JP6404553B2 - Silver solution management method and silver powder production method - Google Patents
Silver solution management method and silver powder production method Download PDFInfo
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本発明は、銀溶液の管理方法および銀粉の製造方法に関し、特に、爆発性を有する雷銀の生成を抑えて安全に銀溶液を管理する方法および銀粉を製造する方法に関する。 The present invention relates to a silver solution management method and a silver powder production method, and more particularly to a method for safely managing a silver solution and a method for producing silver powder while suppressing the formation of explosive thunder silver.
電子機器における配線層や電極などの導電膜の形成には、樹脂型銀ペーストや焼成型銀ペーストのような銀粉を含んだ銀ペーストが多用されている。これら銀ペーストは加熱硬化あるいは加熱焼成によって銀粉が連なり、電気的に接続した電流パスを形成する。従って銀ペーストを塗布又は印刷してから加熱硬化または加熱焼成することにより、所望のパターンを有する導電膜を形成することができる。 For the formation of conductive films such as wiring layers and electrodes in electronic devices, silver paste containing silver powder such as resin-type silver paste and fired-type silver paste is often used. These silver pastes are linked with silver powder by heat curing or heat baking to form an electrically connected current path. Therefore, a conductive film having a desired pattern can be formed by applying or printing a silver paste, followed by heat curing or heat baking.
例えば、樹脂型銀ペーストの場合は、銀粉、樹脂、硬化剤、および溶剤などからなる銀ペーストを回路パターンや端子形状に印刷し、１００℃〜２００℃で加熱硬化させて配線や電極用の導電膜を形成することができる。一方、焼成型銀ペーストの場合は、銀粉、ガラス、および溶剤などからなる銀ペーストを回路パターンや端子形状に印刷し、６００℃〜８００℃で加熱焼成して配線や電極用の導電膜を形成することができる。 For example, in the case of a resin-type silver paste, a silver paste composed of silver powder, resin, curing agent, solvent, etc. is printed on a circuit pattern or terminal shape, and is heated and cured at 100 ° C. to 200 ° C. to conduct electricity for wiring and electrodes. A film can be formed. On the other hand, in the case of fired silver paste, silver paste made of silver powder, glass, solvent, etc. is printed in a circuit pattern or terminal shape, and heated and fired at 600 ° C to 800 ° C to form a conductive film for wiring and electrodes. can do.
かかる銀ペーストに使用する銀粉の粒径は一般に０.１μｍから数μｍ程度であり、形成する配線の幅や電極の厚さに応じて異なる粒径の銀粉が使用される。銀粉はペースト中で均一に分散させることが望ましく、これにより均一な厚みと幅を有する配線や均一な厚みを有する電極を形成することができる。 The particle size of silver powder used for such silver paste is generally about 0.1 μm to several μm, and silver powder having different particle sizes is used depending on the width of the wiring to be formed and the thickness of the electrode. The silver powder is desirably dispersed uniformly in the paste, whereby a wiring having a uniform thickness and width and an electrode having a uniform thickness can be formed.
ところで、銀ペーストの製造では、製造コストに占める割合が高い銀粉のコストを低く抑えることが重要視されており、このため、効率よく銀粉を作製できる湿式還元法が数多く提案されている。例えば特許文献１には、湿式還元法による銀粉の製造方法として、有機酸の存在下で銀錯体を還元する方法が示されている。この方法は、後述する雷銀の生成を回避できるという利点を有しているが、有機酸を用いて銀錯体を生成するため銀量と同じレベルの量の有機酸を添加する必要があり、薬剤コストが高いという問題を有している。また、その廃液はＣＯＤ（化学的酸素要求量）が高い上、残留有機物を分解する必要があるため、その処理にも多額のコストが必要となる。 By the way, in the production of silver paste, it is important to keep the cost of silver powder, which accounts for a high proportion of the production cost, low. For this reason, many wet reduction methods that can efficiently produce silver powder have been proposed. For example, Patent Document 1 discloses a method for reducing a silver complex in the presence of an organic acid as a method for producing silver powder by a wet reduction method. This method has the advantage that generation of thunder silver described later can be avoided, but in order to form a silver complex using an organic acid, it is necessary to add an amount of an organic acid at the same level as the amount of silver, It has the problem of high drug costs. In addition, the waste liquid has a high COD (chemical oxygen demand) and it is necessary to decompose the residual organic matter, so that a large amount of cost is also required for the treatment.
そこで特許文献２では、イオン交換水に硝酸銀およびアンモニアを加えて銀アンミン錯体の溶液を調製した後、還元剤水溶液で銀イオンを還元して銀粉を製造する方法が提案されている。アンモニアは銀イオンと安定な錯体を形成するため還元反応を制御しやすく、湿式還元法による銀粉の製法では有効な成分である。さらにアンモニアは有機酸と比べて薬剤コストが低い上、廃液処理において容易に処理可能な薬剤である。しかし、銀アンミン錯体は、ある条件では爆発性の雷銀を生成することがあるため、製造工程に銀アンミン錯体を用いる場合は安全性に留意する必要があった。例えば、非特許文献１には雷銀の一種である窒化銀の反応性について記載されている。 Therefore, Patent Document 2 proposes a method in which silver nitrate and ammonia are added to ion-exchanged water to prepare a silver ammine complex solution, and then silver ions are reduced with an aqueous reducing agent solution to produce silver powder. Ammonia forms a stable complex with silver ions, making it easy to control the reduction reaction, and is an effective component in the production of silver powder by the wet reduction method. Furthermore, ammonia has a lower drug cost than an organic acid and can be easily treated in waste liquid treatment. However, since silver ammine complexes may generate explosive thunder silver under certain conditions, it is necessary to pay attention to safety when using silver ammine complexes in the production process. For example, Non-Patent Document 1 describes the reactivity of silver nitride, which is a type of lightning silver.
