JP3557274B2 - Stretch film for food packaging - Google Patents

Description

【００１２】
下記式（２）で表されるインデンに、少量のクマロンを共重合した、いわゆるクマロン−インデン樹脂、
【化２】

【００１３】
下記式（３）で表されるα−ピネンに由来する繰り返し単位を主体とするテルペン樹脂またはその水素添加体
【化３】

【００１４】
などを例示することができる。ここで環状オレフインは少なくとも１個の２重結合を有していればよく、例えば環状ジオレフインなども含まれる。
【００１５】
ここで例示した（Ｂ_１ ）成分は、その重合度、共重合成分、水素添加率、使用する触媒系などにより種々の特性のものを得ることができるが、本発明に適合したものは、（Ａ_１ ）成分との関係で、ガラス転移温度が７０℃以上、特に好ましくは８０℃以上のものである。
【００１６】
また（Ｂ_１ ）成分は一般に分子量が大きくなるほど上記（Ａ_１ ）成分との相溶性が悪くなる傾向にあるので、ガラス転移温度と相溶性の両特性面から分子量が概ね７００〜９００の範囲にあるものが好ましく、また分子量分布がシヤープなものが好ましい。
【００１７】
この（Ｂ_１ ）成分は、本来結晶性である（Ａ_１ ）成分に微細オーダーで相溶してその結晶性を低下させるとともに、（Ａ_１ ）成分の応力挙動特性をも変化させて後述のような特性の達成を可能にする。（Ａ_１ ）成分と（Ｂ_１ ）成分の混合比率は、後述の粘弾性に関する基準に沿うように決定される。
【００１８】
本発明フイルムは、動的粘弾性測定により周波数１０Ｈｚ、温度２０℃で測定した貯蔵弾性率（Ｅ´）が５．０×１０^８ 〜５．０×１０^９ （ｄｙｎ／ｃｍ^２ ）の範囲にあり、かつ損失正接（ｔａｎδ）が０．２〜０．８の範囲にあるものである。
ここでＥ´が５．０×１０^８ ｄｙｎ／ｃｍ^２ 未満であると、柔らかくて変形に対し応力が小さすぎるため、作業性が悪く、パツク品のフイルムの張りもなく、ストレツチフイルムとして適さない。また、Ｅ´が５．０×１０^９ ｄｙｎ／ｃｍ^２ を越えると、硬くて伸びにくいフイルムになり、トレーの変形やつぶれが生じやすい。
【００１９】
またｔａｎδが０．２未満であると、フイルムの伸びに対する復元挙動が瞬間的であるため、フイルムをトレーの底に折り込むまでのわずかな間にフイルムが復元してしまい、フイルムがうまく張れずにしわが発生しやすい。また底部のヒートシール状態も、ストレツチ包装の場合は熱による十分な融着がなされにくいので、包装後、輸送中ないし陳列中に次第に底シールの剥がれを生じやすくなる。 また、ｔａｎδが０．８を越えると、包装仕上がりは良好であるものの、塑性的な変形を示し、パツク品の外力に対する張りが弱すぎて、輸送中ないし陳列中の積み重ねなどにより、トレー上面のフイルムがたるみ易く、商品価値が低下しやすい。また自動包装の場合には縦に伸びやすいためチヤツク不良などの問題が生じやすい。ｔａｎδの特に好適な範囲は、０．３０〜０．６０である。
【００２０】
（Ａ_１ ）成分は一般にガラス転移温度が−４０〜０℃であり、２０℃におけるｔａｎδは０．１〜０．１５程度であってそれ単独では本発明の意図する特性が得られない。そこでガラス転移温度が高い（Ｂ_１ ）成分を含有・分散させることにより混合物のガラス転移温度が高くなり、２０℃におけるｔａｎδが大きくなるとともに、結晶性を低下させて、ストレツチフイルムとして好ましい特性が得られる。
【００２１】
上記特性を満たすためには、（Ａ_１ ）成分と（Ｂ_１ ）成分の混合比率が重要である。（Ａ_１ ）成分と（Ｂ_１ ）成分の混合比率は、使用する材料の組み合わせにより異なるため一概には規定し難いが、（Ｂ_１ ）成分が２０重量％未満では、（Ａ_１ ）成分の結晶性が強く残存し、またｔａｎδが低く好ましくない。また３５重量％を越えると、フイルムの貯蔵弾性率（Ｅ´）が低くなり、また強度も低下するため包装作業性などが低下する。さらには、（Ｂ_１ ）成分がフイルム表面に吹き出すなどの問題が生じやすくなる。上記混合比率の目安としては、混合物のガラス転移温度が−１０〜１０℃の範囲に入るように設定することである。
【００２２】
またストレツチフイルムは低温時に使用されることもあり、低温特性（特に伸び）が優れていることが望ましいが、そのためには動的粘弾性測定により周波数１０Ｈｚ、温度０℃で測定したフイルムの貯蔵弾性率（Ｅ´）が１．５×１０^１０ｄｙｎ／ｃｍ^２ 以下の範囲にあることが好ましい。
【００２３】
そのためには、低温特性の優れた（Ａ_１ ）成分の比率を高めるのが有効であり、（Ａ_１ ）成分と（Ｂ_１ ）成分の混合比率を、温度２０℃における粘弾性特性を満足する範囲内で（Ａ_１ ）成分が多めになるように設定することにより達成される。また、上記（Ｂ_１ ）成分はフイルムに粘着性を付与するものが多い。従って上記のように多量に添加するとブロツキングが生じやすくなるので、（Ａ_１ ）成分と（Ｂ_１ ）成分の混合樹脂層に、（Ａ_１ ）成分のみ、あるいは（Ａ_１ ）成分が極めて多い表面層を積層することもできる。
【００２４】
本発明フイルムの材料系の別の例としては、（Ａ_２ ）エチレンを主体とするα−オレフイン単位と環状オレフイン単位との共重合樹脂からなる層、
または（Ａ_２ ）エチレンを主体とするα−オレフイン単位と環状オレフイン単位との共重合樹脂と、（Ｂ_２ ）特性調整材料との組み合わせからなる層を有するものを挙げることができる。
【００２５】
ここで、（Ａ_２ ）成分のエチレンを主体とするα−オレフイン単位は、エチレンを主体とし、必要に応じプロピレン、１−ブテン、４−メチル−１−ペンテン、１−ヘキセン、１−オクテンなどのα−オレフイン単位を含むものである。また環状オレフイン単位としては、例えば下記一般式（４）で示される環状オレフインを挙げることができる。
【００２６】
【化４】

