JP4188093B2 - Heat shrinkable packaging material - Google Patents

Description

上式中Ｒ₃は水素又はアルキル基を示し、好ましくはメチル基である。Ｒ₄は水素又はアルキル基を示し、好ましくは炭素数１〜２０のアルキル基である。
【００２２】
該スチレン−（メタ）アクリル酸エステル共重合体において、最も好適に使用されるスチレン系単量体としてはスチレンであり、（メタ）アクリル酸エステル系単量体としてはブチルアクリレートである。
【００２３】
該スチレン−ブチルアクリレート共重合体におけるスチレン含有量は、一般的には５０〜９８重量％であり、７５〜９５重量％の範囲が好ましい。スチレン含有量が前記下限値未満では、得られる積層フィルムの剛性が低く、好ましくない。一方、上記上限値を越えると、得られる積層フィルムに低温収縮性を付与することが困難となる。
【００２４】
スチレン−ブチルアクリレート共重合体は、優れた低温収縮特性を付与できるが、硬くて脆いため、該樹脂単体での使用は好ましくない。該樹脂にスチレン系単量体と共役ジエン系単量体とからなるブロック共重合体を少なくとも１種以上配合することにより、積層フィルムに耐衝撃性が付与され、好ましい。
【００２５】
環状オレフィン系樹脂としては、ガラス転移温度５０〜９０℃であるものが好ましい。ガラス転移温度が上記下限値未満では得られる積層フィルムの自然収縮（例えば３０℃、３０日保存後の収縮率）が大きく、寸法安定性に欠けるフィルムとなり易く、一方、９０℃を超える場合、低温延伸が困難となり、良好な低温収縮特性が得られにくくなる。
【００２６】
該環状オレフィン系重合体の結合形態は、上述した条件を満足すれば特に制限はなく、下記一般式〔Ｂ〕で表される環状オレフィンとエチレンとのランダム共重合体、環状オレフィン開環（共）重合体、環状オレフィン開環（共）重合体の水素化物、およびこれらの（共）重合体のグラフト変性物などが挙げられる。
【化２】

上式において、R¹〜R¹²は、水素原子または炭化水素基であって、互いに同一でも異なっていてもよい。又、R⁵とR¹⁰又はR¹¹とR¹²は一体化して2価の炭化水素基を形成してよい。また、R³もしくはR¹⁰とR¹¹もしくはR¹²とは環を形成してもよい。ｎは０または正の整数であって、ｎが２以上である場合には、各繰り返し単位におけるR⁵〜R⁸は、互いに同一でも異なっていてもよい。
【００２７】
環状オレフィンの例としては、ビシクロヘプト−２−エン（２−ノルボルネン）およびその誘導体及びテトラシクロ−３−ドデセンおよびその誘導体が挙げられる。ビシクロヘプト−２−エン（２−ノルボルネン）およびその誘導体の例には、ノルボルネン、６−メチルノルボルネン、６−エチルノルボルネン、６−ｎ−ブチルノルボルネン、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、５，６−ジ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が包含される。
【００２８】
テトラシクロ−３−ドデセンおよびその誘導体の例には、８−メチルテトラシクロ−３−ドデセン、８−エチルテトラシクロ−３−ドデセン、８−ヘキシルテトラシクロ−３−ドデセン、２，１０−ジメチルテトラシクロ−３−ドデセン、５，１０−ジメチルテトラシクロ−３−ドデセンなどが包含される。
【００２９】
本発明においては、環状オレフィンとエチレンとのランダム共重合体、例えば、上記一般式〔Ｂ〕で表される環状オレフィンの含有量が、共重合体重量の２０〜５０モル％程度である、該環状オレフィンとエチレンとの共重合体を好適に使用することができる。また、エチレン以外のα−オレフインを含むもの、又、第３成分としてブタジエン、イソプレンなどをさらに含有するものであってもよい。
【００３０】
環状オレフィンの含有量により各種のガラス転移温度を有するものがあり、例えば、三井化学（株）製の「アペル」（商品名）、Ｔｉｃｏｎａ社製の「Ｔｏｐａｓ」（商品名）、日本ゼオン（株）製の「ゼオノア７５０R」（商品名）等を挙げることができる。なお、環状オレフィン系重合体は、例えば、特開昭６０−１６８７０８号公報、特開昭６１−１２０８１６号公報、特開昭６１−１１５９１２号公報、特開昭６１−１１５９１６号公報、特開昭６１−２７１３０８号公報、特開昭６１−２７２２１６号公報、特開昭６２−２５２４０６号公報、特開昭６２−２５２４０７号公報などに記載されている公知の方法に準じて製造することができる。
【００３１】
さらに、本発明において、環状オレフィン系樹脂としては、環状オレフィン系ランダム共重合体、環状オレフィン開環（共）重合体あるいは環状オレフィン開環（共）重合体の水添物を、例えば無水マレイン酸、マレイン酸、無水イタコン酸、イタコン酸、（メタ）アクリル酸等の不飽和カルボン酸あるいはその無水物等の変性剤で変性したグラフト重合体も使用することができる。これらの変性剤は、単独であるいは組み合わせて使用することができる。
【００３２】
積層フィルムの該両外層には、本発明の目的に支障を来たさない範囲で上記の樹脂組成物の他に、汎用ポリスチレン、耐衝撃性ポリスチレン、水添スチレン−ブタジエンブロック共重合体、水添スチレン−イソプレンブロック共重合体、高密度ポリエチレン、低密度ポリエチレン、エチレン−α−オレフィン共重合体、ポリプロピレン系樹脂、プロピレン−α−オレフィン共重合体、さらに脂肪族炭化水素樹脂、脂環族炭化水素樹脂、ロジン誘導体、テルペン樹脂、テルペンフェノール樹脂及びこれらの水素添加物等を混合して使用してもよい。
【００３３】
積層フィルム中間層のオレフィン系樹脂としては、密度が０．９４０g/cm³未満であって、エチレン、プロピレン等の炭素数２〜２０のα−オレフィンを１種又は２種以上含む（共）重合体、及び／又はα−オレフィンと共重合可能なα−オレフィン以外の単量体、例えば酢酸ビニルやアクリル酸及びその誘導体、メタクリル酸及びその誘導体等を含む共重合体、又はこれらの混合樹脂が挙げられる。
【００３４】
上記オレフィン系樹脂として好ましい重合体は、エチレン、又はプロピレンを主成分とし、それ以外の炭素数２〜８のα−オレフィンを１種又は２種以上含むエチレン系共重合体、又はプロピレン系共重合体であり、より好適に使用される重合体は、メタロセン触媒により重合された共重合体である。メタロセン触媒により重合されたエチレン系共重合体やプロピレン系共重合体からなるフィルムは、チーグラー触媒による共重合体からなるフィルムに比べ、機械的特性や透明性等の点で優れるためである。
【００３５】
示差走査熱量計により測定される該オレフィン系樹脂の融点は、好ましくは１６０℃以下であり、１４５℃以下がより好ましく、８０〜１１０℃の範囲が最も好ましい。８０℃未満では、得られる積層フィルムの剛性が低く、フィルムの腰がなくなり好ましくない。また、１６０℃を越える場合は積層フィルムの低温延伸が困難となり、良好な低温収縮特性が得られない場合が生じる。
【００３６】
該オレフィン系樹脂がエチレン系共重合体の場合、該共重合体のメルトフローインデックス（以下、「ＭＩ」と略する。）は、温度１９０℃、荷重２１．１８Ｎで０．５〜２０ｇ／１０分が好ましく、１〜５ｇ／１０分がより好ましい。ＭＩが０．５ｇ／１０分未満の場合は、溶融押出時の押出負荷が大きくなる場合があり、また、２０ｇ／１０分を越えると、延伸安定性が低下する場合がある。
【００３７】
