JP4569727B2 - Silver powder and method for producing the same - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、銀粉およびその製造方法に関し、特に、積層コンデンサの内部電極や回路基板の導体パターンなどの電子部品に使用できる導電性ペースト用の銀粉およびその製造方法に関する。
【０００２】
【従来の技術】
積層コンデンサの内部電極や回路基板の導体パターンなどの電子部品に使用される導電性ペーストとして、銀粉をガラスフリットとともに有機ビヒクル中に加えて混練することにより製造される銀ペーストが使用されている。このような電子部品を小型化したり、銀粉の使用量の低減してコストを削減するため、導電性ペースト用の銀粉は、粒径が適度に小さく、粒度が揃っていることが要求される。
【０００３】
このような導電性ペースト用の銀粉を製造する方法として、銀塩含有水溶液にアルカリまたは錯化剤を加えて、酸化銀含有スラリーまたは銀錯塩含有水溶液を生成した後、還元剤を加えることにより銀粉を還元析出させる湿式還元法が知られている。また、所望の粒径を有する導電性ペースト用の銀粉を製造する方法として、銀塩含有水溶液に錯化剤を加えて銀錯塩含有水溶液（銀アンミン錯体水溶液）を生成した後、微量の有機金属化合物の存在下で還元剤を添加することにより、所望の粒径を有する銀粉を製造する方法が知られている（特開平８−１７６６２０号参照）。この方法によれば、有機金属化合物の添加量を変えることにより、所望の粒径を有する球状銀粉を得ることができる。
【０００４】
【発明が解決しようとする課題】
しかし、従来の銀粉の製造方法によって粒径の小さい銀粉を製造しようとすると、銀粉の粒径を小さくするにしたがって、その銀粉を使用した導電性ペーストの粘度が増大してしまうという問題がある。すなわち、粒径が小さく且つ導電性ペーストに使用した場合の導電性ペーストの粘性が低い銀粉を製造することができないという問題がある。
【０００５】
したがって、本発明は、このような従来の問題点に鑑み、銀の粒径や粒度分布を実質的に変化させることなく銀の粒子表面に存在する凹凸や角張った部分を滑らかにすることにより、粒径が小さく且つ導電性ペーストに使用した場合の導電性ペーストの粘性が低い銀粉およびその製造方法を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明者らは、上記課題を解決するために鋭意研究した結果、銀の粒子同士を機械的に衝突させる表面平滑化処理を施すことにより、銀の粒径や粒度分布を実質的に変化させることなく銀の粒子表面に存在する凹凸や角張った部分を滑らかにすることができることを見出し、本発明を完成するに至った。
【０００７】
すなわち、本発明による銀粉の製造方法は、湿式還元法で製造された銀の粒子同士を機械的に衝突させる表面平滑化処理を施すことを特徴とする。
【０００８】
この表面平滑化処理は、粒子を機械的に流動化できる装置、例えばヘンシェルミキサーなどの筒型高速攪拌機を用いて行うことができる。また、表面平滑化処理によって得られる銀粉の平均粒径は、好ましくは０．１乃至１０μｍ、さらに好ましくは５μｍ以下である。
【０００９】
また、本発明による銀粉は、平均粒径が０．１乃至１０μｍの銀粉であって、この銀粉８０重量％に２５℃で粘度が０．２乃至０．６Ｐａ・ｓｅｃのエポキシ樹脂２０重量％を混練して得られる混練物の粘度をＥ型粘度計により２５℃、１ｒｐｍで測定したときの粘度が１３５Ｐａ・ｓｅｃ以下、または、平均粒径が０．１乃至１０μｍの銀粉であって、この銀粉８０重量％に２５℃で粘度が０．２乃至０．６Ｐａ・ｓｅｃのエポキシ樹脂２０重量％を混練して得られる混練物の粘度をＥ型粘度計により２５℃、３ｒｐｍで測定したときの粘度が９０Ｐａ・ｓｅｃ以下であることを特徴とする。
【００１０】
【発明の実施の形態】
本発明による銀粉の製造方法の実施の形態では、湿式還元法により銀粉を製造した後、銀の粒子同士を機械的に衝突させる表面平滑化処理を施す。
【００１１】
湿式還元法は、銀塩含有水溶液にアルカリまたは錯化剤を加えて、酸化銀含有スラリーまたは銀錯塩含有水溶液を生成した後、還元剤を加えて銀粉を還元析出させる方法である。この湿式還元方法は、二次凝集を防止して単分散した粒子を得ることにより導電性ペーストを使用した電子部品の特性の向上を図るために、還元析出した銀スラリーに対して分散剤を添加する処理、または銀粉を還元析出させる前の銀塩と酸化銀の少なくとも一方を含む水性反応系に対して分散剤を添加する処理を含むことができる。分散剤としては、脂肪酸、脂肪酸塩、界面活性剤、有機金属および保護コロイドのいずれか１種以上を選択して使用することができる。
【００１２】