【００２７】
具体的には、ノルボルネン、５−メチルノルボルネン、５−エチルノルボルネン、５−プロピルノルボルネン、１−メチルノルボルネン、７−メチルノルボルネン、５，５，６−トリメチルノルボルネン、５−フエニルノルボルネン、５−ベンジルノルボルネンなどを挙げることができる。
またこの樹脂には、本発明の目的を損なわない範囲で、必要に応じ他の共重合可能な単量体を含有することができ、その例としては、ブタジエン、イソプレンなどが挙げられる。
【００２８】
（Ａ_２ ）成分からなる層を有する場合には、環状オレフイン単位の種類と共重合比を特定範囲に制御したり、共重合比の異なる２種以上の共重合樹脂をブレンドしたり、また第３成分を共重合するなどして前記Ｅ´やｔａｎδなどの条件を満たすように調整することができる。
【００２９】
ただ、上記のような特性を満たす範囲では、共重合樹脂の結晶性がかなり低くなり、またガラス転移温度も高くないため、共重合樹脂のペレツトがブロツキングしやすいという共重合体製造上の不利が生じることがある。また、２０℃におけるＥ´やｔａｎδを満たす範囲では、０℃におけるＥ´が高くなり、低温適性の点で万全とはいえない場合もある。
【００３０】
この点から、（Ａ_２ ）成分として環状オレフイン含量の高いエチレン−環状オレフイン共重合樹脂を用い、これに（Ｂ_２ ）特性改良材料を混合することもできる。
【００３１】
特性改良材料（Ｂ_２ ）の一例として、低重合度ポリブテンを挙げることができる。すなわち、エチレン−環状オレフイン共重合樹脂として一般的なガラス転移温度が４０℃以上の樹脂に対し、低重合度ポリブテンなどの低ガラス転移温度をもち相溶性のよい材料を混合することにより、可塑化効果によって柔軟性が付与され、ガラス転移温度も低下してストレツチフイルムとしてより好ましい方向への改質がなされる。
【００３２】
ここで低重合度ポリブテンとしては、相溶性や成形後のフイルム表面への吹き出しを考慮して、平均分子量が１００以上、１，０００以下のものが好ましい。またその混合比率は、（Ａ_２ ）成分のガラス転移温度が４０℃以上の場合、（Ａ_２ ）成分１００重量部に対し３５〜５０重量部程度の範囲が好適である。
【００３３】
それ以外に、低ガラス転移温度をもちエチレン−環状オレフイン共重合樹脂との相溶性のよい材料として、ビニル芳香族化合物と共役ジエンとの共重合体、例えばスチレン−ブタジエン−スチレンのトリブロツク共重合体（ＳＢＳ）やスチレン−イソプレン−スチレンのトリブロツク共重合体（Ｓ１Ｓ）などが挙げられる。この場合のスチレン比率は、室温での柔軟性を維持するため３０重量％以下が好ましい。
【００３４】
以上のような特性改良材料による場合、上記改質のみでは、２０℃におけるｔａｎδが大きくなり過ぎる傾向があり、塑性的変形を示してパツク品の張りが弱くなるので、この混合物層に他のｔａｎδが小さい非塩ビ材料層を積層するのが適当である。他の樹脂層としては、ポリオレフイン系重合体が好ましく、これらと積層することにより、粘弾性特性の調整とともに、フイルムの製膜の安定性や耐ブロツキング性、滑り性などを付与することができる。
【００３５】
ここで積層材料としてのポリオレフイン系重合体としては、低密度ポリエチレン、超低密度ポリエチレン（エチレンとα−オレフインとの共重合体）、エチレン−酢酸ビニル共重合体（ＥＶＡ）、エチレン−アルキルアクリレート共重合体、エチレン−アルキルメタクリレート共重合体、エチレン−アクリル酸共重合体、エチレン−メタクリル酸共重合体、低密度ポリエチレンなどのアイオノマ、プロピレン系エラストマ材料などが好適である。
【００３６】
実用上は例えばＥＶＡを好適に使用することができ、このＥＶＡとしては、酢酸ビニル含量が５〜２５重量％、好ましくは１０〜２０重量％、メルトフローレイシヨ（ＭＦＲ）が０．２〜２ｇ／１０分（１９０℃、２．１６ｋｇ荷重）のものが強度や柔軟性、フイルム成形加工性などの面で好適である。
本発明フイルムはさらに、温度２０℃で測定した１５０％伸び時の応力ρ_１５０ と５０％伸び時の応力ρ_５０との比率（ρ_１５０ ／ρ_５０）が縦方向、横方向とも１．３〜２．０の範囲にあるような応力−歪み特性を有するのが好ましい。
【００３７】
比率（ρ_１５０ ／ρ_５０）が１．３未満であると、包装時に不均一な伸びを示し、局部的な伸びによりトレーのコーナー部などで破れを生じやすくなる。またこの比率が２．０を越えると、包装作業時にフイルムを延ばすのに強い力を要する結果となり、作業性が低下し、自動包装機による包装においてはトレーの変形や潰れを生じやすい。
【００３８】
ストレツチフイルムの一般的製法であるインフレーシヨン法によりエチレン系重合体のフイルムを製造すると、ρ_１５０ ／ρ_５０は縦方向に大きく、横方向には小さくなる傾向にあり、特に横方向のρ_１５０ ／ρ_５０を特定の範囲に設定することが重要である。そのためにはインフレーシヨン成形時のブローアツプ比（バブル径／ダイ径）を高めるのが有効であり、ブローアツプ比としては、使用する原料にもよるが一般に４以上、好適には５〜６の範囲から選択することができる。 なお一般に本発明フイルムの厚さは、通常のストレツチ包装用として用いられる範囲、すなわち８〜３０μｍ程度、代表的には１０〜２０μｍ程度の範囲にある。
【００３９】
本発明フイルムは、押出機から材料を溶融押出し、インフレーシヨン成形またはＴダイ成形によりフイルム状に成形することにより得られる。積層フイルムとする場合には多層ダイにより共押出するのが有利である。
実用的には、環状口金から材料樹脂を溶融押出してインフレーシヨン成形するのが好ましい。
