JP2004315871A - Method for producing metal hyperfine particle and production apparatus for metal hyperfine particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for largely producing metal hyperfine particles by a process where flocculation does not occur, production cost is low, and the recycling of the raw material is possible. <P>SOLUTION: The method for producing hyperfine particles comprises: melting raw material metal; obtaining hyperfine particles from a melt of the raw material by a gas atomization method; recovering the hyperfine particles, wherein a gaseous mixture of gaseous H<SB>2</SB>and an inert gas is used as a gas for atomizing. It is preferable that He is used as the inert gas and the volume mixing ratio of the gaseous H<SB>2</SB>prescribed as [the gaseous H<SB>2</SB>/(the gaseous H<SB>2</SB>+the gaseous He)] falls within the range of 0.01 to 30 vol%. <P>COPYRIGHT: (C)2005,JPO&amp;NCIPI

Description

【００１９】
上記の実験式では、用いられる装置特有の装置係数項（実験定数のようなもの）が存在するが、粒径制御因子は、噴射ガス速度、噴射ガスと金属融液動粘度比、噴射ガスと金属融液流量比であることが判明した。実験式内をよく検討すると、噴射ガス速度が粒径を決める因子として一番大きいことが判った。
【００２０】
また、噴射ガス速度は、容器から噴出する気体の速度（下記に示す「Ｚｅｕｎｅｒの公式」及び「気体流速の式」等）として考えることができるが、ガス固有の断熱指数（ガスを構成する分子数により決まる指数で比熱比γ（γ＝定圧比熱Ｃｐ／定積比熱Ｃｖ）とも呼ばれる。例えばＮ_２やＨ_２のような２原子分子気体では約１．４０、ＨｅやＡｒのような単原子分子気体では約１．６６）、ガス定数（一般的に言われているＲ＝８．３１６Ｊ／ｍｏｌのガス定数ではなく、ガス１ｇあたりに換算したガス定数を示す、例えば、Ｎ_２ガスでは０．２９７Ｊ／ｇ．ｋとなり、Ｈｅガスでは２．０７７Ｊ／ｇ・ｋ、Ｈ_２ガスでは４．１４８Ｊ／ｇ・ｋとなる）、温度、断熱指数と噴射圧力、ガス密度、ガス定数より計算できるガス速度係数等が相互に関係していることが判った。
【００２１】
＜Ｚｅｕｎｅｒの公式＞
ｑ＝２γ／（γ−１）＊（Ｐ_０／ρ_０）＊（１−（Ｐ／Ｐ_０）^{（γ―１）／γ}）
断熱変化の場合；Ｃ＝［γ＊（Ｐ／ρ）］^１／２＝［γ＊（Ｒ／ｍ）］^１／２
理想気体の場合；Ｐ＝（Ｒ／ｍ）＊ρ＊Ｔ
【００２２】
＜気体流速の式＞
ｑ＝ｑ_ｍ＊［１−（Ｐ／Ｐ_０）^{（γ―１）／γ}］^１／２
ｑ_ｍ＝［２／（γ―１）］^１／２＊Ｃ_０
【００２３】
さらに、本発明者等は粒径を決める因子として噴射ガスの粉砕エネルギーや噴射ガスと金属融液が接触する距離も関係していることを発見した。
また、ガスアトマイズ法で超微粒子を製造する場合には、造粒メカニズム及び装置構造上、噴射ガスの圧力とガス噴出速度の間に、下記で示される臨界圧力比を考慮しなければならないことを発見した。
【００２４】
＜臨界圧力比の関係式＞
ｐ^＊／ｐ_０＝［２／（γ＋１）］^{γ／（γ―１）}
【００２５】
詳細な数値は省略するが、噴射ガスとしてＮ_２ガスをＨｅガスに変更すると、噴射するガス速度は２．７倍となり、粉砕エネルギーは１．１倍と計算され、その他を同一条件下でガスアトマイズ法により前記同様のＡｇ／Ｃｕ合金を作製した場合、体積平均粒径は８〜１２μｍとなることを実験で確認した。また、存在する最小粒子径は０．５μｍとなり、明らかに粒子全体が微粒子化に向かっていることが確認できた。
【００２６】
なお、Ｎ_２ガスとＨｅガスとを混合した場合の噴射ガス速度や粉砕エネルギーも計算し、実験データとして得られた体積平均粒径と照らし合わせて検討したが、その傾向は混合系のガス特性により大まかに示せるが、実測値と計算値との差が大きく、既存の数式のままで解釈し説明することはできないことが確認された。実際にはガスアトマイズ法による詳細な微粒子化メカニズムを解明することは非常に困難であり、既存の数式では混合ガス系の状態は推定の域を出ない。
【００２７】
しかし、噴射ガスとして用いるガスの各々の特性ではなく、混合ガスにした場合の相乗効果を狙い、電子材料分野において注目されている超微粒子を、凝集がなく、製造コストが安く、原料のリサイクルも可能なプロセスで大量に製造できる製造方法として、本発明者等は、Ｈ_２ガスと不活性ガスとの混合気体を用い、ガスアトマイズ法で用いるガスノズルのガス噴射口にて計算される２５℃におけるガス噴出速度が７００ｍ／ｓ〜１２００ｍ／ｓの範囲にあることを特徴とする金属超微粒子の製造方法を開発するに至った。
【００２８】
本発明においては、Ｈ_２ガスと混合して用いる不活性ガスとしては、Ｎ_２ガス、Ｈｅガス、Ａｒガス、Ｎｅガスを使用することができるが、Ｎ_２ガス、Ｈｅガス、Ａｒガスを使用することが好ましく、Ｈｅガスを用いることがさらに好ましい。
Ｈ_２ガスを使用すると、Ｎ_２ガスに対して３．８倍、Ｈｅガスに対しても１．４倍の噴射ガス速度が得られる計算となる。また、粉砕エネルギーに関しては、Ｎ_２ガスと同等であると計算できるが、前述したが、この数値は実測値とは一致しない。
【００２９】
Ｈ_２ガス特性を考えると、爆発範囲が４〜７５ｖｏｌ％（空気中、室温）で、一般的には圧力が高くなると爆発範囲が広くなると言われている。また、発火温度は５００℃（空気中）である。これらのデータからはＨ_２ガスは工業的に使用するのは非常に難しいように思えるが、本発明者らの実験によれば、不活性ガスとの混合ガスにすることで、上記Ｈ_２単独のガス特性が改良されるようであるが、どのような状態であるかは推測の域を出ない。
【００３０】
実際に計算された２５℃での各単独ガス種におけるガス噴出速度を示すと、Ｈ_２ガスは１２０３ｍ／ｓ、Ｎ_２ガスは３２１ｍ／ｓ、Ｈｅガスは８７９ｍ／ｓ、Ａｒガスは３１１ｍ／ｓ、Ｎｅガスは３９３ｍ／ｓとなる。本発明におけるガス混合系の適切なガス選定と混合割合は、２５℃におけるガス噴出口のガス噴出速度要件より規定される。
【００３１】
次に本発明で用いるガスアトマイズ装置の概要及び特徴について説明する。
後述する製造方法の３つの工程とも関連しているが、ガスアトマイズ装置は大きく分けると、原料金属融解部、ガス噴射により粒子化する噴霧部、及び、得られた粒子を回収する回収部より構成される。本発明者らが使用しているガスアトマイズ装置には、その他付帯設備として、ガス回収ライン、ガスホルダー、ガス圧縮機、水分吸着機が存在するが、本発明の特徴とは直接関係ないので、説明は省略する。
【００３２】
金属融解部とは、作製したい超微粒子の合金組成となるように原料を秤量し、カーボン坩堝内で高周波誘導加熱装置などの加熱装置により融解する部分である。カーボンによる脱酸素（還元効果）もあり、原料を融解する場合には途中まで真空下で融解している。融解後、金属融液を溶融金属ノズルから噴出する際には、不活性ガスにて金属融解部を加圧状態にしている。この際の金属融解部の圧力をａ［ＭＰａ］と規定する。加圧状態にすると、ガス噴射時には、金属融液が噴射ガスの吸引効果で吸い込まれるが、さらに押し出す効果がある。
噴霧部の圧力をｂ［ＭＰａ］とし、ａ＞ｂとなるように圧力を調整する。
【００３３】
金属融液が噴出する部分には超音波振動させるシステムを付帯している。これは超音波振動により、金属融液を振動させることによって、ガス噴射による微粒子化を補助する効果があり、その結果として体積平均粒径を小さくできる。
【００３４】
回収部は、溶媒中に超微粒子が分散された状態で存在する部分であるが、分散状態の超微粒子と溶媒とを分離（イメージとしては濾過或いは濾別）できるように、循環ライン、フィルター及びポンプを付帯している。通常の回収部はこのラインとは別に設けてあり、導電性ペースト製造において、回収スラリー中の超微粒子含有量を多くしたい場合や、多目の溶媒量を装置内に充填した場合に製造した超微粒子を一部回収するためのシステムである。
【００３５】
次に一部重複するが造粒工程、回収工程、分級工程について説明する。
まず、造粒工程とは、原料金属、或いは合金をカーボン坩堝中で融解し、金属融液とし、ガスノズルよりＨ_２ガスと不活性ガスとの所定の割合の混合ガスを噴射することにより、超微粒子化（ガスアトマイズ法、急冷凝固法）する工程を示している。
【００３６】
詳細は回収工程で述べるが、造粒工程と回収工程は１つの装置（ガスアトマイズ装置）内での部分的な名称である。本来、ガスアトマイズ法は乾式造粒法として分類されるものであり、作製した粒子はガスアトマイズ装置下部の回収部より、粉体として回収できる。しかし、本発明においては、作製した超微粒子の凝集を防ぐために、回収部の改良を行っており、敢えて造粒工程と回収工程とを分けている。
【００３７】
回収工程とは次のような工程である。
前述したが、装置としてはガスアトマイズ装置と別個になっている訳ではなく、ガスアトマイズ装置の超微粒子回収部に別途バルブを設け、本体と遮断できるようにしているだけである。その中に極性溶媒を適当量入れた状態で、バルブを閉とし、超微粒子造粒部と隔てた状態をつくる。
【００３８】
その理由はいくつかあるが、例えばガスアトマイズ法をＨ_２ガスとＨｅガスの混合ガス系で行った場合、作製した超微粒子の凝集を防ぐために用いる極性溶媒の蒸気による危険性を排除しているのである。しかし、本質的な状態としては、安全状態を確保できるのであれば、ガスアトマイズ雰囲気に回収部が存在することは何の問題にもならない。
【００３９】