アンモニアを用いた湿式還元法による銀粉の製造方法は、上記したように爆発性の雷銀が生成するリスクを孕んでいる。雷銀の発生メカニズムについて、特許文献２に開示された技術から検討すると、残留する未反応の銀アンミン錯体を含む銀溶液を濃縮した場合に雷銀が生成する可能性がある。これは意図的に濃縮した場合に限られず、例えば反応槽や配管系から飛散した銀溶液が乾燥したり濃縮した場合でも同様に雷銀が生成するリスクがあると考えられる。 The method for producing silver powder by the wet reduction method using ammonia entails the risk of generating explosive thunder silver as described above. When the generation mechanism of lightning silver is examined from the technique disclosed in Patent Document 2, lightning silver may be generated when the silver solution containing the remaining unreacted silver ammine complex is concentrated. This is not limited to the case where it is intentionally concentrated. For example, it is considered that there is a risk that thunder silver is generated even when the silver solution scattered from the reaction vessel or the piping system is dried or concentrated.
本発明はこのような従来の事情に鑑みてなされたものであり、銀アンミン錯体を含む銀溶液を危険な雷銀が発生しないように管理する方法、および危険な雷銀の発生を抑えながら銀アンミン錯体を含む銀溶液から銀粉を製造する方法を提供することを目的としている。 The present invention has been made in view of such conventional circumstances, a method for managing a silver solution containing a silver ammine complex so that dangerous thunder silver is not generated, and silver while suppressing the occurrence of dangerous thunder silver. It aims at providing the method of manufacturing silver powder from the silver solution containing an ammine complex.
本発明の発明者らは、銀アンミン錯体が雷銀を生成する条件について鋭意研究を重ねた結果、銀およびアンモニアを少なくとも含む銀溶液中の特定の成分の濃度を調整することで雷銀の生成を抑え得ることを見出し本発明を完成するに至った。 The inventors of the present invention have made extensive studies on the conditions under which silver ammine complexes generate thunder silver, and as a result, the concentration of specific components in a silver solution containing at least silver and ammonia is adjusted to produce thunder silver. As a result, the present invention has been completed.
即ち、本発明が提供する銀溶液の管理方法は、アンモニア水に塩化物塩および炭酸塩を添加した後、銀塩を溶解することで調製された、銀、アンモニア、塩化物塩および炭酸塩を含有する銀溶液（硫酸が添加されたものを除く）の管理方法であって、銀溶液中の全塩素および全炭酸の合計モル濃度を該銀溶液中の全銀のモル濃度で除した値を１より大きく５以下にすることによって雷銀の生成を抑制することを特徴としている。 That is, the silver solution management method provided by the present invention comprises adding silver chloride and carbonate to aqueous ammonia , and then dissolving silver , ammonia , chloride and carbonate prepared by dissolving the silver salt. a management method of the silver-containing solution (except those added sulfuric acid), the total chlorine and divided by the molar concentration of total silver in the silver solution total molar concentration of all carbonate silver solution It is characterized by suppressing the formation of thunder silver by making it larger than 1 and 5 or less.
また、本発明が提供する銀粉の製造方法は、アンモニア水に塩化物塩および炭酸塩を添加した後、銀塩を溶解する銀溶液を調製する調製工程と、前記調製工程で得た銀、アンモニア、塩化物塩および炭酸塩を含有する銀溶液（硫酸が添加されたものを除く）に還元剤を添加して銀イオンを還元する還元工程とからなる銀粉の製造方法であって、前記銀溶液中の全塩素および全炭酸の合計モル濃度を該銀溶液中の全銀のモル濃度で除した値を１より大きく５以下にすることによって雷銀の生成を抑制することを特徴としている。 Further, the silver powder production method provided by the present invention includes a preparation step of preparing a silver solution for dissolving a silver salt after adding a chloride salt and a carbonate to aqueous ammonia , and silver and ammonia obtained in the preparation step. , A silver powder production method comprising a reduction step of reducing silver ions by adding a reducing agent to a silver solution (excluding those added with sulfuric acid) containing chloride salt and carbonate, The value obtained by dividing the total molar concentration of total chlorine and total carbonic acid in the total by the molar concentration of total silver in the silver solution is set to be larger than 1 and 5 or less, thereby suppressing the formation of thunder silver.
本発明によれば、銀アンミン錯体を含む銀溶液であっても危険な雷銀が発生することがないので、安全且つ低コストに銀溶液を管理又は取り扱うことができ、また安全且つ低コストに銀粉を作製することができる。 According to the present invention, even if a silver solution containing a silver ammine complex does not generate dangerous thunder silver, the silver solution can be managed or handled safely and at low cost, and can be safely and low cost. Silver powder can be produced.
以下、本発明に係る銀粉の製造方法の一具体例について説明する。この本発明の一具体例の銀粉の製造方法は、銀イオンおよびアンモニアを含む銀溶液から銀粉を製造する湿式還元法であり、先ずアンモニアを含む水溶液に銀塩を溶解して銀アンミン錯体を含む銀溶液を作製する。次にこの銀溶液に還元剤を添加することにより銀イオンを還元して銀粉を懸濁させる。この懸濁液を濾過し、得られた固形分を洗浄および乾燥することで銀粉が得られる。この方法は生産性が高く、得られる銀粉の粒径および結晶粒径の制御も容易である。 Hereinafter, a specific example of the method for producing silver powder according to the present invention will be described. The method for producing silver powder according to one embodiment of the present invention is a wet reduction method for producing silver powder from a silver solution containing silver ions and ammonia. First, a silver salt is dissolved in an aqueous solution containing ammonia to contain a silver ammine complex. Make a silver solution. Next, by adding a reducing agent to the silver solution, the silver ions are reduced to suspend the silver powder. The suspension is filtered, and the solid content obtained is washed and dried to obtain silver powder. This method has high productivity, and it is easy to control the grain size and crystal grain size of the silver powder obtained.
しかし、この方法では残留する未反応の銀アンミン錯体を含む溶液が乾燥等の過程で濃縮されると、爆発などの危険性を有する雷銀が生成されることが問題になる。さらに、乾燥等の過程のほか、飛散した銀溶液が乾いて濃縮することで雷銀が生成する恐れもある。ここで雷銀とは、窒化銀、アミド銀、およびイミド銀などの爆発性物質の一般的な総称であり、上記したように銀アンミン錯体を含む溶液を乾燥または加熱したり、アルカリ性物質の添加で該溶液中のアンモニア濃度が下がったりすると雷銀が生成される。 However, in this method, if the solution containing the remaining unreacted silver ammine complex is concentrated in the course of drying or the like, lightning silver having a risk of explosion or the like is generated. Furthermore, in addition to processes such as drying, thunder silver may be generated when the scattered silver solution is dried and concentrated. Here, lightning silver is a general term for explosive substances such as silver nitride, amide silver, and imide silver. As described above, a solution containing a silver ammine complex is dried or heated, or an alkaline substance is added. When the ammonia concentration in the solution decreases, thunder silver is generated.
