JP4929558B2

JP4929558B2 - Method for manufacturing lead-acid battery grid

Info

Publication number: JP4929558B2
Application number: JP2003206742A
Authority: JP
Inventors: 義臣藤原
Original assignee: GS Yuasa International Ltd
Current assignee: GS Yuasa International Ltd
Priority date: 2003-08-08
Filing date: 2003-08-08
Publication date: 2012-05-09
Anticipated expiration: 2023-08-08
Also published as: JP2005056622A

Description

【０００１】
【発明の属する分野】
鉛蓄電池用格子の製造方法に関する。
【０００２】
【従来の技術】
鉛蓄電池の発電要素は、鉛または鉛合金からなる格子の枡目に活物質を充填した構造を有している。前記格子は、鉛または鉛合金を鋳造等によって直接格子状に形成する方法と鉛または鉛合金からなるシートに、ダイスカッターの上・下運動によって該シートに両端部から順に各枡目を形成するレシプロ方式や円板状のカッタ−の回転によってシートに千鳥状のスリットを形成し、該シートを両側から展開してスリットを枡目状に展開するロータリー方式等のエキスパンド加工方式とがある。近年では生産性が優れている点からシートを加工して格子を作製する方式が増えている。
【０００３】
その原料である鉛合金シートの一般的な製造方法として、連続鋳造方式、押出し方式、圧延方式等があげられる。
【０００４】
【発明が解決しようとしている課題】
一般的に連続鋳造方式や押出し方式では、平均結晶粒径の大きい金属組織を有する鉛合金シートが得られる。その場合、強度が小さく、その後のエキスパンド加工が困難である。また、結晶粒界が存在するとその部分にエネルギーが多く蓄積されるので腐食され易く金属組織の平均結晶粒径が大きい場合、腐食が結晶粒界に沿って内部に進行し格子が破断に至る欠点をも有している。しかし、結晶粒界が大きい場合には、腐食の絶対量は少なく、高温下での放置による再結晶化がほとんど起こらないので強度変化が少ない利点を有している。
【０００５】
一方、圧延方式で得たシートは、鋳造や押出しによるシートに比べて平均結晶粒径の小さい金属組織を有している。そのことによって強度が大きく伸びやすいためエキスパンド展開時の加工性が非常に優れている。また金属組織が小さいので、鋳造や押出しによるシートのような内部に進行する腐食は少ない。その反面、結晶粒界が多いため腐食量が多くなる欠点を有している。また、高温下での放置においては、再結晶化が進行し、強度が低下する問題をも有している。したがって、圧延方式による鉛合金シートから得たエキスパンド格子を正極板に使用すると、鋳造格子で見られる粒界に沿った局部的な腐食による破断や突然の劣化は発生しなくなるが、格子全体の腐食量が多くなることや、特に高温下で、再結晶化によって強度が低下して極板が変形・伸張し易く、活物質の脱落や対極板との短絡で短寿命となる問題を抱えている。
【０００６】
本発明が解決しようとする課題は、エキスパンド加工等の加工性が優れ、しかも加工により得た格子の腐食量が少なく、また高温化での再結晶化による強度低下による格子の伸びの少ない鉛蓄電池用格子の製造方法およびそれによって製造された格子を用いた寿命性能の優れた鉛蓄電池を提供することにある。
【０００７】
本発明の課題を解決するための手段として、請求項１によれば、鉛合金シートをエキスパンド加工して鉛蓄電池用格子とする鉛蓄電池用格子の製造方法において、前記シートが中心層と上・下表面層とを備え、前記中心層の平均結晶粒径が２５μｍ〜２５０μｍであり、前記上・下表面層の平均結晶粒径が１０μｍ以下であることを特徴とするものである。
【０００８】
上述したように、小さい平均結晶粒径を有する金属組織は、エキスパンド加工等に対する加工性が優れ、しかも結晶粒界に沿って深く進行する腐食は起こらない。一方、大きな平均結晶粒径を有する金属組織は腐食量が少なく、蓄電池使用中の高温下での強度低下が小さく、格子の変形が抑制されるといった優れた特性を備えている。本願発明は、これらのことを鑑みなされたもので、シートの上・下表面層は小さい平均結晶粒径、中心層は大きな平均結晶粒径からなる３層構造の金属組織にすることによって、上・下表面層の金属組織によりエキスパンド加工等に対する優れた加工特性を維持しながら、中心層の金属組織により正極板の腐食および高温下での極板伸びが低減できることを本願発明者は見出した。
【０００９】
本発明において、「表面層」とはシートの上・下表面からそれぞれシートの総厚みの１０％までの範囲にある層を意味し、「中心層」とは、シートの中心部から上下の厚みがシートの層厚みの１０％を占める、すなわち合計２０％を占める部分を意味する。図２にこの関係を模式的示す。
【００１０】
上記定義は、実施例の項で後述するように平均結晶粒径の小さいことによるシートの加工のし易さは上・下表面層の厚みがそれぞれ１０％であれば維持できること、また中心層の平均結晶粒径が大きいことによる優れた耐食性は、前記中心層の厚みが２０％であれば確保できることによるものである。
【００１１】
なお、平均結晶粒径の測定方法としては、シートを厚み方向に切断し、断面をエッチング・研磨して金属顕微鏡で断面層の金属組織を観察する方法が一例としてあげられる。本願発明においても平均結晶粒径は上記方法で測定した。
【００１２】
前記シートの中心層が０．０００１質量％以上、０．１質量％以下の銀（Ａｇ）を含むと更に好ましい。
【００１３】
上述したように大きな結晶粒径は、耐食性改善に有効であるが、Ａｇを特に中心層に少量添加することによって耐食性がさらに向上することを見出した。その添加量は、０．０００１質量％より少ないと、その効果が十分でなく、０．１質量％より多くしても、耐食性の改善効果がそれ以上期待できないことから、０．０００１質量％以上、０．１質量％以下が好ましい。
【００１４】
―
【００１５】
上記３層構造のシートを加工して作製した格子を正極板に使用した場合、寿命劣化の主原因である正極格子の腐食が抑制され、長寿命の鉛蓄電池が得られる。
【００１６】
【発明の実施の形態】
図１は本発明の実施の形態を模式的に示す鉛合金シートの断面図で、１１は上表層、１２は下表層、２は内層をそれぞれ示す。
【００１７】
図１に示すように、上表面層を含む上表層１１、下表面層を含む下表層１２および中心層を含む内層２の３層構造からなり、上表層１１および下表層１２の平均結晶粒径を内層２のそれに比べて小さい金属組織にしたもので、シートの加工に際しては、上・下表層１１、１２の小さい平均結晶粒径の利点が生かされ加工性に優れ、しかも該シートから作製した格子を正極板に用いた場合には、内層２の大きな平均結晶粒径の利点が生かされ、腐食量が低減され、高温下での強度低下による正極板の伸びも少なく長寿命の鉛蓄電池が得られる。
【００１８】
さらに、前記中心層のみあるいは中心層ならびに上・下表面層に銀（Ａｇ）を添加すれば、耐食性が一層改善されるというものである。
【００１９】
上記では上・下表層と内層との３層構造について説明したが、上・下表面層と中心層との間に、表面層の平均結晶粒径と中心層の平均結晶粒径の間の平均結晶粒径を持つ中間層があってもよい。
【００２０】
【実施例】
本発明を実施例に基づき具体的に説明する。
（実施例１）
実施例１では本発明の請求項１の効果を具体的に示すために行った試験結果について述べる。
【００２１】
Ｐｂ−０．０６質量％Ｃａ−１．３質量％Ｓｎ合金（以降質量は省略）を用い、大きい平均結晶粒径を有するシートの上面および下面に小さい平均結晶粒径を有するシートを当接した後、圧延によって３層を圧着して一体化した３層構造のシートを作製した。その際、大きい平均結晶粒径を有するシートは、鋳造法により作製し、鋳造条件を変えて結晶粒径の異なる２種類のシートを作製した。それらを圧延してさらに平均結晶粒径の異なるシートを作製した。また、小さい平均結晶粒径を有するシートは、多段圧延ロールプレスにより作製し、圧延条件を変えて結晶粒径の異なる３種類のシートを作製した。これらシートを適宜組み合せて３層のシートを圧着により一体化すると共に、前記圧着時の圧延条件を変えることによって、表層および内層の平均結晶粒径の異なるシートを作製した。それらシートの内容を表１に示す。その際、シートの総厚みを１０００μｍとし、上・下表面層を含む上・下表層の厚みがそれぞれ２５０μｍ（合計５００μｍ）、中心層を含む内層の厚みが５００μｍにそれぞれなるように調製した。
【００２２】
従来品は多段圧延式ロールプレスにより厚み１０ｍｍの１枚のスラブから圧延して１層からなる１０００μｍのシートを作製した。前記シートは、平均結晶粒径は約１０μｍを有していた。
【００２３】
【表１】