表面平滑化処理は、乾燥した銀粉を、粒子を機械的に流動化させることができる装置に投入して、銀の粒子同士を機械的に衝突させることにより行う。実際には、攪拌機（ミキサー、ミルなど）を使用して、銀粉の投入量、攪拌機の羽根の回転数および種類、処理時間などを、粒子の流動化と衝突による表面形状の平滑化に最適になるように調整する。この表面平滑化処理により、銀粉の粒子表面の凹凸や角張った部分を滑らかにして、銀の粒径や粒度分布を実質的に変えることなく導電性ペーストの粘度を低下させることができる。
【００１３】
【実施例】
以下、実施例に基づいて本発明による銀粉およびその製造方法について詳細に説明する。
【００１４】
［実施例１］
銀イオンとして２１．７ｇ／Ｌの硝酸銀溶液４９６．８Ｌに、工業用のアンモニア３５Ｌを加えて、銀のアンミン錯体溶液を生成した。生成した銀のアンミン錯体溶液に水４６５Ｌを加えて希釈し、還元剤としてヒドラジンの８０％溶液３．２Ｌを加えた。また、還元剤を加えた直後に、分散剤としてオレイン酸４３．２ｇを加えた。このようにして得られた銀のスラリーをろ過、水洗した後、乾燥し、乾燥した銀１０．３ｋｇを得た。
【００１５】
得られた銀を５ｋｇとり、２０Ｌのヘンシェルミキサー（三井鉱山（株）製のＦＭ２０Ｃ／Ｉ型三井ヘンシェルミキサー）に投入した。このヘンシェルミキサーの上羽根としてＳＴ型の羽根を使用するとともに、下羽根としてせん断力の強いＳｏ型の羽根を使用して、２７５０ｒｐｍで２０分間回転させて表面平滑化処理を行った。
【００１６】
得られた銀粉の粒度（マイクロトラックＤ５０）は１．４４μｍ、比表面積は０．９２ｍ２／ｇ、タップ密度は４．２ｇ／ｍｌであった。また、得られた銀粉８ｇにエポキシ樹脂（油化シェルエポキシ（株）製のエピコート（グレード８１９（２５℃で粘度０．２〜０．６Ｐａ・ｓｅｃ））２ｇを加えてペーストを調整し、このペーストの粘度をＥ型粘度計により２５℃、０．５ｒｐｍ、１ｒｐｍおよび３ｒｐｍで測定したところ、それぞれ１８０Ｐａ・ｓｅｃ、１３０Ｐａ・ｓｅｃおよび８２Ｐａ・ｓｅｃであった。また、図１に示す倍率５０００倍の電子顕微鏡写真からわかるように、本実施例によって得られた銀粉の粒子形状は、表面の凹凸や角張った部分が滑らかになっていた。
【００１７】
［比較例１］
実施例１と同様の方法で得られた乾燥した銀を１０ｋｇとり、実施例１と同じ２０Ｌのヘンシェルミキサーに投入した。このヘンシェルミキサーの上羽根として実施例１と同様にＳＴ型の羽根を使用するとともに、下羽根として実施例１で使用したＳｏ型の羽根よりもせん断力の弱いＡｏ型の羽根を使用して、１２００ｒｐｍで１０分間回転させて解砕処理を行った。
【００１８】
得られた銀粉の粒度（マイクロトラックＤ５０）は１．９４μｍ、比表面積は０．８７ｍ２／ｇ、タップ密度は３．８ｇ／ｍｌ であった。また、得られた銀粉８ｇに実施例１と同じエポキシ樹脂２ｇを加えてペーストを調整し、このペーストの粘度をＥ型粘度計により２５℃、０．５ｒｐｍ、１ｒｐｍおよび３ｒｐｍで測定したところ、それぞれ２１０Ｐａ・ｓｅｃ、１５０Ｐａ・ｓｅｃおよび９５Ｐａ・ｓｅｃであった。また、図２に示す倍率５０００倍の電子顕微鏡写真からわかるように、本比較例によって得られた銀粉の粒子の表面には、凹凸や角張った部分が残ったままであった。
【００１９】
実施例１と比較例１の結果を図９および図１０に示す。図９に示すように、実施例１では、銀粉の粒度が比較例１より小さく、ペーストの粘度も比較例１より低くなっている。また、図９および図１０に示すように、実施例１では、Ｅ型粘度計の回転数が０．５ｒｐｍ、１ｒｐｍおよび３ｒｐｍのいずれの場合も、ペーストの粘度が比較例１より低くなっている。
【００２０】
［実施例２］
銀イオンとして２１．９ｇ／Ｌの硝酸銀溶液４９２．６Ｌに、濃度１００ｇ／Ｌの水酸化ナトリウム溶液４Ｌを加えてｐＨ調整した上で、工業用のアンモニア４５Ｌを加えて、銀のアンミン錯体溶液を生成した。次いで、濃度１００ｇ／Ｌの水酸化ナトリウム溶液をさらに４Ｌ加えてｐＨ調整し、水４６２．５Ｌを加えて希釈し、還元剤として工業用のホルマリン４８．０Ｌを加えた。その直後に、含量９５％のステアリン酸１４．８ｇをエタノール３Ｌに溶かした溶液を加えた。このようにして得られた銀のスラリーをろ過、水洗した後、乾燥し、乾燥した銀１０．７ｋｇを得た。
【００２１】
得られた銀を５ｋｇとり、実施例１と同じ２０Ｌのヘンシェルミキサーに投入した。このヘンシェルミキサーの羽根として実施例１と同じ羽根を使用して、２７５０ｒｐｍで２５分間回転させて表面平滑化処理を行った。
【００２２】
