JP2004307881A

JP2004307881A - Copper powder and manufacturing method therefor

Info

Publication number: JP2004307881A
Application number: JP2003099515A
Authority: JP
Inventors: Yoshihiro Okada; 美洋岡田; Akitsugu Hirata; 晃嗣平田
Original assignee: Dowa Mining Co Ltd
Current assignee: Dowa Holdings Co Ltd
Priority date: 2003-04-02
Filing date: 2003-04-02
Publication date: 2004-11-04
Anticipated expiration: 2023-04-02
Also published as: JP4352121B2

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a copper powder having a suitable particle size distribution for the filler of a conductive paste, by reproducibly manufacturing copper powders each having an aimed and uniform particle size, and mixing the copper powders of different particle sizes. <P>SOLUTION: The method for manufacturing the copper powder having a narrow width of the particle size distribution comprises adding a reducing agent to (1) a mixture comprising a copper powder with an average particle size of 0.1 μm or larger, a solid component consisting of a copper compound, and a liquid medium, (2) a mixture comprising the copper powder with an average particle size of 0.1 μm or larger, and a liquid medium including copper ions, or (3) a mixture comprising the copper powder with the average particle diameter of 0.1 μm or larger, the solid component consisting of the copper compound, and the liquid medium including the copper ions; and reducing the solid component and/or the copper ions to metallic copper. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は，導電性ペーストの導電フィラーに適した粒径が非常にそろった粒度分布幅の狭い銅粉およびその製造法に関する。
【０００２】
【従来の技術】
各種基板の表面や内部あるいは外部に電気回路や電極を形成する手段として導電ペーストが多く使用されている。この導電ペーストに含まれる導電フィラー（金属粉）としては銅粉や銀粉などがあり，粒径が０．１〜２０μｍの粉体が実用に供されている。そのさい，ペーストの焼結性や接着強度を制御する上で，またはそれらの変動をなくす上で，粒径のそろった金属粉は不可欠である。ペーストレオロジーの調整のさいにも，また緻密な導体厚膜や電子部品電極を得るためににも，２〜３種の粒径のそろった金属粉を組み合わせて混合することが有効とされており，このためには，異なる粒径ごとに粒径のそろった金属粉を必要とし，そのための製造技術も必要である。
【０００３】
金属粉の製造方法にはアトマイズ法，電解法，湿式還元法等が良く知られている。銅粉の製造について見ると，アトマイズ法では，得られる銅粉の粒度分布幅が非常に広く，粒径のそろった銅粉を得るには，分級を何度も繰り返さなくてはならず，歩留まりが非常に悪い。電解法は，得られる銅粉の粒度分布幅が広いだけでなく，粒子形状が樹枝状であるため，緻密さを求められる厚膜やチップ電極には適さず，単品で使用することは非常に困難である。
【０００４】
これに対して，湿式還元法は比較的粒径がそろい，粒子形状がほぼ球状の銅粉が得られるので，導電性ペーストに要求される銅粉に最も適しているといえる。湿式還元法による銅粉の製法については，例えば特許文献１および特許文献２に記載されているが，これらの方法によると，不純物の影響やわずかな製造プロセス変動等により，製造ロットごとの粒径のバラツキが大きかったり，粒度分布幅が広かったり，粒径が十分にはそろっていなかったりといった問題があった。
【０００５】
このような問題に対して，同一出願人に係る特許文献３は，湿式還元の途中で酸化工程を導入すると，比較的粒径の揃った銅粉が得られると教示している。
【０００６】
【特許文献１】特公平７−９３０５１号公報
【特許文献２】特開２００１−２４０９０４公報
【特許文献３】特開２０００−１４４２１７号公報
【０００７】
【発明が解決しようとする課題】
特許文献３の方法でも比較的粒径の揃った銅粉を得ることができるが，その粒径の揃う程度は必ずしも十分ではない。また粒径が４μｍを超えるような場合にも粒径の揃ったものが得られるか否かは判然としない。したがって，１μｍ以下の微粒子から１０μｍ以上の粗粒子までといった広い粒径範囲を，目標とするそれぞれの粒径ごとに十分に粒径の揃った銅粉を一貫して制御できる操作性のよい技術は確立されているとは言えなかった。さらに粒径が揃った目標粒径のものを的中率よく再現できればさらに好ましい。
【０００８】
したがって本発明の課題は，銅粉の製造ロットごとの粒径変動を抑え，粒度分布幅が狭く且つ狙った粒径の銅粉を得ることにある。
【０００９】
【課題を解決するための手段】
本発明によれば，平均粒径（Ｄ５０）が０．１μｍ以上の銅粉と，銅の化合物からなる固形成分と，液溶媒とからなる混合物に，還元剤を添加して前記の固形成分を金属銅に還元する銅粉の製造法を提供する。さらに本発明によれば，平均粒径（Ｄ５０）が０．１μｍ以上の銅粉と，銅イオンを含む液溶媒とからなる混合物に，還元剤を添加して前記の銅イオンを金属銅に還元する銅粉の製造法を提供する。また，平均粒径（Ｄ５０）が０．１μｍ以上の銅粉と，銅の化合物からなる固形成分と，銅イオンを含む液溶媒とからなる混合物に，還元剤を添加して前記の固形成分および銅イオンを金属銅に還元することもでき，いずれの場合にも粒度分布幅の狭い銅粉を製造することができる。銅の化合物としては銅の酸化物または水酸化物であることができ，液溶媒としては水であることができる。Ｄ５０は粒度分布における５０％径を表す。
【００１０】
本発明法によれば，混合物中の銅粉以外の銅の総モル数をｎ_０〔モル〕，用いる銅紛の平均粒径（Ｄ５０）をｘ_０〔μｍ〕，使用する銅粉の重量をｗ〔ｇ〕，銅の原子量をＡＷ〔ｇ／モル〕としたとき，製造される銅紛の平均粒径を下記の数２で表されるｘ〔μｍ〕の±２０％以内とすることができる。この場合，製造される銅粉は，その粒度分布における９０％径（Ｄ９０）と１０％径（Ｄ１０）の比率（Ｄ９０／Ｄ１０）が１．５以下であることができ，粒度分布における５０％径（Ｄ５０）は０．１〜２０．０μｍの範囲であることができる。
【００１１】
【数２】

