JP3887009B2

JP3887009B2 - Steel plate for thinned deep-drawn ironing can and manufacturing method thereof

Info

Publication number: JP3887009B2
Application number: JP2002353905A
Authority: JP
Inventors: 利行上田; 聡史大井; 敏山根; 慎一田屋; 政浩甲斐; 晋一青木
Original assignee: Toyo Kohan Co Ltd
Current assignee: Toyo Kohan Co Ltd
Priority date: 2002-12-05
Filing date: 2002-12-05
Publication date: 2007-02-28
Anticipated expiration: 2022-12-05
Also published as: JP2004183074A

Description

【０００１】
【発明の属する技術分野】
本発明は、食品缶、飲料缶等の容器材料に適用することのできる薄肉化深絞りしごき缶用鋼板およびその製造法に係り、特に、深絞り、しごき加工性に優れ、更に成形後に高い強度が得られるとともに、耐肌荒れ性が良く、薄肉化深絞りしごき缶用途に適した薄肉化深絞りしごき缶用鋼板およびその製造法に関するものである。
【０００２】
【従来の技術】
従来、側面無継目（サイドシームレス）缶の成形法として、表面処理鋼板を成形した後の缶の内外に有機塗料を施す方法と、成形前の鋼板にあらかじめ樹脂フィルムを被覆し、その樹脂フィルムを一種の成形潤滑剤とし、缶側壁となる部分の鋼板を薄肉化する、いわゆる薄肉化絞りしごき缶成形法とがある。後者の例として、本発明者らは先に、金属板の平均結晶粒径及び平均表面粗さを特定することにより、製缶後の対肌荒れ性および耐食性に優れた薄肉化絞り缶用の金属板を提案した（例えば、特許文献１参照）。
【０００３】
しかしながら、従来のあらかじめ樹脂フィルムを被覆した金属板を用いて薄肉化絞り缶を成形すると、完成後の缶側壁が極めて肌荒れしやすいという問題がある。この肌荒れ状態が生ずると、外観上、ムラが生じる。また、鉄板の肌荒れに対し、フィルムが完全に追従できず、成形後の缶にフィルム厚みにムラを生じさせる。このフィルムの薄い箇所は耐食性が懸念される。さらに、肌荒れは、ネック加工性に支障を来すなどの問題もある。
【０００４】
また、樹脂被覆鋼板を用いた絞り缶成形時にヘアーを発生させない絞り成形方法が、開示されている（例えば、特許文献２参照）。しかし、絞り加工後、更に数段のしごきダイスによりしごき加工を施す場合には、ヘアーの発生が抑えられないという問題がある。
【０００５】
また、固溶Ｃ及び固溶Ｎを有効に利用することにより、２ピース缶、３ピース缶の薄肉化に対応した高強度化を達成するとともに、製缶する際の加工性も良好な硬質薄鋼板を得ることも提案されている（例えば、特許文献３参照）。
【０００６】
鋼板の薄肉化深絞りしごき加工前の引張り強度と、加工に伴う加工硬化の挙動とを特定の関係に制御することにより、薄肉化深絞りしごき加工において高い加工度を得ることも提案されている（例えば、特許文献４および特許文献５参照）。
【０００７】
本出願に関する先行技術文献情報として次のものがある。
【０００８】
【特許文献１】
特開平４−３１４５３５号公報
【特許文献２】
特許第２５１３３７９号公報
【特許文献３】
特許第３２８３３１３号公報
【特許文献４】
特開２００２−３１７２４７号公報
【特許文献５】
特開２００２−３１７２４８号公報
【０００９】
【発明が解決しようとする課題】
通常、薄肉化深絞り缶は被覆鋼板を円板状に打ち抜き、これを二段階の絞り加工によって成形される。この二段目の絞り加工（再絞り加工）時においては、フランジ部に高いしわ押え力を加え、缶側壁の絞り−張り出し加工を行なうことにより、缶側壁の厚みを減少させている。
【００１０】
上記の加工法において、例えば、ポリエチレンテレフタレートフィルムを被覆した被覆鋼板を円板状に打ち抜いた後にカップ絞り、しごき加工を行うが、原板が高強度の材料では、しごきの段階で面圧が高くなり、この有機皮膜の切り口が非常に微細だが糸状に裂け、連続製缶時に、その糸状の皮膜（以下、「ヘアー」と略す）が剥がれ落ち、製缶ラインに堆積し、作業性を著しく阻害する。したがって、製缶のしごき加工時までは軟質の材料が望ましい。
【００１１】
一方で、過度の軟質な材料では、成形後の缶の段階で強度がなく、落下などにより、不本意に変形するなどの問題がある。
【００１２】
本発明は上記問題点を解決することを目的とし、有機皮膜金属円板がしごき加工時までは軟質状態を維持し、成形後の２００〜２５０℃の熱処理後に硬質状態となる鋼板であり、しかも加工性に優れ、成形時に大きな肌荒れを生じさせない薄肉化深絞りしごき缶用鋼板およびその製造法を提供することを目的とする。
【００１３】
【課題を解決するための手段】
前記目的を達成するために、本発明の薄肉化深絞りしごき缶用鋼板は、無延伸のポリエステル樹脂からなるフィルムをラミネートした樹脂被覆鋼板であって、鋼板が、Ｃ：０．００１〜０．０１０重量％、Ｓｉ：≦０．０５重量％、Ｍｎ：≦０．９重量％、Ｐ：０．１３１〜０．２００重量％、Ｓ：≦０．０４重量％、Ａｌ：０．００６〜０．０８重量％、Ｎ：０．００１０〜０．０１５重量％、残部Ｆｅおよび不可避的不純物からなり、平均結晶粒径が４．０〜１０．０μｍである低炭素鋼板からなることを特徴とする。
【００１４】
この本発明により有機皮膜金属円板がしごき加工時までは軟質状態を維持し、成形後の２００〜２５０℃の熱処理後に硬質状態となる薄肉化深絞りしごき缶用鋼板を得ることができる。
【００１５】
また、本発明の薄肉化深絞りしごき缶用鋼板は、無延伸のポリエステル樹脂からなるフィルムをラミネートした樹脂被覆鋼板であって、鋼板が、Ｃ：０．００１〜０．０１０重量％、Ｓｉ：≦０．０５重量％、Ｍｎ：≦０．９重量％、Ｐ：０．１３１〜０．２００重量％、Ｓ：≦０．０４重量％、Ａｌ：０．００６〜０．０８重量％、Ｎ：０．００１０〜０．０１５重量％、残部Ｆｅおよび不可避的不純物からなる熱延鋼板を、冷間圧延、過時効処理を含むヒートサイクルによる焼鈍、圧延率０．５〜３０％による調質圧延または２次冷間圧延を順次行い、調質圧延後の鋼板の平均結晶粒径が４．０〜１０．０μｍであることを特徴とする。
【００１６】
