JP4204849B2

JP4204849B2 - Production method of fine copper powder

Info

Publication number: JP4204849B2
Application number: JP2002334653A
Authority: JP
Inventors: 美洋岡田; 浩之嶋田
Original assignee: Dowa Electronics Materials Co Ltd
Current assignee: Dowa Electronics Materials Co Ltd
Priority date: 2002-11-12
Filing date: 2002-11-19
Publication date: 2009-01-07
Anticipated expiration: 2022-11-19
Also published as: JP2004211108A

Description

【０００１】
【発明の属する技術分野】
本発明は、粒径が５０ｎｍ以下であっても個々に分散した粒子の集合として存在し得る微粒子銅粉の製法に関する。
【０００２】
【従来の技術】
プリント配線基板の分野で配線の微細化が進んでいるが，それには自ずと限界があることから，近年，インクジェット方式等による新たな超微細配線パターンへの技術開発が行われるようになった。例えばプリンターで採用されているようなインクジェット方式による出力印刷を回路基板に適用し，金や銀等の導電性の微粒子を分散させたインクの噴射で回路基板を製造しようとするものである（例えば，非特許文献１参照）。
【０００３】
金や銀の微粒子（５０ｎｍ以下）を導電フィラーとしたインクまたはペーストは高価であり、また銀ではエレクトロマイグレーションが起きるので、安価で且つエレクトロマイグレーションの問題のない銅の微粒子をインクまたはペーストに用いることが望まれている。
【０００４】
銅粉の製造技術には各種の方法が知られているが，硫酸銅等の銅塩水溶液から直接的にヒドラジン等の還元剤で金属銅にまで還元する方法（例えば特許文献１参照）や，酸化銅粒子を含む水性媒体中でヒドラジン等の還元剤で金属銅に還元する方法（例えば特許文献２参照）等の湿式法による銅粉の製造法が，粒径制御の点や製造性の点で有利である。
【０００５】
【非特許文献１】
雑誌「日経エレクトロニクス」，２００２年６月１７日，Ｐ６７〜６９
【特許文献１】
特開昭６３−１８６８０７号公報
【特許文献２】
特開昭５９−１１６３０３号公報
【０００６】
【発明が解決しようとする課題】
インクジェット方式による回路基板の製造において，銅粉をフイラーとするインクを噴射させるにはその銅粉は微細で且つ粒径が揃っていて凝集せずに粒子の個々が分散している必要がある。
【０００７】
前掲の特許文献１や２の湿式法による銅粉の製法は，粒径制御や製造性の点で乾式法よりも優れているが，粒径を小さくするための反応条件を選ぶと，例えば還元剤を多くするような条件を設定すると，突沸して安定した製造ができなかったり，粒径を小さくすると分散性が悪くなって凝集した二次粒子の生成量が多くなる傾向にある。したがって，微粒子が個々に分散した銅粉を安定して製造することは困難であり，このために，インクジェット方式に適用できるような微粒子の銅粉は市場で入手し難いのが実状である。本発明の課題は，このような要望を満たすことにある。
【０００８】
【課題を解決するための手段】
【０００９】
本発明によれば、短径と長径がいずれも５０ｎｍ以下で、不活性ガス中での焼結開始温度が３００℃以下である、表面に耐酸化性処理が施された銅の粒子が個々に分散している微粒子銅粉を提供する。粒子表面に施す耐酸化性処理としては、銅粒子の表面にベンゾトリアゾールを被着させるのがよい。
【００１０】
このような微粒子銅粉は、硫酸銅等の銅塩水溶液にアルカリを添加して水酸化銅を生成させ、この水酸化銅を還元剤を用いて水性媒体中で金属銅粒子に還元するさいに、還元剤としてヒドラジンまたはヒドラジン化合物を使用すること、当該還元剤の使用量を全水酸化銅の還元に必要な理論当量の３〜５倍とすること、還元剤の全量を５分以内に反応系に添加し終えること、その還元反応を消泡剤存在下で行うこと、および還元反応の前または途中に表面処理剤を添加することを特徴とする微粒子銅粉の製法によって得ることができる。消泡剤にはアルコールを含ませることが好ましく、また、表面処理剤としてベンゾトリアゾールを使用することができる。