また、該オレフィン系樹脂がプロピレン系共重合体の場合、そのＭＩは温度２３０℃、荷重２１．１８Ｎで０．５〜２０ｇ／１０分が好ましく、１〜１０ｇ／１０分がより好ましい。ＭＩが０．５ｇ／１０分未満の場合は、溶融押出時の押出負荷が大きくなる場合があり、また、２０ｇ／１０分を越えると、延伸安定性が低下する場合がある。
【００３８】
さらに、該オレフィン系樹脂の融点が１２０〜１６０℃である場合、積層フィルムの低温収縮特性を向上させる為に、オレフィン系樹脂に石油系樹脂を添加してもよい。該石油系樹脂としては、脂肪族炭化水素樹脂、脂環族炭化水素樹脂、ロジン誘導体、テルペン樹脂、テルペンフェノール樹脂等及びこれらの水素添加物等が挙げられ、耐熱性等の点から水素添加した炭化水素系樹脂の使用が好ましい。市販品としては、例えばアルコン（荒川化学工業（株）製）、クリアロン（ヤスハラケミカル（株）製）等が挙げられる。これらの石油系樹脂の軟化点は、１１０℃以上が好ましく、１２０〜１５０℃がより好ましい。軟化点が、１１０℃未満では、得られる積層フィルムの自然収縮が大きくなる場合があり、好ましくない。
【００３９】
上記オレフィン系樹脂と石油系樹脂とを混合割合は、オレフィン系樹脂／石油系樹脂＝９５〜６０／５〜４０重量％が好ましく、９０〜７０／１０〜３０重量％がより好ましい。石油系樹脂の配合量が５重量％未満の場合、添加する目的である低温収縮特性の改良効果が発現しにくく、また４０重量％を越えると延伸安定性が低下する場合が生じる。
【００４０】
上記両外層と中間層との接着性が低い場合、本発明の目的に支障を来たさない範囲で、両外層と中間層との接着性を向上させる樹脂を中間層、又は／及び両外層へ配合しても良く、さらに、該樹脂を主成分とする層を両外層と中間層との間に接着層として設けても良い。このような樹脂としては、例えば不飽和カルボン酸、不飽和カルボン酸エステル、不飽和カルボン酸無水物及び酢酸ビニルの中から選ばれる１種又は２種以上を含む変成オレフィン系樹脂、ナイロン系樹脂、ポリエステル系樹脂、また、スチレン−ブタジエンブロック共重合体やスチレン−イソプレンブロック共重合体、該ブロック共重合体の水素添加物及び不飽和カルボン酸又はその誘導体で変成した変成物、スチレン−エチレングラフト共重合体、スチレン−エチレンランダム共重合体等が挙げられる。
【００４１】
なお、上記の各樹脂には、必要に応じて、可塑剤、紫外線吸収剤、光安定剤、酸化防止剤、安定剤、着色剤、帯電防止剤、滑剤、無機フィラー等を適宜添加することができる。
【００４２】
上記の積層フィルムの製造は、任意の公知の方法で行うことができるが、上記の各層を構成する樹脂組成物を別々の押出機によって溶融し、これをダイ内で積層させて押し出す共押出成形法が好ましい。押出方法としては、Ｔダイ法、チューブラ法等、任意の方法を採用できる。溶融押出された積層樹脂は、冷却ロール、空気、水等で冷却された後、熱風、温水、赤外線、マイクロウウェーブ等の適当な方法で再加熱され、ロール法、テンター法、チューブラ法等により、一軸又は二軸に延伸される。
【００４３】
延伸温度は、積層フィルムを構成する上記各樹脂の軟化温度や上記積層フィルムに要求される用途によって適宜選択できるが、６０〜１３０℃が好ましく、８０〜１２０℃がより好ましい。６０℃未満では、延伸過程における材料の弾性率が高くなり過ぎて、延伸性が低くなり、フィルムの破断を引き起こし、又は、厚み斑が生じるなど、延伸が不安定になり易い。１３０℃を超えると、所望の収縮特性が得られず、また、延伸過程における材料の弾性率が低過ぎて、材料が自重で垂れ下がって延伸そのものが不可能になる場合がある。
【００４４】
延伸倍率は、積層フィルムの構成組成、延伸手段、延伸温度、目的の製品形態に応じて、２〜８倍とするのがよい。本発明における熱収縮性フィルムは、少なくとも一軸延伸されていることが必要であるが、所望により二軸延伸とすることができる。また、一軸延伸の場合でも、フィルムの機械物性改良の目的等で縦方向に１．０１〜１．８倍程度の弱延伸を付与することも効果的である。また、延伸した後の積層フィルムの分子配向が緩和しない時間内に速やかに冷却するのも、収縮性を付与する上で重要である。
【００４５】
【実施例】
以下、本発明を実施例により説明する。
実施例に示す測定値及び評価は次のように行った。ここで、熱収縮性フィルムの引取り（流れ）方向を「縦」方向、その直行方向を「横」方向と記載する。
（１）密度測定
ＪＩＳ Ｋ７１１２に準拠して温度２３℃において密度勾配管法により、フィルム又は包装材の密度を測定し、水の密度との比にから夫々の密度を算出した。
（２）熱収縮率
包装材を縦１００ｍｍ、横１００ｍｍの大きさに切り取り、８０℃の温水バスに１０秒間浸漬し収縮量を測定した。熱収縮率は、横方向について収縮前の原寸に対する収縮量の比（％）で表した。
（３）自然収縮率
包装材を横に１０００ｍｍの長さでけがき、３０℃の雰囲気の恒温槽に３０日間放置後、けがき間の長さＡ（ｍｍ）を測定し、下記式より自然収縮率（％）を算出した。
自然収縮率（％）＝（１０００−Ａ）／１０００×１００
表２において、自然収縮率が３％以下のものを「A」として、３％を超えるものを「B」として表した。
（４）全ヘ−ズ
熱収縮性フィルムの全ヘーズをＪＩＳＫ７１０５に準拠して測定し、７％以下のものを「A」、７％を超えるものを「B」とした。
（５）収縮仕上がり性
１０ｍｍ間隔の格子目を印刷した包装材を縦１００ｍｍ、横２９８ｍｍの大きさに切り取り、横方向の両端を１０ｍｍ重ねてテトラヒドロフラン／シクロヘキサン＝８／２溶液を用いて、又はヒートシールにより接着し、円筒状とした。この円筒状積層フィルムを、容量１．５リットルの円筒型PETボトルに装着し、蒸気加熱方式で３ｍの収縮トンネル内を回転させずに、１０秒間で通過させた。吹き出し蒸気温度は９７℃、トンネル内雰囲気温度は８７〜９５℃であった。
包装材の被覆後、発生したシワ入り、アバタ、歪みの大きさ及び個数を総合的に評価した。評価基準は、シワ入り、アバタはなく、格子目の歪みも実用上問題なく、かつフィルムの密着性が良好なものを「A」、シワ入り、アバタ、格子目の歪みがあるものを「B」、シワ入り、アバタ、格子目の歪みが目立つか、収縮不足で実用上問題のあるものを「C」とした。
【００４６】
実施例１
エチレン−プロピレン−ブテン三元共重合体（密度０．８９ｇ／ｃｍ^３、ＭＩ＝４ｇ／分（２３０℃、荷重２１．１８Ｎ）、融点１３０℃）５６重量％と軟化点１２５℃の脂環式飽和炭化水素樹脂１４重量％、スチレン３０重量％とブタジエン７０重量％とからなるブロック共重合体を完全水添したＳＥＢＳ（密度０．９１ｇ／ｃｍ^３、ＭＩ５ｇ/１０分（２３０℃、荷重２１．１８Ｎ））３０重量％を同方向２軸押出機を用いて溶融混練し、ペレットを得た。また、スチレン−ブタジエンブロック共重合体（密度１．０２ｇ／ｃｍ^３、ＭＩ６ｇ／１０分（１９０℃、荷重２１．１８Ｎ））５０重量％とスチレン−ブチルアクリレート共重合体（密度１．０５ｇ／ｃｍ^３、ＭＩ４ｇ／１０分（１９０℃、荷重２１．１８Ｎ））５０重量％を同方向２軸押出機を用いて溶融混練し、ペレットを得た。得られたペレットを両外層を形成するための４０ｍｍΦ単軸押出機に入れて、１８０℃〜２２０℃にて溶融混練した。
そして、各層の厚み比が外層：中間層：外層＝１：８：１となるように、各押出機の押出量を設定し、２３０℃に保った３層ダイスより下向きに共押出した。得られた積層体を冷却した後、９０℃の温度雰囲気の三菱重工（株）製テンター延伸設備内で横方向に４．０倍延伸して、厚み６０μｍの積層フィルムを得た。