本発明の薄肉化深絞りしごき缶用鋼板の製造方法は、無延伸のポリエステル樹脂からなるフィルムをラミネートした樹脂被覆鋼板であって、Ｃ：０．００１〜０．０１０重量％、Ｓｉ：≦０．０５重量％、Ｍｎ：≦０．９重量％、Ｐ：０．１３１〜０．２００重量％、Ｓ：≦０．０４重量％、Ａｌ：０．００６〜０．０８重量％、Ｎ：０．００１０〜０．０１５重量％、残部Ｆｅおよび不可避的不純物からなる熱延鋼板を、冷間圧延、過時効処理を含むヒートサイクルによる焼鈍、圧延率０．５〜３０％による調質圧延または２次冷間圧延を順次行って、調質圧延後の鋼板の平均結晶粒径を４．０〜１０．０μｍとすることを特徴とする。
【００１７】
本発明の薄肉化深絞りしごき缶用鋼板の製造方法によれば、有機皮膜金属円板がしごき加工時までは軟質状態を維持し、成形後の２００〜２５０℃の熱処理後に硬質状態となる薄肉化深絞りしごき缶用鋼板を得ることができるとともに、加工性に優れ、成形時に大きな肌荒れを生じさせない用にして薄肉化深絞りしごき缶用鋼板を製造することができる。
【００１８】
【発明の実施の形態】
次に、本発明の実施の形態を説明する。
【００１９】
本発明の薄肉化深絞りしごき缶用鋼板に、ポリエステル等の樹脂フィルムを被覆し、円板状に打ち抜き、これをカップに絞り、連続かつ高速で、ドライまたはウエット方式のいずれの手法において、しごき加工による製缶加工を行っても、ヘアー問題が起きず、しかも成形後の２００〜２５０℃の焼鈍後に缶強度に優れた薄肉化深絞りしごき缶を成形できる。
【００２０】
本用途は、近年における有機皮膜付き２ピース缶をさらに薄肉化するために、成形における高リダクションが要求される。したがって、しごき成形時に高い面圧が鋼板と成形工具間に発生し、有機皮膜の切り口が糸状に剥がれ落ち、問題化する（ヘアー問題）。そこで、しごき加工時の面圧を低減させるために材料を軟質化させ、成形への荷重を低減させることで、ヘアーを最小限にすることを発案した。したがって、鋼板はＣが０．０１重量％以下の軟質な極低炭素鋼板とする。
【００２１】
また、材料が軟質化すると強度不足により缶特性が劣化する。そこで、成形後に成形による有機皮膜に生じた残留ひずみを除去するための焼鈍（２００〜２５０℃）中に、鋼板の時効硬化を利用し、適切な強度にすることを発案した。
【００２２】
しかし、極低炭素鋼板のため、Ｃによる時効が期待できないため、Ｎによる時効硬化を利用することとする。その際、この効果が十分に発揮できるようにＮと化合し、Ｎの時効効果を抑制するＡｌ量を極力抑えるため、０．００６〜０．０５重量％とした。０．００６重量％未満では、脱酸効果がほとんどないため、添加の効果がなく、０．０５重量％を超えると、Ｎの時効効果を抑制するため、問題がある。
【００２３】
さらに、それだけでは鋼板の結晶粒が１次圧延後の焼鈍の際に粗大化し、成形時の肌荒れ現象を引き起こすために、結晶粒の微細化効果があるＰを０．１３１重量％以上添加し、４．０〜１０．０μｍの結晶粒径とすることとした。
【００２４】
以上の成分範囲の選択により、上記の複数の問題を解決することが可能となった。その他の詳細な成分範囲と規定理由を以下に示す。
【００２５】
熱延鋼板の成分
鋼成分はＣ：０．００１〜０．０１０重量％、Ｓｉ：≦０．０５重量％、Ｍｎ：≦０．９重量％、Ｐ：０．１３１〜０．２００重量％、Ｓ：≦０．０４重量％、Ａｌ：０．００６〜０．０８重量％、Ｎ：０．００１０〜０．０１５重量％、残部Ｆｅおよび不可避的不純物より形成される。
【００２６】
以下に鋼成分の規制理由を述べる。
【００２７】
Ｃは０．０１重量％より多くなると硬質化し、ヘアー問題を引き起こす。そこで、Ｃ量は０．０１重量％以下とする。また、缶強度と結晶粒の粗大化抑制から、０．００１重量％以上とする。
【００２８】
Ｓｉは缶用材料として耐食性に有害な元素であるが、Ａｌキルド鋼としては不可避的に含有される元素であり、上限を０．０５重量％とした。
【００２９】
Ｍｎは不純物であるＳによる熱延中の赤熱脆性を防止するために必要な成分であるが、一方、０．９重量％を越えると絞り加工性が劣化することから上限を０．９重量％とした。
【００３０】
Ｐは結晶粒微細化に有効な成分でる。本材料は極低炭素鋼板で、かつ、下記にも示すようにＡｌ量が少なく、ＡｌＮの析出物が少ない。したがって、結晶粒が大きくなり、成形時の肌荒れを引き起こす。そこで、Ｐにより、結晶粒を微細化するため、その下限を０．１３１重量％とした。一方で過多なＰは耐食性を阻害するため、その上限を０．２００重量％とした。
【００３１】
Ｓは熱延中の赤熱脆性を生じる不純物成分であり、極力少ないことが望ましいが、不可避的に含有される元素であり、上限を０．０４重量％とした。
【００３２】
Ａｌは本発明の規制の中で重要な元素である。通常、２ピース缶は成形のリダクションが高く、非金属介在物への感受性が高い。したがって、製鋼における脱酸剤として清浄性が高い鋼板を得るためにＡｌで行うことが一般的である。また、Ａｌは固浴Ｎと反応してＡｌＮとして析出し、結晶粒の細粒化に寄与するなど鋼板の特性面でも大きな役割を果たす。
【００３３】
しかし、本発明の場合、前述したように成形後の焼鈍において、Ｎの時効により、高強度化を図ることにしている。そこで、過多なＡｌはそのＮ時効効果を妨げる。したがって、その上限を０．０８重量％以下とする。０．００６重量％未満では、脱酸効果がほとんどなく好ましくない。
【００３４】
Ｎは本発明においては時効による缶強度特性を満足するために重要な元素である。Ａｌ量を０．００６〜０．０８重量％、また、ＴｉやＮｂなどの窒化物形成元素も不可避な範囲に規制していれば、Ｃと異なり、析出物になることなく、固溶Ｎとして鋼中に存在することが可能であり、０．００１０重量％以上あれば必要な缶特性が得られる。一方、過多なＮは、必要以上に強度を増し、前述したヘアーの原因となる。また、製鋼時に気泡となり、スラブ表面に割れを生じ易くさせ、構造欠陥になる。したがって、上限を０．０１５重量％以下とした。
【００３５】
スラブ加熱温度、熱間圧延条件は、本発明では特定するものではないが、スラブ加熱温度は、Ｎの積極的分解固溶および熱間圧延温度の安定的確保の見地から、１１００℃以上とするのが望ましい。また、熱間圧延における巻取温度は熱延時のコイル幅方向および長手方向の品質安定性を考慮して下限を４５０℃とし、６５０℃を越えると結晶粒が粗大化し、肌荒れが生じるため、巻取温度は４５０〜６５０℃の範囲が望ましい。
【００３６】
冷間圧延工程
圧下率が７５％未満では、焼鈍工程で鋼板の結晶粒粗大化もしくは混粒化をもたらし、結晶粒を十分細粒化することができないので、冷間圧延の圧下率は７５％を下限とすることが望ましい。また、２ピース缶への絞り、しごき成形のために圧延方向に対する鋼板の極度な成形への異方性は好ましくない。したがって、さらに望ましくは８５〜９０％の圧延率にすることである。
【００３７】
焼鈍工程