【００１２】
【発明の実施の形態】
湿式還元法による銅粉の製造において，得られる銅粉の粒径にバラツキが発生する要因としては，その製法に由来して，核発生プロセスの段階と粒子成長プロセスの段階に分けることができる。
【００１３】
核発生の段階は，ｐＨ調整，温度調整（急冷等），還元剤添加，銅イオンの添加，不純物イオンの添加，反応性ガスの導入あるいは光照射等により，銅粒子の核となる金属銅の超微粒子を生成させる段階である。生成させる核数は，目的とする銅粉の粒径に影響する。大きい粒径の銅粉を得る場合は，核発生数を少なく，逆に小さめの粒径の銅粉を得る場合は核発生数を多くすればよい。しかし，実際には不可避的に混入する不純物の量や製造プロセスのわずかな変動によっても核発生数は影響を受けるので，製造される銅粒子径のバラツキが起こり，製造ロットごとの変動を誘発してしまう。
【００１４】
次の粒子成長の段階は，発生させた銅粒子核を徐々に成長させる（銅イオンや酸化銅等を還元して核粒子表面に金属銅を析出させる）ことにより，目的粒径の銅粉に調整する段階である。この段階においても，還元力が強すぎる場合や，発生核の総表面積が小さい場合に粒子成長と同時に，新たな核（二次核）が発生して，粒度分布のブロード化や粒径の微粒化を引き起こしてしまう。
【００１５】
このような核発生プロセスの変動と粒成長の変動を抑えることが，粒径がそろった銅粉を製造ロットごとに変動なく得る上で肝要であるが，本発明によると，これが実現できる。
【００１６】
すなわち本発明においては，（１）平均粒径が０．１μｍ以上の銅粉と，銅の化合物からなる固形成分と，液溶媒とからなる混合物，（２）平均粒径が０．１μｍ以上の銅粉と，銅イオンを含む液溶媒とからなる混合物，または（３）平均粒径が０．１μｍ以上の銅粉と，銅の化合物からなる固形成分と，銅イオンを含む液溶媒とからなる混合物に，還元剤を添加して，銅の化合物または銅イオンを還元するのであるが，これらの方法によると，金属銅粉が反応系に導入されることにより，核発生プロセスが無くなり，これによって，核発生段階での変動を皆無にすることができる。また，金属銅粉の粒径は，通常の核発生時の微小な金属核の粒径よりも大きいので，還元によって生成する金属銅が析出する総表面積が大きくなり，粒成長が促進され二次核発生も抑えられることから，粒成長の変動を抑制することができる。
【００１７】
さらに，本発明においては，前記（１）〜（３）のいずれの混合物においても，混合物中に存在する銅粉以外の銅成分はそのほぼ全てを粒成長に充てることができるので，銅粉以外の銅成分の量（銅粉以外の銅の総モル数），銅粉の粒径，銅粉の添加量を調整することにより，得られる金属粉の粒径を極めて精度良く制御することができるという特徴がある。すなわち，混合物中の銅粉以外の銅の総モル数をｎ_０〔モル〕，銅紛の平均粒径（Ｄ５０）をｘ_０〔μｍ〕，銅粉の重量をｗ〔ｇ〕，銅の原子量をＡＷ〔ｇ／モル〕としたとき，製造される銅紛の平均粒径ｘ〔μｍ〕は下式で表わすことができる。
【００１８】
【数３】

