JP4105565B2 - Aluminum material for electrolytic capacitor electrode, etched aluminum material for electrolytic capacitor electrode, and electrolytic capacitor - Google Patents

Description

【００２３】
【数４】

【００２４】
（５） 前記表層酸化膜における結晶性酸化物粒子の占有面積率は１５％以下である前項１ないし前項４の何れかに記載の電解コンデンサ電極用アルミニウム材。
（６） 前記結晶性酸化物粒子の占有面積率（％）と平均粒径（μｍ）とは、占有面積率（％）／平均粒径（μｍ）＜１００である前項１ないし前項５の何れかに記載の電解コンデンサ電極用アルミニウム材。
（７） 酸化膜の厚さは、ハンターホール法による測定値で２．５〜５ｎｍである前項１ないし前項６の何れかに記載の電解コンデンサ電極用アルミニウム材。
（８） アルミニウム材におけるアルミニウム純度が９９．９質量％以上である前項１ないし前項７の何れかに記載の電解コンデンサ電極用アルミニウム材。
（９） 前記電解コンデンサ電極用アルミニウム材は陽極材である前項１ないし前項８の何れかに記載の電解コンデンサ電極用アルミニウム材。
【００２５】
本発明のエッチングされた電解コンデンサ電極用アルミニウム材は下記の構成を有する。
（１０） 前項１ないし前項９の何れかに記載された電解コンデンサ電極用アルミニウム材において、エッチングピットが形成されてなることを特徴とするエッチングされた電解コンデンサ電極用アルミニウム材。
【００２６】
本発明の電解コンデンサは下記の構成を有する。
（１１） 電極材料として、前項１０に記載されたエッチングされた電解コンデンサ電極用アルミニウム材が用いられてなることを特徴とする電解コンデンサ。
【００２７】
本発明の電解コンデンサ電極用アルミニウム材において、表層の酸化膜に存在する結晶性酸化物粒子の存在密度および分布均一性を規定することによって、エッチングによる実効面積の拡大を確かなものとしている。
【００２８】
結晶性酸化物粒子の存在密度は、１×１０⁴〜１×１０⁷個／ｍｍ²に規定する。結晶性酸化物粒子の存在密度が１×１０⁴個／ｍｍ²未満では、結晶が少なすぎるため生成するエッチピットも少なく、１×１０⁷個／ｍｍ²より多い場合には、エッチング初期において多く生成したエッチピット同士が結合するため大きい実効面積を得ることができない。好ましい存在密度は１×１０⁵〜５×１０⁶個／ｍｍ²である。
【００２９】
また、アルミニウム材の表層酸化膜に存在する結晶性酸化物粒子はエッチピットの核となることから、エッチピット疎密のオーダーの微小領域で均一に分散して存在していることが必要である。本発明においては、表層酸化膜を等しい面積を持つ領域に区切り、各領域に存在する結晶性酸化物粒子の数が１領域あたりの平均結晶性酸化物粒子数に近いほど結晶性酸化物粒子の分布が均一であると評価する。具体的には、１０〜４００μｍ²の等しい面積を持つｍ個の領域について、１領域当たりの平均結晶性酸化物粒子数をＡ個、任意の１領域に含まれる結晶性酸化物粒子数をｘ個としたとき、０．５×Ａ≦ｘ≦１．５×Ａを満たす領域の数を０．５５×ｍ以上と規定する。前記条件を満たす領域数はｍに近いほど分布均一性が高く、０．６５×ｍ以上が好ましい。
【００３０】
前記結晶性酸化物粒子の分布均一性を規定するに際し、１領域の面積を１０〜４００μｍ²とするのは、一般に直流電解エッチングにより生じるエッチピットの疎密が１０〜４００μｍ²程度の領域で発生するからである。また、領域の数が多いほど数値の信頼性が得られるため一サンプル当たり領域数（ｍ）は２０以上であることが好ましい。領域の面積は結晶性酸化物粒子の密度やエッチングにより生成するピット密度により適切な値を選定でき、粒子の存在密度が高いほど小さい領域で観察する。
【００３１】
上述した結晶性酸化物粒子の計数や粒子径の測定は、透過型電子顕微鏡による観察を推奨できる。電解コンデンサ電極用アルミニウム材表面に存在する結晶性酸化物は、アルミニウム材の片面に支持膜としてカーボン等の蒸着膜を形成させた後、例えば臭素−メタノール液に浸漬させることによりアルミニウムを溶解させたサンプルを透過型電子顕微鏡で観察することにより確認できる。上記透過型電子顕微鏡観察サンプル作製時のアルミニウム溶解液の調製に用いる液としては臭素−メタノール液の他に、塩化第二水銀水溶液、ヨウ素−メタノール液等の適用も可能である。
【００３２】
前記結晶性酸化物粒子の種類としてはγ−Ａｌ₂Ｏ₃をはじめとするＡｌ₂Ｏ₃、ベーマイトをはじめとするＡｌＯ（ＯＨ）、アルミニウム以外の含有金属（例えばＭｇ，Ｐｂ，Ｃｕ等）の酸化物および水酸化物、アルミニウムとアルミニウム以外の含有金属（例えばＭｇ，Ｐｂ，Ｃｕ等）との複合金属酸化物あるいは水酸化物であれば特に限定されず、単結晶、多結晶のどちらでも良い。また、単一もしくは複数の結晶が無定形物質に覆われて一つの粒子を形成するものでも良く、凝集した酸化物結晶の間に無定形酸化物が存在していても良い。
【００３３】
前記透過型電子顕微鏡観察領域に存在する結晶性酸化物粒子は各々適切な倍率で観察され、結晶性酸化物であるか否かの区別や結晶性酸化物の同定は、電子線回折およびエネルギー分散型エックス線分析を用いることにより行うことができる。
【００３４】
また、本発明において、電解コンデンサ電極用アルミニウム材の厚さは特に規定されない。箔と称される２００μｍ以下のものはもとより、それ以上の厚さの板、これらを用いた成形体も本発明に含まれる。
【００３５】
前記結晶性酸化物粒子の平均粒子径は０．０５μｍ以上０．４μｍ未満であることが好ましい。平均粒子径が０．０５μｍ未満の場合、結晶がエッチピット核となりにくい。一方０．４μｍ以上では隣接する結晶から生じたエッチピット同士が結合しやすくなって実効面積が十分に拡大されない。特に好ましい粒子径は、０．０５〜０．２９μｍである。なお、結晶性酸化物粒子の形状は特に限定されず、本発明における結晶性酸化物粒子径は投影円相当径即ち粒子の投影面積に等しい円の直径で表す。また、本発明において計数する結晶性酸化物粒子は粒径０．０１μm以上のものとする。０．０１μm未満の超微細粒子は存在確認および同定が極めて困難であり、エッチング特性に及ぼす影響も僅少であるためである。したがって、本発明において結晶性酸化物粒子密度および各々の領域に存在する結晶性酸化物粒子数、後述の平均結晶性酸化物粒子径、結晶性酸化物粒子径の幾何標準偏差および結晶性酸化物粒子占有面積率は粒径０．０１μm以上の結晶性酸化物粒子を対象として求められる。
【００３６】
前記結晶性酸化物粒子径の均一性は幾何標準偏差σ_gで表される。幾何標準偏差σ_gの求め方を下記に示す。
【００３７】
まず、（Ｆ１）式によりｎ個の粒子の幾何平均径Ｍ_gを求める。
【００３８】
【数５】

【００３９】
さらに、幾何平均径Ｍ_gに基づき、（Ｆ２）式より幾何標準偏差σ_gを求める。なお、幾何標準偏差σ_gの信頼性を得るために、ｎ≧５０であることが好ましい。
【００４０】
【数６】

【００４１】
結晶性酸化物粒子の粒子径が全て同一の場合、幾何標準偏差σ_gは１であり、粒径分布が広くなるのに伴って、幾何標準偏差σ_gが大きくなる。従って、幾何標準偏差σ_gが小さく１に近いほど粒子径が均一で粒径分布が狭いことを示す。粒子径が均一なほどエッチピットが均一に生成するため、結晶性酸化物粒子径の幾何標準偏差σ_gは１．５以下であることが好ましい。特に好ましい幾何標準偏差σ_gは１．３５以下である。
【００４２】
表層酸化膜中に結晶性酸化物粒子が占有する面積率は１５％以下であることが好ましい。占有面積が１５％を越えると、エッチング条件によっては全面腐食するおそれがあり、実効面積の拡大が困難となる。特に好ましい結晶性酸化物粒子の占有面積率は０．５〜１０％である。
【００４３】
なお、上述したように結晶性酸化物粒子は非晶質部を含む場合もあるので、酸化物の結晶質部が占有する面積率は、本発明が規定する結晶性酸化物粒子占有面積率よりも小さくなることがある。
【００４４】