本発明においては、鋼板をより軟質化させるために、焼鈍は過時効処理を行うことが望ましいが、極低炭素鋼板のため、過時効効果が十分に発揮されない。したがって、特には規制しないが、必要により、Ｃ量の高い範囲（０．００７〜０．０１重量％）に過時効処理を含むヒートサイクルによる焼鈍を施しても良い。焼鈍は、箱型焼鈍あるいは連続焼鈍のどちらを適用しても良いが、経済性の点で連続焼鈍の方が望ましい。
【００３８】
調質圧延またはＤＲ圧延
調質圧延（ＳＲ，ＳｉｎｇｌｅＲｅｄｕｃｅＲｏｌｌｉｎｇの略）または、ＤＲ圧延（ＤｏｕｂｌｅＲｅｄｕｃｅＲｏｌｌｉｎｇの略、または２次冷間圧延）は、圧延率が０．５〜３０％の範囲であればよい。０．５％未満においては、十分な缶強度が得られず、３０％を越えると鋼板が高強度となり、缶成形加工が困難となる。また、ストレッチャストレインの発生が防止されるため、この範囲が適当である。
【００３９】
本発明においては、過時効処理により前記の鋼中の固溶Ｃ、Ｎを低減してくびれの発生やボイドの連結を抑制して深絞りにおける加工性を向上して、本発明の対象である薄肉化深絞りしごきの加工条件を満たすと共に、圧延率が０．５〜３０％の範囲の調質圧延または２次冷間圧延を行うことによって強度を付与し、これによって、本発明の鋼板は、薄肉化深絞りしごき加工に求められる高度の加工性に併せて加工時の破胴発生を生じない板強度を付与することができる。このように、本発明においては、これら２つの工程が組み合わされて、加工性と板強度それぞれの条件を達成することができる。また、この調質圧延あるいは２次冷間圧延によって極薄厚の缶において求められる所要の缶強度をも達成するものである。この調質圧延あるいは２次冷間圧延は、圧延率等を考慮して適宜選択すればよい。
【００４０】
つぎに、本発明に用いられる鋼板としては、シ−ト状およびコイル状の鋼板、鋼箔およびそれらの鋼板等に表面処理を施したものがあげられる。特に、下層が金属クロム、上層がクロム水和酸化物の２層構造をもつ電解クロム酸処理鋼板あるいは極薄錫めっき鋼板、ニッケルめっき鋼板、亜鉛めっき鋼板およびこれらのめっき鋼板にクロム水和酸化物あるいは上層がクロム水和酸化物、下層が金属クロム層からなる２層構造をもつ表面処理を施したものがポリエステル樹脂との密着性に優れている。
【００４１】
樹脂フィルムのラミネート
本発明に適用する樹脂フィルムは単層フィルムまたは２層以上の複層フィルムのいずれも適用可能であり、熱可塑性樹脂、特にポリエステル樹脂からなるフィルムであることが好ましい。ポリエステル樹脂としては、エチレンテレフタレート、エチレンイソフタレート、ブチレンテレフタレート、ブチレンイソフタレートなどのエステル単位を有するものが好ましく、さらにこれらの中から選択される少なくとも１種類のエステル単位を主体とするポリエステルであることが好ましい。このとき、各エステル単位は共重合されていてもよく、さらには２種類以上の各エステル単位のホモポリマーまたは共重合ポリマーをブレンドして用いてもよい。上記以外のもので、エステル単位の酸成分として、ナフタレンジカルボン酸、アジピン酸、セバシン酸、トリメリット酸などを用いたものなど、またエステル単位のアルコール成分として、プロピレングリコール、ジエチレングリコール、ネオペンチルグリコール、シクロヘキサンジメタノール、ペンタエリスリトールなどを用いたものを用いてもよい。
【００４２】
このポリエステルは、ホモポリエステル或いはコポリエステル、或いはこれらの２種以上からなるブレンド物からなる２種以上のポリエステル層の積層体であってもよい。例えば、ポリエステルフィルムの下層を熱接着性に優れた共重合ポリエステル層とし、その上層を強度や耐熱性更には腐食成分に対するバリアー性に優れたポリエステル層或いは改質ポリエステル層とすることができる。
【００４３】
本発明においては無延伸のポリエステル樹脂からなるフィルムを用いることを前提としており、ポリエステル樹脂フィルムを表面処理鋼板に積層する作業において樹脂が切れたり、ポリエステル樹脂フィルムを積層した表面処理鋼板に絞り加工や絞りしごき加工のような厳しい成形加工を施しても樹脂が削れたり疵付いたりすることがなく、またクラックが生じたり割れたり、さらに剥離することがないようにするため、樹脂の固有粘度を高め、樹脂を強化させる必要がある。
【００４４】
このため、上記のポリエステル樹脂の固有粘度を０．６〜１．４の範囲とすることが好ましく、０．８〜１．２の範囲とすることがより好ましい。固有粘度が０．６未満のポリエステル樹脂を用いた場合は樹脂の強度が極端に低下し、絞り加工や絞りしごき加工を施して成形する缶に適用できない。一方、樹脂の固有粘度が１．４を超えると樹脂を加熱溶融させた際の溶融粘度が極端に高くなり、ポリエステル樹脂フィルムを表面処理鋼板に積層する作業が極めて困難になる。
【００４５】
樹脂フィルムの厚さは単層フィルムの場合は５〜６０μｍであることが好ましく、１０〜４０μｍであることがより好ましい。厚さが５μｍ未満の場合は表面処理鋼板に積層する作業が著しく困難になり、また絞り加工や絞りしごき加工を施した後の樹脂層に欠陥を生じやすく、缶に成形して内容物を充填した際に、腐食成分に対する耐透過性も十分ではない。厚さを増加させると耐透過性は十分となるが、６０μｍを超える厚さにすることは経済的に不利となる。複層フィルムの場合は成形加工性や、耐透過性、あるいは内容物のフレーバーに与える影響などの観点から各層の厚さの比率は変動するが、トータル厚みが５〜６０μｍとなるように、各層の厚さを調整する。
【００４６】
また、樹脂フィルムを製膜加工する際に、樹脂中に必要な特性を損なわない範囲で着色顔料、安定剤、酸化防止剤、滑材などを含有させて、フィルムに製膜してもよい。
【００４７】
無延伸の樹脂フィルムは次のようにして製膜加工する。すなわち、押出機を用いて樹脂ペレットを樹脂の融解温度より２０〜４０℃高い温度で加熱溶融し、溶融樹脂をＴダイからフィルム状に冷却したキャスティングロール上に押し出し、延伸せずに無延伸樹脂フィルムとしてコイラーに巻き取る。
【００４８】
製膜加工された樹脂フィルムを表面処理鋼板に積層するにあたっては、まずコイル状に巻き取られた長尺帯状の表面処理鋼板を解きほどきながら連続的に加熱する。加熱温度は、無延伸樹脂フィルムは樹脂の融解温度以下の温度でも表面処理鋼板に接着することができるが、樹脂フィルム（複層フィルムの場合は表面処理鋼板と接する樹脂層）の融解温度以上に加熱することが好ましい。そして、加熱されて連続的に移動している表面処理鋼板の両面に前記の樹脂フィルムを当接し、１対の加圧ロールで両者を挟み付けて圧着し、直ちに急冷する。以上のようにして本発明の樹脂被覆鋼板が得られる。また、直接、樹脂をコーティングするダイレクト方式でも構わない。
【００４９】
【実施例】
次に、実施例により本発明をさらに説明する。
【００５０】