得られた銀粉の粒度（マイクロトラックＤ５０）は２．８７μｍ、比表面積は０．３５ｍ２／ｇ、タップ密度は５．４ｇ／ｍｌであった。また、得られた銀粉８ｇに実施例１と同じエポキシ樹脂２ｇを加えてペーストを調整し、このペーストの粘度をＥ型粘度計により２５℃、０．５ｒｐｍ、１ｒｐｍおよび３ｒｐｍで測定したところ、それぞれ１１０Ｐａ・ｓｅｃ、１０３Ｐａ・ｓｅｃおよび８５Ｐａ・ｓｅｃであった。また、図３に示す倍率５０００倍の電子顕微鏡写真からわかるように、本実施例によって得られた銀粉の粒子形状は、表面の凹凸や角張った部分が滑らかになっていた。
【００２３】
［比較例２］
実施例２と同様の方法で得られた乾燥した銀を１０ｋｇとり、実施例１と同じ２０Ｌのヘンシェルミキサーに投入した。このヘンシェルミキサーの羽根として比較例１と同じ羽根を使用して、１２００ｒｐｍで１０分間回転させて解砕処理を行った。
【００２４】
得られた銀粉の粒度（マイクロトラックＤ５０）は３．７３μｍ、比表面積は０．３７ｍ２／ｇ、タップ密度は４．４ｇ／ｍｌであった。また、得られた銀粉８ｇに実施例１と同じエポキシ樹脂２ｇを加えてペーストを調整し、このペーストの粘度をＥ型粘度計により２５℃、０．５ｒｐｍ、１ｒｐｍおよび３ｒｐｍで測定したところ、それぞれ１５５Ｐａ・ｓｅｃ、１３９Ｐａ・ｓｅｃおよび１１０Ｐａ・ｓｅｃであった。 また、図４に示す倍率５０００倍の電子顕微鏡写真からわかるように、本比較例によって得られた銀粉の粒子の表面には、凹凸や角張った部分が残ったままであった。
【００２５】
実施例２と比較例２の結果を図９および図１０に示す。図９に示すように、実施例２では、銀粉の粒度が比較例２より小さく、ペーストの粘度も比較例２より低くなっている。また、図９および図１０に示すように、実施例２では、Ｅ型粘度計の回転数が０．５ｒｐｍ、１ｒｐｍおよび３ｒｐｍのいずれの場合も、ペーストの粘度が比較例２より低くなっている。
【００２６】
［実施例３］
銀イオンとして４７．８ｇ／Ｌの硝酸銀溶液４５２．３Ｌに、工業用のアンモニア水７５Ｌを加えて、銀のアンミン錯体溶液を生成した。生成した銀のアンミン錯体溶液に濃度１００ｇ／Ｌの水酸化ナトリウム溶液２００Ｌを加えてｐＨ調整し、水３５０Ｌを加えて希釈し、還元剤として工業用のホルマリン２４．２Ｌを加えた。その直後に、ステアリン酸のエマルジョン（ステアリン酸含量１８％）３６０ｇを加えた。このようにして得られた銀のスラリーをろ過、水洗した後、乾燥し、乾燥した銀２１．６ｋｇを得た。
【００２７】
得られた銀を５ｋｇとり、実施例１と同じ２０Ｌのヘンシェルミキサーに投入した。このヘンシェルミキサーの羽根として実施例１と同じ羽根を使用して、２７５０ｒｐｍで２５分間回転させて表面平滑化処理を行った。
【００２８】
得られた銀粉の粒度（マイクロトラックＤ５０）は１．４１μｍ、比表面積は０．７２ｍ２／ｇ、タップ密度は５．０ｇ／ｍｌであった。また、得られた銀粉８ｇに実施例１と同じエポキシ樹脂２ｇを加えてペーストを調整し、このペーストの粘度をＥ型粘度計により２５℃、０．５ｒｐｍ、１ｒｐｍおよび３ｒｐｍで測定したところ、それぞれ１５７Ｐａ・ｓｅｃ、１２１Ｐａ・ｓｅｃおよび８３Ｐａ・ｓｅｃであった。また、図５に示す倍率５０００倍の電子顕微鏡写真からわかるように、本実施例によって得られた銀粉の粒子形状は、表面の凹凸や角張った部分が滑らかになっていた。
【００２９】
［比較例３］
実施例３と同様の方法で得られた乾燥した銀を１０ｋｇとり、実施例１と同じ２０Ｌのヘンシェルミキサーに投入した。このヘンシェルミキサーの羽根として比較例１と同じ羽根を使用して、１２００ｒｐｍで１０分間回転させて解砕処理を行った。
【００３０】
得られた銀粉の粒度（マイクロトラックＤ５０）は１．９０μｍ、比表面積は０．８１ｍ２／ｇ、タップ密度は４．０ｇ／ｍｌであった。また、得られた銀粉８ｇに実施例１と同じエポキシ樹脂２ｇを加えてペーストを調整し、このペーストの粘度をＥ型粘度計により２５℃、０．５ｒｐｍ、１ｒｐｍおよび３ｒｐｍで測定したところ、それぞれ１９２Ｐａ・ｓｅｃ、１４６Ｐａ・ｓｅｃおよび１００Ｐａ・ｓｅｃであった。また、図６に示す倍率５０００倍の電子顕微鏡写真からわかるように、本比較例によって得られた銀粉の粒子の表面には、表面の凹凸や角張った部分が残ったままであった。
【００３１】
実施例３と比較例３の結果を図９および図１０に示す。図９に示すように、実施例３では、銀粉の粒度が比較例３より小さく、ペーストの粘度も比較例３より低くなっている。また、図９および図１０に示すように、実施例３では、Ｅ型粘度計の回転数が０．５ｒｐｍ、１ｒｐｍおよび３ｒｐｍのいずれの場合も、ペーストの粘度が比較例３より低くなっている。
【００３２】
［実施例４］
銀イオンとして２２．０ｇ／Ｌの硝酸銀溶液４８９．２Ｌに、工業用のアンモニア水４５Ｌを加えて、銀のアンミン錯体溶液を生成した。生成した銀のアンミン錯体溶液に濃度１００ｇ／Ｌの水酸化ナトリウム溶液８Ｌを加えてｐＨ調整し、水４６２Ｌを加えて希釈し、還元剤として工業用のホルマリン４８．０Ｌを加えた。その直後に、オレイン酸を３４．５ｇ加えた。このようにして得られた銀のスラリーをろ過、水洗した後、乾燥し、乾燥した銀１０．０ｋｇを得た。