結晶性酸化物粒子は、上述した表層酸化膜における占有面積率（％）と平均粒径（μｍ）とは、占有面積率（％）／平均粒径（μｍ）＜１００であることが好ましい。両者の比率を規定することにより、エッチングピット同士が過度に結合するのを防止することができる。特に好ましい占有面積率（％）／平均粒径（μｍ）は５〜７０である。
【００４５】
前記酸化膜の厚さは、ハンターホール法による測定値で２．５〜５ｎｍが好ましい。２．５ｎｍ未満ではエッチング初期にアルミニウム材の表面溶解が多く発生し、５ｎｍを越えると結晶性酸化物粒子がエッチングピット核として作用しないおそれがある。前記ハンターホール法とは、M.S.Hunter and P. Fowle, J. Electrochem. Soc., 101[9], 483 (1954)に記載された方法である。特に好ましい酸化皮膜の厚さは２．５〜４．８ｎｍである。
【００４６】
前記アルミニウム材は、その組成を限定するものではなく、電解コンデンサ電極材料として使用されているものを適宜使用することができる。具体的には、不純物量を規制して過溶解によるエッチング特性の低下を防ぐために、アルミニウム純度を９９．９質量％以上であることが好ましく、特に９９．９５質量％以上が好ましい。また、エッチング特性や強度を向上させるために、種々の微量元素が添加されているアルミニウム材も好適に用いることができる。なお、本発明においてアルミニウム材のアルミニウム純度は１００質量％からＦｅ，Ｓｉ，Ｃｕ，Ｍｎ，Ｃｒ，Ｚｎ，ＴｉおよびＧａの合計濃度（質量％）を差し引いた値とする。
【００４７】
本発明のアルミニウム材は、エッチング後の化成処理によって耐電圧性皮膜を形成させても大きい実効面積を有する点で陽極材に適している。さらに、陽極材のうちでも、中圧用および高圧用電解コンデンサ電極材に適している。
【００４８】
この発明のアルミニウム材の製造に際し、アルミニウム材料の溶解・成分調整・スラブ鋳造、均熱処理、熱間圧延、冷間圧延、中間焼鈍、仕上冷間圧延（低圧下圧延）、最終焼鈍は一般法に従えばよく、特に限定すべき工程の指定はない。アルミニウム材の（１００）面積率は９０％以上であることが好ましく、アルミニウム材のエッチング条件との関係で、アルミニウム材の製造工程条件は適宜変更される。なお、圧延工程の途中において前工程の圧延により生じたアルミニウム材の結晶組織の歪みを解消する目的で焼鈍（以後中間焼鈍と称す。）されたものであっても良い。また、中間焼鈍以前の工程で表面の不純物や油分を除去する目的で洗浄を実施しても良い。
【００４９】
また、圧延工程を終了したアルミニウム基材表面には油分や不純物が存在するため、接触加熱前に洗浄を実施してこれらを除去することが好ましい。アルミニウム基材表面にこれらが付着していると、その後の最終焼鈍において結晶性酸化物粒子の均一生成が阻害されるためである。洗浄方法および洗浄液は特に限定されるものではなく、酸洗浄液またはアルカリ洗浄液による浸漬洗浄、スプレー洗浄、ドライエッチング等が利用できる。酸洗浄液の種類としては、塩酸、硫酸、リン酸、硝酸等の無機酸、シュウ酸、酢酸等の有機酸が例示でき、これら酸を少なくとも１種類以上含む水溶液を洗浄液として用いることができる。また、脱脂力を高めるために酸水溶液に界面活性剤を添加しても良い。アルカリ洗浄液の種類としては水酸化ナトリウム、水酸化カリウム、水酸化カルシウム、ケイ酸ナトリウム等が例示でき少なくとも１種類以上のアルカリを含む水溶液を洗浄液として用いることができる。アルカリ洗浄後に酸洗浄を行うといったように複数回の洗浄を実施しても良い。また、圧延工程後の表面が均一な結晶生成に耐える得るものであれば有機溶剤で洗浄しても良い。有機溶剤の例としてはアルコール、トルエンやキシレン等の芳香族炭化水素、ペンタンやヘキサン等の脂肪族炭化水素、アセトン、ケトン、エステル等があげられるが特に限定されるものではなく複数の有機溶剤を混合して用いても良い。また、有機溶剤による洗浄と、上述の酸、アルカリによる洗浄を組み合わせても良い。何れの場合も、洗浄後にアルミニウム表面に付着した洗浄液成分の残留物を除去する目的で水洗を行うことが好ましい。また、また、洗浄は仕上圧延後に限らず、圧延前や圧延パス間に実施しても良い。
最終焼鈍後のアルミニウム表層酸化膜の結晶性酸化物粒子の密度、分布均一性、粒子径、占有面積率を制御する方法の一つとして、接触加熱を用いることができる。
【００５０】
接触加熱の手段は、熱ロール、加熱ベルト、加熱板など接触加熱であれば限定されるものではなく、複数の接触加熱手段を組み合わせても良い。また、アルミニウム材の裏表同時に加熱しても良く、片面ずつ加熱しても良い。加熱体の表面は、アルミニウム材の酸化膜が凝着しない物質で形成されていることが好ましく、ステンレス、メッキ、セラミックス、四フッ化エチレン樹脂、シリコーン樹脂等を例示できる。
【００５１】
前記加熱体の表面温度は５０〜４５０℃が好ましい。加熱体の表面温度が５０℃未満であれば、最終焼鈍後の酸化膜の結晶化率や結晶性酸化物粒子を所定範囲内に制御することが困難であり、４５０℃を越えて高くなると酸化膜が厚くなりすぎ、加熱冷却時に皺が発生する等操業上の問題が生じるおそれがあるからである。さらに好ましい表面温度は８０〜４００℃であり、特に８０〜３００℃が良い。アルミニウム材に加熱体を接触させる時間は０．００１〜３０秒が好ましい。接触時間が０．００１秒未満であるとアルミニウム表面を十分に加熱することが出来ないために、結晶化率や結晶性酸化物粒子を制御するに至らず、３０秒を越えて長く加熱すると酸化膜が厚くなりすぎてエッチピットが発生しにくくなる可能性がある。さらに好ましい接触時間は０．０１〜２０秒であり、特に０．０５〜１５秒が良い。
【００５２】
加熱体表面温度および接触時間は接触加熱前のアルミニウム酸化膜の特性を考慮して適宜選択されるものとする。接触加熱雰囲気は特に限定されず、特別な雰囲気制御も必要なく空気中でも十分である。
【００５３】
洗浄または洗浄後の接触加熱後、アルミニウム材の結晶組織の方位を（１００）方位に整えてエッチング特性を向上させること、および結晶性酸化物粒子を生成させることを主目的とし最終焼鈍がなされる。
【００５４】
最終焼鈍後のアルミニウム材は、前工程で形成された酸化皮膜の厚さをこの工程で増大させ過ぎて結晶性酸化物がエッチング核となり得る可能性を消去させないように、酸化皮膜の合計厚さが上述したハンターホール法による厚さで２．５〜５ｎｍとすることが好ましい。また、（１００）面積率は９０％以上が好ましい。
【００５５】
最終焼鈍の処理雰囲気は特に限定されるものではないが、酸化膜の厚さを増大させすぎないように、水分および酸素の少ない雰囲気中で加熱するのが好ましい。具体的には、アルゴン、窒素等の不活性ガス中あるいは０．１Ｐａ以下の真空の非酸化性雰囲気中で加熱することが好ましい。
【００５６】
最終焼鈍を行う際のアルミニウム材の状態も限定されず、コイルに巻き取った状態でバッチ焼鈍しても良く、コイルを巻き戻し連続焼鈍した後コイルに巻き取っても良く、バッチ焼鈍と連続焼鈍の少なくともどちらかを複数回行っても良い。
【００５７】
さらに、最終焼鈍の保持温度および時間も限定されない。例えばコイルの状態でバッチ焼鈍を行う場合、アルミニウム基材の実体温度を４５０〜６００℃に１０分〜５０時間保持することにより行う。アルミニウム実体温度が４００℃未満、保持時間が１０分未満では酸化皮膜中のエッチピットの核と成り得る結晶性酸化物粒子の生成が十分ではなく、その分散状態が疎となりすぎて、結晶をエッチング核とするエッチング時の拡面効果が期待できない恐れがあり、（１００）面の結晶方位の発達も不十分であるからである。逆に６００℃を越えて焼鈍すると、コイルでバッチ焼鈍する場合にアルミニウム基材が密着を起こし易くなり、また酸化膜が厚くなりすぎるためエッチング特性が低下して実効面積を十分に拡大できないおそれがある。また、５０時間を越えて焼鈍しても実効面積拡大効果は飽和し、却って熱エネルギーコストの増大を招く。特に好ましい温度は、アルミニウム実体温度で４６０〜５６０℃、時間は３０分〜４０時間である。
【００５８】