【００１１】
【発明の実施の形態】
銅粉をフィラーとする導電インクをインクジェット方式で噴射させることによって、印字ヘッドのノズルを詰まらせることなく、一定の線幅を有し且つ低温で焼結可能な微細配線を実現するには、その銅粉は、５０ｎｍ以下の微粒子からなること、その粒径が揃っていること、凝集せずに粒子の個々が分散していること、耐酸化性を有すること、低コストで製造できることが必要である。
【００１２】
本発明者らは、そのような微粒子銅粉を得るべく、種々の試験研究を重ねてきたが、銅塩の水溶液をアルカリで中和して水酸化銅のスラリーとし、これにヒドラジンまたはヒドラジン化合物を添加して銅粒子を析出させる湿式還元法で銅粉を製造するさいに、以下に述べる第１〜４のような処方を採用すると、粒径が５０ｎｍ以下の粒子からなる銅粉を得ることができることを見出した。
【００１３】
先ず第１に，水酸化銅のスラリーへの還元剤の添加速度を適切にすることである。特許文献１〜２のように銅粉の湿式還元法は良く知られているが，水酸化銅のスラリーに対する還元剤の添加速度が粒子サイズに与える影響を積極的に述べているものはない。水酸化銅のスラリーに短時間で還元剤を添加し，核発生から粒成長までを短時間で行うことによって一時に大量の核を発生させ，それらが微粒子サイズまで成長した時点で反応を終結させる方法によると，１００ｎｍ未満の粒子サイズのものを安定して得ることができることがわかった。還元剤の添加時間が長くなると生成する粒子の粒径が増す傾向があり，５分を越えると１００ｎｍ以上の粒子の割合が無視できなくなる。還元剤の添加時間は，好ましくは２分以内，より好ましくは１分以内，最も好ましくは３０秒以内が望ましい。
【００１４】
第２に、添加する還元剤の量も還元に要する理論必要量よりも過剰にして、速やかに反応が進むようにする必要があり、理論当量の３〜５倍の範囲の量を使用するのがよい。３倍未満では少なすぎて良い結果が得られず、５倍以上に増やしても効果が飽和して不経済となる。好ましくは理論当量の３.５〜４.５倍の還元剤を使用するのが望ましい。
【００１５】
しかし，短時間で且つ多量の還元剤を水酸化銅のスラリーに添加すると，反応が一気に進むために，急激な反応による液面上昇が起こり，反応槽から液があふれたり，反応の再現性が確立できなくなり，危険も伴う。
【００１６】
第３に、これを回避するための処方として、適切な消泡剤の存在下で反応を行わせることが有益であることがわかった。すなわち、消泡剤の存在下で短時間で且つ多量の還元剤を水酸化銅のスラリーに添加すると、５０ｎｍ以下の粒径の揃った微粒子銅粉が再現性良く製造できることがわかった。
【００１７】
第４に，還元反応の前または後，若しくは途中に，適切な表面処理剤を液に添加すると，粒径の揃った微粒子銅粉が得られ且つ耐酸化性を付与できることがわかった。このような処理剤としては，ベンゾトリアゾールが有益である。ベンゾトリアゾール（以下，ＢＴＡと略称することがある）は防錆剤として知られているが，ＢＴＡが反応液中に存在すると，生成する微粒子銅粉の溶液中での凝集を妨げる作用を示すことがわかった。それによって，粒径の揃った微粒子にする作用があり，しかも，乾燥後の微粒子銅粉に良好な耐酸化性を付与できることがわかった。
【００１８】
一般に，不活性雰囲気中で乾燥させた粒径が数十ｎｍ程度の，表面処理なしの微粒子銅粉は，表面の活性度が高いので，大気に曝すと激しい酸化が起こり発熱する。しかし，ＢＴＡで表面処理された微粒子銅粉は，このような酸化を緩和することができ，しかも，反応前の銅塩溶液にＢＴＡを添加して反応を進行させると，粒度の揃った微粒子銅粉が得られるという一石二鳥の効果を得ることができ，工程の簡略化，生産性の向上の点でも有利である。
【００１９】