【００１９】
式中のαは補正係数である。これは，粒径の測定方法によっては，得られる粒径値が若干異なったり，粒子形状によっては形状係数が変化したりするので，各測定方法や粒子形状に適合するように係数での補正を加味したものである。この係数αは通常は０．８以上１．２以下の範囲に収まることができる。すなわち，製造される銅粉は，該式の平均粒径ｘの±２０％の範囲内にほぼ収まる。
【００２０】
本発明の実施にさいし，銅粉以外の銅成分（銅の酸化物や水酸化物等の銅化合物）を存在させることにより，製造用銅粉の銅源は，従来の湿式還元法のように金属イオンの溶解度に制限されることはない。このため，銅の供給原となる銅原子の総量を増やすことができる。すなわち，粒成長に寄与する銅原子数の制限が無くなるため，銅粉を所望の粒径に調整しやすくなり，生産性の向上に繋がる。固形成分を用いないで，銅イオンを含む水と銅粉の混合物を還元に供する場合も問題なく実施できる。
【００２１】
銅化合物と銅粉との混合物を用いる場合にその銅化合物の銅の酸化数（一価か二価かといった価数）は小さい方がよい。酸化数が大きい場合，還元反応が数段階になり，複数の還元反応が同時進行する可能性があり，この場合には二次核発生等が危惧される。
【００２２】
銅の化合物からなる固形成分は，共存する銅粉の金属銅粒子の表面で還元されて粒成長に寄与する場合もあれば，反応液中に一度溶出したうえで溶解析出型の反応で粒成長に寄与する場合もあると考えられる。銅の硫酸，硝酸，炭酸，リン酸等のオキソ酸塩，銅のハロゲン化物の塩類，銅の硫化物等のカルコゲナイド，銅のアミノ酸塩あるいはカルボン酸等の有機酸塩類でも，同様の効果が期待できる。本発明で使用できる銅の化合物からなる固形成分として代表的なものは，銅の酸化物または水酸化物である。
【００２３】
反応のための液媒体は，水または有機系の液溶媒，あるいは水と有機系の液溶媒との混合液のいずれでも良い。水を用いる場合や，還元によりガスを発生するような還元剤を使用する場合には，消泡剤や表面張力の低い有機溶媒（例えば，エタノールやイソプロピルアルコール等のアルコール類や，アセトン等のケトン類，ヘキサン等の炭化水素類）を共存させることにより，還元で発生する水素等のガスによる液面上昇を抑えることができるので有益である。
【００２４】
銅イオンと錯体を形成し得る物質（錯化剤）は，急激な反応を抑制し二次核の発生を抑えたり，イオンの溶解度を向上させたり，表面性の良い（表面が滑らかな）粒子を得るのに有効である。錯化剤としては，酒石酸，蓚酸，クエン酸，コハク酸，エチレンジアミン四酢酸等の有機酸や，アンモニアやエチレンジアミン等のアミン類，グリセロールやマンニトール等のアルコール類，アミノ酸類，シアン（青酸）およびそれらの塩が利用できる。また，錯化剤は故意に添加しなくても，原料となる固形成分の金属塩類（例えばカルボン酸塩）に含まれるものや，反応中の副生成物を錯化剤として機能させても良い。
【００２５】
還元剤の添加により還元を進行させるさいには，急激な反応，すなわち二次核発生が抑制されるように，徐々に還元剤を添加するのが良い。具体的には，還元剤の全添加量を数分割し，これらを数分〜数時間おきに回分式に添加する方法や，添加速度を任意に定め，数分〜数時間かけて連続的に添加する方法等が望ましい。
【００２６】
添加する銅粉の粒径は，あまりに小さすぎると，凝集が激しくなって粒度分布幅が広くなったり，二次核が発生したりする場合がある。また，粒子の成長速度は，混合する銅粉の粒径には実質的に依存せず，単位時間あたり数μｍとほぼ一定に維持されるので，粒径が余り大きすぎると，初期粒径に対する粒子成長の比率が小さくなって生産効率が悪くなる。したがって，混合する銅粉の粒径（平均粒径）は０．１μｍ以上，好ましくは０．５μｍ以上，さらに好ましくは１．０μｍ以上で，２０μｍ以下であるの望ましい。
【００２７】
還元反応後に得られる銅粉は粒径が非常にそろったものとなる。例えば粒度分布における９０％径（Ｄ９０）と１０％径（Ｄ１０）の比率（Ｄ９０／Ｄ１０）が１．５以下の粒度分布幅の狭いものとなる。ここで，Ｄ９０およびＤ１０は，横軸に粒径Ｄ（μｍ）をとり，縦軸に粒径Ｄμｍ以下の粒子が存在する容積（Ｑ％）をとった累積粒度曲線において，Ｑ％が９０％および１０％であるときの，それらに対応するそれぞれの粒径Ｄ（μｍ）の値を言う。また例えばＤ５０と言えば，該累積粒度曲線においてＱ％が５０％のときの粒径Ｄの値（μｍ）を言う。このような累積粒度曲線は粒度分布測定装置で描くことができる。Ｄ９０／Ｄ１０の比が１．５を超えるような場合は，粒径が十分には揃っていないため，異なった粒径の銅粉を組合せて導電ペースト用のフイラーとするさいに，意図する粒径分布のものを正確に得るのが困難になる。
【００２８】
還元反応は，雰囲気制御および温調が可能で攪拌機能を備えた反応槽にて実施するのがよい。反応中の雰囲気としては，空気中の酸素による酸化等の副反応の進行を抑えるため，基本的には全体を通じて不活性ガス雰囲気下で行うのがよい。しかし，必要に応じてアンモニア等の反応性ガスや酸素等を導入することによって，液性を制御したり，銅や錯化剤の酸化・還元電位の調整行ったりしても良い。不活性ガスはコスト面から窒素が最適であるが，アルゴン等の希ガスを使用しても問題ない。
【００２９】
金属銅（混合する銅粉）以外の銅化合物の固形成分および／または銅イオンを含む液溶媒（銅粉を添加する前の反応液）は，銅の塩類，銅の水酸化物，銅の酸化物等を純水あるいは純水と有機溶媒の混合液に溶解または懸濁することにより調整する。銅の塩類としては，安価な硫酸銅または塩化銅が望ましいが，銅の硝酸，炭酸，リン酸等のオキソ酸塩類，銅のハロゲン化物塩類，硫化銅等の銅カルコゲナイド類，銅のカルボン酸塩あるいは銅のアミノ酸塩等の有機酸塩類等を使用しても問題ない。また，銅の固形成分として銅の水酸化物および／または酸化物を利用する場合は，溶解した銅塩類を中和等により析出させたものを利用しても良いし，電解法等で製造した亜酸化銅粉末を利用しても良い。
【００３０】
このようにして，銅化合物の固形成分および／または銅イオンを含む液溶媒を反応液として準備し，この反応液に対して，必要に応じて，錯化剤，ｐＨ調整剤，還元剤などを添加混合することによって，液性，固形成分の量や粒径，銅の酸化数等の調整を行うことができる。錯化剤，ｐＨ調整剤，還元剤などの添加に際しては，固体または液体のまま，あるいは純水等に溶解・希釈した後，添加しても構わない。また，銅塩としてカルボン酸塩等を使用した場合は，含有されるカルボン酸に錯化剤としての役割を担わせることもできる。
【００３１】
次いで，銅粉を混合するが，混合する銅粉はある程度粒径が揃い，球状に近いものであれば，アトマイズ法や湿式還元法等で製造された銅粉のいずれでも使用でき，製造履歴には特に制限はない。前記のｘを算出する式における補正係数αは反応系および測定装置が定まると，一義的に定めることが可能であり，再現性よく意図する粒径の且つ粒径分布幅の狭い銅粉を製造することができる。
【００３２】
銅粉を混合したあとは，不活性ガス中で適度な時間リパルプした後，還元剤を徐々に添加して銅化合物の固形成分および／または銅イオンの還元反応を攪拌下で進行ささせる。なお，ここでの還元剤としては，銅化合物の固形成分および銅イオンを金属銅（すなわち酸化数ゼロ）まで還元可能なもの，例えば，含水ヒドラジン，水素化ホウ素化合物，ジメチルアミンボラン，亜鉛華，ホルマリン等を使用できる。
【００３３】
反応の終了は，銅イオン，銅錯体あるいは銅化合物の固形成分の存在が，反応液中に検出できなくなる時点ととする。反応終了後は，ろ過により固液分離し，ろ別分を純水あるいは水溶性の有機溶媒で洗浄する。固液分離はろ過に限らず，遠心分離，スプレードライ等，その他の手段を用いても良い。固液分離して得られたケーキを不活性ガスまたは還元雰囲気下で５０〜３００℃の温度で数〜数十時間かけて乾燥することにより，粒径のそろった導電ペースト用銅粉を得ることができる。不活性ガスとしては，窒素もしくは希ガスを使用し，水素あるいは一酸化炭素等の還元性ガスを混合して使用しても良い。
【００３４】
本発明法は，見方を変えれば，既存の銅粉の粒径を大きくしながら且つ粒径のそろった銅粉に改善する方法であるとも言える。すなわち，本発明は，（１）原料銅粉を，銅の化合物からなる固形成分を含む液媒体と混合し，この混合物に還元剤を添加して前記の固形成分を金属銅に還元することからなる粒度分布幅の狭い銅粉の製造法，（２）原料銅粉を，銅イオンを含む液媒体と混合し，この混合物に還元剤を添加して前記の銅イオンを金属銅に還元することからなる粒度分布幅の狭い銅粉の製造法，および（３）原料銅粉を，銅の化合物からなる固形成分および銅イオンを含む液媒体と混合し，この混合物に還元剤を添加して前記の固形成分および銅イオンを金属銅に還元することからなる粒度分布幅の狭い銅粉の製造法を提供するものであるとも言える。
【００３５】
【実施例】
〔実施例１〕
硫酸銅五水和物２．５ｋｇ（銅のモル数＝１０モル）を室温，窒素雰囲気下にて純水６．１ｋｇに溶解した。この硫酸銅水溶液を１０ｗｔ％の水酸化ナトリウム水溶液９．６ｋｇに添加し，攪拌を開始することにより中和し，水酸化銅を生成させた。
【００３６】
水酸化銅生成後，亜酸化銅までの還元が可能な還元剤として，４２ｗｔ％のブドウ糖水溶液６．５Ｋｇを添加した。そのさい，亜酸化銅の生成を促進させるために７０℃まで昇温し，７０℃で３０分間反応させた。その後，液温７０℃に保持したまま，空気を流速４Ｌ／ｍｉｎで１５０分間導入し，液性を安定化させた。空気を導入してから５０分後，窒素雰囲気に戻して室温まで冷却した。それまでは攪拌を続けた。冷却後は攪拌を止めたうえ，亜酸化銅をデカンテーションにより沈降させた。亜酸化銅が十分に沈降したことを確認し，上澄み液を切ることにより，ウエットな状態の亜酸化銅（切れなかった上澄み液が残存する）２．５ｋｇを得た。銅の収率が１００％であるとすると，この亜酸化銅と残存上澄み液との混合物中に，銅１０モルに相当する亜酸化銅が得られることになる。
【００３７】
前記の亜酸化銅と残存上澄み液の混合物に，純水２．３ｋｇとＤ５０＝４．２３μｍの銅粉５３０ｇを添加した（最終目標銅粉のねらう粒径は５．５μｍである）。このミックスを窒素雰囲気中で６０℃に昇温した後，還元剤として８０％含水ヒドラジン３１ｇを添加して反応を攪拌下で開始した。最初のヒドラジンを添加してから３０分間間隔でヒドラジン３１ｇを追加し続け，３６０分後の段階で亜酸化銅が確認できなくなり，反応が終了した。
【００３８】
反応終了後は，室温まで冷却した後，吸引ろ過により固液分離し，純水８Ｌで洗浄した。洗浄後のケーキを雰囲気制御が可能な乾燥器に入れ，窒素雰囲気中１２０℃で１１時間かけて乾燥し，目的とする銅粉を得た。
【００３９】
得られた銅粉の電子顕微鏡写真を図１に示した。またこの銅粉の粒度分布を，湿式レーザー回折式の粒度分布測定装置（ベックマンコールター社製のＬＳ２３０）にて測定した。その結果，Ｄ５０＝５．４５μｍ，Ｄ９０＝６．４１μｍ，Ｄ１０＝４．７０μｍ（Ｄ９０／Ｄ１０＝１．３６）であった。その粒度分布を図３に示した。これらの結果に見られるように，得られた銅粉はねらい粒径どおりのものであり，粒度分布の非常にシャープな銅粉であった。
【００４０】
〔実施例２〕
Ｄ５０＝４．２３μｍの銅粉５３０ｇに代えて，Ｄ５０＝２．８３μｍの銅粉１００．２ｇを添加した（最終目標銅粉のねらい粒径は５．５μｍである）以外は，実施例１を繰り返した。得られた銅粉は，Ｄ５０＝５．５１μｍ，Ｄ９０＝６．６０μｍ，Ｄ１０＝４．４８μｍ（Ｄ９０／Ｄ１０＝１．４７）であり，図４に示すように粒度分布の非常にシャープな，ねらい粒径どおりのものであった。
【００４１】
〔実施例３〕
Ｄ５０＝４．２３μｍの銅粉５３０ｇに代えて，Ｄ５０＝１．２５μｍの銅粉７．５５ｇを添加した（最終目標銅粉のねらいは粒径５．５μｍである）以外は，実施例１を繰り返した。ただし，実施例１と同様にヒドラジンを添加し続けたが，本例では３９０分後に反応が終了した。得られた銅粉は，Ｄ５０＝５．５７μｍ，Ｄ９０＝６．４４μｍ，Ｄ１０＝４．４２μｍ（Ｄ９０／Ｄ１０＝１．４６）であり，図５に示すように粒度分布の非常にシャープな，ねらい粒径どおりのものであった。
【００４２】
〔実施例４〕
Ｄ５０＝４．２３μｍの銅粉５３０ｇに代えて，Ｄ５０＝５．３６μｍの銅粉２７３ｇを添加した（最終目標銅粉のねらいは粒径８．０μｍである）以外は，実施例１を繰り返した。
【００４３】
得られた銅粉は，Ｄ５０＝７．７８μｍ，Ｄ９０＝９．１１μｍ，Ｄ１０＝６．１４μｍ（Ｄ９０／Ｄ１０＝１．４８）であり，図６に示すように粒度分布の非常にシャープな，ねらい粒径より僅かに粒径が小さい銅粉であった。
【００４４】
〔実施例５〕
Ｄ５０＝４．２３μｍの銅粉５３０ｇに代えて，Ｄ５０＝２．５８μｍの銅粉４４．６ｇを添加した（最終目標銅粉のねらいは粒径６．４μｍである）以外は，実施例１を繰り返した。
【００４５】
得られた銅粉は，Ｄ５０＝６．１３μｍ，Ｄ９０＝７．２０μｍ，Ｄ１０＝５．２５μｍ（Ｄ９０／Ｄ１０＝１．３７）であり，図７に示すように粒度分布の非常にシャープな，ねらい粒径より僅かに粒径が小さい銅粉であった。
【００４６】
さらに，再現性を確認する目的で，硫酸銅五水和物の製造ロットを変えた以外は，本例を繰返したところ，Ｄ５０＝６．１３μｍ，Ｄ９０＝７．２０μｍ，Ｄ１０＝５．２５μｍ（Ｄ９０／Ｄ１０＝１．３７）となり，同一銅粉の製造が，原料や製造ロートの変動をほとんど受けないで再現できることが確認できた。図７には，製造ロットを変えた場合のものを，銅粉２として，その粒度分布を示した。
【００４７】
〔比較例１〕
実施例１と同様にして得た亜酸化銅と残存上澄み液の混合物に，純水２．３ｋｇを添加した。この混合液を用いて粒径５．５μｍをねらって以下の反応を攪拌下で行った。まず，この混合液を窒素雰囲気中で４５℃に昇温した後，８０％含水ヒドラジン１１ｇを添加して反応を開始した。最初のヒドラジンを添加してから３０分間間隔でヒドラジン１１ｇを２７０分まで添加し続け，２７０分より昇温速度０．２５℃／ｍｉｎで８５℃まで昇温した。８５℃に到達（４１０分）と同時に，ヒドラジンの添加を再開し，３０分間間隔で１８．６ｇずつ，５３０分からは，２０分間隔で１５．５ｇずつ添加した。ヒドラジン添加開始時から７１０分後に反応が終了した。反応終了後は実施例１と同様に洗浄・乾燥して銅粉を得た。
【００４８】
得られた銅粉は，Ｄ５０＝６．１９μｍ，Ｄ９０＝８．３１μｍ，Ｄ１０＝４．２８μｍ（Ｄ９０／Ｄ１０＝１．９４）であり，図８に示すように，粒度分布が比較的ブロードな銅粉であった。本例で得られた銅粉の電子顕微鏡写真を図２に示した。なお本比較例では，反応時間が実施例のおよそ２倍の時間を必要としている。
【００４９】
再現性を確認する目的で，硫酸銅五水和物の製造ロットを変えた以外は，本比較例を繰返したところ，Ｄ５０＝７．１８μｍ，Ｄ９０＝９．８４μｍ，Ｄ１０＝４．４２μｍ（Ｄ９０／Ｄ１０＝２．２３）となり，再現性があまりよくなく，製造ロットの変動が大きいことが確認された。
【００５０】
【発明の効果】