ここでは極性溶媒としているが、本発明のガスアトマイズ法では金属或いは合金を坩堝に入れ、高周波誘導加熱により溶融する際、カーボン製坩堝を使用している。そして不活性ガス雰囲気で溶融しているため、金属或いは合金の酸化物はカーボンにより還元されることから、作製する超微粒子の組成によっては、非極性溶媒または弱極性溶媒が使用できる場合がある。但し、水や含水率が非常に高い溶媒は、超微粒子を酸化させるために不適切である。
【００４０】
例えば使用できる極性溶媒としては、アルコール類ではα−テルピネオール、ベンジルアルコール、ヘキサノール等、有機エステル類の酢酸エチル、酢酸ブチル、オレイン酸メチル等であるが、弱極性溶媒であるヘキサン等の長鎖アルカン、シクロヘキサン等の環状アルカン、トルエン、キシレン等の芳香族炭化水素等も使用可能である。
【００４１】
これらの溶媒は単独で用いても、混合溶媒の形で用いても構わない。例えば長鎖アルカンの混合物であるミネラルスピリットでも使用可能である。しかし、溶媒選択に当たっては分散状態と共に分級工程にも関係しているので、溶媒の粘度が低い、蒸気圧が低い、沸点が高い等の物性も考慮し、溶媒を選定することが好ましい。
【００４２】
次に分級工程について説明する。通常ガスアトマイズ法は乾式プロセスであり、作製した粉体はそのまま気流式の分級機等で分級されることが多い。しかし、超微粒子の場合、粒子表面の活性が高く、凝集し易い（分散し難い）状態であり、乾式のまま取り出して分級工程に移ることはほぼ不可能である。そのため、本発明では、極性溶媒中に回収しており、湿式分級工程にて必要粒径に分級することがプロセス上の特徴の１つである。
【００４３】
超微粒子の湿式分級では、極性溶媒中では比較的分散しやすく、超微粒子が金属であるため比重が大きく溶剤との差が確保しやすいという特徴がある。しかし、分級という基本操作においては、分級に使用する流体が気体であるか、液体であるかの違いしかなく、分級基礎理論も同じである。強いて乾式分級との差を挙げれば、ほぼ完全な分散状態をつくれるので、比較的簡単な装置で精度の高い分級が可能である。
【００４４】
湿式分級装置を分類すると、重力分級によるものと遠心分級によるものとがあるが、遠心分級は更に自由渦型と強制渦型とに分類できる。しかし、金属超微粒子を製造する際には、重力分級と遠心分級、さらには粒子サイズ、沈降速度と溶媒の粘度（粒子に対する抗力）、溶媒流速を考慮したカラム型湿式分級を組み合わせることが好ましい。その場合、例えば重力分級により粒径２０μｍ以下程度に分け、遠心分級で１μｍ以下、カラム型湿式分級で超微粒子領域（０．３μｍ以下）に分級する。
【００４５】
本発明では超微粒子を得るために湿式分級を行っているので、湿式分級時の粗粉側に若干製品側の超微粒子が混在しても構わない。一般的には分級収率が低くなるので、粗粉側に製品側の粒子が混在することを避けようする。しかしそのために逆に製品側に粗粉側が混ざってしまうという結果となる。
【００４６】
本発明において、粗粉側に製品側が混ざっても（製品側には粗粉側は混ざらない状態）問題とならない最大の理由は、湿式分級の粗粉側の粒子をガスアトマイズ法の原料としてリサイクル使用できるからである。このリサイクル可能であることが、従来の金属超微粒子製造方法とは決定的な違いである。
【００４７】
リサイクル工程を簡単に説明すると、粗粉側のスラリー（金属粒子と極性溶媒が混ざっている状態）を固液分離する。その後固体側（つまり製造した金属粒子側）を洗浄後、乾燥する。この際金属粒子は酸化されることになるが、前述したように、ガスアトマイズ法での金属融解用坩堝はカーボン製であり、金属酸化物の状態で仕込んでも、高周波誘導加熱にて原料を溶融している途中で、金属に還元される。乾燥工程で酸化する程度の表面酸化であれば、カーボンによる還元が十分に行われる。
【００４８】
なお、金属酸化物の還元では温度が重要な因子であるが、本発明において高周波誘導加熱により金属を溶融する場合には、１５００℃程度まで昇温しており、この温度領域まで昇温することによってカーボン還元が十分に起こる。
【００４９】
次に導電性ペースト組成物、及びその製造方法について説明する。分級工程で得られた超微粒子スラリーを各種バインダーと混合して、導電性ペースト組成物とする。この際、必要に応じて、固液分離して溶媒を少なくする、導電性ペースト組成物として使用する有機溶剤と溶媒置換を行う等しても良い。溶媒置換では溶媒の極性が大きく異なる場合、溶媒の混合状態で超微粒子が凝集する場合があるので、固液分離を併用することが好ましい。
【００５０】
本発明では、一般的に金属・半金属（半導体とも呼ばれている）・希土類金属と呼ばれている、Ｌｉ、Ｎａ、Ｋ、Ｒｂ、Ｃｓ、Ｆｒ、Ｂｅ、Ｍｇ、Ｃａ、Ｓｒ、Ｂａ、Ｒａ、Ｓｃ、Ｙ、Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｐｍ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕ、Ａｃ、Ｔｈ、Ｐａ、Ｕ、Ｎｐ、Ｐｕ、Ｔｉ、Ｚｒ、Ｈｆ、Ｖ、Ｎｂ、Ｔａ、Ｃｒ、Ｍｏ、Ｗ、Ｍｎ、Ｔｃ、Ｒｅ、Ｆｅ、Ｒｕ、Ｏｓ、Ｃｏ、Ｒｈ、Ｉｒ、Ｎｉ、Ｐｄ、Ｐｔ、Ｃｕ、Ａｇ、Ａｕ、Ｚｎ、Ｃｄ、Ｈｇ、Ｂ、Ａｌ、Ｇａ、Ｉｎ、Ｔｌ、Ｓｉ、Ｇｅ、Ｓｎ、Ｐｂ、Ｐ、Ａｓ、Ｓｂ、Ｂｉ、Ｓｅ、Ｔｅ及びＰｏより選ばれる少なくとも１種以上の金属、或いは合金を用いることができる。
【００５１】
しかし、人体への影響、環境への影響、電子材料分野での使用等を考慮すると、本発明で用いる金属は、好ましくは、Ｃｕ、Ｓｎ、Ａｕ、Ａｇ、Ｂｉ、Ｉｎ、Ａｌ、Ｇａ、Ｇｅ、Ｃｏ、Ｓｉ、Ｗ、Ｔｉ、Ｎｉ、Ｐｔ、Ｍｇ、Ｍｏ、Ｍｎ、Ｃｒ及びＰより選ばれる少なくとも１種以上の金属、或いは合金を用いることができる。
【００５２】
用いる金属の選定は、導電性ペースト組成物の用途によって決めることができる。例えば、ハンダペースト、導電性接着剤、異方導電性ペースト、ダイアタッチペースト、回路形成用ペースト、層間接続用ペースト、バンプ形成用ペースト等であれば、Ｃｕ、Ｓｎ、Ａｕ、Ａｇ、Ｂｉ、Ｉｎ、Ａｌ、Ｇａ、Ｇｅ、Ｃｏ、Ｓｉ、Ｗ、Ｔｉ、Ｎｉ、Ｐｔ等を選択することが好ましく、Ｃｕ、Ｓｎ、Ａｕ、Ａｇ、Ｂｉ、Ｉｎ、Ｎｉ等の少なくとも１種以上の金属、或いは合金を選択することがさらに好ましい。
【００５３】
超微粒子の組成は、誘導結合型プラズマ発光分光分析装置（セイコーインスツルメント（株）製、ＳＰＳ−１７００ＨＲＶ型）を用いて測定することができる。本発明に用いる導電性ペースト組成物中の超微粒子の形状としては、製造後は球状であるが、後工程にて多面体状、鱗片状、フレーク状に加工したり、或いはこれらの混合物として用いることもできる。いずれの形状にしても、機械的に粉体を加工する公知の方法を用いることが可能であるが、導電性ペースト組成物を作製するための超微粒子は球状であることが好ましい。
【００５４】
導電性ペースト組成物は、希釈剤としての効果も期待できる沸点が５０℃以上の有機溶剤を含んでいても良い。これは使用時の粘度が高い等の理由で印刷に十分な流動性が得られない場合は粘度調整剤として添加してもよい。好適な添加量は、導電性ペースト組成物全体の３重量％以下である。
【００５５】
粘度を調整するために、モノエポキシ化合物や例えばジメチルアセトアミド、Ｎ−メチルピロリドン、メチルエチルケトン、メチルセロソルブ、メチルカルビトール、カルビトール、カルビトールアセテート、酢酸メチルセロソルブ、トルエン等の溶媒を単独あるいは複数の混合系を適当量混合することも可能である。得られる溶液もしくはペースト状物の粘度が５０００〜４０００００ｃｐ、より好ましくは２００００〜７００００ｃｐであることが作業性の面から好ましい。
【００５６】
本発明に用いられる熱硬化性樹脂は、導電性が得られるものであれば特に制限はない。一般的なものとしては、各種の分子量のレゾール型フェノール樹脂、ノボラック型フェノール樹脂、ビスフェノール型エポキシ樹脂、ノボラック型エポキシ樹脂、および１分子中に１個以上のグリシジル基を有する液状エポキシ化合物、例えばネオペンチルグリコールジグリシジルエーテル、ビスフェノールＡジグリシジルエーテル、プロピレングリコールジグリシジルエーテル、ヘキサンジオールジグリシジルエーテルなどと、アミン、酸無水物等からなるエポキシ硬化剤との組み合わせが好ましい。
【００５７】
その他のバインダー樹脂として、メラミン樹脂、ユリア樹脂、キシレン樹脂、アルキッド樹脂、不飽和ポリエステル樹脂、アクリル樹脂、ポリイミド樹脂、フラン樹脂、ウレタン樹脂、ビスマレイミド−トリアジン樹脂などが挙げられる。また、必要に応じて熱可塑性樹脂や表面処理剤、分散剤などを添加することができる。
【００５８】
エポキシ硬化剤としては一般的なエポキシ硬化剤を用いることができる。例えば、脂肪族ポリアミン系としてトリエチレンテトラミン、ｍ−キシレンジアミンなどがあり、芳香族アミン系としてはｍ−フェニレンジアミン、ジアミノフェニルスルフォンなどがあり、第三級アミン系としてはベンジルジメチルアミン、ジメチルアミノメチルフェノールなどがあり、酸無水物系としては無水フタル酸、ヘキサヒドロ無水フタル酸などがあり、三フッ化ホウ素アミンコンプレックス系としてはＢＦ_３−ピペリンジンコンプレックスなどがある。また、ビスフェノールＡなどのビスフェノール化合物でも良い。
【００５９】
熱可塑性樹脂としては、どの様な熱可塑性樹脂でも使用可能であるが、その構造の中に水素結合性の官能基を有するものが好ましい。水素結合性を有する官能基としては水素基、アミド基、ウレア基、イミド基、エステル基、エーテル基、チオエーテル基、スルホン基、ケトン基などがある。具体的には、１２−ナイロン、６−ナイロン、６，６−ナイロン等のポリアミド樹脂、ポリエチレン、ポリプロピレン等のオレフィン系樹脂、ポリ塩化ビニル、ポリ酢酸ビニル、ポリ塩化ビニリデン、ポリビニルアルコール、エチレン−酢酸ビニル共重合体等のポリビニル系樹脂、エチルアクリレート、メチルメタクリレート及びその変性物等のアクリル樹脂、ポリアクリロニトリル、アクリロニトリル−スチレン共重合体等のアクリロニトリル系樹脂、ポリウレタン系樹脂、ポリアセタール、ポリカーボネート、ポリイミド、ポリスルホン、ポリブチレンテレフタレート、ポリエチレンテレフタレート、ポリアリレート、ポリフェニレンオキシド及びその変性物、ポリエーテルスルホン、ポリフェニレンスルフィド、ポリアミドイミド、ポリオキシベンゼン、ポリエーテルケトン等のエンジニアリングプラスチックと称される樹脂、ポリアラミド、全芳香族ポリエステル、ポリエステルアミド等の液晶樹脂、ポリアミドエラストマー、ポリエステルエラストマー、ポリウレタンエラストマー等の熱可塑性エラストマーであり、これらのうち一種、または二種以上を組み合わせて使用できる。
【００６０】
