silver solution supply pipe for supplying the silver solution. FIG. 2 is a diagram schematically showing an AA ′ cross section of the reaction tube. As shown in FIG. 2, the reaction tube 20 includes a silver solution supply tube 21 that supplies a silver solution containing a silver complex, a reducing agent solution supply tube 22 that supplies a reducing agent solution, a silver solution supply tube 21, and a reduction solution. The agent solution supply pipe 22 is joined and is composed of a mixing tube 23 for mixing the silver solution and the reducing agent solution. In the reaction tube 20 as well, a static mixer may be provided on the downstream side from the joining position of the silver solution and the reducing agent solution in the mixing tube 23.

図２に示すように、反応管２０は、銀溶液の供給方向に対する還元剤溶液の供給方向を０°となるように、すなわち両液を同方向に供給するように、銀溶液供給管２１の内部に還元剤溶液供給管２２の出口を配置させている。これにより、還元剤供給管２２の出口付近に、還元された銀が堆積することを抑制することができる。また、反応管２０では、銀溶液と還元剤溶液とが混合されやすいように、還元剤溶液供給管２２の出口の位置を銀溶液供給管２１の中心位置に配置している。 As shown in FIG. 2, the reaction tube 20 is connected to the silver solution supply tube 21 so that the supply direction of the reducing agent solution with respect to the supply direction of the silver solution is 0 °, that is, both solutions are supplied in the same direction. An outlet of the reducing agent solution supply pipe 22 is disposed inside. Thereby, it is possible to prevent the reduced silver from being deposited near the outlet of the reducing agent supply pipe 22. Further, in the reaction tube 20, the position of the outlet of the reducing agent solution supply pipe 22 is arranged at the center position of the silver solution supply pipe 21 so that the silver solution and the reducing agent solution are easily mixed.

また、銀溶液供給管２１と還元剤溶液供給管２２のそれぞれの径や長さについては、特に限定されるものではなく、各供給管を介して供給される銀溶液と還元剤溶液の流速の違いによって効果的な混合ができるように適宜設定することが好ましい。 Further, the diameters and lengths of the silver solution supply pipe 21 and the reducing agent solution supply pipe 22 are not particularly limited, and the flow rates of the silver solution and the reducing agent solution supplied through the supply pipes are not limited. It is preferable to set appropriately so that effective mixing is possible depending on the difference.

例えば、反応管２０においては、銀溶液供給管２１の内部にその銀溶液供給管２１と同軸に配置された還元剤溶液供給管２２の直線部２２Ａを、還元剤溶液供給管２２の内径の５倍以上の長さに設ける。これにより、還元剤溶液供給管２２の出口から出る還元剤溶液を層流とすることができ、それぞれの溶液の流速の違いによって両液が均一に混合されることになる。 For example, in the reaction tube 20, the straight portion 22 A of the reducing agent solution supply tube 22 disposed coaxially with the silver solution supply tube 21 is arranged inside the silver solution supply tube 21, and the inner diameter of the reducing agent solution supply tube 22 is 5 Provide a length more than double. As a result, the reducing agent solution exiting from the outlet of the reducing agent solution supply pipe 22 can be made into a laminar flow, and both liquids are uniformly mixed due to the difference in the flow rate of each solution.

なお、各供給管の配置等は、各溶液の供給量や流速によっても、適宜変更することができる。また、各供給管の寸法等についても、特に限定されるものではなく、各溶液を供給する際の所望とする流速や流れの状態等に基づいて、適宜設定することができる。 The arrangement of each supply pipe can be changed as appropriate depending on the supply amount and flow rate of each solution. Also, the dimensions and the like of each supply pipe are not particularly limited, and can be set as appropriate based on a desired flow rate or flow state at the time of supplying each solution.

また、銀溶液と還元剤溶液との混合をより迅速に行いたい場合には、流路内における銀溶液の供給方向に対する還元剤溶液の供給方向を、両液の供給方向を含む平面内において９０°を超え、１８０°以下、好ましくは１３５°以上、１８０°以下として混合してもよい。具体的に、例えば銀溶液の供給方向に対する還元剤溶液の供給方向を両液の供給方向を含む平面内において１８０°とする態様としては、銀溶液を供給する配管である銀溶液供給管内に還元剤溶液を供給する配管である還元剤溶液供給管を同軸上に設ける。そして、同軸上に設けた各配管を介して、銀溶液と還元剤溶液とを逆方向に、すなわちそれぞれの流れが向かい合うように流して混合させる。 In addition, when it is desired to mix the silver solution and the reducing agent solution more quickly, the supply direction of the reducing agent solution relative to the supply direction of the silver solution in the flow path is set to 90 in a plane including the supply directions of both solutions. You may mix by exceeding 180 degrees and 180 degrees or less, Preferably it is 135 degrees or more and 180 degrees or less. Specifically, for example, the aspect in which the supply direction of the reducing agent solution with respect to the supply direction of the silver solution is 180 ° in a plane including the supply directions of both solutions is reduced in the silver solution supply pipe which is a pipe for supplying the silver solution A reducing agent solution supply pipe, which is a pipe for supplying the agent solution, is provided on the same axis. Then, the silver solution and the reducing agent solution are mixed in the opposite directions, that is, with the respective flows facing each other, through the respective pipes provided on the same axis.

このように、両液の供給方向をその供給方向を含む平面内において９０°を超え、１８０°以下、好ましくは１３５°以上、１８０°以下として混合することにより、両液の合流時に乱流が生じやすくなり、迅速な混合が可能となる。ただし、この場合には、供給管への銀の堆積が生じる可能性があるため、各溶液の供給量及び流速を調整する必要がある。供給管への銀の堆積を抑制するためには、溶液流量を大きくすることが有効である。なお、供給方向がなす角度以外の構成および条件については、供給方向のなす角度が９０°以下の場合と同様にすればよい。 In this way, by mixing the supply directions of both liquids in a plane including the supply direction in excess of 90 ° and 180 ° or less, preferably 135 ° or more and 180 ° or less, turbulent flow is generated when the two solutions are merged. It tends to occur and quick mixing is possible. However, in this case, since silver may be deposited on the supply pipe, it is necessary to adjust the supply amount and flow rate of each solution. Increasing the solution flow rate is effective for suppressing silver deposition on the supply pipe. The configuration and conditions other than the angle formed by the supply direction may be the same as in the case where the angle formed by the supply direction is 90 ° or less.

本実施の形態に係る銀粉の製造方法においては、銀溶液と還元剤溶液とを混合させた反応液に、分散剤を含有させることが重要である。分散剤が含有されていないと、還元により発生した銀粒子が凝集を起こし、粗大粒子が発生したり、分散性が悪いものとなってしまう。分散剤としては、ポリビニルアルコール、ポリビニルピロリドン、変性シリコンオイル系界面活性剤、ポリエーテル系界面活性剤から選択される少なくとも１種であることが好ましく、又はこれらの２種以上を組合せて用いることがより好ましい。 In the method for producing silver powder according to the present embodiment, it is important to add a dispersing agent to a reaction liquid in which a silver solution and a reducing agent solution are mixed. If the dispersant is not contained, the silver particles generated by the reduction cause agglomeration to generate coarse particles or poor dispersibility. The dispersant is preferably at least one selected from polyvinyl alcohol, polyvinyl pyrrolidone, modified silicone oil surfactants, polyether surfactants, or a combination of two or more of these. More preferred.

分散剤は、予め還元剤溶液に添加しておくことにより、反応液に含有させることが好ましい。分散剤を銀溶液に混合しておくことも選択肢としてはあり得るが、還元剤溶液に混合しておく方が分散性の良い銀粉が得られることが実験的に確認された。これは、還元剤溶液に分散剤を添加しておくことで、銀粒子の生成場に分散剤が存在し、効率よく銀粒子の凝集を抑制できるためと考えられる。なお、分散剤として用いるポリビニルアルコールやポリビニルピロリドンは、還元反応時に発泡する場合があるため、還元剤溶液や銀溶液に消泡剤を添加してもよい。 It is preferable to add the dispersant to the reaction solution by adding it to the reducing agent solution in advance. Mixing the dispersant in the silver solution may be an option, but it has been experimentally confirmed that a silver powder with better dispersibility can be obtained by mixing in the reducing agent solution. This is presumably because by adding a dispersant to the reducing agent solution, the dispersant is present in the silver particle production field, and the aggregation of the silver particles can be efficiently suppressed. In addition, since polyvinyl alcohol and polyvinylpyrrolidone used as a dispersant may foam during the reduction reaction, an antifoaming agent may be added to the reducing agent solution or the silver solution.

分散剤の含有量としては、分散剤の種類及び得ようとする銀粉粒径により適宜決めればよいが、銀溶液中に含有される銀に対して３〜２０質量％とすることが好ましい。分散剤の含有量が３質量％未満であると、銀粒子の凝集抑制効果が十分に得られない可能性があり、一方で含有量が２０質量％を超えても、それ以上に凝集抑制効果の向上はなく、排水処理等の負荷が増加するのみである。 The content of the dispersant may be appropriately determined depending on the type of the dispersant and the silver powder particle size to be obtained, but is preferably 3 to 20% by mass with respect to the silver contained in the silver solution. If the content of the dispersant is less than 3% by mass, the aggregation suppression effect of silver particles may not be sufficiently obtained. On the other hand, even if the content exceeds 20% by mass, the aggregation suppression effect is more than that. There is no improvement and only the load of wastewater treatment etc. increases.

得られた銀スラリーは、濾過した後、洗浄し、乾燥する。洗浄方法としては、特に限定されるものではないが、例えば、銀粒子を水に投入し、撹拌機又は超音波洗浄器を使用して撹拌した後、濾過して銀粉を回収する方法が用いられる。この方法において、銀粒子の水への投入、撹拌洗浄及び濾過からなる操作を、数回繰返して行うことが好ましい。また、洗浄に用いる水は、銀粉に対して有害な不純物元素を含有していない水を使用し、特に純水を使用することが好ましい。 The obtained silver slurry is filtered, washed, and dried. Although it does not specifically limit as a washing | cleaning method, For example, after throwing silver particle into water and stirring using a stirrer or an ultrasonic cleaner, the method of filtering and collect | recovering silver powder is used. . In this method, it is preferable to repeat the operations of adding silver particles into water, stirring and washing, and filtration several times. The water used for washing is water that does not contain an impurity element harmful to silver powder, and it is particularly preferable to use pure water.

そして、水による洗浄を行った後、銀粒子の水分を蒸発させて乾燥させる。乾燥の方法としては、例えば、水洗浄後の銀粒子をステンレスパッド上に置き、大気オーブン又は真空乾燥機等の一般的な乾燥装置を用いて、４０〜８０℃程度の温度で加熱することにより行うことができる。 Then, after washing with water, the moisture of the silver particles is evaporated and dried. As a drying method, for example, the silver particles after washing with water are placed on a stainless steel pad and heated at a temperature of about 40 to 80 ° C. using a general drying device such as an atmospheric oven or a vacuum dryer. It can be carried out.

以上詳述した製造方法により製造された銀粉は、走査型電子顕微鏡観察によって測定される平均粒径、すなわち、一次粒子（銀粒子）の平均粒径が０．３〜２．０μｍであり、粒径の標準偏差をその平均値で除した値が０．３以下である。また、この銀粉のタップ密度は、４〜６ｇ／ｃｍ^３である。ここで、一次粒子とは、外見上から判断して、単位粒子と考えられるものを意味する。また、平均粒径は個数平均の粒径であり、ＳＥＭ観察により３００個以上の一次粒子の粒径測長結果より平均粒径と標準偏差が求められる。 The silver powder produced by the production method described in detail above has an average particle diameter measured by observation with a scanning electron microscope, that is, an average particle diameter of primary particles (silver particles) is 0.3 to 2.0 μm. A value obtained by dividing the standard deviation of the diameter by the average value is 0.3 or less. Moreover, the tap density of this silver powder is 4-6 g / cm < ³ >. Here, the primary particle means what is considered as a unit particle, judging from the appearance. The average particle size is a number average particle size, and the average particle size and standard deviation are obtained from the particle size measurement results of 300 or more primary particles by SEM observation.