【００２４】
このようにして作製した上記鉛合金シートを、常法のロータリーエキスパンド加工により格子を作製した。該格子に正極用のペースト状原料を充填した後、熟成、乾燥を経て、未化成正極板を作製した。この正極板と常法により作製したエキスパンド格子からなる負極板および微孔性のポリエチレンを主体としたセパレータとを組み合せてＪＩＳＤ５３０１に規定される５５Ｄ２３型の自動車用鉛蓄電池を作製した。この蓄電池に所定比重、所定量の希硫酸を注入して化成を行い、蓄電池を完成させた。
【００２５】
これらの蓄電池をＪＩＳＤ５３０１に準ずる軽負荷寿命試験に供した。寿命試験条件を以下に示す。
試験温度：水槽７５℃
放電：２５Ａで４分間
充電：１４．８Ｖ（制限充電電流：２５Ａ）で１０分間
寿命試験は、３，０００サイクルで終了し、そのときの正極板の最大伸びを調査した。その結果を表２に示す。これらの鉛合金シートをエキスパンド加工した時の不良率（加工時に格子桟が破断した割合）を調査した結果も併せて記載した。
【００２６】
加工時の不良率および正極板の最大伸びは、従来品Ｎｏ．１の値を１０とした時の比率で表した。
【００２７】
【表２】

【００２８】
表２に示すように、多段圧延式ロールプレスにより作製した１層からなる平均結晶粒径約１０μｍを有する従来品のシートの加工性はよいが、該シートから加工された格子を用いた正極板の最大伸びが大きかった。一方、本発明の３層構造からなるシートは、シートの加工性が従来品と変わらず、しかもそのシートを加工して作製した格子からなる正極板の最大伸びは大幅に低減できた。
【００２９】
上・下表層の平均結晶粒径に関しては、従来品の１０μｍに対して、さらに平均結晶粒径を約５μｍと小さくしたＮｏ．３、Ｎｏ．５、Ｎｏ．７およびＮｏ．９ではシートの加工性が従来品より約１０％改善された。
【００３０】
一方、正極板の伸びに関しては、表２の結果が示すように、約２５０μｍの正極板の伸びが小さく、内層の平均結晶粒径が小さくなる程、伸びが大きくなる傾向であった。本試験で、内層の平均結晶粒径が約１５μｍと最も小さいＮｏ．８およびＮｏ．９では、正極板の伸びを抑制する効果がかなり劣る結果になり、実用的には、２５μｍ以上が好ましいことがわかった。一方、平均結晶粒径が約２５０μｍより大きい場合は、実用的なシートの総厚みが１０００μｍ程度なので、２５０μｍより大きな平均結晶粒径を有するシートは実用性がなく、２５０μｍ程度が限度といえる。
（実施例２）
実施例２では、シートの上・下表面層を含む上・下表層および中心層を含む内層の厚みを種々変えた場合のシートの加工性ならびに該シートから得た正極板の耐食性について試験した結果について説明する。
【００３１】
実施例１と同じ組成の合金のシートを用いて、シートの総厚みを１０００μｍとし、平均結晶粒径が約１００μｍである中心層を含む内層と約１０μｍの上・下表面層を含む上・下表層との厚み比率を変えたシートを、原料となるシートの厚みおよび圧延条件を種々変えて、３層を圧着して一体化する方法で作製した。その内容を表３に示す。
【００３２】
【表３】

【００３３】
このようにして作製した上記鉛合金シートを、常法のロータリーエキスパンド加工方式により格子を作製し、実施例１と同じ蓄電池を作製すると共に、ＪＩＳＤ５３０１に準ずる軽負荷寿命試験に供した。試験は、３，０００サイクルで終了し、正極板の最大伸びを求めた。また、これらの鉛合金シートをエキスパンド加工した時の不良率を調査した結果も併せて記載した。加工時の不良率および正極板の最大伸びは、実施例１のＮｏ．１の結果を流用し、その値を１０とした時の比率で表した。試験結果を表４に示す。
【００３４】
【表４】