【００４０】
本発明フイルムには、防曇性、帯電防止性、滑り性などの性能を付与するために各種添加剤を添加することができる。例えば、グリセリン脂肪酸エステル、ポリグリセリン脂肪酸エステル、ソルビタン脂肪酸エステル、エチレンオキサイド付加物などの界面活性剤を適宜添加することができる。
【００４１】
【実施例】
以下実施例により、本発明の効果を明らかにする。なおフイルムの特性・性能は、次の方法により測定、評価した。
１）Ｅ´、ｔａｎδ
岩本製作所（株）製粘弾性スペクトロメーターＶＥＳ−Ｆ３を用い、振動周波数１０Ｈｚ、温度２０℃および０℃でフイルムの横方向について測定した。
【００４２】
２）ストレツチ包装適性
幅３５０ｍｍのストレツチフイルムを用い、自動包装機（石田衡器（株）社製ＩＳＨＩＤＡ・Ｗｍｉｎ ＭＫ−ＩＩ）により発泡ポリスチレントレー（長さ２００ｍｍ、幅１３０ｍｍ、高さ３０ｍｍ）を包装し、表４に示す項目について評価した。また同じフイルムおよびトレーを用いて、手包装機（三菱樹脂（株）社製ダイアラッパーＡ−１０５）により包装試験を行った。
３）ρ_１５０ ／ρ_５０
ＪＩＳ Ｋ１７０２に準じて引張速度２００ｍｍ／分で引張試験を行い算出した。
【００４３】
（実施例１）
直鎖状エチレン−ブテン−１共重合体（ブテン−１含量１４重量％、密度０．９０５）７５重量％と、シクロペンタジエンを主体とする石油樹脂の水素添加品（ガラス転移温度８１℃、荒川化学社製アルコンＰ１２５）２５重量％を混合した組成物を中間層（厚さ９μｍ）とし、一方ＥＶＡ（酢酸ビニル含量１５重量％、１９０℃ＭＦＲ２．０ｇ／１０分）１００重量部に対し防曇剤としてジグリセリンモノオレ−ト３重量部を混練した組成物を表裏層として各々厚さ３μｍ配し、ブローアツプ比（ＢＵＲ）６．０で共押出インフレ−シヨン成形により総厚み１５μｍ（３／９／３μｍ）のフイルムを得た。
【００４４】
なお、直鎖状エチレン−ブテン−１共重合体単独で測定した特性は、
０℃における貯蔵弾性率Ｅ´ ２．０×１０^９ ｄｙｎ／ｃｍ^２
２０℃における貯蔵弾性率Ｅ´ １．２×１０^９ ｄｙｎ／ｃｍ^２
２０℃における損失正接ｔａｎδ ０．１２
であった。
また中間層組成物のみで測定した特性は、
０℃における貯蔵弾性率Ｅ´ ６．５×１０^９ ｄｙｎ／ｃｍ^２
２０℃における貯蔵弾性率Ｅ´ １．１×１０^９ ｄｙｎ／ｃｍ^２
２０℃における損失正接ｔａｎδ ０．３５
であった。
【００４５】
（実施例２）
ブローアツプ比を５．０とした以外は実施例１と同様にして、総厚み１５μｍ（３／９／３μｍ）のフイルムを得た。
（実施例３）
ブローアツプ比を４．０とした以外は実施例１と同様にして、総厚み１５μｍ（３／９／３μｍ）のフイルムを得た。
【００４６】
（実施例４）
表裏層としてエチレン−メタクリル酸共重合体（メタクリル酸含量１２重量％、１９０℃ＭＦＲ７．０ｇ／１０分）１００重量部に対し防曇剤としてジグリセリンモノオレ−ト３重量部を混練した組成物を用いた以外は実施例１と同様にして総厚み１５μｍ（３／９／３μｍ）のフイルムを得た。
【００４７】
（比較例１）
表裏層および中間層の厚みを各々６μｍ、３μｍとした以外は実施例１と同様にして総厚み１５μｍ（６／３／６μｍ）のフイルムを得た。
（比較例２）
中間層として、実施例１で用いた直鎖状エチレン−ブテン−１共重合体のみを用いた以外は実施例１と同様にして総厚み１５μｍ（３／９／３μｍ）のフイルムを得た。
【００４８】
（実施例５）
エチレンとノルボルネンからなるエチレン−環状オレフイン共重合体（ガラス転移温度８０℃、三井石油化学社製アペル６５０９）１００重量部に、液状ポリブテン（分子量５００、日本石油社製ＬＶ−１００）を４０重量部混合した樹脂層を中間層（９μｍ）とし、一方実施例１で用いたのと同じＥＶＡ組成物を表裏層として各々３μｍ配し、実施例１と同様にして総厚み１５μｍ（３／９／３μｍ）のフイルムを得た。
【００４９】
なお、エチレン−環状オレフイン共重合体単独で測定した特性は、
０℃における貯蔵弾性率Ｅ´ １．８×１０^１０ｄｙｎ／ｃｍ^２
２０℃における貯蔵弾性率Ｅ´ １．８×１０^１０ｄｙｎ／ｃｍ^２
２０℃における損失正接ｔａｎδ ０．０１
であった。
またエチレン−環状オレフイン共重合体に液状ポリブテンを混合した組成物単独で測定した特性は、
０℃における貯蔵弾性率Ｅ´ １．２×１０^１０ｄｙｎ／ｃｍ^２
２０℃における貯蔵弾性率Ｅ´ ２．５×１０^９ ｄｙｎ／ｃｍ^２
２０℃における損失正接ｔａｎδ ０．６０
であった。
【００５０】
（実施例６）
表裏層および中間層の厚みを各々５μｍ、５μｍとした以外は実施例４と同様にして総厚み１５μｍ（５／５／５μｍ）のフイルムを得た。
（比較例３）
表裏層および中間層の厚みを各々６μｍ、３μｍとした以外は実施例４と同様にして総厚み１５μｍ（６／３／６μｍ）のフイルムを得た。
【００５１】
（比較例４）
中間層として、エチレン−環状オレフイン共重合体１００重量部に液状ポリブテンを３０重量部混合した組成物を用いた以外は実施例４と同様にして総厚み１５μｍ（３／９／３μｍ）のフイルムを得た。
中間層組成物単独で測定した特性は、
０℃における貯蔵弾性率Ｅ´ １．８×１０^１０ｄｙｎ／ｃｍ^２
２０℃における貯蔵弾性率Ｅ´ ８．０×１０^９ ｄｙｎ／ｃｍ^２
２０℃における損失正接ｔａｎδ ０．２２
であった。
【００５２】
（比較例５）
市販のポリ塩化ビニルストレツチフイルム（厚さ１５μｍ）について評価を行った。
これらのフイルムについての特性、性能の測定評価結果を表１〜３に示す。
【００５３】
【表１】

