JP2004006683A - Aluminum material for electrolytic capacitor electrode, etched aluminum material for electrolytic capacitor electrode, and electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum material for the electrodes of an electrolytic capacitor, which can increase its effective area by etching. <P>SOLUTION: In the aluminum material used for the electrodes of the electrolytic capacitor, the existing crystalline oxide particles on a surface oxide film are optimized. That is, the degree of crystallization of the surface oxide film is made larger than 1% but smaller than 3%, and the crystalline oxide particles on the surface oxide film are made at 1×10<SP>4</SP>to 10<SP>7</SP>/mm<SP>2</SP>in density. <P>COPYRIGHT: (C)2004,JPO

Description

【００２２】
【数４】

【００２３】
（４）　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である前項１ないし前項３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。
（５）　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。
【００２４】
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。
（７）　前項１ないし前項６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。
【００２５】
本発明の電解コンデンサは下記の構成を有する。
（８）　電極材料として、前項７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。
【００２６】
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、結晶化率とは、表層の酸化膜に存在する結晶性酸化物部の面積比率を示し、結晶化率を１％より大きく３％より小さい範囲に規定する。結晶化率が１％以下の場合、結晶をエッチピット核として有効に利用できないおそれがあり、結晶化率が３％以上になると結晶から生じた初期ピットが近隣のピットと結合しやすくなって、却って実効面積が減少するおそれがある。好ましい結晶化率は１．１〜２．９％である。
【００２７】
また、結晶性酸化物粒子の存在密度は１×１０^４〜１×１０^７個／ｍｍ^２に規定する。結晶性酸化物粒子の存在密度が１×１０^４個／ｍｍ^２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、１×１０^７個／ｍｍ^２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１×１０^５〜５×１０^６個／ｍｍ^２である。
【００２８】
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。
【００２９】
本発明の電解コンデンサ電極用アルミニウム材は、結晶化率および結晶性酸化物粒子の密度が上記範囲に制御されているため、エッチングによって結晶性酸化物粒子を核とする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て、静電容量が増大される。
【００３０】
前記結晶性酸化物粒子の平均粒子径は０．０５〜１．２μｍあることが好ましい。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。
【００３１】
前記結晶性酸化物平均粒子径が０．０５μｍ未満の場合、結晶がエッチピット核となりにくく、１．２μｍを越えると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０．０６〜０．８μｍである。
【００３２】
前記結晶性酸化物粒子の種類としてはγ−Ａｌ_２Ｏ_３をはじめとするＡｌ_２Ｏ_３、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。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。
【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】
なお、本発明における結晶化率は、アルミニウム材表層の酸化膜に存在する結晶性酸化物部の占める面積比率であるため、結晶性酸化物部と無定形酸化物部が混在する結晶性酸化物粒子が存在する場合の結晶化率は、結晶性酸化物粒子がアルミニウム表層酸化膜において占有する面積比率より小さくなる。
【００３５】
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。
【００３６】
まず、（Ｆ１）式によりｎ個の粒子の幾何平均径Ｍ_ｇを求める。
【００３７】
【数５】