本発明のエッチングされた電解コンデンサ電極用アルミニウム材は、上述した電解コンデンサ電極用アルミニウム材にエッチング処理を施して実効面積を拡大させたものである。エッチング処理によって、表層の酸化膜に存在する結晶性酸化物粒子がエッチピット核となり、多数の深いトンネル状ピットが生成され、表面積が拡大される。エッチング処理条件は特に限定されることはないが、直流エッチング法を採用するのが良い。
【００５９】
エッチングされたアルミニウム材は、さらに化成処理を行って陽極材とすることができ、特に中圧および高圧用電解コンデンサ陽極材に適している。
【００６０】
本発明の電解コンデンサは、電極材料として上述のエッチングされた電解コンデンサ電極用アルミニウム材が用いられたものである。電極材料の実効面積の拡大により高い静電容量が得られる。
【００６１】
【実施例】
以下に、本発明の実施例および比較例を示す。なお、本発明は実施例に限定されない。
【００６２】
アルミニウム基材として、アルミニウム純度９９．９９質量％のアルミニウム材料を常法により１１０μｍに圧延したアルミニウム箔を使用した。このアルミニウム箔は、電解コンデンサ陽極材料として好適に使用できるものである。
（実施例１）
アルミニウム基材を有機溶剤：ｎ−ヘキサンにて脱脂した後、５０℃、０．２質量％オルトケイ酸ナトリウム水溶液に４０秒間浸漬した。その後水洗し、乾燥させた。乾燥後のアルミニウム基材を２５℃、３質量％塩酸水溶液へ６０秒間浸漬し、水洗、乾燥を行った。次に、乾燥後のアルミニウム基材を、表面温度を２００℃に設定した２枚のステンレス製加熱板の間に挟んで大気中で２秒間接触加熱を行った。接触加熱後のアルミニウム基材を重ねた状態で、アルゴン雰囲気中においてアルミニウム基材の実体温度を室温から５４０℃まで５０℃／ｈで昇温させた後、５４０℃にて２４時間保持して最終焼鈍を施し、次いで冷却した後炉出しした。これにより、電解コンデンサ電極用アルミニウム材を得た。
（実施例２）
アルミニウム基材を有機溶剤：ｎ−ヘキサンにて脱脂した後、５０℃、０．２質量％オルトケイ酸ナトリウム水溶液に４０秒間浸漬した。その後水洗し、乾燥させた。乾燥後のアルミニウム基材を２５℃、３質量％硫酸水溶液へ６０秒間浸漬し、水洗、乾燥を行った。次に、乾燥後のアルミニウム基材を、表面温度を２５０℃に設定した２枚のステンレス製加熱板の間に挟んで大気中で２秒間接触加熱を行った。接触加熱後のアルミニウム基材を重ねた状態で、アルゴン雰囲気中においてアルミニウム基材の実体温度を室温から５００℃まで５０℃／ｈで昇温させた後、５００℃にて２４時間保持して最終焼鈍を施し、次いで冷却した後炉出しした。これにより、電解コンデンサ電極用アルミニウム材を得た。
（実施例３）
アルミニウム基材を有機溶剤：ｎ−ヘキサンにて脱脂した後、５０℃、０．２質量％オルトケイ酸ナトリウム水溶液に４０秒間浸漬した。その後水洗し、乾燥させた。乾燥後のアルミニウム基材を、実施例２と同様の条件で接触加熱および最終焼鈍を行い、電解コンデンサ電極用アルミニウム材を得た。
（実施例４）
オルトケイ酸ナトリウム水溶液への浸漬時間を１８０秒間とした以外は、実施例２と同じ処理を施して電解コンデンサ電極用アルミニウム材を得た。
（実施例５〜１８）
塩酸、硫酸、硝酸およびリン酸のうち少なくとも一種類以上を含む水溶液を酸洗浄液として調製した。水酸化ナトリウム、水酸化カリウムおよびオルトケイ酸ナトリウムのうち少なくとも一種類以上含む水溶液をアルカリ洗浄液として調製した。そして、アルミニウム基材を、前記アルカリおよび酸洗浄における洗浄液の種類、浸漬時間を変えて洗浄した後純水に浸漬し空気中で乾燥を行った。次に、アルミニウム基材を２枚のステンレス製加熱板の間に挟んで行う接触加熱を、加熱板の表面温度を８０〜４００℃、加熱時間を０．００１〜３０秒の範囲内で条件を変えて行った。接触加熱後のアルミニウム基材を重ねた状態で不活性ガス雰囲気下もしくは真空中で室温から昇温させ、４００〜６００℃、１０分〜５０時間の範囲内で条件を変えて最終焼鈍した。次いで冷却した後炉出しし、電解コンデンサ電極用アルミニウム材を得た。
（比較例１〜３）
塩酸、硫酸、硝酸およびリン酸のうち少なくとも一種類以上を含む水溶液を酸洗浄液として調製した。水酸化ナトリウム、水酸化カリウムおよびオルトケイ酸ナトリウムのうち少なくとも一種類以上含む水溶液をアルカリ洗浄液として調製した。そして、アルミニウム基材を、前記アルカリ洗浄液および前記酸洗浄液の種類、濃度および浸漬時間を変えて洗浄した後純水に浸漬し空気中で乾燥を行った。次に、接触加熱を行うことなく、アルミニウム基材を重ねた状態で不活性ガス雰囲気中もしくは真空中で室温から昇温させ、４００〜６００℃、１０分〜５０時間の範囲内で条件を変えて最終焼鈍した。次いで冷却した後炉出しし、電解コンデンサ電極用アルミニウム材を得た。
【００６３】
各実施例および比較例で得られた電解コンデンサ電極用アルミニウム材の表層酸化膜について、膜厚さ、結晶性酸化物粒子の存在密度、平均粒子径、分布均一性、幾何標準偏差、占有面積率、占有面積率／平均粒子径を求めた。ここで、結晶性酸化物粒子径は投影円相当径とする。
【００６４】
膜厚さはハンターホール法により測定した。
【００６５】
結晶性酸化物粒子は透過型電子顕微鏡により観察し、粒子個数を計数するとともに、平均粒径、占有面積率を測定した。観察用サンプルは、電解コンデンサ電極用アルミニウム材の片面にカーボン蒸着膜を形成し、臭素−メタノール液に浸漬しアルミニウムを溶解させたものを用いた。また、観察を行う領域は、結晶性酸化物粒子の存在密度が１×１０⁷個／ｍｍ²以上の場合は１０μｍ²（３．３μｍ×３．３μｍの領域）、１×１０⁶個／ｍｍ²以上１×１０⁷個／ｍｍ²未満の場合は１００μｍ²（１０μｍ×１０μｍの領域）、１×１０⁶個／ｍｍ²未満の場合は４００μｍ²（２０μｍ×２０μｍの領域）とし、各サンプルについてそれぞれ１００領域を観察した。なお、各々の粒子が結晶酸化物であるか否かの確認や結晶性酸化物粒子中の結晶部面積の算出は、各視野を拡大して適切な倍率（３万〜２０万倍）で観察、電子線回折、エネルギー分散型エックス線分析を行う方法で行った。
【００６６】
結晶性酸化物粒子の存在密度は、観察した領域面積と計数した粒子個数とから計算した。
【００６７】
結晶性酸化物粒子の幾何標準偏差は、上述の観察・測定結果から（Ｆ１）（Ｆ２）式に基づいて計算した。
【００６８】
また、結晶性酸化物粒子の分布均一性は、観察した１００領域中で０．５×Ａ≦ｘ≦１．５×Ａ（ｘ：平均粒径、Ａ：その領域における粒子数）を満たす領域数とした。
【００６９】
結晶性酸化物粒子の占有面積率（％）／平均粒径（μｍ）はそれぞれの測定値より計算した。
【００７０】
これらの測定値および計算値を表１に示す。
【００７１】
一方、各実施例および各比較例で得られた電解コンデンサ電極用アルミニウム材をＨＣｌ：１．０ｍｏｌ・ｄｍ^-3とＨ₂ＳＯ₄：３．５ｍｏｌ・ｄｍ^-3とを含む液温７５℃の混合水溶液に浸漬した後、電流密度０．２Ａ／ｃｍ²で電解処理を施して電解エッチングを行った。さらに前記組成の塩酸−硫酸混合水溶液に９０℃にて３６０秒浸漬しケミカルエッチングを施してピット径を拡大し、エッチングされたアルミニウム材を得た。得られたエッチングされたアルミニウム材を、化成電圧２７０ＶにてＥＩＡＪ規格に従い化成処理し、ＥＩＡＪ法で静電容量を測定した。測定した静電容量を、比較例３を１００とした時の相対値として表１に示す。
【００７２】
【表１】

【００７３】
表１より、表層の酸化膜の結晶性酸化物粒子を制御することにより、エッチング特性を高めて静電容量を増大させ得ることを確認した。
【００７４】
【発明の効果】
以上の次第で、本発明の電解コンデンサ電極用アルミニウム材は、アルミニウム材の表層酸化膜において、結晶性酸化物粒子の存在密度が１×１０⁴〜１０⁷個／ｍｍ²であり、１０〜４００μｍ²の任意の等しい面積を持つｍ個の領域について、１領域当たりの平均結晶性酸化物粒子数をＡ個、任意の１領域に含まれる結晶性酸化物粒子数をｘ個としたとき、０．５×Ａ≦ｘ≦１．５×Ａを満たす領域の数が０．５５×ｍ以上であるから、エッチングによって、結晶性酸化物粒子を核とする深いトンネル状のエッチングピットが多数かつ均一に生成される。このため、実効面積が拡大され、ひいては静電容量を増大できる。
【００７５】