以上説明したように，本発明によると意図する粒径をもち且つその粒径分布幅の狭い非常に粒径の揃った銅粉が再現性よく製造できる。導電ペースト用のフイラーとして銅粉を用いる場合に，導電ペーストとして所望の特性を付与するために，銅粉の粒度分布を調整することが必要となるが，この場合に異なる粒径のものを混ぜ合わせ意図する粒度分布とするのが便利であるが，そのさい粒径の異なる銅粉そのものがブロードな粒度分布をもつものでは，意図する粒度分布を得ることできない。本発明によれば，異なる粒径の銅粉ごとに，それらの粒径分布幅の狭い銅粉を簡単且つ再現性よく製造することができるので，これらを混ぜ合わせることによって，意図する粒度分布をもつ導電ペースト用銅粉とすることができる。
【図面の簡単な説明】
【図１】本発明に従う粒径のそろった銅粉の電子顕微鏡写真である。
【図２】比較例の銅粉の電子顕微鏡写真である。
【図３】実施例１で用いた原料銅粉と実施例１の反応で得られた銅粉の粒度分布を示す図である。
【図４】実施例２で用いた原料銅粉と実施例２の反応で得られた銅粉の粒度分布を示す図である。
【図５】実施例３で用いた原料銅粉と実施例３の反応で得られた銅粉の粒度分布を示す図である。
【図６】実施例４で用いた原料銅粉と実施例４の反応で得られた銅粉の粒度分布を示す図である。
【図７】実施例５で用いた原料銅粉と実施例５の反応で得られた銅粉の粒度分布を示す図である。
【図８】比較例１で得られた銅粉の粒度分布を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a copper powder having a very uniform particle size and a narrow particle size distribution width suitable for a conductive filler of a conductive paste, and a method for producing the same.
[0002]
[Prior art]
2. Description of the Related Art A conductive paste is often used as a means for forming an electric circuit or an electrode on the surface, inside or outside of various substrates. As the conductive filler (metal powder) contained in the conductive paste, there are copper powder and silver powder, and a powder having a particle size of 0.1 to 20 μm is practically used. At that time, metal powders having uniform particle diameters are indispensable for controlling the sinterability and adhesive strength of the paste, or for eliminating such fluctuations. It is considered effective to adjust the paste rheology and to mix and mix two or three types of metal powders with uniform particle diameters in order to obtain dense conductor thick films and electrodes for electronic components. For this purpose, a metal powder having a uniform particle size is required for each different particle size, and a manufacturing technique for that purpose is also required.
[0003]
Well-known methods for producing metal powder include an atomizing method, an electrolytic method, and a wet reduction method. Regarding the production of copper powder, in the atomization method, the particle size distribution of the obtained copper powder is very wide, and in order to obtain copper powder of uniform particle size, classification must be repeated many times, and the yield is high. Is very bad. The electrolysis method is not suitable for thick films and chip electrodes that require high density, because the obtained copper powder has a wide particle size distribution width and a dendritic particle shape. Have difficulty.
[0004]
On the other hand, the wet reduction method can be said to be most suitable for the copper powder required for the conductive paste since the copper powder having a relatively uniform particle size and a substantially spherical particle shape can be obtained. The methods for producing copper powder by the wet reduction method are described in, for example, Patent Documents 1 and 2, and according to these methods, the particle size of each production lot is affected by the influence of impurities and slight fluctuations in the production process. However, there are problems that the dispersion of the particles is large, the width of the particle size distribution is wide, and the particle size is not sufficiently uniform.
[0005]
To cope with such a problem, Patent Document 3 of the same applicant teaches that if an oxidation step is introduced during wet reduction, copper powder having a relatively uniform particle size can be obtained.
[0006]
[Patent Document 1] Japanese Patent Publication No. Hei 7-93051 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-240904 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-144217 [0007]
[Problems to be solved by the invention]
Although copper powder having a relatively uniform particle size can be obtained by the method of Patent Document 3, the degree of uniformity of the particle size is not always sufficient. Even when the particle size exceeds 4 μm, it is not clear whether or not a product having a uniform particle size can be obtained. Therefore, a technique with good operability capable of consistently controlling a copper powder having a sufficiently uniform particle size for each target particle size in a wide particle size range from fine particles of 1 μm or less to coarse particles of 10 μm or more is required. It was not established. Further, it is more preferable that the target particle having a uniform particle diameter can be reproduced with a good hit ratio.
[0008]
Therefore, an object of the present invention is to suppress the fluctuation of the particle size of each production lot of copper powder and to obtain a copper powder having a narrow particle size distribution width and a target particle size.
[0009]
[Means for Solving the Problems]
According to the present invention, a reducing agent is added to a mixture composed of a copper powder having an average particle diameter (D50) of 0.1 μm or more, a solid component composed of a copper compound, and a liquid solvent, to reduce the solid component. Provided is a method for producing copper powder that reduces to metallic copper. Further, according to the present invention, a reducing agent is added to a mixture of copper powder having an average particle diameter (D50) of 0.1 μm or more and a liquid solvent containing copper ions to reduce the copper ions to metallic copper. To provide a method for producing copper powder. Further, a reducing agent is added to a mixture of copper powder having an average particle diameter (D50) of 0.1 μm or more, a solid component made of a copper compound, and a liquid solvent containing copper ions, and Copper ions can be reduced to metallic copper, and in any case, copper powder having a narrow particle size distribution width can be produced. The copper compound may be a copper oxide or hydroxide, and the liquid solvent may be water. D50 represents a 50% diameter in the particle size distribution.
[0010]
According to the method of the present invention, the total number of moles of copper other than copper powder in the mixture is n ₀ [mol], the average particle size (D50) of the copper powder used is x ₀ [μm], and the weight of the copper powder used is Assuming that w [g] and the atomic weight of copper are AW [g / mol], the average particle size of the copper powder to be produced is within ± 20% of x [μm] expressed by the following equation (2). it can. In this case, the ratio (D90 / D10) of the 90% diameter (D90) and the 10% diameter (D10) in the particle size distribution of the produced copper powder can be 1.5 or less, and the 50% in the particle size distribution. The diameter (D50) can range from 0.1 to 20.0 μm.
[0011]
(Equation 2)