【００３８】
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。
【００３９】
【数６】

【００４０】
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。
【００４１】
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。
【００４２】
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。
【００４３】
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。
【００４４】
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。
【００４５】
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化率、結晶性酸化物粒子の密度および結晶性酸化物粒子の粒子径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。
【００４６】
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。
【００４７】
前記加熱体の表面温度は８０〜４００℃が好ましい。加熱体の表面温度が８０℃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、４００℃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。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。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。
【００４８】
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。
【００４９】
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。
【００５０】
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。
【００５１】
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。
【００５２】
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。
【００５３】
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。
【００５４】
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。
【００５５】
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。
【００５６】
【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。
【００５７】
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秒間浸漬した後水洗した。水洗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５００℃まで５０℃／ｈで昇温させた後、５００℃にて２４時間保持させて最終焼鈍を施し、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秒間浸漬した後水洗した。水洗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、実施例１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秒間浸漬した後水洗し、乾燥させた。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み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時間保持させて最終焼鈍を施し、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４〜３０）
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。次に加熱時間および温度を変化させて接触加熱を行った。接触加熱後のアルミニウム基材を重ねた状態で不活性ガス雰囲気下もしくは真空中で焼鈍温度と時間を変化させ焼鈍し電解コンデンサ電極用アルミニウム材を得た。
（比較例１〜４）
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昇温させたのち４５０〜５８０℃にて保持させ、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。
【００５８】
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、結晶化率、結晶性酸化物粒子の粒子密度、平均粒子径、幾何標準偏差を求めた。ここで、結晶性酸化物粒子径は投影円相当径とする。
【００５９】
膜厚さはハンターホール法により測定した。
【００６０】
結晶性酸化物粒子の粒子密度、平均粒子径および結晶化率は、合計で少なくとも５０個以上の結晶性酸化物粒子が存在する単一もしくは複数の視野を観察する（３０００〜３万倍で観察）ことにより求めた。なお、各々の粒子が結晶し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。
【００６１】
幾何標準偏差は、透過型電子顕微鏡で結晶性酸化物粒子を観察して測定し、あるいは測定した粒子径から（Ｆ１）（Ｆ２）式に基づいて計算した。各電解コンデンサ電極用アルミニウム材の表面に存在する結晶性酸化物粒子の粒径の幾何標準偏差は、５０個以上の粒子の直径より求めた。なお、透過型電子顕微鏡観察用サンプルは、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。これらの結果を表１、２、３に示す。
【００６２】
一方で、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Ｈ_２ＳＯ_４：３．５ｍｏｌ・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／ｃｍ^２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太くし、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１を１００とした時の相対値として表１、２、３に示す。
【００６３】
【表１】

【００６４】
【表２】

【００６５】
【表３】

【００６６】
表１、２、３より、表層の酸化膜の膜厚さ、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。
【００６７】
【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、表層の酸化膜の結晶化率が１％より大きく３％より小さく、該酸化膜における結晶性酸化物粒子の存在密度が１×１０^４〜１０^７個／ｍｍ^２となされているから、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。
【００６８】
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０．０５〜１．２μｍ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。
【００６９】
また、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。
【００７０】
また、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。
【００７１】
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。
【００７２】
、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。
【００７３】
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、前記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。
【００７４】
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]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an aluminum material for an electrolytic capacitor electrode, an etched aluminum material for an electrolytic capacitor electrode, and an electrolytic capacitor.
[0002]
In this specification, the term "aluminum" is used to include its alloy.
[0003]
[Prior art]