表１に示す成分の鋼を転炉で溶製し、常法に従い熱間圧延を行い、表２に示すＣＴ（巻取温度）で巻き取り熱延鋼板とした。その熱延鋼板を酸洗し、０．２２〜０．２８ｍｍの厚さに冷間圧延（圧延率：８５％）後、再結晶温度以上で連続焼鈍を行い、焼鈍後、過時効処理を行った。更に、１．５％の圧延率で調質圧延を施し、０．２０ｍｍの板厚とした。
【００５１】
【表１】

【００５２】
【表２】

【００５３】
評価方法
［抗張力（Ｔ．Ｓ．）］
冷延鋼板からＪＩＳ５号試験片を作成し、テンシロンにより抗張力（Ｔ．Ｓ．）を測定した。
【００５４】
ヘアーと機械強度の関係について、上記したが、有機皮膜の種類や成形の条件、缶の種類などにより、ヘアーが顕著化する強度のしきい値は異なる。したがって、ここでは０．２０ｍｍの鋼板厚みにフィルムをラミネートし、円板を打ち抜いた後に、カップ絞り、さらに３段のしごき加工を加えた場合のしきい値を使って説明する。この場合のヘアーが顕著化しない強度のしきい値は、ＪＩＳ５号片の引張試験における抗張力（Ｔ．Ｓ．）が５３０ＭＰａ（＝Ｎ／ｍｍ²）以下である。また、下限は缶強度から２００ＭＰａ以上とする。
【００５５】
［結晶粒径］
実施例及び比較例で作成した冷延鋼板について、結晶の平均粒径（以下、結晶粒径）を測定した
結晶粒径は成形時の肌荒れ防止の観点から、上限は１０．０μｍ以下が望ましい。また、下限は特には規定しないが、過度な微細粒は、上記のボトム耐圧を上昇させることから、４．０μｍ以上が望ましい。
【００５６】
［耐圧］
実施例及び比較例で作成した冷延鋼板に、下層が金属クロム（付着量：１３０ｍｇ／ｍ²）、上層がクロム水和酸化物（付着量：クロムとして１９ｍｇ／ｍ²）の２層構造をもつ電解クロム酸処理を施し、次いで、缶に成形した際に外面側となる面に、エチレンテレフタレート（８８モル％）とエチレンイソフタレート（１２モル％）からなる共重合ポリエステル樹脂（固有粘度：０．８）に酸化チタン系白色顔料を２０重量％含有させてなる、厚さ１５μｍの無延伸フィルムを、缶に成形した際に内面側となる面に、エチレンテレフタレート（８８モル％）とエチレンイソフタレート（１２モル％）からなる厚さ３０μｍの無延伸の透明共重合ポリエステル樹脂フィルムをそれぞれ当接して圧着し、ＰＥＴフィルム被覆鋼板を得た。このＰＥＴフィルムを被覆した鋼板に次に示す薄肉化深絞りしごき加工を行って、製缶した。絞りしごき加工は、上記のようにして作成された樹脂被覆鋼板から直径１５０ｍｍのブランクを打ち抜き、次いで、白色に着色したフィルムを積層した面が容器の外側となるようにして直径９０ｍｍのポンチで絞る絞り工程（絞り比１．６７）、その後、直径６６ｍｍのポンチで再絞り加工する再絞り工程（再絞り比１．３６）に従い実施した。このカップを、３段のしごき加工ダイスからなるしごき成形装置を用いて缶径６６ｍｍ、缶壁上端部の厚さが０．１５ｍｍの絞りしごき缶に成形加工した。
【００５７】
次いで、上端部をトリミングして高さを１２２ｍｍとし、フィルムのひずみ取りのため、２１５℃で３０秒加熱処理した後、上端部を縮径加工して開口端部の径を５７ｍｍとした。次いで、開口端部を缶の外側に向かって張り出し加工し、フランジ端部の径が６２ｍｍとなるようにフランジ部を形成させ、内容物を充填する前の缶とボトム耐圧を測定した。
【００５８】
ボトム耐圧は、缶強度から、６６０ＭＰａ以上が望ましい。一方、耐圧が高すぎると、例えば、高温時に内容物が膨張した際に、ボトムが変形しにくく、缶のキャップの箇所で破裂する現象が生じ、好ましくない。そこで、ボトム耐圧の上限は７８０ＭＰａとする。
【００５９】
［ヘアーの発生］
実施例及び比較例で作成した冷延鋼板に、耐圧性評価方法で示した製缶方法で内容物を充填する前の缶を作製し、加工後の缶の端面にヘアーがあるかどうか肉眼で評価した。
【００６０】
このような評価方法で、評価した結果を下記に示す。
【００６１】
本発明の実施例Ｎｏ．１〜４は本発明の成分範囲内で、また、比較例の１〜５は本発明の成分範囲外である。その鋼の成分範囲を表１に、特性評価結果を表２に示す。なお、表１で、ＣＴは熱延板の巻取温度を示す。また、総合判定はＴ．Ｓ．、結晶粒径、ボトム耐圧およびヘアー発生無の４項目のすべてを満足するものを○、いずれかひとつでも満足しければ×とした。比較例１はＰが０．０２１重量％と本発明範囲より下回る。その場合、表２に示すように結晶粒が１０．２μｍと大きく、成形でも肉眼で判定できるほどの肌荒れが生じた。また、比較例２はＡｌ量が高く、ＡｌＮの効果から、結晶粒径や原板のＴ．Ｓ．は目標の範囲だが、時効硬化性が乏しく、ボトム耐圧が目標の下限を下回った。比較例３は、Ｎ量が０．０００８重量％と少なく、同じくＮ時効の効果が乏しく、ボトム耐圧が下限を下回った。比較例４はＣが０．０４２％と低炭素鋼板の範疇であり、抗張力（Ｔ．Ｓ．）、ボトム耐圧が高く、好ましくない。最後に比較例５はＭｎ量が１．３重量％と高く、抗張力（Ｔ．Ｓ．）、ボトム耐圧が高く、好ましくない。
【００６２】
【発明の効果】
本発明の薄肉化深絞りしごき缶用鋼板にＰＥＴ等の樹脂フィルムを被覆した鋼板は、成形時の軟質化より、連続高速製缶加工時においても、ヘアーが起きず、しかも、結晶粒の粗大化を抑制したため、肌荒れも問題が無い。さらに、Ｎ時効により缶の強度特性であるボトム耐圧に優れた薄肉化深絞りしごき缶用途に適した鋼板を提供することができる。
【００６３】
なお、本発明により提供される薄肉化深絞りしごき缶用鋼板は、樹脂フィルムと鋼板との間にエポキシ等の接着剤をコーティングした場合でも薄肉化深絞りしごき缶用途に適用できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel plate for a thinned deep-drawn ironing can that can be applied to container materials such as food cans and beverage cans, and a method for producing the same, and in particular, has excellent deep-drawing and ironing workability, and further has high strength after molding. In addition, the present invention relates to a steel sheet for a thinned deep-drawn ironing can suitable for use in a thinned deep-drawn ironing can and a method for producing the same.