【００３３】
得られた銀を５ｋｇとり、実施例１と同じ２０Ｌのヘンシェルミキサーに投入した。このヘンシェルミキサーの羽根として実施例１と同じ羽根を使用して、２７５０ｒｐｍで２５分間回転させて表面平滑化処理を行った。
【００３４】
得られた銀粉の粒度（マイクロトラックＤ５０）は１．８５μｍ、比表面積は０．５９ｍ２／ｇ、タップ密度は５．２ｇ／ｍｌであった。また、得られた銀粉８ｇに実施例１と同じエポキシ樹脂２ｇを加えてペーストを調整し、このペーストの粘度をＥ型粘度計により２５℃、０．５ｒｐｍ、１ｒｐｍおよび３ｒｐｍで測定したところ、それぞれ１３３Ｐａ・ｓｅｃ、１１２Ｐａ・ｓｅｃおよび８４Ｐａ・ｓｅｃであった。また、図７に示す倍率５０００倍の電子顕微鏡写真からわかるように、本実施例によって得られた銀粉の粒子形状は、表面の凹凸や角張った部分が滑らかになっていた。
【００３５】
［比較例４］
実施例４と同様の方法で得られた乾燥した銀を１０ｋｇとり、実施例１と同じ２０Ｌのヘンシェルミキサーに投入した。このヘンシェルミキサーの羽根として比較例１と同じ羽根を使用して、１２００ｒｐｍで１０分間回転させて解砕処理を行った。
【００３６】
得られた銀粉の粒度（マイクロトラックＤ５０）は２．５１μｍ、比表面積は０．５６ｍ２／ｇ、タップ密度は４．２ｇ／ｍｌであった。また、得られた銀粉８ｇに実施例１と同じエポキシ樹脂２ｇを加えてペーストを調整し、このペーストの粘度をＥ型粘度計により２５℃、０．５ｒｐｍ、１ｒｐｍおよび３ｒｐｍで測定したところ、それぞれ１７３Ｐａ・ｓｅｃ、１４３Ｐａ・ｓｅｃおよび１０５Ｐａ・ｓｅｃであった。また、図８に示す倍率５０００倍の電子顕微鏡写真からわかるように、本比較例によって得られた銀粉の粒子の表面には、表面の凹凸や角張った部分が残ったままであった。
【００３７】
実施例４と比較例４の結果を図９および図１０に示す。図９に示すように、実施例４では、銀粉の粒度が比較例４より小さく、ペーストの粘度も比較例４より低くなっている。また、図９および図１０に示すように、実施例４では、Ｅ型粘度計の回転数が０．５ｒｐｍ、１ｒｐｍおよび３ｒｐｍのいずれの場合も、ペーストの粘度が比較例４より低くなっている。
【００３８】
なお、図９および図１０に示すように、実施例１〜４では、Ｅ型粘度計の回転数が１ｒｐｍの場合にペーストの粘度が１３５Ｐａ・ｓｅｃ以下、Ｅ型粘度計の回転数が３ｒｐｍの場合にペーストの粘度が９０Ｐａ・ｓｅｃ以下であり、いずれの場合も比較例１〜４よりペーストの粘度が低くなっている。
【００３９】
【発明の効果】
上述したように、本発明によれば、銀の粒子同士を機械的に衝突させる表面平滑化処理を施すことにより、銀の粒径や粒度分布を実質的に変化させることなく銀の粒子表面に存在する凹凸や角張った部分を滑らかにすることができ、それによって粒径が小さく且つ導電性ペーストに使用した場合のペーストの粘性が低い銀粉を得ることができる。
【図面の簡単な説明】
【図１】実施例１によって得られた銀粉の粒子の表面を示す電子顕微鏡写真。
【図２】比較例１によって得られた銀粉の粒子の表面を示す電子顕微鏡写真。
【図３】実施例２によって得られた銀粉の粒子の表面を示す電子顕微鏡写真。
【図４】比較例２によって得られた銀粉の粒子の表面を示す電子顕微鏡写真。
【図５】実施例３によって得られた銀粉の粒子の表面を示す電子顕微鏡写真。
【図６】比較例３によって得られた銀粉の粒子の表面を示す電子顕微鏡写真。
【図７】実施例４によって得られた銀粉の粒子の表面を示す電子顕微鏡写真。
【図８】比較例４によって得られた銀粉の粒子の表面を示す電子顕微鏡写真。
【図９】実施例１〜４および比較例１〜４の結果を示す表。
【図１０】実施例１〜４および比較例１〜４におけるＥ型粘度計の回転数とペーストの粘度との関係を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to silver powder and a method for producing the same, and more particularly to a silver powder for conductive paste that can be used for electronic components such as internal electrodes of multilayer capacitors and conductor patterns of circuit boards, and a method for producing the same.