このような銀粉は、粒度分布が狭く、高い分散性を有する。そして、このように分散性が良好であることから、電子機器の配線層や電極等の形成に利用される樹脂型銀ペーストや焼成型銀ペースト等のペースト用銀粉として好適に用いることができる。 Such silver powder has a narrow particle size distribution and high dispersibility. And since the dispersibility is good in this way, it can be suitably used as a silver powder for paste such as a resin-type silver paste or a fired-type silver paste used for forming a wiring layer or an electrode of an electronic device.

また、この銀粉は、上述した製造条件を最適化することで、塩素含有量を４０質量ｐｐｍ未満とすることができる。塩素含有量が多い場合には、形成された配線層や電極の電気抵抗を増大させるばかりか、配線間のマイグレーションを起こす要因となる。したがって、これらの観点からも、塩素含有量を低減した銀粉は、電子機器に用いられるペースト用銀粉として好適なものである。 Moreover, this silver powder can make chlorine content less than 40 mass ppm by optimizing the manufacturing conditions mentioned above. When the chlorine content is high, not only the electrical resistance of the formed wiring layer or electrode is increased, but also a cause of migration between wirings. Therefore, also from these viewpoints, the silver powder having a reduced chlorine content is suitable as a silver powder for paste used in electronic equipment.

以下に、本発明の具体的な実施例について説明する。ただし、本発明は、以下の実施例に何ら限定されるものではない。 Specific examples of the present invention will be described below. However, the present invention is not limited to the following examples.

（実施例１）
３８℃の温水ジャケットで加熱した槽中において液温３６℃に保持した２５質量％アンモニア水３６Ｌに、塩化銀１９４０ｇ（住友金属鉱山（株）製、純度９９．９９９９％、水分率１０．５５％）を撹拌しながら投入して銀溶液を作製した。消泡剤（（株）アデカ製、アデカノールＬＧ−１２６）を体積比で１００倍に希釈し、この消泡剤希釈液１７ｍｌを作製した銀溶液に添加して、得られた銀溶液を温浴中において３６℃に保持した。 Example 1
1940 g of silver chloride (Sumitomo Metal Mining Co., Ltd., purity 99.9999%, moisture content of 10.55%) was added to 36 L of 25 mass% ammonia water maintained at a liquid temperature of 36 ° C in a tank heated with a warm water jacket at 38 ° C. ) With stirring to prepare a silver solution. An antifoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times by volume, and 17 ml of this antifoaming agent dilution was added to the prepared silver solution, and the resulting silver solution was heated in a warm bath At 36 ° C.

次に、還元剤のアスコルビン酸９６８ｇ（関東化学（株）製、試薬）を、３０℃の純水５．３５Ｌに溶解した。また、分散剤のポリビニルアルコール２９３ｇ（（株）クラレ製、ＰＶＡ２０５）を５０℃の純水１０Ｌに溶解した。これら２液を混合して還元剤溶液とし、その温度を３６℃に調整した。 Next, 968 g of reducing agent ascorbic acid (manufactured by Kanto Chemical Co., Inc., reagent) was dissolved in 5.35 L of pure water at 30 ° C. Further, 293 g of a polyvinyl alcohol (PVA205, manufactured by Kuraray Co., Ltd.) as a dispersant was dissolved in 10 L of pure water at 50 ° C. These two liquids were mixed to form a reducing agent solution, and the temperature was adjusted to 36 ° C.

銀溶液と還元剤溶液を、スムーズフローポンプ（（株）タクミナ製ＡＰＬ−５、ＢＰＬ−２）を使用して、それぞれ、２．４Ｌ／分、０．８Ｌ／分で反応管に供給し、反応管から排出された反応液を撹拌しながら受槽で保持した。反応管としては、内径１０ｍｍのＹ字管を使用し、銀液と還元剤溶液を供給する管のなす角度を６０°とした。また、反応管には、銀液と還元剤溶液の合流点の下方にスタティックミキサーを配置した。スタティックミキサーは、右と左のエレメントを交互に８個とした。還元反応を送液中に完全に終了させるため、内径１２ｍｍ長さ１０ｍの軟質塩化ビニル樹脂製チューブを反応管出側に接続して、反応液を受槽に送液した。このときの還元速度は、銀量で７８ｇ／分であり、反応液中の銀濃度は２４．５ｇ／Ｌとなる。また、供給速度から求めた銀１モルに対するアスコルビン酸の混合比は０．３５モルとなる。また、分散剤のポリビニルアルコールの量は、混合時の反応液中の銀量に対して１７質量％となる。さらに、銀溶液と還元剤溶液の供給が終了した後、受槽内での攪拌を６０分継続した。 The silver solution and the reducing agent solution are supplied to the reaction tube at 2.4 L / min and 0.8 L / min, respectively, using a smooth flow pump (APL-5, BPL-2 manufactured by Takumina Co., Ltd.) The reaction liquid discharged from the reaction tube was held in a receiving tank while stirring. A Y-tube having an inner diameter of 10 mm was used as the reaction tube, and the angle formed by the tube for supplying the silver solution and the reducing agent solution was 60 °. Moreover, the static mixer was arrange | positioned under the confluence | merging point of silver liquid and a reducing agent solution in the reaction tube. The static mixer had eight right and left elements alternately. In order to complete the reduction reaction during the liquid feeding, a soft vinyl chloride resin tube having an inner diameter of 12 mm and a length of 10 m was connected to the outlet side of the reaction tube, and the reaction liquid was fed to the receiving tank. The reduction rate at this time is 78 g / min in terms of silver, and the silver concentration in the reaction solution is 24.5 g / L. Moreover, the mixing ratio of ascorbic acid to 1 mol of silver determined from the supply rate is 0.35 mol. Moreover, the quantity of the polyvinyl alcohol of a dispersing agent will be 17 mass% with respect to the silver quantity in the reaction liquid at the time of mixing. Furthermore, after the supply of the silver solution and the reducing agent solution was completed, stirring in the receiving tank was continued for 60 minutes.

撹拌終了後の銀溶液を、フィルタープレス機を使用して濾過し、銀粒子を固液分離した。続いて、回収した銀粒子を０．０１ｍｏｌ／ＬのＮａＯＨ水溶液１８Ｌ中に投入し、１５分間撹拌した後、フィルタープレス機で濾過して回収した。ＮａＯＨ水溶液への投入、撹拌、及び濾過からなる操作を更に２回繰返した後、回収した銀粒子を純水１８Ｌ中に投入し、撹拌及び濾過からなる操作を行った。濾過後、銀粒子をステンレスパッドに移し、真空乾燥機にて６０℃で１５時間乾燥して銀粉を得た。 The silver solution after completion of stirring was filtered using a filter press, and the silver particles were separated into solid and liquid. Subsequently, the recovered silver particles were put into 18 L of 0.01 mol / L NaOH aqueous solution, stirred for 15 minutes, and then recovered by filtration with a filter press. The operations consisting of adding to an aqueous NaOH solution, stirring, and filtration were repeated twice more, and then the collected silver particles were put into 18 L of pure water, and operations consisting of stirring and filtration were performed. After filtration, the silver particles were transferred to a stainless steel pad and dried in a vacuum dryer at 60 ° C. for 15 hours to obtain silver powder.

得られた銀粉を走査電子顕微鏡（ＳＥＭ）により観察したところ、ＳＥＭ観察による平均粒径が０．７９μｍであり、粒径の標準偏差（σ）を平均粒径（Ave.）で除した値が０．１５であり、高分散性を有し、ペースト用銀粉として良好であることが確認された。また、銀粉に含有されている塩素濃度について、得られた銀粉を硝酸で分解し、塩化銀をろ過分離した後に還元して遊離した塩化物イオンをイオンクロマトグラフ装置（日本ダイオネクス（株）製、ＩＣＳ−１０００）を用いて分析したところ、塩素濃度は２２ｐｐｍであった。 When the obtained silver powder was observed with a scanning electron microscope (SEM), the average particle diameter by SEM observation was 0.79 μm, and the value obtained by dividing the standard deviation (σ) of the particle diameter by the average particle diameter (Ave.) 0.15, high dispersibility, and good as a silver powder for paste. Moreover, about the chlorine concentration contained in silver powder, the obtained silver powder is decomposed with nitric acid, and the chloride ion which is reduced and reduced after filtration and separation of silver chloride is ion chromatograph device (manufactured by Nippon Dionex Co., Ltd., When analyzed using ICS-1000), the chlorine concentration was 22 ppm.

（実施例２）
３８℃の温水ジャケットで加熱した槽中において液温３６℃に保持した２５質量％アンモニア水３６Ｌに、塩化銀２７０５g（住友金属鉱山（株）製、純度９９.９９９９％、水分率１０．５５％）を撹拌しながら投入して銀溶液を作製した。消泡剤（（株）アデカ製、アデカノールＬＧ−１２６）を体積比で１００倍に希釈し、この消泡剤希釈液２４ｍｌを作製した銀溶液に添加して、得られた銀溶液を温浴中において３６℃に保持した。 (Example 2)
In a tank heated with a hot water jacket at 38 ° C., 25 L ammonia water 36 L maintained at a liquid temperature of 36 ° C., 2705 g of silver chloride (manufactured by Sumitomo Metal Mining Co., Ltd., purity 99.9999%, moisture content 10.55%) ) With stirring to prepare a silver solution. An antifoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times by volume, and 24 ml of this antifoaming agent diluted solution was added to the prepared silver solution, and the resulting silver solution was heated in a warm bath At 36 ° C.

次に、還元剤のアスコルビン酸１２７９ｇ（関東化学（株）製、試薬）を、３０℃の純水４．５５Ｌに溶解した。また、分散剤のポリビニルアルコール３８７ｇ（（株）クラレ製、ＰＶＡ２０５）を５０℃の純水１０Ｌに溶解した。これら２液を混合して還元剤溶液とし、その温度を３６℃に調整した。 Next, 1279 g of a reducing agent, ascorbic acid (manufactured by Kanto Chemical Co., Inc., reagent) was dissolved in 4.55 L of 30 ° C. pure water. Further, 387 g of a polyvinyl alcohol as a dispersant (manufactured by Kuraray Co., Ltd., PVA205) was dissolved in 10 L of pure water at 50 ° C. These two liquids were mixed to form a reducing agent solution, and the temperature was adjusted to 36 ° C.

銀溶液と還元剤溶液を、スムーズフローポンプ（（株）タクミナ製ＡＰＬ−５、ＢＰＬ−２）を使用して、それぞれ、２．４Ｌ／分、０．８Ｌ／分で反応管に供給し、反応管から排出された反応液を撹拌しながら受槽で保持した。反応管としては、内径１０ｍｍのＹ字管を使用し、銀液と還元剤溶液を供給する管のなす角度を６０°とした。また、反応管には、銀液と還元剤溶液の合流点の下方にスタティックミキサーを配置した。スタティックミキサーは、右と左のエレメントを交互に８個とした。還元反応を送液中に完全に終了させるため、内径１２ｍｍ長さ１０ｍの軟質塩化ビニル樹脂製チューブを反応管出側に接続して、反応液を受槽に送液した。このときの還元速度は、銀量で１０９ｇ／分であり、反応液中の銀濃度は３４．０ｇ／Ｌとなる。また、供給速度から求めた銀１モルに対するアスコルビン酸の混合比は０．３５モルとなる。また、分散剤のポリビニルアルコールの量は、混合時の反応液中の銀量に対して１７質量％となる。さらに、銀溶液と還元剤溶液の供給が終了した後、受槽内での攪拌を６０分継続した。 The silver solution and the reducing agent solution are supplied to the reaction tube at 2.4 L / min and 0.8 L / min, respectively, using a smooth flow pump (APL-5, BPL-2 manufactured by Takumina Co., Ltd.) The reaction liquid discharged from the reaction tube was held in a receiving tank while stirring. A Y-tube having an inner diameter of 10 mm was used as the reaction tube, and the angle formed by the tube for supplying the silver solution and the reducing agent solution was 60 °. Moreover, the static mixer was arrange | positioned under the confluence | merging point of silver liquid and a reducing agent solution in the reaction tube. The static mixer had eight right and left elements alternately. In order to complete the reduction reaction during the liquid feeding, a soft vinyl chloride resin tube having an inner diameter of 12 mm and a length of 10 m was connected to the outlet side of the reaction tube, and the reaction liquid was fed to the receiving tank. The reduction rate at this time is 109 g / min in terms of silver, and the silver concentration in the reaction solution is 34.0 g / L. Moreover, the mixing ratio of ascorbic acid to 1 mol of silver determined from the supply rate is 0.35 mol. Moreover, the quantity of the polyvinyl alcohol of a dispersing agent will be 17 mass% with respect to the silver quantity in the reaction liquid at the time of mixing. Furthermore, after the supply of the silver solution and the reducing agent solution was completed, stirring in the receiving tank was continued for 60 minutes.