【００３５】
表４に示すように、平均結晶粒径が約１０μｍからなる上・下表層の合計の厚み比率がシートの総厚み１に対して０．１であるＮｏ．１０は、小さい平均結晶粒径の金属組織の厚み比率が小さいために、従来品のＮｏ．１に比べてエキスパンド加工時の加工性が１０％劣る結果となったが、内層の平均結晶粒径が約１００μｍと大きい効果により、正極板の最大伸びは約５０％低減された。上・下表層の合計の厚み比率をシートの総厚みの０．２にしたＮｏ．１１は、加工時の不良率が従来品並になり、正極板の耐食性も優れ、本発明の効果が明らかになった。しかし、平均結晶粒径の大きい内層の比率が小さくなると、内層の効果が低減し、正極板の伸びが大きくなる傾向であった。したがって、内層の比率が０．１であるＮｏ．１７では正極板の最大伸びの抑制効果があまり得られない結果となった。したがって、シート厚みに対する上・下表層の合計厚み比率は０．２（２０％）以上、０．８（８０％）以下が好ましいことが分かった。
【００３６】
以上の結果が、上・下表面層をシートの総厚みのそれぞれ１０％、中心層を総厚みの２０％と定義したよりどころになっている。
【００３７】
実施例では、平均結晶粒径の小さい上・下表層と粒径の大きい内層の３層からなるシートを作製するにあたって、それぞれ別々のシートを圧着等により一体化する方法について説明したが、圧延方法を工夫することによって単一のスラブで上・下表層の平均結晶粒径が内層のそれに比べて細かい金属組織を有するシートを得ることできる。例えば、多段圧延式ロールプレスにより順次圧延して所望の厚みのシートを得る方式において、通常、ロールの軸はシートの進行方向に対して９０度に設定されているが、ロールプレスの内、少なくとも１段のロールの軸をシートの進行方向に対して９０度より小さい角度に設定することにより、シートがそのロールを通過する際に、シートの表面が内部に比べて大きな摩擦力を受けることになり、上・下表層の平均結晶粒径が内層のそれに比べて小さい金属組織を有するシートが得られることがわかった。
【００３８】
また、多段圧延式ロールプレスにおいて、通常は上・下のロールの線速度は同じに設定されているが、上記ロールプレスの内、少なくとも１段の上・下のロールの線速度を変える方式を採用することによっても、ロール軸の角度を９０度から小さくした場合と同様のシートが得られることを本願発明者は見出した。
（実施例３）
実施例３では、中心層へのＡｇの添加効果を実証するために行った試験結果について述べる。
【００３９】
最終シートの厚みを１０００μｍとして、中心層を含む内層の厚みを５００μｍ、上・下表面層を含む上・下表層の厚みをそれぞれ２５０μｍとした。また、平均結晶粒径に関しては、上・下表層を約１０μｍ、内層のそれを約１００μｍとした。上・下表層の合金組成は実施例１および２と同じＰｂ−０．０６％Ｃａ−１．３％Ｓｎとし、内層の合金組成は、Ｐｂ−０．０６％Ｃａ−１．３％Ｓｎ−Ａｇとし、Ａｇの量を０％から０．２％まで変えたシートを準備し、上・下表層と内層の３層を圧着により一体化してシートを作製した。比較として、総厚み１０００μｍで平均結晶粒径が１００μｍの金属組織のみで構成され、合金組成がＰｂ−０．０６％Ｃａ−１．３％Ｓｎ−０．０１％Ａｇであるシートも試験に供した。それらシートの内容を表５に示す。
【００４０】
【表５】

【００４１】
上記鉛合金シートを、実施例１と同様、常法のロータリーエキスパンド加工方式により格子を作製し、実施例１と同じ蓄電池を作製すると共に、ＪＩＳＤ５３０１に準ずる軽負荷寿命試験に供した。試験は、３，０００サイクルで終了し、正極板の最大伸びを求めた。また、シートを加工した際の不良率の調査結果も併せて記載した。その試験結果を表６に示す。平均結晶粒径が約１０μｍの１層からなる従来品は、実施例１のＮｏ．１の蓄電池のデータを流用し、エキスパンド加工時の不良率および正極板の最大伸びは、これらの値を１０とした時の比率で表した。また、３層からなるシートで中心層にＡｇを含有しないものは、実施例２のＮｏ．１３の蓄電池のデータを流用した。
【００４２】
【表６】

【００４３】
表６に示すように、シートを３層にした本発明品（Ａ）のＮｏ．１３の蓄電池は、既に実施例２で示したように１層からなる従来品Ｎｏ．１と同様の加工性を維持しながら正極板の最大伸びが大幅に低減されたが、その構造で内層にＡｇを添加することによって正極板の最大伸びがさらに抑制されることがわかった。Ａｇの添加量が０．０００１％である比較品Ｎｏ．１８では、Ａｇの効果は認められなかったが、０．０００５％添加したＮｏ．１９の正極板の最大伸びは従来品に比べて６０％低減され、その効果が明らかに認められるようになり、添加量が増加するにしたがって正極板の最大伸びが低減された。しかし、添加量０．１％のＮｏ．２２と０．２％のＮｏ．２３とではその差がほとんどなく、それ以上Ａｇの添加量を多くしても正極板伸びの抑制効果が得られないことが分かった。したがって、シートの中心層を含む内層に添加するＡｇの量は、０．０００１％以上、０．１％以下が好ましいことが明らかになった。
【００４４】
また、シートの平均結晶粒径が約１００μｍの１層からなり、合金組成がＰｂ−０．０６％Ｃａ−１．３％Ｓｎ−０．０１％Ａｇであるシートを用いたＮｏ．２４の蓄電池では、Ｎｏ．１に比べて平均結晶粒径が１００μｍと大きいこととＡｇの効果とが相まって、正極板の最大伸びは、大幅に改善された。しかし、平均結晶粒径が約１００μｍと大きいためにシートの加工性が、従来品のＮｏ．１より２０％劣った。
【００４５】
以上のように、３層構造にすると共に、内層にＡｇを添加することにより、３層構造の優れた耐食性がさらに改善されることがわかった。
（実施例４）
実施例４では、上・下表面層を含む上・下表層と中心層を含む内層の厚み構成および各層の平均結晶粒子径を実施例３と同じにして、上・下表層および内層に含まれるＣａ、ＳｎおよびＡｇの量を変えた場合のシートの加工性および正極板の伸びに及ぼす影響について調べた。また、実施例３では、Ａｇの添加は内層にのみに限った内容であったが本実施例では３層のいずれにもＡｇを添加したシートをも作製し、その影響についても調べた。シートの作製方法は実施例１と同様、上・下表層と内層の３層を圧着により一体化してシートを作製した。合金組成の内容を表７に示す。
【００４６】
【表７】