前記の消泡剤として市販品である例えば第一工業製薬のアンチフロスF-244 を使用できるが，これを使用した場合でも，ＢＴＡを反応系に添加すると，ＢＴＡは発泡しやすいので，突沸が起こることがある。このような場合には，アルコールを併用するのがよい。生成した泡にアルコールを添加しても，また還元前の水酸化銅のスラリーに予め加えておいても，突沸を防止する効果がある。したがって，ＢＴＡを併用する場合には，アルコールを併用するのがよい。
【００２０】
事実，本発明者らの経験によれば，反応系全体に対する重量比で約１０％に相当するイソプロピルアルコール（ＩＰＡ）を水酸化銅スラリーに加えてから還元剤を投入したところ，ほとんど反応中の発泡が見られなかった。また，得られた微粒子銅粉の粒径制御や不純物混入等への悪影響も認められなかった。使用するアルコールは発泡性の物質を溶かすものであればメタノールやエタノールなども利用可能である。なお，アルコールの使用は，ＢＴＡの使用に関わらず，金属アルコキシド等によって銅粉の表面を二次処理するさいにも都合がよい。
【００２１】
このようにして、液中の水酸化銅を還元剤を用いて金属銅粒子に還元するさいに、（１）還元剤としてヒドラジンまたはヒドラジン化合物を使用する、（２）当該還元剤の使用量を全水酸化銅の還元に必要な理論当量の３〜５倍とする、（３）還元剤の添加時間を５分以内とする、（４）還元反応を消泡剤好ましくはアルコール併用の存在下で行う、（５）還元反応の前または途中にベンゾトリアゾール等の表面処理剤を添加することによって、短径と長径がいずれも５０ｎｍ以下で、表面に耐酸化性処理が施された銅の粒子が個々に分散している微粒子銅粉を得ることができる。
【００２２】
この微粒子銅粉は，耐酸化性がよくインクへの分散性がよく，しかも焼結開始温度が３００℃以下であるという特徴がある。このため，本発明に従う微粒子銅粉は導電インクの導電フイラーとして好適に使用でき，インクジェット方式等による超微細配線パターンの形成に役立つ。
【００２３】
ここで，焼結開始温度は，この銅粉の成形体を窒素雰囲気中で所定の速度で昇温したときに焼結を開始する温度を意味しており，その測定は，次のようにして行うことができる。
〔焼結開始温度の測定〕：測定用の銅粉０.５ｇを採取し，これにアクリル系の有機ビヒクル0.03〜0.05ｇを加えて混合し，この混合物を直径５ｍｍの筒体に装填し，上部からポンチを押し込んで１６２３Ｎで１０秒保持する加圧を付与し，高さ約５ｍｍ相当の円柱状に成形する。この成形体を，軸を鉛直方向にして且つ軸方向に１０ｇの荷重を付与した条件で，昇温炉に装填し，窒素流量中で昇温速度１０℃／分，測定範囲：常温〜１０００℃に連続的に昇温してゆき，成形体の高さ変化（膨張・収縮の変化）を自動記録する。横軸に昇温温度（昇温速度が一定である場合には経過時間に対応する）を採り，縦軸に高さ変化の割合（膨張率または収縮率）を記録したものをＴＭＡ曲線と呼ぶ。この昇温につれて，有機ビヒクルの揮発や酸化膜の分解還元などにより徐々に成形体の高さの変化（収縮）が起きる（例えば図４のＡで示す部分）が，焼結温度帯にさしかかると，急激な収縮が始まる（図４のＢで示す部分）。この急激な収縮が始まるときの温度が焼結開始温度であるが，実際には，この温度付近の収縮変化は曲線となり，焼結開始点を正確に判読するのが困難である。このため，さらに昇温して収縮変化を求め（図４のＣで示す部分），Ａの直線部分とＣの直線部分を図上で延長してその交点に対応する温度を焼結開始温度とする。なお，Ｂの部分で実際に焼結が開始したか否かは，同一の別サンプルをＣの部分まで昇温したあと冷却し，得られたサンプルの電気伝導度や色調を調べることによって判別することができる。
【００２４】
【実施例】
〔実施例１〕
硫酸銅五水和物２８０ｇ，ベンゾトリアゾール（ＢＴＡ）１ｇおよび水系消泡剤（第一工業製薬株式会社製の商品名アンチフロスF-244 ）１ｇを，水（Ｈ₂Ｏ）１３３０ｇに溶解し，溶液Ａとする。苛性ソーダ（濃度50% ）２００ｇを水（Ｈ₂Ｏ）９００ｇに希釈し，溶液Ｂとする。ヒドラジン一水和物（濃度８０％）１５０ｇを水１３００ｇで希釈し，溶液Ｃとする。
【００２５】
溶液Ａと溶液Ｂを攪拌しながら混合し，６０℃に温度調整したあと，攪拌を維持しながら，これに溶液Ｃを３０秒以内に全量添加し，約５分程度で反応が終了した。生成したスラリーを固液分離し，真空乾燥して分散性の良い，粒状の銅粉が得られた。電子顕微鏡観察によると，図１に示したように，短軸と長軸がほぼ等しい球形の粒子からなり，その平均粒径は約５０ｎｍであった。