[0002]
[Prior art]
Conventionally, as a method of forming a side seamless can, a method of applying an organic paint to the inside and outside of a can after forming a surface-treated steel sheet, and coating a resin film on the steel sheet before forming, There is a so-called thinned drawn ironing can forming method in which the steel plate at the portion that becomes the can side wall is thinned as a kind of forming lubricant. As an example of the latter, the present inventors previously specified the average crystal grain size and average surface roughness of the metal plate, thereby making the metal for thinned drawn cans excellent in rough skin resistance and corrosion resistance after canning. The board was proposed (for example, refer patent document 1).
[0003]
However, when a thinned drawn can is formed using a conventional metal plate previously coated with a resin film, there is a problem that the finished side wall of the can is extremely rough. When this rough skin state occurs, unevenness occurs in appearance. In addition, the film cannot completely follow the rough skin of the iron plate, causing unevenness in the film thickness of the molded can. There is a concern about the corrosion resistance of the thin part of the film. Furthermore, rough skin also has problems such as hindrance to neck workability.
[0004]
Moreover, the drawing method which does not generate | occur | produce hair at the time of draw can forming using a resin-coated steel plate is disclosed (for example, refer patent document 2). However, there is a problem in that the occurrence of hair cannot be suppressed when ironing is further performed by several steps of ironing dies after drawing.
[0005]
In addition, by using solid solution C and solid solution N effectively, the strength of the two-piece can and the three-piece can can be increased and the workability when making cans is good. It has also been proposed to obtain a steel plate (see, for example, Patent Document 3).
[0006]
It has also been proposed to obtain a high degree of processing in thinning deep-drawing ironing by controlling the tensile strength before thinning deep-drawing ironing and the behavior of work hardening accompanying processing. (For example, see Patent Document 4 and Patent Document 5).
[0007]
Prior art document information relating to the present application includes the following.
[0008]
[Patent Document 1]
JP-A-4-314535 [Patent Document 2]
Japanese Patent No. 2513379 [Patent Document 3]
Japanese Patent No. 3283313 [Patent Document 4]
JP 2002-317247 A [Patent Document 5]
Japanese Patent Laid-Open No. 2002-317248
[Problems to be solved by the invention]
Usually, a thin-walled deep-drawn can is formed by punching a coated steel plate into a disk shape and drawing it in two stages. At the time of the second stage drawing (redrawing), a high wrinkle pressing force is applied to the flange portion to reduce the thickness of the can side wall by drawing and overhanging the can side wall.
[0010]
In the above processing method, for example, a coated steel sheet coated with a polyethylene terephthalate film is punched into a disk shape, and then cup drawing and ironing are performed. However, if the original sheet is a high-strength material, the surface pressure increases at the ironing stage. The cut surface of this organic film is very fine but tears into a thread, and during continuous canning, the thread-like film (hereinafter abbreviated as “hair”) peels off and accumulates on the can-making line, significantly impairing workability. . Therefore, a soft material is desirable until the ironing process of the can.
[0011]
On the other hand, an excessively soft material has a problem that it does not have strength at the stage of a can after molding and deforms unintentionally due to dropping or the like.
[0012]
The present invention aims to solve the above-mentioned problems, and is a steel sheet that maintains a soft state until the organic film metal disc is ironed and becomes a hard state after heat treatment at 200 to 250 ° C. after forming, An object of the present invention is to provide a thin-walled deep-drawn ironing can steel plate that is excellent in workability and does not cause large skin roughness during forming, and a method for producing the same.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the steel sheet for thinned deep-drawn iron can according to the present invention is a resin-coated steel sheet laminated with a film made of an unstretched polyester resin, and the steel sheet has C: 0.001 to 0.00. 010 wt%, Si: ≤ 0.05 wt%, Mn: ≤ 0.9 wt%, P: 0.131 to 0.200 wt%, S: ≤ 0.04 wt%, Al: 0.006 to 0 0.08% by weight, N: 0.0010 to 0.015% by weight, balance Fe and inevitable impurities , and characterized by comprising a low carbon steel plate having an average crystal grain size of 4.0 to 10.0 μm. .
[0014]
According to the present invention, it is possible to obtain a steel plate for a thinned deep-drawn ironing can that maintains a soft state until the organic film metal disc is ironed and becomes a hard state after heat treatment at 200 to 250 ° C. after forming.
[0015]
Moreover, the steel plate for thinned deep-drawn ironing cans of the present invention is a resin-coated steel plate laminated with a film made of an unstretched polyester resin, and the steel plate has C: 0.001 to 0.010% by weight, Si: ≦ 0.05 wt%, Mn: ≦ 0.9 wt%, P: 0.131 to 0.200 wt%, S: ≦ 0.04 wt%, Al: 0.006 to 0.08 wt%, N : 0.0010-0.015% by weight, hot-rolled steel sheet comprising the balance Fe and inevitable impurities, cold rolling, annealing by heat cycle including overaging treatment, temper rolling at a rolling rate of 0.5-30% Alternatively , secondary cold rolling is sequentially performed, and the average grain size of the steel sheet after the temper rolling is 4.0 to 10.0 μm.
[0016]
The method for producing a steel plate for a thinned deep-drawn ironing can according to the present invention is a resin-coated steel plate laminated with a film made of an unstretched polyester resin, C: 0.001 to 0.010% by weight, Si: ≦ 0 0.05% by weight, Mn: ≦ 0.9% by weight, P: 0.131 to 0.200% by weight, S: ≦ 0.04% by weight, Al: 0.006 to 0.08% by weight, N: 0 A hot-rolled steel sheet composed of .0010 to 0.015% by weight, the balance Fe and unavoidable impurities is subjected to cold rolling, annealing by heat cycle including overaging treatment, temper rolling at a rolling rate of 0.5 to 30% or 2 What sequentially rows next cold rolling, characterized in that the average crystal grain size of the steel sheet after temper rolling with 4.0～10.0Myuemu.
[0017]
According to the manufacturing method of a steel sheet for a thinned deep-drawn ironing can according to the present invention, the organic coated metal disk maintains a soft state until the ironing process and becomes a hard state after heat treatment at 200 to 250 ° C. after forming. It is possible to obtain a steel plate for a deep-drawn ironing can, which is excellent in workability and does not cause a large skin roughness during forming, and a steel plate for a thinned deep-drawing ironing can.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described.