ガラスフリットとしては、焼結材料に持ちいられているものであれば特に制約なく用いることができる。例えばＡｌ_２Ｏ_３、ＰｂＯ、ＺｎＯ、Ｂ_２Ｏ_３、ＣｄＯ、ＢａＯ、ＣａＯやそれらの中間体や混合物、または変性剤として含むホウケイ酸塩それらの混合系などである。また、セルロース類、亜酸化銅、アクリル樹脂、ＣｄＯや反応性酸化物などの焼結助剤と呼ばれているものを添加しても構わない。
【００６１】
ロジンとは一般にフラックスとも呼ばれているものであって、樹脂系フラックス、水溶性フラックス、無洗浄タイプフラックス等が使用できるが、特に活性化樹脂フラックスの使用が好ましい。これはロジン系天然樹脂またはその変性樹脂を主成分とし、これに活性剤、有機溶剤、粘度調整剤、その他添加剤が添加されたものである。
【００６２】
一般に、変性樹脂には重合ロジン、フェノール樹脂変性ロジンなど、活性剤には無機系及び有機系フラックス、その中でも特にアミン塩酸塩や有機酸系のフラックス、有機溶剤はカルビトール系、エーテル系のものが用いられる。なお、無機系フラックスを使用することもできる。フラックス形状は、液体フラックス、ペースト状フラックス、水溶性フラックスなど用途に合わせて選択することができる。
【００６３】
滑剤とは超微粒子が導電性ペースト組成物内において適当な分散状態を保持するための潤滑剤的な作用を示す物質であるが、含有可能な滑剤としては、パラフィンワックス、流動パラフィン、ポリエチレンワックス、ポリプロピレンワックス、エステルワックス、カルナウバ、マイクロワックス等のワックス類、ステアリン酸、１２−オキシステアリン酸、ラウリン酸等の脂肪酸類、ステアリン酸亜鉛、ステアリン酸カルシウム、ステアリン酸バリウム、ステアリン酸アルミニウム、ステアリン酸マグネシウム、ラウリン酸カルシウム、リシノール酸亜鉛、リシノール酸カルシウム、２−エチルヘキソイン酸亜鉛等の脂肪酸塩、ステアリン酸アミド、オレイン酸アミド、エルカ酸アミド、ベヘン酸アミド、パルミチン酸アミド、ラウリン酸アミド、ヒドロキシステアリン酸アミド、メチレンビスステアリン酸アミド、エチレンビスステアリン酸アミド、エチレンビスラウリン酸アミド、ジステアリルアジピン酸アミド、エチレンビスオレイン酸アミド、ジオレイルアジピン酸アミド、Ｎ−ステアリルステアリン酸アミド、Ｎ−オレイルステアリン酸アミド、Ｎ−ステアリルエルカ酸アミド、メチロールベヘン酸アミド、メチロールステアリン酸アミド等の脂肪酸アミド、ステアリン酸ブチル等の脂肪酸エステル、エチレングリコール、ステアリルアルコール等のアルコール類、ポリエチレングリコール、ポリプロピレングリコール、ポリテトラメチレングリコール及びこれらの変性物からなるポリエーテル類、シリコーンオイル、シリコングリース等のポリシロキサン類、フッ素系オイル、フッ素系グリース、含フッ素樹脂粉末といったフッ素化合物、窒化珪素、炭化珪素、酸化マグネシウム、アルミナ、シリカゲル等の無機化合物粉体などが挙げられる。
【００６４】
これら滑剤のうちの一種、又は二種以上が用いられるが、ワックス類、ポリエーテル類、脂肪酸アミドのうちの少なくとも一種を滑剤として含有させると、電気接続用金属粉体組成物の成形加工性が大きく向上するために好ましい。滑剤の添加量は、導電性ペースト組成物中に於いて３重量％以下であることが好ましく、さらに好ましくは０．０５〜２重量％である。
【００６５】
カップリング剤とは、金属超微粒子と有機化合物である各種樹脂との接着性を高めるために添加されるものであり、カップリング剤の添加により電気的接続部の強度を高めることも期待できる。カップリング剤にはシラン系、チタン系、アルミニウム系、ジルコニウム系、クロム系、鉄系、錫系等いろいろなものがある。例えば、シラン系カップリング剤としては、フェニルトリメトキシシラン、ジフェニルジメトキシシラン、フェニルトリエトキシシラン、ジフェニルジエトキシシラン等が挙げられる。チタン系では、イソプロピルトリイソステアロイルチタネート、テトライソプロピルチタネート、イソプロピルトリオクタノイルチタネート等が挙げられる。カップリング剤の添加量は導電性ペースト組成物中に於いて３重量％であることが好ましく、さらに好ましくは０．０１〜２重量％である。
【００６６】
導電性ペースト組成物中の各成分は、超微粒子が６０〜９８重量％の範囲、有機バインダーが２〜４０重量％の範囲で含有させることが好ましい。
なお、本発明で製造された超微粒子、或いは導電性ペースト組成物中の超微粒子は、従来技術で製造された粒子のような狭い粒度分布ではなく、広い粒度分布を持つことも特徴としてあげることができる。電子材料分野において使用する場合、充填率の面からも粒度分布が広い方が充填率を上げられる（空隙率を小さくすることができる）ことになり、接続信頼性の面よりも新規性・進歩性があり、産業上の利用価値が高いと考えられる。
【００６７】
【実施例】
次に、実施例及び比較例に基づいて本発明を詳細に説明するが、本発明はこれらの実施例にのみ限定されるものではない。
【００６８】
［実施例１］
Ｓｎ粒子０．９６ｋｇ（純度９９重量％以上）、Ｉｎ粒子１．０４ｋｇ（純度９９重量％以上）をカーボン坩堝に入れ、高周波誘導加熱装置により１５００℃まで加熱、融解した。金属融解部の雰囲気は９９体積％以上のヘリウム中で行ない、圧力は０．０３ＭＰａに設定した。次に、この金属融液をカーボン坩堝の底部に設けたノズルから、ヘリウムガス雰囲気の噴霧槽内に導入し（噴霧部圧力は０．００５ＭＰａに設定した）、カーボン坩堝先端付近に設けたガスノズルから、Ｈ_２／Ｈｅ混合ガス（Ｈ_２濃度２体積％／Ｈｅ濃度９８体積％の混合ガス、混合ガス中の酸素濃度０．００１体積％、圧力２．５ＭＰａＧ）を噴出して金属融液のアトマイズ化し、超微粒子を作製した。この際の計算される２５℃におけるガス噴出速度は、８８５ｍ／ｓとなる。装置下部にはボールバルブで隔てた回収部を設け、ベンジルアルコールを入れておいた。金属融液が全量噴霧され、高周波誘導加熱装置の電源をＯＦＦにした後、噴霧部と回収部と接続しているラインより気化器を通したベンジルアルコールをポンプで押し込み、噴霧部内圧力を０．０１ＭＰａとした。その後、回収部のボールバルブを開け、超微粒子を回収した。体積平均粒径は５μｍであった。一部サンプリングを行い最小粒子径をＳＥＭで確認したところ、０．０８μｍであった。超微粒子の回収量は１．７ｋｇであった。
【００６９】
［実施例２］
実施例１と同じ金属種及び装置を用いて、下記表１に示すアトマイズガスを用いて微粒子を造粒し、回収した。なお、金属融解部圧力：ａ、及び噴霧部内圧力：ｂも同一条件で行った。気体組成とそのガス噴出速度（計算値）を表１に示す。
得られた超微粒子の体積平均粒径は４．５μｍであった。一部サンプリングを行い最小粒子径をＳＥＭで確認したところ、０．０６μｍであった。微粒子の回収量は１．６ｋｇであった。
【００７０】
【表１】

【００７１】
［実施例３］
実施例１と同じ金属種及び装置を用いて、下記表２に示すアトマイズガスを用いて微粒子を造粒し、回収した。なお、金属融解部圧力：ａ、及び噴霧部内圧力：ｂも同一条件で行った。気体組成とそのガス噴出速度（計算値）を表２に示す。
得られた超微粒子の体積平均粒径は５．５μｍであった。一部サンプリングを行い最小粒子径をＳＥＭで確認したところ、０．０９μｍであった。微粒子の回収量は１．８ｋｇであった。
【００７２】
【表２】

【００７３】
［実施例４］
（超微粒子の分級）
本実施例では、実施例１で得られた超微粒子スラリーに対して湿式遠心分級装置を用いて分級処理を行った。分級して得られた超微粒子は、平均粒径が０．８μｍで、最大粒径が１μｍであった。なお、湿式分級後の粗粉側は固液分離し、アセトン洗浄後、６０℃熱風乾燥機にて乾燥した。また、超微粒子の回収量は０．１７ｋｇで、湿式分級収率は１０％であり、乾燥後のリサイクル可能粒子は１．４ｋｇであった。
２段目はカラム型分級機を用いて、湿式分級を行った。超微粒子の回収量は０．１ｋｇであり、湿式分級収率は５９％であった。平均粒径は０．１μｍで、最大粒子系は０．５μｍであった。
【００７４】
［実施例５］
（［導電性ペースト組成物１］の作製と体積抵抗値測定）
上記実施例４で最終的に得られた超微粒子スラリーを脱泡混練機によりデカンテーションを繰り返し、微粒子含有率をあげていった。超微粒子の含有率は６０ｗｔ％となった。有機バインダーとして液状エポキシ樹脂を超微粒子に対して１０重量％、滑剤としてステアリン酸を１重量％、カップリング剤としてチタン系カップリング剤（商品名ＫＲ−ＴＴＳ）を０．５重量％加え、ビーカー内で混練した。混練後、再度脱泡混練機を用いてデカンテーションを実施し、超微粒子含有量を８０ｗｔ％とした。得られた導電性ペースト組成物をガラスエポキシ基板上にガラス棒を用いて評価パターン印刷を行った。このガラスエポキシ基板を、窒素雰囲気下でピーク温度２３０℃に設定された窒素リフロー炉を通過させて熱硬化した。硬化後の硬化物厚みは平均で７０μｍであった。得られた硬化後ガラスエポキシ基板を四端子法により抵抗測定したが、体積抵抗値に換算すると４＊１０^−４Ω・ｃｍであった。
【００７５】
［実施例６］
（［導電性ペースト組成物２］の作製と体積抵抗値測定）
上記実施例４で最終的に得られた超微粒子スラリーを脱泡混練機によりデカンテーションを繰り返し、微粒子含有率をあげていった。この操作を数回繰り返した後、微粒子含有率は６０ｗｔ％となった。有機バインダーとして、ＰｂＯ−ＺｎＯ−Ｂ_２Ｏ_３系のガラスフリットを超微粒子に対して５重量％、エチルセルロースを０．２５重量％、亜酸化銅を１．５重量％入れ、ビーカー内で混練した。混練後、再度脱泡混練機を用いてデカンテーションを実施し、超微粒子含有量を８５ｗｔ％とした。得られた導電性ペースト組成物を９６％アルミナ基板上にスクリーン印刷でテストパターンを印刷し、窒素雰囲気下でピーク温度６５０℃に設定された連続焼成炉を通過させて焼成した。焼成後の導体膜厚は平均で１２μｍであった。得られたアルミナ基板を四端子法により抵抗測定したが、体積抵抗値に換算すると１＊１０^−５Ω・ｃｍであった。
【００７６】
［比較例１］
Ｓｎ粒子０．９６ｋｇ（純度９９重量％以上）、Ｉｎ粒子１．０４ｋｇ（純度９９重量％以上）をカーボン坩堝に入れ、高周波誘導加熱装置により１５００℃まで加熱、融解した。金属融解部の雰囲気は９９体積％以上の窒素中で行ない、圧力は０．０３ＭＰａに設定した。次に、この溶融金属をカーボン坩堝の先端より、ヘリウムガス雰囲気の噴霧槽内に導入した後（噴霧部圧力は０．００５ＭＰａに設定した）、カーボン坩堝先端付近に設けたガスノズルから、窒素ガス（Ｎ_２濃度９９体積％以上、ガス中の酸素濃度０．００１体積％、圧力２．５ＭＰａＧ）を噴出してアトマイズを行い、金属粒子を作製した。この際の計算される２５℃におけるガス噴出速度は、３２１ｍ／ｓとなる。装置下部にはボールバルブで隔てた回収部を設け、中は窒素ガス雰囲気にしておいた。溶融金属が全量噴霧され、高周波誘導加熱装置の電源をＯＦＦにした後、ボールバルブを開け、金属粒子を回収した。体積平均粒径は１２μｍであった。一部サンプリングを行い最小粒子径をＳＥＭで確認したところ、０．７μｍであった。金属粒子の回収量は１．２ｋｇであり、若干回収量が少なかった。