得られた積層フィルムの片面全面に、バーコータを使用して密度１．５５ｇ／ｃｍ^３の銀色インキを印刷して２３℃で２４時間乾燥し、厚み２μｍのインキ塗膜を形成した後上記各評価を行った。
収縮仕上がり性評価で得られた、包装材を装着したPETボトルを粉砕し、液比重分離法により分離したところ、包装材とPETが明瞭に分離した。
【００４７】
実施例２
実施例１と同様の方法で積層フィルムを成形し、得られた積層フィルムの片面全面に、バーコータを使用して、密度１．５５ｇ／ｃｍ^３の銀色インキを印刷して２３℃で２４時間乾燥し、厚み５μｍのインキ塗膜を形成した後上記各評価を行った。
収縮仕上がり性評価で得られた、包装材を装着したＰＥＴボトルを粉砕し、液比重分離により分離したところ、包装材とPETが明瞭に分離した。
【００４８】
実施例３
ガラス転移温度が７０℃である環状オレフィン系重合体（三井化学(株)製、「アペル８００８Ｔ」）８０重量％とメタロセン系エチレン‐α‐オレフィン共重合体（密度０．９０ｇ／ｃｍ³、融点８９℃、ＭＩ４ｇ／１０分（１９０℃、荷重２１．１８Ｎ））２０重量％を同方向２軸押出機を用いて溶融混練し、ペレットを得た。得られたペレットを表裏層を形成するための４０ｍｍφ単軸押出機に入れて１８０〜２３０℃にて溶融混練した。また、メタロセン系エチレン−α−オレフィン共重合体（密度０．９０ｇ／ｃｍ³、融点８９℃、ＭＩ４ｇ／１０分（１９０℃、荷重２１．１８Ｎ））９０重量％と低密度ポリエチレン樹脂（密度０．９２４ｇ／ｃｍ³、融点１２８℃、ＭＩ２ｇ／１０分（１９０℃、荷重２１．１８Ｎ））１０重量％を同方向２軸押出機を用いて溶融混練し、ペレットを得た。得られたペレットを中間層を形成するための６５ｍｍφ単軸押出機に入れて１８０〜２３０℃にて溶融混練した。
そして、各層の厚み比が外層：中間層：外層＝１：４：１となるように、各押出機の押出量を設定し、２３０℃に保った３層ダイスより下向きに共押出した。得られた積層体を冷却した後、８７℃の温度雰囲気の三菱重工（株）製テンター延伸設備内で横方向に４．０倍延伸して、厚み６０μｍの積層フィルムを得た。
得られた積層フィルムの片面に、バーコータを使用して密度1.55ｇ／ｃｍ³の銀色インキを印刷して２３℃で２４時間乾燥し、厚み５μｍのインキ塗膜を形成した後上記各評価を行った。
収縮仕上がり性評価で得られた、包装材を装着したPETボトルを粉砕し、液比重分離法により分離したところ、包装材とPETが明瞭に分離した。
【００４９】
実施例４
実施例３と同様の方法で積層フィルムを成形し、得られた積層フィルムの片面全面に、バーコータを使用して、密度１．５５ｇ/ｃｍ³の銀色インキを印刷して２３≡で２４時間乾燥し、厚み５オｍのインキ塗膜を形成した後上記各評価を行った。
収縮仕上がり性評価で得られた、包装材を装着したＰＥＴボトルを粉砕し、液比重分離により分離したところ、包装材とPETが明瞭に分離した。
【００５０】
比較例１
実施例１において両外層に用いた混合樹脂ペレット（スチレン−ブタジエンブロック共重合体（密度１．０２ｇ／ｃｍ³、ＭＩ６ｇ／１０分（１９０℃、荷重２１．１８Ｎ））５０重量％とスチレン−ブチルアクリレート共重合体（密度１．０５ｇ／ｃｍ³、ＭＩ４ｇ／１０分（１９０℃、荷重２１．１８Ｎ））５０重量％を同方向２軸押出機を用いて溶融混練し、ペレットを得た。これを６５ｍｍφ単軸押出機および両外層を形成するための４０ｍｍφ単軸押出機に入れて、１８０〜２２０℃にて溶融混練し、各層の厚み比が外層：中間層：外層＝１：８：１となるように、各押出機の押出量を設定し、２２０℃に保った３層ダイスより下向きに共押出し、実質単層フィルムを得た。
得られたフィルムを冷却した後、９０℃の温度雰囲気の三菱重工（株）製テンター延伸設備内で横方向に４．０倍延伸して、厚み６０μｍのフィルムを得た。
得られたフィルムの片面に、バーコータを使用して密度1.55ｇ／ｃｍ³の銀色インキを印刷して２３℃で２４時間乾燥し、厚み３μｍのインキ塗膜を形成した後上記各評価を行った。
収縮仕上がり性評価で得られた、包装材を装着したPETボトルを粉砕し、液比重分離法により分離したところ、包装材とPETが共に沈降し、分離することができなかった。
【００５１】
比較例２
実施例３にて中間層に用いた混合樹脂ペレット（メタロセン系エチレン−α−オレフィン共重合体（密度０．９０ｇ／ｃｍ³、融点８９℃、ＭＩ４ｇ／１０分（１９０℃、荷重２１．１８Ｎ））８０重量％と低密度ポリエチレン樹脂（密度０．９２４ｇ／ｃｍ³、融点１２８℃、ＭＩ２ｇ／１０分（１９０℃、荷重２１．１８Ｎ））２０重量％を同方向２軸押出機を用いて溶融混練し、ペレットを得た。これを６５ｍｍφ単軸押出機および両外層を形成するための４０ｍｍφ単軸押出機に入れて、１８０〜２２０℃にて溶融混練し、各層の厚み比が外層：中間層：外層＝１：８：１となるように、各押出機の押出量を設定し、２２０℃に保った３層ダイスより下向きに共押出し、実質単層フィルムを得た。
得られたフィルムを冷却した後、８７℃の温度雰囲気の三菱重工（株）製テンター延伸設備内で横方向に４．０倍延伸して、厚み６０μｍのフィルムを得た。
得られたフィルムの片面に、バーコータを使用して密度1.55ｇ／ｃｍ³の銀色インキを印刷して２３℃で２４時間乾燥し、厚み８μｍのインキ塗膜を形成した後上記各評価を行った。
収縮仕上がり性評価を行ったが、包装材にシワ入り、アバタが見られ、また、収縮不足でボトルに密着しなかった。このように、包装材として実用に供することができないので、本包装材についてはPETとの分離試験は行わなかった。
【００５２】
比較例３
実施例１と同様の方法で積層フィルムを成形し、得られた積層フィルムの片面全面に、バーコータを使用して、密度１．５５ｇ/ｃｍ³の銀色インキを印刷して２３≡で２４時間乾燥し、厚み８オｍのインキ塗膜を形成した後上記各評価を行った。
収縮仕上がり性評価で得られた包装材を装着したPETボトルを粉砕し、液比重分離により分離したところ、包装材とPETが共に沈降し、分離することができなかった。
【００５３】
表１及び表２に各フィルム及び包装材について得られた結果を示す。
【表１】

（上表においてＹ＝（ρ_b−１．０５）／（１．０５−ρ_a）、ρ_a及びρ_bは温度２３℃における密度（g/cm³）であり、ｄ_a及びｄ_bは厚み（μｍ）である。）
【００５４】
【表２】

【００５５】
【発明の効果】
表１及び２から分かるように、本発明の包装材は、熱収縮率、自然収縮率、仕上がり性に優れ、且つ、液比重分離法でPETボトルの粉砕品と精度良く分離することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a packaging material used for shrink packaging, shrink-bound packaging, shrink labels, and the like, and a plastic container equipped with the packaging material, and in particular, can be easily separated from the container when the plastic container is recycled. It relates to packaging materials.