The aluminum foil used as an electrode material for an electrolytic capacitor has an increased surface area by an electrochemical or chemical etching treatment to increase the capacitance, thereby increasing the effective area.
[0004]
Generally, a high-purity aluminum foil for an electrolytic capacitor, which generates tunnel-like pits by a DC etching method, is heated at about 500 ° C. 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. Is finally annealed. Here, the final annealing is a step performed after the finish cold rolling or after the washing after the finish cold rolling.
[0005]
In addition, it is known that the crystalline oxide generated on the aluminum foil surface becomes the nucleus of the etch pit, and it is thought that controlling the density of the crystalline oxide and the particle diameter of the crystal leads to the improvement of the capacitance. (For example, Non-Patent Document 1).
[0006]
The following prior arts relate to crystalline oxide particles on the surface of an aluminum foil (for example, Patent Documents 1, 2, and 3).
[0007]
Patent Literature 1 proposes an aluminum material for an electrolytic capacitor in which γ-alumina crystals are formed on an aluminum foil surface.
[0008]
Patent Document 2 describes that since the surface potential of an amorphous oxide film is locally uniform, etching pits corresponding to electrolysis conditions are formed. It is described that the crystallization ratio of the oxide film is controlled to 1% or less in order to form uniform and deep pits at high density.
[0009]
Patent Document 3 proposes an aluminum foil for an electrolytic capacitor in which crystals having 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 5. ⁴ ~ 2 × 10 ⁹ Pieces / cm ² It is prescribed.
There is fear.
[0010]
[Non-patent document 1]
Nobuo Osawa and Kiyoshi Fukuoka, "Effect of Crystalline Oxide on DC Etching Behavior of Aluminum Foil for Electrolytic Capacitor", Surface Technology, 1999, Vol. 50, No. 7, p. 643-647
[0011]
[Patent Document 1]
JP-A-63-116417
[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 does not provide 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 or the density of γ-alumina particles, and the effects of these on the etching characteristics are not clarified.
[0016]
In the technique described in Patent Document 2, the crystallization ratio is suppressed to 1% or less, and the crystalline oxide particles are not effectively used as etch pit nuclei.
[0017]
In the technology described in Patent Document 3, since the crystalline oxide exists in an area ratio of 3 to 50%, the etch pits generated by using the adjacent crystalline oxide as a nucleus are easily bonded, and the effective area is rather reduced. There is a possibility that.
[0018]
The present invention solves the above-mentioned problems of the prior art, and provides an aluminum material for an electrode for an electrolytic capacitor, an etched aluminum material for an electrode for an electrolytic capacitor, and an electrolytic capacitor that can increase the effective area by etching. The purpose is to do.
[0019]
[Means for Solving the Problems]
The inventors of the present invention have completed the present invention by optimizing the state of the crystalline oxide particles in the aluminum material for the electrolytic capacitor electrode, particularly the surface oxide film of the aluminum material for the anode.
[0020]
That is, the aluminum material for an electrolytic capacitor electrode of the present invention has the following configuration.
(1) The crystallization ratio of the surface oxide film is larger than 1% and smaller than 3%, and the density of crystalline oxide particles in the oxide film is 1 × 10 ⁴ -10 ⁷ Pieces / mm ² An aluminum material for an electrode of an electrolytic capacitor, characterized in that:
(2) The aluminum material for an electrolytic capacitor electrode according to the above (1), wherein the crystalline oxide particles have an average particle diameter of 0.05 to 1.2 μm.
(3) The crystalline oxide particles have a geometric average particle diameter M calculated by the formula (F1). _g Is the geometric standard deviation σ of the particle diameter calculated by equation (F2) using _g 3. The aluminum material for an electrolytic capacitor electrode according to the above item 1 or 2, wherein the aluminum material is 1.5 or less.
[0021]
[Equation 3]

