JP4208042B2 - Resin coated metal plate, metal can and can lid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin-coated metal panel capable of withstanding retort sterilization and the storage condition with the elapse of time in a hot vendor or the like after retort sterilization, and a metal can and a can lid both of which comprise the resin-coated metal panel. SOLUTION: In the resin-coated metal panel consisting of a metal substrate and the thermoplastic resin layer provided on the surface of the metal substrate, the thermoplastic resin layer comprises polyester based on polyethylene terephthalate and an ethylenic polymer and 0.05-3 wt.% of tocopherol or a derivative thereof is added to the resin layer.

Description

で表され、上記式（１）において、Ｒ_１＝Ｒ_２＝Ｒ_３＝ＣＨ_３のα−トコフェロール、Ｒ_１＝Ｒ_３＝ＣＨ_３，Ｒ_２＝Ｈのβ−トコフェロール、Ｒ_２＝Ｒ_３＝ＣＨ_３，Ｒ_１＝Ｈのγ−トコフェロール、Ｒ_３＝ＣＨ_３，Ｒ_１＝Ｒ_２＝Ｈのδ−トコフェロール等を挙げることができる。
また、上記式（１）において２位の不斉炭素原子に関するｄ−，ｌ−の光学異性体の何れでもよく、天然品（ｄ形トコフェロール）、合成品（ｄｌ形トコフェロール）の何れをも用いることができる。中でもα−トコフェロールを有効に使用することができる。
【００２４】
本発明においては、ポリエステル組成物に、それ自体公知の樹脂用配合剤、例えば非晶質シリカ等のアンチブロッキング剤、二酸化チタン（チタン白）等の顔料、各種帯電防止剤、滑剤等を公知の処方に従って配合することもできる。
【００２５】
（金属板）
本発明に用いる金属板としては、各種表面処理鋼板やアルミニウム等の軽金属板が使用される。表面処理鋼板としては、冷圧延鋼板を焼鈍した後二次冷間圧延し、亜鉛メッキ、錫メッキ、ニッケルメッキ、電解クロム酸処理、クロム酸処理等の表面処理の一種または二種以上行ったものを用いることができる。またアルミニウムメッキ、アルミニウム圧延等を施したアルミニウム被覆鋼板が用いられる。
また軽金属板としては、いわゆる純アルミニウム板の他にアルミニウム合金板が使用される。
金属板の元板厚は、金属の種類、容器の用途或いはサイズによっても相違するが、一般に０．１０乃至０．５０ｍｍの厚みを有するのがよく、この中でも表面処理鋼板の場合には０．１０乃至０．３０ｍｍの厚み、軽金属板の場合は０．１５乃至０．４０ｍｍの厚みを有するのがよい。
【００２６】
（樹脂被覆金属板及びその製法）
本発明の樹脂被覆金属板において、金属基体上に設けるポリエステル被覆は、上述したポリエステル組成物単独から成っていても、それ以外の少なくとも１つのポリエステル層との積層体から成る層であってもよい。後者の積層体の場合は、エチレン系重合体及びトコフェロールを含有するポリエステル組成物（以下、単にポリエステル組成物と呼ぶことがある）は、少なくとも金属基体と接する側に存在することが、耐食性、耐高温湿熱性及び耐衝撃性の点で重要である。
【００２７】
図４は、本発明の樹脂被覆金属板の断面構造の一例を示すものであり、この樹脂被覆金属板１は、金属基体２と、容器としたとき内面側となる側に設けられたエチレン系重合体及びトコフェロールを含有するポリエステル組成物から成る層３とから成っている。金属基体２の容器外面側にも熱可塑性ポリエステル層４が形成されているが、この外面側のポリエステル層はポリエステル組成物から成っていても、或いはそれ以外のポリエステル被覆層から成っていてもよい。
樹脂被覆金属基体の他の例を示す図５において、容器内面となる側には、金属基体と接する側に位置するポリエステル組成物から成る下地層３とそれ以外のポリエステル表面層５との積層樹脂層６を設けている以外は図４の場合と同様である。
【００２８】
本発明において、ポリエステル被覆層は全体として１乃至６０μｍ、特に２乃至４０μｍの厚みを有するのが金属基体の保護と加工性とのバランスの点でよく、一方、積層被覆の場合、エチレン系重合体及びトコフェロールを含有するポリエステル組成物から成る層と、それ以外のポリエステル層とは、１：４０乃至４０：１の厚み比、特に１：２０乃至２０：１の厚み比で存在することが、耐食性、耐高温湿熱性及び耐衝撃性等とのバランスの点で好ましい。
【００２９】
本発明において、金属基体へのポリエステル被覆層の形成は任意の手段で行うことができ、例えば、押出コート法、キャストフィルム熱接着法、二軸延伸フィルム熱接着法等により行うことができる。
押出コート法の場合、樹脂の種類に対応する数の押出機を使用し、ダイを通してポリエステルを押出すと共に、これを溶融状態で金属基体上に押出コートして、熱接着させる。
ポリエステルフィルムを用いる場合は、Ｔ−ダイ法やインフレーション製膜法で成形したフィルムを用いる。フィルムとしては、押し出したフィルムを急冷した、キャスト成形法による未延伸フィルムを用いることもでき、また、このフィルムを延伸温度で、逐次或いは同時二軸延伸し、延伸後のフィルムを熱固定することにより製造された二軸延伸フィルムを用いることもできる。
【００３０】
本発明においては、上記層構成以外にも種々の構成を採用することができ、金属基体とポリエステル層の間に、従来公知の接着用プライマーを設けることも可能である。この接着プライマーは、金属素材とフィルムとの両方に優れた接着性を示すものである。密着性と耐腐食性とに優れたプライマー塗料としては、種々のフェノールとホルムアルデヒドから誘導されるレゾール型フェノールアルデヒド樹脂と、ビスフェノール型エポキシ樹脂とから成るフェノールエポキシ系塗料であり、特にフェノール樹脂とエポキシ樹脂を５０：５０乃至１：９９の重量比、特に４０：６０乃至５：９５の重量比で含有する塗料である。接着プライマー層は一般に０．０１乃至１０μｍの厚みに設けるのがよい。接着プライマー層は予め金属素材上に設けてもよく、或いはポリエステルフィルムに設けてもよい。
【００３１】
（金属缶及びその製法）
本発明の樹脂被覆金属板から成る金属缶は、上述した樹脂被覆金属板から形成されている限り、任意の製缶法によるものでよい。この金属缶は側面継ぎ目を有するスリーピース缶であることもできるが、一般にシームレス缶（ツーピース缶）であることが好ましい。このシームレス缶は、上述した樹脂被覆金属板のポリエステル組成物の被覆面が缶内面側となるように、絞り・再しぼり加工、絞り・再絞りによる曲げ伸ばし加工（ストレッチ加工）、絞り・再絞りによる曲げ伸ばし・しごき加工或いは絞り・しごき加工等の従来公知の手段に付すことによって製造される。
本発明の金属缶は、上記手段によって製造されるが、好ましくは再絞りによる曲げ伸ばし加工、及び／又はしごき加工を行って側壁部の薄肉化を行う。
その薄肉化は、底部に比して側壁部は曲げ伸ばし加工、及び／又はしごき加工により、樹脂被覆金属板の素板厚の２０乃至９５％、特に３０乃至８５％の厚みにあるように薄肉化されているのが好ましい。
【００３２】
例えば、絞り・再絞りによる曲げ伸ばし加工によれば、樹脂被覆金属板から絞り比１．１乃至３．０の範囲の絞り加工によって前絞りカップを成形し、このカップを絞り比１．５乃至５．０の範囲で再絞りポンチと再絞りダイスによって再絞り加工を行うと共に、上記再絞りダイスの作用コーナー部の曲率半径（Ｒｄ）を、金属素板厚（ｔＢ）の１乃至２．９倍、特に１．５乃至２．９倍の寸法として曲げ伸ばし加工に付することにより薄肉化を有効に行うことができ、側壁部の下部と上部とにおける厚みの変動が解消され、側壁部全体にわたって均一な薄肉化が可能となる。
一般に、缶胴の側壁部を素板厚（ｔＢ）基準で８０％以下の厚み、４５％まで、特に４０％までの厚みに薄肉化することができる。
また、上記再絞り加工において、再絞りダイの曲げ伸ばし加工部の後方にしごき加工部を配置して、側壁部に対してしごき加工を行うこともできる。
【００３３】
曲げ伸ばし加工及びしごき加工により、下記式（２）
ＲＩ＝｛（ｔＢ−ｔＷ）／ｔＢ｝×１００ …（２）
式中、ｔＢは素板厚であり、ｔＷは側壁部の厚みである。
で定義される薄肉化率ＲＩが２０乃至９５％、特に３０乃至８５％の厚みになるように薄肉化することが好ましい。
【００３４】