[0002]
[Prior art]
The heat-shrinkable film is widely used for shrink wrapping, shrink tying wrapping, shrinkage labels for plastic containers, breakage / scattering prevention wrapping for glass containers, and cap seals. Examples of the material include polyvinyl chloride resin, polystyrene resin, polyester resin, and polyolefin resin.
[0003]
For shrink labels of polyethylene terephthalate resin (hereinafter abbreviated as PET) bottles used as containers for soft drinks, etc., heat-shrinkable films made of polystyrene-based resins or polyester-based resins are used. After use, the PET bottle is recovered for recycling the polyethylene terephthalate resin and recycled as flakes and pellets.
[0004]
Generally, when recycling waste plastic, it is necessary to separate plastics of different materials. As a separation method, a liquid specific gravity separation method based on a difference in specific gravity of plastic is widely used. When an attempt is made to separate a heat-shrinkable label made of polystyrene resin or polyester-based resin from a pulverized PET bottle by this method, the heat-shrinkable label and the PET bottle both have a specific gravity greater than 1 and settle together. Therefore, it is difficult to accurately separate only the pulverized PET bottles. Therefore, a heat-shrinkable polyolefin-based laminated film having a reduced specific gravity so that it can be separated from PET is known (Patent Document 1). However, when the laminated film is used as a packaging material, there is a problem that if an ink coating layer is formed thereon, it cannot be sufficiently separated from PET. Although it is only necessary to make the ink coating layer thinner, there is a practical limit.
[0005]
[Patent Document 1]
JP 2000-209511 (Claims)
[0006]
[Problems to be solved by the invention]
Therefore, the present invention aims to solve the above problems and provide a heat-shrinkable packaging material that can be accurately separated from PET in a liquid specific gravity separation method even when an ink coating layer is formed. .
[0007]
[Means for Solving the Problems]
That is, the present invention is as follows.
A packaging material comprising a single-layer or multilayer heat-shrinkable film and an ink coating film formed on at least one side of the heat-shrinkable film, wherein the heat shrinkage rate (80 ° C.) in at least one direction of the packaging material In warm water for 10 seconds) is greater than 20%, and the thickness (d_a(Μm)) and the thickness of the ink coating (d_b(Μm)) ratio satisfies the relationship of the following formula.
[Expression 2]
d_a/ D_b= NY
(Where Y = (ρ_b-1.05) / (1.05-ρ_a), N> = 2 and ρ_a(G / cm^Three) Is the density of the heat-shrinkable film at a temperature of 23 ° C. (measured according to JIS K7112) and is less than 1.05, and ρ_b(G / cm^Three) Is the density at 23 ° C. in the dry state of the ink coating and is greater than 1.05)
Preferred embodiments of the packaging material are as follows.
n> = 2.5. The packaging material described above, wherein
The density at 23 ° C is 1.05 g / cm^ThreeThe said packaging material characterized by being less than.
Density ρ at 23 ° C. of heat-shrinkable film_a(G / cm^Three) Is 0.92-0.99 (g / cm^ThreeThe above-mentioned packaging material, wherein
Heat shrink film thickness d_a(Μm) is 30 to 80 (μm).
The packaging, wherein the heat-shrinkable film is a coextruded laminated heat-shrinkable film having at least three layers, including both outer layers mainly composed of polystyrene resin or cyclic olefin resin, and an intermediate layer mainly composed of polyolefin resin. Wood.
The above-mentioned packaging material, wherein the polystyrene resin is selected from a styrene-butadiene block copolymer, a styrene-butyl acrylate copolymer, or a mixture thereof.
The above-mentioned packaging material, wherein the cyclic olefin resin is a random copolymer of ethylene and cyclic olefin having a glass transition temperature of 50 to 90 ° C.
The polyolefin resin is composed of one or more α-olefins having 2 to 20 carbon atoms, and the density at 23 ° C. is 0.940 g / cm.^ThreeThe said packaging material characterized by being less than (co) polymer.
The present invention also relates to a polyethylene terephthalate resin container equipped with a heat-shrinkable label made of the packaging material, preferably the container is a bottle.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The packaging material of the present invention includes a heat-shrinkable film and an ink coating film formed on the film. The ink coating film may be formed on the entire surface of the heat-shrinkable film and / or the back surface by a known method such as gravure printing or bar coater. The ink coating film has a density at a temperature of 23 ° C. (hereinafter simply referred to as “density”) measured in accordance with JIS K7112 in a dry state, usually 1.05 g / cm.^ThreeLarger, for example that of silver ink widely used for this application is 1.55 g / cm^ThreeAnd that of white ink is 1.40 g / cm^ThreeIt is. In the present invention, the density of the ink coating film is determined according to JIS K7112, after the ink is solid-printed on a heat-shrinkable film with a bar coater (# 4) and dried at 23 ° C. for 24 hours. The density was measured and obtained by subtracting the density of the heat-shrinkable film from the density.
[0009]
The packaging material of the present invention has a thickness (d_b(Μm)) heat shrink film thickness (d_a(Μm)) ratio satisfies the following formula.
[Equation 3]
d_a/ D_b= NY
In the above formula, n> = 2, preferably n> = 2.5. When n is less than the above lower limit, the packaging material and PET tend to be insufficiently separated. Y = (ρ_b-1.05) / (1.05-ρ_a). Where ρ_a(G / cm^Three) Is the density of the heat-shrinkable film at a temperature of 23 ° C. and is 1.05 (g / cm^Three). The heat-shrinkable film having such a density will be described later. Ρ_b(G / cm^Three) Is the density of the ink coating film at a temperature of 23 ° C. As described above, 1.05 (g / cm^ThreeLarger) It was found that by setting each parameter to satisfy the above formula, a packaging material with good separation from PET can be obtained.