[0022]
(Equation 4)

[0023]
(4) The aluminum material for an electrolytic capacitor electrode according to any one of (1) to (3) above, wherein the oxide film has a thickness of 2.5 to 5 nm as measured by a Hunter Hall method.
(5) The aluminum material for an electrode of an electrolytic capacitor according to any one of the above (1) to (4), wherein the aluminum material has an aluminum purity of 99.9% by mass or more.
(6) The aluminum material for an electrolytic capacitor electrode according to any one of (1) to (5) above, wherein the aluminum material for an electrolytic capacitor electrode is an anode material.
[0024]
The etched aluminum material for an electrolytic capacitor electrode of the present invention has the following configuration.
(7) The aluminum material for an electrolytic capacitor electrode according to any one of the preceding items 1 to 6, wherein an etched pit is formed in the aluminum material for an electrolytic capacitor electrode.
[0025]
The electrolytic capacitor of the present invention has the following configuration.
(8) An electrolytic capacitor, characterized in that the electrode material is the etched aluminum material for an electrolytic capacitor electrode described in the item (7).
[0026]
In the aluminum material for an electrode of an electrolytic capacitor according to the present invention, the crystallization ratio indicates an area ratio of a crystalline oxide portion present in a surface oxide film, and the crystallization ratio is defined in a range of more than 1% and less than 3%. I do. When the crystallization rate is 1% or less, the crystal may not be effectively used as an etch pit nucleus, and when the crystallization rate is 3% or more, initial pits generated from the crystal may be easily combined with neighboring pits. Rather, the effective area may be reduced. The preferred crystallization rate is 1.1 to 2.9%.
[0027]
The density of the crystalline oxide particles is 1 × 10 ⁴ ~ 1 × 10 ⁷ Pieces / mm ² Stipulated. The density of the crystalline oxide particles is 1 × 10 ⁴ Pieces / mm ² If it is less than 1 × 10, the number of generated etch pits is also small because the number of crystals is too small. ⁷ Pieces / mm ² If the number is larger, a large effective area cannot be obtained because many etch pits generated in the initial stage of the etching are connected to each other. The preferred density is 1 × 10 ⁵ ~ 5 × 10 ⁶ Pieces / mm ² It is.
[0028]
In the present invention, the thickness of the aluminum material for an electrolytic capacitor electrode is not particularly limited. The present invention includes a plate having a thickness of 200 μm or less, called a foil, and a plate having a greater thickness, and a molded product using these plates.
[0029]
In the aluminum material for an electrolytic capacitor electrode of the present invention, since the crystallization rate and the density of the crystalline oxide particles are controlled in the above range, a large number of etching pits having the crystalline oxide particles as nuclei are uniformly formed by etching. Generated. For this reason, the effective area is enlarged, and the capacitance is increased.
[0030]
The average particle diameter of the crystalline oxide particles is preferably 0.05 to 1.2 μm. The shape of the crystalline oxide particles 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 particles.
[0031]
When the crystalline oxide average particle diameter is less than 0.05 μm, the crystal is unlikely to become an etch pit nucleus, and when it exceeds 1.2 μm, the etch pits generated from adjacent crystals are easily bonded to each other and the effective area is sufficiently large. Not expanded. A particularly preferred particle size is from 0.06 to 0.8 μm.
[0032]
The type of the crystalline oxide particles is γ-Al ₂ O ₃ And other Al ₂ O ₃ And oxides and hydroxides of AlO (OH), including boehmite, and other metals (eg, Mg, Pb, Cu, etc.) other than aluminum, and aluminum and other metals (eg, Mg, Pb, Cu, etc.) other than aluminum. The composite metal oxide or hydroxide is not particularly limited, and may be a single crystal or a polycrystal. Further, one or a plurality of crystals may be covered with an amorphous substance to form one particle, or an amorphous oxide may be present between aggregated oxide crystals. The crystalline oxide present on the surface of the aluminum material for the electrolytic capacitor electrode was formed by depositing a deposited film of carbon or the like as a support film on one surface of the aluminum material and then dissolving the aluminum by immersion in, for example, a bromine-methanol solution. It can be confirmed by observing the sample with a transmission electron microscope. As the solution used for preparing the aluminum solution at the time of preparing the above-mentioned transmission electron microscope observation sample, an aqueous mercuric chloride solution, an iodine-methanol solution, etc. can be applied in addition to the bromine-methanol solution.
[0033]
The crystalline oxide particles present in the transmission electron microscope observation region are each observed at an appropriate magnification, and whether or not the crystalline oxide is a crystalline oxide or the crystalline oxide is identified by electron diffraction and energy dispersion. It can be performed by using a type X-ray analysis.
[0034]
Note that the crystallization ratio in the present invention is an area ratio of a crystalline oxide portion present in an oxide film on a surface layer of an aluminum material, and therefore, a crystalline oxide portion in which a crystalline oxide portion and an amorphous oxide portion are mixed exists. The crystallization ratio when the particles are present is smaller than the area ratio occupied by the crystalline oxide particles in the aluminum surface oxide film.
[0035]
The uniformity of the crystalline oxide particle diameter is determined by a geometric standard deviation σ. _g Is represented by Geometric standard deviation σ _g Is shown below.
[0036]
First, the geometric mean diameter M of n particles is calculated by equation (F1). _g Ask for.
[0037]
(Equation 5)

[0038]
Furthermore, the geometric mean diameter M _g From formula (F2), the geometric standard deviation σ _g Ask for. Note that the geometric standard deviation σ _g In order to obtain the reliability, it is preferable that n ≧ 50.
[0039]
(Equation 6)