得られた缶は、少なくとも一段の熱処理に付し、加工により生じるフィルムの残留歪みを除去し、加工の際用いた滑剤を表面から揮散させ、更に表面に印刷した印刷インキを乾燥硬化させる。熱処理後の容器は急冷或いは放冷した後、所望により、一段或いは多段のネックイン加工に付し、フランジ加工を行って、巻締用の缶とする。
【００３５】
（缶蓋及びその製法）
本発明の樹脂被覆金属板から成る缶蓋は、上述した樹脂被覆金属板から形成されている限り、従来公知の任意の製蓋法によるものでよい。一般には、ステイ・オン・タブタイプのイージイオープン蓋やフルオープンタイプのイージイオープン蓋に適用される。
【００３６】
【実施例】
本発明を次の例で説明する。
（樹脂被覆金属板の作製）
実施例１〜６，１２〜１７，比較例１〜６については表３に示した組成になるよう、表１に示した共重合乃至ブレンドした組成のポリエステル樹脂、表２に示したエチレン系重合体、及びトコフェロール（チバ・スペシャルティ・ケミカルズ（株）製ＩＲＧＡＮＯＸ Ｅ２０１）をヘンシェルミキサーで予備混合した後、ピンミル等にて粉砕したものを二軸押出機に投入して溶融混練し、Ｔダイを通して厚さ２０μｍとなるように押出したものを冷却ロールにて冷却して得られたフィルムを巻き取りキャストフィルムとした。この際、温度条件は、各樹脂ごとの最適温度を選定した。
【００３７】
但し、実施例１３については、２台の二軸押出機および２層Ｔダイを用い、表３で示した樹脂を下層、表１に示したポリエステル樹脂Ｂを表層にし、表層５μｍ、下層１５μｍの２層キャストフィルムを作製した。
実施例１〜６，１２〜１５、比較例１〜４については,これら作製したキャストフィルムを、ＴＦＳ鋼板（板厚０．１８ｍｍ、金属クロム量１２０ｍｇ／ｍ^２、クロム水和酸化物量１５ｍｇ／ｍ^２ の両面に、熱ラミネートし、直ちに水冷することにより樹脂被覆金属板を得た。このとき、ラミネート前の金属板の温度は、ポリエステル樹脂の融点より１５℃高く設定した。またラミネートロール温度は１５０℃、通板速度は４０ｍ／ｍｉｎでラミネートを行った。
【００３８】
実施例１６，比較例５については、板厚０．２４ｍｍのアルミニウム合金板（Ａ３００４Ｈ３９材）を用いた以外は、実施例１〜６，１２〜１５，比較例１〜４と同様に樹脂被覆金属板を得た。
実施例１７，比較例６については、板厚０．２５ｍｍのアルミニウム合金（Ａ５０５２Ｈ３８材）を用いた以外は、実施例１〜６，１２〜１５，比較例１〜４と同様に樹脂被覆金属板を得た。
【００３９】
実施例７〜１１について、２５０℃に加熱したＴＦＳ鋼板（板厚０．１８ｍｍ、金属クロム量１２０ｍｇ／ｍ^２ 、クロム水和酸化物量１５ｍｇ／ｍ^２）上に、表３に示した組成の樹脂（トコフェロールはチバ・ステシャルティ・ケミカルズ（株）製ＩＲＧＡＮＯＸ Ｅ２１７ＤＦを使用）をドライブレンドしてエクストルージョン・ラミネーション設備を備えたφ６５ｍｍ押出機に供給し、外面側として、厚さ２０μｍとなるように溶融押出しを行いＴＦＳ片面側にラミネートした。次いで、内面側として、同じ樹脂成分をエクストルージョン・ラミネーション設備を備えたφ６５ｍｍ押出機に供給した後、板温度を樹脂の融点より３０℃低い温度に加熱し、厚さ２０μｍとなるように溶融押出を行い、もう一方の面にラミネートし樹脂被覆金属板を得た。
【００４０】
（平板デントＥＲＶ試験）
樹脂被覆金属板を、５℃、湿潤下にて、厚み３ｍｍ、硬度５０°のシリコンゴムに評価すべき被覆面を接触させて、金属板を挟んだ反対側に直径５／８インチの鋼球をおき、１ｋｇのおもりを４０ｍｍの高さから落下させて衝撃張り出し加工を行った。
衝撃加工部の樹脂の被膜割れの程度を電圧６．００Ｖでの電流値で測定し、６個の平均を取り、加工による金属露出の評価を行った。
評価結果は、
○：平均電流値＜０．１ｍＡ
×：平均電流値＞０．１ｍＡ
で示し、表３にまとめた。
【００４１】
（密着性試験）
樹脂被覆金属板を元厚みの５０％の厚みになるまで圧延加工し、その圧延加工した樹脂被覆金属板にカッターでクロスカットを入れ、その部分にセロテープ（ニチバン社製２４ｍｍ）を貼り、そのセロテープを剥離した。
評価はセロテープ剥離後の樹脂被膜の剥離状態から評価した。
評価結果は、
○：フィルムの剥離がない
×：フィルムの剥離がある
で示し、表３にまとめた。
【００４２】
（クロスカット試験）
作製した金属缶の缶壁上部から３ｃｍ×３ｃｍを切り出し、カッターでクロスカットを入れた後、０．１％塩化ナトリウム水溶液に浸し、５０℃で１週間経時した後、腐食状況を観察した。評価はクロスカット部からのフィルムの剥離及びフィルム下腐食の大きさで行った。
評価結果は、
○：１ｍｍ未満のフィルム剥離又はフィルム下腐食
×：１ｍｍ以上のフィルム剥離又はフィルム下腐食
で示し、表３にまとめた。
【００４３】
（レトルト処理試験）
９５℃で蒸留水を充填後、１３５℃３０分のレトルト処理を行い、室温に戻し蒸留水を抜き取り、評価が金属缶である場合は、缶内面、蓋である場合は蓋内面の腐食状態を観察した。
【００４４】
（パック試験）
評価が金属缶である場合は、コーラを充填した缶を横向きに静置した後、５℃において、金属板の圧延方向に対し直角となる缶軸線上で、缶のネック加工部の缶底側終点に、径６５．５ｍｍの球面を有する１ｋｇのおもりを４０ｍｍの高さから球面が缶に当たるように落下させて衝撃を与えた。その後３７℃の温度で貯蔵試験を行い、１年後の缶内面の状態を観察した。
評価が蓋である場合は、コーラを充填した缶を３７℃の温度で貯蔵試験を行い、１年後の蓋内面の状態を観察した。
【００４５】
（実施例１〜１５）
作製した樹脂被覆金属板を平板デントＥＲＶ試験、密着性試験に供した。その結果を表３にまとめた。どの樹脂被覆金属板も耐デント性、密着性に優れたものであった。
これらの樹脂被覆金属板にワックス系潤滑剤を塗布し、直径１６６ｍｍの円盤を打ち抜き、浅絞りカップを得た。次いでこの浅絞りカップを再絞り・しごき加工を行い、深絞り−しごきカップを得た。
この深絞りカップの諸特性は以下の通りであった。
カップ径：６６ｍｍ
カップ高さ：１２８ｍｍ
素板厚に対する缶壁部の厚み：６５％
素板厚に対するフランジ部の厚み：７７％
【００４６】
この深絞りしごきカップを、常法に従いドーミング成形を行い、２２０℃にて熱処理を行った後、カップを放冷後、開口端縁部のトリミング加工、曲面印刷及び焼き付け乾燥、ネック加工、フランジ加工、を行って、３５０ｇ用のシームレス缶を得た。成形上問題はなかった。
次いで、クロスカット試験、パック試験及び蒸留水充填によるレトルト処理試験に供した。
表３に示したように、クロスカット試験における腐食、パック試験におけるデント部腐食、レトルト試験による腐食の発生は認められず、良好であった。これらの結果より、ここで得られたシームレス缶は、飲料保存用に優れたものであると評価された。
【００４７】
（実施例１６）
作製した樹脂被覆金属板を平板デントＥＲＶ試験、密着性試験に供した。その結果を表３にまとめた。この樹脂被覆金属板は耐デント性、密着性に優れたものであった。
この樹脂被覆金属板にワックス系潤滑剤を塗布し、直径１５２ｍｍの円盤を打ち抜き、浅絞りカップを得た。次いでこの浅絞りカップを再絞り・しごき加工を行い、深絞り−しごきカップを得た。
この深絞りカップの諸特性は以下の通りであった。
カップ径：６６ｍｍ
カップ高さ：１２７ｍｍ
素板厚に対する缶壁部の厚み：４５％
素板厚に対するフランジ部の厚み：７７％
【００４８】
この深絞りしごきカップを、常法に従いドーミング成形を行い、２２０℃にて熱処理を行った後、カップを放冷後、開口端縁部のトリミング加工、曲面印刷及び焼き付け乾燥、ネック加工、フランジ加工、を行って、３５０ｇ用のシームレス缶を得た。成形上問題はなかった。
次いで、クロスカット試験、パック試験及び蒸留水充填によるレトルト処理試験に供した。
表３に示したように、クロスカット試験における腐食、パック試験におけるデント部腐食、レトルト試験による腐食の発生は認められず、良好であった。これらの結果より、ここで得られたシームレス缶は、飲料保存用に優れたものであると評価された。
【００４９】
（実施例１７）
作製した樹脂被覆金属板を平板デントＥＲＶ試験、密着性試験に供した。その結果を表３にまとめた。この樹脂被覆金属板は耐デント性、密着性に優れたものであった。
次いで、樹脂被覆金属板を、樹脂被覆面が蓋の内面側となるように直径６８．７ｍｍの蓋を打ち抜き、次いで蓋の外面側にパーシャル開口型のスコア加工（幅２２ｍｍ、スコア残厚１１０μｍ、スコア幅２０μｍ）、リベット加工並びに開封用タブの取り付けを行い、ＳＯＴ蓋の作製を行った。成形上、問題はなかった。
次いで作製したＳＯＴ蓋を用い、パック試験、耐レトルト試験を行った。いずれも腐食の発生は認められず、金属缶用の蓋として優れたものであると評価された。
【００５０】
（比較例１〜４）
作製した樹脂被覆金属板を平板デントＥＲＶ試験、密着性試験に供した。その結果を表３にまとめた。実施例に比較し、耐食性、耐デント性、密着性に劣るものであった。