【００４７】
上記合金組成のシートを実施例１と同様、常法のロータリーエキスパンド加工により格子を作製し、実施例１と同じ蓄電池を作製すると共に、ＪＩＳＤ５３０１に準ずる軽負荷寿命試験に供した。試験は、３，０００サイクルで終了し、正極板の最大伸びを求めた。また、シートを加工した際の不良率の調査結果も併せて記載した。その試験結果を表８に示す。
【００４８】
平均結晶粒径が約１０μｍの金属組織１層からなる従来品は、実施例１のＮｏ．１の蓄電池のデータを流用し、エキスパンド加工時の不良率および正極板の最大伸びは、これらの試験結果の値を１０とした時の比率で表した。また、３層からなるシートで内層にＡｇを含まず、Ｐｂ−０．０６％Ｃａ−１．３％Ｓｎ合金のシートを用いた蓄電池は、実施例２のＮｏ．１３のデータを流用し、上・下表層の合金組成がＰｂ−０．０６％Ｃａ−１．３％Ｓｎで、中心層を含む内層がＰｂ−０．０６％Ｃａ−１．３％Ｓｎ−０．０１％Ａｇの３層からなるシートを用いた蓄電池は、実施例３のＮｏ．２１のデータをそれぞれ流用した。
【００４９】
【表８】