[0010]
Heat shrinkable film thickness (d_a(Μm)) is usually 100 μm or less, preferably 80 μm or less, more preferably 60 μm or less. Moreover, it is preferable that it is 30 micrometers or more from the point of intensity | strength. Ink coating thickness (d_b(Μm)) is obtained from the above equation. Although there is no particular limitation on the lower limit value, it is practically problematic to set it to less than 1 μm. Usually d_b(Μm) is 1 to 10 μm, preferably 2 to 7 μm. When the ink coating is formed on both sides of the heat-shrinkable film, the total thickness of both coatings combined is d_bAnd In the present invention, the thickness was determined by measuring the cross section of the packaging material with an optical microscope.
[0011]
The packaging material of the present invention has a thermal shrinkage rate of 10% in warm water at 80 ° C. in at least one axis direction of greater than 20%, preferably greater than 25%. A film having a heat shrinkage rate of less than 20% is practically unsuitable as a heat shrinkable packaging material.
[0012]
The density of the packaging material of the present invention at a temperature of 23 ° C. is preferably 1.05 g / cm.^ThreeLess, more preferably 1.03 g / cm^ThreeLess, more preferably 1.00 g / cm^ThreeIs less than. With such a density, it can be satisfactorily separated from PET by the liquid density separation method. The lower limit of the density is not particularly limited, but usually 0.92 g / cm^ThreeDegree.
[0013]
The heat-shrinkable film in the present invention preferably has a density of 0.99 g / cm.^ThreeOr less, more preferably 0.96 g / cm^ThreeOr less, most preferably 0.94 g / cm^ThreeIt is as follows. On the other hand, the density is 0.92 g / cm^ThreeIf less than 0.9, the elastic modulus may be insufficient, so 0.92 g / cm^ThreeThe above is preferable.
[0014]
The heat-shrinkable film preferably has a total haze measured in accordance with JISK7105 of 10% or less, more preferably 7% or less, and most preferably 5% or less. In a film in which the total haze exceeds 10%, a clear display effect by the ink coating film is not achieved. Further, the heat shrinkable film preferably has a natural shrinkage rate (for example, 30 ° C., 30 days) of less than 2% in order to store the film.
[0015]
As the resin constituting the heat-shrinkable film, various resins that satisfy the above-described characteristics can be used. For example, JP-A-2001-301101, JP-A-2001-301102, JP-A-2000-246847. The resin described in JP-A-2000-20951 can be used. Preferably, both outer layers mainly composed of a polystyrene-based resin or a cyclic olefin-based resin described in JP 2000-209511, and an intermediate layer mainly composed of an olefin-based resin between the two outer layers are provided. A heat-shrinkable laminated film (hereinafter referred to as a laminated film) that is a laminated film comprising at least three or more layers and that is stretched in at least one axial direction is used.
[0016]
In the laminated film, both outer layers are mainly composed of a polystyrene-based resin or a cyclic olefin-based resin, and are excellent in printability, solvent sealability, and dimensional stability. The intermediate layer is a composition mainly composed of an olefin resin, and the density of the laminated film is 0.99 g / cm.^ThreeIs less than.
[0017]
Examples of the polystyrene resin include polystyrene copolymers mainly composed of one or more styrene monomers such as styrene, α-methylstyrene, and p-methylstyrene, the copolymer block, butadiene, and isoprene. A block copolymer with a conjugated diene copolymer block mainly composed of one or more conjugated diene monomers such as 1,3-pentadiene, and a (meth) acrylic acid ester monomer Examples thereof include styrene- (meth) acrylic acid ester copolymers composed of one or more kinds and the above styrene monomer. Moreover, you may use in combination of 2 or more types of the said polystyrene-type copolymer, a block copolymer, and a styrene- (meth) acrylic acid ester copolymer.
[0018]
The structure of the block copolymer and the structure of each block part are not particularly limited, and the structure of the block copolymer may be, for example, a linear type or a star shape, and the structure of each block part is For example, it may be a completely symmetric block, an asymmetric block, a tetra block, a tapered block, a random block, or the like. Further, two or more block copolymers having different block copolymer structures and block portion structures, molecular weights, and polymerization methods may be blended.
[0019]
As the block copolymer, a styrene-butadiene block copolymer (hereinafter abbreviated as “SBS”) in which the styrene monomer is styrene and the conjugated diene monomer is butadiene is preferably used. The resin is industrially produced in a large number of different types in terms of the type of copolymerization, the structure of the block portion, the molecular weight, etc., and by combining a plurality of different SBS according to the required characteristics Various film properties can be easily controlled.
[0020]
The SBS has a styrene content of 50 to 95% by weight and more preferably 60 to 90% by weight. If the styrene content is less than 50% by weight, the transparency and rigidity of the film and the heat fusion resistance are low. On the other hand, if it exceeds 95% by weight, the impact resistance of the film is low, which is not preferable.
[0021]
Examples of the (meth) acrylic acid ester monomer represented by the following general formula [A] in the styrene- (meth) acrylic acid ester copolymer include methyl (meth) acrylate, butyl (meth) acrylate, Examples include 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, and the like. Here, the (meth) acrylate includes acrylate and / or methacrylate.
[Chemical 1]

R in the above formula_ThreeRepresents hydrogen or an alkyl group, preferably a methyl group. R_FourRepresents hydrogen or an alkyl group, preferably an alkyl group having 1 to 20 carbon atoms.
[0022]
In the styrene- (meth) acrylic acid ester copolymer, the most suitably used styrenic monomer is styrene, and the (meth) acrylic acid ester monomer is butyl acrylate.
[0023]
The styrene content in the styrene-butyl acrylate copolymer is generally 50 to 98% by weight, preferably 75 to 95% by weight. If the styrene content is less than the lower limit, the resulting laminated film has low rigidity, which is not preferable. On the other hand, when the above upper limit is exceeded, it is difficult to impart low temperature shrinkage to the resulting laminated film.
[0024]
The styrene-butyl acrylate copolymer can impart excellent low temperature shrinkage properties, but it is hard and brittle, so it is not preferred to use the resin alone. By adding at least one block copolymer composed of a styrene monomer and a conjugated diene monomer to the resin, impact resistance is imparted to the laminated film, which is preferable.
[0025]
As cyclic olefin resin, what is glass transition temperature 50-90 degreeC is preferable. If the glass transition temperature is less than the above lower limit, the resulting laminated film has a large natural shrinkage (for example, a shrinkage ratio after storage at 30 ° C. for 30 days) and tends to be a film lacking in dimensional stability. It becomes difficult to stretch and it is difficult to obtain good low temperature shrinkage characteristics.
[0026]
The bonding form of the cyclic olefin polymer is not particularly limited as long as the above-described conditions are satisfied. A random copolymer of cyclic olefin and ethylene represented by the following general formula [B], cyclic olefin ring-opening (copolymerization) ) Polymers, cyclic olefin ring-opening (co) polymer hydrides, and graft modified products of these (co) polymers.
[Chemical 2]

Where R¹~ R¹²Are hydrogen atoms or hydrocarbon groups, which may be the same or different. R^FiveAnd R^TenOr R¹¹And R¹²May be integrated to form a divalent hydrocarbon group. R^ThreeOr R^TenAnd R¹¹Or R¹²And may form a ring. n is 0 or a positive integer, and when n is 2 or more, R in each repeating unit^Five~ R⁸May be the same as or different from each other.
[0027]
Examples of cyclic olefins include bicyclohept-2-ene (2-norbornene) and its derivatives and tetracyclo-3-dodecene and its derivatives. Examples of bicyclohept-2-ene (2-norbornene) and its derivatives include norbornene, 6-methylnorbornene, 6-ethylnorbornene, 6-n-butylnorbornene, 5-propylnorbornene, 1-methylnorbornene, 7-methyl Norbornene, 5,6-dimethylnorbornene, 5-phenylnorbornene, 5-benzylnorbornene and the like are included.