【００７７】
［比較例２］
（金属粒子の分級）
上記比較例１で得られた金属粒子を用いて、乾式分級装置を用いて分級を行った。平均粒径が０．８μｍで、最大粒径が１μｍであった。なお、金属粒子の回収量は０．０３ｋｇで、乾式分級収率は４％であり、リサイクル可能粒子は０．８ｋｇであり、凝集によるロスが約０．４ｋｇ（ロス率３７％に相当）であった。
【００７８】
［比較例３］
（［導電性ペースト組成物３］の作製と体積抵抗値測定）
上記比較例２で最終的に得られた金属粒子に、有機バインダーとして液状エポキシ樹脂を金属粒子に対して１０重量％、滑剤を１重量％、カップリング剤を０．５重量％加え、ビーカー内で混練した。さらに三本ロールで混練後、脱泡混練機を用いて脱泡操作をした。得られた導電性ペースト組成物をガラスエポキシ基板上にガラス棒を用いて評価パターン印刷を行った。このガラスエポキシ基板を、窒素雰囲気下でピーク温度２３０℃に設定された窒素リフロー炉を通過させて熱硬化した。硬化後の硬化物厚みは平均で７０μｍであった。得られた硬化後ガラスエポキシ基板を四端子法により抵抗測定したが、体積抵抗値に換算すると４＊１０^−４Ω・ｃｍであった。
【００７９】
［比較例４］
（［導電性ペースト組成物４］の作製と体積抵抗値測定）
上記比較例２で最終的に得られた金属粒子を用いて、有機バインダーとしてＰｂＯ−ＺｎＯ−Ｂ_２Ｏ_３系のガラスフリットを金属粒子に対して５重量％、エチルセルロースを０．２５重量％、亜酸化銅を１．５重量％入れ、ビーカー内で混練した。さらに三本ロールで混練後、脱泡混練機を用いて脱泡操作をした。得られた導電性ペースト組成物を９６％アルミナ基板上にスクリーン印刷でテストパターンを印刷し、窒素雰囲気下でピーク温度６５０℃に設定された連続焼成炉を通過させて焼成した。焼成後の導体膜厚は平均で１２μｍであった。得られたアルミナ基板を四端子法により抵抗測定したが、体積抵抗値に換算すると１＊１０^−５Ω・ｃｍであった。
【００８０】
【発明の効果】
本発明による金属超微粒子の製造方法、製造装置、及び導電性ペースト組成物の製造法を用いることにより、凝集がない状態で超微粒子を得ることができるようになり、超微粒子の表面酸化を防いだまま導電性ペースト組成物を製造することができる。また、大量生産に向いたプロセスとなり、超微粒子のリサイクルも可能となるために、製造コストも従来品と比べ大幅に安価となる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for producing ultrafine metal particles used as a conductive filler, a conductive paste composition using ultrafine metal particles, and a method for producing the same.
[0002]
[Prior art]
Conventionally, as a method for producing ultrafine metal particles, a physical method described in Patent Document 1 and a chemical method (liquid phase reduction method, gas phase reduction method) described in Patent Document 2 have been used.
Specific examples of the production method include physical methods such as an in-gas evaporation method, a sputtering method, a metal vapor synthesis method, and a vacuum evaporation method on fluidized oil.The liquid-phase reduction method includes a colloid method, an alkoxide method, and a co-method. There are a precipitation method, a uniform precipitation method, and the like.₂Medium reduction method, metal chloride O₂Medium oxidation method, metal chloride NH₃Medium nitriding method, H of oxide and hydrated oxide₂There are a medium reduction method, a solvent evaporation method and the like.
[0003]
Ultrafine particles of various metals or alloys are manufactured by these manufacturing methods, and are used as conductive fillers for conductive paste. On the other hand, various metal ultrafine particles have a high activity on the surface of the particles, and when taken out into the atmosphere, there are problems such as aggregation of the particles, oxidation of the particle surface, and poor dispersibility in the organic solvent after the aggregation. Therefore, the metal ultrafine particles obtained by the above-described production method are often subjected to a surface treatment.
[0004]
However, in a manufacturing method generally called a physical method, in a vacuum vessel, and by adjusting the pressure of an inert gas to about several kPa and evaporating the metal to obtain ultrafine metal particles, the purity is high, Despite its features such as good properties and sharp particle size distribution, (1) a process requiring a vacuum vessel, (2) the particle size of the ultrafine metal particles is controlled by the inert gas pressure. Therefore, reproducibility due to pressure fluctuations is not easy. (3) The production volume is small due to the low concentration of ultrafine metal particles in a vacuum apparatus. (4) Surface treatment after ultrafine particle formation to maintain a dispersed state. This is an unsuitable process for mass-producing ultrafine metal particles including the production cost, and there is a need for improvement.
[0005]
In a production method called a liquid phase reduction method, various metal salt solutions are reduced to obtain ultrafine metal particles. However, (1) particles are easily aggregated in a reduction process, and a large amount of a dispersant, a surfactant, and a precipitant are used. (2) low purity due to additives and the like, impurities may be mixed in, (3) ultra-fine metal particles in the colloidal suspension have very low concentration, etc. There's a problem.
[0006]
In the gas phase reduction method, it is possible to produce a colloidal suspension having a high concentration of ultrafine metal particles, but it is very difficult to control the particle size distribution, and the production apparatus is a special apparatus. There is a problem, and as with the physical method, it is an unsuitable process for mass-producing ultrafine metal particles including the production cost, and improvement is desired.