[0002]
[Prior art]
As a conductive paste used for electronic parts such as an internal electrode of a multilayer capacitor and a conductor pattern of a circuit board, a silver paste manufactured by adding silver powder together with glass frit into an organic vehicle and kneading is used. In order to reduce the cost by reducing the size of such electronic components or reducing the amount of silver powder used, the silver powder for conductive paste is required to have an appropriately small particle size and uniform particle size.
[0003]
As a method for producing such silver powder for conductive paste, an alkali or complexing agent is added to a silver salt-containing aqueous solution to form a silver oxide-containing slurry or a silver complex salt-containing aqueous solution, and then a reducing agent is added to the silver powder. A wet reduction method for reducing and precipitating is known. In addition, as a method for producing silver powder for a conductive paste having a desired particle size, a complexing agent is added to a silver salt-containing aqueous solution to form a silver complex salt-containing aqueous solution (silver ammine complex aqueous solution), and then a trace amount of organic metal A method for producing a silver powder having a desired particle size by adding a reducing agent in the presence of a compound is known (see JP-A-8-176620). According to this method, spherical silver powder having a desired particle size can be obtained by changing the amount of the organometallic compound added.
[0004]
[Problems to be solved by the invention]
However, when silver powder having a small particle size is manufactured by a conventional silver powder manufacturing method, there is a problem that the viscosity of the conductive paste using the silver powder increases as the particle size of the silver powder is reduced. That is, there is a problem that silver powder having a small particle size and low viscosity of the conductive paste when used in the conductive paste cannot be produced.
[0005]
Therefore, in view of such a conventional problem, the present invention smoothes irregularities and angular portions present on the surface of silver particles without substantially changing the particle size or particle size distribution of silver, An object of the present invention is to provide a silver powder having a small particle size and a low viscosity of the conductive paste when used in the conductive paste, and a method for producing the same.
[0006]
[Means for Solving the Problems]
As a result of diligent research to solve the above problems, the inventors of the present invention substantially change the particle size and particle size distribution of silver by applying a surface smoothing treatment that mechanically collides silver particles. The present inventors have found that the irregularities and the angular portions present on the surface of the silver particles can be smoothed, and the present invention has been completed.
[0007]
That is, the method for producing silver powder according to the present invention is characterized in that a surface smoothing treatment is performed to mechanically collide silver particles produced by a wet reduction method.
[0008]
This surface smoothing treatment can be performed using an apparatus capable of mechanically fluidizing particles, for example, a cylindrical high-speed stirrer such as a Henschel mixer. Moreover, the average particle diameter of the silver powder obtained by the surface smoothing treatment is preferably 0.1 to 10 μm, more preferably 5 μm or less.
[0009]
Further, the silver powder according to the present invention is a silver powder having an average particle diameter of 0.1 to 10 μm, and 80% by weight of this silver powder is added with 20% by weight of an epoxy resin having a viscosity of 0.2 to 0.6 Pa · sec at 25 ° C. A silver powder having a viscosity of 135 Pa · sec or less or an average particle size of 0.1 to 10 μm when the viscosity of the kneaded product obtained by kneading is measured with an E-type viscometer at 25 ° C. and 1 rpm, Viscosity of a kneaded product obtained by kneading 20% by weight of an epoxy resin having a viscosity of 0.2 to 0.6 Pa · sec at 25 ° C. to 80% by weight with an E-type viscometer at 25 ° C. and 3 rpm. Is 90 Pa · sec or less.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In embodiment of the manufacturing method of the silver powder by this invention, after manufacturing silver powder by the wet reduction method, the surface smoothing process which makes silver particles collide mechanically is performed.
[0011]
The wet reduction method is a method in which an alkali or a complexing agent is added to a silver salt-containing aqueous solution to form a silver oxide-containing slurry or a silver complex salt-containing aqueous solution, and then a reducing agent is added to reduce and precipitate silver powder. In this wet reduction method, a dispersing agent is added to the reduced silver slurry to improve the characteristics of electronic components using conductive paste by preventing secondary aggregation and obtaining monodispersed particles. Or a treatment of adding a dispersant to an aqueous reaction system containing at least one of a silver salt and silver oxide before reducing and precipitating silver powder. As the dispersant, any one or more of fatty acids, fatty acid salts, surfactants, organometallics and protective colloids can be selected and used.
[0012]
The surface smoothing treatment is performed by putting the dried silver powder into an apparatus capable of mechanically fluidizing the particles and mechanically colliding the silver particles. In practice, using a stirrer (mixer, mill, etc.), the amount of silver powder charged, the rotation speed and type of stirrer blades, and the processing time are optimal for fluidizing particles and smoothing the surface shape by collision. Adjust so that By this surface smoothing treatment, irregularities and angular portions on the surface of silver powder particles can be smoothed, and the viscosity of the conductive paste can be reduced without substantially changing the particle size or particle size distribution of silver.
[0013]
【Example】
Hereinafter, based on an Example, the silver powder by this invention and its manufacturing method are demonstrated in detail.