撹拌終了後の銀溶液を、フィルタープレス機を使用して濾過し、銀粒子を固液分離した。続いて、回収した銀粒子を０．０１ｍｏｌ／ＬのＮａＯＨ水溶液２６Ｌ中に投入し、１５分間撹拌した後、フィルタープレス機で濾過して回収した。ＮａＯＨ水溶液への投入、撹拌、及び濾過からなる操作を更に２回繰返した後、回収した銀粒子を純水２６Ｌ中に投入し、撹拌及び濾過からなる操作を行った。濾過後、銀粒子をステンレスパッドに移し、真空乾燥機にて６０℃で１５時間乾燥して銀粉を得た。 The silver solution after completion of stirring was filtered using a filter press, and the silver particles were separated into solid and liquid. Subsequently, the collected silver particles were put into 26 L of 0.01 mol / L NaOH aqueous solution, stirred for 15 minutes, and then collected by filtration with a filter press. The operation consisting of adding to an aqueous NaOH solution, stirring and filtration was repeated twice more, and then the collected silver particles were put into 26 L of pure water, and the operation consisting of stirring and filtration was performed. After filtration, the silver particles were transferred to a stainless steel pad and dried in a vacuum dryer at 60 ° C. for 15 hours to obtain silver powder.

得られた銀粉を走査電子顕微鏡（ＳＥＭ）により観察したところ、ＳＥＭ観察による平均粒径が１．０１μｍであり、粒径の標準偏差を平均粒径で除した値が０．１６であり、高分散性を有し、ペースト用銀粉として良好であることが確認された。また、実施例１と同様にして銀粉に含有されている塩素濃度を分析したところ１９ｐｐｍであった。 When the obtained silver powder was observed with a scanning electron microscope (SEM), the average particle diameter by SEM observation was 1.01 μm, the value obtained by dividing the standard deviation of the particle diameter by the average particle diameter was 0.16, and high It was confirmed that it has dispersibility and is good as a silver powder for paste. Moreover, when the chlorine concentration contained in silver powder was analyzed like Example 1, it was 19 ppm.

（実施例３）
３８℃の温浴中において液温３６℃に保持した２５質量％アンモニア水７．３５Ｌに、塩化銀８１ｇ（住友金属鉱山（株）製、純度９９．９９９９％、水分率１０．５５％）を撹拌しながら投入して銀溶液を作製した。消泡剤（（株）アデカ製、アデカノールＬＧ−１２６）を体積比で１００倍に希釈し、この消泡剤希釈液０．７ｍｌを作製した銀溶液に添加して、得られた銀溶液を温浴中において３６℃に保持した。 (Example 3)
Silver chloride 81g (Sumitomo Metal Mining Co., Ltd., purity 99.9999%, moisture content 10.55%) was stirred into 7.35 L of 25% by mass ammonia water kept at a temperature of 36 ° C. in a 38 ° C. bath. Then, a silver solution was prepared. An antifoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times in volume ratio, and 0.7 ml of this antifoaming agent diluted solution was added to the prepared silver solution. Maintained at 36 ° C. in a warm bath.

次に、還元剤のアスコルビン酸３５ｇ（関東化学（株）製、試薬）を、３０℃の純水１．０Ｌに溶解した。また、分散剤のポリビニルアルコール１１ｇ（（株）クラレ製、ＰＶＡ２０５）を５０℃の純水１．７１Ｌに溶解した。これら２液を混合して還元剤溶液とし、その温度を３６℃に調整した。 Next, 35 g of ascorbic acid as a reducing agent (manufactured by Kanto Chemical Co., Inc., reagent) was dissolved in 1.0 L of pure water at 30 ° C. Moreover, 11 g of polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA205) as a dispersant was dissolved in 1.71 L of pure water at 50 ° C. These two liquids were mixed to form a reducing agent solution, and the temperature was adjusted to 36 ° C.

銀溶液と還元剤溶液を、チューブポンプを使用して、それぞれ、２．７Ｌ／分、０．９Ｌ／分で反応管に供給し、反応管から排出された反応液を撹拌しながら受槽で保持した。反応管としては、銀溶液の供給方向に対する還元剤溶液の供給方向を０°とした、両液を混合撹拌するガラス製の同芯管（銀溶液供給管：内径１０．０ｍｍ、還元剤溶液供給管：内径３．６ｍｍ、混合管長：１００ｍｍ）を使用した。還元反応を送液中に完全に終了させるため、内径１２ｍｍ長さ１０ｍの軟質塩化ビニル樹脂製チューブを反応管出側に接続して、反応液を受槽に送液した。このときの還元速度は、銀量で１８ｇ／分であり、反応液中の銀濃度は５．０ｇ／Ｌとなる。また、供給速度から求めた銀１モルに対するアスコルビン酸の混合比は０．３５モルとなる。また、分散剤のポリビニルアルコールの量は、混合時の反応液中の銀量に対して１７質量％となる。さらに、銀溶液と還元剤溶液の供給が終了した後、受槽内での攪拌を６０分継続した。 The silver solution and the reducing agent solution are supplied to the reaction tube at a rate of 2.7 L / min and 0.9 L / min, respectively, using a tube pump, and the reaction solution discharged from the reaction tube is held in a receiving tank while stirring. did. As a reaction tube, a glass concentric tube (silver solution supply tube: inner diameter 10.0 mm, reducing agent solution supply) in which both solutions are mixed and stirred with the supply direction of the reducing agent solution relative to the supply direction of the silver solution being 0 °. (Tube: inner diameter 3.6 mm, mixing tube length: 100 mm) was used. In order to complete the reduction reaction during the liquid feeding, a soft vinyl chloride resin tube having an inner diameter of 12 mm and a length of 10 m was connected to the outlet side of the reaction tube, and the reaction liquid was fed to the receiving tank. The reduction rate at this time is 18 g / min in terms of silver, and the silver concentration in the reaction solution is 5.0 g / L. Moreover, the mixing ratio of ascorbic acid to 1 mol of silver determined from the supply rate is 0.35 mol. Moreover, the quantity of the polyvinyl alcohol of a dispersing agent will be 17 mass% with respect to the silver quantity in the reaction liquid at the time of mixing. Furthermore, after the supply of the silver solution and the reducing agent solution was completed, stirring in the receiving tank was continued for 60 minutes.

撹拌終了後の銀溶液を、開口径０．１μｍのメンブレンフィルターを使用して濾過し、銀粒子を固液分離した。続いて、回収した銀粒子を０．０１ｍｏｌ／ＬのＮａＯＨ水溶液０．８Ｌ中に投入し、１５分間撹拌した後、開口径０．１μｍのメンブレンフィルターで濾過して回収した。ＮａＯＨ水溶液への投入、撹拌、及び濾過からなる操作を更に２回繰返した後、回収した銀粒子を純水０．８Ｌ中に投入し、撹拌及び濾過からなる操作を行った。濾過後、銀粒子をステンレスパッドに移し、真空乾燥機にて６０℃で１５時間乾燥して銀粉を得た。 The silver solution after stirring was filtered using a membrane filter having an opening diameter of 0.1 μm to separate the silver particles into solid and liquid. Subsequently, the collected silver particles were put into 0.8 L of 0.01 mol / L NaOH aqueous solution, stirred for 15 minutes, and then collected by filtration through a membrane filter having an opening diameter of 0.1 μm. The operation consisting of adding to an aqueous NaOH solution, stirring, and filtration was repeated twice more, and then the collected silver particles were put into 0.8 L of pure water, and the operation consisting of stirring and filtration was performed. After filtration, the silver particles were transferred to a stainless steel pad and dried in a vacuum dryer at 60 ° C. for 15 hours to obtain silver powder.

得られた銀粉を走査電子顕微鏡（ＳＥＭ）により観察したところ、ＳＥＭ観察による平均粒径が０．３９μｍであり、粒径の標準偏差を平均粒径で除した値が０．２０であり、高分散性を有し、ペースト用銀粉として良好であることが確認された。また、実施例１と同様にして銀粉に含有されている塩素濃度を分析したところ２３ｐｐｍであった。 When the obtained silver powder was observed with a scanning electron microscope (SEM), the average particle diameter by SEM observation was 0.39 μm, and the value obtained by dividing the standard deviation of the particle diameter by the average particle diameter was 0.20. It was confirmed that it has dispersibility and is good as a silver powder for paste. Moreover, when the chlorine concentration contained in silver powder was analyzed like Example 1, it was 23 ppm.

（実施例４）
３８℃の温浴中において液温３６℃に保持した２５質量％アンモニア水４．９１Ｌに、塩化銀１２８ｇ（住友金属鉱山（株）製、純度９９．９９９９％、水分率１０．５５％）を撹拌しながら投入して銀溶液を作製した。消泡剤（（株）アデカ製、アデカノールＬＧ−１２６）を体積比で１００倍に希釈し、この消泡剤希釈液１．１ｍｌを作製した銀溶液に添加して、得られた銀溶液を温浴中において３６℃に保持した。 Example 4
Stirring silver chloride 128g (manufactured by Sumitomo Metal Mining Co., Ltd., purity 99.9999%, moisture content 10.55%) to 4.91 L of 25% by mass ammonia water maintained at 36 ° C. in a 38 ° C. bath. Then, a silver solution was prepared. An antifoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times in volume ratio, and 1.1 ml of this antifoaming agent diluted solution was added to the prepared silver solution. Maintained at 36 ° C. in a warm bath.

次に、還元剤のアスコルビン酸５８ｇ（関東化学（株）製、試薬）を、３０℃の純水０．６Ｌに溶解した。また、分散剤のポリビニルアルコール４６ｇ（（株）クラレ製、ＰＶＡ２０５）を５０℃の純水１．３１Ｌに溶解した。これら２液を混合して還元剤溶液とし、その温度を３６℃に調整した。 Next, 58 g of ascorbic acid as a reducing agent (manufactured by Kanto Chemical Co., Inc., reagent) was dissolved in 0.6 L of pure water at 30 ° C. Moreover, 46 g of polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA205) as a dispersant was dissolved in 1.31 L of pure water at 50 ° C. These two liquids were mixed to form a reducing agent solution, and the temperature was adjusted to 36 ° C.