また、この樹脂被覆金属板を用いて、実施例１〜１５と同様の条件で、シームレス缶の作製を試みたが、深絞りカップ成形途中で、フィルムの破断、デラミが発生し、後の評価に供せるシームレス缶を得ることができなかったものもあり、また成形できてもクロスカット試験における腐食、パック試験における腐食、レトルト試験による腐食の発生が認められた。これらの結果より、ここで得られたシームレス缶は飲料保存用に不適であると評価された。
【００５１】
（比較例５）
作製した樹脂被覆金属板を平板デントＥＲＶ試験、密着性試験に供した。その結果を表３にまとめた。実施例に比較し、耐食性、耐デント性、密着性に劣るものであった。
また、この樹脂被覆金属板を用いて、実施例１６と同様の条件にて、シームレス缶を作製した。成形上問題はなかった。
次いで、クロスカット試験、パック試験及び蒸留水充填によるレトルト処理試験に供した。
表３に示したようにクロスカット試験における腐食、パック試験における腐食、レトルト試験による腐食の発生が認められた。これらの結果より、ここで得られたシームレス缶は飲料保存用に不適であると評価された。
【００５２】
（比較例６）
作製した樹脂被覆金属板を平板デントＥＲＶ試験、密着性試験に供した。その結果を表３にまとめた。実施例に比較し、密着性は劣るものであった。
実施例１７と同様にＳＯＴ蓋の作製を試みた結果、スコア部でフィルムの亀裂が認められた。また、パック試験、レトルト試験において、腐食が認められた。このため、金属缶用の蓋として不適のものであると評価された。
【００５３】
【表１】

【００５４】
【表２】

【００５５】
【表３】

【００５６】
【発明の効果】
本発明によれば、金属基体と該基体表面に設けられた熱可塑性樹脂層とから成る樹脂被覆金属板において、前記熱可塑性樹脂層がポリエチレンテレフタレートを主体とするポリエステルとエチレン系重合体から成り、且つ該樹脂層にトコフェロール乃至その誘導体を０．０５乃至３重量％含有することにより、レトルト殺菌やホットベンダー等の過酷な条件下に付された場合にも樹脂被覆金属板に優れた耐食性、耐衝撃性、耐高温湿熱性が付与され、特にレトルト殺菌やホットベンダー等によりクラックが生じた場合でもクラックの部分から腐食が進むことがなく、顕著に耐食性が向上された樹脂被覆金属板を提供することが可能となった。
【図面の簡単な説明】
【図１】本発明に用いるトコフェロールの熱減成について説明する図である。
【図２】本発明に用いるトコフェロールの焦げ抑制効果を説明するための図である。
【図３】本発明に用いるトコフェロールのＰＥＴの分子量への影響を説明するための図である。
【図４】本発明の樹脂被覆金属板の断面構造の一例を示す図である。
【図５】本発明の樹脂被覆金属板の断面構造の他の一例を示す図である。[0001]
[Industrial application fields]
The present invention relates to a resin-coated metal plate in which a film made of a polyester composition is laminated on a metal substrate. More specifically, the polyester composition contains an ethylene polymer and tocopherol or a derivative thereof, thereby providing excellent corrosion resistance. Further, the present invention relates to a resin-coated metal plate having high-temperature wet heat resistance and impact resistance, a metal can having the above-described characteristics, and a can lid formed from the resin-coated metal plate.
[0002]
[Prior art]
Side seamless cans (side seamless cans) are made by applying a metal material such as an aluminum plate, tin plate or tin-free steel plate to at least one stage of drawing between the drawing die and the punch. Formed in a cup consisting of a seamless body part and a bottom part integrally connected to the body part seamlessly, and then the body part is thinned by ironing or bending and stretching to the body part as desired. It has been known.
As an organic coating method for such a side seamless can, a method of previously laminating a resin film on a metal material before molding is known. For example, JP-A-6-172556 discloses an intrinsic viscosity. It is described that a polyester film having [η] of 0.75 or more is used for a metal laminate.
[0003]
In order to improve the heat resistance and impact resistance of polyester used for resin coating, blending an antioxidant with polyester has been frequently performed. For example, JP-A-7-138387 discloses oxidation. A polyester-based film for metal laminates formed from a polyester composition containing 0.01 to 5% by weight of an inhibitor is described. JP-A-7-207039 discloses a diethylene glycol component having a melting point of 120 to 260 ° C. There is described a polyester film for laminating metal plates characterized by containing 0.01 to 1% by weight and containing 0.001 to 1% by weight of an antioxidant.
[0004]
As a practical impact resistance required for actual canned products, there is a so-called dent resistance. This means that even if the canned products fall or if the canned products collide with each other and the dents called dents are formed in the canned products, the adhesion and coverage of the coating can be maintained completely. Is required. In other words, if the coating peels off in the dent test or if pinholes or cracks enter the coating, this part causes metal elution or leakage due to pitting corrosion, resulting in the problem of losing the preservation of the contents. .
[0005]