[0007]
[Patent Document 1]
JP-A-3-34211
[Patent Document 2]
JP-A-11-319538
[Patent Document 3]
JP 2002-121606 A
[0008]
[Problems to be solved by the invention]
As described above, there are methods for producing various types of ultrafine metal particles. However, the use of special equipment increases the production cost, and is only an unsuitable process for mass production. In addition, it is an impossible process to recycle the raw material of the produced ultrafine metal particles.
[0009]
The present invention has been made in view of the above-described problems, and has been developed in such a manner that ultrafine metal particles, which are attracting attention in the field of electronic materials, are produced in a large amount by a process without aggregation, low production cost, and capable of recycling raw materials. It is an object of the present invention to provide a manufacturing method and a manufacturing apparatus that can be manufactured, a conductive paste composition using ultrafine particles obtained by the manufacturing method as a conductive filler, and a manufacturing method thereof.
[0010]
[Means for Solving the Problems]
The present invention has solved the above-mentioned problem by providing the following configuration.
(1) In a method for producing ultrafine particles including a granulation step of obtaining ultrafine particles from a melt of a raw material metal by a gas atomization method and a collection step of collecting the ultrafine particles, H is used as an atomizing gas in the granulation step.₂A method for producing ultrafine metal particles, comprising using a mixed gas of a gas and an inert gas.
(2) The gas injection speed at 25 ° C. calculated at a gas injection port of a gas nozzle for jetting an atomizing gas is in a range of 700 m / s to 1200 m / s, according to the above (1), A method for producing ultrafine metal particles.
(3) The inert gas is He gas, and [H₂Gas / (H₂Gas + He gas)]₂The method for producing ultrafine metal particles according to the above (1) or (2), wherein the gas volume mixing ratio is in the range of 0.01 to 30 vol%.
[0011]
(4) H₂The method for producing ultrafine metal particles according to the above (1) or (2), wherein the gas volume mixing ratio is in the range of 60 to 99 vol%.
(5) He gas and another inert gas are contained as the inert gas, and [(H₂Gas + He gas) / (H₂Gas + He gas + another inert gas)]₂Gas + He gas] volume mixing ratio is in the range of 85 to 99 vol%, and [H₂Gas / (H₂Gas + He gas)]₂The method for producing ultrafine metal particles according to (1) or (2), wherein the gas volume mixing ratio is in the range of 0.01 to 30 vol%.
(6) The method for producing ultrafine metal particles according to any one of the above (1) to (5), wherein the ultrafine particles are recovered in a solvent in the recovery step.
(7) The method for producing ultrafine metal particles according to (6), further comprising a wet classification step of wet-classifying an ultrafine particle slurry obtained by collecting the ultrafine particles in a solvent.
[0012]
(8) The metal ultrafine particles according to claim 7, wherein the raw metal is melted in a carbon crucible, and the ultrafine metal particles collected in the wet classification step are returned to the carbon crucible as a raw material and reused. Production method.
(9) The raw material metals are Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ac, Th, Pa, U, Np, Pu, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, The method for producing ultrafine metal particles according to any one of claims 1 to 8, wherein the method comprises at least one selected from the group consisting of P, As, Sb, Bi, Se, Te and Po.
(10) An organic solvent, a thermosetting resin, a thermoplastic resin, a glass frit, a rosin, a lubricant, and a coupling agent are added to the ultrafine particles produced by the method for producing ultrafine particles according to claim 1. A method for producing a conductive paste composition, characterized by adding at least one of the above.
(11) A conductive paste composition produced by the production method according to claim 10.
[0013]
(12) A raw material melting section, a spray section for obtaining ultrafine particles from the melt of the raw material by a gas atomization method, and a recovery section for the ultrafine particles formed by the spray section, wherein the spray section supplies the raw material melt. A liquid nozzle and a gas nozzle.₂An apparatus for producing ultrafine metal particles, which injects a mixed gas of a gas and an inert gas.
(13) When the pressure of the raw material melting section is defined as aMPa and the pressure of the spray section is defined as bMPa, a pressurizing or depressurizing means for a> b is provided, and an ultrasonic wave is applied to a portion where the raw material melt is jetted. 13. The method according to claim 12, further comprising: means for vibrating; and a means for separating the ultrafine particles and the solvent, wherein the ultrafine particle collection unit accommodates a solvent for dispersing the ultrafine particles formed by spraying. Metal ultrafine particle manufacturing equipment.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
In the present invention, ultrafine metal particles are granulated by a gas atomizing method (sometimes referred to as a rapid solidification method), which is a point of the present invention that is significantly different from the conventional technology. The outline of the gas atomization method is a method in which a predetermined metal or alloy is put in a crucible, a high-frequency induction heating is used to form a metal melt, and the metal melt is turned into particles by injecting a gas into the metal melt as an injection medium. . As a gas to be used, an inert gas or air is often used.
[0015]
Generally, the particle size of the particles obtained is controlled by the gas injection pressure. However, when the present inventors prepared an Ag / Cu alloy (Ag content: 20 wt%) by a gas atomization method, the volume of the obtained particles was reduced. The average particle size is N₂When a gas was used, the thickness was about 18 to 25 μm. The minimum particle size of the existing particles was 0.9 μm.
[0016]
Here, the present inventors examined what kind of particle size control factors exist in the gas atomization method. As the empirical formulas of the gas atomizing method, the following formulas such as “Lavanska's formula” and “Nukiyama fuel injection formula” (external mixing single nozzle airflow injection formula) are known.
[0017]
<Lavanska formula>
d_m/ D_melt= K [ν_m/ Ν_g* 1 / W * (1 + M / A)]^1/2
W = V_ge ²* Ρ_m* D₀/ Σ_m
M = A₀* Ρ_m* C_D(2 * g * h₀)^1/2
A = A_t* ｛Γ * ρ_ge* P_e* [2 / (γ + 1)^{γ + 1 / γ-1}]｝^1/2
[0018]

[0019]
In the above empirical formula, there is a device coefficient term (such as an experimental constant) peculiar to the device used, but the particle diameter control factors are: injection gas speed, injection gas to metal melt kinematic viscosity ratio, injection gas It was found to be the metal melt flow ratio. A close examination of the empirical formula revealed that the jet gas velocity was the largest factor in determining the particle size.
[0020]
The velocity of the injected gas can be considered as the velocity of the gas ejected from the container (such as the “Zeuner's formula” and the “expression of the gas flow rate” described below). An index determined by the number is also called a specific heat ratio γ (γ = constant pressure specific heat Cp / constant volume specific heat Cv).₂And H₂Is about 1.40 for a diatomic molecular gas such as, and about 1.66 for a monoatomic molecular gas such as He or Ar), and a gas constant (a gas constant of R = 8.316 J / mol, which is generally called). Rather, it indicates a gas constant converted per g of gas, for example, N₂0.297 J / g. k, 2.077 J / g · k for He gas, H₂It becomes 4.148 J / g · k for gas), and it was found that the temperature, the adiabatic index, the injection pressure, the gas density, the gas velocity coefficient that can be calculated from the gas constant, and the like are interrelated.
[0021]
<Zeuner's formula>
q = 2γ / (γ-1) * (P₀/ Ρ₀) * (1- (P / P₀)^{(Γ-1) / γ})
In the case of adiabatic change; C = [γ * (P / ρ)]^1/2= [Γ * (R / m)]^1/2
In the case of an ideal gas; P = (R / m) * ρ * T
[0022]
<Expression of gas flow rate>
q = q_m* [1- (P / P₀)^{(Γ-1) / γ}]^1/2
q_m= [2 / (γ-1)]^1/2* C₀
[0023]
Furthermore, the present inventors have found that the grinding energy of the propellant gas and the distance of contact between the propellant gas and the metal melt are related as factors determining the particle size.
In addition, when producing ultrafine particles by the gas atomization method, it was discovered that the critical pressure ratio shown below must be considered between the pressure of the injected gas and the gas ejection speed due to the granulation mechanism and the structure of the device. did.
[0024]
<Relational expression of critical pressure ratio>
p^*/ P₀= [2 / (γ + 1)]^{γ / (γ-1)}
[0025]
Although detailed numerical values are omitted, the injection gas is N₂When the gas is changed to He gas, the gas velocity to be injected becomes 2.7 times, the pulverization energy is calculated to be 1.1 times, and the same Ag / Cu alloy is produced by the gas atomization method under the same conditions. The experiment confirmed that the volume average particle size was 8 to 12 μm. Further, the minimum particle diameter existing was 0.5 μm, and it was clearly confirmed that the entire particles were heading for finer particles.
[0026]
Note that N₂Injection gas velocity and pulverization energy when gas and He gas were mixed were also calculated and examined in light of the volume average particle diameter obtained as experimental data. The tendency can be roughly shown by the gas characteristics of the mixed system. However, it was confirmed that the difference between the actually measured value and the calculated value was so large that it could not be interpreted and explained using existing mathematical expressions. Actually, it is very difficult to elucidate the detailed atomization mechanism by the gas atomization method, and the state of the mixed gas system cannot be estimated with existing mathematical formulas.
[0027]
However, instead of the characteristics of each of the gases used as the propellant gas, aiming for a synergistic effect when a mixed gas is used, ultra-fine particles, which are attracting attention in the field of electronic materials, do not agglomerate, have low manufacturing costs, and can recycle raw materials. As a production method capable of mass production in a possible process, the present inventors have proposed H.₂A metal characterized by using a mixed gas of a gas and an inert gas and having a gas ejection speed at 25 ° C. calculated at a gas injection port of a gas nozzle used in a gas atomization method in a range of 700 m / s to 1200 m / s. A method for producing ultrafine particles has been developed.
[0028]
In the present invention, H₂The inert gas used by mixing with the gas is N 2₂Gas, He gas, Ar gas and Ne gas can be used.₂It is preferable to use gas, He gas, and Ar gas, and it is more preferable to use He gas.
H₂When gas is used, N₂The calculation is such that an injection gas velocity of 3.8 times for gas and 1.4 times for He gas can be obtained. Regarding the grinding energy, N₂Although it can be calculated that it is equivalent to gas, as described above, this numerical value does not match the actually measured value.