【表２】

【表３】

【表４】

【００５４】
実施例１のフイルムは、直鎖状エチレン−ブテン−１共重合体にシクロペンタジエンを主体とする石油樹脂の水素添加品を混合した層を含むことにより、粘弾性特性が本発明で規定する範囲内にあり、諸特性に優れていた。また実施例２〜６のフイルムも同様に優れていたが、実施例３のフイルムはρ_１５０ ／ρ_５０が好適範囲外にあって、やや包装適性が劣っていた。
【００５５】
【発明の効果】
本発明ストレツチフイルムによれば、自動包装機などに使用した場合にフイルムのカツト・搬送やラツピングを問題なく行うことができ、底シール性が良好で、またフイルムの張りがよい包装体を得ることができ、非塩ビ系ストレツチフイルムとして従来にない特徴を有している。[0001]
[Industrial applications]
The present invention relates to a stretch film used for food packaging, and more particularly to a stretch film made of a material containing no chlorine.
[0002]
[Prior art]
Conventionally, as a stretch film for so-called pre-package cages, in which fruits and vegetables, meat, side dishes, etc. are placed on a lightweight tray and overlapped with a film, a polyvinyl chloride-based one has been mainly used. This has good packaging efficiency, good packaging finish, etc., and excellent elastic recovery force that returns to the original state even after deformation such as pressing the film after packing, and good bottom sealability. This is because the merchandise and the consumer have the superiority of the quality that the value of the merchandise does not decrease, for example, the film is hardly peeled off during the transportation display.
[0003]
[Problems to be solved by the present invention]
However, in recent years, problems such as hydrogen chloride gas generated during incineration of a polyvinyl chloride film and elution of a large amount of a plasticizer have been regarded as problems. For this reason, various alternatives to the polyvinyl chloride film have been studied, and in particular, various stretch films using a polyolefin resin have been proposed. For example, a stretch film having a constitution of ethylene-vinyl acetate copolymer (EVA), EVA / polybutene-1 / EVA, EVA / linear ethylene-α-olefin copolymer / EVA, etc. has been proposed. Polyolefin-based resins are easily available, are excellent in water resistance, oil resistance, hygiene, ease of treatment after use, are easy to form films, and are excellent in mechanical strength and the like.
[0004]
However, since the polyolefin resin as described above is generally crystalline, the elongation tends to be uneven. In addition, if the tension is removed in the stretched state, if the tension is removed, it is restored instantaneously, so that there is a problem that the packaging operation is difficult, and it is difficult to satisfy all the characteristics such as packaging workability, packaging finish, elastic recovery force, and bottom sealability.
[0005]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have succeeded in obtaining a non-PVC-based stretch film excellent in the above-mentioned properties, and the gist thereof is that a repeating unit of α-olefin mainly composed of ethylene, Storage elasticity measured at a frequency of 10 Hz and a temperature of 20 ° C. by dynamic viscoelasticity measurement, comprising at least one layer of a mixed resin containing a cyclic olefin repeating unit bonded to or not bonded to α-olefin repeating unit. A stress (E ′) in the range of 5.0 × 10 ⁸ to 5.0 × 10 ⁹ dyn / cm ² and a loss tangent (tan δ) in the range of 0.2 to 0.8. It is in Tsuchifilm.
[0006]
That is, the present invention provides a film that exhibits uniform elongation by reducing crystallinity by allowing bulky cyclic olefin repeating units to coexist with ethylene-based α-olefin repeating units, and further has a specific viscoelasticity. It has been found that by imparting properties, a film having good packaging workability and packaging finish can be obtained.
[0007]
Hereinafter, the present invention will be described in detail. The stretch film of the present invention comprises at least a layer of a mixed resin containing a repeating unit of α-olefin mainly composed of ethylene and a repeating unit of cyclic olefin bonded to or not bonded to the repeating unit of α-olefin. Have more.
[0008]
Specific examples thereof include (A ₁ ) a resin mainly composed of α-olefin repeating units mainly composed of ethylene mixed with a polymer material mainly composed of (B ₁ ) cyclic olefin repeating units mainly. No.
[0009]
The resin (A ₁ ) composed of a repeating unit of α-olefin mainly composed of ethylene includes a unit derived from ethylene or a unit derived from another α-olefin, and / or a unit other than α-olefin. Such as low-density polyethylene, ultra-low-density polyethylene, medium-density polyethylene, ethylene-vinyl acetate copolymer (EVA), ethylene-alkyl acrylate copolymer, and ethylene-alkyl methacrylate. Copolymers, ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, ethylene-propylene copolymers, ethylene-butene-1 copolymers, and polymers such as ionomers of these resins can be given. . Further, an ethylene-cyclic olefin copolymer obtained by copolymerizing a small amount (for example, within 5 mol%) of a cyclic olefin may be used.
[0010]
As these resins, those known per se for films can be used. In general, from the viewpoint of film formability and film strength, the melt flow ratio MFR (190 ° C., 2.16 kg load) is 0.1 to 5 g. Resin for about / 10 minutes can be used. Further, in order to obtain the flexibility required for a stretch film, a resin having an ethylene unit of 60 mol% or more, preferably 80 mol% or more is suitable.
[0011]
On the other hand, as the polymer material having a cyclic olefin unit of (B ₁ ), a petroleum resin mainly composed of a repeating unit derived from cyclopentadiene represented by the following formula (1) or a hydrogenated product thereof,
Embedded image