Moreover, in a can for canning, it is normal to print on the outer surface of the can, and the influence of the heating for baking printing ink arises in a polyester film. Furthermore, in an actual can, the can may be heated for the purpose of stabilizing the distortion removal of the resin coating, and the influence of the heating on the polyester cannot be ignored. Polyester has a tendency to heat deterioration due to heating, that is, molecular weight tends to decrease, and this reduces dent resistance, lowering adhesion to metal substrates or lowering coverage, neck-in processing, winding processing, etc. Sex is reduced.
[0006]
[Problems to be solved by the invention]
Japanese Patent Application Laid-Open No. 10-19183 discloses a resin coating layer of a metal substrate as a resin coating layer of (I) a polyethylene terephthalate segment ( II) per 100 parts by weight of a polyester or polyester composition comprising a polyester segment derived from butylene glycol and an aromatic dibasic acid and (III) a polyester segment derived from butylene glycol and an aliphatic dibasic acid A laminate comprising at least one kind of non-sulfur antioxidant having a molecular weight of 400 or more of 0.01 to 1.5 parts by weight is described.
[0007]
However, in the can made of the above laminate, the dent resistance after receiving a heat history at a high temperature is remarkably improved. However, when the can is subjected to a high-temperature moist heat condition such as retort sterilization or hot Until it was attached to a vendor, satisfactory corrosion resistance and impact resistance were not obtained.
[0008]
Accordingly, an object of the present invention is to provide a resin-coated metal plate having corrosion resistance, impact resistance, high-temperature and high-humidity heat resistance, and the like that can withstand aging with retort sterilization and hot bender after retort sterilization, and the resin-coated metal plate. The present invention provides a metal can and a can lid.
[0009]
[Means for Solving the Problems]
  According to the present invention, in a resin-coated metal plate comprising a metal substrate and a thermoplastic resin layer provided on the surface of the substrate, the thermoplastic resin layer is a polyester mainly composed of polyethylene terephthalate and an ethylene polymer.In a weight ratio of 95: 5 to 50:50And a resin-coated metal sheet comprising 0.05 to 3% by weight of tocopherol or a derivative thereof in the resin layer.
  In the resin-coated metal plate of the present invention,The ethylene polymer preferably contains an ionomer.
  Moreover, according to this invention, the metal can and the can lid | cover characterized by being formed from the said resin-coated metal plate are provided.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, as a resin coating, a polyester mainly composed of polyethylene terephthalate is combined with an ethylene polymer, and tocopherol or a derivative thereof is blended in a proportion of 0.05 to 3% by weight in this polyester composition. This is an important feature that gives the resin-coated metal sheet excellent corrosion resistance, impact resistance, and high temperature and humidity resistance, especially when subjected to harsh conditions such as retort sterilization and hot bender. The point that these characteristics are maintained is an important characteristic.
[0011]
In the present invention, tocopherol blended in a polyester composition comprising a polyester mainly composed of polyethylene terephthalate and an ethylene-based polymer, as a conventional antioxidant, prevents a decrease in molecular weight due to degradation during heat treatment of a polyester resin. Although it is already known that the dent resistance is improved, in the present invention, when this tocopherol is blended with a polyester composition comprising a polyester mainly composed of polyethylene terephthalate and an ethylene polymer, the dent resistance is improved. Not only that, even if the film is cracked due to severe conditions such as retort sterilization or hot bender, the corrosion is prevented from proceeding and the corrosion resistance is remarkably improved. It was possible to get.