【００５０】
表８に示すように、３層にしたシートで、Ｓｎの含有量を１．３％に固定してＣａの含有量を０．０３％にしたＮｏ．２５と０．０６％にしたＮｏ．１３の蓄電池を比較した場合、エキスパンド加工時の不良率および寿命試験後の正極板の最大伸びのいずれにもほとんど差はなく、Ｃａ量の影響は認められなかった。
【００５１】
Ｓｎの含有量についても、Ｃａの含有量０．０３％および０．０６％について、Ｓｎの含有量を０．５、１．０および１．３％と変えたが、この場合もエキスパンド加工時の不良率および寿命試験後の正極板の最大伸びのいずれにもほとんど差はなく、Ｓｎの含有量も影響ないことがわかった。
【００５２】
また、上・下表層の合金組成がＰｂ−０．０３％Ｃａ−０．５％ＳｎおよびＰｂ−０．０３％Ｃａ−１．０％Ｓｎで、内層の合金組成がＰｂ−０．０３％Ｃａ−０．５％Ｓｎ−０．０３％ＡｇおよびＰｂ−０．０３％Ｃａ−１．０％Ｓｎ−０．０３％Ａｇの構成にしたシートを用いた蓄電池Ｎｏ．３０およびＮｏ．３１は、実施例３で示したＮｏ．２１と同様、Ａｇの効果により耐食性が増加したが、Ｓｎの量０．５％と１．０％では差は認められなかった。
【００５３】
さらに、上・下表層および内層の３層のいずれにもＡｇを添加したＰｂ−０．０３％Ｃａ−０．５％Ｓｎ−０．０３％Ａｇの構成であるＮｏ．３２あるいはＰｂ−０．０３％Ｃａ−１．０％Ｓｎ−０．０３％Ａｇの構成であるＮｏ．３３の蓄電池は、耐食性に関しては、上・下表層にＡｇの添加されていないＮｏ．３０およびＮｏ．３１と変わらず、内層にＡｇが添加されている効果が大きかったが、エキスパンドの加工時の不良率では、Ａｇの添加によりシートの強度が若干増加することとシートの平均結晶粒径が１０μｍと細かいことと相まって加工性が１０％改善された。ここでもＳｎの添加量０．５％と１．０％では差は認められなかった。
【００５４】
以上の結果から、３層構造にして、上・下表層の平均結晶粒径を内層の平均結晶粒径より小さくする効果が顕著であって各３層中のＣａおよびＳｎの含有量は影響ないことがわかった。
【００５５】
一方、Ａｇについても、ＣａおよびＳｎの含有量に関係なくＡｇを中心層を含む内層に添加することによる耐食性の改善効果が顕著であった。また、内層に加え、上・下表層にもＡｇを添加した場合、Ａｇによりシートの強度が増加することから、エキスパンド加工時の不良率が若干改善されることがわかった。
【００５６】
なお、上・下表層および内層のＡｇを含有し、合金組成がＮｏ．３２およびＮｏ．３３とほぼ同じにしたシートを上述した多段圧延ロールプレスの内、少なくとも１段のロールの軸をシートの進行方向に対して９０度より小さい８５度に設定した方式により作製した。これらシートについても格子を作製し同様の試験に供した結果、Ｎｏ．３２およびＮｏ．３３と同じ結果が得られ、多段圧延ロールプレスの内、少なくとも１段のロールの軸をシートの進行方向に対して９０度より小さくする方式でも本発明の目的が達せられることがわかった。
【００５７】
【発明の効果】
圧延方式で作製された鉛合金シートは、小さい平均結晶粒径の金属組織を有しておりエキスパンド加工に適しているが、それを加工して作製した格子を正極板に使用した場合、これまでの鋳造格子で見られた粒界に沿った局部的な腐食による破断や突然の劣化は発生しなくなるが、格子全体の腐食量が多くなることや再結晶化による強度低下によって変形して伸びるといった現象が見られ、活物質の脱落や対極板との短絡で短寿命となる問題を抱えていた。これに対して、小さい平均結晶粒径の金属組織の優れた加工性を維持しながら、耐食性を改善する方法として、上・下表面層を含む上・下表層の平均結晶粒径を中心層を含む内層のそれより小さくしたシートを作製し、該シートをエキスパンド等の方法で加工した場合、上・下表層の小さい平均結晶粒径の金属組織により従来と変わらない加工性が維持され、しかも、これを加工して作製した格子を正極板に用いた場合に、シートの内層の大きな平均結晶粒径の金属組織により腐食量が低減され、しかも高温下での再結晶化による格子の強度低下に起因する正極板の伸びも抑制され、さらに、特に前記内層にＡｇを少量添加することによりさらに耐食性が改善され、長寿命の鉛蓄電池が得られその工業的効果が極めて大である。
【図面の簡単な説明】
【図１】上・下表面層を含む上・下表層および中心層を含む内層の３層からなるシートを模式的に示した断面図。
【図２】シートの上・下表面層および中心層を定義した模式図。
【符号の説明】
１１上表面層を含む上表層
１２下表面層を含む下表層
２中心層を含む内層[0001]
[Field of the Invention]
About the production how the grid for a lead storage battery.
[0002]
[Prior art]
A power generation element of a lead storage battery has a structure in which an active material is filled in a grid made of lead or a lead alloy. The grid is formed by directly forming lead or lead alloy into a grid shape by casting or the like and forming a grid on the sheet made of lead or lead alloy in order from the both ends of the sheet by moving the die cutter up and down. There are expanding processing methods such as a reciprocating method and a rotary method in which staggered slits are formed in a sheet by rotating a disc-shaped cutter, and the sheet is developed from both sides and the slits are developed in a grid pattern. In recent years, an increasing number of methods for manufacturing a lattice by processing a sheet from the viewpoint of excellent productivity.
[0003]
As a general method for producing the lead alloy sheet as the raw material, there are a continuous casting method, an extrusion method, a rolling method, and the like.
[0004]
[Problems to be solved by the invention]
In general, a continuous casting method or an extrusion method provides a lead alloy sheet having a metal structure having a large average crystal grain size. In that case, the strength is small, and subsequent expansion processing is difficult. In addition, if there is a grain boundary, a lot of energy is accumulated in that part, so if the average crystal grain size of the metal structure is large, the corrosion progresses inward along the grain boundary and the lattice breaks. It also has. However, when the crystal grain boundary is large, the absolute amount of corrosion is small, and recrystallization due to standing at high temperatures hardly occurs, so that there is an advantage that the strength change is small.
[0005]
On the other hand, a sheet obtained by a rolling method has a metal structure having a smaller average crystal grain size than a sheet obtained by casting or extrusion. As a result, the strength is large and the elongation is easy, and the processability at the time of expanding is extremely excellent. Further, since the metal structure is small, there is little corrosion that progresses to the inside like a sheet by casting or extrusion. On the other hand, since there are many crystal grain boundaries, there is a drawback that the amount of corrosion increases. Further, when left at high temperature, there is a problem that recrystallization proceeds and strength decreases. Therefore, if an expanded grid obtained from a lead alloy sheet obtained by rolling is used for the positive electrode plate, it will not break or suddenly deteriorate due to local corrosion along the grain boundaries found in the cast grid, but the entire grid will be corroded. There is a problem that the amount increases, the strength decreases due to recrystallization, especially at high temperatures, and the electrode plate is easily deformed and stretched, and the active material falls off or short-circuits with the counter electrode, resulting in a short life. .
[0006]
The problem to be solved by the present invention is a lead-acid battery that has excellent processability such as expand processing, has a small amount of corrosion of the lattice obtained by the processing, and has a small lattice elongation due to a decrease in strength due to recrystallization at high temperatures. It is providing the manufacturing method of the grating | lattice for batteries, and the lead storage battery excellent in the lifetime performance using the grating | lattice manufactured by it.
[0007]
As a means for solving the problems of the present invention, according to claim 1, in a method for manufacturing a lead-acid battery grid by expanding a lead alloy sheet into a lead-acid battery grid, the sheet includes a central layer and an upper layer. A lower surface layer, wherein the central layer has an average crystal grain size of 25 μm to 250 μm, and the upper and lower surface layers have an average crystal grain size of 10 μm or less.
[0008]
As described above, a metal structure having a small average crystal grain size is excellent in processability for expanding processing and the like, and further, corrosion that proceeds deeply along the crystal grain boundary does not occur. On the other hand, a metal structure having a large average crystal grain size has excellent properties such as a small amount of corrosion, a small decrease in strength at high temperatures during use of the storage battery, and suppression of lattice deformation. The present invention has been made in view of the above, and the upper and lower surface layers of the sheet have a small average crystal grain size, and the center layer has a three-layer structure having a large average crystal grain size. The inventor of the present application has found that the corrosion of the positive electrode plate and the elongation of the electrode plate under high temperature can be reduced by the metal structure of the central layer while maintaining the excellent processing characteristics for the expanding process or the like by the metal structure of the lower surface layer.
[0009]
In the present invention, the “surface layer” means a layer in the range from the upper and lower surfaces of the sheet to 10% of the total thickness of the sheet, and the “center layer” means the thickness above and below the center of the sheet. Occupies 10% of the layer thickness of the sheet, that is, a portion occupying 20% in total. FIG. 2 schematically shows this relationship.
[0010]
In the above definition, as will be described later in the Examples section, the ease of sheet processing due to the small average crystal grain size can be maintained if the thicknesses of the upper and lower surface layers are 10%, respectively. The excellent corrosion resistance due to the large average crystal grain size is due to the fact that if the thickness of the central layer is 20%, it can be ensured.
[0011]
An example of the method for measuring the average crystal grain size is a method of cutting the sheet in the thickness direction, etching and polishing the cross section, and observing the metal structure of the cross section layer with a metal microscope. Also in the present invention, the average crystal grain size was measured by the above method.
[0012]
Before SL center layer of the sheet 0.0001 mass% or more, further preferably 0.1 mass% or less of silver (Ag).
[0013]
As described above, the large crystal grain size is effective in improving the corrosion resistance, but it has been found that the corrosion resistance is further improved by adding a small amount of Ag, particularly in the central layer. If the addition amount is less than 0.0001% by mass, the effect is not sufficient, and even if it is more than 0.1% by mass, no further improvement in corrosion resistance can be expected. 0.1 mass% or less is preferable.
[0014]
-
[0015]
When a grid produced by processing the sheet having the above three-layer structure is used for a positive electrode plate, corrosion of the positive grid, which is the main cause of life deterioration, is suppressed, and a long-life lead-acid battery is obtained.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a cross-sectional view of a lead alloy sheet schematically showing an embodiment of the present invention. 11 is an upper surface layer, 12 is a lower surface layer, and 2 is an inner layer.
[0017]
As shown in FIG. 1, it has a three-layer structure of an upper surface layer 11 including an upper surface layer, a lower surface layer 12 including a lower surface layer, and an inner layer 2 including a central layer, and the average crystal grain size of the upper surface layer 11 and the lower surface layer 12 In the processing of the sheet, the advantage of the small average crystal grain size of the upper and lower surface layers 11 and 12 was utilized, and the processability was excellent, and the sheet was produced from the sheet. When the grid is used for the positive electrode plate, the advantage of the large average crystal grain size of the inner layer 2 is utilized, the amount of corrosion is reduced, and the positive electrode plate is less stretched due to the strength decrease at high temperature. can get.
[0018]
Furthermore, if silver (Ag) is added only to the center layer or to the center layer and the upper and lower surface layers, the corrosion resistance is further improved.
[0019]
In the above description, the three-layer structure of the upper and lower surface layers and the inner layer has been described, but the average between the average crystal grain size of the surface layer and the average crystal grain size of the central layer is between the upper and lower surface layers and the central layer. There may be an intermediate layer having a crystal grain size.
[0020]
【Example】
The present invention will be specifically described based on examples.
Example 1
Example 1 describes the results of tests conducted to specifically demonstrate the effect of claim 1 of the present invention.
[0021]
Using a Pb-0.06 mass% Ca-1.3 mass% Sn alloy (hereinafter omitted), a sheet having a small average crystal grain size was brought into contact with an upper surface and a lower surface of a sheet having a large average crystal grain size. Thereafter, a three-layer sheet integrated by pressing the three layers by rolling was produced. At that time, a sheet having a large average crystal grain size was produced by a casting method, and two types of sheets having different crystal grain sizes were produced by changing the casting conditions. They were rolled to produce sheets with different average crystal grain sizes. Moreover, the sheet | seat which has a small average crystal grain diameter was produced by the multistage rolling roll press, and three types of sheets from which a crystal grain diameter differs were produced by changing rolling conditions. These sheets were appropriately combined to integrate the three-layer sheets by pressure bonding, and the rolling conditions during the pressure bonding were changed to produce sheets having different average crystal grain sizes for the surface layer and the inner layer. Table 1 shows the contents of these sheets. At that time, the total thickness of the sheet was 1000 μm, the upper and lower surface layers including the upper and lower surface layers were each 250 μm (total 500 μm), and the inner layer including the center layer was 500 μm in thickness.
[0022]
The conventional product was rolled from one slab having a thickness of 10 mm by a multi-stage rolling roll press to produce a 1000 μm sheet consisting of one layer. The sheet had an average crystal grain size of about 10 μm.
[0023]
[Table 1]