[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
In the production of copper powder by the wet reduction method, the factors that cause variation in the particle size of the obtained copper powder can be divided into a nucleation process stage and a particle growth process stage, based on the production method.
[0013]
The stage of nucleation is pH adjustment, temperature adjustment (quenching etc.), addition of reducing agent, addition of copper ions, addition of impurity ions, introduction of reactive gas or light irradiation, etc. This is the step of generating ultrafine particles. The number of generated nuclei affects the target particle size of the copper powder. To obtain a copper powder having a large particle size, the number of nuclei generated may be reduced, and to obtain a copper powder having a small particle size, the number of nuclei generated may be increased. However, in practice, the number of nuclei generated is affected by the amount of impurities that are inevitably mixed and slight variations in the manufacturing process, so that the diameter of the copper particles to be manufactured varies, causing variations between manufacturing lots. Would.
[0014]
In the next particle growth stage, the generated copper particle nuclei are gradually grown (reduced copper ions and copper oxide to precipitate metallic copper on the surface of the core particles), thereby producing copper powder of the target particle size. This is the stage of adjustment. Also at this stage, if the reducing power is too strong or if the total surface area of the generated nuclei is small, new nuclei (secondary nuclei) will be generated at the same time as the particles grow, broadening the particle size distribution and reducing the particle size. Cause the
[0015]
It is important to suppress such fluctuations in the nucleation process and fluctuations in grain growth in order to obtain copper powder having a uniform particle size without variation for each production lot. According to the present invention, this can be realized.
[0016]
That is, in the present invention, (1) a mixture composed of a copper powder having an average particle diameter of 0.1 μm or more, a solid component composed of a copper compound, and a liquid solvent; A mixture of copper powder and a liquid solvent containing copper ions, or (3) a copper powder having an average particle size of 0.1 μm or more, a solid component of a copper compound, and a liquid solvent containing copper ions By adding a reducing agent to the mixture to reduce copper compounds or copper ions, these methods eliminate the nucleation process by introducing metallic copper powder into the reaction system. Therefore, it is possible to eliminate fluctuations at the nucleation stage. In addition, since the particle size of metallic copper powder is larger than the particle size of fine metal nuclei during normal nucleation, the total surface area on which metallic copper generated by reduction precipitates is increased, and grain growth is promoted. Since nucleation is also suppressed, fluctuation in grain growth can be suppressed.
[0017]
Further, in the present invention, in any of the above-mentioned mixtures (1) to (3), almost all of the copper component other than the copper powder present in the mixture can be used for grain growth. By adjusting the amount of copper component (total number of moles of copper other than copper powder), the particle size of copper powder, and the amount of copper powder added, the particle size of the resulting metal powder can be controlled extremely accurately. There is a feature. That is, the total number of moles of copper other than the copper powder in the mixture is n ₀ [mol], the average particle size (D50) of the copper powder is x ₀ [μm], the weight of the copper powder is w [g], and the atomic weight of copper Is defined as AW [g / mol], the average particle size x [μm] of the produced copper powder can be expressed by the following equation.
[0018]
[Equation 3]