銀溶液と還元剤溶液を、チューブポンプを使用して、それぞれ、２．７Ｌ／分、０．９Ｌ／分で反応管に供給し、反応管から排出された反応液を撹拌しながら受槽で保持した。反応管としては、銀溶液の供給方向に対する還元剤溶液の供給方向を０°とした、両液を混合撹拌するガラス製の同芯管（銀溶液供給管：内径１０．０ｍｍ、還元剤溶液供給管：内径３．６ｍｍ、混合管長：１００ｍｍ）を用いた。還元反応を送液中に完全に終了させるため、内径１２ｍｍ長さ１０ｍの軟質塩化ビニル樹脂製チューブを反応管出側に接続して、反応液を受槽に送液した。このときの還元速度は、銀量で４２ｇ／分であり、反応液中の銀濃度は１１．８ｇ／Ｌとなる。また、供給速度から求めた銀１モルに対するアスコルビン酸の混合比は０．３５モルとなる。また、分散剤のポリビニルアルコールの量は、混合時の反応液中の銀量に対して１７質量％となる。さらに、銀溶液と還元剤溶液の供給が終了した後、受槽内での攪拌を６０分継続した。 The silver solution and the reducing agent solution are supplied to the reaction tube at a rate of 2.7 L / min and 0.9 L / min, respectively, using a tube pump, and the reaction solution discharged from the reaction tube is held in a receiving tank while stirring. did. As a reaction tube, a glass concentric tube (silver solution supply tube: inner diameter 10.0 mm, reducing agent solution supply) in which both solutions are mixed and stirred with the supply direction of the reducing agent solution relative to the supply direction of the silver solution being 0 °. (Tube: inner diameter 3.6 mm, mixing tube length: 100 mm) was used. In order to complete the reduction reaction during the liquid feeding, a soft vinyl chloride resin tube having an inner diameter of 12 mm and a length of 10 m was connected to the outlet side of the reaction tube, and the reaction liquid was fed to the receiving tank. The reduction rate at this time is 42 g / min in terms of silver, and the silver concentration in the reaction solution is 11.8 g / L. Moreover, the mixing ratio of ascorbic acid to 1 mol of silver determined from the supply rate is 0.35 mol. Moreover, the quantity of the polyvinyl alcohol of a dispersing agent will be 17 mass% with respect to the silver quantity in the reaction liquid at the time of mixing. Furthermore, after the supply of the silver solution and the reducing agent solution was completed, stirring in the receiving tank was continued for 60 minutes.

撹拌終了後の銀溶液を、開口径０．１μｍのメンブレンフィルターを使用して濾過し、銀粒子を固液分離した。続いて、回収した銀粒子を０．０１ｍｏｌ／ＬのＮａＯＨ水溶液１．２Ｌ中に投入し、１５分間撹拌した後、開口径０．１μｍのメンブレンフィルターで濾過して回収した。ＮａＯＨ水溶液への投入、撹拌、及び濾過からなる操作を更に２回繰返した後、回収した銀粒子を純水１．２Ｌ中に投入し、撹拌及び濾過からなる操作を行った。濾過後、銀粒子をステンレスパッドに移し、真空乾燥機にて６０℃で１５時間乾燥して銀粉を得た。 The silver solution after stirring was filtered using a membrane filter having an opening diameter of 0.1 μm to separate the silver particles into solid and liquid. Subsequently, the collected silver particles were put into 1.2 L of 0.01 mol / L NaOH aqueous solution, stirred for 15 minutes, and then collected by filtration through a membrane filter having an opening diameter of 0.1 μm. The operation consisting of adding to an aqueous NaOH solution, stirring and filtration was repeated twice more, and then the collected silver particles were put into 1.2 L of pure water, and the operation consisting of stirring and filtration was performed. After filtration, the silver particles were transferred to a stainless steel pad and dried in a vacuum dryer at 60 ° C. for 15 hours to obtain silver powder.

得られた銀粉を走査電子顕微鏡（ＳＥＭ）により観察したところ、ＳＥＭ観察による平均粒径が０．５４μｍであり、粒径の標準偏差を平均粒径で除した値が０．２１であり、高分散性を有し、ペースト用銀粉として良好であることが確認された。また、実施例１と同様にして銀粉に含有されている塩素濃度を分析したところ３５ｐｐｍであった。 When the obtained silver powder was observed with a scanning electron microscope (SEM), the average particle diameter by SEM observation was 0.54 μm, and the value obtained by dividing the standard deviation of the particle diameter by the average particle diameter was 0.21. It was confirmed that it has dispersibility and is good as a silver powder for paste. Moreover, when the chlorine concentration contained in silver powder was analyzed like Example 1, it was 35 ppm.

（実施例５）
３８℃の温水ジャケットで加熱した槽中において液温３６℃に保持した２５質量％アンモニア水９０Ｌに、塩化銀５２４９g（住友金属鉱山（株）製、純度９９．９９９９％、水分率１０．５５％）を撹拌しながら投入して銀溶液を作製した。消泡剤（（株）アデカ製、アデカノールＬＧ−１２６）を体積比で１００倍に希釈し、この消泡剤希釈液４６ｍｌを作製した銀溶液に添加して、得られた銀溶液を温浴中において３６℃に保持した。 (Example 5)
In a tank heated with a 38 ° C hot water jacket, 90 L of 25 mass% ammonia water maintained at a liquid temperature of 36 ° C, 5249 g of silver chloride (manufactured by Sumitomo Metal Mining Co., Ltd., purity 99.9999%, moisture content 10.55%) ) With stirring to prepare a silver solution. An antifoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times by volume, and 46 ml of this antifoaming agent diluted solution was added to the prepared silver solution, and the resulting silver solution was heated in a warm bath At 36 ° C.

次に、還元剤のアスコルビン酸２１９９ｇ（関東化学（株）製、試薬）を、３０℃の純水１０Ｌに溶解した。また、分散剤のポリビニルアルコール６６５ｇ（（株）クラレ製、ＰＶＡ２０５）を３６℃の純水２２．２３Ｌに溶解した。これら２液を混合して還元剤溶液とし、その温度を３６℃に調整した。 Next, 2199 g of a reducing agent, ascorbic acid (manufactured by Kanto Chemical Co., Inc., reagent) was dissolved in 10 L of pure water at 30 ° C. In addition, 665 g of polyvinyl alcohol (PVA205, manufactured by Kuraray Co., Ltd.) as a dispersant was dissolved in 22.23 L of pure water at 36 ° C. These two liquids were mixed to form a reducing agent solution, and the temperature was adjusted to 36 ° C.

銀溶液と還元剤溶液を、スムーズフローポンプ（（株）タクミナ製ＡＰＬ−５、ＢＰＬ−２）を使用して、それぞれ、２．７Ｌ／分、０．９Ｌ／分で反応管に供給し、反応管から排出された反応液を撹拌しながら受槽で保持した。反応管としては、銀溶液の供給方向に対する還元剤溶液の供給方向を０°とした、両液を混合撹拌するガラス製の同芯管（銀溶液供給管：内径１０．０ｍｍ、還元剤溶液供給管：内径３．６ｍｍ、混合管長：１００ｍｍ）を用いた。還元反応を送液中に完全に終了させるため、内径１２ｍｍ長さ１０ｍの軟質塩化ビニル樹脂製チューブを反応管出側に接続して、反応液を受槽に送液した。このときの還元速度は、銀量で９５ｇ／分であり、反応液中の銀濃度は２６．５ｇ／Ｌとなる。また、供給速度から求めた銀１モルに対するアスコルビン酸の混合比は０．３５モルとなる。また、分散剤のポリビニルアルコールの量は、混合時の反応液中の銀量に対して１７質量％となる。さらに、銀溶液と還元剤溶液の供給が終了した後、受槽内での攪拌を６０分継続した。 The silver solution and the reducing agent solution were supplied to the reaction tube at a rate of 2.7 L / min and 0.9 L / min, respectively, using a smooth flow pump (APL-5, BPL-2 manufactured by Takumina Co., Ltd.) The reaction liquid discharged from the reaction tube was held in a receiving tank while stirring. As a reaction tube, a glass concentric tube (silver solution supply tube: inner diameter 10.0 mm, reducing agent solution supply) in which both solutions are mixed and stirred with the supply direction of the reducing agent solution relative to the supply direction of the silver solution being 0 °. (Tube: inner diameter 3.6 mm, mixing tube length: 100 mm) was used. In order to complete the reduction reaction during the liquid feeding, a soft vinyl chloride resin tube having an inner diameter of 12 mm and a length of 10 m was connected to the outlet side of the reaction tube, and the reaction liquid was fed to the receiving tank. The reduction rate at this time is 95 g / min in terms of silver, and the silver concentration in the reaction solution is 26.5 g / L. Moreover, the mixing ratio of ascorbic acid to 1 mol of silver determined from the supply rate is 0.35 mol. Moreover, the quantity of the polyvinyl alcohol of a dispersing agent will be 17 mass% with respect to the silver quantity in the reaction liquid at the time of mixing. Furthermore, after the supply of the silver solution and the reducing agent solution was completed, stirring in the receiving tank was continued for 60 minutes.

撹拌終了後の銀溶液を、フィルタープレス機を使用して濾過し、銀粒子を固液分離した。続いて、回収した銀粒子を０．０１ｍｏｌ／ＬのＮａＯＨ水溶液４９Ｌ中に投入し、１５分間撹拌した後、フィルタープレス機で濾過して回収した。ＮａＯＨ水溶液への投入、撹拌、及び濾過からなる操作を更に２回繰返した後、回収した銀粒子を純水４９Ｌ中に投入し、撹拌及び濾過からなる操作を行った。濾過後、銀粒子をステンレスパッドに移し、真空乾燥機にて６０℃で１５時間乾燥して銀粉を得た。 The silver solution after completion of stirring was filtered using a filter press, and the silver particles were separated into solid and liquid. Subsequently, the collected silver particles were put into 49 L of 0.01 mol / L NaOH aqueous solution, stirred for 15 minutes, and then collected by filtration with a filter press. The operations consisting of adding to an aqueous NaOH solution, stirring and filtration were repeated twice more, and then the collected silver particles were put into 49 L of pure water, and operations consisting of stirring and filtration were performed. After filtration, the silver particles were transferred to a stainless steel pad and dried in a vacuum dryer at 60 ° C. for 15 hours to obtain silver powder.

得られた銀粉を走査電子顕微鏡（ＳＥＭ）のより観察したところ、ＳＥＭ観察による平均粒径が０．９１μｍであり、粒径の標準偏差を平均粒径で除した値が０．１５であり、高分散性を有し、ペースト用銀粉として良好であることが確認された。また、実施例１と同様にして銀粉に含有されている塩素濃度を分析したところ２０ｐｐｍであった。 When the obtained silver powder was observed with a scanning electron microscope (SEM), the average particle diameter by SEM observation was 0.91 μm, and the value obtained by dividing the standard deviation of the particle diameter by the average particle diameter was 0.15, It was confirmed that it has high dispersibility and is good as a silver powder for paste. Moreover, when the chlorine concentration contained in silver powder was analyzed like Example 1, it was 20 ppm.

（実施例６）
３８℃の温浴中において液温３６℃に保持した２５質量％アンモニア水４．９１Ｌに、塩化銀４３４ｇ（住友金属鉱山（株）製、純度９９．９９９９％、水分率１０．５５％）を撹拌しながら投入して銀溶液を作製した。消泡剤（（株）アデカ製、アデカノールＬＧ−１２６）を体積比で１００倍に希釈し、この消泡剤希釈液３．８ｍｌを作製した銀溶液に添加して、得られた銀溶液を温浴中において３６℃に保持した。 (Example 6)
Silver chloride 434g (manufactured by Sumitomo Metal Mining Co., Ltd., purity 99.9999%, moisture content 10.55%) was stirred in 4.91 L of 25% by mass ammonia water maintained at 36 ° C in a 38 ° C warm bath. Then, a silver solution was prepared. An antifoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times in volume ratio, and 3.8 ml of this antifoaming agent dilution was added to the prepared silver solution. Maintained at 36 ° C. in a warm bath.

次に、還元剤のアスコルビン酸１９７ｇ（関東化学（株）製、試薬）を、３０℃の純水０．６Ｌに溶解した。また、分散剤のポリビニルアルコール１２．１ｇ（（株）クラレ製、ＰＶＡ２０５）を５０℃の純水１．３１Ｌに溶解した。これら２液を混合して還元剤溶液とし、その温度を３６℃に調整した。 Next, 197 g of a reducing agent, ascorbic acid (manufactured by Kanto Chemical Co., Inc., reagent) was dissolved in 0.6 L of 30 ° C. pure water. Moreover, 12.1 g of polyvinyl alcohol as a dispersant (manufactured by Kuraray Co., Ltd., PVA205) was dissolved in 1.31 L of pure water at 50 ° C. These two liquids were mixed to form a reducing agent solution, and the temperature was adjusted to 36 ° C.