そこで、本発明の一具体例に係る銀粉の製造方法では、アンモニアを含有する銀溶液において、該銀溶液中の全塩素および全炭酸の合計モル濃度を該銀溶液中の全銀のモル濃度で除した値を１と等しくするか又は１より大きく５以下にしている。具体的には、銀イオンを還元する前の該銀溶液に含まれる全塩素のｍｏｌ濃度をＡとし、該銀溶液に含まれる炭酸イオン、炭酸水素イオン、および二酸化炭素分子（以降、これらを合わせて全炭酸とも称する）の合計ｍｏｌ濃度をＢとし、該銀溶液に含まれる全銀のｍｏｌ濃度をＣとした時、これらＡ，Ｂ、およびＣが下記式１または式２のいずれかの関係を満たすように調整する。なお、銀イオンには、銀アンミン錯体［Ａｇ（ＮＨ３）２］＋等の錯イオンや水和したイオンが含まれる。 Therefore, in the method for producing silver powder according to an embodiment of the present invention, in a silver solution containing ammonia, the total molar concentration of all chlorine and total carbonic acid in the silver solution is the molar concentration of all silver in the silver solution. The divided value is made equal to 1 or more than 1 and 5 or less. Specifically, the molar concentration of total chlorine contained in the silver solution before reducing the silver ions is A, and carbonate ions, hydrogen carbonate ions, and carbon dioxide molecules contained in the silver solution (hereinafter these are combined). The total molar concentration of all the carbonic acid) is B, and the molar concentration of total silver contained in the silver solution is C. These A, B, and C are in any one of the following formulas 1 and 2. Adjust to meet. Silver ions include complex ions such as silver ammine complex [Ag (NH 3 ) 2 ] + and hydrated ions.
［式１］
１＝（（Ａ＋Ｂ）／Ｃ）
［式２］
１＜（（Ａ＋Ｂ）／Ｃ）≦５
[Formula 1]
1 = ((A + B) / C)
[Formula 2]
1 <((A + B) / C) ≦ 5
ここで全塩素のｍｏｌ濃度とは、銀溶液中に含まれる塩素および塩素を含む化学物質を塩素原子に換算したｍｏｌ濃度である。この塩素には、Ｃｌ−で示される塩素イオンやＣｌ２で示される塩素分子さらには塩素の化合物が含まれる。これらの化学物質のｍｏｌ濃度は、銀溶液のｐＨ、温度などの諸条件で定まる化学平衡定数や反応速度定数に従って変動する。 Here, the mol concentration of total chlorine is a mol concentration obtained by converting chlorine contained in the silver solution and a chemical substance containing chlorine into chlorine atoms. This chlorine includes a chlorine ion represented by Cl − , a chlorine molecule represented by Cl 2 , and a chlorine compound. The mol concentrations of these chemical substances vary according to chemical equilibrium constants and reaction rate constants determined by various conditions such as pH and temperature of the silver solution.
全炭酸のｍｏｌ濃度とは、銀溶液中に含まれる二酸化炭素や炭酸イオン等の全炭酸を二酸化炭素に換算したｍｏｌ濃度である。この全炭酸には、銀溶液に溶解した状態の二酸化炭素（ＣＯ２）分子、ＣＯ３ −２で示される炭酸イオン、ＨＣＯ３ −で示される炭酸水素イオン、およびこれらの化合物が含まれる。これらの化学物質のｍｏｌ濃度は、銀溶液中のｐＨ、温度などの諸条件で定まる化学平衡定数や反応速度定数に従って変動する。 The mol concentration of total carbonic acid is a mol concentration obtained by converting total carbonic acid such as carbon dioxide and carbonate ions contained in the silver solution into carbon dioxide. This is all the carbonate, the state of being dissolved in silver solution carbon dioxide (CO 2) molecules, CO 3 carbonate ion represented by -2, HCO 3 - bicarbonate ion represented by, and includes these compounds. The mol concentration of these chemical substances varies according to chemical equilibrium constants and reaction rate constants determined by various conditions such as pH and temperature in the silver solution.
全銀のｍｏｌ濃度とは、銀溶液中に含まれる銀の化学種を銀原子に換算したｍｏｌ濃度である。銀溶液中に含まれる銀は、ほとんどが銀アンミン錯体として存在するものであるが、化学平衡により銀アンミン錯体以外の錯体として存在する銀イオンも含まれる。 The mol concentration of total silver is a mol concentration obtained by converting the chemical species of silver contained in the silver solution into silver atoms. Most of the silver contained in the silver solution is present as a silver ammine complex, but also includes silver ions present as a complex other than the silver ammine complex due to chemical equilibrium.
アンモニアが存在する銀溶液について発明者らは鋭意研究を行った結果、銀アンミン錯体とアンモニアが存在する銀溶液において、全塩素のｍｏｌ濃度（Ａ）と全炭酸のｍｏｌ濃度（Ｂ）の合計（Ａ＋Ｂ）と、全銀のｍｏｌ濃度（Ｃ）との関係が上記式１または式２のいずれかを満たす場合は、爆発性の雷銀の発生を回避できることを見出した。これは、反応系内の銀溶液に限るものではなく、例えば反応槽や配管系から漏れたり飛散したりした銀溶液が乾燥あるいは濃縮しても雷銀は生成しない。 As a result of intensive studies on the silver solution in which ammonia is present, in the silver solution in which the silver ammine complex and ammonia are present, the sum of the mol concentration (A) of total chlorine and the mol concentration (B) of total carbonic acid (B) ( It has been found that when the relationship between A + B) and the mol concentration (C) of total silver satisfies either of the above formulas 1 or 2, the occurrence of explosive lightning silver can be avoided. This is not limited to the silver solution in the reaction system. For example, even if the silver solution leaked or scattered from the reaction tank or the piping system is dried or concentrated, thunder silver is not generated.