[0029]
H₂Considering the gas characteristics, the explosion range is 4 to 75 vol% (in air, room temperature), and it is generally said that the explosion range becomes wider as the pressure increases. The ignition temperature is 500 ° C. (in air). From these data, H₂Although it seems that gas is very difficult to use industrially, according to experiments conducted by the present inventors, it has been found that by making a gas mixture with an inert gas, the H₂It seems that the characteristics of the gas alone are improved, but the state of the condition is beyond speculation.
[0030]
The actually calculated gas ejection velocity at 25 ° C. for each single gas type is H₂Gas is 1203 m / s, N₂The gas is 321 m / s, the He gas is 879 m / s, the Ar gas is 311 m / s, and the Ne gas is 393 m / s. The appropriate gas selection and mixing ratio of the gas mixing system in the present invention are determined by the gas ejection speed requirement of the gas ejection port at 25 ° C.
[0031]
Next, the outline and features of the gas atomizing device used in the present invention will be described.
Although it is also related to the three steps of the manufacturing method described later, the gas atomizing apparatus is roughly divided into a raw metal melting unit, a spraying unit for forming particles by gas injection, and a collecting unit for collecting the obtained particles. You. The gas atomizing device used by the present inventors includes a gas recovery line, a gas holder, a gas compressor, and a moisture adsorber as other auxiliary facilities, but they are not directly related to the features of the present invention. Is omitted.
[0032]
The metal melting portion is a portion where a raw material is weighed so as to have an alloy composition of ultrafine particles to be produced, and is melted in a carbon crucible by a heating device such as a high-frequency induction heating device. There is also deoxygenation (reduction effect) by carbon, and when the raw material is melted, it is partially melted under vacuum. After the melting, when the metal melt is ejected from the molten metal nozzle, the metal melting part is pressurized with an inert gas. The pressure of the metal melting part at this time is defined as a [MPa]. In a pressurized state, the metal melt is sucked in by the suction effect of the injection gas at the time of gas injection, but has the effect of being further pushed out.
The pressure of the spray unit is b [MPa], and the pressure is adjusted so that a> b.
[0033]
An ultrasonic vibration system is attached to the part where the metal melt is ejected. This has the effect of assisting the atomization by gas injection by vibrating the metal melt by ultrasonic vibration, and as a result, the volume average particle diameter can be reduced.
[0034]
The collection unit is a part in which ultrafine particles are dispersed in a solvent, and a circulation line, a filter, and a filter are provided so that the ultrafine particles in a dispersed state and the solvent can be separated (filtered or separated as an image). A pump is attached. A normal recovery unit is provided separately from this line, and in the production of conductive paste, it is necessary to increase the content of ultra-fine particles in the recovered slurry or to increase the amount of ultra-fine particles when filling a larger amount of solvent into the device. This is a system for partially recovering fine particles.
[0035]
Next, although partially overlapping, the granulation step, the recovery step, and the classification step will be described.
First, in the granulation step, a raw material metal or alloy is melted in a carbon crucible to form a metal melt, and H₂The figure shows a step of injecting a mixed gas of a predetermined ratio of a gas and an inert gas to form ultrafine particles (gas atomizing method, rapid solidification method).
[0036]
Although the details will be described in the recovery step, the granulation step and the recovery step are partial names in one apparatus (gas atomizing apparatus). Originally, the gas atomization method is classified as a dry granulation method, and the produced particles can be collected as a powder from a collection section below the gas atomization device. However, in the present invention, in order to prevent aggregation of the produced ultrafine particles, the recovery section is improved, and the granulation step and the recovery step are intentionally separated.
[0037]
The recovery step is as follows.
As described above, the apparatus is not necessarily separate from the gas atomizing apparatus, but is simply provided with a separate valve in the ultra-fine particle collecting section of the gas atomizing apparatus so that the gas atomizing apparatus can be shut off from the main body. With the polar solvent in an appropriate amount, the valve is closed to create a state separated from the ultrafine particle granulation section.
[0038]
There are several reasons for this. For example, the gas atomization method₂When the reaction is performed in a mixed gas system of gas and He gas, the danger due to the vapor of the polar solvent used to prevent aggregation of the produced ultrafine particles is eliminated. However, as an essential state, as long as a safe state can be ensured, the existence of the recovery section in the gas atomizing atmosphere does not pose any problem.
[0039]
Here, the polar solvent is used, but in the gas atomizing method of the present invention, when a metal or an alloy is put in a crucible and melted by high-frequency induction heating, a carbon crucible is used. Since the metal or alloy oxide is reduced by carbon because it is melted in an inert gas atmosphere, a nonpolar solvent or a weakly polar solvent may be used depending on the composition of the ultrafine particles to be produced. However, water or a solvent having a very high water content is unsuitable for oxidizing ultrafine particles.
[0040]
For example, polar solvents that can be used include alcohols such as α-terpineol, benzyl alcohol, and hexanol, and organic esters such as ethyl acetate, butyl acetate, and methyl oleate, and long-chain alkanes such as hexane, which is a weakly polar solvent. And cyclic alkane such as cyclohexane, and aromatic hydrocarbon such as toluene and xylene.
[0041]
These solvents may be used alone or in the form of a mixed solvent. For example, mineral spirits, which are mixtures of long-chain alkanes, can be used. However, since the selection of the solvent is related to the classification step as well as the dispersion state, it is preferable to select the solvent in consideration of the physical properties of the solvent such as low viscosity, low vapor pressure, and high boiling point.
[0042]
Next, the classification step will be described. Normally, the gas atomization method is a dry process, and the produced powder is often classified as it is by an airflow classifier or the like. However, in the case of ultrafine particles, the activity on the surface of the particles is high and the particles are easily aggregated (hard to disperse). Therefore, in the present invention, one of the features of the process is that the particles are recovered in a polar solvent and classified to a required particle size in a wet classification step.
[0043]
The wet classification of ultrafine particles is characterized in that it is relatively easy to disperse in a polar solvent, and since the ultrafine particles are a metal, the specific gravity is large and a difference from the solvent is easily secured. However, in the basic operation of classification, the only difference is whether the fluid used for classification is a gas or a liquid, and the basic classification theory is the same. An almost perfect dispersion state can be created by giving a difference from the forced and dry classification, so that highly accurate classification can be performed with a relatively simple apparatus.
[0044]
Wet classification devices are classified into gravity classification and centrifugal classification. The centrifugal classification can be further classified into a free vortex type and a forced vortex type. However, when producing ultrafine metal particles, it is preferable to combine gravity classification and centrifugal classification, and further, column-type wet classification in consideration of particle size, sedimentation velocity, solvent viscosity (drag force against particles), and solvent flow rate. In this case, for example, the particles are divided into particles of about 20 μm or less by gravity classification, and classified into 1 μm or less by centrifugal classification and into ultrafine particles (0.3 μm or less) by column-type wet classification.
[0045]
In the present invention, since wet classification is performed to obtain ultrafine particles, ultrafine particles on the product side may be slightly mixed with the coarse powder during wet classification. In general, the classification yield is low, so that particles of the product side are prevented from being mixed with the coarse powder side. On the contrary, however, the result is that the coarse side mixes with the product side.
[0046]
In the present invention, even if the product side is mixed with the coarse powder side (the coarse side is not mixed with the product side), there is no major problem because the particles of the wet-classified coarse powder side are recycled and used as a raw material for the gas atomization method. Because you can. This recyclability is a decisive difference from the conventional ultrafine metal particle manufacturing method.
[0047]
Briefly describing the recycling process, the slurry on the coarse powder side (a state in which metal particles and a polar solvent are mixed) is subjected to solid-liquid separation. Thereafter, the solid side (that is, the manufactured metal particle side) is washed and then dried. At this time, the metal particles are oxidized, but as described above, the crucible for melting the metal by the gas atomization method is made of carbon, and even when charged in the state of a metal oxide, the raw material is melted by high-frequency induction heating. On the way, it is reduced to metal. If the surface oxidation is such that it is oxidized in the drying step, the reduction by carbon is sufficiently performed.
[0048]
In addition, temperature is an important factor in the reduction of metal oxides. In the present invention, when a metal is melted by high-frequency induction heating, the temperature is raised to about 1500 ° C., and the temperature must be raised to this temperature range. As a result, carbon reduction occurs sufficiently.
[0049]
Next, the conductive paste composition and a method for producing the same will be described. The ultrafine particle slurry obtained in the classification step is mixed with various binders to obtain a conductive paste composition. At this time, if necessary, the solvent may be reduced by solid-liquid separation, or the solvent may be replaced with an organic solvent used as the conductive paste composition. In the case of solvent replacement, if the polarity of the solvent is largely different, ultrafine particles may aggregate in a mixed state of the solvent, and therefore, it is preferable to use solid-liquid separation in combination.
[0050]
In the present invention, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, which are generally called metals, metalloids (also called semiconductors), and rare earth metals, Ra, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ac, Th, Pa, U, Np, Pu, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, At least one metal or alloy selected from Hg, B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, Sb, Bi, Se, Te and Po can be used. .
[0051]
However, in consideration of effects on the human body, effects on the environment, use in the field of electronic materials, and the like, the metal used in the present invention is preferably Cu, Sn, Au, Ag, Bi, In, Al, Ga, Ge. , Co, Si, W, Ti, Ni, Pt, Mg, Mo, Mn, Cr, and at least one or more metals or alloys can be used.
[0052]
The selection of the metal to be used can be determined according to the use of the conductive paste composition. For example, if a solder paste, a conductive adhesive, an anisotropic conductive paste, a die attach paste, a circuit forming paste, an interlayer connecting paste, a bump forming paste, or the like, Cu, Sn, Au, Ag, Bi, In, or the like is used. , Al, Ga, Ge, Co, Si, W, Ti, Ni, Pt, and the like are preferably selected, and at least one or more metals or alloys such as Cu, Sn, Au, Ag, Bi, In, and Ni More preferably, is selected.
[0053]
The composition of the ultrafine particles can be measured using an inductively-coupled plasma emission spectrometer (SPS-1700HRV, manufactured by Seiko Instruments Inc.). The shape of the ultrafine particles in the conductive paste composition used in the present invention is spherical after production, but is processed into a polyhedral shape, flake shape, or flake shape in a later step, or used as a mixture thereof. You can also. Regardless of the shape, a known method of mechanically processing the powder can be used, but the ultrafine particles for producing the conductive paste composition are preferably spherical.