That is, as is clear from the results of Examples described later, when a cross-cut test was performed on a can wall made of a resin-coated metal plate, the can wall made of the resin-coated metal plate of the present invention was almost corroded. It is clear that the corrosion resistance is remarkably improved.
[0012]
As shown in FIG. 1, the tocopherol or its derivative used in the present invention has a weight of 80% or more at a processing temperature of 260 to 270 ° C. which is a processing temperature of polyethylene terephthalate. Since it has a characteristic that it has few heat resistances, even when blended with polyethylene terephthalate, it can exhibit the excellent characteristics of tocopherol without impairing it. Moreover, tocopherol (vitamin E) is safe even when eluted to the contents, and has excellent hygienic properties.
[0013]
The ethylene-based polymer blended as a modifier component in the polyester mainly composed of polyethylene terephthalate improves the impact resistance of the polyester and improves the adhesion and workability to the metal plate. A resin coating is formed. On the other hand, ethylene-based polymers tend to be burned by heating, and blending only an ethylene-based polymer in the polyester is inferior in film-forming properties, and may lead to the occurrence of flaws. By blending tocopherol in a proportion of 0.05 to 3% by weight in a polyester composition comprising a main polyester and an ethylene polymer, in the present invention, such burning of the ethylene polymer is suppressed, It became possible to improve the film forming property.
[0014]
That is, as shown in FIG. 2, a polyester in which 18% by weight of an ionomer resin is blended with polyethylene terephthalate as an ethylene polymer, and a polyester in which 18% by weight of ionomer resin and 0.5% by weight of tocopherol are blended with polyethylene terephthalate, The number of burns in the polyester blended with is significantly reduced. This is thought to be because tocopherol itself is oxidized to prevent oxidation of the ionomer.
[0015]
Also in the present invention, tocopherol can of course effectively suppress a decrease in molecular weight due to thermal degradation of polyethylene terephthalate as an antioxidant. That is, as shown in FIG. 3, when the amount of tocopherol added to the polyester composition composed of poly (ethylene terephthalate) and ethylene polymer is changed and heated (molecular weight before heating: 58000), the molecular weight increases as the amount of tocopherol added increases. Thus, the addition of a certain amount of tocopherol effectively prevents a decrease in molecular weight due to thermal degradation of the polyester, thereby improving the dent resistance.
[0016]
In the present invention, it is necessary that tocophenol or a derivative thereof is contained in the polyester composition in an amount of 0.05 to 3% by weight, particularly preferably 0.1 to 2% by weight. If the amount is less than the above range, the above-described excellent effect obtained by the tocopherol or its derivative cannot be sufficiently expressed in the polyester composition. If the amount is more than the above range, the gelation of the polyester occurs, resulting in the smoothness of the film. Tends to be lost, making it difficult to form seamless cans.
[0017]
In the present invention, the ratio of the polyester mainly composed of polyethylene terephthalate and the ethylene-based polymer is preferably in the range of 95: 5 to 50:50, particularly 90:10 to 70:30. When the amount of the ethylene polymer is less than the above range, the modification of the polyester by the ethylene polymer, that is, the impact resistance of the polyester, the adhesion to the metal plate, and the workability are improved, and it is uniform on the metal plate. There is a possibility that the effect of forming a resin coating may not be sufficiently obtained, and if the amount of the ethylene-based polymer is larger than the above range, the resin is formed on the metal plate due to the generation of butts, gels, fish eyes, etc. It is difficult to form the coating layer with a constant film thickness, and pinholes may occur during processing.
[0018]
(polyester)
The polyester mainly composed of polyethylene terephthalate used in the present invention comprises 50 mol% or more of the aromatic carboxylic acid component composed of a terephthalic acid component, and 50% or more of the alcohol component mainly composed of an aliphatic diol composed of an ethylene glycol component. Means polyester.
As long as the above conditions are satisfied, the polyester may be a homopolyester, a copolyester, or a blend of two or more of these.
[0019]
Examples of carboxylic acid components other than the terephthalic acid component include isophthalic acid, naphthalenedicarboxylic acid, p-β-oxyethoxybenzoic acid, biphenyl-4,4′-dicarboxylic acid, diphenoxyethane-4,4′-dicarboxylic acid, 5 -Sodium sulfoisophthalic acid, hexahydroterephthalic acid, adipic acid, sebacic acid, trimellitic acid, pyromellitic acid, etc. can be mentioned.
[0020]
On the other hand, as alcohol components other than ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexylene glycol, diethylene glycol, triethylene glycol, cyclohexane dimethanol, bisphenol A ethylene oxide adduct, Examples include alcohol components such as glycerol, trimethylolpropane, pentaerythritol, dipentaerythritol, and sorbitan.
The polyester should have a molecular weight in the film forming range, and the intrinsic viscosity [η] measured using a phenol / tetrachloroethane mixed solvent as a solvent is 0.5 or more, particularly in the range of 0.6 to 1.5. This is good in terms of barrier properties against corrosive components and mechanical properties.
[0021]
(Ethylene polymer)
In the present invention, examples of the ethylene-based polymer that is a polyester modifier component include low-, medium-, or high-density polyethylene, linear low density polyethylene, linear ultra-low density polyethylene, and ethylene-propylene. Copolymer, ethylene-butene-1 copolymer, ethylene-propylene-butene-1 copolymer, ethylene-vinyl acetate copolymer, ion-crosslinked olefin copolymer (ionomer), ethylene-acrylic acid ester copolymer Etc.
Among these, the ionomer which is an ionic salt in which a part or all of the carboxyl groups in the copolymer of ethylene and α, β-unsaturated carboxylic acid is neutralized with a metal cation is preferably used. Can do.
[0022]
The α, β-unsaturated carboxylic acid constituting the ionomer resin is an unsaturated carboxylic acid having 3 to 8 carbon atoms, specifically acrylic acid, methacrylic acid, maleic acid, itaconic acid, maleic anhydride, monomethyl maleate Examples thereof include esters and maleic acid monomethyl ester.
Particularly suitable base polymers include ethylene- (meth) acrylic acid copolymers and ethylene- (meth) acrylic acid ester- (meth) acrylic acid copolymers.
Further, as a metal ion for neutralizing the carboxyl group in the copolymer of ethylene and α, β-unsaturated carboxylic acid, Na⁺, K⁺, Li⁺, Zn⁺, Z²⁺, Mg²⁺, Ca²⁺, Co²⁺, Ni²⁺, Mn²⁺, Pb²⁺, Cu²⁺Etc. Further, a part of the remaining carboxyl groups that are not neutralized with metal ions may be esterified with a lower alcohol.