[0028]
Examples of tetracyclo-3-dodecene and its derivatives include 8-methyltetracyclo-3-dodecene, 8-ethyltetracyclo-3-dodecene, 8-hexyltetracyclo-3-dodecene, 2,10-dimethyltetracyclo -3-dodecene, 5,10-dimethyltetracyclo-3-dodecene and the like are included.
[0029]
In the present invention, the content of a cyclic copolymer of cyclic olefin and ethylene, for example, the cyclic olefin represented by the general formula [B] is about 20 to 50 mol% of the copolymer weight, A copolymer of a cyclic olefin and ethylene can be preferably used. Moreover, what contains (alpha)-olefin other than ethylene and also further contains butadiene, isoprene, etc. as a 3rd component.
[0030]
Some have various glass transition temperatures depending on the cyclic olefin content. For example, “Apel” (trade name) manufactured by Mitsui Chemicals, Inc. “Topas” (trade name) manufactured by Ticona, Nippon Zeon Co., Ltd. ) “Zeonor 750R” (trade name) and the like. Examples of the cyclic olefin polymer include, for example, JP-A-60-168708, JP-A-612012016, JP-A-61-115912, JP-A-61-115916, JP-A-6-115916. It can be produced according to known methods described in JP-A Nos. 61-271308, 61-272216, 62-252406, 62-252407 and the like.
[0031]
Further, in the present invention, as the cyclic olefin-based resin, a cyclic olefin-based random copolymer, a cyclic olefin ring-opening (co) polymer, or a hydrogenated product of a cyclic olefin ring-opening (co) polymer, for example, maleic anhydride Graft polymers modified with a modifying agent such as an unsaturated carboxylic acid such as maleic acid, itaconic anhydride, itaconic acid, (meth) acrylic acid, or an anhydride thereof can also be used. These modifiers can be used alone or in combination.
[0032]
In addition to the resin composition described above, both the outer layers of the laminated film do not interfere with the purpose of the present invention, as well as general-purpose polystyrene, impact-resistant polystyrene, hydrogenated styrene-butadiene block copolymer, water Styrene-isoprene block copolymer, high density polyethylene, low density polyethylene, ethylene-α-olefin copolymer, polypropylene resin, propylene-α-olefin copolymer, aliphatic hydrocarbon resin, alicyclic carbonization You may mix and use a hydrogen resin, a rosin derivative, a terpene resin, a terpene phenol resin, these hydrogenated substances, etc.
[0033]
As the olefin resin of the laminated film intermediate layer, the density is 0.940 g / cm.^Three(Co) polymers containing 1 or 2 or more types of α-olefins having 2 to 20 carbon atoms such as ethylene and propylene, and / or simple units other than α-olefins copolymerizable with α-olefins. Examples thereof include copolymers including vinyl acetate, acrylic acid and derivatives thereof, methacrylic acid and derivatives thereof, and mixed resins thereof.
[0034]
A polymer preferable as the olefin resin is an ethylene copolymer or a propylene copolymer containing ethylene or propylene as a main component and one or more kinds of other α-olefins having 2 to 8 carbon atoms. A polymer which is a polymer and is more preferably used is a copolymer polymerized by a metallocene catalyst. This is because a film made of an ethylene copolymer or a propylene copolymer polymerized with a metallocene catalyst is superior in terms of mechanical properties, transparency, etc., compared to a film made of a copolymer with a Ziegler catalyst.
[0035]
The melting point of the olefin-based resin measured by a differential scanning calorimeter is preferably 160 ° C. or lower, more preferably 145 ° C. or lower, and most preferably in the range of 80 to 110 ° C. If it is less than 80 degreeC, the rigidity of the obtained laminated | multilayer film will be low, and the waist of a film will lose and it is not preferable. Moreover, when it exceeds 160 degreeC, the low temperature extending | stretching of a laminated | multilayer film will become difficult, and the case where a favorable low-temperature shrinkage characteristic cannot be obtained will arise.
[0036]
When the olefin resin is an ethylene copolymer, the melt flow index (hereinafter abbreviated as “MI”) of the copolymer is 0.5 to 20 g / 10 at a temperature of 190 ° C. and a load of 21.18 N. Minute is preferable, and 1 to 5 g / 10 minutes is more preferable. When MI is less than 0.5 g / 10 minutes, the extrusion load at the time of melt extrusion may increase, and when it exceeds 20 g / 10 minutes, the stretching stability may decrease.
[0037]
When the olefin resin is a propylene copolymer, its MI is preferably 0.5 to 20 g / 10 min at a temperature of 230 ° C. and a load of 21.18 N, more preferably 1 to 10 g / 10 min. When MI is less than 0.5 g / 10 minutes, the extrusion load at the time of melt extrusion may increase, and when it exceeds 20 g / 10 minutes, the stretching stability may decrease.
[0038]
Furthermore, when the melting point of the olefin resin is 120 to 160 ° C., a petroleum resin may be added to the olefin resin in order to improve the low temperature shrinkage characteristics of the laminated film. Examples of the petroleum-based resin include aliphatic hydrocarbon resins, alicyclic hydrocarbon resins, rosin derivatives, terpene resins, terpene phenol resins, and hydrogenated products thereof. Hydrogenated from the viewpoint of heat resistance and the like. Use of a hydrocarbon resin is preferred. Examples of commercially available products include Alcon (manufactured by Arakawa Chemical Co., Ltd.), Clearon (manufactured by Yashara Chemical Co., Ltd.), and the like. The softening point of these petroleum resins is preferably 110 ° C. or higher, and more preferably 120 to 150 ° C. When the softening point is less than 110 ° C., natural shrinkage of the resulting laminated film may be increased, which is not preferable.
[0039]
The mixing ratio of the olefin resin and the petroleum resin is preferably olefin resin / petroleum resin = 95 to 60/5 to 40% by weight, and more preferably 90 to 70/10 to 30% by weight. When the blending amount of the petroleum-based resin is less than 5% by weight, the effect of improving the low temperature shrinkage property, which is the purpose of addition, is hardly exhibited, and when it exceeds 40% by weight, the stretching stability may be lowered.
[0040]
When the adhesiveness between the outer layer and the intermediate layer is low, a resin for improving the adhesiveness between the outer layer and the intermediate layer is used as an intermediate layer and / or both outer layers as long as the object of the present invention is not hindered. Further, a layer mainly composed of the resin may be provided as an adhesive layer between the outer layer and the intermediate layer. As such a resin, for example, a modified olefin resin, a nylon resin, containing one or more selected from unsaturated carboxylic acid, unsaturated carboxylic acid ester, unsaturated carboxylic acid anhydride and vinyl acetate, Polyester resins, styrene-butadiene block copolymers, styrene-isoprene block copolymers, hydrogenated products of these block copolymers and modified products modified with unsaturated carboxylic acids or derivatives thereof, styrene-ethylene graft copolymers Examples thereof include a polymer and a styrene-ethylene random copolymer.
[0041]
In addition, a plasticizer, an ultraviolet absorber, a light stabilizer, an antioxidant, a stabilizer, a colorant, an antistatic agent, a lubricant, an inorganic filler, and the like may be appropriately added to each of the resins as necessary. it can.
[0042]
The above laminated film can be produced by any known method, but the resin composition constituting each of the above layers is melted by a separate extruder, and this is laminated in a die and extruded. The method is preferred. As the extrusion method, any method such as a T-die method or a tubular method can be adopted. The melt-extruded laminated resin is cooled with a cooling roll, air, water, etc., and then reheated by an appropriate method such as hot air, hot water, infrared rays, microwave, etc., by a roll method, a tenter method, a tubular method, etc. Uniaxially or biaxially.