[0014]
[Example 1]
35L of industrial ammonia was added to 496.8L of a silver nitrate solution of 21.7 g / L as silver ions to form a silver ammine complex solution. The resulting silver ammine complex solution was diluted by adding 465 L of water, and 3.2 L of an 80% hydrazine solution was added as a reducing agent. Immediately after adding the reducing agent, 43.2 g of oleic acid was added as a dispersant. The silver slurry thus obtained was filtered, washed with water and then dried to obtain 10.3 kg of dried silver.
[0015]
5 kg of the obtained silver was taken and introduced into a 20 L Henschel mixer (FM20C / I type Mitsui Henschel mixer manufactured by Mitsui Mining Co., Ltd.). An ST-type blade was used as the upper blade of this Henschel mixer, and a So-type blade having a strong shearing force was used as the lower blade, and the surface was smoothed by rotating at 2750 rpm for 20 minutes.
[0016]
The particle size (Microtrac D 50 ) of the obtained silver powder was 1.44 μm, the specific surface area was 0.92 m 2 / g, and the tap density was 4.2 g / ml. In addition, 2 g of epoxy resin (Epicoat (Grade 819 (viscosity 0.2 to 0.6 Pa · sec at 25 ° C.) at 25 ° C.)) 2 g was added to 8 g of the obtained silver powder to prepare a paste. The viscosity of the paste was measured at 25 ° C., 0.5 rpm, 1 rpm, and 3 rpm with an E-type viscometer, and found to be 180 Pa · sec, 130 Pa · sec, and 82 Pa · sec, respectively, and the magnification of 5000 times shown in FIG. As can be seen from the electron micrograph, the particle shape of the silver powder obtained by this example had smooth surface irregularities and angular portions.
[0017]
[Comparative Example 1]
10 kg of dried silver obtained by the same method as in Example 1 was taken and placed in a 20 L Henschel mixer as in Example 1. As an upper blade of this Henschel mixer, an ST-type blade is used in the same manner as in Example 1, and an Ao-type blade having a lower shearing force than the So-type blade used in Example 1 is used as a lower blade. The crushing process was performed by rotating at 1200 rpm for 10 minutes.
[0018]
The particle size (Microtrac D 50 ) of the obtained silver powder was 1.94 μm, the specific surface area was 0.87 m 2 / g, and the tap density was 3.8 g / ml. Moreover, the same epoxy resin 2g as Example 1 was added to the obtained silver powder 8g, the paste was adjusted, and when the viscosity of this paste was measured at 25 degreeC, 0.5 rpm, 1 rpm, and 3 rpm with the E-type viscosity meter, They were 210 Pa · sec, 150 Pa · sec and 95 Pa · sec. In addition, as can be seen from the electron micrograph at a magnification of 5000 shown in FIG. 2, the surface of the silver dust particles obtained by this comparative example remained uneven and angular.
[0019]
The results of Example 1 and Comparative Example 1 are shown in FIGS. As shown in FIG. 9, in Example 1, the particle size of silver powder is smaller than that of Comparative Example 1, and the viscosity of the paste is also lower than that of Comparative Example 1. Further, as shown in FIGS. 9 and 10, in Example 1, the viscosity of the paste is lower than that in Comparative Example 1 when the rotational speed of the E-type viscometer is 0.5 rpm, 1 rpm, and 3 rpm. .
[0020]
[Example 2]
After adjusting pH by adding 4L of 100g / L sodium hydroxide solution to 492.6L of 21.9g / L silver nitrate solution as silver ion, 45L of industrial ammonia was added to prepare silver ammine complex solution. Generated. Next, 4 L of a sodium hydroxide solution having a concentration of 100 g / L was added to adjust the pH, and 462.5 L of water was added for dilution, and 48.0 L of industrial formalin was added as a reducing agent. Immediately thereafter, a solution of 14.8 g of 95% stearic acid in 3 L of ethanol was added. The silver slurry thus obtained was filtered, washed with water, and then dried to obtain 10.7 kg of dried silver.
[0021]
5 kg of the obtained silver was taken and put into a 20 L Henschel mixer as in Example 1. The same blade as in Example 1 was used as the blade of this Henschel mixer, and the surface was smoothed by rotating at 2750 rpm for 25 minutes.
[0022]
The particle size (Microtrac D 50 ) of the obtained silver powder was 2.87 μm, the specific surface area was 0.35 m 2 / g, and the tap density was 5.4 g / ml. Moreover, the same epoxy resin 2g as Example 1 was added to the obtained silver powder 8g, the paste was adjusted, and when the viscosity of this paste was measured at 25 degreeC, 0.5 rpm, 1 rpm, and 3 rpm with the E-type viscosity meter, They were 110 Pa · sec, 103 Pa · sec, and 85 Pa · sec. Moreover, as can be seen from the electron micrograph at a magnification of 5000 shown in FIG. 3, the particle shape of the silver powder obtained by this example had smooth surface irregularities and angular portions.
[0023]
[Comparative Example 2]
10 kg of dried silver obtained in the same manner as in Example 2 was taken and charged into a 20 L Henschel mixer as in Example 1. The same blade as that of Comparative Example 1 was used as a blade of this Henschel mixer, and the crushing treatment was performed by rotating at 1200 rpm for 10 minutes.