銀溶液と還元剤溶液を、チューブポンプを使用して、それぞれ、２．７Ｌ／分、０．９Ｌ／分で反応管に供給し、反応管から排出された反応液を撹拌しながら受槽で保持した。反応管としては、銀溶液の供給方向に対する還元剤溶液の供給方向を０°とした、両液を混合撹拌するガラス製の同芯管（銀溶液供給管：内径１０．０ｍｍ、還元剤溶液供給管：内径３．６ｍｍ、混合管長：１００ｍｍ）を用いた。還元反応を送液中に完全に終了させるため、内径１２ｍｍ長さ１０ｍの軟質塩化ビニル樹脂製チューブを反応管出側に接続して、反応液を受槽に送液した。このときの還元速度は、銀量で１４４ｇ／分であり、反応液中の銀濃度は４０．１ｇ／Ｌとなる。また、供給速度から求めた銀１モルに対するアスコルビン酸の混合比は０．３５モルとなる。また、分散剤のポリビニルアルコールの量は、混合時の反応液中の銀量に対して１７質量％となる。さらに、銀溶液と還元剤溶液の供給が終了した後、受槽内での攪拌を６０分継続した。 The silver solution and the reducing agent solution are supplied to the reaction tube at a rate of 2.7 L / min and 0.9 L / min, respectively, using a tube pump, and the reaction solution discharged from the reaction tube is held in a receiving tank while stirring. did. As a reaction tube, a glass concentric tube (silver solution supply tube: inner diameter 10.0 mm, reducing agent solution supply) in which both solutions are mixed and stirred with the supply direction of the reducing agent solution relative to the supply direction of the silver solution being 0 °. (Tube: inner diameter 3.6 mm, mixing tube length: 100 mm) was used. In order to complete the reduction reaction during the liquid feeding, a soft vinyl chloride resin tube having an inner diameter of 12 mm and a length of 10 m was connected to the outlet side of the reaction tube, and the reaction liquid was fed to the receiving tank. The reduction rate at this time is 144 g / min in terms of silver, and the silver concentration in the reaction solution is 40.1 g / L. Moreover, the mixing ratio of ascorbic acid to 1 mol of silver determined from the supply rate is 0.35 mol. Moreover, the quantity of the polyvinyl alcohol of a dispersing agent will be 17 mass% with respect to the silver quantity in the reaction liquid at the time of mixing. Furthermore, after the supply of the silver solution and the reducing agent solution was completed, stirring in the receiving tank was continued for 60 minutes.

撹拌終了後の銀溶液を、開口径０．３μｍのメンブレンフィルターを使用して濾過し、銀粒子を固液分離した。続いて、回収した銀粒子を０．０１ｍｏｌ／ＬのＮａＯＨ水溶液４．１Ｌ中に投入し、１５分間撹拌した後、開口径０．３μｍのメンブレンフィルターで濾過して回収した。ＮａＯＨ水溶液への投入、撹拌、及び濾過からなる操作を更に２回繰返した後、回収した銀粒子を純水４．１Ｌ中に投入し、撹拌及び濾過からなる操作を行った。濾過後、銀粒子をステンレスパッドに移し、真空乾燥機にて６０℃で１５時間乾燥して銀粉を得た。 After the stirring, the silver solution was filtered using a membrane filter having an opening diameter of 0.3 μm to separate the silver particles into solid and liquid. Subsequently, the collected silver particles were put into 4.1 L of 0.01 mol / L NaOH aqueous solution, stirred for 15 minutes, and then collected by filtration through a membrane filter having an opening diameter of 0.3 μm. After the operation consisting of adding to an aqueous NaOH solution, stirring and filtration was repeated twice more, the collected silver particles were put into 4.1 L of pure water, and the operation consisting of stirring and filtration was performed. After filtration, the silver particles were transferred to a stainless steel pad and dried in a vacuum dryer at 60 ° C. for 15 hours to obtain silver powder.

得られた銀粉を走査電子顕微鏡（ＳＥＭ）により観察したところ、ＳＥＭ観察による平均粒径が１．１８μｍであり、粒径の標準偏差を平均粒径で除した値が０．２３であり、ペースト用銀粉として良好であることが確認された。 When the obtained silver powder was observed with a scanning electron microscope (SEM), the average particle diameter by SEM observation was 1.18 μm, and the value obtained by dividing the standard deviation of the particle diameter by the average particle diameter was 0.23. It was confirmed that the silver powder for use was good.

（実施例７）
３８℃の温浴中において液温３６℃に保持した２５質量％アンモニア水１．１１Ｌに、塩化銀１７８ｇ（住友金属鉱山（株）製、純度９９．９９９９％、水分率１２．５％）を撹拌しながら投入して銀溶液を作製した。消泡剤（（株）アデカ製、アデカノールＬＧ−１２６）を体積比で１００倍に希釈し、この消泡剤希釈液１．５ｍｌを作製した銀溶液に添加して、得られた銀溶液を温浴中において３６℃に保持した。 (Example 7)
In 1.11 L of 25% by mass ammonia water maintained at a liquid temperature of 36 ° C. in a 38 ° C. bath, 178 g of silver chloride (manufactured by Sumitomo Metal Mining Co., Ltd., purity 99.9999%, moisture content 12.5%) is stirred. Then, a silver solution was prepared. A defoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times by volume, and 1.5 ml of this defoaming agent diluted solution was added to the prepared silver solution. Maintained at 36 ° C. in a warm bath.

次に、還元剤のアスコルビン酸７４ｇ（関東化学（株）製、試薬）を、３０℃の純水０．３Ｌに溶解した。また、分散剤のポリビニルアルコール８ｇ（（株）クラレ製、ＰＶＡ２０５）を５０℃の純水０．１５Ｌに溶解した。これら２液を混合して還元剤溶液とし、その温度を３６℃に調整した。 Next, 74 g of a reducing agent, ascorbic acid (manufactured by Kanto Chemical Co., Inc., reagent) was dissolved in 0.3 L of pure water at 30 ° C. Moreover, 8 g of polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA205) as a dispersant was dissolved in 0.15 L of pure water at 50 ° C. These two liquids were mixed to form a reducing agent solution, and the temperature was adjusted to 36 ° C.

銀溶液と還元剤溶液を、モーノポンプ（兵神装備（株）製３ＮＢ−０６、３ＮＢ−０４）を使用して、それぞれ、０．２４Ｌ／分、０．０８Ｌ／分で反応管に供給し、反応管から排出された反応液を撹拌しながら受槽で保持した。反応管としては、内径１３ｍｍ長さ５００ｍｍのポリエチレン製パイプを約１６°の傾斜で固定したものを使用した。その上端から銀液を流し、その３０ｍｍ下流側から還元液を流した。銀溶液の供給方向に対する還元剤溶液の供給方向を９０°とした。還元反応を送液中に完全に終了させるため、内径１３ｍｍ長さ１ｍの軟質塩化ビニル樹脂製チューブを反応管出側に接続して、反応液を受槽に送液した。このときの還元速度は、銀量で２３ｇ／分であり、反応液中の銀濃度は７１．０ｇ／Ｌとなる。また、供給速度から求めた銀１モルに対するアスコルビン酸の混合比は０．３０モルとなる。また、分散剤のポリビニルアルコールの量は、混合時の反応液中の銀量に対して５質量％となる。さらに、銀溶液と還元剤溶液の供給が終了した後、受槽内での攪拌を３０分継続した。 The silver solution and the reducing agent solution were supplied to the reaction tube at 0.24 L / min and 0.08 L / min, respectively, using a MONO pump (3NB-06, 3NB-04 manufactured by Hyojin Equipment Co., Ltd.) The reaction liquid discharged from the reaction tube was held in a receiving tank while stirring. As the reaction tube, a polyethylene pipe having an inner diameter of 13 mm and a length of 500 mm fixed at an inclination of about 16 ° was used. A silver solution was poured from the upper end, and a reducing solution was fed from the downstream side of 30 mm. The supply direction of the reducing agent solution relative to the supply direction of the silver solution was 90 °. In order to complete the reduction reaction during the liquid feeding, a soft vinyl chloride resin tube having an inner diameter of 13 mm and a length of 1 m was connected to the outlet side of the reaction tube, and the reaction liquid was fed to the receiving tank. The reduction rate at this time is 23 g / min in terms of silver, and the silver concentration in the reaction solution is 71.0 g / L. Moreover, the mixing ratio of ascorbic acid to 1 mol of silver determined from the supply rate is 0.30 mol. Moreover, the quantity of the polyvinyl alcohol of a dispersing agent will be 5 mass% with respect to the silver quantity in the reaction liquid at the time of mixing. Furthermore, after the supply of the silver solution and the reducing agent solution was completed, stirring in the receiving tank was continued for 30 minutes.

撹拌終了後の銀溶液を、開口径０．１μｍのメンブレンフィルターを使用して濾過し、銀粒子を固液分離した。続いて、回収した銀粒子を０．０１ｍｏｌ／ＬのＮａＯＨ水溶液１．８Ｌ中に投入し、１５分間撹拌した後、開口径０．１μｍのメンブレンフィルターで濾過して回収した。ＮａＯＨ水溶液への投入、撹拌、及び濾過からなる操作を更に２回繰返した後、回収した銀粒子を純水１．８Ｌ中に投入し、撹拌及び濾過からなる操作を行った。濾過後、銀粒子をステンレスパッドに移し、真空乾燥機にて６０℃で１５時間乾燥して銀粉を得た。 The silver solution after stirring was filtered using a membrane filter having an opening diameter of 0.1 μm to separate the silver particles into solid and liquid. Subsequently, the collected silver particles were put into 1.8 L of 0.01 mol / L NaOH aqueous solution, stirred for 15 minutes, and then collected by filtration through a membrane filter having an opening diameter of 0.1 μm. The operation consisting of adding to an aqueous NaOH solution, stirring, and filtration was repeated twice more, and then the collected silver particles were put into 1.8 L of pure water, and the operation consisting of stirring and filtration was performed. After filtration, the silver particles were transferred to a stainless steel pad and dried in a vacuum dryer at 60 ° C. for 15 hours to obtain silver powder.

得られた銀粉を走査電子顕微鏡（ＳＥＭ）により観察したところ、ＳＥＭ観察による平均粒径が０．７３μｍであり、粒径の標準偏差を平均粒径で除した値が０．２９であり、ペースト用銀粉として良好であることが確認された。 When the obtained silver powder was observed with a scanning electron microscope (SEM), the average particle diameter by SEM observation was 0.73 μm, and the value obtained by dividing the standard deviation of the particle diameter by the average particle diameter was 0.29. It was confirmed that the silver powder for use was good.

（実施例８）
３８℃の温浴中において液温３６℃に保持した２５質量％アンモニア水１．９２Ｌに、塩化銀２９２ｇ（住友金属鉱山（株）製、純度９９．９９９９％、水分率７．９％）を撹拌しながら投入して銀溶液を作製した。消泡剤（（株）アデカ製、アデカノールＬＧ−１２６）を体積比で１００倍に希釈し、この消泡剤希釈液２．６ｍｌを作製した銀溶液に添加して、得られた銀溶液を温浴中において３６℃に保持した。 (Example 8)
292 g of silver chloride (manufactured by Sumitomo Metal Mining Co., Ltd., purity 99.9999%, water content 7.9%) was stirred in 1.92 L of 25% by mass ammonia water maintained at a liquid temperature of 36 ° C. in a 38 ° C. bath. Then, a silver solution was prepared. An antifoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times by volume, and 2.6 ml of this antifoaming agent diluted solution was added to the prepared silver solution. Maintained at 36 ° C. in a warm bath.