【００２６】
また，得られた銅粉の諸特性を測定した結果を表１に示した。表１において，ＳＥＭ径は電子顕微鏡観察による平均径，ＣＤは圧縮密度，％Ｃは銅粉中のＣ含有量，％Ｏは銅粉中のＯ含有量，ＢＥＴ径はＢＥＴ法で測定された比表面積と密度とから計算される粒子の径，ＢＥＴはＢＥＴ法による比表面積，ＴＡＰはタップ密度を表す。
【００２７】
表１の結果から，ＢＥＴ径とＳＥＭ径は良好な相関を有しており，このことから，本例の銅粉は短径と長径がいずれも５０〜６０ｎｍ付近の銅の微粒子が個々に分散している微粒子銅粉であることがわかる。
【００２８】
〔実施例２〕
溶液ＡにＩＰＡ（イソプロピルアルコール）４６０ｇを加え，これを溶液Ｂと混合した以外は，実施例１を繰り返した。還元反応中はほとんど発泡は見られなかった。得られた銅粉の諸特性を表１に併記した。また，電子顕微鏡観察によれば，本例のものは実施例１のものとほぼ同様の微粒子銅粉であった。
【００２９】
また，得られた真空乾燥後の微粒子銅粉を数時間大気に曝して粒子表面を安定化処理したうえ，本文に記載の焼結開始温度の測定に供した。その結果（ＴＭＡ曲線）を図４に示した。図４には，比較のために，市場で入手し得る，より粒径の大きい銅粉（平均粒径が０.３μｍの銅粉，０.７μｍの銅粉および１.０μｍの銅粉）のＴＭＡ曲線も併記した。
【００３０】
図４の結果から，本例の微粒子銅粉は焼結開始温度約２５０℃であり，他のより粒径の大きなものの焼結開始温度が７００〜７５０℃付近にあるものと対比して，著しく低温側にシフトしていることがわかる。このことから，本例の微粒子銅粉を導電インクのフイラーとしたときに，低温で焼結するので超微細配線パターンを有利に形成できる。
【００３１】
〔実施例３〕
ＢＴＡに代えて，デキストリン１ｇを使用した以外は，実施例１を繰り返した。得られた銅粉の諸特性を表１に併記した。この粉体は，電子顕微鏡観察によると，図２に示したように，分散性の良い球状の粒子からなり，その平均粒径は約３０ｎｍであった。
【００３２】
〔比較例１〕
ＢＴＡを使用しなかった以外は，実施例１を繰り返した。得られた粉体は，微細な一次粒子（粒径が数１０ｎｍ程度）が凝集して数μｍ〜数１０μｍの二次粒子（凝集粒子）の集合となり，分散性のよい微粒子は得られなかった。その電子顕微鏡写真を図３に示した。なお電子顕微鏡観察のための試料は，本例で得られた乾燥粒子をＢＴＡで表面処理して酸化防止を図ったうえで使用した。さらに，得られた銅粉の諸特性を実施例１と同様に測定した結果を表１に併記した。
【００３３】
〔参考例〕
ＢＴＡに代えてデキストリン１ｇを使用した以外は、実施例２を繰り返したところ、高濃度のＩＰＡによりデキストリンがゲル化し、生成物の固液分離（濾過分離）ができなかった。
【００３４】
【表１】

【００３５】
【発明の効果】
以上説明したように、本発明によると、径が５０ｎｍ以下の銅粒子が個々に分散した耐酸化性の良好な微粒子銅粉が得られ、このものは不活性ガス中での焼結開始温度が３００℃以下と低温である。したがって、導電インクのフィラーとして本発明の微粒子銅粉を使用すると、インクジェット方式等による超微細配線パターンを形成するのに好適な導電インクが得られる。
【図面の簡単な説明】
【図１】本発明に従う微粒子銅粉の例（実施例１のもの）を示す電子顕微鏡（ＳＥＭ像）写真である。
【図２】本発明に従う微粒子銅粉の他の例（実施例３のもの）を示す電子顕微鏡（ＳＥＭ像）写真である。
【図３】比較例の銅粉の電子顕微鏡写真である。
【図４】本発明に従う微粒子銅粉の焼結開始温度を測定したＴＭＡ曲線を，従来例の銅粉のＴＭＡ曲線と対比して示した図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing fine copper powder that can exist as an aggregate of individually dispersed particles even when the particle size is 50 nm or less.