[0040]
When the diameters of the crystalline oxide particles are all the same, the geometric standard deviation σ _g Is 1 and the geometric standard deviation σ _g Becomes larger. Therefore, the geometric standard deviation σ _g Is smaller and closer to 1, indicating that the particle size is uniform and the particle size distribution is narrower. Since the etch pits are generated more uniformly as the particle diameter becomes more uniform, the geometric standard deviation σ of the crystalline oxide particle diameter becomes larger. _g Is preferably 1.5 or less.
[0041]
The thickness of the oxide film is preferably 2.5 to 5 nm as measured by the Hunter Hall method. If it is less than 2.5 nm, the surface of the aluminum material is largely dissolved in the initial stage of etching, and if it exceeds 5 nm, the crystalline oxide particles may not act as etching pit nuclei. The Hunter Hall method is described in M.E. S. Hunter and P.M. Fowl, J .; Electrochem. Soc. , 101 [9], 483 (1954).
[0042]
The aluminum material is not limited in its composition, and any material used as an electrode material for an electrolytic capacitor can be appropriately used. Specifically, the aluminum purity is preferably 99.9% by mass or more, and particularly preferably 99.95% by mass or more, in order to control the amount of impurities and prevent deterioration of the etching characteristics due to excessive melting. Further, an aluminum material to which various trace elements are added in order to improve etching characteristics and strength can be suitably used. In the present invention, the aluminum purity of the aluminum material is a value obtained by subtracting the total concentration (% by mass) of Fe, Si, Cu, Mn, Cr, Zn, Ti and Ga from 100% by mass.
[0043]
The aluminum material of the present invention is suitable as an anode material in that it has a large effective area even if a withstand voltage film is formed by a chemical conversion treatment after etching. Further, among the anode materials, it is suitable for electrode materials for medium and high pressure electrolytic capacitors.
[0044]
In the production of the aluminum material of the present invention, the melting, composition adjustment, slab casting, soaking, hot rolling, cold rolling, intermediate annealing, finish cold rolling (low reduction rolling), and final annealing of the aluminum material are generally performed by a general method. The process may be followed, and there is no particular process to be specified. 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 depending on the etching conditions of the aluminum material. In addition, in the middle of the rolling process, the aluminum material may be annealed (hereinafter referred to as intermediate annealing) for the purpose of eliminating the distortion of the crystal structure of the aluminum material caused by the rolling in the preceding process. In addition, cleaning may be performed in order to remove impurities and oil on the surface in a step before the intermediate annealing.
[0045]
Further, since oil and impurities are present on the surface of the aluminum base material after the rolling step, it is preferable to remove these by performing cleaning before contact heating. This is because, when these are adhered to the aluminum base material surface, uniform formation of crystalline oxide particles is hindered in the subsequent final annealing. The cleaning method and the cleaning liquid are not particularly limited, and immersion cleaning, spray cleaning, dry etching, or the like using an acid cleaning liquid or an alkaline cleaning liquid can be used. Examples of the type 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. 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 aqueous acid solution to enhance the degreasing power. Examples of the type of the alkaline cleaning liquid include sodium hydroxide, potassium hydroxide, calcium hydroxide, and sodium silicate, and an aqueous solution containing at least one or more alkalis can be used as the cleaning liquid. A plurality of cleanings may be performed, such as performing acid cleaning after alkali cleaning. Further, if the surface after the rolling step can withstand uniform crystal formation, the surface may be washed with an organic solvent. Examples of organic solvents include alcohols, aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as pentane and hexane, acetone, ketones, esters, and the like, but are not particularly limited, and include a plurality of organic solvents. You may mix and use. Further, washing with an organic solvent and washing with an acid or alkali described above may be combined. In any case, it is preferable to perform water washing for the purpose of removing the residue of the washing liquid component attached to the aluminum surface after washing. Further, the cleaning is not limited to after finishing rolling, but may be performed before rolling or between rolling passes.
Contact heating can be used as one of the methods for controlling the crystallization rate of the aluminum oxide layer after final annealing, the density of the crystalline oxide particles, and the particle size of the crystalline oxide particles.
[0046]
The contact heating means is not limited as long as it is contact heating such as a heat roll, a heating belt, and a heating plate, and a plurality of contact heating means may be combined. In addition, heating may be performed simultaneously on the front and back of the aluminum material, or one surface at a time. The surface of the heating element is preferably formed of a substance to which an oxide film of an aluminum material does not adhere, and examples thereof include stainless steel, plating, ceramics, ethylene tetrafluoride resin, and silicone resin.