[0024]
A lattice was produced from the lead alloy sheet thus produced by a conventional rotary expanding process. After filling the lattice with a paste-form raw material for the positive electrode, aging and drying were performed to produce an unformed positive electrode plate. This positive electrode plate was combined with a negative electrode plate made of an expanded lattice produced by a conventional method and a separator mainly composed of microporous polyethylene to produce a 55D23 type lead acid battery for automobiles defined in JIS D 5301. A predetermined specific gravity and a predetermined amount of dilute sulfuric acid were injected into this storage battery for chemical conversion to complete the storage battery.
[0025]
These storage batteries were subjected to a light load life test according to JIS D 5301. The life test conditions are shown below.
Test temperature: Water tank 75 ° C
Discharge: 4 minutes at 25 A Charge: 14.8 V (limited charge current: 25 A) The 10-minute life test was completed in 3,000 cycles, and the maximum elongation of the positive electrode plate at that time was investigated. The results are shown in Table 2. The results of investigating the defect rate when the lead alloy sheets were expanded (the rate at which the grid bars broke during processing) were also listed.
[0026]
The defect rate at the time of processing and the maximum elongation of the positive electrode plate are the same as those of conventional products. It was expressed as a ratio when the value of 1 was 10.
[0027]
[Table 2]

[0028]
As shown in Table 2, the workability of a conventional sheet having an average crystal grain size of about 10 μm made of one layer produced by a multi-stage rolling roll press is good, but a positive electrode plate using a lattice processed from the sheet The maximum growth of was large. On the other hand, the sheet having the three-layer structure of the present invention has the same processability as that of the conventional product, and the maximum elongation of the positive electrode plate made of a lattice produced by processing the sheet can be greatly reduced.
[0029]
Regarding the average crystal grain size of the upper and lower surface layers, the average crystal grain size is about 5 μm smaller than that of the conventional product of 10 μm. 3, no. 5, no. 7 and no. In No. 9, the workability of the sheet was improved by about 10% compared to the conventional product.
[0030]
On the other hand, by regarding the elongation of the positive electrode plate, as shown by the results in Table 2, small elongation of the positive electrode plate of about 250 [mu] m, greater the average crystal grain size of the inner layer is reduced, tended elongation increases . In this test, the average grain size of the inner layer was about 15 μm, the smallest No. 8 and no. In No. 9, the effect of suppressing the elongation of the positive electrode plate was considerably inferior, and it was found that practically 25 μm or more is preferable. On the other hand, when the average crystal grain size is larger than about 250 μm, the total thickness of the practical sheet is about 1000 μm. Therefore, a sheet having an average crystal grain size larger than 250 μm is not practical and can be said to be about 250 μm.
(Example 2)
In Example 2, the test results of the workability of the sheet when the thicknesses of the upper and lower surface layers including the upper and lower surface layers of the sheet and the inner layer including the center layer were variously changed and the corrosion resistance of the positive electrode plate obtained from the sheet were tested. Will be described.
[0031]
Using an alloy sheet having the same composition as in Example 1, the total thickness of the sheet is 1000 μm, and the upper and lower surfaces include an inner layer including a central layer having an average crystal grain size of approximately 100 μm and upper and lower surface layers of approximately 10 μm. Sheets with different thickness ratios with the surface layer were prepared by a method in which the thickness of the sheet used as a raw material and the rolling conditions were varied, and the three layers were bonded together by pressing. The contents are shown in Table 3.
[0032]
[Table 3]

[0033]
The lead alloy sheet produced as described above was used to produce a lattice by a conventional rotary expanding processing method, to produce the same storage battery as that of Example 1, and to be subjected to a light load life test in accordance with JISD 5301. The test was completed in 3,000 cycles, and the maximum elongation of the positive electrode plate was determined. Moreover, the result of investigating the defective rate when these lead alloy sheets were expanded was also described. The defect rate during processing and the maximum elongation of the positive electrode plate are the same as in No. 1 of Example 1. The result of 1 was diverted and expressed as a ratio when the value was 10. The test results are shown in Table 4.
[0034]
[Table 4]