[0023]
(Tocopherol or its derivative)
Tocopherol (vitamin E) used in the present invention has the following general formula (1)
[Chemical 1]

In the above formula (1), R₁= R₂= R₃= CH₃Α-tocopherol, R₁= R₃= CH₃, R₂= Β-tocopherol of H, R₂= R₃= CH₃, R₁= Γ-tocopherol with H, R₃= CH₃, R₁= R₂And δ-tocopherol with = H.
Further, in the above formula (1), any of the d- and l- optical isomers relating to the asymmetric carbon atom at the 2-position may be used, and either a natural product (d-type tocopherol) or a synthetic product (dl-type tocopherol) is used. be able to. Of these, α-tocopherol can be used effectively.
[0024]
In the present invention, known compounding agents for resins, for example, antiblocking agents such as amorphous silica, pigments such as titanium dioxide (titanium white), various antistatic agents, lubricants and the like are known in the polyester composition. It can also be blended according to the prescription.
[0025]
(Metal plate)
As the metal plate used in the present invention, various surface-treated steel plates and light metal plates such as aluminum are used. As the surface-treated steel sheet, a cold-rolled steel sheet is annealed and then secondary cold-rolled and subjected to one or more surface treatments such as galvanizing, tin-plating, nickel-plating, electrolytic chromic acid treatment, and chromic acid treatment. Can be used. Further, an aluminum-coated steel sheet subjected to aluminum plating, aluminum rolling, or the like is used.
In addition to the so-called pure aluminum plate, an aluminum alloy plate is used as the light metal plate.
The original thickness of the metal plate varies depending on the type of metal and the use or size of the container, but generally it should have a thickness of 0.10 to 0.50 mm. The thickness is preferably 10 to 0.30 mm, and in the case of a light metal plate, the thickness is preferably 0.15 to 0.40 mm.
[0026]
(Resin-coated metal plate and its manufacturing method)
In the resin-coated metal plate of the present invention, the polyester coating provided on the metal substrate may be composed of the above-described polyester composition alone or a layer composed of a laminate with at least one other polyester layer. . In the case of the latter laminate, the polyester composition containing the ethylene-based polymer and tocopherol (hereinafter sometimes simply referred to as the polyester composition) is present at least on the side in contact with the metal substrate so that the corrosion resistance, It is important in terms of high-temperature moist heat resistance and impact resistance.
[0027]
FIG. 4 shows an example of a cross-sectional structure of the resin-coated metal plate of the present invention. This resin-coated metal plate 1 is composed of a metal base 2 and an ethylene-based material provided on the inner surface side when used as a container. And a layer 3 made of a polyester composition containing a polymer and tocopherol. The thermoplastic polyester layer 4 is also formed on the outer surface side of the container of the metal substrate 2, but the outer surface side polyester layer may be made of a polyester composition or other polyester coating layer. .
In FIG. 5 showing another example of the resin-coated metal substrate, the laminated resin of the base layer 3 made of the polyester composition located on the side in contact with the metal substrate and the other polyester surface layer 5 is provided on the side that is the inner surface of the container. Except for the provision of the layer 6, the process is the same as in the case of FIG.
[0028]
In the present invention, the polyester coating layer as a whole may have a thickness of 1 to 60 μm, particularly 2 to 40 μm, in view of the balance between protection of the metal substrate and workability. And the polyester layer containing the tocopherol and the other polyester layer are present in a thickness ratio of 1:40 to 40: 1, particularly 1:20 to 20: 1. From the viewpoint of balance with high temperature and humidity resistance, impact resistance and the like.
[0029]
In the present invention, the polyester coating layer can be formed on the metal substrate by any means, for example, extrusion coating, cast film thermal bonding, biaxially stretched film thermal bonding, or the like.
In the case of the extrusion coating method, the number of extruders corresponding to the type of resin is used to extrude the polyester through a die, and this is extrusion coated onto a metal substrate in a molten state and thermally bonded.
When using a polyester film, a film formed by a T-die method or an inflation film forming method is used. As the film, an unstretched film formed by a cast molding method in which the extruded film is rapidly cooled can be used, and this film is biaxially stretched sequentially or simultaneously at the stretching temperature, and the stretched film is heat-set. It is also possible to use a biaxially stretched film produced by the above method.
[0030]
In the present invention, various configurations other than the above-described layer configuration can be adopted, and a conventionally known adhesion primer can be provided between the metal substrate and the polyester layer. This adhesion primer exhibits excellent adhesion to both the metal material and the film. Primer paints with excellent adhesion and corrosion resistance are phenol epoxy paints composed of resol type phenol aldehyde resins derived from various phenols and formaldehyde and bisphenol type epoxy resins, especially phenol resins and epoxy. It is a paint containing a resin in a weight ratio of 50:50 to 1:99, in particular 40:60 to 5:95. The adhesive primer layer is generally preferably provided with a thickness of 0.01 to 10 μm. The adhesion primer layer may be provided in advance on a metal material, or may be provided on a polyester film.
[0031]
(Metal can and its manufacturing method)
As long as the metal can made of the resin-coated metal plate of the present invention is formed from the above-described resin-coated metal plate, any metal can manufacturing method may be used. The metal can can be a three-piece can having a side seam, but is generally preferably a seamless can (two-piece can). This seamless can is drawn and re-squeezed, bent and stretched by drawing and redrawing (stretching), and drawn and redrawn so that the coated surface of the above-mentioned resin-coated metal sheet is the inner surface of the can. It is manufactured by attaching to a conventionally known means such as bending / stretching or ironing by drawing or drawing / ironing.
The metal can of the present invention is manufactured by the above-mentioned means, but preferably the side wall portion is thinned by performing bending and stretching by redrawing and / or ironing.
As for the thinning, the side wall portion is thinned so as to be 20 to 95%, particularly 30 to 85% of the thickness of the base plate of the resin-coated metal plate, by bending and / or ironing the side wall portion compared to the bottom portion. It is preferable that
[0032]
For example, according to bending and stretching by drawing / redrawing, a front drawn cup is formed from a resin-coated metal plate by drawing in a drawing ratio range of 1.1 to 3.0, and the cup is drawn to a drawing ratio of 1.5 to 3.0. Redrawing is performed by a redrawing punch and a redrawing die within a range of 5.0, and the radius of curvature (Rd) of the working corner portion of the redrawing die is set to 1 to 2.9 of the metal base plate thickness (tB). The thickness can be effectively reduced by bending and stretching to a size of 1.5 times, especially 1.5 to 2.9 times, and the variation in thickness between the lower and upper portions of the side wall portion is eliminated, and the entire side wall portion is eliminated. It is possible to reduce the thickness evenly.
Generally, the side wall of the can body can be thinned to a thickness of 80% or less, 45%, particularly 40%, based on the base plate thickness (tB).