[0047]
The surface temperature of the heating body is preferably from 80 to 400C. If the surface temperature of the heating element is lower than 80 ° C., it is difficult to control the crystallization ratio and crystalline oxide particles of the oxide film after the final annealing within a predetermined range. This is because the film may be too thick, causing operational problems such as generation of wrinkles during heating and cooling. The time for bringing the heating body into contact with the aluminum material is preferably 0.001 to 30 seconds. If the contact time is less than 0.001 second, the aluminum surface cannot be sufficiently heated, so that the crystallization rate and the crystalline oxide particles cannot be controlled. There is a possibility that the film becomes too thick and etch pits hardly occur. The surface temperature of the heater and the contact time are appropriately selected in consideration of the characteristics of the aluminum oxide film before the contact heating. The contact heating atmosphere is not particularly limited, and it is sufficient even in air without any special atmosphere control.
[0048]
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. .
[0049]
The aluminum material after the final annealing has a total thickness of the oxide film so that the thickness of the oxide film formed in the previous step is not excessively increased in this step so as to eliminate the possibility that the crystalline oxide may become an etching nucleus. However, it is preferable to set the thickness by the above-mentioned Hunter Hall method to 2.5 to 5 nm. Further, the (100) area ratio is preferably 90% or more.
[0050]
Although the treatment atmosphere for the final annealing is not particularly limited, it is preferable to heat in an atmosphere with a small amount of moisture and oxygen so that the thickness of the oxide film is not excessively increased. 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.
[0051]
The state of the aluminum material at the time of final annealing is not limited, and may be batch-annealed in a state of being wound on a coil, or may be wound on a coil after rewinding and annealing continuously, and batch annealing and continuous annealing. May be performed a plurality of times.
[0052]
Further, the holding temperature and time of the final annealing are not limited. For example, when performing batch annealing in the state of a coil, it is performed by maintaining the substantial temperature of the aluminum base material at 450 to 600 ° C. for 10 minutes to 50 hours. If the temperature of the aluminum body is less than 400 ° C. and the holding time is less than 10 minutes, the generation of crystalline oxide particles that may become nuclei of etch pits in the oxide film is not sufficient, and the dispersed state is too sparse to etch the crystals. This is because there is a possibility that a surface enlargement effect at the time of etching, which is a nucleus, cannot be expected, and the crystal orientation of the (100) plane is insufficiently developed. Conversely, if the annealing is performed at a temperature higher than 600 ° C., the aluminum base material is likely to adhere when batch annealing is performed with a coil, and the oxide film becomes too thick, so that the etching characteristics deteriorate and the effective area may not be sufficiently enlarged. is there. Further, even if annealing is performed for more than 50 hours, the effect of enlarging the effective area is saturated, which in turn causes an increase in thermal energy cost.
[0053]
The etched aluminum material for an electrolytic capacitor electrode of the present invention is obtained by expanding the effective area by subjecting the above-mentioned aluminum material for an electrolytic capacitor electrode to an etching treatment. By the etching treatment, crystalline oxide particles present in the surface oxide film serve as etch pit nuclei, generating a large number of deep tunnel-like pits and increasing the surface area. Although the etching conditions are not particularly limited, a direct current etching method is preferably used.
[0054]
The etched aluminum material can be further subjected to a chemical conversion treatment to form an anode material, and is particularly suitable as an anode material for medium- and high-pressure electrolytic capacitors.
[0055]
The electrolytic capacitor of the present invention uses the above-described etched aluminum material for an electrolytic capacitor electrode as an electrode material. High capacitance can be obtained by increasing the effective area of the electrode material.
[0056]
【Example】
Hereinafter, Examples and Comparative Examples of the present invention will be described. Note that the present invention is not limited to the embodiments.
[0057]
As the aluminum base material, an aluminum foil obtained by rolling an aluminum material having an aluminum purity of 99.99% by mass to 110 μm by an ordinary method was used. This aluminum foil can be suitably used as an anode material of an electrolytic capacitor.
(Example 1)
The aluminum substrate was degreased with an organic solvent: n-hexane, immersed in a 0.2% by mass aqueous sodium orthosilicate solution at 50 ° C. for 40 seconds, and then washed with water. The washed aluminum substrate was immersed in a 3% by mass aqueous sulfuric acid solution at 25 ° C. for 60 seconds, washed with water and dried. Next, the dried aluminum substrate 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. In a state where the aluminum substrates after the contact heating are stacked, the actual temperature of the aluminum substrate is increased from room temperature to 500 ° C. at a rate of 50 ° C./h in an argon atmosphere, and then maintained at 500 ° C. for 24 hours. After annealing and then cooling, the furnace was taken out. Thus, an aluminum material for an electrolytic capacitor electrode was obtained.