[0054]
The conductive paste composition may include an organic solvent having a boiling point of 50 ° C. or higher, which is also expected to have an effect as a diluent. This may be added as a viscosity modifier if sufficient fluidity for printing cannot be obtained due to high viscosity during use or the like. A suitable addition amount is 3% by weight or less based on the whole conductive paste composition.
[0055]
In order to adjust the viscosity, a monoepoxy compound or a solvent such as dimethylacetamide, N-methylpyrrolidone, methyl ethyl ketone, methyl cellosolve, methyl carbitol, carbitol, carbitol acetate, methyl cellosolve acetate, or a mixture of plural solvents may be used. It is also possible to mix the systems in appropriate amounts. It is preferable from the viewpoint of workability that the viscosity of the obtained solution or paste is 5,000 to 400,000 cp, more preferably 20,000 to 70,000 cp.
[0056]
The thermosetting resin used in the present invention is not particularly limited as long as it can provide conductivity. Commonly used are resol type phenolic resins, novolak type phenolic resins, bisphenol type epoxy resins, novolak type epoxy resins of various molecular weights, and liquid epoxy compounds having one or more glycidyl groups in one molecule, A combination of pentyl glycol diglycidyl ether, bisphenol A diglycidyl ether, propylene glycol diglycidyl ether, hexanediol diglycidyl ether, or the like, and an epoxy curing agent composed of an amine, an acid anhydride, or the like is preferable.
[0057]
Other binder resins include melamine resin, urea resin, xylene resin, alkyd resin, unsaturated polyester resin, acrylic resin, polyimide resin, furan resin, urethane resin, bismaleimide-triazine resin, and the like. In addition, a thermoplastic resin, a surface treatment agent, a dispersant, and the like can be added as needed.
[0058]
As the epoxy curing agent, a general epoxy curing agent can be used. For example, aliphatic polyamines include triethylenetetramine and m-xylenediamine; aromatic amines include m-phenylenediamine and diaminophenylsulfone; and tertiary amines include benzyldimethylamine and dimethylamino. Methyl phenol and the like; acid anhydrides such as phthalic anhydride and hexahydrophthalic anhydride; boron trifluoride amine complex such as BF₃-Piperingin complex. Further, a bisphenol compound such as bisphenol A may be used.
[0059]
Although any thermoplastic resin can be used as the thermoplastic resin, a resin having a hydrogen-bonding functional group in its structure is preferable. Examples of the functional group having hydrogen bonding properties include a hydrogen group, an amide group, a urea group, an imide group, an ester group, an ether group, a thioether group, a sulfone group, and a ketone group. Specifically, polyamide resins such as 12-nylon, 6-nylon and 6,6-nylon, olefin resins such as polyethylene and polypropylene, polyvinyl chloride, polyvinyl acetate, polyvinylidene chloride, polyvinyl alcohol, ethylene-acetic acid Polyvinyl resins such as vinyl copolymers, acrylic resins such as ethyl acrylate, methyl methacrylate and modified products thereof, acrylonitrile resins such as polyacrylonitrile, acrylonitrile-styrene copolymer, polyurethane resins, polyacetal, polycarbonate, polyimide, polysulfone , Polybutylene terephthalate, polyethylene terephthalate, polyarylate, polyphenylene oxide and its modified products, polyether sulfone, polyphenylene sulfide, polyamide imide, Engineering plastics such as oxybenzene and polyetherketone, resins such as polyaramid, wholly aromatic polyesters, liquid crystal resins such as polyesteramides, and thermoplastic elastomers such as polyamide elastomers, polyester elastomers, and polyurethane elastomers. Or a combination of two or more.
[0060]
As the glass frit, any glass frit can be used without any particular limitation as long as it is used in a sintered material. For example, Al₂O₃, PbO, ZnO, B₂O₃, CdO, BaO, CaO, their intermediates and mixtures, or borosilicates containing them as modifiers, and their mixtures. Further, what is called a sintering aid such as celluloses, cuprous oxide, acrylic resin, CdO and reactive oxides may be added.
[0061]
Rosin is generally called a flux, and a resin-based flux, a water-soluble flux, a non-washing type flux, and the like can be used. Particularly, the use of an activated resin flux is preferable. It is mainly composed of a rosin-based natural resin or a modified resin thereof, to which an activator, an organic solvent, a viscosity modifier and other additives are added.
[0062]
In general, modified rosin, phenolic resin modified rosin, etc. for modified resin, inorganic and organic flux for activator, especially amine hydrochloride and organic acid flux, organic solvent for carbitol and ether Is used. Note that an inorganic flux can also be used. The flux shape can be selected according to the application, such as a liquid flux, a paste-like flux, and a water-soluble flux.
[0063]
A lubricant is a substance that exhibits a function as a lubricant for maintaining an appropriate dispersion state in the conductive paste composition in which the ultrafine particles are contained, and as a lubricant that can be contained, paraffin wax, liquid paraffin, polyethylene wax, Waxes such as polypropylene wax, ester wax, carnauba, micro wax, fatty acids such as stearic acid, 12-oxystearic acid, lauric acid, zinc stearate, calcium stearate, barium stearate, aluminum stearate, magnesium stearate, Fatty acid salts such as calcium laurate, zinc ricinoleate, calcium ricinoleate, zinc 2-ethylhexoate, stearamide, oleic amide, erucamide, behenamide, palmitamide, lauric acid amide Amide, hydroxystearic acid amide, methylenebisstearic acid amide, ethylenebisstearic acid amide, ethylenebislauric acid amide, distearyladipamide, ethylenebisoleic acid amide, dioleyladipamide, N-stearylstearic acid amide, Fatty acid amides such as N-oleyl stearamide, N-stearyl erucamide, methylolbehenamide, methylol stearamide, fatty acid esters such as butyl stearate, alcohols such as ethylene glycol and stearyl alcohol, polyethylene glycol, and polypropylene Glycol, polytetramethylene glycol and polyethers composed of modified products thereof, silicone oil, polysiloxanes such as silicone grease, fluorine-based Yl, fluorine-based grease, a fluorine-containing resin powder such as fluorine compounds, silicon nitride, silicon carbide, magnesium oxide, alumina, an inorganic compound powder silica gel, and the like.
[0064]
One or two or more of these lubricants are used, but when at least one of waxes, polyethers, and fatty acid amides is contained as a lubricant, the moldability of the metal powder composition for electrical connection is reduced. It is preferable to greatly improve. The amount of the lubricant to be added is preferably 3% by weight or less, more preferably 0.05 to 2% by weight in the conductive paste composition.
[0065]
The coupling agent is added to enhance the adhesiveness between the ultrafine metal particles and various resins that are organic compounds, and the addition of the coupling agent can also be expected to increase the strength of the electrical connection. There are various coupling agents such as silane, titanium, aluminum, zirconium, chromium, iron and tin. For example, silane-based coupling agents include phenyltrimethoxysilane, diphenyldimethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, and the like. In the case of titanium, isopropyl triisostearoyl titanate, tetraisopropyl titanate, isopropyl trioctanoyl titanate and the like can be mentioned. The amount of the coupling agent added is preferably 3% by weight, more preferably 0.01 to 2% by weight in the conductive paste composition.
[0066]
Each component in the conductive paste composition preferably contains ultrafine particles in a range of 60 to 98% by weight and an organic binder in a range of 2 to 40% by weight.
It should be noted that the ultrafine particles produced in the present invention or the ultrafine particles in the conductive paste composition are characterized by having a wide particle size distribution, not a narrow particle size distribution as particles produced by the prior art. Can be. When used in the field of electronic materials, the wider the particle size distribution from the aspect of the filling rate, the higher the filling rate (the smaller the porosity), and the more novel and advanced the connection reliability. It is considered to have high industrial utility value.
[0067]
【Example】
Next, the present invention will be described in detail based on examples and comparative examples, but the present invention is not limited to only these examples.
[0068]
[Example 1]
0.96 kg of Sn particles (purity of 99% by weight or more) and 1.04 kg of In particles (purity of 99% by weight or more) were placed in a carbon crucible, and heated to 1500 ° C. by a high frequency induction heating device and melted. The atmosphere of the metal melting part was performed in helium of 99% by volume or more, and the pressure was set to 0.03 MPa. Next, the metal melt was introduced from a nozzle provided at the bottom of the carbon crucible into a spray tank in a helium gas atmosphere (the pressure of the spraying section was set to 0.005 MPa). , H₂/ He mixed gas (H₂A mixed gas having a concentration of 2% by volume / 98% by volume of He, an oxygen concentration of 0.001% by volume in the mixed gas, and a pressure of 2.5 MPaG) was jetted to atomize the metal melt to produce ultrafine particles. The calculated gas ejection speed at 25 ° C. at this time is 885 m / s. A collecting part separated by a ball valve was provided at the lower part of the apparatus, and benzyl alcohol was put therein. After the entire amount of the metal melt is sprayed and the power of the high-frequency induction heating device is turned off, benzyl alcohol passed through a vaporizer is pushed in from a line connecting the spraying section and the recovery section with a pump, and the pressure in the spraying section is reduced to 0. 01 MPa. Thereafter, the ball valve of the collection section was opened, and the ultrafine particles were collected. The volume average particle size was 5 μm. Partial sampling was performed and the minimum particle diameter was confirmed by SEM, and it was 0.08 μm. The recovery amount of the ultrafine particles was 1.7 kg.
[0069]
[Example 2]
Using the same metal species and equipment as in Example 1, fine particles were granulated using an atomizing gas shown in Table 1 below and collected. The pressure in the metal melting section: a and the pressure in the spray section: b were also measured under the same conditions. Table 1 shows the gas composition and the gas ejection speed (calculated value).
The volume average particle diameter of the obtained ultrafine particles was 4.5 μm. Partial sampling was performed and the minimum particle diameter was confirmed by SEM, and was 0.06 μm. The recovery amount of the fine particles was 1.6 kg.
[0070]
[Table 1]

[0071]
[Example 3]
Using the same metal species and apparatus as in Example 1, fine particles were granulated using an atomizing gas shown in Table 2 below and collected. The pressure in the metal melting section: a and the pressure in the spray section: b were also measured under the same conditions. Table 2 shows the gas composition and the gas ejection speed (calculated value).