[0002]
[Prior art]
Although the miniaturization of wiring is progressing in the field of printed wiring boards, there is a limit to it naturally, and in recent years, technology development for new ultra-fine wiring patterns by the ink jet method or the like has been carried out. For example, an output printing by an ink jet method used in a printer is applied to a circuit board, and the circuit board is manufactured by ejecting ink in which conductive fine particles such as gold and silver are dispersed (for example, Non-Patent Document 1).
[0003]
Ink or paste using gold or silver fine particles (50 nm or less) as a conductive filler is expensive, and since electromigration occurs in silver, copper fine particles that are inexpensive and have no electromigration problems should be used for the ink or paste. Is desired.
[0004]
Various methods are known for the production technology of copper powder, but a method of reducing copper metal aqueous solution such as copper sulfate directly to metallic copper with a reducing agent such as hydrazine (see, for example, Patent Document 1), A method for producing copper powder by a wet method such as a method of reducing to metallic copper with a reducing agent such as hydrazine in an aqueous medium containing copper oxide particles (for example, refer to Patent Document 2) is advantageous in terms of particle size control and manufacturability. Is advantageous.
[0005]
[Non-Patent Document 1]
Magazine "Nikkei Electronics", June 17, 2002, P67-69
[Patent Document 1]
JP 63-186807 A [Patent Document 2]
JP 59-116303 A [0006]
[Problems to be solved by the invention]
In the production of an ink-jet circuit board, in order to eject ink using copper powder as a filler, the copper powder must be fine and have a uniform particle size so that the individual particles are dispersed without aggregation.
[0007]
The copper powder production method by the wet method described in Patent Documents 1 and 2 is superior to the dry method in terms of particle size control and manufacturability, but if reaction conditions for reducing the particle size are selected, for example, reduction If conditions that increase the amount of the agent are set, stable production cannot be achieved due to bumping, and if the particle size is reduced, the dispersibility becomes poor and the amount of aggregated secondary particles tends to increase. Therefore, it is difficult to stably produce copper powder in which fine particles are individually dispersed. For this reason, it is difficult to obtain fine copper powder that can be applied to the ink jet system in the market. An object of the present invention is to satisfy such a demand.
[0008]
[Means for Solving the Problems]
[0009]
According to the present invention, copper particles whose surface has been subjected to oxidation resistance treatment, each having a minor axis and a major axis of 50 nm or less and a sintering start temperature in an inert gas of 300 ° C. or less are individually provided. Dispersed particulate copper powder is provided. As an oxidation resistance treatment applied to the particle surface, it is preferable to deposit benzotriazole on the surface of the copper particle.
[0010]
Such fine copper powder is produced by adding alkali to an aqueous copper salt solution such as copper sulfate to produce copper hydroxide, and reducing the copper hydroxide to metallic copper particles in an aqueous medium using a reducing agent. , Using hydrazine or a hydrazine compound as a reducing agent, making the amount of the reducing agent used 3-5 times the theoretical equivalent required for reduction of total copper hydroxide, reacting the total amount of reducing agent within 5 minutes It can be obtained by a method for producing fine-particle copper powder characterized by finishing addition to the system, performing the reduction reaction in the presence of an antifoaming agent, and adding a surface treatment agent before or during the reduction reaction. The antifoaming agent preferably contains alcohol, and benzotriazole can be used as the surface treatment agent.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In order to realize a fine wiring that has a constant line width and can be sintered at a low temperature without clogging the nozzles of the print head by ejecting conductive ink containing copper powder as a filler by an inkjet method, The copper powder needs to be composed of fine particles of 50 nm or less, to have a uniform particle size, to be dispersed without particles, to have oxidation resistance, and to be manufactured at low cost. is there.