[0012]
A so-called coumarone-indene resin obtained by copolymerizing a small amount of coumarone with indene represented by the following formula (2):
Embedded image

[0013]
Terpene resin mainly composed of a repeating unit derived from α-pinene represented by the following formula (3) or a hydrogenated product thereof:

[0014]
And the like. Here, the cyclic olefin may have at least one double bond, and includes, for example, a cyclic diolefin.
[0015]
The component (B ₁ ) exemplified here can have various characteristics depending on the degree of polymerization, the copolymerization component, the hydrogenation rate, the catalyst system to be used, and the like. The glass transition temperature is 70 ° C. or higher, particularly preferably 80 ° C. or higher, in relation to the component A ₁ ).
[0016]
In general, as the molecular weight of the component (B ₁ ) increases, the compatibility with the component (A ₁ ) tends to deteriorate. Therefore, the molecular weight is generally in the range of 700 to 900 from both the glass transition temperature and the compatibility. Some are preferred, and those having a sharp molecular weight distribution are preferred.
[0017]
The component (B ₁ ) is compatible with the component (A ₁ ) which is originally crystalline in a fine order to lower its crystallinity, and also changes the stress behavior characteristic of the component (A ₁ ) to be described later. Such characteristics can be achieved. The mixing ratio of the component (A ₁ ) and the component (B ₁ ) is determined in accordance with the viscoelasticity standard described later.
[0018]
The film of the present invention has a storage elastic modulus (E ′) measured at a frequency of 10 Hz and a temperature of 20 ° C. by dynamic viscoelasticity measurement in a range of 5.0 × 10 ⁸ to 5.0 × 10 ⁹ (dyn / cm ² ). And the loss tangent (tan δ) is in the range of 0.2 to 0.8.
If E ′ is less than 5.0 × 10 ⁸ dyn / cm ² , the film is soft and the stress against deformation is too small, so that the workability is poor, the film of the packaged product is not stretched, and the film is suitable as a stretch film. Absent. On the other hand, if E ′ exceeds 5.0 × 10 ⁹ dyn / cm ² , the film becomes hard and hard to expand, and the tray is easily deformed or crushed.
[0019]
If the tan δ is less than 0.2, the film is instantaneously restored to the elongation of the film, so that the film is restored in a short time before the film is folded into the bottom of the tray, and the film does not stretch properly. Wrinkles are easy to occur. Also, in the heat-sealed state of the bottom, in the case of stretch packaging, sufficient fusion by heat is difficult to be performed, so that the bottom seal is likely to peel off during transportation or display after packaging. When tan δ exceeds 0.8, the packaging finish is good, but plastic deformation is exhibited, and the tension against the external force of the packaged product is too weak. The film is easy to sag and the commercial value is easy to decrease. In the case of automatic packaging, problems such as poor chucking tend to occur because the package is easily stretched vertically. A particularly preferred range of tan δ is 0.30 to 0.60.
[0020]
The component (A ₁ ) generally has a glass transition temperature of −40 to 0 ° C., and a tan δ at 20 ° C. of about 0.1 to 0.15, so that the intended properties of the present invention cannot be obtained by itself. Therefore, by containing and dispersing the component (B ₁ ) having a high glass transition temperature, the glass transition temperature of the mixture is increased, the tan δ at 20 ° C. is increased, and the crystallinity is reduced. can get.
[0021]
In order to satisfy the above characteristics, the mixing ratio of the component (A ₁ ) and the component (B ₁ ) is important. Since the mixing ratio of the component (A ₁ ) and the component (B ₁ ) is different depending on the combination of the materials used, it is generally difficult to define the mixing ratio. However, when the component (B ₁ ) is less than 20% by weight, the mixing ratio of the component (A ₁ ) Crystallinity remains strong and tan δ is low, which is not preferable. On the other hand, if it exceeds 35% by weight, the storage elastic modulus (E ') of the film is lowered, and the strength is also lowered, so that the packaging workability and the like are lowered. Further, a problem such as that the component (B ₁ ) blows out to the film surface is likely to occur. As a standard of the mixing ratio, the glass transition temperature of the mixture is set so as to fall within a range of -10 to 10C.
[0022]
The stretch film is sometimes used at a low temperature, and it is desirable that the stretch film has excellent low temperature characteristics (especially, elongation). For this purpose, the storage of the film measured at a frequency of 10 Hz and a temperature of 0 ° C. by dynamic viscoelasticity measurement is required. It is preferable that the elastic modulus (E ′) is in a range of 1.5 × 10 ¹⁰ dyn / cm ² or less.
[0023]
For that purpose, it is effective to increase the ratio of the component (A ₁ ) having excellent low-temperature characteristics. The mixing ratio of the component (A ₁ ) and the component (B ₁ ) satisfies the viscoelasticity at a temperature of 20 ° C. This is achieved by setting the (A ₁ ) component to be relatively large within the range. The component (B ₁ ) often provides the film with tackiness. Therefore, since a blocking when large amounts are added as described above is likely to occur, (A ₁₎ component and the (B ₁₎ mixed resin layer of the components, (A ₁₎ component alone or (A ₁₎ component is extremely large surface Layers can also be stacked.
[0024]
As another example of the material system of the film of the present invention, (A ₂ ) a layer made of a copolymer resin of α-olefin unit and cyclic olefin unit mainly composed of ethylene,
Alternatively, there may be mentioned those having a layer made of a combination of (A ₂ ) a copolymer resin of α-olefin unit mainly composed of ethylene and a cyclic olefin unit, and (B ₂ ) a property adjusting material.
[0025]
Here, the α-olefin unit mainly composed of ethylene as the component (A ₂ ) is mainly composed of ethylene, and if necessary, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, etc. Α-olefin unit of Examples of the cyclic olefin unit include a cyclic olefin represented by the following general formula (4).
[0026]
Embedded image