前記電解コンデンサ電極用アルミニウム材において、結晶性酸化物粒子の平均粒子径が０．０５μｍ以上４μｍ未満である場合は、多数のエッチングピットが隣接ピットと結合することなく形成される。特に平均粒子径が０．０５μｍ〜０．２９μｍである場合には隣接ピットとの結合のおそれがなく、多数のエッチングピットが形成される。
【００７６】
また、前記結晶性酸化物粒子の粒子径の幾何標準偏差σ_gが、１．５以下となされている場合は、特にエッチングピットが均一に形成される。
【００７７】
また、前記表層酸化膜における結晶性酸化物粒子の占有面積率が１５％以下である場合は、エッチング処理において全面溶解することなく、エッチングピットが均一に形成される。
【００７８】
さらに、前記結晶性酸化物粒子の占有面積率（％）と平均粒径（μｍ）とが、占有面積率（％）／平均粒径（μｍ）＜１００である場合は、多数のエッチングピットが隣接ピットと結合することなく形成される。
【００７９】
また、前記酸化膜の厚さが、ハンターホール法による測定値で２．５〜５ｎｍである場合は、特に深いトンネル状のエッチングピットが十分に形成される。
【００８０】
さらに、アルミニウム材におけるアルミニウム純度が９９．９質量％以上である場合は、過溶解を抑制してエッチング特性の低下を防止することができる。
【００８１】
、前記電解コンデンサ電極用アルミニウム材が陽極材として用いられる場合は、実効面積の拡大により高い静電容量を得ることができる。
【００８２】
本発明のエッチングされた電解コンデンサ電極用アルミニウム材は、上述した何れかかの電解コンデンサ電極用アルミニウム材において、エッチングピットが形成されてなるものであるから、多数の深いトンネル状ピットが形成されて、静電容量の増大をなし得るものである。
【００８３】
本発明の電解コンデンサは、電極材料として、上記エッチングされた電解コンデンサ電極用アルミニウム材が用いられてなるものであるから、電極材料の実効面積の拡大により高い静電容量が得られる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an aluminum material for electrolytic capacitor electrodes, an etched aluminum material for electrolytic capacitor electrodes, and an electrolytic capacitor.
[0002]
In this specification, the term “aluminum” is used to include alloys thereof.
[0003]
[Prior art]
An aluminum foil used as an electrode material for an electrolytic capacitor has an effective surface area that is enlarged by an electrochemical or chemical etching process in order to increase the capacitance.
[0004]
Generally, a high-purity aluminum foil for electrolytic capacitors that generates tunnel-like pits by a direct current etching method is used in an inert atmosphere or in a vacuum at a temperature of about 500 ° C. for the purpose of developing the crystal orientation of the (100) plane in the surface layer portion. At the final annealing. Here, the final annealing is a process performed after finish cold rolling or after washing after finish cold rolling.
[0005]
In addition, it is known that the crystalline oxide generated on the surface of the aluminum foil becomes the nucleus of the etch pit, and controlling the density of the crystalline oxide and the crystal particle size will lead to an increase in capacitance. (For example, Non-Patent Document 1).
[0006]
Regarding crystalline oxide particles on the surface of an aluminum foil, there are the following prior arts (for example, Patent Documents 1, 2, and 3).
[0007]
Patent Document 1 proposes an aluminum material for electrolytic capacitors in which γ-alumina crystals are generated on the surface of an aluminum foil.
[0008]
Patent Document 2 describes that an etching oxide pit corresponding to an electrolysis condition is formed because the surface potential of an amorphous oxide film is uniform in place. In order to form uniform and deep pits with high density, it is described that the crystallization rate of the oxide film is controlled to 1% or less.
[0009]
Patent Document 3 proposes an aluminum foil for electrolytic capacitors in which crystals with an average particle size of 0.05 to 0.5 μm occupy 3 to 50% in area ratio, and the density of crystal particles is 1 × 10. ^Four ~ 2x10 ⁹ Piece / cm ² It is prescribed.
[0010]
[Non-Patent Document 1]
Nobuo Osawa, Kiyoshi Fukuoka, “Effect of Crystalline Oxide on DC Etching Behavior of Aluminum Foil for Electrolytic Capacitors”, Surface Technology, 1999, Vol. 50, No. 7, p. 643-647
[0011]
[Patent Document 1]
JP 63-116417 A
[0012]
[Patent Document 2]
JP-A-8-222488
[0013]
[Patent Document 3]
JP-A-8-222487
[0014]
[Problems to be solved by the invention]
However, the above-described prior art has not yet obtained a satisfactory capacitance.