[0012]
In order to obtain such fine-particle copper powder, the present inventors have repeated various test studies, and an aqueous copper salt solution is neutralized with an alkali to form a copper hydroxide slurry, which is then hydrazine or a hydrazine compound. When the prescriptions such as Nos. 1 to 4 described below are adopted when producing copper powder by a wet reduction method in which copper particles are precipitated by adding copper, a copper powder composed of particles having a particle size of 50 nm or less is obtained. I found out that I can.
[0013]
First, the rate of addition of the reducing agent to the copper hydroxide slurry is made appropriate. As described in Patent Documents 1 and 2, the wet reduction method of copper powder is well known, but nothing has positively described the influence of the addition rate of the reducing agent on the copper hydroxide slurry on the particle size. A reducing agent is added to the copper hydroxide slurry in a short time, and a large amount of nuclei are generated at a time by performing the nucleation to grain growth in a short time, and the reaction is terminated when they grow to the fine particle size. According to the method, it was found that particles having a particle size of less than 100 nm can be obtained stably. When the addition time of the reducing agent becomes longer, the particle size of the generated particles tends to increase, and when it exceeds 5 minutes, the proportion of particles of 100 nm or more cannot be ignored. The addition time of the reducing agent is preferably within 2 minutes, more preferably within 1 minute, and most preferably within 30 seconds.
[0014]
Secondly, the amount of the reducing agent to be added must also be larger than the theoretical amount required for reduction so that the reaction proceeds promptly, and an amount in the range of 3 to 5 times the theoretical equivalent is used. Is good. If it is less than 3 times, it is too small to obtain a good result, and even if it is increased to 5 times or more, the effect is saturated and uneconomical. It is preferable to use a reducing agent that is 3.5 to 4.5 times the theoretical equivalent.
[0015]
However, if a large amount of reducing agent is added to the copper hydroxide slurry in a short period of time, the reaction proceeds at a stretch, causing a sudden rise in the liquid level due to a rapid reaction, resulting in overflow of the reaction tank and reproducibility of the reaction. It cannot be established and is dangerous.
[0016]
Third, it has been found beneficial to allow the reaction to occur in the presence of a suitable antifoam as a formulation to avoid this. That is, it was found that when a large amount of a reducing agent was added to a slurry of copper hydroxide in a short time in the presence of an antifoaming agent, fine particle copper powder having a particle size of 50 nm or less could be produced with good reproducibility.
[0017]
Fourthly, it has been found that if an appropriate surface treatment agent is added to the solution before, after, or during the reduction reaction, fine copper powder having a uniform particle size can be obtained and oxidation resistance can be imparted. Benzotriazole is useful as such a treatment agent. Benzotriazole (hereinafter sometimes abbreviated as BTA) is known as a rust inhibitor, but when BTA is present in the reaction solution, it exhibits an action that prevents aggregation of the fine copper powder produced in the solution. I understood. As a result, it has been found that there is an effect of forming fine particles having a uniform particle diameter, and that good oxidation resistance can be imparted to the finely divided copper powder after drying.
[0018]
In general, finely divided copper powder having a particle size of about several tens of nanometers dried in an inert atmosphere and having no surface treatment has high surface activity, and therefore, when exposed to the atmosphere, it undergoes intense oxidation and generates heat. However, the particulate copper powder surface-treated with BTA can alleviate such oxidation. Moreover, when BTA is added to the copper salt solution before the reaction and the reaction proceeds, the particulate copper having a uniform particle size can be obtained. The effect of two birds with one stone that powder can be obtained can be obtained, which is advantageous in terms of simplification of the process and improvement of productivity.
[0019]
For example, Daiichi Kogyo Seiyaku Anti-Floss F-244 can be used as the antifoaming agent. However, even when this is used, if BTA is added to the reaction system, BTA is easy to foam, so that bumping occurs. May happen. In such a case, it is better to use alcohol together. Even if alcohol is added to the generated foam or added to the copper hydroxide slurry before reduction, there is an effect of preventing bumping. Therefore, when using BTA together, it is better to use alcohol together.
[0020]
In fact, according to the experience of the present inventors, when isopropyl alcohol (IPA) corresponding to about 10% by weight with respect to the entire reaction system was added to the copper hydroxide slurry, the reducing agent was added. No foaming was seen. Also, no adverse effects on particle size control and impurity contamination of the obtained fine copper powder were observed. As the alcohol to be used, methanol or ethanol can be used as long as it dissolves a foaming substance. The use of alcohol is also convenient when the surface of the copper powder is secondarily treated with a metal alkoxide or the like regardless of the use of BTA.