[0035]
As shown in Table 4, the total thickness ratio of the upper and lower surface layers having an average crystal grain size of about 10 μm is 0.1 with respect to the total thickness 1 of the sheet. No. 10 is a conventional product No. 10 because the thickness ratio of the metal structure having a small average crystal grain size is small. Although the processability at the time of expanding was inferior by 10% compared to 1, the maximum elongation of the positive electrode plate was reduced by about 50% due to the effect that the average crystal grain size of the inner layer was about 100 μm. No. in which the total thickness ratio of the upper and lower surface layers is 0.2 of the total thickness of the sheet. No. 11 has a defect rate at the time of processing comparable to that of conventional products, and the corrosion resistance of the positive electrode plate is excellent, and the effect of the present invention has been clarified. However, when the ratio of the inner layer having a large average crystal grain size is decreased, the effect of the inner layer is reduced and the elongation of the positive electrode plate tends to be increased. Therefore, the ratio of the inner layer is 0.1. In No. 17, the effect of suppressing the maximum elongation of the positive electrode plate was not obtained so much. Therefore, it was found that the total thickness ratio of the upper and lower surface layers to the sheet thickness is preferably 0.2 (20%) or more and 0.8 (80%) or less.
[0036]
The above results are the basis for defining the upper and lower surface layers as 10% of the total thickness of the sheet and the center layer as 20% of the total thickness, respectively.
[0037]
In the examples, in producing a sheet consisting of three layers of upper and lower surface layers having a small average crystal grain size and an inner layer having a large particle size, a method of integrating separate sheets by pressure bonding or the like has been described. By devising, a sheet having a finer metal structure than that of the inner layer can be obtained with a single slab having an average crystal grain size of the upper and lower surface layers. For example, in a method of obtaining a sheet having a desired thickness by sequentially rolling with a multi-stage rolling roll press, the axis of the roll is usually set to 90 degrees with respect to the traveling direction of the sheet. By setting the axis of the roll of one stage to an angle smaller than 90 degrees with respect to the traveling direction of the sheet, when the sheet passes through the roll, the surface of the sheet receives a larger frictional force than the inside. Thus, it was found that a sheet having a metal structure having an average crystal grain size of the upper and lower surface layers smaller than that of the inner layer can be obtained.
[0038]
In multi-stage rolling roll presses, the linear speeds of the upper and lower rolls are usually set to be the same, but a method of changing the linear speed of at least one upper and lower roll of the roll presses described above. The inventor of the present application has found that the same sheet as that obtained when the angle of the roll shaft is reduced from 90 degrees can be obtained also by adopting it.
(Example 3)
Example 3 describes the results of tests conducted to demonstrate the effect of adding Ag to the central layer .
[0039]
The thickness of the final sheet was 1000 μm, the thickness of the inner layer including the center layer was 500 μm, and the thicknesses of the upper and lower surface layers including the upper and lower surface layers were 250 μm. Regarding the average crystal grain size, the upper and lower surface layers were about 10 μm and the inner layer was about 100 μm. The alloy composition of the upper and lower surface layers is the same as Pb-0.06% Ca-1.3% Sn as in Examples 1 and 2, and the alloy composition of the inner layer is Pb-0.06% Ca-1.3% Sn- A sheet was prepared in which the amount of Ag was changed from 0% to 0.2%, and the upper and lower surface layers and the inner layer were integrated by pressure bonding to produce a sheet. As a comparison, a sheet having only a metal structure with a total thickness of 1000 μm and an average crystal grain size of 100 μm and having an alloy composition of Pb-0.06% Ca-1.3% Sn-0.01% Ag is also used for the test. did. Table 5 shows the contents of these sheets.
[0040]
[Table 5]

[0041]
As in Example 1, the above lead alloy sheet was prepared in the same manner as in Example 1 by using a conventional rotary expanding method to produce a storage battery, and subjected to a light load life test in accordance with JIS D5301. The test was completed in 3,000 cycles, and the maximum elongation of the positive electrode plate was determined. In addition, the survey results of the defective rate when the sheet was processed are also shown. The test results are shown in Table 6. The conventional product consisting of one layer having an average crystal grain size of about 10 μm is No. 1 in Example 1. The data of 1 storage battery was diverted, and the defect rate and the maximum elongation of the positive electrode plate during the expansion process were expressed as ratios when these values were 10. In addition, the three-layer sheet that does not contain Ag in the center layer is No. 2 in Example 2. Data from 13 storage batteries were used.
[0042]
[Table 6]

[0043]
As shown in Table 6, the No. of the product (A) of the present invention having three sheets of sheets. As shown in Example 2, the storage battery of No. 13 is a conventional product No. 1 consisting of one layer. Although the maximum elongation of the positive electrode plate was significantly reduced while maintaining the same processability as in No. 1, it was found that the maximum elongation of the positive electrode plate was further suppressed by adding Ag to the inner layer in the structure. Comparative product No. in which the addition amount of Ag is 0.0001%. 18, the effect of Ag was not observed, but No. 18 added with 0.0005%. The maximum elongation of 19 positive electrode plates was reduced by 60% compared to the conventional product, and the effect was clearly recognized. The maximum elongation of the positive electrode plate was reduced as the amount added was increased. However, no. No. 22 and 0.2% No. It was found that there was almost no difference from the sample No. 23, and that the effect of suppressing the positive electrode plate elongation could not be obtained even if the amount of Ag added was increased. Therefore, it has been clarified that the amount of Ag added to the inner layer including the central layer of the sheet is preferably 0.0001% or more and 0.1% or less.
[0044]
No. 1 using a sheet having an average crystal grain size of about 100 μm and an alloy composition of Pb-0.06% Ca-1.3% Sn-0.01% Ag. In the case of 24 storage batteries, The maximum elongation of the positive electrode plate was significantly improved due to the combined effect of Ag and the large average crystal grain size of 100 μm compared to 1. However, since the average crystal grain size is as large as about 100 μm, the workability of the sheet is no. 20% worse than 1.
[0045]
As described above, it was found that the excellent corrosion resistance of the three-layer structure was further improved by adding Ag to the inner layer while making the three-layer structure.
Example 4
In Example 4, the thickness structure of the upper and lower surface layers including the upper and lower surface layers and the inner layer including the central layer and the average crystal particle diameter of each layer are the same as those in Example 3, and are included in the upper and lower surface layers and the inner layer. The effect on the workability of the sheet and the elongation of the positive electrode plate when the amounts of Ca, Sn and Ag were changed were examined. Further, in Example 3, the addition of Ag was limited to the inner layer only, but in this example, a sheet in which Ag was added to any of the three layers was also produced, and the influence thereof was also examined. In the same manner as in Example 1, the sheet was prepared by integrating the upper and lower surface layers and the inner layer by pressure bonding. The contents of the alloy composition are shown in Table 7.
[0046]
[Table 7]