[0024]
The obtained silver powder had a particle size (Microtrac D 50 ) of 3.73 μm, a specific surface area of 0.37 m 2 / g, and a tap density of 4.4 g / ml. Moreover, the same epoxy resin 2g as Example 1 was added to the obtained silver powder 8g, the paste was adjusted, and when the viscosity of this paste was measured at 25 degreeC, 0.5 rpm, 1 rpm, and 3 rpm with the E-type viscosity meter, They were 155 Pa · sec, 139 Pa · sec, and 110 Pa · sec. Moreover, as can be seen from the electron micrograph at a magnification of 5000 shown in FIG. 4, irregularities and angular portions remained on the surface of the silver powder particles obtained in this comparative example.
[0025]
The results of Example 2 and Comparative Example 2 are shown in FIGS. As shown in FIG. 9, in Example 2, the particle size of the silver powder is smaller than that of Comparative Example 2, and the viscosity of the paste is also lower than that of Comparative Example 2. Moreover, as shown in FIGS. 9 and 10, in Example 2, the viscosity of the paste is lower than that in Comparative Example 2 when the rotational speed of the E-type viscometer is 0.5 rpm, 1 rpm, and 3 rpm. .
[0026]
[Example 3]
Industrial silver water 75L was added to 452.3L of 47.8 g / L silver nitrate solution as silver ions to form a silver ammine complex solution. To the resulting silver ammine complex solution, 200 L of a sodium hydroxide solution having a concentration of 100 g / L was added to adjust the pH, 350 L of water was added for dilution, and 24.2 L of industrial formalin was added as a reducing agent. Immediately thereafter, 360 g of a stearic acid emulsion (stearic acid content 18%) was added. The silver slurry thus obtained was filtered, washed with water, and then dried to obtain 21.6 kg of dried silver.
[0027]
5 kg of the obtained silver was taken and put into a 20 L Henschel mixer as in Example 1. The same blade as in Example 1 was used as the blade of this Henschel mixer, and the surface was smoothed by rotating at 2750 rpm for 25 minutes.
[0028]
The particle size (Microtrac D 50 ) of the obtained silver powder was 1.41 μm, the specific surface area was 0.72 m 2 / g, and the tap density was 5.0 g / ml. Moreover, the same epoxy resin 2g as Example 1 was added to the obtained silver powder 8g, the paste was adjusted, and when the viscosity of this paste was measured at 25 degreeC, 0.5 rpm, 1 rpm, and 3 rpm with the E-type viscosity meter, They were 157 Pa · sec, 121 Pa · sec, and 83 Pa · sec. Further, as can be seen from the electron micrograph at a magnification of 5000 shown in FIG. 5, the particle shape of the silver powder obtained by this example had smooth surface irregularities and angular portions.
[0029]
[Comparative Example 3]
10 kg of dried silver obtained by the same method as in Example 3 was taken and put into a 20 L Henschel mixer as in Example 1. The same blade as that of Comparative Example 1 was used as a blade of this Henschel mixer, and the crushing treatment was performed by rotating at 1200 rpm for 10 minutes.
[0030]
The obtained silver powder had a particle size (Microtrac D 50 ) of 1.90 μm, a specific surface area of 0.81 m 2 / g, and a tap density of 4.0 g / ml. Moreover, the same epoxy resin 2g as Example 1 was added to the obtained silver powder 8g, the paste was adjusted, and when the viscosity of this paste was measured at 25 degreeC, 0.5 rpm, 1 rpm, and 3 rpm with the E-type viscosity meter, They were 192 Pa · sec, 146 Pa · sec, and 100 Pa · sec. Moreover, as can be seen from the electron micrograph at a magnification of 5000 shown in FIG. 6, the surface of the silver powder particles obtained by this comparative example remained uneven and angular.
[0031]
The results of Example 3 and Comparative Example 3 are shown in FIGS. As shown in FIG. 9, in Example 3, the particle size of the silver powder is smaller than that of Comparative Example 3, and the viscosity of the paste is also lower than that of Comparative Example 3. Moreover, as shown in FIGS. 9 and 10, in Example 3, the viscosity of the paste is lower than that of Comparative Example 3 when the rotational speed of the E-type viscometer is 0.5 rpm, 1 rpm, and 3 rpm. .
[0032]
[Example 4]
45L of industrial ammonia water was added to 489.2L of a 22.0 g / L silver nitrate solution as silver ions to form a silver ammine complex solution. The resulting silver ammine complex solution was adjusted to pH by adding 8 L of a sodium hydroxide solution having a concentration of 100 g / L, diluted by adding 462 L of water, and 48.0 L of industrial formalin was added as a reducing agent. Immediately thereafter, 34.5 g of oleic acid was added. The silver slurry thus obtained was filtered, washed with water, and then dried to obtain 10.0 kg of dried silver.
[0033]
5 kg of the obtained silver was taken and put into a 20 L Henschel mixer as in Example 1. The same blade as in Example 1 was used as the blade of this Henschel mixer, and the surface was smoothed by rotating at 2750 rpm for 25 minutes.
[0034]
The resulting silver powder of particle size (Microtrac D 50) of 1.85, a specific surface area of 0.59 m 2 / g, a tap density of 5.2 g / ml. Moreover, the same epoxy resin 2g as Example 1 was added to the obtained silver powder 8g, the paste was adjusted, and when the viscosity of this paste was measured at 25 degreeC, 0.5 rpm, 1 rpm, and 3 rpm with the E-type viscosity meter, They were 133 Pa · sec, 112 Pa · sec, and 84 Pa · sec. Further, as can be seen from the electron micrograph at a magnification of 5000 shown in FIG. 7, the particle shape of the silver powder obtained by this example had smooth surface irregularities and angular portions.