[0021]
Thus, when reducing the copper hydroxide in the liquid to metallic copper particles using a reducing agent, (1) hydrazine or a hydrazine compound is used as the reducing agent, (2) the amount of the reducing agent used is reduced. 3-5 times the theoretical equivalent required for reduction of total copper hydroxide, (3) Addition of reducing agent within 5 minutes, (4) Reduction reaction in the presence of antifoaming agent, preferably alcohol (5) Copper particles whose minor axis and major axis are both 50 nm or less and whose surface is subjected to oxidation resistance treatment by adding a surface treatment agent such as benzotriazole before or during the reduction reaction Can be obtained.
[0022]
This fine particle copper powder is characterized by good oxidation resistance, good dispersibility in ink, and a sintering start temperature of 300 ° C. or lower. For this reason, the fine copper powder according to the present invention can be suitably used as a conductive filler for conductive ink, and is useful for forming an ultrafine wiring pattern by an ink jet method or the like.
[0023]
Here, the sintering start temperature means the temperature at which sintering starts when the copper powder compact is heated at a predetermined rate in a nitrogen atmosphere, and is measured as follows. It can be carried out.
[Measurement of sintering start temperature]: 0.5 g of copper powder for measurement was sampled, 0.03 to 0.05 g of acrylic organic vehicle was added and mixed, and this mixture was loaded into a cylinder having a diameter of 5 mm. A punch is pushed in from above, and a pressure is applied to hold it at 1623 N for 10 seconds, and it is molded into a columnar shape with a height of about 5 mm. This molded body was loaded into a heating furnace under the condition that the shaft was set in the vertical direction and a load of 10 g was applied in the axial direction, the heating rate was 10 ° C./min in the nitrogen flow rate, and the measurement range: normal temperature to 1000 ° C. As the temperature rises continuously, the height change (change in expansion / contraction) of the compact is automatically recorded. A temperature rise temperature (corresponding to elapsed time when the temperature rise rate is constant) is plotted on the horizontal axis, and the rate of change in height (expansion rate or contraction rate) is recorded on the vertical axis is called a TMA curve. . As this temperature rises, the height (shrinkage) of the molded body gradually occurs due to the volatilization of the organic vehicle, decomposition and reduction of the oxide film, etc. (for example, the portion indicated by A in FIG. 4) , Abrupt contraction begins (part indicated by B in FIG. 4). The temperature at which this rapid shrinkage starts is the sintering start temperature. Actually, however, the shrinkage change near this temperature becomes a curve, and it is difficult to accurately interpret the sintering start point. For this reason, the temperature is further raised to obtain the shrinkage change (the portion indicated by C in FIG. 4), the straight line portion A and the straight line portion C are extended on the drawing, and the temperature corresponding to the intersection is defined as the sintering start temperature. To do. Whether or not sintering has actually started in part B is determined by raising the temperature of another identical sample to part C and cooling it, and examining the electrical conductivity and color tone of the obtained sample. be able to.
[0024]
【Example】
[Example 1]
280 g of copper sulfate pentahydrate, 1 g of benzotriazole (BTA) and 1 g of an aqueous antifoaming agent (trade name Antifloss F-244 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) are dissolved in 1330 g of water (H ₂ O). Let it be Solution A. 200 g of caustic soda (concentration 50%) is diluted with 900 g of water (H ₂ O) to obtain Solution B. A solution C is prepared by diluting 150 g of hydrazine monohydrate (concentration 80%) with 1300 g of water.
[0025]
Solution A and Solution B were mixed with stirring, the temperature was adjusted to 60 ° C., and while maintaining stirring, the entire amount of Solution C was added within 30 seconds, and the reaction was completed in about 5 minutes. The resulting slurry was solid-liquid separated and vacuum dried to obtain a granular copper powder with good dispersibility. According to the electron microscope observation, as shown in FIG. 1, it was composed of spherical particles having a short axis and a long axis almost equal, and the average particle diameter was about 50 nm.
[0026]
The results of measuring various properties of the obtained copper powder are shown in Table 1. In Table 1, SEM diameter was measured by electron microscope observation, CD was compressed density,% C was C content in copper powder,% O was O content in copper powder, and BET diameter was measured by BET method. The particle diameter calculated from the specific surface area and density, BET represents the specific surface area by the BET method, and TAP represents the tap density.