[0015]
For example, in the technique described in Patent Document 1, there is no mention of the area ratio of γ-alumina crystals present in the surface oxide film and the density of γ-alumina particles, and the influence of these on the etching characteristics has not been elucidated.
[0016]
In the technique described in Patent Document 2, the crystallization rate is suppressed to 1% or less, and the crystalline oxide particles are not effectively used as etch pit nuclei.
[0017]
In the technique described in Patent Document 3, since the crystalline oxide is present in an area ratio of 3 to 50%, etch pits generated by using the adjacent crystalline oxide as a nucleus are easily combined, and the effective area is decreased instead. There is a risk.
[0018]
Furthermore, the technique described in Patent Document 2 and the technique described in Patent Document 3 both define only the crystallization rate or the area ratio of the crystalline oxide, No consideration is given to the dispersed state, and satisfactory capacitance has not been obtained.
[0019]
The present invention solves the problems of the prior art as described above, and provides an aluminum material for an electrode for an electrolytic capacitor, an aluminum material for an electrolytic capacitor electrode that has been etched, and an electrolytic capacitor that can increase the effective area by etching. The purpose is to do.
[0020]
[Means for Solving the Problems]
The inventors of the present invention have completed the present invention by optimizing the existence state of the crystalline oxide particles in the surface oxide film of the electrolytic capacitor electrode aluminum material, particularly the anode aluminum material.
[0021]
That is, the aluminum material for electrolytic capacitor electrodes of the present invention has the following configuration.
(1) In the surface oxide film of aluminum material, the density of the crystalline oxide particles is 1 × 10 ^Four -10 ⁷ Piece / mm ² 10 to 400 μm ² When the average number of crystalline oxide particles per region is A and the number of crystalline oxide particles contained in any one region is x, m regions having any equal area of 0. An aluminum material for electrolytic capacitor electrodes, wherein the number of regions satisfying 5 × A ≦ x ≦ 1.5 × A is 0.55 × m or more.
(2) The aluminum material for electrolytic capacitor electrodes as recited in the aforementioned Item 1, wherein the crystalline oxide particles have an average particle size of 0.05 μm or more and less than 0.4 μm.
(3) The aluminum material for electrolytic capacitor electrodes as recited in the aforementioned Item 2, wherein the crystalline oxide particles have an average particle size of 0.05 μm to 0.29 μm.
(4) The crystalline oxide particles have a geometric average particle diameter M calculated by the formula (F1). _g The geometric standard deviation σ of the particle diameter calculated by the formula (F2) using _g The aluminum material for electrolytic capacitor electrodes according to any one of the preceding items 1 to 3, wherein is 1.5 or less.
[0022]
[Equation 3]

[0023]
[Expression 4]

[0024]
(5) The aluminum material for electrolytic capacitor electrodes according to any one of (1) to (4), wherein an occupied area ratio of the crystalline oxide particles in the surface oxide film is 15% or less.
(6) The occupied area ratio (%) and the average particle diameter (μm) of the crystalline oxide particles are any one of the preceding items 1 to 5 in which the occupied area ratio (%) / average particle diameter (μm) <100. An aluminum material for electrolytic capacitor electrodes according to claim 1.
(7) The aluminum material for electrolytic capacitor electrodes according to any one of the preceding items 1 to 6, wherein the thickness of the oxide film is 2.5 to 5 nm as measured by a Hunter Hall method.
(8) The aluminum material for electrolytic capacitor electrodes according to any one of the preceding items 1 to 7, wherein the aluminum purity of the aluminum material is 99.9% by mass or more.
(9) The aluminum material for electrolytic capacitor electrodes according to any one of items 1 to 8, wherein the aluminum material for electrolytic capacitor electrodes is an anode material.
[0025]
The etched aluminum material for electrolytic capacitor electrodes of the present invention has the following constitution.
(10) An aluminum material for an electrolytic capacitor electrode etched according to any one of the preceding items 1 to 9, wherein an etching pit is formed.
[0026]
The electrolytic capacitor of the present invention has the following configuration.
(11) An electrolytic capacitor comprising the etched aluminum material for an electrolytic capacitor electrode described in the above item 10 as an electrode material.
[0027]
In the aluminum material for electrolytic capacitor electrodes of the present invention, the effective area by etching is surely expanded by defining the existence density and distribution uniformity of the crystalline oxide particles present in the surface oxide film.
[0028]
The density of the crystalline oxide particles is 1 × 10 ^Four ~ 1x10 ⁷ Piece / mm ² Stipulate. The existence density of crystalline oxide particles is 1 × 10 ^Four Piece / mm ² If it is less than 1, the number of crystals is too small to generate less etch pits. ⁷ Piece / mm ² In the case where the number is larger, etch pits that are generated more in the initial stage of etching are coupled together, so that a large effective area cannot be obtained. The preferred density is 1 × 10 ^Five ~ 5x10 ⁶ Piece / mm ² It is.
[0029]
Further, since the crystalline oxide particles present in the surface oxide film of the aluminum material serve as the nucleus of the etch pit, it is necessary that the crystalline oxide particles be uniformly dispersed in a minute region on the order of the density of the etch pit. In the present invention, the surface oxide film is divided into regions having equal areas, and the closer the number of crystalline oxide particles present in each region is to the average number of crystalline oxide particles per region, Evaluate that the distribution is uniform. Specifically, 10 to 400 μm ² When the average number of crystalline oxide particles per region is A and the number of crystalline oxide particles contained in any one region is x, m × regions having the same area of 0.5 × The number of regions satisfying A ≦ x ≦ 1.5 × A is defined as 0.55 × m or more. As the number of regions satisfying the above condition is closer to m, the distribution uniformity is higher, and is preferably 0.65 × m or more.
[0030]
In defining the distribution uniformity of the crystalline oxide particles, the area of one region is 10 to 400 μm. ² The reason is that the density of etch pits generally generated by direct current electrolytic etching is 10 to 400 μm. ² This is because it occurs in a certain area. Moreover, since the numerical reliability is obtained as the number of regions increases, the number of regions per sample (m) is preferably 20 or more. As the area of the region, an appropriate value can be selected depending on the density of the crystalline oxide particles and the pit density generated by etching. The higher the particle density, the smaller the region.
[0031]
Observation with a transmission electron microscope can be recommended for the above-mentioned counting of the crystalline oxide particles and measurement of the particle diameter. The crystalline oxide present on the surface of the aluminum material for electrolytic capacitor electrodes was formed by forming a deposited film such as carbon as a support film on one surface of the aluminum material, and then dissolving the aluminum by immersing it in a bromine-methanol solution, for example. This can be confirmed by observing the sample with a transmission electron microscope. In addition to bromine-methanol liquid, mercuric chloride aqueous solution, iodine-methanol liquid and the like can be applied as the liquid used for preparing the aluminum solution at the time of preparing the transmission electron microscope observation sample.
[0032]
As the kind of the crystalline oxide particles, γ-Al ₂ O _Three And other Al ₂ O _Three AlO (OH) including boehmite, oxides and hydroxides of metals other than aluminum (eg, Mg, Pb, Cu, etc.), metals contained other than aluminum and aluminum (eg, Mg, Pb, Cu, etc.) The composite metal oxide or hydroxide is not particularly limited, and may be either single crystal or polycrystal. Further, a single or a plurality of crystals may be covered with an amorphous material to form one particle, and an amorphous oxide may exist between aggregated oxide crystals.
[0033]
Crystalline oxide particles present in the transmission electron microscope observation region are each observed at an appropriate magnification. Whether or not it is a crystalline oxide or identification of the crystalline oxide is determined by electron diffraction and energy dispersion. This can be done by using type X-ray analysis.
[0034]
In the present invention, the thickness of the aluminum material for electrolytic capacitor electrodes is not particularly specified. The present invention includes not only those having a thickness of 200 μm or less, which are called foils, but also plates having a thickness greater than that, and molded articles using these.