[0027]
Specifically, norbornene, 5-methylnorbornene, 5-ethylnorbornene, 5-propylnorbornene, 1-methylnorbornene, 7-methylnorbornene, 5,5,6-trimethylnorbornene, 5-phenylnorbornene, 5-benzyl Norbornene and the like can be mentioned.
The resin may contain other copolymerizable monomers, if necessary, as long as the object of the present invention is not impaired. Examples thereof include butadiene and isoprene.
[0028]
When a layer comprising the component (A ₂ ) is provided, the type of the cyclic olefin unit and the copolymerization ratio are controlled to a specific range, two or more copolymer resins having different copolymerization ratios are blended, It can be adjusted to satisfy the conditions such as E ′ and tan δ by copolymerizing the three components.
[0029]
However, as long as the above properties are satisfied, the crystallinity of the copolymer resin is considerably lowered, and the glass transition temperature is not high. May occur. Further, in a range satisfying E ′ or tan δ at 20 ° C., E ′ at 0 ° C. becomes high, and it may not be perfect in terms of low-temperature suitability.
[0030]
From this point, it is also possible to use an ethylene-cyclic olefin copolymer resin having a high cyclic olefin content as the component (A ₂ ) and mix the material (B ₂ ) with the property improving material.
[0031]
As an example of the property improving material (B ₂ ), low polymerization degree polybutene can be mentioned. That is, plasticization is performed by mixing a resin having a low glass transition temperature such as polybutene having a low degree of polymerization with good compatibility with a resin having a glass transition temperature of 40 ° C. or higher, which is a general ethylene-cyclic olefin copolymer resin. The effect imparts flexibility and lowers the glass transition temperature, so that the film is modified in a more preferable direction as a stretch film.
[0032]
Here, as the low polymerization degree polybutene, those having an average molecular weight of 100 or more and 1,000 or less in consideration of compatibility and blowing to the film surface after molding are preferable. When the glass transition temperature of the component (A ₂ ) is 40 ° C. or higher, the mixing ratio is preferably about 35 to 50 parts by weight per 100 parts by weight of the component (A ₂ ).
[0033]
In addition, as a material having a low glass transition temperature and a good compatibility with an ethylene-cyclic olefin copolymer resin, a copolymer of a vinyl aromatic compound and a conjugated diene, for example, a triblock copolymer of styrene-butadiene-styrene, (SBS) and styrene-isoprene-styrene triblock copolymer (S1S). In this case, the styrene ratio is preferably 30% by weight or less in order to maintain flexibility at room temperature.
[0034]
In the case of using the property improving material as described above, tan δ at 20 ° C. tends to be too large by the above-mentioned modification alone, showing plastic deformation and weakening of the packaged product. It is appropriate to laminate a non-PVC material layer having a small thickness. The other resin layer is preferably a polyolefin-based polymer. By laminating the resin layer with the resin layer, it is possible to adjust the viscoelastic properties and to impart stability of film formation, anti-blocking property, slip property and the like.
[0035]
Here, as the polyolefin-based polymer as the laminate material, low-density polyethylene, ultra-low-density polyethylene (copolymer of ethylene and α-olefin), ethylene-vinyl acetate copolymer (EVA), ethylene-alkyl acrylate Polymers, ethylene-alkyl methacrylate copolymers, ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, ionomers such as low-density polyethylene, and propylene-based elastomer materials are preferred.
[0036]
Practically, for example, EVA can be suitably used. The EVA has a vinyl acetate content of 5 to 25% by weight, preferably 10 to 20% by weight, and a melt flow rate (MFR) of 0.2 to 2 g. / 10 minutes (190 ° C., 2.16 kg load) is preferable in terms of strength, flexibility, film formability and the like.
The film of the present invention further has a ratio (ρ ₁₅₀ / ρ ₅₀ ) of a stress ρ ₁₅₀ at 150% elongation measured at a temperature of 20 ° C. and a stress ρ ₅₀ at 50% elongation of 1.3 or less in both the vertical and horizontal directions. It preferably has a stress-strain characteristic in the range of 2.0.
[0037]
If the ratio (ρ ₁₅₀ / ρ ₅₀ ) is less than 1.3, uneven elongation at the time of packaging is exhibited, and local elongation tends to cause tearing at corners of the tray. On the other hand, if the ratio exceeds 2.0, a strong force is required to extend the film during the packaging operation, and the workability is reduced, and the tray is easily deformed or crushed in packaging by an automatic packaging machine.
[0038]
When an ethylene-based polymer film is produced by the inflation method, which is a general method for producing stretch films, ρ ₁₅₀ / ρ ₅₀ tends to be large in the vertical direction and small in the horizontal direction. It is important to set ₁₅₀ / ρ ₅₀ to a specific range. For that purpose, it is effective to increase the blow-up ratio (bubble diameter / die diameter) at the time of inflation molding. The blow-up ratio is generally 4 or more, preferably 5 to 6, depending on the raw material used. You can choose from. In general, the thickness of the film of the present invention is in the range used for ordinary stretch packaging, that is, about 8 to 30 μm, typically about 10 to 20 μm.
[0039]
The film of the present invention is obtained by melt-extruding a material from an extruder and forming the film by inflation molding or T-die molding. In the case of forming a laminated film, it is advantageous to co-extrude with a multilayer die.
Practically, it is preferable to melt extrude the material resin from the annular die to perform inflation molding.
[0040]
Various additives can be added to the film of the present invention in order to impart properties such as antifogging property, antistatic property and slipperiness. For example, a surfactant such as glycerin fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, and ethylene oxide adduct can be appropriately added.