In the redrawing process, the ironing part can be arranged behind the bending and stretching part of the redrawing die to perform ironing on the side wall part.
[0033]
By bending and stretching and ironing, the following formula (2)
RI = {(tB−tW) / tB} × 100 (2)
In the formula, tB is the thickness of the base plate, and tW is the thickness of the side wall.
It is preferable to reduce the thickness so that the thickness reduction ratio RI defined by the above formula is 20 to 95%, particularly 30 to 85%.
[0034]
The obtained can is subjected to at least one stage of heat treatment, the residual distortion of the film generated by processing is removed, the lubricant used in the processing is volatilized from the surface, and the printing ink printed on the surface is dried and cured. The container after the heat treatment is rapidly cooled or allowed to cool, and then subjected to a one-stage or multi-stage neck-in process if necessary, and a flange process is performed to obtain a winding can.
[0035]
(Can lid and its manufacturing method)
The can lid formed of the resin-coated metal plate of the present invention may be formed by any conventionally known lid-making method as long as it is formed of the above-described resin-coated metal plate. In general, the present invention is applied to a stay-on-tab type easy-open lid and a full-open type easy-open lid.
[0036]
【Example】
The invention is illustrated by the following examples.
(Production of resin-coated metal plate)
For Examples 1 to 6, 12 to 17, and Comparative Examples 1 to 6, a polyester resin having a copolymerized or blended composition shown in Table 1 and an ethylene weight shown in Table 2 so as to have the compositions shown in Table 3. After the coalescence and tocopherol (IRGANOX E201 manufactured by Ciba Specialty Chemicals Co., Ltd.) were premixed with a Henschel mixer, the mixture was pulverized with a pin mill or the like, put into a twin screw extruder, melt kneaded, and thickened through a T die. A film obtained by cooling the extruded product to a thickness of 20 μm with a cooling roll was taken up as a cast film. At this time, the optimum temperature for each resin was selected as the temperature condition.
[0037]
However, for Example 13, using two twin-screw extruders and a two-layer T die, the resin shown in Table 3 was the lower layer, the polyester resin B shown in Table 1 was the surface layer, and the surface layer was 5 μm and the lower layer was 15 μm. A two-layer cast film was produced.
For Examples 1 to 6, 12 to 15, and Comparative Examples 1 to 4, these cast films were prepared using TFS steel plates (plate thickness 0.18 mm, metal chromium content 120 mg / m², Chromium hydrated oxide amount 15mg / m² A resin-coated metal plate was obtained by heat laminating on both surfaces and immediately cooling with water. At this time, the temperature of the metal plate before lamination was set 15 ° C. higher than the melting point of the polyester resin. Lamination was performed at a laminating roll temperature of 150 ° C. and a sheet passing speed of 40 m / min.
[0038]
For Example 16 and Comparative Example 5, a resin-coated metal was used in the same manner as in Examples 1 to 6, 12 to 15 and Comparative Examples 1 to 4, except that an aluminum alloy plate (A3004H39 material) having a thickness of 0.24 mm was used. I got a plate.
For Example 17 and Comparative Example 6, a resin-coated metal plate was used in the same manner as in Examples 1 to 6, 12 to 15 and Comparative Examples 1 to 4, except that an aluminum alloy (A5052H38 material) having a plate thickness of 0.25 mm was used. Got.
[0039]
About Examples 7-11, the TFS steel plate (plate thickness of 0.18 mm, metal chromium amount of 120 mg / m) heated to 250 ° C² , Chromium hydrated oxide amount 15mg / m²) Above, dry blended resin with the composition shown in Table 3 (Tocopherol uses IRGANOX E217DF manufactured by Ciba Stablety Chemicals Co., Ltd.) and supplied to a φ65 mm extruder equipped with an extrusion lamination facility. As a side, melt extrusion was performed so as to have a thickness of 20 μm, and lamination was performed on one side of TFS. Next, as the inner surface side, the same resin component was supplied to a φ65 mm extruder equipped with an extrusion lamination facility, and then the plate temperature was heated to a temperature 30 ° C. lower than the melting point of the resin, and melt extrusion was performed so that the thickness became 20 μm. And laminated on the other surface to obtain a resin-coated metal plate.
[0040]
(Flat plate dent ERV test)
A 5/8 inch diameter steel ball is placed on the opposite side of the metal plate, with the coated surface being contacted with silicon rubber having a thickness of 3 mm and a hardness of 50 ° under wet conditions at 5 ° C. A 1 kg weight was dropped from a height of 40 mm, and impact overhanging was performed.
The degree of resin film cracking in the impact-processed portion was measured by a current value at a voltage of 6.00 V, and the average of 6 pieces was taken to evaluate the metal exposure by processing.
The evaluation result is
○: Average current value <0.1 mA
×: Average current value> 0.1 mA
And are summarized in Table 3.
[0041]
(Adhesion test)
The resin-coated metal plate is rolled to a thickness of 50% of the original thickness, the cross-cut is made with a cutter on the rolled resin-coated metal plate, and a cello tape (24 mm made by Nichiban Co., Ltd.) is pasted on that portion. Was peeled off.
The evaluation was performed from the peeled state of the resin film after the cellophane peeling.
The evaluation result is
○: No film peeling
X: There is peeling of the film
And are summarized in Table 3.
[0042]
(Cross cut test)
After cutting 3 cm × 3 cm from the upper part of the can wall of the produced metal can, and making a cross cut with a cutter, it was immersed in a 0.1% sodium chloride aqueous solution, and after aging at 50 ° C. for 1 week, the corrosion state was observed. Evaluation was performed by the magnitude | size of peeling of the film from a crosscut part, and corrosion under a film.
The evaluation result is
○: Film peeling or corrosion below 1mm
×: Film peeling or corrosion under film of 1 mm or more
And are summarized in Table 3.
[0043]
(Retort processing test)
After filling with distilled water at 95 ° C, perform retort treatment at 135 ° C for 30 minutes, return to room temperature, extract distilled water, and if the evaluation is a metal can, the inner surface of the can Observed.
[0044]
(Pack test)
When the evaluation is a metal can, the can filled with cola is left sideways, and then at 5 ° C. on the can axis perpendicular to the rolling direction of the metal plate, the bottom side of the can neck processing part At the end point, a 1 kg weight having a spherical surface with a diameter of 65.5 mm was dropped from a height of 40 mm so that the spherical surface hit the can, and an impact was given. Thereafter, a storage test was performed at a temperature of 37 ° C., and the state of the inner surface of the can after one year was observed.
When the evaluation was a lid, a can filled with cola was subjected to a storage test at a temperature of 37 ° C., and the state of the inner surface of the lid after one year was observed.
[0045]
(Examples 1 to 15)
The produced resin-coated metal plate was subjected to a flat plate dent ERV test and an adhesion test. The results are summarized in Table 3. All the resin-coated metal plates were excellent in dent resistance and adhesion.