[0027]
From the results shown in Table 1, the BET diameter and the SEM diameter have a good correlation. From this, the copper powder of this example has dispersed copper fine particles each having a minor axis and a major axis in the vicinity of 50 to 60 nm. It can be seen that this is a finely divided copper powder.
[0028]
[Example 2]
Example 1 was repeated except that 460 g of IPA (isopropyl alcohol) was added to solution A and mixed with solution B. Little foaming was observed during the reduction reaction. Various characteristics of the obtained copper powder are shown in Table 1. Moreover, according to electron microscope observation, the thing of this example was a fine particle copper powder substantially the same as that of Example 1.
[0029]
The obtained finely divided copper powder after vacuum drying was exposed to the atmosphere for several hours to stabilize the particle surface, and then subjected to the measurement of the sintering start temperature described in the text. The result (TMA curve) is shown in FIG. For comparison, FIG. 4 shows a comparison of commercially available copper powders (copper powder having an average particle diameter of 0.3 μm, copper powder of 0.7 μm, and copper powder of 1.0 μm) that are available on the market. A TMA curve is also shown.
[0030]
From the results shown in FIG. 4, the fine particle copper powder of this example has a sintering start temperature of about 250 ° C., which is remarkably different from those having a larger particle size than those having a sintering start temperature of around 700 to 750 ° C. It turns out that it has shifted to the low temperature side. Therefore, when the fine copper powder of this example is used as a conductive ink filler, it is sintered at a low temperature, so that an ultrafine wiring pattern can be formed advantageously.
[0031]
Example 3
Example 1 was repeated except that 1 g of dextrin was used instead of BTA. Various characteristics of the obtained copper powder are shown in Table 1. According to electron microscope observation, this powder was composed of spherical particles with good dispersibility as shown in FIG. 2, and the average particle size was about 30 nm.
[0032]
[Comparative Example 1]
Example 1 was repeated except that BTA was not used. In the obtained powder, fine primary particles (having a particle size of about several tens of nanometers) aggregate to form an aggregate of secondary particles (aggregated particles) of several μm to several tens of μm, and fine particles with good dispersibility were not obtained. . The electron micrograph is shown in FIG. The sample for electron microscope observation was used after the dry particles obtained in this example were surface-treated with BTA to prevent oxidation. Furthermore, the result of having measured the various characteristics of the obtained copper powder similarly to Example 1 was written together in Table 1.
[0033]
[ Reference example ]
Example 2 was repeated except that 1 g of dextrin was used instead of BTA. As a result, dextrin was gelled by high concentration IPA, and the product could not be separated into solid and liquid (filter separation).
[0034]
[Table 1]

[0035]
【The invention's effect】
As described above, according to the present invention, fine copper powder having excellent oxidation resistance in which copper particles having a diameter of 50 nm or less are individually dispersed is obtained, which has a sintering start temperature in an inert gas. It is a low temperature of 300 ° C. or lower. Accordingly, when the fine particle copper powder of the present invention is used as a filler for the conductive ink, a conductive ink suitable for forming an ultrafine wiring pattern by an ink jet method or the like can be obtained.
[Brief description of the drawings]
FIG. 1 is an electron microscope (SEM image) photograph showing an example (part 1) of fine-particle copper powder according to the present invention.
FIG. 2 is an electron microscope (SEM image) photograph showing another example of the fine-particle copper powder according to the present invention (in Example 3).
FIG. 3 is an electron micrograph of a copper powder of a comparative example.
FIG. 4 is a diagram showing a TMA curve obtained by measuring a sintering start temperature of fine-particle copper powder according to the present invention in comparison with a TMA curve of a copper powder of a conventional example.

Claims

The use of hydrazine or a hydrazine compound as a reducing agent when reducing copper hydroxide in a liquid to metallic copper particles using a reducing agent, and the amount of the reducing agent used is the theory necessary for the reduction of total copper hydroxide. 3 to 5 times the equivalent, finishing adding the total amount of the reducing agent to the reaction system within 5 minutes, performing the reduction reaction in the presence of an antifoaming agent, and the surface before or during the reduction reaction A method for producing fine copper powder, characterized by adding a treating agent.

The method for producing fine-particle copper powder according to claim 1, wherein the surface treatment agent is benzotriazole.

The manufacturing method of the fine-particle copper powder of Claim 1 or 2 which uses alcohol together with the said antifoamer.