[0035]
The average particle diameter of the crystalline oxide particles is preferably 0.05 μm or more and less than 0.4 μm. When the average particle size is less than 0.05 μm, the crystals are difficult to become etch pit nuclei. On the other hand, when the thickness is 0.4 μm or more, etch pits generated from adjacent crystals are easily bonded to each other and the effective area is not sufficiently expanded. A particularly preferable particle diameter is 0.05 to 0.29 μm. The shape of the crystalline oxide particle is not particularly limited, and the crystalline oxide particle diameter in the present invention is represented by a projected circle equivalent diameter, that is, a diameter of a circle equal to the projected area of the particle. In the present invention, the crystalline oxide particles to be counted are those having a particle size of 0.01 μm or more. This is because ultrafine particles of less than 0.01 μm are extremely difficult to confirm and identify, and have little influence on the etching characteristics. Therefore, in the present invention, the crystalline oxide particle density and the number of crystalline oxide particles present in each region, the average crystalline oxide particle diameter described later, the geometric standard deviation of the crystalline oxide particle diameter, and the crystalline oxide The particle occupation area ratio is obtained for crystalline oxide particles having a particle diameter of 0.01 μm or more.
[0036]
The uniformity of the crystalline oxide particle size is geometric standard deviation σ _g It is represented by Geometric standard deviation σ _g The method of obtaining is shown below.
[0037]
First, the geometric mean diameter M of n particles according to the formula (F1) _g Ask for.
[0038]
[Equation 5]

[0039]
Furthermore, geometric mean diameter M _g Based on the above, the geometric standard deviation σ from the formula (F2) _g Ask for. Geometric standard deviation σ _g In order to obtain the reliability of n ≧ 50, it is preferable that n ≧ 50.
[0040]
[Formula 6]

[0041]
When the crystalline oxide particles have the same particle size, the geometric standard deviation σ _g Is 1, and as the particle size distribution becomes wider, the geometric standard deviation σ _g Becomes larger. Therefore, geometric standard deviation σ _g Is smaller and closer to 1, indicating that the particle size is uniform and the particle size distribution is narrow. Since the etch pits are generated more uniformly as the particle size is uniform, the geometric standard deviation σ of the crystalline oxide particle size _g Is preferably 1.5 or less. Particularly preferred geometric standard deviation σ _g Is 1.35 or less.
[0042]
The area ratio occupied by the crystalline oxide particles in the surface oxide film is preferably 15% or less. If the occupied area exceeds 15%, the entire surface may be corroded depending on the etching conditions, and it becomes difficult to expand the effective area. Particularly preferred area ratio of the crystalline oxide particles is 0.5 to 10%.
[0043]
As described above, since the crystalline oxide particles may include an amorphous part, the area ratio occupied by the crystalline part of the oxide is larger than the area ratio occupied by the crystalline oxide particles defined by the present invention. May be smaller.
[0044]
In the crystalline oxide particles, the occupied area ratio (%) and the average particle diameter (μm) in the surface oxide film described above are preferably such that the occupied area ratio (%) / average particle diameter (μm) <100. By defining the ratio between the two, it is possible to prevent the etching pits from being excessively bonded to each other. A particularly preferable occupation area ratio (%) / average particle diameter (μm) is 5 to 70.
[0045]
The thickness of the oxide film is preferably 2.5 to 5 nm as measured by the Hunter Hall method. If the thickness is less than 2.5 nm, the surface of the aluminum material is often dissolved in the initial stage of etching. If the thickness exceeds 5 nm, the crystalline oxide particles may not act as etching pit nuclei. The Hunter Hall method refers to MSHunter and P. Fowle, J. Electrochem. Soc., 101 [9], 483 (1954). A particularly preferable oxide film thickness is 2.5 to 4.8 nm.
[0046]
The aluminum material is not limited in its composition, and those used as electrolytic capacitor electrode materials can be used as appropriate. Specifically, the aluminum purity is preferably 99.9% by mass or more, particularly 99.95% by mass or more, in order to regulate the amount of impurities and prevent deterioration of etching characteristics due to over-dissolution. Moreover, in order to improve an etching characteristic and intensity | strength, the aluminum material to which various trace elements are added can also be used suitably. In the present invention, the aluminum purity of the aluminum material is a value obtained by subtracting the total concentration (mass%) of Fe, Si, Cu, Mn, Cr, Zn, Ti and Ga from 100 mass%.
[0047]
The aluminum material of the present invention is suitable as an anode material in that it has a large effective area even when a voltage-resistant film is formed by chemical conversion after etching. Furthermore, among anode materials, it is suitable for medium and high pressure electrolytic capacitor electrode materials.
[0048]
In the production of the aluminum material of the present invention, melting, component adjustment, slab casting, soaking, hot rolling, cold rolling, intermediate annealing, finish cold rolling (low-pressure rolling), and final annealing are generally used There is no designation of a process that should be particularly limited. The (100) area ratio of the aluminum material is preferably 90% or more, and the manufacturing process conditions of the aluminum material are appropriately changed in relation to the etching conditions of the aluminum material. It may be annealed (hereinafter referred to as intermediate annealing) for the purpose of eliminating the distortion of the crystal structure of the aluminum material produced by rolling in the previous process during the rolling process. Moreover, you may implement washing | cleaning in order to remove surface impurities and oil in the process before intermediate annealing.
[0049]
Further, since oil and impurities are present on the surface of the aluminum base material after the rolling process is completed, it is preferable to remove these by washing before contact heating. This is because if these adhere to the surface of the aluminum substrate, uniform formation of crystalline oxide particles is inhibited in the subsequent final annealing. The cleaning method and the cleaning liquid are not particularly limited, and immersion cleaning, spray cleaning, dry etching, and the like using an acid cleaning liquid or an alkaline cleaning liquid can be used. Examples of the acid cleaning liquid include inorganic acids such as hydrochloric acid, sulfuric acid, phosphoric acid and nitric acid, and organic acids such as oxalic acid and acetic acid, and an aqueous solution containing at least one of these acids can be used as the cleaning liquid. Further, a surfactant may be added to the acid aqueous solution in order to increase the degreasing power. Examples of the alkali cleaning liquid include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium silicate and the like, and an aqueous solution containing at least one kind of alkali can be used as the cleaning liquid. A plurality of cleanings may be performed such that acid cleaning is performed after alkali cleaning. Moreover, you may wash | clean with an organic solvent, as long as the surface after a rolling process can endure uniform crystal production. Examples of organic solvents include alcohols, aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as pentane and hexane, acetone, ketones and esters, but are not particularly limited. You may mix and use. Moreover, you may combine the washing | cleaning by an organic solvent, and the washing | cleaning by the above-mentioned acid and alkali. In any case, it is preferable to perform water washing for the purpose of removing the residue of the cleaning liquid component adhering to the aluminum surface after washing. Further, the cleaning is not limited to after finish rolling, but may be performed before rolling or between rolling passes.
Contact heating can be used as one of the methods for controlling the density, distribution uniformity, particle diameter, and occupied area ratio of the crystalline oxide particles in the aluminum surface oxide film after the final annealing.
[0050]
The contact heating means is not limited as long as it is contact heating such as a heat roll, a heating belt, or a heating plate, and a plurality of contact heating means may be combined. Moreover, the front and back of the aluminum material may be heated simultaneously, or one side may be heated. The surface of the heating body is preferably formed of a material to which an aluminum oxide film does not adhere, and examples thereof include stainless steel, plating, ceramics, tetrafluoroethylene resin, and silicone resin.
[0051]
The surface temperature of the heating body is preferably 50 to 450 ° C. If the surface temperature of the heating body is less than 50 ° C., it is difficult to control the crystallization rate of the oxide film and the crystalline oxide particles within the predetermined range after the final annealing. This is because the film becomes too thick and there is a possibility that operational problems such as generation of wrinkles during heating and cooling may occur. A more preferable surface temperature is 80 to 400 ° C, particularly 80 to 300 ° C. The time for which the heating body is brought into contact with the aluminum material is preferably 0.001 to 30 seconds. If the contact time is less than 0.001 seconds, the aluminum surface cannot be heated sufficiently, so that the crystallization rate and the crystalline oxide particles cannot be controlled, and if heated for longer than 30 seconds, oxidation occurs. There is a possibility that etch pits are less likely to occur because the film becomes too thick. A more preferable contact time is 0.01 to 20 seconds, and 0.05 to 15 seconds is particularly preferable.