[0019]
Α in the equation is a correction coefficient. This is because, depending on the particle size measurement method, the obtained particle size value is slightly different or the shape factor changes depending on the particle shape. It has been added. This coefficient α can usually fall within a range of 0.8 or more and 1.2 or less. That is, the copper powder to be produced almost falls within the range of ± 20% of the average particle diameter x in the above equation.
[0020]
In the practice of the present invention, the presence of copper components (copper compounds such as copper oxides and hydroxides) other than copper powder allows the copper source of the copper powder for production to be used as in the conventional wet reduction method. There is no limitation on the solubility of metal ions. For this reason, the total amount of copper atoms serving as a copper supply source can be increased. That is, since there is no limit on the number of copper atoms contributing to grain growth, the copper powder can be easily adjusted to a desired particle size, leading to an improvement in productivity. Even when a mixture of water containing copper ions and copper powder is subjected to reduction without using a solid component, it can be carried out without any problem.
[0021]
When a mixture of a copper compound and a copper powder is used, the copper oxidation number (valence such as monovalent or divalent) of the copper compound is preferably smaller. When the oxidation number is large, the reduction reaction takes several stages, and there is a possibility that a plurality of reduction reactions proceed simultaneously. In this case, secondary nucleation may occur.
[0022]
In some cases, the solid component consisting of a copper compound is reduced on the surface of metallic copper particles of coexisting copper powder and contributes to grain growth. It is thought that it may contribute to Similar effects are expected with oxoacid salts such as sulfuric acid, nitric acid, carbonic acid and phosphoric acid of copper, salts of copper halides, chalcogenides such as copper sulfides, and organic acid salts such as copper amino acid salts and carboxylic acids. it can. A typical solid component comprising a copper compound that can be used in the present invention is a copper oxide or hydroxide.
[0023]
The liquid medium for the reaction may be water or an organic liquid solvent, or a mixture of water and an organic liquid solvent. When water is used or a reducing agent that generates a gas by reduction is used, an antifoaming agent or an organic solvent having a low surface tension (for example, alcohols such as ethanol and isopropyl alcohol, and ketones such as acetone) And hydrocarbons such as hexane) are advantageous because the rise in liquid level due to a gas such as hydrogen generated by reduction can be suppressed.
[0024]
Substances (complexing agents) that can form a complex with copper ions suppress rapid reactions and suppress the generation of secondary nuclei, improve ion solubility, and have good surface properties (smooth surface). It is effective to get Examples of complexing agents include organic acids such as tartaric acid, oxalic acid, citric acid, succinic acid, and ethylenediaminetetraacetic acid; amines such as ammonia and ethylenediamine; alcohols such as glycerol and mannitol; amino acids; Salt is available. The complexing agent may not be added intentionally, but may be a metal salt (eg, carboxylate) of a solid component as a raw material or a by-product during the reaction functioning as a complexing agent. .
[0025]
When the reduction is promoted by adding the reducing agent, it is preferable to gradually add the reducing agent so as to suppress a sudden reaction, that is, generation of secondary nuclei. Specifically, the total amount of the reducing agent is divided into several parts, and these are added batchwise every few minutes to several hours, or the addition rate is arbitrarily determined, and continuously over several minutes to several hours. It is desirable to use an addition method.
[0026]
If the particle size of the copper powder to be added is too small, agglomeration becomes severe and the particle size distribution width may be widened, or secondary nuclei may be generated. In addition, the growth rate of the particles does not substantially depend on the particle size of the copper powder to be mixed, and is kept almost constant at several μm per unit time. The rate of particle growth is reduced, resulting in poor production efficiency. Therefore, the particle size (average particle size) of the copper powder to be mixed is desirably 0.1 μm or more, preferably 0.5 μm or more, more preferably 1.0 μm or more and 20 μm or less.
[0027]
The copper powder obtained after the reduction reaction has a very uniform particle size. For example, the ratio of the 90% diameter (D90) to the 10% diameter (D10) (D90 / D10) in the particle size distribution is 1.5 or less, and the particle size distribution width is narrow. Here, D90 and D10 have a particle size D (μm) on the horizontal axis and a volume (Q%) on the vertical axis showing the volume of particles having a particle size of Dμm or less, and Q% is 90%. And the values of the respective particle diameters D (μm) when they are 10% and 10%, respectively. Also, for example, D50 means the value (μm) of the particle size D when Q% is 50% in the cumulative particle size curve. Such a cumulative particle size curve can be drawn by a particle size distribution measuring device. If the ratio of D90 / D10 exceeds 1.5, the particle size is not sufficiently uniform. Therefore, when combining copper powders having different particle sizes to form a filler for conductive paste, the intended particle size is required. It is difficult to obtain a diameter distribution accurately.
[0028]
The reduction reaction is preferably performed in a reaction tank capable of controlling the atmosphere and controlling the temperature and having a stirring function. As the atmosphere during the reaction, in order to suppress the progress of side reactions such as oxidation by oxygen in the air, it is basically preferable to carry out the reaction under an inert gas atmosphere throughout. However, if necessary, a reactive gas such as ammonia or oxygen may be introduced to control the liquid properties or to adjust the oxidation / reduction potential of copper or a complexing agent. As the inert gas, nitrogen is optimal from the viewpoint of cost, but there is no problem even if a rare gas such as argon is used.
[0029]
Liquid solvents containing copper compounds other than metallic copper (copper powder to be mixed) and / or copper ions (reaction liquid before adding copper powder) include copper salts, copper hydroxide, and copper oxidation. It is adjusted by dissolving or suspending the substance in pure water or a mixture of pure water and an organic solvent. As the copper salts, inexpensive copper sulfate or copper chloride is preferable, but oxoacid salts such as nitric acid, carbonic acid and phosphoric acid of copper, halide salts of copper, copper chalcogenides such as copper sulfide, and carboxylate salts of copper Alternatively, there is no problem even if an organic acid salt such as an amino acid salt of copper is used. When copper hydroxide and / or oxide is used as a solid component of copper, a solution obtained by precipitating dissolved copper salts by neutralization or the like may be used, or may be produced by an electrolytic method or the like. Cuprous oxide powder may be used.
[0030]
In this way, a liquid solvent containing a solid component of a copper compound and / or copper ions is prepared as a reaction solution, and a complexing agent, a pH adjusting agent, a reducing agent, and the like are added to the reaction solution as necessary. By adding and mixing, it is possible to adjust the liquidity, the amount and particle size of the solid component, the oxidation number of copper, and the like. When adding the complexing agent, the pH adjusting agent, the reducing agent, and the like, they may be added as a solid or liquid, or after being dissolved and diluted in pure water or the like. Further, when a carboxylate or the like is used as a copper salt, the carboxylic acid contained therein can also serve as a complexing agent.
[0031]
Next, copper powder is mixed. If the mixed copper powder has a certain degree of particle size and is close to spherical, any copper powder manufactured by the atomizing method or wet reduction method can be used. Is not particularly limited. The correction coefficient α in the above equation for calculating x can be uniquely determined when the reaction system and the measuring device are determined, and a copper powder having an intended particle size and a narrow particle size distribution width can be produced with good reproducibility. can do.
[0032]
After the copper powder is mixed, the mixture is repulped in an inert gas for an appropriate period of time, and then a reducing agent is gradually added to allow the solid component of the copper compound and / or the copper ion to undergo a reduction reaction with stirring . As the reducing agent, those capable of reducing solid components of copper compounds and copper ions to metallic copper (that is, zero oxidation number), such as hydrazine hydrate, borohydride compounds, dimethylamine borane, zinc white, Formalin or the like can be used.
[0033]
The termination of the reaction is defined as a point in time when the presence of a solid component of copper ions, copper complexes or copper compounds cannot be detected in the reaction solution. After completion of the reaction, solid-liquid separation is performed by filtration, and the separated matter is washed with pure water or a water-soluble organic solvent. Solid-liquid separation is not limited to filtration, and other means such as centrifugation, spray drying and the like may be used. Drying the cake obtained by solid-liquid separation under an inert gas or reducing atmosphere at a temperature of 50 to 300 ° C. for several to several tens of hours to obtain a copper powder for conductive paste having a uniform particle size; Can be. Nitrogen or a rare gas may be used as the inert gas, and a reducing gas such as hydrogen or carbon monoxide may be mixed and used.