[0019]
The steel plate for thinned deep-drawn ironing cans of the present invention is coated with a resin film such as polyester, punched into a disk shape, drawn into a cup, and squeezed in either a dry or wet method continuously and at high speed. Even if the can-making process is performed, a hair problem does not occur, and a thin-drawn deep-drawn iron can with excellent can strength can be formed after annealing at 200 to 250 ° C. after forming.
[0020]
This application requires a high reduction in molding in order to further reduce the thickness of a two-piece can with an organic film in recent years. Accordingly, a high surface pressure is generated between the steel plate and the forming tool during ironing, and the cut end of the organic film is peeled off into a thread shape and becomes a problem (hair problem). Therefore, it was proposed to minimize the hair by softening the material in order to reduce the surface pressure during ironing and reducing the load on the molding. Accordingly, the steel plate is a soft ultra-low carbon steel plate having C of 0.01% by weight or less.
[0021]
Further, when the material becomes soft, the can characteristics deteriorate due to insufficient strength. Therefore, it has been proposed to use the age hardening of the steel sheet to obtain an appropriate strength during annealing (200 to 250 ° C.) for removing the residual strain generated in the organic film by forming after forming.
[0022]
However, since it is an extremely low carbon steel sheet, aging by C cannot be expected, so age hardening by N is used. At that time, in order to combine this with N so that this effect can be sufficiently exerted, and to suppress the amount of Al that suppresses the aging effect of N as much as possible, the content was made 0.006 to 0.05% by weight. If it is less than 0.006% by weight, there is almost no deoxidation effect, so there is no effect of addition, and if it exceeds 0.05% by weight, there is a problem because the aging effect of N is suppressed.
[0023]
Furthermore, by itself, the crystal grains of the steel sheet are coarsened during annealing after the primary rolling, and in order to cause a rough skin phenomenon during forming, 0.13 wt% or more of P having an effect of refining crystal grains is added, The crystal grain size was set to 4.0 to 10.0 μm.
[0024]
By selecting the component ranges described above, it has become possible to solve the above-described problems. Other detailed component ranges and the reasons for their definition are shown below.
[0025]
The component steel components of the hot-rolled steel sheet are: C: 0.001 to 0.010 wt%, Si: ≤ 0.05 wt%, Mn: ≤ 0.9 wt%, P: 0.131 to 0.200 wt%, S: ≦ 0.04 wt%, Al: 0.006 to 0.08 wt%, N: 0.0010 to 0.015 wt%, remaining Fe and inevitable impurities.
[0026]
The reasons for regulating steel components are described below.
[0027]
When C exceeds 0.01% by weight, it hardens and causes hair problems. Therefore, the C amount is 0.01% by weight or less. Further, in view of can strength and suppression of coarsening of crystal grains, the content is made 0.001% by weight or more.
[0028]
Si is an element harmful to corrosion resistance as a material for cans, but is an element inevitably contained as Al killed steel, and the upper limit was set to 0.05% by weight.
[0029]
Mn is a component necessary for preventing red heat brittleness during hot rolling due to S as an impurity. On the other hand, if it exceeds 0.9% by weight, drawability deteriorates, so the upper limit is 0.9% by weight. It was.
[0030]
P is an effective component for grain refinement. This material is an ultra-low carbon steel sheet, and as shown below, the amount of Al is small and AlN precipitates are small. Accordingly, the crystal grains become large and cause rough skin during molding. Therefore, in order to make the crystal grains finer by P, the lower limit is set to 0.131% by weight. On the other hand, excessive P inhibits corrosion resistance, so the upper limit was made 0.200% by weight.
[0031]
S is an impurity component that causes red hot brittleness during hot rolling, and it is desirable that S be as small as possible. However, S is an element that is inevitably contained, and the upper limit is set to 0.04% by weight.
[0032]
Al is an important element in the regulation of the present invention. Usually, a two-piece can has high molding reduction and high sensitivity to non-metallic inclusions. Therefore, in order to obtain a steel plate having high cleanliness as a deoxidizer in steelmaking, it is common to use Al. Further, Al reacts with the solid bath N and precipitates as AlN, which contributes to the refinement of crystal grains and plays a major role in the characteristics of the steel sheet.
[0033]
However, in the case of the present invention, as described above, in the annealing after molding, the strength is increased by the aging of N. Therefore, excessive Al hinders its N aging effect. Therefore, the upper limit is made 0.08% by weight or less. If it is less than 0.006% by weight, there is almost no deoxidation effect, which is not preferable.
[0034]
N is an important element in the present invention in order to satisfy the can strength characteristics due to aging. If the amount of Al is 0.006 to 0.08% by weight, and if nitride-forming elements such as Ti and Nb are also unavoidably restricted, unlike C, it becomes a solid solution N without becoming a precipitate. It can be present in steel, and if it is 0.0010% by weight or more, the necessary can characteristics can be obtained. On the other hand, excessive N increases the strength more than necessary and causes the hair described above. Moreover, it becomes a bubble at the time of steelmaking, makes it easy to produce a crack in the slab surface, and becomes a structural defect. Therefore, the upper limit was made 0.015% by weight or less.
[0035]
Although the slab heating temperature and hot rolling conditions are not specified in the present invention, the slab heating temperature is set to 1100 ° C. or more from the standpoint of positive decomposition and dissolution of N and stable securing of the hot rolling temperature. Is desirable. Further, the coiling temperature in hot rolling is set to 450 ° C. in consideration of the quality stability in the coil width direction and the longitudinal direction during hot rolling, and if it exceeds 650 ° C., crystal grains become coarse and rough skin occurs. The taking temperature is preferably in the range of 450 to 650 ° C.
[0036]
If the rolling reduction ratio of the cold rolling process is less than 75%, the annealing process leads to the coarsening or mixing of the grains in the steel sheet, and the crystal grains cannot be sufficiently refined, so the rolling reduction ratio of the cold rolling is 75%. Is preferably the lower limit. Moreover, the anisotropy to the extreme forming of the steel sheet with respect to the rolling direction due to drawing and ironing to a two-piece can is not preferable. Therefore, it is more desirable to set the rolling rate to 85 to 90%.
[0037]
Annealing Step In the present invention, in order to soften the steel plate, it is desirable to perform an overaging treatment for annealing, but because of the extremely low carbon steel plate, the overaging effect is not sufficiently exhibited. Therefore, although not specifically regulated, if necessary, annealing by heat cycle including overaging treatment may be performed in a high C amount range (0.007 to 0.01% by weight). As the annealing, either box-type annealing or continuous annealing may be applied, but continuous annealing is more preferable from the viewpoint of economy.
[0038]
Temper rolling or DR rolling temper rolling (SR, abbreviation for Single Reduce Rolling) or DR rolling (abbreviation for Double Reduce Rolling, or secondary cold rolling), the rolling rate is in the range of 0.5-30%. I just need it. If it is less than 0.5%, sufficient can strength cannot be obtained, and if it exceeds 30%, the steel sheet has high strength and can molding is difficult. Also, this range is appropriate because the occurrence of stretcher strain is prevented.