The volume average particle diameter of the obtained ultrafine particles was 5.5 μm. Partial sampling was performed, and the minimum particle diameter was confirmed by SEM to be 0.09 μm. The collection amount of the fine particles was 1.8 kg.
[0072]
[Table 2]

[0073]
[Example 4]
(Classification of ultrafine particles)
In the present example, the ultrafine particle slurry obtained in Example 1 was subjected to classification using a wet centrifugal classifier. The ultrafine particles obtained by classification had an average particle size of 0.8 μm and a maximum particle size of 1 μm. The coarse powder after the wet classification was separated into solid and liquid, washed with acetone, and dried with a hot air dryer at 60 ° C. The recovery amount of the ultrafine particles was 0.17 kg, the wet classification yield was 10%, and the recyclable particles after drying were 1.4 kg.
In the second stage, wet classification was performed using a column classifier. The recovery amount of the ultrafine particles was 0.1 kg, and the wet classification yield was 59%. The average particle size was 0.1 μm, and the maximum particle size was 0.5 μm.
[0074]
[Example 5]
(Preparation of [conductive paste composition 1] and measurement of volume resistivity)
The ultrafine particle slurry finally obtained in Example 4 was repeatedly decanted with a defoaming kneader to increase the fine particle content. The content of the ultrafine particles was 60 wt%. A liquid epoxy resin as an organic binder is added at 10% by weight to the ultrafine particles, a stearic acid as a lubricant is added at 1% by weight, a titanium-based coupling agent (trade name: KR-TTS) is added at 0.5% by weight as a coupling agent, and a beaker is added. Kneaded within. After kneading, decantation was again performed using a defoaming kneader to reduce the content of ultrafine particles to 80 wt%. The obtained conductive paste composition was subjected to evaluation pattern printing on a glass epoxy substrate using a glass rod. This glass epoxy substrate was thermally cured in a nitrogen atmosphere by passing through a nitrogen reflow furnace set at a peak temperature of 230 ° C. The cured product thickness after curing was 70 μm on average. The resistance of the obtained glass epoxy substrate after curing was measured by a four-terminal method.^-4Ω · cm.
[0075]
[Example 6]
(Preparation of [Conductive paste composition 2] and volume resistance measurement)
The ultrafine particle slurry finally obtained in Example 4 was repeatedly decanted with a defoaming kneader to increase the fine particle content. After repeating this operation several times, the fine particle content became 60 wt%. PbO-ZnO-B as an organic binder₂O₃5% by weight of the glass frit based on the ultrafine particles, 0.25% by weight of ethylcellulose and 1.5% by weight of cuprous oxide were kneaded in a beaker. After kneading, decantation was again performed using a defoaming kneader to reduce the content of ultrafine particles to 85% by weight. The obtained conductive paste composition was printed with a test pattern on a 96% alumina substrate by screen printing, and fired under a nitrogen atmosphere by passing through a continuous firing furnace set at a peak temperature of 650 ° C. The conductor film thickness after firing was 12 μm on average. The resistance of the obtained alumina substrate was measured by a four-terminal method.^-5Ω · cm.
[0076]
[Comparative Example 1]
0.96 kg of Sn particles (purity of 99% by weight or more) and 1.04 kg of In particles (purity of 99% by weight or more) were placed in a carbon crucible, and heated to 1500 ° C. by a high frequency induction heating device and melted. The atmosphere of the metal melting part was performed in 99% by volume or more of nitrogen, and the pressure was set to 0.03 MPa. Next, after introducing the molten metal from the tip of the carbon crucible into a spray tank in a helium gas atmosphere (the spraying section pressure was set to 0.005 MPa), nitrogen gas (from a gas nozzle provided near the tip of the carbon crucible) was used. N₂A concentration of 99% by volume or more, an oxygen concentration in the gas of 0.001% by volume, and a pressure of 2.5 MPaG were ejected to perform atomization to produce metal particles. The calculated gas ejection velocity at 25 ° C. at this time is 321 m / s. A collecting section separated by a ball valve was provided at the lower part of the apparatus, and the inside was kept in a nitrogen gas atmosphere. After the entire amount of the molten metal was sprayed and the power of the high-frequency induction heating device was turned off, the ball valve was opened to collect the metal particles. The volume average particle size was 12 μm. Partial sampling was performed and the minimum particle diameter was confirmed by SEM, and it was 0.7 μm. The recovered amount of the metal particles was 1.2 kg, and the recovered amount was slightly small.
[0077]
[Comparative Example 2]
(Classification of metal particles)
Using the metal particles obtained in Comparative Example 1, classification was performed using a dry classification device. The average particle size was 0.8 μm and the maximum particle size was 1 μm. The recovery amount of the metal particles was 0.03 kg, the dry classification yield was 4%, the recyclable particles were 0.8 kg, and the loss due to aggregation was about 0.4 kg (corresponding to a loss rate of 37%). there were.
[0078]
[Comparative Example 3]
(Preparation of [Conductive Paste Composition 3] and Volume Resistance Measurement)
To the metal particles finally obtained in Comparative Example 2, 10% by weight of a liquid epoxy resin as an organic binder, 1% by weight of a lubricant, and 0.5% by weight of a coupling agent were added to the metal particles. And kneaded. Furthermore, after kneading with three rolls, defoaming operation was performed using a defoaming kneader. The obtained conductive paste composition was subjected to evaluation pattern printing on a glass epoxy substrate using a glass rod. This glass epoxy substrate was thermally cured in a nitrogen atmosphere by passing through a nitrogen reflow furnace set at a peak temperature of 230 ° C. The cured product thickness after curing was 70 μm on average. The resistance of the obtained glass epoxy substrate after curing was measured by a four-terminal method.^-4Ω · cm.
[0079]
[Comparative Example 4]
(Preparation of [conductive paste composition 4] and measurement of volume resistance value)
Using the metal particles finally obtained in Comparative Example 2, PbO-ZnO-B was used as an organic binder.₂O₃5% by weight of the glass frit based on the metal particles, 0.25% by weight of ethyl cellulose, and 1.5% by weight of cuprous oxide were kneaded in a beaker. Furthermore, after kneading with three rolls, defoaming operation was performed using a defoaming kneader. The obtained conductive paste composition was printed with a test pattern on a 96% alumina substrate by screen printing, and fired under a nitrogen atmosphere by passing through a continuous firing furnace set at a peak temperature of 650 ° C. The conductor film thickness after firing was 12 μm on average. The resistance of the obtained alumina substrate was measured by a four-terminal method.^-5Ω · cm.
[0080]
【The invention's effect】
By using the method for producing ultrafine metal particles, the production apparatus, and the method for producing a conductive paste composition according to the present invention, ultrafine particles can be obtained without aggregation, and surface oxidation of the ultrafine particles is prevented. The conductive paste composition can be manufactured as it is. In addition, since the process is suitable for mass production, and ultra-fine particles can be recycled, the manufacturing cost is significantly lower than conventional products.

Claims (13)

In a method for producing ultrafine particles including a granulation step of obtaining ultrafine particles from a melt of a raw material metal by a gas atomization method and a collection step of collecting the ultrafine particles, H ₂ gas and an inert gas are used as an atomizing gas in the granulation step. A method for producing ultrafine metal particles, comprising using a mixed gas with a gas. 2. The metal ultrafine particles according to claim 1, wherein a gas ejection speed at 25 ° C. calculated at a gas injection port of a gas nozzle that ejects an atomizing gas is in a range of 700 m / s to 1200 m / s. 3. Production method. The inert gas is He gas, and a H ₂ gas volume mixing ratio defined as [H ₂ gas / (H ₂ gas + He gas)] is in a range of 0.01 to 30 vol%. Item 3. The method for producing ultrafine metal particles according to Item 1 or 2. The method for producing ultrafine metal particles according to claim 1, wherein the H ₂ gas volume mixing ratio is in a range of 60 to 99 vol%. [H ₂ gas + He gas] which includes He gas and another inert gas as an inert gas and is defined as [(H ₂ gas + He gas) / (H ₂ gas + He gas + other inert gas)] the volume mixing ratio is in the range of 85～99Vol%, and _{the H 2} gas volume mixing ratio which is defined as _{[H 2} gas / _{(H 2} gas + He gas) is in the range of 0.01～30Vol% The method for producing ultrafine metal particles according to claim 1, wherein: The method for producing ultrafine metal particles according to any one of claims 1 to 5, wherein the ultrafine particles are recovered in a solvent in the recovery step. The method for producing metal ultrafine particles according to claim 6, further comprising a wet classification step of wet-classifying an ultrafine particle slurry obtained by collecting the ultrafine particles in a solvent. The method for producing ultrafine metal particles according to claim 7, wherein the raw metal is melted in a carbon crucible, and the ultrafine metal particles collected in the wet classification step are returned to the carbon crucible as a raw material and reused. The raw material metal is Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb. , Dy, Ho, Er, Tm, Yb, Lu, Ac, Th, Pa, U, Np, Pu, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe , Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As The method for producing ultrafine metal particles according to any one of claims 1 to 8, comprising at least one selected from the group consisting of Sb, Bi, Se, Te and Po. An organic solvent, a thermosetting resin, a thermoplastic resin, a glass frit, a rosin, a lubricant, and a coupling agent are added to the ultrafine particles produced by the method for producing ultrafine particles according to claim 1. A method for producing a conductive paste composition, characterized by adding at least one kind. A conductive paste composition produced by the production method according to claim 10. A melt nozzle for supplying a raw material melt, comprising a raw material melting unit, a spray unit for obtaining ultrafine particles from the raw material melt by a gas atomizing method, and a recovery unit for the ultrafine particles formed by the spray unit. And a gas nozzle, wherein a mixed gas of H ₂ gas and an inert gas is injected from the gas nozzle as an atomizing gas. When the pressure of the raw material melting section is defined as a [MPa] and the pressure of the spraying section is defined as b [MPa], a pressurizing or depressurizing means of a> b is provided, and a portion where the raw material melt is ejected is provided. The apparatus further comprises means for ultrasonically vibrating, and the ultrafine particle collection unit further contains a solvent for dispersing the ultrafine particles formed by spraying, and further comprises means for separating the ultrafine particles from the solvent. 13. The apparatus for producing ultrafine metal particles according to 12.