[0041]
【Example】
The effects of the present invention will be clarified by the following examples. The characteristics and performance of the film were measured and evaluated by the following methods.
1) E ', tan δ
Using a viscoelastic spectrometer VES-F3 manufactured by Iwamoto Seisakusho Co., Ltd., the film was measured in the transverse direction at a vibration frequency of 10 Hz, a temperature of 20 ° C. and 0 ° C.
[0042]
2) Stretch wrapping suitability Using a stretch film with a width of 350 mm, an automatic wrapping machine (ISHIDA / Wmin MK-II, manufactured by Ishida Koki Co., Ltd.) is used to wrap a foamed polystyrene tray (length 200 mm, width 130 mm, height 30 mm). Then, the items shown in Table 4 were evaluated. Using the same film and tray, a packaging test was performed using a hand wrapping machine (Diawrapper A-105 manufactured by Mitsubishi Plastics, Inc.).
3) ρ ₁₅₀ / ρ ₅₀
Calculated by conducting a tensile test at a tensile speed of 200 mm / min according to JIS K1702.
[0043]
(Example 1)
75% by weight of a linear ethylene-butene-1 copolymer (butene-1 content 14% by weight, density 0.905) and a hydrogenated product of a petroleum resin mainly composed of cyclopentadiene (glass transition temperature 81 ° C, Arakawa A composition obtained by mixing 25% by weight of Alcon P125 (manufactured by Kagaku Co.) was used as an intermediate layer (9 μm in thickness), while antifogging was performed on 100 parts by weight of EVA (vinyl acetate content: 15% by weight, 190 ° C. MFR: 2.0 g / 10 minutes) A composition obtained by kneading 3 parts by weight of diglycerin monooleate as an agent was disposed in a thickness of 3 μm each as a front and back layer, and a total thickness of 15 μm (3/9) was formed by coextrusion inflation molding at a blow-up ratio (BUR) of 6.0. / 3 µm).
[0044]
The properties measured with the linear ethylene-butene-1 copolymer alone are as follows:
Storage elastic modulus at 0 ° C. E ′ 2.0 × 10 ⁹ dyn / cm ²
Storage modulus E ′ at 20 ° C. 1.2 × 10 ⁹ dyn / cm ²
Loss tangent tan δ at 20 ° C. 0.12
Met.
The characteristics measured only with the intermediate layer composition are as follows:
Storage modulus E ′ at 0 ° C. 6.5 × 10 ⁹ dyn / cm ²
Storage modulus E ′ at 20 ° C. 1.1 × 10 ⁹ dyn / cm ²
Loss tangent tan δ at 20 ° C. 0.35
Met.
[0045]
(Example 2)
A film having a total thickness of 15 μm (3/9/3 μm) was obtained in the same manner as in Example 1 except that the blow-up ratio was changed to 5.0.
(Example 3)
A film having a total thickness of 15 μm (3/9/3 μm) was obtained in the same manner as in Example 1 except that the blow-up ratio was set to 4.0.
[0046]
(Example 4)
100 parts by weight of an ethylene-methacrylic acid copolymer (methacrylic acid content: 12% by weight, 190 ° C. MFR: 7.0 g / 10 minutes) as front and back layers, and kneaded with 3 parts by weight of diglycerin monooleate as an antifog agent A film having a total thickness of 15 μm (3/9/3 μm) was obtained in the same manner as in Example 1 except for using.
[0047]
(Comparative Example 1)
A film having a total thickness of 15 μm (6/3/6 μm) was obtained in the same manner as in Example 1 except that the thicknesses of the front and back layers and the intermediate layer were changed to 6 μm and 3 μm, respectively.
(Comparative Example 2)
A film having a total thickness of 15 μm (3/9/3 μm) was obtained in the same manner as in Example 1 except that only the linear ethylene-butene-1 copolymer used in Example 1 was used as the intermediate layer.
[0048]
(Example 5)
40 parts by weight of liquid polybutene (molecular weight: 500, LV-100 manufactured by Nippon Oil Co., Ltd.) is added to 100 parts by weight of an ethylene-cyclic olefin copolymer composed of ethylene and norbornene (glass transition temperature: 80 ° C., Apel 6509 manufactured by Mitsui Petrochemical Co., Ltd.) The mixed resin layer was used as an intermediate layer (9 μm). On the other hand, the same EVA composition as used in Example 1 was disposed at 3 μm each as a front and back layer, and the total thickness was 15 μm (3/9/3 μm) as in Example 1. ) Film was obtained.
[0049]
The properties measured with the ethylene-cyclic olefin copolymer alone are as follows:
Storage elastic modulus E ′ at 0 ° C. 1.8 × 10 ¹⁰ dyn / cm ²
Storage elastic modulus E ′ at 20 ° C. 1.8 × 10 ¹⁰ dyn / cm ²
Loss tangent tan δ 0.01 at 20 ° C. 0.01
Met.
In addition, the properties measured with a composition obtained by mixing liquid polybutene with an ethylene-cyclic olefin copolymer alone are as follows:
Storage modulus E ′ at 0 ° C. 1.2 × 10 ¹⁰ dyn / cm ²
Storage elastic modulus at 20 ° C. E ′ 2.5 × 10 ⁹ dyn / cm ²
Loss tangent tan δ at 20 ° C. 0.60
Met.
[0050]
(Example 6)
A film having a total thickness of 15 μm (5/5/5 μm) was obtained in the same manner as in Example 4 except that the thickness of the front and back layers and the thickness of the intermediate layer were 5 μm and 5 μm, respectively.
(Comparative Example 3)
A film having a total thickness of 15 μm (6/3/6 μm) was obtained in the same manner as in Example 4 except that the thicknesses of the front and back layers and the intermediate layer were changed to 6 μm and 3 μm, respectively.
[0051]
(Comparative Example 4)
As the intermediate layer, a film having a total thickness of 15 μm (3/9/3 μm) was prepared in the same manner as in Example 4 except that a composition obtained by mixing 30 parts by weight of liquid polybutene with 100 parts by weight of an ethylene-cyclic olefin copolymer was used. Obtained.
The properties measured with the intermediate layer composition alone are:
Storage modulus E ′ at 0 ° C. 1.8 × 10 ¹⁰ dyn / cm ²
Storage elastic modulus E ′ at 20 ° C. 8.0 × 10 ⁹ dyn / cm ²
Loss tangent tan δ at 20 ° C. 0.22
Met.
[0052]
(Comparative Example 5)
An evaluation was made of a commercially available polyvinyl chloride stretch film (thickness: 15 μm).
Tables 1 to 3 show measurement and evaluation results of characteristics and performances of these films.
[0053]
[Table 1]