しかも、銀イオン還元前の銀溶液を上記式１または上記式２のいずれかの条件を満たすように調整しておけば、還元工程以降の工程においても上記式１または上記式２の関係は維持されるので雷銀が発生することはない。すなわち、銀イオンの還元反応が進むと銀溶液中の銀イオンが銀粉になってその一部は沈降し、銀溶液から分離するので、銀溶液中に懸濁している微細な銀粉を銀溶液中の銀に含めても銀イオン還元前に比べて銀溶液中の全銀の濃度は低下するからである。 In addition, if the silver solution before the reduction of silver ions is adjusted so as to satisfy either of the above formulas 1 and 2, the relationship of the above formula 1 or 2 is maintained in the steps after the reduction step. Therefore, thunder silver will not be generated. That is, as the silver ion reduction reaction proceeds, the silver ions in the silver solution become silver powder, and some of them settle and separate from the silver solution, so that the fine silver powder suspended in the silver solution is removed from the silver solution. This is because the concentration of total silver in the silver solution is lower than that before reduction of silver ions even if it is included in the silver.
なお、上記式２の右側の等号付き不等号は、全塩素のｍｏｌ濃度（Ａ）と全炭酸のｍｏｌ濃度（Ｂ）の合計（Ａ＋Ｂ）が、全銀のｍｏｌ濃度（Ｃ）の５倍以下であることを条件とするものであり、これは銀粉の製造工程の経済性を考慮して導き出されたものである。前述したように、還元工程では全銀のｍｏｌ濃度は減少する傾向にあるので、塩素や二酸化炭素等の合計モル量を銀のモル量の５倍を超えて過剰に投入しなくてもよいことを示している。このように、上記式１または式２のいずれかを満たす条件下で銀粉を製造することにより、安全且つ低コストに銀粉を製造することができ、その工業的価値は極めて大きい。 In addition, the inequality sign with an equal sign on the right side of the above formula 2 indicates that the total concentration (A + B) of mol concentration (A) of total chlorine and mol concentration (B) of total carbonic acid is 5 times or less of mol concentration (C) of total silver This was derived in consideration of the economics of the silver powder production process. As described above, since the mol concentration of total silver tends to decrease in the reduction process, the total molar amount of chlorine, carbon dioxide, etc. does not need to be excessively added more than 5 times the molar amount of silver. Is shown. Thus, by manufacturing silver powder on the conditions which satisfy | fill either the said Formula 1 or Formula 2, silver powder can be manufactured safely and at low cost, The industrial value is very large.
なお、本発明の一具体例に係る銀粉の製造方法において、二酸化炭素を使用しない場合であっても、銀溶液中の全塩素のｍｏｌ濃度と全銀のｍｏｌ濃度とが上記式１または式２のいずれか満たすのであれば同等の効果が得られる。また、銀粉の製造方法において塩素を使用しない場合であっても、銀溶液中の全炭酸のｍｏｌ濃度と全銀のｍｏｌ濃度とが上記式１または式２のいずれか関係を満たすのであれば同等の効果が得られる。 In the method for producing silver powder according to one specific example of the present invention, even when carbon dioxide is not used, the molar concentration of total chlorine and the molar concentration of total silver in the silver solution are the above formula 1 or formula 2. If either of these is satisfied, the same effect can be obtained. Even if chlorine is not used in the method for producing silver powder, it is equivalent if the mol concentration of total carbonic acid in the silver solution and the mol concentration of total silver satisfy either of the above formulas 1 or 2. The effect is obtained.
次に、本発明に係る銀粉の製造方法を工程毎に詳細に説明する。まず、銀と錯化剤としてのアンモニアとを含有するアンモニア溶液に必要に応じて塩化物塩および／または炭酸塩を添加した後、銀塩として酸化銀、炭酸銀、塩化銀、硝酸銀、酢酸銀、および臭化銀からなる群から選ばれる１種類以上を溶解して銀溶液を得る。この銀溶液は前述したように全塩素および／または全炭酸のモル濃度を全銀のモル濃度で除した値が１と等しいか又は１より大きく５以下の範囲内となるように調整する。 Next, the manufacturing method of the silver powder which concerns on this invention is demonstrated in detail for every process. First, after adding a chloride salt and / or carbonate as necessary to an ammonia solution containing silver and ammonia as a complexing agent, silver oxide, silver carbonate, silver chloride, silver nitrate, silver acetate as silver salt And at least one selected from the group consisting of silver bromide is dissolved to obtain a silver solution. As described above, the silver solution is adjusted so that the value obtained by dividing the molar concentration of total chlorine and / or total carbonic acid by the molar concentration of total silver is equal to 1 or in the range of more than 1 and 5 or less.
この時、銀塩の添加だけで上記１と等しいか又は１より大きく５以下の条件を満たすのであれば、基本的に塩化物塩および／または炭酸塩は添加しなくてもよい。例えば、銀塩に塩化銀のみを用いた場合、銀溶液中に銀のモル数と等モルの塩素が存在することになるので、この塩素が脱気などで除去されない限り全塩素のｍｏｌ濃度を全銀のｍｏｌ濃度で除した値は１となるので上記の条件を満たすことになる。 At this time, chloride salt and / or carbonate basically do not need to be added as long as the condition is equal to 1 or more than 1 and not more than 5 by adding silver salt. For example, when only silver chloride is used as the silver salt, chlorine equivalent to the number of moles of silver is present in the silver solution. Therefore, unless this chlorine is removed by deaeration, the mol concentration of all chlorine is reduced. Since the value divided by the mol concentration of total silver is 1, the above condition is satisfied.