[0034]
From a different point of view, the method of the present invention can be said to be a method of increasing the particle size of existing copper powder and improving the copper powder to a uniform particle size. That is, the present invention provides (1) a method in which a raw copper powder is mixed with a liquid medium containing a solid component composed of a copper compound, and a reducing agent is added to the mixture to reduce the solid component to metallic copper. (2) mixing raw copper powder with a liquid medium containing copper ions, and adding a reducing agent to the mixture to reduce the copper ions to metallic copper And (3) mixing the raw copper powder with a liquid medium containing a solid component comprising a copper compound and copper ions, adding a reducing agent to the mixture, and It can be said that the present invention provides a method for producing a copper powder having a narrow particle size distribution, comprising reducing solid components and copper ions to metallic copper.
[0035]
【Example】
[Example 1]
2.5 kg of copper sulfate pentahydrate (the number of moles of copper = 10 mol) was dissolved in 6.1 kg of pure water at room temperature under a nitrogen atmosphere. This aqueous copper sulfate solution was added to 9.6 kg of a 10 wt% aqueous sodium hydroxide solution, and the mixture was neutralized by starting stirring to produce copper hydroxide.
[0036]
After the production of copper hydroxide, 6.5 kg of a 42% by weight aqueous glucose solution was added as a reducing agent capable of reducing to cuprous oxide. At that time, the temperature was raised to 70 ° C. to promote the formation of cuprous oxide, and the reaction was performed at 70 ° C. for 30 minutes. Thereafter, while maintaining the liquid temperature at 70 ° C., air was introduced at a flow rate of 4 L / min for 150 minutes to stabilize the liquid properties. Fifty minutes after the introduction of air, the atmosphere was returned to a nitrogen atmosphere and cooled to room temperature. Until then, stirring was continued. After cooling, stirring was stopped and cuprous oxide was settled by decantation. After confirming that the cuprous oxide had sufficiently settled out, the supernatant was cut to obtain 2.5 kg of wet cuprous oxide (an uncut supernatant remained). Assuming that the yield of copper is 100%, a mixture of the cuprous oxide and the remaining supernatant liquid will provide a cuprous oxide equivalent to 10 moles of copper.
[0037]
2.3 kg of pure water and 530 g of copper powder having a D50 of 4.23 μm were added to the mixture of the cuprous oxide and the remaining supernatant (the target particle diameter of the final target copper powder was 5.5 μm). After the mixture was heated to 60 ° C. in a nitrogen atmosphere, 31 g of 80% aqueous hydrazine was added as a reducing agent, and the reaction was started with stirring. After addition of the first hydrazine, 31 g of hydrazine was continuously added at intervals of 30 minutes, and after 360 minutes, cuprous oxide could not be confirmed, and the reaction was terminated.
[0038]
After completion of the reaction, the mixture was cooled to room temperature, separated into solid and liquid by suction filtration, and washed with 8 L of pure water. The cake after washing was placed in a dryer capable of controlling the atmosphere, and dried at 120 ° C. for 11 hours in a nitrogen atmosphere to obtain a desired copper powder.
[0039]
An electron micrograph of the obtained copper powder is shown in FIG. The particle size distribution of the copper powder was measured with a wet laser diffraction type particle size distribution analyzer (LS230 manufactured by Beckman Coulter, Inc.). As a result, D50 = 5.45 μm, D90 = 6.41 μm, and D10 = 4.70 μm (D90 / D10 = 1.36). The particle size distribution is shown in FIG. As can be seen from these results, the obtained copper powder was of the intended particle size and had a very sharp particle size distribution.
[0040]
[Example 2]
Example 1 was repeated except that 100.2 g of D50 = 2.83 μm copper powder was added instead of 530 g of D50 = 4.23 μm copper powder (the target particle size of the final target copper powder was 5.5 μm). Repeated. The obtained copper powder had D50 = 5.51 μm, D90 = 6.60 μm, D10 = 4.48 μm (D90 / D10 = 1.47), and had a very sharp particle size distribution as shown in FIG. The target particle size was as expected.
[0041]
[Example 3]
Example 1 was repeated except that 7.55 g of D50 = 1.25 μm copper powder was added instead of 530 g of D50 = 4.23 μm copper powder (the aim of the final target copper powder was 5.5 μm particle size). Repeated. However, hydrazine was continuously added as in Example 1, but in this example, the reaction was completed after 390 minutes. The obtained copper powder had D50 = 5.57 μm, D90 = 6.44 μm, D10 = 4.42 μm (D90 / D10 = 1.46), and had a very sharp particle size distribution as shown in FIG. The target particle size was as expected.
[0042]
[Example 4]
Example 1 was repeated, except that 273 g of copper powder of D50 = 5.36 μm was added instead of 530 g of copper powder of D50 = 4.23 μm (the aim of the final target copper powder was 8.0 μm in particle size). .
[0043]
The obtained copper powder had D50 = 7.78 μm, D90 = 9.11 μm, D10 = 6.14 μm (D90 / D10 = 1.48), and had a very sharp particle size distribution as shown in FIG. The copper powder had a particle size slightly smaller than the intended particle size.
[0044]
[Example 5]
Example 1 was repeated except that 44.6 g of copper powder of D50 = 2.58 μm was added instead of 530 g of copper powder of D50 = 4.23 μm (the aim of the final target copper powder was 6.4 μm in particle size). Repeated.
[0045]
The obtained copper powder had D50 = 6.13 μm, D90 = 7.20 μm, D10 = 5.25 μm (D90 / D10 = 1.37), and had a very sharp particle size distribution as shown in FIG. The copper powder had a particle size slightly smaller than the intended particle size.
[0046]
Furthermore, when this example was repeated except that the production lot of copper sulfate pentahydrate was changed for the purpose of confirming reproducibility, D50 = 6.13 μm, D90 = 7.20 μm, D10 = 5.25 μm ( D90 / D10 = 1.37), and it was confirmed that the production of the same copper powder could be reproduced with little change in the raw material and production funnel. FIG. 7 shows the particle size distribution of the copper powder 2 obtained when the production lot was changed.
[0047]
[Comparative Example 1]
2.3 kg of pure water was added to the mixture of cuprous oxide and the remaining supernatant obtained in the same manner as in Example 1. Using this mixture, the following reaction was carried out with stirring, aiming at a particle size of 5.5 μm. First, the temperature of the mixture was raised to 45 ° C. in a nitrogen atmosphere, and 11 g of hydrazine containing 80% water was added to start the reaction. After the first hydrazine was added, hydrazine (11 g) was continuously added at intervals of 30 minutes up to 270 minutes, and the temperature was raised to 85 ° C. at a rate of 0.25 ° C./min from 270 minutes. Upon reaching 85 ° C. (410 minutes), the addition of hydrazine was restarted, and 18.6 g was added at 30 minute intervals and 15.5 g at 20 minute intervals from 530 minutes. The reaction was completed 710 minutes after the start of hydrazine addition. After the completion of the reaction, copper powder was obtained by washing and drying in the same manner as in Example 1.
[0048]
The obtained copper powder had D50 = 6.19 μm, D90 = 8.31 μm, D10 = 4.28 μm (D90 / D10 = 1.94), and as shown in FIG. 8, the particle size distribution was relatively broad. It was copper powder. An electron micrograph of the copper powder obtained in this example is shown in FIG. In this comparative example, the reaction time required was about twice as long as that of the example.
[0049]
This comparative example was repeated except that the production lot of copper sulfate pentahydrate was changed for the purpose of confirming the reproducibility. D50 = 7.18 μm, D90 = 9.84 μm, D10 = 4.42 μm (D90 /D10=2.23), confirming that the reproducibility is not very good and the production lot varies greatly.
[0050]
【The invention's effect】
As described above, according to the present invention, a copper powder having an intended particle size and a narrow particle size distribution range can be produced with excellent reproducibility. When copper powder is used as a filler for the conductive paste, it is necessary to adjust the particle size distribution of the copper powder in order to give the desired properties as the conductive paste. It is convenient to obtain the intended particle size distribution. However, if the copper powders having different particle diameters themselves have a broad particle size distribution, the intended particle size distribution cannot be obtained. According to the present invention, it is possible to easily and reproducibly produce a copper powder having a narrow particle size distribution width for each copper powder having a different particle size. Copper powder for conductive paste.
[Brief description of the drawings]
FIG. 1 is an electron micrograph of a copper powder having a uniform particle size according to the present invention.
FIG. 2 is an electron micrograph of a copper powder of a comparative example.
FIG. 3 is a view showing the particle size distribution of the raw copper powder used in Example 1 and the copper powder obtained by the reaction of Example 1.
FIG. 4 is a view showing the particle size distribution of the raw copper powder used in Example 2 and the copper powder obtained by the reaction of Example 2.
FIG. 5 is a view showing the particle size distribution of the raw copper powder used in Example 3 and the copper powder obtained by the reaction of Example 3.
6 is a view showing the particle size distribution of the raw copper powder used in Example 4 and the copper powder obtained by the reaction of Example 4. FIG.
FIG. 7 is a view showing the particle size distribution of the raw copper powder used in Example 5 and the copper powder obtained by the reaction of Example 5.
FIG. 8 is a view showing the particle size distribution of the copper powder obtained in Comparative Example 1.