[0052]
The heating body surface temperature and the contact time are appropriately selected in consideration of the characteristics of the aluminum oxide film before contact heating. The contact heating atmosphere is not particularly limited, and no special atmosphere control is necessary, and it is sufficient even in the air.
[0053]
After the cleaning or contact heating after the cleaning, final annealing is performed mainly for the purpose of improving the etching characteristics by adjusting the orientation of the crystal structure of the aluminum material to the (100) orientation and generating crystalline oxide particles. .
[0054]
The final thickness of the aluminum material after the final annealing is such that the thickness of the oxide film formed in the previous process is not increased excessively in this process and the possibility that the crystalline oxide can become etching nuclei is not erased. However, the thickness by the Hunter Hall method described above is preferably 2.5 to 5 nm. The (100) area ratio is preferably 90% or more.
[0055]
The treatment atmosphere for the final annealing is not particularly limited, but it is preferable to heat in an atmosphere with less moisture and oxygen so as not to increase the thickness of the oxide film. Specifically, it is preferable to heat in an inert gas such as argon or nitrogen or in a vacuum non-oxidizing atmosphere of 0.1 Pa or less.
[0056]
The state of the aluminum material at the time of final annealing is not limited, and batch annealing may be performed in a state of being wound around a coil, and coil winding may be performed after rewinding and continuous annealing, and batch annealing and continuous annealing. At least one of the above may be performed a plurality of times.
[0057]
Further, the holding temperature and time for the final annealing are not limited. For example, when performing batch annealing in the state of a coil, it carries out by hold | maintaining the solid temperature of an aluminum base material at 450-600 degreeC for 10 minutes-50 hours. When the aluminum body temperature is less than 400 ° C. and the holding time is less than 10 minutes, the crystalline oxide particles that can be the nucleus of the etch pit in the oxide film are not sufficiently generated, and the dispersion state becomes too sparse and the crystal is etched. This is because there is a possibility that the surface expansion effect during etching as a nucleus cannot be expected, and the crystal orientation of the (100) plane is not sufficiently developed. On the other hand, if the annealing temperature exceeds 600 ° C., the aluminum base material tends to adhere when batch annealing is performed with a coil, and the oxide film becomes too thick, so that the etching characteristics may be lowered and the effective area may not be sufficiently expanded. is there. Moreover, even if it anneals over 50 hours, the effective area expansion effect will be saturated and a heat energy cost will be increased on the contrary. A particularly preferable temperature is 460 to 560 ° C. at the aluminum body temperature, and the time is 30 minutes to 40 hours.
[0058]
The etched aluminum material for electrolytic capacitor electrodes of the present invention is obtained by subjecting the above-described aluminum material for electrolytic capacitor electrodes to an etching process to increase the effective area. By the etching process, the crystalline oxide particles present in the surface oxide film become etch pit nuclei, a large number of deep tunnel-like pits are generated, and the surface area is enlarged. Etching conditions are not particularly limited, but a direct current etching method is preferably employed.
[0059]
The etched aluminum material can be further subjected to a chemical conversion treatment to be an anode material, and is particularly suitable for an electrolytic capacitor anode material for medium pressure and high pressure.
[0060]
The electrolytic capacitor of the present invention uses the above-described etched aluminum material for electrolytic capacitor electrodes as an electrode material. High capacitance can be obtained by expanding the effective area of the electrode material.
[0061]
【Example】
Examples of the present invention and comparative examples are shown below. In addition, this invention is not limited to an Example.
[0062]
As the aluminum substrate, an aluminum foil obtained by rolling an aluminum material having an aluminum purity of 99.99% by mass to 110 μm by a conventional method was used. This aluminum foil can be suitably used as an electrolytic capacitor anode material.
(Example 1)
The aluminum substrate was degreased with an organic solvent: n-hexane, and then immersed in a 0.2 mass% sodium orthosilicate aqueous solution at 50 ° C. for 40 seconds. Thereafter, it was washed with water and dried. The aluminum substrate after drying was immersed in a 3% by mass hydrochloric acid aqueous solution for 60 seconds at 25 ° C., washed with water and dried. Next, the aluminum substrate after drying was sandwiched between two stainless steel heating plates whose surface temperature was set to 200 ° C., and contact heating was performed in the atmosphere for 2 seconds. With the aluminum base material after contact heating superimposed, the actual temperature of the aluminum base material was raised from room temperature to 540 ° C. at a rate of 50 ° C./h in an argon atmosphere, and held at 540 ° C. for 24 hours. Annealing was performed, and after cooling, the furnace was discharged. This obtained the aluminum material for electrolytic capacitor electrodes.
(Example 2)
The aluminum base material was degreased with an organic solvent: n-hexane, and then immersed in a 0.2 mass% sodium orthosilicate aqueous solution at 50 ° C. for 40 seconds. Thereafter, it was washed with water and dried. The aluminum substrate after drying was immersed in a 3% by mass sulfuric acid aqueous solution at 25 ° C. for 60 seconds, washed with water and dried. Next, the aluminum substrate after drying was sandwiched between two stainless steel heating plates whose surface temperature was set to 250 ° C., and contact heating was performed in the atmosphere for 2 seconds. In a state where the aluminum base material after contact heating is stacked, the solid temperature of the aluminum base material is raised from room temperature to 500 ° C. at 50 ° C./h in an argon atmosphere, and then held at 500 ° C. for 24 hours to be final. Annealing was performed, and after cooling, the furnace was discharged. This obtained the aluminum material for electrolytic capacitor electrodes.
(Example 3)
The aluminum substrate was degreased with an organic solvent: n-hexane, and then immersed in a 0.2 mass% sodium orthosilicate aqueous solution at 50 ° C. for 40 seconds. Thereafter, it was washed with water and dried. The aluminum substrate after drying was subjected to contact heating and final annealing under the same conditions as in Example 2 to obtain an aluminum material for electrolytic capacitor electrodes.
Example 4
An aluminum material for electrolytic capacitor electrodes was obtained by performing the same treatment as in Example 2 except that the immersion time in the sodium orthosilicate aqueous solution was 180 seconds.
(Examples 5 to 18)
An aqueous solution containing at least one of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid was prepared as an acid cleaning solution. An aqueous solution containing at least one of sodium hydroxide, potassium hydroxide and sodium orthosilicate was prepared as an alkaline cleaning solution. And the aluminum base material was washed by changing the kind of the cleaning liquid and the immersion time in the alkali and acid cleaning, then immersed in pure water and dried in the air. Next, contact heating performed by sandwiching an aluminum substrate between two stainless steel heating plates, changing the surface temperature of the heating plate at 80 to 400 ° C. and the heating time within a range of 0.001 to 30 seconds. went. The temperature was raised from room temperature in an inert gas atmosphere or in a vacuum with the aluminum base material after contact heating being stacked, and final annealing was performed by changing the conditions within a range of 400 to 600 ° C. and 10 minutes to 50 hours. Next, after cooling, the furnace was removed to obtain an aluminum material for electrolytic capacitor electrodes.
(Comparative Examples 1-3)
An aqueous solution containing at least one of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid was prepared as an acid cleaning solution. An aqueous solution containing at least one of sodium hydroxide, potassium hydroxide and sodium orthosilicate was prepared as an alkaline cleaning solution. Then, the aluminum substrate was washed by changing the kind, concentration and immersion time of the alkali cleaning solution and the acid cleaning solution, then immersed in pure water and dried in the air. Next, the temperature is raised from room temperature in an inert gas atmosphere or in a vacuum with the aluminum base material being stacked without performing contact heating, and the conditions are changed within a range of 400 to 600 ° C. and 10 minutes to 50 hours. And finally annealed. Next, after cooling, the furnace was removed to obtain an aluminum material for electrolytic capacitor electrodes.