(Example 2)
The aluminum substrate was degreased with an organic solvent: n-hexane, immersed in a 0.2% by mass aqueous sodium orthosilicate solution at 50 ° C. for 40 seconds, and then washed with water. The washed aluminum substrate was immersed in a 3% by mass aqueous hydrochloric acid solution at 25 ° C. for 60 seconds, washed with water and dried. Next, contact heating and final annealing were performed under the same conditions as in Example 1 to obtain an aluminum material for an electrolytic capacitor electrode.
(Example 3)
The aluminum substrate was degreased with an organic solvent: n-hexane, immersed in a 0.2% by mass aqueous sodium orthosilicate solution at 50 ° C. for 40 seconds, washed with water, and dried. The dried aluminum substrate was sandwiched between two stainless steel heating plates whose surface temperature was set at 250 ° C., and contact heating was performed for 2 seconds. In a state where the aluminum base materials after the contact heating are stacked, the actual temperature of the aluminum base material is increased from room temperature to 540 ° C. at a rate of 50 ° C./h in an argon atmosphere, and then maintained at 540 ° C. for 24 hours. After annealing and then cooling, the furnace was taken out. Thus, an aluminum material for an electrolytic capacitor electrode was obtained.
(Examples 4 to 30)
An aqueous solution containing at least one of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid was prepared as an acid washing 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 base material was washed by changing the type of the washing solution and the immersion time in the alkali and acid washing, immersed in pure water, and dried in air. Next, contact heating was performed while changing the heating time and temperature. The aluminum substrate for the electrolytic capacitor electrode was obtained by changing the annealing temperature and time in an inert gas atmosphere or in a vacuum in a state where the aluminum substrates after the contact heating were stacked, in an inert gas atmosphere or in a vacuum.
(Comparative Examples 1-4)
An aqueous solution containing at least one of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid was prepared as an acid washing 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 base material was washed by changing the types, concentrations, and immersion times of the alkali cleaning solution and the acid cleaning solution, immersed in pure water, and dried in air. Next, without contact heating, the temperature was raised in an inert gas atmosphere or vacuum in a state where the aluminum base materials were stacked, and the temperature was maintained at 450 to 580 ° C. An aluminum material for a capacitor electrode was obtained.
[0058]
With respect to the surface oxide film of the aluminum material for an electrolytic capacitor electrode obtained in each of the examples and comparative examples, the film thickness, the crystallization rate, the particle density of the crystalline oxide particles, the average particle diameter, and the geometric standard deviation were determined. Here, the crystalline oxide particle diameter is a projected circle equivalent diameter.
[0059]
The film thickness was measured by the Hunter Hall method.
[0060]
The particle density, average particle diameter, and crystallization ratio of the crystalline oxide particles are determined by observing a single or a plurality of visual fields in which at least 50 or more crystalline oxide particles are present (observed at 3000 to 30,000 times). ). The confirmation of whether or not each particle is an oxide and the calculation of the crystal part area in the crystalline oxide particles are performed by expanding each field of view and at an appropriate magnification (30,000 to 200,000 times). Observation, electron diffraction, and energy dispersive X-ray analysis were performed.
[0061]
The geometric standard deviation was measured by observing the crystalline oxide particles with a transmission electron microscope, or calculated from the measured particle diameters based on the formulas (F1) and (F2). The geometric standard deviation of the particle size of the crystalline oxide particles present on the surface of the aluminum material for each electrolytic capacitor electrode was determined from the diameters of 50 or more particles. In addition, the sample for observation with a transmission electron microscope was obtained by forming a carbon vapor-deposited film on one surface of an aluminum material for an electrode of an electrolytic capacitor, and immersing the film in a bromine-methanol solution to dissolve aluminum. The results are shown in Tables 1, 2, and 3.
[0062]
On the other hand, the aluminum material for an electrolytic capacitor electrode obtained in each of Examples and Comparative Examples was prepared by adding HCl: 1.0 mol · dm. ^-3 And H ₂ SO ₄ ： 3.5mol ・ dm ^-3 And a current density of 0.2 A / cm ² And electrolytic etching was performed. Further, it was immersed in a hydrochloric acid-sulfuric acid mixed aqueous solution of the above composition at 90 ° C. for 360 seconds and subjected to chemical etching to increase the pit diameter, thereby obtaining an etched aluminum material. The obtained etched aluminum material was subjected to a chemical conversion treatment at a chemical conversion voltage of 270 V according to the EIAJ standard, and the capacitance was measured by the EIAJ method. Tables 1, 2, and 3 show the measured capacitance as a relative value when Comparative Example 1 is set to 100.
[0063]
[Table 1]