Claims

Copper that reduces the solid component to metallic copper by adding a reducing agent to a mixture of a copper powder having an average particle diameter (D50) of 0.1 μm or more, a solid component composed of a copper compound, and a liquid medium. Powder manufacturing method.

A method for producing copper powder wherein a reducing agent is added to a mixture of copper powder having an average particle diameter (D50) of 0.1 μm or more and a liquid medium containing copper ions to reduce the copper ions to metallic copper.

A reducing agent is added to a mixture of copper powder having an average particle diameter (D50) of 0.1 μm or more, a solid component made of a copper compound, and a liquid medium containing copper ions, and the solid component and the copper ions are mixed. Production method of copper powder for reducing copper to metallic copper.

The total number of moles of copper other than the copper powder in the mixture is n ₀ [mol], the average particle diameter (D50) of the copper powder is x ₀ [μm], the weight of the copper powder is w [g], and the atomic weight of the copper is AW. The copper powder according to any one of claims 1 to 3, wherein the average particle size of the produced copper powder is within ± 20% of x [μm] represented by the following formula 1, when [g / mol]. How to make a powder.

The method for producing copper powder according to any one of claims 1 to 4, wherein the mixture contains a substance that forms a complex with copper ions.

5. The method for producing copper powder according to claim 1, wherein the copper compound is an oxide or hydroxide of copper.

The method for producing copper powder according to any one of claims 1 to 6, wherein the reducing agent is gradually added in a continuous or batchwise manner.

8. A copper powder obtained by the production method according to claim 1, wherein a ratio (D90 / D10) of 90% diameter (D90) to 10% diameter (D10) in the particle size distribution is 1.5 or less. .

The copper powder according to claim 8, wherein a 50% diameter (D50) in the particle size distribution is in a range of 0.1 to 20.0 µm.