次に、還元剤のアスコルビン酸１２６ｇ（関東化学（株）製、試薬）を、３０℃の純水１．０２Ｌに溶解した。また、分散剤のポリビニルアルコール１４ｇ（（株）クラレ製、ＰＶＡ２０５）を５０℃の純水０．５１Ｌに溶解した。これら２液を混合して還元剤溶液とし、その温度を３６℃に調整した。 Next, 126 g of ascorbic acid as a reducing agent (manufactured by Kanto Chemical Co., Inc., reagent) was dissolved in 1.02 L of 30 ° C. pure water. In addition, 14 g of polyvinyl alcohol as a dispersant (manufactured by Kuraray Co., Ltd., PVA205) was dissolved in 0.51 L of pure water at 50 ° C. These two liquids were mixed to form a reducing agent solution, and the temperature was adjusted to 36 ° C.

銀溶液と還元剤溶液を、チューブポンプを使用して、それぞれ、２．１Ｌ／分、０．７Ｌ／分で反応管に供給し、反応管から排出された反応液を撹拌しながら受槽で保持した。反応管としては、内径２５ｍｍ長さ７２５ｍｍの硬質塩化ビニル樹脂製パイプを約１６°の傾斜で固定したものを使用した。その上端から銀液を流し、その３０ｍｍ下流側から還元液を流した。銀溶液の供給方向に対する還元剤溶液の供給方向を９０°とした。還元反応を送液中に完全に終了させるため、内径２５ｍｍ長さ１ｍの軟質塩化ビニル樹脂製チューブを反応管出側に接続して、反応液を受槽に送液した。このときの還元速度は、銀量で１００ｇ／分であり、反応液中の銀濃度は３５．５ｇ／Ｌとなる。また、供給速度から求めた銀１モルに対するアスコルビン酸の混合比は０．３０モルとなる。また、分散剤のポリビニルアルコールの量は、混合時の反応液中の銀量に対して５質量％となる。さらに、銀溶液と還元剤溶液の供給が終了した後、受槽内での攪拌を３０分継続した。 The silver solution and the reducing agent solution are supplied to the reaction tube at 2.1 L / min and 0.7 L / min, respectively, using a tube pump, and the reaction solution discharged from the reaction tube is held in a receiving tank while stirring. did. As the reaction tube, a pipe made of rigid vinyl chloride resin having an inner diameter of 25 mm and a length of 725 mm was fixed at an inclination of about 16 °. A silver solution was poured from the upper end, and a reducing solution was fed from the downstream side of 30 mm. The supply direction of the reducing agent solution relative to the supply direction of the silver solution was 90 °. In order to complete the reduction reaction during the liquid feeding, a soft vinyl chloride resin tube having an inner diameter of 25 mm and a length of 1 m was connected to the outlet side of the reaction tube, and the reaction liquid was fed to the receiving tank. The reduction rate at this time is 100 g / min in terms of silver, and the silver concentration in the reaction solution is 35.5 g / L. Moreover, the mixing ratio of ascorbic acid to 1 mol of silver determined from the supply rate is 0.30 mol. Moreover, the quantity of the polyvinyl alcohol of a dispersing agent will be 5 mass% with respect to the silver quantity in the reaction liquid at the time of mixing. Furthermore, after the supply of the silver solution and the reducing agent solution was completed, stirring in the receiving tank was continued for 30 minutes.

撹拌終了後の銀溶液を、開口径０．１μｍのメンブレンフィルターを使用して濾過し、銀粒子を固液分離した。続いて、回収した銀粒子を０．０１ｍｏｌ／ＬのＮａＯＨ水溶液４Ｌ中に投入し、１５分間撹拌した後、開口径０．１μｍのメンブレンフィルターで濾過して回収した。ＮａＯＨ水溶液への投入、撹拌、及び濾過からなる操作を更に２回繰返した後、回収した銀粒子を純水４Ｌ中に投入し、撹拌及び濾過からなる操作を行った。濾過後、銀粒子をステンレスパッドに移し、真空乾燥機にて６０℃で１５時間乾燥して銀粉を得た。 The silver solution after stirring was filtered using a membrane filter having an opening diameter of 0.1 μm to separate the silver particles into solid and liquid. Subsequently, the collected silver particles were put into 4 L of 0.01 mol / L NaOH aqueous solution, stirred for 15 minutes, and then collected by filtration through a membrane filter having an opening diameter of 0.1 μm. The operation consisting of adding to an aqueous NaOH solution, stirring, and filtration was repeated twice more, and then the collected silver particles were put into 4 L of pure water, and the operation consisting of stirring and filtration was performed. After filtration, the silver particles were transferred to a stainless steel pad and dried in a vacuum dryer at 60 ° C. for 15 hours to obtain silver powder.

得られた銀粉を走査電子顕微鏡（ＳＥＭ）により観察したところ、ＳＥＭ観察による平均粒径が０．５４μｍであり、粒径の標準偏差を平均粒径で除した値が０．３０であり、ペースト用銀粉として良好であることが確認された。 When the obtained silver powder was observed with a scanning electron microscope (SEM), the average particle diameter by SEM observation was 0.54 μm, and the value obtained by dividing the standard deviation of the particle diameter by the average particle diameter was 0.30. It was confirmed that the silver powder for use was good.

（実施例９）
３８℃の温水ジャケットで加熱した槽中において液温３６℃に保持した２５質量％アンモニア水１８．６６Ｌに、塩化銀１４７７ｇ（住友金属鉱山（株）製、純度９９．９９９９％、水分率１１．７％）を撹拌しながら投入して銀溶液を作製した。消泡剤（（株）アデカ製、アデカノールＬＧ−１２６）を体積比で１００倍に希釈し、この消泡剤希釈液１３ｍｌを作製した銀溶液に添加して、得られた銀溶液を温浴中において３６℃に保持した。 Example 9
In a tank heated with a warm water jacket at 38 ° C., 18.66 L of 25% by mass ammonia water kept at a liquid temperature of 36 ° C., 1477 g of silver chloride (manufactured by Sumitomo Metal Mining Co., Ltd., purity 99.9999%, moisture content 11. 7%) was added with stirring to prepare a silver solution. An antifoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times in volume ratio, and 13 ml of this antifoaming agent diluted solution was added to the prepared silver solution. At 36 ° C.

次に、還元剤のアスコルビン酸１０１８ｇ（関東化学（株）製、試薬）を、３０℃の純水２Ｌに溶解した。また、分散剤のポリビニルアルコール２１６ｇ（（株）クラレ製、ＰＶＡ２０５）を３６℃の純水５．７９Ｌに溶解した。これら２液を混合して還元剤溶液とし、その温度を３６℃に調整した。 Next, ascorbic acid 1018 g (manufactured by Kanto Chemical Co., Inc., reagent) as a reducing agent was dissolved in 2 L of 30 ° C. pure water. Also, 216 g of polyvinyl alcohol (PVA205, manufactured by Kuraray Co., Ltd.) as a dispersant was dissolved in 5.79 L of pure water at 36 ° C. These two liquids were mixed to form a reducing agent solution, and the temperature was adjusted to 36 ° C.

銀溶液と還元剤溶液を、スムーズフローポンプ（（株）タクミナ製ＡＰＬ−５、ＢＰＬ−２）を使用して、それぞれ、２．７Ｌ／分、０．９Ｌ／分で反応管に供給し、反応管から排出された反応液を撹拌しながら受槽で保持した。反応管としては、銀溶液の供給方向に対する還元剤溶液の供給方向を１８０°とした、両液を混合撹拌するガラス製の同芯管（銀溶液供給管：内径１０．０ｍｍ、還元剤溶液供給管：内径３．６ｍｍ、混合管長：１００ｍｍ）を用いた。還元反応を送液中に完全に終了させるため、内径１２ｍｍ長さ３．６ｍの軟質塩化ビニル樹脂製チューブを反応管出側に接続して、反応液を受槽に送液した。このときの還元速度は、銀量で１２８ｇ／分であり、反応液中の銀濃度は３５．５ｇ／Ｌとなる。また、供給速度から求めた銀１モルに対するアスコルビン酸の混合比は０．５０モルとなる。また、分散剤のポリビニルアルコールの量は、混合時の反応液中の銀量に対して１７質量％となる。さらに、銀溶液と還元剤溶液の供給が終了した後、受槽内での攪拌を６０分継続した。 The silver solution and the reducing agent solution were supplied to the reaction tube at a rate of 2.7 L / min and 0.9 L / min, respectively, using a smooth flow pump (APL-5, BPL-2 manufactured by Takumina Co., Ltd.) The reaction liquid discharged from the reaction tube was held in a receiving tank while stirring. As a reaction tube, a glass concentric tube (silver solution supply tube: inner diameter 10.0 mm, reducing agent solution supply) in which the supply direction of the reducing agent solution with respect to the silver solution supply direction is 180 ° and the two solutions are mixed and stirred. (Tube: inner diameter 3.6 mm, mixing tube length: 100 mm) was used. In order to complete the reduction reaction during liquid feeding, a soft vinyl chloride resin tube having an inner diameter of 12 mm and a length of 3.6 m was connected to the outlet side of the reaction tube, and the reaction liquid was fed to the receiving tank. The reduction rate at this time is 128 g / min in terms of silver, and the silver concentration in the reaction solution is 35.5 g / L. Moreover, the mixing ratio of ascorbic acid to 1 mol of silver determined from the supply rate is 0.50 mol. Moreover, the quantity of the polyvinyl alcohol of a dispersing agent will be 17 mass% with respect to the silver quantity in the reaction liquid at the time of mixing. Furthermore, after the supply of the silver solution and the reducing agent solution was completed, stirring in the receiving tank was continued for 60 minutes.

撹拌終了後の銀溶液を、フィルタープレス機を使用して濾過し、銀粒子を固液分離した。続いて、回収した銀粒子を０．０１ｍｏｌ／ＬのＮａＯＨ水溶液２５Ｌ中に投入し、１５分間撹拌した後、フィルタープレス機で濾過して回収した。ＮａＯＨ水溶液への投入、撹拌、及び濾過からなる操作を更に２回繰返した後、回収した銀粒子を純水２５Ｌ中に投入し、撹拌及び濾過からなる操作を行った。濾過後、銀粒子をステンレスパッドに移し、真空乾燥機にて６０℃で１５時間乾燥して銀粉を得た。 The silver solution after completion of stirring was filtered using a filter press, and the silver particles were separated into solid and liquid. Subsequently, the collected silver particles were put into 25 L of 0.01 mol / L NaOH aqueous solution, stirred for 15 minutes, and then collected by filtration with a filter press. The operations consisting of adding to an aqueous NaOH solution, stirring, and filtration were repeated twice more, and then the collected silver particles were put into 25 L of pure water, and operations consisting of stirring and filtration were performed. After filtration, the silver particles were transferred to a stainless steel pad and dried in a vacuum dryer at 60 ° C. for 15 hours to obtain silver powder.

得られた銀粉を走査電子顕微鏡（ＳＥＭ）により観察したところ、ＳＥＭ観察による平均粒径が０．９９μｍであり、粒径の標準偏差を平均粒径で除した値が０．２８であり、高分散性を有し、ペースト用銀粉として良好であることが確認された。また、実施例１と同様にして銀粉に含有されている塩素濃度を分析したところ３９ｐｐｍであり、塩素濃度が４０ｐｐｍ未満の塩素含有量の少ない銀粉を製造できることが確認された。 When the obtained silver powder was observed with a scanning electron microscope (SEM), the average particle size by SEM observation was 0.99 μm, and the value obtained by dividing the standard deviation of the particle size by the average particle size was 0.28. It was confirmed that it has dispersibility and is good as a silver powder for paste. Moreover, when the chlorine concentration contained in silver powder was analyzed similarly to Example 1, it was 39 ppm, and it was confirmed that silver powder with a small chlorine content whose chlorine concentration is less than 40 ppm can be manufactured.