[Table 2]

[Table 3]

[Table 4]

[0054]
The film of Example 1 contains a layer in which a hydrogenated product of a petroleum resin mainly composed of cyclopentadiene is mixed with a linear ethylene-butene-1 copolymer, so that the viscoelastic property is within the range specified by the present invention. And excellent in various properties. The films of Examples 2 to 6 were similarly excellent, but the film of Example 3 had ρ ₁₅₀ / ρ ₅₀ outside the preferred range, and was somewhat inferior in packaging suitability.
[0055]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the stretch film of this invention, when it uses for an automatic packaging machine etc., the cut-off / transportation and wrapping of a film can be performed without a problem, and the packaging body with good bottom sealing property and good film tension is obtained. It has a unique feature as a non-PVC-based stretch film.

Claims (3)

The following laminated body (1) or (2), wherein the storage elastic modulus (E ′) measured at a frequency of 10 Hz and a temperature of 20 ° C. by dynamic viscoelasticity measurement is from 5.0 × 10 ⁸ to 5.0 × 10 ^9. A stretch film for food packaging, wherein dyn / cm ² and loss tangent (tan δ) are in the range of 0.2 to 0.8.
(1) (A ₁ ) A mixed resin layer composed of a resin mainly composed of α-olefin repeating units mainly composed of ethylene and a polymer material mainly composed of (B ₁ ) cyclic olefin repeating units mainly contains ethylene. Laminate having a surface layer made of a resin mainly composed of a repeating unit of α-olefin whose main component is
(2) (A ₂ ) a copolymer resin of α-olefin units mainly composed of ethylene and cyclic olefin units, (B ₂ ) a low-polymerization degree polybutene, a triblock copolymer of styrene-butadiene-styrene and styrene-isoprene A layer made of an olefin polymer having a loss tangent (tan δ) smaller than that of the mixed resin layer, which is different from the mixed resin layer , in a layer of a mixed resin made of a property improving material selected from a triblock copolymer of styrene. Laminated body made by laminating 2. The film according to claim 1, wherein the storage elastic modulus (E ') of the film measured at a frequency of 10 Hz and a temperature of 0 ° C. by dynamic viscoelasticity measurement is in a range of 1.5 × 10 ¹⁰ dyn / cm ² or less. Stretch film for food packaging. The ratio (ρ ₁₅₀ / ρ ₅₀ ) of the stress ρ ₁₅₀ at 150% elongation and the stress ρ ₅₀ at 50% elongation measured at a temperature of 20 ° C. is in the range of 1.3 to 2.0 in both the vertical and horizontal directions. 2. The stretch film for food packaging according to claim 1, wherein