A wax-based lubricant was applied to these resin-coated metal plates, and a disk having a diameter of 166 mm was punched out to obtain a shallow drawn cup. Subsequently, this shallow drawn cup was redrawn and ironed to obtain a deep drawn-iron cup.
The characteristics of this deep drawn cup were as follows.
Cup diameter: 66mm
Cup height: 128mm
The thickness of the can wall relative to the base plate thickness: 65%
Flange thickness relative to base plate thickness: 77%
[0046]
This deep-drawn ironing cup is domed according to a conventional method, heat-treated at 220 ° C., allowed to cool, and then trimmed the opening edge, curved surface printing and baking drying, neck processing, flange processing The seamless can for 350 g was obtained. There was no problem in molding.
Subsequently, it was subjected to a cross-cut test, a pack test, and a retort treatment test by filling with distilled water.
As shown in Table 3, the occurrence of corrosion in the cross-cut test, dent corrosion in the pack test, and corrosion due to the retort test was not observed, which was good. From these results, it was evaluated that the seamless can obtained here was excellent for beverage storage.
[0047]
(Example 16)
The produced resin-coated metal plate was subjected to a flat plate dent ERV test and an adhesion test. The results are summarized in Table 3. This resin-coated metal plate was excellent in dent resistance and adhesion.
A wax-based lubricant was applied to the resin-coated metal plate, and a disk having a diameter of 152 mm was punched out to obtain a shallow drawn cup. Subsequently, this shallow drawn cup was redrawn and ironed to obtain a deep drawn-iron cup.
The characteristics of this deep drawn cup were as follows.
Cup diameter: 66mm
Cup height: 127mm
The thickness of the can wall relative to the base plate thickness: 45%
Flange thickness relative to base plate thickness: 77%
[0048]
This deep-drawn ironing cup is domed according to a conventional method, heat-treated at 220 ° C., allowed to cool, and then trimmed the opening edge, curved surface printing and baking drying, neck processing, flange processing The seamless can for 350 g was obtained. There was no problem in molding.
Subsequently, it was subjected to a cross-cut test, a pack test, and a retort treatment test by filling with distilled water.
As shown in Table 3, the occurrence of corrosion in the cross-cut test, dent corrosion in the pack test, and corrosion due to the retort test was not observed, which was good. From these results, it was evaluated that the seamless can obtained here was excellent for beverage storage.
[0049]
(Example 17)
The produced resin-coated metal plate was subjected to a flat plate dent ERV test and an adhesion test. The results are summarized in Table 3. This resin-coated metal plate was excellent in dent resistance and adhesion.
Next, the resin-coated metal plate is punched out with a 68.7 mm diameter lid so that the resin-coated surface is on the inner surface side of the lid, and then the partial opening type score processing (width 22 mm, score remaining thickness 110 μm, A score width of 20 μm), riveting, and attachment of a tab for opening were performed to produce an SOT lid. There was no problem in molding.
Next, using the produced SOT lid, a pack test and a retort resistance test were performed. In any case, the occurrence of corrosion was not recognized, and it was evaluated that it was excellent as a lid for a metal can.
[0050]
(Comparative Examples 1-4)
The produced resin-coated metal plate was subjected to a flat plate dent ERV test and an adhesion test. The results are summarized in Table 3. It was inferior to corrosion resistance, dent resistance, and adhesiveness compared with the Example.
In addition, using this resin-coated metal plate, an attempt was made to produce a seamless can under the same conditions as in Examples 1 to 15, but during the deep drawing cup formation, film breakage, delamination occurred, and later evaluation Some seamless cans could not be obtained, and even when molded, corrosion in the cross-cut test, corrosion in the pack test, and corrosion in the retort test were observed. From these results, the seamless cans obtained here were evaluated to be unsuitable for beverage storage.
[0051]
(Comparative Example 5)
The produced resin-coated metal plate was subjected to a flat plate dent ERV test and an adhesion test. The results are summarized in Table 3. It was inferior to corrosion resistance, dent resistance, and adhesiveness compared with the Example.
In addition, seamless cans were produced under the same conditions as in Example 16 using this resin-coated metal plate. There was no problem in molding.
Subsequently, it was subjected to a cross-cut test, a pack test, and a retort treatment test by filling with distilled water.
As shown in Table 3, corrosion in the cross-cut test, corrosion in the pack test, and corrosion due to the retort test were observed. From these results, the seamless cans obtained here were evaluated to be unsuitable for beverage storage.
[0052]
(Comparative Example 6)
The produced resin-coated metal plate was subjected to a flat plate dent ERV test and an adhesion test. The results are summarized in Table 3. Compared with the Examples, the adhesion was inferior.
As a result of attempting to produce an SOT lid in the same manner as in Example 17, cracks in the film were observed in the score portion. Moreover, corrosion was recognized in the pack test and the retort test. For this reason, it was evaluated that it was unsuitable as a lid for metal cans.
[0053]
[Table 1]

[0054]
[Table 2]

[0055]
[Table 3]

[0056]
【The invention's effect】
According to the present invention, in a resin-coated metal plate comprising a metal substrate and a thermoplastic resin layer provided on the surface of the substrate, the thermoplastic resin layer comprises a polyester mainly composed of polyethylene terephthalate and an ethylene polymer, Further, by containing 0.05 to 3% by weight of tocopherol or a derivative thereof in the resin layer, the resin-coated metal plate has excellent corrosion resistance and resistance even when subjected to severe conditions such as retort sterilization and hot bender. Provided is a resin-coated metal sheet that is imparted with impact resistance and high-temperature / humidity resistance, and that does not proceed from the crack even when cracks occur, particularly due to retort sterilization or hot bender, and has significantly improved corrosion resistance. It became possible.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining thermal degradation of tocopherol used in the present invention.
FIG. 2 is a diagram for explaining the scorch suppression effect of tocopherol used in the present invention.
FIG. 3 is a diagram for explaining the influence of tocopherol used in the present invention on the molecular weight of PET.
FIG. 4 is a view showing an example of a cross-sectional structure of a resin-coated metal plate of the present invention.
FIG. 5 is a view showing another example of the cross-sectional structure of the resin-coated metal plate of the present invention.

Claims (4)

In a resin-coated metal plate comprising a metal substrate and a thermoplastic resin layer provided on the surface of the substrate, the thermoplastic resin layer comprises a polyester mainly composed of polyethylene terephthalate and an ethylene polymer of 95: 5 to 50:50. A resin-coated metal sheet comprising: tocopherol or a derivative thereof in an amount of 0.05 to 3% by weight. The resin-coated metal sheet according to claim 1 , wherein the ethylene polymer contains an ionomer. Metal can, characterized in that it is formed from a resin-coated metal plate according to claim 1 or 2. Can lid characterized in that it is formed from a resin-coated metal plate according to claim 1 or 2.

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