[0039]
In the present invention, the solid solution C and N in the steel is reduced by overaging treatment, and the workability in deep drawing is improved by suppressing the occurrence of constriction and the connection of voids, and is the object of the present invention. While satisfying the processing conditions of thinning and deep drawing ironing, the steel sheet of the present invention is given strength by performing temper rolling or secondary cold rolling with a rolling rate in the range of 0.5 to 30%. Further, in addition to the high workability required for thinning and deep drawing ironing, it is possible to impart a plate strength that does not cause fractures during processing. Thus, in the present invention, these two steps can be combined to achieve the conditions of workability and sheet strength. Further, the required can strength required for an extremely thin can is also achieved by this temper rolling or secondary cold rolling. This temper rolling or secondary cold rolling may be appropriately selected in consideration of the rolling rate and the like.
[0040]
Next, examples of the steel sheet used in the present invention include sheet-shaped and coil-shaped steel sheets, steel foils, and steel sheets that have been surface-treated. In particular, chromic hydrated oxide is applied to electrolytic chromic acid-treated steel sheets or ultrathin tin-plated steel sheets, nickel-plated steel sheets, galvanized steel sheets, and these plated steel sheets, with a lower layer of metallic chromium and an upper layer of chromium hydrated oxide. Alternatively, a surface treatment having a two-layer structure in which the upper layer is a hydrated chromium oxide and the lower layer is a metallic chromium layer is excellent in adhesion to the polyester resin.
[0041]
Lamination of Resin Film The resin film applied to the present invention can be either a single layer film or a multilayer film having two or more layers, and is preferably a film made of a thermoplastic resin, particularly a polyester resin. The polyester resin preferably has an ester unit such as ethylene terephthalate, ethylene isophthalate, butylene terephthalate, butylene isophthalate, and is a polyester mainly composed of at least one ester unit selected from these. Is preferred. At this time, each ester unit may be copolymerized, and further, a homopolymer or copolymer of two or more types of ester units may be blended and used. Other than the above, those using naphthalenedicarboxylic acid, adipic acid, sebacic acid, trimellitic acid, etc. as the acid component of the ester unit, and the alcohol component of the ester unit include propylene glycol, diethylene glycol, neopentyl glycol, Those using cyclohexanedimethanol, pentaerythritol, or the like may be used.
[0042]
This polyester may be a laminate of two or more polyester layers made of homopolyester or copolyester, or a blend of two or more thereof. For example, the lower layer of the polyester film can be a copolymerized polyester layer excellent in thermal adhesion, and the upper layer can be a polyester layer or a modified polyester layer excellent in strength, heat resistance, and barrier properties against corrosive components.
[0043]
In the present invention, on the premise that a film made of unstretched polyester resin is used, the resin breaks in the operation of laminating the polyester resin film on the surface-treated steel sheet, or the surface-treated steel sheet laminated with the polyester resin film is drawn or processed. The resin's intrinsic viscosity is increased so that the resin will not be scraped or wrinkled even after severe molding such as squeezing and ironing, and cracking, cracking, and peeling will not occur. It is necessary to strengthen the resin.
[0044]
For this reason, it is preferable to make the intrinsic viscosity of said polyester resin into the range of 0.6-1.4, and it is more preferable to set it as the range of 0.8-1.2. When a polyester resin having an intrinsic viscosity of less than 0.6 is used, the strength of the resin is extremely reduced, and the resin cannot be applied to a can formed by drawing or ironing. On the other hand, if the intrinsic viscosity of the resin exceeds 1.4, the melt viscosity when the resin is heated and melted becomes extremely high, and the operation of laminating the polyester resin film on the surface-treated steel sheet becomes extremely difficult.
[0045]
In the case of a single layer film, the thickness of the resin film is preferably 5 to 60 μm, and more preferably 10 to 40 μm. If the thickness is less than 5 μm, the process of laminating the surface-treated steel sheet becomes extremely difficult, and the resin layer after drawing or drawing and ironing is likely to be defective, and the can is molded into a can and filled with the contents. However, the permeation resistance to corrosive components is not sufficient. When the thickness is increased, the permeation resistance is sufficient, but it is economically disadvantageous to have a thickness exceeding 60 μm. In the case of a multilayer film, the ratio of the thickness of each layer varies from the viewpoints of molding processability, permeation resistance, or the effect on the flavor of the contents, but each layer has a total thickness of 5 to 60 μm. Adjust the thickness.
[0046]
Further, when the resin film is formed into a film, the resin film may be formed by adding a coloring pigment, a stabilizer, an antioxidant, a lubricant, and the like as long as necessary properties are not impaired in the resin.
[0047]
An unstretched resin film is formed as follows. That is, resin pellets are heated and melted at a temperature 20 to 40 ° C. higher than the melting temperature of the resin using an extruder, the molten resin is extruded from a T die onto a casting roll cooled in a film shape, and the unstretched resin is not stretched. It is wound on a coiler as a film.
[0048]
In laminating the film-formed resin film on the surface-treated steel sheet, first, the long-band surface-treated steel sheet wound in a coil shape is continuously heated while being unwound. The heating temperature of the unstretched resin film can be adhered to the surface-treated steel sheet even at a temperature lower than the melting temperature of the resin, but it is higher than the melting temperature of the resin film (the resin layer in contact with the surface-treated steel sheet in the case of a multilayer film). It is preferable to heat. And the said resin film is contact | abutted on both surfaces of the surface treatment steel plate which is heated and moving continuously, both are pinched and crimped | bonded by a pair of pressure roll, and it cools immediately. The resin-coated steel sheet of the present invention is obtained as described above. Further, a direct method in which a resin is directly coated may be used.
[0049]
【Example】
Next, the present invention will be further described with reference to examples.
[0050]
Steels having the components shown in Table 1 were melted in a converter and hot-rolled in accordance with a conventional method, and a rolled hot-rolled steel sheet was obtained by CT (winding temperature) shown in Table 2. The hot-rolled steel sheet is pickled, cold-rolled to a thickness of 0.22 to 0.28 mm (rolling rate: 85%), then subjected to continuous annealing at a recrystallization temperature or higher, and after annealing, an overaging treatment is performed. It was. Further, temper rolling was performed at a rolling rate of 1.5% to obtain a sheet thickness of 0.20 mm.
[0051]
[Table 1]

[0052]
[Table 2]

[0053]
Evaluation Method [Tensile Strength (TS)]
A JIS No. 5 test piece was prepared from the cold rolled steel sheet, and the tensile strength (TS) was measured with Tensilon.
[0054]
Although the relationship between the hair and the mechanical strength is described above, the strength threshold at which the hair becomes prominent differs depending on the type of organic film, molding conditions, the type of can, and the like. Therefore, here, a description will be given using a threshold value when a film is laminated to a steel plate thickness of 0.20 mm, a disc is punched, a cup squeezing and further three steps of ironing are applied. The threshold value of the strength at which the hair does not become noticeable in this case is that the tensile strength (TS) in the tensile test of JIS No. 5 piece is 530 MPa (= N / mm ² ) or less. Further, the lower limit is 200 MPa or more from the can strength.