[0047]
Similarly to Example 1, a sheet having the above alloy composition was prepared by a conventional rotary expanding process to produce a lattice, and the same storage battery as in Example 1 was produced, and a light load life test in accordance with JIS D 5301 was performed. The test was completed in 3,000 cycles, and the maximum elongation of the positive electrode plate was determined. In addition, the survey results of the defective rate when the sheet was processed are also shown. The test results are shown in Table 8.
[0048]
A conventional product consisting of one layer of metal structure with an average crystal grain size of about 10 μm is No. 1 in Example 1. The data of 1 storage battery was diverted, and the defective rate and the maximum elongation of the positive electrode plate during the expansion process were expressed as ratios when the value of these test results was 10. In addition, a storage battery using a sheet made of three layers and not containing Ag in the inner layer and using a sheet of Pb-0.06% Ca-1.3% Sn alloy is No. 2 in Example 2. 13 data is used, the alloy composition of the upper and lower surface layers is Pb-0.06% Ca-1.3% Sn, and the inner layer including the central layer is Pb-0.06% Ca-1.3% Sn- A storage battery using a sheet composed of three layers of 0.01% Ag is No. 3 in Example 3. 21 data were used for each.
[0049]
[Table 8]

[0050]
As shown in Table 8, in the sheet having three layers, the content of Sn was fixed at 1.3% and the content of Ca was 0.03%. No. 25 and 0.06%. When 13 storage batteries were compared, there was almost no difference in any of the defect rate during the expansion process and the maximum elongation of the positive electrode plate after the life test, and the influence of the Ca amount was not recognized.
[0051]
Regarding the Sn content, the Ca content was 0.03% and 0.06%, and the Sn content was changed to 0.5, 1.0, and 1.3%. It was found that there was almost no difference in both the defective rate and the maximum elongation of the positive electrode plate after the life test, and the Sn content was not affected.
[0052]
The upper and lower surface alloy compositions are Pb-0.03% Ca-0.5% Sn and Pb-0.03% Ca-1.0% Sn, and the inner layer alloy composition is Pb-0.03%. Rechargeable battery No. 1 using sheets made of Ca-0.5% Sn-0.03% Ag and Pb-0.03% Ca-1.0% Sn-0.03% Ag. 30 and no. No. 31 is the same as No. 3 shown in Example 3. As with No. 21, the corrosion resistance was increased by the effect of Ag, but no difference was observed between the Sn amount of 0.5% and 1.0%.
[0053]
Furthermore, No. 1 is a structure of Pb-0.03% Ca-0.5% Sn-0.03% Ag in which Ag is added to any of the upper and lower surface layers and the inner layer. No. 32 or Pb-0.03% Ca-1.0% Sn-0.03% Ag No. The No. 33 storage battery is No. with no Ag added to the upper and lower surface layers in terms of corrosion resistance. 30 and no. The effect of adding Ag to the inner layer was great as in the case of 31. However, in the defective rate during processing of the expand, the addition of Ag slightly increased the strength of the sheet and the average crystal grain size of the sheet was 10 μm. Combined with the fine details, the workability was improved by 10%. Again, no difference was observed between the Sn additions of 0.5% and 1.0%.
[0054]
From the above results, the effect of making the average crystal grain size of the upper and lower surface layers smaller than the average crystal grain size of the inner layer with a three-layer structure is remarkable, and the contents of Ca and Sn in each of the three layers are not affected. I understood it.
[0055]
On the other hand, with regard to Ag, the effect of improving the corrosion resistance by adding Ag to the inner layer including the central layer was remarkable regardless of the Ca and Sn contents. Further, it was found that when Ag is added to the upper and lower surface layers in addition to the inner layer, the strength of the sheet is increased by Ag, so that the defect rate during the expanding process is slightly improved.
[0056]
The upper and lower surface layers and the inner layer contain Ag, and the alloy composition is No. 1. 32 and no. A sheet substantially the same as 33 was produced by a system in which at least one roll axis in the multi-stage rolling roll press described above was set to 85 degrees smaller than 90 degrees with respect to the traveling direction of the sheet. As for these sheets, no. 32 and no. The same result as that of No. 33 was obtained, and it was found that the object of the present invention can be achieved even by a method in which the axis of at least one roll of the multi-stage rolling roll press is smaller than 90 degrees with respect to the sheet traveling direction.
[0057]
【Effect of the invention】
The lead alloy sheet produced by the rolling method has a metal structure with a small average crystal grain size and is suitable for expansion processing. However, when a grid produced by processing it is used for a positive electrode plate, Breaking and sudden deterioration due to local corrosion along the grain boundary seen in the cast lattice of, no longer occur, but the amount of corrosion of the entire lattice increases and the deformation decreases due to strength reduction due to recrystallization. The phenomenon was observed, and there was a problem that the life span was shortened due to dropping of the active material or short circuit with the counter electrode plate. On the other hand, as a method for improving the corrosion resistance while maintaining the excellent workability of the metal structure having a small average crystal grain size, the average crystal grain size of the upper and lower surface layers including the upper and lower surface layers is set to the central layer. When a sheet smaller than that of the inner layer is prepared, and the sheet is processed by an expand method or the like, the workability that is not different from conventional ones is maintained by the metal structure of the small average crystal grain size of the upper and lower surface layers, When a grid made by processing this is used for the positive electrode plate, the amount of corrosion is reduced by the metal structure of the large average crystal grain size of the inner layer of the sheet, and the strength of the grid is reduced by recrystallization at high temperature. The resulting elongation of the positive electrode plate is also suppressed, and in particular, by adding a small amount of Ag to the inner layer, the corrosion resistance is further improved, a long-life lead-acid battery is obtained, and its industrial effect is extremely great.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing a sheet composed of three layers of upper and lower surface layers including upper and lower surface layers and an inner layer including a central layer.
FIG. 2 is a schematic diagram defining upper and lower surface layers and a center layer of a sheet.
[Explanation of symbols]
11 Upper surface layer including upper surface layer 12 Lower surface layer including lower surface layer 2 Inner layer including central layer

Claims

In a method for manufacturing a lead storage battery grid by expanding a lead alloy sheet into a lead storage battery grid, the sheet includes a center layer and upper and lower surface layers, and the average crystal grain size of the center layer is 25 μm to 250 μm. The method for producing a lead-acid battery grid, wherein the upper and lower surface layers have an average crystal grain size of 10 μm or less.