銀塩は、比較的安価な原料である、酸化銀、炭酸銀、塩化銀、および硝酸銀の中から選ぶのが好ましく、得られる銀粉への不純物の混入を防止するため、工業用に安定的に製造されている高純度塩化銀を用いることがより好ましい。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。また、アンモニア水の濃度は、通常用いられる２５質量％程度でよく、必要に応じて純水で希釈してもよい。 The silver salt is preferably selected from among relatively inexpensive raw materials such as silver oxide, silver carbonate, silver chloride, and silver nitrate. In order to prevent impurities from being mixed into the resulting silver powder, it is stable for industrial use. It is more preferable to use the high purity silver chloride produced. Ammonia water for dissolving silver chloride may be a normal one used industrially, but in order to prevent contamination with impurities, one having a purity as high as possible is preferable. Further, the concentration of ammonia water may be about 25% by mass which is usually used, and may be diluted with pure water as necessary.
必要に応じて添加する塩化物塩や炭酸塩は、溶解しないものや還元反応中に水酸化物のように沈殿が生じるものでなければ特に限定はなく、塩化物塩では塩化ナトリウム、塩化カリウム、塩化アンモニウム、塩化リチウムなどを使用することができる。一方、炭酸塩では、炭酸ナトリウム、炭酸水素ナトリウム、炭酸カリウム、炭酸アンモニウム、炭酸リチウムなどを使用することができる。 The chloride salt and carbonate added as necessary is not particularly limited as long as it does not dissolve or precipitates like hydroxide during the reduction reaction, and chloride salts include sodium chloride, potassium chloride, Ammonium chloride, lithium chloride, and the like can be used. On the other hand, in carbonate, sodium carbonate, sodium hydrogencarbonate, potassium carbonate, ammonium carbonate, lithium carbonate, etc. can be used.
銀溶液を調製する具体的な方法としては、所定の量のアンモニア水が張り込まれた反応槽に塩化物塩および／または炭酸塩を投入し、これにより得られるアンモニア溶液を２０〜４５℃に保持して撹拌しながら銀塩を投入して十分に溶解すればよい。アンモニア溶液の温度が２０℃未満では、銀塩の溶解度が下がり生産性が悪くなる。一方、アンモニア溶液の温度が４５℃を超えるとアンモニアの揮発が激しくなり、一旦溶解した銀塩がアンモニアの揮発に伴って析出するため、安定した銀溶液が得られなくなる。得られた銀溶液は、引き続き２０〜４５℃に保持するのが好ましく、３５〜４０℃に保持することがより好ましい。 As a specific method for preparing the silver solution, a chloride salt and / or carbonate is introduced into a reaction tank filled with a predetermined amount of aqueous ammonia, and the resulting ammonia solution is brought to 20 to 45 ° C. The silver salt may be added and sufficiently dissolved while holding and stirring. When the temperature of the ammonia solution is less than 20 ° C., the solubility of the silver salt is lowered and the productivity is deteriorated. On the other hand, when the temperature of the ammonia solution exceeds 45 ° C., the volatilization of ammonia becomes violent, and the silver salt once dissolved precipitates with the volatilization of the ammonia, so that a stable silver solution cannot be obtained. The obtained silver solution is preferably kept at 20 to 45 ° C., more preferably 35 to 40 ° C.
上記したアンモニア溶液への銀塩の投入では、得られる銀溶液中の銀濃度が８０〜１００ｇ／Ｌとなるように投入量を調整することが好ましい。この銀濃度が８０ｇ／Ｌ未満であっても得られる銀粉に問題はないが、１バッチ当たりで得られる銀粉の量が少なくなるため生産性が低下する。一方、銀濃度が１００ｇ／Ｌを超えることは、銀塩の析出が開始することから困難である。 When the silver salt is added to the ammonia solution as described above, it is preferable to adjust the input amount so that the silver concentration in the obtained silver solution is 80 to 100 g / L. Even if the silver concentration is less than 80 g / L, there is no problem with the obtained silver powder, but the productivity is lowered because the amount of silver powder obtained per batch is reduced. On the other hand, it is difficult for the silver concentration to exceed 100 g / L since the precipitation of the silver salt starts.
次に、還元剤に分散剤を混合して還元剤混合液を作製する。還元剤には一般的な還元剤を用いることができるが、反応速度や薬剤のコストの面から、ヒドラジン、ヒドラジニウム塩、ホルマリン、アスコルビン酸、酒石酸が好ましい。一方、分散剤には、ポリビニルアルコール、ポリビニルピロリドン、ポリエチレンイミンなどを用いることができる。分散剤にポリビニルアルコールやポリビニルピロリドンを用いる場合は還元反応時に発泡する場合があるため、銀溶液又は還元剤混合液に市販の消泡剤を添加してもよい。また、ポリビニルアルコールを用いる場合は、シリコーン系界面活性剤を添加したものを用いることがより好ましい。 Next, a reducing agent is mixed with a reducing agent to prepare a reducing agent mixed solution. Although a general reducing agent can be used as the reducing agent, hydrazine, hydrazinium salt, formalin, ascorbic acid, and tartaric acid are preferable from the viewpoint of reaction rate and chemical cost. On the other hand, polyvinyl alcohol, polyvinyl pyrrolidone, polyethyleneimine, or the like can be used as the dispersant. When polyvinyl alcohol or polyvinyl pyrrolidone is used as the dispersant, foaming may occur during the reduction reaction, so a commercially available antifoaming agent may be added to the silver solution or the reducing agent mixture. Moreover, when using polyvinyl alcohol, it is more preferable to use what added the silicone type surfactant.
一般的な銀粉の湿式合成においては、還元剤の添加後数時間で銀アンミン錯体が還元されて核生成が起こり、核が成長して銀粒子が形成されると共に銀粒子同士の凝集が生じる。その際、分散剤は生成した銀粒子表面に吸着して、銀粒子同士の凝集を防いで分散させる働きを有する。尚、核が凝集しながら成長すると複数の核が成長してできた多結晶組織で構成される銀粒子となり、核が凝集せずにそのまま成長すると単結晶の銀粒子となる。 In the general wet synthesis of silver powder, the silver ammine complex is reduced within a few hours after the addition of the reducing agent, nucleation occurs, the nucleus grows to form silver particles, and the silver particles aggregate together. At that time, the dispersant has a function of adsorbing on the surface of the generated silver particles and preventing the silver particles from aggregating and dispersing. When the nuclei grow while agglomerating, they become silver particles composed of a polycrystalline structure formed by growing a plurality of nuclei, and when the nuclei grow as they are without agglomeration, they become single crystal silver particles.