[0064]
[Table 2]

[0065]
[Table 3]

[0066]
From Tables 1, 2, and 3, it was confirmed that by controlling the thickness of the oxide film of the surface layer and the crystalline oxide particles, the etching characteristics could be increased and the capacitance could be increased.
[0067]
【The invention's effect】
As described above, in the aluminum material for an electrolytic capacitor electrode according to the present invention, the crystallization ratio of the surface oxide film is larger than 1% and smaller than 3%, and the density of the crystalline oxide particles in the oxide film is 1 × 10 3. ⁴ -10 ⁷ Pieces / mm ² Therefore, the etching produces a large number and uniformity of deep tunnel-shaped etching pits having crystalline oxide particles as nuclei. For this reason, the effective area is enlarged, and the capacitance can be increased.
[0068]
When the average particle diameter of the crystalline oxide particles in the aluminum material for an electrolytic capacitor electrode is 0.05 to 1.2 μm, a large number of etching pits are formed without bonding to adjacent pits.
[0069]
Also, the geometric standard deviation σ of the particle diameter of the crystalline oxide particles _g Is 1.5 or less, etching pits are particularly formed uniformly.
[0070]
When the thickness of the oxide film is 2.5 to 5 nm as measured by the Hunter Hall method, a particularly deep tunnel-shaped etching pit is sufficiently formed.
[0071]
Further, when the aluminum material has an aluminum purity of 99.9% by mass or more, it is possible to suppress overdissolution and prevent deterioration in etching characteristics.
[0072]
When the aluminum material for an electrolytic capacitor electrode is used as an anode material, a high capacitance can be obtained by enlarging the effective area.
[0073]
Since the etched aluminum material for an electrolytic capacitor electrode of the present invention is obtained by forming etching pits in the aluminum material for an electrolytic capacitor electrode, a large number of deep tunnel-like pits are formed, thereby reducing the capacitance. It can increase.
[0074]
Since the electrolytic capacitor of the present invention uses the etched aluminum material for an electrolytic capacitor electrode as the electrode material, a high capacitance can be obtained by enlarging the effective area of the electrode material.

Claims (8)

The crystallization ratio of the surface oxide film is greater than 1% and less than 3%, and the density of the crystalline oxide particles in the oxide film is 1 × 10 ⁴ to 10 ⁷ / mm ^2. Material for electrolytic capacitor electrodes. The aluminum material for an electrolytic capacitor electrode according to claim 1, wherein the average particle diameter of the crystalline oxide particles is 0.05 to 1.2 µm. The crystalline oxide particles have a geometric standard deviation σ _{g of the} particle diameter calculated by the equation (F2) using the geometric average particle diameter M _g calculated by the equation (F1) of 1.5 or less. The aluminum material for an electrode of an electrolytic capacitor according to claim 1 or 2.

The aluminum material for an electrolytic capacitor electrode according to any one of claims 1 to 3, wherein the thickness of the oxide film is 2.5 to 5 nm as measured by a Hunter Hall method. The aluminum material for an electrolytic capacitor electrode according to any one of claims 1 to 4, wherein the aluminum material has an aluminum purity of 99.9% by mass or more. The aluminum material for an electrolytic capacitor electrode according to any one of claims 1 to 5, wherein the aluminum material for an electrolytic capacitor electrode is an anode material. 7. The etched aluminum material for an electrolytic capacitor electrode according to claim 1, wherein etching pits are formed in the aluminum material for an electrolytic capacitor electrode according to claim 1. An electrolytic capacitor, wherein the electrode material is the etched aluminum material for an electrolytic capacitor electrode according to claim 7.