[0055]
[Crystal grain size]
With respect to the cold-rolled steel sheets prepared in Examples and Comparative Examples, the upper limit of the crystal grain size obtained by measuring the average grain size (hereinafter referred to as crystal grain size) is preferably 10.0 μm or less from the viewpoint of preventing rough skin during molding. Moreover, although a minimum is not prescribed | regulated in particular, since an excessive fine grain raises said bottom withstand pressure | voltage, 4.0 micrometers or more are desirable.
[0056]
[Pressure resistance]
The cold-rolled steel sheets prepared in Examples and Comparative Examples have a two-layer structure in which the lower layer is metallic chromium (adhesion amount: 130 mg / m ² ) and the upper layer is chromium hydrated oxide (adhesion amount: 19 mg / m ² as chromium). Next, a copolymer polyester resin (inherent viscosity: 0) made of ethylene terephthalate (88 mol%) and ethylene isophthalate (12 mol%) is formed on the outer surface of the can when it is molded into a can. 8) containing 20% by weight of a titanium oxide-based white pigment, an unstretched film having a thickness of 15 μm is formed on the surface that becomes the inner surface side when formed into a can, with ethylene terephthalate (88 mol%) and ethylene Non-stretched transparent copolyester resin films made of phthalate (12 mol%) with a thickness of 30 μm were brought into contact with each other and pressed to obtain PET film-coated steel sheets. The steel sheet coated with this PET film was subjected to the following thinning deep drawing and ironing to produce a can. In the drawing and ironing process, a blank having a diameter of 150 mm is punched from the resin-coated steel sheet prepared as described above, and then the sheet is squeezed with a punch having a diameter of 90 mm so that the surface on which the white colored film is laminated becomes the outside of the container. The drawing process (drawing ratio: 1.67) was performed, followed by a redrawing process (redrawing ratio: 1.36) for redrawing with a punch having a diameter of 66 mm. This cup was molded into a squeezed and ironed can having a can diameter of 66 mm and a can wall upper end of 0.15 mm using an ironing device comprising three stages of ironing dies.
[0057]
Next, the upper end portion was trimmed to a height of 122 mm, and heat treatment was performed at 215 ° C. for 30 seconds to remove the distortion of the film, and then the upper end portion was reduced in diameter to make the diameter of the open end portion 57 mm. Next, the opening end portion was stretched toward the outside of the can, the flange portion was formed so that the diameter of the flange end portion was 62 mm, and the can and the bottom pressure resistance before filling the contents were measured.
[0058]
The bottom pressure resistance is preferably 660 MPa or more in terms of can strength. On the other hand, when the pressure resistance is too high, for example, when the contents expand at a high temperature, the bottom is not easily deformed, and a phenomenon of bursting at the cap portion of the can occurs. Therefore, the upper limit of the bottom pressure resistance is set to 780 MPa.
[0059]
[Generation of hair]
In the cold-rolled steel sheets created in the examples and comparative examples, a can before filling the contents by the can-making method shown in the pressure resistance evaluation method is prepared, and whether there is hair on the end face of the can after processing with the naked eye evaluated.
[0060]
The results of evaluation by such an evaluation method are shown below.
[0061]
Example No. 5 of the present invention. 1-4 is in the component range of this invention, and 1-5 of a comparative example is outside the component range of this invention. The component ranges of the steel are shown in Table 1, and the property evaluation results are shown in Table 2. In Table 1, CT represents the coiling temperature of the hot rolled sheet. The overall judgment is T.D. S. In addition, a sample satisfying all of the four items of crystal grain size, bottom pressure resistance, and no hair generation was evaluated as “good”, and “×” if any one was satisfied. In Comparative Example 1, P is 0.021% by weight, which is lower than the range of the present invention. In that case, as shown in Table 2, the crystal grains were as large as 10.2 μm, and the skin was rough enough to be judged with the naked eye even after molding. In Comparative Example 2, the amount of Al is high, and due to the effect of AlN, the crystal grain size and T.O. S. Is the target range, but the age hardening is poor, and the bottom pressure resistance is below the lower limit of the target. In Comparative Example 3, the amount of N was as low as 0.0008% by weight, the effect of N aging was also poor, and the bottom breakdown voltage was below the lower limit. In Comparative Example 4, C is 0.042%, which is a category of low carbon steel sheet, and the tensile strength (TS) and the bottom pressure resistance are high, which is not preferable. Finally, Comparative Example 5 is not preferable because the Mn content is as high as 1.3% by weight, the tensile strength (TS) and the bottom pressure resistance are high.
[0062]
【The invention's effect】
The steel sheet coated with a resin film such as PET on the steel sheet for thinned deep-drawn iron can according to the present invention is free of hair even during continuous high-speed can-making due to softening during molding, and the crystal grains are coarse Since the skin is suppressed, there is no problem with rough skin. Furthermore, it is possible to provide a steel sheet suitable for use in a thinned deep-drawn ironing can excellent in bottom strength, which is a strength characteristic of the can, by N aging.
[0063]
In addition, the steel plate for thinning deep drawing ironing cans provided by the present invention can be applied to the use of thinning deep drawing ironing cans even when an adhesive such as epoxy is coated between the resin film and the steel plate.

Claims

A resin-coated steel sheet obtained by laminating a film made of an unstretched polyester resin, the steel sheet being C: 0.001 to 0.010% by weight, Si: ≦ 0.05% by weight, Mn: ≦ 0.9% by weight , P: 0.131 to 0.200 wt%, S: ≤ 0.04 wt%, Al: 0.006 to 0.08 wt%, N: 0.0010 to 0.015 wt%, balance Fe and inevitable A thin-walled deep-drawn ironing can steel plate, characterized by comprising a low-carbon steel plate having an average crystal grain size of 4.0 to 10.0 μm .

A resin-coated steel sheet obtained by laminating a film made of an unstretched polyester resin, the steel sheet being C: 0.001 to 0.010% by weight, Si: ≦ 0.05% by weight, Mn: ≦ 0.9% by weight , P: 0.131 to 0.200 wt%, S: ≤ 0.04 wt%, Al: 0.006 to 0.08 wt%, N: 0.0010 to 0.015 wt%, balance Fe and inevitable Hot-rolled steel sheets made of mechanical impurities are successively subjected to cold rolling, annealing by heat cycle including overaging treatment, temper rolling at a rolling rate of 0.5 to 30% or secondary cold rolling, and after temper rolling A steel plate for a thinned deep-drawn ironing can, characterized in that the average crystal grain size of the steel plate is 4.0 to 10.0 µm.

A resin-coated steel sheet laminated with a film made of unstretched polyester resin, C: 0.001 to 0.010% by weight, Si: ≦ 0.05% by weight, Mn: ≦ 0.9% by weight, P: 0.131 to 0.200 wt%, S: ≤ 0.04 wt%, Al: 0.006 to 0.08 wt%, N: 0.0010 to 0.015 wt%, balance Fe and unavoidable impurities It becomes a hot-rolled steel sheet, cold rolling, annealing by heat cycle comprising overaging, I sequentially line temper rolling or the secondary cold rolling at a rolling rate of from 0.5 to 30%, temper after rolling The manufacturing method of the steel plate for thinning deep drawing ironing cans characterized by the average crystal grain diameter of a steel plate being 4.0-10.0 micrometers .