このように、核生成時から溶液中に分散剤を存在させることにより銀粒子の分散性を向上させて核の成長及び凝集を適度に調整することができる。その際、還元剤を銀溶液に添加する前に、還元剤と分散剤とを予め混合し、還元剤混合液として銀溶液に添加するのが好ましい。これにより、少ない分散剤でも核の表面に効率よく分散剤を吸着させることができる。 In this way, the presence of a dispersing agent in the solution from the time of nucleation can improve the dispersibility of the silver particles and appropriately adjust the growth and aggregation of the nuclei. In that case, before adding a reducing agent to a silver solution, it is preferable to mix a reducing agent and a dispersing agent beforehand, and to add to a silver solution as a reducing agent liquid mixture. Thereby, even with a small amount of dispersant, the dispersant can be efficiently adsorbed on the surface of the core.
還元剤への分散剤の添加量は、分散剤の種類及び作製する銀粉の粒径により適宜決めればよいが、前述したいずれの分散剤を用いる場合であっても、銀溶液中に含まれる銀１００質量部に対して３〜１０質量部とすることが好ましい。また、銀溶液への還元剤混合液の添加量は、添加した還元剤混合液中の還元剤の量が銀溶液中の銀を全て還元できる量であればよく、そのために必要な最少限度の量とすることがコスト面から好ましい。例えば還元剤がアスコルビン酸の場合は、銀溶液中の銀１モル当たり０.２５モルが化学量論量であるので、その添加量は銀１モル当たり０.２５〜１モルが好ましく、０.２５〜０.３５モルがより好ましい。 The amount of the dispersant added to the reducing agent may be appropriately determined depending on the type of the dispersant and the particle size of the silver powder to be produced. Even when any of the above-described dispersants is used, the silver contained in the silver solution It is preferable to set it as 3-10 mass parts with respect to 100 mass parts. Further, the amount of the reducing agent mixed solution added to the silver solution may be an amount in which the amount of the reducing agent in the added reducing agent mixed solution is an amount capable of reducing all the silver in the silver solution. The amount is preferable from the viewpoint of cost. For example, when the reducing agent is ascorbic acid, 0.25 mol per mol of silver in the silver solution is a stoichiometric amount, so the addition amount is preferably 0.25 to 1 mol per mol of silver, and is preferably 0.5. More preferred is 25 to 0.35 mol.
この還元剤混合液を、前述したように好適には２０〜４５℃で保持されている銀溶液の温度以上にして銀溶液に添加する。その際、添加後の銀溶液の温度が２０℃以上５０℃以下となるように温度調節を行うのが好ましい。特に還元反応により温度上昇を伴う場合は、５０℃を超えないように留意することが望ましい。具体的な昇温の程度は、１バッチで作製される銀粉の量、還元剤の投入速度、銀溶液の撹拌状態、反応槽の温度管理状態（冷却機能の有無や放熱性）などにより異なるが、再現性があるため、あらかじめ試験を行うことでどの程度温度が上昇するか把握することができる。この試験結果に基づいて、還元反応時の銀溶液の温度が２０〜５０℃の範囲内に収まるように運転すればよい。その際、還元による温度上昇が大きい場合には、ジャケット付き反応容器を用いて水冷するなど一般的な温度制御を行えばよい。 As described above, this reducing agent mixed solution is preferably added to the silver solution at a temperature higher than the temperature of the silver solution maintained at 20 to 45 ° C. At that time, it is preferable to adjust the temperature so that the temperature of the silver solution after the addition becomes 20 ° C. or more and 50 ° C. or less. In particular, when a temperature increase is caused by a reduction reaction, it is desirable not to exceed 50 ° C. The specific level of temperature rise varies depending on the amount of silver powder produced in one batch, the rate of addition of the reducing agent, the stirring state of the silver solution, the temperature control state of the reaction tank (with or without cooling function or heat dissipation), etc. Because of the reproducibility, it is possible to grasp how much the temperature rises by conducting a test in advance. Based on the test results, the silver solution may be operated so that the temperature of the silver solution during the reduction reaction falls within the range of 20 to 50 ° C. At that time, if the temperature rise due to the reduction is large, general temperature control such as water cooling using a jacketed reaction vessel may be performed.
還元剤混合液を添加した後の銀溶液は、還元反応を均一化させると共に銀粒子同士の凝集を防止するため、連続的に撹拌することが好ましい。撹拌方法には特に限定がなく、一般的な撹拌装置を用いて攪拌すればよい。さらに、必要に応じて還元による銀粒子の生成が終了する前に脂肪酸を添加してもよい。脂肪酸としてはオレイン酸やオレイン酸塩、ステアリン酸やステアリン酸塩、またはこれらをエマルジョン化したものから選択することができる。 The silver solution after adding the reducing agent mixed solution is preferably continuously stirred in order to make the reduction reaction uniform and prevent aggregation of silver particles. There is no particular limitation on the stirring method, and stirring may be performed using a general stirring device. Furthermore, you may add a fatty acid as needed before the production | generation of the silver particle by reduction | restoration is complete | finished. The fatty acid can be selected from oleic acid and oleate, stearic acid and stearate, or an emulsion thereof.
このようにして作製した銀微粒子を含んだ懸濁液を一般的な濾過手段で濾過した後、得られた湿潤状態の銀粉（以降、ケーキとも称する）を洗浄および乾燥することで銀粉が得られる。ケーキの洗浄方法には特に限定はなく、例えば銀粉のケーキを水に投入し、撹拌機又は超音波洗浄器を使用して撹拌した後、再度濾過して銀粉を回収する方法が好ましい。この場合、水への投入、撹拌及び濾過からなる洗浄操作を、複数回繰返すことがより好ましい。この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するのが好ましく、純水の使用が特に好ましい。 After the suspension containing the silver fine particles thus prepared is filtered by a general filtering means, the obtained wet silver powder (hereinafter also referred to as cake) is washed and dried to obtain silver powder. . The method for washing the cake is not particularly limited. For example, a method in which a silver powder cake is put into water, stirred using a stirrer or an ultrasonic cleaner, and then filtered again to collect silver powder is preferable. In this case, it is more preferable to repeat the washing operation consisting of charging into water, stirring and filtration a plurality of times. The water used for this washing is preferably water that does not contain an impurity element harmful to silver powder, and the use of pure water is particularly preferred.