[0043]
The stretching temperature can be appropriately selected depending on the softening temperature of each resin constituting the laminated film and the use required for the laminated film, but is preferably 60 to 130 ° C, more preferably 80 to 120 ° C. If it is less than 60 ° C., the elastic modulus of the material in the stretching process becomes too high, the stretchability becomes low, the film breaks, or the thickness tends to become unstable. If the temperature exceeds 130 ° C., desired shrinkage characteristics cannot be obtained, and the elastic modulus of the material in the stretching process is too low, so that the material hangs down by its own weight and stretching itself may be impossible.
[0044]
The stretching ratio is preferably 2 to 8 times depending on the composition of the laminated film, the stretching means, the stretching temperature, and the desired product form. The heat-shrinkable film in the present invention needs to be at least uniaxially stretched, but can be biaxially stretched if desired. Even in the case of uniaxial stretching, it is also effective to impart weak stretching of about 1.01 to 1.8 times in the longitudinal direction for the purpose of improving the mechanical properties of the film. In addition, it is important for providing shrinkage to cool quickly within a time period in which the molecular orientation of the laminated film after stretching does not relax.
[0045]
【Example】
Hereinafter, the present invention will be described with reference to examples.
The measured values and evaluations shown in the examples were performed as follows. Here, the take-up (flow) direction of the heat-shrinkable film is described as a “longitudinal” direction, and its orthogonal direction is described as a “lateral” direction.
(1) Density measurement
Based on JIS K7112, the density of the film or the packaging material was measured by a density gradient tube method at a temperature of 23 ° C., and each density was calculated from the ratio to the density of water.
(2) Thermal contraction rate
The packaging material was cut into a size of 100 mm in length and 100 mm in width, and immersed in a hot water bath at 80 ° C. for 10 seconds, and the amount of shrinkage was measured. The thermal shrinkage rate was expressed as a ratio (%) of the shrinkage amount to the original size before shrinkage in the lateral direction.
(3) Natural shrinkage rate
Scratch the packaging material to a length of 1000 mm horizontally, leave it in a thermostatic chamber at 30 ° C. for 30 days, measure the length A (mm) between the marks, and calculate the natural shrinkage (%) from the following formula. Calculated.
Natural shrinkage (%) = (1000−A) / 1000 × 100
In Table 2, those having a natural shrinkage rate of 3% or less are represented as “A”, and those having a natural shrinkage ratio exceeding 3% are represented as “B”.
(4) All heads
The total haze of the heat-shrinkable film was measured in accordance with JISK7105, and 7% or less was “A”, and more than 7% was “B”.
(5) Shrinkage finish
A packaging material printed with a 10 mm-interval grid is cut into a size of 100 mm in length and 298 mm in width, and 10 mm at both ends in the horizontal direction and bonded with a tetrahydrofuran / cyclohexane = 8/2 solution or by heat sealing. It was in the shape. This cylindrical laminated film was attached to a cylindrical PET bottle having a capacity of 1.5 liters, and allowed to pass for 10 seconds without rotating through a 3 m shrink tunnel by a steam heating method. The blowing steam temperature was 97 ° C., and the tunnel atmosphere temperature was 87 to 95 ° C.
After covering with the packaging material, wrinkles generated, avatars, distortion magnitude and number were comprehensively evaluated. The evaluation criteria are "A" for wrinkles, no avatars, lattice distortions that have no practical problems and good film adhesion, and "B" for wrinkles, avatars, and grid distortions. “C” was marked with wrinkles, avatars, lattice distortions that were conspicuous, or due to insufficient shrinkage.
[0046]
Example 1
Ethylene-propylene-butene terpolymer (density 0.89 g / cm³, MI = 4 g / min (230℃, Load 21.18 N), melting point 130℃) SEBS (density 0.91 g / cm) fully hydrogenated with a block copolymer consisting of 56% by weight, 14% by weight of alicyclic saturated hydrocarbon resin having a softening point of 125 ° C., 30% by weight of styrene and 70% by weight of butadiene³30 wt% of MI 5 g / 10 min (230 ° C., load 21.18 N)) was melt kneaded using the same-direction twin screw extruder to obtain pellets. Also, styrene-butadiene block copolymer (density 1.02 g / cm³, MI 6g / 10 min (190℃, Load 21.18 N)) 50% by weight and styrene-butyl acrylate copolymer (density 1.05 g / cm³, MI 4 g / 10 min (190 ° C., load 21.18 N)) 50 wt% was melt-kneaded using the same-direction twin screw extruder to obtain pellets. 40 mm for forming both outer layers of the obtained pelletsΦ180 in a single screw extruder℃~ 220℃Was melt kneaded.
  Then, the extrusion amount of each extruder is set so that the thickness ratio of each layer is outer layer: intermediate layer: outer layer = 1: 8: 1, 230℃Co-extruded downward from a three-layer die kept at a constant value. After cooling the resulting laminate, 90℃In a tenter stretching facility manufactured by Mitsubishi Heavy Industries, Ltd. in the temperature atmosphere ofμmA laminated film was obtained.
A density of 1.55 g / cm is applied to the entire surface of one side of the obtained laminated film using a bar coater.³Printed with silver ink and dried at 23 ° C for 24 hours, thickness 2μmAfter the ink coating film was formed, each of the above evaluations was performed.
When the PET bottle equipped with the packaging material obtained by the shrinkage finish evaluation was pulverized and separated by liquid specific gravity separation, the packaging material and PET were clearly separated.
[0047]
Example 2
A laminated film was formed by the same method as in Example 1, and a density of 1.55 g / cm was applied to the entire surface of one side of the obtained laminated film using a bar coater.³23 silver ink is printed℃And dried for 24 hours, thickness 5μmEach of the above evaluations was performed after forming the ink coating film.
When the PET bottle equipped with the packaging material obtained by the shrinkage finish evaluation was pulverized and separated by liquid specific gravity separation, the packaging material and PET were clearly separated.
[0048]
Example 3
Cyclic olefin polymer having a glass transition temperature of 70 ° C. (Mitsui Chemicals, “Apel 8008T”) 80% by weight and metallocene ethylene-α-olefin copolymer (density 0.90 g / cm)^Three, Melting point 89 ° C., MI 4 g / 10 min (190 ° C., load 21.18 N)) 20 wt% was melt-kneaded using the same direction twin screw extruder to obtain pellets. The obtained pellets were put into a 40 mmφ single-screw extruder for forming front and back layers and melt-kneaded at 180 to 230 ° C. In addition, metallocene ethylene-α-olefin copolymer (density 0.90 g / cm^Three, Melting point 89 ° C., MI 4 g / 10 min (190 ° C., load 21.18 N)) 90% by weight and low density polyethylene resin (density 0.924 g / cm^Three, Melting point 128 ° C., MI 2 g / 10 min (190 ° C., load 21.18 N)) 10 wt% was melt-kneaded using the same-direction twin screw extruder to obtain pellets. The obtained pellets were put into a 65 mmφ single screw extruder for forming an intermediate layer and melt-kneaded at 180 to 230 ° C.
And the extrusion amount of each extruder was set so that the thickness ratio of each layer might become outer layer: intermediate layer: outer layer = 1: 4: 1, and it coextruded downward from the 3 layer die kept at 230 degreeC. After cooling the obtained laminate, it was stretched 4.0 times in the transverse direction in a tenter stretching facility manufactured by Mitsubishi Heavy Industries, Ltd. in an atmosphere of 87 ° C. to obtain a laminated film having a thickness of 60 μm.