[0035]
[Comparative Example 4]
10 kg of dried silver obtained by the same method as in Example 4 was taken and put into a 20 L Henschel mixer as in Example 1. The same blade as that of Comparative Example 1 was used as a blade of this Henschel mixer, and the crushing treatment was performed by rotating at 1200 rpm for 10 minutes.
[0036]
The obtained silver powder had a particle size (Microtrac D 50 ) of 2.51 μm, a specific surface area of 0.56 m 2 / g, and a tap density of 4.2 g / ml. Moreover, the same epoxy resin 2g as Example 1 was added to the obtained silver powder 8g, the paste was adjusted, and when the viscosity of this paste was measured at 25 degreeC, 0.5 rpm, 1 rpm, and 3 rpm with the E-type viscosity meter, They were 173 Pa · sec, 143 Pa · sec, and 105 Pa · sec. Moreover, as can be seen from the electron micrograph at a magnification of 5000 shown in FIG. 8, the surface of the silver powder particles obtained by this comparative example remained uneven and angular.
[0037]
The results of Example 4 and Comparative Example 4 are shown in FIGS. As shown in FIG. 9, in Example 4, the particle size of silver powder is smaller than that of Comparative Example 4, and the viscosity of the paste is also lower than that of Comparative Example 4. Moreover, as shown in FIGS. 9 and 10, in Example 4, the viscosity of the paste is lower than that of Comparative Example 4 when the rotational speed of the E-type viscometer is 0.5 rpm, 1 rpm, and 3 rpm. .
[0038]
9 and 10, in Examples 1 to 4, when the rotation speed of the E-type viscometer is 1 rpm, the viscosity of the paste is 135 Pa · sec or less, and the rotation speed of the E-type viscometer is 3 rpm. In some cases, the viscosity of the paste is 90 Pa · sec or less, and in any case, the viscosity of the paste is lower than those of Comparative Examples 1 to 4.
[0039]
【The invention's effect】
As described above, according to the present invention, the surface of the silver particles is substantially changed without changing the particle size or particle size distribution of the silver by performing a surface smoothing process that mechanically collides the silver particles. Existing unevenness and angular portions can be smoothed, whereby a silver powder having a small particle size and low paste viscosity when used in a conductive paste can be obtained.
[Brief description of the drawings]
1 is an electron micrograph showing the surface of silver powder particles obtained in Example 1. FIG.
2 is an electron micrograph showing the surface of silver powder particles obtained in Comparative Example 1. FIG.
3 is an electron micrograph showing the surface of silver powder particles obtained in Example 2. FIG.
4 is an electron micrograph showing the surface of silver powder particles obtained in Comparative Example 2. FIG.
5 is an electron micrograph showing the surface of silver powder particles obtained in Example 3. FIG.
6 is an electron micrograph showing the surface of silver powder particles obtained in Comparative Example 3. FIG.
7 is an electron micrograph showing the surface of silver powder particles obtained in Example 4. FIG.
8 is an electron micrograph showing the surface of silver powder particles obtained in Comparative Example 4. FIG.
FIG. 9 is a table showing the results of Examples 1 to 4 and Comparative Examples 1 to 4.
10 is a graph showing the relationship between the rotational speed of the E-type viscometer and the viscosity of the paste in Examples 1 to 4 and Comparative Examples 1 to 4. FIG.
Claims (4)
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| CN105855562A (en) * | 2016-03-30 | 2016-08-17 | 湖南华信稀贵科技有限公司 | Method for preparing nanometer silver powder |
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| JP4320447B2 (en) * | 2004-02-03 | 2009-08-26 | Ｄｏｗａエレクトロニクス株式会社 | Silver powder and method for producing the same |
| JP2006002228A (en) | 2004-06-18 | 2006-01-05 | Dowa Mining Co Ltd | Spherical silver powder and its production method |
| KR20050122498A (en) * | 2004-06-24 | 2005-12-29 | 삼성에스디아이 주식회사 | A photosensitive paste composition, the pdp electrode prepared therefrom and a pdp comprising the pdp electrode |
| EP1804987A2 (en) * | 2004-10-29 | 2007-07-11 | NanoDynamics, Inc. | Aqueous-based method for producing ultra-fine metal powders |
| JP2006193795A (en) * | 2005-01-14 | 2006-07-27 | Dowa Mining Co Ltd | Spherical silver powder and its production method |
| JP5119526B2 (en) * | 2007-03-07 | 2013-01-16 | Ｄｏｗａエレクトロニクス株式会社 | Silver powder and method for producing the same |
| JP2010180471A (en) * | 2009-02-09 | 2010-08-19 | Dowa Electronics Materials Co Ltd | Flaky silver powder and method for producing the same, and conductive paste |
| KR20140024829A (en) * | 2011-06-16 | 2014-03-03 | 스미토모 긴조쿠 고잔 가부시키가이샤 | Silver powder and method for producing same |
| JP6856350B2 (en) | 2015-10-30 | 2021-04-07 | Ｄｏｗａエレクトロニクス株式会社 | Silver powder and its manufacturing method |
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2000
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102914514A (en) * | 2012-11-08 | 2013-02-06 | 苏州大学 | Hollow gold nano particle sensing membrane and preparation method thereof |
| CN105855562A (en) * | 2016-03-30 | 2016-08-17 | 湖南华信稀贵科技有限公司 | Method for preparing nanometer silver powder |
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