上記洗浄後の銀粉の乾燥方法としては、例えば洗浄後の銀粉のケーキをステンレスパッド上に敷き詰め、大気オーブン又は真空乾燥機などの市販の乾燥装置を用いて、４０〜８０℃の温度で加熱することにより乾燥させるのが好ましい。得られる銀粉の粒径は、用途により異なるが、還元剤混合液の添加方法や撹拌速度などの各種条件を制御することで、平均粒径２μｍ以下の粒度のそろった銀粉を得ることができる。 As a method for drying the washed silver powder, for example, the washed silver powder cake is spread on a stainless steel pad and heated at a temperature of 40 to 80 ° C. using a commercially available drying apparatus such as an atmospheric oven or a vacuum dryer. It is preferable to dry it. The particle size of the obtained silver powder varies depending on the application, but by controlling various conditions such as the method of adding the reducing agent mixed solution and the stirring speed, a silver powder having an average particle size of 2 μm or less can be obtained.
銀およびアンモニアを含む銀溶液を管理する場合においても、上記した本発明の一具体例の銀粉の製造方法と同様に、銀溶液中の全塩素のｍｏｌ濃度および全炭酸のｍｏｌ濃度の合計を全銀のｍｏｌ濃度で除した値が上記した式１に示すように１と等しいか、又は下記式３に示すように１より大きくなるように調整することで雷銀の生成を回避することができる。この銀溶液の管理には、例えばアンモニアを含有する銀溶液の化学分析や廃液処理などを挙げることができる。なお、上記銀溶液の管理の際に例えば銀溶液が床面にこぼれたり飛散したりしてそのまま乾いた場合でも雷銀の生成を回避できる。
［式３］
１＜（（Ａ＋Ｂ）／Ｃ）
Even in the case of managing a silver solution containing silver and ammonia, the total of the mol concentration of all chlorine and the mol concentration of all carbonic acid in the silver solution is the same as in the silver powder production method of one specific example of the present invention described above. By adjusting the value obtained by dividing by the mol concentration of silver to be equal to 1 as shown in the above formula 1 or larger than 1 as shown in the following formula 3, generation of thunder silver can be avoided. . Examples of management of the silver solution include chemical analysis and waste liquid treatment of a silver solution containing ammonia. In addition, when the silver solution is managed, for example, even if the silver solution is spilled or scattered on the floor surface and dried as it is, generation of thunder silver can be avoided.
[Formula 3]
1 <((A + B) / C)
［実施例１］
２８％アンモニア水１ｇに塩化ナトリウムを２８ｍｇを添加し、更に酸化銀（Ｉ）を５０ｍｇ溶解して試料１の銀溶液を作製した。また、塩化ナトリウムの添加量を２８ｍｇに代えてそれぞれ６３ｍｇおよび８５ｍｇにした以外は上記試料１と同様にして試料２および試料３の銀溶液を作製した。更に、塩化ナトリウムおよび酸化銀（Ｉ）の溶解に代えて塩化銀を６２ｍｇ溶解した以外は上記試料１と同様にして試料４の銀溶液を作製した。これら試料１〜４の銀溶液中の塩素のモル濃度を銀のモル濃度で除した値はそれぞれ１.１、２.４、３.４、および１.０となる。
[Example 1]
28 mg of sodium chloride was added to 1 g of 28% ammonia water, and 50 mg of silver (I) was further dissolved to prepare a silver solution of Sample 1. Further, silver solutions of Sample 2 and Sample 3 were prepared in the same manner as Sample 1 except that the addition amount of sodium chloride was changed to 28 mg and replaced with 63 mg and 85 mg, respectively. Further, a silver solution of Sample 4 was prepared in the same manner as Sample 1 except that 62 mg of silver chloride was dissolved instead of dissolution of sodium chloride and silver (I) oxide. The values obtained by dividing the molar concentration of chlorine in the silver solutions of Samples 1 to 4 by the molar concentration of silver are 1.1, 2.4, 3.4, and 1.0, respectively.
これら銀溶液を常温で乾燥したところ、いずれも雷銀を生成することなく塩化銀を生成することができた。ここで雷銀の生成の有無は、乾燥後に得られた固形分をサンプリングし、これに波長９２０ｎｍ〜９４０ｎｍ、パルスピーク出力５Ｗ、パルス幅２ｍ秒の赤外線レーザを照射して起爆試験を行い、爆発しなければ雷銀は生成していないと判断した。なお、このことから、銀溶液は飛散などによって液が乾燥しても安全であることが分かる。
［比較例］
When these silver solutions were dried at room temperature, all were able to produce silver chloride without producing thunder silver. Here, the presence or absence of thunder silver is determined by sampling the solid content obtained after drying, irradiating it with an infrared laser having a wavelength of 920 nm to 940 nm, a pulse peak output of 5 W, and a pulse width of 2 ms, and performing an explosion test. Otherwise, it was judged that thunder silver was not generated. From this, it can be seen that the silver solution is safe even if the solution is dried by scattering or the like.
[Comparative example]
比較のため、２８％アンモニア水１ｇに塩化銀４６ｍｇおよび酸化銀（Ｉ）１３ｍｇを溶解して試料５の銀溶液を作製した。また、２８％アンモニア水１ｇに塩化銀３１ｍｇおよび酸化銀（Ｉ）２５ｍｇを溶解して試料６の銀溶液を作製した。更に、２８％アンモニア水１ｇに塩化銀１６ｍｇおよび酸化銀（Ｉ）３８ｍｇを溶解して試料７の銀溶液を作製した。これら試料５〜７の銀溶液中の塩素のモル濃度を銀のモル濃度で除した値はそれぞれ０.７５、０.５、および０.２５となる。 For comparison, a silver solution of Sample 5 was prepared by dissolving 46 mg of silver chloride and 13 mg of silver (I) oxide in 1 g of 28% aqueous ammonia. Further, 31 mg of silver chloride and 25 mg of silver (I) oxide were dissolved in 1 g of 28% aqueous ammonia to prepare a silver solution of Sample 6. Further, 16 mg of silver chloride and 38 mg of silver (I) oxide were dissolved in 1 g of 28% aqueous ammonia to prepare a silver solution of Sample 7. The values obtained by dividing the molar concentration of chlorine in the silver solutions of Samples 5 to 7 by the molar concentration of silver are 0.75, 0.5, and 0.25, respectively.