On one side of the obtained laminated film, a density of 1.55 g / cm using a bar coater^ThreeThe above silver ink was printed and dried at 23 ° C. for 24 hours to form an ink coating having a thickness of 5 μm.
When the PET bottle equipped with the packaging material obtained by the shrinkage finish evaluation was pulverized and separated by liquid specific gravity separation, the packaging material and PET were clearly separated.
[0049]
Example 4
A laminated film was formed in the same manner as in Example 3, and a density of 1.55 g / cm was applied to the entire surface of one side of the obtained laminated film using a bar coater.^ThreeThe above silver ink was printed and dried at 23≡ for 24 hours to form an ink coating having a thickness of 5 μm, and then the above evaluations were made.
When the PET bottle equipped with the packaging material obtained by the shrinkage finish evaluation was pulverized and separated by liquid specific gravity separation, the packaging material and PET were clearly separated.
[0050]
Comparative Example 1
Mixed resin pellets used in both outer layers in Example 1 (styrene-butadiene block copolymer (density 1.02 g / cm^Three, MI 6 g / 10 min (190 ° C., load 21.18 N)) 50 wt% and styrene-butyl acrylate copolymer (density 1.05 g / cm^Three, MI 4 g / 10 min (190 ° C., load 21.18 N)) 50 wt% was melt-kneaded using the same-direction twin screw extruder to obtain pellets. This was put into a 65 mmφ single screw extruder and a 40 mmφ single screw extruder for forming both outer layers and melt-kneaded at 180 to 220 ° C., and the thickness ratio of each layer was outer layer: intermediate layer: outer layer = 1: 8: The extrusion amount of each extruder was set so as to be 1, and coextruded downward from a three-layer die maintained at 220 ° C. to obtain a substantially single-layer film.
After cooling the obtained film, the film was stretched 4.0 times in the transverse direction in a tenter stretching facility manufactured by Mitsubishi Heavy Industries, Ltd. in a temperature atmosphere of 90 ° C. to obtain a film having a thickness of 60 μm.
A density of 1.55 g / cm using a bar coater on one side of the obtained film^ThreeThe above silver ink was printed and dried at 23 ° C. for 24 hours to form an ink coating having a thickness of 3 μm, and then each of the above evaluations was performed.
When the PET bottle equipped with the packaging material obtained by the shrinkage finish evaluation was pulverized and separated by the liquid specific gravity separation method, the packaging material and the PET both settled and could not be separated.
[0051]
Comparative Example 2
Mixed resin pellets used in the intermediate layer in Example 3 (metallocene ethylene-α-olefin copolymer (density 0.90 g / cm^Three, Melting point 89 ° C., MI 4 g / 10 min (190 ° C., load 21.18 N)) 80% by weight and low density polyethylene resin (density 0.924 g / cm^Three, Melting point 128 ° C., MI 2 g / 10 min (190 ° C., load 21.18 N)) 20 wt% was melt-kneaded using the same direction twin screw extruder to obtain pellets. This was put into a 65 mmφ single screw extruder and a 40 mmφ single screw extruder for forming both outer layers and melt-kneaded at 180 to 220 ° C., and the thickness ratio of each layer was outer layer: intermediate layer: outer layer = 1: 8: The extrusion amount of each extruder was set so as to be 1, and coextruded downward from a three-layer die maintained at 220 ° C. to obtain a substantially single-layer film.
After cooling the obtained film, the film was stretched 4.0 times in the transverse direction in a tenter stretching facility manufactured by Mitsubishi Heavy Industries, Ltd. in an atmosphere of 87 ° C. to obtain a film having a thickness of 60 μm.
A density of 1.55 g / cm using a bar coater on one side of the obtained film^ThreeThe above silver ink was printed and dried at 23 ° C. for 24 hours to form an ink film having a thickness of 8 μm.
The shrinkage finished property was evaluated, but the packaging material was wrinkled, avatars were observed, and the bottle did not adhere to the bottle due to insufficient shrinkage. As described above, since this packaging material cannot be put into practical use, the packaging material was not subjected to a separation test from PET.
[0052]
Comparative Example 3
A laminated film was formed in the same manner as in Example 1, and a density of 1.55 g / cm was applied to the entire surface of one side of the obtained laminated film using a bar coater.^ThreeThe above silver ink was printed and dried at 23≡ for 24 hours to form an ink film having a thickness of 8 μm, and then the above evaluations were made.
When the PET bottle equipped with the packaging material obtained by the shrinkage finish evaluation was pulverized and separated by liquid specific gravity separation, the packaging material and PET both settled and could not be separated.
[0053]
Tables 1 and 2 show the results obtained for each film and packaging material.
[Table 1]

(In the above table, Y = (ρ_b-1.05) / (1.05-ρ_a), Ρ_aAnd ρ_bIs the density at 23 ° C (g / cm^Three) And d_aAnd d_bIs the thickness (μm). )
[0054]
[Table 2]

[0055]
【The invention's effect】
As can be seen from Tables 1 and 2, the packaging material of the present invention is excellent in heat shrinkage rate, natural shrinkage rate and finish, and can be accurately separated from the pulverized PET bottle by the liquid specific gravity separation method.

Claims (11)

A packaging material comprising a single-layer or multilayer heat-shrinkable film and an ink coating film formed on at least one side of the heat-shrinkable film, wherein the heat shrinkage rate (80 ° C.) in at least one direction of the packaging material 10 seconds in hot water) is greater than 20%, and the ratio of the heat shrinkable film thickness (d _a (μm)) and said ink coating film thickness (d _b ([mu] m)) satisfy the relation of the following formula A packaging material characterized by that.

(Where Y = (ρ _b −1.05) / (1.05-ρ _a ), n> = 2, and ρ _a (g / cm ³ ) is the density of the heat-shrinkable film at a temperature of 23 ° C. (Measured in accordance with JIS K7112) and less than 1.05, and ρ _b (g / cm ³ ) is the density at 23 ° C. in the dry state of the ink coating film and is greater than 1.05 ) 2. The packaging material according to claim 1, wherein n> = 2.5. The packaging material according to claim 1 or 2, wherein the density at 23 ° C is less than 1.05 g / cm ³ . 4. The density ρ _a (g / cm ³ ) at _a temperature of 23 ° C. of the heat-shrinkable film is 0.92 to 0.99 (g / cm ³ ). 5. Packaging material. The packaging material according to any one of claims 1 to 4, wherein the heat-shrinkable film has a thickness d _a (µm) of 30 to 80 (µm). The heat-shrinkable film is a coextruded laminated heat-shrinkable film having at least three layers, including both outer layers mainly composed of polystyrene resin or cyclic olefin resin, and an intermediate layer mainly composed of polyolefin resin. The packaging material of any one of 1-5. The packaging material according to claim 6, wherein the polystyrene resin is selected from a styrene-butadiene block copolymer, a styrene-butyl acrylate copolymer, or a mixture thereof. The packaging material according to claim 6, wherein the cyclic olefin resin is a random copolymer of ethylene and a cyclic olefin having a glass transition temperature of 50 to 90 ° C. The polyolefin resin is a (co) polymer comprising one or more of α-olefins having 2 to 20 carbon atoms and a density at 23 ° C. of less than 0.940 g / cm ^3. 6. The packaging material according to 6. A polyethylene terephthalate resin container equipped with a heat-shrinkable label made of the packaging material according to claim 1. The polyethylene terephthalate resin container according to claim 10, wherein the container is a bottle.