[0063]
About the surface oxide film of the aluminum material for electrolytic capacitor electrodes obtained in each Example and Comparative Example, the film thickness, the density of crystalline oxide particles, the average particle diameter, distribution uniformity, geometric standard deviation, occupied area ratio Occupied area ratio / average particle diameter was determined. Here, the crystalline oxide particle diameter is a projected circle equivalent diameter.
[0064]
The film thickness was measured by the Hunter Hall method.
[0065]
The crystalline oxide particles were observed with a transmission electron microscope, the number of particles was counted, and the average particle size and the occupied area ratio were measured. The sample for observation used what formed the carbon vapor deposition film | membrane on the single side | surface of the aluminum material for electrolytic capacitor electrodes, was immersed in the bromine methanol solution, and dissolved aluminum. Further, in the region to be observed, the density of the crystalline oxide particles is 1 × 10 10. ⁷ Piece / mm ² 10μm in the above case ² (3.3 μm × 3.3 μm area), 1 × 10 ⁶ Piece / mm ² 1 × 10 or more ⁷ Piece / mm ² If it is less than 100 μm ² (10 μm × 10 μm area), 1 × 10 ⁶ Piece / mm ² If it is less than 400μm ² (Region of 20 μm × 20 μm), and 100 regions were observed for each sample. In addition, confirmation of whether each particle is a crystalline oxide or calculation of the crystal part area in the crystalline oxide particle is observed at an appropriate magnification (30,000 to 200,000 times) by expanding each field of view. , Electron beam diffraction, and energy dispersive X-ray analysis.
[0066]
The abundance density of the crystalline oxide particles was calculated from the observed area area and the counted number of particles.
[0067]
The geometric standard deviation of the crystalline oxide particles was calculated from the above observation / measurement results based on the formulas (F1) and (F2).
[0068]
The distribution uniformity of the crystalline oxide particles is a region satisfying 0.5 × A ≦ x ≦ 1.5 × A (x: average particle size, A: number of particles in the region) in the observed 100 regions. It was a number.
[0069]
The occupied area ratio (%) / average particle diameter (μm) of the crystalline oxide particles was calculated from each measured value.
[0070]
These measured values and calculated values are shown in Table 1.
[0071]
On the other hand, the aluminum material for electrolytic capacitor electrodes obtained in each example and each comparative example was HCl: 1.0 mol · dm. ^-3 And H ₂ SO _Four : 3.5 mol · dm ^-3 Is immersed in a mixed aqueous solution containing 75 ° C. and a current density of 0.2 A / cm. ² Then, electrolytic treatment was performed by electrolytic treatment. Furthermore, it was immersed in a hydrochloric acid-sulfuric acid mixed aqueous solution having the composition described above at 90 ° C. for 360 seconds, subjected to chemical etching to enlarge the pit diameter, and an etched aluminum material was obtained. The obtained etched aluminum material was subjected to chemical conversion treatment according to the EIAJ standard at a chemical conversion voltage of 270 V, and the capacitance was measured by the EIAJ method. The measured capacitance is shown in Table 1 as a relative value when Comparative Example 3 is 100.
[0072]
[Table 1]

[0073]
From Table 1, it was confirmed that by controlling the crystalline oxide particles of the oxide film on the surface layer, the etching characteristics can be enhanced and the capacitance can be increased.
[0074]
【The invention's effect】
Depending on the above, the aluminum material for electrolytic capacitor electrodes of the present invention has a density of crystalline oxide particles of 1 × 10 in the surface oxide film of the aluminum material. ^Four -10 ⁷ Piece / mm ² 10 to 400 μm ² When the average number of crystalline oxide particles per region is A and the number of crystalline oxide particles contained in any one region is x, m regions having any equal area of 0. Since the number of regions satisfying 5 × A ≦ x ≦ 1.5 × A is 0.55 × m or more, a large number of deep tunnel-shaped etching pits having crystalline oxide particles as nuclei are uniformly formed by etching. Generated. For this reason, an effective area is expanded, and an electrostatic capacitance can be increased by extension.
[0075]
In the aluminum material for electrolytic capacitor electrodes, when the average particle diameter of the crystalline oxide particles is 0.05 μm or more and less than 4 μm, a large number of etching pits are formed without being combined with adjacent pits. In particular, when the average particle diameter is 0.05 μm to 0.29 μm, there is no possibility of bonding with adjacent pits, and a large number of etching pits are formed.
[0076]
Further, the geometric standard deviation σ of the particle diameter of the crystalline oxide particles _g However, when the thickness is 1.5 or less, the etching pits are particularly uniformly formed.
[0077]
Further, when the area ratio of the crystalline oxide particles in the surface oxide film is 15% or less, the etching pits are uniformly formed without dissolving the entire surface in the etching process.
[0078]
Further, when the occupied area ratio (%) and the average particle diameter (μm) of the crystalline oxide particles are the occupied area ratio (%) / average particle diameter (μm) <100, a large number of etching pits are formed. It is formed without combining with adjacent pits.
[0079]
Further, when the thickness of the oxide film is 2.5 to 5 nm as measured by the Hunter hole method, particularly deep tunnel-like etching pits are sufficiently formed.
[0080]
Furthermore, when the aluminum purity in the aluminum material is 99.9% by mass or more, over-dissolution can be suppressed and deterioration of etching characteristics can be prevented.
[0081]
When the aluminum material for electrolytic capacitor electrodes is used as an anode material, a high capacitance can be obtained by expanding the effective area.
[0082]
Since the etched aluminum material for electrolytic capacitor electrodes of the present invention is formed by forming etching pits in any one of the electrolytic capacitor electrode aluminum materials described above, a large number of deep tunnel-like pits are formed. The capacitance can be increased.
[0083]
Since the electrolytic capacitor of the present invention uses the etched aluminum material for electrolytic capacitor electrodes as an electrode material, high capacitance can be obtained by expanding the effective area of the electrode material.

Claims (11)

In the surface layer oxide film of aluminum material, the existence density of crystalline oxide particles is 1 × 10 ⁴ to 10 ⁷ particles / mm ² , and 1 region for m regions having any equal area of 10 to 400 μm ² When the average number of crystalline oxide particles per unit is A and the number of crystalline oxide particles contained in any one region is x, the region satisfying 0.5 × A ≦ x ≦ 1.5 × A An aluminum material for electrolytic capacitor electrodes, wherein the number is 0.55 × m or more. The aluminum material for electrolytic capacitor electrodes according to claim 1, wherein an average particle diameter of the crystalline oxide particles is 0.05 µm or more and less than 0.4 µm. The aluminum material for electrolytic capacitor electrodes according to claim 2, wherein an average particle diameter of the crystalline oxide particles is 0.05 μm to 0.29 μm. The crystalline oxide particles, (F1) geometric standard deviation sigma _g of particle size is calculated by using the geometric mean particle diameter M _g is calculated (F2) formula in formula, wherein less than or equal to 1.5 The aluminum material for electrolytic capacitor electrodes according to any one of claims 1 to 3.

The aluminum material for electrolytic capacitor electrodes according to any one of claims 1 to 4, wherein an area ratio of the crystalline oxide particles in the surface oxide film is 15% or less. 6. The occupied area ratio (%) and the average particle diameter (μm) of the crystalline oxide particles satisfy an occupied area ratio (%) / average particle diameter (μm) <100. The aluminum material for electrolytic capacitor electrodes as described in 2. The aluminum material for electrolytic capacitor electrodes according to any one of claims 1 to 6, wherein the thickness of the oxide film is 2.5 to 5 nm as measured by a Hunter hole method. The aluminum material for electrolytic capacitor electrodes according to any one of claims 1 to 7, wherein the aluminum material has an aluminum purity of 99.9% by mass or more. The aluminum material for electrolytic capacitor electrodes according to any one of claims 1 to 8, wherein the aluminum material for electrolytic capacitor electrodes is an anode material. The aluminum material for electrolytic capacitor electrodes according to any one of claims 1 to 9, wherein etching pits are formed. An electrolytic capacitor comprising the etched aluminum material for an electrolytic capacitor electrode according to claim 10 as an electrode material.