これら試料５〜７の銀溶液についても実施例１と同様にして常温での乾燥を行った。乾燥後に得られた固形分をサンプリングし、実施例１と同様にして起爆試験を行った結果、試料５〜７のいずれも雷銀の生成が部分的に認められた。このことから、試料５〜７の銀溶液は飛散などによって床面に付着して乾燥すると爆発性の雷銀を生成する危険性があることが分かる。 These silver solutions of Samples 5 to 7 were also dried at room temperature in the same manner as in Example 1. The solid content obtained after drying was sampled and subjected to an initiation test in the same manner as in Example 1. As a result, generation of thunder silver was partially recognized in all of Samples 5 to 7. From this, it can be seen that the silver solutions of Samples 5 to 7 have a risk of generating explosive thunder silver if they adhere to the floor surface due to scattering or the like and are dried.
［実施例２］
２８％アンモニア水１ｇに、塩化銀４６ｍｇおよび酸化銀（Ｉ）１３ｍｇを溶解して塩素のモル濃度を銀のモル濃度で除した値を０.７５となる銀溶液を作製した。この銀溶液に更に炭酸ガスを吹き込んで吸収させた後、常温で乾燥した。その結果、雷銀の生成は認められなかった。残留物をフーリエ変換赤外分光法により分析したところ、残留物の組成は塩化銀６０モル％および炭酸銀４０モル％であり、塩素および炭酸のモル濃度を銀のモル濃度で除した値は１.０であった。この銀溶液は飛散などによって液が乾燥しても安全であることが分かる。
[Example 2]
A silver solution was prepared by dissolving 46 mg of silver chloride and 13 mg of silver (I) oxide in 1 g of 28% aqueous ammonia and dividing the molar concentration of chlorine by the molar concentration of silver to be 0.75. Carbon dioxide was blown into the silver solution to absorb it, and then dried at room temperature. As a result, generation of thunder silver was not recognized. When the residue was analyzed by Fourier transform infrared spectroscopy, the composition of the residue was 60 mol% of silver chloride and 40 mol% of silver carbonate, and the value obtained by dividing the molar concentration of chlorine and carbonic acid by the molar concentration of silver was 1. 0.0. It can be seen that this silver solution is safe even if the liquid dries due to scattering or the like.
［実施例３］
実施例１の試料１と同じ組成の銀溶液を銀量が１０ｇ含まれるようにして調製した。また、還元剤であるアスコルビン酸（関東化学製試薬）４.６８ｇを３６℃の純水２０ｍリットルに溶解させた還元剤水溶液を調製した。更に、ポリビニルアルコール（（株）クラレ製、ＰＶＡ２０５）０.５５ｇと界面活性剤（日本エマルジョン（製）、ＳＳ−５６０２）０.０７ｇを分取し、３６℃の純水１０ｍリットルに溶解させた分散剤水溶液を調製した。
[Example 3]
A silver solution having the same composition as Sample 1 of Example 1 was prepared so as to contain 10 g of silver. Further, an aqueous reducing agent solution was prepared by dissolving 4.68 g of ascorbic acid (reagent made by Kanto Chemical), which is a reducing agent, in 20 ml of 36 ° C. pure water. Furthermore, 0.55 g of polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA205) and 0.07 g of a surfactant (Nihon Emulsion Co., Ltd., SS-5602) were separated and dissolved in 10 ml of 36 ° C. pure water. A dispersant aqueous solution was prepared.
上記銀溶液を攪拌しながら、還元剤混合液を投入し、銀溶液を還元して銀粒子を含んだスラリーを得た。このスラリーをメンブレンフィルターを使用して濾過することで銀粒子を固液分離した。次いで、得られた銀粒子のケーキを０.０１ｍｏリットル／リットル水酸化ナトリウム水溶液３００ｍリットル中に投入して１５分間攪拌した後、孔径０.１μｍのメンブレンフィルターで濾過して回収した。これら水酸化ナトリウム水溶液への投入、撹拌および濾過からなる洗浄操作をさらに２回繰り返した。 While stirring the silver solution, a reducing agent mixed solution was added, and the silver solution was reduced to obtain a slurry containing silver particles. The slurry was filtered using a membrane filter to separate the silver particles into solid and liquid. Next, the obtained silver particle cake was put into 300 ml of 0.01 mol / liter sodium hydroxide aqueous solution, stirred for 15 minutes, and then collected by filtration through a membrane filter having a pore size of 0.1 μm. The washing operation consisting of charging into the aqueous sodium hydroxide solution, stirring and filtration was further repeated twice.
こうして得られた銀粒子のケーキを純水３００ｍリットル中に投入して１５分間撹拌した。その後、孔径０.１μｍのメンブレンフィルターで濾過し、回収した湿潤状態の銀粉をステンレスパッドに敷き詰め、真空乾燥機にて６０℃で１０時間乾燥した。乾燥後の銀粒子をジェットミルに導入し、乾燥凝集を解砕して銀粉を得た。この銀粉を１５０００倍で撮影した走査型電子顕微鏡（ＳＥＭ）写真上で２００〜３００個の一次粒子の粒径を測定し、個数平均することにより平均粒径を求めたところ０.６５μｍであった。 The silver particle cake thus obtained was put into 300 ml of pure water and stirred for 15 minutes. Thereafter, the mixture was filtered through a membrane filter having a pore diameter of 0.1 μm, and the collected wet silver powder was spread on a stainless steel pad and dried at 60 ° C. for 10 hours in a vacuum dryer. The dried silver particles were introduced into a jet mill, and the dry agglomeration was crushed to obtain silver powder. The particle size of 200-300 primary particles was measured on a scanning electron microscope (SEM) photograph of this silver powder taken at 15000 times, and the average particle size was determined by number average, and found to be 0.65 μm. .
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