（実施例１０）
３８℃の温水ジャケットで加熱した槽中において液温３６℃に保持した２５質量％アンモニア水１８．６６Ｌに、塩化銀２２７２ｇ（住友金属鉱山（株）製、純度９９.９９９９％、水分率１１．７％）を撹拌しながら投入して銀溶液を作製した。消泡剤（（株）アデカ製、アデカノールＬＧ−１２６）を体積比で１００倍に希釈し、この消泡剤希釈液２０ｍｌを作製した銀溶液に添加して、得られた銀溶液を温浴中において３６℃に保持した。 (Example 10)
In a bath heated by a hot water jacket at 38 ° C., 18.66 L of 25% by mass ammonia water kept at a liquid temperature of 36 ° C., 2272 g of silver chloride (manufactured by Sumitomo Metal Mining Co., Ltd., purity 99.9999%, moisture content 11. 7%) was added with stirring to prepare a silver solution. An antifoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times by volume, and 20 ml of this antifoaming agent diluted solution was added to the prepared silver solution. At 36 ° C.

次に、還元剤のアスコルビン酸１５６６ｇ（関東化学（株）製、試薬）を、３０℃の純水２Ｌに溶解した。また、分散剤のポリビニルアルコール３３２ｇ（（株）クラレ製、ＰＶＡ２０５）を３６℃の純水５．７９Ｌに溶解した。これら２液を混合して還元剤溶液とし、その温度を３６℃に調整した。 Next, 1566 g of ascorbic acid as a reducing agent (manufactured by Kanto Chemical Co., Ltd., reagent) was dissolved in 2 L of 30 ° C. pure water. Further, 332 g of polyvinyl alcohol (PVA205, manufactured by Kuraray Co., Ltd.) as a dispersant was dissolved in 5.79 L of pure water at 36 ° C. These two liquids were mixed to form a reducing agent solution, and the temperature was adjusted to 36 ° C.

銀溶液と還元剤溶液を、スムーズフローポンプ（（株）タクミナ製ＡＰＬ−５、ＢＰＬ−２）を使用して、それぞれ、２．７Ｌ／分、０．９Ｌ／分で反応管に供給し、反応管から排出された反応液を撹拌しながら受槽で保持した。反応管としては、銀溶液の供給方向に対する還元剤溶液の供給方向を１８０°とした、両液を混合撹拌するガラス製の同芯管（銀溶液供給管：内径１０．０ｍｍ、還元剤溶液供給管：内径３．６ｍｍ、混合管長：１００ｍｍ）を用いた。還元反応を送液中に完全に終了させるため、内径１２ｍｍ長さ３．６ｍの軟質塩化ビニル樹脂製チューブを反応管出側に接続して、反応液を受槽に送液した。このときの還元速度は、銀量で１９６ｇ／分であり、反応液中の銀濃度は５４．５ｇ／Ｌとなる。また、供給速度から求めた銀１モルに対するアスコルビン酸の混合比は０．５０モルとなる。また、分散剤のポリビニルアルコールの量は、混合時の反応液中の銀量に対して１７質量％となる。さらに、銀溶液と還元剤溶液の供給が終了した後、受槽内での攪拌を６０分継続した。 The silver solution and the reducing agent solution were supplied to the reaction tube at a rate of 2.7 L / min and 0.9 L / min, respectively, using a smooth flow pump (APL-5, BPL-2 manufactured by Takumina Co., Ltd.) The reaction liquid discharged from the reaction tube was held in a receiving tank while stirring. As a reaction tube, a glass concentric tube (silver solution supply tube: inner diameter 10.0 mm, reducing agent solution supply) in which the supply direction of the reducing agent solution with respect to the silver solution supply direction is 180 ° and the two solutions are mixed and stirred. (Tube: inner diameter 3.6 mm, mixing tube length: 100 mm) was used. In order to complete the reduction reaction during liquid feeding, a soft vinyl chloride resin tube having an inner diameter of 12 mm and a length of 3.6 m was connected to the outlet side of the reaction tube, and the reaction liquid was fed to the receiving tank. The reduction rate at this time is 196 g / min in terms of silver, and the silver concentration in the reaction solution is 54.5 g / L. Moreover, the mixing ratio of ascorbic acid to 1 mol of silver determined from the supply rate is 0.50 mol. Moreover, the quantity of the polyvinyl alcohol of a dispersing agent will be 17 mass% with respect to the silver quantity in the reaction liquid at the time of mixing. Furthermore, after the supply of the silver solution and the reducing agent solution was completed, stirring in the receiving tank was continued for 60 minutes.

得られた銀粉を走査電子顕微鏡（ＳＥＭ）により観察したところ、ＳＥＭ観察による平均粒径が１．３０μｍであり、粒径の標準偏差を平均粒径で除した値が０．２９であり、高分散性を有し、ペースト用銀粉として良好であることが確認された。 When the obtained silver powder was observed with a scanning electron microscope (SEM), the average particle diameter by SEM observation was 1.30 μm, and the value obtained by dividing the standard deviation of the particle diameter by the average particle diameter was 0.29. It was confirmed that it has dispersibility and is good as a silver powder for paste.

（実施例１１）
３８℃の温水ジャケットで加熱した槽中において液温３６℃に保持した２５質量％アンモニア水１４．３８Ｌに、塩化銀２２７７ｇ（住友金属鉱山（株）製、純度９９.９９９９％、水分率１１．７％）を撹拌しながら投入して銀溶液を作製した。消泡剤（（株）アデカ製、アデカノールＬＧ−１２６）を体積比で１００倍に希釈し、この消泡剤希釈液２０ｍｌを作製した銀溶液に添加して、得られた銀溶液を温浴中において３６℃に保持した。 (Example 11)
In a tank heated with a hot water jacket at 38 ° C., 2577% by weight ammonia water 14.38 L kept at a liquid temperature of 36 ° C., 2277 g of silver chloride (manufactured by Sumitomo Metal Mining Co., Ltd., purity 99.9999%, moisture content 11. 7%) was added with stirring to prepare a silver solution. An antifoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times by volume, and 20 ml of this antifoaming agent diluted solution was added to the prepared silver solution. At 36 ° C.

次に、還元剤のアスコルビン酸９７２ｇ（関東化学（株）製、試薬）を、３０℃の純水４．１２Ｌに溶解した。また、分散剤のポリビニルアルコール３４３ｇ（（株）クラレ製、ＰＶＡ２０５）を３６℃の純水２．０８Ｌに溶解した。これら２液を混合して還元剤溶液とし、その温度を３６℃に調整した。 Next, 972 g of a reducing agent, ascorbic acid (manufactured by Kanto Chemical Co., Inc., reagent) was dissolved in 4.12 L of pure water at 30 ° C. Further, 343 g of a dispersant, polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA205) was dissolved in 2.08 L of pure water at 36 ° C. These two liquids were mixed to form a reducing agent solution, and the temperature was adjusted to 36 ° C.

銀溶液と還元剤溶液を、スムーズフローポンプ（（株）タクミナ製ＡＰＬ−５、ＢＰＬ−２）を使用して、それぞれ、２．１Ｌ／分、０．７Ｌ／分で反応管に供給し、反応管から排出された反応液を撹拌しながら受槽で保持した。反応管としては、銀溶液の供給方向に対する還元剤溶液の供給方向を１８０°とした、両液を混合撹拌するガラス製の同芯管（銀溶液供給管：内径１０．０ｍｍ、還元剤溶液供給管：内径３．６ｍｍ、混合管長：１００ｍｍ）を用いた。還元反応を送液中に完全に終了させるため、内径１２ｍｍ長さ３．６ｍの軟質塩化ビニル樹脂製チューブを反応管出側に接続して、反応液を受槽に送液した。このときの還元速度は、銀量で１９９ｇ／分であり、反応液中の銀濃度は７１．０ｇ／Ｌとなる。また、供給速度から求めた銀１モルに対するアスコルビン酸の混合比は０．３０モルとなる。また、分散剤のポリビニルアルコールの量は、混合時の反応液中の銀量に対して１７質量％となる。さらに、銀溶液と還元剤溶液の供給が終了した後、受槽内での攪拌を６０分継続した。 The silver solution and the reducing agent solution were supplied to the reaction tube at 2.1 L / min and 0.7 L / min, respectively, using a smooth flow pump (APL-5, BPL-2 manufactured by Takumina Co., Ltd.) The reaction liquid discharged from the reaction tube was held in a receiving tank while stirring. As a reaction tube, a glass concentric tube (silver solution supply tube: inner diameter 10.0 mm, reducing agent solution supply) in which the supply direction of the reducing agent solution with respect to the silver solution supply direction is 180 ° and the two solutions are mixed and stirred. (Tube: inner diameter 3.6 mm, mixing tube length: 100 mm) was used. In order to complete the reduction reaction during liquid feeding, a soft vinyl chloride resin tube having an inner diameter of 12 mm and a length of 3.6 m was connected to the outlet side of the reaction tube, and the reaction liquid was fed to the receiving tank. The reduction rate at this time is 199 g / min in terms of silver, and the silver concentration in the reaction solution is 71.0 g / L. Moreover, the mixing ratio of ascorbic acid to 1 mol of silver determined from the supply rate is 0.30 mol. Moreover, the quantity of the polyvinyl alcohol of a dispersing agent will be 17 mass% with respect to the silver quantity in the reaction liquid at the time of mixing. Furthermore, after the supply of the silver solution and the reducing agent solution was completed, stirring in the receiving tank was continued for 60 minutes.

得られた銀粉を走査電子顕微鏡（ＳＥＭ）により観察したところ、ＳＥＭ観察による平均粒径が１．４０μｍであり、粒径の標準偏差を平均粒径で除した値が０．２２であり、高分散性を有し、ペースト用銀粉として良好であることが確認された。 When the obtained silver powder was observed with a scanning electron microscope (SEM), the average particle diameter by SEM observation was 1.40 μm, and the value obtained by dividing the standard deviation of the particle diameter by the average particle diameter was 0.22. It was confirmed that it has dispersibility and is good as a silver powder for paste.

（比較例１）
３８℃の温浴中において液温３６℃に保持した２５質量％アンモニア水１４．３４Ｌに、塩化銀２２４２ｇ（住友金属鉱山（株）製、純度９９．９９９９％、水分率１０．６％）を撹拌しながら投入して銀溶液を作製した。消泡剤（（株）アデカ製、アデカノールＬＧ−１２６）を体積比で１００倍に希釈し、この消泡剤希釈液２０ｍｌを作製した銀溶液に添加して、得られた銀溶液を温浴中において３６℃に保持した。 (Comparative Example 1)
Agitate 2242 g of silver chloride (manufactured by Sumitomo Metal Mining Co., Ltd., purity 99.9999%, moisture content 10.6%) in 14.34 L of 25% by mass ammonia water maintained at 36 ° C. in a 38 ° C. bath. Then, a silver solution was prepared. An antifoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times by volume, and 20 ml of this antifoaming agent diluted solution was added to the prepared silver solution. At 36 ° C.

次に、還元剤のアスコルビン酸９４８ｇ（関東化学（株）製、試薬）を、３０℃の純水４Ｌに溶解した。また、分散剤のポリビニルアルコール１１１ｇ（（株）クラレ製、ＰＶＡ２０５）を５０℃の純水２．０３Ｌに溶解した。これら２液を混合して還元剤溶液とし、その温度を３６℃に調整した。 Next, 948 g of a reducing agent, ascorbic acid (manufactured by Kanto Chemical Co., Inc., reagent) was dissolved in 4 L of 30 ° C. pure water. Moreover, 111 g of polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA205) as a dispersant was dissolved in 2.03 L of pure water at 50 ° C. These two liquids were mixed to form a reducing agent solution, and the temperature was adjusted to 36 ° C.

銀溶液と還元剤溶液を、チューブポンプを使用して、それぞれ、２．６Ｌ／分、１．１Ｌ／分で反応管に供給し、反応管から排出された反応液を撹拌しながら受槽で保持した。反応管としては、内径１０ｍｍのＹ字管を使用し、銀液と還元剤溶液を供給する管のなす角度を６０°とした。還元反応を送液中に完全に終了させるため、内径１２ｍｍ長さ１ｍの軟質塩化ビニル樹脂製チューブを反応管出側に接続して、反応液を受槽に送液した。このときの還元速度は、銀量で３００ｇ／分であり、反応液中の銀濃度は８１．０ｇ／Ｌとなる。また、供給速度から求めた銀１モルに対するアスコルビン酸の混合比は０．３０モルとなる。また、分散剤のポリビニルアルコールの量は、混合時の反応液中の銀量に対して７質量％となる。さらに、銀溶液と還元剤溶液の供給が終了した後、受槽内での攪拌を６０分継続した。 The silver solution and the reducing agent solution are supplied to the reaction tube at 2.6 L / min and 1.1 L / min, respectively, using a tube pump, and the reaction solution discharged from the reaction tube is held in a receiving tank while stirring. did. A Y-tube having an inner diameter of 10 mm was used as the reaction tube, and the angle formed by the tube for supplying the silver solution and the reducing agent solution was 60 °. In order to complete the reduction reaction during the liquid feeding, a soft vinyl chloride resin tube having an inner diameter of 12 mm and a length of 1 m was connected to the outlet side of the reaction tube, and the reaction liquid was fed to the receiving tank. The reduction rate at this time is 300 g / min in terms of silver, and the silver concentration in the reaction solution is 81.0 g / L. Moreover, the mixing ratio of ascorbic acid to 1 mol of silver determined from the supply rate is 0.30 mol. Moreover, the quantity of the polyvinyl alcohol of a dispersing agent will be 7 mass% with respect to the silver quantity in the reaction liquid at the time of mixing. Furthermore, after the supply of the silver solution and the reducing agent solution was completed, stirring in the receiving tank was continued for 60 minutes.

撹拌終了後の銀溶液を、フィルタープレス機を使用して濾過し、銀粒子を固液分離した。続いて、回収した銀粒子を０．０１ｍｏｌ／ＬのＮａＯＨ水溶液２０Ｌ中に投入し、１５分間撹拌した後、フィルタープレス機で濾過して回収した。ＮａＯＨ水溶液への投入、撹拌、及び濾過からなる操作を更に２回繰返した後、回収した銀粒子を純水２０Ｌ中に投入し、撹拌及び濾過からなる操作を行った。濾過後、銀粒子をステンレスパッドに移し、真空乾燥機にて６０℃で１５時間乾燥して銀粉を得た。 The silver solution after completion of stirring was filtered using a filter press, and the silver particles were separated into solid and liquid. Subsequently, the collected silver particles were put into 20 L of 0.01 mol / L NaOH aqueous solution, stirred for 15 minutes, and then collected by filtration with a filter press. The operations consisting of adding to an aqueous NaOH solution, stirring and filtration were repeated twice more, and then the collected silver particles were put into 20 L of pure water, and operations consisting of stirring and filtration were performed. After filtration, the silver particles were transferred to a stainless steel pad and dried in a vacuum dryer at 60 ° C. for 15 hours to obtain silver powder.

得られた銀粉を走査電子顕微鏡（ＳＥＭ）により観察したところ、ＳＥＭ観察による平均粒径は０．４５μｍであったものの、粒径の標準偏差を平均粒径で除した値が０．４９であって粒度分布がブロードとなっており、粗大粒子が生成されていた。このような比較例１にて得られた銀粉は、上述した実施例１や２に比べて粒径の分散性が大幅に低下しており、ペースト用銀粉として良好とは言えないものであった。なお、実施例１と同様にして銀粉に含有されている塩素濃度を分析したところ２８ｐｐｍであった。 When the obtained silver powder was observed with a scanning electron microscope (SEM), the average particle size by SEM observation was 0.45 μm, but the value obtained by dividing the standard deviation of the particle size by the average particle size was 0.49. The particle size distribution was broad and coarse particles were generated. The silver powder obtained in Comparative Example 1 had a significantly reduced particle size dispersibility as compared with Examples 1 and 2 described above, and was not good as a silver powder for paste. . In addition, it was 28 ppm when the chlorine concentration contained in silver powder was analyzed like Example 1. FIG.

（比較例２）
３８℃の温浴中において液温３６℃に保持した２５質量％アンモニア水７．３５Ｌに、塩化銀４９ｇ（住友金属鉱山（株）製、純度９９．９９９９％、水分率１０．５５％）を撹拌しながら投入して銀溶液を作製した。消泡剤（（株）アデカ製、アデカノールＬＧ−１２６）を体積比で１００倍に希釈し、この消泡剤希釈液０．４ｍｌを作製した銀溶液に添加して、得られた銀溶液を温浴中において３６℃に保持した。 (Comparative Example 2)
Agitation of 49 g of silver chloride (Sumitomo Metal Mining Co., Ltd., purity 99.9999%, moisture content 10.55%) in 7.35 L of 25% by mass ammonia water kept at 36 ° C. in a 38 ° C. bath Then, a silver solution was prepared. An antifoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times in volume ratio, and 0.4 ml of this antifoaming agent diluted solution was added to the prepared silver solution. Maintained at 36 ° C. in a warm bath.

次に、還元剤のアスコルビン酸２１ｇ（関東化学（株）製、試薬）を、３０℃の純水１．０Ｌに溶解した。また、分散剤のポリビニルアルコール７ｇ（（株）クラレ製、ＰＶＡ２０５）を５０℃の純水１．７１Ｌに溶解した。これら２液を混合して還元剤溶液とし、その温度を３６℃に調整した。 Next, 21 g of ascorbic acid as a reducing agent (manufactured by Kanto Chemical Co., Inc., reagent) was dissolved in 1.0 L of pure water at 30 ° C. Moreover, 7 g of polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA205) as a dispersant was dissolved in 1.71 L of pure water at 50 ° C. These two liquids were mixed to form a reducing agent solution, and the temperature was adjusted to 36 ° C.

銀溶液と還元剤溶液を、チューブポンプを使用して、それぞれ、２．７Ｌ／分、０．９Ｌ／分で反応管に供給し、反応管から排出された反応液を撹拌しながら受槽で保持した。反応管としては、銀溶液の供給方向に対する還元剤溶液の供給方向を０°とした、両液を混合撹拌するガラス製の同芯管（銀溶液供給管：内径１０．０ｍｍ、還元剤溶液供給管：内径３．６ｍｍ、混合管長：１００ｍｍ）を用いた。還元反応を送液中に完全に終了させるため、内径１２ｍｍ長さ１０ｍの軟質塩化ビニル樹脂製チューブを反応管出側に接続して、反応液を受槽に送液した。このときの還元速度は、銀量で１１ｇ／分であり、反応液中の銀濃度は３．０ｇ／Ｌとなる。また、供給速度から求めた銀１モルに対するアスコルビン酸の混合比は０．３５モルとなる。また、分散剤のポリビニルアルコールの量は、混合時の反応液中の銀量に対して１７質量％となる。さらに、銀溶液と還元剤溶液の供給が終了した後、受槽内での攪拌を６０分継続した。 The silver solution and the reducing agent solution are supplied to the reaction tube at a rate of 2.7 L / min and 0.9 L / min, respectively, using a tube pump, and the reaction solution discharged from the reaction tube is held in a receiving tank while stirring. did. As a reaction tube, a glass concentric tube (silver solution supply tube: inner diameter 10.0 mm, reducing agent solution supply) in which both solutions are mixed and stirred with the supply direction of the reducing agent solution relative to the supply direction of the silver solution being 0 °. (Tube: inner diameter 3.6 mm, mixing tube length: 100 mm) was used. In order to complete the reduction reaction during the liquid feeding, a soft vinyl chloride resin tube having an inner diameter of 12 mm and a length of 10 m was connected to the outlet side of the reaction tube, and the reaction liquid was fed to the receiving tank. The reduction rate at this time is 11 g / min in terms of silver, and the silver concentration in the reaction solution is 3.0 g / L. Moreover, the mixing ratio of ascorbic acid to 1 mol of silver determined from the supply rate is 0.35 mol. Moreover, the quantity of the polyvinyl alcohol of a dispersing agent will be 17 mass% with respect to the silver quantity in the reaction liquid at the time of mixing. Furthermore, after the supply of the silver solution and the reducing agent solution was completed, stirring in the receiving tank was continued for 60 minutes.

得られた銀粉を走査電子顕微鏡（ＳＥＭ）により観察したところ、ＳＥＭ観察による平均粒径が０．２８μｍであり非常に微細な粒子が含まれており、また粒径の標準偏差を平均粒径で除した値も０．３５であって粒度分布がブロードとなっていた。このような比較例２にて得られた銀粉では、実施例３と比較すると、粒径の分散性が大幅に低下しており、ペースト用銀粉として良好とは言えないものであった。 When the obtained silver powder was observed with a scanning electron microscope (SEM), the average particle diameter by SEM observation was 0.28 μm, very fine particles were contained, and the standard deviation of the particle diameter was the average particle diameter. The divided value was 0.35, and the particle size distribution was broad. In the silver powder obtained in Comparative Example 2 as described above, the dispersibility of the particle size was greatly reduced as compared with Example 3, and it could not be said that the silver powder for paste was good.

下記表１に、各実施例及び比較例における製造条件、並びに、得られた銀粉についての評価結果をまとめて示す。なお、表１において、「ＰＶＡ濃度」とは、還元剤溶液中に予め添加した分散剤であるポリビニルアルコールの混合後の反応液中の銀量に対する濃度である。また、「ＳＭ」とは、混合管内に設けたスタティックミキサーを意味する。また、「流下時間」とは、流路内で銀溶液と還元剤溶液とが混合されてから流路内を流下して出口（受槽）に出るまでの時間を意味する。 Table 1 below collectively shows the manufacturing conditions in each Example and Comparative Example, and the evaluation results for the obtained silver powder. In Table 1, “PVA concentration” is the concentration relative to the amount of silver in the reaction solution after mixing with polyvinyl alcohol, which is a dispersant added in advance to the reducing agent solution. “SM” means a static mixer provided in the mixing tube. Further, the “flowing time” means the time from when the silver solution and the reducing agent solution are mixed in the flow channel to when it flows down the flow channel and exits to the outlet (receiving tank).

Claims

塩素含有量が４０質量ｐｐｍ未満であり、走査型電子顕微鏡観察によって測定される一次粒子の平均粒径が０．３〜２．０μｍであり、粒径の標準偏差をその平均値で除した値が０．３以下であることを特徴とする銀粉。 The chlorine content is less than 40 mass ppm, the average particle size of primary particles measured by scanning electron microscope observation is 0.3 to 2.0 μm, and the value obtained by dividing the standard deviation of the particle size by the average value The silver powder characterized by being 0.3 or less.

前記一次粒子の平均粒径が０．３９〜２．０μｍであることを特徴とする請求項１に記載の銀粉。 2. The silver powder according to claim 1, wherein an average particle diameter of the primary particles is 0.39 to 2.0 μm.

銀錯体を含む銀溶液とアスコルビン酸を還元剤として含む還元剤溶液とをそれぞれ定量的かつ連続的に流路内に供給し、該銀溶液と該還元剤溶液とを流路内で混合させ、銀濃度を５〜７５ｇ／Ｌ、銀１モルに対してアスコルビン酸を０．２５〜０．５０モルの範囲に調整した反応液に分散剤を含有させ、該反応液中で銀錯体を定量的かつ連続的に還元して得られた請求項１又は請求項２に記載の銀粉。 A silver solution containing a silver complex and a reducing agent solution containing ascorbic acid as a reducing agent are each quantitatively and continuously supplied into the channel, and the silver solution and the reducing agent solution are mixed in the channel, A dispersing agent is contained in the reaction solution in which the silver concentration is adjusted to 5 to 75 g / L and ascorbic acid is adjusted to the range of 0.25 to 0.50 mol with respect to 1 mol of silver, and the silver complex is quantitatively analyzed in the reaction solution. And silver powder of Claim 1 or Claim 2 obtained by reduce | restoring continuously.